KR100383217B1 - A process for toluenediamine recovery - Google Patents

Abstract

The present invention relates to a method for manufacturing and recovering toluene diamine, and more particularly, to a high-boiling tar waste obtained as a side reaction product in a chemical process for producing toluene diisocyanate (TDI) by phosgenating toluene diamine (TDA). The present invention relates to a method for decomposing and recovering an expensive raw material toluenediamine (TDA) by using an aqueous ammonia solution as a reactive medium at high temperature and high pressure chemical reaction conditions before and after the critical temperature of water.

As a result, the method according to the present invention can reduce waste disposal costs, alleviate landfill shortages, and ultimately increase the economics of toluene diisocyanate (TDI) manufacturing process.

Description

Production recovery method of toluenediamine {A process for toluenediamine recovery}

The present invention relates to a method for manufacturing and recovering toluene diamine, and more particularly, to a high-boiling tar waste obtained as a side reaction product in a chemical process for producing toluene diisocyanate (TDI) by phosgenating toluene diamine (TDA). The present invention relates to a method for decomposing and recovering an expensive raw material toluenediamine (TDA) by using an aqueous ammonia solution as a reactive medium at high temperature and high pressure chemical reaction conditions before and after the critical temperature of water.

Conventional methods for treating tar waste generated in toluene diisocyanate (TDI) manufacturing process include the addition of aqueous solutions containing acids or bases such as aqueous ammonia, alkaline earth metal hydroxides, inorganic acids or organic acids, and the like. Method of reacting in a state where gas and liquid coexist at a temperature of 350 ° C. or less, which is much lower than the temperature. Reaction with only steam (superheated steam), supercritical water or critical point limited to process tar that exhibits fluidity at room temperature or low to medium temperature below 100 ℃ including a large amount of low boiling point components such as toluene diisocyanate Decomposition by using subcritical water in the vicinity. In addition, a process of evaporating and removing toluene diisocyanate (TDI) tar using a thin film evaporation apparatus, a rotary evaporation granulation apparatus, or the like under high temperature vacuum is known, but such a process is known. By removing only the low boiling point compound, a large amount of the material having a large molecular weight in the form in which the aromatic rings, which occupy most of the tar component, are connected to each other remains. In flowable tar containing free toluene diisocyanate, the hydrolysis reaction is easily initiated by toluene diisocyanate which remains uniformly in the reaction medium, and the exothermic reaction activates the remaining high molecular weight material so that it can be easily hydrolyzed. Can be. However, high boiling tar solids almost free of toluene diisocyanate have no initiation point for a vigorous hydrolysis reaction that plays this role, and tends to proceed to other side reactions rather than being activated under conditions suitable for hydrolysis.

Toluene Diisocyanate (TDI) Process The yield in the process of decomposing tar to produce toluenediamine (TDA) depends on the chemical affinity between the constituent molecules present in the tar and the reactive medium, more specifically direct or indirectly with a nitrogen atom. It is necessary to create a decomposition environment of low-reactivity high molecular weight materials that are complicatedly connected.

In general, toluene diisocyanate (TDI) is prepared through the phosgenation of toluene diamine (TDA), and the reaction mixture typically contains a process solvent and reaction intermediates, toluene diisocyanate, hydrogen chloride, phosgene, and side reactions. . In order to separate the reaction mixture, the following procedure is usually performed. First, phosgene and hydrogen chloride are flash evaporated in a separation tank and purged with nitrogen. The reaction mixture without phosgene and hydrogen chloride is removed from the process solvent by a distillation operation to obtain a crude toluene diisocyanate mixture. And, toluene diisocyanate tablets are usually obtained by performing purification procedures such as (multistage) flash evaporation steps and / or (vacuum) distillation operations. The high-boiling residue resulting from the liquid mixture and distillation operation in the final flash evaporation step contains a large amount of some free toluene diisocyanate (free TDI) and side reactant impurities. This is referred to as 'toluene diisocyanate manufacturing process tar'.

In the conventional processing methods for hydrolyzing the above-mentioned toluene diisocyanate manufacturing process to obtain toluene diamine, the mixture is quenched in water to produce solid particles, finely ground, and then an acid such as caustic soda solution. Or mixed in a basic hydrolysis medium and heated in a reactor, and the resulting toluenediamine was recovered by distillation. Apart from this method, toluene diisocyanate is recovered as much as possible through a thin film evaporator or a rotary evaporation granulation apparatus at a high temperature vacuum condition at around 250 ° C. and 10 mmHg, and solid residues are embedded or incinerated. There is a method of disposal. Recently, high temperature, high pressure conditions below the critical point of water or supercritical fluid water are used to hydrolyze the liquid bottom residue containing high concentrations of free toluene diisocyanate (free TDI) from 10% to several tens%. Has been developed to recover toluenediamine and incinerate or landfill the remainder. However, when this method is applied to tar in which low boiling point substances such as toluene diisocyanate are almost removed by a thin film evaporator or the like, the conversion yield to toluenediamine is very low. Therefore, preferably, toluene diisocyanate is completely removed from the bottom residue containing predominantly impurities in the toluene diisocyanate manufacturing process by using a thin film evaporator, to maximize the toluene diisocyanate yield, and the high boiling point residue Toluene diamine is produced in yield.

In the process of preparing toluene diisocyanate (TDI) by the phosgenation reaction of toluene diamine (TDA), the side reactions produced by removing most of the free toluene diisocyanate by thin film evaporation apparatus or rotary evaporation granulation apparatus are highly concentrated. In the process of decomposing high-boiling tar solidified at room temperature obtained by conversion to toluenediamine which is a process raw material, it is very difficult to efficiently contact the decomposition medium and the tar constituent side reactions, and by stabilizing high molecular weight constituents The reactivity required for the high yield decomposition reaction is weakened, so that the yield of toluenediamine due to the decomposition reaction is lowered, and the amount of residue after decomposition is insignificant.

In the case of using an aqueous solution containing an acid, an alkali, or the like as a decomposition medium, a large amount of waste acid, waste alkali process wastewater or process waste is generated. From an environmental point of view, the hydrolysis reaction in the above low and medium pressure reaction conditions is undesirable. Under such low and low pressure conditions, the mass transfer characteristics such as the penetration and diffusion rates of the decomposition medium are very limited for the solid waste, which results in a long processing time and an increase in processing equipment.

Toluenediamine (TDA) produced by decomposition is basically basic and forms an ionic amine salt combined with an acid under acidic decomposition conditions, so an additional post-treatment purification process is required to selectively separate toluenediamine. On the other hand, when the high boiling point tar in granule form or free form form in which free toluene diisocyanate (free TDI) is removed is decomposed using supercritical water or subcritical water, mass transfer resistance to solid particles is overcome. However, due to poor reactivity and side reactions, the conversion yield to toluenediamine is low, and the reduction of tar waste is not sufficient. The hydrolysis reaction using water at high temperature and high pressure has the advantage that the toluenediamine is easily separated into the organic phase, the aqueous phase, and the decomposed residue solid as a result of the hydrolysis, but the toluenediamine is economically maintained by maintaining the high temperature and high pressure process conditions. In order to recover, it is necessary to proceed with the conversion reaction at a high yield in consideration of energy costs and high equipment costs.

However, as mentioned above, in high boiling point tar solids in which low boiling point components such as free toluene diisocyanate are mostly removed, many components having a chemical structure convertible to toluenediamine remain stabilized, but are reactive with supercritical water. Due to the competitive progression of shortages and side reactions, the yield of conversion to toluenediamine is limited by this chemical reaction step.

Accordingly, the present invention confronts the problems encountered in the prior art as described above, i.e. when the device is enlarged by adding mass transfer resistance and subsequent separation process, and particularly when decomposing high boiling point toluene diisocyanate process tar. Solving the problem of low reactivity, competitive side reactions, and low decomposition yields, the overall decomposition process, including subsequent separation processes, is simple, rapid decomposition to handle large volumes on a small scale, and to toluenediamine. It is intended to present a decomposition technique where the conversion yield is very high compared to the prior art.

Accordingly, the present invention decomposes a high boiling point toluene diisocyanate manufacturing process tar from which free toluene diisocyanate and the like is removed, converts toluene diamine to be used as a raw material, and converts it to a high yield, resulting in the amount of residue after decomposition. It is an object of the present invention to provide a method for producing and recovering toluene diamine, which greatly reduces the economic efficiency of the toluene diisocyanate-produced phosgenation reaction process, and also contributes to the cleaning of the process.

The present invention relates to a method for producing and recovering a high-boiling tar waste generated in the process of producing toluene diisocyanate by phosgenating toluene diamine (TDA) to convert it to toluenediamine.

A high boiling point tar having a content of free toluene diisocyanate (free TDI) of 1000 ppm or less is decomposed using an aqueous ammonia solution as a decomposition medium at a temperature before and after the critical temperature and near the critical pressure of water to be converted into toluenediamine, and recovered. The method is characterized by that.

Referring to the present invention in more detail as follows.

The present invention is generated in the process of manufacturing toluene diisocyanate and mixed with a high boiling point tar waste from which low boiling point reactive substances such as free toluene diisocyanate have been removed in an aqueous ammonia solution to bring it into a subcritical state near the critical point of water (218 atm, 374 ° C). The present invention relates to a method for producing and recovering toluenediamine by decomposing at a high temperature and high pressure, or decomposing at a high temperature and high pressure in a supercritical fluid state of 218 atm and 374 ° C or higher.

Tar waste discharged from the process of producing toluene diisocyanate by phosgenating toluene diamine (TDA) includes substituted urea, biuret compounds, and diurea compounds produced by side reactions. Carbodimide compounds, uretidione compounds, isocyanurate compounds, allophanate compounds, toluenediisocyanate oligomers and polymers in whole or in part And low boiling point components such as free toluene diisocyanate (free TDI).

In the production recovery method of toluene diamine according to the present invention, the high boiling point toluene diisocyanate process tar from which the low boiling point component has been removed is supplied to the high-pressure decomposition reactor in solid form, for example, in powder form or lump form, and separately The decomposition reaction may be progressed by supplying an aqueous solution to a decomposition reactor, or by preparing a bulk raw tar, paste or slurry previously deposited in an aqueous ammonia solution and supplying it to the reactor. Such conversion reaction techniques can be implemented by constructing the process in a batch, semi-continuous, or continuous manner, and in the case of continuous decomposition reactions, many countercurrent, cocurrent, tar-filled, fixed-bed, and fluidized bed It can be specified by applying process techniques. The type of reactor may be various reactors such as a cylindrical reactor, a tower reactor, a tubular reactor, a back-mixing reactor, a fluidized bed reactor, a fixed bed reactor, and the like. In addition, the technique of the present invention is not limited to the above-described operation method such as the specific batch, semi-continuous, or continuous type, contact method such as countercurrent, cocurrent flow, type of reactor, introduction type of reactants, etc. Applicable

Toluene diisocyanate production process in performing the decomposition process according to the present invention toluene diisocyanate production to remove the low-boiling components contained in the tar by performing a previous step using a thin film evaporation device or a rotary evaporation granulation device Process tar is made into the decomposition process object. It is not difficult to remove the above pretreatment step using conventional process equipment so that it contains less than 1000 ppm of free toluene diisocyanate (free TDI) in tar, and the unit process for this purpose adds extra expense. It is desirable to recover toluene diisocyanate in the range which does not occur and to the maximum possible. This is because the toluene diisocyanate manufacturing process tar contains a significant amount of free toluene diisocyanate, ranging from 10% to several tens of percent, so that the final product is in the form of toluene diisocyanate rather than hydrolyzing and converting it to the raw material of toluene diamine. This is because it is desirable to recover as much as possible.

In the decomposition of high-boiling tar obtained through the above-mentioned step process, in order to overcome mass transfer resistance, the decomposition medium is physically changed into a subcritical state or a supercritical fluid state to overcome the mass transfer resistance. . Long-range fluctuations appear near the critical point, improve mass transfer properties, and especially in supercritical fluids above the critical point, the mass transfer properties become extremely good and the diffusion coefficient increases significantly for solid tar materials. Allow for rapid reaction progress. Therefore, the decomposition reaction according to the present invention is carried out before and after the critical temperature (374 ° C.) and the critical pressure (218 atmospheres) of water, preferably in the temperature range of 350 to 600 ° C. and the range of 170 to 500 atmospheres. Preferably it is performed in the temperature range of 374-500 degreeC, and 218-400 atmospheres.

In addition, the added ammonia or ammonium ions penetrate deeply into the tar sample together with water molecules to enhance the reactivity to decomposition reactions to toluenediamine through the role of catalysts, and to improve the hydrolysis reaction medium such as ionic strength. By modifying the physicochemical properties to control the decomposition reaction and relatively suppress side reactions such as ring condensation, it plays a major role in increasing the production yield to toluenediamine.

In performing the decomposition process according to the present invention, the aqueous ammonia solution is used in an amount of 5 to 2,000 parts by weight, preferably 10 to 1,000 parts by weight, based on dry ammonia, based on 100 parts by weight of the high boiling tar. The aqueous ammonia solution used in the present invention is obtained by dissolving an ammonium salt such as ammonia or ammonium carbonate in water, so as to contain 1 to 40% by weight of dry ammonia. Such aqueous ammonia solution may be prepared by mixing beforehand, or may be directly mixed in a reactor. Ammonia or ammonium ions have the advantage as decomposition process additives or media because they are recovered in the aqueous or gas phase after the reaction, can be recycled, in particular procured inexpensively, and can be handled relatively safely. Ammonia or ammonium ions penetrate deep into the tar-constituting molecular chain together with supercritical water or subcritical water to play a catalytic role in the decomposition to toluenediamine, and relatively suppress the occurrence of malignant solid residues due to condensation reactions. It was confirmed experimentally.

The decomposition of the high boiling tar is carried out for a reaction time or average residence time of 0.01 to 30 minutes, preferably 0.1 to 15 minutes.

The present invention as described above will be described in more detail by the following comparative examples and examples, but the present invention is not limited thereto.

In addition, the gas chromatography (GC), CHN element analyzer, etc. were used for the quantitative analysis which calculates the yield and purity in the following decomposition process. A 30 m long polar capillary column (Alltech, AT210) was used as the gas chromatography separation column, and helium was flowed at 15 ml / min as a mobile phase. Analytical samples were metered in 1 μl through an injector in splitless mode maintained at 285 ° C., and signals for integration were detected at FID maintained at 250 ° C. At this time, the temperature of the oven equipped with the separation column was kept constant at 150 ℃. Toluene diamine conversion yield was calculated by defining the weight fraction of nitrogen recovered in the form of toluenediamine after the reaction in the total nitrogen contained in the raw tar sample quantitatively calculated by CHN element analyzer and the like.

Comparative Example 1

Tar produced as a side reaction in the chemical process of phosgenating toluenediamine (TDA) to produce toluene diisocyanate (TDI) is maintained for about 1 hour in a rotary evaporation granulation apparatus maintained at 260 ° C., 10 mmHg. Low boiling high reactivity materials, including free toluene diisocyanate, were removed by evaporation. And the high boiling point toluene diisocyanate process tar which the obtained free toluene diisocyanate is 500 ppm or less was grind | pulverized about 100 mesh powder. A molten salt thermostat in which the powder tar sample is placed in a high pressure reactor and separately separated by distilled water in a high pressure preheating vessel having a volume of three times the volume of the reactor and then sealed at a constant temperature of 400 ° C. soaked in a bath) and heated. When the temperature of the reactor and the preheater rises to 400 ° C and the pressure of the preheating vessel reaches 250 atmospheres, a shut-off valve isolating the reactor and the preheater to open a portion of the supercritical water on the preheater side. It was penetrated in to cause the decomposition reaction to start, which was regarded as the starting point of the reaction. At this time, the weight of the water introduced into the reactor was calculated to reach about twice the weight of the tar. During the reaction, the pressure in the reaction system varied between 250 atm and 280 atm. After reacting for 1 minute and quenching, the decomposition mixture was recovered and analyzed, and it was confirmed that toluenediamine was produced in a yield of 20%.

Comparative Example 2

The experiment of Comparative Example 1 was repeatedly performed, and the decomposition mixture after 3 minutes of reaction time was quenched, recovered, and analyzed. As a result, the yield of toluenediamine was 27.5%.

Comparative Example 3

The experiment of Comparative Example 1 was repeatedly performed, and the decomposition mixture after 5 minutes of reaction time was quenched, recovered, and analyzed. As a result, the yield of toluenediamine was 24%.

Comparative Example 4

The experiment of Comparative Example 1 was repeated for 1 minute at 450 ℃. The pressure of the reaction system at this time was changed in the range of 250 atmospheres to 340 atmospheres. As a result of analyzing the decomposition mixture by quenching, the production yield of toluenediamine reached 31%.

Comparative Example 5

The experiment of Comparative Example 4 was repeated, and the decomposition mixture after 5 minutes of reaction time was quenched, recovered, and analyzed. As a result, the yield of toluenediamine was 24%. The pressure of the reaction system at this time was changed in the range of 250 atm and 330 atm.

Example 1

Under the same conditions as in Comparative Example 1, 25% ammonia water was added instead of ultrapure water to carry out the decomposition reaction. As a result of analyzing the quenched reaction mixture after reacting for 1 minute, the yield of toluenediamine was 29%, and the yield was increased by about 9% compared to Comparative Example 1. At this time, the weight of ammonia introduced into the reactor was calculated to be about 50% of the tar weight.

Example 2

Under the same conditions as in Comparative Example 2, 25% ammonia water was added instead of ultrapure water to carry out the decomposition reaction. After analyzing the quenched decomposition mixture after reacting for 3 minutes, the yield of toluenediamine reached 41%. Compared with Comparative Example 2, a yield increase of 13.5% was confirmed.

Example 3

Under the same conditions as in Comparative Example 3, 25% ammonia water was added instead of ultrapure water to carry out the decomposition reaction. After reacting for 5 minutes, the quenched decomposition mixture was analyzed, and the yield of toluenediamine reached 52%. A 28% increase in yield was confirmed as compared to Comparative Example 3.

Example 4

Under the same conditions as in Comparative Example 4, 25% ammonia water was added instead of ultrapure water to carry out the decomposition reaction. After the reaction for 1 minute, the quenched decomposition mixture was analyzed, and the yield of toluenediamine reached 40%. Compared with Comparative Example 4, a 9% increase in yield was confirmed.

Example 5

Under the same conditions as in Comparative Example 5, 25% ammonia water was added instead of ultrapure water to carry out the decomposition reaction. After analyzing the quenched decomposition mixture after reacting for 5 minutes, the yield of toluenediamine reached 25%. Compared with Comparative Example 5, a 1% increase in yield was confirmed.

Example 6

Using the reactor and the preheating vessel of Example 1, the decomposition reaction was performed at 400 ° C. by mixing 25% ammonia water about 8 times based on the weight of the high boiling tar powder in the decomposition reactor. After 5 minutes of reaction, the decomposition mixture was quenched and analyzed, and the yield of toluenediamine reached 87.3%. At this time, the weight of ammonia in the decomposition reactor was about twice the weight of tar.

As shown in Comparative Examples and Examples above, in the present invention, the yield of toluenediamine for the same high boiling tar is increased by using an aqueous ammonia solution as compared with the comparative example using pure water as a decomposition medium under high temperature and high pressure. Can be increased more than twice. In addition, the comparative examples and examples described above tend to shorten the reaction time indicating the maximum yield of toluenediamine as the temperature increases, and in the case of the comparative example in which pure water is used as the decomposition medium, the maximum yield point indicates the decomposition of ammonia. It can be seen that the shorter than in the case of using the embodiment, the yield is also very low. That is, side reactions such as a condensation reaction occur competitively with the main decomposition reaction to produce toluenediamine, thereby reducing the conversion yield to toluenediamine. However, when the aqueous ammonia solution is used as the decomposition medium rather than pure water as the decomposition medium, the effects of these side reactions are reduced at the same time, the maximum yield point is increased, and the yield is greatly increased as described above. This is because physicochemical inhibitory effects on side reactions such as condensation reaction and a stabilized tar component are activated in the state decomposable to toluenediamine by ammonia catalysis by ammonia and / or ammonium ions supplied from aqueous ammonia solution. It is interpreted as being caused.

As described above, the decomposition method of the high-boiling toluene diisocyanate process tar according to the present invention has a very high penetration rate into solid or granular raw materials, and almost no generation of decomposed waste and waste water resulting from the decomposition reaction. In addition, the conversion yield to toluenediamine is much higher than that of the conventional technical method, which drastically reduces the processing cost of tar, which is a process waste, and recovers toluenediamine, which is a decomposition product, to be recycled in the phosgenation process for synthesizing toluene diisocyanate. To be able.

Claims (9)

In the method for producing and recovering by converting toluene diamine by converting the high-boiling tar waste generated in the process of producing toluene diisocyanate by phosgenating toluene diamine (TDA), The decomposition reaction is carried out in a temperature range of 350 to 600 ° C. and a pressure range of 170 to 500 atm using ammonia as a decomposition medium in a high boiling point tar containing free toluene diisocyanate (free TDI) of 1,000 ppm or less. Production recovery method of toluenediamine to be. The method for producing and recovering toluenediamine according to claim 1, wherein the high boiling tar is in the form of a powder or a lump. The method of claim 1, wherein the decomposition reaction is carried out at a temperature range of 374 to 500 ℃ and a pressure range of 218 to 400 atmospheres. The method of claim 1, wherein the aqueous ammonia solution is added in an amount corresponding to 5 to 2,000 parts by weight based on dry ammonia with respect to 100 parts by weight of the high boiling tar. 5. The method for producing and recovering toluene diamine according to claim 4, wherein the aqueous ammonia solution is added in an amount corresponding to 10 to 1,000 parts by weight based on 100 parts by weight of the high boiling tar. 6. The production of toluenediamine according to claim 1, 4 or 5, wherein the aqueous ammonia solution is obtained by dissolving ammonia (NH ₃ ) or an ammonium salt in water so as to contain 1 to 40% by weight of dry ammonia. Recovery method. The method of claim 6, wherein the aqueous ammonia solution is prepared in advance and introduced into the reactor, or ammonia (NH ₃ ) or ammonium salt and water are separately added to the reactor and mixed and used. The method of claim 1, wherein the decomposition reaction is carried out so that the reaction time or the average residence contact time is 0.01 to 30 minutes. 10. The method of claim 8, wherein the decomposition reaction is performed such that the reaction time or the average residence contact time is 0.1 to 15 minutes.