Introduction The removal of light hydrocarbons in trace concentrations, such as ethane, propane, and n-butane from exhaust air or process gas is important in multiple environmental and technical applications, e.g. processing... [ view full abstract ]
Introduction
The removal of light hydrocarbons in trace concentrations, such as ethane, propane, and n-butane from exhaust air or process gas is important in multiple environmental and technical applications, e.g. processing of natural gas or separation of olefin/paraffin mixtures. For that purpose, adsorptive processes would be generally suitable. However, experience has shown that the capacity of industrially available adsorbents at ambient conditions is often poor. By lowering the adsorption temperature significantly below ambient temperature, as is possible by energy integration at LNG terminals or low temperature rectification columns, the adsorbent´s capacity could be increased. As yet, there is no thermodynamic data published on the adsorption of light hydrocarbons at temperatures significantly below ambient temperature. Therefore, this work provides adsorption isotherms and isosteric heats of adsorption of light hydrocarbons on microporous activated carbon and zeolite 13X in a temperature range between -80 °C and +60 °C.
Experimental and Theoretical Methods
Dynamic breakthrough experiments of ethane, propane, and n-butane in trace concentrations on microporous activated carbon and zeolite 13X were carried out in a fixed bed adsorption column. From mass balances of the adsorption column, equilibrium loadings were calculated and adsorption isotherms as well as isosteric heats of adsorption were derived. The influence of temperature on the capacity of activated carbon and zeolite 13X is discussed for each adsorptive considering specific interactions between the adsorptive and the adsorbent surface.
Results and Discussion
Adsorption capacity rises with increasing alkane chain length on both adsorbents because the number of molecular bonding sites and molecular polarizability increase. Decreasing temperature improves adsorption capacity of all systems. The shorter the chain the more pronounced is the effect. With temperature dependent isotherm parameters, the Sips isotherm equation is suitable for the modeling of the isotherms. The adsorption process is mainly dominated by van der Waals forces and induced polarization.
Carbon capture and other industrial applications , Challenges and advances in fluid phase equilibria
