Microwave enhanced transesterification of biodiesel from non-edible feedstocks using waste mollusc shells as heterogeneous catalyst

Abstract

Transesterification method is widely used to produce biodiesel at low volume production, which employs a homogenous catalyst and is found effective for processing virgin or highly refined vegetable oils. Hot plate and water bath are the common heat source methods being used to assist in expediting the reaction process. These methods are not only consumed time but they also wasted a lot of water for washing which makes the whole process less environmental friendly and costly. Microwave technology has been reported able to provide rapid heating but the report on its application in the transesterification process is somehow very limited especially involving the catalyst from mollusc shells. Until today, the waste mollusc shells application as the primary heterogeneous catalyst implemented in bulk size in converting high free fatty acid (FFA) feedstock into green and potential biodiesel with the microwave irradiation method is rarely reported. This research aimed to optimise biodiesel production and to identify significant parameters affecting the non-edible biodiesel yield via microwave-assisted transesterification. Waste mollusk shells oxides derived from Corbicula fluminea, Anadara granosa, and Perna viridis as heterogeneous catalysts were utilised to assist the microwave irradiation transesterification process. High FFA of rubber seed oil (RSO), and Jatropha Curcas oil (JCO) were employed as raw feedstock. The mollusc shells were sieved to different particles sizes ranging from 1 mm to 2 mm and were calcined at 900oC for 4 hours at a 10oC/min heating rate. Microwave power and reaction time were varied from 350 W to 450 W and 5 to 9 min respectively. The catalyst characterizations were carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM) and Brunauer- Emmett Teller (BET). A two-step transesterification process was utilised to perform the production. The acid esterification process used sulfuric acid and methanol to reduce the FFA percentage for RSO and JCO. The calcined catalysts mediated the transesterification reaction with feedstock and methanol via domestic microwave heating. Optimisation process was conducted using the Taguchi method of L27(35) orthogonal arrays. According to the analysis of the signal-to-noise ratio and ANOVA, the effect of catalyst loading was the most significant parameter with 45.1% and 47.5% contribution on the biodiesel yield from JCO and RSO, followed by the reaction time and molar ratio of methanol to oil. RSO biodiesel recorded the highest yield conversion of 96.6%, followed by JCO around 95.9% under the optimum parameter of 400 W microwave power and 7 minutes reaction time. It can be concluded that the calcium oxide catalyst derived from waste mollusc shells has a high potential to be used as biodiesel production catalysts in the transesterification of low quality feedstock that fulfill the ASTM D 6751 standard requirement.