WO1995011856A1

WO1995011856A1 - Air purification process

Info

Publication number: WO1995011856A1
Application number: PCT/FR1993/001074
Authority: WO
Inventors: Daniel Gary; François Venet
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 1992-04-24
Filing date: 1993-10-29
Publication date: 1995-05-04
Also published as: FR2690357A1; FR2690357B1; EP0677023A1; JPH08508236A

Abstract

Air purification process for removing the carbon monoxide impurities and hydrogen from the air, particularly in order to prepare high purity nitrogen, wherein (i) the air is brought in contact with a catalytic bed comprising particles of at least one metal selected among copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and rhodium, supported by a support which is chemically inert with respect to water, so as to react the hydrogen and carbon monoxide impurities with the oxygen in the air in order to form respectively carbon dioxide and water; (ii) the water and carbon dioxide impurities contained in the air are removed; (iii) optionally, the nitrogen is separated from the air by cryogenic distillation. The invention also relates to a device for implementing such process.

Description

AIR CLEANING PROCESS

The present invention relates to a simplified process for purifying air into its carbon monoxide and / or hydrogen impurities, in particular with a view to the production of high-purity nitrogen by cryogenic distillation of the purified air.

Large amounts of nitrogen are used in the electronics industry, especially in the manufacture of semiconductors. This nitrogen must be as pure as possible, and in particular it must be free or almost free of impurities such as carbon monoxide and hydrogen which reduce the quality and performance of the semiconductors. Until recently, carbon monoxide and / or hydrogen contents of the order of ppm (parts per million) were still accepted.

But now the electronics industry requires high purity nitrogen containing less than 20 ppb (parts per billion), or even less than 10 ppb in carbon monoxide and / or hydrogen.

Generally, the processes for the preparation of pure or very pure nitrogen, firstly implement a step of separating nitrogen from the air, in particular by cryogenic distillation, the nitrogen obtained then being purified into its impurities , in particular carbon monoxide and / or hydrogen.

US Pat. No. 4,869,883 describes a process of this type according to which nitrogen originating from an air separation unit and containing the oxygen, carbon monoxide and hydrogen impurities is purified by the implementation of the following three steps :

- Oxygen is reacted with carbon monoxide and hydrogen present in the nitrogen, using a catalyst containing reduced copper, at a temperature between 150 ^β C and 250 ° C to form carbon dioxide and water,

- The carbon monoxide and the residual hydrogen are reacted with the oxygen of a catalyst containing copper oxide, at a temperature between 150 ° C and 250 ° C, to form carbon dioxide, water and reduced copper,

- Water and carbon dioxide are removed by adsorption using a molecular sieve. In European patent application 454.531, the applicant has proposed a process for the preparation of ultra-pure nitrogen according to which carbon monoxide and / or hydrogen impurities are removed from the air by passing the air over a bed. catalytic consisting of particles of at least one metallic element chosen from the group consisting of copper, ruthenium, rhodium, palladium, osmium, iridium and platinum, supported on a support having a high specific surface. Said impurities react with oxygen in the air to form carbon dioxide and water.

As a result, the air to be distilled is removed from the water and carbon dioxide, by adsorption, for example, on a molecular sieve, and the nitrogen is separated from the air by cryogenic distillation. The nitrogen thus obtained has carbon monoxide and hydrogen contents which may be less than 10 ppb. Compared to conventional methods in which the purification is carried out on nitrogen, the latter method has the advantage of removing carbon monoxide and / or hydrogen impurities directly from the air which is subsequently cryogenic distilled. Indeed, a purification carried out on nitrogen requires the addition of oxygen in an amount sufficient to oxidize carbon monoxide and hydrogen. However, this oxygen risks contaminating the nitrogen.

A disadvantage of the process described in patent application EP 454,531 consists in having to use a desiccation-decarbonation of air in order to eliminate by adsorption the water and the carbon dioxide which it contains, not only after 1 'removal operation of carbon monoxide and / or hydrogen, but also, prior to this operation. This preliminary desiccation-decarbonation is very particularly required when the removal of carbon monoxide and / or hydrogen is carried out at temperatures below 120 ° C. and in particular at ambient temperature or at a temperature close thereto, either at a temperature between -20 ^e and 50 ^β C.

The Applicant had in fact considered that the prior desiccation-decarbonation operation depending on the temperature used, was necessary in order not to deactivate too quickly with water and / or the carbon dioxide contained in the air, the catalytic bed made up of supported metallic particles.

This deactivation was recently attributed by the applicant, in particular, to the very nature of the support used. However, such a prior desiccation-decarbonation operation involves an additional cost of the air purification device insofar as it is necessary to add a desiccation-decarbonation unit upstream of the catalytic bed.

In addition, it is notable that the air to be distilled must be compressed by a compressor for its cryogenic distillation.

The air leaving this compressor is brought to a temperature usually below 140 ° C, more generally between

5 80 ^β C and 120 ^β C, and at a pressure generally between 5.10 and

3.10 ⁶ Pa.

It is known that conventional devices for desiccation-decarbonation by adsorption are more effective at room temperature. Therefore, when the drying-decarbonation operation is carried out on compressed air, it is generally necessary to cool the air to room temperature, for example by means of a heat exchanger or a cooling unit, then, depending on the nature of the catalytic bed, it may be necessary to reheat the air as it leaves the desiccation-decarbonation device in order to promote the catalytic reaction.

The implementation of such a method therefore requires an apparatus of the heat exchanger or refrigeration unit type, and, generally, a device for heating the air, for example an electric heater. In addition, it involves a significant energy expenditure due to the need to heat the air. Such a process appears to be very expensive.

A first object of the invention consists in a process for purifying the air of its carbon monoxide and / or hydrogen impurities with a view to the preparation of ultra-pure nitrogen, the hydrogen and / or monoxide contents of which of carbon are less than 10 ppb, or even 5 ppb.

A second object of the invention consists in a process for purifying the air of its carbon monoxide and / or hydrogen impurities which can be implemented by means of an installation of reduced cost, not requiring, prior to the 'elimination of these impurities, devices for desiccation-decarbonation by adsorption, heat exchange, cooling unit or air heating. A third object of the invention consists in a process for purifying the air of its carbon monoxide and / or hydrogen impurities, the energy cost of which is reduced, to the extent that on the one hand, it makes it possible to use the energy of the air leaving a compressor and on the other hand, avoids subsequently heating this air in a heater.

Finally, a fourth object of the invention consists of a device for implementing a process for purifying the air of its carbon monoxide and / or hydrogen impurities.

The invention then relates to a process for purifying air of its carbon monoxide and / or hydrogen impurities, in particular for the preparation of ultra-pure nitrogen, characterized in that: (i) the air is put in contact with a catalytic bed comprising particles of at least one metal chosen from copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and rhodium, supported by a chemically inert support with respect to at least water, so as to react the carbon monoxide and / or hydrogen impurities with the oxygen in the air to form carbon dioxide and water respectively,

(ii) removing the carbon dioxide and water impurities contained in the air,

(iii) where appropriate, the nitrogen is separated from the air by cryogenic distillation.

In the context of the invention, the expression "a support which is chemically inert with respect to water" is intended to mean a support which makes it possible to avoid rapid deactivation of the catalytic bed when it is brought into contact with 'water. Such a support is generally hydrophobic, and therefore does not substantially absorb water. A suitable support according to the process of the invention usually adsorbs less than 0.5 g of water per 100 g of support, preferably less than 0.2 g of water per 100 g of support, at 20 ° C. and with a relative humidity less than or equal to 60%.

Preferably, in particular when the air is at ambient temperature, said support is also chemically inert vis-à-vis carbon dioxide. To this end, said support can in particular be chosen so as not to adsorb, substantially, the carbon dioxide.

The invention will be better understood from the following description and the figures. FIG. 1 represents a device for purifying air intended for distillation, comprising a catalytic bed disposed downstream of the air compressor.

FIG. 2 represents a device for purifying air intended for distillation, comprising a catalytic bed arranged upstream of the air compressor.

The process according to the invention is advantageously carried out so that bringing the air into contact with the catalytic bed produced before any air treatment aimed at drying and / or decarbonating this air by adsorption.

According to an advantageous aspect of the invention, the catalytic bed comprises only, or essentially, palladium particles.

The support constituting the catalytic bed is preferably of mineral nature. It may in particular consist of a hydrophobic mineral, such as a hydrophobic zeolite, a hydrophobic silica, an amorphous alumina such as alumina, or a ceramic. An amorphous alumina can be obtained by calcination of a crystalline alumina, preferably under an inert atmosphere, at a temperature between 560 "C and 950 ° C, more generally between 750 ^β C and 850 ° C.

A suitable hydrophobic zeolite can consist in particular of a zeolite ZSM 5, a silicalite or a zeolite Y highly dealuminated, and therefore, whose Si / Ai ratio is high. This ratio can be greater than 50, and preferably it is close to 100. As hydrophobic zeolites which can be used in the process of the invention, mention may also be made of zeolites, such as the treated ordenites, of conventionally, with steam and then with an acid such as nitric acid, so as to remove the hydroxyl groups.

According to an advantageous characteristic of the process of the invention, the support constituting the catalytic bed has a volume of pores

3 less than or equal to 1 cm / g, preferably between 0.3 and 0.5

3 cm / g. The radius of the pores of this support is preferably less than or equal to 25 nm, more preferably between 1 and 15 nm.

The specific surface of said support can advantageously be

2 between 5 and 600 m / g, more generally between 10 and

300 m / g.

The support used can be in various forms, for example in the form of shavings or honeycomb (monolith structure), but preferably it is in the form of balls or grains, which can be placed in a reactor.

The content of metal particles in the catalytic bed is advantageously between 0.1 and 1% by weight, preferably between 0.4 and 0.7% by weight relative to the total weight of said catalytic bed.

The catalytic bed used according to the process of the invention can be prepared according to means known in themselves, for example by the ion exchange technique or, preferably by the impregnation technique. In the latter case, the catalytic bed can be prepared by impregnating the support with an aqueous solution of a copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and / or rhodium salt. , the impregnated support is dried, for example by placing it for 12 to 48 hours in an oven brought to a temperature between 50 ° C. and 150 °. Then it is calcined, preferably at a temperature between 500 ° C and 550 ° C, and the metal particles are reduced, for example by sweeping with a reducing gas such as hydrogen or a mixture of hydrogen and nitrogen . The calcination of the impregnated and dried support can be carried out in air, preferably a purified air such as purified air according to the process of the present invention.

The metal salt in aqueous solution can be a halide, in particular a chloride, but advantageously the metal salt in aqueous solution is a nitrate.

The catalytic purification of air to its carbon monoxide and / or hydrogen impurities by contacting the catalytic bed can be carried out at a temperature between -40 ° C and 140 ° C and at a

5 6 pressure between 5.10 and 3.10 Pa.

When the purification is carried out upstream of the compressor intended to compress the air for its cryogenic distillation, the air is brought into contact with the catalytic bed at ambient temperature or a temperature close to the latter. , either at a temperature between -20 ^β C and 50 ° C and at pressure

5 atmospheric, or a pressure of the order of 10 Pa.

When the purification is carried out downstream of said compressor, the contacting of the air and the catalytic bed can be carried out at a temperature between 80 ° C and 120 "C and at a pressure

5 6 5 between 5.10 and 3.10 Pa preferably between 7.10 and 3.10 Pa. In this case, the temperature and pressure used are advantageously those of the air at its outlet from the compressor.

The water content of the air brought into contact with the catalytic bed is

3 generally greater than 0.5 g / Nm of air; more particularly

3 3 this water content is between 5 and 15 g / Nm of air, (one Nm

3 corresponds to one m of air placed at atmospheric pressure and at a temperature of 0 ^β C). The carbon dioxide content of the air brought into contact with the catalytic bed is generally greater than 300 ppm.

When the air has been purified of its carbon monoxide and / or hydrogen impurities, it is then possible to remove from it the water and the carbon dioxide initially contained in the air and resulting from the reaction of carbon monoxide and hydrogen with oxygen in the air according to the process described above.

This elimination of water and carbon dioxide can be carried out in a conventional manner, for example by means of an adsorbent, such as an adsorbent molecular sieve, of the 13 X zeolite type and / or alumina.

The air purified according to the process of the present invention is usually atmospheric air.

The carbon monoxide and hydrogen contents of the air intended to be treated according to the process of the invention are usually less than 10 ppm, and more generally of the order of 300 ppb to 3 ppm, in each of these impurities .

After purification, according to the method of the invention, the air generally contains less than 10 ppb of hydrogen and less than 5 ppb of carbon monoxide. This purified air can then be distilled cryogenically for the preparation of high purity nitrogen, the hydrogen and carbon monoxide contents of which are generally less than 10 ppb and 5 ppb respectively.

According to another aspect, the invention also relates to a device for implementing the method described above.

Such a device can be that shown in FIG. 1, comprising: a) an air compressor 1, b) a catalytic bed 2 comprising particles of at least one metal chosen from copper, platinum, palladium, l osmium, iridium, ruthenium, rhenium and rhodium, said particles being supported by a chemically inert support at least with respect to water, the inlet of said catalytic bed 2 being connected to the outlet of the compressor d air 1 via a pipe 3, c) an adsorption bed 4 for water and carbon dioxide, the inlet of which is connected to the outlet of the catalytic bed 2 by a pipe 5, d) where appropriate, a cryogenic distillation unit (not shown) communicating with the outlet of the adsorption bed 4.

A variant of this device may consist of the device shown in FIG. 2. The latter comprises: a) a catalytic bed 12 comprising particles of at least one metal chosen from copper, platinum, palladium, osmium, Virridiu, ruthenium, rhenium and rhodium, said particles being supported by a chemically inert support, at least vis-à-vis water, b) an air compressor 11, the inlet of which is connected to the outlet of said catalytic bed 12 via a pipe 6, c) an adsorption bed 14 of water and carbon dioxide, the inlet of which is connected to the outlet of said air compressor 11 via a pipe 7, d) the if necessary, a cryogenic distillation unit (not shown) communicating with the outlet of the adsorption bed 14.

Insofar as the adsorption beds 4, 14 are more efficient when the air is at ambient temperature, the device according to the invention is usually added with means 8, 9, 18, 19 for cooling the air. .

This means is disposed upstream of the adsorption beds, and downstream of the catalytic bed 2 in the case of the device shown in FIG. 1, or of the air compressor 11 in the case of the device shown in FIG. 2. Such a means can for example consist of a water tower 8, 18, a cooling unit 9, 19, or preferably, a water tower 8, 18 associated with a cooling unit 9, 19.

In the latter case, the water tower is advantageously arranged upstream of the refrigeration unit.

The nature of the catalytic bed and the adsorbent bed is as defined above.

The following examples are intended to illustrate the present invention. _ _

Example 1

Preparation of a catalytic bed:

2 Alumina beads, having a specific surface of 331 m / g,

3 a pore volume of 0.45 cm / g and a pore radius of 2.72 nm are calcined for 8 hours at 800 ° C. under a nitrogen atmosphere. After calcination, the specific surface of the alumina beads is 10 2 m / g. These beads are then impregnated with an aqueous solution to

0.5% by weight of palladium nitrate. The beads are dried in an oven at 100 ° C for 24 hours, then calcined at 500 ° C in air.

The palladium particles are then reduced by sweeping with a gas mixture consisting, by volume, of 10% hydrogen and 90% nitrogen. The catalytic bed thus prepared comprises 0.5% by weight of palladium particles.

Example 2

Air cleaning:

Is brought into contact with the catalytic bed prepared in Example 1, air to be distilled comprising 2 ppm of hydrogen, 2 ppm of monoxide

3 carbon and lg of water per Nm. The air cleaning is done at 120 "C and at

5 7.10 Pa. After treatment, the air to be distilled contains less than 10 ppb of hydrogen and less than 3 ppb of carbon monoxide. This purified air is then sent to a double bed consisting of alumina and a 13 X zeolite for the purpose of removal by adsorption at room temperature of water and carbon dioxide.

Example 3 (comparative)

Air to be distilled comprising 2 ppm of hydrogen, 2 ppm of

3 carbon monoxide and 1 g of water per Nm, by bringing it into contact with a catalytic bed comprising 0.5% by weight of palladium particles supported by alumina beads (hydrophilic).

Alumina has a pore radius of 4.6 nm and a specific surface 2 of 250 m / g. The air cleaning is done at 160 ^β C and at

5 7.10 Pa. After treatment, the air still contains 150 ppb of hydrogen and 5 ppb of carbon monoxide.

Such a purification makes it possible to reduce the contents of carbon monoxide and hydrogen impurities. However, the residual contents are still too high for obtaining nitrogen of very high purity as required, for example, in the electronics industry. In addition, it can be seen that the treated air must be brought to a temperature of 160 ° C., which is a higher temperature than that of the air leaving an air compressor. At lower temperatures, the catalytic bed used leads to residual contents of carbon monoxide and hydrogen, which are even greater.

Claims

1. A process for purifying air of its carbon monoxide and hydrogen impurities, in particular for the preparation of high purity nitrogen, characterized in that:

(i) the air is brought into contact with a catalytic bed comprising particles of at least one metal chosen from copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and rhodium, supported by a support chemically inert with respect to water, so as to react the carbon monoxide and hydrogen impurities with the oxygen in the air to form carbon dioxide and water respectively,

(ii) removing the carbon dioxide and water impurities contained in the air,

2. Method according to claim 1, characterized in that said support is also chemically inert with respect to carbon dioxide.

3. Method according to one of claims 1 and 2 characterized in that the contacting of air with said catalytic bed is carried out prior to any treatment of the air by desiccation and / or decarbonation by adsorption.

4. Method according to one of claims 1 to 3 characterized in that said metal is palladium.

5. Method according to one of claims 1 to 4 characterized in that the support is mineral in nature.

6. Method according to claim 5 characterized in that said support consists of a hydrophobic mineral, such as a hydrophobic zeolite, a hydrophobic silica, an amorphous alumina such as Talumine-a or a ceramic.

7. Method according to one of claims 1 to 6, characterized in that the pore volume of the support is less than or equal to 1 cm g, of

3 preferably between 0.3 and 0.5 cm / g.

8. Method according to one of claims 1 to 7 characterized in that the radius of the pores of the support is less than or equal to 15 nm, preferably between 1 and 15 nm.

9. Method according to one of claims 1 to 8 characterized in that

2 the specific surface of said support is between 5 and 600 m / g,

2 preferably between 10 and 300 m / g.

10. Method according to one of claims 1 to 9 characterized in that the content of metal particles in the catalytic bed is between 0.1 and 1% by weight relative to the total weight of said catalytic bed.

11. Method according to one of claims 1 to 10, characterized in that the catalytic bed is prepared by impregnating the support with an aqueous solution of a salt of copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and / or rhodium, the impregnated support is dried, calcined, preferably at a temperature between 500 ° C and 550 ° C, and the metal particles are reduced.

12. The method of claim 11 characterized in that said salt is a nitrate.

13. Method according to one of claims 1 to 12 characterized in that the air is brought into contact with said catalytic bed at a temperature between -40 ^β C and 140 ° C, preferably at a temperature between -20T and 120 ° C.

14. The method of claim 13 characterized in that said temperature is between 80 ° C and 120 ° C.

15. Method according to one of claims 1 to 14 characterized in that the air in contact with said catalytic bed at a pressure between 10 ⁵ and 3.10 ⁶ Pa.

16. Method according to one of claims 14 and 15 characterized in that the air is brought into contact with said catalytic bed at a pressure

5 6 between 5.10 and 3.10 Pa.

17. Method according to one of claims 1 to 16 characterized in that the air brought into contact with the catalytic bed has a water content

3 greater than 0.5 g / Nm, more particularly between 5 and 15 3 g / Nπf

18. Device for implementing the method according to one of claims 1 to 17, characterized in that it comprises: a) an air compressor (1), b) a catalytic bed (2) comprising particles of at least at least one metal chosen from copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and rhodium, said particles being supported by a chemically inert support at least with respect to water, the inlet of said catalytic bed being connected to the outlet of the air compressor (1) by a pipe (3). c) an adsorption bed (4) of water and carbon dioxide, the inlet of which is connected to the outlet of the catalytic bed (2) by a pipe (5), d) where appropriate, a distillation unit cryogenic communicating with the outlet of the adsorption bed (4).

19. Device for implementing the method according to one of claims 1 to 17, characterized in that it comprises: a) a catalytic bed (12) comprising particles of at least one metal chosen from copper, platinum, palladium, osmium, iridium, ruthenium, rhenium and rhodium, said particles being supported by a chemically inert support, at least with respect to water, b) an air compressor ( 11) whose inlet is connected to the outlet of said catalytic bed (12) by a pipe (6), c) an adsorption bed (14) of water and carbon dioxide whose inlet is connected to the outlet said air compressor (11) via a line (7), d) where appropriate, a cryogenic distillation unit communicating with the outlet of the adsorption bed (14). _ _

20. Device according to one of claims 18 to 19 characterized in that it further comprises, disposed upstream of said adsorption bed (4, 14), a means (8, 9, 18, 19) for cooling the air.