Production of fine and bulk chemicals using silage as a renewable resource

The presented work aims for the use of silage as a renewable resource for the fermentative production of bulk- and fine chemicals and is a cooperation with the Institute of Thermal Process Engineering at the University of Kaiserslautern and the Institute of Biochemical Engineering at the Saarland University.
In 2006 321,300 ha of farmland were used for the production of grass and clover, yielding 36,268,000 t of harvested grass clip. Thus, grass clip provides an enormous potential as renewable resource in Germany. Since fresh grass clip is available only during summer and it decays if stored inappropriately, it is conserved by ensiling.
In the ensiling process, the water-soluble carbohydrates are fermented to lactic acid, resulting in a pH-shift and thus the conservation of the silage. The processes in development are to use the remaining carbohydrates, including cellulose and hemicellulose, as well as the lactic acid produced during ensiling. Aspired products are ethanol, 1,2-propanediole, itaconic and succinic acid. Remnants and wastes of the processes should be reuseable as animal food or in biogas production, resulting in a complete substantial and energetic utilisation of the silage.
In the presented work two strategies for the utilization of silage are pursued:
First, a silage juice containing the water-soluble carbohydrates and the lactic acid is won directly from the silage by pressing. This silage juice can either be used directly as a cultivation medium or by the isolation of the contained lactic acid, the main product of ensiling, and its further use.
Secondly, the hydrolysis of the celluloses and hemicelluloses contained in the silage is aspired. After the separation of solid and liquid phases the latter, a mixture of organic acids produced during ensiling and pentoses and hexoses released during hydrolysis, is fermented.
Taken together the described work is able to offer an all-season renewable resource for the production of base and fine chemicals and to increase the value of an agricultural product respectively to improve the economics of biogas production.
The Project is funded by the Fachagentur für Nachwachsende Rohstoffe (22025407 (07NR254)).