oxidative desulfurization process of heavy fuel oil

Abstract

The present invention relates to a process for the oxidative desulfurization of at least one heavy fuel oil, employing a catalyst in the form of platelets having a two-dimensional hexagonal ordered mesoporous structure, and to the use of such a catalyst in the form of platelets having a two-dimensional hexagonal ordered mesoporous structure, for the oxidative desulfurization of at least one heavy fuel oil. Figure for the abstract: Fig. 1

Description

Title of the invention: Oxidation desulfurization process for heavy fuel oil

[0001] The present invention relates to an oxidative desulfurization process (oxidative desulfurization) of at least one heavy fuel oil using a catalyst in the form of platelets having a 2-dimensional hexagonal ordered mesoporous structure, as well as the use of such a catalyst in the form of platelets having a 2-dimensional hexagonal ordered mesoporous structure, for the oxidative desulfurization of at least one heavy fuel oil.

[0002] Regulations concerning the use of low-sulfur marine fuels have been evolving rapidly in recent years. The MARPOL Convention (International Convention for the Prevention of Pollution from Ships), and in particular Annex VI, has mandated since January 1, 2015, the use of fuels on board ships with a maximum sulfur content by mass of 0.1% in emission control areas and 3.5% in the rest of maritime waters. Then, since January 1, 2020, the international maritime organization has limited this maximum sulfur content by mass in marine fuels to 0.5% for all ships operating outside emission control areas. Heavy fuel oil (also known by its English name, "Heavy Fuel Oil," or HFO) is a refining product whose quantity tends to be minimized in refineries in favor of higher value-added products such as diesel.However, its production and consumption remain high, particularly for use as marine fuel. The sulfur content of heavy fuel oil depends on its geographical origin and refining processes, but can legally reach up to 3.5%, which is 3500 times higher than the limit permitted in gasoline used on land.

[0003] On board ships, compliance with regulations is achieved either by using a different grade of fuel oil with a content below the maximum permitted mass content, or by using alternative fuels such as liquefied natural gas, or by implementing flue gas treatment using scrubbers. The use of alternative fuels such as liquefied natural gas requires a complete change in ship technology (propulsion system), which represents a significant cost. Scrubbers spray seawater (or sometimes fresh water) or another aqueous liquid into the ship's exhaust system to precipitate a large portion of the SOx (sulfur oxides) and soot, thus complying with gas emission requirements.However, the acidic, heavy-metal-laden polluted water and sludge generated by this scrubbing process can then be discharged directly into the sea when the treatment is carried out in an open circuit. Furthermore, the flue gas scrubbers put into operation... Methods used for SOx cannot be applied to NOx (nitrogen oxides), which are also subject to increasingly strict limit values. Post-combustion treatment of NOx requires catalytic flue gas scrubbers, the action of which is inhibited by SOx adsorbed onto the catalyst.

[0004] In order to comply with permitted limits, one method that could allow for the production of cleaner fuel from the highly sulfurous residues produced annually by refineries, without modifying ship technology, is desulfurization. Hydrodesulfurization (HDS) is one of the most commonly used processes for reducing the amount of sulfur in light cuts or fractions (such as gasoline, kerosene, and light diesel) obtained from the atmospheric distillation of crude oil. Hydrodesulfurization is carried out in the presence of dihydrogen to form hydrogen sulfide (H2S). It is performed in the presence of a catalyst, for example, consisting of an alumina (Al2O3) support onto which an active phase, generally molybdenum sulfide promoted by cobalt or nickel (CoMoS / NiMoS phase), is deposited.However, the hydrodesulfurization of heavy fuel oils uses dihydrogen under high pressure (up to 200 bar) and high temperature (up to 400°C) conditions, with significant constraints in terms of safety and energy and hydrogen consumption. Furthermore, polycyclic aromatic sulfur compounds such as dibenzothiophene, a major organosulfur compound in marine fuel oil, or 4,6-dimethyldibenzothiophene, are refractory to hydrodesulfurization. Another method involves chemically oxidizing sulfur compounds present in a mixture to generate sulfone groups (R-SO2-R') from sulfide groups (RS-R') incorporated within these sulfur compounds. This chemical oxidation then allows the polarized oxidized compounds to be separated from the rest of the mixture by extraction or adsorption methods.However, the vast majority of prior art oxidative desulfurization processes use model fuels or light fractions with low sulfur content and are not suitable for reducing the sulfur content of heavier fractions and / or high sulfur fractions, and / or for scaling up to industrial production.

[0005] A recent publication by Houda et al., 2021, Catalysis Today, 377, 221-228, describes the oxidesulfurization of marine fuel oils of the "IFO380", "IFO500", and "HSFO700" type, diluted in dodecane or undiluted, with hydrogen peroxide and a catalyst comprising molybdenum oxide supported by alumina. The described process exhibits moderate to low efficiency on the heaviest marine fuel oil, "HSFO700". In particular, dilution of the heavy fuel oil is required to carry out the oxidesulfurization.

[0006] The object of the present invention is therefore to overcome the drawbacks of art previous, and in particular to provide a process for the oxidization of heavy fuel oils which can reduce the sulfur content in order to reach regulatory limit values, while being economical, industrializable, and simple to implement.

[0007] The invention relates first to a process for the oxidization of at least one heavy fuel oil by heterogeneous catalysis, characterized in that it comprises at least the following steps: (i) the reaction of a heavy fuel oil with an oxidizing agent, in the presence of a catalyst comprising at least one metal oxide supported by mesoporous silica, to form one or more oxidized sulfur compounds, ii) the separation of the oxidized sulfur compound(s), and in that: * The catalyst is in the form of platelets and has a two-dimensional ordered hexagonal mesoporous structure, with mesopores having a length of at most approximately 300 nm. * Heavy fuel oil comprises at least 0.5% by mass of sulfur, relative to the total mass of heavy fuel oil, and has a viscosity greater than 180 cSt at 50°C, and * the metal oxide is chosen from titanium, molybdenum, and tungsten oxides.

[0008] The process according to the first object of the invention uses a catalyst based on at least one titanium oxide, at least one molybdenum oxide, or at least one tungsten oxide, supported by a particular mesoporous silica under oxidizing conditions to enable the oxidative desulfurization of a heavy fuel oil. The process is easy to implement, economical because it uses inexpensive raw materials and does not require high temperature and pressure conditions, and scalable for industrial production, while guaranteeing a substantial reduction in the amount of sulfur in heavy fuel oils.

[0009] Step i)

[0010] The International Maritime Organization has proposed a classification of marine fuel oils into different categories according to their mass content of sulfur and their viscosity in ISO 8216 and ISO 8217 standards respectively.

[0011] The heavy fuel oil used in the process of the invention has a viscosity greater than approximately 180 cSt (Centistokes) at 50°C. This corresponds to a viscosity greater than 1.8 x 10⁴ m² / s.

[0012] The heavy fuel oil used in the process of the invention preferably has a viscosity ranging from 250 cSt to 750 cSt at 50°C (i.e., ranging from 2.5 x 10⁴ m² / s to 7.5 x 10⁴ m² / s at 50°C), particularly preferably ranging from 300 cSt to 650 cSt at 50°C (i.e., ranging from 3.0 x 10⁴ m² / s to 6.5 x 10⁴ m² / s at 50°C), and more particularly preferred ranging from 380 to 550 cSt at 50°C (i.e. ranging from 3.8x10⁴ m² / s to 5.5x10⁴ m² / s at 50°C).

[0013] Viscosity can be measured according to ISO 8217, which uses the measurement methods mentioned in ISO 3104.

[0014] The heavy fuel oil used in the process of the invention comprises at least 0.5% by mass of sulfur element.

[0015] In the invention, the element sulfur corresponds to the chemical element with atomic number 16, and symbol S.

[0016] The heavy fuel oil used in the process of the invention preferably comprises at least 0.7% by mass of sulfur element, particularly preferably at least 1% by mass of sulfur element, and more particularly preferably at least 2% by mass of sulfur element, relative to the total mass of the heavy fuel oil.

[0017] The sulfur content of the heavy fuel oil used in the process of the invention can be measured by elemental analysis.

[0018] The heavy fuel oil used in the process of the invention can be an IFO type fuel oil (well known under the anglicism "Intermediate Fuel Oil"), an HSFO type fuel oil (well known under the anglicism "High Sulfur Fuel Oil"), or an RMFO type fuel oil (well known under the anglicism "Residual Marine Fuel Oil").

[0019] The heavy fuel oil used in step i) preferably has a boiling point above approximately 150°C, particularly preferably above approximately 250°C, and even more preferably above approximately 325°C. It is preferably distinguished, in particular, from diesel fuels which have a boiling point of 150°C or less.

[0020] The heavy fuel oil used in step i) preferably has a boiling point less than or equal to about 700°C, and particularly preferably less than or equal to about 650°C.

[0021] Heavy fuel oil may further comprise at least 1% by mass of C7 asphaltenes and / or at least 10 ppm (parts per million by mass) of metals.

[0022] The heavy fuel oil used in the process of the invention preferably has a density ranging from 0.991 to 1.010 at 15°C. The density can be measured according to ISO 3675.

[0023] Heavy fuel oil comprises one or more sulfur compounds which are oxidized during step i) to form one or more oxidized sulfur compounds such as sulfones.

[0024] The sulfur compounds in heavy fuel oil are, in particular, polycyclic aromatic sulfur compounds such as substituted or unsubstituted benzothiophenes, substituted or unsubstituted dibenzothiophenes, substituted or unsubstituted benzonaphthothiophenes, or derivatives of the aforementioned compounds. Examples include For example, dibenzothiophene (DBT) or 4,6-dimethyldibenzothiophene.

[0025] The metal oxide associated with the mesoporous silica represents the active phase of the catalyst. The mesoporous silica itself represents the support.

[0026] The metal oxide is then supported by the mesoporous silica.

[0027] The metal oxide is chosen from titanium oxide (TiO2), molybdenum oxide (MoO3) and tungsten (WO3), and preferably is molybdenum oxide (MoO3).

[0028] The catalyst may comprise several metal oxides supported by mesoporous silica. In this embodiment, the metal oxides are preferably chosen from mixtures of at least two of the aforementioned metal oxides.

[0029] The catalyst may comprise one or more dopants, in particular chosen from cobalt, nickel, phosphorus, and one of their mixtures.

[0030] The metal oxide (or metal oxides) preferably constitutes approximately 5 to 30% by mass, and particularly preferably approximately 10 to 20% by mass, relative to the total mass of the catalyst. When the amount of metal oxide is too high, the conversion to oxidized sulfur compounds during step i) decreases and the final sulfur content in the heavy fuel oil increases.

[0031] The catalyst is preferably made up of one or more metal oxide(s) as defined in the invention and mesoporous silica as defined in the invention.

[0032] According to a preferred embodiment of the invention, the catalyst is in the form of extrudates.

[0033] The catalyst preferably comprises (or is made up of) silicon atoms, oxygen, and at least one of the following metals: titanium, molybdenum, tungsten.

[0034] The catalyst is different from a zeolite. In other words, it does not include aluminium in its structure.

[0035] The catalyst does not preferably comprise any metals other than titanium, molybdenum, and / or tungsten.

[0036] The catalyst preferably has (before shaping) a specific surface area, measured according to the BET method, ranging from approximately 300 m2 / g to 1200 m2 / g, particularly preferably ranging from approximately 350 m2 / g to 800 m2 / g, and even more particularly preferred ranging from approximately 400 m2 / g to 600 m2 / g.

[0037] The catalyst preferably has (before shaping) a porous volume ranging from approximately 0.3 cmVg to 1.6 cmVg, particularly preferably ranging from approximately 0.5 cmVg to 1.2 cmVg, and more particularly preferably from approximately 0.7 cmVg to 1 cmVg.

[0038] The pore volume can be determined by the nitrogen adsorption / desorption method.

[0039] The catalyst has a mesoporous structure. This means that it comprises mesopores, which are defined as pores with an average diameter ranging from 2 to 50 nm. approximately.

[0040] The pore size distribution and the average pore diameter can be determined by the BJH method.

[0041] The catalyst of the invention preferably comprises pores with an average diameter ranging from 2 to 15 nm, particularly preferably ranging from about 3 to 10 nm, and more particularly preferably ranging from about 4.5 to 8 nm.

[0042] The mesopores of the catalyst of the invention preferably have walls with a thickness ranging from approximately 1 to 7 nm, and particularly preferably ranging from approximately 3 to 6 nm.

[0043] The catalyst has an ordered mesoporous structure. In other words, the mesopores are ordered or organized according to a porous network that has a well-defined periodicity.

[0044] The catalyst has a two-dimensional (2D) hexagonal mesoporous structure. In other words, the catalyst exhibits hexagonal 2D symmetry, belongs to the P6m space group, or comprises a hexagonal arrangement of tubular or cylindrical mesopores.

[0045] The mesopores of the catalyst have a length of at most 300 nm, preferably at most about 250 nm, and particularly preferably at most about 200 nm. Thanks to the presence of short, straight mesopores within the catalyst, the penetration of sulfur compounds present in the heavy fuel oil into the catalyst is facilitated, thus allowing a large exchange surface area between the active phase of the catalyst and the heavy fuel oil.

[0046] The mesoporous silica of the catalyst is preferably a mesoporous silica of type COK-12.

[0047] The oxidizing agent is preferably chosen from aqueous peroxides such as hydrogen peroxide, and non-aqueous peroxides such as tert-butyl hydroperoxide (TBHP).

[0048] The oxidizing agent is preferably an aqueous oxidizing agent.

[0049] In the invention, aqueous oxidizing agent means an oxidizing agent that is soluble in water, preferably at room temperature (i.e. 18-25°C).

[0050] Aqueous peroxides such as hydrogen peroxide are particularly preferred.

[0051] The oxidizing agent is preferably diluted in water. This allows for safe oxidative desulfurization and limits the production of organic products. In this embodiment, step i) is carried out in a two-phase medium.

[0052] During step i), the oxidizing agent / sulfur element molar ratio preferably ranges from approximately 2 to 25, particularly preferably from approximately 3 to 10, and in a manner molar ratios from approximately 3 to 6 are particularly preferred. Using such ranges helps limit the consumption of oxidizing agent. Preferably, the molar ratio is above the stoichiometric ratio of 2 due to parallel reactions.

[0053] The oxidative desulfurization process of at least one heavy fuel oil is carried out by heterogeneous catalysis. In other words, the catalyst and the heavy fuel oil are in different phases in the reaction medium used in the process, and in particular during step i).

[0054] Step i) can be carried out at a temperature ranging from approximately 50°C to approximately 100°C, and preferably from approximately 60°C to 80°C, in particular to avoid the degradation of the oxidizing agent. Furthermore, these temperatures correspond to those of the fuel oil circuit on ships, facilitating its handling.

[0055] The oxidizing agent is preferably added to the heavy fuel oil after the reaction medium has reached the required temperature, and, particularly preferably, the oxidizing agent is added at the same time as the catalyst. This prevents its degradation.

[0056] Step i) is preferably carried out at atmospheric pressure.

[0057] Step i) can last from about 5 minutes to about 48 hours, and preferably from about 20 minutes to 2 hours.

[0058] According to a particularly preferred embodiment of the invention, step i) is carried out with vigorous stirring, in particular by imposing a stirring speed greater than approximately 500 rpm. This speed facilitates oxidative desulfurization, while limiting the deterioration of the catalyst, particularly if it is in extruded form.

[0059] In particular, vigorous stirring can be achieved using a magnetic stirrer, preferably oval in shape. In this embodiment, step i) is preferably carried out in a spherical reactor. This promotes contact between the heavy fuel oil and the catalyst and the oxidizing agent, and consequently the oxidative desulfurization reaction.

[0060] Step i) can be carried out in the presence of ultrasound. This improves the contact between the two-phase system (heavy fuel oil + oxidizing agent) and the catalyst, and consequently increases the conversion of sulfur compounds into oxidized sulfur compounds.

[0061] Step i) is preferably carried out in a reactor of volume Vj and in the presence of a volume V2 of heavy fuel oil, so that the volume ratio V2 / Vi is greater than 0.1. This thus makes it possible to promote the oxidative desulfurization reaction.

[0062] According to a preferred embodiment of the invention, step i) uses undiluted heavy fuel oil (in a solvent). In other words, this oxidative desulfurization step i) does not use solvents such as nonpolar solvents. aprotic agents which would then dilute the heavy fuel oil.

[0063] Step ii)

[0064] Step ii) of separation allows the oxidized sulfur compounds to be extracted from the heavy fuel oil.

[0065] Step ii) can be carried out by liquid-liquid extraction, in particular with a polar aprotic organic solvent.

[0066] The polar aprotic organic solvent can be chosen from N,N-dimethylformamide (DMF), γ-butyrolactone, 2-ethoxyethanol, acetonitrile, methanol, λ-methyl-2-pyrrolidone (NMP), polyethylene glycol (e.g., PEG 200), and dimethyl sulfoxide (DMSO).

[0067] The polar aprotic organic solvent makes it possible to remove the oxidized sulfur compounds formed during step i).

[0068] The volume ratio [volume of polar aprotic organic solvent / volume of heavy fuel oil used in step i)] preferably ranges from 0.5 to about 3, and particularly preferably from 0.5 to 1.5.

[0069] In the case where a step A) as described below exists, the volume ratio corresponds to the volume of polar aprotic organic solvent / volume of filtrate.

[0070] In the case where a step C) as described below exists, the volume ratio corresponds to the volume of polar aprotic organic solvent / volume of dilute filtrate.

[0071] Step A)

[0072] The process may further include, before step ii), a step A) of catalyst recovery.

[0073] This step A) can be carried out by filtration. The catalyst is then obtained separated from the filtrate. The filtrate comprises the oxidized heavy fuel oil.

[0074] In this embodiment, step ii) is then carried out on the filtrate.

[0075] Step B)

[0076] The catalyst obtained at the end of step A) can be washed according to a step B), in particular with a nonpolar aprotic organic solvent, then with a polar aprotic organic solvent.

[0077] The nonpolar aprotic organic solvent can be chosen from C5-Ci2 alkanes such as pentane.

[0078] The nonpolar aprotic organic solvent makes it possible in particular to eliminate the remains of heavy fuel oil, including sulfur compounds.

[0079] The polar aprotic organic solvent can be selected from y-butyrolactone, DMF, 2-ethoxyethanol, acetonitrile, methanol, l-methyl-2-pyrrolidone (NMP), a polyethylene glycol (e.g., PEG 200), and dimethyl sulfoxide (DMSO).

[0080] The polar aprotic organic solvent makes it possible in particular to eliminate oxidized sulfur compounds which have attached themselves to the catalyst.

[0081] The catalyst thus recovered and washed can be reused in the process according to the invention according to new steps i) and ii) as defined above.

[0082] Step C)

[0083] The process may further include after step A) and before step ii), a step C) of diluting the filtrate containing the oxidized heavy fuel oil, in particular with a nonpolar aprotic organic solvent.

[0084] The nonpolar aprotic organic solvent can be chosen from alkanes such as dodecane, hexane, and decane.

[0085] In this embodiment, step ii) is then carried out on the diluted filtrate.

[0086] Step a)

[0087] The process may further include, before step i), a step a) of preparation of the mesoporous silica.

[0088] Step a) preferably involves bringing into contact, under pH conditions ranging from 3 to 7, and preferably from 3.5 to 6, a silica precursor and an organic polymer capable of forming mesopores after calcination.

[0089] The organic polymer can be a poly(alkylene oxide), and preferably a triblock copolymer of poly(alkylene oxide) such as a poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol).

[0090] The silica precursor is preferably an alkali silicate such as a sodium silicate.

[0091] The method for preparing mesoporous silica is simple to implement, economical, and rapid. It avoids methods using acidic (pH < 2) or basic (pH > 9) conditions, which can represent a constraint from an industrial standpoint.

[0092] Step a) preferably comprises the following substeps: a-1) prepare a first aqueous solution comprising the silica precursor, a-2) prepare a second aqueous solution comprising the organic polymer and an acid with a pKa in the range of 3 to 9, a-3) add said first aqueous solution to said second aqueous solution, and a-4) filter, dry and calcine the reaction product.

[0093] The acid serves as a buffer solution.

[0094] The acid can be chosen from citric acid, ascorbic acid, succinic acid, benzoic acid, glutaric acid, p-hydroxybenzoic acid, acetic acid, tartaric acid, propionic acid, malonic acid, carbonic acid, phosphoric acid, boric acid.

[0095] When the silica precursor is a sodium silicate, the Na+ / SiO2 molar ratio is preferably from about 2 to 3.

[0096] Mesoporous silica can be in powder form.

[0097] Step a) may include a step of shaping the mesoporous silica, in particular in the form of extrudates.

[0098] Step b)

[0099] The process may further include, before step i), and after step a) if it exists, a step b) of catalyst preparation.

[0100] Step b) preferably comprises impregnating a mesoporous silica in the form of platelets, having an ordered 2-dimensional hexagonal porous structure, with mesopores having a length of at most about 300 nm, with at least one precursor of a metal oxide as defined in the invention.

[0101] The precursor can be selected from ammonium heptamolybdate, molybdenum trioxide, ammonium paratungstate, titanium oxide, and titanium isopropylate.

[0102] This impregnation step b) allows for the uniform dispersion of the metal oxide within the mesoporous silica while ensuring the preservation of the porous structure of the initial mesoporous silica. It is also advantageous in that it allows for the easy, industrial, and rapid production of a high-performance catalyst for the oxidative desulfurization of heavy fuel oil.

[0103] During step b), metal oxide particles are distributed uniformly within the mesoporous silica.

[0104] The impregnation method avoids methods involving the co-condensation of a silicon precursor and a metal precursor, or the condensation of a metal precursor within porous silica, which lead to materials that differ in both pore structure and chemical structure from the catalyst of the invention. These methods employ acidic (pH < 2) or basic (pH > 9) conditions, which can represent a constraint from an industrial standpoint.

[0105] Mesoporous silica preferably has (before shaping) a specific surface area, measured according to the BET method, ranging from approximately 300 m2 / g to 1200 m2 / g, particularly preferably ranging from approximately 350 m2 / g to 800 m2 / g, and more particularly preferably ranging from approximately 400 m2 / g to 600 m2 / g.

[0106] The mesoporous silica preferably has (before shaping) a pore volume ranging from approximately 0.3 cmVg to 1.6 cmVg, particularly preferably ranging from approximately 0.5 cmVg to 1.2 cmVg, and even more particularly preferred ranging from approximately 0.7 cmVg to 1 cmVg.

[0107] Preferably, the mesoporous silica comprises pores with an average diameter ranging from 2 to 15 nm, particularly preferably from 3 to 10 nm, and more particularly preferably from 4.5 to 8 nm.

[0108] The mesopores of mesoporous silica preferably have walls having a thickness ranging from 1 to 7 nm, and particularly preferred ranging from 3 to 6 nm.

[0109] Mesoporous silica has an ordered porous structure. In other words, the mesopores are ordered or organized according to a well-defined periodicity.

[0110] Mesoporous silica has a 2D hexagonal porous structure. In other words, mesoporous silica exhibits 2D hexagonal symmetry or belongs to the space group P6m or comprises a hexagonal arrangement of tubular or cylindrical mesopores.

[0111] Mesoporous silica comprises (or consists of) a network of silica particles interlocked with one another.

[0112] The silica mesopores have a length of at most approximately 300 nm, preferably at most approximately 250 nm, and particularly preferably at most approximately 200 nm. Thanks to the presence of short, straight mesopores within the mesoporous silica, the penetration of the metal oxide during step b) is facilitated, thus allowing a homogeneous distribution of the metal oxide within the catalyst.

[0113] During step b) of impregnation, the initial structure of the mesoporous silica is therefore conserved and imparted to the catalyst.

[0114] According to a preferred embodiment of the invention, the impregnation in step b) is a dry impregnation, also called nascent moisture impregnation. In other words, step b) is carried out by limiting the amount of liquid and / or solvent, so that the volume of liquid or solvent used corresponds to the water absorption volume. The latter, expressed in cm³ per gram of support (mesoporous silica), is determined experimentally by saturating the porous volume of the support with water.

[0115] Dry impregnation can be carried out: - directly onto the shaped mesoporous silica, or - on powdered mesoporous silica (i.e. in powder form), impregnation can be followed by shaping.

[0116] The shaping is preferably extruded shaping.

[0117] Extruded materials are easier to handle, thus avoiding losses of catalyst during its recovery, and to reuse it in other oxidative desulfurizations.

[0118] Step c)

[0119] The process may further include, before step i), a step c) of purifying a heavy fuel oil.

[0120] Step c) may include diluting the heavy fuel oil in a nonpolar aprotic organic solvent, followed by centrifugation. This allows for the recovery of a liquid fuel oil with a reduced asphaltene content, or even without asphaltene.

[0121] The nonpolar aprotic organic solvent can be chosen from alkanes such as dodecane, hexane, and decane.

[0122] The invention has as its second object the use of a catalyst as defined in the first object of the invention for the oxidative desulfurization of at least one heavy fuel oil comprising at least 0.5% by mass of sulfur element, relative to the total mass of the heavy fuel oil, and having a viscosity greater than 180 cSt at 50°C.

[0123] Heavy fuel oil can be as defined in the first object of the invention. Brief description of the drawings

[0124] The accompanying drawings illustrate the invention.

[0125] [Fig-1] Fig. 1 represents low-angle X-ray diffraction incidence of the COK-12 mesoporous silica support.

[0126] [Fig.2] The [Fig.2] represents the X-ray diffraction at high angles of incidence of the mesoporous silica support COK-12, and of the “20 Mo / COK-12” catalyst implemented in the process of the invention.

[0127] [Fig.3] Fig.3 represents the pore size distributions obtained according to the B JH method and the nitrogen adsorption-desorption isotherms of the COK-12 mesoporous silica support and the "20 Mo / COK-12" catalyst in powder form used in the process of the invention.

[0128] [Fig.4] Fig.4 represents a Raman spectrum of the “20 Mo / COK-12” catalyst implemented in the process of the invention.

[0129] [Fig.5] [Fig.5] The [Fig.5] represents the chromatograms of heavy fuel oil RMG380 implemented in step i) ([Fig.5]-a), of heavy fuel oil oxidized at the end of step i) ([Fig.5]-b), of heavy fuel oil oxidized after liquid-liquid extraction ([Fig.5]-c), and of the DMF solvent after liquid-liquid extraction ([Fig.5]-d).

[0130] Other features and advantages of the present invention will become apparent from the description of non-limiting examples of the method of the invention. Examples

[0131] The raw materials used in the examples are listed below: - hydrogen peroxide, 30% by mass in water, Sigma Aldrich, - Ammonium molybdate tetrahydrate, purity > 99%, Sigma Aldrich, - butyrolactone, purity > 99%, Sigma Aldrich, - acetonitrile, environmental grade, 99.7% purity, Alfa Aesar, - 2-ethoxyethanol, 99% purity, ACROS Organics, - N,N-dimethylformamide, 99.8% purity, ACROS Organics, - n-dodecane, purity > 99%, Alfa Aesar, - triblock copolymer, marketed under the reference "P123" by BASF, - citric acid monohydrate, Riedel-de Haen, - trisodium citrate, UCB, - aqueous sodium silicate solution (10% by mass of NaOH, 27% by mass of SiO2), Merck, - boehmite, “Pural SB3”, Sasol - sodium carboxymethylcellulose, purity > 99%, Alfa Aesar - heavy fuel oil under the reference "RMG380" having a viscosity of 380 cSt at 50°C.

[0132] Unless otherwise indicated, all materials were used as received from the manufacturers.

[0133] Characterizations

[0134] The elemental analysis of the content of the elements C, H, N and S in heavy fuel oils was determined by "CHNS" analysis using an apparatus sold under the trade name "EA1110 Thermo Fisher Flash instrument".

[0135] Sulfur compounds were monitored by gas chromatography using an instrument sold under the trade name "Agilent Technologies, 7890B" coupled with a sulfur-specific chemiluminescence detector (SCD) "Agilent Technologies, 8355". A high-temperature-range column, "DB-5HT", was used. An integrated guard column was added due to the heavy nature of the fuel oil used in the process of the invention. The optimized analytical conditions correspond to an initial temperature of 50°C and a final temperature of 260°C with a temperature increase of 5°C / min.

[0136] Alkyl-benzothiophenes (also referred to hereafter as Cx-BTs) were identified by their retention time of between 15 and 27 min; alkyl-dibenzothiophenes (also referred to hereafter as Cx-DBTs) by their retention time of between 27 and 40 min; and DBT was identified by its retention time of around 28 min. During the reaction, and in particular step i), it is thus possible to follow the decay of the sulfur compounds and the simultaneous appearance of peaks attributed to the corresponding oxidized sulfur compounds (sulfones).

[0137] The prepared materials were characterized by X-ray diffraction and N2 physisorption.

[0138] Wide-angle X-ray diffraction characterizations were performed using a Siemens D5000 diffractometer (Cu Ka radiation, λ = 1.5418 Å) with a Lynxeye type fast linear detector and a copper anticathode in Bragg-Brentano geometry at room temperature. Measurements were performed for angle values ​​from 10° to 90° with a scan rate of 0.02° per step and a time of 2 seconds per step.

[0139] Small-angle X-ray diffraction patterns were recorded using a Rigaku device with a measurement step of 0.02°, an acquisition time of 15 seconds, in a range of 20 from 0 to 6°.

[0140] The metal oxide content in the samples can be determined by a spec- X-ray fluorescence tester (“Philips MagiX”) on samples previously compacted into 13 mm diameter pellets.

[0141] Nitrogen physisorption analyses were carried out on an apparatus Micromeritics Tristar II. Samples were first degassed at 200 °C for 5 hours under vacuum. The pore volume was determined at p / p0 = 0.02. The pore size distribution was calculated using the BJH (Barrett-Joyner-Halenda) method on the desorption branch of the isotherm.

[0142] Raman analyses were performed with a device sold under the trade name Dilor XY800 equipped with a krypton laser source with an excitation wavelength of 532 nm.

[0143] Example 1: Preparation of a catalyst as defined in the invention

[0144] 1.1 Preparation of a mesoporous silica of type COK-12 [step a)]

[0145] The process for preparing COK-12 is based on the publication Jammaer et al., 2010, Studies in Surface Science and Catalysis, 175, 681-684, and proceeds as follows.

[0146] 4 g of triblock copolymer “P123” are dissolved in 107.5 g of water. 3.68 g of acid Citric acid monohydrate and 2.84 g of trisodium citrate are added to the aqueous triblock copolymer solution to form a buffer solution. The buffer solution is stirred overnight. 10.4 g of sodium silicate solution is diluted with 30 g of water. This resulting solution is added to the buffer solution while stirring at 175 rpm with a mechanical mixer. Stirring is stopped after 5 minutes, and the resulting mixture is kept at room temperature for 24 hours. The synthesis is carried out in polypropylene bottles, and all solutions are kept at room temperature before mixing. The reaction product is recovered by vacuum filtration and washed with 300 mL of distilled water. The resulting material is dried at 60°C overnight and calcined at 300°C for 8 h and 550°C for another 8 h with heating ramps of 1°C / min.

[0147] Figure 1 shows the low-angle X-ray diffraction of COK-12 as prepared above. COK-12 exhibits a very intense and well-resolved diffraction peak at 0.82° indexed to the (100) reflection. The second peak, observed at 1.43°, is of low intensity and corresponds to the (110) reflections. As reported in the literature, the observed (100) and (110) peaks are indexed according to the p6m hexagonal symmetry.

[0148] 1.2 Preparation of a catalyst in powder form, based on a silica COK-12 type soporific [step b)]

[0149] The catalyst was prepared by dry impregnation with a molybdenum oxide precursor, ammonium heptamolybdate (NH4)6Mo7O24-4H2O, as follows: the water reabsorption volume of COK-12 type mesoporous silica in the form The concentration of a powder was determined and corresponds to 5.8 mL per gram of COK-12 mesoporous silica. An ammonium heptamolybdate solution with a concentration of 4.3 x 10² mol / L is prepared, and an appropriate volume of this solution is added to COK-12 mesoporous silica in powder form, as prepared in Example 1.1, to impregnate it (i.e., completely fill its porous volume) in order to obtain a MoO₃ content of 20% by mass. This solution is dripped onto the mesoporous silica while the mixture is mechanically stirred with a spatula. Capillary action draws the solution into the pores. The subsequent maturation step is carried out at room temperature in a humid atmosphere for 3 hours to allow the solution to penetrate the pores of the mesoporous silica.

[0150] The catalyst is then dried in an oven at 90 °C overnight to remove water and calcined at 480 °C for 3 hours under an air flow (0.3 l.min*), with a temperature ramp of 1 °C.min*. The purpose of this calcination step is to remove foreign counterions not involved in the formation of the active phase and to structure the oxomolybdate phase in order to obtain the oxide precursor.

[0151] Then the catalyst is used in powder form.

[0152] Figure 2 shows the high-angle X-ray diffraction of COK-12 as prepared in step 1.1 (dashed line), and of the catalyst as prepared above (solid line). It indicates the presence of MoO3 crystallites with reflection peaks centered at 20° = 12.9°, 23.7°, 25.8°, 27.4°, and 49.4°. The textural properties of the COK-12 support in powder form and of the "20 Mo / COK-12" catalyst in powder form are shown in Table 1 below.

[0153] [Tables 1] Material Specific surface area (m² / g) Pore volume (cm³ / g) Mean pore diameter (nm) Support COK-12 498 0.94 6.6 Catalyst "20 Mo / COK-12" 445 0.78 6.0

[0154] Table 1 confirms the conservation of the porous characteristics of the initial mesoporous silica, in particular in terms of specific surface area, pore volume, and average pore diameter.

[0155] Figure 3 shows the pore size distributions obtained according to the method BJH ([Fig.3] A) and nitrogen adsorption-desorption isotherms ([Fig.3] B) of the COK-12 support (dotted line) and the “20 Mo / COK-12” catalyst (solid line).

[0156] Nitrogen adsorption revealed type IV isotherms with type hysteresis Hl, characteristic of materials exhibiting open cylindrical mesopores (vertical and nearly parallel branches of the hysteresis loop) with a narrow pore size distribution. A bimodal pore size distribution structure is observed, with similar pore sizes; one centered around 7 nm and another around 8 nm for COK-12. After the addition of molybdenum (Mo), the resulting catalyst retains a type IV isotherm with unimodal porosity and a narrow pore size distribution centered at 6 nm.

[0157] Figure 4 shows two Raman spectra of the “20 Mo / COK-12” catalyst. The spectrum (a) Spectra exhibiting peaks at 243, 293, 343, 671, 820, and 995 cm⁻¹ are characteristic of MoO₃ crystallites present on the substrate surface. Spectrum (b), exhibiting main bands between 940 and 980 cm⁻¹ and a secondary band at 350 cm⁻¹, are characteristic of polymolybdate species well dispersed on the substrate surface.

[0158] 1.3 Shaping of a mesoporous silica of the COK-12 type, in the form of extrudates [step a)]

[0159] The mesoporous silica of type COK-12 as previously obtained is shaped into extrudates of diameter 3 mm.

[0160] A paste is first formed by mechanically mixing with a spatula in a beaker 10.08 g of COK-12; 1.02 g of boehmite and 0.21 g of sodium carboxymethyl-cellulose with 45 g of distilled water.

[0161] This paste is extruded by passing it through a die where it emerges in the form of extrudates. To do this, a single-screw extruder equipped with a die allowing the extrusion of cylindrical extrudates with a diameter of 3 mm is used.

[0162] Next, the raw parts (extruded from the die) are dried overnight at 90°C to evaporate the water. Finally, a high-temperature calcination, 480°C for 3 h under an air flow (0.3 l.min1) with a ramp of 1°C.min*, is carried out to impart the desired textural and mechanical properties to the substrate.

[0163] 1.4 Preparation of a catalyst in the form of extrudates, based on a silica me COK-12 type soporific [step b)]

[0164] The catalyst was prepared by dry impregnation with a molybdenum oxide precursor, ammonium heptamolybdate (NH4)6Mo7O24-4H2O, as follows: the water reabsorption volume of COK-12 type mesoporous silica in extruded form was determined and corresponds to a value of 3.1 ml per gram of COK-12 type mesoporous silica. An ammonium heptamolybdate solution with a concentration of 8.102 mol / 1 is prepared, and an appropriate volume of this solution is added to COK-12 type mesoporous silica in 3 mm diameter extruded form prepared in Example 1.3, to impregnate it (i.e., completely fill its porous volume) so as to obtain a MoO3 content of 20% by mass. This solution is drip-dipped onto the mesoporous silica while The mixture is then mechanically stirred using a spatula. Capillary action draws the solution into the pores. The next maturation step is carried out at room temperature, in a humid atmosphere for 3 hours to allow the solution to penetrate the pores of the mesoporous silica.

[0165] The catalyst is then dried in an oven at 90 °C overnight to remove water and calcined at 480 °C for 3 hours under an air flow (0.3 l.min*), with a temperature ramp of 1 °C.min*. The purpose of this calcination step is to remove foreign counterions not involved in the formation of the active phase and to structure the oxomolybdate phase in order to obtain the oxide precursor.

[0166] The catalyst is used in the form of extrudates.

[0167] The textural properties of the COK-12 support in extruded form and of the “20 Mo / COK-12” catalyst in extruded form are shown in Table 2 below.

[0168] [Tables2] Material Specific surface area (m² / g) Pore volume (cm³ / g) Mean pore diameter (nm) Support COK-12 333 0.65 6.3 Catalyst "20 Mo / COK-12" 395 0.56 5.2

[0169] Example 2: Oxidative desulfurization process of a heavy fuel oil according to a process according to the invention (see steps 1 and 1)1

[0170] 6 g of RMG380 heavy fuel oil having a sulfur content of 1.3% by mass were The mixture was placed in a 100 mL spherical glass reactor at atmospheric pressure, and then 600 mg of 20 Mo / COK-12 catalyst in extruded form, as prepared in Example 1.4 above, were added. The resulting mixture was heated to 80°C under reflux, and then 1.383 mL of an aqueous hydrogen peroxide solution (containing 27% by mass of hydrogen peroxide) was added. The oxidative desulfurization reaction [step i)] was carried out for 60 minutes at 80°C under reflux (reactor equipped with a condenser), under vigorous mechanical stirring with an oval magnetic stirrer and a rotation speed greater than 500 rpm. The oxidizing agent / sulfur molar ratio was 5.

[0171] To perform chromatographic analyses at the end of the reaction and estimate conversion rates, the reaction medium is diluted by a factor of 5 with 24 g of dodecane, and then the catalyst is separated by filtration. The resulting diluted filtrate is then analyzed by gas chromatography using a sulfur chemiluminescence detector (SCD) to determine the conversion of alkylbenzothiophenes (Cx-BTs) and DBT from heavy fuel oil in one or more corresponding oxidized sulfur compounds.

[0172] A liquid-liquid extraction on the diluted filtrate [step ii)] is then carried out with 30 g of DMF (volume ratio of 1.25: volume DMF / volume diluted filtrate) under the following conditions: the mixture is stirred for 1 h under magnetic stirring (500 rpm) and then left for 1 h in the separatory funnel before separation. A sample for analysis by gas chromatography is used to determine the removal rate of alkylbenzothiophenes (Cx-BTs), DBT, and the corresponding oxidized sulfur compounds from the heavy fuel oil.

[0173] A prior art comparative catalyst based on alumina as a support and molybdenum oxide as the active phase "20 Mo / Al" was prepared in the manner described below.

[0174] The catalyst was prepared by dry impregnation with a molybdenum oxide precursor, ammonium heptamolybdate (NH4)6Mo7O24-4H2O, as follows: the pore volume of the alumina was determined and corresponds to a value of 1.08 ml per gram of alumina. An aqueous solution of ammonium heptamolybdate with a concentration of 0.26 mol / L was prepared, and an appropriate volume of this solution was added to the alumina to impregnate it (i.e., to completely fill its pore volume) in order to obtain a MoO3 content of 20% by mass. This solution was impregnated dropwise onto the alumina while mixing the mixture mechanically with a spatula. Capillary action drew the solution into the pores. The next maturation step is carried out at room temperature, in a humid atmosphere for 3 hours to allow the solution to penetrate the pores of the alumina.

[0175] The catalyst obtained is then dried in an oven at 90 °C overnight to remove water and calcined at 480 °C for 3 hours under an air flow (0.3 l.min*), with a temperature ramp of 1 °C.min*. The purpose of this calcination step is to remove foreign counterions not involved in the formation of the active phase and to structure the oxomolybdate phase in order to obtain the oxide precursor.

[0176] The comparative catalyst “20 Mo / Al” is used in the form of extrudates.

[0177] Table 3 below lists the conversion results with this catalyst “20 Mo / COK-12”, and by comparison with the comparative catalyst “20 Mo / Al”, estimated from chromatographic analyses.

[0178] [Tables3] At step i) At step ii) Catalyst in extruded form Cx-BTs conversion (%) DBT conversion (%) Removal of Cx-BTs and oxidized Cx-BTs (%) Removal of DBT and oxidized DBT (%) "20 Mo / COK-12" 81 85 93 ©4 "20 Mo / AI" 65 82 86 92

[0179] The oxidative desulfurization reaction is more efficient using a mesoporous support according to the invention, compared to an alumina-based support, in particular for the conversion of Cx-BTs which is improved from 65 to 81%.

[0180] Figure 5 shows the chromatograms before and after the reaction. For each sample, a triplicate is performed to ensure the reproducibility of the analysis; the conversions are calculated using the averages of the areas under the peaks of the Cx-BTs region (17–29 min) and the area under the DBT peak (29.1–29.3 min). Figure 5 specifically shows the chromatograms of RMG380 heavy fuel oil used in step i) (Fig. 5-a), of the oxidized heavy fuel oil at the end of step i) (Fig. 5-b), of the oxidized heavy fuel oil after liquid-liquid extraction (Fig. 5-c), and of the DMF solvent after liquid-liquid extraction (Fig. 5-d).

Claims

Demands

1. A process for the oxidative desulfurization of at least one heavy fuel oil by heterogeneous catalysis, characterized in that it comprises at least the following steps: i) the reaction of a heavy fuel oil with an oxidizing agent, in the presence of a catalyst comprising at least one metal oxide supported by mesoporous silica, to form one or more oxidized sulfur compounds, ii) the separation of the oxidized sulfur compound(s), and in that: * the catalyst is in the form of platelets and has a two-dimensional ordered hexagonal mesoporous structure, with mesopores having a length of at most 300 nm, * the heavy fuel oil comprises at least 0.5% by mass of elemental sulfur, relative to the total mass of the heavy fuel oil, and has a viscosity greater than 1.8 x 10⁴ m² / s at 50°C, and * the metal oxide is selected from titanium, molybdenum, and oxides. tungsten.

2. The method according to claim 1, characterized in that the metal oxide is molybdenum oxide.

3. A process according to claim 1 or 2, characterized in that the metal oxide represents from 5 to 30% by mass, relative to the total mass of the catalyst.

4. A method according to any one of the preceding claims, characterized in that the catalyst is in the form of extrudates.

5. A process according to any one of the preceding claims, characterized in that the catalyst has a specific surface area, measured according to the BET method, ranging from 400 m2 / g to 600 m2 / g.

6. A method according to any one of the preceding claims, characterized in that the catalyst has a pore volume ranging from 0.7 cmVg to 1 cmVg.

7. A method according to any one of the preceding claims, characterized in that the catalyst comprises pores with an average diameter of 4.5 to 8 nm.

8. A method according to any one of the preceding claims, characterized in that it further comprises, prior to step i), a step a) of preparing mesoporous silica involving the implementation of contact under pH conditions ranging from 3 to 7 of a silica precursor and an organic polymer capable of forming mesopores after calcination.

9. A process according to any one of the preceding claims, characterized in that the heavy fuel oil used in step i) has a boiling point above 150°C.

10. A process according to any one of the preceding claims, characterized in that the oxidizing agent is hydrogen peroxide.

11. Use of a catalyst as defined in any one of claims 1 to 7, for the oxidative desulfurization of at least one heavy fuel oil comprising at least 0.5% by mass of sulfur element, relative to the total mass of the heavy fuel oil, and having a viscosity greater than 1.8 x 0.4 m2 / s at 50°C.

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