React. Kinet. Catal. Lett., Vol. 22, Nos 1 -2 , 215-219 (1983)

A L K Y L A T I O N OF T O L U E N E WITH M E T H A N O L ON Mg-CONTAINING Y Z E O L I T E S

Mai Tuyen and Chr. Dimitrov

Department of Chemistry, University of Sofia, Sofia, Bulgaria

Received April 29, 1982 Accepted November 9, 1982

On Mg-containing Y zeolites and in the presence of methanol, toluene undergoes mainly alkylation. It is established, that for this reaction strong adsorption and acid centers are not necessary.

Tonyon, B IIpHCyTCTBHH MeTaHOJ'la rl Mg-co~ep~Ka!/LvIx Y I~eOJIHTOB, FJIaBHbIM o6pa3oM, a.rIIcd, IylHpyeTe~I. YCTaHOB~IeHO, qTO ~;l~l aTO~ peaKI~HI, I Heo6xo/IHlVlbI a~cop6tLVloHHble H KHCIIOTHBIe ILeHTpI:,I e He~oYISIMofl CHTIO~.

Upon studying the catalytic conversions of aromatic hydrocarbons of various structures over Mg-containing Y zeolites with various degrees of ion-exchange and Si/A1 ratios, or treated under different conditions we showed / 1 - 3 / that cations in the cationic positions of the zeolite lattice accessible for aromatic hydrocarbon molecules are also responsible for the activation of reacting molecules. New proofs in favor of this supposition are expected to be obtained upon studying the be- havior of toluene in the presence of methanol over three series of Mg-containing Y zeolites, sirlce hydrocarbon and alcohol molecules are sharply distinguished in their adsorption properties. For comparison, experiments were carried out under analogous conditions also with cumene.

EXPERIMENTAL

Dealumination of the zeolite Na-Y, FAU (Na20 - 12.01; A1203 - 19.87 and SiO2 - 67.86 wt. %)was carried out by EDTA solution. Ion-exchange of Na § for Mg 2§ of the parent zeolite to degrees 13, 27, 34, 48, 54 and 80%, and in dealu- minated samples with Si/A1 ratios of 3.7, 4.8 and 7.1 to degrees 61.6, 53.8 and 66.4%, respectively, were completed by treatment with MgCI2 solutions. The sample ex Nao.19(NH4)o.81-Y, FAU was obtained by treating Na-Y, FAU with

215

MAI TUYEN, DIMITROV: ALKYLATION OF TOLUENE

Ntt4C1 solution at 100 ~ An ultrastable sample (US-ZY) was obtained by 3-fold treatment of sample ex Na0.19(NH4)o.sl-Y, FAU with water vapor at 550 ~ and ad- ditional exchange with NH4C1 solution after every heating. From sample

eX eX e x e x Mg~.22Nao.46(NH4)o.a2-Y , FAU, sample Ho.29Mg~.asNao.23-Y , FAU was obtained by deep bed treatment at 550 ~ followed by additional exchange with NH4C1

1--1 e x ILl e x V and MgC12 solutions, and sample . lo.ls, ,go.84-_ , FAU by steaming at 550 ~ for 3 h folloved by the same additional exchange.

Toluene and methanol were p.a. grade and used in a toluene/methanol ratio of 1. Catalytic apparatus, procedure and analysis were described /1/. The extent of alkylation was determined from the sum of xylenes and trimethylbenzenes; disproportionation from the amount of benzene, and isomerization from the

p-+o- decrease of the r a t i o - xylenes, because it is known that toluene alkylation

m -

in the aromatic ring is preferent in o- and p-positions.

RESULTS AND DISCUSSION

It can be seen from Fig. 1, that the starting Na-Y, FAU is inactive in the al- kylation of toluene with methanol. The partial exchange of Na § for Mg 2§ makes the samples active for alkylation as well as for toluene disproportionation and isomerization of xylenes produced. However, while in the disproportionation and isomerization reactions, analogously to cumene dealkylation (Fig. 2) a stable tendency is observed for increasing the respective reaction products for alkylation; this dependence passes through a maximum for the sample with 34% exchange. A decrease in alkylation for samples with higher exchange degrees can hardly be explained by a more intensive decomposition of the alkylating agent, as it is known that an increase in the toluene: methanol ratio is more favorable for al- kylation /4, 5/. Hence this fact is more probably due to a change in the chemistry of the zeolite surface, which favors competitive disproportionation. Really, for ion- exchange degrees up to 34%, the acidity is characterized by the presence of rela- tively weak centers /6/. These centers, however, seem to be sufficient for activat- ing the oxygen-containing molecules and their participation in the alkylation of the aromatic ring. In support of this suggestion is the fact that, for isopropanol dehydration over (H ex, Na)-Y, FAU, modification by ion-exchange of about 30% is the most suitable /8/. The further increase in the Mg 2§ content is accompanied by a sharp increase in total acidity and mainly in the concentration of stronger acid centers (HR = --6.6) /6/, that is, better conditions are created for the for-

216

MAI TUYEN, DIMITROV: ALKYLATION OF TOLUENE

1 Total conversion

2 Alkyiotion

3 Disproportionation 5O

4 Isomerizat ion Z~ I

' .,J ~o \4

2o ~-~--z._~ 10

0 - ~ i 0 20 40 60 80

Ion exchonge (%)

30 o E

2.5

2.0

1 . 5

1.0

0.5

Fig. 1. Toluene conversion in the presence of methanol and the change of xylene ratio ~" +o- m -

on (Ng, Na)-Y, FAU as functions of the Mg content at 355 ~

30

20

E

10

0 0 20 ~0 60 80

Ion exchange {%)

Fig. 2. Cumene dealkylation on (Mg, Na)-Y, FAU depending on the Mg content at 240 ~

mation of adsorption complexes with the participation of two toluene molecules,

responsible for the disproportionation reaction /7/. Upon increasing the Si/A1 ratio from 2.9 to 7.1, cumene dealkylation passes

through a maximum at the sample with a Si/AI ratio o f 4.8 (Fig. 3), alkylation

217

MAI TUYEN, DIMITROV: ALKYLATION OF TOLUENE

E

30

20

10 I I I I I

3 4 5 6 ?

Si/Al

Fig. 3. Cumene dealkylation on (Mg, Na)-Y, FAU depending on the Si/A1 ratio at 240 ~

20

"6 E 10

1. Tofol conversion 2. A lky la t i on

3. Disproport ionation 4. ] somer i za t i on

I / \

3 4 5 6 7

5 i /A l

E

t,.0

3.0

2.0

1.0

Fig. 4. Toluene conversion in the presence of methanol and change of the xylene ratio in dependence of the Si/A1 ratio at 297 ~

218

No.

MAI TUYEN, DIMITROV: ALKYLATION OF TOLUENE

Table 1

Toluene alkylation with methanol at 260 ~ and cumene dealkylation at 240 ~ mol %

Catalyst _ _ Toluene alkylation Cumene

Benzene Toluene X + TMB § dealkylation

H~X81Na0.19-Y, FAU 2.4

US-ZY 4.7 e x e x Ho.3Mgo.2Na-Y, FAU 2.1 e x e x Ho.sMg0.3Na-Y , FAU 3.5 e X e X H0.1 sMgo.84-Y , FAU 8.9

+Xylenes plus trimethylbenzenes

2.4

4.7

2.1

3.5

8.9

76.6

62.1

79.9

67.9

56.3

20.9

23.2

18.0

28.6

34.9

54.7

71.0

54.1

88.8

90.8

continues to increase with increasing this parameter (Fig. 4). This fact correlates

relatively well to the change in the concentration o f weak acid centers with

He = 3.3.

The steaming of NH~X-Y, FAU (samples 2 and 5, Table 1) increases significantly

the activity towards toluene, conversions are increased from 2 0 - 2 3 mol % (for not

steamed samples Nos. 1 and 3) to 3 8 - 4 4 mol % (for steamed samples). In agree-

ment with the stronger acidity o f these samples, judged by their higher cumene

dealkylation activity, the increases observed in activity are more pronounced for disproportionation than for alkylation.

An increase in the toluene conversion to 32 mol % by keeping a relatively good

selectivity for alkylation is reached by the ammonium treated sample, containing

less Mg (sample 4, Table 1). These results show that the presence o f Mg cations

in the supercages leads to the formation of adsorption and active centers with higher strength, which favor toluene disproportionation.

REFERENCES

1. Chr. Dimitrov et al.: React. Kinet. Catal. Lett., 8, 101 (1978). 2. Mai Tuyen, Chr. Dimitrov: React. Kinet. Catal. Lett., 16, 289 (1981); 18, 217 (1981). 3. Mai Tuyen, Chr. Dimitrov: Appl. Catal., (in press). 4. T. Yashima et al.: J. Catal., 16, 273 (1970). 5. B. Doughlan et aL: Chem. Ind., 14, 480 (1979). 6. Z. Popova et al.: Acad. Bulg. Sei., 30, 1569 (1977). 7. Y. Izumi, T. Shiba: Bull. Chem. Soc. Japan, 37, 1797 (1964). 8. K. V. Topchieva, H. S. Thoang: Kinet. Katal., 14, 398 (1973). it

219