Method of operating a plant for the continuous production of isocyanates

Abstract

The present invention relates to a method for operating a plant for continuously producing isocyanates by converting primary amine A using phosgene P, while maintaining phosgene in a stoichiometric excess based on the amino group of the primary amine in the liquid phase in the presence of solvent L, using a first reaction chamber operated adiabatically and a second reaction chamber operated isothermally. The method is characterized by a combination of measures, in particular maintaining a sufficiently high starting pressure and a sufficiently high starting temperature, to start the plant from a production shutdown state and return it to a target state, which is a standard operating state.

Description

Technology Field

[0001] The present invention relates to a method for operating a plant for continuously producing isocyanates by reacting primary amine A with phosgene P, using a first reaction zone operated adiabatically and a second reaction zone operated isothermally, while maintaining phosgene in a stoichiometric excess based on the amino group of the primary amine in the liquid phase in the presence of solvent L. The method is characterized by a combination of measures, in particular maintaining a sufficiently high starting pressure and a sufficiently high starting temperature, to return the plant to a target state, i.e., a normal operating state, from a state of production shutdown (e.g., after maintenance, a shortage of feedstock, or a shutdown due to a lack of demand for the isocyanates produced in the plant). Background Technology

[0002] Isocyanates are manufactured in large quantities and primarily serve as starting materials for the production of polyurethanes. They are typically produced by reacting a corresponding amine with phosgene using a stoichiometric excess of phosgene. The reaction between the amine and phosgene can be carried out in a gaseous or liquid phase, whereby the reaction can be performed discontinuously or continuously. By the phosgenesis reaction (in the case of gaseous phosgenesis, after quenching the initially obtained gaseous reaction product), a liquid phase containing the desired isocyanate is obtained.

[0003] Processes for preparing organic isocyanates from primary amines and phosgene have been widely described previously; the following literature is to be referenced purely as an exemplary basis:

[0004] DE-A-34 03 204 describes a continuous manufacturing process for organic polyisocyanates in which a temperature increase of 100 to 220°C is established in a reaction including partial circulation at a pressure of 5 to 100 bar.

[0005] DE-A-17 68 439 describes a continuous process for producing organic isocyanates, in which amine and phosgene feedstocks are first preheated, then the preheated components are combined in a reaction zone under high pressure and reacted under isothermal conditions, that is, under heat exchange with the surrounding environment.

[0006] DE-A-102 22 968 describes a process for continuously producing polyisocyanates by reacting primary amines with phosgene in a cascade of temperature-adjustable reaction tubes of various sizes.

[0007] EP 1 873 142 A1 describes a three-stage process form in which the pressure between the mixer of the first stage and the first phosgenation reactor of the second stage is kept equal or increased, and the pressure of the phosgen removal device in the third stage is lower than that in the second stage. The reaction may proceed adiabatically or isothermally.

[0008] Of interest on an industrial scale are aromatic isocyanates, such as methylene diphenylene diisocyanate (hereinafter MMDI – “monomerical MDI”), mixtures of MMDI and polymethylene polyphenylene polyisocyanate (the latter is a higher homologue of MMDI, hereinafter referred to as PMDI, “polymerical MDI”), or tolylene diisocyanate (TDI), and aliphatic isocyanates, such as both pentane 1,5-diisocyanate (PDI), hexamethylene 1,6-diisocyanate (HDI), or isophorone diisocyanate (IPDI). Additionally, isocyanates having benzyl isocyanate groups are also important; here, xylylene diisocyanate (XDI) should be mentioned in particular. The present invention relates particularly to the manufacture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate (hereinafter collectively referred to as MDI).

[0009] In most known processes, the desired reaction temperature is established using temperature-controlled reactors through various modifications (jacket heating, heat exchangers, or heating via special reactor internals). However, in the synthesis of isocyanates by the phosgenation of amines, external control of the reactor temperature often presents a problem because high temperatures on the reactor wall surfaces promote or even induce the formation of byproducts, negatively impacting yield and / or product characteristics. Furthermore, since precipitates form within the reactor in such cases, the reactor must be shut down and cleaned periodically. However, this leads to a loss of plant capacity and consequently results in economic disadvantages. Additionally, heat transfer systems incur additional capital costs, which likewise worsens the economic viability of the process. To solve these problems, EP 1 616 857 A1 proposes a two-step process form in which, in step 1 a), an amine and phosgene are reacted adiabatically, wherein the reaction temperature is limited to 100 to 220°C by setting the absolute pressure in the reactor to a value of 8 to 50 bar through depressurization, and the temperature is maintained at 100 to 220°C until at least 80% phosgene conversion rate is obtained, and then in step 2 b), the reaction mixture from step 1 is depressurized to an absolute pressure in the range of 1 to 15 bar and, typically, heat is supplied to continue the conversion at a temperature of 90 to 240°C. This process form may be referred to as an adiabatic-isothermal process form. Essential to the described process is to control the reaction temperature (100°C to 220°C, preferably 115°C to 180°C, more preferably 120°C to 150°C) within an adiabatically operated reactor through the pressure within the reactor. This control through pressure is achieved by opening a valve attached to the reactor to allow a portion of the reaction mixture to exit the reactor, thereby implementing a controlled reduction of pressure (see paragraph

[0016] ).The reaction mixture exiting the adiabatic reactor is further converted under isothermal conditions in the second stage and depressurized to a lower pressure than in the first stage (see paragraph

[0019] ). At the outlet of the isothermal reactor, the liquid and gaseous phases containing isocyanate are withdrawn separately therefrom.

[0010] European patent application EP 3 653 605 A1 describes a method comprising: I) providing an amine solution and adjusting its temperature in a heat exchanger; II) providing a phosgene solution and adjusting its temperature in a heat exchanger; III) mixing the amine solution with the phosgene solution in a mixing unit; then IV) further converting in an adiabatically operated reaction zone and removing the gaseous phase formed as a result of the chemical reaction in a separation zone; V) depressurizing the remaining liquid phase; VI) further converting the liquid phase remaining after depressurization in an indirectly heated reaction zone; VII) isolating the isocyanate from the reaction solution obtained therefrom; wherein, for closed-loop control of the temperature of the primary amine solution provided in step I) and / or the temperature of the phosgene solution provided in step II) by means of the heat exchanger used to adjust the temperature of each solution, a target value for the temperature of the reaction mixture from step III) is set within the range of 110°C to 145°C, and the reaction zone and separation zone are controlled using the actual temperature of the reaction mixture from step III) measured continuously or intermittently. The present invention relates to a process for producing isocyanates by reacting a primary amine with phosgene, including adjusting the internal temperature.

[0011] European patent application EP 3 653 604 A1 relates to a process for producing an isocyanate by reacting a primary amine with phosgene, comprising: I) providing an amine solution; II) providing a phosgene solution; III) mixing the amine solution with the phosgene solution in a mixing device; IV) further reacting in an adiabatic reaction zone and separating the gaseous phase formed as a result of the chemical reaction in a separation zone; v) depressurizing the remaining liquid phase in 2-3 steps; VI) further reacting the remaining liquid phase after the final depressurization step in an indirectly heated reaction zone; and VII) isolating the isocyanate from the reaction solution obtained therefrom.

[0012] The quality of a process for producing isocyanates is, first, defined by the content of unwanted by-products included in the process product. Second, the quality of the process is defined by the fact that the entire initiation and manufacturing operation can be carried out in normal operation until the process is stopped without technical manufacturing stoppages or problems requiring operational intervention, and that there is no loss of feedstocks, intermediates, or final products. In this context, international patent application WO 2015 / 144658 A1 relates to a process for producing isocyanates by phosgenerating a corresponding amine, wherein the problem caused by the formation of a precipitate in the device within the reaction zone during the initiation and shutdown of the process is avoided by chemical manipulation measures, particularly by ensuring a very large excess of phosgene compared to the amine being phosgenerated during the main initiation and shutdown steps of the process. To this end, a continuous process for producing isocyanates by reacting a corresponding amine with phosgene in the presence of an inert solvent is proposed, wherein the process comprises sequentially performing (A) a step of initiating continuous production, (B) a step of continuous production, and (C) a step of stopping continuous production, wherein in step (A),

[0013] The mixing zone and the reaction zone positioned downstream thereof are initially (i) charged only with at least partially inert solvent, then heated to a desired reaction temperature, then additionally charged with phosgene but not with amine, or (ii) charged at least partially with inert solvent and phosgene and not with amine, then heated to a desired reaction temperature;

[0014] Subsequently only, the amine, additional phosgene, and additional inert solvent are continuously supplied to the reaction zone through the mixing zone;

[0015] Here, continuous production is stopped by initially terminating only the supply of amine while continuing the continuous supply of phosgene and inert solvent in step (C). These literatures do not contain details regarding a two-step adiabatic-isothermal process mode.

[0016] However, experience indicates that findings from "conventional" phosgenation processes cannot simply be converted to a two-stage adiabatic-isothermal process mode. The present invention is based on the finding that in a two-stage adiabatic-isothermal phosgenation process, several factors must be satisfied simultaneously to allow for problem-free initiation. These include, in particular, a sufficiently high starting pressure and a sufficiently high (but not excessively high) starting temperature. Specific details for implementing the invention

[0017] Taking these findings into consideration, the present invention provides the following:

[0018] A method for operating a plant for continuously producing isocyanates by reacting primary amine A with phosgene P while maintaining phosgene in a stoichiometric excess based on the amino group of the primary amine in the liquid phase in the presence of solvent S, and

[0019] Here plant is doing Plant section :

[0020] (I) Compound for providing amine solution AS by mixing primary amine A and solvent S. First mixing device ,

[0021] (II) Composed of mixing phosgene P and solvent S to provide a phosgene solution PS. Second mixing device ,

[0022] (III) Compound to provide a reaction mixture by mixing an amine solution and a phosgene solution. Third mixing device ,

[0023] (IV) Composed for the adiabatic reaction of the reaction mixture First reaction zone , and configured to form a first liquid phase and a first gas phase, disposed downstream of the reaction zone Depressure zone (Here, the reaction zone and the depressurization zone are (a) two different devices, i.e. First reactor and First pressure reduction device (b) placed in, or entirely First reactor (placed in a common device constituting),

[0024] (V) configured to depressurize the first liquid phase to form a second liquid phase and a second gas phase (in the case of (a) The second ) Pressure reducing device (= reduced pressure zone of the plant part (V) placed in the dedicated device),

[0025] (VI) Configured to form a third liquid phase and a third gas phase by isothermally reacting the second liquid phase. Second reaction zone (= 2nd reactor),

[0026] (VII) For obtaining isocyanate from the third liquid phase Post-processing unit

[0027] Including;

[0028] Here in the target state (normal operation) method silver

[0029] Target concentration of amine in amine solution c(A) 목표 , and target flow rates of amine (A) 목표 and the first target flow rate of the solvent (SA) 목표 Target flow rate of the amine solution obtained from (AS) 목표 An amine solution having and

[0030] Target concentration of phosgene in phosgene solution c(P) 목표 Target flow rates of , and phosgene (P) 목표 and the second target flow rate of the solvent (SP) 목표 Target flow rate of the phosgene solution obtained from (PS) 목표 of a phosgene solution having

[0031] It includes a continuous reaction,

[0032] Here

[0033] Condition in which the amine solution is not supplied to the third mixing device (i.e., instantaneous flow rate of the amine solution) Starting from (AS) is 0, and therefore the production of isocyanate is stopped), the following steps:

[0034] (i) (a) Target concentration c(P) from the second mixing device 목표 and target flow rate (PS) 목표 A phosgene solution having a temperature in the range of 100°C to 125°C, preferably 100°C to 105°C, and (simultaneously, prior or subsequent)

[0035] (b) First target flow rate from the first mixing device (SA) 목표 A solvent having a temperature in the range of 70°C to 100°C, preferably 90°C to 95°C (not accompanied by amine)

[0036] A step of continuously supplying to a third mixing device, and from thereto continuously supplying to a post-treatment unit through a first reaction zone, a pressure reduction zone, a pressure reduction device, and a second reaction zone,

[0037] (ii) Start a continuous supply of amine to a first mixing device in which the solvent stream established in step (i)(b) continues to flow, at the target flow rate of amine (A) 목표 Starting flow rate of amine lower than (A) 출발 A step of forming an amine solution in such a way that the temperature of the amine solution exiting the first mixing device is in the range of 85°C to 105°C, preferably 95°C to 100°C, and the temperature of the reaction mixture exiting the third mixing device is in the range of 130°C to 145°C, preferably 138°C to 142°C (= starting temperature), wherein the point in time at which the continuous supply of amine A to the first mixing device begins is selected such that, at the first contact between the amine solution and the phosgene solution in the third mixing device, the pressure within the reduced pressure zone of the plant part (IV) is in the range of 16 to 25 bar, preferably 16 bar to 20 bar (= starting pressure).

[0038] (iii) the flow rate of amine (A) 출발 from (A) 목표 A step of increasing (stepwise or continuously) the temperature of the phosgene solution withdrawn from the second mixing device at the same time as lowering it to a value in the range of 0°C to 10°C, preferably 0°C to 5°C, so that the temperature of the reaction mixture exiting the third mixing device is maintained within the range established in step ii), and the pressure in the reduced pressure zone of the plant part (IV) is increased to a value in the range of 20 bar to 30 bar, preferably 20 bar to 25 bar,

[0039] (iv) After the target flow rate of amine is achieved (i.e. (A) = (A) 목표), by lowering the temperature of the amine solution withdrawn from the first mixing device to a value in the range of 50°C to 80°C, preferably 50°C to 60°C, so that in the target state, the temperature of the reaction mixture exiting the third mixing device is in the range of 125°C to 135°C, preferably 128°C to 132°C, and the pressure in the reduced pressure zone of the plant part (IV) is maintained in the range of 20 bar to 30 bar, preferably 20 bar to 25 bar.

[0040] A method of achieving a target state by performing.

[0041] Here and below, all pressures must be understood to mean absolute pressure.

[0042] According to the present invention, phosgene is used as a "stoichiometric excess" based on the amino group of a primary amine. Theoretically, 1 mole of phosgene reacts with 1 mole of a primary amino group (1 R-NH2 + 1 COCl2 → 1 R-NCO + 2 HCl). Therefore, the phosgene excess x% relative to the primary amino group is It corresponds to the molar ratio n(phosgene) / n(-NH2) (n = molar amount), that is, for example, an excess of 40% phosgene is = corresponds to 1.40, and for example, a phosgene excess of 120% is = Corresponds to 2.2.

[0043] Now regarding various possible embodiments of the present invention Brief summary This continues.

[0044] In the first embodiment of the present invention which can be combined with all other embodiments, in step (i)

[0045] · The temperature of the phosgene solution is set to a value in the range of 100℃ to 105℃, and

[0046] · The temperature of the solvent is set to a value in the range of 90℃ to 95℃, and

[0047] In step (ii)

[0048] · At the time of the first contact between the amine solution and the phosgene solution in the third mixing device, the pressure in the reduced pressure zone of the plant part (IV) is in the range of 16 bar to 20 bar;

[0049] · The temperature of the amine solution exiting the first mixing device is in the range of 95℃ to 100℃;

[0050] · The temperature of the reaction mixture exiting the third mixing device is in the range of 138℃ to 142℃;

[0051] In step (iii)

[0052] · The temperature of the phosgene solution withdrawn from the second mixing device is lowered to a value in the range of 0°C to 5°C, and

[0053] · The pressure in the depressurization zone of the plant section (IV) is increased to a value in the range of 20 bar to 25 bar, and

[0054] In step (iv)

[0055] · The temperature of the amine solution withdrawn from the first mixing device is lowered to a value in the range of 50°C to 60°C, and

[0056] · The temperature of the reaction mixture exiting the third mixing device in the target state is in the range of 128℃ to 132℃, and

[0057] · The pressure in the reduced pressure zone of the plant section (IV) is maintained in the range of 20 bar to 25 bar.

[0058] In a second embodiment of the present invention which can be combined with all other embodiments, the pressure in the reduced pressure zone of the plant part (IV), established in step (iii), is greater than the pressure in the reduced pressure zone of the plant part (IV) when the continuous supply of amine to the first mixing device is started in step (ii).

[0059] In the third embodiment of the present invention, which is an alternative to the fourth embodiment described below but can be combined with all other embodiments, the reaction zone and the depressurization zone of the plant part (IV) are placed in two different devices (a first reactor and a first depressurization device).

[0060] In a fourth embodiment of the present invention, which is an alternative to the third embodiment described above but can be combined with all other embodiments, the reaction zone and the depressurization zone of the plant portion (IV) are located in a common device (constituting the first reactor entirely).

[0061] In the fifth embodiment of the present invention, which can be combined with all other embodiments, in step (ii), the pressure in the depressurization zone of the plant part (IV) is adjusted through degassing of phosgene, addition of an inert gas (particularly nitrogen), and / or addition of hydrogen chloride.

[0062] In the sixth embodiment of the invention, which is a specific embodiment of the fifth embodiment, the pressure in the depressurization zone of the plant part (IV) is adjusted by the addition of hydrogen chloride, wherein the hydrogen chloride is drawn from the first, second, and / or third gas phase.

[0063] In the seventh embodiment of the present invention, which is an alternative to the eighth and ninth embodiments described below but can be combined with all other embodiments, the performance of step (i)(b) is started simultaneously with step (i)(a).

[0064] In the eighth embodiment of the present invention, which is an alternative to the seventh embodiment described above and the ninth embodiment described below but can be combined with all other embodiments, the performance of step (i)(b) is started before step (i)(a).

[0065] In the ninth embodiment of the present invention, which is an alternative to the seventh embodiment described above but can be combined with all other embodiments, the performance of step (i)(b) begins after step (i)(a).

[0066] In the 10th embodiment of the present invention, which can be combined with all other embodiments, the post-processing unit is

[0067] · A first distillation apparatus configured to separate a phosgene-containing fourth gaseous phase from a third liquid phase to provide a fourth liquid phase depleted of phosgene,

[0068] · A second distillation apparatus configured to separate a solvent-containing fifth gaseous phase from a fourth liquid phase to provide a fifth liquid phase depleted of phosgene and solvent, and

[0069] · A third distillation apparatus configured to provide isocyanate from the fifth liquid phase

[0070] Includes

[0071] In the eleventh embodiment of the present invention, which can be combined with all other embodiments, after the target state is achieved (and after the plant is operated to the target state), the continuous reaction of the amine solution and the phosgene solution is stopped, wherein the following step:

[0072] (v) A step of increasing the temperature of the phosgene solution and the temperature of the amine solution at flow rates of the phosgene solution and the amine solution that have not changed compared to the target state;

[0073] (vi) When the temperature of the reaction mixture exiting the third mixing device is achieved to be in the range of > 135℃ to 140℃,

[0074] A step of maintaining the supply of solvent to the first mixing device and maintaining the supply of phosgene solution to the second mixing device while terminating the supply of amine to the first mixing device;

[0075] (vii) a step of maintaining the supply of solvent to the second mixing device and maintaining the supply of solvent to the first mixing device while terminating the supply of phosgene to the second mixing device;

[0076] (viii) After the concentration of phosgene in the solvent exiting the second mixing device has dropped below a predetermined critical concentration,

[0077] Step of terminating the supply of solvent to the second mixing device; and

[0078] (viii) Step of terminating the supply of solvent to the first mixing device

[0079] Execute the above interruption by performing.

[0080] In the 12th embodiment of the present invention, which is a specific form of the 11th embodiment, in step (v), the temperature of the phosgene solution is raised to a value in the range of 100°C to 125°C and the temperature of the amine solution is raised to a value in the range of 100°C to 125°C.

[0081] In the 13th embodiment of the present invention, which is a specific form of the 11th and 12th embodiments, the amine supply is terminated as soon as the temperature of the reaction mixture exiting the third mixing device in step (vi) reaches a range of > 135°C to 137°C.

[0082] In the 14th embodiment of the present invention, which may be combined with all other embodiments, the primary amine is methylene diphenylene diamine (providing methylene diphenylene diisocyanate), polymethylene polyphenylene polyamine (providing polymethylene polyphenylene polyisocyanate), a mixture of methylene diphenylene diamine and polymethylene polyphenylene polyamine (providing a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate), tolylene diamine (providing tolylene diisocyanate), xylylene diamine (providing xylylene diisocyanate), pentane-1,5-diamine (providing pentane 1,5-diisocyanate), hexamethylene-1,6-diamine (providing hexamethylene 1,6-diisocyanate), isophorone diamine (providing isophorone diisocyanate), and naphthyl diamine (naphthyl It is selected from (providing diisocyanates).

[0083] The embodiments briefly outlined above and additional possible embodiments of the present invention are as follows: It is explained in more detail. All embodiments may be combined with one another as desired, unless otherwise noted or clearly evident from the context.

[0084] Operation of the plant in the target state (normal operation)

[0085] Before describing specific details regarding the initiation of manufacturing according to the present invention, the operation of the plant in the target state (= normal operation) will be described in more detail. As would be immediately apparent to a person skilled in the art, many aspects outlined below apply equally to the initiation operating state (e.g., the type of device used or the method of temperature-controlling the reactants). To avoid unnecessary repetition, these aspects are not described in further detail below.

[0086] The target state is the flow rate of the amine solution (A) is a value (AS) 목표 = (A) 목표 + (SA) 목표 It is achieved as soon as it is achieved (where, in the case of the concentration of amine A c(A) in amine solution AS, c(A) = c(A) 목표 (Im). The process for manufacturing isocyanate in the target state comprises the following steps (process steps numbered by Arabic numerals ((1), (2) etc.) described below are carried out in corresponding plant parts numbered by Roman numerals ((I), (II) etc.):

[0087] (1) A solution of primary amine A corresponding to the isocyanate in solvent L First mixing device Steps provided using;

[0088] (2) Solution of phosgene P in solvent L Second mixing device Steps provided using;

[0089] (3) the solution of the primary amine provided in step (1) and the solution of the phosgene provided in step (2) are maintained in a stoichiometric excess of phosgene based on the amino group of the primary amine, preferably in the range of 40% to 200% of the theoretical value, particularly preferably in the range of 40% to 120% of the theoretical value, very particularly preferably in the range of 50% to 100% of the theoretical value, and particularly preferably in the range of 50% to 75% of the theoretical value. Third mixing device A step of mixing to provide a reaction mixture having a temperature in the range of 125°C to 135°C, preferably 128°C to 132°C;

[0090] (4) A step of passing the liquid reaction mixture obtained in step (3) through a first reaction zone of a plant part (IV) and a first reduced pressure zone disposed downstream of the first reaction zone to form a first gaseous phase and a first liquid phase under a pressure of 20 bar to 30 bar, preferably 20 bar to 25 bar, wherein the first reaction zone and the reduced pressure zone are neither heated nor cooled (i.e., both are operated adiabatically);

[0091] (5) The first liquid phase withdrawn from the depressurization zone in step (4) of the plant part (V) Pressure reducing device A step of depressurizing (in one or multiple stages) to form a second liquid phase and a second gas phase;

[0092] (6) The second liquid phase obtained after depressurization in step (5). Second reaction zone A step of passing through to form a third liquid phase (containing isocyanate and solvent) and a third gaseous phase (containing hydrogen chloride and phosgene and also generally a portion of the evaporated solvent), wherein the second reaction zone is heated indirectly, i.e., operated isothermally;

[0093] (7) The third liquid phase obtained in step (6) Post-processing unitA step of recovering the solvent and obtaining the isocyanate through post-processing.

[0094] A pressure zone of the plant section (IV) is positioned "downstream" of the first reaction zone (which should also be understood as meaning an open fluidic connection between the two zones in the terminology of the present invention), and furthermore, since the first reaction zone and the pressure zone of the plant section (IV) are "neither heated nor cooled" (= adiabatic process mode), all points of the first reaction zone and the pressure zone of the plant section (IV) have a temperature substantially determined by the reaction enthalpy of the chemical process (described below) occurring at a given temperature of the reaction mixture from step (3), apart from heat loss through the incomplete insulation of the device used. The established pressure is also primarily determined by the chemical process occurring. However, the pressure zone of the plant section (IV) is preferably provided with a pressure control valve for the formed gaseous phase and a liquid level control means for the liquid phase so as to safely ensure that the pressure is within the aforementioned range (20 bar to 30 bar, preferably 20 bar to 25 bar). Therefore, the temperature in step (4) ultimately depends on the temperature of the reaction mixture supplied to this step.

[0095] Step 1) In, Provision of the amine solution required for phosgenationThis can be carried out through any method known from the prior art. The amine used is determined by the desired isocyanate. In principle, the process of the present invention is suitable for the production of any desired aromatic, aliphatic, and ar aliphatic isocyanate. The process according to the present invention comprises: methylene diphenylene diisocyanate (from methylene diphenylene diamine); polymethylene polyphenylene polyisocyanate (from polymethylene polyphenylene polyamine); a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate (such a mixture is hereinafter referred to as MDI and starting amine mixture MDA); tolylene diisocyanate (from tolylene diamine); xylylene diisocyanate (from xylylene diamine); pentane 1,5-diisocyanate (from pentane-1,5-diamine); hexamethylene diisocyanate (from hexamethylene diamine); isophorone diisocyanate (from isophorone diamine); and naphthyl diisocyanate (from naphthyl diamine), more preferably methylene diphenylene diisocyanate, methylene diphenylene diisocyanate and polymethylene It is preferable to use it for the production of mixtures of polyphenylene polyisocyanates and tolylene diisocyanates. The process according to the present invention is most preferably suitable for the production of methylene diphenylene diisocyanates and mixtures of methylene diphenylene diisocyanates and polymethylene polyphenylene polyisocyanates. Methylene diphenylene diisocyanates are also referred to as diphenylmethane-based diamines. Polymethylene polyphenylene polyisocyanates are also referred to as diphenylmethane-based polyamines.

[0096] The manufacturing process of the mentioned amine is known to a person skilled in the art, so no further explanation is required at this time.

[0097] In step (1), the amine to be phosgenerated is dissolved in a solvent. As the first mixing apparatus required for this purpose, a mixing apparatus known in itself to a person skilled in the art may be used. A mixing tube having a static mixer as an internal component (often referred to simply as a static mixer) is particularly suitable. Suitable solvents available according to the present invention are solvents that are inert under reaction conditions, such as monochlorobenzene, dichlorobenzene (especially the ortho isomer), dioxane, toluene, xylene, methylene chloride, perchloroethylene, trichlorofluoromethane, or butyl acetate. Since the solvent is preferably not essentially isocyanate (target mass fraction < 100 ppm) and not essentially phosgene (target mass fraction < 100 ppm), this should be kept in mind when using a recirculation stream. Therefore, it is preferable to work using a process as described in EP 1 854 783 A2. The solvent may be used individually or in the form of any desired mixture of the solvents mentioned as examples. It is preferable to use monochlorobenzene (MCB) or ortho-dichlorobenzene (oDCB), most preferably monochlorobenzene (MCB).

[0098] The temperature of the resulting amine solution is intended to be in the range of 50°C to 80°C, particularly preferably 50°C to 60°C. This can, in principle, be achieved by appropriately controlling the temperatures of the starting materials, the amine and the solvent, while taking into account the enthalpy of the solution. However, according to the present invention, in addition to controlling the temperature of the starting materials specifically mentioned, it is desirable to provide a heat exchanger downstream of the mixing process of the amine and the solvent, which allows the amine solution to be precisely adjusted to a desired temperature within the mentioned range, thereby enabling heating or cooling depending on the temperature immediately downstream of the mixing process of the starting materials. Heat exchangers known to those skilled in the art, such as shell-tube heat exchangers and plate heat exchangers, are suitable for this purpose.

[0099] Regarding the amine concentration in the solution provided in step (1), it is desirable to adjust the mass fraction of primary amines based on the total mass of the solution to a value in the range of 25% to 50%, particularly in the range of 30% to 45%.

[0100] Providing the phosgene solution required for phosgenesis Step 2) can likewise be carried out through any method known from the prior art. The same mixing apparatus and solvent described above for the primary amine are suitable. It is particularly desirable to dissolve the primary amine in Step (1) and the phosgene in Step (2) in the same solvent in each case, that is, very particularly preferably in MCB. Since the process for manufacturing phosgene is known to those skilled in the art, no further explanation is required at this time.

[0101] The temperature of the resulting phosgene solution is intended to be in the range of 0°C to 10°C, preferably 0°C to 5°C. This can, in principle, be achieved by appropriately controlling the temperatures of the starting materials, phosgene and the solvent, while taking into account the enthalpy of the solution. However, according to the present invention, in addition to controlling the temperature of the starting materials specifically mentioned, it is desirable to provide a heat exchanger downstream of the mixing process of phosgene and the solvent, which allows the phosgene solution to be precisely adjusted to a desired temperature within the aforementioned range, thereby enabling heating or cooling depending on the temperature immediately downstream of the mixing process of the starting materials. Suitable mixing units and solvents are the same as those described above for primary amines.

[0102] Regarding the phosgene concentration in the solution provided in step (2), it is desirable to adjust the mass fraction of phosgene based on the total mass of the solution to a value in the range of 45% to 90%, particularly in the range of 55% to 80%.

[0103] In step (3), Mix the solution of primary amine provided in step (1) with the solution of phosgene provided in step (2). Mixing devices known by themselves to a person skilled in the art, such as static or dynamic mixers, are suitable as the third mixing device required for this purpose. A static mixer is characterized by not having moving parts; in particular, a mixing tube having a static mixer as an internal component (often referred to simply as a static mixer) or a mixing tube having a nozzle should be mentioned here. In contrast, a dynamic mixer includes moving parts, for example, an agitator unit. In particular, a rotor-stator system known in EP 0 830 894 A1 and EP 2 077 150 A1 should also be mentioned here. A dynamic mixer, particularly of the rotor-stator type, is preferred for use in the present invention.

[0104] The mixing unit from step (3) is preferably neither heated nor cooled, which means that the temperature of the resulting reaction mixture is determined only by the reaction enthalpy and mixing enthalpy already set in the mixing unit. The transport conduit for the reaction mixture between the outlet of the third mixing unit and the inlet of the first reaction zone is also preferably neither heated nor cooled, but is preferably insulated.

[0105] According to the present invention, in the mixing at step (3), the stoichiometric excess of phosgene based on the amino group of the primary amine is observed to be preferably in the range of 40% to 200% of the theoretical value, particularly preferably in the range of 40% to 120% of the theoretical value, very particularly preferably in the range of 50% to 100% of the theoretical value, and particularly preferably in the range of 50% to 75% of the theoretical value.

[0106] First major part of the reaction to provide isocyanate (Apart from the chemical reaction already started in the third mixing device), in step (4), especially Adiabatic conditions It is performed under. This should be understood to mean that the reaction mixture that has undergone step (4) is neither heated nor cooled during the reaction. Since the device used is insulated against heat loss, the temperature profile is determined by the reaction enthalpy of the reaction occurring.

[0107] Although not intended to be bound by a specific theory, it can be assumed that multiple reactions proceed simultaneously in step (4) (in some cases, already in step (3)). Primary amines react with phosgene to provide a known carbamoyl chloride intermediate (exothermic reaction). The hydrogen chloride released here reacts with the amine that has not yet been converted to provide amine hydrochloride (exothermic reaction), which dissolves in the solvent used (endothermic reaction). The cleavage of carbamoyl chloride to provide the desired isocyanate and hydrogen chloride also occurs partially in step (4) (endothermic reaction). Temperature changes depend on the interaction of all these reactions. Generally, only slight temperature changes are observed in step (4), which suggests that the exothermic and endothermic reactions are in "balance." In any case, the reactions in step (4) result in the formation of a first gaseous phase separated from the first liquid phase remaining in the first reduced-pressure zone of the plant section (IV).

[0108] According to the present invention, it is possible to use two separate devices as the first reaction zone and the pressure reduction zone of the plant portion (IV). In this case, the device comprising the first reaction zone is referred to as the first reactor in the terminology of the present invention, and the device comprising the first pressure reduction zone is referred to as the first pressure reduction device. A suitable first pressure reduction device is a gas-liquid separation vessel (also known as a gas separator) that is known to a person skilled in the art.

[0109] (b) Likewise, according to the present invention, it is possible and preferable to place the first reaction zone and the first reduced pressure zone in a common device collectively referred to as the first reactor in the terminology of the present invention.

[0110] Regardless of whether modification mode (a) or modification mode (b) is used, a suitable first reactor is a conventional phosgenation reactor known to those skilled in the art, such as, in particular, an upright tubular reactor (tube reactor; also referred to as a tower reactor or reactor tower when the height-to-diameter ratio is relatively small). Such a reactor may also operate as a bubble column. To narrow the residence time distribution, the first reaction chamber placed in the first reactor may be divided by an internal structure known to those skilled in the art. The reaction mixture obtained in step (3) preferably flows through the first reactor from bottom to top. In the preferred case (b), the first depressurization zone is a gaseous zone in the upper region of the first reactor, from which the first liquid phase and the first gaseous phase are removed separately. Regardless of whether modification mode (a) or modification mode (b) is used, phase separation occurs spontaneously.

[0111] In step (5), the first liquid phase obtained in step (4) is Single-stage or multi-stage depressurization It is applied to, preferably, a pressure in the range of 1.0 bar to 20 bar measured in the gas phase obtained in the final stage, which is referred to in the term of the present invention as the second gas phase in the case of multi-stage depressurization. A suitable (in the case of (a): the second) depressurization device is a gas-liquid separation vessel (also known as a gas separator) that is known to a person skilled in the art in itself. In the case of multi-stage depressurization in step (5), a corresponding number of such gas separators are arranged in series, wherein, in the term of the present invention, all gas-liquid separation vessels constitute the depressurization device of the plant part (V). A gas phase containing hydrogen chloride and unconverted phosgene is formed in all stages. This multi-stage depressurization proceeds such that the liquid phase obtained after depressurization in the first stage becomes the feedstock for the second stage.

[0112] It is possible to place a gas-liquid separation vessel for depressurization (in the case of multi-stage depressurization used for final depressurization) and a second (indirectly heated) reaction zone from step (6) in a common device. An example of a possible embodiment is described below.

[0113] In step (6), the second liquid phase obtained in step (5) is in the second reaction zone. React additionally , a third liquid phase containing the desired isocyanate and a third gaseous phase (containing hydrogen chloride- and phosgene-) are formed ("isothermal process mode"). This can be carried out in a heatable reactor known to those skilled in the art. A shell-tube reactor (vertically positioned) is particularly suitable for this purpose. The second liquid phase may flow through the interior of the tubes of the shell-tube reactor (inside the tubes), or through the zone between the tubes of the shell-tube reactor (outside the tubes), separated from the outside by the reactor walls surrounding the tube bundle. Thus, the heating medium, such as a heat carrier, salt melt, steam, etc., flows through each different zone so as not to come into physical contact with the liquid process product to be converted (indirect heating). The liquid phase obtained in step (4) preferably flows from top to bottom through a vertically positioned shell-tube reactor. In a preferred embodiment of the present invention, when the gas-liquid separation vessel provided for the depressurization of step (5) / the final depressurization step of step (5) is integrated with the device in which the second reaction zone from step (5) is located, the gas-liquid phase separation is performed in a cap located at the top of the shell-tube reactor.

[0114] In the post-processing unit, Post-processing the third liquid phase obtained in step (6) In step (7), the desired isocyanate is isolated and the solvent is recovered. This step can be performed by a process known in itself from the prior art and generally Dephosphogenation , Solvent separation and Final Refining Includes dissolved phosgene ( Fourth gas phase(separated as) is preferably removed as completely as possible, as early as possible, from the third liquid phase in a first distillation apparatus (so-called "dephosgenesis column"), so that the phosgene is depleted Fourth liquid phase A solvent ( Fifth gas phase Separated as) is preferably removed as completely as possible in a second distillation apparatus (so-called "solvent column") so that the phosgene-depleted Fifth liquid phase Obtain the recovered phosgene and solvent, which are advantageously recycled.

[0115] The fifth liquid phase is applied to the final purification in a third distillation apparatus, which includes homologue separation, if necessary. Depending on the type of isocyanate, the final purification may also include isomer separation. In a preferred embodiment, the present invention relates to the preparation of methylene diphenylene diisocyanate and the preparation of a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate. In this case, a fifth liquid phase containing a mixture of all crude isocyanates (homologous and isomers) is preferably initially fed to a distillation homologous separation (so-called "polymer separation") to obtain a distillate of methylene diphenylene diisocyanate (containing trace amounts of polymethylene polyphenylene polyisocyanate) and a bottom product of polymethylene polyphenylene polyisocyanate and methylene diphenylene diisocyanate (wherein the proportion of methylene diphenylene diisocyanate is reduced compared to the fifth liquid phase according to the amount of methylene-diphenylene diisocyanate distilled off in the homologous separation). In at least one additional distillation step, low-boiling and high-boiling impurities are removed from the distillate of methylene diphenylene diisocyanate and separated into various isomer fractions. The separation of isomers preferably comprises obtaining a fraction of 4,4'-methylene diphenylene diisocyanate and a fraction of a mixture of 2,4'-methylene diphenylene diisocyanate and 4,4'-methylene diphenylene diisocyanate. Step (7), which is outlined only briefly herein, is described in detail in the prior art; reference should be made, for example, to WO 2017 / 050776 A1.

[0116] Steps (4), (5), and (6) provide a gas phase (i.e., the first, second, and third gas phases) containing hydrogen chloride, phosgene, and any entrained solvent. This gas phase is preferably applied to post-treatment for the recovery of a similarly valuable product. The post-treatment serves to separate phosgene and hydrogen chloride from each other, for example, by absorbing phosgene into a solvent or by distillation separation after compression and liquefaction. The obtained hydrogen chloride gas is suitable for further oxidation to chlorine, which is required for the production of phosgene required in step (2). Oxidation can be carried out by electrolysis or catalysis using oxygen (so-called decon( Deacon ) process). A portion of the recovered hydrogen chloride can also be used to establish the starting pressure as described below. Optionally, the recovered phosgene containing solvent can also be used in step (2).

[0117] In any case, it is advantageous to adjust the gas phases obtained in steps (4), (5) and (6) to a common pressure and combine them upstream of the post-processing process.

[0118] In principle, this can be accomplished by depressurizing all gas phases to the lowest pressure (i.e., the pressure of the third gas phase obtained in step (6)) or a much lower pressure, and then further purifying it. This procedure is particularly desirable in the case of post-treatment by absorption.

[0119] Start of manufacturing (transitioning the plant to the target state)

[0120] In the case of the disclosed process of the present invention, the amine solution is not supplied to the third mixing device (i.e., the instantaneous flow rate of the amine solution). Starting from (AS) being 0 and therefore the production of isocyanate being stopped), the target state is achieved by performing steps (i) through (iv) described above (the plant is switched to normal operation as described above). In a preferred embodiment,

[0121] In step (i)

[0122] · The temperature of the phosgene solution is set to a value in the range of 100℃ to 105℃, and

[0123] · The temperature of the solvent is set to a value in the range of 90℃ to 95℃;

[0124] By the procedure in step (ii)

[0125] · At the time of the first contact between the amine solution and the phosgene solution in the third mixing device, the pressure in the reduced pressure zone of the plant part (IV) is in the range of 16 bar to 20 bar;

[0126] · The temperature of the amine solution exiting the first mixing device is in the range of 95℃ to 100℃;

[0127] · The temperature of the reaction mixture exiting the third mixing device is in the range of 138℃ to 142℃;

[0128] Also, by the procedure in step (iii)

[0129] · The temperature of the phosgene solution withdrawn from the second mixing device is lowered to a value in the range of 0°C to 5°C, and

[0130] · The pressure in the depressurization zone of the plant section (IV) is increased to a value in the range of 20 bar to 25 bar, and

[0131] Finally, by the procedure in step (iv)

[0132] · The temperature of the amine solution withdrawn from the first mixing device is lowered to a value in the range of 50℃ to 60℃, and

[0133] · The temperature of the reaction mixture exiting the third mixing device in the target state is in the range of 128℃ to 132℃, and

[0134] · The pressure in the reduced pressure zone of the plant section (IV) is maintained in the range of 20 bar to 25 bar.

[0135] Preferably, in the case of the pressure within the reduced pressure zone of the plant part (IV) established in step (iii), a value higher than the pressure within this reduced pressure zone is selected when the continuous supply of amine to the first mixing device is started in step (ii). This ensures that the reaction does not stop even when the excess phosgene is reduced as a result of continuously increasing the concentration of the supplied aniline solution.

[0136] Depending on the pressure and temperature conditions selected in step (ii), the dissolved phosgene is partially converted from the liquid phase to the gaseous state (degassing). This causes the pressure within the depressurization zone of the plant section (IV) to increase. In the process according to the present invention, when the pressure within the depressurization zone of the plant section (IV) is in the range of 16 bar to 25 bar, preferably 16 bar to 20 bar (starting pressure), the amine solution and the phosgene solution first come into contact with each other in the third mixing device. Here, the residence time of the amine solution from the start of the supply of amine to the first mixing device until the amine solution first arrives in the third mixing device, which can be easily determined for a given plant, should be taken into account. Unless any specific measures are taken, in addition to the pressure caused by the given boundary conditions, the pressure within the depressurization plant section (IV) may be adjusted by the addition of an inert gas (particularly nitrogen) and / or hydrogen chloride. Hydrogen chloride can advantageously be drawn from the first, second, and / or third gas phases, wherein such hydrogen chloride can also originate from the initial manufacturing period for the production of isocyanate (stored in a suitable storage container during the process) if necessary.

[0137] After step (iv) is performed, the plant operates normally and can continue to operate until the next manufacturing shutdown as described above.

[0138] Manufacturing shutdown (transition of the plant from the target state to the plant shutdown state)

[0139] Any continuous manufacturing process must be interrupted from time to time because demand for the manufactured product drops or work on the plant (maintenance, inspection, etc.) is required. To this end, in the context of the present invention, it is preferable to proceed as follows:

[0140] When the flow rate does not change compared to the target state (normal operation), the temperature of the phosgene and amine solutions is initially raised. This has the effect of avoiding a temperature drop after the third mixing device, which could potentially lead to fouling of the reactor. The temperature of the phosgene solution is raised from its target value for normal operation in the range of 0°C to 10°C to a value preferably in the range of 100°C to 125°C. The temperature of the amine solution is raised from its target value for normal operation in the range of 50°C to 80°C to a value preferably in the range of 100°C to 125°C. As a result, the temperature of the reaction mixture exiting the third mixing device is raised to a higher value than its target value for normal operation in the range of 125°C to 135°C. When a temperature in the range of > 135°C to 140°C, preferably > 135°C to 137°C, is achieved, the additional supply of amine is stopped, whereas, in contrast, the flow of solvent through the first mixing device to the third mixing device is maintained, wherein this flow rate may also be higher or lower than in the case of normal operation, and may be particularly higher (to control the temperature at the outlet of the third mixing device). The temperature at the outlet of the third mixing device decreases as the dilution rate increases. This temperature is preferably maintained in the range of 115°C to 125°C.

[0141] In order to clean the used apparatus and react any amine still present inside, a phosgene solution is continued to be added through the second mixing apparatus, the third mixing apparatus, and the apparatus placed downstream thereof for a period preferably ranging from 15 minutes to 3 hours, e.g., 20 minutes, even after the amine supply has been stopped. After this period has elapsed, the phosgene supply is also stopped, and only the solvent for diluting / cleaning the phosgene solution still present in the apparatus is pumped through the second mixing apparatus to the third mixing apparatus and from the apparatus placed downstream thereof. When sufficient phosgene has been transferred (i.e., to a predetermined critical concentration), the metering of the solvent through the second mixing apparatus is stopped. Thereafter (particularly after 10 to 20 minutes, e.g., after 15 minutes), the supply of the solvent through the first mixing apparatus is also stopped.

[0142] The extent to which phosgene must be depleted in the plant varies depending on the situation. In the case of a relatively short manufacturing shutdown where no work is performed in the phosgene-transfer plant section, a complete replacement of phosgene is generally not necessary. However, if the plant is taken off-line for an extended period or if work needs to be performed in the phosgene-transfer plant section, it is necessary to completely replace and / or decompose phosgene through a subsequent cleaning step, such as a reaction with ammonia.

[0143] The present invention is described in more detail below with reference to examples.

[0144] Example:

[0145] Percentage concentration is a mass percentage based on the total mass of each substance stream. Refer to the above description for the definition of phosgene excess.

[0146] The example was carried out in a mini-plant, in which, at the target state, an amine solution consisting of about 11.6 kg / h of MDA and about 27 kg / h of MCB from the first mixing device was mixed with a phosgene solution with about 60% phosgene excess from the second mixing device in a dynamic mixer (third mixing device), and the resulting mixture was fed to an adiabatically operated bubble column reactor (diabatically operated reaction zone, first reactor). The product mixture from the bubble column reactor was depressurized in two depressurization devices (a first depressurization device corresponding to the depressurization zone of plant part (IV) and a second depressurization device of plant part (V), and the obtained liquid phase was fed to a falling membrane evaporator (an isothermally operated reaction zone, second reactor). The liquid phase obtained therefrom was fed to a distillation column, in which MDI was obtained as a bottom stream and a phosgene- and hydrogen chloride-containing gaseous phase was obtained as an top stream. The gas phase obtained from two depressurization devices was combined with this gas phase.

[0147] Example 1 (for comparison - excessively low starting pressure):

[0148] A 60% phosgene solution is prepared by mixing monochlorobenzene (MCB) and phosgene, and the solution is used at a mass flow rate = 51.4 kg / h and at a temperature of 120℃, it was transferred from the second mixing device to the third mixing device. The MCB heated to 95℃ was subsequently transferred at a mass flow rate = 30 kg / h was transferred from the first mixing device to the third mixing device. Subsequently, the supply of MDA to the second mixing device and from there to the third mixing device was started. As a result, the temperature of the amine solution reached 100°C. The reaction was initiated at an amine solution concentration of 25% (corresponding to an amount of MDA of approximately 9.7 kg / h and an amount of MCB of approximately 28.9 kg / h). After about 7 minutes, the amine solution reached the third mixing device and the reaction began. At this point, the pressure within the reduced pressure zone (= starting pressure) was 15 bar. As a result of the reaction initiation, the temperature at the outlet of the third mixing device rose from 100°C to 135°C over a period of 5 minutes. As soon as the temperature rise stopped, the concentration of the amine solution was increased to 30% (corresponding to an amount of MDA of approximately 11.6 kg / h and an amount of MCB of approximately 27 kg / h). As a result of these changes, the temperature at the outlet of the third mixing device rose to 140°C. The pressure in the reduced pressure zone increased to 20 bar.

[0149] While taking into account the temperature at the outlet of the third mixing device (which must not fall below 135°C), the temperature of the phosgene solution was lowered from 120°C to 0°C over 90 minutes. About 10 minutes after the temperature of the phosgene solution began to decrease, the excess phosgene was reduced stepwise from 210% to 60% by continuously increasing the mass flow rate and concentration of the amine solution (the final value was about 60 kg / h of an amine solution with a concentration of 30%). At the same time, the pressure in the depressurization zone was increased to 26 bar. It took about 60 minutes to reduce the excess phosgene (while maintaining the temperature at the outlet of the third mixing device at least at 135°C).

[0150] While still reducing the phosgene excess, it was observed that gas generation in the depressurization zone decreased. At a pressure of 24 bar in the depressurization zone and about 60% phosgene excess, a temperature drop occurred at the outlet of the third mixing device (implying that the reaction was in a "stopped" state). The experiment had to be terminated to avoid contamination of the reactor.

[0151] Example 2 (for comparison - starting pressure is sufficiently high, but the temperature at the outlet of the third mixing device is excessively high):

[0152] A 60% phosgene solution is prepared by mixing monochlorobenzene (MCB) and phosgene, and the solution is used at a mass flow rate = 51.4 kg / h and was transferred from the second mixing device to the third mixing device at a temperature of 120℃. The MCB heated to 80℃ was subsequently transferred at a mass flow rate = 30 kg / h was transferred from the first mixing device to the third mixing device. Subsequently, the supply of MDA to the second mixing device and from there to the third mixing device was started. As a result, the temperature of the amine solution became 95°C. The initiation was carried out at an amine solution concentration of 25% (corresponding to an amount of MDA of about 9.7 kg / h and an amount of MCB of about 28.9 kg / h). After about 7 minutes, the amine solution reached the third mixing device and the reaction began. The pressure in the reduced pressure zone prior to the start of the reaction was 15 bar, and was increased to 20 bar (= starting pressure) by adding nitrogen within a suitable time before the MDA and phosgene first came into contact. As a result of the reaction initiation, the temperature at the outlet of the third mixing device rose from 100°C to 135°C over 5 minutes. As soon as the temperature rise stopped, the concentration of the amine solution increased to 30% (corresponding to an amount of MDA of about 11.6 kg / h and an amount of MCB of about 27 kg / h). As a result of this change, the temperature at the outlet of the third mixing device rose to 140°C. As the reaction proceeded, the pressure in the reduced pressure zone increased to 26 bar over 10 minutes.

[0153] Without considering the temperature at the outlet of the third mixing device, the temperature of the phosgene solution was lowered from 120°C to 0°C over 90 minutes. About 10 minutes after the temperature of the phosgene solution began to decrease, the excess phosgene was reduced stepwise from 210% to 60% by continuously increasing the mass flow rate and concentration of the amine solution (the final value was about 60 kg / h of an amine solution with a concentration of 30%). (Also without considering the temperature at the outlet of the third mixing device) it took about 30 minutes to reduce the excess phosgene. The temperature at the outlet of the third mixing device rose to 150°C, and along with this, more solid was formed and the inner reactor walls were coated with solid. The experiment was terminated to avoid further contamination of the reactor.

[0154] Example 3 (according to the present invention - the starting pressure is sufficiently high and the temperature at the outlet of the third mixing device is within a suitable range):

[0155] A 60% phosgene solution is prepared by mixing monochlorobenzene (MCB) and phosgene, and the solution is used at a mass flow rate = 51.4 kg / h and was transferred from the second mixing device to the third mixing device at a temperature of 120℃. The MCB heated to 80℃ was subsequently transferred at a mass flow rate = 30 kg / h was transferred from the first mixing device to the third mixing device. Subsequently, the supply of MDA to the second mixing device and from there to the third mixing device was started. As a result, the temperature of the amine solution became 95°C. The initiation was carried out at an amine solution concentration of 25% (corresponding to an amount of MDA of about 9.7 kg / h and an amount of MCB of about 28.9 kg / h). After about 7 minutes, the amine solution reached the third mixing device and the reaction began. The pressure in the reduced pressure zone prior to the start of the reaction was 15 bar, and was increased to 20 bar (= starting pressure) by adding nitrogen within a suitable time before the MDA and phosgene first came into contact. As a result of the reaction initiation, the temperature at the outlet of the third mixing device rose from 100°C to 135°C over 5 minutes. As soon as the temperature rise stopped, the concentration of the amine solution increased to 30% (corresponding to an amount of MDA of about 11.6 kg / h and an amount of MCB of about 27 kg / h). As a result of this change, the temperature at the outlet of the third mixing device rose to 140°C. As the reaction proceeded, the pressure in the reduced pressure zone increased to 26 bar over 10 minutes.

[0156] While taking into account the temperature at the outlet of the third mixing device (which should be maintained at approximately 140°C), the temperature of the phosgene solution was lowered from 120°C to 0°C over 90 minutes. About 10 minutes after the temperature of the phosgene solution began to decrease, the excess phosgene was reduced stepwise from 210% to 60% by continuously increasing the mass flow rate and concentration of the amine solution (the final value was about 60 kg / h of an amine solution with a concentration of 30%). It took about 30 minutes to reduce the excess phosgene (while maintaining the temperature at the outlet of the third mixing device at approximately 140°C).

[0157] After achieving a 60% phosgene excess, the temperature of the amine solution was lowered from 95°C to 55°C over 30 minutes. Under these conditions (amine solution temperature 55°C, phosgene solution temperature 0°C, phosgene excess 60%, pressure in the reduced pressure zone 26 bar), the temperature of the reaction mixture at the outlet of the third mixing device becomes 130°C. Thus, the system is in the target state. The time from the start to the achievement of the target state was approximately 4 hours.

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