Hysteresis in the cyclic adsorption of acetone, ethanol and ethyl acetate on activated carbon

This paper describes the adsorption behaviour of three solvents (ethyl acetate, ethanol and acetone) on BASF activated carbon at various temperatures (15-80 degrees C). The adsorption isotherms show hysteresis which persists to very low pressures (Low Pressure Hysteresis, LPH). After prolonged outgassing (<10(-2) mbar) at 473-523 K we found that LPH still remains. This LPH is more pronounced for ethyl acetate at higher temperatures. Due to its importance on Pressure Swing Adsorption (PSA) units design and operation we discuss the adsorption behaviour when adsorption/desorption cycles are applied. We concluded that after approximately five cycles the system reaches what we called 'limiting isotherm' where adsorption and desorption branches cannot be distinguished within experimental error. This isotherm is independent of system history if a sufficiently low pressure and/or a sufficiently high pressure is used for cycling and in these conditions the adsorbent has higher capacity than when fresh. Also the Langmuir equation correlates quite well with the limiting isotherms. (C) 2000 Elsevier Science Ltd. All rights reserved.