It is known to catalytically crack non-aromatic gasoline boiling range hydrocarbons (in particular paraffin and olefins) to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene, and xylenes) in the presence of catalysts which contain a zeolite (such as ZSM-5), as is described in an article by N.Y. Chen et al in Industrial & Engineering Chemistry Process Design and Development, Volume 25, 1986, pages 151-155. The reaction product of this catalytic cracking process contains a multitude of hydrocarbons such as unconverted C5+ alkanes, lower alkanes (methane, ethane, propane), lower alkenes (ethylene and propylene), C6-C8 aromatic hydrocarbons (benzene, toluene, xylenes, and ethylbenzene), and C9+ aromatic hydrocarbons. Depending upon the relative market prices of the individual reaction products, it can be desirable to increase the yield of certain of the more valuable products relative to the others.

One concern with the use of zeolite catalysts in the conversion of hydrocarbons to aromatic hydrocarbons and lower olefins is the excessive production of coke during the conversion reaction. Coke formed during the zeolite catalyzed aromatization of hydrocarbons tends to cause catalyst deactivation. It is desirable to improve processes for the aromatization of hydrocarbons and the formation of lower olefins from hydrocarbons by minimizing the amount of coke formed during such processes. It is also desirable to have a zeolite catalyst that is useful in producing significant quantities of the aromatic and olefin conversion products.

The invention deals with hydrocarbon conversion processes which at least partially convert hydrocarbons to ethylene, propylene and BTX (benzene, toluene, xylene and ethylbenzene) aromatics.

The invention further provides hydrocarbon conversion processes

which have an acceptably low coke production rate and/or which produces a conversion product containing suitable quantities of olefins and BTX aromatics.

Also provided is an improved zeolite material and/or a method for making an improved zeolite material having such desirable properties as providing for lower coke production and favorable production of olefins and BTX aromatics when used in the conversion of hydrocarbons.

One aspect of the invention deals with a process for the conversion of non-aromatic hydrocarbons to aromatic hydrocarbons and lower olefins by contacting under conversion conditions a hydrocarbon feed with a silicon impregnated calcined mixture of an acid treated zeolite and zinc.

Another aspect of the invention is a novel composition used in the conversion of hydrocarbons. The novel composition comprises a silicon impregnated calcined mixture of an acid treated zeolite and zinc.

The novel composition may be made by mixing an acid treated zeolite and zinc to form a mixture and calcining the mixture which is thereafter impregnated with silicon.

The inventive composition includes a calcined mixture of zinc and a zeolite starting material that has been treated with an acid to provide an acid treated zeolite. The calcined mixture is impregnated with silicon to thereby give the inventive composition comprising a silicon impregnated calcined mixture of an acid treated zeolite and zinc.

Any suitable means or method can be used to treat the zeolite starting material with acid. It is preferred for the zeolite to be soaked with an acid solution by any suitable means known in the art for contacting the zeolite with such acid solution. The acid solution used to treat the zeolite can be a solution of any acid that suitably provides for the leaching of aluminum atoms from the zeolite particles.

Preferably, the acid concentration in this solution is about 1-10 equivalents per liter.

Examples of such suitable acids include sulfuric, phosphoric, nitric and hydrochloric. The preferred acid solution is aqueous hydrochloric acid. The zeolite is soaked in the acid solution (preferably at a temperature of about 50-100"C) for a period upwardly to about 15 hours, but, preferably from 0.1 hour to 12 hours.

After soaking, the resultant acid treated zeolite is washed free of the acid and then

can be dried or calcined, or both.

The zeolite starting material used in the composition of the invention can be any zeolite which is effective in the conversion of non-aromatics to aromatics when contacted under suitable reaction conditions with non-aromatic hydrocarbons. Preferably, the zeolite has a constraint index (as defined in U.S.

Patent 4,097,367, which is incorporated herein by reference) in the range of about 0.4 to about 12, preferably about 2-9. Generally, the molar ratio of SiO2 to A1203 in the crystalline framework of the zeolite is at least about 5:1 and can range up to infinity. Preferably the molar ratio of SiO2 to A1203 in the zeolite framework is about 8:1 to about 200:1, more preferably about 12:1 to about 100:1. Preferred zeolites include ZSM-5, ZSM-8, ZSM-ll, ZSM-12, ZSM-35, ZSM-38, and mixtures thereof. Some of these zeolites are also known as "MFI" or "Pentasil" zeolites.

The presently more preferred zeolite is ZSM-5.

As used herein, the term "zinc" refers to elemental zinc, inorganic zinc compounds, organic zinc compounds and mixtures of any two or more thereof.

Examples of potentially suitable zinc compounds include zinc acetate dihydrate, zinc acetylacetonate hydrate, zinc bromide, zinc carbonate hydroxide, zinc chloride, zinc borate, zinc silicate, zinc aluminate, zinc chromite, zinc cyclohexanebutyrate dihydrate, zinc 2-ethylhexanoate, zinc fluoride, zinc hexafluoroacetylacetonate dihydrate, zinc iodide, zinc molybdate, zinc naphthenate, zinc nitrate hexahydrate, zinc oxide, zinc perchlorate hexahydrate, zinc phosphate hydrate, zinc phosphide, zinc protoporphyrin, zinc sulfate monohydrate, zinc sulfide, zinc telluride, zinc tetrafluoroborate hydrate, zinc titanate, and zinc trifluoromethanesulfonate.

Inorganic zinc compounds are particularly preferred. The most preferred zinc compound is zinc chloride.

Zinc is mixed or incorporated or impregnated into the acid treated zeolite to form a mixture of acid treated zeolite and zinc. The zinc may be incorporated into the acid treated zeolite by any suitable means or method known in the art for incorporating metallic elements into a substrate material. A presently preferred method is to mix the acid treated zeolite with at least one anhydrous zinc compound, followed by calcining, preferably at about 700-800"C for about 1-10 hours in an inert gas stream. Another suitable method uses a liquid impregnation

solution containing a concentration of zinc so as to ultimately provide the final inventive composition having a concentration of zinc in the required range.

If zinc is incorporated into the acid treated zeolite with an aqueous solution of a zinc compound, the preferred impregnation solution is an aqueous solution formed by dissolving a salt of zinc (preferably ZnCl2) in water. However, it is acceptable to use somewhat of an acidic solution to aid in the dissolution of the zinc salt. The zinc-impregnated, acid-treated zeolite is then calcined, preferably at about 700-800"C for about 1-10 hours in an inert gas stream.

The amount of the zinc incorporated or impregnated into or mixed with the acid treated zeolite should be such as to give a concentration effective in providing the desirable properties of favorable aromatics and olefin conversion yields with low coke production when the inventive composition is employed in the conversion of a hydrocarbon feed. Generally, the weight percent of zinc present in the mixture of acid treated zeolite and zinc should be such as to provide a concentration generally in the range upwardly to about 10 weight percent of the inventive composition comprising a silicon impregnated calcined mixture of an acid treated zeolite and zinc. The preferred concentration of zinc in the final inventive composition is in the range of from or about 0.05 to or about 8 weight percent and, most preferably, from 0.1 to 6 weight percent.

The mixture of acid treated zeolite and zinc can be subjected to a heat treating step (calcination) whereby it is exposed by any suitable method known in the art to a gaseous atmosphere under temperature and pressure conditions and for a period of time that suitably provide a calcined mixture of acid treated zeolite and zinc. The gas used in the heat treatment of the mixture of acid treated zeolite and zinc can be selected from the group consisting of inert gases (for example, nitrogen, helium and argon gases), reducing gases (for example, carbon monoxide and hydrogen gases), air, oxygen and steam. The preferred gas is selected from the group consisting of air, oxygen, nitrogen, steam and mixtures thereof. Most preferably, the heat treatment gas is selected from the group consisting of air, oxygen, nitrogen and mixtures of one or more thereof.

The heat treatment may be conducted at any pressure and temperature conditions that suitably provide a heat treated mixture of acid treated zeolite and

zinc. Generally, the heat treatment may be conducted at a pressure from below atmospheric upwardly to about 1000 pounds per square inch absolute (psia). More typical pressures, however, are in the range of from or about atmospheric to or about 100 psia. The heat treatment temperature is generally in the range of from or about 200"C to or about 1000"C. Preferably, this temperature range is from about 300"C to about 800"C and, most preferably, the heat treatment temperature is in the range of from 350"C to 7500C.

The time period for conducting the heat treatment step must be sufficient to provide a substantially dry, i.e., free of water, material. Generally, the period for exposing the mixture of acid treated zeolite and zinc to the gas atmosphere at appropriate temperature and pressure conditions can range from or about 0.1 hour to or about 30 hours. Preferably, the heat treatment step is conducted for a period of from or about 0.25 hour to or about 25 hours and, most preferably, from 0.5 hour to 20 hours.

The calcined mixture of acid treated zeolite and zinc is then impregnated with silicon to provide the novel silicon impregnated calcined mixture of an acid treated zeolite and zinc. The silicon may be incorporated into the calcined mixture of acid leached zeolite and zinc by any suitable means or method known in the art for incorporating metallic elements into a substrate material. A preferred method is the use of any standard incipient wetness technique for impregnating the calcined mixture of acid leached zeolite and zinc substrate with the silicon. The preferred method uses a liquid impregnation solution containing the desirable concentrations of silicon so as to ultimately provide the final inventive composition having the required concentration of silicon.

It is particularly desirable to use for the impregnation of the calcined mixture of acid treated zeolite and zinc a solution of the silicon that is incorporated into the calcined mixture. The solution of silicon may be an aqueous solution or a nonaqueous solution. The preferred impregnation solution is one formed by dissolving an organic silicon compound in a hydrocarbon solvent, preferably, cyclohexane.

As used herein, the term "silicon" refers to elemental silicon, inorganic silicon compounds and organic silicon compounds and mixtures of any

two or more thereof. Organic silicon compounds are particularly preferred and most preferred are silicon compounds are selected from the group consisting of poly(methylphenylsiloxane), tetraethoxysilicon and mixtures thereof.

The amount of silicon incorporated or impregnated into the calcined mixture should be such as to give a concentration of silicon in the final inventive composition that is effective in providing the desirable properties of favorable aromatics and olefin conversion yields with low coke production when the inventive composition is employed in the conversion of a hydrocarbon feed. The weight percent of silicon present in the silicon impregnated calcined mixture of acid treated zeolite and zinc is generally in the range upwardly to about 50 weight percent of the silicon impregnated calcined mixture of acid treated zeolite and zinc. The preferred concentration of silicon in the silicon impregnated calcined mixture of acid treated zeolite and zinc is in the range of from about 0.05 to about 30 weight percent and, most preferably, from 0.1 to 20 weight percent.

The inventive composition described herein can also be combined with an inorganic binder (also called matrix material) preferably selected from the group consisting of alumina, silica, alumina-silica, aluminum phosphate, clays (such as bentonite), and mixtures thereof. The content of the silicon impregnated calcined mixture of acid treated zeolite and zinc component of the combined mixture is about 1-99 (preferably about 5-80) weight-%, and the content of the above-listed inorganic binders in the combined mixture is about 1-50 weight-%. Generally, the silicon impregnated calcined mixture of acid treated zeolite and zinc and the inorganic binder components are compounded and subsequently shaped (such as by pelletizing, extruding or tableting). Generally, the surface area of the compounded composition is about 50-700 m2/g, and its particle size is about 1-10 mm.

The atomic ratio of silicon to zinc in the silicon impregnated calcined mixture of acid treated zeolite and zinc should be such as to provide the desirable properties as described elsewhere herein. Generally, the atomic ratio of silicon to zinc in the silicon impregnated calcined mixture of acid treated zeolite and zinc is in the range of from or about 1:1 to about 30:1. A preferred atomic ratio of silicon to zinc is in the range of from or about 2:1 to about 25:1 and, most preferably, the - atomic ratio is in the range of from 3:1 to 20:1.

Any suitable hydrocarbon feedstock which comprises paraffins (alkanes) and/or olefins (alkenes) and/or naphthenes (cycloalkanes), wherein each of these hydrocarbons contains 2-16 carbon atoms per molecule can be used as the feed to be contacted with the inventive composition under suitable process conditions for obtaining a reaction product comprising lower alkenes containing 2-5 carbon atoms per molecule and aromatic hydrocarbons. Frequently, these feedstocks also contain aromatic hydrocarbons. Non-limiting examples of suitable, available feedstocks include gasolines from catalytic oil cracking (e.g., FCC and hydrocracking) processes, pyrolysis gasolines from thermal hydrocarbon (e.g., ethane, propane, and naphtha) cracking processes, naphthas, gas oils, reformates, straight-run gasoline and the like. The preferred feed is a gasoline-boiling range hydrocarbon feedstock suitable for use as at least a gasoline blend stock generally having a boiling range of from or about 30"C to or about 210"C. Generally, the content of paraffins exceeds the combined content of olefins, naphthenes and aromatics (if present).

The hydrocarbon feedstock can be contacted by any suitable manner with the inventive compositions described herein contained within a reaction zone.

The contacting step can be operated as a batch process step or, preferably, as a continuous process step. In the latter operation, a solid catalyst bed or a moving catalyst bed or a fluidized catalyst bed can be employed. Any of these operational modes have advantages and disadvantages, and those skilled in the art can select the one most suitable for a particular feed and catalyst.

The contacting step is preferably carried out within a conversion reaction zone, wherein is contained the inventive composition, and under reaction conditions that suitably promote the formation of olefins, preferably light olefins, and aromatics, preferably BTX, from at least a portion of the hydrocarbons of the hydrocarbon feedstock. The reaction temperature of the contacting step is more particularly in the range of from or about 400"C to or about 800"C, preferably, from or about 450"C to or about 750"C and, most preferably, from 500"C to 7000C.

The contacting pressure can range from subatmospheric pressure upwardly to or about 500 psia, preferably, from or about atmospheric to or about 450 psia and, most preferably, from 20 psia to 400 psia.

The flow rate at which the hydrocarbon feedstock is charged to the conversion reaction zone is such as to provide a weight hourly space velocity ("WHSV") in the range of from exceeding 0 hours upwardly to or about 1000 hours The term "weight hourly space velocity", as used herein, shall mean the numerical ratio of the rate at which a hydrocarbon feedstock is charged to the conversion reaction zone in pounds per hour divided by the pounds of catalyst contained in the conversion reaction zone to which the hydrocarbon is charged. The preferred WHSV of the feed to the conversion reaction zone or contacting zone can be in the range of from or about 0.25 hours to or about 250 hours and, most preferably, from 0.5 hours to 100 hour~'.

The following examples are presented to further illustrate this invention and are not to be construed as unduly limiting its scope.

Example I This example illustrates the preparation of several catalysts which were subsequently tested as catalysts in the conversion of a gasoline sample, which had been produced in a commercial fluidized catalytic cracking unit (FCC), to aromatics.

Catalyst A - Acid Treated Zeolite A commercially available ZSM-5 catalyst (provided by United Catalysts Inc., Louisville, KY, under product designation "T-4480") was treated by acid leaching. To acid leach the catalyst, 50 grams of "T-4480" was soaked in 100 grams of an aqueous HC1 solution, having a concentration of approximately 6 gram- equivalents HC1 per liter solution (approximately 6N), for two hours at a constant temperature of about 90"C. After soaking, the catalyst was separated frorn the acid solution, thoroughly washed with water, and dried at 900C for 2 hours. The acid soaked, washed and dried catalyst was calcined at a temperature of about 525"C for four hours.

Catalyst B - Acid Treated Zeolite Impregnated with Silicon A 12.58 gram quantity of the above described acid-treated zeolite was impregnated with 8.22 grams of a solution of 50 weight percent poly(methylphenylsiloxane) in cyclohexane to incipient wetness. The resultant catalyst was dried in air at room temperature and then calcined at 5380C for 6 hours

to obtain 13.75 grams of silylated acid-leached zeolite.

Catalyst C - Untreated Zeolite Implanted with Zinc A mixture of 20 grams of precalcined zeolite and 3 grams of anhydrous zinc chloride (ZnCl2) was heated to 7500C in flowing helium (flow rate of 20 ml per minute) for 2 hours and then cooled to approximately room temperature. The resultant catalyst was then washed with 400 ml of an aqueous 1M ammonium nitrate (NH4NO3) solution. The washed catalyst was filtered, washed with deionized water, dried at 900C for 2 hours, and calcined in air at 5350C for 6 hours to obtain 19.32 grams of zinc-incorporated zeolite, wherein the zeolite had not been treated with acid.

Catalyst D - Untreated Zeolite Implanted with Zinc and Impregnated with Silicon A mixture of 20 grams of precalcined zeolite and 6.0 grams of anhy- drous zinc chloride (ZnCl2) was heated to 7500C in flowing helium (flow rate: 20 ml/minute) for 4 hours and then cooled. The resultant catalyst was then washed with 200 ml of an aqueous 1M ammonium nitrate (NH4NO3) solution. The washed catalyst was filtered, washed with deionized water, dried at 900C for 2 hours and calcined in air at 5250C for 6 hours to obtain a zinc-incorporated zeolite. The zinc- incorporated zeolite was impregnated with a solution of 50 weight percent poly- (methylphenyl siloxane) in cyclohexane to incipient wetness. The resultant zinc incorporated zeolite impregnated with silicon was then calcined at 5300C for 6 hours to obtain a silylated zinc-implanted zeolite, wherein the zeolite had not been treated with an acid.

Catalyst E - Silicon Impregnated Calcined Mixture of Acid Treated Zeolite and Zinc A 10.00 gram quantity of above-described acid-treated ZSM-5 catalyst (Catalyst A) was mixed with a 4.0 gram quantity of anhydrous zinc chloride (ZnCl2). This mixture of acid leached zeolite and zinc chloride was then heated in flowing helium (flow rate: 50 ml/minute) at a temperature of 750"C for 4 hours, followed by soaking in a 1.0 molar aqueous solution of ammonium nitrate (NH4NO3), drying for 16 hours at 900C and heating for 5 hours at 5000C. The - resulting material was impregnated with a solution of 50 weight percent

poly(methylphenylsiloxane) in cyclohexane solvent. The thus impregnated material was then heated for 6 hours at 5380C. The final product contained 7.43 weight percent silicon dioxide (SiO2) and 1.03 weight percent zinc.

EXAMPLE II This example illustrates the use of the zeolite materials described in Example I as catalysts in the conversion of a gasoline feed to benzene, toluene and xylenes (BTX) and lower olefins (ethylene, propylene).

For each of the test runs, a 5.0 g sample of the catalyst materials described in Example I was placed into a stainless steel tube reactor (length: about 18 inches; inner diameter: about 0.5 inch). Gasoline boiling range feedstock from a catalytic cracking unit of a refinery was passed through the reactor at a flow rate of about 14 ml/hour, at a temperature of about 600"C and at atmospheric pressure (about 0 psig). The formed reaction product exited the reactor tube and passed through several ice-cooled traps. The liquid portion remained in these traps and was weighed, whereas the volume of the gaseous portion which exited the traps was measured in a "wet test meter". Liquid and gaseous product samples (collected at hourly intervals) were analyzed by means of a gas chromatograph. Results of five test runs for Catalysts A through E are summarized in Table I. All test data were obtained after 8 hours on stream.

Table I BTX Light Olefin Sum of Description of Coke Catalyst Yield Yield* BTX and Catalyst (Wt-%) (Wt-%) (Wt-%) Olefin A Acid Leached Zeolite 48 15 63 1.7 Acid Leached Zeolite B 32 28 60 0.46 Impregnated with Silicon Zeolite (untreated) C 48 18 66 2.7 Implanted with Zinc Zeolite (untreated) D Implanted with Zinc and 33 24 57 1.18 Impregnated with Silicon Silicon Impregnated E Calcined Mixture of 40 26 66 0.15 Acid Treated Zeolite and Zinc * Ethylene + Propylene

The test data presented in Table 1 show that the inventive Catalyst E exhibited considerably less coking (which results in excessive catalyst deactivation) and yielded comparable, if not more, BTX and light olefins than the control catalysts. The improvement in catalyst performance is believed to be due to the unique combination of treatment and modification of the starting zeolite.

It is also noted that the untreated zeolite containing only zinc produced a significant amount of coke with a somewhat reasonable yield of BTX and light olefins. The acid leached zeolite impregnated with silicon lowered the coke production rate, but it also undesirably reduced BTX yield. The novel composition (Catalyst E) suppressed coke formation while also providing for a good yield of BTX and olefins.

Reasonable variations, modifications, and adaptations can be made within the scope of the disclosure and the appended claims without departing from the scope of this invention.