Study On Plasma Treated Of Solid-base Catalysts For The Synthesis Of Biodiesel

Biodiesel are the mixtures of fatty acid esters synthetized by vegetable oils, animal fat or long chain fatty acids with methanol or other low carbon alcohol. Biodiesel is an environmental friendly renewable fuel, and it can play a great role in solving the problems of energy shortage and environmental pollution. The homogeneous catalysts are mainly used in the transesterification to produce biodiesel. However, the high quality requirement to raw materials is necessary when using homogeneous catalysts, and a large amount of waste water, which is not benefit for the environment, is produced in the processes of separating the catalyst from reaction system and cleaning products. In order to overcome the above problems, synthesis of biodiesel with solid base catalyst has received extensive attention. Presently, two kinds of solid base catalysts, i.e. Ca/Al composite oxides and NaAlO2/MgO have been prepared by our research group, which could be high reactivity, mild reaction conditions and easy to be separated for recycling in the process of production of biodiesel. However, higher activity and stability of the solid base catalysts are still needed for industrial production of biodiesel. Taking the above into consideration, plasma treatment of the solid-base catalyst was further investigated in this paper.Firstly, the influences of acid value and water content in material on the yield of methyl ester were respectively investigated during the process of the transesterification of vegetable oil with methanol to produce biodiesel catalyzed by Ca/Al composite oxides and NaAlO2/MgO. The results showed that the influences of acid value and water content in material on the yields of methyl ester were smaller when using Ca/Al composite oxides or NaAlO2/MgO as catalyst compared that of using the homogeneous base catalyst. The stability of Ca/Al composite oxides and NaAlO₂/MgO were also studied, and the results showed that the yields of methyl ester were still all above 90% when Ca/Al composite oxides catalyst was used repeatedly for 5 cycles. And the yields of methyl ester were decreased from 88.3% to 76.0% when NaAlO₂/MgO was used repeatedly for 4 cycles.Secondly, the solid base catalysts of Ca/Al composite oxides and NaAlO2/MgO were treated with air dielectric barrier discharges (DBD). The influences of some factors, such as applied voltage, treatment time and discharge gap on the activity of the catalysts were investigated, and the optimum conditions of plasma treatment were obtained. The results demonstrated that when the plasma treated Ca/Al composite oxides was used as catalyst to produce biodiesel, the yield of methyl ester can be high up to 95.9% compared to that of 91.9% with the untreated catalyst. Similarly, when the plasma treated NaAlO2/MgO was used as catalyst to produce biodiesel, the yield of methyl ester can be high up to 92.5% compared to that of 86.3% with the untreated catalyst. However, the stability of both catalysts was slightly increased. In addition, the two kinds of plasma treated catalysts under the optimum conditions were characterized with IR,BET,XPS,XRD and SEM. The results indicated that the specific surfaces of both plasma treated catalysts were increased, while the crystal structure and surface composition has not changed.Finally, Jatropha oil was used as raw material for synthesis of biodiesel catlyzed by Ca/Al composite oxides catalyst. Different raw material processing methods were investigated and compared. The results indicated that the acid value of Jatropha oil was much higher than that of general vegetable oils. When solid base catalyst of Ca/Al composite oxides was employed for synthesis of biodiesel, preesterification of Jatropha oil may be necessary in order to reduce its content of free fatty acid and gelatin.