Biohydrogen

As Biohydrogen is hydrogen (H ₂ ) denotes that of biomass or by means of live biomass is produced. Per Kværner-process produced hydrogen from natural gas , the usual form of industrial production of hydrogen is not called biohydrogen although the energy needed for this comes from biomass.

Hydrogen is an energy-rich gas that z. B. can be used in fuel cells to generate electricity, in internal combustion engines as fuel or in the chemical industry. At the moment, energy use does not yet play an economically relevant role. As part of the energy transition , hydrogen is being discussed as a form of storage and transport of energy in a so-called hydrogen economy .

Manufacturing

The production of hydrogen requires energy, which in the case of bio-hydrogen comes either from the biomass used as raw material or from solar energy , which is absorbed by living biomass during photosynthesis . On the other hand, the element hydrogen is required. This comes from the biomass used as a raw material or is added to the manufacturing or production process as a component of water.

Production from biomass

The production of hydrogen from biomass can take place through biological and chemical processes:

fermentation

On a laboratory scale, high-energy organic compounds in the biomass (e.g. carbohydrates , fats , proteins ) can be converted into H ₂ by fermenting bacteria in addition to CO ₂ and oxidized organic compounds . In this anaerobic process, only part of the energy contained in the biomass can be tapped by the bacteria, since oxygen is not available as an oxidizing agent . The biohydrogen formed can thus contain a large proportion of the remaining energy.

Thermochemical processing

On an industrial scale, biohydrogen can be produced from biomass (wood, straw, grass clippings, etc.) but also from other bioenergy sources ( biogas , bioethanol, etc.) through thermochemical processing (gasification or pyrolysis) and subsequent or direct steam reforming . The synthesis gas formed during gasification consists of different proportions of carbon dioxide (CO ₂ ), carbon monoxide (CO), methane (CH ₄ ), hydrogen and other components , depending on the raw material used . During steam reforming, chemical reactions take place between the water vapor and the synthesis gas components, which can increase the hydrogen yield.

${\displaystyle \mathrm {CH_{4}+H_{2}O\;{\overrightarrow {\leftarrow }}\;CO+3\ H_{2},\ \Delta H=+201,4kJ/mol} }$

( Methane + water vapor → carbon monoxide + hydrogen ; endothermic ; other equations also possible)

${\displaystyle \mathrm {CO+H_{2}O\;{\overrightarrow {\leftarrow }}\;CO_{2}+H_{2},\ \ \ \Delta H=-41,2kJ/mol} }$

( Shift reaction ; slightly exothermic )

This method of hydrogen production is used on a large scale in the production of hydrogen from natural gas, e.g. B. for the production of ammonia for nitrogen fertilizers ( Haber-Bosch process ).

The end products are essentially hydrogen (with a conversion efficiency of around 78%), carbon dioxide and mineral ash . The high-energy synthesis gas can be used to start up the plant. The process should then be energetically self-sustaining through exothermic reactions. Hydrogen production on the basis of thermochemical biomass gasification is in the experimental stage.

Advantages and disadvantages of bio-hydrogen from biomass

The use of bio-hydrogen offers various advantages and disadvantages. The evaluation depends in detail on the raw materials used, the manufacturing process and the type of use. The assessment is made more difficult by the lack of practical experience and the previously lacking relevance of bio-hydrogen production.

advantages

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In the production of hydrogen by thermochemical biomass processing ("gasification"), the process can be controlled in such a way that charcoal-like biochar granules are produced, which, together with the mineral ash that has accumulated in biomass arable land, improve soil fertility and water retention. Fortune improved especially in sandy soils.

At the same time, this procedure reduces the amount of carbon dioxide in the atmosphere. Without the introduction of biochar into the soil, only as much CO _{2 would be} released as was previously absorbed during the formation of the biomass. The carbon cycle would be closed and this type of energy would therefore be classified as almost climate-neutral. However, in order to create a correct climate balance, all upstream energy expenditure and emissions of the overall process (plant cultivation, fertilization, processing, transport, etc.) must be taken into account.

The dependence on energy imports is reduced if biomass and bio-hydrogen are produced regionally.

There is a controversial discussion about the modification effort required to make the gas supply network capable of transporting hydrogen to the end-use points. It should be taken into account that the town gas previously produced by coking plants through coal gasification already consisted of around 60% hydrogen.

disadvantage

Blue Tower in Herten in an early variant from 2003

The processing of biomass, intermediate products in production and the end product is complex. When nutrients are extracted and returned from the processed biomass in the form of mineral ash to the cultivated areas, certain elements such as nitrogen and sulfur can be lost. These then have to be replaced by the appropriate artificial fertilizer additions. Most of the processes for producing bio-hydrogen have so far only been successfully tested in pilot plants. The foundation stone for a larger demonstration facility at the Blauer Turm Herten was laid in 2009. The planned plant should produce 150 m³ of hydrogen per hour. However, the main investor, Solar Millennium , went bankrupt at the end of 2011 and the project was abandoned.

Production using biomass

Hydrogen production using algae on a laboratory scale

Living biomass (e.g. cyanobacteria , algae ) can also be used to produce biohydrogen . In some metabolic processes (e.g. photosynthesis , nitrogen fixation ) by certain enzymes (e.g. nitrogenases , hydrogenases ), hydrogen can be produced. A distinction can be made between oxygenic and anoxygenic photosynthesis.

Oxygen photosynthesis

The typical photosynthesis, e.g. B. from land plants and algae, is referred to as oxygen (oxygen-forming, see oxygenic photosynthesis ), since oxygen is released as the product of water splitting:

${\displaystyle {\begin{matrix}\mathrm {6\;CO_{2}+12\;H_{2}O\quad {\xrightarrow {h\nu }}\;C_{6}H_{12}O_{6}+6\;O_{2}+6\;H_{2}O} \qquad \Delta H^{0}=+2870\ {\frac {\mathrm {kJ} }{\mathrm {mol} }}\end{matrix}}}$

Gross reaction equation for oxygenic photosynthesis

The purpose of photosynthesis is to provide energy. However, the release of high-energy biohydrogen means a loss of energy. These processes therefore only occur under certain circumstances:

• Cyanobacteria are able to convert the important nutrient nitrogen from the difficult to access form N ₂ (e.g. present in the air or dissolved in water) into biologically accessible compounds through nitrogenases . The basis is this reaction of nitrogen fixation:

${\displaystyle \mathrm {N_{2}+8\ H^{+}+8\ e^{-}\longrightarrow 2\ NH_{3}+H_{2}\!} }$

The electrons (e ^- ) and protons (H ⁺ ) can come from the photosynthetic water splitting of the oxygen-forming photosynthesis, which is operated in parallel. The product or product gas thus contains both oxygen and hydrogen.

• Green algae also carry out oxygenic photosynthesis. Under certain circumstances, the energy-rich electrons provided during photosynthetic water splitting are not used to reduce carbon dioxide, but are converted into hydrogen molecules in a kind of idle reaction with protons (from the surrounding aqueous phase). This reaction, catalyzed by hydrogenases , is induced, for example, in the absence of oxygen.

The absorbed solar energy is not initially stored in biomass, but can be converted directly into hydrogen. Attempts are being made to make this process usable in hydrogen bioreactors .

Anoxygenic photosynthesis

During anoxygenic photosynthesis , H ₂ and CO ₂ or oxidized sulfur compounds can be formed from organic substrates or reduced sulfur compounds by phototrophic bacteria using solar energy .

Advantages and disadvantages of bio hydrogen from solar energy

The production of biohydrogen from solar energy by means of metabolic processes differ significantly or completely from the production from biomass. Thus, there are also other advantages and disadvantages.

Photosynthetic algae cultivated in algae reactors or photobioreactors can have a significantly higher energetic productivity per area than plants. During the photosynthetic production of hydrogen, the solar energy is converted directly into a final energy carrier. Conversion losses compared to the production and use of carbon-based biomass (wood, bioethanol, biodiesel , biogas etc.) could theoretically be reduced.

The cultivation of algae and bacteria is associated with high investment and operating costs. There is currently no commercial production of hydrogen using biomass. The metabolic processes in which hydrogen is generated occur in nature only to a small extent or under special conditions (stressful situations). A transfer from laboratory to production conditions is not yet in sight.

costs

According to a study by the Fraunhofer Institute for Systems and Innovation Research, the specific costs ("manufacturing costs without transport") for bio-hydrogen produced with allothermal fluidized bed gasification are around 59.0 EUR / GJ H2 (or 7.1 EUR / kg H2 ); the specific costs arising from the generation with fermentation-based plants are between 76.1 EUR / GJ H2 (or 9.1 EUR / kg H2) and 54.2 EUR / GJ H2 (or 6.5 EUR / kg H2).

Comparison with gasoline on a bulk basis

If you compare this with the "pump price" of petrol (as of January 2015) of approx. 1.20 EUR per liter (1.6 EUR / kg petrol), bio-hydrogen is at least 4 to 5.6 times more expensive than petrol .

Comparison with gasoline on a calorific value basis

This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.

This section has no evidence. - Trinitrix ( discussion ) 09:56, May 16, 2016 (CEST)

Hydrogen has a calorific value of approx. 142 MJ / kg. In terms of calorific value, the production costs of bio-hydrogen would be somewhere between

4.5 ct / MJ and 6.4 ct / MJ. Petrol has a calorific value of 43 MJ / kg, which corresponds to costs of 2.7 ct / MJ (as of January 2015). In terms of calorific value, hydrogen would be at least 1.6 to 2.37 times more expensive than gasoline.

Comparison with gasoline on a km basis

For 100 km of mileage in a petrol MPV, costs (as of January 2015) are around EUR 7.44. A comparable fuel cell vehicle currently consumes approx. 0.970 kg H2 / 100 km, which corresponds to bio-hydrogen costs of EUR 6.30 to EUR 8.82 per 100 km of travel.

perspective

The processes for the production of biohydrogen are still in development or in prototype use. Practical experience in large-scale use is still lacking. The production of hydrogen from biomass competes with biomass liquefaction . The fuels obtained in this way have a higher energy density as an energy source and are easier to handle. A final assessment is e.g. Not possible at the moment.

See also

• Renewable energy
• Hydrogen bioreactor
• Hydrogen production
• Hydrogen economy
• List of hydrogen technologies

Individual evidence

1. ↑ ^{a b} Biowasserstoff.de , private information page from Röbbe Wünschiers (Hochschule Mittweida), accessed on November 30, 2009.
2. ↑ ^{a b} Hydrogen from Biomass , Gülzower Expert Discussions, Volume 25, (PDF; 6.3 MB) published by the Agency for Renewable Raw Materials , 2006.
3. ^ TU Vienna, September 30, 2013: Energy from wood - Finally environmentally friendly hydrogen production , accessed October 8, 2013.
4. ↑ The Blue Tower ( Memento of the original from November 2, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (Source: Hydrogen Competence Center Herten). 
5. ↑ - "Light-driven hydrogen production with a" living "catalyst" , article on a BMBF project at www.innovations-report.de.
6. ↑ - www.biotechnologie.de ( Memento of the original from April 4, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Information page of the BMBF, accessed on November 30, 2009.  
7. ↑ University of Cologne, original text made available by the author Röbbe Wünschiers (version from July 18, 2007, accessed July 15, 2008), also available from Perspective on Biowasserstoff.de ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , private information page from Röbbe Wünschiers (Hochschule Mittweida), version from January 15, 2010, accessed on August 31, 2014. 
8. ↑ - Report of the Federal Environment Agency on the use of microalgae ( Memento of July 21, 2009 in the Internet Archive ), last update on March 16, 2009, accessed on December 4, 2009.
9. ^ Roman Büttner, Christoph Stockburger: The hydrogen offensive of Peter Ramsauer . MIRROR ONLINE. June 19, 2012. Retrieved January 28, 2019.
10. ↑ Ulf Bossel, Theory and Practice, April 2006: Hydrogen does not solve energy problems , accessed September 24, 2014

Web links

• Hy-NOW Evaluation of the processes and technologies for the supply of hydrogen on the basis of biomass
• Thermochemical production of hydrogen from biomass with special consideration of raw gas reforming
• Bio hydrogen economy
• Wired-Mutant Algae Is Hydrogen Factory (English)
• FAO - Hydrogen production (English)
• Maximizing Light Utilization Efficiency and Hydrogen Production in Microalgal Cultures (English, 384 kB, PDF file)