Turning waste into a valuable biofuel through innovative mineral-based filtration

If you’ve ever seen a McDonald’s truck with “We recycle all our used cooking oil into biodiesel” written across the side, you may have wondered how the liquid that crisps up your French fries end up in a fuel tank.

It’s down to a filterable adsorbent that uses diatomaceous earth to turn waste into something of value.

Biofuel mandates are increasing demand for renewable raw materials

Biofuels, including those using waste-based feedstocks, have proved to be as effective as fossil fuels – if filtered properly – as well as being cleaner for the environment.

To help reduce greenhouse gas emissions as part of international climate change frameworks, such as the Kyoto Protocol, governments are steadily increasing the proportion of biodiesel required as a blend in fuel.

More than 60 countries—most in the EU—now have such policies in place. For example, France’s biodiesel roadmap is aiming for a 15% incorporation rate by 2030. Indonesia has had a requirement for a 20% biomix since 2018. And Brazil mandates a minimum of 27% ethanol content.

As the world’s leading supplier of soybean oil, Argentina generates about $1.7 billion a year in revenue from biodiesel exports. Biofuel is not just good for the environment – it’s big business.

To make this sustainable future a reality, there is an increasing need for renewable raw materials, including virgin oils, such as palm, sunflower and rapeseed oil, as well as lower-quality waste-based feedstocks. Hydrotreated vegetable oil (HVO) is proving a particularly attractive proposition, as it is suitable as a 100% fuel source – it doesn’t need to be blended with petroleum-based diesel.

Whatever the source, the feedstock needs to be refined before it can be blended and put in your fuel tank – either filtered or water-washed with a centrifuge.

The latter process effectively scrubs away the contaminants but has a few drawbacks. It uses a lot of water, which is not good for the environment – and because the water is used to remove contaminants, it cannot be returned to the river until it is treated, which is a significant cost.

For that reason, more biofuel suppliers are moving towards filtration.

Image

Effective filtration removes contaminants from waste-based feedstocks

So, back to that McDonald’s truck. Waste-based feedstocks – such as used cooking oils from restaurants – are taken to a refiner, where they are purified through a filtration process to convert them into a sustainable fuel source.

David Gittins, Imerys’ Science & Technology Director for Filtration & Life Sciences, explains: “With waste fats, you have different types of feedstock coming in from different sources and containing different types of contamination. Cooking oil from a restaurant, for example, has lots of burnt chips and fatty acids in it. You have to remove all those impurities, as well as trace metals and phosphorus.”

The filtration process for waste-based feedstocks, therefore, needs to be second to none.

“What comes out needs to be super clean and must meet the specification for biofuel conversion”, says David. “Traditional filter processes don’t work as well on waste-based feedstocks because there are more contaminants to remove. It’s like using 10 filter papers for your morning coffee. It’s going to take a lot longer for the coffee to get through.”

Diatomite’s high porosity makes it ideal for filtration

Imerys has engineered a product that is both a filter aid and an adsorbent, improving its filtration performance and removing the risk of blockage. CynerSorb® uses diatomite, an effective mineral for filtration – its huge amount of small pores increases the surface area and enables quicker and more thorough filtration.

CynerSorb’s superior characteristics mean even the most heavily contaminated waste feedstock can be filtered.

A credible source of biodiesel for sustainable transport of the future

Renewable diesel is principally used to power cars, but the potential is for airlines to adopt a cleaner fuel source and reduce their environmental footprint.

“When we talk about cutting pollution from transport, we’re looking at electric trucks and battery-operated cars,” says David. “Airplanes won’t run on batteries – but you could run a plane on HVO. Aside from technical developments, that’s the only way airlines are going to decrease their emissions. The industry is starting to build HVO plants and is carrying out research to ensure it’s safe and won’t corrode.”

Progress is being made. In July 2020, Repsol produced Spain’s first batch of sustainable aviation fuel. Those 7,000 tons of biojet will prevent the release of 440 tons of CO2 emissions. Using something that has been used already turns a waste product into something of value. Even a 130-tonne fatberg found in London’s sewers in 2017 was converted into enough biofuel to fuel 350 London buses for a day.

Matt Jordan, Imerys’ Technical Support Manager for Filtration & Life Sciences, says: “There is a growing trend to move away from using virgin vegetable oils as a fuel source when there are plenty of waste sources that can be used instead. People don’t want something in their cars that could be used as food, and many governments don’t want to have to import oils produced elsewhere.”

David adds: “Anything that has fat in it can be turned into a waste-based feedstock. Consider livestock. We want the nice bits for food, but for health reasons, you can’t grind up the rest of an animal and use it as feed for other animals, so the carcass ends up in a landfill. Instead, you can render this tallow – the saturated fat in animals – and use it as a feedstock.”

Improved filtration opens up more opportunities to use any waste-based feedstock as a credible source for biofuel ­– and that has the potential to drive real environmental change.

David concludes: “Every gallon of biofuel used is one less gallon of crude oil extracted from the ground.”