基于SAXS的不同变质程度煤纳米级孔隙结构特征研究

SAXS-based nano-scale pore structure characteristics of coals with different metamorphic degrees

为揭示不同变质程度煤岩纳米级孔隙特征,运用小角X射线散射方法(SAXS),采集镜质体反射率R_(max)在0.31%~6.24%的15个样品,基于散射数据获取的煤岩孔隙率、孔径分布、比表面积和分形维数,讨论了煤化过程对煤岩纳米孔隙(0.3~100nm)结构的影响,并用低温CO_(2)和N_(2)吸附DFT模型结果对孔径分布进行了验证。结果表明:在R_(max)<0.5%时,煤岩孔隙率和比表面积随着变质程度的增加而增加,微孔(<2nm)含量增长较少,介孔(2~50nm)和大孔(50~100nm)含量大幅增加,煤岩表面逐渐光滑;在R_(max)=0.5%~1.4%时,孔隙率和比表面积减小,各类孔隙含量均减少,煤岩表面逐渐光滑;在R_(max)=1.4%~4.0%时,煤岩孔隙率和比表面积增大,微孔含量大幅增加,介孔和大孔含量近乎稳定,煤岩表面逐渐粗糙;在R_(max)>4.0%后,煤岩孔隙率和比表面积缓慢增加,微孔增长幅度变缓,煤岩表面逐渐光滑。SAXS在0.3~100nm孔径分布(本次实验范围)中用球形形状因子与低温CO_(2)和N_(2)吸附结果契合度较高,煤中纳米级孔隙率及比表面积主要由微孔贡献。

In order to reveal the characteristics of nano-scale pores in coals with different metamorphic degrees,the small-angle X-ray scattering method(SAXS)is used to obtain the porosity,pore size distribution,specific surface area and fractal dimension of 15 samples whose vitrinite reflectance R_(max)is 0.31%-6.24%,and the low temperature CO_(2)and N_(2)adsorption DFT model results are used to verify the pore size distribution.The results show:during coalification process,when R_(max)is<0.5%,the porosity and the specific surface area of coal increase with the increase of metamorphic degree,the micropores(<2 nm)content increases seldomly,the mesoporous(2-50 nm)and microporous(50-100 nm)content increase greatly,and the surface of coal is gradually smooth.When R_(max)=0.5%-1.4%,the porosity and the specific surface area decrease,and each type of pore content is reduced,and the surface of coal is gradually smooth.When R_(max)=1.4%-4.0%,the porosity and specific surface area of coal rock increase,the microporous content increases,and the mesoporous and microporous content are nearly stable,and the surface of the coal is gradually rough.When R_(max)>4.0%,the porosity and specific surface area of coal increase,the microporous growth is slow,and the surface of coal is gradually smooth.