Study On The Preparation Of Solid Catalyst For Biodiesel Production

Currently, the research on alternative liquid fuel has been carried out extensively as a result of rising price of international crude oil and tension of oil supply, which will bring great effects on our country's economy construction.Biodiesel, a mixture of methyl esters of fatty acids, is an environment-friendly transportation fuel produced by transesterification reaction of vegetable oils or animal fat with a short-chain alcohol in the presence of catalyst. Biodiesel is a renewable, alternative, non-toxic and biodegradable diesel fuel. Many studies have shown that the properties of biodiesel are very close to diesel fuel. Therefore, biodiesel can be used in diesel engines with little or no modification.Solid acid (base) refers to solids that can adsorb base (acid), or be defined as solids that give (accept) proton or accept (give) electron. The transesterification reactions catalyzed by solid base may avoid the problems in traditional homogeneous acid/base catalyzing process that the separation of transesterification products with used catalyst is very difficult and discharge of waste catalyst induces environmental problems, it is meaningful for both the production and application of biodiesel, especially for the rising biodiesel industry to study heterogeneous base catalysts and transesterification process.Biodiesel production using heterogeneous base catalyst is a new process, which is little reported home and abroad. The purpose of this paper is to prepare highly-activated and highly-selective solid alkali catalyst and explore new methods of increasing stability and reusable times of solid base by analyzing the reason for which catalysts lost activity and got toxic.The preparation, application and reutilization of Cs2O/γ-Al2O3 catalyst were investigated in this paper. The main results are as follows:1. The preparation of solid base catalysts with four kinds of compounds based on cesium of Cs₂CO₃, CsC₂H₃O₂, CsNO₃ and CsCl and the effects of different kinds of supports on performance of catalysts were studied. The results show that solid super-base catalysts can be prepared with Cs₂CO₃ or CsC₂H₃O₂ loading onγ-Al₂O₃, CaO and MgO. It is the most suitable for preparation of catalysts to select Cs2CO3 as precursor andγ-Al₂O₃ as support due to simplicity of preparation technology and high base strength. Cs₂O/γ-Al₂O₃ catalyst, prepared by immersing Cs₂CO₃ into water, then loading onγ-Al₂O₃, finally calcining in nitrogen atmosphere, whose Hammett value is more than 37, which is higher than those of catalysts prepared with potassium, sodium and calcium under the same conditions.2. Cs2O/γ-Al2O3 catalyst was characterized by BET, XRD, XRF and FTIR. The results suggest that significant catalytic activity substance is Cs₂O dispersing over the support and prepared solid base has three alkali centers.3.The highest transesterification rate of 95.5% was obtained in ester-exchange reactions of rapeseed oil and methanol catalyzed by Cs₂O/γ- Al₂O₃ solid base whose loading amount was 2.5mmol/g, and the transesterification rate amounted to 93.7% in catalyzing ester-exchange reactions of tallow and methanol with the catalyst. The loading amount of 4 mmol/g could be achieved when using nano-γ-Al2O3 as support and the less methanol dosage, the shorter reaction time and 98.5% transesterification rate could be obtained in catalyzing ester-exchange reactions of rapeseed oil and methanol, and the transesterification rate was over 80% when this catalyst was used more than ten times.4. The reasons for toxicosis and loss of activity of catalyst were investigated. It's suggested that the effective detoxifcation method is to calcine toxic catalyst again in nitrogen atmosphere and the method of resuming activity of catalyst is to supply activated components.