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Contaminated cooking oil transformed into usable biodiesel with new process

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A new method to turn used cooking oil and agricultural waste into biodiesel and food scraps and plastic rubbish into high-value products has been developed by researchers at Australia’s RMIT University.

It hinges on the use of a new type of ultra-efficient catalyst that can make low-carbon biodiesel and other valuable complex molecules out of diverse, impure raw materials.

Waste cooking oil currently has to go through an energy-intensive cleaning process to be used in biodiesel because commercial production methods struggle to handle feedstock with more than 1-2 per cent contaminants.

The researchers said their new catalyst was “so tough” that biodiesel can still be created from low-grade ingredients that contain up to 50 per cent contaminants.

It also opens the door to doubling the productivity of manufacturing processes 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.

Co-lead investigator Professor Adam Lee, RMIT, said that conventional catalyst technologies depended on high-purity feedstocks and required expensive engineering solutions to compensate for their poor efficiency.

“The quality of modern life is critically dependent on complex molecules to maintain our health and provide nutritious food, clean water and cheap energy,” Lee said.

“These molecules are currently produced through unsustainable chemical processes that pollute the atmosphere, soil and waterways.

“Our new catalysts can help us get the full value of resources that would ordinarily go to waste - from rancid used cooking oil to rice husks and vegetable peelings - to advance the circular economy.

“And by radically boosting efficiency, they could help us significantly reduce environmental pollution from chemical manufacturing and bring us closer to the green chemistry revolution.”

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.

Co-lead investigator Professor Karen Wilson, also from RMIT, said the new catalyst design mimicked the way that enzymes in human cells coordinated 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,” Wilson said.

“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.”

The sponge-like catalysts are cheap to manufacture, use no precious metals and could advance biofuel production and reduce reliance on fossil fuel-derived diesel.

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