甲烷在褐煤煤焦上的裂解反应研究

Methane cracking over lignite char

采用石英管固定床反应器,分别考察了不同温度(1123K、1173K、1223K、1273K)及不同浓度(10%、15%、20%)下,甲烷在褐煤煤焦上的裂解反应。结果表明,褐煤煤焦对甲烷裂解反应具有良好的催化活性,在所考察温度范围内,甲烷的初始转化率最高达99.5%,温度越高,甲烷的初始转化率越高;但随着反应的进行,转化率逐渐降低;甲烷进气浓度越高,初始转化率越低,而且催化剂失活也越快。反应前后煤焦电镜扫描照片及物性参数的比较表明,甲烷裂解生成炭沉积在煤焦表面,导致煤焦比表面积随反应的进行逐渐降低,与甲烷裂解转化率的变化趋势一致;反应后煤焦的孔容及微孔容都有所降低,平均孔径增大,说明甲烷的裂解生成炭造成了煤焦孔道尤其是微孔的堵塞,比表面积减小,导致了甲烷的转化率降低。

Methane cracking over a lignite char was studied in a fixed bed reactor. The experiments were performed at temperature range from 1123K to 1273K and atmospheric pressure. The total flow rate was 250 mL/min with methane concentrations of 10% , 15% and 20% , respectively. The lignite char shows a significant catalytic activity on methane cracking. The maximum conversion of methane of 99.5% is achieved at 1273K in the initial stage. However, the methane conversion decreases with reaction time due to deactivation of the lignite char by carbon deposition on surface of the char. The results also show that higher initial methane conversion is achieved at higher temperature. Furthermore, the higher the methane concentration, the lower the methane conversion and the faster the deactivation of the char occurs. During the reaction the carbon deposits on the surface of the char. The spent char shows a lower surface area, total pore and micropore volumes, and larger pore diameters than those of the fresh char. This observation seems to suggest that the carbon deposition takes place in the pores, especially in the micropores of the char, leading to blockage of the pores for continuing catalytic cracking of methane.