JPH0662594B2 - Recovery method of ethylene oxide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing ethylene oxide obtained by catalytic vapor-phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst. For more details,
The reaction product gas containing ethylene oxide, which is obtained by catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst, is led to an absorption tower and absorbed in the absorbing liquid to recover ethylene oxide, and then the absorption containing ethylene oxide. The liquid is sent to the stripping tower and ethylene oxide is stripped from the top of the stripping tower by heating, and a part of the liquid extracted from the bottom of the stripping tower is introduced to the absorption tower and recycled as an absorbing liquid. It is about the method.

(Prior Art) In the step of recovering ethylene oxide, a reaction product gas is absorbed by an absorption liquid mainly containing water and recovered as an ethylene oxide aqueous solution, and ethylene oxide is diffused from this aqueous solution to obtain ethylene oxide. Ethylene oxide is generally recovered as follows. A reaction product gas containing ethylene oxide produced by catalytic gas-phase oxidation of ethylene and a molecular oxygen-containing gas on a silver catalyst is introduced to an absorption tower and counter-currently contacted with an absorption liquid mainly containing water to recover 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 stripping tower with heating steam. Of ethylene oxide, water, carbon dioxide, inert gas (nitrogen, argon, methane, ethane, etc.) and low boiling point impurities such as formaldehyde and high boiling point impurities such as acetaldehyde and acetic acid are dehydrated and separated into light components. And purifying ethylene oxide through each of the heavy and heavy separation processes to produce ethylene oxide. It can be.

(Problems to be Solved by the Invention) However, such a method for recovering ethylene oxide has a problem of consuming a large amount of heating vapor in the ethylene oxide stripping tower. The conventional method is 100-130.
The liquid at the bottom of the ethylene oxide stripping tower at 0 ° C. was heat-exchanged with the liquid at the bottom of the ethylene oxide absorption tower, and after recovering the amount of heat, it was cooled to obtain the absorption liquid in the absorption tower. As a result of research on energy saving in these ethylene oxide recovery steps, the present invention was completed with the aim of effectively utilizing the energy of the bottom liquid of the ethylene oxide stripping column.

(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 in the presence of a silver catalyst into an absorption tower for absorption. The solution is brought into countercurrent contact with the liquid, the gas from the top of the absorption tower circulates to the carbon dioxide absorption step and / or the ethylene oxidation reaction step, the absorption tower bottom liquid containing ethylene oxide is supplied to the stripping tower, and ethylene oxide is stripped from the top of the stripping tower. In the process of sending a part of the liquid extracted from the bottom of the stripping tower to the absorption tower and circulating it as an absorbing liquid, and sending the rest to the by-product ethylene glycol concentration tower to concentrate the ethylene glycol contained in the liquid, the stripping tower. The liquid extracted from the bottom is flushed, separated into a gas phase part and a liquid phase part, the gas phase part is compressed and introduced to the bottom of the stripping tower, and the liquid phase part is the absorption liquid of the absorption tower. The present invention relates to a method for recovering ethylene oxide, which is characterized in that In the present invention, the temperature of the absorption liquid supplied to the absorption tower is 5 to 40 ° C., preferably 10 to 35 ° C., and the composition of the absorption liquid is PH 5 to 12, preferably 6 to 11, ethylene glycol concentration 1 -40% by weight, preferably 5-30% by weight, antifoaming agent concentration is 0.1 ppm or more, preferably 1-1
It is controlled to the range of 00 ppm and the remaining water. To keep the ethylene glycol concentration in the absorption liquid constant, a part of the absorption liquid that circulates in the absorption tower and the ethylene oxide diffusion tower is extracted from the bottom of the diffusion tower and sent to the by-product ethylene glycol concentration tower, where necessary fresh water is 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. Specifically, the additive is 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 a defoaming effect on the absorbing solution. It is effective because it has excellent dispersibility, dilution stability, and thermal stability.

The operating conditions of the absorption tower are such that the concentration of ethylene oxide in the reaction product gas is 0.05 to 5% by volume, preferably 0.1 to 4% by volume, and the operating pressure of the absorption tower is ^{2 to} 40 kg / cm ² G, preferably Is 10 to 30 kg / cm ² G.

The operating conditions of the stripping tower are: the stripping tower top pressure 0 to 1 kg / cm ² G,
Preferably 0.3-0.6 kg / cm ² G, stripping tower top temperature 8
5 to 110 ° C., the bottom temperature of the stripping tower is 110 to 130 ° C., and the ethylene oxide concentration in the bottom of the stripping tower is 10 ppm or less, preferably 0.5 ppm or less.

A feature of the present invention is that the liquid discharged from the bottom of the stripping column is introduced into a flash tank operated at normal pressure or slightly reduced pressure to generate low-pressure steam. The generation of water vapor is endothermic and has the effect of lowering the temperature of the solution. The generated steam is pressurized by an electrically driven centrifugal compressor, screw compressor, or reciprocating compressor and supplied to the gas phase at the bottom of the stripping tower to become part of the heat source of the stripping tower, heating the stripping tower. Bring down the source water vapor. Further, the remaining liquid that generated low-pressure steam is heat-exchanged with the liquid from the bottom of the absorption tower to recover heat.

On the other hand, the absorption tower bottom liquid is heat-exchanged with the remaining liquid that has generated low-pressure steam, and then the light fraction gas is separated in a flush tank, and then is supplied to the top of the stripping tower to release ethylene oxide. What is diffused from the stripping tower in the present invention is mostly low-boiling impurities such as ethylene oxide and water, a small portion of carbon dioxide and a trace amount of oxygen, ethylene, an inert gas (nitrogen, argon, methane, ethane), formaldehyde and the like. , A high-boiling point impurity such as acetaldehyde and acetic acid.

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

In FIG. 1, 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 (1) through a packed tower or a plate tower type absorption tower ( 2) to the lower part, and from the conduit (24) to the upper part of the absorption tower (2), the temperature is 40 ° C or lower, pH = 6 or higher, ethylene glycol concentration = 1 to 20% by weight, antifoaming agent (water-soluble silicone emulsion). ) Concentration = 1
An absorption liquid consisting of ˜50 ppm and the balance being water was introduced and countercurrently contacted with the reaction product gas so that the ethylene oxide in the reaction product gas was absorbed by the absorption liquid. Here, 99% by weight or more of ethylene oxide in the reaction product gas is recovered. Gases such as ethylene, oxygen, carbon dioxide, inert gases (nitrogen, argon, methane, ethane), aldehydes and acidic substances that have not been absorbed from the top of the absorption tower (2) are absorbed through the conduit (3) in the carbon dioxide absorption step. And / or recycled to the oxidation reaction step.

In the ethylene oxide absorption process, in addition to ethylene oxide, ethylene, oxygen, carbon dioxide, inert gas (nitrogen,
Argon, methane, ethane, and low boiling impurities such as formaldehyde produced in the ethylene oxidation reaction step,
High boiling impurities such as acetaldehyde and acetic acid are simultaneously absorbed in substantial amounts.

The bottom liquid of the absorption tower (2) is sent to the conduit (4) and the heat exchanger (5) to exchange heat with the diffusion bottom liquid, and the temperature is raised to 70 to 110 ° C.
It is sent to the gas-liquid separation tank (7) through the conduit (6), and the light component gas of the inert gas partially containing ethylene oxide and water is separated through the conduit (8). The remaining absorption liquid after flushing the light component gas is passed through the conduit (9) and the pressure is set to 0.1 to 0.1.
It is supplied to the upper part of the stripping tower (10) at ² kg / cm ² G and a temperature of 90 to 120 ° C., and it passes through a conduit (13) to a heater (12) of the stripping tower (10) through a conduit (13). ) Or the like, or by directly introducing steam into the bottom of the stripping tower to heat it, and heating at a temperature of 100 at which ethylene oxide is not substantially contained from the bottom of the stripping tower (10).
A part of the bottom liquid of the stripping tower at ˜130 ° C. is supplied to the flash tank (41) through the conduit (14) and the conduit (16), and the pressure is reduced to atmospheric pressure or slightly reduced pressure to generate low-pressure steam, and the solution is generated. Result in a decrease in temperature. The low pressure steam generated in the flash tank (41) is introduced into the conduit (42).
Through a vapor compressor (43) and is compressed to a pressure slightly higher than the bottom pressure of 0.5 kg / cm ² G of the desorption column (10) by a conduit (44) to a gas phase section at the bottom of the desorption column (10). Sent in. The remaining liquid flashed in the flash tank (41) is passed through the conduit (45), the heat exchanger (5) and the cooler (18), through the conduit (21), water, and through the conduit (22), an aqueous potassium hydroxide solution and the conduit ( 23)
Add a defoamer (water-soluble silicone emulsion),
It can be introduced into the absorption tower (2) through a conduit (24).

On the other hand, the remaining absorption liquid extracted from the bottom of the stripping tower (10) through the conduit (14) can be sent to the by-product ethylene glycol concentration tower through the conduit (15).

In order to describe the present invention in more detail, a conventionally known method will be described with reference to FIG.

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 (1) and a packed tower or a plate tower type absorption tower ( 2) is supplied to the lower part, and the absorption liquid is introduced from the conduit (24) to the upper part of the absorption tower (2),
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, carbon dioxide, which was not absorbed from the top of the absorption tower (2),
Inert gases (nitrogen, argon, methane, ethane), aldehydes, acidic substances and other gases are circulated through the conduit (3) to 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 absorption tower (2) is sent to the heat exchanger (5) through the conduit (4) and exchanges heat with the diffusion bottom liquid to raise the temperature to 70 to 110 ° C., and the gas-liquid separation tank ( 7) and the inert gas is separated by the conduit (8). Liquid containing part of ethylene oxide and water is piped (9)
Through column top pressure 0.1 to ² kg / cm ² G, temperature 90 to 1
It is supplied to the upper part of the diffusion tower (10) at 20 ° C., and the diffusion tower (1
Heated by steam or a heating medium such as Dowsome (commercially available from Dow) from the heater (12) of 0), or directly by a heating method of introducing steam to the lower part of the stripping tower (10) to obtain the absorption liquid. 99% by weight of ethylene oxide contained
The above is diffused, and a part of the bottom liquid of the stripping tower at a temperature of 100 to 130 ° C. which does not substantially contain ethylene oxide from the bottom of the stripping tower (10) is passed through the conduit (14) and the conduit (16) to the heat exchanger (5). At that time, heat exchange is performed with the feed liquid of the stripping tower (10), cooling is performed by a cooler (18), and then fresh water is introduced through a conduit (21) to adjust the ethylene glycol concentration in the absorbing liquid. An aqueous potassium hydroxide solution is added through a conduit (22) to adjust the pH in the absorbing liquid, and a conduit (23) to adjust the concentration of the defoaming agent in the absorbing liquid.
An antifoaming agent can be introduced through. 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 stripping column (10) is withdrawn from the bottom of the stripping column (10) through conduits (14) and (15) and sent to the concentration step.

(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 by this embodiment alone.

Example 1 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 passed through a conduit (1) and a plate column type absorption tower ( 2) is supplied to the lower part and the conduit (24) is supplied to the upper part of the absorption tower (2) at a temperature of 29.6 ° C., pH = 6, ethylene glycol concentration = 9.0% by weight, an antifoaming agent (water-soluble silicone emulsion). ) Concentration = 3 ppm and the balance was water, and an absorption liquid was introduced and countercurrently contacted with the reaction product gas to absorb ethylene oxide in the reaction product gas into the absorption liquid.
Here, 99% by weight or more of ethylene oxide in the reaction product gas is recovered. Ethylene, oxygen, carbon dioxide, inert gas (nitrogen, nitrogen, etc.) not absorbed from the top of the absorption tower (2)
Gases such as argon, methane, ethane), aldehydes, acidic substances, etc. are passed through the conduit (3) to the carbon dioxide absorption step and / or
Alternatively, it was recycled to the oxidation reaction step.

The bottom liquid of the absorption tower (2) is fed with a conduit (4), a heat exchanger (5),
It is sent to the gas-liquid separation tank (7) through the conduit (6), and the light component gas of the inert gas partially containing ethylene oxide and water is separated through the conduit (8). The residual absorption liquid after flushing the light gas is passed through the conduit (9) to the diffusion tower (1
0) and the heater (12) of the stripping tower (10).
Steam is supplied through the conduit (13) to heat and the stripping bottom liquid containing substantially no ethylene oxide is withdrawn from the bottom of the stripping tower (10) through the conduit (14), part of which is passed through the conduit (16). Flash tank (41)
And is reduced to a pressure of normal pressure or slightly reduced pressure to generate low-pressure steam, which lowers the temperature of the solution. The low-pressure vapor generated in the flash tank (41) is sent to the vapor compressor (43) through the conduit (42) and compressed to a pressure slightly higher than the bottom pressure of 0.5 kg / cm ² G of the desorption tower (10). By (44), it is fed into the vapor phase section at the bottom of the stripping tower (10). The remaining liquid flushed in the flash tank (41) is passed through the conduit (45), the heat exchanger (5) and the cooler (18), the water is supplied through the conduit (21), the potassium hydroxide aqueous solution is supplied through the conduit (22), and the conduit (22). 23) Defoamer (water-soluble silicone emulsion)
Can be added and introduced into the absorption tower (2) through the conduit (24).

On the other hand, the remaining absorption liquid extracted from the bottom of the stripping tower (10) through the conduit (14) was sent to the by-product ethylene glycol concentration tower through the conduit (15). Table 1 shows the operating conditions of this process all together.

Comparative 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 (1) and a plate column type absorption tower ( 2), and the absorption liquid is introduced from the conduit (24) to the upper part of the absorption tower (2) at a temperature of 29.6.
° C, pH = 6, ethylene glycol concentration = 9.0% by weight,
An antifoaming agent (water-soluble silicone emulsion) concentration = 3 ppm and the balance of water was introduced, and the mixture was countercurrently contacted with the reaction product gas to absorb ethylene oxide in the reaction product gas. Gases such as ethylene, oxygen, carbon dioxide, inert gases (nitrogen, argon, methane, ethane), aldehydes and acidic substances that have not been absorbed from the top of the absorption tower (2) are absorbed through the conduit (3) in the carbon dioxide absorption step. And / or recycled to the oxidation reaction step. The bottom liquid of the absorption tower (4) is sent to a gas-liquid separation tank (7) through a conduit (4), a heat exchanger (5) and a conduit (6), and an inert gas containing ethylene oxide and water is partially generated. Separated by conduit (8). The remaining absorption liquid after flushing the light gas was fed to the upper part of the stripping column (10) through the conduit (9). Dispersion tower (10)
Steam is supplied to the heater (12) through the conduit (13) for heating, and the bottom liquid of the desorption column, which is substantially free of ethylene oxide, is withdrawn through the conduit (14) from the bottom of the desorption column (10). A part through a conduit (16), through a heat exchanger (5) and a cooler (18), through a conduit (21)
Water, an aqueous potassium hydroxide solution from a conduit (22), and an antifoaming agent (water-soluble silicone emulsion) from a conduit (23) are added, and the mixture is supplied to the top of the absorption tower through a conduit (24).

On the other hand, the remaining absorption liquid extracted from the bottom of the stripping tower (10) through the conduit (14) was sent to the by-product ethylene glycol concentration tower through the conduit (15). Table 2 shows the operating conditions of this process all together.

(Effects of the Invention) According to the method of the present invention, the vapor generated when flushing the bottom liquid of the ethylene oxide stripping tower is separated from the flash drum, and is compressed to a little higher than the pressure at the bottom of the ethylene oxide stripping tower by the compression means. By introducing it into the bottom of the tower, the effect of making it possible to greatly reduce the amount of heating required to heat the ethylene oxide stripping tower is exhibited. Further, by carrying out this method, the heat load of the cooling water for cooling the absorption liquid sent to the ethylene oxide absorption tower is reduced.

[Brief description of drawings]

FIG. 1 is an example showing a preferred specific example of the ethylene oxide recovery method of the present invention. FIG. 2 is an example showing a known ethylene oxide recovery method related to the present invention. (2) …… Absorption tower (5) …… Heat exchanger (7) …… Gas-liquid separation tank (10) …… Dissipation tower (12) …… Heater (18) …… Cooler (41) …… Flash tank (43) …… Compressor

Claims (1)

[Claims] 1. A reaction product gas containing ethylene oxide produced by catalytic vapor-phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst is introduced into an absorption tower and is brought into countercurrent contact with the absorbing liquid to absorb it. The gas from the tower top is circulated to the carbon dioxide absorption step and / or ethylene oxidation reaction step, the absorption tower bottom liquid containing ethylene oxide is supplied to the ethylene oxide stripping tower, ethylene oxide is stripped off from the stripping tower top, and withdrawn from the stripping tower bottom. In the process of sending the liquid to the absorption tower and the by-product ethylene glycol concentrating tower, the liquid extracted from the bottom of the stripping tower is subjected to flash treatment, separated into a gas phase portion and a liquid phase portion, and the gas phase portion is compressed to the stripping tower. A method for recovering ethylene oxide, characterized in that the liquid phase is introduced into the absorption liquid of an absorption tower.