褐煤半焦直接加氢制甲烷反应特性及其孔结构和表面形态变化

在高温高压(1 000 ℃、12 MPa)固定床反应器上对内蒙古褐煤半焦的加氢甲烷化反应特性进行了研究,采用氮吸附和扫描电镜(SEM)对甲烷化残渣比表面积、孔结构和表面形态进行了表征。结果表明,半焦加氢甲烷化可分为加氢热解、快速加氢和慢速加氢等三个反应阶段,每阶段分别发生含氧官能团和烷基侧链加氢反应、芳环结构加氢反应以及贫氢骨架碳结构加氢反应。半焦加氢甲烷化最优反应温度为800 ℃,反应压力为3.0~4.0 MPa;提高升温速率可以缩短前段(碳转化率低于46%)反应过程时间,对后段(碳转化率高于46%)反应过程影响较小。半焦甲烷化残渣的吸附-脱附等温线呈反S型,滞后环呈H3回线形状;在甲烷化反应过程中,半焦平均孔径先减小后增大,总孔容积和介孔容积逐渐增大,微孔容积和比表面积先增大后减小。

Hydrogasification of lignite semicoke to produce methane and the textural properties of coke residues

The hydrogasification of Inner Mongolia lignite semicoke to produce methane was investigated in a high-temperature and high-pressure (1 000 ℃, 12 MPa) fixed bed reactor; the specific surface area, pore structure and surface feature of the coke residues were characterized by nitrogen physisorption and scanning electron microscope (SEM). The results showed that the hydrogasification process of semicoke can be divided into three stages, viz., hydropyrolysis, rapid hydrogenation and slow hydrogenation, in which the hydrogenation of oxygen-containing functional group and alkyl side chain, the hydrogenation of aromatic structure, and the hydrogenation of hydrogen depleted carbon skeleton structure take place successively. The optimum reaction temperature and pressure for the semicoke hydrogasification are 800 ℃ and 3.0~4.0 MPa, respectively. An increase of heating rate may shorten the reaction time of earlier hydrogasification stage with a carbon conversion below 46%, but has little effect on the later stage with a carbon conversion above 46%. The nitrogen physisorption of the coke residues exhibits a reversed S-shape isotherm with a H3 hysteresis loop. Along with the progress of hydrogasification, the average pore size of semicoke decreases first and then increases, the total pore volume and mesopore volume increase gradually, whereas the micropore volume and specific surface area increase first and then decrease.