Memorandum from the Royal Society of Chemistry
The RSC is the largest organisation in Europe
for advancing the chemical sciences.
Supported by a network of 45,000 members worldwide
and an internationally acclaimed publishing business, our activities
span education and training, conferences and science policy, and
the promotion of the chemical sciences to the public.
This document represents the views of the RSC
and has been put together by our Environment, Sustainability and
Energy Forum in consultation with the Energy Policy working group.
The RSC's Royal Charter obliges it to serve the public interest
by acting in an independent advisory capacity, and we would therefore
be very happy for this submission to be put into the public domain.
The document has been written from the perspective
of the Royal Society of Chemistry consequently our comments relate
to only parts of the consultation document. However, the chemical
sciences and chemical scientists will play an essential role in
driving forward technological breakthroughs in the capture, storage
and conversion of carbon dioxide.
The evidence submitted was in the most part
published in an RSC report entitled "Chemical Science
Priorities for Sustainable Energy Solutions" [www.rsc.org/Gateway/Subject/EnvEnergy/].
The response can essentially be divided into
four key sections:
1. State of the art in trapping and storing
2. Research and development priorities for
trapping and storing CO2
3. Chemical conversion of CO2 in chemicals
4. Key funding needs
In CO2 capture and storage, capture technologies
constitute a critical component of zero emission power generation
schemes. The major thrust of research is in the optimisation of
solvent absorption systems, development of new separation systems
(membranes and adsorption systems), a move to achieving more concentrated
gas streams by way of, for example, pre-combustion decarbonisation
or flue gas recirculation with oxygen addition ("oxyfuel")
and research into the conversion of CO2 into inert or commercially
viable materials. CO2 storage in North Sea oil and gas fields
must be addressed now, as this sector moves into the decline phase,
to avail of this storage mechanism. Areas which will warrant further
attention include collaborative research by chemists, geologists
and engineers into: corrosion of well completions and long-term
sealing; geochemical and geomechanical impact on the reservoir
cap rock and overlying seals (long-term integrity); maximising
storage potential and surveillance and monitoring.
1. STATE OF
This section summarises the state of the art
and discusses those gaps in technology that should be addressed
to encourage greater deployment of CO2 capture and storage (CCS).
Much of the following is based on discussions and documented outputs
of the CO2NET thematic network on carbon capture and storage sponsored
by the EU Framework Programme and published in more detail at
1.1 CO2 Capture
CO2 capture is a well-known technology in different
sectors to separate CO2 from flue gas, natural gas and hydrogen
(in syngas). Captured CO2 is vented, used for enhanced oil recovery
or purified to produce high purity CO2 for niche market applications
(eg the food and beverage industry). Three process routes are
1.1.1 Pre-combustion capture
In pre-combustion capture, CO2 is captured from
a gas mixture which is produced by partial oxidation of natural
gas, coal oil residuals or biomass. This gas mixture contains
predominantly H2 gas and CO2 (15-40%) at a high pressure (15-40
bar). Separating CO2 from H2 is the main task in pre-combustion
capture. Physical absorption is the leading option (when partial
pressure is sufficiently high), but membranes and cryogenics might
become interesting alternatives in the future.
1.1.2 Post-combustion capture
In post-combustion capture, CO2 is captured
at low pressure and low CO2 content from flue gas by separation
from N2 and O2. This technology can be applied to large power
plants such as pulverized coal plants and natural gas turbine
fired combined cycles, cement kilns and industrial boilers and
furnaces. The leading technology in post-combustion capture is
chemical absorption using monoethanolamine. Alternative options
to capture CO2 from flue gasses are adsorption, cryogenics and
membranes, but these options are still relatively expensive.
Pre-combustion capture is considered to be a
key technology for the production of hydrogen from fossil fuels,
especially in integrated coal gasification combined cycle plants,
where CO2 capture could be cheaper and more efficient compared
to capture at pulverized coal plants.
1.1.3 Oxyfuel combustion
A concentrated stream of carbon dioxide can
be produced by the exclusion of nitrogen before or during the
combustion/conversion process. The difference with previous process
routes is that here the separation is targeted to produce oxygen
from air (ie separation of oxygen from mainly nitrogen), thereby
avoiding the need for CO2 separation. Cryogenic separation is
the conventional technology to produce pure oxygen, separating
air into liquid oxygen and gaseous nitrogen, argon (which can
be sold) and some trace components. Fossil fuels are then burned
in an atmosphere of pure or enriched oxygen. A part of the flue
gas, which consists mainly of CO2 and H2O, is recycled to the
combustion chamber to enhance the CO2 content for subsequent removal.
This also helps to control the flame temperature, since current
materials applied in the power industry cannot handle such high
temperatures. Finally, water is condensed from the flue gas that
is not recycled and CO2 is removed by compression. Since the volume
of inert gas in the boiler is lower than conventional systems,
the boiler efficiency is increased.
This technology has already been applied in
some glass, steel and iron industries but has yet to be widely
deployed due to the high costs and the energy requirements of
the oxygen separation technologies.
1.1.4 Biological Capture and Mineralisation
About 90 gigatonnes of carbon are exchanged
between the ocean and the atmosphere each year with a net uptake
by the ocean of 2.2 gigatonnes. The upper warmer ocean layer contains
about 1,030 gigatonnes of carbon whereas the deeper ocean stores
around 38,100 gigatonnes, drawing 1.7 gigatonnes from the surface
layer each year. Acceleration of mineral formation from dissolved
CO2 in a controlled manner would enhance the capacity of the ocean
as a CO2 sink without the potentially damaging ecological impacts
of elevated CO2 concentrations. Wright has suggested that microbial
consortia mediate precipitation of a range of carbonates including
dolomite and magnetite in ephemeral, highly saline lakes that
occur in arid parts of the world. The way in which iron reducing
bacteria convert atmospheric carbon dioxide to calcite, aragonite
and siderite in ash collection ponds is being examined by Oak
Ridge under US DOE funding as a means of sequestering CO2. This
has the added advantage of stabilising fly ash into a stable mineral.
Several claims are made for this research including combination
with agricultural and food processing waste treatment to provide
energy for microbial growth.
1.1.5 Direct Capture of CO2 from the Atmosphere
In 2001, Lackner, Grimes and Ziock argued that
it is technically feasible to capture CO2 from natural airflow
at a rate that far exceeds natural photosynthesis. Their idea
is based on the construction of many 300 metre tall, 115 metre
diameter convection towers, where a down draft is created by cold
water pumped to the top of the tower. Air flowing out of the bottom
of the tower would pass 9,500 tonnes of CO2 per day through a
Ca(OH)2 absorbent. The absorbent would then be regenerated to
release a concentrated stream of CO2 for disposal. The authors
estimate that the process would cost $10-15 per tonne of CO2.
The focus of their paper is to suggest a viable and cost effective
alternative to changing the transportation infrastructure to non-carbonaceous
fuels and they conclude that all of the CO2 produced by the consumption
of transportation fossil fuels could be captured for $0.09-0.14
per gallon of gasoline. Additional costs would be incurred to
store or sequester the captured CO2.
1.2 Carbon Storage
An example of CO2 storage is the Sleipner West
natural gas field production operated by Statoil, in the Norwegian
sector of the North Sea. In order to meet market specifications,
the CO2 content in the natural gas has to be reduced from 9% to
2.5%. Rather than emit this CO2 to the atmosphere, as is a normal
practice, Statoil decided to store the CO2 underground. Since
1996, Statoil have been storing approximately 1 megatonne of CO2
per year in a saline aquifer. The saline aquifer is similar to
a sandstone reservoir, that contains oil and/or gas, but contains
saline porewater instead.
Another example is the Weyburn oilfield in Saskatchewan,
Canada. Here, Encana, the field operator, is injecting CO2 to
enhance oil recovery (EOR). CO2 is a good solvent for oil that
allows the oil to move more easily through the reservoir, aided
by a slight increase in the oil volume and improved sweep efficiency
of the CO2. The CO2 for this EOR operation is supplied from flue
gas from the Dakota Gasification Company in North Dakota. At the
end of the EOR operation the CO2 will be left behind in the reservoir.
The oil industry, especially in the onshore oilfields of Texas,
has been using CO2 for EOR for several decades. Hence the technologies
and experience of injecting CO2 underground are already well established.
There are three broad options for CO2 storage:
depleted oil and gas fields; deep saline aquifers; and unmineable
coal seams. The potential for storage in unmineable coal seams
is very small in the UK and will not be considered further in
this document. Depleted oil and gas fields offer the advantages
of having, by definition, a proven trapping mechanism (though
some fields do allow hydrocarbons to migrate out of the main reservoir,
occasionally to the surface). Also, due to the exploration and
production history, much is known about these traps in terms of
their geology, size, storage capacity, sealing caprocks etc In
contrast, saline aquifers have not been studied previously and
although their theoretical storage capacity is very large, geologists
have not had opportunities to establish this absolutely.
2. RESEARCH AND
IN CO2 CAPTURE
Amine scrubbing is currently the most widely
used process for CO2 capture and has been used, for example, in
the Sleipner plant since 1996 to remove CO2 from natural gas.
Considerable technical experience exists with respect to generation
of relatively small amounts of food-grade CO2 and for relatively
low volume industrial purposes such as cooling and fire fighting
equipment. However, the process is costly and inefficient when
used with the dilute streams of CO2 found in the stack gases from
the current generation of fossil fuel power plants. It accounts
for more than 80% of the overall cost of the carbon capture and
storage (CCS) chain. The development of other more cost effective
methods of CO2 capture is one of the key issues relating to CCS
(along with public acceptance of geological storage).
Alternatives to amine absorption currently under
development include polymers such as polyethyleneimine impregnated
on high surface area silicas, activated carbons or fly ashes that
are effective and regenerable adsorbents. The key issues for adsorption
separation are to develop an adsorbent with high CO2 separation
selectivity and adsorption capacity. A significant programme on
adsorption has been established at the University of Nottingham.
Other methods are under examination (eg membrane
or cryogenic separation), but the major thrust of research is
aimed at achieving more concentrated gas streams by way of, for
example, pre-combustion decarbonisation or "oxyfuel"
ie use of a low nitrogen, high carbon dioxide gas stream for combustion.
More specifically, further research is needed
into post-combustion decarbonisation technologies, with a view
to validation of absorption technologies in integrated pilot plants
and development of novel chemical solvents and associated process
technologies with significantly reduced capture costs and energy
consumption. Other separation processes to be investigated include
membranes, adsorption, high temperature solid sorbents, as well
as cryogenic approaches. Similarly, within the field of pre-combustion
decarbonisation there is a need for validation of absorption technologies
in integrated pilot plants as well as the development of novel
reactor concepts for H2/CO2 separation (eg membrane, adsorption
and absorption for the enhanced reforming/gasification process).
Some concepts for generation of multiple products,
including CO2 capture, warrant further study. Validation of de-nitrogenation/oxyfuel
technologies in integrated pilot plants is also essential, as
are novel concepts for oxygen production or oxygen transfer. Further
development of fuel conversion technologies should focus on drastic
improvements in capture processes or avoidance of separation processes.
Capture technologies constitute a critical component
of zero emission power generation schemes. It is necessary to
work on the development and validation of new integrated processes
providing near complete CO2 capture, while at the same time trying
to achieve higher energy efficiencies and/or lower costs. This
could also include incorporation of biomass co-combustion and
partial CO2 capture as well as multi-pollutant removal concepts
addressing, for example, sulphur components, NOX and trace metals.
It is essential that the development of capture
processes is properly integrated into complete CO2 mitigation
chains, providing enhanced uptake through:
integration with improved combustion
and synergistic approaches for CO2
capture and CO2 storage.
2.2 Storage in Oil and Gas Fields
The CO2 storage capacity of old and current
oil and gas fields in Western Europe amounts to approximately
37 billion tonnes. Although this is only a few per cent of the
estimated storage capacity of aquifers, these fields offer a potentially
useful test bed and niche market for larger-scale commercial sequestration.
If the injection of CO2 into such reservoirs can generate a marketable
by-product, through EOR, the net costs of CO2 sequestration could
be reduced and this might encourage oil companies with substantial
prior experience to participate in the programme. Additional information
gained with this type of application will also be relevant for
the more general aquifer storage of CO2. Regulatory issues are
also likely to be simpler and potential sites could become available
earlier than for aquifers.
Most experience of CO2 EOR has been gained onshore
in the US and Canada. Operating offshore in the North Sea is a
more difficult proposition, though much of the on-shore experience
is still relevant. There is, however, an issue of timing. Already
many of the large early discoveries in the North Sea are in the
decline phase, as is the entire British offshore sector, and the
Norwegian and Danish North Sea sectors are predicted to move into
the decline phase within a few years. A concern is that older
oil and gas fields may be decommissioned before CO2 EOR and enhanced
gas recovery (ERG) projects can be implemented.
Many of the major international oil companies,
needing a rate of return of 12%, are moving their interests to
lower risk areas elsewhere in the world and leaving the North
Sea to smaller independent operators. These low cost operators
can operate at the end of the maturity line of a field, by operating
at a rate of return of 8%, but this leaves little tolerance on
such tight margins for new technology in the North Sea. Small
operators cannot afford or risk using new technology, as the major
operators could. The window of opportunity is therefore shortening.
Issues for which further R&D is either necessary
or desirable to optimise storage potential as opposed to the present
norm of minimising CO2 generation include the following:
Geophysical and geotechnical explorations
of potential wells;
Corrosion of well completions and
long term sealing;
Geochemical and geomechanical impacts
on the reservoir cap rock and overlying seals (long-term integrity);
Maximising storage potential;
Surveillance and monitoring; and
2.3 Aquifer Storage
Deep saline aquifers constitute by far the greatest
potential for geological storage of CO2, being capable, in principle,
of storing several hundred years' worth of Europe's power plant-derived
CO2. Suitable aquifers are, however, unevenly distributed throughout
Europe, with the majority of the theoretical storage potential
located in the North Sea, far away from the main power plants
and other major emission points. It should be noted that the UK
has one of the largest capacities in Europe for offshore CO2 storage
in aquifers. Very considerable aquifer potential does still exist
onshore and near-shore, but detailed assessment of the aquifer
potential at any given location is a prerequisite to understanding
the regional, national or local storage capacity. The information
available about saline aquifers is often scant and considerable
effort is required to assess the capacity and suitability of various
Although a number of technical issues dealing
with storage safety, monitoring and longevity are still outstanding,
the public acceptance of geological storage is probably the overriding
issue. To address public acceptance, it is important to carry
out a number of onshore geological storage pilot projects, selected
to represent a geographical spread and a range of geological conditions.
The European Commission's 6th Framework Programme will provide
the first such small scale demonstration. Following these projects,
there will be a need for several other small projects, as well
as a few concerted projects at greater scale, bringing European
policies and the main players together in one or just a few activities.
The rolling out of geological storage demonstrations
across Europe is perceived to constitute the main scientific bottleneck
to the successful deployment of CCS. In other words, it does not
matter how much CO2 can be captured, and at what cost, if geological
storage cannot obtain public acceptance as a safe, long term CO2
With respect to subsurface processes, further
research requirements include laboratory experiments to improve
knowledge of the behaviour and physical properties of CO2 at reservoir
conditions that include increased temperatures, pressures, and
salinities, and account for the presence of other fluids and organics.
These complex conditions can affect the chemistry of CO2/rock/reservoir
fluid interactions and compromise the sealing capacities of overlying
caprocks. In conjunction with the improved knowledge at the small-scale,
it is essential that in-situ field experiments are conducted.
These should aim to elucidate the effects of different geological
settings, geological variance, CO2 migration and long term processes
using and integrating natural analogues and laboratory experiments,
as well as identifying suitable sites for demonstrations. In addition,
research should focus on the potential impacts on both offshore
and onshore ecosystems of spatially restricted but very high concentration
CO2 leaks, thereby helping to define site performance and safety
criteria. Methodologies and protocols should be developed for
long term performance assessment of storage sites. These will
integrate much of the disparate research needs and knowledge described
above into long-term predictions of probable risks and potential
impacts of CO2 leaks.
In the field of material and equipment development,
the utilisation of aquifers requires further development of corrosion
resistant material (eg pipes, pumps, cements) and cheap, long-life
measuring sensors for down-hole (eg leak detection, pressure and
temperature gauges) as well as surface uses (eg gas sniffers,
seismology and compaction sensors). There is also a need for the
further development of new cheap, high resolution CO2 plume monitoring
2.4 The chemistry of CO2/rock/reservoir fluid
There is a growing literature regarding the
long-term interactions between CO2 and the minerals present in
the receiving reservoir both as solids and in solution. These
interactions will play a major role in determining the eventual
form of the stored CO2 and hence the risks associated with leakage
and escape to the atmosphere. The long-term geochemical interactions
in both the reservoir and caprock, which prevents the fluid (CO2,
hydrocarbons or water) moving upwards, are very important in CCS.
Predicating these reactions over geological timescales with confidence
can be challenging since increased temperatures, pressures, and
salinities, must be accounted for. If the CO2 could be more permanently
locked up through precipitation as a carbonate within the reservoir
this would increase the security of storage. In addition saline
porewaters saturated with CO2 are denser than the surrounding
porewaters so they would tend to "sink" rather than
the "pure" supercritical CO2 fluid which has much lower
density and hence naturally buoyant and wants to rise up, increasing
the risk of leakage. One of the key issues for storage is the
stability of cements over long (geological) periods used to seal
the boreholes. Low pH porewaters resulting from injected CO2 can
readily dissolve cements, which therefore necessitate an investigation
into the pH evolution of porewaters, since pH essentially controls
the precipitation of carbonates as well.
It is important to note that the majority of
the technologies discussed so far involve trapping and storage
of CO2, however, from a chemical science perspective CO2 can also
be seen as potential feedstock for the manufacture of useful chemicals
and as such chemical conversion of significantly large amounts
of carbon dioxide to inert or commercially useful material is
an option that cannot be ignored. This is a key challenge that
the chemical sciences will rise to meet if a framework of continued
and dedicated funding is in place to reflect the significant research
effort that is required. In this section a number of ongoing research
projects are detailed.
A substantial amount of research has been carried
out to find an economic route to the preparation of carbon monoxide
(CO), methane and methanol by chemically reducing carbon dioxide.
For example, CO2 will react with hydrogen over a nickel catalyst
in the Sabatier reaction to generate methane, and the reverse
water-gas shift reaction can be used to convert CO2 to carbon
monoxide as a feedstock for higher hydrocarbon production. These
two reactions have both been explored for space exploration as
a means of recycling CO2. Syn gas may also be generated by reforming
natural gas with CO2 as well as with steam.
Less conventional routes have also been proposed
for the reduction of CO2. In 2002 Nakamichi Yamasaki of the Tokushima
Industrial Technology Center in Japan claimed that carbon dioxide
and hydrochloric acid in the presence of iron powder at 300C and
100 atmospheres will yield substantial amounts of methane, ethane,
propane and butane. However, these promising observations don't
seem to have led to anything yet.
The search for catalysts that will unlock a
commercial route to the activation of CO2 will no doubt continue
and is founded on a growing body of published literature.
More recently there has been growing interest
in understanding the photochemical processes by which plants algae
and certain bacteria are able to utilise light to drive charge
separation processes within the cell that eventually lead to the
reduction of carbon dioxide and the synthesis of carbohydrates.
Over the last 15 years, much research effort
has been devoted to finding ways of mimicking the mechanism of
photosynthesis for conversion of CO2. One approach has been to
construct artificial photocatalytic systems, which are able to
use light energy for the reduction of CO2. However, there is a
need for fundamental research to overcome the key problems that
still remain to be solved in this very complex area of photocatalytic
CO2 activation, particularly understanding how to increase the
present unsatisfactory efficiency both with respect to the value
of the reduction products of CO2 (usually C1 products) and also
to the oxidation products of the sacrificial electron donor. The
University of Nottingham is currently looking into developing
catalyst materials that can mediate the photochemical reduction
of CO2 with water using near UV/visible light to produce fuels.
This holds promise to develop systems that can mediate CO2 photoreduction
with sunlight. Substantial progress has already been made in this
field with the demonstration of photo-reduction of CO2 to methanol
using a variety of transition metal complexes.
An alternative electrochemical route is being
pursued by CSIRO who are investigating the use of a 200 nm porous
Au electrode, supported on a polymer membrane, for electrochemically
reducing CO2 to carbon monoxide (CO) at near-ambient pressures.
Finally, another potential chemical approach
to sequestration is the transformation of CO2 into inert, long-lived
materials, such as magnesium carbonate. This process is known
as mineral carbonation and mimics the natural weathering of silicate
rocks. Although the reaction is thermodynamically favoured, it
is extremely slow and the challenge is to increase the reaction
in order to be able to design an economically viable process.
At this stage it is clear that the transformation
of CO2 into useful chemicals can be achieved either by chemical
processes or by moving towards artificial photosynthesis. There
are considerable scientific and economic challenges to be overcome
in this area of research before such processes are feasible on
a large-scale, but it is important to note that this research
offers a genuine use for CO2 rather than a "storage option".
With the correct funding and political framework in place this
research could lead to a future scenario where significant quantities
of fuels and chemicals are synthesised from CO2.
5. KEY FUNDING
Government needs to put into place
a framework to provide incentives (most likely fiscal incentives
such as R&D tax credits) to promote R&D associated with
sustainable energy technologies.
Significant long-term funding is
required for fundamental chemistry and application specific chemistry
to stimulate and encourage energy related research; innovative,
ground-breaking energy related R&D will rely on a strong chemical
science base (eg materials chemistry, catalysis and combustion
chemistry) in the UK.
Significant and continued funding
for the chemical science research and demonstration of technologies
for the chemical conversion of CO2 into inert or useful chemicals
is required if the opportunities for utilising trapped CO2 is
to be realised.
Incentives are required to recruit
and retain outstanding, internationally competitive scientists
to work on energy related research in the UK. Incentives to attract
international researchers to work in these areas are required
to ensure that R&D happens now.
Funding is needed for pilot studies
of the above CO2 sequestration methods. These pilot studies are
required in order to assure public acceptance and praise once
the required fundamental research is complete.