Methane and Carbon Dioxide Adsorption Capacity Estimation and Modeling on Coals

Open Access
Zhang, Rui
Graduate Program:
Energy and Mineral Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 15, 2015
Committee Members:
  • Shimin Liu, Thesis Advisor
  • methane
  • carbon dioxide
  • adsorption
  • modeling
  • coal
Characterization of gas sorption behavior on coals plays an important role on coalbed methane (CBM) and CO2-enhanced CBM industry. In this study, the excess adsorption capacities were estimated for four coal samples with different ranks including San Juan sub-bituminous coal, Pittsburgh No. 8 bituminous coal, Hazleton anthracite and Good Spring anthracite by the volumetric adsorption experimental method. Adsorption and desorption isotherms of methane and CO2 were directly measured for these four coal samples. Langmuir based models and Dubinin-Astakhov (D-A) based models were used to model adsorption behavior of both methane and CO2. The experimental results showed that CH4/CO2 excess adsorption capacity ratio varied from 1:1.1 to 1:1.6 at maximum equilibrium pressure on these coals. Higher rank coals have higher excess adsorption capacities than lower rank coals across the experimental pressure range. Hysteresis of CO2 is discernable and larger than methane for all coals. Higher rank coals have negligible methane hysteresis but larger CO2 hysteresis than lower rank coals. From the modeling results, maximum CO2 adsorption capacities are larger than methane capacities for all coals. In general, D-A based models were modeled better than Langmuir based models for these coals. Added k term reduced modeling error for both Langmuir and D-A series models. In addition, the modified Langmuir model-1 have relatively high errors for all coal samples.