Hydrophobic activated carbon for elevated-temperature pressure swing adsorption

Elevated temperature pressure swing adsorption is a newly developed gas purification technology, wherein the product gas recovery rate can be significantly improved by adding a steam rinse and purge. Furthermore, high temperature industrial syngas can be directly purified at elevated temperatures, so the temperature variation during purification process is not as large as that in Selexol, Rectisol or some other methods, which benefits to the simplification of heat management and improvement of energy efficiency. At working temperatures of approximately 200 °C, activated carbon is considered to be a promising adsorbent. Nevertheless, activated carbon also adsorbs large amounts of steam during rinse and purge, which affects its adsorption capacity. Herein, hydrophobic activated carbon was synthesized by impregnation and characterized, achieving a contact angle with a water droplet of up to 134°. When exposed to wet air, the weight increase of the hydrophobic adsorbent was 0.3%, whereas it was approximately 12% for the commercial activated carbon, which can be mainly attributed to vapor adsorption. The CO₂ adsorption capacity was tested under humid conditions at 200 °C on a fixed bed. The effect of steam on the hydrophobic adsorbent was much smaller than that on the commercial adsorbent. The working capacity decreased from 0.091 to 0.009 mmol/g when the commercial activated carbon was operated under steam at 1 atm, whereas the hydrophobic material exhibited a stable and desired working capacity at the same condition, which was around 0.05 mmol/g. Steam rinse and purge were demonstrated to be feasible for the hydrophobic adsorbent and the introducing of steam rinse could not only compensate for the deterioration of adsorption capacity resulting from impregnation, but further improve the purification efficiency.