Wastewater treatment of 4-aminophenol_Kain Industrial Additive

Background and overview^[1][2]

4-Aminophenol, also known as “p-hydroxyaniline”, obtains rhombic flake crystals from water and turns purple in the air. 4-Aminophenol (PAP) is a widely used organic synthesis intermediate. Body, widely used in dyes, medicine, rubber and other fields. In the pharmaceutical industry, 4-aminophenol is an intermediate for the synthesis of paracetamol, paramethacin, acetaminophen, vitamin B1, compound agent nicotinamide, etc.; in the rubber industry, 4-aminophenol is mainly used in antioxidants 4010MA, 4020, The synthesis of 4030, etc., these products are supporting antioxidants for radial tire products that are currently very promising.

Preparation^[2]

At present, the production of 4-aminophenol is divided into p-nitrophenol method and nitrobenzene method according to the raw material route. The p-nitrophenol reduction method is the earliest traditional production method used in the production of 4-aminophenol. This method uses p-nitrochlorobenzene as raw material, and obtains p-nitrophenol through hydrolysis and acidification. The p-nitrophenol is then reduced 4-Aminophenol is obtained. Using cheap nitrobenzene as raw material to synthesize 4-aminophenol has obvious raw material advantages compared to the p-nitrophenol method. According to different reduction methods, it is divided into two processes: nitrobenzene catalytic hydrogenation method and nitrobenzene electrolytic reduction method. The nitrobenzene catalytic hydrogenation reduction method uses precious metals as hydrogenation catalysts to generate 4-aminophenol through direct hydrogenation in dilute sulfuric acid medium.

This method is characterized by short process flow, low energy consumption, high yield of 4-aminophenol, and good product quality. It is the most widely used synthesis method in the production of 4-aminophenol. Industrial catalytic hydrogenation of nitrobenzene to synthesize p-aminophenol usually uses precious metals such as platinum, rhodium, and palladium supported on activated carbon as catalysts, and the reaction is carried out in a sulfuric acid medium with a concentration of 10% to 20%. At present, most of the research on catalysts for this synthesis process in the literature focuses on the effects of different metal active components, different carriers, metal loadings, addition of additives, etc. on the reaction performance of the synthesis of 4-aminophenol.

US patent US3715397 believes that Pt has the best catalytic effect among precious metal catalysts. Using Pt/C as the catalyst, the yield of 4-aminophenol can reach more than 80% under appropriate conditions. At present, the main problem of this process in industrial production is the difficulty in separating the catalyst and the product. The catalyst used in the traditional process is Pt/C, and the carrier used is powdered activated carbon. The catalyst not only has a small particle size, but also has a small specific gravity. It is extremely difficult to separate it from the reaction mixture, resulting in serious catalyst losses and high production costs.

Chinese patent CN1562467 discloses a method for synthesizing 4-aminophenol using Pt/SiO₂ as a catalyst. The separation and recovery rate of the catalyst after the reaction has been improved, but the reaction process still cannot be completely avoided. Catalyst loss problems due to carrier pulverization and filtration operations.

In view of the problems of filtration, separation and loss of supported catalysts used in the current industrial production of nitrobenzene to synthesize 4-aminophenol, CN201410525627.9 provides a simple preparation method for immobilizing active components on the surface of reactor components. The active reaction component is a method for hydrogenating nitrobenzene to synthesize 4-aminophenol using the active reaction component. Since the catalytic reaction is carried out directly on the surface of the reactor component, there is no need to add a catalyst during the reaction. There is no separation problem of the catalyst after the reaction. The equipment and production process are simple, and the loss of the catalyst is effectively avoided.

In the first step, put 1.0g of Pt/C catalyst with a Pt loading of 0.1% after roasting at 100°C and 100g of solvent water into a 200ml kettle reactor with a glass wall material. There is a stirring paddle and a thermowell made of zirconium. The ratio of the surface area of the metal component in contact with the reaction liquid to the volume of the reaction liquid is 0.1cm²/1cm³;

In the second step, in the above reactor, replace the air with N₂ for 8 to 12 minutes, then introduce H₂ at a temperature of 80°C until H ₂The partial pressure is 0.1MPa, and the processing time is 1 hour;

The third step. After the second step of treatment, lower the reactor to room temperature and filter the catalyst. The filtered catalyst can be used for related catalytic reactions after drying. The filtrate can be reused as a treatment liquid for the next treatment process. ;

The fourth step is to pour the filtrate filtered in the third step back into the reactor as the treatment liquid, and re-add the same supported catalyst according to the amount in the first step;

The fifth step is to repeat the above-mentioned second to fourth steps 4 times. After completing the third step of the fourth time, a reactor with active reaction components is obtained.

The sixth step, add 100ml water, 10ml concentrated sulfuric acid (mass concentration is 98%, the following examples are all at this concentration), 0.01g cetyltrimethyl Ammonium bromide and 2 ml nitrobenzene, the ratio of the surface area of the active reaction component in contact with the reaction solution to the volume of the reaction solution is 0.09cm²/1cm³, with N₂ After replacing the air for 8 to 12 minutes, raise the temperature to 200°C, then introduce H₂ until the hydrogen partial pressure is 0.1MPa, and react for 2 hours to convert nitrobenzene into 4-Aminophenol, nitrobenzene conversion rate is 95.2%, 4-aminophenol yield is 75.2%;

After the seventh and sixth steps are completed, the reaction liquid is pumped into the intermediate tank for product separation, and the reactor is prepared for the next batch of reaction processes.

The beneficial effects of the present invention are:

(1) The present invention provides a process for hydrogenating nitrobenzene to synthesize 4-aminophenol using active reaction components. Compared with the current industrial synthesis process using Pt/C catalyst, the hydrogenation reaction of nitrobenzene is It is carried out directly on the surface of the active component without the influence of internal diffusion. The reaction process does not require the addition of an external catalyst. There is no separation problem between the reactants and the catalyst after the reaction. The equipment and process are simple.

Wastewater treatment^[3]

CN201710350051.0 discloses a resource treatment method for 4-aminophenol production wastewater, which includes the following steps:

(1) Pretreatment: Adjust the 4-aminophenol production wastewater to neutral or alkaline, add coagulant for coagulation, and filter to obtain filtrate I and filter residue;

(2) Primary recovery of p-nitrophenol: Wash the filter residue with hot water, adjust the washing water to acidity and cool it, filter to obtain filtrate II and p-nitrophenol crystals, recover p-nitrophenol, and circulate filtrate II Used for washing filter residue;

(3) Secondary recovery of p-nitrophenol: Adjust the pH of filtrate I to 0.5-4, and use resin adsorption to recover p-nitrophenol;

(4) Post-processing: Post-process the resin adsorption water to recover inorganic salts. The treatment process of the present invention takes “neutralization and flocculation, primary recovery of p-nitrophenol – secondary recovery of p-nitrophenol – post-treatment” as the main line, realizing resource recovery and treatment of waste water and achieving “zero discharge”, which is remarkable Reduce secondary pollution.