Phenol can be manufactured from Benzene using several ways

• • Benzene hydrochlorination to form Benzyl chloride followed by hydrolysis of benzyl chloride to form phenol.
• • Benzene chlorination to form benzyl chloride which is transformed to sodium benzoate and eventually to phenol using NaOH and HCl
• • Benzene sulfonate process: In this process, benzene is convered to benzene sulfonate using sulphuric acid and eventually through neutralization, fusion and acidification, the benzene sulfonate is gradually transformed to phenol.
• • In this lecture, we restrict our discussion to the manufacture of phenol from
  

• Benzene hydrochlorination route • Benzene from chlorobenzene route

23.2 Phenol using Hydro chlorination route

23.2.1 Reactions

First reaction

• Benzene + HCl + Oxygen → Benzyl chloride + Water

• Catalyst: FeCl₃ + CuCl₂

• Operating conditions: 240°C and atmospheric pressure

Second reaction

• Benzyl chloride + water → Phenol + HCl

• Catalyst: SiO₂

• Here, HCl is regenerated and will be recycled.

• Operating conditions: 350°C and atmospheric pressure

23.2.2 Process Technology (Figure 23.1)

Figure 23.1 Flow sheet of manufacture of phenol using hydro chlorination route

 

• In this process, Benzene is used to extract phenol from phenol +water mixture. This unit is termed as an extraction unit (liquid liquid extraction principle). Therefore, this unit takes up fresh benzene and phenol + water mixture and produces two streams namely water stream (bottom product) and benzene + phenol stream (top product). The water stream is fed to a scrubber unit (i.e., Unit B that will be described later).

• Then onwards, the organic mixture is fed to a distillation column that produces purer benzene as the top product. The bottom product is phenol with other impurities.

• The bottom phenol rich product is sent to the phenol fractionator to obtain waste product as top product and pure phenol as bottom product.

• The purer benzene then enters the hydrochlorination reactor in which a mixture of HCl and O₂ is fed at 220°C. Under these conditions, Benzene will be also in vapour state.

• Therefore, the reactor is a gas solid reactor.

• The conversions are pretty low and not more than 20% of the benzene is converted to benzyl chloride.

• Eventually, the products are sent to two fractionators that separate unreacted benzene, crude benzyl chloride and poly benzyl chlorides as various products. The unreacted benzene is sent back to the hydrochlorination reactor as a recycle stream.

• The crude benzyl chloride then enters an absorber unit A where phenol is used to purify the benzyl chloride from other organic compounds (such as benzene and polybenzyl chlorides).

• The purified benzyl chloride stream then enters the hydrolysis reactor in which water is passed along with benzyl chloride over the silica catalyst. The reactor itself is a furnace with catalyst loaded in the tubes and hot fuel gases are circulated in the shell to obtain the desired higher temperature.

• Under these conditions, both reactants are in vapour state (with the benzyl chloride boiling point of 179°C) and therefore, the reaction is also a gas solid reaction.

• After hydrolysis reaction, the product vapors are sent to a partial condenser that separates the HCl from the organic phase.

• The HCl is recycled to the hydrochlorination reactor.

• The phenol rich product stream is sent as a solvent for the scrubber (unit A) that purifies crude benzyl chloride to purer benzyl chloride. The bottom product from the scrubber (i.e., unit A) enters another scrubber (unit B) that receives water from the extractor.

• The unit B enables washing of the phenol to remove any water soluble impurities. The water from the unit B enters the hydrolysis reactor.