In situ water removal by vapor permeation membrane for enhanced amino acid esterification

Catalyst-membrane coupling reactor (CMCR) was fabricated for enhancing amino acid esterification. • In situ water separation was achieved by a PVA/Al 2 O 3 hollow fiber membrane. • HCl promoted the vapor permeation performance of the PVA/Al 2 O 3 membrane. • The HND-2 solid acid resin catalyst and PVA/Al 2 O 3 membrane exhibited excellent reusability. • CMCR also demonstrated good universality for various amino acid esterifications. . Amino acid ester hydrochlorides are critical intermediates used to produce pharmaceuticals and fine chemicals. The synthesis of amino acid ester hydrochlorides industrially adopted thionyl chloride (SOCl 2 )-mediated route, from which substantial SO 2 is generated and poses a great threat to the environment. In this study, a SOCl 2 -free catalyst-membrane coupling reactor (CMCR) was fabricated for amino acid esterification, which integrated HND-2 solid acid resin catalyst and polyvinyl alcohol (PVA) membrane supported on a four-channel α-Al 2 O 3 hollow fiber. Karl Fischer titration directly confirmed the effective water removal ability of the PVA/Al 2 O 3 membrane. In the esterification of DL-serine with methanol, the CMCR achieved a DL-serine conversion of 93.1%, outperforming the traditional reactor without membrane (86.5%). In addition, it was found that HCl dissolved in methanol improved the solubility and conversion of DL-serine. More importantly, vapor permeation experiments and simulation calculations indicated that HCl resulted in a 3.3-fold increase in water flux and ∼83.7% improvement in H 2 O/MeOH separation factor by promoting the water vaporization. The CMCR also demonstrated excellent reusability and universality for the esterification of other amino acids with alcohols. This work proposes a green and efficient reaction-separation coupling strategy for the synthesis of amino acid ester hydrochlorides, providing a viable alternative to replace the SOCl 2 -mediated route. Researchers have developed a reaction-separation coupling system that intensifies the esterification of serine with methanol to produce serine methyl ester hydrochloride, via the synergistic coupling of solid acid HND-2 and a PVA/Al 2 O 3 dehydration membrane. This system efficiently separates water generated during the esterification reaction, overcomes the thermodynamic equilibrium constraints, and significantly enhances the conversion efficiency of the reactants. Furthermore, this study reveals that hydrogen chloride can effectively facilitate the separation of water throughout the reaction process. Collectively, this work affords a novel strategy for the green synthesis of amino acid esters in industrial production. Download: Download high-res image (213KB) Download: Download full-size image