HYDROCARBON CONVERSION This invention relates to the conversion of n-alkenes into other useful hydrocarbon products. n-butenes and n-pentenes can be converted to isobutene or isopentene, or cyclized to form aromatic compounds. Isobutene can be polymerized to form polyisobutene, while isobutene or isopentene can be reacted with methanol in an etherification to form methyl tertiary alkyl ethers (MTBE or T.AME) octane improvers for gasoline. The isobutene or isopentene may be made by isomerization of n-butene or n-pentene respectively, e.g. over a specific tectometaUosilicate catalyst, e.g. a TON catalyst such as Theta 1 as in our EP 247802 or an MF1 one, e.g. ZSM 5 as in EP-A-0026041, or a FER catalyst such as the ferrierite ZSM 35 as in USP 4016245, 4107195, 41511892, 4584286, 4925548 and 4252499 the disclosures of which are herein incorporated by reference. The n-alkene feedstocks may be made by hydrogenation of a diene, but if the alkene is contaminated with unreacted diene then the catalyst activity is short lived because of the formation of oligomers.

We have now discovered how to convert the 4 or 5 carbon n- alkenes into useful hydrocarbon products, especially iso-alkenes, even in the presence of a diene.

Accordingly, the present invention provides a process for the conversion of a hydrocarbon feed comprising a C or C5 n-alkene into other hydrocarbon products which comprises contacting the feed with a tectometaUosilicate in the H-form at elevated temperature, characterized in that, the process is carried out in the presence of

hydrogen, the feed also comprises a C or C5 alkadiene and the tectometaUosilicate comprises a Group VIII metal.

The present invention provides a process for isomerising an olefin with a double bond in an alpha position. Preferably, the product is an olefin with the double bond in an internal position in the molecule.

The feedstock comprises an n-alkene which is n-butene or n- pentene with at least some butadiene, methyl butadiene or isoprene. Suitably, the butadiene, methyl butadiene or isoprene is present at 0.01-500%, by weight (based on the n-alkene weight)for example, preferably 0.1-10% (eg 0.1-3%) or 50-250%. The feedstock may also comprise at least one other component which is an alkane (preferably gaseous) or internal or iso-alkene, e.g. of 1-4 carbons such as ethane, propane or -butane, an inert gas, e.g. nitrogen and/or carbon oxide, e.g. carbon monoxide; the total amount of other component(s) may suitably be 50-500% (by weight based on the weight of said n-alkene), preferably 200-450%. Preferably, the amount of saturated C alkanes is 50-250% w/w (based on said n-alkene).

The feedstock may be at least partly derived from a refining process, e.g. the product of selective hydrogenation of a diene which is butadiene or isoprene over a catalyst, which is a platinum group metal on a support, e.g. of clay or alumina, or the product remaining after selective removal of diene by extraction from a mixed C or C5 refinery gas stream, e.g. from a gas cracker for C diene or fluid catalytic cracker for a C5 diene or the product before said removal (e.g. said gas stream).

The feedstock contacts the tectometaUosilicate in the presence of hydrogen, which may be mixed with the feedstock before entering the reactor, accomodating the tectometaUosilicate, or may be fed separately to said reactor. The amount of hydrogen may suitably be 50-500 mole % (relative to the diene), preferably eg 80-150 especially 90-110 mole %(relative to the diene) or suitably 1-500% moles (relative to the n-alkene) or suitably 20-300 molar (relative to the total of diene and alkenes) , preferably 40-80% molar (relative to the total of diene and alkenes) .

For high selectivity of the conversion of n-alkenes to iso- alkenes the tectometaUosilicate is usually a zeo-type catalyst whose framework structure includes channels defined by 10- or 12-membered rings which are not intersected by channels having 10- or 12-membered rings. Zeo-type catalysts which may be used in the process include TON (Theta-1, Nu-10, ZSM-22, KZ-2, ISI-1), MTT (ZSM-23, EU-13, ISI-4, KZ-1), EUO (EU-1 TP2-3, ZSM-50), AEL (SAPO-ll) and FER (ferrierite, FU-9, Nu-23, ISI-6, ZSM-35) . For higher selectivities towards aromatics, albeit with some alkanes, the tectometaUosilicate may be a zeo-type catalyst whose framework structure includes channels defined by 10- or 12-membered rings which are intersected by channels having 10- or 12-membered rings, such as MFl- and MEL-types, e.g. ZSM 5 and 11.

Information on zeo-type structures is given in the Atlas of Zeolite Structure types by Meier WM and Olsen DH, 1992 published by Butterworths, Zeolites vol 2, No. 15, June 1992. All of the above zeo-type structures can be prepared by published literature methods. Typical general methods are given, for example, in "Synthesis of High Silica Aluminosilicate Zeolites" by P A Jacobs and J A Martens, Studies in Surface Science and Catalysis, Vol 33, Elsevier, 1987 and "Zeolite Molecular Sieves" by D S Breck, John Wiley 1974.

A synthetic zeolite immediately after synthesis contains cations which depending upon the precise synthesis method used, may be hydrogen, aluminium, alkali metals, organic nitrogen cations or any combination thereof. The zeo-type catalyst used in the process of the present invention is at least partly and preferably substantially in the hydrogen form. The hydrogen form may be achieved by, in the case of organic containing zeo-type catalysts, calcination to remove the organics followed by either ammonium ion exchange or proton exchange with an acid solution or a combination of both. In the case of a zeo-type catalyst synthesised in the absence of an organic nitrogen containing compound, the hydrogen form could be prepared by either direct ammonium ion-exchange followed by calcination or proton exchange with an acid solution or a combination of both. If so desired, the hydrogen form of the zeo-type catalyst

may suitably be partially exchanged or impregnated with a metal such as gallium or magnesium and used in the process of the present invention.

The zeo-type catalyst may be modified to alter its acidity or shape selectivity in such a way to improve the catalytic performance. The modifications may include a calcination regime steam treatment, acid/steam treatment, chemical treatment, e.g. with a dealuminating agent such as SiCl , mineral acids, ammonium fluoride or bifluoride, EDTA, etc. or an aluminating agent such as sodium aluminate, aluminium chloride or inclusion of a phosphorus compound, a Lewis base, hydrogen fluoride, etc. The treatment step may be carried out during the preparation of the hydrogen-form or may be carried out after the preparation of the hydrogen form.

The zeo-type catalyst may be bound in a suitable binding material. Suitably, the binder may be one of the conventional binders such as alumina, silica, clay or may be an aluminophosphate binder or a combination of binders.

In the catalyst the Group VIII metal is usually present in a weight % of the tectometaUosilicate of suitably up to 10%, preferably up to 5%, especially 0.01-1% or 0.05 - 0.3%. The metal is of Group VIII of the Periodic Table and is especially a platinum group metal of the second and particularly the third long periods. Thus the metal may be at least one of iron, cobalt or nickel, but is preferably at least one of platinum, ruthenium, iridium or rhodium; it is especially palladium. The metal is preferably present at least in part in an elemental form. For illustration the invention will be described with respect to a platinum group metal, but the general techniques apply too for the other metals.

The catalyst for use in the present process may be made by incorporating the platinum group metal in the tectometaUosilicate either during its preparation or by incorporating the metal in the prepared tectometaUosilicate. Thus suitable techniques include impregnation, precipitation and gelation.

A suitable method, for example, comprises impregnating the support with a soluble thermally decomposable compound of platinum

group metal. A mineral acid, for example nitric acid, may be added to the impregnation solution or solutions in order to facilitate better the dispersion of the metallic component. Alternatively, the platinum group metal may be incorporated during the production of the zeo-type support.

The tectometaUosilicate support for use in the process of the invention may be made by a process which comprises forming a hydrogel comprising water, a source of alumina, a source of alkali or alkaline earth metal, a source of silica and an organic nitrogen-containing compound and thereafter crystallising the hydrogel at elevated temperature; the process also comprising if desired incorporating a source of a platinum group metal before or after crystallisation of the hydrogel.

The platinum groups metals may if desired be added to the gel in the form of a salt or complex thereof. Platinum, for example, may suitably be added in the form of tetrammine platinum dihydroxide or dihalide, for example dichloride, while palladium may be added as the dihalide, e.g. dichloride or the nitrate especially the palladium tetrammine dinitrate. Halides and nitrates are generally suitable for all the other Group VIII metals.

Suitable sources of silica include, for example, sodium silicate, silica hydrosol, silica gel, silica sol and silicic acid. A preferred source of silica is an aqueous colloidal dispersion of silica particles. A suitable commercially available source of silica is LUDOX (Trade Mark) Colloidal Silica supplied by Du Pont

The organic nitrogen-containing compound may suitably be an amine, for example diethylamine, ethylene diammine, butane diamine or 1,6-diaminohexane, pyrolidine an alkanolamine, for example diethanolamine, or a tetraalkyl ammonium compound, for example tetrapropylammonium hydroxide or tetrabutyl ammonium hydroxide, a tripyrolium hydroxide or a bis (N-methyl pyridyl) ethylinium compound; other examples are given in the above patents.

The source of aluminium may be an aluminium salt, aluminium hydroxide, aluminium oxide, or preferably a metal aluminate, e.g. sodium aluminate.

The source of the alkali or alkaline earth metal may for example be an alkali or alkaline earth metal hydroxide, for example sodium, potassium, magnesium or calcium hydroxide. A mixture of different materials, for example sodium hydroxide plus potassium hydroxide, may be used. It is especially preferred that the reaction mixture contains an alkali metal with atomic number of at least 19. In addition to water, the hydrogel may if desired contain an alcohol, for example, methanol or ethanol.

The proportions in which the water, silica and alumina source and organic nitrogen-containing compound are present in the hydrogel are such as to form the zeo-type material; details of these proportions are given in the above patents.

Crystallisation may suitably be effected at a temperature greater than 100°C, preferably in the range from 140 to 220°C. The pressure may suitably be autogeneous, that is the pressure generated within a closed vessel at the temperature employed. The crystallisation period will depend upon a number of factors including the rate of stirring and the temperature. Typically, within the preferred temperature range the crystallisation period may suitably be from 1 to 4 days.

The support may be recovered, suitably by filtration or centrifugation, and washed, suitably with water at a temperature in "the range, for example, of from 15 to 95°C.

Before use in the process of the invention the support is preferably activated, suitably by a thermal treatment, for the purpose of decomposing thermally decomposable compounds. The thermal treatment may suitably be effected in the presence of an inert gas, for example, nitrogen or air. Alternatively, or in addition the catalyst may be reductively activated by heating in the presence of a reducing gas, for example, hydrogen. It is possible to combine the thermal treatment and the reductive treatment into a single operation.

If a source of platinum group metal was not present during preparation of the hydrogel, this may be incorporated by impregnation before or after activation of the catalyst.

The process of the present invention may be suitably carried out at a temperature of from 200 to 700°C, preferably 300 to 600°C, especially 350-550°C. The process may be carried out under reduced or elevated pressure relative to atmospheric pressure. Suitably a pressure of from 0.1 to 100 bar absolute, preferably 0.5 to 50 bar absolute may be used. The reactive time may be 5 mins to 200 hr, especially 1-20 hours.

The weight hourly space velocity of the feedstock over the tectometaUosilicate is suitably in the range of 1-100 WHSV such as 2-30 or 20-80 WHSV/hr.

The process of the present invention with the zeo-type catalyst (a) gives isobutene or isopentene with a high selectivity usually with low selectivity to aromatics and hydrocarbons of 3 or less carbons and especially with a long catalyst life. With zeo-type catalyst (b) a higher proportion of aromatics is obtained. The products of the process may be separated, e.g. by distillation or by molecular sieving or selective adsorption, or may if desired be used as such as a petrochemical feedstock to produce polyolefins or olefin oligomers (for gasoline blending) alcohols, ethers and other oxygenates, surfactants and alkylaromatics, or as an aromatic feedstock.

The invention is illustrated in the following examples. Example 1(a) - Synthesis of Theta-1 Zeolite

Theta-1 was synthesised using ammonia as the templating agent. Sodium aluminate (30g, ex BDH, 40 wt% Al ₂ 0 ₃ , 30 wt% Na ₂ 0 and 30 wt% H2O) and sodium hydroxide (15.6g ex BDH) were dissolved in distilled water (240g) . Ammonia solution (1400g, SG 0.90° containing 25% NH3) was added with gentle mixing. Ludox AS40 (Trade Mark) (1200g) which contained 40 wt% silica was added over fifteen minutes with stirring to maintain a homogeneous hydrogel. The molar composition of the hydrogel was: -

2.9 Na ₂ 0:175 NH3: 1.0 Al ₂ 0 ₃ ^:68 Si0 ₂ :950 H ₂ 0 The mixture was then loaded into a 5 litre Parr autoclave and crystallised at 175°C for 25 hours under autogeneous pressure whilst mixing by a mechanical stirring action. At the end of the

crystallisation period the autoclave was cooled, and the product filtered, washed and dried in an air oven at 100°C. The crystallinity and the purity of the zeolite were determined by X-ray powder diffraction. The sample was Theta-1 with an estimated cristobalite content of less than 5%. Example Kb) - Preparation of the H-form Theta-1 Zeolite

The Theta-1 as synthesised in Example 1 which contained both Na ⁺ and NH4 ⁺ ions was directly ion exchanged in order to remove the Na ⁺ ions. The zeolite was mixed for 1 hour with an aqueous ammonium nitrate solution (1M, zeolite to solution weight ratio of 1:20). The zeolite was filtered, washed and the ion exchange treatment repeated twice. The ammonium form of the zeolite was then dried at 100°C and calcined overnight in air at 550°C to convert to the hydrogen form. The X-ray diffraction pattern of the H-Form is shown in Table 1. TABLE 1 : XRD OF PRODUCT OF EXAMPLE (b)

Variation in intensities of ± 20%

Variation in 20 peak positions of + 0.2° with corresponding Variation in D spacings

Peaks below 10% of I _max Excluded Copper alpha 1 wavelengths, 1.54060.

X-Ray Diffractometer Philips PW 1820/10

Slits 1/4°, 0.2°, 1/4°

20 Scan 2° - 32°

Step Size 0.025°

Time 4 sec

Example 1(c) - Impregnation of Palladium

The H-form Theta-1 Zeolite from Exl(b) (14g) was added to distilled water (600ml) in a glass beaker stirred reasonably vigorously with a PTFE stirrer. To the slurry obtained was added over 30 mins at ambient temperature (ca 22°C), 27 ml of an aqueous solution of palladium tetra ammine dinitrate (containing 8.08% Pd by wt) . The slurry was stirred for 4 hours and subsequently filtered in air. The separated solids were dried in air overnight at 60°C and then calcined in air with a temperature profile of heating the solids at 2°C/min to 210°C, and then maintenance of that temperature for 6 hr. The product contained 0.12% Pd by weight. Example 2 - Catalyst Preparation and Testing

The zeolite powder prepared in Ex 1(b) was pressed into tablets under 10 tonnes pressure. The tablets were broken and sieved into granules to pass 1500 micron but not 600 micron sieves. 5cc of the catalyst granules (2.19g) were loaded into a tubular reactor with a coaxial thermocouple well. The catalyst was reduced at 150C under a hydrogen flow of 200ml/min. The catalyst was then brought up to its testing temperature of 500°C under a nitrogen flow of 200ml/min. A hydrogen gas stream was fed into the reactor cocurrent with a hydrocarbon feed comprising n-butene and 1, 3-butadiene.

Table 2 provides the product and feed stream data analysis. The process gave a product comprising isobutene. Glossary of Table Terms Set temperature = Heater applied temperature in Deg C.

Bed temperature = Measured temperature in Thermowell in the

Catalyst Bed in Deg C. WHSV = Weight Hourly Space Velocity ie the Weight of

Total hydrocarbon feed per weight of catalyst per hour. H0S = Hours on stream after hydrocarbon feed

released onto the catalyst bed.

Conversion Defined as the

100% x Initial Mass - Final Mass of Same Initial Mass of Component

Selectivity Mass Yield of Component x 100% Mass Conversion

Table 2

Catalyst Vol/ml 5.0 Plant Pressure/bara 1.44 Catalyst Mass/g 2.19 Atms Pressure/mmHg 745.75 Set temperature 492°C Room Temp/°C 19.50 H0S 2 hours Bed temperature °C 501

Hydrocarbon Feedrate ml/min 0.54 Hydrogen/butadiene molar ratio 1:1 Hydrocarbon Feedrate ml/min 34.0 WHSV 8.87

Analysis of streams

Feed Wt% Product Wt%

Propene 0.01 1.70

Isobutane 5.83 3.99

Normal butane 19.29 18.06

Trans butene-2 5.24 5.03

Cis butene-2 1.99 4.63

Butene-1 14.47 3.42

Isobutene 3.77 7.63

1,3 Butadiene 25.03 0.14

Normal Pentane 9.65 0.2

Isopentane 0.65

Pentenes 11.26

Hexanes 3.93

Hexenes 2.07

Heptenes 16.79

Octeneε 14.71 9.26

Heavy Hydrocarbons 11.23 greater than Octenes

1,3 Butadiene Conversion = 99%