NO149492B - CATALYST MATERIAL AND PROCEDURE FOR SELECTIVE PREPARATION OF P-DIALKYL SUBSTITUTED BENZENES - Google Patents

Description

This invention relates to a catalyst material for the

tive preparation of para-dialkyl-substituted benzenes, including

tended a crystalline aluminosilicate zeolite with a SiC^/A^O-j ratio of 12 - 3000 and a "constraint index" within the range 1 - 12. Furthermore, the invention relates to a method for the selective production of para-dialkyl-benzenes, where each alkyl group contains 1-4 carbon atoms, especially p-xylene, p-diethylbenzene or

ler p-ethyltoluene, by which method catalyst materials

light according to the invention is used.

Disproportionation of aromatic hydrocarbons in the presence

of zeolite catalysts is described by Grandio et. eel. in Oil and Gas Journal, vol. 69, No. 48 (1971). In US Patent Nos.

3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961 describe vapor phase disproportionation of toluene over different catalyses

sators. In these processes, the xylenes obtained show an equilibrium composition, namely approx. 24 percent para-, 54 percent meta- and 22 percent ortho-xylene.

Of the xylene isomers, meta-xylene is the least desirable, as para-xylene has particular value in the production of terephthalic acid,

which is an intermediate product in the manufacture of synthetic fibres. Mixtures of xylene isomers, either alone or together with ethylbenzene, which generally contain the equilibrium concentration of para-xylene, have previously been separated by super-fractionation and multi-stage cooling, which entail large costs.

The invention relates to a catalyst material for the selective production of para-dialkyl-substituted benzenes, comprising a crystalline aluminum silicate zeolite with a SiO2/Al2O2_for-

hold of 12 - 3000 and a "constraint index" within the range 1 - 12, characterized in that it has an activity, alpha, of 2 - 5000, preferably 5 - 200, a xylene sorption capacity greater than 1g/100g zeolite and an ortho -xylene sorption time for 30% of said capacity of over 10 minutes, where the sorption capacity and sorption time are measured at 120°C and 4.5 ± 0.8 mm Hg.

A catalyst that meets the requirements mentioned

above, and which can thus take part in transformations of the aforementioned kind with the desired selectivity, can be provided in several forms

different forms, of which the ones indicated below constitute preferred embodiments of the invention. According to a first out-

embodiment, the crystal size of the zeolite is thus a determining factor, and preferably at least part of the zeolite is present as crystals with sizes from 0.5 to 20 µm, preferably 1-6 nm.

According to another embodiment, the catalyst acquires its properties by coking, in particular in that it carries a deposit of coke in an amount between 15 and 75 percent by weight, preferably 20-40 percent by weight, calculated on the weight of the catalyst without coke deposit.

According to a third embodiment, the prescribed activity and sorption properties are linked to a zeolite which is intimately associated with 2 - 30%, calculated on the weight of the zeolite, of one or more stable, difficult-to-reduce oxides, in particular oxides of antimony, phosphorus, boron, uranium, magnesium, zinc and/or calcium, as the percentages apply to each of these oxides.

In a preferred embodiment of this embodiment is

the zeolite associated with 2-25 percent by weight of an oxide of phosphorus and an oxide of magnesium, the preferred content of phosphorus oxide being between 0.7 and 15 percent by weight and of magnesium oxide between 1 and 15 percent by weight.

According to a fourth embodiment, the prescribed properties are achieved in that the zeolite in its internal crystalline structure contains 0.1 - 10%, calculated on the weight of the zeolite, of added amorphous silicon dioxide; preferably the amount of SiC>2

2-10 percent by weight. According to one of the more convenient production methods, the added amorphous silicon dioxide is the cleavage product of a silicon compound which is able to penetrate into the pores of the zeolite, e.g. a silicone, siloxane or polysilane or a mono-methyl, chloro or fluoro derivative thereof. Particularly suitable are silicon compounds with the formula SiR^I^R^*^/ where R and R2 are hydrogen, fluorine, chlorine, methyl, ethyl, amino, methoxy or ethoxy, R^ is hydrogen, fluorine, chlorine, methyl or amino, and R 1 is hydrogen or fluorine; other well-usable silicon compounds are silane, dimethylsilane, dichlorosilane, methylsilane or silicon tetrafluoride.

A fifth embodiment deviates i.a. from the fourth wood

that the desired properties are due to silica which is not present in the internal crystalline structure. According to this execu-

typically, the zeolite has a coating of silica on its outer surface in an amount between 0.5 and 30% by weight of the zeolite. This silica can also here be the cleavage product of a silicon compound that is unable to penetrate the zeolite's pores, e.g. a compound of the formula [ (R.j) (I^) SiO] , where and R 2 represent fluorine, hydroxy, alkyl, aralkyl or alkaryl or fluoroalkyl and may be the same or different except that only R^ may be hydrogen, and where n is from 10 to 1000 and the number of carbon atoms in R 1 or R 2 is from 1 to 10. The silicone compound preferably has a molecular weight of 500 - 20,000, preferably 1,000 - 10,000, and compounds which have been found to be particularly effective, are dimethylsilicone, diethylsilicone, phenylmethylsilicone, methylhydrogensilicone, ethylhydrogensilicone, phenylhydrogensilicone, methylethylsilicone, phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone, ethyltrifluoropropylsilicone, polydimethylsilicone, tetrachlorophenylmethylsilicone, tetrachlorophenylethylsilicone, tetrachlorophenylhydrogensilicone, tetrachlorophenylphenylsilicone, methylvinylsilicone and ethylvinylsilicone.

The preferred zeolites used in the catalysts according to the invention are zeolites ZSM-5, ZSM-11, ZSM-12, ZSM-35 or ZSM-38; it is usually advantageous to use them in a form characterized by the presence of hydrogen cations. The preferred catalysts are those in which the zeolite has an activity, alpha, within the range 5 - 200.

It is by no means necessary that the catalyst consist of zeolite; it may as well be a composite of a zeolite as mentioned with a binder, e.g. a naturally occurring or synthetic heat-resistant oxide. Suitable naturally occurring oxides are montmorillonite or kaolin clay; suitable synthetic oxides are silicon dioxide, aluminum oxide, magnesium oxide, zirconium oxide, thorium oxide, beryllium oxide and/or titanium dioxide. When a binder is used, it constitutes 1 - 99, preferably 20 - 95 percent by weight of the catalyst, and a particularly favorable proportion is 30 - 40 percent by weight.

According to another aspect of the invention, a method is provided for the "selective preparation of para-dialkyl-benzenes, where each alkyl group contains 1-4 carbon atoms, in particular p-xylene, p-diethylbenzene or p-ethyltoluene, by which method a C - C₁-monoalkyl-substituted benzene, a C₁-C₂-olefin and/or a -C₂-paraffin, or a mixture of one or more of these with benzene, under conversion conditions is brought into contact with a catalyst as indicated above The preferred conditions include a temperature of 250-750°C, a pressure between 0.1 and 100 atmospheres and a space velocity between 0.1 and 2000.

By using a temperature of 400 - 700°C, a pressure of 1-100 atmospheres and a space velocity of 0.1 - 100, toluene can be disproportionated, or alkylated with an alkylating agent with 1-4 carbon atoms, with very good results. A preferred space velocity for the aforementioned two conversions is 1 - 50. The same conditions are also favorable for the use of -C 2 -paraffins as starting material. By using a temperature of 300 - 700°C, a pressure of 1 - 100 atmospheres and a space velocity of 1 - 1000, - C 1 -olefins can be brought into contact with the catalyst and give the desired p-dialkylbenzenes.

Among the very useful products that can be produced according to the invention are p-xylene, p-diethyl-benzene or p-ethyl-toluene; under some circumstances, the yield can be increased if the reaction is carried out in the presence of hydrogen, in which case the molar ratio of hydrogen to added hydrocarbon is conveniently from 2 to 20.

The above-mentioned catalyst exhibits special properties

for the production of para-dialkyl-substituted benzenes containing alkyl groups with 1-4 carbon atoms in that a suitable hydrocarbon, such as mono-alkyl-substituted benzenes with 1-4 carbon atoms in the alkyl substituent, - C^-olefins or a C^- paraffin or a mixture thereof, under conversion conditions is brought into contact with the catalyst.

According to a preferred embodiment, the present method comprises the conversion of the specified compounds into xylenes in which the proportion of para-xylene is substantially greater than the normal equilibrium concentration and preferably greater than 40% by weight of the xylene product which is formed in the presence of the specified catalyst at a temperature between approx. . 250 and 750°C, and a pressure between 0.1 and 100 atmospheres using a space velocity between 0.1 and 2000- This space velocity is based on the weight of the catalyst materials, i.e. the combined weight of active catalyst and binder. The flowing product is separated and distilled to recover the desired product, for example para-xylene, and the unreacted product is recycled for further reaction.

The drawing's fig. 1 shows the change in the para-xylene selectivity with varying ortho-xylene sorption time for 30 percent of the xylene sorption capacity of the zeolite catalyst used. Fig. 2 shows a comparison regarding the para-xylene selectivity obtained with crystalline aluminosilicate zeolite catalyst with small and large crystals. Fig. 3 shows the changes in toluene conversion and para-xylene selectivity as a function of time using a simultaneous feed of toluene and hydrogen.

The hydrocarbon compound used as starting material in the method according to the invention can be a mono-alkyl-substituted benzene with 1-4 carbon atoms in the alkyl substituent, e.g. toluene; a C„-C. c-olefin, e.g. ethylene,

<L lol

propylene, butenes, pentenes, hexenes, heptenes, octenes, nonenes, decenes, pentadecenes, or mixtures thereof with each other or a <C>^<->C^ paraffin, such as butane, hexane, octane, dodecane, eicosane, dotriacontane , tetracontane, or mixtures of these with each other. The paraffins are preferably unbranched or only slightly branched paraffins.

Typical of the processes that can be discussed here are

disproportionation of toluene to benzene and xylene, where the proportion of para-xylene obtained is far greater than the normal equilibrium concentration. Such a process is effectively carried out at a temperature between 400 and 700°C at a pressure between 1 atmosphere and 100 atmospheres using a space velocity between 1 and 50.

Another starting material which is suitable for use in the method according to the invention is a stream with a high content of C 2 -C 1,5-olefin. Thus, ethylene, propylene, butenes, pentenes, hexenes, dienes such as butadiene, pentadienes, cycloolefins such as cyclopentene and cyclohexene, alkyl-substituted cycloolefins such as ethylcyclopentene, cyclopentadiene and cyclo-.hexadiene can be efficiently converted into para-dialkyl-substituted benzenes with high yield using the catalyst described above. When using such an olefin starting material, the conversion is carried out at a temperature within the approximate range of 300-700°c, a pressure between atmospheric pressure and 100 atmospheres, using a space velocity between 1 and.

As sources for the olefin reactant, one can use either mainly pure streams of C 2 -C 2 , -- olefin or refinery or chemical streams which have a high content of this reactant, i.e. usually over 25 percent by volume.

A further starting material which can be used with good results according to the invention for the selective production of para-dialkyl-substituted benzenes containing alkyl groups with 1-4 carbon atoms, includes paraffinic hydrocarbons having between 3 and 44 carbon atoms. Examples of such paraffins are butanes, pentanes, hexanes, heptanes, octanes, dodecanes, eicosane, dotriacontane, tetracontane and alkyl-substituted derivatives of these paraffins. When using such paraffinic starting materials, the reaction conditions will include contact with the above-described zeolite catalyst based on crystalline aluminosilicate at a temperature of 400-700°C, a pressure between 1 and 100 atmospheres and a space velocity between 0.1 and 100.

Mixed aromatics can also be used as starting material. For example, a mixture of ethylbenzene and toluene is selectively converted into a mixture rich in p-diethylbenzene and p-ethyltoluene, predominantly the latter when the ratio between the starting material's content of toluene and ethylbenzene is high.

Reaction between benzene, toluene, ethylbenzene, propylbenzene or butylbenzene with C2-C20 olefins or <C>5~C25 paraffins at 250-500 C gives p-dialkyl benzenes. This reaction is preferably carried out under pressure above 13.6 ato.

For example, benzene and ethylene give a molar ratio of

1:2 to 10:1 p-diethylbenzene in addition to ethylbenzene (p=27.2 ato, temperature 426.7°C); toluene and 1-octene give p-ethyltoluene and a mixture of n- and isopropyltoluene with a high content of the p-isomer.

Without the addition of aromatics, C2~C^^-olefins as well as C^-C^-paraffins give a mixture of aromatics rich in p-dialkylbenzenes. The olefins and the higher paraffins are more reactive and require less drastic operating conditions, e.g. a temperature of 250-600°C, preferably 300-550°C, while the lower paraffins, for example C^-C,.-paraffins give aromatics at a practically usable rate only above 400 oC. The aromatization can be carried out at atmospheric pressure or at elevated pressure; low-pressure hydrogen can be used to delay catalyst ageing, but high hydrogen partial pressure above 13.6 ato reduces aromatics formation. Production of p-dialkylated benzenes containing alkyl groups larger than , is favored by higher pressure and lower temperature; for example, p-ethyltoluene is formed from dodecane or 1-butene at 400°C, while p-xylene is the preferred dialkylbenzene which is formed at a higher temperature.

Methylation of toluene in the presence of the catalyst described above, in particular a catalyst on which coke has been deposited, is carried out by bringing the toluene into contact with a methylating agent, preferably methanol, at a temperature between 300 and preferably between 400 and approx. 700°c. At the higher temperatures, those zeolites which have a high silica/alumina ratio are preferred. For example, ZSM-5 with a Si02/Al20g ratio of 300 and above is very stable at high temperatures. The reaction is usually carried out at atmospheric pressure, but the pressure may be in the approximate range between 1 atmosphere and 68 ato. A space velocity between 1 and 2000 is used. The molar ratio between methylating agent and toluene is generally between 0.05 and 5. When methanol is used as methylating agent, a molar ratio between methanol and toluene of approx. 0.1-8 mol methanol per moles of toluene have been found to be appropriate. When using other methylating agents, such as methyl chloride, methyl bromide, dimethyl ether or dimethyl sulphide, the molar ratio between methylating agent and toluene can vary within the range indicated above. The reaction is conveniently carried out using a space velocity between 1 and 2000, preferably between 5 and 1500, weight units charge per weight unit of catalyst per hour. The reaction product, consisting predominantly of para-xylene, together with relatively small amounts of meta-xylene and ortho-xylene, can be separated in any suitable manner, such as by passing the material through a water condenser, after which the organic phase is passed through a column in which

a chromatographic separation of the xylene isomers is carried out.

According to the present invention, the starting compounds described above are brought into contact with a layer comprising a particulate catalyst containing a crystalline aluminosilicate, and which has: (1) an activity, expressed by the alpha value, between 2 and 5000, (2) a xylene sorption capacity of more than 1 g per 100 g of zeolite and (3) an ortho-xylene sorption time for 30 percent of said capacity of over 10 minutes, where the sorption capacity and sorption time are measured at 120°C

and a xylene pressure of 4.5 + 0.8 mm Hg.

The alpha value is a measure of the catalyst's relative activity in relation to a high activity silica-alumina cracking catalyst. To determine the alpha value, as this term is used here, the n-hexane conversion is determined at 538°c. The conversion is varied by varying the space velocity so that

a conversion of 10-60 per cent of the n-hexane is obtained and converted to a rate constant per unit volume of zeolite and is compared with the value for the silica-alumina catalyst which is normalized to a reference activity for 538°C. The catalytic activity of the catalysts is expressed as a multiple of this standard, i.e. the silica-alumina standard. This silica-alumina reference catalyst contains approx. 10 weight percent A^O^, the rest SiO2» This method of determining alpha, modified as described above, is more fully described in the Journal of Catalysis,

Vol. VI, pp. 278-287, 1966.

The measurements of hydrocarbon sorption capacities and rates are conveniently carried out using a thermobalance. In particular, it has been found that an equilibrium sorption capacity for xylene, which can be either para-, meta-, ortho-xylene or a mixture thereof, preferably para-xylene as this isomer reaches equilibrium in the shortest time, of at least 1 g per 100 g of zeolite, measured at 120°C and a xylene pressure of 4.5 + 0.8 mm Hg, and an orthoxylene sorption time for 30 percent of said capacity of more than 10 minutes (at the same temperature and pressure conditions) is required to obtain of the desired selective formation of para-dialkyl-substituted benzenes.

It has been found that zeolites exhibiting very high selectivity for the formation of para-dialkylbenzene require a very long time, up to and exceeding 1000 minutes, to sorb o-xylene in an amount of 30% of the entire xylene sorption capacity. For these materials it is more convenient to determine the sorption time for a lower degree of sorption, e.g. 5%, 10% or 20% of capacity, and calculate the time for 30% sorption using the following multiplication factor F, as illustrated for 5% sorption:

t 0.3 = F.t 0.05

When determining the zeolite crystal size, conventional scanning electron microscopy can be used, with the smallest crystal dimension of a given crystal being taken as a dimension reference. The crystalline aluminosilicate zeolites used in the present invention in a significant proportion are essentially characterized by a crystal size greater than 0.5 µm. The aim is that the amount of zeolite with such a crystal size will be such that it exerts a direct influence on the selective production of para-dialkyl-substituted benzenes. In general, the amount of zeolite with such a crystal size will be present in a predominant proportion, i.e. in an amount that exceeds 50% by weight and can preferably amount to 100% by weight of the total zeolite used.

In addition to scanning electron microscopy as a tool in the selection of an effective crystalline aluminosilicate zeolite for use in the catalyst used here, measurement of the hydrocarbon sorption capacity and rate has been useful when it comes to characterizing the catalyst. Such measurements are conveniently carried out gravimetrically using a thermo balance.

The carbonaceous coating applied to the catalyst, commonly referred to as "coke" and resulting from the cracking of hydrocarbons, is generally deposited at high temperature in the presence of the catalyst in question during a reaction such as the methylation of toluene. In general, a pre-coking of the catalyst will be achieved by initially using the uncoked catalyst in the reaction in question, during which coke is deposited on the catalyst surface and then regulated within the above-mentioned range of 15 to 75 percent by weight by periodic regeneration by exposure to an oxygen-containing atmosphere at elevated temperature.

An advantage that comes with the use of the catalyst described here is that it can easily be regenerated. After using

the pre-coked catalyst to carry out the desired reaction over a period of time so that the activity of the catalyst decreases to a point where further use becomes uneconomical, it can thus be easily regenerated by burning off excess coke in an oxygen-containing atmosphere, for example air, at a temperature that is generally within - the range 4 00 - 700°C. The catalyst can thereby be made mainly free of coke,

which makes it necessary to subject the catalyst to pre-coking. Alternatively, the catalyst can be partially freed of coke during the regenerative combustion step, so that it

remains a residue of coke on the surface of the catalyst, the amount of which is within the aforementioned range from 15 to 75 percent by weight of coke. The regenerated catalyst can then be used again to achieve the desired selective formation of para-xylene.

In a preferred embodiment, the crystalline aluminosilicate zeolites used may have undergone modification prior to use by selective pre-coking to deposit at least 1 percent by weight and generally between 2 and 40 percent by weight of coke, based on the weight of the entire catalyst. If zeolite is used in mainly pure form or in combination with

a low coke-forming binder, such as silica, then coke is

the amount usually in the range of 2-10 percent by weight. When the zeolite is combined with a binder with a strong coke-forming tendency,

such as aluminum oxide, the coke content of the overall catalyst is normally in the range of 10-40 percent by weight. Pre-coking can be achieved by bringing the catalyst into contact with

a hydrocarbon charge, for example toluene, under harsh reaction conditions or alternatively at a reduced hydrogen/hydrocarbon concentration, i.e. 0-1 mol hydrogen per moles of hydrocarbon,

for a sufficiently long time for the desired amount of coke to be deposited.

Pre-modification of the zeolite can also be conveniently carried out by combining the zeolite with a small amount, usually

show within the range from 2 to 30 percent by weight, of a difficult-to-reduce oxide, such as oxides of antimony, phosphorus, boron, magnesium, uranium, zinc and/or calcium. Combination of that

desired oxide with the zeolite can be readily obtained by contacting the zeolite with a solution of a suitable compound of the element to be introduced, followed by drying and calcination to convert the compound into the oxide form.

According to an advantageous embodiment of the above-mentioned modification, the difficult-to-reduce oxides are oxides of phosphorus and magnesium, both of which are then present at the same time. The production of the catalyst (which is particularly effective in toluene disproportionation) is carried out in two stages, the zeolite crystals being in a mainly alkali metal-free form, i.e. containing less than 1.5 percent by weight of alkali metal and preferably having received at least part of the associated, original cations replaced by hydrogen, are first brought into contact with a phosphorus compound.

Representative phosphorus-containing compounds include derivatives of groups represented by PX^/ RPX2' R2PX' R3P' X3P0'

(X03)PO, (XO)3P, R3P=0, R3P=S, RP02, PPS2, RP(O) (0X)2,

RP(S) (SX)2, R2P(0)OX, R2P(S)SX, RP(OX)2/RP(SX)2, ROP(OX)2, RSP(SX)2, (RS)2PSP( SR)2 and (RO)2POP(OR)2, where R is an alkyl or aryl group, such as a phenyl radical, and X is hydrogen, R or halide. These compounds include primary (RPH2), secondary (R2PH) and tertiary (R3-P) phosphines such as butylphosphine;

tertiary phosphine oxides, R3PO, such as tributylphosphine oxide; tertiary phosphine sulfides, R3?S; primary (RP(0)(OX)2) and secondary (R2P(0)OX) phosphonic acids, such as benzenephosphonic acid; the corresponding sulfur derivatives, such as RP(S)(SX)2 and R2P(S)SX, esters of the phosphonic acids, such as diethylphosphonate, (RO)2P(0)H, dialkyl alkylphosphonates, (RO)2P(0 )R, and alkyl-dialkylphosphinates, (RO)P(O)R2; phosphine acids, R2P0X, such as diethylphosphine acid, primary (RO)P(OX)2# secondary, (RO)2POX, and tertiary, (RO)3P, phosphites; and esters thereof such as the monopropyl ester, alkyl-dialkylphosphinites, (RO)PR2, and dialkyl-alkylphosphonite, (RO)2PR esters. Corresponding sulfur derivatives can also be used, including (RS)2P(S)H, (RS)2P(S)R, (RS)P(S)R2, R2PSX, (RS)P(SX)2, (R<S> )2PSX, (RS)3P, (RS)PR2 and (RS)2PR. Examples of phosphite testers include trimethyl phosphite, triethyl phosphite, diisopropyl phosphite, butyl phosphite; and.pyro-phosphites such as tetraethyl pyrophosphite. The alkyl groups in the aforementioned compounds contain 1-4 carbon atoms.

Other suitable phosphorus-containing compounds include phosphorus halides, e.g. phosphorus trichloride, -bromide and -iodide, alkyl-phosphorus dichloridites, (R0)PC12, dialkyl-phosphorus chloridites, (RO)2PX, dialkyl-phosphine chloridites, R2PCl, alkyl-alkylphosphonic chloridates, (RO)(R)P(0)Cl, dialkyl phosphine chlorides, R2P(0)C1 and RP(0)C12- Useful corresponding sulfur derivatives include (RS)PC12, (RS)2PX, (RS)(R)P(S)C1 and R P(S)Cl.

Preferred phosphorus-containing compounds include diphenylphosphine chloride, trimethylphosphite and phosphorus trichloride, phosphoric acid, phenylphosphine oxychloride, trimethylphosphate, diphenylphosphine acid, diphenylphosphine acid, diethylchlorothiophosphate, acid methylphosphate and other alcohol-P20, reaction products.

The reaction between the zeolite and the phosphorus compound is carried out by bringing the zeolite into contact with said compound. When the phosphorus compound used in the treatment is a liquid, the compound can be dissolved in a solvent during the treatment of the zeolite. Any solvent which is relatively inert to the treating compound and the zeolite can be used. Suitable solvents include water and aliphatic, aromatic or alcoholic liquids. When the phosphorus-containing compound is, for example, trimethylphosphite or liquid phosphorus trichloride, a hydrocarbon solvent such as n-octane can be used. The phosphorus-containing compound can be used without a solvent, i.e. it can be used as a liquid. When the phosphorus-containing compound is in a gaseous state, such as when gaseous phosphorus trichloride is used, the treating compound can be used alone, or it can be used in admixture with a gaseous diluent which is relatively inert to the phosphorus-containing compound and the zeolite, e.g. air or nitrogen, or in mixture with an organic solvent, such as octane or toluene.

Before the reaction between the zeolite and the phosphorus-containing compound, the zeolite can be dried. The drying can take place in air. Elevated temperatures can be used. However, the temperature must not be so high that the zeolite's crystal structure is destroyed.

Heating the phosphorus-containing catalyst after production and before use is also preferable. The heating can be carried out in the presence of oxygen, e.g. air. The heating can take place at a temperature of approx. 150°C. Higher temperatures, i.e. up to approx. 500°C, however, is preferable. The heating is generally carried out for 1-5 hours, but can be extended to 24 hours or more. Heating temperatures above 500°C can be used, but they are not required. At temperatures of approx. At 1000°C, the zeolite's crystal structure tends to be damaged. After heating in air at elevated temperatures, phosphorus is present in the oxide form.

The amount of phosphorus oxide that is incorporated into the zeolite should be at least 0.25% by weight. However, it is preferred that the amount of phosphorus oxide in the zeolite is at least 2% by weight, particularly when it is combined with a binder, e.g. 35% aluminum oxide by weight. The amount of phosphorus oxide can be as high as approx. 25% by weight or more depending on the amount and type of binder. The amount of phosphorus oxide added to the zeolite is preferably between 0.7 and 15 percent by weight.

The amount of phosphorus oxide that is incorporated into the zeolite by reaction with elemental phosphorus or a phosphorus-containing compound will depend on several factors. One of these is the reaction time, i.e. the time the zeolite and the phosphorus-containing material are kept in contact with each other. With longer reaction times, a greater amount of phosphorus is incorporated into the zeolite, if all other factors are kept constant. Other factors that affect the amount of phosphorus incorporated into the zeolite include the reaction temperature, the concentration of the treating compound in the reaction mixture, the degree to which the zeolite has been dried prior to reaction with the phosphorus-containing compound, the conditions of drying the zeolite after the reaction between the zeolite and the treating compound, as well as the amount and type of binder incorporated into the zeolite.

The zeolite containing phosphorus oxide is then further combined with magnesium oxide by contact with a suitable magnesium compound. Representative magnesium-containing compounds include magnesium acetate, magnesium nitrate, magnesium benzoate, magnesium propionate, magnesium 2-ethylhexoate, magnesium carbonate, magnesium formate, magnesium oxylate, magnesium amide, magnesium bromide, magnesium hydride, magnesium lactate, magnesium laurate, magnesium oleate, magnesium palmitate, magnesium silicylate, magnesium stearate and magnesium sulfide.

The reaction between the zeolite and the treating magnesium compound is carried out by bringing the zeolite into contact with said compound. When the treating compound is a liquid, the compound may be dissolved in a solvent during the treatment of the zeolite. Any solvent which is relatively inert to the treating magnesium compound and the zeolite can be used. Suitable solvents include water and aliphatic, aromatic or alcoholic liquids. The treating compound can also be used without a solvent, i.e. it can be used in the form of a liquid. When the treating compound is in a gaseous state, it can be used alone, or it can be used in admixture with a gaseous diluent that is relatively inert to the treating compound and the zeolite, such as helium or nitrogen, or in admixture with an organic solvent, such such as octane or toluene.

Heating of the catalyst impregnated with the magnesium compound after production and before use is preferred. The heating can be carried out in the presence of oxygen, e.g. air. The heating can be carried out at a temperature of approx. 150°c. Higher temperatures, i.e. up to approx. 500°C, however, is preferable. The heating is generally carried out for 1-5 hours, but can be extended to 24 hours or more. Heating temperatures above 500°C can be used, but are generally not required. At temperatures of approx. At 1000°C, the zeolite's crystal structure tends to be damaged. After heating in air at elevated temperatures, the oxide form of magnesium is present.

The amount of magnesium oxide that is incorporated into the calcined phosphorus oxide-containing zeolite should be at least 0.25 percent by weight. However, it is preferred that the amount of magnesium oxide in the zeolite is at least 1% by weight, particularly when it is combined with a binder, for example 35% by weight of aluminum oxide. The amount of magnesium oxide can be as high as approx. 25% by weight or more depending on the amount and type of binder. The amount of magnesium oxide added to the zeolite is preferably between 1 and 15 percent by weight.

The amount of magnesium oxide that is incorporated into the zeolite by reaction with the treating solution and subsequent calcination in air will depend on several factors. One of these is the reaction time, i.e. the time during which the zeolite and the magnesium-containing material are kept in contact with each other. When all other factors are kept constant, increasing reaction time will result in an increasing amount of magnesium oxide incorporated in the zeolite. Other factors

which is important for the amount of magnesium oxide that is incorporated

in the zeolite, include the reaction temperature, the concentration of the treating compound in the reaction mixture, the degree to which the zeolite has been dried prior to reaction with the treating compound, the conditions of drying the zeolite after the reaction between the zeolite and the magnesium compound, and the amount and type of binder incorporated in the zeolite.

After the treatment of the phosphorus oxide-containing zeolite with the magnesium reagent, the resulting composite is dried and heated in a similar manner as in the preparation of the phosphorus oxide-containing zeolite.

A further embodiment of the catalyst according to the invention, which again has particular applicability in the selective disproportionation of toluene to p-xylene, is an embodiment in which the zeolite contains, interdispersed in its internal crystalline structure, amorphous silica added to the crystalline zeolite after that this is formed, in an amount of at least 0.1 percent by weight and generally within the range of 2-10 percent by weight.

It has been found that such a catalyst can conveniently be prepared by sorption of a silicon-containing compound,

generally a silane, into the pores of a crystalline aluminosilicate zeolite which has the above-mentioned silica/alumina ratio and constraint index. The molecular dimensions of the silicon compound used are such that it is easily sorbed into the pores of the aluminosilicate zeolite. The sorbed silicon compound contained in the pores of the crystalline aluminosilicate is subjected to catalyzed hydrolysis, either by base-catalyzed hydrolysis, for example by contact with a solution of aqueous ammonia, or by acid-catalyzed hydrolysis in the presence of Lewis or Brohsted acids, e.g. by contact with an aqueous solution of hydrochloric acid, followed by calcination in air at a temperature between 300 and 700°C with the formation of amorphous silica inside the pores of the aluminosilicate zeolite.

According to a preferred manufacturing technique, the zeolite crystals in essentially alkali metal-free form, i.e. they contain less than 1.5 percent by weight of alkali metal and preferably have had at least part of the original cations thus connected replaced by hydrogen, are brought into contact with a silicon-containing compound whose molecular dimensions are such that it is easily sorbed into the zeolite's pores. In general, the silicon-containing compound used is a silane with the following formula:

where and R 2 are hydrogen, fluorine, chlorine, methyl, ethyl, amino, methoxy or ethoxy; R 1 is hydrogen, fluorine, chlorine, methyl, amino or methoxy; and R 4 is hydrogen or fluorine. Other suitable silicon-containing compounds include siloxanes such as di-siloxanes, tri-siloxanes and higher siloxanes up to deca-siloxanes, and polysilanes such as di-silanes, tri-silanes and higher silanes up to deca-silanes. The aim is also to use derivatives of the above-mentioned siloxanes and polysilanes with methyl, chlorine or fluorine substituents, where the silicon atom does not contain more than one of these substituents.

The silicon compound used can either be in the form of a liquid or a gas under the conditions under which it is brought into contact with the zeolite. The pores of the zeolite are preferably, but not necessarily, saturated with the liquid or gaseous silicon compound. The silicon compound then undergoes catalyzed hydrolysis as described above, for example by bringing the zeolite containing the sorbed silicon compound into contact with a suitable acid or base for a sufficiently long time for the desired hydrolysis to take place with the evolution of hydrogen. The resulting product is then calcined in an oxygen-containing atmosphere, such as air, at a temperature between 300 and 700°C for 1-24 hours, whereby a zeolite catalyst of the specified crystalline aluminosilicate is obtained, the zeolite containing silica in its internal structure..

The amount of silica that is incorporated into the zeolite will depend on several factors. One of these is the time during which the zeolite and the silicon-containing material are kept in contact with each other. When all other factors are kept constant, increasing contact time will result in an increasing amount of silica in the zeolite. Other factors that affect the amount of silica incorporated into the zeolite include the temperature, the concentration of the treating compound in the contact media used, the degree to which the zeolite has been dried prior to contact with the silicon-containing compound, the conditions of the hydrolysis and calcination of the zeolite after this has been brought into contact with the treating compound, and the amount and type of binder that is incorporated into the zeolite.

According to an alternative embodiment, the zeolite has a coating of silica deposited on its outer surface. This coating covers the outer surface of the zeolite and is mainly completely located on the outer surface, although it will be understood that a number of factors affect the final location of this silica. The coating of silica is deposited on the surface of the zeolite by bringing it into contact with a silicone compound of such a molecular size that it cannot penetrate the zeolite's pores, and subsequent heating in an oxygen-containing atmosphere, such as air, to a temperature above 300° C, but below a temperature at which the crystallinity of the zeolite is adversely affected, at such a rate that the silicone compound does not volatilize before it

oxidized to silica.

The silicone compound used to form the silica coating has the following general formula:

where R 1 is hydrogen, fluoro, hydroxy, alkyl, aralkyl, alkaryl or fluoroalkyl. The hydrocarbon substituents generally contain 1-10 carbon atoms and are preferably methyl or

ethyl groups. R 2 is selected from the same group as R 1 , with the exception of hydrogen, and n is an integer of at least 10 and generally within the range 10-1000. The silicone compound's molecular weight is generally between 500 and 20,000 and preferably in the range 1,000-10,000. Representative silicone compounds include dimethyl silicone, diethyl silicone,

phenylmethylsilicone, methylhydrogensilicone, ethylhydrogensilicone, phenylhydrogensilicone, methylethylsilicone, phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone, ethyltrifluoropropylsilicone, polydimethylsilicone, tetrachlorophenylmethylsilicone, tetrachlorophenylethylsilicone, tetrachlorophenylhydrogensilicone, tetrachlorophenylphenylsilicone, methylvinylsilicone and ethylvinylsilicone.

The silicone compound dissolved in a suitable solvent, e.g. n-hexane, pentane, heptane, benzene, toluene, chloroform, carbon tetrachloride, are kept in contact with the above-mentioned zeolite at a temperature between 10 and 100°C for a sufficiently long time for the finally desired amount of silicone to be deposited. The contact time will generally be within the range of 0.2-5 hours, during which the mixture is appropriately subjected to evaporation.

The resulting residue is then calcined in an oxygen-containing atmosphere, preferably air, at a heating rate of 0.2-5°C/minute to a temperature above 300°C, but below a temperature at which the crystallinity of the zeolite is adversely affected. In general, this temperature will be below 600°C. The calcination temperature is preferably within about

advised 350-550°C. The product is kept at the calcination temperature, usually for 1-24 hours, whereby a silica-coated zeolite is obtained which contains between 0.5 and 30 weight percent and preferably between 1 and 15 weight percent silica.

Zeolites such as zeolite X, zeolite Y, ZSM-4, faujasite, mordenite, ferrierite and offretite which exhibit the above-mentioned activity and sorption properties fall within the scope of the invention. As mentioned above, the zeolites exhibit a silica/alumina ratio of at least 12 and a constraint index in the range 1-12. These zeolites effect profound conversions of aliphatic hydrocarbons to aromatic hydrocarbons with commercially satisfactory yields and are generally very effective in conversion reactions where aromatic hydrocarbons are involved. Although they have an unusually low alumina content, i.e. high silica/alumina ratio, they are very active even when the silica/alumina ratio exceeds 30. The activity is surprising, as catalytic activity is generally attributed to skeletal aluminum atoms and cations that are connected with these aluminum atoms. These zeolites retain their crystallinity for a long time despite the presence of water vapor at high temperature which causes irreversible breakdown of the skeleton in other zeolites, for example of the X and A type. Furthermore, carbonaceous deposits, when formed, can be removed

by burning at temperatures above normal, whereby the activity is restored. In many environments, the zeolites of this class show very little coke-forming ability, which helps to extend the service life between burn-off regenerations.

An important feature of the crystal structure of this class

of zeolites is that it results in restricted access to and exit from the intracrystalline free space due to the fact that it has a pore dimension greater than approx. 5 Å and pore windows whose size approximates those produced by 10-membered rings of oxygen atoms. It will of course be understood that these rings are those formed by the regular arrangement of the tetrahedra which make up the anionic skeleton of the crystalline aluminosilicate, the oxygen atoms being bound to the silicon or aluminum atoms in the centers of the tetrahedra. The preferred zeolite type which is used according to the invention, in short, exhibits the following combination: a silica/alumina mole ratio of at least 12, and a structure which gives restricted access to the free space in the crystal structure. v

The aforementioned ratio between silica and alumina can be determined by conventional analysis. It is intended that this ratio should represent, as accurately as possible, the ratio in the rigid anionic skeleton of the zeolite crystal, and that aluminum in the binder or in cationic or other form inside the channels is not taken into account. Although zeolites with a silica/alumina ratio of

at least 12 can be used, it is preferred to use zeolites with a higher ratio of at least 30. After activation, such zeolites have an intracrystalline sorption capacity for normal hexane that is greater than for water, i.e. that they exhibit "hydrophobic" properties. It is believed that this hydrophobic character is advantageous in the present invention.

The type of zeolites that can be used according to the invention sorbs normal hexane well and has a pore size greater than <5> A. The structure must also provide restricted access for larger molecules. It is sometimes possible to judge from a known crystal structure whether such restricted access exists. If e.g. the only pore windows in a crystal are formed by 8-membered rings of oxygen atoms, then molecules with a larger cross-section than normal hexane are prevented, and the zeolite is then not of the desired type. Windows formed by 10-membered rings are preferred, although excessive crimping or blocking of pores can in some cases render these zeolites ineffective. Twelve-membered rings generally do not seem to offer sufficient constraint to give the beneficial transformations, although wrinkled structures do exist, such as TMA offretite, which is a known effective zeolite. Furthermore, structures can be envisaged which may be usable due to pore blocking or other reasons.

Instead of trying to judge from the crystal structure whether a zeolite has the necessary inhibited access or availability, one can carry out a simple determination of the "inhibition index" by continuously feeding a mixture of equal amounts by weight of normal hexane and 3 -methylpentane over a small sample, approx. 1 g or less, of catalyst at atmospheric pressure according to the following procedure: a sample of the zeolite in the form of pellets or extruded material is crushed to a particle size approximately that of coarse sand and arranged in a glass tube. Before the test, the zeolite is treated with a stream of air at 538°C for at least 15 minutes. The zeolite is then flushed with helium, and the temperature is set to between 288°C and 510°C, which gives an overall conversion between 10 and 60%. The mixture of hydrocarbons is passed at a space velocity on a liquid basis (ie 1 volume unit of liquid hydrocarbon per unit volume of zeolite per hour) over the zeolite with a helium dilution which gives a mole ratio between helium and total hydrocarbon of 4:1. After 20 minutes of flow through, a sample is taken of the flowing product, which is analysed, most appropriately by gas chromatography, to determine the proportion that remains unchanged for each of the two hydrocarbons. The "constraint index" is calculated as follows:

The inhibition index roughly corresponds to the ratio of the cracking rate constants of the two hydrocarbons. Zeolites which are suitable for use according to the invention are those which have an inhibition index within the approximate range of 1-12. Values for this index (Cl) for some of the typical zeolites are:

It will be understood that the above-mentioned inhibition index values typically characterize the indicated zeolites, but that they are the cumulative result of several variables used in the determination and calculation thereof. For a given zeolite, the inhibition index can thus, depending on the temperature used within the above-mentioned range of 288-510°C, with conversion between 10 and 60%, vary within the indicated range of 1 - 12.

Likewise, other variables, such as the crystal size of the zeolite, the presence of possible entrapped contaminants and binders intimately united with the zeolite, can affect the inhibition index. Accordingly, it will be understood by those skilled in the art that the inhibition index, as used herein, although a very useful means of characterizing the zeolites of interest, is approximate or approximated, in view of the manner in which which it is determined, with the probability that - in some cases - extreme values for the variables are merged. With a temperature within the above-mentioned range of 288-510°C, however, the inhibition index will in all cases have a value for any given zeolite of interest here, within the aforementioned range of 1-12.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-11, ZSM-12, ZSM-35, ZSM-38, and other similar materials. U.S. Patent No. 3,702,886, to which reference is made, describes ZSM-5.

ZSM-11 is described more particularly in U.S. Patent No. 3,709,979, to which reference is made.

ZSM-12 is more particularly described in U.S. Patent No. 3,832,449, which is incorporated herein by reference.

ZSM-38 can be identified, using molar ratios between oxides and in the anhydrous state, as follows:

where R is an organic nitrogen-containing cation derived from a 2-(hydroxyalkyl)-trialkylammonium compound, and M is an alkali metal cation and is characterized by a specified powder X-ray diffraction pattern.

In a preferred synthesized form, the zeolite has a formula, given by molar ratio between oxides and in the anhydrous state, as follows:

where R is an organic nitrogen-containing cation derived from a 2-(hydroxyalkyl)trialkylammonium compound, where the alkyl group is methyl, ethyl or a combination thereof, M is an alkali metal, especially sodium, and x is greater than 8 and up to about . 50.

The synthetic ZSM-38 zeolite has a certain distinctive crystal structure whose X-ray diffraction pattern shows essentially the significant lines indicated in Table I. It will be seen that this X-ray diffraction pattern (significant lines) corresponds to the lines of natural ferrierite, with the notable exception that natural ferrierite exhibits a significant line at 11.33Å.

A further property of ZSM-38 is its sorption capacity which means that this zeolite has increased capacity for 2-methylpentane (with respect to n-hexane sorption at the n-hexane/2-methylpentane ratio) when compared to a hydrogen form of natural ferrierite obtained by calcination of an ammonium-exchanged form. The characteristic n-hexane/2-methylpentane sorption ratio for ZSM-38 (after calcination at 600°C) is less than 10, while the ratio for the natural ferrierite is substantially greater than 10, as high as 34 or higher.

Zeolite ZSM-38 can conveniently be prepared by preparing a solution containing sources of an alkali metal oxide, preferably sodium oxide, an organic nitrogen-containing oxide, an oxide of aluminium, an oxide of silicon and water, and which has a composition, expressed by mole ratio between oxides, within the following ranges:

where R is an organic nitrogen-containing cation derived from a 2-(hydroxyalkyl)-trialkylammonium compound, and M is an alkali metal ion, from which mixture crystals of zeolite are formed. (The amount of 0H~ is calculated only from the inorganic sources of alkali without any contribution from organic base). The crystals are then separated from the liquid and recovered. Typical reaction conditions consist in heating the above-mentioned reaction mixture to a temperature between 90°C and 400°C for a time between 6 hours and 100 days. A more preferred temperature range is from 150 to 400°C and a period of time at a temperature within this range from 6 hours to 80 days.

The treatment of the gel particles is carried out until crystals are formed. The solid product is separated from the reaction medium, e.g. by cooling the whole to room temperature, filtering and washing with water. The crystalline product is then dried, for example at 110°C for 8-24 hours.

ZSM-35 can be identified; using molar ratios between oxides and in the anhydrous state, as follows: (0.3-2.5)R20 : (0-0.8)M20 : Al203 : >8 Si02

where R is an organic nitrogen-containing cation derived from ethylenediamine or pyrrolidine, and M is an alkali metal cation, and is characterized by a specified powder X-ray diffraction pattern.

In a preferred synthesized form, the zeolite has a formula, expressed in molar ratio between oxides and in the anhydrous state, as follows: (0.4-2.5)R20 : (0.0.6)M20 : Al^ : xSiC >2

where R is an organic nitrogen-containing cation derived from ethylenediamine or pyrrolidine, M is an alkali metal, especially sodium, and x is greater than 8 and up to about 50.

The synthetic ZSM-35 zeolite has a certain distinctive crystalline structure whose X-ray diffraction pattern shows substantially the significant lines indicated in Table II. It will be seen that this X-ray diffraction pattern (with respect to significant lines) corresponds to that of native ferrierite, with the notable exception that native ferrierite exhibits a significant line at 11.33Å. Closer examination of some individual samples of ZSM-35 can show a very weak line at 11.3-11.5Å. However, this very weak line is not found to be a significant line for ZSM-35.

A further property of ZSM-35 is its sorption capacity, which means that this zeolite has increased capacity for 2-methylpentane (with respect to n-hexane sorption at the n-hexane/2-methylpentane ratio) when compared to a hydrogen form of natural ferrierite obtained by calcination of an ammonium-- exchanged form. The characteristic sorption ratio n-hexane/2-methylpentane for ZSM-35 (after calcination at 600°C) is less than 10, while the ratio for the natural ferrierite is significantly greater than 10, for example as high as 34 or higher.

Zeolite ZSM-35 can conveniently be prepared by preparing a solution containing sources of an alkali metal oxide, preferably sodium oxide, an organic nitrogen-containing oxide, an oxide of aluminum, an oxide of silicon and water, and which has a composition, expressed by mole ratio between oxides, within the following ranges:

where R is an organic nitrogenous cation derived from pyrrolidine or ethylenediamine, and M is an alkali metal ion, from which mixture crystals of zeolite are formed. (The amount of 0H~ is calculated only from the inorganic sources for alkali without any contribution from organic base). The crystals are then separated from the liquid and recovered. Typical reaction conditions consist in heating the above-mentioned reaction mixture to a temperature between 90 and 400°C for a period of time between 6 hours and 100

days. A more preferred temperature range is between 150 and 400°C for a period between 6 hours and 80 days.

The treatment of the gel particles is carried out until crystals are formed. The solid product is separated from the reaction medium, e.g. by cooling the whole to room temperature, filtering and washing with water. The crystalline product is dried, e.g. at 110°C

for 8-24 hours.

The specific zeolites described are catalytically inactive when prepared in the presence of organic cations, possibly because the intracrystalline free space is occupied by organic cations from the preparation solution. They can be activated by heating in an inert atmosphere at 538°C for 1 hour, for example, followed by base exchange with ammonium salts followed by calcination at 538°C in air. The presence of organic cations in the preparation solution may not be absolutely necessary for the formation of this zeolite type, but the presence of these cations has been found to favor the formation of this particular zeolite type. More generally, it is desirable to activate this type of catalyst by base exchange with ammonium salts followed by calcination in air at approx. 538°C for a period between 15 minutes and 24 hours.

Natural zeolites can sometimes be converted into this type of zeolite catalyst by various activation methods and other treatments, such as base exchange, steam treatment, alumina extraction and calcination, in combinations. Natural minerals that can be treated in this way include ferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite, and clinoptilolite. The preferred crystalline aluminosilicate is ZSM-5, ZSM-11, ZSM-12, ZSM-38 and ZSM-35, with ZSM-5 being particularly preferred.

According to a preferred feature of the invention, the zeolites are selected as those zeolites which have a crystal skeleton density, in the dry hydrogen form, of not substantially less than 1.6 g/cm 3. It has been found that zeolites which fulfill all these three criteria are the most preferred, because they are apt to maximize the formation of hydrocarbon products boiling in the gasoline range. The preferred zeolites are therefore those which (in addition to an inhibition index as indicated above of 1 to 12 and a silica/alumina ratio of at least 12) have a dry crystal density of at least 1.6 g/cm 3 . The density for known , dry structures can be calculated from the number of silicon atoms plus aluminum atoms per 1000 cubic Angstroms, as shown for example on page 19 of the article on "Zeolite Structure" by W. M. Meier. This paper, the entire contents of which are hereby incorporated by reference, is included in the "Proceedings of the Conference on Molecular Sieves, London, April 1967", published by the "Society of Chemical Industry", London, 1968. When the crystal structure is unknown, the crystal skeleton can be the density is determined by a common pycnometer technique. For example, it can be determined by immersing the dry zeolite in the hydrogen form in an organic solvent that is not sorbed by the crystal. It is possible that the unusual activity and stability of this class of zeolites is related to the high crystal density of the anionic skeleton of at least 1.6 g/cm . This high density must of course be related to a relatively small amount of "free space" inside the crystal, which should be expected to result in more stable structures. However, this "free space" is important as the site of catalytic activity.

Crystal skeleton densities of some typical zeolites are:

When the zeolite is synthesized in the alkali metal form, it is conveniently converted to the hydrogen form, generally by intermediate formation of the ammonium form as a result of ammonium ion exchange and calcination of the ammonium form while forming the hydrogen form. Besides the hydrogen form, other forms of the zeolite in which the original alkali metal has been reduced to less than 1.5% by weight can be used. The zeolite's original alkali metal can thus be replaced by ion exchange with other suitable ions from groups IB-VIII in the periodic table of the elements, including, for example, nickel, copper, zinc, palladium, calcium or rare earth metals.

When carrying out the desired conversion process, it is desirable to incorporate the above-described crystalline aluminosilicate zeolite in another material which can withstand the temperatures and other conditions used in the process. Such matrix materials include synthetic or naturally occurring substances as well as inorganic materials such as clay, silica and/or metal oxides. The latter can either be naturally occurring or in the form of gelatinase precipitated materials or gels, including mixtures of silica and metal oxides. Naturally occurring clays that may be used with the zeolite include materials from the montmorillonite and kaolin groups, which groups include sub-bentonites and kaolins commonly known as Dixie, McNamee-Georgia and Florida clays, or others in in which the most important mineral constituent is halloysite, kaolinite, dickite, nacritte or anauxite. Such clay species can be used in their raw state as they are at the time of extraction, or they can first be subjected to - calcination, acid treatment or chemical modification.

In addition to the above-mentioned materials, the zeolites used according to the invention can form composites together with a porous matrix material, such as alumina, silicon dioxide-alumina, silicon dioxide-magnesium oxide, silicon dioxide-zirconium oxide, silicon dioxide-thorium oxide, silicon dioxide-beryllium oxide, silicon dioxide-titanium dioxide . The relative proportions of zeolite component and gel base mass of inorganic oxide can vary within wide limits, where the zeolite content is between 1 and 99 weight percent and more, usually within the range between 5 and 80 weight percent of the composite material.

The conversion process can be carried out batchwise, semi-continuously or continuously using a stationary or moving catalyst layer. After use, the catalyst is taken to a regeneration zone where coke is burned off from the catalyst in an oxygen-containing atmosphere, for example air, at an elevated temperature, after which the regenerated catalyst is recycled to the conversion zone for further contact with the starting material. It is particularly possible to carry out the desired conversion in the presence of hydrogen using a ratio between hydrogen and starting compound between 2 and 20, where the hydrogen pressure is from 1 atmosphere and up to 100 atmospheres. The presence of hydrogen in the reaction zone has been found to reduce the aging rate of the catalyst very significantly.

The method is described above in connection with the selective production of para-dimethyl-substituted benzenes, such as para-xylene, but it is also aimed at the selective production of other para-dialkyl-substituted benzenes where the alkyl group contains 1-4 carbon atoms. By using the described technique, a mixture of ethylbenzene and toluene can be selectively converted into para-ethyltoluene by suitable choice of starting compound; likewise, para-ethyl-toluene is formed from dodecane or 1-butene, in addition to para-xylene; ethylbenzene can be selectively converted to diethylbenzene, propylbenzene can be converted to dipropylbenzene, and butylbenzene can be selectively converted to dibutylbenzene.

The following examples, of which examples 6, 7, 11, 12, 16, 17-19, 22, 23, 37, 38, 68, 72, 73 and 81 are comparative examples, will serve to illustrate the catalyst and the method according to the invention.

Example 1 19.6 kg of sodium silicate ("Q-Brand") was mixed with 23.97 kg of water. The resulting solution was designated solution A. 0.613 kg of commercial grade aluminum sulfate [Al2(SO4)3 • 14H20], 7.19 kg of commercial grade NaCl, and 1.60 kg of H2SO4 (96.5% by weight H2SO4) were mixed with 32.78 kg of water. The resulting solution was designated as solution B. 1.18 kg of water was added to an autoclave equipped with an agitator. Solution A and solution B were simultaneously mixed in a nozzle and injected into the autoclave. The resulting gel was mixed in the autoclave at ambient temperature for 1 hour. 1.29 kg of tri-n-propylamine and 1.11 kg of n-propyl bromide were added to the contents of the autoclave. The mixture was reacted at 160°C with stirring. After 20 hours at 160°C, a sample of the autoclave contents was examined and the solid product was found to be 100% ZSM-5 by X-ray diffraction. After a total reaction time of 28.7 hours at 160°C, the contents of the autoclave were cooled. The resulting solid product was washed with deionized water containing 3500 ppm "Primafloc" C-7 (polyammonium bisulfate), decanting the wash water until the wash water was chloride free. The solid product was filtered and dried at 121°C.

500 g of the dried filter cake was calcined in nitrogen for three hours at 538°C. 444 g of the calcined product was mixed with 2220 ml of 1 N NH4N03 solution for one hour at ambient

temperature. The mixture was vacuum filtered. The ion exchange treatment was repeated. The filter cake was washed, with 1776 ml of water, and the solid product was dried at 121°C. The sodium content of the final product was less than 0.01%.

The resulting catalyst had a crystal size

of 1-2 yum, an alpha activity of 162, a para-xylene sorption capacity of 6.5 percent by weight and an ortho-xylene sorption time for 30 percent of said capacity of 92 minutes. The two latter measurements were carried out at 120°C. In the para-xylene sorption, the partial pressure of the hydrocarbon was 5.1 mm Hg. For the ortho-xylene sorption time, the hydrocarbon partial pressure was 3.8 mm Hg.

Example 2

The toluene was passed over the catalyst according to example 1

at 550°C and a pressure of 2 6.53 ato at a weight basis space velocity of 50 and a hydrogen/hydrocarbon ratio of 6. The toluene conversion was 20.1% by weight, and the yield of para-xylene, as a percentage of xylene , was 30 percent.

Example 3

The catalyst according to example 1 was treated with toluene

for five hours at 640°C and at a space velocity on a weight basis of 50

and a pressure of 1 atmosphere, whereby approx. 4% by weight of coke on the catalyst. The treated catalyst sorbed 6.1 g of para-xylene per 100 g of zeolite at 120°C and a para-xylene pressure of 5.1 mm Hg. At 120°C and an ortho-xylene pressure on

3.8 mm Hg, the time for sorption of 30 percent of the xylene capacity was 6000 minutes. The catalyst had an alpha value of 281.

The catalyst, which contained approx. 4 weight percent coke, was brought into contact with toluene at 550°C, a pressure of 40.82 ato,

a space velocity on a weight basis of 40 and a hydrogen/hydrocarbon mole ratio of 10. The liquid product contained 80.7 weight percent toluene (19', 3 percent conversion) and 9.6 weight percent xylenes in addition to benzene. The xylene fraction contained 82 percent para-xylene.

Example 4

3 g of the catalyst according to example 1 was brought into contact with a solution containing 1.02 g of magnesium acetate tetrahydrate in 4 ml of water. The resulting slurry was evaporated to dryness over 24 hours and then air calcined for 10 hours at 538°C, whereby a HZSM-5 product containing 6% MgO by weight was obtained. The catalyst sorbed 6.3 g of para-xylene per 100 g of zeolite at 120°c and a para-xylene pressure of 5.1 mm Hg. At 120°C and an ortho-xylene pressure of 3.8 mm Hg, the time for sorption of 30 percent of the xylene capacity was 583 minutes. The catalyst had an alpha value of 129.

Example 5

The catalyst of Example 4 was contacted with toluene at 550°C, a pressure of 40.82 ato, a weighted space velocity of 40 and a hydrogen/hydrocarbon ratio of 4. The toluene conversion was 29.4 percent; the liquid product contained 15.3 weight percent xylene, which consisted of 53 percent of the para isomer.

Example 6

HZSM-5 with a crystallite size of approx. 0.03 µm was prepared as follows:

a) Preparation of solution

Silicate solution

41.27 kg sodium silicate (Q-Brand)

23.88 kg H20

118 g "Daxad 27 Dispersant" (the sodium salt of polymerized substituted benzenoid alkyl sulfonic acid combined with a suspending agent)

Acid solution

1430 g Al2(SO4)3-xH20 (molecular weight=595)

3440 g of H 2 SO 4

4890 g NaCl

24.52 kg H20

Additional solids

2840 g NaCl

2390 g of n-propyl bromide

4590 g of methyl ethyl ketone

Additional liquid

1180 g of H2O

b) Method of work

The silicate solution and the acid solution were mixed in one

mixing nozzle, whereby a gel was formed which was fed to a 113 liter autoclave to which 1180 g of H 2 O had previously been added.

The gel was whipped by agitation, and 2840 g of NaCl was added and thoroughly mixed. The agitation was stopped, and the solution of organic substances was added as a layer on top of the gel. The autoclave was closed and heated to approx. 104.4°C without agitation and held at this temperature for 14-15 hours, whereby the organic substances are reacted in advance. After this preliminary reaction, the agitation and thus the initial crystallization period was started. After approx. 75-80 hours, the temperature was raised to 160°C and held there for approx. three hours for the completion of the crystallization. The excess of unreacted organic substances was evaporated, and the contents of the autoclave were cooled and withdrawn. The product was analyzed by X-ray diffraction and shown to be 100% crystalline ZSM-5. Chemical analysis of the thoroughly washed crystalline product showed:

After thorough washing and drying at approx. 121°C, the zeolite was converted to the catalytic form by the following steps: a) Pre-calcination in a 100% N2 atmosphere for three hours at 538°C and atmospheric pressure, using a programmed heating rate of 2.78° C per minute from the ambient temperature to 538°C.

b) Ion exchange with IN NH4N03 at room temperature for one hour using 5 ml exchange solution per grams dry

zeolite.

c) Washing with four volumes of water.

d) Repeating steps (b) and (c) and drying at 121°C in air.

The exchange-treated zeolite was analyzed and was

found to contain 0.01% by weight sodium and to have an alpha value of 162. It was characterized by an ortho-xylene sorption capacity of 5.6% by weight and an ortho-xylene sorption time for 30% of said capacity of less than 1 ,3 minutes. Both of the latter measurements were carried out at 120°C and a hydrocarbon partial pressure of approx. 3.8 mm Hg.

Example 7

Toluene was passed over the microcrystalline HZSM-5 catalyst of Example 6 at 1 atmosphere pressure, 600°C, and a space velocity on a weight basis of 50. The toluene conversion was 15 percent by weight, and the yield of p-xylene, as a percent of xylenes,

was 25%, i.e. approximately the normal equilibrium concentration of p-xylene.

Example 8

Catalyst prepared as in example 6 was combined with alumina to produce an extruded catalyst containing 65 weight percent zeolite and 35 weight percent alumina. After use for toluene disproportionation under a variety of conditions and regeneration, toluene was passed over this catalyst at 474-521°C, space velocity (weight basis) = 5-6.3,

pressure = 30.6 ato, and a hydrogen/hydrocarbon ratio of 0.5, for 38 days.

The coke content was 45 g per 100 g of catalyst. The capacity for sorption of p-xylene, measured by a p-xylene pressure of

5.1 mm Hg, was 2 g per 100 g of zeolite, and the o-xylene sorption time for 30% of the xylene sorption capacity was 2900 minutes; this measurement was performed at an o-xylene pressure of 3.8 mm Hg. The catalyst had an alpha value of 20. The toluene was passed over the catalyst at 521°C, 30.6 ato, a space velocity of 6.3 and a hydrogen/hydrocarbon ratio of 0.5. The toluene conversion was 37% by weight, and the yield of p-xylene, as a percentage of xylenes produced, was 43.

Example 9

A catalyst was prepared by adding 3 g of the catalyst according to Example 1 to a solution prepared from 0.3 g of magnesium nitrate hexahydrate in 2.2 ml of water. The slurry was thoroughly mixed and air-calcined by heating at a rate of 1.67°C per minute. minute at 538°C, followed by 10 hours at 538°C. The resulting catalyst contained 2.4 weight percent magnesium. It absorbed 5.2 g of p-xylene per 100 g of zeolite at 120°C and a p-xylene pressure of 5.1 mm Hg. At 120°C and an o-xylene pressure of 3.8 mm Hg, the time for sorption of 30 percent of the xylene capacity was 2600 minutes. The catalyst had an alpha value of 36.

Example 10

The toluene was passed over the catalyst of Example 9 at 550°C, 40.82 ato, a hydrogen/hydrocarbon ratio of 4, and a space velocity of 10. The toluene conversion was 20% by weight, and the yield of p-xylene, as a percent of xylenes, was 45.

Example 11

A 5 g sample of the HZSM-5 catalyst of the type described in Example 6 was placed in a glass tube provided with a disc of fritted glass. Dimethylsilane was passed through the bed of HZSM-5 at a rate of 40 ml/minute. After 15 minutes, the HZSM-5 material had sorbed 0.60 g of dimethylsilane. The product was added to 200 ml of 15% aqueous ammonia for hydrolysis to the silane. Hydrogen was quickly developed. After one hour, the product was filtered and calcined by heating at a rate of 1°C/minute to 538°C and then held at this temperature for 6 hours.

The above procedure was repeated a total of three times, whereby silica-containing HZSM-5 containing 5% by weight of added silica was obtained.

This catalyst sorbed 4.1 g of o-xylene per 100 g of zeolite at 120°C and an o-xylene pressure of 3.8 mm Hg. A sorption of 30 percent of the capacity was achieved in 2.7 minutes. The catalyst had an alpha value of 75.

Example 12

The toluene was passed over the catalyst of Example 11 at 600°C, one atmosphere pressure, a space velocity of 40 and a hydrogen/hydrocarbon ratio of 2. The toluene conversion was 2% by weight and the p-xylene yield, as a percentage of xylenes, was 62 .

In a more realistic toluene conversion, e.g. 20 percent, the selectivity to para-xylene was only 27 percent, i.e. essentially the same as at equilibrium, indicating that the sorption time to reach 30 percent of capacity, only 2.7 minutes, was far too low.

Example 13

20 g of NH 2 -ZSM-5 with a crystal size of 0.03 µm was suspended in a solution of 5.35 g of ortho-boric acid in 40 ml of water at a temperature of 80°C. After standing overnight (16.5 hours) at 90°C, the contents were poured into a 30 mm x 50 mm crystallization dish and placed in an oven at 110°C. The contents were stirred frequently until a uniform dry powder was formed. The temperature was gradually increased to 200°C, after which the catalyst was allowed to stand for 1-2 hours. It was then transferred to an oven at 500°C, in air, in the same open crystallization dish for 17.5 hours. The theoretical amount of boron, present as the oxide, was 4.06 wt% B. The powder was pressed into wafers, crushed and screened to 14-20 mesh size for use.

This catalyst sorbed 3.1 g of p-xylene at 120°C and a p-xylene pressure of 5.1 mm Hg. At 120°C and an o-xylene pressure on

3.8 mm Hg, the time for sorption of 30 percent of the capacity was 2 70 minutes. The catalyst had an alpha value of 3.8.

Example 14

The toluene was passed over 5 g of the catalyst according to Example 13 at 600°C, one atmosphere pressure and a space velocity of 4.5. The toluene conversion was 11.9% by weight, and the yield of p-xylene, as a percentage of xylenes, was 74.

Example 15

10.0 g of zeolite of the type described in example 6 was mixed with 6.5 g of antimony trimethoxy and 75 ml of p-xylene. This slurry was heated under reflux in a nitrogen atmosphere for 17 hours. The solids were then washed with 100 ml of toluene, then 100 ml of methanol, followed by 100 ml of n-hexane. The product was air-dried and then placed in a vacuum oven at 100°C for 3 hours. It was then air-calcined for 10 hours at 538°C. The product contained 24% antimony by weight.

The catalyst sorbed 3.5 g of p-xylene per 100 g of zeolite at 120°C and a p-xylene pressure of 5.1 mm Hg. At 120°C and an o-xylene pressure of 3.8 mm Hg, the time for sorption of 30 percent of the xylene capacity was 89 minutes. The catalyst had an alpha value of 8.

Example 16

10 g of the ammonium form of ZSM-5 was suspended in a solution of 5 g of uranium dioxide dinitrate hexahydrate in 20 ml of water. The slurry was heated to a temperature of 73°C and allowed to stand overnight. The total contents of the flask were then poured into a crystallization dish and placed in an oven at 130°c. The catalyst was stirred at 30 minute intervals. After approx. After 2 hours, the catalyst had a dry appearance. It was then placed in an oven at 500°C and allowed to stand overnight. The final weight of the calcined catalyst was 12.17 g. The catalyst had a xylene sorption capacity at 120°C and a xylene pressure of 4.5 + 0.8 mm Hg of 6.3 g xylene per 100 g zeolite. The time for sorption of ortho-xylene at 120°C and a pressure of 3.8 mm Hg corresponding to 30 percent of the capacity was 4.8 minutes. The catalyst had an alpha value of 83.

Example 17

The toluene was passed over the catalyst of Example 16 at 550°C, one atmosphere pressure and a space velocity of 3.5.

The toluene conversion was 46% by weight, and the yield of p-xylene,

as a percentage of xylenes, was 24.

Example 18

11.6 g of magnesium acetate tetrahydrate was dissolved in 25 ml of water. To this was added 10 g 1/8 pellets of the ammonium form of ZSM-5 zeolite crystal. After a few minutes, the excess liquid was separated and stored. The catalyst was placed in an oven to drive off the water. After cooling, the dry catalyst was placed in the remaining solution of magnesium acetate. Excess liquid was separated and the wet catalyst was placed in an oven for drying. This procedure was repeated until the entire amount of liquid had been absorbed by the catalyst.

Finally, the catalyst was placed in an oven at 500°C overnight. The weight of the final catalyst was 11.56 g. The catalyst had a xylene sorption capacity at 120°C and a xylene pressure of 4.5 + 0.8 mm Hg of 4.2 g xylene per 100 g zeolite. The time for sorption of ortho-xylene at 120°C and 3.8 mm Hg in an amount corresponding to 30 percent of the capacity was 7.5 minutes. The catalyst had an alpha value of 21.

Example 19

The toluene was placed over the catalyst of Example 18 at 550°C, one atmosphere pressure and a space velocity of 3.5. The toluene conversion was 12% by weight, and the yield of p-xylene, as a percentage of xylenes, was 25.

Example 20

10 g of ammonium ZSM-5 was added to a solution of 7.28 g of zinc nitrate hexahydrate in 20 ml of water. The suspension was heated to approx. 90°C and set aside overnight. The entire contents of the flask were then poured into a crystallization dish and placed in an oven at approx. 130°C. After approx. 2 hours, the catalyst was placed in an oven at 500°C and allowed to stand for approx. 8 hours. The final weight of the catalyst after calcination was 11.21 g. The catalyst had a xylene sorption capacity at 120°C and a xylene pressure of 4.5 + 0.8 mm Hg of 4.9 g xylene per 100 g zeolite. The time for sorption of ortho-xylene at 120°C and a pressure of

3.8 mm Hg in an amount corresponding to 30% by weight of the capacity was 38 minutes. The catalyst had an alpha value of 504.

Example 21

The toluene was passed over the catalyst of Example 20 at 550°C, one atmosphere pressure and a space velocity of 3.5. The toluene conversion was 20% by weight, and the yield of p-xylene, as a percentage of xylenes, was 28.

Example 22

10 g of the acid form of ZSM-5 was suspended in a solution of 12.9 g of calcium nitrate tetrahydrate in 25 ml of water. The slurry was heated to 88°C and left overnight. The entire contents were then poured into a crystallization dish and placed in an oven at 100-130°C. After approx. 4 hours, the temperature was raised to 200°C, which was maintained for approx. 2 hours. The catalyst was then placed in an oven at 500°C overnight. The catalyst's final weight after calcination was 12.80 g. The catalyst had a xylene sorption capacity at 120°C and a xylene pressure of 4.5 + 0.8 mm Hg of 1.2 g xylene per 100 g zeolite. The time for sorption of ortho-xylene at 120°C and a pressure of

3.8 mm Hg in an amount corresponding to 30% by weight of the capacity was 116 minutes. The catalyst had an alpha value of 0.9.

Example 23

The toluene was passed over the catalyst of Example 22 at 550°C, one atmosphere pressure and a space velocity of 3.5. The toluene conversion was 0.4% by weight, and the yield of p-xylene, as a percentage of xylenes, was 67.

Example 24

10 g of the ammonium form of ZSM-5 was placed in powder form in a solution of 11.6 g of magnesium acetate tetrahydrate in 25 ml of water. The suspension was heated to a temperature of 95°C and left overnight. The entire contents of the flask were then poured into a crystallization dish and placed in an oven at 56°C. The temperature was then raised to 100-120°C. The slurry was frequently stirred until the catalyst eventually took on a dry appearance. The temperature was then gradually raised to 200°C, which was maintained for approx. 1 hour. The catalyst was then placed in an oven at 500°C overnight. The catalyst's final weight was 11.37 g. The catalyst had a xylene sorption capacity at 120°C and a xylene pressure of 4.5 + 0.8 mm Hg of 4.4 g xylene per

100 g zeolite. The time for sorption of ortho-xylene at 120°C and a pressure of 3.8 mm Hg in an amount corresponding to 30 percent of the capacity was 655 minutes. The catalyst had an alpha value of 24.

Example 25

The toluene was passed over the catalyst of Example 24 at 550°C, one atmosphere pressure and a space velocity of 4.5. The toluene conversion was 16% by weight, and the yield of p-xylene, as a percentage of xylenes, was 59.

Example 26

A boron-containing ZSM-5 catalyst was prepared according to the method in example 13, with the exception that 0.22 g of ortho-boric acid was used per grams of ammonium-ZSM-5. The final catalyst was calculated to contain 3.34 wt% B, which was probably present as the oxide.

Propylene was passed over the above catalyst at a space velocity of 2.6 and a temperature of 400°C. The conversion was 94%. The aromatics that were formed (25% by weight) contained 31% xylenes. The content of p-xylene in the xylene fraction was 56%.

Example 27

A sample of HZSM-5 was mixed with S^O^ in the ratio

0.43 g Sb203 per gram HZSM-5. After pressing and sieving to 8/14 mesh, approx. lg added to a glass microreactor with a length of 15-20 cm and a diameter of 14-18 mm. A 4-6 mm thermo-cavity was arranged in the catalyst layer. The catalyst was heated to 525°C during one hour in flowing nitrogen, the flow rate of which was 50 ml/minute, and was held in nitrogen for three hours at 500-525°CL and then in air (50 ml/minute) for 0 .5 hours. The resulting catalyst contained 30% S₂O₂.

Example 28

A sample of 30% Sb 2 O 3 /HZSM-5, prepared according to Example 27, was placed in a vertical flow reactor; propylene was passed over the catalyst at 400°C and a space velocity of 3.0. The propylene conversion was 90.3%. Aromatics were formed with a selectivity of 14.8% and contained as main components benzene, toluene, xylenes and ethyltoluene. The largest fraction (34%) was xylene which contained 91% of the para isomer.

Example 29

Another sample of 30% Sb 2 O 3 /HZSM-5 according to Example 27

was used for selective toluene disproportionation. The toluene was passed over the catalyst in a vertical flow, stationary bed reactor at 550°C, atmospheric pressure and a space velocity of 1.0. After 6 hours, the toluene conversion was 20%. The products were benzene and xylenes. The xylenes contained 81% of the para isomer.

Example 30

Another sample of Sb203~ZSM-5 was prepared according to the procedure in example 27 with the exception that 0.33 g of Sb203 per gram HZSM-5. The resulting catalyst contained nominally 25% Sb 2 O 3 .

Example 31

The catalyst prepared in Example 30 was used in toluene disproportionation to benzene and xylene at atmospheric pressure, 550°C and a space velocity of 1. After 6 hours the toluene conversion was 9.5%. The xylene fraction contained 83% p-xylene.

The catalyst sorbed 1.39 g of p-xylene per 100 g of zeolite at 120°C and a p-xylene pressure of 5.1 mm Hg. At 120°C and an 0-xylene pressure of 3.8 mm Hg, the time for sorption of 30% of the xylene capacity, tQ 3 , was longer than 300 minutes.

Example 32

The catalyst of Example 1 was contacted with 1-butene at 400°C, a space velocity on a weight basis of 4 and 1 atmosphere pressure. The liquid product, which made up 89 percent of the charge's weight, contained 13.4 percent by weight xylene and 3.9 percent by weight ethyltoluene. The xylene fraction contained 37 percent p-xylene, and the ethyltoluene fraction contained 43 percent para-ethyltoluene. The equilibrium values for these para isomers are 24 and 32 percent respectively.

Example 33

The catalyst of Example 1 was contacted with dodecane at 400°C, a weighted space velocity of 10 and 1 atmosphere pressure. The liquid product, which made up 41% by weight of the charge, consisted of 12.6% by weight xylene and 4.3% by weight ethyltoluene. The xylene fraction contained 63 percent para-xylene, and the ethyltoluene fraction contained 58 percent para-ethyltoluene.

Example 34

This example illustrates the production of p-diethylbenzene using the catalyst according to example 1 pretreated with toluene as in example 3, whereby approx. 4% by weight of coke was deposited. A mixture of benzene and ethylene in a molar ratio of 1:2 (fresh material) is mixed with a recycle stream containing benzene and ethylbenzene and passed over the catalyst at a temperature of 441-454°C, a pressure of 20.4 ato and a space velocity of 2, based on weight units of ethylene per hour per unit weight catalyst. The effluent product from the reactor is distilled, thereby obtaining a distilled fraction (recycling stream) consisting of benzene, ethylbenzene and unreacted ethylene, which is recycled to the reactor, and a bottom fraction containing the desired product, p-diethylbenzene.

The specific selectivity with respect to para-dialkyl aromatics that can be achieved with the catalysts described herein depends on the particular starting material and the operating conditions used. In the case of toluene disproportionation, the content of para-xylene in the xylenes obtained is highest at low toluene conversion. Furthermore, the catalysts according to the invention have been found to exhibit a very surprising and unusual phenomenon, namely that the para-xylene selectivity at a given percent toluene conversion increases with increasing temperature over (approximately) the temperature range 400 - 700°C.

When different catalysts are to be compared with regard to para-selectivity, it is therefore desirable that they be compared at the same temperature, for example 550°C, and the same percentage toluene conversion, for example 20%, which can be achieved by regulating the supply rate for the toluene . For these reference conditions, the para-selectivity can be obtained directly or by extrapolation on the basis of other applied operating conditions.

Para-xylene selectivities (% p-xylene in the total content of xylenes) for the above standard conditions (20% toluene conversion at 550°C) and ortho-xylene sorption times, tQ ^ (30% of capacity at 120°C) , is shown in the following table:

The above data is presented graphically in the drawing's fig. 1, where the selectivity factor for para-xylene is shown as a function of the ortho-xylene sorption time for 30 percent of the capacity. It will be seen from the figure that catalysts which have a xylene sorption time for 30 percent of the xylene sorption capacity longer than 10 minutes are para-xylene-selective.

Example 35

19.2 kg of sodium silicate (Q-Brand) was mixed with 24.0 kg of water. The resulting solution was designated solution A.

■613 g aluminum sulfate (Al2(S04)^•14 H,,0) of commercial quality, 7.20 kg of NaCl of commercial quality and 1.60 kg of H2S04 (96.06% by weight

H2SO4) was mixed with 32.6 kg of water. The resulting solution was designated solution B. Solution A and solution B were simultaneously mixed in a nozzle and injected into an autoclave equipped with a stirring arm. 1.29 kg of tri-n-propylamine and 1.10 kg of n-propyl bromide were added to the autoclave. The mixture was reacted at 158°C with stirring at a rate of 121 revolutions per minute. minute. After 14.1 hours at 158°C, the solid product was analyzed by X-ray diffraction and found to be 100% ZSM-5, with a SiO2/Al2O3 ratio of 70.

A 10 g sample of the above ZSM-5 was treated with

500 ml of 1 N NH^Cl solution. Three ion exchange steps were performed, the first at 100°C for 2 hours, the second at room temperature for 18 hours and the third at 100°C for 3 hours. The ion-exchanged product was then calcined by heating to 538°C at a rate of 1°C/minute, after which this temperature was maintained for 10 hours. The resulting HZSM-5 had a crystallite size of 1-2 µm. The material also showed a sorption capacity for para-xylene of 6 percent by weight and an ortho-xylene sorption ion time for 30 percent of said capacity of 116 minutes. Both of the latter measurements were carried out at 120°C. For the para-xylene sorption, the hydrocarbon partial pressure was

5.1 mm Hg. For the ortho-xylene sorption time, the hydrocarbon partial pressure was 3.8 mm Hg.

Example 36

The toluene was passed over large crystals of the HZSM-5 catalyst according to example 1 at 1 atmosphere pressure and a temperature between approx. 400 and approx. 650°C at a space velocity on a weight basis between 5 and 100. The reaction conditions and results in weight percent are given in the following Table IV.

From the above results, it will be seen that para-xylene was formed selectively in an amount above the thermodynamic equilibrium concentration in the mixture of xylenes obtained. Furthermore, it will be seen that increasing temperature within the range 400-650°C acted to increase the para-xylene selectivity significantly.

Example 37

HZSM-5 with a crystallite size of approx. 0.03 µm was prepared as follows:

a) Preparation of the solution

S1ikat- opiösn ing

41.27 kg sodium silicate (Q-Brand)

23.88 kg H20

118 g dispersant ("Daxad" 27)

Acid solution

1430 g A12(SO4)3 xH20 (molecular weight 595)

3440 g of H 2 SO 4

4890 g NaCl

24.52 kg H20

Additional solids

2840 g NaCl

2390 g of n-propyl bromide

4590 g MEK

Additional liquid

1180 g of H2O

b) Procedure

The silicate solution and the acid solution were mixed in one

mixing nozzle while forming a gel which was added to a 113 liter autoclave to which 1180 g of H 2 O had previously been added. The gel was whipped by stirring, and 2840 g of NaCl was added and thoroughly mixed. The stirring was stopped, and the solution of organic substances was added as a layer on top of the gel. The autoclave was closed and heated to approx. 104.4°C without stirring and held at this temperature for 14-15 hours, whereby the organic substances were pre-reacted. The stirring was then started

- 90 revolutions per minute - and the initial or first

crystallization period began. After approx. 75-80 hours, the temperature was raised to 160°c, which was maintained for approx. 3 hours for the completion of the crystallization. The excess of unreacted organic substances was removed, and the contents of the autoclave were cooled and withdrawn. The product was analyzed by X-ray diffraction and shown to be 100% crystalline ZSM-5, based on a standard sample. Chemical analysis of the thoroughly washed, crystalline product

knew:

After thorough washing and drying at approx. 121°C, the zeolite was converted to the catalytic form by the following steps: a) Pre-calcination in an atmosphere of 100% N2 for three hours at 538°C and atmospheric pressure using a programmed heating rate of 2.78°C/minute to 538°C from ambient temperature.

b) ion exchange with IN NH^NO^ at room temperature for one hour using 5 ml of ion exchange solution per grams dry

zeolite.

c) Washing with four volume units of water.

d) Repeating steps (b) and (c) and drying at 121.1°C in air.

The ion-exchanged zeolite was analyzed and found to contain 0.01 wt% Na. It exhibited an ortho-xylene sorption capacity of 5.6 percent by weight and an ortho-xylene sorption time for 30 percent of capacity of less than 1.3 minutes. Both of the latter measurements were carried out at 120°C and a hydrocarbon partial pressure of approx. 3.8 mm Hg.

Example 38

The toluene was passed over the microcrystalline HZSM-5 catalyst of Example 3 at a pressure of 1 atmosphere and at temperatures of 600-650°C and a space velocity on a weight basis between 20 and 100. The reaction conditions and the results expressed in weight percent are given in the following table V.

From the above results, it will be seen that the amount of para-xylene in the total xylenes obtained practically corresponded to the thermodynamic equilibrium concentration.

The drawing's fig. 2 illustrates a comparison between HZSM-5 with small crystals, i.e. approx. 0.03 µm, and HZSM-5 with large crystals, i.e. approx. 1 ^ura, with respect to para-xylene selectivity. It will be seen that the para-xylene selectivity was greatly improved by using a material with large crystals. At 10 per cent toluene conversion, use of the large crystals thus showed a para-xylene selectivity of 48 per cent, while in comparison it was 27 per cent when using the small crystals.

Example 39

A sample of the HZSM-5 catalyst of Example 35 with large crystals was steam-treated for 2 hours at 560°C in 1 atmosphere of steam.

Example 40

The toluene was passed over the HZSM-5 catalyst of Example 39 with large crystals at 1 atmosphere pressure and a temperature of approx. 650°C at a space velocity on a weight basis of 20. The reaction conditions and results are set forth in the following Table VI:

Here too, it will be seen that when using HZSM-5 with large crystals, para-xylene was formed in an amount significantly greater than that which corresponds to the equilibrium concentration, the amount rising to 100 per cent after 5-6 hours.

Example 41

The toluene and hydrogen in a hydrogen/hydrocarbon mole ratio of 2 were passed over the HZSM-5 catalyst of Example 39 (large crystals) at 1 atmosphere pressure, a temperature of approx. 650°C and a space velocity on a weight basis of 10. The reaction conditions and results are set forth in the following Table VII.

When comparing the results in table VI and table VII, it will be seen that the presence of hydrogen, even at a total pressure of 1 atmosphere, greatly reduces the catalyst's aging rate and thus significantly extends the catalyst's effective life and reduces the need for frequent regeneration.

Example 42

The toluene was passed over a sample of the HZSM-5 catalyst of Example 39 (large crystals) at ca. 625°C, a space velocity on a weight basis of 20 and a pressure of 25.51 ato in the presence of hydrogen, the mole ratio of hydrogen to hydrocarbon being 6.

The initial conversion was 24.8 percent by weight with a para-xylene selectivity (as a percent of xylenes) of 45 percent. After 14 days, the conversion and para-xylene selectivity were 21 percent and 82 percent, respectively.

The changes in toluene conversion and para-xylene selectivity that occur over the 14 days are shown in Fig. 3. It will be seen, cf. especially fig. 3, that the aging rate was slow, as it entailed a relative conversion loss per day of 1.2 percent. Furthermore, it will be seen that the para-xylene selectivity (as a percentage of xylenes) during this time period increased by 2.9 per cent per day.

Example 43

A catalyst was prepared by heating 8.5 g of ZSM-5 consisting of approx. 10 percent twin crystals with up to 3.um minimum dimension and approx. 90 percent 5-10 µm polycrystalline spheroids for 5 hours at 538 oC in air, followed by three ion exchanges, at room temperature, with 500 ml of 1 N NH^Cl solution for 15.3 hours, 3.8 respectively hours and 3.0 hours. This material was then air-calcined for 10 hours at 538°C. The resulting product showed a para-xylene sorption capacity of 6.2 percent by weight and an ortho-xylene sorption time for 30 percent of said capacity of 43 minutes. The two latter measurements were carried out at 120°C. For the para-xylene sorption, the hydrocarbon partial pressure was

5.1 mm Hg. For the ortho-xylene sorption time, the hydrocarbon partial pressure was 3.8 mm Hg.

The toluene was passed over the catalyst of Example 43 at 600°C, a weight basis space velocity of 50 and 1 atmosphere pressure. The toluene conversion was 10.6% by weight. The product consisted of 5.1% by weight benzene, 89.4% by weight toluene and 5.5% by weight xylenes. The xylene fraction contained 35.2 percent para-xylene.

Example 44

19.16 kg of sodium silicate (Q-Brand) was mixed with 23.97 kg of water. The resulting solution is designated solution A. 0.613 kg of commercial grade aluminum sulfate (Al 2 (SO 4 ) 3 .14 H 2 O), 7.191 kg of commercial grade NaCl and 1.598 kg of H 2 SO 4 (96.5 wt% H 2 SO 4 ) were mixed with 32.78 kg of water. The resulting solution is referred to as solution B. 1.180 kg of water was added to an autoclave equipped with a high shear agitator. Solution A and solution B were mixed simultaneously in a nozzle and injected into the autoclave. The resulting gel was mixed in the autoclave at 90 rpm. minute and the ambient temperature for 1 hour. 1.289 kg of tri-n-propylamine and 1.108 kg of n-propyl bromide were added to the contents of the autoclave. The mixture was reacted at 160.0°C with stirring at 90 rpm. minute. After 20 hours at 160°C, samples were taken of the contents of the autoclave, and the solid product was found to be 100% ZSM-5 by X-ray diffraction analysis. After a total reaction time of

28.7 hours at 160°C, the contents of the autoclave were cooled. The resulting solid product, using decantation, was washed with deionized water and 3500 ppm "Primafloc" C-7 (Rohm & Haas) until the decanted water was chloride free. The solid product was filtered off and dried at 121.1°C.

500 g of the dried filter cake product was calcined in N2 for three hours at 538°C.

444 g of the calcined product was mixed with 2220 ml

1 N NH.NO., solution for 1 hour at ambient temperature. The mixture was vacuum filtered. the ion exchange treatment was repeated. The filter cake was washed with 1776 ml of water, and the solid product was dried at 121.1 °C. The sodium content of the final product was less than 0.01%.

The resulting catalyst had a crystal size of 1-2 µm, a para-xylene sorption capacity of 6.5 percent by weight and showed an ortho-xylene sorption time for 30 percent of said capacity of 92 minutes. The two latter measurements were carried out at 120°C. For the para-xylene sorption, the hydrocarbon partial pressure was 5.1 mm Hg. For the ortho-xylene sorption time, the hydrocarbon partial pressure was 3.8 mm Hg.

Example 45

The catalyst of Example 11 was treated with 1-butene at 400°C, a space velocity on a weight basis of 4 and 1 atmosphere pressure. The liquid product, which made up 89% by weight of the charge, contained 13.4% by weight xylene and 3.9% by weight ethyltoluene. The xylene fraction contained 37 percent p-xylene, and the ethyltoluene fraction contained 43 percent para-ethyltoluene. The equilibrium values for these para isomers are 24 and 32 percent respectively.

Example 46

The catalyst of Example 44 was treated with dodecane at 400°C, a weighted space velocity of 10 and 1 atmosphere pressure. The liquid product, which made up 41% by weight of the charge, consisted of 12.6% by weight xylene and 4.3% by weight ethyl toluene. The xylene fraction contained 63 percent para-xylene, and the ethyltoluene fraction contained 58 percent paxa-ethyltoluene.

Example 47

The catalyst of Example 44 was treated with toluene at 550°C, a weight-based space velocity of 50, a pressure of 25.51 ato, and a mole ratio of hydrogen to hydrocarbon of 6. The liquid product, which contained 20 percent by weight converted toluene, consisted of 12.1 percent by weight xylenes in addition to benzene, where the xylene fraction contained 30 percent para-xylene.

Example 48

The catalyst of Example 44 was treated with toluene for five hours at 640°C, a weighted space velocity of 50 and a pressure of 1 atmosphere. After this treatment, the catalyst, which was found to contain approx. 4 wt.% coke, treated with toluene at 550°C, a pressure of 40.82 ato, a weight-based space velocity of 40, and a mole ratio of hydrogen to hydrocarbon of 10. The liquid product contained 80.7 wt.% toluene (19, 3 percent conversion) and 9.6 percent by weight xylenes in addition to benzene. The xylene fraction contained 82 percent para-xylene.

Example 49

3 g of the catalyst according to example 44 was treated with a solution consisting of 1.02 g of magnesium acetate tetrahydrate in 4 ml of water. The resulting slurry was evaporated to dryness over 24 hours and then air-calcined for 10 hours at 538°C, yielding a HZSM-5 product containing 6 wt% MgO.

Example 50

The catalyst of Example 49 was treated with toluene at 550°C, a pressure of 40.82 ato, a space velocity on a weight basis of 40 and a hydrogen/hydrocarbon ratio of 4. The toluene conversion was 29.4 percent. The liquid product contained 15.03 percent by weight xylene, which contained 53 percent of the para isomer.

Example 51

This example illustrates the production of p-diethylbenzene using the catalyst according to example 44 pre-treated with toluene as in example 15, whereby approx. 4% by weight of coke was deposited. A mixture of benzene and ethylene in a molar ratio of 1:2 (fresh material) is mixed with a recycle stream containing benzene and ethylbenzene and passed over the catalyst at a temperature of 441.5-454.4°C, a pressure of 20, 41 ato and a space velocity of 2, based on weight units of ethylene per hour per unit weight catalyst. The effluent product from the reactor is distilled, whereby a fraction (recycling stream) consisting of benzene, ethylbenzene and unreacted ethylene is distilled off, which is recycled to the reactor, and a bottom fraction containing the desired product, p-diethylbenzene.

Example 52

A 5 g sample of HZSM-5 with a crystal size of 0.02-0.05 µm was placed in a glass tube fitted with a fritted glass disc, Dimethylsilane was passed through the layer of HZSM-5 at a rate of 40 ml /minute. After 15 minutes, the HZSM-5 material had sorbed 0.60 g of dimethylsilane. The product was added to 200 ml of 15% aqueous ammonia to hydrolyze the silane. Hydrogen was developed quickly. After 1 hour, the product was filtered and calcined by heating to 538°C at a rate of 1°C/minute and held at this temperature for 6 hours.

The above procedure was repeated a total of three times, whereby a silica-containing HZSM-5 containing 5% by weight of added silica was obtained.

Example 53

A silica-modified HZSM-5 catalyst was prepared as in Example 52 using HZSM-5 with a crystal size of 1-2 µm instead of the above crystal size of

0.02-0.05 um.

The toluene (5.2 parts by weight) was contacted with 0.13 parts by weight of the above catalyst at 600°C and a liquid-based space velocity of 20. The para-xylene content of the xylene product was found by gas chromatography to be 79 percent. This is significantly higher than the 30 percent xylene content found using the HZSM-5 parent material under similar reaction conditions.

Example 54

To 1.42 g of phenylmethylsilicone (molecular weight 1686) dissolved in 40 ml of n-hexane was added 4 g of NH 3 ZSM-5 with a crystallite size of 1-2 µm. This sample of NH^ ZSM-5 contained 35 percent alumina as binder. The mixture was evaporated slowly over 2 hours using a rotary evaporator. The residue was calcined in air by heating to 538°C at a rate of 1°C/minute and maintaining this temperature for 7 hours, whereby silica-modified HZSM-5 containing 14 weight percent silica was obtained.

Example 55

To 0.73 g of phenylmethylsilicone (molecular weight 1686) dissolved in 40 ml of n-hexane was added 4 g of NH 3 ZSM-5 with a crystallite size of 1-2 µm. The mixture was evaporated over 1/2 hour using a rotary evaporator. The residue was calcined in air by heating to 538°C at a rate of 1°C/minute and maintaining this temperature for 7 hours, whereby silica-modified HZSM-5 containing 7.5 weight percent silica was obtained.

Example 56

To 0.32 g of methyl hydrogen silicone (molecular weight 3087) dissolved in 40 ml of n-hexane was added 4 g of NH 3 ZSM-5 with a crystallite size of 1-2 µm. The mixture was evaporated over 1/2 hour using a rotary evaporator. The residue was calcined in air by heating to 538°C at a rate of 1°C/minute and maintaining this temperature for 7 hours, whereby silica-modified HZSM-5 containing 7.5 weight percent silica was obtained.

Example 57

To 0.40 g of dimethyl silicone (molecular weight 4385) dissolved in 40 ml of n-hexane was added 4 g of NH 4 ZSM-5 with a crystallite size of 1-2 µm. The mixture was evaporated over 1/2 hour using a rotary evaporator. The residue was calcined in air by heating to 538°C at a rate of 1°C/minute and maintaining this temperature for 7 hours, whereby silica-modified HZSM-5 containing 7.5 weight percent silica was obtained.

Example 58

A sample of silica-modified HZSM-5 prepared as in Example 57 was pelletized, pellet size corresponding to 14-30 mesh, and tested in a reactor for toluene disproportionation at atmospheric pressure using flowing hydrogen and a hydrogen to hydrocarbon mole ratio of 2. The reaction was carried out at 550-600°C using space velocities on a weight basis of 8-22. The results are set forth in the following Table VIII.

It will be seen from the above data that the selectivity of

para-xylene at the same conversion and temperature was significantly higher after modification with silica, and that this selectivity ! remained high after regeneration of the catalyst by combustion of deposited carbon in air at 540°C.

Example 59

A sample of silica-modified HZSM-5 prepared as in Example 55 was pelletized, pellet size corresponding to 14-30 mesh, and tested for toluene disproportionation at atmospheric pressure using flowing hydrogen and a

mole ratio between hydrogen and hydrocarbon of 2. The reaction

i was performed at a temperature of 550°C using space velocities on a weight basis of 6-25. The results are set forth in the following Table IX.

in

It will be seen from the above results that the silica-modified HZSM-5 catalyst can be completely regenerated (in air at 540°C) and shows significantly higher selectivity to para-xylene compared to the unmodified catalyst at the same conversion and temperature.

Example 60

A silica-modified HZSM-5 catalyst prepared in a similar manner to Example 55, but containing 1.9 weight percent silica, was tested for toluene disproportionation in a reactor at atmospheric pressure using flowing hydrogen and a hydrogen to hydrocarbon mole ratio of 2. The reaction was carried out at 550°C using space velocities on a weight basis of 5-20. The results are given in the following table X.

Example 61

A sample of silica-modified HZSM-5 prepared as in Example 56 was tested for toluene disproportionation as in Example 60. The results are given in the following

table XI.

Example 62

Toluene disproportionation was performed with a sample of a silica-modified HZSM-5 catalyst prepared as in Example 54. The reaction was performed at 500°C and 40.82 ato. The mole ratio of hydrogen to hydrocarbon was 2, and the space velocity on a weight basis was 7. After the experiment had been running for 18 days, the toluene conversion decreased slightly, from 38 percent to 35 percent, while the para-xylene content of the xylene increased from 58 percent to 70 percent.

Example 63

Alkylation of toluene with methanol was carried out in the presence of a sample of silica-modified HZSM-5 prepared as in Example 55. The molar ratio of toluene to methanol was 4, and a pelletized catalyst, pellet size 14-30 mesh, was used . The reaction was carried out at a temperature of 400-550°C and atmospheric pressure at a space velocity on a weight basis of 10, using flowing hydrogen and a mole ratio of hydrogen to hydrocarbon of 2. The results, which are set forth in the following Table XII , shows high selectivity to para-xylene.

Example 64

ZSM-5 crystals were prepared using the following reactants:

Silicate solution

19.16 kg sodium silicate (Na20/Si02 = 3.3) (Q-Brand) 23.97 kg water

Acid solution

612 g of aluminum sulfate

1600 g sulfuric acid

7190 g of sodium chloride

32.78 kg of water

Organic substances

12 90 g tri-n-propylamine

1110 g of n-propyl bromide

The silicate solution and the acid solution were mixed in a nozzle, whereby a gelatinous material was obtained, which was fed to a 113 liter autoclave equipped with a stirrer. After gelatinization was complete, the organics were added and the temperature raised to 157.2°C with stirring. The reaction mixture was maintained at this temperature for 17 hours with stirring at a rate of 121 rpm. minute. The product was now analyzed by X-ray diffraction and found to be ZSM-5. The product was then washed free of soluble salts and dried. Analysis of the product gave the following result expressed in mole ratio:

The thus prepared ZSM-5 was pre-calcined in air at 370°C and then ammonium-exchanged by 2 times treatment with 5N NH^Cl solution at 100°C (15 ml per gram of zeolite), the first time for 16 hours , a second time for 4 hours, filtered, washed free of chloride and air-dried.

The resulting ammonium form of ZSM-5 was converted to the hydrogen form by calcination in air by heating to 538°C at a rate of 1°C/minute and maintaining this temperature for 10 hours.

A mixture of toluene (1715 g) and methanol (426 g) in a molar ratio of 1.4/1 was passed over 5 g of the thus prepared HZSM-5 at 550°C and a space velocity of 5 parts by weight charge per weight part catalyst per hour for a total of 85 hours. The activity of the catalyst decreased from an initial conversion of toluene of 70% by weight to zero at the end of the 85 hours. Catalyst weight increased by 77 percent due to coke formation.

A portion of the coke-containing catalyst was regenerated in air at 550°C overnight. Alkylation of toluene with methanol was carried out by passing a mixture of toluene and methanol in a molar ratio of 1.4:1 over 0.8 g of the regenerated catalyst containing approx. 30 weight percent coke at a temperature of 490°C and a space velocity of 11.5 weight parts charge per weight part catalyst per hour. The toluene conversion was 60 percent, and the para/meta/ortho ratio in the xylene product was 50/33/17.

Example 65

After use in the method according to example 64,

the catalyst regenerated in air at 550°C for 16 hours. Alkylation of toluene with methanol was carried out by passing a mixture of toluene and methanol in the molar ratio 1.4:1 over 0.8 g of the regenerated catalyst containing approx. 30 weight percent coke at a temperature of 490°c and a space velocity of 18 (weight units charge per weight unit catalyst per hour). The toluene conversion was 49 percent and the para/meta/ortho ratio was 52/32/16.

Example 66

A catalyst was prepared by mixing 5% by weight HZSM-5 and 95% by weight silica gel.

Toluene and methanol in a molar ratio of 1:1 was passed over this catalyst at a temperature of 550°C and a space velocity on a weight basis of 250. The methanol conversion was 11% by weight. The xylene content of the aromatic product was 50% by weight After 32.5 hours of the experiment, the catalyst was significantly deactivated due to accumulation of coke on the catalyst and exhibited 100 percent selectivity to para-xylene at about 1 percent toluene conversion.

Example 67

A catalyst was prepared by mixing 5 weight percent HZSM-5 extrudate (containing 65 weight percent HZSM-5 and 35 weight percent A^O^ binder) and 95 weight percent silica gel.

Toluene and methanol in a mole ratio of 1:1 was passed over this catalyst at a temperature of 550°C and a space velocity on a weight basis of 241. The methanol conversion was 10 weight percent. The xylene content of the aromatic product was 100% by weight. After 4.5 hours of the experiment, the catalyst was significantly deactivated due to accumulation of coke on the catalyst and showed 100 percent selectivity to para-xylene at approx. 1 percent toluene conversion.

Example 68

A toluene starting material was contacted with methyl alcohol in a molar ratio of toluene to alcohol of 2:1, using a stationary bed of extruded catalyst containing 35% by weight alumina and 65% by weight HZSM-5, prepared as in Example 1 in U.S. Patent No. 3,751,506. The temperature at the reactor inlet was 465.6°c, and the pressure in the reactor was atmospheric pressure. The space velocity for the total added material was 4. The composition of the liquid product was as follows:

It will be clear from the above results that the amount of coke on the catalyst, i.e. 3.6% by weight, was insufficient to give selective formation of para-xylene, as the para/meta/ortho-xylene concentration mainly corresponded to the equilibrium mixture - concentration on.

Examples 69-71

An extruded catalyst of the same nature as that of Example 68 was pretreated to deposit coke prior to the alkylation. The starting material and conditions of the reaction were the same as

in the preceding example. The composition of the liquid product was as follows:

From the above results, it will be seen that when the amount of coke deposited on the catalyst was within the range of 26 - 30 percent by weight, para-xylene was formed in amounts significantly greater than the corresponding amount in the equilibrium mixture.

Examples 72-80

A HZSM-5 catalyst prepared as in Example 64 was used in the methylation of toluene using a 2:1 mole ratio of toluene to methyl alcohol. The temperature in the reactor inlet was 465.6°C, the pressure was atmospheric pressure, and the space velocity on a weight basis was 4. The catalyst used in example 72 was not pre-treated for the deposition of coke, while the catalysts used in the other examples were pretreated to deposit varying amounts of coke on the catalyst as indicated. The composition of the liquid products obtained in each case is given in Table XIII below.

From the results above, it will be seen that a minimum provision of approx. 15% by weight of coke on the catalyst is required before selective formation of para-xylene is achieved. From the results in example 72, it will thus be clear that even with a deposited amount of coke on the catalyst of over 8% by weight, the para/meta/ortho-xylene concentration was essentially equal to the concentration in the equilibrium mixture.

Example 81

This example serves to illustrate disproportionation of toluene in the presence of a catalyst of HZSM-5 not modified with phosphorus and magnesium.

A catalyst containing 65 weight percent acid ZSM-5 and 35 weight percent alumina was prepared as follows: A sodium silicate solution was prepared by mixing 3832 kg of sodium silicate (Q Brand - 28.9 weight percent SiC^,

8.9 weight percent Na 2 O and 62.2 weight percent H 2 O) and 2215 1 water. After adding 10.90 kg of a dispersant consisting of a sodium salt of polymerized substituted benzenoid alkyl sulfonic acid combined with an inert inorganic suspending agent ("Daxad" 27), the solution was cooled to approx. 12.8°C. An acidic alum solution was prepared by adding 138.5 kg of aluminum sulphate

(17.2 Al 2 O 3 ), 332.8 kg of sulfuric acid (93%'s) and 171.2 kg of sodium chloride were dissolved in 2275 1 of water. The solutions were gelled in a mixing nozzle and fed into an autoclave equipped with a stirrer. During this mixing operation, 545 kg of sodium chloride was added to the gel and thoroughly mixed. The resulting gel

was thoroughly agitated and heated to 93.3°C in a closed container. After reducing the agitation, an organic solution was prepared by mixing 258 kg of tri-n-propylamine, 221.6 kg of n-propyl bromide and 427 kg of methyl ethyl ketone added to the gel. This mixture was reacted for 14 hours at a temperature of 93.3-98.9°C. Then the agitation was increased and these conditions maintained until the crystallinity of the product reached at least 65% ZSM-5, as determined by X-ray diffraction. The temperature was then increased to 160°C until crystallization was complete. The remaining organics were removed from the autoclave and the product slurry was cooled.

The product was washed using decantation and a defoamer based on polyammonium hydrogen sulfate. The washed product containing less than 1% sodium was filtered and dried. The weight of dried zeolite was approx. 1044 kg.

The dried product was mixed with alpha alumina monohydrate and water (65% zeolite, 35% alumina binder on annealed basis) and then extruded to approx. 1.6 mm pellets with particle density <0.98 gram/ml and crushing strength >3.57 kg/linear cm.

After drying, the extruded pellets were calcined in nitrogen (19.8-28.3 m^ per minute) for 3 hours at 538°C, cooled,

and air of ambient temperature was passed through the layer for 5 hours. The pellet product was then ammonium-exchanged for 1 hour at ambient temperature (109 kg ammonium nitrate dissolved in approx. 3024 1 de-ionized water). The exchange was repeated and the product washed and dried. The sodium content in the exchanged pellet product was less than 0.05 percent by weight.

The dried pellet product was calcined in a mixture of nitrogen and air (10-12.5% air, 90-87.5% nitrogen) for 6 hours at 538°C and cooled in nitrogen alone.

This catalyst was used for the disproportionation of toluene by passing it over 6.0 g of the catalyst at a space velocity on a weight basis of 3.5-3.6 and a temperature between 450 and 600°C. The conditions and results are set forth in the following Table XIV.

It will be seen from the above results that the unmodified catalyst gave a xylene product in which the para isomer was present in its normal equilibrium concentration of about 24% by weight of the xylene fraction.

Example 82

To a solution of 8 g of 85% H 3 PO 4 in 10 ml of water was added 10 g of HZSM-5 extrudate which was allowed to stand overnight at room temperature. After filtering and drying at 120°C

for 3 hours, the material was calcined at 500°C for 3 hours, whereby 11.5 g of phosphorus-modified ZSM-5 was obtained. 10 g of the above phosphorus-modified ZSM-5 was then added to a solution of 25 g of magnesium acetate tetrahydrate in 20 ml of water, which was allowed to stand overnight at room temperature. After filtering and drying at 120°C, the material was calcined at 500°C for 3 hours, whereby 10.6 g of magnesium-phosphorus-modified ZSM-5 was obtained. Analysis showed concentrations of the

modifying elements of 9.2 weight percent phosphorus and 3.0 weight percent magnesium.

Example 83

The toluene was passed over 5 g of the catalyst of Example 82 at a weighted space velocity of 3.5 (based on the total catalyst) at 600°C. The conversion of toluene was 24 per cent, and the concentration of para-xylene in the total xylenes was 98.2 per cent.

Example 84

The toluene was passed over 5 g of the catalyst of Example 82 at a space velocity on a weight basis of 0.5 (based on the total catalyst) at 550°C. The conversion of toluene was 32.5 per cent, and the concentration of para-xylene in the total xylenes was 91.2 per cent.

Example 85

The procedure in Example 82 was repeated with the exception that 7 g of 85% H 3 PO 4 were used. The final catalyst weighed 10.9 g. Analysis showed concentrations of the modifying elements of 7.4 weight percent phosphorus and 4.2 weight percent magnesium.

Example 86

The toluene was passed over 5 g of the catalyst of Example 85 at a weight basis space velocity of 3.5 (based on the total catalyst) at 600°C. The conversion of toluene was 27.2 per cent, and the concentration of para-xylene in the total xylenes was 96.6 per cent.

By repeating the above experiment at varying temperatures and space velocities, the following results were obtained:

Example 87

To a solution of 3 g of 85% H3PO4 in 12 ml of water was added 10 g of HZSM-5 extrudate, which was allowed to stand overnight at room temperature. The water was evaporated at 130°C with occasional stirring, after which the material was dried at 200°C for 2 hours. After calcination at 500°C, the material weighed 11.2 g. Analysis showed a phosphorus content of 7.5 percent by weight.

To a solution of 11 g of Mg(OAc)2•4H20 in 20 ml of water was added 10 g of the above-mentioned phosphorus-modified ZSM-5 extrudate, which was left overnight at room temperature. The mixture was evaporated to dryness and then heated to 200°C. It was then calcined at 500°C for 2 hours, whereby 11.3 g of magnesium-phosphorus modified ZSM-5 was obtained. Analysis showed concentrations of the modifying elements of 5.4 weight percent phosphorus and 8.5 weight percent magnesium.

Example 88

The toluene was passed over 5 g of the catalyst of Example 87 at a space velocity on a weight basis of 3.5 (based on the total catalyst) at 600°C. The conversion of toluene was 18.2 per cent, and the concentration of para-xylene in the total xylenes was 85.5 per cent.

Example 89

The toluene was passed over 5 g of the catalyst of Example 87 at a weight basis space velocity of 0.4 at 550°C. The conversion of toluene was 30.6 per cent, and the concentration of para-xylene in the total xylenes was 40 per cent.

Example 90

The general method of preparation according to example 82 was repeated, whereby a magnesium-phosphorus-modified ZSM-5 catalyst was obtained. Analysis showed modifier concentrations of 10.2 weight percent phosphorus and 4.7 weight percent magnesium.

Example 91

The toluene was passed over 5 g of the catalyst of Example 90 at a weight basis space velocity of 3.5 (based on the total catalyst) at 600°C. The conversion of toluene was 21.8 per cent, and the concentration of para-xylene in the total xylenes was 65.2 per cent.

Example 92

The toluene was passed over 5 g of the catalyst of Example 90 at a weighted space velocity of 0.4 (based on the total catalyst) at 550°C. The conversion of toluene was 35.7 per cent, and the concentration of para-xylene in the total xylenes was 38.4 per cent.

From the above results, it will be clear that high selectivities to the para isomer were obtained in the xylene product using the modified zeolite catalyst described herein. Unmodified catalysts gave, under the same reaction conditions as in the previous examples, para-xylene in an equilibrium ratio of 24 percent.

Claims (7)

1. Catalyst material for the selective production of para-dialkyl-substituted benzenes, comprising a crystalline aluminosilicate zeolite with a SiO2/Al203 ratio of 12-3000 and a "constraint index" within the range 1-12, characterized by that it has an activity, alpha, of 2-5000, preferably 5-200, a xylene sorption capacity greater than 1g/100 g zeolite and an ortho-xylene sorption time for 30% of said capacity of over 10 minutes, where the sorption capacity and the sorption time is measured at 120°C and 4.5 - 0.8 mm Hg. 2. Catalyst according to claim 1, characterized in that at least part of the zeolite is present as crystals with sizes between 0.5 and 20 µm, preferably within the range 1-6 µm. 3. Catalyst according to one of the preceding claims, characterized in that coke is deposited on the catalyst in an amount of 15-75% by weight, preferably 20-40% by weight, calculated on the weight of the catalyst without coke. 4. Catalyst according to claim 1 or 2, characterized in that the zeolite is intimately connected with 2-30% by weight of one or more stable, difficult-to-reduce oxides, where the percentage applies to each of these and is based on the weight of the zeolite. 5. Catalyst according to claim 4, characterized in that the zeolite is combined with 2-25% by weight of an oxide of phosphorus and of an oxide of magnesium. 6. Catalyst according to claim 1 or 2, characterized in that the zeolite's internal crystalline structure contains 0.1-10%, calculated on the weight of the zeolite, of added amorphous silicon dioxide. 7. Process for the selective preparation of para-dialkyl-benzenes, where each alkyl group contains 1-4 carbon atoms, in particular p-xylene, p-diethylbenzene or p-ethyltoluene, whereby a C1 - C4-monoalkyl-benzene, a C2 - C15- olefin and/or a C3 - C3 paraffin, or a mixture of any of these with benzene, under conversion conditions is brought into contact with a catalyst, optionally in the presence of hydrogen, in particular by disproportionation of toluene or by alkylation of toluene with an alkylating agent containing 1-4 carbon atoms, characterized in that a catalyst material according to one of claims 1-6 is used as catalyst.