Study On The Preparation Of Biodiesel By In Situ Esterification Of Bio-based Fatty Acid

Fatty acid ester is one of the important chemical products.Because of the environmental problems and shortage of fossil resources,the route from biobased fatty acid to ester derivatives is becoming an international research hot spot.However,the concentration of products by bioconversion is much lower than that through chemical methods and only the 5 g/L level could be obtained.On the other side,the procedure for the isolation and purification of biobased compounds from water solvent is tedious and high cost,which is one of the key restraining factors for the industrialization process.In this paper,surfactants-metal ion chelating materials(S-M),phosphotungstic acid modified porous coordination polymer materials(PCP(Cr)-PTA)and supported phosphotungstic acid MCM-41 molecular sieve and hydrophobic functional treatment of the materials(OTS-PTA-MCM-41)were synthesized by precipitation method,hydrothermal method and sol-gel method,respectively.The three materials were used in the synthesis of biodiesel in the aqueous phase,investigated the effects of reaction conditions such as catalyst dosage,reaction temperature,reaction time and different water-alcohol ratio on palmitic acid esterification rate,the following experimental results were obtained.The optimum reaction conditions of DBS-Sn(IV)for the preparation of biodiesel from palmitic acid were as follows: molar ratio of palmitic acid methanol 1:25,catalyst addition amount 50 mg,reaction temperature 70 ℃,reaction time 3 h.At this time the yield of methyl palmitate was as high as 97.4%.The catalyst was repeated in five reaction cycles,and the palmitic acid yield did not decrease substantially.The reaction temperature was 110 ℃,the reaction time was 3 h,the amount of catalyst was 100 mg,and the yield of methyl palmitate was 87.4% at the time of the esterification experiment of DBS-Sn(IV)catalytic fermentation liquid.Under the same conditions,the catalytic yield of palmitic acid in the fermentation broth was 89.1%.The optimum reaction conditions of PCP(Cr)-PTA catalyzed palmitic acid-derived biodiesel were as follows: the ratio of alcohol to water was 1: 9,the reaction temperature was 130 ℃,the reaction time was 3 hours,the amount of catalyst was 5% The yield of methyl methacrylate reached 84.7%,and the yield of palmitic acid did not decrease in the five reaction cycles.The yield of methyl palmitate was 80.0% using the above reaction conditions using PCP(Cr)-PTA in the esterification reaction of the catalytic fermentation liquid.OTS-PTA-MCM-41 catalyst was used to catalyze the fermentation of liquid fatty acids in OTS-PTA-MCM-41(C14)The yields of methyl laurate,methyl myristate and methyl palmitate were 91.1%,87.9% and 90.7%,respectively,at 150 ° C for 3 hours.Besides,we will also analyze the tertiary structure of heteropoly acid,the surface and pore size distribution of carrier material,the loading efficiency of heteropoly acid and the hydrophobicity of catalyst.Based on the relationship between the catalyst structure and the reaction activity,the improvement of catalyst will be studied and the esterification of fatty acid in the fermentation solution will be realized finally.These studies will provide a scientific basis for the hydrophobic heterogeneous system,a new alternate route for the transformation of fatty acid into high value-added esters and guidance for the dehydration reaction in water solvent.The new method would make the combination of fermentation and separation easy to get,achieve the natural separation of ester from water and lower production costs.