Thermodynamicand kinetic characteristics of gas adsorption by coal under temperature effect

doi:10.16265/j.cnki.issn1003-3033.2023.07.1934

Abstract

Abstract:

In order to study the thermodynamic and kinetic characteristics of the interaction between coal and gas, the isothermal adsorption tests of coal at 298, 308, 318, 328 and 338 K were carried out. In this paper, the thermodynamic parameters and adsorption kinetic characteristics of coal gas adsorption under temperatures effect were analyzed by using the self-developed coal gas-solid coupling test platform. The results show that with the increase in temperature, the gas adsorption capacity of coal decreases gradually, and the isothermal adsorption curve conforms to the Langmuir type change rule. The isosteric adsorption heat of coal increases with the increase of adsorption capacity, and the variation range is -10.191 to -7.127 kJ/mol. The adsorption of coal gas is an exothermic physical process. The increase in temperature inhibits the adsorption capacity of coal gas, and the limited adsorption heat of coal is -11.369 kJ/mol. The adsorption free energy and adsorption entropy at different temperatures were less than 0, which were -6.958 to -2.452 kJ/mol and -14.085 to -12.607 J/(mol·K), respectively. In the kinetic model fitting, the gas adsorption amount at adsorption equilibrium decreases with the temperature increase, and the adsorption rate constant is positively linear with temperature. The adsorption of coal gas is a dynamic exothermic process. With the increase in temperature, the molecular energy of gas is gradually greater than the adsorption potential energy of coal pores. The adsorbed gas gradually transforms into free gas, and the adsorption capacity of coal gas decreases.

Key words: gas adsorption, temperature effect, isothermal adsorption, adsorption thermodynamics, kinetic characteristic.

QIU Yue, LONG Hang, BAI Yang, LIN Haifei, YAN Min, XIAO Tong. Thermodynamicand kinetic characteristics of gas adsorption by coal under temperature effect[J]. China Safety Science Journal, 2023, 33(7): 147-155.

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吸附试验温度T/K	吸附数据的 Langmuir 拟合
吸附试验温度T/K	a	b	拟合相关系数
298	41.728	0.177	0.999
308	41.264	0.154	0.996
318	40.031	0.110	0.998
328	39.076	0.100	0.998
338	34.029	0.094	0.998

Q/ (mmol·g^-1)	等量吸附线拟合公式	ΔH/ (kJ·mol^-1)
0.200	lnP^*=2.933-857.232T^-1	-7.127
0.250	lnP^*=3.253-909.872T^-1	-7.565
0.300	lnP^*=3.572-962.513T^-1	-8.002
0.350	lnP^*=3.893-1015.154T^-1	-8.440
0.400	lnP^*=4.213-1067.794T^-1	-8.878
0.450	lnP^*=4.532-1120.435T^-1	-9.315
0.500	lnP^*=4.852-1173.075T^-1	-9.753
0.550	lnP^*=5.172-1225.716T^-1	-10.191

Q/ (mmol·g^-1)	ΔS/(J·mol^-1·K^-1)
Q/ (mmol·g^-1)	298 K	308 K	318 K	328 K	338 K
0.200	0.612	0.548	2.370	2.191	2.856
0.250	4.190	4.081	5.868	5.654	6.328
0.300	7.436	7.283	9.035	8.787	9.472
0.350	10.457	10.260	11.977	11.696	12.397
0.400	13.315	13.075	14.758	14.444	15.165
0.450	16.052	15.768	17.419	17.072	17.819
0.500	18.696	18.369	19.988	19.610	20.388
0.550	21.268	20.898	22.486	22.078	22.894

T/K	Q_e1/(cm³·g^-1)	k₁/ h^-1	拟合相关系数
298	3.245	12.016	0.862
308	3.124	15.634	0.870
318	3.072	16.844	0.923
328	2.969	18.300	0.948
338	2.865	23.833	0.938

T/K	Q_e2/(cm³·g^-1)	k₂/h^-1	拟合相关系数
298	3.408	6.063	0.952
308	3.266	8.561	0.963
318	3.199	9.728	0.980
328	3.089	11.053	0.991
338	2.968	15.885	0.990