Assignment

Problems 1 through 4 deal with this situation.

1,3-butadiene is produced by dehydrogenating n-butane in the presence of steam via the reaction

C_4 H_10 (g)→C_4 H_6 (g)+2H_2 (g)

The reaction takes place at 925 K and 1 bar.

1. Draw the I/O diagram for a process that uses pure butane as a raw material and produces 100 kmol/h of a product that is 95% 1,3-butadiene and 5% n-butane. Complete the mass balances around it.

2. The reactor effluent contains 1-3 butadiene, hydrogen, water, and a small amount of n-butane.Draw the recycle structure for this process that is consistent with your I/O structure. List all species in each stream.

3. Using the table below, synthesize a separation sequence. What physical property difference should you exploit to recover the water? What physical property difference will you exploit to separate hydrogen from the C4 species?

4.  Your customer would like a purer grade of butadiene, but this reaction is equilibrium limited, and, as the table shows, butane and 1,3-butadiene are difficult to separate. What could you do to shift the reaction equilibrium so as to reduce the amount of butane in the reactor effluent?

5. A heat exchanger network has several hot streams and one cold stream. The hot composite stream is plotted on the TQ diagram, shown below. The cold stream enters the network at 30^oC and leaves at 90^oC, and has a flowrate-heat capacity of 10 kW/K.

a. Sketch the cold composite curve for the case where there is no cold utility. Is this feasible? Why or why not?

b. The minimum temperature difference for heat transfer is 10^oC. Sketch the cold composite curve for the minimum utility case. What is the minimum steam consumption in kW? What is minimum cooling water consumption in kW? Where is the pinch point?

Problems 6 through 9 deal with this situation.

n-butanol (NB) has been proposed as an alternative fuel. It can be produced from an azeotropic mixture of ethanol (E) and water (W) via the reaction

2E→NB+W

The reaction takes place in the presence of a heterogeneous catalyst at 150^oC and 1 atm. The per-pass conversion of ethanol is 37%. Normal boiling points are given below.

In addition, please note that water can be removed from n-butanol using a zeolite adsorbent.

6. What should be done with the unreacted ethanol in the reactor effluent?

a. Dispose of it as waste
b. Sell it as a byproduct
c. Recycle it to the reactor in a pure ethanol stream
d. Recycle it to the reactor in a stream containing the ethanol/water azeotrope.

Briefly explain your answer:

7. Draw the I/O diagram for a process that produces 75 kmol/h of NB, using an azeotropic mixture of ethanol and water as a feed, and is consistent with your answer to question 6. Complete the mass balances around it.

8. Draw a recycle structure for this process that is consistent with your answers to questions 6 and 7. Number your streams, complete the mass balances, and then enter the component flow rates in the stream table template at the bottom of the page. (You may use fewer than 10 streams. If you need more than 10, add them to the right.

9. Synthesize a separation sequence and draw your flowsheet in the space below.

10. A silica adsorbent will be used in a pressure swing adsorption system. The adsorption step takes 15 minutes. Regenerating the bed takes 30 minutes. How many beds do I need in my PSA system?

11. A zeolite bed adsorbs 18 kg/h of water. The bed must operate for 2 hours before regenerating. The adsorption capacity of the zeolite is 0.3 g water/g zeolite, and the bulk density of the zeolite is 0.6 kg/L. What is the volume of the adsorption bed?

12. Consider the attached TQ diagram. The minimum temperature difference for heat transfer is 10^oC. What is the minimum steam consumption in kW? What is minimum cooling water consumption in kW? Where is the pinch point?