Catalytic Transfer Hydrogenation Of Fatty Acid Methyl Esters Under Mild Conditions

Biodiesel is an effective and clean-burning alternative fuel.Although biodiesel shows many advantages,there are some drawbacks in it,such as poor cold flow property and low oxidative stability.The drawbacks of biodiesel have been limited largely to the application of biodiesel.In this work,FAMEs,the main component of biodiesel produced by transesterification,was selected for the study.The catalytic transfer hydrogenation of FAMEs using using sodium borohydride as hydrogen donor with Ni-La-B catalyst was studied.The main research results were as followed:(1)Ni-B alloy catalysts with different modifiers used for catalytic transfer hydrogenation of FAMEs under mild conditions was prepared by chemical reduction method.The addition of La in Ni-B catalyst exhibited higher catalytic activity compared with Cu,Zr and Co.The conversion ratio of methyl linoleate(C18:2)using La added Ni-B catalyst increased by 31.45%.Characterization of Ni-La-B and Ni-B were achieved by scanning electron microscope,X-ray diffraction,and X-ray photoelectron spectrosc.It was found that the obtained Ni-La-B catalyst had amorphous structure,small particle size,and loose structure.In addition,the repeatability experiments of the Ni-La-B catalyst were carried out.It was found that the Ni-La-B catalyst after the first cycle of using showed obviously deactivated.After the ethanol cleaning of used Ni-La-B catalyst,the repeatability of the catalyst was effectively improved,and the conversion ratio of C18:2 still reached about 60 % after four recycling times.(2)The optimum conditions for catalytic transfer hydrogenation of FAME using sodium borohydride as hydrogen donor with Ni-La-B catalyst were as follows: catalyst loading 10 wt.%,reaction time 150 min,reaction temperature 85 °C,sodium borohydride amount 1.14 g,and water quantity 40 g.Under the optimum conditions,the conversion ratio of C18:2 reached 95.4 %.The FAMEs have been successfully upgraded by using sodium borohydride as hydrogen donor under mild reaction conditions.Both the oxidative stability and the combustion quality of FAMEs were significantly improved and the major properties of hydrogenated FAMEs met the requirements of both Chinese and European standards for biodiesel.Based on the results,the possible mechanisms involved in hydrogenation of FAMEs using sodium borohydride as hydrogen donor were presented.(3)The catalytic transfer hydrogenation of FAMEs was carried out by ultrasound assisted.The optimum conditions for catalytic transfer hydrogenation of FAMEs under ultrasound assisted were as follows: catalyst loading 10 wt.%,reaction time 120 min,reaction temperature 35 °C,sodium borohydride amount 1.51 g.Under the optimum conditions,it was found that the hydrogenated FAMEs met the Chinese and European standards.In comparison with catalytic transfer hydrogenation of FAMEs under non ultrasound assisted,the use of ultrasound can be established as the reduction in the reaction time(from 150 to 120 min)and significant reduction in the temperature(from 85 to 35℃).Also the trans-isomer formation was much lower under ultrasound assisted.