Effects of alkaline additives on the formation of lactic acid in sorbitol hydrogenolysis over Ni/C catalyst

Lactic acid is produced as a major byproduct during sorbitol hydrogenolysis under alkaline conditions. We investigated the effects of two different alkaline additives, Ca(OH)2 and La(OH)3, on lactic acid formation during sorbitol hydrogenolysis over Ni/C catalyst. In the case of Ca(OH)2, the selectivity of lactic acid was 8.9%. In contrast, the inclusion of La(OH)3 resulted in a sorbitol conversion of 99% with only trace quantities of lactic acid being detected. In addition, the total selectivity towards the C2 and C4 products increased from 20.0% to 24.5% going from Ca(OH)2 to La(OH)3. These results therefore indicated that La(OH)3 could be used as an efficient alkaline additive to enhance the conversion of sorbitol. Pyruvic aldehyde, which is formed as an intermediate during sorbitol hydrogenolysis, can be converted to both 1,2-propylene glycol and lactic acid by hydrogenation and rearrangement reactions, respectively. Notably, these two reactions are competitive. When Ca(OH)2 was used as an additive for sorbitol hydrogenolysis, both the hydrogenation and rearrangement reactions occurred. In contrast, the use of La(OH)3 favored the hydrogenation reaction, with only trace quantities of lactic acid being formed.