A Study of Residual Oils Recovered from Spent Bleaching Earth: Their Characteristics and Applications

This study described the extraction of residual oils of spent bleaching earth (SBE) from palm oil refining industry, the properties and applications of residual oils obtained there from. Residual oils of SBE (acid-activated, WAC and neutral, NC) were recovered via solvent and supercritical-fluid (SC-CO2) extraction. The yields of residual oils recovered from WAC were higher than those from NC using solvent and SC-CO2 extraction respectively. Both the residual oils recovered from WAC and NC had fatty acids composition (FAC) similar to that of crude palm oil. These oils exhibited poor qualities in terms of free fatty acids (FFA) content and peroxide value (PV). As the residual oils had very high FFA value (more than 10%), they were no longer suitable for food applications. Alternatively, these oils can be converted to their respective methyl esters for biofuel and other non-food applications as they were thermally and chemically stable with induction period of up to 29 h in Rancimat test. The methyl esters conversion via esterification and transesterification gave optimum yields of more than 80%. The methyl esters obtained have comparable fuel properties as petroleum diesel; hence, they can be used as diesel substitute.