Adsorption and Desorption of a Mixture of Volatile Organic Compounds: The Impact of Activated Carbon Porosity

Cyclic adsorption-desorption on activated carbon is typically used to mitigate Volatile Organic Compounds (VOCs) emissions from automotive paint booths. In this study, the impact of activated carbon porosity on adsorption/desorption performance is investigated using a mixture of industrially relevant surrogate VOCs as feed gas. To that end, 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 contribution of carbon porosity. Effluent streams during adsorption/desorption were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). Overall, BACs with higher total pore volume achieved higher VOC uptake and longer adsorption breakthrough time. For adsorption/desorption kinetics, however, BACs with a higher share of mesopores showed faster kinetics. High boiling point VOCs in the mixture displaced low boiling point VOCs via competitive adsorption, with this phenomenon being more apparent in mesoporous BACs. Traces of high boiling point VOCs were retained on all BACs at the end of the desorption step, owing to strong physical adsorption. Closure analysis based on mass balance was consistent with GC-MS results obtained during adsorption and desorption.