Spring 2000                                                                

ChE 250  Exam IV

Name _____________________

 

This is a closed-book examState any assumptions you use explicitly to ensure adequate credit.  Write only on the front of each page, and turn in all pages in order with the exam on top. 

 

Problem 1 (30 points)

Instead of disposing of waste HCl generated by the old glycerin process, we could use the Deacon process to regenerate chlorine (HCl +  O2    à Cl2 + H2O ,  reaction not yet balanced). For materials and reaction kinetics reasons, the reaction should be conducted in an adiabatic reactor operating in the range 200-400°C.

a)   Determine the standard-state heat of reaction for your balanced reaction. Is this exo- or endothermic?

b)      The reactor feed is 1000 mole/hr HCl with the theoretical amount of air, all at 250°C. Determine the maximum conversion allowed by the operating temperature range, and the outlet chlorine mole fraction.

c)      Suggest two changes in operation that would allow higher conversion of HCl.

 

Problem 2 - Short Answer (40 points)

a) Define “upper heating value” and “lower heating value” for a fuel, and describe why they differ.

b) Give the heat capacity of liquid water, near 20°C, in both English units and SI units.

c) What is the adiabatic flame temperature for methanol (liquid fuel) burned in stoichiometric air?

d) What is Hess’s Law? Give an example of its application.

 

Problem 3 (30 points)

Benzene is readily alkylated to toluene in the following reaction:

C6H6 + CH3OH  à C6H5CH3 + H2O

Xylenes are also produced in the undesired side reaction:

C6H5CH3 + CH3OH  à C6H4(CH3)2 + H2O

The reactor feed is 60 moles/min of 2:1 benzene:methanol, to keep xylene production low, and the reactor runs isothermally at 5 atm and 120°C with reaction in the gas phase over a solid acid catalyst. The methanol is completely reacted. After leaving the reactor, the reaction products are condensed to separate the water from the organics, and the organic product stream is found to be 60% benzene, 30% toluene, and 10% xylenes

a)   Calculate DHreaction at 120°C for both reactions.

b)   Determine the rate of heating or cooling required to maintain the reactor at 120°C.

 

Component Properties

                                cp                D Hocombustion

Species             (J/mole°C)            (kJ/mole)                   

benzene (g)             120                  -3301.5                    

toluene (g)              162                  -3947.9                    

xylenes (g)              202                  -4595.2                    

methanol (g)            59                    -764.0                     

methanol (l)             90                    -726.6                     

CO2 (g)                   70                        -

  methanol DHvap = 35.27 kJ/mole at 64.7°C, 1 atm

 

Standard state for D Hocombustion products:

          CO2(g), H2O(l) at 25°C, 1 atm

                                cp                 D Hoformation

Species             (J/mole°C)            (kJ/mole)                   

chlorine (g)              36                        -

HCl(g)                     28                    -92.31

H2O(l)                     75                   -285.84

H2O(g)                    33                   -241.83

N2(g)                       29                        -

O2(g)                       31                        -

water  DHvap = 40.6 kJ/mole at 100°C, 1 atm