JPH0574404B2 - - Google Patents

Description

[Detailed description of the invention]

Object of the present invention The present invention relates to a method for adsorbing and separating CO from CO-containing gases, and in particular from multi-component gases containing CO and _N2 produced in steel plants, autothermal partial oxidation methods, air-blown coal gasification plants, etc. This paper relates to a CO adsorption separation method. Overview of conventional technology and its drawbacks Autothermal partial oxidation method using off-gas from steel plants, natural gas, liquefied petroleum gas, and naphtha as raw materials and air as a combustion improver, and air-blown coal gasification plants that produce CO, N ₂ , and CO ₂ , H ₂ O, H ₂ etc. are produced as main components. Selective enrichment of CO from this gas mixture is CO
It is extremely meaningful and important because it has various uses. One use of CO is as a raw material for methanol synthesis from a mixed gas of CO and _H2 . For other uses, CO can be regarded as an H ₂ source since it generates H ₂ through a shift reaction in the coexistence of H ₂ O gas. Another possible use is as a raw material for a carbonylation method in which acetic acid is produced by reacting CO with methanol. Particularly in recent years, prospects for the practical application of gasoline synthesis using methanol as a raw material are opening up, and this is important in that sense as well. Conventionally, CO is separated using copper aluminum chloride (CuAlCl ₄ ).
The liquid phase absorption method using a toluene solution is said to have the best performance. In this method, the absorption reaction of CO as shown in equation (1) causes equimolar absorption with copper aluminum chloride. CuAlCl ₄ +COCuAlCl ₄・CO (1) Usually, CO is absorbed into the above absorption liquid through the absorption reaction of equation (1) above at around room temperature, and the CO that has been absorbed is released and recovered at a high temperature of 100°C or higher. be. In this method, the CO absorption capacity increases as the pressure increases, so a slightly higher pressure of several ata may be used to reduce the initial cost. or,
With this method, there is almost no CO and accompanying gas, so
The concentration of CO gas obtained is extremely high, around 99%.
And the recovery rate is also high. In addition to this method, there are CO concentration methods such as copper liquid washing method and cryogenic separation method, but the liquid phase absorption method mentioned above is the mainstream method because it is superior in terms of equipment cost, power cost, and CO concentration obtained. It is becoming. However, due to toluene solution of aluminum copper chloride
The biggest drawback of the CO absorption and separation method is that H ₂ O, H ₂ S, SO _2, etc. that are mixed in due to incorrect operation etc.
CuAlCl ₄ reacts to form CuCl, HCl, CuAlCl ₆
It decomposes into (OH), etc., causing depletion of aluminum copper chloride, and the recovered CO is accompanied by HCl, significantly reducing the quality of the product. The next drawback is that olefin and acetylene react with CuAlCl ₄ to form a precipitate, and this reaction is irreversible, so make-up of CuAlCl ₄ is required. Also, since toluene is used as a solvent, off-gas and
Since toluene accompanies all CO recovery (stripper) units, a toluene recovery unit that uses activated carbon as an adsorbent and uses water vapor as regeneration gas is required, and of course, toluene make-up is also required. There is a drawback. In terms of power costs, this method has the advantage of being able to operate the absorption process at near atmospheric pressure and consumes little electricity; of water vapor is required, and the amount of heat to generate this water vapor is equivalent to 2 to 3 times the above power consumption in terms of electricity.
This is equivalent to double the power consumption, which is not economical as the power consumption is large. Purpose of the present invention The present invention is a method of selectively adsorbing only CO from a mixed gas mainly containing CO, _N2 , etc. at relatively low pressure (above atmospheric pressure) and recovering it under reduced pressure conditions of 0.5 ata or less. The purpose of the present invention is to provide a CO recovery method that uses an extremely simple process, requires little chemical make-up, and is easy to maintain and operate. New Points of the Present Invention The present invention is novel in that sodium phaujasite, a mineral represented by Na-X, is used as a selective adsorbent for CO. The adsorption density diameter of these adsorbents is estimated to be 3.8 to 4.0 Å, judging from examples of separation from two-component systems of N ₂ and O ₂ . The Na-X type zeolite referred to herein refers to the following. Chemical formula M _K/o・(Al ₂ O ₃ ) _K・SiO ₂ (where M is an exchangeable metal ion, n is its valence, and K is AlO ₂ /
_SiO2 ratio), usually with water of crystallization,
In aluminosilicate, which exhibits gas adsorption ability by releasing crystal water without changing the crystal structure by heating and degassing, M is Na ion and K = 0.67.
〜0.83, n=1 is called Na-X type zeolite. This adsorbent is packed into at least two or more adsorption towers, and the temperature of the adsorption towers is set at -30°C or higher and 25°C or lower (room temperature), and one or more gases containing CO and _N2 are packed into each tower.
5 ata to adsorb CO, and in another column, the previously adsorbed CO is reduced to 0.05 ata to 0.5 ata to become _N2.
Another novel feature is the ability to recover CO at high temperatures while suppressing its co-adsorption. Furthermore, the recovered CO flows down into the adsorption tower immediately after the adsorption step in the same gas flow direction as the adsorption step to scavenge the remaining N ₂ in the tower and improve the concentration of CO recovered during reduced pressure regeneration. This is a preferred embodiment. That is, the present invention provides at least two adsorption towers filled with the mineral name sodium faugiasite represented by Na-X as a CO adsorbent.
A mixed gas mainly containing CO, _N2 , etc. is introduced and CO adsorption is performed under operating conditions of adsorption pressure 1 to 5 ata and adsorption temperature room temperature to -30℃, followed by desorption pressure of 0.05.
This invention relates to a CO adsorption separation method characterized by desorbing CO under operating conditions of ~0.5ata. Field of application of the present invention The present invention can be advantageously applied to the _H2 manufacturing industry, methanol industry, acetic acid industry, synthetic gasoline industry (C1 chemical industry), and can also be used to improve the calorific value of boiler fuel such as off gas and process gas. You can make it useful. Description of Specific Examples of the Present Invention Hereinafter, specific embodiments of the present invention will be described with reference to FIG. In FIG. 1, 1 is a CO and H ₂ synthesis gas production apparatus using propane as a raw material and using a partial oxidation method using oxygen-enriched air as a combustion improver. The CO,
Table 1 shows an example of the gas composition in the H ₂ synthesis gas production apparatus 1.

[Table] The synthesis gas in the CO, H ₂ synthesis gas production apparatus 1 is pressurized by the compressor 3 through the flow path 2. The pressurized synthesis gas passes through channel 4 to valve 5 . At this time, the valves 5 and 6 are open, and the synthesis gas flows through the adsorption tower 8. In the adsorption towers 8 and 8', the inlet half is filled with activated alumina, and the rear half is filled with activated carbon. Therefore, water is adsorbed at the front of the tower 8, and CO ₂ is adsorbed at the rear. On the other hand, once adsorbed
H ₂ O and CO ₂ are in the state of the adsorption tower 8', that is, in the vacuum desorption process, and the valve 7' is open;
6' is closed. Channel 9 leading to valves 7, 7'
communicates with the vacuum pump 10 on the other side. The adsorption tower 8' reaches a maximum pressure of 0.05ata, and H ₂ O, CO ₂
Remove and play. The adsorption towers 8, 8' are switched alternately every 2 to 10 minutes to continuously dehumidify and remove _CO2 . The dehumidified and CO _2- removed synthesis gas is passed through the flow path 11,
The gas passes through the surge tank 12 to a heat exchanger 13 and a refrigerator 14, where the gas temperature is cooled to an arbitrary temperature from room temperature to -60°C, and then reaches a valve 15. Valves 15 and 16 are in an open state. Table 2 shows the gas composition of the flowing synthesis gas in the channel 11.

[Table] CO is adsorbed from the synthesis gas flowing through the CO adsorption tower 18, and N ₂ is co-adsorbed depending on the selectivity of the CO adsorbent. Adsorption of _H2 is negligible. The adsorption tower 18' where CO adsorption has been completed is operated by valve 1.
5', 16', and 17 are closed, and the valve 17' is open, and the CO adsorbed in the adsorption tower 18' is discharged from the flow path 21 under reduced pressure through the flow path 19, the heat exchanger 13', and the vacuum pump 20. Collected at high concentration. By repeating this operation alternately every 1 to 5 minutes, high-concentration CO is continuously recovered. The heat exchanger 22 is installed to cool the product CO after the vacuum pump because the temperature rises to about 150°C. One-way adsorption tower 18, flow path 23 through valve 16
Gas with low CO concentration flows through. Note that since the low CO gas in the flow path 23 contains H ₂ at a high concentration, a high concentration of H 2 can be obtained by removing N ₂ with an adsorbent having a large amount of N ₂ adsorption, such as Ca-substituted Na-A _zeolite . Furthermore, even if N ₂ is liquefied and removed by cryogenic separation, highly pure H ₂ can be obtained in the same way. Moreover, if the gas in the flow path 23 is used as fuel, heat can be recovered. In addition, in terms of heat balance, the gas in the flow path 11, the gas in the flow path 19, and the gas in the flow path 23 are connected to the heat exchangers 13 and 1.
Since gas-gas heat exchange is performed at 3' and 13'', the power consumption of the refrigerator 14 is extremely low. In the present invention, the adsorption towers 18 and 18' and their surrounding piping and valves are installed in the cold box 24. Using the above equipment configuration and gas composition, we performed the operations shown in Table 3 to attempt to recover CO.

【table】

[Table] Shows the CO recovery results under the above operating conditions. Figure 2 shows the adsorption temperature at 0℃ and desorption pressure at 0.1ata.
The performance of the adsorbent during CO recovery is plotted on the horizontal axis with adsorption pressure and
The vertical axis shows CO concentration. Figure 3 shows the CO recovery performance of the adsorbent at an adsorption pressure of 1.2 ata and an adsorption temperature of 0°C, with the horizontal axis representing the desorption pressure and the vertical axis representing the CO recovery performance.
This is a selection of CO concentrations. Figure 4 shows the CO recovery performance of the adsorbent at an adsorption pressure of 1.2 ata and a desorption pressure of 0.1 ata, with the horizontal axis representing the temperature during adsorption and the vertical axis representing the CO concentration. As you can see above, Na-X type zeolite
Highly effective while minimizing adsorption of _N2 from CO, _N2, etc.
It was shown that it can be recovered with CO selectivity. This thing is
This is something that has not been previously known, and provides a new method for adsorption and separation of CO. Note that the CO recovery rate in the method of the present invention depends on the raw material.
Although it depends largely on the CO concentration, it is around 90% when the raw material CO concentration (after removing CO ₂ and H ₂ O in the flow path 11) is 50 vol%. The CO recovery rate is: CO recovery rate = CO amount recovered per unit time in the product CO flow path 21 / CO flowing in per unit time in the inlet flow path 11
It is defined as amount x 100%. In Figure 3, the recovered CO concentration increases as the regeneration pressure approaches absolute vacuum. But 0.05ata
Below this, the power consumption of the vacuum pump increases and the capacity is limited, so it cannot be said to be industrially effective. In Figure 4, it shows good performance even at low temperatures below -30℃.
It can be seen that it shows CO adsorption performance. However, if it is above -30℃, the unitary refrigerant
The refrigerator consists of stage compressors. However, −30℃
Below this, it becomes difficult to use equipment because two or more types of refrigerants are required and two stages of compressors are required. Furthermore, the power consumption during refrigeration also increases significantly. Another embodiment of the invention is shown in FIG. In FIG. 5, the same reference numerals as in FIG. 1 indicate the same parts as in FIG. As shown in FIG. 5, the flow path 19 and the heat exchanger 13'
The CO recovered from the adsorption tower 18' by the vacuum pump 20 under reduced pressure conditions is taken out to the flow path 21 through the heat exchanger 22. At this time, focusing on the adsorption tower 18, the raw material CO gas flows into the front of the adsorption tower 18, and as it goes to the rear of the tower,
_N2 concentration is rising. In the embodiment (Fig. 1), CO
Since the CO was recovered, the N ₂ remaining in the voids of the tower accompanied the CO and lowered the concentration of CO. Therefore, immediately after the adsorption process is completed, a part of the gas in the product tank 25 is passed through the flow path 26 and the heat exchanger 13, and the product CO is scavenged from the valves 27 and 15 which are in an open state. Therefore, residual N ₂ in the void portion of the adsorption tower 18 is discharged to the outside of the system through the open valve 16, the flow path 23, and the heat exchanger 13'. Note that as the CO concentration in tower 18 increases,
Not only N ₂ but also part of the co-adsorbed N ₂ is removed. Note that approximately 10% of the CO recovered as a product is sufficient for scavenging the void area with product CO. In the present invention, for samples A, B, and C, the adsorption pressure
Scavenging with product CO was carried out at a regeneration pressure of 1.2 ata, 0.1 ata, and a tower temperature of 0°C, and CO with a concentration of over 99% could be obtained in both cases. An example of valve operation is shown below.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a flowchart explaining one embodiment of the present invention, and Figure 2 is a flowchart for explaining an embodiment of the present invention.
The performance of the adsorbent during CO recovery is plotted on the horizontal axis with adsorption pressure and
Figure 3 shows the CO recovery performance of the adsorbent at an adsorption temperature of 0°C, the horizontal axis shows the desorption pressure, and the vertical axis shows the CO concentration. The figure shows the CO recovery performance of the adsorbent at an adsorption pressure of 1.2 ata and a desorption pressure of 0.1 ata, with the horizontal axis representing the temperature during adsorption and
FIG. 5, a graph in which CO concentration is selected on the vertical axis, is a flow for explaining another embodiment of the present invention.

Claims (1)

[Claims] 1. A mixed gas mainly containing CO, _N2, etc. is introduced into at least two or more adsorption towers filled with the mineral name sodium faugiasite represented by Na-X as a CO adsorbent, Adsorption pressure 1~5ata,
After CO adsorption is performed under operating conditions with an adsorption temperature of room temperature to -30°C, CO is adsorbed under operating conditions with a desorption pressure of 0.05 to 0.5 ata.
A CO adsorption separation method characterized by desorbing CO. 2. The method according to claim 1, wherein the adsorption column at the end of adsorption is scavenged with the recovered CO gas with a gas flow in the same direction as during adsorption, and then the desorption operation is performed.