Reaction pathways and kinetics of cholesterol in high-temperature water

•Cholesterol was reacted in high-temperature water at 300, 325, and 350 °C.•Cholesta-3,5-diene was the sole primary reaction product.•Rate constants and Arrhenius parameters for cholesterol dehydration were calculated.•Products consisted nearly entirely of cholestadienes.•A reaction network for major product pathways was proposed.

We investigated the reaction of cholesterol, a model compound for sterols in microalgae, in high-temperature water at 300, 325, and 350 °C. Products nearly entirely consisted of cholestadienes, with cholesta-2,4-diene, cholesta-3,5-diene, and cholesta-4,6-diene being the most abundant isomers. Cholesta-3,5-diene was the only primary product, formed via dehydration of cholesterol. Cholesta-2,4-diene and cholesta-4,6-diene likely formed from cholesta-3,5-diene by double-bond migration. We report conversion and product molar yields for each reaction condition. The initial rate of disappearance of cholesterol was first-order with an activation energy of Ea = 127 ± 12 kJ mol−1 and A = 108.35±2.41 s−1. We used a delplot analysis and mechanistic considerations to develop a reaction network for conditions relevant to hydrothermal liquefaction of microalgae.