Preparation Of Heterogeneous Catalysts And Its Application In The Synthesis Of Biodiesel In The Transesterification

Biodiesel, a typical bio-renewable alternative fuel, is generally produced by transesterification of vegetable oils or animal fats with short-chain alcohols in the presence of catalysts. Conventional synthesis techniques rely on homogeneous acid and basic catalysts; however, removal of these catalysts is technically difficult and brings extra cost to the final product. Heterogeneous catalysts could improve the synthesis methods by eliminating the additional processing costs associated with homogeneous catalysts. Unfortunately, the application of heterogeneous catalyst has been restricted because of its low activity. So, the design of high catalytic activity of heterogeneous catalyst is one of the key technologies in preparing biodiesel at present. In this paper, two kinds of heterogeneous catalysts are prepared and characterized by the methods of TGA-DSC, XRD, SEM, BET, NH3-TPD. The relationships between catalytic performance and structure of the catalysts were studied in transesterification of vegetable oils to biodiesel.1. The eggshell catalyst, which was used in transesterification of vegetable oils to biodiesel, was prepared by calcining waste eggshell in different temperatures. Effect of calcination temperatures on the structure and activity of eggshell catalyst was investigated and reaction conditions were optimized. It was found that the calcination temperature affected the catalytic activity of eggshell catalyst and the optimum calcination temperature are above 800℃. The experimental results showed that a 9:1 molar ratio of methanol to oil, addition of 3 wt% eggshell-derived catalysts, 65℃reaction temperatures gave the best results, and the biodiesel yield reached 98% at 3 h. Besides, the reuse of the catalyst was studied. The result showed that catalytic activity of the eggshell-derived catalyst was still high after recycled 14 times. In this study, high active, reusable solid catalyst was obtained by just calcining eggshell. The method of reusing eggshell waste to prepare catalyst could recycle the waste, minimizing contaminants, reducing the production costs of biodiesel and making the process to produce biodiesel fully ecologically friendly.2. Zr(HPO₄)₂ (solid acid), ZrPO (acid-base bifunctional properties) and ZrPON (solid base), were prepared by precipitation method. The catalytic properties of them were studied in the reaction of biodiesel synthesis. The result showed that catalytic activity of ZrPO were higher than Zr(HPO₄)₂ and ZrPON. ZrPON showed medium activity and Zr(HPO₄)₂ had lowest activity. The catalytic performance of the heterogeneous Zirconium phosphate oxygen compounds was closely related to their acid-base property. ZrPO contained both acid and basic sites. Its high catalytic activity may be due to acid-base bifunctional mechanism. The study provides a new way to design a high-performance solid catalyst in preparation of biodiesel.