Propylene is converted to butyraldehyde and n-butanol in the following reaction sequence:

C3H6 + CO + H2 → C3H7CHO (butyraldehyde)

C3H7CHO + H2 → C4H9OH (n-butanol)

Liquid propylene, gaseous carbon monoxide and hydrogen, and a soluble cobalt catalyst are fed to a high-pressure catalytic reactor. The reactor effluent goes to a flash tank, where all of the solution constituents are vaporized except the catalyst, which is recycled to the reactor. The reaction products are separated from unconsumed reactants in a multiple-unit process, and the product stream, which contains both butyraldehyde and n-butanol, is subjected to additional hydrogenation with excess hydrogen, converting all of the butyraldehyde to butanol.

(a) Redraw and label the flowchart, including in the labeling the molar flow rates of all stream components, the temperatures of each stream, and the heat duties (Q) for each unit. If all of a species entering a process unit leaves in a single product stream, use the same variable label at the inlet and outlet. Calculate the number of degrees of freedom for each sub process (the reactor, flash tank, separation process, and hydrogenator) and then the number for the entire process.

(b) Why must the catalyst circulation rate be a design variable?