Converting carbs to lactic acid with catalysts

By Lisa Gibson
Posted May 19, 2010, at 3:29 p.m. CST

A team of researchers from Haldor Topsøe A/S, a Danish catalyst research and development company, and the Technical University of Denmark's Department of Chemistry have developed a process to convert carbohydrates from biomass into lactic acid using only catalysis.

Traditionally, fermentation is used in the conversion process, but the researchers modified the acidity of a zeolite material catalyst, which is made of silicone oxide and aluminum oxide, to carry out their process, according to Esben Taarning, researcher with Haldor Topsøe. "It is the aluminum oxide that makes the zeolites acidic and by changing the composition of the zeolite to one that is composed of silicon oxide and e.g. tin oxide (no aluminum oxide), the acidic properties change as well," he said. "In fact, the acidic properties change so dramatically that the modified zeolites are able to catalyze the conversion of carbohydrates to lactic acid derivatives. In comparison, a conventional zeolite is too acidic to afford any useful products at a high selectivity and primarily catalyze dehydration reactions." Lactic acid products can be used in manufacturing biodegradable plastics and solvents.

So far, the team has only used pure substrates of monosaccharides such as glucose and fructose, as well as the disaccharide sucrose in its research. But any carbohydrate source can in principle be used as long as there is a pre-step to break down components such as cellulose to glucose, Taarning said. The primary catalyst is zeolite beta because it has large pores into which monosaccharides will diffuse where they react. The catalyst can be modified with elements such as tin, zirconium and titanium to achieve different acidities, but the best results are obtained with tin, Taarning said. "So in short, many different catalysts can be effective for this conversion," he said. He added that the catalysts are highly hydrophobic, meaning they are repelled by water and often cluster together, which may seem a bit odd since they are used to convert carbohydrates.

"The significance of the discovery should be seen in the light that very few chemicals can be made directly from carbohydrates using catalysts," Taarning said, citing, gluconic acid from glucose, sorbitol from glucose and 5-hydroxymethylfurfural from fructose/glucose. "Therefore, having a process for the conversion of glucose/fructose to lactic acid derivatives will add new possibilities to make value-added products from biomass using catalysis only." A catalytic process to lactic acid derivatives could turn out to be advantageous since more process options are available when using a heterogeneous catalyst compared with yeast or bacteria, he added. "One of the next steps in the research is to improve the catalyst and the process, so higher yields of lactic acid products are obtainable from carbohydrates."