A desalination method

Abstract

The invention provides a method for desalting RT base by recovering alkali. Aniline and recovered alkali are placed in a desalting reactor, a desalting agent is added to carry out a desalting reaction, the reactor is allowed to stand, filtered, and nitrobenzene is added to the filtrate to carry out a condensation reaction, wherein the desalting rate is above 80%.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemical industry, and in particular relates to a desalination method for recovering alkali in an RT base production device. Background Art

[0002] RT base is an important intermediate in the production of rubber antioxidants and is widely used in dyes, textiles, printing, pharmaceuticals and rubber additives. The industrial production routes of RT base include aniline method, diphenylamine method, formanilide method and nitrobenzene method. Among them, the nitrobenzene method is the most widely used method for producing RT base due to its mild conditions, few by-products and advanced technology.

[0003] Aniline and nitrobenzene undergo condensation reaction under the action of condensation catalyst tetramethylammonium hydroxide. After the condensation is completed, hydrogenation reaction is carried out in the presence of a reduction catalyst. After the hydrogenation is completed, methanol is distilled from the aqueous phase containing tetramethylammonium hydroxide and then alkali is concentrated. The alkali is recovered and used in the condensation process. Tetramethylammonium hydroxide is a two-phase catalyst with strong alkalinity and is easy to absorb carbon dioxide in the air. The carbonate in the recovered alkali affects the normal progress of the condensation reaction and the reduction reaction. The recovered alkali needs to be desalted to remove the carbonate before recycling.

[0004] Patent CN 201610354725.X uses calcium hydroxide, calcium oxide or calcium hydroxide aqueous solution as a desalting agent to desalinate the aqueous phase of RT base extraction using nitrobenzene method to reduce the carbonate ion content in the organic base.

[0005] Patent CN 201710164449.5 adds extraction solvent to recover quaternary ammonium base, stirs, and stands to separate water phase and oil phase. The oil phase is transported to the distillation system to recover aniline and para-aminodiphenylamine.

[0006] Patent CN 201710164449.5 adds a centrifugal separation process to separate and recover p-aminodiphenylamine and large molecular viscous organic substances in the quaternary ammonium base, thereby reducing the content of p-aminodiphenylamine and large molecular viscous organic substances in the recovered quaternary ammonium base.

[0007] When using sodium hydroxide for desalination, sodium carbonate will be brought into the system due to its high solubility, affecting the condensation and reduction reactions. Centrifugal separation has high requirements for production equipment. When using the extraction water phase for desalination, the amount of water is large and the cost is high. Summary of the invention

[0008] The purpose of the present invention is to provide a method for recovering alkali and desalting RT base, which has a high desalination rate and can be used in industrial production.

[0009] The invention provides a method for desalting RT base by recovering alkali. Aniline and recovered alkali are placed in a desalting reactor, a desalting agent is added to carry out desalting reaction, the reactor is allowed to stand, filtered, and nitrobenzene is added to the filtrate to carry out condensation reaction.

[0010] The recovered alkali is a tetramethylammonium hydroxide aqueous solution recovered from the RT base production device.

[0011] The mass ratio of the aniline to the recovered alkali is 0.5-2.

[0012] The concentration of carbonate in the recovered alkali is 0.5% to 5%.

[0013] The concentration of hydroxide in the recovered alkali is 10% to 22%.

[0014] The desalination reaction temperature is 50°C to 90°C, and the desalination reaction time is 0.5h to 5h.

[0015] The desalination reaction is carried out under certain stirring, and the stirring speed is 100~800r / min.

[0016] After the desalination reaction, the standing time is 0.5h~5h.

[0017] The desalting agent is barium hydroxide, barium oxide, or an aqueous solution of barium hydroxide.

[0018] The molar ratio of the desalting agent to the carbonate in the recovered alkali is 0.8-1.5.

[0019] Compared with the prior art, the method of the present invention has the following advantages:

[0020] 1) Use a mixture of aniline and recovered alkali for desalination, and directly add nitrobenzene after desalination for condensation reaction;

[0021] 2) Use barium salts for desalination, taking advantage of the difference in solubility to convert all carbonate ions into barium carbonate precipitates, which are easy to filter and separate;

[0022] 3) Salt removal rate is above 80%. DETAILED DESCRIPTION

[0023] The method of the present invention is described in detail below with reference to the embodiments.

[0024] Example 1

[0025] 150 g of aniline and 75 g of recovered alkali were placed in a flask, 9.21 g of barium hydroxide was added, and the mixture was stirred at 50°C for desalination reaction at a stirring speed of 100 r / min and a reaction time of 0.5 h. The mixture was allowed to stand for 5 h and filtered. The carbonate concentration in the recovered alkali was 4.3%, the carbonate concentration in the filtrate was 0.11%, and the desalination rate was 92.3%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 99.5%.

[0026] Comparative Example 1

[0027] 150 g of aniline and 75 g of recovered alkali were placed in a flask, the concentration of carbonate in the recovered alkali was 4%, 40 g of nitrobenzene was added, the vacuum degree was 0.094 MPa, the condensation reaction was carried out at 68°C, and the reaction conversion rate was 90%.

[0028] Example 2

[0029] 150 g of aniline and 300 g of recovered alkali were placed in a flask, 3.43 g of barium hydroxide was added, and the desalination reaction was carried out by stirring at 50°C, with a stirring speed of 500 r / min and a reaction time of 5 h. The mixture was allowed to stand for 0.5 h and filtered. The carbonate concentration in the recovered alkali was 0.5%, the carbonate concentration in the filtrate was 0.1%, and the desalination rate was 70%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 99.6%.

[0030] Example 3

[0031] 150 g of aniline and 75 g of recovered alkali were placed in a flask, 15.3 g of barium hydroxide was added, and the mixture was stirred at 50°C for desalination reaction at a stirring speed of 200 r / min and a reaction time of 2.5 h. The mixture was allowed to stand for 1.5 h and filtered. The carbonate concentration in the recovered alkali was 5.1%, the carbonate concentration in the filtrate was 0.03%, and the desalination rate was 98.2%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 99.4%.

[0032] Example 4

[0033] 150 g of aniline and 150 g of recovered alkali were placed in a flask, 13.8 g of barium hydroxide was added, and the mixture was stirred at 50°C for desalination reaction at a stirring speed of 300 r / min and a reaction time of 1.5 h. The mixture was allowed to stand for 3.5 h and filtered. The carbonate concentration in the recovered alkali was 3.6%, the carbonate concentration in the filtrate was 0.36%, and the desalination rate was 81%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 98.4%.

[0034] Example 5

[0035] 150 g of aniline and 75 g of recovered alkali were placed in a flask, 6.21 g of barium hydroxide was added, and the mixture was stirred at 50°C for desalination reaction at a stirring speed of 250 r / min and a reaction time of 2 h. The mixture was allowed to stand for 1 h and filtered. The carbonate concentration in the recovered alkali was 2.9%, the carbonate concentration in the filtrate was 0.12%, and the desalination rate was 87.6%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 96.4%.

[0036] Example 6

[0037] 150 g of aniline and 250 g of recovered alkali were placed in a flask, 17.6 g of barium hydroxide was added, and the mixture was stirred at 50°C for desalination reaction at a stirring speed of 350 r / min and a reaction time of 3 h. The mixture was allowed to stand for 3 h and filtered. The carbonate concentration in the recovered alkali was 2.5%, the carbonate concentration in the filtrate was 0.03%, and the desalination rate was 98.0%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 99.4%.

[0038] Example 7

[0039] 150 g of aniline and 150 g of recovered alkali were placed in a flask, 6.12 g of barium hydroxide was added, and the mixture was stirred at 50°C for desalination reaction at a stirring speed of 200 r / min and a reaction time of 2 h. The mixture was allowed to stand for 2 h and filtered. The carbonate concentration in the recovered alkali was 1.5%, the carbonate concentration in the filtrate was 0.07%, and the desalination rate was 90.5%. 40 g of nitrobenzene was added to the filtrate, and the vacuum degree was 0.094 MPa. The condensation reaction was carried out at 68°C, and the reaction conversion rate was 99.4%.

Claims

1. A desalination method, characterized in that: Aniline and recovered alkali are placed in a desalination reactor, a desalting agent is added to carry out a desalination reaction, the reactor is allowed to stand, filtered, and nitrobenzene is added to the filtrate to carry out a condensation reaction; the recovered alkali is a tetramethylammonium hydroxide aqueous solution recovered from an RT base production device, the mass ratio of aniline to the recovered alkali is 0.5-2, and the concentration of carbonate in the recovered alkali is 0.5%-5%; the desalting agent is one or more of a barium hydroxide aqueous solution, barium oxide, and barium hydroxide.

2. The method according to claim 1, characterized in that The concentration of tetramethylammonium hydroxide in the recovered alkali is 10% to 22%.

3. The method according to claim 1, characterized in that The desalination reaction temperature is 50℃~90℃, and the desalination reaction time is 0.5h~5h.

4. The method according to claim 1, characterized in that The desalination reaction is carried out under stirring, and the stirring speed is 100~800r / min.

5. The method according to claim 1, characterized in that After the desalting reaction, the standing time is 0.5h~5h.

6. The method according to claim 1, characterized in that The molar ratio of the desalting agent to the carbonate in the recovered alkali is 0.8-1.5.