Reaction pathways and kinetics of cholesterol in high-temperature water

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 E_a=127±12kJmol^-1 and A=10^8.35±2.41s^-1. We used a delplot analysis and mechanistic considerations to develop a reaction network for conditions relevant to hydrothermal liquefaction of microalgae.