In Situ-Generated Supported Potassium Lactate: Stable Catalysis for Vapor-Phase Dehydration of Lactic Acid to Acrylic...

We have studied unsupported, silica gel- and amorphous silica-alumina-supported catalysts derived from K salts for the vapor-phase dehydration of lactic acid (LA) to acrylic acid (AA). A catalytic study shows that the supported catalysts improve the activity and selectivity for the production of AA and decrease the selectivity for the production of propionic acid (PA). The silica-alumina-supported catalysts remain fairly stable in the catalytic performance during 90 h of reaction. The IR spectroscopic characterization combined with the catalytic study demonstrates that potassium lactate (C₃H₅KO₃) in situ generated from LA and a K salt is an important reaction intermediate for the production of AA and the catalytic stability is associated with the chemical stability of C₃H₅KO₃ and the activity for the regeneration of C₃H₅KO₃ in the catalytic cycle. On silica-alumina, C₃H₅KO₃ is well stabilized and smoothly regenerated during the reaction, leading to the good catalytic stability. This work suggests for the first time that lactate salt acts as the true catalytic active species for the dehydration of LA to AA. We also propose a predominant reaction pathway for the vapor-phase dehydration of LA to AA with K salt catalyst systems.