Chemical Engineering 301
Mid Term Exam  10/13/04

Return to AL B216 by 1PM on 10/20/04

Open text, notes and computer  including 
all material in the ceng301 Directories of Web pages, 
problem and text example solutions.

Three hour total time limit, but you may take a break in the middle.
During the break, you are encouraged to contact the instructors
if you have any questions about the problems, but you may not
study material in the course.  
Sending e-mail to shdavis@rice.edu or kyzy@rice.edu
should be the most efficient way to contact us.

Note that all material connected with your solution of this exam
must be stored in your protected ceng301 directory.

1)	20 Points
Categorize each of the following systems as being:
•	steady state or dynamic
•	open or closed
•	reactive or non-reactive
a)	a distillation column used to separate petroleum into fractions in a chemical plant,
b)	a greenhouse used to grow plants,
c)	a housing unit built on the moon.
In each case list assumptions you made to come to your conclusions.
Our general mass balance is: 
input + generation - output – consumption = accumulation
For each case list the terms in this balance which can be neglected in determining the total mass in the system.

2)	60 Points total
One unit (made up of several sub units) in a chemical plant produces ethylene oxide for use in making glycol.  One feed stream to the unit contains 95 mol% ethylene and 5 mol% ethane.  The other feed is air.  The hydrocarbon stream is fed at the rate: 100 kmols per hour and the air feed is set to just give enough oxygen to react completely all the ethylene to ethylene oxide. 

The following reactions are assumed to take place in the system:

•	Ethylene reacts with O2 to produce Ethylene oxide
•	Ethylene reacts with O2 to make CO and H2O
•	Ethane reacts with O2 to make CO2 and H2O
•	CO reacts with O2 to make CO2

Assume air is 21 mol% O2 and the rest N2
a)	20 points 
Draw a flow diagram of the process labeling  all streams and the flow of compounds in them.  Use a Degree of Freedom analysis based on compound flows and reactions to determine how many specifications can be set for the system: call this number DoF.
b)	25 points
Choose DoF specifications from the following list to give a process that can be analyzed.

•	The conversion of ethylene is 90%.
•	The yield of Ethylene oxide is 98% of the ethylene that reacts
•	2% of the ethane that is fed reacts
•	The ratio of CO2 to CO in the product is 0.25
•	No O2 is present in the product gas

For this set of specifications find the flows of all compounds in all streams in the system.  Is the answer you found reasonable?  Are all flow rates in the product stream positive?
c)	15 points
Use a Degree of Freedom analysis based on the flow of elements in and out of the system to determine the number of allowed specifications in the case descried in part a).  Does it agree with what you found in part a)? 
3)	20 points
Work parts (a) and (b) of problem 4.54 in Felder and Rousseau.

4)	10 points bonus
Work part (c) of problem 4.54

Note: You may find property data in Table B.1 useful in these problems.

Pledge