Microemulsion based residual oil recovery for spent bleaching earth from biodiesel production

Abstract

Spent bleaching earth (SBE), an industrial solid waste generated at bleaching process of vegetable oil refinery, usually recovers oil retained in SBE through solvent extraction which can lead to environmental impact and high cost of disposal. Consequently, this work investigated the use of microemulsion extraction technique to extract residual oil adsorbed on SBE. The most important criterion of this method is the ability of lowering interfacial tension (IFT) between oil and aqueous surfactant solution in order to liberate oil from SBE. The surfactant systems with different structure (anionic extended and nonionic ethoxylated surfactant) were selected to formulate middle phase microemulsion (Winsor type III) with crude palm oil. In the oil extraction, the predetermined optimum formulations were selected to study the effect of extraction parameters based on total oil extraction efficiency. In addition, the extracted oil qualities were evaluated. The result showed that C12,13-(PO)4-SO4Na and C12,13-(PO)8-SO4Na produced an ultralow IFT (<0.1 mN/m) with crude palm oil whereas C12,14-(EO)3-OH and C12,14-(EO)9-OH were not observed due to limited temperature. The C12,13-(PO)8-SO4Na system provided the highest of total oil extraction efficiency (25%) at the optimum surfactant concentration of 1 wt.% with 2.5 wt.% NaCl at stirring 1000 rpm, using solid to liquid ratio (g/ml) of 2/15 and contact time 20 min. Microemulsion technology could not replaced a solvent technique due to the interactions between surfactant and waxy solid in vegetable oil is limited compared to that of vegetable oil in liquid form. However, the extracted oil obtained aqueous microemulsion based extraction had superior oil quality in terms of low free fatty acid.