Hydrogen production by methane cracking over different coal chars

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 pyrolysing four parent coals of different ranks, namely, Jincheng anthracite, Binxian bituminous coal, Xiaolongtan 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 surfaces and pores of coal chars were covered with carbon deposits produced by methane cracking as evident 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. (C) 2011 Elsevier Ltd. All rights reserved.