Adsorption of alkali metal vapor from high-temperature coal-derived gas by solid sorbents

Seven sorbents for alkali metal removal from high-temperature coal-derived gas were tested in a fixed-bed reactor at 840 °C. NaCl was used as an alkali metal model compound. It was found that five sorbents, including the second grade alumina, bauxite, kaoline, acidic white clay and activated Al2O3, present higher adsorption efficiency, and activated Al2O3 shows the highest capture capacity. In capturing time of 3 h, the adsorption efficiency and sodium content absorbed by activated Al2O3 are, respectively, up to 98.20% and 6.20 mg/g. The tests indicate the removal of alkali metal vapor with activated Al2O3 is a physical adsorption process in the absence of moisture. The adsorption kinetics of activated Al2O3 with NaCl indicates that there are critical times at which adsorption constants begin to change. The critical time is at about 4–5 h.