(German title: Gewinnung von Milchsäure sowie 1,2-Propandiol aus Grassilage)

Grass is a globally widespread renewable raw material with high biomass yields. For industrial use, however, the problem of storing grass cuttings must be taken into account. Ensiling is a good way of making grass cuttings suitable for long-term storage. The lactic acid fermentation that takes place during this process leads to the preservation of the grass cuttings on the one hand and on the other hand already results in an initial increase in value, as lactic acid is one of the most important platform chemicals for plastics made from renewable raw materials. In the project Utilization of silage and silage press juice as a raw material for the production of basic and fine chemicals, methods for the production of lactic acid and ethanol from silage were developed. These methods are to be further optimized and expanded in a second project phase. The second project phase is aimed at the extraction of lactic acid as an exclusive product.

A key step in a green biorefinery is the extraction and storage of raw materials in the form of silage. To date, ensiling has been optimised with regard to the properties of the silage as animal feed. As the resulting silage does not have to be optimal for a green biorefinery, the aim is to optimise the silage to improve its hydrolysability.

Typical for green biorefineries is a pressing step as primary refining, as lactic acid can be obtained from the pressed juice as an important product and the press cake can be further processed. In this project, the entire silage is to be converted into lactic acid. Therefore, the hydrolysis of the entire silage without prior separation of the organic acids from the ensiling process is being investigated as an alternative. Acidic and enzymatic hydrolysis processes are used, which will be further optimised during the course of the project.

The hydrolysates obtained in this way are used as a medium for lactic acid fermentation. Here, the influence of potential inhibitors on the fermentation must be analysed and the process adapted to the substrate. In addition, an in situ process analysis is established. Finally, the lactic acid is processed and converted to 1,2-propanediol. In addition to the processes from the first project phase, further innovative methods will be used.