JPS6358613B2 - - 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 set for (a) separation and concentration. Equipment costs (b) 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 example of a conventional oxygen/nitrogen separation process is a cryogenic separation device that cools air to an extremely low temperature and separates oxygen and nitrogen based on their different boiling points. 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 improves the drawbacks of the above oxygen production equipment,
This proposal aims to significantly reduce the cost of oxygen production and significantly downsize the equipment for the oxygen production process by providing a preferential adsorbent for oxygen. 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 iron having a charge number of at least two or more 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, which selects oxygen. It was found that the properties of the two components increased and the amount of oxygen adsorbed in a one-component system increased. In addition, the present inventors discovered that as the temperature decreases, Na-A type zeolite also increases its selective adsorption of oxygen in a two-component system of oxygen and nitrogen.
It was further discovered that the Na-A zeolite dissolved in Na-A zeolite has superior oxygen selectivity at higher temperatures than the Na-A zeolite. The oxygen selectivity of such Na-A type zeolite in which Fe is dissolved has not been clarified at all in conventional studies on adsorption of oxygen and nitrogen. The present inventors carried out the following treatment in order to obtain the above-described Fe-dissolved Na-A type zeolite. First, the present inventors thoroughly washed Na-A type zeolite powder manufactured by UCC with water and further heated it at 100°C with an aqueous NaCl solution.
After boiling for 1 hour, the product 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 w % and 1 w %, were adjusted by adjusting the amount of FeCl ₃ dropped. After this, water is removed from the Fe-adhered Na-A zeolite using a vacuum filter, and then pre-dried at 100℃ in an air bath, and then in a vacuum heating bath.
It was produced by heating at 450° C. for 1 hour under vacuum evacuation conditions of 0.1 Torr to cause Fe to dissolve in Na-A type zeolite. Quality control of dissolution of Fe into Na-A type zeolite is confirmed by checking the position of Fe in the crystal by ESR and the concentration distribution of Fe in the cross section of the crystal by scanning electron microscopy. 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.

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This is thought to be due to the formation of a bond such as [Formula]. However, details are currently unknown. The adsorption and separation properties of Na-A type zeolite in which Fe is dissolved from air will be explained below with reference to the figures. FIG. 1 is a schematic explanatory diagram of an apparatus prototyped by the present inventors to measure the air separation characteristics of Na-A type zeolite. 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 valve 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
does not have any 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, and 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,
Filled with 15g of Na-A type zeolite powder with no dissolved Fe, Na-A type zeolite powder with 0.5w% Fe dissolved, Na-A type zeolite powder with 1w% Fe dissolved, and the inlet gas flow rate was set to 100Nml/ minutes,
The inlet air pressure was set at 5ata and the change in outlet oxygen concentration over time was measured. Figure 2 shows an example of the change in outlet oxygen concentration over time at room temperature (25°C). In FIG. 2, the horizontal axis 14 is elapsed time;
One scale is one minute. The vertical axis 15 is the O ₂ concentration, and the unit is volume %.
To indicate the oxygen concentration on the inlet side, the air oxygen concentration is 20.8
A reference line 16 is drawn at %. In addition, in Figure 2, the time-course curve of the outlet oxygen concentration is shown as a solid line for Na-A type zeolite powder with no dissolved Fe, and a solid line for Na-A zeolite powder with 0.5 w% Fe dissolved.
The A-type synthetic zeolite powder is shown by a broken line, and the powder containing 1w% Fe is shown by a dashed-dotted 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 is
It 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 circulation. 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. Regarding these points, the present inventors found that when Fe is dissolved in Na-A type zeolite with the above adjustment,
We have discovered that new properties that have not been described in conventional literature arise. Does not dissolve Fe at all
Although Na-A type zeolite showed only weak oxygen selectivity as mentioned above, when Fe was dissolved in Na-A type zeolite, the minimum value of the outlet oxygen concentration decreased as the amount of dissolved Fe increased, and the maximum value will also decrease. This means that the nitrogen adsorption rate is reduced compared to the oxygen adsorption rate, and under dynamic adsorption conditions such as in an adsorption tower, an extremely high selective adsorption of oxygen can be obtained. The effectiveness of the present invention will be explained below with reference to FIG. For 0.5w% Fe-dissolved Na-A type zeolite, the lowest value of outlet oxygen concentration is 14%, the highest value is 30%, 1w%
In the Fe-dissolved Na-A type zeolite, the minimum value of the outlet oxygen concentration is 6% and the maximum value is 24%. As can be seen from these properties, the dissolution of Fe into the Na-A type zeolite shows that the nitrogen adsorption rate is significantly reduced compared to the oxygen adsorption rate. In addition, when measuring the isothermal adsorption amount of oxygen in a one-component system, it is 2.2 ml/g at 25°C 1ata condition when no Fe is dissolved, whereas it is 3 ml/g when 0.5 w% Fe is dissolved. , 3.8 for 1w% Fe dissolved
ml/g, it is thought that the decrease in the minimum value of the outlet oxygen concentration with the increase in the amount of dissolved Fe is caused not only by the oxygen adsorption rate but also by the increase in the amount of oxygen adsorption. Furthermore, when the above adsorbents were used to adsorb oxygen from air after cooling to a temperature below room temperature, a new phenomenon occurred in addition to the properties at room temperature. Figure 3 shows the time course of the outlet oxygen concentration at 0°C, and Figure 4 shows the
The figure shows data on changes in outlet oxygen concentration over time at -30°C. As shown in Figure 3, under the condition of 0℃, the minimum value of the outlet oxygen concentration decreases for all of the adsorbents ~, especially for the 0.5w% Fe-dissolved one.
At 1.5vol%, it is hardly detected at the exit. Moreover, the maximum value of the outlet oxygen concentration also decreased in all of the cases of ~, and in particular, in the case of 1w% Fe dissolved therein, no adsorption was observed at all. Furthermore, as shown in Figure 4, under -30°C conditions, Na-A zeolite, which does not dissolve Fe at all, has the lowest outlet oxygen concentration (1.5 vol%);
The minimum value of the outlet oxygen concentration increases, which is not due to the increase in the amount of dissolved Fe. However, in this experiment, with dissolved Fe, the maximum outlet oxygen concentration never exceeded the inlet oxygen concentration, indicating that the oxygen adsorption rate was only decreasing, and the oxygen selectivity continued to increase. . To summarize the above cases, (1) When Fe is dissolved in Na-A type zeolite, Fe
As the dissolved amount of nitric acid increases, the nitrogen adsorption rate decreases significantly compared to the oxygen adsorption rate, and under dynamic adsorption conditions such as in an adsorption column, it provides a significantly high oxygen selectivity. (2) The oxygen selectivity of both Na-A type zeolite and its Fe-dissolved version improves as the temperature decreases, but this tendency is more pronounced as the amount of dissolved Fe increases, and dynamic adsorption Complete oxygen selectivity under these conditions can be achieved at higher temperatures with dissolved Fe than with no Fe dissolved at all. (3) In the case of Na-A type zeolite in which Fe is dissolved, at too low a temperature, the nitrogen adsorption rate can be completely ignored, and even a decrease in the oxygen adsorption rate is such that it becomes a practical problem. 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. Note that under the conditions of flow rate (100 ml/min) and pressure (5 ata) in the present invention, almost perfect oxygen selectivity was exhibited upon cooling to 0°C. In addition, under this condition, the flow rate, pressure,
How the outlet oxygen concentration changes depending on the cross-sectional area of the adsorption tower, the length of the adsorption tower, etc. can be estimated from "Basics and Design of Adsorption Kitagawa, Suzuki, pp. 89-92." Furthermore, on the side higher than this temperature, the rate of nitrogen adsorption cannot be ignored, so it is sufficient to analyze a two-component system. According to these results, the larger the amount of Fe dissolved and the lower the temperature, the wider the mass transfer coefficients of oxygen and nitrogen become.Practically speaking, this means that the larger the amount of Fe dissolved, the lower the temperature becomes. A lower inlet flow rate is allowed, and a higher inlet flow rate must be set on the room temperature side. 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℃, and when the expansion turbine is driven by flowing high-pressure _N2 gas, the temperature between -30 and -50℃ is preferable, and the temperature selection in the low-temperature range rather depends on the mode of cooling. do. An example 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 will be described below. 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 by a heat exchanger 27 and sent to an adsorption tower 25 through a valve 20, where oxygen in the pressurized air is selectively adsorbed by an adsorbent in the tower, and the nitrogen-enriched air is passed through a valve 17. Sent from the same tower. At this time, the valve 1 attached to the adsorption tower 25
7 and 20 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 are extracted by continuously repeating the adsorption step and the regeneration step. In the example of the present invention, an adsorption tower with an inner diameter of 50 mm and a length of 600 mm was filled with 1 kg of Na-A type zeolite in which 1 wt% Fe was dissolved and molded into a sphere with a diameter of about 1 mm using a tablet molding machine, and the supplied air was The pressure was swung between 1 ata and 5 ata, the inlet air flow rate was 16 Nl/min, and the adsorption separation was performed at a low temperature of 0°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 2 shows the product oxygen concentration behind No. 23 and the amount of recovered oxygen. Note that at 25° C., no product nitrogen was obtained from behind the valves 17 and 21, and 45% of oxygen passed through. This seems to be 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, and Figures 2, 3, and 4 show substantially pure Na-A zeolite and Fe dissolution amount of 0.5wt. %, a graph showing the dynamic adsorption amount of 1wt% Na-A type zeolite at room temperature, 0°C, and -30°C, and Fig. 5 shows the flow of the embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. An oxygen adsorbent from a binary mixed gas of oxygen and nitrogen, which is obtained by dissolving iron having a charge number of at least two valences in substantially pure Na-A type zeolite. 2. Converting a binary gas mixture of oxygen and nitrogen at a relatively high pressure in a temperature range below room temperature to substantially pure Na-
Nitrogen gas is collected by passing through an oxygen adsorbent packed bed made by dissolving iron having a valence of at least two or more in A-type zeolite, and selectively adsorbing oxygen to the adsorbent. A method for separating a two-component mixed gas of oxygen and nitrogen into oxygen and nitrogen, which is characterized by collecting adsorbed oxygen by applying a relatively low pressure to an adsorbent packed bed.