闪热解对烟煤焦结构及活化过程孔隙生成的影响

采用闪热解方式在不同温度(500,800和1 000℃)和停留时间(10和40 min)条件下制备分级孔活性炭。使用SEM分析煤焦表面形貌,N_2吸附获得孔结构参数、XRD和Raman分别获得芳香层片尺寸和不同杂化炭结构参数。通过活化过程与慢速热解焦结构参数的变化进行对比,探究不同煤焦的碳损失与孔隙形成机制。研究结果表明,闪热解终温是控制中孔生成的主要因素,停留时间影响微晶形态及其空间结构的变化。慢速热解焦(M800-10)烧失率为53.6%时,其比表面积为663.19 m~2/g,微孔孔容为0.246 m~3/g,颗粒表面已被严重刻蚀。闪热解焦(K800-40)烧失率为25.2%时,比表面积为859.14 m~2/g,微孔孔容为0.34 m~3/g,具有明显分级孔结构特征,外部无明显刻蚀。在最佳的闪热解工况下制备前驱体煤焦,可有效消除活化气体和活化产物的内扩散阻力,使颗粒内部和表面同时发生烧失生成大量微孔,有效抑制了颗粒表面烧失并降低活性炭制备成本。

Effect of flash pyrolysis on bituminous char structure and pore development during activation

The activated carbon with hierarchical porous structure was prepared by flash pyrolysis method under different temperatures(500,800 and 1 000 ℃) and residence times(10 and 40 min).The apparent morphology,pore size and carbon structure parameters of chars were obtained by SEM(scanning electron microscope),nitrogen adsorption,XRD(X-ray diffraction) and Raman spectroscopy,respectively.The mechanism on the carbon loss and pore formation of two chars was illustrated by comparing the structural change of chars produced by flash and slow pyrolysis during activation.Results show that the flash pyrolysis temperature controls the formation of mesoporous,and the residence time has an importance on the change of morphology and spatial structure of microcrystalline.The char(M800-10) produced by slow pyrolysis has the specific surface area(SBET) of 663.19 m2/g and the microporous volume of 0.246 m3/g at a burn-off of 53.6%,meanwhile,its surface has been burned severely.The char(K800-40) produced by flash pyrolysis has the SBET of 859.14 m2/g and the microporous volume of 0.34 m3/g at a burn-off of 25.2%,it already has the obvious micro-mesoporous hierarchical structure and no apparent carbon loss outside of the particles.The precursor char prepared by flash pyrolysis under optimal conditions can eliminate the inner diffusion resistance of the activated gas and the activation product.A large number of micropores are developed from the external and internal particles simultaneously,which results in the reduction of carbon loss on particles surface and the cost of activated carbon.