Kinetic analysis and reaction mechanism of hydrothermal hydrolysis of rapeseed hulls to produce polyphenols

Hydrothermal hydrolysis of rapeseed hulls to produce polyphenols was studied by treatment of aqueous slurries of 3.3 wt% rapeseed hulls at 120‒220°C for 30 min‒3 h. Polyphenol production, hull dissolution ratio, and total carbon yield increased with increasing temperature. The time profile of treatment at 180°C indicated that the hydrolysis proceeded rapidly in the initial 30 min and then slowed. Hydrolysis was assumed to be the main reaction pathway for polyphenol production in the initial stage of reaction, and kinetic analysis was performed. The hydrolysis rates of compounds containing ether bonds in the literature were analyzed and found to follow the enthalpy-entropy compensation rule. With the exception of phenyl ethers, the hydrolysis rates of these compounds all fell on a single line, indicating that the hydrolysis occurred through a similar reaction mechanism. Based on the enthalpy-entropy compensation rule, it is suggested that the polyphenols produced by hydrothermal hydrolysis of rapeseed hulls were derived from glycoside structures.