DE1280225B - Process for separating an oxygen-nitrogen gas mixture into its components - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

German class:

Number:
File number:
Registration date:
Display day:

COIb

BOId

12 i-13/02

12 e-3/02

P 12 80 225.4-41 (U 8299)

August 26, 1961

17th October 1968

It is known to contain oxygen and nitrogen To separate the gas mixture into its constituent parts by placing it over or through a stationary, crystalline, zeolitic molecular sieve conducts. It is also known that sodium zeolites A and X are at 5 - 75 ° C absorb nitrogen to a greater extent than oxygen.

It has now been found that such a separation of gas mixtures consisting essentially of oxygen and nitrogen, in particular air, ^{can be carried out particularly effectively at a temperature between 0 and -15O 0} C if a zeolitic material with an apparent pore diameter of at least 4 angstrom units used.

It has also been found that zeolites of certain composition are particularly good for performing of the procedure are suitable. Zeolites are known to be metal-aluminum silicates in general formula

χ Me ₁ O: Al ₂ O ₃ : y SiO ₂ : ζ H ₂ O
η

In this form) Me means a metal and η its valence. Excellent zeolites for the process according to the invention are those in which Me means lithium, strontium, barium, nickel, calcium, sodium and / or rubidium, χ a value of about 0.9 ± 0.2, y a value of about 2.5 ± 0 , 5 and ζ has a weri up to about 8. Zeolites are also suitable, where Me means calcium, χ has a value of about 1.0 ± 0.2, y has a value of about 1.85 ± 0.5 and ζ has a value of up to about 6. Such zeolites are described in German patents 1,038,016 and 1,038,017. Molecular sieves can be removed by dewatering these zeolites. produce an apparent pore diameter greater than 4 angstroms. Dewatering can be carried out in a known manner, e.g. B. by heating to about 350 ° C in a vacuum or in a stream of air. In many cases, complete dehydration is not required because the water of crystallization is removed during the process.

The "apparent pore diameter" means the maximum diameter of molecules that are under under normal conditions are just barely adsorbed by the molecular sieve in question. This apparent pore diameter is always larger than the actual diameter of the pores.

Natural zeolites, ζ. B. Chabazite, Erionite or Faujasite, or synthetic zeolites, were used for separation processes

an oxygen-nitrogen gas mixture

into its constituent parts

Applicant:

Union Carbide Corporation,

New York, N.Y. (V. St. A.)

Representative:

Dipl.-Ing. H. Görtz, patent attorney,

6000 Frankfurt, Schneckenhofstr. 27

Named as inventor:

Robert Paul Hamlen, Scotia, N.Y .;

Kazuo Kiyonaga,

Henry William McRobbie, Buffalo, N, Y .;

Douglas William McKee,

Schenectady, N. Y. (V. St. A.)

Claimed priority:

V. St. v. America on August 26, 1960 (52134),

dated December 1, 1960

(73 029),

dated December 2, 1960

(73 215, 73 216)

the. The desired cations can be incorporated in a manner known per se by ion exchange.

Zeolitic molecular sieves of the type described have good adsorption capacity for mixtures from nitrogen and oxygen and a high selectivity. In the table below are some Values included. The first column of this table shows the type of cation, the second column in percent the degree of exchange de? original cation against that contained in the molecular sieve. the The third column gives the adsorption capacity per gram of the activated zeolite in milliliters of a mixture from 25% oxygen and 75% nitrogen, calculated at normal pressure and normal temperature. the fourth column contains the separation factor, which is calculated using the following formula:

adsorbed

[O ₂ ] adsorbed

[O ₂ ] gas
[N ₂ ] gas

809 627/1402

Here, [N2] and [O2] represent the concentrations of the gases in volume percent in the two phases' in all cases, a mixture of 25 volume percent oxygen and 75 volume percent nitrogen at a total pressure of 1 atmosphere and a temperature of -78 ⁰ C was investigated .

Adsorption
middle Degree of exchange • Adsorption
capability Separation factor % ml Mg ⁺⁺ X 56 50.1 2.4 Ca ⁺⁺ X 96 37.8 3.5 Li ⁺ X 86 111.8 7.6 Sr ⁺⁺ X 96 52.7 • 8.6 Ba ⁺ + X • 85 62.7 15.8 Cs ⁺ X 50 26.3 1.5 Ni ⁺⁺ X 38 41.6 6.2 Rb ^ X 56 30.0 3.5 Ca ⁺⁺ A 80 116.0 4.4 Na ⁺ X 100 72.4 4.9 K ⁺ X 100 58.7 2.2

IO

15th

20th

temperature Adsorptive capacity Separation factor ml ■ -95 4.9 103 -78 5.5 86.7 -45 6.0 44.5 -32 6.6 ' 37.0 0 6.8 20.0

The following table shows the dependence of the adsorption capacity and the separation factor on the temperature when using a lithium zeolite to separate a mixture of 20% oxygen and 80 ° / ₀ nitrogen at a total pressure of 1 atmosphere.

35

40

The table shows that the separation factor decreases with increasing temperature.

When carrying out the process, a higher separation factor has the advantage that one to generate a certain amount of oxygen of a certain purity a, smaller amount of Adsorption material needs.

Although you can perform the procedure of the invention at temperatures from 0 to -150 ⁰ C, it is recommended in most cases to work from -30 to -50 ^0C. The following must be taken into account that ^u C take place during the adsorption and desorption temperatures ranging from about 20 microns. If you want to work at an equilibrium temperature of about -30 ° C, the incoming gas mixture should be precooled ^{to about -5O 0 C.} A temperature range between -30 and -5O ⁰ C has the advantage that the molecular sieves are not worn out by frequent heating and cooling and the associated expansion and contraction, and that ordinary steel can be used as the equipment material which is not yet brittle at these temperatures and that no great expenditure is required to maintain very low temperatures.

The process according to the invention can be carried out in one or more stages. With the two-stage It is recommended to use the cooled filling of a process for cooling in the first process stage To use recuperator and the recuperator by means of the desorption from the zeolitic To cool material obtained nitrogen.

An advantageous embodiment of the method is that the contact between the gas mixture and the zeolitic material takes place alternately in two separate zones. Here, in one zone is adsorbed while the other zone is regenerated at the same time.

In all cases it has proven to be useful to remove the gas mixture to be separated before contact with to cool the zeolitic material from the outside to a temperature below room temperature lies.

The drawings show, for example, some embodiments of the method.

According to FIG. 1, a gas containing oxygen and nitrogen, for example air, is fed to line 10 at room temperature and a first higher pressure, passed through a compressor reversing valve 12 and then fed to feed gas cooler 14, where it is countercurrently with heat exchange at about 10 to 40 ^° C. the oxygen-containing tail gas in line 16 occurs when such a gas is recovered. From the cooler 14, the gas passes into the line 18 and via one of the two inlet valves 20 to drying devices 22, where moisture contained in it is removed.

This drying is necessary for the best effectiveness of the adsorber. At moisture levels of a few parts per million or less, the nitrogen adsorbers according to the present Process operated continuously at temperatures below 0 ° C for one year or more will. An increase in the 'temperature during the regeneration of the adsorber, an increase in Increase the amount of purge gas and an increase in pressure when adsorbing compared to regeneration the effectiveness of the regeneration and therefore extend the operating time before a drainage of the Adsorbers is required.

The dryer can be regenerated by a flushing gas, for example hot air, over the Line 24 and one of the inlet valves 26 initiated and through the decommissioned drying device 22 is passed through. The purging gas containing moisture is drawn off through one of the valves 28 drained from the drying device 22 and preferably via the valve 30 in the line 32 deducted from the system.

The dried feed gas is discharged from one of the two drying devices 22 and the valves 34 discharged to line 36 and enters the heat exchanger 38, where the heat of adsorption through a corresponding coolant, for example water, is derived, which flows through the line 40. It will be understood that the application of the heat exchanger 38 for the implementation of the Invention is not essential. If in a given plant, the temperature of the dried feed gas is above the temperature of the cooling water available at the location concerned, the cooling device preferably used to reduce the heat load on the recuperator and the subsequent cooling system

to decrease. The dried feed gas is fed via the control valve 42 to the first recuperator 44, which is filled with a suitable cold-storing material, for example with pebbles, aluminum, copper or other refractory materials such as AbQi. The recuperator 44 was previously cooled by passing through cold nitrogen desorbate gas and can, for example, cool ^{the feed gas from 20 to about -3O 0 C.}

To achieve maximum efficiency of the oxygen-nitrogen separation at affordable cost and complexity of the required cooling system to ensure progressively lower temperatures, the nitrogen adsorption is preferably, but not necessarily, carried out in a temperature range of -30 to -5O ⁰ C. For this purpose, an external cooling system with a heat exchanger 46 and a line 48 can be provided. The partially cooled feed gas exiting from the first recuperator 44 is fed via the line 45 to the first external heat exchanger 46 for further cooling to approximately -10 to -60 C. The coolant for this further cooling is guided upwards through the line 48 and can, for example, evaporate will. Suitable coolants are ammonia, monochlorotifluoromethane, monochlorodifluoromethane and dichlorodifluoromethane, the latter being preferably used. The heated coolant exiting from the upper end of the line 48 is fed via the line 50 and the line 52 connected to it to the cooling device 54, where it is compressed and condensed again and via the line 56 and the subsequent branch line 58 to the first outdoor heat exchanger 46 is returned.

The coolant flowing back is throttled via the valve 60 before it enters the exchanger 46 entry

The further cooled feed gas from the first Außenwnrmeaustauscher 46 having a temperature of preferably -40 to - outlet 50 ⁰ C, is fed via line 60 to the bottom of the first adsorber 62, a corresponding crystalline zeolitic molecular sieve material having an apparent pore size of at least 4 Contains angstrom. At the beginning of the adsorption process, the first adsorber 62 is at a second, lower pressure, since the nitrogen desorbate was drawn from it at such a pressure during the previous regeneration. Preferably nitrogen is adsorbed from the feed gas during adsorption. When the pressure in the first adsorber 62 approaches atmospheric pressure, the bypass valve 12 is closed and the compressor 64 is started. When the first adsorber pressure is a certain desired value, preferably in the range of about 1.4 to 3.5 kg / cm ² , e.g. B. about 1.8 kg / cm ² , the outlet valve 66 is opened in the line 68, and oxygen-containing exhaust gas sjröint for example at -3O ⁰ C through this valve and through the control valve 70 through to the edible oil cooler 14. The heated exhaust gas is fed via the line 72 to the gas storage 74 and then to the oxygen compressor 76, where it is compressed to the desired pressure, for example to about 175 kg / cm-. The compressed. Oxygen-containing gas of, for example, 93% purity is discharged from compressor 76 into line 78 for consumption.

While the adsorption takes place in the first adsorber 62, the second adsorber 80 is regenerated, so that adsorption can take place in it when the first adsorber has absorbed sufficient nitrogen Has. For this purpose, the pressure of the second adsorber 80 is first via the line 82, the bypass valve 84 and the second recuperator 86 drained to practically atmospheric pressure. In this way the considerable cold content of the nitrogen desorbate is absorbed by the recuperative material, to later to the incoming oxygen-nitrogen gas stream in the manner described above treat. The heated nitrogen desorbate gas emerging from the lower end of the second recuperator 86 flows via the line 88 and the control valve 90 to the connecting line 92, which the Vacuum pump 94 bypasses. Line 92 includes a control valve 96 and a control valve 98, and that Nitrogen desorbate is discharged from there to the outside.

The vacuum pump 94 is started when the pressure in the second adsorber 80 is substantially atmospheric, and the adsorber 80 is then set to the desired second lower pressure, preferably in the range of about 0.007 to about 0.28 kg / cm ² , e.g. , 07 kg / cm ² , evacuated. Since there is no advantage in passing the nitrogen desorbate through the second outdoor heat exchanger 100, it is preferably bypassed during the regeneration. The time required for depressurization and repressurization is reduced in this way.

The pressure difference between adsorption and desorption generally increases the loading of the zeolitic molecular sieve with the adsorbable component. In the case of nitrogen-oxygen separation the pressure can also influence the separation factor. Next is the economic compromise the cost of compressing the entire feed stream with the cost of subtracting the Note that desorbates have a smaller volume than the feed gas.

If the first adsorber 62 is filled with nitrogen, the gas flows can be switched so that the Adsorber 62 is regenerated and the adsorption in the second adsorber 80 continues. This can be done because the relevant adsorbers 62 and 80, the external heat exchangers 46 and 100 and the recuperators 44 and 86 in the circuit parallel to Hegen. So feed gas is passed through the second one after the other Recuperator 86 and the second outdoor heat exchanger 100 fed to the second adsorber 80. on this way, the cooling heat of the nitrogen desorbate, which is first fed to the second recuperator 86 was fed in, recovered by the incoming feed gas.

F i g. Fig. 2 shows a further embodiment of the invention in which oxygen-containing tail gas continuously generated and instead of two external heat exchangers only a single heat exchanger for further cooling of the oxygen-nitrogen mixture is used. Although additional valves are required, their cost is increased by the Saving an outdoor heat exchanger more than made up for it. In the flow diagram of FIG. 2 is just that Recuperator - external heat exchanger - and

Adsorber section shown. The remaining part is the same as that described above and shown in FIG. 1 illustrated identically. The feed gas is fed via line 136 to the first recuperator 144, where it is cooled by previously stored cold. The cooled gas is discharged via line 145 and control valve 147 to outdoor heat exchanger 146, where it is further cooled by coolant in line 148. _{The further cooled feed gas ro} coming from the exchanger 146 into the line 160 flows via the control valve 161 into the first adsorber 162, where the nitrogen is removed in the manner described above.

During the pressure relief taking place during the regeneration of the second adsorber 180, the cold nitrogen desorbate gas delivered to the second recuperator 186 via the control valve 183 and cools this. The heated desorbate is then discharged. The flow of gas through the pipe 163 through to the outdoor heat exchanger 146 is prevented by closing the control valve 165.

As explained above, the flow of the oxygen-enriched exhaust gas can be made continuous when depressurizing, evacuating and repressurizing an adsorber during that Part of the overall cycle take place in which the product is withdrawn from the other adsorber. When operated in this way, however, a larger vacuum pump is required to withdraw a certain amount of gas than is the case! would be if the pump operated continuously would be.

The use of three adsorbers and three recuperators according to FIG. 3 allows continuous lending Acceptance of the product as well as continuous operation of the vacuum pump for separate Adsorber, while a third adsorber is either drained or re-pressurized. The feed gas flows through the line 236 and the control valve 242 to the first recuperator 244. where it is cooled. The cooled gas passes through line 245 and is in the outdoor heat exchanger 246 continued to be cooled. The cold oxygen-nitrogen mixture obtained is passed through the line 260 fed to the first adsorber, v / o the nitrogen is drawn off. The tail gas containing oxygen is discharged via the line 268 with the control valve 270 arranged therein. Meanwhile the second adsorber 280 with feed gas re-pressurized by removing some of this gas from the Line 236 is diverted to the second recuperator 286 via the branch line 241 and the Em-! Aßsieuerventil 243 will. The cooled feed gas flowing out of this is via the control valve 249 of the line 282 dsm is supplied to the second adsorber 280, which is thereby pressurized again. Here after the inlet valve 243 can be closed to repressurize the second adsorber 286 shut off until adsorption is to take place in it. The repressurization can also be timed be dimensioned so that it is completed just before the first adsorber switched to regeneration will.

While the first adsorber 262 is switched on and the second adsorber 280 is pressurized, the third adsorber 281 is evacuated and the third recuperator 287 is cooled again. This happens, in that cold nitrogen desorbate gas is drawn off from the third adsorber 281 by means of the vacuum pump 294 will. The cold withdrawn gas flows via line 285 and the control valve provided in it 289 to the third recuperator 287 and cools it. The heated gas enters line 291 and runs through the control valve 293 to the pump 294. The warm nitrogen gas is then via the line 292 discharged from the system with the valve 298.

The three adsorbers 262, 280 and 281 and the three recuperators 244, 286 and 287 are connected in parallel and are all connected to the outdoor heat exchanger 246. There are also corresponding Valves are provided so that the various flows in and out in an appropriate manner can be switched off. If, for example, the adsorption in the first adsorber 262 is ended and If this is switched to regeneration, the second adsorber 280 is switched to adsorption and the previously evacuated third adsorber 281 is pressurized again. Thereafter, the third adsorber 281 Feed gas is supplied, the second adsorber 280 is evacuated and the first adsorber 262 is again under pressure set. The next following changes in the flow represent the conditions originally described again.

According to FIG. 4, the feed gas is supplied by the blower 310 through line 311 to heat exchanger 313, where it is cooled by a colder α gas in the ti thermal contact stationary pipe 312th In the heat exchanger 313, the Speisegns should not be cooled below about 0 ⁰ C, otherwise attsfriert in this gas contained moisture and the line 312 and the line 311 blocked. The cooled air is then conducted via line 311 to drum 314, where the condensed water is drawn off and discharged via line 315 with valve 316 extending from the bottom of the drum. The air is vented from the drum 314 through the line 317 at the top and is preferably directed to the drying device 318, whereby the water vapor concentration is further reduced. The drying device 318 may contain an appropriate adsorbent or silica gel.

The dried air then flows through line 319 and is heated to the desired adsorption temperature, e.g. B. -40 "C, through heat exchange with an appropriate coolant, for example: liquid ammonia or a halogenated hydrocarbon, further cooled in the thermal contact line 320. Depending on whether the valve 321 or the valve 322 is open, this is cooled feed gas fed to the adsorbent column 323 or 324, which are parallel in flow. According to the drawing, the control valve 321 is open, and the cold feed gas passes through the valve to the inlet end of the first adsorbent column 323, where the nitrogen through the adsorbent contained in the column Will get removed.

The essentially pure oxygen gas flows from the outlet end of the first column 323 via the line 323 a and the control valve 325 at a temperature of about -3O ⁰ C. The cooling heat of the cold oxygen stream is recovered by flowing through the line 312 a of the heat exchanger 312, wherein the air feed stream is partially cooled in the manner described above. The heated oxygen can via line 324 to

Consumption point or a corresponding memory.

While the adsorption takes place in the first adsorption column 323 , the nitrogen adsorbate is removed from the second adsorption column 324 and this column is prepared for the subsequent activation. This is preferably done by holding the valve 326 at the discharge end of the second adsorption column 324 in the closed position and evacuating the column from the feed gas inlet end via the line 327 by connecting the line 330 via the valve 329 .

Appropriate means, for example a vacuum pump 331, are provided at the discharge end of the line 330 in order to achieve the required evacuation, and from there the nitrogen is released into the atmosphere via the line 332 or released for further use.

When the nitrogen-enriched adsorption front approaches the discharge end of the first column 323 or when the column is almost saturated with the equilibrium oxygen-nitrogen mixture, the connections between the two columns are switched so that desorption occurs in the first column 323 and in the second column 324 the adsorption takes place. The position of the enriched nitrogen "adsorption front can be determined, for example by means of thermocouples or other similar devices. In order to change the gas flow, the valve is closed 321 and the valve is opened 322 in the conduit 333 at the inlet end of the second adsorber 324th At the discharge the valve 325 is closed and the valve 326 of the discharge line 324 opened. To desorb the nitrogen component from the first column 323 , the valve 335 in the line 328 is opened and the desorbate via the inlet end of the column 323 into the line 328 and via the connecting line 330 in the previously described Way to vacuum pump 331 withdrawn.

Claims (2)

Patent claims: 1. A method for separating gas mixtures consisting essentially of oxygen and nitrogen, in particular air, into their constituents by passing them over or through a static crystalline zeolitic molecular sieve at a temperature between 0 and -15O ⁰ C, characterized in that a zeolitic material with an apparent pore diameter of at least 4 angstrom units is used. 2. The method according to claim 1, characterized in that one is used as a zeolitic material Zeolite with lithium, strontium, barium, nickel, calcium, sodium and / or rubidium as a cation used. . Considered publications:
French Patent No. 1,223,261;
U.S. Patent Nos. 2,882,243, 2,882,244. 1 sheet of drawings 809 627/1402 10.68 Θ Bundesdruckerei Berlin