Design a plant to produce 20,000 tonnes/year of mono-chlorobenzene together with not less than 2000 tonnes/year of dichlorobenzene, by the direct chlorination of benzene. Process description Liquid benzene (which must contain less than 30 ppm by weight of water) is fed into a reactor system consisting of two continuous stirred tanks operating in series at 2.4 bar. Gaseous chlorine is fed in parallel to both tanks. Ferric chloride acts as a catalyst and is produced in situ by the action of hydrogen chloride on mild steel. Cooling is required to maintain the operating temperature at 328 K. The hydrogen chloride gas leaving the reactors is first cooled to condense most of the organic impurities. It then passes to an activated carbon adsorber where the final traces of impurity are removed before it leaves the plant for use elsewhere. The crude liquid chlorobenzenes stream leaving the second reactor is washed with water and caustic soda solution to remove all dissolved hydrogen chloride. The product recovery system consists of two distillation columns in series. In the first column (the benzene column ) unreacted benzene is recovered as top product and recycled. In the second column (the chlorobenzene column ) the mono- and dichlorobenzenes are separated. The recovered benzene from the first column is mixed with the raw benzene feed and this combined stream is fed to a distillation column (the drying column ) where water is removed as overhead. The benzene stream from the bottom of the drying column is fed to the reaction system. Feed specifications (1) (ii) Product specifications (1) (III) Chlorine: 293 K, atmospheric pressure, 100 per cent purity. Benzene: 293 K, atmospheric pressure, 99.95 wt per cent benzene, 0.05 wt per cent water. Utilities (1) Monochlorobenzene: 99.7 wt per cent. Dichlorobenzene: 99.6 wt per cent. Hydrogen chloride gas: less than 250 ppm by weight benzene. Stream: dry saturated at 8 bar and at 28 bar. Cooling water: 293 K. (III) (iv) (v) Process water: 293 K. Caustic soda solution: 5 wt per cent NaOH, 293 K. Electricity: 440 V, 50 Hz, 3 phase. Scope of assignment 1. Describe the suggested process and justify the selection of the process route. 2. Perform a preliminary environmental impact assessment and determine the likely feasibility of the project based on these factors. Decide whether the project should proceed to the next design stage. List all assumptions upon which your decision is based 3. Present a bock flow diagram for your selected process, together with a preliminary material balance for the whole plant 4. Scrutinise the suggested flowsheet, and suggest modifications, with justification. You may modify the details of the flowsheet at any point during your project.