JPH0360523B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial usage method) The present invention uses a carbon monoxide selective adsorbent to
Pressure swing adsorption method (hereinafter abbreviated as PSA method)
This invention relates to a method for separating and recovering carbon monoxide from a mixed gas. (Prior art and its problems) Recently, in order to effectively utilize carbon monoxide contained in converter gas, electric furnace gas, blast furnace gas, etc., a method of separating carbon monoxide from these gases using PSA has been developed. , has been extensively studied. For example, in JP-A-59-22625, etc., a general zeolite-based adsorbent is used to remove PSA from converter gas, etc.
proposed a method for concentrating carbon monoxide. However, the adsorbent used in this method adsorbs more carbon dioxide, which coexists with carbon monoxide, than carbon monoxide. For this reason, this method requires a pretreatment device such as CO ₂ -PSA for removing carbon dioxide in the first stage, which complicates the process and increases the cost of the device. Also, with this method,
Attempts to increase carbon monoxide concentration will increase the amount of purge, significantly reducing the recovery rate, and
In CO-PSA, since a general zeolite adsorbent is used, the co-adsorption of nitrogen becomes large.
There is a drawback that it becomes difficult to sufficiently reduce the nitrogen concentration. Further, JP-A-61-21906 and JP-A-61-26506 disclose a method of separating carbon monoxide using PSA using an adsorbent that selectively adsorbs carbon monoxide. Here, an adsorbent that selectively adsorbs carbon monoxide against other gas components that coexist with carbon monoxide, such as nitrogen, carbon dioxide, hydrogen, and oxygen, is used, and a raw material mixed gas containing these components is Disclosed is a method for recovering carbon monoxide through a vacuum desorption process after passing through an adsorption tower, passing through each step of pressurization and adsorption, and connecting it to another tower where the vacuum desorption process has been completed to perform a cocurrent depressurization process. Furthermore, in order to further improve the purity, a method of adding a product processing step and a vacuum evacuation step after the co-current depressurization step is shown. However, according to the example described in this publication, the raw material mixed gas concentration is CO90.0%, _N2 9.2%,
For CO ₂ 0.8%, the product gas concentration is CO 96.2%,
N ₂ was 2.7% and CO ₂ was 1.10%, so the product purity had not improved that much. Moreover, the CO ₂ concentration is higher than that of the raw material mixed gas. Therefore, it can be said that gas purging is insufficient with this method. Furthermore, Japanese Patent Publication No. 54-3822 describes a method for separating easily adsorbable components from mixed gases with high purity.
A method of purging with product gas under the same pressure as during adsorption before desorption is shown. Also, special public service in 1977-
In order to continuously separate and recover difficult-to-adsorb and easily-adsorbed components from a mixed gas with high purity, 3823 requires a pressure increase process using tail gas before supplying the mixed gas, and an adsorption process using product gas before the desorption process. A method of purging under the same pressure is described. However, purging with product gas does not necessarily have to be carried out at the same pressure as during adsorption, and although increasing the pressure with tail gas may seem at first glance to be useful for improving the recovery rate, it actually co-adsorbs the second most adsorbable component. This has the disadvantage that the purge operation becomes difficult because of the increase in the amount of water. (Technical Problems to be Solved by the Invention) The present invention is a system that can separate and recover carbon monoxide in one step with high purity and high recovery rate from a mixed gas containing carbon monoxide, carbon dioxide, nitrogen, etc. The purpose of the present invention is to provide a method for separating and recovering carbon oxide. (Means for Solving the Technical Problems) This invention involves passing a mixed gas containing carbon monoxide as one of the main components and containing at least carbon dioxide and/or nitrogen through a column containing a carbon monoxide selective adsorbent. In a method for separating and recovering carbon monoxide in which carbon monoxide is selectively adsorbed and then desorbed, a pressurization step of supplying the mixed gas to a tower where desorption and recovery of carbon monoxide has been completed and increasing the pressure to at least atmospheric pressure; An adsorption process in which a mixed gas at a pressure higher than atmospheric pressure is passed through the tower after the pressure raising process until at least the component with the highest amount of adsorption next to carbon monoxide begins to break through, and a purge process in which the adsorption process is completed in the tower. A preliminary purge step in which the outlet gas is supplied while depressurizing to purge other adsorbed components except for carbon monoxide and the component with the second largest amount of adsorption after carbon monoxide, and the outlet end of the tower after the preliminary purge step is completed. a post-purging gas recovery process in which the gas at the outlet of the purge process is recovered by closing the purge process, and a post-purging gas recovery process in which the product gas after desorption and recovery is pressurized to a pressure exceeding the adsorption pressure in the adsorption process, heated by the adiabatic heat of compression, and then transferred to the post-purging process. There is a purge step in which gas is supplied to the inlet end of the tower where the gas recovery step has been completed, and the outlet end is simultaneously opened to purge the adsorbed components that have the second largest adsorption amount after carbon monoxide.After the purge step, the tower is depressurized and concentrated. This is a carbon monoxide separation and recovery method in which a desorption and recovery step for recovering carbon monoxide is sequentially repeated. (Specific Description of the Invention) In order to separate and recover easily adsorbable components (here, carbon monoxide) with high purity from a mixed gas containing carbon monoxide, carbon dioxide, nitrogen, etc., in one stage PSA, the coexisting mixed gas must be It is essential to use an adsorbent that best adsorbs carbon monoxide among the components, and it is also necessary to replace and adsorb other co-adsorbed components (carbon dioxide, nitrogen, etc.) with reflux of the product gas (carbon monoxide). In other words, the most important point is how efficiently the purge operation can be performed. The present inventors have already disclosed a method for producing such an adsorbent and its excellent adsorption performance in Japanese Patent Application Laid-Open No. 17413/1983. That is, this adsorbent is
Zeolite with a silica/alumina ratio of 10 or less, Ni,
One or more metals selected from Mn, Rh, Cu(), Ag, and mixtures thereof are loaded on the adsorbent, and the manufacturing method for this adsorbent is to attach zeolite to zeolite in the first step by an ion exchange method. In this method, the metal is supported by an impregnation method in the second step. As a result of further studies on the breakthrough and purge characteristics of these carbon monoxide selective adsorbents, the inventors found that the following two points are important in order to perform the purge process efficiently. (1) Raise the purge temperature. (2) Increase the amount of purge gas. That is, the higher the temperature at which displacement adsorption is performed, the more the selective adsorption ability of carbon monoxide of this adsorbent increases, and the mass transfer rate increases, so that purging can be performed quickly. Furthermore, when the purge pressure is increased, the amount of desorption increases, so the amount of purge can be increased without changing the amount of carbon monoxide recovered. Furthermore, it was found that by increasing the pressure of the purge gas, a synergistic effect could be obtained in that the temperature of the purge gas could be increased by the heat of adiabatic compression. And the inventor has efficiently exploited these characteristics.
We have completed the present invention as a process that can be reflected in the PSA system and improve the purity and recovery rate of carbon monoxide. Table 1 and FIG. 1 show one example of the method of the present invention. Here, four adsorption towers A to D are used to form a cycle in which the steps of pressurization, adsorption, preliminary purge, post-purging gas recovery purge, and desorption/recovery are performed in one order in eight steps. By using at least four adsorption towers, supply of raw material mixed gas, supply of purge gas, and recovery of product gas can be performed continuously. Here, in order to explain the process in an easy-to-understand manner, only basic operations are shown, but the present invention is not limited thereto. In addition, converter gas (CO80%, CO ₂ 10%, N ₂ 9%, H ₂ 1
%). First, let's focus on Tower D and explain it. Step 1 shows the pressure increasing step. The D column in this step has completed the desorption and recovery step and is in a vacuum state, and the raw material mixed gas is introduced from the inlet end of the D column using a blower. The end point of this process is when the blowing pressure reaches about atmospheric pressure or blower pressure. The reason why the raw material mixed gas is directly blown in this process and the tail gas (described later) is not supplied is because the tail gas is
Because the carbon monoxide concentration is lower than that of the raw material mixed gas,
This is because if the pressure is increased with this tail gas, it becomes difficult to purge the co-adsorbed components after this step. Tower D in step 2 represents the adsorption step. In this step, the outlet end is opened and the raw material mixed gas is circulated using a blower. It is sufficient for the pressure of the raw material mixed gas to be increased by a blower, and may be 0 to 0.5 kg/cm ² G. Through this process, hydrogen and oxygen, which have a small adsorption capacity, can easily break through. The end point of this process is at least until nitrogen has broken through and carbon dioxide has begun to break through. This point is the end point of step 2. Note that if adsorption continues even after carbon dioxide breakthrough ends, the recovery rate of carbon monoxide will decrease. The reason for lowering the adsorption pressure is to minimize co-adsorption of components other than carbon monoxide. Another advantage is that a booster is not required to supply the raw material mixed gas, and only a blower is required. Step 3, column D, represents a preliminary purge step.
In this step, the purged outlet gas from the C tower outlet is introduced from the inlet end. Since the breakthrough has not been completed on the column outlet side after the adsorption process is completed, the tail gas with a high concentration of nitrogen and carbon dioxide is exhausted by opening the column outlet end. This process is
This is carried out at least up to the point at which displacement desorption of the co-adsorbed carbon dioxide begins, ie, the point at which purge begins. Note that it is not preferable to continue this step beyond the carbon dioxide purge starting point because the recovery rate of carbon monoxide will decrease. Step 4, Tower D, represents a post-purging gas recovery step. Here, the outlet end is closed and the purged gas at the outlet of the C column is recovered and pressurized. Since the carbon monoxide concentration in the column is high even in the gas after purging, this step improves the recovery rate. Additionally, the nitrogen and carbon dioxide adsorption zones move to the outlet end, facilitating the next purge step. Step 5, column D, represents a purge step. In this step, pressurized product gas (gas mainly composed of desorbed and recovered carbon monoxide) is introduced from the tower inlet via a booster. The purged gas from the outlet end enters the inlet end of the A column. The pressure of the purge gas is at least higher than the adsorption pressure and not more than 5 kg/cm ² G, preferably higher than the adsorption pressure and not more than 2 kg/cm ² G, and is arbitrarily set depending on the purity of the product gas. The purge gas is heated by the heat of adiabatic compression accompanying pressure increase, improving purge efficiency. Tower D in step 6 shows a purge step with pressurized product gas similar to step 5. In this step, since the outlet end of column A is closed, purging is performed while the pressure inside column D is increased. The purity of the product gas used in this purge step (steps 5 and 6) improves as the amount increases, but if the amount is too large, the throughput decreases, so the product gas used in the desorption and recovery step should preferably be at most 80% or less. It is best to keep it below 60%. Step 7 shows the column just after the purge step is completed. Here, the pressure in the purge step is released to atmospheric pressure or a pressure near atmospheric pressure. Furthermore, when the pressure reaches atmospheric pressure or near atmospheric pressure, it is depressurized and desorbed via a vacuum pump. In step 8, decompression is subsequently carried out using a vacuum pump. Since the carbon monoxide adsorption capacity of the adsorbent is high below atmospheric pressure, the degree of vacuum here is preferably as low as possible, at least 150 Torr or less, preferably
Must be 100Torr or less. In the illustrated example, steps 1 to 8 described above are
It is equipped with four towers A to D, which perform these steps sequentially. In each column, steps 1 to 8 are staggered as shown in Table 1 so that carbon monoxide can be separated and recovered continuously. The connections of each tower in each step are as shown in FIG. The structure for continuously operating each column is as shown in FIG. 2, and the equipment shown is controlled by a computer. Reference numeral 1 indicates a blower, which sequentially sends the raw material mixed gas F to the towers A to D. Also vacuum pump 2
The pressure in columns A to D is sequentially reduced. The booster 3 sequentially sends a part of the product gas R in the gas holder 4 to the columns A to D. In the figure, 5 to 8 indicate flow rate adjustment valves, and 9 to 29 indicate switching valves. T indicates tail gas. Note that the raw material mixed gas to which the present invention can be applied can contain any components as long as an adsorbent that adsorbs the largest amount of carbon monoxide under the temperature, pressure, and time conditions in the adsorption step and purge step is used. You can stay there. However, this does not apply to impurities that reduce the carbon monoxide adsorption ability of the adsorbent. Such raw material mixed gas includes off-gas generated from converters, blast furnaces, electric furnaces, etc., but is not limited to these. In addition, if the adsorbent used in the present invention selectively adsorbs carbon monoxide with respect to other components,
It can be anything. In the present invention, at least four adsorption towers are required to continuously operate the supply of raw material mixed gas, the supply of purge gas, and the recovery of product gas.

[Table] Examples are shown below. Example 1 A 1N solution of CuCl ₂ was prepared, and 10 g of Na-Y type zeolite (1.5 mmφ, 5 mm L pellet, containing 20% binder) and 50 g of 1N CuCl ₂ solution were placed in a 100 ml round bottom flask.
ml was added, a condenser was attached to the round bottom flask, and the mixture was heated under reflux at 100°C for 2 hours using a mantle heater. After standing still, the supernatant was collected by decantation, and 50 ml of 1NCuCl ₂ solution was added thereto, followed by refluxing in the same manner. The reflux operation was performed a total of 5 times, and the zeolite was thoroughly washed with pure water and dried at 110℃.
An adsorbent was created by firing in an electric furnace at 550°C for 2 hours.
The ion exchange rate was measured by mixing the recovered supernatant and filtrate and determining the amount of Na released by luminescence analysis.
The amount was 8.87wt%. This Cu()-Y type zeolite (1.5mmφ, 5mm
Weigh out 10g of pellets), put them in a 100ml eggplant-shaped flask, set it in a rotary vacuum evaporator, and vacuum degas it at 95°C or above. After degassing, the sample is cooled to room temperature while applying a vacuum. On the other hand, 8.3 g of CuCl ₂ .2H ₂ O was dissolved in water at room temperature to make 20 ml. This results in an approximately saturated solution of CuCl ₂ . A capillary is attached to the leak tank of the rotary vacuum evaporator, and while the inside of the eggplant-shaped flask is maintained in vacuum, the adsorbent is impregnated with 2 to 3 drops of the above solution. When the adsorbent leaks out evenly, stop dropping and return the inside of the flask to normal pressure. Then, transfer the impregnated sample to a suction filter equipped with a wire mesh, pour the remaining solution onto the sample, filter it with suction for about 30 minutes, spread it on a magnetic plate, and air dry it overnight. The air-dried sample was vacuum-dried at 110° C. for 3 hours in a vacuum dryer to obtain an adsorbent of the present invention. The amount of Cu supported on this adsorbent is 15.96wt
It was %. Cu()Y-CUCl ₂ obtained in this way,
Cu content 16wt%, 1.5mmφ, 5mmL pellets were placed in an adsorption tower with an inner diameter of 50mmφ and a height of 800mm (dry).
The chamber was filled with CO gas with a purity of 99.9% or higher at 250°C for 2 hours at a rate of about 1 Nl/min to reduce Cu ²⁺ to Cu ⁺ . While supplying the CO gas, the temperature inside the column was lowered to 60° C. and maintained at approximately atmospheric pressure. Applicable
Stop the CO gas supply, connect the vacuum pump, and
It was evacuated for a minute. The pressure inside the column after 5 minutes is 80Torr.
It was hot. A standard gas (CO8 0.0% by volume, CO ₂ 10.5% by volume, H ₂ 1.0% by volume, N ₂ 8.5% by volume) is added at 1.4Nl/into the adsorption tower under reduced pressure from the inlet end.
After reaching 0.3 Kg/cm ² G, the outlet end was opened and the CO and CO ₂ concentrations at the tower outlet were continuously measured using a CO/CO ₂ gas analyzer using a non-dispersive infrared absorption method.
When the outlet gas concentration almost matches the inlet gas concentration,
Stopping the flow of standard gas and supplying 99.9% more CO gas.
Similarly, the flow was conducted at 1.4 Nl/min and 0.3 Kg/cm ² G, and the outlet gas concentration was measured. Similarly, breakthrough was achieved by setting the inside of the tower to 70℃.
Purge measurements were performed. Figure 3 shows the results of purge measurements at 60°C and 70°C. The purge characteristics for H ₂ and N ₂ are almost the same, but for CO ₂ the width of the adsorption zone is smaller in the 70°C method, indicating that the displacement adsorption of CO ₂ is easier at higher temperatures. Examples 2 to 7 Cu()Y- produced by the method shown in Example 1
CUCl ₂ , Cu content 16wt%, 1.5mmφ, 5mmL pellets were placed in four adsorption towers with an inner diameter of 50mmφ and a height of 800mm.
Each was filled with 1000 g (dry) and installed in the apparatus shown in Figure 2. To activate the adsorbent, pure hydrogen gas was passed at 1Nl/min at 120°C for 2 hours to remove Cu ²⁺ .
Reduced to Cu ⁺ . After setting the tower internal temperature to the specified operating temperature, the dedusted and dehumidified converter gas (CO78~82% by volume, _CO2 9
~11% by volume, _N2 7-10% by volume, _H2 0.8-2% by volume,
PSA was performed using the system shown in the method of the _present invention, and CO was separated. The cycle time was 20 minutes in each case, 2 minutes for step 1, and 3 minutes for step 2. Each experiment was operated for more than 20 cycles, and after the flow rate and concentration were both stable, the flow rate and concentration at each part were measured. The results of Examples 2 to 7 are shown in Table 2. Note that with the throughput of this experimental device, the temperature increase due to adiabatic compression of the purge gas was slight and no influence was observed, but the results were good.

[Table] (Effects of the invention) According to this invention, no tail gas is used in the pressure increase process, and all raw material mixed gas is used, and the product gas is pressurized and heated by adiabatic compression in the purge process. , the selective adsorption capacity of carbon monoxide of the adsorbent is increased, and the mass transfer rate is increased, so that the purge process can be carried out efficiently.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining one side of the flow of each gas in the separation and recovery method of the present invention, FIG. 2 is a diagram showing a four-column PSA apparatus for carrying out the separation and recovery method of the present invention, and FIG. 3 This is a diagram showing the change in the CO concentration at the outlet by flowing CO purge gas through the tower where adsorption has been completed. 1...Blower, 2...Vacuum pump, 4...Booster, 4
...Gas holder, 5-8...Flow rate control valve, 9-29
...Switching valve, A to D...Adsorption tower, F...Raw material mixed gas,
P...Purge gas, T...Tail gas, De...Desorption gas.

Claims (1)

[Claims] 1 A mixed gas containing carbon monoxide as one of the main components and containing at least carbon dioxide and/or nitrogen is passed through a column containing a carbon monoxide selective adsorbent to select carbon monoxide. In the separation and recovery method for carbon monoxide, which is adsorbed and then desorbed, the above-mentioned mixed gas is supplied to the column where the desorption and recovery of carbon monoxide has been completed, and the pressure is increased to at least atmospheric pressure; There is an adsorption process in which a mixed gas at a pressure higher than atmospheric pressure is passed through the tower until at least the component with the highest amount of adsorption next to carbon monoxide begins to break through, and the outlet gas from the purge process is released into the tower after the adsorption process has been completed. A preliminary purge step in which carbon monoxide and other adsorbed components except for the component with the second largest amount of adsorption after carbon monoxide are purged by supplying the product under pressure, and a purge step in which the outlet end of the tower is closed after the preliminary purge step is completed. The product gas after desorption and recovery is pressurized to a pressure higher than the adsorption pressure in the adsorption step, and its temperature is raised by the heat of adiabatic compression, and then the gas is collected at the end of the post-purging gas recovery step. There is a purge step in which carbon monoxide is supplied to the inlet end of the tower, and at the same time the outlet end is opened to purge the adsorbed component, which has the second largest amount of adsorption after carbon monoxide.After the purge step, the tower is depressurized to remove the concentrated carbon monoxide. A method for separating and recovering carbon monoxide by sequentially repeating the desorption and recovery process. 2 The carbon monoxide selective adsorbent uses zeolite with a silica/alumina ratio of 10 or less, Ni, Mn, Rh, and Cu.
1 selected from ( ), Ag and mixtures thereof
The carbon monoxide separation and recovery method according to claim 1, wherein the carbon monoxide separation and recovery method is one in which two or more metals are supported.