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A method of producing Hydrogen from water

Preamble to the Description

[0001] The following specification particularly describes the invention and the manner in which it is to be performed.


Technical field of the invention

[0002] The present invention relates to a method to produce hydrogen from water. The invention is specifically a method of producing hydrogen economically and which is free from carbon emission.

Background of the invention

[0003] Hydrogen is a very important source of energy in today’s world. Its production, storage and transportation constitute an important branch of study and research. Many path-breaking industrial processes have been devised and attempted to undertake profitable production of hydrogen from various sources. Further many of the known methods of producing hydrogen result in carbon emission due to use of fossil fuels.

[0004] The current industrial method of hydrogen production gets us hydrogen at a price comparable to that of gasoline. The industrial method uses the Steam Methane Reformation (SMR) technique as mentioned in US patent number 9,233,847 (2005) which is based on reacting natural gas (mostly methane) with water for Hydrogen production. Calculations show that for each ton of hydrogen that is produced, 8.1 tons of CO2 is generated. The production cost works to about 1.65$/kg of Hydrogen. This is cheap, particularly now, due to fracturing the oil shales and driving out the contained hydrocarbons with CO2 which is called fracking. It is a very destructive process causing mini-earthquakes.

[0005] Electrolysis of water is another method which produces hydrogen with little or no carbon emission, but the method is very energy intensive and if this energy comes from fossil fuel, it adds up to the pollution problem. C. Philbert (2017) Commentary titled “Producing industrial hydrogen from renewable Energy”. Based on reference“Gerlach, A.-K et al. (2011), PV and wind power -complementary technologies, 26th European Photovoltaic Solar Energy Conference Hamburg (GE), 5-9 September” discloses one such process wherein price for a kilogram of ¾ could be as low as $3.0 per kilogram using electrolysis of water.

[0006] US patent number 7892521B2 titled“Synthesis and use of metal hydrides for vehicular and other applications” discloses a method of producing Hydrogen using metal hydride which is convenient and safe for transportation. The Magnesium hydride used for Hydrogen production is formed either by combining hydrogen with magnesium metal as shown in reaction (1)

Mg (s) + H2 (g) ^MgH2 (s) - (1)

Or by adjusting the proportions of Mg and water in the reaction as shown in the

reaction (2) below-

[0007] Reaction (1) requires hydrogen already produced by the SMR technique as referred above and based on fossil fuel. Hydrogen is then obtained by heating the hydride or by further reacting with water or other oxides. The patented process for production of hydride is (2) in the invention wherein use of fossil fuel is avoided. However, the cost of production in this process is high due to price of Magnesium. There is one additional MgO to be recycled.

[0008] Magnesium hydride is an excellent hydrogen storage material and can be transported in a powder form or as oil-based slurry. It releases hydrogen on demand without requiring any substantial energy input.

[0009] The reaction (2) mentioned above is an exothermic reaction and require no significant energy. However, both the elements Mg and ¾ require expensive methods for their extraction from their respective oxide, which is their principal mode of occurrence. There are kinetic problems in the hydrolysis of Mg but by adjusting the temperature and grain size, such problems are solved.

[0010] Krishnan, A, Pal, U.B. and Lu,X. (2005) Solid Oxide Membrane Process for Magnesium Production Directly From Magnesium Oxide, Metallurgical and Materials Transactions B 36(4):463-473 mentions a method for Mg production by electrolytic method using solid oxide membrane as shown below:

MgO -> Mg

If the above process does not use coal as a source of energy it can be made emission free while the corresponding process using coal power results in emission of 11.28 kg of CC per Kg of Magnesium produced.

[0011] The patent application US20090202413A1 relates to a system of processes for sequestering carbon in coal- burning power plant and producing hydrogen gas that take advantage of emission of CO and CO2 and heat from the plants. The use of this invention leads to cheap hydrogen and hydride production and carbon sequestration and reduced global warming.

[0012] Kojima et ah, 2002 discloses a hydrogen generation method using sodium borohydride solution and metal catalyst coated on metal oxide, wherein the hydrogen generation was accelerated based on the crystal size of the catalyst.

[0013] The US patent application US20070025908A1 discloses activated aluminium hydride composition having one or more hydrogen desorption stimulant which includes oxides of metal as metal catalyst for desorption of hydrogen. However, the cost efficiency of Hydrogen production depends on the ratio of the hydride to the stimulant and there is no mention of carbon emission involved in the process.

[0014] Therefore, there is a need for a process for production of hydrogen from water which is most cost effective and reduces the carbon emission. In our case the hydride is produced from reaction of water with double the amount of magnesium. The extra cost of recycling MgO is adjusted by co-producing a metal which sells for a much higher price than magnesium.

Summary of the invention

[0015] The present invention relates to a method of producing hydrogen from water by using metal oxide and metal hydride economically without causing any environmental pollution. Magnesium hydride (MglT) is a convenient and easily storable solid metal hydride which can be used to produce hydrogen on demand for any application.

[0016] Hydrogen can be generated by coproducing it with certain metals by reducing the metal oxide with Mg¾ or with metal and water. The coproduction of metals and hydrogen makes hydrogen a by-product and therefore it is cost effective and highly profitable.

[0017] The invention provides to produce hydrogen along with metal either by reaction of a metal oxide or metal sulphide with magnesium hydride or reaction of metal oxide or metal sulphide with magnesium and water. The products are MgO, metal and Hydrogen. The former process is the Hydride method and the latter one is the Direct method.

[0018] The process of the present invention results in coproduction of Hydrogen and metal (from reduced oxide ore), both of which are economically profitable. Further, most of the reactions involved in the process are exothermic and do not require external heating. This makes the process highly viable from energy consumption point of view.

[0019] The metal oxides used in the Hydride process include H2O, S1O2, AI2O3, (¾03, TiC , SnC , ZrC , CuO, ZnO, WO3, Ta20s, Mn02, Cs2Cr207, CsOH and the metal sulphides include CuS and CuFeS2. In the Direct method, metals like Mg, Al, Si or Ca combine with water and react with metal oxides. The metal-oxides include S1O2, (¾(¾, T1O2, SnC , ZrC , CuO, ZnO, WO3, Ta20s, Cs2Cr207 or CsOH to produce hydrogen and metal. The process is highly profitable since the cost of metal used in the process is more than offset by the value of the hydrogen and metal (from reduction of the ore) obtained as the product of the process.

Brief description of the drawings

[0020] The foregoing and other features of embodiments will become more apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings.

[0021] Figure 1 is a phase diagram depicting the stability of Mg¾ formed by combining different proportion of Mg and water at various temperatures.

[0022] Figure 2 is a diagram of a reactor used to produce hydrogen from the direct method.

[0023] Figure 3 is another embodiment of the reactor shown in figure 2 which uses the hydride method.

Detailed description of the invention

[0024] Reference will now be made in detail to the description of the present subject matter, one or more examples of which are shown in figures. Each example is provided to explain the subject matter and is not a limitation. Various changes and modifications obvious to one skilled in the art to which the invention pertains are deemed to be within the spirit, scope and contemplation of the invention.

[0025] The present invention relates to a method to produce hydrogen from water. It could be via an already produced MgH2 or via a reaction of water and magnesium. Magnesium hydride (Mgth) is a convenient and easily storable solid which contains hydrogen. Hydrogen can be generated by coproducing it with certain metals. The process is accomplished by reacting magnesium hydride with a metal oxide or sulfide. Hydrogen can also be coproduced with metal by reaction of a metal such as Mg, Al, Si, or Ca with water and a metal oxide (oxide ore). The coproduction of metals and hydrogen makes hydrogen a by-product and therefore there is no specific cost involved and hence the process is highly profitable. The method is largely carbon emission free depending on mode of production of Magnesium.

[0026] The Magnesium required as a reactant in the process is obtained by electrolytic reduction of MgO by the solid oxide membrane (SOM) technique. This process requires close to 12 kWh of electricity and results in generating 11.28 Kg of CO2 for each kg of Mg when thermal power is used. This emission is reduced to almost zero, if alternate forms of energy (hydro, nuclear, solar, wind) are used.

[0027] When one mole of Mg reacts with one mole of H2 Magnesium hydride is obtained according to equation (1) shown below:

Mg (s) + H2 (g) -> MgH2 (s) DH = -6.2E-02 kW T=300 K - (1)

[0028] When a metal such as Mg is reacted with water, we get the reaction as shown in (3) and not the hydride producing reaction as shown in (4):

Mg+ HiO ^ MgH2 + 0.502 - (4)

[0029] The two-step process (reactions 1 and 3) can be changed to one step by using different proportions of Mg and water in (3) to get

[0030] There is an important difference between the hydride produced from reactions (1) and (3) and reaction (5). The hydride in reaction (5) is produced without involvement of any fossil fuel, except if Mg production leads to some carbon emission.

[0031] On heating, the hydride produces hydrogen according to equation (6)

MgH2 (s) Mg + H2 T=566 K DH = 1.2E4 J - (6)

The price of the hydrogen will depend on the price of Mg used in the overall process.

[0032] Coproduction of metal and hydrogen: There are two ways of coproducing hydrogen and the metal. They are as follows:

[0033] 1. The hydride method: This method to generate hydrogen is to carry the hydride to any site where it is required and apply some heat (reaction 6). MgH2 releases hydrogen on reacting with an oxide, usually with H20. Other oxides which react with the hydride are CuO or CuFeS2, Fe203, Fe304, Si02, Sn02, Zr02, Al203 and Cr203. In each case MgO forms along with hydrogen and the added oxide is reduced to the corresponding metal.

[0034] The metals which are produced in the process are very expensive and their production along with hydrogen is very profitable. Further hydrogen being a byproduct is produced at no cost. The overall cost of production is reduced since the recycling cost of MgO will be easily recovered by the sale of the products namely the metal and hydrogen. The reactions of metal oxides with Magnesium Hydride presented below occur at a temperature of 300 K to 400 K. The temperature can be higher if kinetics are slow. All reactions are exothermic except

(9). All AH values are in Joules.

Mn02 + 2 MgH2- 2MgO + Mn + 2 H2 AH=-3.6E5 - (20)

7MgH2 + Cs2Cr207 -»2 Cs + 7MgO + 2 Cr +7 H2 AH=-1.59E6 - (21)

MgH2 + CsOH^Cs +MgO +1.5H2 AH=-1.087E5 - (22)

[0035] Reactions (7) to (22) are thermo-chemically possible. The kinetic barrier in these reactions may be overcome by using higher temperatures if needed. Hence, these reactions proceed even in the absence of catalysts.

[0036] 2. Direct method: In this method metal and hydrogen are produced without the use of hydride by the direct reaction of Metals such as Magnesium, Silicon, Aluminium or Calcium with water and metal-oxide. A few examples of such reactions are as follows:

3Mg + Si02 + H20 = Si + 3 MgO + H2 AH= -6.01E5 - (23)

(The reaction not useful because Mg is higher in price than Si)

2A1+ Si02 + H20 = Si +A1203 + H2 AH= -5.23E5 - (24)

4Mg+Cr203+H20 = 4MgO + 2 Cr + H2 AH =-1.04E6 - (25)

3 Mg + TΪ02+H20 = 3 MgO + TiH2 AH =-7.47E5 - (26)

2A1 + TΪ02+H20 = A1203+TΪH2 AH= -5.9E5 - (27)

3 Ca + Ti02+ H20 = 3CaO +TiH2 AH =-8.27E5 - (28)

3 Mg + Sn02+H20 = 3MgO + Sn + H2 AH =-9.85E5 - (29)

3 Ca + Sn02+H20 = 3CaO + Sn + H2 -1.086E6 - (30)

2A1 +Sn02+H20 = A1203+Sn+ H2 AH= -8.62E5 - (31)

Mg + CuO +H20 = 2MgO + Cu + H2 T= 400 AH =-8.05E5 - (32)

Ca + CuO +H2O = 2CaO + Cu + H2 T= 400 AH =-8.75E5 - (33)

1.34 A1 + CuO + H20 = Cu + .67 A1203 + H2 AH =-71.19E5 - (34)

1.5 Si + Sn02 + H20 = 1.5 Si02 + Sn + H2 AH =- 5.46E5 - (35)

2Mg + .5 Zr02 + H20 = 0.5 ZrH2 + 2MgO +.5 H2 DH =-4.861E4

3Ca + Zr02+ H20 = 3 CaO+ZrH2 DH =-7.35E5 -

2 A1 +Zr02+H20 = A1203 +ZrH2 AH =-5.05E5 - (38)

2Mg + ZnO + H20 = 2MgO + Zn + H2 AH =-6.15E5 - (39) 2Ca + ZnO + H20 = 2CaO + Zn + H2 AH =-6.77E5 - (40)

E334 A1 + ZnO +H20 = Zn + .667 A1203 + H2 AH =-5.24 E5 - (41)

Si +ZnO + H20 = Zn + Si02 +H2 DH= -3.19E5 - (42)

2 Si + W03 +H20 = 2 Si02+W + H2 AH =-7.37E5 - (43)

4 Mg + W03 +H20 = 4 MgO +W + H2 AH= -1.45 E6 - (44) 3 A1 +W03 + H20 = 1.333 A1203 + W + H2 AH =-1.15E5 - (45)

6 Mg + Ta205 + H20 = 6 MgO+2 Ta +H2 AH =-1.32E6 - (46)

6 Ca + Ta205 + H20 = 6 CaO+2 Ta +H2 AH =-1.52E6 - (47)

4 A1 + Ta205+ H20 = 2 A1203 + 2 Ta + H2 AH =-1.064E5 - (48)

4 Si + Ta205 + H20 = 3 Si02 + Ta2Si +H2 AH =-5.7E5 - (49) 8Mg + Cs2Cr207 + H20 = 2 Cs + 8MgO + 2 Cr + H2 DH=-2.48E - (50)

8Ca + Cs2Cr207 + H20 = 2 Cs + 8CaO + 2 Cr + H2 DH=-2.75E6 - (51)

5.5 A1+ Cs2Cr207 + H20 = 2 Cs + 2.67A1203 + 2 Cr + H2 DH=-2.14E6— - (52)

5.5 Si + Cs2Cr207 + H20 = 2 Cs + 4 Si02 + .75 CrSi + .25 Cr5Si3 +H2 - (53)

AH=- 1.42E6

Mg + CsOH + H20 = Cs -1-MgO +1.5

Si + CsOH + H2O = Cs +Si02 +1.5 H2 DH= -2.53 E5 - (55)

2 Ca+ CsOH + H20 = Cs +2 CaO + H2 DH =-6.12E5 - (56)

2 A1 + CsOH +2 H20 = Cs +A1203 + 2.5 H2 DH =-7.75E5 - (57)

[0037] The reactions (23) to (57) are thermo-chemically possible and the kinetic barrier is overcome by the temperature conditions of the reaction. The reactions therefore proceed to completion.

[0038] Reactors: Fluidized bed reactors made of iron-alloy are used for these reactions. The finely ground charge consists of one of the metals including Magnesium, Silicon, Aluminium and Calcium. The metal oxides include Si02, Cr203, Ti02, Sn02, Zr02, CuO, ZnO, WO3, Ta2Os, Cs2Cr207 or CsOH. The grinding of the charge is done in inert gas sealed metal jars in a planetary ball mill. The reactor is maintained at a homogeneous temperature between 25°C and 1000°C. All reactions consist of reacting one of the four elements Magnesium,

Aluminium, Silicon or Calcium with water and the metal-oxides as mentioned above. The molar proportions of the reactants as shown in the equations are used as the reactant proportion. The detailed design of the reactors may require additional features to remove any difficulties due to the exothermic nature of the reactants.

[0039] Figure 1 depicts the stability of MgH2 formed by combining different proportion of Mg and water at various temperatures. The figure shows that below T= 566 K, MgH2 is stable and therefore can be synthesized directly from water and Mg.

[0040] Figure 2 is a fluidized bed reactor used to co-produce hydrogen with metal. In Figure 2, (1) is the inlet of the reactor wherein a mixture of the metal and metal oxide is fed. Hot steam is fed through the inlet pipe (2). The reaction chamber (3) containing fluidized bed of metal oxide and metal is the place where the reaction takes place. The outlet (4) is where the products MgO and metal is collected. The hydrogen evolved through the anterior outlet (6) is collected for use. The high temperature membrane (5) allows only hydrogen to pass through it preventing the outflow of other undesirable gases.

[0041] Figure 3 is another embodiment of the reactor shown in figure 2. The inlet (1) is used to feed Mg¾ and metal oxide. Hot inert gas is fed through inlet (2). The reaction chamber (3) contains fluidized bed of MgH2, metal oxide and hot inert gas where the reaction takes place. The outlet (4) is used to collect MgO and reduced metal. The hot temperature membrane (5) allows only hydrogen to pass through it. The evolved hydrogen is collected through outlet (6).

[0042] Evaluation of the production cost and the sales cost of the obtained products reveal that the overall process is highly cost effective and economically beneficial. The process is very profitable as the price of magnesium used in the reaction is more than offset by the cost of metal obtained as the byproduct.

[0043] The present invention is a method of co-producing hydrogen and metal, the method comprises of the steps of reacting Magnesium hydride and metal oxide or Magnesium hydride and metal sulphide in a fluidized bed reactor, collecting the hydrogen gas evolved, collecting and separating the metal and MgO produced. The reaction occurs in a sealed inert gas flushed reaction chamber which is heated between 25°C and 1000°C.

[0044] The metal oxide or metal sulphide used in the process include ¾0, S1O2, AI2O3, (¾03, Ti02, Sn02, Zr02, CuO, CuS, CuFeS2, ZnO, WO3, Ta20s, Mn02, Cs2Cr207 and CsOH.

[0045] The invention also pertains to a method of co-producing hydrogen and metal, the method comprises the steps of reacting a metal and metal oxide with water in a fluidized bed reactor, collecting the hydrogen gas evolved, collecting and separating the metal and MgO. The reaction occurs in a sealed inert gas flushed reaction chamber which is heated between 25°C and 1000°C.

[0046] The metal used in the process is one of Magnesium, Calcium, Aluminium or Silicon. The metal oxide used in the process is one of SiC , Cr203, T1O2, SnC , ZrC , CuO, ZnO, WO3, Ta20s, Cs2Cr207 or CsOH.

[0047] An example of the present invention is when tin oxide is added to magnesium hydride it gives us magnesium oxide, tin and hydrogen as in the equation represented below:

MgH2 + 0.5 Sn02^ MgO + 0.5 Sn + H2

[0048] Production cost per mole of Mg¾ works to 36-38 dollars by using electrolytic or Steam Methane Reformation method with Solid Oxide Membrane. The produced hydride when reacted with CuS by the hydride method of the invention results in producing hydrogen and copper yielding a net profit of 176 dollars (per mole) in the overall process.

[0049] When hydrogen is produced by reacting the hydride with a metal oxide, for some oxides, a kilogram of hydrogen results in production of metals worth many hundred dollars. The calculations are based on the prices of metal and hydride only, costs of oxides and energy are ignored.

[0050] In various embodiments of the reaction, production cost using Mgth and S1O2, Cr203, T1O2, ZrC and CsOH as the metal oxide reactant have also revealed the process to be economically beneficial and viable.

[0051] The cost analysis of the direct method also indicates that the process is highly profitable and carbon emission free as long as the method of isolating the metal used in the reaction are obtained by using non-fossil sources of energy. [0052] While at least a few exemplary embodiments have been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.