WO2024059990A1

WO2024059990A1 - Methods and apparatus for indirect production of hydrogen peroxide using amyl-anthraquinone for hydrogen transport

Info

Publication number: WO2024059990A1
Application number: PCT/CN2022/119784
Authority: WO
Inventors: Curtis Berlinguette; Arthur Fink; Renate Schwiedernoch; Javier DIAZ-MAROTO CARPINTERO
Original assignee: The University Of British Columbia; Solvay Sa; Solvay (China) Co., Ltd.
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2024-03-28

Abstract

Apparatuses and methods for producing hydrogen peroxide by performing coupled chemical and electrochemical reactions are disclosed. An electrochemical cell has a chemical reaction chamber configured to hydrogenate amyl-anthraquinone (AAQ) and an electrochemical chamber configured to electrochemically dissociate water to form hydrogen ions at an anode, and to reduce the hydrogen ions to atomic hydrogen at a cathode. The chemical reaction chamber and the anode chamber are separated by a metallic membrane. The metallic membrane acts as a cathode of the cell, a hydrogen-selective layer and a catalyst. The metallic membrane may comprise a layer of palladium or a palladium alloy. A layer of co-catalyst may optionally be electrodeposited on the layer of palladium or palladium alloy. An ion exchange membrane separates the metallic membrane and the anode chamber. The hydrogenated AAQ may be supplied to a reactor for contacting an oxygen-containing gas to yield hydrogen peroxide.

Description

METHODS AND APPARATUS FOR INDIRECT PRODUCTION OF HYDROGEN PEROXIDE USING AMYL-ANTHRAQUINONE FOR HYDROGEN TRANSPORT

Field

This invention relates generally to apparatuses and methods for indirect production of hydrogen peroxide. Specific embodiments provide electrochemical cells and methods which apply such cells for the indirect synthesis of hydrogen peroxide.

Background

The synthesis of hydrogen peroxide generally involves the use of large quantities of hydrogen gas. Hydrogen gas is very flammable. It is typically derived from a carbon-and energy-intensive process known as steam–methane reforming. Steam–methane reforming involves an endothermic reaction that requires high temperature conditions to produce CO and H ₂ (1: 3 molar ratio) . A subsequent exothermic reaction converts CO into H ₂ and CO ₂ (1: 1 molar ratio) in a water-gas shift reactor in the presence of water . Steam–methane reforming produces an equivalent of 0.25 CO ₂ for every H ₂O ₂ molecule (i.e., 2.8 Mt _CO2 y ^–1) and requires ～8.6 GW y ^–1. Creating hydrogen gas through steam-methane reforming is therefore very expensive, dangerous, requires a lot of energy, and is harmful to the environment.

The inventors have recognised a general need for improved apparatuses and methods for the synthesis of hydrogen peroxide. There is a particular need for such methods and apparatuses which do not require a supply of hydrogen gas.

Summary

This application has a number of aspects. These include, without limitation: methods and apparatuses for indirect production of hydrogen peroxide which pair an electrochemical reaction that generates hydrogen ions from water and a chemical reaction in which atomic hydrogen is reacted with amyl-anthraquinone (AAQ) to yield hydrogenated amyl-anthraquinone and the hydrogenated amyl-anthraquinone is then used in the synthesis of hydrogen peroxide.

One aspect of the invention provides a method for producing hydrogen peroxide by performing coupled chemical and electrochemical reactions. The method comprises electrochemically dissociating, at an anode, a hydrogen-containing compound to form one or more hydrogen ions (H ⁺) . The hydrogen ions may be transported through an ion exchange membrane to a metallic membrane. Upon reaching the metallic membrane, the hydrogen ions are reduced to form hydrogen atoms. The hydrogen atoms are diffused through the metallic membrane into a chemical reaction chamber. The diffused hydrogen atoms react with amyl-anthraquinone (AAQ in the chemical reaction chamber to form hydrogenated amyl-anthraquinone. In some embodiments, the reaction between the diffused hydrogen atoms and AAQ occurs on a surface of the metallic membrane. In some embodiments the surface comprises a catalyst layer. The catalyst layer may be electrodeposited. In some embodiments the catalyst layer is augmented by nanoparticles coated with a catalyst (e.g. palladium on carbon nanoparticles) . The nanoparticles may be spray coated onto the catalyst layer. The nanoparticles may be mixed with a polar or apolar binder such as PTFE or a sulfonated tetrafluoroethylene based fluoropolymer-copolymer such as Nafion ^TM.

The hydrogenated AAQ is transported from the chemical reaction chamber and is caused to react with a gas to form a product comprising hydrogen peroxide.

In some embodiments, reacting the hydrogen atoms with the AAQ is performed in a solvent mix comprising an aprotic solvent and a protic solvent. In some embodiments the solvent mix comprises a higher proportion by weight of the aprotic solvent and a relatively lower proportion by weight of the protic solvent. For example the solvent mix may comprise a weight ratio of the aprotic solvent to the protic solvent in the range of 2.5: 1 to 3: 1 (e.g. 2.75: 1) .

In some embodiments the aprotic solvent is a naphtha-based solvent. In some embodiments the aprotic solvent is a petroleum hydrocarbon solvent. The petroleum hydrocarbon solvent may have an aromatic content. In some embodiments the aprotic solvent comprises a C9 to C11 hydrocarbon fraction. The C9 to C11 hydrocarbon fraction may comprise a mixture of aromatic compounds having from 9 to 11 carbon atoms. In some embodiments, the C9 to C11 hydrocarbon fraction consists of a mixture of aromatic compounds having from 9 to 11 carbon atoms. In some embodiments the mixture of aromatic compounds in the C9 to C11 hydrocarbon fraction comprises predominantly (i.e., over 50%, or over 70%, or over 85%) aromatic compounds with 10 carbon atoms. The aprotic solvent may comprise heavy naphtha aromatics. For example, the aprotic solvent may be Solvesso ^TM which is a naphtha based solvent available from ExxonMobil Chemicals. In some embodiments, the aprotic solvent is Solvesso ^TM 150. In some embodiments the protic solvent is diisobutyl carbinol (DIBC) .

In some embodiments, a weight ratio of the aprotic solvent to the protic solvent is in the range of 2.5: 1 to 3: 1. In some embodiments, a weight ratio of the aprotic solvent to the protic solvent is approximately 2.75: 1.

In some embodiments, a concentration of AAQ in the chemical reaction chamber is at least 0.5M or at least 0.7M or at least 0.8M.

In some embodiments, the method involves introducing a constant flow of AAQ into the chemical reaction chamber.

In some embodiments, the hydrogen-containing compound is water. The electrochemical dissociation of water forms oxygen and hydrogen ions. In some embodiments, the electrochemical dissociation of the hydrogen-containing compound (e.g., water) at the anode is performed in an aqueous electrolyte solution.

The metallic membrane comprises a dense metallic hydrogen selective layer. The hydrogen selective layer may for example comprise a layer of palladium or a palladium alloy. In some embodiments, a layer of co-catalyst is deposited on the hydrogen selective layer. The layer of co-catalyst may be deposited by electrodeposition or shutter-deposition. In some embodiments, the co-catalyst comprises one or more transition metals. In example embodiments, the co-catalyst comprises one or both of palladium or gold. In some embodiments, the co-catalyst comprises palladium black. In some embodiments, the co-catalyst comprises a layer of palladium on carbon nanoparticles. In some example embodiments, the palladium on carbon nanoparticles are mixed with a polymeric binder. The polymeric binder may comprise PTFE or a sulfonated tetrafluoroethylene based fluoropolymer-copolymer.

In some embodiments, the method comprises maintaining a current density at the metallic membrane of at least 100 mA/cm ^-2.

In some embodiments, the method comprises maintaining a temperature in the of the chemical reaction chamber in the range of 25℃ to 80℃.

In some embodiments, the metallic membrane comprises a dense metallic hydrogen selective layer. The hydrogen selective layer may comprise a layer of palladium or palladium alloy.

In example embodiments, the gas that is being reacted with the hydrogenated AAQ comprises an oxygen-containing gas. The oxygen-containing gas may for example comprise gaseous oxygen or a gas mixture comprising the gaseous oxygen. The gas mixture may for example comprise oxygen and a second gas such as nitrogen or an inert gas.

In some embodiments, the ratio of unreacted AAQ to hydrogenated AAQ being fed to the reactor to contact the oxygen-containing gas is less than 3: 2 including 1: 2, 2: 3, 1: 4, 1: 9, etc. In some embodiments, the ratio of unreacted AAQ to hydrogenated AAQ being fed to the reactor to contact the oxygen-containing gas is at least 1: 10, or, at least 1: 20.

In some embodiments, reacting the oxygen-containing gas with the hydrogenated AAQ produces the product comprising hydrogen peroxide and regenerated AAQ. Downstream processes may be provided to recover the hydrogen peroxide. The regenerated AAQ may be returned to the chemical reaction chamber.

In some embodiments, the aqueous hydrogen peroxide solution is concentrated and/or stabilized with a stabilizing agent before storage.

An aspect of the invention relates to a system for producing hydrogen peroxide. The system comprises an electrolyzer and a reactor. The reactor may be arranged downstream of the electrolyzer. The electrolyzer comprises a chemical reaction chamber, an anode chamber, a cathode and a metallic membrane. An anode is exposed in the anode chamber and is adapted to oxidize a hydrogen-containing compound to form hydrogen ions. The metallic membrane provides a hydrogen selective layer between the chemical reaction chamber and the cathode chamber. The metallic membrane is adapted to electrochemically reduce hydrogen ions to hydrogen atoms at the cathode chamber and to allow the hydrogen atoms to diffuse through the membrane to react with AAQ in the chemical reaction chamber to yield hydrogenated AAQ. A fluid inlet and/or a fluid outlet may be provided at the chemical reaction chamber. The fluid inlet may be fluidly connected to a reservoir containing a solution of AAQ dissolved in a solvent. The system includes one or more pumps arranged to drive a flow of the dissolved AAQ to the chemical reaction chamber. The fluid outlet may be fluidly connected to an inlet of a reactor for flowing the hydrogenated AAQ to the reactor. An ion exchange membrane may be arranged to separate the cathode chamber and the anode chamber. The reactor may be configured to contact a gas with the hydrogenated AAQ to yield a product comprising hydrogen peroxide.

In some embodiments, the metallic membrane is arranged to contact the ion exchange membrane.

In some embodiments, the system further comprises a separator arranged downstream of the reactor for separating hydrogen peroxide from the product, a purifier arranged downstream of the separator for purifying the separated hydrogen peroxide and a concentrator arranged downstream of the purifier for concentrating the purified hydrogen peroxide.

Further aspects and example embodiments are illustrated in the accompanying drawings and/or described in the following description.

Brief Description of the Drawings

The accompanying drawings illustrate non-limiting example embodiments of the invention,

FIG. 1 is a schematic illustration showing an apparatus for synthesizing hydrogen peroxide according to an example embodiment of this invention.

FIG. 2A is a flow chart showing the steps of a method for producing hydrogenated AAQ using the FIG. 1 electrochemical cell according to an example embodiment of the invention. FIG. 2B is a flow chart showing steps of a method for producing hydrogen peroxide using hydrogenated AAQ according to an example embodiment of the invention.

FIG. 3 is an exploded view of a reactor according to an example embodiment of the invention.

FIG. 4 is a schematic diagram showing an example electrochemical cell showing chemical reactions that may occur in each of the reaction zones of the cell according to an example embodiment.

Fig. 5 is a graph that shows current efficiency as a function of solvent composition of an AAQ solution.

Fig. 6 is a graph showing current efficiency as a function of solvent composition for different concentrations of AAQ.

Fig. 7 is a graph showing the percentage of hydrogenation of AAQ as a function of time.

Fig. 8 is a graph showing the percentage of hydrogenation of AAQ as a function of time with different added catalyst layers.

Detailed Description

Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive sense.

Definitions

“Selectivity” refers to the product selectivity of a reaction. Selectivity is measured by the ratio of the desired product formed to the undesired product (s) formed. For example, if a particular reaction yields 4 moles of a desired product and 3 moles of undesired products then the reaction has a selectivity of 4/3. Higher selectivity is generally better.

“Hydrogen” is any isotope of the element with atomic number 1.

“Hydrogen ion” is ionized hydrogen (H ⁺) . A proton is an example of a hydrogen ion.

“Hydrogenation” includes any reaction between hydrogen atoms or hydrogen molecules (H ₂) and a reactant. Hydrogenation includes reactions which result in a hydrogen atom being added to a reactant to form a product of the reaction. For example, a hydrogenation reaction may reduce a double or triple bond in a hydrocarbon. One example of a hydrogenation reaction is adding hydrogen atoms to AAQ compound to yield hydrogenated AAQ. Another example of a hydrogenation reaction is a reaction which adds hydrogen atoms to oxygen molecules to yield hydrogen peroxide.

"Palladium" is used herein broadly and comprises various composition of matter, including alloys and other combinations of palladium metal with other materials. For example, a "palladium membrane" may be formed by electrodepositing one or more layers of palladium onto a substrate (which may be a palladium foil, or a porous polymer) . In one example, the substrate may be a rolled Pd wafer bar. Without being bound to any particular theory, the electrodeposited palladium may provide increased surface area that may increase the rate of reaction. Any suitable method for depositing palladium on a substrate, membrane foil, or other dense deuterium selective material may be used.

"H-cell" is used herein broadly and comprises a two-reaction zone reactor architecture. For illustration purposes only, and not to limit the scope of the invention, an exemplary illustration of a design of an H-cell is shown in FIG. 4.

"ePMR" refers to an "electrocatalytic palladium membrane reactor" that includes an electrochemical reaction zone and hydrogenation reaction zone separated by a palladium membrane further comprising a transition metal catalyst.

"ePMR flow cell" is used herein as an abbreviation for "electrocatalytic palladium membrane reactor flow cell" .

Example Embodiments

Aspects of the invention relate to methods and apparatuses of producing hydrogen peroxide (H ₂O ₂) . The methods and apparatuses do not require the use of hydrogen gas (H ₂) as a hydrogen source. Water is used as the hydrogen source in some embodiments.

The methods involve indirect production of hydrogen peroxide using AAQ as a shuttle molecule. The AAQ is hydrogenated. The hydrogenated AAQ is subsequently caused to react in a chemical reaction to produce hydrogen peroxide. The hydrogen that hydrogenates the AAQ may, for example, be produced by electrochemical dissociation of water or another hydrogen-containing compound. The resulting hydrogen ions may be reduced to hydrogen atoms before reacting to hydrogenate the AAQ.

The methods may be performed in systems that include an electrochemical cell that is operative to produce hydrogen ions. The hydrogen ions are reduced to hydrogen atoms prior to participating in a reaction with AAQ molecules to yield hydrogenated AAQ. The pairing of an electrochemical reaction which generates hydrogen ions at an anode with a chemical reaction in which hydrogen atoms participate in a hydrogenation reaction with AAQ can provide a highly efficient means for providing hydrogenated AAQ.

Proof of concept demonstrations of the method using the electrochemical cell described herein have shown that very high rates (rates of greater than 95%current efficiency at 100 mA cm ^-2) of conversion of AAQ to hydrogenated AAQ can be achieved.

Overview of Apparatus and Methods for Producing H ₂O ₂

FIG. 1 is a schematic diagram that illustrates an example system 10 that includes an electrochemical cell 11 for hydrogenating AAQ molecules 36. Hydrogenated AAQ molecules 38 may be supplied to a reaction chamber 72 where the hydrogenated AAQ molecules may react with an oxygen-containing gas to yield hydrogen peroxide.

Cell 11 comprises a hydrogen selective membrane 12 that separates a chemical reaction zone 52 comprising a chemical reaction chamber 14 from an electrochemical reaction zone 16. Electrochemical reaction zone 16 may be operated as described below to generate hydrogen ions and to supply the hydrogen ions to hydrogen selective membrane 12. Hydrogen selective membrane 12 is operative to pass atomic hydrogen into chemical reaction chamber 14.

Hydrogen ions which reach membrane 12 are reduced to hydrogen atoms. Membrane 12 absorbs the hydrogen ions. Membrane 12 selectively allows absorbed hydrogen atoms 32 to pass through membrane 12 while membrane 12 essentially blocks passage of all ions, electrolytes and solvents. Membrane 12 may be referred to as a “hydrogen selective layer” .

In currently preferred embodiments, hydrogen selective membrane 12 comprises or consists of a metallic membrane. In the following description membrane 12 is described as “metallic membrane 12” .

In some embodiments, including the embodiment illustrated in Fig. 1 electrochemical reaction zone 16 comprises a cathode chamber 18 and an anode chamber 20. In some embodiments, metallic membrane 12 separates chemical reaction chamber 14 from cathode chamber 18. In such embodiments, a first surface 22 of metallic membrane 12 is exposed to cathode chamber 18 and an opposing second surface 24 of metallic membrane 12 is exposed to chemical reaction chamber 14.

An anode 28 is exposed to anode chamber 20. Anode 28 may comprise platinum metal, for example. Other suitable materials may be used as anode 28. For example, metals such as palladium metal and metal oxides such as a nickel oxide (NiO _x) or ruthenium (IV) oxide (RuO ₂) may be used for anode 28. Carbonaceous materials such as graphite may also be used as anode 28.

A power source 26 is connected to apply a potential difference between anode 28 and metallic membrane 12. Metallic membrane 12 serves as a cathode.

Power source 26 may be configured to maintain a desired electric current between metallic membrane 12 and anode 28 and/or maintain a potential difference between metallic membrane 12 and anode 28 at a desired level or in a desired range.

Anode chamber 20 and cathode chamber 18 are optionally defined by an ion exchange membrane 46 that divides electrochemical reaction zone 16 into two parts. Ion exchange membrane 46 is a membrane that is selectively permeable to certain dissolved ions while blocking other ions or neutral molecules. In example embodiments, ion exchange membrane 46 is a cation exchange membrane. For example, membrane 46 may comprise a commercially available cation exchange membrane such as those marketed under the product name Nafion ^TM. In example embodiments, ion exchange membrane 46 is selectively permeable to hydrogen ions. In the illustrated embodiments, ion exchange membrane 46 advantageously blocks oxygen gas 47 that is produced at anode 28 from migrating to cathode chamber 18 where the oxygen could undesirably be reduced at metallic membrane 12

A suitable anolyte 60 is supplied to anode chamber 20. A suitable anolyte 60 facilitates first electrochemical reaction 50 at anode 28 by providing electrons to reactant 56 to yield hydrogen ions (H ⁺) . Anolytes may be acidic or basic. Non-limiting examples of suitable anolytes include H ₂SO ₄, HCl, H ₃PO ₄, KHCO ₃, KOH.

A suitable catholyte 62 is supplied to cathode chamber 18. A suitable catholyte 62 facilitates a second electrochemical reaction 64 at metallic membrane 12 by providing a medium within which hydrogen ions 48 travel to metallic membrane 12 where the hydrogen ions are reduced to yield atomic hydrogens 32. A suitable acid may, for example be used for catholyte 62. Non-limiting examples of suitable catholyte 62 include H ₂SO ₄, HCl, H ₃PO ₄.

In some embodiments, the same electrolyte solution is used as both anolyte 60 and catholyte 62. In other embodiments, different electrolyte solutions are used as anolyte 60 and catholyte 62.

One or more reactants 56 are supplied to anode chamber 20 to participate in a first electrochemical reaction 50 at anode 28 to yield hydrogen ions 48. In some embodiments, first electrochemical reaction 50 is an oxidation reaction, for example a dehydrogenation reaction.

In some embodiments, reactant 56 comprises water (H ₂O) . In such embodiments, the electrochemical dissociation of water at anode 28 yields oxygen gas 47 and hydrogen ions 48. First electrochemical reaction 50 may however comprise any other oxidation reaction which produces hydrogen ions (H ⁺) .

In some embodiments, oxygen gas 47 is supplied to apparatuses downstream from cell 11 for use as a reactant in other chemical reactions. For example, oxygen gas 47 may be supplied for reaction with hydrogenated AAQ 38 to yield hydrogen peroxide.

Hydrogen ions 48 are released into anode chamber 20 and migrate through ion exchange membrane 46 (if present) to reach metallic membrane 12. Hydrogen ions 48 participate in a second electrochemical reaction 64 at metallic membrane 12 to yield hydrogen atoms 32. Second electrochemical reaction 64 is a reduction reaction. The hydrogen atoms are absorbed into metallic membrane 12 and permeate through metallic membrane 12 to second surface 24 where they are available to react with AAQ in chemical reaction chamber 14. In doing so, hydrogen atoms 32 transition from first surface 22 into the bulk of a lattice 34, and transition to the opposing second surface 24 within chemical reaction chamber 14.

Chemical reaction chamber 14 comprises chemical reaction zone 52 containing AAQ molecules 36 dissolved in a suitable solvent 54. AAQ molecules 36 undergo hydrogenation reaction 40 with hydrogen atoms 32 which have diffused through metallic membrane 12 to chemical reaction chamber 14 to yield a product 33 comprising hydrogenated AAQ molecules 38 (e.g. molecules of amyl-anthrahydroquinone) .

In some embodiments, hydrogenation reaction 40 takes place on second surface 24 of metallic membrane 12. The supply of AAQ molecules 36 at second surface 24 may be matched to the rate at which hydrogen atoms 32 are presented at second surface 24 so that substantially all hydrogen atoms 32 that reach second surface 24 participate in hydrogenation reaction 40. This advantageously reduces the likelihood of or prevents hydrogen atoms 32 from forming hydrogen gas (H ₂) in chemical reaction chamber 14.

The balance between the availability of hydrogen atoms 32 and AAQ molecules 36 at second surface 24 may be adjusted to ensure that there are least enough AAQ molecules 36 to consume substantially all hydrogen atoms 32 that make it to second surface 14 by, for example, any of or any combination of: adjusting the availability of reactants 56 in anode chamber 20, adjusting power source 26 to alter the current driving electrochemical reaction 50, adjusting the concentration of AAQ molecules 36 in chemical reaction chamber 14, and/or adjusting the flow of solvent 54 that brings AAQ molecules 36 into chemical reaction chamber 54.

In some embodiments, a constant supply of AAQ molecules 36 is fed to chemical reaction chamber 14 to provide at least an amount of AAQ molecules 36 sufficient to react with all hydrogen atoms 32 that pass through metallic membrane 12..

In some embodiments hydrogenation reaction 40 is catalyzed by the material of metallic membrane 12 and/or by a catalyst provided on or adjacent to second surface 24 of metallic membrane 12. The hydrogenated AAQ molecules 38 may be subsequently reacted to yield hydrogen peroxide at apparatus downstream from chemical reaction chamber 14.

AAQ has a reversible redox chemistry which allows AAQ to reversibly be hydrogenated and to give up hydrogen to be returned to its original unhydrogenated state.

In some embodiments, the concentration of shuttle molecule 36 fed to chemical reaction chamber 14 to perform hydrogenation reaction 40 is in the range of from 0.1 M to about 3 M. In an example embodiment, the concentration of shuttle molecule 36 fed to chemical reaction chamber 14 to perform hydrogenation reaction 40 is in the range of from 0.80 M to 0.90 M.

Solvent 54 for performing hydrogenation reaction 40 may be selected based on one or more of the following:

● solubility of AAQ molecule 36 and the corresponding hydrogenated AAQ molecule 38;

● compatibility with hydrogenation reaction 40 and downstream reaction with oxygen-containing gas and/or separation processes (e.g., low solubility in water is desired in embodiments in which water extraction methods are used) ;

● low solubility in aqueous hydrogen peroxide solutions;

● low volatility (e.g., high boiling point and flash point) ; and

● low toxicity.

In some embodiments, solvent 54 is an organic solvent or a mixture of organic solvents.

In some embodiments, solvent 54 comprises an aprotic solvent 55, a mixture of aprotic solvents 55 or a mixture of one or more aprotic solvents 55 with one or more protic solvents 57.

In some embodiments, solvent 54 comprises a mixture of aprotic solvent (s) 55 and protic solvent (s) 57. In some embodiments solvent 54 is made up of more aprotic solvent 55 by weight than protic solvent 57.

In a specific example embodiment, solvent 54 comprises a mixture of a naptha based aprotic solvent (e.g. Solvesso ^TM ) and diisobutyl carbinol (DIBC) . SOLVESSO ^TM is the brand name for an aromatic hydrocarbon solvent that is available from ExxonMobil Chemical Company, Inc. For example, any one or more of SOLVESSO ^TM 100, SOLVESSO ^TM 150, SOLVESSO ^TM 150ND, SOLVESSO ^TM 200 and SOLVESSO ^TM 200ND may be suitable for use as aprotic solvent 55. Other suitable commercially available aromatic hydrocarbon solvents may also be used as aprotic solvent 55such as the aromatic solvent products sold under the trademark SHELLSOL ^TM.

In embodiments in which solvent 54 is a mixture of Solvesso and DIBC it has been found that the rate of hydrogenation reaction 40 tends to increase as the ratio of the protic solvent to the protic solvent is increased.

In some embodiments, the weight ratio of aprotic solvent 55 to protic solvent 57 in solvent 54 is in the range of from 1: 1 to 5: 1. In some embodiments, the weight ratio of aprotic solvent 55 to protic solvent 57 in solvent 54 is in the range of from 1: 1 to 3: 1. In one example embodiment solvent 54 comprises Solvesso and DIBC in a weight ratio of approximately or about 2.75: 1.

Non-limiting examples of suitable aprotic solvents 55 include alkanes (e.g., pentane, hexane, heptane, octane, etc. ) , benzene, chloroform, diethyl ether, dichloromethane, tetrahydrofuran (THF) , ethyl acetate, acetonitrile, dimethylformamide (DMF) , dimethyl sulfoxide, acetone, hexamethylphosphoric triamde (HMPT) .

In some embodiments, aprotic solvent 55 comprises one or more aromatic hydrocarbon solvents. Aprotic solvent 55 may comprise C5-C20 hydrocarbons. Non-limiting examples of suitable aromatic hydrocarbons that may be used as aprotic solvent 55 include one or more of alkylbenzenes such as toluene, xylene, trimethylbenzene, ethylbenzene, methylethylbenzene, methylpropylbenzene, dimethylethylbenzene, and octacylbenzene, monoalkylbenzenes, dialkylbenzenes and trialkylbenzenes, naphthalenes, alkylnaphthalenes such as monoalkylnaphthalene, dialkylnaphthalene, trialkylnaphthalene, phenylxylylethane and 1-phenyl-1-ethylphenylethane.

In some embodiments, solvent 54 comprises a protic solvent 57 or a mixture of protic solvents 57. Protic solvents are molecules that have at least one hydrogen atom connected to an electronegative atom such as a fluoride, nitrogen or oxygen. The molecules of protic solvents can readily donate hydrogen ions to solutes. Non-limiting examples of suitable protic solvents 57 include water, alcohols such as methanol, ethanol, butanol, isopropanol, acetic acid, hydrogen fluoride, ammonia, alkyl phosphates (e.g., tris- (2-ethylhexyl) phosphate (TOP) ) , nonyl alcohols (e.g., Diisobutyl Carbinol) , alkylcyclohexanol esters (e.g., 2-methylcyclohexyl acetate) , N, Ndibutyl propionamide, N-ethyl-N-phenyl benzamide, 2-ethylhexyl-N-butylcarbamate, tetra-n-butylurea, dihexyl propyleneurea, N, N-dibutyl-N′-methyl-N′-phenylurea, N-octylpyrrolidone, N-octylcaprolactam, etc. In some example embodiments, protic solvent 57 comprises diisobutyl carbinol (DIBC) .

With the sole exception of hydrogen which can be transported through metallic membrane 12, AAQ molecules 36, solvent 54 and hydrogenated AAQ molecules 38 in chemical reaction zone 52 can be kept isolated from reactant 56, anolyte 60 and catholyte 62 in electrochemical reaction zone 16. The near complete isolation provided by metallic membrane 12 allows materials that are incompatible to be present at opposite sides of metallic membrane 12. For example, AAQ molecules 36 may be dissolved in a solvent 54 that is an organic solvent or a mixture of organic solvents while an aqueous electrolyte is used as anolyte 60 and/or catholyte 62 without concerns of incompatibility.

Aspects of the invention relate to combining methods and apparatuses for hydrogenating AAQ molecules with downstream processes and apparatuses for synthesizing hydrogen peroxide by reacting the hydrogenated AAQ molecules (e.g. with an oxygen-containing gas) . FIG. 1 illustrates example apparatuses that may be arranged downstream of electrochemical cell 11 for reacting the hydrogenated AAQ to yield hydrogen peroxide, and for processing the unprocessed hydrogen peroxide solution to form a hydrogen peroxide product.

First product 33 comprising hydrogenated AAQ molecules 38 produced from hydrogenation reaction 40 and solvent 54 may be removed from chemical reaction chamber 14. First product 33 may be processed at a suitable separator 70 to remove undesired impurities such as any undesired byproducts of hydrogenation reaction 40. Separator 70 may implement any suitable separation methods and apparatuses may be used such as any physical separation methods (e.g., filtration and distillation) and/or chemical separation methods (e.g., extraction) .

The mixture of hydrogenated AAQ molecules 38 and solvent 54 is supplied to a reactor 72, for example an oxidation reactor 72. An oxygen-containing gas 74 is supplied to reactor 72. A pump 75 may be arranged to deliver oxygen-containing gas 74 to reactor 72. Oxygen-containing gas 74 may be pure oxygen gas (O ₂) or a mixture of gases comprising oxygen and one or more other gases. The one or more other gases may include an inert gas such as nitrogen gas (N ₂) . In some embodiments, oxygen-containing gas 74 comprises air.

Hydrogenated AAQ molecules 38 react in reaction 76 with oxygen-containing gas 74 to form a second product 80. Second product 80 comprises hydrogen peroxide 78.

In some embodiments, reaction 76 converts hydrogenated AAQ molecule 38 back to a non-hydrogenated AAQ molecule 36 such that second product 80 also comprises regenerated AAQ molecule 36.

In some embodiments, reaction 76 is a redox reaction. Reaction 76 may be an auto-oxidation reaction (i.e., a chemical reaction in which a substance oxidizes spontaneously, for example in the absence of a catalyst) . In some embodiments, reaction 76 is performed at a temperature in the range of from about 30℃ to 70℃.

One or more separators 80 may be arranged downstream of reactor 72 to separate hydrogen peroxide 78 from second product 80 comprising regenerated AAQ molecules 36.

In some embodiments, separator 80 comprises an extraction column. An example is a liquid-liquid extraction column. In example embodiments, water is used as an extracting agent. Water may be supplied to the extraction column with second product 80. Hydrogen peroxide is miscible in water and may preferentially migrate into a water phase. An aqueous hydrogen peroxide product (i.e. a hydrogen peroxide-water layer) may be removed from the extraction column.

In some embodiments, a pump 82 is arranged to deliver regenerated AAQ molecules 36 to chemical reaction chamber 14 for use in subsequent hydrogenation reactions 40. In some embodiments, solvent 54 containing the regenerated AAQ molecules 36 is purified to remove impurities before recycling back to chemical reaction chamber 14.

In some embodiments, a purifier 84 is arranged downstream of separator 80. Purifier 84 may be operable to purify the aqueous hydrogen peroxide product to remove impurities. Such impurities may include for example solvent 54, AAQ molecules 36 and/or hydrogenated AAQ molecules 38. Any suitable apparatuses and methods suitable for purifying the aqueous hydrogen peroxide product may be used. In one example embodiment, purifier 84 comprises a scrubber. An organic solvent such as toluene may be used as a scrubbing agent to remove organic impurities contained in the aqueous hydrogen peroxide product.

A concentrator 86 may be arranged to concentrate the aqueous hydrogen peroxide product. In example embodiments, concentrator 86 comprises a distillation apparatus. Distillation apparatus may for example comprise a sample reservoir containing the aqueous hydrogen peroxide product to be distilled, a heat source, a rectification column, a condenser, and a collector for receiving the concentrated hydrogen peroxide product. A vacuum source may be provided to reduce the pressure during the distillation process. In such example embodiments, hydrogen peroxide is concentrated by evaporating at least partially the aqueous hydrogen peroxide product contained in the sample reservoir. The vapors from the evaporated product are rectified by passing through the rectification column, and are collected as hydrogen peroxide which are of higher concentration and/or purity.

In some embodiments, a device 88 is provided for contacting a stabilizing agent with the recovered hydrogen peroxide. A suitable stabilizing agent may be provided to deactivate the catalytic activities which could result in the decomposition of hydrogen peroxide (particularly when the hydrogen peroxide is in the presence of impurities such as metal ions) . Examples of suitable stabilizing agents that may be used include sodium citrate, sodium malonate, sodium phytate, dipicolinic acid (DPA) , ethylenediamine tetra acetic acid compounds (EDTA) , etc.

A storage container 90 may be arranged downstream of device 88 to collect the stabilized hydrogen peroxide product.

Example Constructions for Metallic Membrane 12

Metallic membrane 12 is made of a material which is selectively permeable to absorbed hydrogen atoms 32.

Metallic membrane 12 may serve as all of: 1) a cathode; 2) a hydrogen selective layer which allows passage of hydrogen atoms (i.e. any isotope of hydrogen) and blocks other reactants including hydrogen ions; 3) a physical barrier which separates a solvent and the shuttle molecule in the chemical reaction chamber from the different solution or solutions used in the electrochemical compartment; and 4) a catalyst which helps to promote the hydrogenation reaction. The physical barrier advantageously allows for the use of solvent or solvents in the chemical reaction chamber that is incompatible with the electrolyte solution or solutions selected for the electrochemical compartment.

Metallic membrane 12 is made up of at least one metal. The metal, may, for example, have a crystalline lattice that provides interstitial sites that can accept hydrogen atoms. In example embodiments, metallic membrane 12 is made from palladium (Pd) metal. Palladium is highly selective for passing hydrogen and is impermeable to most practical solvents and electrolytes. Palladium metal has a face centered cubic crystal lattice that is capable of hosting hydrogen atoms up to a hydrogen/palladium ratio (H: Pd) of approximately 0.7 (PdH _0.7) . Another example metal that may be used as metallic membrane 12 is a hydrogen permeable pallidum alloy. Examples of palladium alloys that may be used to make metallic membrane 12 include but are not limited to: Pd-Ag, Pd-Sn, Pd-Au, Pd-Pb, Pd-B, Pd-Pt, Pd-Rh, Pd-Ni and Pd-Cu. Other metals that have high permeability to hydrogen include niobium, vanadium and tantalum.

In some embodiments, metallic membrane 12 is formed of one or more layers. The one or more layers may be formed by electrodeposition and/or sputtering. The one or more layers may comprise a metal such as palladium or a palladium alloy and/or a layer of co-catalyst 42.

In some embodiments, layer of catalyst 42 is applied on second surface 24 of metallic membrane 12 to promote hydrogenation reaction 40 in chemical reaction chamber 14. Catalyst 42 may be called a “co-catalyst” . Co-catalyst 42 may be porous. Co-catalyst 42 may be heterogeneous.

In some embodiments, co-catalyst 42 comprises one or more transition metals. “Transition metals” include elements that have (or readily form) partially filled d-orbitals, for example those located in groups 3-12 of the periodic table. Examples of suitable elements that may be used as co-catalyst 42 include but are not limited to gold, iridium, palladium, platinum and ruthenium. In some embodiments, co-catalyst 42 comprises a palladium alloy. In one example embodiment, the palladium alloy is a gold palladium (AuPd) alloy.

In some embodiments, the thickness of the layer of co-catalyst 42 is in the range of from 3 nm to 20 nm, including any value therebetween, such as 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, etc.

In some embodiments, metallic membrane 12 comprises a self-supporting member made of a hydrogen selective material as described herein. The member may, for example have the form of a sheet, plate, corrugated sheet or plate, casting or the like. In some embodiments, metallic membrane 12 is formed on or attached to a permeable substrate that helps to support metallic membrane 12.

In example embodiments, metallic membrane 12 is formed by electrodepositing one or more layers of palladium on one or both sides of a palladium foil or a hydrogen selective membrane. Such membrane 12 may be called a “Pd/Pd membrane” , Without being bound to theory, the electrodepositing of one or more layers of palladium may result in a morphology that provides greater surface area of the membrane. The one or more layers may for example be made of palladium electrodeposited from a solution comprising a palladium salt. In example embodiments, the palladium salt comprises palladium chloride (PdCl ₂) .

In some embodiments, the layer of co-catalyst 42 comprises one or more of co-catalysts selected from: gold, and a gold palladium (AuPd) alloy. Gold or a mixture of gold and palladium may for example be sputtered on a Pd/Pd membrane. Without being bound to theory, providing a layer of Au or AuPd alloy on metallic membrane 12 serves to both increase the surface area of metallic membrane 12 and suppress H ₂O ₂ decomposition by suppressing O-O bond cleavage. The atomic ratio Au: Pd of the AuPd alloy may for example be in the range of from 1: 0 to 20: 0, including any value therebetween such as 2: 0, 3: 0, 4: 0, 5: 0, 6: 0, 7: 0, 8: 0, 9: 0, 10: 0, 11: 0, 12: 0, 13: 0, 14: 0, 15: 0, 16: 0, 17: 0, 18: 0, 19: 0, etc.

Any suitable method for electro-depositing and/or sputter-depositing palladium salt and/or the layer of co-catalyst on a hydrogen selective membrane may be used. In an example electro-deposition process, an Ag/AgCl electrode is used as a reference electrode and a Pt mesh electrode is used as the counter electrode. The electrodeposition may be performed in an acidic PdCl ₂ solution. For example, the solution may comprise 15.9 mM PdCl ₂ dissolved in 1 M HCl. Roughly -0.2 V vs. Ag/AgCl potential is applied to the electrodes. The electrodeposition is complete when a desired thickness of palladium has been deposited. Completion may be determined by measuring a charge passed in the electrodeposition circuit. For example some satisfactory electrodeposited palladium layers were made by terminating the electrodeposition when a charge of about 7.5 C/cm ² of the membrane had passed in the circuit.

In some embodiments, an electrodeposition current in the range of about 20 mA to about 100 mA is applied to electrodeposit a co-catalyst on metallic membrane 12. The magnitude of the electrical current may be set based on the type of co-catalyst to be deposited. For example, the electrical current may be maintained at about 30 mA in embodiments in which gold and or platinum are selected as the co-catalyst and 70 mA in embodiments in which iridium is selected as the co-catalyst.

In some embodiments, the co-catalyst is sputter-deposited at a rate in a range from about 0.1 to about 1 mm/s. In example embodiments, the co-catalyst is sputter-deposited at a rate of about 0.2 mm/s.

In example embodiments, membrane 12 comprises a palladium foil. The density of the palladium foil may be about 11.9 g/cm ³. The thickness of the palladium foil may for example be in the range from 25 μm to 150 μm.

Example Methods for Producing H ₂O ₂

FIGS. 2A and 2B are flow charts illustrating the steps of an example method 100 of producing hydrogen peroxide. Referring to FIG. 2A, in block 112, an electrical current and/or potential is applied between an anode and a metallic membrane which serves as a cathode. In block 114, a hydrogen-containing compound such as water is supplied at the anode. In block 116, the hydrogen-containing compound undergoes an oxidation reaction to produce hydrogen ions (H ⁺) . The hydrogen ions (H ⁺) migrate toward the metallic membrane (block 118) . In block 120, the hydrogen ions (H ⁺) undergo a reduction reaction on a first surface of the metallic membrane to form hydrogen atoms. The hydrogen atoms pass through the metallic membrane as absorbed hydrogen atoms and appear on a second surface of the metallic membrane (block 122) . In block 124, a solvent comprising a shuttle molecule is supplied to a chemical reaction chamber. The shuttle molecule undergoes a chemical reaction by reacting with the hydrogen atoms to produce a hydrogenated shuttle molecule in the chemical reaction chamber (block 126) . The oxidation reaction at block 116 may be performed in tandem with the reduction reaction at block 120 and the chemical reaction at block 126.

In some embodiments, the AAQ molecule or the solution of AAQ in solvent 54 is heated before supplying into the chemical reaction chamber. In example embodiments, the AAQ solution in the chemical reaction chamber is at a temperature in the range of from about 40 to 120℃. In some embodiments, the AAQ solution in the chemical reaction chamber is at a temperature in the range of from about 40 to 80℃.

As described above, the chemical reaction between AAQ molecules and the hydrogen atoms typically occurs on the second surface 24 of metallic membrane 12 (in block 126) . The method may comprise balancing the supply of hydrogen atoms and the supply of AAQ molecules as described above. In some embodiments, a constant supply of AAQ molecules is fed to the chemical reaction chamber to provide a sufficient amount of AAQ molecules to be available for reaction with substantially all hydrogen atoms that reach the second surface of the metallic membrane. The flow rate at which the AAQ molecules or the solvent containing the AAQ molecules is supplied into the chemical reaction chamber may be adjusted to ensure that a sufficient and/or an excess amount of AAQ molecules is present in react with the hydrogen atoms.

In some embodiments, the hydrogen ions (H ⁺) produced at the anode in block 116 migrate to an ion exchange membrane and pass through the ion exchange membrane (block 128) before migrating to the metallic membrane (block 118) to participate in the reduction reaction at block 120.

Referring to Figure 2B, in block 130, the hydrogenated AAQ molecule produced in the chemical reaction chamber at block 126 reacts with an oxygen-containing gas. The oxidation reaction yields a product comprising hydrogen peroxide. The product may also comprise regenerated AAQ molecules. In block 132, the hydrogen peroxide is separated from impurities such as the solvent, regenerated AAQ molecules and/or unreacted hydrogenated AAQ molecules. Such separation may for example be done by a water extraction process. The unprocessed hydrogen peroxide solution may be purified, concentrated and stabilized (blocks 134-138) to yield a recovered hydrogen peroxide product before storage at block 140.

In some embodiments, the mixture comprising the regenerated AAQ molecules and solvent is recycled to the chemical reaction chamber for re-use in subsequent chemical reactions (block 144) . The mixture comprising the regenerated AAQ molecule and solvent is optionally purified to remove impurities prior to returning to the chemical reaction chamber (block 142) .

In some embodiments, the products of the chemical reaction released into the chemical reaction chamber comprising the hydrogenated AAQ molecules may be separated to remove impurities (block 146) before reacting with the oxygen-containing gas at block 130.

Method 100 may be tuned to optimize one or more of product selectivity, current efficiency and reaction rate of each of the electrochemical reactions and chemical reactions by adjusting one or more of:

● characteristics of the metallic membrane such as the particular metal or metals used to make the membrane hydrogen selective and its surface area, density and thickness, and/or

● additional catalysts present; and/or

● conditions of the flow cell such as temperature, pH, pressure, etc.; and/or

● the choice of solvent and electrolyte in the area where each reaction takes place; and/or

● the concentration of AAQ in the chemical reaction chamber;

● flow rate of the AAQ molecule and/or solvent; and/or

● flow rate and/or composition of the reactants and/or solvent and/or catholyte and/or anolyte; and/or

● characteristics of the ion exchange membrane such as the thickness, porosity, etc.; and/or

● electrical operating conditions such as the applied electrical potential; and/or

● characteristics of the cathode and/or anode electrodes such as the material and method of fabrication; and/or

● nature of the cathode and/or anode catalyst;

● etc.

At least some of these factors may be separately optimized for each of the electrochemical and chemical reactions to achieve high rates of formation of the products and/or high selectivity of the desired products at each of the electrochemical and the chemical reaction chambers. The physical barrier provided by metallic membrane 12 advantageously allows the electrochemical and chemical reaction conditions in chemical reaction chamber 14 and electrochemical reaction zone 16 to be controlled independently. Examples of conditions that can be independently controlled are: catalysts, choice of solvent, choice of electrolytes or other additives, etc. Although apparatus as described herein may be operated at low temperatures (e.g. room temperature) and at low pressures (e.g. atmospheric pressure) it is possible to operate one or both electrochemical reaction zone 16 and chemical reaction zone 52 of metallic membrane 12 at pressures above or below atmospheric pressure and/or at temperatures above and/or below room temperature. Within limits imposed by the physical design of metallic membrane 12, it is possible to independently control temperature and/or pressure on either side of metallic membrane 12.

In some embodiments, an electrical potential difference applied between the anode and the metallic membrane introduces a current density at the metallic membrane of at least about 100 mA cm ^-2 . For example, in some embodiments the current density at the metallic membrane is maintained in the range of about 100 mA cm ^-2 to about 500 mA cm ^-2, including any value therebetween such as 100 mA cm ^-2, 150 mA cm ^-2, 200 mA cm ^-2, 250 mA cm ^-2, 300 mA cm ^-2, 350 mA cm ^-2, 400 mA cm ^-2, 450 mA cm ^-2, etc. In some embodiments, the current density is maintained at a level of at least 100 mA cm ^-2.

In some embodiments, electrochemical cell 11 is maintained at a temperature in a range of from about 25℃ to about 80℃, including any value therebetween such as 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, etc.

In some embodiments, the concentration of AAQ molecules in the solvent being supplied to the chemical reaction chamber is in the range of from about 0.1 M to about 1 M, including any value therebetween such as 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, etc.

Fig. 3 is a schematic diagram illustrating an example reactor 300 which may be used to perform paired electrochemical and chemical reactions in the production of hydrogen peroxide (H ₂O ₂) . Reactor 300 comprises a hydrogenation reaction zone 302, an anode reaction zone 306 and a cathode reaction zone 304 between hydrogenation and

anode reaction zones

302, 306. Anode reaction zone 306 and cathode reaction zone 304 form an electrochemical reaction zone 308. An anode (not shown) may be exposed to anode reaction zone 306, for example through anode port 307.

A metallic membrane 309 which acts both as a cathode and as a hydrogen permeable barrier is positioned between hydrogenation reaction zone 302 and cathode reaction zone 304. In the illustrated embodiment, a compression plate 312 holds metallic membrane 309 against a flow field 302A.

Hydrogenation reaction zone 302 comprises an inlet 310. An AAQ solution is supplied to hydrogenation reaction zone 302 through inlet 310. In reactor 300 hydrogenation reaction zone 302 comprises flow field 302A which provides a chemical reaction chamber at which flowing AAQ solution is brought into contact with hydrogen atoms at a face of metallic membrane 309. AAQ molecules become hydrogenated in a hydrogenation reaction and then exit hydrogenation reaction zone 302 at outlet 311.

In some embodiments, an ion exchange membrane (not shown) separates cathode reaction zone 304 from anode reaction zone 306. In such embodiments the composition of an anolyte can be different from the composition of a catholyte.

In some embodiments, anode reaction zone 306 contains water and a suitable electrolyte (e.g. H ₂SO ₄) . In some embodiments, anode reaction zone 306 comprises an inlet (not shown) . The water and/or electrolyte may be supplied to anode reaction zone 306 through the inlet. In some embodiments an electrolyte solution is flowed through anode reaction zone 306.

The components of cell 300 are compressed together between

end plates

314A and 314B.

FIG. 4 is a schematic diagram showing another example reactor 400 which may be used in the production of hydrogen peroxide (H ₂O ₂) by a method which involves hydrogenating AAQ in a chemical reaction paired with an electrochemical reaction which produces hydrogen atoms.

Reactor 400 comprises a flow cell that comprises a cathode plate 410 that is pressed against a first surface 412 of metallic membrane 414. An anode plate 416 is pressed against an anode 418. A hydrogenation flow plate 420 is pressed against an opposing second surface 422 of metallic membrane 414.

An inlet 424 of hydrogenation flow plate 420 is fluidly connected to a reservoir 426. that contains an AAQ solution. Inlet 424 is fluidly connected to deliver AAQ solution 426 to chemical reaction chamber 428. An outlet 430 of hydrogenation flow plate 420 may be fluidly connected to a collector (not shown) . Product comprising hydrogenated AAQ molecules dissolved in solvent may flow out of reactor 400 by way of outlet 430.

The product comprising hydrogenated AAQ molecules may be supplied to a reactor 428 for reaction with an oxygen-containing gas. This reaction yields a product comprising hydrogen peroxide. The reaction may regenerate non-hydrogenated AAQ molecules (which may be returned to reservoir 426 and/or to reactor 400) .

The product is separated to recover hydrogen peroxide. The product may undergo one or more of separation, purification, concentration and/or stabilization. The recovered hydrogen peroxide may be stored in a collector.

In example embodiments, anode plate 416 comprises an anode chamber which contains an anolyte comprising a hydrogen-containing compound such as water as the reactant. Cathode plate 410 may comprise a cathode chamber which contains a catholyte which may be the same as or different from the anolyte.

In some embodiments, anode plate 416 comprises an anode flow field which has an inlet that is fluidly connected to an anolyte source (which may comprise a reservoir) . The anolyte source supplies anolyte which may be delivered to anode 418 by flowing through the anode flow field. Anode flow plate 416 may also include an outlet. The outlet may be connected to recirculate anolyte to an anolyte reservoir or to deliver anolyte to a drain. Unreacted water and/or unwanted materials may flow out through the outlet.

Housings 432, 434 may be arranged to press against hydrogenation flow plate and

anode plate

420, 416 respectively.

The invention is further described with reference to the following specific examples, which are not meant to limit the invention, but rather to further illustrate it. EXAMPLES

Example 1 –Indirect hydrogen peroxide synthesis

An electrochemical cell of the type illustrated in FIG. 1 and the method illustrated in FIG. 2A were used to oxidize water 56 at anode 28 which releases hydrogen ions (H ⁺) in anode chamber 20, and to hydrogenate AAQ molecules 36 in chemical reaction chamber 14. In the example embodiment, metallic membrane 12 which separates the chemical and electrochemical reaction zones is a palladium membrane.

Metallic membrane 12 used in the example embodiments was formed from a 1 oz palladium wafer bar which was rolled to palladium foil with a thickness of about 150 μm.The palladium foil was then rolled to a thickness of about 25 μm. The 25 μm thickness was annealed in an inert atmosphere (under argon, Ar) at 850℃ for 1.5 hours. Before use, the annealed foils were cleaned using 0.5: 0.5: 1 vol. %concentration of HNO ₃: H ₂O: 30%H ₂O ₂. The co-catalyst comprises palladium. The co-catalyst was electrodeposited on the palladium foil. The electrodeposition was performed in 15.9 mM PdCl ₂ in 1 M HCl solution. The foil was placed into the cell as the working electrode. An Ag/AgCl electrode was used as a reference electrode and a Pt mesh electrode was used as the counter electrode. Roughly -0.2 V vs. Ag/AgCl potential was applied to the electrodes. The electrodeposition is complete when a charge of about 25 C/cm ² has been passed in the circuit, which provided about 5 mg of co-catalyst material on the palladium foil.

Example 2 –Indirect hydrogen peroxide synthesis using AAQ as a shuttle molecule in a solvent comprising protic and aprotic solvents

An electrochemical flow reactor of the type illustrated in FIG. 3 was used to investigate the effect of solvent composition on current efficiency when hydrogenating AAQ. The reactor was maintained at a temperature of 55℃ in an oven for these experiments. The electrolyte in the electrochemical side of the reactor was 1M H ₂SO ₄. Current density at the metallic membrane was set to either 100 mA cm ^-2 or 200 mA cm ^-2. The metallic membrane was a palladium foil coated with palladium black on the face exposed to flow field 302A.

In each run of the experiment, 15 ml of AAQ solution was circulated through flow field 302A for 15 minutes. Current efficiencies were extrapolated by measuring the amount of AAQ that had been converted to hydrogenated AAQ after 15 minutes of electrolysis to produce hydrogen atoms. The amount of AAQ that had been converted to hydrogenated AAQ was measured by iodometric titration. Iodometric titration was performed by reacting hydrogenated AAQ with iodine (I ₂) to form hydrogen iodide (HI) and AAQ. Excess I ₂ that was left in the solution was titrated against a solution of thiosulfate with an iodometric color indicator. 100%current efficiency corresponds to the case where one AAQ molecule is hydrogenated for every two electrons flowing in the cathode (each AAQ molecule can carry two hydrogen atoms) . The solvent was a mixture of Solvesso 150 and DIBC.

For the experiments at a current density of 100 mA cm ^-1 the concentration of AAQ in the AAQ solution was 0.78M. For the experiments at a current density of 200 mA cm ^-1 the concentration of AAQ in the AAQ solution was 0.83M. Table 1 provides the composition of the AAQ solution for these experiments.

Fig. 5 is a graph that shows current efficiency as a function of solvent composition based on data acquired in the experiments of Table 1.

A current efficiency of 59.3%was achieved for a weight ratio of Solvesso: DIBC = 2.75 at 200 mA cm ^-2. As compared to the electrolysis being operated at 100 mA cm ^-2, a higher production rate of hydrogenated AAQ was achieved (about 1.184 times higher) at 200 mA cm ^-2.

Example 3 –Effect of AAQ concentration on current efficiency

Fig. 6 is a graph showing current efficiency as a function of solvent composition for different concentrations of AAQ. Conditions were the same as for runs A and C of Table 1 with current density of 100 mA cm ^-2 .

Fig. 6 demonstrates that current efficiencies are higher when:

● the weight ratio of Solvesso: DIBC is decreased from 4: 1 to 1: 1; and

● AAQ concentration is increased.

Example 4 –Rate of hydrogenation of AAQ

Fig. 7 is a graph showing the percentage of hydrogenation of AAQ as a function of time. Conditions were the same as run D of Table 1.30.9%of the AAQ molecules in the 15 ml sample were converted to hydrogenated AAQ after 1 h running at a current density of 200 mA cm ^-2.

The rate of hydrogenation of AAQ may be retained by adding a Pd/C nanoparticle catalyst to the surface of the metallic membrane in addition to an electrodeposited catalyst (e.g. Pd black) . These results demonstrate that nanoparticle catalysts may be used without negatively impacting the rate of hydrogenation of AAQ. The Pd/C catalyst may be bound to the surface of the metallic membrane using a suitable binder such as polytetrafluoroethylene (PTFE) or Nafion ^TM. Using PTFE (an apolar polymer) or Nafion ^TM (a negatively charged polymer) as a catalyst binder is believed to assist with the transport of polar AAQ molecules and polar hydrogenated AAQ molecules to and away from the catalyst respectively.

Palladium on carbon nanoparticles (with a polymeric binder) may be spray-coated onto a metallic membrane to increase surface area of the electrodeposited palladium catalyst ( “Pd black” ) . The binder may also help to bind the electrodeposited catalyst to the metallic membrane.

Fig. 8 is a graph that includes curves showing the percentage of hydrogenation of AAQ as a function of time for:

● Pd/C nanoparticle catalyst bound to Pd black with 5%Nafion (curve 81)

● Pd/C nanoparticle catalyst bound to Pd black with 5%PTFE (curve 82)

● Pd/C nanoparticle catalyst bound to Pd black with 2.5%Nafion (curve 83)

● Pd/C nanoparticle catalyst bound to Pd black with 5%Sustanion ^TM (curve 84) In each case the Pd/C nanoparticle catalyst was spray coated onto the Pd black surface of the metallic membrane. The Pd/C nanoparticle catalyst was observed to delaminate from the metallic membrane in the samples used for

curves

83 and 84.

Summary of Experimental Results

A membrane reactor as described herein is effective for hydrogenating AAQ in a solvent which comprises an aprotic solvent (Solvesso) mixed with a protic solvent (DIBC) . 59.3%current efficiency was achieved during electrolysis at 200 mA cm ^-2 .

Rates of hydrogenation are higher for high fractions of aprotic solvent (e.g., Solvesso) as compared to protic solvent (e.g., DIBC) . A weight ratio of Solvesso: DIBC of 2.75 was found to be best. Specifically, high current efficiencies were achieved at a weight ratio of Solvesso: DIBC of 2.75.

Higher concentrations of AAQ (e.g. 0.83M) tended to yield higher rates of hydrogenation than lower concentrations of AAQ.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout the description and the claims:

● “comprise” , “comprising” , and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to” ;

● “connected” , “coupled” , or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof;

● “herein” , “above” , “below” , and words of similar import, when used to describe this specification, shall refer to this specification as a whole, and not to any particular portions of this specification;

● “or” , in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list;

● the singular forms “a” , “an” , and “the” also include the meaning of any appropriate plural forms. These terms ( “a” , “an” , and “the” ) mean one or more unless stated otherwise;

● “and/or” is used to indicate one or both stated cases may occur, for example A and/or Β includes both (A and Β) and (A or Β) ;

● “approximately” when applied to a numerical value means the numerical value ± 10%;

● where a feature is described as being “optional” or “optionally” present or described as being present “in some embodiments” it is intended that the present disclosure encompasses embodiments where that feature is present and other embodiments where that feature is not necessarily present and other embodiments where that feature is excluded. Further, where any combination of features is described in this application this statement is intended to serve as antecedent basis for the use of exclusive terminology such as "solely, " "only" and the like in relation to the combination of features as well as the use of "negative" limitation (s) ” to exclude the presence of other features; and

● “first” and “second” are used for descriptive purposes and cannot be understood as indicating or implying relative importance or indicating the number of indicated technical features.

Words that indicate directions such as “vertical” , “transverse” , “horizontal” , “upward” , “downward” , “forward” , “backward” , “inward” , “outward” , “left” , “right” , “front” , “back” , “top” , “bottom” , “below” , “above” , “under” , and the like, used in this description and any accompanying claims (where present) , depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

Where a range for a value is stated, the stated range includes all sub-ranges of the range. It is intended that the statement of a range supports the value being at an endpoint of the range as well as at any intervening value to the tenth of the unit of the lower limit of the range, as well as any subrange or sets of sub ranges of the range unless the context clearly dictates otherwise or any portion (s) of the stated range is specifically excluded. Where the stated range includes one or both endpoints of the range, ranges excluding either or both of those included endpoints are also included in the invention.

Certain numerical values described herein are preceded by "about" . In this context, "about" provides literal support for the exact numerical value that it precedes, the exact numerical value ±5%, as well as all other numerical values that are near to or approximately equal to that numerical value. Unless otherwise indicated a particular numerical value is included in “about” a specifically recited numerical value where the particular numerical value provides the substantial equivalent of the specifically recited numerical value in the context in which the specifically recited numerical value is presented. For example, a statement that something has the numerical value of “about 10”is to be interpreted as: the set of statements:

● in some embodiments the numerical value is 10;

● in some embodiments the numerical value is in the range of 9.5 to 10.5; and if from the context the person of ordinary skill in the art would understand that values within a certain range are substantially equivalent to 10 because the values with the range would be understood to provide substantially the same result as the value 10 then “about 10” also includes:

● in some embodiments the numerical value is in the range of C to D where C and D are respectively lower and upper endpoints of the range that encompasses all of those values that provide a substantial equivalent to the value 10.

Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any other described embodiment (s) without departiang from the scope of the present invention.

Any aspects described above in reference to apparatus may also apply to methods and vice versa.

Any recited method can be carried out in the order of events recited or in any other order which is logically possible. For example, while processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, simultaneously or at different times.

Various features are described herein as being present in “some embodiments” . Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. All possible combinations of such features are contemplated by this disclosure even where such features are shown in different drawings and/or described in different sections or paragraphs. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible) . This is the case even if features A and B are illustrated in different drawings and/or mentioned in different paragraphs, sections or sentences.

It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions, and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

A method for producing hydrogen peroxide comprising:

applying an electrical potential between an anode and a metallic membrane;

electrochemically dissociating, at the anode, a hydrogen-containing compound to form hydrogen ions;

transporting the hydrogen ions to the metallic membrane;

at the metallic membrane, reducing the hydrogen ions to form hydrogen atoms;

diffusing the hydrogen atoms through the metallic membrane into a chemical reaction chamber;

reacting the hydrogen atoms with amyl-anthraquinone (AAQ) at a surface of the metallic membrane in the chemical reaction chamber to form hydrogenated AAQ; and

reacting the hydrogenated AAQ with oxygen to yield a product comprising hydrogen peroxide.
The method according to claim 1 wherein the reacting of the hydrogenated AAQ is performed outside of the chemical reaction chamber and the method comprises transporting the hydrogenated AAQ out of the chemical reaction chamber before reacting the hydrogenated AAQ with oxygen.
The method according to claim 2 wherein reacting the hydrogenated AAQ with oxygen yields regenerated AAQ and the method comprises recycling the regenerated AAQ to the chemical reaction chamber.
The method according to any one of the preceding claims, wherein reacting the hydrogen atoms with the AAQ is performed in a solvent.
The method according to claim 4, wherein the solvent comprises a mixture of an aprotic solvent and a protic solvent.
The method according to claim 4 wherein the solvent comprises more of the aprotic solvent by weight than the protic solvent.
The method according to any of claims 5 to 6 wherein the protic solvent comprises diisobutyl carbinol (DIBC) .
The method according to any of claims 5 to 7 wherein the aprotic solvent comprises a naphtha based solvent.
The method according to any of claims 5 to 8, wherein the aprotic solvent comprises a C9 to C11 hydrocarbon fraction.
The method according to claim 9, wherein the C9 to C11 hydrocarbon comprises a mixture of aromatic compounds.
The method according to any of claims 5 to 10, wherein the aprotic solvent comprises heavy naphtha aromatics.
The method according to any of claims 5 to 11 wherein a weight ratio of the aprotic solvent to the protic solvent is in the range of 2.5: 1 to 3: 1.
The method according to claim 12 wherein the weight ratio of the aprotic solvent to the protic solvent is approximately 2.75: 1.
The method according to any of claims 4 to 13 wherein a concentration of the AAQ is at least 0.5 M.
The method according to any of claims 4 to 13 wherein a concentration of the AAQ is at least 0.8 M.
The method according to any of the preceding claims wherein the chemical reaction chamber comprises a flow field that is in contact with the metallic membrane and the method comprises flowing the AAQ through the flow field.
The method according to any one of the preceding claims, wherein electrochemical dissociation of the hydrogen-containing compound at the anode is performed in an aqueous electrolyte solution.
The method according to any of the preceding claims, wherein reacting the hydrogen atoms with AAQ is catalyzed by a co-catalyst on the metallic membrane.
The method according to claim 18, wherein the co-catalyst comprises one or more transition metals.
The method according to claim 18 or 19, wherein the co-catalyst comprises one or both of palladium and gold.
The method according to claim 20, wherein co-catalyst comprises Palladium black.
The method according to any of claims 18 to 21 wherein the co-catalyst comprises a layer of Palladium on carbon nanoparticles.
The method according to claim 22 wherein the Palladium on carbon nanoparticles are mixed with a polymeric binder.
The method according to claim 23 wherein the polymeric binder comprises PTFE or a sulfonated tetrafluoroethylene based fluoropolymer-copolymer.
The method according to any of the preceding claims comprising transporting the hydrogen ions through an ion exchange membrane located between the anode and the metallic membrane.
The method according to any of the preceding claims, wherein the method comprises maintaining a current density at the metallic membrane of at least 100 mA/cm ^-2.
The method according to any one of the preceding claims, wherein the method comprises maintaining a temperature at the chemical reaction chamber in the range of 25℃ to 80℃.
The method according to any one of the preceding claims, wherein the metallic membrane comprises a dense metallic hydrogen selective layer.
The method according to claim 28, wherein the hydrogen selective layer comprises a layer of palladium or a palladium alloy.
Apparatus having any new and inventive feature, combination of features, or sub-combination of features as described herein.
Methods having any new and inventive steps, acts, combination of steps and/or acts or sub-combination of steps and/or acts as described herein.