1 Korean J. Chem. Eng., 31(4), 1-8 (2014) DOI: 10.1007/s11814-014-0273-2 INVITED REVIEW PAPER pISSN: 0256-1115 eISSN: 1975-7220 INVITED REVIEW PAPER † To whom correspondence should be addressed. E-mail: rathersami@gmail.com, yhamed@kau.edu.sa Copyright by The Korean Institute of Chemical Engineers. Preparation of activated carbon from fly ash and its application for CO 2 capture Yahia Abobakor Alhamed * , ** ,† , Sami Ullah Rather * , ** ,† , Ahmad Hasan El-Shazly * , ** , Sharif Fakhruz Zaman * , ** , Mohammad Abdulrhaman Daous * , ** , and Abdulrahim Ahmad Al-Zahrani * , ** *Chemical and Materials Engineering Department, King Abdulaziz University, P. O. Box 80204, Jeddah 21589, Saudi Arabia **Center of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80216, Jeddah 21589, Saudi Arabia (Received 5 May 2014 • accepted 11 September 2014) Abstract-Power and desalination plants are one of the main anthropogenic sources for CO 2 generation, which is one of the key elements to cause greenhouse gas effect and thus contribute to the global warming. Fly ash (FA) generated in desalination and power plants was converted into activated carbon (AC) treated with KOH at higher temperature and tested for CO 2 capturing efficiency. Morphological characteristics of FA such as BET specific surface area (SSA), pore volume, pore diameter, and pore size distribution (PSD) were performed using N 2 adsorption isotherm. CO 2 adsorp- tion capacity and adsorption isotherms of CO 2 over AC were measured by performing thermogravimetric analysis at different temperatures. BET SSA of 161 m 2 g -1 and adsorption capacity of 26 mg CO 2 /g AC can be obtained by activa- tion at KOH/FA ratio of 5 at 700 o C and activation time of 2 h. Therefore, great potential exists for producing AC from FA, which will have the positive effect of reducing the landfill problem and global warming. Keywords: Fly Ash, Activated Carbon, CO 2 Capture, KOH Activation, Global Warming INTRODUCTION Global warming is attributed mainly to the increase of CO 2 emis- sion to the atmosphere, and subsequently worst climate changes are predicted if CO 2 emission is not reduced immediately [1]. Power generation plants and seawater desalination units utilizing various fossil fuels are considered as a major contributors to this continu- ally increasing CO 2 emission problem. This environmental prob- lem is further aggravated by fly ash (FA) generated in these plants as a solid waste residue, which creates not only a solid waste dis- posal problem, but also a particulate pollution problem in the atmo- sphere and in the surrounding land area. The FA is being captured from flue-gas of these industries using suitable particulate collec- tor. Currently, disposal of larger quantity of this solid waste, gener- ated in industries, is being done in landfills, mostly without pre- treatment. This has created an increasing environmental concern regarding possible leaching of heavy metals present in the FA into ground water adjacent to FA dumping sites, in addition to dust- ing problems [2-6]. Various utilization of FA has been implemented, tested or pro- posed in literature. Strength developments for cement mortars con- taining FA are modified by altering physical, mineralogical, mor- phological, and chemical properties by mechanical grinding [7-9]. FA particles and precipitated silica are used in fillers to improve the vulcanization properties of rubbers [10]. Effects of silica and alumina contents vary the setting, phase development, and physical properties of FA [11]. Nonetheless, FA whether treated or untreated, is considered as a solid waste that creates a serious pollution prob- lem in these plants, its surroundings, and in its landfill areas. Re- searchers have been investigating utilization of FA with two-fold applicability, i.e., reduction of solid waste generation and handling problem and use FA generated AC to capture CO 2 emitted from these industries [12-14]. There are mainly two different processes for preparation of AC, chemical and physical activation [15-17]. An important advantage of chemical activation is its ability to take place at lower tempera- tures and shorter time than those used in physical activation. In addition, higher surface area and higher yield of carbon can be ob- tained by using chemical activation [18-20]. Many researchers have shown that AC produced by KOH activation from carbonaceous materials such as coke, charcoal, coal, and char provides a high BET SSA of over 2,000 m 2 g -1 . In addition, KOH chemical activation is a very effective method for the production of AC with a narrow PSD and a well-developed porosity [21-26]. The aim of the present work was to investigate FA generated AC by KOH produced in power and desalination plants for removal of CO 2 . EXPERIMENTAL 1. Raw Material The FA used for this study was obtained from Shuaiba desalina- tion plants, 70 km south of Jeddah, Saudi Arabia. The fuel used in the desalination plant was heavy vacuum gas oil (Bunker “C”). Burning this type of fuel emits enormous amounts of obnoxious and toxic pollutants to the environment along with a large amount of a high carbon (92%) content FA (36 tons per day) [4]. The properties of raw FA generated from desalination plant are shown in Table 1. 2. Activation and Purification About 10 g of as-received FA was mixed vigorously with 0.16 M