Effect of MoO3 loading on product selectivity for calcium pyrophosphate catalyzed vapor phase lactic acid dehydration

Abstract

Calcium pyrophosphate and hydroxyapatite catalysts with varying C/P ratios have been previously used by our group for vapor phase dehydration of lactic acid to acrylic acid with almost 100% conversion and up to 78% acrylic acid selectivity. The activity was highly sensitive to acidity and basicity of the catalyst. Hence the catalyst with maximum activity, calcium pyrophosphate, was modified with MoO3 for modifying its acidity and to study its effect on product selectivity for lactic acid dehydration. The MoO3 modified calcium pyrophosphate with 5% MoO3 loading was used for vapor phase dehydration of lactic acid at 375°C using 50% lactic acid concentration with WHSV of 3 h-1. The activity was compared with nonmodified calcium pyrophosphate catalyst. Surprisingly, deoxygenation was predominant compared to dehydration. Acidity was observed to play a crucial role in product selectivity (i.e,. with less acidic support, calcium pyrophosphate with 5 wt% MoO3 showed more deoxygenation activity as compared to acidic support γ-Al2O3 as well as SiO2 with same MoO3 loading). Higher acidity led to formation of acetaldehyde as the only product. The results confirmed formation of propionic acid by deoxygenation of lactic acid using in situ generated hydrogen after decarboxylation of lactic acid to acetaldehyde.