Making biodiesel from old cooking oil is now easier than ever


Researchers have developed a powerful, low-cost method for recycling used cooking oil and agricultural waste into biodiesel, and turning food scraps and plastic rubbish into high-value products.

The method uses a new type of ultra-efficient catalyst that can make low-carbon biodiesel and other valuable complex molecules out of a range of impure raw materials.

The new catalyst can make biodiesel from low-grade ingredients, known as feedstocks, with up to 50 per cent contaminants compared to the current energy-intensive production method that can only use feedstocks with one to two per cent contaminants.

The new process is so efficient that it could double manufacturing productivity for transforming rubbish like food scraps, microplastics and old tyres into high-value chemical precursors used to make anything from medicines and fertilisers to biodegradable packaging.

Dr Simon Beaumont from Durham University, part of the international research team, said: “Current technology used to make many of the complex molecules that support our daily lives is overly reliant on expensive engineering solutions and can pollute our environment.

“A big problem is that high purity feedstocks must be prepared for conventional chemical reactions. This is possible if you have single source for feedstocks, like natural gas from the North Sea, but not if you want to use distributed resources like plant materials (biomass) or waste streams like cooking oil instead of fossil fuels. It then becomes prohibitively expensive to move them all to one big chemical plant.

He added: “Instead we have developed new catalysts that carry out the separations, such as the rancid part of used cooking oil from the parts we can turn into biodiesel, and then carry out the chemical microscopic reactions by themselves – – about the size of a red blood cell.

“These new materials are really exciting as they provide a key step towards using greener resources efficiently, with complete solutions that could be deployed anywhere as an alternative to what currently takes place in large chemical plants.”

To make the new ultra-efficient catalyst, the team fabricated a micron-sized ceramic sponge (100 times thinner than a human hair) that is highly porous and contains different specialised active components.

Molecules initially enter the sponge through large pores, where they undergo a first chemical reaction, and then pass into smaller pores where they undergo a second reaction.

It is the first time a multi-functional catalyst that can perform several chemical reactions in sequence within a single catalyst particle has been developed, and they are cheaper to manufacture using non precious metals.

Co-lead investigator Professor Karen Wilson, from RMIT (formerly known as the Royal Melbourne Institute of Technology and Melbourne Technical College), said: “The new catalyst design mimics the way that enzymes in human cells coordinate complex chemical reactions.

“Catalysts have previously been developed that can perform multiple simultaneous reactions, but these approaches offer little control over the chemistry and tend to be inefficient and unpredictable.

“Our bio-inspired approach looks to nature’s catalysts – enzymes – to develop a powerful and precise way of performing multiple reactions in a set sequence. It’s like having a nanoscale production line for chemical reactions, all housed in one tiny and super-efficient catalyst particle.”

Making low-carbon biodiesel from agricultural waste with these catalysts requires little more than a large container and some gentle heating and stirring, so this low technology, low-cost approach could advance distributed biofuel production and reduce reliance on fossil fuel-derived diesel.

Professor Wilson added: “This is particularly important in developing countries where diesel is the primary fuel for powering household electricity generators.

“If we could empower farmers to produce biodiesel directly from agricultural waste, like rice bran, cashew nut and castor seed shells, on their own land, this would help address the critical issues of energy poverty and carbon emissions.”

While the new catalysts can be used immediately for biodiesel production, with further development they could be easily tailored to produce jet fuel from agricultural and forestry waste, old rubber tyres, and even algae.

The next steps for the Science Research Team are scaling up the catalyst fabrication from grams to kilograms and adopting 3D printing technologies to get the product to market quicker.