EQUIPMENT AND METHODS FOR SEPARATING MIXTURES CONTAINING THERMALLY INSTABILITIES

Abstract

The invention relates to an apparatus and a method based on such apparatus for the continuous purification of a high-boiling-point thermally unstable compound from a more volatile impurity by continuous selective distillation of a medium fed into the apparatus. The apparatus is a column-like device containing at least three zones arranged in series: a mass transfer zone, an evaporation zone, and a cooling zone, wherein the evaporation zone is a membrane evaporator with gravity flow directed vertically with a fixed residence time of the thermally unstable mixture in the evaporator zone. In particular, examples of high-boiling-point thermally unstable media are mixtures of aromatic polyamines, for example, mixtures of methylenediphenylamine (MDA) and its higher homologues; as well as mixtures of aromatic polyisocyanates, for example, mixtures of methylenediphenylisocyanate (MDI) and its higher homologues.The method is based on a device that makes it possible to obtain the aforementioned purified medium with an excess content of more volatile solvents, such as chlorinated aniline or benzene, not exceeding a few tens of ppm, while the residence time of the medium being evaporated in the evaporator zone is no longer than 100 seconds, without significantly altering the color of the heat-unstable medium.

Description

[0001] DEVICE AND METHOD FOR SEPARATION OF A MIXTURE CONTAINING THERMOLABILITY SUBSTANCES

[0002] Field of technology to which the invention relates

[0003] The invention relates to a device for separating a mixture containing at least one heat-labile substance. In particular, the invention relates to a column-type device consisting of at least three successive sections located one above the other and connected by a fluid medium: a mass-exchange, an evaporation and a cooling section. The invention also relates to a method for separating a mixture containing at least one heat-labile substance, in particular to a method for separating polyamines and polyisocyanates. In particular, a device and method are proposed for continuously purifying high-boiling heat-labile compounds from more volatile impurities by selective continuous distillation of a medium fed to the device.

[0004] State of the art

[0005] Separation of mixtures containing heat-labile substances, i.e. substances that are subject to thermal destruction, is one of the most common processes in industry. In this case, both the separation processes themselves, i.e. obtaining two or more different products, and the purification processes, i.e. removing unwanted impurities from the initial medium, are implemented in industry. From here on, separation will also mean purification processes. Examples of separation processes for heat-labile mixtures are: separation of water-glycol solutions, separation of high-boiling aromatic compounds and pharmacological substances, purification of polyamines and polyisocyanates from unreacted initial compounds or solvents. It is the sensitivity of heat-labile substances to temperature changes that leads to a number of limitations associated with the design features of the devices used and their operating modes.

[0006] In accordance with the state of the art, most processes of separation of media by the method of continuous distillation are carried out using evaporators, the design of which assumes prolonged heating and stay of the evaporated medium in the evaporator zone and outside its perimeter under significant temperature loads. Examples of such evaporators are evaporators with a steam space or waste heat boilers, vertical tubular evaporators of volumetric boiling and thermosyphons. The listed evaporators in combination with the volume of the space for accumulation of the lower product in the lower section of the distillation column lead to the presence of high-boiling media under temperature loads in periods from tens of minutes to several hours.

[0007] One of the key representatives of heat-labile media are mixtures of polyamines and polyisocyanates. Raw (poly)diaminodiphenylmethane (pMDA) is an unrefined mixture of di- and polyamines obtained as a result of the synthesis of di- and polyamines by the condensation of aniline and formaldehyde. Later, pMDA is used as a feedstock in the production of polyisocyanates (pMDI) by phosgenation of pMDA. The noted media are highly sensitive even to low temperature loads, not exceeding 200-250 °C, and with prolonged heating undergo irreversible structural changes associated with the processes of thermal destruction and resinification.For the phosgenation stage, it is critical that the initial PMDA does not contain water, which promotes the formation of a corrosive environment and reduces the service life of the equipment, and aniline, which promotes the accumulation of phenyl isocyanate, which is difficult to separate from the mixture of di- and polyisocyanates and is a poison for subsequent processes of obtaining polyurethane compositions.

[0008] A volatile component of a distilled thermolabile mixture may be a component with a higher volatility relative to the closest thermolabile component in terms of volatility under the conditions of the distillation. The most common thermolabile media, such as mixtures of pMDA and pMDI, contain the volatile components aniline and mono- or dichlorobenzene, respectively, having a relative volatility in mixtures of more than 3 units at a residual pressure of less than 20 mbar.

[0009] Thus, document US7312362 (published 25.12.2007 by Bayer Material Science AG [DE]) discloses various variations of the processes of separation of di- and polyamines by distillation. The document proposes to carry out the final purification of the target components from aniline and water in column apparatuses, where the use of sharp water vapor is proposed as a heating agent. The separation processes include preliminary evaporation, distillation and cooling. The disadvantages of this method are the high final proportion of water and aniline impurities in the target product - more than 100 ppm of water, which, as noted above, adversely affect the process of further phosgenation of the amine medium.

[0010] Document WO2019115213 (published 20.06.2019 by Sulzer Chemtech [CH]) describes a process and device for distilling a highly thermostable mixture of di- and polyisocyanates. Thus, according to the proposed solution, the evaporator of the distillation column is an evaporator with a falling film. However, the implementation of this method requires forced circulation of the bottom product and a long residence time of the medium, which accumulates in the lower section of the column, at its boiling temperature.

[0011] The authors of DE202013003950 (published 25.06.2013 by Huntsman LLC) propose to perform final purification of PMDA in a column apparatus using additional purging of volatile components with a stream of heated nitrogen. This solution has all the above-mentioned disadvantages, and, in addition, the load on the vacuum-creating unit is increased when pumping the purge gas.

[0012] Thus, the problem of organizing the process of separating mixtures containing heat-labile substances, which allows achieving a high degree of purity of the separation products in the absence of a negative thermal decomposition process, remains relevant.

[0013] The essence of the invention

[0014] The objective of the present invention is to organize a process for separating mixtures containing high-boiling, heat-labile substances, characterized by the absence of a negative thermal decomposition process.

[0015] The technical result consists in obtaining separation products containing high-boiling, heat-labile substances with a residual content of volatile substances of no more than 100 ppm and a small change in the original color.

[0016] This technical problem is solved and the achievement of the technical result is ensured by using, in the process of separating mixtures containing heat-labile substances, a device that includes a mass-exchange section with an inlet for the mixture, an evaporation section located under the mass-exchange section and connected to it via a fluid medium, and a cooling section located under the evaporation section and connected to it via a fluid medium with an outlet for a liquid flow containing a heat-labile substance, wherein the evaporation section contains a vertical film evaporator with a distribution device located in its upper part for forming a film on the inner surface of the vertical film evaporator from the mixture coming from the mass-exchange section, wherein the vertical film evaporator is designed with the possibility of heating the film with the formation of a vapor phase of the mixture and a liquid flow containing a heat-labile substance,wherein the distribution device is additionally configured to allow the vapor phase of the mixture to pass through it from the vertical film evaporator into the mass exchange section, wherein the mass exchange section is configured to provide contact between the mixture introduced into the mass exchange section and the vapor phase of the mixture coming from the evaporation section, wherein the vertical film evaporator is configured to move the liquid flow containing the thermolabile substance from the evaporation section into the cooling section for cooling it.

[0017] Without wishing to be bound by a particular theory, the author of the present invention believes that the use of the device described above reduces the residence time of heat-labile substances in the high-temperature zone of the evaporation section, which makes it possible to avoid undesirable processes of their decomposition, but at the same time makes it possible to achieve a low content of undesirable volatile impurities (water, unreacted starting compounds, reaction by-products, etc.) in the separation product.

[0018] Effective separation of mixtures containing high-boiling heat-labile substances, characterized by the absence of a negative thermal decomposition process, is achieved by sequentially arranging three key sections - a mass-exchange section, in which the separation of the supplied mixture occurs due to mass exchange between the liquid and vapor phases of the mixture, an evaporation section, in which the vapor phase is generated from a film of heat-labile liquid, which then enters the mass-exchange section, and a cooling section, which limits the residence time of the medium at a high temperature after the evaporation section.

[0019] Effective separation of mixtures is achieved by mass-exchange processes occurring in the mass-exchange section of the device between the descending flow of feed liquid supplied to the device (irrigation flow in the upper section of the mass-exchange section) and the ascending flow of saturated steam generated in the evaporation section. In this case, the vertically oriented film evaporator in the evaporation section ensures gravity movement of the film along its inner surface, which ensures the residence time of thermolabile substances in the zone of elevated temperatures, excluding their thermal decomposition. For amine and isocyanate media, the residence time of the medium in the evaporation section does not exceed 100 sec.

[0020] According to one embodiment of the present invention, the film evaporator comprises vertically oriented tubes. Preferably, the length of the tubes is:

[0021] L[M]=T_Film*wcp, where i Film is the average residence time of the film flow on the inner surface of the heat exchange tubes, ranging from 1 to 100 seconds, wcp is the average speed of gravity flow of the film along the inner surface of the tubes.

[0022] Preferably, the length of the tubes is selected to provide a residence time of the film flow i Film from 20 to 80 seconds. More preferably, the length of the tubes is selected to provide a residence time of the film flow i Film from 30 to 60 seconds.

[0023] In this case, the distribution device is designed with the possibility of forming a film on the inner surface of the film evaporator tubes.

[0024] According to one embodiment of the present invention, the distribution device for forming a film from the mixture coming from the mass exchange section on the inner surface of the vertical film evaporator is a blind plate.

[0025] The device according to the present invention can be preferably used for separating a mixture of di- or polyamines or di- or polyisocyanates. Preferably, the mass transfer section is a packed column with an internal contact device based on mesh or sheet structured packing elements.

[0026] Preferably, the internal contact device has a specific surface area of ​​400-1000 m 2 / m 3 and the proportion of volumetric voids is more than 80%.

[0027] In the device according to the present invention, the cooling section is or includes an inclined gravity-flow tubular heat exchanger of the "pipe in pipe" type or a heat exchanger-recuperator. Preferably, the gravity-flow tubular heat exchanger has an angle of inclination of the heat exchanger axis to the overall horizontality of the device of 1 -90°.

[0028] Another aspect of the present invention, providing for the achievement of the above-mentioned technical result, is a method for separating a mixture containing at least one heat-labile substance, using a device for separating a mixture, comprising a mass-exchange section, located under the mass-exchange section and connected thereto via a fluid medium, an evaporation section, comprising a vertical film evaporator, and a cooling section located under the evaporation section and connected thereto via a fluid medium, wherein the mixture containing at least one heat-labile substance is introduced into the mass-exchange section, after which it enters the vertical film evaporator of the evaporation section with the formation of a film, which moves by gravity along the inner surface of the film evaporator under the action of gravity,wherein the gravity-flowing film of the mixture in the vertical film evaporator is heated to obtain a vapor phase of the mixture and a liquid stream containing a thermolabile substance, wherein the vapor phase of the mixture rises into the mass exchange section for mass exchange due to contact between the vapor phase of the mixture and the mixture introduced into the mass exchange section, wherein the liquid stream containing a thermolabile substance moves from the evaporation section into the cooling section, where it is cooled and removed as a separation product containing a thermolabile substance.

[0029] Preferably, the method is used to separate a mixture of di- or polyamines or di- or polyisocyanates. Preferably, the method is used to separate (poly)diaminodiphenylmethane (pMDA) or polydiaminodiphenylisocyanates (pMDI) to obtain two or more streams of pMDA or pMDI.

[0030] According to the present invention, the residence time of the film flow in the vertical film evaporator is from 1 to 100 seconds.

[0031] Description of figures

[0032] Fig. illustrates the device according to the invention, where I is a mass-exchange section, II is an evaporation section, III is a cooling section, 1 is a vapor phase outlet, 2 is a mist separator or a strengthening section of the mass-exchange part of the device, 3 is a mixture inlet for separation / purification, 4 is a collector-distributor of vapor-liquid flows, 5 is a contact device, 6 are support elements, 7 is a distributor for the vapor and liquid phase, 8 is a gravity-flow vertically oriented film evaporator, 9 is a heat carrier, 10 is a cooler, 11 is an outlet of separation products.

[0033] Detailed disclosure of the invention

[0034] The main aspects of the present invention are disclosed in detail below.

[0035] The device according to the present invention is a column-type device consisting of at least three successive sections: mass exchange (I), evaporation (II) and cooling (III).

[0036] The mass-exchange section (I) of the column device is a section of the column into which a mixture containing heat-labile substances is fed for separation through the inlet 3, equipped with an internal contact device 5 (ICD) and support elements 6 for its fastening. The contact devices 5 of the mass-exchange part can be selected from any contact devices known from the prior art, including mass-exchange trays, structured packed elements, etc. It is most preferable to use mesh or sheet structured packed elements with a specific surface area of ​​400-1000 m as a contact device. 2 / m 3and a proportion of volumetric voids of more than 80%, since this type of contact device has an optimal number of separation stages per unit of column height, as well as an acceptable hydraulic pressure drop under normal distillation process conditions at low residual pressure.

[0037] Depending on the physicochemical properties and vapor-liquid equilibria of the components of the mixture being separated, the material design of the VKU and the optimal number of separation stages of the mass-exchange part of the device are different. For example, the optimal number of stages for separating a mixture of polyamines with water and aniline or a mixture of polyisocyanates with a chloroaromatic solvent, such as monochlorobenzene, is from 3 to 20, more preferably from 4 to 10, and even more preferably from 5 to 8; in this case, the optimal material design of the VKU is austenitic stainless steel, such as AISI304 / 316.

[0038] Optionally, for intensification and organization of optimal operation of the device, the mass transfer part of the column device can be equipped with a drip separator 2 and a collector-distributor 4. The drip separator 2 is any device available for the purpose of preventing drip entrainment, for example, a structured packing element with a specific surface area of ​​100-2000 m 2 / m 3 .

[0039] Optionally, the mist separator 2 can be replaced or modified to organize a strengthening section of the column and reduce the proportion of high-boiling substances in the overhead product flow. However, even without significant additional changes, in the case of feeding the device with an amine or isocyanate medium, the noted section can have an affinity for mass exchange between the retained drops and the rising vapor phase of more volatile components of the medium.

[0040] The vapor phase can be removed through outlet 1, located in the upper section of the mass transfer section.

[0041] The evaporation section (II) of the device is a gravity-flow vertically oriented film evaporator 8 located below the mass-exchange section. Film evaporator 8 is of the single-pass tube evaporator type, close in geometric characteristics to tubular heat exchangers that meet international TEMA standards. The vapor phase for the mass-exchange process is generated on the inner surface of the vertically oriented tube bundle in the film mode. Unlike typical volumetric boiling devices, in which the vapor phase is generated in the volume of liquid in the form of gas bubbles, in the film mode the equilibrium vapor phase is formed above the surface of a sequentially heated thin film flowing down the vertical surface. In this case, the movement of the liquid and vapor phase of the evaporator is carried out countercurrently.

[0042] The gravity vertically oriented film evaporator 8 according to the present invention is a film evaporator without forced circulation of the mixture. Such a vertically oriented film gravity evaporator ensures a fixed residence time of the mixture containing heat-labile substances.

[0043] The evaporation section is equipped with a distribution device 7, which is any available distribution device for the described level of technology and allows for uniform distribution of the liquid phase on the inner surface of the evaporator or evaporator tubes. It is most preferable to use distribution devices for direct irrigation of the wetted perimeter of the tubes, in which the liquid entering the evaporator wets the tubes due to flow under the action of gravity forces.

[0044] The film mode in the vertical tubular evaporator 8 according to the invention is set arbitrarily at a certain irrigation density due to the natural flow of liquid medium through the distribution device 7 onto the inner surface of the evaporator 8, in particular onto the inner surface of the evaporator tubes.

[0045] In the evaporator 8 according to the invention, no forced means are used to create and / or maintain a film regime on the inner surface of the evaporator or the bundle of evaporator tubes, such as, for example, pumps, combs, etc. It is this feature that is defined in the present invention as gravity flow. In the evaporator 8, no means are used other than the natural barrier of the distributor 7, which allows for the formation of a sufficient irrigation density for the stability of the film regime.

[0046] The advantage of such an evaporator is the low residence time of the mixture containing heat-labile substances on the surface of the heat exchange tubes, which is limited by the time of gravity movement of the liquid film from the distribution element of the evaporator to the next section of the column apparatus - the cooling section. Another advantage of the described type of evaporator is the absence of the need to use a high-temperature expensive circulation pump, which is often used to organize the separation process, but, at the same time, is the most vulnerable zone for depressurization and contact of the mixture containing heat-labile and / or highly reactive substances with oxygen in the ambient air.

[0047] It is obvious to a specialist in this field of technology that the specific geometric parameters of the described device depend on the characteristics of the mixtures being separated. In this case, to describe the geometric characteristics of the evaporative part of the device, it is relevant to use the noted set of formulas:

[0048] (1) Re=(4*Gop [kg / (m*s)]) / (c [Pa*s]), where Re is the Reynolds number; Gop is the irrigation density calculated using formula (2); c is the dynamic viscosity of the separated mixture passing through the evaporator.

[0049] (2) G_op=(G (Nl liq) [kg / (m*s)]) / (£ [Ptr] [m]), where G (Nl liq) is the amount of liquid absorbed for evaporator irrigation; Ptr is the internal perimeter of the wetted heat exchange tube of the evaporator. where Зср is the average thickness of the liquid film formed on the inner surface of the heat exchange tubes, р is the density of the separated medium passing through the evaporator (kg / m 3 ); g=9.8 - free acceleration coefficient. where w aver is the average speed of gravity flow of the film along the inner surface of the pipes [m / sec].

[0050] (5) T_Film=(L [M]) / WCP, where L is the length of the heat exchange tubes of the film evaporator, i Film is the average residence time of the liquid on the inner surface of the heat exchange tubes.

[0051] When feeding the device with a polyamine or polyisocyanate medium, the preferred range of the Reynolds number is 0.1-10000, more preferably 1-1000, even more preferably 1-50.

[0052] The length of the pipes can be selected from the standard size range of heat exchangers of the TEMA type BEM standards. When feeding the device with an amine or isocyanate medium, the preferred length of the pipes is such that the time of gravity movement of the liquid film is in the range from 1 to 100 sec, preferably from 20 to 80 sec, more preferably from 30 to 60 sec.

[0053] Heating of the film evaporator of the proposed design can be carried out by any available and effective heat carrier 9, for example, water vapor of the appropriate pressure or a high-boiling organic heat carrier, for example, organosilicon heat carriers or heat carriers based on polyalkylbenzenes, with suitable thermophysical characteristics.

[0054] The third section (III) of the device is a cooler 10 for the flow containing heat-labile substances, exiting from the lower section of the film evaporator 8. The cooler 10 can be any available cooling device from the prior art, including, but not limited to: gravity inclined tubular heat exchangers, heat exchangers-recuperators. A suitable example of such a device can be an inclined tubular heat exchanger of the "pipe in pipe" type, with an axis inclination relative to the general horizontal in the range of 1-90 degrees, more preferably 15-60 degrees. The advantage of this section is that it limits the stay of the flow containing heat-labile substances at a high temperature in the perimeter of the film evaporator 8, which reduces the stay time of the heat-labile medium at a high temperature to the time of gravity movement of the flowing film along the inner surface of the tubes of the evaporator 8.This ensures that the risk of thermal destruction of heat-labile substances is minimized and, accordingly, the physical and mechanical properties and color index of the medium are preserved.

[0055] The flow exiting the lower part of the device can be directed as a feedstock for further chemical transformations or sent to the production of a commercial form.

[0056] Condensation of the vapors formed in the upper part of the device can be carried out by any method known from the state of the art. The most preferred method of condensation is the method of condensing the vapor phase on the outer surface of a horizontally oriented tube bundle of a shell-and-tube heat exchanger. The advantage of this method is the low hydraulic pressure drop in the vapor phase condensation system. A specific example of separating a mixture containing thermolabile substances is the separation of di- and polyamines, water and aniline. This description is given only as an example and does not limit it, as is obvious to a person skilled in the art.

[0057] The feed of the device (input 3) is preferably fed with a crude mixture of di- and polyamines (pMDA) mixed with water and aniline. The proportion of water in the initial raw pMDA may be 0-15 wt.%, more preferably 0-8 wt.%. In order to reduce the steam load of the mass-exchange section (I) of the device, it is possible to pre-dry the raw pMDA by any method available in the prior art. The most preferred method of pre-drying is a single-stage evaporation of the mixture in an evaporator-separator (flash), where under mild conditions at a temperature of up to 150°C and a pressure of at least 200 mbar it is possible to remove a significant proportion of water from the mixture in the form of an evaporated water-aniline azeotrope. The proportion of aniline in the crude mixture may be 0-60 wt.%, more preferably 0-30 wt.%. The distillation process of the mixture of di- and polyamines is carried out at a residual pressure in the range of 1-50 mbar, more preferably 2-20 mbar, even more preferably 3-10 mbar.The temperatures of the upper and lower sections of the mass-exchange section (I) are set in accordance with the oligomeric composition of the polyamines, the temperature of the inlet stream of the raw material and the requirement for the extraction of the components of the oligomeric composition. The temperature of the evaporation section (II), depending on the oligomeric composition of the polyamines, is 200-280°C, more preferably 220-250°C. The temperature of the cooling section (III) is set sufficient to cool the amine medium to a temperature of no more than 150°C, more preferably no more than 100-120°C. Due to the high viscosity of the resulting medium, the amine medium is stored before final transportation at a temperature of no lower than 60-100°C.

[0058] The achieved residual content of volatile components is individual for specific thermolabile media and components extracted from them. More specifically, the capabilities of the device are disclosed in examples using the example of distillation of such thermolabile media as PMDA and PMDI in a mixture with aniline and monochlorobenzene, respectively.

[0059] The achieved improvement of color and viscosity of thermolabile products output from the lower section of the device (through output 11) is individual for a specific thermolabile medium supplied to power the device. Due to the fact that the described characteristics for thermolabile media are a function of time at specific temperature stresses, it is obvious that the described device with a short contact time allows to a greater extent to avoid negative results of thermal destruction.

[0060] More specifically, the capabilities of the device are disclosed in examples using the example of distillation of such heat-labile media as PMDA and PMDI in a mixture with aniline and monochlorobenzene, respectively.

[0061] Examples of the invention

[0062] Methods of analysis:

[0063] 1. The mass fractions of oligomers and aniline in the pMDA samples were determined by liquid chromatography (HPLC) on an Agilent 1260 Infinity II liquid chromatograph equipped with a 1260 DAD WR diode array detector and a Kinetex C18, 250^4.6, 5 μm, 100 A chromatographic column. The samples were pre-dissolved in acetonitrile with the addition of DMSO. The calculation was performed using the absolute calibration method.

[0064] 2. The residual water content in the PMDA samples was determined by the coulometric Karl Fischer titration method on an automatic titrator according to GOST 24614 "Liquids and gases that do not interact with the Fischer reagent. Coulometric method for determining water". The following reagents were used to determine water: Hydranal-Coulomat AK and Hydranal-Coulomat SK.

[0065] 3. The mass fraction of water in aniline was determined by gas chromatography (GC) on an Agilent 7890A gas chromatograph equipped with a thermal conductivity detector and a DB-FFAP capillary column (30 m x 0.32 mm x 0.25 μm). The mass fraction of water was calculated using the absolute calibration method.

[0066] 4. The viscosity of pMDA was determined on an Anton Paar MCR 102 modular compact rheometer equipped with a PP 25 measuring system (plate / plate type) based on measuring the moment of resistance to rotation of the measuring device plate by the test sample at different rotation speeds (shear rates) and calculating the shear stress and dynamic viscosity. 5. The color of pMDA and pMDI samples was determined using a Lovibond PFXi-995 spectrophotometric colorimeter and a cuvette made of commercial optical glass with an optical path length of 10 mm. The method is based on measuring the color coordinates and color of the samples diluted with a solvent (ethyl acetate for pMDA, monochlorobenzene for pMDI; 20-25% by weight) in the wavelength range from 420 to 710 nm. The result is given in color units of the iodine scale.

[0067] 6. The mass fractions of oligomers in the PMDI samples were determined by HPLC with preliminary derivatization of the samples with methanol and subsequent analysis of the resulting reaction mass on an Agilent 1260 Infinity II liquid chromatograph equipped with a 1260 DAD WR diode array detector and a Kinetex C18, 250^4.6, 5 μm, 100 A chromatographic column. The content of oligomers in the samples was determined by the internal normalization of peak areas.

[0068] 7. The mass fractions of phenyl isocyanate and 4,4'-methylene diphenyl diisocyanate impurities in the MHB distillate samples were determined by GC on an Agilent 7890A gas chromatograph equipped with a flame ionization detector and a DB-35 capillary column (30 m x 0.25 mm x 0.25 μm). The calculation was performed using the absolute calibration method.

[0069] 8. The dynamic viscosity of PMDI was determined by calculation using kinematic viscosity and density.

[0070] 8.1 Kinematic viscosity was determined using capillary viscometers of the VPZh-1 type. The determination consists of measuring the flow time, in seconds, of a certain volume of the test liquid under the influence of gravity at a constant temperature using a calibrated glass viscometer. Kinematic viscosity is the product of the measured flow time and the viscometer constant.

[0071] 8.2 The density of pMDI was determined at a temperature of 25 °C according to GOST 18995.1 “Liquid chemical products. Methods for determining density”.

[0072] Example 1 (according to the invention)

[0073] The device, according to Fig., consisted of a mass-exchange section, which was a tube made of stainless steel AISI316 with an internal diameter of 50 mm, which was filled with structured Sulzer CY packed elements with a total height of the packed part of 0.8 m; a drip-eliminator section, which was a tube made of stainless steel AISI316 with an internal diameter of 50 mm, which was filled with structured Sulzer CY packed elements with a total height of the packed layer of 160 mm; a multi-point liquid distributor with a specific distribution capacity of about 1000 points / m 2 In order to minimize heat loss, local areas of the column body were heated using electric heating to a temperature of about 200°C and insulated with mineral wool.

[0074] The device, according to Fig., consisted of an evaporation section, which was a vertical shell-and-tube heat exchanger with an internal shell diameter of 80 mm and three heat-exchange tubes 28x1.5 mm and 400 mm long, which were heated by feeding hot silicone oil of the Thermolan Lab5 brand. The distribution device was a blind plate, and the film was created by overflowing the liquid through the wetted perimeter of the tubes. The calculated hydrodynamic regime of the film flow was characterized by a Reynolds number of about 30 and a residence time of about 30 sec.

[0075] The device, according to Fig., consisted of a cooling section, which was an inclined gravity-flow heat exchanger of the “pipe in pipe” type with an internal diameter of the inner tube of 25 mm and a total slope relative to the plane of the column placement of 105° into the intertube space, from which silicone oil of the PMS10 brand was supplied.

[0076] The raw pMDA for testing the device was obtained using the method described in Patent CN100422239. The initial color of the raw pMDA was 23 units on the iodine scale. The device was fed with raw pMDA of the following average composition: water content 0.25-0.5 wt.%, aniline content 16.33 wt.%, and the rest was a mixture of MDA and its oligomers. The raw material consumption for feeding was 1.1-1.15 kg / h, and the input flow temperature was maintained at 80°C using electric heating.

[0077] In the upper section of the mass-exchange section of the device, a residual pressure of 6-8 mbar was maintained, and in the evaporation section, a coolant temperature of 245-250°C was maintained. The pressure drop from the upper section of the mass-exchange section to the bottom of the evaporation section was less than 1.5 mbar. The temperature of the outgoing vapors was 55-65°C, and the temperature of the vapors in the lower section was about 235°C.

[0078] At the outlet of the evaporator, the PMDA flow in the amount of 950-1000 g / h was cooled in the cooling section to a temperature of 100-120°C, and then collected in a 12-liter receiving tank equipped with external electric heating.

[0079] The distilled vapor phase in the amount of 100-200 g / h was condensed in a shell-and-tube heat exchanger-condenser on the outer surface of a bundle of finned tubes with a specific surface of about 1 m 2 . A water-glycol coolant with a temperature of 10-25°C was directed into the tube space of the condenser. The condensed aniline fraction was collected in a 12-liter receiving tank equipped with an external jacket, into the annular gap of which the water-glycol coolant was directed after the vapor condenser.

[0080] The accumulated fractions of the upper and lower products were discharged periodically every 4-6 hours of continuous operation of the device, and then samples were taken from the fractions for quantitative and qualitative analysis using the HPLC method.

[0081] The condensate fraction, which was predominantly a mixture of aniline and water, contained up to 0.001 wt.% MDA. The bottom product of the device, purified pMDA, contained less than 10 ppm water and less than 20 ppm aniline. The color of purified pMDA was 43 units on the iodine scale. The viscosity of purified pMDA was 34 mPa*sec at 100 °C.

[0082] Example 2. (according to the invention)

[0083] The device described in Example 1 was used to extract from a flow of 950-980 g / h pMDA of the following average composition: water content less than 10 ppm, aniline content less than 40 ppm, MDA content 48 wt.%, content of higher oligomers of MDA - the rest; MDA flow in an amount of 2-25% of the mass flow of the device feed. The color of the pMDA feed flow according to the iodine scale was 43 units. The temperature of the feed flow was maintained at 150-200°C using electric heating. The calculated hydrodynamic mode of the film evaporator was characterized by a Reynolds number of about 20 and a residence time of pMDA of about 30 sec.

[0084] In the upper section of the mass-exchange section of the device, a residual pressure of 3-4 mbar was maintained, and in the evaporation section, a coolant temperature of 225-235°C was maintained. The pressure drop from the upper section of the mass-exchange section to the bottom of the evaporation section was less than 1.5 mbar. The temperature of the outgoing vapors was 200-210°C, and the temperature of the vapors in the lower section was 220-230°C.

[0085] At the outlet of the evaporator, the PMDA flow in the amount of 850-950 g / h was cooled in the cooling section to a temperature of 120°C, and then collected in a 12-liter receiving tank equipped with external electric heating.

[0086] The distilled vapor phase in the amount of 50-150 g / h was condensed in a shell-and-tube heat exchanger-condenser on the outer surface of a bundle of finned tubes with a specific surface of about 1 m 2. An organosilicon coolant with a temperature of 110°C was directed into the tube space of the condenser. The condensed fraction was collected in a receiving tank with a volume of 12 l, equipped with an external jacket, into the annular gap of which the organosilicon coolant was directed after the vapor condenser.

[0087] Depending on the inlet flow temperature and the heat load on the evaporator, the proportion of MDA recovery from the inlet flow was 2–25 wt.% of the total feed flow.

[0088] The accumulated fractions of the upper and lower products were discharged periodically every 4-6 hours of continuous operation of the device, and then samples were taken from the fractions for quantitative and qualitative analysis using the HPLC method.

[0089] The condensate fraction, which is an MDA melt, contained up to 0.3 wt.% M3 A. The bottom product of the device - purified PMDA with a reduced proportion of MDA, contained less than 1 ppm of water and less than 10 ppm of aniline. The change in the color of PMDA after distillation of MDA was less than 10 units on the iodine scale. The viscosity of PMDA was 48 mPa*sec at 100 °C.

[0090] Example 3. (according to the invention)

[0091] The purified pMDA obtained in Example 2 was subjected to phosgenation according to the method described in WO2023 / 063852. After phosgenation and preliminary filtration purification of the isocyanate medium, the obtained product was sent to the column apparatus described in Example 1 for separation and the excess solvent feed stream. Thus, 1100-1150 g / h of raw pMDA of the following average composition was sent to feed the device: the proportion of monochlorobenzene is 10-15% by weight, the proportion of pMDA is the rest. The temperature of the feed stream was maintained at 50-80°C using electric heating. The calculated hydrodynamic mode of the film evaporator was characterized by a Reynolds number of about 20 and a residence time of pMDA of about 30 sec.

[0092] In the upper section of the mass-exchange section of the device, a residual pressure of 5-10 mbar was maintained, and in the evaporation section, a coolant temperature of about 200°C was maintained. The pressure drop from the upper section of the mass-exchange section to the bottom of the evaporation section was less than 1.5 mbar. The temperature of the outgoing vapors was 40-45°C, and the temperature of the vapors in the lower section was up to 200°C.

[0093] At the outlet of the evaporator, the PMDI flow in the amount of 1000 g / h was cooled in the cooling section to a temperature of 60-70°C, and then collected in a 12-liter receiving tank equipped with external electric heating.

[0094] The distilled vapor phase in the amount of 100-150 g / h was condensed in a shell-and-tube heat exchanger-condenser on the outer surface of a bundle of finned tubes with a specific surface of about 1 m 2. An organosilicon coolant with a temperature of -20°C was directed into the tube space of the condenser. The condensed fraction was collected in a receiving tank with a volume of 12 l, equipped with an external jacket, into the annular gap of which the organosilicon coolant was directed after the vapor condenser.

[0095] The accumulated fractions of the upper and lower products were discharged periodically every 4-6 hours of continuous operation of the device, and then samples were taken from the fractions for quantitative and qualitative analysis using the HPLC method.

[0096] The condensate fraction, which is MCB, contained trace amounts of MDI isomers. The distillate product of the device - purified PMDI, contained less than 30% of MCB. The color of PMDI on the iodine scale was no higher than 110 units, the viscosity of PMDI was 180 mPa*sec at 25 °C.

[0097] Example 4. (Comparative)

[0098] Raw pMDA obtained in accordance with the method described in the source Patent. CN100422239 and having the following average composition: proportion of water 0.25-0.5 wt.%, proportion of aniline 16.33 wt.%, proportion of a mixture of MDA and its oligomers - the rest; was subjected to sequential purification from water and aniline and extraction of the recycled fraction of MDA in an amount of up to 25% by weight of the initial mass of the polyamine medium, by periodic distillation fractionation in a device representing a laboratory distillation flask with a volume of 500 ml, equipped with a magnetic stirrer and placed in an electric heating mantle connected to a receiver of the vapor fraction by the "trap to trap" method and the corresponding air heaters and coolers of the vapor flows.

[0099] The distillation process was carried out at temperature and pressure readings close to the process conditions of the processes described in examples 1 and 2, respectively. The residence time of the bottom product during the sequential execution of all stages of distillation purification of the medium was from 45 min to 90 min.

[0100] In the process of fractionation of 150 g of loaded raw MDA, about 26 g of water-aniline fraction and about 13 g of MDA fraction were obtained. At the end of fractionation, samples were taken from the upper fractions and bottom product for quantitative and qualitative analysis by HPLC.

[0101] The distillate obtained in the fractionation process, purified pMDA, contained less than 100% aniline and had a color of 66 units on the iodine scale and a viscosity of 56 mPa*sec at 100 °C.

[0102] Example 5. (Comparative)

[0103] The crude pMDI obtained in Example 3 was subjected to periodic fractionation in a device similar to the device described in Comparative Example 4, except that the distillation flask and the receiver of the distillate fraction were connected to each other by a direct condenser, for the cooling of which a chilled organosilicon coolant was supplied.

[0104] The distillation process was carried out at temperatures and pressures close to the process conditions described in Example 3. The residence time of the bottoms product in the fractionation process was from 45 min to 90 min. About 16 g of the MCB fraction were obtained during the fractionation of 150 g of the loaded raw PMDI. Upon completion of the fractionation, samples were taken from the upper fraction and the bottoms product for quantitative and qualitative analysis using the HPLC method. The bottoms product obtained in the fractionation process, purified PMDI, contained less than 300 MCB and had a color of 305 units on the iodine scale and a viscosity of 233 mPa*sec at 25 °C.

[0105] Table 1. Summary table of characteristics of examples

Claims

CLAUSE OF INVENTION 1. A device for separating a mixture containing at least one heat-labile substance, wherein the device includes: a mass-exchange section with an inlet for the mixture, an evaporation section located under the mass-exchange section and connected to it via a fluid medium, and a cooling section located under the evaporation section and connected to it via a fluid medium with an outlet for a liquid flow containing a heat-labile substance, wherein the evaporation section contains a vertical film evaporator with a distribution device located in its upper part for forming a film on the inner surface of the vertical film evaporator from the mixture coming from the mass-exchange section, wherein the vertical film evaporator is designed with the possibility of heating the film with the formation of a vapor phase of the mixture and a liquid flow containing a heat-labile substance,wherein the distribution device is additionally configured to allow the vapor phase of the mixture to pass through it from the vertical film evaporator into the mass exchange section, wherein the mass exchange section is configured to provide contact between the mixture introduced into the mass exchange section and the vapor phase of the mixture coming from the evaporation section, wherein the vertical film evaporator is configured to move the liquid flow containing the thermolabile substance from the evaporation section into the cooling section for cooling it.

2. The device according to 1, in which the film evaporator contains vertically oriented tubes.

3. The device according to item 2, in which the length of the pipes is: L[M]=T_Film*wcp, where T_Film is the average residence time of the film flow on the inner surface of the heat exchange tubes, ranging from 1 to 100 seconds, wcp is the average speed of gravity flow of the film along the inner surface of the tubes.

4. The device according to item 3, in which the length of the pipes is selected to ensure the residence time of the film flow i Film from 20 to 80 seconds.

5. The device according to item 4, in which the length of the tubes is selected to ensure a residence time of the film flow i Film from 30 to 60 seconds.

6. The device according to item 2, in which the distribution device is designed with the possibility of forming a film on the inner surface of the tubes of the film evaporator.

7. The device according to claim 1, wherein the distribution device is a blind plate.

8. A device according to item 1, intended for separating a mixture of di- or polyamines or di- or polyisocyanates.

9. The device according to claim 1, wherein the mass transfer section is a packed column with an internal contact device based on mesh or sheet structured packed elements.

10. The device according to claim 9, in which the internal contact device has a specific surface area of ​​400-1000 m2 / m 3 and the proportion of volumetric voids is more than 80%.

11. The device according to claim 1, wherein the cooling section is or includes an inclined gravity-flow tubular heat exchanger of the “pipe in pipe” type or a heat exchanger-recuperator.

12. The device according to item 11, in which the gravity tubular heat exchanger has an angle of inclination of the heat exchanger axis to the overall horizontality of the device of 1 - 90°.

13. A method for separating a mixture containing at least one heat-labile substance using a device for separating a mixture comprising a mass-exchange section located under the mass-exchange section and connected thereto via a fluid medium, an evaporation section containing a vertical film evaporator, and a cooling section located under the evaporation section and connected thereto via a fluid medium, wherein the mixture containing at least one heat-labile substance is introduced into the mass-exchange section, after which it enters the vertical film evaporator of the evaporation section with the formation of a film that moves by gravity along the inner surface of the film evaporator under the action of gravity, wherein the gravity-moving film of the mixture in the vertical film evaporator is heated to obtain a vapor phase of the mixture and a liquid stream containing a heat-labile substance, wherein the vapor phase of the mixture rises into the mass exchange section for mass exchange due to contact between the vapor phase of the mixture and the mixture introduced into the mass exchange section, wherein the liquid stream containing the heat-labile substance moves from the evaporation section into the cooling section, where it is cooled and removed as a separation product containing the heat-labile substance.

14. The method according to claim 13, in which the residence time of the film flow in the vertical film evaporator is from 1 to 100 seconds.

15. The method according to claim 13, in which a mixture of di- or polyamines or di- or polyisocyanates is separated.