23.3. Phenol from Chlorobenzene route

23.4 Reactions

There are three reactions to convert benzene to phenol using chlorination route

23.4.1 Chlorination

• Benzene + Cl₂ → monochloro benzene

• Operating temperature: 85°C

• Catalyst: Fe or FeCl₃ catalyst

23.4.2 Causticization

• Benzyl chloride + NaOH → sodium benzoate

• NaOH is in aqueous media

• Operating conditions: 425°C and 350 atms

• Exothermic reaction

23.4.3 Hydrolysis

• Sodium benzoate + HCl (aq) → Phenol + NaCl (aq)

• Operating conditions: Nothing specific

23.4.4 Process Technology (Figure 23.2)

Figure 23.2 Flow sheet of manufacture of phenol from chlorobenzene route

• Benzene is first dried. Dry benzene and FeCl₃ catalyst enters the chlorination reactor.

• After the solid-gas-liquid reaction, the products are further heated up to enter a fractionator.

• The fractionator separates benzene as a top product and monochloro benzene as the bottom product. The top product also consists of HCl off gas that is obtained as the vapour stream from the partial condenser.

• The benzene is further cooled and sent back to the reactor and also as a reflux to the fractionator.

• The bottom product monochloro benzene is mixed with 10% NaOH solution and diphenyl oxide to enter a high pressure pump followed with heat integrated heat exchanger that pre-heats the feed to higher temperature.

• The feed then enters the causticization reactor which has cooling water tubes to control the temperature.

• The product stream is cooled using heat integrated exchanger and then enters a neutralizer that is fed with the HCl obtained from the fractionator partial condenser.

• After neutralization, the product phenol is separated from the aqueous phase using gravity settling principle.

• The organic layer rich in phenol is sent to a vacuum column to separate the phenol from diphenyl oxide (bottom product). The bottom product is partially recycled to enter the cauticization reactor.