Preparation of Solid Acid Catalyst from Rice Husk and Investigation of Its Catalytic Performance in Esterification

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Addis Ababa University


The fundamental reaction in organic synthesis is esterification of carboxylic acid and alcohol which can produce high value of material in the areas of cosmetics, plastics, food, medicines, intermediates, etc. Furthermore, this reaction is used in the pretreatment step for biodiesel production from low cost, lower quality feedstocks (with high free fatty acid content) to improve the economics of production. The cost of utilization of virgin oil (higher feedstock with lower FFA content) as a raw material for biodiesel production constitutes 70% of the total biodiesel production cost. Homogeneous acid catalysts, such as sulfuric acid and phosphoric acid, are conventional catalysts for esterification. However, the uses of these homogeneous acid catalysts are limited in a practical application due to corrosion, environmental pollution, side reactions and a more tedious separation process. Alternatively, a number of prospective heterogeneous acid catalysts, which are easily separated from the reactants and products through suction filtration, get attractive routes for biodiesel production and could eliminate the problems mentioned above. A sulfonated carbon-based solid acid catalyst was prepared by sulfonating rice husk char with concentrated sulphuric acid and the catalytic activity was validated through the esterification of oleic acid with ethanol for biodiesel production. Characterization methods of X-ray diffraction (XRD),Fourier transform infrared spectroscopy(FT-IR), thermogravimetry analysis and acid density tests was carried out to reveal the physical and chemical characteristics of the prepared catalyst. The effects of catalyst preparation conditions and esterification reaction conditions on the performance of the catalyst were investigated using the esterification of oleic acid and ethanol as the probe reaction. The results showed that 4500C and 1100C were suitable carbonization and sulfonation temperatures respectively. The catalyst prepared at these conditions exhibited high catalytic performance and 98% conversion of oleic acid was obtained under the optimal reaction conditions with a catalyst loading of 5.73%, ethanol to oleic acid molar ratio of 10.6:1, and a reaction time of 2.65 hr. The conversion still reached 94.89% after five cycles of successive reuse, which indicated that the catalyst stability was excellent. These results clearly show that the rice husk-derived catalyst is promising, economic and eco-friendly for biodiesel production from low-cost feedstocks and potentially substituted for homogeneous sulfuric acid catalyst for esterification in industries in the near future.



Esterification, solid acid catalyst, rice husk, biodiesel