XPRIZE

To address climate change, the 2016 Paris Agreement saw 194 states and the European Union agree to limit the rise in global temperature to below two degrees Celsius over this century. With carbon dioxide levels still climbing, as Nasa's monitoring shows, solving climate change needs more than just reducing emissions – we're going to have to take back the CO2 and technology can help.

Eight months before the Paris Agreement was signed, the moonshot XPRIZE team that helped inspire the first commercial spaceflight, started its $20 million NRG COSIA Carbon XPRIZE – aimed at literally pulling CO2 out of the air and converting it in to something useful.


To win a place in the finals, the teams had to demonstrate their technologies at pilot scale – in a location of their choosing. To win the big prize, the finalists have been divided into two tracks – five teams have been given a coal-fired power plant in Gillette, Wyoming and five teams are working at a natural gas-fired power plant in Alberta, Canada. Starting in June, they will need to demonstrate the ability to trap at least two tonnes of CO2 per day – although the winning team in each track will be the one that converts the most CO2. All of the shortlisted teams get to share $5 million – each winner earns an additional $7.5 million.

So what can we learn about their unusual approaches to fighting climate change?

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C4X

XPRIZE

“China produces about one quarter of the world’s CO2, which is around 90 million metric tonnes per year,” according to Wayne Song, who’s leading the team from Suzhou, China. “Our solution is really aimed at cleaning up China first.”



C4X’s two step process takes place in two separate reactors. In the first, purified flue gas with a high CO2 content is heated with ethylene oxide and a catalyst – initially cobalt but now a cheaper aluminium or copper oxide - to create ethylene carbonate… a process very similar to the Shell OMEGA process. Currently, C4X’s reactors can fix around 70kg of CO2 every four hours, says Song.


The ethylene carbonate is then pumped into the second chamber with a stream of pure hydrogen where fresh catalytic surfaces and more heat convert it into ethylene glycol and methanol – two fuels currently in high demand in China. Song hopes to replace fossil fuels with these biofuels.

“The process is very energy intensive,” Song admits. “Right now, to save energy we are only converting 50 per cent of the carbonate to the glycol but we’re hoping to use this stage in the prize to increase our energy efficiency.”

Breathe

“India consumes about two million tons of methanol, blending it with gasoline to reduce fossil fuel use - and only 20 per cent of that is produced locally,” explains Sebastian Chirambatte Peter, who leads the team from Bangalore, India. India’s $1.5 billion methanol market, the team hopes, will make their CO2 to methanol conversion process into big business.

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Breathe’s three-metre-high reactors pass purified CO2 from flue gas and pure hydrogen across a range of copper, zine, aluminium and iron-based catalysts which speed up a variant of the so-called Fischer–Tropsch process, as used in the international space station to combine waste hydrogen and CO2 to produce methane and water. The last couple of years have seen breakthroughs in catalytic hydrogenation of CO2 to methanol. A single reactor in Bangalore is currently converting 300kg of CO2 to methanol daily.


The downside? The reaction requires high temperatures – around 250° Celsius – and high pressures. “At the moment we’re using electricity to power the reaction,” says Peter. “Our challenge is to use the excess heat from the power plant and the reaction itself.”

Carbon Capture Machine

Dr Mohammed Salah-Eldin Imbabi’s Aberdeen based team has built a device that appears to be a complex collection of tubes and stirrers some five square metres in size. The Carbon Capture Machine’s tubes pump flue gas directly into slightly alkaline water where it dissolves to produce carbonate, in a process similar in principle to carbonating fizzy drinks.

This carbonated water is then mixed with brine – water with a high concentration of salt which contains dissolved calcium and magnesium ions. “Industrial or desalination brine is perfect,” Imbabi explains. The resulting solution precipitates out calcium carbonate – used in everything from stomach antacids to ceramic tiles and PVC – and magnesium carbonate – used to make bricks, toothpaste, athlete’s chalk, neoprene rubber and laxatives.

“It’s inherently simple and straightforward – but the devil is in the detail,” Imbabi explains. “One of the highest costs - in terms of CO2 emissions and in cash – is in producing the alkaline solution. So, the challenge is that you need to produce exactly the right amount - no more, no less.”

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CarbonCure

XPRIZE

Unlike many of the XPRIZE finalists, CarbonCure is already installed in some concrete plants across the US and Canada. The process works on the same principle as coral – created by tiny soft bodied invertebrates combining CO2 with calcium to create calcium carbonate.

CarbonCure takes carbon dioxide from a factory or power plant, purifies and liquefies it in pressurised tanks which are distributed to concrete manufacturers. When CO2 is injected into wet concrete during mixing, it reacts with water to form carbonate ions. These react with calcium in the cement to form nano-sized pieces of calcium carbonate – or limestone – permanently bound within the concrete.

These nano-particles strengthen the concrete by around ten per cent and reduce the use of cement by around eight per cent according to CarbonCure CEO Robert Niven. “We can retrofit to existing plants – all it takes is a CO2 tank for the plant and new lines injecting into the concrete. It’s like dry ice being added to concrete mixer.”

Carbon Upcycling UCLA

Civil engineer Gaurav Sant leads the UCLA based team also focussing on concrete. “Not only does cement manufacture produce CO2 – we make five billion tonnes of cement and 30bn tonnes of concrete per year,” he explains. “If you can use that as a sink for CO2 then you can deal with a lot of CO2.”

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The team has integrated of several technologies into a closed-loop. Exhaust fumes from power plants and cement plants are enriched using waste heat from the same flue. This is injected into LEGO-shaped moulds – depending on the shape or use of the resulting concrete - where it mixes with calcium hydroxide, otherwise known as portlandite, as well as aggregates and chemical admixtures to form a patented building material the team has branded CO2NCRETE.

The process needs speeding up, says Sant. The pilot programme produced a couple of metric tonnes of CO2NCRETE in 24 hours. “The bonus is,” he adds, “Portlandite absorbs CO2 rapidly under ambient conditions – which brings down the costs and energy needs.”

C2CNT

“Most carbon capture technology needs purified or concentrated CO2,” Dr Stuart Licht, who leads the Virginia, US-based C2CNT team. “Our process works equally well with flue gas or even atmospheric levels of CO2.”



The C2CNT process transforms CO2 to carbon nanotubes using molten electrolysis with inexpensive nickel and steel electrodes and a low voltage current. The teams 25 by 25 metre chamber is connected to flue exhaust fumes, CO2 flows into a molten carbonate, then – in a process resembling aluminium electrolysis – the team run a current between a steel cathode and a nickel anode, creating thin carbon nanotubes at the cathode and pure oxygen at the anode.

These rolled graphene tubes are 100 times stronger than steel, only one-sixth as heavy and conduct electricity more efficiently than copper. “To date, carbon nanotubes have been so expensive – hundreds of dollars per gram,” Licht explains. "Our process is self-heating after a kick start and the vision is to use solar for the initial bust – and we can produce nanotubes for a fraction of the current price.”

Carbicrete

XPRIZE

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“We are making cement free concrete – which means the concrete we produce is actually carbon negative,” explains Dr Mehrdad Mahoutian, who leads the Montreal, Canada, based team. “Making a block of concrete typically releases two kilograms of CO2 into the atmosphere because of the cement that’s been manufactured to make it. We don’t use cement, saving those two kilos, then inject another kilo of CO2 into the concrete.”

Carbicrete’s process takes steel slag – the complex silicate and oxide rich waste products from a steel plant currently dumped in slag piles at steel works – and mixes it with purified CO2 in an enclosed chamber. Flue gas is roughly eight per cent CO2 – and Carbicrete needs to get that up to fifty or sixty per cent working with commercial carbon capture partners. “The CO2 gas reacts with the calcium and silicate in the slag to create a product that behaves like cement,” Mahoutian explains. “We’re already fixing 200kg CO2 per day – the next step is scaling up to two tonnes.”

Newlight

When you put a piece of bread in your mouth and chew for a long time, you’ll find it suddenly tastes sweet. This is thanks to the enzyme in your mouth called alpha-amylase that converts starch into sugar. It’s known as a biocatalyst and it jump starts the conversion process that breaks down complex foods into the simple compounds your body needs.

“We use something similar,” explains Mark Herrema, who heads up the Huntington Beach, California based team. “It’s a naturally-occurring microorganism-based biocatalyst that pulls carbon out of the CO2 that’s present in a dilute air stream and combines it with hydrogen and oxygen to produce a naturally-occurring biopolymer material — which behaves just like a very tough plastic.”

The company has been using the process to break down methane – and in 2016 IKEA agreed to buy 10 billion pounds of the resulting plastic in exchange for the exclusive rights to use the patented material in home furnishings.

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Carbon Upcycling Technologies

XPRIZE

“At the heart of a CO2 molecule there’s a strong double bond that’s created with the energy used when you burn fuel,” explains Apoorv Sinha, who leads the Calgary, Canada based team. “Most carbon technologies break this bond – which requires yet more energy. Instead, we capture CO2 molecules and bond them to a solid, requiring far less energy.”

Carbon Upcycling Technologies’s process involves pumping purified CO2 into a rotating cylinder where it mixes with a feed stock – chosen from one of a number of solid powder chemicals that trap the CO2. To date, the team has focused on graphite as feed stock – “it’s cheap and available,” Sinha explains – to create graphene nanoplatelets. These resemble graphene – a one-atom-thick sheet of carbon that’s 200 times stronger than steel – but GNP packs layers to between 80 and 100 molecules thick. The result, says Sinha, looks like a business card – long, wide and thin.

In the future, they plan on combining CO2 with coal to create photo luminescent graphene quantum dots, which can increase the efficiency of quantum based solar cells – as well as graphene oxide, an effective drug delivery agent that can load on high doses of cancer drugs as well as lowers the body’s toxicity response.


CERT

The University of Toronto team, explains team leader Alex Ip, “takes CO2, water and renewable electricity – along with a catalyst material we’ve developed – to make ethylene, ethanol, methanol or pretty much any of the building block molecules that you typically get from fossil fuels.”

The CERT device is essentially a vertical sheet of porous electrolysed catalyst – a type of chemical that speeds up reactions without being consumed by them, along which a current runs. Up one side the team pumps a stream of CO2 and down the other a liquid electrolyte – using different electrolytes depending on the molecules to be made. The CO2 diffuses through the catalyst and reacts with the electrolyte, splitting the CO2 molecule up to create new carbon products.

“It’s a modular process,” Ip explains. “We’re making cells you can stack in series – in multiple stacks – so we can be installed in small niche industries or a large refinery pumping out tonnes of CO2.”