NEW SULFUR ADDITIVES AND ANTI-FOULING COMPOUNDS FOR BIOFUEL PRODUCTION

Abstract

The present invention relates to a process for producing biofuel from a feed comprising an unsaturated oil derived from a bio-based raw material and / or waste, characterized in that a mercaptan of the following general formula (I): XR1-Y(I) is added upstream or at the inlet of the preheating device, wherein: R1 is a linear or branched (C1-C30)alkylene; X is selected from a hydrogen atom, HO-, HOOC-, or HS-(CH2)nC(O)-O-, with n being an integer between 1 and 8; Y is an -SH group or a hydrogen atom; and wherein if Y is a hydrogen atom, then X is an -OC(O)-(CH2)n-SH group. The mercaptan can also be combined with another sulfur compound, in particular dimethyl disulfide.

Description

Title of the invention: NEW SULFUR ADDITIVES AND ANTI-FOULING COMPOSITIONS FOR THE PRODUCTION OF BIOFUELS Scope of the invention

[0001] The present invention relates to a biofuel production process comprising a step of adding a mercaptan as an antifouling additive, as well as the use of this mercaptan as an antifouling additive for a preheating device. The present invention also relates to a composition comprising a mercaptan according to the invention and dimethyl disulfide, particularly useful as an antifouling composition for a preheating device. Technical background

[0002] Today, environmental issues associated with fossil fuel consumption are paramount, and reducing this consumption is a major challenge on a global scale. Alternative fuels, called biofuels, derived from biomass or waste, have therefore been developed to reduce greenhouse gas emissions and to anticipate the depletion of global fossil fuel reserves. These biofuels also allow for the valorization of previously unused waste such as cooking oils or plastic waste. Their use, alone or blended with fossil fuels, represents one of the alternative and renewable solutions available to us for reducing our dependence on fossil fuels.

[0003] Thus, there are two main biofuel production sectors: the "gasoline" sector and the "biodiesel" sector. The "gasoline" sector includes bioethanol, its derivative ETBE (ethyl tert-butyl ether), and synthetic biogasolines. The diesel biofuel sector, often grouped under the name "biodiesel," includes various biofuels, which can be produced primarily by transesterification or hydrotreatment. In the latter case, they can also be called renewable diesels.

[0004] The transesterification reaction consists of reacting a fat (the triglycerides contained in oils or fats) with an alcohol (methanol or ethanol) to obtain fatty acid esters (generally, fatty acid methyl ester or fatty acid methyl ester “FAME” in English), usable as a biofuel.

[0005] Hydrotreatment consists of treating fatty substances such as vegetable oils, oils derived from animal fats or oils derived from waste with hydrogen. This process yields, under a generic designation, Hydrotreated Vegetable Oils for Diesel (HVHTG). Hydrotreatment can be carried out in a dedicated unit such as a biorefinery or as co-treatment within a refinery: the oil is mixed upstream of the hydrotreatment unit with a diesel fuel stream. This process is called co-processing. Such processes are widely known and described, for example in US patents 3,425,810, FR 2,538,813 A1, and US patent 2022 / 0145193.

[0006] As indicated above, the raw materials used to produce biofuels by hydrotreatment come from very diverse sources: biomass, agricultural waste, forestry waste, municipal waste, used cooking oil, or even recycled plastics.Depending on the origin of the raw material used, the properties of the oils to be hydrotreated will vary considerably: different levels of free fatty acids and / or glycerides, different number and position of unsaturates, variable hydrocarbon chain lengths, or the presence of specific impurities. The nature and variability of the raw materials will have consequences for the biofuel production process by hydrotreatment.

[0007] Indeed, the oils used contain unsaturated fatty acids and / or glycerides and / or other types of unsaturated compounds. When heated, these compounds can react together, giving rise to dimers, which are again reactive, and oligomers. Their accumulation leads to the formation of fouling deposits, particularly in the raw material preheating devices.Organic debris (e.g., cellulose or lignin) or inorganic debris (e.g., sand) that are insoluble and contribute to the formation of these deposits can also be found in the raw material stream. It should be noted that other types of deposits can form in the hydrotreating reaction zone: these are generally linked to the formation of highly aromatic by-products (coke), leading to a loss of catalyst activity.

[0008] Fouling deposits that form in preheating devices require specific treatment and represent a real problem for (bio)refiners. They lead to a loss of raw material and a loss of efficiency. They can form a more or less thick and insulating layer inside the preheating devices, which makes it more difficult for the raw materials to reach the desired temperature. Energy consumption must then be increased to preheat to the required temperature. Moreover, as these deposits accumulate, they can eventually clog the installations. Very costly shutdowns of the production unit for cleaning are then necessary.

[0009] There is therefore a need for an improved biofuel production process, in which fouling of the elements upstream of the hydrotreating reactor, in particular of the preheating devices, is limited or even avoided.

[0010] Document WO 2013 / 016256 describes the use of organic polysulfides to reduce this type of fouling. These polysulfides have the general formula R-Sx-R, where R is a linear or branched alkyl containing 2 to 15 carbon atoms and x is an integer between 1 and 8. However, when such compounds are used over the long term, other types of deposits form. Above 170 °C, these polysulfides decompose, and this decomposition can lead to the formation of a deposit called "Carsul," which consists of sulfur-containing polyaromatic molecules. This solution is therefore not entirely satisfactory.

[0011] Thus, there is still a need for additives or antifouling compositions, particularly for heating devices, which are effective and suitable for biofuel production.

[0012] An objective of the present invention is to provide a process for the production of biofuels in which fouling of the elements upstream of the hydrotreating reactor, in particular of the preheating devices, is limited or even avoided.

[0013] Another objective of the present invention is to provide a new additive or a new composition which makes it possible to treat and / or limit and / or prevent fouling of the elements upstream of the hydrotreating reactor, in particular of preheating devices, of biofuel production units.

[0014] Another objective of the present invention is to provide a new antifouling additive or composition that can be easily introduced into biofuel production units (biorefineries or refineries), and more particularly without modification of the production line. Brief description of the invention

[0015] The present invention fulfills, in whole or in part, the above objectives. The inventors have discovered that mercaptans of general formula (I) as defined below have antifouling activity on preheating devices, particularly on preheating devices used upstream of hydrotreating reactors. In particular, they are more effective than the organic polysulfides described for this application.

[0016] Moreover, they exhibit an even improved antifouling activity when combined with another sulfur compound, of the following general formula (II):

[0017] R2-Sm-R3 (II)

[0018] in which: - R2 and R3, identical or different, are chosen from among the hydrogen atom, the methyl radical and the ethyl radical; - m is an integer equal to 1 or 2; and

[0019] provided that if R2 is an ethyl radical, then R3 is a hydrogen atom.

[0020] In a particularly preferred manner, the sulfur compound of general formula (II) is dimethyl disulfide (hereinafter DMDS, of formula CH3-SS-CH3). Such a combination exhibits an improved antifouling effect and is perfectly suited to industrial applications.

[0021] The injection of these new anti-fouling additives can, for example, be carried out via the injection points of the sulfur compound of general formula (II), in particular DMDS, which may sometimes already be present in the process. It can therefore be done without additional cost or adaptation required for (bio)refineries.

[0022] Thus, the present invention relates to a process for producing biofuel from a stream comprising an unsaturated oil derived from a bio-based raw material and / or waste, said process comprising the following steps:

[0023] a / said flow is introduced into a preheating device;

[0024] b / said preheated stream is introduced into a hydrotreating reactor;

[0025] c / the hydrotreatment of said stream is carried out with hydrogen, in the presence of a hydrotreating catalyst, in order to obtain a hydrotreated stream;

[0026] d / Optionally, the hydrotreated stream obtained at the outlet of the hydrotreating reactor is separated in order to obtain:

[0027] - a hydrotreated organic stream,

[0028] - a gaseous flow comprising H2, H2S and possibly CO and / or CO2, And

[0029] - an aqueous flow;

[0030] e / optionally, an isomerization and / or cracking reaction is carried out on the hydrotreated stream recovered at the end of step c) and / or step d), with hydrogen, in the presence of an isomerization and / or cracking catalyst; and

[0031] f / the biofuel obtained at the end of one of the steps c), d) or e) is recovered;

[0032] said process being characterized in that upstream or at the inlet of the preheating device a mercaptan of general formula (I) following: X-Rl-Y (I)

[0033] in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched; - X is chosen from a hydrogen atom, HO-, HOOC- or HS-(CH2)nC(O)-O- with n being an integer between 1 and 8, preferably between 1 and 4, preferably n is equal to 1 or 2; - Y is an -SH group or a hydrogen atom;

[0034] and in which if Y is a hydrogen atom, then X is a -OC(O)-(CH2)n-SH group.

[0035] The present invention also relates to the use of a mercaptan as an antifouling additive for a preheating device of a stream comprising an unsaturated oil, preferably from a bio-based raw material and / or waste, said mercaptan having the following general formula (I): X-Rl-Y (I)

[0036] in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched; - X is chosen from a hydrogen atom, HO-, HOOC- or HS-(CH2)nC(O)-O- with n being an integer between 1 and 8, preferably between 1 and 4, preferably n is equal to 1 or 2; - Y is an -SH group or a hydrogen atom;

[0037] and in which if Y is a hydrogen atom, then X is a -OC(O)-(CH2)n-SH group.

[0038] The present invention relates to a composition comprising mercaptan of general formula (I) as according to the invention and dimethyl disulfide, and its use as an antifouling composition for a preheating device of a stream comprising an unsaturated oil, preferably from a bio-based raw material and / or waste.

[0039] The present invention also relates to a method for combating fouling of a preheating device of a flow comprising an unsaturated oil, preferably from a bio-based raw material and / or waste, said method comprising a step of adding upstream or at the inlet of the preheating device a mercaptan of general formula (I) such as according to the invention or of a composition such as according to the invention. Detailed description of the invention

[0040] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the following description.

[0041] It is specified that the expressions "from ... to ..." and "between ... and ..." used in this description should be understood as including each of the limits mentioned.

[0042] Biofuels are liquid or gaseous fuels obtained from the transformation of non-fossil organic raw materials. According to the invention, the unsaturated oil used can be derived from a bio-based raw material and / or waste. "Bio-based raw material" means, in particular, a raw material derived from biomass. "Biomass" means, in particular, organic matter of plant, animal, bacterial, or fungal origin (usable as energy source). Biomass can in particular be considered a renewable raw material (when its consumption is at least equal to its regeneration).

[0043] Preferably, the biofuels according to the invention are renewable fuels. More particularly, they are bionaphtha, renewable diesels, and / or sustainable aviation fuels, preferably sustainable aviation fuels. The biofuels obtained according to the invention can be blended with other petroleum fractions such as gasoline, kerosene, or diesel. They can be "drop-in fuels," meaning they can completely replace petroleum-based fuels.

[0044] As previously stated, they can be produced by hydrotreating processes that treat fatty substances such as vegetable oils, animal oils or oils derived from animal fats, or even waste oils, with hydrogen. This yields Hydrotreated Vegetable Oils for Diesel (called HVHTG).

[0045] To produce biofuels using this method, two reactors are generally required: a hydrotreating reactor, similar to conventional petroleum hydrotreating units, and an isomerization and / or light cracking reactor. There are two main types of production units for these biofuels: - the so-called "single stage" units where the two reactors are in series, and - the "two-stage" units where the hydrotreated stream is purified before reaching the isomerization and / or light cracking reactor.

[0046] Chemically, these processes hydrogenate the unsaturates in the fat chains and eliminate unwanted oxygen from the raw materials by hydrodeoxygenation (which produces H2O), and / or by hydrogenation and decarbonylation (which produces carbon monoxide C(O)), and / or by hydrogenation and decarboxylation (which produces carbon dioxide CO2). Such processes are widely known to those skilled in the art.

[0047] The biofuel production process according to the invention can be carried out in any type of hydrotreating unit having a device for preheating the raw materials (i.e., placed upstream of the hydrotreating reactor(s)). The preheating device can be a heat exchanger and / or a preheating furnace. The preheating furnace is particularly useful at startup. Subsequently, the exothermic nature of the reaction may allow the use of only a heat exchanger (although the stream containing the unsaturated oil can still pass through the preheating furnace).

[0048] Thus, the stream comprising the unsaturated oil is introduced into the preheating device (step a)). The stream comprising the unsaturated oil may also include saturated hydrocarbons of fossil and / or bio-based origin. These mixtures make it possible to reduce the number of functions to be hydrogenated and thus limit The exothermic reaction occurs in the hydrotreating reactor(s). The preheating device is used to heat the stream containing the unsaturated oil to a temperature close to the hydrotreating reaction temperature or to the hydrotreating reaction temperature itself. "Temperature close to the hydrotreating reaction" means, in particular, a temperature between 0 °C and 100 °C lower than that of the hydrotreating reaction. For example, the temperature of the stream containing the unsaturated oil exiting the preheating device is between 150 °C and 430 °C, for example between 200 °C and 400 °C, preferably between 250 °C and 380 °C, and more preferably between 250 °C and 330 °C. The stream containing the unsaturated oil is thus preheated in the preheating device and then introduced into the hydrotreating reactor for hydrotreating (step b)).

[0049] Step c) of hydrotreating is known to those skilled in the art. It can be carried out at temperatures ranging from 150 to 430 °C, preferably from 200 °C to 400 °C, and / or at a pressure ranging from 0.1 to 25 MPa, preferably from 1 to 20 MPa. When the hydrotreating reaction is carried out in a single reaction zone, the temperature can range from 200 to 400 °C, preferably from 250 to 380 °C. When there are two or more hydrotreating steps, the temperature in each reaction zone can be lower, as a milder hydrotreating process can be performed. In such embodiments, the temperature can range from 150 to 300 °C, for example, from 200 to 300 °C. Furthermore, the temperature in the first reaction zone may be lower than the temperature in the second (or subsequent) reaction zone.

[0050] Step c) of hydrotreating is carried out with hydrogen and in the presence of a hydrotreating catalyst. The hydrogen used may be fresh or recycled (from the process itself or from another unit of the (bio)refinery). It may be substantially pure or contain impurities and / or by-products, preferably such that the chemical nature and / or concentration of these impurities and / or by-products in the hydrogen does not cause a significant reduction in the activity and / or lifetime of the catalyst to which the hydrogen is exposed.

[0051] The hydrogen content can be between 50 Nm³ / m³ and 1000 Nm³ / m³ of catalyst. When relatively mild hydrotreating conditions are desired, the hydrogen content can be between 75 Nm³ / m³ and 300 Nm³ / m³, preferably between 100 Nm³ / m³ and 250 Nm³ / m³. When relatively more severe hydrotreating conditions are desired, the hydrogen content can be between 300 Nm³ / m³ and 650 Nm³ / m³, preferably between 350 Nm³ / m³ and 550 Nm³ / m³.

[0052] The catalyst used is known to those skilled in the art. It includes, in particular, one or more metals from Group VIII (columns 8, 9 and 10 of the periodic table). elements) and / or one or more metals from group VIA (column 6 of the periodic table of elements), for example Ni and / or Co and / or W and / or Mo. Preferably, the catalyst comprises a NiMo or CoMo combination, or a ternary combination such as Ni, Co and Mo or Ni, Mo and W. These metals may be in the form of oxides, sulfides or oxysulfides.

[0053] The hydrotreating catalyst is generally supported on an oxide such as alumina, silica, zirconia, titanium, or a combination thereof, or another known support material such as carbon. The catalyst may also contain other components such as promoters. By way of illustration, suitable hydrotreating catalysts are described in one or more of U.S. Patent Nos. 6,156,695; 6,299,760; 6,783,663; 7,288,182; 7,410,924 and 7,544,632, U.S. Patent Application Publications Nos. 2007 / 0084754 and 2008 / 012407, and International Publication WO 2007 / 084439.

[0054] A combination of catalysts may be used, optionally in a mixture, in the first and / or second (or subsequent) hydrotreating reaction zones. These catalysts may be arranged in a stacked bed. Alternatively, one catalyst may be used in the first hydrotreating reaction zone and a second catalyst in the second (or subsequent) hydrotreating reaction zones. For example, the first hydrotreating reaction zone may comprise a stacked bed of NiMo catalyst, followed by a CoMo catalyst. The second reaction zone may comprise a CoMo catalyst. In another example, the NiMo catalyst in the first hydrotreating zone may be replaced by a catalyst containing Ni and W metals or a catalyst containing Ni, W, and Mo metals.

[0055] Hydrotreating can be carried out at liquid space hour velocities (LHSV) of about 0.1 to about 10 h⁻¹, for example, from about 0.3 to about 5 h⁻¹ or from about 0.5 to about 5 h⁻¹. In embodiments where there are two or more hydrotreating steps, the conditions in each reaction zone (or each reactor, when the reaction zones are in separate reactors) can be milder, and as noted above, this can be achieved using lower temperatures. In such an embodiment, the LHSV is preferably from about 1 to about 5 h⁻¹.

[0056] The hydrotreated stream obtained at the outlet of the hydrotreating reactor can then be separated (step d)) in order to obtain:

[0057] - a hydrotreated organic stream (liquid stream), - a gaseous flow comprising H2, H2S and possibly CO and / or CO2, and - an aqueous flow.

[0058] Such separation can be achieved by any means known to a person skilled in the art, for example by evaporation and / or decantation.

[0059] The hydrotreated stream from step c) and / or step d) can then be recovered to carry out an isomerization and / or cracking reaction (step e)) with hydrogen, in the presence of an isomerization and / or cracking catalyst. This type of reaction is conventional and is used, in particular, to obtain liquid fuels. It is described in US patent 2022 / 0145193 (see in particular paragraphs

[0051] to

[0075] ). The catalyst can be either a catalyst (of the NiW / zeolite type) or a catalyst comprising a noble metal (for example, Pt / Al2O3), preferably a sulfide. The temperature of the isomerization and / or cracking reaction can be between 150 °C and 450 °C and the pressure can be between 1 MPa and 15 MPa.

[0060] Unsaturated oil:

[0061] The term "unsaturated oil" includes, in particular, any oil comprising at least one unsaturated organic compound, that is, an organic compound with at least one C=C double bond. Preferably, said organic compound comprises one, two, or three C=C double bonds. This oil is derived, in particular, from a raw material of vegetable and / or animal origin and / or from waste. Advantageously, said unsaturated oil may be derived from a renewable raw material.

[0062] In particular, the unsaturated oil comprises (as an unsaturated compound):

[0063] - at least one unsaturated free fatty acid; and / or

[0064] - at least one glyceride (formed from unsaturated fatty acid(s), which may be a mono-, di- or triglyceride), preferably a triglyceride; and / or

[0065] - at least one unsaturated fatty acid ester other than a glyceride, for example Ci-C5 alkyl esters of unsaturated fatty acids, such as methyl and / or ethyl esters of unsaturated fatty acids (known as FAME or FAEE in English); and / or

[0066] - an unsaturated hydrocarbon chain.

[0067] Preferably, said unsaturated oil comprises an unsaturated free fatty acid and / or a triglyceride formed from unsaturated fatty acid(s). Said fatty acids comprise in particular from 4 to 36 carbon atoms, preferably from 8 to 24 carbon atoms, preferably again from 12 to 18 carbon atoms.

[0068] More particularly, said unsaturated oil comprises at least 40% by weight, preferably at least 50% by weight, preferably still at least 60% by weight of said unsaturated compound relative to the total weight of the oil.

[0069] Said unsaturated oil may be chosen from vegetable oils, animal oils or oils derived from animal fat(s), oils derived from algae, used oils such as that used cooking oils (e.g. frying oils), pyrolysis oils from plastic(s), oils from waste and their mixtures.

[0070] Among vegetable oils, we can mention:

[0071] almond oil, peanut oil, babassu oil, camelina oil, hemp oil, canola oil, safflower oil, rapeseed oil, jatropha oil, jojoba oil, linseed oil, corn oil, mustard oil, coconut oil, olive oil, palm oil, palm kernel oil, grapeseed oil, castor oil, soybean oil, sunflower oil, rice bran oil, Jatropha curcas (Ratanjot, Wild Castor, Jangli Erandi) oil, Madhuca indica (Mohuwa) oil, Pongamia pinnata (Karanji, Honge) oil, Calophyllum inophyllum oil, Moringa oil oleifera and Azadirachta indica (Neem) oil, their derivatives and mixtures.

[0072] Among animal oils and fats (hereinafter referred to as animal oils), the following may be mentioned:

[0073] fish oil(s), lard, tallow, suet, beef fat, pork fat, whale fat, milk fats, and mixtures thereof.

[0074] Among oils derived from algae, oils derived from microalgae such as diatoms and chlorophytes are preferred.

[0075] Regarding oils derived from waste, examples include waste and recycled products from the plastics industry, the paper industry such as tall oil, and forestry. This waste is generally pyrolyzed to obtain an oil. For example, the pyrolysis of polystyrene can yield triphenylbenzene.

[0076] In particular, said unsaturated oil is selected from used cooking oils, linseed oil, rapeseed oil, soybean oil, corn oil, palm oil, animal oils, pyrolysis oils of plastic(s) and mixtures thereof.

[0077] The process according to the invention may include a preliminary step of transforming a raw material into oil, for example, transforming animal fat into oil by melting it. It may also include a preliminary step of purifying and / or filtering the unsaturated oil.

[0078] The process according to the invention includes a step of adding, upstream or at the inlet of the preheating device, a mercaptan of general formula (I) as defined below. Said mercaptan may be in the form of a composition comprising said mercaptan and DMDS.

[0079] This step helps prevent unsaturated compounds present in the oil from forming dimers and / or oligomers. They can indeed form molecules with a high molar mass (the molar mass of these molecules can vary depending on the nature of the unsaturated compound). These dimers and oligomers can to form deposits and thus foul the preheating device. In particular, the mercaptan of general formula (I) according to the invention or the composition according to the invention is added upstream or at the inlet of the preheating device to eliminate and / or reduce and / or prevent fouling. It is added in sufficient quantity to eliminate and / or reduce and / or prevent fouling of said preheating device. More particularly, said mercaptan or said composition is added intermittently, semi-continuously or continuously, preferably continuously.

[0080] For its introduction, said mercaptan or composition may be pre-mixed with the stream comprising said unsaturated oil. It is, for example, mixed upstream or at the inlet of the preheating device. In this case, preferably:

[0081] - the quantity of said mercaptan is between 1 ppm and 1000 ppm, preferably between 10 ppm and 500 ppm, and more preferably between 25 ppm and 150 ppm, relative to the total weight of said flux; or

[0082] - the quantity of said composition is between 1 and 5000 ppm, preferably between 1 ppm and 2000 ppm, preferably still between 50 ppm and 1800 ppm, and more preferably between 100 ppm and 1500 ppm, relative to the total weight of said flux.

[0083] Alternatively, the mercaptan or the composition can be introduced directly at the inlet of the preheating device, without prior mixing with the stream comprising the unsaturated oil.

[0084] The addition of the mercaptan or the composition can be done by any technique known to a person skilled in the art (for example with a pump), who can adapt the quantities introduced according to the production conditions or the nature of the unsaturated oil.

[0085] General formula mercaptan (I):

[0086] The mercaptan according to the invention has the following general formula (I): X-Rl-Y (I)

[0087] in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched; - X is chosen from a hydrogen atom, HO-, HOOC- or HS-(CH2)nC(O)-O- with n being an integer between 1 and 8, preferably between 1 and 4, preferably n is equal to 1 or 2; - Y is an -SH group or a hydrogen atom;

[0088] and in which if Y is a hydrogen atom, then X is a -OC(O)-(CH2)n-SH group.

[0089] By "alkylene" is meant in particular a divalent, saturated, linear or branched alkane group comprising from 1 to 30 carbon atom(s).

[0090] Preferably, Ri is a (C4-C30)alkylene, more preferably a (C4-Ci2)alkylene, and even more preferably a (C8-Ci2)alkylene. Most preferably, Ri is a branched alkylene as defined above. This branching is, in particular, a (Ci-C4)alkyl branch. For example, said alkylene is branched by the presence of at least one methyl and / or ethyl group, attached to the main chain.

[0091] In particular, said mercaptan corresponds to one of the following three general formulas:

[0092] R a -SH (la); HS-(CH2)nC(O)-O-Ra (Ib); HOOC-R1-SH (the);

[0093] in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched (as defined above); - Ra is a (Ci-C30)alkyl, linear or branched, preferably branched; - n is an integer between 1 and 8, preferably between 1 and 4, preferably equal to 1 or 2.

[0094] Preferably, Ra is a (C4-C30)alkyl, more preferably a (C4-Ci2)alkyl, for example a (C8-Ci2)alkyl.

[0095] Preferably, said mercaptan is of general formula (la) or (Ib), more preferably (la).

[0096] Preferably, said mercaptan is selected from the group consisting of:

[0097] 2-mercaptoethanol, n-octylmercaptan (NOM), n-dodecylmercaptan (NDM), tert-dodecyl mercaptan (TDM), tert-nonyl mercaptan (TNM), tert-butyl mercaptan (TBM), 2-ethylhexyl thioglycolate (2-EHTG), isooctyl thioglycolate (IOTG), 2-methylheptyl thioglycolate (2-MHTG), methyl thioglycolate (MTG), 1'-ethyl thioglycolate, 3-mercaptopropionic acid, methyl 3-mercaptopropionate, ethyl 3-mercaptopropionate, butyl 3-mercaptopropionate, 2-ethylhexyl 3-mercaptopropionate, isooctyl 3-mercaptopropionate, octadecyl 3-mercaptopropionate, and acid thioglycolic, preferably tert-dodecylmercaptan and 2-ethylhexyl thioglycolate.

[0098] The structure of these compounds is given in the following Table 1:

[0099] [Tables 1] 2-mercaptoethanol CAS No. 60-24-2 H n-octylmercaptan (NOM) or 1-octanethiol CAS No. 111-88-6 n-dodecylmercaptan (NDM) or 1-dodecanethiol CAS No. 112-55-0 CH3(CH2)1oCH2SH tert-dodecylmercaptan (TDM) or tert-dodecanethiol CAS No. 25103-58-06 ch3 c9h19 sf ch3 tert-nonylmercaptan (TNM) or tert-nonanethiol CAS No. 25360-10-5 C6Hi3^SH h3c gh3 tert-butylmercaptan (TBM) or tert-butylthiol CAS No. 75-66-1 ^3 h3c'ch3 thioglycolic acid (ATG) or acid mercaptoacetic acid CAS No. 68-11-1 2-ethylhexyl thioglycolate (2-EHTG) CAS No. 7659-86-1 isooctyl thioglycolate (IOTG) CAS 25103-09-7 2-methylheptyl thioglycolate (2-MHTG) H3^Af XQX r methyl thioglycolate (MTG) CAS No. 2365-48-2 O HS JI UGng ethyl thioglycolate CAS No. 623-51-8 0 HS. A / -x O ch3 3-mercaptopropionic acid CAS No. 107-96-0 O methyl 3-mercaptopropionate CAS No. 2935-90-2 O HS'^^OCHs ethyl 3-mercaptopropionate CAS No. 5466-06-8 O butyl 3-mercaptopropionate CAS No. 16215-21-7 O 2-ethylhexyl 3-mercaptopropionate CAS No. 50448-95-8 O ^CHS isooctyl 3-mercaptopropionate CAS No. 30374-01-7 Q .✓X / -x / CH3 HS OY ° ch3 octadecyl 3-mercaptopropionate CAS No. 31778-15-l

[0100] Preferably, said mercaptan is chosen from the group consisting of:

[0101] tert-dodecyl mercaptan (TDM), tert-nonyl mercaptan (TNM), tert-butyl mercaptan (TBM), 2-ethylhexyl thioglycolate (2-EHTG), isooctyl thioglycolate (IOTG), 2-methylheptyl thioglycolate (2-MHTG), butyl 3-mercaptopropionate, 2-ethylhexyl 3-mercaptopropionate and isooctyl 3-mercaptopropionate. Particularly preferred mercaptans are tert-dodecyl mercaptan and 2-ethylhexyl thioglycolate.

[0102] The mercaptan of general formula (I) as defined above can be used as an antifouling additive for a preheating device of a stream comprising an unsaturated oil, preferably from a bio-based raw material and / or waste.

[0103] Sulphur compound of general formula (II):

[0104] Surprisingly, the present inventors have discovered that the mercaptan of general formula (I) as defined above can be combined with a sulfur compound of the following general formula (II):

[0105] R2-Sm-R3 (II)

[0106] in which: - R2 and R3, identical or different, are chosen from among the hydrogen atom, the methyl radical and the ethyl radical; - m is an integer equal to 1 or 2; and

[0107] provided that if R2 is an ethyl radical, then R3 is a hydrogen atom.

[0108] In particular, the sulfur compound of general formula (II) is chosen from the group consisting of: hydrogen sulfide (H2S), methyl mercaptan (CH3-SH), dimethyl sulfide (CH3-S-CH3), dimethyl disulfide (CH3-SS-CH3) and ethyl mercaptan (CH3-CH2-SH), preferably hydrogen sulfide and dimethyl disulfide.

[0109] Preferably, R2 and R3, whether identical or different, are a hydrogen atom or a methyl radical. Most preferably, the sulfur compound of general formula (II) is dimethyl disulfide (DMDS).

[0110] This combination makes it possible in particular to improve the anti-fouling effect of the preheating device. Thus, the sulfur compound of general formula (II) following can also be added to the process according to the invention.

[0111] According to one embodiment, the mercaptan of general formula (I) and the sulfur compound of general formula (II) are introduced separately into the biofuel production process according to the invention. In this embodiment, said mercaptan is added independently of said sulfur compound, and its addition is carried out as described above. The sulfur compound of general formula (II) is sometimes used for the proper functioning of the process because it helps maintain the catalysts in a sulfuric state: it is preferably injected upstream or at the inlet of the preheating device. It can thus be injected into the stream containing the unsaturated oil. In this case, it can be introduced at concentrations ranging from 10 to 2000 ppm, preferably from 50 to 1000 ppm, and even more preferably from 75 to 800 ppm (relative to the total weight of the stream containing the unsaturated oil).

[0112] According to another embodiment, the mercaptan of general formula (I) and the sulfur compound of general formula (II) are in the form of a composition, in particular as defined below. Such a composition is preferably made with DMDS as the sulfur compound of general formula (II).

[0113] Thus, the present invention also relates to a composition comprising a mercaptan of general formula (I) such as according to the invention and DMDS.

[0114] In particular, said composition comprises at least 30%, preferably at least 65%, more preferably at least 85%, for example at least 95%, by weight of DMDS, relative to the total weight of the composition.

[0115] Preferably, said composition comprises between 1 and 50% by weight, preferably between 5 and 45% by weight, preferably again between 10 and 40% by weight, of mercaptan of general formula (I) as defined above, relative to the total weight of the composition.

[0116] Compositions comprising tert-dodecylmercaptan and DMDS or 2-ethylhexyl thioglycolate and DMDS are particularly preferred.

[0117] For example, a composition according to the invention may include, among other things: - 5 and 45% by weight, preferably between 10 and 40%, for example 15% or 35% by weight of mercaptan of general formula (I), preferably tert-dodecyl mercaptan, relative to the total weight of the composition; and - between 55 and 95% by weight of DMDS, preferably between 60 and 90% by weight, for example 65% or 85% by weight of DMDS, relative to the total weight of the composition.

[0118] Said composition may also contain one or more odor-masking agents (see, for example, international application WO 2011 / 012815A1). DMDS is commercially available. An example is DMDS Evolution® E2 marketed by ARKEMA.

[0119] Such a composition can be introduced into the process according to the invention as mentioned above.

[0120] The composition as defined above can be used as an antifouling composition for a preheating device of a flow comprising an unsaturated oil, preferably from a bio-based raw material and / or waste.

[0121] The following examples are given for illustrative purposes only and do not limit the present invention. EXAMPLES

[0122] Example 1: Anti-fouling effect of mercaptans according to the invention

[0123] Operating procedure:

[0124] Samples of 50 g of unsaturated oil used as raw material for biofuels are heated in an oven, possibly in the presence of 100 ppm of sulfur additive.

[0125] The samples are heated in capsules that simulate the behavior of an unsaturated oil in the preheaters of vegetable oil hydrotreating units, where the gaseous air has been replaced by nitrogen.

[0126] After being heated for 80 hours at 240 °C, the capsules are removed from the oven and samples are taken. The percentage by weight of high molar mass molecules (corresponding to the dimers and / or oligomers formed), relative to the total weight of the unsaturated oil, is measured by size exclusion chromatography.

[0127] The molar mass of the dimers and / or oligomers formed varies depending on the nature of the unsaturated oil tested. For linseed oil, the percentage by weight of molecules with a molar mass greater than 3500 g / mol is determined, relative to the total weight of the unsaturated oil (hereinafter referred to as "% greater than 3500"). 1) Test 1: Linseed oil alone

[0128] Linseed oil is heated without additives, as a control, according to the procedure mentioned above. The percentage by weight of molecules with a molar mass greater than 3500 g / mol is determined, relative to the total weight of the unsaturated oil.

[0129] The results are given in Table 2 below.

[0130] [Tables2] Linseed oil Unheated Heated according to protocol % greater than 3500 0 18

[0131] 2) Test 2: Linseed oil with anti-fouling additive

[0132] In this series of tests, according to the procedure mentioned above, the heated oil is linseed oil and various anti-fouling sulfur additives were added at a level of 100 ppm: - 2-EHTG: 2-Ethylhexyl thioglycolate (marketed by Arkema) - DTDDS: Di-tert-dodecyl disulfide (marketed by Arkema)

[0133] - DMDS: Dimethyl disulfide (marketed by Arkema) - Sulfrzol® 54: Di-tert-butyl polysulfide (marketed by Lubrizol) - TDM: Tert-dodecyl mercaptan (marketed by Arkema) - TPS® 20: Di-tert-dodecyl polysulfide (marketed by Arkema) - TPS® 54: Di-tert-butyl polysulfide (formerly marketed by Arkema)

[0134] The percentage by weight of molecules with a molar mass greater than 3500 g / mol is determined, relative to the total weight of the unsaturated oil.

[0135] The results are given in Table 3 below.

[0136] [Tables3] Oil + additive % greater than 3500 2-EHTG (invention) 12% TDM (invention) 12% DTDDS (comparative WO 2013 / 016256) 14% DMDS (comparative) 14% Sufrzol 54® (comparative WO 2013 / 016256) 14% TPS 20 (comparative WO 2013 / 016256) 14% TPS 54 (comparative WO 2013 / 016256) 14%

[0137] The results show that mercaptans such as those according to the invention make it possible to reduce the formation of high molar mass molecules (such as dimers and / or oligomers) when the oil is heated: they therefore have an anti-fouling activity.

[0138] In particular, this anti-fouling effect is improved compared to the polysulfides described for this application in document WO 2013 / 016256.

[0139] 3) Test 3: Linseed oil with antifouling additive and DMDS

[0140] In this series of tests, according to the procedure mentioned above, the heated oil is linseed oil and the mercaptans according to the invention or DMDS were added at a level of 100 ppm, with 100 ppm of additional DMDS.

[0141] The percentage by weight of molecules with a molar mass greater than 3500 g / mol is determined, relative to the total weight of the unsaturated oil.

[0142] The results are given in Table 4 below.

[0143] [Tables4] Linseed oil + 100 ppm mercaptan + 100 ppm DMDS 2-EHTG + DMDS (invention) TDM + DMDS (invention) DMDS (200 ppm) % greater than 3500 11% 11% 15%

[0144] The results show improved anti-fouling effectiveness, or even synergy, between the mercaptans according to the invention and DMDS: an even greater reduction in the presence of molecules with a molar mass greater than 3500 g.mol1 is observed.

Claims

1. Demands Process for producing biofuel from a stream comprising an unsaturated oil derived from a bio-based raw material and / or waste, said process comprising the following steps: a / the stream is introduced into a preheating device; b / the preheated stream is introduced into a hydrotreating reactor; c / the hydrotreating of said stream is carried out with hydrogen, in the presence of a hydrotreating catalyst, in order to obtain a hydrotreated stream; d / Optionally, the hydrotreated stream obtained at the outlet of the hydrotreating reactor is separated in order to obtain: - a hydrotreated organic stream, - a gaseous flow comprising H2, H2S and possibly CO and / or CO2, and - an aqueous flow; e / Optionally, an isomerization and / or cracking reaction is carried out on the hydrotreated stream recovered at the end of step c) and / or step d), with hydrogen, in the presence of an isomerization and / or cracking catalyst; and f / we recover the biofuel obtained at the end of one of the steps c), d) or e); said process being characterized in that a mercaptan of the following general formula (I) is added upstream or at the inlet of the preheating device: X-RrY U) in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched; - X is chosen from a hydrogen atom, HO-, HOOC- or HS-(CH2)nC(O)-O- with n being an integer between 1 and 8, preferably between 1 and 4, preferably n is equal to 1 or 2; - Y is an -SH group or a hydrogen atom; and in which if Y is a hydrogen atom, then X is a -OC(O)-(CH2)n-SH group.

2. A process for producing biofuel according to claim 1, wherein said mercaptan is pre-mixed with the stream comprising the unsaturated oil.

3. A biofuel production process according to claim 2, wherein the amount of said mercaptan is between 1 ppm and 1000 ppm, preferably between 10 ppm and 500 ppm, and more preferably between 25 ppm and 150 ppm, relative to the total weight of said stream.

4. A method for producing biofuel according to any one of the preceding claims, wherein the preheating device is a heat exchanger and / or a preheating furnace.

5. A biofuel production process according to any one of the preceding claims, wherein said mercaptan is selected from the group consisting of: 2-mercaptoethanol, n-octylmercaptan (NOM), n-dodecylmercaptan (NDM), tert-dodecylmercaptan (TDM), tert-nonyl mercaptan (TNM), tert-butylmercaptan (TBM), 2-ethylhexyl thioglycolate (2-EHTG), isooctyl thioglycolate (IOTG), 2-methylheptyl thioglycolate (2-MHTG), methyl thioglycolate (MTG), ethyl thioglycolate, 3-mercaptopropionic acid, methyl 3-mercaptopropionate, ethyl 3-mercaptopropionate butyl, 2-ethylhexyl 3-mercaptopropionate, isooctyl 3-mercaptopropionate, octadecyl 3-mercaptopropionate, and thioglycolic acid, preferably tert-dodecyl mercaptan and 2-ethylhexyl thioglycolate.

6. A process for producing biofuel according to any one of the preceding claims, wherein the unsaturated oil is selected from vegetable oils, animal oils or oils derived from animal fat(s), oils derived from algae, used oils such as used cooking oils, pyrolysis oils from plastic(s), oils derived from waste and mixtures thereof.

7. A process for producing biofuel according to any one of the preceding claims, wherein said unsaturated oil is selected from used cooking oils, linseed oil, rapeseed oil, soybean oil, corn oil, palm oil, animal oils, plastic pyrolysis oils and mixtures thereof.

8. A biofuel production process according to any one of the preceding claims, wherein a sulfur compound of the following general formula (II) is also added: R2-Sm-R3 (II) in which: - R2 and R3, identical or different, are chosen from the hydrogen atom, the methyl radical and the ethyl radical; - m is an integer equal to 1 or 2; and on the condition that if R2 is an ethyl radical, then R3 is a hydrogen atom.

9. A method for producing biofuel according to any one of the preceding claims, wherein said biofuel is a bionaphtha, a renewable diesel and / or a sustainable aviation fuel.

10. Use of a mercaptan as an antifouling additive for a preheating device of a stream comprising an unsaturated oil, preferably derived from a bio-based raw material and / or waste, said mercaptan having the following general formula (I): XR x -Y (I) in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched; - X is selected from a hydrogen atom, HO-, HOOC- or HS-(CH2)nC(O)-O- with n being an integer between 1 and 8, preferably between 1 and 4, preferably n is equal to 1 or 2; - Y is an -SH group or a hydrogen atom; and in which if Y is a hydrogen atom, then X is an -OC(O)-(CH2)n-SH group.

11. Composition comprising: - a mercaptan of the following general formula (I): XR x -Y (I) in which: - Ri is a (Ci-C30)alkylene, linear or branched, preferably branched; - X is chosen from a hydrogen atom, HO-, HOOC- or HS-(CH2)nC(O)-O- with n being an integer between 1 and 8, preferably between 1 and 4, preferably n is equal to 1 or 2; - Y is a -SH group or a hydrogen atom; and in which if Y is a hydrogen atom, then X is a -OC(O)-(CH2)n-SH group; and - dimethyl disulfide.

12. Composition according to claim 11, comprising: - between 5 and 45% by weight, preferably between 10 and 40%, for example 15% or 35% by weight, of mercaptan of general formula (I), relative to the total weight of the composition; and - between 55 and 95% by weight of DMDS, preferably between 60 and 90% by weight, for example 65% or 85% by weight of DMDS, relative to the total weight of the composition.

13. Use of a composition as defined in claim 11 or 12, as an anti-fouling composition for a preheating device of a stream comprising an unsaturated oil, preferably derived from a bio-based raw material and / or waste.