(340e) The Impact of Activated Carbon's Pore Size Distribution on Heel Formation during Adsorption of Organic Vapors

This research investigates the effect of activated carbon pore size distribution (PSD) on heel formation during adsorption of organic vapors typically emitted from automotive painting operations. For this purpose five types of commercially available beaded activated carbons (BAC) were used. Micropore surface analysis, X-ray photoelectron spectroscopy, and derivative thermo-gravimetric (DTG) analysis were used to assess differences in the physical and chemical properties of these adsorbents. The samples have similar chemical characteristics (e.g. surface oxygen content) but different physical properties (e.g., surface area, total pore volume, micropore volume, and pore size distribution), allowing for isolating the contribution of carbon porosity on heel formation. The samples were tested for 5 consecutive adsorption/regeneration cycles using a mixture of nine organic compounds representing different organic groups. Mass balance cumulative heel was similar for BACs with similar micropore volume and it was 20% higher than heel for BAC with the lowest micropore volume, showing a strong correlation with the adsorbent micropore volume. Contrary to this, adsorption capacities and adsorption breakthrough times correlated with total pore volumes of the BACs not the micropore volumes. BET surface area, micropore volume, and total pore volume of the regenerated BACs decreased proportionally with the cumulative heel. PSD and pore volume reduction confirmed that the heel was mainly accumulated in narrow micropores, which can be occupied or blocked by some of the adsorbates. The results from this study help explain the heel formation mechanism and how it relates to adsorbent structure.