Regeneration of spent bleaching earth and conversion of recovered oil to biodiesel

A large amount of spent bleaching earth (SBE) solid waste is generated by the vegetable oil refining industry. This spent bleaching earth contains entrapped crude oil and in most cases, it is disposed of in its pristine state, which is considered an environmental hazard. In this work, the regeneration of SBE by pyrolysis or solvent extraction, and the conversion of the recovered entrapped vegetable oil to biodiesel are investigated. The entrapped oil was extracted using n-hexane, methanol or steam as solvents, and the SBE was regenerated by pyrolysis under inert environment of Nitrogen at 450 °C, 550 °C and 650 °C. After oil extraction, the regenerated bleaching earth (RBE) was activated and employed in virgin vegetable oil bleaching. Peroxide activated samples of methanol-extracted and pyrolyzed regenerated bleaching earth at 450 °C and 650 °C exhibit superior bleaching property; demonstrating that the SBE could be regenerated to have superior bleaching capacity over fresh bleaching earth. Thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) analysis of the SBE show that methanol extracted 23.5% out of the 35% residual oil (i.e. 67% efficiency) compared to 15.7% (i.e. 45% efficiency) by n-hexane, while pyrolysis extracted 33% out of the 35% residual oil (i.e. 95% efficiency). GC–MS analysis of the produced biodiesel shows that the n-hexane extracted oil produces more fatty acid methyl esters (FAME). Therefore, the choice of solvent depends on the intended application; as methanol regenerates the SBE better while retaining its adsorptive properties, while n-hexane gives a better biodiesel yield.