14-02: Biomass pretreatment by a continuous flow of superheated steam

It is known that the lignocellulosic complex can be broken under acidic conditions at high temperatures. In case heating is carried out by steam injection, most of the time such steam is stagnant and saturated. The use of super heated steam that flows through the biomass is an alternative with several advantages. By passing steam through heaps of straw an efficient and uniform heat transfer is established. Tests were carried out with wheat straw and reaction conditions were varied. The straw could be successfully pretreated within a few minutes at dry matter concentrations between 30% and 65%, steam pressures of 6 bara and temperatures of 160-180°C. High dry matter concentrations reduce heating costs and required acid concentrations are rapidly reached because of the low amount of water present. In addition, high biomass concentrations are favorable for the economy of the fermentation process and down stream processing. A large part of the volatile compounds such as furfural was stripped from the biomass, thus reducing toxicity of the biomass. During super heated steam treatment hemicellulose was 90% hydrolyzed into its monomers. After cooling and neutralization the cellulose could be 90-95% converted into glucose by the use of enzymes. Such pretreatment can be carried out in conventional steam dryers, with some modifications. In such systems the continuous feed in and out of relatively dry pieces of biomass through the super heated steam process, against a pressure drop of 6 bara, is easy: the inlet and outlet systems are proven technology.