The Chemistry of Carbon Capture and Storage

Richard Pike, CEO, Royal Soc. of Chemistry

Editor’s note: This is the third installment of a yearlong series designed to stimulate discussion in research and development. The oil and gas industry faces the prospect of progressively increasing CO2 production because of the presence of CO2 in produced natural gas and the fact that petroleum production is becoming heavier. However, the industry is uniquely positioned to sequester CO2, no matter the source. This article features the perspective of an expert outside the oil and gas industry regarding the challenges associated with CO2 capture and storage. Comments on articles in the Technology Tomorrow series are welcome. Please send any questions, comments, or ideas to vik.rao@halliburton.com.

Evidence linking anthropogenic carbon emissions with climate change is accepted by many experts, and the key challenge now is to act to avert disaster. Countries signed on to the Kyoto Protocol and those that have set more stringent domestic targets are now defining energy policies that balance energy efficiency and energy technologies alongside measures for energy security. In the U.K., the government is currently reviewing its energy policy and is examining a range of policy and technological measures that will secure clean and affordable energy for the long term while meeting the U.K. target of reducing carbon emissions 60% by 2050 (based on 1990 levels). It is widely expected that the U.K. will continue to rely upon fossil fuels for electricity, transportation, and heating for the foreseeable future, and, therefore, it is important that carbon-abatement technologies are employed when feasible.

The chemical sciences have played a crucial role in optimizing energy output from fossil fuels through developments in areas such as combustion chemistry and fuel additives. The chemical sciences will be critical in providing future energy technologies such as batteries, fuel cells, solar power, microgeneration, energy-efficient lighting, new nuclear power and nuclear waste management, and carbon capture and storage (CCS).

CCS is not a new technology. In fact, there are a number of examples of its application around the globe (e.g., in ammonia production). It has been predicted that CCS technologies could reduce carbon dioxide (CO2) emissions from power plants (and other energy-intensive processes such as oil refining and steel and cement manufacturing) by up to 85%. However, the technology will reduce the energy efficiency of power plants significantly and increase the cost of energy production, according to the Intergovernmental Panel on Climate Change (Table 1).

CCS technologies will be fully realized only when significant technological and social challenges are overcome by multidisciplinary teams of scientists and engineers and receive critical input from chemical scientists. CCS can essentially be considered as three interconnecting processes:

CO2 from the combustion of fossil (or other) fuel is captured efficiently in a form from which it can be readily released.
CO2 is transported from where it is captured to where it ultimately will be stored.
CO2 is stored permanently at specially selected sites and is continuously monitored for leakage.

Each of these steps provides significant challenges to be addressed. The key challenges for the chemical sciences are discussed here.

Carbon Capture

CO2 capture is a well-known technology and one that has been used to separate CO2 from flue gas, from natural gas, and during ammonia production. However, none of these technologies have been demonstrated at the scale required for a large power plant. Three possible mechanisms are proposed for CO2 capture:

Precombustion—in which CO2 is captured from a mixture of predominantly hydrogen and CO2 formed from the partial oxidation (deliberate incomplete combustion) of a feedstock such as natural gas, coal, or biomass. The hydrogen then can be combusted directly to make electricity and heat (this forms the basis of BP’s Decarbonized Fuels Project based on the U.K. Peterhead Power Plant and the U.K. Continental Shelf Miller Field), mixed with natural gas to reduce combustion carbon emissions, used to power fuel cells, or used as a chemical feedstock.
Post-combustion—in which low-pressure CO2 is captured after combustion from flue gas. This technology will be applied in the recently announced RWE n-power “clean coal” power plant feasibility study at Tilbury in the U.K. This technology could be applied to large power plants and industrial processes; however, retrofitting aging and inefficient plants with CCS technologies may not be economically feasible because it will reduce the thermal efficiency of the plants.
Oxyfuel combustion—in which fossil fuel is burned in the presence of pure oxygen (typically, cryogenically separated from air). This results in a flue gas containing predominantly CO2 and water, which are readily separable. To progress this technology from the laboratory stage, further research is required on materials to withstand the high combustion temperatures and options for reducing the cost of the pure oxygen feedstock.

Alongside the role for the chemical sciences in combustion chemistry and materials design there is also an important research priority in the design of systems to separate CO2 from other gases. Key technologies include improved solvent scrubbing systems (for post-combustion processes), new regenerable and efficient solid adsorbents, and robust and selective membranes that allow only the desired gas to pass through.

Carbon Storage

Several options exist for CO2 storage, including depleting/depleted oil and gas fields, deep saline aquifers, the deep ocean, unmineable coal seams, and through mineral carbonization. Of these options, the first two are considered most suitable for the U.K. The basic principle entails trapping CO2 in a liquid-like state in pores (gaps) in sedimentary rocks. Worldwide, there are a number of planned and ongoing demonstration projects including:

EOR—in which CO2 is pumped into existing oil fields improving oil yields and total recovery while leaving the CO2 trapped behind. More than 70 projects exist worldwide (more than 50 of which are in Texas).
Saline aquifers—The best known project is Sleipner, which is operated commercially by Statoil, in which CO2 is separated from commercially produced hydrocarbons and injected into an aquifer 1000 m below sea level at 1 million tonnes per year.

There are several key challenges that need to be resolved to fully demonstrate carbon storage, including:

Identifying optimal storage sites.
Understanding corrosion and long-term sealing of wells.
Understanding the behavior, interactions, and physical properties of CO2 under storage conditions.
Maximizing storage potential.
Monitoring storage sites in the long term.
Demonstrating successful projects to build confidence in the technology.

These challenges will be overcome only through the collaborative work of national and international multidisciplinary teams of scientists and engineers. It is important to appreciate that carbon storage poses social as well as technological challenges. It cannot be assumed that storing huge quantities of CO2 in the Earth is publicly acceptable. Therefore, alongside R&D into the technological aspects of CCS there must also be a program of stakeholder engagement and education to ensure that the risks and benefits of CCS are understood fully.

Conversion of CO2 to Chemicals

From a chemical science perspective, CO2 must be seen as potential feedstock for the manufacture of useful chemicals, and, as such, the chemical conversion of significantly large amounts of carbon dioxide to inert or commercially useful material is an option that cannot be ignored. A number of projects are currently under way and include the reaction of CO2 to form useful chemicals, fuels, and polymers and photochemical processes designed to mimic nature’s pathways for converting CO2 into useful chemicals. The Royal Soc. of Chemistry Environment, Sustainability, and Energy Forum will host a technical workshop to explore this opportunity on 27 July.

Conclusion

The Royal Soc. of Chemistry believes that if fossil fuels are to continue to contribute to the energy mix in the future, CO2 must be sequestered permanently. CCS technologies could offer a cost-effective mechanism to achieve this in the medium term and should be considered in national and international energy policies alongside energy efficiency measures and other low-carbon technologies. It is vital that scientists and engineers from a wide range of disciplines collaborate both nationally and internationally to ensure that CCS technologies are developed as soon as possible. In particular, significant international effort should be focused on the development of an oxyfuel-combustion demonstration plant. It is also critically important that we look ahead and ensure that there will be a sufficient number of skilled scientists and engineers available—after all, we need someone to actually build these plants.

Richard Pike is Chief Executive Officer (CEO) of the Royal Soc. of Chemistry, a U.K. professional organization for chemical scientists. He held a number of technical and commercial positions during his 25-year career with BP, including Technical Manager of the Sullom Voe Terminal in Shetland, Scotland; General Manager, Chemicals, BP Far East; President, BP Chemicals, Japan; and Director, Samsung-BP Chemicals, South Korea. After leaving Japan, Pike was Director General of the Inst. of Mechanical Engineers for 5 years and was Executive Vice Chairman, Professional Engineering Publishing. He later moved to become Senior Associate at Gaffney, Cline, and Assocs., advising on corporate strategy within the oil and gas industry, and leading international technical, commercial, and organizational assignments throughout the energy supply chain, from reservoir management to processing facilities, petrochemicals, and power. Pike earned bachelor’s and doctorate degrees in engineering from Cambridge U. He is a chartered scientist and chartered engineer and is a fellow of five major professional bodies.