JPS6258773B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oxygen separation method for separating, removing or concentrating oxygen in the air. 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 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
N ₂ /100 ₄ g at NTP), which selectively removes nitrogen from the air and separates oxygen.
A concentration process has been put into practical use. In reality, 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. , in the air
Since the N ₂ /O ₂ molar ratio is 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 is proposed with the aim of achieving a significant reduction in oxygen production costs and a significant downsizing of equipment for the oxygen production process by providing an oxygen separation method that improves the drawbacks of the above-mentioned oxygen production equipment. . In connection with adsorption separation of oxygen and nitrogen in the air, the present inventors have conducted intensive research on the oxygen and nitrogen adsorption ability of type A zeolite exchanged with various metal ions. The present invention was achieved by discovering that zeolite exhibits remarkable oxygen selective adsorption properties when subjected to low-temperature adsorption operations at temperatures below 25°C within a certain range of Zn exchange. The present invention will be explained in detail below. Regarding A-type zeolite having Zn and K as exchange ions (hereinafter abbreviated as Zn-K-A type zeolite), a manufacturing method is described in Japanese Patent Publication No. 18159/1983, and the method for producing the same is described in Japanese Patent Publication No. 18159/1983, with a Zn exchange rate of 66.7 to 83.3%. It is stated that it exhibits unique adsorption properties. Here, the Zn exchange rate (%) is defined by equation (1). Zn exchange rate (%) = 2 [Zn] / 2 [Zn] + [K] × 10
0......(1) [Zn]: Zn molar concentration in zeolite [K]: [K molar concentration] Estimated from the contents of Japanese Patent Publication No. 52-18159, Zn exchange rate of Zn-K-A type zeolite The relationship between the window diameter of the adsorbent and the window diameter of the adsorbent is shown in Table 1.

[Table] On the other hand, the apparent shape of each oxygen and nitrogen molecule is as shown in Figure 9, and the size is as shown in Table 2. In order to adsorb to
It is necessary that the thickness be slightly smaller than Å, and this is also suggested by Japanese Patent Application No. 1983-67100, which was filed separately by the present inventors.

[Table] Although Japanese Patent Publication No. 52-18159 does not mention anything about the separation of oxygen and nitrogen using Zn-K-A type zeolite, the molecular shapes of oxygen and nitrogen and the Zn exchange rate shown in Table 1 are Predicting the adsorption of oxygen and nitrogen based on the window diameter, the Zn exchange rate is 66.7%.
Below, neither oxygen nor nitrogen is adsorbed, and above 66.7%, although there is a stepwise change in the window diameter, oxygen and nitrogen co-adsorption or nitrogen selective adsorption is predicted. In contrast, the present inventors conducted a test on the adsorption of oxygen and nitrogen by Zn-K-A type zeolite, and found that Zn-K-A type zeolite was able to absorb oxygen and nitrogen from the two components in the region of Zn exchange rate of 30 to 70%. We found an effect that could not be predicted from the description in Japanese Patent Publication No. 18159/1983, which states that only oxygen is selectively adsorbed. This seems to be due to a completely different phenomenon.
Furthermore, we found that this tendency becomes more pronounced as the temperature decreases. The present inventors performed the following treatment in order to obtain the above-mentioned Zn-K-A type zeolite. First, the present inventors thoroughly washed K-A type zeolite powder manufactured by UCC with water, and further washed it with a KCl aqueous solution for 100 min.
After boiling at ℃ for 1 hour, the mixture was washed again with water and used as a raw material. This is true for K-A type zeolite powder.
Impurities such as approximately 5wt% Na, 0.05wt% Ca, and 0.05wt% Mg are usually mixed in, but the above treatment can purify the total impurity amount to 0.1wt% or less. It is from. From this
50 g was taken out and added to the pure water from Step 1. While stirring to form a slurry, an aqueous ZnCl ₂ solution was added dropwise, and stirring was continued for an additional hour. Here, ZnCl ₂ becomes a precipitate such as Zn(OH) ₂ when the pH of the aqueous solution exceeds 5.5, so use a very small amount of HCl to lower the pH of the slurry to 4.5.
The Zn exchange rate was adjusted to ~5.5 and exchanged with K ions to achieve the desired Zn exchange rate. After this, after dehydration, the first
The adsorption tower shown in the figure was filled. In addition, in this experiment,
Four types of Zn-K-A type zeolites with Zn exchange rates of 20, 40, 60, and 80% were prepared by adjusting the amount of dropped _ZnCl2 , and for comparison, K-A type zeolite was prepared.
type zeolite was subjected to an adsorption separation test. After filling the adsorption tower, water is removed from the Zn-K-A type zeolite using a vacuum filter, and then heated to 100℃ in an air bath.
After pre-drying the mixture, it was heated in a vacuum heating bath at 350 to 450°C for 1 hour under vacuum conditions of 0.1 Torr to develop adsorption activity. The adsorption and separation properties of Zn-K-A type zeolite 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 Zn-K-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 a valve 3. A Bourdon tube type pressure gauge 4 is installed between the pressure reducer 2 and the valve 3, and it is possible to measure the pressure.
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, valves 3 and 5
was opened to allow high-pressure air to flow through it, and the flow rate was measured 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 an automatic recorder 13. The Zn exchange rate and test conditions of the sample subjected to the adsorption separation test conducted using the experimental apparatus shown in Figure 1 were
Shown in the table.

[Table] Figures 2 and 3 show the outlet oxygen concentration in air adsorption separation tests conducted using samples Zn-K-A-0 and Zn-K-A-20 at 25℃ and -30℃. In FIGS. 2 and 3, which are graphs showing changes over time, the horizontal axis 14 is the flow time, and one scale is one minute. The vertical axis 15 is the outlet oxygen concentration, and the unit is volume %. In order to indicate the oxygen concentration on the inlet side, a reference line 16 was drawn at the air oxygen concentration of 20.8%. In FIGS. 2 and 3, the correspondence between the outlet oxygen concentration change curve over time and the sample is distinguished by writing the sample name in the figure. According to the data on changes in outlet oxygen concentration over time shown in Figures 2 and 3, at 25°C and -30°C, for both Zn-K-A-0 and Zn-K-A-20 samples. The outlet oxygen concentration remains constant regardless of the passage of time and matches the reference line 16.
It can be seen that neither oxygen nor nitrogen is adsorbed. Figures 4 and 5 show samples Zn-K-A-40 and
This is a graph showing the change in outlet oxygen concentration over time in an air adsorption separation test conducted at 25°C and -30°C using Zn-K-A-60, and the numbers in the figure indicate the same locations as in Figure 2. . According to the temporal change data of the outlet oxygen concentration for Zn-K-A-40 shown in Figure 4, the outlet oxygen concentration decreased from 20.8% to 4% at the initial stage, and then 23%.
%, then gradually decreases. Similarly, in the case of Zn-K-A-60, the outlet oxygen concentration initially decreases from 20.8% to 12%, then increases relatively rapidly to 28%, and then gradually decreases. 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, it gradually decreases. Furthermore, Zn-K- at -30℃ shown in Figure 5
Regarding the change over time in the outlet oxygen concentration for A-40, it initially decreases from 20.8% to 2%, stays around 2% for a while, then increases, and then breaks through after about 5 minutes.
A similar trend was observed in the case of Zn-K-A-60, with the outlet oxygen concentration decreasing from 20.8% to 0.5% at the initial stage.
After staying around 0.5% for a while, it quickly rises to 22% and then gradually decreases. As can be seen from this data, Zn-K-A-40
In both cases, the amount of oxygen adsorbed per unit time overwhelmingly exceeds the amount of nitrogen adsorbed, and the amount of nitrogen adsorbed is negligible, indicating selective adsorption of oxygen. significantly high in gender. The area surrounded by the reference line 16 and the time course curve of outlet oxygen concentration is proportional to the apparent amount of oxygen adsorbed per packed adsorbent. Figures 6 and 7 are graphs showing changes in outlet oxygen concentration over time in air adsorption separation tests conducted at 25°C and -30°C using sample Zn-K-A-80. indicates the same tube place as in Fig. 2. According to Figure 6, for Zn-K-A-80
The outlet oxygen concentration at 25℃ initially ranges from 20.8% to 48%.
%, then gradually decreased and reached breakthrough in about 6 minutes. Also, Zn-K-A shown in Figure 7
According to the data on the time course of the outlet oxygen concentration at −30℃ for −80℃, the outlet oxygen concentration initially
It increased from 20.8% to 42% and then gradually decreased. In FIGS. 6 and 7, the area surrounded by the reference line 16 and the time-course curve of outlet oxygen concentration is proportional to the apparent amount of nitrogen adsorbed per packed adsorbent. As can be seen from this data, in the case of Zn-K-A-80, the amount of nitrogen adsorbed by the adsorbent per unit time exceeds the amount of oxygen adsorbed, and is a so-called nitrogen selective type. Summarizing the above results, the oxygen and nitrogen selectivity for each sample, the apparent oxygen and nitrogen adsorption amount (adsorption amount in g per 100g of adsorbent in terms of 1ata standard conditions), the minimum oxygen concentration reached (O ₂ vol%), The maximum oxygen concentration (O ₂ vol%) achieved is shown in Table 4.

【table】

[Table] As detailed above, the Zn exchange rate of the present invention is 30 to 70.
% of Zn-K-A type zeolite is
This is a completely new oxygen-selective adsorbent that has not been suggested in any existing literature, including Publication No. 18159, and has the characteristic of adsorbing an extremely large amount of oxygen, and this tendency is particularly noticeable at low temperatures.
The amount of oxygen adsorbed at 30°C is approximately seven times the amount of oxygen adsorbed at room temperature. This adsorbent 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 it can be applied to conventional N ₂
The adsorption performance far exceeds that of adsorption-type molecular sieves, paving the way for smaller equipment and lower cost oxygen concentration. Furthermore, if this adsorbent is used to remove oxygen from other component gases, an extremely inexpensive oxygen adsorption/removal agent will be provided. Furthermore, under the conditions of flow rate (100ml/min) and pressure (5ata) in oxygen separation using this adsorbent, Zn
In the region of exchange rate of 30 to 70%, almost complete oxygen selectivity was exhibited by cooling to 0°C. 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 P89-P92". Further, at temperatures higher than this temperature, the co-adsorption of nitrogen cannot be ignored, but it is sufficient to analyze the two-component system of oxygen and nitrogen. These results indicate that in the region where the Zn exchange rate is 30 to 70%, the lower the temperature, the more the mass transfer coefficients of oxygen and nitrogen open up.This means that in practical terms, the lower the temperature, the lower the inlet flow velocity. On the room temperature side, a higher inlet flow rate must be set. In any case, if the data on changes in outlet oxygen concentration over time shown in FIGS. 2 to 7 are obtained, the design of the adsorption tower and its operation can be carried out within the conventional technical range. 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 about -10℃, and if the expansion turbine is driven by flowing high-pressure _N2 gas, the temperature between -30℃ and -180℃ is preferable.The temperature selection in the low-temperature range is rather based on the mode of cooling. Dependent. Next, 30% to 70% of the ion-exchangeable cations of type A zeolite are converted to zinc ions, and 70% to 30%
A method for selectively adsorbing and separating oxygen from a binary gas mixture of oxygen and nitrogen by using Zn-K-A type zeolite with % exchanged with potassium ions as an adsorbent and performing a low-temperature adsorption operation at 25°C or lower; That is, the above-mentioned Zn-K-A type zeolite is packed in an adsorbent packed bed, and a relatively high pressure two-component mixed gas of oxygen and nitrogen is passed through the bed at a temperature below room temperature to select oxygen as the adsorbent. A specific example will be described in which a method of collecting nitrogen gas by adsorbing nitrogen gas and then collecting adsorbed oxygen using the adsorbent packed bed at a relatively low pressure is applied to a pressure swing type oxygen production apparatus. FIG. 8 is a schematic explanatory diagram of a pressure swing type oxygen production apparatus. In FIG. 8, 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,
An adsorption tower for decarbonizing gas, 29 a bleak cooler, 30 an air compressor, 31 an air strainer, 32 a throttle valve, and a control device for controlling automatic switching valves and the like are 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 bleed cooler 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 adsorption operation is being performed in the adsorption tower 25, 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 an 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 Zn-K-A type zeolite with a Zn exchange rate of 60%, molded into a sphere with a diameter of about 1 mm using a tablet molding machine, and then supplied. Swing the air pressure between 1 ata and 5 ata, inlet air flow rate at 16Nl/min, temperature -
Adsorption separation was carried out at a low temperature of 30°C. At this time, in FIG. 8, the product nitrogen concentration behind valves 17 and 21, the amount of nitrogen separated, the valve 19,
Table 5 shows the product oxygen concentration behind No. 23 and the amount of recovered oxygen. Note that at 25° C., the product nitrogen flowed from behind the valves 17 and 21 with an oxygen concentration of about 5%. This seems to be because the 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. 25℃
In the vicinity, larger inlet flow velocities may be required.

【table】 [Brief explanation of the drawing]

Figure 1 shows the flow of the experimental equipment used to confirm the effects of the present invention, and Figures 2 to 7 show the flow of the experimental equipment used to confirm the effects of the present invention.
A graph showing the dynamic adsorption amount of Zn-K-A type zeolite with different Zn exchange rates at room temperature and -30°C,
FIG. 8 is a diagram showing a flow of an embodiment of the oxygen separation method of the present invention, and FIG. 9 is a diagram showing a two-atom molecular model of oxygen and nitrogen.

Claims (1)

[Claims] 1 Zn-K-A type zeolite, in which 30% to 70% of the ion-exchangeable cations of type A zeolite are exchanged with zinc ions and 70% to 30% with potassium ions, is used as an adsorbent, and the An oxygen separation method characterized by selectively adsorbing and separating oxygen from air by low-temperature adsorption operation.