CO2 to SAF: A one-step solution

Oxford spinout OXCCU has launched a demonstration plant at London Oxford Airport to trial its one-step process of turning CO2 into sustainable aviation fuel (SAF). Aniqah Majid visited the plant to investigate the benefits of its “novel” catalyst

OVERLOOKING two grooved runways, the distinctive electric blue of OXCCU’s two-storey SAF demonstration plant immediately marks it out from the surrounding grey buildings of London Oxford Airport.

The plant, named OX1, has been built to evolve a novel catalytic process developed by the University of Oxford spinout which sees CO2 and H2 converted directly into SAF.

The aviation industry, which accounts for 2.5% of global CO2 emissions, has set a goal of achieving net zero emissions by 2050. SAF, where fuel is made from largely renewable sources, has emerged as a promising technology in the race to decarbonise. According to the International Air Transport Association (IATA), SAF production is expected to reach 1.5m t this year, accounting for 0.53% of aviation fuel need.

An alternative to traditional kerosene-based fuel, SAF has mostly been trialled using biomass from cooking oils.

However, with other hard-to-abate sectors, including road transport, taking precedence, the UK government has capped the use of hydroprocessed esters and fatty acids (HEFA) in aviation to ensure feedstocks are not diverted from zero emission road vehicles.

Alternative HEFA feedstocks produced from palm or soy oil, meanwhile come with unfavourable land use impacts and produce more emissions than conventional hydrocarbon-based jet fuel, according to aviation intelligence company IBA.

As Andrew Symes, the CEO of OXCCU, says: “We will still need hydrocarbons, even in a net zero world. There are three non-negotiables; chemicals and plastics, because they are carbon-based, and aviation fuel.”

Enter power-to-liquids (PtL) or eFuels, a synthetic hydrocarbon fuel made through electrification, CO2, and water. 

The one-step solution

In 2010, researchers that would go on to make up the OXCCU team found early success in converting CO2 and H2 into jet fuel-range hydrocarbons using a one-step process.

Now, along with the US startup Infinium, OXCCU is one of the few companies using PtL to develop aviation fuel. But unlike its competitor, which is using a two-step indirect process of converting CO2 and H2 into syngas (H2 and CO) and then into jet fuel, OXCCU has found success in skipping the syngas step altogether through CO2 hydrogenation.

“The problem with eFuels right now is cost, and we believe the solution to this is using catalysts,” says Symes.

OX•EFUEL uses an iron-based catalyst containing manganese, potassium, and organic fuel compounds, a mix that has proven to be highly effective in producing jet fuel synthesis via the hydrogenation of CO2.

This catalyst reduces CO2 and H2 into CO and H2 via a reverse water gas shift (RWGS) process, and then subsequently turns it into jet fuel and water via Fischer-Tropsch (FT).

Charles Yiu, OXCCU’s head of engineering, explains: “The traditional two-step process will make CO and H2 by putting it through a traditional FT reactor. However, CO2 is poisonous to the traditional catalyst, making it unable to tolerate CO2, so another step of recycling of the CO2 would be involved for the RWGS process.”

“Here, we can take the CO2 directly to form the FT process. Though CO does form on the surface of the catalyst, it continues to react and is immediately consumed, so from a reactor in and out point of view, you do not see a lot of CO.”

The scale journey

OX1 is part of the research and development stage of OXCCU’s wider plan to get its SAF off the ground, following the success of its lab trials in 2022, where its catalyst ran in a stable condition for 3,000 hours.

OXCCU says the demonstration plant will be open-ended, allowing it to run for “as long as they want” for the company to test out how long its catalyst can last before it needs to be changed out.

The plant is expected to produce around 1.2 l/d of liquid fuel, starting from this month.

The fuel from the facility will not be going into any planes just yet, as it was built specifically to expand OXCCU’s research into its SAF and build a case to aviation bodies that the fuel is safe and usable.

“We are in the commissioning phase with OX1, where we test the equipment to make sure it is leak tight and that everything works.” says Yiu.

High-flying standards

Before any type of aviation fuel is put into a plane, it must adhere to a set of standards, including the international American Society for Testing and Materials (ASTM) D1655 standard specification.

“There are specific aviation standards we need to adhere to, called ASTM,” says Symes. “And in addition to the jet fuel spec, we have got to be on one of the approved pathways.”

There are several pathways for certified SAF, including ethanol-to-jet and HEFA. OXCCU’s SAF is looking to qualify via the FT pathway, where syngas is converted to fuel.

To pass the ASTM standard, the company will have to ensure the fuel is fit-for-purpose when blended with conventional fuel at its maximum ratio. The UK government is planning to introduce PtL obligations into aviation fuel at a ratio of 0.2% in 2028, and 3.5% by 2040.

Once OXCCU passes these standards, it can set the wheels in motion for its next scaleup, the OX2 plant, which will be situated around 180 miles north of Oxford at the Saltend Chemicals Park in Hull.

The facility will sit alongside energy heavyweights like bp, INEOS, and Mitsubishi Chemicals and is expected to produce 200 l/d of fuel.

OXCCU is currently working on the designs for the plant but expects it to be up and running by 2026, with its next commercial-scale plant, which will produce 10,000 l/d of fuel, expected to begin operation in 2028.

“Our plan is to license our technology globally towards the end of this decade,” says Symes. “We are looking at sites in the UK near the industrial clusters where there is existing chemical infrastructure, but we are also looking at sites in the Middle East, Canada, Texas, and South America.”

He adds: “We think that OXCCU’s catalyst will enable us to fly without a climate impact. We know we're not the only part of this puzzle, but we do think that we're a key part of it, because we can produce the efficient conversion of CO2 and H2 to fuel.”