Problem 11 Operating Time for Catalytic Polymerization Reactor to Reach Minimum Allowable Conversion
A catalytic polymerization plant is to operate continuously with a special catalyst with properties and results as given below. Under the following specified operating conditions, how many days could each reactor remain on stream from the time of fresh (catalyst age zero) catalyst charge until the percent propylene conversion through the catalyst bed drops to 93.75 percent. What will the pressure drop across the catalyst bed be at that time? How often should a new recharged unit come on stream if all units are to operate on identical staggered schedules (i.e., how many days will each unit be down for dumping and recharging)?
Total feed stream is 15,000 barrels per day and is 40 percent by volume propylene and 60 percent by volume propane.
Five reactors are available, each holding 20,000 lb of the catalyst.
All reactors will operate on identical staggered schedules.
The unit will be operated with the same flow rate in four of the reactors while the fifth one is down for dumping and catalyst recharging, with this dumping and recharging requiring at least 5 days but no more than 8 days.
The temperature in the reactors will be maintained constant at 430°F. 0.715 barrel of polymer is obtained for every barrel of propylene converted. One barrel equals 42 gallons.
gallons of polymer produced since catalyst charging
pounds of catalyst charged
[/,f.F(i) dt ] [conversion factors to give gallons of polymer] arjth ave
^ pounds of catalyst t = time, days
D = time in days at which A P/F 2 is to be calculated F = F(t) = reactor total feed rate as thousands of barrels/day AP = pressure drop across reactors, psi
At the operating pressure and temperature of 430°F, the following data apply for the special catalyst used:
A plot of leg A P/F 2 versus catalyst age, A, is linear with A P/F2 = 0.2 at A = 0 and hP/F2 = 100 at A = 84.90.
(Resultant equation is leg A P/F2 = 0.03179,4 - 0.699.) The conversion of propylene to polymer at the time of fresh catalyst charge (catalyst age zero) is 97.66 percent.
The following data apply for the catalyst and indicated temperature (linear interpolation is satisfactory):
% conversion of propylene at catalyst age A
% conversion of propylene at catalyst age zero
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