Fractionation of synthetic oils using liquefied gases

PIZZANO, A.; ZABALOY MARCELO, S; HEGEL PABLO, E; RODRIGUEZ REARTES SBRINA, B

Itaici, Indaiatuba

Congreso; XII IBEROAMERICAN CONFERENCE ON PHASE EQUILIBRIA AND FLUID PROPERTIES FOR PROCESS DESIGN; 2022

University of Campinas

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 presenceof residual monomers and oligomers that alter the product quality and its viscosity index. The removalof these non-desired minor compounds from the oily lubricants by classical vacuum distillation is difficultand 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 modernprocess.In this work we evaluate the performance of CO2 + propane (C3) liquid solvent mixtures in the liquid-liquidextraction of minor components (monomers and oligomers) present in synthetic oils. CO2+propane solventmixtures have shown interesting properties for the extraction and fractionation of viscous fluids regardingenvironmental aspects, selectivity, and non-flammability. In a previous work (CB Termo 2019) we evaluatedphase 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 solventmixtures of up to 37 C3 wt.% exhibit partial liquid miscibility with silicone oils, turning feasible a liquid-liquidfractionation 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 preparedfrom two silicone oils (MW: 8000, and a D5 monomer MW: 370) is used as a model lubricant to evaluatethe technical feasibility of the separation technology proposed in this work. Liquefied CO2+C3 mixtures inthe range from 9 C3 wt.% to 37 C3 wt.% are used to evaluate their effect on the solubility of the silicone oil andand of D5 monomers in the solvent liquid phase. Then, semi-batch liquid-liquid extractions are carried out toevaluate the effectivity of different CO2 + propane solvent mixtures. The liquid-liquid distribution coefficientof D5 monomers (solvent free weight fraction basis) varied roughly in the range from 1.5 to 20, according tothe 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 siliconeoils than pure CO2, or than liquefied CO2+C3 mixtures with low propane content (< 20 wt.%), due tothe lower operating pressure observed in the system, the high solvent power and the suitable selectivity toextract minor monomer components.