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Kinetics of COx Formation in MC Oxidation of p-Xylene
Weizhen SUN, Meiying AN, Weimin ZHONG, and Ling ZHAO*
State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China
sunwz@ecust.edu.cn
July 14, 20111/17
Outline
Introduction
Mechanism & Kinetic Model
Experimental
Results
Conclusion
2/17
Introduction
/2 2
metals bromidesolventHydrocarbon O oxygenate H O+ ⎯⎯⎯⎯⎯→ +
The Amoco MC method is defined by:
• High activity• High selectivity• Easy separation
22
( )( )
3 2 2( ) ( )Co OACMn OACHBr
HOACAr n CH O Ar n COOH nH O− + ⎯⎯⎯⎯→ − + n =1-4
3/17
Major by-products (>0.1% yield)
Introduction
Catalytic cycles for PX oxidation suggested by Partenheimer.
Partenheimer, W. Catalysis of Organic Reactions, (Ed.: D. W. Blackburn): 321-346, Marcel Dekker: New York, 1990.
Oxidation of PX to TPA
+ +
4/17
The formation of COx (CO2 and CO) can be used to estimate side reactions in PX oxidation.
Outline
Introduction
Mechanism & Kinetic Model
Experimental
Results
Conclusion
5/17
Mechanism & Kinetic Model
(i) Formation of CO2
(1)2
IkIII IIAr COOH Co Ar CO Co− + → + +i
3 3
IIk
CH COOH ROO ROOH CH COO+ → +i i (2)
Partenheimer, W. Catalysis of Organic Reactions, (Ed.: D. W. Blackburn): 321-346, Marcel Dekker: New York, 1990. Kenigsberg, T. P.; Ariko, N. G.; Agabekov, V. Energy Convers. Mgmt., 1995, 677-680.
3 3 2CH COO CH CO→ +i i (3)
IIIk
Ar COOH ROO ROOH Ar COO− + → + −i i (4)2 3[ ] [ ] [ ] [ ]III
CO I IIr k Ar COOH Co k CH COOH ROO= ⋅ − ⋅ + ⋅ ⋅ i (5)
2 1 2[ ] [ ]COr k Ar COOH k ROO= ⋅ − + ⋅ i (6)
Kinetic Model of CO2 Formation:
6/17
Mechanism & Kinetic Model
(ii) Formation of CO
(7)
(8)
(9)
(10)
IVkIII IIAr CHO Co Ar CO Co− + → + +i
Vk
Ar CO Ar CO− → +i i
[ ] [ ] [ ]IIICO IV Vr k Ar CHO Co k Ar CO= ⋅ − ⋅ + ⋅ − i
3 4[ ] [ ]COr k Ar CHO k Ar CO= ⋅ − + ⋅ − i
Kinetic Model of CO Formation:
7/17
Outline
Introduction
Mechanism & Kinetic Model
Experimental
Results
Conclusion
8/17
Experimental
Experimental setup
2
[ ] 0.79(1 [ ] [ ]) 22.4x
x AirCO
x sol
CO QrO CO M
⋅ ⋅=
− − ⋅ ⋅ (11)
9/17
Outline
Introduction
Mechanism & Kinetic Model
Experimental
Results
Conclusion
10/17
Results
[ ]1 2PX
PX PXOdC k C k C C
dt= − −
[ ] [ ]1 3PX
TALDTALD TALDO O
dC CC k C k C Cdt
= − −
[ ] [ ]1 4TALD
p TAp TA p TAO O
dCCC k C k C C
dt−
− −= − −
[ ][ ] [ ] [ ] [ ] [ ]1 2 6 ( )PX
PX PX PX
OPX PXO O O O O
dCk C k C C CC k C C C
dt= + − − +
[ ][ ] [ ] [ ] [ ] [ ]1 3 6 ( )TALD
TALD TALD TALD
OTALD TALDO O O O O
dCk C k C C CC k C C C
dt= + − − +
(12)
(13)
(14)
(15)
(16)
Weizhen Sun, Ling Zhao. Ind. Eng. Chem. Res., 2011, 50: 2548-2553.Weizhen Sun, Yi Pan, Ling Zhao, Xinggui Zhou. Chem. Eng. Technol., 2008, 31: 1402-1409.
Determination of intermediates and free radicals
11/17
Results
[ ] [ ]4
1 4 5 4p TA
CBACBA CBAO O
dC CC k C k C Cdt −
−− −= − −
[ ]4 CBA
TPAO
dC CCdt −
=
[ ][ ] [ ] [ ] [ ] [ ]1 4 6 ( )p TA
p TA p TA p TA
O
p TA p TAO O O O O
dCk C k C C CC k C C C
dt−
− − −− −= + − − +
[ ][ ] [ ] [ ] [ ] [ ]
4
4 4 41 4 5 4 6 ( )CBA
CBA CBA CBA
OCBA CBAO O O O O
dCk C k C C CC k C C C
dt−
− − −− −= + − − +
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]4
4 4 4
26 ( )
PX TALD PX p TA PX CBA TALD p TA TALD CBA p TA CBA
i O jO O O O O O O O O O O O O
dCk C C C C C C C C C C C C C
dt − − − − − −
− − = − − − − − −
4[ ] [ ] [ ] [ ] [ ]
2 3 4 5 4
( )
( )PX TALD p TA CBAO O O O O
PX TALD p TA CBA
C C C C C
C k C k C k C k C− −
− −
= + + +
= + + +where
(17)
(18)
(19)
(20)
(21)
Weizhen Sun, Ling Zhao. Ind. Eng. Chem. Res., 2011, 50: 2548-2553.Weizhen Sun, Yi Pan, Ling Zhao, Xinggui Zhou. Chem. Eng. Technol., 2008, 31: 1402-1409. 12/17
Determination of intermediates and free radicals
Results
k2×10-3 k3 ×10-3 k4×10-3 k5×10-3 k6
15.88±0.62 17.09±0.53 3.28±0.13 9.81±0.28 0.54±0.02
Table 1a. Estimated rate constants (kg/mol/min)
Initiation rate constants Case 1 Case 2 Case 3
k1, 10-5min-1, for PX oxidation 6.29 5.50 4.03
Table 1b. Initiation rate constants
Model parameters for main reaction
13/17
2 4/ 4.8k k =
Hammett structure-reactivity relationship:
0 2 4log( / ) / 4.9k k k kσ ρ= ⋅ ⇒ =
Results
Model fitting to the formation rate of CO2
Preliminary fitting
Model fitting to the formation rate of CO
14/17
2 1 2[ ] [ ]COr k Ar COOH k ROO= ⋅ − + ⋅ i (6) (10)3 4[ ] [ ]COr k Ar CHO k Ar CO= ⋅ − + ⋅ − i
Results
Model fitting to the formation rate of CO2Model fitting to the formation rate of CO
Revised fitting
Co/Mn/Br, 10-6 kg/kg k1 *103, min-1 k3 *103, min-1 k4, min-1
350/350/700 3.8±0.5 12.9±2.5 700/350/700 5.6±0.7 18.1±2.1 350/700/700 3.2±0.4 14.9±2.0 350/350/1400 3.1±0.1 10.3±2.4
5.4±4.0
Table 2. Summary of Rate Constants
15/17
Outline
Introduction
Mechanism & Kinetic Model
Experimental
Results
Conclusion
16/17
Conclusion
1. The MC oxidation of PX was carried out semi-continuously and the formation kinetics of COx was measured. The simplified elementary steps of COx formation were summarized, on the basis of which the kinetic model of COx formation was established.
2. For the formation of CO2, the fitting curve is in agreement with the experiments. The rate constants of elementary step for decarboxylation of alkyl aromatics were determined with narrow confidence intervals.
3. There are two peaks for the formation rate of CO as a function of time, in which the first is captured successfully by the model. In initial stage, the CO formation has two main sources, including the decarbonylation of aldehyde group and the direct decarbonylation of carbonyl radical. The rate constants of thesetwo elementary steps were determined.
17/17
The End!
Thank you for your attentions!
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