In order to study the difference in adsorption/desorption characteristics and the desorption hysteresis of CH

4

in different coal ranks

low

medium

and high coal rank samples are collected for the experiments of micro-component determination

liquid nitrogen adsorption

and isothermal adsorption/desorption to systematically

analyze the composition

pore structure

differences in adsorption/desorption characteristics and desorption hysteresis effects of different coal rank sample materials. Combined with the calculation results of methane adsorption heat

the mechanism of coalbed methane desorption hysteresis from the energy perspective is discussed. The results show that: ①The reflectance

R

o

max

of the vitrinite group of coal samples are 0.43 %

1.26 %

and 3.27 %

respectively. Low-rank coal samples have low vitrinite group content

high inert matter group content

high volatile content and fixed carbon. Medium-rank and high-rank samples are reversed. The degree of coal metamorphism increases. Porosity

BET specific surface area

BJH total pore volume

and fractal dimension D

2

change in a “V” shape

and D

1

changes in an inverted “V” shape. ②Under isothermal condition

the residual adsorption amount becomes larger as the coal rank rises

and the desorption becomes more difficult. As the temperature rises

the residual adsorption capacity increases first and then decreases. With 40 ℃ as the inflection point

the temperature influences both the degree of activation of gas molecules and the pore structure of coal. ③When the pressure is the same

the higher the coal rank

the faster the methane adsorption rate at the low-pressure stage（

p

4 MPa）

the adsorption capacity increases rapidly at the high-pressure stage（

p

4 MPa）

and the adsorption capacity does not increase significantly. ④For the three coal samples

DFS4

#

SGZ11

#

and SH3

#

in the desorption process

their isosteric heat of adsorption are all greater than that in the adsorption process

indicating that the desorption process needs to continuously absorb heat from outside. Therefore

the methane in the adsorption state needs to absorb energy from the external environment

and the energy difference between the adsorption and desorption processes will cause desorption hysteresis. The methan

e in the free state enters into the micropores due to high pressure

resulting in the expansion and deformation of coal matrix

changes in pore structure

limit of methane desorption

and finally a desorption hysteresis effect.