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          Green Hydrogen

Here’s some basic information on one of our current projects. Using hydrogen for energy has many advantages, such as being clean – no carbon dioxide or global warming gases are produced. But there are challenges as well, especially with doing it cost effectively. Our work shows how we can develop a green hydrogen economy profitably.

Hydrogen from fossil fuel, cheap and well established

Green energy is a matter of intensive research. Any time we use fossil fuel to operate our machines and devices, we emit carbon dioxide. Most materials when they are oxidized (burnt) evolve thermal energy which can then be converted into electricity. Hydrogen is one such material which when burnt produces energy and water. The production of hydrogen on an industrial scale is a major problem. Hydrogen occurs combined with carbon as hydrocarbons such as methane and methanol or with oxygen as water. Currently hydrogen is produced from methane by the steam methane reformation (SMR) technique. In doing so for each ton of hydrogen, we generate close to 8 tons of carbon dioxide. Hydrogen can be obtained by splitting water into hydrogen and oxygen by electrolysis, which is a very energy intensive process. However, if such energy can be produced from green alternatives (wind and solar, for example), we can get hydrogen with no carbon emission.

Water and Earth to our rescue

Elements such as Mg, Al or Si are not used to react with natural oxide/sulfide ores to produce metals because they are usually expensive. Instead the oxides are reduced to the metals by such processes as carbothermal reduction. Abundantly and cheaply available coal is used in metallurgical processes adding enormously harmful carbon emission to the atmosphere. It is time to examine the myth that the elements are rare and expensive and cannot be used on an industrial scale in metallurgical processes. Elements such as Mg, Si and Al form  oxides that are major components of the Earth’s crust and are available in inexhaustible quantities. If it is feasible to obtain these elements without significant carbon emission, we can then in turn use many chemical reactions to reduce other oxide ores in the metallurgical processes and if water can be part of that reaction, we may have hydrogen coproduced with a metal. The coproduction of metals and hydrogen makes hydrogen a byproduct and therefore the production is free or highly profitable and the cost of the reactant element (e.g. Mg) is easily accommodated. 

Water is two atoms of hydrogen and an atom of oxygen; when oxygen combines with hydrogen a lot of energy is released, so hydrogen is a carrier of energy. Hydrogen does not occur as a free element on Earth in any substantial amounts; it is almost always a constituent of water. In the following table, a comparison of the energies obtainable from different solid or liquid sources – and the carbon dioxide produced – shows how important hydrogen is.



A hydride, produced from water and a metal, is reacted with an oxide ore to yield a metal and hydrogen with significant profit.

Current industrial method of hydrogen production

The current industrial method of hydrogen production gets us hydrogen at a price under $2 per kilogram, which is good – 1 kilogram of hydrogen is equivalent in energy to a gallon of gasoline – however this method uses fossil fuels. This industrial method is SMR (Steam Methane Reformation) which is based on reacting natural gas (mostly methane) with water: CH4 + H2O = CO + 3H2  and CO + H2O = CO2 + H2. As we see, this process produces carbon dioxide, a major greenhouse gas. Calculations show that for each ton of hydrogen we produce using this method, we generate 8.1 tons of CO2. Natural gas is cheap, particularly now due to fracking in USA (fracking implies fracturing the oil shales and driving out the contained hydrocarbons with CO2 fluxes; It is a very destructive process causing mini-earthquakes). So what we have now is cheap and plentiful gas, making the pursuit of any alternate renewable energy initiatives difficult. We can run our vehicles on fossil fuel in various forms (e.g. LNG, liquified natural gas or CNG, condensed natural gas) or on hydrogen obtained from the SMR process. The latter does only a little to reduce pollution but may be helpful to localize it. 

Method of reactant element: hydrogen from water

To avoid this pollution, instead of natural gas, we can use a metal to react with water. For example, Mg + H2O = MgO + H2. Unfortunately, magnesium and similar metals do not occur as free metal in the crust. Only oxides of metals occur freely and must be dissociated in order to separate the metal from the oxygen. In addition, to use hydrogen for transportation (such as to power an automobile), we need it in a more convenient, easily storable form. Hydrogen, being the smallest atom in the periodic table, will tend to diffuse out of most containers. We can liquify it, but that’s expensive. An ideal storage method would be a solid that contains hydrogen, and which releases hydrogen on demand without requiring any substantial energy input.  Magnesium hydride (MgH2) is just such a solid. 

The critical challenge is the cost of magnesium and the cost of hydrogen, when produced without fossil fuels. We assumed that Mg might cost only $2 per kilogram, but, the cost in China (via Alibaba.com) puts the price at between $1 to $10.0. That translates to many dollars per kilogram of hydrogen. This cost imbalance of producing hydrogen with renewable sources as opposed to gasoline with conventional methods makes green production and use of hydrogen a tough sell.


There is a hopeful alternative. We can produce a hydride directly by the reaction (US patent #789251(patented by me 10 years ago and then buried because of being too costly):

2 Mg + H2O = MgO + MgH2

 This produces a hydride without any emissions of carbon dioxide. It happens when we manipulate the amount of the reactants in a reactor. We get one Mg recycled back when we dissociate the hydride (MgH2) to get H2, but now one Mg is oxidized. This MgO can be sold (as a highly reactive chemical) to recover some of the cost, but still the overall price is not favorable when compared to gasoline. However, if the price of one kilogram of Mg can be brought down to between $1 to $2 /kg, calculations show that we will be able to bring down the price of a kilogram of hydrogen (equivalent in energy to 1 gallon of gas) to under $4, making it competitive with gasoline.  There are efforts to bring down the cost of producing magnesium via reducing the oxide to metal, for example the SOM (Solid Oxide Membrane) technique price of a kg of Mg is less than $1.50. 

Following figure from S.Das, JOM (2008),vol.60,no.11,p.63

Hy

The invented process (patent pending, USPTO 62725440)

The prices indicated above should be possible soon. Hydrogen from methane reformation is cheap but it is not good for the environment. To figure out a method to reduce hydrogen prices, it is proposed that we coproduce hydrogen with something that sells for a high enough price and

compensates for the high price of hydrogen (electrolysis). The invented process involves reacting the magnesium hydride with one metal oxide (ore), whereby the oxide is reduced to metal and hydrogen is released e.g. tin oxide is added to magnesium hydride which gives us magnesium oxide, tin and hydrogen (MgH2 + .5 SnO2 = MgO +.5 Sn + H2). The price of half a mole of tin (in kg) is $1305, which means that production of one mole of hydrogen gives a profit close to $1300.0. This calculation considers the materials only.

Patented process: Contact surendrasaxena8@gmail.com

Fig.1. CuS and MgH2. CuS ore  is reduced over large T-X areas; the gas is all hydrogen. A simiar phase diagram may be drawn for hydride with the tin ore cassiterite.

The prices indicated above should be possible soon. Hydrogen from methane reformation is cheap but it is not good for the environment. To figure out a method to reduce hydrogen prices, it is proposed that we coproduce hydrogen with something that sells for a high enough price and compensates for the high price of hydrogen (electrolysis). The invented process involves reacting the magnesium hydride with one metal oxide (ore), whereby the oxide is reduced to metal and hydrogen is released e.g. tin oxide is added to magnesium hydride which gives us magnesium oxide, tin and hydrogen (MgH2 + .5 SnO2 = MgO +.5 Sn + H2). The price of half a mole of tin (in kg) is $1305, which means that production of one mole of hydrogen gives a profit close to $1300.0. This calculation considers the materials only.

There are many ways to use solid hydrides; for example to power a house.

Fig.2. A solar-hydro house with a hydride container of 0.4×0.4×0.4 meters, which accommodates enough hydride for a week’s worth of typical energy use. A portion of this hydride is fed into a smaller container, which is then heated (using solar energy or another source), releasing hydrogen for daily energy consumption. This hydrogen can be fed to a fuel cell for later use, including at night. Hydrogen also has many other household uses.

Fig.3. Energy for various uses.

Using a stored hydride, large buildings, tankers and even cruise boats can be run on a combination of hydride and solar energy.  The figure above shows the amount of solar energy needed to generate hydrogen for the fuel cells that can power a house, large building or a ship (this figure is dedicated to Elon Musk!). Magnesium hydrides thus have the potential for bringing a green hydrogen economy into reality.

Surendra K Saxena is currently emeritus professor in Florida International University, Miami, Florida and at Geocentrum, Uppsala University, Sweden. He has published 452 papers and 6 books in the field of Earth and Planetary Science, High-pressure Physics and Materials Science.He is member of the Royal Swedish Academy of Sciences, Stockholm, Sweden, a recipient of La Laurea Ad Honorem in Scienze Geologiche, Padova University, Italy, 2001 and the Rudbeck Medal for academic excellence, Uppsala University, Sweden, 2007.

Also see 

more details in https://drive.google.com/file/d/18GNRBf9eFvAlI00hd90xd4H80kiaBmOB/view?usp=sharing

Sivaprasad and Saxena: Environmentally friendly electricity can come from municipal waste. Journal of Natural gas and electricity, January 2019, DOI 10.1002/gas/ Wiley or

Periodicals.https://drive.google.com/file/d/1UMQmgQk3yB5D6ttwOLcplWSn4gpaSAOA/view?usp=sharing

Saxena, S. K. Splitting CO2 into carbon and oxygen, US provisional patent 

Saxena, S.K. Splitting methane into carbon and hydrogen,  under review.