Regeneration of beaded activated carbon saturated with volatile organic compounds by a novel electrothermal swing adsorption system

A commercially available beaded activated carbon (KBAC) was selected for combination with a novel electrothermal swing system in examining the Joule heating effects on the physical and chemical properties of activated carbon and its adsorption regenerability at various regeneration temperatures (120, 140, and 160 °C) after saturation by toluene (TOL) and methylethylketone (MEK). The specific surface area (1278 m2 g− 1) and micropore volume (0.48 cm3 g− 1) for KBAC after one adsorption/desorption cycle were slightly reduced, while KBAC micropore surface area (1158 m2 g− 1) and micropore volume decreased significantly after six adsorption/desorption cycles. It can be inferred that the pores of KBAC, especially micropores, are blocked by heel buildup caused mainly by formation of cracked TOL and MEK coke generated by cyclic Joule heating. The desorption efficiencies of TOL-KBAC and MEK-KBAC (KBAC saturated with TOL and MEK, respectively) evaluated per the gravimetric method ranged from 55 to 80 and 85–90%, respectively, and both showed great correlation between regeneration temperature and desorption efficiency. Notably, the desorption efficiencies calculated from the integral method based on breakthrough curves were 8 and 16% lower than those directly obtained by the gravitational method for TOL-KBAC and MEK-KBAC, respectively. The larger difference in desorption efficiency evaluated by the two methods for MEK-KBAC is likely caused by the decomposition of MEK into CO or CO2, which was less prominent in TOL-KBAC. In the cyclic adsorption/desorption tests, the adsorption capacities of both TOL-KBAC and MEK-KBAC decreased after the 6-cycle electrothermal swing regeneration, such that TOL-KBAC adsorption capacity significantly reduced to around 50%, while that of MEK-KBAC retained around 70% of their respective original adsorption capacities. As aforementioned, heel buildup blocks the pores and leads to decreasing adsorption, especially for TOL.