Enhancement Of CO₂ Bubbling Separation Process Of Volatile Solvents In Solid Particles

Unconventional petroleum ores（oil sands,oil shale,asphaltite,etc.）are rich in reserves.They are the important supplements for the crude oil.As a general separation method for unconventional petroleum ores（especially oil-bearing ores with high asphaltene content）,solvent extraction has been extensively studied and pilot tested.This paper focuses on the recovery of residual solvent in the extracted sands after solvent extraction of oil sands.Based on the CO₂bubbling separation method of residual solvent proposed by our research group,the enhancement effect and mechanism of chemical additives and micro-nano bubbles on the bubbling separation efficiency were further studied.In this paper,from the perspective of chemical enhancement,different types of surfactants（anionic surfactants,cationic surfactants,amphiphilic surfactants and polymer surfactants）were used to enhance the CO₂bubbling separation process to remove residual organic solvents in the extracted sand.The results show that the anionic surfactant（SDS）has a positive effect on the CO₂bubbling separation process.When the bubbling time is less than 10 minutes,the introduction of SDS can reduce5-10%residual toluene in the system;when the bubbling time exceeds 10 minutes,the introduction of SDS can reduce 26%-56%residual toluene in the system.This is mainly because the presence of SDS increases the hydrophilicity of the solid particles and facilitates the separation of solvent molecules from the solid surface.However,cationic surfactants（tetradecyl trimethyl ammonium bromide）and amphiphilic surfactants（lauryl betaine）showed an inhibitory effect on the CO₂bubbling separation process.This is because the hydrophobicity of the solid surface treated with C₁₄TAB and SB-12 is enhanced（The contact angle is bigger）.Unlike surfactant enhancement,when the micro-nano bubbles（10-200 nm and 1-20μm）were introduced into the system,they could cooperate with large CO₂bubbles（2mm）to enhance the bubbling separation process.The results show that the fixed water flow rate is 10 L/min,when the bubbling time is 10 min,the introduction of micro-nano bubbles can reduce 56.14%residual toluene in the system.By exploring the influence of the amount of micro-nano bubbles and the amount of water on the bubbling separation process,the optimal operating conditions of the micro-nano bubble enhancement experiments of bubbling separation process are obtained.Polymer surfactants increase the viscosity of the solution,hinder the mass transfer of toluene,and inhibit the bubbling separation process.Through molecular dynamics simulation,it was found that compared with the large CO₂bubbles,the electrostatic attraction between the nano-sized bubbles and the oil droplets is stronger and easier to coalesce.Meanwhile,when asphaltenes（residual oil fraction during solvent extraction）accumulate at the oil-water interface,the asphaltene interface film can weaken the electrostatic attraction between the nano-sized bubbles and the oil droplets,and hinder the coalescence of nano-bubbles and droplets.Based on the results of the above two different enhancement measures,the general applicability of the surfactants enhancement and micro-nano bubbles enhancement measures were further explored for the different solvents.It was found that SDS and micro-nano bubbles have the same influence on bubbling separation process for the different solvents.The above two different enhancement measures are suitable for oily solvents and some non-oily solvents that are not easily separated from the surface of solids.The research results of this paper will provide basic data and theoretical references for the separation and recovery of residual solvents in the extracted sand produced by the solvent extraction.It will also help promote the industrial application of the solvent extraction technology and the bubbling separation process technology.