Conversion of lactic acid to acrylic acid in near-critical water

The dehydration of lactic acid is studied in a Hastelloy C-276 annular reactor in near-critical water. Experiments are performed at a pressure of 310 bar, at temperatures of 120-400°C, at residence times of 25-110 s, and with various catalysts, including disodium hydrogen phosphate, phosphoric acid, and sodium hydroxide. Three main reaction pathways are investigated and evaluated. A temperature of 160°C optimizes the formation of acrylic acid with molar yields as high as 58%, based on conversion. The presence of phosphate salts and/or base increases the yields of acrylic acid by suppressing the competing pathways. The aging of the Hastelloy reactor for 60-70 h decreases the degradation reactions resulting in higher yields of acrylic acid