Temperature effect on extraction and purification of used motor oil by supercritical carbon dioxide

Supercritical carbon dioxide (SC-CO2) was used for the extraction of used motor oil (UMO) from two types of contaminated sand (sieved and not sieved) at 70–80 °C and 35–65 MPa. The presence of fine sand in Sand 1 contributed to the increase of UMO recovery, decrease of outgassing losses and better purification of extracted UMO samples. All samples extracted at 70 °C from both sands were clean from engine wear residues and transparent while most of the samples extracted at 80 °C were black. This implies that the temperature has most significant effect on purification of UMO achieved by depositing residues in the sand and extracting base oil fraction. Therefore, remediation of sands using SC-CO2 attained by removal of UMO can be obtained at higher temperatures, but the purification of UMO requires lower temperatures.