Application of walnut shell ash/ZnO/K2CO3 as a new composite catalyst for biodiesel generation from Moringa oleifera oil

Abstract

A novel heterogeneous catalyst based on walnut shell ash (WSA)/ZnO/K2CO3 composite was synthesized and applied for the production of biodiesel via the transesterification process of Moringa oleifera non-edible oil. Chemical precipitation and calcination processes were used to produce the catalyst. The results showed that the specific active surface areas for free WSA, ZnO, and WSA/ZnO/K2CO3 composite samples were 8.1, 24.1, and 1.9 m2.g−1, respectively. XRD and FTIR tests were confirmed the occurrence of different functional groups or compounds in the structure of the synthesized catalyst and indicated the activity potential of the catalyst. A response surface method-central composite design (RSM-CCD) was used to investigate the effect of independent variables including the temperature and time of reaction, the methanol to oil ratio, and catalyst concentration on the process efficiency. A probability value (P-value) < 0.0001 and a Fisher value (F-value) of 192.16 were obtained indicating the high capability of the proposed model. The value of C.V.% of 1.10 showed that there is a little deviation between the experimental and the predicted data by the model, which shows the high accuracy of the model. In addition, R2 and Adj. R2 parameters confirmed the high ability and accuracy of the model. Based on RSM-CCD results, the maximum efficiency of 97.34 % was obtained using a reaction temperature of 65 °C, a reaction time of 4 h, a catalyst content of 4 wt%, and methanol to oil ratio of 18:1. Moreover, it was shown that that the synthesized catalyst can be re-cycled for multiple usages in the biodiesel generation process. The E factor showed that the produced fuel is biocompatible. The properties of the produced biodiesel showed that it has good compliance with ASTM-D6751 and EN-14214 and can replace diesel-derived fuels as a suitable fuel source.