(German title: Verbundvorhaben: Pilotprojekt Lignocellulose-Bioraffinerie, Teilvorhaben 1: Extraktverarbeitung, Enzymtechnologie, verfahrenstechnische Untersuchungen, Ökobilanzierung, Wirtschaftlichkeitsberechnungen)

The economic dependence on fossil fuels such as oil, coal and natural gas and the associated harmful effects on our climate have led to an intensive search for alternative raw materials for energy generation and the production of chemicals. Sugar building blocks from plant biomass are a particularly promising source here, as they can be used as starting materials for a variety of chemicals such as ethanol or citric acid. In the processes established to date, mainly sugar beet and sugar cane or starchy plants (e.g. maize) are used as an energy source for the production of bioethanol. As these plants play an important role in the food supply, their use as a raw material poses an ethical and moral problem.

With the aim of using an alternative raw material source, the 'Fachagentur für nachwachsende Rohstoffe' (FNR e.V.) funded the pilot project on the use of wood as a raw material for the production of platform chemicals. The aim was to develop a sustainable, integrated process for the pulping and component separation of beech and poplar wood containing lignocellulose, in which all components of the starting material can be used for the production of basic and fine chemicals.

Wood consists mainly of three different polymers, which are collectively referred to as lignocellulose and represent the skeletal substance of plants. Specifically, these are cellulose (consisting of glucose monomers), hemicellulose (mainly composed of xylose) and lignin (polymer of phenolic compounds). These components were broken down and fractionated by a project partner to improve further processing.

The bioprocess engineering department dealt with the enzymatic hydrolysis of cellulose and hemicellulose fractions with commercially available cellulases and xylanases into their basic components glucose and xylose and their further conversion by fermentation into valuable products such as ethanol and itaconic acid.

The enzymatic hydrolysis was optimized without the addition of buffer substances and approx. 80 % of the cellulose contained in the pulp could be converted. Fed-batch hydrolysis proved to be the best method for achieving high glucose concentrations.

The use of wood hydrolysates for the production of ethanol by means of the co-fermentation of the yeasts S. cerevisiae and P. tannophilus could be realized in different operating modes. Yields of 60 - 80 % of the theoretically possible yield were achieved. The hydrolysates were also used for the production of biomass. Industrial yeasts were cultivated and high biomass yields were achieved.

Furthermore, experiments on simultaneous saccharification and fermentation (SSF) were carried out. These showed that neither the suboptimal temperature during this mode of operation nor the ethanol produced had a negative influence on the conversion. In addition, the ethanol concentration could be approximately doubled compared to the 2-stage process (separate hydrolysis and fermentation).