Scientific American: Plastic from plants

By David Biello

Glucose is the main carbohydrate product of photosynthesis and a primary source of energy in most living things. It is a sugar and the human body's main source of fuel. And, because of its ubiquity, it is a leading candidate to replace oil as an abundant source for fuels, plastics and other petroleum products.

Unfortunately, converting the stuff into useable forms remains a difficult process. For example, using acid catalysts to transform it into a basic building block for plastics also yields a vat of impurities (such as levulinic and formic acids). But now chemists at the Pacific Northwest National Laboratory (PNNL) in Richland, Wash., have come up with a way to efficiently and cleanly turn such naturally occurring sugars into plastics, making Tupperware from trees a real possibility.

Chemist Conrad Zhang and colleagues at PNNL tested a variety of metal catalysts—compounds that speed chemical reactions—in their search for an efficient method of transforming glucose and other natural sugars into hydroxymethylfurfural (HMF), a molecule that can easily be manipulated into a variety of chemicals and plastics.

"Because glucose can be derived directly from cellulose and starch, it is nature's most abundant carbohydrate building block," Zhang says. "HMF from renewable carbohydrates, such as fructose and glucose, is a versatile platform chemical from which hundreds of other chemicals can be produced."

The chemists detail in Science how they used metal chlorides—chromium, copper and other metals paired with two or more chlorine atoms—to transform 70 percent of glucose and nearly 90 percent of fructose into HMF. They report that chromium chloride (CrCl2) worked best, apparently by boosting a sugar molecule's ability to open up and shift atoms in its structure as it changed form, although the exact mechanism remains unknown, Zhang says.

The research could become the basis of a process that turns biomass such as trees, cornstalks and algae into feedstock for chemicals, plastics and fuels at roughly 100 degrees Celsius (212 degrees Fahrenheit), which is a lot cooler than the 600 degrees C (1,112 degrees F) needed for oil refining or the high temperatures (as well as pressure) such oil must undergo when it is formed naturally.

"A number of steps, including process development and optimization, have to take place before full-scale commercialization," Zhang notes. "It may take several years to reach that stage."

Ultimately, the plastic in a fork used at a backyard barbeque may be as directly plant-based as charcoal in the grill and the chef's polyester apron. "Direct utilization of cellulosic biomass for chemicals and fuel production is a challenging goal," Zhang adds. "Our results point to a potential process for the production of HMF from the most abundant renewable sources."