Thermochemical Refining of Biomass

The consistent use of renewable energy sources reduces the dependence on fossil raw materials and also contributes to the reduction of CO₂ emissions. Whereas water power, geothermal energy, solar energy and wind power are suitable primarily for the generation of electric power and heat, biomass is the only renewable carbon source and thus is of particular importance for the production of fuels and organic key chemicals. Accordingly, the efficient use of this unique property of biomass is of particular importance.

 

In this context, the department is making contributions in two future-oriented fields:

 

1. Preparation of synthesis gas and synthetic fuels from dry biomass

The bioliq® process allows preparation of synthetic fuels from dry residual biomass. They have higher purity and therefore better environmental compatibility and provide higher power than petroleum-based fuels and can be tailored to the requirements of automotive manufacturers also in view of the ever more stringent exhaust gas standards. Our development is directed primarily at using relatively low-cost, previously largely unused biomass, such as crop straw, animal hay or residual wood. They contain more ash and heteroatoms than, for example, bark-free wood and make it necessary to develop suitably adapted processes. The obstacles that have often prevented an efficient use of biomass were its low energy density and its regionally variable distribution, requiring long transport routes, making their use uneconomical. This problem is solved by the bioliq concept, by first subjecting the biomass to fast pyrolysis in decentralized plants, producing an energy-dense intermediate composed of pyrolysis oil and pyrolysis char. The resulting bio slurry is then reacted in a large-sized central entrained flow pressurized gasifier at pressures of up to 80 bar and temperatures above 1200°C to give synthesis gas, from which fuels, but also a large variety of other organic key chemicals can be prepared using customary chemical processes.

 

2. Generation of Hydrogen from Wet Biomass

The second process development is used for the generation of hydrogen by hydrothermal gasification of wet biomass. Hydrogen is of great interest as secondary energy source, in particular against the backdrop of its use in fuel cells. The handling of hydrogen also raises issues concerning safety or its storage based on nanomaterials. These will be dealt with in the interdisciplinary research group of the research centre, the HyTechGroup. The starting materials of hydrothermal gasification are biomasses having a water content of up to 90%. They can be residues from agriculture, but also from the foodstuff or beverage industries. At temperatures of up to 700°C and pressures of up to 300 bar, the biomass reacts almost completely with water to give hydrogen, methane and carbon dioxide as the main products. The carbon dioxide can be efficiently removed from the product gas down to a small residual content by means of a water wash under pressure. In the experimental plant VERENA, the technical development of this process is pushed ahead. In parallel fundamental issues regarding the chemical sequence of hydrothermal conversion of biomass are investigated. The results of this work will allow the process to be improved in terms of reaction engineering and to be applied to other applications, such as the direct liquefaction of biomass, which may lead to other possible uses.