Solid-liquid extraction of chlorogenic acid from Eucommia ulmoides Oliver leaves: Kinetic and mass transfer studies

Chlorogenic acid is an important natural active compound in Eucommia ulmoides Oliver leaves. A second-order kinetic model was considered applicable for the solid-liquid extraction process and revealed the positive effects of reducing the particle size, increasing the liquid-solid ratio and temperature on accelerating the extraction rate and increasing the equilibrium yield. An empirical model on the studied variables was developed to predict the extraction process and its feasibility was verified. The activation energy was 19.67 kJ mol−1. The mass transfer process was investigated based on Fick's second law, where the extraction rate depends on the internal diffusion of the compound and the internal resistance was the main factor affecting the extraction process. Temperature and liquid-solid ratio significantly changed the effective diffusion coefficient and mass transfer coefficient in different ways, and the Biot number was related to the liquid-solid ratio. Overall, these findings provided fundamental datas and theoretical guidances for the extraction of chlorogenic acid.