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US20070227951A1 - Novel Process for Removing Sulfur from Fuels - Google Patents

Novel Process for Removing Sulfur from Fuels Download PDF

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US20070227951A1
US20070227951A1 US11/598,000 US59800004A US2007227951A1 US 20070227951 A1 US20070227951 A1 US 20070227951A1 US 59800004 A US59800004 A US 59800004A US 2007227951 A1 US2007227951 A1 US 2007227951A1
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fuel
sulfur
catalyst
compounds
contacting
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Jeyagorwy Thirugnanasampanthar
Rong Xu
Frits Dautzenberg
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Agency for Science Technology and Research Singapore
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    • C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
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    • C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
    • C10G21/06—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents characterised by the solvent used
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    • C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
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    • C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
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    • C10G25/02—Refining of hydrocarbon oils in the absence of hydrogen, with solid sorbents with ion-exchange material
    • C10G25/03—Refining of hydrocarbon oils in the absence of hydrogen, with solid sorbents with ion-exchange material with crystalline alumino-silicates, e.g. molecular sieves
    • C10G25/05—Removal of non-hydrocarbon compounds, e.g. sulfur compounds
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    • C10G27/00—Refining of hydrocarbon oils in the absence of hydrogen, by oxidation
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    • C10G45/00—Refining of hydrocarbon oils using hydrogen or hydrogen-generating compounds
    • C10G45/02—Refining of hydrocarbon oils using hydrogen or hydrogen-generating compounds to eliminate hetero atoms without changing the skeleton of the hydrocarbon involved and without cracking into lower boiling hydrocarbons; Hydrofinishing
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    • C10G53/00—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes
    • C10G53/02—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only
    • C10G53/04—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only including at least one extraction step
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    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
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    • C10G53/00—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes
    • C10G53/02—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only
    • C10G53/08—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only including at least one sorption step
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    • C10G53/00—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes
    • C10G53/02—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only
    • C10G53/14—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only including at least one oxidation step
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
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    • C10G67/00—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only
    • C10G67/02—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only
    • C10G67/04—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only including solvent extraction as the refining step in the absence of hydrogen
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    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
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    • C10G67/00—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only
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    • C10G67/06—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only including a sorption process as the refining step in the absence of hydrogen
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
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    • C10G67/00—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only
    • C10G67/02—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only
    • C10G67/12—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only including oxidation as the refining step in the absence of hydrogen
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
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    • C10G67/00—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only
    • C10G67/02—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only
    • C10G67/14—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one process for refining in the absence of hydrogen only plural serial stages only including at least two different refining steps in the absence of hydrogen

Definitions

  • This invention relates to a novel process for removing sulfur-containing organic compounds from fuels by oxidative desulfurisation.
  • HDS hydro-desulfurization
  • HDS is less effective in removing certain residual sulfur-containing compounds present in petroleum distillates, particularly heterocyclic sulfur-containing compounds such as thiophenes, benzothiophenes (BT), dibenzothiophenes (DBT), especially DBTs having alkyl substituents on their 4 and/or 6 positions (Ind. Eng. Chem. Res. 2002, 41, 4362-4375), as well as higher homologs of these compounds.
  • heterocyclic sulfur-containing compounds such as thiophenes, benzothiophenes (BT), dibenzothiophenes (DBT), especially DBTs having alkyl substituents on their 4 and/or 6 positions (Ind. Eng. Chem. Res. 2002, 41, 4362-4375), as well as higher homologs of these compounds.
  • BT benzothiophenes
  • DBT dibenzothiophenes
  • heterocyclic sulfur compounds may be removed by optionally increasing the severity of HDS reaction conditions, the onset of other side reactions leading to the formation of coke, degradation of the octane level of the fuel, as well as the accompanying increase in energy and hydrogen consumption, makes the HDS option undesirable from an economic perspective.
  • Deep desulfurisation is carried out on fuels which have already undergone HDS and thus have sulfur contents that have been lowered from the initial level of several thousand ppm to several hundred ppm. Deep desulfurisation is thus distinguished from conventional HDS in that it the oxidation of sulfur occurs at a sulfur concentration that is by comparison much lower. From the perspective of reaction kinetics, reactions that are first order or higher with respect to the reactant become more difficult to carry out as the concentration of the reactant becomes gradually lower.
  • One current approach to the deep desulfurisation of fuels include the use of transition metal adsorbents for removing the sulfur compounds, as disclosed in US Patent Application No. 2004/0007506, for example.
  • ODS oxidative desulfurisation
  • fuel is contacted with oxidants such as hydrogen peroxide, ozone, nitrogen dioxide, and tert-butyl-hydroperoxide, in order to selectively oxidise the sulfur compounds present in the fuel to polar organic compounds.
  • oxidants such as hydrogen peroxide, ozone, nitrogen dioxide, and tert-butyl-hydroperoxide
  • polar compounds can be easily separated from the hydrophobic hydrocarbon based fuel via solvent (liquid) extraction using solvents such as alcohols, amines, ketones or aldehydes, for example.
  • U.S. Pat. No. 3,847,800 discloses an ODS process in which nitrogen dioxide gas is used as an oxidant to oxidise sulfur-containing compounds in diesel fuel. Methanol and ethanol are subsequently used as non-miscible solvents for extracting the oxidised compounds.
  • the European Patent Application No. EP 0 565 324 A1 discloses a method of recovering organic sulfur compounds from liquid oil.
  • the method involves a pure redox-based process between the sulfur compounds and the oxidant.
  • the liquid oil to be processed is treated with an oxidising agent, such as ozone gas, chlorine gas, peracetic acid or hydrogen peroxide to oxidise the sulfur compounds in the oil into sulfones or sulfoxides.
  • an oxidising agent such as ozone gas, chlorine gas, peracetic acid or hydrogen peroxide to oxidise the sulfur compounds in the oil into sulfones or sulfoxides.
  • the oxidised products are separated using a combination of means such as distillation, solvent extraction and adsorption.
  • gaseous or liquid oxidants such as hydrogen peroxide, ozone, dioxirane and ethylene oxide to convert the sulfur compounds present in fuels into sulfones is also disclosed in U.S. Pat. No. 6,160,193.
  • the oxidants are contacted with fuel in liquid phase, and the oxidised products thus formed are subsequently extracted from the fuel by adding dimethyl sulfoxide to the reaction mixture.
  • metal catalysts can be used to accelerate the decomposition of the hydrogen peroxide to form the reactive oxidising species.
  • the dimethyl sulfoxide forms an aqueous phase which is separable from the hydrocarbon phase by gravity separation or centrifugation. Oxidation is reportedly carried out at about 30° C. to 100° C. at pressures of about 150 psig (about 12.5 bars) or preferably at a pressure of 30 psig (about 2.5 bars).
  • U.S. Pat. No. 6,402,940 further discloses a method for the oxidative removal of sulfur using an oxidising aqueous solution that comprises hydrogen peroxide and formic acid in specific molar ratios.
  • This oxidising solution is mixed with liquid fuel at temperatures of 50 to 130° C., thereby oxidising the sulfur compounds into polar compounds.
  • the polar compounds are subsequently removed by simple extraction and phase separation.
  • the PCT application WO 03/051798 discloses a method for carrying out ODS in which the fuel and oxidant are contacted in the gas-phase.
  • the fuel is first vapourised and then contacted with a supported metal oxide catalyst in the presence of oxygen.
  • Sulfur is liberated from hydrocarbon molecules in the fuel as sulfur dioxide gas, which is subsequently removed with an ion exchange column.
  • oxidative desulfurisation processes the removal of sulfur-containing compounds from petroleum-based hydrocarbon fuels is carried out by oxidising the sulfur-containing compounds using a suitable oxidant.
  • the sulfur containing compounds are converted into compounds having increased polarity relative to the fuel, and then subsequently extracted.
  • oxidation is accomplished by contacting liquid fuel with air in the presence of transition metal oxide catalysts that selectively facilitates the oxidation of the residual sulphur compounds.
  • One advantage of the invention comes from the use of gaseous oxygen found in air. While costly oxidants such as hydrogen peroxide or ozone are required in some of the current desulfurisation processes, the present process only requires the use of air as oxidant. Since air is abundant and freely obtainable from the atmosphere, the present process can be carried out very economically. The use of air also eliminates the need to carry out any oxidant recovery process that is usually required if liquid oxidants such as hydrogen peroxide are used.
  • Another advantage of the inventive process comes from treating fuel in liquid phase, which allows mild process conditions (low process temperatures and pressures) to be used for the efficient oxidation of sulfur compounds, as compared to other desulfurisation processes known in the art in which more severe conditions are needed.
  • Mild process conditions also mean that energy consumption for the process is low, thus resulting in further cost savings.
  • Yet another advantage of the present invention is the ease of integration into any existing refinery for the production of diesel, as afforded by the mild process conditions of liquid phase contacting and the use of air.
  • the use of a selective oxidation catalyst also permits the tuning of experimental parameters such as temperature and contacting time to achieve optimal conversion and selectivity. Conversions as high as 95% have been achieved in the present invention.
  • the present process is suitable for processing fuels having sulfur content ranging from several hundred to several thousand parts per million (ppm) by weight, effectively reducing the sulfur content to less than 100 ppm.
  • Sulfur content of a fuel that is to be treated may vary, depending for example on the geographical location from which the original crude oil is obtained, as well as the type of fuel treated (e.g. whether the fuel is cracked or straight run).
  • the present invention is sufficiently versatile to be implemented as a primary desulfurisation process or as a secondary desulfurisation process for treating fuels.
  • fuels which can be treated by this invention include gasoline, kerosene, diesel, jet fuel, furnace oils, lube oils and residual oils.
  • the fuels that can be processed are not limited to straight-run fractions, i.e. fractions obtained directly from atmospheric or vacuum distillation in refineries, but include cracked fuels and residues which are obtained from catalytic cracking of heavy crude oil fractions.
  • the invention can substitute conventional HDS processes to process straight-run fuels which typically have high sulfur content of several thousand ppm, even up to 10000 ppm (1%) or more.
  • the present invention can be used for treating fuels that have been undergone HDS treatment and thus have sulfur content of 500 ppm or less.
  • HDS is first carried out to lower sulfur content to the range of about 300 to 800 ppm.
  • the process of the present invention can be used to further lower sulfur content to less than 100 ppm or even less than 50 ppm, if desired.
  • the initial removal of high levels of sulfur from fuel is more suitably carried out by a conventional HDS process.
  • the fuel comprises diesel that has been treated in a hydrodesulfurization (HDS) process.
  • HDS hydrodesulfurization
  • the present process is most preferably used-for processing low viscosity fuels such as diesel and other fuels having viscosities that are comparable or lower than diesel. Nevertheless, if required, this process can still be applied to heavier fractions such as lube oils and residual oils.
  • lowered sulfur content refers to fuel that has sulfur content of less than 500 ppm by weight.
  • the present invention is able to reduce sulfur content in fuels to less than 500 ppm, preferably less than 200 ppm, and more preferably less than 100 ppm, and most preferably less than 50 ppm.
  • Sulfur-containing compounds that are typically found in petroleum fractions and which can be removed by the process of the invention include aliphatic or aromatic sulfur-containing compounds such as sulfides (e.g. diphenylsulfide, dibutylsulfide, methylphenylsulfide), disulfides, and mercaptans, as well as heterocyclic sulfur-containing compounds such as thiophene, benzothiophene (BT), dibenzothiophene (DBT), 4-methyl-dibenzothiophene (mDBT), 4,6-dimethyl-dibenzothiophene (dmDBT) and tribenzothiophene, and other derivatives thereof, for example.
  • sulfides e.g. diphenylsulfide, dibutylsulfide, methylphenylsulfide
  • disulfides e.g. diphenylsulfide
  • mercaptans e.g. diphenyl
  • Simple sulfur-containing compounds such as aliphatic or aromatic mercaptans and sulfides are generally more easily oxidized than heterocyclic sulfur-containing compounds.
  • Heterocyclic compounds typically comprise thiophenic substances such as thiophenes, BT, DBT, akylated DBTs such as 4-methyl-dibenzothiophene, 4,6-dimethyl-dibenzothiophene as well as other higher boiling point derivatives.
  • One possible reason for the resistance to oxidation in the latter class of sulfur-containing compounds is the shielding of the sulfur by bulky hydrocarbon structures in the molecule. This class of sulfur-containing compounds are not easily oxidised or decoupled from the hydrocarbons by means of conventional HDS processes, and have thus become known as ‘hard’ or ‘refractory’ sulfur compounds.
  • the conversion of thiophenic compounds into polar sulfones and/or sulfoxides using air as oxidant is the principal reaction carried out in the invention.
  • the general reaction scheme for the ODS process is as follows: As can be seen from scheme (I), the sulfones can decompose to liberate SO 2 , while leaving behind a useful hydrocarbon compounds that can be utilised.
  • Air is utilised in the present invention to oxidise the residual sulfur compounds mainly into their corresponding sulfones. While it is theoretically possible that some of the thiophenic sulfur compounds may be converted into other oxidised forms than sulfones, e.g. sulfoxides, gas chromatography data obtained from experiments according to the examples reveal that virtually no other sulfur compounds were formed. Without wishing to be bound by theory, it is believed that the sulfoxide species is unstable and will be oxidised into a corresponding sulfone by the process of the present invention. Accordingly, the present invention can be employed to convert sulfur compounds in fuels almost completely into sulfones, which can subsequently be extracted in a convenient manner.
  • the contacting of fuel with air can typically be carried out in any suitable continuous flow or batch reactor.
  • Suitable continuous-flow reactors can, for example, be any commercially available tubular or packed-bed column reactor.
  • Typical single fixed bed catalyst packing configurations found in hydrodesulfurisation processes can be used in the present invention.
  • the transition metal oxide catalyst can be held in any commercially available structured packing that can improve contact between the fuel, air and the metal oxide catalyst.
  • the treated fuel leaving the ODS reactor contains both desulfurised fuel and oxidised sulfur compounds which can be readily separated by means of any suitable separation process such as solvent extraction or distillation.
  • a batch reactor If a batch reactor is used, a fixed amount of fuel can be placed in the batch reactor while air is bubbled into the fuel. Once the reaction is complete, the oxidised sulfur compounds may be separated from the treated fuel using any suitable separation technique. If desired, treated fuel may be processed in a second run of the oxidation process to further reduce sulfur content in the fuel.
  • the contacting of fuel with air is carried out at a temperature range of between 90° C. to 250° C., more preferably from 90° C. to 200° C.
  • the choice of the reaction temperature is typically influenced by factors such as the boiling range of the fuel being treated and the desired level of conversion.
  • the boiling point of fuels that can be processed typically range from less than 100° C. to several hundred degrees Celsius. For example, if the boiling range of the fuel is above 180° C., a reaction temperature range of 130° C. to 180° C. is used. Fuels having such a boiling range include kerosene, diesel, gas oil and heavy gas oils.
  • one advantage of the present invention is that the treatment of fuel takes place in the liquid phase, meaning that the contacting generally takes place at temperatures lower than the boiling range of the fuel for a given reaction pressure. It is known that an elevated reaction temperature is desirable for improving the kinetics of the oxidation reaction, thereby obtaining higher conversion levels. However, due to the exothermicity of the oxidation reaction, high temperatures can be inhibitory from a thermodynamic viewpoint. Furthermore, an elevated temperature is associated with unwanted side reactions that can result in the formation of undesirable polymers and coke. Accordingly, an optimal reaction temperature range that takes into consideration these opposing factors would be beneficial in carrying out the invention.
  • the contacting of fuel with air is carried out at a temperature range of about 110° C. to 190° C., and preferably between 130° C. and 180° C., and more preferably between 130° C. to 160° C.
  • a particularly preferred temperature range is between 130° C. and 150° C., including about 130° C. to 140° C., or even more preferably about 140° C.
  • a preferred reaction temperature is about 150° C.
  • a preferred reaction temperature is about 130° C.
  • reaction pressures that are typically used in the invention may be about 1 bar or may range from less than 1 bar to slightly above 1 bar (about 1.2 bar) or about 2.5 bars or about 5 bars. Carrying out the oxidation reaction at elevated reaction pressures may be advantageous as the elevated pressure may improve the oxidant concentration in the reaction system.
  • the contacting takes place at ambient pressure, meaning at about 1 bar.
  • the oxidation reaction which is carried out in the present invention involves the use of air as the (sole) oxidant for carrying out the oxidation of sulfur-containing compounds in the fuel.
  • air as used herein is to be understood in its regular meaning.
  • the term thus refers to a mixture of atmospheric gases comprising gases such as nitrogen, oxygen, carbon dioxide, trace amounts of other gases and optionally also water vapour.
  • Gaseous oxygen is involved in the oxidation of the sulfur-containing compounds, while other gases such as nitrogen passes through the reactor without being involved in any reaction, given the mild reacting conditions of the process.
  • the oxygen content in air is typically known to be about 21% by volume, although this level of oxygen may vary.
  • the oxygen content of air that is used here may be at about its regular level in the atmosphere, i.e. 21%. It may, however, also be lower, e.g. if oxygen depleted air is used, or may be higher, if oxygen enriched air is used.
  • the flowrate of air into the reaction environment can be adjusted dynamically by implementing a conventional feedback control, based for example based on the measured oxygen content of the air introduced into the reactor.
  • the reaction environment can be dynamically supplemented with a high purity oxygen stream using a feedback control.
  • the present invention makes use of a transition metal oxide catalyst for the oxidation of the sulfur-containing compounds.
  • any transition metal oxide exhibiting catalytic activity towards the oxidation of sulfur compounds preferably hard sulfur compounds such as thiophenic compounds and the higher homologs thereof, may be used in the invention.
  • suitable catalytic transition metal oxides include but is not limited to oxides of transition metals such as vanadium, chromium, manganese, cobalt, nickel, zirconium, niobium, molybdenum, rhenium, tantalum, and tungsten.
  • Specific examples of transition metal oxides include MnO 2 , Cr 2 O 3 , V 2 O 5 , NiO 2 , MoO 3 and Co 3 O 4 .
  • transition metal oxides are those that exhibit highly catalytic activity towards the selective oxidation of sulfur containing compounds, especially thiophenic compounds.
  • the transition metal oxide is an oxide of a metal selected from Groups 6, 7, 8 or 9 of the Periodic Table (IUPAC 1990), with oxides of manganese, cobalt, iron and chromium being presently preferred in the invention.
  • the catalyst may comprise a single transition metal oxide or a mixture of transition metal oxides.
  • the transition metal oxide catalyst can be present in a single or in multiple oxidation states.
  • Solid catalysts are preferably used in the invention.
  • the catalyst can be present in any useable form, such as powders, pellets, extruded structures, monoliths or crushed structures, for example.
  • Conventional techniques can be used prepare the catalysts in the desired form for use in the present invention. For example, in order to prepare powder catalysts, it is possible to calcine the corresponding metal nitrates or metal acetates under static air for 3 hours, using a calcination temperature in the range of 500-600° C. in order to obtain the metal oxides.
  • the heating rate can be pre-determined by thermal gravimetric analysis.
  • solid catalysts are preferably employed in the form of porous pellets.
  • Porous catalyst pellets are commonly known and can be produced according to any conventional method. For example, it is possible to mix the catalyst components into a paste and extrude the paste as pellets, which are then baked at a high temperature. In order to obtain supported catalysts, it is possible to dope a support pellet with the transition metal oxide catalyst by immersing the support pellet in a salt solution of the transition metal. Additionally, pellets can adopt any suitable shape, including pellets that are spherical, cylindrical, star shaped or ring shaped, for example.
  • the catalyst used is mounted/supported on a porous support.
  • Supported catalysts are typically porous pellets having catalytic material deposited as a thin film onto its surface.
  • the porous support can comprise a chemically inert material having no effect on the oxidation reaction, or it can comprise a material that exerts a promoting effect on the catalyst which it supports, thereby improving the oxidation ability of the catalyst, e.g. silica carrier promotes chromia catalyst.
  • catalyst pellets can comprise solely of catalytic material, it is usually not economically attractive since a substantial mass of catalytic material remains locked within the pellet and is thus not effectively exposed for contact with reactants.
  • porous support helps to increase the surface area to volume ratio of the supported catalyst, thus providing a larger surface area for the oxidation reaction to take place.
  • any variety of porous support may be used, including microporous (d ⁇ 2 nm), mesoporous (2 ⁇ d ⁇ 50 nm) and macroporous (d ⁇ 50 nm) supports.
  • Materials which can be used as the porous support include metal oxides such as titania, alumina, ceria, magnesia, zirconia and tin oxide.
  • Refractory materials that can withstand high reaction temperatures, such as ceramic materials can also be used, and examples include silica or alumina based ceramic materials.
  • Suitable materials include activated carbon, as well as members of the zeolite mineral group, for instance Y-zeolites, mordenite, clinoptilolite, chabazite, and phillipsite. It is presently possible that the support comprises one single material or a mixture or combination of several materials, such as amorphous silica-alumina.
  • the support comprises aluminium oxide (alumina), preferably ⁇ -alumina.
  • Alumina supports can be in the form of pellets or extrudates, and can be obtained by any conventional method, such as drop coagulation of an alumina suspension, or via agglomeration.
  • catalyst and support that are suitable for use in the invention include CoO/Al 2 O 3 , Co 3 O 4 /Al 2 O 3 , MnO 2 /Al 2 O 3 , Mn 2 O 3 /Al 2 O 3 , CoO;Co 3 O 4 /Al 2 O 3 , Co 3 O 4 ;MnO 2 /Al 2 O 3 , CoO;MnO 2 /Al 2 O 3 , CoO/SiO 2 , Co 3 O 4 /SiO 2 , MnO 2 /SiO 2 , Mn 2 O 3 /SiO 2 , CoO;Co 3 O 4 /SiO 2 , Co 3 O 4 ;MnO 2 /SiO 2 , CoO;MnO 2 /SiO 2 , MoO 2 /Al 2 O 3 , MoO 3 /Al 2 O 3 , Ru/SiO 2 , Mg;Al/SiO 2 , CoO 2
  • catalyst loading is defined as the weight percentage of transition metal oxide present with respect to the support, preferably with respect to the weight of the support before loading the support with the catalyst.
  • catalyst loading can be determined once calcination has been carried out on the catalyst in which the transition metal salt is converted into the corresponding transition metal oxide.
  • the respective metal will be present after calcination as a homogenous oxide with a uniform oxidation state, for example as MnO 2 , NiO 2 , or Co 3 O 4 .
  • ICP Inductively coupled plasma spectroscopy
  • SEM Scanning Electron Microscopy
  • EDAX X-Ray
  • Loading levels that fall below the optimal range may result in lower yields, while loading levels that are increased above the empirically determined optimal range may provide diminishing returns in terms of conversion.
  • the catalyst loading is in the range of 1 to 17%, more preferably between 2 to 13%, of the weight of the support used.
  • any conventional impregnation method known in the art may be used to prepare the catalysts. Such methods include incipient wetness, adsorption, deposition and grafting. If the incipient wetness method is used, for example, a solution containing a salt of the catalytic transition metal is first prepared. The support on which the catalyst is to be mounted may be subjected to pre-drying at elevated temperatures overnight before impregnation. This drying step helps to remove the adsorbed moisture from the pores and to fully utilize the pores for efficient and uniform impregnation of the metal salt solution. The concentration of the salt solution is prepared according to the desired catalyst loading level.
  • log of pre-dried ⁇ -alumina can be impregnated in a solution containing 1.409 g of Mn(II) acetate ⁇ 4H 2 O (molecular weight 245.09) dissolved in 8.0 ml deionised water.
  • Mn(II) acetate ⁇ 4H 2 O molecular weight 245.09
  • the wetted support is subsequently left to dry. The drying may be carried out by baking the wetted supports in an oven to calcine the catalyst. Calcination of the metal salt leads to the formation of a layer of metal oxide on the support.
  • the impregnation and baking steps can be sequentially performed with the salt solution of each respective transition metal.
  • the salt that is used to prepare a salt solution is known as the catalyst precursor.
  • Suitable precursors include crystalline salts of the transition metal such as nitrates, chlorides, sulphates, bromides, iodides, phosphates, carbonates, as well as organic compounds of the metals, such as acetates, benzoates, acrylates and alkoxides. It should be noted that in order to form a solution using these salts, they should be water soluble or soluble in an organic solvent. Methods of preparing suitable supported or bulk catalysts for use in the present invention are described in Example 1 as well as taught in WO 03/051798 and the references cited therein, for example.
  • the catalyst formulation can additionally include other components, such as promoters which can enhance catalyst activity or prolong the process lifespan of the catalyst. It may also be desirable that the catalysts are presulfided before use.
  • the process of the present invention may be supplemented by other suitable pre- or post-treatment steps.
  • the fuel to be treated can be subjected to prior chemical or thermal treatment before it is contacted with air. It is also possible to pre-heat the process air prior to introducing the air into the reactor. Once the contacting has been performed, it is also possible to carry out a variety post-processing steps, such as separation steps to separate the oxidised sulfur compounds from the fuel or to remove any sulfur dioxide gas from the exhaust air prior to releasing it into the atmosphere.
  • one embodiment of the present invention further comprises adding a polar organic solvent to the treated fuel after contacting with air, thereby extracting the oxidised sulfur-containing compounds from the treated fuel, and separating the polar organic solvent and the oxidised sulfur-containing compounds from the treated fuel.
  • This embodiment is based on liquid-liquid extraction using polar solvents that are insoluble in the hydrocarbon fuel.
  • the choice of solvent is influenced by several factors, such as selectivity of the oxidised sulfur compounds in the solvent, density of the solvent, insolubility of the solvent in the treated fuel, and recoverability of the solvent.
  • selectivity of the oxidised sulfur compounds in the solvent is the selectivity of the solvent towards the polar oxidised sulfur-containing compounds.
  • organic compounds having high polarity, as observed from their Hildebrand's solubility parameter are selective towards the solvation of the oxidised sulfur compounds.
  • Selectivity of extraction is important because the extraction of valuable carbonyl and aromatic hydrocarbons from the fuel should be minimised.
  • the selected fuel should preferably also be one that is immiscible (partition coefficient) in the fuel and has a different density from the treated fuel, so that the fuel/solvent mixture can be easily separated by conventional means such as gravity separation or centrifugation. It may also be helpful to choose a solvent that has a boiling point that is different from the boiling point of the sulfones to be extracted, so that distillation can be readily carried out to separate the sulfones from the solvent subsequently.
  • Various types of equipment can be used for solvent extraction, and its selection can depend on factors such as cost, size of equipment or process throughput, for example.
  • a single stage mixer-settlers can be used, or if better extraction is desired, multi-stage cascades may be used instead.
  • sieve tray extraction towers may also be used.
  • the extracting step between about 1 to 4 parts by volume of fuel is contacted with about 1 part by volume of polar organic solvent.
  • the quantity of solvent used in solvent extraction affects the extent of extraction. While increasing the quantity of solvent improves the extraction of the oxidised sulfur compounds from the fuel, this advantage is counteracted by other considerations such as increased costs due to the larger amounts of solvent being used as well as increase in the scale of solvent recovery operations.
  • polar organic substances can be used for the solvent extraction of the oxidised sulfur compounds. These include acetonitrile (AcN), dimethyl sulfoxide, N,N′-dimethyl-acetamide, N-methyl-pyrolidinone, trimethylphosphate, hexamethylphosphoric amide, methanol (MeOH), ethanol, propanol, butanol, carbon disulfide, pyridine, propylene glycol, ethylene glycol or any mixture thereof etc.
  • the polar organic solvent comprises N,N′-dimethyl-formamide (DMF), 1-methyl-2-pyrrolidone (NMP), acetone or any mixture thereof.
  • the solvent can also be diluted with water, if desired.
  • the polar organic solvent and the dissolved oxidised sulfur compounds can be separated from the fuel by gravity separation or centrifuging.
  • the organic solvent can subsequently be recovered using any conventional separation method, such as evaporation, distillation or chromatography, to recover the solvent for recycle.
  • the desulphurised fuel can be further processed, such as by washing with water or adsorption using silica gel or alumina, to remove traces of the solvent.
  • the fuel thus obtained has sulfur-content of typically less than 100 ppm, or preferably less than 50 ppm.
  • the treated fuel is contacted with a basic adsorbent.
  • the basic adsorbents used herein should exhibit a tendency towards the preferential adsorption of any acidic species present in the fuel.
  • the contacting step in this embodiment can be advantageously carried out after the separation/extraction step to eliminate remaining traces of the sulfones in the fuel.
  • sulfones are weakly acidic in nature
  • the use of a basic adsorbent can remove them as well as other acidic impurities such as other sulfur-based or nitrogen-based impurities from the fuel.
  • Examples of such basic adsorbents include zeolites, activated carbon, and layered-double hydroxides (LDH).
  • LDHs are preferably used in some embodiments and examples of suitable LDHs include those based on the metals Mn, Co, Ni, Cr, Al, Mg, Cu, Zn and Zr coupled with exchangeable anions such as NO 3 ⁇ , CO 3 2 ⁇ and/or Cl ⁇ , for example.
  • the adsorption process can be carried out in any suitable furnace reactor, such as in a continuous flow tube furnace with the absorbent packed as a fixed bed.
  • a base can be added to the adsorption column to regenerate the adsorbent.
  • the overall recovery that can be achieved with a combination of solvent extraction and adsorption can be as high as 92%.
  • FIG. 1 shows the simplified process flowsheet of the oxidative desulfurisation (ODS) process according to the invention.
  • FIG. 2 shows the process flowsheet of a specific embodiment of the ODS process according to the present invention.
  • ODS is carried out as a secondary desulfurisation process for fuels that have been treated by conventional HDS.
  • the treated fuel is channelled to a stirred/mixing tank containing a solvent for removing the oxidised sulfur compounds.
  • the fuel/solvent mixture is then channelled to a settler where the treated fuel is separated from the solvent.
  • FIG. 3 shows another embodiment of the process shown in FIG. 2 , in which the treated fuel is further passed through basic adsorbent column for further removal of the remaining sulfur-containing (which is slightly acidic in nature) compounds in the fuel.
  • the fuel passing out of the adsorption column is sulfur-free.
  • FIG. 4 shows the results of the analysis of the prepared catalysts based on the Brunauer, Emmett and Teller (BET) method.
  • FIGS. 5A to 5 D show the results of analysis carried out with a gas chromatography Flame Ionisation Detector (GC-FID) on model diesel before oxidation was carried out (a) and after oxidation was carried out using the present invention (b). After solvent extraction using NMP was performed, the fuel and the solvent layers were each analysed. Figures (c) and (d) shows the analysis results of the n-tetradecane layer the NMP layer, respectively.
  • GC-FID gas chromatography Flame Ionisation Detector
  • FIGS. 6A to 6 H show the individual gas chromatograms of specific samples of treated model diesel.
  • the catalyst used was 5% MnO 2 / ⁇ -alumina. Treatment temperature was 130° C.
  • FIG. 6A shows the analysis result before treatment
  • FIG. 6B shows the analysis result after treatment.
  • FIGS. 6C & 6D show the GC results of model diesel treated in the absence of catalyst at a temperature of 130° C., before treatment and after 18 hours of treatment, respectively. No oxidation was observed.
  • FIG. 6E & 6F show the GC analysis results of model diesel treated with 5% MnO 2 / ⁇ -alumina catalyst at a temperature of 150° C., before treatment and after 18 hours of treatment, respectively.
  • FIG. 6G & 6H show the GC analysis results of model diesel treated with 8% MnO 2 / ⁇ -alumina catalyst at a temp. 150° C., before treatment and after 18 hours of treatment, respectively.
  • FIG. 7 shows the conversion of DBT vs. time in model diesel at 130° C. for manganese ( ⁇ )- and cobalt ( ⁇ )-containing catalysts.
  • FIG. 8A shows the gas chromatography-atomic emission detection (GC-AED) chromatogram of untreated real diesel used in the examples.
  • FIG. 8B shows a table of data from X-ray florescence (XFR) analysis of sulfur content in untreated diesel that has undergone only solvent extraction.
  • XFR X-ray florescence
  • FIG. 9 shows a table of data from XRF analysis of sulfur content in real diesel that has been treated with either Co 3 O 4 or MnO 2 catalyst supported on ⁇ -alumina, and solvent extraction carried out with AcN, DMF, NMP and methanol. Treatment temperature was about 130° C.
  • FIG. 10 shows a table of data from XRF analysis of sulfur content in real diesel that has been treated with MnO 2 catalyst supported on ⁇ -alumina, and single or multiple solvent extraction carried out with AcN, DMF, NMP and methanol. Treatment temperature was either 130° C. or 150° C.
  • FIGS. 11A to 11 C show sulfur AED chromatograms of treated samples marked with superscript 3Ci, 3Cii and 3Ciii in the table in FIG. 10 .
  • FIG. 12 shows a table of data from XRF analysis of sulfur content in real diesel that has been treated with MnO 2 catalyst supported on ⁇ -alumina. Comparisons can be made between the effectiveness of sulfur removal employing a single solvent extraction using NMP and without employing any solvent extraction step. Treatment temperature was at 150° C. The initial sulfur content of the real diesel was 440-454 ppm. Sulfur content measurements were taken by ASTM 2622 (Brucker XRF).
  • FIG. 13 shows the graph of sulfur content in a treated fuel sample vs ratio of solvent to diesel fuel applied in the solvent extraction process. It will be noted that sulfur content is generally reduced as solvent to fuel ratio is increased.
  • the catalysts to be prepared comprise transition metal oxides and porous support with high specific surface area have been prepared by impregnation using incipient wetness method.
  • the total metal oxides loading with respect to ⁇ -alumina ranged from 2 to 13 wt %.
  • the impregnated sample was left on the roller which was set at 25 rpm for approximately 18 h to obtain better dispersion.
  • the sample was then dried at 120° C. in the oven for 18 h for removal of the water content.
  • the dried sample was calcined in a static furnace at 550° C. for 5 hours with a ramp of 5° C./min.
  • Powder X-ray diffraction (XRD) showed that the catalysts were amorphous and that no distinguishable crystallographic properties could be observed among the catalysts.
  • the prepared catalysts were also characterised by N 2 adsorption/desorption, and thermogravimetric analysis (TGA) in order to obtain the information on surface area, pore size distribution and pore volume, crystallography and thermal decomposition of the samples.
  • TGA thermogravimetric analysis
  • the BET method of measurement were used to determine the catalyst surface area.
  • the characterisation data for the prepared catalysts used in the subsequent examples are summed up in the table in FIG. 4 .
  • DBT and/or 4-MDBT were chosen to prepare model diesel by dissolving them in n-tetradecane with a total sulphur content of 500-800 ppm.
  • sulfur content in the model diesel was introduced by adding only DBT.
  • both 4-MDBT and DBT were added.
  • the oxidation experiments were carried out in a stirred batch reactor.
  • the mixture was then transferred into a separating funnel for the model diesel and polar organic solvent to be separated into different layers.
  • the thus-treated model diesel was analysed with GC.
  • the sulphur-containing polar solvent layer was then collected and analysed by GC.
  • the methanol solvent was removed by the rotary evaporator.
  • the remaining solid product was collected and analysed by the GC after re-dissolving into methanol or NMP (1-methyl-2-pyrrolidone) solvent.
  • FIGS. 5A to 5 D shows the results of sulfur analysis from a gas chromatography-atomic emission detector (GC-FID) of the model diesel before and after the oxidative process of the present invention carried out on model diesel.
  • GC-FID gas chromatography-atomic emission detector
  • FIGS. 6A-6D show that the catalyst is important for the selective oxidation of dibenzothiophene to corresponding sulfone at 130° C.
  • FIGS. 6E-6H further show that the catalytic activity of 5-8% MnO2 loaded on gamma alumina for model diesel and a reaction temperature of 150° C. provide advantageous conditions for selective oxidation of dibenzothiophene without oxidising the hydrocarbons such as tetradecane or pentadecane.

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