Adsorption and desorption of a mixture of volatile organic Compounds: Impact of activated carbon porosity

Cyclic adsorption-desorption on activated carbon is typically used to control volatile organic compound (VOC) emissions from automotive paint booths. In this study, the impact of activated carbon porosity on adsorption-desorption performance was investigated using a mixture of industrially relevant surrogate VOCs (alcohol, ester, ketone, glycol ether, aromatic hydrocarbons, n-alkane) as a feed stream. Three commercially available beaded activated carbons (BACs) with similar chemical properties (e.g., surface oxygen content) but different structural properties (e.g., surface area, pore volume, microporosity) were used, allowing for isolating the effect of carbon porosity on competitive adsorption. Effluent streams during adsorption and desorption were analyzed by gas chromatography-mass spectrometry (GC-MS) and flame-ionization detector (FID). Overall, BACs with higher total pore volume achieved higher VOC uptake and longer adsorption breakthrough time. For adsorption and desorption kinetics, however, BACs with a higher share of mesopores showed faster kinetics in both cases. Overall, VOCs with higher boiling points, larger molecular weights, and/or lower polarity displaced VOCs with lower boiling points, smaller molecular weights, and/or higher polarity, via competitive adsorption, with this phenomenon being more apparent in mesoporous BACs. Traces of high-boiling-point, nonpolar VOCs were retained on all BACs at the end of the desorption step, owing to strong physical adsorption. Closure analysis based on gravimetric measurements was consistent with GC-MS results obtained during adsorption and desorption. The findings have important implications for industrial applications, indicating that the adsorber should be designed to ensure effective control of different VOCs with varying adsorption affinities.