Catalytic reactions of tetralin on HZSM-5 zeolite

Applied Catalysis A: General, 95 (1993)

221

221-236

Elsevier Science Publishers B.V., Amsterdam APCAT

A2450

Catalytic reactions of tetralin on HZSM-5 zeolite A.T. Townsend and J. Abbot Chemistry Department,

University

of Tasmania, Hobart, Tasmania (Australia)

(Received 18 September 1992)

Abstract Studies of catalytic reactions of tetralin on HZSMd at 400°C show that this feedstock is much less reactive on the pentasil compared to reaction on HY. At low feedstock conversions, thermal products contributed a large proportion of the total product species observed. Eight initial catalytic products were determined on HZSM-5, compared with approximately 20 found on the faujasite under similar conditions. As previously found for the HY zeolite, naphthalene, methylindans and benzene were the major initial products formed on HZSM-5. Even though a small number of initial catalytic products were formed on the pentasil, a complete network of initial reaction pathways could still not be clearly determined.

Keywords: cracking; hydrogen transfer; H-ZSM-5; isomerixation; tetralin; zeolites

INTRODUCTION

Industrial cracking feedstocks contain a wide variety of hydrocarbon types [ 11. The reactions of alkanes [ 2,3], isoalkanes [4,5], cycloalkanes [ 6,7] and alkylaromatics [ 8,9] have been extensively studied under cracking conditions. In contrast, cracking of molecules containing both naphthenic and aromatic characteristics, such as tetralin, have received comparatively little attention [ 10-121. This structural type is known to be of importance in feedstocks derived from the hydrogenation of heavy gas-oils and coal-derived liquids [ 131, being produced through the partial saturation of extended aromatic structures. Early work (1944) on the reactions of tetralin in the presence of a silicaalumina-zirconia cracking catalyst carried out by Bloch and Thomas [ 141 identified naphthalene as the major reaction product in the range 400-500°C. The formation of cycloalkanes and alkylbenzenes was taken as evidence that Correspondence

to: Dr. J. Abbot, Chemistry Department,

mania, Australia.

0926-860X/93/$06.00

Tel. (+61-02)202178,

University fax. (+61-02)234074.

0 1993 Elsevier Science Publishers B.V.

of Tasmania,

All rights reserved.

Hobart,

Tas-

222

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

hydrogen transfer processes were occurring on this catalyst. Tetralin was also thought to be converted to bicycloalkanes, presumably decalin. At about the same time, Greensfelder et al. [lo] also studied the cracking of a range of aromatic molecules, including tetralin, over a silica-zirconia-alumina catalyst at ca. 500°C. Dehydrogenation of tetralin was found to produce naphthalene, while benzene, toluene and Cl,, reaction products were also readily identified, along with the possibility of indan and methylindans. Little further work was reported on the reactions of tetralin over acid catalysts until recently (1990) when Mostad et al. [ 111 studied the reactions of tetralin and decalin over a USY-zeolite at 480°C. Reactions of tetralin were found to be dominated by two competing processes: ( 1) the cleavage of the alicyclic ring to produce alkylbenzene structures and (2) dehydrogenation to naphthalene, with over forty different product types identified. This work was limited however, by the fact that the cracking products were identified only at high conversion, making it virtually impossible to differentiate between initial and secondary reaction processes. In a recent study [ 121 we described the reactions of tetralin at 400” C on HY zeolite. Conversions of tetralin ranging from 5 to 87% were used to determine both initial and secondary products. Under these conditions initial and secondary reaction processes were found to be very complex, with extensive bimolecular processes occurring in conjunction with hydrogen transfer. The system was found to be sufficiently complex that even a reaction network describing only initial catalytic processes was difficult to formulate in detail, despite identification of all products involved. Reaction processes on HZSM5 often lead to fewer products and simpler reaction networks than found for reaction of the same feedstocks on HY [ 151. In this study we have investigated reactions of tetralin on HZSM-5 and have attempted to elucidate the reaction networks involved. EXPERIMENTAL

Tetralin (98.227% ) was obtained from Aldrich and used without further purification. The major impurities in the feed [ 121 are listed in Table 1. The presence of these impurities was taken into account in the calculation of the initial selectivities from reaction processes. HZSM-5 zeolite (Si/Al ratio of 105) was obtained from Snamprogetti, Italy and was calcined at 500’ C for 24 h under a flowing stream of dry air prior to use. All experiments were performed by using an integral, fixed-bed gas phase plug flow reactor with an independently controlled three zone heater. The experimental apparatus and procedures employed were similar to those reported previously [3]. All reactions were carried out at 400°C at atmospheric pressure. The catalyst was regenerated in dry air at 500°C after each cracking experiment.

A. T. Townsend and J. AbbotlAppl.

Catal. A 95 (1993) 221-236

223

TABLE 1 Tetralin feedstock impurities and major thermal cracking products At 600 s time-on-stream at 400 ’ C Product Toluene Ethylbenzene Indene Indan n-Propylbenzene Naphthalene’ CIJ-L,,~~ Methylindans’ CIOHIB~= Decalin”” C,,H,,O Methyltetralins Dimethylnaphthalenes Ethylnaphthalene CJ-Lrl= Dimethyltetralins Pyrene/fluorene CJ-L,” W-L,” C,&s” Tetralin Total

Feedstock impurity (wt.-% 1 0.03 0.06 0.24

0.29 0.09

0.21

Thermal (wt.-%) 0.20 0.06 0.07 0.16 0.50 1.10 0.16 0.03 0.36 0.30

0.07 0.63 0.08 0.16 0.02 0.02 0.04 0.66 0.21 98.23

100.0

“Structure not determined. *Valuesmay include some indene. “Cl0 Structure similar to tetralin.

Reaction products were analysed using Hewlett-Packard gas chromatographs. Liquid products were analysed using an SGE BP-10 capillary column and gaseous products were determined using a Chrompak capillary column, both with flame ionisation detection. Molecular hydrogen was detected using a packed molecular sieve column and a thermal conductivity detector. Hydrocarbon identification was facilitated by a Hewlett-Packard gas chromatograph-mass spectrometer. RESULTS AND DISCUSSION

Tetralin was found to be significantly less reactive on HZSM-5 in comparison to reactions on HY zeolite [ 121 under similar conditions at 400” C. A max-

224

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

imum conversion of only ca. 27% using a catalyst to feed ratio (C/F) of 0.2 was achieved on HZSM-5, whereas a conversion of ca. 87% was found for a C/ F = 0.02 on HY. With the high reactivity of tetralin on HY zeolite, feedstock conversions below 10% were virtually impossible to obtain at 400°C with a measurable amount of catalyst present in the reactor [ 12 1. Observations at low conversion levels are important in determining the initial catalytic processes taking place on the zeolite. It was hoped that the lower level of activity of the HZSM-5 towards tetralin cracking would provide additional insight into initial reaction processes occurring on acidic sites on zeolite catalysts.

Feedstock impurities, thermal reactions and catalytic cracking Impurities detected in the tetralin feedstock are shown in Table 1. We have previously reported that thermal reactions of tetralin at 400’ C are more significant than observed for other classes of hydrocarbons [ 12 1. Fig. 1 shows that thermal conversions in the range ca. 2-3.5% were observed under the conditions investigated. Hydrocarbons identified as thermal products from tetralin at 400°C are also given in Table 1 [ 121, which shows that 55% of the total thermally produced species retain the original Cl,, structure. The thermal products identified are similar to those reported in previous work [ 161 using a batch autoclave reactor to study the thermal dissociation of tetralin between 300 and 450” C. The presence of feedstock impurities, as well as thermal prod-

TIME ON STREAM

(sets)

Fig. 1. Tetralin conversion on HZSM-5 at 400°C plotted against time-on-stream for a range of

catalyst-to-feed ratios, including blank runs (thermal reactions). (m) Blank (thermal cracking); (0)

C/F=0.02;

(0)

C/F=0.04;

(A) C/F=O.l;

(0)

C/F=0.2.

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

225

ucts must be taken into account in attempting to elucidate the reaction networks arising from catalytic processes. Plots of yield against conversion for primary products are shown in Figs. 2 and 3. In some cases the contribution of a particular hydrocarbon impurity or thermal product has been included in the yield-conversion plots by indicating the presence of a finite amount at zero catalytic conversion. This is shown, for example, for toluene and ethylbenzene in Fig. 2 and for naphthalene and methylindans in Fig. 3. The total amount of each product present at any particular conversion level can be considered as the sum of the contributions from impurity levels, thermal processes and catalytic processes. In the cases illustrated in Figs. 2 and 3 the individual hydrocarbon species are clearly produced as primary products of the catalytic reaction of tetralin, as indicated by the initial slopes of these plots approaching zero catalytic conversion of tetralin. Other types of product hydrocarbon species show a different type of yieldconversion profile as shown in Fig. 4. For example, the level of n-propylbenzene present (Fig. 4a) remains approximately constant over the range of conversion studied. It appears that this thermal product does not react further in the presence of the zeolite catalyst at 400°C. Benzyltetralin (C&H,,) (Fig. 0.60

(a)

0

(b)

0.40

/

0

0.26

0.6

Max.

Thermal

Conversion

CONVERSION

(wt%)

Fig. 2. Yield-conversion plots for initial producta from reaction of tetralin on HZSM-5 at 400” C. (a) C3 Gazes, (b) benzene, (c) toluene, (d) ethylbenzene.

A.T. Townsend and J. Abbot/Appl. Catal. A 95 (1993) 221--236

226

8.0

0.60

6.0

t-lax.

se

1.2

z

1.0

z z=

0.8

Thermal

Max.

Conversion

Thermal

Conversion

Thermal

Conversion

8.0

(d) 6.0

0.6

/ii..ii -Max.

ro CONVERSION

20

30

(wtX)

Fig. 3. Yield-conversion plots for initial products from reaction of tetralin on HZSM-5 at 400°C. (a) Indan, (b) methylindans, (c) 5- and6-methyltetralin, (d) naphthalene.

4b) and the unsaturated species C,,H,, (Fig. 4c) are formed as major thermal products. However their concentrations decline as catalytic conversion increases. The concentration of benzyltetralin declines continuously, reaching zero at approximately 20% catalytic conversion. The amount of C!,,H,, reaches a constant value at higher conversions. It is possible that this species is an intermediate in the debydrogenation of tetralin to naphthalene, a major stable product of catalytic reactions (Fig. 3d). This structure has been previously identified in hydrocracking studies of tetralin at 500°C [ 171. In our previous work with tetralin on HY [ 12 ] , the product C&H,, was also detected, but due to the conversion levels of tetralin observed on the faujasite, this product was hardly seen in the presence of co-eluting methyltetralins (C,,H,,), and any C,,H,, observed was hence included in the C,,H,, data. Fig. 4d shows that decalin (C,,H,,) is not a stable catalytic reaction product, its concentration declining steadily from levels attributable to thermal activity and initial feedstock impurities. Decalin results are complicated by the presence of indene, which has a similar chromatographic retention time to cisdecahn under the conditions employed in the analysis. However, even with this

A.T. Townsend and J. Abbot/Appl.

227

Catal. A 95 (1993) 221-236

0.80 ax. Thermal

Conversion

0.60

Max.

Thermal

Conversion

0.40 0.20 0

0

IO

Max.

o-

O

20

Thermal

0

30

0

10

20

30

1 0

IO

20

30

Converslon

30

0.30

CONVERSION

(wt%)

Fig. 4. Yield-conversion plots for thermal products of tetralin removed in the presence of HZSM5 at 400°C. (a) n-Propylbenzene, (b) benzyltetralin, (c) CJIlo, (d) decalin.

possible interference taken into account, our results show that decalin is produced only in relatively small amounts, in agreement with Mostad et al. [ 111. Fig. 5 shows the profiles for molecular hydrogen and coke from catalytic processes over the conversion range studied. Molecular hydrogen was detected as a thermal product [ 121, and it is interesting to note that levels of hydrogen initially decline as catalytic processes are introduced. At higher levels of catalytic conversion, molecular hydrogen is evolved, an observed behaviour more typical of other hydrocarbon systems previously investigated under cracking conditions [ 18,191. Previous results [12] have shown that a thermal “coke” deposition occurs at 4OO”C, despite low tetralin conversion levels ( < 3.5% ). The yield-conversion plot for coke is similar to other products considered in this section, with a reduction in yield as feedstock conversion increased. For most classes of hydrocarbon previously reported, levels of coke increase with increasing feedstock conversion [ 3,20,21]. The unusual coke profile illustrated in Fig. 5b shows that the carbonaceous residue initially formed thermally from tetralii can apparently react further with the feedstock (or secondary hydrocarbon products) in bimolecular processes yielding smaller more volatile product species. Other

228

A.T. Townsend and J. Abbot/Appl.

0.002

I 0

0 IO

20

30

CONVERSION Fig. 5. Yield-conversion on HZSM-5 at 400 ’ C.

I-.

Catal. A 95 (1993) 221-236

.I

0

-I IO

20

30

(wt%)

plota for (a) molecular hydrogen and (b) coke from reaction of tetralin

products showing similar behaviour in the presence of the pentasil included propylnaphthalene,diphenylethane,CllH12, CllH14,C,,H,, and C.&H,,, although these were not observed as either thermal products or feedstock impurities. Initial products from catalytic cracking

Table 2 shows selectivitiesof initial catalyticproducts,determinedfrom the initialslopes of the respectiveyield-conversionplots, aftertakinginto account effects due to impuritiesand thermalcracking.Only eight individualprimary products were found on HZSM-5 (Table 2), compared to 20 previously reported on HY undersimilarcrackingconditions [ 121.As found for the reaction of tetralin on the faujasite,benzene, naphthaleneand the isomerisationproducts, methylindanswere the major initial species produced on HZSM-5. As significantamounts of thermal products formed at low conversion levels can complicate the accurate calculation of initial selectivities,an alternativeapproach was used to check the validity of the values reported in Table 2. The normal&d yields of primary products at 610% conversion, prior to significant formation of secondary reaction products (Figs. 6 and 7), are in good agreementwith the normalisedinitial molar selectivitiesas shown in Table 3. Despite the small number of primaryproduct species observedon HZSM-5, a detailedexaminationof selectivitiesin Table 2 revealsthat a simple and complete reaction network is difficult to devise. The only simple monomolecularprocess which can be postulatedis isomerisation of tetralinto methylmdans.

A.T. Townsend and J. Abbot/Appl.

229

Catal. A 95 (1993) 221-236

TABLE 2 Initial products formed from catalytic reaction of tetrahn on HZSM-5 and HY at 400°C Product

C3 Gases Benzene Toluene Ethylbenzene Indan Naphthalene Methylindans Methyltetralins

HZSM-5 initial selectivity Type”

Weightb

Molar

Typd

WeighP

Molar

1u 1u 1s 1u 1u 1s 1s 1s

0.024 0.267 0.080 0.026 0.073 0.236 0.315 0.044

0.074 0.452 0.115 0.032 0.082 0.243 0.315 0.042

1s (1+2)s (1+2)s (1+2)s (1+2)s 1u 1u

0.126 0.019 0.013 0.025 0.244 0.245 0.114

0.213 0.027 0.016 0.028 0.252 0.245 0.103

(1+2)s (1+2)s (1+2)&s 1u 1u 1u (1+2)s 1u 1u 1u

0.0001 0.005 0.003 0.023 0.122 0.015 0.021 0.005 0.004 0.017

0.007 0.008 0.004 0.025 0.120 0.014 0.020 0.004 0.003 0.013

(1+2)s 1u (1+2)s

0.002 0.007 0.003

0.002 0.005 0.003

Hydrogen Methylcyclopentane Methylcyclohexane Propylbenzene Butylbenzenes (&Hi, Methylnaphthalenes C;-Naphthalenes Dimethyltetrahns C,-Naphthalenes Anthracene/Phenanthrene C;-Naphthalenes Coke Total

HY initial selectivity

1.065

1.013

“( 1) Primary; (2) secondary; (S) stable; (U) unstable. batheinitial weight selectivity is determined by the initial slope of the corresponding yield-conversion plot.

The initial selectivity for the formation of methylindans (0.315) is comparable to that observed on HY (0.245). On the basis of boiling points, the isomers l-, 2- and 4-methylindan were identified as reaction products of tetralin on both HZSM-5 and HY. Mostad et al. [ 111 have previously identified l-methylindan as the most abundant isomer on USY zeolite at 480 oC. In the present study virtually equal amounts of l- and 2-methylindan were formed, these isomers being attributed to a simple contraction of the six-membered ring in the feedstock [ 7,221. For reaction on HZSM-5 the isomer 4-methylindan was identified only at high feedstock conversions, and comprised less than 2.5% (by weight) of the total methylindans found at the highest conversion level (ca. 27% ). Similarly, on the faujasite only l- and 2-methylindans were detected at low conversion of tetralin.

A.T. Townsend and J. Abbot/Appl. Catal. A 95 (1993) 221-236

230 0.002

0.001 = 2 0

g R

0.005

5 0

0.004

z 3

0.003

IO

20

30

IO

20

30

(d)

0.002 0.00

1 0

-?

0 CONVERSION

(wt%)

Fig. 6. Yield-conversion plots for secondary alkane products from reaction of tetralin on HZSM5 at 400°C. (a) Methane, (b) ethane, (c) n-butane, (d) isobutane.

TABLE 3 Normal&d

molar selectivities

Product

from reaction of tetralin on HZSM-5 at 400” C Normalised

molar selectivities

Initial

At 810%

C3 Gases Benzene Toluene Ethylbenzene Indan Naphthalene Methylindans 5 and 6-Methyltetralin

0.055 0.334 0.085 0.024 0.061 0.179 0.232 0.031

0.070 0.349 0.041 0.020 0.035 0.177 0.286 0.022

Total

1.001

1.006

“Allowance was made for any thermal contribution

conversion”

to these values.

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

231

0.30

0.08 0.06

0.20 0.04 0.10 0.02 0 IO

0

R !E (3 w 3

0

30

20

0.008 0.006 0.004

(cl

IO

0

30

(d)

0

L

20

-

0.002

0.010

0.00

0

I

0

0

0.002 0

10

20

30

CONVERSION

0

0

(wt%)

Fig. 7. Yield-conversion plots for secondary alkene products from reaction of tetralin on HZSM5 at 400°C. (a) Ethene, (h) 1-butene, (c) ck-2-butene, (d) 2-methyl-2-butene.

Simple cracking or hydrogen transfer processes cannot easily account for the remaining initial products. Formation of naphthalene cannot occur through simple monomolecular or bimolecular processes such as: + 2H2 and:

as neither molecular hydrogen nor decalin are observed as initial catalytic products (Table 2). Bimolecular processes involving a methyl transfer could account in part for the formation of indan and methyltetralins.

Apart from propane and propene, Table 3 shows that there is a lack of small acyclic primary cracking fragments which would complement the direct mon-

232

A.T. Townsend and J. Abbot/Appl. Catal. A 95 (1993) 221-236

omolecular formation of benzene, toluene and ethylbenzene by a single cracking process. Neither do these fragments appear as alkyl substituents on other cyclic product species observed. These phenomena raise a number of questions. For example, assuming that benzene is produced from the aromatic nucleus of the tetralin feedstock, what is the fate of the residual C, fragment? The low initial selectivity for coke in Table 2 shows that formation of carbonaceous residues from small hydrocarbon fragments does not provide a plausible explanation [ 231. As we have previously suggested for the reaction of tetralin on HY, it seems that the only explanation is to assume that the cracking fragments are transformed into aromatics through bimolecular processes involving extensive hydrogen transfer. Formation of aromatics on HZSMB type zeolites from small alkane and alkene molecules is well documented [ 23-251. Product distributions at higher conversions and secondary products An extensive range of secondary products were also found from the reaction of tetralin on HZSM-5. Examples of yield-conversion plots for these product types are shown in Figs. 6 and 7. It is clear that the slopes of these plots are zero at low feedstock conversion levels. A complete list of secondary products is given in Table 4. Secondary products listed as not detected (n.d.) at 20% conversion were identified only at higher conversions. It is evident that on HY at 20% conversion the majority of secondary products identified at high conversions were not yet evident. The formation of all products, both secondary and initial, can be followed by grouping together similar molecular types, as for example, the benzene types, which includes benzene, toluene, ethylbenzene etc. Products have been classified by type in this study as follows: alkanes, alkenes, alicyclics, benzenes, tetralins and naphthalenes. Comparisons of product formation by product type on both HZSM-5 and HY are shown in Figs. 8-10. Combined aromatics (benzenes, tetralins and naphthalenes) account for ca. 92% of the total products formed on both catalysts under similar conditions (on a molar basis), agreeing with the value of 90% found by Mostad et al. [ 111. Fig. 8 shows that benzene type products are favoured on HZSM-5 whereas naphthalene and its derivatives are favoured on HY, probably as a direct result of pore size constraints within the pentasil. The parent molecules benzene and naphthalene were the major components in their respective groups on both catalysts. Table 4 shows that there were fewer individual aromatic secondary products detected on HZSM-5 compared with reaction on HY. Xylenes were found on both zeolites as secondary products, while alkylated naphthalenes and heavier aromatics were formed only on HY. Alkylated species are likely to arise from disproportionation reactions [ 111. Small acyclic cracking fragments in the range C,-C, are formed as alkanes and alkenes as illustrated in Fig. 9. Alkenes are formed on both catalysts only

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

233

TABLE 4 Secondary products formed from the catalytic reaction of tetralin at 400°C on HZSM-5 and HY at 20% conversion n.d., Not detected, only found at tetralin conversions

in excess of 20%

class

product

HZSM-5 (wt.-% )

HY (wt.-%)

Alkanes

Methane Ethane Propane Isobutane n-Butane Isopentane n-Pentane 2-Methylpentane 3-Methylpentane 2-Methylhexane 3-Methylhexane

0.0009 0.0009

0.0002 0.0005 0.020 0.030 0.075 0.030 n.d. n.d. n.d. n.d. n.d. n.d.

0.020 0.0014 0.0040

CL& Alkenes

Ethene Propene Isobutene trans-2-Butene cis-2-Butene CsHa trans-2-Pentene cis-2-Pentene GH,o 2-Methyl-1-butene 2-Methyl-2-butene

0.040 0.11 0.0050 0.0035

n.d. n.d. 0.0070

0.0050 0.030 0.015 0.020 0.010 n.d. 0.00050 n.d. n.d. 0.00010

Alicyclics

Cyclopentane Cyclohexane Dimethylcyclopentanes Ethylcyclopentane Dimethylcyclohexanes

n.d.

n.d. n.d. n.d. n.d. n.d.

Aromatics

Xylenes

0.14

C&k, C,,H,, Methylnaphthalenes

n.d. n.d. n.d.

0.45

C,lHl, Dimethylnaphthalenes Ethylnaphthalenes Ethyltetralins C,zHlG C,,H,, CUH~~ C,,H,, Propylnaphthalenes C,-Tetralins C,-Tetralins Pyrene/fluoranthene CwH12

n.d. n.d. 0.050 0.10 0.55 n.d. 0.080 n.d. n.d. 0.080 0.090 n.d. n.d.

234

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

0.014 0.012 0.010 0.006 0.006 0.004 0.002

Max. Thermal

0 0

IO

20

IO

Conversion 40

50

0

60

CONVERSION

IO

20

30

40

50

60

(wt%)

Fig. 8. Molar yields of (a) benzene type products and (b) naphthalene type products from tetralin reaction on HZSM-5 and HY at 400°C. (0 ) HZSM-5; (0 ) HY. 0.002 L 2 B a IL 0

0.0006

0.001

In 2 E 0

IO

20

30

40

50

60

CONVERSION

0

IO

20

30

40

50

60

(wt%l

Fig. 9. Molar yields of (a) alkane type products and (b ) alkene type products from tetralin reaction on HZSM-5 and HY at 400 oC. ( 0 ) HZSM-5; ( 0 ) HY.

as secondary products. On HY, alkanes are also observed only as secondary products during reactions of tetralin. A greater diversity of individual alkane and alkene species were found on the HY zeolite. However, on both catalysts these cracking products represented less than 9% of the total products at the highest feedstock conversion levels studied. Fig. 10a shows that while tetralin species are produced in similar amounts at low conversion levels on both catalysts, there is a higher tendency towards secondary tetralin types on the pentasil as conversion increases. On HZSM-5, in addition to the 5- and 6-methyltetralins seen as primary products shown in Table 2, ethyl-, C3- and C!,-tetralins were observed as secondary products as shown in Table 4. The apparent stability of these products on HSZM-5 may

A.T. Townsend and J. Abbot/Appl. 0.010

I

Catal. A 95 (1993) 221-236 0.002

,

1I

235

(a) 0

0.006

f

0.001 0.004 0.002

0

0 0

10

20

30

40

50

60

CONVERSION

0

10

20

30

40

50

60

(wt%)

Fig. 10. Molar yields of (a) tetralin type products and (b) alicyclic type products from tetralin reaction on HZSM-5 and HY at 400°C. (0 ) HZSM-5; (0 ) HY.

be associated with steric constraints limiting their diffusion into the zeolite or their ability to take part in bimolecular processes leading to further reactions. Fig. lob shows that while alicyclic types are observed on HY as secondary products, they are not produced on HZSM-5. On HY, in addition to alicyclic products listed in Table 2, cyclopentane, cyclohexane, ethylcyclopentane, dimethylcyclopentanes and dimethylcyclohexanes were also detected as secondary products, as shown in Table 4. The only secondary alicyclic product detected from the reaction of tetralin on HZSM-5 was cyclopentane. The alicyclic components described in Fig. lob also include decalin, the individual behaviour of which has been discussed previously. CONCLUSION

A detailed study of catalytic reactions of tetralin on HZSM-5 has been undertaken, accounting for feedstock impurities and thermal reaction products. Although the initial catalytic reaction network on HZSM-5 involves only 8 products compared to 20 on HY, apart from isomerisation through simple ring contraction to methylindans, formation of the remaining products must include more complex bimolecular processes with extensive hydrogen transfer. ACKNOWLEDGEMENTS

Financial support for this work was provided by the Australian Research Council and the University of Tasmania. The authors are grateful to Mr. N.W. Davies (Central Science Laboratory) for gas chromatography-mass spectrometry identification of products, and the assistance and useful comments of Mr. F.N. Guerzoni.

236

A.T. Townsend and J. Abbot/Appl.

Catal. A 95 (1993) 221-236

REFERENCES 1 P.B. Venuto and E.T. Habib, Catal. Rev. Sci. Eng., 18 (1978) 1. 2 Y.V. Kissin, J. Catal., 126 (1990) 600. 3 J. Abbot and F.N. Guerzoni, Appl. Catal. A, 85 (1992) 173. 4 E.A. Lombard0 and W.K. Hall, J. Catal., 112 (1986) 565. 5 G. Bourdillon, C. Gueguen and M. Guisnet, Appl. Catal., 61 (1990) 123. 6 A. Corma and A. Lopez Agudo, React. Kinet. Catal. Lett., 16 (1981) 253. 7 J. Abbot, J. Catal., 123 (1990) 383. 8 D. Best and B.W. Wojciechowski, J. Catal., 47 (1977) 11. 9 A. Corma, P.J. Miguel, A.V. Orchilles and G.S. Koermer, J. Catal., 135 (1992) 45. 10 B.S. Greensfelder, H.H. Voge and G.M. Good, Ind. Eng. Chem., 37 (1945) 1168. 11 H.B. Mostad, T.U. Riis and O.H. Ellestad, Appl. Catal., 63 (1990) 345. 12 A.T. Townsend and J. Abbot, Appl. Catal. A, 90 (1992) 97. 13 M. Nomura, T. Yoshida, P. Philp and T. Gilbert, Fuel, 64 (1985) 108. 14 H.S. Bloch and C.L. Thomas, J. Am. Chem. Sot., 66 (1944) 1589. 15 H. Krannila, W.O. Haag and B.C. Gates, J. Catal., 135 (1992) 115. 16 R.J. Hooper, H.A.J. Battaerd and D.G. Evans, Fuel, 58 (1979) 132. 17 J.M.L. Penninger, Int. J. Chem. Kinet., 14 (1982) 761. 18 J. Abbot and B.W. Wojciechowski, in Proc. of the 9th Int. Cong. on Catalysis, Calgary, Canada, 1988, The Chemical Institute of Canada, Ottawa, 1988. 19 J. Abbot and J.D. Head, J. Catal., 125 (1990) 187. 20 P.E. Eberly Jr., C.N. Kimberlin Jr., W.H. Miller and H.V. Drushel, Ind. Eng. Chem. Proc. Des. Dev., 5 (1966) 193. 21 B.W. Wojciechowski and A, Corma, Catalytic Cracking Catalysts, Chemistry and Kinetics, Chemical Industries Series, Vol. 25, Marcel Dekker, New York, 1986. 22 J. Abbot and B.W. Wojciechowski, J. Catal., 107 (1987) 571. 23 L. Kubelkova’, J. Novakova, M. Tupd and Z. Tvaruzkova, Acta Phys. Chem., 31 (1985) 649. 24 P. Dejaifve, J.C. Vedrine, V. Bolis and E.G. Derouane, J. Catal., 63 (1980) 331. 25 MS. Scurrell, Appl. Catal., 41 (1988) 89.