JPH0156070B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing ethylene oxide by catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas. The preheating section 6 is composed of a partition plate 4 that partitions the side 16 and the shell side 11 of the cooling section 8 and a large number of reaction tubes 5, and the inlet section of the reaction tube 5 is filled with an inert filler, and the inlet section of the reaction tube 5. A vertical multi-tubular heat exchange reactor 9 is equipped with a reaction section 7 filled with a silver catalyst between the tube and the outlet, and a cooling section 8 filled with an inert filler at the outlet of the reaction tube 5. ~180℃
of hot water is supplied to the shell side 11 through the conduit 10, and brought into contact with the outside of the reaction tube 5 through which the reaction product gas of 200 to 300°C in the cooling section 8 passes, thereby exchanging heat with the reaction product gas containing ethylene, ethylene oxide, and oxygen. did
The hot water at 200 to 250°C is sent to the gas-liquid separation tank 13 through the conduit 12, and the hot water separated in the gas-liquid separation tank 13 is introduced into the shell side 16 of the reaction section 7 through the conduit 15, and the hot water is sent to the gas-liquid separation tank 13 through the conduit 12. The hot water in a gas-liquid mixed phase state boiled in the reaction section 7 is brought into contact with the outside of the reaction tube 5 in the preheating section 6 to preheat the raw material gas and pass through the conduit 17 for gas-liquid separation. The present invention relates to a method for producing ethylene oxide, which is characterized by natural circulation in a tank 13. The present invention relates to a method for producing ethylene oxide by reacting ethylene with a molecular oxygen-containing gas in a method for producing ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen.

In the catalytic gas phase oxidation reaction of hydrocarbons, for example, in the process of producing ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen in the presence of a silver catalyst, in addition to ethylene, saturated hydrocarbons such as methane and ethane, and nitrogen After a hydrocarbon-containing gas containing carbon dioxide, argon, oxygen, etc. and a molecular oxygen-containing gas consisting of air, oxygen-enriched air, or pure oxygen are mixed in a predetermined ratio, a silver catalyst is filled. A catalytic gas phase reaction introduced into the reactor takes place. In the case of ethylene, the exothermic reaction exhibited by most hydrocarbons is as follows: When ethylene is reacted with molecular oxygen in the presence of a silver catalyst, C ₂ H ₄ + 1/2O ₂ →C ₂ H ₄ O + 29Kca1/mol (1 ) C ₂ H ₄ +3O ₂ →2CO ₂ +2H ₂ O + 316Kca1/mol (2) An exothermic reaction occurs.

Among these exothermic reactions, in order to improve the yield of ethylene oxide, the rate at which the reaction shown by reaction formula (1) proceeds should be increased, and silver catalysts and reaction methods are being studied. There is. However, at present, it is impossible to avoid the occurrence of reaction formula (2), that is, the complete oxidation reaction of ethylene, which has a large reaction heat.

In addition to the above formulas (1) and (2), there is another reaction that affects the yield of ethylene oxide.
It is an isomerization reaction of ethylene oxide to acetaldehyde that proceeds according to the reaction formula shown in the following formula (3).

Therefore, no matter how high the selectivity of ethylene to ethylene oxide is, if there are many isomerization reactions of the generated ethylene oxide to acetaldehyde, the yield of ethylene oxide will decrease. Minimizing reactions is also a challenge in ethylene oxide production.

In recent years, as the demand for ethylene oxide has increased, and in order to reduce the production cost of ethylene oxide, ethylene oxide production plants have been increasing in size. Therefore, the amount of reaction heat in the reactor per ethylene oxide production plant is large, as understood from the above reaction formula, although the yield has been considerably improved. How to safely and effectively recover and use this large amount of reaction heat is an important issue from a safety and economic standpoint when producing ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen. That's a problem.

Generally, in the catalytic gas phase oxidation of hydrocarbons using molecular oxygen, a method is known in which the reaction product gas is passed through a cooling zone filled with packing to suppress side reactions (U.S. Pat. No. 3,147,084). ). It is also known to apply such a method to a method for producing ethylene oxide by catalytic gas phase oxidation of ethylene using molecular oxygen. For example, according to JP-A-51-4101, the reaction product obtained in the reaction zone is passed through a cooling zone, which may or may not be adjacent to the reaction zone and may or may not contain an inert material. Also, JP-A-53
According to No. 2409, the reaction product is passed through a cooling zone filled with inert refractory granules having a surface area of less than 0.1 m ² /g. However, the reaction equipment used in these methods removes heat by circulating a high boiling point heat medium such as Dowsum or a low boiling point heat medium such as water in the reaction zone, and the cooling zone is Methods using high boiling point heat carriers such as Dowsum have been adopted, but these methods have the drawbacks that the heat carriers are hazardous materials with high boiling points and are difficult to handle, and the equipment is complex and operation is not easy. have.
Therefore, the purpose of the present application is to easily circulate or pass hot water through the preheating section, reaction section, and cooling section of the reactor, and to recover the supplied hot water as steam. The object of the present invention is to provide a method and apparatus for catalytic gas-phase oxidation of hydrocarbons that can achieve effective heat recovery.

Conventionally, as a reactor for producing ethylene oxide through catalytic gas phase oxidation of ethylene and molecular oxygen, a multi-tubular heat exchange reactor is used between the outside of the reaction tube and a heat exchanger structured to generate water vapor. The reaction tube is cooled by forcibly circulating a heat medium with a high boiling point, such as Dow Sam (trade name, manufactured by The Dow Company), using a pump, and the heat medium at an elevated temperature is heated by removing the reaction heat. A multi-tubular heat exchange reactor is known, which has a structure in which heat is applied to water in an exchanger to generate steam, and the heat medium cooled here is recirculated to cool the outside of the reaction tube.

In addition, when a heat medium that evaporates, such as water, is used as a heat medium, water vapor is directly generated on the shell side of the multi-tubular heat exchange reactor, so a heat exchanger with a structure that generates water vapor as described above is used. A multi-tubular heat exchange type reactor is also known, which does not require a reactor and also does not require pump equipment because hot water can be circulated naturally.

However, in the above method, the temperature of the reaction gas from the reactor outlet is high, and the heat exchange performed in the heat exchanger between the reaction raw material gas and the product gas causes the raw material gas to become high temperature, and the inside of the pipe up to the reactor entrance is high temperature. is maintained. As a result, the oxygen concentration in the raw material gas has to be controlled low at the expense of productivity in order to keep it below the lower explosive limit at that temperature.

Another object of the present invention is to not only reduce the risk of explosion of the high-temperature explosive gas of the reaction product gas containing ethylene, ethylene oxide, and oxygen that has flowed out from the catalyst layer, but also to Another object of the present invention is to provide a method for catalytic gas phase oxidation of hydrocarbons in which productivity can be expected to be improved by increasing the oxygen concentration in the hydrocarbons.

Other objects of the invention will become apparent from the description below.

The present invention relates to a method for producing ethylene oxide by catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas. It consists of a partition plate 4 that partitions the shell side 11 and a large number of reaction tubes 5, and a preheating section 6 in which the inlet of the reaction tube 5 is filled with an inert filler, and a silver plate between the inlet and outlet of the reaction tube 5. A vertical multi-tubular heat exchange reactor 9, which is equipped with a reaction section 7 filled with a catalyst and a cooling section 8 filled with an inert filler at the outlet of the reaction tube 5, is heated to a temperature of 130 to 180°C.
of hot water is supplied to the shell side 11 through the conduit 10, and brought into contact with the outside of the reaction tube 5 through which the reaction product gas of 200 to 300°C in the cooling section 8 passes, thereby exchanging heat with the reaction product gas containing ethylene, ethylene oxide, and oxygen. did
The hot water at 200 to 250°C is sent to the gas-liquid separation tank 13 through the conduit 12, and the hot water separated in the gas-liquid separation tank 13 is introduced into the shell side 16 of the reaction section 7 through the conduit 15, and the hot water is sent to the gas-liquid separation tank 13 through the conduit 12. The hot water in a gas-liquid mixed phase state boiled in the reaction section 7 is brought into contact with the outside of the reaction tube 5 in the preheating section 6 to preheat the raw material gas and pass through the conduit 17 for gas-liquid separation. The present invention relates to a method for producing ethylene oxide, which is characterized by natural circulation in a tank 13.

In the present invention, the preheating section is a region in which the inlet of the reaction tube is filled with an inert filler, the reaction section is a region in which silver catalyst is filled between the inlet and outlet of the reaction tube, and the cooling section is a region in which a silver catalyst is filled between the inlet and outlet of the reaction tube. This is a region filled with an inert filler at the outlet of the reaction tube.

The inert filler to be filled in the preheating section and the cooling section of the reactor of the present invention may be any inert refractory material, including spheres, hemispheres, pellets, rings, and amorphous materials. Preferred are alumina, silica alumina, zirconia, magnesia, silicon carbide, etc., which are commonly used as carriers for silver catalysts, and α-alumina and zirconia are particularly preferred. The shape, size, pores, specific surface area, apparent porosity, etc. of these inert refractory carriers can be appropriately selected in consideration of pressure loss and mechanical strength when filled into a reaction tube. The average particle size is usually 1/
The diameter is 16 to 1/2 inches, preferably 3/16 to 1/2 inches, and spheres or rings are preferred. Further, it is preferable to use a carrier in which at least one selected from sodium, potassium, rubidium, cesium, lithium, calcium, strontium, barium, and thallium is precipitated on the above-mentioned inert refractory carrier, and in particular, sodium, potassium, rubidium,
Cesium and thallium are preferred. In particular, it is preferable to fill the reaction tube 5 of the cooling section 8 with these.

By partitioning the shell side of the vertical multi-tubular heat exchange type reactor used in the present invention into a reaction section and a cooling section with a partition plate, 200 ml of hydrocarbons containing hydrocarbons, their oxidation products, and oxygen flowing out from the catalyst layer can be separated into a reaction section and a cooling section. The reaction product gas at a high temperature of ~300℃ is cooled by supplying hot water with a temperature of 130 to 180℃ to the shell side in a cooling section filled with inert fillers, and the reaction product gas at the outlet of the cooling section is cooled to a temperature of 150 to 250℃.
The temperature can be controlled in ℃. Providing this cooling section is important because, for example, when ethylene oxide is produced by catalytic gas phase oxidation of ethylene using molecular oxygen, the oxidation reaction is carried out at a temperature of 200 to 300°C, so naturally the temperature of the produced gas is is the same level or higher, causing an isomerization reaction of ethylene oxide to acetaldehyde. Therefore, by providing a cooling section immediately after the reaction product gas leaves the reaction section, the effect of reducing the isomerization reaction of ethylene oxide to acetaldehyde can be reduced. bring.

In the present invention, since hot water is used as a heat medium in the reaction device, there is no danger of ignition, and by using hot water, natural circulation is possible and no circulation pump equipment is required. Therefore, there is no problem of abnormal temperature rise in the reaction section due to sudden stoppage of the circulation pump. Further, when hot water is used, heat transfer is good, so heat can be removed efficiently, and as a result, there is an advantage that the reaction rate can be higher than when other heat media are used.

In the present invention, the reaction product gas containing ethylene and oxygen flowing out from the reaction section is cooled to 150 to 250
By cooling to ℃, the temperature of the raw material gas can be suppressed to 100 to 200℃ in heat exchangers that preheat the raw material gas with the reaction product gas, and the oxygen concentration in the raw material gas can be increased. It is something to do. Furthermore, by using the reaction apparatus of the present invention, the hot water supplied as a heat medium can directly generate steam on the reactor shell side, and moreover, it has the effect of recovering steam commensurate with the supplied hot water. It is. Furthermore, using the hot water exiting the cooling section to replenish the cooling medium in the reaction section is advantageous in terms of economics such as utilization of thermal energy, construction, and equipment costs.

As mentioned above, the method of passing or circulating a cooling medium through the cooling section and the reaction section separately is known, and the effect on the reaction surface is the same.

However, the method of the present invention is different in that it can generate a large amount of high-pressure steam with a high energy level that is advantageous for later energy utilization, and is also different in terms of economy in terms of construction and equipment due to the simplification of the process. There is.

As the process and reaction conditions to which the method of the present invention can be applied, any of the processes and reaction conditions conventionally known in this field can be applied. For example, the process of producing ethylene oxide by catalytic catalytic oxidation of ethylene with molecular oxygen includes an air oxidation method using air as an oxygen source and an oxygen oxidation method using pure oxygen. It can also be effectively applied. In particular, an oxygen oxidation method that can increase the reaction amount per passage of the catalyst layer and increase the ethylene oxide concentration can be effectively applied.

The operating conditions are that the raw material gas mixture consists of ethylene, oxygen, carbon dioxide, nitrogen, argon, methane, ethane, dichloroethane, etc. to suppress the reaction, and the higher the ethylene concentration, the more advantageous it is, but it should not exceed 40% by volume. It is. Carbon dioxide gas is less than 10% by volume. Also, when methane or ethane is present in the gas, methane shifts the explosive range to the safe side,
Since it has the effect of narrowing the explosion range, it is effective to be present in fairly high concentrations as a reactant gas diluent.

Reaction pressure is 0~40Kg/ ^cm2G , preferably 10~30G
Kg/cm ² G. The reaction temperature is 150-300°C, preferably 180-280°C. Space velocity is 1000 ~
10,000 hr ⁻¹ , preferably 2,000 to 8,000 hr ⁻¹ .

Any conventionally known silver catalyst can be used as the catalyst filled in the reaction section, but the specific surface area is 20 m ² /g or less, preferably 0.01 to 10 m 2 /g, and the apparent porosity is 20 m ² /g or less.
Preferably, fine particles of metallic silver are precipitated and supported on an inert refractory carrier in an amount of 20% by volume or more, preferably 30 to 70% by volume, and a reaction accelerator containing alkali metals, alkaline earth metals, thallium, antimony, tin, etc. It is preferable to add at least one selected one. As the carrier material, inert refractory carriers such as alumina, silica alumina, silicon carbide, zirconia, and magnesia can be used, and inert refractory carriers containing α-alumina as a main component are particularly preferred. The shape of the carrier includes spheres, hemispheres, rings, pellets, etc., but spheres and rings are preferred. The average particle diameter is preferably 1/16 to 1/2 inch, particularly preferably 3/16 to 5/16 inch. The amount of silver supported in the catalyst may be from 1 to 20% by weight, in particular from 5 to 15% by weight, which is substantially economical.

BRIEF DESCRIPTION OF THE DRAWINGS In order to explain the present invention in more detail, the present invention will be explained with reference to the drawings. The drawings show an embodiment and an apparatus used for catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst, and do not limit the present invention.

In Figure 1, the shell plate 1, the upper tube plate 2, the lower tube plate 3, the shell side 16 of the reaction section 7, and the cooling section 8
The preheating section 6 is composed of a partition plate 4 that partitions the shell side 11 of the reaction tube 4 and a large number of reaction tubes 5, and the inlet section of the reaction tube 5 is filled with an inert filler. A reaction section 7 filled with a silver catalyst, a cooling section 8 filled with an inert filler at the outlet of the reaction tube 5
A vertical multi-tubular heat exchange reactor 9 equipped with a temperature
Hot water of 130 to 180℃ is passed through the conduit 10 to the shell side 1.
1, and the outside of the reaction tube 5 through which the reaction product gas of 200 to 300°C in the cooling section 8 passes is brought into contact with ethylene,
The hot water of 200 to 250°C that has undergone heat exchange with the reaction product gas containing ethylene oxide and oxygen is sent to the gas-liquid separation tank 13 through the conduit 12, and the hot water separated in the gas-liquid separation tank 13 is sent to the shell of the reaction section 7 through the conduit 15. side 16
and brought into contact with the outside of the reaction tube 5 of the reaction section 7,
The gas-liquid mixed-phase hot water that absorbs the reaction heat and boils in the reaction section 7 contacts the outside of the reaction tube 5 in the preheating section 6 to preheat the raw material gas, and passes through the conduit 17 to the gas-liquid separation tank 13.
The water is naturally circulated, mixed with hot water from the conduit 12, and the temperature is lowered. Temperature separated in gas-liquid separation tank 13
Water vapor at a temperature of 210 to 250° C. and a pressure of 20 to 40 kg/cm ² G can be recovered through the conduit 14. On the other hand, conduit 18
A raw material gas containing ethylene and molecular oxygen at a temperature of 10 to 80°C is introduced, and passed through a heat exchanger 19 to a temperature of 100 to 80°C.
It is preheated to 200°C, introduced into the reaction tube 5 of the vertical multi-tubular heat exchange reactor 9 through the conduit 20, passed through the preheating section 6, the reaction section 7 and the cooling section 8, and then passed through the conduit 22.
The reaction product gas at 150 to 250°C can be sent to the heat exchanger 19 to preheat the raw material gas.

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, this example is one aspect of the invention, and does not limit the invention.

Example 1 Consisting of a shell plate 1, an upper tube plate 2, a lower tube plate 3, a partition plate 4 that partitions the shell side 16 of the reaction section 7 and the shell side 11 of the cooling section 8, and a large number of reaction tubes 5, and, A preheating section 6 filled with an inert refractory alumina carrier at the inlet of the reaction tube 5, a reaction section 7 filled with a silver catalyst between the inlet and outlet of the reaction tube 5, and cesium at the outlet of the reaction tube 5. Hot water at a temperature of 145° C. is passed through a conduit 10 into a vertical multi-tubular heat exchange reactor 9 equipped with a cooling section 8 filled with supported inert refractory alumina carrier at a rate of 90 kg/hour. Ethylene, ethylene oxide, and oxygen at a temperature of 255°C are supplied to the shell side 11 from the reaction tube 5 of the reaction section 7.
The outside of the reaction tube 5 in the cooling section 8 through which the reaction product gas containing carbon dioxide passes is cooled, and the reaction heat is removed to bring the temperature to 240.
The hot water heated to ℃ is sent to the gas-liquid separation tank 13 through the conduit 12, where it is separated into gas and liquid.The hot water at a temperature of 240℃ is sent from the bottom of the gas-liquid separation tank 13 to the conduit 15 at a rate of 4500 kg/hour. It is introduced into the shell side 16 of the reaction section 7 through the tube, contacts the outside of the reaction tube 5 of the reaction section 7 and the preheating section 6 in a boiling gas-liquid mixed phase state, and leads to the gas-liquid separation tank 13 through the conduit 17. The pressure of 33.1Kg/
Steam at a temperature of 240° C. and cm ² G was collected through conduit 14 at a rate of 90 kg/hour.

On the other hand, a raw material gas containing ethylene and molecular oxygen at a temperature of 45°C is introduced into the shell side of the heat exchanger 19 through the conduit 18, and a reaction product at a temperature of 210°C is introduced into the tube side of the heat exchanger 19 through the conduit 21. The reaction product gas, which was subjected to heat exchange with the gas and cooled to a temperature of 75° C., was sent through conduit 22 to the ethylene oxide absorption step. On the other hand, the raw material gas preheated to a temperature of 180°C is introduced into the reaction tube 5 of the vertical multi-tubular heat exchange reactor 9 through the conduit 20 at a space velocity of 5000 hr ^-1 , and is introduced into the preheating section 6, reaction section 7 and After passing through the cooling section 8, the reaction product gas was sent to the heat exchanger 19 through the conduit 21.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of an apparatus for producing ethylene oxide.

Claims (1)

[Claims] 1 In a method for producing ethylene oxide by catalytic gas phase oxidation of ethylene with a molecular oxygen-containing gas, shell plate 1, upper tube plate 2, lower tube plate 3, shell side 16 of reaction section 7 and shell side of cooling section 8 11
A preheating section 6 is composed of a partition plate 4 and a large number of reaction tubes 5, and the inlet of the reaction tube 5 is filled with an inert filler, and a silver catalyst is filled between the inlet and outlet of the reaction tube 5. Hot water at a temperature of 130 to 180° C. is passed through a conduit 10 into a vertical multi-tubular heat exchange reactor 9, which is equipped with a reaction section 7 and a cooling section 8 filled with an inert filler at the outlet of the reaction tube 5. Reaction tube 5 which is supplied to the shell side 11 and through which reaction product gas of 200 to 300°C in the cooling section 8 passes
200~ where the outside of the gas was brought into contact and heat exchanged with reaction product gas containing ethylene, ethylene oxide, and oxygen.
250°C hot water passes through conduit 12 to gas-liquid separation tank 13
The hot water separated in the gas-liquid separation tank 13 is sent to the conduit 1
5 into the shell side 16 of the reaction section 7, the outside of the reaction tube 5 of the reaction section 7 is brought into contact with the outside of the reaction tube 5 of the reaction section 7, and the gas-liquid mixed phase hot water boiled in the reaction section 7 removes the reaction heat and flows into the reaction tube of the preheating section 6. 5, the raw material gas is preheated, and is naturally circulated through a conduit 17 to a gas-liquid separation tank 13.