Fabrication of a solid catalyst using coal fly ash and its utilization for producing biodiesel

Abstract

To recycle raw fly ash (RFA), a waste from thermal power plants, it was used to prepare solid catalysts which have many advantages compared with homogenous catalysts. When biodiesel was produced from soybean oil using RFA, only 1.2% of biodiesel conversion was obtained. A metal hydroxide, NaOH, KOH or Ca(OH)2, was mixed with the acid-treated fly ash (ATFA), and the mixture was calcined at 700°C for 3 h to prepare the solid catalyst. The solid catalyst prepared by mixing ATFA with NaOH, designated as SC-Na, showed a better performance than those prepared by mixing ATFA with KOH or Ca(OH)2, respectively. The optimal mass ratio of ATFA with NaOH was 1:3, at which the proportion of Na2O increased to 60.2% in SC-Na, and 97.8% of biodiesel conversion was achieved under optimal reaction conditions (2 w% SC-Na relative to oil and 5 mL-methanol/g-oil at 50°C for 4 h). Finally, a batch operation was repeatedly carried out to test the feasibility of reusing the solid catalyst, and more than 96% biodiesel conversion was stably achieved for the third round of operations. This study shows that RFA was successfully recycled to solid catalysts through a simple preparation method, and the solid catalyst was reused for the production of biodiesel with high conversion.