A recycle reactor allows a portion of the product stream from a plug flow reactor to be returned to its entrance, providing varying degrees of backmixing. Advantages include improved conversion rates compared to traditional plug flow reactors, but higher fixed and operating costs due to increased reactor volume. This type of reactor is particularly useful in the petroleum industry and for processes requiring the recycling of enzyme-rich streams.

1. SUBJECT - CHEMICAL REACTION ENGINEERING – 1

2. What Is Recycle Reactor ??
 In certain situations it is found to be advantageous to
divide the product stream from a plug flow reactor and
return a portion of it to the entrance of the reactor.
 Let the recycle ratio R be defined as :

3. What Is Recycle Reactor ??
 This recycle ratio can be made to vary from zero to
infinity.
 Reflection suggests that as the recycle ratio is
raised the behaviour shifts from plug (R=0) to
mixed flow.
 Thus recycling provides a means for obtaining
various degrees of backmixing with a plug flow
reactor.
 Let us develop the performance equation for the
recycle reactor.

4. Recycle Reactor
 Figure of Recycle Reactor :

5. Derivation Of Performance
Equation
 Consider a recycle reactor with nomenclature as shown
in figure. Across the reactor itself equation for plug flow
gives,
 ---------(1)
 Where F’A0 would be the feed rate of A if the stream
entering the reactor (fresh feed plus recycle) were
unconverted.

6. Derivation Of Performance
Equation
 Since F’A0 and XA1 are not known directly, they
must be written in terms of known quantities before
the above equation can be used.
 The flow entering the reactor includes both fresh
feed and the recycle stream. Measuring the flow
split at point L we then have

7.  Now to evaluate XA1 from above equation we can
write ;
 ------- (2)
 Now, equation of CA1 can be written as ;
----(3)

8. Combining Eqns (2) & (3) we will get ;
----------(4)
Finally putting value of (4) in Eqn (1) we will get ;
Conversion :
Concentration :

9. These expressions are represented graphically in Fig. 6.14.

13. Advantages
 Less time required for desired
conversion than the PFR due to Back
Mixing
 We can get different percentage of
conversion by only changing Recycle
Ratio

14. Disadvantages
 Fixed cost is high because of higher
volume of reactor required
 Operating cost is also high due to
recycle
 Volume requred is higher than PFR
due to recycle
 Conversion is also less than PFR

15. Application
 The production unit in which we want
high conversion as well as production
in Lesser time then we can use this
type of reactor.
 It is generally used in petroleum
industry and when the system is
needed to recycle such as Enzyme
Rich stream back into the reactor.