Carbon-neutral hydrogen can be produced from farm waste

Hydrogen could be made using agricultural waste under a new production process that uses less energy than existing methods and emits no greenhouse gases.

The novel process turns bioethanol into clean hydrogen and acetic acid, a substance found in vinegar that is also used in the chemicals, food and pharmaceutical industries.

Most hydrogen is produced from natural gas; the process is energy-intensive and expensive. Hydrogen can also be produced from water using renewable electricity, but this approach is even more expensive than using natural gas.

Graham Hutchings at the University of Cardiff, UK, and his colleagues have developed an alternative method that relies on a catalyst made of platinum and iridium to extract hydrogen from bioethanol and water, without releasing any carbon dioxide. The bioethanol used in the process can be made from waste plant material, Hutchings says.

“We don’t make CO2, and so we are not making something that is an environmental burden,” says Hutchings. “We are taking a biologically sustainable source of carbon and hydrogen, and we are turning that into renewable hydrogen and renewable acetic acid. That’s quite neat.”

The team says the process is likely to be scalable and commercially viable, requiring much less energy to run than making hydrogen from natural gas. The next step is to attract commercial investment to set up a demonstration plant, says Hutchings.

Clean hydrogen production will need to scale up radically to enable global decarbonisation, with industries such as steel, chemicals and long-haul transportation expected to need hydrogen fuel.

But the world uses only around 15 million tonnes of acetic acid a year, limiting the potential role this new process could play in meeting demand for zero-carbon hydrogen.

“On a molecule basis we make twice as much hydrogen as acetic acid,” says Hutchings. “But acetic acid is much heavier than hydrogen.” That means producing 15 million tonnes of acetic acid – the world’s entire annual demand – in this way would yield only just over 1 million tonnes of hydrogen, far less than the demand of a net-zero world. “In terms of scale, there’s a bit of a mismatch,” says Klaus Hellgardt at Imperial College London.

Rather, the new process could offer a potential path to decarbonising part of the chemicals industry, with clean hydrogen production an attractive byproduct, says Hutchings. “Acetic acid at the moment is effectively made from fossil carbon. And here we are, we can make it from sustainable sources of carbon,” he says.