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The University of Western Ontario

Faculty of Engineering

Assignment 3

CBE 2220a- Chemical Process Calculations

06-10- 2014 (DUE October 13, 2014 BY 5 PM) 

Q. 1. Case Study: Extractive Distillation Process for Acetone

A mixture containing 50.0 wt% acetone and 50.0 wt% water is to be separated into two streams-

one enriched in acetone, the other in water. The separation process consists of extraction of theacetone from the water into a solvent methyl isobutyl ketone (MIBK), which dissolves acetone but is

nearly immiscible with water. The process is shown below:

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(water in this process) is referred to as the Raffinate and the phase rich in the solvent (MIBK) is

termed the Extract. The first “mixer settler “ combination is the First Stage Extractor Unit for the

process. The raffinate then passes to a second “mixer-settler” combination or second extractor unit.

Here the raffinate is contacted with a second stream of pure MIBK which permits the transfer of

more acetone from the raffinate to the solvent. The phases separate in the settler of the second

extractor unit. The extracts from the two extraction steps are combined while raffinate 2 which is

very low in acetone is discarded. The combined extracts are fed to a distillation column where the

acetone and MIBK are separated. The overhead from the distillation column is rich in acetone and is

the required product. The bottom effluent from the distillation column is rich in MIBK. This could be

treated further and eventually recycled back to the process as pure MIBK.

In a pilot scale study, for every 100 Kg of acetone-water fed to the first extraction stage, 100 Kg of

MIBK is fed to the first extractor and 75 Kg to the second extractor. The extract from the first stage

is found to contain 27.5% (w/w) acetone, The second stage raffinate has a mass of 43.1 Kg and

contains 5.3% acetone, 1.6% MIBK and the rest water. The second stage extract contains 9.0%

acetone, 88.0% MIBK and 3.0% water. The overhead product from the distillation column contains

2.0% MIBK, 1.0% water and the rest acetone. Taking a basis of calculation of 100 Kg acetone-water

feed:

1. 

Show a simplified schematic by combining mixer settler into one (extractor) for the process?

2. 

Do a DF analysis around the 2 extractor subsystem.

3. 

Show a DF analysis for the OVERALL process.

4. 

Show a DF analysis for first extractor; second extractor; around the mixing point; and around thedistillation column.

5. 

Write mass balances around the 2 extractor unit and solve.

6. 

Write mass balances around the mxing point and solve.

7. 

Write mass balances around extractor 1 and etractor 2 and solve.

8 Why cannot we completely solve for the process?

 

Q 2. A reactor is fed an equi-molar mixture of three chemicals A,B, and C. The product D is

 produced via the reaction below:A + 2B + 1.5C 2D + E

The conversion in the reactor is 50% based on the limiting reactant.

(a) What is the limiting reactant?

b) How many moles of D are produced per 100 moles of total feed to the reactor? (b) How many moles of D are produced per 100 moles of total feed to the reactor?

 

The acetone (solute)-water (diluents) mixture is first contacted with the MIBK (solvent) in a mixer

that provides a good contact between the two liquid phases. A portion of the acetone in the feed

(water) transfers to the organic solvent (MIBK) phase in this step. The mixture passes into the

settling tank where the phases separate and are separately withdrawn. The phase rich in diluents