FR2661170A1 - Process for the production of ultrapure nitrogen - Google Patents

Abstract

Process for the production of ultrapure nitrogen with an impurities content of less than 100 ppb (parts per billion), characterised in that the impurities consisting of carbon monoxide (CO) and/or hydrogen (H2) are removed by bringing the gas to be purified from at least one of these two constituents into contact with a particulate support of zeolite type which has a metal incorporated: copper (Cu), according to the ion mutation technique, or palladium (Pd), according to the impregnation technique. This technique makes it possible to obtain ultrapure nitrogen by applying it either to distillation nitrogen or to air, with additional removal of CO2 and H2O, before distillation.

Description

 The present invention relates to the production of ultra-pure nitrogen, with an impurity content of less than 100 ppb (parts per billion), even less than a few tens of ppb, or even less than 10 ppb, and even less of the order of 1 ppb.

 Pure nitrogen is generally obtained by cryogenic distillation of the air, which allows to separate the oxygen, while the carbon dioxide and water vapor are previously removed by stopping on adsorbent before distillation.

 However, carbon monoxide (CO) and hydrogen (H2) contained in the air are found after distillation in nitrogen, except, for hydrogen, to add an additional distillation column, which would be particularly expensive.

 This is the reason why, at present, it is carried out catalytically using noble metals such as platinum and palladium on an alumina support and at an elevated temperature above 1000C or, for the carbon monoxide of the oxide. CuD copper at a temperature of about 1500C, air treatment, and this after compression and before sending to the desiccator-decarbonation battery and then to the distillation column, but this high temperature operation is performed on the entire air flow is expensive and it is difficult to reach the target limit of 10 ppb, both for carbon monoxide and for hydrogen, whose residual contents remain of the order of 100 ppb.

 On the other hand, purifiers that treat nitrogen to remove 00, 002> H2O, H2 gui which function by stopping oxygen and oxidation of OO and H2 on active element CuO and or (forming for the oxygen impurity of CuO from Cu, and for the purity 00 and H2 of C102 and H20 respectively), then stop 002 and HO on molecular sieves, where appropriate preceded by a bed of alumina.

Such scrubbers are relatively complex in operation and, in particular, require reactivation of the Cu / CuO active element with a gas such as hydrogen.

 It has been tried to stop OO and H2 by adsorption, but conventional adsorbents or sieves are ineffective for H2 and not very effective for 00 (13X molecular sieves that stop 002 and very little 00). However, it is known that these products can be improved by copper ion (Cu) exchange or palladium (Pd) impregnation.There are some examples of these improvements (saturation rate increase), but no proposals have yet been made. been made to adapt this technique to the development of ultra-pure nitrogen.

The problem of the present invention was the discovery of the effectiveness of these products (Cu exchanged zeolites or Pd-impregnated zeolites) in the production of ultra-pure nitrogen by achieving the following double objective.
a lower stop threshold of the order of 10 ppb
- with a ratio of amount of gas to be treated / quantity of product
stop that is economical.

 These objectives of the invention are achieved in that the impurities constituted by carbon monoxide (OO) and / or hydrogen (H2) are eliminated by passing the gas to be purified on a particulate support of the zeolite type, with incorporation of a copper (Cu) or palladium (Pd) metal element made according to the known technique of ion exchange and / or impregnation.

 In particular, the impurity 00 is removed by adsorption on the molecular support of the zeolite genus in which the incorporation of the Cu metal has been ensured by nutation of ions by a metal ion W. By "exchanged" zeolites, we mean in a known manner, a transformation of the zeolites of the comnerce, which are formed of a calcium or sodium alumino-silicate carrier with crystalline structure, having, according to the type of crystalline structure, pores of different diameters which are measured in Angstrom (A), these structures being associated with different cations (sodiun, calcium). Such commercial zeolites are capable of trapping certain gases, within certain limits, however.This substitution, or exchange, takes place in an aqueous solution by exchange of the alkaline or alkaline-earth ions of a synthetic or natural zeolite by metal ions. a solution of a metal salt such as Cucul2, PdC12. The zeolite is then dried moderately under a nitrogen sweep before it can be used.

By impregnation is meant the implementation of the following operations. contacting a zeolite with a solution of a salt evaporation of water from the solution. moderate drying under neutral gas reduction reduction by reducing gas, for example hydrogen or a mixture
of hydrogen and nitrogen.

 According to another embodiment, for the substantial elimination of the impurity H2 and also a bed of zeolites in which the incorporation of the palladium metal (Pd) ~ has been ensured by impregnation of the zeolite.

The invention applies firstly to the final purification of cryogenic distillation nitrogen from air, where the main elimination of the hydrogen impurity is ensured by passing nitrogen at room temperature on a bed of zeolites impregnated with palladium, the action of which is completed by one of the following provisions - or the impurity carbon monoxide is first stopped by passage
nitrogen at room temperature on a bed of mutated zeolites
copper - either carbon monoxide is substantially stopped at
ambient temperature by passing nitrogen on said bed of
palladium impregnated zeolites sized accordingly.

 In this form of implementation operating on nitrogen, the invention also relates to an ultrapure nitrogen making device, wherein at least one hydrogen and carbon monoxide stop bed is disposed in a single enclosure the operation is performed using two identical speakers, one operating at room temperature for purification, while the other is in regeneration at high temperature, under the effect of a rise in temperature and / or a lowering of pressure, if necessary below atmospheric pressure and / or an elution sweep by the nitrogen to be purified or purified.

The invention also applies to the purification of air prior to its distillation by passage of air at room temperature after elimination, in a desiccator-decarbonator, of carbon dioxide, water vapor and impurities. other than carbon monoxide and hydrogen, on a bed of palladium impregnated zeolites for
Substantial stopping of hydrogen, and / or for substantially stopping carbon monoxide by passage at ambient temperature on a bed of copper mutated zeolites, and / or by passage at ambient temperature on said bed of palladium-impregnated zeolites, if necessary dimensioned accordingly.

 In this form of implementation operating on air, the invention relates to an air purifying device intended to be distilled, the hydrogen and carbon monoxide stopping beds being grouped with the adsorbent beds. water vapor (such as alumina) and molecular sieve (such as 13X zeolite) for stopping carbon dioxide, water vapor and other pollutants, in a single enclosure stop.

Preferably, the hydrogen and carbon monoxide stopping beds being disposed downstream of the carbon dioxide and water vapor stopping beds and other pollutants, and furthermore, the enclosure of stop includes downstream H2 and 00 stop beds, smaller beds for the final stop of traces of water vapor and carbon dioxide.

 The invention also relates to a process for producing ultra-pure nitrogen in which air is passed at an elevated temperature of the order of 1000.degree. C. to 3000.degree. C. prior to distillation by a bed of such particulate zeolite supports, either in a single bed which is a palladium impregnated bed, or a bed of copper mutated zeolites, either in a double bed which is a bed of copper mutated zeolites and a palladium-impregnated zeolite bed, or in a single bed of copper mutated zeolites and doped with palladium.

The invention is now illustrated by the following examples of implementation, which highlight certain results in accordance with the invention and other inoperative
Results - ABOUT AZCIE A TEMEbU4DURE Afiq3IANTE
Sieve mutated Cu no stop H2
stop of 00: <2 ppb
drilling adsorption rate
= 0.42 Ncm3 / g (Ncm3 of CO per gratine
adsorbent)
Impregnated sieve Pd oo = 15 ppb
H2 <10 ppb
drilling adsorption rate
= 0.27 Ncm3 / g (Name3 of CO and H2
per gram of adsorbent adsorbent)
Milled sieve Cu + impregnated sieve Pd CO <2 ppb
H2 <3 ppb
drilling adsorption rate
= 0.67 Nom3 / g (Ncm3 of CD and H2
per gram of adsorbent)
We have both low thresholds and interesting rates.

Reversibility has been mounted by renewing the tests.

- ON AMBIENT TEMPERATURE AIR
Sieve mutated Cu no stop H2
OO stop threshold = 6 ppb
drilling adsorption rate
= 0,16 Nom3 / g (Ncm3 of CO per gram
adsorbent)
Impregnated sieve Pd OO = 6 ppb
H2 = 10 to 20 ppb for 10 days
Formation of 002 in the reactor which is then eliminated at
room temperature - ON AIR AT HIGH TEMPERATURE
Sieve mutated Cu + impregnated sieve Pd
at 1002C
H2 <10 ppb
OO = 7 ppb
Sieve mutated Cu doped Pd
at 1500C
H2 = 35 ppb
OO = 5 ppb EXAMPLES OF IMPLEMENTATION
A first bed of SA type zeolites (24.6 g) is prepared, of which 60% of the ions are exchanged with Cu ions and a second bed of mordenite (23 g) impregnated at 3.5% (weight) with palladium, in two columns having a diameter of 12 mm and a length of 250 mm and the following tests are carried out
FIRST TRY :
Cryogenic nitrogen (N2) at a flow rate of 126 Nl / h at 7 bar at room temperature is passed through the columns, having a water content of less than 150 ppb, an OO content of 2 ppn (part by million 6) and a hydrogen content of 1.7 ppm. At the outlet, the nitrogen contains only an ace content of about ppb and a hydrogen content of less than 3 ppb. This result is ensured for a period of 67 hours.

SED3N3 TEST
In the columns, at a flow rate of 126 Nl / h at 7 bar, air having a water content of less than 150 ppn, a content of 00 of 2 ppn and an H2 content of 1.3 ppm. The outgoing air has a content of 00 of 6 ppb and a hydrogen content of 10 to 20 ppb for a minimum of 10 days.

ISDISIEDdE TRIAL
This test is identical to the second test with the difference that the air is heated to 100 ° C. The outgoing air has a content of 0.07 ppb and a hydrogen content of less than 10 ppb.

 The invention applies to the preparation of ultra pure nitrogen, especially used in the electronics industry.

Claims (11)

THESE # DICATICNS  1. A process for producing ultra-pure nitrogen using an air distillation, characterized in that at least substantially eliminates the impurities constituted by carbon monoxide (00) and / or hydrogen (H2 ) by passing the gas to be purified in at least one of these two constituents onto a particulate support of the zeolite type incorporating a copper (Cu) or palladium (Pd) metal element, according to the known technique of ion exchange and / or impregnation.  2. Process for the production of ultra-pure nitrogen, the nitrogen component of which has been separated by cryogenic distillation according to claim 1, characterized in that the elimination of the carbon monoxide impurity is first ensured by passage of the nitrogen at room temperature on a bed of copper-exchanged zeolites and / or on a bed of palladium-impregnated zeolites, whereas the elimination of the hydrogen impurity is ensured by passage of nitrogen at ambient temperature over a bed of impregnated zeolites of palladium.  3. Process for the production of ultra-pure nitrogen, the nitrogen component of which has been separated by cryogenic distillation according to claim 1, characterized in that the elimination of the carbon monoxide impurity is ensured by passage to ambient temperature of the nitrogen at room temperature on a bed of zeolites exchanged copper.  4. Device for producing ultra-pure nitrogen implementing the process according to claim 2 or 3, characterized in that at least one hydrogen and / or carbon monoxide stopping bed is arranged in a single chamber, the operation taking place by means of two identical enclosures, one operating at ambient temperature and under pressure for purification, while the other is in regeneration under the effect of a rise in temperature and / or a lowering of pressure, if necessary below atmospheric pressure and / or an elution sweep by the nitrogen to be purified or purified.  5. A process for producing ultra pure nitrogen according to claim 1 by passing air at room temperature, prior to distillation, in a desiccator-decarbonator, characterized in that the air thus released from carbon dioxide and water vapor and impurities other than carbon monoxide and hydrogen also pass to room temperature on a bed of copper-exchanged zeolites and / or on a bed of palladium-impregnated zeolites for stopping carbon monoxide, and then on a bed of palladium-impregnated zeolites for stopping hydrogen.  6. A process for producing ultra-pure nitrogen according to claim 1 by passage of air at ambient temperature, prior to distillation, in a desiccator-decarbonator, characterized in that the air thus freed from carbon dioxide and water vapor and impurities other than carbon monoxide and hydrogen also pass to room temperature on a bed of copper-exchanged zeolites for stopping carbon monoxide.  7. Air purifying device intended to be distilled, implementing the method according to claim 5 or 6, characterized in that the hydrogen and carbon monoxide stopping beds are grouped with the adsorbent beds of water vapor (such as alumina) or molecular sieves (such as 13X zeolite) for stopping carbon dioxide, water vapor and other pollutants, in a single stopping chamber.  8. air purifying device according to claim 7, characterized in that the stop beds of hydrogen and carbon monoxide type palladium impregnated molecular sieve and / or copper mutated are arranged downstream of the beds stopping carbon dioxide and water vapor and other pollutants.  9. Air purifying device according to claim 8, characterized in that the stop chamber comprises, downstream of the hydrogen stopping beds and carbon monoxide, beds of smaller dimensions for stopping. final traces of water vapor and carbon dioxide.  10. Process for producing ultra-pure nitrogen according to claim 1, characterized in that the air is treated at an elevated temperature of the order of 1000C to 3000C prior to the distillation by a bed of such particulate zeolite supports, either a single palladium impregnated bed or a copper mutant bed, or a double bed which is a copper mutated zeolite bed and a palladium impregnated bed, or a single bed of palladium doped mutated copper zeolites.  11. A process for producing ultra-pure nitrogen according to claim 10, characterized in that the first desiccation-decarbonation is carried out, then the treatment at high temperature on said beds of zeolites, finally to desiccation- final complementary decarbonation.