WO2017125610A1

WO2017125610A1 - Process and system

Info

Publication number: WO2017125610A1
Application number: PCT/EP2017/051345
Authority: WO
Inventors: Kyle Teamey
Original assignee: Avantium Knowledge Centre B.V.
Priority date: 2016-01-22
Filing date: 2017-01-23
Publication date: 2017-07-27

Abstract

A process comprising: - converting water in an electrolyzer to thereby produce oxygen and hydrogen; - hydrogenating one or more carbon-based compounds with the hydrogen in a hydrogenation reactor to thereby produce one or more hydrogenated carbon-based compounds and water; - oxidizing the one or more hydrogenated carbon-based compounds at an anode of a fuel cell, whilst simultaneously reducing oxygen at a cathode of the fuel cell, to thereby produce electricity, one or more carbon-based compounds and water; - recycling the one or more carbon-based compounds. And a system comprising: - an electrolyzer, which electrolyzer is provided with one or more inlets means for water and one or more outlet means for hydrogen and oxygen; - a hydrogenation reactor, which hydrogenation reactor is provided with one or more inlet means for hydrogen and one or more carbon-based compounds and one or more outlet means for one or more hydrogenated carbon-based compounds and water, wherein the inlet means for hydrogen of the hydrogenation reactor are fluidly connected to the outlet means for hydrogen of the electrolyzer; - a fuel cell, which fuel cell is provided with an anode compartment and a cathode compartment and wherein the anode compartment is provided with one or more inlet means for one or more hydrogenated carbon-based compounds and one or more outlet means for one or more carbon-based compounds and wherein the cathode compartment is provided with one or more inlet means for oxygen and one or more outlet means for water.

Description

PROCESS AND SYSTEM

FIELD OF THE INVENTION

[0001] The present invention relates to a process and system suitable for hydrogen energy storage.

BACKGROUND TO THE INVENTION

[0002] The combustion of fossil fuels in activities such as electricity generation, transportation, and manufacturing produces billions of tons of carbon dioxide annually. Research since the 1970s indicates increasing concentrations of carbon dioxide in the atmosphere may be responsible for altering the Earth's climate, changing the pH of the ocean and other potentially damaging effects. Countries around the world, including the United States, are seeking ways to mitigate emissions of carbon dioxide.

[0003] A mechanism for mitigating emissions is to convert carbon dioxide into economically valuable materials such as fuels and industrial chemicals. If the carbon dioxide is converted using energy from renewable sources, both mitigation of carbon dioxide emissions and conversion of renewable energy into a chemical form that can be stored for later use will be possible.

[0004] Renewable energy sources such as solar and wind power are clean but intermittent. The sun only shines during the day and the wind doesn't always blow. Intermittency necessitates the incorporation of energy storage. Many energy storage media have been proposed, but all suffer from a weakness that makes their commercialization difficult.

[0005] According to EP2717372 there is a very significant instability in solar energy, wind energy and others, which prevents them from well merging into the existing grid system. Also EP2717372 mentions a need for high-performance energy storage facilities. EP2717372 mentions hydrogen energy as a clean and harmless possible solution and describes a direct fuel cell based on a mixture of liquid unsaturated heterocyclic aromatic compounds, the fuel cell comprising a fuel cell unit and a hydrogen storage unit. The liquid unsaturated heterocyclic aromatic compounds mentioned by EP2717372, such as carbazole, N-methyl carbazole, N-ethyl carbozole, indole or quinolone are, however, complex in their manufacture and their use is not economically advantageous.

[0006] In passing, EP2717372 mentions that direct fuel cells of small alcohol molecules are disadvantageous as their battery products, C02 and H20 come from complete oxidation of the alcohols, which are difficult to reversely be electrolyzed back to the alcohols to store electric energy as chemical energy. EP2717372 therefore concludes that as a result, these cannot be used for "peak-cutting and valley-filling" of intermittent renewable electric energy.

[0007] It would hence be an advancement in the art to have a process and/or system with which similar, better, or economically more advantageous results can be achieved.

SUMMARY OF THE INVENTION

[0008] Such a process and system have been achieved with the processes and systems according to the invention.

[0009] Accordingly, the present invention provides a process comprising the following steps:

1 ) converting water in an electrolyzer (also referred to herein as "first electrochemical cell") to thereby produce oxygen and hydrogen;

2) hydrogenating one or more carbon-based compounds, which one or more carbon-based compounds preferably comprise or consist of oxalic acid and/or glycolic acid, with the hydrogen in a hydrogenation reactor to thereby produce one or more hydrogenated carbon-based compounds and water;

3) optionally removing water produced in step 2 from a mixture of the one or more hydrogenated carbon-based compounds and water;

4) optionally storing the one or more hydrogenated carbon-based compounds at a time t1 and retrieving the stored one or more hydrogenated carbon-based compounds at a time t2, wherein t2 is later than t1 ;

5) oxidizing the one or more hydrogenated carbon-based compounds at an anode of a fuel cell (also referred to herein as "second electrochemical cell"), whilst simultaneously reducing oxygen at a cathode of the fuel cell, to thereby produce electricity, one or more carbon-based compounds and water; 6) optionally removing water generated in step 5 from a mixture of the one or more carbon-based compounds and water;

7) optionally storing the one or more carbon-based compounds at a time t3 and retrieving the stored one or more carbon-based compounds at a time t4, wherein t4 is later than t3;

8) recycling the one or more carbon-based compounds to step 2).

[0010] In addition, the present invention provides a system comprising:

a) an electrolyzer (also referred to herein as "first electrochemical cell"), which electrolyzer is provided with one or more inlets means for water and one or more outlet means for hydrogen and oxygen;

b) a hydrogenation reactor, which hydrogenation reactor is provided with one or more inlet means for hydrogen and one or more carbon-based compounds and one or more outlet means for one or more hydrogenated carbon-based compounds and water, wherein the inlet means for hydrogen of the hydrogenation reactor are f luidly connected to the outlet means for hydrogen of the electrolyzer ;

c) optionally a first storage tank for storage of hydrogenated carbon-based compounds;

d) a fuel cell (also referred to herein as "second electrochemical cell"), which fuel cell is provided with an anode compartment and a cathode compartment and wherein the anode compartment is provided with one or more inlet means for one or more hydrogenated carbon-based compounds and one or more outlet means for one or more carbon-based compounds and wherein the cathode compartment is provided with one or more inlet means for oxygen and one or more outlet means for water;

e) optionally a second storage tank for storage of carbon-based compounds.

[0011] Both the above process as well as the above system are suitable for hydrogen energy storage. The present invention hence advantageously provides a process and system for closed-loop hydrogen energy storage utilizing organic compounds, that is, carbon-based compounds. Embodiments of the invention can advantageously provide a closed-loop process of energy storage and production employing an energy dense chemical that can be easily stored and transported and may be used for stationary or portable power. Embodiments of the invention can advantageously provide a closed-loop energy storage and production system that uses/reuses a carbon-based material to store and transport hydrogen, and provide hydrogen for energy production via fuel cells.

[0012] Surprisingly, it was found that with the processes and systems according to the invention, small alcohol molecules, such as mono-ethylene glycol, can be used to store and/or release electric energy as chemical energy.

[0013] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the present disclosure. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate subject matter of the disclosure. Together, the descriptions and the drawings serve to explain the principles of the disclosure.

[0014] In this patent application, the words "method" and "process" are interchangeable and wherever the word "process" is used "method" can be read or vice versa. Further, the words "first electrochemical cell" and "electrolyzer" are interchangeable and wherever the word "first electrochemical cell" is used "electrolyzer" can be read or vice versa. In addition, the words "second electrochemical cell" and "fuel cell" are interchangeable and wherever the word "second electrochemical cell" is used "fuel cell" can be read or vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The processes and systems of the invention are illustrated by the accompanying figure 1 which illustrates a non-limiting example of a process and system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hydrogen has been widely touted as an energy storage medium that could be used for both energy production and transportation. Without wishing to be bound by any kind of theory it is believed that hydrogen has high energy content on a mass basis, and can be either combusted or utilized in a fuel cell with high efficiency and no emissions. However, hydrogen is a gas that is difficult to store in tanks or onboard vehicles. The present invention advantageously provides a process of storing hydrogen by reacting it with a carbon- based material or chemical that may serve as a hydrogen carrier. While these can be completely oxidized to water and carbon dioxide, this is not preferred because of the difficulty of reducing carbon dioxide relative to more reduced organic compounds. Examples might include the reduction of formic acid to methanol with hydrogen during a "charging" phase, followed by partial oxidation back to formic acid during a "discharge" phase; or the reduction of oxalic acid to ethylene glycol followed by oxidation back to oxalic acid. The latter reaction and related reactions employing glycolic acid may be preferable because the partial oxidation of ethylene glycol or glycolic acid may be done in a fuel cell without completely oxidizing the energy storage medium to carbon dioxide.

[0017] Preferably, water may be converted to oxygen and hydrogen (water splitting) in an electrolyzer (also referred to herein as "first electrochemical cell"), using electricity that may come from a renewable source such as solar, hydroelectric or wind power. The resulting hydrogen may be reacted with oxalic acid or another carbon-based compound (herein also abbreviated to "carbon compound") in a hydrogenation reaction. For example, oxalic acid may be hydrogenated to glycolic acid and/or ethylene glycol. Glycolic acid and/or ethylene glycol may then be used to generate electricity in a fuel cell. The fuel cell may be located either as a stationary power plant or a portable power plant, such as a power plant of a vehicle. After the glycolic acid and/or ethylene glycol has been oxidized to oxalic acid in the fuel cell, the oxalic acid may be returned to the hydrogenation reactor to be re- hydrogenated and re-used as fuel. "Make-up" oxalic acid for the process may be produced electrochemically from carbon dioxide in a separate electrochemical cell. Excess water from the hydrogenation and oxidation reactions may be recovered for use in the water-splitting electrolyzer.

[0018] It is also possible to combine an electrolyzer with a hydrogenation reactor such that the carbon-based material or scaffold material is hydrogenated electrochemically.

[0019] The invention further provides a reversible system that combines an electrolyzer, hydrogenation reactor, and fuel cell into one apparatus.

[0020] The invention can advantageously be used in the manufacture of chemicals in such a manner that "load leveling" is achieved.

[0021] Hydrogen may be produced at night during periods of low power demand. Some of the hydrogenation products (also referred to herein as hydrogenated carbon-based compounds or simply hydrogenated carbon-based compounds) may be stored for use during the day and some are used immediately in the manufacture of chemicals. For example, oxalic acid or another carbon-based compound may be produced electrochemically or otherwise provided. Hydrogen, made at night when electric power is less expensive, may be used to hydrogenate the oxalic acid or another carbon compound to a more reduced species, such as formaldehyde, methanol, methane, glycolic acid, acetic acid, ethanol, ethylene glycol, and the like. The compound may then be sold as a fuel or as a chemical, such that load leveling and/or energy storage services are provided for the electric power grid concurrent with the production of the carbon compound. Hence, the process according to the invention may be a process wherein the one or more hydrogenated carbon-based compounds are stored at night-time at a time t1 and retrieved at day-time at time t2, wherein t2 is later than t1 ; and/or the one or more carbon-based compounds are stored at day-time at a time t3 and retrieved at night-time at time t4, wherein t4 is later than t3.

[0022] On the other hand, solar power may only be available during the day and hence the process according to the invention may also be a process wherein the one or more hydrogenated carbon-based compounds are stored at day-time at a time t1 and retrieved at night-time at time t2, wherein t2 is later than t1 ; and/or the one or more carbon-based compounds are stored at night-time at a time t3 and retrieved at day-time at time t4, wherein t4 is later than t3.

[0023] The use of oxalic acid as the carbon-based compound upon which hydrogen is stored in the form of glycolic acid or ethylene glycol may be advantageous for several reasons. The first is the relatively high energy density of these materials. The second is their relatively low toxicity and biodegradability. Furthermore, ethylene glycol has the additional benefit of lowering the freezing point of water. Without wishing to be bound by any kind of theory it is believed that aqueous ethylene glycol mixtures will remain a liquid even at relatively low temperatures. For example, a mixture of 60% ethylene glycol and 40% water freezes at -45 °C. In addition, ethylene glycol has a low vapor pressure. Thus it can be stored, pumped, and transported under a variety of conditions. Because glycolic acid and ethylene glycol may be partially oxidized to oxalic acid in a fuel cell with little or no production of carbon dioxide, energy can be generated with zero emissions. Any oxalic acid and water remaining after fuel cell energy production may be recycled such that the cycle approaches a closed-loop with very little water, oxalic acid, or other resources consumed. Preferably oxygen may also be recycled for use in the fuel cell to make a completely closed-loop process.

[0001 ] An exemplary complete cycle for ethylene glycol and oxalic acid is illustrated below:

- Electrolyzer (also referred to herein as "first electrochemical cell"):

4H₂0→ 4H₂ + 20₂

-Hydrogenation (as suitably carried out in a hydrogenation reactor):

C₂0₄H₂ (oxalic acid) + 4H₂→ C₂H₆0₂ (ethylene glycol) + 2H₂0

-Oxidation (as suitably carried out in a second electrochemical cell or "fuel cell"):

C₂H₆0₂ (ethylene glycol) + 20₂→ C₂0₄H₂ (oxalic acid) + 2H₂0

[0002] An exemplary cycle for ethylene glycol and glycolic acid is illustrated below.

- Electrolyzer (also referred to herein as "first electrochemical cell"):

2 H₂0→2H₂ + 0₂

- Hydrogenation (as suitably carried out in a hydrogenation reactor):

C₂H₄C>3 (glycolic acid) + 2 H₂→ C₂H₆0₂ (ethylene glycol) + H₂0

- Oxidation (as suitably carried out in a second electrochemical cell or "fuel cell"): C₂H₆0₂ (ethylene glycol) + 0₂→ C₂H₄03 (glycolic acid) + H₂0

[0003] An exemplary cycle for glycolic acid and oxalic acid is illustrated below.

- Electrolyzer (also referred to herein as "first electrochemical cell"):

2 H₂0→ 2 H₂ + 0₂

- Hydrogenation (as suitably carried out in a hydrogenation reactor):

C₂0₄H₂ (oxalid acid) + 2 H₂2→ C₂H₄0₃ (glycolic acid) + H₂0

- Oxidation (as suitably carried out in a second electrochemical cell or "fuel cell"): C₂H₄0₃ (glycolic acid) + 02→ C₂0₄H₂ (oxalic acid) + H₂0

[0004] When used in a stationary application, the process and system may for example suitably be as described below:

[0005] Step 1 . Water, optionally from a storage tank, may be provided to an electrolyzer (also referred to herein as "first electrochemical cell"). Make-up water, if needed, may come from another source. Hydrogen may be produced in the electrolyzer from water by passing an electric current through the water. The electric current may be provided by a renewable energy source, such as solar, wind, or hydroelectric power. Oxygen produced in the electrolyzer may be stored for later use, utilized in another process, or released to the atmosphere.

[0006] Step 2. Hydrogen is provided to a hydrogenation reactor. Glycolic acid and/or oxalic acid may be provided to the hydrogenation reactor, optionally from a storage tank, and hydrogenated to ethylene glycol and/or glycolic acid and water.

[0007] Step 3. Excess water produced in step 2 may be removed from the mixture of ethylene glycol and/or glycolic acid. The water may be returned to the electrolyzer (also referred to herein as "first electrochemical cell") for use in step 1 , stored for later usage, or used for another purpose.

[0008] Step 4. Ethylene glycol and/or glycolic acid produced in step 2 may be stored for later use.

[0009] Step 5. Ethylene glycol and/or glycolic acid produced in step 2 and stored in step 3 may be provided to the anode compartment of a fuel cell. Either air or oxygen produced in step 1 may be provided to the cathode compartment of the fuel cell. The outputs of the fuel cell are electricity, water, glycolic acid and/or oxalic acid. The electricity produced may be used for power and/or sold onto the electric grid.

[0010] Step 6. Excess water produced in step 5 may be removed from the mixture of ethylene glycol and/or glycolic acid. The water may be returned to the electrolyzer in step 1 , stored for later usage, or used for another purpose.

[001 1 ] Step 7. Glycolic acid and/or oxalic acid may be stored for use in step 2.

[0012] When used in a portable application, the process and system may for example suitably be as described below:

[0013] Step 1 . Water, optionally from a storage tank, may be provided to an electrolyzer. Make-up water, if needed, may come from another source. Hydrogen may be produced in the electrolyzer from water by passing an electric current through the water. The electric current may be provided by a renewable energy source, such as solar, wind, or hydroelectric power. Oxygen produced in the electrolyzer may be stored for later use, utilized in another process, or released to the atmosphere.

[0014] Step 2. Hydrogen may be provided to a hydrogenation reactor. Glycolic acid and/or oxalic acid, optionally from a storage tank, may be provided to the hydrogenation reactor and hydrogenated to produce ethylene glycol and/or glycolic acid and water.

[0015] Step 3. Excess water produced in step 2 may be removed from the mixture of ethylene glycol and/or glycolic acid. The water may be returned to the electrolyzer in step 1 , stored for later usage, or used for another purpose.

[0016] Step 4. Ethylene glycol and/or glycolic acid produced in step 2 may be stored for later use.

[0017] Step 5. Ethylene glycol and/or glycolic acid from step 4 may be provided to a vehicle or to a portable power generation unit. A vehicle, or a portable power generation unit, may comprise a storage unit for ethylene glycol and/or glycolic acid.

[0018] Step 6. Ethylene glycol and/or glycolic acid from step 5 may be introduced to the anode of a fuel cell. Air may be introduced to the cathode of the fuel cell. The fuel cell products are electricity, water, glycolic acid and/or oxalic acid. The fuel cell may be part of a vehicle, in which case the electricity produced may be used to provide power to the vehicle.

[0019] Step 7. Glycolic acid and/or oxalic acid from step 6 may be taken to a facility for removal and recycling.

[0020] The process according to the invention can thus preferably be a process comprising the following steps:

[0021 ] 1 ) electrochemically converting water in an electrolyzer, which water is optionally at least partly taken from a water storage tank, to thereby produce oxygen and hydrogen;

[0022] 2) hydrogenating one or more carbon-based compounds, which one or more carbon-based compounds comprise or consist of oxalic acid and/or glycolic acid, with the hydrogen produced in step 1 in a hydrogenation reactor to thereby produce a mixture of one or more hydrogenated carbon-based compounds and water;

[0023] removing water produced in step 2 from the mixture of the one or more hydrogenated carbon-based compounds and water, and optionally recycling such water to step 1 and/or storing such water in a water storage tank;

[0024] 4) storing the one or more hydrogenated carbon-based compounds at a time t1 , for example in a hydrogenated carbon-based compound storage tank, and retrieving the stored one or more hydrogenated carbon-based compounds at a time t2, wherein t2 is later than t1 ;

[0025] 5) oxidizing the one or more hydrogenated carbon-based compounds, retrieved in step 4, at an anode of a fuel cell (also referred to herein as "second electrochemical cell"), whilst simultaneously reducing oxygen, which oxygen is preferably at least partly taken from step 1 ), at a cathode of the second electrochemical cell, to thereby produce electricity and a mixture of one or more carbon-based compounds and water;

[0026] 6) removing water generated in step 5 from the mixture of the one or more carbon-based compounds and water, and optionally recycling such water to step 1 and/or storing such water in a water storage tank;

[0027] 7) storing the one or more carbon-based compounds at a time t3, for example in a carbon-based compound storage tank, and retrieving the stored one or more carbon-based compounds at a time t4, wherein t4 is later than t3;

[0028] 8) recycling the one or more carbon-based compounds to step 2).

[0029] It is contemplated that the structure and operation of the electrolyzers and/or fuels cells, or more in general of the electrochemical cells, employed in the process and system of the invention may be adjusted by the person skilled in the art. It should be understood that the words "first electrochemical cell" and "electrolyzer" may be used interchangeably and the words "second electrochemical cell" and "fuel cell" may be used interchangeably. For example, the electrochemical cell or cells may operate at higher pressures, such as pressure above atmospheric pressure which may increase current efficiency and allow operation of the electrochemical cell at higher current densities.

[0030] Additionally, the cathode and anode of the electrochemical cell or cells may include a high surface area electrode structure with a void volume which may range from 30% to 98%. The electrode void volume percentage may refer to the percentage of empty space that the electrode is not occupying in the total volume space of the electrode. The advantage in using a high void volume electrode is that the structure has a lower pressure drop for liquid flow through the structure. The specific surface area of the electrode base structure may be from 2 cm²/cm³ to 500 cm²/cm³ or higher. The electrode specific surface area is a ratio of the base electrode structure surface area divided by the total physical volume of the entire electrode. It is contemplated that surface areas also may be defined as a total area of the electrode base substrate in comparison to the projected geometric area of the current distributor/conductor back plate, with a preferred range of 2x to 1000x or more. The actual total active surface area of the electrode structure is a function of the properties of the electrode catalyst deposited on the physical electrode structure which may be 2 to 1000 times higher in surface area than the physical electrode base structure.

[0031] Cathode may be selected from a number of high surface area materials to include copper, stainless steels, transition metals and their alloys, carbon, and silicon, which may be further coated with a layer of material which may be a conductive metal or semiconductor. The base structure of cathode may be in the form of fibrous, metal foams, reticulated, or sintered powder materials made from metals, carbon, or other conductive materials including polymers. The materials may be a very thin plastic screen incorporated against the cathode side of the membrane to prevent the membrane from directly touching the high surface area cathode structure. The high surface area cathode structure may be mechanically pressed against a cathode current distributor backplate, which may be composed of material that has the same surface composition as the high surface area cathode.

[0032] In addition, cathode may be a suitable conductive electrode, such as Al, Au, Ag, Bi, C, Cd, Co, Cr, Cu, Cu alloys (e.g., brass and bronze), Ga, Hg, In, Mo, Nb, Ni, NiCo₂0₄, Ni alloys (e.g., Ni 625, NiHX), Ni-Fe alloys, Pb, Pd alloys (e.g., PdAg), Pt, Pt alloys (e.g., PtRh), Rh, Sn, Sn alloys (e.g., SnAg, SnPb, SnSb), Ti, V, W, Zn, stainless steel (SS) (e.g., SS 2205, SS 304, SS 316, SS 321 ), austenitic steel, ferritic steel, duplex steel, martensitic steel, Nichrome (e.g., NiCr 60:16 (with Fe)), elgiloy (e.g., Co-Ni-Cr), degenerately doped n-Si, degenerately doped n-Si:As, degenerately doped n-Si:B, degenerately doped n-Si, degenerately doped n-Si:As, and degenerately doped n-Si:B. Other conductive electrodes may be implemented to meet the criteria of a particular application. For photoelectrochemical reductions, cathode 122 may be a p-type semiconductor electrode, such as p-GaAs, p-GaP, p-lnN, p-lnP, p-CdTe, p-GalnP₂ and p-Si, or an n-type semiconductor, such as n-GaAs, n-GaP, n-lnN, n-lnP, n-CdTe, n-GalnP₂ and n-Si. Other semiconductor electrodes may be implemented to meet the criteria of a particular application including, but not limited to, CoS, MoS₂, TiB, WS₂, SnS, Ag₂S, CoP₂, Fe₃P, Mn₃P₂, MoP, Ni₂Si, MoSi₂, WSi2, CoSi₂, Ti₄0₇, Sn0₂, GaAs, GaSb, Ge, and CdSe.

[0033] The catholyte may include a pH range from 1 to 12, preferably from pH 4 to pH 10. The selected operating pH may be a function of any catalysts utilized in operation of the electrochemical cell. Preferably, catholyte and catalysts may be selected to prevent corrosion at the electrochemical cell. The catholyte may include homogeneous catalysts. Homogeneous catalysts are defined as aromatic heterocyclic amines and may include, but are not limited to, unsubstituted and substituted pyridines and imidazoles. Substituted pyridines and imidazoles may include, but are not limited to mono and disubstituted pyridines and imidazoles. For example, suitable catalysts may include straight chain or branched chain lower alkyl (e.g. , C1 -C10) mono and disubstituted compounds such as 2-methylpyridine, 4-tertbutyl pyridine, 2,6 dimethylpyridine (2,6-lutidine); bipyridines, such as 4,4'- bipyridine; amino-substituted pyridines, such as 4- dimethylamino pyridine; and hydroxyl-substituted pyridines (e.g. , 4-hydroxy-pyridine) and substituted or unsubstituted quinoline or isoquinolines. The catalysts may also suitably include substituted or unsubstituted dinitrogen heterocyclic amines, such as pyrazine, pyridazine and pyrimidine. Other catalysts generally include azoles, imidazoles, indoles, oxazoles, thiazoles, substituted species and complex multi-ring amines such as adenine, pterin, pteridine, benzimidazole, phenonthroline and the like.

[0034] The catholyte may include an electrolyte. Catholyte electrolytes may include alkali metal bicarbonates, carbonates, sulfates, phosphates, borates, and hydroxides. Non-aqueous electrolytes, such as propylene carbonate, methanesulfonic acid, methanol, and other ionic conducting liquids may be used rather than water and using salt addition electrolytes such as alkali metal salts. The electrolyte may comprise one or more of Na₂S0₄, KCl, NaN0₃, NaCl, NaF, NaCl0₄, KC10₄, K₂Si0₃, CaCl₂, a guanidinium cation, a H cation, an alkali metal cation, an ammonium cation, an alkylammonium cation, a tetraalkyl ammonium cation, a halide anion, an alkyl amine, a borate, a carbonate, a guanidinium derivative, a nitrite, a nitrate, a phosphate, a polyphosphate, a perchlorate, a silicate, a sulfate, and a hydroxide.

[0035] The catholyte may further include an aqueous or non-aqueous solvent. An aqueous solvent may include greater than 5% water. A non-aqueous solvent may include as much as 5% water. A solvent may contain one or more of water, a protic solvent, or an aprotic polar solvent. Representative solvents include methanol, ethanol, acetonitrile, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethylsulfoxide, dimethylformamide, acetonitrile, acetone, tetrahydrofuran, N,N-dimethylacetaminde, dimethoxyethane, diethylene glycol dimethyl ester, butyrolnitrile, 1 ,2- difluorobenzene, γ-butyrolactone, N-methyl-2-pyrrolidone, sulfolane, 1 ,4-dioxane, nitrobenzene, nitromethane, acetic anhydride, ionic liquids, and mixtures thereof.

[0036] In one embodiment, a catholyte/anolyte flowrate may include a catholyte/anolyte cross sectional area flow rate range such as 2 - 3,000 gpm/ft² or more ( 0.0076 - 11.36 m³/m²). A flow velocity range may be 0.002 to 20 ft/sec ( 0.0006 to 6.1 m/sec). Operation of the electrochemical cell catholyte at a higher operating pressure allows more dissolved carbon dioxide to dissolve in the aqueous solution. Typically, electrochemical cells can operate at pressures up to about 20 to 30 psig in multi-cell stack designs, although with modifications, the electrochemical cells may operate at up to 100 psig. The electrochemical cell may operate the anolyte and the catholyte at the same pressure range to minimize the pressure differential on a separator or membrane separating the two regions. Special electrochemical designs may be employed to operate electrochemical units at higher operating pressures up to about 60 to 100 atmospheres or greater, which is in the liquid C0₂ and supercritical C0₂ operating range.

[0037] In another embodiment, a portion of a catholyte recycle stream may be separately pressurized using a flow restriction with backpressure or using a pump, with C0₂ injection, such that the pressurized stream is then injected into the catholyte region of the electrochemical cell which may increase the amount of dissolved C0₂ in the aqueous solution to improve the conversion yield. In addition, microbubble generation of carbon dioxide can be conducted by various means in the catholyte recycle stream to maximize carbon dioxide solubility in the solution.

[0038] Catholyte may be operated at a temperature range of -10 to 95 °C, more preferably 5 - 60° C. The lower temperature will be limited by the catholytes used and their freezing points. In general, the lower the temperature, the higher the solubility of C0₂ in an aqueous solution phase of the catholyte, which would help in obtaining higher conversion and current efficiencies. The drawback is that the operating electrochemical cell voltages may be higher, so there is an optimization that would be done to produce the chemicals at the lowest operating cost. In addition, the catholyte may require cooling, so an external heat exchanger may be employed, flowing a portion, or all, of the catholyte through the heat exchanger and using cooling water to remove the heat and control the catholyte temperature.

[0039] Anolyte operating temperatures may be in the same ranges as the ranges for the catholyte, and may be in a range of 0°C to 95 °C. In addition, the anolyte may require cooling, so an external heat exchanger may be employed, flowing a portion, or all, of the anolyte through the heat exchanger and using cooling water to remove the heat and control the anolyte temperature.

[0040] Electrochemical cells may include various types of designs. These designs may include zero gap designs with a finite or zero gap between the electrodes and membrane, flow-by and flow-through designs with a recirculating catholyte electrolyte utilizing various high surface area cathode materials. The electrochemical cell may include flooded co-current and counter-current packed and trickle bed designs with the various high surface area cathode materials. Also, bipolar stack cell designs and high pressure cell designs may also be employed for the electrochemical cells.

[0041] Anode electrodes may be the same as cathode electrodes or different. For sulfur dioxide and hydrogen sulfide anode oxidation chemistry under acid conditions, the preferred electrocatalytic coatings may include precious metal oxides such as ruthenium and iridium oxides, as well as platinum and gold and their combinations as metals and oxides on valve metal substrates such as titanium, tantalum, zirconium, or niobium. Carbon and graphite may also be suitable for use as anodes in addition to boron-doped diamond films on metal or other electrically conductive substrates. For other sulfur based reactants in the anolyte such as sodium sulfide or hydrogen sulfide being oxidized under alkaline conditions, such as in a hydroxide containing electrolyte, selected anode materials may include carbon, transition metals, transitional metal oxides carbon steel, stainless steels, and their alloys and combinations which are stable as anodes. Anode 124 may include electrocatalytic coatings applied to the surfaces of the base anode structure. Anolytes may be the same as catholytes or different. The anolyte electrolytes may be the same as catholyte electrolytes or different. The anolyte may comprise solvent. The anolyte solvent may be the same as catholyte solvent or different. For example, for acid anolytes containing S0₂ as the sulfur-based reactant, the preferred electrocatalytic coatings may include precious metal oxides such as ruthenium and iridium oxides, as well as platinum and gold and their combinations as metals and oxides on valve metal substrates such as titanium, tantalum, zirconium, or niobium. For other anolytes, comprising alkaline or hydroxide electrolytes, anodes may include carbon, cobalt oxides, stainless steels, transition metals, and their alloys, oxides, and combinations. High surface area anode structures that may be used which would help promote the reactions at the anode. The high surface area anode base material may be in a reticulated form composed of fibers, sintered powder, sintered screens, and the like, and may be sintered, welded, or mechanically connected to a current distributor back plate that is commonly used in bipolar cell assemblies. In addition, the high surface area reticulated anode structure may also contain areas where additional applied catalysts on and near the electrocatalytic active surfaces of the anode surface structure to enhance and promote reactions that may occur in the bulk solution away from the anode surface such as the the introduction of S0₂ into the anolyte . The anode structure may be gradated, so that the suitable of the may vary in the vertical or horizontal direction to allow the easier escape of gases from the anode structure. In this gradation, there may be a distribution of particles of materials mixed in the anode structure that may contain catalysts, such as transition metal based oxides, such as those based on the transition metals such as Co, Ni, Mn, Zn, Cu and Fe as well as precious metals and their oxides based on platinum, gold, silver and palladium which may be deposited on inorganic supports within cathode compartment space or externally, such as in the second product extractor or a separate reactor.

[0042] A separator of the electrochemical cell, also referred to as a membrane, may be placed between an anode region and a cathode region of the electrochemical cell. Separator may include cation ion exchange type membranes. Cation ion exchange membranes which have a high rejection efficiency to anions may be preferred. Examples of such cation ion exchange membranes may include perfluorinated sulfonic acid based ion exchange membranes such as DuPont Nafion brand unreinforced types N117 and N120 series, more preferred PTFE fiber reinforced N324 and N424 types, and similar related membranes manufactured by Japanese companies under the supplier trade names such as AGC Engineering (Asahi Glass) under their tradename Flemion^®. Other multi-layer perfluorinated ion exchange membranes used in the chlor alkali industry may have a bilayer construction of a sulfonic acid based membrane layer bonded to a carboxylic acid based membrane layer, which efficiently operates with an anolyte and catholyte above a pH of about 2 or higher. These membranes may have a higher anion rejection efficiency. These are sold by DuPont under their Nafion^® trademark as the N900 series, such as the N90209, N966, N982, and the 2000 series, such as the N2010, N2020, and N2030 and all of their types and subtypes. Hydrocarbon based membranes, which are made from of various cation ion exchange materials can also be used if a lower the anion rejection eficiency is not as important, such as those sold by Sybron under their trade name lonac^®, AGC Engineering (Asahi Glass) under their trade name under their Selemion^® trade name, and Tokuyama Soda, among others on the market. Ceramic based membranes may also be employed, including those that are called under the general name of NASICON (for sodium super-ionic conductors) which are chemically stable over a wide pH range for various chemicals and selectively transports sodium ions, the composition is Nai+xZr₂Si_xP3-xOi2, and well as other ceramic based conductive membranes based on titanium oxides, zirconium oxides and yttrium oxides, and beta aluminum oxides. Alternative membranes that may be used are those with different structural backbones such as polyphosphazene and sulfonated polyphosphazene membranes in addition to crown ether based membranes. Preferably, the membrane or separator is chemically resistant to the anolyte and catholyte.

[0043] A rate of the generation of reactant formed in the anolyte compartment and the catholyte compartment may be proportional to the applied current to the electrochemical cell. The operation of an extractor and its selected separation method, for example fractional distillation or packed tower scrubbing, the actual products produced, and the selectivity of the wanted reaction would determine the optimum molar ratio of the reactant to the generated reactant.

[0044] The electrochemical cell may be easily operated at a current density of greater than 3 kA/m² (300 mA/cm²), or in suitable range of 0.5 to 5 kA/m² or higher if needed. The anode preferably has a high surface area structure with a specific surface area of 50 cm²/cm³ or more that fills the gap between the cathode backplate and the membrane, thus having a zero gap anode configuration. Metal and/or metal oxide catalysts may be added to the anode in order to decrease anode potential and/or increase anode current density. Stainless steels or nickel may also be used as anode materials with for sodium sulfide oxidation under alkaline conditions.

[0045] In respect of the preferences for the second electrochemical cell (also referred to a "fuel cell") the following references are hereby incorporated herein by reference in their entirety: Ogumi and Miyazaki, "Fuel Cells - Direct Alcohol Fuel Cells - Direct Ethylene Glycol Fuel Cells," Encyclopedia of Electrochemical Power Sources," (2009), pp 412-419. Zhao, et al, "Performance of a Direct Ethylene Glycol Fuel Cell with Anion Exchange Membrane," International Journal of Hydrogen Energy, 35 (2010), pp 4329-4335. Li, et al, "Electrocatalytic oxidation of ethylene glycol on supported Au and Pt catalysts in alkaline media: Reaction pathway investigation in three electrode cell and fuel cell reactors," Applied Catalysis B: Environmental, 125 (2012), pp 85-94. Puckett et al, US7615671 , Hydrogenation process for preparation of 1 ,2 diols, (2009). Gresham, US2607805, Hydrogenation of glycolic acid to ethylene glycol, (1952) and U.S. Patents 4,088,682, 4,453,026, 4,551 ,565 and 4,789,451. The fuel cell may be designed as or operated as described therein.

[0046] For example, if, in a process according to the invention, the carbon-based compound is oxalic acid and the hydrogenated carbon-based is ethylene glycol, the fuel cell may be a fuel cell as illustrated in section 2 of the article of Zhao, et al, "Performance of a Direct Ethylene Glycol Fuel Cell with Anion Exchange Membrane," International Journal of Hydrogen Energy, 35 (2010), pp 4329-4335 and it may be operated as described in such article.

[0047] The hydrogenation in step 2 is suitably a catalytic hydrogenation. That is, the hydrogenation is suitably carried out in the presence of a homogeneous or heterogeneous catalyst. The hydrogenation in step 2 can for example suitably be carried out as described in, and with catalysts and/or at temperatures and/or pressures as described in for example US2607805 and US7615671. [0048] Figure 1 illustrates a non-limiting example of the process and system according to the invention, wherein a stream of water (101 ) is obtained from a water storage tank (102) via outlet means (103) of such water storage tank (102).

[0049] The stream of water (101 ) is fed via inlet means (111 ) into a divided or undivided first electrochemical cell, also referred to herein as electrolyzer, (112), comprising an anode and cathode (not shown). In the electrolyzer (112) the stream of water (101 ) is electrochemically converted with electricity originating from solar power to thereby produce a stream of hydrogen (113) at the cathode and a stream of oxygen (114) at the anode. The stream of hydrogen (113) leaves the electrolyzer (112) via outlet means (115) and the stream of oxygen (114) leaves the electrolyzer (112) via outlet means (116).

[0050] The stream of hydrogen (113) is fed via inlet means (121 ) into hydrogenation reactor (122). In addition a stream of carbon-based compounds, such as for example oxalic acid, (154) is fed via inlet means (123) into hydrogenation reactor (122). In the hydrogenation reactor (122) the stream of carbon-based compounds, such as for example oxalic acid (154) is hydrogenated with the stream of hydrogen (113) to thereby produce a mixture of hydrogenated carbon-based compounds, such as for example ethylene glycol, and water (124). The mixture of hydrogenated carbon-based compounds, such as for example ethylene glycol, and water (124) leaves the hydrogenation reactor (122) via outlet means (125) and is split in a separator (not explicitly shown) in a stream of water (126) and a stream of hydrogenated carbon-based compounds, such as for example ethylene glycol (127).

[0051] The stream of hydrogenated carbon-based compounds, such as for example ethylene glycol (127) is fed via inlet means (131 ) into a storage tank (132) at daytime at a time t1 and retrieved via outlet means (133) as a stream (134) at nighttime at a time t2, which time t2 is later than time t1.

[0052] The stream of hydrogenated carbon-based compounds, such as for example ethylene glycol (134) is fed via inlet means (141 ) into an anode compartment (142), which anode compartment (142) comprises an anode (not shown), of fuel cell (143). Simultaneously a steam of oxygen (144) is fed via inlet means (145) into a cathode compartment (146), which cathode compartment (146) comprises a cathode (not shown), of fuel cell (143). The stream of oxygen (144) may at least partly be obtained from the stream of oxygen (114) generated by the electrolyzer (112) and can partly be obtained externally, for example from the air. In addition the fuel cell (143) may contain one or more separator membranes (not shown) between the anode and the cathode. In the fuel cell (143) the one or more hydrogenated carbon-based compounds, such as for example ethylene glycol, are oxidized, that is dehydrogenated, into one or more dehydrogenated carbon-based compounds, such as for example oxalic acid, and a stream of carbon-based compounds, such as for example oxalic acid (147), leaves the fuel cell (143) via outlet means (148). The stream of oxygen (144) is reduced into water, and a stream of water (149) leaves fuel cell (143) via outlet means (150). During this process electricity is generated.

[0053] The stream of carbon-based compounds, such as for example oxalic acid (147) is fed via inlet means (151 ) into storage tank (152) at night-time at a time t3 and retrieved via outlet means (153) as a stream (154) at day-time at a time t4, which time t4 is later than time t3. This stream of carbon-based compounds, such as for example oxalic acid, (154) can suitably be recycled again via inlet means (123) into hydrogenation reactor (122).

[0054] One or more of the streams of water (149) (shown) and/or (126) (not shown) can suitably be recycled via a water storage tank (102) to electrolyzer (112).

[0055] Unless explicitly indicated otherwise, the above mentioned preferences and descriptions are applicable to all embodiments of the invention. It is believed that the present disclosure and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory, and it is the intention of the following claims to encompass and include such changes.

Claims

1. A process comprising the following steps:

1 ) converting water in an electrolyzer to thereby produce oxygen and hydrogen; 2) hydrogenating one or more carbon-based compounds with the hydrogen in a hydrogenation reactor to thereby produce one or more hydrogenated carbon-based compounds and water;

5) oxidizing the one or more hydrogenated carbon-based compounds at an anode of a fuel cell, whilst simultaneously reducing oxygen at a cathode of the fuel cell, to thereby produce electricity, one or more carbon-based compounds and water;

6) optionally removing water generated in step 5 from a mixture of the one or more carbon-based compounds and water;

8) recycling the one or more carbon-based compounds to step 2).

2. The process according to claim 1 , wherein the one or more carbon-based compounds comprise or consist of oxalic acid and/or glycolic acid and the one or more hydrogenated carbon-based compounds comprise or consist of ethylene glycol.

3. The process according to claim 1 , wherein the one or more carbon-based compounds comprise or consist of oxalic acid and the one or more hydrogenated carbon-based compounds comprise or consist of ethylene glycol and/or glycolic acid.

4. The process according to anyone of claims 1 to 3, wherein step 1 ) comprises electrochemically converting water in an electrolyzer using electricity from solar, hydroelectric or wind power, to thereby produce oxygen and hydrogen.

5. The process according to anyone of claims 1 to 4, wherein oxygen in step 5 is obtained from the air and/or from step 1 ).

6. The process according to anyone of claims 1 to 5, wherein:

- step 3) is included and the water removed is recycled to step 1 ; and/or

- step 6) is included and the water removed is recycled to step 1 .

7. The process according to claim 6, wherein the water that is recycled is first stored in a water storage tank.

8. The process according to anyone of claims 1 to 7, wherein

- the one or more hydrogenated carbon-based compounds are stored at day-time at a time t1 and retrieved at night-time at time t2, wherein time t2 is later than time t1 ; and/or

- the one or more carbon-based compounds are stored at night-time at a time t3 and retrieved at day-time at time t4, wherein time t4 is later than time t3.

9. The process according to anyone of claims 1 to 7, wherein

- the one or more hydrogenated carbon-based compounds are stored at night-time at a time t1 and retrieved at day-time at time t2, wherein time t2 is later than time t1 ; and/or

- the one or more carbon-based compounds are stored at day-time at a time t3 and retrieved at night-time at time t4, wherein time t4 is later than time t3.

10. A system comprising:

a) an electrolyzer, which electrolyzer is provided with one or more inlets means for water and one or more outlet means for hydrogen and oxygen;

b) a hydrogenation reactor, which hydrogenation reactor is provided with one or more inlet means for hydrogen and one or more carbon-based compounds and one or more outlet means for one or more hydrogenated carbon-based compounds and water, wherein the inlet means for hydrogen of the hydrogenation reactor are fluidly connected to the outlet means for hydrogen of the electrolyzer ;

d) a fuel cell, which fuel cell is provided with an anode compartment and a cathode compartment and wherein the anode compartment is provided with one or more inlet means for one or more hydrogenated carbon-based compounds and one or more outlet means for one or more carbon-based compounds and wherein the cathode compartment is provided with one or more inlet means for oxygen and one or more outlet means for water;

e) optionally a second storage tank for storage of carbon-based compounds.

1 1 . Use of the process according to anyone of claims 1 to 9 or a system according to claim 10 for hydrogen energy storage.

12. Use of the process according to anyone of claims 1 to 9 or a system according to claim 10 in a stationary application.

13. Use of the process according to anyone of claims 1 to 9 or a system according to claim 10 in a portable application.

14. Use of the process according to anyone of claims 1 to 9 or a system according to claim 10 in a vehicle.