Recycling CO2

10th March 2014


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Richard Failey

Julian Jackson discovers alternatives to capturing and storing carbon emissions

There is an obvious problem with human-caused emissions of carbon dioxide in that the chemical compound is a major contributor to the heating of the Earth’s atmosphere. That said, this colourless, odourless gas is also quite useful.

For years it has been suggested that CO2 and other pollutants should be “scrubbed” from power station chimneys and pumped into depleted oil wells, such as those in the North Sea. But there are problems with the concept of carbon capture and storage (CCS), notably that it is expensive and energy intensive – it takes energy to power the CCS process, therefore you need to generate more energy to keep it going, which results in more emissions. There is also the risk that the CO2 might leak out of the oil wells.

Although a lot of money and effort has been put into CCS research it looks unlikely to be a major part of any solution for greenhouse-gas (GHG) emissions at present. According to Peter Styring, professor of chemical engineering and chemistry at the University of Sheffield: “The rate at which CCS projects are currently deployed and the emissions reductions they achieve may be insufficient to reach the 80% reduction in global carbon emissions required by 2050.”

However, quietly in the background, scientists and engineers have been working on a different approach: capture the CO2 and use it as a feedstock. Carbon dioxide is an extremely useful chemical that is vital for the survival of plants, for example. Various scientific projects are developing processes that use CO2 to create durable objects, which include building materials, polyurethane foam and other plastics, as well as synthetic fuels, which can substitute for petrol or diesel.

The sky’s the landfill

The simplest way to think of this use of carbon dioxide is to envisage it as a form of recycling. Instead of recycling solid objects into something new in place of putting them in landfill, such projects recycle carbon dioxide gas, using it productively, instead of sending it into the great landfill in the sky. Putting carbon into building blocks, for example, fixes the gas so it won’t go into the atmosphere for a long time, if ever, and renders the product as a valuable building material instead of expensive waste.

One reason that capturing CO2 and using it productively has not had more exposure is a lack of agreement on what to call it. Terms include: carbon dioxide utilisation (CDU); carbon capture and utilisation (CCU); and carbon capture, utilisation and storage (CCUS – the term favoured by the US department of energy). Whatever the name, using CO2 in this way is opening a new industrial frontier where the UK and some other countries including Germany are creating novel, financially viable products.

Norwegian risk-management business DNV calculates that the carbon utilisation technologies have, between them, the potential to reduce CO2 emissions by at least 3.7 gigatonnes a year (Gt/y) – approximately 10% of annual global carbon emissions – either directly or by reducing use of fossil fuels. It also predicts that much greater reductions are possible if the technologies are adopted more widely.

Using CO2 can help to reduce the UK’s dependence on fossil fuels by creating valuable chemicals, fuels and other products, according to the 2011 report Carbon capture and utilisation in the green economy, written by Styring and Daan Jensen at ECN, the energy research centre in the Netherlands.

Researchers at Newcastle University calculated that a CCU plant creating mineral carbonates had a payback time of less than two years and could generate profits in excess of £1.4 billion over 15 years if the carbonates continued to be sold at current market prices. So there are potentially significant financial rewards for the economies that adopt such technologies, in addition to emissions reductions.

Fuelling change?

Several British startups are pushing forward CDU technologies and have created innovative products. One is Air Fuel Synthesis (AFS), which has developed a method of turning carbon dioxide and hydrogen in water into a “sustainable” fuel.

The Darlington-based company uses renewable energy to do what nature does with photosynthesis and geological time: make carbon dioxide into oil. The firm uses electricity to convert carbon dioxide and water into synthetic hydrocarbon liquids from which sustainable fuels or other oil-based products can be made. The fuels it has created include petrol, diesel and aviation kerosene.

The creation of alternative fuels obviously does not remove carbon dioxide from the air permanently, but it is recycling it, so the product is deemed carbon-neutral. “Our main raw material is electricity,” explains AFS chief executive Peter Harrison. “When we make petrol from ethanol the process generates heat, so we are working on utilising that heat to power earlier stages of the process.”

AFS is focused on making their process a fully functional commercial product without the need for subsidy. Harrison, however, is cautious about the amount of hydrogen that would be needed for industrial scale production, emphasising that it is a new sector and that the supply chain is incomplete.

Another example of CDU is the “carbon buster” building block from Lignacite. The block, made from 50% recycled material, includes aggregate created by new company Carbon8. The firm, which is based in Chatham, Kent, next to a Lignacite plant, uses carbon dioxide to manufacture pellets of aggregate from waste by combining CO2 with ashes from industrial incinerators and water. The so-called “accelerated carbonation” technology converts the CO2 gas into calcium carbonate, a solid material. Carbon8 takes the pure CO2 output from a sugar beet factory and captures it in the new construction material, eliminating waste from landfill and removing carbon that would normally go into the atmosphere.

This approach creates a triple revenue stream: the sugar beet factory saves on landfill tax; Carbon8 receives a gate fee for handling hazardous wastes; and the blocks made by Lignacite are sold to builders, replacing GHG-emitting ones.

“Carbon8 aggregates have taken a technology developed in a university laboratory through to commercial reality,” says the firm’s managing director, Dr Paula Carey. “We use accelerated carbonation to produce the world’s only carbon-negative aggregate, which in turn is used to manufacture the world’s first carbon-negative concrete block.”

A third example of CDU technology in the UK is the mineral carbonation process developed by Cambridge Carbon Capture (CCC). The process bonds carbon dioxide molecules to mineral silicates to produce zero-carbon lime and magnesia, and sequesters CO2 safely.

“Our process reacts directly with power station flue gases and converts them into geologically stable solids,” explains CCC founder and chief technology officer Michael Priestnall. The company claims that its electrochemical process releases 15% more energy than it uses, making it potentially a huge leap forward.

CCC uses a magnesium silicate called olivine, which is present in the Earth’s crust in huge quantities, to capture the carbon. CCC plans to extract residual metals from the waste to provide another income stream. It is also exploring using the process to remove emissions from ships in partnership with exploration company Polarcus, which carries out marine seismic surveys around the world and is aiming to develop a fleet of the greenest vessels on the planet.

Meanwhile, German chemical giant Bayer is also developing ways to recycle carbon dioxide. Dr Tony Van Osselaer, head of industrial operations at Bayer Material Science, says: “Carbon dioxide is too precious to simply let it escape into the atmosphere. We aim to turn this waste gas into a useful and profitable raw material. This makes us a front-runner for an entirely different approach to the production of high-quality foams.”

Bayer has already produced a polyurethane foam that incorporates CO2 for use in mattresses. The foam performs as well in tests as fossil-fuel derived materials, and could have many other applications, including in cars, furniture and as insulation.

In 2010, Bayer launched CO2RRECT, a programme aimed at using surplus renewable energy to produce hydrogen from water by electrolysis. The gas is then combined with CO2 and used as a feedstock in chemical production. The German federal ministry of education and research is backing the study with €118 million of funding. It is an exciting project in many ways – for example, by using excess renewable energy that cannot be stored when more is produced than needed – but Bayer admits that it is “blue sky” research at the moment and concrete results are not expected before 2020.

Another interesting CDU application currently at the laboratory stage is the production of microalgae for biofuels. Using flue gases from power plants as a nutrient supply and CO2 source, the cultivation of microalgae in open ponds or photobioreactors could directly capture and use carbon dioxide. Australian firm Algae Tec and the country’s largest electricity generator Macquarie Generation agreed a deal last year to construct an “algae carbon capture and biofuels” production facility next to a coal-fired power station near Sydney. The station will feed waste CO2 into an enclosed algae growth system.

Early days

CDU is a largely nascent technology that could be part of the solution to reducing carbon emissions. There are many difficulties on the road from the laboratory to industrial production, but saving 10% of global GHG emissions is a goal worth aiming for, and there are the additional benefits of creating a new, high-tech industry.

“It’s like solar power,” says Priestnall at CCC. “[CDU] is a distributed, modular technology that you can deploy, make profit from and go through the learning curve at small scale, and then expand the operation while bringing down costs.”

The success of carbon dioxide recycling will largely depend on governments following Germany’s example and providing funds for research and development.

“The UK government needs to invest in research and development for carbon capture and utilisation, and investors need to be made aware of the potential benefits of the technology so that barriers can be brought down,” argues Styring.

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