React. Kinet. Catal. Lett., Vol. 51, No. i, 177-181 (1993)

RKCL2153

SELECTIVE CYCLODEHYDRAT!ON OF DIOLS ON ZEOLITES

C.P. Bezouhanova and F.A. Jabur

University of Sofia, Faculty of Chemistry

i, J. Bourchier Ave, Sofia 1126, Bulgaria

Received October 8, 1992 Accepted May 6, 1993

1,4-Butanediol, 2,5-hexanediol and 1,5-pentanediol

were selectively converted to tetrahydrofuran and

tetrahydropyran in the presence of LaHY, CaHY and

H-ZSM-6 zeolites. The advantage of these zeolites

is in their high stability and faster regeneration.

The use of zeolites as acid catalysts for organic reac-

tions has found considerable interest [11. The selectivity of

the catalyst appeared to be of great importance for its pre-

parative application. Earlier investigations on the dehydra-

tion of 1,4-butanediol on synthetic A and X zeolites showed

that tetrahydrofuran can be obtained with high selectivity and

very good yield using HNaX zeolite as catalyst [23. The yield

of tetrahydrofuran diminished after 14 hours on stream and it

has not been shown how long the catalyst could be regenerated.

In another investigation [3J NaHY was applied for 2,5-hexane-

diol and 1,5-pentanediol conversion. The temperature was higher

than hhat in E43, where Al(III)-montmorillonite was the cata-

lyst and data on catalyst deactivation have not been presented.

It is well known that HNaX and HNaY zeolites are easily deac-

tivated by coking [51. The introduction of multivalent cations

stabilizes the zeolite structure and improves the catalytic ac-

tivity. The stability of the zeolite structure as well as de-

Akad4miai Kiad6, Budapest

BEZOUHANOVA, JABUR: CYCLODEHYDRATION OF DIOLS

activation by coking depends also on the ratio Si/AI. In this

respect high-silica zeolites of the pentasil type (ZSM-5) have

been found to possess very stable structures and low rate of

deactivation because of the channel dimensions, which do not

allow the formation of the bulky coke deposits. Taking into ac-

count the improved stability of faujasites containing multi-

valent cations and the low coking ability of H-ZSM-5 zeolites,

we checked the activity and selectivity of LaHY, CaHY and

H-ZSM-5 zeolites in cyclodehydration of 1,4-butanediol, 2,5-

hexanediol and 1,5-pentanediol.

EXPERIMENTAL

Catalysts

LaHY and CaHY were prepared by ion exchange of NaY zeolite

with NH4CI and the corresponding salts under conditions de-

scribed in [5]. H-ZSM-5 (Si/AI=40) was obtained by HCl-solution

treatment of Czechoslovak commercial Na-ZSM-5 zeolite. The ac-

tivation and regeneration of the used catalysts was performed

at 773 K in air flow.

Reagents

The diols were commercial products. 1,4-Butanediol and

1,5-pentanediol were from Fluka; 2,5-hexanediol (isomer mix-

ture) from Merck-Schuchardt.

Apparatus

The catalytic experiments were performed in a fixed bed

flow reactor with different catalyst quantities (0.05-1 g),

pressed, crushed and sieved to particles of 1.25-2.5 nm size.

Before the experiments the catalysts were flushed with nitro-

gen. The diols were introduced using a calibrated syringe.

Analysis

GC analysis of the reaction products were performed on a

2 m column with 15% Reoplex-400 on Chromosorb P/NAW 30-60 mesh

at 453 K.

178

BEZOUHANOVA, JABUR: CYCLODEHYDRATION OF DIOLS

RESULTS AND DISCUSSION

The experimental conditions have been determined for the

selective cyclodehydration of 1,4- and 1,5-diols. It has been

established that at 523 K 1,4-butanediol was completely con-

verted to tetrahydrofuran (Fig. i) in the presence of LaHY. The

selectivity of the three zeolite catalysts used was 100%. This

fact has been verified by GC analysis and IR spectra of the

products. The catalyst activity diminished at smaller contact

times (greater WHSV).

100-

80- > C 0 U

60-

I I I I

1.2 2.4 6.1 12.2

WHSV h -1

Fig. I. 1,4-Butanediol conversion on LaHY (A), CaHY (e)

and H-ZSM-5 (o) zeolites at 523 K, 1 h on stream

Similar results have been obtained using Al(III)-montmo-

rillonite as catalyst [43. The advantage of the zeolite cata-

lysts is in the simple apparatus (not in autoclave) and the

better reproducibility of zeolite preparation.

As in the case of pinacole conversion [6], LaHY showed

the best performance, followed by CaHY. The activities of CaHY

and H-ZSM-5 zeolites in 1,4-butanediol conversion were compara-

ble. From 2,5-hexanediol, with zeolite catalysts, a mixture of

cis- and trans-isomers of 2,5-dimethyltetrahydrofuran [7] has

179

100

8O

50 c o o

40

20

i [ I i i 075 15 3.4 ~5 15

WHSV h - I

BEZOHHANOVA, JABUR: CYCLODEHYDRATION OF DIOLS

Fig. 2. 2,5-Hexanediol conversion on zeolites at 503 K

(notation as in Fig. i)

been obtained (Fig. 2). The conversion was 100% at greater con-

tact times in the presence of LaHY or CaHY, while H-ZSM-5 was

less active. At shorter contact times the conversion dropped

rather sharply.

Tetrahydropyran was selectively obtained by the dehydra-

tion of 1,5-pentanediol on LaHY, CaHY and H-ZSM-5 zeolites

(Fig. 3). The results were similar to those in E43. A high se-

lectivity in cyclodehydration of the zeolite catalysts studied

has been achieved at temperatures slightly higher than with

Al(III)-montmorillonite [43, but lower than with NaHY [3]. Our

experiments showed that the activity of LaHY remained constant

for 12 h, while that of CaHY for 8 h on stream. No deactiva-

tion of H-ZSM-5 was observed.

In conclusion LaHY, CaHY and H-ZSM-5 zeolites are selec-

tive catalysts for the cyclodehydration of 1,4-diols to tetra-

hydrofuran derivatives and of 1,5-diols to tetrahydropyrans.

The advantage of these catalysts is in their lower deactiva-

180

BEZOUHANOVA, JABUR: CYCLODEHYDRATION OF DIOLS

t-

O o

I00

BO

60

40

20 \

I I t

0.75 I'50 3.00 7150 15.00

WHSV h - I

Fig. 3. 1,5-Pentanediol conversion on zeolites at 533 K

(notation as in Fig. i)

tion and better regeneration.

REFERENCES

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Engl., 27, 226 (1988).

2. Kh.I. Areshidze, G.O. Chivadze: Khim. Geterotsikl. Soed.,

195 (1969).

3. A. Moln~r, I. Bucsi, M. Bart6k: in Proc. Int. Symp. on

Zeolite Catalysis, Si6fok, Hungary, May 13-16. 1985, p.571.

4. D. Kotkar, P.K. Ghosh: J. Chem. Soc. Chem. Commun., 650

(1986).

5. C.P. Bezouhanova, P. Kovacheva, Kh. Dimitrov, Y. Kurteva:

Kinet. Katal., 19, 760 (1978), and refs therein.

6. C. Bezouhanova, F.A. Jabur: in preparation

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222 (1959).

181