Adsorption of light hydrocarbons on liquid-modified adsorbents

Abstract

Adsorption isotherms of propane and butane were determined at three temperatures on a graphitized carbon black adsorbent (Carbopack C) both uncoated and coated with 0.2% Carbowax 1500. In addition, the specific retention volumes of each alkane were determined as a function of the amount of the other alkane adsorbed on the normal and liquid-modified surfaces. The equilibrium isotherms for both alkanes on the liquid modified adsorbent were almost linear, but segmented into two distinct regions. The low-pressure adsorption was postulated to be adsorption on the portion of the solid not covered by the polymeric modifier. At higher pressures, adsorption occurred on the preadsorbed adsorbate and/or the polymer itself. Cooperative adsorption caused by lateral interactions on the surface was observed for both propane and butane on the uncoated adsorbent, and a similar effect between adsorbate and liquid modifier was used to explain the adsorption data for liquid-modified adsorbent. In general, the effects of volatile and nonvolatile modifiers on the adsorptive properties of a surface are similar and involve concurrent cooperative and competitive adsorption processes. However, volatile modifiers provide much more flexibility and greater potential for control of the physical and chemical activity of adsorbents and catalysts.