JP5175235B2 - Method and apparatus for producing dinitrotoluene - Google Patents

Description

  The present invention relates to a production method and production apparatus for dinitrotoluene, and more particularly to a method for producing dinitrotoluene by reacting toluene with a mixed acid of nitric acid and sulfuric acid, and a production apparatus used for the method.

  Dinitrotoluene is industrially produced by a two-stage reaction of mononitrating and dinitrating toluene using a mixed acid of nitric acid and sulfuric acid. In the first stage, it is discharged in the second stage. The secondary waste acid is used together with fresh nitric acid to mononitrate toluene to produce mononitrotoluene. In the second stage, a concentrated solution obtained by concentrating the primary waste acid discharged in the first stage is added to a new solution. It is produced by dinitrating mononitrotoluene with nitric acid (for example, see Patent Document 1).

JP 60-204748 A

  However, in the production method described above, the secondary waste acid discharged in the second stage is separated from the crude dinitrotoluene and used as it is for mononitration of toluene in the first stage. Therefore, the water contained in the secondary waste acid used in the first stage dilutes the new nitric acid supplied in the first stage, and the first stage of the secondary waste acid discharged in the second stage. As the reflux to is repeated, the nitric acid concentration decreases and the reaction yield of mononitrotoluene due to the mononitration of toluene in the first stage decreases.

On the other hand, if only a part of the secondary waste acid discharged in the second stage is circulated to the first stage, such a decrease in the reaction yield of mononitrotoluene in the first stage can be prevented. However, in such a case, the reuse rate of the secondary waste acid discharged in the second stage is lowered.
As described above, when the secondary waste acid discharged in the second stage is recycled to the first stage and reused, the reaction yield of mononitrotoluene in the first stage is lowered or discharged in the second stage. There is a problem that the reuse rate of the secondary waste acid is reduced.

  An object of the present invention is to provide a production method of dinitrotoluene and a production apparatus used in the method for efficiently producing dinitrotoluene by efficiently reusing secondary waste acid. is there.

  In order to achieve the above object, the method for producing dinitrotoluene of the present invention comprises a first step of producing mononitrotoluene by reacting toluene with a mixed acid of nitric acid and sulfuric acid, and mononitrotoluene obtained in the first step, Obtained in the second step of producing dinitrotoluene by reacting with a mixed acid of nitric acid and sulfuric acid, the first mixing step of mixing mononitrotoluene with the secondary waste acid discharged from the second step, and the first mixing step. Separation process for separating the tertiary waste acid from the first mixed liquid in which mononitrotoluene is mixed with the secondary waste acid, the concentration process for concentrating the tertiary waste acid separated in the separation process, and the concentration process. It is characterized by comprising a first recirculation step for recirculating the concentrated solution to the second step.

In this method, since the secondary waste acid discharged from the second step is concentrated and circulated to the second step, the secondary waste acid can be efficiently reused, and the secondary waste acid can be reused. The rate can be significantly improved.
Moreover, in this method, since mononitrotoluene is mixed with the secondary waste acid discharged | emitted from the 2nd process, nitric acid in secondary waste acid is reduced by reaction with the mixed mononitrotoluene and secondary waste acid. be able to. Therefore, the sulfuric acid concentration in the secondary waste acid can be increased. In addition, mononitrotoluene has good compatibility with dinitrotoluene, and tertiary waste acid can be efficiently separated from the first mixed solution in the next separation step.

Furthermore, since the tertiary waste acid is concentrated after separation from the first mixed liquid, crystallization due to the concentration of the first mixed liquid can be prevented, and the tertiary waste acid is concentrated to the optimum concentration. Can do.
Moreover, in the manufacturing method of the dinitrotoluene of this invention, it is suitable that the mononitrotoluene mixed with the secondary waste acid discharged | emitted from the said 2nd process is the mononitrotoluene obtained in the said 1st process.

In this method, since the mononitrotoluene obtained in the first step is mixed with the secondary waste acid discharged from the second step, the production efficiency can be improved.
Moreover, in the manufacturing method of the dinitrotoluene of this invention, it is suitable to provide the 2nd recirculation | circulation process which recirculate | circulates the separation liquid from which the tertiary waste acid was isolate | separated to the said 2nd process in the said separation process.
In this method, since the separated liquid is circulated to the second step without discarding, mononitrotoluene can be used efficiently.

Further, in the method for producing dinitrotoluene of the present invention, the secondary waste acid discharged from the second step is partially refluxed to the first step before the mononitrotoluene is mixed in the first mixing step. It is preferable to provide a three-circulation process.
In this method, since the secondary waste acid discharged from the second step and mixed with mononitrotoluene is partially circulated to the first step, the concentrations of sulfuric acid and nitric acid in the first step are partially circulated. Further, it can be adjusted to an optimum concentration by secondary waste acid. Moreover, this can also adjust the quantity of the secondary waste acid which should be concentrated in a concentration process, and can achieve efficient concentration.

In the method for producing dinitrotoluene of the present invention, it is preferable to concentrate the tertiary waste acid so that the sulfuric acid concentration becomes 80% by weight or more in the concentration step.
In this method, since the concentration of sulfuric acid in the concentrated solution is 80% by weight or more, the yield of dinitrotoluene can be improved in the second step.
In the method for producing dinitrotoluene of the present invention, the first mixing step is performed in a tubular reactor including a tube and a line mixer connected to the tube, and the flow rate in the line mixer is 20 cm / s. The residence time in the tubular reactor is preferably 60 seconds or longer.

  In this method, the first mixing step is carried out in a tubular reactor, and the flow rate in the line mixer is set to 20 cm / s or more and the residence time is set to 60 seconds or more. The nitric acid in the acid can be reacted efficiently. Moreover, the residence time required for reaction can be reduced by setting the flow rate in a line mixer to said range.

In the method for producing dinitrotoluene of the present invention, the primary waste acid discharged in the first step is partly mixed with the tertiary waste acid before being separated in the separation step and concentrated in the concentration step. It is preferable to provide a second mixing step.
In this method, the primary waste acid discharged in the first step can be effectively reused without being discarded as it is. Moreover, since the obtained waste sulfuric acid is partly mixed with the tertiary waste acid separated in the separation step, the reuse amount of the waste sulfuric acid to be reused can be adjusted. Further, the mixing ratio of sulfuric acid and nitric acid in the concentrated liquid that is subsequently concentrated and then refluxed and reused can be adjusted to an optimum value. Furthermore, the amount of new mixed acid added in the second step can be reduced.

Further, in the method for producing dinitrotoluene of the present invention, the waste sulfuric acid obtained by denitrating the primary waste acid is separated into the tertiary waste acid before being separated in the separation step and concentrated in the concentration step. It is preferable to partially mix.
In this method, by denitrating the primary waste acid, the load of waste nitric acid treatment in the concentration step can be reduced.

  The apparatus for producing dinitrotoluene according to the present invention includes a first reaction tank for producing mononitrotoluene by reacting toluene with a mixed acid of nitric acid and sulfuric acid, and mononitrotoluene obtained in the first reaction tank, A second reaction tank for producing dinitrotoluene by reacting with the mixed acid, a first mixing means for mixing mononitrotoluene with the secondary waste acid discharged from the second reaction tank, and the first mixing means Separation means for separating the tertiary waste acid from the first mixed liquid obtained by mixing mononitrotoluene with the secondary waste acid, a concentration means for concentrating the tertiary waste acid separated in the separation means, And the 1st recirculation means for recirculating the concentrate obtained in the said concentration means to the said 2nd reaction tank is characterized by the above-mentioned.

In this apparatus, the secondary waste acid discharged from the second reaction tank is concentrated by the concentration means and circulated to the second reaction tank by the first reflux means, so that the secondary waste acid is efficiently reused. It is possible to remarkably improve the reuse rate of the secondary waste acid.
Moreover, in this apparatus, since mononitrotoluene is mixed with the secondary waste acid discharged | emitted from the 2nd reaction tank by the 1st mixing means, secondary waste is produced | generated by reaction with the mixed mononitrotoluene and secondary waste acid. Nitric acid in the acid can be reduced. Therefore, the sulfuric acid concentration in the secondary waste acid can be increased. In addition, mononitrotoluene has good compatibility with dinitrotoluene, and the tertiary waste acid can be efficiently separated from the first mixed solution by the separation means.

Further, since the tertiary waste acid is concentrated by the concentrating means after being separated from the first mixed solution by the separating means, crystallization of dinitrotoluene in the apparatus due to the concentration of the first mixed liquid is prevented. The tertiary waste acid can be stably concentrated to the optimum concentration.
In the dinitrotoluene production apparatus of the present invention, it is preferable that the first mixing unit mixes the mononitrotoluene obtained in the first reaction tank.

In this apparatus, since the mononitrotoluene obtained in the first reaction tank is mixed with the secondary waste acid discharged from the second reaction tank by the first mixing means, the production efficiency can be improved.
In the apparatus for producing dinitrotoluene of the present invention, it is preferable that the separation means further comprises a second reflux means for circulating the separated liquid from which the tertiary waste acid has been separated into the second reaction tank.

In this apparatus, since the separated liquid is circulated to the second reaction tank by the second circulator without discarding the separated liquid, mononitrotoluene can be used efficiently.
In the dinitrotoluene production apparatus of the present invention, the secondary waste acid discharged from the second reaction tank is partially recirculated to the first reaction tank before the mononitrotoluene is mixed by the first mixing means. It is preferable to provide a third reflux means for the purpose.

  In this apparatus, the secondary waste acid that has been discharged from the second reaction tank and has not been mixed with mononitrotoluene by the first mixing means is partially circulated to the first reaction tank by the third refluxing means. The concentration of sulfuric acid and nitric acid in the tank can be adjusted to the optimum concentration by the secondary waste acid partially refluxed. This also allows the amount of secondary waste acid to be concentrated in the concentration means to be adjusted, and efficient concentration can be achieved.

In the dinitrotoluene production apparatus of the present invention, the denitration means for denitrating the primary waste acid discharged from the first reaction tank, and the waste sulfuric acid obtained in the denitration means are used. And a second mixing means for partially mixing the tertiary waste acid before being separated by the separating means and concentrated by the concentrating means.
In this apparatus, the primary waste acid discharged | emitted by the 1st reaction tank can be reused effectively, without discarding as it is. Also, the waste sulfuric acid obtained by denitrating the primary waste acid is partially mixed with the tertiary waste acid separated by the separation means, so the amount of reused waste sulfuric acid can be adjusted. Can do. In addition, the mixing ratio of sulfuric acid and nitric acid in the concentrated liquid that is concentrated and then recirculated to the second reaction tank and reused can be adjusted to an optimum value. Furthermore, the amount of new mixed acid added in the second reaction tank can be reduced.

  According to the production method and production apparatus of dinitrotoluene of the present invention, dinitrotoluene can be produced efficiently by efficiently reusing the secondary waste acid.

It is a schematic block diagram which shows one Embodiment of the dinitrotoluene manufacturing apparatus of this invention.

FIG. 1 is a schematic configuration diagram showing an embodiment of a dinitrotoluene production apparatus of the present invention. In the following description, “upstream side” and “downstream side” are based on the liquid flow direction in each apparatus.
In FIG. 1, the dinitrotoluene production apparatus 1 includes a mononitration reaction unit 2, a dinitration reaction unit 3, and a waste acid treatment unit 4.

The mononitration reaction unit 2 includes a first reaction tank 5 and a first separator 6.
The first reaction tank 5 is not particularly limited as long as it is a reaction tank for reacting toluene with a mixed acid of nitric acid and sulfuric acid (hereinafter abbreviated as mixed acid). For example, a reactor equipped with a stirring blade is used. Etc. are used. The first reaction tank 5 may be either a continuous reactor or a batch reactor, but preferably a continuous reactor is used, more preferably a multistage continuous reactor.

A toluene supply pipe 7 for supplying toluene, which is a starting material of dinitrotoluene, and a mixed acid supply pipe 8 for supplying mixed acid are connected to the first reaction tank 5.
The toluene supplied from the toluene supply pipe 7 is not particularly limited as long as it is toluene used for the production of dinitrotoluene, and toluene available as an industrial product is used. Moreover, toluene is supplied to the 1st reaction tank 5 with the supply amount of 1000-10000 kg / h from the toluene supply pipe | tube 7, for example.

Further, the mixed acid supplied from the mixed acid supply pipe 8 is not particularly limited as long as it is a mixed acid used in the production of dinitrotoluene, and contains nitric acid, sulfuric acid and water. For example, nitric acid is 50 to 95% by weight, sulfuric acid Is contained in a proportion of 5 to 50% by weight. Further, the mixed acid is supplied from the mixed acid supply pipe 8 to the first reaction tank 5 at a supply rate of 1000 to 10,000 kg / h, for example.
In the first reaction tank 5, for example, toluene is mononitrated with a mixed acid at a reaction temperature of 30 to 90 ° C. (first step). In this mononitration reaction of toluene, mononitrotoluene is produced as an organic phase component, and primary waste acid is produced as an aqueous phase component. In addition, since the secondary waste acid is circulated to the first reaction tank 5 from a third reflux line 16 described later, specifically, the organic phase component contains, for example, mononitrotoluene and dinitrotoluene, 60% to 95% by weight of mononitrotoluene and 5% to 40% by weight of dinitrotoluene, for example.

The primary waste acid contains nitric acid, sulfuric acid and water, and toluene, mononitrotoluene and dinitrotoluene. For example, nitric acid is 0.1 to 2% by weight, sulfuric acid is 60 to 75% by weight, and toluene is 1% by weight. Hereinafter, mononitrotoluene is contained at a ratio of 3% by weight or less and dinitrotoluene is contained at a ratio of 3% by weight or less.
The first separator 6 is connected to the first reaction tank 5 through a pipe 30.

Although the 1st separator 6 will not be restrict | limited especially if it is a separator for isolate | separating the mononitrotoluene and primary waste acid which were obtained in the 1st process, For example, a non-powered type extraction apparatus, a stirring type extraction apparatus An extraction device such as a pulsation / vibration extraction device or a centrifugal extraction device is used.
Then, when the reaction liquid is supplied from the first reaction tank 5 to the first separator 6 via the pipe 30, the mononitrotoluene obtained in the first step and the primary waste in the first separator 6. Acid is separated.

The first separator 6 is connected to the upstream end of the mononitrotoluene supply pipe 9 and the upstream end of the primary waste acid discharge pipe 10.
The dinitration reaction unit 3 includes a second reaction tank 11 and a second separator 12.
The second reaction tank 11 is not particularly limited as long as it is a reaction tank for reacting mononitrotoluene with a mixed acid. For example, a reactor equipped with a stirring blade is used. The second reaction tank 11 may be either a continuous reactor or a batch reactor, but preferably a continuous reactor is used, more preferably a multistage continuous reactor.

The second reaction tank 11 is connected to the downstream end of the mononitrotoluene supply pipe 9 and a mixed acid supply pipe 13 for supplying mixed acid.
Mononitrotoluene obtained in the first step is supplied to the second reaction tank 11 through the mononitrotoluene supply pipe 9. Mononitrotoluene is supplied at a supply amount of 1500 to 15000 kg / h, for example.

The mixed acid supplied from the mixed acid supply pipe 13 contains nitric acid, sulfuric acid, and water. For example, nitric acid is contained in a proportion of 50 to 95% by weight and sulfuric acid is contained in a proportion of 5 to 50% by weight. Further, the mixed acid is supplied from the mixed acid supply pipe 13 to the second reaction tank 11 at a supply rate of 1000 to 10,000 kg / h, for example.
In the second reaction tank 11, for example, mononitrotoluene is reacted with a mixed acid and dinitrated at a reaction temperature of 40 to 90 ° C. (second step). In the dinitration reaction of mononitrotoluene, dinitrotoluene is produced as an organic phase component, and secondary waste acid is produced as an aqueous phase component.

The secondary waste acid contains nitric acid, sulfuric acid and water, and toluene, mononitrotoluene and dinitrotoluene. For example, nitric acid is 0.5 to 5% by weight, sulfuric acid is 65 to 80% by weight, and toluene is 0.00. 5 wt% or less, mononitrotoluene 0.5 wt% or less, and dinitrotoluene 0.5 to 5 wt%.
A second separator 12 is connected to the second reaction tank 11 through a pipe 30.

The second separator 12 is not particularly limited as long as it is a separator for separating dinitrotoluene and secondary waste acid obtained in the second step. For example, the non-powered extraction device, the stirring extraction device An extraction device such as a pulsation / vibration extraction device or a centrifugal extraction device is used.
Then, when the reaction liquid is supplied from the second reaction tank 11 to the second separator 12 via the pipe 30, the dinitrotoluene obtained in the second step and the secondary waste are obtained in the second separator 12. Acid is separated.

Further, the upstream end of the dinitrotoluene discharge pipe 14 and the upstream end of the secondary waste acid discharge pipe 15 are connected to the second separator 12.
The separated dinitrotoluene is taken out from the dinitrotoluene discharge pipe 14 and used as a raw material for producing tolylene diisocyanate which is a raw material of polyurethane.
The waste acid treatment unit 4 includes a mixer 17 as a first mixing means, a third separator 18 as a separation means, a denitration treatment tank 19 as a denitration treatment means, and a second relay as a second mixing means. A tank 20 and a concentrator 21 as a concentration means are provided.

The mixer 17 is not particularly limited as long as it is a mixer for mixing mononitrotoluene with the secondary waste acid discharged from the second step. For example, a tubular reactor, a stirring tank, or the like is used. The mixer 17 may be either a continuous type or a batch type, but is preferably a continuous type. As the mixer 17, a continuous tubular reactor is preferably used.
The tubular reactor includes, for example, a tube (flexible tube) 41 and a plurality of line mixers (static mixers) 42 connected to the tube 41. The line mixer 42 is arranged with an interval between the tubes 41 in the liquid flow direction.

The interval between the line mixers 42 in the liquid flow direction is set so that the liquid flowing through the tubular reactor is stirred by the line mixer 42 every 150 seconds or less, for example.
By using a tubular reactor as the mixer 17, nitric acid in the secondary waste acid and mononitrotoluene can be reacted efficiently.
The mixer 17 is connected to the downstream end of the secondary waste acid discharge pipe 15.

Further, an upstream end portion of a third reflux line 16 as a third reflux means is connected to the secondary waste acid discharge pipe 15 in the middle. The downstream end of the third reflux line 16 is connected to the first reaction tank 5. Thereby, a part of the secondary waste acid discharged from the second separator 12 is circulated to the first reaction tank 5 via the third circulatory line 16 (third circulatory step).
The secondary waste acid recirculated to the first reaction tank 5 via the third recirculation line 16 is recirculated at a recirculation flow rate of 1000 to 15000 kg / h, for example.

Further, the secondary waste acid recirculated to the first reaction tank 5 through the third recirculation line 16 has a recirculation ratio (the secondary waste acid recirculated to the first reaction tank 5 through the third recirculation line 16). The circulation flow rate / the supply amount of the mixed acid supplied from the mixed acid supply pipe 8) is circulated at 1/1 to 5/1, for example.
In the middle of the secondary waste acid discharge pipe 15, the downstream end of the mononitrotoluene branch supply pipe 26 branched from the mononitrotoluene supply pipe 9 is connected downstream of the connection position of the third reflux line 16. Yes. As a result, the mononitrotoluene discharged from the first separator 6 joins and is supplied to the mixer 17 together with the secondary waste acid discharged from the second separator 12.

The secondary waste acid is supplied to the mixer 17 through the secondary waste acid discharge pipe 15 at a supply amount of 1000 to 20000 kg / h, for example.
Mononitrotoluene is fed from the mononitrotoluene branch supply pipe 26 to the mixer 17 via the secondary waste acid discharge pipe 15, for example, 2 to 30 moles, preferably 3 to 3 moles of nitric acid in the secondary waste acid. It is supplied at a ratio of 20 times mole.

  In the mixer 17, for example, when using a tubular reactor, the flow rate in the line mixer 42 is 20 cm / s or more, preferably 25 cm / s or more, and the residence time in the tubular reactor is, for example, 60 seconds or more. Preferably, the secondary spent acid and mononitrotoluene are mixed in 100 to 1500 seconds, more preferably 100 to 1000 seconds, particularly preferably 150 to 600 seconds, and the nitric acid in the secondary spent acid is mixed. Reaction with mononitrotoluene (first mixing step). Thereby, the 1st liquid mixture with which mononitrotoluene was mixed with the secondary waste acid is obtained. In addition, this makes it possible to efficiently react nitric acid in the secondary waste acid with mononitrotoluene. Moreover, the residence time required for reaction can be reduced by setting the flow velocity in the line mixer 42 to 20 cm / s or more.

The mixer 17 is connected to a third separator 18 as a separating means via a pipe 30.
The third separator 18 is not particularly limited as long as it is a separator for separating the first mixed liquid obtained in the mixer 17 into the quaternary waste acid and the separated liquid. For example, the non-powered extraction device An extraction device such as a stirring extraction device, a pulsating / vibration extraction device, or a centrifugal extraction device is used.

Then, when the first mixed solution is supplied from the mixer 17 to the third separator 18 via the pipe 30, the first mixed solution is separated into the quaternary waste acid and the separated solution (separation step). .
The quaternary waste acid (tertiary waste acid separated from the first mixed solution) contains, for example, nitric acid, sulfuric acid and water, and toluene, mononitrotoluene and dinitrotoluene. % Or less, sulfuric acid 65 to 80% by weight, toluene 0.2% or less, mononitrotoluene 0.2 to 3% by weight, dinitrotoluene 0.1 to 2% by weight.

The separation liquid contains, for example, 30 to 80% by weight of mononitrotoluene and 20 to 70% by weight of dinitrotoluene.
The third separator 18 is connected to an upstream end of a separation liquid recirculation line 22 as a second recirculation means and an upstream end of a quaternary waste acid discharge pipe 23.
The downstream end of the separation liquid recirculation line 22 is connected to the second reaction tank 11. As a result, the separation liquid discharged from the third separator 18 is circulated to the second reaction tank 11 via the separation liquid recirculation line 22 (second recirculation step). The separation liquid is circulated at a circulation flow rate of 100 to 5000 kg / h, for example.

Further, the separation liquid recirculated to the second reaction tank 11 via the separation liquid recirculation line 22 has a recirculation ratio (the recirculation flow rate of the separation liquid recirculated to the second reaction tank 11 via the separation liquid recirculation line 22 / mono. The supply amount of mononitrotoluene supplied to the second reaction tank 11 via the nitrotoluene supply pipe 9 is circulated at, for example, 1/10 to 5/10.
The denitration treatment tank 19 is not particularly limited as long as it is a treatment tank for denitrating the primary waste acid discharged in the first step to obtain waste sulfuric acid. For example, a distillation tower or the like is used.

The downstream end of the primary waste acid discharge pipe 10 is connected to the denitration treatment tank 19.
And when the primary waste acid discharged | emitted by the 1st process is supplied to the denitration processing tank 19 via the primary waste acid discharge pipe 10, in this denitration processing tank 19, primary waste acid will be It is denitrated to obtain waste sulfuric acid. The denitration treatment is performed, for example, by steam distillation.
The upstream end portion of the waste sulfuric acid supply pipe 27 is connected to the denitration treatment tank 19.

The waste sulfuric acid contains, for example, nitric acid, sulfuric acid and water, and contains, for example, sulfuric acid in a proportion of 60 to 75% by weight and nitric acid in an amount of 0.1% by weight or less.
The relay tank 20 is a mixing tank in which a part of the waste sulfuric acid obtained in the denitration treatment tank 19 is mixed with the quaternary waste acid separated in the separation step and temporarily stored.
The downstream end of the quaternary waste acid discharge pipe 23 and the downstream end of the waste sulfuric acid supply pipe 27 are connected to the relay tank 20. Thus, the quaternary waste acid separated by the third separator 18 is supplied to the relay tank 20 via the quaternary waste acid discharge pipe 23, and the waste sulfuric acid discharged from the denitration treatment tank 19 is supplied. Is supplied via a waste sulfuric acid supply pipe 27.

Further, the downstream end of the primary waste acid supply pipe 31 is connected to the relay tank 20. The upstream end of the primary waste acid supply pipe 31 is connected to the middle of the primary waste acid discharge pipe 10. Thereby, a part of the primary waste acid discharged from the first separator 6 is supplied to the relay tank 20 through the primary waste acid supply pipe 31.
A waste sulfuric acid discharge pipe 24 is connected in the middle of the waste sulfuric acid supply pipe 27. Thereby, the remaining portion of the waste sulfuric acid discharged from the denitration treatment tank 19 through the waste sulfuric acid supply pipe 27 is discharged from the waste sulfuric acid discharge pipe 24.

In the relay tank 20, the quaternary waste acid, the waste sulfuric acid, and the primary waste acid are mixed to obtain a quaternary waste acid (a tertiary waste acid that is concentrated in the concentration step described below). 2 mixing steps).
The fourth waste acid is supplied to the relay tank 20 through the quaternary waste acid discharge pipe 23, for example, at a supply amount of 1000 to 20000 kg / h.
The waste sulfuric acid is supplied to the relay tank 20 through the waste sulfuric acid supply pipe 27 at, for example, a supply amount of 10,000 kg / h or less.

The primary waste acid is supplied to the relay tank 20 through the primary waste acid supply pipe 31, for example, at a supply rate of 10,000 kg / h or less.
The mixing ratio between the quaternary waste acid supplied to the relay tank 20 via the quaternary waste acid discharge pipe 23 and the waste sulfuric acid supplied to the relay tank 20 via the waste sulfuric acid supply pipe 27 is, for example, With respect to the supply amount 1 of the quaternary waste acid, the waste sulfuric acid supply amount 2 or less is mixed. The primary waste acid supplied to the relay tank 20 via the primary waste acid supply pipe 31 and the waste sulfuric acid supplied to the relay tank 20 via the waste sulfuric acid supply pipe 27 have a mixing ratio of, for example, The primary waste acid supply amount 1 is mixed with the waste sulfuric acid supply amount 2 or less.

The quaternary waste acid contains, for example, nitric acid, sulfuric acid and water, and toluene, mononitrotoluene and dinitrotoluene. For example, nitric acid is 0.2% by weight or less, sulfuric acid is 60 to 80% by weight, and toluene is 0%. 0.5 wt% or less, mononitrotoluene in a proportion of 0.1 to 3 wt%, and dinitrotoluene in a proportion of 0.1 to 3 wt%.
A concentrator 21 is connected to the relay tank 20 via a pipe 30.

The concentrator 21 is not particularly limited as long as it is a concentrator that concentrates the fifth-order waste acid obtained in the second mixing step. For example, an evaporator such as a flash evaporator or a vacuum evaporator is used.
And if the 5th waste acid from the relay tank 20 is supplied to the concentrator 21 via the piping 30, in this concentrator 21, the 5th waste acid will have the sulfuric acid concentration, for example, 80 weight%. As described above, it is preferably concentrated at a temperature of 150 to 250 ° C. until it becomes 83 wt% or more, and more preferably 85 wt% or more (concentration step). Thereby, the concentrate which concentrated the 5th-order waste acid is obtained.

As described above, since the concentration of sulfuric acid in the concentrated solution is 80% by weight or more, as described later, the concentrated solution is circulated to the second step to improve the yield of dinitrotoluene in the second step. Can do.
The concentrator 21 is connected to an upstream end of a first circulation line 25 as a first circulation means.

The first reflux line 25 is connected to the second reaction tank 11 at its downstream end in order to circulate the concentrated liquid obtained in the concentration process to the second process.
Then, the concentrate obtained in the concentration step is circulated from the concentrator 21 to the second reaction tank 11 via the first circulatory line 25 (first circulatory step). In the first circulation line 25, the concentrated liquid is circulated at a circulation flow rate of 1000 to 40000 kg / h, for example.

In addition, the concentrated liquid that is refluxed to the second reaction tank 11 via the first reflux line 25 has a reflux ratio (circular flow rate / mixed acid of the concentrated liquid that is refluxed to the second reaction tank 11 via the first reflux line 25. The supply amount of the mixed acid supplied to the second reaction tank 11 via the supply pipe 13 is circulated at, for example, 1/1 to 5/1.
Thus, in this dinitrotoluene production apparatus 1, in the first reaction tank 5, toluene is reacted with a mixed acid of nitric acid and sulfuric acid to produce mononitrotoluene, and this mononitrotoluene is nitric acid in the second reaction tank 11. And dinitrotoluene by reaction with a mixed acid of sulfuric acid. Then, in the mixer 17, the secondary waste acid discharged from the second reaction tank 11 and mononitrotoluene are mixed to obtain a first mixed solution, and in the third separator 18, 4 from the first mixed solution is obtained. The secondary waste acid is separated and further mixed with waste sulfuric acid in the relay tank 20 to form the fifth waste acid, and then the fifth waste acid is concentrated in the concentrator 21 to obtain a concentrated liquid. The concentrated liquid is circulated to the second reaction tank 11.

Therefore, the secondary waste acid discharged | emitted from the 2nd reaction tank 11 can be reused efficiently, and the remarkably improvement of the reuse rate of a secondary waste acid can be aimed at.
In the mixer 17, the secondary waste acid discharged from the second reaction tank 11 and mononitrotoluene are mixed, and nitric acid in the secondary waste acid is obtained by the reaction of the mixed secondary waste acid and mononitrotoluene. Can be reduced. Therefore, the sulfuric acid concentration in the secondary waste acid can be increased. Mononitrotoluene has good compatibility with dinitrotoluene, and the third separator 18 can efficiently separate the quaternary waste acid from the first mixed solution.

Further, the quaternary waste acid is concentrated by the concentrator 21 as the fifth waste acid mixed with the waste sulfuric acid after being separated from the first mixture by the third separator 18, so that the first mixture is left as it is. Crystallization of dinitrotoluene in the apparatus due to the concentration can be prevented, and the quintic waste acid can be concentrated to an optimum concentration.
In the dinitrotoluene production apparatus 1, the mononitrotoluene obtained in the first reaction tank 5 is mixed with the secondary waste acid separated and discharged from the second reaction tank 11 by the second separator 12 in the mixer 17. Therefore, the manufacturing efficiency can be improved.

Further, in this dinitrotoluene production apparatus 1, the separation liquid from which the quaternary waste acid has been separated by the third separator 18 is circulated to the second reaction tank 11 by the separation liquid recirculation line 22, so the separation liquid is discarded. Without using mononitrotoluene.
In the dinitrotoluene production apparatus 1, the secondary waste acid separated and discharged from the second reaction tank 11 by the second separator 12 by the third reflux line 16 is mixed with the mononitrotoluene by the mixer 17. Since a part of the first reaction tank 5 is circulated, the concentration of sulfuric acid and nitric acid in the first reaction tank 5 can be adjusted to the optimum concentration by the secondary waste acid partially circulated. This also allows the amount of secondary waste acid to be concentrated in the concentrator 21 to be adjusted, and efficient concentration can be achieved.

  Further, in the dinitrotoluene production apparatus 1, the primary waste acid discharged from the first reaction tank 5 is denitrated in the denitration treatment tank 19, and a part of the obtained waste sulfuric acid is third separated. In the relay tank 20, the primary waste acid discharged from the first reaction tank 5 is not discarded as it is because it is mixed in the relay tank 20 with the quaternary waste acid that has been separated in the vessel 18 and concentrated in the concentrator 21. Can be reused effectively. Moreover, since the reuse amount of the waste sulfuric acid to be reused can be adjusted, the mixing ratio of sulfuric acid and nitric acid in the concentrated liquid to be reused after being concentrated and then recirculated to the second reaction tank 11 is optimal. Can be adjusted to the value. Furthermore, the amount of new mixed acid added in the second reaction tank 11 can be reduced.

DESCRIPTION OF SYMBOLS 1 Dinitrotoluene manufacturing apparatus 5 1st reaction tank 11 2nd reaction tank 16 3rd reflux line 17 Mixer 18 3rd separator 19 Denitration treatment tank 20 Relay tank 21 Concentrator 22 Separation liquid reflux line 25 1st reflux line

Claims (13)

A first step of producing mononitrotoluene by reacting toluene with a mixed acid of nitric acid and sulfuric acid,
A second step of producing dinitrotoluene by reacting the mononitrotoluene obtained in the first step with a mixed acid of nitric acid and sulfuric acid,
A first mixing step of mixing mononitrotoluene with the secondary waste acid discharged from the second step;
A separation step of separating the tertiary waste acid from the first mixed solution obtained in the first mixing step, wherein the secondary waste acid is mixed with mononitrotoluene;
A concentration step of concentrating the tertiary waste acid separated in the separation step; and
A method for producing dinitrotoluene, comprising a first refluxing step of refluxing the concentrated liquid obtained in the concentration step to the second step.   The method for producing dinitrotoluene according to claim 1, wherein the mononitrotoluene mixed with the secondary waste acid discharged from the second step is the mononitrotoluene obtained in the first step.   The method for producing dinitrotoluene according to claim 1 or 2, further comprising a second reflux step in which the separation liquid from which the tertiary waste acid is separated is refluxed to the second step in the separation step.   The secondary waste acid discharged from the second step includes a third reflux step in which the secondary waste acid is partially refluxed to the first step before the mononitrotoluene is mixed in the first mixing step. Item 4. A method for producing dinitrotoluene according to any one of Items 1 to 3.   The method for producing dinitrotoluene according to any one of claims 1 to 4, wherein in the concentration step, the tertiary waste acid is concentrated so that the sulfuric acid concentration becomes 80 wt% or more.   The first mixing step is performed in a tubular reactor including a tube and a line mixer connected to the tube, the flow rate in the line mixer is 20 cm / s or more, and the residence in the tubular reactor is The method for producing dinitrotoluene according to any one of claims 1 to 5, wherein the time is 60 seconds or more.   The primary waste acid discharged in the first step is separated in the separation step and includes a second mixing step of partially mixing with the tertiary waste acid before being concentrated in the concentration step. The manufacturing method of dinitrotoluene in any one of Claims 1-6.   The waste sulfuric acid obtained by denitrating a primary waste acid is partly mixed with the tertiary waste acid before being separated in the separation step and concentrated in the concentration step. 8. The method for producing dinitrotoluene according to 7. A first reactor for reacting toluene with a mixed acid of nitric acid and sulfuric acid to produce mononitrotoluene;
A second reaction tank for producing mononitrotoluene by reacting the mononitrotoluene obtained in the first reaction tank with a mixed acid of nitric acid and sulfuric acid;
A first mixing means for mixing mononitrotoluene with the secondary waste acid discharged from the second reaction tank;
Separation means for separating tertiary waste acid from the first mixed liquid obtained in the first mixing means and mixed with mononitrotoluene in the secondary waste acid;
A concentration means for concentrating the tertiary waste acid separated in the separation means, and
An apparatus for producing dinitrotoluene, comprising: first refluxing means for circulating the concentrate obtained in the concentration means to the second reaction tank.   The apparatus for producing dinitrotoluene according to claim 9, wherein the first mixing means mixes mononitrotoluene obtained in the first reaction tank.   11. The apparatus for producing dinitrotoluene according to claim 9, further comprising: a second reflux unit that circulates the separation liquid from which the tertiary waste acid has been separated in the separation unit to the second reaction tank. .   The secondary waste acid discharged from the second reaction tank is provided with a third reflux means for partly circulating the secondary waste acid into the first reaction tank before mixing the mononitrotoluene with the first mixing means. The apparatus for producing dinitrotoluene according to any one of claims 9 to 11. A denitrification means for denitrating the primary waste acid discharged from the first reaction tank;
And a second mixing means for partially mixing the waste sulfuric acid obtained in the denitration treatment means with the tertiary waste acid before being separated by the separation means and concentrated by the concentration means. The apparatus for producing dinitrotoluene according to any one of claims 9 to 12.

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