DE2329210A1 - ZEOLITE A WITH IMPROVED PROPERTIES - Google Patents

Description

Zeolite A with improved properties

Type A zeolites that make up the composition

1.0 + 0.2

Al ₂ O,. 1.85 + 0.5

where M is a metal and η is its valence, are widely used in adsorption technology. Zeolites A are primarily used for drying or after shaping with binders into pellets, spheres or granules Fine cleaning of gas and liquid flows. Binder-free moldings of zeolite A are also used.

In the drying and fine cleaning processes, relatively small amounts of H ₂ O or other impurities such as CO ₂ , H ₂ S, acetylene, NH, etc. are removed from the fluid. If, on the other hand, it is a matter of the adsorptive separation of components which are contained in the fluid in a higher concentration, this is referred to as material separation.

The effect of type A zeolites in the adsorption processes mentioned can be based on two completely different principles. First, molecules can be different Cross-sectional projections are separated from each other in that only the smaller ones are more uniform through the Zeollthporen Size step through and so access to the real Have adsorption cavities (sieve effect). Secondly

Le A 15 074

409881/0592

Thanks to the polar structure of the inner surface of the zeolite crystals, more polar molecules are preferentially adsorbed in front of less polar, and more polarizable, preferred over less polarizable (polarity effect), provided that the molecular shape allows passage through the zeolite pores. Some of those carried out in the art with zeolite A. Adsorption process is based on the sieve effect, another part on the polarity effect, with some both principles work at the same time.

The pore size of type A zeolites can be influenced by the cations. During the synthesis, zeolite A is generally obtained in the Na form, which has a pore size of approx. 4 Å. Through ion exchange, the more voluminous K ⁺ ions can now be introduced instead of the Na ⁺ ions, whereby the pores are narrowed to approx. Z> Ä. On the other hand will be

+ 2+

When the Na ions are exchanged for the divalent Ca ions, the pores are expanded to approx. 5 Å, because instead of 2 Na ⁺ ions

2+
only 1 Ca ion with approximately the same ion radius enters the lattice. This change in the pore size naturally affects the selectivity of the zeolites due to the sieving effect, but other properties that are important for technical application are also changed. By introducing the bivalent ions, the polarity of the lattice increases, and as a result of the pore widening, faster adsorption and desorption of the molecules is observed.

The expansion of pores through the introduction of divalent ions is not proportional to the amount of exchanged in zeolite A Ions, but occurs suddenly in a relatively narrow range of the degree of exchange. E.g. occurs - as in the German patent 1 215 650 executed - the pore widening from 4 to 5 8 units when replacing the

Le A 15 074 - 2 -

409881/0592

Sodium ions are exchanged for calcium ions within the narrow range of 25 - 40 % , ie if the exchange is only 25% or less, the material has the sieving characteristics of sodium ions, but if an exchange of 40 % or more occurs the sieving characteristics of calcium zeolite A. These limits can shift somewhat with other bivalent ions.

In technology, the pore opening of zeolite A from 4 S to .5 Å is mainly effected by ion exchange with calcium ions, the exchange being carried out far beyond the 40 # required for pore opening for safety reasons. In general, these zeolites referred to as "Zeolite 5 A ^M " have a degree of exchange of 60-70 % . Since not all ion exchange sites in the starting zeolite are usually occupied by sodium ions, but rather partially by H ions, the degree of exchange does not depend on the proportion of related to distant Na ⁺ ions,

2+ but as a molar ratio of Ca to AlpO in the zeolite

Are defined.

Zeolites 5 A are used in technology for the adsorption of straight-chain hydrocarbons, for gas drying, for the adsorption of CO ₂ , CO, N ₂ , NH, among others. In some cases, when selecting the type, zeolite 5 A competes with zeolites with a different effective pore size; this applies, for example, to the adsorption of CO ₂ . When removing CO ₂ from natural gas, sodium zeolite A with a pore size of 4 Å is chosen in order to exclude the coadsorption of propane and higher n-alkanes. In contrast, zeolite 5 A is preferred for COg removal from combustion gases to generate protective gas or for COp removal from the intake air of air separation plants

Le A 15 074 - 3 -

4098 81/0592

the adsorption and desorption through the further pores is rapid and a shorter mass discharge zone is achieved becomes, which increases the economy of the process.

For the assessment of the performance of zeolites, equilibrium values of the loading are first used the temperature, so-called adsorption isotherms, are used. Before measuring such isotherms and in general, before any adsorption process, the first step must be the preparation of the zeolite water bound in the pores can be removed, which is done by heating and applying a vacuum or a dry purge gas is significantly accelerated. This process is called "activation" or "regeneration" designated.

When measuring the adsorption isotherms, only small amounts of sample, e.g. Ig or less, are used are usually activated in a high vacuum. Such activation can be described as very careful and gentle will.

In contrast, zeolites are seldom activated with the help of a vacuum in technical applications: one usually works with a hot gas stream passed through the adsorber, which at the same time supplies heat and desorbed water vapor or other desorbates removed from bed. If water vapor is desorbed or the activating gas itself is already not dry, such an activation or regeneration is not as gentle as that in the laboratory High vacuum method used for measurements, as zeolites protect against the simultaneous action of water vapor and

Le A 15 074

409881/0592

higher temperatures are sensitive, i.e. a gradual Suffering changes in the crystal lattice.

It has been proven that the manner of activation has an influence on the adsorption performance of the zeolites. This is particularly true for adsorption at relatively low loads, ie for the adsorption of substances that are only slightly adsorbable at the given temperature, such as N ₂ , CH ₂ ^, CO, at temperatures well above the boiling point, e.g. room temperature. The same applies to substances that can be easily adsorbed per se at very low partial pressures, such as COp from atmospheric air. It is therefore not surprising that the measured values of samples which have been gently activated in the laboratory using a high vacuum are in no way to be equated with the adsorption values of the zeolites, which were subjected to regeneration in technical adsorbers, possibly repeated many times in the presence of water vapor .

It has been found that the adsorption performance of a zeolite 5 A for Np is already through at room temperature a one-time activation at atmospheric pressure and the presence of water vapor as opposed to vacuum activation considerably deteriorated and, depending on the duration of the water vapor exposure, drop to less than half can. This phenomenon occurs not only with Ca-containing 5 A zeolites, but also with other 2-valent zeolites Metals, such as strontium, exchanged type A zeolites.

In the case of processes for the enrichment of oxygen from air, however, the highest possible Np loading at room temperature is required required. These procedures are winning in recent years

Le A 15 074 - 5 -

409881/0592

Time is considerably more important. Enriched oxygen is used in technology, among other things, for oxidation reactions, the generation hot flames and for fermentative processes such as wastewater treatment.

Another process in which a high Ng load on the zeolite is decisive for economic viability is the production of pure hydrogen from ammonia cracked gas. A similar problem arises with other production processes for hydrogen, in which traces of N ₂ , CO ₂ , CO and CHu have to be removed from a raw gas.

Zeolites 5 A, which are used in adsorption systems for binding N ₂ or other components that are difficult to adsorb, should therefore be activated in a vacuum to achieve an optimal effect. Although this is not a problem with small amounts, on an industrial scale this is hampered by the poor heat transfer in a vacuum and the outlay on equipment. In addition, it must be taken into account that adsorber fillings may have to be reactivated in situ when a certain amount of moisture has been absorbed.

The invention is therefore based on the object of a zeolitic To provide adsorbent after activation in the hot air stream, which may not even needs to be dried, has a high adsorption capacity in the area of low loadings.

It has now been shown, surprisingly, that 5 A zeolites whose degree of exchange is at least 80 % far above the limit necessary for pore opening are far less sensitive to hot gas activation than the commercially available 5 A zeolites.

Le A 15 074 - 6 -

409881/0592

The subject of the present invention are therefore zeolites of type A of the general formula

χ Me ¹¹ O. η Me ^ O. Al ₂ O ^. 1.85 + 0.5 SiO ₂ ,

whereby

Me monovalent metals, especially sodium,

Me represents divalent metals and

χ has a value of at least Ο, ΘΟ and

η has a value of (1.0 +0.2) - χ.

Such zeolites are ideal for separation of polar or polarizable molecules of those that are less polar or polarizable.

Me can, for example, consist of Mg, Ca, Sr or a bivalent metal the series of subgroup elements of the periodic system, e.g. Mn. Calcium is popular because of its low price and the favorable location of the ion exchange equilibrium.

In the preparation of the zeolites according to the invention, it is best to start from Na zeolite A, the starting material being can be in powder form or already as a shaped body. The material will; in aqueous suspension the exchange e.g. Subjected to calcium salt solutions. The ion exchange can take place at room temperature or at a higher temperature, with An increase in temperature with otherwise constant reaction conditions leads to higher degrees of exchange. The concentration the exchange solution is generally between 0.1 m and 3 m calcium; low concentrations lead to higher ones Degrees of exchange, however, naturally deliver lower space yields. In powder samples, the ion exchange is within

Le A 15 074 - 7 -

409881/0592

finished one hour; Shaped bodies need depending on size and porosity response times up to about 8 hours. To achieve the degree of exchange according to the invention can several exchange steps follow one another.

The difference in the adsorption behavior between the zeolites according to the invention with a degree of exchange of at least 80% of divalent cations and the known 5 Å zeolites with a lower degree of exchange can be shown on the basis of isothermal measurements. For example, a Mc Bain quartz spring balance was used to measure Np loads on binder-free zeolite Α granules with different degrees of Ca exchange of 83 % (sample 1) and 73 Jt (sample 2) depending on the pretreatment. The replacement products were made from the same batch of Na zeolite Α granules. The samples were first activated in a vacuum at 0.5 Torr and 350 ° C. for 8 hours, with the recipient being filled Z> times with dry helium and evacuated again _{towards the end of the activation to flush out residual H 2 O traces.} After the first measurement, the samples were then exposed to a moist stream of hot gas in order to simulate the activation conditions in practice. For this purpose, it was for 4 hours 300 ⁰ C hot air that had been saturated at 20 ° C and the water vapor passed over the sample. Activation then took place in a vacuum as for the first measurement, in order to obtain the comparable, anhydrous state for the second measurement. The following measured values show the superiority of the over 80 % exchanged sample:

Le A 15 O74 - 8 -

409881/0592

Sample treatment N ~ uptake at OC in

^d g / 100 g

800 torr 100 torr 1 activation in vacuum 2.60 0.62

1 exposure to moisture
Hot air, then activation in a vacuum 2.65 0.66

2 activation in vacuum 2.29 0.6 ^

2 exposure to moisture
Hot air, then activation in a vacuum 1.90 O, j54

More meaningful than such equilibrium measurements of absolute loads of pure gases are the measurements of separation effects, Degrees of enrichment or yields in cyclic adsorption processes, as they are in the following examples to be discribed. Since larger amounts of substance are used here, there are uncertainties in the inhomogeneity the sample could be justified, automatically switched off. In addition, those for technical recovery likewise important properties of the zeolites with regard to the adsorption and desorption kinetics and their changes in the dynamic measurements are also recorded.

The method according to the invention is to be explained in more detail using the following examples:

Le A 15 074 - 9 -

409881/0592

Example 1:

Production of Ca-Na-Zeolite A with different degrees of exchange:

a) 1,200 g of binder-free Na zeolite A pearl granules of the sieve fraction 1-4 mm (corresponding to 4.4 mol of Na zeolite A) were placed in a glass column and filled with 7.0 1 of 1.25 molar CaClp solution at 80 ° C exchanged. The CaClg solution was continuously circulated through the column with a pump for 3 hours. Then the solution was allowed to run off and the whole process was repeated with 7.0 l of fresh CaCl ₂ solution (1.25 m) for 3 hours at 80 ° C. The granules were washed free of chloride with water and air-dried. The Ca-Na zeolite A obtained had the following composition, based on anhydrous substance:

0.86 CaO. 0.08 Na ₂ O. Al ₃ O ₃ . 2.03 SiO ₃

b) 1.200 g of the same binder-free zeolite Na-A-Perlgranulats as in Example 1 a) were for 1 hour with 1.5 1 1.2 molar CaClg solution at 50 ⁰ C by pumping the solution over the zeolite contained in a column exchanged as in Example 1 a). Then the solution was drained and the process repeated with fresh 1.5 1 CaClg solution (1.2 m), the Umpumpdauer 6 hours and the temperature was 50 ⁰ C. The product obtained had the following composition based on anhydrous substance:

0.58 CaO. 0.34 Na ₂ O. Al ₃ O. 2.04

Le A 15 074 - 10 -

409881/0592

Example 2: ty

The two Ca-Na zeolites prepared according to Example 1 a) and 1 b) A were assessed on their adsorption capacity in the oxygenation of air at room temperature in the apparatus described below tested. Before the actual test, the samples were activated, initially by baking in a tube provided with an electrical heating coil at a vacuum of 1 Torr. Between A cooled zeolite column was installed to absorb the desorbed water vapor. The final temperature during activation was −20 ° C., this The temperature was kept constant for 2 hours.

The samples were then subjected to the first performance measurement (such as described later) and then spread out in a dish for 3 days to saturate with water vapor left to stand in the air.

This was followed by renewed activation, but this time with hot gas, as is generally used in technical adsorbers. For this purpose, the granulate was poured into a well-insulated column and hot air flowed through it, which was set to a dew point of + 20 ^° C. by being moistened in a water saturator. After reaching 320 ⁰ C the Wassersättiger was bypassed with a bypass line and continue activating at 320 ⁰ C for 2 hours with carefully dried air in order to ensure a comparable Vakuumaktivlerung the residual water loading on the zeolite.

The actual performance measurement of the zeolite took place in the apparatus shown in the accompanying figure. Where 1) is the

Le A 15 074 - 11 -

409881/0592

Recipient for the batch of zeolite to be tested, he has one inside diameter of 48 mm, a length of the cylindrical part of 69Ο mm and a usable filling volume of 1.250 ml. The inlet side of the test tube can be connected to a vacuum pump 3) via the shut-off valve 2 a) Gas outlet is connected to a gas meter 4) for the purpose of measuring the amount of gas pumped out. On the other hand, the inlet side of the test pipe via the shut-off valve 2 b) to a Dried air source can be connected. The dried compressed air coming from line 5) is in the reducing valve 6) relaxes and passes through line 7), the buffer tank 8), line 9) and the shut-off valve 2 b) into the Test tube 1). Line 7) is also connected to a check valve 10), which leads to an immersion 11), with the aid of which the desired adsorption pressure is finely adjusted by the height of the liquid column in 11). In the tests, the overpressure was 20 mm Hg column.

The outlet side of the test pipe 1) is via the shut-off valve 12 a) and the shut-off valves 13 a), 12 b) and 13 c) with calibrated gasometers 14 a), 14 b) and 14 c) tied together. On the other hand, the amount of gas flowing out of the test tube can optionally be controlled via the shut-off valve 12 b) can also be fed to the gas meter 15). The pressure or the vacuum at the outlet end of the test tube is with the Mercury manometer l6) measured.

After filling the zeolite into the recipient and adjusting the reducing valve 6), so that by immersion 11) a stream of gas bubbles escapes, the cyclic loading cycle that results from the cycles A) evacuation, B) filling insists on adsorption pressure and C) transferring at constant pressure, carried out as follows:

Le A 15 074 - 12 -

409881/0592

-ty

A) Evacuate:

With closed valves 2b), 12 a) and 12 b) and open Valve 2 a) is the recipient with the help of the vacuum pump 3) to a constant pressure of 95 Torr (= 1/8 atmosphere) evacuated and then the valve 2 a) also closed. The amount of gas pumped out during the evacuation process is measured with the gas meter 4).

B) Filling up to adsorption pressure:

By slowly opening valve 2 b), dried air is allowed to enter the recipient. The filling is finished, if gas bubbles escape again as a result of the immersion.

C) transfer at constant pressure:

When valves 2 a), 12 a), 12 b) are closed from the previous cycle and valve 2 b) is open, one opens now valve 12 b) and lets air flow over the zeolite until the gas meter 15) shows an exit gas quantity of 5 l. Then valve 2 b) is closed first and then valve 12 b).

This cycle is repeated a few times until the volume measured by gas meter 4) is the volume pumped out during evacuation Gas quantity results in completely constant values. Then, in the 3rd cycle of a cycle, the one emerging from the test column becomes Gas is not sent through the gas meter as previously described, but with the valve 12 b) closed and the valves open 12 a) and 13 a) passed into the gasometer 14 a) until a predetermined amount of gas, e.g., 3 liters, has been collected there; then the gas flow is directed e.g. to the gasometer 14 b) and catches a further 2 1, so that on the whole again 5 1 of the outlet gas were taken off in this cycle. The content of the gasometer is based on its oxygen

Le A 15 074 - 13 -

409881/0592

content (in Vol.-Ji) analyzed. The cycle can meanwhile continue as described above and possibly repeat the collection of the gas for the purpose of analysis. The single ones Measures take about 50 seconds to 1 minute.

The tests are evaluated in such a way that the average concentration of 5 liters of product gas determines if necessary, is calculated from the individual results in the case of separate analysis of partial quantities. Since the valuation of Og-Ng mixtures are not proportional to the Og content, is used as a measure of the enrichment effect according to the usual procedure in air separation technology, the amount of "Excreted nitrogen" determined. This number is a measure of the separation effect achieved, it results from of the following formula:

b - a (0.0476 x-1)

where b = amount of Np £ ~ N liter_ / a * amount of gas / ~ N liter_7 χ = O ₂ content / ~ volume-#_7

On the other hand, the quotient of the amount of gas pumped out and the excreted N “sets the pumping work involved in relation to the achieved separation performance. This quotient should therefore have the lowest possible values. The following are measured values from Op enrichment experiments with the two produced according to Example 1 a) and 1 b) Products juxtaposed; all series of measurements were carried out twice:

Le A 15 074 - 14 -

A09881 / 0592

cn co ιο

1 2 3 4 5 6th 7th 8th product lot Vol.-Ji O ₂ in
the liters
1 + 2 + 3 4 + 5 voi. -ji
O ₂
middle excluded
N ₂
N liters abep.
gas
N liters quotient
columns
7: 6 Example 1 a) Vacuum activity
tion 872 48.4 26.2
48.6 26.4 39.5
39 * 7 4.40
4.45 9.07
9.15 2.06
2.06 Activation with
moist hot air 874 47.0 25.4
47.2 25.4 38.4
38.5 4.14
4.16 8.19
8.24 1.98
1.98 Example 1 b) Vacuum act i ν i e-
tion 862 49.0 26.6
49.0 26.6 40.0
40.0 4.51
4.51 9.14
9.18 2.03
2.04 Activation with
moist hot air 868 40.0 23.2
40.2 23.4 33.3
33.5 2.93
2.96 6.56
6.58 2.24
2.22

Le A 15

- 15 -

The two products according to Example 1 a) and 1 b), which are made from the same starting material and thus also with regard to grain size spectrum, macroporosity and bulk density are comparable, practically do not differ after the gentle activation in a vacuum. The differences emerge only after the damaging influence of water vapor at high temperature. While the first, highly exchanged Product according to example 1 a) has only decreased insignificantly in its performance, the product according to 1 b) shows with a lower degree of exchange, there is a sharp drop in the separation performance.

Example 3:

The 5 8 zeolites according to the invention with a degree of exchange by divalent cations of at least 80 % were tested in the present example for the removal of COp traces from air, a typical fine cleaning process with removal of a polarizable component at minimal partial pressures. This system is of great importance in technology for cleaning the intake air of air separation plants based on the Linde principle.

The testing took place in a test column with a diameter of 21 mm and a bed height of 1,500 mm. According to the invention In the process, a product of the following composition was used as the zeolite:

Sample 1: 0.84 CaO. 0.1? Na ₃ O. Al ₉ O. 2.16

A lower exchanged zeolite was also used for comparison measured with the following composition:

Sample 2: 0.75 CaO. 0.18 Na ₃ O. Al ₃ O ₃ . 1.99 Le A 15 O74 - 16 -

409881/0592

The zeolite granules were activated with carefully dried (dew point below -7O ° C), hot air at 50O ⁰ C. The test gas was ppm by volume of dried air of 23 ⁰ C and 6.5 atm with a cog content of 420th The flow rate, based on the empty column, was 20.5 cm / sec.

The evaluation of the experiment was carried out in such a way that behind the zeolite column, the amount of purified air with measured by a gas meter. From the amount of air purified up to the breakthrough of 1 ppm COp, the mean COp loading of the zeolite, which calculates the "breakthrough loading" which is important for the design of technical adsorbers. In addition, with the help of a number of gas analysis nozzles distributed over the length of the column, the length of the mass transition zone could be determined (dimension transfer zone = MTZ) can be determined. The experimental values listed below show the clear Superiority of 5 8 zeolite with one degree of ion exchange of over 8O # according to the invention:

Product Amount breakthrough loading Length of the MTZ

gg C0 ₂ / l00 grams of zeolite cm

Sample 1,398 2.72 60

Sample 2 38O 1.90 92

Le A 15 074 - 17 -

409881/0 5 92

Claims (7)

Patent claims: Type A zeolites of the general formula χ Me ¹¹ O. η Me ₂ O. Al ₂ O ^ . 1.85 + 0.5 SiO ₂ Me monovalent metals, Me represents divalent metals and χ has a value of at least 0.80 and η has a value of (1.0 +0.2) - χ. 2) Type A zeolites according to claim 1, characterized in that Me is calcium and Me is sodium. 3) Process for the production of zeolites of type A according to one of claims 1 to 2, characterized in that zeolites of the Na-A type are treated with the aid of Me salt solutions. 4) Use of zeolites according to one of claims 1 to 2 for the separation of polar or polarizable elements or compounds from those which are less polar or polarizable. 5) A method for separating polar or polarizable substances from those which are less polar or polarizable, characterized in that zeolites according to one of claims 1 to 2 are used. Le A 15 074 - 18 - 409881/0592 6) Method according to claim 5, characterized in that nitrogen is adsorbed or separated from atmospheric air or from oxygen-nitrogen mixtures. 7) Method according to claim 5j, characterized in that is adsorbed or separated from gas mixtures COg. Le A 15 074 - 19 - 409881/0592 Blank page