Optimization of Microwave-Assisted Extraction of Residual Soybean Oil from Spent Bleaching Earth

Abstract

Spent bleaching earth (SBE) which is generated from bleaching process is a valuable industrial waste of edible vegetable oil production because of residual edible vegetable oil absorbed. The residual oil in spent bleaching earth can be recovered and reused for application in the industries such as the production of biodiesel and lubricant. Currently, microwave-assisted extraction (MAE) technique is widely used because this method has a shorter extraction time and less solvent consumption when compared with traditional methods. In this study, MAE combined with solvent reflux was optimized using solvent screening experiments and response surface methodology (RSM) to obtain the highest yield of MAE extraction of residual soybean oil from spent bleaching earth. The extraction yield of residual soybean oil obtained from selected solvent were hexane-ethanol mixture (2:1 v/v, 10.19%) > hexane-ethanol mixture (1:1 v/v, 10.00%) >hexane-ethanol mixture (1:2 v/v, 9.98%) > hexane-ethanol mixture (1:3 v/v, 9.83%) > hexane-ethanol mixture (3:1 v/v, 8.59%) > hexane (8.17%) > acetone (7.73%). The regression coefficient (R-squared = 0.9852) expresses the accuracy of the regression and indicates the relationship between experimental data and predicted result, with high regression coefficient close to 1, which is remarkably desired. The experiment conditions for optimal MAE extraction of residual soybean oil from SBE were hexane-ethanol mixture (2:1 v/v), liquid to solid ratio 15.56:1 mL/g, extraction time 12.22 min, and microwave power 350 W. Under such conditions, the highest predicted value of the extraction yield of residual soybean oil was 10.43%.