Research On Selective Adsorption Of VOCs On Activated Carbon

Single-component fixed-bed thermostatic adsorption experiments and correlation analysis on the effect of activated carbon and adsorbate properties on adsorption behavior were conducted, where three kinds of granular activated carbons acted as adsorbent, toluene, acetone, xylene, methanol and 1,2-dichloroethane acted as adsorbate. Besides, two component adsorption experiments were also carried out with toluene, acetone and 1,2-dichloroethane, then the mechanism of selective adsorption and competitive adsorption were analyzed.(1)Three types of activated carbon were chosen as adsorbents. Their surface area, pore volume, pore structure and surface functional groups were tested, while single-component fixed-bed thermostatic adsorption experiments were conducted using five organic gases, including toluene, acetone, xylene, methanol and 1,2-dichloroethane, as adsorbate. The results showed that there existed diversity of activated carbon property; as for different adsorbate, the adsorption capacity, breakthrough time and saturation time on the same activated carbon were various; when it came to different activated carbon, the adsorption behavior of the same adsorbate was also diverse.(2)Combined with activated carbon properties and experimental results, the influence of activated carbon surface area, pore volume, pore structure and surface functional groups on the adsorption behavior were analyzed. The results showed that there was no obvious correlation between specific surface area, pore volume and adsorption capacity; the key parameter affected adsorption properties was pore structure; different types of surface functional groups had different effects on the adsorption for adsorbate.(3) Correlation analysis between adsorbate properties and adsorption behavior on activated carbon was conducted. It was illustrated that saturated adsorption capacity increased with adsorbat molecular weight, molecular dynamics diameter and boiling point increased; while decreased with adsorbat molecular polarity and vapor pressure increased; there was no obvious correlation between saturated adsorption capacity and adsorbat melting point and density.(4) Two-component experiments demonstrated that the adsorption for toluene and 1,2-dichloroethane showed preferential adsorption. Based on the difference of activated carbon and adsorbate properties, preferential adsorption and competitive adsorption could give rise to invalid pore interval, one-component selective adsorption pore interval, two-component selective adsorption pore interval and channel pore interval. Selective adsorption stage was the body zone, the mechanism of competitive adsorption mainly included pore diameter banked-up competition, effective absorption center competition and vicarious absorption competition. Adsorption energy could reflect selective adsorption strength of activated carbon to a certain extent; larger adsorption energy adsorbate was more favorable during competitive adsorption. Adsorption energy calculation showed that activated carbon adsorption energy for toluene was higher than that for acetone, while for 1,2-dichloroethane was higher than that for methanol.