Chinese Journal of Chemical Engineering, 20(3) 497 504 (2012) Systematic Analysis of Carbon Dioxide Activation of Waste Tire by Factorial Design P.P.M. Fung, W.H. Cheung * and G. McKay Department of Chemical and Biomolecular Engineering, the Hong Kong University of Science and Technology, Hong Kong, China Abstract In this study, waste tire was used as raw material for the production of activated carbons through pyro- lysis. Tire char was first produced by carbonization at 550°C under nitrogen. A two factorial design was used to op- timize the production of activated carbon from tire char. The effects of several factors controlling the activation process, such as temperature (850 950 °C), time (2 6 h) and percentage of carbon dioxide (70% 100%) were in- vestigated. The production was described mathematically as a function of these three factors. First order modeling equations were developed for surface area, yield and mesopore volume. It was concluded that the yield, BET sur- face area and mesopore volume of activated carbon were most sensitive to activation temperature and time while percentage of carbon dioxide in the activation gas was a less significant factor. Keywords activated carbon, waste tire, factorial design, carbon dioxide 1 INTRODUCTION As economies develop and living standards improve, growth of motor vehicle ownership is noted in many developed or developing countries. In the United States, motor vehicle registration rose by about 40 million between 1996 and 2006; while in China, ownership of civil motor vehicles tripled during the same period. As ownership of motor vehicles is widespread in the world, it is not surprising that a substantial amount of used tires is generated everyday. Over 5 million tons of waste tires are disposed annually worldwide [1]. In Hong Kong, about 12 tons waste tires are shredded and disposed in landfills per day on average [2]. Un- doubtedly, there is a pressing need to seek a good method to deal with such a huge amount of waste tires generated annually throughout the world. However, waste tires are problematic when it comes to disposal. On one hand, they are in huge amounts and take up significant space in landfills, which makes them a concern to most developed countries where land is scarce and expensive. Furthermore, waste tires pose serious environmental problems due to their special nature; tires are immune to biological degradation and stay intact in the landfill for years. Also, when tires are landfilled in large quantities, they can be a potential fire and health hazard. In addition, industries have a problem in finding an economically feasible method of removing pollutants such as organics, dyestuff and metals from effluents. A range of conventional wastewater treatment technologies has been investigated extensively [3 10] such as the trickling filter, activated sludge, chemical coagulation, carbon adsorption and photodegradation processes. Liquid phase adsorption has been shown to be an effec- tive method for the removal of suspended solids, odors, organic materials, metal ions and dyestuffs by the ap- plication of activated carbon [11]. Although carbon adsorption is used globally, this process remains ex- pensive due to the relatively high cost of activated carbon. Recently, the production of activated carbon from various agricultural and industrial wastes is of interest [12 17]. Several studies on pollutants adsorp- tion have been conducted using activated carbon pro- duced from these low cost materials [18 25]. While waste tires can be problematic if they are to be disposed in landfills, sometimes it is overlooked that waste tires contain useful materials, like rubber and carbon black, which can be recycled and reused in other applications. Tires contain vulcanized rubber and various reinforcing materials. Although compositions may vary among tires producers, the content of tires is generally similar. The typical composition of tire rub- ber is styrene butadiene rubber (60% 65%), carbon black (29% 31%), zinc oxide (2% 3%) and sulfur (1% 2%) [26]. The high content of carbon black in tire makes it a good precursor for activated carbon pro- duction. Several studies have shown that good quality activated carbon can be produced from waste tires [27 32]. However, at present there is no systematic analysis to investigate the physical properties such as surface area, porosity and yield of produced carbon with the activating parameters including activation time, activating agent concentration and temperature. Recently, statistical analysis especially factorial design has been gaining interest to investigate the influential factors together with their mutual interactions in acti- vated carbon production [33 38]. In the present study, the production of activated carbon from waste tires was investigated. The project mainly focused on the impacts of activating conditions, such as activation time, activation temperature and composition of activation agent, on the characteristics of the activated carbon produced by the physical acti- vation method. A systematic approach using factorial design was used to identify factors that affected the Received 2012-02-06, accepted 2012-05-03. * To whom correspondence should be addressed. E-mail: alex.cheung@scottwilson.com.hk