Free chlorine refers to HClO, ClO- and Cl2 during the chlorine disinfection process.
In contrast, combined chlorine refers to chloramine compounds (NH2Cl, NHCl2, NCl3)
There are various production methods for p-chlorophenol and ortho-chlorophenol (see below), but Neither can be produced directly from p-chlorotoluene or o-chlorotoluene as raw materials.
Production methods that can co-produce p-chlorophenol and o-chlorophenol include: phenol sulfuryl chloride method, phenol chlorination method, and phenol copper chloride method.
The most widely used industrial production method at present is the phenol chlorination method. Its biggest advantage is that it can use the same set of equipment to produce p-chlorophenol, o-chlorophenol, 2,4-dichlorophenol, 2,6- Dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol and other chlorinated phenol derivatives have been serialized to facilitate enterprises to adjust production according to market demand. The output ratio of p-chlorophenol and o-chlorophenol can be adjusted by adopting different process conditions (especially catalysts).
2.1 Production methods of p-chlorophenol
The production methods of p-chlorophenol that have been developed include: phenol sulfuryl chloride method, p-aminophenol method, p-chloroaniline method, The direct chlorination method of phenol and the phenol copper chloride method are introduced below respectively.
2.1.1 Phenol sulfuryl chloride method
P-chlorophenol is produced by reacting phenol and sulfuryl chloride in the presence of iron catalyst, and there is 25 to 30% of by-product o-chlorophenol. generate.
The specific process is as follows: After heating and melting the phenol, cool it to 40°C, slowly add sulfuryl chloride, it will take about 40 to 45 minutes to complete the addition, stir for 4 hours, raise the temperature to 43 to 47°C, and continue to keep it warm. 4 hours, after the reaction is completed, cool to room temperature, wash with water, 10% sodium carbonate solution, and water in sequence, collect the 110-11.5°C (20mm mercury) fraction by distillation under reduced pressure, and obtain p-chlorophenol, with 25-30% by-products. The product o-chlorophenol is generated. For every 1 ton of p-chlorophenol produced, approximately 1 ton of phenol and approximately 2 tons of sulfuryl chloride are consumed.
2.1.2 Para-aminophenol method
It is obtained by diazotization and replacement of para-aminophenol.
The specific process is as follows: add water, p-aminophenol and hydrochloric acid to the reaction kettle, stir and cool to below 10°C, add NaNO3 solution dropwise to the end of the reaction, the reaction temperature does not exceed 15°C. Add this diazo liquid to the cuprous chloride hydrochloric acid solution, slowly raise the temperature to 105~108°C and reflux for 1 hour, cool to room temperature and let stand, extract the oil layer, distill under reduced pressure, and collect 130~140°C (10~20mm mercury Column) fraction to obtain p-chlorophenol.
2.1.3 Para-chloroaniline method
It is obtained by diazotization and hydrolysis of para-chloroaniline.
The specific process is as follows: add water and p-chloroaniline to the reaction kettle, then add [wiki]sulfuric acid[/wiki] while stirring, then raise the temperature to 90°C and stir for half an hour, then lower to 25°C. Next, add NaNO2 solution dropwise to the end of the reaction, raise the temperature and reflux for 2 hours, cool and separate into layers, extract the oil layer, distill under reduced pressure, and collect the 130~140°C (10~20mm mercury) fraction to obtain p-chlorophenol.
2.1.4 Direct chlorination of phenol method
It is produced by chlorination of phenol by introducing chlorine gas and then distilling under reduced pressure.
The specific process is as follows: After heating and melting the phenol, the temperature is lowered to 45°C, and chlorine gas is introduced. According to the speed from slow to fast, and finally gradually slowing down, the chlorine flow is completed within 2.5 to 3 hours, and then the deacidification is blown off, distilled under reduced pressure, and the 85 to 132°C (15mm mercury column) fraction is collected to obtain p-chlorophenol. At the same time, o-chlorophenol and 2,4-dichlorophenol are produced as by-products. During the reaction process, since the para-position effect of the phenolic hydroxyl group is greater than the ortho-position effect, the probability of a chlorine atom replacing a [wiki]hydrogen[/wiki] atom in the para-position is high, and the resulting p-chlorophenol accounts for a larger proportion in the product. Large, respectively: p-chlorophenol ≥ 50%; o-chlorophenol about 30%; 2,4-dichlorophenol about 8%.
2.1.5 Phenol copper chloride method
Shaanxi Province [wiki] Petroleum [/wiki] [wiki] Chemical Industry [/wiki] Research and Design Institute Liu Jiang and Cai Yaozong focused on the traditional Due to the problems existing in the sulfuryl chloride method and the direct chlorination method of phenol, a new synthesis method, namely the phenol copper chloride method, was studied. Using this method, the average yield of para position reaches more than 70%, and the para-ortho ratio is more than 10:1; the purity of p-chlorophenol can reach more than 99.8%; copper chloride can be used repeatedly; the reaction conditions are easy to control, and the phenol utilization rate is high. It is easy to be industrialized and the cost is lower than the sulfuryl chloride method and the direct chlorination method.
2.2 Production methods of o-chlorophenol
The production methods of o-chlorophenol that have been developed include: sodium phenol chloride acid precipitation method, traditional phenol chlorination method, and phenol catalytic chlorine The chemical methods are introduced below.
2.2.1 Sodium phenolate chloride and acid precipitation method
It is prepared by chlorination and acid precipitation of sodium phenolate.
The specific process is as follows: Stir the mixture of sodium phenolate, water and ice, slowly add NaClO solution below 20°C, and control the temperature below 20°C. After chlorination is completed, leave it at room temperature overnight, add concentrated hydrochloric acid with stirring until the pH is 2, wash it once with water, and then wash it with 5% sodium carbonate solution until the pH value is 4 to 5. After cooling, separate the oil layer and carry out normal pressure Fractional distillation and then distillation under reduced pressure.
2.2.2 Traditional phenol chlorination method
It is obtained by chlorination and distillation of phenol by passing chlorine gas into the solvent benzene.
The specific process is as follows: add molten phenol to benzene under stirring, and introduce chlorine gas at 26±2℃ until the specific gravity of the chlorinated solution reaches 0.954 (23~25℃). After eliminating hydrogen chloride The benzene is steamed out and recovered, steamed to 125°C (160mm mercury), cooled to 60°C, fractionated under reduced pressure, and the 75°C (20~25mm mercury) fraction was collected to obtain o-chlorophenol. The chlorination reaction also produces p-chlorophenol and 2,4-dichlorophenol, which are collected as high boilers during fractionation under reduced pressure and can be used as by-products after separation. The yield of o-chlorophenol (more than 95%) is nearly 50%, and the yield of p-chlorophenol (more than 95%) is about 25.5%.
2.2.3 Phenol catalytic chlorination method
Using phenol as raw material, selective chlorination is carried out with a specific catalyst in the solvent tetrachlorethylene, and is obtained by distillation and purification. The reaction equation is as follows:
The specific process is as follows: add molten phenol to tetrachlorethylene under stirring, then add the catalyst, stir thoroughly for 20 minutes, while raising the temperature to 110±5°C, and pass in the Chlorine reaction. After the reaction is completed, the hydrogen chloride is removed, the temperature is raised to evaporate the solvent, and then o-chlorophenol is obtained by distillation under reduced pressure.
Feng Tianyang of the Institute of Chemical Engineering of Tianjin University successfully developed a process for the catalytic chlorination of phenol to synthesize o-chlorophenol. Qingdao Jiaonan Chemical Plant Research Institute also conducted trial production based on European patent EP0l96260, with a phenol conversion rate of 75%. Has been used in industrial production.
Residual chlorine can be divided into combined residual chlorine (referring to the compounds of chlorine and ammonia in water, including NH2Cl, NHCl2 and NHCl3. NHCl2 is more stable and has better sterilization effect), also called combined residual chlorine. ; Free residual chlorine (referring to OC1+, HOCl, Cl2, etc. in water, which has fast sterilization speed and strong bactericidal power, but disappears quickly), also called free residual chlorine; total residual chlorine is the combination of combined residual chlorine and free residual chlorine. and.