Process for the preparation of a non-discoloring phenylenediamine and the product obtained

Abstract

This invention provides a method for preparing anti-discoloration o-phenylenediamine and the resulting product. The preparation method includes the following steps: o-phenylenediamine raw material is added to a reaction vessel along with an alkaline solution. After nitrogen purging, an alkaline hydrolysis reaction is carried out, reacting easily discolorable substances such as o-chloroaniline, o-aminophenol, and phenol in the o-phenylenediamine raw material to generate corresponding phenolates. Then, the alkaline hydrolysate is dehydrated and subjected to thin-film evaporation to obtain the anti-discoloration o-phenylenediamine product. Compared to traditional o-phenylenediamine purification processes, this invention effectively reacts the easily discolorable components, and the generated phenolates are removed as heavy components via thin-film evaporation. Simultaneously, it can also treat the already discolored product to obtain anti-discoloration o-phenylenediamine. This invention has a short process flow, significant effects, and the finished o-phenylenediamine exhibits good anti-discoloration properties, does not discolor during long-term storage, and has high industrial application value.

Description

Technical Field

[0001] This invention relates to the field of chemical post-processing technology, specifically to a method for preparing anti-discoloration o-phenylenediamine and the resulting product. Background Technology

[0002] o-Phenylenediamine is mainly used in the preparation of pesticide fungicides, such as carbendazim and benomyl. It can also be used as an important component in the preparation of dyes, photosensitive materials, antifreeze agents, and surfactants. Some high-value-added products have stringent appearance requirements, but existing o-Phenylenediamine products contain trace amounts of o-aminophenol, o-chloroaniline, phenol, and other easily discolored substances, resulting in products that are prone to discoloration (non-discoloration time < 30 days), thus failing to meet the demands of the high-end market.

[0003] Currently, the main industrial preparation method for o-phenylenediamine is as follows: o-nitroaniline is hydrogenated to synthesize o-phenylenediamine, and the hydrogenation solution is then subjected to solvent removal, light component removal, and distillation to obtain the o-phenylenediamine product. However, because the o-phenylenediamine product contains trace amounts of light components such as o-aminophenol, o-chloroaniline, and phenol that cannot be completely removed through the light component removal process, the finished product is prone to discoloration.

[0004] Patent application CN101462966 A discloses a method for purifying high-quality o-phenylenediamine. The method involves purifying o-phenylenediamine through distillation and then flake-forming it under nitrogen protection to obtain high-quality o-phenylenediamine. This process is conventional, yielding a product with a purity of only 99.5%. The finished product still contains small amounts of easily discolored components such as o-chloroaniline, which are prone to discoloration during prolonged storage.

[0005] Patent application CN107286025 A discloses a method for purifying o-phenylenediamine. The crude o-phenylenediamine is distilled through a packed column containing 7A molecular sieves and silica adsorbent, followed by the addition of a protective agent to form flakes. This process still does not address the small amount of easily discolored substances, and the addition of the protective agent introduces additional impurities, which may affect downstream products.

[0006] Patent application CN109879762 A discloses a method for purifying o-phenylenediamine, which involves recrystallizing o-phenylenediamine in an aqueous solution, filtering the crystallized material, dehydrating it, and flake-forming it to obtain the finished o-phenylenediamine product. However, this crystallization process is energy-intensive and has low production capacity. Furthermore, trace amounts of easily discoloring substances dissolved in water cannot be completely removed through crystallization.

[0007] Therefore, in order to further remove trace amounts of o-aminophenol, o-chloroaniline, phenol and other easily discolored substances contained in o-phenylenediamine products and meet the demands of the high-end market, it is essential to provide a novel purification method for o-phenylenediamine to prepare anti-discoloration o-phenylenediamine. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing anti-color-changing o-phenylenediamine and the resulting product.

[0009] The technical solution adopted in this invention is as follows:

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

[0011] (1) Add o-phenylenediamine raw material into the reactor and add alkaline solution. After nitrogen replacement, carry out alkaline hydrolysis reaction to react the o-chloroaniline, o-aminophenol, phenol and other substances in the o-phenylenediamine raw material that are prone to discoloration to generate the corresponding phenol salts.

[0012] (2) The alkaline hydrolysate after the reaction is dehydrated and evaporated to obtain the anti-discoloration o-phenylenediamine product.

[0013] The present invention is further configured such that the o-phenylenediamine content in the o-phenylenediamine raw material in step (1) is >99.5%, and is conventional o-phenylenediamine or color-changing o-phenylenediamine, that is, the o-phenylenediamine raw material is crude o-phenylenediamine that has changed color or has not changed color.

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

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

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

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

[0018] In step (2), water is removed from the alkaline solution and the water generated in the reaction by dehydration to obtain o-phenylenediamine containing a small amount of alkaline hydrolysis product, namely phenol salt; the dehydration is performed under negative pressure at a pressure of 5-10 kPa, the dehydration endpoint is when no water is discharged, and the kettle temperature is about 130-150℃.

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

[0020] Another aspect of the present invention is to provide an anti-color-changing o-phenylenediamine, which is prepared by the above-described 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 existing o-phenylenediamine purification processes, this process has the following advantages:

[0022] (1) Compared with existing physical purification processes such as crystallization or distillation, this scheme adopts alkaline hydrolysis process to remove the easily discolored components through chemical reaction and prepare anti-discoloration o-phenylenediamine. After alkaline hydrolysis, o-phenylenediamine and the phenolic salt generated by the reaction can be separated by thin-film evaporation to remove the heavy component phenolic salt. Thin-film evaporation has high efficiency and short product heating time, which is suitable for preparing anti-discoloration o-phenylenediamine.

[0023] (2) This process can not only treat conventional o-phenylenediamine products, but also treat products that have changed color to obtain anti-discoloration o-phenylenediamine.

[0024] (3) The anti-discoloration o-phenylenediamine prepared by this process has high purity. 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. There is no distillation step. The process flow is short, energy consumption is low, and the effect is significant. The finished o-phenylenediamine has good anti-discoloration properties and does not change color after long-term storage, which meets the needs of the high-end market and has high industrial application value. Attached Figure Description

[0026] Figure 1 A flowchart of the process for preparing anti-color-changing o-phenylenediamine. Detailed Implementation

[0027] This invention provides a method for preparing anti-color-changing o-phenylenediamine, see [link to relevant documentation]. Figure 1 The preparation method includes the following steps:

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

[0029] (2) The alkaline hydrolysate is dehydrated under negative pressure until no material is discharged. Then the residue in the dehydration vessel is sent to a thin-film evaporator to remove the heavy components obtained from the alkaline hydrolysis reaction and obtain the anti-discoloration o-phenylenediamine product.

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

[0031]

[0032]

[0033] The content (gas spectral normalized content) of conventional o-phenylenediamine / color-changing o-phenylenediamine is >99.5%, and the main content meets the requirements for Grade I o-phenylenediamine in HG / T3310-2017, wherein the content of individual components such as o-chloroaniline, o-aminophenol, phenol, and p-phenylenediamine is <0.5%. The composition of color-changing o-phenylenediamine is basically unchanged compared to conventional o-phenylenediamine; the color change is caused by trace amounts of color-changing impurities. The following examples mainly use conventional o-phenylenediamine as an example.

[0034] In Examples 1-9 below, a conventional o-phenylenediamine was used as a raw material, wherein the o-phenylenediamine content was 99.6%, the o-chloroaniline content was 0.15%, the phenol content was 0.11%, the o-aminophenol content was 0.06%, and the p-phenylenediamine content was 0.08%. This conventional o-phenylenediamine changed color after being stored at room temperature for 20 days.

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

[0036] In the following examples, gas chromatography was used to detect and analyze the product components. Specific detection conditions were as follows: 1g sample was diluted with 10ml of methanol, and the following chromatographic conditions were used for injection analysis: vaporization chamber temperature: 300℃; detector temperature: 250℃; column temperature: initial temperature 120℃ (hold for 2 min), then increased to 240℃ at a rate of 20℃ / min (hold for 17 min); carrier gas (N2) 2 ) : 10.152 psi; H2: 30 mL / min; Air: 300 mL / min; Purging (N 2 ): 20 mL / min; split ratio: 5:1; injection volume: 1.0 μL.

[0037] In the following embodiments, the product yield is calculated using the following formula:

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

[0039] Example 1

[0040] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, along with 100 kg of 1 wt% NaOH aqueous solution. After nitrogen purging, the temperature was raised to 120 °C, and alkaline hydrolysis was carried out at a pressure of 1 MPa for 2 hours, yielding a total of 199.8 kg of hydrolysate.

[0041] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no more product was produced, with the kettle temperature at 135°C. 98.9 kg of water was discharged, leaving 100.8 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C, with a vacuum 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 was obtained, with 1.4 kg of recombinant components.

[0042] The anti-discoloration o-phenylenediamine product has a content of 99.95%, with o-chloroaniline, phenol, and o-aminophenol not detected, and p-phenylenediamine at 0.050%. The yield of anti-discoloration o-phenylenediamine is 99.3%, and the product does not change color after 180 days of storage at room temperature.

[0043] Example 2

[0044] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, and 50 kg of 1 wt% NaOH aqueous solution was added. After nitrogen purging, the temperature was raised to 120 °C and alkaline hydrolysis was carried out at a pressure of 1 MPa for 2 hours, yielding a total of 149.6 kg of alkaline hydrolysate.

[0045] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no more product was produced, with the kettle temperature at 133°C. 49.3 kg of water was discharged, leaving 100.2 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.5 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 160°C, and the condenser temperature was 105°C. A total of 99.1 kg of anti-discoloration o-phenylenediamine was obtained, with 1.0 kg of recombinant components.

[0046] The anti-discoloration o-phenylenediamine product has a content of 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 120 days of storage at room temperature.

[0047] Example 3

[0048] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, and 200 kg of 1 wt% NaOH aqueous solution was added. After nitrogen purging, the temperature was raised to 120 °C and alkaline hydrolysis was carried out at a pressure of 1 MPa for 2 hours, yielding a total of 298.8 kg of alkaline hydrolysate.

[0049] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no more product was produced, with a kettle temperature of 138°C. 196.6 kg of water was discharged, leaving 102.1 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.5 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 160°C, and the condenser temperature was 105°C. A total of 98.3 kg of anti-discoloration o-phenylenediamine was obtained, with a recombinant composition of 3.7 kg.

[0050] The anti-discoloration o-phenylenediamine product has a content of 99.951%, including 0.001% o-chloroaniline, no detectable phenol or o-aminophenol, and 0.048% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 98.3%, and the product does not change color after 180 days of storage at room temperature.

[0051] Example 4

[0052] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, and 300 kg of 1 wt% NaOH aqueous solution was added. After nitrogen purging, the temperature was raised to 120 °C and alkaline hydrolysis was carried out at a pressure of 1 MPa for 2 hours, yielding a total of 398.6 kg of alkaline hydrolysate.

[0053] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no more product was produced, with the kettle temperature at 140°C. 295.6 kg of water was discharged, leaving 102.9 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.5 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 160°C, and the condenser temperature was 105°C. A total of 97.6 kg of anti-discoloration o-phenylenediamine was obtained, with 5.2 kg of recombinant components.

[0054] The anti-discoloration o-phenylenediamine product has a content of 99.943%, including 0.001% o-chloroaniline, no detectable phenol or o-aminophenol, and 0.056% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 97.6%, and the product does not change color after 180 days of storage at room temperature.

[0055] Example 5

[0056] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, along with 100 kg of 1 wt% KOH aqueous solution. After nitrogen purging, the temperature was raised to 120 °C, and alkaline hydrolysis was carried out at a pressure of 1 MPa for 2 hours, yielding a total of 199.7 kg of hydrolysate.

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

[0058] The anti-discoloration o-phenylenediamine product has a content of 99.946%, including 0.001% o-chloroaniline, no detectable phenol or o-aminophenol, and 0.053% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 99.2%, and the product does not change color after 180 days of storage at room temperature.

[0059] Example 6

[0060] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, and 150 kg of 0.5 wt% NaOH aqueous solution was added. After nitrogen purging, the temperature was raised to 150 °C and alkaline hydrolysis was carried out at a pressure of 2 MPa for 1 hour, yielding a total of 249.5 kg of alkaline hydrolysate.

[0061] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 10 kPa until no more product was produced, with the kettle temperature at 148°C. 148.6 kg of water was discharged, leaving 100.8 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 1 kPa, the evaporator scraper speed was 200 rpm, the heater temperature was 180°C, and the condenser temperature was 100°C. A total of 97.5 kg of anti-discoloration o-phenylenediamine was obtained, with a recombinant composition of 3.2 kg.

[0062] The anti-discoloration o-phenylenediamine product has a content of 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 48 days of storage at room temperature.

[0063] Example 7

[0064] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, along with 100 kg of 5 wt% NaOH aqueous solution. After nitrogen purging, the temperature was raised to 80 °C, and alkaline hydrolysis was carried out at a pressure of 0.2 MPa for 5 hours, yielding a total of 199.6 kg of hydrolysate.

[0065] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 7 kPa until no more product was produced, with the kettle temperature at 143°C. 94.4 kg of water was discharged, leaving 105.1 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.3 kPa, the evaporator scraper speed was 250 rpm, the heater temperature was 150°C, and the condenser temperature was 100°C. A total of 97.9 kg of anti-discoloration o-phenylenediamine was obtained, with 7.1 kg of recombinant components.

[0066] The anti-discoloration o-phenylenediamine product has a content of 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 76 days of storage at room temperature.

[0067] Example 8

[0068] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, and 100 kg of 3 wt% NaOH aqueous solution was added. After nitrogen purging, the temperature was raised to 100 °C and alkaline hydrolysis was carried out at a pressure of 0.5 MPa for 0.5 h, yielding a total of 199.7 kg of alkaline hydrolysate.

[0069] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 8 kPa until no more product was produced, with the kettle temperature at 145°C. 96.8 kg of water was discharged, leaving 102.8 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.8 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 170°C, and the condenser temperature was 105°C. A total of 97.2 kg of anti-discoloration o-phenylenediamine was obtained, with 5.5 kg of recombinant components.

[0070] The anti-discoloration o-phenylenediamine product has a content of 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 97 days of storage at room temperature.

[0071] Example 9

[0072] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, along with 100 kg of 2 wt% NaOH aqueous solution. After nitrogen purging, the temperature was raised to 130 °C, and alkaline hydrolysis was carried out at a pressure of 1.5 MPa for 3 hours, yielding a total of 199.7 kg of hydrolysate.

[0073] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 6 kPa until no more product was produced, with a kettle temperature of 141°C. 97.5 kg of water was discharged, leaving 102.1 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.1 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 155°C, and the condenser temperature was 105°C. A total of 98.1 kg of anti-discoloration o-phenylenediamine was obtained, with a recombinant composition of 3.9 kg.

[0074] The anti-discoloration o-phenylenediamine product has a content of 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 148 days of storage at room temperature.

[0075] Example 10

[0076] Step (1) 100 kg of color-changing o-phenylenediamine was added to the reactor, and 100 kg of 1 wt% NaOH aqueous solution was added. After nitrogen purging, the temperature was raised to 120°C and the pressure was 1 MPa for alkaline hydrolysis for 2 hours, and a total of 199.8 kg of alkaline hydrolysate was obtained.

[0077] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no more product was produced, with the kettle temperature at 135°C. 98.8 kg of water was discharged, leaving 100.9 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.5 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 160°C, and the condenser temperature was 105°C. A total of 99.1 kg of anti-discoloration o-phenylenediamine was obtained, with a total recombinant fraction of 1.8 kg.

[0078] The anti-discoloration o-phenylenediamine product has a content of 99.951%, including 0.001% o-chloroaniline, no detectable phenol or o-aminophenol, and 0.048% p-phenylenediamine. The yield of anti-discoloration o-phenylenediamine is 99.1%, and the product does not change color after 180 days of storage at room temperature.

[0079] Comparative Example 1

[0080] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, along with 100 kg of 1 wt% NaOH aqueous solution. After nitrogen purging, the temperature was raised to 100 °C, and alkaline hydrolysis was carried out under normal pressure for 2 hours, yielding a total of 199.9 kg of hydrolysate.

[0081] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no more product was produced, with the kettle temperature at 135°C. 98.7 kg of water was discharged, leaving 101.1 kg of residue in the dehydrated kettle. The residue was then pumped into a thin-film evaporator at a temperature controlled at 100-110°C. The vacuum was 0.5 kPa, the evaporator scraper speed was 300 rpm, the heater temperature was 160°C, and the condenser temperature was 105°C. A total of 98.5 kg of anti-discoloration o-phenylenediamine was obtained, with a recombinant fraction of 2.6 kg.

[0082] The anti-discoloration o-phenylenediamine product has a content of 99.809%, including 0.08% o-chloroaniline, 0.03% phenol, 0.01% o-aminophenol, and 0.071% p-phenylenediamine. The yield of the anti-discoloration o-phenylenediamine is 98.5%, and the product does not change color after 32 days of storage at room temperature. When the alkaline hydrolysis reaction is carried out under normal pressure, the changes in the content of o-phenylenediamine and the anti-discoloration properties of the purified product are not significant.

[0083] Comparative Example 2

[0084] Step (1) 100 kg of conventional o-phenylenediamine was added to the reactor, along with 100 kg of 1 wt% NaOH aqueous solution. After nitrogen purging, the temperature was raised to 120 °C, and alkaline hydrolysis was carried out at a pressure of 1 MPa for 2 hours, yielding a total of 199.8 kg of hydrolysate.

[0085] Step (2) The alkaline hydrolysate from the previous step was dehydrated under negative pressure at a vacuum of 5 kPa until no product was discharged, with the kettle temperature at 135°C. 98.9 kg of water was discharged, leaving 100.8 kg of residue in the dehydration kettle. The residue was then pumped into a distillation column at 100-110°C to separate the heavy components. The conditions were a vacuum of 0.5 kPa, 20 theoretical plates in the distillation column, and a reflux ratio of 3:1. A total of 95.1 kg of anti-discoloration o-phenylenediamine and 5.6 kg of heavy components were obtained.

[0086] The anti-discoloration o-phenylenediamine product had a content of 99.921%, including 0.008% o-chloroaniline, 0.003% phenol, 0.002% o-aminophenol, and 0.066% p-phenylenediamine. The yield of the anti-discoloration o-phenylenediamine was 95.1%, and the product did not change color after 85 days of storage at room temperature. Conventional distillation was used to separate the residue from the dehydration vessel. Compared with Example 1, the separation effect was worse than that of thin-film evaporation, with more heavy components, a lower yield, and a significantly reduced anti-discoloration time.

Claims

1. A method for preparing anti-color-changing o-phenylenediamine, characterized in that, Includes the following steps: (1) Add o-phenylenediamine raw material and alkaline solution to the reactor, replace with nitrogen, and carry out alkaline hydrolysis reaction; (2) The alkaline hydrolysate is dehydrated and evaporated in a thin film to obtain the anti-discoloration o-phenylenediamine product; The alkaline hydrolysis temperature in step (1) is 80-150℃, the alkaline hydrolysis pressure is 0.2-2MPa, the alkaline solution concentration is 0.5%-5%, and the o-phenylenediamine raw material includes o-chloroaniline, o-aminophenol, and phenol. The vacuum degree of the thin film evaporation is 0.1-1 kPa; the feed temperature of the thin film evaporation is 100-110℃, the heating temperature is 150-180℃, and the condensation temperature is 100-105℃; the scraper rotation speed used in the thin film evaporation is 200-300 rpm.

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

3. The preparation method according to claim 1, characterized in that, The alkaline solution in step (1) is an aqueous solution of NaOH or KOH.

4. The preparation method according to claim 3, characterized in that, The concentration of the alkali solution in step (1) is 1%-2%.

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

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

7. The preparation method according to claim 1, characterized in that, The alkaline hydrolysis temperature in step (1) is 100-130℃; the alkaline hydrolysis pressure is 0.5-1.5 MPa.

8. The preparation method according to claim 7, characterized in that, The alkaline hydrolysis temperature in step (1) is 100-120℃; the alkaline hydrolysis pressure is 0.5-1 MPa.

9. The preparation method according to claim 1, characterized in that, In step (1), the alkaline hydrolysis time is 0.5-5h.

10. The preparation method according to claim 9, characterized in that, In step (1), the alkaline hydrolysis time is 1-3 hours.

11. The preparation method according to claim 10, characterized in that, In step (1), the alkaline hydrolysis time is 1-2 hours.

12. The preparation method according to claim 1, characterized in that, In step (2), the dehydration is negative pressure dehydration with a pressure of 5-10 kPa, and the dehydration endpoint is when no water is discharged.

13. The preparation method according to claim 1, characterized in that, The vacuum degree of the thin film evaporation is 0.3-0.5 kPa.

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