Fractionation of synthetic oils using liquefied gases

PIZZANO, ALDANA; RODRIGUEZ REARTES, SABRINA BELÉN; ZABALOY, MARCELO SANTIAGO; HEGEL, PABLO EZEQUIEL

Campinas

Conferencia; XII Iberoamerican Conference on Phase Equilibria and Fluid Properties for Process Design (Equifase 2022) / X Congresso Brasileiro de Termodinâmica Aplicada (CBTermo, 2022); 2022

UNICAMP

Special lubricants used in compressors, turbines, pumps, and other devices in different industrial sectors (energy, food industry or medical applications) have strict composition regulations regarding the presence of residual monomers and oligomers that alter the product quality and its viscosity index. The removal of these non-desired minor compounds from the oily lubricants by classical vacuum distillation is difficult and expensive because of the required high temperatures. Thus, organic solvents like methyl-ethyl ketone (MEK)/toluene, or phenol are normally used for the lubricant purification in liquid/liquid extraction processes. These solvents are toxic and non-environmentally safe, so they should be replaced by benign options in modern process.In this work we evaluate the performance of CO2 + propane (C3) liquid solvent mixtures in the liquid-liquid extraction of minor components (monomers and oligomers) present in synthetic oils. CO2+propane solvent mixtures have shown interesting properties for the extraction and fractionation of viscous fluids regarding environmental aspects, selectivity, and non-flammability. In a previous work (CB Termo 2019) we evaluated phase transitions for silicone oils + CO2 + propane systems at varying solvent compositions (CO2/propane: 60/40 to 90/10) and temperatures (T: 298 K to 323 K), and concluded that, at 303 K, liquefied CO2+C3 solvent mixtures of up to 37 C3 wt.% exhibit partial liquid miscibility with silicone oils, turning feasible a liquid-liquid fractionation process. A high-pressure view cell is used in this work to study the liquid-liquid-vapor equilibria in silicone oil + CO2 + propane systems at 303 K and at varying CO2+C3 solvent mixture compositions. A synthetic oil mixture prepared from two silicone oils (MW: 8000, and a D5 monomer MW: 370) is used as a model lubricant to evaluate the technical feasibility of the separation technology proposed in this work. Liquefied CO2+C3 mixtures in the range from 9 C3 wt.% to 37 C3 wt.% are used to evaluate their effect on the solubility of the silicone oil and and of D5 monomers in the solvent liquid phase. Then, semi-batch liquid-liquid extractions are carried out to evaluate the effectivity of different CO2 + propane solvent mixtures. The liquid-liquid distribution coefficient of D5 monomers (solvent free weight fraction basis) varied roughly in the range from 1.5 to 20, according to the solvent composition (37 C3 wt.% to 9 C3 wt.%).Experiments show that liquefied CO2+C3 mixtures of 30 wt.% propane are more suitable to fractionate silicone oils than pure CO2, or than liquefied CO2+C3 mixtures with low propane content (< 20 wt.%), due to the lower operating pressure observed in the system, the high solvent power and the suitable selectivity to extract minor monomer components.