Porous material polymerizes carbon dioxide at natural gas wellheads; less costly and energy-intensive approach
|Particles of nitrogen-containing porous carbon polymerize CO2 from natural gas under pressure at a wellhead. When the pressure is released, the CO2 returns to gaseous form. Courtesy of the Tour Group. Click to enlarge.|
Scientists in the Rice University lab of chemist James Tour have developed materials that offer a lower cost, less energy-intensive way to separate carbon dioxide from natural gas at wellheads. The nucleophilic porous carbons, synthesized from simple and inexpensive carbon–sulphur and carbon–nitrogen precursors, pull only carbon dioxide molecules from flowing natural gas and polymerize them while under pressure naturally provided by the well.
When the pressure is released, the carbon dioxide spontaneously depolymerizes and frees the sorbent material to collect more. All of this works in ambient temperatures, unlike current high-temperature capture technologies that use up a portion of the energy being produced.
|Illustration by Tanyia Johnson/Rice University. Click to enlarge.|
The Tour lab patented material, developed with assistance from the National Institute of Standards and Technology (NIST), shows promise to replace more costly and energy-intensive processes. Results from the research appear in the journal Nature Communications.
Natural gas is the cleanest fossil fuel, but still requires clean-up before use—such as the removal of carbon dioxide to meet pipeline specifications. Development of cost-effective means to separate carbon dioxide during the production process will improve its advantage over other fossil fuels and enable the economic production of gas resources with higher carbon dioxide content that would be too costly to recover using current carbon capture technologies, Tour said.
If the oil and gas industry does not respond to concerns about carbon dioxide and other emissions, it could well face new regulations. Our technique allows one to specifically remove carbon dioxide at the source. It doesn’t have to be transported to a collection station to do the separation. This will be especially effective offshore, where the footprint of traditional methods that involve scrubbing towers or membranes are too cumbersome. This will enable companies to pump carbon dioxide directly back downhole, where it’s been for millions of years, or use it for enhanced oil recovery to further the release of oil and natural gas. Or they can package and sell it for other industrial applications.—James Tour
The Rice material, a nanoporous solid of carbon with nitrogen or sulfur, is inexpensive and simple to produce compared with the liquid amine-based scrubbers used now, Tour said.
Amines are corrosive and hard on equipment. They do capture carbon dioxide, but they need to be heated to about 140 degrees Celsius to release it for permanent storage. That’s a terrible waste of energy.—James Tour
Rice graduate student Chih-Chau Hwang, lead author of the paper, first tried to combine amines with porous carbon; this approach still required heating to break the covalent bonds between the amine and carbon dioxide molecules, he said. Hwang also considered metal oxide frameworks that trap carbon dioxide molecules, but they had the unfortunate side effect of capturing the desired methane as well and they are far too expensive to make for this application.
The porous carbon powder has a surface area of 2,500 square meters per gram. The researchers treated the carbon source with potassium hydroxide at 600 ˚C to produce the powders with either sulfur or nitrogen atoms evenly distributed through the resulting porous material. The sulfur-infused powder performed best, absorbing 82% of its weight in carbon dioxide. The nitrogen-infused powder was nearly as good and improved with further processing.
Nobody’s ever seen a mechanism like this. You’ve got to have that nucleophile (the sulfur or nitrogen atoms) to start the polymerization reaction. This would never work on simple activated carbon; the key is that the polymer forms and provides continuous selectivity for carbon dioxide.—James Tour
Methane, ethane and propane molecules that make up natural gas may try to stick to the carbon, but the growing polymer chains simply push them off, he said. Tour said the material did not degrade over many cycles.
Apache Corp., a Houston-based oil and gas exploration and production company, funded the research at Rice and licensed the technology. Tour expected it will take time and more work on manufacturing and engineering aspects to commercialize.
The paper’s co-authors are undergraduate Josiah Tour, research scientist Carter Kittrell and senior research scientist Lawrence Alemany, all of Rice, and Laura Espinal, an associate at NIST. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and nanoengineering and of computer science.
Chih-Chau Hwang, Josiah J. Tour, Carter Kittrell, Laura Espinal, Lawrence B. Alemany & James M. Tour (2014) “Capturing carbon dioxide as a polymer from natural gas,” Nature Communications 5, Article number: 3961 doi: 10.1038/ncomms4961