Page 208 - Separation process engineering

problems:
a. Separation of phenol from p-cresol. F = 100, z = 0.6, q = 0.4, x = 0.04, x = 0.98, α = 1.76,
F B D
and L/D = 4.00.
b. Separation of benzene from toluene. F = 200, z = 0.4, q = 1.3, x = 0.0005, x = 0.98, α = 2.5,
D
B
F
and L/D = 2.00.
c. Since the relative volatility of benzene and toluene can vary from 2.61 for pure benzene to
2.315 for pure toluene, repeat part b for α = 2.315, 2.4, and 2.61.

Write your program so that it will calculate the fractional number of stages required. Check your
program by doing a hand calculation.

H. Spreadsheet Problems

H1. [VBA required] Using the spreadsheet in Appendix B of Chapter 4 or your own spreadsheet,
solve the following problem. A methanol water mixture is being distilled in a distillation column
with a total condenser and a partial reboiler. The pressure is 1.0 atm, and the reflux is returned as
a saturated liquid. The feed rate is 250 kmol/h and is a saturated vapor. The feed is 40 mol%
methanol. We desire a bottoms product that is 1.1 mol% methanol and a distillate product that is
99.3 mol% methanol. L/D = 4.5. Find the optimum feed stage, the total number of stages, D and B.
Assume CMO is valid. Equilibrium data are available in Table 2-7. Use Excel to fit this data with
a 6th-order polynomial. After solving the problem, do “What if?” simulations to see what happens

if the products are made purer and if L/D is decreased.
H2. [VBA required] Using the spreadsheet in Appendix B of Chapter 4 or your own spreadsheet, find
the minimum L/D by trial and error for a saturated vapor feed of ethanol and water with z = 0.1,
x = 0.7, and x = 0.0001.
B
D
H3. [VBA required] Write a spreadsheet for binary distillation with CMO that automatically
calculates (L/D) min , determines L/D = (Multiplier) (L/D) min , then calculates the number of stages

when the feed stage is specified. Use this program to find (L/D) min , the optimum feed stage, and
the total number of stages for distillation of a 0.17 mole fraction ethanol and 0.83 mole fraction
water feed with q = 0.5, x = 0.7, x = 0.0001, and Multiplier = 1.05.
D
B
Chapter 4 Appendix A. Computer Simulations for Binary Distillation

Although binary distillation problems can be done conveniently on a McCabe-Thiele diagram, Chapter 6
will show that multicomponent distillation problems are easiest to solve as matrix solutions for
simulation problems (the number of stages and feed locations are known). Commercial simulators
typically solve all problems this way. Lab 3 in this appendix provides an opportunity to use a process
simulator for binary distillation. Although the instructions discuss Aspen Plus, other simulators will be
similar.

Prerequisite: This appendix assumes you are familiar with Appendix 2A [in Chapter 2], which included
Labs 1 and 2, and that you are able to do basic steps with your simulator. If you need to, use the
instructions in Lab 1 as a refresher on how to use Aspen Plus. If problems persist while trying to run the
simulations, see Appendix A, “Aspen Plus Separations Trouble Shooting Guide,” at the end of the book.

Lab 3. The goals of this lab are: 1) to become familiar with Aspen Plus simulations using RADFRAC for
binary distillation systems, and 2) to explore the effect of changing operating variables on the results of
the binary distillation. There is no assignment to hand in. However, understanding this material should
help you understand the textbook and will help you do later labs.