JPH06178933A - Oxygen adsorbent and separation of oxygen and nitrogen - Google Patents

Abstract

PURPOSE:To provide an oxygen adsorbent which adsorbs a large quantity of oxygen under low temperature and low pressure adsorptive conditions and excels in oxygen selectivity and to provide a method for separating oxygen and nitrogen where oxygen of high purity is easily obtained at extremely low unit requirement of power by using the adsorbent. CONSTITUTION:(1) An oxygen adsorbent which after 3-20% of Na ions of Na-A type zeolite is given ion exchange by K ions, heat treatment is performed at atmospheric pressare and at a temperature of 600-760 deg.C to form is provided. (2) A method for separating oxygen and nitrogen where not less than two adsorbers packed with the oxygen adsorbent are kept at not more than room temperature and mixed gas of oxygen and nitrogen is fed to one a adsorption tower at a pressure of atmospheric to data to make oxygen selectively adsorbed, causing nitrogen of high purity or nitrogen-rich gas to flow out and the other adsorption tower is given pressure decrease to 0.08-0.5ata to regenerate the adsorbent, causing oxygen-rich gas to be recovered and continuous switching between the adsorption process and the regeneration process is performed is provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen adsorbent which selectively adsorbs oxygen at a lower temperature than a mixed gas containing oxygen and nitrogen as main components, and an oxygen adsorbent using the adsorbent. On how to separate.

[0002]

2. Description of the Related Art The method of adsorbing and separating oxygen and nitrogen from air using an oxygen adsorbent has the advantages that the device is small and simple and does not require maintenance as much as unmanned operation. In recent years, the number of uses has increased as a medium- and small-sized nitrogen production device with an amount of about 10 to 3000 Nm ³ -N ₂ / h, and replacement of the case of transporting and using liquid nitrogen produced by a cryogenic separation device is also in progress. is doing. There, activated carbon type molecular sieves carbon 4A is most often used as an oxygen adsorbent.

The above adsorption / separation method is carried out in an apparatus comprising an air compressor, two or more oxygen adsorption towers, and in some cases a vacuum pump. Sending compressed air to one adsorption tower,
Oxygen in the air is adsorbed and separated by the oxygen adsorbent filled in the adsorption tower, and the remaining high-pressure nitrogen is recovered from the rear of the adsorption tower. Then, the other adsorption tower decompresses and recovers oxygen to regenerate the adsorbent by decompressing, if necessary countercurrently flowing a part of nitrogen of the product, or by strongly sucking with a vacuum pump. . By repeating this operation, oxygen and nitrogen are continuously separated.

A typical example of the oxygen adsorbent used in the above adsorption separation method is carbon molecular sieves put to practical use by Bergbau Forsung, which is estimated to have a window diameter of about 4 angstroms. Oxygen is selectively adsorbed from a binary gas mixture by utilizing the difference in adsorption rate.

Although the above-mentioned adsorption separation method is said to be advantageous in the area of small and medium-sized equipment, in order to produce 1 Nm ³ of nitrogen, 0.45 Kwh with 99% nitrogen and 0.15% with 99.9% nitrogen. It requires 65 Kwh of power and consumes more power than 0.28 Kwh of the large-capacity cryogenic separation method. In addition, when oxygen of 1 Nm ³ is produced under the above operating conditions for oxygen, 25 to 30% of oxygen-enriched air is 3.5 to 4 from the desorption side.
Recovered at Nm ³ . However, there are few examples in which oxygen is specifically recovered by this method. This is because the obtained oxygen concentration remains low as described above, and on the other hand, since high pressure air is used, the power consumption is 0.8 kwh / Nm ³ -O.
_It is considered that this is because it exceeds ₂ (pure oxygen equivalent). Further, in the nitrogen production, there is little economies of scale with respect to the increase of the apparatus capacity, and it is said that it is not possible to compete with the cryogenic separation method in the region of 1000 Nm ³ −N ₂ / h or more, and the situation is even more difficult in the oxygen production.

Therefore, looking at the reduction of power consumption,
It is conceivable to lower the blast pressure to perform the adsorption operation at a low pressure, but the oxygen adsorption amount decreases almost in proportion to the pressure, so the capacity of the device becomes extremely large. Further, in order to increase the oxygen production amount (oxygen-enriched air amount), it is conceivable to shorten the cycle time, but the valve, the adsorbent, the rotating machine, and the like are largely consumed, which naturally limits the cycle time.

[0007]

Therefore, the present invention solves the above-mentioned drawbacks and provides an oxygen adsorbent having a large oxygen adsorption amount under low temperature and low pressure adsorption conditions and excellent oxygen selectivity, and It is an object of the present invention to provide a method for separating oxygen and nitrogen, which can easily obtain high-purity oxygen with an extremely small power unit by using the adsorbent.

[0008]

The present invention provides (1) Na-A
An oxygen adsorbent obtained by subjecting 3 to 20% of the total zeolite of the type zeolite to ion exchange with K and then heat-treating at a temperature of 600 to 760 ° C. under normal pressure, and (2) filling the oxygen adsorbent described above with 2 The adsorption towers above are kept at room temperature or below, and a mixed gas containing oxygen and nitrogen as main components is supplied to the adsorption tower in the adsorption step at a pressure of atmospheric pressure to 3 ata to selectively adsorb oxygen, and the adsorption tower High-purity nitrogen or nitrogen-enriched gas is discharged from the column, the adsorbent in the regeneration step is decompressed to a pressure of 0.08 to 0.5 ata to regenerate the adsorbent, and the oxygen-enriched gas is recovered. The method for separating oxygen and nitrogen is characterized in that the regeneration step and the regeneration step are continuously switched.

[0009]

The present inventors, while earnestly researching a method for efficiently separating oxygen and nitrogen under low temperature and low pressure adsorption conditions,
3-20% of Na ions contained in Na-A type zeolite
The oxygen adsorbent activated by heat exchange at 600 to 760 ° C. after ion exchange with K ion increases the amount of oxygen adsorbed under low temperature and low pressure adsorption conditions and is excellent in oxygen selective adsorption. Therefore, compared with high-pressure adsorption in the room temperature range and regeneration under atmospheric pressure (vacuum decompression), it is possible to significantly reduce the power consumption without increasing the capacity of the adsorption tower and to separate oxygen and nitrogen. Has been completed.

A production example of the oxygen adsorbent according to the present invention will be described below. First, a 0.1 M KCl aqueous solution is added to a Na-A type zeolite slurry solution to ion-exchange 3 to 20% of all Na contained in the zeolite with K in terms of mol. Then, filtration and washing are carried out, then kaolin and silica sol are added as binders, and after molding, they are fired at a high temperature of 600 to 760 ° C. for 2 hours to obtain an oxygen adsorbent. Using this oxygen adsorbent, an attempt was made to separate oxygen and nitrogen from air using the air separation device shown in FIG.

The air separation operation will be described below with reference to FIG. The air is sent to the compressor 2 through the inlet line 1, is pressurized to 1.05 to 3 ata, is sent to the dehumidifying / decarbonizing tower 4 through the flow path 3, and becomes extremely clean pressurized air. . The pressurized air flows through the flow path 3 ′, the valve 5, the flow path 6,
It is supplied to the adsorption tower 8 in the adsorption process through the valve 7,
Oxygen is adsorbed and separated by the oxygen adsorbent 9 filled in the tower. At that time, the nitrogen concentration increases toward the rear of the tower. Then, the nitrogen-enriched air is collected in the product nitrogen tank 13 via the valves 10 and 11, and taken out of the system via the valve 12 and the product nitrogen flow passage 21 as necessary.

On the other hand, the adsorption tower 8'in the regeneration step is decompressed by the vacuum pump 18 through the valve 16 'and the flow path 17, and the oxygen adsorbed on the oxygen adsorbent 9'is easily desorbed. , Will be played in a short time. Oxygen adsorbent 9 in adsorption tower 8
Are saturated and the oxygen adsorbent 9'of the adsorption tower 8'is regenerated, the inlet air flow path 6 is switched to 6 ', the adsorption tower 8 is changed from the adsorption step to the regeneration step, and the adsorption tower 8'is regenerated step. To the adsorption step. Thus, by sequentially switching the above steps, product nitrogen and oxygen-enriched air can be continuously recovered.

A heat exchanger 19 is provided between the flow path 3'for supplying clean pressurized air at the inlet and the flow path 17 for discharging the gas containing desorbed oxygen as a main component. Road 2
1 and the above-mentioned pressurized air flow path 3 ′ are also connected to the heat exchanger 22.
Is provided to enable heat exchange. By installing the compression refrigerator 20 in the pressurized air flow path 3 ′, the adsorption tower can be cooled very efficiently and a predetermined low temperature condition can be obtained.

In addition, when switching the adsorption tower, not only is the flow path simply switched between 6 and 6 ', but also the inlet air is prevented from being blown through due to pressurization immediately after the switching, and it remains behind the adsorption tower. In order to minimize the release of nitrogen and forward pressurized air out of the system, first, the valve 10,
10 ′ is fully opened, and the residual nitrogen behind the adsorption tower 8 immediately after adsorption is partially transferred to the adsorption tower 8 ′ immediately after regeneration. At this time, the pressure of the adsorption tower 8 is P _O (ata), and the pressure of the adsorption tower 8'is P ₁ (ata).
(Ata), the pressure after equalization is approximately (P _O + P ₁ ).
/ 2. After this, the adsorption tower 8 ′ having a pressure of about (P _O + P ₁ ) / 2 is opened by opening the valves 10 ′ and 11 ′ to equalize the product nitrogen tank 13 and the adsorption tower so that the adsorption tower 8 ′ has a higher pressure. Fill with nitrogen. Pressure P when equalizing product tank 13
₂ (ata), assuming that the dead volume of the adsorption towers 8 and 8 ′ is V ₁ (liter) and the capacity of the product nitrogen tank 13 is V ₂ (liter), the pressure of the product nitrogen tank 13 before pressure equalization is P _O. If they are substantially equal, the pressure equalizing pressure P ₂ is roughly as follows. P ₂ = [(P _O + P ₁ ) / 2 · V ₁ + P _O · V ₂ ] /
(V ₁ + V ₂ )

Thus, when simply switching the tower, P
Compared to the rapid boosting from ₁ to P _O
Since the pressure is gently increased to P ₁ , (P _O + P ₁ ) / 2, P ₂ , P _O , blow-through of air such as pressure increase is prevented, and residual nitrogen and high pressure air in the desorption process are released to the outside of the system. Can be minimized. It should be noted that in the operation whose main theme is the recovery of oxygen-enriched air in the regeneration process, the above operation is not effective because it lowers the product oxygen concentration.

[0016]

EXAMPLE Air separation was carried out using the apparatus shown in FIG. The operation specifications at that time are as follows. Adsorption tower diameter 25mm, length 2600m
m Adsorbent filling amount 1.5 kg / tower Number of towers 2 towers Switching time 60 seconds Outlet product flow rate 2 N liter / switching time Adsorption tower pressure 1-5 ata Regeneration tower pressure 0.1-1 ata Adsorption tower temperature 20--100 ° C Adsorption Type of agent Na-KA type zeolite

FIG. 2 shows N contained in Na-A type zeolite.
3 to 15 mol% of a is ion-exchanged with K to obtain 60 under normal pressure.
Using Na-KA type zeolite heat-treated at 0 to 760 ° C as an oxygen adsorbent, the change in oxygen concentration (vol%) in the desorbed gas was examined when changing the K ion exchange rate (mol%). is there. The adsorption pressure (P _O ) is 1.2
ata, regeneration pressure (P ₁ ) is 0.1 ata, adsorption temperature-
The temperature was set to 30 ° C. and the outlet nitrogen concentration was 97%.

As is clear from FIG. 2, the oxygen-enriched air concentration exceeds 30 vol% as a standard for oxygen production (membrane separation, etc.) in the ion exchange ratio range of 3 to 15%. The power consumption per unit at this time is 0.09 kW on an oxygen-enriched air basis.
the h / Nm ³ -O _2. In this example, in order to separate oxygen from air, it is assumed that oxygen corresponding to product nitrogen is brought in from the raw material air, and purely produced oxygen is the amount of oxygen in the product minus this carried-in oxygen. Power evaluation was performed by doing. That is, carry-in oxygen Ci = 20.6 / 78.5 (1- _CO ), where _CO : oxygen concentration in oxygen-enriched air Pure oxygen content Cp = _CO- 20.6 / 78.5 (1- C _O) = so 1.26C _O -0.26 oxygen concentration of the oxygen-enriched air is the highest 48 vol% at Cp = 0.34 nm ^3, a power consumption rate 0.2
The 6kwh / Nm ³ -O _2.

Here, according to the explanation of the molecular sieve effect of conventional Na-A, the window diameter of Na-A is 4Å, and as shown in FIG. 3, oxygen (2.8 × 3. 8
Nitrogen (3.2 × 4.2Å), which is a large molecule, is also adsorbed. On the other hand, in KA, it was said that the window diameter was reduced to 3Å and neither oxygen nor nitrogen was adsorbed. According to this explanation,
Even if a part of Na is ion-exchanged with K, only a window in which neither oxygen nor nitrogen is adsorbed is increased, and no further effect appears. However, in the present invention, the adsorbent that has undergone the above-mentioned ion exchange is subjected to the heat treatment described below, thereby succeeding in imparting the selective adsorption property of oxygen in the low temperature adsorption operation.

FIG. 4 shows the oxygen concentration in the oxygen-enriched air recovered during desorption by changing the heat treatment temperature for Na-K-A whose K exchange rate is 12 mol% which is the optimum condition of FIG. It shows the result of examining (vol%). Incidentally, the adsorption pressure (P _O) is 1.2Ata, the regeneration pressure (P ₁₎ was set 0.1Ata, adsorption temperature -30 ° C., the outlet nitrogen concentration of 97%. As is clear from FIG. 4, the oxygen concentration is 30 v in the heat treatment temperature range of 600 to 760 ° C.
The optimum heat treatment temperature exceeded ol% and was around 740 ° C. That is, the optimal preparation conditions of Na-A type zeolite are: i) K exchange rate: in the range of 3 to 15%, maximum value is near 12% ii) Heat treatment temperature: in the range of 600 to 760 ° C, maximum value is 7
Near 40 ° C. Therefore, the following characteristics were investigated for the separation of oxygen and nitrogen using a Na-KA oxygen adsorbent that had been treated at a heat exchange temperature of 740 ° C for 2 hours with a K exchange rate of 12%.

FIG. 5 shows an adsorption temperature of -30 ° C. and a desorption pressure P.
₁ is set to 0.1 ata and outlet nitrogen concentration is 99.9%,
It is the result of investigating the power consumption unit (kwh / Nm ³ −N ₂ ) when the adsorption pressure P ₀ was changed in the range of 1.05 to 4.5 ata. As is clear from FIG. 5, the power consumption rate is drastically reduced as the adsorption pressure decreases, and when the adsorption pressure is 3 ata or less, the carbon molecular sieve 4A has 0.65 k.
It has been found that nitrogen and oxygen enriched air can be separated from air with smaller power units for wh / Nm ³ -N ₂ (99.9% N ₂ ).

In FIG. 6, of the conditions of FIG. 5, the adsorption pressure P _O is 1.2 ata, and only the desorption pressure P ₁ is 0.1 to 0.5.
It is the result of investigating the power consumption unit when changing within the range of ata. As is clear from FIG. 5, the desorption pressure P ₁ =
The range of 0.1 to 0.3 ata can separate nitrogen- and oxygen-enriched air from air with a power unit smaller than 0.65 kwh / Nm ³ -N ₂ (99.9% N ₂ ) of carbon molecular sieve 4A. Do you get it.

In FIG. 7, the adsorption pressure P _O is set to 1.2 ata, the desorption pressure P ₁ is set to 0.1 ata, and the outlet nitrogen concentration is set to 99.9% under the conditions of FIG.
It is the result of investigating the power consumption unit when changing in the range of 00 ° C. This is because when the above low temperature conditions are set, an increase in adsorption amount and an improvement in oxygen selectivity generally occur.
This is because the breakthrough zone at the time of adsorption can be reduced, which can be expected to reduce the size of the device and improve the separation efficiency. As is clear from FIG.
The power consumption rate continued to decrease with the decrease in adsorption temperature. Up to −60 ° C., the power consumption unit was examined with the above apparatus, but there was no particular problem regarding air separation. In addition, small scale studies up to −100 ° C. did not lose their effectiveness. However, at temperatures below -70,
The power consumption required for cooling is about 4 times as high as -30 ° C and twice as high as -60 ° C, and the equipment cost is also high, which is not practically preferable.

Next, in FIG. 8, the empty cylinder speed U is set to 0.4 cm / sec and the adsorption temperature is set to 4 under the same conditions as those in FIG.
It is the result of examining the oxygen concentration in the nitrogen at the outlet of the adsorption tower when the temperature was changed from 0 to -100 ° C. As is clear from FIG. 8, the oxygen concentration in the nitrogen at the outlet of the adsorption tower was significantly reduced in the low temperature region as the temperature decreased. Above, mainly power costs,
Having described in relation to oxygen purity, it will now be described in relation to initial equipment costs.

In FIG. 9, the adsorption pressure P _O is 1.2 ata, the desorption pressure P ₁ is 0.1 ata, and the product nitrogen sampling amount is adjusted so that the oxygen concentration in the outlet product nitrogen is 0.1%. Temperature is changed from 40 ℃ to -100 ℃, 1Nm
It is the result of evaluating the adsorbent weight (kg) required to collect ³ / h of nitrogen (oxygen concentration 0.1%). Carbon molecular sieve is 1N / h under adsorption conditions of room temperature and 4-6 atm
The adsorbent weight required to produce m ³ of nitrogen is 25 kg
However, as is clear from FIG. 9, under this adsorption condition, even if the pressure is reduced to around atmospheric pressure, it is 25 at the temperature condition of −30 ° C.
There was not much difference from kg.

As can be seen from the above, 3-20% of Na contained in the Na-A type zeolite is ion-exchanged with K and heat-treated at a temperature of 600-760 ° C under normal pressure.
When KA type zeolite is used, the adsorption pressure is set to 3ata or less, the desorption pressure is set to 0.1 to 0.3ata, the adsorption temperature is set to room temperature or less, and the oxygen and nitrogen mixed gas is separated by the pressure swing adsorption separation method. , The power consumption required to produce 1 Nm ³ of nitrogen per hour is 0.4 by the conventional cryogenic separation method.
5 ~ 0.65kWh, 0.65kWw with current adsorption separation method
What required h or more can be reduced to around 0.25 kwh all at once, and the amount of adsorbent used can be maintained at the same level as in the current adsorption separation method.

The production of nitrogen has been mainly described above. Next, the production of oxygen-enriched air will be described. In this case, since air can be blown in the vicinity of atmospheric pressure, the power consumption does not rise even if oxygen is accompanied by nitrogen flowing out from the rear of the oxygen adsorption tower. Rather, it is desirable because the oxygen concentration in the outlet nitrogen rises, the oxygen partial pressure in the oxygen adsorption tower rises, and the recovered oxygen concentration rises.

Specifically, using the apparatus of FIG. 1, the inlet air amount was 10 N liter / switching time, the oxygen concentration in the outlet nitrogen was raised to 5%, the adsorption temperature was -30 ° C., and the adsorption pressure was 1. When 1 ata and the regeneration pressure are set at 0.1 ata,
4N liters of oxygen-enriched air having an oxygen concentration of about 50% could be collected from the desorption side regeneration line. Furthermore, when a part of the recovered oxygen was passed through the column immediately after the adsorption in the same direction as the air flow to purge residual nitrogen, the oxygen concentration could be increased to about 80%. Calculating the power consumption rate based on the material balance under these conditions, it will be 0.2% in terms of 100% -O _2.
It becomes 7 kwh / Nm ³ —O ₂ , which can be an extremely effective method for producing oxygen-enriched air.

[0029]

EFFECTS OF THE INVENTION By adopting the above construction, the present invention is excellent in selective adsorption of oxygen when operating at a lower desorption pressure side and a lower adsorption temperature side, and a large oxygen adsorption capacity. Can provide an oxygen adsorbent with a quantity,
With the method of separating oxygen and nitrogen using the adsorbent, it has become possible to easily obtain high-purity nitrogen with an extremely small power unit.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an apparatus for carrying out an oxygen / nitrogen separation method of the present invention.

FIG. 2 is a graph showing the relationship between the K ion exchange rate of Na-A type zeolite and the oxygen concentration in the desorption gas in Examples.

FIG. 3 is a diagram for explaining the molecular sieving effect of the zeolite of the present invention by comparing the adsorption window diameters of Na-A, Na-KA, and KA type zeolites and the molecular shapes of oxygen and nitrogen.

FIG. 4 is a graph showing the relationship between the heat treatment temperature of Na—KA and the oxygen concentration in the desorption gas in the examples.

FIG. 5 shows the adsorption pressure and power consumption rate (kw) in the examples.
It is a graph showing the relationship between h / Nm ³ -N _2).

FIG. 6 shows desorption pressure and power consumption rate (kw) in Examples.
It is a graph showing the relationship between h / Nm ³ -N _2).

FIG. 7 shows adsorption temperature and power consumption rate (kw) in Examples.
It is a graph showing the relationship between h / Nm ³ -N _2).

FIG. 8 is a graph showing the relationship between the adsorption temperature and the oxygen concentration in the nitrogen at the outlet of the adsorption tower in the examples.

FIG. 9 shows the adsorption temperature and 1 Nm ³ —N _{2 in} Examples.
3 is a graph showing the relationship with the adsorbent weight necessary for producing / h nitrogen.

[Explanation of symbols]

1 air line, 2 compressor, 4 dehumidification decarbonization tower, 8 adsorption tower, 8'adsorption tower, 13 product nitrogen tank, 18 vacuum pump, 19 heat exchanger, 2
0 compression type refrigerator, 21 heat exchanger, 22 heat exchanger.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akinori Yasutake 5-717-1, Fukagiki-cho, Nagasaki-shi, Nagasaki Sanryo Heavy Industries Co., Ltd. Nagasaki Research Institute (72) Inventor Kazuaki Oshima 1-Atsunoura-cho, Nagasaki-shi, Nagasaki Prefecture No. 1 Mitsubishi Heavy Industries Ltd. Nagasaki Shipyard

Claims (2)

[Claims] 1. The total Na of the Na-A type zeolite is 3 to 3.
After ion exchange of 20% with K, the temperature is 600 ~ under normal pressure.
An oxygen adsorbent obtained by heat treatment at 760 ° C. 2. A filled with the oxygen adsorbent according to claim 1.
The adsorption towers above are kept at room temperature or below, and a mixed gas containing oxygen and nitrogen as main components is supplied to the adsorption tower in the adsorption step at a pressure of atmospheric pressure to 3 ata to selectively adsorb oxygen, and the adsorption tower High-purity nitrogen or nitrogen-enriched gas is discharged from the column, the adsorbent in the regeneration step is decompressed to a pressure of 0.08 to 0.5 ata to regenerate the adsorbent, and the oxygen-enriched gas is recovered. And a method for separating oxygen and nitrogen, characterized in that the regeneration process is continuously switched.