| Energy is an indispensable and important material foundation for society and economic development of the countries and closely related to the survival and development of mankind.With the process of industrialization in the world,the demand for energy is constantly increasing,and the traditional non-renewable fossil fuels have been excessively consumed,resulting in energy shortage,serious environmental pollution and greenhouse effect.Therefore,the development and utilization of clean and renewable green energy as a substitute for fossil fuels have become a research hotspot.Biodiesel,as the renewable and environment-friendly biomass energy,has a wide range of raw materials and similar physical and chemical properties to diesel fuel.It has been considered as an ideal substitute for petrochemical diesel,and has attracted widespread attention.The transesterification method,which is s safe and simple method and can be conducted under low temperature and normal pressure,is the main method for the production of biodiesel in the current industry.However,due to the difference in the composition of biodiesel feedstock,the produced biodiesel usually contains a high content of polyunsaturated fatty acid methyl esters（FAMEs）,resulting in low-quality product with poor oxidation stability and poor cold flow property,which restricts the application of biodiesel.Therefore,in order to hydrogenate the polyunsaturated FAMEs in biodiesel produced by transesterification method into stable cis-monounsaturated FAMEs with high-quality,and to avoid the formation of both saturated FAMEs and trans-monounsaturated FAMEs,which can lead to poor cold flow property,it is of great significance to design and prepare a high-efficient hydrogenation catalyst for the upgrading of biodiesel.In this work,low-cost bentonite was modified organically by cetyltrimethylammonium bromide（CTAB）and utilized as a support to synthesize a novel organobentonite-supported Pd composite catalyst with lipophilicity via chemical reduction method.The effects of preparation conditions on the catalytic activity of the composite catalyst were investigated and the optimum synthesis conditions of the catalyst were established.The structural features of the composite catalyst were analyzed by a series of characterizations.Moreover,the lipophilicity of the composite catalyst was studied,and the circulation and regeneration of the catalyst were also explored.In addition,the catalytic transfer hydrogenation（CTH）of polyunsaturated FAMEs,which used ammonium formate as hydrogen donor and water as solvent,was investigated with the assistance of microwave.The effects of CTH reaction conditions on the CTH of FAMEs were investigated,and the optimum process conditions of CTH were obtained.Furthermore,a comparative study between the microwave heating and the conventional heating for CTH of FAMEs has been conducted.And the reaction kinetic of the CTH of polyunsaturated FAMEs was also studied.Overall,the efficient CTH of polyunsaturated FAMEs under mild conditions of CTH was achieved.The main research results were as followed:（1）Optimum preparation conditions of Pd/organobentonite composite catalyst were as follows:CTAB amount 14 wt.%,Pd content 3 wt.%,Pd/B molar ratio 1:5,reduction time 5 h and drying temperature 80℃.The composite catalyst prepared was characterized and analysed.The characterization results showed that the hydrophobicity of bentonite was enhanced by modifying bentonite with CTAB,and the prepared composite catalyst was a layered mesoporous material with narrow pores,and with smooth surface and loose structure.Moreover,the particle sizes of active metal Pd in the catalyst was small and the metal Pd particles uniformly dispersed in the interior and on the surface of the composite catalyst.The result about the effect of lipophilicity of composite catalyst on the catalytic activity of the catalyst showed that with the increase of CTAB content in the catalyst,the lipophilicity of the catalyst enhanced,which could effectively enhance the hydrogenation activity of the catalyst and promote the CTH of FAMEs.Compared with nano-Pd catalyst,the prepared Pd/organobentonite composite catalyst exhibited high hydrogenation activity and selectivity towards both C18:1 and c-C18:1.Moreover,according to the results of circulation and regenerability of composite catalyst,when the catalyst was washed with anhydrous ether,the prepared Pd/organobentonite composite catalyst remained excellent activity and stability after the reuse for five cycles consecutively in the CTH of FAMEs.（2）The optimum process conditions of microwave-assisted CTH of polyunsaturated FAMEs using ammonium formate as hydrogen donor and water as solvent were as follows:ammonium formate amount 40 g,water amount 60 g,catalyst dosage 8 wt.%,reaction temperature 80℃,reaction time 140 minutes and agitation speed 350 rpm.Under the optimum CTH conditions,the CRC182of hydrogenated FAMEs reached 78.56%,the yield of C18:1 was 72.22%,the selectivity towards c-C18:1 was 70.29%,the C18:0 content was low of 2.44wt.%and the iodine value of FAMEs was 94.0.The results mentioned above indicated that during the CTH reaction,the polyunsaturated C18:2 was mainly hydrogenated into the monounsaturated FAMEs and there was no deep hydrogenation of C18:1 transformed into C18:0.Thus,the efficient CTH of polyunsaturated FAMEs under mild conditions of CTH was achieved.Moreover,microwave presented the obvious process intensification effect for the CTH of FAMEs,which increased the C18:2 conversion ratio and enhanced the reaction rate with a reduction in the reaction time.The results of CTH reaction kinetic for polyunsaturated FAMEs indicated that the microwave-assisted CTH of polyunsaturated FAMEs using composite catalyst could be described by a pseudo-first-order kinetic model.Furthermore,the results of catalyst regenerability suggested that after being regenerated with anhydrous ether,the composite catalyst maintained excellent catalytic activity and stability after the reuse for five cycles consecutively in the CTH of FAMEs. |
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