Study Of Essential Oil Extraction And Activated Carbon Preparation From Citrus Peel And Its Applications

In order to realize the high-value utilization of citrus peel waste,the high-performance activated carbon and high-yield essential oil were obtained by using a novel distillation-pyrolysis method.Potassium carbonate(K2CO3)was used to assist the extraction of essential oils and served as the activating agent for the further preparation of activated carbons.A common alkali metal salt,K2CO3,is verified to be effective in promoting the extraction of essential oils from citrus peel.Compared to the 2.4 wt.%extraction rate of essential oil obtained using regular steam distillation,a 6.2 wt.%extraction rate was achieved when the citrus peel was pretreated with a K2CO3 solution.Meanwhile,its chemical composition remained stable,indicating that these additional essential oils can also be directly used in areas that have already been developed in the industries such as perfume and fragrance.The solid residue collected after essential oil extraction was further used as the precursor for activated carbons.The specific surface area of the activated carbon reached up to 1848 m2/g at a carbonization temperature of 800 ℃ and time of 1 h,and it exhibited a highly developed microporous structure.For the purpose of improving the adsorption performance of activated carbon on phenolic pollutants,the pore structure and surface chemistry of carbons were modified by base treatment.The performance-improved activated carbon derived from orange peel was obtained by urea modification.Meanwhile,the optimum process conditions for the adsorption of hydroquinone onto activated carbon was determined and the adsorption mechanism was explored.At an initial concentration of hydroquinone of 200 mg/L and the pH value of 7.0,the equilibrium adsorption capacity of modified activated carbon for hydroquinone was 385.26 mg/g,which was increased by 37.07%compared to the unmodified one.The adsorption of hydroquinone onto the activated carbon was observed to follow the pseudo-second order model,indicating that the chemisorption may be existed,and the adsorption is controlled by film diffusion and intra-particle diffusion.The equilibrium isotherm was mainly subj ect to the Freundlich model which reveals the heterogeneous surface of activated carbons.The thermodynamic parameters indicated that the adsorption was an exothermic reaction and could occur spontaneously.The activated carbon/nano Fe2O3 composite was prepared by using pomelo peel as a carbon source and ferric nitrate as an iron source.Meanwhile,the morphology,structure and electrochemical properties of this composite were further studied.The results showed that the use of nano Fe2O3 improved the electrochemical performance of activated carbons.At 1 A/g of current density,the specific capacitance increased from 159.6 F/g of activated carbon to 276.0 F/g of the composite.Furthermore,in a symmetric supercapacitor,an energy density of 9.39 Wh/kg was obtained at a power density of 360 W/kg.The synergistic effect between activated carbon and Fe2O3 contributed this composite to be a promising electrode material for supercapacitors.