Carbon capture made easy

Gasification plants may be one of the keys to a hydrogen economy, if capture and sequestration of carbon dioxide (CO2) becomes technically and economically feasible. These plants would transform fossil fuel feedstock, including coal, biomass and municipal wastes, into clean-burning hydrogen gas where the only byproduct is water. But there are problems to solve. In addition to producing hydrogen, coal gasification produces CO2. Current methods for CO2 capture use large volumes of chemical solvents that must be cycled through dramatic changes in pressure and temperature to absorb and then release CO2. These pressure and temperature swings use a lot of energy and increase costs of electricity production by 15 to 30 percent.

Researchers at Pacific Northwest National Laboratory are developing a new class of materials for CO2 capture that aims to significantly reduce the energy penalty for CO2 capture. The PNNL process does not require dramatic pressure and temperature swings, making it more energy-efficient. And the concept integrates CO2 capture with a water-gas shift reaction into a single, more efficient unit, reducing costs and creating a near-zero emissions system. Integrating the process improves the efficiency of the water-gas shift reaction, which converts carbon monoxide to CO2 and hydrogen by reacting with water vapor, ultimately producing more CO2 and more hydrogen, the desired product.

A unique nanomaterial will be instrumental in the integrated process. “We are working with a nano-structured material called an organic clathrate that can be engineered to attract CO2 and other gases into its molecular cages,” said Laboratory Fellow Pete McGrail, who is leading the carbon capture work. Organic clathrates can hold several gas molecules in each of their cavities. The material is a solid that could be packed into an absorber column to collect CO2 from the gas stream.

“The water-gas shift reaction of interest takes place at 230 to 260 degrees Celsius,” said Praveen Thallapally, who is leading the materials synthesis work. “We have created a new clathrate material that can absorb CO2 at 220 degrees Celsius so we believe it’s possible, with additional research, to create materials that will perform at the temperatures necessary for this application.”

McGrail and his team also are using molecular dynamics simulations in their studies. Instead of the timeconsuming conventional method of constructing a material, synthesizing it and evaluating it, they are using computer simulations to help guide their materials development and discovery effort.