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 and fuels
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 www.co2net.com.
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 available:
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
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
1.1.5 Direct Capture of CO2 from the
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
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
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
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
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 aquifers.
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 abatement method.
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 methodologies.
2.4 The chemistry of CO2/rock/reservoir
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
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
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.