Liquid adsorption of linear and branched paraffins onto microporous adsorbents: Influence of adsorbent structure and Si/Al molar ratio

Abstract

Liquid phase adsorption (298 K, batch technique) of linear and branched paraffins (tetradecane, 3-methylpentane, 2,3-dimethylpentane and 2,2,4-trimethylpentane) has been studied onto several microporous adsorbents with different structures and Si/Al molar ratios: H-Beta (BEA), H-ZSM-5 and S-1 (MFI) and SAPO-11 (AEL). MFI samples showed no adsorption of the geminal paraffin due to molecular sieve effect, as well as a preferential adsorption of the linear paraffin. A competitive adsorption between the mono- and dibranched paraffins was observed onto MFI samples, showing an increase in adsorption capacity for 3-methylpentane at higher Si/Al molar ratios. AEL and BEA samples adsorbed significant amounts of all adsorptives. A mixture of C 13 isomers containing different amounts of tridecane, monomethyldodecanes, dimethylundecanes, trimethyldecanes, ethylundecanes and other polimethyl paraffins was also tested onto commercial H-ZSM-5, pure (Si/Al = 13, 16, 54) and agglomerated (Si/Al = 24, 45, 200), as well as onto two commercial pure silicalites. Only dimethyl, monomethyl and linear paraffins were significantly adsorbed. Adsorption capacities of the five monomethyl isomers increased following the sequence 6M–C 12 > 5M–C 12 > 4M–C 13 > 3M–C 12 > 2M–C 12, specially at low Si/Al molar ratios.