Determination of multi-component gas and water equilibrium and non-equilibrium sorption isotherms in carbonaceous solids from early-time measurements

Abstract

A rapid method is presented for determination of the multi-component gas and water sorption isotherms on carbonaceous solids from the non-equilibrium sorption data. This approach alleviates the long-time data requirement of the traditional volumetric gas adsorption technique used to construct gas isotherms requiring a series of equilibrium sorption measurements by successive pressure increments, particularly resorted in the coalbed methane industry. This is accomplished by the application of the non-equilibrium thermodynamics, multi-component material balance, gas sorption, and dissolution kinetic considerations for the gas adsorbed by carbonaceous solids and the gas dissolved in water under the effect of pressure, temperature, and grain size. The capabilities of the new technique in reducing the time required for construction of an isotherm are demonstrated by analyzing a series of the non-equilibrium sorption measurements and projecting the results to the equilibrium case. Moreover, it is demonstrated that the present model enables constructing both the equilibrium and non-equilibrium multi-component gas and water sorption isotherms in any carbonaceous solids and particularly coals simultaneously in relatively shorter time and with higher accuracy.