JP2929393B2 - Xylene production apparatus and production method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus and a method for producing xylenes, and more particularly to a production method for efficiently producing xylene using at least toluene as a raw material. The present invention relates to an apparatus and a manufacturing method.

[Conventional technology and problems to be solved by the invention]

Conventionally, xylene is mainly due to disproportionation of toluene,
In some cases, toluene, for example, are manufactured using both the trans alkylation or disproportionation and trans alkylation of the reacting an aromatic hydrocarbon of C _9, such as trimethylbenzene. In this production, a great amount of energy is consumed for separating and recovering xylenes.

In particular, in general, the substance contained in the reaction product liquid in the largest amount is unreacted toluene, and a large amount of energy is required for this separation, and the energy removed by the separated toluene is a large amount. Despite its quantity, this energy was discarded with little or no effective use.

[Means and actions for solving the problem]

The present inventors have intensively studied to overcome the above-mentioned drawbacks in the conventional xylene production method using toluene as a raw material, and effectively use a large amount of energy carried away by toluene in the separation of toluene. By utilizing the present invention, the present invention was finally developed to develop an apparatus and a method for efficiently producing xylenes.

That is, one of the present invention is a reaction step including a reactor for converting toluene into xylene and benzene using at least toluene as a raw material, and a reaction product liquid containing at least benzene, toluene and xylene discharged from the reaction step. A benzene column for separating each of benzene, toluene and xylene by distillation and a distillation step having a toluene and a column, and a para-xylene recovery step for separating and recovering para-xylene from the xylene fraction from the distillation step. In the connected xylene manufacturing equipment, two condensers are arranged at the top of the toluene tower, one of which is used as a reboiler for the benzene tower, and the other condenser is used for waste heat recovery. Xylene manufacturing equipment It is.

Further, another invention of the present invention is to obtain a reaction product liquid containing at least benzene, toluene and xylene using at least toluene as a raw material, and separate benzene, toluene and xylenes from the reaction product solution by distillation, Next, in a method for producing xylenes for separating and recovering para-xylene from a xylene fraction, toluene vapor distilled from the top of a toluene column for separating toluene by distillation is divided into at least two, and one of them is reboiler in a benzene column. Characterized in that the xylene is used as a heat source, and the remainder is used as an energy source of equipment in a xylene production apparatus.

The apparatus of the present invention is provided with a reaction step, a distillation step, and a para-xylene recovery step sequentially.

The reaction step includes a reactor for converting toluene to xylene by disproportionation or in combination with disproportionation and transalkylation. The reactor may be any of a batch type and a continuous type, but a continuous type is preferred in practice. In general, hydrogen gas is fed into the reactor. In this case, at the outlet of the reactor, the hydrogen gas mixed with the reaction product liquid is separated by a flash separator. The compressed hydrogen is pressurized by a compressor, returned to the reactor and reused. This compressor is
Although both a turbo type and a positive displacement type can be used, a turbo type and a rotary positive displacement type are preferred.

The reaction product liquid from which the hydrogen gas has been removed is sent to a distillation step.

In the distillation step, a low-boiling tower, a benzene tower, a toluene tower, a xylene tower, and a high-boiling tower for sequentially separating low-boiling components, benzene, toluene, xylene, and high-boiling components in the reaction product liquid by distillation from the upstream side. Are generally provided.

The type of the distillation column is not particularly limited, but both a column column and a packed column can be used.

The xylene column is omitted when there are few components having a higher boiling point than the xylenes in the reaction product solution, the content of single xylene is high, and the content of single xylene in the bottom solution of the toluene column is high. be able to.

Further, in order to separate the xylenes further each xylene adsorption separation method in place of the distillation, it can also be caused by HF-BF ₃ and a method and solvent extraction method utilizing complex reaction with xylene.

The xylene fractions obtained in the distillation step, such as the bottom liquid of the toluene column containing xylene or the top liquid of the xylene tower, are sent to the para-xylene recovery step in order to separate and recover xylene.

 The para-xylene recovery step is usually performed by a crystallization method.

As the crystallization method, both the high pressure crystallization method and the cooling crystallization method can be used, but the cooling crystallization method is preferable. As the cooling crystallization method, for example, JP-A-59-66
The "countercurrent cooling and refining method" as described in JP-A-305 is most preferred. This "counter-flow cooling and refining method"
A combination of a cooling type crystallization tank having a fining unit at the top and a heating unit at the top with a fining unit at the bottom, and a solid purification tower operating at a higher temperature than the crystallization tank. The generated crystals are led to the clarifying sedimentation section at the top of the purification tower, and further, a crystal packed layer section is generated at the middle stage of the purification tower. This is a method in which a part of the product is taken out as a product, the other part is raised as a reflux liquid, the crystal layer moving to the lower part is washed, and the clarified liquid at the upper part of the purification tower is led to the clarifying sedimentation part of the crystallization tank.

The crystallization tank used here is not particularly limited as long as it is a crystallization tank in which the upper portion becomes a clarifying section.
The "scraping circulation type crystallizer" described in 109403 is preferably used. In this "scraping circulation type crystallizer", a draft tube is provided in a scraping mechanism that rotates inside a scraping type crystallization tank, and stirring blades for generating a circulating flow are installed inside and outside the draft tube. A baffle having a certain curvature inserted outside and inside the draft tube from the top lid and the bottom plate of the crystallization tank to near the support boom of the scraping mechanism for changing the swirling flow to upstream and downstream. This is a crystallization tank.

As the rigid purification column used here, for example, a "purification apparatus" described in JP-B-62-59603 is suitably used. This "purifying device" is a device provided with a heatable partition shelf having an opening.

The refrigerant for cooling the crystallization tank is not particularly limited, but usually ammonia is used. As a refrigeration system using ammonia as a refrigerant, any of a so-called compression refrigeration system and an absorption refrigeration system can be used, but the latter is preferable in practical use.

Of the toluene vapor distilled from the top of the toluene column, a part is used as a heat source of the benzene column and the energy of the remaining toluene vapor is, for example, in the para-xylene recovery step, the reboiler heat source of the ammonia distillation column in the absorption refrigeration method, As a heat source for the reflux of the above-mentioned rigid purification tower, or as a power source for a compressor for hydrogen compression, or as an energy source for a turbine generator for obtaining power such as lighting, control, and pumps in the apparatus or It can be utilized as a heat source for removing the solvent used for solvent extraction.

Usually, the former or the former will consume most of the remaining toluene vapor energy,
If there is a surplus, it can be used as the other energy source.

That is, when this toluene vapor is used directly as an energy source, the waste heat condenser is, for example,
It is a reboiler at the lower part of the ammonia distillation tower and a heating part at the lower part of the rigid purification tower. In this case, the waste heat recovery condenser is divided into two or more.

On the other hand, when steam is generated using this toluene vapor as a heat source and the steam is used as an energy source, the waste heat recovery condenser is a steam boiler.

Since this steam has a low pressure as it is, for example, when it is used as a power source such as a turbine drive compressor for hydrogen compression and a turbine generator, a medium pressure to high pressure steam heated and pressurized is used. Must.

In addition, the toluene tower reboiler can be heated using a heat medium such as a high-temperature heat transfer medium oil, but the heat source of the toluene tower reboiler drives a turbine generator for powering the xylene device of the present invention. It is possible and preferred to use a back pressure steam and / or a steam turbine back pressure steam for driving a hydrogen compressor.

The BFW of the boiler for generating steam for the turbine generator and the steam turbine for driving the hydrogen compressor (boiler feed water-the same applies hereinafter) is generally performed by a direct heating furnace. Steam from the waste heat condenser can also be applied.

FIG. 1 shows a flow sheet of a typical example of the xylene production apparatus of the present invention. The xylene production apparatus shown in the flow sheet of FIG. 1 does not have a xylene tower, and uses a countercurrent cooling crystallization purification apparatus having three crystallization tanks and a solid purification tower for the recovery system. Ammonia, which is a refrigerant of the countercurrent cooling crystallization purification device, is cooled by an absorption refrigeration system.

The raw material toluene is combined with the toluene separated and collected in the toluene tower 17 and condensed, preheated by the reaction product liquid from the reactor 2 in the heat exchanger 3, and further heated to a predetermined temperature in the heating furnace 1 to react. Is supplied to the vessel 2. On the other hand, hydrogen gas is supplied to the reactor 2. The toluene is reacted in the reactor 2, and the reaction product liquid mainly containing toluene, benzene and xylene, and also a low-boiling component and hydrogen gas from the reactor 2 is sent to a flash separator 4 where hydrogen gas is separated. This hydrogen gas is combined with newly supplied hydrogen gas as required, and is pressurized by the hydrogen compressor 5 and circulated to the reactor 2. The reaction product liquid discharged from the flash separator 4 after the heat exchange with the supply liquid is sent to the pressure release flash tank 6, where the vapor component in the reaction product liquid discharged and flashed is condensed and discharged. Further, the liquid component is sent from the bottom of the discharge flash tank 6 to the low boiling column 10.

In the low boiling tower 10, low boiling components such as light hydrocarbons in the reaction product liquid are removed by distillation. The removed low-boiling components are condensed by a low-boiling column condenser 11, one part of which is refluxed and the remaining part is discharged outside the column. The reaction product liquid from which the low boiling components have been removed is sent to the benzene tower 14 as a low boiling tower bottom liquid.
Here, benzene in the lower column bottom liquid is removed by distillation, and this benzene is condensed by the benzene column condenser 15, a part of which is refluxed, and the remaining part is discharged outside the column. Further, the benzene column bottom liquid containing substantially no benzene is sent to the toluene column 17. Here, the toluene in the bottom liquid of the benzene tower is separated by distillation, and this toluene is discharged from the top of the toluene tower 17 and divided into two streams. One stream is used as a heat source of the benzene tower reboiler 16. It is condensed. The other stream is sent to the waste heat recovery condenser 18 and used as a heat source for generating steam, while toluene is condensed. Part of the toluene agglomerated in each of the benzene tower reboiler 16 and the waste heat recovery condenser 18 is refluxed, and the remainder is returned to the reactor 2 in combination with the raw toluene.

The toluene bottom liquid which is substantially made only of xylenes is sent to a para-xylene recovery step. The three crystallization tanks in the para-xylene recovery process have a clarifying part at the top.
This is a scraping circulation type crystallizer described in JP-A-55-109403. Liquid ammonia is flowed through the jackets of these crystallization tanks and cooled by the latent heat of vaporization of the liquid ammonia.

The first tank for these crystal layers is connected to a rigid purification tower. This rigid purification tower is a purifying apparatus described in Japanese Patent Publication No. 62-59603.

The bottom liquid of the toluene column is supplied to the first crystallization tank 50. First
The clarified liquid above the crystallization tank 50 is sent to the second crystallization tank 51, and the clarified liquid above the second crystallization tank 51 is similarly sent to the third crystallization tank 52, and the clarified liquid above the third crystallization tank 52 is clarified. The liquid is discharged out of the apparatus as a residue. The crystal slurry in the third crystallization tank 52 is the second
The crystallization slurry in the second crystallization tank 51 is sent to the first crystallization tank 50, and the crystal slurry in the first crystallization tank 50 is sent to the upper part of the rigid purification column 53. Here, the crystal slurry is settled to the lower part, and is heated and melted by the lower heater 54. A part of the melt is taken out from the lower part of the compact purification column 53 to obtain high-purity para-xylene as a product. The remaining melt rises in the rigid purification column 53 and is brought into contact with crystals descending in the column to wash the crystals. The clarified liquid in the upper part of the solid purification column 53 is returned to the first crystallization tank 50.

Ammonia vapor from the jacket of the third crystallization tank 52 reaches the first ejector via the first super heater 41, where it is mixed with dilute ammonia water, and the mixture is then mixed with the first low-pressure condenser 34 and the first lean solution. Liquid receiving tank and first booster pump
It is sent to the second ejector via 36 in sequence.

Ammonia vapor from the respective outer jackets of the second crystallization tank 51 and the first crystallization tank 50 reaches the second ejector via the second superheater 40, where it is pressurized and diluted by the first pressure pump 36. Mixed with aqueous ammonia, the mixture
Boost pump 37, second dilute liquid receiving tank 38, and third booster pump
It is sent to the second ammonia distillation column 29 via the second ammonia distillation column heat exchanger 33 through the path 39 sequentially. Here, ammonia vapor is separated by distillation. Second
The bottom liquid of the ammonia distillation tower 29 is diluted ammonia water, and this bottom liquid reaches the first ejector via the second ammonia distillation tower exchanger 33, where it is mixed with ammonia vapor. Ammonia vapor from the top of the second ammonia distillation column 29 is supplied to the second ammonia distillation column condenser 30 and the second ammonia distillation column.
The liquid component is removed via the reflux drum 31 of the ammonia distillation tower. This ammonia vapor is mixed with diluted ammonia water, which is the bottom liquid of the first ammonia distillation tower 20, to form concentrated ammonia water. It is sent to the first ammonia distillation column 20 via 24, where the pressurized ammonia vapor is separated by distillation. The bottom solution of the first ammonia distillation column 20 is pressurized diluted ammonia water, and this bottom solution passes through the first ammonia distillation column heat exchanger 24 and from the top of the second ammonia distillation column 29. And pressurized ammonia vapor.

The pressurized ammonia vapor from the first ammonia distillation column 20 is liquefied by the first ammonia distillation column condenser 22, and this liquefied ammonia is sent to the reflux drum 23, and a part of the liquefied ammonia is returned to the ammonia distillation column 20. The remainder is divided into two streams, one of which is sent to the jacket of the first crystallization tank 50 via the second superheater 40, and the other is sent via the first superheater 41. Second
It is sent to the respective jackets of the crystallization tank 51 and the third crystallization tank 52.

The water vapor obtained by the waste heat condenser 18 using toluene vapor from the toluene tower 17 as a heat source is guided to a first ammonia distillation tower reboiler 21 and a second ammonia distillation tower reboiler 32, and used as a heat source for both distillation towers. The remaining steam is guided to the solid refining tower heater 54 and used as a heat source for the solid refining tower.

A typical example of the heating method of the toluene tower will be described with reference to respective flow sheets in FIGS. 2 and 3.

In FIG. 2, BFW is supplied to a boiler 61 and converted into steam. The obtained steam (high-pressure steam) rotates the steam turbine 62 to drive the generator 63. After the turbine 62 is rotated, the waste heat steam (medium-pressure steam) is guided to the toluene tower reboiler 19, Used as a heat source for tower 17.

In FIG. 3, the steam turbine 71 is rotated with steam (high-pressure steam) obtained in the same manner as in FIG. 2 to drive the generator 72 and also drive the hydrogen compressor 5,
The waste steam (medium pressure steam) after rotating the steam turbine 71 is guided to the toluene tower reboiler 19 and used as a heat source of the toluene tower 17.

In the above, in order to preheat part or all of the BFW to the boiler 61, steam generated by the waste heat recovery condenser 18 may be used.

In the reactor 1, the raw material toluene can be converted to xylene by disproportionation of toluene or disproportionation of toluene and transalkylation of toluene and an alkylbenzene having 9 carbon atoms such as trimethylbenzene. And benzene is by-produced. These reactions are carried out, for example, in the presence of a solid acid catalyst such as silica alumina and a catalyst in which a noble metal is supported on silica alumina, at 30 to 60 bar and at a temperature of 300 to 350 ° C., based on toluene fed with the amount of hydrogen used. The reaction is carried out under ordinary conditions of 3 to 8 times the molar amount. Examples include the TATORAY process by Toray, the ARCO-xylene plus method by Atlantic Richfiekd Co., and the STDP (Selective Process) by Mobile.
Reaction conditions in Toluence disproportionation and the like can be employed.

Of these, it is preferable to employ the reaction conditions in STDP because paraxylene having high utility value is highly selective and can be obtained efficiently.

The toluene used in this reaction can be the one used for general industrial raw materials. For example, ASTM (American Society of Testing Material-
Specified in the American Society for Testing and Materials-Standard) D362-80, and
Those having a purity of 99.9% by weight or more are preferably used.

The number of stages in each distillation column in the distillation step, and the conditions such as the supply stage, the temperature, the pressure, and the reflux ratio vary depending on the composition of the reaction product solution and the like. It is as follows. That is, When a xylene tower is provided, the number of stages is 20 to 3
0, supply stage 5-10 stages, temperature 160-180 ℃ at the top, 1 at the bottom
90-230 ° C., the pressure is 1-3 bar at the top. In this case, if the xylene tower condenser is used as a waste heat boiler, steam at 140 to 160 ° C. is obtained, and this steam can also be used as an energy source of the same plant, and is preferable.

In the para-xylene recovery step, the temperature of each tank when using a countercurrent cooling crystallization purification device depends on the composition of the xylene tower bottom liquid and the xylene tower liquid containing xylene supplied to the first crystallization tank. Different.

For example, when the xylene content of the liquid supplied to the first crystallization tank is 60 to 80 wt%, the first crystallization tank is -5 to 0 ° C,
2nd crystallization tank -15 ° C, 3rd crystallization tank -25 ~ -35 ° C and 4th
Crystal tank -65 to -45 ° C and upper part of the rigid purification tower -3 to 3 ° C
It is preferable that

When the content of para-xylene is 25 to 35 wt%, the supply liquid is supplied to the second crystallization tank, and
The temperature is preferably set to -15 ° C, the second crystallization tank at -30 ° C, the third crystallization tank at -45 ° C and the fourth tank at -65 ° C, and the upper part of the rigid purification tower at -2 ° C.

In addition, the conditions for freezing ammonia, which is a refrigerant in the para-xylene recovery step, are appropriately determined by the composition and amount of the liquid supplied to the para-xylene recovery step.

〔Example〕

 The present invention will be described more specifically with reference to examples.

The present invention is not limited by the embodiments.

Example 1 p-xylene was produced using the apparatus shown in the flow sheet of FIG.

1. Reaction process The reaction was carried out using zeolite catalyst ZSM-5. (1) Catalyst ZSM-5 (2) Toluene ASTM D362 crude, 99.9wt% toluene (3) Toluene feed rate 5kg / catalyst 1kg / hr (replenishment toluene: circulating toluene = 1: 3.3) (4) Hydrogen Feed rate 2kg-mol / toluene kg-mol / hr (5) Pressure 30bar (6) Temperature 400 ° C (7) Discharge amount of reaction product 8403 kg / hr (8) Composition of reaction product (after removing hydrogen gas) mol% C ₅ below: 5.20 benzene: 15.83 toluene: 66.80 p-xylene: 10.14 m-xylene: 1.80 o-xylene: 0.19 C ₉ or higher: 0.04 2. distillation step The reboiler of the toluene tower used a high-temperature heat transfer oil, and its inlet and outlet temperatures were 240 ° C. and 200 ° C., respectively.

3. Xylene recovery process All three crystallization tanks are 1.8m in diameter and 2.4m in height.
The heat transfer area was 10 m ² .

The operating conditions in the three crystallization tanks were as follows.

In addition, a residue having the following composition was obtained from the third crystallization tank.
6.7 kg / hr was discharged.

Composition of the residue (mol%) Toluene 1.50 Ethylbenzene 13.93 p-xylene 28.84 o-xylene 37.18 m-xylene 6.53 C ₉ or more 12.02 The specifications and operating conditions of the rigid purification tower were as follows.

Composition mol% Toluene 0.4 Ethylbenzene 4.0 p-xylene 79.4 o-xylene 10.8 m-xylene 1.9 C ₉ or more 3.5 Crystal slurry supply rate kg / hr 1172.0 Slurry concentration wt% 45 Melt discharge kg / hr 293.0 p-xylene purity% 99.9 4. Absorption refrigeration process The operating conditions of the absorption refrigeration system were as follows.

5. Comparison of energy amount Product p-xylene 1k in distillation process and recovery process
The amount of energy required per g is
It was 1.8 kilojoules. On the other hand, when the waste heat of toluene in the toluene tower was not used, it was 3.3 kJ.

〔The invention's effect〕

In the present invention, high-purity xylene can be efficiently obtained with a relatively small amount of energy.

[Brief description of the drawings]

1 to 3 are flow sheets showing an embodiment of the present invention. In the drawing, 1 ... heating furnace, 2 ... reactor 4 ... flash separator 5 ... hydrogen compressor 6 ... releasing pressure flash tank 10 ... low boiling tower, 14 ... benzene tower 17 ... toluene tower 18 ... Waste heat recovery condenser 20 First ammonia distillation tower 26 Reflux drum 27 Solution pump 29 Second ammonia distillation tower 35 First dilute liquid receiving tank 36 First booster pump 38 Second diluted liquid receiving tank 39 Third booster pump 40 Second superheater 41 First superheater 50 First crystal tank 51 Second crystal tank 52 Third crystal tank 53 …… Rigid refining tower 61 …… Boiler, 62… Steam turbine 63 …… Generator, 71 …… Steam turbine 72 …… Generator

Continuation of front page (72) Inventor Koji Miwa 2-17-15 Tsukuda, Chuo-ku, Tokyo Inside Tsukishima Kikai Co., Ltd. (56) References JP-A-58-167683 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) C07C 15 / 08,6 / 12,7 / 04,7 / 14

Claims (8)

(57) [Claims] 1. A reaction step including a reactor for converting toluene into benzene and xylene using at least toluene as a raw material, and converting a reaction product liquid containing at least benzene, toluene and xylene discharged from the reaction step into benzene, A xylene production apparatus having a distillation step having at least a benzene column and a toluene column for separating toluene and xylene by distillation, and a para-xylene recovery step for separating and recovering para-xylene from a xylene fraction from the distillation step Wherein two condensers are disposed at the top of the toluene tower, one of which is a reboiler for the benzene tower, and the other one is a condenser for waste heat recovery. Xylene production equipment. 2. The apparatus for producing xylenes according to claim 1, wherein the para-xylene recovery step is performed by a cooling crystallization method. 3. The apparatus for producing xylenes according to claim 1, wherein the para-xylene recovery step is carried out by a countercurrent cooling / melting / refining method. 4. The apparatus for producing xylenes according to claim 2, wherein the equipment for producing a refrigerant for cooling the para-xylene recovery step by the cooling crystallization method is of an absorption refrigeration system. 5. A condenser other than the reboiler of the benzene tower among the two condensers disposed at the top of the toluene tower is connected to the reboiler of the ammonia distillation tower in the refrigeration equipment of the absorption refrigeration system. The apparatus for producing xylenes according to claim (1) or (4). 6. A condenser, other than a reboiler of a benzene tower, of the two condensers disposed at the top of the toluene tower is connected to a lower part of the solid purification tower in the para-xylene recovery step. An apparatus for producing xylenes according to (1) or (3). 7. The para-xylene recovery step is based on a countercurrent cooling / melt refining method, and the apparatus for producing a cooling medium for cooling in the para-xylene recovery step is based on an absorption refrigeration system. Of the two condensers disposed in the benzene tower, a condenser other than the reboiler is connected to the lower part of the ammonia distillation tower in the refrigeration facility and the solid purification tower in the xylene recovery step. Claims (1), (3), (4), (5)
Or the apparatus for producing xylenes according to (6). 8. A reaction product containing at least toluene as a raw material and containing at least benzene, toluene and xylene, and benzene,
In a xylene production method of separating toluene and xylenes, and then separating and recovering para-xylene from the xylene fraction, at least two toluene vapors distilled from the top of a toluene tower for separating toluene by distillation are separated. A method for producing xylenes, wherein one is used as a heat source of a reboiler of a benzene tower, and the other is used as an energy source of equipment in a xylene production apparatus.