Hydrogen production
Encyclopedia
Hydrogen production is the family of industrial methods for generating hydrogen. Currently the dominant technology for direct production is steam reforming
from hydrocarbon
s. Many other methods are known including electrolysis
and thermolysis. The discovery and development of less expensive methods of production of bulk hydrogen is relevant to the establishment of a hydrogen economy
.
In 2006, the United States was estimated to have a production capacity of 11 million tonnes of hydrogen. 5 million tonnes of hydrogen were consumed on-site in oil refining, and in the production of ammonia (Haber process
) and methanol (reduction of carbon monoxide
). 0.4 tonnes were an incidental by-product of the chlor-alkali process.
with approximately 80% efficiency, or from other hydrocarbon
s to a varying degree of efficiency. Specifically, bulk hydrogen is usually produced by the steam reforming
of methane or natural gas At high temperatures (700–1100 °C), steam (H2O) reacts with methane
(CH4) to yield syngas
.
In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction
, performed at about 130 °C:
Essentially, the oxygen
(O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
(CO2). Since the production is concentrated in one facility, it is possible to separate the CO2 and dispose of it properly, for example by injecting it in an oil or gas reservoir (see carbon capture), although this is not currently done in most cases. A carbon dioxide injection project has been started by a Norwegian
company StatoilHydro
in the North Sea
, at the Sleipner field
. This is disputed in The Hype about Hydrogen
: Fact and Fiction in the Race to Save the Climate, a book by Joseph J. Romm
, published in 2004 by Island Press and updated in 2005. Romm says that directly burning fossil fuels generates less CO2 than hydrogen production.
Integrated steam reforming / co-generation - It is possible to combine steam reforming and co-generation of steam
and power
into a single plant. This can deliver benefits for an oil refinery
because it is more efficient than separate hydrogen
, steam
and power
plants. Air Products recently built an integrated steam reforming / co-generation plant in Port Arthur, Texas
.
reaction occurs when a substoichiometric
fuel-air mixture is partially combusted
in a reformer, creating a hydrogen-rich syngas
. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX). The chemical reaction takes the general form:
Idealized examples for heating oil and coal, assuming compositions C12H24 and C24H12 respectively, are as follows:
or Kvaerner carbon black
& hydrogen
process (CB&H) is a plasma reforming method, developed in the 1980s by a Norwegian
company of the same name, for the production of hydrogen and carbon black
from liquid hydrocarbons (CnHm). Of the available energy of the feed, approximately 48% is contained in the hydrogen, 40% is contained in activated carbon
and 10% in superheated steam. CO2 is not produced in the process.
A variation of this process is presented in 2009 using plasma arc waste disposal
technology for the production of hydrogen, heat and carbon from methane and natural gas in a plasma converter
can be converted into syngas
and methane
, also known as town gas, via coal gasification
. Syngas consists of hydrogen and carbon monoxide. Another method for conversion is low temperature and high temperature coal carbonization.
-stabilized zirconium together with nickel.
(S-I cycle) is a thermochemical process which generates hydrogen from water, but at a much higher efficiency than water splitting. The sulfur and iodine used in the process are recovered and reused, and not consumed by the process. It is well suited to production of hydrogen by high-temperature nuclear reactors or by concentrating solar power systems (CSP).
and waste streams can in principle be converted into biohydrogen
with biomass gasification
, steam reforming or biological conversion like biocatalysed electrolysis or fermentative hydrogen production.
is the fermentative conversion of organic substrate to biohydrogen
manifested by a diverse group of bacteria
using multi enzyme
systems involving three steps similar to anaerobic conversion
. Dark fermentation
reactions do not require light energy, so they are capable of constantly producing hydrogen
from organic compounds throughout the day and night. Photofermentation
differs from dark fermentation
because it only proceeds in the presence of light
. For example photo-fermentation with Rhodobacter sphaeroides
SH2C can be employed to convert small molecular fatty acids into hydrogen.
Fermentative hydrogen production can be done using direct biophotolysis by green algae, indirect biophotolysis by cyanobacteria, photo-fermentation by anaerobic photosynthetic bacteria and dark fermentation by anaerobic fermentative bacteria. For example studies on hydrogen production using H. salinarium, an anaerobic photosynthetic bacteria, coupled to a hydrogenase donor like E. coli, are reported in literature.
Biohydrogen can be produced in bioreactors that utilize feedstocks, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO2. The CO2 can be sequestered successfully by several methods, leaving hydrogen gas. A prototype hydrogen bioreactor using waste as a feedstock is in operation at Welch's grape juice factory in North East, Pennsylvania (U.S.).
The key technology is cell-free synthetic enzymatic pathway biotransformation (SyPaB). A biochemist can understand it as "glucose oxidation by using water as oxidant". A chemist can describe it as "water splitting by energy in carbohydrate". A thermodynamics scientist can describe it as the first entropy-driving chemical reaction that can produce hydrogen by absorbing waste heat
. In 2009, cellulosic materials were first used to generate high-yield hydrogen. Furthermore, the use of carbohydrate as a high-density hydrogen carrier was proposed so to solve the largest obstacle to the hydrogen economy and propose the concept of sugar fuel cell vehicles.
Synthetic biology
(electrolysis using microbes) is another possibility. Using microbial fuel cell
s, wastewater or plants can be used to generate power. Biocatalysed electrolysis should not be confused with biological hydrogen production
, as the latter only uses algae and with the latter, the algae itself generates the hydrogen instantly, where with biocatalysed electrolysis, this happens after running through the microbial fuel cell and a variety of aquatic plants can be used. These include reed sweetgrass
, cordgrass, rice, tomatoes, lupines, algae
to produce hydrogen in a steam reformer, and the other is to use renewable power to produce hydrogen from electrolysis. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is a renewable fuel.
.
Hydrogen
is mainly used for the production of ammonia
via Haber process
. In this case, the hydrogen is produced in situ. Ammonia is the major component of most fertilizer
s.
Earlier it was common to vent the surplus hydrogen
off, nowadays the process systems are balanced with hydrogen pinch
to collect hydrogen
for further use.
Hydrogen
is also produced as a by-product
of industrial chlorine production by electrolysis. Although requiring expensive technologies, hydrogen can be cooled, compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.
Steam reforming
Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...
from hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s. Many other methods are known including electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
and thermolysis. The discovery and development of less expensive methods of production of bulk hydrogen is relevant to the establishment of a hydrogen economy
Hydrogen economy
The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
.
In 2006, the United States was estimated to have a production capacity of 11 million tonnes of hydrogen. 5 million tonnes of hydrogen were consumed on-site in oil refining, and in the production of ammonia (Haber process
Haber process
The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron or ruthenium catalyst, which is used to industrially produce ammonia....
) and methanol (reduction of carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
). 0.4 tonnes were an incidental by-product of the chlor-alkali process.
Steam reforming
Fossil fuels are the dominant source of industrial hydrogen. Hydrogen can be generated from natural gasNatural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
with approximately 80% efficiency, or from other hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s to a varying degree of efficiency. Specifically, bulk hydrogen is usually produced by the steam reforming
Steam reforming
Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...
of methane or natural gas At high temperatures (700–1100 °C), steam (H2O) reacts with methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
(CH4) to yield syngas
Syngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...
.
- CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol
Water gas shift reaction
The water-gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen:The water-gas shift reaction is an important industrial reaction. It is often used in conjunction with steam reforming of methane or other hydrocarbons, which is...
, performed at about 130 °C:
- CO + H2O → CO2 + H2 - 40.4 kJ/mol
Essentially, the oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
CO2 sequestration
Steam reforming generates carbon dioxideCarbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2). Since the production is concentrated in one facility, it is possible to separate the CO2 and dispose of it properly, for example by injecting it in an oil or gas reservoir (see carbon capture), although this is not currently done in most cases. A carbon dioxide injection project has been started by a Norwegian
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
company StatoilHydro
StatoilHydro
Statoil ASA, trading as Statoil and formerly known as StatoilHydro, is a Norwegian energy company, formed by the 2007 merger of Statoil with the oil and gas division of Norsk Hydro. The Government of Norway is the largest shareholder in Statoil with 67% of the shares...
in the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
, at the Sleipner field
Sleipner gas field
The Sleipner gas field is a natural gas field in the North Sea, about west of Stavanger, Norway. Two parts of the field are in production, Sleipner West , and Sleipner East . The field produces natural gas and light oil condensates from sandstone structures about below sea level. It is operated...
. This is disputed in The Hype about Hydrogen
The Hype about Hydrogen
The Hype about Hydrogen: Fact and Fiction in the Race to Save the Climate is a book by Joseph J. Romm, published in 2004 by Island Press and updated in 2005. The book has been translated into German as Der Wasserstoff-Boom...
: Fact and Fiction in the Race to Save the Climate, a book by Joseph J. Romm
Joseph J. Romm
Joseph J. Romm is an American author, blogger, physicist and climate expert who concentrates on methods of reducing greenhouse gas emissions and global warming and increasing energy security through energy efficiency, green energy technologies and green transportation technologies...
, published in 2004 by Island Press and updated in 2005. Romm says that directly burning fossil fuels generates less CO2 than hydrogen production.
Integrated steam reforming / co-generation - It is possible to combine steam reforming and co-generation of steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
and power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
into a single plant. This can deliver benefits for an oil refinery
Oil refinery
An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...
because it is more efficient than separate hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
and power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
plants. Air Products recently built an integrated steam reforming / co-generation plant in Port Arthur, Texas
Port Arthur, Texas
-Demographics:As of the 2000 census, there were 57,755 people, 21,839 households, and 14,675 families residing in the city. The population density was 696.5 people per square mile . There were 24,713 housing units at an average density of 298.0 per square mile...
.
Partial oxidation
The partial oxidationPartial oxidation
Partial oxidation is a type of chemical reaction. It occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas which can then be put to further use, for example in a fuel cell...
reaction occurs when a substoichiometric
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
fuel-air mixture is partially combusted
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
in a reformer, creating a hydrogen-rich syngas
Syngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...
. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX). The chemical reaction takes the general form:
- CnHm + n/2 O2 → n CO + m/2 H2
Idealized examples for heating oil and coal, assuming compositions C12H24 and C24H12 respectively, are as follows:
- C12H24 + 6 O2 → 12 CO + 12 H2
- C24H12 + 12 O2 → 24 CO + 6 H2
Plasma reforming
The Kværner-processKværner-process
The Kværner-process or Kvaerner carbon black & hydrogen process is a method, developed in the 1980s by Aker Solutions of Norway, for the production of hydrogen from hydrocarbons , such as methane, natural gas and biogas.- Description :...
or Kvaerner carbon black
Carbon black
Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
& hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
process (CB&H) is a plasma reforming method, developed in the 1980s by a Norwegian
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
company of the same name, for the production of hydrogen and carbon black
Carbon black
Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
from liquid hydrocarbons (CnHm). Of the available energy of the feed, approximately 48% is contained in the hydrogen, 40% is contained in activated carbon
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...
and 10% in superheated steam. CO2 is not produced in the process.
A variation of this process is presented in 2009 using plasma arc waste disposal
Plasma arc waste disposal
Plasma arc gasification or Plasma Gasification Process abbreviated PGP is a waste treatment technology that uses electrical energy and the high temperatures created by an electric arc gasifier. This arc breaks down waste primarily into elemental gas and solid waste , in a device called a plasma...
technology for the production of hydrogen, heat and carbon from methane and natural gas in a plasma converter
Coal
CoalCoal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
can be converted into syngas
Syngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...
and methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, also known as town gas, via coal gasification
Coal gasification
Coal gasification is the process of producing coal gas, a type of syngas–a mixture of carbon monoxide , hydrogen , carbon dioxide and water vapour –from coal...
. Syngas consists of hydrogen and carbon monoxide. Another method for conversion is low temperature and high temperature coal carbonization.
From water
Many technologies have been explored but it should be noted that as of 2007 "Thermal, thermochemical, biochemical and photochemical processes have so far not found industrial applications." Only high temperature electrolysis of alkaline solutions finds some applications.Electrolysis
Approximately 5% of industrial hydrogen is produced by the electrolysis. Two types of cells are popular, solid oxide electrolysis cells (SOEC's) and alkaline electrolysis cells (AEC's) . These cells optimally operate at high concentrations electrolyte (KOH or potassium carbonate) and at high temperatures, often near 200 °C. Typical catalysts are yttriumYttrium
Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...
-stabilized zirconium together with nickel.
Thermolysis
Water spontaneously dissociates at around 2500 C, but this thermolysis occurs at temperatures too high for usual process piping and equipment. Catalysts are required to reduce the dissociation temperature.Photocatalytic water splitting
The conversion of solar energy to hydrogen by means of water splitting process is one of the most interesting ways to achieve clean and renewable energy systems. However if this process is assisted by photocatalysts suspended directly in water instead of using photovoltaic and an electrolytic system the reaction is in just one step, therefore it can be more efficient.Sulfur-iodine cycle
The sulfur-iodine cycleSulfur-iodine cycle
The sulfur–iodine cycle is a three-step thermochemical cycle used to produce hydrogen.The S–I cycle consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen. All other chemicals are recycled...
(S-I cycle) is a thermochemical process which generates hydrogen from water, but at a much higher efficiency than water splitting. The sulfur and iodine used in the process are recovered and reused, and not consumed by the process. It is well suited to production of hydrogen by high-temperature nuclear reactors or by concentrating solar power systems (CSP).
Biohydrogen routes
Although of no industrial significance, biomassBiomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
and waste streams can in principle be converted into biohydrogen
Biohydrogen
Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.-Introduction:...
with biomass gasification
Gasification
Gasification is a process that converts organic or fossil based carbonaceous materials into carbon monoxide, hydrogen, carbon dioxide and methane. This is achieved by reacting the material at high temperatures , without combustion, with a controlled amount of oxygen and/or steam...
, steam reforming or biological conversion like biocatalysed electrolysis or fermentative hydrogen production.
Fermentative hydrogen production
Fermentative hydrogen productionFermentative hydrogen production
Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are...
is the fermentative conversion of organic substrate to biohydrogen
Biohydrogen
Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.-Introduction:...
manifested by a diverse group of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
using multi enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
systems involving three steps similar to anaerobic conversion
Anaerobic digestion
Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. It is used for industrial or domestic purposes to manage waste and/or to release energy....
. Dark fermentation
Dark fermentation
Dark fermentation is the fermentative conversion of organic substrate to biohydrogen. It is a complex process manifested by diverse group of bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion...
reactions do not require light energy, so they are capable of constantly producing hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
from organic compounds throughout the day and night. Photofermentation
Photofermentation
Photofermentation is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of photosynthetic bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion...
differs from dark fermentation
Dark fermentation
Dark fermentation is the fermentative conversion of organic substrate to biohydrogen. It is a complex process manifested by diverse group of bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion...
because it only proceeds in the presence of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. For example photo-fermentation with Rhodobacter sphaeroides
Rhodobacter sphaeroides
Rhodobacter sphaeroides is a kind of purple bacteria; a group of bacteria that can obtain energy through photosynthesis. Its best growth conditions are anaerobic phototrophy and aerobic chemoheterotrophy in the absence of light. R. sphaeroides is also able to fix nitrogen...
SH2C can be employed to convert small molecular fatty acids into hydrogen.
Fermentative hydrogen production can be done using direct biophotolysis by green algae, indirect biophotolysis by cyanobacteria, photo-fermentation by anaerobic photosynthetic bacteria and dark fermentation by anaerobic fermentative bacteria. For example studies on hydrogen production using H. salinarium, an anaerobic photosynthetic bacteria, coupled to a hydrogenase donor like E. coli, are reported in literature.
Biohydrogen can be produced in bioreactors that utilize feedstocks, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO2. The CO2 can be sequestered successfully by several methods, leaving hydrogen gas. A prototype hydrogen bioreactor using waste as a feedstock is in operation at Welch's grape juice factory in North East, Pennsylvania (U.S.).
Enzymatic hydrogen generation
Due to the Thauer limit (four H2/glucose) for dark fermentation, a non-natural enzymatic pathway was designed that can generate 12 moles of hydrogen per mole of glucose units of polysaccharides and water in 2007. The stoichiometric reaction is:- C6H10O5 + 7 H2O → 12 H2 + 6 CO2
The key technology is cell-free synthetic enzymatic pathway biotransformation (SyPaB). A biochemist can understand it as "glucose oxidation by using water as oxidant". A chemist can describe it as "water splitting by energy in carbohydrate". A thermodynamics scientist can describe it as the first entropy-driving chemical reaction that can produce hydrogen by absorbing waste heat
Waste heat
Waste heat sometimes called Secondary heat or Low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat...
. In 2009, cellulosic materials were first used to generate high-yield hydrogen. Furthermore, the use of carbohydrate as a high-density hydrogen carrier was proposed so to solve the largest obstacle to the hydrogen economy and propose the concept of sugar fuel cell vehicles.
Synthetic biology
Synthetic biology
Synthetic biology is a new area of biological research that combines science and engineering. It encompasses a variety of different approaches, methodologies, and disciplines with a variety of definitions...
Biocatalysed electrolysis
Besides dark fermentation, electrohydrogenesisElectrohydrogenesis
Electrohydrogenesis or biocatalyzed electrolysis is the name given to a process for generating hydrogen gas from organic matter being decomposed by bacteria. This process uses a modified fuel cell to contain the organic matter and water...
(electrolysis using microbes) is another possibility. Using microbial fuel cell
Microbial fuel cell
A microbial fuel cell or biological fuel cell is a bio-electrochemical system that drives a current by mimicking bacterial interactions found in nature....
s, wastewater or plants can be used to generate power. Biocatalysed electrolysis should not be confused with biological hydrogen production
Biological hydrogen production
Biohydrogen reactors use a method of photobiological water splitting which is done in a closed photobioreactor based on the production of hydrogen by algae. Algae produce hydrogen under certain conditions. In 2000 it was discovered that if C...
, as the latter only uses algae and with the latter, the algae itself generates the hydrogen instantly, where with biocatalysed electrolysis, this happens after running through the microbial fuel cell and a variety of aquatic plants can be used. These include reed sweetgrass
Glyceria maxima
Glyceria maxima Holmb. is a species of rhizomatous perennial grasses in the mannagrass genus native to Europe and Western Siberia and growing in wet areas such as riverbanks and ponds...
, cordgrass, rice, tomatoes, lupines, algae
Renewable hydrogen
Currently there are several practical ways of producing hydrogen in a renewable industrial process. One is to use landfill gasLandfill gas
Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill.-Production:Landfill gas production results from chemical reactions and microbes acting upon the waste as the putrescible materials begins to break down in the landfill...
to produce hydrogen in a steam reformer, and the other is to use renewable power to produce hydrogen from electrolysis. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is a renewable fuel.
Use of hydrogen
Hydrogen is mainly used for the conversion of heavy petroleum fractions into lighter ones via the process of hydrocracking and other petroleum fractions (dehydrocyclization and the aromatization process). It is also required for cleaning fossil fuels via hydrodesulfurizationHydrodesulfurization
Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur from natural gas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils...
.
Hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
is mainly used for the production of ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
via Haber process
Haber process
The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron or ruthenium catalyst, which is used to industrially produce ammonia....
. In this case, the hydrogen is produced in situ. Ammonia is the major component of most fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
s.
Earlier it was common to vent the surplus hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
off, nowadays the process systems are balanced with hydrogen pinch
Hydrogen pinch
Hydrogen pinch analysis is a hydrogen management method that originates from the concept of heat pinch analysis. HPA is a systematic technique for reducing hydrogen consumption and hydrogen generation through integration of hydrogen-using activities or processes in the petrochemical industry,...
to collect hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
for further use.
Hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
is also produced as a by-product
By-product
A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....
of industrial chlorine production by electrolysis. Although requiring expensive technologies, hydrogen can be cooled, compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.