Selective adsorption of sulfur compounds: Isotherms, heats, and relationship between adsorption from vapor and liquid solution

Adsorption isotherms were measured for thiophenic sulfur compounds, thiophene (T), benzothiophene (BT), 2-methylbenzothiophene (2-MBT), and dibenzothiophene (DBT), from their binary solutions in n-octane. Two sulfur-selective, π-complexation sorbents were studied: Cu(I)-Y zeolite and PdCl₂ impregnated on activated carbon (PdCl₂/AC). Vapor-phase isotherms of n-octane and thiophene were also measured. The selectivity of adsorption from liquid solutions followed the order, T < BT < 2-MBT < DBT for PdCl₂AC, and T < DBT < 2-MBT < BT for Cu(I)-Y zeolite. The adsorption bond energies, which approximate the heats of vapor-phase adsorption, followed the order, T < BT < 2-MBT < DBT. This order was not followed for adsorption from liquid solutions on Cu-Y zeolite. The heats of adsorption were obtained by the temperature dependence of the isotherms. A simple theory was proposed for estimating the relationship between the heat of adsorption from liquid solution and that from vapor phase. The experimental results were in fair agreement with the theory.