To support the sustainability of the future hydrogen economy, hydrogen has to come from renewable resources. Therefore hydrogen should be produced from water using green electricity from solar or wind energy or from biomass
In HyTIME, 6 industries, 2 universities and 1 research organisation have worked together to develop a process for production of hydrogen, at low temperature, from biomass resources having a high moisture content. This process is based on fermentation with natural micro-organisms and is an alternative to gasification of biomass. HyTIME leans heavily on the technology of anaerobic digestion but is special in having hydrogen as its product. In anaerobic digestion hydrogen is an intermediate product which is immediately consumed by hydrogen eating bacteria which make methane. In HyTIME the processes in anaerobic digestion are separated to make first a hydrogen fermentation which is then followed by methane production in separate anaerobic digester. Hydrogen is harvested and purified to make a product whereas the methane in the biogas is used to cover the heat demand of the process.
HyTIME has started with the successful mobilization of sugars from verge grass and wheat straw using mechanical and chemical pretreatment, followed by enzymatic hydrolysis. Hydrogen and subsequent methane production from wheat straw hydrolysates were successfully tested in simple stirred tank reactors. Although the hydrogen concentration in the raw gas was high (44% v/v), productivity and yield were fairly low. Hydrogen production from verge grass hydrolysate was tested in a dedicated high cell density reactor. Here hydrogen productivity and yield were high but the hydrogen concentration in the raw gas was lower (19%) due to dilution with nitrogen which is used as stripping gas in the dedicated reactor. Methane production using the effluent from the hydrogen reactor was successful. The volume of the dedicated hydrogen reactor was scaled up to 225L but as a result of contamination causing a decrease in yield, hydrogen productivity halted at 109 g hydrogen/day. For online monitoring and control of the fermentation special devices to measure performance indicators were developed and installed together with sensors for pH, pressure flow rate etc. Automation and visualization was realized to facilitate the management of the fermentation by means of a smart phone.
In order to enable efficient hydrogen upgrading, several membrane contactors were tested for removal of carbon dioxide from the fermenter off gas and the proof of principle was delivered by connecting 2 modules to the hydrogen reactor. At the same time, applicability and cost effects of conventional gas upgrading methods (VSA and PSA) were modelled and simulated for the recovery of hydrogen from the raw gas at low volumetric concentration, pressure and temperature.
For system integration all technological data over the entire process chain were collected to form the backbone of the simulation model for the techno-economic assessment at commercial scale. Optimization options for the process were identified. The foreseen methane production in the anaerobic digester would be sufficient to cover the heat demand of optimized process. Among the assessed process routes the chemical pretreatment of verge grass with lime seems to be the most favorable route concerning economics. In general, major cost contributions to hydrogen production costs resulted from biomass pretreatment. Besides lowering enzyme and chemical costs an increase of sugar yields and avoidance of sugar losses would improve the techno-economic results.