10. Product Separation and Recycle
Overall Conversion is a formula used to
calculate how much of the reactant has taken part in the overall reaction:
(Reactant input to process – reactant output from process)/reactant input to
process
Single-pass conversion is a formula used
to calculate the amount of reactant taken part in a single-pass:
(Reactant input to reactor- reactant
output from reactor)/reactant input reactor
To find the percentage conversions
multiply by 100%. Single pass overall pass extent of reactions
Purging
Recycle
stream is a term denoting a process stream that returns material from
downstream of a process unit back to the process unit.
Purge
Stream
Purge stream is a stream bled off to
remove an accumulation of inerts or unwanted material that might otherwise
build up in the recycle stream.
A great example would be one by Prof. Manolito
E Bambase Jr. Department of Chemical Engineering.
University of the Philippines Los Baños
Example
12-1. Distillation of Benzene and Toluene
A
distillation column separates 10,000 kg/hr of a mixture containing equal mass
of benzene and toluene. The product D recovered from the condenser at the top
of the column contains 95% benzene, and the bottom W from the column contains
96% toluene. The vapor V entering the condenser from the top of the column is
8000 kg/hr. A portion of the product from the
condenser
is returned to the column as reflux R, and the rest is withdrawn as the final
product D. Assume that V, R, and D are identical in composition since V is
condensed completely.
Find
the ratio of the amount refluxed R to the product withdrawn D.
Overall
Process
Total
Balance: 10,000 = D + W
Benzene
Balance: 10,000(0.50) = D(0.95) + W(0.04)
Solving
simultaneously, D = 5050 kg/hr ; W = 4950 kg/hr
Total
balance around the separator:
8000
= R + D
R
= 2950 kg/hr
Ratio
(R/D) = (2950/5050) = 0.58
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