Production of Methyl Lactate with Sn-USY and Sn-β: Insights into Real Hemicellulose Valorization

Potassium exchanged Sn-β and Sn-USY zeolites have been tested for the transformation of various aldoses (hexoses and pentoses), exhibiting outstanding catalytic activity and selectivity toward methyl lactate. Insights into the transformation pathways using reaction intermediates—dihydroxyacetone and glycolaldehyde—as substrates revealed a very high catalytic proficiency of both zeolites in aldol and retro-aldol reactions, showcasing their ability to convert small sugars into large sugars, and vice versa. This feature makes the studied Sn-zeolites outstanding catalysts for the transformation of a wide variety of sugars into a limited range of commercially valuable alkyl lactates and derivatives. [K]Sn-β proved to be superior to [K]Sn-USY in terms of shape selectivity, exerting tight control on the distribution of produced α-hydroxy methyl esters. This shape selectivity was evident in the transformation of several complex sugar mixtures emulating different hemicelluloses—sugar cane bagasse, Scots pine, and white birch—that, despite showing very different sugar compositions, were almost exclusively converted into methyl lactate and methyl vinyl glycolate in very similar proportions. Moreover, the conversion of a real hemicellulose hydrolysate obtained from Scots pine through a simple GVL-based organosolv process confirmed the high activity and selectivity of [K]Sn-β in the studied transformation, opening new pathways for the chemical valorization of this plentiful, but underutilized, sugar feedstock.

. Stoichiometric coefficients considered in the calculation of product yields -carbon basisas a function of the starting substrate.
Table S2.Composition of hemicellulose hydrolysate recovered from different biomass sources as determined through NREL/TP-510-42623 standard.Extraction and recovery efficiencies for pentoses and hexoses.
Table S3.Impurities and their concentration found in GLV-organosolv Scots Pine hemicellulose hydrolysate.

TABLES
Table S3.Impurities and their concentration found in GLV-organosolv Scots Pine hemicellulose hydrolysate.

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Instituto de Tecnologías para la Sostenibilidad.Universidad Rey Juan Carlos.C/ Tulipan s/n Scheme S1.Detailed transformation pathways occurring in the treatment of hemicellulose monosaccharaides in the presence of [K]Sn-USY and [K]Sn-β zeolites in methanol media.

Figure S4 .
Figure S4.Product distribution obtained in the second use of Sn-USY and Sn-β catalyst in the transformation of hemicellulose monosaccharides (A, glucose; B, mannose; C, xylose and D,

Figure S8 .
Figure S8. 13C (A) and 1 H (B) NMR spectra of Sn-β spent catalyst in the transformation of dihydroxyacetone (DHA) and glycolaldehyde (GLA) (black solid lines) and the liquid-extracted compounds after washing with CD 3 Cl (solid red lines).

Figure S4 .
Figure S4.Product distribution obtained in the second use of Sn-USY and Sn-β catalyst in the

Figure S6 .Figure S7 .
Figure S6.Product distribution obtained in the second use of Sn-USY and Sn-β catalyst in the

Figure S8 .
Figure S8. 13C (A) and 1 H (B) NMR spectra of Sn-β spent catalyst in the transformation of

Table S1 .
Stoichiometric coefficients considered in the calculation of product yields -carbon basisas a function of the starting substrate.

Table S2 .
Composition of hemicellulose hydrolysate recovered from different biomass sources as determined through NREL/TP-510-42623 standard.Extraction and recovery efficiencies for pentoses and hexoses.