Predicting Coal Deformation During Gas Adsorption

This project (Corrente et al., 2021) developed a novel thermodynamic approach to predict how nanoporous materials deform when exposed to gas mixtures, with particular focus on coal swelling during CO2-enhanced methane recovery - a promising technique for both natural gas production and carbon sequestration.

Key Contributions

Developed a rigorous thermodynamic framework for predicting material deformation during multicomponent gas adsorption
Validated model predictions against experimental data for CH₄/CO₂ mixtures on coal samples
Projected coal swelling behavior under realistic geological conditions at varying depths
Demonstrated model’s potential for optimizing CO₂ sequestration and enhanced gas recovery

Theoretical Framework

We developed a thermodynamic model based on the adsorption stress concept, where material deformation is determined by:

External pressure (Pext)
Adsorption stress (σₐ) from guest molecules
Material’s volumetric modulus (K)

Adsorption and strain isotherms for pure CO₂, CH₄, and their mixtures on coal. Points show experimental data, lines show model predictions.

Key Findings

Model Validation
- Excellent agreement between predicted and measured adsorption behavior
- Successfully captured both contraction and swelling effects
- Accurately predicted mixture behavior from pure component data
Geological Predictions
- Quantified coal swelling at depths up to 2000m
- Revealed nonmonotonic behavior with depth due to competing temperature and pressure effects
- Projected maximum volumetric strain of ~1.55% at 1000m depth
Practical Implications
- Provided insights for CO₂ sequestration optimization
- Enabled prediction of reservoir permeability changes
- Framework adaptable to other nanoporous materials

Temperature and Pressure Effects

At geological conditions, both temperature and pressure increase with depth:

Temperature gradient: 0.03 K/m
Pressure gradient: 0.01 MPa/m

Predicted adsorption and strain behavior at different depths, showing nonmonotonic behavior due to competing temperature and pressure effects.

Impact

This work provides crucial insights for:

Optimizing CO₂-enhanced methane recovery
Predicting reservoir behavior during gas injection
Understanding environmental impacts of carbon sequestration
Designing better gas separation processes

The theoretical framework developed here can be extended to other flexible nanoporous materials, including metal-organic frameworks (MOFs) and zeolites, making it valuable for various industrial applications beyond geological carbon storage.

Methods

Thermodynamic modeling
In-situ strain measurements
Gas chromatography
Volumetric adsorption measurements

This research advances our understanding of material behavior during multicomponent adsorption and provides practical tools for optimizing energy and environmental technologies.