Abstract：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 density functional theory( DFT). Further,using by the theory of Kakei's multi-stage adsorption,the difference of adsorption capacity 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 nanopores decrease firstly and then increase,and the distribution of the pores with different pore diameter is more homogeneous with the deepening of the coalification. The nitrogen adsorption capacity of coal mainly has a good relationship with the BET specific surface area,but the amount of meso-pores and micro-pores in coal is the 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 change laws 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 modes monolayer adsorption,multi-molecular layer adsorption,capillary condensation and micropore filling.

Keyword：coal with different ranks;nano-pores;liguid nitrogen adsorption at low temperature;mechanism of multi-stage adsorption;