Shape-selective alkylation of naphthalene with isopropanol over mordenite catalysts

MICROPOROUS MATERIALS ELSEVIER

Microporous Materials 2 (1994) 467476

Shape-selective alkylation of naphthalene with isopropanol over mordenite catalysts Chunshan Song*, Stephen Kirby Fuel Science Program, Department of Materials Science and Engineering, The Pennsylvania State University, 209 Academic Projects Building, University Park, PA 16802, USA (Received 13 November 1993; accepted 13 March 1994)

Abstract

Naphthalene alkylation with isopropanol was studied at 250°C using several proton-form mordenites (HM) and Y-zeolites. HM catalysts afforded 2-isopropylnaphthalene (ZIPN) as the dominant product, whereas the Y-zeolites (HY and LaHY) gave l-IPN as a major product. HM displayed better selectivity to 2-IPN and 2,6-diisopropylnaphthalene (2,6-DIPN), although HY showed higher activity for naphthalene conversion. HM catalysts with SiOJA1203 ratios of 20-35 appear to be effective for shape-selective synthesis of 2-IPN and 2,6-DIPN. These catalysts displayed over 73% /&selectivity to 2-IPN among the two IPN isomers, and over 65% /?,/?‘-selectivity to the desired 2,6-DIPN among all DIPN isomers with 2,6-DIPN/2,7-DIPN ratios of about 3. The isopropanol-tonaphthalene ratios and the solvent type are also influential for both activity and selectivity of mordenite catalysts. Key words: Naphthalene;

Alkylation;

Isopropanol;

Mordenite; Catalyst; Shape selectivity

1. Introduction Shape-selective catalysis was first reported over thirty years ago by Weisz et al. [ 1,2] using zeolites A and X. About twenty-five years ago, Venuto and Landis published their seminal paper on molecular sieve catalysis in synthetic organic chemistry [3] and reported their own work on selective alkylation of benzene and alkylbenzenes using crystalline aluminosilicates [4,5]. Since these pioneering studies reported in the 196Os, shape-selective catalysis has made great strides, and has led to the development of many industrial processes. The remarkable progresses in the fundamental chemistry and industrial applications of zeolite catalysis in the past three decades have been reviewed in

* Corresponding author. 0927-6513/94/%7.00 0 1994Elsevier Science B.V. All rights reserved SSDZO927-6513(94)00024-P

several recent publications [6-l 11. As Weisz pointed out [6], the unique role and purpose of a catalyst are to provide selectivity to direct the chemical transformation along a very specific, desired path. What makes zeolites unique is that their pores are uniform in size and that they are in the same size range as relatively small molecules [ 111. There are three types of shape selectivity involved in zeolite catalysis [ 71. The first is reactant selectivity occurring with reactions of mixed feedstocks containing molecules with different sizes or shapes. The second is product selectivity where only some of the products formed within the pores have the proper dimensions for out-of-pore diffusions. The third is restricted transition-state selectivity that occurs when reactions are prevented because the corresponding transition state would require more space than available in the cavities [7,91.

468

C. Song, S. Kirbylikficroporous

Materials2

As a part of our effort to develop valueadded chemicals from polyaromatic hydrocarbons [ 12,131, the present study is concerned with selective alkylation of naphthalene with isopropanol. Many high-value aromatic chemicals and the important monomers from one- to four-membered ring aromatic compounds for advanced aromatic polymer materials and engineering plastics have been discussed in our recent review [ 121. The key to the large-volume application of these materials (as fibers, films, resins, and engineering plastics) is the development of highly efficient catalytic processes for making the desired monomers. In particular, 2,6_dialkylnaphthalene (2,6-DAN) has recently become a very important building block for advanced polymer materials such as poly(ethylene naphthalate) (PEN), poly(butylene naphthalate) (PBN), and liquid crystalline polymers (LCP) [ 121. Scheme 1 shows the structures of some advanced polymer materials containing naphthalene in the main chain. The monomers for these advanced polymer materials can be prepared through shape-selective synthesis of 2,6-DAN. Selective alkylation of benzene and alkylbenzenes over various zeolites has been studied extensively since the 196Os, as summarized in many reports [4-10,14,15]. However, alkylation of twomembered ring aromatics such as naphthalene [ 16- 181 and biphenyl [ 19,201 received relatively little attention until recently. Due to the need for

(1994) 447-476

monomers for making the advanced polymer materials shown in Scheme 1, /?-selective naphthalene alkylation has become an important subject. At the onset of our work [ 13,211, literature information on shape-selective alkylation of naphthalene was very limited [ 16,171. On the basis of benzene alkylation processes, several methods are possible for naphthalene alkylation. However, there is a difficult problem with the selectivity in positioning the alkyl group on the ring, because the number of dialkylnaphthalene isomers (ten) is much larger than that of dialkylbenzene (three) [21]. One way to increase the /?-selectivity of naphthalene alkylation is to use a bulky substituent (e.g., isopropyl instead of methyl), as suggested by earlier work of Olah and Olah [22] on Friedel-Crafts reaction using Al&. For isopropylation of biphenyl, Lee et al. [ 191 and Sugi et al. [20] demonstrated that synthetic mordenites behave as shape-selective catalysts. Recently, Katayama et al. [ 171 and Felhnan et al. [23] have described shape-selective naphthalene isopropylation over mordenites. It should be noted that propylene was used as the alkylating agent in the prior studies [ 17,19,23]. However, isopropanol was used as the alkylating agent in the present work. From both a practical and a fundamental point of view it is of interest to examine naphthalene alkylation with isopropanol. This paper reports our preliminary results on the selective

Polyester fibers, films, resins and engineering plastics

Poly(ethylene naphthalate) (PEN)/Teijin, Amoco

Poly(butylene naphthalate) (PBN)/Teijin

Thermotropic polyester liquid crystalline polymers (LCPs)

+-@Q+&J; &3-Q

Hoe&t

Celanese’s Vectra LCP

Hoechst Celanese’s LCP

Scheme 1. Structures

of some naphthalene-based

advanced

polymer

materials.

469

C. Song, S. Kirby/Microporous Materials 2 (1994) 447-476

naphthalene alkylation with isopropanol to produce 2-isopropylnaphthalene (2-IPN) and 2,6-diisopropylnaphthalene (2,6-DIPN) using Hmordenite and Y-zeolite catalysts.

2. Experimental 2.1. Catalysts and reaction Table 1 shows the properties of the catalysts. Three H-mordenites (HM) with different molar ratios of SiOZ to Al,O, were prepared by heat treatment of three commercial ammonium mordenite samples. Hydrogen-Y zeolite (HY) and a La ion-exchanged Y zeolite (LaHY) were prepared according to the method described in a previous paper [ 241. Naphthalene, isopropanol, decalin, and 1,3,5_trimethylbenzene (TrMB) were reagentgrade chemicals of highest commercially available purity, and were used as received. In a typical run, about 4 g (31 mmol) of naphthalene, 0.5 g of a catalyst, 4 ml of decalin or TrMB as solvent, and a given amount of isopropanol were transferred into a 25 ml tubing bomb microreactor. The reactor was then sealed, flushed with Nz several times and then pressurized with N, to 0.7 MPa at room temperature. The reactions were conducted by submerging the reactor in a fluidized sand bath preheated to 250°C with continuous shaking of the horizontal reactor tube in the vertical direction (about 200 strokes per minute) for a given time period. After reaction, the reactor was quenched in a water bath.

2.2. Product analysis

The contents of the reactor were washed out with acetone and filtered on a membrane of 0.45 pm pore size. Liquid products were identified by capillary gas chromatography-mass spectrometry (GC-MS) on a HP 5890GC5971MSD system, and quantified by capillary GC on a Perkin-Elmer 8500 gas chromatograph equipped with a flame ionization detector. The columns used for both GC-MS and GC were identical: 30 m x 0.25 mm I.D. fused silica capillary column coated with 100% phenyhnethylpolysiloxane (DB- 17) with a film thickness of 0.25 l.ur~.The gas chromatograph in both instruments was operated in the split injection mode using helium as carrier gas, and temperatureprogrammed after injection: 5 min hold at 40°C heating to 280°C at 4”C/min, followed by a 10 min hold. Because most DIPN isomers are not commercially available for calibration, their GC-flame ionization detection (FID) response factors are assumed to be the same on the basis of weight. This assumption may introduce a few percentage error in quantification. However, it has been shown that the isomers of methylnaphthalene and dimethylnaphthalene have very similar FID response factors on a weight basis [25]. The confidence level of the data reported here is 90-95%.

3. Results and discussion

Fig. 1 presents a representative GC-MS total ion chromatogram of the products from naphtha-

Table 1 Properties of mordenite and Y-zeolite catalysts Catalyst

HM20A HM30A HML8 HY LaHYb

Precursor type

NH,-M NH,-M NH,-M NH,-Y NH.,-Y

Final thermal treatment’ (“C)

SiOJAl,O, molar ratio

SUrfaCe

area (m’/g)

Micropore volume (cm3/g)

Mesopore volume (cm3/g)

515 515 515 500 500

20 35 17 4.8 4.6

600 600 480 646 662

0.207 0.167 ND ND ND

0.110 0.126 ND ND ND

’ In air for 4 h. b By ion-exchange method. The La content determined by ICP-AES is 8.4 wt% as La,O,.

C. Song, S. KirbyJMicroporous Materials 2 (1994) 467-476

470 Abundance

a? 00

2e+07-

1.8e+07

-

1.6e+07

-

1.4e+07

-

1.2e+07

-

le+07

03 00

-

>rcox

8000000-

00

6000000-

+a@$

4000000-

2000000-

h

1

0 Time

->

!

I

rU] il ‘3

1

1’

35.00

YlA

1.

40.00

4’

i'

I

*I

,

45.00

T

.,.

,-

,

_,

,

50.00

Fig. 1. W-MS profile of products from naphthalene alkylation with isopropanol over HM20A catalyst using decalin at 250°C for 2 h (C,H,OH/naphthalene molar ratio = 0.5).

lene alkylation over HM20A catalyst using isopropanol as alkylating agent and decalin as solvent at 250°C for 2 h. Our experience shows that it is easy to separate l- and 2-alkylnaphthalene with most commercial capillary columns, but careful selection of coating phase and column dimensions, as well as GC oven temperature program are necessary for good separation of 2,6- and 2,7-DAN. It should be mentioned that 2,6- and 2,7-DAN can co-elute on some widely used capillary columns such as those coated with dimethylpolysiloxane, but they resolve on the column coated with phenylmethylpolysiloxane under the programmed conditions used in this work, as shown in Fig. 1. 3.1.

Effect

of catalyst type

Table 2 shows the effect of zeolite type on the catalytic isopropylation. HY and LaHY gave 1-isopropylnaphthalene ( l-IPN) as a major pro-

duct, whereas H-mordenites (HML8, HM20A, HM30A) afforded more 2-IPN. While the conversion with each catalyst is also dependent upon the ratio of isopropanol to naphthalene and the solvent, HY generally showed higher activity for naphthalene conversion. Regardless of which solvent was used, the two Y-zeolite catalysts promoted the formation of l-IPN (> 60%). On the other hand, H-mordenites generally displayed over 67% /?-selectivity to 2-IPN among the two IPN isomers, and over 66% /J-selectivity to 2,6-DIPN among all DIPN isomers. Acid-catalyzed alkylation is one type of the Friedel-Crafts substitution reactions. Naphthalene isopropylation over an acidic catalyst can proceed through two different pathways, one via l-IPN and the other through 2-IPN, as shown in Scheme 2. Zeolites can catalyze such reactions because of the strong acidity of their protons. It is known that the electron density of the l-position

C. Song, S. Kirby/Microporous Materials 2 (1994) 467-476

471

Table 2 Effect of zeolite type on naphthalene isopropylation at 250°C for 2 h Conversion (mol-%)

Condition

Other DIPN

p (2-IPN)

P*P (2,6-DIPN)

1.5 0.7 8.0

3.4 0.9 2.6

30.9 32.7 75.7

29.9 42.9 75.4

30.3 20.3 17.3

3.9 8.3 8.7

1.2 3.8 4.4

66.9 76.9 80.1

76.4 68.4 66.5

59.9 28.5 9.6

1.5 5.1 10.7

8.0 2.0 5.2

33.8 69.3 88.6

16.0 70.8 67.0

2-IPN

I-IPN

21.5 15.8 7.1

29.4 31.0 67.7

65.7 63.8 21.7

1.O 1.0 1.1

4.0 12.9 15.1

61.4 67.6 69.6

0.5 0.6 0.6

38.2 11.3 27.6

30.5 64.4 14.5

Zeolite

Solvent

ROH/ naphthalene

HY LaHY HM20A

Decalin Decalin Decalin

1.4 1.3 1.3

HMLI HM20A HM30A

Decalin Decalin Decalin

HY HMLS HM3OA

TrMB TrMB TrMB

Selectivity (%)

Product distribution (%) 2,6-DIPN

Scheme 3. Selective isopropylation pore of H-mordenite catalyst.

Scheme 2. peaction pathways for naphthalene alkylation with isopropanol over acidic catalysts.

(0.362) of naphthalene is higher than that of the 2-position (0.138) [26,27]. Because of the electrophilic nature of the alkylation over acidic catalyst, substitution at the l-position of naphthalene Therefore, more kinetically favored. is l-alkylnaphthalene will be formed on conventional acidic catalysts. This is the case with Y-zeolites including HY and LaHY (Table 2) whose pores are large enough to facilitate alkylation on the electron-rich l-position of naphthalene. However, the transition state leading to l-IPN formation gives rise to considerable steric hindrance in the elliptical and narrower pore channel of mordenites. As a result, HM catalysts greatly suppress the formation of l-IPN and its subsequent alkylation in the channel of mordenites, as can be seen from Table 2. Scheme 3 gives a conceptual explanation of the shape-selective isopropylation of naphthalene inside the elliptical pore of a mordenite catalyst. The l-IPN product with mordenitesis probably

of naphthalene inside the

due to external surface. On the other hand, l-IPN can isomerize into thermodynamically more stable 2-IPN. Isomerization of 1-alkylnaphthalene is known to occur with acid catalysts such as AlCl, at low temperature [22]. This isomerization ean also occur with zeolitic catalysts under the conditions employed, as depicted in Scheme 2. 3.2. E#ect of SiO,JAI,O, ratio of mordenites With an attempt to examine the effect of dealumination, we compared three H-mordenites with SiO,/Al,OJ molar ratios ranging from 17 to 35. It is the substitution of trivalent aluminum for tetravalent silicon that produces the negatively charged frameworks in zeolites [ 111. Therefore, the zeolite acidity is associated with the aluminum ions. The removal of Al from mordenites also affects the channel structure, increasing the mesopore volume and thus the diffusivity of reactant and product molecules to and from active sites. Therefore, dealumination of mordenites is generally accompanied by a decrease in the number of acidic sites, an increase in acid strength, and increased diffusiv-

C. Song, S. KirbylMicroporous Materials 2 (1994) 467476

472

ity. It is not easy to predict the combined effect. Table 2 suggests that the H-mordenites with relatively larger SiOJA1,03 ratio exhibits higher activity and higher &selectivity when decalin was used as the solvent. Both naphthalene conversion and /?-selectivity increased in the order of HML8 < HM20A < HM30A. This trend is qualitatively in good agreement with the recent findings of Lee et al. [19], who observed the enhanced biphenyl isopropylation upon dealumination of mordenites. They also proposed an interesting concept of reactant-assisted shape selectivity, where biphenyl diffuses through the relatively large channel (6.7 x 7.0 A) but propylene fills the sidepocket channel (2.9 x 5.7 A) of mordenite.

(1.3) seems to give slightly higher selectivity to 2,6-DIPN. 3.4. ESf^t of solvent and reaction time As can be seen from Table 4, increasing the reaction time at 250°C from 2 to 4 h (with C3H,0H/C,,,Hs ratios at about 0.5 and 1.0) increased the conversion over HM20A and selectivity to 2,6-DIPN. This is not surprising since a consecutive pathway is expected to lead to 2,6-DIPN (Scheme 2). As shown in Table 5, the nature of the solvent is also influential for both activity and selectivity of mordenite catalysts. For runs at 250°C for 4 h, replacing decalin with TrMB as solvent increased the naphthalene conversion and selectivity to 2-IPN, but decreased the selectivity to 2,6-DIPN. This trend was observed for runs with HM20A at two different C3H70H&,H8 molar ratios.

3.3. Eflect of isopropanol/naphthalene ratio It is also interesting to note the effect of isopropanol/naphthalene (C3H,0H/C10Hs) molar ratio from data in Table 3. Due to the sample availability, we used HM20A rather than HM30A for this part of the work. Although C3H,0H is the alkylating agent and the reaction stoichiometry for DIPN requires a C3H70H/C1,,H8 molar ratio of 2, Table 3 shows that increasing this ratio from 0.5 to 1.3 tends to lower the catalyst activity in view of decreased conversion. This indicates that using excess QH,OH results in fast deactivation of the active sites, which may be attributed to the passivation of active sites by the strong adsorption of either the excessive alcohol molecules or the water produced from the reaction of alcohol. On the other hand, higher C3H,0H/C10Hs molar ratio Table 3 Effect of ROH/naphthalene

3.5. p,j3’-Selectivity towards 2,6-DIPN While /?-selective alkylation can produce both 2,6- and 2,7-DIPN, the former (/?,/.I’)is the desired product [ 12,17,23]. Table 6 compares the shapeselectivity data for naphthalene isopropylation reported by four different groups including ours, over four mordenites with similar SiOz/A1203 ratios. In the presence of non-shape-selective catalysts such as silica-alumina, the highest percentage of 2,6-DIPN among all DIPN isomers at equilibrium is 39%, and the ratio of 2,6-DIPN to 2,7-DIPN at equilibrium is about 1.0 [23]. As can

ratio on alkylation with isopropanol over HMZOA at 250°C Conversion (mol-%)

Condition Solvent

ROH/ naphthalene

Tie

Decalin Decalin Decalin

0.5 1.0 1.3

2 2 2

TrMB TrMB

0.6 1.0

4 4

Product distribution (%)

Selectivity (%)

2-IPN

1-1PN

2,6-DIPN

Other DIPN

fl (2-IPN)

8>8 (2,6-DIPN)

20.0 12.9 7.1

67.3 67.6 67.7

16.6 20.3 21.7

8.1 8.3 8.0

4.3 3.8 2.6

80.2 76.9 75.7

65.3 68.4 75.4

25.3 20.0

72.5 70.4

13.9 16.6

9.4 9.7

4.1 3.3

83.9 81.0

69.6 74.2

(h)

C. Song, S. KirbyJMicroporous Materials 2 (1994) 467-476

413

Table 4 Effect of reaction time on naphthalene isopropylation over HMZOA at 250°C in decalin Conversion (mol-%)

Condition ROH/Naph

Time (h)

0.5 0.6

2 4

1.0 1.1

2 4

Selectivity (%)

Product distribution (%) 2-IPN

I-IPN

2,6-DIPN

Other DIPN

/I (2-IPN)

/l,B’ (2,6-DIPN)

20.0 20.5

67.3 66.0

16.6 20.1

8.1 10.1

4.3 2.2

80.2 16.1

65.3 82.0

12.9 10.7

67.6 66.0

20.3 23.6

8.3 8.6

3.8 1.8

16.9 73.7

68.4 82.0

Table 5 Effect of solvent on naphthalene alkylation with isopropanol over HMZOA at 250°C for 4 h Conversion (mol-%)

Condition Solvent

ROH/Naph

Decalin TrMB

0.6 0.6

Decalin TrMB

1.1 1.0

Selectivity (%)

Product distribution (%) I-IPN

l-IPN

2,6-DIPN

Other DIPN

/3 (2-IPN)

/I,/?’(2,6-DIPN)

20.5 25.3

66.0 12.5

20.1 13.9

10.1 9.4

2.2 4.1

76.7 83.9

82.0 69.6

10.7 20.0

66.0 70.4

23.6 16.6

8.6 9.1

1.8 3.3

13.1 81.0

82.0 14.2

be seen clearly from Table 6 and Fig. 1, in the naphthalene alkylation with isopropanol over the HM20A catalyst, we observed the preferential formation of 2,6-DIPN among all DIPN isomers, with /?,/I’-selectivity (65%) far exceeding the equilibrium value (39%). The 2,6-DIPN/2,7-DIPN ratio with HM20A is around 3, which is much higher than the corresponding ratio at thermodynamic equilibrium, 1.O (Table 6). The high shape selectivity to 2,6-DIPN observed for alkylation with isopropanol in this work is consistent with the findings of Katayama et al. [17] and Felhnan et al. [23] on the reaction with propylene over HM catalysts (Table 6). It is encouraging to note that the /I,/?‘-selectivity of naphthalene alkylation in this work and that claimed in the recent patent [23] reached the same level, with a 2,6-DIPN/2,7-DIPN ratio of around 3 (although different mordenites were used in different reaction systems with different alkylating agents). Comparison of our results with those of Katayama et al. [ 171 suggests that relative to the alkylation with propylene, alkylation with isopropanol under similar conditions can alford higher

j?,/3’-selectivity but lower naphthalene conversion. This trend has also been verified in a collateral research in this laboratory [28]. It is not easy to explain the higher 2,6-DIPN/2,7-DIPN ratio, although the higher /Iselectivity of HM catalysts towards 2-IPN has been rationalized (Scheme 3). While the recently published patent of Fellman et al. [23] contains detailed and important information, it provides no rationale for the high 2,6-DIPN/2,7-DIPN ratio with mordenites. In the present work, possible factors that contribute to the higher selectivity of 2,6-DIPN against 2,7-DIPN with the HM catalysts include the differences in their critical diameters, in their diffusion rates, and in the steric structures of the transition state leading to their formation. The difference in molecular diameter between 2,6- and 2,7-DIPN was not considered in the two recent studies, where the diameter of both compounds was reported to be 6.5 A [ 17,181. In the present study, however, an energy minimization on computer using PC-Model software reveals that there is small but definite difference in the critical diameter between 2,6- and 2,7-DIPN. Critical

25 25 25 21

SiOJAl,O,

comparison

7

Propylene Propylene Propylene

Isopropanol Propylene Propylene Isopropylbromide

Alkylating reagent

for naphthalene

’ /?,B-selectivity to 2,6-DIPN + 2,7-DIPN. b B,/?‘-selectivity to 2,6-DIPN among all DIPN ’ See Table 3.

HY Si02-Al,03 Si02-Al,O,

Reference catalyst

HMZOA HM HM7b HM3

H-Mordenite

Catalyst

Table 6 Shape selectivity

isomers.

24O”C/8 h 275°C 275°C

96.1 23.4 94.2

20.0 35.6 27.1 16.0

Naphalene conversion

over mordenites

25O”C/2 h 24O”C/2 h 275”C/O.5 h 2OO”C/24 h

Reaction temp./time

isopropylation

(%)

< 50.4 91.9 31.1

83.9 < 84.0 83.1 55.0

% IPN

49.6 8.1 51.5

12.4 16.0 16.4 34.0

% DIPN

63.8 73.6 75.9

87.1 75.7 92.1 80.0

% 2,6 + 2,7”

32.6 36.8 38.5

65.3 51.7 69.2 41.1

“/LzB Selectivityb

1.1 1.0 1.0

3.0 2.2 3.0 1.1

2961227 ratio

17 23 23

This work” 17 23 18

Ref.

n

C. Song, S. Kirby1Microporou.s Materials 2 (1994) 467-476

diameter is defined as the smallest diameter of a cylinder through which the molecule can pass without distortion. 2,6-DIPN has a more linear structure and a smaller critical diameter compared to 2,7-DIPN. Although the difference in critical diameter is within 1 A, it may lead to substantially higher diffusivity of 2,6-DIPN relative to that of 2,7-DIPN. This can account for, at least in part, the preferential formation of 2,6-DIPN over mordenite catalysts. Another factor that may also contribute to higher 2,6-DIPN/2,7-DIPN ratio with mordenite is the relative ease of transition-state formation for these two isomers. Since the isopropyl groups are attached to the different positions in 2,6- and 2,7-DIPN, different location of acidic sites or different steric configurations may be required for the formation of transition states. In this context, there is a possibility that mordenite may favor the formation of the transition state from 2-IPN and isopropanol which leads to 2,6-DIPN. Katayama et al. [ 171 also deduced that the activated complex for the production of 2,6-DIPN is formed more easily as compared to that for the formation of 2,7-DIPN over mordenite. Further study is needed to clarify these issues. The almost equimolar yields of 2,6- and 2,7-DIPN over Y zeolites (Table 6), imply that the cavity in HY zeolites is large enough to facilitate the formation of transition states for both isomers and their out-of-pore diffusion. It should be mentioned that Moreau et al. [ 181 recently carried out naphthalene alkylation with isopropylbromide over mordenites at 200°C for 1 to 24 h. They reported that H-mordenites promoted p-selective alkylation, but afforded almost equimolar yields of 2,6- and 2,7-DIPN. The selectivity data with both untreated and CVD-modified H-mordenites, however, are very similar to those obtained with non-shape selective Si02-A&O3 (for the run with propylene) [23], as also listed in Table 6 for comparison. Apparently, the alkylation with isopropanol or propylene over H-mordenites is distinctly different from that with isopropylbromide. 4. Conclusions For naphthalene alkylation with isopropanol at 25O”C, H-mordenites display higher P-selectivity

415

2-IPN and 2,6-DIPN, while Y-zeolites show higher activity for naphthalene conversion. Increasing the Si0,/A1203 ratio (the degree of dealumination) of the H-mordenite catalysts from 17 to 35 seems to increase catalyst activity and flselectivity. Using dealuminated H-mordenites (with Si02/A1203 ratios of 20-35) can achieve over 73% P-selectivity among the monoisopropyl products, and over 65% /I$‘-selectivity to 2,6-DIPN among the diisopropyl products with a 2,6DIPN/2,7-DIPN ratio of about 3. Although isopropanol is the alkylating agent, increasing the C3H,0H/C10H8 mol ratio from 0.5 to 1.3 tends to lower the catalyst activity in terms of a decrease in conversion. The nature of the solvent and reaction time are also intluential for both activity and selectivity of mordenite and Y-zeolite catalysts. The data reported in this paper, though still preliminary, point to a promising direction in selectively producing 2-alkylnaphthalene which is a useful intermediate in synthetic chemical industry, and 2,6_dialkylnaphthalene which is a very important building block for advanced polymer materials such as poly(ethylene naphthalate), poly(butylene naphthalate) and liquid crystalline polymers (Scheme 1). A known disadvantage with mordenite is its non-intersecting channel, which can lead to rapid catalyst deactivation by pore blockage. However, it has been demonstrated [ 19,231 that dealumination can significantly mitigate the deactivation of mordenite catalysts.

to

Acknowledgements We are grateful to Dr. T. Golden and Dr. V. Schillinger for providing the mordenite samples and to the following members in this laboratory: Dr. W.-C. Lai for assistance in GC-MS, Dr. A. Schmitz for performing two control experiments, Dr. J.-L. Faulon for evaluating the molecular size, and Dr. S.-D. Lin for helpful discussion. C.S. thanks Prof. P.B. Weisz and Dr. P.B. Venuto for their encouragement. 6. References [l] P.B. Weisz and V.J. Frilette, J. Phys. Chem., 64 (1960) 382. [2] P.B. Weisz, V.J. Frilette, R.W. Maatman and E.B. Mower, J. Catal., 1(1962) 307-312.

476

C. Song, S. KirbyJh4icroporou.s Materials 2 (1994) 467-476

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