461302 Synthesis and Adsorption Performance of Zeolites for Separating Alkanes in 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 ℃. 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 ℃, crystallization for 48 h at 180 ℃ 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.
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