Refining of synthetic lubricants through liquefied CO2 + propane

PIZZANO, ALDANA; RODRIGUEZ REARTES, SABRINA BELÉN; HEGEL, PABLO EZEQUIEL

La Pineda, Tarragona

Conferencia; 16th International Conference on Properties and Phase Equilibria for Product and Process Design; 2023

Universitat Rovira i Virgili and Khalifa University

Lubricants are fluids used to reduce friction and wear, and prevent corrosion and overheating of various kinds of devices. Thus, they play an important role in different sectors from energy generation, metal-working and chemical production, to food/drink industry, and pharmaceutical laboratories. The production of lubricants requires strict control of their composition and viscosity index, which makes complex the fractionation and purification operations during its production. In this work we evaluate the use of liquid solvent mixtures of CO2 + propane for the extraction of minority compounds present in synthetic oil lubricants. The use of these liquefied gases for extraction of viscous fluids is attractive due to its proved selectivity, non-flammability and for guaranteeing a safe operation, both for people and for the environment [1]. In the industry, lubricants have strict composition regulations regarding the presence of residual monomers and oligomers that alter the product viscosity index. Liquid/liquid extraction is commonly employed to carry out the fractionation process, in which organic solvents (e.g., methyl ethyl ketone/toluene) are used for mineral lubricant purification. Liquefied gases mixtures appear as less toxic and environmentally friendly options which can replace the current solvents, and utilize CO2. Moreover, liquefied gases can play an important role in the purification of bio-based lubricants, which need also make use of renewable solvents for its production processes[2]. The design of extraction processes requires a detailed study, adapted to the specific product of interest.To study the technical feasibility of CO2 + propane as liquefied solvent mixtures for lubricant purification, a model lubricant is prepared from a Silicone oil (polydimethylsiloxane, MW: ≈8000) and Decamethylcyclopentasiloxane (D5, MW: ≈371). To set preliminary operating conditions, the liquid-liquid-vapor phase behavior of the multicomponent system is studied in a high-pressure view cell. The effect of the variables governing the separation process are studied, such as solvent composition (CO2/propane: 60/40 to 90/10) and temperature (298 K to 323 K). The composition of the system under equilibrium is also determined by an analytical method and the distribution coefficient of D5 in the liquid phases is calculated. Experimental and modeling results evidence that liquefied gases with propane concentrations between 10 and 26 wt.% are suitable to remove the monomers from the raw lubricant oils with good selectivity and extraction yields. The thermodynamic modeling of the mixtures involved is performed by means of Sanchez-Lacombe equation [3]. A conceptual engineering design of the liquid-liquid fractionation process is made to determine the suitable solvent composition to completely remove the monomers present in the lubricant oil and determine the recovery of the lubricant oil.