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Plastics get fruity

June 29, 2006 By Philip Ball This article courtesy of Nature News.

Sugar can provide the raw materials for polystyrene.

Apple juice and corn, rather than petroleum, could be the raw materials for some of the plastics and pharmaceuticals of the future, thanks to a new chemical process devised by researchers at the University of Wisconsin in Madison.

Chemical engineer James Dumesic and his colleagues have figured out how to convert fructose, a sugar found in fruit, corn syrup and honey, into an important component in the making of several products of the chemicals industry.

The ingredient, called 5-hydroxymethylfurfural (HMF), can be converted into one of the building blocks of polyester, meaning that the plastic could in theory be made entirely from plants, rather than petrochemicals. HMF can also be used in making diesel fuel.

"There's lots of things you can make from HMF," says Jeff Hardy, manager of the Environment, Sustainability and Energy Forum at the Royal Society of Chemistry in London, UK, and a specialist in green chemistry. "Any process that makes these building blocks from renewable resources is good."

Milk and honey

HMF is formed when heat breaks down sugars. It appears in many heat-processed foods, including fruit juices, milk and honey, and is thought to be harmless at low levels.

You normally get something of a witches' brew.
Jeff Hardy,
Royal Society of Chemistry, London.
But simply boiling up sugar is not an efficient way to make HMF, as it produces all manner of other compounds. "When you start with this kind of natural product, you normally get something of a witches' brew," says Hardy.

There are more efficient ways of converting fructose into HMF, but they use lots of energy, expensive catalysts and organic solvents. Dumesic's team wanted to find a way to decompose fructose mostly into HMF and extract it in a cost-effective way that industry could use.

An acid is needed to break down the sugar. The researchers used either hydrochloric acid or a solid acidic resin, both of which generated few side-products. Four-fifths of the fructose broken down gets turned into HMF this way, they report in Science1.

Salad dressing

The key problem was extracting the HMF from the water in which the reaction takes place. To do this, the researchers put a layer of oily solvent on top of the sugar solution, like layers of oil and vinegar in a salad dressing.

As the fructose breaks down to HMF, the HMF jumps from the water layer into the oil. This collects and purifies the HMF, and prevents it being broken down in the water.

Additives in both solvents helped to ensure that the fructose is decomposed mostly to HMF, and that the HMF then passes into the oily layer, from which it can be extracted by evaporating the solvent in a vacuum.

"Selectivity and separation are the two key issues," says Hardy. He says that the current process is "a good step in the right direction", but suspects that an industrial process might need even better conversion of sugar into HMF, without producing side-products, and a simpler way of separating it.

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  1. Romn-Leshko Y., et al. Science, 312. 1933 - 1937 (2006).


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