isomerization of mixed xylene – ethylbenzene feeds over ... · pdf filecumene phenol,...

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Thomas F. Degnan, Jr., David H. Olson, and B. K. HuhExxonMobil Research and Engineering CompanyAmerican Institute of Chemical Engineers Annual MeetingSan Francisco, CAMonday, November 4, 2013

Isomerization of Mixed Xylene –Ethylbenzene Feeds over ZSM-5:Analysis of Kinetics and Diffusion of C10 Transalkylation ProductsIn Honor of Professor W. Nicholas Delgass 2012 R. H. Wilhelm Award Recipient

2

Congratulations Nick!

Great friend, wonderful colleague, and inspirational teacher

• 2003 Purdue University Outstanding Undergraduate Teaching Award in memory of Charles B. Murphy.

• Dean A.A. Potter Teaching Award, Purdue, Schools of Engineering, 1990. • R.N. Shreve Teaching Award, Purdue School of Chemical Engineering, 1983,

1986, 1989,1991, 2000 and 2002. • Purdue Schools of Engineering Mentoring Excellence Award 2003. • New York Catalysis Society Excellence in Catalysis Award, 2006• Inaugural North American Catalysis Society (NACS) Award for Distinguished

Service in the Advancement of Catalysis, 2010• AIChE R. H. Wilhelm Award, 2012

3

Manufacture of High Value Alkylaromatics

Alkylaromatic Major Uses WW Production, lbs/yr Ethylbenzene Styrene, Polystyrene 60 BillionCumene Phenol, Bisphenol-A, Polycarbonate 18 BillionPara-Xylene Terephthalic acid, Polyester 36 Billion

Reformer

Fractionation TransalkylationC9

+ , C6/C7

Isomerization

Disproportionation

Cumene Synthesis

EB Synthesis

Xylene

Toluene

Benzene

C2=

C3=

Ethylbenzene

Cumene

Para-Xylene

BenzeneCracker / Separations

2011

4

Manufacture of High Value Alkylaromatics

Alkylaromatic Major Uses WW Production, lbs/yr Ethylbenzene Styrene, Polystyrene 60 BillionCumene Phenol, Bisphenol-A, Polycarbonate 18 BillionPara-Xylene Terephthalic acid, Polyester 36 Billion

Reformer

Fractionation TransalkylationC9

+ , C6/C7

Isomerization

Disproportionation

Cumene Synthesis

EB Synthesis

Xylene

Toluene

Benzene

C2=

C3=

Ethylbenzene

Cumene

Para-Xylene

BenzeneCracker / Separations

2011

5

Para-Xylene Can be Produced Via Equilibrium or Selective Processes

+2

+2

Xylene Isomerization Toluene Disproportionation

XylenesAt

Equilibrium

SelectiveProcesses

EquilibriumProcesses

Transalkylation

Selective TolueneDisproportionation

22% Ortho- 54% Meta- 24% Para-

Para- >> 24%

Para- ~ 24%

Para- ~ 24%

All ProcessesRequire

Separation

+ 2

6

ExxonMobil’s Xylene IsomerizationProcess Development HistoryContinuous Development and Improvement for 35+ Years

Lower pX Concentration in Isom feeds(e.g. from adsorption)

Higher pX Concentration in Isom feeds(e.g. from crystallizers)

MHAI1990

MHTI1981

MLPI1978

MVPI1975

AdvancedMobilHighActivityIsom.

MobilHighActivityIsom.

MobilHighTemperatureIsom.

MobilLowPressureIsom.

MobilVaporPhaseIsom.

7

ExxonMobil MHAIXylene Isomerization Process

p-Xylene recovery

Unit

C9+ Aromatics

Make-up Hydrogen

Separator

Compressor Hydrogen Recycle

Gas

Benzene &Toluene

Isomerate

CW

Stabilizer

Reactor

Furnace

XyleneColumn

Para-xylene

C8AromaticHeart-cut

EBConversion

Xylene Isomerization

Catalysts

+

8

ExxonMobil MHAIXylene Isomerization Process

p-Xylene recovery

Unit

C9+ Aromatics

Make-up Hydrogen

Separator

Compressor Hydrogen Recycle

Gas

Benzene &Toluene

Isomerate

CW

Stabilizer

Reactor

Furnace

XyleneColumn

Para-xylene

C8AromaticHeart-cut

EBConversion

Xylene Isomerization

Catalysts

+

9

Transalkylation Reactions inthe Ethylbenzene – Xylene System

+

+

E , E

E , X+

X , E++

X , X+ +

Ref: D. H. Olson and W. O. Haag, ACS Symp.Ser. 248, pp. 275 – 307 (1984)

+

10

Xylene – EB TransalkylationProduces C9 and C10 Aromatics

ZSM-5 Crystal

+ +

+

+ +

+

+ +

DEB

DMEB

kE,E

kX,E kE,X

kX,X

11

Xylene – EB TransalkylationProduces C9 and C10 Aromatics

ZSM-5 Crystal

+ +

+

+ +

+

+ +

DEB

DMEB

kE,E

kX,E kE,X

kX,X

Changes in DEB/DMEBRatio are indicators ofIntracrystallinediffusivity

12

Transalkylation Kinetic Parametersin EB – Xylene System

Relative Rate ConstantsReaction ZSM-4 Mordenite ZSM-5

E, E 10.4 20.8 125.0E, X 2.2 3.6 16.8X, E 1.3 1.5 3.6X, X 1.0 1.0 1.0

Ethyl vs. Methyl TransferkE,E / kX,E 8.0 13.9 34.7kE,X / kX,X 2.2 3.6 16.8

Ethylbenzene vs. XylenekE,E / kE,X 4.7 5.8 7.4kX,E / kX,X 1.3 1.5 3.6Memo: Conditions: 250 – 280oC, 2800 kPa, WHSV = 2 to 20 hr-1


13

Aromatic Kinetic Diameters areClose to Pore Diameters of ZSM-5

Straight Channel5.4 x 5.6 Å

Sinusoidal Channel5.1 x 5.5 Å

Kinetic Diameter of Aromatics Close to the Pore Size of ZSM-56.8 6.8 5.8 5.8 5.8 5.8

~ ~ ~ ~

Ortho-Xylene Meta-Xylene Para-Xylene Ethylbenzene

>

Toluene Benzene

14

The Role of Shape Selective Zeolites in C8 – C10 Aromatic Reactions

Reactant Selectivity (Hydrodealkylation)

Product or Isomer Selectivity (Selective Toluene Disproportionation)

+ H 2 +

+2

Csicsery, J Catal 1971, 23, 124

5.8 Å6.8 Å 6.8 Å

Metal

Transition State Selectivity (C8 Aromatics Disproportionation)

+very low

yields+ +Bulky

15

Study Objectives

• Examine the diffusional characteristics of C10 transalkylation products (DMEB and DEB) in ZSM-5 catalyzed Isomerization of Xylene: Ethylbenzene Feeds

• ZSM-5 catalyzed isomerization of a mixed Xylene: EB feed• Mixed Xylenes (86 wt%) : Ethylbenzene (14 wt%)• Temperatures: 350o – 390oC• WHSV = 2 to 150 hr-1

• H2 : Hydrocarbon molar ratios = 2 to 4• Pressure = 1480 kPa

16

ZSM-5 Catalysts

Designation Relative Activity (C6 cracking)

D/r2 , sec-1

(p-Xylene uptake method)

SCLA 1.5 3.2 x 10-4

MCLA 1.0 4.7 x 10-5

LCLA 1.3 6.3 x 10-6

SCMA 13.3 3.4 x 10-4

MCMA 17.5 4.5 x 10-5

LCMA 6.7 5.7 x 10-6

SCHA 70.0 3.1 x 10-4

MCHA 58.3 3.3 x 10-5

LCHA 54.7 5.0 x 10-6

Memo: SC - Small Crystal; MC - Midsize Crystal; LC - Large Crystal; LA – Low Activity; MA – Moderate Activity; HA – High Activity

17

Effect of ZSM-5 Acidity onDiethylbenzene (DEB) Yield

EB Conversion, mole pct.

DE

B Y

ield

, mol

e pc

t.

Temperature: 370oCWHSV = 2 to 150 hr-1

H2 : Hydrocarbon molar ratios = 2 to 4Pressure = 1480 kPa

Large Crystal

Low activityModerate activityHigh activity

18

Small Crystal

Medium Crystal

Large Crystal

Effect of Crystal Size onDiethylbenzene (DEB) Yield




DE

B Y

ield

, mol

e pc

t.

19

Small Crystal

Medium Crystal

Large Crystal

Effect of Crystal Size onDimethylethylbenzene (DMEB) Yield




DM

EB

Yie

ld, m

ole

pct.

20

Small Crystal

Medium Crystal

Large Crystal

Effect of Crystal Size onDEB / DMEB Ratio




DE

B /

DM

EB

Rat

io, m

olar

21

Summary: Effects of ZSM-5 Crystal Size

• DEB yield is a direct function of the zeolite acidity, or number of acid sites.

• DEB yield is a strong function of EB conversion and a mild function of crystal size.

• Conversely, DMEB yield is a strong function of crystal size, indicating that it is more strongly influenced by intracrystalline diffusivity and crystal size.

• DEB/DMEB Ratio increases with ZSM-5 crystal size and activity which is consistent with differences in the intracrystalline diffusivities of DEB and DMEB

22

0.1

1

10

0 0.02 0.04 0.06 0.08

DEB and DMEB:First Order Kinetics

1/WHSV

kDEB = 60 hr-1

Small Crystal; Low Activity ZSM-5370oC1515 kPa

kDEB = k E E kDMEB= k X E

1/WHSV

DMEB

Production of Diethylbenzene andDimethylethylbenzene are both governed by First Order Kinetics

DEB

No diffusion limitation expected - withlow crystal activities and small crystal

0.01

0.1

1

0 0.02 0.04 0.06 0.08

kDMEB = 6 hr-1

Olson and Haag This (1984) Study

kDEB / kDMEB 7.4 10.0

Frac

tion

DM

EB

in P

rodu

ct, m

olar

Frac

tion

DM

EB

in P

rodu

ct, m

olar


23

Transalkylation Kinetic Parametersin EB – Xylene System

Relative Rate ConstantsReaction ZSM-4 Mordenite ZSM-5

E, E 10.4 20.8 125.0E, X 2.2 3.6 16.8X, E 1.3 1.5 3.6X, X 1.0 1.0 1.0

Ethyl vs. Methyl TransferkE,E / kX,E 8.0 13.9 34.7kE,X / kX,X 2.2 3.6 16.8

Ethylbenzene vs. XylenekE,E / kE,X 4.7 5.8 7.4kX,E / kX,X 1.3 1.5 3.6Memo: Conditions: 250 – 280oC, 2800 kPa, WHSV = 2 to 20 hr-1


24

Diffusional Considerations

kobs = k

= R(k/D)1/2

= f (

Then, from Haag et al.,

= tanh R(k/D)1/2

and kH ~ alpha (hexane cracking activity)

Ref: W. O. Haag, R. M. Lago, and P. B. Weisz, Trans. Faraday Soc. pp 317-330 (1981)

ZSM-5 Crystal as a flat plate

25

Transalkylation of EB to DEB

Crystal R,m

Activity,kH

kDEB obs

hr-1

Selectiv.kDEB obs

kH

R(kDEB obs)1/2

X 105 kintrins

sec-1

R2 kintrins

cm2/sec

SCLA 0.025 1.5 60 34 1.7 1 2.8E-04 1.0E-13

SCMA 0.02 13.3 532 34 4.2 0.97 2.8E-04 5.9E-13

SCHA 0.08 70 1235 15 259 0.42 1.2E-04 5.0E-11

MCLA 0.12 1 38 34 7.1 0.95 2.6E-04 1.6E-12

MCMA 0.15 17.5 600 29 33.9 0.83 2.3E-04 4.4E-11

MCHA 0.15 58.3 706 10 368 0.31 8.6E-05 1.5E-10

LCLA 1.25 1.3 32.941 26 66.2 0.75 2.1E-04 2.3E-10

LCMA 1.4 6.7 158.82 20.1 162 0.57 1.6E-04 1.5E-09

LCHA 5.5 54.7 289.41 4.5 862 0.13 3.6E-05 1.8E-07

26

Effectiveness Factor Plot

Flat Plate

Ref: W. O. Haag, R. M. Lago, and P. B. Weisz, Trans. Faraday Soc. Pp 317-330 (1981)

27

R(k)1/2

, C

ryst

al E

ffect

iven

ess

Fact

or

Effectiveness Factor Plot : DEB Production over ZSM-5 via Transalkylation

0.1

1.0

1 10 100 1000

0.2

0.3

0.4

0.5

0.7

T = 350oC

28

Transalkylation of EB and Xylene to DMEB

Crystal R,m

Activity,kH

kDMEB obs

hr-1

Selectiv.kDMEBobs

kH

R(kDMEBobs)1/2 kintrins R2 kintrins

cm2/sec

SCLA 0.025 1.5 6 4.0 0.06 1.00 1.7E-04 1.0E-15

SCMA 0.02 13.3 53.2 4.0 0.15 1.00 1.5E-03 5.9E-15

SCHA 0.08 70 72.2 1.3 5.20 0.32 4.5E-01 2.9E-11

MCLA 0.12 1 3.8 3.8 0.23 0.95 1.1E-04 1.6E-14

MCMA 0.15 17.5 60.0 3.4 1.16 0.86 1.9E-03 4.4E-13

MCHA 0.15 58.3 57.1 0.9 10.20 0.22 5.7E-01 1.3E-10

LCLA 1.25 1.3 3.3 2.5 2.27 0.63 1.4E-04 2.3E-12

LCMA 1.4 6.7 8.2 1.2 2.90 0.59 3.8E-03 7.5E-11

LCHA 5.5 54.7 8.9 0.16 29.59 0.04 1.6E-02 4.9E-09

29

R(k)1/2

Effectiveness Factor Plot : DMEB Production over ZSM-5 via Transalkylation

T = 350oC

0.01

0.10

1.00

0.01 0.10 1.00 10.00 100.00

, C

ryst

al E

ffect

iven

ess

Fact

or

30

Effectiveness Factor Plot : vs R(k)1/2

for DEB and DMEB

R(k)1/2

=

tanh

Dimethylethyl

benzene (DMEB)

Diethylbenzene (DEB)

0.01

0.10

1.00

0.01 0.10 1.00 10.00 100.00 1000.00

T = 350oC

31

Determination of DiffusionCoefficient, D for DEB and DMEB

Since, = tanh and R(k/D)1/2

If we know and R and k,

then we can calculate D for Diethylbenzene (DEB) production at T = 350oC

For large values of = 1 then

For = 0.31; R2kintrins = 1.5x10-10 cm2/sec; kintrins = 8.6x10-5/sec,

DDEB = 1.5 x 10-11 cm2/sec

Similarly,

DDMEB = 1.0 x 10-11 cm2/sec

32

Aromatics Diffusion in ZSM-5Comparison with Other Studies

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

250 300 350 400 450 500 550 600 650

Temperature, oK

Diff

usio

n C

oeffi

cien

t, cm

2 /sec Para-Xylene

Ortho-XylenePara-Ethyltoluene2,Methyl NaphthaleneDimethylethylbenzene (this study)Diethylbenzene (this study)

Refs: S. F. Garcia and P. B. Weisz, J. Catal. 121, 294 (1990);S. F. Garcia and P. B. Weisz, J. Catal. 142, 692 (1993) and others

33

Impact of Temperature on DEB and DMEB Diffusion Coefficients in ZSM-5

Diffusion Coefficient, cm2/sec350oC 370oC 390oC

DDEB 1.5 x 10-11 2.1 x 10-11 2.4 x 10-11

DDMEB 1.0 x 10-11 1.3 x 10-11 1.6 x 10-11

• Temperature has small effect on the Diffusion Coefficients of DEB and DMEB in ZSM-5

• Ea – activation energy of intracrystalline Diffusion Coefficients, for bothDEB and DMEB are less than 1.0 kcal/mole – consistent with other studiesby Weisz et al.

34

Conclusions

• We have evaluated the kinetics and diffusion characteristics associated with the formation of C10 aromatics in the isomerization of mixed ethylbenzene and xylene feeds (EB:Xylene) over ZSM-5 catalysts of differing crystal sizes and activities (’s)

• The formation of diethylbenzene (DEB) and dimethylethylbenzene (DMEB) are controlled by intracrystalline diffusion rather than transition state (spatio-) selectivity in the ZSM-5 channels and channel intersections

• The intracrystalline diffusivity of DMEB is approximately 66% of that of DEB

• Intracrystalline diffusivities for both DEB and DMEB are vritually independent of temperature

• The classical Thiele Modulus – Effectiveness Factor analysis is applicable to diffusion of alkylated aromatics in ZSM-5

35

Back-up

36

Ethylbenzene (EB) Conversion is First Order in ZSM-5 Isomerization

0.60 0.05 0.1 0.15 0.2

0.7

0.8

0.9

1.0

1/ WHSV

Frac

tion

of E

thyl

benz

ene

(EB

) Rem

aini

ng

37

Para-Xylene Can be Produced Via Equilibrium or Selective Processes

+2

+2

Xylene Isomerization Toluene Disproportionation

XylenesAt

Equilibrium

SelectiveProcesses

EquilibriumProcesses

Transalkylation

Selective TolueneDisproportionation

22% Ortho- 54% Meta- 24% Para-

Para- >> 24%

Para- ~ 24%

Para- ~ 24%

All ProcessesRequire

Separation

+ 2

38

The Role of Shape Selective Zeolites in C8 Aromatic Reactions

Reactant Selectivity (Hydrodealkylation)

Product or Isomer Selectivity (Selective Toluene Disproportionation)

+ H 2 +

+2

Ref: S. Csicsery, J Catal 23, 124 (1971)

5.8 Å6.8 Å 6.8 Å

Metal

Transition State (or Spatio-) Selectivity (C8 – C10 Aromatics Disproportionation)

+very low

yields+ +Bulky

isomerization of mixed xylene – ethylbenzene feeds over ... · pdf filecumene phenol,...

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