AU640039B2 - Hydrocarbon fuel - Google Patents

Description

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AUSTRALIA

Patent Act COMPLETE SPECIFICATION

(ORIGINAL)

Class I i0039 nt. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: L Xt Names(s) of Applicant(s): TECHNISEARCH LIMITED Actual Inventor(s): ANDOR LASZLO SALUSINSZKY tie t t Our Address for service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street MELBOURNE, Australia 3000 Complete Specification for the invention entitled: HYDROCARBON FUEL The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 0804N 0804N -2- HYDROCARBON FUEL The present invention relates to a process for the preparation of a hydrocarbon fuel having reduced benzene content and increased octane number.

Benzene is contained in several blendstocks which form the gasoline pool of oil refineries, particularly in catalytic reformate, cracked gasoline and pyrolisis gasoline. In the latter two streams benzene concentration depends mainly on the process of its production. On the other hand benzene content of catalytic reformate depends on feedstock composition and severity of operations.

Benzene has a high octane number and a suitable boiling point for a gasoline blendstock. However, its carcinogenic properties render it an undesirable component, especially at high concentrations. The oil industry adheres to an internal standard keeping benzene confer\ of finished gasoline below 5 volume percent.

Meeting this limitation has become in some refinery configurations difficult due to .ead phase out which required more extreme operational conditions in the catalytic reformers. The benzene problem is expected to become even more critical due to moves, mainly in United States of America and Germany, but which could spread world-wide, to limit benzene content to 1 volume percent.

Reducing benzene content of finished gasoline will require operational changes in most oil refineries.

A relatively simple process of benzene reduction suggested in the prior art is the removal of cyloparaffins, the main precursors of benzene formation in catalytic reforming, from the charge to the catalytic reformer. This change in operation reduces benzene content of catalytic reformate from the usual 5 to 10 weight percent. However, it also reduces availability of feed to the catalytic reformer and adds relatively low octane components to the gasoline pool.

Another possible process of benzene reduction suggested in the prior art is the alkylation of benzene with light olefins, such as ethylene, propylene or butylene. The alkyl benzenes formed have a higher: octane number than benzene. However the polyalkylated benzenes

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O1 which form always as by products boil outside the accepted gasoline boiling range. In addition in most oil refineries there are no excess olefins available for benzene alkylation.

Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties related to the prior art.

Accordingly, in a first aspect, the present invention provides a process for the preparation of a hydrocarbon fuel having reduced benzene content which process includes providing a hydrocarbon feedstock including -4efnencande aliphatic hydrocarbons c f< les) 15 v4% benzene at least one hydrogenation or isomerisation catalyst, and a first source of hydrogen; and mixing the feedstock with the first hydrogen source to form a mixed vapor; and contacting the mixed vapor with the catalyst.

The process may reduce benzene content via hydrogenation to cyclohexane and to methyl cyclopentane.

The hydrogenation/isomerisation process described has as its main objective to reduce benzene content of motor spirit below 1 volume By changing feedstock fractionation, it is possible to reduce total aromatics content of motor spirit to below 25 volume as required by the United States Clean Air Act of November, 1990.

Further the aliphatic hydrocarbons may be partially isomerised to increase the octane number of the fuel. Simultaneously a portion of cycloparaffins present may undergo ring opening. The hydrogenation of benzene to a mixture of methylcyclopentane and cyclohexane, the isomerisation of aliphatic hydrocarbons and the ring opening of cycloparaffins also increase product volume.

Octane number increase is attained by the partial isomerisation of the normal paraffins in the feed.

The hydrocarbon feedstock may be derived from an oil refinery stream. The hydrocarbon feedstock may 000

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eJ 3 C- I I -I I I I include from approximately up to 50% by weight of benzene.

The hydrocarbon feedstock may include a catalytic reformate or other benzene-rich feedstock stream. The hydrocarbon feedstock may be provided by separation of benzene-rich feedstock stream containing as little toluene as practical.

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t I 3A Accordingly, in a preferred aspect, the process of the present invention includes the preliminary step of providing a catalytic reformate feedstock; subjecting the feedstock to a distillation process; and recovering a benzene-rich feedstock stream as overhead product.

j The process may include charging, for example, a stabilised catalytic reformate to a distillation tower.

The distillation process will recover most of the benzene content of the feed as overhead product while leaving components boiling at higher temperatures than benzene, for instance toluene, in the bottom product. In most i cases the overhead product will contain benzene in excess i 15 of approximately 10 vol. This may represent at least Sapproximately 70% vol. of the benzene in the catalytic reformate.

The process may be carried out on a "stand-alone" i basis. The process may preferably be integrated with a catalytic reformer unit. In the case of integration with a catalytic reformer unit the whole liquid effluent from the high pressure separator of the reformer may be charged to a benzene/toluene splitter. The overhead product of the splitter, even without condensation, may be charged to the hydrogenation/isomerisation unit. After condensing the reactor(s) effluent, the liquid product may be fed to a catalystic reformer stabiliser.

Isomerisation of aliphatic hydrocarbons may be conducted simultaneously with benzene hydrogenation or sequentially. The effluent from the hydrogenation reactor may be charged to an isomerisation reactor containing an f isomerisation catalyst. Other hydrocarbon feedstock streams containing aliphatic hydrocarbons, for example, light naphtha or condensate, may be added at this stage.

Since isomerisation is thermally an almost neutral reaction, the isomerisation reactor may be an adiabatic reactor.

Accordingly, in a further preferred aspect of the present invention the mixed vapour is first charged to a I I, i "ag, 1 1- 1 1 1-1- I I reactor containing an hydrogenation ctalyst and the effluent therefrom is charged to a second reactor containing an isomerisation catalyst.

Preferably the first and/or second reactor is a heat exchanger. More preferably the heat exchanger is a tubular reactor. The tubular reactor may include one or several paths. In the case of multiple paths the number of tubes may, in each path, be the same or different.

The tubes may be filled with the same or with different catalyst. For example in a two path reactor the first path may be filled with a hydrogenation catalyst and the second path with an isomerisation catalyst.

The tubular reactor heat may optionally be used, in a preferred embodiment, for temperature control. This may be achieved by injecting a material in liquid or vapour from which material would not affect the reaction.

Thus, where the reactor for the exothermal reaction is in the form of a heat exchanger, including a number of tubes defining multiple paths, and the catalyst is contained in the tubes where the tubes are distributed in two or more path and the return head is used for temperature control.

The same system may be used, alternatively or in addition, to inject catalyst activators into the system.

For example carbon tetrachloride may be utilised as a catalyst activator for an isomerisation catalyst, e.g. a catalyst containing platinum on an alumina support.

Preferably the first reactor is an isothermal tubular reactor and the second reactor is isothermal or adiabatic.

More preferably the effluent from the first reactor may be mixed with a second source of hydrogen prior to charging to the second reactor.

The hydrocarbon feedstock may be enriched in aliphatic hydrocarbons. This will increase the octane number of the reaction product. Alkanes such as pentane and hexane may be added to the hydrocarbon feedstock.

Other streams such as streams containing light straight naphtha or condensate may be added to enrich the hydrocarbon feedstock.

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Ij I Cr 4 t O~ For example, as discussed above where two reactors are used, the effluent from the first reactor is mixed with a second hydrocarbon feedstock, including aliphatic hydrocarbons, prior to charging to the second reactor.

The source of hydrogen utilised in the hydrogenation step according to the present invention may be of any suitable type. A gas including from approximately 50 to 100% H 2 may be used. The hydrogen gas may be provided in gas cylinders. The hydrogen stream may be mixed directly with the hydrocarbon feedstock.

The hydrogen gas may be present in any suitable amounts. The molar ratio of hydrogen to benzene will affect the composition of product produced. Higher hydrogen to benzene molar ratio in the reaction increases the methylcyclopentane to cyclohexane ratio. In the case of hydrogen shortage, recycling of unreacted hydrogen can be avoided in mixing the benzene containing stream to the hydrogen stream in two or more steps. The hydrogen to benzene molar ratio may be within the range of approximately 3:1 to 20:1.

The at least one catalyst used in the process may be of any suitable type. The at least one catalyst may be S: o a '.4 .4.4' 44 t 5A i -6selected from metals Group VIII or Group III, or mixtures thereof, optionally deposited on a carrier. These catalyst may ensure saturation and promote paraffin isomerisation in accordance with the invention. In certain cases the efficiency of these metal catalysts can be enhanced by applying them in the form of bifunctional catalysts, that is depositing them on a carrier such as alumina or zeolite.

It has been found that metal-containing zeolite catalysts which may also be used according to the present invention include ZSM-5, ZSM-11, ZSM-12, ZSM-35, ZSM-38 and other similar materials. The catalyst may have deposited therein a suitable metal. ZSM-5 type zeolite catalysts are not only catalytically selective but also shape selective, so that they preferably catalyze the reaction of normal paraffins.

Preferably the catalyst is a platinum/nickel catalyst deposited on an alumina carrier.

Hydrogenation and isomerisation may be carried out simultaneously or sequentially with the same ctalyst or with two different catalysts containing the same or different metals.

The process of the invention converts benzene to the mixture of cyclohexane and methylcyclopentane. The main properties of the three components involved in the S process are tabulated in the following (octane number data are based on A.P.I. research project Benzene Cyclohexane Methylcyclopentane Boiling Point, Degree C. 80 81 72 Specific Gravity 0.8845 0.784 0.754 Clear Blending RON 99 110 107 Clear Blending MON 91 97 99 Volumetric conversion 1 1.128 1.173 Since methylcyclopentane has about the same blending octane numbers as cyclohexane but a lower specific gravity, that is volume gain due to the conversion of benzene is higher, reaction conditions are orPsr-

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applied which favour the formation of methylcyclopentane.

For example the thermodynamic equilibrium at a 5:1 hydrogen to benzene molar ratio, the optimum temperature for maximising methylcyclopentane yield is between approximately 250 0 C and 300 0 C. This temperature range also allows removing the large quantity of heat generated in the exothermic reaction as high pressure steam.

However, lower temperatures of 150 0 C to 200 0 C favour increased isomerisation of normal paraffins. Accordingly optimum temperatures depend on feedstock composition.

Thus the hydrogenation and isomerisation reaction may be conducted at a temperature of approximately 150 0

C

to 350 0 C, preferably approximately 230 0 C to 270 0 C. The hydrogenation step may be conducted under pressures of from approximately 5 to 25 bar, preferably 10 to 20 bar.

The process may be conducted at a weight hourly space velocity of approximately 0.5 to 5, preferably 1 to S 2.

t The present invention will now be more fully described with reference to the accompanying examples. It should be understood, however, that the following description is illustrative only and should not be taken in any way as a restriction on the generality of the invention specified above.

EXAMPLE 1 A feedstock was prepared containing 24 weight percent of pure benzene and 76 weight percent of light naphtha, a mixture of pentane and hexane. The hydrogenation mixture was heated together with pure hydrogen withdrawn from a cylinder to 150 0 C, the molar ratio of hydrogen to benzene was maintained at 5:1. The ,ti mixture was charged to a laboratory pilot plant isothermal reactor filled with 70 g of a commercial platinum/nickel containing catalyst at a Weight Hourly Space Velocity (WHSV) of 4.3. The 10 mm diameter reactor was cooled on the outside with water. By controlling the level of the water bath reaction temperature was controlled at 200 0

C

while pressure by a back pressure contrclled at 500 KPa, Gas chromatographic analysis s that benzene Ji -8concentration dropped to 0.2 weight percent and isohexane to normal hexane ratio increased from 1.5 in the feed to 3.2 in the product.

EXAMPLE 2 From a stabilised reformate produced in an oil refinery a fraction boiling up to 90°C was separated in the laboratory. This fraction comprised 33.1 weight percent of the stabilised reformate.

The light reformate was vaporised and mixed in a 10:1 mole ratio with hydrogen and fed at 10 bar pressure to an isothermal reactor containing a catalyst from Group VIII platinum/nickel catalyst. The vapors leaving the reactor were cooled by ice water and the liquid product separated.

I 4 ft tI t t I t1 The collected liquid effluent was vaporised, mixed in 9:1 mole ratio with hydrogen and fed under 9 bar pressure to a second isothermal reactor. In the second reactor the catalyst was doped with a metal from Group

VIII.

The combined material balance from the two stage reaction was the following (in weight percent).

Feed Product

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3 0.3 2.2

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4 3.1 6.1

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5

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6

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Cyclohexane 10.8 36.9 4.0 44.4 10.9 4 C

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7 24.5 16.3 M-Cyclohexane 0.1

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8 0.2 0.6 Benzene 18.5 Toluene 1.6 In this process the density of the stream decreased from 0.6907 to 0.6793.

Finally, it is to be understood that various other modifications and/or alterations may be made without departing from the spirit of the present invention as outlined herein.

Claims (11)

1. A process for the preparation of a hydrocarbon fuel having reduced benzene content which process includes providing a light reformate feedstock including aliphatic hydrocarbons and at least 15 wt% benzene, at least one hydrogenation and isornerisation catalyst; and a first source of hydrogen; and mixing the feedstock with the first hydrogen source to form a mixed vapor; and contacting the mixed vapor with the catalyst at a pressure of 5-25 bar and temperature of 150°C to 350 0 C, so that the benzene content is hydrogenated to a mixture of methylcyclopentane and cyclohexane.

2. A process according to Claim 1, wherein a portion of the aliphatic hydrocarbons are partially isomerised to increase the octane number of the hydrocarbon fuel. 4* *o o f a Z Oai -or ~mnar -9- The claims defining the inventon -a-es follows. A process for the preparation of a hydrocarbon fue having reduced benzene content which process includes roviding a hydrocarbon feedstock including benzene and all atic hydrocarbons, at le t one hydrogenation and isomerisation catalyst; and a first source f hydrogen; and mixing the feedstoc ith the first hydrogen sourc' to form a mixed vapor; and contacting the mixed vapor with he catalyst. 2. A process according to claim 1, wheein a portion of the benzene content is hydrogenated to cycl exane and to methylcyclopentane, and portion of the a i hatic i hydrocarbons are partially isomerised to increase he i~ -ctane number of the hydrocarbon fuel. S3. A process according to claim 2, wherein the A .hy.rc rb feedstock includes from up to 50% by weight of benzene.

4. A process according to claim 3, wherein the Shydrocarbon feedstock includes a catalytic reformate or other benzene-rich feedstock stream. A process according to claim 4, which process includes the preliminary step of providing a catalytic reformate feedstock; subjecting the feedstock to a distillation process; and recovering a benzene-rich feedstock stream as overhead product.

6. A process according to claim 1, wherein at least one catalyst is selected from metals Group VIII or Group III, or mixtures thereof, optionally deposited on a carrier.

7. A process according to claim 6, wherein the catalyst is a platinum/nickel catalyst deposited on an alumina carrier.

8. A process according to claim 1, wherein hydrogen is present in a molar ratio of hydrogen: benzene of 3:1+0o2:l, 1. <c 1 V O I aately h 1 to 20;1 and tho hydrogonation and isomerisation reLnt:oa nis conducted at a temperature of approximately 150 0 C to 350-C ressure of

9. A process according to claim 8, wherein the hydrogenation and isomerisation reaction is conducted at a weight hourly space velocity of aproximtly 0.5 to A process according to claim 1, wherein the mixed vapour is first charged to a reactor containing an hydrogenation ctalyst and the effluent therefrom is charged to a second reactor containing an isomerisation catalyst.

11. A process according to claim 9, wherein the first reactor is an isothermal tubular reactor and the second reactor is isothermal or adiabatic.

12. A process according to claim 10, wherein the effluent from the first reactor is mixed with a second source of hydrogen prior to charging to the second reactor. S13. A process according to claim 10, wherein the effluent from the first reactor is mixed with a second hydrocarbon feedstock, including aliphatic hydrocarbons, 't prior to charging to the second reactor.

14. A process according to claim 1, substantially as hereinbefore described with reference to Example 1 or 2.

15. A hydrocarbon fuel having reduced benzene content when prepared according to any one of claims 1 to 14. DATED: 30th August, 1991 PHILLIPS ORMONDE FITZPATRICK Attorneys for: TECHNISEARCH LIMITED 0 8989G PT AO j W ABSTRACT A process for the preparation of a hydrocarbon fuel having reduced benzene content which process includes providing a hydrocarbon feedstock including benzene and aliphatic hydrocarbons, at least one hydrogenation and isomerisation catalyst; and a first source of hydrogen; and mixing the feedstock with the first hydrogen source to form a mixed vapor; and contacting the mixed vapor with the catalyst. re I i k, I 4 I.-.,,jimm TIui >«iiir n T nl')iH V( M tl*r ff T me g s o B I ABSTRAC