Fuel mixture comprising marine fuel and BIO-oil

Abstract

Fuel mixture comprising: (a) from 65% by weight to 98% by weight, preferably from 70% by weight to 97% by weight, of marine fuel; (b) from 2% by weight to 35% by weight, preferably from 3% by weight to 30% by weight, of bio-oil with a glyceride content comprised between 70% by weight and 100% by weight, preferably between 75% by weight and 100% by weight, with respect to the total weight of the bio-oil; the sum of (a) + (b) being equal to 100; wherein said marine fuel has the following characteristics: - a density, at 15°C, comprised between 890 kg / m3 and 1020 kg / m3, preferably comprised between 910 kg / m3 and 1010 kg / m3; - a kinematic viscosity, at 50°C, comprised between 6 mm2 / s and 1950 mm2 / s, preferably comprised between 20 mm2 / s and 1900 mm2 / s, more preferably comprised between 35 mm2 / s and 1850 mm2 / s; - a total amount of hot post-filtration sediment (TSA - Total Sediment Aged) less than or equal to 0.1% m / m; - an acidity (TAN - Total Acid Number) less than or equal to 1 mg KOH / g, preferably comprised between 0.05 mg KOH / g and 0.5 mg KOH / g; - a Conradson carbon residue (CCR) less than or equal to 20% m / m. Said fuel mixture can advantageously be used, as such, or mixed with other renewable or fossil marine fuels, in combustion engines for ships.

Description

[0001] FUEL MIXTURE COMPRISING MARINE FUEL AND BIO-OIL

[0002] The present invention relates to a fuel mixture comprising marine fuel and bio-oil.

[0003] More particularly, the present invention relates to a fuel mixture comprising marine fuel and bio-oil, in specific amounts, said marine fuel having specific characteristics.

[0004] Said fuel mixture can advantageously be used, as such, or mixed with other renewable or fossil marine fuels, in combustion engines for ships.

[0005] Therefore, the present invention also relates to the use of said fuel mixture as such, or mixed with other renewable or fossil marine fuels, in combustion engines for ships.

[0006] Marine fuels are traditionally produced by the distillation of oil, but due to the strong environmental impact these fuels have, it has become necessary to study marine fuels that can reduce greenhouse gas (GHG) emissions. In fact, the International Maritime Organisation (IMO) has the goal of achieving “net-zero” total annual greenhouse gas emissions from international shipping by 2050.

[0007] There are two basic types of marine fuel: distillate based marine fuel, also known as Marine Gas Oil (MGO) or Marine Diesel Oil (MDO); and residual based marine fuel [Residual Marine Fuel Oil (RMFO)], also known as Heavy Marine Fuel Oil (HMFO)].

[0008] Large ocean-going vessels have relied on residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)], to power large combustion engines for over 50 years.

[0009] However, the high content of heavy substances, and in particular aromatic- based substances (for example, polynuclear aromatic compounds, asphaltenes) in residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)] may be critical for optimal combustion in the combustion engines in which it is used. Furthermore, when said residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)] is stored for a long period of time and / or heated, its stability begins to deteriorate and aromatic substances (for example, polynuclear aromatic compounds, asphaltenes) precipitate in the fuel causing an increase in the amount of sediment.

[0010] In particular, the stability of asphaltenes in residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO) is of paramount importance for several reasons such as, for example: sludge formation as asphaltenes tend to clump together, forming sticky, highly viscous sludge in storage tanks; their formation can cause operational problems, clog filters and reduce the efficiency of the engine supply system; impact on combustion because when they burn, asphaltenes can form carbon deposits on the internal surfaces of engines, including pistons and valves; said carbon deposits can reduce engine efficiency and cause maintenance problems; emissions of pollutants as the presence of asphaltenes can influence the composition of emissions produced during combustion; for example, it can contribute to the formation of particulate matter (PM) and nitrogen oxides (NOX), which are harmful air pollutants.

[0011] In summary, the stability of asphaltenes is crucial to ensure the efficient and sustainable operation of ships, reduce pollution and maintain operational safety.

[0012] In order to reduce the total annual greenhouse gas emissions from international shipping, several studies have been carried out on alternative marine fuels that have improved stability and can improve combustion in the combustion engines in which they are used.

[0013] For example, international patent application WO 2023 / 037049 relates to a mixture of marine fuel having a kinematic viscosity comprised between 1 mm2 / s and 700 mm2 / s measured at 50°C according to standard EN ISO 3104: 1996, and comprising 0.5% by volume to 50% by volume of refined cashew nutshell liquid, said refined cashew nutshell liquid comprising at least 50% by weight of cardanol, said marine fuel mixture having at least one of the characteristics in accordance with standard ISO 8217:2017(E) for residual and distillate based marine fuels. Said patent application also mentions the use of said refined cashew nutshell liquid comprising at least 50% by weight of cardanol as an asphaltene stabiliser in residual and distillate based marine fuels. The aforementioned mixture is said to reduce greenhouse gas emissions and be more stable due to the increased stability of the asphaltenes.

[0014] International patent application WO 2023 / 037050 relates to a mixture of marine fuel having a kinematic viscosity comprised between 1 mm2 / s and 700 mm2 / s measured at 50°C according to standard EN ISO 3104:2020, and comprising 0.5% by volume to 50% by volume of palm oil effluent sludge bottom, said marine fuel mixture having at least one of the characteristics in accordance with standard ISO 8217:2017(E) for residual and distillate based marine fuels. The aforementioned mixture is said to meet the characteristics of standard marine fuels.

[0015] International patent application WO 2022 / 129681 relates to a method for producing marine fuel components comprising: a) supplying a feedstock comprising tall oil pitch, b) subjecting the feedstock to hydrotreatment to produce a hydrotreated tall oil pitch, wherein said hydrotreatment is carried out at a pressure comprised between 30 barg and 200 barg, at a temperature comprised between 300°C and 350°C, in the presence of a hydrogen stream and one or more hydrotreatment catalysts, and c) fractionation of the hydrotreated tall oil pitch into a first fraction and a second fraction, wherein the second fraction is the marine fuel component. The aforementioned second fraction is said to be usable as marine fuel as such or, alternatively, in a mixture with other renewable or fossil marine fuel components.

[0016] US patent application US 2022 / 0259510 relates to a method for improving or maintaining the stability and / or compatibility of a hydrocarbon residual fuel comprising: (a) mixing at least 5% m / m-95% m / m of a residual hydrocarbon component with at least 5% m / m-80% m / m of an alkyl fatty acid ester component or (b) mixing at least 5% m / m-80% m / m of an alkyl fatty acid ester component with a stable residual carbon composition comprising (i) at least 5% m / m-95% m / m of a residual hydrocarbon component and (ii) up to 90% m / m of a non-hydrotreated hydrocarbon, a hydrotreated hydrocarbon or any combination thereof; wherein the fatty acid alkyl ester component is mixed with the stable residual fuel composition before at least one other fuel composition is added which reduces the solvent power of the asphaltenes of the residual fuel composition.

[0017] International patent application WO 2024 / 015295 relates to a marine fuel or a fuel mixture comprising: a mixture of heavy residual fuel oil and one or more of: a) biodiesel distillation residues and b) renewable diesel comprising at least 70% n- paraffins, wherein said marine fuel or fuel mixture contains less than 3.5% by weight of sulphur. The aforementioned marine fuel or fuel mixture are said to be able to reduce carbon emissions during their life cycle.

[0018] The European Renewable Energy Directive III (RED III), in Annex IX, lists feedstocks that can be used for the production of biofuels and biogas. These include feedstocks such as, for example: vegetable oils not competing with the food chain, oils from cultivation on marginal land, animal fats (comprising glycerides and / or fatty acids), lignocellulosic biomass, waste from industrial processes, and the like. However, not all feedstocks can be used as feed in traditional biorefinery processes, thus preventing their exploitation: this may be due either to their chemical nature, which would lead to end products that are not in specification [for example, in the case of cashew nutshell liquid (CNSL) oil, which would increase the aromatics content in the end product beyond the limits], or because of the pollutants they contain that could cause problems with catalyst poisoning and / or problems with the integrity of the system (for example, in the case of the presence of many acidic components or many chlorides that could give rise to corrosion phenomena). In order to be used in the production of biofuels, said feedstocks (for example, vegetable oils and animal fats) often have to undergo upgrading processes such as de-oxygenation and isomerisation processes in order to obtain products that are directly usable as fuels, in particular as fuels for automotive diesel engines [for example, HVO (Hydrotreated Vegetable Oil), or for aviation].

[0019] The Applicant set out to solve the problem of utilising feedstocks containing glycerides, in particular bio-oils containing glycerides, directly, in the absence of upgrading processes, into marine fuels, in particular residual based marine fuel [Residual Marine Fuel Oils (RMFO) or Heavy Marine Fuel Oils (HMFO)]. In particular, the Applicant set out to solve the problem of finding a fuel mixture comprising marine fuel, in particular residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)], and bio-oil having a specific glyceride content, that could be obtained through a simple, low-energy process, that would reduce greenhouse gas (GHG) emissions and increase the stability of asphaltenes.

[0020] The Applicant has now found a fuel mixture comprising marine fuel, in particular residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)], and bio-oil having a specific glyceride content, in specific amounts, said marine fuel having specific characteristics, which can be obtained by means of a simple, low-energy process, and exhibits an improvement in the stability of the asphaltenes with respect to the initial marine fuel without adversely affecting the remaining characteristics such as, for example, density and viscosity. Said improvement in the stability of asphaltenes inhibits the formation of deposits in engines that are produced on injectors, pistons and piston rings, which could give rise to tribological phenomena (abrasive wear) and delayed combustion (increased flame area in the cylinder), with a reduction in the lubricating power exerted by the fuel itself. Said fuel mixture also has a reduction in greenhouse gas (GHG) emissions. Said fuel mixture can advantageously be used, as such, or mixed with other renewable or fossil marine fuels, in combustion engines for ships.

[0021] The object of the present invention is therefore a fuel mixture comprising:

[0022] (a) from 65% by weight to 98% by weight, preferably from 70% by weight to

[0023] 97% by weight, of marine fuel;

[0024] (b) from 2% by weight to 35% by weight, preferably from 3% by weight to 30% by weight, of bio-oil with a glyceride content comprised between 70% by weight and 100% by weight, preferably comprised between 75% by weight and 100% by weight, with respect to the total weight of the bio-oil; the sum of (a) + (b) being equal to 100; wherein said marine fuel has the following characteristics: a density, at 15°C, comprised between 890 kg / m3and 1020 kg / m3, preferably comprised between 910 kg / m3and 1010 kg / m3; a kinematic viscosity, at 50°C, comprised between 6 mm2 / s and 1950 mm2 / s, preferably comprised between 20 mm2 / s and 1900 mm2 / s, more preferably comprised between 35 mm2 / s and 1850 mm2 / s; a total amount of hot post-filtration sediment (TSA - Total Sediment Aged) less than or equal to 0.1% m / m; an acidity (TAN - Total Acid Number) less than or equal to 1 mg KOH / g, preferably comprised between 0.05 mg KOH / g and 0.5 mg KOH / g; a Conradson carbon residue (CCR) less than or equal to 20% m / m.

[0025] For the purpose of the present description and of the following claims, the characteristics of marine fuel have been measured in accordance with standard ISO 8217:2017.

[0026] For the purpose of the present description and of the following claims, the definitions of the numeric ranges always include the extremes unless specified otherwise.

[0027] For the purpose of the present description and of the following claims, the term “comprising” also includes the terms “which essentially consists of’ or “which consists of’.

[0028] In accordance with a preferred embodiment of the present invention, said marine fuel is a residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)].

[0029] For the purpose of the present description and of the following claims, the term “bio-oil” means any oil from a renewable (bio) source, including plant sources (for example, vegetable fats, vegetable oils, vegetable waxes), animal sources (for example, lard, tallow, yellow fat, brown fat, animal oils, animal waxes, fish fats, fish oils and fish waxes), microbial sources (for example, algae, bacteria, moulds, filamentous fungi). The re-use of waste oils from the food industry is also considered a renewable source, as are oils from the conversion of waste, such as municipal and slaughterhouse waste.

[0030] In accordance with a preferred embodiment of the present invention, the glycerides contained in said bio-oil have general formula (I): wherein Ri, R2 and R3, equal to or different from each other, represent a hydrogen atom, or are selected from C10-C28, preferably C12-C24, alkyl groups, linear or branched, saturated or unsaturated, provided that at least one of Ri, R2 and R3 represents an alkyl group.

[0031] In accordance with a preferred embodiment of the present invention, said biooil may contain free fatty acids comprising from 10 to 28 carbon atoms, preferably from 12 to 24 carbon atoms.

[0032] In accordance with a preferred embodiment of the present invention, said biooil may have a free fatty acid content comprised between 0.1% by weight and 30% by weight, preferably comprised between 0.5% by weight and 25% by weight, with respect to the total weight of said bio-oil.

[0033] In accordance with a further embodiment of the present invention, said biooil may contain further compounds such as, for example: aromatic compounds such as, for example, alkyl phenols; proteins and / or compounds resulting from the degradation of proteins such as, for example, amides, amino acids; carbohydrates and / or compounds resulting from the degradation of carbohydrates such as, for example, sugars, alcohols.

[0034] In accordance with a preferred embodiment of the present invention, said biooil may have a content of further compounds, when present, comprised between 0.01% by weight and 15% by weight, preferably comprised between 0.1% by weight and 10% by weight, with respect to the total weight of said bio-oil.

[0035] As mentioned above, said fuel mixture can advantageously be used, as such, or mixed with other renewable or fossil marine fuels, in combustion engines for ships.

[0036] Accordingly, it is a further object of the present invention the use of the fuel mixture as such, or mixed with other renewable or fossil marine fuels, in combustion engines for ships.

[0037] EXAMPLES

[0038] The analysis and characterization methods reported below were used. Turbiscan Stability Index (TSI)

[0039] The stability of asphaltenes in the fuel mixtures obtained in the following examples was assessed using Turbiscan Tower® (MICROTRAC Particle Characterizati on) .

[0040] For this purpose, 0.2 ml of the fuel mixture and 19.8 ml of / / -heptane (Merck) were placed in the analysis cell: everything was shaken, at room temperature (25°C), for 10 seconds, and then placed in the scanning station.

[0041] The aforementioned Turbiscan Tower® works by using light scattering to detect particle migration and cluster formation in the liquid dispersion. It has two detectors, working in transmittance (T) and backscatter (BS) mode (A = 880 nm), and therefore transparent and opaque samples were analysed.

[0042] For an objective stability comparison, it was necessary to take global destabilisation into account: this means that the extent of destabilisation in the entire sample to be analysed must be compared quantitatively.

[0043] The Turbiscan Stability Index (TSI) was calculated using a personal computer equipped with Turbisoft software (MICROTRAC Particle Characterization). Peptization index (“P-value”)

[0044] The peptization index (“P-value”) was measured in accordance with standard UNI20011-NOM139.

[0045] Measurement of the amount of glycerides (% by weight), the amount of free fatty acids (% by weight) and alkyl phenols (% by weight) of bio-oils

[0046] The amount of glycerides was determined by13C-NMR spectroscopic analysis by operating as follows.

[0047] The bio-oil sample to be analysed was diluted in deuterated chloroform (CDCL) so as to obtain a solution with a concentration of 20 mg bio-oil per ml chloroform, and the analysis was carried out using a Varian 500 MHz spectrometer, at a temperature of 298 K, with the following instrumental parameters:

[0048] The integration of the spectral areas shown in Figure 1 of the13C-NMR spectrum allows the quantification of the different types of alkyl chains and to obtain information concerning mono-, di- and tri-glycerides. Knowing the relative quantities of13C signals, and using the method described by Vlahov G. in “Progress in Nuclear Magnetic Resonance" (1999), Vol. 35, pages 341-357, the percentage of molecules present can be calculated.

[0049] The areas of the F and E signals in the13C-NMR spectrum shown in Figure 1, provide the relative amount of free fatty acids with respect to the amount of esterified chains: free fatty acids (% by weight = 100 ■ F E + F) glycerides (% by weight) = 100 — free fatty acids (% by weight).

[0050] The alkyl phenols were evaluated from the aromatic carbons zone between 100 ppm and 165 ppm in the13C-NMR spectrum. The amounts of the four different species of alkyl phenols were evaluated using the four signals summarised in the following table:

[0051] Table

[0052] REGION 13C SHIFT QUANTIFIED (ppm) SPECIES

[0053] Alkyl- 163 Anacardic acid phenols 120 Cardanol

[0054] 155 2-methylcardol

[0055] 100 Cardol The above four key areas represent one phenolic carbon per molecule except in the case of 2-methylcardol. In fact, the 100 ppm signal that was used for its quantification is given by 2 equivalent carbons; therefore, the area obtained was divided by 2. The values obtained from the integration of these areas were divided by the total, i.e. by the sum of the CX areas of all the species present (that of 2- methylcardol divided by 2) to obtain the molar distribution:

[0056] Table 1 and Table 2 show the characteristics of the marine fuels and bio-oils used in the following examples.

[0057] Table 1

[0058] Table 2

[0059] (1),(2)and(3): PUREA - Austria GmbH;

[0060] 5(4): obtained by pressing cottonseed operating as described below;

[0061] (5)and(6): Bunge Italia S.p.A.;

[0062] (7): Fatty Acid Methyl Esters standard Mixture - Merck.

[0063] Cotton oil preparation

[0064] For this purpose, 10 g of cottonseed were subjected to Sohxlet extraction 10 operating as follows. The cottonseeds were placed in the extraction chamber of a Sohxlet extractor, inside a cartridge filter made from solvent-permeable filter paper, while the solvent [200 ml of / / -hexane (Merck)] was loaded into the lower flask. At the end of the extraction process, after 24 hours, at room temperature (25°C), the solvent was removed by means of a rotary evaporator (Rotavapor), obtaining an 15 oily phase consisting of cotton oil.

[0065] Examples 1-8 (Invention)

[0066] Marine fuel and bio-oil mixtures

[0067] Marine fuel was placed in a 1 -litre beaker [Fuel oil (2) - Fuel Oil 380 mm2 / s RMG380 0.5%S - Eni S.p.A having a kinematic viscosity, at 50°C, of 299.3 mm2 / s] 20 (the amounts are provided in Table 3) and, after keeping the beaker at 90°C for 24 hours, bio-oil was added (the amounts are provided in Table 3): the temperature was allowed to drop spontaneously to 70°C and the whole was kept at said temperature, under stirring, for 30 minutes, obtaining a fuel mixture that was subjected to Turbiscan Stability Index (TSI) analysis operating as described above: the data obtained are shown in Table 4, Figure 2 and Figure 3 [the ordinate shows the values of the Turbiscan stability index (TSI) at 30 minutes; the abscissa shows the number of the reference mixture. Figure 2 and Figure 3 also show both the Turbiscan Stability Index (TSI) of the marine fuel obtained by operating as described above, and the theoretical Turbiscan Stability Index (TSI) of the marine fuel calculated according to the following formula:

[0068] TSIfheoretical TSI Marine fuel used * (100 - % by W eightbio-oil) / 100. Table 3 Table 4

[0069] EXAMPLES 9 -13 (invention) and 14 (comparative)

[0070] Marine fuel and bio-oil mixtures Marine fuel was placed in a 1 -litre beaker [Fuel oil (3) - Fuel Oil 380 mm2 / s

[0071] RMG380 3.5%S - Eni S.p.A having a kinematic viscosity, at 50°C, of 165.8 mm2 / s] (the amounts are provided in Table 5) and, after keeping the flask at 90°C for 24 hours, bio-oil was added (the amounts are provided in Table 5): the temperature was allowed to drop spontaneously to 70°C and the whole was kept at said temperature, under stirring, for 30 minutes, obtaining a fuel mixture that was subjected to Turbiscan Stability Index (TSI) analysis operating as described above: the data obtained are shown in Table 6 and Figure 4 [the ordinate shows the values of the Turbiscan stability index (TSI) at 30 minutes; the abscissa shows the number of the reference mixture. Figure 4 also shows both the Turbiscan Stability Index (TSI) of the marine fuel obtained by operating as described above, and the Turbiscan Stability Index (TSI) of the marine fuel theoretically calculated as described above in Examples 1-8.

[0072] Table 5

[0073] Table 6

[0074] Examples 15-19 (Invention)

[0075] Marine fuel and bio-oil mixtures

[0076] Marine fuel was placed in a 1 -litre beaker [Fuel oil (4) - Fuel Oil 700 mm2 / s RMK700 3.5%S max - Eni S.p.A having a kinematic viscosity, at 50°C, of 676.3 mm2 / s] (the amounts are provided in Table 7) and, after keeping the flask at 90°C for 24 hours, bio-oil was added (the amounts are provided in Table 7): the temperature was allowed to drop spontaneously to 70°C and the whole was kept, at said temperature, under stirring, for 30 minutes, obtaining a fuel mixture that was subjected to Turbiscan Stability Index (TSI) analysis operating as described above: the data obtained are shown in Table 8, Figure 5 and Figure 6 [the ordinate shows the values of the Turbiscan stability index (TSI) at 30 minutes; the abscissa shows the number of the reference mixture. Figure 5 and Figure 6 also show both the Turbiscan Stability Index (TSI) of the marine fuel obtained by operating as described above, and the theoretical Turbiscan Stability Index (TSI) of the marine fuel calculated as described above in Examples 1-8.

[0077] Table 7 Table 8

[0078] EXAMPLES 20-29 (invention) and 30-31 (comparative)

[0079] Marine fuel and bio-oil mixtures

[0080] Marine fuel was placed in a 1 -litre flask [Fuel oil (5) - Fuel Oil 700 mm2 / s 5 RMK700 3.5%S max - Eni S.p.A having a kinematic viscosity, at 50°C, of 1786 mm2 / s] (the quantities are provided in Table 9) and, after keeping the flask at 90°C for 24 hours, bio-oil was added (the amounts are provided in Table 9): the temperature was allowed to drop spontaneously to 70°C and the whole was kept, at said temperature, under stirring, for 30 minutes, obtaining a fuel mixture that was 0 subjected to Turbiscan Stability Index (TSI) analysis operating as described above: the data obtained are shown in Table 10, Figure 7 and Figure 8 [the ordinate shows the values of the Turbiscan stability index (TSI) at 30 minutes; the abscissa shows the number of the reference mixture. Figure 7 and Figure 8 also show both the Turbiscan Stability Index (TSI) of the marine fuel obtained by operating as 5 described above, and the theoretical Turbiscan Stability Index (TSI) of the marine fuel calculated as described above in Examples 1-8.

[0081] Table 9

[0082]

[0083] Table 10

Claims

CLAIMS1. Fuel mixture comprising:(a) from 65% by weight to 98% by weight, preferably from 70% by weight to 97% by weight, of marine fuel;(b) 2% by weight to 35% by weight, preferably from 3% by weight to 30% by weight, of bio-oil with a glyceride content comprised between 70% by weight and 100% by weight, preferably comprised between 75% by weight and 100% by weight, with respect to the total weight of the bio-oil; the sum of (a) + (b) being equal to 100; wherein said marine fuel has the following characteristics: a density, at 15°C, comprised between 890 kg / m3and 1020 kg / m3, preferably comprised between 910 kg / m3and 1010 kg / m3; a kinematic viscosity, at 50°C, comprised between 6 mm2 / s and 1950 mm2 / s, preferably comprised between 20 mm2 / s and 1900 mm2 / s, more preferably comprised between 35 mm2 / s and 1850 mm2 / s; a total amount of hot post-filtration sediment (TSA - Total Sediment Aged) less than or equal to 0.1% m / m; an acidity (TAN - Total Acid Number) less than or equal to 1 mg KOH / g, preferably comprised between 0.05 mg KOH / g and 0.5 mg KOH / g; a Conradson carbon residue (CCR) less than or equal to 20% m / m.

2. Fuel mixture according to claim 1, wherein said marine fuel is a residual based marine fuel [Residual Marine Fuel Oil (RMFO) or Heavy Marine Fuel Oil (HMFO)].

3. Fuel mixture according to claim 1 or 2, wherein the glycerides contained in said bio-oil have the general formula (I):wherein Ri, R2 and R3, equal to or different from each other, represent a hydrogenatom, or are selected from C10-C28, preferably C12-C24, alkyl groups, linear or branched, saturated or unsaturated, provided that at least one of Ri, R2 and R3 represents an alkyl group.

4. Fuel mixture according to any one of the preceding claims, wherein said biooil contains free fatty acids, said free fatty acids comprising 10 to 28 carbon atoms, preferably 12 to 24 carbon atoms.

5. Fuel mixture according to claim 4, wherein said bio-oil has a free fatty acid content comprised between 0.1% by weight and 30% by weight, preferably comprised between 0.5% by weight and 25% by weight, with respect to the total weight of said bio-oil.

6. Fuel mixture according to any one of the preceding claims, wherein said biooil contains further compounds such as aromatic compounds such as, alkyl phenols; proteins and / or compounds resulting from the degradation of proteins such as, amides, amino acids; carbohydrates and / or compounds resulting from the degradation of carbohydrates such as, sugars, alcohols.

7. Fuel mixture according to claim 6, wherein said bio-oil has a content of further compounds, when present, comprised between 0.01% by weight and 15% by weight, preferably comprised between 0.1% by weight and 10% by weight, with respect to the total weight of said bio-oil.

8. Use of the fuel mixture according to any one of claims 1 to 7, as such, or in a mixture with other renewable or fossil marine fuels, in combustion engines for ships.

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