Adsorption Thermodynamics and Kinetics of Light Hydrocarbons on Microporous Activated Carbon at Low Temperatures

Abstract

The removal of light hydrocarbons from exhaust air and process gas is important for a variety of applications, e.g., in natural-gas treatment. However, particularly at lower concentrations, the removal of C1 and C2 hydrocarbons is either very expensive or unfeasible with standard technology. Adsorption processes at temperatures below 0 °C may provide a technical solution, but until today, no systematic study on the dynamics of trace adsorption at low temperatures is available. Therefore, in this work, we present breakthrough curve experiments of ethane, propane, and n-butane over a temperature range from +20 to −80 °C and a concentration range from 5 to 1000 Pa on microporous activated carbon. Equilibrium loadings are calculated and modeled with the temperature-dependent Toth equation. From dynamic simulations of the experimental breakthrough curves, kinetic parameters are determined. The lowering of temperature results in the slowdown of kinetics, which, however, is overcompensated by a simultaneous capacity gain.

Adsorption of Light Alkanes and Alkenes on Activated Carbon and Zeolite 13X at Low Temperatures

“…Lowering the temperature below ambient temperature by integrating energy into the process can significantly increase the efficiency of an adsorber bed. This is especially beneficial for short-chain adsorptives, as shown in the authors’ preliminary work. − …”

“…To compare the equilibrium data, the isotherms of alkanes and alkenes of the same number of carbon atoms are displayed in one plot. The isotherm data of the adsorption of ethane and propane on the AC NORIT RX 1.5 Extra were experimentally determined and published by Birkmann et al using the same setup …”

“…The isotherm data of the adsorption of ethane and propane on the AC NORIT RX 1.5 Extra were experimentally determined and published by Birkmann et al using the same setup. 7 Ethane reaches significantly higher loads than ethylene over all temperatures. Both molecules interact with the mainly nonpolar surface of the AC by dispersion interactions and by lateral interactions with neighboring molecules.…”

“…The adsorbents were already characterized in previous studies. − Table lists the results of nitrogen sorption measurements at 77 K. The Brunauer–Emmett–Teller (BET) method (DIN ISO 9277) was used for calculating the inner surface area. The pore and micropore volumes were determined according to the Gurvich rule at p / p 0 = 0.98 and Dubinin–Radushkevich rule (DIN 66135-3).…”

“…Scheme displays a schematic flow diagram of the experimental plant, which has already been described in detail in previous publications. − In a gas mixing chamber (1) a defined gas mixture of carrier gas and adsorptive is produced with mass flow controllers 2–4, which are located in a tempered box. The process temperature is adjusted with a cryogenic circulation thermostat (2).…”