Process-driven glycerol catalytic conversion to lactic acid over nickel-doped hydroxyapatite: Effects of temperature and CO₂ pressure

This study investigates the roles of CO 2 and reaction temperature in the catalytic conversion of glycerol to lactic acid (LA). The hydrothermal reaction between glycerol and KOH is conducted over a nickel-doped hydroxyapatite catalyst in a high-pressure autoclave reactor. CO 2 pressure was varied at 10, 26, and 42 bar and compared to the process without CO 2 . The results indicate that the presence of CO₂ has a significant influence on glycerol conversion. At a CO 2 of 26 bar, the reaction yielded the highest glycerol conversion and concentration. It facilitates effective coupling between Ni-catalyzed dehydrogenation and base-driven rearrangement to LA. Furthermore, over a range of 150 to 250°C, temperature is the dominant driving force for LA formation under CO₂-rich conditions. LA yield increases linearly with temperature. The optimum condition is considered at 225°C and 26 bar CO 2 , where the LA yield and glycerol conversion 39% and 46.4%, respectively. The synergistic effects observed in the glycerol conversion indicate that the reaction mechanism is primarily governed by glycerol dehydrogenation, with in situ-generated hydrogen serving as the reducing agent. Keywords: CO 2 ; dehydrogenation; glycerol conversion; hydrothermal; lactic acid; Ni-HAp