不同煤级煤低温氮的多段吸附特征

The multi-stage adsorption characteristics of coals with different ranks under the condition of cryogenic liquid nitrogen

基于不同煤级煤的低温液氮吸附性能测试,采用毛细管凝聚理论(BJH法)和密度泛函理论(DFT法),对煤的低温氮吸附曲线进行解析,结合Kakei的多段吸附理论,探讨不同煤级煤的吸附量、吸附曲线形态的差异,以及多段吸附特征及其机理。结果表明,随着煤化作用的加深,煤中纳米级孔隙呈现先减少后增加的趋势,孔隙的孔径分布更加均一;煤的液氮吸附量主要与BET比表面积有一定的关系,但中、微孔孔隙含量是造成液氮吸附量差异的主因;煤级的增加,液氮吸附曲线呈现由简单→复杂→简单的变化规律,表现为多段性吸附特征,暗示着吸附机理的变化,存在着单分子层吸附、多层吸附、毛细孔凝聚及微孔填充等多种吸附模式。

Based on the test results of the adsorption of coal with different ranks for liquid nitrogen at low temperature,the adsorption curves were analyzed by means of capillary condensation theory （ BJH ） and densityfunctional theory（DFT） . Further,using by the theory of Kakei5 s multi-stage adsorption, the difference of adsorptioncapacity and the adsorption curve on coal samples with different ranks are discussed. In addition,the laws of multi-stage adsorption and its mechanism are also investigated. The results show that the nanoporesdecrease firstly and then increase, and the distribution of the pores with different pore diameter is morehomogeneous with the deepening of the coalification. The nitrogen adsorption capacity of coal mainly has agood relationship with the BET specific surface area, but the amount of meso-pores and micro-pores in coal isthe main reason that causes the change of adsorption capacity of coal for liquid nitrogen at low temperature.As the increase of coal metamorphism degree, the adsorption curves of coal for liquid nitrogen have the changelaws from simplicity to complexity and then to simplicity, showing the characteristics of multi-stage adsorption, and also indicating the variation of adsorption mechanism, including the following adsorption modesmonolayer adsorption, multi-molecular layer adsorption, capillary condensation and micropore filling.