Conversion of methanol to light olefins over zeolite H-T

Chem. Eng. Technol. 12 (1989) 155 - 161 155

Conversion of Methanol to light Olefins over Zeolite H-T

Dietmar Gubisch and Friedhelm Bandermann*

The conversion of methanol over zeolite H-T was investigated in a fixed bed reactor. H-T was prepared from Na-T by ion exchange with HC1 and NH4Cl solutions. The HCl solutions caused appreciable dealumination. High yields of ethene were obtained with NH,Cl exchanged zeolites Na-T with 45 % decationization, high propene yields with low HC1 or NH4C1 exchanged catalysts. Low methanol partial pressures and short residence times favoured the formation of lower olefins. Lowest coking rates.were observed at a reaction temperature of 693 K. The catalytic activity decreased slowly with the number of reactiontregeneration cycles. The distribution of products > C, could be described by the most probable distribution of Schulz and Flory.

1 Introduction

After Mobil Oil had shown that zeolites of the pentasil type can act as catalysts for the conversion of methanol to high octane gasoline [ 1, 21, strenuous efforts were made to establish the conditions for the production of light olefins such as ethene and propene. This was more or less achieved, e.g. by modifying zeolite ZSM-5 by treatment with phosphorous compounds [3], by replacing aluminium in zeolite synthesis by other elements such as boron [4] or by use of small pore zeolites such as chabazite, erionite and offretite [5 - 81.

Zeolite H-T (H-T), an intergrowth of erionite and offretite, was used by Chang [5], Ceckiewicz [9 - 121, Marquart and Fetting [13, 141, Fleckenstein et al. [15] and Langner [16]. The products of methanol conversion over H-T were mainly olefins but coking was rapid.

In this paper, we wish to report on investigations to produce lower olefins from methanol over zeolite H-T by a correct ad- justment of chemical and process variables.

2 Experimental

Zeolite Na-T was synthesized according to Breck [17] and characterized by chemical analysis and x-ray diffraction. All data coincided well with those published. The raw material was ground in a ball mill and sieved. The fraction between 90 and 125 pm was used in all investigations.

Catalytic studies were performed in fixed bed reactors heated electrically or in a fludized sand bath (type Techne SB24). All catalysts were calcined at reaction temperature for 1 h in a stream of helium (calcination times in excess of 1 h showed no effect on catalytic activity). Pure methanol was charged by a metering pump (Precidor, type 5003, Infors AG) into a helium stream preheated to reaction temperature before entering the reactor. Products were analyzed by on-line gas chromatography (gas chromatograph 5730 A, Hewlett Packard, equipped with

* Dr. D. Gubisch and Prof. Dr. F. Bandermann, Institut f i r Technische Chemie, Universitiit-Gesamthochschule Essen, Universititsstr. 5 , D-4300 Essen 1.

FID and TCD, two integration terminals, 6 m 17% sebaconitrile column (C, - C, hydrocarbons), 2 m Porapak Q and 1 m Porapak R columns (MeOH, CO, C02, ethene and ethane)). In order to investigate the coking behaviour of the catalysts, a reactor tube was mounted under the pan of an analytical balance (type 2007 MPGE, Sartorius AG) and the increase in mass of the reactor during the reaction of methanol on H-T was measured continuously. The C/H ratio of coke was determined according to Enterman and van Leuven [ 181.

3 Results

3. I Preparation of Catalysts

For the preparation of catalysts, zeolite Na-T was ion exchanged by HCl and NH4C1 treatment.

3.1.1 Treatment with HCl

For decationization, zeolite Na-T was treated under stimng with 0.1, 0.05,0.025,0.01,0.005 and 0.0025 M HC1 at room temperature. After two hours, decationization ceased and dealumination changed only slightly. Both values were calculated according to Cichocki [19]. We observed an upper limit of decationization, corresponding to an equilibrium value for each HC1 concentration. This is reached when the ratio m of acid equivalents to alkali cation equivalents exceeds 3, while dealumination still slightly increases above this value (Fig. 1). Fig. 2 shows the relationship between dealumination and decationization for 0.005 to 0.1 M HC1 solutions and m values from 1 to 5. The points may be approximated by a straight line not passing through the origin, i.e. with weak HCl solutions, decationization occurs without appreciable dealumination. For comparison, corresponding exchange results of Cichocki [ 191 are also shown (0.11 HC1,22 "C, 24 h). It can be seen that, under the applied exchange conditions, with weak HCl solutions and stimng , higher decationization without any dealumination may be obtained than by the method of Cichocki. The agreement between the two results with respect to the slopes of the lines is satisfactory. Furthermore, in contrast to Cichocki, we observed no appreciable decrease in crystallinity with increasing dealumination.

0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1989 0930-7516/89/0204-0155 $02.50/0

156 Chem. Eng. Technol. 12 (1989) 155- 161

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x' A' &'' -

X- x/x-x

A-A-A A- 0-

X/ 80 -

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9 12 15

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3.1.2 Treatment with NH,Cl

A second modification of zeolite H-T was obtained by treating Na-T with 0.OO5,0.01,0.1,0.5 and 1 .O M NH,Cl solutions for 90 min at room temperature (Fig. 3).

Here, higher m values than with HCl are necessary to obtain the same decationization. No dealumination was observed, again in contrast to Cichocki, but we carried out the exchange under more carefully controlled conditions so that our results are not unexpected. Meanwhile, Delannay and Ceckiewicz [20] showed by TEM and X.P.S. measurements that the surface of HCl treated zeolite Na-T samples may be covered by a thin layer of amorphous material and that the surface layer was much more decationized and dealuminated than the bulk.

Hence, it may be assumed that the difference in bulk composi- tion of HCl and NH4C1 exchanged zeolite Na-T would cause an appreciably different catalytic behaviour in the conversion of methanol to hydrocarbons.

m

3.2 Search for an Optimal Reaction Temperature

m

It is known that, at temperatures below 573 K, methanol is converted .over zeolites mainly to dimethyl ether. Appreciable amounts of hydrocarbons are only obtained at higher temperatures, Since coke formation and hence deactivation are also enhanced with rising temperature, we measured for a more detailed description of the overall process not only the product distributions but also coke formation rates as functions of reaction temperature between 623 and 793 K. In these experiments, 0.79g MeOH in 3.73 l,He/(g catalyst h) was fed onto lg zeolite H-T (decationization 41.5%, dealumination 10.2%) in a reactor, 1.5 cm in diameter. Time-yield curves were integrated for

fig. 1. ~ ~ ~ t i ~ k ~ t i ~ ~ and dd-ation of zeolite N ~ - T after a reaction time of 120 min, the amounts of coke and its C/H with HCl solutions versus ratio m of proton equivalents to alkali cation ratio determined as described above. Fig. 4 shows the equivalents. [HClI (molll): (*I 0.005; (1) 0.01; (0) 0.025; ( A 0.05; ( x ) dependence of coke yield on reaction temperature. The coke 0.1.

decationization I YO m Fig. 2. Dealumination versus decationization of zeolite Na-T after ion exchange with HCI solutions. [HCll (molll): (0) 0.005; ( X ) 0.1; ( A ) values of Cichocki [19].

fig. 3. Decationization of zeolite Na-T after treatment with NH,Cl solutions versus ratio m of proton equivalents to alkali cation equivalents. [NH,Cl] (molll): (*) 0.005; (I) 0.01; (0) 0.1; ( A ) 0.5; ( x ) 1.0.

Chem. Eng. Technol. 12 (1989) 155- 161 157

reaction temperature I K

I I 1 I I 600 650 700 750 800

reaction temperature I K

Fig. 4. Coke yield within 120 min versus reaction temperature during con- Fig. 6. Molar C/H ratio of coke formed during conversion of methanol over version of methanol over HC1 exchanged zeolite Na-T (decationization HCl exchanged zeolite Na-T (decationization 41.5%, dealumination 41.5%, dealumination 10.2%). WHSV = 0.79g/(g catalyst h), pMleOH = 10.2%) versus reaction temperature. WHSV = 0.79g/(g catalyst h), pMeOH 0.13 bar, residence time T = 3.74 x lo-, h. = 0.13 bar, residence time T = 3.74 x h.

yield passes through a minimum at about 693 K. At the same temperature, the yields of propene and C,-olefiis show a maximum (Fig. 5). We suggest that, at first, coke formation decreases with rising temperature because the desorption of all reaction products from zeolite is enhanced. At higher temperatures, consecutive reactions, especially of adsorbed reaction products >C,, may occur forming coke molecules which cannot escape from the interior of the zeolite, on account of their size. Thus, coke formation increases again. Our inter- pretation is confirmed by the change in the C/H ratio of the coke, which increases linearly with temperature, indicating that the coke is becoming more and more unsaturated (Fig. 6). This points to the formation of larger molecules with increasing

L 35 3

- 30

4 .- 25

20

15

10

5

x

I I 1 I

reaction temperature I K 600 650 700 750 800

aromatic character. The yields of methane and ethene increase continuously over the whole temperature range (Fig. 5). We assume that both compounds are formed not only by cracking but also by a reaction mechanism different from that of higher hydrocarbons, since their formation cannot be described by the most probable distribution (cf. 4). Hence, in all subsequent investigations, the reaction temperature was set at 693 K because of the lowest coking tendency at this value. We know [21] that the total amount of MeOH converted over H-T, up to the beginning of deactivation, decreases slightly with increasing calcination temperature. However, since according to the authors' ex- perience, the influence of calcination temperature on selectivity is small, calcination at reaction temperature for 1 h is recom- mended. Longer calcination times show no effect on catalytic activity.

3.3 Comparison of Catalytic Activity of HC1 and NH,Cl Exchanged Zeolite Na-T

Five catalysts exchanged with HC1 and four exchanged with NH,Cl were prepared. Before use, the latter ones were precalcined for 4 h at 823 K in a stream of helium in order to obtain the H-form of the zeolite. After calcination at reaction temperature, 0.5g of each catalyst was used in the conversion of methanol (carrier gas helium, 3.72 lN/(g cat h), WHSV = 0.73g MeOH/(g cat h), pMMeOH = 0.12 atm, residence time T = 3.8 x h).

Fig. 7 shows the amount of MeOH per g catalyst, being converted to hydrocarbons up to the time when conversion fell to below 100% under our reaction conditions, as a function of decationization. For the HC1 exchanged catalysts, the total amount of converted MeOH increases at first due to an increas-

20-25% decationization. At higher exchange values, less MeOH is converted, i.e. the onset of deactivation by coke for-

Fig. 5. Yields of methane ( A ), ethene (*), propene ( X ) and C,-olefins (0) within 120 min, during conversion of methanol over HCl exchanged zeolite

(g catalyst h), versus reaction temperature. pMeoH = 0.13 bar, residence time 7 = 3.74 x h.

Na-T (decationkation 41.5%, &alumination 10,2%), WHSV = 0.79g/ ing number Of active centres. An Optimum is reached at

158 Chem. Eng. Technol. 12 (1989) 155- 161

decationization I YO Fig. 7. Mass of converted methanol up to the beginning of deactivation per g catalyst versus decationization of HCI exchanged (0) and NH,CI exchanged ( X ) zeolite Na-T. WHSV = 0.73g/(g catalyst h), pMeOH = 0.12 bar, residence time T = 3.8 x h.

mation is earlier. We suggest that this is due to dealumination becoming significant in this decationization range. As shown by Delannay and Ceckiewicz [20], amorphous material covers the surface of HCl exchanged zeolite Na-T, blocking the pore open- ings. This may hinder the product molecules in diffusing out of the zeolite and enhance coking in this way. On the other hand, the dependence of the total amount of converted MeOH on decationization is much weaker for the NH4C1 exchanged catalysts than for the HC1 exchanged ones. After a steep rise at low decationization, again due to an increasing number of active centres, there is a slow fall with increasing exchange. Since there is no dealumination, this decrease can only result from a growing number of active centres, catalyzing hydrogen transfer reactions. Near the optimum, the total amount of converted MeOH is smaller for the NH4C1 treated zeolites Na-T than for the HC1 treated ones. We know from other investigations [21] that the activity of NH4C1 exchanged zeolite Na-T depends on the calcination temperature. The samples used in the experiments described here were precalcined at 823 K, in order to obtain the H-form of the zeolite. Usually, such catalysts subsequently show a lower activity in MeOH conversion. Tables 1 and 2 give the product distributions as functions of decationization. On HC1 treated zeolite Na-T, above 25% ion exchange, equal amounts of ethene and propene are formed while, on NH4C1 treated samples, ethene yield increases and propene yield decreases appreciably with decationization, with maximum ethene yield at about 45 % ion exchange. The molar C/H ratio of the coke is higher for the NH,Cl exchanged zeolite samples than for the HC1 ones (Fig. 8). Obviously, dehydration reactions can proceed to a larger extent with the former catalysts than with the latter ones. In such dehydration reactions, which lead to coke, propene is more active than ethene. This may ex- plain the different yields of these two compounds. The total C,-C4-olefin production is usually higher on HC1 exchanged catalysts. Thus, for high yields of ethene, NH,Cl exchanged zeolite Na-T should be used with decationization of about 45 % and, for high yields of propene, low exchange HC1 or NH4Cl treated catalysts.

Table 1. Integral product distribution during conversion of methanol up to the beginning of deactivation over HCl exchanged zeolite Na-T at different decationizations and dealuminations. WHSV = 0.73 g MeOH/(g catalyst h), pMeOH = 0.12 bar, residence time T = 3.8 x lo-, h.

Decationi- zation [%I: 59.3 52.6 37.3 22.5 14.0 Dealumi- nation [%I: 27.1 20.9 10.2 2.2 0.1

g MeOH converted per g catalyst 0.8 1.29 2.0 2.5 1.4

coke Cl C, =

c, C, =

c3 C, =

c4

c5 +

[wt-%I [wt-%I [wt-%I [wt-%l [wt- % I [wt-%I [wt- %I [wt-%I [wt-%I

11.8 11.6 9.8 9.8 9.8 3.0 3.0 3.1 2.9 3.2

29.1 29.4 29.2 31.3 16.7 0.9 0.9 0.9 0.9 0.7

30.0 30.6 31.9 30.9 39.2 9.5 8.4 5.1 5.0 1.9 8.6 9.9 13.8 12.4 16.3 3.0 2.3 0.2 1.1 1.8 4.1 3.9 6.0 5.7 10.4

Table 2. Integral product distribution during conversion of methanol up to the beginning of deactivation over NH,Cl exchanged zeolite Na-T at different decationizations. WHSV = 0.73 g MeOH/(g catalyst h), pMeOH = 0.12 bar, residence time T = 3.8 x lo-, h.

Decationi- zation [%I: 84.5 45.5 18.0 8.0

g MeOH converted per g catalyst 1.16 1.61 1.70 1.70

coke [wt-%] 13.7 13.3 12.2 9.2 c, [wt-%I 3.9 4.0 2.5 3.2 c,= [wt-%I 33.2 35.3 29.2 21.9 c, [wt-%I 1.9 1.2 1.0 0.5 c,= [wt-%I 18.2 19.7 25.3 33.7 c3 [wt-%I 15.4 12.4 9.1 5.3

c5+ [wt-%I 3.6 4.2 6.9 9.9

c,= [wt-%I 6.8 7.2 10.9 14.0 c, [wt-%I 3.3 2.7 2.9 2.3

3.4 Znfluence of Process Variables on the Conversion of Methanol over Zeolite H-T

Another kind of variables, the so-called process variables, in- fluencing the conversion of MeOH over H-T, are the methanol partial pressure, pMeOH, the residence time 7, and deduced from these two the weight hourly space velocity, WHSV. If one of these three variables is kept constant, experiments can only be performed in such a way that the other two vary together.

In the first set of runs, we variedp,,,, (and hence also WHSV) at a constant residence time, thus investigating the influence of concentration on MeOH conversion. Table 3 gives the values of all the variables and product distributions. It may be concluded that, with increasing pMeOH and WHSV, the yields of paraffins and coke increase while those of olefins decrease, pointing to a growing influence of hydrogen transfer reactions on the product distribution. Surprisingly, at the lowest pMMeOH and WHSV values, the conversion of MeOH is low. Some paraffins and a

Chem. Eng. Technol. 12 (1989) 155 - 161 159

2.0 0 .- ; 1.8 L

I 1.6 I

G 1.L L

2 1.2

1.0 0

W Y 2 0.8

0.6

0.2 o.L I 0 10 20 30 LO 50 60 70 80 90 100

decationization I YO Fig. 8. Molar C/H ratio of coke formed during conversion of methanol up to the beginning of deactivation over HCl exchanged (0) and NH,CI exchanged ( x ) zeolite Na-T versus decationization. WHSV = 0.73g/ (g catalyst h), pMeoH = 0.12 bar, residence time 7 = 3.8 x lo-, h.

little coke are formed. Under these conditions, methane becomes the most important product apart from dimethyl ether.

In the second series of runs, we variedpMeOH and r a t a constant WHSV level, thus investigating not only the influence of concentration but also that of residence time. Table 4 lists the values of all the variables and product distributions. Again, with increasing pMeOH and 7, the yields of paraffins and coke increase and those of olefins decrease.

3.5 Regeneration of Deactivated Catalysts

Though coke formation during conversion of MeOH over H-T may be somewhat reduced by an optimal choice of variables, it cannot be avoided completely. Fig. 9 shows some typical time-yield curves. At first, the yields of C&, hydrocarbons

Table 3. Integral product distribution after conversion of 2.37g MeOH/g catalyst over HCl exchanged zeolite Na-T (decationization 41.2%, dealumination 10.2%) as a function ofp,,,,. Residence time 7 = 6.4 x

h.

P M ~ O H Par]: 0.014 0.14 0.41 0.68

WHSV [g MeOH/g catalyst h] 0.2 2.0 5.9 9.9

coke [wt-%I c, [wt-%l c,= [wt-%] c, [wt-%I c,= [wt-%] c, [wt-%I c,= [wt-%] c, [wt-%I c5+ [wt-%I

[wt-%] MeOH/DME

4.7 4.3

25.6 0.8

17.7 0.5 5.1 0.1 1.6

39.6

7.9 2.0

26.9 0.8

26.2 6.3

10.0 1.6 4.9

13.4

9.7 2.0

21.2 1 .o

24.1 8.0 8.0 4.6 6.0

15.4

11.1 2.0

20.5 1.3

20.4 8.6 8.6 4.1 6.1

17.3 __

Table 4. Integral product distribution during conversion of methanol up to the beginning of deactivation over HCl echanged zeolite Na-T (decationization 41.2%, dealumination 10.2%) at different pMleoH and residence times 7. WHSV = 0.79g MeOH/(g catalyst h).

P M ~ O H [barl: 0.71 0.55 0.27 0.17 10) [hi: 0.82 0.52 0.25 0.16

g MeOH converted per g catalyst

coke [wt-%I c, [wt-%l c,= [wt-%I c, [wt-%] c,= [wt-%] c, [wt-%l c,= [wt-%] c, [wt-%l CS+ [Wt-%l

1 .o 1.35 1.85

15.7 12.1 4.9 3.5

24.6 27.8 1.2 1 .o

16.0 24.1 17.7 12.6 7.8 8.8 5.7 4.3 6.4 5.8

9.5 3.0

29.3 0.8

28.6 9.3

10.0 3.4 6.1

1.8

8.2 2.3

32.1 0.9

31.4 7.5

11.1 1.6 4.9

decrease slowly but then with increasing rate when the coking curves (Fig. 10) begin to flatten. From now on the products con- tain more and more MeOH and dimethyl ether. The explanation of these results is quite simple. As Fig. 10 shows, coke is formed all the time. The lifetimes of the catalysts increase with increasing degree of exchange, due to the growing number of active centres. Coke formation blocks the active centres, thus reducing their number in the catalysis of the reaction to hydrocarbons so that, at the end, methanol and dimethyl ether break through. The yields of C,-C, hydrocarbons are less dependent on the coking state, again a reason to assume that they are formed by a different reaction mechanism.

We investigated the regeneration behaviour and development of catalytic activity over a number of reactionlregeneration cycles at different regeneration temperatures. The amount of burnt-off coke increases the faster, the higher is the reaction temperature.

3 701 i L\ - 60-\

'5, 50

LO

-0 W -

- - -

X

20

10

- -

60 120 180 2LO 300 0 time / min

Fig. 9. Yield profiles of methanol and dimethyl ether (o), C,-C, hydrocarbons ( x ) and C,-C, hydrocarbons ( 0 ) during conversion of methanol over HCl exchanged zeolite Na-T (decationization 52.6%, dealumination 20.9%). WHSV = 0.73g/(g catalyst h), pMeoH = 0.12 bar, residence time 7 = 3.8 x lo-, h.

160 Chem. Eng. Technol. 12 (1989) 155- 161

x 0 - 5 1 2 - 0) . 0 10

S 8 -

? .!! 6 -

- . 0

x Q,

u 5 L -

2 -

n , , . I ,

" 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 L.0 L.5 fed MeOH l g I g catalyst

Fig. 10. Coke yield versus fed methanol during conversion of methanol over HCl exchanged zeolite Na-T. Ratio of decationization to dealumination (%/%): ( x ) 59/27; ( A ) 52.6/20.9; ( 0 ) 37.3/10.2; (I) 22.5/2.2; (0) 14/0.1. WHSV = 0.73g/(g catalyst h), pMcOH = 0.12 bar, residence time 7 = 3.8 x h.

Catalyst activity slowly decreases from cycle to cycle, almost independently of the regeneration temperature (Fig. 11). Therefore, in the case of a series of fixed bed reactors, regeneration of coked catalysts can be effected by changing the feed from methanol to air at reaction temperature. The rise in bed temperature, occurring in the meantime, would not exert a large influence on catalytic activity and selectivity.

4 Discussion

Formation of hydrocarbons from MeOH over zeolites can be compared to chain polymerization catalyzed by active centres

* 50

30

20

I "0 2 L 6 8 10 12 14 16

reaction cycle number

Fig. 11. Conversion of methanol within 120 min over HCI exchanged zeolite Na-T (decationization 41.2%, dealumination 10.2%) versus number of reactiodregeneration cycles. WHSV = 0.79 g MeOH/(g catalyst h), pMleOH = 0.13 bar, residence time 7 = 3.74 x h (0): regeneration at 793 K, 1 h; ( x ) regeneration at 693 K, 5 h.

on the zeolite surface. For an equal propagation probability p of formation of all C-C bonds, irrespective of chain length, the resulting molar mass distribution is the "most probable distribution", derived by Schulz and Flory [22, 231

In this equation, Sci ist the C-selectivity of hydrocarbons with i C-atoms, p the ratio of C-C-bond formation rate r,, to the sum of r, and the desorption rate r, of hydrocarbon chains from the active centres. Product distributions in the presented experiments showed a significant departure from linearity for the methane and ethene points, indicating a formation mechanism of these two compounds, different from that for C, + hydrocarbons. (Similar results were published by Wu and Kaeding [24]). Therefore, it is reasonable to base product distributions on C, +

hydrocarbons [25]

(1 -p)2 i $ 1

1 - (l-p)2 - 2 ( l - p ) ' p SCi' =

Also taking into account the formation of coke and denoting the experimental selectivities of methane, ethene and ethane, and coke by Sc *, S2* and SC,coke* respectively, the selectivity related to all the hydrocarbons is obtained

SCi = SCi'(1 - SCi* - Sc2* - .

The values of p were determined with this equation so that the calculated C,-selectivities coincided well with the experimental ones. In all cases, the selectivities of all the other hydrocarbons could be well predicted with these p values [2 11.

For HC1 exchanged zeolite Na-T, p decreases linearly with decationization (Fig. 12, - x- ,). For NH,C1 exchanged samples (Fig. 12, -0-), this linear decrease in p is only observed up to 45 % decationization and then the curve flattens. Obviously, with increasing decationization, the MeOH feed is

o.22 t 1 0 . 2 0 " " ~ " " "

0 10 20 30 LO 50 60 70 80 90 100 decationization I %

Fig. 12. Propagation probability p for C,-C, hydrocarbons versus decationization during conversion of methanol over zeolite Na-T, exchanged with HCI (x) or with NH,Cl (0).

Chem. Eng. Technol. 12 (1989) 155 - 161 161

distributed to an increasing number of active centres so that suc- cessive reactions can only proceed to a lesser extent. We can only speculate about the cause of the difference in p at higher decationization for HC1 and NH,C1 exchanged zeolite Na-T. It may be caused by a different environment of the active centres, resulting from a higher dealumination in the HC1 exchanged samples. The dependence of p on pMeOH and WHSV (Fig. 13) is quite easily understood. It increases with increasing values of these parameters, thus relating the formation of longer chains to higher MeOH concentrations (Fig. 13). ButpMeOH should not be too low sincep then decreases on account of low MeOH concentrations at the active centres. Methane and dimethyl ether are then the main products.

WHSV / g MeOH I ( g catalyst hl 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

. A c

0 13

a C 0

0 [I, 0 a 0

a

- a ?

._ +-

c

methanol partial pressure I bar

Fig. 13. Propagation probability p for C,-C, hydrocarbons versus methanol partial pressure (x) and weight hourly space velocity (WHSV) (0) during conversion of methanol over HCl exchanged zeolite Na-T (decationization 41.2 %, dealumination 10.2 %).

5 Conclusions

From a practical viewpoint, zeolite H-T is suitable for the production of lower olefins from methanol. It may be prepared from zeolite Na-T by HCl or NH,C1 treatment. In the former case, the exchange is accompanied by appreciable dealumination, especially at higher HCl concentrations. High ethene yields are obtained with NH4C1 treated zeolite Na-T at about 45 % decationization, high yields of propene with low exchanged HC1 or NH,Cl treated catalysts. Therefore, and because high

dealumination may favour the collapse of the zeolite structure, ion exchange of zeolite Na-T with NH,Cl is to be recommend- ed. High MeOH partial pressure, long residence times, and high WHSV favour the formation of higher hydrocarbons. On the other hand, pMeOH should not be too low for ethene production because then methane and dimethyl ether become the main products. Regeneration is possible at the reaction temperature over a large number of reactionlregeneration cycles with low decay of catalyst activity, which constitutes an important advantage, compared to processes in which the reactor has to be heated during regeneration. Other experiments, not described here [21], indicate that catalysts with low particle sizes, arranged in flat layers should be used for high olefin yields.

Received: March 1, 1988 [CET 1331

References

Meisel, S.L., McCullough, J.P., Lechthaler, C.H., Weisz, P.B., Chemtech 6 (1976) p . 86. Chang, C.D., Silvestri, A.J., J. Cutul. 47 (1977) p. 249. Kaeding, W.W., Butter, S.A., J . Cutul. 61, (1980) p. 155. DOS 2830787, 1980, BASF AG (Inv.: L. Marosi, J. Stabenow, M. Schwarzmann); Chem. Abstr. 93 (1980) 13864e. DOS 2438252, 1975, Mobil Oil Corp. (Inv.: S.A. Butter, C.D. Chang, A.T. Jurewicz, W.W. Kaeding, W.H. Lang, A. Silvestri, R.L. Smith); Chem. Abstr. 83 (1975) 78810~. Singh, B.B., Lin, F.N., Anthony, R.G., Chem. Eng Commun. 4 (1980) p. 749. Wunder, F. A., Leupold, E.I., Angew. Chem. Inr. Ed. Engl. 19 (1980) p. 126. ' Dettmeier, U., Leupold, E.T., Litterer, H., Baltes, H., Herzog, W., Wunder, F.A., Erdoel Kohle 36 (1983) p. 365. Ceckiewicz, S., Bull. Acud. Pol. Sci., Ser. Sci. Chim. 27(1979) p. 629. Ceckiewicz, S., React. Kine?. Curd Lett. 16 (1981) p. 11. Ceckiewicz, S., J . Chem. SOC., Furaday Trans. I , 77(1981) p. 269. Ceckiewicz, S., J . Chem. Soc., Faraday Trans. I , 80 (1984) p. 2989. Marquart, R., Dissenution, TH Darmstadt 1984. Marquart, R., Fetting, F., Chem.-Ing.-Tech. 57 (1985) p. 982. Fleckenstein, T., Belendorff, K., Fetting, F., Gem.-1ng.-Tech. 57 (1985) p. 800; Ger. Chem. Eng 9 (1986) p. 346. Langner, B., Appl. Curd. 2 (1982) p. 289. U.S. Pat. 2950952, 1960, Union Carbide Corp. (Inv. D.W. Breck, N.A. Acara); Chem. Absrr. 55 (1961) 1968h. Enterman, W., van Leuven, H.C.E., Anal. Chem. 44 (1972) p. 589. Cichocki, A., Krist. Tech. 15 (1980) p. 869. Delannay, F., Ceckiewicz, S., Zeolites 5, (1985) p. 69. Gubisch, D., Dissenution, Univ.-GHS Essen 1985. Schulz, G.V., Z. Phys. Chem. B 30 (1935) p. 379. Flory, P.J., J. Am. Chem. SOC. 58 (1936) p. 1877. Wu, M.M., Kaeding, W.W., J . Cutul. 88 (1984) p. 478. Konig, L., Gaube, J., Chem.-Zng.-Tech. 55 (1983) p. 14.

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Conversion of methanol to light olefins over zeolite H-T