甲烷在活性炭上裂解制氢研究

Hydrogen production from methane pyrolytic decomposition over activated carbons

在连续流动石英固定床反应器上研究了甲烷在活性炭上裂解制氢的反应,并对反应前后活性炭的比表面积以及孔径分布等的变化进行了测定。结果表明,甲烷在五种活性炭上的裂解行为基本相同,反应初期转化率最高,随着反应进行转化率逐渐降低直至一个平稳的状态;降低甲烷分压和增加甲烷与活性炭的接触时间可提高甲烷转化率;温度的升高有利于初始转化率的提高,但不利于活性炭的稳定性;反应后活性炭比表面积、孔容及微孔孔容都明显降低,平均孔径增大,孔径分布向中孔方向迁移,说明甲烷的裂解导致了活性炭孔特别是微孔内的炭沉积以及进一步的孔堵塞。

The hydrogen production by the direct thermal decomposition of natural gas is an promising approach for its nearly zero emission of COx and lower energy consumption compared to the traditional methane steam reforming. The activated carbon （AC） as the catalyst for methane decomposition has many advantages over the metal ones, such as low cost, rich supply and so on, while there is little literature reported on the detailed methane decomposition over ACs and the properties changes of the ACs. In this work, the hydrogen production from the methane decomposition over activated carbons was studied in a fixed-bed quartz-tube reactor and at the same time the surface properties changes of the ACs including surface area, pore volume, micropore volume and pore distribution before and after use were analyzed. The results indicate that the methane decomposition over different ACs shows a similar behavior, i. e. , the maximum methane conversion is reached in the initial stage and then gradually fallen down to a stable stage along with the reaction time, which shows that the mechanisms of methane decomposition over ACs are same. The deactivation of the AC catalysts is due to the carbon deposition produced by the methane decomposition, which corresponds to the weight gain of the deactivated AC catalysts. The methane conversion increases with the increase of temperature, residence time and the decrease of methane partial pressure. However, high temperature is unfavorable of the stability of ACs because of the too rapid reaction rate and the great amount of carbon deposition in the initial stage. The spent ACs after methane decomposition have lower surface area, pore and micropore volme, and larger pore diameter than those of fresh ones, which shows that the carbon deposition takes place in the pores especially in the micropores of ACs and leads to the block of the pores.