Study Of Heterogeneous Base Catalysts For Biodiesel Production

Nowadays, biodiesel is gaining more and more attention due to the earths' diminishing fossil fuel resources and its environmental merits. Having almost the same characteristics as diesel fuel, biodiesel can be used directly in diesel engines. Fuels from renewable biomass have advantages to lower the combustion emission of carbon monoxide, particulate matter, and sulfur compounds and limit greenhouse emissions because of the closed carbon dioxide cycle.Biodiesel is usually synthesized in the presence of homogeneous catalysts. However, the formation of soap lowers the biodiesel yield and renders the separation of ester and glycerol, making the washing process difficult. At the same time, the catalysts can't be reused. In order to solve this problem, at present, more and more research works have focused on the use of heterogeneous catalysts. Heterogeneous catalysts have several advantages including easier operational procedures, catalyst separation, reusability and reduction of environment pollutants, among others.Taking transesterification of vegetable oil and methanol with heterogeneous base catalysts as the main research objects, analyzed the FAME components from three vegetable oils, studied four solid base catalysts KF/MgO, sodium aluminate, K2CO3/La2O3 and KF/La2O3 in the transesterification reaction of biodiesel synthesis, characterized the catalysts thoroughly, and studied the overall reaction kinetics of three catalysts sodium aluminate, K2CO3/La2O3 and KF/La2O3 in the transesterification of soybean oil and methanol. The main contents are as follows:The rapeseed biodiesel was qualified analyzed with GC-MS apparatus, the results showed four main components:palmitic acid methyl ester (16:0), oleic acid methyl ester (18:1), linoleic acid methyl ester (18:2), linolenic acid methyl ester (18:3). Biodiesel from Rapeseed, soybean and cottonseed were quantified analyzed by gas chromatography. Rapeseed biodiesel:palmitic acid methyl ester 6.32%, oleic acid methyl ester 49.26%, linoleic acid methyl ester 16.35%, linolenic acid methyl ester 25.73%. Soybean biodiesel:palmitic acid methyl ester 12.13%, oleic acid methyl ester 84.25%. Cottonseed biodiesel:palmitic acid methyl ester 28.64%, oleic acid methyl ester 69.13%. At the same time, rapeseed biodiesel's reaction yield was tested with internal standard method. High-performance liquid chromatography (HPLC) was used for the determination of compounds occurring during the production of biodiesel from rapeseed oil, soybean oil and cottonseed oil. HPLC method:reservoir A contained methanol, reservoir B contained a mixture of 2-propanol-hexane (5:4, v/v). A linear gradient from 100% A to 50% A+50% B in 15-35 min was employed.1H nuclear magnetic resonance (NMR) spectroscopy to quantitate directly the methyl esters in the reaction mixture was build. The relevant signals chosen for integration were those of methoxy groups in the methyl esters at 3.7 ppm (singlet) and of the (x-carbonyl methylene groups present in all fatty ester derivatives at 2.3 ppm. The determination was accurate and simple.The synthesis of biodiesel from rapeseed oil by transesterification was carried out over Magnesium oxide loaded with KF. The catalytic activity strongly depends on the loading amount of KF and calcined temperature. We found that the reaction reached a 79.37% yield when the loading amount was at 35 wt% and calcined at 500℃. The simply dried 30% KF/MgO at 80℃was found to give equally good results from the catalyst calcined at 500℃, avoiding the usual activation at high temperature. The catalysts were characterized by the Hammett indicator method, BET, TG/DTG, XRD, NMR, EDS, and FT-IR. According to the instrumental analysis, the activity in the transesterification probably belonged to coordinately unsaturated F-and liberation of hydroxide during preparation. The effects of methanol/oil ratio and catalyst amounts on the conversion were also studied.The production of biodiesel from soybean oil by transesterification was carried out over sodium aluminate as a heterogeneous catalyst. The solid base showed high catalytic activity for methanolysis reaching a 93.9% yield under optimal reaction conditions (reflux temperature,1.5 wt% of catalyst,12:1 molar ratio of methanol/oil, and 50 min). The catalyst treated at different temperatures was characterized by ICP-OES, XRD, TG/DTG and FT-IR. The reaction contained homogeneous and heterogeneous contributions at the same time. Removing water and carbon dioxide was an effective way to elevate the catalyst stability in methanol.The transesterification of soybean oil with methanol was carried out over K2CO3/La2O3 and KF/La2O3 as solid base catalysts. The catalysts preparation of different loading amount and calcination temperature were studied. Under the reaction conditions of methanol/oil molar ratio 12:1, catalyst amount 4%, reaction temperature 60℃, reaction time 20 min, the 25 wt% K2CO3/La2O3 calcined at 600℃reached a conversion of 93%, and 15 wt% KF/La2O3 achieved 93.9% ester yield in 40 min.According to the characteristics of two catalysts, LaKO(CO3) was formed in the calcined process of K2CO3/La2O3, and K2CO3 interacted with La2O3 leaded to the basic site La-O-K. Beside the active site La-O-K, KF/La2O3 also had component like La[(OH)x---Fy], whose basic site came from the nearest oxide atom close to fluoride atom.The apparent reaction order, rate constant and activation energy were calculated from kinetic data of three catalysts. From the results, the concentration of reactors had bigger effect on K2CO3/La2O3 than KF/La2O3 as a catalyst. The reaction of NaAlO2 under 50℃, reaction rate fell down with the rising of reactor's concentration. The sensitivity of temperature was:K2CO3/La2O3＞KF/La2O3.