WO1996018705A1

WO1996018705A1 - Process for the isomerisation of a hydrocarbonaceous feedstock

Info

Publication number: WO1996018705A1
Application number: PCT/EP1995/004997
Authority: WO
Inventors: Erwin Blomsma; Pierre August Jacobs; Johan Adriaan Martens; Donald Reinalda
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Canada Limited
Priority date: 1994-12-13
Filing date: 1995-12-12
Publication date: 1996-06-20
Also published as: AU4345796A; JPH10510568A; EP0797650A1; CZ160897A3; MX9704292A

Abstract

Process for isomerisation of a hydrocarbonaceous feedstock substantially boiling in the gasoline range which feedstock comprises linear paraffins having at least five carbon atoms wherein the feedstock is contacted in the presence of hydrogen at elevated temperature and pressure with a catalyst comprising in combination platinum (Pt) and palladium (Pd) each in metallic form supported on an acidic amorphous alumina or molecular sieve, and isomerised hydrocarbons preprared by the process.

Description

PROCESS FOR THE ISOMERISATION OF A HYDROCARBONACEOUS FEEDSTOCK

The present invention relates to a process for upgrading hydrocarbonaceous feedstocks more particularly for isomerisation of a feedstock substantially boiling in the gasoline range which feedstock comprises linear paraffins having at least five carbon atoms.

An increasing demand placed on oil refiners is the production of gasolines meeting environmental requirements and having high octane numbers. The requirement to reduce the content of aromatics, in particular benzene, and of olefins, to reduce gasoline vapour pressure and to dispense with lead-containing additives has made necessary the identification and production of alternative high octane gasoline components. Such components, for example branched gasoline range paraffins, are not typically available from main refining processes and must be obtained by upgrading of refinery fractions and added to the gasoline pool. It is an object of the present invention to provide a process for the production of such branched paraffins. Processes are known for isomerisation of linear C4- CI _Q paraffinic feeds by contacting with certain zeolitic or amorphous catalysts in the presence of hydrogen. It has been found that bifunctional catalysts comprising certain hydrogenating-dehydrogenating metals supported on a zeolite or amorphous metal oxide, such as commercially available platinum supported on mordenite (MOR) and platinum supported on chlorided alumina, give both good selectivity of reaction and improvement in stability of performance and catalyst life resulting from the presence of the hydrogenating-dehydrogenating metal. Moreover in European Patent no 0 398 416 is disclosed a similar process comprising contacting a similar feedstock with a catalyst comprising zeolite beta (BEA) and a hydrogenating-dehydrogenating metal or a compound thereof, the BEA having been treated with a solution having a pH of at least 9 and thereafter calcined, the metal being suitably selected from Group VIII of the Periodic Table of the Elements.

These processes give attractive yields of the desired product, notably in the upgrading of C5-C6 paraffinic feeds, with some yield loss incurred as a result of paraffin hydrogenolysis and cracking. In view of the fact that these processes are sensitive to catalyst deactivation as a result of poisoning by sulphur contaminants contained in the feed, it is common practice to operate feed pretreatment for removal or conversion of sulphur for example by adsorption or hydrotreatment, prior to carrying out the upgrading reaction.

It has now surprisingly been found that still further improvement in product yields and selectivities can be obtained with a process employing a catalyst comprising a specific bimetallic hydrogenation-dehydrogenation function. Moreover it would appear that these catalysts display reduced hydrogenolysis activity and increased sulphur tolerance, thereby reducing feed pretreatment duty.

Accordingly the present invention relates to a process for isomerization of a hydrocarbonaceous feedstock substantially boiling in the gasoline range which feedstock comprises linear paraffins having at least five carbon atoms wherein the feedstock is contacted in the presence of hydrogen at elevated temperature and pressure with a catalyst comprising in combination platinum and palladium each in metallic form supported on an acidic amorphous alumina or molecular sieve .

Reference herein to "metallic form" is to the zero valent state of substantially all of both platinum (Pt) and palladium (Pd) present on the catalyst. It is to be appreciated that the catalyst may be employed without prior reduction of the metal components to the metallic state, whereby reduction is achieved in situ under the prevailing conditions including the presence of hydrogen. Accordingly reference herein to "metallic form" is to the form effective during the contacting.

Reference herein to "molecular sieve" is to both zeolitic and non-zeolitic types, i.e. to molecular sieves comprised of silicoaluminate or otherwise. Preferred molecular sieves are of the "10 ring" or "12 ring" type, i.e. comprise 10 or 12 membered rings of oxygen atoms.

It is of particular advantage that the process of the present invention may be employed in the upgrading by means of isomerisation of a feed comprising paraffins of varying carbon number, for example having carbon number 5 up to 8, in a single stage. This is of particular advantage since the conversion of C7₊ component of a hydrocarbonaceous feedstock introduces problem of cracking to undesired products which problem is less prevalent with the conversion of the C5_Cg component. Addressing this problem by operating the process with a reduced acidity catalyst is not attractive since this of course leads to reduced conversion and the need for enhanced recycle of unreacted feedstock. Remaining options for addressing this problem include operation in two stages with use in each stage of a catalyst selective for the conversion of each component. It has now moreover been found that the process of the invention enables the isomerisation of normal paraffins to multibranched paraffins in significant yield in a single stage. Alternatively the process of the invention enables operation with lower total metal loading than in conventional processes without incurring yield and selectivity loss. These advantages would of course contribute to the economics of a commercial process. It has been found that the influence of Pt and Pd in combination on catalyst selectivity is greater than the sum influence of both components individually. The indication is therefore that in the process employing the bimetallic catalyst, a certain synergy in selectivity takes place.

Suitably the Pt and Pd are uniformly dispersed throughout the catalyst thereby enhancing their cooperative effect. Without being limited to the following theory, it is thought that the presence of one or both metals has an effect on the other metal, in particular the presence of the Pd seems to have a positive effect on the dispersion or the state of the Pt, whereby the metals are better brought into or retained in the metallic form. Preferably in a process employing fixed bed or other operation, the Pt and Pd are both present in the same catalyst locus, more preferably on the same catalyst particle, most preferably on the same particle of amorphous alumina or molecular sieve. The catalyst to be used in accordance with the present invention may comprise in addition to the amorphous alumina or molecular sieve (hereinafter the active catalyst structure) , a binder material comprising one or more refractory oxides.

The Pt and Pd metals may be present on the active catalyst structure or may be present on a separate carrier (e.g. the binder) comprising for instance one or more refractory oxides, e.g. alumina. Preferably the Pt and Pd are present on the active catalyst structure. Suitably the Pt and Pd are loaded onto the active catalyst structure by methods known in the art, for example by means of (competitive) ion-exchange, (competitive) pore volume (incipient wetness) impregnation, controlled deposition precipitation, comulling in a suitable mixing device a precursor of the metallic components onto the active catalyst structure and/or binder. Preferably the metals are loaded onto the active catalyst structure by means of incipient wetness impregnation of an aqueous solution of the tetramine- dichloride salt, or by means of competitive ion exchange in the presence of ammonium as competitive ion.

In a further advantage, the process of the invention is substantially independent of the manner in which the metals are loaded onto the catalyst. This is in contrast to processes using catalysts comprising only Pt or only Pd, whereby process performance can be affected by manner of loading of metal onto the active catalyst structure.

In particular, known processes employing catalysts prepared by competitive ion exchange of only Pt or only Pd display stable, high performance operation over a typical temperature range, which we believe is the result of improved metal dispersion and reduced excess acidity, and with respect to the platinum component, reduced hydrogenolysis activity.

It is found that the present process advantageously provides improved catalyst performance which would seem to override any improvement available by manner of catalyst synthesis. Without being limited to the following theory, it is thought that the catalysts employed in the process of the present invention are characterized by improved metal dispersion and reduction to the metallic state when compared with the known monometallic catalysts.

Suitably the metals are introduced simultaneously. Suitably the metals are distributed in the active catalyst structure. Suitably distribution is controlled by means of control of solution composition during introduction, for example by control of solution pH and competitive anions and cations content. Suitably the metals are brought into metallic form by reduction procedures known in the art. Suitably the catalyst comprises from 0.01 to 5% by weight of Pt and Pd in combination based on total weight of active catalyst structure, preferably from 0.1 to 3% by weight of combined Pt and Pd based on total weight of active catalyst structure. Suitably the Pt and Pd are present in an atomic ratio of Pt/ (Pt + Pd) of between 0.0 and 1.0, preferably of substantially 0.1 to 0.8, more preferably of substantially 0.1 to 0.5.

Amorphous alumina catalysts which may be employed in the process of the present invention include those known in the art. Suitably amorphous alumina catalysts are characterised by moderate to low surface area, preferably surface area of 100-500 m*-*/g. More preferably amorphous alumina catalysts comprise eta alumina or gamma alumina, of 320-430 m²/g or 170-220 m²/g respectively.

The amorphous alumina may comprise an additional acidic component. Suitably amorphous alumina catalysts comprise a chloride component whereby acidity is enhanced. Suitably amorphous alumina catalysts are chlorided by known means including subliming AICI3 and reaction with COCI2, CCI4 etc. Suitably acidic components are present at a level suitable to achieve the desired acidity. In particular eta alumina may comprise chlorine in amount of 5-15%, gamma alumina in an amount of 3-8%. Molecular sieves which may be employed in the present invention include any zeolitic or non-zeolitic molecular sieves capable of selective conversion of feed molecules in the range above defined. Typically such molecular sieves are, but are not limited to, those typically known as medium pore type natural or synthetic molecular sieves. Preferred zeolites are of the "10 ring" or "12 ring" type, i.e. comprise 10 or 12 membered rings of oxygen atoms, and are preferably of the twelve ring type including as non-limiting example MCM-22 and AEL, AFI, AFR, AFS, AFY, ATO, ATS, BEA, BOG, BPH, CAV, EHT, FAU, GME, LTL, MAZ, MEI, MOR, MTW and OFF as described in "Zeolites" Vol. 12 No. 5 (1992), with the exception of MCM-22 which is described in US Patent 4,954,325. More prefered are AEL, BEA, FAU, MOR, MTW and OFF. Non-zeolitic molecular sieves given as non-limiting example, in particular AEL, AFI, AFR, AFS, AFY, ATD and ATS, which include a metal component, suitably include a Group VIII metal component, preferably selected from magnesium, manganese, cobalt and zinc, more preferably cobalt.

Molecular sieves of the zeolite or non-zeolite type may be selected or modified to obtain a desired level of acidity. Zeolites may be conveniently modified or synthesised in manner to attain a given ratio of Siθ2 to AI2O3, whereby the acidity is determined. Suitable ratios of Siθ2 to AI2O3 are dependent on the individual zeolite to be employed. Typically for example a zeolite of the MOR type may be employed with a Siθ2*Al2θ3 ratio of 10 to 60, preferably 15 to 30, for example of approximately 20. The zeolite may further be modified to optimise selectivity for example by treatment of non-selective acidic sites, typically non pore-internal acid sites, which treatment or modification is well known, and may comprise acid or base treatment or modification. Suitably the process is carried out at a temperature of 50 to 400 °C, a pressure of up to 5 x 10⁶ Pa (50 bar), a space velocity of 0.5 to 10 kg/kg.h and a hydrogen to feedstock molar ratio of up to 10.0.

When use is made of an amorphous alumina catalyst the process is suitably carried out at a temperature of from 50 to 250 °C, preferably of from 100 to 150 °C, a total pressure of 1.5 x 10⁶ to 4 x 10⁶ Pa (15 to 40 bar), preferably of 3 x lO*-* Pa (30 bar), a space velocity of 0.3 to 10 kg/kg.hr, preferably of 0.5 to 5 kg/kg.hr and a hydrogen to feedstock molar ratio of up to 10.0, preferably of from 0.01 to 3.0.

When use is made of a zeolite molecular sieve catalyst, the process is suitably carried out at a temperature of from 150 to 350 °C, preferably of from 180 to 280 °C, a total pressure of 1.5 x 10⁶ to 3.5 x 10⁶ Pa (15 to 35 bar), for example approximately 2.5 x lO*-⁵ Pa (25 bar), a space velocity of 0.5 to 5 kg/kg.hr and a hydrogen to feedstock molar ratio of up to 5.0, preferably of from 0.5 to 4.0. When use is made of a non-zeolite molecular sieve catalyst, the process is suitably carried out at a temperature of from 250 to 450 °C, preferably of from 275 to 400 °C, a total pressure of up to 1 x 10⁷ Pa (100 bar), preferably of from 1 x 10⁶ to 5 x 10⁶ Pa (10 to 50 bar), a space velocity of from 0.5 to 10.0 kg/kg.h, preferably of from 1.0 to 5.0 kg/kg.h and a hydrogen to feedstock molar ratio of up to 5.0, preferably of from 1.0 to 3.0.

The hydrocarbonaceous feedstock substantially boiling in the gasoline range can suitably be obtained by fractionating any paraffinic gasoline-containing hydrocarbonaceous feedstock.

Preferably the feedstock substantially boiling in the gasoline range is obtained by subjecting a straight run hydrocarbon oil to a f actionation, preferably atmospheric distillation. Other suitable hydro¬ carbonaceous feedstocks substantially boiling in the gasoline range include product fractions obtained from cracking processes such as catalytic cracking, thermal cracking, delayed coking, visbreaking and flexicoking. Hydrocarbonaceous feedstocks containing unacceptable levels of sulphur and nitrogen may be subjected to a hydrotreatment before they are subjected to the process according to the present invention, whereby particularly advantageous results may be obtained. Suitably the hydrocarbonaceous feedstock boiling in the gasoline range has a low sulphur content, preferably less than 10 ppmw on feed.

The hydrocarbonaceous feedstock may consist entirely of a fraction boiling in the gasoline range, i.e. in the range of C4-22O °C. While the full gasoline boiling range fraction may be included in the hydrocarbonaceous feedstock, it may be preferred to employ as hydrocarbonaceous feedstock a cut thereof having a boiling point up to 180 °C. Optionally, the hydrocarbonaceous feedstock may be blended with a reformate fraction.

Suitably, the hydrocarbonaceous feedstock substantially boiling in the gasoline range may substantially comprise linear paraffins having at least five carbon atoms, i.e. the feedstock may substantially consist of one or more different types of linear paraffins having at least five carbon atoms.

Preferably, the hydrocarbonaceous feedstock boiling in the gasoline range substantially comprises linear paraffins having five to ten carbon atoms. More preferably, the hydrocarbonaceous feedstock substantially comprises linear paraffins having five to seven carbon atoms. Suitably, the hydrocarbonaceous feedstock substantially comprises n-hexane and/or n-heptane.

In a further advantage the process of the present invention is characterised by an enhanced performance in the conversion of sulphur contaminated feedstocks, by virtue of the enhanced total activity observed. Moreover it would seem that the process is characterised by an enhanced resilience to the poisoning effect of sulphur contaminants present in feedstocks to be converted. It is of particular advantage to process a refinery feedstock without the need for a preliminary feed purification step, or with the possibility to reduce the duty of feed pretreatment.

Accordingly the present invention relates in a further embodiment to a process for isomerisation of a hydrocarbonaceous feedstock substantially boiling in the gasoline range which feedstock comprises linear paraffins having at least five carbon atoms and has a sulphur content of greater than or equal to 10 ppm wherein the feedstock is contacted in the presence of hydrogen at elevated temperature and pressure with a catalyst comprising in combination Pt and Pd each in metallic form supported on an acidic amorphous alumina or molecular sieve.

Suitably the process comprises isomerization of a feedstock as above defined having a sulphur content in the range of 10 to 100 ppm, preferably 10 to 50 ppm, more preferably 10 to 30 ppm, for example approximately 20 ppm. Suitably operation with higher sulphur content feeds is performed at slightly higher severity, for example at temperatures slightly greater than required with conversion of low sulphur content feedstocks.

Suitably unconverted linear paraffins are separated from branched paraffins downstream of the reaction zone in which the isomerisation is carried out, and recycled to the reaction zone. Separation can suitably be carried out by means of molecular sieve or of distillation. The process is suitably initiated by loading the reaction vessel with catalyst and heating the bed with simultaneous activation of the catalyst by contacting with flowing oxygen at elevated temperature and subsequently with flowing hydrogen at elevated temperature. The feedstock to be isomerised is suitably preheated to elevated temperature which may be less than or equal to the operating temperature and is introduced at a desired rate together with hydrogen in desired molar ratio.

The reaction is suitably terminated on partial or complete deactivation of the catalyst, and catalyst regeneration performed. Regeneration may be performed after terminating the feedstock supply, by introducing a suitable regeneration medium or by raising the catalyst to elevated temperature for combustion of deactivating hydrocarbonaceous deposits. Suitable regeneration media include reactive or adsorptive fluids as known in the art, for example a combustion gas such as diluted air or oxygen/nitrogen mixtures.

The process may be carried out in any desired reactor, and is suitably carried out in a fixed bed, slurry or fluidised bed reactor, in batch, semi- continuous or continuous mode. A plurality of reactors may be employed in series or parallel. Regeneration of the catalyst may be carried out in one or more reactors simultaneously with operation of the process in one or more of the remaining reactors.

In a further aspect the present invention relates to isomerised paraffinic hydrocarbons whenever prepared by a process as hereinbefore described.

The invention will now be illustrated in non-limiting manner by means of the following examples. Example 1 - Preparation of bifunctional bimetallic Catalysts A

Samples of BEA zeolite of Si to Al atomic ratio of 12.5, surface area of 750 rn-^/g and crystal size of 0.1 to 0.7 micron were converted to the ammonium form by contacting the sample with an aqueous solution of ammonium chloride at a pH of 8. Platinum (Pt) and palladium (Pd) were then introduced onto the samples in desired amounts by contacting the samples with a Pt/Pd tetramine dichloride solution, by known technique of competitive ion exchange in the presence of ammonium as competitive ion. The samples thus obtained were activated in situ by calcination in flowing oxygen (15 mol/kg.s) at 400 °C, followed by reduction in flowing hydrogen (15 mol/kg.s) at 400 °C. Catalysts A were thus obtained having both Pt and Pd present in independently varied amounts, expressed as ratio Pt/ (Pt + Pd) of between 0.0 and 1.0. Total metal loading (Pt + Pd) included 0.5 wt%, 1.0 wt% and 1.5 wt% on weight of active catalyst structure for different samples. Example 2 (Comparative) - Preparation of bifunctional monometallic Catalysts B and C

Catalysts B and C were prepared following the same procedure as given in Example 1 above, with the exception that for each sample of ammonium form BEA zeolite only one of platinum and palladium metal was introduced. Catalysts B were obtained having only Pt present in varied amounts equal to the total metal loading of Catalysts A, and Catalysts C were obtained having only Pd present in varied amounts equal to the total metal loading of Catalysts A, expressed as ratio Pt/ (Pt + Pd) of 1.0 and of 0.0 respectively.

Example 3 - Isomerisation of n-heptane feedstock

Heptane conversion was carried out in a fully automated continuous flow tubular microreactor. A sample of Catalyst A, B, C or mixture of B and C prepared in Example 1 or 2 above was activated in situ in the reactor as above described. A stream of hydrogen saturated with heptane vapour was then generated using a thermostatted saturator. The purity of heptane was at least 99%, with 1% or less impurities comprised mainly of isomers of heptane. Reaction products were analysed on line by gas chromatography. Conversion was maintained at 82.5%, by means of adjusting the space velocity. Conversion was carried out at 220 °C, a hydrogen to heptane molar ratio of 60 and a total pressure of 0.3 MPa (3 bar). Product obtained comprised a mixture of cracked hydrocarbons having less than 7 carbon atoms, and of isomerised hydrocarbons having 7 carbon atoms. The results are given in Tables 1 to 3 below.

TABLE 1 - Isomer Yield (%) as a function of Pt/(Pt + Pd) ratio for isomerisation of heptane over Catalysts A, B, C, B and C.

ISOMER YIELD {%)

CATALYST (Pt + Pd) - (Pt + Pd)= (Pt + Pd)= A,B,C,B + C 0.5 wt% 1.0 wt% 1.5 wt% Pt/(Pt + Pd)

C 0.00 73.0

A 0.23 75.0 (72.1)

A 0.50 74.6 (71.0)

A 0.69 73.3 (70.3)

B 1.00 69.1

C 0.00 73.4

A 0.35 74.8 (70.5)

A 0.85 71.7 (69.3)

B 1.00 65.0

C 0.00 + < 60.0 B 1.00

A 0.33 74.0

In the table, values in brackets correspond to the calculated value which would be expected with a bimetallic catalyst having performance equal to the additive performance of the individual metal components, this value is calculated as a simple additive function.

From the table it is apparent that the isomer yields of Catalysts A comprising both Pt and Pd in combination exceed the calculated sum isomer yields of Catalysts B and C, and significantly exceed the measured sum isomer yield (physical mixture Catalysts B + C) . This is seen to be reproducible for different absolute metal loadings, with preference for catalysts having Pt/(Pt + Pd) of 0.1 to 0.5.

TABLE 2 - Yield of monobranched and multibranched isomers (%) as a function of Pt/(Pt + Pd) ratio for isomerisation of heptane over Catalysts A, B and C.

MONOBRANCHED (%) MULTIBRANCHED (%)

CATALYST (Pt + Pd) - (Pt + Pd)= (Pt + Pd) = (Pt + Pd) - (Pt + Pd)= (Pt + Pd) - A,B,C 0.5 wt% 1.0 wt% 1.5 wt% 0.5 wt% 1.0 wt% 1.5 wt% Pt/(Pt + Pd)

0.00 (C) 51.5 21.6

0.23 (A) 51.6 (51.0) 23.4 (21.2)

0.50 (A) 53.6 (50.4) 21.0 (20.7)

0.69 (A) 52.7 (50.0) 20.6 (20.4)

1.00 (B) 49.3 19.8

0.00 (C) 51.2 22.2

0.35 (A) 50.9 23.9 i (50.3) (22.1)

0.85 (A) 49.8 21.9 (49.1) (21.9)

1.00 (B) 46.4 18.6

0.33 (A) 52.4 21.6

In the table, values in brackets correspond to the calculated value which would be expected with a bimetallic catalyst having performance equal to the additive performance of the individual metal components. This value is calculated as a simple additive function.

From the Table it is apparent that the yields of mono and of multibranched isomers obtained with Catalysts A exceed the sum monobranched isomer and sum multibranched isomer yields of the process using Catalysts B and C. Moreover for Catalysts A wherein Pt/ (Pt + Pd) is 0.1 to

0.5, enhancement of isomer yield comprising predominantly multibranched isomers is obtained in a single step according to the process of the invention. TABLE 3 - Product Yield breakdown of process Example 3 Total product breakdown is given in the following

Table, for the process using Catalyst A, Pt/(Pt + Pd) = 0.23, Pt + Pd = 0.5 wt% and for the process using Catalyst C, Pd = 0.5 wt%, and using Catalyst B, Pt = 0.5 wt%.

Product Octane Yield (mol %) Product: Yield

Rating (mol %)

(RON) A C B A C B n C7 0 17.5 17.5 17.5 Cl 0.0 0 0.3

2-MeCβ 42.4 24.8 25.1 24.0 c 0.0 0 0.4

3-MeCg 52.0 25.1 24.6 23.6 C₃ 3.7 4.6 5.8

3-EtC₅ 65.0 1.7 1.8 1.7 nC4 0.0 0.1 1.4

2,2- 92.8 6.7 6.1 5.3 iC4 3.8 4.8 4.5 diMeCs

2,4- 83.1 5.8 6.0 5.7 C5 0.0 0 0.4 diMeCs

3,3- 3.0 2.5 2.0 c₆ 0.0 0 0.5 diMeC5

2,3- 91.1 7.7 6.6 6.6 diMeCs

2,2,3- >100 0.3 0.4 0.3 triMeC

From the above Table it is clear that improved quality of product is obtained by the process of the present invention, with substantially no cracking of feed molecules taking place, and with attractive yields of high octane rating multibranched components. Octane ratings are obtained from "Automotive Fuels Handbook" K. Owen, T. Coley, SAE International 1990 p. 564 (ISBN 1- 56091-064-x) . For other Catalysts A, with total metal loadings up to 1.5 wt%, product quality was almost identical. In comparison, the product yields obtained with the Catalyst B and C show a substantial amount of cracked C3 and C4 product and less attractive yields of high octane rating components.

Claims

C L A I S

1. Process for isomerisation of a hydrocarbonaceous feedstock substantially boiling in the gasoline range which feedstock comprises linear paraffins having at least five carbon atoms wherein the feedstock is contacted in the presence of hydrogen at elevated temperature and pressure with a catalyst comprising in combination platinum (Pt) and palladium (Pd) each in metallic form supported on an acidic amorphous alumina or molecular sieve.

2. Process according to claim 1 wherein the Pt and Pd are both present on the same locus, more preferably on the same catalyst particle, most preferably on the same particle of amorphous alumina or molecular sieve.

3. Process according to claim 1 or 2 wherein the catalyst comprises from 0.01 to 5% by weight of Pt and Pd in combination based on total weight of active catalyst structure, preferably from 0.1 to 3% by weight thereof.

4. Process according to any of claims 1 to 3 wherein Pt and Pd are present in an atomic ratio of Pt/(Pt + Pd) of between 0.0 and 1.0, preferably of substantially 0.1 to 0.8, more preferably of substantially 0.1 to 0.5.

5. Process according to any of claims 1 to 4 wherein an amorphous alumina catalyst comprises a moderate to low surface area, preferably surface area of 100-500 m-^/g.

6. Process according to any of claims 1 to 5 wherein the amorphous alumina comprises an additional acidic component.

7. Process according to any of claims 1 to 6 wherein acidic molecular sieve is of the "twelve ring type" as hereinbefore defined, including for example MCM-22 and AEL, AFI, AFR, AFS, AFY, ATO, ATS, BEA, BOG, BPH, CAV, EHT, FAU, GME, LTL, MAZ, MEI, MOR, MTW and OFF as hereinbefore defined.

8. Process according to any of claims 1 to 7 which is carried out at a temperature of 50 to 400 °C, a pressure of up to 5 x lO⁶ Pa (50 bar), a space velocity of 0.5 to 10 kg/kg.h and a hydrogen to feedstock molar ratio of up to 10.0.

9. Process according to any of claims 1 to 8 wherein the feedstock is obtained by fractionating any paraffinic gasoline-containing hydrocarbonaceous feedstock, preferably by subjecting a straight run hydrocarbon oil to fractionation, more preferably atmospheric distillation.

10. Process according to any of claims 1 to 9 wherein the feedstock substantially comprises linear paraffins having five to ten carbon atoms.

11. Process according to any of claims 1 to 10 wherein the feedstock has a sulphur content of greater than or equal to 10 ppm, suitably in the range of 10 to 100 ppm, preferably 10 to 50 ppm, more preferably 10 to 30 ppm, for example approximately 20 ppm.

12. Process according to claim 11 wherein unconverted linear paraffins are separated from branched paraffins downstream of the reaction zone in which the isomerisation is carried out, and recycled to the reaction zone.

13. Isomerised paraffinic hydrocarbons whenever prepared by a process according to any one of claims 1 to 12.