Method for storing mixture containing toluene diisocynate and high-boiling compound and method for post-processing crude reaction product containing toluene diisocynate
By stirring and adjusting component ratios and controlling viscosity, the viscosity problem of toluene diisocyanate residue in storage and treatment is solved, the storage period is extended and the loss of TDI is reduced, and the stable operation of the equipment and efficient reuse of TDI is achieved. .
Patent Information
- Application Number
- CN202380036481.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-04-26
- Filing Date
- 2023-04-25
- Publication Date
- 2024-12-31
AI Technical Summary
In the prior art, when storing and treating toluene diisocyanate (TDI) residues, there are viscosity problems that lead to a high risk of equipment failure, and the increase in storage instability and viscosity lead to loss of TDI, making it difficult to effectively store and reuse them in the intermediate state.
By stirring the mixture containing 20-80% toluene diisocyanate, the viscosity is controlled below 1 Pas, the component ratio is adjusted using solvent or TDI, combined with appropriate temperature and pressure conditions, the storage time is extended and the fluidity is maintained, and the scaling and precipitation is prevented.
It effectively reduces the loss of TDI, extends the storage period, ensures the stable operation of the equipment and the efficient reuse of TDI, and reduces the risk of equipment failure.
Smart Images
Figure CN119233965A_ABST
Abstract
Description
[0001] manual
[0002] The present invention relates to a method for storing a mixture containing toluene diisocyanate and high boiling point compounds, the mixture containing 20% to 80% by weight of toluene diisocyanate. The present invention also relates to a method for post-processing a crude reaction product containing toluene diisocyanate, the method comprising removing a solvent from the crude reaction product containing toluene diisocyanate, thereby obtaining crude toluene diisocyanate; removing toluene diisocyanate from the crude toluene diisocyanate, thereby obtaining purified toluene diisocyanate as a product and a residue containing toluene diisocyanate; feeding the residue containing toluene diisocyanate to a dryer, obtaining a stream substantially containing toluene diisocyanate and a dryer residue in the dryer; and recycling the stream substantially containing toluene diisocyanate to the step of removing toluene diisocyanate from the crude toluene diisocyanate.
[0003] Toluene diisocyanate (TDI) is used in particular as an intermediate product in the preparation of polyurethanes and is usually prepared by phosgenation of toluenediamine (TDA) in the gas or liquid phase.
[0004] The crude reaction product obtained by the phosgenation process contains impurities and is post-treated to obtain purified TDI as a product. The post-treatment of the crude reaction product usually includes at least one distillation step for removing low-boiling compounds such as solvents and a further distillation step in which TDI is removed as a product. In this distillation, a distillation residue is obtained which still contains a large amount of TDI.
[0005] To recover TDI from the distillation residue, a dryer can be used in which the TDI is evaporated and recycled back to the distillation step. The remaining dryer residue is usually used for heating, for example as a substitute for fuels such as activated carbon for sewage sludge incineration or for heating cement kilns. Alternatively, the dryer residue can be decomposed, for example in a hydrolysis process and recycled as TDA.
[0006] Processes for working up distillation residues are described, for example, in DE-A 28 46 815, DE-A 29 15830 or DE-A 43 17 669.
[0007] However, a disadvantage of all known processes is that the distillation residues are highly viscous and form solids during reprocessing, so that the plant components for working up the distillation residues are subject to a certain risk of failure. Since the distillation residues are unstable in storage and are subject to a continuous increase in viscosity, the distillation residues are currently fed directly to thermal applications in order to prevent such failures. The direct use of the distillation residues in thermal applications results in significant losses of TDI. In addition, an incinerator of sufficient size must also be provided.
[0008] In order to reduce TDI losses, in particular in the event of a dryer failure, an intermediate storage device is required until the shut-down plant part can be restarted.
[0009] It was therefore an object of the present invention to provide a process which allows the storage of mixtures containing TDI.It was a further object of the present invention to provide a process for working up a crude reaction product comprising toluene diisocyanate, in which the loss of TDI is minimized.
[0010] This object is achieved by a method for storing a mixture containing toluene diisocyanate and a high boiling point compound, the mixture containing 20% to 80% by weight of toluene diisocyanate, the method comprising:
[0011] (a) feeding a mixture containing toluene diisocyanate and a high boiling point compound into a storage container; and
[0012] (b) A mixture containing toluene diisocyanate and a high boiling point compound is stirred.
[0013] Surprisingly, it has been found that it is possible to store a mixture containing TDI and high boilers for a certain period of time if the stored mixture is stirred, even though such a mixture containing TDI and high boilers is generally unstable in storage.
[0014] In the context of the present invention, "storage" means delivering residence time without separating the components of the feed mixture. This means in particular that during storage, the separation between TDI and high boiling point compounds is as low as possible, preferably, no separation occurs between TDI and high boiling point compounds, and no evaporation of the expected reaction or gaseous product occurs. However, composition changes caused by adding higher or lower boiling point components or by time-related reactions (e.g., dimerization of TDI, trimerization and / or reactions of other components in the mixture with each other) are not excluded herein, and these composition changes may have an impact on the viscosity of the stored mixture. In addition, the evaporation caused by low boiling point components such as dissolved inert gases, reaction products such as carbon dioxide due to storage temperature (especially when the temperature of the stored mixture changes) cannot be excluded. However, "storage" in the sense of the present invention does not include expected evaporation and setting temperature so that low boiling point compounds must evaporate.
[0015] The mixture containing TDI and high boiling point compounds that can be stored using the method of the present invention contains 20% to 80% by weight, preferably 30% to 70% by weight, particularly 40% to 60% by weight of TDI, and can be used, for example, as a residue obtained by post-processing a crude reaction product containing TDI. High boiling point compounds in the context of the present invention are all components whose boiling point is higher than the boiling point of TDI. Such high boiling point compounds particularly include urea compounds, uretdione (uretdione), isocyanurate, carbodiimide and high-order condensation or polymerized compounds, particularly polymerized TDI.
[0016] Properties of a mixture containing TDI and high boiling point compounds, such as viscosity or the amounts of components in a mixture containing TDI and high boiling point compounds, always relate to the complete mixture which may contain other components besides TDI and high boiling point compounds, such as low boiling point compounds or solvents.
[0017] During storage, in particular TDI polymerizes, which leads to an increase in the viscosity of the mixture containing TDI and high boiling point compounds. Although the viscosity increases due to stirring, the mixture containing TDI and high boiling point compounds can maintain sufficient fluidity for a certain period of time. This allows intermediate storage and feeding the stored mixture containing TDI and high boiling point compounds into another process step, in particular into the dryer of the next stage.
[0018] If the viscosity of the mixture containing TDI and high boiling point compounds is reduced, the storage period can be extended. Preferably, the viscosity of the mixture containing TDI and high boiling point compounds is set so that after a predetermined storage time, the viscosity is below 1 Pas, particularly preferably below 500 mPas. According to DIN 53019-1:2008, DIN 53019-2:2001 and DIN 53019-3:2008, the viscosity is determined, for example, using a rotational viscometer, a capillary viscometer or online by a tuning fork or other resonant frequency viscometer, or can be measured indirectly, for example, by the power requirement of the stirrer or circulating pump.
[0019] The viscosity of the mixture containing TDI and high boiling point compounds can be set before being fed into the storage container, or alternatively or in addition thereto, in the storage container. The viscosity can be set, for example, by setting the content of the solvent or TDI in the mixture containing TDI and high boiling point compounds or by setting the temperature. If the viscosity is set by adding TDI to the mixture containing TDI and high boiling point compounds, the amount of TDI preferably added to the mixture containing TDI and high boiling point compounds is selected to increase the content of TDI in the mixture containing TDI and high boiling point compounds by at least 1 weight %, more preferably at least 5 weight %, and particularly at least 10 weight %. If the viscosity is set by adding a solvent to the mixture containing TDI and high boiling point compounds, the amount of the solvent added to the mixture containing TDI and high boiling point compounds is selected to not drop below 20 weight %, preferably not drop below 30 weight %, and particularly not drop below 40 weight %.
[0020] If a solvent or TDI is used to set the viscosity of the mixture comprising TDI and high boiling point compounds in the storage container, the solvent or TDI can first be introduced into the storage container and the mixture comprising TDI and high boiling point compounds can subsequently be fed into the storage container. Alternatively or in addition, it is also possible to feed the mixture comprising TDI and high boiling point compounds into the storage container and then add the solvent or TDI. This further allows additional addition of solvent or TDI in case the viscosity increases during storage and reaches a predetermined maximum value.
[0021] If a solvent is used to set the viscosity, any solvent in which TDI is soluble can be used. Suitable solvents are selected, for example, from chlorinated aromatic hydrocarbons such as dichlorobenzene, monochlorobenzene or trichlorobenzene or mixtures thereof, aromatic or aliphatic hydrocarbons such as toluene, xylene, benzene, pentane, hexane, heptane, octane, cyclohexane, biphenyl, ketones such as 2-butanone, methyl isobutyl ketone, esters such as diethyl isophthalate, ethyl acetate, butyl acetate, nitriles such as acetonitrile, sulfolane and mixtures thereof. Particularly preferably, the solvent used to set the viscosity of the mixture comprising TDI and the high boiling point compound is the same as the solvent used in the preparation method of TDI. Preferably, the solvent is monochlorobenzene, dichlorobenzene, trichlorobenzene, toluene or any mixture thereof, in particular monochlorobenzene, dichlorobenzene or toluene.
[0022] Whether the viscosity is set by adding solvent or by adding TDI, if the solvent or TDI is added before the mixture containing TDI and high boiling point compounds is fed into the storage container, the amount of solvent or TDI is selected so that the viscosity of the mixture containing TDI and high boiling point compounds after the predetermined storage time is less than 1 Pas, preferably less than 500 mPas. The storage time is preferably selected so that it corresponds to the shutdown time of the dryer usually for maintenance, for example 1 day to 10 days. However, when a sufficient amount of solvent and / or TDI is added, a storage time of more than 10 days and possibly in the range of 20 days to 50 days or even longer days can be achieved. If the mixture containing TDI and high boiling point compounds is mixed with the solvent in a ratio of 4:1, for example, a storage time of about 20 days can be achieved, and if the mixture containing TDI and high boiling point compounds is mixed with the solvent in a ratio of 1:1, a storage time of more than 50 days can be achieved.
[0023] When a mixture containing TDI and a high boiling point compound is mixed with TDI in a 1:1 ratio, a storage time of more than 50 days can also be achieved.
[0024] Alternatively, the viscosity of the mixture containing TDI and high boiling point compounds can be set by setting the temperature in the storage container. The lower the temperature in the storage container, the slower the viscosity of the mixture containing TDI and high boiling point compounds increases. In order to set the temperature, the mixture containing TDI and high boiling point compounds is preferably cooled to a desired temperature before being fed into the storage container. In addition, in order to heat or cool the mixture containing TDI and high boiling point compounds stored in the storage container, the storage container may include a temperature control unit (e.g., a double jacket or a temperature control coil), and / or a heater cooler unit is provided in an external recirculation loop.
[0025] The temperature in the storage container is preferably in the range of 20°C to 100°C, in particular in the range of 35°C to 85°C. In order to set the temperature in the storage container, any suitable device for setting the temperature can be used. Such devices for setting the temperature include, for example, a storage container with a double jacket through which a heating medium flows or a heating coil in the storage container or on the outer wall of the storage container. The heating coil can be a pipe or pipe fitting through which the heating medium flows, or an electric heating coil. In addition, any other device known to the technician for setting the temperature can be used, such as an external heat exchanger or a heater in an external circuit. The heater in the external circuit can be an electric heater or a heater using a heating medium.
[0026] The pressure in the storage container is preferably in the range from 500 mbar (absolute pressure) to 2 bar (absolute pressure), in particular in the range from 800 mbar (absolute pressure) to 1.5 bar (absolute pressure).
[0027] In order to reduce or prevent the fouling caused due to high boiling point compound precipitation, stir the mixture containing TDI and high boiling point compound.Through stirring, the mixture containing TDI and high boiling point compound keeps moving, and due to this motion, realizes the uniform distribution of high boiling point compound, these high boiling point compounds can be the form of particle, high viscosity droplet or are dissolved in the mixture containing TDI and high boiling point compound.The stirring of the mixture containing TDI and high boiling point compound can be realized by using the recirculation loop passed by the stored toluene diisocyanate or by using the agitator in the storage container.If use agitator, then can use any suitable agitator that makes the mixture containing TDI and high boiling point compound keep moving, for example axial conveying agitator or radial conveying agitator.Suitable agitator is for example propeller mixer, paddle mixer or anchor agitator.
[0028] If agitation of the mixture containing TDI and high boiling point compounds is achieved by using a recirculation loop, a stream containing the mixture of TDI and high boiling point compounds is withdrawn from a storage vessel, conveyed by a pump through the recirculation loop and returned to the storage vessel. The pump used in the recirculation loop may be any pump suitable for conveying viscous materials, such as a centrifugal pump, a displacement pump, a diaphragm pump or a tank motor pump.
[0029] Instead of using either an agitator or a recirculation loop to agitate the mixture containing TDI and high boilers, it is also possible to provide both an agitator and a recirculation loop.
[0030] In order to reduce or prevent scaling, it is further preferred that if the storage container, the connecting lines leading to the storage container and other equipment parts through which the mixture containing TDI and high boiling point compounds flows have no dead space, and if the line for extracting the mixture containing TDI and high boiling point compounds from the storage container leaves at the bottom of the container, the bottom is inclined so that the line for extracting the mixture containing TDI and high boiling point compounds is connected to the storage container at the lowest point of the storage container.
[0031] In order to carry out pressure compensation during filling or emptying, the storage container can be connected to an inert gas supply source. During emptying the storage container, an inert gas is fed into the storage container, and during filling the storage container with a mixture containing TDI and high boiling point compounds, an inert gas is extracted from the storage container. In this way, by feeding an inert gas into the storage container or extracting an inert gas from the storage container, liquid level changes can also be compensated. In addition, it is preferred to purge the storage container with an inert gas before starting to fill the mixture containing TDI and high boiling point compounds into the storage container. In order to avoid reacting with the components in the gas phase, it is further preferred to cover the mixture containing TDI and high boiling point compounds in the storage container with an inert gas phase. The inert gas used for pressure compensation, for purging and / or for covering the mixture containing TDI and high boiling point compounds can be any gas that does not contain any component that reacts with the components of the mixture containing TDI and high boiling point compounds. Suitable inert gases are, for example, nitrogen, rare gases such as argon or carbon dioxide. Particularly preferably, the inert gas is nitrogen. If the storage container is connected to an inert gas supply, it is further preferred to use inert gas to set the pressure in the storage container.
[0032] In order to prevent the gas from being introduced directly into the atmosphere, the storage container can also be connected to an exhaust gas system or a filter system in which the gas extracted from the storage container is purified before being introduced into the atmosphere.
[0033] The mixture containing TDI and high boiling point compounds stored in the storage container can be any mixture containing TDI and high boiling point compounds. However, preferably, the mixture containing TDI and high boiling point compounds is a residue containing TDI obtained by post-processing a crude reaction product containing TDI.
[0034] The process for working up the crude reaction product comprising TDI preferably comprises:
[0035] (a) removing a solvent from a crude reaction product containing toluene diisocyanate in a solvent removal step, thereby obtaining crude toluene diisocyanate;
[0036] (b) removing toluene diisocyanate from crude toluene diisocyanate in a toluene diisocyanate removal step, thereby obtaining purified toluene diisocyanate as a product and a residue containing toluene diisocyanate;
[0037] (c) feeding the residue comprising toluene diisocyanate to a dryer, in which a stream comprising essentially toluene diisocyanate and a dryer residue are obtained, and recycling the stream comprising essentially toluene diisocyanate to the toluene diisocyanate removal step in step (b), or feeding the residue comprising toluene diisocyanate to a hydrolysis step, in which toluene diisocyanate is hydrolyzed to form the corresponding toluenediamine;
[0038] According to the invention, at least a portion of the residue comprising toluene diisocyanate is at least temporarily stored in a storage container.
[0039] The crude reaction product comprising TDI can be obtained by any suitable method for preparing TDI known to those skilled in the art.Usually, TDI is formed by reacting toluenediamine (TDA) and phosgene in the presence of a solvent.Therefore, the crude reaction product comprising TDI obtained in the reaction contains phosgene, solvent, hydrochloride and the by-product also formed in the reaction in addition.For post-treatment of the crude reaction product, unreacted phosgene and hydrochloride are removed in a first step.The crude reaction product comprising TDI by the inventive method post-treatment is the composition obtained after removing phosgene and hydrochloride.
[0040] The removal of the solvent in step (a) and the removal of the TDI in step (b) can be carried out as described in DE-A 102 60 092.
[0041] For post-treatment, in the first step (a), the solvent is removed from the crude reaction product containing TDI, thereby obtaining crude TDI. Preferably, the solvent is removed by a first distillation process. The first distillation process may include one distillation stage or more than one distillation stage, such as two or three distillation stages. If the first distillation process is carried out in more than one distillation stage, each distillation stage is usually carried out in a separate distillation tower. Usually, the solvent is a low-boiling compound, which means that the boiling point of the solvent is lower than the boiling point of TDI. Therefore, if distillation is carried out in a distillation tower, the solvent is removed at the top of the distillation tower, and the crude TDI is taken out at the bottom of the distillation tower. The crude TDI contains high-boiling compounds and residual solvent. The first distillation process for removing the solvent from the crude reaction product containing TDI is preferably carried out at a column bottom temperature of 90° C. to 260° C., more preferably at a column bottom temperature of 120° C. to 220° C., and in particular at a column bottom temperature of 150° C. to 200° C., and at a pressure in the range of 2 mbar to 1000 mbar (absolute pressure), preferably in the range of 50 mbar to 200 mbar (absolute pressure). If the first distillation process is carried out in more than one distillation column, the distillation columns are usually operated at decreasing pressures within the above range.
[0042] From the crude TDI thus obtained, purified TDI is removed as product in step (b). The removal of TDI from the crude TDI is also preferably carried out by distillation. In this second distillation, the purified TDI obtained as product can be obtained as a top stream or, if further low-boiling compounds are removed in the second distillation, as a side stream. If purified TDI is obtained as a side stream, further low-boiling compounds are removed as a top stream. In each case, the bottom stream of the second distillation is a residue comprising TDI. This residue comprising TDI can still contain 20% to 80% by weight of TDI, preferably 40% to 60% by weight of TDI. The second distillation process for removing purified TDI from the crude TDI is preferably carried out at a column bottom temperature of 90° C. to 260° C., more preferably at a column bottom temperature of 100° C. to 200° C., and in particular at a column bottom temperature of 110° C. to 150° C., and at a pressure in the range of 2 mbar to 1000 mbar (absolute pressure), preferably in the range of 5 mbar to 50 mbar (absolute pressure). The second distillation can comprise one distillation stage or more than one distillation stage, for example two or three distillation stages. It is also possible to carry out the distillation in a dividing wall column. If the second distillation is carried out in more than one distillation stage, each distillation stage is usually carried out in a separate distillation column.
[0043] In step (c), the residue containing TDI is fed to a dryer to recover the TDI obtained in the residue containing TDI and thus increase the yield of the process, or alternatively to a hydrolysis unit in which the TDI is hydrolyzed to form the corresponding toluenediamine (TDA). The stream essentially containing TDI is preferably recycled to step (b), in which purified TDI is taken out from the crude TDI. Dryer residues, which in particular contain highly viscous or even solid components, are usually fed to thermal uses, for example as a substitute for fuels such as activated carbon for sewage sludge incineration or for heating cement kilns. Alternatively, the desiccant residue can be fed to a hydrolysis step in which the TDI can be decomposed and recycled as TDA.
[0044] The dryer may be any suitable dryer, in particular a mechanical direct dryer, such as an extruder dryer, a paddle dryer, a fluidized bed dryer or a thin film dryer.
[0045] Furthermore, the dryer may comprise a fluidized bed as described, for example, in DE-A 29 15 830 .
[0046] The separation of TDI from the TDI-comprising residue is generally carried out at a temperature in the range of 100 to 350° C., more preferably in the range of 150 to 300° C., in particular in the range of 180 to 270° C. and at a pressure in the range of 5 to 300 mbar (absolute pressure), more preferably in the range of 10 to 200 mbar (absolute pressure), in particular in the range of 20 to 150 mbar (absolute pressure).
[0047] According to the invention, at least a portion of the TDI-comprising residue obtained in step (b) is stored in a storage container.
[0048] In order to store the at least part of the residue containing TDI, it is possible to continuously separate a part of the residue containing TDI and feed this separated part into a storage container. However, preferably, only the residue containing TDI is fed into the storage container when the dryer or the hydrolysis is not in operation, for example if the dryer fails and / or shuts down. By feeding the residue containing TDI into the storage container, it is possible to recover the contained TDI at a later time when the dryer is in operation again. Therefore, according to the prior art, the yield can be significantly increased in case the entire residue containing TDI is incinerated when the dryer is not in operation.
[0049] In particular in the case where the dryer or the hydrolysis is not in operation, the entire residue containing TDI obtained in step (b) is fed into the storage container until the storage container is completely filled. Also in the process according to the invention, after complete filling, it is necessary to remove the residue containing TDI from the process and feed it to a thermal use. Preferably, however, the storage container is dimensioned so that the entire residue containing TDI obtained during the normal shutdown period of the dryer can be fed into the storage container.
[0050] As mentioned above, if the viscosity of the TDI-containing residue is reduced, the storage period can be extended. Preferably, the viscosity of the at least part of the TDI-containing residue stored in the storage container is set so that after a predetermined storage time, the viscosity is below 1 Pas, in particular below 500 mPas, and can be set, for example, by setting the content of solvent or by the content of TDI in the TDI-containing residue or by setting the temperature in the storage container.
[0051] In addition to the above-described method of setting the TDI content and thereby the viscosity in the residue comprising TDI by adding TDI, it is also possible in the process according to the invention for working up a crude reaction product comprising TDI to set the amount of TDI in the residue comprising TDI and thereby the viscosity of said at least part of the residue comprising TDI by withdrawing TDI in step (b). This can be achieved, for example, by reducing the amount of purified TDI withdrawn from the apparatus for carrying out step (b). If a distillation column or an evaporator is used to withdraw TDI from the crude TDI, this can be achieved, for example, by reducing the column bottom temperature or by reducing the evaporation temperature, respectively.
[0052] In order to avoid precipitation of high-boiling compounds contained in the residue containing TDI, it is preferred to stir the residue containing TDI in the storage container. Stirring can be carried out by stirring the residue containing TDI in the storage container using a stirrer as described above and / or by connecting the storage container to a recirculation loop through which the stored residue containing TDI passes.
[0053] In the process for working up a crude reaction product comprising TDI, the recirculation loop can be a separate loop or a part of a pipeline for conveying the residue comprising TDI from the storage vessel back into the process for working up TDI.
[0054] If the pipeline for conveying the residue containing TDI is used as a recirculation loop, an additional connection is usually required, through which the residue containing TDI can be fed back into the storage container from the pipeline through which the residue containing TDI in the storage container is extracted. For this purpose, a connecting line is preferably provided, which connects the pipeline through which the residue containing TDI is extracted from the storage container to the storage container. In order to allow the residue containing TDI to be recycled into the method or to be taken out of the method, it is preferred that the connecting line includes a control element for closing the connecting line, such as a valve, a tap or a piston. In addition, in order to recirculate the residue containing TDI for stirring, at least one additional control element for closing the pipeline is provided in the pipeline through which the residue containing TDI is extracted upstream of the connection point of the connecting line.
[0055] By closing the control element in the line for withdrawing the residue containing TDI and opening the control element in the connecting line, the residue containing TDI is recirculated from the storage container via the line for withdrawing the residue containing TDI and the connecting line back to the storage container, and by closing the control element in the connecting line and opening the control element in the line for withdrawing the residue containing TDI, the residue containing TDI can be withdrawn and recycled to the workup process or withdrawn from the process and fed, for example, to thermal use. After use, the storage container must be cleaned by flushing with TDI or solvents to avoid clogging or scaling.
[0056] An embodiment of the process according to the invention for working up a crude reaction product comprising TDI is shown in the single FIGURE.
[0057] The Figure schematically shows a process for working up a crude reaction product comprising TDI.
[0058] For the work-up of the crude reaction product 1 containing TDI, the crude reaction product 1 is fed to a solvent removal step 3. In the solvent removal step 3, the solvent 5 is preferably removed from the crude reaction product 1 by distillation or by evaporation. The solvent 5 is usually a low-boiling compound, so that TDI and high-boiling compounds form one fraction and the solvent forms a second fraction. If applicable, the solvent 5 removed from the crude reaction product containing TDI can be recycled to the preparation process of TDI after further work-up (by which low-boiling impurities are removed from the solvent before the solvent is recycled into the preparation process, which low-boiling impurities can also be removed in the solvent removal step 3).
[0059] A second fraction comprising TDI and high boiling point compounds is withdrawn from the solvent removal step 3 as crude TDI 7 and fed to the TDI withdrawal step 9. In the TDI withdrawal step, a portion of TDI is separated from the crude TDI and withdrawn from the TDI withdrawal step as purified TDI 11, which is the product of the work-up process.
[0060] The remaining TDI and high boiling point compounds form a residue 13 containing TDI, which is also removed from the TDI removal step 9. In a normal work-up method, the residue 13 containing TDI is fed to a dryer 15. In the dryer 15, TDI and other components that are optionally evaporated in the dryer are removed and recycled to the TDI removal step 9 as recovered TDI 17. As an alternative, the residue 13 containing TDI can be fed to a hydrolysis step, in which TDI is hydrolyzed to form the corresponding TDA. The TDA can then be worked up to remove water and recycled to the reaction to form TDI.
[0061] All components which are not evaporated in the dryer 15 form a dryer residue 19 which is removed from the dryer 15 and generally fed to a thermal use 21. In addition to the thermal use 21, the dryer residue can also be fed to any other use. However, generally, the dryer residue is incinerated to produce energy, as a substitute for activated carbon for sewage sludge incineration or for heating cement kilns. Alternatively, the dryer residue can be decomposed, for example, in a hydrolysis process and recycled as TDA.
[0062] According to the invention, during normal workup of the crude reaction product comprising TDI, a portion of the residue 13 comprising TDI may be fed into the storage container 23. Preferably, however, during normal operation, the entire amount of the residue 13 comprising TDI is fed into the hydrolysis step or the dryer 15, and only in the event that the hydrolysis step or the dryer 15 is shut down, for example for maintenance purposes or during a possible malfunction of the hydrolysis step or the dryer, the entire residue 13 comprising TDI formed in the TDI removal step 9 is fed into the storage container 23.
[0063] In order to be able to further process the residue 13 containing TDI stored in the storage container 23 after restarting the dryer or the hydrolysis step, for example after completing maintenance or after solving a malfunction, it is necessary to keep the residue 13 containing TDI in a flowable condition and further avoid precipitation of components from the residue 13 containing TDI, in particular high boiling point compounds that may form solids.
[0064] In order to keep the residue 13 containing TDI in a flowable condition, the viscosity of the residue containing TDI is preferably set so that it is below 1 Pas, preferably below 500 mPas. In order to set the viscosity of the residue containing TDI, it is possible, for example, to set the content of solvent or TDI in the residue containing TDI 13. In order to set the content of solvent, solvent can be fed into the storage container 23 via the feed line 25. Therefore, if the viscosity is set by the amount of TDI in the residue containing TDI, the viscosity can also be set by adding TDI via the feed line 25. If the viscosity is set by the amount of TDI in the residue containing TDI, it is alternatively or additionally possible to operate the TDI removal step 9 in such a way that the amount of purified TDI 11 is reduced and the amount of TDI in the residue containing TDI 13 is increased. If the TDI removal step 9 comprises distillation or evaporation, this can be achieved by reducing the temperature or increasing the pressure in the TDI removal step 9.
[0065] If a solvent or TDI is used to set the viscosity of the residue containing TDI in the storage container 23, the solvent or TDI can first be introduced into the storage container 23 and then the residue containing TDI 13 can be fed into the storage container 23. Alternatively or in addition, it is also possible to feed the residue containing TDI 13 into the storage container 23 and then add the solvent or TDI via the feed line 25. This further allows additional addition of solvent or TDI in case the viscosity increases during storage and reaches a predetermined maximum value. However, preferably, the solvent or TDI is first introduced into the storage container 23 and then the residue containing TDI 13 is introduced.
[0066] Alternatively or in addition, the viscosity of the residue containing TDI in the storage container 23 can be set by setting the temperature in the storage container. The lower the temperature in the storage container 23, the slower the reaction of components in the residue containing TDI to form high boiling point components such as oligomers or polymers. Therefore, the viscosity of the residue containing TDI in the storage container 23 increases more slowly than at a higher storage temperature.
[0067] In order to reduce precipitation from the residue containing TDI, it is preferred to stir the residue containing TDI in the storage container 23. For this purpose, a stirrer may be provided in the storage container 23. By stirring with the stirrer, the residue containing TDI in the storage container 23 is kept in motion, and thereby all components in the residue containing TDI are kept in a substantially uniform mixture.
[0068] As an alternative to or in addition to the stirrer, a recirculation loop 31 can be provided for stirring the residue comprising TDI. Such a recirculation loop 31 can be a separate loop or part of the pipeline of a device for working up the crude reaction product comprising TDI.
[0069] If the recirculation loop 31 is a separate loop, the recirculation line 33 is connected to the storage container 23 in particular at the bottom of the storage container 23 and ends in the storage container 23, for example, at a side inlet of the storage container 23 or at the top of the storage container 23. In order to recirculate the residue containing TDI, the recirculation line is equipped with a pump. The pump can be any pump that can convey the residue containing TDI, for example a centrifugal pump, a displacement pump, a diaphragm pump or a tank motor pump.
[0070] As an alternative to a separate recirculation line, a recirculation loop can also be realized by using the piping of the device. In this case, for recirculation, the residue containing TDI can be extracted from the storage container 23 by recycling the residue containing TDI to the pipeline through which it is passed in the process or by feeding the residue containing TDI to the pipeline through which it is passed in the thermal use 21. The connecting line branches off from the corresponding line for recirculation and ends in the storage container 23. By closing the corresponding extraction line upstream of the branching point of the connecting line and opening the connecting line, the residue containing TDI can be recirculated for stirring.
[0071] As a further alternative, if a solvent is used to set the viscosity, it is also possible to recycle the TDI-containing residue back to the storage container 23 via the solvent removal step 3, the TDI withdrawal step 9, or if the viscosity is set by the TDI content in the TDI-containing residue or by the temperature of the storage container, it is also possible to recycle the TDI-containing residue back to the storage container 23 via the TDI withdrawal step 9.
[0072] After the process can be returned to normal operation, the residue comprising TDI stored in the storage vessel 23 is recycled into the process.
[0073] If a solvent is added for the purpose of storing the residue containing TDI, the residue containing TDI diluted with the solvent 27 is introduced into the solvent removal step 3. Here, the solvent is removed from the residue containing TDI diluted with the solvent, and the remaining TDI and high boiling point compounds are fed to the TDI removal step 9 together with the crude TDI obtained from the crude reaction product containing TDI.
[0074] If TDI is added for storage of the TDI-containing residue or the TDI withdrawal step is performed in such a way that the TDI amount in the TDI-containing residue satisfies the viscosity condition, the TDI-containing residue 29 diluted with TDI or the TDI-containing residue is fed to the TDI withdrawal step 9.
[0075] By recycling the residue comprising TDI, the residue comprising TDI diluted with solvent or the residue comprising TDI diluted with TDI, the yield can be increased since the amount of TDI withdrawn from the process during possible shutdowns of the dryer or the hydrolysis step is minimized.
[0076] However, if the shutdown of the dryer or the hydrolysis step lasts for a period of time such that the storage container 23 is completely filled with TDI-containing residues during the continuation of the work-up process, the TDI-containing residues formed after the storage container 23 is completely filled cannot be stored but must be withdrawn from the process. In this case, the TDI-containing residues can be introduced directly into the thermal use 21. Alternatively, if the TDI-containing residues are further fed into the storage container 23, the TDI-containing residues are withdrawn from the storage container 23 and introduced into the thermal use 21. In this case, the amount of TDI-containing residues withdrawn from the storage container 23 and introduced into the thermal use 21 preferably corresponds to the amount of TDI-containing residues fed into the storage container 23 from the TDI withdrawal step 9.
[0077] In addition, also in the case that the TDI-containing residue stored in the storage container 23 has been altered in such a way that further use is not possible, this altered material can be fed to the thermal use 21. This may be the case, for example, if the storage period exceeds a maximum storage period and the TDI in the TDI-containing residue polymerizes in such an amount that reuse of the TDI-containing residue is uneconomical.
[0078] The residue comprising TDI is withdrawn directly from the TDI removal step 9 or from the storage vessel 23 and fed to a thermal use as indicated by the dashed line in the figure. Example
[0079] The crude reaction product containing TDI was worked up in two stages by removing the solvent in a first distillation and removing TDI as product in a second distillation. In the second distillation, a residue containing TDI was formed, which had an NCO value of 33.7 g / 100 g and a viscosity of 120 mPas at 80° C. The residue containing TDI was stored in a storage container.
[0080] The storage time of the residue containing TDI with the addition of different solvents or TDI is shown in Table 1. The storage temperature was kept constant at 80°C and the rotational viscometer was used at the same temperature and for 250 s -1 The viscosity is measured at a shear rate of 1.
[0081] In the comparative example, no solvent or TDI was added, and the residue containing TDI extracted from the second distillation was stored.
[0082] In Example 1, the residue containing TDI was mixed with chlorobenzene as a solvent at a ratio of 1:1 of the residue containing TDI:chlorobenzene, in Example 2, the residue containing TDI was mixed with chlorobenzene as a solvent at a ratio of 2:1 of the residue containing TDI:chlorobenzene, and in Example 3, the residue containing TDI was mixed with chlorobenzene as a solvent at a ratio of 4:1 of the residue containing TDI:chlorobenzene. In Example 4, the residue containing TDI was mixed with TDI at a ratio of 1:1 of the residue containing TDI:TDI.
[0083] Table 1: Viscosity increase
[0084] Storage time (days) 0 1 5 7 10 Comparative Example <![CDATA[80℃、250s -1 Viscosity (mPas)]]> 120.5 223 1537 - - Example 1 <![CDATA[80℃、250s -1 Viscosity (mPas)]]> 9.3 9.3 10.7 12.9 15.0 Example 2 <![CDATA[80℃、250s -1 Viscosity (mPas)]]> 12.9 15 49 58.7 107 Example 3 <![CDATA[80℃、250s -1 Viscosity (mPas)]]> 27 30.4 665 1260 - Example 4 <![CDATA[80℃、250s -1 Viscosity (mPas)]]> 17.2 32.2 48.0 60.1
[0085] In the comparative example, the viscosity increased so that after a storage time of 3 days, the viscosity exceeded 1000 mPas, and was therefore too viscous to allow further use.
[0086] The greater the amount of solvent mixed into the TDI-containing residue, the longer the diluted TDI-containing residue can be stored. In Example 2, even after a storage time of 20 days, the viscosity was still below 1000 mPas, and in Example 1, even after 50 days, the viscosity did not reach 1000 mPas.
[0087] The stored and diluted TDI-comprising residue can be recycled into the workup process of the TDI-comprising crude reaction product.
[0088] In addition to adding solvents or TDI, if the storage temperature is lowered, the viscosity can be kept below 1000 mPas for several days and the storage period can be extended further.
[0089] Table 2 shows the viscosity increase as a function of storage time. The mixture used for Examples 5 to 7 corresponds to the mixture of Example 4, wherein a TDI-containing residue having the same composition as in Examples 1 to 4 was mixed with TDI in a ratio of 1:1.
[0090] In Example 5, the mixture of TDI-containing residue and TDI was stored at a temperature of 40° C., in Example 6 at a temperature of 60° C. and in Example 7 at a temperature of 80° C. The viscosity at the storage temperature was respectively measured using the same method as described above.
[0091] Table 2: Viscosity increase depending on storage temperature
[0092] Storage time (days) 1 5 10 15 20 Example 5 <![CDATA[40℃、250s -1 Viscosity (mPas)]]> 35.8 40.8 - 58.7 69.4 Example 6 <![CDATA[60℃、250s -1 Viscosity (mPas)]]> 23.7 33.6 - 74.5 95.2 Example 7 <![CDATA[80℃、250s -1 Viscosity (mPas)]]> 17.2 32.2 60.1 99.5 113
[0093] By lowering the storage temperature, the storage time can also be extended. As can be seen in Table 2, Example 7, even at a storage temperature of 80° C. it is possible to store the TDI-containing residue for well over 20 days before the viscosity reaches the limit of 1000 mPas.
Claims
1. A method for storing a mixture containing toluene diisocyanate and a high boiling point compound, wherein the mixture contains 20% to 80% by weight of toluene diisocyanate, the method comprising: (a) feeding the mixture containing toluene diisocyanate and a high boiling point compound into a storage container (23); as well as (b) stirring the mixture containing toluene diisocyanate and the high boiling point compound. 2 . The method according to claim 1 , wherein the viscosity of the mixture containing toluene diisocyanate and the high-boiling compound is set so that after a predetermined storage time, the viscosity is below 1 Pas.
3. The method according to claim 2, wherein the viscosity of the mixture containing toluene diisocyanate and a high boiling point compound is set by the content of the solvent or toluene diisocyanate in the mixture containing toluene diisocyanate and a high boiling point compound or by setting the temperature.
4. The process according to any one of claims 1 to 3, wherein the mixture containing toluene diisocyanate and high boiling point compounds is stirred by using a recirculation loop through which stored toluene diisocyanate passes or by using a stirrer in the storage container.
5. The process according to any one of claims 1 to 4, wherein the mixture containing toluene diisocyanate and high boiling point compounds is a residue containing toluene diisocyanate obtained by post-processing a crude reaction product containing toluene diisocyanate.
6. A method for post-treating a crude reaction product containing toluene diisocyanate, the method comprising: (a) removing the solvent from the crude reaction product (1) containing toluene diisocyanate in a solvent removal step (3) to obtain crude toluene diisocyanate (7); (b) removing toluene diisocyanate from the crude toluene diisocyanate (7) in a toluene diisocyanate removal step (9), thereby obtaining purified toluene diisocyanate (11) as a product and a residue (13) containing toluene diisocyanate; (c) feeding the residue (13) comprising toluene diisocyanate to a dryer (15), in which a stream (17) substantially comprising toluene diisocyanate and a dryer residue (19) are obtained, and the stream (17) substantially comprising toluene diisocyanate is recycled to the toluene diisocyanate removal step (9) in step (b), or feeding the residue (13) comprising toluene diisocyanate to a hydrolysis step, in which the toluene diisocyanate is hydrolyzed to form the corresponding toluenediamine; At least a portion of the residue (13) comprising toluene diisocyanate is stored in a storage container (23).
7. The method according to claim 6, wherein the residue (13) comprising toluene diisocyanate is fed into the storage container (23) when the dryer (15) or the hydrolysis is not in operation.
8. The method according to claim 6 or 7, wherein the viscosity of the at least part of the residue (13) comprising toluene diisocyanate stored in the storage container (23) is set so that after a predetermined storage time the viscosity is below 1 Pas.
9. The method according to claim 8, wherein the viscosity of the at least part of the residue (13) comprising toluene diisocyanate is set by the content of solvent or by the content of toluene diisocyanate in the residue (13) comprising toluene diisocyanate.
10. The process according to claim 9, wherein the solvent is selected from the group consisting of chlorinated aromatic hydrocarbons, aromatic or aliphatic hydrocarbons, ketones, esters, nitriles, sulfolane and mixtures thereof.
11. The method according to any one of claims 8 to 10, wherein the viscosity of the at least part of the residue (13) comprising toluene diisocyanate is set by setting the temperature in the storage container (23).
12. The method according to any one of claims 8 to 11, wherein the amount of toluene diisocyanate in the residue (13) containing toluene diisocyanate is set by removing toluene diisocyanate in (b), thereby setting the viscosity of the at least part of the residue (13) containing toluene diisocyanate.
13. The method according to any one of claims 6 to 12, wherein the residue (13) comprising toluene diisocyanate in the storage container (23) is stirred.
14. The method according to claim 13, wherein the storage container (23) is connected for stirring to a recirculation loop (31) through which the stored residue (13) comprising toluene diisocyanate passes.
15. The method according to claim 13 or 14, wherein for stirring, the storage container comprises a stirrer for stirring the residue containing toluene diisocyanate in the storage container.