Carbon Dioxide (CO₂) Capture, Conversion and Utilization-

Economical Sequestration of Carbon Dioxide from Power Plants

The project team is developing a highly selective gas separation membrane to capture carbon dioxide from the flue gas of a power plant. Polymeric based membranes for capturing carbon dioxide at room temperature or in a high temperature environment are being pursued. The team is also working on a new approach for the efficient conversion of CO₂ into fuel (formic acid & methanol).

Goals of the research include:

1) Establish scientific basis for dry gas CO₂ separation, adsorption, storage and conversion into fuel.

2) Establish proof of concept: efficient CO₂ capture from flue gas and conversion for use in a hydrogen fuel cell in a near zero-energy loss power cycle.

The alternatives for CO₂ sequestration such as geologic sequestration, conversion into other materials or deep ocean storage pose a safety hazard or are not economically sustainable. The background behind CO₂ sequestration supports the research path that we are pursuing.

The greenhouse effect is the trapping of solar energy by certain gases of which the most important include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and chlorofluorocarbons (CFCs). Unprecedented and increasing emissions of CO₂ have led to substantive climatic changes which are now supported by measurable data. These include the rise in the global mean air temperature over land and sea, satellite observations of microwave emissions from the atmosphere since 1979, records of the width and density of tree rings, changes in the extent of alpine glaciers, sea ice, seasonal snow cover, length of the growing season and increasing oceanic pH concentration levels [1]. The current atmospheric CO₂ concentration level of 364 ppm marks a 30% increase from the pre-industrial level of 280 ppm, which cyclically fluctuated by 3.5%. Figure 1 & 2 demonstrates the correlation between CO₂ concentration level and the average temperature change. The evidence was further corroborated when the Intergovernmental Panel on Climate Change declared in 1996 that, “the balance of the evidence suggests a discernable human influence on climate change” [1,5]. As seen upon a closer inspection of figure 2, average atmospheric temperatures underwent fairly cyclic swings in the past, but substantial, acyclical increases in atmospheric temperature began after the industrial age and have risen even more sharply over the last two decades.

Recognizing the potential impact of global warming on life on the planet, 141 nations have come together to form a pact to mitigate CO₂ and other greenhouse gas emissions. The pact, called the Kyoto Treaty, went into effect on Feb. 16, 2005 and calls for a 2% reduction in atmospheric concentrations of greenhouse gasses below 1990 levels, by 2012 [10]. In order to meet this goal, treaty signatories will rely on the development of carbon sinks, new clean energy technologies and advanced technologies to curtail greenhouse gas emissions, and CO₂ in particular, since it has the highest concentration in the atmosphere. Domestically, another green house gas mitigation approach has been adopted under the auspices, U.S. Global Climate Change Initiative which calls for a voluntary reduction emissions intensity (ratio of CO₂ emissions to GDP) by 18% before 2012.

Despite the great body of research that has been pursued to control global warming through the sequestration of CO₂ from power plants (the largest single source emitters of CO₂), major shortcomings, namely environmental and safety concerns, inefficient capture rates and high costs still exist [2,3,5,7]. Though geologic sequestration is most popular for its attractiveness as a long-term solution, it poses grave human health and environmental threats [4]. Any geologic shift could trigger the release of the CO₂, which asphyxiates any life-form that relies on oxygen. This tragic reality was seen when over 1,700 people and thousands of animals lost their lives in Cameroon, West Africa in 1986 when the underground volcano beneath Lake Nyos unexpectedly released trapped CO₂ [9]. Most other alternatives for CO₂ sequestration are prohibitively expensive. Deep ocean sequestration, in the form of hydrates, costs approximately $510/ton CO₂, conversion of CO₂ by biological systems and conversion to mineral carbonates vary from $80 to $100/ton CO₂ [4].

None of the proposed technologies or research paths consider CO₂ as a useful fuel source capable of lowering the energy requirement of capture. It is well established that CO₂ can be converted into carbon monoxide (CO) with a 95% yield by heating at 800^oC or through a low-cost catalytic process at 400^oC. Several pathways exist for economically converting the CO to useful fuel: 1) A nickel catalyst can be used to convert the CO to methane (CH₄) at 200-300^oC in normal pressure; 2) A zinc oxide catalyst activated with copper and aluminum oxide can be used for conversion to methanol (CH₃OH) between 200-400^oC at 200 atm pressure; or 3) CO can be reacted catalytically with water to form hydrogen plus more CO₂. Given the nominal waste heat temperature of 200-400^oC available at the typical power plant, the conversion of CO₂ could be done with no additional energy requirement. The energy produced from the fuel cell using any one of these three fuels could then be used to supply additional electricity to the power plant, thereby creating a near zero-loss power cycle. Refer to Figure 3 for a diagram of the project goal.

The key concerns that highlight the technological advantages of the UIUC CO₂ sequestration project:

• Safety – the transportation and storage of CO₂ is probably the most CRUCIAL issue regarding the acceptance and use of sequestration technology. There are inherent safety concerns with geologic and deep ocean storage. Our project avoids the hazard of transporting and storing CO₂ long-term by immediate conversion of the CO₂ into fuel.
• Liability – an important concern to power plants. In mitigating CO₂, power plants want to avoid collateral damage that could arise from mechanical or technical failures. Hence, the simpler the CO₂ capture device, process or scheme, the more comfortable power plants will be. Our project is working to develop a two-stage membrane separation system to maximize CO₂ capture without extraneous steps or processes.
• Cost-effectiveness – power plants want to get as much bang for their buck as possible while still complying with governmental regulations. However, traditional capture technologies coupled with the storage options are not only expensive, but also reduce the power efficiency of the plants. Our project aims to lower the capture costs by developing low-cost membranes capable of regeneration and recycling the waste heat from the power plant for the CO₂ conversion process into fuel for producing electricity with a hydrogen fuel cell.

Important background information which explains the drive behind this project is explained here.

The underlying goal behind the UIUC CO₂ Sequestration & Utilization Project is to capture CO₂ in an efficient manner from the effluent of a power plant and convert it to a useful fuel source using the power plant's own waste heat. Previous work in Dr. Economy's research group has demonstrated the synthesis of polymeric membranes with high selectivity for acidic gasses [11]. Recently, a low cost technique incorporating the polyethyleneimine (PEIM) polymer in a network of primary, secondary and tertiary amines coated on a glass substrate with crosslinked epoxy has demonstrated far superior selectivity and storage capacity for CO₂. The new membranes are highly porous, mechanically strong, thermally stable at high temperatures and regenerable up to 4 times using temperature swing absorption. Refer to figure 4 for an SEM, FTIR scan confirming the PEI/epoxy structure and the regeneration profile of the membranes. The key properties that we are targeting include high selectivity, high reactivity, high adsorption capacity, low cost, good mechanical strength, stable adsorption capacity after cycles.

Figure 4: SEM, FTIR & Regeneration

The key areas of focus for the membranes include:

• Improving CO₂ adsorption selectivity and storage capacity
• Determining the adsorption / desorption kinetics and regeneration properties using pressure swing absorption
• Evaluating the effect of competing gasses and water vapor.

Efficient conversion of carbon dioxide into useful materials continues to be a lingering energetic challenge. Researchers have attempted to convert carbon dioxide using a number of techniques which include but are not limited to:

1. Thermally induced conversion to mineral carbonates

2. Conversion to O₂ using algae ponds

3. Catalytic conversion to carbon monoxide (CO), methanol (CH₃OH) and hydrogen (H₂) using the following pathways:

Ø CO₂ + C = CO * (800^oC for 94% Conversion – FeC catalyst to reduce temperature)

Ø CO₂ + CH₄ = 2CO + 2H₂0 (300-400^oC at norm press. – Fe catalyst)

Ø CO + H₂0 = H₂ + CO₂

Ø 2CO + 3H₂ = CH₄ + H₂O * (200-300^oC at norm press. – Ni or Co catalyst)

Ø CO + 2H₂ = CH₃OH * (200-400^oC at 200-300atm – ZnO activated with Cu and Al₂O₃)

Our unique approach employs microelectrochemical cells, which utilize the waste heat of the power plant to reduce the energy of conversion. The captured carbon dioxide from the waste stream is first converted to formic acid which could be further converted to methanol for utilization in a fuel cell or storage and retail in the commercial markets.

Electrochemical conversion of CO₂ to formic acid (HCOOH)

Electrochemical conversion of CO₂ to methanol (CH₃OH)

Figure 5: Electrochemical Cell for carbon dioxide conversion.

Key opportunities envisioned from the project include:

• Cost-effective mitigation option for limiting greenhouse gas emissions and ultimately stabilizing the greenhouse gas concentrations in the atmosphere.

• Long-term greenhouse gas mitigation emissions options that allows for continued large-scale use of the abundant fossil energy resources.
• Potential to control sulfur dioxide (SO₂) and nitrous oxide (NO_x)

References

1. D.J Wuebbles, Fuel Process Technology, 71:99-119 (2001)
2. Z. Yong, Separation and Purification Technology, 26:195-205 (2001)
3. X. Xu, Microporous and Mesoporous Materials. 62:29-45 (2003)
4. P. Freund, Energy Conversion Management, 38 Suppl.:S259-264 (1997)
5. H. Herzog, A Research Needs Assessment for the Capture, Utilization and Disposal of Carbon Dioxide from Fossil Fuel-Fired Power Plants, DOE/ER-30194, US Department of Energy, Washington, DC (1993).
6. Inventory of Electrical Utility Power Plants in the US 2000 Energy Information Administration, DOE/EIA-0095, US Department of Energy, Washington, DC (2000).
7. A. Corti, Journal of Energy, 3:11 (2004)
8. “CO₂ Capture Project.” http://www.CO2CaptureProject.com
9. Degasssing Lake Nyos, Earth Science News. February (2002)
10. Kyoto Emissions Pact Kicks Off http://www.swissinfo.org. February 16, 2005.
11. A.G. Andreopoulos and J. Economy, Polymers for Advanced Technologies, 2:87-91 (1991).

Gordon Nangmenyi