Abstract:

Using coal char, de-ashed coal char, coal ash and quartz as catalysts, cracking of methane is studied in a fixed bed reactor at 1123 K and atmospheric pressure. Methane conversion and hydrogen yield over fresh and de-ashed coal chars show certain difference. The initial methane conversion of 9.81% and hydrogen yield of 8.14% is achieved at 1123 K over coal ash. The results show that coal ash is of certain catalytic activity for methane cracking. The conversion and hydrogen yield over coal char decrease gradually with the reaction time, indicating the deactivation of coal char. Lignite char and de-ashed char before and after reaction were characterized by using scanning electron microscope and specific surface area determinator. The results shows that the surface area and micro-pore volume of coal chars decrease and average pore diameter increases after methane decomposition reaction, implying that the micro-pore could be blocking by deposition of carbon formed in methane cracking, and the part surface of coal char has been covered by carbon of deposition, which makes catalytic activity of coal char decrease gradually.

Key words: methane cracking, hydrogen, fixed-bed, coal char, coal ash, catalysis, deactivation

摘要：

利用煤焦作为催化剂,采用小型石英管固定床为反应装置,对甲烷在煤焦、脱灰煤焦、煤灰以及石英砂床层上在温度为1123 K下的裂解反应进行了较为详细的研究。甲烷在脱灰煤焦上和新鲜的褐煤焦上的转化率和氢气收率有一定的差别。煤灰作为催化剂时,甲烷初始转化率和氢气初始收率分别为9.81%和8.14%。表明煤焦中的灰成分对甲烷裂解有一定的影响。随着反应时间的增加,甲烷的转化率和氢气的收率都逐渐降低。通过扫描电子显微镜和比表面积测定仪对反应前后的褐煤焦、脱灰煤焦进行了表征。甲烷裂解后煤焦比表面积、微孔容都明显降低,平均孔径增大。说明甲烷裂解生成的积炭堵塞煤焦的微孔。SEM照片显示甲烷裂解后积炭覆盖在煤焦的表面,使煤焦的催化活性逐渐降低。

关键词: 甲烷裂解, 氢, 固定床, 煤焦, 灰成分, 催化活性, 失活