Adding water to asphalt-derived porous carbon improves its ability to sequester carbon dioxide at natural gas wellheads. The porous particles in the illustration are combined with water and then heated to remove excess water from the pores. The water that remains binds to pore structures, and at pressures above 20 atmospheres, the filter material sequesters carbon dioxide and allows methane molecules to pass through. Source: Almaz JalilovAdding water to asphalt-derived porous carbon improves its ability to sequester carbon dioxide at natural gas wellheads. The porous particles in the illustration are combined with water and then heated to remove excess water from the pores. The water that remains binds to pore structures, and at pressures above 20 atmospheres, the filter material sequesters carbon dioxide and allows methane molecules to pass through. Source: Almaz Jalilov

Carbon dioxide emission control is an issue for natural gas producers, as gas at the wellhead typically contains 3-7 percent CO2 but is as high as 70 percent at some sites. Sequestration of this gas is usually attempted with membranes, solid sorbents or other physical schemes that have poor selectivity. Chemical approaches offer better selectivity but are corrosive and incur higher costs.

A new material developed at Rice University delivers high CO2 uptake capacity and captures more than 200 percent by weight. Adding water to grains of inexpensive Gilsonite asphalt results in a material that adsorbs more than two times its weight in the greenhouse gas. The treated asphalt selects carbon dioxide over valuable methane at a ratio of more than 200-to-1. Coating the pore surfaces with water adds weak chemical absorption and high selectivity while retaining the material’s strong physical adsorption.

The material performs well at ambient temperatures and under the pressures typically found at wellheads. When the pressure abates, the material releases the carbon dioxide, which can then be stored, sold for other industrial uses or pumped back downhole.

Combining water and Gilsonite forms a hydrate within pore microstructures that greatly increases the binding selectivity of CO2 over methane. The micropores are far larger than the target molecules, but addition of water tightens the pores and decreases the pore volume through which the molecules must travel. The prepared Gilsonite has a surface area of 4,200 square meters per gram, so adding water leaves plenty of room to capture the gas.

Material degradation was demonstrated to be negligible over multiple testing cycles at various pressures and temperatures between freezing and 50 degrees Celsius. While about 1 percent weight of the water content is lost during cycling, the researchers say the water content of natural gas itself would likely replace that.

To contact the author of this article, email shimmelstein@globalspec.com