JP5785728B2 - Unsaturated nitrile distillation method and distillation apparatus, and unsaturated nitrile production method - Google Patents

Description

  The present invention relates to an unsaturated nitrile distillation method and distillation apparatus, and an unsaturated nitrile production method.

  Acrylonitrile is one of the most important organic chemical intermediates available among the many types of unsaturated nitriles, and is the main intermediate in the manufacture of a wide range of products, plastics, synthetic rubbers, synthetic fibers, soil conditioners, etc. It is used as a body. In many applications, acrylonitrile must be of high purity, and thus commercially distributed acrylonitrile has strict product specifications.

  In an industrial production process for producing acrylonitrile from propylene and / or propane, ammonia and oxygen, the reaction effluent contains significant amounts of hydrogen cyanide and acetonitrile as by-products in addition to acrylonitrile, and succinonitrile and Contains other impurities such as nitriles. The exact composition of the effluent and the by-products and impurities contained in the effluent will vary considerably depending on the reaction conditions and catalyst of the ammoxidation. Other unsaturated nitrile production effluents similarly contain various by-products and impurities.

  In the production of acrylonitrile by catalytic ammoxidation of propylene with ammonia and oxygen, crude acetonitrile is produced as one of the by-products. Crude acetonitrile may include hydrogen cyanide, acrylonitrile, acetaldehyde, acetone, methanol, acrolein, oxazole, cis- and trans-crotononitrile, methacrylonitrile and allyl alcohol in addition to acetonitrile. The relative proportions of the components of crude acetonitrile can vary widely depending on various conditions. In the past, crude acetonitrile was disposed of by incineration. However, in recent years, acetonitrile has been recovered, purified and sold.

Although the production of unsaturated nitriles has been carried out industrially for many years, there is room for improvement with substantial benefits. One of these improvements is a reduction in product standard deviations. In industrial production of unsaturated nitriles, stable operation of the recovery tower (distillation tower) in the process of recovery and purification of unsaturated nitrile and its by-products is the product quality standard, that is, impurities It is important in reducing the content, and improvement measures are desired.
For example, in the process of producing acrylonitrile by reacting propylene and / or propane, ammonia and molecular oxygen, there is a recovery tower for separating acetonitrile from the produced acrylonitrile, acetonitrile and hydrocyanic acid and recovering acrylonitrile and hydrocyanic acid. . Acrylonitrile and hydrocyanic acid are recovered from the top of this recovery tower, but it is important to operate so as not to entrain acetonitrile at this time in order to prevent production of non-standard product acrylonitrile. At the same time, surplus water is extracted from the bottom of the recovery tower and processed in the wastewater treatment facility. It is important to reduce the cost of wastewater treatment by operating so that acrylonitrile, acetonitrile and hydrocyanic acid are not mixed in this bottom liquid. It is.
In view of the above circumstances, the present invention provides a stable operation of the recovery tower in the recovery and purification process of unsaturated nitrile and its by-products when industrially producing unsaturated nitrile such as acrylonitrile. An object is to provide a distillation method and a distillation apparatus for saturated nitrile.
Furthermore, when industrially producing unsaturated nitriles such as acrylonitrile, the recovery tower is stably operated in the recovery and purification process of unsaturated nitriles and their by-products to produce high purity unsaturated nitriles. It aims at providing the manufacturing method of an unsaturated nitrile which can be obtained over a long period of time.

Usually, the middle part of the recovery tower has a large temperature fluctuation compared to the top and bottom of the tower, and the influence on stable operation is large. When the temperature of the middle stage is higher than the control temperature, acetonitrile is easily distilled from the top of the column, and when the temperature of the middle stage is lower than the control temperature, acrylonitrile, acetonitrile and hydrocyanic acid are easily output from the bottom of the tower. It is considered that the temperature fluctuation in the middle stage can be reduced by detecting the temperature of the part where the fluctuation is intense and controlling the flow rate of the heat source supplied to the reboiler of the recovery tower. However, since the flow rate of the heat source supplied to the reboiler of the recovery tower is large, if this flow rate is controlled, the temperature of each part of the recovery tower fluctuates and it is difficult to keep the temperature of the middle stage constant.
Conventionally, as shown in FIG. 16, the temperature control of the middle part of the recovery tower has been performed by the heat source flow rate adjustment valve 19 of the reboiler 2. The flow rate adjustment valve 19 is controlled based on the measured value of the thermometer 15 in the middle part of the recovery tower, or the flow rate adjustment valve 17 is installed on the flow rate adjustment valve, and the temperature indication adjustment meter 16 is installed on the thermometer 15. It has been electronically controlled by connecting with electrical wiring 18. However, even with such control, it is difficult to keep the temperature of the middle stage constant.
Conventionally, as shown in FIG. 17, the temperature control of the middle stage of the recovery tower has been performed by the heat source flow rate adjustment valve 19 of the auxiliary boiling unit 3. The auxiliary boiling device 3 reheats a part of the bottom stream flowing out from the reboiler 2 and returns it to the reboiler 2 through a line 13. The flow rate adjustment valve 19 is controlled based on the measured value of the thermometer 15 in the middle part of the recovery tower, or the flow rate adjustment valve 17 is installed on the flow rate adjustment valve, and the temperature indication adjustment meter 16 is installed on the thermometer 15. It has been electronically controlled by connecting with electrical wiring 18. However, even with such control, it is difficult to keep the temperature of the middle stage constant.
As a result of intensive studies on the temperature control method for the recovery tower, the inventor has connected the first and second heating paths to the recovery tower, and the amount of heat supplied to the recovery tower by the second heating path Further, the present inventors have found that the temperature fluctuation in the middle part of the recovery tower can be reduced by controlling it to 1 to 20% with respect to the sum of heat supplied to the recovery tower through the second heating path.

That is, the present invention is as follows.
[1]
A method for distilling unsaturated nitriles, comprising:
Distilling the unsaturated nitrile through a recovery tower connected to the first and second heating paths;
The amount of heat supplied to the recovery tower by the second heating path is 1 to 20% with respect to the sum of heat amounts supplied to the recovery tower by the first and second heating paths,
An unsaturated nitrile distillation method in which a tower bottom stream reheated from the first heating path is supplied to the recovery tower, and water vapor is supplied to the recovery tower from the second heating path.
[2]
The distillation method according to [1] above, wherein the water vapor is supplied to a lower portion of the recovery tower.
[3]
A reboiler using steam as a heat medium is provided in the second heating path, and a tower bottom stream reheated from the first heating path is supplied to the recovery tower, and the second heating path The unsaturated nitrile distillation method according to the above [1], wherein a tower bottom stream and / or a tower internal stream heated by a reboiler is supplied to the recovery tower.
[4]
Producing a gas containing an unsaturated nitrile by ammoxidizing at least one selected from the group consisting of propane, propylene, isobutane and isobutylene in the presence of a catalyst;
A step of obtaining an aqueous mixture containing an unsaturated nitrile by contacting the gas with an aqueous liquid in a quenching tower and then absorbing the gas in contact with a liquid containing water in the absorption tower;
Distilling the aqueous mixture containing the resulting unsaturated nitrile,
A method for producing an unsaturated nitrile comprising:
Supplying a reheated bottom stream and water vapor to a recovery tower for distilling the unsaturated nitrile from the aqueous mixture.
[5]
A distillation apparatus having a recovery tower and first and second heating paths connected to the recovery tower,
The amount of heat supplied to the recovery tower by the second heating path is 1 to 20% with respect to the sum of heat amounts supplied to the recovery tower by the first and second heating paths,
The second heating path includes a steam generator;
The tower bottom stream is heated by the first heating path, and the heated tower bottom stream is supplied to the recovery tower,
The steam generating apparatus generates steam that is not derived from the bottoms stream, and that to supply steam which is not derived from the bottoms stream to said recovery column, distillation apparatus unsaturated nitrile.
[6]
The unsaturated nitrile distillation apparatus according to [5], wherein the water vapor is supplied to a lower portion of the recovery tower.
[7]
The second heating path includes a reboiler using steam as a heat medium, the bottom stream is heated by the first heating path, and the bottom stream and / or the inner stream is heated by the reboiler. The unsaturated nitrile distillation apparatus according to [5] above.
[8]
The unsaturated nitrile distillation apparatus according to the above [7], wherein the bottom stream and / or the inner stream at the bottom of the recovery tower is reheated by the reboiler and supplied to the recovery tower.
[9]
A reactor, a quenching tower connected to the reactor, an absorption tower connected to the quenching tower, and a recovery tower connected to the absorption tower,
A reboiler and a steam generator are connected to the recovery tower,
In the reactor, a gas containing an unsaturated nitrile is generated by at least one ammoxidation selected from the group consisting of propane, propylene, isobutane and isobutylene in the presence of a catalyst;
The gas is contacted with an aqueous liquid in the quenching tower, and then contacted with a liquid containing water in the absorption tower to obtain an aqueous mixture containing an unsaturated nitrile,
An unsaturated nitrile production apparatus in which an aqueous mixture containing the obtained unsaturated nitrile is distilled in a recovery tower,
The unsaturated nitrile manufacturing apparatus in which the bottom stream flowing out of the recovery tower is heated by the reboiler and returned to the recovery tower, and the water vapor generated by the steam generator is supplied to the recovery tower.

  According to the distillation method of the present invention, stable operation with reduced temperature fluctuation in the recovery tower can be achieved in the industrial production process of unsaturated nitrile.

It is the schematic which shows an example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. It is the schematic which shows another example of the distillation apparatus of this embodiment. 1 is a schematic diagram of an acrylonitrile production process by catalytic ammoxidation of propylene using ammonia and oxygen. FIG. It is the schematic which shows an example of the conventional distillation apparatus. It is the schematic which shows another example of the conventional distillation apparatus. It is a figure which shows the time-dependent change of 59-stage temperature of the collection | recovery tower which supplied the water vapor | steam in Example 1. FIG. It is a figure which shows the time-dependent change of the 59 stage temperature of the collection | recovery tower which does not supply the water vapor | steam in the comparative example 1. FIG.

Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.
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. The dimensional ratios of the devices and members are not limited to the illustrated ratios.

The method for distilling unsaturated nitrile in the present embodiment is a method for distilling unsaturated nitrile, including a step of distilling unsaturated nitrile using a recovery tower connected to first and second heating paths, An unsaturated nitrile distillation method wherein the amount of heat supplied to the recovery tower through two heating paths is 1 to 20% of the sum of heat supplied to the recovery tower through the first and second heating paths. .
Further, the unsaturated nitrile manufacturing apparatus in the present embodiment is a manufacturing apparatus having a recovery tower and first and second heating paths connected to the recovery tower, wherein the second heating path is used to In the distillation apparatus, the amount of heat supplied to the recovery tower is 1 to 20% with respect to the sum of heat supplied to the recovery tower through the first and second heating paths.

FIG. 1 is a schematic diagram showing an example of a distillation apparatus according to the present embodiment, and shows an example of a distillation apparatus for separating and recovering acetonitrile from the produced acrylonitrile, acetonitrile, hydrocyanic acid and water in the process of producing acrylonitrile. . The recovery tower 1 is connected to the first and second heating paths, and is supplied with heat from both heating paths. An introduction line 4 is connected to the recovery tower 1, and an aqueous mixture obtained by absorbing water produced by a reactor (not shown) into the recovery tower 1 enters the recovery tower 1 through the introduction line 4. The position where the introduction line 4 is connected to the recovery tower 1 is generally set so that the composition of the introduction liquid and the composition in the recovery tower are closest.
The typical concentration of acrylonitrile in the aqueous mixture fed to the recovery tower 1 from line 4 is 5-15 wt%, preferably 5-10 wt%. The flow rate of the aqueous mixture to be supplied depends on the production amount of acrylonitrile, but is preferably 2.5 to 30 T with respect to 1 T of acrylonitrile production amount from the viewpoint of industrially producing acrylonitrile efficiently.

The distillation apparatus is provided with a reboiler 2, and the bottom stream enters the reboiler 2 through the bottom line 6 and returns to the bottom of the tower through the line 8 (first heating path). The flow in the tower is extracted through a line 10 connected to the first stage of the bottom of the recovery tower 1, and after the temperature is lowered, it is introduced into the top of the recovery tower 1 as solvent water. The heat generated by the temperature drop of the liquid in the tower is preferably used as a heat source for the heat exchanger 11 in the process. In the recovery tower 1, acetonitrile is extracted and separated by extractive distillation, acrylonitrile, hydrocyanic acid and water are extracted from the top of the tower through line 5, and acetonitrile is extracted from the tower side through line 9.
A preferable position of the line 9 can be determined approximately by optimizing each component contained in the solution supplied to the recovery tower 1 and its ratio, and optimizing based on the boiling point of each component. Computer programs for performing such calculations are well known and are used in the design of recovery towers. Generally, it is preferable to connect the line 9 within a range of 5 stages before and after the number of stages in which the concentration of acetonitrile in the column becomes maximum.

The internal structure of the recovery tower 1 is not particularly limited, and a general internal structure can be accommodated in principle. Examples of internal structures include irregular packings such as trays, packing and / or Raschig rings and pole rings, and regular packings such as melapacks. In general, in the case of a plate tower, the total number of trays is preferably 40 to 150 from the viewpoint of managing the composition of the fluid discharged from the tower top, tower bottom and tower side, that is, from the viewpoint of separation efficiency in the entire recovery tower.
The temperature at the bottom of the recovery tower 1 is preferably 90 to 130 ° C, and the top temperature is preferably 50 to 80 ° C. The heat load during operation in the recovery tower 1 is preferably managed at the temperature of the middle stage that greatly affects the composition of the discharged fluid. In this specification, “middle part” indicates a line 4 to a line 9. Further, the “temperature control unit” is set to one stage in the middle stage. In general, it is preferable to set a thermometer at a position where the temperature in the tower is 80 to 105 ° C. in the middle stage portion to form a temperature control section and to manage the temperature.

The reboiler 2 reheats the recovery tower bottom stream before supplying the recovery tower bottom stream flowing out from the line 6 to the recovery tower 1. A heating medium is supplied to the reboiler 2 through the line 14, and the heating medium may be steam prepared for the purpose of heating the reboiler 2, but high-temperature steam generated at any step in the process ( It may contain water as a main component and also contains a trace amount of reaction products such as acetonitrile and hydrocyanic acid). For example, steam generated from a wastewater concentration facility (not shown) can be used. Of course, it is also possible to use them together. From the viewpoint of appropriate temperature control, the preferred heat medium is steam, and the temperature at the bottom of the column is maintained by continuously circulating steam maintained at 100 to 160 ° C. under a pressure of 101 to 638 kPa. be able to.
A part of the bottom stream of the recovery tower is heated in the reboiler 2 and returned to the recovery tower 1, and the remaining bottom stream is withdrawn from the bottom of the reboiler 2 through the line 12 as waste water.

Water vapor is supplied to the lower part of the recovery tower 1 through the flow rate adjusting valve 19 (second heating path). From the viewpoint of temperature adjustment, the preferred form of water vapor is saturated steam. In addition to the tower bottom flow reheated by the first heating path, the steam in the tower of the recovery tower 1 can be effectively suppressed by supplying water vapor through the second heating path.
In this specification, the “lower part” of the recovery tower 1 means below the line 9, includes the bottom of the recovery tower, and includes the reboiler outlet line 8 in addition to the inside of the tower. In particular, an aspect in which steam is supplied to the bottom of the recovery tower 1 including the reboiler outlet line is preferable in that the heat load of the entire recovery tower 1 can be reduced.
The amount of heat supplied to the recovery tower by steam (the amount of heat supplied to the recovery tower by the second heating path) is the amount of heat supplied to the recovery tower by the bottom stream (the amount of heat supplied to the recovery tower by the first heating path) and the water vapor. To 1 to 20% of the sum of the amount of heat supplied to the recovery tower. By controlling the amount of heat supplied to the recovery tower by steam within the above range, temperature fluctuations inside the recovery tower can be suppressed. When the amount of heat supplied to the recovery tower by the water vapor exceeds 20%, it is earnestly studied that the temperature fluctuation inside the recovery tower occurs as in the case where the heat quantity is supplied to the recovery tower only by the tower bottom flow using the reboiler. I understood the result.

Here, in this embodiment, the amount of heat supplied to the recovery tower through the first and second heating paths can be measured as follows.
The amount of heat supplied from the reboiler can be estimated from the amount of enthalpy change calculated from the temperature and pressure before and after the reboiler of the heating medium or tower bottom flow. The amount of heat supplied by the water vapor can be estimated from the amount of enthalpy calculated from the temperature and pressure of the water vapor supplied.

  Water in the column is the most water, and fluctuations in the column composition can be minimized by supplying water vapor into the column as a heat source. From the viewpoint of reducing impurities in the tower, the water vapor is preferably generated from water that does not originate from the tower bottom flow in a steam generator connected to the recovery tower.

  The temperature control of the middle stage can be performed by the steam flow rate adjustment valve 19. The flow rate adjustment valve 19 is controlled in accordance with the measured value of the thermometer 15 in the middle part of the recovery tower. Preferably, the flow rate adjustment valve 17 is installed in the flow rate adjustment valve, and the temperature indication adjustment meter 16 is installed in the thermometer 15. They are connected by electrical wiring 18 to perform electronic control.

  FIG. 2 is a schematic view showing another example of the distillation apparatus of the present embodiment. The apparatus shown in FIG. 2 is substantially the same as the example shown in FIG. 1 except that the recovery tower is separated into an upper recovery tower 1a and a lower recovery tower 1b, and only the differences will be described below. The upper recovery tower 1a and the lower recovery tower 1b are operated so as to perform distillation as a unit. The component that descends and the component that rises in the recovery tower are connected so that they can travel between the upper recovery tower 1a and the lower recovery tower 1b. As long as the upper recovery tower 1a and the lower recovery tower 1b are functionally separated, the top and bottom may be physically separated or may be continuous. From the viewpoint of the composition of the introduced liquid, the line 4 is connected to the upper side 1a, and the aqueous mixture that has flowed in is separated while coming and going from the lower recovery tower 1b. From the viewpoint of economic efficiency during construction of the apparatus, the line 9 is preferably branched from between the upper recovery tower 1a and the lower recovery tower 1b, and the fraction containing acetonitrile is discharged.

FIG. 3 is a schematic view showing still another example of the distillation apparatus of the present embodiment. Since the apparatus shown in FIG. 3 is substantially the same as the example shown in FIG. 1 except that the auxiliary boiling device 3 is connected to the reboiler 2, only the differences will be described. The auxiliary boiling device 3 reheats a part of the bottom stream flowing out from the reboiler 2 and returns it to the reboiler 2 through a line 13. The heat medium is supplied to the auxiliary boiling device 3 through the line 14. If the amount of heat is sufficiently supplied to the auxiliary boiling device 3, the reboiler 2 to which the bottom stream reheated by the auxiliary boiling device 3 is supplied is also heated. The auxiliary boiling device 3 has a function of concentrating the waste water flowing out from the reboiler 2. By using the steam generated during the concentration of the wastewater as a heating medium for the reboiler 2, the heat in the process can be used effectively.
Water vapor is supplied to the auxiliary boiling device 3 through the line 14 as a heating medium. From the viewpoint of contamination of the heat transfer surface, the water vapor is preferably generated from water that does not originate from the tower bottom flow in a steam generator connected to the auxiliary boiling device 3.

  FIG. 5 is a schematic view showing still another example of the distillation apparatus of the present embodiment. The apparatus shown in FIG. 5 is substantially the same as the apparatus shown in FIG. 3 except that water vapor is supplied to the line 8, and only the differences will be described below. In the apparatus shown in FIG. 5, when the steam supply position is set to line 8, when the existing reboiler is remodeled and steam is supplied, it is not necessary to replace the nozzle inside the recovery tower. It will be easy.

  FIG. 7 is a schematic view showing still another example of the distillation apparatus of the present embodiment. The apparatus shown in FIG. 7 is almost the same as the apparatus shown in FIG. 3 except that water vapor is supplied between the temperature control unit and the line 9 in the recovery tower 1, and only the differences will be described next. . In the apparatus shown in FIG. 7, the temperature fluctuation range of the temperature control unit can be further reduced by supplying water vapor to the bottom by supplying water vapor in the vicinity of the temperature control unit that is important for the composition management of the discharged fluid.

  4, 6 and 8 are schematic views showing still another example of the distillation apparatus of the present embodiment. The apparatus shown in FIGS. 4, 6, and 8 is the same as that shown in FIG. 2, except that the recovery tower is separated into an upper recovery tower 1a and a lower recovery tower 1b, respectively. Is almost the same.

FIG. 9 is a schematic view showing still another example of the distillation apparatus of the present embodiment. Since the apparatus shown in FIG. 9 is substantially the same as the example shown in FIG. 1 except that the second reboiler 20 is provided in the second heating path, only the differences will be described below. A part of the bottom stream flows into the first reboiler 2, but a further part of the remainder flows into the second reboiler 20. Regarding the ratio of the bottom flow rate allocated to the first and second reboilers, from the viewpoint of temperature adjustment, the bottom flow rate allocated to the second reboiler is allocated to the first reboiler. The flow rate is preferably 50% or less. Steam is supplied as a heat medium to the reboiler 20 installed at the lower part of the recovery tower 1 through the flow rate adjusting valve 19. From the viewpoint of temperature adjustment, the preferred form of water vapor is saturated steam. In addition to the tower bottom stream reheated in the tower bottom reboiler 2, the tower interior temperature of the recovery tower 1 is supplied by reheating the tower stream in the reboiler 20 using steam as a heating medium. The fluctuation can be suppressed more effectively. Water vapor is supplied to the second reboiler 20 via the flow rate indicating regulator 17. The flow rate indicating / adjusting meter 17 is connected to the temperature indicating / adjusting meter 16, and the flow rate of water vapor is adjusted according to the temperature in the tower.
The use of a reboiler with steam as a heat medium is more disadvantageous from the viewpoint of economics during construction and operation of the apparatus than when steam is directly supplied to the recovery tower, but the amount of heat supplied is easy to adjust. preferable.
In particular, an embodiment in which a reboiler using steam as a heat medium is installed at the bottom of the recovery tower 1 and the tower bottom flow is reheated together with the existing tower bottom reboiler can reduce the heat load of the entire recovery tower 1. This is preferable.
The amount of heat supplied to the recovery tower by the second reboiler is based on the sum of the amount of heat supplied to the recovery tower by the tower bottom flow and the amount of heat supplied to the recovery tower by the second reboiler using the steam as a heat medium. 1 to 20%. By controlling the amount of heat supplied to the recovery tower by the second reboiler using steam as a heating medium, the temperature fluctuation inside the recovery tower can be suppressed. When the amount of heat supplied to the recovery tower by the second reboiler exceeds 20%, as in the case of supplying heat to the recovery tower only by the tower bottom flow using the first reboiler, As a result of intensive studies, it was found that temperature fluctuations occur.

  The temperature control of the middle stage can be performed by the steam flow rate adjustment valve 19. The control of the flow rate adjusting valve 19 is performed in accordance with the measured value of the thermometer 15 in the middle part of the recovery tower 1, preferably the flow rate adjusting valve 17 is installed in the flow rate adjusting valve, and the temperature indicating adjuster 16 is installed in the thermometer 15, The two are connected by electrical wiring 18 to perform electronic control.

  10 and 11 are schematic views showing still another example of the distillation apparatus of the present embodiment. The apparatus shown in FIG. 10 is substantially the same as the example shown in FIG. 2 except that the second reboiler 20 is provided in the second heating path. FIG. 11 is substantially the same as the example shown in FIG. 3 except that the second reboiler 20 is provided in the second heating path.

  The apparatus shown in FIG. 13 is a schematic view showing still another example of the distillation apparatus of the present embodiment. The apparatus shown in FIG. 13 is substantially the same as the apparatus shown in FIG. 10 except that a reboiler using steam as a heat medium is installed between the temperature control unit and the line 9 in the recovery tower 1. Only the differences will be described next. In the apparatus shown in FIG. 13, the flow in the tower near the temperature control unit important for the composition management of the discharged fluid is reheated and supplied by a reboiler using steam as a heat medium. The temperature fluctuation range can be further reduced as compared with the case where a reboiler using steam as a heat medium is installed at the bottom.

  12 and 14 are schematic views showing still another example of the distillation apparatus of the present embodiment. The apparatus shown in FIGS. 12 and 14 is substantially the same as the apparatus shown in FIGS. 11 and 13 except that the recovery tower is separated into an upper recovery tower 1a and a lower recovery tower 1b as in FIG.

The method for producing an unsaturated nitrile in the present embodiment is as follows:
A step of generating a gas containing an unsaturated nitrile by ammoxidizing at least one selected from the group consisting of propane, propylene, isobutane and isobutylene in the presence of a catalyst (step A);
A step of bringing the gas into contact with an aqueous liquid in a quenching tower and then bringing it into contact with a liquid containing water in the absorption tower to absorb it to obtain an aqueous mixture containing an unsaturated nitrile (step B);
A step (step C) of distilling the aqueous mixture containing the obtained unsaturated nitrile,
A method for producing an unsaturated nitrile comprising:
The method includes a step of supplying a reheated tower bottom stream and water vapor to a recovery tower for distilling the unsaturated nitrile from the aqueous mixture.

Here, the manufacturing method of unsaturated nitrile can be performed using the manufacturing apparatus shown in FIG. 15, for example.
FIG. 15 shows a schematic diagram of a process for producing acrylonitrile by catalytic ammoxidation of propylene using ammonia and oxygen. As shown in FIG. 15, propylene, ammonia, and molecular oxygen (usually using air) are introduced into a reactor in which a catalyst is previously stored, and these come into contact with the catalyst to generate a gas containing acrylonitrile. (Process A). The generated gas flows out from the top of the reactor, flows into the quenching tower, and is cooled in the process of contacting the aqueous liquid (typically water) in the quenching tower, and some of the high-boiling organic compounds, etc. The components are eluted in the cooling water, but the main product containing acrylonitrile flows out from the top of the column in a gaseous state and is introduced into the absorption tower. Absorption water is supplied to the absorption tower from the top of the tower, and acrylonitrile, acetonitrile, hydrocyanic acid and water in the gas are absorbed into the absorption water (step B). Of the components contained in the gas, propylene and / or propane, oxygen, nitrogen, produced carbon dioxide and carbon monoxide that are not absorbed flow out from the top of the absorption tower. From the bottom of the absorption tower, an aqueous mixture containing acrylonitrile (an aqueous solution containing acrylonitrile, acetonitrile and hydrocyanic acid) flows out and is supplied to the recovery tower for distillation (step C).
In the above method, the ammoxidation reaction can be carried out using at least one selected from the group consisting of propylene, isobutane and isobutylene instead of or together with propane.
Moreover, the said distillation process (process C) can be performed using the collection | recovery tower to which the 1st and 2nd heating path | route was connected similarly to the method mentioned above.

Although the present embodiment will be specifically described based on examples, the present embodiment is not limited to the following examples. Further, the present embodiment is not limited to a tower having a specific number of trays, and is not limited to a tower having trays. In addition, a packed tower may alternatively be used.
In Examples and Comparative Examples, the calorific value was measured as follows.
Here, in this embodiment, the amount of heat supplied from the reboiler is estimated from the enthalpy change amount calculated from the temperature and pressure before and after the reboiler of the heating medium or the bottom flow. The amount of heat supplied by the steam supplied directly into the tower was estimated from the amount of enthalpy calculated from the temperature and pressure of the supplied steam.

[Example 1]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting propylene, ammonia and air, a liquid containing 7.1 wt% acrylonitrile, 0.4 wt% acetonitrile, 0.4 wt% hydrocyanic acid, and 92.1 wt% water was used. It was supplied to the upper 37 stages of the recovery tower at a flow rate of 363 T / hr. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 12.2 wt% of acetonitrile and 87.5 wt% of water was extracted at a flow rate of 4 T / hr from the middle 45 stages of the tower (the pipe between the two towers), and was separated by distillation in the subsequent purification step to obtain product acetonitrile. The liquid in the tower extracted from the first stage of the lower stage was subjected to heat exchange in the process and cooled to 47 ° C., and then this liquid was supplied to stage 114 of the tower at a flow rate of 133 T / hr.
The bottom liquid was acetonitrile 29 wt. It contains ppb, 0.2 wt% of hydrocyanic acid, and 96.3 wt% of water. This liquid was extracted from the bottom of the column, a part was heated through a reboiler and returned to the bottom of the column, and the rest was extracted at a flow rate of 17 T / hr. .
Separately from the reheated tower bottom stream, 475 kPa of water vapor not derived from the tower bottom stream was supplied to the outlet line of the reboiler at the bottom of the tower based on 1.7 T / hr. The amount of heat supplied by the steam 1.7 T / hr was 1.3% with respect to the sum of the amount of heat supplied by the tower bottom flow and the amount of heat supplied by the steam.
The tower top management temperature was 73 ° C., the tower bottom management temperature was 116 ° C., and the 59-stage management temperature was 99 ° C. The temperature control inside the tower was 59 stages, and the reboiler conditions were kept constant, and only the amount of steam supplied to the tower bottom was implemented. Although it was operated for 2 years under these operating conditions, the fluctuation range was a maximum of 5 ° C. at 59-stage temperature, which is important for product management, and there was no deviation from the product standard due to the temperature management of the recovery tower. FIG. 18 shows the change over time in the 59-stage temperature of the recovery tower.

[Example 2]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting propylene, ammonia and air, a liquid containing 6.6% by weight of acrylonitrile, 0.2% by weight of acetonitrile, 0.1% by weight of hydrocyanic acid and 91.5% by weight of water It was supplied at a flow rate of 165 T / hr to the upper 37 stages of the recovery tower. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 16.5 wt% of acetonitrile and 80.5 wt% of water was extracted at a flow rate of 1.7 T / hr from the middle 45 stages of the tower (pipe between the two towers), and was separated by distillation in the subsequent purification step to produce product acetonitrile and did. The liquid in the tower extracted from the first stage of the lower stage was subjected to heat exchange in the process and cooled to 47 ° C., and then this liquid was supplied to stage 114 of the tower at a flow rate of 69 T / hr.
The liquid at the bottom of the tower contains 0.01% by weight of hydrocyanic acid and 98.6% by weight of water. This liquid is withdrawn from the bottom of the tower, and part of the liquid is heated through a reboiler and returned to the bottom of the tower. Extracted.
Separately from the reheated tower bottom stream, 475 kPa of water vapor not derived from the tower bottom stream was directly supplied to 46 stages of the tower based on 2.7 T / hr. The amount of heat supplied by the steam 2.7 T / hr was 15.0% with respect to the sum of the amount of heat supplied by the tower bottom flow and the amount of heat supplied by the steam.
The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. The temperature control inside the tower was 75 stages, and the reboiler condition was kept constant, and only the amount of steam supplied to the bottom of the tower was implemented. It was operated for 1.5 years under these operating conditions, but the fluctuation range was 3 ° C at 75 ° C, which is important for product management, and there was no deviation from the product standard due to the temperature management of the recovery tower. .

[Example 3]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from a reaction product obtained by reacting propylene, ammonia and air, a liquid containing 6.4% by weight of acrylonitrile, 0.2% by weight of acetonitrile, 0.6% by weight of hydrocyanic acid, and 92.7% by weight of water is obtained. It was supplied to 82 stages of the recovery tower at a flow rate of 394 T / hr. However, this recovery tower was a recovery tower having a sieve tray having 110 plates.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 18.7 wt% of acetonitrile and 79.6 wt% of water was extracted from the middle 41 of the column at a flow rate of 3.3 T / hr, and was distilled and separated in the subsequent purification step to obtain product acetonitrile. The liquid in the tower extracted from the lower stage 1 was heat-exchanged in the process and cooled to 47 ° C., and then this liquid was supplied to the 110th stage of the tower at a flow rate of 155 T / hr.
The liquid at the bottom of the column contains 6 ppm of acetonitrile, 0.01 wt% of hydrocyanic acid and 99.9 wt% of water. This liquid is extracted from the bottom of the tower, and part of the liquid is heated through a reboiler and returned to the bottom of the tower. / Hr.
Separately from the reheated tower bottom stream, 475 kPa of water vapor not derived from the tower bottom stream was directly supplied to the 42 stage of the tower based on 1.1 T / hr. The amount of heat supplied by the steam 1.1 T / hr was 2.7% with respect to the sum of the amount of heat supplied by the tower bottom flow and the amount of heat supplied by the steam.
The tower top management temperature was 70 ° C, the tower bottom management temperature was 116 ° C, and the 55 stage management temperature was 99 ° C. The temperature control in the tower was performed for only the amount of steam supplied to the bottom of the tower while maintaining the conditions of the reboiler at a constant of 55 stages. Although it was operated for 2 years under these operating conditions, the fluctuation range was 3 ° C. at the maximum 55 stage temperature, which is important for product management, and there was no deviation from the product standard due to the temperature management of the recovery tower.

[Example 4]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting tertiary butyl alcohol, ammonia and air, methacrylonitrile 6.9 wt%, acetonitrile 2.1 wt%, cyanic acid 1.1 wt% and water 88.8 wt% Was supplied to the upper 37 stages of the recovery tower at a flow rate of 82 T / hr. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of methacrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product methacrylonitrile and product hydrocyanic acid. A liquid containing 2.7 wt% of acetonitrile and 95.4 wt% of water was extracted at a flow rate of 64.7 T / hr from the middle 45 stages of the tower (piping between the two towers), and after the heat exchange in the process, the absorption tower of the previous step Used as absorbed water. The liquid in the tower extracted from the first stage of the lower stage was subjected to heat exchange in the process and cooled to 44 ° C., and then this liquid was supplied to stage 114 of the tower at a flow rate of 66 T / hr.
The bottom liquid contains 0.09 wt% of cyanic acid and 99.5 wt% of water. This liquid is extracted from the bottom of the tower, partly heated through a reboiler and returned to the bottom of the tower, and the rest at a flow rate of 14 T / hr. Extracted.
Separately from the reheated tower bottom stream, 475 kPa of water vapor not derived from the tower bottom stream was directly supplied to 46 stages of the tower based on 0.9 T / hr. The amount of heat supplied by the steam 0.9 T / hr was 8.2% with respect to the sum of the amount of heat supplied by the tower bottom flow and the amount of heat supplied by the steam.
The tower top management temperature was 76 ° C., the tower bottom management temperature was 113 ° C., and the 75 stage management temperature was 88 ° C. The temperature control inside the tower was 75 stages, and the reboiler condition was kept constant, and only the amount of steam supplied to the bottom of the tower was implemented. The operation was continued for one month under these operating conditions, but the fluctuation range was 3 ° C. at a maximum at 75-stage temperature, which is important for product management.

[Example 5]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting propylene, ammonia and air, a liquid containing 6.6% by weight of acrylonitrile, 0.2% by weight of acetonitrile, 0.1% by weight of hydrocyanic acid and 91.5% by weight of water It was supplied at a flow rate of 128 T / hr to the upper 37 stages of the recovery tower. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a sheave tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 12.5 wt% of acetonitrile and 80.5 wt% of water was extracted at a flow rate of 1.3 T / hr from the middle 45 stages of the tower (pipe between the two towers), and was separated by distillation in the subsequent purification step, did. The liquid in the tower extracted from the lower stage 1 was heat-exchanged in the process and cooled to 47 ° C., and then this liquid was supplied to 114 stages of the tower at a flow rate of 64 T / hr.
The bottom liquid contains 0.09 wt% of cyanic acid and 98.6 wt% of water. This liquid is extracted from the bottom of the tower and partly heated through the reboiler (first reboiler) and returned to the bottom of the tower. The remainder was extracted at a flow rate of 18 T / hr.
Separately from the reheated tower bottom stream, 475 kPa of steam not derived from the tower bottom stream is supplied to another reboiler (second reboiler) as a heating medium based on 3.3 T / hr to heat the tower bottom stream. did. The amount of heat supplied by the second reboiler using the water vapor as a heat medium is the amount of heat supplied by the first reboiler and the amount of heat supplied by the second reboiler using the water vapor as a heat medium. It was 19.0% with respect to the sum.
The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. The temperature control inside the tower was 75 stages, and the reboiler condition was kept constant, and only the amount of steam supplied to the bottom of the tower was implemented. It was operated for 1.5 years under these operating conditions, but the fluctuation range was 3 ° C at 75 ° C, which is important for product management, and there was no deviation from the product standard due to the temperature management of the recovery tower. .

[Example 6]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting propylene, ammonia and air, a liquid containing 6.7% by weight of acrylonitrile, 0.2% by weight of acetonitrile, 0.1% by weight of hydrocyanic acid and 91.6% by weight of water It was supplied to the upper 82 stages of the recovery tower at a flow rate of 160 T / hr. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a sheave tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 12.5 wt% of acetonitrile and 80.5 wt% of water was extracted at a flow rate of 1.5 T / hr from the middle 45 stages of the tower (the pipe between the two towers), and was separated by distillation in the subsequent purification step. did. The liquid in the tower extracted from the first stage of the lower stage was subjected to heat exchange in the process and cooled to 47 ° C., and then this liquid was supplied to the stage 114 of the tower at a flow rate of 65 T / hr.
The bottom liquid contains 0.07 wt% of cyanic acid and 98.5 wt% of water. This liquid is extracted from the bottom of the tower and partly heated through the reboiler (first reboiler) and returned to the bottom of the tower. The remainder was extracted at a flow rate of 18 T / hr.
Separately from the reheated bottom stream, 475 kPa of water vapor not derived from the bottom stream is supplied to another reboiler (second reboiler) as a heating medium based on 0.8 T / hr to heat the bottom stream. did. The amount of heat supplied by the second reboiler using the water vapor as a heat medium is the amount of heat supplied by the first reboiler and the amount of heat supplied by the second reboiler using the water vapor as a heat medium. It was 4.1% with respect to the sum.
The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. The temperature control inside the tower was 75 stages, and the reboiler condition was kept constant, and only the amount of steam supplied to the bottom of the tower was implemented. The system was operated for 1 year under these operating conditions, but the fluctuation range was 2 ° C. at a maximum of 75 ° C., which is important for product management, and stable operation was possible without any deviation from the product standard due to the temperature management of the recovery tower.

[Example 7]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting propylene, ammonia and air, a liquid containing 6.6% by weight of acrylonitrile, 0.2% by weight of acetonitrile, 0.1% by weight of hydrocyanic acid and 91.5% by weight of water The gas was supplied to the upper 82 stages of the recovery tower at a flow rate of 105 T / hr. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a sheave tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 12.6 wt% of acetonitrile and 80.6 wt% of water was extracted at a flow rate of 1.4 T / hr from the middle 45 stages of the tower (the pipe between the two towers), and was separated by distillation in the subsequent purification step, did. The liquid in the tower extracted from the first stage of the lower stage was subjected to heat exchange in the process and cooled to 47 ° C., and then this liquid was supplied to the 114th stage of the tower at a flow rate of 51 T / hr.
The bottom liquid contains 0.07 wt% of cyanic acid and 98.5 wt% of water. This liquid is extracted from the bottom of the tower and partly heated through the reboiler (first reboiler) and returned to the bottom of the tower. The remainder was extracted at a flow rate of 18 T / hr.
In addition to the reheated tower bottom stream, 475 kPa of water vapor not derived from the tower bottom stream is supplied to another reboiler (second reboiler) as a heating medium on the basis of 3.0 T / hr to enter the 45-stage tower. The stream was heated. The amount of heat supplied by the second reboiler using the water vapor as a heat medium is the amount of heat supplied by the first reboiler and the amount of heat supplied by the second reboiler using the water vapor as a heat medium. It was 16.9% with respect to the sum.
The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. The temperature control inside the tower was 75 stages, and the reboiler condition was kept constant, and only the amount of steam supplied to the bottom of the tower was implemented. The system was operated for 1 year under these operating conditions, but the fluctuation range was 2 ° C. at a maximum of 75 ° C., which is important for product management, and stable operation was possible without any deviation from the product standard due to the temperature management of the recovery tower.

[Example 8]
Distillation was performed using the distillation apparatus shown in FIG.
In order to separate acetonitrile from the reaction product obtained by reacting propylene, ammonia and air, a liquid containing 6.6% by weight of acrylonitrile, 0.2% by weight of acetonitrile, 0.1% by weight of hydrocyanic acid and 91.5% by weight of water It was supplied at a flow rate of 118 T / hr to the upper 82 stages of the recovery tower. However, this recovery tower was divided into two towers having an upper 69 stage having a dual tray and a sheave tray and a lower 45 stage, and the tower bottom of the upper tower and the tower top of the lower tower were connected by a pipe.
A mixed gas of acrylonitrile, hydrocyanic acid, and water was extracted from the top of the column, and was separated by distillation in a subsequent purification step to obtain product acrylonitrile and product hydrocyanic acid. A liquid containing 12.6 wt% of acetonitrile and 80.6 wt% of water was extracted at a flow rate of 1.3 T / hr from the middle 45 stages of the tower (pipe between the two towers), and was separated by distillation in the subsequent purification step, did. The liquid in the tower extracted from the first stage of the lower stage was subjected to heat exchange in the process and cooled to 47 ° C., and then this liquid was supplied to the stage 114 of the tower at a flow rate of 56 T / hr.
The tower bottom liquid contains 0.09 wt% of cyanic acid and 98.5 wt% of water. This liquid is withdrawn from the tower bottom and partly heated through the reboiler (first reboiler) and returned to the tower bottom. The remainder was extracted at a flow rate of 11 T / hr.
Separately from the reheated tower bottom stream, 475 kPa of water vapor not derived from the tower bottom stream is supplied to another reboiler (second reboiler) as a heating medium on the basis of 0.8 T / hr. The stream was heated. The amount of heat supplied by the second reboiler using the water vapor as a heat medium is the amount of heat supplied by the first reboiler and the amount of heat supplied by the second reboiler using the water vapor as a heat medium. It was 4.9% with respect to the sum.
The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. The temperature control inside the tower was 75 stages, and the reboiler condition was kept constant, and only the amount of steam supplied to the bottom of the tower was implemented. The system was operated for 1 year under these operating conditions, but the fluctuation range was 2 ° C. at a maximum of 75 ° C., which is important for product management, and stable operation was possible without any deviation from the product standard due to the temperature management of the recovery tower.

[Comparative Example 1]
In the recovery tower shown in FIG. 6, water vapor is not supplied to the outlet line of the reboiler at the bottom of the tower, that is, the total amount of heat is supplied and adjusted through the reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 1 was supplied to the same recovery tower as in Example 1 at the same flow rate. The other flow rates were the same as in Example 1, and the temperature and pressure were also operated in the same manner as in Example 1. The tower top management temperature was 73 ° C., the tower bottom management temperature was 116 ° C., the 59 stage management temperature was 99 ° C., and the 45 stage management temperature was 109 ° C. Although it was operated for 2 years under these operating conditions, the fluctuation range was a maximum of 10 ° C. at 59-stage temperature, and non-standard products were temporarily generated. FIG. 19 shows the change over time in the 59-stage temperature of the recovery tower.

[Comparative Example 2]
In the recovery tower shown in FIG. 8, no steam was supplied to 46 stages in the vicinity of the temperature controller, that is, the total heat was supplied and adjusted through a reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 2 was supplied to the same recovery tower as in Example 2 at the same flow rate. The other flow rates were the same as in Example 2, and the temperature and pressure were also operated in the same manner as in Example 2. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 1.5 years under these operating conditions, the fluctuation range was a maximum of 7 ° C. at 75-stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 3]
In the recovery tower shown in FIG. 1, no steam was supplied to the 42 stages near the temperature control section, that is, the total amount of heat was supplied and adjusted through the reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 3 was supplied to the same recovery tower as in Example 3 at the same flow rate. The other flow rates were the same as in Example 3, and the temperature and pressure were also operated in the same manner as in Example 3. The tower top management temperature was 70 ° C, the tower bottom management temperature was 116 ° C, and the 55 stage management temperature was 99 ° C. Although it was operated for 2 years under these operating conditions, the fluctuation range was a maximum of 8 ° C. at 55-stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 4]
In the recovery tower shown in FIG. 8, no steam was supplied to 46 stages in the vicinity of the temperature controller, that is, the total heat was supplied and adjusted through a reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 4 was supplied to the same recovery tower as in Example 4 at the same flow rate. The other flow rates were the same as in Example 2, and the temperature and pressure were also operated in the same manner as in Example 4. The tower top management temperature was 76 ° C., the tower bottom management temperature was 113 ° C., and the 75 stage management temperature was 88 ° C. Although it was operated for one month under these operating conditions, the fluctuation range was a maximum of 8 ° C. at 65-stage temperature, and non-standard products were temporarily generated.

[Comparative Example 5]
The recovery tower shown in FIG. 10 is not provided with a reboiler using steam as a heat medium, that is, except that the total amount of heat was supplied and adjusted through the reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 5 was supplied to the same recovery tower as in Example 5 at the same flow rate. The other flow rates were the same as in Example 5, and the temperature and pressure were also operated in the same manner as in Example 5. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 1.5 years under these operating conditions, the fluctuation range was a maximum of 8 ° C. at 75-stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 6]
In the recovery tower shown in FIG. 11, a reboiler using steam as a heat medium is not installed, that is, the total amount of heat is supplied and adjusted through the reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 6 was supplied to the same recovery tower as in Example 6 at the same flow rate. The other flow rates were the same as in Example 6, and the temperature and pressure were also operated in the same manner as in Example 6. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 1 year under these operating conditions, the fluctuation range was a maximum of 6 ° C. at 75 stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 7]
The recovery tower shown in FIG. 14 is not provided with a reboiler that uses steam as a heat medium, that is, except that the total amount of heat is supplied and adjusted through the reboiler at the bottom of the tower without using the second heating path. The same reaction product solution as in Example 7 was supplied to the same recovery tower as in Example 7 at the same flow rate. The other flow rates were the same as in Example 7, and the temperature and pressure were also operated in the same manner as in Example 7. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 1 year under these operating conditions, the fluctuation range became a maximum of 7 ° C. at 75 stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 8]
In the recovery tower shown in FIG. 6, the same reaction product solution as in Example 1 was used at the same flow rate except that the amount of steam supplied to the outlet line of the reboiler at the bottom of the tower was changed to 32.9 T / hr. 1 was fed to the same recovery tower. The other flow rates were the same as in Example 1, and the temperature and pressure were also operated in the same manner as in Example 1. The amount of heat supplied by the steam 32.9 T / hr was 20.3% with respect to the sum of the amount of heat supplied by the reheated tower bottom flow and the amount of heat supplied by the steam. The tower top management temperature was 73 ° C., the tower bottom management temperature was 116 ° C., the 59 stage management temperature was 99 ° C., and the 45 stage management temperature was 109 ° C. Although it was operated for 2 weeks under these operating conditions, the fluctuation range was a maximum of 7 ° C. at 59-stage temperature, and non-standard products were temporarily generated.

[Comparative Example 9]
In the recovery tower shown in FIG. 8, the same reaction product solution as in Example 2 was used at the same flow rate as in Example 2, except that the amount of steam supplied to 46 stages of towers was changed to 4.1 T / hr. Supplied to. The other flow rates were the same as in Example 2, and the temperature and pressure were also operated in the same manner as in Example 2. The amount of heat supplied by the steam 4.1 T / hr was 21.1% with respect to the sum of the amount of heat supplied by the reheated tower bottom flow and the amount of heat supplied by the steam. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 1 month under these operating conditions, the fluctuation range was a maximum of 8 ° C. at 75-stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 10]
In the recovery tower shown in FIG. 1, the same reaction product solution as in Example 3 is used at the same flow rate, except that the amount of steam supplied to 42 stages of the tower is changed to 12.0 T / hr. Supplied to. The other flow rates were the same as in Example 3, and the temperature and pressure were also operated in the same manner as in Example 3. The amount of heat supplied by the steam 12.0 T / hr was 23.2% with respect to the sum of the amount of heat supplied by the reheated tower bottom flow and the amount of heat supplied by the steam. The tower top management temperature was 70 ° C, the tower bottom management temperature was 116 ° C, and the 55 stage management temperature was 99 ° C. Although it was operated for 1 month under these operating conditions, the fluctuation range reached a maximum of 10 ° C. at 55-stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 11]
In the recovery tower shown in FIG. 8, the same reaction product liquid as in Example 4 is used at the same flow rate, except that the amount of steam supplied to 46 stages of the tower is changed to 3.0 T / hr. Supplied to. The other flow rates were the same as in Example 2, and the temperature and pressure were also operated in the same manner as in Example 4. The amount of heat supplied by the steam 3.0 T / hr was 22.9% with respect to the sum of the amount of heat supplied by the reheated tower bottom flow and the amount of heat supplied by the steam. The tower top management temperature was 76 ° C., the tower bottom management temperature was 113 ° C., and the 75 stage management temperature was 88 ° C. Although it was operated for 2 weeks under these operating conditions, the fluctuation range reached a maximum of 8 ° C. at 65-stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 12]
10 except that the amount of steam supplied to the reboiler using steam as a heat medium in the recovery tower shown in FIG. 10 was changed to 4.0 T / hr. 5 was supplied to the same recovery tower as in No. 5. The other flow rates were the same as in Example 5, and the temperature and pressure were also operated in the same manner as in Example 5. The amount of heat supplied by the reboiler using the steam as a heat medium is the sum of the amount of heat supplied by the reboiler “derived from the bottom stream” and the amount of heat supplied by the reboiler using the steam as a heat medium. It was 22.1%. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 1 month under these operating conditions, the fluctuation range was 9 ° C. at the 75th stage temperature, and non-standard products were temporarily generated.

[Comparative Example 13]
In the recovery tower shown in FIG. 11, the same reaction product solution as in Example 6 was used at the same flow rate except that the amount of steam supplied to the reboiler using steam as a heat medium was changed to 4.8 T / hr. 6 was supplied to the same recovery tower as in No. 6. The other flow rates were the same as in Example 6, and the temperature and pressure were also operated in the same manner as in Example 6. The amount of heat supplied by the reboiler using the steam as a heat medium is the sum of the amount of heat supplied by the reboiler “derived from the bottom stream” and the amount of heat supplied by the reboiler using the steam as a heat medium. It was 20.4%. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 2 months under these operating conditions, the fluctuation range became a maximum of 7 ° C. at 75 stage temperature, and a non-standard product was temporarily generated.

[Comparative Example 14]
14 except that the amount of steam supplied to the reboiler using steam as a heat medium in the recovery tower shown in FIG. 14 was changed to 4.0 T / hr. 7 was supplied to the same recovery tower. The other flow rates were the same as in Example 7, and the temperature and pressure were also operated in the same manner as in Example 7. The amount of heat supplied by the reboiler using the steam as a heat medium is the sum of the amount of heat supplied by the reboiler “derived from the bottom stream” and the amount of heat supplied by the reboiler using the steam as a heat medium. It was 21.3%. The tower top management temperature was 71 ° C., the tower bottom management temperature was 117 ° C., and the 75 stage management temperature was 85 ° C. Although it was operated for 2 weeks under these operating conditions, the fluctuation range was 8 ° C. at the 75th stage temperature, and non-standard products were temporarily generated.

  The distillation method and distillation apparatus of the present invention can be usefully used in the industrial production process of unsaturated nitriles.

1: Recovery tower 2, 3: Reboiler 11: Heat exchanger in process 15: Thermometer in recovery tower 16: Temperature indicator regulator 17: Flow indicator regulator 18: Electrical wiring 19: Flow regulator 20: No. Second reboiler 4-10, 12, 13, 14: line

Claims (9)

A method for distilling unsaturated nitriles, comprising:
Distilling the unsaturated nitrile through a recovery tower connected to the first and second heating paths;
The amount of heat supplied to the recovery tower by the second heating path is 1 to 20% with respect to the sum of heat amounts supplied to the recovery tower by the first and second heating paths,
An unsaturated nitrile distillation method in which a tower bottom stream reheated from the first heating path is supplied to the recovery tower, and water vapor is supplied to the recovery tower from the second heating path.   The distillation method according to claim 1, wherein the water vapor is supplied to a lower portion of the recovery tower.   A reboiler using steam as a heat medium is provided in the second heating path, and a tower bottom stream reheated from the first heating path is supplied to the recovery tower, and the second heating path The unsaturated nitrile distillation method according to claim 1, wherein a tower bottom stream and / or a tower inner stream heated by a reboiler are supplied to the recovery tower. Producing a gas containing an unsaturated nitrile by ammoxidizing at least one selected from the group consisting of propane, propylene, isobutane and isobutylene in the presence of a catalyst;
A step of obtaining an aqueous mixture containing an unsaturated nitrile by contacting the gas with an aqueous liquid in a quenching tower and then absorbing the gas in contact with a liquid containing water in the absorption tower;
Distilling the aqueous mixture containing the resulting unsaturated nitrile,
A method for producing an unsaturated nitrile comprising:
Supplying a reheated bottom stream and water vapor to a recovery tower for distilling the unsaturated nitrile from the aqueous mixture. A distillation apparatus having a recovery tower and first and second heating paths connected to the recovery tower,
The amount of heat supplied to the recovery tower by the second heating path is 1 to 20% with respect to the sum of heat amounts supplied to the recovery tower by the first and second heating paths,
The second heating path includes a steam generator;
The tower bottom stream is heated by the first heating path, and the heated tower bottom stream is supplied to the recovery tower,
The steam generating apparatus generates steam that is not derived from the bottoms stream, and that to supply steam which is not derived from the bottoms stream to said recovery column, distillation apparatus unsaturated nitrile. The unsaturated nitrile distillation apparatus according to claim 5, wherein the water vapor is supplied to a lower portion of the recovery tower.   The second heating path includes a reboiler using steam as a heat medium, the bottom stream is heated by the first heating path, and the bottom stream and / or the inner stream is heated by the reboiler. The unsaturated nitrile distillation apparatus according to claim 5. 8. The unsaturated nitrile distillation apparatus according to claim 7, wherein a tower bottom stream and / or an inner stream at a lower part of the recovery tower are reheated by the reboiler and supplied to the recovery tower. A reactor, a quenching tower connected to the reactor, an absorption tower connected to the quenching tower, and a recovery tower connected to the absorption tower,
A reboiler and a steam generator are connected to the recovery tower,
In the reactor, a gas containing an unsaturated nitrile is generated by at least one ammoxidation selected from the group consisting of propane, propylene, isobutane and isobutylene in the presence of a catalyst;
The gas is contacted with an aqueous liquid in the quenching tower, and then contacted with a liquid containing water in the absorption tower to obtain an aqueous mixture containing an unsaturated nitrile,
An unsaturated nitrile production apparatus in which an aqueous mixture containing the obtained unsaturated nitrile is distilled in a recovery tower,
The unsaturated nitrile manufacturing apparatus in which the bottom stream flowing out of the recovery tower is heated by the reboiler and returned to the recovery tower, and the water vapor generated by the steam generator is supplied to the recovery tower.