Deep eutectic solvents used as the green media for the efficient extraction of caffeine from Chinese dark tea

•DESs were firstly developed as green media for the extraction of caffeine from CDT.•The major factors influencing the extraction were optimized by RSM.•The Kamlet-Taft polarity parameters for the DESs solution were measured.•The extraction kinetics model was established using the Fick’s Second Law. In recent years, more and more attention are paid to the green media in the extraction field. Deep eutectic solvents (DESs) are considered as excellent substitutes to traditional organic solvents and ionic liquids (ILs). In this work, DESs were used to extract caffeine from Chinese dark tea (CDT), then caffeine was recovered from the crude DES extract using macroporous resins. The factors affecting the solid-liquid extraction, including DES concentration, liquid-solid ratio, extraction time, extraction temperature, and system pH were studied in the single factor experiments. The Kamlet-Taft polarity parameters of DESs were determined to analyze the proper hydrogen-bond interaction between DESs and caffeine. Then the major factors of DES concentration, liquid-solid ratio, and extraction time were optimized by response surface methodology (RSM). The results showed that the maximum extraction yield of 26.78 mg/g were obtained using the DES choline chloride-lactic acid (ChCl-LA) as extractant under the optimized conditions. Moreover, the kinetics model of caffeine extraction was established using the Fick’s Second Law, the experimental results were well fitted by this model. This extraction of caffeine from CDT using DESs is much simpler and environmentally friendly with low cost and high extraction efficiency.