Plastic growing on the trees?

Chemists have succeeded in converting cellulose - the most common plant carbohydrate - directly into a chemical building block called HMF in one step

Researchers hope to convert plants into renewable and non-polluting alternatives to crude oil. To do this, they must learn how to convert plant biomass into building blocks for the efficient and cheap preparation of plastics and fuels. In a new study in this field, chemists were able to convert cellulose - the most common plant carbohydrate - directly into a chemical building block called HMF in one step.

The new findings are based on previous research conducted by researchers from the Department of Energy at the Pacific Northwest National Laboratory. In this study, the scientists were able to produce HMF from simple sugars derived from cellulose. The researchers were able to develop a way that bypassed the sugar creation step and went directly from cellulose to HMF. This simple process produces the important material with high utilization and enables the use of raw cellulose as the starting material.

"In biomasses, such as wood, corn stalks and sugarcane, cellulose is the most common polymer that researchers are trying to convert into biofuels and plastics," said chemist Z. Conrad Zhang, one of the leaders of the new study.

HMF, also known by its scientific name 5-hydroxymethylfurfural, can be used as a building block for plastics and biofuels such as gasoline and diesel, which are fuels very similar to those obtained from the processing of crude oil. In their previous study, the researchers used a chemical and solvent known as an ionic liquid to convert simple sugars into HMF.

The chemical, a chloride salt of a metal known as chromium chloride, was able to convert sugar into extremely clean HMF. However, for cellulose to be used as a direct source material from nature, the research team still had to break down the cellulose into simpler sugars. The researchers wanted to examine how this step could be completely skipped.

The ionic liquid has the added advantage of being able to dissolve the cellulose, a process that is normally not so simple. Substances known as catalysts speed up the conversion of cellulose into HMF material. After trying different catalysts from the metal chloride family that worked in the ionic solvent, the researchers found a pair of catalysts that worked well: a combination of copper chloride and chromium chloride at a temperature of 120 degrees Celsius was able to break down the cellulose without the formation of unwanted by-products.

In additional experiments, the researchers tested the effectiveness of their method in comparison to the use of acid - a well-known and common method for dissolving cellulose. The system of metal chlorides within the ionic liquid worked ten times faster than acid alone and at much lower temperatures. In addition, the pair of catalysts allowed the researchers to avoid the use of another tested compound - a mineral acid known to break down the substance HMF.

While optimizing their method, the researchers found that they were able to consistently achieve a high utilization of the substance HMF - converting fifty-seven percent of the sugar content in cellulose to HMF in one step. The researchers were able to obtain more than ninety percent of the extracted material and the final product of the entire process was ninety-six percent pure.

Moreover, the system of the metal chlorides and the ionic liquid can be used several times without loss of its effectiveness. The ability to recycle the materials in the process will further reduce the production cost of the essential material HMF.

"Our article is a tremendous breakthrough. By coupling the steps of cellulose breakdown and sugar conversion, we are very close to a one-step method of converting raw biomass from nature into an important chemical - one that can be easily used to make motor fuel or to synthesize plastics or other petroleum products," said Jim Amonette, geochemist and co-author of the article. "These kinds of advances could help us reduce our dependence on fossil fuels."

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