FR3040002A1 - PROCESS FOR TRAPPING OXYGEN - Google Patents

Abstract

The present invention relates to an oxygen scavenging method in which gaseous oxygen is brought into contact with an anion exchange support, said anion exchange support comprising fixed cationic groups and free anions X-, X - being an anion selected from the group consisting of SO32-; S2O52-; S2O72-, NO2-; and their mixtures.

Description

PROCESS FOR TRAPPING THE OXYGEN FIELD OF THE INVENTION

The present invention relates to a method for trapping oxygen in the form of gas through the use of an anion exchange medium. It also relates to the device for implementing this method.

The field of use of the present invention relates to any application requiring the elimination of gaseous oxygen, in particular hydrogen generators.

PRIOR STATE OF THE TECHNIQUE

Many applications require anaerobic conditions, especially to prevent corrosion of iron or cobalt materials. For this, various technologies have been developed to remove oxygen, whether it is dissolved in a solution or it is in the form of gas. By way of example, document CA 2 233 420 describes a method for limiting corrosion in a boiler by using sulphite ions in the boiler water.

US 4,231,869 discloses a process wherein a cobalt catalyst accelerates the reaction between solution dissolved oxygen and sulfite ions to form sulfate ions.

These solutions may be satisfactory in liquid media; however, some applications require the removal of gaseous oxygen. This is particularly the case of the generation of hydrogen from the catalyzed hydrolysis of a solution based on chemical hydride (more exactly based on borohydride) in a hydrogen generator, as described in the documents WO 2010/051557 and WO 2012/003112.

During the storage of the hydrogen generator, before its operation, it is essential to remove the oxygen present in order to maintain the performance of the catalyst by preventing its oxidation. For this, the hydrogen generator is generally purged before being packaged in a sealed package.

However, it is possible for oxygen to enter the interior of the hydrogen generator during its operation, in particular by permeation through the materials constituting the generator. It may be an amount of oxygen of the order of 1 μL per day to 5 mL per day.

In order to remedy this problem, gaseous oxygen absorbers have been developed to be positioned in the hydrogen generator. These include iron-based compounds, for example iron oxides, iron 0 or iron boride (FeBx).

To be effective, these absorbers generally require the presence of water or must be in the form of nanoparticles. Their use or preparation is therefore restrictive.

The present invention solves this technical problem by trapping oxygen gas without the need for water and without using nanoparticles.

SUMMARY OF THE INVENTION

The Applicant has developed a new process for trapping gaseous oxygen through the use of an anion exchange support (polymer or inorganic support). The entrapment of gaseous oxygen may be carried out in the presence or absence of water.

Ion exchange polymers (anions or cations) are commonly referred to as ion exchange resins. These are polymers capable of exchanging ions (anions or cations). This type of polymer is used in the present invention to trap oxygen gas.

More specifically, the present invention relates to an oxygen scavenging process according to which gaseous oxygen is brought into contact with an anion exchange support, said anion exchange support comprising fixed cationic groups and free anions X '. X 'being an anion selected from the group consisting of SO32', s2o52-, S2O72-, NO2 ', and mixtures thereof. One of the main advantages of the present invention resides in the trapping of gaseous oxygen by means of an anion exchanger carrier in solid form. Unlike the processes of the prior art employing SO32 'free sulfite ions, oxygen scavenging is advantageously carried out in the absence of a catalyst or solvent such as water. However, according to a particular embodiment, a transition metal catalyst may be used, for example a cobalt salt.

The present invention can be implemented in any type of application that requires trapping gaseous oxygen.

Thus, another subject of the invention relates to a process for trapping gaseous oxygen in a hydrogen generator, comprising the following steps: placing in a hydrogen generator, at least one anion exchange support comprising groups fixed cationic and free anions X ', X' being an anion chosen from the group comprising SO32 ', S2052', S2O72 ', NO2 ", and mixtures thereof, gaseous oxygen is trapped by contacting the oxygen gaseous with the anion exchanger carrier, hydrogen is generated, oxygen can also be trapped after hydrogen generation, in particular by contacting the gases (H2 and O2) with the anion exchange support

The present invention can be implemented in any type of application which requires trapping gaseous oxygen and the elimination of any basic and / or anionic and / or cationic impurities.

Thus, another subject of the invention relates to a process for trapping gaseous oxygen and for purifying hydrogen in a hydrogen generator, comprising the following steps: a hydrogen exchanger support is placed in a hydrogen generator. ions comprising: at least one anion exchange support comprising fixed cationic groups and free anions X ', X' being an anion selected from the group consisting of SO32 ', S2052', S2O72 ', NO2', and mixtures thereof; and at least one cation exchange support comprising Ct + free cations; gaseous oxygen is trapped by contacting the gaseous oxygen with the ion exchange support; hydrogen is generated; the hydrogen is purified by contacting the generated hydrogen with the ion exchange support.

Free anions X 'of the anion exchange support react with gaseous oxygen to form S042' ions (for S032 'anions), S2062' ions (for S2O52 anions), S20x2 ions (for S2O72 anions). ') and NO3' ions (for NO2 anions).

In general, any type of anion or cation exchange medium can be used in the present invention from the moment when these supports respectively have free anions X '(S032', S2052 ', S2072', N02 ', and their mixtures) and Ct + free cations.

The anion exchange support may be a polymeric support or a mineral support such as, for example, zeolites or grafted silicas.

Advantageously, the anion exchange support is a polymer of at least one monomer chosen from the group comprising styrene; divinylbenzene; acrylic; and their mixtures.

Acrylic polymers include polymers synthesized from acrylates, methacrylates or acrylonitrile. They are generally crosslinked by divinylbenzene in the presence of a radical initiator according to conventional techniques forming part of the knowledge of those skilled in the art.

The monomers and other starting substances may preferentially be chosen from the following list: monomers: styrene or acrylic (styrene, acrylates, methacrylates, acrylonitrile); crosslinking agent: divinylbenzene; activation catalysts: azobisisobutyronitrile (AIBN), peroxides; agents for chloromethylation: chloromethyl methyl ether CH2CIOCH3 in the presence of a catalyst AICI3OU SnCU.

The anion exchange support can in particular be a polymer support chosen from the group comprising: polymers with quaternary amine groups of the polymer-NR3 + / X 'and / or N-polymer (ROH) (R') 2+ / X 'type ; polymers with tertiary amine groups of the polymer-NHR 2+ / X 'type; polymers with secondary and / or primary amine groups of the polymer-NH 2 R + / X 'and / or polymer-NH 3 + / X' type; polymers with sulfonium groups of the polymer-SR2 + / X 'type; R and R 'being defined above as alkyl groups or aryl groups. The groups R and R 'are advantageously a CH 3 group.

The anion exchange medium can in particular be a copolymer of styrene and divinylbenzene or a copolymer of acrylic and divinylbenzene. Divinylbenzene then plays the role of crosslinking agent. The anion-exchange polymer support can in particular correspond to the functionalized copolymer (free anions X ') of styrene and divinylbenzene corresponding to the CAS number 60177-39-1.

As already indicated, the anion exchange support comprises fixed cationic groups.

The cationic fixed groups of the anion exchange support are advantageously groups chosen from the group comprising: -NH 3 +; -NR3 +; -NHR2 +; -NH2R +; -N (ROH) (R ') 2+; and -SR2 +; R and R 'being alkyl or aryl. The groups R and R 'are advantageously a CH 3 group.

The present invention can also implement a cation exchange support comprising Ct + free cations. These free Ct + cations are advantageously chosen from the group comprising Na + ions; H +; K +; and their mixtures.

Advantageously, the cation exchange support comprising Ct + free cations comprises fixed anions which can be chosen from -SO 3 '; -H2P (V; -COCT; and -CH2-COO '.

The cation exchange support may be a polymer of at least one monomer selected from the group consisting of styrene; divinylbenzene; acrylic; and their mixtures.

It can in particular be a cation exchange support selected from the group comprising: polymers with sulfonic groups of the polymer-SCh "/ Ct + type, polymers with phosphorus groups of the polymer-HiPOf / Ct + type, and polymer with groupings carboxylic polymers of the polymer-COO '/ Ct + type; polymers containing carboxymethyl groups of the polymer-CH2-COO' / Ct + type.

According to a particular embodiment, a mixture of at least one anion exchange support and at least one cation exchange support can be used. In this case, the oxygen and any impurities from the generation of hydrogen can be simultaneously trapped. This mixture may especially correspond to the functionalized copolymer (free anions X ', free Ct + cations) of styrene and divinylbenzene corresponding to the CAS number 79956-14-2.

The preparation of the anion exchange or cation carriers used in the invention is carried out according to the conventional techniques forming part of the general knowledge of those skilled in the art. By way of example, an anion exchange support can be functionalized with SO32 'anions by passing an SO32' ion-based solution, for example an aqueous solution of Na2SO3 or of KHSO3. Exchange between the anions of the anion exchange carrier, for example OH 'ions, and SO32' sulfite ions is carried out. The sulphite ions then functionalize the anion exchange support.

The number of effectively functionalized sites can be optimized by carrying out several passages of an anion solution X 'or Ct + cations, or by adjusting the concentration.

Partial functionalization may be advantageous when the anion exchange carrier is also used to trap impurities resulting from the hydrogen generation reaction. Thus, an anion exchange support comprising both free anions X 'and free anions OH' can fulfill this double role of oxygen scavenger gaseous and impurities.

Advantageously, the ion exchange support (anions or cations) has an exchange capacity of between 0.8 eq / L and 4.5 eq / L, more advantageously between 4 and 4.5 eq / L (1 eq / l). L = 1 equivalent per liter of ion exchange support).

The exchange capacity makes it possible to express the number of sites of the polymer that can exchange charges. An equivalent corresponds to one mole of +1 or -1 charge ions or half a mole of +2 or -2 charge ions.

The greater the exchange capacity, the more ion exchange medium comprises of ions that can be substituted, and the greater the amount of oxygen or impurities that can be trapped.

As already indicated, according to a particular embodiment, the anion exchange medium may be a mixture of anion exchange support and cation exchange support. In addition to the anions X ', the anion exchange support can thus comprise free anions OH', Cl ', SO42 ", HCO3" and / or free Na +, H +, K + cations.

The simultaneous presence of anion and cation exchange groups makes it possible: to absorb oxygen, for example by oxidation of free ions SO32 'to SO42'; to filter the impurities that may result from the generation of hydrogen, for example. As already indicated, it may be impurities NaB02 or NaOH resulting from the hydrolysis reaction of NaBEL.

In fact, in a hydrogen generator, the hydrogen can advantageously be generated by hydrolysis of a borohydride, more advantageously by hydrolysis of the NaBLL borohydride according to the following reaction:

NaBLL + (2 + x) H 2 O -> 4H 2 + NaBO 2 .xH 2 O

This reaction is generally facilitated by the presence of a catalyst, the activity of which is maintained by preventing its oxidation, by trapping oxygen according to the invention.

Generally speaking, in a process according to the invention, the anion exchange support is kept out of any solution in order to avoid any exchange between the free anions X 'serving to trap oxygen and anions present in solution. for example the anions BH4 'or B02'. In addition, the presence of the ion exchange medium (anions and / or cations) in solution would not purify the generated hydrogen.

The present invention also relates to a device comprising the free anion exchange support X 'for the purpose of trapping gaseous oxygen.

More specifically, the device for trapping gaseous oxygen according to the invention comprises an anion exchange support, said anion exchange support comprising fixed cationic groups and free anions X ', X' being an anion chosen from the group comprising SO32 "; S2O52"; S2O72 ', NO2 "and mixtures thereof.

This device can be integrated into a hydrogen generator. Thus, the hydrogen generated can in particular be purified by eliminating the possible oxygen gas present, by passing through the device according to the invention. The invention and the advantages thereof will become more apparent from the following figures and examples given in order to illustrate the invention and not in a limiting manner.

DESCRIPTION OF THE FIGURES

Figure 1 illustrates a conventional hydrogen generator.

Figure 2 illustrates the method of operation! the SO32 'anions on an ion exchange support and the absorption of oxygen on this ion exchange support.

Figures 3 and 4 illustrate the method according to the invention for trapping gaseous oxygen present in a hydrogen generator.

FIG. 5 illustrates the evolution of the pressure of the hydrogen generator as a function of time in the presence of an ion exchange support according to the invention (functionalized SO32 -) or solid Na2SO3.

FIG. 6 illustrates the evolution of the absorbed oxygen volume as a function of time in the presence of an ion exchange support according to the invention (functionalized SO32 ') or solid Na2SC> 3.

Figure 7 shows a device comprising a hydrogen generator and a condensate collector from the hydrogen generator.

Figure 8 illustrates the partial functionalization of an anion and cation exchange support with SO32 'and Na + ions.

Figure 9 illustrates the entrapment of oxygen and the purification of hydrogen according to the invention.

FIG. 10 represents the evolution of the pressure of the hydrogen generator as a function of time in the presence of an ion exchange support (functionalized SO32 ') according to the invention.

FIG. 11 represents the pH of the condensates coming from the generator during the hydrolysis of NaBLL according to one embodiment of the invention and according to a counterexample.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 represents a conventional hydrogen generator (1) comprising: a reaction medium (2) making it possible to generate hydrogen, in particular by hydrolysis of borohydride; a catalyst (3); a chamber (4) providing the interface between the reaction medium (2) and the outlet valve (6) of the generated hydrogen; a membrane (5) porous to gases (hydrogen and oxygen) and preferably liquid impermeable for the entry of hydrogen into the chamber (4).

FIG. 2 illustrates the functionalization of an ion exchange support by exchange of free OH 'anions with free anions X' = SO32 '. Once the functionalization is carried out at least partially, the support can be used in the context of the present invention according to the oxygen scavenging step also illustrated in Figure 2. The fixed cations of this support are ammonium-NR3 +.

The ion exchange support (7) can be positioned in any location of the hydrogen generator (1). However, and advantageously, it is not totally immersed in the reaction medium (2), so as to avoid any rapid exchange between the free anions X 'of the ion exchange support (7) and for example the type BH4 'that can include the reaction medium (2).

According to a preferred embodiment of the invention, the ion exchange support (7) (anions and optionally cations) is advantageously positioned in the chamber (4) (FIG. 3). Thus, it makes it possible to trap the oxygen gas present in the hydrogen generator and thus prevents the aging of the catalyst (3) by oxidation (FIG. 4). The oxygen scavenging is therefore advantageously carried out before the start of hydrogen generation. However, the present invention allows for the continuous entrapment of gaseous oxygen during the generation of hydrogen.

Once the hydrogen is generated, it is removed from the hydrogen generator (1) by the valve (6) after being brought into contact with the ion exchange medium (7). Optionally, the hydrogen can then be purified by passing through a device (8) allowing the condensation of any impurities, and by passing through a filter (9) (Figure 7).

As already indicated, the main role of the ion exchange support (7) is to trap the oxygen gas by means of the free anions X '.

According to a particular embodiment, the ion exchange support (7) can trap oxygen gas thanks to the free anions X 'and any impurities resulting from the hydrogen generation. In this case, the ion exchange support (7) may be the mixture of an anion exchange support comprising free anions X 'and a cation exchange support comprising Ct + free cations.

FIG. 8 represents the partial functionalization of a mixture containing: an anion exchange support having fixed groups -NR.3 + and free anions OH '; a cation exchange support having fixed groups -SO3 'and free cations H +.

According to the particular embodiment illustrated in FIG. 8, the simultaneous functionalization of these two supports is carried out by exchange with a solution of Na 2 SO 3. At the end of the partial functionalization, the free anions SO32 'and OH' as well as the free Na + and H + cations can trap oxygen gas and any X + and anionic cationic impurities Y '(FIG. 9).

Thus, a cation exchange support can be used to generate an acidic condensate, while a mixture of anion exchange media and cations can generate a condensate with a neutral pH, indicating that all the contaminants have been trapped by the support and the gaseous hydrogen is free or essentially free of contaminants

This hydrogen purification step can be very important especially when the hydrogen is intended to be used in a fuel cell.

EXAMPLES OF CARRYING OUT THE INVENTION

Two types of anion exchange carriers were functionalized with sulfite ions (INV-1 and INV-3) and compared with solid sodium sulfite (CE-1) or with a cation exchange support (CE-2). 1 / Comparison between an anion exchange support according to the invention and Na ^ SQ? 1.1 / Preparation of an anion exchange medium having sulphite ions according to the invention (INV-1)

A commercial anion exchange support (polymer referenced Amberjet 4200 from Dow Chemical) having the following properties has been functionalized: spherical beads having a diameter of between 0.58 and 0.70 mm; polymer matrix: copolymer of styrene and divinylbenzene; fixed functional group: tertiary ammonium cation (trimethylammonium); free ionic form: OH '; total exchange capacity of 1.2 eq / L.

It has been functionalized in the laboratory with sulphite ions.

The functionalization is carried out according to the following steps (FIG. 2): 4 g of a solution containing 5% by weight of Na 2 SO 3 (1.6 mmol) in distilled water are passed through 2.6 ml of support (Amberjet polymer). 4,200 to Dow Chemical); the support (polymer) thus functionalized is dried under vacuum for 24 hours at room temperature.

The drying of the functionalized polymer with the SO32 'anions is not essential. On the other hand, this step makes it possible to validate the oxygen scavenging tests by loss of pressure (FIG. 5). Indeed, the oxygen can not be dissolved in the polymer support, it is not wet. The oxygen is necessarily trapped by reaction with the sulphite ions as illustrated in FIG.

Thus, the functionalized polymeric support is evaluated in the absence of any other compound.

It is possible to determine the exact amount of sulphite ions of the support thus functionalized, for example by measuring the difference in concentration of sulphite ions in the functionalization solution, that is to say by comparing the concentration of sulphite ions before and after the functionalization. Conventional techniques can be implemented, including iodometric or infrared spectroscopy titration. 1.2 / Evaluation of the anion exchange medium having sulphite ions according to the invention (INV-1) relative to solid sodium sulphite (CE-1)

Oxygen trapping is evaluated in a stainless steel device comprising a 5mL tank connected to a pressure sensor. The total volume is 71 mL (Figures 3 and 4). 2.6mL of functionalized polymer support (INV-1) are placed in the reservoir.

A monitoring of the pressure inside the device is performed (Figure 5).

The same experiment (CE-1) is carried out by placing 200mg of solid Na2SO3 (0.0016 moles of SO32-) in the tank 1.3 / Results for oxygen scavenging (INV-1, CE-1)

A depression is observed in the reservoir containing the functionalized polymer support according to the invention (INV-1). There has therefore been oxygen uptake (FIG. 6).

On the other hand, no variation of pressure is observed for the counterexample CE-1 (Na2SC> 3 solid). The trapping of oxygen therefore requires that the sulphite be in ionic form. The present invention makes it possible to have a support having fixed cations and free anions which make it possible to trap oxygen. 2 / Trapping of oxygen and impurities: comparison between a mixture of anion and cation exchange carriers (INV-3) according to the invention and the absence of ion exchange support (CE-3) 2.1 Preparation of a mixture of anion exchange media and cations according to the invention (INV-3)

An anion and cation exchange commercial support (polymer referenced Amberlite IRN 150 from Dow Chemical, CAS 79956-14-2) is functionalized with sulphite ions. This polymeric support has the following properties: spherical beads having a diameter of between 0.58 and 0.70 mm; polymer matrix: copolymer of styrene and divinylbenzene; fixed functional group: tertiary ammonium cation (trimethylammonium) for the anion exchange polymer and SO32 'anions for the cation exchange polymer; free ion form: OH 'for the anion exchange polymer and H + for the cation exchange polymer; total exchange capacity of 1.2 eq / L for the free anionic functions OH 'and 1.9 eq / L for the free cationic functions H +.

This ion exchange polymer support comprises 50% of free cationic functions H + and 50% of free anionic functions OH '.

The functionalization is carried out according to the following steps: 5.5 ml of a solution containing 5% by weight of Na.sub.2 SO.sub.3 in distilled water is passed through 7.2 ml of the anion and cation exchange support; drying the ion exchange support under vacuum for 24 hours at room temperature.

Considering an exchange efficiency of 100%, 50% of the free anionic sites are exchanged with SO32 'ions. The ion exchange support is thus partially functionalized with the sulphite ions (FIG. 8). 2.2 / Entrapment of oxygen (INV-3)

Oxygen trapping is evaluated in a stainless steel device comprising a 5mL tank connected to a pressure sensor (Figure 7). The total volume is 71mL. 1.6 g of ion exchange medium are placed in the tank (INV-3), more precisely in the chamber connected to the hydrogen outlet valve (FIG. 7). This generator corresponds to the device in point 1.2 / above.

A monitoring of the pressure inside the device is performed (Figure 10).

Depression is observed in the hydrogen generator, which demonstrates oxygen scavenging. 2.3 / Entrapment of impurities (INV-3, CE-3)

The hydrogen generator of item 2.2 / above is activated to generate hydrogen by hydrolysis of 10 g of NaBH4. 160mg of ion exchange support are used.

Throughout the life of the hydrogen generator, the condensate from the generator is trapped and collected (Figure 7). Once the hydrogen generation is complete, a measurement of the pH of the condensate is carried out (FIG. 11).

A comparison is made with a generator containing no ion exchange support, the chamber connected to the hydrogen outlet valve being empty (CE-3).

The pH of the condensate from the generator containing the partially functionalized ion exchange support (INV-3) is neutral while the pH of the condensate from the generator does not contain ion exchange support (CE-3) is basic (FIG. 11).

The impurities resulting from the hydrolysis reaction of NaBH 4 in the presence of the cobalt-based catalyst are trapped by the ion exchange support which fulfills the filter function.

Thus, this type of partially functionalized ion exchange support makes it possible to trap the oxygen present in the free volume and the ionic impurities resulting from the hydrolysis of NaBH 4.

Claims (10)

1. Oxygen scavenging process according to which gaseous oxygen is brought into contact with an anion exchange support, said anion exchange support comprising fixed cationic groups and free anions X ', X' being an anion selected from the group consisting of SO32 '; S2O52 '; S2O72 ', NO2'; and their mixtures. 2. oxygen scavenging process according to claim 1, characterized in that the anion exchange carrier is a polymer support or a mineral carrier. 3. oxygen scavenging process according to claim 1 or 2, characterized in that the fixed cationic groups of the anion exchange support are groups selected from the group comprising -NH3 +; -NR.3 +; -NHR.2 +; -NH2R +; -N (ROH) (R ') 2+; and -SR2 +; R and R 'being alkyl or aryl. 4. Oxygen scavenging method according to one of claims 1 to 3, characterized in that the anion exchange carrier is a polymer support selected from the group comprising: polymers with quaternary amine groups polymer type-NR3 + / X 'and / or N-polymer (ROH) (R') 2+ / X '; polymers with tertiary amine groups of the polymer-NHR 2+ / X 'type; polymers with secondary amine groups and / or primary polymer type-NH 2 R + / X "and / or polymer-NH 3 + / X"; polymers with sulfonium groups of the polymer-SR2 + / X 'type; R and R 'being alkyl or aryl. 5. oxygen scavenging process according to one of claims 1 to 4, characterized in that the anion exchange carrier is a copolymer of styrene and divinylbenzene or a copolymer of acrylic and divinylbenzene. 6. oxygen scavenging process according to one of claims 1 to 5, characterized in that the anion exchange carrier has an exchange capacity of between 0.8 eq / L and 4.5 eq / L. 7. Process for trapping gaseous oxygen in a hydrogen generator, comprising the following steps: placing in a hydrogen generator at least one anion exchange support comprising fixed cationic groups and free anions x; X 'being an anion selected from the group consisting of SO32', S2O52 ', S2O72', NO2 ', and mixtures thereof, gaseous oxygen is trapped according to one of claims 1 to 6 and hydrogen is generated. 8. Process for trapping gaseous oxygen and for purifying hydrogen in a hydrogen generator, comprising the following steps: placing in a hydrogen generator an ion exchange support consisting of: at least one exchanger support anion composition comprising fixed cationic groups and free anions X ', X' being an anion selected from the group consisting of S032 ', S2052', S2072 ', NO2' and mixtures thereof; and at least one cation exchange support comprising free C, + cations; oxygen gas is trapped according to one of claims 1 to 6; hydrogen is generated; the hydrogen is purified by contacting the generated hydrogen with the ion exchange support. 9. Process according to claim 8, characterized in that the free cations Q + are chosen from the group comprising the ions Na +, H +, K +, and their mixtures. Apparatus for trapping gaseous oxygen, comprising an anion exchange support, said anion exchange support comprising fixed cationic groups and free anions X ', X' being an anion chosen from the group comprising SO32 ', S2052 ', S2O72', NO2 ', and mixtures thereof.