JP6538922B2 - Method of producing ethylene oxide - Google Patents

Description

  The present invention relates to a process for the production of ethylene oxide.

Ethylene oxide is today produced by catalytic gas phase oxidation of ethylene with a molecular oxygen containing gas in the presence of a silver catalyst. And the purification method in the manufacturing process of ethylene oxide is as follows roughly (for example, refer to patent documents 1).

First, ethylene and a molecular oxygen-containing gas are subjected to catalytic gas phase oxidation on a silver catalyst to obtain a reaction product gas containing ethylene oxide (reaction step). Next, the reaction product gas obtained is introduced into an ethylene oxide absorber, and brought into contact with an absorbing solution containing water as a main component to recover ethylene oxide as an aqueous solution (absorption step). The recovered aqueous ethylene oxide solution is then sent to the ethylene oxide purification system, and high purity ethylene oxide is obtained through several steps.
The ethylene oxide purification system usually comprises a diffusion step, a dehydration step, a light component separation step, a heavy component separation (purification) step and the like.

Here, with regard to the exhaust gas containing unreacted ethylene discharged from the top of the ethylene oxide absorber, by-product carbon dioxide and water, and further inert gases (nitrogen, argon, methane, ethane, etc.), ethylene oxidation is carried out as it is. Cycle through the process, or take out part of it,
It is a common practice to introduce to a carbon dioxide absorption tower to selectively absorb carbon dioxide with an alkaline absorbing solution and to diffuse and recover carbon dioxide from the absorbing solution.

On the other hand, the molecular oxygen-containing gas that is the reaction raw material contains argon, and as described above, the process circulation can be performed only by circulating the exhaust gas from the top of the ethylene oxide absorber into the ethylene oxidation step or the carbon dioxide absorption step. Argon builds up in the gas. Accumulation of argon in the process circulation gas may increase the pressure of the reaction system, making it impossible to operate at a constant pressure. In addition, when the argon concentration in the process recycle gas becomes too high, the ethylene concentration and the oxygen concentration may decrease to lower the EO reaction rate. Therefore, extracting and purging a part of the exhaust gas from the top of the ethylene oxide absorber (argon purge)
Is usually done.

As described above, the exhaust gas (absorber exhaust gas) from the top of the absorber which is purged with argon contains ethylene which is a raw material for producing ethylene oxide, and the ethylene loss by argon purge is supplied to the ethylene oxidation reactor. Reaches 0.55% of the amount of ethylene
For this reason, it is required to reduce the argon purge amount.

JP-A-62-103072

The present invention has been made in view of the conventional situation as described above, and it is an object of the present invention to provide a novel technology capable of further reducing the amount of argon purge in the process of producing ethylene oxide.

The present inventors have intensively studied in view of the above-mentioned problems. In the process, mixing of trace amounts of nitrogen and argon contained in the molecular oxygen-containing gas supplied into the system from outside the system for use in catalytic gas phase oxidation reaction in the ethylene oxidation reactor causes argon purge It was found that it was one of the causes of the volume increase.

And by controlling the concentration of molecular oxygen (O ₂ ) in the molecular oxygen-containing gas to a predetermined value or more, it is possible to suppress the mixing of nitrogen and argon into the process derived from the molecular oxygen-containing gas. As a result, it has been found that the amount of argon purge can be reduced, and the present invention has been completed.

That is, one aspect of the present invention relates to a method for producing ethylene oxide. In the production method, first, ethylene is absorbed by ethylene oxide in the ethylene oxidation reaction step in an ethylene oxidation reactor by catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst. A step of supplying to a column and contacting with the absorbing solution supplied to the ethylene oxide absorber, supplying a bottom liquid of the ethylene oxide absorber containing ethylene oxide to an ethylene oxide purification system, and purifying ethylene oxide in the ethylene oxide purification system Including. Moreover, the said manufacturing method supplies the carbon dioxide gas absorption column by supplying at least one part of the carbon dioxide gas containing gas discharged | emitted from the tower | column top part of the said ethylene oxide absorption column, and makes the said carbon dioxide gas containing gas contact an absorption liquid. The gas-rich absorbent is withdrawn as the bottom liquid of the carbon dioxide absorption column and supplied to the upper part of the carbon dioxide gas diffusion tower, carbon dioxide is diffused from the carbon dioxide-rich absorbent liquid, and the exhaust gas is discharged from the top of the carbon dioxide tower. Including the step of

And, the method for producing ethylene oxide according to the present embodiment is characterized in that the concentration of molecular oxygen (O ₂ ) in the molecular oxygen-containing gas supplied from the outside of the system into the system is 99.7% by volume or more. is there.

According to the present invention, in the process of producing ethylene oxide, the concentration of molecular oxygen (O ₂ ) in the molecular oxygen-containing gas supplied from the outside of the system to the inside of the system is 99.7% by volume or more. Contamination of nitrogen and argon derived from the gaseous oxygen-containing gas into the process is suppressed.
As a result, it is possible to reduce the amount of argon purge in the ethylene oxide production process.

It is a block diagram showing an example of composition of a process which enforces a manufacturing method of ethylene oxide concerning one embodiment of the present invention. It is a block diagram showing an example of composition of a process which enforces a manufacturing method of ethylene oxide concerning one embodiment of the present invention. It is a block diagram which shows the structural example of the purification process until the ethylene oxide diffused is finally refine | purified.

Hereinafter, specific modes for carrying out the present invention will be described in detail with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the claims,
It is not limited only to the following forms.

«Reaction system»
First, a system for producing ethylene oxide by the oxidation reaction of ethylene (hereinafter, also simply referred to as a “reaction system”) will be described with reference to FIG. FIG. 1 is a block diagram showing an example of the configuration of a process for carrying out the method for producing ethylene oxide according to an embodiment of the present invention.
The production process of ethylene oxide shown in FIG. 1 is roughly divided into three systems of a reaction system, a carbon dioxide gas system, and a purification system.

The "ethylene oxide-containing reaction product gas" used in the present invention is produced in the step of catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst (hereinafter also referred to as "ethylene oxidation reaction step") What is necessary is just that. The technology itself of this catalytic gas phase oxidation reaction is widely known, and conventional knowledge can be appropriately referred to in the practice of the present invention. In addition, there is no restriction | limiting in particular in a concrete form, such as composition of reaction product gas. As an example, the reaction product gas is usually added to a gas such as unreacted oxygen, unreacted ethylene, produced water, carbon dioxide, nitrogen, argon, methane, ethane, etc. in addition to formaldehyde, in addition to 0.5 to 5% by volume ethylene oxide And a trace amount of organic acids such as aldehydes of acetaldehyde and acetic acid.

Referring to FIG. 1, first, the raw material gas containing ethylene or molecular oxygen is supplied to the booster blower 4.
The pressure is increased by the pressure, and then heated by a heat exchanger (not shown) to be supplied to the ethylene oxidation reactor 1. The ethylene oxidation reactor 1 is usually a multi-tubular reactor provided with a large number of reaction tubes filled with a silver catalyst. The reaction product gas produced in the ethylene oxidation reaction step is cooled by passing through a heat exchanger (not shown), and then an ethylene oxide absorber (hereinafter simply referred to as "absorbent tower") 2
Supplied to Specifically, the reaction product gas is supplied from the bottom of the absorber 2. On the other hand, from the top of the absorption tower 2, an absorption liquid containing water as a main component is supplied. Thereby, countercurrent contact of gas and liquid is performed in the inside of absorption tower 2, and ethylene oxide (usually 99 mass% or more) contained in reaction product gas is absorbed by absorption liquid. In addition to ethylene oxide, ethylene, oxygen, carbon dioxide, inert gases (nitrogen, argon, methane, ethane, etc.), low boiling impurities such as formaldehyde produced in the ethylene oxidation reaction step, acetaldehyde, acetic acid, etc. A substantial amount of boiling impurities is also absorbed at the same time. The temperature of the reaction product gas supplied to the absorption tower 2 is preferably about 20 to 80 ° C. The composition of the absorbing solution is not particularly limited, and in addition to one containing water as a main component, propylene carbonate as disclosed in JP-A-8-127573 may be used as the absorbing solution. Also, if necessary, additives may be added to the absorbing solution. As an additive which may be added to absorption liquid, an antifoamer and a pH adjuster are mentioned, for example. As the antifoaming agent, any antifoaming agent may be used as long as it is inert to ethylene oxide and by-product ethylene glycol etc. and has the defoaming effect of the absorbing liquid, but as a representative example, The water-soluble silicone emulsion is effective because it is excellent in the dispersibility in the absorbing liquid, the dilution stability, and the thermal stability. Moreover, as a pH adjuster, the compound which can melt | dissolve in absorption liquid, such as hydroxide and carbonate of alkali metals, such as potassium and sodium, is mentioned, for example, and potassium hydroxide or sodium hydroxide is preferable. The pH of the absorbing solution is preferably 5 to 12, more preferably 6 to 11.

As the absorption tower 2, a tray type or packed tower type absorption tower can usually be used. As the operating conditions of the absorption tower 2, the ethylene oxide concentration in the reaction product gas is 0.5 to 5% by volume,
Preferably, it is 1.0 to 4% by volume, and the operating pressure of the absorption tower 2 is 0.2 to 4.0 MPa gau
It is ge, preferably 1.0 to 3.0 MPa gauge. The absorption operation is more advantageous as the pressure is higher, but the possible value can be determined according to the operating pressure of the oxidation reactor. The molar flow ratio (L / V) of the absorbing solution to the reaction product gas is usually 0.30 to 2.00. In addition, the space linear velocity (GHSV [NTP]) in the standard state of the reaction product gas is usually 400 to
It is 6000 h ⁻¹ .

Ethylene, oxygen, carbon dioxide, inert gas (nitrogen, not absorbed in the absorption tower 2
A gas containing argon, methane, ethane), an aldehyde, an acidic substance and the like is discharged from the top of the absorber 2 through a conduit 3. Then, the exhaust gas is pressurized by the pressure raising blower 4 and then circulated to the ethylene oxidation reactor 1 through the conduit 5. The details of the ethylene oxidation reaction step are as described above. Here, the ethylene oxidation reaction step is usually carried out under pressure (1.0 to 3.0) in an oxidation reactor equipped with a large number of reaction tubes filled with a silver catalyst.
It is carried out under the conditions of pressure (about MPa gauge). For this reason, before circulating the exhaust gas from the top of the absorption tower 2 to the ethylene oxidation reaction step, it is necessary to increase the pressure using a pressurizing means such as the pressurizing blower 4 or the like.

In the present invention, molecular oxygen (O ₂₎ in a molecular oxygen-containing gas supplied from the outside of the system into the system is
Is characterized by having a concentration of 99.7% by volume or more. Here, “molecular oxygen-containing gas supplied from outside the system into the system” refers to molecular oxygen-containing gas supplied to the conduit 3 connecting the top of the absorption tower 2 and the booster blower 4 (see FIG. 1). Mean “as shown as“ O ₂ ”.

As described above, in the process of aiming to reduce the amount of argon purge in the process of producing ethylene oxide, the present inventors are supplied from the outside of the system into the system for use in the catalytic gas phase oxidation reaction in the ethylene oxidation reactor. It has been found that the incorporation of trace amounts of nitrogen and argon contained in the molecular oxygen-containing gas into the process is one of the causes of the increase in the amount of argon purge. And by controlling the concentration of molecular oxygen (O ₂ ) in the molecular oxygen-containing gas to a predetermined value or more, it is possible to suppress the mixing of nitrogen and argon into the process derived from the molecular oxygen-containing gas. It has been found that it is possible to reduce the amount of argon purge, and to complete the present invention.

In the present invention, molecular oxygen (O 2) in the molecular oxygen-containing gas supplied into the system
The concentration of ₂ ) needs to be 99.7% by volume or more, but there is no particular limitation on the specific method for obtaining the molecular oxygen-containing gas containing such a high concentration of O ₂ . For example, it is possible to obtain the above-described high concentration molecular oxygen-containing gas by a technique such as a cryogenic separation method or a PSA method.

The inventors of the present invention also studied reduction of the argon purge amount from the viewpoint different from the above, and the shaft seal device of the pressure-boosting blower for pressurizing the source gas supplied to the ethylene oxidation reactor ( It was also found that the incorporation of nitrogen from the so-called shaft seal) into the process was also one of the causes of the increased argon purge amount. And it discovered that mixing of nitrogen to the process from the said pressure rising blower could be suppressed also by employ | adopting the centrifugal compressor whose sealing system of a shaft sealing apparatus is a dry gas sealing system as said pressure rising blower.

The dry gas seal system generates gas pressure by rotation at the narrow seal portion of the vertical end face, and makes the gas film non-contact (the gap is a few microns level) and exerts the function of the seal while generating a minimal gas leak It is a thing. In addition, the centrifugal compressor itself provided with a dry gas seal as a shaft seal device belongs to a well-known technology, and a large number of documents regarding this also exist.

Here, according to the study by the present inventors based on the above findings, theoretically, a molecular oxygen-containing gas having a concentration of molecular oxygen (O ₂ ) of 99.7% by volume or more is used, and It was thought that argon purge would be unnecessary if the above-mentioned predetermined centrifugal compressor was used as a pressure rising blower. For this reason, when the process of producing ethylene oxide was carried out using the above two techniques in combination and without performing the argon purge, it is surprisingly considered that only the argon purge can be discharged out of the system. A phenomenon was observed that the amount of nitrogen during the process was significantly reduced over time. As described above, if the amount of nitrogen in the process is significantly reduced with time, an imbalance occurs in the mass balance of the raw material gas supplied to the ethylene oxidation reactor, specifically, the operation in the reaction system. There is a new problem that the pressure decreases.
Therefore, when carrying out the process for producing ethylene oxide without using the above two techniques in combination and without performing the argon purge, an inert gas (nitrogen, argon, etc. (preferably nitrogen, etc.) with a molecular oxygen-containing gas) It has been found that it is preferable to carry out the reaction while feeding it into the system (see Example 2).

«Carbon dioxide system»
As shown in FIG. 1, at least a portion of the gas (carbon dioxide gas-containing gas) discharged from the top of the absorption tower 2 is boosted by the pressurizing means such as the pressure-boosting blower 4 and the like to the carbon dioxide absorption tower 7 through the conduit 6. Supplied. Hereinafter, a carbon dioxide gas recovery system (hereinafter, also simply referred to as “carbon dioxide gas system”) starting with the introduction of gas to the carbon dioxide gas absorption tower 7 will be described with reference to FIG. 1.

As described above, the gas discharged from the top of the absorption tower 2 is pressurized (through the conduit 6)
When introduced into the carbon dioxide absorption tower 7, the gas pressure at that time is 0.5 to 4.0 MPa gau
The gas temperature is adjusted to about 80 to 120 ° C. The carbon dioxide gas diffusion tower 8 is installed at the rear stage of the carbon dioxide gas absorption tower 7, and the alkaline absorbing liquid is supplied from the bottom of the carbon dioxide gas diffusion tower 8 to the upper portion of the carbon dioxide gas absorption tower 7. Then, carbon dioxide gas contained in the gas introduced into the carbon dioxide gas absorption column 7 in a countercurrent contact with the alkaline absorbing liquid, a small amount of inert gas (eg, ethylene, methane, ethane, oxygen, nitrogen, argon, etc.) ) Is absorbed. The unabsorbed gas discharged from the top of the carbon dioxide absorber 7 is recycled to the conduit 3 and mixed with oxygen, ethylene, methane and the like to be newly replenished, and then recycled to the ethylene oxidation reactor 1.

The carbon dioxide-rich absorbent which has absorbed carbon dioxide gas in the carbon dioxide absorption column 7 is withdrawn from the bottom of the carbon dioxide absorption column, and then the pressure 0.01 to 0.5 MPa gauge, temperature 80 to 1
The temperature is adjusted to about 20 ° C., and is supplied to the top of the carbon dioxide gas stripping tower 8 equipped with a reboiler 9 at the bottom. In the liquid supply section at the upper part of the carbon dioxide gas diffusion tower 8, the absorbing liquid causes a pressure flash due to the pressure difference between the carbon dioxide gas absorption tower 7 and the carbon dioxide gas diffusion tower 8. Thereby, 10 to 8 in the absorbing solution
0% by volume of carbon dioxide gas and most of the inert gas are separated from the absorption liquid, and carbon dioxide gas stripping tower 8
It is discharged as exhaust gas from the top of the tower. In the present embodiment, as shown in FIG. 1, it is preferable to use the exhaust heat of the exhaust gas as a heat source of the ethylene oxide purification tower in the purification system (this will be described later in detail). Here, from the viewpoint of reducing the amount of steam supplied to the reboiler 9 of the carbon dioxide gas diffusion tower 8, the smaller the operating pressure of the carbon dioxide gas diffusion tower 8, the better. Specifically, the operating pressure of the carbon dioxide gas diffusion tower 8 is preferably 0 to 0.1 MPa gau
ge, more preferably 0.01 to 0.015 MPa gauge.

The remaining carbon dioxide-absorbing liquid from which part of carbon dioxide gas has been separated by the above-described pressure flash enters the gas-liquid contact unit 10 provided below the liquid supply unit, and the vapor and gas-liquid generated from the reboiler 9 In a countercurrent contact with a gas mainly composed of carbon dioxide gas generated from the portion below the contact portion 10, a part of carbon dioxide gas in the absorbing solution and most of the other inert gases are separated from the absorbing solution. From the top of the gas-liquid contact portion 10 by the series of processes in the carbon dioxide gas system, preferably the carbon dioxide gas diffusion tower 8 in the lower portion of the gas-liquid contact portion 10 corresponds to one theoretical plate number or more required for gas-liquid contact. From the inside, carbon dioxide of high purity is obtained. That is, the inert gas in the carbon dioxide absorbing liquid at the gas-liquid contact portion 10 is dissipated by causing a countercurrent gas-liquid contact with the carbon dioxide gas containing a very small amount of inert gas rising from the lower part and water vapor, This makes the concentration of inert gas extremely low. Therefore, carbon dioxide gas with high purity can be obtained by taking out the released gas.

«Purification system»
The absorption liquid which absorbed ethylene oxide in the absorption tower 2 is sent to an ethylene oxide purification system (hereinafter, also simply referred to as "purification system") as the bottom liquid of the absorption tower 2. There is no restriction | limiting in particular about the specific form of a refinement | purification system, The conventionally well-known knowledge may be referred suitably. As an example, the purification system usually comprises a diffusion step, a dehydration step, a light separation step, a heavy separation (purification) step and the like. Hereinafter, a purification system consisting of several of these steps will be described with reference to FIGS. 2 and 3. FIG. 2 is a block diagram showing an exemplary configuration of a process for carrying out a process for producing ethylene oxide according to an embodiment of the present invention.

The bottom liquid (absorption liquid) of the absorption tower 2 is usually preheated to a temperature suitable for the emission in the separation tower 11 before being supplied to the ethylene oxide separation tower (hereinafter, also simply referred to as “the separation tower”) 11 Be done. Specifically, as shown in FIG. 2, the bottom liquid (absorbent liquid) of the absorber 2 is supplied to the heat exchanger 13 through the conduit 12. Then, in this heat exchanger 13, heat exchange is performed with the bottom liquid of the diffusion tower 11, and if necessary, it is heated by the heater 14, and the bottom liquid (absorption liquid) of the absorption tower 2 Is heated to a temperature of about 70 to 110.degree. In the present embodiment, the bottom liquid (absorption liquid) of the absorption tower 2 heated by heat exchange with the bottom liquid of the diffusion tower 11 is
The gas-liquid separation tank 16 is supplied through the conduit 15. In the gas-liquid separation tank 16, the light gas of the inert gas including a part of ethylene oxide and water is separated, discharged through the conduit 17, and supplied to the ethylene oxide reabsorption tower (not shown). On the other hand, the remaining absorption liquid that has flashed the light gas is supplied to the top of the diffusion tower 11 through the conduit 18. The residence time of the absorbing liquid can be shortened by considering as short as possible the arrangement distance of the portion where ethylene oxide coexists with water particularly under high temperature conditions as in the case of the conduit 18 As a result, it can contribute to the prevention of by-production of ethylene glycol.

Subsequently, for example, as shown in FIG. 2, a heating medium such as water vapor is supplied to the reboiler 19 and the diffusion tower 11 is heated using the heating medium heated in the reboiler 19 or the tower of the diffusion tower 11 The diffusion tower 11 is heated by supplying steam directly to the bottom. By heating the diffusion tower 11 in this manner, ethylene oxide (usually 99% by mass or more) contained in the absorbing liquid supplied from the top of the diffusion tower 11 is dissipated, and the conduit from the top of the diffusion tower 11 Exhausted after 20 hours. In addition, the operating condition of the stripping tower 11 is that the overhead pressure is usually 0
. 01 to 0.20MPa gauge, preferably 0.03 to 0.06MPa gaug
e. The lower the pressure at the top of the column, the lower the temperature in the column, and as a result, there is a tendency that by-production of ethylene glycol from ethylene oxide in the column is suppressed. However,
Since ethylene oxide is a relatively easily ignited substance, from the viewpoint of preventing the leakage of oxygen into the system, the operation below the atmospheric pressure is not usually performed, and as described above, at a pressure slightly higher than the atmospheric pressure It is driven. The temperature at the top of the stripping tower 11 is usually 8 at the top.
The temperature is 5 to 120 ° C., and the bottom temperature is usually 100 to 130 ° C.

The remaining absorption liquid after ethylene oxide is released is extracted as the bottom liquid of the separation tower 11 as shown in FIG. 2, and is supplied to the upper part of the absorption tower 2 as the absorption liquid in the absorption tower 2, and is circulated and used It can be done. However, in order to adjust the composition of the absorbing solution, fresh water and, if necessary, the additives described above may be supplied to the absorber 2 through a separately provided conduit. In addition, absorption tower 2
It is preferable to keep the concentration of ethylene glycol in the absorbing solution to be supplied constant. For this reason, a part of the absorption liquid circulating between the absorption tower 2 and the stripping tower 11 is extracted from the bottom of the stripping tower 11. Here, the bottom liquid of the stripping tower 11 contains substantially no ethylene oxide. Specifically, the concentration of ethylene oxide contained in the bottom solution is preferably 10 ppm by mass
Or less, more preferably 0.5 mass ppm or less. The bottom liquid contains ethylene glycol by-produced in the absorbing liquid between the ethylene oxidation reaction step and the ethylene oxide releasing step, and a portion thereof is withdrawn through the conduit 21 and the conduit 22. The liquid withdrawn through the conduit 22 is subjected to a combustion process or supplied to an ethylene glycol concentration step for concentrating and recovering the ethylene glycol contained therein. Furthermore, depending on the case, ethylene glycol contained in the extracted solution is as it is or after being subjected to an ethylene glycol concentration step, as disclosed in Japanese Patent Publication No. 45-9926 or Japanese Patent Publication No. 4-28247. In addition to chemical treatments, it is also possible to recover as a fiber grade product by applying physical treatments in some cases. In addition, since the bottom liquid of the diffusion tower 11 also contains low boiling impurities such as formaldehyde and high boiling impurities such as acetaldehyde and acetic acid, part of the bottom liquid is extracted outside the system as described above. The advantage is also obtained that the accumulation of these impurities in the absorption liquid circulated to the absorption tower 2 can be prevented. On the other hand, the bottom of the stripping tower which has not been withdrawn through the conduit 22 is cooled by heat exchange with the bottom of the absorber 2 by passing through the heat exchanger 13, to the top of the absorber 2. It is circulated with.

The ethylene oxide-laden emissions that are dissipated from the top of the stripping tower 11 are sent through the conduit 20 to the stripping tower condenser 25 where the cooling water passes through the conduit 23 and the conduit 24, and the condensate is discharged from the conduit 2.
6 to the top of the stripping tower 11, and the uncondensed vapor is supplied to the dewatering tower 28 (FIG. 3) through the conduit 27.

The ethylene oxide-containing vapor supplied to the dewatering tower 28 comes in contact with the liquid to be refluxed through the conduit 29 to become a higher ethylene oxide concentration vapor, and the liquid with low ethylene oxide concentration withdrawn from the bottom is the stripping condenser through the conduit Sent to 25

The ethylene oxide-containing vapor discharged from the top of the dewatering tower 28 is sent to the dewatering tower condenser 33 through which the cooling water passes through the conduit 30 and the conduit 31 and the conduit 32, and a part of the condensate is dewatered through the conduit 29. Reflux to the top of the column 28 and uncondensed vapor (deoxidized gas containing ethylene oxide) of the dehydrating column condenser 33 passes through the conduit 34 and an ethylene oxide reabsorption column (not shown)
Supplied to In the ethylene oxide reabsorption tower, ethylene oxide is resorbed by the countercurrent contact with the absorbing liquid as in the absorption tower 2 described above. Here, with regard to the composition and pH of the absorbent used for the reabsorption of ethylene oxide in the reabsorption tower, the form of the reabsorption tower (plate column type or packed column type), the operating conditions, etc. Is the same as The bottom liquid of the ethylene oxide reabsorption column is a purification system (the same as the bottom liquid of absorption column 2 described above)
Specifically, in the present embodiment, the gas is circulated to the stripping tower 11). On the other hand, uncondensed gas that has not been absorbed in the ethylene oxide reabsorption column is discharged from the top of the column. The uncondensed gas discharged from the ethylene oxide reabsorption column is circulated to the absorption column 2 or the carbon dioxide gas absorption column 7 after the pressure is increased by the pressurizing means (not shown in the embodiment shown in FIG. 1). , To the absorption tower 2). However, preferably, the uncondensed gas is circulated to the carbon dioxide gas absorption tower 7. Since the non-condensed gas contains a large amount of carbon dioxide gas (usually about 5 to 60% by volume), the gas supplied from the absorption tower 2 to the carbon dioxide gas absorption tower 7 with such a configuration It is possible to increase the concentration of carbon dioxide in the medium. As a result, the occurrence of a problem caused by the increase in the amount of carbon dioxide in the gas supplied to the carbon dioxide absorption tower 7 can be prevented, and the carbon dioxide can be recovered more efficiently from the ethylene oxide production process. More specifically, by reducing the amount of steam input to the reboiler 9 of the carbon dioxide gas diffusion tower 8, reducing the input amount of carbon dioxide absorption promoter, and reducing the gas volume sent from the absorption tower 2 to the carbon dioxide absorption tower 7. At least one industrially very advantageous effect is obtained: reduction of power of boost blower, miniaturization of equipment of carbon dioxide gas absorption column 7, improvement of ethylene oxide yield by reduction of carbon dioxide concentration at the inlet of ethylene oxidation reactor 1 .

The remainder of the condensate from the dewatering column condenser 33 is supplied to the light separation column 37 through a conduit 36.
The ethylene oxide vapor which is heated by the reboiler 38 of the light separation column 37 is heated by a heating medium such as steam through the conduit 39, and the ethylene oxide vapor containing light from the top of the light separation column 37 flows into the conduit 41 and the conduit 42 through the conduit 40 The coolant is sent to the light separation column condenser 43 through which the cooling water passes, and the condensate is refluxed to the top of the light separation column 37 through the conduit 44, and the uncondensed vapor of the light separation column condenser 43 (ethylene oxide containing noncondensed gas) Is fed through conduit 45 to the ethylene oxide reabsorption column to recover ethylene oxide.

The bottom liquid of the light separation column 37 is an ethylene oxide purification column (hereinafter referred to simply as “
To the purification tower) 47). The purification tower 47 is provided with a reboiler 48 at the bottom. And, in this embodiment, the reboiler 48 of the purification tower 47 is
As a heating medium for heating, steam having a pressure of about 0.05 to 0.10 MPa gauge is supplied. However, the heating medium may be another one, for example, glycol aqueous solution, warm water, etc. may be used.

As described above, the heating medium for heating the reboiler 48 of the purification tower 47 is preferably heated by heat exchange with the exhaust gas from the top of the carbon dioxide gas stripping tower 8 described above. In order to achieve this, a heat exchanger 57 is installed on the circulation path 56 to the reboiler 48 of the heating medium (steam). Then, the exhaust gas from the top of the carbon dioxide gas diffusion tower 8 is supplied to the heat exchanger 57 through the conduit 58, whereby heat exchange occurs with the heating medium (steam), and the heating medium is heated. (Water vapor) is heated. The exhaust gas after heat exchange in the heat exchanger 57 may be circulated to the gas-liquid separation unit 10 of the carbon dioxide gas diffusion tower 8 again as shown in FIG.

Here, the purification tower 47 is characterized in that the temperature of the purification tower 47 is lower in operating temperature than other distillation towers, since the operation at high temperature is not preferable for safety reasons. The top temperature of the carbon dioxide gas stripping column 8 is a relatively low temperature of 87 ° C., and if the exhaust gas of this temperature is used, the refining tower 47 can be used as a heat source. That is, the exhaust gas from the top of the carbon dioxide gas diffusion tower 8 is a vapor containing carbon dioxide gas, and in order to enhance the heat recovery efficiency of the vapor in the exhaust gas, it is preferable that the temperature difference between the materials to be exchanged is large. Thus, the lower the temperature at which the exhaust gas is used for heat exchange, the better.

As described above, by supplying the heating medium to the reboiler 48, the purification is performed with the column bottom temperature of the purification column 47 at 35 to 80 ° C. and the column pressure of 0.1 to 0.80 MPa gauge. From the top of 47, the top temperature 12 to 75 ° C., the top pressure 0.10 to 0.8
A 0 MPa gauge ethylene oxide vapor is sent to the purification tower condenser 51 where the cooling water passes through the conduit 49 and the conduit 50. Then, ethylene oxide is liquefied in the purification column condenser 51, and a part thereof is supplied as a reflux solution to the top of the purification column 47 through the conduit 52, and the remainder is withdrawn as the product ethylene oxide (product EO) through the conduit 53. The uncondensed vapor (ethylene oxide-containing uncondensed gas) of the purification column condenser 51 is supplied through the conduit 54 to the ethylene oxide reabsorption column to recover ethylene oxide.

The bottom liquid of the purification column 47 is withdrawn through the conduit 55 as necessary for heavy fraction separation of high boiling impurities such as acetaldehyde, water, and acetic acid.

As described above, the uncondensed vapor discharged from the purification system (in the embodiment shown in FIG. 3, the uncondensed vapor derived from the dehydration column condenser 33, the light separation column condenser 43, and the purification column condenser 51) Contains ethylene oxide. For this reason, these uncondensed vapors are supplied to the above-mentioned ethylene oxide reabsorption tower.

Hereinafter, although the embodiment of the present invention is described in more detail using an example, the technical scope of the present invention is not limited to only the following form.

[Comparative example]
Ethylene oxide was produced by the process for producing ethylene oxide shown in FIGS. In the present comparative example, centrifugal compressors (two units) provided with oil film seals were used as the pressure rising blower 4 as the shaft sealing device. Also, a conduit 3 connecting the top of the absorption tower 2 and the booster blower 4
As the molecular oxygen-containing gas to be supplied to, the one having an O ₂ concentration of 99.60% by volume (the balance being argon) was used. Here, the circled numbers 1 to 5 shown in FIG.
The component amounts and operating conditions (flow rate, pressure, temperature) at each site up to are shown in Table 1 below.

Example 1
Ethylene oxide was produced by the process for producing ethylene oxide shown in FIGS. In the present embodiment, centrifugal compressors (two units) provided with oil film seals are used as the pressure rising blower 4 as the shaft sealing device. Also, a conduit 3 connecting the top of the absorption tower 2 and the booster blower 4
As the molecular oxygen-containing gas to be supplied to, the one having an O ₂ concentration of 99.95% by volume (the balance being argon) was used. Here, the circled numbers 1 to 5 shown in FIG. 1 during steady operation of the present embodiment.
The component amounts and operating conditions (flow rate, pressure, temperature) at each site up to are shown in Table 2 below.

Example 2
Ethylene oxide was produced by the process for producing ethylene oxide shown in FIGS. In the present embodiment, centrifugal compressors (two units) provided with a dry gas seal were used as the pressure rising blower 4 as the shaft sealing device. Further, as the molecular oxygen-containing gas supplied to the conduit 3 connecting the top of the absorption tower 2 and the booster blower 4, one having an O ₂ concentration of 99.95% by volume (remaining argon) was used. Here, the component amounts and the operating conditions (flow rate, pressure, temperature) in each part from the circled number 1 to the circled number 5 shown in FIG. 1 during steady operation of this example are shown in Table 3 below. In the present embodiment, since the argon purge is not performed, the flow rate in the circled number 5 is zero. Also, by supplying nitrogen (N ₂ ) gas together with molecular oxygen-containing gas at a flow rate of 1.1 Nm ³ / minute to the conduit 3 connecting the top of the absorption tower 2 and the booster blower 4, the material balance is balanced. I did.

The amount of methane and the amount of ethylene loss in the argon purge calculated from the above-described comparative example and Examples 1 and 2 were calculated as follows.

From the results shown in Table 4, it is understood that the argon purge amount can be reduced by adopting the configuration of the present invention (supplying the high concentration O ₂ -containing gas into the system) (Example 1). Also,
It can be seen that, by further using a centrifugal compressor equipped with a dry gas seal as a shaft seal device as a pressure-boosting blower, it is possible to carry out an ethylene oxide manufacturing process without performing the argon purge operation itself (Example 2). In this case, it is also necessary to separately supply an inert gas such as nitrogen together with the molecular oxygen-containing gas in the system in order to balance the mass balance.

From the above, according to the present invention (further in combination with the above-described predetermined centrifugal compressor),
It can be seen that a very economical process for producing ethylene oxide is provided.

DESCRIPTION OF SYMBOLS 1 ethylene oxidation reactor 2 ethylene oxide absorption tower 4 pressure | voltage rise blower 7 carbon dioxide gas absorption tower 8 carbon dioxide gas diffusion tower 9 reboiler 10 gas-liquid contact part 11 ethylene oxide diffusion tower 13 heat exchanger 14 reboiler 16 gas-liquid separation tank 19 diffusion tower reboiler 25 emission Tower condenser 28 Dewatering tower 33 Dewatering tower condenser 37 Light separation column 38 Light separation column reboiler 43 Light separation column condenser 47 Ethylene oxide purification tower 48 Purification tower reboiler 51 Purification tower condenser 56 Circulation path 57 Heat exchanger 58 conduit

Claims (3)

A reaction product gas containing ethylene oxide generated in an ethylene oxidation reaction step in an ethylene oxidation reactor is fed to an ethylene oxide absorption tower, wherein ethylene is catalytically vapor phase oxidized with a molecular oxygen-containing gas in the presence of a silver catalyst. Contacting the absorbing liquid supplied to the absorption column, supplying the bottom of the ethylene oxide absorption column containing ethylene oxide to an ethylene oxide purification system, and purifying ethylene oxide in the ethylene oxide purification system;
At least a part of the carbon dioxide gas-containing gas discharged from the top of the ethylene oxide absorber is supplied to the carbon dioxide gas absorption tower, and the carbon dioxide gas rich absorbent obtained by bringing the carbon dioxide gas-containing gas into contact with the absorbent Extracting the bottom liquid of the gas absorption column and supplying it to the upper part of the carbon dioxide gas diffusion column, desorbing carbon dioxide gas from the carbon dioxide gas rich absorption liquid, and discharging the carbon dioxide gas from the top of the carbon dioxide gas diffusion column as exhaust gas;
A process for producing ethylene oxide containing
Der concentration 99.7% by volume or more of molecular oxygen (O ₂₎ in the molecular oxygen-containing gas supplied from outside the system into the system it is,
The manufacturing method of ethylene oxide which pressurizes the said source gas containing ethylene using the centrifugal compressor provided with the dry gas seal as a shaft seal apparatus, and supplies the said source gas pressure | voltage-risen to the said ethylene oxidation reactor . The method for producing ethylene oxide according to claim 1 , wherein the argon purge is not performed. The method for producing ethylene oxide according to claim 1, which is performed while supplying an inert gas into the system together with the molecular oxygen-containing gas.