JPS6358614B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oxygen selective adsorbent for separating, removing, or concentrating oxygen in the air, and a method for separating oxygen and nitrogen using the same. The biggest problem in separating, removing, or concentrating oxygen from air is that since the raw material is usually air, there is no raw material cost, and the price added to oxygen is (a) the cost of equipment installed for separation and concentration. (b) The power costs necessary to operate the equipment; (c) If a separation medium is required, it depends on its price and replenishment costs. Further, the separation and concentration process may be carried out by either of the two methods, oxygen separation or nitrogen separation, as long as air is used as the raw material. From these points of view, the economically advantageous ones are:
A typical oxygen and nitrogen separation process that has been carried out in the past involves cooling air to a cryogenic temperature to remove oxygen and nitrogen.
An example is a cryogenic separation device that separates nitrogen based on the difference in boiling point. This device is suitable for large-capacity oxygen production, and most of the domestic oxygen and nitrogen production relies on the cryogenic separation process, but it has the disadvantage of requiring large amounts of electricity and large equipment. Another separation method recently developed and put into practical use by Union Carbide and others uses an aluminosilicate polymer adsorbent.
Among these, molecular sieves 5A and 13X (manufactured by Union Carbide, trade name) have extremely high adsorption capacity for nitrogen (1.2g
_N2 /100gat NTP), and a process for selectively removing nitrogen from the air and separating and concentrating oxygen has been put into practical use. in fact,
The adsorption capacity of 5A and 13X type molecular sieves follows the Langmuir type adsorption isotherm, and when the pressure reaches 1.5 ata, the adsorption capacity does not increase as much as the pressure increases. ₂ /
Due to the O ₂ molar ratio of 4, a very large amount of nitrogen needs to be removed. Therefore, the merits of scale associated with increasing the capacity of the device are small, and the actual situation is that the device is limited to small-capacity equipment. Another possibility is to use a transition metal-based organic complex that selectively absorbs oxygen. For example, a cyclic cobalt complex called sarcomine absorbs 1 mole of oxygen with 2 moles of sarcomine. Since this absorption is reversible with respect to changes in temperature and pressure, separation and concentration of oxygen can be achieved in principle by the heating-lowering cycle and pressure-raising-lowering cycle of the air. In reality, the deterioration due to absorption and release is severe, and since it is expensive, its application will be limited to use as a very special oxygen carrier. In addition to these, there are oxygen selective permeation filters, oxygen pumps using zirconium oxide, etc. that have not yet been put into practical use but are sufficiently possible in principle. As described above, in terms of oxygen separation, concentration, and removal, in practical small-capacity oxygen production processes, a pressure swing process is adopted in which nitrogen is removed from the air using molecular sieves. In addition, large-capacity types employ a cryogenic separation process using cryogenic cooling of air, but it is thought that all of these methods have almost reached their limits in terms of reducing power and equipment costs. The present invention aims to improve the above-mentioned drawbacks of the oxygen production process, provide a preferential adsorbent for oxygen, and achieve a significant reduction in oxygen production costs and a significant reduction in the size of equipment for the oxygen production process. This is a proposal. The present inventors have discovered that among the above-mentioned molecular sieves, Na-A type zeolite hardly selectively adsorbs oxygen even when it is packed in an adsorption tower and air is passed through it at high pressure at room temperature; Although it behaves as a nitrogen selective adsorbent like 5A and 13X,
After contacting Na-A type zeolite with Fe having a valence of at least 2 or higher in a wet state, heat treatment is performed at a temperature of around 450°C to dissolve Fe in the Na-A type zeolite crystals. Na-type zeolite (hereinafter referred to as Fe-dissolved Na-
K-A type zeolite) is significantly different from pure Na-A type zeolite in which part of the Na is replaced with K (hereinafter referred to as Na-K-A type zeolite), and has increased oxygen selectivity. We also found that the amount of oxygen adsorption increases in O ₂ one-component systems. They also discovered that although the rate of oxygen adsorption decreases as the temperature decreases, no nitrogen is adsorbed at all, making it possible to remove oxygen from extremely highly concentrated nitrogen gas. The oxygen selectivity of such Fe-dissolved Na-K-A type zeolite has not been clarified at all in conventional research on adsorption of oxygen and nitrogen. The present inventors performed the following treatment in order to obtain the above-mentioned Fe-dissolved Na-K-A type zeolite. First, the present inventors thoroughly washed Na-A type zeolite powder manufactured by UCC with water, and then diluted it with NaCl aqueous solution for 100 mL.
After boiling at ℃ for 1 hour, the mixture was washed again with water and used as a raw material. This means that Na-A type zeolite powder has
K about 0.1wt%, Ca about 0.05wt%, 0.05wt%
This is because although a certain amount of impurities such as Mg are usually mixed in, the above treatment can purify the total amount of impurities to 0.1 wt% or less. From this, 50 g was taken out and added to the pure water from step 1. While stirring to form a slurry, dissolved oxygen was removed by bubbling with N ₂ gas to prevent the progress of oxidation of Fe ions. After that, an aqueous FeCl ₃ solution was added dropwise, and stirring was continued for an additional hour. FeCl ₃ is thought to exist as Fe(OH) ₃ colloid because the slurry aqueous solution has a pH of about 8.5 to 9, but most of it is
Adheres to Na-A type zeolite powder. Thereafter, it was dehydrated and packed into an adsorption tower as shown in FIG. 1, and its oxygen adsorption characteristics from air were confirmed. In this experiment, two types of Fe ₂ O ₃ equivalent weight %, 0.5 wt % and 1 wt %, were adjusted by adjusting the amount of FeCl ₃ dropped. After that, water was removed from the Fe-adhered Na-A zeolite using a vacuum filter, and the water was removed from the Na-A type zeolite using an air bath.
After pre-drying at ℃, the Fe was heated in a vacuum heating bath at 450℃ for 1 hour under vacuum evacuation conditions of 0.1 Torr.
It was bath-dissolved in Na-A type zeolite. Fe Na−
ESR is used for quality control of dissolution into A-type zeolite.
This has been confirmed based on the position of Fe in the crystal and the Fe concentration distribution in the cross section of the crystal using a scanning electron microscope. In addition, in addition to the above-mentioned FeCl ₃ , FeCl ₂ , Fe(CH 3 CO 2 ) 2 , Fe(CH ₃ CO ₂ ) ₂ ,
Although Fe(NO ₃ ) ₂ , Fe(NO ₃ ) _3, etc. were used, the final adsorption properties did not change. Probably after slurry dripping
Fe(OH) ₂ and Fe(OH) ₃ are formed and eventually Na-A zeolite is formed as a result of dehydration.

【formula】

【formula】

【formula】

This is thought to be due to the formation of a bond such as [Formula]. After this, Na-A type zeolite in which Fe was dissolved was added.
Exchangeable Fe was removed by boiling in a NaCl aqueous solution for 30 minutes, washed with water, and further immersed in a KCl aqueous solution to remove exchangeable Fe.
Part of the exchangeable Na of A is exchanged with K, and Fe is dissolved.
Na-K-A type zeolite was produced. In this experiment, two types were prepared with a K exchange rate of 10% and 20%. Also, for reference, pure
Using Na-A type zeolite, two kinds of K-exchanged products were prepared using the above-mentioned K-exchange method: 10% and 20% K-exchange rate. Here, to discuss the influence of anions on K exchange, instead of Cl ^- , SO ₄ ^2- , PO ₄ ^3- ,
When CH ₃ CO ₂ ^- etc. were used, there was no change, but when OH ^- was used, the adsorption capacity decreased significantly unless sufficient washing with water was carried out. The adsorption and separation properties of Fe-dissolving Na-A type zeolite from air will be explained below with reference to the figures. Figure 1 shows the inventors' work to measure the air separation characteristics of Na-A type zeolite, Na-K-A type zeolite, Fe-dissolved Na-A type zeolite, and Fe-dissolved Na-K-A type zeolite of the present invention. FIG. 1 is a schematic explanatory diagram of a device prototyped by et al. 1 is a high pressure air cylinder. High pressure air leaving the cylinder 1 passes through a pressure reducer 2 and reaches the cylinder 3. A Bourdon tube pressure gauge 4 is installed between the pressure reducer 2 and the cylinder 3, and it is possible to measure the pressure.In this test, the inlet pressure was measured at 5ata using the pressure reducer 2 and the Bourdon tube pressure gauge 4
It was set to Adsorbent 7 immediately after washing inserted into a stainless steel adsorption tower 6 with an inner diameter of 10 mmφ and a length of 300 mm
has no adsorption capacity. For this reason, in this test, a temperature-controlled bath 8 whose temperature can be adjusted from -70℃ to 600℃ was used.
The adsorption tower 6 is installed at
The pressure inside the adsorption tower was reduced to 0.1 Torr, and the temperature control bath 8 was
Heat treatment was performed at 450°C for 1 hour, also serving as dehydration. Then, after cooling to room temperature again, valve 3
and 5 were opened to allow high-pressure air to flow through and measure the flow rate with a float type flow meter 11.Then, the entire amount was allowed to flow into an oxygen concentration meter 12 to measure the outlet oxygen concentration, and the data was further recorded with a self-recording recorder 13. In the adsorption tower 6 using the experimental equipment shown in Figure 1,
Na-A type zeolite powder with no Fe dissolved at all, 10% K exchanger of this sample, also 20
%K exchanger, 1wt% Fe dissolved Na-A type zeolite 1wtFe dissolved 10% K exchanged Na-K-A type zeolite, 1wt% Fe dissolved 20% K exchanged Na-K-A
Fill 15g of type zeolite and adjust the inlet gas flow rate.
The time-dependent change in outlet oxygen concentration was measured with the inlet air pressure set at 100 Nml/min and 5ata. Room temperature (25℃)
Figure 2 shows an example of the change in outlet oxygen concentration over time. In FIG. 2, the horizontal axis represents elapsed time, and one scale is one minute. The vertical axis is O ₂ concentration, and the unit is volume %. In addition, to indicate the oxygen concentration on the inlet side,
A reference line α was drawn at the air oxygen concentration of 20.8%. In addition, in Figure 2, the time-course curve of outlet oxygen concentration is shown as a solid line for the Na-A type zeolite powder that does not dissolve any Fe, a broken line for the 10% K exchanger of this sample, and a broken line for the 20% K exchanger as well. The body is indicated by a dashed line. In Figure 2, first of all, Na has no dissolved Fe at all.
- This will be explained based on data on changes over time in outlet oxygen concentration of type A zeolite. In this sample, the outlet oxygen concentration initially decreased from 20.8% to 18%, then rapidly increased to 46%, and then gradually decreased, reaching a breakthrough in about 5 minutes after air flow. As can be seen from this data, at the initial stage of adsorption, the amount of oxygen adsorbed per unit time exceeds the amount of nitrogen adsorbed, and therefore the outlet oxygen concentration decreases. However, as time passes, the amount of nitrogen adsorbed exceeds the amount of oxygen adsorbed per unit time, and the outlet oxygen concentration increases. Furthermore, since the adsorbent becomes saturated with oxygen and nitrogen, the concentration gradually decreases and becomes equal to the gas concentration on the inlet side. On the other hand, regarding the adsorption amount of oxygen and nitrogen single component systems of Na-A type zeolite, please refer to “Basics and Design of Adsorption”.
20℃, as described in “Kitagawa, Suzuki P.226”
It adsorbs 6.2ml of nitrogen and 2.2ml of oxygen per 1g under 1ata condition. Taking all these facts together, the amount of nitrogen adsorbed is about three times larger, so the outlet oxygen concentration should originally be higher, but since the diffusion rate of oxygen into the adsorbent is greater than that of nitrogen, It is assumed that the following phenomenon occurs. However, as can be seen from the ability of Na-A zeolite to separate oxygen and nitrogen from air,
The selective adsorption of oxygen is too weak and it is economically difficult to use it practically. Even if part of the Na in such Na-A type zeolite is replaced with K, the performance of the adsorbent is not improved at all. In other words, in Figure 2, the data for the 10% K exchanger shows that the maximum value of the outlet oxygen concentration is 32% and the minimum value is 17%.
Therefore, according to the data of 20% and the exchanger, the maximum value of the outlet oxygen concentration is 22% and the minimum value is 19%. In addition,
A 30% K exchanger no longer adsorbs oxygen and nitrogen. Next, the effectiveness of the Fe-dissolved Na-K-A type zeolite of the present invention will be explained with reference to FIG. Figure 3, like Figure 2, shows the change in outlet oxygen concentration over time at room temperature (25°C), with the horizontal axis
The vertical axis and reference line α have the same meaning as in FIG. In Fig. 3, the minimum value of the outlet oxygen concentration of the 1wt% Fe-dissolved Na-A zeolite is reduced to 6% even without K exchange, which is much improved compared to the above-mentioned one in which Fe is not dissolved. It can be seen that Furthermore, 1wt% Fe dissolved 10% K exchanged Na-K-
For A-type zeolite, the minimum value of outlet oxygen concentration is 4
%, indicating strong oxygen selectivity.
In addition, in the case of 1 wt% Fe-dissolved 20% K-exchanged Na-K-A type zeolite, the minimum value of the outlet oxygen concentration increases to 7%, but it should be noted that the outlet oxygen concentration is 20.8% of the air oxygen concentration, that is, the reference line α It adsorbs almost no _N2 , making it a perfect oxygen-selective adsorbent. Of the three types of adsorbents above, 1wt% Fe dissolution 10
When oxygen and nitrogen were separated from air using %K-exchanged Na-K-A type zeolite under adsorption conditions on the low temperature side, the above effects were obtained even when operated at room temperature, but even under lower temperature conditions A further increase in efficiency was observed by adding This will be explained with reference to FIG. In FIG. 4, the data at 25°C are the same as in FIG. ' is the one in which the adsorption operation was carried out at 0°C, and although the minimum value of the outlet oxygen concentration increased to 8%, no nitrogen was adsorbed at all, and the amount of adsorption increased more than twice. In addition, "" is the one in which the adsorption operation was carried out at -25°C, and the minimum value of the outlet oxygen concentration further increases to 12%, and the air separation performance decreases, but complete oxygen selectivity is sufficiently present. To summarize the above cases, (1) When Fe is dissolved in Na-A type zeolite,
The selectivity of oxygen adsorption from a two-component system of oxygen and nitrogen such as air at room temperature increases, but this
Exchanging part of the Na with K further increases the selectivity, and under dynamic adsorption conditions such as in an adsorption column, complete oxygen selectivity is achieved. (2) Partial K exchangers do not adsorb nitrogen at all in the temperature range from room temperature to low temperatures, but K exchange to obtain complete oxygen selectivity requires a high K exchange rate at high temperatures and a low K exchange rate at low temperatures. The K exchange rate is sufficient. (3) In the case of a low temperature side and a high K exchange rate, the peak value of the outlet oxygen concentration is high (that is, the separation of oxygen and nitrogen is insufficient). This is because it is too small compared to the column velocity, and in such a case, it is necessary to reduce the superficial velocity of the air in the adsorption column. As explained above, the oxygen adsorbent of the present invention is a completely new oxygen-selective adsorbent that has not been suggested in any conventional literature, and it has an oxygen adsorption capacity of 1.5 to 2 times that of Na-A type zeolite, which does not dissolve Fe. It has the excellent advantage of adsorbing oxygen. The oxygen adsorbent of the present invention has a very wide range of applications, for example, when applied to oxygen concentrators using molecular sieves, it can be applied to both temperature swing and pressure swing methods, and can be applied to conventional N ₂ adsorption methods. The adsorption performance far exceeds that of type molecular sieves, paving the way for smaller equipment and lower cost oxygen concentration. Furthermore, if the oxygen adsorbent of the present invention is used to remove oxygen from other component gases, an extremely inexpensive oxygen adsorption/removal agent will be provided. In addition, the flow rate (100ml/
min), under pressure (5ata) conditions, 1wt% Fe dissolution20
% K-exchanged Na-K-A type zeolite showed almost perfect oxygen selectivity. In addition, under this condition, the flow rate, pressure,
How the outlet oxygen concentration changes depending on the adsorption tower cross-sectional area, adsorption tower length, etc. can be estimated from "Basics and Design of Adsorption Kitagawa, Suzuki, P.89-P.92". In addition, under the conditions of high temperature, low K exchange rate, and low Fe dissolution amount, the nitrogen adsorption rate cannot be ignored, so 2
All you have to do is analyze the component system. According to these results, the larger the amount of dissolved Fe, the more
This means that the higher the K exchange rate and the lower the temperature, the wider the mass transfer coefficients of oxygen and nitrogen become.Practically speaking, this means that the larger the dissolved amount of Fe, the higher the K exchange rate, and the higher the K exchange rate. As the temperature decreases, a lower inlet flow rate is allowed, and a higher inlet flow rate must be set at room temperature, low K exchange rate, and low Fe dissolution amount. In any case, the design of the adsorption tower and its operation can be carried out within the conventional technical range if the data on the change in outlet oxygen concentration over time shown in FIGS. 2 to 4 are obtained. Note that the selection of the low-temperature conditions is not determined solely by the properties of the adsorbent. For example, an absorption chiller may be used under conditions where sufficient waste heat can be obtained, and in this case _the optimal temperature is around -25℃. When combined with a tube tube, the optimum temperature is around -10°C, and if the expansion turbine is driven by flowing high-pressure _N2 gas, -30 to -50°C is preferable, and the temperature selection in the low-temperature range rather depends on the mode of cooling. do. Hereinafter, an example will be described in which the method for selective adsorption and separation of oxygen of the present invention is applied to a pressure swing type oxygen production apparatus. FIG. 5 is a schematic explanatory diagram of a pressure swing type oxygen production apparatus. In FIG. 5, 17 to 24 are automatic switching valves, 25 and 26 are adsorption towers filled with the oxygen adsorbent of the present invention, 27 is a heat exchanger for low-temperature cooling, 28 is a dehumidifier,
29 is a pre-cooler, 30 is an air compressor, 31 is an air strainer, 32 is a throttle valve, and a control device for controlling an automatic switching valve and the like is not shown. Assume now that the adsorption tower 25 is in the adsorption process and the adsorption tower 26 is in the regeneration process. air strainer 3
The air from which dust has been removed through 1 is pressurized by an air compressor 30, then roughly dehydrated and cooled to room temperature in a precooler 29, further dehumidified and decarboxylated in an adsorption tower 28, and then cooled at a low temperature. The air is cooled to -30°C by the heat exchanger 27 and sent to the adsorption tower 25 through the valve 20, where the oxygen in the pressurized air is selectively adsorbed by the adsorbent in the tower, and the nitrogen-enriched air is passed through the valve. 17 and is sent out from the same tower. At this time, valves 17 and 20 attached to adsorption tower 25 are open, and valves 18 and 19 are closed. On the other hand, while the adsorption tower 25 is performing an adsorption operation, the adsorption tower 26 first performs vacuum regeneration of the adsorbent within the adsorption tower 26 . That is, at this time, the adsorption tower 26
Of the valves 21 to 24 attached to the valves 21, 22,
24 is closed and the valve 23 is opened to reduce the pressure inside the adsorption tower 26 to atmospheric pressure (or negative pressure), desorb some of the adsorbed components adsorbed in the adsorption process, and oxygen-enriched air flows through the valve. 23 and is sent out from the same tower. At the same time as the pressure reduction process is completed, the valve 22 is opened, and the atmosphere is sent to the throttle valve 3 by a blowing means (not shown).
2 and into the adsorption tower 26 through the valve 22,
A scavenging process is performed in which the oxygen-rich void gas and residual adsorbed components in the column are sent out of the column through the valve 23. At the same time as the above steps are completed, the adsorption tower 26 moves to the adsorption step, and at the same time, the adsorption tower 25 moves to the regeneration step. As mentioned above, oxygen-enriched air and/or nitrogen-enriched air is extracted by continuously repeating the adsorption step and the regeneration step. In this example, an adsorption tower with an inner diameter of 50 mm and a length of 600 mm was filled with 1 kg of 1 wt% Fe-dissolved 20% K-exchanged Na-K-A zeolite molded into a sphere with a diameter of 1 mm using a tablet molding machine. Swing pressure between 1 ata and 5 ata, inlet air flow rate at 2.8Nl/min, temperature
Adsorption separation was carried out under room temperature conditions of 25°C. At this time, in FIG. 5, the product nitrogen concentration behind valves 17 and 21, the amount of nitrogen separated, the valve 19,
Table 1 shows the product oxygen concentration behind No. 23 and the amount of recovered oxygen. In addition, in the case of pure Na-A type zeolite, 25
℃, no product nitrogen was obtained from behind the valves 17 and 21, and 45% of oxygen passed through. this is,
This is probably because the slight decrease in oxygen concentration at the initial stage of adsorption, which was observed in the small air separation tester shown in Figure 1, was canceled out by the subsequent nitrogen adsorption. Around 25°C, higher inlet flow rates may be required.

【table】

【table】 [Brief explanation of drawings]

Figure 1 shows the flow of the experimental equipment used to confirm the effects of the present invention, Figures 2, 3 and 4 show substantially pure Na-A type zeolite, 10% of the zeolite , 20% K exchanger, 1wt%
Fe-dissolved Na-A type zeolite, 1wt% Fe-dissolved 10%
K-exchanged Na-K-A type zeolite and 1wt%Fe
Dissolve 20% K-exchanged Na-K-A type zeolite at room temperature,
A graph showing the dynamic adsorption amount at temperatures of 0°C and -25°C,
FIG. 5 shows the flow of an embodiment of the present invention.

Claims (1)

[Claims] 1. Iron having a valence of at least two or more is dissolved in substantially pure Na-A zeolite, and
An oxygen adsorbent from a two-component mixed gas of oxygen and nitrogen, which is made by exchanging part of Na with K. 2. In a low temperature range below room temperature, a two-component mixed gas of oxygen and nitrogen is dissolved in substantially pure Na-A type zeolite, and iron having a valence of at least 2 is dissolved, and part of the Na is dissolved in K. A method for separating a two-component mixed gas of oxygen and nitrogen into oxygen and nitrogen, characterized in that the gas is passed through an oxygen adsorbent packed bed formed by exchanging the gas with oxygen, and the oxygen is selectively adsorbed by the adsorbent.