DE2847310A1 - PROCESS FOR SEPARATING GASES - Google Patents

Description

DR. BERG DIFL.-ING. STAPF DIPL.-ING. SCHWABE DR. DR. SANDMAiR

P.O. Box 860245 8000 Munich 86

Attorney's file 29 350 October 31, 1978

MORSANTO GOMPAIiY, St. Louis, Missouri / USA

Process for separating gases

- Expectations -

r (089) 988272 Telegrams: Bank accounts: Hypo-Bank Munich 4410122850

⁹⁸⁸²⁷³ BERGSTAPFPATENTJtUtachen- ι λ / <«λ λ λ (BLZ 70020011) Swill Code: HYPO DE MM

⁹⁸⁸²⁷⁴ TELEX: yUiSÖ IGf I U4 <B »yec Veransbank Munich 453100 (bank code 70020270) ⁹⁸³³¹⁰ 0524560BERGd Postscheck Munich 65343-808 (bank code 70010080)

The invention relates to a method of separating of gases by means of membranes which are permeable to at least one gas of a gas mixture. In particular, the Invention to a method for separating gases by selective gas diffusion through membranes, in which the efficiency of the separation at individual membrane separation stages without increasing what is necessary for the separation Labor or changing the characteristics of the membranes used is improved.

In recent years, membranes for separating a variety of Gases evolved from mixtures of the same with other gases and vapors. The separation of gases by diffusion or penetration through membranes depends in large part on those on either side of such membranes prevailing pressure differences. The pressures to be applied differ largely from the pressures with who work when separating liquids using semi-permeable membranes.

In general, the passage of one or more gases through a semipermeable membrane increases with the increase in the difference in the pressures prevailing on both sides of the membrane. The applicable In any case, however, pressure differences have a practical limit which is usually determined by the strength of the The membranes used are given, regardless of whether they are designed as a flat film or as a hollow fiber membrane. Another economic limit arises from the

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Cost of compressing gases or gas mixtures at the separation stages arranged one behind the other.

A method of separating would therefore be of great advantage of gases or gas mixtures up to a high degree of purity, at which the work required for compression the gases did not need to be increased excessively.

The invention provides such a method for separating gases to an increased purity or concentration of the gas or gases to be separated without unduly increasing the amount of work required for compression. The method is applicable for the separation of gas mixtures, which by penetration or diffusion through membranes are separable therethrough, but using a single membrane to achieve the desired purity of the separating gases is not achievable. The procedure is thus in the form of an additional stage in a multi-stage Gas separation process applicable.

In a method of the type mentioned, it is provided according to the invention that a starting gas mixture is compressed and with a first one for at least one chemical gas permeable membrane is contacted, so that a first concentrate is formed that compresses the first concentrate and is brought into contact with a second membrane permeable to at least one gas contained therein, so that a second concentrate and a second depleted mixture result, that the second depleted mixture

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with one for the at least one gas contained therein permeable return membrane is contacted so that a concentrated reflux mixture arises that the concentrated reflux mixture is added to the first concentrate prior to compression and that the second concentrated mixture is collected.

In the following exemplary embodiments of the invention are explained with reference to the drawing. Show it:

Fig. 1 is a schematic representation of a known Method for separating at least one gas from a mixture thereof with other gases among Use of two membrane separation stages arranged one behind the other,

2 shows a schematic representation of a method for separating gas mixtures using two Membrane separation stages and a return arrangement in a first embodiment of the invention and

3 shows a schematic representation of a multi-stage Method for separating gases using a return arrangement in another embodiment of the invention to achieve a high purity of the gas to be obtained.

Fig. 1 shows a typical two stage gas separation process known type, in which a gas or gas mixture concentrated in a first stage by means of a membrane in a second stage by means of a further membrane

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is centered. A starting gas mixture 1 is by means of a first compressor 2 and fed to a separating device 3 containing a first membrane. In The first separating device or stage 3 produces a gas mixture 4 enriched with the gas to be concentrated and a mixture retained by the membrane and depleted of the gas to be concentrated 5 »which each depending on its composition, it can be discharged into the open, burned or otherwise disposed of.

The enriched mixture 4- is made using a second Compressor 7 again, optionally compressed to a higher pressure and one containing a further membrane second separation stage 8 supplied. In this then a still further enriched second concentrate 9 and is created a mixture 10 depleted of the desired gases. This can optionally be carried out on one of the first compressor following point 2 can be added to the starting gas mixture or otherwise used or derived. That Concentrate 9 formed at the second stage 8 usually provides the desired product in the form of a concentrated one Gas or gas mixture.

The degree of concentration or purity that can be achieved in such a cascade arrangement is limited by the Permeability of the membrane used in the individual stages for the desired gas or gas mixture the selectivity of the membranes with regard to the desired gas or mixture over others in the starting mixture

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retained gases and the resistance of the membranes to pressure differences acting on them. Accordingly, additional separation steps are often required to achieve the desired concentration or purity necessary, at which the gases are compressed and separated by means of membranes, which increases the cost of devices and costs increased considerably. In many cases the cost is compared to other methods and devices for separating or concentrating the desired gases not portable, so that membrane separators Not used.

In a first embodiment of the invention shown in FIG. 2, a starting gas mixture 11 is by means of a Compressor 12 is compressed and in a first separation stage 13 working with a membrane in a first depleted one Mixture 15 and a first enriched mixture 14 separately. The latter is again by means of a further compressor 17, if necessary to a higher pressure compressed and fed to a second membrane separation stage 18 as described above. To achieve an increased The efficiency of the arrangement will be the second depleted Mixture 20 fed to a third or reflux membrane separation stage 21. There is no further compression, i.e. no further work is necessary, since the second depleted mixture 20 is essentially has the same pressure as the enriched mixture 14 fed to the second separation stage 18.

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Stage 21 creates an enriched return mixture 22, which corresponds to the enriched from the first separation stage
Mixture 14 can be added. This happens at
one between the first separation stage 13 and the compressor 17 for the second separation stage 24. At the return separation stage 21 there is also a depleted return mixture 23, which is the starting gas mixture at a point 25 between the first compressor 12 and the inlet of the first Separation stage 13 can be added. The membrane of the reflux separation stage is preferably dimensioned so that the depleted reflux mixture 23 is approximately
has the same composition as the starting mixture 11, so that the work required to compress the first concentrated mixture 14 by the compressor 17 can be reduced to a minimum. In addition, since the pressure of the
depleted reflux mixture 23 is approximately equal to the pressure of the starting mixture fed to the first separation stage 13, the effort required for the compression in the entire process can be limited to a minimum.

The process, which works in several stages with gas recirculation, offers various advantages. The thereby obtained Gas mixture 19 has an increased concentration of the desired gas or gases, i.e. increased purity.

This increased concentration or purity is with no additional compression labor and no change the separation characteristics of the membranes used can be achieved and does not require the use of membranes,

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the characteristics of which differ from those of membranes used in known multi-stage gas separation arrangements. That The method is therefore for an improved separation of gases or gas mixtures which can be separated by means of given membranes applicable without these membranes or their characteristics having to be changed.

For example, it has been found that in a two-step process of the type shown in FIG Separation of oxygen from air with the same pressure differences in both separation stages and when using Fiber membranes with the same separation factor and the same permeability for oxygen with respect to nitrogen as in the process shown in FIG. 1, with the same gas weight per hour, the concentration of oxygen in the enriched mixture or concentrate of the second stage from 81.2% by volume to 90.3% by volume, without the The workload for the two compression stages compared to the arrangement according to FIG. 1 needs to be increased. This increase in efficiency is also associated with a reduced total area of the membranes of the same type achievable. So have the three in the arrangement according to

Fig. 2 membranes used a total area of 5360 m, while the two used in the arrangement of FIG

ο membranes have a total area of 7116 m.

In order to improve the efficiency, the method according to the invention can also be used for separation systems, which three, four or more membrane separation stages in a row

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exhibit. The return separation stage can be assigned to any two successive separation stages. However, in order to keep the cost of additional facilities as low as possible, the return flow separation stage preferably fed with the depleted mixture of the last separation stage and provides an enriched reflux mixture, which is added to the enriched mixture of the penultimate separation stage, while the depleted Return mixture is added to the enriched mixture fed to the penultimate separation stage. Such a one The arrangement is explained below with reference to FIG.

In the arrangement of FIG. 3, an output gas mixture is compressed by means of a compressor 32 and in a first membrane separation stage 35 into an enriched mixture 34 and a depleted mixture 35 are separated. That of the The mixture 35 depleted of gases to be concentrated can be fed to a pressure reducer 36 before it is removed to recover the energy of the compressed mixture. The recovered energy can then be used in the Procedure or for other purposes. In the arrangement of FIG. 2 can in the same way by means a pressure reducer 16, energy can be recovered from the depleted mixture 15 of the first separation stage. The enriched mixture 3 ^ of the first separation stage is by means of a second compressor 37 again or compressed to a higher pressure, a second membrane separating

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stage 38 is fed and from this in a second depleted Mixture 40 and a second enriched mixture are separated. The depleted mixture 40 can be compressed Starting mixture 31 at a point 50 before the are added to the first separation stage. The enriched mixture 39 of the second stage is by means of a compressor 41 compressed again or to an even higher pressure and fed to a third membrane separation stage 42. from an even more enriched mixture and a third depleted mixture 44 are then discharged from this. This still has essentially the same pressure as the mixture at the inlet of the third stage 42 and becomes a reflux separation stage 45 forwarded. This is dimensioned so that an enriched return mixture derived therefrom is approximately the has the same composition as the compressed mixture fed to the second separation stage 38, which it at a before the inlet of the second separation stage 38 is added point. An accumulating at the return separation stage 45, enriched reflux mixture 46 has approximately the same composition as that from the second separation stage 38 discharged enriched mixture 39 and is added to this at a point 48 located upstream of the compressor 41 of the third separation stage.

The multi-stage separation process shown in FIG. 3 also provides increased efficiency and offers essentially the same advantages as explained above with regard to the two-stage separation process.

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When using the three-stage shown in FIG Process with gas recirculation for the recovery of oxygen from air, the oxygen concentration in the of the mixture discharged from the third stage compared to one with the same hollow fiber membranes and the same pressure differences, but without gas recirculation working three-stage process with the same gas weight per hour without Increase the workload for the three compression levels from 94.5% by volume to 96.6% by volume. So that one for the secured mixture 47 of the return flow separation stage the same composition as for the enriched mixture of the first separation stage and for the enriched mixture Mixture 40 of the second stage ^ approximately the same composition as obtained for the starting gas mixture 3 ^, proved in the production of oxygen it is necessary to adjust the total area of the four membranes in the arrangement Fig. 3 to enlarge compared to that of the three membranes in a conventional separation plant.

The method according to the invention for separating gas mixtures can be used for concentration, purification and separation of gases which are made up of mixtures using membranes which are permeable to at least one gas in each case can be separated with other gases or vapors, for example to separate oxygen or nitrogen from air, from water vapor from any gas mixture, from hydrogen from carbon monoxide, carbon dioxide, helium, nitrogen, Argon, ammonia gas, alkanes such as methane, ethane and the like,

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and alkenes such as ethylene, propylene and the like, from ammonia gas of hydrogen, nitrogen, argon, water vapor, alkanes and the like, of carbon monoxide of carbon dioxide, hydrogen, Nitrogen, argon, alkanes and the like. From carbon dioxide from hydrogen, nitrogen, carbon monoxide, alkanes and the like, from hydrogen sulfide from hydrogen, nitrogen, Carbon dioxide and the like, from alkanes such as methane from hydrogen, nitrogen, ammonia, carbon monoxide, carbon dioxide, Methanol, water vapor and the like, from alkanols such as methanol or ethanol from hydrogen, carbon monoxide, Carbon dioxide, nitrogen and alkanes such as methane, ethane and the like. As well as any other by means of semi-permeable Membranes of separable gases or vapors such as isotopes of vaporizable metals or salts thereof, such as uranium, Uranium hexafluoride and the like.

Any semipermeable membranes suitable for the separation of gases can be used for the process. These can be in the form of asymmetrical or symmetrical films, which are constrained or self-supporting, tubular can be rolled up or flat. To achieve the largest possible membrane areas in devices of economic Dimensions, the gas separation membranes are preferably formed from hollow fibers. Such hollow fiber membranes can also be symmetrical or asymmetrical, isotropic or anisotropic and in terms of their composition be homogeneous. Furthermore, they can be designed as composite or multi-component hollow fiber membranes

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which hollow fibers made of one material are coated on the inside and / or outside with other substances. When separating different gases show such composite or multi-component membranes a superior selectivity and Permeability to certain gases, which is why they are often used to achieve high separation efficiency will. If hollow fiber membranes are used at all for the separation of desired gases from gas mixtures of the above are suitable, they are preferably used for the method according to the invention.

The invention is also not limited to specific gas separation systems. Any device is suitable in which a gas mixture can be contacted with a membrane and which has an inlet for a gas mixture and outlets for an enriched mixture let through by the membrane and one retained by the membrane Has mixture. When using the preferred hollow fiber membranes, any device is suitable in which an arrangement of hollow fiber membranes can be attached in such a way that a gas stream supplied to the outside of the hollow fibers coated and gases not allowed through by these can be discharged from it, while one of the hollow fibers permeated gas stream is discharged on the inside of the same. Otherwise, the gas flow can also be the Inside of the hollow fibers are supplied and the gas flow that has passed through can be discharged from the outside of the same. Such a device needs an outer housing,

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one connected to the outside or inside of the hollow fibers Inlet and outlets connected to the outside and inside of the hollow fibers. The device can be used for rectilinear Be set up through flow, the fibers then being connected to both ends of the housing. Otherwise the hollow fibers can also only be connected to one end of the housing and are U-shaped within the same be returned. Furthermore, other arrangements are also possible with which an effective separation in each case at least a gas or steam from a gas and / or steam mixture can be achieved.

The other devices of the arrangements shown schematically in the drawing, such as compressors, pressure reducers and lines between the individual stages may be of a conventional type and do not form part of the invention.

The invention is not limited to the exemplary embodiments described, but extends to the ver ^ various changes and modifications of the same.

Thus, the multi-stage arrangement according to FIG. 3 is not limited to a single return stage. " In a number of η stages can be used, for example, η - 1 return stages.

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Claims (20)

DR. BERG DIPL. ING. STAPF DIPL.-ING. SCHWABE DR. DR. SANDMAIR 28 47310 PATENTANWÄLTE Postfach 860245-8000 Munich 86 Lawyer files 29 530 P_a_t_e_n_t_a_n_s_ £ _r_ü_c_h_e 1. A method for separating gas mixtures, characterized in that a starting gas mixture Compressed to superatmospheric pressure and with a first permeable to at least one gas of the mixture Membrane is contacted, so that a first enriched or concentrated mixture and a first depleted Mixtures arise that the first enriched mixture is compressed and with one for the at least one gas in it permeable second membrane is contacted, so that a second, more enriched or concentrated Mixture and a second secured mixture arise that the second depleted mixture under substantially the same pressure with a for the at least one gas permeable therein, contacted special return membrane so that an enriched or concentrated reflux mixture and a depleted reflux mixture arise, that the enriched return mixture before the Compressing the first enriched mixture is mixed therewith, and that the second enriched mixture f (089) 988272 Telegrams: jUSo I θ / I Ui ί Bank accounts: Hypo-Bank Munich 4410122850 988273 BERGSTAPFPATENT Munich (BLZ 70020011) Swift Code: HYPO DE MM 82 74 TELEX: Bayer Vereinsbank Munich 453100 (bank code 700 202 70) 983310 0524560BERGd Postscheck Munich 65343-808 (BLZ 70010080) is caught. 2. The method according to claim 1, characterized in that the depleted return mixture
is mixed with the starting gas mixture. 3. The method according to claim 1, characterized in that the first depleted mixture for Elimination is discharged. 4. The method according to claim 3, characterized in that the first depleted mixture for Pressure reduction is relaxed with recovery of energy. 5. The method according to claim 1, characterized in that the return membrane is dimensioned so that the concentrated return mixture is approximately the same
Gas composition gets enriched like the first
Mixture. 6. The method according to claim 2, characterized in that the return membrane is dimensioned so that the depleted return mixture is approximately the same
Concentration is maintained like the starting gas mixture. 7- The method according to claim 1, characterized in that the at least one gas is permeable Membranes are hollow fiber membranes. 8. The method according to claim 1, characterized in that the through- 909818/1022 Permeable membranes are multi-component hollow fiber membranes. 9. The method according to claim 1, characterized in that the second enriched mixture before its recovery is compressed and separated again. 10. A method for separating gas mixtures, characterized in that a gas mixture several times compressed one after the other and permeable to at least one gas of the mixture under superatmospheric pressure Diaphragms is contacted, so that on the diaphragm of a second or later stage one enriched with one gas Concentrate and a mixture depleted of the at least one gas arise that the depleted Mixture from the membrane of the second or later stage under substantially the same pressure with one for the at least one gas-permeable return membrane is contacted so that a concentrated reflux mixture enriched with the at least one gas is formed, that the concentrated reflux mixture prior to compressing the concentrate from a membrane of a previous one Stage is mixed with this, and that the resulting on the membrane of the second or later stage concentrated Mixture is recompressed and separated and / or collected. 11. A method for separating gas mixtures, characterized in that a gas mixture several times one after the other compressed to superatmospheric pressure and permeable to at least one gas of the mixture 9 09818/1022 Membranes is contacted, so that a penultimate concentrated mixture enriched with the at least one gas and a penultimate mixture depleted of the at least one gas is formed that the penultimate one is concentrated Compressed mixture and contacted with a last membrane permeable to the at least one gas contained therein is, so that a further enriched with the at least one gas, the last concentrated mixture and a last mixture depleted of the at least one gas is produced, that the last mixture depleted essentially under the same pressure with a separate return membrane permeable to the at least one gas is contacted, so that a concentrated reflux mixture enriched with the at least one gas and a reflux mixture which is further depleted of the at least one gas is produced, that the concentrated reflux mixture before the compression of the penultimate concentrated mixture is mixed with this and that the last concentrated mixture is collected. 12. The method according to claim 11, characterized in that the depleted return mixture the gas mixture supplied to the membrane of the penultimate stage is added. 13. Method according to claim 11, characterized in that the return membrane is dimensioned in such a way that that the concentrated reflux mixture is about the same Composition gets concentrated like the penultimate 909818/1022 Mixture. 14-. Method according to claim 12, characterized in that the return membrane is dimensioned so that the depleted return mixture is approximately the same
The composition of gases is the same as that of the gas mixture supplied to the membrane of the penultimate stage. 15 · The method according to claim 11, characterized in that the depleted mixture of the penultimate Stage is admixed with the gas mixture fed to the membrane of a previous stage. 16. The method according to claim 15, characterized in that the membrane of the penultimate stage
is dimensioned so that the penultimate depleted mixture has approximately the same composition as the gas mixture fed to the membrane of the previous stage. 17. The method according to claim 11, characterized in that the at least one gas is permeable Membranes are hollow fiber membranes. 18. The method according to claim 11, characterized in that the permeable to the at least one gas Membranes are multi-component hollow fiber membranes. 19 · Method according to claim 11, characterized in that one at one of the penultimate stage
upstream stage accumulating, depleted gas mixture 909818/1022 is relaxed to a reduced pressure with recovery of energy. 20. The method according to at least one of claims 1 and / or 11, characterized in that the gas mixture contains at least one gas and at least one other gas or at least one vapor and that the at least one gas by selective diffusion through a semipermeable membrane from the at least another gas or vapor is separable. 909818/1022