Coal Gas Adsorption/Desorption Isotherms versus Diffusion Process

Abstract

In the present work, the authors studied two meta-anthracite samples from Douro Coalfield (NW of Portugal) in which classical sorption isotherms were carried out, using CO2 only. Results have demonstrated that whenever the CO2 is adsorbed in the coal pores/matrix it will be enduringly fixed up to, approximately, pressures of 32 bar in sample A and 34 bar in sample B. Since the gas release process it intensely related to diffusion coefficients, it is crucial to define their evolution on the two analyses reported in this paper. So, during adsorption, diffusion coefficients decrease in sample A from 4.66736E-08 to 1.23490E-09 cm2/sec (6.72 and 48.13 bar) and during desorption they increase from 7.61829E-09 to 1.09908E-08 cm2/sec (45.68 and 11.48 bar). In sample B, diffusion coefficients decrease from 2.47409E-08 to 2.11813E-09 cm2/sec (7.53 and 47.17 bar) in adsorption and increase in desorption from 1.48767E-09 to 2.83736E-08 cm2/sec (42.22 and 7.71 bar).