DE2826913A1 - Argon purificn. by adsorption of oxygen and nitrogen - using mixt. of type 4A and 5A zeolitic mol. sieves with super-additive effect - Google Patents

Abstract

In the sepn. of O2 and/or H2 from crude Ar by adsorption on type A zeolitic mol. sieves, mixts. of types 4A and 5A are employed, pref. in 1:10 to 10:1 (1:4 to 4:1) ratio. Sepn. is achieved very economically. The selectivity of the mixt. for O2 adsorption is much greater than would result from a purely additive effect. Pref. the mol. sieve mixt. is heated to 400-700 (500-650) degrees C before use. Adsorption takes place at 15 degrees C pref. between 0 degree C and -70 degrees C.

Description

Process for the adsorptive separation of

Oxygen and nitrogen from crude argon The invention relates to a Process for the separation of oxygen and / or nitrogen from crude argon by adsorption on zeolitic molecular sieves of type A.

Such a process, however, only focuses on the separation of oxygen from crude argon is known from DE-OS 2,457,842. There will the separation of oxygen and argon on zeolitic molecular sieves of the type A carried out, the entrance window of which have a diameter of up to 4.2 i. These zeolites can thus be assigned to type 4A. Recalling the Fact that the selective uptake of oxygen from the raw argon initially occurs a Temperature range between 93 and 108 K is limited and a temperature increase over 108 K would lead to a standstill of the cleaning process are in the specified Special procedural measures provided to keep the work area up expand to temperatures of 140 K. Among other things, several hours of bakeout will be required proposed at 4000c before the intended use of the zeolitic molecular sieve serves to remove the moisture practically completely from this. By targeted cation substitution that results in a reduction in the diameter of the entry window is connected, according to the cited document, the temperature range of the selective The absorption of oxygen from the raw argon can be significantly expanded. The reason it can be seen that the oxygen molecule has a smaller diameter than the argon atom. This suggests that the expansion of the Entry window to a reduction in the selectivity with regard to oxygen adsorption should lead.

According to DE-AS 1 444 435, the separation of argon and oxygen on a zeolite of the type 4A in that the flow rate of the Gas mixture is kept higher by the adsorbent than it is for the setting the adsorption equilibrium for argon and oxygen would be required. Included the fact that the Adsorption rates of the two components at some distance from the equilibrium state are very different can be, whereby this effect obviously increases with decreasing temperature and for example at -78.5 C is much more pronounced than at OOC. Here too is it is therefore only possible through special procedural measures, bypassing the fact that the zeolite 4A only weakly for argon and oxygen at the adsorption equilibrium has different loading capacities to obtain an acceptable separation result.

DE-PS 1 235 271 discloses a process for the separation of oxygen-nitrogen mixtures known, in which, inter alia, zeolite 5A is used. Regarding the separation of these two components of argon, however, there is only a hint. '# th, that argon behaves towards the zeolite 5A like oxygen, so that one under Economically interesting separating effect of this molecular sieve for a nitrogen-argon mixture, but not for an oxygen-argon mixture is to be expected.

From the prior art it was found that for the separation of oxygen and nitrogen from raw argon under the zeolitic molecular sieves at most type 4A comes into question, whereby a special, sometimes complicated process management is a prerequisite.

There is thus still an interest in better adsorbents for the purification of raw argon, since the den Adsorptively experienced counterparts Cleaning processes, which essentially consist of burning over Deoxo catalysts, Drying and rectification removal of excess hydrogen and nitrogen exist, are very expensive in terms of apparatus and process technology.

The present invention is therefore based on the object for a Process for the adsorptive separation of oxygen and / or nitrogen from crude argon to provide an adsorbent with the help of which it is possible to carry out the separation to be carried out as economically as possible.

This object is achieved according to the invention in that mixtures zeolitic molecular sieves of types 4A and 5A can be used.

Corresponding measurements have surprisingly shown that that when using a mixture of the molecular sieve types mentioned, a selectivity with regard to the oxygen uptake is achieved, which has an additive effect of the Mixture components goes far beyond. This is supposed to be done with the help of the discussed below Measurement results are clarified.

An advantageous development of the invention is that the molecular sieve mixture before its use for adsorptive oxygen and / or Nitrogen separation at temperatures between 400 and 7000J, preferably between 500 and 6500c is baked out. In contrast to the one quoted at the beginning specification from the prior art, which only provides for heating at 4oo0c, shows it turns out that by heating in the specified preferred temperature range far better results can be achieved.

The investigation of the most favorable temperature range for adsorption found to be particularly advantageous that the adsorptive separation of oxygen and / or Nitrogen from Rohgargon at temperatures below 150C, preferably between 00G and -700C is performed. With that, there are also considerable advances in terms of of the temperature range to be observed has been achieved, as in the DE-OS process 2 457 842 temperatures below 140 K are prescribed and also from the DE-AS i 444 435 can be seen that the optimal selectivity only below of the temperature range preferred here occurs.

The proportions of types 4A and 5A in the mixture should be Values between 1:10 and 10: 1, preferably between 1: 4 and 4: 1.

For measurements made with 96.75% by volume argon, 2.2% by volume raw argon mixture consisting of oxygen and 1.05% by volume of nitrogen 4.4 bar and -110 ° C were carried out, it was already clear that a molecular sieve mixture, which consisted in equal parts of types 4A and 5A and previously baked out at 25,000 compared to the in individual components pretreated in the same way 4A and 5A show considerable advantages in terms of oxygen receptivity having. If a separation column is optionally filled with these molecular sieves is charged with the aforementioned raw argon mixture, the result is a breakthrough charge with regard to oxygen, defined by the occurrence of approx.

1 ppm oxygen downstream of the separation column, a value in the case of type 4A of 14.7 Ncm3 / kg molecular sieve, for type 5A a value of 22.2 Ncm3 / kg, while for a mixture of the two types in a ratio of 1: 1 already has a value of 44.4 Ncm3 / kg is measured. This corresponds to an increase in loadability by one Factor 3 or 2.

The others carried out on the basis of this first result Measurements are shown in the diagrams in Figures 1 and 2.

Figure 1 shows the breakthrough loading with respect to oxygen, measured at a pressure of 4.5 bar and plotted in Ncm3 / kg molecular sieve the temperature in OC.

Figure 2 shows the retention times on a logarithmic scale of nitrogen and oxygen on different molecular sieves or molecular sieve mixtures, plotted in minutes over the reciprocal absolute temperature.

The curves in Figure 1 were taken from three different column fillings measured. Curve 1 relates to one baked out at 25000, too Molecular sieve mixture consisting of equal parts of types 4A and 5A, curve 2 on a molecular sieve mixture of the same composition after heating at 60,000, Curve 3 shows a pure filling of type 5A after heating at 60,000. The curves clearly show, on the one hand, the positive effect of bakeout at 60,000 and, on the other hand, the absolute superiority of those composed in equal parts of types 4A and 5A Molecular sieve mixture in the temperature range between OOC and 7000 compared to the pure filling of type 5A with the same pretreatment. In addition, it results that in the entire temperature range below 1500 the selectivity of the molecular sieve mixture that of the pure component exceeds 5A.

The measurements shown in Figure 2 were made on a 2 m long and 4 mm diameter separating column carried out with baked at 30,000 Molecular sieve fillings was provided. Pure argon flowing into the separation column a small amount of air was briefly let in. Then the retention times were measured for the components nitrogen and oxygen. The curves 1 and 4 relate refer to a pure filling of type 5A, curves 2 and 5 to a mixture of Types 4A and 5A in a ratio of 1: 1 and curves 3 and 6 to such a ratio Mix in a quantity ratio of 2: 1.

The measurement results show, on the one hand, that the nitrogen of all three fillings is preferred, and on the other hand that both molecular sieve mixtures with regard to the readiness to take up oxygen compared to the pure filling of type 5A are cheaper by a factor of approx. 1.5. From this it can be concluded that the numerical value of the mixing ratio is obvious plays a subordinate role.

Overall, the measurements show that there is nitrogen and oxygen with the aid of molecular sieve mixtures of the composition indicated better to remove adsorptively from crude argon than with the help of the pure individual components.

Claims (4)

Claims 1. A method for separating oxygen and / or Nitrogen from crude argon by adsorption on zeolitic molecular sieves of the type A, characterized in that mixtures of types 4A and 5A are used. 2. The method according to claim 1, characterized in that the molecular sieve mixture prior to their use for adsorptive oxygen and / or nitrogen separation Temperatures between 400 and 70,000, preferably between 500 and 65,000, baked out will. 3. The method according to claim 2, characterized in that the adsorptive Separation of oxygen and / or nitrogen from the raw argon at temperatures below of 15 C, preferably between 00 0 and -70 ° C is carried out. 4. The method according to any one of claims 1 to 3, characterized in that that the quantity ratio of types 4A and 5A in the mixture at values between 1: 10 and 10: 1, preferably between 1: 4 and 4: 1.