Hydrogen production by methane cracking over different coal chars Ling Wei a,b , Yi-sheng Tan a , Yi-zhuo Han a , Jian-tao Zhao a , Jinhu Wu d , Dongke Zhang a,c,d,⇑ a Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China b Graduate School of Chinese Academy of Sciences, Beijing 100039, China c Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia d Qingdao Institute of Bioenergy and Bioprocessing Technology, Chinese Academy of Sciences, Qingdao 266101, China article info Article history: Received 17 May 2011 Received in revised form 11 June 2011 Accepted 13 June 2011 Available online 12 July 2011 Keywords: BET Coal char Hydrogen Methane cracking Pyrolysis abstract Hydrogen production by methane cracking over a bed of different coal chars has been studied using a fixed bed reactor system operating at atmospheric pressure and 1123 K. The chars were prepared by pyr- olysing four parent coals of different ranks, namely, Jincheng anthracite, Binxian bituminous coal, Xiao- longtan lignite and Shengli lignite, in nitrogen in the same fixed bed reactor operating at different pyrolysis temperatures and times. Hydrogen was the only gas-phase product detected with a GC during methane cracking. Both methane conversion and hydrogen yield decreased with increasing time on stream and pyrolysis temperature. The lower the coal rank, the greater the catalytic effect of the char. While the Shengli lignite char achieved the highest methane conversion and hydrogen yield in methane cracking amongst all chars prepared at pyrolysis temperature of 1173 K for 30 min, a higher catalytic activity was observed for the Xiaolongtan lignite char prepared at 973 K, indicating the importance of the nature of char surfaces. The catalytic activity of the coal chars were reduced by the carbon deposition. The coal chars had legible faces and sharp apertures before being subjected to methane cracking. The sur- faces and pores of coal chars were covered with carbon deposits produced by methane cracking as evi- dent in the SEM images. The results of BET surfaces areas of the coal chars revealed that the presence of micropores in the chars was not an exclusive reason for the catalytic effect of the chars in methane cracking. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The use of coal-bed methane (CBM) as a feedstock for hydrogen production presents an alternative pathway for utilization of the huge but largely un-tapped CBM resources. In a series of recent studies involving the present authors, hydrogen has proven to be the primary gas-phase product in methane cracking over coal chars [1]. Compared with the conventional hydrogen production meth- ods using natural gas as a feedstock such as steam methane reforming (SMR), auto-thermal reforming (ATR) and partial oxida- tion reforming (POR) [2], cracking of coal-bed methane has many advantages in terms of process economy [3] as it can be easily inte- grated with existing coal conversion operations, avoiding the use of expensive metal catalysts and of course, eliminating the need of expensive new infrastructure. A detailed comparison of methane cracking and steam reforming reactors in hydrogen production showed that methane cracking can save about 40% of the unit en- ergy consumption [4,5]. Many literature reports have focused on the catalytic decompo- sition of methane over transition metals, such as Ni, Fe, Co, which can be easily deactivated by carbon deposition [6]. Recently, the carbon-based catalysts for decomposition of methane to produce hydrogen were proposed. Muradov [7] investigated several types of carbon including activated carbon, carbon black, graphite, dia- mond, carbon fibers and carbon nanotubes as catalysts for meth- ane cracking in a fixed bed reactor. It was shown that the best catalyst is the activated carbon prepared at 1123 K. The methane conversion over the carbon materials is much lower than that on the metal catalysts, but the use of carbon-based catalysts offers other advantages: being tolerant to sulfur and high temperatures, production of marketable byproduct carbon and no need of catalyst regeneration process [8]. Muradov et al. [7,8] considered that the carbon-based catalytic methane cracking can also produce valuable carbon byproduct, which can be used in several applica- tions such as structural materials, power generation, soil amendment and environmental remediation [9]. Lee et al. [10] used carbon blacks as catalysts for methane decomposition with CO 2 -free hydrogen production which showed more stable catalytic activity and lower activation energies than activated carbons. Methane cracking studies have been performed over a bed of coal 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.06.053 ⇑ Corresponding author at: Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Tel.: +61 8 6488 7600. E-mail address: Dongke.Zhang@uwa.edu.au (D. Zhang). Fuel 90 (2011) 3473–3479 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel