WO2025068470A1 - Method for producing middle distillates, in particular kerosene, from an alcohol feedstock - Google Patents

Abstract

The present invention relates to a method for producing middle distillate hydrocarbon bases from an alcohol feedstock, the method comprising the following steps: a) dehydrating the alcohol feedstock, and obtaining at least one dehydration effluent comprising: - at least 80% by weight ethylene, relative to the total weight of the dry effluent; - compounds having at least three carbon atoms, wherein the dehydration step is carried out in the presence of an amorphous acid or zeolite acid catalyst; b) separating the dehydration effluent obtained in step a) and obtaining at least: - one fraction essentially comprising ethylene; - a fraction essentially comprising compounds having at least three carbon atoms; c) oligomerising at least one portion of the fraction essentially comprising ethylene obtained from step b) and obtaining at least one olefin effluent comprising at least 80% by weight olefins having a number of carbon atoms greater than or equal to four, relative to the total weight of the olefins contained in the olefin effluent, wherein the oligomerisation step is carried out in the presence of a homogeneous catalyst; d) oligomerising at least: - one portion of the effluent from step c); - a portion of the fraction essentially comprising compounds having at least three carbon atoms obtained from step b); - and obtaining a middle distillate effluent, wherein the oligomerisation step is carried out in the presence of an amorphous or zeolite heterogeneous catalyst; e) fractionating the middle distillate effluent obtained from step d).

Description

PROCESS FOR THE PRODUCTION OF MIDDLE DISTILLES, IN PARTICULAR KEROSENE FROM AN ALCOHOLIC FEED

TECHNICAL FIELD

The present invention relates to the transformation of an alcoholic feedstock and more particularly of an ethanol feedstock, preferably bioethanol, into middle distillates, in particular into diesel and/or kerosene fuel bases, using a process comprising a step of dehydration of the feedstock and two successive steps of oligomerization.

PRIOR TECHNIQUE

The demand for the use of biomass as an at least partial replacement for petroleum resources for fuel synthesis is growing. The use of bioethanol for the synthesis of fuel bases is therefore receiving increasing interest.

Bioethanol is ethanol of agricultural origin, meaning that it is produced from a renewable source of biomass such as living plant matter.

Most bioethanol is produced today by fermenting the sugars contained in raw materials of plant origin. From sugar plants, the first stage of processing consists of obtaining a sweet juice by hot water extraction for beet or by crushing and pressing for sugar cane. After possible concentration, these juices or syrups are introduced into fermenters where the biological transformation of sugars into ethanol takes place with the co-production of CO2 under the action of microorganisms (yeast). The wines obtained contain approximately 10% alcohol in water. A distillation stage allows the azeotropic composition of the ethanol/water binary (8% water) to be achieved. In order to obtain complete dehydration, a passage through a molecular sieve is necessary. In cereal plants (corn, wheat), the fermentable sugars into ethanol are present in the form of a polymer called starch; to release them, a preliminary hydrolysis stage catalyzed by enzymes is necessary.

Technologies for the transformation of lignocellulosic biomass (wood, grass, straw and other agricultural waste, etc.) into bioethanol have also recently become available. These technologies make it possible to use resources that do not compete with human or animal food (in the sense of livestock farming).

There are also technologies for obtaining ethanol from waste gas from steelmaking or household waste incineration, using gasification of this waste followed by microbial fermentation from the CO and part of the CO2 in the gas, and nutrient inputs for the microorganisms. Ethanol is primarily used for gasoline production, not diesel and kerosene. Another promising avenue is the use of ethanol as a biofuel in diesel engines. E-Diesel biofuel is a blend consisting of 85% to 95% diesel, anhydrous ethanol (without water), and a specially designed additive package to improve the stability of the blend and overcome some of the drawbacks of bioethanol, such as its low cetane index and poor lubricity.

Blending conventional diesel with ethanol and the additive improves combustion performance and slightly increases fuel volatility. The main result is a reduction in regulated pollutant gas emissions such as particulate matter (PM 10) and smoke. This reduction is due to the oxygen content of the biofuel, which limits the formation of particles during fuel combustion. Indeed, these oxygenated molecules significantly improve combustion quality due to the presence of oxidizer at the very point where the oxidation reaction takes place. Blending bioethanol with diesel also has the main consequence and disadvantage of reducing the flash point.

Blending conventional jet fuel (called Jet A1 in the customs specification) with ethanol is not accepted by equipment manufacturers in the current commercial specification (ASTM D7566), mainly due to problems with flammability (flash point), stability, water uptake and energy content per liter. These defects suggest that even if it is possible to fly small aircraft on ethanol, use on existing fleets would not be possible simply.

The transformation of ethanol into hydrocarbons is therefore an interesting way to use renewable resources for fuels.

The literature is very rich on the transformation of alcohols, for example of the methanol type, into olefins or aromatics to produce a gasoline cut on acid catalysts, often zeolitic.

The production of ethylene from ethanol is a well-known process that has been developed on an industrial scale in a few units. For example, ethanol dehydration units into ethylene were built in Brazil during the 1970s, following the oil crisis. Ethanol is catalytically converted into ethylene at temperatures above 300°C. The catalysts used can be of different types: activated alumina, silica-alumina, etc.

Scientific Design has developed its own technology for dehydrating ethanol into ethylene and, following the development of a new catalyst, introduced on an industrial unit, has published an article ("Ethylene from Ethanol", NK Kochar, R. Merims, and AS Padia, CEP, June 1981). US patents 4,232,179, US 4,396,789, US 4,234,752, US 4,396,789, US 4,698,452 may also be cited. Documents FR2959750 and FR2959752 in the name of IFPEN disclose processes for producing middle distillate hydrocarbon bases from an ethanol feedstock comprising ethanol dehydration steps followed by two oligomerization steps, respectively in homogeneous and heterogeneous phase. Patent US9840676 discloses a process for converting ethanol into diesel and/or kerosene, by dehydration, conversion of the ethylene obtained into hexene and then di- or trimerization, to obtain a mixture comprising C12 hydrocarbon compounds. These documents do not disclose a step for recovering compounds having 3 or more carbon atoms (C3+) from the dehydration effluent which are considered undesirable.

An objective of the present invention is therefore to provide a process for producing middle distillate hydrocarbon bases (diesel and/or kerosene) and preferably kerosene bases which can be incorporated into the fuel pool, from an alcoholic feedstock, preferably ethanol, produced from a renewable source derived from biomass also called bioethanol, with a yield higher than the processes of the prior art.

The applicant has surprisingly demonstrated that by recovering the C3+ compounds formed during the dehydration stage of the alcoholic feedstock, by sending them to the heterogeneous phase oligomerization stage, the yield of olefins of interest is increased (of the order of 0.5 to 10% of the carbon yield of the transformation) for obtaining middle distillates and more particularly kerosene. The advantages are mainly economic by recovering initially undesirable compounds at the end of dehydration.

SUMMARY OF THE INVENTION

The present invention relates to a process for producing hydrocarbon bases of the middle distillate type and preferably kerosene hydrocarbon base from an alcoholic feedstock, comprising at least one mono-alcohol, preferably comprising ethanol, said process comprising: a) a step of dehydrating the alcoholic feedstock comprising at least one mono-alcohol, preferably comprising ethanol, and obtaining at least one dehydration effluent comprising:

- at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight of ethylene, relative to the total weight of the effluent considered dry,

- compounds having at least 3 carbon atoms (C3+), preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms, said dehydration step being carried out in the presence of an amorphous acid catalyst or a zeolitic acid catalyst; b) a step of separating the dehydration effluent obtained in step a) and obtaining at least:

- a fraction comprising essentially ethylene,

- a fraction essentially comprising compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, more preferably between 3 and 6 carbon atoms; c) a first step of oligomerization of at least a portion of the fraction essentially comprising ethylene from step b) and obtaining at least one olefinic effluent comprising at least 80% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total mass of olefins contained in said olefinic effluent, said first oligomerization step being carried out in the presence of a homogeneous catalyst; d) a second step of oligomerization of at least:

- part of the effluent from step c),

- a part of the fraction essentially comprising compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably between 3 and 6 carbon atoms, from step b), and obtaining an effluent of the middle distillate type, said second oligomerization step being carried out in the presence of a heterogeneous amorphous or zeolitic catalyst; e) a step of fractionation of the effluent of the middle distillate type from step d).

“Considered dry” means the effluent ideally separated from the water produced during the dehydration reaction and/or any solvents added in addition to the alcoholic feedstock before the dehydration stage.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, the expression "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values of the interval are included in the range of values described. If this is not the case and the limit values are not included in the range described, such precision will be provided by the present invention.

In the sense of the present invention, different parameter ranges for a given step such as pressure ranges and temperature ranges can be used. alone or in combination. For example, within the meaning of the present invention, a preferred pressure range may be combined with a more preferred temperature range.

In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when technically feasible.

Charge

According to the invention, the feedstock treated in the process according to the invention is an alcoholic feedstock (or an alcohol feedstock), containing at least one mono-alcohol. Preferably, said mono-alcohol is ethanol.

Advantageously, said alcohol feedstock of the process according to the invention comprises at least 35% by weight of said mono-alcohol, preferably from 35% by weight to 99.9% by weight of said mono-alcohol. Said alcoholic feedstock may also comprise between 0 and 65% of water. Said alcoholic feedstock may also comprise impurities of mineral type (such as Na, Ca, P, Al, Si, K, SO4), of organic type such as a mono-alcohol other than the targeted mono-alcohol, for example methanol or n-butanol in an ethanolic feedstock, aldehydes, ketones, and the corresponding acids, for example furanic, acetic, isobutyric acid. Said alcoholic feedstock may also comprise, in particular, inorganic nitrogen and/or sulfur compounds, such as ammonia, or organic nitrogen and/or sulfur compounds, preferably basic, such as amines, amides, imines and sulfur compounds (thiol, thiophenes, mercaptans, thioethers, sulfides, disulfides, etc.). The nitrogen content and the sulfur content, of organic and mineral origin, of said alcoholic feedstock are preferably each less than or equal to 0.5% by weight, preferably less than or equal to 0.2% by weight, the weight percentages being expressed relative to the total weight of said alcoholic feedstock. According to the invention, by nitrogen content and sulfur content, it is necessary to understand the contents of elemental nitrogen and elemental sulfur provided respectively by the nitrogen and sulfur impurities present in the streams considered, in particular in said alcoholic feedstock of the process of the invention. Preferably, the elemental nitrogen content is advantageously determined by combustion and chemiluminescence detection and the elemental sulfur content is determined by combustion and UV fluorescence detection.

Advantageously, said alcoholic feedstock may come from non-fossil resources. Preferably, the alcoholic feedstock treated in the process according to the invention is produced from renewable resources derived from biomass, preferably by fermentation of sugars derived for example from sugar plant crops such as sugar cane (sucrose, glucose, fructose, and sucrose), beets, or starchy plants (starch) or lignocellulosic biomass or hydrolyzed cellulose (mainly glucose and xylose, galactose), containing variable quantities of water. For a more complete description of classic fermentation processes, please refer to the book 'Biofuels, State of play, perspectives and challenges of development, Daniel Ballerini, Editions Technip'.

Said alcoholic charge can also advantageously be obtained from synthesis gas.

The alcoholic feedstock treated in the process according to the invention can also optionally be obtained by a process for synthesizing alcohol from fossil resources such as, for example, from coal, natural gas or carbon waste.

Said alcoholic feedstock of the process according to the invention can also be obtained by hydrogenation of the corresponding acids or esters. In this case, the acetic acid or the acetic esters are advantageously hydrogenated using hydrogen to ethanol. Acetic acid can, for example, be obtained by carbonylation of methanol or by fermentation of carbohydrates.

Very preferably, the alcoholic feedstock treated in the process according to the invention is an alcohol feedstock produced from renewable resources derived from biomass, more particularly bioethanol.

In one embodiment, the alcoholic feedstock may undergo a pretreatment step so as to produce a pretreated alcoholic feedstock.

Said pretreatment step is advantageously carried out on at least one acidic solid. Said acidic solid may be chosen from all solids known to those skilled in the art. Said acidic solid may thus be selected from the group consisting of: acidic clays, zeolites, sulfated zirconias, acidic resins, etc. For example, said acidic solid may be chosen from commercially available acidic solids, such as clays treated with acids to make them acidic (such as montmorillonite) and zeolites preferably having a silica to alumina molar ratio in the crystal lattice of 2.5 to 100.

Preferably, said acidic solid is an acidic resin, in particular an ion exchange resin, preferably a cation exchange resin, in particular which has an exchange capacity (or acid strength) of at least 0.1 mmol H+ equivalent per gram, the exchange capacity (or acid strength) being determined by assay, preferably by conductimetry, of the H+ ions released by the acidic resin after exchange by Na+ ions (see in particular ASTM D4266). For example, the acidic solid is a commercial acidic resin sold under the reference TA801 by the company Axens. Advantageously, said pretreatment step makes it possible to trap and therefore eliminate cationic and possibly anionic impurities, basic, complexing, chelating impurities, inorganic or organic impurities, in particular metal salts (such as salts of K, Na, Ca, Fe, Cu, P, Cl) and nitrogenous and/or sulfurous impurities, such as basic nitrogenous compounds present in the feedstock, for example in the form of ammonia and/or in the form of organic and basic species, for example in the form of amine, amide, imine or nitrile.

Advantageously, the alcoholic load is pretreated according to the teachings of application FR3090393.

Operating conditions and catalysts

Step a) dehydration

The process according to the invention comprises a step a) of dehydration of the alcoholic feedstock containing at least one mono-alcohol, preferably containing ethanol, and obtaining at least one dehydration effluent comprising:

- at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight of ethylene, relative to the total weight of the effluent considered dry.

- compounds having at least 3 carbon atoms (C3+), preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms, said dehydration step being carried out in the presence of an amorphous acid catalyst or a zeolitic acid catalyst.

Non-limiting examples of compounds having 3 or more carbon atoms are olefins, for example: propylene, linear butene, isobutene, methyl butene and methyl pentene; aromatics such as: toluene and xylene, and paraffins for example: propane, butane, pentane, hexane.

Advantageously, the dehydration effluent comprises at least 1% by weight, preferably at least 5% by weight, more preferably at least 8% by weight of compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, more preferably having between 3 and 6 carbon atoms, relative to the total weight of the effluent considered dry. Very advantageously, the dehydration effluent has a content of said compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, more preferably having between 3 and 6 carbon atoms, less than 20% by weight, preferably less than 15% by weight, more preferably less than 10% by weight relative to the total weight of the effluent considered dry. Advantageously, the compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms comprise olefins, preferably at least 50% by weight, preferably at least 60%, preferentially at least 70% by weight of olefins relative to the total weight of the compounds having at least 3 carbon atoms.

In one embodiment, the dehydration effluent comprises, in addition to olefins, aromatic compounds, preferably between 1 and 10% by weight of aromatic compounds relative to the total weight of compounds having at least 3 carbon atoms.

In the case where the catalyst used in dehydration step a) is a zeolitic catalyst, said catalyst comprises at least one zeolite chosen from zeolites having at least pore openings containing 8, 10 or 12 oxygen atoms (8 MR, 10 MR or 12 MR). It is known in fact to define the pore size of the zeolites by the number of oxygen atoms forming the annular section of the channels of the zeolites, called "member ring" or MR in English. Preferably, said zeolitic dehydration catalyst comprises at least one zeolite having a structural type chosen from the structural types MFI, FAU, MOR, FER, SAPO, TON, CHA, EUO, MEL and BEA. Preferably, said zeolitic dehydration catalyst comprises a zeolite of structural type MFI and preferably a zeolite ZSM-5.

Said zeolite can advantageously be modified by dealumination or desilication according to any dealumination or desilication method known to those skilled in the art.

Said zeolite may advantageously be modified by an agent capable of reducing its total acidity and improving its hydrothermal resistance properties. Preferably, said zeolite or said catalyst advantageously comprises phosphorus, preferably added in H3PO4 form followed by steam treatment after neutralization of the excess acid by a basic precursor such as, for example, calcium Ca. Preferably, said zeolite comprises a phosphorus content of between 1 and 4.5% by weight, preferably between 1.5 and 3.1% by weight relative to the total weight of the catalyst.

In the case where the catalyst used in dehydration step a) is an amorphous acid catalyst, said catalyst comprises at least one porous refractory oxide chosen from alumina, alumina activated by a mineral acid deposit and silica alumina.

Said amorphous or zeolitic dehydration catalyst used in step a) of the process according to the invention may advantageously also comprise at least one oxide-type matrix also called binder. By matrix according to the invention, we mean an amorphous or poorly crystallized matrix. Said matrix is advantageously chosen from the elements of the group formed by clays (such as for example among natural clays such as kaolin or bentonite), magnesia, aluminas, silicas, silica-aluminas, aluminates, titanium oxide, boron oxide, zirconia, aluminum phosphates, titanium phosphates, zirconium phosphates, and coal. Preferably said matrix is chosen from the elements of the group formed by aluminas, silicas and clays.

The dehydration catalyst used in step a) of the process according to the invention is advantageously shaped in the form of grains of different shapes and sizes. It is advantageously used in the form of cylindrical or polylobed extrudates such as bilobed, trilobed, polylobed of straight or twisted shape, but can optionally be manufactured and used in the form of crushed powder, tablets, rings, balls, wheels, spheres, stars. Preferably, said catalyst is in the form of extrudates or balls.

Dehydration step a) of the process according to the invention advantageously operates at a temperature of between 250 and 600°C, preferably between 300 and 600°C and preferably between 300 and 500°C, at an absolute pressure of between 0.1 and 5 MPa, preferably between 0.1 and 2.5 MPa and preferably between 0.1 and 1 MPa and preferably at an hourly weight rate of between 0.1 and 50 h' ¹ and preferably between 0.5 and 15h- ¹ .

The hourly weight rate is defined as the ratio of the mass flow rate of the feed entering step a) to the mass of catalyst.

The conversion of the alcoholic feed in step a) is advantageously greater than 90%, preferably 95% and more preferably greater than 98%.

Conversion of the alcoholic feedstock is understood to mean the ratio of the difference between the mass flow rate of the inlet alcoholic feedstock and the mass flow rate of the outlet alcoholic feedstock from step a) relative to the mass flow rate of the inlet alcoholic feedstock, said ratio being expressed as a percentage.

Advantageously, prior to separation step b), the water present in the dehydration effluent is separated by any method known to those skilled in the art.

Dehydration step a) can be advantageously implemented according to the teachings of applications WO2014083260 or WO2014083261.

An example of a process for dehydrating an alcoholic feedstock is the Atol® process marketed by the company Axens.

Step b) separation The process according to the invention comprises a step b) of separating the dehydration effluent obtained in step a) and obtaining at least:

- a fraction comprising essentially ethylene,

- a fraction essentially comprising compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, more preferably having between 3 and 6 carbon atoms.

The term "essentially" means at least 95% by weight, preferably at least 97% by weight, more preferably at least 99% by weight of desired compounds relative to the total weight of the fraction considered.

Advantageously, the compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms comprise olefins, preferably at least 50% by weight, preferably at least 60%, preferentially at least 70% by weight of olefins relative to the total weight of the compounds having at least 3 carbon atoms.

In a particular embodiment of the invention, the fraction essentially comprising compounds having at least 3 carbon atoms undergoes an additional separation step to obtain at least:

- an olefinic fraction comprising essentially olefins having between 3 and 6 carbon atoms,

- a heavy fraction comprising aromatics, preferably having between 6 and 9 carbon atoms.

In this particular embodiment, it is the olefinic fraction essentially comprising olefins having between 3 and 6 carbon atoms which is sent to the second oligomerization step d). The heavy fraction comprising aromatics, preferably having between 6 and 9 carbon atoms, may also comprise unsaturated olefinic or diolefinic compounds, preferably having between 6 and 9 carbon atoms. Said heavy fraction advantageously undergoes a step of selective hydrogenation of the unsaturated olefinic or diolefinic compounds contained therein and then the effluent obtained is sent to the fractionation step e). The step of selective hydrogenation of the heavy fraction makes it possible to purify this fraction in order to improve its stability to oxidation. Indeed, the presence of heavy olefins makes the heavy fraction sensitive to peroxidation, ultimately giving rise to the presence of gums in the final fuel.

Separation step b) can be carried out by any method known to those skilled in the art, for example by distillation, in particular continuous distillation, successive distillations or Continuous or batch multi-cut distillations, possibly with a side draw to extract the intermediate boiling cut. Internally walled columns can also be used to achieve this separation while reducing energy consumption. Molecular sieves or separating membranes can also be used to complement or replace distillation methods.

Preferably, the dehydration effluent from step a) undergoes at least one step of purification of said effluent prior to separation step b). This purification step makes it possible to eliminate impurities harmful to the oligomerization catalysts used for the implementation of steps c) and d) placed downstream and in particular allows the elimination of oxygenated compounds present in said dehydration effluent.

The optional purification step can advantageously be implemented according to any method known to those skilled in the art, such as, for example, the successive combination of treatment in a water washing column, then passage through an absorption column with MDEA (methyldiethylamine) or other amine and through a washing column with sodium hydroxide or any other means known to those skilled in the art. Dryers can advantageously be implemented so as to achieve a water content compatible with the oligomerization catalysts used downstream in oligomerization steps d) and e). The water content of the fraction sent to first oligomerization step c) is advantageously between 0 and 500 ppm and preferably less than 100 ppm, very preferably less than 1 ppm.

Step c) of first oligomerization

The process according to the invention comprises a first step c) of oligomerization of at least part of the fraction essentially comprising ethylene from step b) and obtaining at least one olefinic effluent comprising at least 80% by weight, preferably 90% by weight of olefins having a number of carbon atoms greater than or equal to 4 (C4+), relative to the total mass of olefins contained in said olefinic effluent, said first oligomerization step being carried out in the presence of a homogeneous catalyst.

Advantageously, at least a portion, i.e. at least 50% by weight, preferably at least 90% by weight of the fraction essentially comprising ethylene from step b) and preferably all of said fraction is subjected to said first oligomerization step.

Advantageously, said olefinic effluent from said first oligomerization step c) comprises less than 20% by weight, preferably less than 10% by weight of ethylene, in particular not converted during the first oligomerization step c), the percentages being expressed in weight percentages relative to the total mass of olefins contained in said olefinic effluent produced.

In a particular embodiment, said olefinic effluent is rich in olefinic hydrocarbons having a number of carbon atoms between 4 and 8 and also comprises olefinic hydrocarbons having at least 10 carbon atoms (C10+). More particularly, said olefinic effluent produced during the first oligomerization step c), advantageously comprises at least 80% by weight, preferably at least 90% by weight, of olefinic compounds having predominantly a number of carbon atoms between 4 and 8 and less than 20% by weight and preferably less than 10% by weight, of olefinic compounds having predominantly a number of carbon atoms greater than or equal to 10, the weight percentages being expressed relative to the total mass of olefins contained in said olefinic effluent produced.

In accordance with step c) of the process according to the invention, the catalyst used in the first oligomerization step c) is a homogeneous catalyst, i.e. the catalyst is soluble in the liquid phase composed of dissolved ethylene and its oligomerization products.

Advantageously, the homogeneous catalyst used in step c) of oligomerization of the process according to the invention comprises:

- at least one nickel precursor with oxidation state (+II),

- and at least one activating agent chosen from the group formed by chlorinated and brominated hydrocarbylaluminium compounds, taken alone or as a mixture.

Optionally, the homogeneous catalyst used in step c) of oligomerization of the process according to the invention further comprises at least one organic Brônsted acid, or at least one carboxylic acid anhydride, or at least one phosphine ligand of formula PR1 R2R3 in which the groups R1, R2 and R3, identical or different from each other, linked or not to each other.

Nickel compounds of oxidation state (+II) are preferably compounds soluble at more than one gram per liter in hydrocarbon medium, and more particularly in the reagents and the reaction medium and preferably, nickel carboxylates of general formula (RCOO)2Ni where R is a hydrocarbyl radical, for example alkyl, cycloalkyl, alkenyl, aryl, aralkyl or alkaryl containing up to 20 carbon atoms, preferably a hydrocarbyl radical of 5 to 20 carbon atoms. The radical R can be substituted by one or more halogen atoms, by one or more hydroxyl, ketone, nitro, cyano groups or other groups which do not hinder the reaction. The two radicals R can also constitute an alkylene radical of 6 to 18 carbon atoms. The bivalent nickel compounds are advantageously chosen from the following divalent nickel salts: octoate, ethyl-2-hexanoate, decanoate, stearate, oleate, salicylate and hydroxydecanoate, taken alone or as a mixture and preferably, the divalent nickel compound is nickel ethyl-2-hexanoate.

The activating agent is chosen from the group formed by chlorinated and brominated hydrocarbylaluminium compounds corresponding to the formula AIRX ₂ , in which R is a hydrocarbyl radical and X is a halogen chosen from chlorine and bromine taken alone or in a mixture. The hydrocarbylaluminium halides are advantageously chosen from dichloroethylaluminium, dichloroisobutylaluminium and dibromoethylaluminium. These hydrocarbylaluminium dihalides can be advantageously enriched with aluminium trihalides (AIX3) such as aluminium trichloride.

The organic Brônsted acid compounds preferably correspond to the formula HY, where Y is an organic anion, for example carboxylic, sulfonic or phenolic. Said compounds preferably have a pKa at 20°C at most equal to 3 and are preferably chosen from the group formed by halogenocarboxylic acids of formula RCOOH in which R is a halogenated alkyl radical and preferably a halogenated alkyl radical containing at least one halogen atom alpha to the -COOH group with a total of 2 to 10 carbon atoms. Preferably, a halogenoacetic acid of formula CXpHs-p-COOH is used in which X is fluorine, chloro, bromine or iodine, with p being an integer from 1 to 3. By way of example, mention may be made of trifluoroacetic, difluoroacetic, fluoroacetic, trichloroacetic, dichoroacetic and chloroacetic acids. These examples are not limiting, and it is also possible to use arylsulfonic, alkylsulfonic, fluoroalkylsulfonic acids, picric acid, nitroacetic acid.

The catalyst used in the first oligomerization step c) may also contain at least one carboxylic acid anhydride of formula (RCO) ₂ O in which R is a hydrocarbyl radical which may advantageously contain one or more halogen atoms. The carboxylic acid anhydrides are advantageously chosen from octoic, ethyl-2-hexanoic, decanoic, stearic, oleic, trifluoroacetic, monofluoroacetic, trichloroacetic, monochloroacetic, pentafluoropropionic or heptafluorobutyric anhydrides, taken alone or as a mixture. Preferably, the carboxylic acid anhydride is trifluoroacetic acid anhydride.

Finally, the catalyst used in the first oligomerization step c) may also contain a phosphine ligand of formula PR1 R2R3 in which the groups R1, R2 and R3, identical or different from each other, linked or not to each other. The hydrocarbyl groups R1, R2 and R3 of the phosphine ligand PR1 R2R3 advantageously comprise 1 to 20 carbon atoms, preferably 2 to 15 carbon atoms, preferably between 3 and 10 carbon atoms. of carbon. Preferably, the hydrocarbyl groups R1, R2 and R3 of the phosphine ligand PR1 R2R3 are chosen from the group formed by the methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, cyclopentyl, cyclohexyl, benzyl, adamantyl groups.

Preconditioning of the catalyst may be carried out before contacting the catalyst with ethylene. Preconditioning of the catalytic composition consists of mixing the three components in a hydrocarbon solvent, for example an alkane or an aromatic hydrocarbon, or a halogenated hydrocarbon, or preferably the olefins produced in the oligomerization reaction, with stirring and under an inert atmosphere, for example under nitrogen or argon, at a controlled temperature of between 0 and 80°C, preferably between 10 and 60°C, for a period of 1 minute to 5 hours, preferably 5 minutes to 1 hour. The solution thus obtained is then transferred under an inert atmosphere into the oligomerization reactor.

This preconditioning of the catalyst makes it possible to increase the activity of the catalyst in the oligomerization of ethylene.

The catalyst present in said unit carrying out oligomerization step c) is in liquid form. Depending on the chemical composition of said catalyst, the weight proportions of each of the catalyst components must be controlled during the synthesis of the catalyst. The molar ratio of hydrocarbylaluminium halide to nickel compound, expressed by the Al/Ni ratio, is advantageously from 2/1 to 50/1, and preferably from 2/1 to 20/1.

The molar ratio of Bronsted acid to nickel compound is advantageously from 0.25/1 to 10/1, and preferably from 0.25/1 to 5/1. If the catalyst comprises carboxylic acid anhydride, the molar ratio of carboxylic acid anhydride to nickel compound is advantageously between 0.001/1 and 1/1, very advantageously between 0.01/1 and 0.5/1. If the catalyst comprises a phosphine ligand, the molar ratio of phosphine ligand to nickel compound is advantageously between 2 and 25, preferably between 5 and 20, more preferably between 5 and 15.

In one embodiment, said homogeneous catalyst is the catalyst described in document WO2017017087.

The first step c) of oligomerization implemented by homogeneous catalysis is advantageously carried out continuously: the catalytic solution is injected into the unit carrying out the oligomerization step and the ethylene is injected therein continuously. The unit carrying out said step of oligomerization of ethylene by homogeneous catalysis comprises one or more reactors of the perfectly stirred type, in series, with recycle of at least part of the effluent from the reactor into the reactor, this recycle having been advantageously cooled. The first oligomerization step c) can advantageously be implemented in a reactor with one or more reaction stages in series, the predominantly ethylenic feedstock and/or the previously preconditioned catalytic composition being introduced continuously, either into the first stage or into the first and any other of the stages.

The operating conditions in the reactor(s) carrying out step c) of oligomerization by homogeneous catalysis are such that the temperature is between -20°C and +80°C and the pressure is sufficient to allow the existence of a liquid phase in the reactor(s). Preferably, the absolute total pressure in the reactor(s) is between 0.5 and 8 MPa.

At the outlet of the first oligomerization stage c), the homogeneous catalytic system is mixed with the olefinic effluent produced during stage c) and the unreacted ethylene.

Advantageously, said olefinic effluent produced during the first oligomerization step c) preferably undergoes at least one step c’) of treatment/separation of the homogeneous catalytic system of said effluent before being sent to the second oligomerization step d).

The term “step of treatment/separation of the homogeneous catalytic system” means a step in which said catalytic system is deactivated and separated from the homogeneous reaction medium and in particular from the olefinic effluent resulting from the first step c) of oligomerization. Step c’) of treatment/separation of the homogeneous catalytic system can implement different methods adapted to this treatment and known to those skilled in the art. By way of non-limiting example, the 3 methods below can be cited:

1) either by the use of capture mass,

2) either by treatment with a base and/or an acid, of the olefinic effluent from the first stage c) of oligomerization, neutralized or not by a base,

3) either by separating said olefinic effluent from the first oligomerization step c), neutralized or not by a base, into a first effluent comprising at least a portion of the C10+ olefinic compounds and also the homogeneous catalytic system and into a second olefinic effluent free from the catalytic system, said separation being followed by treatment of the effluent comprising at least a portion of the C10+ compounds and the homogeneous catalytic system by acid and/or basic washing or by using capture mass.

Please refer to the description of patent FR2959752 for more details on this step of treatment/separation of the homogeneous catalytic system.

Advantageously, the olefinic effluent having possibly undergone a step c') of treatment/separation of the homogeneous catalytic system, is sent to a step c”) of optional separation, this step allows the separation of said olefinic effluent from the first oligomerization step c) or from the treatment/separation step c') of the homogeneous catalytic system, into at least one olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 4 (C4+) and into at least one light olefinic effluent C2.

Said separation step c”) can advantageously be implemented by any method known to those skilled in the art, such as, for example, the combination of one or more high and/or low pressure and high and/or low temperature separator flasks, and/or distillation steps comprising one or more distillation columns.

The term “light olefinic effluent C2” means an effluent advantageously comprising a content of at least 50% by weight and preferably at least 65% by weight of olefinic compounds having a number of carbon atoms less than 4.

Advantageously, a part, preferably all of said light olefinic effluent C2 is recycled in the first oligomerization stage c).

The term “olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 4 (or C4+ olefinic effluent)” means an effluent advantageously comprising a content of at least 80% by weight, preferably at least 90% by weight, of olefinic compounds having a number of carbon atoms between 4 and 8 (C4-C8). The C4+ olefinic effluent may also comprise olefinic compounds having a number of carbon atoms greater than or equal to 10 (C10+ compounds).

According to a first variant, in the case where the olefinic effluent from said step c) or c’) undergoes said optional separation step c”), all of the olefinic effluent O4+ from said optional separation step c”), comprising the C4-C8 olefinic compounds and possibly the C10+ olefinic compounds, is advantageously sent to the second oligomerization step d).

According to a second variant, still in the case where the olefinic effluent from step c) or c') undergoes said optional separation step c”), the olefinic effluent O4+ is advantageously separated in a second optional separation step c'”), into at least one olefinic effluent comprising compounds having a number of carbon atoms between 4 and 8 (C4-C8) and at least one olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 10 (C10+ compounds). In this case, said C4-C8 olefinic effluent is advantageously sent to the second oligomerization step d) and said olefinic effluent O10+ is advantageously optionally hydrogenated and sent to the fractionation step e). This embodiment makes it possible to limit the formation of heavy products (excluding the kerosene cut) and therefore to increase the yield of kerosene cut. It also allows the use of reactors during the second oligomerization stage d), of reduced size.

Said C4-C8 olefinic effluent is defined as being an effluent comprising olefinic compounds distributed according to the following distribution: at least 50% by weight and preferably at least 70% by weight of olefinic compounds having a number of carbon atoms between 4 and 8 and less than 50% by weight and preferably less than 30% by weight of other olefinic compounds, the weight percentages being expressed relative to the total mass of olefins present in the C4-C8 olefinic effluent.

In the same way, said C10+ olefinic effluent is defined as being an effluent comprising olefinic compounds distributed according to the following distribution: at least 50% by weight and preferably at least 70% by weight of olefinic compounds having a number of carbon atoms greater than or equal to 10 and also advantageously comprising less than 50% by weight and preferably less than 30% by weight of compounds having a number of carbon atoms less than 10, the weight percentages being expressed relative to the total mass of olefins present in the C10+ olefinic effluent.

Thus, the input charge of the second oligomerization step d) advantageously comprises at least one part:

- all of the olefinic effluent from the first oligomerization stage c) in the case where no stage c’) of treatment/separation of the homogeneous catalytic system and/or c”) of optional separation is implemented between the first and second oligomerization stages, or

- the entire C4+ olefinic effluent (i.e. a part of the olefinic effluent from the first oligomerization stage c), and separated from the light olefinic effluent (C2-C4), in the case where at least one stage c’) of treatment/separation of the homogeneous catalytic system and one stage c”) of optional separation are implemented between the first and second oligomerization stages, or

- the entirety of said C4-C8 olefinic effluent, in the case where at least one step c’) of treatment/separation of the homogeneous catalytic system and two successive steps c”) and c’”) of optional separation are implemented between the first and second oligomerization steps.

An example of the first oligomerization step c) is the DimEne-B® process marketed by the company Axens.

Another example of the first oligomerization step c) is the Dimersol-E® process marketed by the Axens company. Step d) of second oligomerization

The process according to the invention comprises a second step d) of oligomerization of at least:

- part of the olefinic effluent from step c),

- a part of the fraction essentially comprising compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms from step b).

The second stage d) of oligomerization allows the production of a middle distillate type effluent.

The said second oligomerization step is carried out in the presence of a heterogeneous amorphous or zeolitic catalyst.

According to a preferred embodiment, the catalyst used in the second oligomerization step d) is an amorphous heterogeneous catalyst comprising, and preferably consisting of, an amorphous mineral material chosen from silica-aluminas and siliceous aluminas.

According to another preferred embodiment of the invention, the second oligomerization step d) is carried out in the presence of a heterogeneous zeolitic catalyst, i.e. a heterogeneous catalyst comprising at least one zeolite, preferably having at least pore openings containing 10 or 12 oxygen atoms (10MR or 12MR), and advantageously chosen from aluminosilicate type zeolites having an overall Si/Al molar ratio greater than 10.

In one embodiment, said catalyst used in the second oligomerization step d) comprises at least one zeolite chosen from zeolites of structural type MFI, MTW, MOR, TON, MEL, MFS, MTT, taken alone or as a mixture.

In one embodiment, said catalyst used in the second oligomerization step d) comprises at least one zeolite chosen from the zeolites ZSM-5, ZSM-12, NU-86, Mordenite, ZSM-22, NU-10, ZBM-30, ZSM-48, ZSM-11, ZSM-57, IZM-2, ITQ-6 and IM-5, taken alone or in a mixture, preferably from the zeolites ZSM-5, NU-10 and ZBM-30, taken alone or in a mixture, very preferably the zeolite is ZBM-30 and even more preferably, the zeolite is ZBM-30 synthesized in the presence of the structuring agent triethylenetetramine.

The zeolite used in the catalyst used in step d) of the process according to the invention can advantageously undergo several post-treatments known to those skilled in the art, such as, for example, being modified by dealumination or desilication according to any method of dealumination, external surface passivation or desilication known to those skilled in the art, with the aim of improving its activity and/or its stability.

According to a very particular embodiment in which a silica-alumina is used as a catalyst for the second oligomerization step d), said silica-alumina makes it possible to carry out said oligomerization, in particular of at least a portion of the effluent from step c) and at least a portion of the fraction essentially comprising compounds having at least 3 carbon atoms from step b), with better control of the reactivity of the olefins, making it possible in particular to operate at a low-pass conversion level and very advantageously to optimize the selectivity towards the desired olefins, in comparison with oligomerization in the presence of other catalysts, for example zeolites. In addition, coke formation appears less significant and less rapidly in the presence of silica-alumina than in the presence of zeolites. Thus, silica-alumina requires regenerations at a lower frequency than those of zeolites.

Said catalyst used in step d) of the process according to the invention also advantageously comprises at least one oxide type matrix also called binder. By matrix according to the invention is meant an amorphous or poorly crystallized matrix.

Said matrix is advantageously chosen from the elements of the group formed by clays (such as for example among natural clays such as kaolin or bentonite), magnesia, aluminas, silicas, silica-aluminas, aluminates, titanium oxide, boron oxide, zirconia, aluminum phosphates, titanium phosphates, zirconium phosphates, and coal. Preferably said matrix is chosen from the elements of the group formed by aluminas, clays and silicas, more preferably said matrix is chosen from aluminas, and even more preferably said matrix is gamma alumina.

The catalyst used in step d) of the process according to the invention is advantageously shaped in the form of grains (or particles) of different shapes and sizes. They are advantageously used in the form of cylindrical or polylobed extrudates such as bilobed, trilobed, polylobed of straight or twisted shape, but can optionally be manufactured and used in the form of crushed powder, tablets, rings, balls, wheels, spheres. Preferably, said catalysts are in the form of extrudates of size between 1 and 10 mm.

The second stage d) of oligomerization is advantageously implemented in at least one fixed bed reactor. In one embodiment, in the second oligomerization step d), at least a portion of the gasoline-type cut from fractionation step e) is also oligomerized.

The second oligomerization step d) of the process according to the invention advantageously operates at a temperature of between 50 and 400°C, preferably between 100 and 350°C and preferably between 100 and 300°C, at an absolute pressure of between 2 and 15 MPa, preferably between 2 and 8 MPa and preferably between 3 and 8 MPa and at an hourly weight rate of between 0.1 and 10 h-1 and preferably between 0.4 and 5 h-1.

The hourly weight rate is defined here as the ratio of the mass flow rate of the “fresh” charge entering step d) to the mass of catalyst without taking into account any recycles.

The middle distillate effluent produced by the second oligomerization step d) is an olefinic effluent comprising at least 80% by weight and preferably at least 90% by weight of olefins comprising a number of carbon atoms greater than 4, and less than 20%, preferably less than 10% of C4 olefins, in particular not converted during the second oligomerization step d) (C4 meaning comprising 4 carbon atoms), the weight percentages being expressed relative to the total weight of the olefins contained in the middle distillate effluent produced.

The middle distillate type effluent advantageously comprises at most 50% by weight and preferably at most 40% by weight of C4-C8 olefinic compounds, and at least 50% by weight and preferably at least 60% by weight of C10+ olefinic compounds (i.e. comprising 10 carbon atoms or more), the weight percentages being expressed relative to the total mass of olefins present in said effluent.

The process according to the invention is a flexible process in the sense that the operating conditions and the choice of catalyst in the second stage d) of oligomerization make it possible to direct the reaction towards one or other of the target products, namely in one case towards the majority production of a hydrocarbon base of the diesel type and in the other of a hydrocarbon base of the kerosene type.

In the case where the majority production of hydrocarbon base of the diesel type is more particularly sought, the second stage d) of oligomerization advantageously operates in the presence of a catalyst comprising at least one zeolite chosen from aluminosilicate type zeolites having an overall Si/AI ratio greater than 10 and a pore structure of 10 or 12MR and at a temperature of between 200 and 300°C, at a pressure of between 3 and 7MPa and at an hourly weight rate of between 0.1 and 5 h' ¹ . In the case where the majority production of kerosene-type hydrocarbon base is more particularly sought, the second oligomerization step d) advantageously operates in the presence of an amorphous catalyst, preferably comprising and preferably consisting of silica alumina at a temperature between 100 and 300°C, at a pressure between 2 and 6 MPa and at an hourly weight rate between 0.1 and 5 h ^-1 .

An example of a second oligomerization step d) is the Polynaphtha® process marketed by the company Axens.

Step e) of fractionation

The process according to the present invention comprises a step e) of fractionation of the middle distillate type effluent from step d).

Fractionation step e) is advantageously carried out in at least one distillation column so as to separate said middle distillate type effluent into at least two cuts:

- A gasoline cup,

- A middle distillate cut (diesel and/or kerosene).

A light effluent comprising C2-C4 compounds can also be separated for recovery pure or as a mixture.

A heavy fraction having an initial boiling point between 350 and 370°C can also be advantageously separated.

The term “gasoline” cut means the cut comprising hydrocarbon compounds whose boiling point is between room temperature and 220°C.

The term “middle distillates” refers to the fraction comprising hydrocarbon compounds with a boiling point between 140 and 360°C.

At least part of the gasoline cut from fractionation step e) can advantageously be recycled in the second oligomerization step d) of the process according to the invention.

In one embodiment, the C4 olefins not converted during the second oligomerization step d) are separated from the effluent from step d) and then recycled to the inlet of the second oligomerization step d).

One of the objectives of the present invention being to maximize the yield of middle distillate base and preferably of kerosene base, said light effluent (comprising C2-C4 compounds) and the gasoline cut (corresponding to the C4-C8 compounds), which are not desired, are advantageously oligomerized again respectively in step c) and in step d). of the process according to the invention, allowing the increase of their molecular weight and thus the increase of their boiling point and their compatibility with the desired use.

At least a portion, preferably all of the middle distillate cut (diesel and/or kerosene) from fractionation step e) advantageously undergoes an optional step f) of hydrogenation of the olefins, to make them incorporable into the fuel pool. Preferably, at least a portion and preferably all of the middle distillate cut (diesel and/or kerosene) from fractionation step e) is brought into contact with a hydrogen-rich gas in the presence of a catalyst comprising at least one metal from group VIII, advantageously chosen from palladium and nickel taken alone or as a mixture, and a support advantageously chosen from alumina, silica or silica-alumina.

The catalyst used in the optional hydrogenation step f) comprises a palladium content advantageously between 0.1 and 10% by weight and/or a nickel content, advantageously between 1 and 60% by weight relative to the total mass of the catalyst.

The optional hydrogenation step f) advantageously operates at a temperature between 100 and 250°C at the reactor inlet, at a pressure between 2 and 5 MPa and at an hourly weight rate between 0.05 and 8h-1.

The performance of the hydrogenation is validated by a measurement of the bromine number which is advantageously at most 5 g Br/100 g, in the case where one wishes to saturate all the unsaturated compounds present in the cut to be hydrogenated.

The effluent from the optional hydrogenation step f) mainly contains hydrocarbons that can be recovered and incorporated into the kerosene and/or diesel pool, and preferably kerosene.

An optional final separation step g) can advantageously be implemented after the optional hydrogenation step f), to allow the fractionation of the effluent from step f) into a kerosene cut and/or a diesel cut and/or a cut having a boiling point above 360°C.

The term “diesel” cut means the cut comprising hydrocarbon compounds with a boiling point between 220 and 360°C.

The term “kerosene” cut means the cut comprising hydrocarbon compounds with a boiling point between 140 and 300°C.

According to one embodiment, at least a portion of said effluent from the optional hydrogenation step f) can advantageously be recycled into the first oligomerization step c) so as to constitute a diluent for the feedstock of said step c) and thus stabilize the catalyst. When the desired fuel is kerosene, the olefin hydrogenation step is essential.

EXAMPLES

Example: Process for producing middle distillates from an ethanol feedstock:

Step a): dehydration of the load

The charge is a bioethanol charge with the following characteristics:

Sugarcane ethanol, containing 92% by weight ethanol, 500 ppm by weight organic impurities (heavy alcohols, methanol, esters, acids), the remainder being water.

This charge is dehydrated in the presence of a PZSM-5 zeolite catalyst at a temperature of 400°C, at a pressure of 0.6 MPa, and at an hourly weight rate of 7h ¹ .

The composition of the dehydration effluent is given in the following table:

Table 1

The composition of C3+ is 74.3% by weight of olefins (20.1% propylene, 45.4% butene, 8.8% C5-C6 olefins), 19.9% by weight of paraffins (13.5% C3-C4 paraffins, 6.4% C5-C6 paraffins) and 5.9% aromatics.

Step b) separation

The effluent is introduced into a cryogenic distillation column after drying, compression and removal of CO, CO2 and acetaldehyde by capture masses and molecular sieves (deoxo mass with Cu/ZN, 3A and 13X sieves) at 2.28 MPa. This column uses structured packing for a height equivalent to 40 theoretical plates. At the top of the column, at -22°C, an ethylene-rich cut is produced, with traces of propylene present. The bottom cut is separated in a second distillation column (20 theoretical plates) 0.7 MPa 30°C at the top, producing a top fraction rich in C3-C5 (and without ethylene) and a bottom cut rich in aromatics. The top cut of this second column is sent to the oligomerization step d), the bottom cut is in our case used as fuel in the process furnaces. The composition of the top cut is:

Table 2

First oligomerization step c) The ethylene-rich fraction from separation step b) is sent to the first oligomerization step c) which operates in the presence of a homogeneous catalyst comprising a bivalent nickel compound, with a dichloroethylaluminium (EADC) co-catalyst, and at a temperature of 50°C, at a pressure of 1 MPa. The Al/Ni molar ratio is set at 15.

The composition of C4+ compounds in the olefinic effluent from step c) is given in the following table:

Table 3

The selectivities of the different cuts are as follows:

- 41% weight in C4 olefins - 35% weight in C6 olefins

- 14.5% weight in C8 olefins

- 9.5% weight in C10+ olefins

The effluent at the outlet of step c) is separated into 2 sections:

- A cut containing the C4, C6 and C8 olefins sent to step d)

- A cut containing the C10+ olefins sent to step f)

Step d) of second oligomerization

In case 1 (comparison according to the prior art) the cut containing the C4, C6 and C8 olefins from step c) of the first oligomerization is sent to step d).

In case 2 (according to the invention), the cut containing the C4, C6 and C8 olefins from step c) of the first oligomerization is sent to step d) together with the C3-C5 rich fraction from step b) of separation.

Step d) of the second oligomerization operates in the presence of a heterogeneous aluminosilicate catalyst at a temperature of 110°C, at an absolute pressure of 6.0 MPa and at an hourly volumetric flow rate of 0.2 h' ¹ .

The effluent from the second oligomerization is separated in a first column into two fractions:

- A recycled C4 cut at the input of step d) or output from the process in the form of purge

- A C6+ cut sent to a second column

The C6+ cut from this first column is separated in a second column into two fractions:

- A C6-C8 cut recycled at the input of step d) or output from the process in the form of purge

- An oligomer sent to step e)

The recycling rate of the C6-C8 cut from fractionation step e) relative to the feed entering step d) is 3.5.

The recycling rate of C4 not converted in step d) and separated in step e) relative to the feed entering step d) is 1.5.

The composition of the effluent from the second oligomerization stage is described in the following table: Table 4

Step e) of hydrogenation and fractionation:

The oligomerate obtained in step d) is hydrogenated together with the cut containing the C10+ olefins from step c) of the first oligomerization after separation. This step is carried out with a Ni-on-alumina catalyst, at a temperature of 180°C, at a pressure of 1.5 MPa and at an hourly volumetric flow rate of 0.5 h' ¹ .

The hydrogenated effluent is sent to a fractionation column where a kerosene cut and a diesel cut are recovered. The fuel yield of the effluent from the dehydrogenation and fractionation step e) is described in the following table:

Table 5

The overall efficiency of the process is described in the following table:

On observe donc que le procédé selon l’invention comprenant l’envoi des composés C3+ issus de l’étape a) de déshydratation vers la deuxième étape d’oligomérisation d) permet l’obtention d’un meilleur rendement en Kérosène (+3,8% = 54,3% - 50,5%, par rapport au poids de la charge entrante du procédé) et dans une moindre mesure un meilleur rendement en Gazole (+0,2% = 2,6% - 2,4%) par rapport au poids de la charge entrante du procédé). Table 6

It is therefore observed that the process according to the invention comprising the sending of the C3+ compounds from the dehydration step a) to the second oligomerization step d) allows the obtaining of a better yield in Kerosene (+3.8% = 54.3% - 50.5%, relative to the weight of the feedstock entering the process) and to a lesser extent a better yield in Diesel (+0.2% = 2.6% - 2.4%) relative to the weight of the feedstock entering the process).

Claims

1. Process for the production of hydrocarbon bases of the middle distillate type and preferably kerosene hydrocarbon base from an alcoholic feedstock, comprising at least one mono-alcohol, preferably comprising ethanol, said process comprising: a) a step of dehydration of the alcoholic feedstock comprising at least one mono-alcohol, preferably comprising ethanol, and obtaining at least one dehydration effluent comprising: - at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight of ethylene, relative to the total weight of the effluent considered dry, - compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms, said dehydration step being carried out in the presence of an amorphous acid catalyst or a zeolitic acid catalyst; b) a step of separating the dehydration effluent obtained in step a) and obtaining at least: - a fraction comprising essentially ethylene, - a fraction essentially comprising compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, more preferably between 3 and 6 carbon atoms; c) a first step of oligomerization of at least a portion of the fraction essentially comprising ethylene from step b) and obtaining at least one olefinic effluent comprising at least 80% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total mass of olefins contained in said olefinic effluent, said first oligomerization step being carried out in the presence of a homogeneous catalyst; d) a second step of oligomerization of at least: - part of the effluent from step c), - a part of the fraction essentially comprising compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably between 3 and 6 carbon atoms, from step b), and obtaining an effluent of the middle distillate type, said second oligomerization step being carried out in the presence of an amorphous or zeolitic heterogeneous catalyst; e) a step of fractionation of the middle distillate type effluent from step d). 2. Process according to claim 1 in which the dehydration effluent comprises at least 1% by weight, preferably at least 5% by weight, more preferably at least 8% by weight of compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, more preferably having between 3 and 6 carbon atoms, relative to the total weight of the effluent considered dry. 3. Process according to any one of the preceding claims, in which the compounds having at least 3 carbon atoms, preferably having between 3 and 9 carbon atoms, preferably having between 3 and 6 carbon atoms, comprise olefins, preferably at least 50% by weight, preferably at least 60%, preferentially at least 70% by weight of olefins relative to the total weight of the compounds having at least 3 carbon atoms. 4. Process according to any one of the preceding claims, in which the fraction essentially comprising compounds having at least 3 carbon atoms from step b) undergoes an additional separation step to obtain at least: - an olefinic fraction comprising essentially olefins having between 3 and 6 carbon atoms, - a heavy fraction comprising aromatics, preferably having between 6 and 9 carbon atoms. 5. Process according to claim 4 in which the heavy fraction advantageously undergoes a step of selective hydrogenation of the unsaturated olefinic or diolefinic compounds contained therein and then the effluent obtained is sent to the fractionation step e). 6. Process according to any one of the preceding claims, in which the olefinic effluent from the first oligomerization stage c) comprises less than 20% by weight, preferably less than 10% by weight of ethylene, the percentages being expressed as percentages by weight relative to the total mass of olefins contained in said olefinic effluent produced. 7. Process according to any one of the preceding claims, in which the homogeneous catalyst used in step c) of oligomerization comprises: - at least one nickel precursor with oxidation state (+II), - and at least one activating agent chosen from the group formed by chlorinated and brominated hydrocarbylaluminium compounds, taken alone or as a mixture. 8. Process according to any one of the preceding claims, in which the olefinic effluent from step c) is sent to a separation step c”), this step allowing the separation of said olefinic effluent from the first oligomerization step c), into at least one olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 4 and into at least one light olefinic effluent C2. 9. Process according to claim 8 in which a part, preferably all of the light olefinic effluent C2 is recycled in the first oligomerization stage c). 10. Process according to claim 8 or 9 in which the olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 4 is separated in a second separation step c’”), into at least one olefinic effluent comprising compounds having a number of carbon atoms between 4 and 8 and at least one olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 10. 11. Process according to claim 10 in which the olefinic effluent comprising compounds having a number of carbon atoms greater than or equal to 10 is hydrogenated and sent to the fractionation step e). 12. Process according to any one of the preceding claims, in which the middle distillate effluent produced by the second oligomerization step d) is an olefinic effluent comprising at least 80% by weight and preferably at least 90% by weight of olefins comprising a number of carbon atoms greater than 4, and less than 20%, preferably less than 10% of C4 olefins, the weight percentages being expressed relative to the total weight of the olefins contained in the middle distillate effluent produced. 13. Process according to any one of the preceding claims, in which the fractionation step e) is carried out in at least one distillation column so as to separate the middle distillate type effluent from step d) into at least two cuts: - A gasoline cup, - A cut of middle distillates. 14. Process according to claim 13 in which at least a portion, preferably all of the middle distillate cut from fractionation step e) undergoes a step f) of hydrogenation of the olefins. 15. Process according to any one of the preceding claims, in which the C4 olefins not converted during the second oligomerization step d) are separated from the effluent from step d) and then recycled to the inlet of the second oligomerization step d).