Selection and Adsorption Behavior of Resin for the Decaffeination of Tea

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.