WO1996019423A1

WO1996019423A1 - Catalytic conversion of paraffinic feedstocks with improved catalyst

Info

Publication number: WO1996019423A1
Application number: PCT/US1995/012683
Authority: WO
Inventors: Sharon Brawner Mccullen; Lilian Ann Rankel
Original assignee: Mobil Oil Corporation
Priority date: 1994-12-22
Filing date: 1995-10-03
Publication date: 1996-06-27
Also published as: AU3687495A

Abstract

A process is provided for converting paraffinic feedstock over a particular catalyst composition to produce upgraded conversion product hydrocarbon compounds. The catalyst composition for use herein comprises crystalline material having the structure of ZSM-48 which has been synthesized in a particular way to impart thereto improved properties for use herein. The improved ZSM-48 for use herein is the product of digesting boron-containing zeolite Beta with a mineral base and a particular organic compound at elevated temperature to produce ZSM-48 crystals, treating the ZSM-48 with soluble aluminum-containing species and/or mixing, extruding, or pelletizing the ZSM-48 with alumina, and recovering the improved ZSM-48 catalyst.

Description

CATALYTIC CONVERSION OF PARAFFINIC

FEEDSTOCKS WITH IMPROVED CATALYST

- The present invention relates to a process for converting a hydrocarbon feed comprising paraffins over a particular catalyst composition to produce upgraded conversion product. The catalyst composition for use herein comprises crystalline material having the structure of ZSM-48 which has been synthesized in a particular way to impart thereto improved properties for use herein. The improved ZSM-48 for use herein is the product of digesting boron-containing zeolite Beta with a mineral base and a particular organic compound at elevated temperature to produce ZSM-48 crystals, treating the ZSM-48 with soluble aluminum-containing species and/or mixing, extruding, or pelletizing the ZSM-48 with alumina, and recovering the improved ZSM-48 catalyst. ZSM-48 and its usual synthesis methods are taught in

U.S. Patents 4,397,827; 4,423,021; and 4,585,747. Zeolite Beta and its synthesis are taught in U.S. Patents 3,308,069; Re. 28,341; 4,923,690; and 5,139,759. Preparation of zeolites including ZSM-48 from reaction mixtures containing boron-containing zeolite Beta as a source of silicon and boron oxide is disclosed in U.S. Patent 5,187,132.

A unit process frequently encountered in petroleum refining involves conversion of paraffinic feedstock to upgraded product. One such process comprises paraffin isomerization of linear (straight chain) paraffins to produce branched chain paraffins. In such a process, as conventionally operated, low molecular weight C. - C- paraffins are converted to isoparaffins in the presence of an acidic catalyst such as chlorided alumina. Non- regenerable Lewis and Bronsted acid catalysts are disclosed in U.S. Patent Nos. 3,766,286; 3,852,184; 3,855,346; 3,839,489; 4,144,282; and 4,814,544. Recently, C_c+ , preferably C._n+ n-paraffins, have been isomerized, in the presence of large pore size zeolites to produce branched chain paraffins by skeletal rearrangement. The latter process can find application in dewaxing.

Naphtha reforming involves the mechanisms of several reactions to upgrade a low octane naphtha to a higher octane effluent. One of the octane enhancing reactions which occurs during reforming is the conversion of n- paraffins to isoparaffins. Under the process conditions of reforming, other reactions which occur are aromatization (or dehydrocyclization) , dehydrogenation, with some cracking.

Paraffin conversion catalysts may also be employed as ring opening catalysts for removal of cyclic aromatic precursors from reformer feedstocks. For example, cyclohexane, a precursor to benzene, is rearranged over commercial paraffin conversion catalysts to a mixture of branched paraffins. Branched paraffins are only partly aromatized in reforming whereas cyclohexane is completely converted to aromatics, mostly benzene. Application of paraffin conversion catalysts for ring opening aromatics precursors will no doubt become more important as environmental regulations limiting aromatics in gasoline become more stringent.

The conversion of paraffins, especially light paraffins, is a useful refining process for providing additional feedstock for alkylation units or to convert relatively low octane linear paraffins to higher octane, branched chain isomers which can be blended into the gasoline pool. An alternative type of catalyst used in a number of commercial processes comprises a metal hydrogenation/ dehydrogenation component, usually platinum, on a porous support. An example of this process is the Penex process (UOP) in which isomerization is carried out in the presence of hydrogen and a platinum catalyst. The Iso- Kel process (M.W. Kellogg) also employs a precious metal catalyst with hydrogen circulation and the Pentafining (Arco/Englehardt) and Butamer (UOP) processes also employ platinum on supports with external hydrogen circulation. Processes of this kind are disclosed, for example, in U.S. Patent Nos. 4,834,866 and 4,783,575.

Paraffin conversion catalysts may also be employed as ring opening catalysts for the removal of cyclic aromatic precursors from reformer feedstocks as disclosed in above-cited U.S. 4,783,575 and U.S. 4,834,866. For example, cyclohexane, a precursor of benzene, may be isomerized to a mixture of branched paraffins which are only partly aromatized in the reformer so as to minimize the production of benzene. U.S. Patent No. 3,631,117 describes a process for the hydroisomerization of cyclic hydrocarbons that uses a zeolite supported Group VIII metal as a catalyst for ring opening and paraffin isomerization. The utilization of paraffin isomerization for ring opening aromatic precursors, especially cyclohexane, is likely to become more important in the future as environmental regulations limit the aromatic content of motor gasoline.

Isomerization processes utilizing metal components on supports comprising a molecular sieve are disclosed in U.S. Patent Nos. 3,842,114; 3,836,597; 4,778,944 and 4,374,296.

U.S. Patent No. 5,107,054 describes the use of a zeolite, designated MCM-22, to catalyze the conversion of certain paraffins, such as those included in a low octane, light straight run naphtha. The present invention provides a process for converting feedstock comprising paraffinic hydrocarbon compounds to product hydrocarbon compounds which comprises contacting the feedstock at conversion conditions with catalyst comprising crystalline material having the structure of ZSM-48 which has been synthesized by a particular method imparting thereto improved catalytic activity and paraffin isomerization selectivity.

The paraffins of the feedstock converted by the present process may be comprised of from 3 to 10 carbon atoms, usually from 4 to 8 carbon atoms, e.g., butane, pentane and hexane.

The ZSM-48 catalyst composition for use herein is prepared by the steps of digesting boron-containing zeolite Beta with a mineral base, e.g. , KOH, and particular organic compound, e.g., pyrrolidine, in an aqueous reaction mixture at conditions sufficient to crystallize ZSM-48, e.g, elevated temperature of from about 90*C to about 175*C; treating the ZSM-48 under conditions sufficient to insert aluminum into the crystal structure, e.g., contacting said ZSM-48 with soluble aluminum-containing species, such as, for example, A1(N0₃)₃ or Na₃AlF₆ and/or mixing said ZSM-48 with alumina and extruding or pelletizing the mixture; and recovering said treated ZSM-48 catalyst composition. The catalytic conversion process described herein may be used to increase the octane and reduce the vapor pressure of low octane naphthas containing C₈-C₁₀ n- paraffins and/or mono-methyl branched paraffins, which under conventional reforming conditions, are the most difficult components to upgrade. Particular uses of the present improved conversion process include upgrading refinery streams rich in C.-C₆ n-paraffins.

In accordance with an embodiment described herein, conversion is undertaken in the presence of a catalyst comprising the specially prepared ZSM-48. During the conversion, n-paraffinic and mono-methyl branched paraffinic components are converted to higher branched paraffins which are generally better octane boosters. By way of illustration, the significance of these reactions can be gleaned from a review of the following table of octane numbers of pure hydrocarbons from Catalvsis. P.H. Emmett (ed.), vol. VI (1958).

Octane Numbers of Pure Hydrocarbons

Blending Research Octane Number fcleari

Paraffin Hydrocarbons n-heptane 0

2-methylhexane 41

3-methylhexane 56 2,2-dimethylpentane 89

2,3-dimethylpentane 87

2,2,3-trimethylbutane 113

Further, the Research Octane Number of isobutane is reported to be 102, compared to 92 for n-butane; and 92 for isopentane compared to 62 for n-pentane.

The feedstock for the present process may contain significant amounts of C₅+ normal and/or slightly branched paraffins, especially normal and/or slightly branched paraffins in the Co-.-C1,U_ range. Accordingly, normal hexane and normal heptane as well as the various mono-methyl branched isomers alone or in admixture may be employed as the feedstock in the present process. In addition, the feedstock may contain monocyclic aromatic compounds and/or cyclic paraffins, such as cyclohexane. The feedstock to the present conversion process can be straight-run, thermal, or catalytically cracked naphtha. Typically, naphthas boil at from 80°F to 400"F. Preferably, for high increases in octane numbers of the feed, the charge to the process is a naphtha rich in C_β to C . paraffins. Naphtha rich in C and C_η paraffins is generally difficult to reform selectively using conventional catalysts (such as chlorided Pt-alumina) . Naphthas can be obtained by separating the charge into two fractions: a light naphtha and a heavy naphtha. Conventionally such separation is by distillation. The boiling range of the light naphtha may be from 80°F to 400°F and the boiling range of the heavy naphtha may be up to 650°F. The light naphtha may be rich in Cg-C.. paraffins, and specifically C_g and C_ paraffins. When the light naphtha is upgraded in accordance with the present process, the heavy naphtha may be processed by conventional reforming.

Generally, the feeds for the present process do not contain bicyclic and polycyclic aromatics. Bicyclic and polycyclic aromatics are commonly found in the higher boiling fractions (IBP over 340*C) , than those which are generally used as feeds in the process of the invention. Single ring (monocyclic) aromatics which are readily hydrogenated over an optional metal component of the catalyst can be tolerated, and at the higher end of the range of temperature conditions of the present process may be subject to ring opening to form branched chain paraffin compounds. The aromatic content may, for preference, be held below 10 weight percent although slightly greater amounts up to 30 weight percent might be tolerated if the proportion of monocyclic aromatics is sufficiently high and if a sufficiently strong hydrogenation component such as platinum is present on the catalyst.

The feed may, optionally, be pretreated in an aromatics saturator prior to contact with the present catalyst. Aromatics, such as benzene, may be hydrogenated to form saturated cyclics, such as cyclohexane, when reacted with hydrogen over a non- acidic, hydrogenation catalyst, such as platinum on amorphous alumina, in an aromatics saturator reactor. Reaction conditions required for the present improved process include a temperature of from 400'C to 650 ° C, preferably from 500*C to 600"C; a pressure of from 101 kPa (atmospheric) to 13,790 kPa (2000 psig) , preferably from 689 kPa (100 psig) to 2,758 kPa (400 psig); and a liquid hourly space velocity of from 0.1 hr"¹ to 20 hr"¹, preferably from 1 hr"¹ to 10 hr"¹.

Catalyst The catalyst for use in the present invention comprises a small crystal, i.e., from 0.05 to 0.5 micron, material having the structure of ZSM-48 which exhibits much higher catalytic activity than usual and significantly higher isoparaffin selectivity than would be expected from ZSM-48 synthesized by usual methods. Synthesis of this catalyst comprises:

(i) preparing an aqueous mixture comprising a mineral base (MB) , pyrrolidine (PYR) and boron-containing crystalline material having the structure of zeolite Beta, said mixture having the following composition, expressed in moles/mole Si0₂:

Broad Preferred

Al-O-j/SiO- 0 to 0.005 0 to 0.001

B₂0₃/Si0₂ 0.001 to 0.5 0.01 to 0.1

MB/Si0₂ 0.005 to 0.15 0.02 to 0.10 PYR/Si0₂ 0.01 to 0.5 0.05 to 0.5

H₂0/Si0₂ 5 to 100 20 to 50

(ii) maintaining said mixture at crystallization conditions, including a temperature of from 90^*C to 175^βC, preferably from 110"C to 160°C, until crystals having the structure of ZSM-48 are formed, usually from 24 to 96 hours,

(iii) separating said crystals having the ZSM-48 structure from the reaction mixture, (iv) treating the separated ZSM-48 to increase its acid activity and create a catalyst by replacing structural boron with structural aluminum, such as by (a) contacting with a soluble aluminum-containing species, non-limiting examples of which include A1(N0₃)₃, Na₃AlF₆, and (NH_«)₃A1F₆, or (b) mixing with alumina and extruding or pelletizing the mixture, or (c) contacting with a soluble aluminum-containing species and mixing with alumina and extruding or pelletizing, and

(v) recovering the treated ZSM-48 catalyst. The mineral base for use in the synthesis method step (i) must produce hydroxyl ions when added to water. Non-limiting examples of such materials for use herein include KOH, NaOH, and Na₂C0₃.

The boron-containing zeolite Beta may be made, if desired, as in U.S. Patent 5,139,759 or as in Example 1 of U.S. Patent 4,788,169 and will have a composition, expressed on an anhydrous basis and in terms of moles/mole of Si0₂, comprising the components:

(0.08 to 0.02)B₂O₃: (0.0001 to 0.002) Al₂0₃:Si0₂. The catalysts for use herein are ammonium ion exchanged followed by calcination to provide the hydrogen form. The operational requirements of these procedures are well known in the art.

The source of the ammonium ion is not critical; thus the source can be ammonium hydroxide or an ammonium salt such as ammonium nitrate, ammonium sulfate, ammonium chloride and mixtures thereof. These reagents are usually in aqueous solutions. By way of illustration, aqueous solutions of IN NH₄0H, IN NH₄N0₃, IN NH₄C1, and IN NH.Cl/NH.OH have been used to effect ammonium ion exchange. The pH of the ion exchange is not critical but is generally maintained at 7 to 10. Ammonium exchange may be conducted for a period of time ranging from 0.5 to 20 hours at a temperature ranging from ambient up to 100 ° C . The ion exchange may be conducted in a single stage or in multiple stages. Calcination of the ammonium exchanged zeolite will produce its acid form.

Calcination can be effected at temperatures up to 550"C. In general, the relative proportions of finely divided, crystalline ZSM-48 component of the final improved catalyst for use herein will range from 20 to 90 percent by weight, and more usually from 40 to 80 weight percent of the final catalyst product.

In order to more fully illustrate the nature of the invention and the manner of practicing same, the following examples are presented.

Example 1 Boron-containing zeolite Beta was prepared as in

Example 1 of U.S. Patent 4,788,169. The zeolite Beta was then calcined by heating in nitrogen at 2°C/minute to 538*C, then holding at 530*C for 2 hours. The sample was then cooled in nitrogen to 250"C at which temperature air was introduced followed by heating at 2"C/minute to 538*C and holding for 2 hours. The calcined zeolite was exchanged twice with IM NH₄N0₃ at room temperature for one hour. Following exchange, the zeolite Beta was calcined in air at 2'C/minute to 538"C and holding for two hours at that temperature.

Example 2 A solution was prepared with 0.5 gram di-n- propylamine, 0.18 gram KOH and 26 gram deionized water. Two grams of the boron-containing zeolite Beta of Example 1 were added to this solution. The resulting mixture was crystallized at 150°C for two days in a Parr bomb to yield boron-containing ZSM-48 as determined by X-ray diffraction analysis.

Sixty-eight milligrams of A1(N0₃)₃ were dissolved in 10 ml deionized water. This solution was mixed with 0.5 gram of the boron-containing ZSM-48 for two hours at room temperature then filtered, and the solid washed and dried. The recovered solid was calcined by heating in air at 2'C/minute to 538°C and holding at 538'C for two hours. The calcined product was then exchanged twice with 1 M NH_«N0₃ at room temperature for one hour each.

ExfrWPle ? Boron-containing zeolite Beta was prepared as in Example 1 of U.S. Patent 4,788,169. The zeolite Beta was then calcined by heating at 2^βC/minute in nitrogen to 538"C, then holding at that temperature for 2 hours. The sample was then cooled in nitrogen to 250^βC at which temperature air was introduced followed by heating at 2'C/minute to 538°C and holding at that temperature for two hours. The calcined zeolite was exchanged twice with 1 M NH₄(acetate) at room temperature for one hour each. Following exchange, the zeolite was calcined in air at 2^*C/minute to 538"C and holding for two hours at temperature.

Example 4 A solution was prepared with 2.25 grams di-n-propyl- amine, 0.54 gram KOH and 78 grams deionized water. Six grams of the boron-containing zeolite Beta of Example 3 were added to this solution. The reaction mixture was crystallized at 150"C for two days in a small Parr bomb to yield product crystals identified by X-ray diffraction analysis as pure ZSM-48.

One gram of ZSM-48 was calcined as described in Example 1 and added to a solution of 280 milligrams of A1(N0₃)₃ and 40 ml deionized water. The solution was mixed for two hours at room temperature then filtered, and the solid washed and dried. The recovered solid was air calcined by heating in air at 2°C/minute to 538°C for two hours and then exchanged twice with 1 M NH₄N0₃ at room temperature for one hour each. Example 5 A solution was prepared with 0.7 gram of pyrrolidine, 0.14 gram 50% NaOH and 14 grams deionized water, to which two grams of boron-containing zeolite Beta of Example 3 were added. The reactive mixture was crystallized in a Parr bomb at 150"C for four days. The recovered product was determined by X-ray diffraction analysis to be boron-containing ZSM-48.

A 0.5 gram portion of the product ZSM-48 was calcined as described in Example 1 and added to a solution of 140 milligrams of A1(N0₃)₃ and 20 ml deionized water. The solution was mixed for two hours at room temperature then filtered, and the solid washed and dried. The recovered solid was air calcined by heating in air at 2'C/minute to 538"C and holding for two hours at that temperature. The calcined product was then exchanged twice with 1 M NH₄N0₃ at room temperature for one hour each.

Example 6 A 1 gram portion of the as-synthesized boron- containing ZSM-48 of Example 5 was calcined as described in Example 1 and added to a solution of 280 milligrams of A1(N0₃)₃ and 40 ml deionized water. This solution was mixed for two hours at room temperature then filtered, and the solid washed and dried. The recovered solid was air calcined by heating in air at 2"C/minute to 538°C and holding at that temperature for two hours. The calcined product was then exchanged twice with 1 M NH₄N0₃ at room temperature for one hour each.

Example 7

A solution was prepared with 0.74 gram of pyrrolidine, 0.05 gram KOH and 14 grams deionized water, to which two grams of boron-containing zeolite Beta of Example 3 were added. The reaction mixture was crystallized in a small Parr bomb at 150°C for four days. The recovered product was determined by X-ray diffraction to be boron-containing ZSM-48.

A 1 gram portion of the product ZSM-48 was calcined as described in Example 1 and added to a solution of 280 milligrams of A1(N0₃)₃ and 40 ml deionized water. This solution was mixed for two hours at room temperature then filtered and the solid washed and dried. The recovered solid was air calcined by heating in air at 2°C/minute to 538°C, and holding for two hours at 538*C. The calcined product was then exchanged twice with 1 M NH₄N0₃ at room temperature for one hour each.

Example 8 A solution was prepared with 0.5 gram di-n- propylamine, 0.18 gram KOH and 26 grams deionized water. Two grams of the boron-containing zeolite Beta of Example 1 were added to this solution. The resulting mixture was crystallized at 150"C for two days in a Parr bomb to yield boron-containing ZSM-48 as determined by X-ray diffraction analysis.

Sixty-eight milligrams of A1(N0₃)₃ were dissolved in 10 ml deionized water. This solution was mixed with 0.5 gram of the boron-containing ZSM- 8 for two hours at room temperature then filtered, and the solid washed and dried. The recovered solid was calcined by heating in air at 2"C/minute to 538"C and holding at 538°C for two hours. The calcined product was then exchanged twice with 1 M NH₄N0₃ at room temperature for one hour each.

Example 9 ZSM-48 was prepared as in Example 14 of European

Patent Application 142,317. The iodide salt of diquat-6 was used as the directing agent and the crystallization temperature was maintained at 160 ° C with stirring of the reaction mixture. The product ZSM-48 crystals were treated by calcination and exchange as in Example 7.

Example 10 ZSM-5 crystals were prepared as in U.S. Patent 3,702,886 having a silica/alumina mole ratio of 70/1. The product was steamed to control its acid activity to that which was used in Example 11.

Example 11 To test the products of the above examples for catalytic activity and selectivities for isoparaffins, i.e. isopentane/n-pentane and isobutane/n-butane. Alpha Tests were conducted. The Alpha Test provides an approximate indication of the catalytic activity of a catalyst compared to a standard catalyst and it gives the relative rate constant (rate of normal hexane conversion per volume of catalyst per unit time) . It is based on the activity of silica-alumina catalyst taken as an Alpha of 1 (Rate Constant = 0.016 sec"¹). The Alpha Test is described in U.S. Patent 3,354,078; in the Journal of Catalvsis. 4, 527 (1965); 6, 278 (1966); and 61, 395 (1980) , each incorporated herein by reference as to that description. The experimental conditions of the test used herein include a constant temperature of 538^βC, hexane vapor pressure of 100 Torr and a variable flow rate as described in detail in the Journal of Catalvsis. 61, 395. Gas selectivities for iC₅/nC₅ and iC₄/nC₄ were determined at about 10% n-hexane conversion. Mole selectivities for iC₄ and iC₅ products were also determined. Results of the Alpha Testing and mole gas selectivities for ic₄ and ic₅ are shown in Table 1 for the catalyst products of Examples 4-10.

10

As shown in Table 1, the Alpha values of the catalysts made with pyrrolidine as the organic directing agent, Examples 5-7, have much higher hexane conversion activity (-75-93 Alpha) than the samples made with di-n- propylamine (-1-10 Alpha) despite reactions with the same moles Al*³/gram zeolite. These pyrrolidine templated samples also have higher selectivities for iC₄ and iC₅ products compared to ZSM-5 which has low activity for iC₄ and iC₅. This translates into potentially higher octane fuels or raw materials for MTBE/TAME and/or alkylation reactions. Products of Examples 5 and 6 were synthesized in the same way and illustrate the reproducibility of the present ZSM-48 preparations to give equivalent Alpha activity and similar isomerized product slates.

Claims

What js Cl^iweq js:

1. A process for converting paraffinic feedstock to product hydrocarbon compounds which process comprises contacting said feedstock at reaction conditions with a catalyst composition comprising crystalline material having the structure of ZSM-48 manufactured by the method comprising the steps of:

Al₂0₃/Si0₂ 0 to 0.005

B₂0₃/Si0₂ 0.001 to 0.5

MB/Si0₂ 0.005 to 0.15 PYR/Si0₂ 0.01 to 0.5

H₂0/Si0₂ 5 to 100,

(ii) maintaining said mixture at crystallization conditions until crystals having the structure of ZSM- 8 are formed,

(iii) separating said crystals having the structure of ZSM-48 from the reaction mixture,

(iv) treating the separated ZSM-48 crystals by (a) contacting with a soluble aluminum-containing species, or (b) mixing with alumina and extruding or pelletizing the mixture, or (c) contacting with a soluble aluminum- containing species and mixing with alumina and extruding or pelletizing, and

(v) recovering the treated ZSM-48 catalyst.

2. The process of claim 1 wherein the mixture of step (i) has the following composition:

Al₂0₃/Si0₂ 0 to 0.001

B₂0₃/Si0₂ 0.01 to 0.1

MB/Si0₂ 0.02 to 0.10

PYR/Si0₂ 0.05 to 0.5

H₂0/Si0₂ 20 to 50.

3. The process of claim 1 or 2 wherein the crystallization conditions of step (ii) include a temperature of from about 90'C to about 175^βC.

4. The process of claim 1, 2 or 3 wherein the soluble aluminum-containing species of step (iv) is selected from the group consisting of A1(N0₃)₃, Na₃AlF₆, (NH₄)₃A1F₆, and combinations thereof.

5. The process of claim 1, 2, 3 or 4 wherein said mineral base of step (i) is selected from the group consisting of KOH, NaOH, Na₂C0₃, and combinations thereof.

6. The process of claim 1, 2, 3, 4 or 5 wherein said boron-containing crystalline material having the structure of zeolite Beta of step (i) has a composition expressed on an anhydrous basis and in terms of moles/mole of Si0₂ as follows:

(0.08 to 0.02) B₂0₃: (0.0001 to 0.002)Al₂0₃:Si0₂.

7. The process of claim 1, 2, 3, 4, 5 or 6 wherein said reaction conditions include a temperature of from 400°C to 650°C, pressure of from 101 kPa (atmospheric) to 13,790 kPa (2000 psig), and a liquid hourly space velocity of from 0.1 hr^"1 to 20 hr"¹.

8. The process of claim 7 wherein said reaction conditions include a temperature of from about 500*C to 600"C, a pressure of from 689 kPa (100 psig) to 2,758 kPa (400 psig) , and a liquid hourly space velocity of from 1 hr"¹ to 10 hr"¹.

9. The process of claim 1, 2, 3, 4 or 5 wherein said feedstock comprises paraffins having from 3 to 10 carbon atoms.

10. The process of claim 1, 2, 3, 4 or 5 wherein said feedstock comprises paraffins having from 4 to 8 carbon atoms.

11. A process for converting feedstock comprising hexane to a product comprising isoparaffins of 4 to 5 carbon atoms which comprises contacting said feedstock at reaction conditions including a temperature of from 400*C to 650*C with a catalyst composition comprising crystalline material having the structure of ZSM-48 manufactured by the method comprising the steps of :

Al₂0₃/Si0₂ 0 to 0.005

B₂0₃/Si0₂ 0.001 to 0.5 MB/Si0₂ 0.005 to 0.15

PYR/Si0₂ 0.01 to 0.5

H₂0/Si0₂ 5 to 100,

(ii) maintaining said mixture at crystallization conditions until crystals having the structure of ZSM-48 are formed. (iii) separating said crystals having the structure of ZSM-48 from the reaction mixture,

(iv) treating the separated ZSM-48 crystals by (a) contacting with a soluble aluminum-containing species, or (b) mixing with alumina and extruding or pelletizing the mixture, or (c) contacting with a soluble aluminum- containing species and mixing with alumina and extruding or pelletizing, and (v) recovering the treated ZSM-48 catalyst.