Base heterogeneous catalytic transesterification of rice bran oil to biodiesel using calcium oxide nanostructured

Abstract

Biodiesel or fatty acid ester is commonly produced by transesterification of vegetable oil or animal fat. Commercially, biodiesel was synthesized using homogeneous base catalysts such as NaOH and KOH. However, homogeneous base catalyst adsorped into the vegetable oil or animal fat. Thus, a large amount of water is required to clean the biodiesel and might lead to saponification or soap formation. As a result, this will lower the biodiesel quality and makes the biodiesel production becomes difficult, producing waste water, expensive and complicated. This research focused on the use of heterogeneous base catalyst, calcium oxide (CaO), an alkaline earth metal oxide that make the biodiesel easily separated, low cost and environmental friendly. The aim of this research is to investigate the potential of commercial calcium carbonate, CM-CaCO3 to be transformed to nanostructured CaO and used as a heterogeneous base catalyst for single step transesterification of rice bran oil to biodiesel. The CaO samples were prepared by calcination at 100°C to 700°C under vacuum at 10-3 mbar. The prepared CaO nanostructured was characterized by thermogravimetric analysis-differential thermal analysis (TGA-DTA), Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), nitrogen gas adsorption analysis (NA), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX). The basicity of the prepared CaO nanostructured was determined via back titration method. TGA-DTA result showed that the calcination temperature for CM-CaCO3 to form CaO must be higher than 600°C. This was supported by FTIR results which indicated the complete formation of CaO at 700°C. XRD showed that at this temperature, the rhombohedral CaCO3 and hexagonal Ca(OH)2 were totally disappeared leaving only crystalline cubic CaO. CaO obtained at 700°C (CaO-700) showed the highest BET surface area of 11.49 m2g-1. FESEM image showed the spherical particles coagulated to form agglomeration with nanoparticle size. The EDX further supported the formation of CaO and indicated to contain 53.56% of oxygen and 46.44% of calcium. It was found that CaO-700 has the highest basicity with 1.959 mmol/g. After optimization process, the prepared nanostructured CaO-700 was selected and applied for single step transesterification reaction of rice bran oil to produce biodiesel. The biodiesel produced was characterized using FTIR, NMR and GC-FID. The catalytic activity was further studied on the effect of time of reaction, percentage catalyst loading and a mechanism reaction was proposed. FTIR and NMR results further confirmed that biodiesel was successfully formed. In this study, the optimum reaction conditions to produce the highest biodiesel of 89% was at 60 minutes reaction time with 1.0% catalyst loading.