Synthesis And Adsorption Performance Of Adsorbent Material For Alkanes In Naphtha

The utilaitzation efficiency of naphtha can be improved remarkably by separating group compositions in naphtha based on molecular scale management. In order to meeting the raw material requirements of ethylene industry and aromatics industry, zeolites was prepared and used for the adsorption separation of alkanes rich in n-paraffins and monomethyl iso-paraffins in naphtha.Firstly, ZSM-5 zeolites was selected for its adsorption performance of monomethyl iso-paraffins based on theoretical analysis and experimental comparison of six kinds of zeolites. The adsorption capacity of the synthesized ZSM-5 zeolites for 2-methylpentane was 0.0383 g/g at 25℃, which was 49% higher than that of the reference ZSM-5 zeolites. The optimal conditions for the synthesis of ZSM-5 zeolites were: n(SiO2):n(Al2O3):n(Na2O):n(H2O)= 80:1:7:2450, aging for 36 hat 25℃, crystallization for 48 hat 180℃and using n-butylamine as a template. The characterization results showed the synthesized ZSM-5 zeolites had a higher degree of crystallinity, the specific surface area and pore volume than those of the reference ZSM-5 zeolites. The average pore size of synthesized ZSM-5 zeolites was about 0.58 nm.Then the molding conditions of synthesized zeolites were investigated. The optimal formula for the ZSM-5molding was pseudo bohemite of 8%, nitric acid content of 5% and sesbania powder 5%. The mechanical strength of adsorbent pellet with a diameter of 5 mm was 29 N and the adsorption capacity for 2-methylpentane was 0.0351 g/g at 25℃.The adsorption kinetics of monomethyl iso-paraffins on ZSM-5 pellet was investigated. The diffusion coefficients were gained and the diffusion activation energies of 2-methylpentane, 3-methylpentane,2-methylheptane and 3-methylheptane were 15.57 kJ/mol、20.49 kJ/mol、 17.82 kJ/mol and 21.68 kJ/mol. The activation energy of long chain isoparaffin was higher than that of short chain isoparaffin and activation energy of 3-methyl-isoparaffins was higher than that of the corresponding 2-methyl-isoparaffins.The adsorption separation performance of synthesized ZSM-5 zeolite was studied in a fixed bed adsorption column. The adsorption capacities of n-paraffins, monomethyl iso-paraffins and aromatics in ZSM-5 zeolites were 0.0529 g/g> 0.0158 g/g and 0.023 g/g. The multimethyl iso-paraffins and cycloalkane were not adsorbed. N-paraffins and monomethyl iso-paraffins, which were 30.4% 11.8% of naphtha were separated by ZSM-5 adsorbent. The potential aromatic content of raffinate oil increased to 31.63%, which was 10 percent higher than that of naphtha.