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

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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

+ +

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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

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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:

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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:

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Outline

Introduction

Mechanism & Kinetic Model

Experimental

Results

Conclusion

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Experimental

Experimental setup

2

[ ] 0.79(1 [ ] [ ]) 22.4x

x AirCO

x sol

CO QrO CO M

⋅ ⋅=

− − ⋅ ⋅ (11)

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Outline

Introduction

Mechanism & Kinetic Model

Experimental

Results

Conclusion

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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

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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

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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

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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

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Outline

Introduction

Mechanism & Kinetic Model

Experimental

Results

Conclusion

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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.

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The End!

Thank you for your attentions!