(210d) A New Model for the Depolymerisation of Polysaccharides Originating from Biomass

Controlled depolymerisation of polysaccharides is one of the key issues in the utilisation of biomass as a source for fine and specialty chemicals. The aim is to break down the glycosidic bonds of polysaccharides, such as cellulose, hemicelluloses and starch in such a way that oligomeric and monomeric sugars are obtained, but no low-molecular degradation products. This can be achieved by applying hydrolysis of polysaccharides under mild conditions in the precence of a homogeneous or heterogeneous acid catalyst. It has been demonstrated that this is possible, e.g. by using solid ion-exchangers as catalysts and interesting self-accelerating effects have been discovered. To progress further, a model for the depolymerisation kinetics is needed; a model which can predict the distribution of the oligomers and monomers as a function of the reaction time.

A new theoretical model for the depolymerisation kinetics of polysaccharides in batch and continuous reactors was developed. The main idea of the model is that the depolymerisation reactivities of the polymer bonds depend parabolically on the distance of the bonds from the central bond in the polysaccharide polymer. The model is able to describe the self-acceleration of the depolymerisation process as the polymer chains become shorter. A software was developed to be able to calculate the product distribution for an arbitrary mixture of initial polymers. The model was successfully tested on existing experimental depolymerisation data of O-acetylgalactoglucomannan, a hemicellulose appearing in softwood.