Prepraration Of Solid Acid Catalysts And Solid Base Catalysts And Their Application In Synthesis Of Biodiesel

The price of fossil diesel is soaring in these two years,and it will be exhausted some day. Thus, looking for an alterative way to develop a substitute for diesel is an imperious task for humans. Biodiesel derived from a renewable lipid feedstock, such as vegetable oil or animal fat.There is growing interest in biodiesel (fatty acid methyl ester or FAME) because of the similarity in its properties when compared to those of diesel fuels. Waste cooking oils (WCO): which contain large amounts of free fatty acids should be disposed in a suitable way. The difficulty with alkaline-transesterification of these oils is that they often contain large amounts of free fatty acids (FFA).These free fatty acids quickly react with the alkaline catalyst to produce soaps that inhibit the separation of the ester and glycerin. In this research, a two step catalyzed process was adopted to prepare biodiesel from waste cooking oil whose acid value was 91 mgKOH/g. The free fatty acids of WCO were esterified with methanol catalyzed by solid acid in the first step, and the triglycerides (TGs) in WCO were transesterified with methanol catalyzed by solid base in the second step.The main contents of the thesis are as follows:1.Prepraration,characterization of solid acid and study on the esterification of biodiesel. In this paper the synthesis of modified SBA-15 samples with different hydrophobic properties and adjusted acid sites by direct synthesis method and grafting method.Catalytic properties of the modified SBA-15 samples in the esterification of FFA and methanol were mainly investigated. Firstly, after the synthesis of SBA-15,incorporation of different hydrophobic groups on the external of SBA-15 was carried,and then the templates were wiped off. Subsequently sulfonic groups were attached on the internal surface of SBA-15.So the modified SBA-15 samples were attained by grafting method. XRD spectra showed the modified SBA-15 samples reserved periodic hexagonal channels. The results of IR, contact angle and titration measurements showed the organic groups had been successfully incorporated on both internal and external surfaces.The results of TGA also showed the organic groups had high thermal stability. Secondly, the modified SBA-15 catalysts were prepared by direct synthesis method through simultaneous reaction of condensable inorganic silica species and silylated organic compounds in the acidic condition while PEO20-PPO70-PEO20 was used as surfactant. XRD spectra showed the modified SBA-15 samples also had periodic hexagonal channels except the samples in which the proportion of organic groups reached 26%. The results of IR, contact angle and titration measurements showed the organic groups had been successfully incorporated on the surface and had better effects than which incorporated by grafting method. Moreover, the wetting contact angle of the sample named d-C16H33-SBA-15-SO3H (α=0.11)reached 91.90°and its acid content was 0.98mmol H+/g. The results of TGA also showed the organic groups had high thermal stability. Thirdly, the catalytic properties of organic modified SBA-15 for the esterification of of FFA and methanol were studied. The results indicated that the sample named d-C16H33-SBA-15-SO3H (α=0.11)had excellent activity and stability. Under the conditions as follows:catalyst ratio to FFA:6%, reaction time:4 hours, the yield of biodiesel reached 91.2%. The catalyst could be reused. Catalytic activity of seven inorganic salts in the esterification of high acid value oil with methanol was studied.Results showed that catalytic activity of NaHSO4 and Ti(SO4)2 were good. The optimal parameters of esterification were as follows: molar ratio of methanol to oil 10:1,reaction time 4h and the amount of NaHSO4 4%,the transformation rate was 90.5%.using the same conditions,the transformation rate of Ti (SO4)2 was 97.2%.The catalyst could be recovered easily and used repeatedly.2.Prepraration,characterization of calcium oxide based solid base and study on the transesterification of biodiesel.CaO based solid base catalyst was prepared by impregnation method (CaO/C) and pugging method(CaO-C)respectively. Besides, some instrumental methods, such as XRD,CO2-TPD,BET were used to reveal the matrix structure, the specific surface area and the base strength of catalysts respectively. The catalytic mechanism in the transesterification reaction of calcium oxides catalysts were also detailedly investigated to study. In addition, transesterification of oils with methanol were also carried out. It was found that,two types CaO based solid base catalysts have similar base strength and high catalytic activity. The influences of reaction conditions were studied and the optimized parameters were the methanol/oil mole ratio of 10:1,reaction time 1h and the catalyst dosage of 3%(weight of catalyst/weight of oil).The reaction is rather slow at the beginning because methanol is insoluble in oil.It speeds up with increasing mutual oil-methanol solubility while mono-or di-glycerides forms in the reaction process.The catalyst is tolerant to free acid and water to some extent.3.Preparation of biodiesel from high fatty acid oil by solid acid and solid base. Waste oil have high free fatty acids (FFA).Due to its high FFA,the waste oil was processed in two steps: the solid acid catalyzed esterification followed by the solid base catalyzed transesterification. FFA of waste oil was esterified with methanol catalyzed by titanium sulfate in the first step, and then triglyceride(TG) of waste oil was transesterified with methanol catalyzed by porous CaO.Results showed that titanium sulfate had strong activity to catalyze the estersification. Under the optimal condition,the esterification rate of free fatty acid was 97.1%.The porous CaO have strong transesterification activitives,the conversion of oil feed was 96.1%.Using hydrophobic mesoporous molecular sieves SBA-15-SO3H solid acid catalyzed esterification two times, without seperating methanol and water in second step,using solid base catalyzed transesterafication directly.The solid base catalyst is tolerant to free acid and water to some extent. This new process presented many advantages, such as no acidic waste water, high efficiency, low cost equipment,and the recovery of catalyst.