脱茶叶咖啡碱树脂的筛选及吸附行为的研究

Selection and Adsorption Behavior of Resin for the Decaffeination of Tea

摘要:

以茶汤中咖啡碱的吸附率及吸附量为指标，比较了静态吸附条件下10种树脂对茶叶咖啡碱的吸附效果，筛选出吸附效果最佳的树脂AL-1，并对AL-1的吸附热力学及动力学特性进行了研究。结果表明，AL-1对茶叶咖啡碱的吸附率高达98.58%，吸附晗变ΔH=21.84 kJ/mol，说明AL-1对咖啡碱的吸附是吸热的物理吸附过程，吸附自由能均为正值，且随吸附温度增加而减少，说明环境温度越高，吸附越容易。平衡吸附数据符合Langmuir和Freundlich等温吸附方程，说明吸附属单分子层吸附，吸附速率符合准一级动力学方程，吸附过程主要受液膜控制。

Abstract:

Taking the adsorption rate and adsorption capacity as indexes, the adsorption abilities of 10 kinds of resins were compared and the resin AL-1 was shown to be the best one with its caffeine-adsorption rate of 98.58%. Based on the thermodynamics and kinetics characteristics of the resin AL-1, the change of enthalpy was 21.84 kJ/mol, which indicated that the adsorption was exothermic physical absorption process. The value of free energy was positive and was reduced with the gradual increase of temperature. It indicated that the higher ambient temperature, the more easily caffeine was adsorbed. Equilibrium adsorption data was consistent with both Langmuir and Freundlich isotherms equation, which showed that it was single molecule layer adsorption. A Lagergren pseudo-first order rate equation was suitable to the adsorption process, which was mainly controlled by liquid film.