JPH0141379B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a low-temperature product that selectively adsorbs N ₂ at a lower temperature than a mixed gas mainly composed of O ₂ and N ₂ such as air.
The present invention relates to an N ₂ adsorbent and a method for separating O ₂ and N ₂ from air using the N ₂ adsorbent. The adsorption separation method of O ₂ and N ₂ from air using N ₂ adsorbent has the advantage that the equipment is small and simple and requires almost no maintenance, _which is close to unmanned operation. In recent years, the use of small and medium-sized devices with a capacity of about ³ −O ₂ /h has been increasing, and alternatives to cases in which liquid acid produced in cryogenic separation devices is transported and used are progressing. To give an overview of a typical device, the device consists of an air compressor, two or more N ₂ adsorption towers, and in some cases a vacuum pump. In this device, when compressed air is sent to one tower, the N ₂ in the air is adsorbed and removed by the N ₂ adsorbent filled, and the remaining high-pressure O ₂ flows out to the rear of the adsorption tower and is recovered. On the other hand, in other towers, the adsorbed N ₂ is released under reduced pressure conditions (sometimes a part of the product O ₂ is flowed in a countercurrent, or a vacuum pump is used to powerfully remove N ₂ ) for regeneration. This is repeated alternately to continuously separate O ₂ and N ₂ . A typical N ₂ adsorbent packed in the above adsorption tower is a 60-70% Ca exchanger of Na-A type zeolite commercialized by Union Carbide, which absorbs O ₂ and N ₂ components. It selectively adsorbs N ₂ from a mixed gas, and co-adsorption of O ₂ under air conditions is estimated to be less than 10% of N ₂ adsorption. It was stated that this O ₂ and N ₂ separation device using adsorption is advantageous in small and medium-sized areas, but it is not suitable for producing 1Nm ³ of O ₂ .
It requires 0.75 to 1Kwh, which is higher than the 0.45Kwh of O ₂ produced by large-capacity cryogenic separation.
Furthermore, it is said that there is little merit of scale for increasing the capacity of the equipment, and that it cannot compete with the cryogenic separation method in the region of 3000 Nm ³ -O ₂ /h or more. Therefore, various methods for improving these drawbacks are conceivable, but when describing the improvement methods in relation to the present invention, the following obstacles usually appear. First, to reduce power consumption, it is possible to lower the blowing pressure and perform adsorption operation at low pressure, but since the amount of _N2 adsorption decreases almost in proportion to the pressure,
The capacity of the device increases significantly. Next, in order to increase the adsorption amount, it is possible to perform adsorption operation under low temperature conditions, but in this case, although the amount of _N2 adsorption increases, the adsorption/desorption rate decreases significantly, so The O ₂ concentration of the product is actually lower than it is at room temperature. Also, as the temperature decreases, _N2 adsorption
Since the amount of O ₂ co-adsorption increases, the power consumption rate gradually increases. Therefore, the present inventor has developed a low-temperature solution that improves the above-mentioned drawbacks.
In the process of conducting intensive research and experiments on a high-performance separation method for O ₂ and N ₂ under low-pressure adsorption conditions, we discovered that Na-X
At least 1% by weight or more of alumina sol Al(OH) ₃ is added to the mineral name sodium phaujasite represented by Na-Y type zeolite, and the temperature is 450℃.
By heat-treating under the above conditions, untreated Na
Compared to phaujasites such as -X and Na-Y types, the amount of N ₂ adsorbed is increased under low temperature and low pressure adsorption conditions, and the N ₂ adsorption rate can be maintained within a practical range, and the N ₂ adsorption selectivity is also increased. The present invention was completed based on the discovery that the decrease in . Below, first, the adsorbent of the present invention will be explained. When alumina sol is added to sodium faugiasite, the alumina sol invades the defective parts of the faugiasite, and this is presumed to have some effect on N ₂ adsorption. Next, a detailed explanation will be given using a specific example. As a representative of faugiasite, the present inventors used Na-X type zeolite in consideration of economic efficiency. First, Na-X type zeolite was prepared under each adjustment condition.
Add 30-300g of Al(OH) ₃ sol for a total of 3Kg
Take a portion and mix until homogeneous. From this mixture, use an extruder to
It was granulated into φ pellets. Thereafter, the mixture was activated by heat treatment in an electric furnace at 450° C. for 1 hour, and three types of Na-X type zeolite, each weighing 3 kg, were produced as shown in Table 1.

[Table] Using these adsorbents, we attempted to separate O ₂ and N ₂ from air using the air separation device shown in Figure 1. The air separation operation carried out will be described below based on FIG. 1.05 to 3 ata in compressor 2 through inlet side line 1
The pressurized air enters the dehumidification and CO ₂ removal tower 4 through the flow path 3, and becomes extremely clean pressurized air. A valve 5 installed at the rear of the flow path 3' is open, and clean pressurized air enters the adsorption tower 8 through the flow path 6 and the open valve 7. The pressurized air that has entered the adsorption tower 8 has N ₂ adsorbed and removed by the N ₂ adsorbent 9, and the O ₂ concentration increases as it moves toward the rear. After this, pressurized air is supplied to the open valves 10, 11, 12 and the product O ₂ tank 1 inserted between the valves 11, 12.
3 is recovered as product _O2 . On the other hand, a part of the product O ₂ is transferred to a pressure reducing valve 15 located in the middle of the flow path 14.
The pressure is reduced at , and the gas enters the adsorption tower 8' through the open valve 10'. The adsorption tower 8' has a valve 16 in an open state.
and a vacuum pump 18 connected through a flow path 17.
Therefore, part of the product O ₂ flowed in the opposite direction to the air flow in the adsorption tower 8' under negative pressure, and was adsorbed by the N ₂ adsorbent 9' in the adsorption tower 8'. N ₂ is easily desorbed and the N ₂ adsorbent 9' is regenerated in a short time. The N ₂ adsorbent 9 of the adsorption tower 8 is saturated,
On the other hand, when N ₂ is removed from the N ₂ adsorbent 9' in the adsorption tower 8' and regeneration is completed, the inlet air flow path 6 is switched to 6' and the method described so far is performed alternately _. Can be collected continuously. A heat exchanger 19 is installed between the clean pressurized air line 3' at the inlet and the gas line 17 whose main component is separated _N2 , and the product _O2 line 21 is connected to the flow path. 3', heat exchange is also possible with a heat exchanger 22. Also, since a compression refrigerator 20 is installed in the flow path 3',
Very efficiently the adsorption columns 8 and 8' are cooled and set to low temperature conditions. In addition, when switching the adsorption tower, it is not only necessary to simply switch the flow path from 6 to 6' (or vice versa), but also to prevent the inlet air from blowing through due to the pressure increase immediately after switching, and to remain behind
In order to minimize the release of O ₂ and the pressurized air from the front to the outside of the system, first, the valves 10, 15, 10' are fully opened, and the residual O ₂ at the rear of the adsorption tower 8 immediately after adsorption is removed from the adsorption immediately after regeneration. Partially transferred to tower 8'. At this time, adsorption tower 8
The pressure in the adsorption tower 8' is P ₀ (ata), and the pressure in the adsorption tower 8' is P ₁ (ata).
Then, the pressure after pressure equalization will be approximately P ₀ +P ₁ /2 (ata). After this, the adsorption tower 8', which has reached about P ₀ + P ₁ /2 (ata), opens the valves 10' and 11' to equalize the pressure between the product O ₂ tank 13 and the adsorption tower, and further increases the pressure of the adsorption tower 8'. Fill with high pressure _O2 . The pressure P ₂ (ata) at the time of pressure equalization with the product tank 13 is the dead volume of the adsorption towers 8, 8', V ₁
(), the capacity of the product O ₂ tank 13 is V ₂ (), then the pressure of the product O ₂ tank 13 before pressure equalization is P ₀ (ata)
, the equalization pressure P ₂ (ata) is approximately P ₂ = P ₀ + P ₁ /2V ₁ + P ₀ V ₂ /V ₁ + V ₂ , and is simply calculated from P ₁ (ata) when switching columns.
Compared to _the rapid increase in pressure to _{P 0} (ata), _{the above} operation reduces _the
) Since the pressure is increased gradually, it is possible to prevent air from blowing through due to pressure increase, and to minimize the release of residual O ₂ and high-pressure air to the outside of the system during the desorption process. Air separation was carried out using the apparatus shown in FIG. 1 using the operating method described above. Table 2 shows the operating specifications of the device at this time.

[Table] O ₂ and N ₂ were separated from air under the operating conditions shown in Table 2. The results are summarized in Figures 2-7. Below, the pressure swing type adsorption separation of O ₂ and N ₂ from air using the adsorbent of the present invention will be sequentially shown in Figures 2 to 7 under low temperature conditions using an untreated Na- For air separation,
Explain how much it will improve. In FIG. 2, the horizontal axis represents the weight percentage (%) of added Al(OH) ₃ , and the vertical axis represents the power consumption required to produce 1 Nm ³ of O ₂ per hour, that is, the power unit. Evaluation was carried out by filling the adsorbent shown in Table 1. The ○ mark indicates the power unit when the adsorption operation temperature was changed to 20°C, the □ mark to 0°C, and the △ mark to -30°C. The adsorption pressure (hereinafter P ₀ ) is 1.5ata, the regeneration pressure (hereinafter P ₁ ) is 0.2ata, and the air flow rate (hereinafter u) is
It was set to 0.8cm/sec. In Figure 3, the horizontal axis is Al as in Figure 2.
It is the amount of (OH) ₃ added, and the vertical axis is the outlet O ₂ concentration. The 〇, □, and △ marks representing temperatures in the figure are the same as in FIG. 2, and P ₀ , P ₁ , and u are also the same as in FIG. 2. As can be seen from Figure 2, the amount of Al(OH) ₃ added is 1wt.
%, the power consumption rate during Na-X filling rapidly decreases. This property is maintained both at room temperature and at low temperatures. Further, as shown in FIG. 3, the O ₂ concentration at the outlet of the adsorption tower increases with the treatment of the present invention, which is effective both at room temperature and low temperature ranges, as well as the effect of reducing power consumption. Next, regarding the heat treatment temperature, Figure 4 evaluates this property from the perspective of the O ₂ concentration on the outlet side.
The horizontal axis is the heat treatment temperature, and the vertical axis is the outlet _O2 concentration.
The □ and △ marks correspond to Figure 2, P ₀ is 1.5ata, P ₁ is
0.2ata, u is 0.8cm/sec, and the sample is
10 wt% Al(OH) ₃ added (i.e. the first
No. 3) in the table was used. As can be seen from Figure 4, the specified performance is reached at a temperature of 450°C or higher. As can be seen from the above, the huauja sites represented by Na-X, Na-Y, etc. are at least
After adding 1wt% or more of alumina sol Al(OH) ₃ , heat treatment at 450℃ or higher can reduce power consumption by approximately 12%. Furthermore, the outlet O ₂ concentration has improved by more than 10% for the same column length, demonstrating that additional benefits are being generated in terms of product quality. Note that the alumina sol added this time is also used as a binder, and it goes without saying that it also has pellet forming ability at the same time. Next, the amount of alumina sol added was adjusted to 10wt%.
The O ₂ and N ₂ separation characteristics of Na-X from air were evaluated (Figures 5 to 7). In FIG. 5, the horizontal axis shows the adsorption pressure, and the vertical axis shows the power consumption rate. In the figure, ● indicates untreated Na
-X is the amount of alumina sol Al(OH) ₃ added.
10wt% of the present invention is shown. In addition, P ₁
is 0.2ata, u is 0.8cm/sec, adsorption operation temperature is 20℃
And so. As can be seen from Figure 5, compared to untreated Na-X,
A 12% reduction in power consumption is expected. Also,
Power unit for cryogenic separation method: 0.45 to 0.6 Kwh/Nm ³ −
Considering O ₂ and 0.7Kwh/Nm ³ −O ₂ of the current N ₂ adsorbent, the adsorption pressure P ₀ is 3 ata to atmospheric pressure, more preferably
A low pressure range of 2ata to atmospheric pressure is appropriate. In Figure 6, the horizontal axis represents the desorption pressure P ₁ , and the vertical axis represents the power consumption unit.
Corresponding to the figure, P ₀ was 1.5 ata, u was 0.8 cm/sec, and the adsorption operation temperature was 20°C. As can be seen from Fig. 6, the desorption pressure P ₁ is
In terms of competitiveness with cryogenic separation method and current N ₂ adsorption method
It seems desirable to be around 0.08 to 0.5 ata, more preferably around 0.1 to 0.3 ata. In Fig. 7, the horizontal axis shows the adsorption temperature, and the vertical axis shows _the O ₂ concentration at the outlet of the adsorption tower _. 0.2ata, u
was set to 0.8 cm/sec. As can be seen from FIG. 7, under the same column length, the O ₂ concentration on the outlet side gradually increases with cooling, but in consideration of economic efficiency, a preferable range is 0 to 60°C. The outlet O ₂ concentration is always higher with the inventive Na-X with addition of alumina sol Al(OH) ₃ than with untreated Na-X. Further, when the same test as above was conducted on Na-Y type zeolite, the same results as above were obtained. The effect of the additive heat treatment of alumina sol described above has not been suggested in any conventional literature.
Furthermore, by operating under appropriate adsorption pressure, desorption pressure, and cooling conditions, it is possible to provide a method for easily obtaining O ₂ with a high purity of over 90% with extremely low power consumption.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the apparatus used to carry out the O ₂ and N ₂ separation method of the present invention, and Figures 2 to 7 are the
1 is a chart showing the results of a test using the apparatus shown in the figure.

Claims (1)

[Claims] 1 N ₂ adsorption for low temperature, which is obtained by adding at least 1% by weight or more of alumina sol to sodium phaujasite represented by Na-X and Na-Y, and then heat-treating the mixture at 450°C or higher. agent. 2 At least 2 types filled with a low-temperature N ₂ adsorbent made by adding at least 1% by weight or more of alumina sol to sodium phaujasite represented by Na-X and Na-Y and then heat-treated at 450°C or higher. In adsorption towers larger than the first adsorption tower, air is pumped so that the pressure in the first adsorption tower is between atmospheric pressure and 3ata.
High purity O ₂ is produced from the adsorption tower by selectively adsorbing N ₂ .
Alternatively, the O ₂ enriched air is discharged, and the other second adsorption tower is depressurized to a pressure of 0.5 ata to 0.08 ata, and the adsorbed N ₂ is discharged to regenerate the above adsorbent, and the entire process is carried out at a temperature below room temperature. A method for separating O ₂ and N ₂ from air, which is carried out under cooling conditions.