WO2000015338A1

WO2000015338A1 - An improved zeolite

Info

Publication number: WO2000015338A1
Application number: PCT/US1999/020536
Authority: WO
Inventors: Charles A. Drake; An-Hsiang Wu
Original assignee: Phillips Petroleum Company
Priority date: 1998-09-16
Filing date: 1999-09-08
Publication date: 2000-03-23
Also published as: AU5815099A

Abstract

A composition is prepared by a method comprising contacting a zeolite with a compound containing zinc and a metal selected from the group consisting of Group IIIA and Group VIB of the periodic table of the elements. The thus-obtained composition is employed as a catalyst in the conversion of hydrocarbons to aromatics.

Description

AN IMPROVED ZEOLITE Background of the Invention

The invention relates to catalyst compositions useful in hydrocarbon upgrading processes and to methods for their production and use. In another aspect, this invention relates to processes for converting hydrocarbons to aromatic and olefin (ethylene and propylene) hydrocarbons with an increase in BTX (benzene, toluene and xylenes) yield resulting from the conversion of such hydrocarbons in the presence of such catalyst compositions.

It is known to catalytically crack non-aromatic gasoline boiling range hydrocarbons (in particular paraffin and olefin hydrocarbons) to olefms and aromatic hydrocarbons 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. alkanes (methane, ethane, propane), 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. Summary of the Invention

It is desirable to provide an improved process for the conversion of hydrocarbons in which the yield of BTX is increased.

It is also desirable to provide an improved zeolite material which when used in the conversion of hydrocarbons results in increased BTX yield. Yet again it is desirable to provide a method for making an improved zeolite material having such desirable properties as providing for increased BTX yield when used in the conversion of hydrocarbons.

The inventive composition comprises a zeolite, a zinc component and a metal selected from the group consisting of Group IIIA and Group VIB of the periodic table of the elements. CAS version, Hawley's Condensed Chemical

Dictionary, eleventh edition, copyright 1987. The inventive composition may be prepared by incorporating a zinc component and a metal selected from the group consisting of Group IIIA and Group VIB into a zeolite. The inventive composition may be used in the conversion of a hydrocarbon or hydrocarbon mixture to aromatic and olefin hydrocarbons by contacting, under conversion conditions, a hydrocarbon feedstock with the inventive composition. Other advantages of the invention will become apparent from the detailed description and the appended claims.

Detailed Description of the Invention The zeolite material used in preparing the inventive composition can be any zeolite that is effective in the conversion of non-aromatic hydrocarbons to aromatic hydrocarbons 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, the disclosure of which is incorporated herein by reference) in the range of from about 0.4 to about 12, preferably from about 2 to about 9. Generally, the molar ratio of SiO₂ to Al₂O₃ in the crystalline framework of the zeolite is at least about 5:1 and can range up to infinity. Preferably the molar ratio of SiO, to Al₂O₃ in the zeolite framework is in the range of from about 8:1 to about 200:1, more preferably in the range of from about 12:1 to about 100:1. Preferred zeolites include, but are not limited to, ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-35, ZSM-38, and mixtures of any two or more thereof. Some of these zeolites are also known as "MFI" or "Pentasil" zeolites. The presently more preferred zeolite is ZSM-5.

Any suitable means or method can be used to treat the zeolite starting material with acid to give an acid-leached zeolite. 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-leached zeolite is washed free of the acid and then can be dried or calcined, or both.

The inventive composition is a material that comprises a zeolite which may or may not have been acid-leached, a zinc component and a metal selected from the group consisting of Group IIIA and Group VIB. The zinc component and metal can be incorporated into the acid-leached zeolite 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 zeolite substrate with the metal promoters. The preferred method uses a liquid impregnation solution containing the desirable concentrations of zinc and the metal selected from the group consisting of Group IIIA and Group VIB so as to ultimately provide the final inventive composition having the required concentrations of zinc and the metal selected from the group consisting of Group IIIA and Group VIB.

It is particularly desirable to use for the impregnation of the zeolite, which may or may not have been acid-leached, an aqueous solution containing the zinc component and the metal. The preferred impregnation solution is an aqueous solution formed by dissolving a compound comprising zinc and a metal selected from the group consisting of Group IIIA and Group VIB in water. It is preferable to use somewhat of an acidic solution to aid in the dissolution of the compound. The acid used to acidify the impregnation solution is preferably nitric acid. Examples of suitable compounds comprising zinc and a metal selected from the group consisting of Group IIIA and Group VIB for incorporating into the zeolite, which may or may not have been acid-leached, include, but are not limited to, zinc borate, zinc molybdate, zinc chromate, zinc tungstate and zinc aluminate.

The amounts of zinc and the metal selected from the group consisting of Group IIIA and Group VIB incorporated or impregnated into the zeolite, which may or may not have been acid-leached, should be such as to give concentrations effective in providing the desirable properties of increased BTX yield when the inventive composition is employed in the conversion of a hydrocarbon feed.

The weight percent of the compound comprising zinc and the metal selected from the group consisting of Group IIIA and Group VIB present in the impregnated zeolite, which may or may not have been acid-leached, is generally in the range upwardly to about 10 weight percent based on the total weight of the impregnated zeolite. The preferred concentration of the compound in the impregnated zeolite is in the range of from about 0.05 to about 9 weight percent and, most preferably, from 0.1 to 8 weight percent based on the total weight of the impregnated zeolite.

The impregnated zeolite, which may or may not have been acid- leached, can be dried or calcined, or both. The drying step is generally performed in the presence of air at a temperature in the range of from about 20°C to about 125°C and over a time period of from about 0.1 hour to about 4 hours. The calcination temperature is generally in the range of from about 300°C to about 1000°C. The calcination can be performed in either an air atmosphere or an inert atmosphere or a combination thereof for a time period of from about 0.1 hour to about 30 hours. Any suitable hydrocarbon feed which comprises paraffins (alkanes) and/or olefins (alkenes) and/or naphthenes (cycloalkanes), wherein each of these hydrocarbons contains from 2 to 16 carbon atoms per molecule can be used as a feed to be contacted with the inventive composition under suitable process conditions for obtaining a reaction product comprising alkenes containing from 2 to 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 about 30-210°C. Generally, the content of paraffins exceeds the combined content of olefins, naphthenes and aromatics (if present).

The hydrocarbon feed stream can be contacted in any suitable manner with the inventive compositions described herein contained within a conversion 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 has 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 aromatics, preferably BTX, from at least a portion of the hydrocarbons of the hydrocarbon feed. The reaction temperature of the contacting step is generally in the range of from about 400°C to about 800°C, preferably, from about 450°C to about 750°C and, most preferably, from 500°C to 700°C. The contacting pressure can range from subatmospheric pressure upwardly to about 500 psia, preferably, from about atmospheric to about 450 psia and, most preferably, from 20 psia to 400 psia.

The flow rate at which the hydrocarbon feed 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 hour^"1 upwardly to about 1000 hour^"1. The term "weight hourly space velocity", as used herein, shall mean the numerical ratio of the rate at which a hydrocarbon feed 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 can be in the range of from about 0.25 hour^"1 to about 250 hour^"1 and, most preferably, from 0.5 hour^"1 to 100 hour^"1.

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 catalysts which were subsequently tested as catalysts in the conversion of a hydrocarbon feedstock to aromatics (BTX). Acid-leached ZSM-5

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, it was soaked in an aqueous HCl solution, having a concentration of 38 weight percent HCl (approximately 6N), for two hours at a constant temperature of about 90°C. After soaking, the catalyst was separated from the acid solution and thoroughly washed with water and dried. Catalyst A (Control)

A sample of the above-described acid-leached ZSM-5 catalyst was calcined at a temperature of about 525°C for four hours. Catalyst B (Control)

A 10 gram quantity of the above-described acid-leached ZSM-5 catalyst was combined with 10 ml. water and 0.5 ml. nitric acid. The excess liquid was drained off and the catalyst was dried and then calcined at a temperature of about 500°C for 3 hours. Catalyst C (Invention)

A 20.0 gram quantity of the above-described acid-leached ZSM-5 catalyst was impregnated by an incipient wetness technique with a solution containing 1.4 grams zinc hexaborate, 20 grams water, and 1.4 grams nitric acid. This impregnated, acid-leached ZSM-5 catalyst was dried and then calcined at a temperature of about 500°C for three hours. Catalyst D (Invention)

A 20.0 gram quantity of the above-described acid-leached ZSM-5 catalyst was impregnated by an incipient wetness technique with a solution containing 1.4 grams zinc molybdate, 20 grams water and 2.8 grams nitric acid. This impregnated, acid-leached ZSM-5 catalyst was dried and then calcined at a temperature of about 500°C for three hours.

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 olefins (ethylene, propylene).

For each of the Runs 1, 2, 3 and 4, a 5.0 g sample of the catalyst materials described in Example I, that is, Catalysts A, B, C and D, respectively, was placed into a stainless steel tube reactor (length: about 46 cms (about 18 inches); inner diameter: about 1-3 cms (about 0.5 inch)). Gasoline boiling range feedstock from a catalytic cracking unit of a refinery was passed downwardly 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 were analyzed by means of a gas chromatograph. Test results for Runs 1 , 2, 3 and 4 for Catalysts A, B, C and D, respectively, are summarized in Table I. All test data were obtained after about 8 hours on stream.

*Ethylene and Propylene

The test data presented in Table I show that the use of the inventive Catalysts C and D in Runs 3 and 4 produced considerably higher yields of BTX than control Catalysts A (Run 1) and B (Run 2).

Inventive Run 3 demonstrated 26% and 21% increases in BTX yield over control Runs 1 and 2. respectively.

Inventive Run 4 demonstrated 27% and 22% increases in BTX yield over control Runs 1 and 2, respectively.

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.

Claims

C L A I M S

1. A composition comprising a zeolite contacted with a compound containing zinc and a metal selected from the group consisting of Group IIIA and

Group VIB of the periodic table of the elements to form a treated zeolite.

2. A composition as recited in claim 1 wherein said compound is present in said treated zeolite in an amount in the range upwardly to about 10 weight percent based on the total weight of said treated zeolite.

3. A composition as recited in claim 1 wherein said zeolite is ZSM-5.

4. A composition as recited in claim 1 wherein said zeolite has been treated by contacting said zeolite with an acid prior to said contact with said compound.

5. A composition as recited in claim 4 wherein said acid is hydrochloric acid.

6. A composition as recited in claim 1 wherein the contacting of said zeolite includes contacting said zeolite with a solution containing an acid and said compound.

7. A composition as recited in claim 6 wherein said acid is nitric acid.

8. A composition as recited in claim 1 wherein said treated zeolite has been calcined subsequent to treatment with said compound.

9. A composition as recited in claim 8 wherein the calcining of said treated zeolite is conducted at a temperature in the range of from about 300┬░C to about 1000┬░C and for a time period of from about 0.1 hour to about 30 hours.

10. A composition as recited in claim 1 wherein said metal is boron.

11. A composition as recited in claim 10 wherein said compound is zinc borate.

12. A composition as recited in claim 1 wherein said metal is molybdenum.

13. A composition as recited in claim 12 wherein said compound is zinc molybdate.

14. A method of forming a treated zeolite comprising contacting a zeolite with a compound containing zinc and a metal selected from the group consisting of Group IIIA and Group VIB of the periodic table of the elements to form a treated zeolite.

15. A method as recited in claim 14 wherein said compound is present in said treated zeolite in an amount in the range upwardly to about 10 weight percent based on the total weight of said treated zeolite.

16. A method as recited in claim 14 wherein said zeolite is ZSM-5.

17. A method as recited in claim 14 wherein said zeolite is treated by contacting said zeolite with an acid prior to said contact with said compound.

18. A method as recited in claim 17 wherein said acid is hydrochloric acid.

19. A method as recited in claim 14 wherein the contacting of said zeolite includes contacting said zeolite with a solution containing an acid and said compound.

20. A method as recited in claim 19 wherein said acid is nitric acid.

21. A method as recited in claim 14 further comprising the step of calcining said treated zeolite subsequent to said contacting step.

22. A method as recited in claim 21 wherein the calcining of said treated zeolite is conducted at a temperature in the range of from about 300┬░C to about

1000┬░C and for a time period of from about 0.1 hour to about 30 hours.

23. A method as recited in claim 14 wherein said metal is boron.

24. A method as recited in claim 23 wherein said compound is zinc borate.

25. A method as recited in claim 14 wherein said metal is molybdenum.

26. A method as recited in claim 25 wherein said compound is zinc molybdate.

27. A process comprising contacting, under conversion conditions, a hydrocarbon feed with the composition of any one of preceding claims 1-13, to thereby produce a conversion product comprising aromatics.

28. A process as recited in claim 27 wherein said conversion product has a weight % of aromatics in excess of the weight % of aromatics in the hydrocarbon

feed.

29. A process as recited in claim 27, wherein said hydrocarbon feed

comprises cracked gasoline.

30. A process as recited in claim 29, wherein said conversion conditions include a reaction temperature in the range of from about 400┬░C to about 800┬░C, a contacting pressure in the range of from about 0 psia to about 500 psia and a charge rate of said hydrocarbon feed such that the weight hourly space velocity is in the range of from about 0.1 hour^"1 to about 1000 hour^"1.