Dissolution of polycyclic aromatic hydrocarbons in super critical cyclohexane:A molecular dynamics simulation study
A large number of polycyclic aromatic hydrocarbons in heavy oil will undergo a condensation reaction to form polycyclic aromatic hydrocarbons(PAHs),and the limitation of dissolution and diffusion will cause the polymerization between polycyclic aromatic hydrocarbons to form residual coke,which greatly reduces the utiliza-tion rate of heavy oil.Therefore,dissolution and diffusion in the pyrolysis process of PAHS is one of the key fac-tors for the improvement of heavy oil.Based on the good solubility of cyclohexane to hydrocarbons,the molecular dynamics simulation method was used to study the dissolution behavior of polycyclic aromatic hydrocarbons and their mixtures in supercritical cyclohexane.Critical cyclohexane has good solubility for NAP,while temperature has little effect on the dissolution of Bghip.During the dissolution of oil droplets in the PAH mixture,NAP was preferentially dissolved into the cyclohexane phase,while Bghip was concentrated in the oil droplets with reduced particle size.By calculating the radial distribution function and solvation free energy of PAHs in the system,it is found that cyclohexane and PAHs can attract each other,and the solvent shell formed by cyclohexane around PAH molecules can inhibit of intermolecular polymerization PAHs.The increase in temperature and the decrease in density will lead to a decrease in the cohesive energy density of PAHs,increasing the interaction between PAHs and supercritical cyclohexane.The lower density of cyclohexane and the increase in temperature can pro-mote the dissolution of polycyclic aromatic hydrocarbons or mixtures of polycyclic aromatic hydrocarbons in super-critical cyclohexane.
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