reactors' problems

Reaction Engineering I, Problem Set 1

Mass Balances in Batch and Steady State Isothermal Reactors

1. Show that for a first order reversible reaction A  B, the rate of reaction dt

dC A can be

expressed as the product of a constant, multiplied by the driving force )( ,eqAA

CC  , where

CA,eq is the equilibrium concentration of component A. Assume that the initial

concentration of B is zero and that the temperature is constant.

2. A CSTR is used to decompose a dilute solution of A by a first order irreversible reaction. The value of the kinetic constant is 3.45 hr

-1 . The reactor volume is 10 m

3 . Calculate the

flow rate of feed solution that can be treated if 95% decomposition is required? Neglect

any volume change upon reaction.

3. What volume of reactor would be required to achieve the same conversion in a plug flow reactor, using the same volumetric flow rate?

4. Repeat problem 2 and 3 for xA = 0.5. Explain qualitatively the change in the difference between the sizes of the CSTR and PFR.

5. The liquid phase reactions:

i. 2A  products, rA = k CA 2

ii. A + B  products, rA = k CA CB

iii. 3A  products rA = k CA 3

are separately carried out in isothermal plug-flow reactors at steady state. Assuming

constant mass density, derive expressions showing how the flow rate nA,e (at which ‘A’

leaves the reactor) is related to reactor volume. P across the reactor may be neglected.

6. For the same liquid phase reactions as in problem 5, derive expressions showing how in a batch system the final conversion is related to reaction time. Compare these expressions

with those found in problem 5.