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Indian Journal of Chemical TechnologyVol. 3 November 2001, pp. 469-472

Isopropylation of naphthalene over large pore zeoliteslshwarya Mathew, Smita Sabneb, S Mayadevib*, SA Pardhyb S Sivasankerb

Department of Applied Chemistry, Cochin University of Science and Technology, Cochin 682 022, Indiab National Chemical Laboratory, Pune 411 008, India

Received 22 November 2 ; revised 3 May 2 1; accepted 8 June 2 1Isopropylation of naphthalene with isopropanol (IPA) proceeds at 200C over the large pore zeolites HY, H-

Mordenite and REY in the presence of N2. Over H ~ , conversion is more in N2 than when cyclohexane is used as solvent orin absence of N2. Conversions and selectivities to diisopropyl naphthalenes fall in the sequence > REY > HM > HY, but2,6: 2,7 ratio is greatest with HM. With conversion is maximum at 200C, and increasing the IPA : naphthalene ratioleads to deactivation of the catalyst.

Isopropylation of naphthalene to produce 2,6-diisopropylnaphthalene (2,6-DIPN) is a commerciallyimportant reaction. 2,6-DIPN is an important intermediate for making advanced new polymer materials.Isopropylation of naphthalene has been studied inboth the liquid I J and gas45 phases over zeolitecatalysts, with the aim of achieving high yield of 2,6-DIPN. Different alkylating agents, such as propene6,isopropanoe and isopropyl bromide 1 have been usedfor this reaction over zeolite catalysts. Song andKirbl reported that the 2,6-/2,7-DIPN ratio wasdependent on the alkylating agent used. Theyobtained a 2,6-/2,7-ratio between 2 and 3 usingisopropanoUpropene, whereas an earlier study7reported 2,6- and 2,7- in equal proportions whenisopropyl bromide was used. High ~ - M I P N ~ - m o n o isopropylnaphthalene; 2-isopropylnaphthalene) selectivity was observed for isopropylation of naphthalenewhen HM (H-Mordenite) was used as the catalyst. Ithas been shown by several research groups1368 that2,6-DIPN can be obtained with high selectivities overHM by alkylation of naphthalene with propene and 2-propanol. The preferential formation of 2,6-DIPNwithin the HM framework may be due to thedifference in diffusion kinetics between thedialkylnaphthalenes9 Song and co-workers 10- 2explained the improvement in selectivity ondealumination of mordenite to be due to reducedcontribution of external acid sites and reduction of*For correspondence (Fax: +91-(0)20-589 3041.E-mail : maya@che.ncl.res.in)

unit cell dimensions 3' 4 Poisoning of external acidsites by silylation7, by adsorption of water 3, and bydeposition of cerium oxide 13 , was found to enhancethe selectivity of HM for 2,6-DIPN formation.

Though considerable literature is available on theisopropylation of naphthalene over zeolite catalysts,studies using isopropyl alcohol or bromide asalkylating agents have been carried out in thepresence of an organic solvent1367 2 The study ofalkylation in the absence of organic solvents is ofinterest as it reduces the load on down streamseparation. The present work has been undertaken tostudy the isopropylation of naphthalene on differentzeolites in the absence of organic solvent. Activity ofdifferent zeolites has been compared for theisopropylation reaction and the selectivity for 2,6-DIPN. The influences of reaction parameters on theisopropylation reaction have also been studied.Experimental Procedure

The N ~ - f o r m s of zeolites beta ~ ) . Y andmordenite (M) were obtained from PQ Corp., USA.The zeolites were converted into the H-forrn bycalcination at 450C for 4h. The calcined powderswere pressed into pellets, crushed and sieved to obtainparticles of size, 0.8 - 2 mm. A commercial sample ofREY (15 RE20 3) was also used in the studies. Thesized zeolite particles were activated at 450C for 4hbefore use. XRD patterns of the zeolites matched wellwith their standard patterns. Compositional analysesof the zeolites were done by chemical methods.

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470 INDIAN J. CHEM. TECHNOL., NOVEMBER 2001

Isopropylation experiments were carried out inbatch mode in a 300 mL stainless steel Parr autoclave.The catalyst lg) enclosed in a stainless steel wiremesh was attached to the stirrer blades to ensure goodcontact with reacting fluids . The reactor was loadedwith the required amount of naphthalene andisopropy lalcohol (IPA), and filled with nitrogen to therequired pressure. After carrying out the reaction forthe desired time, the reactor and its contents werecooled, the product mixture dissolved in diethyl ether,and ana lyzed by GC (Perkin-Elmer Auto System XL;column: Ultra 2 (cross linked 5 % PHME siloxane),film thickness: 0.52 Jlm, length: 25 m; i.d .: 0.32 mm)with FID detector.Results a nd Discussion

The isopropylation of naphthalene was carried outover H ~ , HY, REY and HM . The studies were alsocarried out at different process conditions (temperature between 175 and 225C, pressures (with N2 of15 to 90 bars, IPA/naphthalene mol ratios of 1 to 3and different periods of time (1.5 - 9h)) in the case of

H ~ .Isopropylation of naphthalene produces first the a-

and ~ i s o p r o p y l n a p h t h l e n e s (1- and 2-IPN). The twoisomers undergo further alkylation to produce thedialkylnaphthalenes. The isopropanol rapidly dehydrates into propene, which is the major alkylatingagent. The various isopropylnaphthalenes that are

formed in the reaction are shown in Scheme IInterconversions between the various isomers throughisomerization have not been shown in the scheme.

omparison of activities of zeolitesThe results of the isopropylation of naphthalenewith IPA at simi lar reaction conditions are presented

in Table 2. The zeolites may be arranged in thefo llowing orders based on their performance w.r.t.naphthalene conversion, diisopropylnaphthalene(DIPN) selectivity and 2,6-/2,7-DIPN ratio.

H ~ > REY > HM > HY (conversion; DIPN selectivity)HM > > HY > REY (2,6-/2,7-DIPN)

Naphthalene conversion is the highest for H ~ andREY followed by HM. The lower conversion overHY is probably due to its possessing weaker acidity as~ ~ 0 000 / 1.4-DrPN 1.5-DIPN 1.8-DIPNy I-lPN ~ r i f ~ ~ ; O O ~~ 0 0 ( 1.2-DIPN 1.3-DIPN 1.6-DIPN 1.7-D PN

2- IPN _pg{W2,3-DIPN 2.6-DIPN 2.7-DIPN

Scheme 1

Table I--Composition and surface area of the zeolites

Zeolite

HMHY

REY

Zeo lite Si/AI Unit cell composition Ss Tm2/g)15.49 HJ_s Na

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MATHEW eta / : ISOPROPYLATION OF NAPHTHALENE 471

a result of its high AI content. Due to the presence ofRE-ions, REY possesses stronger acidity than HY.The high conversion observed over H ~ can beattributed to a combination of two factors; the 3-Dchannel system made up of twelve-membered ringsenabling rapid diffusion of the reactant and productmolecules and the strong acidity arising from its largeSi/AI ratio. Even though one would expect HM topossess strong acid sites as in H ~ . its activity is lowerdue to its unidimensional pores (pore dimensions:

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - ~- - Naphthalene Conversion- - MIPN Yieldl

60

- -

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