JPH08127573A - Recovery of ethylene oxide - Google Patents

Abstract

PURPOSE: To recover ethylene oxide with a small loss in recovery and a small energy consumption by using propylene carbonate as an absorbent in recovering the ethylene oxide from a gas mixture containing the ethylene oxide. CONSTITUTION: A gas mixture containing ethylene oxide (preferably at 0.5-5vol.% ethylene oxide concentration) is brought into contact with propylene carbonate as an absorbent to absorb the ethylene oxide therein. The absorbed ethylene oxide is then stripped and separated from the absorbent to recover the ethylene oxide. Although the propylene carbonate may be used alone, a mixture of the propylene carbonate with ethylene carbonate containing at least 40wt.% propylene carbonate may be used. The absorption of the ethylene oxide is preferably carried out at 5-50 deg.C under 2-40kg/cm<2> G pressure and the stripping is preferably performed with heat at 80-140 deg.C under 0.1-3kg/cm<2> G pressure.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for recovering ethylene oxide. More specifically, the present invention provides
A reaction product gas containing ethylene oxide produced by vapor-phase catalytic oxidation of ethylene with oxygen in the presence of a silver catalyst is led to an absorption tower of ethylene oxide, and the absorption liquid containing propylene carbonate absorbs ethylene oxide, and then this liquid is absorbed. To a stripping tower for stripping and separating ethylene oxide to recover ethylene oxide. This recovery method has less recovery loss of ethylene oxide in the absorption and diffusion steps and less energy consumption as compared with the conventional method using an absorbent containing water as a main component.

[0002]

2. Description of the Related Art Conventionally, the recovery of ethylene oxide has been carried out as follows by using an absorbent containing water as a main component. That is, a reaction product gas containing 0.5 to 5% of ethylene oxide obtained by vapor-phase catalytic oxidation of ethylene with oxygen in the presence of a silver catalyst is first introduced into an ethylene oxide absorption tower, where water is used as a main component. The absorbent is allowed to come into countercurrent contact with the absorbent at 5 to 40 ° C., and ethylene oxide is absorbed in the absorbent. Next, this liquid is sent to an ethylene oxide stripping tower, and a gas mainly containing ethylene oxide is stripped from the tower top at a temperature of 85 to 140 ° C. by lowering the pressure and stripping with heated steam to recover the ethylene oxide.

Mainly the recovered ethylene oxide, water,
A gas containing nitrogen, an inert gas such as carbon dioxide, methane, ethane, a hydrocarbon such as ethylene and an aldehyde is sent to a refining process to obtain high-purity ethylene oxide as a product. The water after the emission of ethylene oxide is recycled to the absorption tower for reuse. However, this method of recovering ethylene oxide using an absorbent containing water as a main component has two major problems.

One is the problem of by-product of ethylene glycol during recovery. That is, water reacts with ethylene oxide to produce ethylene glycol, absorbs ethylene oxide gas, transfers the liquid, and in the process of heat dissipation,
The conversion of a part of ethylene oxide into ethylene glycol cannot be suppressed. This amount ranges from 3 to 15% of the total ethylene oxide. Due to recent economic and social conditions, it is often demanded to produce the whole amount of ethylene oxide without producing ethylene glycol. In such a case, however, a system using water as an absorbing solution causes a great production loss. Even when ethylene glycol is produced for the purpose of converting a part or the whole amount of ethylene oxide to ethylene glycol, ethylene glycol produced as a by-product in the ethylene oxide recovery step is aldehyde or organic acid produced in the ethylene oxidation reaction step. Since it contains a large amount of impurities such as, it is difficult to obtain a highly pure product as an industrial product.

The second problem is the problem of energy loss during recovery. The absorption of ethylene oxide is preferably at a relatively low temperature, generally 5 to 40 ° C., and the emission needs to be higher than that, generally at a temperature of 85 to 130 ° C. Therefore, the absorbing liquid containing water as a main component is repeatedly heated during the time it is sent from the absorption tower to the desorption tower and cooled during the time it is circulated from the desorption tower to the absorption tower. In this process, some energy is recovered by using it for heating other low temperature fluids, but it is difficult to economically recover energy from water equivalent to hot water. Generally, it is difficult to recover the energy of hot water of 70 to 100 ° C. or less, and the heat is discharged to the outside of the process as heat dissipation to the cooling water. Since water has a large specific heat, this results in a great loss of heat energy.

Several methods have been proposed as prior art to solve the problems when water is used as an absorbent for ethylene oxide. For example, JP-A-49-94612
The publication proposes a method of simultaneously separating ethylene oxide and carbon dioxide from a gas mixture obtained by catalytic oxidation of ethylene with oxygen using methanol as an absorbing liquid. Since the specific heat of methanol is less than half that of water, if the heat recovery system can be assembled properly, the heat loss, which is a drawback when using water, can be reduced. However, since methanol has a low boiling point of 65 ° C. and reacts with ethylene oxide like water to form methyl glycol ether, absorption of ethylene oxide must be carried out at a low temperature of −15 to −50 ° C., which is effective. The heat recovery system is difficult to assemble. In addition, when ethylene oxide is absorbed at a higher temperature than this, not only is the loss of methanol scattered increased, but when the gas after absorbing and removing ethylene oxide is circulated to the oxidation reactor, methanol is contained in the gas. As a result, the oxidation reaction of ethylene has an unfavorable influence such as the combustion of alcohol.

Japanese Patent Publication No. 61-35190 and Japanese Patent Application Laid-Open No. 58-92674 propose a method of using carbon dioxide in the supercritical or (near) supercritical state together with water as an absorbent. In this case, the process up to the step of absorbing ethylene oxide from the gas from the ethylene oxidation reactor using water is the same as the conventional method. Next, without heating the water that absorbed ethylene oxide, it was contacted with carbon dioxide in the (near) supercritical state to extract ethylene oxide into the carbon dioxide solvent side, and then carbon dioxide was separated by depressurizing distillation operation. Ethylene oxide is recovered, and the pressure of carbon dioxide is increased by a compressor and circulated as an extraction solvent again. According to this method, it is possible to prevent heat recovery loss due to heating and cooling of water. However, on the other hand, this method has two drawbacks. One is that although the heat recovery loss can be prevented, the amount of carbon dioxide in the (near) supercritical state is about 35 times as large as that of ethylene oxide to be absorbed, and as an example of sufficient pressure for extraction, 88 kg / cm ² is 73 kg / cm ² G as an example of sufficient pressure to separate ethylene oxide and carbon dioxide, and the pressure difference between the ^two is a large value of 15 kg / cm ² G, so a large amount of energy is required to pressurize carbon dioxide. Is required. That is, there is a tendency that the heat recovery loss merely changes into a boosting energy loss. Furthermore,
The state of carbon dioxide in this (near) supercritical state is maintained (the critical condition of carbon dioxide is 31 ° C., 75.1 kg / c
m ² G), the operating pressure becomes high as described above, and the equipment cost is higher than that of the conventional method which is carried out at the emission pressure of about 0.1 to ² kg / cm ² G. Have. Therefore, this method also cannot be an essential solution.

Japanese Patent Publication No. 1-31506 proposes a method of using ethylene carbonate (ethylene carbonate) as an absorbent for ethylene oxide. Ethylene carbonate has a specific heat of only about 40% of water and a boiling point of 2
Since the temperature is as high as 39 ° C., the compound is characterized as having less scattering loss than water, having the ability to absorb ethylene oxide more than water, and being stable without reacting directly with ethylene oxide. By using this ethylene carbonate, it is possible to prevent the by-product of ethylene glycol and to reduce the heat recovery loss by about 60%.

[0009]

However, the above method has the following problems. First, since the freezing point is high, it is not possible to operate with an efficient absorption liquid amount, and it is impossible to realize the above-mentioned reduction of heat recovery loss. The temperature of the conventional absorption operation using water is 5 to 40 ° C. However, since ethylene carbonate is a substance having a freezing point of 39 ° C., it is impossible to operate at such a temperature, and in order to prevent troubles due to solidification at any point in the process, it is practically at least 50. ℃
It must be maintained at a temperature above 10 ° C. Therefore, the absorption operation using ethylene carbonate has a smaller absorption capacity as compared with the case where water is used and must be treated at a temperature higher than 10 ° C., and the amount of circulating absorption liquid must be increased. -The effect of reducing the heat recovery loss during heat dissipation will be greatly impaired.

Secondly, since ethylene carbonate has a high freezing point, it is necessary to keep a large amount of the absorbing solution warm even when the plant is out of operation, which requires the cost of heating equipment and utilities. Even if the temperature of ethylene carbonate is kept high as described above, the temperature difference with ethylene carbonate is usually required to be 15 to 20 ° C. at the time of indirect heat exchange with cooling water of low temperature. In this case, there are serious problems in terms of operation, heat retention, and maintenance, such as partial solidification, which tends to reduce heat exchange efficiency and tend to clog pipes. As mentioned above, none of the technologies have sufficient ability to be used as an absorbent of ethylene oxide, which replaces the currently practiced water. When the conditions required for the ethylene oxide absorbent are summarized, it is preferable that 1) the ethylene oxide absorption capacity per weight is excellent, and that it is at least equal to or higher than that of water. 2) Small specific heat. 3) It has no reactivity with ethylene oxide or side reaction products. 4) No solidification or deterioration within the normal operating condition range of the plant. 5) The boiling point is high, and the loss of emission and scattering is small.

[0011]

Means for Solving the Problems The inventors of the present invention, as a result of intensive studies under such a background, found that propylene carbonate, as an ethylene oxide absorbent, satisfies all the above conditions, and a process using the same was found. The present invention has been completed by assembling the above. That is, the present invention is a method of contacting a gas mixture containing ethylene oxide with an absorbing liquid to absorb the ethylene oxide, and then releasing and separating the ethylene oxide from the absorbing liquid to recover ethylene oxide. A method for recovering ethylene oxide is characterized by using a carbonate. That is, propylene carbonate has an absorption capacity of 1) ethylene oxide per weight, which is 50% higher than water and 40% higher than ethylene carbonate. 2) The specific heat is as low as 0.4 cal / g · ° C. like ethylene carbonate. 3) Not only is it stable with no direct reactivity with ethylene oxide, but it is also extremely stable against aldehydes and acids that are by-produced in the ethylene oxidation reaction step, and this stability is superior to ethylene carbonate. 4) The freezing point is -49 ° C,
Absorption of ethylene oxide at 5 to 40 ° C. can be adopted without any problem so that coagulation does not become a problem at all under actual operating conditions and the facility cost does not become excessive. Due to such excellent properties, heat recovery when cooling the absorption liquid at the stage of sending the absorption liquid from the desorption process to the absorption process without generating impurities that consume ethylene oxide such as ethylene glycol It is possible to construct an ethylene oxide absorption / emission system that can reduce the loss to about one-third as compared with the case of using water. Hereinafter, each requirement of the method of the present invention will be specifically described.

(Propylene Carbonate) The propylene carbonate used in the present invention is not particularly limited, and industrially used grades can be used as they are. Propylene carbonate may be used alone or as a mixture of propylene carbonate and ethylene carbonate containing at least 40% by weight, preferably at least 50% by weight of propylene carbonate. Hereinafter, propylene carbonate or a mixed solution of propylene carbonate and ethylene carbonate containing at least 40% by weight of propylene carbonate is collectively referred to as propylene carbonate for convenience. As will be described later, the absorption capacity of ethylene oxide is higher when propylene carbonate alone is used, but if the propylene carbonate concentration is 40% by weight or more, it should be used as an ethylene oxide absorption liquid without significantly impairing the characteristics of this propylene carbonate. You can That is, the decrease in absorption capacity is around 10%, and solidification and blockage at the pipe interface of the heat exchanger for cooling do not occur.

(Gas Mixture Containing Ethylene Oxide) The gas mixture containing ethylene oxide used in the present invention refers to a mixture of ethylene oxide and another gas, a typical example of which is ethylene in the presence of a silver catalyst. It is a reaction product gas containing ethylene oxide produced by vapor phase catalytic oxidation with lower oxygen. The reaction product gas is usually 0.5 to 5% of ethylene oxide, unreacted oxygen, unreacted ethylene, generated water, carbon dioxide gas, nitrogen, methane, ethane and the like gas, formaldehyde and acetaldehyde aldehydes, Contains trace amounts of organic acids such as acetic acid.

(Operation for absorbing ethylene oxide) The reaction product gas is cooled and then introduced into an ethylene oxide absorption tower. Here, the reaction product gas is supplied from the bottom of the tower, and the absorbing liquid propylene carbonate is supplied from the top of the tower to carry out countercurrent contact of gas and liquid. The temperature of the ethylene oxide-containing mixed gas supplied to the absorption tower is preferably in the range of about 20-80 ° C. The temperature of the absorbing liquid supplied to the absorption tower is about 10
It is preferably in the range of 35 ° C. By this operation, most of ethylene oxide is absorbed by propylene carbonate. Since propylene carbonate is also a good absorbent for carbon dioxide gas, carbon dioxide gas is partially absorbed at the same time. Experimental results have shown that most of the produced water is absorbed as well. However, the amount of other nitrogen, methane, ethylene, ethane, oxygen, etc. absorbed is very small as in the case of using water. These gases other than ethylene oxide are diffused together with ethylene oxide in a later desorption tower, so these non-condensable gas and ethylene oxide gas are separated, and the non-condensable gas circulates to the absorption tower inlet. .

The operating condition of the absorption tower is that the molar flow ratio of the absorbing liquid to the amount of ethylene oxide supplied (L / V is usually 0.10 to 0.35. In addition, in the standard state of the mixed gas containing ethylene oxide. Space linear velocity (GHSV [NT
P]) is usually 400 to 4000 hr ⁻¹ . Further, the operating temperature of the absorption tower, that is, the absorption of ethylene oxide,
It is usually carried out at 5 to 50 ° C, preferably 10 to 45 ° C. The lower the absorption capacity, the greater the absorption capacity, but if it is too low, the heat energy loss when cooling the absorption liquid to that temperature increases, and it is disadvantageous that a special cooling medium must be used. On the other hand, if the operating temperature is raised too high, the amount of absorbing liquid required becomes large, not only a large amount of energy is required for liquid circulation but also heat recovery loss increases as a result. Furthermore, if the absorption of ethylene oxide is insufficient, unabsorbed ethylene oxide will be circulated to the oxidation reactor, leading to a production loss. Therefore, the above temperature range is suitable. Since propylene carbonate has a larger ethylene oxide absorption capacity than ethylene carbonate, it can be economically operated even at a temperature exceeding 40 ° C.

The operating pressure of the absorption tower is usually 2 to 40 kg /
cm ² G, preferably 10 to 30 kg / cm ² g. The higher the pressure of the absorption operation, the more advantageous it is, but the value that can be taken is almost determined by the operating pressure of the oxidation reactor. As a result of the absorption experiment by the present inventors, the absorption capacity of ethylene oxide per unit weight of the absorption liquid is about 1.5 times that of propylene carbonate and 1.1 times that of ethylene carbonate as compared with water. There was found. Therefore, it is possible to reduce the amount of the absorbing liquid by 40 to 50% or raise the operating temperature of the absorption tower, as compared with the conventional method using water.

(Propagation and Separation Operation of Ethylene Oxide) The propylene carbonate liquid that has absorbed ethylene oxide is heated and then supplied to the top of the ethylene oxide diffusion column, and gas-liquid contact is made with the emission gas supplied to the bottom of the column. This releases ethylene oxide. Operating conditions are such that the temperature is usually 80-at the top of the tower.
The temperature is 140 ° C., preferably 85 to 120 ° C., and the pressure is usually 0.1 to 3 kg / cm ² G, preferably 0.3 to 1.
It is 5 kg / cm ² G. The bottom of the column becomes high temperature and high temperature due to the pressure loss due to the tray or packing provided in the column for gas-liquid contact. Usually, the temperature is 10 to 25 ° C higher than that at the top of the tower.

In the conventional system using water, steam in which absorbed water itself is heated is used as a gas for diffusion.
This is because even if a non-condensable gas such as nitrogen or carbon dioxide is used, the atmospheric boiling point of water is as low as 100 ° C., and it is difficult to avoid entrainment of a large amount of water. However, the latent heat of vaporization of water is about 50.
Although it is as large as 0 kcal / kg, the tower top temperature is 80 to 14
Since the temperature was as low as 0 ° C, it was difficult to efficiently recover the heat carried away by the entrained steam with little loss. In the present invention using propylene carbonate, it is sufficient to dissipate heat without using a gas for dissipation in the dissipation step. Further, a diffusion gas may be used, and as the diffusion gas, carbon dioxide gas separated and recovered in the carbon dioxide gas removing step, ethylene as a raw material for the catalytic oxidation reaction, or methane as a diluent gas at the catalytic oxidation reaction is used. Non-condensable gases such as Even if these gases are used, the boiling point of propylene carbonate is as high as 242 ° C., so that the amount of propylene carbonate emitted along with ethylene oxide and other components can be negligibly reduced. The water produced by the side reaction in the oxidation reactor can be emitted in an amount corresponding to the amount of the side reaction produced in the emission step. At the same time, some aldehydes and organic acids are also emitted along with them.

Further, in the conventional absorption / desorption system using water, it is sufficient for the process of heating the absorption water which has absorbed ethylene oxide in the absorption tower toward the desorption tower and for producing ethylene glycol in the desorption tower. Since it is exposed to high temperature (80 to 140 ° C), it cannot avoid a large amount of ethylene glycol by-product. The reaction amount of ethylene oxide here ranges from 3 to 15% of the total amount of ethylene oxide. Furthermore, since this absorbed water contains aldehydes and organic acids that are by-products of the oxidation reaction, it is extremely difficult to recover high-quality ethylene glycol from this absorbed water, and much energy is required. In the present invention, there is almost no water in the absorbing liquid, and
It is around% by weight. Therefore, the production of ethylene glycol can be reduced to a small amount of several thousand to several hundreds or less as compared with the case of using water as the absorbed water. The lower the venting pressure is, the more advantageous it is, and the amount of the venting gas is small, but the pressure is required to allow the gas or liquid to flow down in the step of purifying ethylene oxide after the venting, and the above-mentioned pressure is maintained.

The propylene carbonate liquid from which ethylene oxide gas has been diffused is withdrawn from the bottom of the diffusion tower, cooled and circulated to the ethylene oxide absorption tower. The bottom liquid of the stripping tower preferably exchanges heat with the bottom liquid of the absorption tower.
In that case, the temperature of the bottom liquid of the stripping tower is cooled to a range of about 10 to 35 ° C by the heat exchange, while the temperature of the bottom liquid of the absorption tower is adjusted to a range of about 70 to 150 ° C. Preferably. By such heat exchange, a part of the retained heat amount is recovered, but when the temperature falls to a temperature level of hot water of 70 to 100 ° C. or lower, further heat recovery causes a too small temperature difference with the low temperature side medium. However, practical recovery is generally difficult and is removed outside the system by heat exchange with cooling water (sea water at about 10 to 30 ° C., re-cooled water, industrial water, etc.) that is not heat recovered. In the conventional system using water, the specific heat of water is 1 kc
The specific heat of the propylene carbonate of the present invention is about 0.4 kcal / kg ° C. and about 4 ° C.
Only 0%. Therefore, even when the amount (weight) of the absorbent used is the same as that of water, the heat recovery loss in the cooling process as described above can be reduced to about 60%. Furthermore, compared to water, propylene carbonate has 1.5 times the capacity of ethylene carbonate and 1.1 times the capacity of ethylene carbonate, so it is possible to reduce the amount of absorbing liquid or raise the operating temperature of the absorption tower. Therefore, the heat recovery loss can be further reduced, and as a result, the heat recovery loss can be reduced to 25 to 30% of that of the water system.

In a long-term operation, aldehydes, organic acids, and trace amounts of ethylene glycol accumulate in propylene carbonate, which is the absorbing liquid, in very small amounts. There is. But,
This amount may be about 0.002% of the circulating absorbent per hour, which is negligible compared to the reaction amount of ethylene oxide when conventional water is used. Furthermore, since the extracted absorption liquid has a very large difference in boiling point between impurities and propylene carbonate, it can be recovered as propylene carbonate that can be reused by a normal distillation operation or the like. Furthermore, in order to prevent equipment corrosion, operations such as adding a stabilizer such as a neutralizing agent to the absorption liquid or passing the absorption liquid through a device filled with an adsorbent to remove these impurities May be performed, and those operations do not impair the effects of the present invention.

(Process Flow) A structural example of the process according to the present invention will be described with reference to FIG. The configuration of each unit operation device and piping can be implemented with almost the same configuration as the existing water system. The reaction product gas containing ethylene oxide obtained by vapor-phase catalytic oxidation of ethylene with oxygen in the presence of a silver catalyst is
It is supplied to the lower part of the ethylene oxide absorption tower (2) through the pipe (1). This reaction product gas is supplied to the pipe (11) at the top of the tower.
It is countercurrently contacted with the propylene carbonate absorption liquid supplied from the above and absorbs 99% by weight or more of ethylene oxide. In addition to carbon dioxide, some of the produced water and gases such as ethylene are also absorbed at the same time. The gas that is not absorbed (containing ethylene, oxygen, carbon dioxide, nitrogen, argon, methane, ethane, etc.) is circulated through the pipe (3) to the carbon dioxide separation step and the oxidation reaction step. The absorbent that absorbed ethylene oxide exchanges heat with the bottom liquid of the ethylene oxide stripping tower (6) through the pipe of (4), and is further heated to a temperature sufficient for stripping the ethylene oxide from the pipe (5). A stripping gas required for stripping is supplied from a pipe (8) from the bottom of the stripping column, which is guided to the column (6).
A gas centering on carbon dioxide, ethylene, which is a raw material gas for the oxidation reaction, and a part of methane, which is a dilution gas at the time of the oxidation reaction, can be used as the diffusion gas. The gas (7) mainly composed of the released ethylene oxide gas is sent to the ethylene oxide refining step for separating water and light boiling gas after cooling (not shown in the figure). In addition, a part of the light boiling gas separated in this refining step is circulated in the pipe (8) as a gas for releasing ethylene oxide. The propylene carbonate liquid after the stripping is withdrawn from the bottom of the stripping tower through a pipe (9), and a small part is withdrawn from the system through a pipe (10) to prevent the accumulation of aldehydes and acidic substances. After heat exchange with the liquid and further cooling, it is circulated in the pipe (11) as an ethylene oxide absorbing liquid.

[0023]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to this embodiment.

Examples 1 to 11 and Comparative Examples 1 to 9 Using an autoclave having a content of 1.5 L, ethylene oxide was absorbed into water, propylene carbonate, ethylene carbonate and a mixture of propylene carbonate and ethylene carbonate. Equilibrium was measured. Charge 500cc of any of the above liquids into the autoclave,
After purging the inside with nitrogen, heating was performed to a predetermined temperature, and after the temperature was stabilized, the pressure was adjusted to 0.2 kg / cm ² G. Thereafter, a predetermined amount of ethylene oxide was supplied through the raw material supply pipe. To ensure that ethylene oxide remaining in the supply pipe is also supplied to the autoclave, 0.2 kg / cm
Ethylene oxide (EO) in the feed pipe was fed into the autoclave by feeding nitrogen for ² minutes from the same feed pipe. After stirring for 4 hours (600 rpm) and temperature control were continued, the pressure was recorded, the gas and liquid were sampled, and the composition of the gas phase and the liquid phase was determined by gas chromatography. The EO concentration in the gas phase was calculated from the partial pressure measurement value and compared with the gas chromatography analysis value.
Within%, both showed good agreement. The measurement results are shown in Table 1.
Shown in

Examples 1 to 7 are propylene carbonate (PC), Examples 8 to 11 are mixed liquids of propylene carbonate and ethylene carbonate (MIX), Comparative Examples 1 to 1
5 is water and Comparative Examples 6 to 9 are ethylene carbonate (EC)
Is the respective absorption data for. These data are shown graphically and shown in Figures 2-4. FIG. 2 is a comparison of PC and water. The EO concentration in the liquid phase at the same gas phase EO concentration and the same temperature is, for example, as shown in the example of FIG.
At a concentration of 15 mol%, the liquid phase EO concentration at 40 ° C. is 2.6% by weight with water and 4.0% by weight with PC. From FIG. 2, it was found that PC had about 1.5 times the absorption capacity, and PC had about 1.5 times the absorption capacity of water. FIG.
It is a comparison between PC and EC. Similarly, it was found that PC has an absorption capacity about 1.4 times that of EC at the same temperature. Although this is a comparison at the same temperature, EC is difficult to operate below about 50 ° C due to the problem of solidification,
There is no problem if you use a PC. As an example, comparing the absorption capacities of EC at 50 ° C. and PC at 20 ° C., it can be seen that there is a difference in absorption capacity of about 4 times. FIG. 4 is a comparison between a mixed solution of PC and EC (PC: EC = 40: 60) and EC. In the same manner, the mixed solution has an EC of about 1.
It was confirmed that it had three times the absorption capacity.

[0026]

[Table 1]

Example 12 Outflow gas from ethylene oxide reactor 100 Nm ³ / hr
Was used to operate an ethylene oxide absorption tower using propylene carbonate as an absorption liquid. The effluent gas from the ethylene oxide reactor was supplied to the bottom of an ethylene oxide absorption column filled with a Raschig ring-shaped packing in order to achieve good mixed contact of gas and liquid. The effluent gas from the reactor contains ethylene oxide, ethylene, oxygen, carbon dioxide and water as reaction byproducts, inert gas (nitrogen, methane, argon, ethane), and aldehyde, in addition to ethylene oxide. Table 2 shows the absorption rate of ethylene oxide and water corresponding to the operating conditions of the absorption tower and each operating condition.
It was shown to. Almost no components other than those shown in Table 2 were absorbed. In Table 2, “L / V” is the molar flow rate ratio of the absorbing liquid to the supplied EO gas amount.

Comparative Example 10 The same conditions as in Example 12 except that ethylene carbonate was used as the absorbent in Example 12, the temperature of the absorbent at the inlet of the absorption tower was 40 ° C., and the pressure was 18 kg / cm ² G. When the operation was carried out at 1, the absorption liquid coagulated in the absorption liquid supply pipe having an external cooling jacket for temperature adjustment, the continuous supply of the absorption liquid could not be satisfactorily performed, and stable absorption of ethylene oxide could not be achieved.

[0029]

[Table 2]

Examples 13 to 15 Examples 13 and 14 show the results when the operating temperature of the absorption tower was raised from 20 ° C to 30 ° C and 40 ° C. Although it was necessary to increase the amount of absorbing liquid as the absorption temperature increased, ethylene oxide could be absorbed well by this. Further, the results of using a mixed solution of propylene carbonate and ethylene carbonate are shown in Example 15.

Example 16 In order to recover ethylene oxide from the propylene carbonate liquid which absorbed ethylene oxide by the operation of Example 12, this liquid was led to an ethylene oxide stripping tower. At the same time, the pressure was released, and at the same time, carbon dioxide was used as a diffusion gas to diffuse ethylene oxide. Table 3 shows the operating conditions and emission results. This stripping tower was also filled with a Raschig ring-shaped packing in order to improve the contact between the stripping carbon dioxide from the bottom and the propylene carbonate flowing down from the top. It was possible to dissipate most of the water produced in the oxidation reactor. This prevents water from accumulating in the propylene carbonate liquid, and in combination with the fact that propylene carbonate has no reactivity with ethylene oxide, it prevents the formation of substances that consume ethylene oxide such as ethylene glycol. I was able to. As described above, the reaction product contains some aldehydes and acidic substances (acetic acid, etc.). Some of these (especially for aldehydes)
When ethylene oxide was released, it was released at the same time. However, it was difficult to dissipate the whole amount. Therefore, it was decided to extract a small part of the absorbing liquid and add a new absorbing liquid, but as a result of the trial, the amount was 0.
It was found that it is sufficient to extract the liquid corresponding to 002%. This is a negligible amount compared to the loss of ethylene oxide caused by the reaction of 3 to 15% of the ethylene oxide produced in the oxidation reactor when conventional water is used as the absorbing liquid. The above operation was carried out continuously for 35 days, and it was tracked whether there was any change in the deterioration or dissipation of the absorption liquid, the absorption rate, or the emission rate. No such changes were observed, and stable operation was possible. It was In addition, in Table 3,
“L / V” is the molar flow ratio of the absorbing liquid to the amount of supplied EO gas.

[0032]

[Table 3]

Examples 17 to 19 The results of ethylene oxide stripped from the absorbents of Examples 13 to 15 by the stripping tower used in Example 16 are shown in Tables 3 to 17, respectively. The operating temperature of the stripping tower was changed to 105 ° C., 120 ° C., and 105 ° C. (mixed solution) for testing. In all cases, ethylene oxide and water could be recovered well.

[0034]

The propylene carbonate of the present invention,
Alternatively, a mixture of propylene carbonate and ethylene carbonate containing 40% by weight or more of propylene carbonate is used as an ethylene oxide absorbent compared with conventional water,
It has the following outstanding capabilities: 1) High absorption capacity of ethylene oxide per unit weight. About 4 compared to water
It has an absorption capacity of 0 to 50%. 2) Small specific heat,
It is about 40% of water. From this characteristic and the characteristic of the preceding paragraph, the heat recovery loss during repeated heating and cooling in the absorption / dissipation system can be reduced to 25 to 30% of that in the water system. With ethylene carbonate alone, such a reduction is not possible due to coagulation problems. 3) It is extremely stable against ethylene oxide and aldehydes and organic acids that are by-products from the ethylene oxide reactor. For this reason, it is possible to recover almost all the amount of ethylene oxide as ethylene oxide, without producing by-products such as ethylene glycol. Therefore, it is possible to adopt a flexible production system according to the recent economic situation and production demand. 4) Since the freezing point is at least below the freezing point, solidification or blockage does not occur at the contact interface with the cooling heat exchanger. Further, it is not necessary to perform special curing for preventing solidification even when the plant is stopped.
5) Since the boiling point is as high as about 240 ° C, there is almost no scattering loss in the absorption / emission process. Due to the above characteristics, an economically superior and flexible ethylene oxide plant can be constructed.

[Brief description of drawings]

FIG. 1 shows an example of the configuration of a process according to the present invention.

FIG. 2 shows the ethylene oxide absorption capacity of PC and water. The example is at the same vapor phase EO concentration of 1 at 40 ° C.
With respect to 5 mol%, the EO concentration in the liquid phase was as follows: water (point A): 2.6% by weight dissolved PC (point B): 4.0% by weight dissolved It shows that it has an absorption capacity of 4.0 / 2.6≈1.5 times.

FIG. 3 shows the ethylene oxide absorption capacity of PC and EC.

FIG. 4 shows a mixed solution of PC and EC and EC absorption capacity of ethylene oxide.

[Explanation of symbols]

 1: Pipe for supplying an ethylene oxide-containing gas mixture 2: Pipe for absorbing an ethylene oxide 3: Pipe for discharging a non-absorbing gas 4: Pipe for flowing out a liquid at the bottom of an absorption tower 5: Pipe for supplying a liquid at a bottom of an absorption tower 6: Ethylene oxide diffusion tower 7: Pipe for recovering ethylene oxide 8: Pipe for supplying gas for diffusion 9: Pipe for discharging liquid at the bottom of the diffusion tower 10: Pipe for discharging liquid at the bottom of the diffusion tower 11: Pipe for circulating liquid at the bottom of the diffusion tower

Claims (13)

[Claims] 1. A method for recovering ethylene oxide by contacting a gas mixture containing ethylene oxide with an absorbing solution to absorb the ethylene oxide, then releasing and separating ethylene oxide from the absorbing solution, and collecting ethylene oxide as the absorbing solution. A method for recovering ethylene oxide, which comprises using 2. The method according to claim 1, characterized in that an absorption liquid comprising a mixture of propylene carbonate and ethylene carbonate containing at least 40% by weight of propylene carbonate is used as the absorption liquid. 3. An ethylene oxide-containing gas mixture is brought into contact with an absorption liquid in an absorption tower to absorb the ethylene oxide into the absorption liquid, and the obtained absorption liquid (a) is led to a diffusion tower where the ethylene oxide is diffused. The absorption liquid (b) is recovered from the top of the tower, while the remaining absorption liquid (b) is circulated to the absorption tower while the absorption liquid (a) is being collected.
The temperature of the absorbing liquid (b) is 10 to 3 by heat exchange between the absorbing liquid (b) and another heating or heat exchange with a cooling medium.
Within the range of 5 ° C., and the temperature of the absorption liquid (a) is 70 to 1
The method according to claim 1 or 2, wherein the temperature is adjusted within the range of 50 ° C. 4. The method according to claim 3, wherein the temperature of the ethylene oxide-containing gas mixture supplied to the absorption tower is 20 to 80 ° C. 5. The temperature of the absorption liquid supplied to the absorption tower is 10
The method according to claim 3 or 4, wherein the temperature is adjusted to ~ 35 ° C. 6. The method according to claim 1, wherein the ethylene oxide concentration of the gas mixture containing ethylene oxide is 0.5 to 5% by volume. 7. A gas mixture containing ethylene oxide comprises:
7. The method according to claim 1, which is a gas containing ethylene oxide produced by vapor-phase catalytic oxidation of ethylene with oxygen in the presence of a silver catalyst. 8. The process according to claim 1, wherein the absorption of ethylene oxide is carried out at a temperature of 5 to 50 ° C. 9. The absorption of ethylene oxide is 2 to 40 kg / c.
9. The method according to claim 1, which is carried out under a pressure of m ² G. 10. Emission of ethylene oxide is carried out in a stripping tower at a top temperature of 80 to 140 ° C.
Either way. 11. The emission of ethylene oxide is 0.1 to 3 kg.
Method according to any of claims 1 to 10 carried out under a pressure of / cm ² G. 12. The method according to claim 1, wherein the emission of ethylene oxide is carried out by heat. 13. Emission of ethylene oxide is performed using a gas for diffusion, and as the gas, steam; carbon dioxide which is a by-product of the catalytic oxidation reaction; ethylene which is a raw material of the catalytic oxidation reaction; or a catalytic oxidation reaction 13. The method according to claim 1, wherein methane is used as the diluting gas.