Plant oils give petroleum a run for the money

Plant oil from crops such as soybeans may become an essential renewable energy resource

July 18, 2000
Web posted at: 12:19 p.m. EDT (1619 GMT)

By Environmental News Network staff

When Bernie Tao talks to farmers, he tells them that they're oil barons.

The oil they control isn't below the ground, however. It's growing on top, contained in the corn and soybean plants in their fields.

It may be green gold instead of black gold, but Tao predicts that over the next several decades, plant oil will become just as essential to everyday life as fossil fuels are today.

"In the 1970s we got our first taste of what it was like when the fuel begins to go away," said Tao, an associate professor of agricultural and biological engineering at Purdue University. "Three decades later we're beginning to see the start of another large petroleum crunch. And part of that is consumer demand, which has greatly increased. Consumers like this stuff!"

Anyone standing at a gasoline pump this summer watching the digits scroll by may wonder whether prices are going to go down. Over the long term, Tao pointed out, they won't.

"One-time-use resources, which are also known as non-renewable resources such as petroleum, are a problem because you eventually run out," he said. "Eventually we will have to switch from using non-renewable resources to using renewable resources."

But Tao and others say that the potential is already there for common field crops, such as corn and soybeans, to replace petroleum oil as the driver of our economy. And the change may come within a few decades.

"With a bio-based economy, you can produce new raw materials every year, so you don't have this type of problem," he said.

Although most biofuel discussions center on ethanol, that's not the only option, Tao said. "The obvious substitutes for petroleum are plant oils and fats because they have the same base chemical structure as petroleum," he said.

Ethanol is a type of alcohol made by fermenting plant material. Although it makes a good fuel, it has drawbacks, Tao said. "The economics of ethanol production are improving as the technology improves," he said. "But ethanol has two problems: It doesn't explode like gasoline, and it can absorb water, which can cause oxidation, rust and corrosion."

By manipulating plant oils, Tao said it's possible to create a petroleum substitute.

Fossil fuels were plants once, millions of years ago, and so it makes sense that both the fossil fuels we use today and oils produced by plants are chemically similar. Both are made up of chains of chemicals known as hydrocarbons.

A hydrocarbon is a carbon atom surrounded by hydrogen atoms. Methane, the simplest hydrocarbon, is a single carbon atom surrounded by four hydrogen atoms. Gasoline varies from seven to 10 hydrocarbons long. "In fact, the word 'octane' means eight carbons in a chain," Tao said.

The shorter the chain of carbons, the more explosive the fuel is, and the more power it offers an engine.

The problem is that plant oils are 14 to 18 carbons in length. "Diesel fuel is 15 carbons long, which is close to the same size as plant oils. That is why the first applications are as biodiesel fuel," Tao said. "You couldn't burn vegetable oils in today's gasoline engines because their hydrocarbon chains are too long."

Tao said the possibility exists to make a type of plant gasoline from plant oils that have shorter carbon chains.

"Not surprisingly, shorter-chain vegetable oils do exist," he said. "Coconut oil, tropical oils and similar plant oils might make a reasonable gasoline-like fuel. It might also be possible to transgenetically modify crops to produce plants with those lengths of fatty acids."

Corn has a high oil yield for conversion to other products

Tao said future scientists could genetically modify corn and soybeans, two of the highest oil-yielding plants, to produce plant oils that could be converted into a type of gasoline. "Could you produce a fuel by combining vegetable oil and ethanol? Actually, the combination of those would seem to fit nicely into today's engine structures," he said.

Fuels aren't the only uses of petroleum, Tao said. "If you look at where petroleum is used, the largest number of applications is in inks, paints and coatings."

Chemists have known for decades how to alter the hydrocarbon chains in petroleum through processes known as cracking and reforming. Shortened hydrocarbon chains are used as solvent bases for paints and chemicals. Longer chains — as many as 200 hydrocarbons are known as plastics. But these products also can be made from plants.

According to Tao, before World War II, most paints, coatings and adhesives were made from vegetable oils or other plant products. "In the very near future, some of these products will go back to using vegetable oils instead of petroleum," Tao said. "There are latex paints that will be appearing on the market very soon."

This isn't a new idea: Henry Ford famously made everything from clothing to automobile bumpers from vegetable oils just to show that it could be done. And this past January, Dow Chemical Co. and Cargill Inc. said they will begin production of new plastics made from corn.

Despite this, most products are still made from petroleum instead of plants. Tao said a look around will show thousands of products that were once made from plants that are now made from petroleum products. "Candles, for one," he said, holding up a blueberry-scented candle made from soybean oil. "It's only been in the last 60 to 70 years that paraffin wax candles were common.

"As we change from a black gold economy to a green gold economy, we'll need engineers who know how to make products out of plant materials."

The need for petroleum is never going to go away; the question is how are we going to use it, Tao said. "Plastics are made from petroleum chains 200 carbons long," he said, tapping the case of his computer monitor. "We'll be saving petroleum to make things that we can't make in any other way."

Copyright 2000, Environmental News Network, All Rights Reserved

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Biodiesel Web Site
Purdue University
Plants for a future
Corn Refiners Association
soybeans
The American Petroleum Institute
The Agricultural Research Center

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