# 7.42: Untitled Page 187

## Chapter 7

entering the dryer is equivalent to 50 mm Hg. For this condition, calculate the total molar flow rate of fresh air entering the system (Stream #1) and the total molar flow rate of the recycle stream (Stream #6). Assume that the process operates at atmospheric pressure (760 mm Hg).

Figure 7.31. Air dryer with recycle stream

7‐32. Solve problem 7‐31 using one of the iterative procedures described in Appendix B. Assume that the partial pressure of water in the fresh air stream tream

(S

#1) is 20 mm Hg and that the maximum partial pressure in the stream leaving the unit (Stream #5), does not exceed 180 mm Hg. If you use a spreadsheet or a Matlab program to solve this problem, make sure all variables are conveniently

ed.

label

Use a convergence criteria of 1 mm Hg for Stream #6.

7 33. By manipulating the operating conditions (temperature, pressure and catalyst) in the reactor described in Example 7.5, the conversion can be increased from 0.30 to 0.47, i.e.,

 RC H Cl

2

4

2

C  Conversion of C H Cl

 0 . 47

2

4

2

( M

)

C2H4Cl2 2

For this conversion, what are the changes in the molar flow rate of vinyl chloride in Stream #4 and the molar flow rate of dichloroethane in Stream #5?

7‐34. For the conditions given in Example 7.5, determine the total molar flow rate and composition in Stream #3.

7‐35. Metallic silver can be obtained from sulfide ores by roasting to sulfates, leaching with water, and precipitating the silver with copper. It is this latter process, involving the chemical reaction   Material Balances for Complex Systems

351

Ag SO

 Cu  2Ag  CuSO

2

4

4

that we wish to consider here. In the system illustrated in Figure 7.35, the product leaving the second separator contains 90% (by mass) silver and 10%

copper. The percent of excess copper in Stream #1 is defined by

 molar flow rate 

 molar rate of

of copper entering

 consumption of

 in the feed stream 

copper in the reactor

percent of

 

 100

excess copper

 molar rate of

 consumption of 

copper

in the reactor 

and the conversion of silver sulfate is defined by

molar rate of consumption

 of Ag SO in reactor

R

2

4

Ag SO

C 

2

4

molar flow rate of Ag SO 

( M

)

2

4 

Ag2SO4 3

 entering the reactor

For the conditions given, what is the percent of excess copper? If the conversion is given by C  0 . 75 , what is m

/ m ?

6

5

Figure 7.35. Metallic silver production  352