Abstract
Inorganic zeolite/geopolymer composite (Z/GP) was synthesized by controlled zeolitization of synthetic geopolymer from kaolinite and diatomite to be used as a potential catalyst in the transesterification of commercial spent cooking oil (SCO). The Z/GP composite demonstrates promising microstructural properties (106 m2/g surface area and 4.2 nm average pore diameter) and chemical structural enrich in OH and Na+ ions as active basic and catalytic centers. The Z/GP composite as catalyst was applied in the transesterification of SCO according to suggested experiment conditions from statistical design which was built based on the Response Surface Methodology. The measured biodiesel yield from SCO over Z/GP catalyst is 98.1% at experimental conditions of 40 °C as temperature, 90 min as time, 12:1 as methanol/SCO ratio, and 3.25 wt, % as Z/GP loading value. The theoretical optimization function of the statistical design suggested potential enhancement for the performance of the reaction to achieve a yield of 99% by adjusting the values of the studied factors at 54.9 °C, 81.9 min, at 12:1, and 3.48 wt, % for the temperature, time, methanol/SCO ratio, and Z/GP loading. The physical properties of the produced SCO-based biodiesel over Z/GP demonstrate the suitability of the product to be used as biofuels considering the criteria to international standards. The kinetic properties of the transesterification reactions of SCO over Z/GP catalyst follow the Pseudo-First order kinetic assumption and occurred with low activation energy. Finally, the synthetic Z/GP as a solid basic catalyst is of significant reusability and reused five times with remarkable biodiesel yields.
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•Zeolite/geopolymer composite was prepared as basic catalyst of high activity.•It was used in transesterification of waste-cooking oil based on statistical design.•It achieved actual and predicted biodiesel yields of 98% and 99%, respectively.•The produced biodiesel samples match the international specifications of biofuels.•It is of high recyclability, Pseudo-first-order kinetics, and low activation energy.