Modified Coconut Shell as Active Heterogeneous Catalyst for the Transesterification of Waste Cooking Oil

M. O. Ekeoma, P. A. C. Okoye, V.I.E. Ajiwe, B. H. Hameed


The potential of selected metal-based clay and carbon-based bio-waste materials were investigated for their performance as heterogeneous catalysts in the transesterification of waste cooking oil. Li-supported on activated carbon (Li/AC), Na-supported on activated carbon (Na/AC), Na-supported on sapiolite (Na/sapiolite), Ca-based clay (calcium powder), K-based clay (potassium powder), and Na-based clay (sodium powder) were variously screened heterogeneous catalysts for their catalytic effects in the transesterification of waste cooing oil (WCO) at similar reaction conditions. Coconut shell modified with sodium carbonate (Na/Ac) came out the most effective heterogeneous catalyst for the transesterification of waste cooking oil with the highest fatty acid methyl ester (FAME) yield after the screening and was therefore used for further optimization and characterization studies. For the catalyst characterization, the surface area and pore-size distribution of catalyst were determined by Braunner Emmett Teller (BET) method to be 893.16m2g-1 and 20.30 Å respective. The weight percent of Na element on calcined catalyst from energy dispersive spectroscopy (EDX) was 3.71 wt. % compared with the theoretical value 17.36 wt. %. Fourier Transform Infra-red (FTIR) analysis of calcined Na/Ac catalyst revealed two functional groups at 1400 – 1500 cm-1 (-CH2 bending) and 3300 – 4000 cm-1 (O-H bonding). The scanning electron microscopy (SEM) of raw and calcined Na/Ac catalyst revealed well developed pores after calcination resulting in the observed large surface area and pore structure which were the reasons for enhanced adsorption and subsequent high yield of FAME. Optimum conditions of 550 oC calcination temperature of Na/Ac catalyst gave 99% FAME yield at 70 oC reaction temperature, 7 h reaction time, 4.48 wt. % of catalyst loading and 6:1 methanol/oil molar ratio. Coconut shell which is a non-degradable material and an environmental concern could find use as efficient heterogeneous catalyst for bio-diesel production, a green energy source.

Keyword: Coconut shell, FAME yield, Transesterification, Heterogenous catalyst, Bio-diesel

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