JP2015098455A - Method for producing unsaturated nitrile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing unsaturated nitrile, in which clogging of a heat exchanger arranged on an outlet line of a reactor and clogging of a quick cooling tower arranged in the downstream of the heat exchanger can be prevented.SOLUTION: The method for producing unsaturated nitrile by an ammoxidation reaction comprises the steps of: feeding a gaseous raw material containing at least one selected from the group consisting of alkane, olefin and alcohol to a catalyst-packed reactor to advance the ammoxidation reaction in the reactor; introducing the reaction product gas produced by the ammoxidation reaction into a heat exchanger to cool the introduced reaction product gas; and introducing the reaction product gas cooled in the heat exchanger into a quick cooling tower to cool the introduced reaction product gas. A liquid or a gas of 110°C or higher temperature is used as a cooling medium for cooling the reaction product gas in the heat exchanger. The quick cooling tower is an empty tower having no packed layer, or has a packed layer having 1.5 m or less height or 90% or higher void volume.

Description

  The present invention relates to a method for producing an unsaturated nitrile.

  Conventionally, as a method for producing an unsaturated nitrile of a hydrocarbon compound, a method for producing an α, β-unsaturated nitrile by an ammoxidation reaction of propylene, isobutene or tertiary butanol is well known. In recent years, a method for producing an α, β-unsaturated nitrile having the same carbon number by subjecting a saturated hydrocarbon such as propane or isobutane to ammoxidation has been put into practical use. In these ammoxidation reactions, a fluidized bed reactor is generally used. When olefin is used as a raw material, molybdenum and / or antimony composite oxide is used as a catalyst. When paraffin is used as a raw material, a molybdenum / vanadium composite oxide is generally used as a catalyst.

  When an unsaturated nitrile is produced by an ammoxidation reaction using a fluidized bed reactor, a heat exchanger is installed in the reactor outlet line in order to cool a high-temperature reaction product gas produced by the reaction. Further, the product gas cooled by the heat exchanger is introduced into the quenching tower.

  Patent Document 1 discloses a method using a multistage quenching tower as the quenching tower used in this method. According to the method described in Patent Document 1, the quenching tower is divided into two upper and lower sections, and the reaction product gas is first guided to the lower section of the quenching tower, where it is cooled and washed with the first cooling water containing sulfuric acid. Then, neutralization of unreacted ammonia in the reaction product gas, separation and removal of high boiling point by-products, polymer, and flying catalyst are performed. Subsequently, the reaction product gas is guided to the upper section of the quenching tower and is cooled again with the second cooling water containing sulfuric acid, and unreacted ammonia is separated from the reaction product gas. According to this method, the cooler is installed in both the first and second cooling water circulation lines.

US Pat. No. 3,649,179

  In the reaction product gas produced by the ammoxidation reaction, there are high-boiling by-products in addition to useful components and water produced by the reaction. Although the ammoxidation reaction proceeds at a high temperature, a heat exchanger is installed at the outlet line of the reactor in order to recover the heat of the generated high-temperature reaction gas (typically 400 to 500 ° C.). ing. The high boiling point by-product generated by the ammoxidation reaction condenses and aggregates near the heat transfer member of the heat exchanger (for example, near the side pipe in the case of a tube heat exchanger), and heat transfer of the heat exchanger It adheres to the member surface and causes clogging of the product gas flow path. As a result, there is a technical problem that the pressure in the reactor rises and it becomes difficult to keep the operation of the reactor stably for a long time.

  In addition, even if the reaction product gas flow path can be prevented from clogging in the heat exchanger installed in the reactor outlet line, the high-boiling by-product that has passed through the heat exchanger is liquid circulation provided in the quenching tower. This may cause line contamination and clogging. Further, when a cooler is provided in the liquid circulation line, the frequency of cleaning the cooler increases due to contamination and clogging of the cooler. Furthermore, if there is a packed bed filled with packing in the quenching tower and the quenching tower does not function as desired due to contamination and clogging of the packed bed, the entire unsaturated nitrile production apparatus including the reactor is Since it becomes necessary to stop the operation and perform maintenance of the quenching tower, it becomes difficult to continue the operation of the apparatus for a long time.

  The present invention has been made in view of the above problems, and it is possible to prevent unsaturated nitriles that can prevent clogging of the heat exchanger installed in the reactor outlet line and the quenching tower downstream thereof, particularly clogging inside the tower. An object is to provide a manufacturing method.

  The present inventors provide a method for preventing clogging of a heat exchanger installed in a reactor outlet line and also preventing clogging of a quenching tower installed downstream of the heat exchanger, particularly clogging inside the tower. , Earnestly studied. As a result, it is possible to solve clogging of the heat exchanger and the quenching tower at once by using a refrigerant having a predetermined temperature as the refrigerant used in the heat exchanger and making the packed bed in the quenching tower a predetermined one. As a result, the present invention has been completed.

That is, the present invention is as follows.
[1] A method for producing an unsaturated nitrile by an ammoxidation reaction, wherein a raw material gas containing at least one selected from the group consisting of an alkane, an olefin, and an alcohol is supplied to a reactor filled with a catalyst, A first step of advancing the ammoxidation reaction in the reactor, a second step of introducing and cooling the reaction product gas generated by the ammoxidation reaction into a heat exchanger, and cooling in the heat exchanger A third step of introducing the reaction product gas into a quenching tower and cooling it, and using a liquid or gas at 110 ° C. or higher as a refrigerant for cooling the reaction product gas in the heat exchanger, and The method for producing an unsaturated nitrile, wherein the quenching tower is an empty tower having no packed bed, or has a packed bed having a height of 1.5 m or less or a porosity of 90% or more.
[2] The method for producing the unsaturated nitrile, wherein the temperature of the refrigerant is 140 to 260 ° C.
[3] In the third step, the reaction product gas is cooled with 65 to 95 ° C. cooling water. [4] The temperature of the liquid extracted from the bottom of the quenching tower is 75. The manufacturing method of the said unsaturated nitrile which is -98 degreeC.
[5] The method for producing the unsaturated nitrile, wherein the temperature of the gas flowing out from the quenching tower is 65 to 95 ° C., and the gas contains water vapor having a saturated water vapor pressure.
[6] The method for producing the unsaturated nitrile, wherein the specific gravity of the liquid extracted from the bottom of the quenching tower is 1.10 to 1.20.
[7] The method for producing an unsaturated nitrile, wherein the source gas includes at least one selected from the group consisting of propylene, isobutene, tertiary butanol, propane, and isobutane.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the unsaturated nitrile which can prevent clogging of the heat exchanger installed in the reactor exit line and the quenching tower of the downstream can be provided.

It is a flowchart which shows typically an example of the apparatus used for the manufacturing method of the unsaturated nitrile of this invention.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. However, the present invention is limited to the following embodiment. It is not a thing. The present invention can be variously modified without departing from the gist thereof. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  The method for producing an unsaturated nitrile according to the present embodiment is a method for producing an unsaturated nitrile by an ammoxidation reaction, and at least one selected from the group consisting of an alkane, an olefin, and an alcohol in a reactor filled with a catalyst. And a reaction product gas generated by the ammoxidation reaction (hereinafter also referred to simply as “product gas”) to the heat exchanger. A refrigerant that has a second step of introducing and cooling and a third step of introducing and cooling the reaction product gas cooled in the heat exchanger into the quenching tower, and cooling the reaction product gas in the heat exchanger As above, a liquid or gas at 110 ° C. or higher is used, and the quenching tower is an empty tower without a packed bed, or the height is 1.5 m or less or the porosity is 90% or more and not 100%. Those having a packed bed. According to such a production method, it is possible to solve simultaneously the prevention of clogging of the heat exchanger installed in the outlet line of the reactor and the prevention of clogging of the quenching tower installed downstream of the heat exchanger, particularly inside the tower.

(1) First step (reaction step)
The first step is a reaction step in which a raw material gas containing at least one selected from the group consisting of alkanes, olefins, and alcohols is supplied to a reactor filled with a catalyst, and an ammoxidation reaction proceeds in the reactor. . The source gas preferably contains at least one selected from the group consisting of propylene, isobutene, tertiary butanol, propane and isobutane. The reaction system in the reactor may be a fluidized bed reaction or a fixed bed reaction. The fluidized bed reaction is a gas phase ammoxidation reaction, for example, production of acrylonitrile by a gas phase ammoxidation reaction using propane or propylene, ammonia and oxygen as raw materials, isobutene, tertiary butanol or isobutane, ammonia and oxygen as raw materials. It is often used when the production of methacrylonitrile by the gas phase ammoxidation reaction is carried out on an industrial scale. Also in this embodiment, such a fluidized bed reaction is preferable.

In the fluidized bed reactor, it is necessary that the catalyst particles are maintained in a fluidized state. The catalyst may be a catalyst conventionally known as a catalyst used when an unsaturated nitrile is produced from the raw material gas by an ammoxidation reaction. For example, in the ammoxidation reaction of olefin, a composite oxide mainly composed of molybdenum and / or antimony may be used. Moreover, as a catalyst used for the ammoxidation reaction of paraffin, the composite oxide which has molybdenum or vanadium as a main component is mentioned, for example. The reaction pressure in the fluidized bed reactor is not particularly limited, and may be, for example, 1.5 kg / cm ² G or less. The reaction temperature is not particularly limited as long as the raw materials react in a gas phase, and may be 400 to 500 ° C.

(2) Second step (Production gas cooling step by heat exchanger)
The second step is a cooling step in which the reaction product gas generated by the ammoxidation reaction is introduced into the heat exchanger and cooled by the refrigerant. Preferably, the product gas produced by the fluidized bed reaction flows out of the reactor, and flows into a heat exchanger installed in the reactor outlet line to be cooled. The heat exchanger is not particularly limited in its method and structure as long as it has an appropriate cooling capacity. However, from the viewpoint of cooling efficiency in the heat exchanger, a shell / tube heat exchanger is preferable. The product gas from the reactor is introduced to the tube side (inside the tube) which is the heat transfer member of this heat exchanger, and the refrigerant is introduced to the shell side (outside the tube), and heat exchange between them The heat of the product gas is recovered.

  The temperature of the refrigerant introduced into the heat exchanger is 110 ° C. or higher, and what is previously heated to that temperature may be used. By using a refrigerant heated to 110 ° C. or higher, the temperature is kept higher than the temperature of the high-boiling by-product in the product gas, and blockage due to condensation of the high-boiling by-product in the heat exchanger of the reactor outlet line is prevented. be able to.

  The catalyst used in the reaction step is, for example, fine particles having an average particle size of around 50 μm, and the catalyst particles are contained in the product gas. From the viewpoint of more effectively preventing such catalyst particles from accumulating in the heat exchanger, when a shell / tube type heat exchanger is used, the tube is preferably a straight tube. A structure in which the product gas passes through the gas in one pass is preferable.

  From the viewpoint of more effectively and reliably preventing the high-boiling by-product from adhering to the wall surface of the product gas flow path of the heat exchanger, it is preferable to control the temperature by monitoring the temperature of the refrigerant introduced into the heat exchanger. . The gas temperature in the product gas flow path becomes lower as it goes downstream, and high-boiling byproducts are likely to adhere. Therefore, when the refrigerant is introduced from the downstream side of the product gas flow path, that is, the counterflow type, and the inlet temperature (supply temperature) of the refrigerant to the heat exchanger is controlled, the temperature on the downstream side of the product gas is also increased. This is preferable because it is easy to manage. From the same point of view, the temperature and / or flow rate of the refrigerant introduced into the heat exchanger can be controlled by monitoring the temperature of the product gas at the outlet of the heat exchanger so that the temperature becomes a certain temperature or higher. preferable. However, it is not always necessary to accurately measure the temperature of the product gas heat exchanger outlet, and there is a certain relationship between the temperature of the product gas heat exchanger outlet and the temperature of the refrigerant introduced into the heat exchanger. May be monitored, the temperature of the refrigerant introduced into the heat exchanger may be monitored to control the temperature and / or flow rate of the refrigerant.

  The refrigerant introduced into the heat exchanger may be liquid or gas. The liquid used as the refrigerant is preferably water, and examples thereof include pure water, industrial water, seawater, and a mixture of two or more thereof. Such a refrigerant may be pressurized and heated by a boiler and adjusted to a temperature of 110 ° C. or higher. Examples of the gas used as the refrigerant include water vapor, air, nitrogen, carbon dioxide, or a mixture of two or more thereof. What is necessary is just to heat such a refrigerant | coolant with a boiler etc. and to adjust to 110 degreeC or more. From the viewpoint of more effectively and reliably suppressing the high boiling point by-product contained in the product gas from adhering to the inner wall of the heat exchanger (for example, the surface of the heat transfer member), the temperature of the refrigerant introduced into the heat exchanger is: Preferably it is 140-260 degreeC, More preferably, it is 170-240 degreeC. In order to control the temperature of the refrigerant to a desired temperature, the amount and temperature of the preheated refrigerant supplied to the heat exchanger may be adjusted. The temperature of the product gas flowing out of the reactor is generally the same as the reaction temperature, and is generally 400 to 500 ° C. Therefore, even if the temperature of the refrigerant is in the above range, the product gas can be cooled without any problem.

(3) Third step (product gas cooling step in the quenching tower)
The third step is a cooling step of cooling the product gas with 75 to 95 ° C. cooling water. First, the product gas cooled by the heat exchanger in the reactor outlet line is introduced into the quenching tower. In the quenching tower, in addition to the target product, a product gas containing a high-boiling by-product that is secondaryly generated by an ammoxidation reaction in the first step, unreacted ammonia, a catalyst scattered from the reactor, and the like. Cooled with cooling water and washed. The cooling water preferably contains an acid in addition to water. Thereby, the unreacted ammonia that can be contained in the product gas is neutralized by the acid to produce an ammonium salt.

  Moreover, it is preferable that at least a part of the cooling water is circulated in the quenching tower. That is, it is preferable that the cooling water flows into the quenching tower again after cooling the product gas and flowing out of the quenching tower. In this case, it is more preferable that the cooling water is at least partially cooled after flowing out of the quenching tower and flows into the quenching tower again. For example, a cooling water circulation line may be provided in the quenching tower, and a heat exchanger for cooling the cooling water flowing out of the quenching tower may be installed in the circulation line. Thereby, even if it is a case where cooling water is circulated, the temperature of cooling water can be controlled easily. The cooling water is circulated in the quenching tower using, for example, a pump provided in the circulation line. The circulation amount is not particularly limited, but is, for example, 40 to 60 t per 1 t of unsaturated nitrile contained in the product gas.

  The cooling water may be circulated and reused as described above, but at least a part of it may be newly supplied to the quenching tower (make-up water). Details of the makeup water will be described later.

  In the product gas cooling step, the product gas introduced into the quenching tower is cooled, and at the same time, the product gas and the cooling water are in direct contact with each other, so that moisture in the product gas generated by the reaction can be condensed. Further, when the product gas is introduced into the quenching tower, it is cooled by increasing the humidity by evaporation of the cooling water.

  The cooling water is preferably sprayed from a spray nozzle installed inside the quenching tower. This further promotes contact between the product gas and the cooling water.

  Further, for the purpose of cooling with cooling water in the quenching tower, the quenching tower may be filled with a packing for efficiently bringing the product gas and cooling water into contact with each other. However, high-boiling by-products contained in the product gas that has passed through the heat exchanger installed in the reactor outlet line cause dirt and clogging (clogging) in the quenching tower. It becomes more pronounced when the tower is equipped with packing. Accordingly, by reducing the packing that causes clogging, clogging inside the tower of the quenching tower can be more effectively and reliably suppressed. Specifically, the porosity of the packed bed is 90% or more, or the height of the packed bed is 1.5 m or less. Here, the “filled layer” is a space in which the filler is present, and a gap between the fillers, a hole portion of the filler, and the like are regarded as a part of the packed layer.

  When the porosity of the packed bed is used as an index, the porosity of the packed bed is 90% or more, preferably 92% or more. When the porosity of the packed bed is 90% or more, blockage due to dirt can be further suppressed. In the specification, the “porosity” of the packed bed is the ratio of the gaps between the packings and the pores of the packing to the volume (volume) of the whole packed bed. Since the porosity of the packed bed depends on the shape of the packing filled in the packed bed, a filler having a shape that allows the porosity to be in the above range may be used to adjust the porosity. Examples of the filler capable of adjusting the porosity within such a range include a pole ring type and a Raschig (registered trademark) ring type filler. The method for measuring the porosity of the packed bed is as follows. That is, a container with a known volume is filled with the filling, water is filled up to the height of the edge of the container, and the volume of the water is measured. When filling the container with water, the bubbles cannot be calculated accurately if they are present. When the volume of the container is A and the volume of water is B, the value calculated by B / A × 100 is the porosity (%) of the packed bed.

  When the height of the packed bed is used as an index, the height of the packed bed is 1.5 m or less, and more preferably 1.0 m or less. Since the product gas moves at least in the height direction of the packed bed in the quenching tower, the height of the packed bed is 1.5 m or less, which shortens the distance in the moving direction of the product gas and clogs the quenching tower. Is less likely to occur.

  Furthermore, from the viewpoint of further suppressing clogging of the quenching tower, it is preferable to satisfy the above-described conditions of the porosity of the packed bed and the height of the packed bed at the same time. Specifically, the porosity of the packed bed is preferably 90% or more, the height of the packed bed is preferably 1.5 m or less, the porosity of the packed bed is 92% or more, and The height of the layer is more preferably 1.0 m or less, and an empty tower is particularly preferable. In addition, an empty tower here means that a quenching tower does not have a packed bed.

  In industrial production of unsaturated nitriles, the height of the quenching tower is usually 5 to 7 m regardless of the production capacity. On the other hand, the diameter of the quenching tower is generally different according to the production capacity of unsaturated nitrile.

When the porosity of the packed bed is 90% or more, or when the height of the packed bed is 1.5 m or less, the contact efficiency between the product gas and the cooling water tends to decrease. Therefore, it is desirable to increase the contact between the product gas and the cooling water by providing a spray nozzle inside the quenching tower. In this case, when a spray nozzle is installed inside the quenching tower, cooling water is uniformly sprayed from the spray nozzle in order to cool the generated gas introduced into the quenching tower. The number of spray nozzles, the installation density, the model, and the like are appropriately adjusted so that the cooling water is sprayed more uniformly on the generated gas. In order to cool the product gas more sufficiently, it is desirable that the spray nozzles are installed in multiple stages in the height direction of the quenching tower. Examples of the type of spray nozzle to be used include a hollow cone type and a full cone type, preferably a hollow cone type. The installation density of the spray nozzles is preferably 2 to 5 / m ² with respect to the cross-sectional area of the quenching tower (cross-sectional area when cut perpendicular to the height).

  In the case of the conventional general acrylonitrile manufacturing process, from the viewpoint of improving the efficiency of gas-liquid contact in the quenching tower, the porosity of the packed bed is approximately 80% or less, and the height of the packed bed is 2 m or more. is there.

  Since a high-boiling by-product and ammonium sulfate (ammonium sulfate) stay at the bottom of the quenching tower and concentrate, the liquid existing in the bottom of the tower (hereinafter referred to as “column bottom liquid”) is continuously or batch-type. It is preferable to withdraw from the quenching tower. The amount of the bottom liquid may be such that the high-boiling by-product and ammonium sulfate in the bottom liquid are not excessively concentrated, for example, 0.1 to 0.3 t with respect to 1 t of unsaturated nitrile. As will be described later, it is preferable to adjust the extraction amount of the column bottom liquid while confirming the specific gravity (concentration) of the column bottom liquid.

  In order to prevent overconcentration of the column bottom liquid, the amount of the column bottom liquid extracted is preferably managed based on its specific gravity. A standard for the specific gravity of the bottom liquid is preferably 1.10 to 1.20. However, the specific gravity of the column bottom liquid is not limited to this numerical range, and there is no problem as long as the degree of concentration is such that clogging of pipes is suppressed and the column bottom liquid can be sent by a pump. The specific gravity of the tower bottom liquid can also be adjusted by the amount of makeup water newly supplied to the quenching tower. In addition, it is preferable that the temperature of tower bottom liquid is 75-98 degreeC, and it is more preferable that it is 80-95 degreeC from a viewpoint of further suppressing clogging of the extraction pipe of tower bottom liquid.

  The quenching tower is preferably supplied with makeup water in order to adjust the water balance, that is, to maintain the amount of water in the system within a certain range. For example, in the case of ammoxidation of olefins, the product gas cooled by the heat exchanger installed in the reactor outlet line is a dry gas of 200 to 300 ° C., and is saturated with humidity. Has not reached. Since water accompanying the product gas flowing out from the quenching tower is also present, the amount of makeup water is preferably 0.1 to 0.5 t per 1 t of unsaturated nitrile. In addition, the temperature of the cooling water preferable for adjusting the water balance and the temperature of the gas flowing out from the quenching tower (preferably the top of the quenching tower) (hereinafter also referred to as “quenching tower outlet gas”) are 65. It is -95 degreeC, More preferably, it is 75-95 degreeC. The preferred quench tower outlet gas temperature may vary somewhat depending on the composition of the reaction product from the reactor and the reaction pressure, but the effect is limited. However, the quenching tower outlet gas temperature may be higher than the temperature of the cooling water, or may be higher in the range of 10 ° C. or less than the temperature of the cooling water.

  The temperature of the circulating cooling water, the temperature of the tower bottom liquid, and the temperature of the quenching tower outlet gas can be controlled by installing a cooler in the cooling water circulation line. The cooler may be a heat exchanger. In addition, a bypass line may be installed in case the circulation line is blocked. If the heat exchanger is not installed in the quenching tower circulation line for cooling the circulating cooling water, the upper cooling water temperature, the bottom liquid temperature, and the quenching tower outlet gas temperature are substantially the same. .

  As the make-up water, waste water generated in other steps of the production method of unsaturated nitrile, condensed water generated by cooling the quenching tower outlet gas, or the like can be used. In general, wastewater is a component in which components other than water contained therein are concentrated and may be heated for that purpose. By using the waste water as makeup water for the quenching tower, the heat of the generated gas can be used efficiently and the amount of heat required for concentration can be reduced. From the standpoint of efficiently concentrating, the quench tower outlet gas preferably has a higher humidity or water vapor pressure, and most preferably has a humidity of 100%, that is, a saturated water vapor pressure. In order to increase the humidity of the exit gas from the quenching tower, it is desirable to take sufficient residence time of the product gas.

The average residence time of the product gas in the quenching tower is preferably 2 seconds or more, more preferably from the viewpoint of neutralization of unreacted ammonia, separation and removal of high-boiling byproducts, polymers, and flying catalysts. Is 3 seconds or more. The average residence time of the product gas in the quenching tower is the capacity of the product gas flowing into the quenching tower in the standard state (0 ° C., 1 atm), and the actual temperature and pressure of the product gas at the quenching tower inlet (operation) Although it depends on the conditions, for example, it can be determined from the actual gas capacity converted at 300 ° C. and 0.7 kg / cm ² G) and the volume of the quenching tower.

(Other processes and equipment)
An apparatus for removing mist (water) contained in a gas by providing an apparatus such as a mist separator and a liquid cyclone at a gas outlet of a quenching tower in the method for producing an unsaturated nitrile of the present embodiment and the apparatus used therefor May be installed.

(4) Specific Aspect A preferred embodiment of the method for producing an unsaturated nitrile of the present embodiment will be described by taking a production method using a gas phase ammoxidation reaction using propylene as an example. However, the manufacturing method of this embodiment is not limited to this. The apparatus shown in FIG. 1 is an apparatus used for this production method, a reactor 1 that is a fluidized bed reactor, a heat exchanger 2 for cooling the product gas generated in the reactor 1, a cleaning of the product gas, A quenching tower 3 for cooling is provided.

  The reactor 1 contains a catalyst containing molybdenum and / or antimony, and propylene, ammonia gas and air, which are raw material gases, are supplied from lines 13A and 13B, and a product containing acrylonitrile by an ammoxidation reaction. Gas is generated. The reaction temperature is maintained at 400-500 ° C. The product gas passes through the line 6 and the heat exchanger 2 and is introduced into the quenching tower 3 for cleaning and cooling the product gas through the line 7. The heat exchanger 2 is a shell / tube heat exchanger, and boiler water is introduced to the shell side (external to the tube), thereby cooling the generated gas flowing on the tube side (in the tube) of the heat exchanger 2. Is done. In order to prevent condensation of the high boiling point by-product in the product gas in the heat exchanger 2, the temperature of the boiler water poured into the shell side is controlled to be 140 to 260 ° C.

  Although the cooling heat exchanger 9 is installed in the circulation line 11 of the quenching tower 3, it is not essential in the manufacturing method of this embodiment. Inside the quenching tower 3, a packed bed 8 and a spray nozzle 12 for spraying cooling water are installed. The product gas introduced into the quenching tower 3 from the line 7 is cooled and washed by the cooling water sprayed from the spray nozzle 12, and particularly in the packed bed 8, the contact with the cooling water is more efficiently performed. Thoroughly cooled and washed. The quenching tower 3 is supplied with makeup water from the line 5 as necessary. A part of the tower bottom liquid containing the makeup water and the cooling water used for cooling the generated gas is discharged out of the system via the line 10, and the other part is passed through the circulation line 11. It is cooled by the heat exchanger 9 and supplied to the quenching tower 3.

  The product gas that has passed through the quenching tower 3 is introduced into the absorption tower via the line 4 via a further product gas cooling tower (not shown). Thereafter, useful components such as acrylonitrile absorbed in water by the absorption tower are purified in the order of a normal process, that is, a recovery tower and a purification tower, to obtain a product acrylonitrile.

  According to the method for producing an unsaturated nitrile of this embodiment, when producing an unsaturated nitrile by an ammoxidation reaction using a reactor, particularly a fluidized bed reactor, the blockage in the heat exchanger and the quenching tower is suppressed, Stable operation is possible.

  Hereinafter, the fluidized bed reaction method of the present invention will be described in more detail with reference to a method for producing acrylonitrile by a gas phase ammoxidation reaction using propylene as a raw material and a methacrylonitrile by a gas phase ammoxidation reaction using tertiary butyl alcohol as a raw material. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, the clogging of the heat exchanger and the quenching tower installed in the reactor outlet line is suppressed, when the product gas flow rate is the same, the rate of increase in pressure loss of the heat exchanger and the quenching tower disappears or I confirmed that it was slow. The pressure loss of the heat exchanger was measured with an underwater manometer by installing pressure taps on the product gas inlet line and outlet line of the heat exchanger. Moreover, the temperature of the preheated refrigerant | coolant supplied to a heat exchanger was measured with the thermometer installed in the refrigerant | coolant inlet line of the heat exchanger. Table 1 shows the operating conditions of the heat exchanger and quenching tower installed in the reactor outlet line in each example, and Table 2 shows the operating results.

[Example 1]
Propylene, ammonia gas and air were supplied to an apparatus including the same configuration as shown in FIG. 1 to produce acrylonitrile. A reactor having a diameter of 5.3 m was used, and a molybdenum-bismuth-iron-based silica-supported catalyst having a particle diameter of 10 to 100 μm and an average particle diameter of 50 μm was used as the catalyst. As a heat exchanger installed in the outlet line of the reactor, a tube with a diameter of 1.4 m, a length of 5.0 m, a tube inner diameter / outer diameter of 36.0 mm / 43.2 mm, and 531 tubes, one pass tube / A shell type heat exchanger was used. Boiler water was used as the refrigerant. The reaction pressure is 0.7 kg / cm ² G, the reaction product gas amount is 38000 Nm ³ / hr, the product gas inlet temperature to the heat exchanger is 420 ° C., and the inlet temperature of the refrigerant (boiler water) of the heat exchanger is Set to 235 ° C., continuous operation was performed.

A quenching tower having an inner diameter of 3.7 m and a height of 7 m and having spray nozzles installed above and below the packed bed was used. The spray nozzle was of a hollow cone type, and the spray nozzle was installed at 4 pieces / m ² with respect to the cross-sectional area of the quenching tower to ensure the cleaning and cooling of the generated gas.

  A cooler was installed in the circulation line of the quenching tower. As the cooler, a tube / shell type heat exchanger having a diameter of 0.85 m, a length of 4.66 m, a tube inner diameter / outer diameter of 17.7 mm / 21.7 mm, and 558 tubes and one pass on the tube side was used. . Below the upper spray nozzle, a pole ring type filler made of metal and having a length and a diameter of 3 inches was irregularly filled so that the height of the packed bed was 1.5 m. The packing was selected so that the porosity of the packed bed was 96%. The makeup water was supplied at an amount of 1.3 t / hr from a position below the spray nozzle at the lower stage of the quenching tower and above the liquid level of the bottom liquid. The circulation rate of the cooling water was 420/250 t / hr for each of the upper and lower stages, and the amount of the bottom liquid extracted was adjusted so that the specific gravity of the bottom liquid was 1.15, and it was 1.3 t / hr. The temperature of the upper cooling water, the temperature of the tower bottom liquid, and the temperature of the quenching tower outlet gas were controlled to the temperatures shown in Table 1 using a cooler installed in the cooling water circulation line.

[Example 2]
The boiler water inlet temperature of the heat exchanger is changed to 205 ° C., the height of the packed bed of the quenching tower is changed to 1.2 m, the temperature of the upper cooling water, the temperature of the bottom liquid, and the quenching tower outlet gas Acrylonitrile was produced under the same conditions as in Example 1 except that the temperature was changed to the temperature shown in Table 1.

[Example 3]
The boiler water inlet temperature of the heat exchanger is changed to 150 ° C, the height of the packed bed of the quenching tower is changed to 0.8 m, the temperature of the upper cooling water, the temperature of the bottom liquid, and the quenching tower outlet gas Acrylonitrile was produced under the same conditions as in Example 1 except that the temperature was changed to the temperature shown in Table 1.

[Example 4]
Change the boiler water inlet temperature of the heat exchanger to 135 ° C, change the height of the packed bed of the quenching tower to 0.5m, the temperature of the upper cooling water, the temperature of the bottom liquid, and the quenching tower outlet gas Acrylonitrile was produced under the same conditions as in Example 1 except that the temperature was changed to the temperature shown in Table 1.

[Example 5]
The quenching tower packing was changed to a pole ring type packing made of metal and having a length and diameter of 3 inches (with a porosity of 92% in the packed bed), and the height of the packed bed Is changed to 0.5 m, and the temperature of the upper cooling water, the temperature of the tower bottom liquid, and the temperature of the quenching tower outlet gas are changed to the temperatures shown in Table 1 under the same conditions as in Example 2. Acrylonitrile was produced.

[Example 6]
Except for changing the quenching tower to an empty tower not filled with packing, and changing the temperature of the upper cooling water, the temperature of the bottom liquid, and the temperature of the quenching tower outlet gas to the temperatures shown in Table 1, Acrylonitrile was produced under the same conditions as in Example 2.

[Examples 7 and 8]
Except for changing the height of the packed bed of the quenching tower to 0.8 m and changing the temperature of the upper cooling water, the temperature of the tower bottom liquid, and the temperature of the quenching tower outlet gas to the temperatures shown in Table 1. Under the same conditions as in Example 2, acrylonitrile was produced.

[Example 9]
The supply amount of makeup water is changed so that the specific gravity of the bottom liquid of the quenching tower becomes 1.21 to 1.25, the height of the packed bed is changed to 0.5 m, the temperature of the upper cooling water, the tower Acrylonitrile was produced under the same conditions as in Example 2 except that the temperature of the bottom liquid and the temperature of the quenching tower outlet gas were changed to the temperatures shown in Table 1.

[Example 10]
The supply amount of makeup water is changed so that the specific gravity of the bottom liquid of the quenching tower is 0.95 to 1.0, and the temperature of the upper cooling water, the temperature of the bottom liquid, and the temperature of the quenching tower outlet gas are changed. Acrylonitrile was produced under the same conditions as in Example 9 except that the temperature was changed to the temperature shown in Table 1.

[Example 11]
Change the packing of the quenching tower to metal and use a Raschig (R) ring type packing (with a porosity of 89% packed bed) that is 3 inches in length and diameter. Example 2 except that the height of the layer was changed to 0.8 m, and the temperature of the upper cooling water, the temperature of the bottom liquid, and the temperature of the quenching tower outlet gas were changed to the temperatures shown in Table 1. Under the same conditions, acrylonitrile was produced.

[Example 12]
Tertiary butyl alcohol, ammonia gas, and air were supplied to an apparatus including the same configuration as shown in FIG. 1 to produce methacrylonitrile. A reactor having a diameter of 5.3 m was used, and a molybdenum-bismuth-iron-based silica-supported catalyst having a particle diameter of 10 to 100 μm and an average particle diameter of 50 μm was used as the catalyst. As a heat exchanger installed in the outlet line of the reactor, a tube having a diameter of 1.27 m, a length of 4.65 m, a tube inner diameter / outer diameter of 34.0 mm / 40.8 mm, and 733 tubes, one-pass tube / A shell type heat exchanger was used. Boiler water was used as the refrigerant. The reaction pressure is 0.78 kg / cm ² G, the reaction product gas amount is 36500 Nm ³ / hr, the product gas inlet temperature to the heat exchanger is 440 ° C., and the inlet temperature of the refrigerant (boiler water) of the heat exchanger is A continuous operation was performed at 245 ° C.

A quenching tower having an inner diameter of 3.7 m and a height of 12.3 m, and having spray nozzles installed above and below the packed bed was used. The spray nozzle was of a hollow cone type, and the spray nozzle was installed at 4 pieces / m ² with respect to the cross-sectional area of the quenching tower to ensure the cleaning and cooling of the generated gas.

  A cooler was installed in the circulation line of the quenching tower. As a cooler, a tube / shell type heat exchanger having a diameter of 0.75 m, a length of 6.05 m, a tube inner diameter / outer diameter of 17.7 mm / 21.7 mm, and 332 tubes on one side of the tube was used. . Below the upper spray nozzle, a Raschig® ring-type packing made of metal and having a length and diameter of 3 inches is irregular so that the height of the packed bed is 1.5 m. Filled. The filler was selected so that the porosity of the packed bed was 95%. The make-up water was supplied in an amount of 3.0 t / hr from a position below the spray nozzle at the lower stage of the quenching tower and above the liquid level of the bottom liquid. The circulating amount of the cooling water was 470/400 t / hr for each of the upper stage and the lower stage, and the amount of the bottom liquid extracted was adjusted so that the specific gravity of the bottom liquid was 1.13, which was 3.5 t / hr. The temperature of the upper cooling water, the temperature of the tower bottom liquid, and the temperature of the quenching tower outlet gas were controlled to the temperatures shown in Table 1 using a cooler installed in the cooling water circulation line.

[Example 13]
As a heat exchanger installed in the outlet line of the reactor, a tube having a diameter of 1.27 m, a length of 8.41 m, a tube inner diameter / outer diameter of 34.0 mm / 40.8 mm, and 733 tubes, one-pass tube / Methacrylonitrile was produced under the same conditions as in Example 12 except that two shell-type heat exchangers were installed in parallel and the refrigerant was changed to heated air.

[Comparative Example 1]
The quenching tower packing was changed to a pole ring type packing made of ceramic and having a length and diameter of 3 inches (with a porosity of 79% in the packed bed), and the height of the packed bed Was changed to 1.6 m, and under the same conditions as in Example 2 except that the temperature of the upper cooling water, the temperature of the bottom liquid, and the temperature of the quenching tower outlet gas were changed to the temperatures shown in Table 1. Acrylonitrile was produced.

[Comparative Example 2]
The boiler water inlet temperature of the heat exchanger is changed to 108 ° C., the height of the packed bed of the quenching tower is changed to 1.5 m, the temperature of the upper cooling water, the temperature of the bottom liquid, and the quenching tower outlet gas The acrylonitrile was produced under the same conditions as in Example 2 except that the temperature was changed to the temperature shown in Table 1.

[Comparative Example 3]
The quenching tower packing was changed to that used in Example 11 (the porosity of the packed bed was 89%), the height of the packed bed was changed to 1.7 m, the temperature of the upper cooling water, Acrylonitrile was produced under the same conditions as in Example 2 except that the temperature of the column bottom liquid and the temperature of the quenching tower outlet gas were changed to the temperatures shown in Table 1.

[Comparative Example 4]
The quenching tower packing is changed to a Rashihi (registered trademark) ring type packing (with a porosity of 75% in the packed bed) made of porcelain and having a length and diameter of 3 inches. Example 12 except that the height of the layer was changed to 1.7 m, and the temperature of the upper cooling water, the temperature of the bottom liquid, and the temperature of the quenching tower outlet gas were changed to the temperatures shown in Table 1. Under the same conditions, methacrylonitrile was produced.

[Comparative Example 5]
The quenching tower packing is changed to a Rashihi (registered trademark) ring type packing (with a porosity of 75% in the packed bed) made of porcelain and having a length and diameter of 3 inches. Example 13 and Example 13 except that the height of the layer was changed to 1.7 m and the temperature of the upper cooling water, the temperature of the bottom liquid, and the temperature of the quenching tower outlet gas were changed to the temperatures shown in Table 1. Under the same conditions, methacrylonitrile was produced.

  The present invention can provide a method for producing an unsaturated nitrile capable of preventing clogging of a heat exchanger installed in a reactor outlet line and a quenching tower downstream thereof, and therefore the group consisting of an olefin and an alcohol. There is an industrial applicability to produce an unsaturated nitrile by an ammoxidation reaction from a source gas containing at least one selected from the above.

  DESCRIPTION OF SYMBOLS 1 ... Fluidized bed reactor, 2 ... Heat exchanger, 3 ... Quench tower, 4, 5, 6, 7, 10, 11, 13A, 13B ... Line (pipe), 8 ... Packed bed, 9 ... Cooler, 12 …spray nozzle.

Claims (7)

A method for producing an unsaturated nitrile by an ammoxidation reaction,
Supplying a source gas containing at least one selected from the group consisting of alkanes, olefins, and alcohols to a reactor filled with a catalyst, and advancing an ammoxidation reaction in the reactor;
A second step of introducing and cooling the reaction product gas generated by the ammoxidation reaction into a heat exchanger;
A third step of introducing the reaction product gas cooled in the heat exchanger into a quenching tower and cooling it;
Have
As a refrigerant for cooling the reaction product gas in the heat exchanger, a liquid or gas of 110 ° C. or higher is used, and
The method for producing an unsaturated nitrile, wherein the quenching tower is an empty tower having no packed bed, or has a packed bed having a height of 1.5 m or less or a porosity of 90% or more.   The manufacturing method of the unsaturated nitrile of Claim 1 whose temperature of the said refrigerant | coolant is 140-260 degreeC.   The method for producing an unsaturated nitrile according to claim 1 or 2, wherein, in the third step, the reaction product gas is cooled with 65 to 95 ° C cooling water.   The manufacturing method of the unsaturated nitrile of any one of Claims 1-3 whose temperature of the liquid extracted from the bottom part of the said quenching tower is 75-98 degreeC.   The method for producing an unsaturated nitrile according to any one of claims 1 to 4, wherein the temperature of the gas flowing out of the quenching tower is 65 to 95 ° C, and the gas contains water vapor having a saturated water vapor pressure.   The method for producing an unsaturated nitrile according to any one of claims 1 to 5, wherein the specific gravity of the liquid extracted from the bottom of the quenching tower is 1.10 to 1.20.   The method for producing an unsaturated nitrile according to any one of claims 1 to 6, wherein the source gas contains at least one selected from the group consisting of propylene, isobutene, tertiary butanol, propane, and isobutane.

Images