Assessment of the Potential of Electrochemical Steps in Direct Air Capture through Techno-Economic Analysis

Direct air capture (DAC) technologies are proposed to reduce the atmospheric CO2 concentration to mitigate climate change and simultaneously provide carbon as a feedstock independent of fossil resources. The currently high energy demand and cost of DAC technologies are challenging and could limit the significance of DAC processes. The present work estimates the potential energy demand and the levelized cost of capture (LCOC) of liquid solvent absorption and solid adsorption DAC processes in the long term. A consistent framework is applied to compare nonelectrochemical to electrochemical DAC processes and estimate the LCOC depending on the electricity price. We determine the equivalent cell voltage needed for the electrochemical steps to achieve comparable or lower energy demand than nonelectrochemical processes. The capital expenses (CapEx) of the electrochemical steps are estimated using analogies to processes that are similar in function. The results are calculated for a range of initial data of CapEx and energy demand to include uncertainties in the data.


Absorption via chemical looping (ACL)
Figure S1 shows the flowsheet of the ACL plant.The sorbent replacement  sorb,OpEx per ton of CO2 is adopted from Keith et al.. 1 For calculation of  sorb , sorbent raw material costs for lab-scale application are taken from Sigma-Aldrich and converted to large-scale application. 2As the sorbent is commercially available, no utility, labor, maintenance or synthesis costs must be included.Therefore, the purchase cost equals the overall sorbent cost.

Absorption with electrochemical regeneration (AEC)
Figure S2 shows the flowsheet of the AEC plant.The sorbent material (costs) are assumed to be part of the CapEx.

Temperature-vacuum swing adsorption (TVSA)
Figure S3 shows the flowsheet of the TVSA plant.A breakdown of capital costs and energy demand for the TVSA plant is listed in Table S2.The values adopted from the National Academy of Sciences (Table 5.10) 3 refer to an annualized payment and were calculated to absolute capital costs using a payback period of 30 years and an interest rate of 12% (according to Equation 4).The energy demand was adopted from Table 5.7 3 and recalculated from GJ/tCO2 to MWh/tCO2.Note that implementing a heat pump reduces the initial energy demand by a factor of 3.5, which is the coefficient of performance (COP).

Electro-swing adsorption (ESA)
Figure S4 shows the flowsheet of the ESA plant.The sorbent material (costs) are assumed to be part of the CapEx.

Calculation of water loss
The relative water content of air  is calculated according to: with   as the gas constant of air,   as the gas constant of vapour,  as the relative humidity,   as the saturated pressure pf the vapour at given temperature, and   as the overall pressure (ambient pressure).The water loss  is calculated according to: where   is the amount of air and   is the vapour content at saturation.Table S3 lists the respective values at 20 °C.  1695 t

Review of techno-economic studies
Table S4 lists the values and sources that were used to prepare Figure 3 in the main article.

Net LCOC
The net LCOC is calculated for carbon intensities of 18/57/800 kgCO2e/MWh, an electricity price of 200 $/MWh, and a CIC of 1 MtCO2/a and 1 GtCO2/a, respectively, and given in Table S5.

Fig. S1
Fig. S1 Flow sheet of the absorption plant with chemical looping.

Fig. S2 :
Fig. S2: Flow sheet of the absorption plant with electrochemical regeneration.

Table S1 lists
sorb,OpEx and  sorb of CaCO3 needed to capture 1 MtCO2/a.The CO2 capture rate is 125 t/h.

Table S1 :
Large-scale raw material quantity and sorbent purchase cost  sorb for ACL sorbent.

Table S2 :
3reakdown of capital costs (CapEx) and energy demand of the TVSA plant recalculated from the National Academy of Sciences.3

Table S3 :
Paramters for water loss calculation at 20 °C.

Table S4 :
The levelized cost of capture (LCOC) for absorption with chemical looping (ACL), absorption with electrochemical regeneration (AEC), and temperature vacuum swing adsorption (TVSA) from different sources.

Table S5 :
The net LCOC for carbon intensities of 18/57/800 kgCO2e/MWh, an electricity price of 200 $/MWh, and a CIC of 1 MtCO2/a and 1 GtCO2/a (cn: carbon-neagtive) for the lower and upper limit of the considered range.