Tuesday, June 19, 2007

Plastics from Sugar

New catalysts convert glucose into a valuable chemical feedstock.

By Prachi Patel-Predd

Sugar synthesis: Researchers at Pacific Northwest National Laboratory have taken an important step toward the goal of plant-derived sugars to replace the petroleum-based compounds that are currently used to make polyester and other plastics, industrial chemicals, and fuels. They have developed an easy, inexpensive catalytic process to directly convert glucose into a versatile chemical feedstock. Credit: Pacific Northwest National Laboratory, Technology Review

Researchers at Pacific Northwest National Laboratory (PNNL) have come up with an easy, inexpensive method to directly convert glucose into a chemical that can be used to make polyester and other plastics, industrial chemicals, and even fuels.

Petroleum is commonly used to make plastics and various chemical products, such as fertilizers and solvents. But researchers are trying to find a simple and affordable way to convert the sugars, including glucose and fructose, in plants into compounds that can replace petroleum feedstocks. If successful, such technology could use a chemical made from corn, potatoes, and even grass to substitute for ones derived from oil.

While previous studies have shown various ways to chemically convert fructose and glucose into plastic intermediates and even fuels, these conversion processes are complicated and costly, and are only efficient for converting fructose. Glucose is a much more common sugar because it can be derived directly from starch and cellulose, both plentiful in plant material. "The major bottleneck has been to utilize nature's most abundant building block, which is glucose," says Z. Conrad Zhang, a scientist at PNL's Institute for Interfacial Catalysis, who led the work.

Zhang and his colleagues have developed a catalysis process to transform the sugars into an organic compound called hydroxymethylfurfural, or HMF, which can be converted into polyester and a diesel-like fuel. The technique, which the researchers describe in last week's Science, yields almost 90 percent of HMF from fructose and 70 percent from glucose.

The yield from fructose is similar to that reported in the past by other research groups, Zhang says. But he claims that his process is simpler, involving fewer steps, which would make it more cost-effective. Previous methods use an acidic catalyst, and the chemical reactions take place in a water-based solution, producing high levels of impurities. Instead of an aqueous solution, the PNL researchers use solvents known as ionic liquids, and they use metal chlorides as catalysts. The resulting chemical reaction gives nearly pure HMF, getting rid of the cost of purification, Zhang says.

After trying various metal chlorides, the researchers found that chromium chloride is the best catalyst for glucose. It gets the most HMF from glucose and works at temperatures of 80 °C for fructose and 100 °C for glucose.

The ability to make HMF directly from glucose and in relatively high yields has caught the attention of some experts. The new technique is a step in the right direction, says Leo Manzer, president of Catalytic Insights, a consulting firm based in Wilmington, DE. "What folks have been looking for is a cheaper feedstock and a good way to make HMF," he says. "This is a very unique, remarkable system that [Zhang] has discovered."

The ultimate goal will be to build an economical reactor that can convert cellulosic biomass, such as grass and plant stalks, into HMF. Zhang says that his research team is already working on a method to utilize cellulose directly. However, he says, the first step will be to develop a commercial process for converting glucose into HMF, and that will take several years.