23.1 Introduction
Phenol can be manufactured from Benzene using several ways
23.2 Phenol using Hydro chlorination route
23.2.1 Reactions
First reaction
Second reaction
23.2.2 Process Technology (Figure 23.1)
Figure 23.1 Flow sheet of manufacture of phenol using hydro chlorination route
23.2.3 Technical questions
1. Discuss the merits of the process from waste minimization perspective?
In this flow sheet, the raw material itself is used as a solvent to extract the product. Also, one of the reactants (water) is used as another absorbent. The usage of raw materials and intermediates in the process as absorbents itself is very attractive from waste minimization perspective as waste water streams are not produced significantly. Also, the solvent used is benzene itself which reduces the complexity of using another solvent and subsequent safety related issues.
2. Comment upon the corrosion issues of the processes?
HCl is very corrosive and therefore, enough precaution shall be taken towards the plant and process design.
3. What impurities are removed in the unit B scrubber using water?
Benzyl chloride has limited solubility with water. Therefore, it is expected that benzyl chloride is dissolved to some extent in the unit B scrubber where benzyl chloride as an impurity in minor amounts can be removed from phenol.
4. Why do you think make up HCl is required?
Some HCl gets reacted to form poly benzyl chlorides. Some HCl gets lost as a vapour in various operations. Therefore, some make up HCl is definitely required in the process though, HCl is largely regenerated.
5. Compared to other Benzene based phenol production processes, what advantage this process has towards phenol production?
In this process, very little quantities of other raw materials are required. These are HCl. Air is inexpensive and is freely available. Therefore, the plant can be build easily as many other auxillary processes are not required provided benzene is available in large quantities in the vicinity. However, one basic drawback is that the fixed costs of units will be high in this case as HCl is involved.
23.3 Phenol from Chlorobenzene route
23.4 Reactions
23.4.1Chlorination
23.4.2Causticization
23.4.3 Hydrolysis
23.4.4 Process Technology (Figure 23.2)
Figure 23.2 Flow sheet of manufacture of phenol from chlorobenzene route
23.4.5 Technical questions
1. Why is diphenyl oxide added to the causticization reactor?
Ans: To suppress the formation of more diphenyl oxide at the causticization reactor.
2. How can you regenerate Cl2 for this process?
Ans: Brine when subjected to electrolysis will produce Cl2 and NaOH. Therefore, electrolytic process will be beneficial to produce Cl2 and us e it to the requirements as well as produce excess NaOH and sell it too. This way, the process becomes more commercially attractive.
3. Can the chlorinator and the fractionators be integrated into a single unit where the bottom section is a reactor and the top section is a fractionator?
Ans: Yes, this is possible, as after chlorination the products are in vapour state and they can enter the trays above the reactor section of a single column. The heavier product in this case is the monochlorobenzene from fractionation perspective and this is the product as well. Therefore, integrating both reactor and separator in a single unit can reduce the costs significantly.
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