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Electronic State of Low-Rank Coals with Exchanged Sodium Cations

Yuji Shinohara
Yuji Shinohara
Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan
More by Yuji Shinohara
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Naoto Tsubouchi*
Naoto Tsubouchi
Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan
*E-mail: [email protected]
More by Naoto Tsubouchi

Cite this: ACS Omega 2020, 5, 3, 1688–1697

Publication Date (Web):January 10, 2020

https://doi.org/10.1021/acsomega.9b03780

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Abstract

Our previous experimental study showed that Na⁺-exchanged coal prepared from low-cost natural soda ash is an excellent catalyst for steam gasification of low-rank coals using fixed-bed quartz reactors. However, it is difficult to experimentally clarify the effect of Na ion exchange on low-rank coal. In order to investigate the influence of Na⁺ ions on low-rank coal, this study determined the electronic state between the Na⁺-exchanged coal model and raw coal model and compared them using RHF/6-311G* and B3LYP/6-31G*. The experiments revealed that Na ion exchange has a significant effect on low-rank coal gasification. The model structure of low-rank coal is considered to change significantly in terms of the electronic state before and after Na exchange even with a simple main molecular structure. Molecular models where H of COOH/OH was ion-exchanged with one, two, and three Na ions were developed, and quantum chemical calculations were performed. The results showed that when the number of Na⁺-exchanged sites is increased, the electron state on the coal molecule becomes more negatively charged in the case of the Na⁺-exchange coal model. It is presumed that this contributes to enhancing the reactivity of low-rank coal and water vapor. In addition, weak bonds in the Na⁺-exchanged coal molecule were examined by calculating the difference in the value of the Mulliken and Löwdin bond orders before and after Na⁺ exchange. The results showed that the increase in the number of exchanged Na⁺ in the low-rank coal molecule model increased the number of weak bonds in the molecule. It is presumed that this contributes to enhancing the decomposition of low-rank coal.

Introduction

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Coal combustion accounts for about a fourth of the total world energy consumption, and coal plays an important role in satisfying the world’s primary energy demand. (1) However, at the current rate of annual use, global coal deposits will last for about 150 years. (2) One means of reducing coal consumption is improving the utilization efficiency of heat obtained from coal. To achieve this aim, various technologies, such as supercritical thermal power generation, integrated gasification combined cycle, and polygeneration, have been developed. The use of low-rank coal (brown coal), a potentially abundant resource, is also important for establishing stable energy supply in the future. Nevertheless, at present, the use of low-rank coal as energy source has few advantages because of high production costs. Low-rank coal is generally characterized by a high volatile component and moisture content and low ignition temperature. In addition, low-rank coal has a higher oxygen content (15–30%) in oxygen-containing functional groups than high-rank coal does. (3) Therefore, since low-rank coal tends to adsorb moisture, a large amount of energy is required to remove it. (4)

Accordingly, several attempts have been made to overcome this limitation. For example, the Strategic Technical Platform for Clean Coal Technology in Japan has aimed to achieve low-rank coal gasification at 900 °C or less using a catalyst. To achieve this aim, many studies have been conducted on the use of Ni or K carbonate catalysts in the gasification of low-rank coal. (5−7) As an example, gasification at 600 °C using Ni-supported Yallourn low-rank coal with a fluid bed reactor yielded high conversion rates (≥80 wt %). (8) K catalysts also have excellent gasification properties, and Exxon has developed a pilot-scale fluidized-bed coal gasifier operating at 3 MPa and 700 °C using steam or H₂ with K catalysts. (9,10) However, this process has been shown to produce methane-rich products, and no commercially viable gasification catalysts have been developed hitherto.

Numerous studies have attempted to understand the chemical structure of coal to gasify coal. Mathews and Chaffee (11) summarized the structures of many types of coal. Quantum chemical calculations of coal regarding the interaction between steam and benzene rings have been conducted, and C═O–K bonds in the benzene ring have been analyzed, completely neglecting differential overlap. (12) Many studies have also investigated the interaction between water and coal through computer simulations. (13−16) However, the influence of substituting H with Na in carboxyl or hydroxyl groups on the structure of low-rank coal has not been studied.

In a previous study, our group found that Na⁺ ion exchange of H in Austrian Loy Yang (LY) low-rank coal and Indonesian Adaro (AD) bituminous coal-promoted gasification. (17) In particular, the samples used mainly had particle sizes of 250–500 μm, and ion exchange was performed at room temperature using natural soda ash powder (Na₂CO₃ > 99%) produced in the United States; a gasification test was also performed. Na⁺ was exchanged into LY and AD using the natural soda ash powder. According to the results, 2.7 mass % Na⁺-exchanged LY and 1.6 mass % Na⁺-exchanged AD were obtained. Table 1 presents char conversion during gasification after 1 and 2 h at 700 °C. The conversion was about 15–20% after 2 h irrespective of the coal type, but with the addition of Na⁺, the conversion of LY reached approximately 100% after 1 h, and that of AD also increased to 75%. As described above, our group clarified that Na⁺-exchanged coal remarkably promoted steam gasification.

Table 1. Changes in Char Conversion with Reaction Time for the Steam Gasification of Raw and Na⁺-Exchanged Coals at 700 °C

	char conversion, mass % (dacfa)
sample code	reaction time (1 h)	reaction time (2 h)
raw AD coal	15–18	15–20
raw LY coal	15–18	15–20
1.6 mass % Na⁺/AD coal	75	100
2.7 mass % Na⁺/LY coal	100

^{^a}

daf = dry, ash-catalyst-free basis.

However, many other studies have only experimentally shown that these additives are effective for coal gasification. The effect of Na catalyst ion exchange on the structure of coal has not been clarified. Since the reaction between water molecules and low-rank coal occurs at 700 °C, low-rank coal may decompose and react with water molecules. Consequently, determining the decomposition reaction between water molecules and low-rank coal via quantum chemical calculations involves many uncertainties, and the effect of Na addition has not been accurately evaluated. Therefore, this study focused on changes in the electronic state of low-rank coal before and after ion exchange and performed quantum chemistry calculations.

In this study, we used a molecular model based on analytical values of Yallourn low-rank coal (Australia), which is a typical structure of low-rank coal, and analyzed using the molecular orbital method. (18) The chemical structure of Yallourn low-rank coal has been discussed in detail, and other researchers have used it for molecular dynamics calculations. (19) In addition, low-rank coal has a smaller number of atoms and smaller molecular weight than bituminous coal, no large aromatic ring structure, and a unique minimum unit structure. Therefore, examining the interaction with the additive based on the minimum unit structure is significant because it can simplify the characterization of low-rank coal. In addition, the electronic state of Na⁺ ion-exchanged low-rank coal is considered to change before the gasification reaction. It is believed that changes in the electronic state facilitate reaction and promote gasification. Therefore, if changes in the electronic state and bond order during the exchange of H⁺ and Na⁺ in COOH and OH groups of simple low-rank coal are investigated, the influence of Na⁺ on low-rank coal molecules can be determined. Accordingly, this study extends the potential to the search for additional coal gasification catalysts and discovery of more catalyst species.

Results and Discussion

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Structure of low-rank coal used in the calculation and substitution position of Na⁺

In the gasification of low-rank coal, experimental results show that gasification is promoted by ion exchange of the COOH group or OH group with an alkali metal, alkaline earth metal, or the like. (17,20) Therefore, we adopted a molecular model constructed based on the analytical values of a typical low-rank coal, namely, Yallourn low-rank coal. The unit structure of the low-rank coal used for the calculations is shown in Figure 1. The ends of the bond were capped with hydrogen atoms without nitrogen and sulfur. Several possible combinations of reactions between Na⁺ and the COOH and/or OH groups of the Yallourn coal model structure exist, and all combinations are shown in Figure 2. Therefore, molecular orbital calculations were performed on structures with one (Na-1, Na-2, Na-3), two (2Na-1, 2Na-2, 2Na-3), and three Na ions exchanged (3Na) per Yallourn coal model structure (Figure 2).

Figure 1. Model structure of Yallourn low-rank coal.

Figure 2. Number and location of sodium exchange for low-rank coal.

Structure and total energy after structure optimization

Each structure substituted by Na⁺ was optimized, the most stable structure with the lowest energy and the same substitution number of Na⁺ were extracted, and their energies were compared. Figure 3 shows the calculation results using the restricted Hartree–Fock method (RHF)/6-311G*, and Figure 4 shows those using Becke, 3-parameter, Lee–Yang–Parr (B3LYP)/6-31G* considering the interactions between electrons. According to the calculated total energies, structures with Na⁺ ions reacting with carboxyl groups were stable. The structure in which H in a COOH group was ion-exchanged with Na was found to be the most stable regardless of the number of Na. A previous study using infrared spectroscopy confirmed that the Ca²⁺ ion reacted with a carboxyl group. (20) Therefore, this calculation result could be considered as correct. Furthermore, in the model with the substitution of 1, 2, and 3 Na ions, the electronic and bonding states were examined only for the structure in which H in the COOH group was ion-exchanged. These structures with the lowest total energies were compared using electrostatic potential maps.

Figure 3. Relationship between the number of Na⁺ and total energy using RHF/6-311G*.

Figure 4. Relationship between the number of Na⁺ and total energy using B3LYP/6-31G*.

Next, the electrostatic potential was superimposed on the structure of each low-rank coal. Figures 5 and 6 show the calculation results using RHF/6-311G* and B3LYP/6-31G*, respectively. The electrostatic potential map showed the interaction energy, which the positive charge of unit electric quantity exerted on the electron distribution of the molecule. It indicated the electrostatic potential at various points on an electron density surface corresponding to the overall molecular size. The map was used to determine the polar area of the Na⁺-exchanged structures, encompassing the area of the electron density surface where the electrostatic potential is indicated in red (large negative values of potential) or blue (large positive values of potential). (21) Comparing the low-rank coal before and after Na⁺ exchange, the Na⁺-exchanged structure was found to be in the form of a horizontally elongated rod. The interaction of Na with the opposite O atom was found to stabilize the shape of the rod. Therefore, this part is blue when Na⁺ exchange increased. Furthermore, this part of the benzene ring is indicated in red. That is, the positive charge accumulated in this Na⁺ portion, and the negative charge was pushed out to the benzene ring. In the case of low-rank coal without ion exchange, the oxygen atom portion was negatively charged, and the electron state was not charged in the benzene ring portion. In addition, the charge of the benzene ring gradually became more negative in the case of two or three Na substitutions. This suggested an enhancement of the reactivity of the basic structure of low-rank coal, and Na⁺-exchanged low-rank coal is considered to react with molecules, such as water vapor, during gasification to promote decomposition. It is presumed that decomposition due to gasification was likely to occur by increasing the Na⁺ ion exchange. In fact, although different types of coal were used in the experiment, the gasification of 2.7 mass % LY coal was higher than that of 1.6 mass % AD coal (Table 1).

Figure 5. Relationship between the number of Na⁺ and electrostatic potential map using RHF/6-311G*.

Figure 6. Relationship between the number of Na⁺ and electrostatic potential map using B3LYP/6-31G*.

Furthermore, to determine the part of the structure of low-rank coal affected by Na⁺, the strength of each bond in the coal structures was determined using Mulliken population analysis. (22) Löwdin population analysis was also performed to support the Mulliken population analysis of symmetric orthogonal basis functions. (23) In this study, the difference in bond order between the raw coal and ion-exchanged structure was determined. Although the bond state from the bond order may change, caution is required because absolute values have little physical significance. A bond that has a large difference in the Mulliken and Löwdin bond orders may have either a weak or strong bond. As a precaution, the bond orders of benzene, (1R)-1,2,3,4-tetrahydronaphthalene-1-carboxylic acid, 4-methylbenzene-1,3-diol, and raw low-rank coal were calculated using RHF/6-311G* (Figures 7 and 8). The calculations confirmed that raw low-rank coal had a bond order that was similar to that of each of the molecules that made up the structure. This suggested that the raw low-rank coal had a unit structure similar to that of a very stable single molecule.

Figure 7. Mulliken bond orders using RHF/6-311G*.

Figure 8. Löwdin bond orders using RHF/6-311G*.

The differences between the bond orders of Na⁺-exchanged and raw coal are indicated in Figures 9 and 10. The values in red indicate the bond order of Na⁺-exchanged coal, which is lower than that of raw coal by 0.05 or less. The blue characters indicate the bond order of Na⁺-exchanged coal, higher by 0.05 or more. From this point onwards, the red lines indicate weaker bonds. The blue characters mean that bonds became stronger. In addition, charge transfer was found to occur between the C═O and C–ONa bonds in the carboxyl group. However, because the conjugation suggested charge transfer, only the change in the bond order of the main structure was considered here. Therefore, the difference in cleaving energy was estimated using B3LYP/6-31G* when the difference in Mulliken bond order was 0.06 (Löwdin bond order was 0.05).

Figure 9. Mulliken bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond order of raw coal; blue letters indicate increased bond orders by 0.05 or more).

Figure 10. Löwdin bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond order of raw coal; blue letters indicate increased bond orders by 0.05 or more).

Figure 11 shows the bond order of the raw low-rank coal. It was calculated to separate bond A from 1.410 to 5.410 Å in 20 steps with respect to the most stable structure of raw coal. The relationship between the bond distance and total energy is also shown in Figure 11. In the raw coal, the energy for the cleaving bond A was 171.692 kcal/mol. Next, as shown in Figure 12, calculation was performed to cleave bond A in 20 steps from 1.425 to 5.425 Å in the model (2Na-1). The energy for cleaving the bond at that time was 122.101 kcal/mol in the model. Therefore, the cleavage energy of 49.591 kcal/mol was found to decrease with decreasing Mulliken and Löwdin bond orders (0.06 and 0.05, respectively). Accordingly, the ease of bond cleavage was evaluated with a bond order difference of 0.05.

Figure 11. Mulliken bond orders of the original raw low-rank coal using B3LYP-6-31G* and the relationship between bond distance and total energy (calculation was performed to separate bond A from 1.410 to 5.410 Å in 20 steps).

Figure 12. Mulliken bond orders of the model (2Na-1) using B3LYP/6-31G* and the relationship between bond distance and total energy (calculation was performed to separate bond A from 1.425 to 5.425 Å in 20 steps).

Next, Figures 13 and 14 show the Mulliken and Löwdin bonding orders of the molecular structures (Na-1, 2Na-1, and 3Na) using RHF/6-311G*. Similar to Figures 9 and 10, red values indicate that the bond order of the Na⁺-exchanged coal decreased by 0.05 or less relative to that of raw coal. Blue values indicate an increase in the bond order by 0.05 or more. Figures 13 and 14 further show that the bonds weaken with the increasing number of Na⁺ ions. Figures 15 and 16 show the results of B3LYP/6-31G* considering the interaction between electrons with Mulliken and Löwdin bonding orders. Figures 13–16 show that the bond of the benzene ring structure tended to weaken with Na⁺-exchange in both calculation methods. That is, the electronic state of the structure appeared to be biased, and the bond was easily broken when H in the COOH or OH groups of low-rank coal was exchanged with Na ions. Moreover, decomposition may be promoted by the progress of ion exchange. In our experiment, although the coal differed, the decomposition rate was faster for 2.7% LY coal than for 1.6% AD coal. (17)

Figure 13. Comparisons between the number of Na⁺ and Mulliken bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).

Figure 14. Comparisons between the number of Na⁺ and Löwdin bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).

Figure 15. Comparisons between the number of Na⁺ and Mulliken bond orders using B3LYP/6-31G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).

Figure 16. Comparisons between the number of Na⁺ and Löwdin bond orders using B3LYP/6-31G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).

In summary, in Na and C atoms, electrons appear to be attracted to C atoms even with a simple index such as Pauling’s electronegativity. According to this study, the substituent in raw coal was located where it was likely to affect the main structure via ion exchange. According to the results of this study, the ease of steam gasification with low-rank coal can conceivably be evaluated using the bond order of the main structure before and after ion exchange, and, as an evaluation method, it may be useful to future catalyst research and development.

Conclusions

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The experiments in the previous study showed that the steam gasification reaction proceeded readily via ion exchange between low-rank coal molecules and Na. (17) The purpose of this study was to investigate the effect of Na in low-rank coal molecules on the molecule structure using quantum chemical calculations. As a result, according to the calculated total energies, structures with Na⁺ ions reacting with carboxyl groups were stable. The structure in which H in a COOH group was ion-exchanged with Na was found to be the most stable regardless of the number of Na⁺ ions. Previous research confirmed that Ca²⁺ ions reacted with carboxyl groups. (20) Therefore, the calculation results in this study can be considered correct. Moreover, the Na catalyst affected the electronic state and weak intramolecular bonding of low-rank coal molecules and caused electron localization. The quantum chemistry calculations for low-rank coal and Na⁺ exchange showed that the Na⁺-exchange model had a weak bond compared to the bond strength (bond order) of the raw coal model. Bond strength was found to decrease with increasing number of Na⁺ ions in Na⁺-exchanged coal. Although different types of coal were used in the experiments, gasification of 2.7 mass % LY coal occurred more readily than that of 1.6 mass % AD coal did. Consequently, both thermal decomposition and steam gasification reactivity may be improved. Analysis of the electronic state of the heating process through quantum chemical calculations will likely be an important research topic in the future.

Calculation Method

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For geometry optimization and estimation of the electronic states, Spartan’16 V2.0.7 for Windows (Wavefunction, Inc.) installed on DELL XPS 8930 (Intel Core i7–8700, system memory 16 GB Double-Data-Rate4 Synchronous Dynamic Random Access Memory 2666 MHz, and hard disk drive 1 TB, SSD 256 GB) was used for the quantum chemical calculation. (21) The conformations of the model structure of low-rank coal were first analyzed using a molecular dynamics method (Merck molecular force field). (24) Five low-energy and roughly different structures were selected from the results. These structures were then calculated using optimized geometry with RHF/3-21G*. (25) For Na⁺-exchanged coal, all possible combination models exchanged with Na⁺ in the raw coal were constructed. These models were also subjected to geometrical optimization. Finally, the structures calculated with RHF/3-21G* were used as input data for the calculation using RHF/6-311G*, B3LYP (exchange-correlation functional), and 6-31G* to obtain accurate results. (26,27) B3LYP included all electron interactions other than classical Coulomb interactions. Therefore, using B3LYP, an accurate solution considering the relationship between exchange interaction and electron correlation could be obtained, which is not included in the RHF method.

Author Information

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Corresponding Author
- Naoto Tsubouchi - Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan; Email: [email protected]
Author
- Yuji Shinohara - Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan
Notes
The authors declare no competing financial interest.

Acknowledgments

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The present study was supported in part by Hokkaido Electric Power Co., Inc.

NOMENCLATURE

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B3LYP	Becke, 3-parameter, Lee–Yang–Parr
AD	Adaro
LY	Loy Yang
RHF	Restricted Hartree–Fock method

References

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This article references 27 other publications.

1
Zhang, Y.; Schauer, J. J.; Zhang, Y.; Zeng, L.; Wei, Y.; Liu, Y.; Shao, M. Characteristics of particulate carbon emissions from realworld Chinese coal combustion. Environ. Sci. Technol. 2008, 42, 5068– 5073, DOI: 10.1021/es7022576
[ACS Full Text ], [CAS], Google Scholar
1
Characteristics of Particulate Carbon Emissions from Real-World Chinese Coal Combustion
Zhang, Yuanxun; Schauer, James Jay; Zhang, Yuanhang; Zeng, Limin; Wei, Yongjie; Liu, Yuan; Shao, Min
Environmental Science & Technology (2008), 42 (14), 5068-5073CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
Particulate matter emissions from different Chinese coal combustion systems were collected and analyzed for elemental and org. C (EC, OC), and mol. markers. Emissions from industrial boilers and residential stoves were examd. Coal included anthracite, bituminous, brown, and commonly used Chinese coal briquettes produced for residential combustion. Results showed significant differences in the contribution of carbonaceous species to particulate mass emissions. Industrial boilers had much higher C burn-out, yielding particulate emissions with much lower OC, EC, and speciated org. compd. concns.; residential stoves had significantly higher carbonaceous particulate emissions with rates ∼100 times greater than industrial boilers. Quantified org. compds. emitted from industrial boilers were dominated by oxygenated compds., of which 46-68% were org. acids; the dominant species quantified in residential stove emissions were polycyclic arom. hydrocarbons (PAH, 38%) and n-alkanes (20%). An important observation was that PAH emission factors and hopanoid distribution were different than those emissions from industrial and residential coal combustion, even when the same coal was burned. Although particulate matter emissions by industrial and residential combustion were different, picene was detected in all samples with detectable OC mass concns., supporting the use of this org. tracer for OC from all types of coal combustion. 17α(H),21β(H)-29-norhopane was the predominant hopanoid in coal combustion emissions, which was different from mobile source emissions and may be used to distinguish emissions from different fossil fuel sources.
>> More from SciFinder ^®
https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXmvVGqtb4%253D&md5=73fbd50ff822e49b7aa46e588f2f52d7
2
Thielemann, T.; Schmidt, S.; Peter Gerling, J. Lignite and hard coal: energy suppliers for world needs until the year 2100—An outlook. Int. J. Coal Geol. 2007, 72, 1– 14, DOI: 10.1016/j.coal.2007.04.003
[Crossref], [CAS], Google Scholar
2
Lignite and hard coal: Energy suppliers for world needs until the year 2100 - an outlook
Thielemann, Thomas; Schmidt, Sandro; Gerling, J. Peter
International Journal of Coal Geology (2007), 72 (1), 1-14CODEN: IJCGDE; ISSN:0166-5162. (Elsevier B.V.)
For three years, international hard coal prices have been at rather expensive levels. Some argue that these higher prices might indicate the threat of a phys. scarcity of fossil fuels - similar to the situation with oil and gas. This is not true. The supply situations with lignite and hard coal appear to be largely not crit. Adjusted to the rise in global coal consumption, which is expected until 2100, nature by and large can meet the world's coal demand. This is shown for lignite in this article and it is illustrated for hard coal here, differentiated in space and time for a world divided into eight regions and viewed for the years 2005, 2020, 2030, 2050, and 2100. The only area of potential concern is Asia (esp. China). But today's and coming eager efforts in China to convert coal resources into reserves will most likely deliver the coal needed for the Chinese market. Up to the year 2100, and from a geoscientific point of view, there will be no bottleneck in coal supplies on this planet.
>> More from SciFinder ^®
https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpt1Srtr8%253D&md5=501ef4734f23e96fc9e9b33d7f771b57
3
Jia, R.; Harris, G. H.; Fuerstenau, D. W. An improved class of universal collectors for the flotation of oxidized and / or low-rank coal. Int. J. Miner. Process. 2000, 58, 99– 118, DOI: 10.1016/S0301-7516(99)00024-1
[Crossref], [CAS], Google Scholar
3
An improved class of universal collectors for the flotation of oxidized and/or low-rank coal
Jia, R.; Harris, G. H.; Fuerstenau, D. W.
International Journal of Mineral Processing (2000), 58 (1-4), 99-118CODEN: IJMPBL; ISSN:0301-7516. (Elsevier Science B.V.)
Ash minerals, including pyrite, can be sepd. from coal by flotation, primarily making use of the natural hydrophobicity of the carbonaceous matter in coal. However, to overcome the deleterious effect of oxygen functional groups on the coal surface, an org. collector is required. The most common industrial coal flotation collector is fuel oil, but the addn. of oxygenated functional groups to the collector mol. markedly enhances the flotation of lower rank and oxidized coals. This paper summarizes the results of detailed study of the flotation response of two high-sulfur coals, Illinois No. 6 coal and Pittsburgh No. 8, using different nonionic oxygenated surfactants as the collector. The performance of these reagents is compared with that of two oily collectors, namely dodecane and nonylbenzene, and mechanisms for the interaction of these compds. with coal are suggested.
>> More from SciFinder ^®
https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhslSrtbY%253D&md5=5737fe24e379637ee18305e4fa1b57e8
4
Tahmasebi, A.; Yu, J.; Han, Y.; Zhao, H.; Bhattacharya, S. Thermogravimetric study and modeling for the drying of a Chinese lignite. Asia-Pac. J. Chem. Eng. 2013, 8, 793– 803, DOI: 10.1002/apj.1722
[Crossref], [CAS], Google Scholar
4
Thermogravimetric study and modeling for the drying of a Chinese lignite
Tahmasebi, Arash; Yu, Jianglong; Han, Yanna; Zhao, Huan; Bhattacharya, Sankar
Asia-Pacific Journal of Chemical Engineering (2013), 8 (6), 793-803CODEN: AJCEBK; ISSN:1932-2135. (John Wiley & Sons Ltd.)
Study of drying characteristics and kinetics of coal is necessary in order to optimize drying operation and design a dryer in industrial scale. Drying characteristics of Chinese lignite was investigated exptl. using thermogravimetric method, and the effect of drying variables on drying rate was systematically studied. For CFD modeling and scale-up purposes, it is useful to have an algebraic equation that describes the drying process of lignite. Therefore, different thin layer drying models given in the literature were employed to analyze coal drying kinetics under different conditions. During studying the consistency of all the models, statistical tests such as χ2, residual sum of squares (RSS), F-value, and the coeff. of detn. R2 were employed. It was found that the Midilli-Kucuk model best describes the drying process within 99.9% accuracy. The effects of drying temp. and coal sample wt. on the consts. and coeffs. of the selected model were also studied by multiple regression anal. Apparent diffusion coeff. of moisture from sample was calcd. using the exptl. kinetics data. Higher drying temps. and smaller sample wts. resulted in higher diffusion coeff., which was consistent with exptl. data. Activation energy of moisture evapn. calcd. from Arrhenius equation for drying process was 21.17 kJ/mol. The selected algebraic drying model can be used for CFD modeling during scale-up of drying facility for industrial applications. © 2013 Curtin University of Technol. and John Wiley & Sons, Ltd.
>> More from SciFinder ^®
https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXisVGktb0%253D&md5=6df59aa7ba3dcef96368381b8bfb967f
5
Tomita, A.; Tamai, Y. Low-temperature gasification of Yallourn coal catalysed by nickel. Fuel 1981, 60, 992– 994, DOI: 10.1016/0016-2361(81)90099-5
[Crossref], [CAS], Google Scholar
5
Low-temperature gasification of Yallourn coal catalyzed by nickel
Tomita, Akira; Tamai, Yasukatsu
Fuel (1981), 60 (10), 992-4CODEN: FUELAC; ISSN:0016-2361.
Ni catalyst enhanced the gasification of the Yallourn coal in a similar manner obsd. for activated C. At present the mechanism of this high activity is unclear, but the following characteristics of this coal might account for this activity: porosity, S content, functional groups, maceral compn., ash yield, and ash components.
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6
Tomita, A.; Ohtsuka, Y.; Tamai, Y. Low-temperature gasification of brown coals catalysed by nickel. Fuel 1983, 62, 150– 154, DOI: 10.1016/0016-2361(83)90187-4
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6
Low-temperature gasification of brown coals catalyzed by nickel
Tomita, Akira; Ohtsuka, Yasuo; Tamai, Yasukatsu
Fuel (1983), 62 (2), 150-4CODEN: FUELAC; ISSN:0016-2361.
Ni catalysts exhibited an extremely high activity in the gasification of some low rank coals at a temp. as low as 750 K. Approx. 85% of Yallourn coal was converted within 30 min in steam at 773 K. A high Ni loading (>4 wt.%) was necessary. It seems essential for high-O low-S coal to be gasified in this manner. O-contg. functional groups on the coal surface seemed to play an important role in keeping the Ni catalysts in a finely dispersed state. H2S was strongly adsorbed on the Ni catalyst and retarded this reaction. H and CO2 were the main products of low-temp. steam gasification. Similar low-temp. gasification reactions were also obsd. in H and in CO2.
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7
Ohtsuka, Y.; Tomita, A.; Tamai, Y. Catalysis of nickel in low temperature gasification of brown coal. Appl. Catal. 1986, 28, 105– 117, DOI: 10.1016/S0166-9834(00)82496-3
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7
Catalysis of nickel in low temperature gasification of brown coal
Ohtsuka, Yasuo; Tomita, Akira; Tamai, Yasukatsu
Applied Catalysis (1986), 28 (1-2), 105-17CODEN: APCADI; ISSN:0166-9834.
The low-temp. gasification of brown coal in the presence of a Ni catalyst was investigated. The Ni catalyst exhibited an extremely high activity in the gasification both with steam and in H at 773-873 K. The activity depended strongly on the kind of starting Ni salts for both gasifying agents. It correlated with the dispersivity of metallic Ni at the devolatilization stage of coal. The presence of O-contg. functional groups such as carboxyl group in the step of catalyst impregnation was essential for the formation of finely dispersed Ni. The catalytic activity of Ni in steam was increased markedly by K but decreased by Ca.
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Tomita, A.; Watanabe, Y.; Takarada, T.; Ohtsuka, Y.; Tamai, Y. Nickel-catalysed gasification of brown coal in a fluidized bed reactor at atmospheric pressure. Fuel 1985, 64, 795– 800, DOI: 10.1016/0016-2361(85)90012-2
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8
Nickel-catalyzed gasification of brown coal in a fluidized bed reactor at atmospheric pressure
Tomita, Akira; Watanabe, Yoshihiko; Takarada, Takayuki; Ohtsuka, Yasuo; Tamai, Yasukatsu
Fuel (1985), 64 (6), 795-800CODEN: FUELAC; ISSN:0016-2361.
Pyrolysis and steam gasification of Ni-loaded Yallourn coal were carried out in a fluidized-bed reactor at ambient pressure. Pyrolysis was influenced by addn. of Ni catalyst. The yield of total volatile matter decreased whereas the gas yield markedly increased, when compared with uncatalyzed pyrolysis. This is due to tar decompg. on the catalyst and being converted to gases and deposited C. For the catalyzed steam gasification, ∼80 wt.% coal conversion was obtained at 873 K and the gas yield was 12 times that for the uncatalyzed reaction. The homogeneous equil. in the gas phase controlled the compn. of the product gas. The product gas contained little tarry material and a negligible amt. of H2S. Ni was efficiently recovered from the residue by an NH3-leaching method.
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9
Nahas, N. C. Exxon catalytic coal gasification process: Fundamental to flowsheets. Fuel 1983, 62, 239– 241, DOI: 10.1016/0016-2361(83)90207-7
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9
Exxon catalytic coal gasification process. Fundamentals to flowsheets
Nahas, N. C.
Fuel (1983), 62 (2), 239-41CODEN: FUELAC; ISSN:0016-2361.
A review with 4 refs. Basic features of the reaction kinetics of K-catalyzed coal gasification are presented. How small-scale data were used for the conceptual design of large fluidized-bed gasifiers is described. Other subjects discussed are how K was chosen from among the alkali metals and the importance of the methanation and steam conversion reactions.
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10
Jüntgen, H. Application of catalysts to coal gasification processes. Incentives and perspectives. Fuel 1983, 62, 234– 238, DOI: 10.1016/0016-2361(83)90206-5
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10
Application of catalysts to coal gasification processes. Incentives and perspectives
Juentgen, Harald
Fuel (1983), 62 (2), 234-8CODEN: FUELAC; ISSN:0016-2361.
The state of reaction kinetics of the noncatalyzed and catalyzed steam-C reaction as the basic coal gasification reaction (e.g., in moving-bed, fluidized-bed, and entrained-bed reactors) is discussed. Catalysts only affect gasification rates in the temp. range of chem. reaction or pore diffusion control. Furthermore, increase in rates by catalysts can also be reached without using catalysts. Therefore, the application of catalysts seems not to be attractive in conventional gasification processes because advantages (less coal and O consumption and lower heat losses) are compensated by disadvantages (addnl. costs, side effects). Only for processes in which a temp. increase is limited for different reasons does the application of catalysts have significant advantages. Such processes are allothermal gasification using nuclear heat and processes leading to synthetic natural gas.
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11
Mathews, J. P.; Chaffee, A. L. The molecular representations of coal - A review. Fuel 2012, 96, 1– 14, DOI: 10.1016/j.fuel.2011.11.025
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11
The molecular representations of coal - A review
Mathews, Jonathan P.; Chaffee, Alan L.
Fuel (2012), 96 (), 1-14CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
A review. Between 1942 and 2010 there were >134 proposed mol. level representations (models) of coal. While they spanned the rank range, bituminous representations are the bulk, with far fewer lignite, and very few subbituminous or anthracite representations. They have transitioned from predominantly 2D pen and paper drawings into 3D computational structures, and have recently increased in complexity, and to a limited degree, in scale. Advances in anal. techniques as well as modeling software, and computation power have resulted in improved partial representations of coal structure. Computer aided design has helped to overcome some of the challenges in model construction for a few models. Yet generally it is the capturing of the constitution of coal that remains elusive. Evaluation of phys. parameters and behavior observations has aided our confidence in the representations but models are typically generated for a specific use. No model has faced the gambit of "tests".
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12
Chen, S. G.; Yang, R. T. The active surface species in alkali-catalyzed carbon gasification: phenolate (C-O-M) groups vs clusters (particles). J. Catal. 1993, 141, 102– 113, DOI: 10.1006/jcat.1993.1122
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12
The active surface species in alkali-catalyzed carbon gasification: phenolate (C-O-M) groups vs clusters (particles)
Chen, S. G.; Yang, R. T.
Journal of Catalysis (1993), 141 (1), 102-13CODEN: JCTLA5; ISSN:0021-9517.
The activities and catalytic roles of different species of K in the gasification reactions of graphite by H2O and CO2 were investigated, using TEM techniques to measure the rates of monolayer edge recession (uncatalyzed and C-O-K catalyzed) and rates of monolayer channeling (catalyzed by particles) on the basal plane of graphite reacting with 21 torr H2O at 700°. The turnover frequencies for carbon gasification were 0.08/s (uncatalyzed), 0.15/s (catalyzed by C-O-K groups), and 7.8/s (catalyzed by particles). TGA and literature results using mixts. of carbon and alkali salts showed a sigmoidal dependence of gasification rates on catalyst loading, which is a result of catalyst dispersion and competition between the C-O-K groups and alkali particles. A CNDO semi-empirical MO calcn. was performed on model graphite substrates with -O and -O-K groups bonded to the {101l} zigzag face and {112l} armchair face. On the zigzag face, the carbon atom bridging two C-O-K groups gains a large neg. charge (-0.486) and hence is a favorable site for binding an O atom. The surface C-C bonds in this structure are substantially weakened by adding O atoms on the bridging C atoms, leading to CO release. The O atoms are supplied by the dissocn. of H2O and CO2. The possible reason for the alkali particles being more active than the C-O-M (M = alkali) groups is that the particles can dissoc. H2O and CO2 at higher rates, by providing either more active sites or higher activities. The CNDO results also predict that the C-O-K groups have an inhibiting effect on the armchair face; an inhibiting effect has indeed been obsd. earlier.
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Kumagai, H.; Hayashi, J.; Chiba, T.; Nakamura, K. Change in physical and chemical characteristics of brown coal along with a progress of moisture release. In: Abstracts of papers of the American Chemical Society, vol. 218. American Chemical Society: Washington, DC, 1999; pp U611- U611
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14
Given, P. H. The Distribution of Hydrogen in Coal and Its Relation to Coal Structure. Fuel 1960, 39, 147– 153
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14
The distribution of hydrogen in coals and its relation to coal structure
Given, P. H.
(1960), 39 (), 147-53 ISSN:.
Estimates of the ratio (C-Haromatic)/(C-Haliphatic) obtained by methods of infrared and proton magnetic resonance spectroscopy are examd. The ratio is important because if the estd. values are correct the no. of types of structure that can be assigned to the vitrinites of bituminous coals is severely limited. A no. of possible mol. models are considered. A polymeric structure is suggested (and illustrated) in which the hydrocarbon structure of the monomer is of a type that can have the correct analysis for typical vitrinites and H ratios equal to or slightly higher than those estd. by Brown (CA 49, 9255eh) with infrared spectroscopic methods. A model structure is shown to illustrate 1 way in which such monomer units can be linked together and substituted with O groups. The probable properties of the model are compared with those observed for vitrinite, and it is concluded that they correspond reasonably closely in several respects.
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15
Vu, T.; Chaffee, A.; Yarovsky, I. Investigation of lignin-water interactions by molecular simulation. Mol. Simul. 2002, 28, 981– 991, DOI: 10.1080/089270204000002610
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15
Investigation of lignin-water interactions by molecular simulation
Vu, Tham; Chaffee, Alan; Yarovsky, Irene
Molecular Simulation (2002), 28 (10-11), 981-991CODEN: MOSIEA; ISSN:0892-7022. (Taylor & Francis Ltd.)
The results of mol. dynamics simulations of 3 lignin-water systems are presented. Static and dynamic properties of each system are compared to a benchmark system consisting entirely of water mols. The significantly decreased mobility of water mols. local to lignin OH regions is attributed to hydrogen bond formation, whereas the slightly decreased mobility of water mols. in the vicinity of lignin methoxy groups results from a hydrophobic effect that causes water mols. to structure themselves around these groups. The av. diffusion of water in each system correlates with the no. of methoxy groups present in the system. As the no. of methoxy groups in the system increases, so too does the av. diffusion const. of water in that system. The bulky methoxy groups obstruct water from accessing lignin OH regions where hydrogen bond formation is anticipated and the hydrogen-bonded water lowers the av. diffusion const.
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Gao, Z.; Ding, Y.; Yang, W.; Han, W. DFT study of water adsorption on lignite molecule surface. J. Mol. Model. 2017, 23, 27, DOI: 10.1007/s00894-016-3194-7
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16
DFT study of water adsorption on lignite molecule surface
Gao Zhengyang; Ding Yi; Yang Weijie; Han Wentao
Journal of molecular modeling (2017), 23 (1), 27 ISSN:.
High moisture content is a main characteristic of low-rank coal, such as lignite. Numerous oxygen containing functional groups in lignite make it represent some special properties, and these functional groups affect the adsorption mechanisms of water molecules on lignite surface. This study reports some typical water · · · lignite conformations, along with a detailed analysis of the geometry, electrostatic potential distribution, reduced density gradient of interaction, and interaction energy decomposition. The results show that water molecules tend to aggregate around functional groups, and hydrogen bonds play a dominant role in the interaction. The adsorption energy of water cluster on lignite surface is larger than that of isolated water molecule, a good linear relationship between the interaction distance and adsorption energy of layers has been found. Since water is a polar molecule, the local minima and maxima of electrostatic potential in conformations increase along with more water adsorbing on lignite surface. Reduced density gradient analysis shows that H-bonds, van der Waals interaction, and a little steric make up the interaction between water cluster and lignite molecule. In these studied conformations which mainly are H-bond complexes, electrostatic and exchange repulsion play a dominant role, whereas polarization and dispersion make relatively small contribution to the interaction. Attractive and repulsive interaction both affect the stability of water · · · lignite conformations.
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Tsubouchi, N.; Mochizuki, Y.; Byambajav, E.; Hanaoka, Y.; Kikuchi, T.; Ohtsuka, Y. Steam gasification of low-rank coals with ion-exchanged sodium catalysts prepared using natural soda ash. Energy Fuels 2017, 31, 2565– 2571, DOI: 10.1021/acs.energyfuels.6b02905
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Steam Gasification of Low-Rank Coals with Ion-Exchanged Sodium Catalysts Prepared Using Natural Soda Ash
Tsubouchi, Naoto; Mochizuki, Yuuki; Byambajav, Enkhsaruul; Hanaoka, Yuu; Kikuchi, Takemitsu; Ohtsuka, Yasuo
Energy & Fuels (2017), 31 (3), 2565-2571CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
Ion-exchange reactions of brown and sub-bituminous coals with natural soda ash, composed of >99% Na2CO3, have been studied at 20-40 °C without any pH-adjusting reagents, and the pyrolysis and subsequent steam gasification of the resulting Na+-exchanged coals have been conducted using a fixed-bed quartz reactor at 700 °C. When the Na+ concn. and pH of an aq. mixt. of coal and soda ash are monitored during the ion-exchange process, both values decrease at a greater rate with brown coal with a higher content of COOH groups, indicating that ion exchange of Na+ with H+ of the COOH group is the predominant process. About 65% of COOH can be exchanged with Na+ ions under optimal conditions, irresp. of the coal type. The reactivity of these raw coals in steam at 700 °C is similar, with char conversions of less than 20 mass %, even after 2 h of reaction. Exchanged Na promoted the gasification of both coals at this temp., but the rate profiles were different: conversion of brown coal increased linearly with time and reached nearly 100% at 1 h, whereas sub-bituminous coal needed approx. 2 h to be gasified completely. The temp. dependence of the conversion with this coal revealed that the use of a Na catalyst can lower the reaction temp. by about 120 °C, and the apparent activation energies were estd. to be 190 and 120 kJ/mol without and with the catalyst, resp., from Arrhenius plots of the initial specific rate. The SEM-electron probe microanal. and X-ray diffraction anal. of Na-contg. chars recovered after pyrolysis and gasification suggested that the Na catalysts were finely dispersed at the initial stage of the reaction but that they may be deactivated by the formation of sodium silicates at high char conversions at temps. higher than 90%, even at the low temp. of 700 °C.
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Murata, S.; Miura, M.; Nomura, M.; Takanohashi, T.; Iino, M.; kumagai, H.; Sanada, Y.; Nakamura, K. Application of computer chemistry to the study of coal chemical structure. J. Jpn. Inst. Energy. 1995, 74, 342– 351
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There is no corresponding record for this reference.
19
Isoda, T.; Takagi, H.; Saiki, H.; Kusakabe, K.; Morooka, S. Analysis for initial stage reaction of coal pyrolysis by molecular orbital calculation. J. Jpn. Inst. Energy. 2000, 79, 511– 521, DOI: 10.3775/jie.79.511
[Crossref], [CAS], Google Scholar
19
Analysis for initial stage reaction of coal pyrolysis by molecular orbital calculation
Isoda, Takaaki; Takagi, Hideyuki; Sajki, Hideharu; Kusakabe, Katsuki; Morooka, Shigeharu
Nippon Enerugi Gakkaishi (2000), 79 (6), 511-521CODEN: NENGEM; ISSN:0916-8753. (Nippon Enerugi Gakkai)
Coals with carbon contents of 60-80% daf were pyrolyzed using a Curie point pyrolyzer at 764-1,040° for 5 s. In order to explain the effect of coal ranks on product distribution, the cleaving energies of the unit structures of coal were estd. by a reaction coordinate anal. based on the MO calcn. using the WinMOPAC program. The coal pyrolysis reactivity and product distributions were then discussed on the basis of the cleaving energies of the unit structures.
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Nabatame, T.; Ohtsuka, Y.; Takarada, T.; Tomita, A. Steam gasification of brown coal impregnated with calcium hydroxide. J. Fuel Soc. Jpn. 1986, 65, 53– 58, DOI: 10.3775/jie.65.53
[Crossref], [CAS], Google Scholar
20
Steam-gasification of brown coal with calcium hydroxide catalyst
Nabatame, Toshihide; Ohtsuka, Yasuo; Takarada, Takayuki; Tomita, Akira
Nenryo Kyokaishi (1986), 65 (1), 53-8CODEN: NENKAU; ISSN:0369-3775.
In the steam gasification of Australian Yallourn coal impregnated with Ca(OH)2, the conversion increased with the amt. of impregnated Ca(OH)2 up to 1.5 wt.% concn.. Ion-exchanged Ca was transformed to finely dispersed CaCO3 upon pyrolysis and extensive crystal growth of CaCO3 was obsd. during the steam gasification. Near the end of gasification, CaCO3 was converted to CaO due to the decrease of CO2 content in the atm.
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21
Spartan’ 16 for windows; Wavefunction, Inc. Spartan16Manual, https://www.wavefun.com/.
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There is no corresponding record for this reference.
22
Mulliken, R. S. Electronic Population Analysis on LCAO-MO Molecular Wave Functions. I. J. Chem. Phys. 1955, 23, 1833– 1840, DOI: 10.1063/1.1740588
[Crossref], [CAS], Google Scholar
22
Electronic population analysis on LCAO-MO [linear combination of atomic orbital-molecular orbital] molecular wave functions. I
Mulliken, R. S.
Journal of Chemical Physics (1955), 23 (), 1833-40CODEN: JCPSA6; ISSN:0021-9606.
An analysis in quant. form was given in terms of breakdowns of the electronic population into partial and total "gross at. populations," or into partial and total "net at. populations" together with "overlap populations." Gross at. populations distribute the electrons almost perfectly among the various at. orbitals of the various atoms in the mol. From these nos., a definite figure is obtained for the amt. of promotion (e.g. from 2s to 2p) in each atom; and also for the gross charge Q on each atom if the bonds are polar. The total overlap population for any pair of atoms in a mol. is in general made up of pos. and neg. contributions. If the total overlap population between 2 atoms is pos., they are bonded; if neg., they are antibonded. Tables of gross at. populations and overlap populations were calcd. for CO and H2O. The amt. of s-p promotion was nearly the same for the O atom in CO and in H2O (0.14 electron in CO and 0.15e in H2O). For the C atom in CO it is 0.50e. For the N atom in N2 it is 0.26e. In spite of very strong polarity in the π bonds in CO, the σ and π overlap populations are very similar to those in N. In CO the total overlap population for the π electrons is about twice that for the σ electrons. The most easily ionized electrons of CO are in a mol. orbital such that its gross at. population is 94% localized on the C atom; these electrons account for the weak electron donor properties of CO.
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Löwdin, P.-O. Quantum Theory of Many-Particle Systems. I. Physical Interpretations by Means of Density Matrices, Natural Spin-Orbitals, and Convergence Problems in the Method of Configurational Interaction. Phys. Rev. 1955, 97, 1474– 1489, DOI: 10.1103/PhysRev.97.1474
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There is no corresponding record for this reference.
24
Halgren, T. A. Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94. J. Comput. Chem. 1996, 17, 490– 519, DOI: 10.1002/(SICI)1096-987X(199604)17:5/6<490::AID-JCC1>3.0.CO;2-P
[Crossref], [CAS], Google Scholar
24
Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94
Halgren, Thomas A.
Journal of Computational Chemistry (1996), 17 (5 & 6), 490-519CODEN: JCCHDD; ISSN:0192-8651. (Wiley)
This article introduces MMFF94, the initial published version of the Merck mol. force field (MMFF). It describes the objectives set for MMFF, the form it takes, and the range of systems to which it applies. This study also outlines the methodol. employed in parameterizing MMFF94 and summarizes its performance in reproducing computational and exptl. data. Though similar to MM3 in some respects, MMFF94 differs in ways intended to facilitate application to condensed-phase processes in mol.-dynamics simulations. Indeed, MMFF94 seeks to achieve MM3-like accuracy for small mols. in a combined "org./protein" force field that is equally applicable to proteins and other systems of biol. significance. A second distinguishing feature is that the core protion of MMFF94 has primarily been derived from high-quality computational data-ca. 500 mol. structures optimized at the HF/6-31G* level, 475 structures optimized at the MP2/6-31G* level, 380 MP2/6-31* structures evaluated at a defined approxn. to the MP4SDQ/TZP level, and 1450 structures partly derived from MP2/6-31G* geometries and evaluated at the MP2/TZP level. A third distinguishing feature is that MMFF94 has been parameterized for a wide variety of chem. systems of interest to org. and combinations of functional groups for which little, if any, useful exptl. data are available. The methodol. used in parameterizing MMFF94 represents a fourth distinguishing feature. Rather than using the common "functional group" approach, nearly all MMFF parameters have been detd. in a mutually consistent fashion from the full set of available computational data. MMFF94 reproduces the computational data used in its parameterization very well. In addn., MMFF94 reproduces exptl. bond lengths (0.014 Å root mean square [rms]), bond angles (1.2° rms), vibrational frequencies (61 cm-1 rms), conformational energies (0.38 kcal/mol rms), and rotational barriers (0.39 kcal/mol rms) very nearly as well as does MM3 for comparable systems. MMFF94 also describes intermol. interactions in hydrogen-bonded systems in a way that closely parallels that given by the highly regarded OPLS force field.
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25
Szabo, A.; Ostlund, N. S. Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory; Courier Corporation 1996, ISBN 0–486–69186-1.
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There is no corresponding record for this reference.
26
Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648– 5652, DOI: 10.1063/1.464913
[Crossref], [CAS], Google Scholar
26
Density-functional thermochemistry. III. The role of exact exchange
Becke, Axel D.
Journal of Chemical Physics (1993), 98 (7), 5648-52CODEN: JCPSA6; ISSN:0021-9606.
Despite the remarkable thermochem. accuracy of Kohn-Sham d.-functional theories with gradient corrections for exchange-correlation, the author believes that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional (contg. local-spin-d., gradient, and exact-exchange terms) is tested for 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total at. energies of first- and second-row systems. This functional performs better than previous functionals with gradient corrections only, and fits expt. atomization energies with an impressively small av. abs. deviation of 2.4 kcal/mol.
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Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem. 1994, 98, 11623– 11627, DOI: 10.1021/j100096a001
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27
Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields
Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J.
Journal of Physical Chemistry (1994), 98 (45), 11623-7CODEN: JPCHAX; ISSN:0022-3654.
The unpolarized absorption and CD spectra of the fundamental vibrational transitions of the chiral mol. 4-methyl-2-oxetanone are calcd. ab initio. Harmonic force fields are obtained using d. functional theory (DFT), MP2 and SCF methodologies, and a [5s4p2d/3s2p] (TZ2P) basis set. DFT calcns. use the LSDA, BLYP, and Becke3LYP (B3LYP) d. functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with expt. The MP2 force field yields spectra in slightly worse agreement with expt. than the B3LYP force field. The SCF force field yields spectra in poor agreement with expt. The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreement with expt.
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Ronnachai Tipo, Chatchawan Chaichana, Reiji Noda, Suparin Chaiklangmuang. Influence of coal treatments on the Ni loading mechanism of Ni-loaded lignite char catalysts. RSC Advances 2021, 11 (56) , 35624-35643. https://doi.org/10.1039/D1RA05046J

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Abstract
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Figure 1
Figure 1. Model structure of Yallourn low-rank coal.
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Figure 2
Figure 2. Number and location of sodium exchange for low-rank coal.
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Figure 3
Figure 3. Relationship between the number of Na⁺ and total energy using RHF/6-311G*.
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Figure 4
Figure 4. Relationship between the number of Na⁺ and total energy using B3LYP/6-31G*.
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Figure 5
Figure 5. Relationship between the number of Na⁺ and electrostatic potential map using RHF/6-311G*.
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Figure 6
Figure 6. Relationship between the number of Na⁺ and electrostatic potential map using B3LYP/6-31G*.
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Figure 7
Figure 7. Mulliken bond orders using RHF/6-311G*.
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Figure 8
Figure 8. Löwdin bond orders using RHF/6-311G*.
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Figure 9
Figure 9. Mulliken bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond order of raw coal; blue letters indicate increased bond orders by 0.05 or more).
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Figure 10
Figure 10. Löwdin bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond order of raw coal; blue letters indicate increased bond orders by 0.05 or more).
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Figure 11
Figure 11. Mulliken bond orders of the original raw low-rank coal using B3LYP-6-31G* and the relationship between bond distance and total energy (calculation was performed to separate bond A from 1.410 to 5.410 Å in 20 steps).
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Figure 12
Figure 12. Mulliken bond orders of the model (2Na-1) using B3LYP/6-31G* and the relationship between bond distance and total energy (calculation was performed to separate bond A from 1.425 to 5.425 Å in 20 steps).
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Figure 13
Figure 13. Comparisons between the number of Na⁺ and Mulliken bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).
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Figure 14
Figure 14. Comparisons between the number of Na⁺ and Löwdin bond orders using RHF/6-311G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).
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Figure 15
Figure 15. Comparisons between the number of Na⁺ and Mulliken bond orders using B3LYP/6-31G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).
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Figure 16
Figure 16. Comparisons between the number of Na⁺ and Löwdin bond orders using B3LYP/6-31G* (red letters indicate increased bond orders of Na⁺-exchanged coal by 0.05 or less, relative to the bond orders of raw coal; blue letters indicate increased bond orders by 0.05 or more).
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This article references 27 other publications.
1. 1
  Zhang, Y.; Schauer, J. J.; Zhang, Y.; Zeng, L.; Wei, Y.; Liu, Y.; Shao, M. Characteristics of particulate carbon emissions from realworld Chinese coal combustion. Environ. Sci. Technol. 2008, 42, 5068– 5073, DOI: 10.1021/es7022576
  [ACS Full Text ], [CAS], Google Scholar
  1
  Characteristics of Particulate Carbon Emissions from Real-World Chinese Coal Combustion
  Zhang, Yuanxun; Schauer, James Jay; Zhang, Yuanhang; Zeng, Limin; Wei, Yongjie; Liu, Yuan; Shao, Min
  Environmental Science & Technology (2008), 42 (14), 5068-5073CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
  Particulate matter emissions from different Chinese coal combustion systems were collected and analyzed for elemental and org. C (EC, OC), and mol. markers. Emissions from industrial boilers and residential stoves were examd. Coal included anthracite, bituminous, brown, and commonly used Chinese coal briquettes produced for residential combustion. Results showed significant differences in the contribution of carbonaceous species to particulate mass emissions. Industrial boilers had much higher C burn-out, yielding particulate emissions with much lower OC, EC, and speciated org. compd. concns.; residential stoves had significantly higher carbonaceous particulate emissions with rates ∼100 times greater than industrial boilers. Quantified org. compds. emitted from industrial boilers were dominated by oxygenated compds., of which 46-68% were org. acids; the dominant species quantified in residential stove emissions were polycyclic arom. hydrocarbons (PAH, 38%) and n-alkanes (20%). An important observation was that PAH emission factors and hopanoid distribution were different than those emissions from industrial and residential coal combustion, even when the same coal was burned. Although particulate matter emissions by industrial and residential combustion were different, picene was detected in all samples with detectable OC mass concns., supporting the use of this org. tracer for OC from all types of coal combustion. 17α(H),21β(H)-29-norhopane was the predominant hopanoid in coal combustion emissions, which was different from mobile source emissions and may be used to distinguish emissions from different fossil fuel sources.
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2. 2
  Thielemann, T.; Schmidt, S.; Peter Gerling, J. Lignite and hard coal: energy suppliers for world needs until the year 2100—An outlook. Int. J. Coal Geol. 2007, 72, 1– 14, DOI: 10.1016/j.coal.2007.04.003
  [Crossref], [CAS], Google Scholar
  2
  Lignite and hard coal: Energy suppliers for world needs until the year 2100 - an outlook
  Thielemann, Thomas; Schmidt, Sandro; Gerling, J. Peter
  International Journal of Coal Geology (2007), 72 (1), 1-14CODEN: IJCGDE; ISSN:0166-5162. (Elsevier B.V.)
  For three years, international hard coal prices have been at rather expensive levels. Some argue that these higher prices might indicate the threat of a phys. scarcity of fossil fuels - similar to the situation with oil and gas. This is not true. The supply situations with lignite and hard coal appear to be largely not crit. Adjusted to the rise in global coal consumption, which is expected until 2100, nature by and large can meet the world's coal demand. This is shown for lignite in this article and it is illustrated for hard coal here, differentiated in space and time for a world divided into eight regions and viewed for the years 2005, 2020, 2030, 2050, and 2100. The only area of potential concern is Asia (esp. China). But today's and coming eager efforts in China to convert coal resources into reserves will most likely deliver the coal needed for the Chinese market. Up to the year 2100, and from a geoscientific point of view, there will be no bottleneck in coal supplies on this planet.
  >> More from SciFinder ^®
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3. 3
  Jia, R.; Harris, G. H.; Fuerstenau, D. W. An improved class of universal collectors for the flotation of oxidized and / or low-rank coal. Int. J. Miner. Process. 2000, 58, 99– 118, DOI: 10.1016/S0301-7516(99)00024-1
  [Crossref], [CAS], Google Scholar
  3
  An improved class of universal collectors for the flotation of oxidized and/or low-rank coal
  Jia, R.; Harris, G. H.; Fuerstenau, D. W.
  International Journal of Mineral Processing (2000), 58 (1-4), 99-118CODEN: IJMPBL; ISSN:0301-7516. (Elsevier Science B.V.)
  Ash minerals, including pyrite, can be sepd. from coal by flotation, primarily making use of the natural hydrophobicity of the carbonaceous matter in coal. However, to overcome the deleterious effect of oxygen functional groups on the coal surface, an org. collector is required. The most common industrial coal flotation collector is fuel oil, but the addn. of oxygenated functional groups to the collector mol. markedly enhances the flotation of lower rank and oxidized coals. This paper summarizes the results of detailed study of the flotation response of two high-sulfur coals, Illinois No. 6 coal and Pittsburgh No. 8, using different nonionic oxygenated surfactants as the collector. The performance of these reagents is compared with that of two oily collectors, namely dodecane and nonylbenzene, and mechanisms for the interaction of these compds. with coal are suggested.
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4. 4
  Tahmasebi, A.; Yu, J.; Han, Y.; Zhao, H.; Bhattacharya, S. Thermogravimetric study and modeling for the drying of a Chinese lignite. Asia-Pac. J. Chem. Eng. 2013, 8, 793– 803, DOI: 10.1002/apj.1722
  [Crossref], [CAS], Google Scholar
  4
  Thermogravimetric study and modeling for the drying of a Chinese lignite
  Tahmasebi, Arash; Yu, Jianglong; Han, Yanna; Zhao, Huan; Bhattacharya, Sankar
  Asia-Pacific Journal of Chemical Engineering (2013), 8 (6), 793-803CODEN: AJCEBK; ISSN:1932-2135. (John Wiley & Sons Ltd.)
  Study of drying characteristics and kinetics of coal is necessary in order to optimize drying operation and design a dryer in industrial scale. Drying characteristics of Chinese lignite was investigated exptl. using thermogravimetric method, and the effect of drying variables on drying rate was systematically studied. For CFD modeling and scale-up purposes, it is useful to have an algebraic equation that describes the drying process of lignite. Therefore, different thin layer drying models given in the literature were employed to analyze coal drying kinetics under different conditions. During studying the consistency of all the models, statistical tests such as χ2, residual sum of squares (RSS), F-value, and the coeff. of detn. R2 were employed. It was found that the Midilli-Kucuk model best describes the drying process within 99.9% accuracy. The effects of drying temp. and coal sample wt. on the consts. and coeffs. of the selected model were also studied by multiple regression anal. Apparent diffusion coeff. of moisture from sample was calcd. using the exptl. kinetics data. Higher drying temps. and smaller sample wts. resulted in higher diffusion coeff., which was consistent with exptl. data. Activation energy of moisture evapn. calcd. from Arrhenius equation for drying process was 21.17 kJ/mol. The selected algebraic drying model can be used for CFD modeling during scale-up of drying facility for industrial applications. © 2013 Curtin University of Technol. and John Wiley & Sons, Ltd.
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5. 5
  Tomita, A.; Tamai, Y. Low-temperature gasification of Yallourn coal catalysed by nickel. Fuel 1981, 60, 992– 994, DOI: 10.1016/0016-2361(81)90099-5
  [Crossref], [CAS], Google Scholar
  5
  Low-temperature gasification of Yallourn coal catalyzed by nickel
  Tomita, Akira; Tamai, Yasukatsu
  Fuel (1981), 60 (10), 992-4CODEN: FUELAC; ISSN:0016-2361.
  Ni catalyst enhanced the gasification of the Yallourn coal in a similar manner obsd. for activated C. At present the mechanism of this high activity is unclear, but the following characteristics of this coal might account for this activity: porosity, S content, functional groups, maceral compn., ash yield, and ash components.
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6. 6
  Tomita, A.; Ohtsuka, Y.; Tamai, Y. Low-temperature gasification of brown coals catalysed by nickel. Fuel 1983, 62, 150– 154, DOI: 10.1016/0016-2361(83)90187-4
  [Crossref], [CAS], Google Scholar
  6
  Low-temperature gasification of brown coals catalyzed by nickel
  Tomita, Akira; Ohtsuka, Yasuo; Tamai, Yasukatsu
  Fuel (1983), 62 (2), 150-4CODEN: FUELAC; ISSN:0016-2361.
  Ni catalysts exhibited an extremely high activity in the gasification of some low rank coals at a temp. as low as 750 K. Approx. 85% of Yallourn coal was converted within 30 min in steam at 773 K. A high Ni loading (>4 wt.%) was necessary. It seems essential for high-O low-S coal to be gasified in this manner. O-contg. functional groups on the coal surface seemed to play an important role in keeping the Ni catalysts in a finely dispersed state. H2S was strongly adsorbed on the Ni catalyst and retarded this reaction. H and CO2 were the main products of low-temp. steam gasification. Similar low-temp. gasification reactions were also obsd. in H and in CO2.
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7. 7
  Ohtsuka, Y.; Tomita, A.; Tamai, Y. Catalysis of nickel in low temperature gasification of brown coal. Appl. Catal. 1986, 28, 105– 117, DOI: 10.1016/S0166-9834(00)82496-3
  [Crossref], [CAS], Google Scholar
  7
  Catalysis of nickel in low temperature gasification of brown coal
  Ohtsuka, Yasuo; Tomita, Akira; Tamai, Yasukatsu
  Applied Catalysis (1986), 28 (1-2), 105-17CODEN: APCADI; ISSN:0166-9834.
  The low-temp. gasification of brown coal in the presence of a Ni catalyst was investigated. The Ni catalyst exhibited an extremely high activity in the gasification both with steam and in H at 773-873 K. The activity depended strongly on the kind of starting Ni salts for both gasifying agents. It correlated with the dispersivity of metallic Ni at the devolatilization stage of coal. The presence of O-contg. functional groups such as carboxyl group in the step of catalyst impregnation was essential for the formation of finely dispersed Ni. The catalytic activity of Ni in steam was increased markedly by K but decreased by Ca.
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8. 8
  Tomita, A.; Watanabe, Y.; Takarada, T.; Ohtsuka, Y.; Tamai, Y. Nickel-catalysed gasification of brown coal in a fluidized bed reactor at atmospheric pressure. Fuel 1985, 64, 795– 800, DOI: 10.1016/0016-2361(85)90012-2
  [Crossref], [CAS], Google Scholar
  8
  Nickel-catalyzed gasification of brown coal in a fluidized bed reactor at atmospheric pressure
  Tomita, Akira; Watanabe, Yoshihiko; Takarada, Takayuki; Ohtsuka, Yasuo; Tamai, Yasukatsu
  Fuel (1985), 64 (6), 795-800CODEN: FUELAC; ISSN:0016-2361.
  Pyrolysis and steam gasification of Ni-loaded Yallourn coal were carried out in a fluidized-bed reactor at ambient pressure. Pyrolysis was influenced by addn. of Ni catalyst. The yield of total volatile matter decreased whereas the gas yield markedly increased, when compared with uncatalyzed pyrolysis. This is due to tar decompg. on the catalyst and being converted to gases and deposited C. For the catalyzed steam gasification, ∼80 wt.% coal conversion was obtained at 873 K and the gas yield was 12 times that for the uncatalyzed reaction. The homogeneous equil. in the gas phase controlled the compn. of the product gas. The product gas contained little tarry material and a negligible amt. of H2S. Ni was efficiently recovered from the residue by an NH3-leaching method.
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9. 9
  Nahas, N. C. Exxon catalytic coal gasification process: Fundamental to flowsheets. Fuel 1983, 62, 239– 241, DOI: 10.1016/0016-2361(83)90207-7
  [Crossref], [CAS], Google Scholar
  9
  Exxon catalytic coal gasification process. Fundamentals to flowsheets
  Nahas, N. C.
  Fuel (1983), 62 (2), 239-41CODEN: FUELAC; ISSN:0016-2361.
  A review with 4 refs. Basic features of the reaction kinetics of K-catalyzed coal gasification are presented. How small-scale data were used for the conceptual design of large fluidized-bed gasifiers is described. Other subjects discussed are how K was chosen from among the alkali metals and the importance of the methanation and steam conversion reactions.
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10. 10
  Jüntgen, H. Application of catalysts to coal gasification processes. Incentives and perspectives. Fuel 1983, 62, 234– 238, DOI: 10.1016/0016-2361(83)90206-5
  [Crossref], [CAS], Google Scholar
  10
  Application of catalysts to coal gasification processes. Incentives and perspectives
  Juentgen, Harald
  Fuel (1983), 62 (2), 234-8CODEN: FUELAC; ISSN:0016-2361.
  The state of reaction kinetics of the noncatalyzed and catalyzed steam-C reaction as the basic coal gasification reaction (e.g., in moving-bed, fluidized-bed, and entrained-bed reactors) is discussed. Catalysts only affect gasification rates in the temp. range of chem. reaction or pore diffusion control. Furthermore, increase in rates by catalysts can also be reached without using catalysts. Therefore, the application of catalysts seems not to be attractive in conventional gasification processes because advantages (less coal and O consumption and lower heat losses) are compensated by disadvantages (addnl. costs, side effects). Only for processes in which a temp. increase is limited for different reasons does the application of catalysts have significant advantages. Such processes are allothermal gasification using nuclear heat and processes leading to synthetic natural gas.
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11. 11
  Mathews, J. P.; Chaffee, A. L. The molecular representations of coal - A review. Fuel 2012, 96, 1– 14, DOI: 10.1016/j.fuel.2011.11.025
  [Crossref], [CAS], Google Scholar
  11
  The molecular representations of coal - A review
  Mathews, Jonathan P.; Chaffee, Alan L.
  Fuel (2012), 96 (), 1-14CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
  A review. Between 1942 and 2010 there were >134 proposed mol. level representations (models) of coal. While they spanned the rank range, bituminous representations are the bulk, with far fewer lignite, and very few subbituminous or anthracite representations. They have transitioned from predominantly 2D pen and paper drawings into 3D computational structures, and have recently increased in complexity, and to a limited degree, in scale. Advances in anal. techniques as well as modeling software, and computation power have resulted in improved partial representations of coal structure. Computer aided design has helped to overcome some of the challenges in model construction for a few models. Yet generally it is the capturing of the constitution of coal that remains elusive. Evaluation of phys. parameters and behavior observations has aided our confidence in the representations but models are typically generated for a specific use. No model has faced the gambit of "tests".
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12. 12
  Chen, S. G.; Yang, R. T. The active surface species in alkali-catalyzed carbon gasification: phenolate (C-O-M) groups vs clusters (particles). J. Catal. 1993, 141, 102– 113, DOI: 10.1006/jcat.1993.1122
  [Crossref], [CAS], Google Scholar
  12
  The active surface species in alkali-catalyzed carbon gasification: phenolate (C-O-M) groups vs clusters (particles)
  Chen, S. G.; Yang, R. T.
  Journal of Catalysis (1993), 141 (1), 102-13CODEN: JCTLA5; ISSN:0021-9517.
  The activities and catalytic roles of different species of K in the gasification reactions of graphite by H2O and CO2 were investigated, using TEM techniques to measure the rates of monolayer edge recession (uncatalyzed and C-O-K catalyzed) and rates of monolayer channeling (catalyzed by particles) on the basal plane of graphite reacting with 21 torr H2O at 700°. The turnover frequencies for carbon gasification were 0.08/s (uncatalyzed), 0.15/s (catalyzed by C-O-K groups), and 7.8/s (catalyzed by particles). TGA and literature results using mixts. of carbon and alkali salts showed a sigmoidal dependence of gasification rates on catalyst loading, which is a result of catalyst dispersion and competition between the C-O-K groups and alkali particles. A CNDO semi-empirical MO calcn. was performed on model graphite substrates with -O and -O-K groups bonded to the {101l} zigzag face and {112l} armchair face. On the zigzag face, the carbon atom bridging two C-O-K groups gains a large neg. charge (-0.486) and hence is a favorable site for binding an O atom. The surface C-C bonds in this structure are substantially weakened by adding O atoms on the bridging C atoms, leading to CO release. The O atoms are supplied by the dissocn. of H2O and CO2. The possible reason for the alkali particles being more active than the C-O-M (M = alkali) groups is that the particles can dissoc. H2O and CO2 at higher rates, by providing either more active sites or higher activities. The CNDO results also predict that the C-O-K groups have an inhibiting effect on the armchair face; an inhibiting effect has indeed been obsd. earlier.
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13. 13
  Kumagai, H.; Hayashi, J.; Chiba, T.; Nakamura, K. Change in physical and chemical characteristics of brown coal along with a progress of moisture release. In: Abstracts of papers of the American Chemical Society, vol. 218. American Chemical Society: Washington, DC, 1999; pp U611- U611
  Google Scholar
  There is no corresponding record for this reference.
14. 14
  Given, P. H. The Distribution of Hydrogen in Coal and Its Relation to Coal Structure. Fuel 1960, 39, 147– 153
  [CAS], Google Scholar
  14
  The distribution of hydrogen in coals and its relation to coal structure
  Given, P. H.
  (1960), 39 (), 147-53 ISSN:.
  Estimates of the ratio (C-Haromatic)/(C-Haliphatic) obtained by methods of infrared and proton magnetic resonance spectroscopy are examd. The ratio is important because if the estd. values are correct the no. of types of structure that can be assigned to the vitrinites of bituminous coals is severely limited. A no. of possible mol. models are considered. A polymeric structure is suggested (and illustrated) in which the hydrocarbon structure of the monomer is of a type that can have the correct analysis for typical vitrinites and H ratios equal to or slightly higher than those estd. by Brown (CA 49, 9255eh) with infrared spectroscopic methods. A model structure is shown to illustrate 1 way in which such monomer units can be linked together and substituted with O groups. The probable properties of the model are compared with those observed for vitrinite, and it is concluded that they correspond reasonably closely in several respects.
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15. 15
  Vu, T.; Chaffee, A.; Yarovsky, I. Investigation of lignin-water interactions by molecular simulation. Mol. Simul. 2002, 28, 981– 991, DOI: 10.1080/089270204000002610
  [Crossref], [CAS], Google Scholar
  15
  Investigation of lignin-water interactions by molecular simulation
  Vu, Tham; Chaffee, Alan; Yarovsky, Irene
  Molecular Simulation (2002), 28 (10-11), 981-991CODEN: MOSIEA; ISSN:0892-7022. (Taylor & Francis Ltd.)
  The results of mol. dynamics simulations of 3 lignin-water systems are presented. Static and dynamic properties of each system are compared to a benchmark system consisting entirely of water mols. The significantly decreased mobility of water mols. local to lignin OH regions is attributed to hydrogen bond formation, whereas the slightly decreased mobility of water mols. in the vicinity of lignin methoxy groups results from a hydrophobic effect that causes water mols. to structure themselves around these groups. The av. diffusion of water in each system correlates with the no. of methoxy groups present in the system. As the no. of methoxy groups in the system increases, so too does the av. diffusion const. of water in that system. The bulky methoxy groups obstruct water from accessing lignin OH regions where hydrogen bond formation is anticipated and the hydrogen-bonded water lowers the av. diffusion const.
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16. 16
  Gao, Z.; Ding, Y.; Yang, W.; Han, W. DFT study of water adsorption on lignite molecule surface. J. Mol. Model. 2017, 23, 27, DOI: 10.1007/s00894-016-3194-7
  [Crossref], [PubMed], [CAS], Google Scholar
  16
  DFT study of water adsorption on lignite molecule surface
  Gao Zhengyang; Ding Yi; Yang Weijie; Han Wentao
  Journal of molecular modeling (2017), 23 (1), 27 ISSN:.
  High moisture content is a main characteristic of low-rank coal, such as lignite. Numerous oxygen containing functional groups in lignite make it represent some special properties, and these functional groups affect the adsorption mechanisms of water molecules on lignite surface. This study reports some typical water · · · lignite conformations, along with a detailed analysis of the geometry, electrostatic potential distribution, reduced density gradient of interaction, and interaction energy decomposition. The results show that water molecules tend to aggregate around functional groups, and hydrogen bonds play a dominant role in the interaction. The adsorption energy of water cluster on lignite surface is larger than that of isolated water molecule, a good linear relationship between the interaction distance and adsorption energy of layers has been found. Since water is a polar molecule, the local minima and maxima of electrostatic potential in conformations increase along with more water adsorbing on lignite surface. Reduced density gradient analysis shows that H-bonds, van der Waals interaction, and a little steric make up the interaction between water cluster and lignite molecule. In these studied conformations which mainly are H-bond complexes, electrostatic and exchange repulsion play a dominant role, whereas polarization and dispersion make relatively small contribution to the interaction. Attractive and repulsive interaction both affect the stability of water · · · lignite conformations.
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17. 17
  Tsubouchi, N.; Mochizuki, Y.; Byambajav, E.; Hanaoka, Y.; Kikuchi, T.; Ohtsuka, Y. Steam gasification of low-rank coals with ion-exchanged sodium catalysts prepared using natural soda ash. Energy Fuels 2017, 31, 2565– 2571, DOI: 10.1021/acs.energyfuels.6b02905
  [ACS Full Text ], [CAS], Google Scholar
  17
  Steam Gasification of Low-Rank Coals with Ion-Exchanged Sodium Catalysts Prepared Using Natural Soda Ash
  Tsubouchi, Naoto; Mochizuki, Yuuki; Byambajav, Enkhsaruul; Hanaoka, Yuu; Kikuchi, Takemitsu; Ohtsuka, Yasuo
  Energy & Fuels (2017), 31 (3), 2565-2571CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
  Ion-exchange reactions of brown and sub-bituminous coals with natural soda ash, composed of >99% Na2CO3, have been studied at 20-40 °C without any pH-adjusting reagents, and the pyrolysis and subsequent steam gasification of the resulting Na+-exchanged coals have been conducted using a fixed-bed quartz reactor at 700 °C. When the Na+ concn. and pH of an aq. mixt. of coal and soda ash are monitored during the ion-exchange process, both values decrease at a greater rate with brown coal with a higher content of COOH groups, indicating that ion exchange of Na+ with H+ of the COOH group is the predominant process. About 65% of COOH can be exchanged with Na+ ions under optimal conditions, irresp. of the coal type. The reactivity of these raw coals in steam at 700 °C is similar, with char conversions of less than 20 mass %, even after 2 h of reaction. Exchanged Na promoted the gasification of both coals at this temp., but the rate profiles were different: conversion of brown coal increased linearly with time and reached nearly 100% at 1 h, whereas sub-bituminous coal needed approx. 2 h to be gasified completely. The temp. dependence of the conversion with this coal revealed that the use of a Na catalyst can lower the reaction temp. by about 120 °C, and the apparent activation energies were estd. to be 190 and 120 kJ/mol without and with the catalyst, resp., from Arrhenius plots of the initial specific rate. The SEM-electron probe microanal. and X-ray diffraction anal. of Na-contg. chars recovered after pyrolysis and gasification suggested that the Na catalysts were finely dispersed at the initial stage of the reaction but that they may be deactivated by the formation of sodium silicates at high char conversions at temps. higher than 90%, even at the low temp. of 700 °C.
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18. 18
  Murata, S.; Miura, M.; Nomura, M.; Takanohashi, T.; Iino, M.; kumagai, H.; Sanada, Y.; Nakamura, K. Application of computer chemistry to the study of coal chemical structure. J. Jpn. Inst. Energy. 1995, 74, 342– 351
  Google Scholar
  There is no corresponding record for this reference.
19. 19
  Isoda, T.; Takagi, H.; Saiki, H.; Kusakabe, K.; Morooka, S. Analysis for initial stage reaction of coal pyrolysis by molecular orbital calculation. J. Jpn. Inst. Energy. 2000, 79, 511– 521, DOI: 10.3775/jie.79.511
  [Crossref], [CAS], Google Scholar
  19
  Analysis for initial stage reaction of coal pyrolysis by molecular orbital calculation
  Isoda, Takaaki; Takagi, Hideyuki; Sajki, Hideharu; Kusakabe, Katsuki; Morooka, Shigeharu
  Nippon Enerugi Gakkaishi (2000), 79 (6), 511-521CODEN: NENGEM; ISSN:0916-8753. (Nippon Enerugi Gakkai)
  Coals with carbon contents of 60-80% daf were pyrolyzed using a Curie point pyrolyzer at 764-1,040° for 5 s. In order to explain the effect of coal ranks on product distribution, the cleaving energies of the unit structures of coal were estd. by a reaction coordinate anal. based on the MO calcn. using the WinMOPAC program. The coal pyrolysis reactivity and product distributions were then discussed on the basis of the cleaving energies of the unit structures.
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20. 20
  Nabatame, T.; Ohtsuka, Y.; Takarada, T.; Tomita, A. Steam gasification of brown coal impregnated with calcium hydroxide. J. Fuel Soc. Jpn. 1986, 65, 53– 58, DOI: 10.3775/jie.65.53
  [Crossref], [CAS], Google Scholar
  20
  Steam-gasification of brown coal with calcium hydroxide catalyst
  Nabatame, Toshihide; Ohtsuka, Yasuo; Takarada, Takayuki; Tomita, Akira
  Nenryo Kyokaishi (1986), 65 (1), 53-8CODEN: NENKAU; ISSN:0369-3775.
  In the steam gasification of Australian Yallourn coal impregnated with Ca(OH)2, the conversion increased with the amt. of impregnated Ca(OH)2 up to 1.5 wt.% concn.. Ion-exchanged Ca was transformed to finely dispersed CaCO3 upon pyrolysis and extensive crystal growth of CaCO3 was obsd. during the steam gasification. Near the end of gasification, CaCO3 was converted to CaO due to the decrease of CO2 content in the atm.
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21. 21
  Spartan’ 16 for windows; Wavefunction, Inc. Spartan16Manual, https://www.wavefun.com/.
  Google Scholar
  There is no corresponding record for this reference.
22. 22
  Mulliken, R. S. Electronic Population Analysis on LCAO-MO Molecular Wave Functions. I. J. Chem. Phys. 1955, 23, 1833– 1840, DOI: 10.1063/1.1740588
  [Crossref], [CAS], Google Scholar
  22
  Electronic population analysis on LCAO-MO [linear combination of atomic orbital-molecular orbital] molecular wave functions. I
  Mulliken, R. S.
  Journal of Chemical Physics (1955), 23 (), 1833-40CODEN: JCPSA6; ISSN:0021-9606.
  An analysis in quant. form was given in terms of breakdowns of the electronic population into partial and total "gross at. populations," or into partial and total "net at. populations" together with "overlap populations." Gross at. populations distribute the electrons almost perfectly among the various at. orbitals of the various atoms in the mol. From these nos., a definite figure is obtained for the amt. of promotion (e.g. from 2s to 2p) in each atom; and also for the gross charge Q on each atom if the bonds are polar. The total overlap population for any pair of atoms in a mol. is in general made up of pos. and neg. contributions. If the total overlap population between 2 atoms is pos., they are bonded; if neg., they are antibonded. Tables of gross at. populations and overlap populations were calcd. for CO and H2O. The amt. of s-p promotion was nearly the same for the O atom in CO and in H2O (0.14 electron in CO and 0.15e in H2O). For the C atom in CO it is 0.50e. For the N atom in N2 it is 0.26e. In spite of very strong polarity in the π bonds in CO, the σ and π overlap populations are very similar to those in N. In CO the total overlap population for the π electrons is about twice that for the σ electrons. The most easily ionized electrons of CO are in a mol. orbital such that its gross at. population is 94% localized on the C atom; these electrons account for the weak electron donor properties of CO.
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23. 23
  Löwdin, P.-O. Quantum Theory of Many-Particle Systems. I. Physical Interpretations by Means of Density Matrices, Natural Spin-Orbitals, and Convergence Problems in the Method of Configurational Interaction. Phys. Rev. 1955, 97, 1474– 1489, DOI: 10.1103/PhysRev.97.1474
  [Crossref], Google Scholar
  There is no corresponding record for this reference.
24. 24
  Halgren, T. A. Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94. J. Comput. Chem. 1996, 17, 490– 519, DOI: 10.1002/(SICI)1096-987X(199604)17:5/6<490::AID-JCC1>3.0.CO;2-P
  [Crossref], [CAS], Google Scholar
  24
  Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94
  Halgren, Thomas A.
  Journal of Computational Chemistry (1996), 17 (5 & 6), 490-519CODEN: JCCHDD; ISSN:0192-8651. (Wiley)
  This article introduces MMFF94, the initial published version of the Merck mol. force field (MMFF). It describes the objectives set for MMFF, the form it takes, and the range of systems to which it applies. This study also outlines the methodol. employed in parameterizing MMFF94 and summarizes its performance in reproducing computational and exptl. data. Though similar to MM3 in some respects, MMFF94 differs in ways intended to facilitate application to condensed-phase processes in mol.-dynamics simulations. Indeed, MMFF94 seeks to achieve MM3-like accuracy for small mols. in a combined "org./protein" force field that is equally applicable to proteins and other systems of biol. significance. A second distinguishing feature is that the core protion of MMFF94 has primarily been derived from high-quality computational data-ca. 500 mol. structures optimized at the HF/6-31G* level, 475 structures optimized at the MP2/6-31G* level, 380 MP2/6-31* structures evaluated at a defined approxn. to the MP4SDQ/TZP level, and 1450 structures partly derived from MP2/6-31G* geometries and evaluated at the MP2/TZP level. A third distinguishing feature is that MMFF94 has been parameterized for a wide variety of chem. systems of interest to org. and combinations of functional groups for which little, if any, useful exptl. data are available. The methodol. used in parameterizing MMFF94 represents a fourth distinguishing feature. Rather than using the common "functional group" approach, nearly all MMFF parameters have been detd. in a mutually consistent fashion from the full set of available computational data. MMFF94 reproduces the computational data used in its parameterization very well. In addn., MMFF94 reproduces exptl. bond lengths (0.014 Å root mean square [rms]), bond angles (1.2° rms), vibrational frequencies (61 cm-1 rms), conformational energies (0.38 kcal/mol rms), and rotational barriers (0.39 kcal/mol rms) very nearly as well as does MM3 for comparable systems. MMFF94 also describes intermol. interactions in hydrogen-bonded systems in a way that closely parallels that given by the highly regarded OPLS force field.
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25. 25
  Szabo, A.; Ostlund, N. S. Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory; Courier Corporation 1996, ISBN 0–486–69186-1.
  Google Scholar
  There is no corresponding record for this reference.
26. 26
  Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648– 5652, DOI: 10.1063/1.464913
  [Crossref], [CAS], Google Scholar
  26
  Density-functional thermochemistry. III. The role of exact exchange
  Becke, Axel D.
  Journal of Chemical Physics (1993), 98 (7), 5648-52CODEN: JCPSA6; ISSN:0021-9606.
  Despite the remarkable thermochem. accuracy of Kohn-Sham d.-functional theories with gradient corrections for exchange-correlation, the author believes that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional (contg. local-spin-d., gradient, and exact-exchange terms) is tested for 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total at. energies of first- and second-row systems. This functional performs better than previous functionals with gradient corrections only, and fits expt. atomization energies with an impressively small av. abs. deviation of 2.4 kcal/mol.
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27. 27
  Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem. 1994, 98, 11623– 11627, DOI: 10.1021/j100096a001
  [ACS Full Text ], [CAS], Google Scholar
  27
  Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields
  Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J.
  Journal of Physical Chemistry (1994), 98 (45), 11623-7CODEN: JPCHAX; ISSN:0022-3654.
  The unpolarized absorption and CD spectra of the fundamental vibrational transitions of the chiral mol. 4-methyl-2-oxetanone are calcd. ab initio. Harmonic force fields are obtained using d. functional theory (DFT), MP2 and SCF methodologies, and a [5s4p2d/3s2p] (TZ2P) basis set. DFT calcns. use the LSDA, BLYP, and Becke3LYP (B3LYP) d. functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with expt. The MP2 force field yields spectra in slightly worse agreement with expt. than the B3LYP force field. The SCF force field yields spectra in poor agreement with expt. The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreement with expt.
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Electronic State of Low-Rank Coals with Exchanged Sodium Cations

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Abstract

Introduction

Results and Discussion

Structure of low-rank coal used in the calculation and substitution position of Na+

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Structure and total energy after structure optimization

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Conclusions

Calculation Method

Author Information

Acknowledgments

NOMENCLATURE

References

Cited By

Abstract

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References

STEP 1:

STEP 2:

Structure of low-rank coal used in the calculation and substitution position of Na⁺