Sample Problem Set 2: (10/1/2001 TBC)

I.

The production of ethanol by hydration of ethylene is given by RXN1 but with some undesired side reaction given by RXN2.

Fresh feed rate of 210 moles/min (containing 38.1 mol% C2H4, 38.1 mol% H2O, 23.8 mol% inerts) is mixed with a recycle stream and fed to a reactor. The reactor effluents are then passed to a separator in which two streams emerge. One stream is the liquid product containing ethanol (C2H5OH), diethyl ether ( (C2H5)2OH ), water, ethylene and no inerts. The ratio of H20 to C2H4 to in the product stream was found to be 15 mol-H20/mol-C2H4. The selectivity of ethanol to ether in the product stream was found to be 2.889 mol-C2H5OH/mol-(C2H5)2O.

The other stream coming out the separator ( containing ethanol, ether, water, ethylene and inerts) is then further split into two streams: 5% comes out as a purge stream and 95% as a recycle stream. The purge stream contains 30.11 mol% C2H4, 4.30 mol% C2H5OH, 1.08 mol% (C2H5)2O , 10.75 mol% H2O and 53.76 mol% inerts.

Determine the molar flow rate and molar composition of the product stream, and the single pass conversion of the reactor.
 
 

II.

A reactor-separator system shown in figure 1 is used to produce the compound AB using the reaction

Figure 1.

Show that the overall conversion of A, OCA, is related to the single pass conversion of A, SCA, by the following equation:
where, r is the moles of recycle/moles of fresh feed,

xR,A is the mole fraction of A in the fresh feed

xFF,A is the mole fraction of A in the recycle

 (Thus, the overall conversion of A is always larger than single pass conversion.)
 

III.
Feed composed of 20 mol% A, 20 mol% B2C and 60 mol% inerts undergoes the reaction

6 A + 3 B2C   ¾¾¾®    6 AB + C3

The product from the reactor contains 63 mol% inerts. What is the composition of the products?
 

IV.
Propane is fed with 20% excess dry air  to a furnace.  However, part of the fuel undergoes only partial combustion. Also, some propane did not burn.  The stack gas coming out of the furnace was analyzed under dry basis to contain 30 mol% CO2 and 10 mol% CO plus some unreacted O2, C3H8 and N2.

a) Determine the composition of the feed.
b) Determine the amount of H2O produced per kmol of feed.