WO2015181744A1

WO2015181744A1 - Process for producing a diesel hydrocarbon fraction starting from a renewable feedstock

Info

Publication number: WO2015181744A1
Application number: PCT/IB2015/053971
Authority: WO
Inventors: Giuseppe Bellussi; Daniele MOLINARI; Alberto Renato DE ANGELIS; Vincenzo Calemma
Original assignee: Eni S.P.A.
Priority date: 2014-05-29
Filing date: 2015-05-27
Publication date: 2015-12-03

Abstract

The present invention relates to a process for preparing a diesel hydrocarbon fraction, comprising the following steps: (a) reacting at least a renewable feedstock comprising glycerides with ammonia at a temperature within the range of 130–250°C and a pressure within the range of 1-8 MPa, forming at least a mixture of fatty acid amides and glycerine; (b) separating said glycerine from said mixture of amides; (c) subjecting said mixture of amides to catalytic hydrotreatment in the presence of hydrogen, obtaining a reaction product comprising: (i) at least one gaseous effluent comprising ammonia, hydrogen, water vapour and CO, (ii) at least one diesel hydrocarbon fraction comprising a mixture of substantially linear paraffins; (d) separating said diesel hydrocarbon fraction from said reaction product. Said mixture of linear paraffins is advantageously subjected to a further hydroisomerization step for converting the linear paraffins into branched paraffins.

Description

PROCESS FOR PRODUCING A DIESEL HYDROCARBON FRACTION STARTING FROM A RENEWABLE FEEDSTOCK

The present invention relates to a process for producing a diesel fraction starting from a renewable feedstock, such as, for example, a vegetable oil or a fat of an animal origin.

As is known, the increase in the extraction costs of petroleum due to the progressive exhaustion of natural reserves and a growing awareness with respect to problems relating to pollution of the environment have increased the necessity for using fuels alternative to fuels of a fossil origin, in particular fuels obtained from renewable energy sources, such as, for example, vegetable oils, fats of an animal origin, biomasses and algae.

Various processes are currently available in the specific field of fuels for diesel engines (diesel fuels), through which hydrocarbon fractions can be obtained which can be used as such as diesel fuels, or as components to be added to the diesel fuels obtained from fossil energy sources (so-called "biocomponents" ) .

One of the technologies available for converting renewable feedstocks into diesel hydrocarbon fractions is a conversion process in two steps which comprises a first hydrotreating step of the starting feedstock followed by a subsequent hydroisomerization step.

The hydrotreating step envisages the treatment of the renewable feedstock with hydrogen in the presence of a catalyst. In this step, the feedstock is subjected to a catalytic hydrogenation reaction through which the saturation is obtained of the double bonds of the hydrocarbon chains of glycerides and the contemporaneous elimination of the oxygen atoms present on these chains. The above catalytic hydrogenation reaction, also called "hydrodeoxygenation" reaction, leads to the formation of a mixture of prevalently linear paraffins having a length substantially corresponding to that of the hydrocarbon chains of fatty acids which form glycerides. In the hydrodeoxygenation reaction, the glycerine part of the structure of the esters of fatty acids with glycerine, under the reaction conditions, is converted to propane. Further by-products are ¾0, and fuel gas.

The paraffins obtained through hydrotreatment have a boiling point within the distillation temperature range of hydrocarbons which typically form diesel fuels and kerosene. These paraffins, however, due to their linearity, are a diesel fuel with poor cold flow properties. This drawback can be overcome by subjecting the linear paraffins to a subsequent hydroisomerization step, in which the paraffinic mixture is treated with hydrogen in the presence of a hydroisomerization catalyst. In this step, most of the linear paraffins are converted to branched paraffins, without substantially undergoing the cracking of the alkyl chain. The mixture of branched paraffins thus obtained can be used as diesel fuel or as biocomponent for fuels of a fossil origin with adequate performances also at low temperatures.

Examples of treatment processes of renewable feedstocks which include the hydrotreatment and isomerization steps described above are provided in WO 2008/058664 and US 2009/0077867. Although the treatment process of the known art described above is successfully applied industrially, it has various disadvantages.

First of all, the above conversion process requires a high hydrogen consumption. This high consumption is due to the inevitable hydrogenation reaction of the glycerine part of the structure of the fatty acid esters with glycerine, with the formation of propane and water, which takes place during the hydrotreating step. The transformation of the glycerine part into propane, moreover, wastes the possibility of recovering this part in the form of glycerine and using it as raw material for subsequent uses, such as, for example, the production of biocomponents for diesel fuels.

A second drawback is the limited production capacity of the treatment process. As the hydrodeoxygenation reaction is a strongly exothermic reaction, in industrial practice, the hydrotreating step is generally effected by recirculating a part of the reaction effluent containing linear paraffins, to this step, so as to control the process temperature. In some cases, the recirculation of the paraffins can reach values higher than 80% by weight referring to the weight of the stream at the inlet of this step, according to what is described, for example, in patent EP1741768 assigned to Neste Oil Oyi . This represents an evident limit to the full utilization of the production capacity of the process.

A further disadvantage lies in the risk of corrosion of the treatment plants due to the acidity of the renewable feedstocks. At present, in order to prevent corrosion phenomena, various sections of the treatment plants are produced with anti-corrosion materials, such as, for example, AISI 316 stainless steel or even higher alloyed steel, with a consequent increase in the construction costs of the plants.

The objective of the present invention is to overcome the highlighted drawbacks of the state of the art .

In particular, a specific objective of the present invention is to provide a process for preparing a diesel hydrocarbon fraction starting from a renewable feedstock which leads to a reduced hydrogen consumption .

A second objective of the present invention is to provide a process for preparing the above diesel hydrocarbon fraction which can be effected industrially with a higher production yield with respect to the refining processes of the known art.

A third objective of the present invention is to provide a process for preparing the above diesel hydrocarbon fraction in which there are reduced risks of corrosion of the production equipment.

The Applicant has now found that these and other objectives, which will be better illustrated in the following description, can be achieved by effecting a process for preparing a diesel hydrocarbon fraction, comprising the following phases:

(a) reacting at least a renewable feedstock comprising glycerides with ammonia at a temperature within the range of 130-250°C and a pressure within the range of 1-8 MPa, forming at least a mixture of fatty acid amides and glycerine;

(b) separating said glycerine from said mixture of amides ;

(c) subjecting said mixture of amides to catalytic hydrotreatment in the presence of hydrogen, obtaining a reaction product comprising:

(i) at least one gaseous effluent comprising ammonia, hydrogen, water vapour and CO,

(ii) at least one diesel hydrocarbon fraction comprising a mixture of substantially linear paraffins;

(d) separating said diesel hydrocarbon fraction from said reaction product.

According to a preferred embodiment, the process of the present invention also comprises at least one phase (e) in which said diesel hydrocarbon fraction substantially comprising linear paraffins is subjected to catalytic hydroisomerization in the presence of hydrogen, so as to convert at least one part of said linear paraffins into branched paraffins and obtain a diesel hydrocarbon fraction with improved cold flow properties .

According to the present invention, the renewable feedstock containing glycerides, in particular triglycerides, is treated initially with ammonia in order to cause the splitting of the glycerides into glycerine and corresponding fatty acids amides (phase a) . The glycerine is then separated (phase b) from the fatty acid amides, so as to avoid being subjected to hydrogenation in the subsequent hydrotreating step (phase c) . In the hydrotreatment step, the amides are transformed into a diesel hydrocarbon fraction comprising substantially linear paraffins, which, in the possible subsequent hydroisomerization phase (phase e) , can be at least partly converted into branched paraffins .

As the glycerine component of the structure of the fatty acid esters is eliminated by the renewable feedstock, upstream of the hydrotreatment phase, its transformation into propane is avoided, significantly reducing the hydrogen consumption in this step. Furthermore, thanks to this separation, the glycerine recovered can be upgraded either as raw material for further uses or by purifying it to obtain a product having a higher commercial value.

As already indicated, the present invention relates to a process for preparing a diesel hydrocarbon fraction. For the purposes of the present invention, the expression "diesel hydrocarbon fraction" indicates a mixture of hydrocarbons having a total number of carbon atoms ranging from 9 to 22 and a boiling point at atmospheric pressure within the temperature range of hydrocarbons which typically form the diesel cut obtained from petroleum (180°C - 360°C), in particular the kerosene cut (C9-C14, boiling range 180°C - 240°C, so-called jet fuel) and the gasoil cut (C₁ -C22_A boiling range 240°C - 360°C) .

This diesel hydrocarbon fraction is obtained starting from a renewable feedstock.

For the purposes of the present invention, the expression "renewable feedstock" (hereinafter also indicated as "feedstock") includes feedstocks different from feedstocks deriving from petroleum.

The renewable feedstocks that can be used for the purposes of the present invention comprise glycerides. The glycerides are generally in the form of triglycerides, but monoglycerides and diglycerides can also be present.

The hydrocarbon chain of fatty acids which form glycerides can typically contain from 11 to 21 carbon atoms, preferably from 14 to 20 carbon atoms, and can be mono-unsaturated or poly-unsaturated.

The renewable feedstocks can be selected, for example, from vegetable oils, vegetable fats, animal fats, fish oils or mixtures thereof.

Some examples of renewable feedstocks are: sunflower oil, rapeseed. oil, canola oil, palm oil, soybean oil, hempseed oil, olive oil, linseed oil, peanut oil, castor oil, mustard oil, coconut oil, oils deriving from algae or fatty oils contained in the pulp of pine trees ("tall oil") . The animal oils and fats can be selected from lard, tallow, milk fat or fats obtained from the poultry industry (chicken fat) . Recycled oils and fats of the food industry, of both an animal and vegetable origin, can also be used. The vegetable oils or fats can also derive from plants selected by genetic manipulation . The above renewable feedstocks can be used alone or mixed with each other.

The renewable feedstocks can also contain free fatty acids. When present, the concentration of said free fatty acids can typically reach 30% by weight of the renewable feedstock. In the particular case of renewable feedstocks deriving from microalgae, the concentration of free fatty acids can also reach 60% by weight of the feedstock.

In the process according to the present invention, mixtures of renewable feedstocks together with hydrocarbons of petroleum origin, can also be used.

Phase (a) of the process according to the present invention, also called ammonolysis , envisages the treatment of the renewable feedstock with ammonia at a temperature within the range of 130-250°C and a pressure within the range of 1-8 MPa. Phase (a) can be carried out either without catalysts or in the presence of catalysts. Examples of catalysts that can be used comprise ammonium salts, such as ammonium acetate, ammonium stearate, ammonium palmitate or ammonium oleate .

The ammonia is preferably used in a substantially pure state, i.e. in anhydrous form. It is preferable, in fact, to avoid the use of aqueous solutions of ammonia in the ammonolysis reaction so as not to introduce water into the reaction environment, which would counteract the reaction for the formation of amides .

Under the above reaction conditions, the glycerides of the feedstock are split, forming a mixture of fatty acid amides and glycerine. The alkyl chains of the amides thus obtained substantially correspond to the hydrocarbon chains of the glycerides, as, during the ammonolysis, substantially no other reactions take place .

The ammonolysis can be carried out in one or more reactors operating batchwise (e.g. an autoclave) .

At the end of the ammonolysis phase, the reaction product is a mixture comprising the fatty acid amides which formed the glycerides, and glycerine.

The ammonolysis treatment with ammonia substantially also completely eliminates the free fatty acids present in the feedstock, transforming them into the corresponding amides. In a subsequent phase, the mixture is treated to separate the amides from the glycerine (phase b) according to separation methods known in the art.

The separation of the glycerine from said mixture can be effected, for example, by washing the mixture with water, preferably hot water, so as to form an aqueous fraction containing dissolved glycerine. Once the amides have been separated, the glycerine can be recovered from said aqueous fraction by means of distillation.

The mixture of amides free of glycerine is fed to the subsequent catalytic hydrotreating step (phase c) where it is put in contact with a hydrotreatment catalyst in the presence of hydrogen.

In this step, there is the saturation of the unsaturated portions (e.g. double bonds) of the aliphatic chains that form the amides and the removal of the oxygen atoms ( deoxygenation) and nitrogen atoms from the same chains. The above saturation, deoxygenation, particularly decarbonylation, and denitrogenation reactions are indicated as a whole with the term "hydrotreatment".

Hydrotreatment catalysts that can be used for the purposes of the present invention comprise hydrotreatment catalysts known in the state of the art.

The hydrotreatment catalysts generally comprise one or more metals selected from Ni and Co supported on a solid substrate with a high surface area (typically higher than 100 m²/g) .

Examples of solid substrates with a high surface area suitable for the purposes of the present invention are: γ-alumina, silica, activated carbon or oxides of one or more elements of groups IIIB and/or IVB, preferably titania, zirconia and ceria. The above substrates can be used alone or combined with each other .

The substrate can be amorphous or crystalline. The substrate preferably does not substantially have active acid sites, typically Br0nsted acid sites.

For the purposes of the present invention, the catalyst preferably comprises one or more metals selected from Co and Ni and mixtures thereof. In addition to these metals, the catalyst can also comprise one or more metals of group VIB of the periodic table, preferably Mo and/or W.

In a particularly preferred embodiment, the catalyst comprises at least one pair of metals selected from Ni-Mo, Ni-W, Co-Mo, Co-W and mixtures thereof, more preferably Ni-Mo and/or Co-Mo.

The metals Co and/or Ni are preferably present in the catalyst in an overall quantity ranging from 3 to 8% by weight with respect to the total weight of the catalyst; when one or more metals of group VI are present, their overall quantity ranges from 10 to 30% by weight with respect to the total weight of the catalyst (the weight percentage of the metal refers to the metal content expressed as metallic element) .

The above catalysts can also comprise phosphorous. The catalysts are typically prepared by impregnation of the substrate with a solution containing a precursor of the metals of interest. The impregnation is then followed by a thermal treatment in an oxidizing atmosphere to decompose the precursor and obtain the metals dispersed on the surface of the substrate, and an activation treatment by sulfidation. The sulfidation treatment is carried out according to the methods of the known art.

Subsequent impregnations can be effected for reaching the desired charge level of the metal. Processes are also known for the production of the above supported metal catalysts by precipitation of the metal precursor from a saline solution of the same metal on a carrier, or by co-precipitation of the various components of the catalyst, i.e. the metal and the carrier.

Catalysts that can be used in the hydrotreatment step of the present invention are described, for example, in "Hydrocracking science and technology" J. Scherzer and A. J. Gruia, chapters 3 and 4, Marcel Dekker, 1996.

In order to keep the catalyst in sulfidized form during the reaction, a sulfiding agent (for example, dimethyldisulfide) can be added to the mixture of amides. The total sulfur content in the mixture of amides, can range, for example, from 0.02% to 0.5% by weight (140-3400 ppm of sulfur) . Alternatively, a "straight run" gasoil with a high sulfur content (S >1% by weight) can be co-fed in a ratio of gasoil/mixture of amides which is such as to obtain the above S content in the feedstock.

The hydrotreating reaction can be carried out in a reaction zone comprising one or more catalytic beds, in one or more reactors. According to a preferred aspect, the reaction is carried out in a hydrotreatment reactor containing one or more fixed catalytic beds. The streams containing hydrogen and the mixture of amides can be fed in equicurrent or in countercurrent .

As this is an exothermic reaction, with the production of heat, in every catalytic bed will occur a temperature rise as the reaction proceeds. In order to control the temperature of the reaction environment, a stream of hydrogen and/or a liquid feedstock can be fed, at a defined temperature, between one catalytic bed and the next, so as to create a constant or increasing temperature profile in the reaction area. This operating mode is normally indicated as " splitted feed" .

In order to control the thermal profile in the reactor with adiabatic layers, the reactor can be run by recirculating a part of the effluents leaving the same hydrotreatment step, according to the type known as recycling reactor. The function of the recycling is to dilute the fresh feedstock in the reactor, thus limiting the thermal peaks due to the exothermic nature of the reaction.

In this respect, it should be observed that, unlike the processes of the known art, the hydrotreatment reaction of the process according to the present invention is carried out on a mixture of amides rather than on a mixture of triglycerides. The heat developed during the reaction is significantly lower with respect to the case of triglycerides, with the result that the temperature control by the addition of a diluting feedstock becomes simpler. In particular, considering that there is less heat to be dissipated, the process according to the present invention can be carried out by feeding a smaller quantity of diluting feedstock, with a consequent significant increase in the production yield of the process.

According to the present invention, for example, an adequate temperature control can be obtained by feeding a diluting feedstock equal to or lower than 50% by weight, preferably lower than 30% by weight, with respect to the weight of the total feedstock being fed to the inlet of phase (c), wherein total feedstock refers to the sum of the diluting feedstock and mixture of amides.

The diluting feedstock, which can advantageously be a portion of the diesel hydrocarbon fraction produced in the hydrotreatment step, can be recycled in a weight ratio within the range of 0.05 - 0.43 with respect to the weight of the mixture of amides entering phase (c) .

The hydrotreatment reaction of the amides is preferably carried out at a pressure ranging from 4 to 15 MPa, preferably ranging from 6 to 10 MPa.

The temperature at which the reaction is carried out preferably ranges from 250°C to 400°C, preferably from 300°C to 350°C.

It is preferable to operate at a space velocity of the liquid (LHSV) ranging from 0.5 to 2 hours^-1, even more preferably from 0.5 to 1 hours^-1.

The molar ratio H2/mixture of amides preferably ranges from 5 to 30.

The product leaving the hydrotreatment reactor is an effluent which comprises a liquid portion and a gaseous portion. The liquid portion substantially comprises a mixture of paraffins. The paraffins are substantially composed of linear alkyl chains.

The gaseous portion comprises hydrogen, ammonia, water vapour, CO. Small quantities of hydrogen sulfide (H₂S) can also be present.

The above gaseous and liquid portions can be separated by feeding said effluent to a high-pressure gas-liquid separator. The separator generally operates at a pressure ranging from 0.7 MPa to 14 MPa and at a temperature ranging from 40°C to 350°C.

The gaseous phase recovered from the separator essentially consists of hydrogen and ammonia.

The gaseous phase can be treated in order to recover the hydrogen and ammonia. The hydrogen can be recycled, for example, to the hydrotreatment step or to the hydroisomerization step.

The ammonia, on the other hand, can be advantageously recycled to the ammonolysis phase (a) of the renewable feedstock.

The recovery of the hydrogen and ammonia can be effected by means of conventional industrial methods.

The ammonia, for example, can be separated by washing the gaseous effluent with aqueous acid solutions (e.g. diluted sulfuric acid) . More preferably, the ammonia can be separated by absorption on acid zeolites. After absorption, the gaseous ammonia can be easily recovered by heating the zeolites.

Alternatively, the ammonia can be burnt and used as fuel, exploiting its combustion heat.

The liquid portion separated in the high-pressure separator substantially comprises a mixture of linear paraffins with a number of carbon atoms typically ranging from 14 to 21, prevalently from 15 to 19. The liquid portion also contains an aqueous fraction in which the ammonium sulfide formed by reaction of ammonia with ¾S, is dissolved, which in turn is formed in the reaction environment while keeping the catalyst in sulfided form. After separation of said aqueous phase, a portion of the remaining liquid phase can be recycled at the head to the hydrodeoxygenation step as diluting feedstock for controlling the temperature of the process, as described above.

The liquid portion can be advantageously treated with a gaseous hydrocarbon, for example CH₄, or nitrogen or hydrogen, in a stripper, in order to further reduce the water content.

The mixture of paraffins obtained from the hydrotreatment step can be used as diesel fuel or as jet fuel. As this fraction substantially comprises linear paraffins, however, it is a low-quality fuel under low temperature conditions.

If the cold flow properties of this fraction are to be improved, at least a part of said fraction can be subjected to a further catalytic hydroisomerization step so as to convert at least a part of said linear paraffins into branched paraffins. This step can be effected by putting the hydrocarbon fraction comprising linear paraffins in contact with a hydroisomerization catalyst in the presence of hydrogen.

The hydroisomerization can be carried out in accordance with techniques known to skilled persons in the field, using hydroisomerization catalysts known in the art .

The hydroisomerization step can be carried out in a reaction area comprising one or more catalytic beds in one or more reactors.

Hydroisomerization catalysts that can be used are, for example, catalysts comprising one or more metals of group VIII supported on at least one substrate.

The substrate can be amorphous or crystalline.

Examples of substrates suitable for the purposes of the present invention are: zeolites in acid form, silico-alumina, ASA (amorphous silica-alumina) , SAPO, MSA, MSA-P (mesoporous silica-alumina with phosphorous) or mixtures thereof.

Zeolite in acid form refers to a zeolite containing Si and Al in the crystalline lattice, in which the cationic sites are prevalently or completely occupied by H⁺ ions .

The catalyst preferably comprises at least one zeolite as substrate, said zeolite preferably being selected from: zeolite Y, zeolite Beta, ZSM-22, ZSM-23, ZSM-12 and ZSM-5.

Preferred metals of group VIII are Pt, Pd, Ir, and mixtures thereof. The metals are not subjected to sulfidation treatment.

Further preferred catalysts are catalysts comprising a mixed substrate, such as, for example, Pt/ZSM-22/Al₂0₃ and Pt/ZSM-23/Al₂0₃ : in said catalysts, the alumina (A1₂0₃) does not act as carrier but as ligand .

According to a particularly preferred aspect of the present invention, in accordance with what is described in WO 2008/058664 and in WO 2008/113492, a catalyst can be used, consisting of a catalytic composition comprising :

(a) a carrier of an acid nature comprising an amorphous micro-mesoporous silico-alumina having a molar ratio S1O₂/AI₂O₃ ranging from 30 to 500, a surface area greater than 500 m²/g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter less than 40 A,

(b) a metallic component comprising one or more metals of group VIII.

Completely amorphous micro-mesoporous silico- aluminas that can be used as carrier (a) of the catalytic compositions of the hydroisomerization step of the present invention are described, for example, in US 5049536, EP 659478, EP 812804, and called MSA. MSAs have a substantially amorphous crystallographic structure, as their XRD powder spectrum does not reveal any significant peak. US 5049536, EP 659478, EP 812804 describe various methods for preparing silico-aluminas suitable as carrier (a) .

As far as the metals of the metallic component (b) of the above catalytic compositions are concerned, these are selected from metals of group VIII.

The metal (s) of group VIII are preferably selected from Pt, Pd, Ir and mixtures thereof.

The metal of group VIII is preferably present in a quantity ranging from 0.1% to 5% by weight with respect to the weight of the catalytic composition.

The weight percentage of the metal (s) refers to the content of metal expressed as metallic element; in the final catalyst, after calcination, said metal is in oxide form.

The catalysts are typically prepared by impregnation of the substrate with a solution containing a precursor of the metals of interest. The impregnation is then followed by a thermal treatment in an oxidizing atmosphere to decompose the precursor and obtain the metals dispersed on the surface of the substrate, this is followed by a suitable activation treatment by means of a pre-treatment effected in a stream of hydrogen, at a temperature ranging from 250 to 350°C.

Catalytic compositions that can be used in the hydroisomerization step containing one or more metals of group VIII are described, for example, in WO2005/103207.

The hydroisomerization catalyst can be formulated and formed into extruded products having various forms (e.g. cylinders, trilobates, etc.), as described, for example, in EP 1101813.

The hydroisomerization step can be effected in a fixed-bed reactor. The thermal control in this case is not critical as the reaction is weakly exothermic. For this reason, a reactor with adiabatic layers is appropriate .

The mixture of paraffins deriving from the hydrotreatment step can be fed to the hydroisomerization area in equicurrent or in countercurrent with respect to the hydrogen.

The hydroisomerization can be carried out, for example, at a temperature ranging from 250°C to 450°C, preferably from 280°C to 380°C, and at a pressure ranging from 2.5 MPa to 10.0 MPa, preferably from 3.0 MPa to 5.0 MPa. It is preferable to operate at a space velocity (LHSV) ranging from 0.5 to 2 hours^-1. The volumetric ratio H2/mixture of paraffins preferably ranges from 200 to 1,000 Nl (H₂) /l (paraffins) .

The conditions under which the hydroisomerization reaction is carried out can be suitably selected to obtain a final product having the desired characteristics. By varying the reaction conditions, for example, mixtures of paraffins can be obtained with improved cold flow properties and therefore more similar to those of diesel fuel or jet fuel with which the hydroisomerization product can be subsequently combined as bio-component.

By suitably varying the reaction conditions of the second step, in addition to varying the isomerization degree of the paraffins, it is also possible to change the distribution of the products maximizing the yield to either the gasoil cut or jet fuel cut.

The mixture obtained in the hydroisomerization step can be subjected to distillation to obtain said jet fuel and gasoil hydrocarbon fractions to be used as fuel or as bio-component in fuels of a petroleum origin. A naphtha fraction (C5-C9, boiling range 80°C - 180°C) which can be used as gasoline component, can also be recovered from the distillation.

An embodiment example of the process according to the present invention is described hereunder with reference to the scheme of the enclosed Figure 1. The following example is provided for purely illustrative purposes of the present invention and should not be considered as limiting the protection scope defined by the enclosed claims.

With reference to Figure 1, the renewable feedstock is fed to the hydrolysis reactor (a) through line 1. The ammonia necessary for the ammonolysis reaction is fed to the same reactor (a) through line 2. The mixture resulting from the ammonolysis, substantially containing amides, glycerine and water is sent, through line 3, to a first separator (b) . In said first separator (b) , the mixture resulting from the ammonolysis is washed with water in order to separate the organic fraction containing amides and an aqueous fraction containing glycerine. The aqueous fraction leaving the above first separator (b) is fed, through line 4, to a second separator (f), for example a distillation column, where the glycerine is recovered, through line 12, and the remaining water, through line 13. The aqueous fraction containing glycerine can be possibly subjected to a treatment with exchange resins, before being distilled, in order to remove any possible salts present.

The glycerine leaving the second separator (f), through line 12, is fed to a subsequent reaction area (g) where it is used as raw material for producing bio- components for diesel fuel (line 14), for example through the process described in patent application WO 2013150457.

The organic phase containing amides leaving the first separator (b) is fed, through line 5, to a catalytic hydrotreatment reactor (c) , where it is reacted with a stream of hydrogen which is fed to the same reactor (c) , through line 6. The mixture leaving the catalytic hydrodeoxygenation reactor (c) , is sent to a high-pressure gas-liquid separator (d) , through line 7. The gaseous phase comprising hydrogen, ammonia, water vapour and CO is recovered at the outlet of the separator (d) , through line 8, whereas the liquid phase containing linear paraffins is recovered, through line 9, which is subsequently fed to a hydroisomerization reactor (e) . A separator (not indicated in the figure) is present on line 9, to allow the aqueous solution of ammonium sulfide to be removed. The gaseous phase leaving the separator (d) is sent through line 8 to a further separator (h) , where the ammonia is recovered, which is recycled to the ammonolysis step through line 15. The hydrogen necessary for the hydroisomerization reaction is fed to said reactor (e) , through line 10. The mixture containing the isomerized paraffins is recovered, at the outlet of the reactor (e) , through line 11.

EXAMPLE 1 - Ammonolysis of olive oil

31.40 g of a renewable feedstock consisting of olive oil are charged into a steel autoclave having a volume of 250 cc.

The autoclave is then subjected to two filling cycles with nitrogen and subsequent degassing under vacuum.

The autoclave is then cooled to -50°C. 10 ml of liquid ammonia are introduced into the autoclave at this temperature. The autoclave is then heated up to 170°C. The reaction mixture is kept under stirring at this temperature for a period of 6 hours. After cooling the autoclave to room temperature, the gaseous phase containing non-reacted ammonia is removed.

In order to remove the glycerine, the reaction product is washed with three aliquots of hot water (50 ml each), which are then joined (aqueous phase) . At the end of the washing, the reaction product is a solid residue consisting of a mixture of amides having the following composition (% moles) : oleamide 80%, linoleic acid amide 12%, palmitic acid amide 8%.

The solid residue has the following characteristics: melting point 73-74°C, iodine number 83.2, acidity number 1.5. The yield to amides is equal to 98%.

The aqueous phase substantially consists of glycerine and water.

EXAMPLE 2 - Ammonolysis of castor oil

31.40 g of a renewable feedstock consisting of castor oil are charged into a steel autoclave having a volume of 250 cc.

In order to remove the glycerine, the reaction product is washed with three aliquots of hot water (50 ml each), which are then joined (aqueous phase) . At the end of the washing, the reaction product is a solid residue consisting of a mixture of amides having the following composition (% moles): ricinoleic acid amide 92%, oleic acid amide 7%, linoleic acid amide 1%.

The solid residue has the following characteristics: melting point 62-64°C, iodine number 85.6, acidity number 1.4. The yield to amides is equal to 99%.

The aqueous phase substantially consists of glycerine and water.

EXAMPLE 3 - Hydrotreatment of a mixture of fatty acid amides

The solid residue obtained according to what is described in Example 1, was subjected to hydrotreatment with hydrogen on a pre-sulfided catalyst Ni-Mo dispersed on alumina.

The catalyst was prepared as follows: 40 ml of an aqueous solution containing 5.5 g of Mo₇ (NH ) 6Ο2 * 4¾0 are added to 10 g of γ-alumina placed in a rotary evaporator (60 rpm) . The mixture is left under stirring for 16 hours, the water is then evaporated at 110°C in air for 1 hour. A second impregnation is then effected following the same procedure described above using an aqueous solution containing 1.5 g of Ni(NC>3)2*6 ¾0. The mixture is left under stirring for 16 hours and the water is then evaporated at 110°C in air for 1 hour. The powder thus obtained is calcined in a muffle furnace at 500°C for 4 hours in air, heating at a rate of 3°C min^-1. The calcined powder is pressed into tablets at a pressure of 3.5 t/cm², the tablets are then crushed and the powder fraction having a particle-size within the range of 0.40-0.85 mm is used for the reaction .

The catalyst proves to contain 27.2% by weight of Mo and 3.2% by weight of Ni and has a BET surface area

The catalyst was sulfided using dodecane containing dimethyldisulfide (DDMS) having a sulfur concentration of 1% by weight.

The solution of DDMS in dodecane is fed together with hydrogen under the following conditions:

space velocity (LHSV) = 1 hf¹, hydrogen flow-rate 40 Nl/h, pressure 40 bar, temperature 25°C. The temperature of the reactor is then increased from 25 to 120°C, at a rate of 5°C per minute; this temperature is maintained for an hour at 120°C, and is then increased to 230°C at 10°C per minute and this temperature (230°C) is maintained for eight hours; finally, the temperature is increased up to 315°C at a rate of 10°C per minute to 315°C and is kept at this temperature (315°C) for four hours.

The hydrotreatment reaction was carried out in a fixed-bed reactor, at a pressure of 4 MPa, with a space velocity of the liquid (LHSV) equal to 1 hf¹ and at a temperature of 330°C.

A flow of n-dodecane was fed to the reactor together with the mixture of amides, in order to simulate the recirculation conditions of a fraction of linear paraffins which can be obtained from the HDO reaction. The feedstock fed to the reactor contained 30% by weight of n-dodecane and 70% by weight of amides .

In order to keep the catalyst in a sulfided state, dimethylsulfide was added to the above feedstock in a concentration equal to 0.5% by weight with respect to the weight of the feedstock.

The volumetric feeding ratio between hydrogen and feedstock fed was equal to 900 Nl ¾/l of feedstock fed.

The reaction products (mixture of paraffins) were removed and analyzed by means of gas chromatography. A complete conversion of the mixture of amides was revealed by the gas chromatographic analysis.

Table 1 below indicates the selectivity values of the paraffins obtained from the hydrotreatment reaction in relation to the reaction time. The selectivities are expressed as:

molar percentage of the sum of paraffins having from 15 to 18 carbon atoms (C15 - Cis) with respect to the initial moles of fatty acid fed;

molar percentage of the sum of paraffins having a number of carbon atoms equal to or lower than 14 (C≤i ) referring to the number of total carbon moles present in the feedstock fed to the reactor (excluding n-dodecane) .

Table 1

EXAMPLE 4 - I someri zation of the mixture of paraffins

The mixture of paraffins obtained according to what is described in Example 3, was subjected to a hydroisomerization reaction on a catalyst of Pt dispersed on amorphous silico-alumina in the presence of hydrogen. The Pt content is equal to 0.6% by weight with respect to the weight of the catalyst. The catalyst was prepared according to what is described in patent EP 1101813 Al ("preparative example 2") .

The hydroisomerization reaction was carried out in a fixed-bed reactor at a pressure of 5 MPa, with a space velocity of the liquid equal to 1.5 h^~ (LHSV) and at a temperature of 320°C.

In the effluent fed to the reactor, the volumetric ratio between hydrogen and feedstock of paraffins was equal to 400 Nl of ¾/l of feedstock of paraffins.

The reaction products were removed and analyzed by means of gas chromatography.

Table 2 below indicates the distribution of the hydroisomerization reaction products in relation to the reaction time.

The distribution of the products is expressed as weight percentage of the paraffins having from 15 to 18 carbon atoms (C15 - Cis) and paraffins having a number of carbon atoms equal to or lower than 14 (C≤i ) referring to the total weight of paraffins fed to the reactor.

Table 2

* Ratio between the total weight of C15-C18 iso- paraffins and the total weight of the fraction of C15-C18 paraffins.

Claims

1. A process for preparing a diesel hydrocarbon fraction which comprises the following phases:

(b) separating said glycerine from said mixture of amides;

(d) separating said diesel hydrocarbon fraction from said reaction product.

2. The process according to claim 1, also comprising a phase (e) for subjecting said diesel hydrocarbon fraction separated in said separation phase (d) to catalytic hydroisomerization in the presence of hydrogen .

3. The process according to any of the previous claims, wherein said diesel hydrocarbon fraction separated in said separation phase (d) and substantially comprising linear paraffins, is partly recycled to said phase (c) .

4. The process according to the previous claim, wherein said diesel hydrocarbon fraction is recycled in a weight ratio within the range of 0.05 - 0.43 with respect to the weight of the mixture of amides.

5. The process according to any of the previous claims, wherein said hydrogen is separated from said gaseous effluent and at least partly recycled to said hydrotreatment phase (c) and/or said hydroisomerization phase (e) .

6. The process according to any of the previous claims, wherein said ammonia is separated from said gaseous effluent and at least partly recycled to said reaction phase (a) with said renewable feedstock.

7. The process according to any of the previous claims, wherein said glycerine is used as raw material for producing biocomponents for fuels.

8. The process according to any of the previous claims, wherein said catalytic hydrotreatment is carried out at a temperature within the range of 250- 400°C.

9. The process according to any of the previous claims, wherein said catalytic hydrotreatment is carried out at a pressure within the range of 4-15 MPa .

10. The process according to any of the previous claims, wherein said catalytic hydrotreatment is carried out in the presence of a hydrotreatment catalyst comprising at least one or more metals selected from Co and Ni, possibly combined with one or more metals of group VIB, supported on a solid substrate .

11. The process according to the previous claim, wherein said solid substrate is selected from alumina, γ-alumina, silica, activated carbon, oxides of one or more elements of groups IIIB and/or IVB, and mixtures thereof .

12. The process according to claim 10 or 11, wherein said hydrotreatment catalyst comprises at least a pair of metals selected from Ni-Mo, Ni-W, Co-Mo and Co-W.

13. The process according to the previous claim, wherein said hydrotreatment catalyst is a sulfided catalyst .

14. The process according to any of the previous claims, wherein said hydroisomerization phase (e) is carried out at a temperature within the range of 250- 450°C.

15. The process according to any of the previous claims, wherein said hydroisomerization phase (e) is carried out at a pressure within the range of 2.5 - 10.0 MPa.

16. The process according to any of the previous claims, wherein said hydroisomerization phase (e) is carried out in the presence of a catalytic composition comprising one or more metals selected from metals of group VIIIB supported on a substrate selected from: acid zeolite, silico-alumina, amorphous silico-alumina, ASA, SAPO, MSA, MSA-P and mixtures thereof.