Enzymatic degradation of pre-treated wood

The economic dependency on fossil fuels and the changes of climate due to them has led to an intensive search for renewable resources for the production of chemicals and fuels. At present there are several processes established which use sugar cane and corn for the production of bioethanol. As these crops are commonly used as food there is an ethical drive to use alternative resources for industrial processes. Promising feedstock for the chemical and fuel production are in this context the fermentable sugars derived from wooden celluloses and hemicelluloses by enzymatic hydrolysis. The great challenge in this regard is to design new simple and beneficial processes that can compete against conventional petrochemical production processes.
The most important step in these processes is the hydrolysis of the lignocellulosic material into the corresponding sugar monomers, which can be fermented to ethanol for example. The aim of the presented work is to optimize the enzymatic hydrolysis with regard to the used substrates and the usage of hydrolysates for the fermentation of alcohol. The substrates are cellulose and hemicellulose fractions obtained by thermo-chemical pre-treatment of beech wood. This pre-treatment is carried out by our project partner at the Johann Heinrich von Thünen Institute, Hamburg, Germany.
Several commercially available enzymes, even thermo stable ones were tested on their ability to degrade these fractions. In first experiments it could be shown, that the enzymes can hydrolyse up to 40 % of the cellulosic fraction into fermentable sugars within 24 h. The hemicellulosic fraction already contains some monomeric sugars which can be fermented. For this fraction the use of hemicellulases is investigated. All sugar containing hydrolysates and fractions were tested for their suitability as carbon source for a co-fermentation of two different yeasts to produce ethanol. The results showed that the addition of a nitrogen source, vitamins and trace-elements is the only necessary preliminary step for the fermentation. To increase the yield of sugars in the hydrolysates further optimizations were made, e.g. the increase of substrate concentration and the amount of added enzymes was investigated.