Design Project

$2024$

LL

Design Statement $1$

The Design

Design a process to produce $20,000$ tons per year of monochlorobenzene together with not less than $2,000$ tons per year of dichlorobenzene, by the direct chlorination of benzene.

The Process

Liquid benzene $($which must contain less than $30ppm$ by weight of water$)$ is fed into a reactor system consisting of two continuous stirred tanks operating in series at $2\mathrm{.}4$ bar. Gaseous chlorine is fed in parallel to both tanks. Ferric chloride acts as a catalyst, and is produced in situ by the reaction of hydrogen chloride on mild steel. Cooling is required to maintain the operating temperature at $328K.$ 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 the 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

i$.$ Chlorine: $293K,$ atmospheric pressure, $100\%$ purity.

ii$.$ Benzene: $293K,$ atmospheric pressure, $99\mathrm{.}95wt\%$ benzene, $0\mathrm{.}05wt\%$ water.

Product Specifications

i$.$ Monochlorobenzene: $99\mathrm{.}7wt\%.$

ii$.$ Dichlorobenzene: $99\mathrm{.}6wt\%.$

iii. Hydrogen chloride gas: less than $250$ ppm by weight benzene.

Utilities

i$.$ Stream: dry saturated at $8$ bar and at $28$ bar.

ii$.$ Cooling water: $293K.$

iii. Process water: $293K.$

iv$.$ Caustic soda solution: $5wt\%$NaOH,$293K.$

Aspects of the design work required

Process Design

a$.$ Present a materials balance for the process including an analysis of each reactor stage $($the kinetics of the chlorination reactions are given below$).$ Onstream time may be taken as $330$ days per year.

b$.$ Present energy balances for the first reactor and for the chlorobenzene column $($take the reflux ratio for this column as twice the minimum reflux ratio$).$

c$.$ Present a process flow diagram for the design. This should show the major items of equipment, pipelines and instrumentation with an indication of stream data presented in a flow sheet. Temperatures and pressures should also be indicated.

d$.$ Give a safety analysis.

Chemical Engineering Design

Present a sieve$-$plate column design for the chlorobenzene distillation.

Data

The Reactions: $1.C_6{H}_6+C{l}_2=C_6{H}_{5}Cl+HCl,2.C_6{H}_{5}Cl+C{l}_2=C_6{H}_{4}C{l}_2+HCl$