Dehydration of lactic acid to acrylic acid in high temperature water at high pressures

Reaction of lactic acid was investigated with a flow apparatus in water at high temperatures (450 °C) and high pressures (40–100 MPa). The major products obtained from the reaction of lactic acid were acrylic acid, acetaldehyde, and the minor products were acetic acid and propionic acid. The maximum selectivity of acrylic acid was 44% at 23% lactic acid conversion that was obtained at 450 °C, 100 MPa and a residence time of 0.8 s. The reaction kinetics could be modeled by considering two pathways defined as a dehydration pathway to acrylic acid and a combined reaction pathway that consisted of decarboxylation and decarbonylation to acetaldehyde. The data and the kinetic analysis consistently show that both dehydration and the combined decarboxylation and decarbonylation reactions continue to be promoted in supercritical water as pressure (water density) increases. However, high water densities increase the selectivity of the dehydration reaction.