EP2661314A1

EP2661314A1 - Zeolite composition adapted for air purification

Info

Publication number: EP2661314A1
Application number: EP12700625.2A
Authority: EP
Inventors: Christian Monereau
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2011-01-07
Filing date: 2012-01-04
Publication date: 2013-11-13
Also published as: FR2970184B1; CN103313769B; US20130269524A1; FR2970184A1; CN103313769A; WO2012093141A1; US9242237B2

Abstract

The invention relates to an adsorbent zeolite-based material comprising for 100 mass %: an amount different from zero of a zeolite selected from X zeolites or LSX zeolites; the balance up to 100 mass % consisting of an amount different from zero of a cation-exchanged zeolite, said cation-exchanged zeolite being selected from cation-exchanged X zeolites and cation-exchanged LSX zeolites.

Description

Zeolite composition adapted to air purification

The object of the present invention is to provide a process for pretreatment or purification of a gas stream consisting of atmospheric air, prior to the cryogenic separation of said air, in particular by cryogenic distillation.

It is known that the atmospheric air contains compounds to be removed before the introduction of said air into the heat exchangers of the cold box of an air separation unit, in particular the carbon dioxide (C0 ₂ ), steam water (H ₂ O), hydrocarbons (C _n H _m ) and nitrogen oxides.

Indeed, in the absence of such pretreatment of the air to remove its impurities C0 ₂ and water vapor, there is a condensation and an ice solidification of these impurities during cooling of the air at cryogenic temperature, which can result in clogging problems of the equipment, including heat exchangers, distillation columns ...

In addition, it is also customary to remove hydrocarbon impurities that may be present in the air in order to avoid any risk of deterioration of the equipment, in particular of the distillation column or columns located downstream of the reactor. the cold box.

Currently, this pretreatment of the air is carried out, as the case may be, by TSA (Temperature Swing Adsorption) method, that is to say a temperature variation adsorption process, or by PSA (Pressure Swing Adsorption) method. that is, a pressure swing adsorption process; PSA process is understood to mean PSA processes proper, VSA (Vacuum Swing Adsorption) processes, VPSA (Vacuum / Pressure Swing Adsorption) processes, that is to say vacuum adsorption processes during regeneration.

The invention essentially relates to the TSA method.

Conventionally, a TSA process cycle of air purification comprises the following steps:

a) purification of air by adsorption of impurities at superatmospheric pressure ( ³ × ¹⁰ ⁵ Pa at 35 × 10 ⁵ Pa (3 bar at 15 bar abs) and at room temperature (from 5 ° C. to 50 ° C.),

b) depressurization of the adsorber to atmospheric pressure (or even below atmospheric pressure),

c) regeneration of the adsorbent at atmospheric pressure, in particular by waste gases or waste gases, typically impure nitrogen originating from a separation unit air and heated to a temperature above 70 ° C by means of one or more heat exchangers,

d) cooling at ambient or sub-ambient temperature of the adsorbent, especially by continuing to introduce said waste gas from the air separation unit, but not reheated,

e) repressurization of the adsorber with purified air from, for example, another adsorber in the production phase.

Many variants may exist depending on the downstream process and / or the operating conditions; for example, the cooling step can be skipped, the repressurization is done in moist air, the regeneration be carried out at medium pressure ...

Generally, the air pretreatment devices comprise two adsorbers, operating alternately, that is to say that one of the adsorbers is in the production phase, while the other is in the regeneration phase.

Such TSA methods of air purification are described in particular in US-A-3,738,084 and FR-A-7725845.

In general, the removal of CO ₂ and water vapor is carried out on one or more beds of adsorbents, preferably several beds of adsorbents, namely generally a first adsorbent intended to preferentially stop water, by For example, a bed of activated alumina, silica gel or zeolites, and a second adsorbent bed for preferentially stopping C0 ₂ , for example a zeolite. As such, there may be mentioned in particular documents US-A-5,531, 808, US-A-5,587,003 and US-A-4,233,038.

Thus, it is customary to use a 13X type zeolite to eliminate CO ₂ since zeolite 13X is deemed to be particularly effective for stopping small amounts of CO ₂ and possibly water because it has a high affinity and selectivity for these polar molecules. In addition, zeolite X has micropore diameters among the largest, which allows it to adsorb with good kinetics kinetic diameter molecules up to 0.8 nm.

However, zeolite 13X does not stop all the harmful molecules that may be present in a gas stream.

Indeed, the gaseous molecules adsorbed by zeolite 13X are essentially and by increasing affinity: methane, ethane, propane, nitrous oxide, ethylene, carbon dioxide, butane, propylene (C ₃ H ₆ ), acetylene ( C ₂ H ₂ ), toluene and methylcyclohexane. It follows that a strictly sized industrial unit for stopping carbon dioxide with a standard 13X zeolite only partially halts ethylene, propane and nitrous oxide.

The commercialization of LSX with a Si / Al ratio of 1 significantly improved the C0 ₂ stoppage but much less the cessation of the other impurities mentioned above.

The use of zeolite exchanged with calcium and / or barium has, in turn, improved the stopping of ethylene and / or propane and / or nitrous oxide but at the expense of stopping the C0 ₂ .

Then we will use the term zeolite X (or NaX or 13X) to talk about a zeolite

X whose main cations are sodium cations and zeolite LSX to speak as explained above of a zeolite X with an Si / Al ratio of 1 or close to 1 and whose main cations are sodium cations and / or potassium.

Three types of solution are used today to reach the residual levels of impurities sought:

- Use of a bed of NaX (13X standard) or LSX oversized compared to the stop of C0 ₂

- Use of a double bed of NaX or LSX followed by a bed of zeolite exchanged with calcium or barium

- Use of a partially exchanged zeolite bed with calcium and / or barium to stop up to the required thresholds C0 ₂ , C ₂ H ₄ , N ₂ 0 and C ₃ H ₈ .

This latter method is illustrated by WO 03/041858.

The main interest in using a single bed instead of multi beds is largely related to the use of radial adsorber.

Indeed, each type of additional adsorbent results in the presence of an additional separation grid to hold in place the adsorbents, which complicates the manufacture of said adsorbers.

In this way, it is possible to obtain a residual C0 ₂ content in the range of 500ppb to 100ppb with ethylene stopping rates of 75% to 99%, of propane of 50% to 99% and of N ₂ 0 from 65 to 97% -98% depending on the type of solution retained.

Given the levels of secondary impurities in the air, from a few tens to a few hundred ppb, the residual amount of these impurities is in absolute very low, of the order of ppb. New low pressure cryogenic processes or consideration of higher safety or reliability levels lead to want to limit the total amount of impurities introduced into the cryogenic unit.

Since the residual water content is very low, the residual C0 ₂ content should be reduced by an order of magnitude or more.

The 3 solutions listed above can be adapted to this new situation:

- Oversize the bed of NaX or LSX to obtain 10 ppb of C0 ₂ ,

- Over-sizing of the first bed of NaX or LSX

- Over-sizing of the exchanged zeolite bed

These 3 solutions have their disadvantage: significant volume for the first and third solutions with residual contents of secondary impurities (C ₂ H ₄ , C ₃ H ₈ , N ₂ 0) lower than necessary because the dimensioning is carried out for C0 ₂ ; double bed for stopping C0 ₂ and secondary impurities in the second solution with the corresponding complexity in the case of radial adsorber.

From there, a problem is to provide an improved air purification process that is to say, to minimize the total volume of adsorbent while maintaining a minimum number of beds (1 or 2 maximum ) for stopping all impurities, water included at the level required by the process.

A solution of the present invention is a zeolitic adsorbent material consisting of 100% by mass:

A non-zero proportion of a zeolite chosen from X zeolites or LSX zeolites; and

the 100% by weight supplement of a non-cation-exchanged zeolite fraction, said cation-exchanged zeolite being selected from cation-exchanged X-zeolite or cation exchanged LSX zeolites.

In the context of the invention, exchanged by cations is meant that the cations are considered those associated with AI0 ₂ tetrahedral units ^"of zeolite (zeolite phase), which exchanged cations play a role in the mechanism of adsorption of the gaseous compounds to be eliminated.

Similarly, exchangeable cations means cations that can be substituted or replaced by other cations by implementing an ion exchange process.

By exchange rate of a cation x is meant the number of charges borne by the X cations present in the zeolite relative to the total number of charges of all the cations. The exchange rate varies between 0% and 100%. The total positive charge borne by cations is equal to the total negative charge carried by the groups AI0 ₂ ^" .The stoichiometric amount corresponds to this total charge.

It should be noted that the quantities of zeolites X or LSX and of zeolites exchanged are determined as a function of the level of residual impurities required and of the composition of the air to be purified.

Depending on the case, the adsorbent material according to the invention may have one or more of the following characteristics:

the mixture is formed of particles consisting of zeolite X or LSX crystals and zeolite crystals exchanged with cations agglomerated together;

the mixture is formed of zeolite X or LSX particles and zeolite particles exchanged with cations; By particles is meant solids of size ranging from a few hundred microns to a few millimeters and of various shapes, preferably rods, pellets or essentially spherical beads;

the zeolite exchanged with cations is exchanged with calcium, barium, magnesium, strontium and / or lithium cations, preferably with calcium and barium cations;

the cation-exchanged zeolite is exchanged from 10 to 90% by calcium cations and from 10 to 90% by barium cations, preferably from 10 to 50% by calcium cations and from 10 to 50% by barium cations; more preferably 15 to 40% by calcium cations and 15 to 40% by barium cations;

the X or LSX zeolites and the zeolites exchanged with cations are distributed uniformly or almost uniformly in said material;

The present invention also relates to an adsorber comprising an adsorbent material according to the present invention;

The adsorber is preferably a radial adsorber.

Moreover, either the adsorbent material according to the present invention is placed in a single bed; or said adsorber comprises a first bed for removing at least partly the water of a gas stream and a second bed comprising the adsorbent material according to the invention. If the second alternative is chosen, the first bed may comprise activated alumina, silica gel or a sieve (zeolite).

The present invention also relates to a process for purifying or separating a gas or a gaseous mixture using a zeolitic adsorbent material consisting of a mixture of zeolite X or LSX and zeolite exchanged with cations according to the invention. Depending on the case, the purification or separation process according to the invention may have one or more of the following characteristics:

the gas is air, preferably air intended to be fractionated by a cryogenic unit;

at least one first impurity selected from CO ₂ , ethylene, propane and N ₂ 0 is removed;

at least one second impurity selected from water, butane and acetylene is removed;

said process is a TSA process;

the adsorption pressure is between 3 and 35 bar abs, preferably between 3 and 10 bar abs, the adsorption temperature is between 5 and 50 ° C, the adsorption time is between 30 and 480 minutes, preferably between 60 and 180 minutes, and even more preferably between 90 and 150 minutes;

- The regeneration temperature is between 70 ° C and 200 ° C, preferably between 100 and 160 ° C, the regeneration pressure is less than 5 bar abs, preferably close to atmospheric pressure;

the regeneration gas of the adsorbent is nitrogen or a mixture of nitrogen and oxygen containing a small proportion of oxygen (a few% in vol;), preferably the nitrogen / oxygen mixture used to regenerate the oxygen; adsorbent is a waste gas or a waste gas from a cryogenic air separation unit;

- The method of the invention is implemented in at least one adsorber, preferably in at least two adsorbers operating alternately.

The invention also relates to a first process for producing a zeolitic adsorbent material consisting of a mixture of particles consisting of zeolite X or LSX crystals and zeolite X or LSX crystals exchanged with calcium and barium cations agglomerated together, in which :

(a) a zeolite X or LSX containing sodium and / or potassium cations is subjected to at least one ion exchange by contact with a solution containing calcium and / or barium ions,

(b) if necessary, step (a) is repeated until the desired exchange rate for each of said barium and calcium cations is reached,

(c) crystals of zeolite X or LSX exchanged with calcium and barium cations are recovered; (d) the crystals of zeolite X or LSX exchanged with calcium and barium cations from step (c) and zeolite X or LSX crystals are agglomerated to form agglomerated particles, and

(e) heat treatment is performed to dry and activate said particles

Activation essentially means removing by heating the water molecules that obscure the active sites without damaging the crystal structure of the zeolite. The heating rate, the heating time, the maximum temperature depend on the nature of the zeolite

In step (a), for carrying out the ion exchange, a solution of calcium and / or barium salts, such as a chloride solution, is preferably used at a pH below about 6.

The contacting between the zeolite and the saline solution takes place for example by immersion of the entire zeolite in as short a time as possible, this to ensure a homogeneous ion exchange in the zeolite.

Alternatively, the zeolite powder can be suspended in water and slowly added the calcium and / or barium salt solution, with stirring sufficient to distribute the solution throughout the suspended volume. In all cases, the contacting must be carried out under conditions in which the calcium salt and / or barium will be distributed throughout the volume of zeolite, before the exchange has had time to be done, this for ensure that calcium and / or barium will be evenly distributed throughout the mass of the zeolite.

The molarities in salt are between 1 M and 0.01 M, the temperature between 20 ° C and 100 C, and the contact time between 20 minutes and 3 hours.

In the agglomeration step (d), the zeolite can be mixed with a binder, such as clay, silica gel or the like.

Finally, the invention relates to a second process for manufacturing a zeolitic adsorbent material consisting of a mixture of zeolite X or LSX particles and particles of zeolite X or LSX exchanged with calcium and barium cations, distributed uniformly or almost uniformly in said material.

The mixture of said particles can be done continuously or discontinuously by passing through a mixer. Preferably, we will use

- a batch process, in which:

(a) placing the X or LSX zeolite particles and the calcium and barium exchanged X or LSX zeolite particles in a vessel comprising a residual vacuum of at least 15%, and (b) the container is subjected to rotational movements along an axis different from the axis of symmetry of the container.

Either a continuous process, in which the respective quantities of zeolite X or LSX particles and the zeolite X or LSX particles exchanged with calcium and barium cations are introduced simultaneously into an in-line mixer and the mixture then sent to an intermediate storage (silo) or to the delivery packaging (drums, "big bags").

The invention will now be described in the case of a monolitic radial adsorber, that is to say that a single bed consisting of an adsorbent material of homogeneous composition is used to stop the water, the C0 ₂ acetylene, ethylene, propane, butane and N ₂ O up to the required residual level. This charge can also stop traces of other compounds such as certain acid gases or other easily adsorbable compounds possibly even accidentally present in the air (NH ₃ , combustion residues, VOC ...). On such a charge, among the normal impurities mentioned, the water is adsorbed preferentially and the acetylene and butane are also completely stopped.

The traces of methane and ethane can be found in the dried and decarbonated gas but do not pose any particular problem in the cryogenic separation unit.

The choice of the adsorbent charge will therefore depend on the respective contents of C0 ₂ , C ₂ H ₄ , C ₃ H ₈ and N ₂ O in the air and the residual contents required at the inlet of the cryogenic unit for operate it reliably and safely.

The operation of a radial adsorber comprising such an adsorbent charge is shown in FIG.

The fluid to be purified 1 containing the impurities mentioned above enters the lower part of the radial adsorber 10, passes through the adsorbent mass 20 and the product leaves the upper part 2. During the regeneration, the regeneration fluid 3 is counter-balanced. current through the upper part, desorbs the impurities contained in the adsorbent mass 20 and the waste gas 4 leaves at the bottom.

The adsorber itself 10 consists of a cylindrical shell of vertical axis AA and 2 funds. The adsorbent mass 20 is held in place by means of a perforated external grid 11 and an internally perforated internal grid 12 fixed on one side to the upper bottom and on the other side to a solid plate 13 in part. lower. The gas 1 circulates vertically at the periphery in the outer free zone 14 between the cylindrical shell and the external grid, passes radially through the adsorbent mass 20 and then flows vertically in the internal free zone 15 before leaving the adsorber from above. Regeneration is carried out in the opposite direction. In the description above, the gas to be purified during the adsorption phase circulates from the periphery to the center: it is called centripetal circulation in adsorption. The corresponding regeneration is then carried out centrifugally, that is to say from the center to the outside. This is the most general configuration, but the radial adsorbers can be used in the same way with reverse circulation directions, that is to say in adsorption, for example, the gas to be treated will go from the inside towards the outside while in regeneration, the regeneration gas will circulate from outside to inside. Another possible arrangement is to add a circular sealing disc to split the adsorbent mass in two parts. It is then possible in the same radial adsorber to have in adsorption phase for example a centrifugal circulation in a first volume of adsorbent followed by a centripetal circulation in the upper volume of adsorbent.

The adsorbent material relating to the invention consists of a homogeneous mixture consisting of half LSX-type zeolite particles (Low Silica / Alumina ratio) and half CaBaX type zeolite. (This is 50% weight)

More specifically, the LSX is in the form of spherical balls with a diameter of between 1.9mm and 2.15mm and packed density of between 650kg / m ³ and 665kg / m ³ .

CaBaX is also in the form of spherical balls with a diameter of between 2 and 2.30mm and packed density around 700kg / m ³ . The exchange rate for both calcium and barium is 20% of the exchangeable cations. With secondary compounds, this second adsorbent is therefore an Na60 type zeolite; Ca20; Ba20 X. These characteristics were measured on 5 samples taken in 5 different manufacturing batches for each of the adsorbents. The color of the two adsorbents is slightly different allowing visually to identify each of the products. The mixture was carried out before filling in drums filled successively with 50% LSX and then with 50% CaBaX.

The barrels are thus filled to about 80% of their maximum capacity and then the mixing is carried out in an industrial drum mixer which imposes eccentric rotational movements on the drums ... Small samples taken before filling and during the filling shows the stability of the mixture. Visually, there is no evidence of segregation. This confirms the results of laboratory tests. Particles having a maximum diameter ratio of 1, 21 and a density ratio of 1. 08 form a stable mixture as long as the transport of the drums, the filling of the adsorber and the operating conditions of the unit are carried out. according to the rules of art.

The use of a 50/50 mixture makes it possible to aim at a very low residual C0 _{2 content of} less than 10ppb and a 95% stoppage rate for the other impurities. The use of only one of these adsorbents would make it possible to obtain the required specifications but at the cost of a higher investment: higher adsorbent volume, larger adsorber.

The use of a double bed would also optimize the purification unit but at the cost of a complexification of the adsorber. The addition of an additional grid results in particular for the largest radial adsorbers crucial problems of realization, in particular of successive threading of the grids holding the adsorbents.

The choice of the optimum distribution LSX / CaBaX can be made from laboratory tests under the operating conditions but it can also be done preferably via adsorption simulation software as commercially available or as described extensively in the literature.

FIG. 1 depicts the simplest radial adsorber with a single adsorbent material consisting of equal parts of LSX and CaBaX particles. With the same zeolite mixture, it is possible to use a double bed, preferably in this case an activated alumina bed intended to stop the water and the composite zeolitic bed. As an alternative to the base case or the double bed case, the zeolitic material may consist of zeolite beads agglomerating from a mixture of LSX powder and CaBaX. Such a mixture must, in principle, be carried out by the adsorbent supplier, who must preferentially produce the two species of adsorbents himself.

The mixture of adsorbent particles of different composition requires the additional final mixing step but offers a greater flexibility of implementation. It can be two adsorbents from different suppliers, the mixture can be made from commercial products in stock and in any proportion.

Claims

claims

1. Zeolite adsorbent material constituted for 100% by mass:

A non-zero proportion of a zeolite chosen from X zeolites or LSX zeolites; and

The 100% by weight supplement of a non-cation-exchanged zeolite fraction, said cation-exchanged zeolite being selected from cation exchanged X-zeolite or cation-exchanged LSX zeolites.

2. Material as defined in claim 1, characterized in that the cation-exchanged zeolite is exchanged with calcium, barium, magnesium, strontium and / or lithium cations, preferably calcium and barium cations.

3. Adsorbent material according to claim 2, characterized in that said cation-exchanged zeolite is exchanged from 10 to 90% by calcium cations and from 10 to 90% by barium cations, preferably from 10 to 50% by weight. calcium and 10 to 50% cations by barium cations.

4. adsorbent material according to any one of claims 1 to 3, characterized in that the X or LSX zeolites and zeolites exchanged with cations are distributed uniformly or almost uniformly in said material.

5. Adsorber comprising an adsorbent material as defined in any one of claims 1 to 4.

6. Adsorber according to claim 5, characterized in that said adsorber is a radial adsorber.

7. Adsorber according to any one of claims 5 or 6, characterized in that said adsorber comprises a single bed of adsorbent material.

8. Adsorber, characterized in that said adsorber comprises a first bed for removing at least partly the water of a gas stream and a second bed comprising the adsorbent material according to one of claims 1 to 4.

9. A process for purifying or separating a gas or a gaseous mixture using a zeolitic adsorbent material as defined in any one of claims 1 to 4.

The method of claim 9, wherein the gas is air.

A process according to any one of claims 9 or 10, wherein at least one impurity selected from CO ₂ , ethylene, propane and N ₂ O is removed.

12. Process according to any one of claims 9 to 11, characterized in that said process is a TSA process.

A process for preparing a zeolitic adsorbent material as defined in any one of claims 2 or 3, wherein:

(a) - a zeolite X or LSX containing sodium and / or potassium cations is subjected to at least one ion exchange by placing in contact with a solution containing calcium and / or barium ions,

(c) - crystals of zeolite X or LSX exchanged with calcium and barium cations are recovered;

(d) - The crystals of zeolite X or LSX exchanged with calcium and barium cations from step (c) and zeolite X or LSX crystals are agglomerated to form agglomerated particles, and

(e) - A heat treatment is carried out to dry and activate said particles

14. A method of manufacturing a zeolitic adsorbent material as defined in any one of claims 2 or 3, wherein:

(a) - The zeolite X or LSX particles and the zeolite X or LSX particles exchanged with calcium and barium cations are placed in a container comprising a residual vacuum of at least 15%, and

(b) - The container is subjected to rotational movements along an axis different from the axis of symmetry of the container.

15. A method of manufacturing a zeolitic adsorbent material as defined in claim 4, wherein:

(a) - The zeolite X or LSX particles and the zeolite X or LSX particles exchanged with calcium and barium cations are introduced simultaneously into an in-line mixer, and

(b) - This mixture is then sent to an intermediate storage or to the delivery packaging.