A method for salt formation and purification in the production of rt-pcr

Abstract

The present application relates to rubber antioxidant intermediate-RT production technical field, especially disclose a kind of salt-removing method in RT production process.This application provides a kind of efficient, convenient, low-cost method for removing carbonate in RT production system of nitrobenzene method.The method is extracted by hydrogen reduction liquid, oil-water separation, water phase demethanolization, evaporation concentration to obtain the recovery alkali material liquid containing higher tetramethylammonium hydroxide concentration and condensation reaction liquid are extracted in two directions, while realizing the enrichment of carbonate ion and the removal of RT and other organic matters in recovery alkali water phase, and a small amount of condensation reaction raw material liquid is extracted to the recovery alkali water phase enriched with carbonate, and finally the carbonate is removed by salt-alkali conversion.The salt removal efficiency of the present application is high, the treatment method is simple, the generation of three wastes is less, energy saving and environmental protection, and the economy is good.

Description

Technical Field

[0001] The present invention relates to the technical field of production of RT base, an intermediate of a rubber antioxidant, and in particular to a salt-forming and impurity-removing method in the production process of RT base. Background Art

[0002] The preparation of p-aminodiphenylamine (RT-base), a key intermediate in p-phenylenediamine rubber antioxidants, is a two-step process. First, aniline and nitrobenzene react in the presence of tetramethylammonium hydroxide as a catalyst to produce a condensation solution containing p-nitrodiphenylamine and p-nitrosodiphenylamine. This condensation solution is then subjected to catalytic hydrogenation to produce a hydrogenated reduction solution containing RT-base. After filtering through the catalyst, the hydrogenated reduction solution contains RT-base, aniline, methanol, and tetramethylammonium hydroxide. Diluting the solution with water separates the oil and water phases, with the RT-base primarily entering the oil phase. The aqueous phase is then demethanolated and concentrated by evaporation to recover the spent condensation catalyst, commonly known as "recovery base," which is then reused.

[0003] The condensation catalyst, tetramethylammonium hydroxide, is a strong base. During the condensation reaction, hydrogenation reaction, and material transportation and storage processes, the tetramethylammonium hydroxide partially decomposes and inevitably comes into contact with small amounts of CO2 to form carbonates. As the recovered base continuously circulates within the system, the carbonates continue to accumulate, and their content gradually increases. Carbonates not only affect the binding of tetramethylammonium hydroxide with aniline, thereby reducing the selectivity of the condensation reaction, but also lead to post-use concentration and difficulty in recovering the condensation catalyst. They can even reduce the activity of the hydrogenation catalyst and exacerbate side reactions. Therefore, regular removal of accumulated carbonate ions within the reaction system (commonly known as "desalting") is necessary.

[0004] A review of existing RT-base process technologies reveals that desalination processes are currently divided into two main operating modes: recovery alkali desalination and condensation liquid desalination. The recovery alkali desalination process typically involves adding a desalting agent to the aqueous phase of the hydrogenated liquid after dilution, extraction, and stratification. This converts the carbonate ions present in the aqueous phase into inorganic carbonates, which are then removed to achieve desalination. A disadvantage of this process is that during hydrogenated liquid extraction, a large amount of water is typically added to increase the density difference between the oil and water phases and improve oil-water stratification. This results in a high water content in the final recovery alkali aqueous phase, low concentrations of methylammonium hydroxide and carbonate ions, and low salt formation efficiency. It also dissolves a large amount of calcium and sodium ions into the system, accelerating equipment scaling or causing catalyst deactivation. Furthermore, the recovery alkali typically contains a small amount of methanol, which inevitably dissolves some organic matter, such as RT-base. This not only affects salt formation but also exacerbates side reactions when introduced into the condensation reaction system.

[0005] The condensation liquid desalination process is to control the water content in the condensation reaction system of nitrobenzene and aniline, by maintaining a certain amount of water in the reaction system, or adding a certain amount of water to the reaction system, the carbonate in the reaction material is dissolved in the aqueous phase, and then by adding a desalting agent to the aqueous phase or directly removing the carbonate in the form of discarded aqueous phase. However, the above-mentioned process also has obvious drawbacks, that is, the water content in the condensation reaction system needs to be accurately controlled, if the amount of water is too much, not only will it lead to low salt formation efficiency after adding a desalting agent, but also dissolve too much calcium and sodium cations into the reaction system, and also cause the adverse effects such as the condensation reaction speed slowing down and the nitrobenzene surplus increasing, and if the amount of water is too little, it will not only affect the dissolution and enrichment of carbonate ions in the system, but also aggravate the decomposition and consumption of the condensation catalyst. Therefore, the condensation liquid desalination process has high requirements for the water content control of the condensation reaction, and not only needs to consider the reaction speed and the degree of reaction, but also needs to consider the dissolution and removal of carbonate, which will greatly increase the difficulty of process operation. Furthermore, the tetramethylammonium hydroxide in the condensation solution primarily dissolves in the oil phase, leaving a low concentration in the aqueous phase. This significantly increases the dissolution of alkali metal cations such as calcium and sodium during salt formation in the aqueous phase. Furthermore, the aqueous phase directly separated from the condensation reaction contains some 4-nitrodiphenylamine and 4-nitrosodiphenylamine, which can affect salt formation. Directly discarding the aqueous phase significantly increases the consumption of the condensation catalyst, resulting in waste and increased production costs.

[0006] Therefore, there is an urgent need to develop an efficient, convenient, and low-cost salt-forming and impurity-removing method to remove carbonate ions in the reaction system, which is of great significance for the high-quality and efficient production of RT base. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the present invention provides an efficient, convenient and low-cost method for salt formation and impurity removal in the RT base production process.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for salt formation and impurity removal in the RT base production process, treating a recovered alkali liquid obtained by subjecting the hydrogenated reduction liquid in the RT base preparation to water extraction, oil-water separation, methanol removal from the aqueous phase, and evaporation concentration, comprising the following steps:

[0010] (1) Add the recovered alkali liquid to the extraction kettle, then add the nitrobenzene and aniline condensation reaction liquid, heat and stir thoroughly to mix and extract, cool the treated mixed liquid and let it stand in the extraction kettle to separate layers, the oil phase returns to the system and enters the hydrogenation section for hydrogenation reduction, the water phase remains in the extraction kettle, and then adds the condensation reaction liquid, continues to stir and mix to extract, and let it stand to separate layers until the carbonate concentration in the recovered alkali water phase reaches the salt formation requirement;

[0011] (2) adding an extractant M to the recovered alkaline aqueous phase rich in carbonate obtained in step (1), heating the feed solution, stirring and extracting the mixture, cooling the treated mixed solution, standing and separating the layers, and returning the extractant oil phase as a raw material for the condensation reaction directly to the condensation reaction system;

[0012] (3) Sodium hydroxide is added to the recovered alkaline aqueous phase obtained in step (2) to carry out a salt-forming reaction. After the reaction is completed, the feed liquid is sent to a filter for filtration. The filter residue includes the generated sodium carbonate and unreacted sodium hydroxide. The obtained filtrate is recycled as a recovered condensation catalyst.

[0013] The present invention addresses the problems existing in existing alkali recovery desalination and condensation liquid desalination processes. The invention adopts a recovered alkali feed liquid containing a relatively high tetramethylammonium hydroxide concentration obtained by subjecting a hydrogenated reduction liquid to water extraction, oil-water separation, aqueous phase methanol removal, and evaporation concentration, as a carbonate enriched aqueous phase. The feed liquid resulting from the condensation reaction of nitrobenzene and aniline is used as an oil phase, and the two are subjected to bidirectional extraction. That is, the recovered alkali feed liquid is used as the aqueous phase, and carbonate ions contained in the condensation liquid can be effectively extracted, enriched, and transferred thereto until they are enriched to a concentration required for salt formation. Moreover, since the condensation liquid contains a large amount of aniline, p-nitrosodiphenylamine, and p-nitrodiphenylamine, organic substances such as RT base dissolved in the recovered alkali feed liquid can be efficiently extracted and transferred thereto.

[0014] The bidirectional extraction strategy of the present invention not only enriches carbonate ions but also removes organic matter such as RT base from the recovered alkaline aqueous phase, thus preventing any impact on subsequent desalination. Furthermore, extracting the carbonate-enriched recovered alkaline aqueous phase with a small amount of aniline or nitrobenzene removes small amounts of dissolved p-nitrosodiphenylamine and p-nitrodiphenylamine, thus preventing any impact on subsequent desalination. The used aniline or nitrobenzene requires no treatment and can be directly returned to the system as a raw material for the condensation reaction.

[0015] A better technical solution of the present invention is:

[0016] In step (1), in the recovered alkali solution, the mass concentration of tetramethylammonium hydroxide is 15-25%, and the mass concentration of carbonate ion is 0.5-2.0%.

[0017] Further preferably, the mass ratio of the recovered alkali liquid to the condensation reaction liquid is 0.03-0.1:1, the extraction temperature is 55-80°C, and the standing stratification temperature is 50-75°C.

[0018] More preferably, in the recovered alkaline aqueous phase, the carbonate ion concentration is enriched to reach the mass concentration required for salt formation of 4-15%.

[0019] In step (2), the extractant M is nitrobenzene or aniline, and the mass ratio of the extractant M to the recovered alkaline aqueous phase is 0.03-0.1.

[0020] More preferably, the extraction temperature is 30-70°C and the stratification temperature is 25-60°C.

[0021] In step (3), the molar ratio of sodium hydroxide to carbonate in the recovered alkaline aqueous phase is 2-5.

[0022] More preferably, after adding sodium hydroxide, the reaction temperature of the mixed liquid is 40-75° C., and the reaction time is maintained for 0.5-3 h.

[0023] Compared with the prior art, the present invention has the following outstanding progress and advantages: (1) the control operation of the condensation reaction process is simplified; (2) the bidirectional extraction operation removes organic matter while enriching carbonate ions, significantly improving the removal efficiency of carbonate ions; (3) the alkaline aqueous phase contains a high concentration of tetramethylammonium hydroxide, which effectively improves the salt formation efficiency and greatly reduces the amount of sodium ions introduced into the system; (4) the use of additional extraction solvents is avoided, and the amount of waste liquid and waste residue generated during the treatment process is small, which is green, environmentally friendly and economical. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0025] Example 1: A method for salt formation and impurity removal in the production process of RT base.

[0026] The recovered alkali solution obtained from the hydrogenation reduction liquid during the RT base preparation process, which undergoes water extraction, oil-water separation, aqueous phase methanol removal, and evaporation concentration, was used as the treatment object. Analysis revealed that the recovered alkali solution contained a tetramethylammonium hydroxide concentration of 15.5%, a carbonate concentration of 0.75%, and an RT base content of 1.05%. The salt formation and impurity removal method specifically includes the following steps:

[0027] (1) Take 5 kg of recovered alkali liquid as the aqueous phase and add it to the extraction kettle, then add 100 kg of nitrobenzene and aniline condensation reaction liquid as the oil phase, heat it to 70 ° C and stir and mix it thoroughly for 1 hour, cool the treated mixed liquid to 55 ° C and let it stand in the extraction kettle for stratification, the oil phase returns to the system and enters the hydrogenation section for hydrogenation reduction, the aqueous phase remains in the extraction kettle, the aqueous phase is sampled and measured, and the carbonate content is 4.44%; then add 100 kg of condensation reaction liquid, continue to stir and mix and extract according to the above conditions and let it stand for stratification, the oil phase is also returned to the system and enters the hydrogenation section for hydrogenation reduction, a total of 5.70 kg of aqueous phase is obtained, the aqueous phase is sampled and measured, and the carbonate content is 6.72%, which meets the salt formation requirements, the RT base content is reduced to 0.058%, and the total content of 4-nitrodiphenylamine and 4-nitrosodiphenylamine is 0.23%.

[0028] (2) 0.57 kg of nitrobenzene was added to the carbonate-rich recovered alkaline aqueous phase obtained in step (1). The feed solution was fully stirred and extracted at 65°C for 1 hour. The treated mixed solution was cooled to 40°C and then allowed to stand for stratification. The extracted oil phase was directly returned to the condensation reaction system as a raw material for the condensation reaction. After extraction and separation, 5.65 kg of recovered alkaline aqueous phase was obtained. The aqueous phase was sampled and measured. The mass concentration of tetramethylammonium hydroxide was 16.3%, the carbonate content was 6.78%, the RT base content was reduced to 0.014%, and the total content of 4-nitrodiphenylamine and 4-nitrosodiphenylamine was reduced to 0.012%.

[0029] (3) 0.64 kg of sodium hydroxide was added to the recovered alkaline aqueous phase obtained in step (2), and the temperature was raised to 65° C. for reaction for 1 hour. The feed liquid was then filtered to obtain 5.46 kg of filtrate. The filtrate was sampled and measured. The mass concentration of tetramethylammonium hydroxide was 34.2%, the carbonate content was reduced to 0.23%, and the residual sodium ion content was 0.088%. The carbonate removal rate was 96.6%. The filtrate can be recycled as a recovered condensation catalyst.

[0030] Example 2: A method for salt formation and impurity removal in the production process of RT base.

[0031] The same batch of recovered alkali solution and nitrobenzene and aniline condensation reaction solution as in Example 1 were used. The salt-forming and impurity-removing method specifically comprises the following steps:

[0032] (1) Take 10 kg of recovered alkali liquid as the aqueous phase and add it to the extraction kettle, then add 100 kg of nitrobenzene and aniline condensation reaction liquid as the oil phase, heat it to 75 ° C and stir and mix it for 1 hour, cool the treated mixed liquid to 60 ° C and let it stand in the extraction kettle for stratification, return the oil phase to the system and enter the hydrogenation section for hydrogenation reduction, and leave the aqueous phase in the extraction kettle; add 100 kg of condensation reaction liquid again, continue to stir and mix and extract according to the above conditions and let it stand for stratification, and return the oil phase to the system and enter the hydrogenation section for hydrogenation reduction; carry out the above extraction operation 3 times in total; obtain a total of 10.4 kg of aqueous phase, sample the aqueous phase for determination, and the carbonate content is 8.14%, which meets the salt formation requirement, the RT base content is reduced to 0.045%, and the total content of 4-nitrodiphenylamine and 4-nitrosodiphenylamine is 0.26%.

[0033] (2) 0.69 kg of aniline was added to the carbonate-rich recovered alkaline aqueous phase obtained in step (1). The feed solution was fully stirred and extracted at 65°C for 1 hour. The treated mixed solution was cooled to 40°C and allowed to stand for stratification. The extracted oil phase was directly returned to the condensation reaction system as a raw material for the condensation reaction. After extraction and separation, 10.3 kg of recovered alkaline aqueous phase was obtained. The aqueous phase was sampled and measured. The mass concentration of tetramethylammonium hydroxide was 16.6%, the carbonate content was 8.18%, the RT base content was reduced to 0.012%, and the total content of 4-nitrodiphenylamine and 4-nitrosodiphenylamine was reduced to 0.015%.

[0034] (3) 1.12 kg of sodium hydroxide was added to the recovered alkaline aqueous phase obtained in step (2), and the temperature was raised to 65° C. for reaction for 1 hour. The feed liquid was then filtered to obtain 10.18 kg of filtrate. The filtrate was sampled and measured. The mass concentration of tetramethylammonium hydroxide was 37.6%, the carbonate content was reduced to 0.32%, and the residual sodium ion content was 0.075%. The carbonate removal rate was 96.1%. The filtrate can be recycled as a recovered condensation catalyst.

[0035] Example 3 (Comparative Example 1):

[0036] The same batch of recovered alkali solution and nitrobenzene and aniline condensation reaction solution as in Example 1 was used.

[0037] The salt-forming and impurity-removal method is as follows: first, an aqueous phase is obtained by the same method as in step (1) of Example 2. 1.12 kg of sodium hydroxide is directly added to the aqueous phase without undergoing the extraction step of step (2) of Example 2. The temperature is raised to 65°C and the reaction is carried out for 1 hour. The feed liquid is then filtered to obtain approximately 10.2 kg of filtrate. The filtrate is sampled and measured, and the mass concentration of tetramethylammonium hydroxide is 32.4%, the carbonate content is 1.58%, and the residual sodium ion content is 0.08%. The carbonate removal rate is approximately 80.6%.

[0038] It can be judged that the total content of 4-nitrodiphenylamine and 4-nitrosodiphenylamine in the aqueous phase is about 0.26%, which will affect the salt-forming reaction and thus affect the removal of carbonate ions.

[0039] Example 4 (Comparative Example 2):

[0040] The same batch of recovered alkali solution as in Example 1 was used. This recovered alkali solution was concentrated by evaporation at -0.095 MPa and 55-60°C, with an appropriate amount of CO2 introduced to adjust the carbonate content. Sampling and analysis of the concentrated recovered alkali solution revealed a tetramethylammonium hydroxide concentration of 33.5%, a carbonate concentration of 6.55%, and an RT-base content of 2.96%.

[0041] 10 kg of the recovered alkaline aqueous phase after the concentration treatment was added with 1.1 kg of sodium hydroxide, and the temperature was raised to 65°C for 1 hour. The liquid was then filtered to obtain 9.8 kg of filtrate. Samples of this filtrate were measured and found to contain 31.2% tetramethylammonium hydroxide, 1.22% carbonate, and 0.105% residual sodium ion. The carbonate removal rate was approximately 81%.

[0042] Example 5: Condensation reaction verification experiment

[0043] The recovered alkaline aqueous phases obtained through desalination treatment in Examples 1, 2, and 4 were used as condensation reaction catalysts to verify their effects on the aniline-nitrobenzene condensation reaction. The recovered alkaline aqueous phases obtained through desalination treatment in Examples 1, 2, and 4 were designated as S1, S2, and S4, respectively.

[0044] The condensation reaction was performed as follows: 1.2 kg of aniline, 0.2 kg of nitrobenzene, and a certain amount of recovered alkaline aqueous phase (S1, S2, and S4) were added to a condensation reactor. The recovered alkaline aqueous phase was metered to a molar ratio of 1.2:1 between tetramethylammonium hydroxide and 0.2 kg of nitrobenzene. After nitrogen substitution, the dehydration condensation reaction was carried out at a temperature of 70°C and a pressure of -0.09 MPa for 2 hours. After completion of the reaction, the liquid was sampled and analyzed by high-performance liquid chromatography. The results are shown below.

[0045]

[0046] As can be seen from the above analysis results, when the recovery bases S1 and S2 obtained by processing in Examples 1 and 2 are used as condensation reaction catalysts, the raw nitrobenzene can be basically completely converted, and the tar impurities generated by the reaction are small, indicating that the use of S1 and S2 as catalysts has no adverse effect on the condensation reaction. In contrast, when the recovery base S4 obtained by processing in Example 4 is used as a condensation reaction catalyst, the raw nitrobenzene cannot be completely converted, and the tar impurities generated by the reaction increase significantly. Based on this, it can be judged that the introduction of excessive organic matter such as RT base into the recovery base has a relatively significant adverse effect on the condensation reaction, which will aggravate the occurrence of side reactions.

[0047] Obviously, the embodiments described above are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

Claims

1. A method for removing impurities from salt in the RT base production process, wherein the recovered alkali liquid obtained by subjecting the hydrogenated reduction liquid in the RT base preparation to water extraction, oil-water separation, methanol removal from the aqueous phase, and evaporation concentration is treated as the processing object, and the method is characterized by: The steps include: (1) Add the recovered alkali liquid to the extraction kettle, then add the nitrobenzene and aniline condensation reaction liquid, heat and fully stir to mix and extract, cool the treated mixed liquid and let it stand in the extraction kettle to separate into layers, the oil phase returns to the system and enters the hydrogenation section for hydrogenation reduction, the water phase remains in the extraction kettle, then add the nitrobenzene and aniline condensation reaction liquid, continue to stir and extract, let it stand to separate into layers, until the carbonate concentration in the recovered alkali water phase reaches the salt formation requirement; (2) adding an extractant M to the recovered alkaline aqueous phase rich in carbonate obtained in step (1), heating the feed solution, stirring and extracting the mixture, cooling the treated mixed solution, standing and separating the layers, and returning the extractant oil phase as a raw material for the condensation reaction directly to the condensation reaction system; The extractant M is nitrobenzene or aniline; (3) Sodium hydroxide is added to the recovered alkaline aqueous phase obtained in step (2) to carry out a salt-forming reaction. After the reaction is completed, the feed liquid is sent to a filter for filtration. The filter residue includes the generated sodium carbonate and unreacted sodium hydroxide. The obtained filtrate is recycled as a recovered condensation catalyst.

2. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (1), in the recovered alkali solution, the mass concentration of tetramethylammonium hydroxide is 15-25%, and the mass concentration of carbonate ion is 0.5-2.0%.

3. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (1), the mass ratio of the recovered alkali liquid to the condensation reaction liquid is 0.03-0.1:1, the extraction temperature is 55-80°C, and the standing stratification temperature is 50-75°C.

4. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (1), the carbonate concentration in the recovered alkaline aqueous phase is enriched to reach the mass concentration required for salt formation, which is 4-15%.

5. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (2), the mass ratio of the extractant M to the recovered alkaline aqueous phase is 0.03-0.

1.

6. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (2), the extraction temperature is 30-70°C, and the standing temperature for stratification is 25-60°C.

7. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (3), the molar ratio of sodium hydroxide to carbonate in the recovered alkaline aqueous phase is 2-5.

8. The method for salt formation and impurity removal in the RT base production process according to claim 1, wherein: In step (3), after adding sodium hydroxide, the reaction temperature of the mixed liquid is 40-75°C, and the reaction time is maintained for 0.5-3h.

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