Regeneration of geothermal-sludge based sodium silicate catalyst for transesterification of palm oil with methanol

Abstract

Sodium silicate synthesized from geothermal sludge of a geothermal power plant in Indonesia was applied as a solid catalyst to catalyze transesterification reaction of palm oil with methanol. In our previous study, it has been found that the catalyst deactivated due to hydrocarbon contamination on its surface. In the present work, 3 (three) different regeneration methods were studied for reactivation of the catalyst. The studied methods were: 1) calcination at 400oC for 3 hours with a ramp of 20°C/minutes, 2) 1x-washing with methanol at room temperature, and 3) 3x-washing with methanol at 60°C. The performance of the catalyst was studied by sequential reaction batches to monitor the reaction yield from time to time. The sequence consisted of 4 (four) transesterification reaction cycles, with a catalyst regeneration process before reused in subsequence cycle. Experimental results showed that although none of the regeneration processes regained catalyst activity as high as that of the freshly-activated catalyst, the third regeneration method, i.e. 3x-washing with methanol at 60°C regained higher catalyst activity compared to the other two studied methods. The method could maintain the reaction conversion at about 50% after four cycles of reaction and regeneration, Furthermore, the kinetics of the catalytic transesterification reaction was studied by fitting the experimental data with calculated yield obtained from mathematical modelling. It was found that among the first, second, and third order reaction kinetics, the experimental data was best fitted by the calculated results from the first order reaction kinetics. Results from this work suggested that even though 3x-washing regeneration of sodium silicate catalyst with methanol at 60°C offered relatively high reactivation, further study for improvement is still needed.