GB2366803A

GB2366803A - Sulphur removal from a hydrocarbon stream

Info

Publication number: GB2366803A
Application number: GB0116679A
Authority: GB
Inventors: Sally Anne Jones; Peter Edward James Abbott; John Leonello Casci; Edmund Hugh Stitt
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 2000-08-14
Filing date: 2001-07-09
Publication date: 2002-03-20
Also published as: GB0019807D0; GB0116679D0

Abstract

Sulphur compounds from a liquid hydrocarbon stream, e.g. a FCC gasoline stream, are converted to higher boiling point sulphur compounds by contact with hydrogen peroxide and a catalyst, effective to catalyse the reaction of hydrogen peroxide with sulphur compounds. A higher boiling point fraction containing said higher boiling point sulphur compounds is subsequently separated from the hydrocarbon stream. Before separation of the higher boiling fraction, residual hydrogen peroxide is preferably decomposed catalytically using e.g. a nickel catalyst.

Description

<Desc/Clms Page number 1> Sulphur removal This invention relates to sulphur removal and in particular to the removal of sulphur compounds from liquid hydrocarbons, particularly gasoline FCC fractions produced by cracking naphtha. Such FCC fractions generally have an atmospheric pressure boiling range of up to 220'C and generally contain hydrocarbons containing 5 to 12 carbon atoms, in particular paraffins, olefins, cycloparaffins and aromatic hydrocarbons. The olefin content is usually at least 20% on a molar basis. Unfortunately, the FCC fractions generally also contain sulphur compounds, in particular mercaptans and thiophenic compounds.

There is growing environmental and legislative pressure on reducing the sulphur compound content of gasoline.

One known method is hydro-treating wherein the hydrocarbon is reacted with hydrogen in the presence of a suitable catalyst, often a nickel or cobalt molybdate, so the sulphur compounds are hydrogenated to form hydrogen sulphide. The hydrogen sulphide may then be removed by absorption in a regenerable wash system, e.g. amine scrubbing. However hydro- treating processes are liable to effect hydrogenation of valuable components such as aromatics or olefins in the hydrocarbon stream, This leads to a reduction in the octane number of the gasoline, which is a disadvantage with respect to its performance.

It has been proposed in US 5318690 to overcome this problem by fractionating a catalytically cracked naphtha to give a light and a heavy fraction. The light fraction, which contains the olefin components and the low boiling sulphur compounds such as mercaptans, is subjected to an oxidative sweetening process, while the heavy fraction containing higher sulphur compounds such as thiophenes is subjected to hydro-desulphurisation and then the hydro-desulphurised higher fraction is subjected to a controlled cracking to increase the octane rating thereof. Since the cracking produces olefins which may combine with the hydrogen sulphide produced in the hydro-desulphurisation stage, the product is subjected to a further hydro-desulphurisation step and then combined with the sweetened light fraction after removal of the sulphides and disulphides therefrom.

The oxidative sweetening process of FCC gasoline fractions is well known, see for example US 4206043, GIB 2071134 and US 4574121, and comprises contacting the liquid fraction with an oxygen-containing gas, e.g. air, in the presence of a suitable catalyst, e.g. cobalt phthalocyanine, often dispersed in an aqueous caustic solution. As a result of the oxidative sweetening, the mercaptans are converted to sulphides and/or di-sulphides. However this oxidative sweetening does not affect oxidation of the thiophenic sulphur compounds.

US 3816301 discloses that thiophenic sulphur compounds in heavy hydrocarbons can be oxidised using hydroperoxides, for example tertiary butyl hydroperoxide formed by the oxidation of isobutane with a gas containing free oxygen.

It is also known that sulphur compounds in hydrocarbons can be oxidised to sulphoxides and/or sulphones. Thus GB 2262942 and EP 0565324 describe the non-catalytic oxidative treatment of both light and heavy liquid hydrocarbons, for example ranging from naphtha, through gasoline, kerosene and gas oil to heavy fuel oils, containing sulphur compounds to give the corresponding sulphoxide and/or sulphone having increased boiling points compared to the un-oxiclised sulphur compounds and suggest that the sulphur compounds may be separated by subjecting the hydrocarbon to distillation leaving the oxidised sulphur compound as a component of the distillation residue.

Hereinafter, boiling points refer to the boiling points at atmospheric pressure. For example dimethyl sulphide has a boiling point of about 38*C whereas the oxidation product, dimethyl sulphoxide, has a boiling point of 190*C and the further oxidation product, dimethyl sulphone, has a boiling point of 2380C. Likewise, thiophene has a boiling point of 84'C while thiophene suiphoxide has a boiling point of about 215-2200C.

We have realised that the process of the aforementioned US 5318690 may be simplified if the FCC stream can be oxidised under conditions effective to convert the sulphur compounds to sulphoxides or sulphones with minimal oxidation of the olefins present. The treated FCC stream can then be subjected to fractional distillation to separate the lighter components of the FCC stream, including the olefin components, as a gasoline fraction having a greatly reduced sulphur content, leaving a small higher boiling fraction containing the oxidised sulphur compounds. If desired, as described in US 5318690 this higher boiling fraction may be desulphurised by conventional techniques such as hydro-desulphurisation and then mixed with the lighter fraction. Alternatively the higher boiling fraction, after hydro-desulphurisation if desired, can be added to the heavy FCC fraction (boiling range typically >2000C), which may be hydrotreated before being added to the diesel pool.

We have described in our co-pending PCT application WO 00/47696 that, surprisingly, hydroperoxides can be used to oxidise the sulphur compounds in FCC streams to higher boiling compounds with minimal oxidation of the aromatics and olefinic components thereof.

The use of tertiary hydroperoxides while beneficial for the aforesaid process is limited in some cases by the complexity of their synthesis and the resulting economic considerations. Consequently, a process using the more readily available hydrogen peroxide would be desirable. However, it is known that hydrogen peroxide can oxidise olefins, even at low temperatures. Such processes are described for example in BE 1011375, WO 00/007965 and US 5744619. Such oxidation would result in a reduced level of olefins which is deleterious to the performance of the gasoline.

We have found, surprisingly, that hydrogen peroxide can be used to oxidise the sulphur compounds in FCC streams to higher boiling compounds with minimal oxidation of the aromatics and olefinic components thereof. Thus it is believed that, at least at low temperatures, the presence of sulphur compounds inhibits the oxidation of the olefin and

aromatic components, despite the latter generally being present in much larger proportions than the sulphur compounds.

Accordingly, the present invention provides a process for the removal of sulphur compounds from a liquid hydrocarbon FCC stream containing olefins and thiophenic sulphur compounds comprising contacting said hydrocarbon stream with hydrogen peroxide and a catalyst effective to catalyse the reaction of hydrogen peroxide with sulphur compounds, whereby the sulphur compounds are converted to higher boiling point sulphur compounds, and thereafter separating a higher boiling point fraction containing said higher boiling point sulphur compounds from said hydrocarbon stream.

Suitable catalysts may be selected from the group comprising aluminas, silicas, aluminosilicates, zeolites and metal silicate zeotypes and carbon-based catalysts such as carbon or Pd on carbon. Examples of such catalysts include silica, alumina, an aluminosilicate zeolite catalyst of FAU framework type with an approximate Si02 : A1203 molar ratio in the range of 2:1 to 80:1, titanosilicate zeotypes including Ti-MR, TWEL, Ti-BEA* and Ti-MTW; titanoaluminasilicate zeotypes including TiAl-MR, TiAl-MEL, TiAl-BEA* and TiAl-MTW; titanovanadosilicate zeotypes; titanium-containing mesoporous materials such as Ti-MCM-41, Ti-MCM-48 and Ti-SBA-2; and vanadium silicate zeotypes. Additionally mixtures of these catalysts may be used in the present invention.

The catalyst is desirably selective for the oxidation of sulphur species without loss of hydrogen peroxide to oxygen gas and water. Preferably the catalyst is selected from silica; alumina-, an aluminosilicate zeolite catalyst of FAU framework type with an approximate Si02 A1203 molar ratio in the range of 5:1 to 40:1 and most preferably with an approximate Si02 A1203 molar ratio of 20 : 1; a titanosilicate having a MFI framework-, or mixtures of these, for example a mixture of silica and a titanosilicate zeotype.

The reaction is effected by contacting the catalyst with the hydrocarbon stream in the liquid state and containing the hydrogen peroxide. Hydrogen peroxide may be added in any form to the process of the present invention. Typically, hydrogen peroxide is supplied as aqueous solutions in concentrations up to 35% by weight. Preferably, the hydrogen peroxide concentration should be between 2% wt. and 35% wt. Since hydrogen peroxide tends to decompose at relatively low temperatures, the reaction is preferably effected adiabatically with the hydrocarbon stream being fed to the catalyst at a temperature in the range 20 to 1 OOOC' and preferably in the range 60 to 800C. The amount of hydrogen peroxide required will normally depend on the amount and nature of the sulphur compounds. Thus, generally there should be at least one mole of hydrogen peroxide per mole of sulphur compound. Preferably, the amount of hydrogen peroxide should be limited to avoid undue risk of olefin oxidation. Preferably the molar ratio of sulphur to hydrogen peroxide is between 1:1 and 1:50 (sulphur hydrogen peroxide).

The pressure of the process may be in the range I to 20 bar abs., preferably in the range I to 15 bar abs. and most preferably at 2 to 5 bar abs.

In a preferred embodiment, the sulphur oxidation catalyst is disposed as a fixed bed in a column. The FCC stream and hydrogen peroxide are passed down through the bed where oxidation of the sulphur compounds takes place.

Effective contacting of the aqueous hydrogen peroxide solution, FCC stream and catalyst is important for maximising the process efficiency. This may be carried out in a number of different operations. For example, the mixing of FCC stream and hydrogen peroxide may be carried out in a separate vessel to that containing the sulphur compound oxidation catalyst, but preferably is effected within the same vessel by means of a suitable mixing nozzle, designed to produce a fine dispersion of organic phase and aqueous phase droplets, disposed above the bed of sulphur oxidation catalyst.

Alternatively the sulphur compound oxidation catalyst may be disposed as a slurry in the FCC stream and high-shear mixing performed on the slurry to disperse the aqueous phase containing the hydrogen peroxide.

Following the sulphur compound oxidation step, the aqueous phase should preferably be separated from the treated hydrocarbon phase. This may be carried out by means of a separate separation vessel or decanter in which natural coalescence of the separate phases is effected under low or no shear conditions. The aqueous phase containing any unreacted hydrogen peroxide thus separated may be recycled to the hydrogen peroxide feed for the sulphur compound oxidation reaction. A purge from the recycle line can be used to control the level of dilution of the hydrogen peroxide feed with water formed in the sulphur oxidation step and present with unreacted hydrogen peroxide after the sulphur compound oxidation step.

After the phase separation step, the hydrocarbon phase will normally contain some residual hydrogen peroxide. These residues are preferably decomposed before separation of the oxidised sulphur compounds. The residues of hydrogen peroxide may be decomposed by heating the mixture, e.g. to a temperature above 1 OOOC, but this is less preferred as the residual hydrogen peroxide may tend to react with other components, e.g. aromatic or olefinic components, of the hydrocarbon stream which not only may result is loss of desired products, but also may produce gums or other undesirable compounds.

In a preferred arrangement the residual hydrogen peroxide may be decomposed by passing the hydrocarbon stream over a suitable hydrogen peroxide decomposition catalyst, for example a catalyst comprising oxides of at least one metal selected from iron, nickel, cobalt and copper, preferably nickel, for example in the form of porous shaped particles containing 10 to 70% by weight of nickel oxide and a calcium aluminate cement as a binder. Such catalysts decompose the residual hydrogen peroxide with the formation of oxygen and water. The catalyst used for the decomposition of the residual hydrogen peroxide may be disposed in the same vessel as the sulphur compound oxidation catalyst but is preferably disposed as a fixed

bed in a separate vessel. Catalytic decomposition of the residual hydrogen peroxide is preferably effected at substantially the same temperature and pressure as was employed for the sulphur compound oxidation step.

The liquid hourly space velocity through each catalyst bed is typically in the range 1 to 10 11-1.

After the sulphur compound oxidation step, phase separation step and preferably after a residual hydrogen peroxide decomposition step, the hydrocarbon stream is subjected to a separation process, e.g. fractional distillation, to separate a higher boiling point stream containing the oxidised sulphur compounds. As indicated above, the higher boiling stream may be added to the heavy FCC fraction. The oxidised sulphur compounds can be removed from this stream by the conventional hydrotreating employed for sulphur reduction of diesel. Alternatively, the higher boiling stream, which will be largely free from olefinic compounds, may be subjected to conventional sulphur removal, e.g. hydrotreatment and sulphur absorption and then returned to the lower boiling fraction or otherwise used.

The reaction of the hydrogen peroxide with the sulphur compounds, and the subsequent decomposition of residual hydrogen peroxide in the FCC stream, both give rise to water. In the case of reaction between hydrogen peroxide and sulphur compounds, the water can be separated from the hydrocarbon in a phase separation step and removed or recycled with any unreacted hydrogen peroxide. In the case of decomposition of hydrogen peroxide residues in the FCC stream, the water may be removed during fractional distillation by means known to those skilled in the art. For example, the water may be collected in a trap at the base of an overhead condensate receiver for the fractional distillation column. Decomposition of residual hydrogen peroxide also gives rise to oxygen. This oxygen may be purged from the vessel in which residual hydrogen peroxide is being catalytically decomposed or may be removed during fractional distillation.

The invention is illustrated with reference to the accompanying drawing, which is a diagrammatic flowsheet of one embodiment of the process.

In this embodiment, the FCC stream 10 is fed via a heat exchanger 11 and line 12 to vessel 13 wherein a mixing nozzle 14 combines the FCC stream with aqueous hydrogen peroxide solution fed via line 15. The mixture is then contacted with a bed of catalyst 16 e.g. a titanosilicate zeotype having MFI framework. The FCC stream, containing the sulphur compounds and the hydrogen peroxide, pass down through the sulphur-compound oxidation catalyst bed 16 wherein the hydrogen peroxide oxidises the sulphur compounds to higher boiling point compounds. Typically, the FCC stream is fed at a pressure in then range 2 to 5 bar abs., and at a temperature in the range 20 to 1 00*C. The mixture is the fed via line 17 to a separator 18 wherein the hydrocarbon and aqueous phases separate. The aqueous phase 19 containing unreacted hydrogen peroxide may be recycled to the hydrogen peroxide feed line 15 via pump 20 and line 21. A purge line 22, controlled by valve 23, is present to

remove the excess aqueous hydrogen peroxide recycle if desired. The hydrocarbon phase is fed via line 24 to a second vessel 25 and passed through a bed of hydrogen peroxide decomposition catalyst 26, e.g. nickel oxide supported on alumina or calcium aluminate, wherein the residual hydrogen peroxide is decomposed. The treated FCC stream may then be passed via line 27 to a fractional distillation unit (not shown). A high boiling point fraction, containing the oxidised sulphur compounds, is separated in the distillation unit. Typically, about 2-10% of the product stream 27 will be separated as the high boiling point stream in the subsequent fractional distillation. This separated stream will contain little olefinic components and so the octane rating of the light fraction will not be significantly reduced.

The invention is illustrated by the following examples in which all percentages and parts per million (ppm) figures are expressed by weight.

Example 1 100 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as tetrahydrothiophene and 10 ml (3.84 g) of silica (in the form of spheres of diameter 2-4 mm, having a purity of over 99%, a total surface area of about 330 M2 /g and a pore volume of about 1. 1 CM3/g) as catalyst, were added to a 250 ml round-bottomed flask equipped with magnetic follower and reflux condenser. The mixture was heated to 60'C. 1.1 ml of 30% aqueous hydrogen peroxide was added to the flask. After 30 minutes, no tetrahydrothiophene was detected. 100% of the sulphur containing compounds present was tetramethylene sulphone.

The experiment was repeated with 10 ml (5.926 g) of y-alumina (in the form of extrudates of about 2-3 mm length and having a surface area of 180 M2jg , e.g. AL 3992-E TM ) as catalyst. By 120 minutes > 97% of tetrahydrothiophene had been converted to tetramethylene sulphone. No tetramethylene sulphoxide was detected.

When the experiment was repeated with 10 ml (2.870 g) of an aluminosilicate zeolite catalyst of FAU framework type with an approximate Si02:AI203 molar ratio of 20:1, no tetrahydrothiophene was detected after 5 minutes reaction. 76% of the sulphur containing compounds present was tetramethylene sulphone with the remaining 24% being tetramethylene sulphoxide. By 120 minutes, only tetramethylene sulphone was detected.

Example 2 A sample of a titanosilicate MFI structure type was prepared from a reaction mixture of; molar composition: 60 Si02 2 Ti02 1OTPAOH 2400 H20 where TPAOH is tetrapropylammoniurn hydroxide.

The reaction mixture was prepared by mixing the appropriate amounts of tetraethylorthosilicate (Fluka), titanium ethoxide (Fluka), tetrapropylammonium hydroxide (20%w/w aqueous solution; Sigma-Aldrich) and de-mineralised water.

The titanium ethoxide was added slowly, with stirring, to the tetraethylorthosilicate. The water was then added slowly to the above mixture with stirring, followed by the tetra propylam mon iu m hydroxide solution. The resulting mixture was stirred for 5 minutes then charged to a 1 litre, stainless steel autoclave and reacted at 160'C with stirring (4 x 450 pitched paddle impellers) at 300 rpm. The reaction was terminated after 66 hours and crash-cooled (by means of a cooling coil located in the autoclave) to ambient temperature (20-23'C) then discharged. The solid material was separated and washed by repeated sedimentation and decantation (4 times) before being dried, at 11 O'C, then calcined in static air at 4500C for 24 hours followed by 5500C for 24 hours.

The resulting titanosilicate material was examined by powder x-ray diffraction and found to be a highly crystalline MFI type zeolite.

75 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as butanethiol and 10 ml (4.660 g) of the titanosilicate catalyst were added to a 250 ml round-bottomed flask equipped with a magnetic follower and reflux condenser. The mixture was heated to 80'C and 75 ml of 2% aqueous hydrogen peroxide was added to the flask. All of the butanethiol was converted to dibutylsulphide after 30 minutes.

The reaction was repeated such that 100 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as butanethiol and 10 ml (3.031 g) of an aluminosilicate zeolite catalyst of FAU framework type with an approximate Si02:AI203 molar ratio of 20:1, were added to a 250 ml round-bottomed flask equipped with magnetic follower and reflux condenser. The mixture was heated to 80'C. 1.1 ml of 30% aqueous hydrogen peroxide was added to the flask. All butanethiol was converted to dibutylsulphide by 30 minutes and complete conversion of the dibutylsulphide to undefined higher boiling sulphur compounds was achieved after 1 hour.

Example 3 75 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as thiophene and 6 ml (3.688 g) of the titanosilicate zeotype catalyst prepared as described in Example 2 were added to a 250 ml round-bottomed flask equipped with an overhead mechanical stirrer. The mixture was heated to 800C. 0.55 ml of 30% aqueous hydrogen peroxide was added to the flask. (This quantity equates to sufficient for 100% conversion of thiophene to thiophene-1, I -dioxide). After 120 minutes, only 16 ppm thiophene remained in the gasoline. This equates to consumption of 98.4% of the hydrogen peroxide for the oxidation of the thiophene. No oxidised olefin was detected.

Example 4 100 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as tetra hydroth iophene and 10 ml

(3.870 g) of a gel silica catalyst (in the form of spheres of diameter in the range 2-4 mm having a purity of over 99%, a total surface area of about 300-350 M2/g. and a pore volume of 1.04 CM3/g with 76% of the pore volume provided by pores having a diameter in the range 7-23 nm) were added to a 250 ml round-bottomed flask equipped with magnetic follower and reflux condenser. The mixture was heated to 60'C. 0.55 ml of 30% aqueous hydrogen peroxide was added to the flask, this quantity being only sufficient for conversion of tetrahydrothiophene to tetramethylene sulphone. After 30 minutes, no tetrahydrothiophene was detected. By 240 minutes, 99.5% of the sulphur containing compounds present was tetrarnethylene sulphone with the remaining 0.5% being tetramethylene sulphoxide. This equates to 99.8% consumption of the hydrogen peroxide. No oxidised olefin was detected.

Example 5 75 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as thiophene and 20 ml (12.625 g) of the titanosilicate zeotype catalyst prepared as described in Example 2 were added to a 250 ml round-bottomed flask equipped with magnetic follower and reflux condenser. The mixture was heated to 80'C. 75 ml of 2% aqueous hydrogen peroxide was added to the flask, this quantity being in excess to that required for complete conversion of the thiophene to thiophene-1,1- dioxide. By 30 minutes, >97% thiophene conversion was achieved. The Ti02 content of both the fresh and used catalyst was 2.0% indicating that no leaching of the active metal component had taken place. The sulphur absorbed on the catalyst at the end of the reaction was measured to be 0. 101 % by weight on the catalyst, equivalent to 85 ppm of the originally added sulphur. Such a low level of absorbed sulphur indicates that sulphur compounds are not significantly absorbed by the oxidation catalyst. No oxidised o(efin was detected.

Example 6 75 ml of a model gasoline fraction comprising octane, octene and para-xylene in the ratio 50:30:20 parts by volume, containing 1000 ppm sulphur as thiophene and 6 ml (3.790 g) of the titanosilicate zeotype catalyst prepared as described in Example 2 were added to a 250 ml round-bottomed flask equipped with an overhead mechanical stirrer. The mixture was heated to 80'C. 75 ml of 2% aqueous hydrogen peroxide was added. By 30 minutes 94.6% conversion was achieved which increased to >99% after 120 minutes. The final sulphur content of the gasoline was 7 ppm.

Claims

Claims. I A process for the removal of sulphur compounds from a liquid hydrocarbon FCC stream containing olefins and thiophenic sulphur compounds comprising contacting said hydrocarbon stream with hydrogen peroxide and a catalyst effective to catalyse the reaction of hydrogen peroxide with sulphur compounds, whereby the sulphur compounds are converted to higher boiling point sulphur compounds and thereafter separating a higher boiling point fraction containing said higher boiling point sulphur compounds from said hydrocarbon stream.
2. A process according to claim 1 wherein the reaction is effected adiabatically with the hydrocarbon stream being fed to the catalyst at a temperature in the range 20 to 1 OOOC and at a pressure in the range 1 to 20 bar abs.
3. A process according to claim 1 or claim 2 wherein the hydrogen peroxide is in the form of an aqueous solution having a hydrogen peroxide concentration between 2 and 35% by weight.
4. A process according to any one of claims 1 to 3 wherein the sulphur compound oxidation catalyst is selected from the group consisting of aluminas, silicas, aluminosilicates, zeolites and metal silicate zeotypes, or mixtures of these, and carbon or Pd on carbon.
5. A process according to claim 4 wherein the sulphur compound oxidation catalyst is an aluminosilicate zeolite catalyst of FAU framework type with an approximate Si02: A1203 molar ratio in the range 2:1 to 80:1,
6. A process according to claim 4 wherein the sulphur compound oxidation catalyst is a titanosilicate having a MFI framework.
7. A process according to any one of claims 1 to 6 wherein the sulphur compound oxidation catalyst is disposed as a fixed bed.
8. A process according to any one of claims 1 to 7 wherein, after passage through the bed of catalyst effective to catalyse the reaction of hydrogen peroxide with sulphur compounds, the mixture of aqueous hydrogen peroxide and liquid hydrocarbon FCC stream is allowed to separate into an aqueous phase and a hydrocarbon phase.

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9. A process according to claim 8 wherein the separated aqueous phase is recycled to be at least part of that contacted with said hydrocarbon stream to effect oxidation of said sulphur compounds.
10. A process according to any one of claims I to 9 wherein, after passage through the bed of the catalyst effective to catalyse the reaction of hydrogen peroxide with sulphur compounds, residual hydrogen peroxide in the hydrocarbon stream is decomposed by passing the hydrocarbon stream over a hydrogen peroxide decomposition catalyst before the higher boiling point fraction containing the higher boiling point sulphur compounds is separated from the hydrocarbon stream.
11. A process according to claim 10 wherein the hydrogen peroxide decomposition catalyst comprises oxides of at least one metal selected from iron, nickel, cobalt and copper.
12. A process according to claim 10 or claim 11 wherein the hydrogen peroxide decomposition catalyst is disposed as a fixed bed in a separate vessel to that used for the oxidation of sulphur compounds.