Preparation method of anti-tarnish o-phenylenediamine and obtained product

Abstract

The invention provides a preparation method of anti-discoloration o-phenylenediamine and an obtained product, and the preparation method comprises the following steps: putting an o-phenylenediamine raw material into a reaction kettle, adding alkali liquor, carrying out nitrogen replacement, carrying out an alkaline hydrolysis reaction, and carrying out a reaction on easily discoloration o-chloroaniline, o-aminophenol, phenol and other substances in the o-phenylenediamine raw material to generate corresponding phenate; and then carrying out dehydration and thin film evaporation on the alkaline hydrolysis solution to obtain an anti-tarnish o-phenylenediamine finished product. Compared with the traditional purification process of o-phenylenediamine, the method has the advantages that components which are easy to change color are effectively reacted, the generated phenate serves as a heavy component and is removed through thin film evaporation, and meanwhile, the discolored product can be treated to obtain the discoloration-resistant o-phenylenediamine. The method is short in technological process and remarkable in effect, and the finished o-phenylenediamine product is good in discoloration resistance, does not discolor after being stored for a long time and has high industrial application value.

Description

Technical Field

[0001] The invention relates to the technical field of chemical post-processing, and in particular to a preparation method of anti-discoloration o-phenylenediamine and the obtained product. Background Art

[0002] O-phenylenediamine is mainly used to prepare pesticide fungicides, such as carbendazim and benomyl, and can also be used as an important component in the preparation of dyes, photosensitive materials, antifreeze agents, surfactants, etc. Some high value-added products have high requirements for appearance, but the existing o-phenylenediamine products contain trace amounts of o-aminophenol, o-chloroaniline, phenol and other easily discolored substances, which makes the product easy to discolor (no discoloration time <30 days), and cannot meet the needs of the high-end market.

[0003] At present, the industrial preparation method of o-phenylenediamine is mainly: o-nitroaniline is hydrogenated to synthesize o-phenylenediamine, and the hydrogenated liquid is subjected to solvent removal, light removal, and distillation to prepare the o-phenylenediamine finished product. Since a small amount of light components such as o-aminophenol, o-chloroaniline, and phenol contained in the o-phenylenediamine finished product cannot be completely removed through the light removal process, the finished product is prone to discoloration.

[0004] Patent application CN101462966 A discloses a method for purifying fine o-phenylenediamine, which purifies o-phenylenediamine by distillation and flakes under nitrogen protection to obtain fine o-phenylenediamine. This process is a conventional processing process, and the product content is only 99.5%. The finished product still contains a small amount of o-chloroaniline and other easily discolored components, which are prone to discoloration when stored for a long time.

[0005] Patent application CN107286025 A discloses a method for purifying o-phenylenediamine, wherein the crude o-phenylenediamine is distilled in a tower filled with 7A molecular sieve and silica adsorbent, and then a protective agent is added for flake formation. This process still does not handle a small amount of easily discolored substances, and the addition of a protective agent introduces additional impurities, which may affect downstream products.

[0006] Patent application CN109879762 A discloses a method for purifying o-phenylenediamine, wherein o-phenylenediamine is recrystallized in an aqueous solution, and the crystallized material is filtered, dehydrated, and flaked to obtain a finished o-phenylenediamine product. The crystallization process has high energy consumption and low production capacity, and trace discoloration substances dissolved in water cannot be completely removed by the crystallization process.

[0007] Therefore, in order to further remove the trace o-aminophenol, o-chloroaniline, phenol and other easily discolored substances contained in the o-phenylenediamine product to meet the high-end market demand, it is very necessary to provide a new method for refining and purifying o-phenylenediamine to prepare anti-discoloration o-phenylenediamine. Summary of the invention

[0008] In order to overcome the deficiencies of the prior art, the present invention aims to provide a method for preparing anti-discoloration o-phenylenediamine and the obtained product.

[0009] The technical solution adopted by the present invention is:

[0010] A method for preparing anti-discoloration o-phenylenediamine, the preparation method comprising the following steps:

[0011] (1) adding an o-phenylenediamine raw material and an alkali solution into a reaction kettle, and after nitrogen substitution, performing an alkaline hydrolysis reaction to react the o-chloroaniline, o-aminophenol, phenol and other substances in the o-phenylenediamine raw material that are easy to change color to generate corresponding phenol salts;

[0012] (2) dehydrating and evaporating the alkaline solution after the reaction to obtain the anti-discoloration o-phenylenediamine finished product.

[0013] The present invention is further configured that the content of o-phenylenediamine in the o-phenylenediamine raw material in step (1) is greater than 99.5%, and is conventional o-phenylenediamine or discolored o-phenylenediamine, that is, the o-phenylenediamine raw material is a discolored or undiscolored crude o-phenylenediamine.

[0014] The alkali solution in step (1) is an aqueous solution of alkali, wherein the alkali is NaOH or KOH, and the alkali solution is preferably a dilute alkali solution, and the concentration of the alkali solution is 0.5%-5%, preferably 1-2%.

[0015] The amount of the alkali solution in step (1) is 0.5-3 times the mass of the o-phenylenediamine raw material, preferably 1-1.5 times; the content of alkali in the alkali solution is 0.5%-5% of the mass of the o-phenylenediamine raw material, preferably 1%-2%.

[0016] Before the alkaline hydrolysis reaction in step (1), the reactor needs to be replaced with nitrogen. The alkaline hydrolysis temperature is 80-150° C., preferably 100-130° C., more preferably 100-120° C.; the alkaline hydrolysis pressure is 0.2-2 MPa, preferably 0.5-1.5 MPa, more preferably 0.5-1 MPa.

[0017] In step (1), the alkaline hydrolysis time is 0.5-5h, preferably 1-3h, more preferably 1-2h.

[0018] In step (2), water in the alkali solution and water generated by the reaction are removed by dehydration to obtain o-phenylenediamine containing a small amount of alkaline hydrolysis product, i.e., phenolate; the dehydration is negative pressure dehydration with a pressure of 5-10 KPa, the end point of the dehydration is no water discharge, and the kettle temperature is about 130-150°C.

[0019] In step (2), the evaporation is preferably thin film evaporation, which effectively separates the light component o-phenylenediamine and the heavy component phenolate. The vacuum degree of thin film evaporation is 0.1-1Kpa, preferably 0.3-0.5Kpa, and the scraper speed of the thin film evaporator used in the thin film evaporation is 200-300 rpm; the feed temperature of the thin film evaporation is 100-110°C, the heating temperature is 150-180°C, and the condensation temperature is 100-105°C.

[0020] Another aspect of the present invention is to provide an anti-discoloration o-phenylenediamine, which is prepared by the above-mentioned preparation method, wherein the content of o-chloroaniline is not higher than 0.011%, the content of o-aminophenol is not higher than 0.005%, and the content of phenol is not higher than 0.003%; preferably, the content of o-chloroaniline is not higher than 0.005%, the content of o-aminophenol is not higher than 0.001%, and the content of phenol is not higher than 0.003%.

[0021] Compared with the existing o-phenylenediamine purification process, this process has the following beneficial effects:

[0022] (1) Compared with the existing physical purification process of crystallization or distillation, this scheme adopts an alkaline hydrolysis process to remove the easily discolored components through chemical reaction to prepare anti-discoloration o-phenylenediamine; after the alkaline hydrolysis process, o-phenylenediamine and the phenol salt generated by the reaction can be separated by thin film evaporation to remove the heavy component phenol salt. The thin film evaporation process has high efficiency and the product is heated for a short time, which is suitable for the preparation of anti-discoloration o-phenylenediamine.

[0023] (2) This process can be used not only to treat conventional o-phenylenediamine products, but also to treat discolored products to obtain anti-discoloration o-phenylenediamine.

[0024] (3) The anti-discoloration o-phenylenediamine prepared by this process has high purity, and no antioxidants or other additives are added during the process, which does not affect downstream use.

[0025] (4) This process only includes three steps: alkaline hydrolysis, dehydration, and thin film evaporation, without a distillation step. The process is short, the energy consumption is low, the effect is significant, and the finished o-phenylenediamine has good anti-discoloration performance and does not change color after long-term storage, which meets the needs of the high-end market and has high industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a process flow chart for the preparation of anti-discoloration o-phenylenediamine. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing anti-discoloration o-phenylenediamine, see Figure 1 , the preparation method comprises the following steps:

[0028] (1) A certain amount of conventional o-phenylenediamine / color-changing o-phenylenediamine is added into a reactor, and a certain amount of alkali solution is added. After nitrogen substitution, an alkaline hydrolysis reaction is carried out at a certain temperature and pressure to obtain an alkaline hydrolysis solution, so that the color-changing substance reacts completely.

[0029] (2) Dehydrating the alkaline hydrolysis liquid under negative pressure until no more material is discharged, and then sending the residue of the dehydration kettle to a thin film evaporator to remove the heavy components obtained by the alkaline hydrolysis reaction to obtain the anti-discoloration o-phenylenediamine finished product.

[0030] Taking NaOH as an example, the reaction equation of alkaline hydrolysis is as follows:

[0031]

[0032]

[0033] The content of conventional o-phenylenediamine / color-changing o-phenylenediamine (gas spectrum normalized content) is greater than 99.5%, and the main content meets the first-class requirements of o-phenylenediamine in HG / T3310-2017, wherein the content of single components such as o-chloroaniline, o-aminophenol, phenol, and p-phenylenediamine is less than 0.5%. The composition of color-changing o-phenylenediamine is basically unchanged compared to conventional o-phenylenediamine, and the color change is caused by trace color-changing impurities. The following examples mainly take conventional o-phenylenediamine as an example.

[0034] In the following Examples 1-9, a conventional o-phenylenediamine is used as a raw material, wherein the o-phenylenediamine content is 99.6%, the o-chloroaniline content is 0.15%, the phenol content is 0.11%, the o-aminophenol content is 0.06%, and the p-phenylenediamine content is 0.08%. The conventional o-phenylenediamine changes color when stored at room temperature for 20 days.

[0035] In Example 10, a color-changed o-phenylenediamine is used as a raw material, wherein the o-phenylenediamine content is 99.51%, the o-chloroaniline content is 0.19%, the phenol content is 0.14%, the o-aminophenol content is 0.10%, and the p-phenylenediamine content is 0.06%.

[0036] In the following embodiments, gas chromatography was used to detect and analyze the product components. The specific detection conditions were as follows: 1 g of sample was diluted with 10 ml of methanol, and the injection analysis was performed under the following chromatographic conditions: vaporizer temperature: 300°C; detector temperature: 250°C; column temperature: initial temperature 120°C (maintained for 2 min), 20°C / min to 240°C (maintained for 17 min); carrier gas (N 2 ): 10.152psi; H 2 :30mL / min;Air:300mL / min;Tail blowing(N 2 ): 20mL / min; split ratio: 5:1; injection volume: 1.0μL.

[0037] In the following examples, the product yield is calculated by the following formula:

[0038] Product yield = weight of anti-discoloration o-phenylenediamine / weight of feed o-phenylenediamine*100%.

[0039] Example 1

[0040] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 1 wt% NaOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 120° C. and alkaline hydrolysis was performed at a pressure of 1 MPa for 2 hours to obtain 199.8 kg of alkaline hydrolysis liquid.

[0041] Step (2) Dehydrating the alkaline solution of the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrating until no material is discharged, and the kettle temperature is 135° C. Among them, 98.9 kg of water is discharged, and 100.8 kg of dehydration kettle residue is left. The dehydration kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator, with a vacuum degree of 0.5 KPa, a scraper speed of 300 rpm, a heater temperature of 160° C., and a condenser temperature of 105° C. A total of 99.3 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 1.4 kg.

[0042] The content of the anti-discoloration o-phenylenediamine finished product is 99.95%, of which o-chloroaniline, phenol, o-aminophenol, and p-phenylenediamine are not detected. The yield of anti-discoloration o-phenylenediamine is 99.3%, and the product does not change color after being stored at room temperature for 180 days.

[0043] Example 2

[0044] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 50 kg of 1 wt% NaOH aqueous solution was added. After nitrogen substitution, the temperature was raised to 120° C. and alkaline hydrolysis was performed at a pressure of 1 MPa for 2 hours to obtain 149.6 kg of alkaline hydrolysis liquid.

[0045] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 133° C. 49.3 kg of water is discharged, and 100.2 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.5 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 160° C., and the condenser temperature is 105° C. A total of 99.1 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 1.0 kg.

[0046] The content of the anti-discoloration o-phenylenediamine finished product is 99.932%, including 0.005% o-chloroaniline, 0.001% phenol, 0.001% o-aminophenol, and 0.061% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 99.1%, and the product does not change color after being stored at room temperature for 120 days.

[0047] Example 3

[0048] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 200 kg of 1 wt% NaOH aqueous solution was added. After nitrogen substitution, the temperature was raised to 120° C. and alkaline hydrolysis was performed at a pressure of 1 MPa for 2 hours to obtain 298.8 kg of alkaline hydrolysis liquid.

[0049] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 138° C. 196.6 kg of water is discharged, and 102.1 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.5 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 160° C., and the condenser temperature is 105° C. A total of 98.3 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 3.7 kg.

[0050] The content of the anti-discoloration o-phenylenediamine finished product is 99.951%, of which o-chloroaniline is 0.001%, phenol is not detected, o-aminophenol is not detected, and p-phenylenediamine is 0.048%. The yield of anti-discoloration o-phenylenediamine is 98.3%, and the product does not change color after being stored at room temperature for 180 days.

[0051] Example 4

[0052] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 300 kg of 1 wt% NaOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 120° C. and alkaline hydrolysis was performed at a pressure of 1 MPa for 2 hours to obtain 398.6 kg of alkaline hydrolysis liquid.

[0053] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 140° C. 295.6 kg of water is discharged, and 102.9 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.5 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 160° C., and the condenser temperature is 105° C. A total of 97.6 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 5.2 kg.

[0054] The content of the anti-discoloration o-phenylenediamine finished product is 99.943%, of which o-chloroaniline is 0.001%, phenol is not detected, o-aminophenol is not detected, and p-phenylenediamine is 0.056%. The yield of anti-discoloration o-phenylenediamine is 97.6%, and the product does not change color after being stored at room temperature for 180 days.

[0055] Example 5

[0056] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 1 wt% KOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 120° C. and alkaline hydrolysis was performed at a pressure of 1 MPa for 2 hours to obtain 199.7 kg of alkaline hydrolysis liquid.

[0057] Step (2) Dehydrate the alkaline hydrolyzate in the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 135° C. 99.0 kg of water is discharged, and 100.7 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.5 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 160° C., and the condenser temperature is 105° C. A total of 99.2 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 1.5 kg.

[0058] The content of the anti-discoloration o-phenylenediamine finished product is 99.946%, of which o-chloroaniline is 0.001%, phenol is not detected, o-aminophenol is not detected, and p-phenylenediamine is 0.053%. The yield of anti-discoloration o-phenylenediamine is 99.2%, and the product does not change color after being stored at room temperature for 180 days.

[0059] Example 6

[0060] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 150 kg of 0.5 wt% NaOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 150° C. and alkaline hydrolysis was performed at a pressure of 2 MPa for 1 hour to obtain 249.5 kg of alkaline hydrolysis liquid.

[0061] Step (2) Dehydrating the alkaline solution of the previous step under negative pressure, with a vacuum degree of 10 KPa, dehydrating until no material is discharged, and the kettle temperature is 148° C. 148.6 kg of water is discharged, and 100.8 kg of the dehydration kettle residue is left. The dehydration kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 1 KPa, the scraper speed of the thin film evaporator is 200 rpm, the heater temperature is 180° C., and the condenser temperature is 100° C. A total of 97.5 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 3.2 kg.

[0062] The content of the anti-discoloration o-phenylenediamine finished product is 99.919%, including 0.011% o-chloroaniline, 0.003% phenol, 0.005% o-aminophenol and 0.062% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 97.5%, and the product does not change color after being stored at room temperature for 48 days.

[0063] Example 7

[0064] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 5 wt% NaOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 80° C. and alkaline hydrolysis was performed at a pressure of 0.2 MPa for 5 hours to obtain 199.6 kg of alkaline hydrolysis liquid.

[0065] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 7 KPa, dehydrate until no material is discharged, and the kettle temperature is 143° C. 94.4 kg of water is discharged, and 105.1 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.3 KPa, the scraper speed of the thin film evaporator is 250 rpm, the heater temperature is 150° C., and the condenser temperature is 100° C. A total of 97.9 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 7.1 kg.

[0066] The content of the anti-discoloration o-phenylenediamine finished product is 99.922%, including 0.006% o-chloroaniline, 0.001% phenol, 0.003% o-aminophenol and 0.068% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 97.9%, and the product does not change color after being stored at room temperature for 76 days.

[0067] Example 8

[0068] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 3 wt% NaOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 100° C. and alkaline hydrolysis was performed at a pressure of 0.5 MPa for 0.5 h to obtain 199.7 kg of alkaline hydrolysis liquid.

[0069] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 8 KPa, dehydrate until no material is discharged, and the kettle temperature is 145° C. 96.8 kg of water is discharged, and 102.8 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.8 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 170° C., and the condenser temperature is 105° C. A total of 97.2 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 5.5 kg.

[0070] The content of the anti-discoloration o-phenylenediamine finished product is 99.927%, including 0.004% o-chloroaniline, 0.003% phenol, 0.001% o-aminophenol and 0.065% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 97.2%, and the product does not change color after being stored at room temperature for 97 days.

[0071] Example 9

[0072] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 2 wt% NaOH aqueous solution was added. After nitrogen substitution, the temperature was raised to 130° C. and alkaline hydrolysis was performed at a pressure of 1.5 MPa for 3 hours to obtain 199.7 kg of alkaline hydrolysis liquid.

[0073] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 6 KPa, dehydrate until no material is discharged, and the kettle temperature is 141° C. 97.5 kg of water is discharged, and 102.1 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.1 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 155° C., and the condenser temperature is 105° C. A total of 98.1 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 3.9 kg.

[0074] The content of the anti-discoloration o-phenylenediamine finished product is 99.936%, including 0.003% o-chloroaniline, 0.002% phenol, 0.001% o-aminophenol and 0.058% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 98.1%, and the product does not change color after being stored at room temperature for 148 days.

[0075] Example 10

[0076] Step (1) 100 kg of color-changing o-phenylenediamine is put into a reaction kettle, and 100 kg of 1 wt% NaOH aqueous solution is added. After nitrogen substitution, the temperature is raised to 120° C. and the pressure is 1 MPa for alkaline hydrolysis. The alkaline hydrolysis time is 2 hours, and a total of 199.8 kg of alkaline hydrolysis liquid is obtained.

[0077] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 135° C. 98.8 kg of water is discharged, and 100.9 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.5 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 160° C., and the condenser temperature is 105° C. A total of 99.1 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 1.8 kg.

[0078] The content of the anti-discoloration o-phenylenediamine finished product is 99.951%, of which o-chloroaniline is 0.001%, phenol is not detected, o-aminophenol is not detected, and p-phenylenediamine is 0.048%. The yield of anti-discoloration o-phenylenediamine is 99.1%, and the product does not change color after being stored at room temperature for 180 days.

[0079] Comparative Example 1

[0080] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 1 wt% NaOH aqueous solution was added. After nitrogen substitution, the temperature was raised to 100° C. and alkaline hydrolysis was performed under normal pressure for 2 hours to obtain 199.9 kg of alkaline hydrolysis liquid.

[0081] Step (2) Dehydrate the alkaline solution of the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 135° C. 98.7 kg of water is discharged, and 101.1 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a thin film evaporator. The vacuum degree is 0.5 KPa, the scraper speed of the thin film evaporator is 300 rpm, the heater temperature is 160° C., and the condenser temperature is 105° C. A total of 98.5 kg of anti-discoloration o-phenylenediamine is obtained, and the recombinant fraction is 2.6 kg.

[0082] The content of the anti-discoloration o-phenylenediamine finished product is 99.809%, including 0.08% o-chloroaniline, 0.03% phenol, 0.01% o-aminophenol and 0.071% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 98.5%, and the product does not change color when stored at room temperature for 32 days. When the alkaline hydrolysis reaction is carried out under normal pressure, the content of the refined o-phenylenediamine finished product and the anti-discoloration performance do not change significantly.

[0083] Comparative Example 2

[0084] Step (1) 100 kg of conventional o-phenylenediamine was put into a reaction kettle, and 100 kg of 1 wt% NaOH aqueous solution was added. After nitrogen replacement, the temperature was raised to 120° C. and alkaline hydrolysis was performed at a pressure of 1 MPa for 2 hours to obtain 199.8 kg of alkaline hydrolysis liquid.

[0085] Step (2) Dehydrate the alkaline hydrolyzate in the previous step under negative pressure, with a vacuum degree of 5 KPa, dehydrate until no material is discharged, and the kettle temperature is 135° C. 98.9 kg of water is discharged, and 100.8 kg of the dehydrated kettle residue is left. The dehydrated kettle residue is controlled at 100-110° C. and pumped into a distillation tower to separate the heavy components, under the conditions of a vacuum of 0.5 KPa, 20 theoretical plates of the distillation tower, and a distillation reflux ratio of 3:1. A total of 95.1 kg of anti-discoloration o-phenylenediamine is obtained, and the heavy components are 5.6 kg.

[0086] The content of the anti-discoloration o-phenylenediamine finished product is 99.921%, of which o-chloroaniline is 0.008%, phenol is 0.003%, o-aminophenol is 0.002%, and p-phenylenediamine is 0.066%. The yield of the anti-discoloration o-phenylenediamine is 95.1%, and the product does not change color when stored at room temperature for 85 days. The dehydration kettle residue is separated by conventional distillation means. Compared with Example 1, the separation effect is poorer than that of thin film evaporation, the heavy components are more, the yield is lower, and the anti-discoloration time is significantly reduced.

Claims

1. A method for preparing anti-discoloration o-phenylenediamine, characterized in that: The following steps are involved: (1) adding o-phenylenediamine raw material into a reactor and adding alkali solution, and then performing alkaline hydrolysis reaction after nitrogen substitution; (2) dehydrating and evaporating the alkaline hydrolysis solution to obtain the anti-discoloration o-phenylenediamine finished product.

2. The preparation method according to claim 1, characterized in that: The o-phenylenediamine raw material in step (1) is selected from uncolored or colored crude o-phenylenediamine, wherein the content of o-phenylenediamine is greater than 99.5%.

3. The preparation method according to claim 1, characterized in that: The alkali solution in step (1) is an aqueous solution of NaOH or KOH, and the concentration of the alkali solution is 0.5%-5%, preferably 1-2%.

4. The preparation method according to claim 1, characterized in that: The amount of the alkali solution in step (1) is 0.5-3 times the mass of the o-phenylenediamine raw material, preferably 1-1.5 times; the content of alkali in the alkali solution is 0.5%-5% of the mass of the o-phenylenediamine raw material, preferably 1%-2%.

5. The preparation method according to claim 1, characterized in that: The alkaline hydrolysis temperature in step (1) is 80-150° C., preferably 100-130° C., more preferably 100-120° C.; the alkaline hydrolysis pressure is 0.2-2 MPa, preferably 0.5-1.5 MPa, more preferably 0.5-1 MPa.

6. The preparation method according to claim 1, characterized in that: In the step (1), the alkaline hydrolysis time is 0.5-5 h, preferably 1-3 h, and more preferably 1-2 h.

7. The preparation method according to claim 1, characterized in that: In the step (2), the dehydration is negative pressure dehydration with a pressure of 5-10 KPa, and the end point of dehydration is no water discharge.

8. The preparation method according to claim 1, characterized in that: In the step (2), the evaporation is thin film evaporation.

9. The preparation method according to claim 8, characterized in that: The vacuum degree of the thin film evaporation is 0.1-1Kpa, preferably 0.3-0.5Kpa; the feed temperature of the thin film evaporation is 100-110°C, the heating temperature is 150-180°C, and the condensation temperature is 100-105°C; the scraper speed used in the thin film evaporation is 200-300 rpm.

10. An anti-discoloration o-phenylenediamine, characterized in that: The method is prepared by any one of the preparation methods described in claims 1 to 9, wherein the content of o-chloroaniline is not higher than 0.011%, the content of o-aminophenol is not higher than 0.005%, and the content of phenol is not higher than 0.003%; preferably, the content of o-chloroaniline is not higher than 0.005%, the content of o-aminophenol is not higher than 0.001%, and the content of phenol is not higher than 0.003%.

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