Computational modeling of cellulose decomposition.

One of the visions of sustainable development is often expressed as ‘from the cradle to the cradle’, where all ‘waste’ materials can be used as sources for new, useful products such as energy.  Together with other actors in the Sjuhärad region, such as Borås Energy & Miljö AB (BEM), SP and the Waste Refinery Excellence Center, the School of Engineering (IH) at the University of  Borås (HB) is working towards finding new and improved techniques to convert waste to ethanol and biogas. 

 As shown in the diagram below, pretreatment of lignocellulosic materials is needed when using it to produce ethanol or biogas.  Hence, optimizing this step is central to production of both forms of energy.  The chemical structure of the wastes, which include lignocellulose, need to be broken down before they can be used to obtain energy.  Since very little is known about the decomposition of these structures at the molecular level, a huge variety of methods have been tested and are still being tested to improve the pretreatment.  The computational modeling used in this project complements  these resource-intensive studies. 

The cellulose chains are packed by strong hydrogen bonds in so-called ‘elementary fibrils’. These elementary fibrils are attached to each other by hemicelluloses, amorphous polymers of different sugars as well as other polymers such as pectin, and covered by lignin. The microfibrils are often associated in the form of bundles or macrofibrils. This tightly-packed structure makes cellulose resistant to the biological and chemical pretreatments.

The figure below shows the unit structure of the cellulose molecule (called cellobiose) in the left panel and the microfibril that contains 36 cellulose molecule in the right panel.

Our calculations will identify the type and strength of bonding that prevents easy decomposition of cellulose, as well as suggest ways to improve the chemistry to make the decomposition more efficient.  This may also involve calculating activation energies and Arrhenius pre-exponentials, which can then be used to obtain the decomposition kinetics.  Our long term goals are to study keratin and wastes from the textile industry.

This research, which is performed in close collaboration with the experimental studies at IH, is funded by Stiftelsen Sjuhäradsparbanken.