2th Generation Ethanol: Converting Cellulose to Sugars

Switch from cellulose to small molecules of sugars

A team of scientists from the Max Planck Institute for Carbon Research (MPI-KoFo) in Mühlheim-sur-la-Ruhr has developed a new method that allows cellulose to be broken down relatively easily into its building blocks, sugars. This could open the door to the production of raw materials and biofuels from biomass derived from wood or plant waste, therefore without competition with food products.

Cellulose, the most common organic molecule on earth, is the main component of plant cells. As it is particularly stable, it was heretofore difficult for the industry to cleave it into its elementary components. A significant amount of energy was thus left unused.

Roberto Rinaldi, Regina Palkovits and Ferdi Schüth from MPI-KoFo have now managed to overcome this obstacle, using an acidic solid catalyst and an ionic medium. The resulting process allows long chains of cellulose to be selectively split into small pieces in a matter of hours or less. In addition, an advantage is that few by-products appear, which reduces the risk of complications following treatment. The catalyst can be recovered and reused at the end of the reaction.

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First, the researchers place the cellulose molecule in an ionic solution. It is a salt, liquid at room temperature, which contains positively and negatively charged elements. "This step makes the long chains of cellulose accessible for the following chemical reactions, and the cellulose is thus attackable by solid catalysts", explains F. Schüth.

The MPI-KoFo team has meanwhile determined which properties a catalyst must have in order to cleave cellulose. The material must be acidic, that is, be able to give H + protons. It must also have a large surface area and pores of the correct size, because the cellulose dissolved in the ionic solution is very viscous, which complicates the transport of the chains to the catalyst. "We have discovered that the chemically modified resin is particularly well suited to cleavage of the sugar bonds of cellulose", continues Ferdi Schüth.

With the addition of water, the thus shortened sugar chains sink to the bottom, so that it is easy to separate them from the solution. The researchers then filter the solution and recover the catalyst. "In order to finally achieve the smallest building blocks of cellulose, an additional step is necessary via, for example, the use of enzymes." These cut the short chains into isolated sugar molecules. This process of "breaking down" - from cellulose to glucose molecules - is called depolymerization.

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The new method allows, among other things, to cut very stable plant components, such as micro-crystalline cellulose, or even wood. "We can thus say that, thanks to this method, the dismantling of wood into sugars is possible", comments F. Schüth.

This cellulose treatment opens up many avenues of application. The sugar molecules thus obtained could be subjected to alcoholic fermentation and the ethanol then produced as a biofuel, without competing with food products. Scraps of wood or straw could be used as basic material. However, significant development work remains to be done before using this method on a large scale. In particular, ionic solutions are very expensive, which necessitates their reuse in the production cycle, and therefore the development of a recycling approach.

Ferdi Schüth - Max-Planck-Institut für Kohlenforschung, Mühlheim an der Ruhr - tel: +49 208 306 2373 - email: schueth@mpi-muehlheim.mpg.de

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Source: BE Germany

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