Epsilon Archive for Student Projects

Abstract

A transition in the current energy system is needed for multiple reasons. For example, fossil fuels are depleting and have a major impact on the climate. A shortage of renewable ener-gies, under and over production at peak times are examples of the challenges the indus-try/research are facing today. Current research shows that Hydrogen can be a component to renewable energy integration, and thus a positive component in the energy transition towards a sustainable and stable power supply. However, producing hydrogen requires large amounts of electric energy, but can’t be easily stored.

To facilitate transportation and storage, hydrogen can be converted into organic acids. Pri-marily acetic acid with a process that incorporates carbon dioxide and hydrogen in a trickle-bed reactor. It is known that acetic acid plays a key role in biogas plants, where it contrib-utes to methane generation. This thesis explores the conversion of hydrogen into organic acids under different environmental conditions to identify the factors that achieve the high-est production rates. The resulting liquid product is then tested as a substrate in a biogas reactor, and its impact on gas production is compared with that of two reference reactors.

Through the analytical methods used in this research—including measurements of volatile fatty acids, gas composition, gas flow, temperature, and pH—it was shown that, at its peak, the trickle-bed reactor achieved an acetic acid concentration of 12.4 g/L with a maximum production rate of 3.83 g/L per day. The process performed better at higher pH values around 9 compared to lower pH values around 6. Using this acetate substrate, methane gas production in the biogas reactor was 36% higher than in the reference system over one retention time. The results show that higher pH levels in the trickle-bed reactor improve the conversion of hydrogen to acetic acid and increase methane production, supporting its use in microbial Power-to-Gas solutions and as renewable energy storage.