Method for purifying m-phenylenediamine through crystallization

Abstract

The invention discloses a method for purifying m-phenylenediamine through crystallization. A phenylenediamine mixture is sequentially subjected to cooling through a first cooling heat exchanger, crystallization through a first stirring tank and separation through a first vacuum filter, and primary m-phenylenediamine crystals and mother liquor are obtained; m-phenylenediamine seed crystals exist in the first stirring tank; in the phenylenediamine mixture, m-phenylenediamine is more than 68% by mass, o-phenylenediamine is less than 22% by mass, and p-phenylenediamine is less than 10% by mass; the temperature of the phenylenediamine mixture at the inlet of the first cooling heat exchanger is 70-75 DEG C; the temperature difference between the inlet temperature and the outlet temperature of the phenylenediamine mixture at the first cooling heat exchanger is 10-30 DEG C; the crystallization temperature of the first stirring tank is controlled to be 40-60 DEG C; according to the invention, m-phenylenediamine can be effectively purified, and the construction cost and the operation difficulty are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of separation of metaphenylenediamine, and in particular to a method for purifying metaphenylenediamine by crystallization. Background Art

[0002] 1,3-phenylenediamine (also known as m-phenylenediamine) is an important dye intermediate that can be used to synthesize various basic dyes. It is also an important aromatic amine curing agent and is widely used in the fields of composite materials and plastics.

[0003] With the rapid development of high-performance polyaromatic amide materials and aramid materials in recent years, the use of m-phenylenediamine has been newly expanded. It has broad market prospects in the synthesis of high-temperature resistant aramid 1313. At the same time, it also puts forward new requirements and challenges for the preparation of high-quality m-phenylenediamine. When producing m-phenylenediamine, its isomers o-phenylenediamine and p-phenylenediamine are also generated at the same time, so the effective purification of m-phenylenediamine is an important topic.

[0004] Although m-phenylenediamine and the other two isomers do not have a common azeotropic point, due to their close boiling points, the highest atmospheric boiling point of m-phenylenediamine is 283°C; the atmospheric boiling point of p-phenylenediamine is 267°C, and the lowest atmospheric boiling point of o-phenylenediamine is 252°C. The temperature difference between the highest and lowest is only 30°C. If distillation is used for separation, the required theoretical plate number is extremely high, and the boiling point is also very high, so the required heat energy is also quite high, so crystallization is often used for purification.

[0005] For example, the patent specification with publication number CN113754546A discloses a method for purifying m-phenylenediamine, which utilizes a static crystallizer to purify m-phenylenediamine from a mixture of m-phenylenediamine, o-phenylenediamine and p-phenylenediamine by controlling key process conditions such as material temperature, crystallization plate cooling rate, crystallization plate final temperature and sweating temperature in the static crystallizer. The patented technology requires that the components and weight fractions of the mixture entering the static crystallizer are: 85% ≥ m-phenylenediamine ≥ 80%, 12% ≤ o-phenylenediamine ≤ 15%, and 3% ≤ p-phenylenediamine ≤ 5%.

[0006] For another example, the patent specification with the publication number CN115304490A discloses a system and method for continuous separation of m-, p- and o-phenylenediamine, and its technical points are: including a holding tank, and also including: a first crystallizer, the outlet of the first crystallizer passes through a first solid-liquid separator, the mother liquid is connected to the first distillation tower through a connecting pipe, and the first solid-liquid separator is provided with a first crystallization precipitation tube; and a second crystallizer, the outlet of the second crystallizer passes through a second solid-liquid separator, the mother liquid is connected to the second distillation tower through a connecting pipe, and the second solid-liquid separator is provided with a second crystallization precipitation tube; the outlet of the third crystallizer passes through a third solid-liquid separator, the mother liquid is connected to the holding tank through a connecting pipe, and the third solid-liquid separator is provided with a third crystallization precipitation tube, and a set of separation systems designed by using solid-liquid separation and gas-liquid separation complement each other, so as to effectively separate the mixture of m-, p- and o-phenylenediamine isomers, which not only improves the recovery purity, but also improves the recovery rate. This patent technology does not propose a specific method for purifying m-phenylenediamine.

[0007] Conventional cooling crystallizers need to make the difference between the feed temperature T1 and the temperature T2 inside the crystallizer as large as possible to ensure the high yield of the product from the pure liquid state of the phenylenediamine mixture to the solid-liquid coexistence state and the crystallization product. However, a large temperature drop will cause the cooling heat exchanger to crystallize when the temperature drops, resulting in pollution and blockage of the cooling heat exchanger pipeline. In order to avoid this situation, the temperature difference between the inlet temperature T3 and the outlet temperature T4 of the cooling heat exchanger needs to be as small as possible. Therefore, in order to simultaneously meet the large temperature difference between T1 and T2 and the small temperature difference between T3 and T4, the mother liquor in the cooling crystallizer is generally mixed with the feed through a precision tubular filter at a flow rate several times or even a hundred times that of the feed before flowing into the cooling heat exchanger. However, due to the presence of fine crystals, the precision tubular filter will be blocked, and backwashing is usually required to keep the filter unobstructed. At the same time, the pipeline also needs to be fully polished, but this combination also has the risk of heat loss. The above disadvantages limit the application of cooling crystallizers. Summary of the invention

[0008] The inventors have found that m-phenylenediamine has a large metastable region. Even if there is a large temperature difference between the inlet temperature T3 and the outlet temperature T4 when passing through the cooling heat exchanger, as long as T4 is still in the metastable region, crystallization will not occur without the addition of seed crystals, so there is no need to worry about pipeline contamination and blockage. As long as there is enough time for crystal growth, the grown crystals can be separated and purified using an ordinary vacuum filter.

[0009] The present invention uses a conventional stirring tank to replace a conventional cooling crystallization system with a large number of cycles and a precision tube filter, so there is no need to worry about heat loss. Then, the coarse crystallization is achieved by adding seed crystals to the conventional stirring tank and then crystallizing to replace the cooling crystallizer. Since most of the impurities are between the m-phenylenediamine crystals, the impurities are easily removed after washing with mother liquor / sweat.

[0010] The specific technical solutions are as follows:

[0011] A method for crystallizing and purifying m-phenylenediamine, wherein a phenylenediamine mixture is cooled by a first cooling heat exchanger, crystallized by a first stirring tank, and separated by a first vacuum filter to obtain primary m-phenylenediamine crystals and a mother liquor; and m-phenylenediamine seed crystals are present in the first stirring tank;

[0012] In terms of mass fraction, in the phenylenediamine mixture, m-phenylenediamine>68%, o-phenylenediamine<22%, and p-phenylenediamine<10%;

[0013] The inlet temperature of the phenylenediamine mixture at the first cooling heat exchanger is 70-75° C.;

[0014] The difference between the inlet temperature and the outlet temperature of the phenylenediamine mixture in the first cooling heat exchanger is 10 to 30° C.;

[0015] The crystallization temperature of the first stirring tank is controlled at 40-60°C.

[0016] Preferably, in the phenylenediamine mixture, by mass fraction, m-phenylenediamine>82%, o-phenylenediamine<12%, and p-phenylenediamine<6%.

[0017] In a preferred embodiment, the primary metaphenylenediamine crystals are sequentially heated and melted in an intermediate storage tank, cooled in a second cooling heat exchanger, crystallized in a second stirring tank, and separated by a second vacuum filter to obtain metaphenylenediamine crystals and mother liquor; metaphenylenediamine seed crystals exist in the second stirring tank;

[0018] The temperature at which the primary m-phenylenediamine crystals are heated and melted in the intermediate storage tank is controlled at 70-75° C.;

[0019] The temperature reduction range of the second cooling heat exchanger is 8 to 15°C;

[0020] The crystallization temperature of the second stirring tank is controlled at 55-62°C.

[0021] The purity of the metaphenylenediamine in the metaphenylenediamine mixture is relatively low (>68%, preferably>82%), and the crystallization temperature of the metaphenylenediamine mixture is lower than that of a single crystal, so the outlet temperature of the first cooling heat exchanger and the crystallization temperature of the first stirring tank are lower than the outlet temperature of the second cooling heat exchanger and the second stirring tank, for example, the outlet temperature of the first cooling heat exchanger and the crystallization temperature of the first stirring tank are preferably 40-50° C. By the time of the second cooling heat exchanger and the second stirring tank, the purity of the metaphenylenediamine in the primary metaphenylenediamine crystals has reached more than 96%, so the outlet temperature of the second cooling heat exchanger and the crystallization temperature of the second stirring tank can be close to the crystallization point of pure metaphenylenediamine (61-63° C.), for example, it can be 60-62° C.

[0022] The intermediate storage tank can be heated and insulated by a jacket to keep the primary metaphenylenediamine crystals in a molten state. The primary metaphenylenediamine crystals can be temporarily stored in the intermediate storage tank for insulation, and the primary metaphenylenediamine in the intermediate storage tank is transported to the second cooling heat exchanger for cooling.

[0023] In another preferred embodiment, the primary metaphenylenediamine crystals are heated and melted in the first storage tank and then enter the melt crystallizer for crystallization and sweating solid-liquid separation to produce sweat and metaphenylenediamine crystals. The first storage tank can be heated by a jacket to melt the primary metaphenylenediamine crystals.

[0024] Specifically, the primary meta-phenylenediamine crystals may enter the first storage tank by gravity.

[0025] Specifically, the primary meta-phenylenediamine crystals melted in the first storage tank can enter the melt crystallizer by gravity.

[0026] The heating temperature of the first storage tank may be 65-70°C.

[0027] After the primary metaphenylenediamine crystals enter the melt crystallizer in a molten state, they are first cooled to completely crystallize. The purity of the metaphenylenediamine in the primary metaphenylenediamine crystals has reached more than 96%, so the crystallization temperature of the melt crystallizer can be close to the crystallization point of pure metaphenylenediamine. Preferably, the crystallization temperature of the melt crystallizer is controlled at 55-61°C. Then, the metaphenylenediamine crystals obtained by crystallization in the melt crystallizer are heated to near the crystallization point to sweat away impurities. Preferably, the sweating temperature of the melt crystallizer is controlled at 61-63°C.

[0028] Furthermore, the sweat can be recovered and used to clean the primary metaphenylenediamine crystals.

[0029] Preferably, the sweat is recovered in the second storage tank and kept at 40-50°C, and then the sweat is output from the second storage tank for washing the primary metaphenylenediamine crystals. The sweat is kept at 40-50°C in the second storage tank, which is close to or even consistent with the temperature of the primary metaphenylenediamine crystals separated by the first vacuum filter, which is conducive to better washing and impurity removal. The second storage tank can be jacketed for heat preservation.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention designs a method for crystallization purification of m-phenylenediamine based on the large metastable region of m-phenylenediamine, uses a cooling heat exchanger and a conventional stirring tank with crystal seeds to replace the conventional cooling crystallizer to complete the initial crystallization, and can be further purified by secondary crystallization or melt crystallization, and even the sweat after melt crystallization can be used to clean the primary crystal. The present invention can effectively purify m-phenylenediamine while reducing the construction cost and operation difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A basic schematic diagram of a method for crystallizing and purifying m-phenylenediamine provided by the present invention.

[0033] Figure 2 A schematic diagram of a recrystallization version of a method for purifying meta-phenylenediamine by crystallization provided by the present invention.

[0034] Figure 3 This is a schematic diagram of melt crystallization version I of a method for crystallization purification of m-phenylenediamine provided by the present invention.

[0035] Figure 4 This is a schematic diagram of melt crystallization version II of a method for crystallization purification of m-phenylenediamine provided by the present invention.

[0036] Figure 5 This is the solid-liquid equilibrium diagram of phenylenediamine isomers. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0038] The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0039] The present invention provides a method for crystallizing and purifying m-phenylenediamine. Figure 1 In view of the large metastable region of m-phenylenediamine, a first cooling heat exchanger 1 and a conventional first stirring tank 2 with seed crystals can replace the conventional cooling crystallizer. The outlet of the first stirring tank 2 is connected to a first vacuum filter 3. The first vacuum filter 3 separates the mother liquor and the coarse crystals (i.e., primary m-phenylenediamine crystals) into solid and liquid. The mother liquor can be emptied. For the recrystallization version, see Figure 2 After the crude crystals are separated from the base version, the crude crystals are remelted in the intermediate storage tank 5 with a jacket, and then secondary crystallization is carried out through the second cooling heat exchanger 6 and the second stirring tank 7 with crystal seeds, and then the mother liquor and m-phenylenediamine crystals are separated from the solid and liquid through the second vacuum filter 8. The mother liquor can be emptied, and the m-phenylenediamine crystals are the recrystallization version products; see the melt crystallization version I Figure 3 After the crude crystals are separated from the base version, the crude crystals are allowed to enter the first storage tank 10 with a jacket by gravity and heated and melted. The primary metaphenylenediamine crystals melted in the first storage tank 10 enter the melt crystallizer 9 by gravity. The melt crystallizer 9 separates sweat and metaphenylenediamine crystals through crystallization and sweating. The sweat can be emptied. The metaphenylenediamine crystals are the melt crystallization version products; see the melt crystallization II version Figure 4On the basis of melt crystallization version I, a second storage tank 4 with a jacket for heat preservation of sweat and a process of washing coarse crystals in the first vacuum filter 3 with sweat are added to further improve the purity of the m-phenylenediamine crystal product.

[0040] For conventional cooling crystallizers, the difference between the feed temperature T1 and the temperature T2 inside the crystallizer should be as large as possible to ensure the high yield of the product from the pure liquid state of the phenylenediamine mixture to the solid-liquid coexistence state and the crystallization product. However, a large temperature drop will cause the cooling heat exchanger to crystallize when the temperature drops, resulting in pollution and blockage of the pipeline. In order to avoid this situation, the temperature T3 at the inlet of the cooling heat exchanger and the outlet temperature T4 need to be as small as possible. Therefore, in order to simultaneously meet the large temperature difference between T1 and T2 (10-20℃ or even larger temperature difference) and the small temperature difference between T3 and T4 (0.5-1℃ temperature difference), the mother liquor in the cooling crystallizer is generally allowed to pass through a precision tubular filter at a flow rate several times or even a hundred times that of the phenylenediamine mixture feed and then mixed with the phenylenediamine mixture feed and then flow into the cooling heat exchanger. At the same time, the pipeline also needs to be fully polished, but this combination also has the risk of high energy consumption and heat loss. The present invention utilizes the larger metastable region of m-phenylenediamine, and can directly increase the temperature difference between the inlet temperature T3 and the outlet temperature T4 of the cooling heat exchanger (specifically, the temperature difference can reach 10 to 30°C). In the present invention, even if there is a large temperature difference of 10 to 30°C between the inlet and outlet of the cooling heat exchanger, crystallization will not occur without the addition of seed crystals. The present invention can ensure that T3 and T4 are rapidly crystallized in the agitator under the condition of a large temperature difference without worrying about pipeline pollution and blockage. Compared with jackets and coils, the cooling heat exchanger of the present invention has a faster cooling rate at a large flow rate and a better subsequent crystallization effect. The present invention does not use a large number of cycles with precision tubular filters, so there is no need to worry about heat loss. Afterwards, coarse crystallization or secondary crystallization is achieved by replacing the cooling crystallizer with crystallization after adding seed crystals in a conventional stirring tank.

[0041] Figure 5 The solid-liquid equilibrium diagram of phenylenediamine isomers is shown. In terms of mass fraction, in the phenylenediamine mixture, metaphenylenediamine>68%, o-phenylenediamine<22%, and p-phenylenediamine<10%, preferably, metaphenylenediamine>82%, o-phenylenediamine<12%, and p-phenylenediamine<6%, and the feed component of the phenylenediamine mixture is located in the metaphenylenediamine region.

[0042] The present invention provides a specific embodiment here, firstly, a phenylenediamine mixture of 110 t / h is fed, and the phenylenediamine mixture is composed of 11.5 wt% of o-phenylenediamine, 82.8 wt% of m-phenylenediamine and 5.7 wt% of p-phenylenediamine, then the fed phenylenediamine mixture is transported to the first cooling heat exchanger 1, the mixture temperature is reduced from 70°C at the inlet of the first cooling heat exchanger 1 to 47°C at the outlet of the first cooling heat exchanger 1, and then the outlet phenylenediamine mixture is transported to the conventional first stirring tank 2. Then, the m-phenylenediamine is crystallized by adding m-phenylenediamine seed crystals to the first stirring tank 2, the crystallization temperature of the first stirring tank 2 is controlled at 47°C, the crystallization amount is 20 t / h, and the purity of the crude crystal m-phenylenediamine separated by the first vacuum filter 3 is 96.63%, so that the basic version of the crystallization purification method of m-phenylenediamine is completed.

[0043] On the basis of the above basic version of the method for purifying m-phenylenediamine by crystallization, after separating crude crystals with a purity of 96.63% of m-phenylenediamine, the crude crystals are heated and kept warm at 70°C to be re-melted, and then cooled to 62°C by the second cooling heat exchanger 6 and then secondary crystallization is carried out in the second stirring tank 7 with crystal seeds. The crystallization temperature of the second stirring tank 7 is controlled at 62°C, and then the mother liquor and m-phenylenediamine crystals are separated by solid-liquid separation through the second vacuum filter 8. The crystallization amount is 16 t / h, and the crystal purity of m-phenylenediamine after secondary crystallization is 98.58%. The recrystallization version of the method for purifying m-phenylenediamine by crystallization is completed.

[0044] On the basis of the above basic version of the crystallization method for purifying m-phenylenediamine, after separating the crude crystals with a purity of 96.63% of m-phenylenediamine, the crude crystals are allowed to enter the first storage tank 10 with a jacket by gravity, and the temperature of the first storage tank 10 is controlled at 70°C to completely melt the crude crystals, and then enter the melt crystallizer 9 by gravity, and the crystallization temperature is controlled at 60°C. After complete crystallization, the temperature is raised to 62°C to start sweating. The sweat and m-phenylenediamine crystals are separated by sweating, and the crystallization amount is 16t / h. After sweating, the crystals (m-phenylenediamine crystal purity is 99.90%) are heated to 70°C and discharged as liquid products, thus completing the method of crystallization purification of m-phenylenediamine of melt crystallization version I.

[0045] Based on the above-mentioned method of crystallization and purification of metaphenylenediamine by melt crystallization version I, a second storage tank 4 with a jacket is added to collect sweat. The sweat temperature in the second storage tank 4 is controlled at 47-48°C. The collected sweat is used to clean the coarse crystals in the first vacuum filter 3 to further improve the purity of the metaphenylenediamine crystal product. The method of crystallization and purification of metaphenylenediamine by melt crystallization version II is completed. The crystal purity of metaphenylenediamine in melt crystallization version II is 99.99%.

[0046] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for crystallizing and purifying m-phenylenediamine, characterized in that: The phenylenediamine mixture is cooled by a first cooling heat exchanger, crystallized in a first stirring tank, and separated by a first vacuum filter to obtain primary metaphenylenediamine crystals and mother liquor; metaphenylenediamine seed crystals exist in the first stirring tank; In terms of mass fraction, in the phenylenediamine mixture, m-phenylenediamine>68%, o-phenylenediamine<22%, and p-phenylenediamine<10%; The inlet temperature of the phenylenediamine mixture at the first cooling heat exchanger is 70-75° C.; The difference between the inlet temperature and the outlet temperature of the phenylenediamine mixture in the first cooling heat exchanger is 10 to 30° C.; The crystallization temperature of the first stirring tank is controlled at 40-60°C.

2. The method according to claim 1, characterized in that In terms of mass fraction, in the phenylenediamine mixture, m-phenylenediamine>82%, o-phenylenediamine<12%, and p-phenylenediamine<6%.

3. The method according to claim 1, characterized in that The primary metaphenylenediamine crystals are sequentially heated and melted in an intermediate storage tank, cooled in a second cooling heat exchanger, crystallized in a second stirring tank, and separated in a second vacuum filter to obtain metaphenylenediamine crystals and a mother liquor; metaphenylenediamine seed crystals are present in the second stirring tank; The temperature at which the primary m-phenylenediamine crystals are heated and melted in the intermediate storage tank is controlled at 70-75° C.; The temperature reduction range of the second cooling heat exchanger is 8 to 15°C; The crystallization temperature of the second stirring tank is controlled at 55-62°C.

4. The method according to claim 1, characterized in that: The primary metaphenylenediamine crystals are heated and melted in the first storage tank and then enter the melting crystallizer for crystallization and sweating to separate the sweat and metaphenylenediamine crystals.

5. The method according to claim 4, characterized in that The primary metaphenylenediamine crystals enter the first storage tank by gravity; The primary meta-phenylenediamine crystals melted in the first storage tank enter the melt crystallizer by gravity.

6. The method according to claim 4, characterized in that The heating temperature of the first storage tank is 65-70°C.

7. The method according to claim 4, characterized in that The crystallization temperature of the melt crystallizer is controlled at 55-61°C, and the sweating temperature is controlled at 61-63°C.

8. The method according to any one of claims 4 to 7, characterized in that: The sweat recovery is used to clean the primary meta-phenylenediamine crystals.

9. The method according to claim 8, characterized in that The sweat is recovered in the second storage tank and kept at 40-50° C., and then the sweat is output from the second storage tank for washing the primary metaphenylenediamine crystals.

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