PERGAMON Carbon 39 (2001) 523–534 Effects of pore structure and temperature on VOC adsorption on activated carbon a , b c * Yu-Chun Chiang, Pen-ChiChiang ,Chin-Pao Huang a Department of Mechanical Engineering , Yuan Ze University , 135 Yuan-Tung Rd ., Chung-Li , Taoyuan , Taiwan b Graduate Institute of Environmental Engineering , National Taiwan University , 71 Chou-Shan Rd ., Taipei , Taiwan c Department of Civiland Environmental Engineering , University of Delaware , Newark , DE 19716, USA Received 19 February 2000; accepted 9 June 2000 Abstract This research was undertaken to investigate the pore structure of three activated carbons and determine the tempe dependence of the adsorption of VOCs onto activated carbon. Three kinds of activated carbon made of different raw materials and four VOC species were chosen. The microporosity of activated carbon was assessed by the pore size distribution. The adsorption of VOCs showed that only C H exhibited the activated entry effect. The VOC adsorption 6 6 capacity of peat-derived carbon was less dependent on temperature. A characteristic curve was observed for the pea carbon. Benzene adsorption was the most preferable compared to other three VOCs because of higher heats of adsor lower entropy change. Results indicate physical adsorption played a critical role during adsorption processes in this study system.  2001 Elsevier Science Ltd. All rights reserved. Keywords : A. Activated carbon; C. Adsorption, BET surface area; D. Porosity, Thermodynamic properties 1. Introduction structure of porousactivated carbons. According to the BET classification of isotherm, in general, adsorption on Due to ubiquity in the environment and risk to human porous solids would belong to the Type IV isotherm [1], health, volatile organic compounds (VOCs) have received which is characterized by a hysteresis loop. de Boer[2] greatattention in the field of environmental control. The firstproposed fivemajordistincthysteresis loops.The adsorptionof VOCs ontoporousadsorbents, such as IUPAC (International Union of Pure & Applied Chemistry) activated carbons, has been suggested as an innovative laterrecommended a different classification system and treatment technology. Activatedcarbonadsorptionhas categorized hysteresis loopsinto fourgroups, Type H1, been considered to be one of the promising methods for H2, H3 and H4 [3]. The lowerclosurepointof the controlling VOCs of low concentrations with potential to hysteresis loop occursat a relativepressurewhich is recovervaluable vapors. Activated carbon characterizedalmost independent of the nature of adsorbent butmainly with heterogeneously porous structures, generally, can be relies on the properties of the adsorbate. Forexample, it made from a variety of raw materials such as peat, coal, occursat P/P 60.42 for nitrogen at77 K and at P/ o nutshell,lignite, saw dust, and synthetic polymers. P 60.28 for benzene at 298 K [4]. o The adsorption capacity of activated carbon depends The profile of hysteresis loop is closely related to both strongly on its surface microstructure. Consequently, in- the shapes of pores and the pore size distribution. Kelvin formation on the surface characteristics of activated carbon was the first to calculate the pore size using a cylindrical is important to adsorption process design.To date,ad- model [1]. However, the Kelvin equation is only applicable sorption isotherms of inertgases,such asnitrogen and in the range of P/P .0.42. In orderto predicthe pore o argon, are the most widely used to determine the physical size distribution under low pressure conditions, Lippens and de Boer [5] developed the t-method which was later modified by Mikhail et al. [6] proposing the micropore *Corresponding author. Tel.:1886-3-463-8800 ext. 476; fax: method, MP-method. Horvath and Kawazoe [7] based on 1886-3-455-8013. E-mailaddress : ycchiang@saturn.yzu.edu.tw (Y.-C. Chiang). the concept of average potential function, developed a slit 0008-6223 / 01 / $ – see front matter  2001 Elsevier Science Ltd. All rights reserved. P I I : S 0 0 0 8 - 6 2 2 3 ( 0 0 ) 0 0 1 6 1 - 5