Abstract
Bentonite sample enriched in organic matters (oil shale) was functionalized with -SO3H sulfonated carbonaceous bentonite (S-CB) by sulfonation process as a low-cost and effective acidic catalyst for the transesterification spent sunflower oil (SFO). The sulfonation effect was followed by several analytic techniques including X-ray diffraction, Fourier transform infrared, and scanning electron microscopy analysis. The catalytic performance of the sulfonated product was evaluated based on a statistical design which was built according to the response surface methodology and the central composite rotatable design. Using the S-CB acidic catalyst in the transesterification of spent SFO resulted in an actual biodiesel yield of 96% at studied conditions of 85 min at reaction interval, 50 °C as temperature,15:1 as methanol/oil ratio, and 3.5 wt % as S-CB loading. Moreover, the optimization function suggested enhancement to obtained yield up to 97.9% by selecting the values of temperature at 62 °C, the time at 98.5 min, the methanol/SFO ratio at 14.4:1, and S-CB loading at 3.4 wt %. The technical evaluation of the SFO biodiesel reflected the suitability of the product to be used as biofuels according to international standards. The kinetic behavior of the SFO transesterification reaction over S-CB is of pseudo-first order properties and of low activation energy. Finally, the synthetic S-CB as a solid acidic catalyst is of significant reusability and was reused five times with remarkable biodiesel yields.