Heterogeneous Catalytic Liquid Phase Reaction - Concentration Profile false


i have some problems with a heterogeneous catalytic liquid phase reaction in a plug flow reactor in terms of the production of cumene by benzene with propylene. The concentration profile a long the reactor length seems to be wrong while all other solutions makes sense.

the reaction set during the alkylation is

R1: benzene (R1) + propylene (R2) --> cumene (P1)
R2: propylene (R1) + cumene (R2) --> DIPB (P1)

Almost every reaction happens at the beginning of the reactor which cannot be true. The reactions are independet of the length and volume, too.

Kinetics of liquid phase reaction can be expressed as simple first order equations where the concentration of propylen is determing the rate.

R1: k1*R2, with k1=6510exp(-52564/R/T) and R2=c_propylene, R=8.3148 kJ/kmol
R2: k2*R1, with k2=450exp(-55000/R/T) and R1=c_propylene, , R=8.3148 kJ/kmol

Activation energy in kJ/kmol, reaction rate in kmol/(m3*s), k in 1/s. Maybe here's the problem, i cannot choose the right unit in velocity settings at reaction settings?

Reactor and Catalysator settings

reactor volume: 9,1m3
reactor length: 7m
catalyst loading: 1000kg/m3
catalyst particle diameter: 2,4mm
catalyst void fraction: 0,4

The feed to the pfr is composed as follows:

molar flow: 511,1 kmol/h
temperature: 165°C
pressure: 35,5 bar
benzene: 0,78262571
Propane: 0,021737429
propylene: 0,19563686
cumene: 0
dipb: 0

Property Package is Peng Robinson. I also attached my .dwxmz file for you to check.

BTW1: I also simulated the gasphase alkylation where the problem does not appear.
BTW2: All the Information about the kinetics are out of the book 'Chemical Process Design, Alexandre C. Dimian and Costin Sorin Bildea'

DWSIM 22-07-21, 6:56 a.m. willex
Here a picture of the profile, i dont know why but i cant upload the .dwxmz file..
22-07-21, 7:05 a.m. willex

  1. Could you check the the reaction rates with their units? this is one source of issue
  2. the space velocity (and hence the residence time) will affect the conversion, so could you check you have used the correct values?
Sharing the main reference for kinetics and your implementation will help to debug your simulation more easily
27-08-21, 3:50 p.m. atronoush

More comments I checked you feed is two phases and your reaction only works in liquid phase! The residence time is very low? check your data
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