Carbon Capture and Utilization
Using CO2 to manufacture fuel, chemicals, and materials
Centre for Low Carbon Futures | July 25, 2011
Capture and storage of CO2 is defined by most international bodies, including the UK Department of Energy and Climate Change (DECC), as referring to capture of CO2 from point sources combined with geological storage of CO2. While carbon capture and geological storage (CCS) can make a significant contribution to carbon dioxide abatement in the United Kingdom and abroad, there is also the possibility of CO2 utilisation in building material production, for fuels or in the chemical industry. This paper explains that, in parallel to CCS, capture and utilisation of CO2 (CCU) can contribute to a green economy and suggests that possibilities for funding technology development be considered.
The United Kingdom has laid down deep greenhouse gas emission reductions in legislation. Next to climate change mitigation, however, economic stability, sustainability of the UK industry to maintain jobs and energy security are important political themes. CCS in some sectors provides cost-effective emission reductions, but has significant shortcomings: it has high investment costs, the potential storage capacity has uncertainties, public resistance to CCS has been increasing, and it costs energy. Moreover, if the UK is to maintain and improve on its current standard of living, access to a secure supply of chemical feedstocks and fuels is essential. Although only a partial solution to the CO2 problem, under some conditions using CO2 for CCU rather than storing it underground can add value as well as offsetting some of the CCS costs. The economic potential of CCU is limited by scale, but some options can be attractive enough to pursue.
Mainland Europe, and in particular Germany, the US and Australia are well advanced in research and development of CCU technologies. Substantial investment has been made in those countries by extending CCS technology to incorporate utilisation in addition to storage. New data are emerging daily and so this policy document reflects a snapshot of a point in time. At the time of going to press the Danish government has stated that it will aim to go to a zerofossil fuel energy economy by 2050. CCU could play a significant role in achieving that aim.
In this policy document, we highlight progress in CCU globally and discuss the opportunities for implementation in the UK in three primary areas: chemical conversion, mineral carbonation and biofuels from algae.
Chemical conversion to chemical feedstocks and fuelsRather than treating CO2 as waste, it can be regarded as a chemical feedstock for the synthesis of other chemicals that do not rely on a petrochemical source. The energy required for this would be best facilitated by renewable energy sources, such as wind or solar energy. New catalysts are also necessary. This process can build on current post-combustion CCS technologies to give value-added products that can in theory offset the costs of plant investment or even make the process profitable. Currently, pilot scale technologies only take a slipstream from the main flue gas supply but have the potential and economic viability to be scaled-up. Continuous flow reactor technology and the development of new active and selective catalysts will need to be developed if this CCU option is to play a role at a commercial scale.
Accelerated mineralisation through carbonisation of rocks
Mineral carbonation involves reaction of minerals (mostly calcium or magnesium silicates) with CO2 into inert carbonates. These carbonates can then be used for example as construction materials. Since the energy state of magnesium and calcium carbonates is lower than CO2, theoretically, the process not only requires no energy inputs, but could generate heat. The current bottleneck, however, for a viable mineral carbonation process on an industrial scale is the reaction rate of carbonation. To enhance reaction rates, heat, pressure, chemical processing and mechanical treatment (grinding) of the mineral could be applied, but these treatments are expensive (!60-100/t CO2 stored), cost energy and lead to environmental impacts. The potential, globally and in the UK, is considered very large, but the technology is in the R&D phase.
Biorenewable fuels and materials from algae
Microalgae have a high biomass productivity compared to terrestrial crops and can be cultivated on non-arable land. Many species can grow in salty water. These characteristics could enable sustainable manufacture of products such as biooils, chemicals, fertilizers and fuels, replacing fossil fuel-based products. Using flue gases as nutrient supply and CO2 source, the cultivation of microalgae in open ponds or photobioreactors could directly capture and utilise CO2. Per tonne of algae biomass ca. 0.5 tonne carbon (from 1.8 tonnes of absorbed CO2) can be fixed and converted. Microalgae technology is in the R&D phase, and not yet ready for commercial implementation. To achieve cost and energy requirement reductions, leading to viable large-scale algal production, significant RD&D investments are needed.
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