Transcript Slide 1

The Oxidation of Cyclohexane in a Stirred Tank
R. Jevtic, P.A. Ramachandran, M. P. Dudukovic
ODRPACK, a collection of Fortran subroutines for fitting a model to data, is
used to determine kinetic constants
Results
Motivation
Reaction condition: 50% O2, T=130ºC, P=15 atm
•Green et al. (US 5,780,683 patent 1998) performed the
oxidation of cyclohexane with pure oxygen in a Liquid-phase
Oxidation Reactor (LOR).
Conventional
technology
Invention
% Oxygen
21
100
Temperature, 0C
160
149
Residence time, min
36
8
4
4
Cyclohexanol %
42
44
Cyclohexanone, %
20
34
Total
78
84
0.45
1.85
Conversion, cyclohexane %
Yield (Y): Product formed relative to the amount of cyclohexane at the beginning of the reaction
Selectivity (S): Amount of desired products formed relative to the reacted cyclohexane
Assumptions:
constant temperature; both gas and liquid phase fully back-mixed; ideal gas law valid
G:
VG
 Conclusion from Green et al: Reaction temperature and
residence time are reduced while selectivity and productivity are
increased.
 LOR results using pure oxygen were compared to those of the
existing process, which uses air.
 No conclusive evidence for the cause of improvement: might
be due to higher mass transfer rate in the LOR reactor.
VL
130ºC
k0
(m3mol-1s-1)
k1
(s-1)
k2
(s-1)
k3
(m3mol-1s-1)
k4
(m3mol-1s-1)
6.19e-6
1.01e-3
5.58e-4
8.60e-5
3.15e-4
2.66e-5
4.8e-3
1.3e-3
5.0e-4
3.7e-4
160ºC
Volumetric mass transfer coefficient
 The model equations for the gas and the liquid phase solved simultaneously with all
the parameters
 A stiff ODE solver from Netlib library (LSODE) used
% oxygen in the gas
phase
21% O2, 160ºC, P=15 atm
Kinetic models
Spielman(1964), Alagy et al. (1964)
k1
-0.5O2
RH
+O2
Time (min) to achieve Selectivity (%) for cyclohexanol,
4% cyclohexane
cyclohexanone, and cyclohexylconversion
hydroperoxide
20
34.4
89.4
50
14.2
92.6
75
9.8
93.9
100
7.4
94.9
For fixed conversion of cyclohexane, higher oxygen content in gas phase
yields lower residence time and higher selectivity.
ROH
k3 +0.5O2
ROOH
k0
k2
Complete set of temporal data on cyclohexane conversion
and selectivity is necessary to systematically investigate
the effect of increased oxygen availability
Henry’s constants for component i
NR
dci
pi
 kLa (
 ci )   ki rk
dt
Hi
k 1
L:
Selectivity:
Productivity, gmol/hrL
VG dpi
pi
 k L a (
 ci )VL
RT dt
Hi
Obtain kinetic constants:
RO
+(n-1)O2
k4
Byproducts
Summary
Kharkova et al. (1989)
Figure 1. Concentration of products and reactant of
cyclohexane oxidation using kinetic model from
Alagy et al(1964)
 Design, set up and experimental study in stirred autoclave operated in
the batch mode is completed.
Increased oxygen content in the gas phase yielded higher concentration of
desired products but also lower selectivity.
Experimental Setup
To draw any definite conclusion on the effect of oxygen availability, oxygen
partial pressure should be kept constant.
 Design, set up and preliminary experimental study in stirred autoclave
operated in the semibatch mode is completed.
Figure 2. Concentration of products and reactant of
cyclohexane oxidation using kinetic model from
Reaction condition: 50% Kharakova
O2, T=160ºet
C,alP=15
atm
(1989)
Again, increased oxygen percentage in the gas phase will result in higher
yields of cyclohexanol and cyclohexanone but lower selectivity.
However, for fixed conversion of cyclohexane, higher oxygen content in
gas phase requires lower residence time and leads to higher productivity.
Experimental setup:
References
Parr Mini autoclave (operated in a batch and a
semibatch mode), T=1300C, P=15 bar and 30 bar, mol.
fraction of O2 in gas phase=0.2 and 0.5, VG/VL=2.33,
total liquid volume=7.5ml, 900 RPM
1.
2.
3.
4.
Figure 3. Experimental and modeling results for yields of
cyclohexanol (ROH) and cyclohexanone (RO) in time for
catalytic reaction
Greene, M. I.; Sumner, C.; Gartside, R. J. Cyclohexane oxidation. 5,780,683, 1998.
Jevtic et al., AIChE Annual Meeting, Cincinnati, OH, November, 2005
Jevtic et al., AIChE Annual Meeting, San Francisco, CA, November, 2006
Jevtic et al. NASCRE-2, Houston, TX, February, 2007
Figure 4. Experimental results for yields of
cyclohexanol (ROH) and cyclohexanone (RO) in
time for non-catalytic reaction
Chemical Reaction Engineering Laboratory