Regeneration of waste lubricant oil with distinct properties by extraction-flocculation using green solvents

Abstract

This work aims to study the removal of contaminants from waste lubricating oil (WLO) with distinct properties by solvent extraction to recover the base oil. 1-Butanol and methyl ethyl ketone (MEK) were selected as green solvents. Three WLO samples (class A, B, and C) with substantially different properties were considered. Class A is the most common type of WLO; Class B corresponds to mineral oil with low level of contaminants (e.g. oxidation products and additives); Class C is mainly constituted by synthetic ester base oils. The analysis involved the response surface methodology and the desirability function to model two response variables (Yield and percent sludge removal - PSR) and to find the best operating conditions for the most influential factors (solvent/oil ratio and KOH dosage). The rates of contaminant removal were very dependent on the type of WLO. The maximum PSR achieved were 8.5 and 6.5% using 1-Butanol for class A and C oils, respectively, while 6.3 and 4.7% were observed for MEK. Thus, 1-Butanol is the most efficient extracting agent than MEK for both classes A and C. The extraction process was not effective for class B (PSR ≈ 0%), and this oil can bypass the deasphalting stage, saving materials and energy. The addition of KOH as flocculation agent in class C was less effective than to other classes due to the saponifiable matter content in the oil. However, the solvent extraction is a suitable treatment route for the regeneration of synthetic ester-based oils (class C). Reasonably accurate models regarding the response variables were obtained for both solvents and class A and C oils. Considering desirability functions, a solvent/oil ratio of 5 w/w and KOH dosage of 1.5 or 2 g/L were found as optimal conditions.