Method for oxydesulfurization of a heavy fuel oil

Abstract

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

Description

[0001] Oxydesulfurization process for heavy fuel oil

[0002] The present invention relates to a process for the oxydesulfurization (oxidative desulfurization) of at least one heavy fuel oil using a catalyst in the form of platelets having an ordered mesoporous structure in 2 hexagonal dimensions, as well as the use of such a catalyst in the form of platelets having an ordered mesoporous structure in 2 hexagonal dimensions, for the oxydesulfurization of at least one heavy fuel oil.

[0003] Regulations on 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 required the use of fuels on board ships with a maximum sulfur content of 0.1% by mass in emission control areas and 3.5% in other maritime waters since 1 January 2015. Then, since 1 erSince January 2020, the International Maritime Organization has limited this maximum mass content of sulfur in marine fuels to 0.5% for all vessels operating outside emission control areas. Heavy fuel oil (also known as "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 a boat fuel. The mass content of sulfur in heavy fuel oil depends on the geographical origin and refining processes but can reach up to 3.5% by regulation, which is 3,500 times higher than the limit tolerated in land-based gasoline.

[0004] On board ships, compliance with the regulations is achieved either by using another 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 fume scrubbers. The use of alternative fuels such as liquefied natural gas requires a complete change in ship technology (propulsion mode), which represents a significant cost. Flue gas scrubbers spray seawater (or sometimes fresh water) or another aqueous liquid into the ship's exhaust duct to solubilize a large portion of the SOx (sulfur oxides) and remove soot, and thus comply with gas emission requirements.However, the polluted acidic and heavy metal-laden water and sludge generated by this washing can then be discharged directly into the sea when the treatment is carried out in an open circuit. Furthermore, the flue gas scrubbers used for SOx cannot be used for NOx (nitrogen oxides), which are also subject to increasingly strict limit values. Post-combustion treatment of NOx requires catalytic flue gas scrubbers whose action is inhibited by the SOx adsorbed on the catalyst.

[0005] In order to comply with the authorized limits, one of the methods that could make it possible to produce a cleaner fuel from the highly sulfurous residues produced each year by refineries, while not changing ship technology, is desulfurization. Hydrodesulfurization (HDS) is one of the most commonly used processes to reduce the amount of sulfur in light cuts or fractions (such as gasoline, kerosene, light diesel) resulting from the atmospheric distillation of crude oil. Hydrodesulfurization is carried out in the presence of dihydrogen to form hydrogen sulfide (H2S). It is carried out in the presence of a catalyst, for example formed from an alumina support (AI2O3) on which is deposited an active phase generally consisting of molybdenum sulfide promoted by cobalt or nickel (CoMoS / NiMoS phase).However, the hydrodesulfurization of heavy fuel oils uses dihydrogen under high pressure (up to 200 bars) and high temperature (up to 400°C), with significant constraints in terms of safety and energy and hydrogen consumption. In addition, polycyclic aromatic sulfur compounds such as dibenzothiophene, which is an organosulfur compound present in marine fuel oil, or 4,6-dimethyldibenzothiophene, are refractory to hydrodesulfurization. Another method consists of chemically oxidizing sulfur compounds present in a mixture, so as to generate sulfone functions (R-SO2-R'), from sulfide functions (RS-R') incorporated in said sulfur compounds. This chemical oxidation then makes it possible to separate the oxidized compounds that have become polar from the rest of the mixture by extraction or adsorption methods.However, the vast majority of prior art oxydesulfurization 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 fractions with high sulfur contents, and / or for considering a transition to industrial scale. Furthermore, extrapolation of the phenomena occurring during the oxydesulfurization of a model feedstock to the oxydesulfurization of a real feedstock is impossible. The complexity of the real matrix, the presence of other oxidizable molecules, impurities, or even the differences in solubility of the compounds within the two types of feedstock do not allow a direct correlation to be established between the model feedstock and the real feedstock. A recent publication by Houda et al., 2021, Catalysis Today, 377, 221-228 describes the oxydesulfurization of marine fuel oils of the type “IFO380”, “IFO500” and “HSF0700” diluted in dodecane or crude (i.e.undiluted) with hydrogen peroxide and a catalyst comprising molybdenum oxide supported by alumina. The process described has moderate or even low efficiency on the heaviest marine fuel oil "HSF0700". In particular, dilution of the heavy fuel oil is required to be able to carry out oxydesulfurization.

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

[0007] The first subject of the invention is a process for the oxydesulfurization 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 a mesoporous silica, to form one or more oxidized sulfur compounds, ii) the separation of the oxidized sulfur compound(s), and in that:

[0008] * the catalyst is in the form of platelets and has an ordered mesoporous structure in 2 hexagonal dimensions, with mesopores having a length of at most approximately 300 nm,

[0009] * heavy fuel oil contains at least 0.5% by mass of the element sulfur, relative to the total mass of the heavy fuel oil, and has a viscosity greater than 180 cSt at 50°C, and

[0010] * the metal oxide is chosen from titanium, molybdenum and tungsten oxides. The process according to the first subject 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 allow the oxydesulfurization of a heavy fuel oil. The process is easy to implement, economical in that it uses inexpensive raw materials and does not require high temperature and pressure conditions, industrializable, while guaranteeing a substantial reduction in the quantity of sulfur in heavy fuel oils.

[0011] Step i)

[0012] The International Maritime Organization has proposed a classification of marine fuel oils into different categories according to their mass sulfur content and viscosity in ISO 8216 and ISO 8217 standards respectively.

[0013] 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 1.8x10 -4 m 2 / s.

[0014] 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 2.5x10 -4 m 2 / s at 7.5x10 -4 m 2 / s at 50°C), particularly preferably ranging from 300 cSt to 650 cSt at 50°C (i.e. ranging from 3.0x10 -4 m 2 / s at 6.5x10 -4 m 2 / s at 50°C), and more particularly preferably ranging from 380 to 550 cSt at 50°C (i.e. ranging from 3.8x10 -4 m 2 / s at 5.5x10 -4 m 2 / s at 50°C).

[0015] Viscosity can be measured according to ISO 8217 which uses the measurement methods mentioned in ISO 3104.

[0016] The heavy fuel oil used in the process of the invention comprises at least 0.5% by mass of sulfur element.

[0017] In the invention, the element sulfur corresponds to the chemical element with atomic number 16, and symbol S.

[0018] The heavy fuel oil used in the process of the invention preferably comprises at least 0.7% by mass of element sulfur, particularly preferably at least 1% by mass of element sulfur, and more particularly preferably at least 2% by mass of element sulfur, relative to the total mass of the heavy fuel oil. The sulfur content of the heavy fuel oil used in the process of the invention can be measured by elemental analysis.

[0019] The heavy fuel oil used in the process of the invention may be a fuel oil of the IFO type (well known by the Anglicism "Intermediate Fuel Oil"), of the HSFO type (well known by the Anglicism "High Sulfur Fuel Oil"), or of the RMFO type (well known by the Anglicism "Residual Marine Fuel Oil").

[0020] The heavy fuel oil used in step i) preferably has a boiling point greater than approximately 150°C, particularly preferably greater than approximately 250°C, and more particularly preferably greater than approximately 325°C. It is preferably distinguished in particular from diesels which have a boiling point less than or equal to 150°C.

[0021] The heavy fuel oil used in step i) preferably has a boiling point less than or equal to approximately 700°C, and particularly preferably less than or equal to approximately 650°C.

[0022] 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.

[0023] 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 the ISO 3675 standard.

[0024] 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.

[0025] 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 above-mentioned compounds. Examples include dibenzothiophene (DBT) or 4,6-dimethyldibenzothiophene.

[0026] The metal oxide associated with the mesoporous silica represents the active phase of the catalyst. The mesoporous silica represents the support.

[0027] The metal oxide is then supported by the mesoporous silica.

[0028] The metal oxide is selected from titanium (TiO2), molybdenum (MoOs) and tungsten (WO3) oxides, and is preferably molybdenum oxide (MoOs). The catalyst may comprise several metal oxides supported by the mesoporous silica. In this embodiment, the metal oxides are preferably selected 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 represents from 5 to 30% by mass approximately, and particularly preferably from 10 to 20% by mass approximately, relative to the total mass of the catalyst. When the quantity of metal oxide is too high, the conversion into oxidized sulfur compounds during step i) decreases and the final sulfur content in the heavy fuel oil increases.

[0031] The catalyst preferably consists 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 consists of) atoms of silicon, 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 aluminum within its structure.

[0035] The catalyst preferably does not comprise 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 300 m 2 / g at 1200 m 2 / g approximately, particularly preferably ranging from 350 m 2 / g at 800 m 2 / g approximately, and more particularly preferably ranging from 400 m 2 / g at 600 m 2 / g approximately.

[0037] The catalyst preferably has (before shaping) a pore volume ranging from 0.3 cm 3 / g at 1.6 cm 3 / g approximately, particularly preferably ranging from 0.5 cm 3 / g at 1.2 cm 3 / g approximately, and more particularly preferably 0.7 cm 3 / g at 1 cm 3 / g approximately.

[0038] The pore volume can be determined by the nitrogen adsorption / desorption method. The catalyst has a mesoporous structure. This means that it contains mesopores, which are defined as pores with an average diameter ranging from about 2 to 50 nm.

[0039] The pore size distribution and average pore diameter can be determined by the BJH method.

[0040] The catalyst of the invention preferably comprises pores with an average diameter ranging from 2 to 15 nm, particularly preferably ranging from approximately 3 to 10 nm, and more particularly preferably ranging from approximately 4.5 to 8 nm.

[0041] The mesopores of the catalyst of the invention preferably have walls having a thickness ranging from approximately 1 to 7 nm, and particularly preferably ranging from approximately 3 to 6 nm.

[0042] The catalyst has an ordered mesoporous structure. In other words, the mesopores are ordered or organized into a porous network that has a well-defined periodicity.

[0043] The catalyst has a hexagonal 2-dimensional (2D) mesoporous structure. In other words, the catalyst has hexagonal 2D symmetry or belongs to the P6m space group or comprises a hexagonal arrangement of tubular or cylindrical mesopores.

[0044] 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 and straight mesopores within the catalyst, the penetration of the sulfur compounds present in the heavy fuel oil into the catalyst is favored, and thus allows a large exchange surface between the active phase of the catalyst and the heavy fuel oil.

[0045] The mesoporous silica of the catalyst is preferably a mesoporous silica of type COK-12.

[0046] According to one embodiment, the oxidizing agent is a non-gaseous oxidizing agent. This ensures greater safety in the implementation of the method. Furthermore, the use of gaseous oxidizing agents very often requires higher temperature conditions and / or specific pressure conditions. The oxidizing agent is preferably chosen from aqueous peroxides such as hydrogen peroxide, and non-aqueous peroxides such as tetrabutyl hydroperoxide (TBHP).

[0047] The oxidizing agent is preferably an aqueous oxidizing agent.

[0048] In the invention, the term “aqueous oxidizing agent” means an oxidizing agent which is soluble in water, preferably at room temperature (i.e. 18-25°C).

[0049] Aqueous peroxides such as hydrogen peroxide are particularly preferred.

[0050] The oxidizing agent is preferably diluted in water. This allows oxidative desulfurization to be carried out safely and limits the production of organic products. In this embodiment, step i) is carried out in a two-phase medium (i.e. aqueous medium comprising the aqueous oxidizing agent and organic medium comprising fuel oil), or even three-phase (if the catalyst, which is solid, is also taken into account).

[0051] In step i), the oxidizing agent / sulfur element molar ratio preferably ranges from approximately 2 to 25, particularly preferably from approximately 3 to 10, and more particularly preferably from approximately 3 to 6. The use of such molar ratio ranges makes it possible to limit the consumption of oxidizing agent. Preferably, the molar ratio is above the stoichiometric ratio of 2 due to the parallel reactions.

[0052] The process for the oxydesulfurization 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).

[0053] Step i) may 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 degradation of the oxidizing agent. In addition, these temperatures correspond to those of the fuel oil circuit on ships, facilitating its handling.

[0054] The oxidizing agent is preferably added to the heavy fuel oil after the temperature of the reaction medium has risen, and particularly preferably the oxidizing agent is added at the same time as the catalyst. This thus prevents its degradation.

[0055] Step i) is preferably carried out at atmospheric pressure. Step i) can last from approximately 5 minutes to approximately 48 hours, and preferably from approximately 20 minutes to 2 hours.

[0056] 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 revolutions per minute. This speed makes it possible to facilitate oxidative desulfurization, while limiting deterioration of the catalyst, in particular if it is in the form of extrudates.

[0057] In particular, the vigorous stirring may be carried out by means of a magnetic stirrer, preferably of oval shape. In this embodiment, step i) is preferably carried out in a spherical reactor. This thus makes it possible to promote the contacting of the heavy fuel oil with the catalyst and the oxidizing agent, and consequently the oxidative desulfurization reaction.

[0058] 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 therefore increases the conversion of sulfur compounds into oxidized sulfur compounds.

[0059] Step i) is preferably carried out in a reactor of volume Vi and in the presence of a volume V2 of heavy fuel oil, so that the volume ratio V2 / V1 is greater than 0.1. This thus makes it possible to promote the oxidative desulfurization reaction.

[0060] According to a preferred embodiment of the invention, step i) uses undiluted heavy fuel oil (in a solvent). In other words, this oxydesulfurization step i) does not use solvents such as apolar aprotic solvents which would then dilute the heavy fuel oil.

[0061] Step ii)

[0062] Separation step ii) allows the extraction of oxidized sulfur compounds from heavy fuel oil.

[0063] Step ii) can be carried out by liquid-liquid extraction, in particular with a polar aprotic organic solvent.

[0064] The polar aprotic organic solvent may be selected from N,N-dimethylformamide (DMF), γ-butyrolactone, 2-ethoxyethanol, acetonitrile, methanol, 1-methyl-2pyrrolidone (NMP), a polyethylene glycol (e.g. PEG 200), and dimethyl sulfoxide (DMSO). The polar aprotic organic solvent can be used to remove the oxidized sulfur compounds formed during step i).

[0065] The volume ratio [volume of polar aprotic organic solvent / volume of heavy fuel oil used in step i)] preferably ranges from approximately 0.5 to 3, and particularly preferably from 0.5 to 1.5.

[0066] 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.

[0067] 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 diluted filtrate.

[0068] Step A)

[0069] The process may further comprise, before step ii), a step A) of recovering the catalyst.

[0070] This step A) can be carried out by filtration. The catalyst is then obtained, separated from the filtrate. The filtrate includes the oxidized heavy fuel oil.

[0071] In this embodiment, step ii) is then carried out on the filtrate.

[0072] Step B)

[0073] The catalyst obtained at the end of step A) can be washed according to step B), in particular with an apolar aprotic organic solvent, then a polar aprotic organic solvent.

[0074] The apolar aprotic organic solvent can be chosen from C5-C12 alkanes such as pentane.

[0075] The apolar aprotic organic solvent is used in particular to eliminate heavy fuel oil residues, including sulfur compounds.

[0076] The polar aprotic organic solvent may be selected from γ-butyrolactone, DMF, 2-ethoxyethanol, acetonitrile, methanol, 1-methyl-2pyrrolidone (NMP), a polyethylene glycol (eg PEG 200), and dimethyl sulfoxide (DMSO).

[0077] The polar aprotic organic solvent makes it possible in particular to eliminate the oxidized sulfur compounds which have attached to the catalyst.

[0078] 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.

[0079] Step C) The process may further comprise, after step A) and before step ii), a step C) of diluting the filtrate containing the oxidized heavy fuel oil, in particular with an apolar aprotic organic solvent.

[0080] The apolar aprotic organic solvent can be selected from alkanes such as dodecane, hexane, and decane.

[0081] In this embodiment, step ii) is then carried out on the diluted filtrate.

[0082] Step a)

[0083] The method may further comprise, before step i), a step a) of preparing the mesoporous silica.

[0084] Step a) preferably involves bringing into contact, under pH conditions ranging from 3 to 7, and preferably ranging from 3.5 to 6, a silica precursor and an organic polymer capable of forming mesopores after calcination.

[0085] The organic polymer may be a poly(alkylene oxide), and preferably a poly(alkylene oxide) triblock copolymer such as a poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol).

[0086] The silica precursor is preferably an alkali silicate such as sodium silicate.

[0087] 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 on the industrial level.

[0088] Step a) preferably comprises the following sub-steps: a-1) preparing a first aqueous solution comprising the silica precursor, a-2) preparing a second aqueous solution comprising the organic polymer and an acid with a pKa in the range of 3 to 9, a-3) adding said first aqueous solution to said second aqueous solution, and a-4) filtering, drying and calcining the reaction product.

[0089] The acid serves as a buffer solution.

[0090] The acid may 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. When the silica precursor is a sodium silicate, the molar ratio Na + / SiO2 preferably ranges from about 2 to 3.

[0091] Mesoporous silica can be in powder form.

[0092] Step a) may comprise a step of shaping the mesoporous silica, in particular in the form of extrudates.

[0093] Step b)

[0094] The process may further comprise, before step i), and after step a) if it exists, a step b) of preparing the catalyst.

[0095] Step b) preferably comprises the impregnation with at least one precursor of a metal oxide as defined in the invention, of a mesoporous silica in the form of platelets, having an ordered 2-dimensional hexagonal porous structure, with mesopores having a length of at most approximately 300 nm.

[0096] The precursor may be selected from ammonium heptamolybdate, molybdenum trioxide, ammonium paratungstate, titanium oxide, and titanium isopropoxide.

[0097] This impregnation step b) makes it possible to uniformly disperse 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 makes it possible to easily, industrially, and quickly obtain a high-performance catalyst for the oxydesulfurization of heavy fuel oil.

[0098] During step b), particles of the metal oxide are distributed uniformly within the mesoporous silica.

[0099] The impregnation method makes it possible to avoid methods involving the cocondensation of a silicon precursor and a metal precursor, or the condensation of a metal precursor within a porous silica, which lead to materials that are different both in terms of porous structure and in terms of chemical structure compared to the catalyst of the invention. These methods use acidic (pH < 2) or basic (pH > 9) conditions that can represent a constraint on the industrial level.

[0100] Mesoporous silica preferably has (before shaping) a specific surface area, measured according to the BET method, ranging from 300 m 2 / g at 1200 m 2 / g approximately, particularly preferably ranging from 350 m 2 / g at 800 m 2 / g approximately, and more particularly preferably ranging from 400 m 2 / g at 600 m 2 / g approximately. Mesoporous silica preferably has (before shaping) a pore volume ranging from 0.3 cm 3 / g at 1.6 cm 3 / g approximately, particularly preferably ranging from 0.5 cm 3 / g at 1.2 cm 3 / g approximately, and more particularly preferably ranging from 0.7 cm 3 / g at 1 cm 3 / g approximately.

[0101] Preferably, the mesoporous silica comprises pores with an average diameter ranging from 2 to 15 nm, particularly preferably ranging from 3 to 10 nm, and more particularly preferably ranging from 4.5 to 8 nm.

[0102] The mesopores of mesoporous silica preferably have walls with a thickness ranging from 1 to 7 nm, and particularly preferably from 3 to 6 nm. Mesoporous silica has an ordered porous structure. In other words, the mesopores are ordered or organized according to a well-defined periodicity.

[0103] Mesoporous silica has a hexagonal 2-dimensional (2D) porous structure. In other words, mesoporous silica has hexagonal 2D symmetry or belongs to the P6m space group or comprises a hexagonal arrangement of tubular or cylindrical mesopores.

[0104] The mesopores of the silica have a length of at most about 300 nm, preferably at most about 250 nm, and particularly preferably at most about 200 nm. Thanks to the presence of short and straight mesopores within the mesoporous silica, the penetration of the metal oxide during step b) is promoted, and thus allows a homogeneous distribution of the metal oxide within the catalyst.

[0105] During the impregnation step b), the initial structure of the mesoporous silica is therefore preserved and conferred on the catalyst.

[0106] According to a preferred embodiment of the invention, the impregnation of step b) is a dry impregnation, also called incipient wetness impregnation. In other words, step b) is carried out by limiting the quantity of liquid and / or solvent, so that the volume of liquid or solvent used corresponds to the water uptake volume. The latter, expressed in cm 3 per gram of support (mesoporous silica), is determined experimentally by saturating the pore volume of the support with water.

[0107] Dry impregnation can be carried out:

[0108] - directly on the shaped mesoporous silica, or

[0109] - on powdered mesoporous silica (i.e. in the form of a powder). Impregnation can be followed by shaping.

[0110] The shaping is preferably extruded shaping.

[0111] Extrudates are easier to handle, thus avoiding catalyst losses during recovery and allowing it to be reused in other oxidative desulfurizations.

[0112] Step c)

[0113] The process may further comprise, before step i), a step c) of purifying a heavy fuel oil.

[0114] Step c) may include diluting the heavy fuel oil in a non-polar aprotic organic solvent, followed by centrifugation. This allows the recovery of a liquid fuel oil with a reduced asphaltene content, or even without asphaltenes.

[0115] The apolar aprotic organic solvent can be selected from alkanes such as dodecane, hexane, and decane.

[0116] The second subject of the invention is the use of a catalyst as defined in the first subject 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.

[0117] Heavy fuel oil may be as defined in the first subject of the invention.

[0118] Brief description of the drawings

[0119] The accompanying drawings illustrate the invention.

[0120] Figure 1 shows the low-angle X-ray diffraction of the mesoporous silica support COK-12.

[0121] Figure 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 used in the process of the invention.

[0122] Figure 3 represents the pore size distributions obtained according to the BJH method and the nitrogen adsorption-desorption isotherms of the mesoporous silica support COK-12 and the “20 Mo / COK-12” catalyst in powder form used in the process of the invention.

[0123] Figure 4 represents a Raman spectrum of the “20 Mo / COK-12” catalyst used in the process of the invention. Figure 5 represents the chromatograms of the RMG380 heavy fuel oil used in step i) (Figure 5-a), of the oxidized heavy fuel oil at the end of step i) (Figure 5-b), of the oxidized heavy fuel oil after liquid-liquid extraction (Figure 5-c), and of the DMF solvent after liquid-liquid extraction (Figure 5-d).

[0124] Other features and advantages of the present invention will become apparent from the description of non-limiting examples of the method of the invention.

[0125] Examples

[0126] The raw materials used in the examples are listed below:

[0127] - hydrogen peroxide, 30% by mass in water, Sigma Aldrich,

[0128] - ammonium molybdate tetrahydrate, purity > 99%, Sigma Aldrich,

[0129] - butyrolactone, purity > 99%, Sigma Aldrich,

[0130] - acetonitrile, environmental grade, purity 99.7%, Alfa Aesar,

[0131] - 2-ethoxyethanol, purity 99%, ACROS Organics,

[0132] - N,N-dimethylformamide, purity 99.8%, ACROS Organics,

[0133] - n-dodecane, purity > 99%, Alfa Aesar,

[0134] - triblock copolymer, marketed under the reference “P123” by BASF,

[0135] - citric acid monohydrate, Riedel-de Haen,

[0136] - trisodium citrate, UCB,

[0137] - aqueous sodium silicate solution (10% by mass of NaOH, 27% by mass of SiO2), Merck,

[0138] - boehmite, “Rural SB3”, Sasol,

[0139] - sodium carboxymethylcellulose, purity > 99%, Alfa Aesar,

[0140] - heavy fuel oil under the reference “RMG380” having a viscosity of 380 cSt at 50°C.

[0141] Unless otherwise stated, all materials were used as received from the manufacturers.

[0142] Characterizations

[0143] The elemental analysis of the content of C, H, N and S elements in heavy fuel oils was determined by “CHNS” analysis using a device sold under the trade name “EA1110 Thermo Fisher Flash instrument”. The sulfur compounds were monitored by gas chromatography using a device sold under the trade name “Agilent Technologies, 7890B” coupled with a sulfur-specific chemiluminescence detector SCD “Agilent Technologies, 8355”. A high temperature range column was used “DB-5HT”. An integrated guard column was added due to the heavy nature of the fuel oil used in the process of the invention. The optimized analysis conditions correspond to an initial temperature of 50°C and a final temperature of 260°C with a temperature increase of 5°C / min.

[0144] Alkyl-benzothiophenes (also referred to hereinafter as Cx-BTs) were identified by their retention time between 15 and 27 min; alkyl-dibenzothiophenes (also referred to hereinafter as Cx-DBTs) by their retention time between 27 and 40 min; and DBT was identified by its retention time around 28 min. During the reaction, and in particular during 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).

[0145] The prepared materials were characterized by X-ray diffraction and N2 physisorption.

[0146] X-ray diffraction characterizations (wide angle) were performed using a “Siemens D5000” diffractometer (Cu Ka radiation, λ = 1.5418 A) with a fast linear detector of the “Lynxeye” type and a copper anticathode, in “Bragg Brentano” geometry at room temperature. The measurements were performed for angle values ​​20 from 10° to 90° with a scanning speed of 0.02° per step and a time of 2 seconds per step.

[0147] 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°.

[0148] The metal oxide content in the samples can be determined by an X-ray fluorescence spectrometer (“Philips MagiX”) on samples previously compacted into 13 mm diameter pellets.

[0149] Nitrogen physisorption analyses were performed on a Micromeritics Tristar II apparatus. Samples were first degassed at 200°C for 5 hours under vacuum. The pore volume was determined to be p / po = 0.02. The pore size distribution was calculated by the BJH (Barrett-Joyner-Halenda) method on the desorption branch of the isotherm.

[0150] 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.

[0151] Example 1: Preparation of a catalyst as defined in the invention

[0152] 1.1 Preparation of a mesoporous silica of type COK-12 [step a)]

[0153] The preparation process of COK-12 is based on the publication Jammaer et al., 2010, Studies in Surface Science and Catalysis, 175, 681-684, and proceeds as follows.

[0154] 4 g of triblock copolymer “P123” are dissolved in 107.5 g of water. 3.68 g of 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 a sodium silicate solution is diluted in 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 collected by vacuum filtration and washed with 300 ml of distilled water. The obtained material is dried at 60°C for 1 night and calcined at 300°C for 8 h and 550°C for another 8 h with heating ramps of 1°C / min.

[0155] Figure 1 shows the X-ray diffraction at low incidence angles of COK-12 as prepared above. COK-12 shows 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), (110) peaks are indexed according to the p6m hexagonal symmetry.

[0156] 1.2 Preparation of a catalyst in the form of a powder, based on a mesoporous silica of the COK-12 type [step b)]

[0157] The catalyst was prepared by dry impregnation with a molybdenum oxide precursor ammonium heptamolybdate (NH4)6Mo?O24-4H2O as follows: the water uptake volume of COK-12 type mesoporous silica in powder form was determined and corresponds to a value of 5.8 ml per gram of COK-12 type mesoporous silica. An ammonium heptamolybdate solution of concentration 4.3.10 -2mol / l is prepared and an appropriate volume of this solution is added to mesoporous silica of type COK-12 in the form of a powder prepared in Example 1.1 to impregnate it (i.e. completely fill its pore volume) so as to obtain a content of 20% by mass of MoOs. This solution is impregnated drop by drop onto the mesoporous silica while mixing the whole by mechanical action 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 into the pores of the mesoporous silica.

[0158] 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 -1 ), with a temperature ramp of 1°C. min -1The aim of this calcination step is to eliminate foreign counterions not involved in the formation of the active phase and to structure the oxomolybdate phase in order to obtain the corresponding oxide.

[0159] Then the catalyst is used in the form of a powder.

[0160] Figure 2 shows the high angle X-ray diffraction of COK-12 as prepared in point 1.1 (dotted line), and of the catalyst as prepared above (solid line). It indicates the presence of MoOs crystallites with reflection peaks centered at 29 = 12.9; 23.7; 25.8; 27.4 and 49.4°. The textural properties of the COK-12 support in powder form and the “20 Mo / COK-12” catalyst in powder form are shown in Table 1 below.

[0161] TABLE 1

[0162] Table 1 confirms the preservation of the porous characteristics of the initial mesoporous silica, particularly in terms of specific surface area, pore volume, and average pore diameter. Figure 3 shows the pore size distributions obtained using the BJH method (Figure 3 A) and the nitrogen adsorption-desorption isotherms (Figure 3 B) of the COK-12 support (dotted line) and the “20 Mo / COK-12” catalyst (solid line).

[0163] Nitrogen adsorption revealed type IV isotherms with H1-type hysteresis, characteristic of materials with 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 close 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 monomodal porosity and a narrow pore size distribution centered at 6 nm.

[0164] Figure 4 shows two Raman spectra of the “20 Mo / COK-12” catalyst. Spectrum (a) shows peaks at 243, 293, 343, 671, 820 and 995 cm -1 is characteristic of MoOs crystallites present on the surface of the support. The spectrum (b) showing main bands between 940-980 cm -1and a secondary band at 350 cm -1 is characteristic of polymolybdate species well dispersed on the surface of the support.

[0165] 1.3 Shaping of a mesoporous silica of type COK-12, in the form of extrudates [step a)]

[0166] The mesoporous silica of type COK-12 as obtained previously is shaped into extrudates of diameter 3 mm.

[0167] A paste is first formed by mechanical mixing using a spatula in a beaker of 10.08 g of COK-12; 1.02 g of boehmite and 0.21 g of sodium carboxymethylcellulose with 45 g of distilled water.

[0168] This paste is extruded by passing it through a die from which it comes out 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.

[0169] Then, the raw parts (extruded at the outlet of the die) are dried overnight at 90°C to evaporate the water. Finally, a high temperature calcination, 480°C for 3 hours under air flow (0.3 l.min -1 ) with a ramp of 1°C. min -1 , is carried out to give the desired textural and mechanical properties to the support.

[0170] 1.4 Preparation of a catalyst in the form of extrudates, based on a mesoporous silica of the COK-12 type [step b)] The catalyst was prepared by dry impregnation with a molybdenum oxide precursor ammonium heptamolybdate (Nh ^Mo C^ ^hhO) as follows: the water uptake volume of the mesoporous silica of the COK-12 type in the form of extrudates was determined and corresponds to a value of 3.1 ml per gram of mesoporous silica of the COK-12 type. A solution of ammonium heptamolybdate of concentration 8.10 -2mol / l is prepared and an appropriate volume of this solution is added to mesoporous silica of type COK-12 in the form of 3 mm diameter extrudates prepared in Example 1.3, to impregnate it (i.e. completely fill its pore volume) so as to obtain a content of 20% by mass of MoOs. This solution is impregnated drop by drop onto the mesoporous silica while mixing the whole by mechanical action 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 into the pores of the mesoporous silica.

[0171] 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 -1 ), with a temperature ramp of 1°C. min -1The aim of this calcination step is to eliminate foreign counterions not involved in the formation of the active phase and to structure the oxomolybdate phase in order to obtain the corresponding oxide.

[0172] The catalyst is used in the form of extrudates.

[0173] The textural properties of the COK-12 support in the form of extrudates and the “20 Mo / COK-12” catalyst in the form of extrudates are presented in Table 2 below.

[0174] TABLE 2

[0175] Example 2: process for the oxidative desulfurization of a heavy fuel oil according to a process in accordance with the invention [steps i) and ii)l

[0176] 6 g of RMG380 heavy fuel oil having a sulfur content of 1.3% by mass were placed in a 100 ml spherical glass reactor at atmospheric pressure and then 600 mg of “20 Mo / COK-12” catalyst in the form of extrudates as prepared in Example 1.4 above were added. The resulting medium was heated to 80°C under reflux and then 1.383 ml of an aqueous hydrogen peroxide solution (comprising 27% by mass of hydrogen peroxide) were 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 element molar ratio is 5.

[0177] To perform the chromatographic analyses at the end of the reaction and estimate the 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, in order to determine the conversion of alkyl-benzothiophenes (Cx-BTs) and DBT from heavy fuel oil into one or more corresponding oxidized sulfur compounds.

[0178] A liquid-liquid extraction on the diluted filtrate [step ii)] is then carried out with 30 g of DMF (volume ratio of 1.25: DMF volume / diluted filtrate volume) under the following conditions: the mixture is stirred for 1 h under magnetic stirring (500 rpm) then left for 1 h in the separating funnel before separation. A sample for gas chromatographic analysis makes it possible to determine the elimination rate of alkyl-benzothiophenes (Cx-BTs), DBT and the corresponding oxidized sulfur compounds from the heavy fuel oil.

[0179] A comparative prior art catalyst based on alumina as a support and molybdenum oxide as an active phase "20 Mo / Al" was prepared as described below.

[0180] The catalyst was prepared by dry impregnation with a molybdenum oxide precursor, ammonium heptamolybdate (NF jeMo C^ ^FhO, 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 is prepared and an appropriate volume of this solution is added to the alumina to impregnate it (i.e. completely fill its pore volume) so as to obtain a content of 20% by mass of MoOs. This solution is impregnated dropwise onto the alumina while mixing the whole by mechanical action 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 into the pores of alumina.

[0181] The obtained catalyst is then dried in an oven at 90°C overnight to remove the water and calcined at 480°C for 3 hours under an air flow (0.3 l.min -1 ), with a temperature ramp of 1°C. min -1 The aim of this calcination step is to eliminate foreign counterions not involved in the formation of the active phase and to structure the oxomolybdate phase in order to obtain the corresponding oxide.

[0182] The comparative catalyst “20 Mo / AI” is used in the form of extrudates.

[0183] Table 3 below lists the conversion results with this “20 Mo / COK-12” catalyst, and in comparison with the comparative “20 Mo / AI” catalyst, estimated from chromatographic analyses.

[0184] TABLE 3

[0185] 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 by 65 to 81%.

[0186] Figure 5 represents the chromatograms before and after reaction. For each sample, a triplicate is carried out to ensure the reproducibility of the analysis, the conversions are calculated with 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 represents in particular the chromatograms of the RMG380 heavy fuel oil used in step i) (figure 5-a), of the oxidized heavy fuel oil at the end of step i) (figure 5-b), of the oxidized heavy fuel oil after liquid-liquid extraction (figure 5-c), and of the DMF solvent after liquid-liquid extraction (figure 5-d).

Claims

Claims 1. Process for the oxydesulfurization 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 a 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 an ordered 2-dimensional hexagonal mesoporous structure, with mesopores having a length of at most 300 nm, * heavy fuel oil contains at least 0.5% by mass of the element sulfur, relative to the total mass of the heavy fuel oil, and has a viscosity greater than 1.8x10 -4 m 2 / s at 50°C, and * the metal oxide is chosen from titanium, molybdenum, and tungsten oxides.

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

3. 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. Process according to any one of the preceding claims, characterized in that the catalyst is in the form of extrudates.

5. Method 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 m 2 / g at 600 m 2 / g.

6. Method according to any one of the preceding claims, characterized in that the catalyst has a pore volume ranging from 0.7 cm 3 / g at 1 cm 3 / g.

7. 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. Method according to any one of the preceding claims, characterized in that the mesopores of the catalyst have walls having a thickness ranging from 3 to 6 nm.

9. Method according to any one of the preceding claims, characterized in that it further comprises, before step i), a step a) of preparation of the mesoporous silica involving the contacting under pH conditions ranging from 3 to 7 of a silica precursor and an organic polymer capable of forming mesopores after calcination.

10. Method according to any one of the preceding claims, characterized in that the heavy fuel oil used in step i) has a boiling temperature greater than 150°C.

11. Method according to any one of the preceding claims, characterized in that the oxidizing agent is hydrogen peroxide.

12. Method according to any one of the preceding claims, characterized in that step i) is carried out at a temperature ranging from 50°C to 100°C.

13. Method according to any one of the preceding claims, characterized in that step i) is carried out with vigorous stirring, imposing a stirring speed greater than 500 revolutions per min.

14. Method according to any one of the preceding claims, characterized in that step i) is carried out in a reactor of volume Vi and in the presence of a volume V2 of heavy fuel oil, so that the volume ratio V2 / V1 is greater than 0.

1.

15. Use of a catalyst as defined in any one of claims 1 to 8, for the oxidative desulfurization of at least one heavy fuel oil comprising at least 0.5% by mass of element sulfur, relative to the total mass of the heavy fuel oil, and having a viscosity greater than 1.8x10 -4 m 2 / s at 50°C.

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