(80f) Synthesis and Adsorption Performance of Zeolites for Separating Alkanes in Naphtha

The utilization 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 including n-paraffins and monomethyl iso-paraffins in naphtha, which is a more reasonable strategy than the separation of n-paraffins from naphtha.

MFI zeolites were synthesized for its adsorption performance of monomethyl iso-paraffins based on theoretical analysis and experimental investigation. The adsorption capacity of the synthesized MFI zeolites for 2-methylpentane was 0.0383 g/g at 25 â??. The optimal conditions for the synthesis of MFI zeolites were: n(SiO2):n(Al2O3): n(Na2O):n(H2O) = 80:1:7:2450, aging for 36 h at 25 â??, crystallization for 48 h at 180 â?? and using n-butylamine as a template. The characterization results showed the synthesized MFI zeolites had a high degree of crystallinity. The average pore size of synthesized MFI zeolites was about 0.58 nm.

The adsorption kinetics of monomethyl iso-paraffins on MFI zeolites 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 MFI zeolites was studied in a fixed bed adsorption column. The adsorption capacities of n-paraffins, monomethyl iso-paraffins and aromatics in MFI 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% and 11.8% of naphtha were separated by MFI zeolites. The potential aromatic content of raffinate oil increased to 31.63 %, which was 10 percent higher than that of naphtha.