15 Dec, 2005 Presented in CHEMCON 2005 1

Study of Alkylation of Diphenyl Oxide with Benzyl Alcohol over HZSM-5 as Catalyst

Ranjeet Kumar, D. Venkatesan and S. Sengupta*Department of Chemical Engineering

IIT Kharagpur- 721302

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ALKYLATION REACTIONS

Used in Pharmaceuticals, Agrochemicals, Resins, Additives, Polymerization inhibitors, Antioxidants, etc

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Catalysts used for alkylation of aromatics

Friedel-Craft catalysts- AlCl3 , BF3 ,

H3PO4, H2SO4

Super acid catalysts Cation-exchange resins Zeolite type catalysts

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Problems with Friedel-Craft alkylation:---

---heavy environmental pollution due to waste generation ---troublesome product recovery & purification, ---catalysts cannot be reused, ---lower stability at higher temperature ---poor selectivity ---use of expensive acid-resistant material of construction

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Cation exchange resins

lower stability at higher temperature low activity and selectivity

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Zeolites as an alternative

Molecular-sieve properties -Selective adsorption of reaction product

-Displacement of equilibrium in chemical transform

Higher surface area & absorption capacity

These increase rate of Hydrogen transfer thus reduce unsaturation

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Fig 3.1 Schematic Diagram of Experimental Set-Up

M Motor C Condenser R Glass Reactor T Thermometer OB Oil Bath TI Temperature Indicator / Controller

Experimental Set-upFully baffled glass reactor with electrically heated oil bathFully baffled glass reactor with electrically heated oil bath

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Experimental procedure

diphenyl oxide benzyl alcohol. a speed of agitation of 1100 rpm at 1200C for 3hrs catalyst loading was 100kg/m3 of

total reactants.

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Method of Analysis

gas chromatogram HPLC and TLC two peaks on HPLC chromatogram

and two spots in TLC plate So an isomeric mixture (ortho and

para) of benzyl-diphenyl-oxide in reaction product.

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Chemical equation

(B) (A)HZ

SM

-5

12

00C

benzyl alcohol is protonated and the carbocation formed, then it combines with diphenyloxide in ortho and para position to give two isomericmixtures as products

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Kinetic Studies

solid –liquid reaction involving the transfer of benzyl alcohol (A) and diphenyl oxide (B) to the surface of the catalyst particles

followed by intraparticle diffusion, adsorption, surface reactions and desorption of the products

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Kinetic Studies

To develop a true kinetic model Experimental analyses were done

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Kinetic Studies

Effect of Speed of agitation on conversion of Benzyl alcohol

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Co

nve

rsio

n %

Time (sec)

700 rpm 900 rpm 1100 rpm 1300 rpm

Absence of solid-liq MT resistance as stirring wentbeyond 1100rpm

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Kinetic Studies

Effect of particle size on conversion of benzyl alcohol

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Con

vers

ion

%

Time(sec)

1.5 mm 1.33 mm 0.85 mm

The conversion remained practically same within therange of the catalyst sizes.So intraparticle mass transferresistance is insignificant & this support rxn as surfacecontrolled.

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Kinetic Studies

Effect of catalyst loading on conversion of benzyl alcohol

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Co

nve

rsio

n %

Time (sec)

50 Kg/m3

80 Kg/m3

100 Kg/m3

120 Kg/m3 Due to increase inavailable acid sites,conversion increaseslinearly with increase In catalyst loading.

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Kinetic Studies

Plot of initial rate of reaction (r0i) against catalyst loading (w)

0 20 40 60 80 100 1200.00000

0.00001

0.00002

0.00003

0.00004

0.00005

0.00006

Initi

al r

ate

(km

ol/m

3 .s)

Catalyst loading( kg/m3)

Due to increase in available acid sites,initial rate of reactionincreases linearly withincrease in catalystloading.

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Kinetic Studies

Effect of mole ratio on conversion of Benzyl alcohol

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Co

nve

rsio

n %

Time (sec)

2 : 1 3 : 1 5 : 1 7 : 1 Mole ratio is diphenyl oxide

to benzyl alcohol, no effecton diphenyl oxide conversion,whereas benzyl Alcoholconversion increased Withincrease in ratio

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Kinetic Studies

Effect of temperatures on conversion of Benzyl alcohol

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Co

nve

rsio

n %

Time (sec)

373o K

383o K

393o K

403o K

Clearly, conversionincreases with increasein temperature

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Kinetic Studies

Kinetic plots for various temperatures

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5000 10000 15000

Time (sec)

-ln (1

-XA)

373 K

383 K

393 K

403 K

Rate constants, k1 =2.26*10-5 (373K),2.93*10-5 (383K),3.689*10-5 (393K),4.265*10-5 (403K), s-1

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Kinetic Studies

Arrhenius plot

0.00245 0.00250 0.00255 0.00260 0.00265 0.00270

-10.7

-10.6

-10.5

-10.4

-10.3

-10.2

-10.1

-10.0

ln (

K)

1/T (K-1)

From the slope of this graphApparent activation energy was calculated, Ea=26.74KJ/molHigh value of Ea shows that rxnis kinetically controlled & occursat the surface of catalyst

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Kinetic Studies

First order reaction plots: effect of catalyst loading

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

-ln(1

-XA)

Time(sec)

50 kg/m3

80 kg/m3

100 kg/m3

120 kg/m3

plot of –ln (1-XA) vs. time was made for this reaction at various catalysts loading. All of these plots show straight lines passing through the origin. Their linearity confirms the first order reaction

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Kinetic Studies

Effect of reuse of catalyst

0 2000 4000 6000 8000 10000 120000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Co

nve

rsio

n %

Time (sec)

Fresh

1st reuse

2nd reuse

3rd reuse

Reusability of catalyst…Filtered from rxn mixture& heated at 550oC to burnoff the reactants & productsfrom pores. Conversion of Benzyl alcoholbecame 31.82 to 18.77% from fresh to 1st reuse

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CONCLUSIONS

Kinetics of alkylation of diphenyl oxide with benzyl alcohol catalysed by HZSM-5 was established. Reaction is pseudo 1st order.

Internal mass transfer resistance was negligible External mass transfer can be eliminated by adjusting

proper stirring rate. Activation energy is 26.74 kj/mol Catalyst is reusable.

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References

1. H.Scott Fogler., Elements of Chemical Reaction Engineering (3rd edition). 2. Smith J.M., Van Ness H.C and Abbott M.M., Introduction to Chemical Engineering

Thermodynamics (Fifth edition). 3. R. T. Morrison and Robert Neilson Boyd., Organic chemistry (6th edition). 4. S.M.Mukherji and S.P.Singh., Reaction mechanism in organic chemistry (3rd

edition). 5.G.D.Yadav and S. Sengupta, Friedel-Crafts Alkylation of Diphenyl oxide with

Benzyl chloride, Organic process research &Development .6, 252-262, (2002). 6. Bhat. Y. S. and Halgeri. A. B Kinetics of toluene alkylation With methanol on

HZSM-8 zeolite catalyst, Ind.Eng.Chem.Res. Res., 28, 894-899, (1989). 7.Chandavar K. H, et al. Alkylation of benzene to propyl and isopropyl benzenes

over ZSM-5 zeolite. J.Chem.technol. J. Chem. 34,165-173, (1984). 8.Chandavar. K. H., Kulkarni. S. B and Ratnaswami. P., Alkylation of benzene with

ethanol over ZSM-5 zeolites. Appl.cata. 4, 287-295, (1982). 9.Chandra. K. G and Sharma M. M., Alkylation of phenol with MTBE and other tert-

butyl ethers, Cation exchange resins as catalyst.Catal.lett, 19, 309-317, (1993). 10.Chaudhuri, B and Sharma, M. M., Alkylation of phenol with α-methylstyrene,

propylene, butenes, isoamylene, I-octene, and diisobutyle heterogeneous vs homogeneous catalysts. Ind .Eng.Chem.Res. 30, 227-231, (1991).

15 Dec, 2005 Presented in CHEMCON 2005 25

THANKS!