Studies On The Directional Separation Of Hydrocarbon Molecules In Naphtha Based On Molecular Scale Management

The directional separation and efficient utilization of hydrocarbon molecules is the key to improve the utilization efficiency of naphtha.Based on the synthesis of the ZSM-5 zeolites,the directional separation of n-alkanes,aromatics and monomethyl iso-paraffins in naphtha were studied using the combination of 5A zeolites,13X zeolites and ZSM-5 zeolites.Firstly,ZSM-5 zeolites was synthesized by hydrothermal method and the channels were adjusted by ion exchange method.The optimal Si/Al ratio was 80.After exchanging with 0.1 mol/L Ni2+ for 4h at 60 ?,the adsorption capacity of 2-methylpentane in modified ZSM-5 zeolites was 4.8g/100g at 25?,which was 9.1%higher than that in the original zeolites.Under the same conditions,the adsorption capacities of 2-methyl iso-paraffins in the modified ZSM-5 zeolites were greater than those of 3-methyl iso-paraffins.The adsorption capacities of monomethyl iso-paraffins with the same methyl positions decreased with the increase of carbon numbers.The adsorption isotherm of monomethyl iso-paraffins in ZSM-5 zeolites can be described by Langmuir equation.The apparent diffusion coefficients of 2-methyl iso-paraffins with the same carbon numbers were higher than those of 3-methyl iso-paraffins at 25?.The diffusion activation energies of 2-methyl and 3-methyl hexane were 19.17kjJ/mol and 21.14kJ/mol,respectively.Adsorption separation of normal alkanes,aromatics and monomethyl iso-paraffins using 5A zeolites,13X zeolites,and modified ZSM-5 zeolites as well as their binary and ternary combinations were investigated in a fixed bed adsorber.Under the optimal conditions,the adsorption capacity of n-alkanes in 5A zeolites was 5.9g/100g,and the adsorption capacity of aromatics in 13X zeolites was 1.9g/100g,and the adsorption capacity of monomethyl iso-paraffins in the modified ZSM-5 zeolites was 1.8g/100g.After adsorption separation of 5A and ZSM-5 zeolites,the contents of n-alkanes and monomethyl iso-paraffins decreased from 31.9%and 23.5%in naphtha to 0.6%and 3.8%,respectively.After adsorption separation of 5A,13X and ZSM-5 zeolites,the contents of n-alkanes,aromatics and monomethyl iso-paraffins decreased from 31.90%,12.80%and 23.50%in naphtha to 0.65%,2.02%and 1.74%.respectively.