Biohydrogen (gasification)

Besides production of biohydrogen from biogas, it can also be produced through gasification of biomass, similar to the production of bio-SNG, which was discussed above. A gasification method has to be used that produces a gas with higher hydrogen content. Otherwise, additional steam reforming is needed to convert methane into hydrogen. Water gas shift is used to increase the hydrogen yield. Then the remaining CO2 is removed by pressure swing adsorption or ceramic membrane separation, which leaves bio-hydrogen, which is to be used as an automotive fuel. In order to use it in this way, it has to be compressed or liquefied, or stored in metal hydrides. Hydrogen can be used in either internal combustion engines or fuel cells. Since fuel cell vehicles are not commercially available yet and a distribution infrastructure for hydrogen cannot be realised in the short term, bio-hydrogen is considered a longer-term option for the transport sector.

The main challenges for further development of biohydrogen are similar to those of other gasification-derived biofuels (except SNG), which have been discussed earlier in this section. Supercritical gasification, which was discussed earlier in this section as an option for the production of SNG, is also a useful technology for production of biohydrogen. However, in that case, steam reforming is necessary to convert the formed methane into hydrogen, which makes the process more expensive. Another option to produce hydrogen from wet biomass, which is also still at lab scale, is a technology called dark and photo fermentation. Hydrogen can be produced directly by anaerobic digestion (biogas), which was discussed earlier. Dark fermentation is a similar process, however, it is manipulated in such a way that the desired end-product - hydrogen - is produced directly without the forming of methane, whereas hydrogen is normally an intermediate product in anaerobic digestion. During dark fermentation, besides hydrogen, organic acids are produced, which can be converted to hydrogen by a process called photo fermentation.