WO2014091101A1 - Process and device for producing pure hydrogen under pressure, by permeation through a metallic membrane in contact with protic liquid solution - Google Patents

Abstract

The present invention describes a process for producing pure, dry hydrogen under pressure by electrolysis and permeation through a metallic wall immersed in a protic liquid solution containing a promoter for entry of the hydrogen into the metal. The invention also relates to the device for implementing said process.

Description

 PROCESS AND DEVICE FOR PRODUCING PURE HYDROGEN UNDER PRESSURE BY PERMEATION THROUGH A METAL MEMBRANE

 IN CONTACT WITH A PROTIC LIQUID SOLUTION

FIELD OF THE INVENTION

The present invention describes a process for producing hydrogen under high pressure, high purity and very low water content, by exploiting the permeability property of certain metals (such as steel) with hydrogen (atomic or pro tonic). In this process, hydrogen is generated on the surface of the metal by an electrochemical reduction reaction, and its entry into the metal is favored by the presence of a chemical species called "hydrogen input promoter", for example H ₂ S.

 This phenomenon is rather known to cause corrosion of steels, as well as embrittlement by hydrogen. In the context of the present invention, the corrosion phenomenon is avoided by applying a polarization of the immersed metal membrane within the protic liquid medium, which also makes it possible to increase the flow of hydrogen produced by electrochemical reaction, as well as to increase the equilibrium hydrogen gas pressure which is established on the other side of the metal membrane.

The hydrogen embrittlement phenomenon is generally treated using specific grades of steel or other resistant metal alloys.

 The process for producing H 2 according to the present invention makes it possible to maximize the flow (or flux) of hydrogen through the metal membrane, so as to produce directly compressed hydrogen.

The process thus intrinsically provides low energy cost pressurization, and high purity of product hydrogen which may be of interest in certain applications, such as fuel cells for example. The purity of the hydrogen obtained is greater than 99.999% by weight and the water content is less than 0.01 ppm H ₂

The pressure level of the hydrogen produced is a function of the choice of metal membrane, in a preferred range of 10 to 500 bar.

EXAMINATION OF THE PRIOR ART

We are not aware of relevant prior art on such a principle of production SUMMARY DESCRIPTION OF THE FIGURES

FIG. 1 schematically represents the method according to the invention with its main elements: the capillary tube system (1), the hydrogen collector (2), the protic liquid medium containing a hydrogen entry promoter (3) , the electrical circuit providing cathodic polarization (4), the counter electrode (5), the safety valve (6), the discharger (7) and the pressurized H ₂ tank (8).

 A flow of hydrogen (A) is generated inside the capillary tubes (1), and the hydrogen thus produced (B) is stored under pressure in the reservoir (8).

SUMMARY DESCRIPTION OF THE INVENTION

The present invention can be defined as a process for producing pure gaseous hydrogen gas under pressure using a metal membrane (1), one of whose faces is in contact with a protic liquid solution (3) containing a hydrogenated species in which hydrogen is at an oxidation state greater than zero, and a so-called "hydrogen entry promoter" species in the metal. Hydrogen is introduced into the metal membrane (1) by the effect of an electrochemical reduction reaction of said hydrogenated species, then diffuses through said metal membrane under the action of a hydrogen activity gradient. through the thickness, and recombines into gaseous hydrogen on the second side of the metal membrane (1) in contact with a closed compartment containing pressurized hydrogen, which acts as a receptacle for hydrogen thus generated.

The hydrogen inlet promoter in the metal membrane is preferably chosen from the following bodies: H ₂ S, H ₃ As, HP, HSCN.

 The protic liquid solution (3) is preferably a deaerated aqueous solution, with an acidic pH of between 0 and 6, preferably between 2 and 5, and more preferably between 3 and 4.

The metal membrane (1) is preferably made of a grade steel resistant to embrittlement by hydrogen, or any other hydrogen-permeable metallic material, such as iron, palladium, niobium, thallium or alloys combining at least two of these different elements. The electrochemical reduction reaction leading to the formation of hydrogen is favored by cathodic polarization of the surface of the membrane (1) at a potential of between -0.9 V and -1.5 V relative to a standard calomel electrode. saturated.

The temperature of the aqueous solution (3) is generally between 20 ° C and 800 ° C, and preferably between 20 ° C and 100 ° C.

 In the process for producing hydrogen under pressure according to the present invention, the pressure of the liquid electrolytic solution is preferably maintained at a pressure greater than the saturation vapor pressure of the electrolyte.

 In general, the hydrogen is generated at a pressure of between 1 and 2000 bar, and preferably between 10 and 500 bar. Of course, the choice of the thickness of the membrane and its volume takes into account the desired level of pressure.

 For example, for membranes consisting of a set of capillary tubes with a diameter of about 200 microns, a thickness of between 80 and 130 microns makes it possible to withstand hydrogen pressures generated of the order of 100 bar.

 The present invention also consists of a device allowing the implementation of the method, a device consisting of:

 A set of capillary tubes (1) arranged in parallel, each tube being closed at one of its ends, and whose open ends communicate with a collector (2), said collector (2) supplying the steam circuit on which find a safety valve (6), a discharge (7), and a reservoir for collecting the product hydrogen (8),

 An electrical circuit allowing the cathodic polarization of the capillary tubes (1) and of an anode (5),

- An electrolytic medium (3) consisting of an aqueous solution supplied with H ₂ S in which is immersed all of the capillary tubes (1) and the anode (5).

The overflow (7) serves to maintain a pressure of hydrogen gas in contact with the outlet face of the metal membrane, less than the equilibrium pressure at the inlet of said membrane. This pressure difference between the inlet face and the outlet face is necessary to maintain a hydrogen activity gradient in the thickness of the membrane, and thus promote the transport of hydrogen from the face in contact with the protic solution (3) towards the face in contact with the hydrogen produced. The thickness of the capillary tubes (1) used in the context of the present invention is generally between 20 microns and 500 microns for internal diameters of tubes of between 50 microns and 2 mm.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is to exploit the phenomenon of permeation through a metal wall to produce hydrogen under pressure. A metal membrane (1) of steel or other metal alloy permeable to hydrogen, such as palladium, niobium, thallium (or alloys combining these elements), is used to produce hydrogen by an electrochemical reaction of reduction, then to separate it and to pressurize it.

 In the natural state, this phenomenon induces the corrosion of the steel or metal alloy in contact with the protic liquid solution, according to the electrochemical reactions (R 1) and (R 2).

H ⁺ (solution) + e ^~ -> - ^ H (steel) (R. l) Fe (steel) → Fe ²⁺ + 2e ^~ (R.2)

In the example above, the reaction (R. 1) reflects the reduction of the proton followed by the entry of hydrogen into the steel, and the reaction (R.2) reflects the corrosion of the iron.

The reaction (R. 1) leads to the introduction into the metal of a hydrogen atom. In the context of the present invention, the reagent (H ⁺ ) in the reaction (R. 1) can be replaced by any hydrogenated chemical compound in which the hydrogen is present at an oxidation state greater than zero.

 In the context of the present invention, a cathodic electric polarization is applied by an external current source to the steel or metal alloy membrane (1).

This polarization leads to a modification of the kinetics of the reactions (R. 1) and (R.2), in the sense of an increase in the hydrogen production rate (R 1) and a decrease or even a cancellation of the corrosion rate (R.2).

The polarization of the metal surface (1) subjected to the protic liquid medium (3) therefore has a double advantage: on the one hand, it greatly reduces the dissolution rate of the metal (reaction R.2) and secondly it increases the flow of hydrogen penetrating into the metal (R 1 reaction), which is the phenomenon sought in the context of the present invention.

Moreover, this polarization also leads to increasing the equilibrium pressure which is established on the other side of the metal membrane (1), not exposed to the protic liquid medium (3).

 The increase in the flow of hydrogen is however not monotonous with the polarization potential: beyond a limiting potential, the efficiency of the mechanism of entry, then of permeation of the hydrogen through the metallic membrane ( 1) decreases.

Part of the hydrogen generated by the electrochemical reaction is then likely to degass at the inlet surface, instead of passing through the metal membrane (1). This hydrogen then remains on the side of the protic liquid solution (3) and no longer crosses the metal membrane (1).

 On this principle, the proposed invention also consists of a device for producing hydrogen under pressure which can be described as follows:

 The device consists of one or more steel tubes (1) of small diameter and small thickness but sufficient for the tube to withstand the desired hydrogen pressure, potentially up to several hundred bars. This type of tube is generally called a "capillary tube".

The metal capillary tubes (1), are closed at one of their ends (by any method known to those skilled in the art, crushing, welding ...) and all connected to a collector (2) of greater thickness, him- even connected to an overflow (7) and a safety valve (6). Downstream of the discharger (7) is the reservoir (8) in which the hydrogen is accumulated under pressure. The capillary tubes (1) are exposed on their outer face to a protic liquid solution (3), preferably a deaerated aqueous solution and at an acidic pH, called loading solution. This loading solution contains promoter elements of hydrogen loading, which may be, for example, but not exhaustively, H ₂ S, H ₃ As, H ₃ P, HSCN.

 The collector (2) is electrically insulated from the rest of the gas line.

The capillary tubes (1) are immersed in the aqueous solution (3) constituting the electrolytic medium in the presence of a counter electrode (5) with an area greater than or equal to the cumulative surface area of the capillary tubes (1). The counter electrode (5) makes it possible to circulate the electric current induced by the cathodic polarization of the metal tubes. The counterelectrode (5) is preferably made of an inert metal so as not to undergo parasitic electrochemical reactions. Among the materials that can be used to form the counterelectrode (5), platinum, carbon or stainless steel may be mentioned in a non-exhaustive manner.

 In a variant of the present device, this counter-electrode (5) can be separated from the protic liquid solution (3) in contact with the metal tubes (1), and placed in another liquid compartment connected to the loading solution ( 3) through an ion exchange membrane or a porous separator.

EXAMPLES ACCORDING TO THE INVENTION Example 1

An aqueous solution (3) saturated with H ₂ S dissolved under a partial pressure p (H ₂ S) = 50 mbar (1 mbar = 10 ^-3 bar = 10 ² Pa) is obtained, pH = 4.5, T = 20 ° C,

 We apply a potential of -1,1V vs. Ag / AgCl between an inert counter electrode (5) and a set of capillary tubes (1)

 Steel capillary tubes (1) are used: thickness e = 80 μιη and diameter 0 = 200 μιη. The pressure of the overflow device (7) is set at 100 bar.

For the 480 capillary tubes immersed in the aqueous solution (3) over a height of 15 cm, the deployed surface of the tubes is 4520 cm ² .

An H ₂ flow rate of 0.36 mol / J is obtained, ie 8 NL / h ₂ H ₂ at a pressure which may be greater than 100 bars.

Example 2

 Several parameters can be used to increase the flow of hydrogen produced.

In an aqueous solution containing dissolved H ₂ S, the hydrogen flow produced increases as the acidity of the solution increases, as the concentration of dissolved H ₂ S increases, and as the temperature increases.

 Example No. 2 applies these principles to lead to a process for increasing the flow rate of hydrogen produced.

In this example, the aqueous solution (3) is saturated with H ₂ S dissolved under a partial pressure p (H ₂ S) = 10 bars, at pH = 3.5, and at a temperature of 80 ° C. We apply a potential of -1,1V vs. Ag / AgCl between an inert counter electrode (5) and the set of capillary tubes (1).

 A set of capillary tubes (1) made of steel is used: of thickness e = 80 μιη and of diameter 0 = 200 μπι.

 The pressure of the overflow (7) is set to 200 bar.

For the 480 capillary tubes immersed in the aqueous solution (3) over a height of 15 cm, the deployed surface of the tubes is 4520 cm ² .

An H ₂ flow rate of 195 mol / h is obtained, ie 4367 NL / h ₂ H ₂ at a pressure of 200 bar.

Claims

1. A process for producing pure gaseous hydrogen (that is to say purity greater than 99.999% by weight) and dry (that is to say water content less than 0.01 ppm H ₂ 0) and under pressure, using a metal membrane (1) permeable to hydrogen and made of steel resistant to hydrogen embrittlement or other hydrogen permeable metallic material, such as iron, palladium, niobium, thallium, one of whose faces is in contact with a protic liquid solution (3) of pH between 0 and 6, and containing a hydrogenated species in which the hydrogen is at an oxidation state greater than zero, and a so-called "input promoter" species of hydrogen in the metal chosen from H ₂ S, H ₃ As, H ₃ P, HSCN, a process in which hydrogen is introduced into the metal membrane (1) by the effect of a cathodic polarization of the surface of said membrane at a potential of -0.9 and -1.5 V per compared to a standard saturated calomel electrode, all of these characteristics leading to an electrochemical reaction (R. l) reducing said hydrogenated species, H ⁺ (solution) + e ^~ H (steel) (Rl) the atomic hydrogen diffuses through said metal membrane under the action of a gradient of hydrogen activity through the thickness, and recombines hydrogen gas on the second side of the metal membrane delimiting a closed compartment which acts as a receptacle for the hydrogen thus generated. Process for the production of pressurized hydrogen according to claim 1, in which the protic liquid solution (3) is a deaerated aqueous solution, preferably with an acidic pH of between 2 and 5 and more preferably between 2 and 4. The process for producing pressurized hydrogen according to claim 1, wherein the metal membrane (1) is made of a hydrogen-permeable metallic material, such as iron, palladium, niobium, thallium or alloys combining at least two of these different elements. The process for producing hydrogen under pressure according to claim 1, wherein the temperature of the aqueous solution (3) is between 20 ° C and 800 ° C, and preferably between 20 ° C and 100 ° C. The process for producing pressurized hydrogen according to claim 1, wherein the pressure of the liquid electrolyte solution is maintained at a pressure higher than the saturating vapor pressure of the electrolyte. 6. A process for producing hydrogen under pressure according to claim 1, wherein the hydrogen is generated at a pressure of between 1 and 2000 bar, and preferably between 10 and 500 bar. 7. Device for implementing the method according to claim 1, consisting of: A set of capillary tubes (1) arranged in parallel, each tube being closed at one of its ends, and whose open ends communicate with a collector (2), said collector (2) supplying the steam circuit on which find a safety valve (6), a discharge (7), and a reservoir for collecting the product hydrogen (8),  An electrical circuit allowing the cathodic polarization of the capillary tubes (1) and of an anode (5),  - An electrolytic medium (3) consisting of an aqueous solution containing a hydrogen inlet promoter in which the whole of the capillary tubes (1) and the anode (5) are immersed.