Chapter 4, Problem 4.75P

A catalytic reactor is used to produce formaldehyde from methanol in the reaction CH₃OH - HCHO + H₂

A single-pass conversion of 60.0% is achieved in the reactor. The methanol in the reactor product is separated from the formaldehyde and hydrogen in a multiple-unit process. The production rate of formaldehyde is 900.0 kg/h.

1. Calculate the required feed rate of methanol to the process (kmol/h) if there is no recycle.

Suppose the unreacted methanol is recovered and recycled to the reactor and the single-pass conversion remains 60%. Without doing any calculations, prove that you have enough information to determine the required fresh feed rate of methanol (kmol/h) and the rates (kmol/h) at which methanol enters and leaves the reactor. Then perform the calculations.

The single-pass conversion in the reactor, X^. affects the costs of the reactor (C_r) and the separation process and recycle line (C₅). What effect would you expect an increased X_sp would have on each of these costs for a fixed formaldehyde production rate? (Hint: To get a 100% singlepass conversion you would need an infinitely large reactor, and lowering the single-pass conversion leads to a need to process greater amounts of fluid through both process units and the recycle line.) What would you expect a plot of (C, + C₅) versus X_sp to look like? What does the design specification X_sp = 60% probably represent?