Purification of synthetic oils using liquefied gases of reduced flammability

Abstract

In this work we evaluate the technical feasibility of using liquefied CO2 + propane as a solvent for the purification of lubricant oils. A model lubricant made of a silicone oil (polydimethylsiloxane, MW ≈6000) and Decamethylcyclopentasiloxane (D5, MW: ≈371) is prepared to study the extraction process. The phase behavior of the CO2 +propane+silicone oil system is evaluated in a high-pressure view cell to set the window of operating conditions where the system exhibits partial liquid miscibility (298–323 K). Then, we add D5 monomer (2 mass % in the silicone oil) to the previous ternary mixture, and we assess the effect of solvent composition (CO2/propane: 60/40–90/10) over the fractionation process by means of new equilibrium measurements. The solvent-free distribution coefficient of D5 between the liquid phases is determined from experimental determinations. Results evidence that liquefied gases with propane concentrations between 10 and 26 mass % are suitable to remove the monomers from the raw lubricant oils with good selectivity and extraction yields. Conceptual engineering designs of the liquid-liquid fractionation process are performed to determine the suitable solvent composition that completely removes the monomer present in the lubricant oil and to assess the recovery of the lubricant oil.