Process for fractionation and purification of synthetic lubricants using liquefied CO2 + propane as solvent

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

CABA

Congreso; 11th World Congress of Chemical Engineering, WCCE11; 2023

Asociación Argentina de Ingenieros Químicos

Carbon capture, storage and utilization could help reduce emissions from the used of non-renewable carbon-containing fuels. Different technologies are being developed and tested by several energy companies worldwide [1]. In this work we study the purification of synthetic oil lubricants using liquefied CO2 + propane mixtures as solvent. These liquefied gases have shown interesting properties for extraction of viscous fluids regarding CO2 utilization, environmental aspects, high selectivity, and reduced flammability properties [2]. Particularly, CO2 can play an interesting role in the fractionation and purification process of special lubricants used in compressors, turbines, pumps, and other devices at different industrial sectors (energy, food industry or medical applications). These lubricants have strict composition regulations regarding the presence of residual monomers and oligomers that alter the product quality and its viscosity index. However, the removal of these non-desired minor compounds from the oily lubricants by classical vacuum distillation is difficult and expensive because of the high temperatures governing the process. Organic solvents like methyl-ethyl ketone (MEK)/toluene, or phenol are normally used for the lubricant purification in liquid/liquid extraction processes [3]. These solvents are toxic and non-environmentally safe, so they should be replaced for benign options in modern process. Moreover, the production process of biolubricants in a near future to replace mineral oils must consider the used of renewable solvents with a low environmental impact and CO2 can play an important role [4]. To evaluate the technical feasibility of CO2 + propane as liquefied solvent mixtures for the purification of lubricant oils, we consider a synthetic oil mixture prepared from a Silicone oil (MW: ≈8000) and Decamethylcyclopentasiloxane (D5, MW: ≈371) as a lubricant model. The liquid-liquid-vapor phase behavior of the multicomponent system is studied in a high-pressure view cell to set preliminary operating conditions. The effect of the different variables governing the separation process such as solvent composition (CO2/propane: 60/40 to 90/10) and temperature (T: 298 K to 323 K) are studied to determine its effect in the system. Then, an analytical method is used to evaluate the composition of the system under equilibrium and to determine the distribution coefficient of D5 in the liquid phases. Experimental and modeling results are pointing out liquefied gases with propane concentrations between 10 and 26 wt.% are suitable to remove the monomers from the raw lubricant oils due to its good selectivity and extraction yield. A conceptual engineering design of the liquid-liquid fractionation process shows a liquefied gases with 85 wt.% CO2 enables the removal of 99 % of the monomers present in the lubricant oil with an oil recovery greater than 90 % at the end of the purification process.