KR20130086643A - Method for purifying acrylonitrile - Google Patents

Abstract

A method for purifying acrylonitrile comprising distilling a solution containing acrylonitrile, hydrogen cyanide and water by using a distillation column and a distillation apparatus having a top gas condenser connected to the distillation column. It provides a method comprising the step of maintaining a constant temperature of the temperature control stage located above the feed stage and below the top of the distillation column.

Description

Purification method of acrylonitrile {METHOD FOR PURIFYING ACRYLONITRILE}

The present invention relates to a method for purifying acrylonitrile by distilling a solution containing acrylonitrile, hydrogen cyanide and water.

In the process of producing acrylonitrile by reacting propylene and / or propane, ammonia and oxygen in the presence of a catalyst, first, the reaction product gas containing the produced acrylonitrile, acetonitrile and hydrogen cyanide is cooled in a quench tower. The unreacted ammonia is neutralized and removed with sulfuric acid. The reaction product gas is then sent to an absorption tower, where acrylonitrile, acetonitrile and hydrogen cyanide are absorbed in water. Subsequently, an aqueous solution containing acrylonitrile or the like obtained from the absorption tower is introduced into the recovery column, and from the aqueous solution, an oil containing acetonitrile and most of water, and acrylonitrile or cyanide by distillation. Separate into fractions containing most of the hydrogen. Subsequently, an oil containing most of acrylonitrile or hydrogen cyanide is introduced into the decleaning dehydration column to separate hydrogen cyanide and water, and then the column bottom liquid is introduced into the product column, and acrylonitrile is removed by distillation. Purification produces a product conforming to product specifications.

Patent Literature 1 discloses a method of suppressing polymerization of acrylonitrile and hydrogen cyanide by adding an acid and hydroquinone to a dehydrochloric acid dehydration tower in purifying acrylonitrile.

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-39403

In the decleaning dehydration column, a solution containing acrylonitrile, hydrogen cyanide, and water is distilled, a vapor containing hydrogen cyanide flows out from the column top, and a solution containing acrylonitrile is extracted from the column bottom. do. The gas containing hydrogen cyanide flowing out from the column top is partially condensed by cooling with a condenser, and since hydrogen cyanide containing few impurities which are not condensed is used as a raw material of the hydrogen cyanide derivative, acryl in the hydrogen cyanide gas flowing out from the column top It is desirable to keep the nitrile concentration low. For this reason, even if the tower top temperature is maintained at the target temperature according to a general distillation technique, the acrylonitrile concentration in the hydrogen cyanide gas flowing out of the tower top is not stable, and the acrylonitrile concentration in the hydrogen cyanide gas is a prescribed value. It is often seen that ascending beyond. When this phenomenon occurs, not only the quality of the hydrogen cyanide derivative raw material is not stable, but also the quality of the acrylonitrile product is not stable, and may also be a factor in the polymerization of acrylonitrile and hydrogen cyanide in a dehydrochlorination dehydration tower. .

Conventionally, much attention has been paid to the increase in the yield of acrylonitrile which is a product, and has been studied. On the other hand, in addition to the improvement aimed at the direct effect of the increase in quantity, the indirect improvement such as the stabilization of the product quality has great merits both technically and economically, but the present situation has not been examined in detail so far.

In view of the above circumstances, the problem to be solved by the present invention is to provide a method for stabilizing product quality in the manufacturing process of acrylonitrile.

MEANS TO SOLVE THE PROBLEM This inventor stabilizes product quality by controlling so that the temperature of the specific stage of a distillation column in the process of distilling the solution containing acrylonitrile, hydrogen cyanide, and water in the process of manufacturing an acrylonitrile is constant. It was found that the process load can be reduced, and the present invention was completed.

That is, the present invention is as follows.

[1] A method for purifying acrylonitrile comprising distilling a solution containing acrylonitrile, hydrogen cyanide and water using a distillation column having a distillation column and a condenser of a top gas connected to the distillation column.

And maintaining a constant temperature of a temperature control stage positioned above the feed stage of the distillation column and below the top of the distillation column.

[2] an adjustment valve is provided in the pipe for supplying the refrigerant to the condenser and / or the pipe for discharging the refrigerant from the condenser, and a thermometer is provided in the temperature control stage.

Setting a target temperature of the temperature control stage,

When the temperature of the temperature control stage is higher than the target temperature, the opening of the control valve is adjusted to increase the supply amount of the refrigerant,

The method according to the above [1], wherein when the temperature of the temperature control stage is lower than the target temperature, the temperature of the temperature control stage is kept constant by adjusting the opening degree of the regulating valve to reduce the supply amount of the refrigerant.

[3] setting the upper limit value and the lower limit value of the temperature of the temperature control stage, and adjusting the supply amount of the refrigerant by the regulating valve so that the temperature of the temperature control stage is changed above the lower limit value and below the upper limit value. 2].

[4] increase and decrease the amount of heat removed from the condenser while providing a constant amount of heat from the reboiler to the distillation column,

In each heat removal amount, the temperature of each stage located above the feed stage of the said distillation column, and below the upper end of the said distillation column,

Acrylonitrile concentration and hydrogen cyanide concentration in each said stage are measured,

A stage positioned above the feed stage of the distillation column and below the top stage of the distillation column, wherein the lowest stage (lowest stage) among the stages where the acrylonitrile concentration is lower than the hydrogen cyanide concentration is set as a temperature control stage,

[1]-comprising the step of determining a target temperature of the temperature control stage such that the concentration of acrylonitrile flowing out of the column top of the distillation column is minimum from the temperature of each stage in the respective heat removal amounts. The method for purifying acrylonitrile according to any one of [3].

[5] increase and decrease the amount of heat removed from the condenser while providing a constant amount of heat from the reboiler to the distillation column,

In each heat removal amount, the temperature of each stage located above the feed stage of the said distillation column, and below the upper end of the said distillation column,

Acrylonitrile concentration and hydrogen cyanide concentration in each said stage are measured,

A stage positioned above the feed stage of the distillation column and below the top stage of the distillation column, among the stages where the acrylonitrile concentration is higher than the hydrogen cyanide concentration, the uppermost stage (top) is set as a temperature control stage,

[1]-comprising the step of determining a target temperature of the temperature control stage such that the concentration of acrylonitrile flowing out of the column top of the distillation column is minimum from the temperature of each stage in the respective heat removal amounts. The method for purifying acrylonitrile according to any one of [3].

[6] distillation towers,

A thermometer provided at a temperature control stage positioned above the feed stage of the distillation column and below the top of the distillation column;

A condenser connected to the distillation column,

A pipe for supplying a coolant connected to the condenser and a pipe for discharging the coolant;

A distillation apparatus having an adjustment valve for adjusting a supply amount of a refrigerant attached to a pipe for supplying the coolant and / or a pipe for discharging the coolant,

The thermometer is connected to the control valve via a temperature controller;

The temperature of the temperature control stage is transmitted to the temperature controller by the thermometer,

When the temperature of the temperature control stage is higher than a target temperature by the temperature controller, the opening of the control valve is adjusted to increase the supply amount of the refrigerant.

The distillation apparatus as described above, when the temperature of the temperature control stage is lower than a target temperature, the supply amount of the refrigerant is reduced by adjusting the opening degree of the adjustment valve.

According to the present invention, in the manufacturing process of acrylonitrile, a high quality product can be stably obtained for a long time.

1 is a schematic diagram conceptually illustrating an example of an acrylonitrile manufacturing process.
FIG. 2 is a schematic diagram conceptually showing an example of a decleaning dewatering tower and a facility connected thereto.
3 is a schematic diagram conceptually showing another example of a decleaning dewatering tower and a facility connected thereto.

EMBODIMENT OF THE INVENTION Hereinafter, the form (following this embodiment) for implementing this invention is demonstrated in detail. In addition, this invention is not limited to this embodiment, It can variously deform and implement within the range of the summary.

EMBODIMENT OF THE INVENTION Hereinafter, this embodiment is described in detail, referring drawings as needed. In addition, the same code | symbol is attached | subjected to the same element in drawing, and the overlapping description is abbreviate | omitted. In addition, the positional relationship of up, down, left, right, etc. shall be based on the positional relationship shown in drawing unless there is particular notice. The dimension ratio of an apparatus or a member is not limited to the ratio shown.

The purification method of the acrylonitrile of this embodiment is

A method for purifying acrylonitrile comprising distilling a solution containing acrylonitrile, hydrogen cyanide and water by using a distillation column and a distillation apparatus having a top gas condenser connected to the distillation column.

And a step of maintaining a constant temperature of the temperature control stage positioned above the feed stage of the distillation column and below the top of the distillation column.

1 is a schematic diagram schematically showing an example of an acrylonitrile manufacturing process, and FIG. 2 is a schematic diagram conceptually showing an example of a decleaning dehydration tower and equipment connected thereto. In addition, although the "distillation tower" in this embodiment is demonstrated as a "demineralization dehydration tower," as a "distillation tower", it is not limited to the "declaration acid dehydration tower" heretofore, as long as it is a tower which can distill, all this embodiment It is included in the range of "distillation tower" of.

In the acrylonitrile manufacturing process, first, a gaseous propylene and / or propane is obtained from line 2, ammonia from line 3, and oxygen (usually using air) from line 4, respectively. It is supplied to the charged fluidized bed reactor 1, and propylene and / or propane are subjected to ammoxidation reaction. The obtained reaction product gas is taken out from the line 5 and introduced into the quench tower 6. In the quench tower 6, the reaction product gas and water are brought in direct contact with each other to cool the reaction product gas to remove the fluidized bed catalyst contained in a small amount in the high boiling point material and the gas. In addition, the unreacted ammonia is neutralized and removed with sulfuric acid. These high boiling point substances, catalysts, and oils are extracted out of the process system from the line 7 at the bottom of the quench tower 6.

The gas taken out from the top of the quench tower 6 is introduced into the absorption tower 9 by the line 8. Water extracted from the recovery column 12 to the top of the absorption tower 9 is supplied from the line 14 as absorption water, and acrylonitrile, acetonitrile and hydrogen cyanide in the reaction product gas are absorbed into the water. Propylene, propane, oxygen, nitrogen, carbon dioxide, carbon monoxide and the like and trace organic matters which are not absorbed are extracted from the top line 11 of the absorption tower. The column bottom liquid of the absorption tower 9 is supplied from the line 10 to the recovery tower 12.

Extraction water is introduced into the column top of the recovery column 12 from the line 15, and acetonitrile is extracted and separated by extractive distillation. Acetonitrile exits the process system from line 16. In addition, most of the water is discharged from the line 13 out of the process system. Acrylonitrile, hydrogen cyanide and water flow out from the top of the recovery column by line 17, condensate with a condenser (not shown), and separate into two layers, an organic layer and a water layer, with a decanter (not shown). An organic layer comprising acrylonitrile, hydrogen cyanide and a small amount of water is fed to the decleaning dehydration tower 18. The aqueous layer is recycled to the previous step as a recovery tower feed liquid (from line 10) or extraction water (from line 15) or the like.

The vapor containing hydrogen cyanide flows out from the line 19 from the tower top of the decleaning dehydration tower 18, is sent to the condenser 20, and it cools and partially condenses. The condensed hydrogen cyanide liquid is refluxed to the column top by the line 22, and the crude hydrogen cyanide gas containing few impurities which have not condensed is taken out from the line 21 out of the system. Hydrogen cyanide gas is refine | purified in the distillation tower which is not shown in figure as needed, and is used as a raw material of a hydrogen cyanide derivative. As the condenser 20, a vertical type is preferable, and acetic acid is sprayed on the upper tube plate to suppress the polymerization of hydrogen cyanide. As the coolant 20a used for the condenser 20, water or methanol aqueous solution whose supply temperature is 0-35 degreeC, Preferably 3-30 degreeC is used.

The column inner liquid is extracted by the line 23 from the chimney tray D at the stop of the decleaning dewatering tower 18, and cooled to the line 23c after cooling by the refrigerant 23a with the side cut cooler 23b. It supplies to the decanter 23d, and separates into two layers, an organic layer and an aqueous layer, by the decanter 23d. In the present embodiment, the "interruption" refers to a portion above the bottom of the tower information, and in the case of a multi-stage distillation column, one stage between the tower bottom and the top of the column. For example, in the case of a distillation column having 50 to 65 stages in total, it is preferable to set the line 23 to 20 to 30 stages from the bottom of the column from the viewpoint of efficiently separating water from the crude acrylonitrile. As the coolant 23a, the same coolant as the coolant 20a can be used. The heat removal amount in the side cut cooler 23b is adjusted with reference to the thermometer (not shown) for measuring the temperature of the liquid installed in the decanter 23d. It is preferable to control so that liquid temperature in a decanter may become constant in the range of 20-40 degreeC. The water layer in the decanter is recycled to the previous steps such as the recovery tower 12 by the line 23f. The organic layer in the decanter is returned to the stage below the stage where the above-mentioned columnar liquid is extracted by the line 23e. This organic layer may be preheated and returned.

The heat required for distillation is supplied from the reboiler 24a via the line 24c. As the fruit 24b, high temperature process water taken out from the bottom of the column (lines 14 and 15) and / or the bottom (line 13) of the steam or recovery column 12 is used.

The amount of heat provided to the distillation column by the reboiler 24a is 180 × 10 ³ to 260 × 10 ³ dl / h / from the viewpoint of efficiently separating and collecting the acrylonitrile in the desalination dewatering tower 18. t-acrylonitrile is preferred, and 190 x 10 ³ to 230 x 10 ³ dl / h / t-acrylonitrile is more preferred. Here, the mass of acrylonitrile is the mass (t) of acrylonitrile obtained as a product from a product tower, and since the above-mentioned numerical value shows calorie per mass of acrylonitrile, it can be called a "calorie source unit." have.

The crude acrylonitrile is extracted by the line 24 from the bottom of the decleaning dehydration tower 18 and sent to the product tower 25. In addition, a part of the column bottom liquid extracted by the line 24 is supplied to the reboiler 24a.

The product tower 25 is a tray-type distillation column operated under a pressure lower than atmospheric pressure. The effluent vapor of the product tower 25 is discharged through the line 26 and sent to the condenser 30 to condense. The condensate is refluxed to the product column 25 via the line 31, and a part of the liquid is discharged through the line 29. The bottom liquid containing the high boiling point material is drawn out from the line 28. In the process shown in FIG. 1, acrylonitrile is acquired as a product from the line 27. FIG.

In the manufacturing process of acrylonitrile, even if it is normal operation, the production amount of acrylonitrile may increase or decrease from a production plan etc. in some cases. In this case, the amount of solution fed to the decleaning dewatering tower 18 increases and decreases, and the necessity of adjusting the operating conditions of the distillation apparatus arises. In the present embodiment, the "distillation apparatus" is a concept including the auxiliary equipment of a distillation column including a reboiler and a condenser, and extracts a part of the solution from the stop of the distillation column, and cools and / or separates the stop extract. If so, a cooler and / or oil / water separator are also included in the distillation apparatus.

The decleaning dehydration tower 18 is a tray-type distillation column operated under normal pressure, and the number of shelves is preferably 50 stages to 65 stages. Although the shelf to be used has a kind of a sieve tray, a dual flow tray, etc., it is not limited to these.

The feed liquid to the decleaning dehydration tower is supplied to the feed stage A from the line 17. The position of the said feed stage A is the upper part of chimney tray D, Preferably it is the 10th-25th upper part of chimney tray D. When the feed liquid is supplied, steam rises in the tower, and steam containing hydrogen cyanide flows out of the line 19 from the column top. The outflow steam is sent to the condenser 20, cooled and partially condensed. The condensed hydrogen cyanide liquid is refluxed to the top end C of the column by the line 22, and the crude hydrogen cyanide gas containing less uncondensed impurities is taken out of the system from the line 21. The reflux liquid which flows down in a column and the vapor which rises in a column come into contact, and distillation purification is performed.

In the method of this embodiment, the temperature of the stage B located below the upper end C of the upper part and the tower from the feed end A is kept constant. Here, the feed end A itself is not included in the "above the feed end A", and the upper end C itself is not included in the "lower than the top end C". In this embodiment, "keeping a temperature constant" shows keeping to the set target temperature, and when setting the upper limit and lower limit mentioned later, it also includes maintaining in the temperature range more than an upper limit and less than a lower limit. In addition, the amplitude by hunting of the meter measurement value is included. Here, the "end B" does not mean a whole end located above the feed end A and below the top end of the tower, but is a specific step in which the thermometer 22b selected from the steps between them is provided. Is referred to as " temperature control stage ". More preferably, the temperature of the specific stage B, which is located between the upper three stages of the feed stage A and the lower three stages of the top of the tower, is kept constant.

The target temperature is preferably set to a specific point temperature, but in practice, even when the temperature of the temperature control stage is out of the target temperature, the distillation separation at the target temperature is acceptable. There is an upper limit and a lower limit. In this embodiment, the value is called an upper limit and a lower limit, respectively. It is preferable that the upper limit and the lower limit are approximately the upper limit = target temperature x 1.05 and the lower limit = target temperature x 0.95. For example, when the upper limit is the target temperature + 2 ° C and the lower limit is the target temperature -2 ° C, the temperature of the temperature control stage is kept within the target temperature ± 2 ° C.

The thermometer 22b is connected to the flow rate control valve 20b of the coolant 20a provided in the pipe for discharging the coolant via the temperature controller 22a, and is connected to the temperature control stage B by the thermometer 22b. Temperature is transmitted to the temperature controller 22a, and when the temperature of the temperature control stage B is higher than the target temperature, the supply amount of the refrigerant is increased by adjusting the opening degree of the adjustment valve 20b, and the temperature control stage B Is lower than the target temperature, the supply amount of the coolant is reduced by adjusting the opening degree of the adjustment valve 20b. There are two aspects of "adjusting the opening degree" of an adjustment valve: the aspect which opens a valve | bulb largely, ie, opens a valve, and the aspect which makes opening degree small, ie, closes a valve. When the adjustment valve is provided in the discharge pipe as shown in the example shown in FIG. 2, since the refrigerant 20a is discharged by opening the adjustment valve 20b, a refrigerant having a lower temperature than the refrigerant discharged flows into the condenser 20. The cooling effect of the condenser 20 becomes high. On the contrary, by closing the adjustment valve 20b, the discharge of the coolant 20a is suppressed, and since the coolant having a lower temperature than the discharged coolant is prevented from flowing into the condenser 20, the cooling effect of the condenser 20 is lowered. . Thus, by changing the supply amount of the coolant 20a by the control valve 20b, the temperature of the reflux liquid returned from the condenser 20 to the tower is changed, and the temperature of the temperature control stage B is kept constant. .

When setting the upper limit value and the lower limit value of the temperature of the temperature control stage, the supply amount of the coolant can be adjusted by the adjustment valve so that the temperature of the temperature control stage changes from the lower limit value to the upper limit value.

The target temperature of the temperature control stage (B) is 40 to 55 ° C from the viewpoint of lowering the acrylonitrile concentration in the effluent vapor, increasing the hydrogen cyanide purity, and decreasing the hydrogen cyanide concentration in the column bottom liquid, and raising the acrylonitrile purity. Is preferable and 45-50 degreeC is more preferable. If the temperature of the temperature control stage (B) is higher than the target temperature, the acrylonitrile concentration in the effluent vapor rises, leading to loss of acrylonitrile, and the purity of the outflowing hydrogen cyanide decreases, thereby reducing the quality of the hydrogen cyanide derivative. Give adverse effects. On the other hand, when the temperature of the temperature control stage B is lower than the target temperature, the hydrogen cyanide concentration in the column bottom liquid rises and cannot be sufficiently removed from the downstream product column, which may cause the acrylonitrile product to become off-spec. have.

In this embodiment, "target temperature" is an optimal temperature derived from the acrylonitrile distillation experiment in a laboratory and / or the experiment regarding the temperature dependence of the distillation separation performance using the commercial scale distillation apparatus. For example, the relationship between each temperature distribution (hereinafter referred to as "temperature profile") of the column bottom from the column top of the distillation column, the concentration of the key material of the column top, and the concentration of the key material of the column bottom is examined. Here, a key substance is a substance used as a guide in distillation separation, and generally refers to a trace impurity, and it is not preferable in purification if a large amount of the substance is mixed. It is preferable to set a specification of the concentration of the key substance and use this as a separation specification for operation management of the distillation column.

3 is a schematic diagram showing another example of the decleaning dewatering tower 18 and equipment connected thereto. Since the flow rate control valve 20b 'connecting the supply pipe and the discharge pipe of the refrigerant 20a of the condenser is provided, it is almost the same as the example shown in FIG. When the control valve 20b 'is opened, part of the coolant 20a flows into the discharge pipe without passing through the condenser from the supply pipe, so that the supply amount of the coolant 20a is reduced by opening the control valve 20b'. The thermometer 22b is connected to the flow control valves 20b and 20b 'via the temperature controller 22a, the temperature of the temperature control stage B is transmitted to the temperature controller 22a, and the temperature control stage ( When the temperature of B) is higher than the target temperature, the regulating valve 20b is opened, and / or the regulating valve 20b 'is closed to increase the supply amount of the coolant 20a. When the temperature of the temperature control stage B is lower than the target temperature, the control valve 20b is closed, and / or the control valve 20b 'is opened to reduce the supply amount of the refrigerant 20a, thereby reducing the temperature control stage ( The temperature of B) is kept constant.

In the example shown in FIG. 3, although both of the flow control valves 20b and 20b 'operate | move by the command from the thermostat 22a, it exhibits the function of "keeping the temperature of a temperature control stage constant." As long as both of them do not need to be opened or closed by the temperature controller 22a, only the flow control valve 20b is opened and closed by the temperature controller 22a, and the flow control valve 20b 'may be manual. When the control valve 20b 'is manual, the opening degree of the control valve 20b' is made constant, and the temperature of the temperature control stage B is operated by operating the control valve 20b similarly to the example shown in FIG. Keep it constant.

In a commercial scale acrylonitrile distillation apparatus, it is preferable to use acrylonitrile as a top key material of a top top, and hydrogen cyanide and water as a key material of a top bottom. By keeping the acrylonitrile in the hydrogen cyanide gas flowing out from the column top at a low concentration, it is possible to prevent the mass reduction of the acrylonitrile obtained as a product. In addition, hydrogen cyanide is one of commercially available products, and although it is used in various hydrogen cyanide derivatives, methyl methacrylate obtained by, for example, acetone cyanhydrin (ACH) by keeping the concentration of acrylonitrile in hydrogen cyanide low. Undesirable coloring of (MMA) and the like can be prevented. Even if acrylonitrile leaks from the column top, it is possible to increase the purity of hydrogen cyanide by further separating by distillation or the like. It becomes. Therefore, in consideration of using hydrogen cyanide, it is preferable to keep the concentration of acrylonitrile in the hydrogen cyanide flowing out from the column top low. The acrylonitrile concentration in the hydrogen cyanide flowing out from the column top is preferably 1000 ppm or less, more preferably 700 ppm or less, and still more preferably 500 ppm or less.

When a lot of hydrogen cyanide mixes in the acrylonitrile extracted from a tower bottom, it becomes a cause of coloring of the acrylic fiber or ABS resin obtained using this acrylonitrile. In addition, when much water is mixed, the purity of the product acrylonitrile is inferior. The hydrogen cyanide concentration in the acrylonitrile extracted from the column bottom is preferably 100 ppm or less, more preferably 70 ppm or less, and still more preferably 50 ppm or less.

By increasing or decreasing the heating amount of the reboiler and / or the heat removal amount of the condenser, the temperature profile in the column is changed, and the change in the concentration of the key material in the column and the column bottom is measured. From the measurement result, the position of the preferable temperature control stage for forming a profile inside the column which shows good distillation separation performance, and its target temperature are determined.

Below, an example of the position of a temperature control stage and the determination method of target temperature is shown.

First, the heating amount of a reboiler and the heat removal amount of a condenser are made constant, and the density | concentration (mass%) of a key substance is investigated in each stage (concentration profile). In addition, the temperature of each stage is also measured (temperature profile). Subsequently, the heating amount of the reboiler is not changed, only the heat removal amount of the condenser is changed, and the concentration profile and the temperature profile are measured. Comparing the temperature profile in each column when the amount of heat removal of the condenser is different, if the temperatures of the feed stages and the top temperatures are the same in each case, they are located above and below the feed stage. The temperature of each stage may be different, and at this time, a difference occurs in the concentration of the key material of the top and the bottom of each case. That is, even if only the temperature at the feed stage and / or the top stage is monitored, the concentration of the key material at the top and the bottom cannot be controlled. The inventors have found that the temperature change of the stage located above the feed stage and below the top stage affects the key material concentration.

The concentration of the key material at the top and the bottom in the concentration profile is reversed, specifically, the temperature of the lowest stage (lowest stage) among the stages where the acrylonitrile concentration is lower than the hydrogen cyanide concentration, and / or the acrylic It was found that among the stages where the ronitrile concentration is higher than the hydrogen cyanide concentration, the uppermost stage (topmost) has a strong correlation with the key material concentration of the top and / or the bottom.

Since acrylonitrile is high at the bottom and hydrogen cyanide is high at the top, the concentration of protons is reversed at any stage, which is above the feed stage and located below the top stage. The temperature affects the concentration of the key material at the top and / or the bottom. Therefore, with reference to the concentration profile, it is preferable to determine, as the position of the temperature control stage, the stage at which the key substance concentration reverses. And a target temperature can be set from the temperature of the temperature control stage in a preferable temperature profile. In general, in a preferable temperature profile, the temperature of the temperature control stage shows a drastic change, and the inflection point of the temperature profile often corresponds to the temperature control stage.

That is, as a suitable aspect in the method of this embodiment,

Increase or decrease the heat removal amount of the condenser while providing a constant amount of heat from the reboiler to the distillation column,

In each heat removal amount, the temperature of each stage located above the feed stage of the said distillation column, and below the upper end of the said distillation column,

Acrylonitrile concentration and hydrogen cyanide concentration in each said stage are measured,

A stage positioned above the feed stage of the distillation column and below the top stage of the distillation column, wherein the acrylonitrile concentration is lower than the hydrogen cyanide concentration, and the lowest stage (lowest stage) and / or the acrylonitrile concentration. Sets the uppermost stage (topmost) among the stages higher than the hydrogen cyanide concentration as the temperature control stage,

And a step of determining a target temperature of the temperature control stage such that the concentration of acrylonitrile flowing out of the column top of the distillation column is minimum from the temperature of each stage in the respective heat removal amounts.

From the viewpoint of purifying acrylonitrile to satisfy the separation specification of the key material, referring to the concentration profile and the temperature profile, it is a preferred embodiment to locate the temperature control stage and its target temperature.

At the start of operation of the distillation column, an increase in the heating amount of the reboiler and an increase in the heat removal amount of the condenser are repeated in parallel. Increasing or decreasing the parameters related to the calories at a time makes it difficult to operate the distillation column stably. Therefore, from the viewpoint of determining the position of the temperature control stage and the target temperature while stably operating the distillation column, the reboiler has a constant heating amount in the range of 180 × 10 ³ to 260 × 10 ³ dl / h / t-acrylonitrile. It is preferable to control the temperature of the temperature control stage of the distillation column to be the target temperature by increasing or decreasing the amount of heat removed of the condenser while providing. By doing in this way, there exists a tendency which can pull out the favorable separation performance of a distillation column early, and can suppress the amount of off-spec products which need refining. In addition, it is possible to speed up the time of product acquisition.

In the manufacturing process of acrylonitrile, even if it is normal operation, the production amount of acrylonitrile may increase or decrease from a production plan etc. in some cases. In this case, the amount of solution fed to the decleaning dehydration tower 18 is increased or decreased. The product amount according to the mass change of the feed liquid and the amount of heat applied to the reboiler from the above-described reboiler calorie source unit (hereinafter referred to as "reboiler heating amount") are adjusted and changed. When the reboiler heating amount is increased or decreased, the amount of steam inside the distillation column changes. For example, when the reboiler heating amount is increased, acrylonitrile may boil to the top of the column, and the rate of outflow in hydrogen cyanide may increase. On the contrary, when the reboiler heating amount is reduced, the hydrogen cyanide may fall to the bottom of the column, and the ratio present in the column bottom extraction liquid may increase. These all adversely affect the purity of the product (acrylonitrile, hydrogen cyanide derivative). In order to prevent these, it is useful to adjust distillation column temperature suitably according to the increase and decrease of the reboiler heating amount.

Although it does not specifically limit as an apparatus for performing the purification method of this embodiment, For example, it can carry out using the following distillation apparatus.

Distillation column,

A thermometer provided at a temperature control stage positioned above the feed stage of the distillation column and below the top of the distillation column;

A condenser connected to the distillation column,

A pipe for supplying a coolant connected to the condenser and a pipe for discharging the coolant;

A distillation apparatus having an adjustment valve for adjusting a supply amount of a refrigerant attached to a pipe for supplying the coolant and / or a pipe for discharging the coolant,

The thermometer is connected to the control valve via a temperature controller;

The temperature of the temperature control stage is transmitted to the temperature controller by the thermometer,

When the temperature of the temperature control stage exceeds the target temperature by the temperature controller, the supply amount of the refrigerant is increased by adjusting the opening degree of the control valve, and when the temperature of the temperature control stage is less than the target temperature, A distillation apparatus wherein the supply amount of the refrigerant is reduced by adjusting the opening degree.

Example

Although an Example is shown to the following and this embodiment is demonstrated in more detail, this embodiment is not limited by the Example described below. In addition, the acrylonitrile manufacturing process in an Example is the same as that shown in FIG. In addition, the deoxidation dehydration tower in an Example is the same as that shown in FIG.

Analysis of acrylonitrile was performed by gas chromatography on the following apparatuses and conditions.

Gas chromatography used Shimadzu GC-17A as an apparatus, and the column used TC-FFAP 60 m x 0.32 film thickness 0.25 micrometer. The detector used FID and helium for the carrier gas.

Column temperature conditions were as follows.

Initial temperature: 50 ℃

Heating rate: 5 ° C / min

Final temperature 1: 180 ° C. 15 min HOLD

Heating rate: 10 ° C / min

Final temperature 2: 230 ° C. 10 min HOLD

Final temperature 3: 50 ° C 5 min HOLD

The analysis of hydrogen cyanide and water was performed by the silver nitrate titration method and the Karl Fischer method, respectively.

As the flow meter and the thermometer, the followings were used.

Flowmeter: YOKOGAWA differential pressure type flow meter (orifice type) Differential Pressure Transmitter DP harp EJX

Thermometer: OKAZAKI Manufacture Resistance Thermometer Resistance Thermometer, Temperature Trans

Example 1

Propylene, ammonia, and air were supplied to a vertical cylindrical fluidized bed reactor 1 having an internal diameter of 8 m and a length of 20 m, and the ammoxidation reaction of propylene was carried out as follows. The fluidized bed reactor 1 had a source gas dispersion tube, a dispersion plate, a heat removal tube, and a cyclone therein. The decleaning dewatering tower 18 is composed of 55 stages of sheave trays, and has a feed stage (A) at the 37th stage and a chimney tray (D) at the 24th stage and counts side cuts at the 24th stage. (23) and a line (23e) for returning the organic layer in the decanter at the 23rd stage through the side cut cooler (23b) and the decanter (23d).

The fluidized bed catalyst was packed so as to have a stop bed height of 2.7 m using a molybdenum-bismuth-iron based supported catalyst having a particle diameter of 10 to 100 µm and an average particle diameter of 55 µm. 56000 Nm 3 / h of air was supplied from the air dispersion plate, and 6200 Nm 3 / h of propylene and 6600 Nm 3 / h of ammonia were supplied from the source gas dispersion tube. The reaction temperature was controlled by a heat removal tube so as to be 440 ° C. The pressure was 0.70 kg / cm 2 G.

The reaction product gas was introduced into the quench tower 6 and brought into countercurrent contact with water to neutralize and remove the unreacted ammonia with sulfuric acid. The gas which flowed out from the quench tower 6 was introduced into the absorption tower 9 from the line 8. Absorption water was introduced from the line 14 at the top of the absorption tower 9, brought into countercurrent contact with the gas, and acrylonitrile, acetonitrile and hydrogen cyanide in the gas were absorbed into the water. The amount of water absorbed was adjusted so that the acrylonitrile concentration in the gas discharged from the absorption tower column top was 100 vol ppm. The gas which was not absorbed was taken out from the absorption tower top line 11, and was incinerated.

The absorption tower column bottom liquid was preheated at 80 degreeC, and was supplied to the recovery tower 12. Acetonitrile and most of the water were separated in recovery column 12, and acrylonitrile, hydrogen cyanide and water were distilled from column top line 17. The effluent steam was condensed to form an organic layer and a water layer using a recovery tower decanter (not shown), and the aqueous layer was recycled to the supply line 10 of the recovery tower 12, and the organic layer was supplied to the decleaning dehydration tower 18. .

The feed liquid to the deoxidation dehydration tower 18 measured the mass and temperature with the flow meter and thermometer which are not shown in the line 17 which were not shown. Measured values were 13595 kg / h and 35.0 degreeC, respectively.

Hydrogen cyanide gas was taken out from the top line 19 of the decleaning dehydration tower 18, it was sent to the condenser 20, it cooled, and it partially condensed. The refrigerant 20a used for the condenser 20 was water at 6 ° C. The condensed hydrogen cyanide liquid was refluxed to the column top, and the hydrogen cyanide gas containing few uncondensed impurities was taken out from the line 21 to the outside of the system.

The column internal liquid was taken out from 24 stages of the decleaning | dehydration tower | water dehydration tower 18, and it cooled by the side cut cooler 23b. The refrigerant 23a used for the side cut cooler 23b was water at 25 ° C. The heat removal amount Q3 of the side cut cooler was adjusted to the flow rate of the refrigerant 23a so that the liquid temperature of the decanter 23d was 30 ° C. The side stream extracted from the tower was separated into two layers of an organic layer and an aqueous layer by a decanter 23d, and the aqueous layer was extracted by a line 23f and recycled to the supply liquid of the recovery column 12. The organic layer was returned to the 23rd stage of the tower by the line 23e.

As a heat source of the reboiler 24a, the process water of 110 degreeC extracted from the recovery tower 12 lower part was used. The amount of heat Q1 provided was 200 × 10 ³ dl / h / t-acrylonitrile. Since the mass of acrylonitrile obtained as a product in the product column 25 was 11.5 t per hour, 2300 × 10 ^{3 3} The flow rate of the process water 24b passing through the reboiler 24a was adjusted to be / h.

Crude acrylonitrile was taken out from the tower bottom line 24, and it sent to the product tower 25. The column bottom extraction liquid measured the mass with the flowmeter not shown in the line 24, and the measured value was 11585 kg / h. The temperature of the column bottom extraction liquid was 86 degreeC similar to the liquid temperature of the column bottom of the decleaning | dehydration dehydration tower 18.

Here, the acrylonitrile concentration and hydrogen cyanide concentration in each stage above the feed stage were measured by making the heating amount of the reboiler 24a and the heat removal amount of the condenser 20 constant, and as a result, acrylonitrile concentration was measured. Among the stages lower than the hydrogen cyanide concentration, the lowermost stage was 51, counting from the bottom.

Next, with the heating amount of the reboiler 24a being constant, the heat removal amount of the condenser was adjusted so that the acrylonitrile concentration in the hydrogen cyanide flowing out from the column top became 300 ppm. As a result, the temperature of the stage was 48 ° C. .

Here, the heat removal amount of the condenser was adjusted so that the temperature of the stage was 48 ° C., with the temperature control stage B, the thermometer provided at the stage, the thermometer 22b, and the target temperature of the stage be 48 ° C.

The operation was continued for about 6 months when acrylonitrile production was 11.5 0.2 t / h. In the meantime, the temperature of the temperature control stage was 48 ± 0.4 degreeC.

The decleaning dehydration column can be operated stably, during which the concentration of acrylonitrile in the hydrogen cyanide flowing out from the top of the decleaning dehydration tower is 300 ± 20 ppm, and the concentration of hydrogen cyanide in the acrylonitrile extracted from the tower bottom is 40 ±. 10 ppm. In the meantime, the hydrogen cyanide concentration in the acrylonitrile product was 5 ppm or less, and a high quality acrylonitrile product could be obtained stably. In addition, the purity of hydrogen cyanide was stable, and there was no problem in the quality of the hydrogen cyanide derivative.

[Example 2]

An acrylonitrile was produced by the same equipment and method as in Example 1, except that the acrylonitrile yield was increased to 12.7 t / h due to the change in the production plan.

Reboiler calories were increased to 2540 × 10 ³ kW / h. The flow rate control valve 20b of the coolant 20a was controlled via the temperature controller 22a so that the temperature of the temperature control stage B of the decleaning dehydration tower 18 was 48 ° C. The temperatures in the tower of the decleaning dewatering tower 18 and the temperatures of the decanter 23d were almost the same as those in the first embodiment.

The operation was continued for about 3 months when acrylonitrile production was 12.7 ± 0.2 t / h. In the meantime, the temperature of the temperature control stage was 48 ± 0.4 degreeC. The decleaning dehydration tower 18 can be operated stably, during which the acrylonitrile concentration in the hydrogen cyanide flowing out from the top of the decleaning dewatering tower is 300 ± 20 ppm, and the concentration of hydrogen cyanide in the acrylonitrile extracted from the tower bottom. Was 40 ± 10 ppm. In the meantime, the hydrogen cyanide concentration in the acrylonitrile product was 5 ppm or less, and a high quality acrylonitrile product could be obtained stably. In addition, the purity of hydrogen cyanide was stable, and there was no problem in the quality of the hydrogen cyanide derivative.

[Example 3]

Acrylonitrile is manufactured on the conditions similar to Example 1, the heating amount of the reboiler 24a and the heat removal amount of the condenser 20 are made constant, and the acrylonitrile density | concentration in each stage upper than a feed stage is made constant. As a result of measuring the hydrogen cyanide concentration, among the stages where the acrylonitrile concentration was higher than the hydrogen cyanide concentration, the lowest stage was counted from the bottom and 50 stages.

Next, with the heating amount of the reboiler 24a being constant, the heat removal amount of the condenser was adjusted so that the acrylonitrile concentration in the hydrogen cyanide flowing out from the column top became 300 ppm. As a result, the temperature of the stage was 51 ° C. .

Here, the heat control amount of the condenser was adjusted so that the temperature of the stage was 51 ° C, with the temperature control stage B, the thermometer provided at the stage, the thermometer 22b, and the target temperature of the stage being 48 ° C.

The operation was continued for about 6 months when acrylonitrile production was 11.5 0.2 t / h. In the meantime, the temperature of the temperature control stage was 51 ± 0.4 degreeC. The decleaning dehydration column can be operated stably, during which the concentration of acrylonitrile in the hydrogen cyanide flowing out from the top of the decleaning dehydration tower is 300 ± 20 ppm, and the concentration of hydrogen cyanide in the acrylonitrile extracted from the tower bottom is 40 ±. 10 ppm. In the meantime, the hydrogen cyanide concentration in the acrylonitrile product was 5 ppm or less, and a high quality acrylonitrile product could be obtained stably. In addition, the purity of hydrogen cyanide was stable, and there was no problem in the quality of the hydrogen cyanide derivative.

Example 4

Propane, ammonia and air were supplied to the fluidized bed reactor 1 as in Example 1, and the ammonia oxidation reaction of propane was performed as follows.

The fluidized bed catalyst was packed so as to have a stationary bed height of 2.2 m using a molybdenum-vanadium-based supported catalyst having a particle diameter of 10 to 100 µm and an average particle diameter of 55 µm. 64500 Nm 3 / h of air was supplied from the air dispersion plate, and 4300 Nm 3 / h of propane and 4300 Nm 3 / h of ammonia were supplied from the source gas dispersion tube. The reaction temperature was controlled by a heat removal tube so as to be 440 ° C. The pressure was 0.75 kg / cm 2 G.

The reaction product gas was introduced into the quench tower 6 and brought in countercurrent contact with water. In addition, unreacted ammonia was neutralized and removed with sulfuric acid.

The gas taken out from the quench tower 6 was introduced into the absorption tower 9 from the line 8. Absorbed water was introduced from the overhead line 14 and countercurrently contacted with the gas to absorb acrylonitrile, acetonitrile and hydrogen cyanide in the gas in water. Unabsorbed gas was taken out from the absorption tower top line 11, and was incinerated. The amount of absorption water was adjusted so that the acrylonitrile concentration in the gas taken out from the top of the absorption tower became 100 vol ppm.

The absorption tower column bottom liquid was preheated and supplied to the recovery tower 12. Acetonitrile and most of the water were separated in the recovery tower and acrylonitrile, hydrogen cyanide and water were drained from the tower line (17). The effluent vapor was condensed to form an organic layer and an aqueous layer, the aqueous layer was recycled to the supply line 10 of the recovery tower, and the organic layer was supplied to the decleaning dehydration tower 18.

The feed liquid to the deoxidation dehydration tower 18 measured the mass and temperature with the flow meter and thermometer which are not shown in the line 17 which were not shown. The measured values were 6219 kg / h and 35.0 degreeC, respectively.

Hydrogen cyanide gas was taken out from the top line 19 of the decleaning dehydration tower 18, it was sent to the condenser 20, it cooled, and it partially condensed. The refrigerant 20a used for the condenser 20 was water at 6 ° C. The condensed hydrogen cyanide liquid was refluxed to the top of the column, and hydrogen cyanide gas containing less condensed impurities was taken out from the line 21 to the outside of the system.

The column internal liquid was taken out from 24 stages of the decleaning | dehydration tower | water dehydration tower 18, and it cooled by the side cut cooler 23b. The refrigerant 23a used for the side cut cooler 23b was water at 25 ° C. The heat removal amount Q3 of the side cut cooler was adjusted to the flow rate of the refrigerant 23a so that the liquid temperature of the decanter 23d was 30 ° C. The side stream extracted from the tower was separated into two layers of an organic layer and an aqueous layer by a decanter 23d, and the aqueous layer was extracted by a line 23f and recycled to the supply liquid of the recovery column 12. The organic layer was returned to the 23rd stage of the tower by the line 23e.

As a heat source of the reboiler 24a, the process water of 110 degreeC extracted from the recovery tower 12 lower part was used. The amount of heat Q1 provided was 250 × 10 ³ dl / h / t-acrylonitrile, and the mass of acrylonitrile obtained as a product in the product column 25 was 5.22 t per hour, so 1305 × 10 ³ The flow volume of the process water 24b which passed the reboiler 24a was adjusted so that it might be d / h.

Crude acrylonitrile was taken out from the tower bottom line 24, and it supplied to the product tower 25. The tower bottom extraction liquid measured the mass with the flowmeter not shown in the line 24, and the measured value was 5312 kg / h. The temperature of the column bottom extraction liquid was 86 degreeC similar to the liquid temperature of the column bottom of the decleaning | dehydration dehydration tower 18.

Here, the acrylonitrile concentration and hydrogen cyanide concentration in each stage above the feed stage were measured by making the heating amount of the reboiler 24a and the heat removal amount of the condenser 20 constant, and as a result, acrylonitrile concentration was measured. Among the stages lower than the hydrogen cyanide concentration, the lowermost stage was 51, counting from the bottom.

Next, with the heating amount of the reboiler 24a being constant, the heat removal amount of the condenser was adjusted so that the acrylonitrile concentration in the hydrogen cyanide flowing out from the column top became 300 ppm. As a result, the temperature of the stage was 48 ° C. .

Here, the heat removal amount of the condenser was adjusted so that the temperature of the stage was 48 ° C., with the temperature control stage B, the thermometer provided at the stage, the thermometer 22b, and the target temperature of the stage be 48 ° C.

The operation was continued for about 4 months when acrylonitrile production was 5.22 ± 0.17 t / h. In the meantime, the temperature of the temperature control stage B was 48 +/- 0.4 degreeC. The decleaning dehydration tower can be operated stably, during which the concentration of acrylonitrile in the hydrogen cyanide flowing out from the top of the decleaning dehydration tower is 300 ± 10 ppm, and the concentration of hydrogen cyanide in the acrylonitrile extracted from the tower bottom is 40 ±. 10 ppm or less. In the meantime, the hydrogen cyanide concentration in the acrylonitrile product was 5 ppm or less, and a high quality acrylonitrile product could be obtained stably. In addition, the purity of hydrogen cyanide was stable, and there was no problem in the quality of the hydrogen cyanide derivative.

[Example 5]

Acrylonitrile is manufactured on the conditions similar to Example 4, the heating amount of the reboiler 24a and the heat removal amount of the condenser 20 are made constant, and the acrylonitrile density | concentration in each stage upper than a feed stage is made constant. As a result of measuring the hydrogen cyanide concentration, among the stages where the acrylonitrile concentration was higher than the hydrogen cyanide concentration, the lowest stage was counted from the bottom and 50 stages.

Next, with the heating amount of the reboiler 24a being constant, the heat removal amount of the condenser was adjusted so that the acrylonitrile concentration in the hydrogen cyanide flowing out from the column top became 300 ppm. As a result, the temperature of the stage was 51 ° C. .

Here, the heat control amount of the condenser was adjusted so that the temperature of the stage was 51 ° C, with the temperature control stage B, the thermometer provided at the stage, the thermometer 22b, and the target temperature of the stage being 48 ° C.

The operation was continued for about 4 months when acrylonitrile production was 5.22 ± 0.17 t / h. In the meantime, the temperature of the temperature control stage B was 51 +/- 0.4 degreeC. The decleaning dehydration column can be operated stably, during which the concentration of acrylonitrile in the hydrogen cyanide flowing out from the top of the decleaning dehydration tower is 300 ± 20 ppm, and the concentration of hydrogen cyanide in the acrylonitrile extracted from the tower bottom is 40 ±. 10 ppm. In the meantime, the hydrogen cyanide concentration in the acrylonitrile product was 5 ppm or less, and a high quality acrylonitrile product could be obtained stably. In addition, the purity of hydrogen cyanide was stable, and there was no problem in the quality of the hydrogen cyanide derivative.

Comparative Example 1

Ammonia oxidation reaction of propylene was carried out by the same equipment and method as in Example 1, except that the uppermost stage of the desorption dehydration tower was operated as a temperature control stage, and the stage temperature was 30 ° C. Was prepared. In the meantime, although the temperature of the temperature control stage did not change to 30 degreeC, the acrylonitrile density | concentration in hydrogen cyanide which flowed out from the tower top of a deoxidation dehydration tower rose to 1000 ppm 1 month after the start of manufacture. Determining that the amount of heat removal Q2 of the condenser was insufficient, the flow rate of the refrigerant passing through the condenser was increased to increase Q2. The temperature at the top of the decleaning dehydration column did not change to 30 ° C., but the hydrogen cyanide flowed out of the tower. The acrylonitrile concentration in it decreased to 300 ppm.

Two months after the start of production, the concentration of hydrogen cyanide in acrylonitrile obtained as a product was increased to 20 ppm to become an off spec product. At this time, the hydrogen cyanide concentration in the bottom liquid of the decleaning dehydration tower was 120 wt ppm. It was judged that the amount of heat removal Q2 of the condenser was excessive, and the flow rate of the refrigerant passing through the condenser was lowered to decrease Q2. As a result, the hydrogen cyanide concentration in acrylonitrile obtained as a product decreased to 5 ppm, resulting in a specification product. Moreover, the ratio of the acrylonitrile which flowed out in the hydrogen cyanide flowing out from a column top rose to 600 ppm, and the quality of the hydrogen cyanide derivative was inferior. In the meantime, the temperature of the uppermost stage of the deoxidation dehydration tower did not change to 30 degreeC.

Comparative Example 2

Ammonia oxidation of propane was carried out using the same equipment and method as in Example 4, except that the uppermost stage of the demineralization dehydration tower was operated as a temperature control stage, and the stage temperature was 30 ° C. Nitrile was prepared. In the meantime, although the temperature of the temperature control stage did not change to 30 degreeC, after 2 weeks from the start of manufacture, the acrylonitrile concentration in the hydrogen cyanide which flowed out from the tower top of a deoxidation dehydration tower rose to 1000 ppm. Determining that the amount of heat removal Q2 of the condenser was insufficient, the flow rate of the refrigerant passing through the condenser was increased to increase Q2. The temperature at the top of the decleaning dehydration column did not change to 30 ° C., but the hydrogen cyanide flowed out of the tower. The acrylonitrile concentration in it decreased to 300 ppm.

After 4 weeks from the start of production, the concentration of hydrogen cyanide in acrylonitrile obtained as a product was increased to 20 ppm to become an off spec product. At this time, the hydrogen cyanide concentration in the bottom liquid of the decleaning dehydration tower was 120 wt ppm. It was judged that the amount of heat removal Q2 of the condenser was excessive, and the flow rate of the refrigerant passing through the condenser was lowered to decrease Q2. As a result, the hydrogen cyanide concentration in acrylonitrile obtained as a product decreased to 5 ppm, resulting in a specification product. Moreover, the ratio of the acrylonitrile which flowed out in the hydrogen cyanide flowing out from a column top rose to 600 ppm, and the quality of the hydrogen cyanide derivative was inferior. In the meantime, the temperature of the uppermost stage of the deoxidation dehydration tower did not change to 30 degreeC.

This application is based on the JP Patent application (patent application 2010-290914) of the Japan Patent Office on December 27, 2010, The content is taken in here as a reference.

The method of the present invention has industrial applicability in the production process of acrylonitrile in which propylene and / or propane, ammonia and oxygen are reacted in the presence of a catalyst.

1 fluidized bed reactor
2 supply lines for propylene and / or propane
3 supply line of ammonia
4 supply pipe of air (oxygen)
6 quench tower
5, 7, 8 lines
9 absorption tower
10, 11 lines
12 Recovery Tower
13, 14, 15, 16, 17 lines
18 Desalination Dewatering Tower
19 lines
20 Desalination Dewatering Tower Condenser
20a Refrigerant Feed to De-Cleaning Dewatering Tower Condenser
Flow Control Valve of Refrigerant Supply to 20b Desalination Dewatering Tower Condenser
Flow regulating valve connecting supply and discharge pipes of refrigerant of 20b 'condenser
21, 22 lines
22a thermostat
22b temperature detector (thermometer)
23, 23c, 23e, 23f line
23a Refrigerant Supply to De-Cleaning Dewatering Tower Side Cut Cooler
23b Desalination Dewatering Tower Side Cut Cooler
23d Desalination Dewatering Tower Decanter
24, 24c line
24a De-Cleaning Dewatering Tower Reboiler
Fruits Feeding 24b De-Clearing Dewatering Tower Reboiler
25 Product Tower
26, 27, 28, 29 lines
30 Product Tower Condenser
31 lines
A feed stage
B temperature control stage
C top
D chimney tray

Claims (6)

A method for purifying acrylonitrile comprising distilling a solution containing acrylonitrile, hydrogen cyanide and water by using a distillation column and a distillation apparatus having a top gas condenser connected to the distillation column.
And maintaining a constant temperature of a temperature control stage positioned above the feed stage of the distillation column and below the top of the distillation column. The method of claim 1,
An adjustment valve is provided in the tube for supplying the refrigerant to the condenser and / or the tube for discharging the refrigerant from the condenser, and the thermometer is provided in the temperature control stage.
Setting a target temperature of the temperature control stage,
When the temperature of the temperature control stage is higher than the target temperature, the opening of the control valve is adjusted to increase the supply amount of the refrigerant,
If the temperature of the temperature control stage is lower than the target temperature, the temperature of the temperature control stage is kept constant by adjusting the opening degree of the control valve to reduce the supply amount of the refrigerant. 3. The method according to claim 2, wherein the upper limit value and the lower limit value of the temperature of the temperature control stage are set, and the supply amount of the refrigerant is adjusted by the regulating valve so that the temperature of the temperature control stage is changed above the lower limit and below the upper limit. Way. 4. The method according to any one of claims 1 to 3,
Increase or decrease the heat removal amount of the condenser while providing a constant amount of heat from the reboiler to the distillation column,
In each heat removal amount, the temperature of each stage located above the feed stage of the said distillation column, and below the upper end of the said distillation column,
Acrylonitrile concentration and hydrogen cyanide concentration in each said stage are measured,
A stage positioned above the feed stage of the distillation column and below the top stage of the distillation column, wherein the lowest stage (lowest stage) among the stages where the acrylonitrile concentration is lower than the hydrogen cyanide concentration is set as a temperature control stage,
Acryl furnace comprising the step of determining a target temperature of the temperature control stage such that the concentration of acrylonitrile flowing out of the column top of the distillation column is minimized from the temperature of each stage in the respective heat removal amounts. Method for Purifying Nitrile. 4. The method according to any one of claims 1 to 3,
Increase or decrease the heat removal amount of the condenser while providing a constant amount of heat from the reboiler to the distillation column,
In each heat removal amount, the temperature of each stage located above the feed stage of the said distillation column, and below the upper end of the said distillation column,
Acrylonitrile concentration and hydrogen cyanide concentration in each said stage are measured,
A stage positioned above the feed stage of the distillation column and below the top stage of the distillation column, among the stages where the acrylonitrile concentration is higher than the hydrogen cyanide concentration, the uppermost stage (top) is set as a temperature control stage,
A method for purifying acrylonitrile comprising the step of determining a target temperature of the temperature control stage such that the concentration of acrylonitrile flowing out of the column top of the distillation column is minimum from the temperature of each stage in the respective heat removal amounts. . Distillation column,
A thermometer provided at a temperature control stage positioned above the feed stage of the distillation column and below the top of the distillation column;
A condenser connected to the distillation column,
A pipe for supplying a coolant connected to the condenser and a pipe for discharging the coolant;
Control valve for adjusting the supply amount of the refrigerant attached to the pipe for supplying the refrigerant and / or the pipe for discharging the refrigerant
A distillation apparatus having
The thermometer is connected to the control valve via a temperature controller;
The temperature of the temperature control stage is transmitted to the temperature controller by the thermometer,
When the temperature of the temperature control stage is higher than a target temperature by the temperature controller, the opening of the control valve is adjusted to increase the supply amount of the refrigerant.
The distillation apparatus of which the supply amount of refrigerant | coolant is reduced by adjusting the opening degree of the said control valve, when the temperature of the said temperature control stage is lower than target temperature.

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