基于低温氮吸附的动态超临界CO2对煤纳米孔隙结构的影响

基于动态SCCO₂萃取平台,模拟了SCCO₂(温度55℃和压力12 MPa)与焦煤和瘦煤的动态相互作用。通过低温氮吸附技术分析了SCCO₂作用前后煤纳米孔隙结构的变化特征,探讨了SCCO₂对煤纳米孔隙结构的影响。结果表明:SCCO₂不会改变纳米孔隙形状,SCCO₂作用后,焦煤的比表面积和孔体积增大,微孔含量显著升高,中孔孔隙度下降,平均孔径降低,瘦煤表现出相反的趋势;分形分析表明SCCO₂增强了焦煤纳米孔隙表面的非均质性,但瘦煤孔隙表面变得光滑;SCCO₂的萃取效应和SCCO₂吸附引发的溶胀效应的净作用是上述焦煤和瘦煤纳米孔隙差异变化的主因,对于焦煤,萃取作用强于溶胀作用,对纳米孔隙结构产生增孔效应,瘦煤则相反。

Influence of dynamic supercritical CO_2 on nanopore structure of coals based on low-temperature nitrogen adsorption

The dynamic interaction of SCCO₂ with coking coal and lean coal was simulated on a dynamic SCCO₂ extraction system under conditions of temperature of 55 ℃ and pressure of 12 MPa. The low-temperature nitrogen adsorption was adopted to address the alterations in nanopore structure of coal samples, and the influence of SCCO₂ on nanopore structure of coal samples was discussed. The results show that SCCO₂ cannot alter pore shape of nanopores. For coking coal after SCCO₂ exposure, the specific surface area and pore volume increase, the microporosity rapidly increases, while the mesoporosity and average pore size decline.However, the reverse trend is found for lean coal after SCCO₂ exposure. Fractal analysis shows that SCCO₂ enhances the heterogeneity of nanopore surface of coking coal, while the nanopore surface of lean coal after SCCO₂ exposure becomes smooth.The net effect of SCCO₂ extraction and swelling effect due to SCCO₂ adsorption contributes to the different variations in nanopore structure of coking coal and lean coal. For coking coal, SCCO₂ extraction effect is superior to swelling effect, which is favorable to the development of nanopores, while the reverse trend occurs in lean coal.