Activated diffusion of methane from coals at elevated pressures

Diffusion of methane from three coals ranging in rank from anthracite to HVA bituminous has been studied at initial methane pressures up to about 2.76 MPa (400 psi). Unsteady-state diffusion conditions existed, the methane pressure within the coal particle decreasing with time while the methane pressure outside the particles remained at atmospheric. The diffusion parameter $\text{D}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{r}{}_0$ increased with increasing methane concentration at high values of methane sorption. Diffusion was activated but the exact magnitude of the activation energy is uncertain owing to the suspected contribution of the heat of sorption to the temperature coefficient. $\text{D}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{r}{}_0$ increased with decreasing particle size of coal studied, but r₀ is clearly less than the particle radius.