Study On Solvent Screening Of Extractive Distillation In Comprehensive Utilization Of Reformed Raffinate Oil

Reformed raffinate oil is the the byproduct fraction with low content of aromatic,sulfur,nitrogen,heavy metals and other impurities,and high content of n-hexane,methyl cyclopentane,n-heptane,methylcyclohexane and other saturated hydrocarbons,which is produced from aromatics extraction of catalytic reforming and is quite appropriate to be used to produce high quality,high value-added fine chemical raw materials.The boiling point difference of n-hexane and methyl cyclopentane is 2.5 oC,n-heptane and methylcyclohexane is 3.1 oC,effective separation can be done by enlarge reflux ratio or theoretical plate number through ordinary distillation.In this paper,the separation and purification of n-hexane and methyl cyclopentane system,n-heptane and methylcyclohexane system was studied by extractive distillation.Several solvents were picked out according to some empirical and qualitative rules.In order to overcome the drawbacks of theoretical prediction and experimental selection,UNIFAC method and vapor-liquid equilibrium experiments were combined in this paper to select solvent for n-hexane and methyl cyclopentane system,n-heptane and methyl cyclohexane system,and benzyl alcohol was chosed as extractive solvent for both systerms.Vapor-liquid equilibrium experiments of n-hexane-ethylene glycol dimethyl ether,nhexane-isobutyl acetate,n-hexane-sec-butyl acetate,methyl cyclopentane-ethylene glycol dimethyl ether,methyl cyclopentane-isobutyl acetate,n-heptane-sec-butyl acetate,methyl cyclohexane-sec-butyl acetate,n-hexane-benzyl alcohol,methyl cyclopentane-benzyl alcohol,methyl cyclohexane-benzyl alcohol,were conducted under atmospheric pressure.The experiment data were correlated by Wilson equation,the calculation results of Wilson model matched well with the experiment data,the obtained binary interaction parameters can be used for process simulation and distillation and design.Simulation calculation was conducted with Aspen Plus,of extractive distillation separating n-hexane and methyl cyclopentane system,n-heptane and methyl cyclohexane system,benzyl alcohol as solvent.Effects of the solvent feed stage,the feed stage,the reflux ratio and mass ration of solvent to feed(solvent ratio)were studied,operation conditions were obtained.Effective separation of n-hexane and methyl cyclopentane system,n-heptane and methyl cyclohexane system,can be realized by using extractive distillation with benzyl alcohol as solvent,and this paper can be taken use to guide the research and application of extractive distillation separating both systerms.