Current legislation in many parts of the world for hydrocarbon fuels, such as e. g. gasoline, diesel and jet fuel requires upper limits on the content of sulphur compounds in the fuel for environmental reasons. The main commercial processes used to lower the content of sulphur compounds involve hydrotreatment of the fuel with a high sulphur level in the presence of gaseous hydrogen and a hydrodesulphurisation catalyst wherein the organic sulphur compounds are converted to hydrogen sulphide which is subsequeuntly removed.

However there is a continual requirement to improve desulphurisation processes to produce hydrocarbon fuels with lower sulphur content and the present invention provides a single liquid phase desulphurisation process which eliminates the requirement of recycle gas compressors.

Accordingly the present invention provides a process for reducing the sulphur content of a liquid hydrocarbon feed comprising organic sulphur species wherein said process comprises a) contacting the liquid hydrocarbon feed comprising organic sulphur species with a hydrogen containing gas stream to produce a liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content b) contacting the liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content with a catalyst at elevated temperature and presurre in a reaction zone to generate a liquid hydrocarbon feed with a decreased organic sulphur

species content and an increased hydrogen sulphide content c) passing the liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide content to a hydrogen sulphide removal zone to produce a liquid hydrocarbon feed with a decreased organic sulphur species content and decreased hydrogen sulphide content.

The liquid hydrocarbon feed comprising organic sulphur species is usually a liquid at a temperature of 25°C and at a pressure of lbarg and is generally directly or indirectly derived from a crude oil distillation. The liquid hydrocarbon feed usually contains saturated hydrocarbons e. g. branched and unbranched alkanes and alicyclic hydrocarbons as well as variable amounts of aromatics and/or unsaturated compounds such as olefins.

The liquid hydrocarbon feed comprising organic sulphur species may be a middle distillate which may be one or more petroleum fractions with a boiling range of 150- 450°C, preferably 190-390°C. Advantageously the middle distillate stream is a combination of said petroleum fractions. Examples of suitable petroleum fractions include light gas oils (LGO), heavy gas oils (HGO), light cycle oils (LCO), coker gas oils (CGO) and Visbroken gas oils (VBGO). Preferably the liquid hydrocarbon feed comprising organic sulphur species is diesel, gasoline, kerosene or jet fuel and is advantageously diesel or jet fuel.

The organic sulphur species usually comprise mercaptans, sulphides, thiophenes, benzothiophenes and dibenzothiophenenes (DBTs), especially hindered alkyl substituted dibenzothiophenes. The liquid hydrocarbon feed comprising organic sulphur species usually has a total sulphur content (expressed as elemental S) of 1000-50000ppm S, preferably 5000-20000ppm S e. g. 15000ppm S, a DBT content of 100-20000ppm S, preferably 1000-5000ppm S e. g. 3000ppm S, and a hindered-DBT content of 50- 5000ppm S, preferably 100-1000ppm S e. g. 500ppm S. When the liquid hydrocarbon comprising organic sulphur species is diesel the diesel may contain contaminant sulphur in the range of 10-lOOppm (expressed as elemental S).

The liquid hydrocarbon feed comprising organic sulphur species is contacted with the hydrogen containing gas stream to produce a liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content.

The hydrogen containing gas stream may be provided by a reformer off gas stream

but is preferably substantially pure hydrogen. The liquid hydrocarbon comprising organic sulphur species is typically saturated with gaseous hydrogen in a saturator vessel wherein hydrogen is passed through the body of the liquid.

The liquid hydrocarbon comprising organic sulphur species is typically saturated with gaseous hydrogen at a temperature of between 250°C-500°C, e. g. 300-400°C e. g.

340°C or 380°C, and at pressure of between 1-100 bar, preferably between 10-60bar e. g.

20-40 bar. The liquid hydrocarbon comprising organic sulphur species usually contains 1-100, preferably 10-90 and especially 20-60 Nm3 of hydrogen per m3.

The liquid hydrocarbon feed comprising organic sulphur species may be saturated with hydrogen at location remote from the reaction zone. Alternatively the liquid hydrocarbon feed comprising organic sulphur species may be saturated with hydrogen immediately upstream of the reaction zone.

The liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content is then contacted with a catalyst at elevated temperature and presurre in a reaction zone to generate a liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide content.

Any suitable catalyst may be used in the reaction zone. Such a catalyst may comprise one or more active components which are dispersed on a catalyst support.

Examples of active components include, molybdenum, tungsten, platinum, palladium, ruthenium, nickel, cobalt, iron, copper, cerium or rhenium. Preferably the catalyst comprises at least two metals selected from the above group and most preferably the catalyst comprises molybdenum or tungsten and at least one additional metal selected from nickel and cobalt.

The active component or components, may be supported on any suitable catalyst support, such as silica, alumina, silica-alumina, carbon, titania, activated carbon or an alumino-silicate such as a zeolite. The support may be pretreated to incorporate a promoter such as phosphorus or fluorine. The catalyst support may be mixed with a binder such as alumina or silica.

The total weight of metal may be between 0.1-70% by weight (as metal) based on the weight of support, preferably between 0.2-20% by weight (as metal) based on the weight of support. The metal (s) may be introduced to the support by any of the well known techniques employed in catalyst preparation e. g. impregnation wherein the pores

of the support are filled at least partly with an impregnating solution comprising a soluble precursor salt of the desired metal and the impregnated resulting support material is subsequently dried, optionally calcined and sulphided. The impregnating solution is usually an aqueous solution of a metal nitrate, oxalate, formate, propionate, acetate, chloride, carbonate, or bicarbonate in particular a metal nitrate, chloride or carbonate. Alternatively the impregnating solution may comprise a metal compound dissolved in an organic solvent e. g. an organometallic compound such as a metal acetylacetonates, metal naphthenates or metal carbonyls.

Wherein the catalyst comprises at least two metals the second metal may also be introduced to the support as described above before or after the incorporation of the initial metal or the incorporation of the additional metal may be simultaneous with the incorporation of the initial metal.

When a catalyst comprising molybdenum or tungsten and at least one additional metal selected from nickel and cobalt is being prepared the impregnating solutions are usually ammonium paramolybdate and cobalt or nickel nitrate and when a catalyst comprising tungsten and at least one additional metal selected from nickel and cobalt is being prepared the impregnating solutions are usually ammonium paratungstate and cobalt or nickel nitrate.

The catalyst usually comprises at least 1% by weight of molybdenum or tungsten (based on the weight of support), usually between 1-50% by weight of molybdenum or tungsten and preferably between 20-30% by weight of molybdenum or tungsten and at least 0. 1% by weight of nickel and/or cobalt (based on the weight of support), usually between 0.1-20% by weight of nickel and/or cobalt and preferably between 3-10% by weight of nickel and/or cobalt.

After metal incorporation the catalyst may be post treated. The post treatment usually involves calcination in air, nitrogen or helium at a temperature within the range of 200-800°C, preferably 300-700°C e. g. 350-500°C. After calcination the catalyst is advantageously sulphided using a sulphiding agent such as hydrogen sulphide or dimethyl disulphide. The catalyst is usually sulphided at a temperature within the range of 100-400°C, preferably within the range of 250-350°C.

Prior to contacting the liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content with the catalyst the catalyst is usually

pretreated. The pretreatment usually involves calcination in air, nitrogen or helium at a temperature within the range of 200-800°C preferably 300-700°C e. g. 350-500°C.

Optionally the catalyst is reduced at a temperature within the range of 100-800°C preferably 200-700°C with a flowing gas such as hydrogen, carbon monoxide or a light hydrocarbon e. g. Cl-C4 hydrocarbon. Alternatively after calcination the catalyst is sulphided using a sulphiding agent such as hydrogen sulphide or dimethyxl disulphide.

The catalyst is usually sulphided at a temperature within the range of 100-400°C, preferably within the range of 250-350°C.

The liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content is preferably contacted with the catalyst at a temperature of between 250°C-500°C, e. g. 300-400°C e. g. 340°C or 380°C, and at pressure of between 1-100 bar, preferably between 10-60bar e. g. 20-40 bar.

The reaction zone usually comprises a fixed bed catalyst contained within a vessel. The vessel may be one capable of withstanding temperatures of up to 500°C and pressures of up to 100 bar, e. g. a steel pressure vessel.

The reaction zone generates a liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide content and this is advantageously passed directly (i. e. in the absence of any recycle to the reaction zone) to the hydrogen sulphide removal zone to generate a liquid hydrocarbon feed with a decreased organic sulphur species content and a decreased hydrogen sulphide content.

The hydrogen sulphide removal zone may comprise a zone that is maintained at a lower pressure than that of the reaction zone. Consequently the hydrogen sulphide and hydrogen present in the liquid hydrocarbon feed exiting the reaction zone is vapourised in the removal zone and removed from the liquid hydrocarbon product.

Advantageously a gaseous stream may be passed through the hydrogen sulphide removal zone to facilitate the removal of the hydrogen sulphide. The gaseous stream may be comprise an inert gas e. g. nitrogen but is preferably hydrogen.

Wherein the gaseous stream is hydrogen the gas exiting the hydrogen sulphide removal zone may then be advantageously employed to in step (a) of the present invention.

In a preferred embodiment of the invention the hydrogen sulphide removal zone comprises an adsorbent in an adsorption zone wherein the process comprises contacting

the liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide content with an adsorbent in an adsorption zone to produce a liquid hydrocarbon feed with a decreased organic sulphur species content and decreased hydrogen sulphide content and an adsorbent with an increased sulphur content.

Suitable adsorbents may be provided by porous oxides e. g. metal or non metal oxides. The metal oxides are advantageously di, tri and tetravalent metals, which may be transition or non transition metals or rare earth metals, such as zinc oxide, alumina, titania, cobaltic oxide, zirconia, ceria, molybdenum oxide, magnesia and tungsten oxide.

An example of a non metal oxide is silica. More than one type of adsorbent may be present. Advantageously the adsorbent is selected from zinc oxide, alumina and magnesia or any combinations thereof.

The adsorbent may comprise incorporated elemental metal usually selected from the metal Groups VIIIA, IB, IIB, niB, IVB and VB in particular group VEA e. g. nickel, cobalt and especially the platinum metals e. g. platinum, palladium, ruthenium, rhodium, osmium, and iridium. The groups are as described in the Periodic Table in Basic Inorganic Chemistry by F. A. Cotton, G. Wilkinson and P. L Gaus Publ. John Wiley & Sons, Inc. New York 2nd Ed. 1986. Advantageously the adsorbent comprises nickel with one or more platinum group metals e. g. platinum.

Alternatively the adsorbent may comprise a zeolite. These zeolites may be synthetic e. g. zeolites A, X, Y and L or naturally occurring zeolites e. g. faujasite. The zeolite may also comprise a group VBIA metal as elemental metal, in particular palladium or platinum.

In another embodiment of the invention the adsorbent may be carbon based e. g. activated carbon.

The liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide is preferably contacted with the adsorbent at a temperature of between 50°C-200°C, advantageously between 100-150°C e. g. 120°C or 140°C, and at pressure of between 1-50 bar, preferably between 2-20bar e. g. 10-15 bar.

The adsorption zone usually comprises a fixed bed of adsorbent contained within a vessel. The vessel may be one capable of withstanding temperatures of up to 500°C and pressures of up to 100 bar, e. g. a steel pressure vessel.

The adsorbent of increased sulphur content is preferably stripped of its sulphur content by contact with a stripping gas e. g. nitrogen, oxygen, hydrogen or steam or a sulphur free hydrocarbon gas to give an adsorbent substantially free of adsorbed sulphur compounds. The sulphur containing adsorbent is usually contacted with the stripping gas at a temperature elevated above the temperature of adsorption. Usually the stripping gas is contacted with the adsorbent at temperatures in the range of 100-600°C e. g. 150- 350°C and at a pressure of between 1-100 bar.

In an alternative embodiment of the invention the hydrogen sulphide removal zone may comprise an amine or a caustic solution wherein the process comprises passing the liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide content through a vessel containing an amine or a caustic solution e. g. potassium hydroxide solution or sodium hydroxide solution to produce a liquid hydrocarbon feed with a decreased organic sulphur species content and a decreased hydrogen sulphide content.

The liquid hydrocarbon feed with a decreased organic sulphur species content and decreased hydrogen sulphide content usually contains a total amount of the sulphur containing compounds of less than 500ppmS e. g. 200-400ppmS, preferably less than 200ppmS e. g. 50-100ppmS, more preferablyless than 50ppmS e. g. 20-40ppmS and advantageously less than l OppmS e. g. 0. 1-5ppm (expressed by weight as elemental S).

The invention will now be described and illustrated with reference to the accompanying drawing in which Fig. 1 shows a reservoir (1) containing a liquid hydrocarbon feed comprising organic sulphur species. The liquid hydrocarbon feed comprising organic sulphur species is passed to a hydrogen saturator (2) via a liquid feed pump (3) wherein it is contacted with gaseous hydrogen which is passed to the hydrogen saturator (2) via line (4) and exits the hydrogen saturator (2) via vent (5).

A liquid hydrocarbon feed comprising organic sulphur species and an increased hydrogen content exits the hydrogen saturator via line (6) and is passed into a reaction zone (7) which contains a fixed bed of hydrodesuphurisation catalyst.

A liquid hydrocarbon feed with a decreased organic sulphur species content and an increased hydrogen sulphide content exits the reaction zone (7) and is passed via line (8) to an adsorption zone (9) which contains a fixed bed of adsorbent. A liquid hydrocarbon feed with a decreased organic sulphur species content and a decreased

hydrogen sulphide content exits the adsorption zone (9) via line (10).

The invention is illustrated in the following example.

Example 1 A test rig comprising a liquid feed reservoir, a liquid feed pump, a hydrogen supply, a saturator vessel and a reactor contained within an oven for temperature control was employed. The reactor comprised a steel tube with an internal diameter of 4mm and a length of 1.3m and contained a fixed bed of a presulphided cobalt-molydenum on alumina hydrotreating catalyst. The reactor temperature was varied between 360°C- 400°C and the pressure was varied between of 30-70barg.

A gas oil containing 260ppm of total sulphur (expressed as elemental S) was passed to the hydrogen saturator wherein it was saturated with gaseous hydrogen and then subsequently passed to the reactor with a Liquid Hourly Space Velocity LHSV of between 1.0-1. 4h-l. The gas oil exiting the reactor was passed to hydrogen sulphide removal zone wherein the hydrogen sulphide was removed The sulphur content of the gas oil product was monitored at different reactor temperatures and pressures and at different contact times. The results are shown in table 1.

Table 1 Pressure (barg) Temperature (°C) LHSV (h'') S-content (ppm) 30 360 1. 0 46 30 370 1. 2 35 30 380 1. 4 46 30 390 1. 2 24 60 400 1. 1 3 70 360 1. 1 30 Example 2.

Example 1 was repeated. The reactor temperature was maintained at 360°C and the pressure was varied between of 10-30barg.

A gas oil containing 32ppm of total sulphur (expressed as elemental S) was passed to the hydrogen saturator wherein it was saturated with gaseous hydrogen and then subsequently passed to the reactor with a Liquid Hourly Space Velocity LHSV of

between 1-45 h'1. The gas oil exiting the reactor was passed to hydrogen sulphide removal zone wherein the hydrogen sulphide was removed The sulphur content of the gas oil product was monitored at different reactor pressures and at different contact times. The results are shown in table 2.

Table 2 Pressure (barg) Temperature (°C) LHSV (h-l) S-content (ppm) 30 360 1. 1 : 5 30 360 43.1 6 10 360 1.4 zu 10 360 10. 1 6 Example 2 illustrates that a product with less than l Oppm can be produced from a gas oil that has been already pretreated.

Example 3 The catalyst was replaced with a fixed bed of a US-Y zeolite containing 42% by weight of Al203 and 2.7% by weight of Re203. The zeolite was pretreated with nitrogen at 200°C for 1 hour. The reactor temperature was varied between 300-360°C and the pressure was varied between of 10-30barg.

A gas oil containing 32ppm of total sulphur (expressed as elemental S) was passed to the hydrogen saturator wherein it was saturated with gaseous hydrogen and then subsequently passed to the reactor with a Liquid Hourly Space Velocity LHSV of between 7-35 h-1. The gas oil exiting the reactor was passed to hydrogen sulphide removal zone wherein the hydrogen sulphide was removed The sulphur content of the gas oil product was monitored at different reactor temperatures, pressures and at different contact times. The results are shown in table 3.

Table 3 Pressure (barg) Temperature (°C) LHSV (h-l) S-content (ppm) 50 300 8 28 50 330 7 19 50 360 7 11 50 360 35 14

Example 4.

The US-Y zeolite was replaced with a copper-cerium on zeolite catalyst. The reactor temperature was varied between 300-360°C and the pressure was maintained at 50barg.

A gas oil containing 32ppm of total sulphur (expressed as elemental S) was passed to the hydrogen saturator wherein it was saturated with gaseous hydrogen and then subsequently passed to the reactor with a Liquid Hourly Space Velocity LHSV of between 6.9-7. 3 h-l. The gas oil exiting the reactor was passed to hydrogen sulphide removal zone wherein the hydrogen sulphide was removed The sulphur content of the gas oil product was monitored at different reactor temperatures and different contact times. The results are shown in table 4.

Table 4 Pressure (barg) Temperature (°C) LHSV (h-1] S-content (ppm) 50 300 6. 9 18 50 330 7 13 50 360 7. 3 8