Extractive Deterpenation Of Citrus Essential Oils Using Quaternary Ammonium-based Deep Eutectic Solvents

Essential oil,as a natural product with high added commercial value,has been widely used in human health care,food seasoning,and cosmetics production.Among many essential oil products,citrus essential oil accounts for more than half of the essential oil market due to its wide range of raw materials.Citrus essential oil is mainly composed of terpenes and a small amount of terpenoids.Terpenes contribute little to the flavor of citrus essential oil.However,they are easily oxidized and polymerized to form resin substances in the air condition,which are potential factors for deterioration and odour production of citrus essential oil.Therefore,developing a green and efficient deterpene process of citrus essential oil is necessary to effectively separate terpenoids from terpenes to improve the essential oil product value.In this work,the separation of terpene and terpoid in citrus essential oil with quaternary ammonium salt-based deep eutectic solvent(DES)as extractant was proposed.The mixture of limonene and linalool was used as the model oil.Firstly,based on the COSMO-RS calculations and the feasibility of DES formation,19 kinds of DESs were selected to extract linalool from model citrus essential oil.The effects of the structure of hydrogen bond acceptors(HBA)and donors(HBD)in DESs on the extraction performance,namely distribution coefficient and selectivity,were investigated.It was found that the DESs with long alkyl chain in HBA and HBD exhibited higher distribution coefficient.The DESs with chloride ion in HBA had higher distribution coefficient and selectivity than those with bromide ion in HBA.Taking the distribution coefficient and selectivity into account,the extraction performance index(PI)value was used as the screening critria.The DES formed by tetrabutylammonium chloride and 1,3-butanediol with the molar ratio of 1:2,TBAC:13BD(1:2),was selected as the optimal extractant,due to its high PI value(68.98).The liquid-liquid equilibrium of the system including model oil and TBAC:13BD(1:2)was studied,and the pseudo-ternary phase diagram of {limonene+linalool+TBAC:13BD(1:2)} was obtained.The binary interaction parameters of NRTL equation were then fitted.TBAC:13BD(1:2)showed high extraction performance at different temperatures and linalool contents.The effects of the water content,dosage of extractant,and extraction temperature were further investigated to obtain better process operation conditions.TBAC:13BD(1:2)also showed good extraction performance in extraction of actual citrus essential oil.Quaternary ammonium salt-based DESs showed high extractive deterpenation performance in both model and actual citrus essential oil,which could be used as ideal solvents for extracting terpenoids in the downstream processing of citrus essential oil.