In your analysis, Reppe process as illustrated in FIGURE Q$1$ is studied. The raw materials needed for Reppe process are formaldehyde $(C{H}_{2}O),$ acetylene $(C_2{H}_2)$ and hydrogen $(H_2).$ Formaldehyde and acetylene are fed into two batch reactors which operate at $5$ bar, $80C$ and are arranged in parallel. Formaldehyde is reacted with acetylene in the presence of copper, bismuth and silicon dioxide supporting catalyst to produce $1,4-$butynediol as an intermediate product with a conversion rate of $60\%.$ Aqueous sodium hydroxide and hydrochloric acid are used to maintain the $pH$ of the medium in the reactor within the range of $pH6$ to $8.$ The product from the batch reactors is sent to a tank and is stored for approximately $1-30h$ before feeding to a distillation column for further separation. After separation, the bottom product stream of the distillation column is rich in $1,4-$butynediol and is fed to a trickling and hydrogenation reactor for further reaction to produce $1,4-$butanediol as the main product with a conversion rate of $90\%.$ The operating condition of this reactor is $160C$ and $150$ bar. Currently, standard feedback controllers are employed for controlling the key variables in the distillation column. To convince the top$-$level management on the benefits of advanced control, it is imperative for your team to prove that enhanced control can work on this part.

You are required to perform the following:

a$.$ Identify the key control objectives and possible disturbances for the distillation column.

$[10$ marks$]$

b$.$ Design enhanced control strategies for energy efficiency and product purity of the distillation column. Your design must include the appropriate schematic diagram of the proposed control strategies, detailed justification on the selection of the proposed control strategies, and explanation on the effectiveness of the proposed strategy in improving energy efficiency and product purity. Cite all references.