A simple, low-temperature process that converts waste cooking oil to biodiesel could reduce the cost and energy use for making the alternative fuel. The method, reported in the journal Energy & Fuels, could help to make the use of sustainable biodiesel more widespread, and help bring down emissions from transportation and heavy industry.
Most of today’s freight-lugging trucks, and many trains, boats, and heavy machinery, burn petroleum-based diesel for fuel. In the U.S. alone, the transportation sector burned approximately 3 million barrels of diesel every day in 2022. That resulted in 10% of the country’s total energy-related carbon dioxide emissions.
Diesel made from vegetable oils is a renewable, low-carbon alternative that can be used in conventional diesel engines. Currently, nearly 60% of the biodiesel in the US is made from soybean oil.
But there is a push for using waste oil collected from restaurants and food processing plants. Renewable diesel made from used cooking oil results in fewer greenhouse gas emissions than those made from new vegetable oils. And as an added bonus, reusing cooking grease helps reduce the amount of waste that would otherwise end up in landfills or sewage systems.
Known processes to convert cooking oils and vegetable oils into biodiesel require high temperatures. They also produce glycerin and other soapy molecules, which adds purification costs and energy use.
The new method developed by chemists at the University of Santa Cruz relies on a chemical called sodium tetramethoxyborate. The researchers tested the process on waste cooking oil from a major fast-food chain, and also on soybean oil, corn oil, olive oil, and animal fat.
The reaction is completed in under an hour at temperatures as low as 40°C, saving energy and cost. At the end, the byproducts form a solid material, so it’s easy to separate the biodiesel by simply pouring it out of the reactor. The method converts about 85% used cooking oil into industry-standard biodiesel.
Besides being affordable, the simple process can be done at just above room temperature and does not require a refinery, UC Santa Cruz chemistry professor Scott Oliver said in a press release. “You can potentially use this method on a farm.”
Source: Kevin C. Lofgren et al. Borate Pathway to FAMEs at Near-Ambient Conditions from Used Oil, Energy & Fuels, 2024.
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