Process for hydrotreatment and hydroisomerization of feedstocks resulting from biomass in which the effluent to be hydrotreated and the hydrogen stream contain a limited carbon monoxide content Field of the invention In an international context marked by the rapid increase in the need for fuels, in particular diesel bases and kerosenes in the European community, research into novel sources of renewable energy which can be integrated into the traditional refining layout and the production of fuels constitutes a major challenge.
In this regard, integrating novel products of vegetable origin into the refining pro- cess obtained from the conversion of lignocellulosic biomass or obtained from the production of vegetable oils or animal fats has in recent years enjoyed a robust re- — newal of interest due to the increase in the cost of fossil materials.
At the same time, traditional biofuels (principally ethanol or methyl esters of vegetable oils) have acguired genuine status as a supplement for oil type fuels in fuel pools.
Fur- thermore, current known processes using vegetable oils or animal fats are the basis of CO: emissions which are known to have negative effects on the environment. — Better use of these bioresources such as, for example, integrating them into the fuel pool, would thus be of definite advantage.
The great demand for diesel and kerosene fuels coupled with the importance of en- vironmental considerations reinforces the importance of using feeds obtained from — renewable sources, also known as biosourced feeds.
Examples of these feeds which may be cited are vegetable oils, animal fats, which are unrefined or which have un- dergone a prior treatment, as well as mixtures of such feeds.
These feeds in particu- lar contain triglyceride type chemical structures or esters or fatty acids, the structure and length of the hydrocarbon chain of these latter being compatible with the hy- — drocarbons present in diesels and kerosene.
One possible pathway is the catalytic transformation of the feed obtained from a renewable source of paraffinic fuel deoxygenated in the presence of hydrogen (hy- drotreatment). One of the major disadvantages of the hydrotreatment of vegetable oils derives from their high consumption of hydrogen.
Depending on the nature of — the oils, this may exceed 3% by weight with respect to the feed.
However, the new European directive 2009/28/CE insists on “durability criteria” for the energy sources, in particular with a major emphasis on the “reduction of greenhouse gas emissions resulting from the use of biofuels and bioliguids which must be at least 35% (50% in 2017 and 60% in 2018)”.
In order to overcome this disadvantage, a number of solutions have been pro- posed in the prior art, including recycling to the hydrotreatment step of hydrogen which is not converted during said hydrotreatment step.
However, during hy- drotreatment of the feed obtained from a renewable source, decarboxyla-
— tion/decarbonylation reactions of the fatty acid compounds result in the formation of gas such as carbon dioxide CO», methane CH4, and carbon monoxide CO, mixed with the unconverted hydrogen.
However, carbon monoxide CO, may have a nega- tive impact on the hydrodeoxygenating activity of the catalyst.
— Patent US 2009/0300971 describes a process for the preparation of naphtha starting from a feed obtained from a renewable source comprising a hydrotreatment step, a gas/liguid separation step, followed by a hydroisomerization step.
The hydrogen recycled to the hydrotreatment and/or hydroisomerization step may optionally be purified in order to separate ammonia, oxides of carbon and hydrogen sulphide be-
— fore being sent to said hydrotreatment and hydroisomerization steps.
It indicates that prior elimination of the contaminants present in the hydrogen stream preserves the catalytic activity and selectivity of the hydrotreatment and hydroisomerization catalysts.
However, no precise indication as to the purity of the hydrogen employed in the hydroisomerization step is mentioned.
Patent US 7 982 075 describes a process for the preparation of diesel starting from a feed obtained from a renewable source, comprising a hydrotreatment step,
a gas/liquid separation step followed by a hydroisomerization step.
The first step is carried out by injecting FbS in order to promote the formation of odd- numbered paraffins and thus of CO and CO2. The liquid effluent produced has to be completely free of water, CO, CO? or any other impurity so as not to have a deleterious effect on the isomerization activity.
The gases obtained from this first step may undergo several treatments in order to eliminate light hydrocarbons, ammonia and CO2. In the case in which the gas obtained from the first step has sufficiently low oxide of carbon contents, this may then be recycled to the hy- drotreatment section.
However, no precise indication as to the purity of the hydro- gen employed in the hydrotreatment step is mentioned.
Application WO 2006/100584 describes a process for the preparation of a diesel and naphtha cut from a feed obtained from a renewable source, comprising a step for hydrotreatment and hydroisomerization inside the same reactor, a gas/liguid separation step followed by a naphtha/diesel fractionation step.
The gas obtained from the gas/liguid separation undergoes a first purification in order to eliminate light compounds using a selective membrane or PSA (Pressure Swing Absorption). The hydrogen separated from the other by-products may then be recycled to the hydrotreatment and hydroisomerization step.
Patent US 2011/166396 describes a process for the production of diesel starting from a renewable feed containing triglycerides or free fatty acids and a fossil hy- drocarbon by hydrotreatment on a catalyst Mo/support, separation of the gaseous fraction from the hydrotreated effluent, purification of said gaseous fraction in — order to eliminate H2S, NH3, CO, CO, and the light hydrocarbons, recycle of the purified gas to the hydrotreatment step and catalytic hydroisomerization of the hy- drotreated liquid effluent.
Next, the gaseous fraction is usually separated from the effluent leaving the hy- — drotreatment reactor then re-injected into the reactor after passing through a treatment system in order to eliminate gases such as CO thereby.
Elimination of CO from the gases or reducing its quantity to very low contents ne- cessitates using complex and expensive treatment systems.
In addition, the pres- ence of such treatment systems can drop the recycled hydrogen yield (up to 25% hydrogen loss with a treatment using PSA). Thus, there is still a need for providing more economic, better-performing processes.
The Applicant’s research has led to the development of a process which can be used to recycle hydrogen without a prior step for purification of said recycled hydrogen.
The present invention proposes a process for the production of middle distillates starting from a feed comprising at least one fraction of feed obtained from a renew- able source, comprising at least: a) a step for hydrotreatment of said feed in the presence of a fixed bed of catalyst under predetermined conditions; b) a step for separation of at least a portion of the effluent obtained from step a) into at least one gaseous fraction and at least one liquid hydrocarbon effluent; c) a step for hydroi- somerization of at least a portion of the liquid hydrocarbon effluent separated in step b), in the presence of a fixed bed of hydroisomerization catalyst; d) a step for frac- tionation of the effluent obtained from step c) in order to obtain at least one middle distillate fraction, in which process at least a portion of the gaseous fraction separat- — edin step b) is returned to step a), said gaseous fraction returned to step a) compris- ing a quantity of CO in the range 0.5% to 3% by volume.
Detailed description of the invention — The present invention is dedicated to the preparation of diesel and/or kerosene fuel bases which comply with new environmental specifications, starting from a feed comprising at least one fraction of a feed obtained from renewable sources.
The present invention concerns a process for the production of middle distillates starting from a feed comprising at least one fraction of a feed obtained from a re- newable source, comprising at least: a) a hydrotreatment step in which said feed is brought into contact with a fixed bed of hydrotreatment catalyst, said catalyst com-
prising a hydrodehydrogenating function and an amorphous support, at a tempera- ture in the range 200°C to 450°C, at a pressure in the range 1 MPa to 10 MPa, at an hourly space velocity in the range 0.1 h™ to 10 h' and in the presence of a total quantity of hydrogen mixed with the feed such that the hydrogen/feed ratio is in the 5 range 70 to 1000 Nm? of hydrogen/m* of feed; b) a step for separation of at least a portion of the effluent obtained from step a) into at least one gaseous fraction com- prising hydrogen, at least CO and CO2 and C4" compounds, and at least one liquid hydrocarbon effluent; c) a step for hydroisomerization of at least a portion of the liquid hydrocarbon effluent separated in step b), in the presence of a fixed bed of — hydroisomerization catalyst; d) a step for fractionation of the effluent obtained from step c) in order to obtain at least one middle distillate fraction, in which at least a portion of the gaseous fraction separated in step b) is returned to step a), said gase- ous fraction returned to step a) comprising a quantity of CO in the range 0.5% to 3% by volume, in which the gaseous fraction separated in step b) is recycled to step a) at the same time as a makeup of fresh hydrogen, and in which the total gaseous fraction recycled combined with the makeup of fresh hydrogen comprises a quantity of CO in the range 0.5% to 3% by volume. The gaseous fraction returned to step a) contains a quantity of CO in the range
0.5% to 3% by volume, more preferably in the range 0.5% to 2.5% by volume, still more preferably in the range 0.5% to 2% by volume, and highly preferably in the range 0.5% to 1.5% by volume. Advantageously in accordance with the invention, the gaseous fraction separated — in step b) undergoes a step for purification of the CO? before being recycled to the hydrotreatment step a). Carrying out the process of the invention has the advantage of overcoming the problems linked to the large consumption of hydrogen during the hydrotreatment — of the feeds comprising at least one fraction of a feed obtained from a renewable source. The process of the invention can be used to save on costs linked to using systems for purification of the hydrogen recycled to the hydrotreatment step. Fur-
thermore, by avoiding having to use such purification systems, the present inven- tion has the advantage of increasing the hydrogen recycle yield.
Feed
The feed of the invention comprises at least one fraction of a feed obtained from a renewable source.
A feed obtained from a renewable source, also known as a biosourced feed, as used in the context of the present invention, should be under- stood to mean a feed advantageously comprising at least oils and fats of vegetable — or animal origin, or mixtures of such feeds, containing triglycerides and/or free fatty acids and/or esters.
The vegetable oils may advantageously be unrefined or refined, completely or partially, and obtained from the following plants: rape, sun- flower, soya, African, palm kernel, olive, coconut, jatropha; this list is not limiting, Algal oils or fish oils are also pertinent.
The animal fats are advantageously select- — ed from lard or fats composed of food industry residues or obtained from catering industries.
These feeds essentially contain chemical structures of the triglyceride type, which the skilled person also knows as fatty acid triesters, as well as free fatty acids.
A fatty acid triester is thus composed of three fatty acid chains.
These fatty acid chains, in the form of a triester or in the form of free fatty acids, have a number of unsaturated bonds per chain, which are also known as carbon-carbon double bonds per chain, which is generally in the range 0 to 3, but which may be higher, in partic- ular for oils obtained from algae which generally contain 5 or 6 unsaturated bonds per chain.
The molecules present in the feeds obtained from renewable sources used in the present invention thus have a number of unsaturated bonds, expressed per molecule of triglyceride, which is advantageously in the range 0 to 18. In these feeds, the degree of unsaturation, expressed as the number of unsaturated bonds per hydrocar- bon fatty chain, is advantageously in the range 0 to 6.
The feeds obtained from renewable sources also comprise different impurities, in particular heteroatoms such as nitrogen.
The quantity of nitrogen in the vegetable oils is generally in the approximate range 1 ppm to 100 ppm by weight, depending on their nature.
The feed of the invention may also comprise at least one fraction of hydrocarbon feed (co-processing). In the context of the present invention, said hydrocarbon feed should be understood to mean a fraction of feed which may advantageously contain at least coal, petcoke, natural gas, oil residues, crude oil, topped crude oils,
deasphalted oils, deasphalted asphalts, oil conversion process derivatives (such as for example: HCO, FCC slurry, heavy GO/coking VGO, visbreaking residue or similar thermal process residues, etc.), bituminous sands or their derivatives, shale gases and shale oil or their derivatives.
In accordance with the process of the inven- tion, said hydrocarbon feed fraction may be a fraction of a gaseous, solid or liquid hydrocarbon feed or a mixture thereof.
Advantageously, the feed used in the process of the invention comprises a fraction of at least 20%, preferably at least 50%, more preferably at least 70%, and highly preferably at least 90% of the feed obtained from a renewable source.
In a preferred embodiment, prior to step a) of the process of the invention, the feed undergoes a step for pre-treatment or pre-refining so as to eliminate contaminants such as metals and alkaline compounds by means of an appropriate treatment, for example over ion exchange resins, alkaline-earths and phosphorus.
Examples of
— appropriate treatments may be thermal and/or chemical treatments which are well known to the skilled person.
Hydrotreatment step a)
In accordance with step a) of the process of the invention, the feed, which may have been pre-treated, is brought into contact with a fixed bed of catalyst at a temperature in the range 200°C to 450°C, preferably in the range 220°C to 350°C,
more preferably in the range 220°C to 320°C, and still more preferably in the range 220°C to 310°C. The pressure is in the range 1 MPa to 10 MPa, preferably in the range 1 MPa to 6 MPa and still more preferably in the range 1 MPa to 4
MPa. The hourly space velocity, i.e. the volume of feed per volume of catalyst per hour, is in the range 0.1 h' to 10 h'. The feed is brought into contact with the catalyst in the presence of hydrogen. The total quantity of hydrogen mixed with the feed is such that the hydrogen/feed ratio is in the range 70 to 1000 Nm? of hydrogen/m* of feed, and preferably in the range 150 to 750 Nm? of hydrogen/m* of feed. In step a) of the process of the invention, the fixed bed catalyst is advantageously a hydrotreatment catalyst comprising a hydrodehydrogenating function compris- ing at least one metal from group VIII and/or group VIB, used alone or as a mix- ture, and a support selected from the group formed by alumina, silica, silica- aluminas, magnesia, clays and mixtures of at least two of these minerals. This support may also advantageously comprise other compounds, for example oxides selected from the group formed by boron oxide, zirconia, titanium oxide, and phosphoric anhydride. The preferred support is an alumina support, highly prefera- bly n, 6 or y alumina. Said catalyst is advantageously a catalyst comprising metals from group VIII, pref- erably selected from nickel and cobalt, used alone or as a mixture, preferably in association with at least one metal from group VIB, preferably selected from mo- lybdenum and tungsten, used alone or as a mixture. The quantity of oxides of metals from group VIII, preferably nickel oxide, is advan- tageously in the range 0.5% to 10% by weight of nickel oxide (NiO), preferably in the range 1% to 5% by weight of nickel oxide, and the quantity of oxides of metals from group VIB, preferably molybdenum trioxide (MoQs3), is advantageously in the range 1% to 30% by weight, preferably in the range 5% to 25% by weight, the per- centages being expressed as the percentage by weight with respect to the total cata- lyst mass.
The total quantity of oxides of metals from groups VIB and VIII in the catalyst used in step a) is advantageously in the range 5% to 40% by weight, preferably in the range 6% to 30% by weight with respect to the total catalyst mass.
Said catalyst used in step a) of the process of the invention is advantageously char- acterized by a high hydrogenating power in order to orientate the selectivity of the reaction as far as possible towards a hydrogenation conserving the number of car- bon atoms in the fatty chains, i.e. the hydrodeoxygenation pathway, in order to max- 1imize the yield of hydrocarbons within the kerosenes and/or diesels distillation range.
Advantageously, the operating temperature is relatively low.
Maximizing the hydrogenating function also means that polymerization and/or condensation reactions can be limited as they lead to the formation of coke which would degrade the stability of the catalytic performance.
Preferably, a Ni or NiMo type catalyst is — used.
Said catalyst used in hydrotreatment step a) of the process of the invention may also advantageously contain a doping element selected from phosphorus and boron, used alone or as a mixture.
Said doping element may be introduced into the matrix or, as — is preferable, deposited on the support.
It is also possible to deposit silicon onto the support, alone or with phosphorus and/or boron and/or fluorine.
The quantity by weight of the oxide of said doping element is advantageously below 20% and pref- erably less than 10%, and it is advantageously at least 0.001%. — Preferred catalysts are the catalysts described in patent application FR 2 943 071 describing catalysts with a high selectivity for hydrodeoxygenation reactions.
Other preferred catalysts are the catalysts described in patent application EP 2 210 663, which describes bulk or supported catalysts comprising an active phase consti- tuted by a sulphurized element from group VIB, the element from group VIB being molybdenum.
The metals of the catalysts used in the hydrotreatment step a) of the process of the invention are sulphurized metals or metallic phases, preferably sulphurized metals.
The context of the present invention also encompasses using a single catalyst or — several different catalysts in step a) of the process of the invention, simultaneously or in succession.
This step may be carried out on an industrial scale in one or more reactors with one or more catalytic beds, preferably with a downflow of liquid.
Step b) for gas/liquid separation of the effluent obtained from step a)
In accordance with step b) of the process of the invention, a step for separation of at least a portion, preferably all of the effluent obtained from step a) is carried out.
Step b) of the process of the invention can be used to separate the effluent ob- tained from step a) into at least one gaseous fraction essentially comprising hy- drogen and at least one liquid hydrocarbon effluent.
In accordance with the invention, said gaseous fraction comprises unconverted hydrogen, the gases containing at least one oxygen atom and the C4 compounds.
Said gases are essentially obtained from the decomposition of oxygen-containing — compounds during the hydrotreatment step.
In accordance with the invention, the term “gas containing at least one oxygen atom” is intended to mean the gas containing at least CO and CO». — In accordance with the invention, the term “C4” compounds” is intended to mean C1 to C4 compounds preferably with a final boiling point of less than 20°C.
In accordance with the invention, the gaseous fraction obtained from step b) ad- vantageously undergoes a step for purification of the CO? before being recycled to the hydrotreatment step a). Said step for purification of CO? is advantageously carried out by washing said gaseous fraction with amines or any technique which is known to the skilled person.
Step b) of the invention can be used to separate the gas from the liquid, in particular to recover at least one gaseous fraction which is rich in hydrogen and containing CO and the C4 compounds on the one hand and at least one liquid hydrocarbon effluent on the other hand. In accordance with the invention, at least a portion, preferably the whole of the gas- eous fraction separated in step b) is recycled to step a). In accordance with the in- vention, the gaseous fraction separated in step b) and recycled to step a) comprises a CO content in the range 0.5% to 3% by volume, still more preferably in the range
0.5% to 2.5% by volume, highly preferably in the range 0.5% to 2% by volume. In a highly preferred variation of the process, said CO content in said gaseous fraction recycled to step a) is in the range 0.5% to 1.5% by volume. — In accordance with the invention, said gaseous fraction separated in step b) is recy- cled to step a) at the same time as a makeup of fresh hydrogen. In accordance with the invention, the total recycled gaseous fraction combined with the makeup of fresh hydrogen has a CO content in the range 0.5% to 3% by volume, still more preferably in the range 0.5% to 2.5% by volume, highly preferably in the range
0.5% to 2% by volume. In a highly preferred variation of the process, said CO con- tent in said gaseous fraction recycled to step a) is in the range 0.5% to 1.5% by vol-
ume. Without wishing to be bound to a particular theory, it would appear, apart from the — specific conditions of the hydrotreatment step of the invention, that tolerating the presence of CO in quantities which may be up to 3% by volume could be linked to the reaction equilibrium for the conversion of carbon monoxide with steam (Water- Gas-Shift), which produces hydrogen by consuming carbon monoxide (CO) and water obtained from the reaction for hydrotreatment of the vegetable feed. The liquid hydrocarbon effluent separated in step b) preferably has a sulphur con- tent of less than 10 ppm by weight, a nitrogen content of less than 2 ppm by weight.
Separation step b) may advantageously be carried out by any method which is known to the skilled person, such as for example the combination of one or more high and/or low pressure separators and/or distillation steps and/or high and/or low — pressure stripping.
Step c) for hydroisomerization of the liquid hydrocarbon effluent In accordance with step c) of the process of the invention, at least a portion, pref- erably all of the liquid hydrocarbon effluent obtained from step b) of the process of the invention is hydroisomerized in the presence of a fixed bed of hydroisom- erization catalyst, said hydroisomerization step being carried out at a temperature in the range 150°C to 500°C, a pressure in the range 1 MPa to 10 MPa, an hourly space velocity in the range 0.1 to 10 h? in the presence of a total quantity of hy- drogen mixed with the feed such that the hydrogen/feed ratio is in the range 70 to 1000 Nm*/m of feed and in the presence of hydrogen.
In accordance with the invention, the hydrogen used in step c) is advantageously generated by processes which are known to the skilled person such as, for exam- — ple, a process for catalytic reforming or catalytic cracking of the gases.
Depending on the nature of the various sources, the hydrogen used in step c) in the process of the invention may or may not contain impurities.
The quantity of atomic oxygen in said hydrogen stream may be measured using any method — known to the skilled person such as gas phase chromatography, for example.
Preferably, the hydrogen used in step c) may be fresh hydrogen or recycled hydro- gen, i.e. hydrogen not converted during the hydroisomerization step c) and separat- ed in fractionation step d), or a mixture thereof.
Preferably, the hydrogen used in step c) undergoes a purification step to eliminate oxygen-containing compounds such as CO and CO? therefrom.
Said step for purifi-
cation of the hydrogen used in step c) may advantageously be carried out using any method known to the skilled person.
Preferably, said purification step is advantageously carried out in accordance with — pressure swing adsorption (PSA) methods or temperature swing adsorption (TSA) methods, amine washing, methanation, preferential oxidation, or membrane pro- cesses, used alone or in combination.
When the process employs recycling of hydrogen not converted during the hydroi- — somerization step c) and separated in the fractionation step d) (recycled hydrogen), a purge of said recycled hydrogen may advantageously be carried out in order to limit the accumulation of molecules containing at least one oxygen atom such as CO or CO? and thus to limit the quantity of atomic oxygen in said hydrogen stream.
In another embodiment of the invention, the hydrogen used in step c) derives at least in part from the gaseous fraction separated in step b). The operating conditions for the hydroisomerization step are adjusted in order to carry out hydroisomerization of the feed which is not being converted.
This means that the hydroisomerization is carried out with a conversion of the 150°C" fraction into the 150°C" fraction of less than 20% by weight, preferably less than 10% by weight and highly preferably less than 5% by weight.
Advantageously, the hydroisomerization step c) of the process of the invention is — operated at a temperature in the range 150°C to 450°C, highly preferably in the range 200°C to 450°C, at a pressure in the range 2 MPa to 10 MPa and highly pref- erably in the range 1 MPa to 9 MPa, at an hourly space velocity which is advanta- geously in the range 0.2 to 7 h", highly preferably in the range 0.5 to 5 h”', at a hy- drogen flow rate such that the hydrogen/hydrocarbon volume ratio is advantageous- ly in the range 100 to 1000 normal m? of hydrogen per m? of feed, preferably in the range 150 to 1000 normal m? of hydrogen per m” of feed.
The hydroisomerization catalyst comprises at least one hydrodehydrogenating metal selected from the group formed by metals from group VIB and VIII of the periodic classification of the elements and at least one solid Bronsted acid, and optionally a binder.
Preferably, the hydroisomerization catalyst comprises either at least one noble metal from group VIII selected from platinum and palladium, used alone or as a mixture, either active or in their reduced form, or at least one non-noble metal from group VIII selected from nickel and cobalt in combination with at least one metal from — group VI selected from molybdenum and tungsten, used alone or as a mixture, and preferably used in their sulphurized form.
In the case in which the hydroisomerization catalyst comprises at least one noble metal from group VIII, the quantity of noble metal of said hydroisomerization cata- — lyst is advantageously in the range 0.01% to 5% by weight with respect to the fin- ished catalyst, preferably in the range 0.05% to 4% by weight and highly preferably in the range 0.10% to 2% by weight.
In the case in which the hydroisomerization catalyst comprises at least one metal — from group VI in combination with at least one non-noble metal from group VIII, the guantity of metal from group VI of said third hydroisomerization catalyst is ad- vantageously in the range 5% to 40% by weight as the oxide eguivalent with respect to the finished catalyst weight, preferably in the range 10% to 35% by weight and highly preferably in the range 15% to 30% by weight and the guantity of metal from — group VIII of said catalyst is advantageously in the range 0.5% to 10% by weight as the oxide eguivalent with respect to the finished catalyst weight, preferably in the range 1% to 8% by weight and highly preferably in the range 1.5% to 6% by weight.
The metallic function is advantageously introduced into the catalyst using any method which is known to the skilled person, such as co-mixing, dry impregnation or impregnation by exchange for example.
Preferably, the solid Bronsted acid is constituted by silica-alumina or Y zeolite, SAPO-11, SAPO-41, ZSM-22, ferrierite, ZSM-23, ZSM-48, ZBM-30, IZM-1, or COK-7. Optionally, a binder may advanta- geously also be used during the step for shaping the support.
Preferably, a binder is used when zeolite is employed.
Said binder is advantageously selected from silica (S102), alumina (A203), clays, titanium oxide (TiO2), boron oxide (B203) and zirconia (ZrO2), used alone or as a mixture.
Preferably, said binder is selected from silica and alumina and still more preferably, said binder is alumina in any of its forms which are known to the skilled — person, such as gamma alumina, for example.
A preferred hydroisomerization catalyst used in the process of the invention advan- tageously comprises at least one noble metal, said noble metal being platinum, and a solid silica-alumina type Bronsted acid, with no binder.
The quantity of silica and silica-alumina, expressed as a percentage by weight, is generally in the range 1% to 95%, advantageously in the range 5% to 95%, and preferably in the range 10% to 80% by weight and more preferably in the range 20% to 70% and in the range 22% to 45%. This silica content is ideally measured with the aid of X ray fluorescence. — Several preferred catalysts used in the hydroisomerization step c) of the process of the invention are described below.
A preferred catalyst used in the process of the invention comprises a particular silica-alumina.
More precisely, said catalyst comprises (and preferably is essen- — tially constituted by) 0.05% to 10% by weight and preferably in the range 0.1% to 5% by weight of at least one noble metal from group VIII, preferably selected from platinum and palladium and preferably, said noble metal is platinum, depos- ited on a silica-alumina support, without any binder, containing a quantity of silica (S102) in the range 1% to 95%, expressed as a percentage by weight, preferably in the range 5% to 95%, preferably in the range 10% to 80% and highly preferably in the range 20% to 70% and still more preferably in the range 22% to 45%, said catalyst having:
— a BET specific surface area of 100 to 500 m?/g, preferably in the range 200 m”/g to 450 m”/g and highly preferably in the range 250 m?/g to 450 m?/g; — a mean mesopore diameter in the range 3 to 12 nm, preferably in the range 3 nm to 11 nm and highly preferably in the range 4 nm to 10.5 nm; — a pore volume of pores with a diameter in the range between the mean diameter as de- fined above reduced by 3 nm and the mean diameter as defined above increased by 3 nm of more than 40% of the total pore volume, preferably in the range 50% to 90% of the total pore volume and highly preferably in the range 50% to 70% of the total pore volume; — a total pore volume in the range 0.4 to 1.2 mL/g, preferably in the range 0.5 to 1.0 mL/g and highly preferably in the range 0.5 to 0.9 mL/g; — a quantity of alkaline or alkaline-earth compounds of less than 300 ppm by weight, prefer- ably less than 200 ppm by weight. The mean mesopore diameter is defined as being the diameter corresponding to cancellation of the derivative of the curve for the intrusion volume of mercury obtained from the mercury porosity curve for pore diameters in the range 2 to 50 nm. The mean mesopore diameter of the catalyst is advantageously measured from the pore distribution profile obtained using a mercury porosimeter. Preferably, the dispersion of the metal of said preferred catalyst is advantageously in the range 20% to 100%, preferably in the range 30% to 100% and highly preferably in the range 40% to 100%. The dispersion, representing the fraction of the metal accessible to the reagent with respect to the total guantity of metal of the catalyst, is advantageously measured, for example, by H2/O? titration or by transmission elec- tron microscopy. Preferably, the distribution coefficient of the noble metal of said preferred catalyst is more than 0.1, preferably more than 0.2 and highly preferably more than 0.4. The distribution of the noble metal represents the distribution of the metal inside the catalyst grain, the metal possibly being dispersed well or poorly. Thus, it is possible to obtain poorly distributed platinum (for example detected in a ring the thickness of which is substantially less than the radius of the grain) but well dispersed, i.e. all of the platinum atoms located in the ring will be accessible to the reagents. The distri-
bution coefficient of the noble metal may be measured using a Castaing micro- probe. The noble metal salt is advantageously introduced by one of the usual methods em- ployed to deposit the metal on the surface of a solid. One of the preferred methods is dry impregnation, which consists of introducing a metal salt into a volume of solution which is equal to the pore volume of the mass of the solid to be impregnat-
ed. Before the reduction operation, the catalyst may advantageously undergo cal- cining such as, for example, a treatment in dry air at a temperature of 300°C to 750°C, preferably at a temperature equal to 520°C, for 0.25 to 10 hours, preferably for 2 hours. Another preferred catalyst in the process of the invention comprises a second par- ticular silica-alumina. More precisely, said catalyst comprises at least one hydrode- — hydrogenating element selected from the group formed by elements from group VIB and group VIII of the periodic classification of the elements, 0.01% to 5.5% by weight of oxide of a doping element selected from phosphorus, boron and silicon and a non-zeolitic support based on silica-alumina containing a guantity of more than 5% by weight and less than or equal to 95% by weight of silica (SiOz), said catalyst having the following characteristics: — a mean mesopore diameter, measured by mercury porosimetry, in the range 2 to 14 nm; — a total pore volume, measured by mercury porosimetry, in the range 0.1 mL/g to 0.5 mL/g; — a total pore volume, measured by nitrogen porosimetry, in the range 0.1 mL/g to 0.5 mL/g; — a BET specific surface area in the range 100 to 550 m%g; — a pore volume, measured by mercury porosimetry, included in pores with a diameter of more than 14 nm, of less than 0.1 mL/g; — a pore volume, measured by mercury porosimetry, included in pores with a diameter of more than 16 nm, of less than 0.1 mL/g;
— a pore volume, measured by mercury porosimetry, included in pores with a diameter of more than 20 nm, of less than 0.1 mL/g;
— a pore volume, measured by mercury porosimetry, included in pores with a diameter of more than 50 nm, of less than 0.1 mL/g;
— an X ray diffraction pattern which contains at least the principal charac- teristic lines of at least one of the transition aluminas included in the group composed of alpha, rho, chi, eta, gamma, kappa, theta and delta aluminas;
— a settled packing density of more than 0.75 g/mL.
Another preferred catalyst used in the process of the invention comprises (and is preferably essentially constituted by) 0.05% to 10% by weight, preferably 0.1% to 5% by weight of at least one noble metal from group VIII, preferably selected from platinum and palladium; preferably, said noble metal is platinum deposited on a silica-alumina support without any binder, containing a quantity of silica (S102) in the range 1% to 95%, expressed as a percentage by weight, preferably in the range 5% to 95%, preferably in the range 10% to 80% and highly preferably in the range 20% to 70% and still more preferably in the range 22% to 45%, said cata- lyst having:
— a BET specific surface area of 200 to 600 m?/g, preferably in the range 250 m*/g to 500 m?/g;
— a mean mesopore diameter in the range 3 to 12 nm, preferably in the range 3 nm to 11 nm and highly preferably in the range 4 nm to 10.5 nm;
— a pore volume of pores with a diameter in the range between the mean diameter as de- fined above reduced by 3 nm and the mean diameter as defined above increased by 3 nm of more than 60% of the total pore volume, preferably more than 70% of the total pore vol- ume and highly preferably more than 80% of the total pore volume;
— a total pore volume of less than 1 mL/g, preferably in the range 0.1 to 0.9 mL/g and highly preferably in the range 0.2 to 0.7 mL/g;
— a quantity of alkaline or alkaline-earth compounds of less than 300 ppm by weight, prefer-
ably less than 200 ppm by weight.
Preferably, the dispersion of the noble metal of said preferred catalyst used in step d) of the process of the invention is advantageously in the range 20% to 100%, preferably in the range 30% to 100% and highly preferably in the range 40% to 100%. Preferably, the distribution coefficient of the noble metal of said preferred catalyst used in step c) of the process of the invention is more than 0.1, preferably more than
0.2 and highly preferably more than 0.4. This distribution coefficient is measured by Castaing microprobe. Another preferred catalyst used in the process of the invention comprises a silica- alumina and at least one metal from group VIIIB and at least one metal from group VIB, said catalyst being sulphurized. The quantity of these elements is advanta- geously in the range 5% to 40% by weight as the oxide equivalent with respect to the finished catalyst, preferably in the range 10% to 35% by weight and highly pref- erably in the range 15% to 30% by weight, and the quantity of metal from group VIII of said catalyst is advantageously in the range 0.5% to 10% by weight as the oxide equivalent with respect to the finished catalyst, preferably in the range 1% to 8% by weight and highly preferably in the range 1.5% to 6% by weight. The metallic hydrodehydrogenating function may advantageously be introduced onto said catalyst using any method which is known to the skilled person, such as co-mixing, dry impregnation or exchange impregnation, for example. Said hydroi- somerization catalyst comprises at least one amorphous mineral support as the hy- — droisomerization function, said one amorphous mineral support being selected from silica-aluminas and siliceous aluminas, preferably silica-aluminas, containing a quantity of more than 5% by weight to 95% by weight or less of silica (SiOz). Step d) for fractionation of the liquid effluent obtained from step c) In accordance with step d) of the process of the invention, the hydroisomerized effluent obtained from step c) undergoes a fractionation step, preferably in a dis-
tillation train which integrates atmospheric distillation and optionally vacuum distillation, in order to obtain at least one middle distillate fraction.
The aim of said step d) is to separate the effluent obtained from hydroisomerization step c) into at least one gaseous fraction comprising hydrogen not converted during the hydroisomerization step c), at least one diesel cut, at least one kerosene cut and at least one naphtha cut.
Upgrading the naphtha cut is not the aim of the present invention, but this cut may advantageously be sent to a steam cracking or catalytic reforming unit.
EXAMPLES Example 1: Preparation of a hydrotreatment catalyst (C1)
The catalyst was an industrial catalyst based on nickel, molybdenum and phos- phorus on alumina with quantities of molybdenum oxide, MoOs3, of 16% by weight, of nickel oxide, NiO, of 3% by weight and of phosphorous oxide, P2Os, of 6% by weight with respect to the total finished catalyst weight, supplied by AXENS.
Example 2: Hydrotreatment of a feed obtained from a renewable source using a process which is not in accordance with the invention Step a): hydrotreatment
92 g/h of pre-refined rapeseed oil with a density of 920 kg/m? with an oxygen con- tent of 11% by weight and a sulphur content of 5 ppm by weight was introduced into a temperature-regulated reactor so as to provide for isothermal operation also having a fixed bed charged with 110 mL of hydrotreatment catalyst C1, which had already been sulphurized.
The cetane number was 35 and the fatty acid distribution for the rapeseed oil is detailed in Table 1.
Table 1: Characteristics of rapeseed oil used as feed for hydrotreatment step a)
Fatty acid composi-
es”
14:0 0.1
16:0 5.0
16:1 0.3
17:0 0.1
17:1 0.1
18:0 1.5
18:1 trans <0.1
18:1 cis 60.1
18:2 trans <0.1
18:2 cis 20.4
18:3 trans <0.1
18:3 cis 9.6
20:0 0.5
20:1 1.2
22:0 0.3
22:1 0.2
24:0 0.1
24:1 0.2 700 Nm” of pure hydrogen/m* of feed was introduced into the reactor maintained at a temperature of 300°C, at an hourly space velocity of 1 h' and at a pressure of
5 MPa.
Step b): separation of the effluent obtained from hydrotreatment step a) The whole of the hydrotreated effluent obtained from step a) was separated with the aid of a gas/liquid separator so as to recover a light fraction containing mainly hydrogen, propane, water in the form of a vapour, oxides of carbon (CO and CO?) and ammonia and a liquid hydrocarbon effluent mainly constituted by linear hydrocarbons (150+ cut). The water present in the liquid hydrocarbon effluent was eliminated by decanting. The liquid hydrocarbon effluent thus obtained con- tained an atomic oxygen content of less than 80 ppm by weight, said quantity of atomic oxygen being measured by the infrared adsorption technique described in — patent application US 2009/0018374, and a sulphur content of 1 ppm by weight and a nitrogen content of less than 1 ppm by weight. The principal yields for the fractions of the effluent produced are reported in Table