Effect of Adsorption and Regeneration Temperature on Irreversible Adsorption of Organic Vapors on Beaded Activated Carbon Masoud Jahandar Lashaki, † Mohammadreza Fayaz, † Haiyan (Helena) Wang, † Zaher Hashisho,* ,† John H. Philips, ‡ James E. Anderson, § and Mark Nichols § † University of Alberta, Department of Civil and Environmental Engineering, Edmonton, AB T6G 2W2, Canada ‡ Ford Motor Company, Environmental Quality Office, Dearborn, Michigan 48126, United States § Ford Motor Company, Research and Advanced Engineering, Dearborn, Michigan 48121, United States ABSTRACT: This paper investigates the effect of adsorption and regeneration temperature on the irreversible adsorption of a mixture of organic compounds typically emitted from automobile painting operations. Adsorption of the organic vapors mixture onto microporous beaded activated carbon (BAC) and regeneration of the saturated BAC were completed under different conditions. Results indicated that increasing the adsorption temperature from 25 to 35 or 45 °C increased heel buildup on BAC by about 30% irrespective of the regeneration temperature due to chemisorption. The adsorption capacity (for the first cycle) of the mixture onto the BAC at these three temperatures remained almost unchanged indicating chem- isorption of some of these compounds onto the BAC. Increasing the regeneration temperature from 288 to 400 °C resulted in 61% reduction in the heel at all adsorption temperatures, possibly due to desorption of chemicals from narrow micropores. BET area and pore volumes of the BAC decreased proportionally to the cumulative heel. Pore size distribution and pore volume reduction confirmed that the heel was mainly built up in narrow micropores which can be occupied or blocked by some of the adsorbates. ■ INTRODUCTION Vehicle painting operations are the primary source of volatile organic compound (VOCs) emissions from the automobile manufacturing sector. 1,2 These emissions consist of a mixture of high and low molecular weight compounds including aromatic hydrocarbons, esters, ketones, alcohols, and glycol ethers. 1,2 On average, 6.58 kg of VOCs is used as paint solvents per vehicle in typical automotive plants in North America. 2 VOC emissions are of concern because of their health effects and/or ozone formation potential, 2-5 so, the gaseous stream needs to be treated before discharging to the atmosphere. 6 Methods to control emission of organic vapors include adsorption, absorption, oxidation, biofiltration, condensation, and mem- brane separation. 4,5,7-13 Among these methods, adsorption is widely used because of its cost effectiveness, high efficiency at low concentrations, i.e., ppm for recovering the VOCs from gaseous streams, and ability to recover the adsorbate for reuse. 1,12,14-17 Adsorption can be categorized into physical adsorption and chemical adsorption. In chemical adsorption or chemisorption, the adsorbate reacts on the surface of the adsorbent and adheres through chemical bonds; consequently, the heat of adsorption is high and approaches the energy of chemical bonds. 18 Chemisorbed species are generally difficult to desorb and as a result they accumulate on the surface of the adsorbent and reduce its adsorption capacity. Higher temperatures during adsorption can favor chemisorption as it provides the activation energy needed for the formation of adsorbate-adsorbent complex. 19 Other factors promoting chemisorption include the presence of adsorbates with electron-donating functional groups such as amine (-NH 2 ) and hydroxyl (-OH), 20-23 the difference between the boiling point of the adsorbate and the regeneration temperature, 23 and π-π electron donor- acceptor interaction between the aromatic ring and unsaturated bond on the carbon. 24 Due to its low cost and high surface area, activated carbon is one of the most commonly used adsorbents in air and water treatment. 10,25-29 One of the challenges of capturing organic vapors from painting operations is the irreversible adsorption (aka build-up of heel) of these compounds onto activated carbon which reduces the lifetime of the adsorbent and increases the operation and maintenance cost of the system due to the cost of the adsorbent, disposal of the spent adsorbent, and labor cost to replace the adsorbent. Irreversible adsorption on an adsorbent surface can be described as the combined result of formation of permanent bonds between the adsorbate and the surface (chemisorption) and the irreversible trans- Received: January 4, 2012 Revised: February 15, 2012 Accepted: March 13, 2012 Published: March 13, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 4083 dx.doi.org/10.1021/es3000195 | Environ. Sci. Technol. 2012, 46, 4083-4090