Recrystallization of tri-sodium phosphate from Thai monazite concentrate decomposition as solid catalyst for biodiesel production

Abstract

Tri-sodium phosphate (TSP) obtained from alkaline baking process of Thai monazite concentrate was used as raw material to synthesize the solid catalyst for biodiesel production. The TSP catalysts were prepared via recrystallization method with the ratio of Na₃PO₄·12H₂O: H₂O of 1:15 by lower temperature from 80 to 30 °C using stirring rate of 400 rpm and calcined at 300–700 °C. The catalytic performances were evaluated in the transesterification of palm oil with methanol. According to the results, the radioactive material (uranium) of < 10 mg kg^-1 was detected after recrystallization, which was considered safe to use as catalyst. The TSP calcined at 600 °C showed active pure tetragonal phase with high basic sites strength and basicity, and can produce the highest fatty acid methyl ester (FAME) content of 91 % under the reaction conditions: the molar ratio of oil to methanol of 1:9, the catalyst loading of 5 wt %, the reaction temperature of 80 °C and the reaction time of 5 h. There was a significant leaching of active Na⁺ during the reaction. The improvement of stability and reusability of the catalyst and economic analysis will be further investigated for its utilization in the large-scale biodiesel production. This development can enhance the economic value of TSP as by product obtained from mineral monazite processing and also provides an idea for designing the economic viability of rare earth production.