Decaffeination of tea extracts by using poly(acrylamide-co-ethylene glycol dimethylacrylate) as adsorbent

Poly(acrylamide-co-ethylene glycol dimethacrylate) was synthesized by thermal polymerization. The adsorption properties of the polymers for catechins and caffeine were studied. Adsorption kinetics showed the polymers preferred to adsorb the catechins rather than caffeine, and adsorption of catechins and caffeine onto the polymers could be described by the pseudo-second-order model. Isothermal equilibrium curves of catechins and caffeine showed a good fit with Langmuir model. The maximum monolayer adsorption capacity (Qm) of total catechins (192.85–171.11 mg g−1) was 3.9–5.2-folds of caffeine. Adsorption of catechins and caffeine was spontaneous and exothermic process as the change in free energy and enthalpy were negative. Lower temperature was favorable for the adsorption process. Caffeine and catechins were well separated and recovered by eluting polymers-packed column with gradient ethanol, i.e., 30% ethanol elution for separating caffeine, and 80% ethanol elution for recovering catechins. Thus, the synthetic poly(acrylamide-co-ethylene glycol dimethacrylate) could be used as a new adsorbent candidate for producing the decaffeined catechins.