JPH0791282B2 - Method for purifying ethylene oxide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying ethylene oxide. In the presence of a silver catalyst, a reaction product gas containing ethylene oxide produced by catalytic gas-phase oxidation of ethylene with a molecular oxygen-containing gas is introduced into an ethylene oxide absorption tower and brought into countercurrent contact with the absorption liquid, and the ethylene oxide absorption tower top The gas is circulated to the ethylene oxidation reaction step, the bottom liquid of the ethylene oxide absorption tower containing ethylene oxide is supplied to the ethylene oxide diffusion tower, ethylene oxide is diffused from the top of the ethylene oxide diffusion tower, the distillate containing ethylene oxide and water is condensed, and the dehydration tower In a method for purifying ethylene oxide, which comprises the steps of separating water with a light fraction separator, separating light fraction with a light fraction separator, and then rectifying ethylene oxide with an ethylene oxide fractionator, heating the ethylene oxide fractionator and / or the light fraction separator. Energy-saving ethylene oxide It relates to the purification process.

(Prior Art) Ethylene oxide is generally purified as follows. A reaction product gas containing ethylene oxide produced by catalytic gas-phase oxidation of ethylene and a gas containing molecular oxygen on a silver catalyst is introduced to an ethylene oxide absorption tower and countercurrently contacted with an absorption liquid mainly composed of water to recover as an ethylene oxide aqueous solution. Then, it is sent to an ethylene oxide stripping tower and ethylene oxide is stripped from the aqueous solution by heating the bottom of the ethylene oxide stripping tower with heating steam, and the aqueous solution containing substantially no ethylene oxide from the bottom of the ethylene oxide stripping tower is circulated and used as an absorption liquid. Dehydration process of light emission products including ethylene oxide, water, carbon dioxide, inert gas (nitrogen, argon, methane, ethane) and other low boiling point impurities such as formaldehyde and high boiling point impurities such as acetaldehyde and acetic acid released from the top. Separation process and Purification over each quality component separation step can be produced ethylene oxide. Various proposals have been made regarding a method for recovering ethylene oxide. For example, U.S. Patent No. 3,165,539, U.S. Patent No. 2,771,473, U.S. Patent No. 4,028,070, U.S. Patent No. 3,097,215, U.S. Patent No. 3,217,466, U.S. Patent No. 3,745,092, U.S. Patent No. 3,
729,899, U.S. Pat.No. 3,766,714 and U.S. Pat.
964,980 and the like.

The conventionally known method will be described in detail. For example, in FIG. 1, a reaction product gas containing ethylene oxide produced by catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst is charged through a conduit 1 to fill the reaction product gas. It is supplied to the lower part of a tower or plate tower type ethylene oxide absorption tower 2, and the absorption liquid is introduced from the conduit 3 to the upper part of the ethylene oxide absorption tower 2, and is brought into countercurrent contact with the reaction product gas, thereby
99% by weight or more of ethylene oxide was recovered, and gases such as ethylene, oxygen, carbon dioxide, inert gases (nitrogen, argon, methane, ethane) aldehydes, and acidic substances that were not absorbed from the top of the ethylene oxide absorption tower 2 Conduit 4
Through the carbon dioxide absorption step and / or the oxidation reaction step. In this absorption process, in addition to ethylene oxide, ethylene, oxygen, carbon dioxide, inert gases (nitrogen, argon, methane, ethane, etc.) and low boiling impurities such as formaldehyde produced in the ethylene oxidation reaction process, high boiling points such as acetaldehyde and acetic acid. A substantial amount of impurities is absorbed at the same time. The bottom liquid of the ethylene oxide absorption tower 2 is sent to the heat exchanger 6 through the conduit 5 to exchange heat with the ethylene oxide diffusion tower bottom liquid to raise the temperature to 70 to 110 ° C., which is sent to the flash tank 8 through the conduit 7 and partially ethylene oxide and water. An inert gas light component gas containing is separated by the conduit 9. The remaining absorption liquid after flushing the light gas is passed through the conduit 10 to obtain a top pressure of 0.1 to ² Kg / cm ² G and a top temperature.
It is supplied to the upper part of the ethylene oxide stripping tower 11 at 85 to 120 ° C., and heated from a heater 12 of the ethylene oxide stripping tower 11 with a heating medium such as steam or Dowsome (Dow Company, a heating medium product) through a conduit 13 or direct ethylene oxide. It is heated by a heating method of introducing water vapor into the bottom of the desorption tower 11 to disperse 99% by weight or more of ethylene oxide contained in the absorption liquid, and a temperature 110-150 at which ethylene oxide is not substantially contained from the bottom of the ethylene oxide desorption tower 11. Part of bottom liquid of ethylene oxide stripping tower at ℃
Heat is exchanged with the bottom liquid of the ethylene oxide absorption tower 2 through the heat exchanger 6 through 15, and cooled by the cooler 17 through which the cooling water passes through the conduit 16 and the conduits 18 and 19, and then the ethylene glycol concentration in the absorbent is Fresh water is introduced through conduit 21 to adjust the
The aqueous solution of potassium hydroxide can be added to adjust the temperature, and the antifoaming agent can be introduced into the ethylene oxide absorption tower 2 to adjust the concentration of the defoaming agent in the absorbing liquid. Low boiling point impurities such as by-produced ethylene glycol and formaldehyde, and high boiling points such as acetaldehyde and acetic acid, which are produced by the hydrolysis reaction of ethylene oxide and water in the absorption liquid between the oxidation step of oxidizing ethylene with molecular oxygen and the ethylene oxide emission step In order to prevent the increase of impurities, the bottom liquid of the ethylene oxide stripping tower 11 is extracted from the bottom of the ethylene oxide stripping tower 11 through conduits 14 and 22 and sent to the by-product ethylene glycol concentration step.

On the other hand, the emitted vapor containing ethylene oxide which is emitted from the top of the ethylene oxide stripping tower 11 passes through the conduit 23,
The cooling water is sent to the condenser 24 through which the conduits 25 and 26 are passed, the condensate is refluxed to the top of the ethylene oxide stripping column 11 through the conduit 27, and the uncondensed vapor is supplied to the dehydration column 29 through the conduit 28.

The dehydrator 29 is heated by a heater 30 of the dehydration tower 29 with steam or a heating medium such as Dowsome (commercial product of Dow Company) through a conduit 31 or by a heating method of directly introducing steam to the lower part of the dehydration tower 29. Water that is substantially free of ethylene oxide is withdrawn from the bottom of the column through conduit 32.

The vapor containing ethylene oxide from the top of the dehydration tower 29 is sent through the conduit 33 to the condenser 34 through which cooling water or brine passes through the conduits 35 and 36, and the condensate is refluxed through the conduit 37 to the top of the dehydration tower 29, The uncondensed vapor in the condenser 34 is a conduit
It is supplied through 39 to a re-ethylene oxide absorption column (not shown). The other part of the condensate of the condenser 34 is supplied to the light fraction separation column 40 through a conduit 38.

The light source separation tower 40 is heated by a heater 41 of the light content separation tower 40 with a heating medium such as steam or Dowsome (commercial product of Dow Company) through a conduit 42, and the ethylene oxide vapor containing the light fraction is supplied from the top of the light content separation tower 40 through a conduit. 43 through condenser 44
To the recycle ethylene oxide absorber column (not shown) for recovery of ethylene oxide via conduit 48.

On the other hand, the ethylene oxide from which the light components have been separated is supplied to the ethylene oxide rectification column 50 from the bottom of the light components separation column 40 through a conduit 49.

Pressure from conduit 59 to heater 58 of ethylene oxide rectification column 50
0.5 to 3.0 kg / cm ² G of steam is supplied, the bottom temperature of the ethylene oxide rectification column 50 is 35 to 85 ° C., and the bottom pressure of the ethylene oxide rectification column is 1.2 to 8.2 kg / cm ² G to perform rectification. From the top of the distillation column, the temperature at the top of the column is 29-81 ℃, the pressure at the top of the column is 1.0-
8.0 kg / cm ² G of ethylene oxide vapor was sent to the condenser 52 through the conduit 51, the ethylene oxide vapor was liquefied, and a part of the liquefied liquid was introduced as the reflux liquid to the top of the ethylene oxide rectification column 50 through the conduit 56. The other portion of the liquefied liquid is withdrawn as ethylene oxide product through conduit 57.

The uncondensed vapor in condenser 52 of ethylene oxide rectification column 50 is fed through conduit 55 to a re-ethylene oxide absorber (not shown) for recovery of ethylene oxide.

The bottom liquid of the ethylene oxide rectification column 50 is withdrawn through a conduit 67 as necessary for separating heavy components such as acetaldehyde, water, and high-boiling impurities such as acetic acid.

(Problems to be Solved by the Invention) However, such a method for purifying ethylene oxide is such that the heat of condensation of the vapor of the ethylene oxide stripping tower and the heat energy of the liquid extracted from the bottom of the ethylene oxide stripping tower are collected. However, there was a problem that a large amount of heat was discarded outside the system. In the conventional method, the bottom liquid of the ethylene oxide stripping tower at 100 to 150 ° C. is heat-exchanged with the bottom liquid of the ethylene oxide absorption tower, and after recovering the heat quantity, it is cooled to obtain the absorption liquid of the ethylene oxide absorption tower. Further, the method for purifying ethylene oxide has a problem that a large amount of heating vapor is consumed in the ethylene oxide rectification column and the light fraction separation column.

Therefore, it is an object of the present invention to provide a novel method for purifying ethylene oxide.

Another object of the present invention is to provide a method for purifying ethylene oxide, which utilizes the energy of the bottom liquid of the ethylene oxide stripping tower effectively.

(Means for Solving Problems) The present invention introduces a reaction product gas containing ethylene oxide produced by catalytic vapor-phase oxidation of ethylene with a molecular oxygen-containing gas into an ethylene oxide absorption tower to countercurrently flow with an absorption liquid. The gas from the top of the ethylene oxide absorption tower is circulated to the ethylene oxidation reaction step, and the bottom liquid of the ethylene oxide absorption tower containing ethylene oxide is supplied to the ethylene oxide diffusion tower to diffuse the ethylene oxide from the top of the ethylene oxide absorption tower, containing ethylene oxide and water. In the method for purifying ethylene oxide, which comprises the steps of condensing a distillate, separating water in a dehydration tower, separating light components in a light fraction separating tower, and then rectifying ethylene oxide in an ethylene oxide rectifying tower, the top of the ethylene oxide stripping tower From the ethylene oxide Used as a heat source for the distillation column, part of the liquid extracted from the bottom of the ethylene oxide stripping column is heat-exchanged with the bottom liquid of the ethylene oxide absorption column, and then the heat source of the ethylene oxide rectification column and / or the heat source of the light fraction separation column. The present invention relates to a method for purifying ethylene oxide, which is characterized by being used for. These various purposes were to introduce a reaction product gas containing ethylene oxide produced by catalytic vapor-phase oxidation of ethylene with a molecular oxygen-containing gas into an ethylene oxide absorption tower to make countercurrent contact with the absorbing liquid, Part of the gas is circulated to the ethylene oxidation reaction step, the bottom liquid of the ethylene oxide absorption tower containing ethylene oxide is supplied to the ethylene oxide diffusion tower, ethylene oxide is diffused from the top of the ethylene oxide diffusion tower, and the distillate containing ethylene oxide and water is condensed. In the method for purifying ethylene oxide, which comprises separating the water in the dehydration tower, separating the light fraction in the light fraction separation tower, and then purifying ethylene oxide in the ethylene oxide rectification tower, the emission products emitted from the top of the ethylene oxide diffusion tower As a heating source for the ethylene oxide rectification column And use, part of the liquid extracted from the ethylene oxide stripper bottom is achieved by the purification process of ethylene oxide, characterized in that it uses the heat source of the heat sources and / or light fraction separation of ethylene fractionator.

FIG. 1 is a flow chart showing an example of a known method for purifying ethylene oxide, and FIGS. 2 to 5 are flow charts showing an embodiment of the method for purifying ethylene oxide according to the present invention.

In the present invention, the temperature of the absorption liquid supplied to the ethylene oxide absorption tower is 5 to 40 ° C, preferably 10 to 35 ° C, and the composition of the absorption liquid has a pH of 5 to 12, preferably 6 to 11, and an ethylene glycol concentration of 1 to 40% by weight, preferably 5 to 30% by weight, the antifoaming agent concentration is 0.1 ppm or more, preferably 1 to 100 ppm,
It is controlled by the range of the remaining water. In order to keep the ethylene glycol concentration in the absorption liquid constant, a part of the absorption liquid that circulates in the ethylene oxide absorption tower and the ethylene oxide diffusion tower is withdrawn from the bottom of the ethylene oxide diffusion tower and sent to the by-product ethylene glycol concentration tower, with fresh water if necessary. Are introduced and controlled. The pH is preferably adjusted by adding a compound that is soluble in an absorbing solution such as a hydroxide or carbonate of an alkali metal such as potassium or sodium, and the additive is specifically potassium hydroxide or Sodium hydroxide is preferred.

The defoaming agent is inert to ethylene oxide, by-product ethylene glycol, etc., and any defoaming agent can be used as long as it has the defoaming effect of the absorbing liquid. As a typical example, water-soluble silicone emulsion is absorbed. It is effective because it has excellent dispersibility in a liquid, dilution stability, and thermal stability.

The operating conditions of the ethylene oxide absorption tower are that the concentration of ethylene oxide 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 ethylene oxide absorption tower is ^{2 to} 40 Kg / cm ² G, preferably 10 to 30 Kg / cm ² G. The operating conditions of the ethylene oxide stripping tower are such that the ethylene oxide stripping tower top pressure is 0.1 to ² kg / cm ² G, preferably 0.3 to
0.6Kg / cm ² G, ethylene oxide stripping tower top temperature 85-120
C., the bottom temperature of the ethylene oxide diffusion column is 100 to 150.degree. C., and the ethylene oxide concentration at the bottom of the ethylene oxide diffusion column is 10 ppm or less, preferably 0.5 ppm or less.

The first feature of the present invention is to introduce the vapor emitted from the top of the ethylene oxide stripping column into the heater of the ethylene oxide rectifying column so that the heating amount from the outside required to heat the ethylene oxide rectifying column can be increased. It exerts the effect that it can be greatly reduced. Furthermore, by carrying out this method, the heat load of the cooling water for cooling the vapor phase generated at the top of the ethylene oxide stripping tower is reduced. The second feature of the present invention is that after a part of the liquid extracted from the bottom of the ethylene oxide stripping column is heat-exchanged with the liquid from the bottom of the ethylene oxide absorption column, it is used as a heating source for the ethylene oxide rectification column and the light fraction separation column. By doing so, the heating vapor of the ethylene oxide rectification column and the light fraction separation column can be reduced. Further, the heat load of the cooling water for cooling the absorption liquid to the ethylene oxide absorption tower is reduced.

In the present invention, the temperature of the supply steam supplied to the ethylene oxide dehydration tower is 5 to 60 ° C, preferably 10 to 50 ° C,
The ethylene oxide concentration of the feed steam is in the range of 80-98% by weight.

The operating conditions of the ethylene oxide dehydration tower are such that the dehydration tower top pressure is 0 to ² kg / cm ² G, preferably 0.3 to 0.6 kg / cm ² G, the dehydration tower top temperature is 10 to 40 ° C., and the dehydration tower bottom temperature is 100 to 130 ° C. Is. The ethylene oxide concentration in the bottom of the dehydration column is 100 ppm or less, preferably 10 ppm or less.

In the present invention, the temperature of the feed liquid supplied to the ethylene oxide light fraction separation column is 0 to 50 ° C., preferably 5 to 30 ° C., and the composition of the feed liquid is mostly ethylene oxide, and a small amount of aldehydes such as formaldehyde and Contains water.

The operating conditions of the light separation column are:
Kg / cm ² G preferably 3~7Kg / cm ² G, light fraction separating column head temperature 30 to 90 ° C., in the range of light fraction separating column bottom temperature 30 to 90 ° C..

The ethylene oxide concentration at the bottom of the light fraction separation column is 99.5% by weight or more, preferably 99.95% by weight or more.

In the present invention, the ethylene oxide rectification column includes a plate column type and a packed column type.

There are various trays of the tray column type distillation column, and examples thereof include a bubble cap tray, a uniflux tray, a turbo grid tray, a lip tray, a flexi tray, a sieve tray, and a ballast tray. As the packing of the packed column type rectification tower, Raschig ring, pole ring, saddle type ring, spiral ring, McMahon packing, interlock metal packing, packing having a pressure loss of 10 mmHg or less per logical stage, woven fabric Alternatively, a wire mesh laminated plate having a knit structure may be used.

In the present invention, the ethylene oxide rectification column and the light fraction separation column are 20 mmHg or less per one theoretical plate, preferably 15 mmHg.
The plate column type and packed column type having the following pressure loss are preferable.

The temperature of the feed liquid supplied to the ethylene oxide rectification column in the present invention is 30 to 90 ° C, preferably 50 to 70 ° C, and the composition of the feed liquid has an ethylene oxide concentration of 99.5% by weight or more,
It is preferably controlled in the range of 99.95% by weight or more.

The operating conditions of the ethylene oxide rectification column are the top pressure of the rectification column.
1.0 to 8.0 Kg / cm ² G, preferably 1.2 to 5.0 Kg / cm ² G, rectification column top temperature 29 to 81 ° C., rectification column bottom temperature 35 to 85 ° C., ethylene oxide rectification column bottom ethylene oxide concentration is 30 to 90% by weight,
It is preferably in the range of 40 to 80% by weight.

In the present invention, the bottom liquid of the ethylene oxide rectification column is composed of high boiling impurities such as acetaldehyde, water and acetic acid in addition to ethylene oxide.

Therefore, the above characteristics, in the presence of a silver catalyst, ethylene, a reaction product gas containing ethylene oxide produced by catalytic vapor phase oxidation with a molecular oxygen-containing gas is introduced into an ethylene oxide absorption tower, and brought into countercurrent contact with the absorbing liquid, A part of the gas from the top of the ethylene oxide absorption tower is circulated to the ethylene oxidation reaction step, the bottom liquid of the ethylene oxide absorption tower containing ethylene oxide is supplied to the ethylene oxide diffusion tower, and ethylene oxide is diffused from the top of the ethylene oxide diffusion tower, A part of the extracted liquid is heat-exchanged with the bottom of the ethylene oxide absorption tower by a heat exchanger, cooled by a cooler, introduced to an ethylene oxide absorption tower and circulated as an absorption liquid, and the rest is ethylene contained in the liquid. Send to ethylene glycol concentration tower as a by-product to concentrate glycol In step, the thermal energy is recovered with the steam to dissipate from the ethylene oxide stripper top, is to measure the effective use of the recovered heat energy. As a means for this, the vapor that is diffused from the top of the ethylene oxide stripping tower is sent to the heater of the ethylene oxide rectifying tower, the heat exchange is performed and the stripped material is liquefied, the condensed liquid is refluxed to the ethylene oxide stripping tower, and the uncondensed gas is sent to the dehydration tower. The supply method is adopted. Further, the liquid withdrawn from the bottom of the ethylene oxide stripping column is heat-exchanged with the bottom liquid of the ethylene oxide absorption column to recover the heat quantity, and then introduced into the heater of the ethylene oxide rectification column and / or the light fraction separation column, and the ethylene oxide rectification column and / or Alternatively, it is used as a part of the heat source of the light fraction separation column, then cooled with cooling water and led to the ethylene oxide absorption column.

On the other hand, the bottom liquid of the ethylene oxide absorption tower is heat-exchanged with the hot liquid from the bottom of the ethylene oxide stripping tower, and then the light component gas is separated in the flash tank, and then the ethylene oxide is stripped off by being supplied to the top of the ethylene oxide stripping tower. In the present invention, those emitted from the top of the ethylene oxide stripping tower are mostly low in water, ethylene oxide, low in carbon dioxide, trace amounts of oxygen, ethylene, inert gas (nitrogen, argon, methane, ethane), formaldehyde and the like. It is a release product consisting of high-boiling impurities such as boiling impurities and acetaldehyde and acetic acid.

The present invention will be described in more detail with reference to the drawings.

In FIG. 2, a reaction product gas containing ethylene oxide, which is produced by catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst, is passed through a conduit 301 to a packed tower or a tray tower type ethylene oxide absorption tower 302. Is supplied to the lower part of the ethylene oxide absorption tower 302 through the waveguide 303 and brought into countercurrent contact with the reaction product gas to recover 99% by weight or more of ethylene oxide in the reaction product gas and absorb the ethylene oxide. Ethylene, oxygen, carbon dioxide, inert gas (nitrogen, nitrogen, etc.) not absorbed from the top of the tower 302
Gases such as argon, methane, ethane), aldehydes, acidic substances, etc. are passed through the conduit 304 to the carbon dioxide absorption step and / or
It is also recycled to the oxidation reaction step. In this absorption process, in addition to ethylene oxide, ethylene, oxygen, carbon dioxide,
A substantial amount of inert gas (nitrogen, argon, methane, ethane) and low boiling point impurities such as formaldehyde and high boiling point impurities such as acetaldehyde and acetic acid generated in the ethylene oxidation reaction step are simultaneously absorbed. The bottom liquid of the ethylene oxide absorption tower 302 is sent to the heat exchanger 306 through the conduit 305 and heat-exchanged with the bottom liquid of the ethylene oxide diffusion tower 311 to obtain a temperature of 7
The temperature is raised to 0 to 110 ° C., and is sent to a flash tank 308 by a conduit 307, and a light component gas of an inert gas including a part of ethylene oxide and water is separated by a conduit 309. The remaining absorption liquid after flushing the light gas is supplied to the upper portion of the ethylene oxide stripping column 311 at a column top pressure of 0.1 to ₂ kg / cm C ₂ G and a temperature of 90 to 120 ° C through a conduit 310, and the ethylene oxide stripping column 311 is supplied.
Water vapor or Dowsome from the heater 312 of the Dow (Dow company product)
It is heated through a conduit 313 with a heating medium such as, or is heated by a heating method in which steam is directly introduced into the bottom of the ethylene oxide diffusion tower 311 to disperse 99% by weight or more of ethylene oxide contained in the absorption liquid, and the ethylene oxide diffusion tower Part of the bottom liquid of the stripping column at a temperature of 100 to 150 ° C that does not substantially contain ethylene oxide from the bottom of 311 is pipe 314 and pipe 315.
Through a heat exchanger 306 to exchange heat with the bottom liquid of the ethylene oxide absorption tower 302, and then is sent to a heater 358 of the ethylene oxide rectification tower 350 through a conduit 380 and used as a heating source, and then the conduit 31
6 and further cooled by a cooler 317 through which cooling water passes through conduits 318 and 319, and then fresh water is introduced through conduit 321 to adjust the ethylene glycol concentration in the absorption liquid, and if necessary, the pH in the absorption liquid. The aqueous solution of potassium hydroxide can be added to adjust the concentration of the defoaming agent, and the defoaming agent can be introduced into the ethylene oxide absorption tower 302 to adjust the concentration of the defoaming agent in the absorbent.

Low boiling point impurities such as by-product ethylene glycol and formaldehyde and high boiling point such as acetaldehyde and acetic acid produced by the hydrolysis reaction of ethylene oxide with water in the absorbing solution between the oxidation step of oxidizing ethylene with molecular oxygen and the ethylene oxide stripping step In order to prevent the increase of impurities, the bottom liquid of the ethylene oxide stripping tower 311 is withdrawn from the bottom of the ethylene oxide stripping tower 311 through conduits 314 and 322.
It is sent to the by-product ethylene glycol concentration step.

On the other hand, the vaporized vapor containing ethylene oxide emitted from the top of the ethylene oxide stripping tower 311 is sent to a heater 360 of the ethylene oxide rectification tower 350 through a conduit 323 and used as a heating source. The pipe 362 and the condenser 364 through which the cooling water passes through the pipe 363 are sent, and the condensate is fed through the pipe 365 to the ethylene oxide stripping tower 3
After refluxing to the top of the column 11, the uncondensed vapor is supplied to the dehydration column 329 through the conduit 366.

The heater 330 of the dehydration tower 329 heats it with a heating medium such as steam or Dowsome (commercial product of Dow Company) through the conduit 331, or heats it by a heating method of directly introducing steam to the lower part of the dehydration tower 329, Water substantially free of ethylene oxide is withdrawn from the bottom of the column through a conduit 332.

The vapor containing ethylene oxide from the top of the dehydration tower 329 is sent to the condenser 334 through which the cooling water or brine passes through the conduit 333 and the conduit 335 through the conduit 333, and a part of the condensate is passed through the conduit 337 to the top of the dehydration tower 329. Reflux and condenser 334
Of uncondensed vapor is fed to a re-ethylene oxide absorber column (not shown) via conduit 339.

The other part of the condensate of the condenser 334 is supplied to the light fraction separation column 340 through the conduit 338. From the top of the light fraction separation column 340, ethylene oxide vapor containing light fraction gas is sent to the condenser 344 through the conduit 343, the condensate is refluxed to the top of the light fraction separation column 340 through the conduit 347, and the uncondensed vapor is conduit 348. Is fed to a re-ethylene oxide absorption column (not shown) to recover ethylene oxide.

The bottom liquid of the light fraction separation column 340 is supplied to the ethylene oxide rectification column 350 through a conduit 349.

The emission from the top of the ethylene oxide stripping tower 311 is supplied to the heater 360 of the ethylene oxide rectification tower 350, and the liquid from the bottom of the ethylene oxide stripping tower 311 is supplied to the heater 358 of the ethylene oxide rectification tower 350 from the bottom of the ethylene oxide absorption tower. After the heat exchange with the liquid of (1), it is heated by a heating system introduced through a conduit 380, the bottom temperature of the ethylene oxide rectification column 350 is 35 to 85 ° C, the ethylene oxide rectification column bottom pressure is 1.2 to
The rectification is performed at 8.2 kg / cm ² G, and the ethylene oxide rectification tower 3
From the 50th section, tower top temperature 29-81 ℃, tower top pressure 1-8kg / cm
² G of ethylene oxide vapor is sent to an ethylene oxide condenser 352 through a pipe 351 to liquefy ethylene oxide, and a part of the ethylene oxide rectification tower 350 is passed through a pipe 356.
Is fed to the top of the column as reflux and the other part is withdrawn as ethylene oxide product through conduit 357.

The bottom liquid of the ethylene oxide rectification column 350 contains acetaldehyde, water and acetic acid in addition to ethylene oxide, and is withdrawn through a conduit 367 if necessary.

The bottom liquid of the ethylene oxide stripping tower 311 is heat-exchanged with the liquid from the bottom of the ethylene oxide absorption tower 302 by a heat exchanger 306, and then a heater of the ethylene oxide rectification tower 350 via a conduit 380.
Supplied to 358 and used as a heating source, then conduit 316
Is sent to a cooler 317 to be cooled and further circulated to an ethylene oxide absorption tower 302 via conduits 320 and 303.

FIG. 3 shows another embodiment of the present invention. In a method similar to the method shown in FIG. 2, the bottom liquid of the ethylene oxide stripping column is heated by the heat exchanger 406 to obtain the ethylene oxide absorption column 4.
02 After heat exchange with the liquid from the bottom, it is supplied to the heater 441 of the light fraction separation column 440 via the conduit 442 and used as a heating source, and then sent to the cooler 417 via the conduit 416 for cooling, It is circulated to the ethylene oxide absorption tower 402 via conduits 420 and 403.

Note that the reference numerals in which 100 is added to the reference numerals in FIG. 2 represent the same members in FIG.

FIG. 4 shows another embodiment of the present invention. In a method similar to the method shown in FIG. 2, the bottom liquid of the ethylene oxide stripping tower is heated by the heat exchanger 506 to obtain the ethylene oxide absorption tower 5.
After heat exchange with the liquid from 02, conduits 580 and 581,542
Supplied to a heater 558 of the ethylene oxide rectification column 550 and a heater 541 of the light fraction separation column 540 for use as a heating source, and then cooled via conduits 582, 583 and 516.
It is sent to 517 for cooling, and is further circulated to the ethylene oxide absorption tower 502 via conduits 520 and 503.

The reference numeral in FIG. 2 plus 200 indicates the same member in FIG.

FIG. 5 shows still another embodiment of the present invention,
In a method similar to that shown in FIG. 2, the bottom liquid of the ethylene oxide stripping tower is heat-exchanged with the liquid from the ethylene oxide absorption tower 602 by the heat exchanger 606, and then the heater 658 of the ethylene oxide rectification tower 650 via the conduit 680. Is supplied to the heater 641 of the light separation column 640 via the conduit 642 and is used as a heating source.
Then, it is sent to a cooler 617 via a conduit 616 for cooling, and further, via an conduit 620 and 603, an ethylene oxide absorption tower 60.
Cycled to 2.

The reference numeral in FIG. 2 plus 300 indicates the same member in FIG.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention does not limit the scope of the present invention only by this embodiment.

Example 1 In FIG. 2, a reaction product gas containing ethylene oxide produced by catalytic gas-phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst is passed through a conduit 301, and a packed column or plate column type ethylene oxide is produced. It is supplied to the lower part of the absorption tower 302, and the temperature is 29.6 ° C. or lower from the conduit 303 to the upper part of the ethylene oxide absorption tower 302, pH = 6, ethylene glycol concentration = 9.0% by weight, defoaming agent (water-soluble silicone emulsion) concentration 3 ppm, and the balance is Introduce an absorbing liquid consisting of water,
The reaction product gas was brought into countercurrent contact with the reaction product gas to recover 99% by weight or more of ethylene oxide, and ethylene, oxygen, which was not absorbed from the top of the ethylene oxide absorption tower 302,
Gases such as carbon dioxide, inert gases (nitrogen, argon, methane, ethane), aldehydes and acidic substances were circulated to the carbon dioxide absorption step and / or the oxidation reaction step through the conduit 304. In this absorption process, in addition to ethylene oxide, ethylene, oxygen, carbon dioxide, inert gas (nitrogen,
Argon, methane, and ethane) and low boiling point impurities such as formaldehyde produced in the ethylene oxidation reaction step, and high boiling point impurities such as acetaldehyde and acetic acid were also absorbed in substantial amounts. The bottom liquid of the ethylene oxide absorption tower 302 is sent to the heat exchanger 306 through the conduit 305 to exchange heat with the ethylene oxide diffusion bottom liquid to raise the temperature to 105.5 ° C., and is sent to the flash tank 308 by the conduit 307 and contains a part of ethylene oxide and water. The inert gas light fraction gas was separated by conduit 309. The remaining absorption liquid after flushing the light gas was passed through the conduit 310 and the top pressure was 0.4 kg / cm ² G and the temperature was 99.6 ° C.
99% by weight of the ethylene oxide contained in the absorption liquid after being supplied to the upper part of the ethylene oxide diffusion tower 311 and heated through steam from the heater 312 of the ethylene oxide diffusion tower 311.
The above was diffused, and the temperature was 113.8 ° C at which ethylene oxide was not substantially contained from the bottom of the ethylene oxide stripping tower 311.
Part of the bottom liquid of the ethylene oxide stripping tower is passed through conduits 314 and 315 in the heat exchanger 306 to the ethylene oxide absorption tower.
After heat exchange with the bottom liquid of 302, it is sent to the heater 358 of the ethylene oxide rectification column 350 by a conduit 380 and used as a heating source, and then through a conduit 316, and by a cooler 317 through which cooling water passes through conduits 318 and 319. Cool water and then add fresh water to conduit 321 to adjust the ethylene glycol concentration in the absorbent.
Introduced through. Low boiling point impurities such as by-product ethylene glycol and formaldehyde and high boiling point such as acetaldehyde and acetic acid produced by the hydrolysis reaction of ethylene oxide with water in the absorbing solution between the oxidation step of oxidizing ethylene with molecular oxygen and the ethylene oxide stripping step In order to prevent the increase of impurities, the ethylene oxide stripping tower 311 is passed through the conduits 314 and 322 from the bottom of the ethylene oxide stripping tower 311.
The bottom liquid was extracted and sent to the by-product ethylene glycol concentration step.

On the other hand, the vaporized vapor containing ethylene oxide emitted from the top of the ethylene oxide stripping tower 311 is sent to a heater 360 of the ethylene oxide rectification tower 350 through a conduit 323 and used as a heating source. The pipe 362 and the condenser 364 through which the cooling water passes through the pipe 363 are sent, and the condensate is fed through the pipe 365 to the ethylene oxide stripping tower 3
It was refluxed to the top of the column 11, and the uncondensed vapor was supplied to the dehydration column 329 through the conduit 366.

Water was heated by the heater 330 of the dehydration tower 329 by a heating method of heating steam through the conduit 331, and water substantially free of ethylene oxide was extracted from the bottom of the dehydration tower 329 through the conduit 332.

The vapor containing ethylene oxide from the top of the dehydration tower 329 is sent through the conduit 333 to the condenser 334 through which the brine passes through the conduits 335 and 336, and a part of the condensate is refluxed to the top of the dehydration tower 329 through the conduit 337, The uncondensed vapor in condenser 334 was fed via conduit 339 to a reethylene oxide absorber (not shown). The other part of the condensate was supplied to the light fraction separation column 340 through the conduit 338. From the top of the light separation column 340, the ethylene oxide vapor containing the light gas is introduced into the conduit 34.
3 to the condenser 344, the condensate is refluxed to the top of the light separation column 340 through the conduit 347, and the uncondensed vapor is conduit 3
It was fed to a re-ethylene oxide absorption column (not shown) to recover ethylene oxide through 48. The bottom liquid of the light fraction separation column 340 was supplied to the ethylene oxide rectification column 350 through a conduit 349.

The emissions from the ethylene oxide stripping tower are supplied to the heater 360 of the ethylene oxide rectifying tower 350, and the liquid at the bottom of the ethylene oxide stripping tower 311 is recovered by the heat exchanger 306 to the heater 358 of the ethylene oxide rectifying tower 350, and then the conduit 380 is introduced into the heater 358 and heated by the heating method, and the ethylene oxide rectification column 350 is rectified at a bottom temperature of 45 ° C. and an ethylene oxide rectification column bottom pressure of 2.0 kg / cm ² G. Tower top temperature 39 ℃, Tower top pressure 1.8kg / cm
² G of ethylene oxide vapor is sent to an ethylene oxide condenser 352 through a pipe 351 to liquefy ethylene oxide, and a part of the ethylene oxide rectification tower 350 is passed through a pipe 356.
Was fed to the top of the column as a reflux liquid, and the other part was withdrawn as an ethylene oxide product through a conduit 357.

The uncondensed vapor of ethylene oxide condenser 352 was fed through conduit 355 to a re-ethylene oxide absorber (not shown) to recover ethylene oxide.

The bottom liquid of the ethylene oxide rectification column 350 was withdrawn through a conduit 367 as necessary due to high boiling impurities such as acetaldehyde, water and acetic acid in addition to ethylene oxide.

Table 1 shows the continuous operating conditions of this process all together.

Example 2 As shown in FIG. 3, in the same manner as in Example 1,
The bottom liquid of the ethylene oxide diffusion tower 411 exchanges heat with the liquid from the ethylene oxide absorption tower 402 by the heat exchanger 406,
It is supplied to the heater 441 of the light separation column 440 via the conduit 442 for use as a heating source, and then sent to the heat exchanger 417 via the conduit 416 for cooling, and further to the ethylene oxide absorption tower 402 via the conduits 420 and 403. A similar method was used except that it was circulated.

Table 2 collectively shows the continuous conditions of this process.

Example 3 As shown in FIG. 4, in the same manner as in Example 1,
The bottom liquid of the ethylene oxide stripping tower is heat-exchanged with the liquid from the ethylene oxide absorption tower 502 by a heat exchanger 506, and then the ethylene oxide rectification tower 550 is passed through conduits 580 and 581, 542.
To the heater 558 of the light separation column 540 and the heater 541 of the light fraction separation column 540 to be used as a heating source, and then the conduits 582,583
And 516 to cooler 517 for cooling and further conduit
A similar method was carried out except that the ethylene oxide absorption tower 502 was circulated via 520 and 503.

Table 3 collectively shows the continuous conditions of this process.

Example 4 As shown in FIG. 4, when the same method was used except that the operating conditions of each part were changed in the method of Example 3, the results in Table 4 were obtained.

Example 5 As shown in FIG. 5, in the same manner as in Example 1, the bottom liquid of the ethylene oxide stripping tower was heat-exchanged with the liquid from the ethylene oxide absorption tower 602 by the heat exchanger 606, and then ethylene oxide was passed through the conduit 680. Rectification tower 650 heater
After being supplied to 658 and used as a heating source, it is supplied to the heater 641 of the light separation column 640 through a conduit 642 and used as a heating source, and then sent to a cooler 617 via a conduit 616 for cooling, Further, the same method was performed except that the ethylene oxide absorption tower 602 was circulated through conduits 620 and 603.

Table 5 collectively shows the continuous conditions of this process.

Comparative Example 1 As shown in FIG. 1, in the same manner as in Example 1,
Dispersed vapor containing ethylene oxide, which is dissipated from the top of the ethylene oxide stripping tower 11, passes through a pipe 23 and a pipe 25.
Then, the cooling water was sent to a condenser 24 through which a conduit 26 was passed, the condensate was refluxed to the top of the ethylene oxide stripping column 11 through a conduit 27, and the uncondensed vapor was supplied to a dehydration column 29 through a conduit 28.

The heater 30 of the dehydration tower 29 is heated by a heating system in which steam is heated through the conduit 31 and the conduit 32 is supplied from the bottom of the dehydration tower 29.
Water substantially free of ethylene oxide was withdrawn through. Except for this, the same method as in Example 1 was performed.

Table 6 collectively shows the continuous conditions of this process.

(Effect of the invention) According to the method of the present invention, by introducing the vapor diffused from the top of the ethylene oxide stripping tower into the heater of the ethylene oxide fractionating tower, it is necessary to heat the ethylene oxide fractionating tower from the outside. The effect of making it possible to greatly reduce the amount of heating heat of is exhibited. Furthermore, by carrying out this method, the heat load of the cooling water for cooling the vapor phase generated at the top of the ethylene oxide stripping tower is reduced. In addition, a part of the liquid extracted from the bottom of the ethylene oxide stripping column is heat-exchanged with the liquid from the bottom of the ethylene oxide absorption column, and then used as a heating source for the ethylene oxide rectification column and / or the light fraction separation column. This will reduce the heating steam of the rectification column and the light fraction separation column. Further, it has an effect of reducing the heat load of the cooling water for cooling the absorption liquid to the ethylene oxide absorption tower.

(Effects of the Invention) In a method for purifying ethylene oxide from an ethylene oxide-containing reaction product gas produced by catalytic vapor-phase oxidation of ethylene with a gas containing molecular oxygen, in the method of heating the ethylene oxide rectification column, the emissions emitted from the ethylene oxide stripping column are heated. It is a method for purifying ethylene oxide used as a source, and the bottom product of the stripping column can also be used as a heating source for a rectification column and / or a light fraction separation column.

[Brief description of drawings]

FIG. 1 is an example showing a known ethylene oxide recovery method related to the present invention. 2 to 5 are examples showing preferred specific examples of the ethylene oxide recovery method of the present invention. (302) …… Ethylene oxide absorption tower (317) …… Cooler (308) …… Flash tank (311) …… Ethylene oxide diffusion tower (312) …… Ethylene oxide diffusion tower heater (364) …… Ethylene oxide diffusion tower condenser (329) …… Dehydration tower (330) …… Dehydration tower heater (334) …… Dehydration tower condenser (340) …… Light fraction separation tower (341) …… Light fraction separation heater (344) …… Light fraction separation tower condenser (350) …… Ethylene oxide rectification tower (352) …… Ethylene oxide rectification tower condenser (358) …… Ethylene oxide rectification tower heater (360) …… Ethylene oxide rectification tower heater (306) )……Heat exchanger

 ─────────────────────────────────────────────────── ─── Continued Front Page (56) References US Pat. No. 3,766,714 (US, A)

Claims (6)

[Claims] 1. A reaction product gas containing ethylene oxide produced by catalytic vapor-phase oxidation of ethylene with a gas containing molecular oxygen is introduced into an ethylene oxide absorption tower and is brought into countercurrent contact with an absorbing liquid to remove the ethylene oxide absorption tower from the top. The gas is circulated to the ethylene oxidation reaction step, the bottom liquid of the ethylene oxide absorption tower containing ethylene oxide is supplied to the ethylene oxide diffusion tower to disperse ethylene oxide from the top of the ethylene oxide diffusion tower, the distillate containing ethylene oxide and water is condensed, and the dehydration tower In the method for producing ethylene oxide, which comprises the steps of separating water with a light fraction separator, separating the light fraction with a light fraction separation column, and then rectifying ethylene oxide with an ethylene oxide rectification column, the emissions emitted from the ethylene oxide stripping column are rectified with ethylene oxide. Used as a heating source for the tower, METHOD generation of ethylene oxide portion of liquid extracted from Sid stripping column, characterized in that the used heat source and / or heating source light fraction separating column of ethylene fractionator. 2. The method according to claim 1, wherein the stripper bottom liquid temperature is 100 to 150 ° C. 3. The method according to claim 1, wherein a part of the liquid extracted from the bottom of the ethylene oxide stripping column is used as a heating source for the ethylene oxide rectifying column. 4. The method according to claim 1, wherein a part of the liquid withdrawn from the bottom of the ethylene oxide stripping column is used as a heating source for the light fraction separation column. 5. The method according to claim 1, wherein a part of the liquid withdrawn from the bottom of the ethylene oxide stripping column is used as a heating source for the ethylene oxide rectification column and the light fraction separation column. 6. The method according to claim 1, wherein a part of the liquid extracted from the bottom of the ethylene oxide stripping column is used together with a heating source of the ethylene oxide rectification column, and then used as a heating source for light fraction separation and the like. The method described in 1).