One step potassium hydroxide activated and calcium oxide doped carbon catalyst for transesterification of rice bran oil

Abstract

Palm kernel shell are a cheap and abundant biomass from palm oil industries in many tropical countries like Malaysia and Indonesia. This agricultural by-product can be a good source for the production of activated carbon. Activated carbon can be used as catalyst support in transesterification reaction to produce biodiesel. Catalyst support is important to reduce the effects of leaching in heterogeneous catalyst process. Typical preparation of activated carbon catalyst support for transesterification reaction employs a two-step process. In this study, doped activated carbon was prepared in one step using palm kernel shell activated by potassium hydroxide (KOH) and doped with calcium oxide (CaO). The modified carbon was prepared via wet impregnation method using different amount of CaO while maintaining the same percentage concentration of KOH at 25% by weight before calcined at 500oC for 5 hours. The prepared carbon was then used as a heterogeneous base catalyst in transesterification reaction of rice bran oil with methanol. The modified carbon was characterized using thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR), nitrogen adsorption analysis, field emission scanning electron microscope (FESEM), X-ray powder diffraction spectroscopy (XRD) and X-ray fluorescence spectroscopy (XRF). The basic strength of the sample was determined by back titration method. The final product of transesterification was then analysed using gas-chromatography-flame ionization detection (GC-FID) and gas-chromatography-mass spectrometry (GC-MS). XRF was employed to check the possibility of leaching of the metal catalyst into the biodiesel. TGA analysis indicates that complete calcination of palm kernel shells occur at 500oC. Thus, the activation of the modified carbon was done at 500oC. FTIR analysis of raw palm kernel shell shows the presence of various functional groups. However, after activation, most of the functional groups disappeared. BET surface area of 3.62 m2/g was obtained from the 25% CaO/KOH/C due to the filling of the metal catalyst into the cavities and pores of the modified carbon. This was confirmed by washing the modified carbon several times with hot water, which later increase the BET surface area to 443.84 m2/g. From the basicity analysis, increase in the percentage concentration of CaO increased the basicity of the prepared modified carbon. The performance of prepared modified CaO/KOH/C was identified by measuring the percentage yield of fatty acid methyl esters (FAMEs) in the transesterification of rice bran oil with methanol. The percentage yield of FAMEs for 0%, 10%, 15%, 20%, 25% and 30% CaO/KOH/C were 80.9%, 86.2%, 90.4%, 92.8%, 93.6% and 94.3%, respectively. Recyclability for the 25% CaO/KOH/C were studied and the catalyst can be reused for three consecutive runs with acceptable yield. Thus, it can be concluded that the preparation of one step KOH activated and CaO modified carbon from palm kernel shell can be used as catalyst in biodiesel production.