Abstract
Kaolinite nanotubes were synthesized by exfoliation and scrolling process for kaolinite sheets and then doped with potassium ions (K+/KNTs) forming a novel basic catalyst of promising activity in the transesterification reactions. The synthetic K+/KNTs catalyst displayed well-developed nanotube morphology with an average pore diameter of 14.5 nm, surface area of 112 m2/g, and total basicity of 7.43 mmol OH/g. The catalyst was applied in the transesterification of waste samples for sunflower cooking oil based on statistical design. The statistical design was built based on the response surface methodology in conjunction with the central composite design. The obtained results considering the interaction between the different factors (time, temperature, catalyst loading, and methanol-to-oil ratio) reflected achieving maximum biodiesel yield of 98%. This value was obtained after conducting the test for 4 h using 6 wt, of K+/KNTs as catalyst loading in the presence of 15:1 methanol-to-oil ratio at a reaction temperature of 90 °C. Considering the suggested optimization solutions from the design, K+/KNTs catalyst can achieve biodiesel yield of 99.4% if the conditions adjusted at 5.5 h as time interval, 4.96 wt, % as loading, 103.3 °C as temperature, and 14.64:1 as a methanol-to-oil ratio. The properties of the biodiesel sample at the best conditions match the technical limitations of both EN 14214 and ASTM D-6751 standards.
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•K+ doped clay nanotubes were synthesized as basic catalyst for transesterification reaction.•The catalyst is of 14.5 nm pore diameter, 112 m2/g surface area, and 7.43 mmol OH/g total basicity.•It is applied effectively in transesterification of waste sunflower oil with maximum yield of 98%.•The best conditions are 4 h, 6 wt,% loading, 90 °C and 15:1 alcohol/oil using statistical design.•The resulted biodiesel matches mostly the requirements of the international standards.