CN116217439A - Circulation solvent for preparing MDI by phosgenation and purification method thereof - Google Patents

Circulation solvent for preparing MDI by phosgenation and purification method thereof Download PDF

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CN116217439A
CN116217439A CN202310003120.6A CN202310003120A CN116217439A CN 116217439 A CN116217439 A CN 116217439A CN 202310003120 A CN202310003120 A CN 202310003120A CN 116217439 A CN116217439 A CN 116217439A
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solvent
tower
reaction
partition
phosgenation
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董超
赵东科
张金强
文放
张宏科
周宇杰
黄荐
朱健
范石晓
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Wanhua Chemical Group Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C263/00—Preparation of derivatives of isocyanic acid
    • C07C263/10—Preparation of derivatives of isocyanic acid by reaction of amines with carbonyl halides, e.g. with phosgene
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C263/00—Preparation of derivatives of isocyanic acid
    • C07C263/18—Separation; Purification; Stabilisation; Use of additives
    • C07C263/20—Separation; Purification
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C265/00—Derivatives of isocyanic acid
    • C07C265/14—Derivatives of isocyanic acid containing at least two isocyanate groups bound to the same carbon skeleton
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency

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  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

The invention discloses a circulating solvent for preparing MDI by phosgenation and a purification method thereof, which can improve the quality of products and reduce the color number of the products by controlling the mass content of halogenated hydrocarbon substances in the circulating solvent. The partition tower is combined with multi-effect rectification, so that the high-efficiency separation of halogenated hydrocarbon substances and solvents can be realized, the product quality is greatly improved, and the product can be directly recycled. The method combines the degassing and desolventizing systems in the refining process of the crude isocyanate, saves a solvent purifying unit, realizes complete coupling of energy, has simple and reliable process, and can greatly reduce investment and operation cost.

Description

Circulation solvent for preparing MDI by phosgenation and purification method thereof
Technical Field
The invention belongs to the field of isocyanate, and in particular relates to a circulating solvent for preparing MDI by phosgenation and a purification method thereof.
Technical Field
Isocyanate is one of the most important raw materials in the synthesis process of polyurethane materials, and has very wide application in the aspects of polyurethane foam plastics, rubber, fibers, coatings, adhesives, synthetic leather and the like. Most of the current industrialized isocyanate production methods adopt a phosgenation method, and organic primary amine and phosgene react in an inert solvent and are prepared and generated through a series of post-treatment and separation processes. In the process of producing diphenylmethane diisocyanate (MDI) by a liquid-phase phosgene method, a large amount of inert solvent is added into phosgene and diphenylmethane diamine (MDA) simultaneously to improve the reaction quality and reduce the occurrence of side reactions, and the solvent is recycled through a series of product purification and solvent refining processes, wherein impurities possibly brought into the recycled solvent participate in the phosgenation reaction to influence the reaction and the product quality, which is very undesirable.
Patent US3410888 discloses a process for separating aromatic diisocyanates from reaction mixtures, wherein the isocyanates have two benzene rings and wherein the isocyanate functions are attached to carbon atoms of the different benzene rings. The solvent and isocyanate are separated by distillation, and the isocyanate product and the intermediate colored component are also removed together during the removal of the solvent, and then the partially separated mixture of isocyanate and solvent is returned as feed to the solvent removal process or to a separate evaporation or fractionation process to concentrate the isocyanate. The method has the defects that part of isocyanate separated in the solvent removal process is required to be distilled and purified again, so that energy consumption is wasted, and meanwhile, the removed solvent possibly contains isocyanate, and the isocyanate is recycled to be mixed with amine to react to generate urea, so that abnormal system blockage or product quality is reduced.
Patent CN 101302174a discloses a process for producing isocyanates by reacting an amine with phosgene in a solvent to produce the corresponding isocyanate, and recovering the solvent by distillation, the solvent being recycled. The patent mentions that reducing the phosgene and isocyanate content of the solvent is beneficial for improving the product quality and does not limit the reaction affecting other substances in the solvent, such as halogenated hydrocarbon substances.
The patent CN 114380714A discloses a circulating solvent and a method for removing impurities in the production of phosgenation reaction, and the method comprises the steps of mixing the solvent and amine in a solvent reaction kettle in advance, and then carrying out solid-liquid separation to ensure that the total amount of amine consumption substances in the circulating solvent is reasonably controlled and reduce the generation of solid byproducts in the phosgenation reaction. The present invention focuses on substances capable of reacting with amines in solvents, reduces the effect on the reaction by consuming the starting amine, resulting in waste of starting materials and increase in running cost, while the method does not consider the effect of substances not reacting with amines on the system.
The above patents focus mainly on the description protection of part of impurities in the solvent during the purification of isocyanate and the preparation thereof, which are all conventional processes, and the influence of halogenated hydrocarbon impurities in the solvent on the reaction quality is not recognized. In the actual MDI production process, the quality of the phosgenation reaction is poor and the color of the product is even deepened, so that a new circulating solvent for preparing MDI by phosgenation and a purification method thereof are needed to be developed, and the circulating solvent is separated and purified from the reaction mixture in a more efficient and lower cost manner, so that the content of halogenated hydrocarbon in the solvent is reduced.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a circulating solvent for preparing MDI by phosgenation and a purification method thereof, which can greatly reduce the content of halogenated hydrocarbon in the circulating solvent, greatly simplify the process flow and reduce the operation cost.
A circulating solvent for preparing MDI by phosgenation, wherein the mass content of halogenated hydrocarbon substances in the circulating solvent is 0.1-200ppm, preferably 1-150ppm, more preferably 10-100ppm.
In the present invention, the halogenated hydrocarbon substance refers to methane or ethylene substance substituted by chlorine and/or bromine, and includes carbon tetrachloride, trichlorobromomethane, dichlorobromomethane, tetrachloroethylene, dichloroethylene, trichloroethylene, dibromoethylene, etc.
In the present invention, the circulating solvent is preferably one or more of chlorinated aromatic hydrocarbon, dialkyl terephthalate, diethyl phthalate, toluene and xylene, more preferably one or more of chlorobenzene, dichlorobenzene, toluene and xylene, still more preferably chlorobenzene.
In the MDI production process, a series of purification treatment processes including HCl removal, phosgene removal, solvent removal and the like are required, and the removed solvent usually contains HCl, phosgene, water and other light component impurities, and is required to be removed by further refining treatment of the solvent. The inventor discovers through continuous research that halogenated hydrocarbon substances exist in the circulating solvent at the same time, the boiling point of the halogenated hydrocarbon substances is not different from that of the solvent, the halogenated hydrocarbon substances are difficult to remove by a common refining process, the halogenated hydrocarbon substances can exist in the solvent stably, and the reaction quality is influenced along with the circulation of the solvent and the participation of the solvent in the phosgenation reaction.
It is another object of the present invention to provide a process for purifying a recycle solvent for the phosgenation of MDI, said process comprising the steps of:
a. phosgenation reaction: carrying out phosgenation reaction on diphenyl Methane Diamine (MDA) and phosgene under an inert solvent to generate photochemical reaction liquid;
b. separation of partition walls: separating and purifying the reaction liquid in a partition tower, extracting light components containing phosgene and HCl from the tower top, extracting a gaseous solvent from the tower as an extracted solvent, and delivering a tower kettle concentrated solution to a solvent removal unit;
c. and (3) solvent removal: and c, further distilling the tower kettle concentrated solution from the step b in a solvent removal tower under reduced pressure, wherein the tower top condensate of the solvent removal tower is taken as a condensing solvent.
The recycled solvent includes the produced solvent and the condensed solvent.
The extracted solvent from the step b can be used as a heat source of a reboiler of a solvent removal tower kettle, and is combined with the condensed solvent at the top of the solvent removal tower after heat exchange to be used as a circulating solvent.
In a preferred embodiment of the present invention, the inert solvent in the step a is preferably one or more of chlorinated aromatic hydrocarbon, dialkyl terephthalate, diethyl phthalate, toluene and xylene, more preferably one or more of chlorobenzene, dichlorobenzene, toluene and xylene, and still more preferably chlorobenzene.
In a preferred embodiment of the present invention, the inert solvent in step a is recycled, and the mass content of halogenated hydrocarbon in the recycled solvent is 0.1 to 200ppm, preferably 1 to 150ppm, more preferably 10 to 100ppm.
In the present invention, the halogenated hydrocarbon substance refers to methane or ethylene substance substituted by chlorine and/or bromine, and includes carbon tetrachloride, trichlorobromomethane, dichlorobromomethane, tetrachloroethylene, dichloroethylene, trichloroethylene, dibromoethylene, etc.
In some preferred embodiments of the invention, the MDA and inert solvent are added in step a in a mass ratio of 1 (1-8), preferably 1 (2-5).
In some preferred embodiments of the invention, the MDA and phosgene are added in a mass ratio of 1 (1-15), preferably 1 (2-5) in step a.
In some preferred schemes of the invention, the phosgenation reaction in the step a is divided into a cold reaction and a hot reaction, wherein the cold reaction temperature is 60-120 ℃, the pressure is 0.2-3.0MPaA, and the reaction time is within 5min; the thermal reaction temperature is 90-150 ℃, the pressure is 0.2-0.6MpaA, and the reaction residence time is 0.5-3h.
In some preferred embodiments of the invention, the phosgene concentration in the photochemical reaction solution in step a is from 0.1 to 10% and the solvent concentration is from 30 to 90%.
In some preferred embodiments of the present invention, in the step b, a vertical partition is disposed in the middle of the partition tower, and the tower type is one of a plate tower and a packed tower or a combination thereof, and in order to reduce the blockage of the tower tray, the tower tray is preferably in a fixed valve type.
In some preferred schemes of the invention, a partition wall tower is divided into a pre-separation section and a side line extraction section by a partition wall tower middle partition plate in the step b, the lower part of the partition wall is a public stripping section, and the upper part of the partition wall is a public rectifying section;
preferably, the intermediate partition has a height of 2-12m, preferably 4-8m; the height of the public stripping section is 1-8m, preferably 2-5m;
preferably, the bottom of the middle partition plate is provided with a radial adjusting rotary adjusting device for controlling the sectional area ratio of the bottom of the pre-separation section to the side line extraction section to be 1 (0.5-2), more preferably 1: (0.8-1.8), thereby controlling the gas phase flow rate passing through the pre-separation section and the side line extraction section from bottom to top and realizing reasonable distribution of gas phase.
Preferably, the pre-separation section is provided with a reflux flow regulating device, and the ratio of the reflux flow to the feed flow is controlled to be 1: (5-30) preventing the heavy component from being carried out from the gas phase, and realizing the effective separation of the light and heavy components.
In some preferred embodiments of the present invention, after the reaction solution is separated and purified by a dividing wall column, the halogenated hydrocarbon substance is mostly carried out of the gaseous light component at the top of the column. In some preferred embodiments of the present invention, the solvent extracted from the tower in the step b is gas phase extraction, the mass content of halogenated hydrocarbon substances in the solvent extracted is 0.1-300ppm, and the mass flow rate of the solvent extracted accounts for 30% -60% of the total solvent flow rate.
In some preferred embodiments of the present invention, the temperature of the column bottom in the partition wall in the step b is 170-210 ℃ and the pressure is 0.1-0.3MpaA.
In some preferred embodiments of the present invention, the solvent removal column in step c is one of a tray column, a packed column, or a combination thereof, and the solvent is recovered by condensing at the top of the column.
In some preferred embodiments of the present invention, the solvent removal column bottoms temperature in step c is 120-180 ℃, preferably 130-170 ℃; the pressure is 2-50KPaA, preferably 5-20KPaA.
In some preferred embodiments of the invention, the solvent removal overhead condensing temperature in step c is from 40 to 90 ℃, preferably from 60 to 80 ℃; the content of halogenated hydrocarbon substances in the condensed solvent at the top of the tower is 0.1-50ppm (mass ratio).
In some preferred embodiments of the present invention, the solvent withdrawn from the column in step b is used as a heat source for the reboiler of the solvent removal column in step c, and the reboiler outlet temperature is controlled to be 140-180 ℃. And c, combining the extracted solvent with a condensing solvent at the top of the solvent removal tower after heat exchange to serve as a circulating solvent, and returning the circulating solvent to the step a for phosgenation.
The vertical partition board is arranged in the middle of the partition board tower, the partition board tower is divided into a pre-separation side and a main tower side, the partition board can enable a single tower to realize the functions of the two towers, back mixing of intermediate components in the flow of the two towers is avoided, materials are pre-separated at the feeding side of the partition board, further rectifying and separating are carried out at the other side, the mixing effect near the feeding section is reduced, the thermodynamic efficiency is improved, the energy consumption is greatly reduced, and the multi-component separation effect of the single tower is realized. Meanwhile, by adopting the partition tower technology, one rectifying tower and auxiliary equipment, including a condenser, a reboiler, a reflux tank, a reflux pump and the like, can be saved, and the equipment investment and the occupied area are reduced.
Compared with the prior art, the invention has the following positive effects:
(1) The invention can realize the high-efficiency separation of the halogenated hydrocarbon substances and the solvent, the purity of the obtained circulating solvent is high, the content of the halogenated hydrocarbon substances can be reduced to 0.1-200ppm (mass ratio), the quality of the product is greatly improved, the product can be directly recycled, a solvent purification unit is saved, and the process is simple and reliable.
(2) Compared with the conventional separation and rectification process, the separation effect of multiple towers is realized by adopting the partition tower, the equipment investment and the occupied area are greatly reduced, and the gas phase solvent extracted from the partition tower is used as a heat source of a reboiler of the crude product purification tower, so that the complete coupling of energy is realized, and the operation cost is greatly reduced. Meanwhile, the partition tower rectification technology and the multi-effect rectification technology are combined, so that production equipment and process flow are simplified, and energy consumption in the production process is reduced.
Drawings
FIG. 1 is a flow chart of a process for purifying the circulating solvent in the preparation of MDI according to the invention.
Wherein 1 is a mixed solution of MDA and solvent, 2 is phosgene feed, 3 is a mixer, 4 is a reactor, 5 is phosgenation reaction liquid, 6 is a partition tower, 7 is a rotation adjusting mechanism, 8 is a produced solvent, 9 is concentrated solution, 10 is a partition tower reboiler, 11 is a solvent removal tower, 12 is MDI,13 is a solvent removal tower reboiler, 14 is condensed solvent, and 15 is circulating solvent.
Detailed Description
The invention will now be further illustrated by means of specific examples which are given solely by way of illustration of the invention and do not limit the scope thereof.
The main raw material sources involved in examples and comparative examples are as follows:
phosgene: MDI devices in the smoke counter vanning industrial park produce, industrial products;
diphenylmethane diamine (MDA): MDI devices in the smoke counter vanning industrial park produce, industrial products;
chlorobenzene: producing a TDI device in a smoke-box Wanhua industrial park, and an industrial product;
the sample analysis methods involved in the examples and comparative examples are as follows:
the method for analyzing the halogenated hydrocarbon substances in the solvent comprises the following steps:
after diluting the solvent by 100 times of volume with methanol, the total amount of stable halogenated hydrocarbon substances is measured by a gas chromatograph and an ECD detector;
gas chromatography conditions: the temperature of the column box is kept at 35 ℃ for 8min, the temperature is increased to 100 ℃ at the speed of 5 ℃/min, and then the temperature is increased to 200 ℃ at the speed of 10 ℃/min and kept for 5min; column flow rate: 1.5ml/min; sample inlet temperature: 220 ℃; detector temperature: 320 ℃; split ratio: 5:1; tail blow flow rate: 60ml/min.
L color analysis of MDI: the L, a, b values are determined by the CIE color system known to those skilled in the art.
[ example 1 ]
Phosgenation reaction: 10t/h MDA and 10t/h chlorobenzene are mixed in advance and react with 10t/h phosgene to generate a phosgenation reaction solution. The phosgenation reaction is divided into two steps of cold and hot reaction, wherein the cold reaction temperature is 60 ℃, the pressure is 0.2MPaA, and the reaction time is 2min; the thermal reaction temperature was 90℃and the pressure was 0.2MpaA, and the reaction residence time was 0.5h. The phosgene concentration in the reaction solution was 10%.
Separation of partition walls: the reaction liquid is sent to a partition tower for separation and purification, a middle partition plate which is vertically arranged is arranged in the middle of the partition tower, the partition tower is divided into a feed pre-separation side and a side line extraction side, the lower part of the partition plate is a public stripping section, the upper part of the partition plate is a public rectifying section, the bottom of the middle partition plate is provided with a rotary adjusting device which is radially adjusted, and the top of the middle partition plate is provided with a reflux adjusting device. After the reaction liquid is separated and purified by a partition tower, light components such as phosgene, HCl, halogenated hydrocarbon substances and the like are extracted from the tower top, a gaseous solvent chlorobenzene is extracted from the tower, and a tower kettle concentrated solution is sent to a solvent removal unit. The tower tray of the dividing wall tower adopts a fixed valve type, the height of the middle partition plate is 2m, the height of the lower public stripping section is 1m, the height of the upper public rectifying section is 1m, the cross-sectional area ratio of the feed pre-separation side to the side extraction side is 1:0.5, the mass ratio of the reflux flow of the pre-separation section to the feed flow is 1:5, the temperature of the tower bottom of the dividing wall tower is 170 ℃, and the tower pressure is 0.1MPaA.
And (3) solvent removal: and (3) delivering the concentrate of the separation wall tower kettle into a solvent removal tower for further reduced pressure rectification to obtain MDI, wherein the temperature of the solvent removal tower kettle is 140 ℃, the pressure is 2KPaA, gas-phase chlorobenzene extracted from the side line of the separation wall tower is used as a heat source of a reboiler of the solvent removal tower kettle, the outlet temperature of the reboiler is controlled to be 150 ℃, and the gas-phase chlorobenzene after heat exchange with the chlorobenzene is combined with condensed chlorobenzene at the top of the solvent removal tower to be used as a circulating solvent.
[ example 2 ]
Phosgenation reaction: 10t/h MDA and 80t/h chlorobenzene are mixed in advance and react with 150t/h phosgene to generate a phosgenation reaction solution. The phosgenation reaction is divided into two steps of cold and hot reaction, wherein the cold reaction temperature is 120 ℃, the pressure is 3MPaA, and the reaction time is 4min; the thermal reaction temperature was 150℃and the pressure was 0.6MpaA, and the reaction residence time was 3h. The phosgene concentration in the reaction solution was 0.1%.
Separation of partition walls: the reaction liquid is sent to a partition tower for separation and purification, a middle partition plate which is vertically arranged is arranged in the middle of the partition tower, the partition tower is divided into a feed pre-separation side and a side line extraction side, the lower part of the partition plate is a public stripping section, the upper part of the partition plate is a public rectifying section, the bottom of the middle partition plate is provided with a rotary adjusting device which is radially adjusted, and the top of the middle partition plate is provided with a reflux adjusting device. After the reaction liquid is separated and purified by a partition tower, light components such as phosgene, HCl, halogenated hydrocarbon substances and the like are extracted from the tower top, a gaseous solvent chlorobenzene is extracted from the tower, and a tower kettle concentrated solution is sent to a solvent removal unit. The tower tray of the dividing wall tower adopts a fixed valve type, the height of the middle partition plate is 12m, the height of the lower public stripping section is 8m, the height of the upper public rectifying section is 8m, the cross-sectional area ratio of the feed pre-separation section to the side line extraction side is 1:2, the mass ratio of the reflux flow of the pre-separation section to the feed flow is 1:30, the temperature of the tower bottom of the dividing wall tower is 210 ℃, and the tower pressure is 0.3MPaA.
And (3) solvent removal: and (3) delivering the concentrate of the separation wall tower kettle into a solvent removal tower for further reduced pressure rectification to obtain MDI, wherein the temperature of the solvent removal tower kettle is 180 ℃, the pressure is 50KPaA, gas-phase chlorobenzene extracted from the side line of the separation wall tower is used as a heat source of a reboiler of the solvent removal tower kettle, the outlet temperature of the reboiler is controlled to be 190 ℃, and the gas-phase chlorobenzene after heat exchange with the chlorobenzene is combined with condensed chlorobenzene at the top of the solvent removal tower to be used as a circulating solvent.
[ example 3 ]
Phosgenation reaction: 10t/h MDA and 20t/h chlorobenzene are mixed in advance and react with 10t/h phosgene to generate a phosgenation reaction solution. The phosgenation reaction is divided into two steps of cold and hot reaction, wherein the cold reaction temperature is 70 ℃, the pressure is 0.5MPaA, and the reaction time is 2min; the thermal reaction temperature was 100℃and the pressure was 0.3MpaA, and the reaction residence time was 1h. The phosgene concentration in the reaction solution was 8%.
Separation of partition walls: the reaction liquid is sent to a partition tower for separation and purification, a middle partition plate which is vertically arranged is arranged in the middle of the partition tower, the partition tower is divided into a feed pre-separation side and a side line extraction side, the lower part of the partition plate is a public stripping section, the upper part of the partition plate is a public rectifying section, the bottom of the middle partition plate is provided with a rotary adjusting device which is radially adjusted, and the top of the middle partition plate is provided with a reflux adjusting device. After the reaction liquid is separated and purified by a partition tower, light components such as phosgene, HCl, halogenated hydrocarbon substances and the like are extracted from the tower top, a gaseous solvent chlorobenzene is extracted from the tower, and a tower kettle concentrated solution is sent to a solvent removal unit. The tower tray of the dividing wall tower adopts a fixed valve type, the height of the middle partition plate is 4m, the height of the lower public stripping section is 2m, the height of the upper public rectifying section is 2m, the cross-sectional area ratio of the feed pre-separation section to the side line extraction side is 1:0.8, the mass ratio of the reflux flow of the pre-separation section to the feed flow is 1:8, the temperature of the tower bottom of the dividing wall tower is 180 ℃, and the tower pressure is 0.15MPaA.
And (3) solvent removal: and (3) delivering the concentrate of the separation wall tower kettle into a solvent removal tower for further reduced pressure rectification to obtain MDI, wherein the temperature of the solvent removal tower kettle is 150 ℃, the pressure is 5KPaA, gas-phase chlorobenzene extracted from the side line of the separation wall tower is used as a heat source of a reboiler of the solvent removal tower kettle, the outlet temperature of the reboiler is controlled to 160 ℃, and the gas-phase chlorobenzene after heat exchange with the chlorobenzene is combined with condensed chlorobenzene at the top of the solvent removal tower to be used as a circulating solvent.
[ example 4 ]
Phosgenation reaction: 10t/h MDA and 50t/h chlorobenzene are mixed in advance and react with 50t/h phosgene to generate a phosgenation reaction solution. The phosgenation reaction is divided into two steps of cold and hot reaction, wherein the cold reaction temperature is 110 ℃, the pressure is 2.5MPaA, and the reaction time is 4min; the thermal reaction temperature was 140℃and the pressure was 0.5MpaA, and the reaction residence time was 2h. The phosgene concentration in the reaction solution was 1%.
Separation of partition walls: the reaction liquid is sent to a partition tower for separation and purification, a middle partition plate which is vertically arranged is arranged in the middle of the partition tower, the partition tower is divided into a feed pre-separation side and a side line extraction side, the lower part of the partition plate is a public stripping section, the upper part of the partition plate is a public rectifying section, the bottom of the middle partition plate is provided with a rotary adjusting device which is radially adjusted, and the top of the middle partition plate is provided with a reflux adjusting device. After the reaction liquid is separated and purified by a partition tower, light components such as phosgene, HCl, halogenated hydrocarbon substances and the like are extracted from the tower top, a gaseous solvent chlorobenzene is extracted from the tower, and a tower kettle concentrated solution is sent to a solvent removal unit. The tower tray of the dividing wall tower adopts a fixed valve type, the height of the middle baffle plate is 10m, the height of the lower public stripping section is 7m, the height of the upper public rectifying section is 7m, the cross-sectional area ratio of the feed pre-separation section to the side line extraction side is 1:1.8, the mass ratio of the reflux flow of the pre-separation section to the feed flow is 1:25, the temperature of the tower kettle of the dividing wall tower is 200 ℃, the tower pressure is 0.25MPaA, and the concentration of chlorobenzene in the concentrated solution of the tower kettle is 40%.
And (3) solvent removal: and (3) delivering the concentrate of the separation wall tower kettle into a solvent removal tower for further reduced pressure rectification to obtain MDI, wherein the temperature of the solvent removal tower kettle is 170 ℃, the pressure is 20KPaA, gas-phase chlorobenzene extracted from the side line of the separation wall tower is used as a heat source of a reboiler of the solvent removal tower kettle, the outlet temperature of the reboiler is controlled to be 180 ℃, and the gas-phase chlorobenzene after heat exchange with the chlorobenzene is combined with condensed chlorobenzene at the top of the solvent removal tower to be used as a circulating solvent.
[ example 5 ]
Phosgenation reaction: 10t/h MDA and 35t/h chlorobenzene are mixed in advance and react with 35t/h phosgene to generate a phosgenation reaction solution. The phosgenation reaction is divided into two steps of cold and hot reaction, wherein the cold reaction temperature is 100 ℃, the pressure is 1.5MPaA, and the reaction time is 3min; the thermal reaction temperature was 120℃and the pressure was 0.4MpaA, and the reaction residence time was 1.5h. The phosgene concentration in the reaction solution was 3%.
Separation of partition walls: the reaction liquid is sent to a partition tower for separation and purification, a middle partition plate which is vertically arranged is arranged in the middle of the partition tower, the partition tower is divided into a feed pre-separation side and a side line extraction side, the lower part of the partition plate is a public stripping section, the upper part of the partition plate is a public rectifying section, the bottom of the middle partition plate is provided with a rotary adjusting device which is radially adjusted, and the top of the middle partition plate is provided with a reflux adjusting device. After the reaction liquid is separated and purified by a partition tower, light components such as phosgene, HCl, halogenated hydrocarbon substances and the like are extracted from the tower top, a gaseous solvent chlorobenzene is extracted from the tower, and a tower kettle concentrated solution is sent to a solvent removal unit. The tower tray of the dividing wall tower adopts a fixed valve type, the height of the middle baffle plate is 8m, the height of the lower public stripping section is 5m, the height of the upper public rectifying section is 5m, the cross-sectional area ratio of the feed pre-separation section to the side line extraction side is 1:1.2, the mass ratio of the reflux flow of the pre-separation section to the feed flow is 1:15, the temperature of the tower kettle of the dividing wall tower is 190 ℃, the tower pressure is 0.2MPaA, and the concentration of chlorobenzene in the concentrated solution of the tower kettle is 30%.
And (3) solvent removal: and (3) delivering the concentrate of the separation wall tower kettle into a solvent removal tower for further reduced pressure rectification to obtain MDI, wherein the temperature of the solvent removal tower kettle is 160 ℃, the pressure is 12KPaA, gas-phase chlorobenzene extracted from the side line of the separation wall tower is used as a heat source of a reboiler of the solvent removal tower kettle, the outlet temperature of the reboiler is controlled to 170 ℃, and the gas-phase chlorobenzene after heat exchange with the chlorobenzene is combined with condensed chlorobenzene at the top of the solvent removal tower to be used as a circulating solvent.
Comparative example 1
Phosgenation the reaction: the same procedure as in example 3 was followed for the phosgenation reaction.
And (3) light component removal: and (3) delivering the reaction solution into a conventional rectifying tower to remove light components such as phosgene, HCl and the like by rectification, wherein the temperature of a tower kettle is 140 ℃, and the pressure is 120KPaA.
Purifying a crude product: and (3) delivering the concentrated solution in the rectifying tower kettle to a solvent removal tower for further reduced pressure rectification to obtain MDI, condensing the gas phase component at the tower top, and recycling the chlorobenzene which is taken out as a solvent, wherein the temperature in the solvent removal tower kettle is 140 ℃, and the pressure is 2KPaA.
Comparative example 2
Phosgenation reaction: the same procedure was followed for the phosgenation reaction as in example 4.
And (3) light component removal: and (3) delivering the reaction solution into a conventional rectifying tower to remove light components such as phosgene, HCl and the like by rectification, wherein the temperature of a tower kettle is 140 ℃, and the pressure is 120KPaA.
Purifying a crude product: and (3) delivering the concentrated solution in the rectifying tower kettle to a solvent removal tower for further reduced pressure rectification to obtain MDI, condensing the gas phase component at the tower top, and recycling the chlorobenzene which is taken out as a solvent, wherein the temperature in the solvent removal tower kettle is 140 ℃, and the pressure is 2KPaA.
[ comparative example 3 ]
Phosgenation reaction: the same procedure as in example 5 was followed for the phosgenation reaction.
And (3) light component removal: and (3) delivering the reaction solution into a conventional rectifying tower to remove light components such as phosgene, HCl and the like by rectification, wherein the temperature of a tower kettle is 140 ℃, and the pressure is 120KPaA.
Purifying a crude product: and (3) delivering the concentrated solution in the rectifying tower kettle to a solvent removal tower for further reduced pressure rectification to obtain MDI, condensing the gas phase component at the tower top, and recycling the chlorobenzene which is taken out as a solvent, wherein the temperature in the solvent removal tower kettle is 140 ℃, and the pressure is 2KPaA.
The halogenated hydrocarbon contents in the produced solvent, the condensed solvent and the recycled solvent in the above examples and comparative examples were analyzed and tested, and the test results are shown in table 1.
Table 1, performance data of examples and comparative examples
Figure BDA0004034804970000141
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and additions may be made to those skilled in the art without departing from the method of the present invention, which modifications and additions are also to be considered as within the scope of the present invention.

Claims (9)

1. A circulating solvent for preparing MDI by phosgenation, characterized in that the mass content of halogenated hydrocarbon substances in the circulating solvent is 0.1-200ppm, preferably 1-150ppm, more preferably 10-100ppm;
preferably, the halogenated hydrocarbon substance refers to methane or ethylene substance substituted by chlorine and/or bromine, and comprises carbon tetrachloride, trichlorobromomethane, dichlorobromomethane, tetrachloroethylene, dichloroethylene, trichloroethylene and dibromoethylene substance.
2. The circulating solvent according to claim 1, characterized in that the circulating solvent is one or more of chlorinated aromatic hydrocarbon, dialkyl terephthalate, diethyl phthalate, toluene and xylene, more preferably one or more of chlorobenzene, dichlorobenzene, toluene and xylene, still more preferably chlorobenzene.
3. A method for purifying a circulating solvent for phosgenation to produce MDI, the method comprising the steps of:
a. phosgenation reaction: carrying out phosgenation reaction on diphenyl methane diamine and phosgene under an inert solvent to generate photochemical reaction liquid;
b. separation of partition walls: separating and purifying the reaction liquid in a partition tower, extracting light components containing phosgene and HCl from the tower top, extracting a gaseous solvent from the tower as an extracted solvent, and delivering a tower kettle concentrated solution to a solvent removal unit;
c. and (3) solvent removal: c, further distilling the tower kettle concentrated solution from the step b in a solvent removal tower under reduced pressure, wherein condensate on the top of the solvent removal tower is used as a condensing solvent;
the inert solvent in the step a is recycled, and the mass content of the halogenated hydrocarbon substance in the recycled solvent is 0.1-200ppm, preferably 1-150ppm, more preferably 10-100ppm;
the recycled solvent includes the produced solvent and the condensed solvent.
4. The purification method according to claim 3, wherein the produced solvent in the step b is used as a heat source of a reboiler of a solvent removal tower, and is combined with a condensed solvent at the top of the solvent removal tower as a circulating solvent after heat exchange;
preferably, the inert solvent in the step a is preferably one or more of chlorinated aromatic hydrocarbon, dialkyl terephthalate, diethyl phthalate, toluene and xylene, more preferably one or more of chlorobenzene, dichlorobenzene, toluene and xylene, and still more preferably chlorobenzene;
preferably, the halogenated hydrocarbon substance refers to methane or ethylene substance substituted by chlorine and/or bromine, and comprises carbon tetrachloride, trichlorobromomethane, dichlorobromomethane, tetrachloroethylene, dichloroethylene, trichloroethylene, dibromoethylene and the like.
5. A purification process according to claim 3, wherein in step a the mass ratio of MDA to inert solvent addition is 1 (1-8), preferably 1 (2-5);
preferably, the mass ratio of MDA to phosgene added in step a is 1 (1-15), preferably 1 (2-5).
6. The purification method according to claim 3, wherein the phosgenation reaction in the step a is divided into two steps of cold and hot reactions, wherein the cold reaction temperature is 60-120 ℃, the pressure is 0.2-3.0MPaA, and the reaction time is within 5min; the thermal reaction temperature is 90-150 ℃, the pressure is 0.2-0.6MpaA, and the reaction residence time is 0.5-3h;
preferably, the concentration of phosgene in the photochemical reaction solution in the step a is 0.1-10% and the concentration of the solvent is 30-90%.
7. A purification process according to claim 3, wherein in step b a vertical partition is provided in the middle of the dividing wall column, the column type is one of a tray type, a packed column type or a combination thereof, and in order to reduce tray blockage, the trays are preferably of a fixed valve type;
preferably, in the step b, a partition tower is divided into a pre-separation section and a side line extraction section by a partition plate in the middle of the partition tower, the lower part of the partition plate is a public stripping section, and the upper part of the partition plate is a public rectifying section;
preferably, the intermediate partition has a height of 2-12m, preferably 4-8m; the height of the public stripping section is 1-8m, preferably 2-5m;
preferably, the bottom of the middle partition plate is provided with a radial adjusting rotary adjusting device for controlling the sectional area ratio of the bottom of the pre-separation section to the side line extraction section to be 1 (0.5-2), more preferably 1: (0.8-1.8); the material flow ratio is 1: (5-30);
preferably, after the reaction liquid is separated and purified by a partition tower, most of halogenated hydrocarbon substances are carried out from the gas phase light components at the top of the tower.
8. The purification method according to any one of claims 3 to 7, wherein the extraction solvent in the column in the step b is gas phase extraction, the mass content of halogenated hydrocarbon substances in the extraction solvent is 0.1 to 300ppm, and the mass flow rate of the extraction solvent is 30 to 60 percent of the total solvent flow rate;
preferably, the temperature of the isolation tower kettle in the step b is 170-210 ℃ and the pressure is 0.1-0.3Mpa A.
9. The purification process according to any one of claims 3 to 8, wherein the solvent removal column in step c is one of a tray column, a packed column or a combination thereof, and the solvent is recovered by condensing at the top of the column;
preferably, the temperature of the solvent removal tower kettle in the step c is 120-180 ℃, preferably 130-170 ℃; the pressure is 2-50KPaA, preferably 5-20KPaA;
preferably, the condensing temperature of the top of the solvent removal tower in the step c is 40-90 ℃, preferably 60-80 ℃; the content of halogenated hydrocarbon substances in the condensed solvent at the top of the tower is 0.1-50ppm;
preferably, the solvent extracted from the tower in the step b is used as a heat source of a reboiler of the solvent removal tower in the step c, and the outlet temperature of the reboiler is controlled to be 140-180 ℃;
preferably, the extracted solvent is combined with the condensed solvent at the top of the solvent removal tower after heat exchange to be used as a circulating solvent, and the circulating solvent is returned to the step a for phosgenation.
CN202310003120.6A 2023-01-03 2023-01-03 Circulation solvent for preparing MDI by phosgenation and purification method thereof Pending CN116217439A (en)

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