MXPA96003167A - A process to prepare toluylendiisocyanate, toluylendiamines and water specific mixtures, and mixtures use to prepare toluylendiisocyanate - Google Patents

Abstract

The present invention refers to toluylendiisocyanate produced by toluene nitration to produce dinitrotoluene, nitrotoluene hydrogenation, optionally in presence of a solvent or diluent, to produce a toluylendiamine crude solution and reaction water, processing toluylendiaminecrude solution and water to produce a toluylendiamine and water intermediate mixture, wherein processing is interrupted to give as result a water content of approximately 1-40 percent by weight, preferably approximately 2-10 percent by weight of intermediate mixture, carrying this intermediate mixture from a first yielding media to a second yielding media, thereby terminating TDA and water intermediate mixture, to yield commercial quality dry toluylendiamine, and then phosgenating toluylendiamine to yield toluylendiisocyanate. Is optionally dry before phosgenation. Invention also refers to toluylendiamine and water intermediate mixtures having a solidification point of 95øC at the most, and to these intermediate mixtures use to produce toluylendiisocyanate. It is preferable that these intermediate mixtures use to produce toluylendiisocyanate is performed in a site (or location) different from toluylendiamine and water intermediate mixtures yielding site.

Description

A PROCESS FOR THE PREPARATION OF TOLUILEN-DIISOCYANATE, SPECIFIC MIXTURES OF TOLUILEND AMINE AND WATER, AND THE USE OF MIXTURES TO PREPARE TOLUILENDIISOCIANATO.

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to a process for the preparation of toluylene diisocyanate. This process comprises reacting toluene with nitric acid to produce dinitrotoluene • (DNT), hydrogenating the resulting dinitrotoluene (DNT) to produce toluene diamine (TDA) and water of reaction, and reacting toluene diamine with phosgene to give TDI. However, the process steps to form toluylenediamine (TDA) are performed in a first production plant where the crude solution of toluylenediamine (TDA) and water from the hydrogenation step is distilled to form an intermediate mixture of toluylenediamine containing about 1 to 40%. in weight of water. This intermediate mixture is transported to a second production plant located at some distance from the first floor. In the second production plant, the distillation of the intermediate mixture of toluylenediamine (TDA) and water is REF: 22828 ends to produce dry toluylenediamine which is then phosgenated to produce toluylene diisocyanate (TDI). The present invention also relates to specific mixtures of toluene diamine and water, and to the use of these mixtures to prepare tolylene diisocyanate in a location that is different from the location at which the toluene diamine and water mixture was obtained or prepared. Typically, large-scale production of TDI is performed using the process steps of reacting toluene with nitric acid to produce DNT and water, reacting the DNT with hydrogen to produce TDA and water, followed by reacting the dry, processed TDA. , with phosgene to produce TDI and hydrogen chloride where the production units for each stage of the process are joined together in a production plant. However, it can be advantageous to carry out the process steps in two production plants located at some distance from each other, where the process steps up to the production of TDA are carried out in a production plant and the reaction of TDA with phosgene and The processing to give a final product of marketable TDI, are made in the second production plant. This type of procedure can be economically attractive, if for example, the appropriate raw materials and infrastructure are easily available in one area, but a large purchase market with the need for local production of the final product is provided in another area located at a considerable distance. In addition, it may also be economically advantageous to supply a variety of small phosgene units in various locations from an integrated, central amine plant located at a distance away. However, this mode of production and / or operation becomes considerably more difficult, due to the fact that the intermediate product, TDA, has a high melting point. This means that the TDA can only be transported if it is in the solid form or as a hot melt at a temperature of more than 100 ° C. When the ADT is transported in the solid form, the ADD first has to be subjected to an expensive processing step such as, for example, producing flakes, in order to be able to melt the product again after transport for use in its reaction. final phosgenation. On the other hand, overseas transport as a melt requires the use of containers with heatable tanks and appropriate heating means in the house such as, for example, connections for heating steam or for electrical energy, or, in the case of transport as bulk goods, the use of tankers whose cargo holds can be heated to a temperature of 105-100 ° C. The first case, which requires the use of containers with heatable tanks, is very expensive and ineconomic for the transportation of large quantities of TDA. In the second case, the transport as a bulk merchandise in ships with heatable cargo holds, will also be very expensive and therefore, ineconomic because the conventional tanks and the trans-shipment devices in the docks are not proposed for use at high temperature. This method will first require that the tankers and the trans-shipment devices be adapted for this purpose, which would be a great expense. Finally, the problem of the elimination of the pads of cargo holdings of the ships would have to be overcome, optionally by means of special procedures, costly incineration of waste. - US Patent No. 5,449,832 describes a process for storing and transporting toluene diamine (TDA) .This process comprises dinitrate toluene to produce the 2,4- and 2,6-isomers of dinitrotoluene, hydrogenate the dinitrotoluene to produce the 2,4 - and 2,6-isomers of toluenediamine, and distilling toluenediamine to produce essentially the anhydrous product of 2,4- and 2,6-toluenediamine, which is then cooled and transferred for storage and / or shipment. / or shipment of toluene diamine (TDA), the melting point of the TDA is reduced by adding water in an amount of about 5 to 15, preferably 7 to 10% by weight (based on the weight of the anhydrous TDA) , and by controlling the temperature of the resulting TDA-water mixture such that the final temperature of the TDA-water mixture is at or below the boiling point.It is this mixture that is suitable for long-term storage and transportation. The water added to the anhydrous TDA It is hot demineralized water, deionized water, or distilled water under pressure. The final temperature level of the addition of water to the anhydrous TDA provides sufficient internal heat to maintain the TDA-water mixture in a liquid state for a prolonged period of time, and thus allows for storage and / or storage. transport of the mixture.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides TDA formulations that can be stored or transported in the liquid form at a temperature below 95 ° C without the settlement of solids. A further object is to modify the process for the production of TDI by nitration of toluene to produce DNT, the hydrogenation of DN to produce TDA and water, and the reaction of dry TDA with phosgene to produce TDI in such a way that it is possible transport the TDA in tanker vessels or bulk goods from a first production plant to a second production facility located at a distance away, without the disadvantages mentioned above. This object is achieved by the blends and the process of the present invention. Now, it has surprisingly been shown that specific mixtures of TDA and water, having a water content of 1-40%, preferably 2-10%, have clearly decreased the melting points and thus are substantially easier to handle and are more cost effective to transport over long distances as bulk goods in tankers than is pure TDA. Tank vessels designed to transport chemicals are generally capable of keeping the goods being transported at temperatures in the range of about 65 to 70 ° C during transport, and also to discharge the chemicals over a similar temperature range . In this way, an object of the process according to the invention is to obtain TDA / water mixtures whose melting characteristics allow their transport as bulk goods in conventional tank vessels. The mixtures according to the invention can be produced, in principle, by mixing pure TDA, ie mixtures of industrial, conventional isomers containing about 80% by weight of 2,4-TDA and about 20% by weight of 2, 6-TDA, with water. These mixtures are more easily accessible, however if during the distillation step of the hydrogenation product containing TDA and water, the industrial process is interrupted at a suitable point such that an intermediate mixture of TDA and water having a content of water for about 1 to 40% by weight, instead of the anhydrous TDA as in conventional processes.

Thus, the present invention provides a process for the production of toluene diisocyanate which comprises reacting toluene with nitric acid to produce dinitrotoluene, hydrogenating the dinitrotoluene to produce a crude solution of toluene diamine and water of reaction, and distilling the crude solution of toluene diamine and the reaction water to form an intermediate mixture of toluene diamine and water containing from about 1 to 40%, preferably from about 2 to 10% by weight of water, then transporting this intermediate mixture of toluene diamine and water from a first production plant to a second production plant, followed by distillation of the intermediate mixture of toluylenediamine and water completely in the second production plant to produce dry toluylenediamine and to phosgenate the dry toluylenediamine to produce toluylene diisocyanate. In another embodiment, the dinitrotoluene is hydrogenated in the presence of a solvent or diluent. This solvent or diluent can be either completely or partially removed or separated from the crude solution of toluene diamine and water of reaction in an additional step before the distillation of the crude solution of toluene diamine and the water of reaction to produce the intermediate mixture of toluene diamine. and water that is suitable for storage and / or transportation. In another embodiment, the dried toluene diamine, after which it is completely distilled in a second production plant, can be subjected to the additional processing steps before phosgenation to produce tolylene diisocyanate in a manner known per se.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram illustrating the removal of water from the raw solutions of TDA and water to produce raw TDA in the traditional process as described in the prior art.

Figure 2 is a schematic diagram illustrating the process according to the present invention, through the second distillation step.

Diagram 1 illustrates the variation of the solidification point of a crude solution of TDA and water.

Diagram 2 is a phase equilibrium diagram of the raw solution of TDA and water.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, it is preferred that: the toluylenediamine comprises 2,4-toluylenediamine, 2,6-toluylenediamine or any mixture of these isomers, and optionally with 2,3-toluylenediamine, 3,4-toluylenediamine, or mixtures thereof, in any quantity, and - no solvent or diluent is present during the hydrogenation of the dinitrotoluene.

The invention also relates to mixtures of toluylenediamine and water in which the solidification point of these mixtures is at most 95 ° C. According to the invention, mixtures with a solidification point in the range from approximately 60-95 ° C, more preferably from 65-70 ° C, which consist of 2,4- and / or 2, 6-toluylenediamine and water, and - containing 1-40 parts by weight of water, more preferably 2-10 parts by weight of water, to 100 parts by weight of toluylenediamine and.

In addition to the water content given above, the mixtures according to the invention may optionally contain a maximum concentration of homogenously dissolved, organic solvent or diluent of about 10% by weight. Suitable solvents or diluents in this case are, in particular, lower alcohols, preferably methanol, ethanol, n-propanol and isopropanol, lower ketones, specifically acetones and diols, specifically ethylene glycol, or also toluene. The invention also provides the use of intermediate mixtures of TDA and water to prepare tolylene diisocyanate by phosgenation, with the previous removal of water. It is preferred that the proposed intermediate blends for preparing toluylene diisocyanate are transported to a production plant that moves spatially from the mixing preparation site. The industrial production of TDA from dinitrotoluene is generally achieved by using a continuous process by reducing the nitrogen groups in the DNT with hydrogen under high pressure in a dispersed powder catalyst such as, for example, palladium in activated carbon or Raney nickel, and optionally in the presence of * a diluent or solvent. A large number of processes have been described for preparing aromatic amines such as TDA by the catalytic hydrogenation of the corresponding nitro compound, 'DNT, in the present invention. These processes are described in for example, DE-OS 1,542,544, 1,947,851, 2,016,644, 2,135,154, 2,214,056, 2,456,308, BE PS 631,964, 661,047, 661,946, FR-PS 1,359,438, GB-PS 768,111, EP-A 0,124,010. Suitable solvents or diluents include compounds such as, for example, methanol, ethanol, or propanol (Ullmann, 4th edition, 1977, vol.13, page 14). The presence of these solvents or diluents helps distribute the high heat of reaction (about 418 kJ per mole of nitro groups) throughout a large amount of reaction and to facilitate its removal as well as to increase the availability of dinitrotoluene in the suspension when improving the solubility Opposing these desirable properties is the presence of solvents which is associated with the additional costs of distillation for their separation, thus minimizing the use of the solvent while simultaneously observing the requirements of The safety and reaction of this stage represents an optimization objective Therefore, the continuous production of TDA without the use of solvents is preferred for the process according to the invention, since it is possible to use the reactors according to U.S. Patent No. 5,387,396, the description of which is incorporated herein by reference, (it is believed to correspond to DE-OS 3,635,217). These reactors are constructed in such a way as to allow particularly efficient removal of the heat by means of cooling by evaporation, that is, by the production of, for example, water vapor on the side of the cooling fluid. Thus, in the case of dinitrotoluene, these reactors allow the reaction to be carried out at a temperature higher than that of normal, ie at 180-200 ° C instead of 100 ° C, and without the use of a solvent. The crude solution obtained during the reaction of dinitrotoluene with hydrogen comprises approximately 60% by weight of TDA, with approximately 40% by weight of water of reaction, and optionally, the diluent or solvent used. This crude solution also contains, after the isolation of the solid catalyst, such as, for example, by distillation or sedimentation, the by-products of the process. These byproducts are mainly 2,3-TDA and 3,4-TDA, and may account for approximately 3 to 5% by weight of crude solution. Other byproducts may also exist, including some that have high molecular weights. In order to achieve separation of a suitable starting product that can be used for the phosgenation, water and optionally, any diluent or solvent present can be completely removed in a manner known per se such as, for example, by distillation. Furthermore, in order to achieve the highest possible production of TDI, it is also convenient to remove the byproducts by distillation, after which the conventional purity of the commercially available TDA is obtained. Conventional, pure ADT comprises approximately 80% by weight of 2, 4-tolulendiamine and approximately 20% by weight of 2,6-toluylenediamine. Before the removal of the reaction water that is produced during the homogenization of the dinitrotoluene, any solvent present must first be removed from the crude solution, free of toluene diamine catalyst (TDA) and the water of reaction. The removal of the solvent generally takes place, in a known manner, by distillation in a continuously operated distillation column, where the solvent is recovered in a state of purity, by means of process control, which can be completely reused in the process without further purification. It is also possible to separate, from the raw solution of TDA and the water of reaction, the solvent together with some (or all) of the water formed by means of distillation, and then recover the solvent with the required degree of purity to from the mixture of solvent and water in an additional stage of the process. When the reaction is carried out without the addition of the solvent, the isolation of the solvent is obviously not required. In an industrial process, conventional for the production of toluylene diisocyanate (TDI), the drying process of the dry solution of TDA and water then continues. This procedure completely removes all the water of reaction that is present in the raw solution of TDA and the water of reaction. Water generally accounts for up to about 40% by weight of the crude solution. In principle, this can be achieved by simply removing the water by heating the raw solution under vacuum and removing the vapors that are formed. However, the isolated water obtained by this simple procedure does not occur in the purity required for the direct elimination of the waste, because it is always more or less contaminated with TDA. Therefore, it is better to remove the water of reaction by distillation in an appropriate distillation apparatus, in this case, for example, the crude solution of TDA and the water of reaction is heated to a temperature of more than 200 ° C in the base of a column; thus producing water in the pure form at the top of the column. These distillation columns used in conventional processes are operated at atmospheric pressure or with slight excess pressure, having approximately 20 to 30 bubble plates (ie, practical plates), and the TDA is removed from the base, with the last traces of water that are removed when decompressing in a vacuum of 30 to 50 mbar. Figure 1 is a schematic diagram of the traditional process (ie, the prior art process) for the removal of water from the TDA.

In Figure 1: A represents: crude solution of TDA and water containing approximately 60% by weight of TDA; B represents: removal of water; C represents: mixture of TDA / water returned to A; D represents »removal of ADD (dry); and 25 represents: the number of bubble plates in the distillation column.

However, the present invention differs from the conventional course of the process for producing ADT described above. More specifically, the present invention differs from conventional processes in that the step of separating the water from the crude solution of TDA and the water of reaction is carried out in two steps. In fact, the crude solution of TDA and the water of reaction, which contains approximately 40% by weight of water, has the very low solidification point of about 45 ° C. Therefore, this crude solution of TDA and reaction water would be suitable for bulk transport in tankers. The solidification point, as used herein, is understood to be the temperature at which the transition from a liquid state to a solid state takes place. However, the transportation of the TDA crude solution and water of reaction will mean that the expensive cargo hold will be greatly wasted in the transport of water. Therefore, in the process according to the invention, partial removal of the reaction water is made from the crude solution of TDA and reaction water, to produce an intermediate mixture of TDA and water, where the residual concentration of water "in the intermediate mixture is adjusted so that the solidification point of the resulting intermediate mixture is not above the controlled temperature range normally used in tankers.The variation of the solidification point of a mixture of TDA and water As shown in Diagram 1, it is used as a basis to determine the appropriate concentrations of water in these intermediate mixtures to produce the appropriate mixtures for storage and / or transportation, Diagram 1 illustrates the solidification points of the TDA mixtures and More specifically, the TDA comprises 80% by weight of 2,4-TDA and "20% by weight of 2,6-TDA. The axis of the x represents the water content and the% by weight, and the y axis represents the solidification point in C. According to this diagram a solidification point of, for example, 65 ° C corresponds to a content of water of 7% by weight. The process used for the partial removal of water from the crude solution of TDA and water of reaction is much simpler than the apparatus for drying the TDA in a conventional process as described above. It is preferred that the partial removal of water be via a simple distillation at atmospheric pressure. In the process according to the invention, a distillation column having only 5 bubble plates (i.e., practical plates) is more than adequate to produce the top products containing no TDA. Since the main proportion of the water has already been removed in this way, the vacuum distillation apparatus required in the final distillation, that is, a second production plant, to produce dry ADT, needs only to have approximately 10 plates (i.e. , practical plates). In this manner, the vacuum distillation apparatus required by the present invention is smaller than the conventional vacuum distillation apparatus required in conventional industrial processes to produce TDA. Accordingly, the distillation apparatus of the present invention is also more economically efficient. Distillation columns suitable for the present invention to produce dry TDA are designed in a manner known per se, by taking into account the phase equilibrium diagram for the TDA / water system (predominant: 1013 mbar, thin: 100 mbar) ( see diagram 2). In diagram 2, the axis of x represents the molar concentration of water in the liquid phase and the y axis represents the molar concentration of water in the vapor phase. An additional advantage in accordance with the present invention is problem-free elimination, of the waste of the pads of the tanks of the ship. Since the vessel can be rinsed with water and the distillation of the intermediate mixture of TDA and water is completed at each final destination, processing of the rinsing water containing TDA is also possible at the final destination. Therefore, special, expensive waste incineration procedures are not required. Further processing of the dry TDA to give TDI at the ultimate (or final) destination is also performed using conventional methods known to those skilled in the art. The 2,3- and 3,4-isomers of the TDA and other by-products can first be removed optionally from the mixture of TDA isomers. Suitable methods for the removal of these isomers and other by-products are described in for example, U.S. Patent Nos. 3,420,752 and 3,414,619, the descriptions of which are incorporated herein by reference. The final step of the total process for producing TDI by phosgenation of the TDA proceeds in a known manner. See for example, Becker / Braun, Kunststof f-Handbuch, 2a. edition, 1983, volume. 7, page 63 et seq. Carl-Hanser Verlag, Munich, and the literature cited therein. Accordingly, the present invention provides a process for the production of TDI by nitration of toluene to give dinitrotoluene (DNT), hydrogenation of DNT to give a crude solution of toluene diamine (TDA) and water of reaction, optionally in the presence of a solvent or diluent, however, preferably without the use of these, optionally, either completely or partially removing the solvent, and distilling the aqueous solution of TDA and the water of reaction to form an intermediate mixture of TDA and water where the distillation is stopped at a point such that the intermediate mixture of TDA and water contains from about 1 and up to 40% by weight of water. This intermediate mixture is then transported from a first production means to a second production means. In the second production medium, the intermediate mixture of TDA and water is completely distilled to produce dry TDA. Any by-products including, for example, 2,3-TDA and / or 3,4-TDA can also be removed by either this second distillation step or another processing step to produce commercial grade dry TDA. Then, the dry TDA is phosgenated to produce TDI. Suitable compounds for the process according to the invention are 2,3-toluylenediamine and various isomeric mixtures of toluylenediamine. The commercial grade ADT is typically a mixture of the 2,4-isomer and the 2,6-isomer, where the isomer ratios of -2.4-TDA to 2.6-TDA is approximately 65:35 or 80: twenty. Suitable intermediate mixtures of TDA and water that can be transported from a production plant to a second production facility include the isomeric mixtures of 2,4-TDA and / or 2,6-TDA with various concentrations of the 2, 3- and 3,4-isomers of TDA. These intermediate mixtures also contain reaction by-products. Typically, 2,3- and / or 3,4-isomers are present in these intermediate mixtures in amounts from about 0.05 to 5.0% by weight. These intermediate mixtures of TDA and water also contain various proportions of products that have high molecular weights. These by-products with molecular weights. Higher amounts are typically present in amounts from about 0.01 to 2.5% by weight, usually from 0.2 to 1.8% by weight. The following examples further illustrate the details for the process of this invention. The invention, which is set forth in the foregoing description, is not to be limited either in spirit or scope by these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless stated otherwise, all temperatures are in degrees Celsius and all percentages are percentages by weight.

EXAMPLES Example 1 Production of a TDA / water mixture according to the invention a) Preparation of dinitrotoluene Dinitrotoluene (DNT) was prepared in two stirred tank reactors which were cooled with water. Each reactor had a working volume of 500 1 and was equipped with an overflow or lateral spill in separate flasks, each flask containing a volume of 100 1. On the degassing side, the apparatus was connected to a gas collection line of vent that was operated at atmospheric pressure. Before the start of the reaction, both vessels were filled with sulfuric acid with a concentration of 92% until overflow, the agitator was switched on. In the first tank were fed 93 kg / h of toluene and lOO kg / h of nitric acid with a concentration of 65% as well as sulfuric acid that has been introduced into the second tank as acid in a concentration of 92% to 665 kg / There was a spill in the downstream sedimentation flask. The overflow from the first separate tank, in the associated settling flask, in a phase of sulfuric acid, which was made for processing, and an organic phase consisting mainly of mononitrotoluene (MNT). The organic phase was continuously pumped into the second tank, where, in addition to the 92% sulfuric acid mentioned above, another 105 kg / h of nitric acid with a concentration of 65% was added. The temperature in the second tank was 70 ° C. The overflow or spill from the second separate tank, in the associated settling flask, into a sulfuric acid phase as mentioned above, which was then pumped into the first tank, and an organic phase that contained crude DNT and traces of entrained acid . To purify the product, the crude DNT was continuously passed through a 3-stage mixer / settler battery maintained at 70 ° C where the crude DNT was washed, in sequence, with 50 1 / h of hot water (70 ° C). C), 50 1 / h of caustic soda solution with a concentration of 2% (70 ° C), and 50 1 / h of deionized water (70 ° C). An aqueous extract of the resulting DNT had a pH of 7.6. The aqueous phase was rejected as an effluent. b) Hydrogenation of DNT to produce TDA A 500 1 autoclave equipped with cooling and heating media, a gaseous dispersion stirrer, a thermometer and a level gauge was used to hydrogenate the DNT to produce toluene diamine (TDA). A mixture of 70 kg of water and 150 kg of toluylenediamine- at 80 ° C was initially introduced into the autoclave, and then 7 kg of Raney nickel, dispersed in approximately 30 1 of water, was added to this mixture. The autoclave was filled 10 times with hydrogen at a pressure of 10 bar, and then decompressed at atmospheric pressure each time. Then, hydrogen was introduced at a pressure of 22 bar, the agitator was switched on, and the addition of DNT in the reaction mixture was started, via a submerged tube, at a rate of 182 kg / h. After about 2 minutes, initiation of the reaction was detected by rapid increase of the temperature inside the autoclave. After the change from the heating process to a cooling procedure, the temperature was controlled at 190 ° C. The consumption of hydrogen was compensated by the addition of fresh hydrogen such that the pressure inside the autoclave remained constant at 22 bar. A gas stream of 25 Nm3 / h was removed from the gas space. When the liquid had filled 75% of the autoclave, the product was removed via the immersion product. The product flowed into a filter vessel having a capacity of approximately 20 1, in which a cartridge of the synthesized metal filter 3 was previously inserted. Approximately 50 1 / h of the reaction mixture enriched with catalyst was returned from the vessel of reaction to the reactor using a pump, while the pressure of the reaction mixture flowing through the filter cartridge was reduced to 3 bar in a decompression vessel with a reflux condenser, via a regulating valve that was controlled by the level in the reactor. The decompressed gases were discharged as exhaust gas. The reaction mixture flowed continuously from the decompression vessel into a first distillation column with 5 bubble plates, where the distillation column was about 2.5 m in length and about 200 mm in diameter. The column was operated at room temperature and the base was heated to 135 ° C using a plug-in evaporator and a 6 bar steam. At the top of the column, water containing approximately 25 ppm of TDA was removed at a reflux (reflux / derivation) ratio = 3. The product from the base of the column was an intermediate mixture of TDA and water that contained approximately 7% by weight of water, and had a solidification point of approximately 65 ° C. This contained the different isomers of TDA, specifically the 2,3-, 2,4-, 3-4- and 2,6-isomers, as well as the high molecular weight byproducts. No solid was sedimented from this reaction mixture of TDA and water after it was stored for 4 weeks at about 70 ° C. In this way, the intermediate mixture of TDA and water was suitable for bulk transport at 70 ° C in a warehouse.

Example 2 Production of toluylene diisocyanate from an intermediate mixture of TDA and water according to the invention.- ' The residual water was removed from the intermediate mixture of TDA and water (ie, the product of the first distillation column described in Example Ib above) under vacuum at 100 mbar at the top and 205 ° C at the collector at a second distillation column with 10 bubble plates. This second distillation column was approximately 4.5 m in length and approximately 300 mm in diameter. The base of the column was heated using 30 bar steam. This distillation produced essentially dry ADT (which contained approximately 400 ppm of water) at the base of the column with the water that occurs at the top of the column (which contained approximately 10 ppm of TDA) when (reflux / derivation) = 4. A schematic diagram of the process according to the present invention, through the second distillation step, is shown in Figure 2.

In Figure 2: A represents: supply of DNT B represents: hydrogen supply; C represents: venting gas; D represents: heat removal; E represents: catalytic conversion of DNT to TDA (185 ° C, 25-30 bar, 2-3% by weight of catalyst); F represents: catalyst separation; G represents: decompression at 130 ° C, 3 bar; H represents: supply to column 1; I represents: water removal (TDA content: 25 ppm); J represents: withdrawal of the intermediate; mixture of TDA and water (according to the invention); K represents: storage and / or temporary transport of the intermediate mixture of TDA and water (according to the present invention), 80 ° C; L represents: removal of TDA from column 2 (water content: 400 ppm); M represents: withdrawal of water from column 2 (TDA content: 10 ppm) 1) represents: first distillation column where: 5 represents: the number of bubble plates in column 1 and 2) represents: second distillation column where 10 represents: the number of bubbling plates in column 2.

The dry TDA is then reacted with phosgene to produce TDI. This step was carried out in a continuously operated apparatus consisting essentially of two stirred tanks, heated with steam of 30 bar, each having a capacity of 2 m, and two distillation columns. 800 kg / h of phosgene was fed in the form of a solution with 50% concentration in orthodichlorobenzene (ODB) in the first of the two stirred tanks, and heated to 90 ° C at a pressure of 1.9 bar. The overflow or spillage flowed • to the second agitated tank that was connected to the first tank on the degassing side that was maintained at a temperature of approximately 135 ° C. The TDA, which was removed from the TDA solution tank at 120 kg / h at 45 ° C in the form of a solution with a concentration of 5% in ODB via a pump, was mixed with the phosgene solution that was introduced into the tank. the first stirred tank. A centrifugal pump with an open impeller was used to intensively mix the two solutions. After leaving the second stirred tank, the reaction mixture was heated to 190 ° C in a 30 bar steam operated heat exchanger. The vapors discharged from the stirred tanks and from the heat exchanger were passed through a washing column having a diameter of about 500 ml, a length of about 4 mm containing 10 bubbling plates. A condenser cooled with ODB at 60 ° C in the upper part of the column condensed some of the reaction mixture that was added to the column as a refluxing medium. The discharge from the column was returned to the first stirred tank below the liquid level. The vapors emerging from the column were passed in a recovery apparatus to remove the excess phosgene used from the hydrogen chloride produced. The reaction mixture at 190 ° C emerging from the heat exchanger (mentioned above) was introduced into the base of the solvent column which had a diameter of approximately 450 mm, a length of approximately 6 m and which contained the packing at a height of approximately 4 m. The base of the solvent column was heated to about 185 ° C with steam at 30 bar using an enclosed evaporator, and the pressure at the top of the column was 330 mbar.A reflux ratio was established R: E = 2 using a condenser operating with cold water The ODB withdrawal did not contain TDI and was used again to prepare the TDA solution and the phosgene solution (as described above that entered the first tank). the base of the solvent column was heated with approximately 10% ODB in a downstream thin layer evaporator (TLE), which was steam heated to 30 bar and maintained at a pressure of 100 mbar, and the ODB was removed The distillate from the TLE was condensed in a condenser using cold water and returned to the solvent column.The discharge from the base of the TLE was separated into approximately 90% of the product from the top and approximately 10% of the fon products in a second thin-film evaporator which was also heated with steam at 30 bar and a pressure of 10 mbar was maintained. The bottom products were placed in a distillation kettle with a volume of 2 m and evaporated batchwise using steam at 30 bar at 220 ° C / 5 mbar until a viscous melt had formed. The viscous melt was drained while hot, solidified in cardboard vats, and removed by a waste incineration process. In addition to the high boiling product by-products that were formed during the phosgenation, it also contained the high molecular weight by-product from the TDA feed. The distillate from the distillation of the boiler was fed, together with the distillate from the second TLE, to the TDI column. The TDI column had a total height of approximately 5 m, a diameter of 250 mm and contained the packing at a height of approximately 3.5 m. - At the top of the column was a condenser that caused the total reflux. Removal of the product from the TDI column took place approximately 400 mm below the top of the inner package by means of a removal plate. The reflux ratio R: E was 15. There was a pressure of 15 mbar at the top of the column. The base of the TDI column had a volume of approximately 100 1 and was heated with steam at 30 bar by means of a plug-in evaporator so that the temperature was 163 ° C. The contents of the base portion were reduced by approximately 30 1 at regular intervals - from 6 h and the removal of the product was added to the feed material at the second TLE mentioned above. The withdrawal of the TDI product from the TDI column had the following analytical characteristics: 79. 4% 2, 4-isomer 20.6% 2, 6 isomer 0.005% hydrolysable chloride less than 0.005% ODB Therefore, the TDI product of this example corresponded to the quality of the commercial TDI. The yield in all stages of manufacture from toluene to toluylene diisocyanate was approximately 85%. Although the invention has been described in detail in the foregoing for the purpose of illustration, it should be understood that this detail is only for this purpose and that variations may be made therein by those skilled in the art without departing from the spirit and scope of the invention except as may be limited by the claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property:

Claims (14)

1. A process for the production of toluene diisocyanate, characterized in that it comprises the steps of: 1) reacting toluene with nitric acid to produce dinitrotoluene, 2) hydrogenating the dinitrotoluene to form a crude solution of toluene diamine and water of reaction, 3) distilling the solution crude oil of toluene diamine and the reaction mixture to form an intermediate mixture of toluene diamine and water, the distillation which is interrupted at a point where the water content of the intermediate mixture is from about 1 to 40% by weight, 4) to transport the intermediate mixture of toluene diamine and water from a first reaction plant to a second reaction plant, followed by 5) distilling the intermediate mixture of toluene diamine and water completely in the second production plant to produce dry toluene diamine, and 6) phosgenation toluylenediamine dry to produce toluylene diisocyanate.

2. The process according to claim 1, characterized in that the hydrogenation of the dinitrotoluene is in the presence of a solvent or diluent, and is followed by the removal of the diluent solvent, either partially or completely, from the crude solution of toluylenediamine before the distillation of the crude solution of toluylenediamine and water of reaction to produce the intermediate mixture of toluylenediamine and water.

3. The process according to claim 1, characterized in that the distillation of the crude solution of toluene diamine and the water of reaction to produce the intermediate mixture of toluene diamine and water is interrupted at a point where the water content of the intermediate mixture is from approximately 2 to 10%.

4. The process according to claim 1, characterized in that the toluene diamine comprises the 2,4-isomer, the 2,6-isomer, or mixture thereof.

5. The process according to claim 4, characterized in that the toluenediamine comprises the 2,4-isomer, the 2,6-isomer, or mixtures thereof, in combination with the 2,3-isomer, the 3,4-isomer , or mixtures thereof.

6. A mixture of toluylenediamine and water, the mixture that has a freezing point of at most 95 ° C.

7. The mixture according to claim 6, characterized in that the freezing point is in the range of 60 to 95 ° C.

8. The mixture according to claim 6, characterized in that the freezing point is in the range of 65 to 70 ° C.

9. The mixture according to claim 6, characterized in that the toluylenediamine consists of the 2,4-isomer and the 2,6-isomer.

10. The mixtures according to claim 6, characterized in that the toluenediamine consists of the 2,4-isomer, the 2,6-isomer, or mixtures thereof, in combination with the 3,4-isomer 3,4-isomer, or mixtures thereof, and high molecular weight byproducts.

11. The mixture according to claim 6, characterized in that the mixture contains from about 1 to 40 parts by weight of water to about 100 parts by weight of toluene diamine.

12. The mixture according to claim 6, characterized in that the mixture contains from about 2 to 10 parts by weight of water to about 100 parts by weight of toluene diamine.

13. In a process for the production of toluene diisocyanate, which comprises the phosgenation of the to-luylenediamine to produce the toluene diisocyanate, the improvement is characterized in that the toluene diamine comprises the mixture of claim 6 which was distilled to remove the water content before it was dissolved. submit to phosgenation.

14. The process according to claim 13, characterized in that the mixture of claim 6 was transported to a production plant that moves spatially from the production site of this mixture. SUMMARY OF THE INVENTION Toluene diisocyanate is produced by the nitration of toluene to produce dinitrotoluene, the hydrogenation of the nitrotolunene, optionally the presence of a solvent or diluent, to produce a crude solution of toluylenediamine and water of reaction, processing the crude solution of toluene diamine and water to produce an intermediate mixture of toluene diamine and water where processing is interrupted to result in a water content of about 1-40% by weight, preferably about 2-10% by weight of the intermediate mixture, by transporting this intermediate mixture from a first production medium to a second production medium, with which the intermediate mixture of TDA and water is terminated to produce commercial grade dry toluylenediamine, and followed by the phosgenation of the toluylenediamine to toluylene diisocyanate. It is optional to further process the dry toluylenediamine before phosgenation. The invention also relates to intermediate mixtures of toluylenediamine and water having a solidification point of at most 95 ° C, and to the use of these intermediate mixtures to produce toluylene diisocyanate. It is preferable that the use of these intermediate mixtures to produce toluylene diisocyanate be carried out at a site (or location) that is different from the production site of the intermediate mixtures of toluylenediamine and water.