Post-combustion Sorbents for Carbon Capture

Post-combustion Sorbents for Carbon Capture

Background
Carbon capture and storage from fossil-based power generation is a critical component of realistic strategies for arresting the rise in atmospheric CO2 concentrations, but capturing substantial amounts of CO2 using current technology would result in a prohibitive rise in the cost of producing energy. The National Energy Technologies Laboratory-Regional University Alliance (NETL-RUA) is pursuing a multifaceted approach, which leverages cutting-edge research facilities, world-class scientists and engineers, and strategic collaborations to foster the discovery, development, and demonstration of efficient and economical approaches to carbon capture.

Sorbents are high surface area solid materials designed to sorb CO2 reversibly. Upon saturation of CO2 on the solid sorbent, regeneration via heat or pressure swing is performed to produce high purity CO2, separating the CO2 from the flue gas. Solid sorbents have the potential to drastically reduce the energy required to release the CO2 due to their potentially higher CO2 loading, lower heat capacity, and reduced heat of reaction. The result is a lower overall cost for CO2 capture and separation. Many different types of solid materials have been investigated for CO2 capture, including supported amines, carbon-based sorbents, supported carbonates, and zeolites. Each of these sorbent types has specific advantages, disadvantages, and challenges associated with its implementation for CO2 capture.

Approach
The NETL-RUA is taking a broad approach to solid sorbent research in which technologies are moved from concept to testing on real flue gas from a power plant in a staged process. One example is a highly developed amine-based solid sorbent which is to be tested under real flue gas conditions in FY2014. This amine-based sorbent is the result of considerable optimization and is well characterized for a variety of potential conditions. The sorbent has shown favorable regeneration properties and the ability to repel the potentially damaging effects of moisture. Another class of sorbents that has recently moved from concept to reality is the creation of sorbents based on layered-double-hydroxides. The materials were selected using high throughput computational screening. The screening approach provided a few sorbent candidates that have favorable properties, which were then synthesized. Additionally, NETL is investigating a novel process which removes moisture to allow low cost CO2 removal from flue gas. Removing the moisture from the flue gas allows for a very low energy method of CO2 separation known as physical sorption. Physical sorption is generally not economical if moisture is present, so a low cost moisture removal technology is required to utilize physical adsorption of CO2 in a post-combustion atmosphere. This project has developed a method for low cost moisture removal and is investigating the overall advantages and disadvantages of the entire moisture and carbon removal process.

 

 Figure 1. Micrograph of the amine-based solid sorbent.

 Figure 2. Supported amine sorbent ready for testing.
 

Accomplishments
The amine-based solid sorbent is the most developed of the capture technologies currently being examined by the NETL-RUA. It has been tested at a variety of scales including in a continuous cycle, full circulation capture unit, and it has performed well. It was selected as one of R&D Magazine’s 100 most innovative technologies in 2012. This award is significant because it demonstrates the larger community’s recognition of the ability of the new material to reduce the cost of CO2 separation over traditional aqueous amine-based solvents. The layered-double-hydroxide sorbent demonstrates the NETL-RUA’s exceptional ability to take the results from computational models and convert them into effective capture materials, and the moisture removal technology demonstrates is an example of innovation at the systems level.

NETL received an R&D 100 award for the supported amine sorbents in 2012.

Expected Outcomes
Sorbent technologies will be developed and evaluated under realistic testing conditions at successively larger scales with eventual bench scale testing in the presence of real flue gas at the National Carbon Capture Center. The technologies will then be transferred to industrial partners for further scale up and commercialization.


Benefits
The research will accelerate the development (ranging from the discovery of innovative materials through evaluation in real flue gas) of efficient, cost-effective fossil fuel conversion systems that meet the programmatic goal of capturing 90 percent of the CO2 produced by a pulverized coal power plant at a cost of less than $40/tonne CO2.

Figure 3. Full circulation carbon capture performance testing unit.

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