| In the process of high value utilization of biomass resources turpentine, the esterification reaction of ?-pinene has important industrial value, but it has many disadvantages such as conversion, selectivity, post-processing technique. In order to solve these problems, this paper studies on esterification reaction of the ?-pinene and acetic acid, using GC and GC-MS for analysis and characterization. The reaction mechanism and reaction direction under the different catalytic conditions has been discussed. And according to the characters of reaction system, a series of acidic ionic liquid catalyst based on heteropoly acid have been designed and synthesized, and applied in the esterification reaction of ?-pinene. The structure of synthesised catalysts is characterized using 1H NMR, FT-IR, and their thermal stability is analysed using thermogravimetric. Moreover, potentiometric titration method is used to measure catalyst acidity. Combining with their melting points and solubility property, structure-activity relationships of zwitterion between catalysts are studied.It is found that sulfonic acid functionalized heteropoly acid salt catalyst [MIMPS] H2PW12O40- shows good catalytic performance with chloroactic acid as a co-catalyst. Under the optimal reaction conditions as follows: m(?-pinene) = 6.8 g, n(?-pinene): n(chloroacetate): n(acetic acid) = 1:1:3, m(cat.) = 3 g, t = 7 h, T = 70 ?, the ?-pinene conversion is 97 %, and the esterification product selectivity is 45 %. After the reaction, the catalyst does not dissolve in oil and acetic acid, being solid deposit in the bottom of the container, reaction system is divided into three phases, and the catalyst can be recycled by simple separation without significant decrease of catalytic activity.Study shows that the co-catalyst chloroacetic acid plays a key role in the esterification reaction of ?-pinene since the nuclear capability of its carboxyl functional groups. However, its good solubility both in water phase and in organic phase is not conducive to recycling reusable. To solve this problem, chloroacetic acid, dichloroacetic acid and N-methyl imidazole and pyridine are used as raw materials to introduce carboxyl functional groups to the cationic of ionic liquid in this paper to prepare a series of carboxyl functionalized ionic liquids. It is found that the esterification of ?-pinene with acetic acid catalyzed by carboxyl functionalized ionic liquids [TEACH(Cl)COOH]HSO4 catalyst can give 31.5 % ?-pinene conversion and 27.9% selectivity for esterification products.Moreover, amino acids with natural carboxyl structure unit have been used to synthesize functional heteropoly ionic liquid. More than 97 % conversion of ?-pinene and 30.8% esterification selectivity are achieved with [Glu]H2PW12O40 as the catalyst and under the optimum reaction conditions: m(?-pinene) = 6.8 g, n(acetic acid): n(?-pinene) = 3:1, m(cat.) = 3.0 g, T = 50 ?, t = 3 h. The catalyst does not dissolve in organic phase so that it can be simple separated after reaction and has good repetition of usability.Polyether type octadecylamine ionic liquids or polyethylene glycol type diproton ionic liquids with surfactivity are also prepared and used for ?-pinene esterification, which can lead the reaction system into microemulsion phase at the reaction temperature. After reaction, catalyst can be simple separated by centrifugal method. Degree of polymerization of the catalyst has greatly effect on esterification reaction. Under [AC(-Cl CHCOOH)-18-80]HSO4, the conversion of ?-pinene is 98.4 % and the selectivity is 22.8 %. Using PEG1000-DAIL catalytic esterification conversion can reach 98.8 %, the selectivity can reach 17.5 %, and the catalyst can automatically layer after reaction, when polyethylene glycol(PEG) has low molecular weight, reaction selectivity reduces, and with bigger molecular weight, the lower hydrophilic lessens its catalytic activity.The purpose of this paper is to explore new catalyst for esterification of ?-pinene without auxiliary chloroacetic acid and other organic acids, provide a new way for environment friendly conversion technology of biomass. |
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