Hydrogen production

Originally on Earth, hydrogen existed mainly as water. Then plants split water into hydrogen and oxygen to form carbohydrates and protein. So huge amounts of hydrogen are combined with carbon as biomass and over time this became gas, oil, and coal.

To produce hydrogen we can:

  • split it from water
  • remove it from an organic compound,
  • steam reforming - a combination of both
Water H2O
Biomass CH2O
Gas - e.g. Methane CH4
Oil - e.g. Octane C8H18
Coal     C135H96O9NS

 

    Sources of hydrogen

    From water

    • Electrolysis of water
    • Heating water with a catalyst to split the water directly
    • Sunlight on water with a catalyst
    • Microorganisms can produce hydrogen
    • Photobiological Water Splitting

    From organic compounds

    • Fermentation: Biomass is converted into sugar-rich feedstocks that can be fermented to produce hydrogen.
    • partially burning methane or any hydrocarbon 
    • Thermal decomposition of methane (pyrolysis)

    From organic compound plus water - reforming

    Sources of global hydrogen production:

    • 50% via steam reforming of natural gas,
    • 30% from oil/naphtha reforming
    • 18% from coal gasification,
    • 3.9% from water electrolysis, and
    • 0.1% from other sources. Source

    Worldwide hydrogen production causes about 5% of the global CO2 emissions.  Source

    One kilogram of hydrogen has the same energy as 3 KG of petrol / gasoline. 

    Hydrogen is used mainly for:

    • production of NH3 - ammonia for fertiliser,
    • Reforming of oil to petrol
    • Reduction of metals from ore

    In future it will be needed for:

    • Fuel cell cars
    • Industrial heating
    • Storage of energy
    • Steelmaking

    Splitting water

    Electrolysis  

    Passing electricity through water is one of the simplest ways of producing hydrogen. If the electricity is from renewable sources, then this process produces no greenhouse gases. One aim is to have excess electricity produce hydrogen that can then be used to produce electricity when required. Like a battery, it would iron out the peaks and lows.

    Energy content of Hydrogen is 147 MJ/kg. At an efficiency of  80%, 50 kWh (180 MJ) of electricity produces 1 kilogram of hydrogen.  

    1 KG of hydrogen has the same energy as 3 KG of petrol.

    Electrolysis at Low temp.

    Low temperature electrolysis is carried out at <100oC,  with an electrolyte of an alkaline (hydroxyl ion conducting) solution, or a polymer membrane (proton conducting).

    Low temperature electrolysis is expensive, but has a few advantages:

    • on-demand (distributed) generation,
    • high purity hydrogen, 
    • unit modularity,
    • fast start-up and shutdown,
    • good load following capability that makes them suitable for integrating with intermittent renewable energy source

    Polymer electrolyte membrane (PEM)-based electrolysis systems offer additional advantages over alkaline systems:

    • higher current densities and production rate,
    • solid state system requiring no alkaline solutions or electrolyte top-up, 
    • higher purity hydrogen and
    • hydrogen generation at higher pressures 

    Companies selling Low Temp electrolysis are:

    Efficiency is 50-55%.

    Source

    Electrolysis at high temp.

    If the water, or steam, temperature is around 1000oC, then the process is more efficient because up to one third of the energy can come from  a heat source, such as solar mirrors, or nuclear. The ceramic yttria stabilised zirconia electrolyte, can transfer either O2- or H+ ions. It is the same as a solid oxide fuel cell.

    - Sunfire

    Sunfire's reversible electrolysis combines both fuel cell and electrolysis in one single device. The process electrolyses steam under high pressure (> 20 bar) and temperatures over 800 deg C. 

    Their website claims various efficiencies of 70-90 %  (Energy in H2 / electrical energy used.)  A Solid Oxide Power Core ) generates hydrogen. 

    They use the hydrogen to produce liquid fuels (-CH2-), such as diesel, or methane (CH4) by combining H2 with CO2. This is a convenient way to store H2Sunfire

    Electrolysis Very high temp nuclear hydrogen 

    One plan is to use a very high temperature (850-1,000oC) next generation nuclear reactor to generate hydrogen by high temperature electolysis. The plan is for the reactor to generate electricity by day, and hydrogen at night.

    Electrolysis at high pressure

    3% of the energy can be saved by electrolysing water at 120–200 bar (1740–2900 psi). Compressing water takes almost no energy, and the hydrogen is produced, already compressed.

    Electrolysis with catalysts

    In 2012 MIT discoved that a catalyst using cobalt and phosphate makes electrolysis more efficient.

    A startup company called Sun Catalytics was formed to exploit this discovery. It was bought by Lockheed Martin and is working on flow batteries with no mention of the catalyst.  ref  ref2

    Catalyst - Cobalt atoms on graphene 

    The best catalyst for helping the splitting of water is platinum. But it is expensive. Scientists at Rice university have taken graphene, doped it with nitrogen, and added with cobalt atoms. It can split water as well as platinum, and a lot more cheaply. It uses very little cobalt as every atom is exposed to the water because it is on the surface of the graphen, not locked up inside a metal particle.

    Water reacts at the anode to form oxygen and positively charged hydrogen ions (protons).

    The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode.

    At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas.
    Anode Reaction:    2H2O → O2 + 4H+ + 4e-
    Cathode Reaction: 4H+ + 4e- → 2H2

    ALKALINE ELECTROLYZERS

    Alkaline electrolyzers operate via transport of hydroxide ions (OH-) through the electrolyte from the cathode to the anode with hydrogen being generated on the cathode side. Electrolyzers using a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte have been commercially available for many years. Newer approaches using solid alkaline exchange membranes as the electrolyte are showing promise on the lab scale.

    SOLID OXIDE ELECTROLYZERS

    Solid oxide electrolyzers, which use a solid ceramic material as the electrolyte that selectively conducts negatively charged oxygen ions (O2-) at elevated temperatures, generate hydrogen in a slightly different way.

    Water at the cathode combines with electrons from the external circuit to form hydrogen gas and negatively charged oxygen ions.

    The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and generate electrons for the external circuit.

    Solid oxide electrolyzers must operate at temperatures high enough for the solid oxide membranes to function properly (about 700°–800°C, compared to PEM electrolyzers, which operate at 70°–90°C, and commercial alkaline electrolyzers, which operate at 100°–150°C). The solid oxide electrolyzers can effectively use heat available at these elevated temperatures (from various sources, including nuclear energy) to decrease the amount of electrical energy needed to produce hydrogen from water.  USDOE

     

     

    Graphene is an incredible single sheet of graphite.

    A new catalyst just 15 microns thick has proven nearly as effective as platinum-based catalysts but at a much lower cost, according to scientists at Rice University. The catalyst is made of nitrogen-doped graphene with individual cobalt atoms that activate the process. (Credit: Tour Group/Rice University)

    Photo-electrolysis

    The photoelectrode is a semiconducting device absorbing solar energy and simultaneously creating the necessary voltage for the direct decomposition of water molecule into oxygen and hydrogen.

    If the semiconductor photoelectrode is submerged in an aqueous electrolyte exposed to solar radiation, it will generate enough electrical energy to support the generated reactions of hydrogen and oxygen. The voltage necessary for electrolysis is about 1.35 V.

    A catalyst on the surface improves efficiency.

    Photocatalytic

    There is a lot of research into making an artificial leaf. Sunlight hits a catalyst, which then splits water molecules producing hydrogen. There are many catalysts, most are quite complex.

    Photosynthesis is about 1% efficient.  Wikipedia   Ref

    Chemical - Olivine

    Hydrogen is produced when water meets the mineral olivine under the high temperatures and pressure. In the process, olivine turns into the mineral serpentine and water splits into its components, hydrogen and oxygen. Serpentinite can be used to fix carbon dioxide. Source

    Some Photo Catalysts % Effic.
    Nickel-Molybdenum-Zinc 10%
    Pt/TiO2  - Platinum + Titanium Oxide  
    MoS2 - Molybdenum sulfide  
    molybdenum-oxo metal complex  
    WSe2 - Tungsten Diselenide  
    Bismuth 5%
    Cobalt based systems  
    NaTaO3:La 56%
    K3Ta3B2O12 6.5%
    Graphene with CdS 22%
    Iron Oxide + Titanium Oxide -  may reach 16%

      Splitting water - heat

      At 2200 °C about three percent of all H2O molecules are dissociated into various combinations of hydrogen and oxygen atoms, H, H2, O, O2, and OH. At 3000 °C more than half of the water molecules split.

      The main problem for commercial production is finding material to withstand the high temperature.

      Thermochemical cycles

      A way oif reducing thiis temperature is to use thermochemical cycles involves a series of chemical reactions driven by heat alone. Hydrogen is produced, and the chemicals recycled.

      The heat would come from solar mirrors, or nuclear reactor.

      There are over 300 processes whereby heat and chemicals can be used to produce hydrogen from water. The temperatures are around 1,000oC.

      E,G, Zinc oxide powder passes through a reactor heated by a solar concentrator operating at about 1,900°C. The zinc oxide dissociates to zinc and oxygen. The zinc reacts with water to form hydrogen gas and zinc oxide.  Source 

      2ZnO + heat → 2Zn + O2
      2Zn + 2H2O → 2ZnO + 2H2

      Thermochemical cycles

      The US Dept of Energy USDOE is developing a Very High temperature Reactor VHTR for the production of hydrogen and electricity. This would be a gen. IV nuclear reactor. The plan is to build one of 50 MW by 2017. Then it would be used to produce hydrogen by the best method discovered to date.

      In Europe, the high temperature gas cooled reactor was exploring ways of using the high temperatures produced. This work was followed up in the US by the The Gas research Institute (now the Gas Technology Institute). They looked at:

      • 200 thermochemical cycles were considered
      • 125 were considered feasible
      • 80 were tested in the lab.

      The best were:

      • Hybrid sulfur,
      • Sulfur-iodine,
      • hybrid copper sulphate 

      See end of this page for more details.

      Splitting water Photobiological

      See page on BioHydrogen

      Hydrogen from hydrocarbons

      Hydrogen can be produced from hydrocarbon fuels through four basic technologies:

      1. steam reforming (SR),
      2. partial oxidation (POX),
      3. autothermal reforming (ATR).  Source
      4. Biological processes - see Biohydrogen page

      Steam Reforming

      Reforming is a process by which the molecular structure of a hydrocarbon is rearranged to alter its properties.

      Steam methane reforming

      Steam reacts with methane to yield carbon monoxide and hydrogen.   This is the most common method of producing hydrogen.

      CH4 + H2O ⇌ CO + 3 H2

      It  is carried out at 700 – 1100 °C, with nickel based catalyst. This reaction consumes heat (endothermic, ΔHr= 206 kJ/mol)

      Next, steam is reacted with CO which removes the oxygen to leave hydrogen. 

      CO + H2O ⇌ CO2 + H2

      This is called a water gas shift reaction. It gives off heat, (exothermic,  ΔHr= -41 kJ/mol).

      Renewable Liquid Reforming: Renewable liquid fuels, such as methanol or ethanol, are reacted with high-temperature steam to produce hydrogen near the point of end use.

      Reforming of Methane - Solar gas.

      CSIRO has been developing a method of using concentrating solar thermal heat to convert methane to H2 and CO2Solar gas

      Plasma reforming

      Plasmatrons can generate temperatures >2000°C. They supply the heat for the steam reforming reaction. They are compact, and can be shut Down quickly.

      Hydrogen is generated mainly from methane and coal involving three major steps requiring separate reactors, all operating at temperatures in excess of 500°C:

      1. Methane reforming or coal gasification to produce syngas (a mixture of hydrogen and carbon monoxide) at temperatures close to 800°C;
      2. water gas shift reaction to convert carbon monoxide to hydrogen and carbon dioxide at around 500°C; and
      3. H2/CO2 separation and gas cleaning.

      Partial oxidation - Hydrocarbons, coal or biomass

      Gasification of coal

      Coal is partially burned to produce heat and CO.

      This produces synthesis gas (syngas), a mixture of CO and H2. It is how coal is gasified for use in gas turbines. For hydrogen production autothermal reforming is needed.

      Gasification of biomass

      Biomass is a bit more difficult. The feedstock is moist, and tars are produced. Small plant normally cannot afford the oxygen production equipment. If they use air, then the gas is diluted with nitrogen. The main costs are the transport of biomass, and the removal of the tars.

      CH4 + O2  ⇌  CO + 2H2

      CH4 +H2O ⇌ CO + 3H2

       

       

      Autothermal reforming

      The steam reforming process is endothermic, so needs a source of heat.  If the heat is not available, then the hydrocarbon can be partially burnt to supply the heat. Then steam is added for steam reforming to convert CO to H2 and CO2.

      CO + H2O ⇌ CO2 + H2

      Pyrolysis of hydrocarbons

      The process takes place in the absence of oxygen and air, and therefore the formation of dioxins can be almost ruled out. The products are hydrogen and carbon.  No CO2 is produced.

      Splitting of methane - Pyrolysis

      Thermal decomposition of methane in a high-temperature bubble column reactor. The column is filled with liquid metal (Pb, Sn, etc) that is at 600-1000°C. Methane rises up to the surface and is decomposed as it rises. The process is experimental

      Pyrolysis to hydrogen and carbon fibres

      A pyrolysis process, developed by Eden with the University of Queensland produces hydrogen and carbon nanofibres or carbon nanotubes. The fibres ae being used to strengthen concrete. So far it in creaseing strength about 25%.

      If successful on a commercial scale, the process could have important implications. Eden Energy

      Methane is bubbled up a liquid-metal bubble column reactor filled with molten tin at 750-900oC. The ascending methane bubbles are decomposed into hydrogen and carbon, Ref 

       

      Hydrogen may be obtained from methane by pyrolysis in the temperature range 1000°−1200°C. 

       

      Economics of Hydrogen Production

       At present, the most widely used and cheapest method for hydrogen production is the steam reforming of methane (natural gas). This method includes about half of the world hydrogen production, and hydrogen price is about US$7/GJ. A comparable price for hydrogen is provided by partial oxidation of hydrocarbons. However, greenhouse gases generated by thermochemical processes must be captured and stored, and thus, an increase in the hydrogen price by 25–30% must be considered.

      The further used thermochemical processes include gasification and pyrolysis of biomass. The price of hydrogen thus obtained is about three times greater than the price of hydrogen obtained by the steam reforming process. Therefore, these processes are generally not considered as cost competitive of steam reforming. The price of hydrogen from gasification of biomass ranges from US$10–14 /GJ and that from pyrolysis US$8.9–15.5 /GJ. It depends on the equipment, availability, and cost of feedstock.

      Electrolysis of water is one of the simplest technologies for producing hydrogen without byproducts. Electrolytic processes can be classified as highly effective. On the other hand, the input electricity cost is relatively high and plays a key role in the price of hydrogen obtained. Source

       ,

       

       

       

      Where Will the Hydrogen Come From?

        NATURAL GAS NUCLEAR SOLAR WIND BIOMASS COAL
        Gas station-size facilities using steam reformation Very High Temperature Reactors providing heat for electrolysis or for thermochemical cycles Photovoltaic systems providing electricity for electrolysis with 10% efficiency Turbines producing electricity for electrolysis, assuming they operate at 30% capacity Gasification plants using steam reformation FutureGen plants using coal gasification then steam reformation
      Raw
      Materials
      Required
      15.9 million
      cu. ft. of natural gas — only a fraction of current U.S. annual consumption
      240,000
      tons of unenriched uranium, five times today's global production
      2500
      kilowatt-hours of sun per square meter per year, found in the Southwestern states of the Sun Belt
      7
      meters per second average wind speed, typically found in many parts of the country
      1.5 billion
      tons of dry biomass (initially byproducts such as peanut shells, then concentrated crops)
      1 billion
      tons of coal — which would require doubling current U.S. domestic production
      Infrastructure 777,000
      facilities; though a more likely scenario would include a mix of larger central production plants
      2000
      600-megawatt next-generation nuclear power plants; only 103 nuclear power plants operate in the States today
      113 million
      40-kilowatt systems, covering 50% of more than 300 million acres — an area three size the size of Nevada
      1 million
      2-megawatt wind turbines, covering 5% of 120 million acres, or an area larger than California
      3300
      gasification plants, and up to 113.4 million acres — or 11% of U.S. farmland — dedicated to growing the biomass
      1000
      275-megawatt plants; only 12 sites were proposed for a DOE demonstration plant — not all met the requirements
      Total Cost $1 trillion $840 billion $22 trillion $3 trillion $565 billion $500 billion
      Price Per GGE
      (Gallon of Gas Equivalent)
      $3.00 $2.50 $9.50 $3.00 $1.90 $1
      CO2 Emissions
      measured in tons
      300 million 0 0 0 600 million* 600 million**
        *Zero net emissions because crops pull CO2 from the air. **90% will be captured and stored underground.
      Time Frame There are four fueling stations that now produce hydrogen from natural gas. The first Very High Temperature Reactor in the U.S. will be built at Idaho National Laboratory in 2021. Honda built an experimental solar-powered hydrogen refueling station at its lab in California in 2001. A 100-kilowatt turbine is now being built at the National Renewable Energy Lab in Colorado. Government funded bio-mass research will be transferred to private industry in 2015. By 2012, the first FutureGen demonstration plant should be running at 50% capacity

      Source
      Read more: Truth About Hydrogen Power - Hydrogen Energy and Fuel - Popular Mechanics 
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