FR3143125A1 - Method for analyzing the cold properties of hydrocarbon cuts - Google Patents

Abstract

The present invention relates to an analytical method for determining the cold properties of a hydrocarbon cut comprising in part compounds derived from renewable material, and comprising a diesel and/or kerosene fraction, said method comprising the following steps: a) Measurement of a Simulated Distillation of the hydrocarbon cut by the ASTM D2887 method; b) Calculation of the yield of the diesel and/or kerosene fraction in the hydrocarbon cut using the result of Simulated Distillation; c) Calculation of the nC18 and/or nC16 content in the hydrocarbon cut via the integration of the peaks of the chromatogram obtained by Simulated Distillation; d) Calculation of the nC18 and/or nC16 content in the diesel and/or kerosene fraction using the results of steps b) and c); e) Calculation of the cloud point and/or the disappearance point of the crystals from the following equations: with xw,nC18 the content of nC18 in the diesel fraction; with xw,nC16 the content of nC16 in the kerosene fraction.

Description

Method for analyzing the cold properties of hydrocarbon fractions

The co-processing of feedstocks from renewable and lipidic materials such as vegetable oils and/or animal fats and/or fish oils and/or used cooking oils with conventional petroleum feedstocks in hydrotreatment aims to produce biofuels such as biodiesel and biokerosene. The conversion of triglycerides by hydrotreatment present in oils and fats leads overwhelmingly to the production of linear paraffins with boiling points (Normal Boiling Point or NBP according to the Anglo-Saxon terminology) corresponding to the fossil diesel cuts: n-hexadecane (nC16, NBP = 287°C), and n-octadecane (nC18, NBP = 317°C).

These paraffins improve density and cetane index but significantly degrade cold properties such as the cloud point of diesel and the disappearance point of kerosene crystals.

On pilot plants or industrial plants, the refiner is required to measure the cold properties of the kerosene and diesel fractions to verify fuel specifications. In order to obtain the kerosene and diesel fractions, a distillation operation is often necessary. This operation is long, costly and consumes a large sample volume. For example, in High-Throughput Experimentation (HTE) applications, the quantities of samples available are of the order of a few milliliters and a preparative distillation to obtain diesel and kerosene fractions is impossible.

The object of the present invention is to estimate the cold properties by a simulated distillation (SD) type analysis according to the ASTM D2887 standard, conventionally used in the oil industry, applied to a hydrocarbon cut leaving a reactor. The objective is to propose a methodology that is valid regardless of the load and the process used and without the need for physical distillation.

In the context of the reduction of greenhouse gas emissions, refiners are forced to increase the proportion of components of biological origin in fuels. The public authorities aim to promote the use of biofuels in transport, not only road transport (diesel engines) but also air transport. For example, the roadmap of Ancre (National Alliance for the Coordination of Research for Energy), published in June 2018, assesses the French potential of aviation biofuel production sectors, taking into account the maturity and development time of these industrial sectors, the following deployment trajectory therefore reflects the French ambition for 2030 of an incorporation of aviation biofuels in France of 5%. In addition, the National Low-Carbon Strategy (SNBC) revised in 2018 sets a long-term direction for air transport by 2050, aiming at a 50% substitution of conventional fossil fuels with biofuels. Biofuel production has therefore been promoted in recent years and will continue to be strengthened in the years to come.

It is well known that biofuels can be produced from lipid feedstocks, which contain triglyceride compounds, free fatty acids and esters, such as vegetable oils (rapeseed oil, sunflower oil, palm oil), animal fat, fish oil and used cooking oil. These feedstocks mentioned above are processed alone or in co-processing with fossil oil feedstocks to incorporate the “bio” proportion into the final fuels.

Hydrotreatment, hydrocracking or hydroconversion processes make it possible to convert the above biological feedstocks into biofuels. In said processes, using a hydrogen pressure ranging from 20 to 200 bars and in the presence of catalysts, the triglycerides and free fatty acids in the biological feedstocks are converted according to the different reactions presented below.

In the hydrotreatment reactor(s), the reactions implemented are the hydrogenation of the olefinic bonds by the addition of hydrogen molecules, and deoxygenation according to two reaction pathways:

- hydrodeoxygenation: oxygen is eliminated in the form of water by consumption of hydrogen while keeping the same number of carbons in the starting carboxylic acid chain, and

- decarbonylation/decarboxylation: oxygen is eliminated in the form of CO and _CO2 , so the number of carbons in the hydrocarbon chain is reduced by one atom compared to the initial carboxylic acid chain.

Under the operating conditions of hydrotreatment, the renewable triglyceride feedstocks are completely converted into paraffinic hydrocarbons.

Subsequently, in the hydrocracking reactor(s), in the presence of one or more acid catalysts, the paraffinic hydrocarbon chains from the triglycerides are partially converted by the cracking reactions, making it possible to obtain hydrocarbons that are shorter than the initial chains.

In the total effluent leaving the reactor, n-paraffins from oils will be mainly found in fuel cuts such as kerosene and diesel and will therefore have an impact on cold properties such as the crystal disappearance point of the kerosene fraction and the cloud point of the diesel fraction. However, these are key properties of fuels, determining their approval and commercial use. It is therefore essential to control the flow properties of the products and to manage operating conditions to meet product specifications, i.e. concretely the crystal disappearance point below -47°C for Jet-A1 kerosene and the cloud point below 5°C for summer diesel fuel or below -5°C for winter diesel fuel (Euro V standard).

The products from refining processes come in the form of several fractions such as: gas, light naphtha, heavy naphtha, kerosene, diesel and the unconverted heavy fraction. In the majority of laboratory-scale refining process units, the pilot units are not equipped with a fractionation section to separate the product fractions of interest. Consequently, operators are forced to carry out a separate distillation (outside the pilot unit) to recover the desired products and then measure their cold properties. This approach consumes a lot of time, energy and product, and will therefore not allow the operating conditions of the processes to be quickly controlled. In addition, it requires the production of a large volume of product to be able to carry out a distillation.

Therefore, it is desirable to find a robust and rapid methodology allowing access to these cold flow properties without the need for a distillation step.

In the literature, there are many studies on the molecular understanding of cold properties in fuels. These studies systematically mention the determining role of normal paraffins on cold properties. Indeed, normal paraffins, due to their linear and flexible structure, can easily align and form stable crystals with cooling. Another important factor is the length of the normal paraffins. The longer a paraffin is (typically normal paraffins with a carbon number in the chain greater than 15 carbon atoms), the more the axial interactions by Van der Waals forces between n-paraffins are important in the crystals. On the other hand, for short linear paraffins, the interactions between the ends are also important and not negligible and disrupt the organization of the crystals.

In the paper Tang et al. (Solubility and crystallisability of the ternary system: Hexadecane and octadecane representative in fuel solvents. Fuel, 2018, 226, 665-674) the solubility and crystallization of the ternary system of hexadecane and octadecane in three fossil solvents: dodecane, toluene and kerosene are studied. It was found that mixtures of alkane form less stable and therefore more soluble crystals than pure alkanes; the solubility of the crystals decreases with an increase in the size of the aliphatic chains; the shape and size of the crystals is the same in the three solvents studied and the solubility of linear paraffins in C16 and C18 is better in a similar solvent (aliphatic and non-polar). The order of most soluble to least soluble solvent is therefore as follows: dodecane (linear paraffin), followed by kerosene (mixture of paraffins and aromatics) and lastly toluene (aromatic).

Krishna et al. (Correlation of pour point of gas oil and vacuum gas oil fractions with compositional parameters. Energy Fuels 1989;3(1):15–20) also demonstrated a dependence of the pour point value on the final cut point of the diesels studied. The higher the final cut point, the greater the pour point value. A lesser influence of short n-paraffins (chain length less than 15 carbons) on the cold property was found. It was also found that the pour point varies in a non-linear manner with the concentration of n-paraffin in the cuts and mathematical correlations with a logarithmic form were proposed.

Crystal Disappearance Point (Kerosene)

The freezing point (FP) of a kerosene corresponds to the lowest temperature at which the fuel does not contain any solid crystals. The FP measurement is carried out using the D5972, D7153, D7154 (automated methods) or D2386 (manual method) standards. These four standards are accepted for the certification of a kerosene fuel according to ASTM D1655-20d. However, the minimum and maximum temperature limits for the application of these four methods are not the same. The recommended methods for certification or re-certification are the ASTM D5972 and/or ASTM D7153 automated methods.

In the determination of FP, the sample is cooled in a standardized apparatus, being vigorously agitated, thus simulating the cooling conditions that can be encountered during a flight. The temperature at which the crystals appear is the crystallization temperature and is detected by the optical detection system (opacity and crystal). The sample is then heated until the opacity disappears.

At this stage, the temperature is increased until the crystal detector detects the disappearance of crystals. If this temperature is higher than the temperature at which the first crystals form, the crystal disappearance point is reached.

In the literature there are several correlative models to estimate the FP of a kerosene. However, all of the proposed correlations most often require a detailed analysis of the kerosene cut obtained by high-performance liquid chromatography (HPLC), gas chromatography (GC) and ¹³ C nuclear magnetic resonance (NMR) (Cookson et al. Investigation of the chemical basis of kerosene (jet fuel) specification properties. Energy Fuels 1(5): 438–447.), or gas chromatography coupled with a mass spectrometry detector (GC-MS) (Liu et al. Artificial neural network approaches on composition–property relationships of jet fuels based on GC–MS. Fuel 86(16):2551–2559) or two-dimensional gas chromatography coupled with a mass spectrometry detector and a flame ionization detector (GCxGC-MS/FID) (Shi et al. Quantitative composition property relationship of aviation hydrocarbon fuel based on comprehensive two-dimensional gas chromatography with mass spectrometry and flame ionization detector. Fuel 200: 395–406). Indeed, most of these correlations are based on knowledge of the detailed molecular structure and the mass or molar composition of kerosene in n-paraffins, iso-paraffins, naphthenes and aromatics. Other correlations have been obtained from statistical (chemometric) models applied to data obtained from Fourier transform infrared spectroscopy (FT-IR) (Scheuermenn et al. In-depth interpretation of mid-infrared spectra of various synthetic fuels for the chemometric prediction of aviation fuel blend properties. Energy Fuels 31(3): 2934–2943). Finally, all these correlations have been developed directly on the kerosene fraction and thus require a distillation operation of the total effluent leaving the reactor and a more or less detailed characterization of the cut.

Trouble point (Diesel)

The cold resistance of a diesel can be characterized by three properties: the filterability limit temperature (FLT), the cloud point (CP) and the pour point (FP). These properties generally follow the same trend with the concentration of normal paraffins present in the diesel and are fairly well correlated with each other. In general, the crystallization of a fluid occurs in two stages: the first is nucleation with the appearance of crystals and the second stage is the agglomeration and growth of crystals. The CP therefore characterizes the first stage when the first crystals appear; the FLT characterizes the moment during cooling from which the size of the crystals becomes too large for them to pass through a filter and the FP characterizes the temperature from which the product can no longer flow because it becomes solid. Consequently, the following order is observed in temperature: CP > FLT > FP. It should be noted that PT and TLF are defined in diesel specifications according to ASTM D975-20c “Standard Specification for Diesel Fuel” unlike pour point.

The measurement of the PT or "cloud point" according to the Anglo-Saxon terminology is carried out according to the standards ASTM D2500-11 or NF ISO EN 23015. These methods are used for PT below 49 ° C. In the determination, the sample is heated at least 15 ° C above the supposed PT and placed in a test tube closed with a stopper. A thermometer inside the tube touches the bottom of it. It is then cooled gradually, using increasingly cold cooling baths and the clarity of the product is manually checked every degree. The PT is the temperature at which a distinct cloudiness appears at the bottom of the test tube. It is reported from degree to degree. There are other equivalent automated methods that are also accepted for the certification of diesel (ASTM D975-20c) in particular the AFNOR ISO 3015 standard and ASTM D5773. However, in the event of a discrepancy between two values given by different standards, the ASTM D2500 method is the authoritative method. This method is expensive and also requires distillation, particularly by hydrocracking.

A set of correlations have been developed (Riazi MR. Characterization and properties of petroleum fractions. W. Conshohocken, PA: ASTM International; 2005). However, they are generally valid for a single range of process, feed, and operating conditions.

In Cookson et al. (Composition-property relations for jet and diesel fuels of variable boiling range. Fuel 1995;74(1):70–8.) models were proposed for diesel cuts with variable boiling range (with an initial boiling point between 230°C and 250°C and a final boiling point between 320°C and 370°C), emphasizing the need to introduce information on the cut points. The proposed models for PT and PE are given in the following equations:

Or and the are the model parameters, and And respectively denote the percentages of n-paraffinic and aromatic carbons estimated from ¹³ C NMR data. are the temperatures of the analyzed DS carried out by gas chromatography. The main disadvantage of these methods is that the quantities And are not directly accessible in the refinery.

In his thesis, JJ. Da Costa (2017) (Molecular understanding and prediction of physicochemical properties in petroleum products) proposed a model for predicting PT in hydrocracking from basic properties:

- the conversion rate X ₃₇₀ ,

- the temperature T ₉₅ obtained by DS,

- the nitrogen content contained in the original vacuum distillate charge.

Two models have been developed:

- A linear regression model

- A Kriging model (J. J. Da Costa, F. Chainet, Molecular understanding and prediction of physicochemical properties in petroleum products, B. Celse, M. Lacoue-Nègre, C. Ruckebusch, and D. Espinat, Energy & Fuels 2018 32 (4), 5623-5634)

The prediction by these above-mentioned models is relatively good but the drawback is that the correlation is only valid for conventional hydrocracking (without co-treatment with lipid feedstocks).

The applicant has surprisingly demonstrated that, during co-treatment of biological feedstocks with fossil feedstocks in hydrotreatment or hydroconversion processes, the cold properties of the kerosene and diesel fractions are governed by the content of normal paraffins generated by the biological feedstocks.

The applicant's work shows that the FP is directly related to the content of longer normal paraffins in the kerosene cut and more precisely to nC16 in the context of co-treatment with lipid feedstocks. Whatever the hydroconversion processes, whatever the feedstocks and whatever the operating conditions, the correlation of the FP of kerosene with the nC16 content in the cut is unique and the FP can be calculated according to a particular equation.

The applicant's work also shows that the PT of diesel is directly related to the nC18 content in the diesel. Whatever the hydroconversion processes, whatever the loads and whatever the operating conditions, the correlation of the PT of diesel with the nC18 content in the cut is unique while the amount of nC18 is in the majority and the PT can be calculated according to a particular equation.

Unexpectedly, these correlations are unique for different process types and different load types at iso cut point.

This allows refiners and/or operators to control the installations without carrying out direct measurements of FP or PT and without carrying out distillation of the effluents.

The present invention relates to an analytical method for determining the cold properties of a hydrocarbon cut partly comprising compounds derived from renewable material, and comprising a diesel and/or kerosene fraction, said method comprising the following steps:

a) Measurement of a Simulated Distillation (SD) of the hydrocarbon cut by the ASTM D2887 method;

b) Calculation of the yield of the diesel and/or kerosene fraction in the hydrocarbon cut using the result of the Simulated Distillation;

c) Calculation of the nC18 and/or nC16 content in the hydrocarbon cut via the integration of the peaks of the chromatogram obtained by Simulated Distillation;

(d) Calculation of the nC18 and/or nC16 content in the diesel and/or kerosene fraction using the results of steps (b) and (c);

e) Calculation of the cloud point (CP) and/or the crystal disappearance point (CP) from the following equations:

with x _w,nC18 the nC18 content in the diesel fraction;

with x _w,nC16 the nC16 content in the kerosene fraction.

This simplified, robust and easily accessible analytical method for refiners and scientific researchers in the refining and biomass field, allows to quickly obtain cold flow property analyses of diesel and kerosene fractions. It allows to follow these cold flow properties without the need for distillation and without the need for physical measurements of the cloud point and the crystal disappearance point.

This analytical method therefore makes it possible to quickly control the parameters of hydrocarbon feedstock treatment processes while ensuring that the properties of the fuels are controlled.

This invention can be applied for the control of industrial or laboratory units, for refining processes (such as hydrotreatment, hydrocracking, hydroisomerization, hydroconversion) using feedstocks from renewable materials (such as vegetable oils and animal fats and fish fats) mixed with petroleum feedstocks.

BRIEF DESCRIPTION OF THE FIGURES

: Correlation of the FP of a kerosene cut with the nC16 content in the cut.

: Correlation of the PT of a diesel cut with the nC18 content in the cut.

: DS calibration curve.

: Integrated DS curve.

: Chromatogram obtained under DS conditions.

: Valley-to-valley integration of the nC18 peak in a DS chromatogram.

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.

For the purposes of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges may be used alone or in combination. For example, for the purposes of the present invention, a preferred pressure value range may be combined with a more preferred temperature value 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 this is technically feasible.

Hydrocarbon cut

The present invention relates to an analytical method for determining the cold properties of a hydrocarbon cut partly comprising compounds derived from renewable material, and comprising a diesel and/or kerosene fraction.

Advantageously, the hydrocarbon fraction has an initial boiling temperature greater than 100°C and a final boiling temperature less than 420°C according to the simulated distillation method ASTM D2887, preferably an initial boiling temperature greater than 120°C and a final boiling temperature less than 400°C according to the simulated distillation method ASTM D2887.

Advantageously, the hydrocarbon fraction is obtained from refining processes such as hydrotreatment, hydrocracking, hydroisomerization, hydroconversion, using feedstocks from renewable materials mixed with fossil oil feedstocks with at least 1% by weight of feedstocks from renewable materials. These feedstocks are detailed below:

- The feedstocks from renewable materials that can be used in refining processes are chosen from vegetable oils, animal fats, fish fats, effluents from Fischer-Tropsch conversion rich in paraffinic compounds, or a mixture of these.

- Fossil petroleum feedstocks usable in refining processes are feedstocks having an initial boiling point greater than or equal to 120°C and a final boiling point less than or equal to 600°C, preferably petroleum feedstocks comprising compounds boiling between 150 and 550°C according to the ASTM D2887 simulated distillation method. The feedstocks can range from a kerosene-type cut to a vacuum distillate-type cut.

Advantageously, the hydrocarbon cut can also be obtained from mixtures of fractions from the fossil petroleum feedstocks described above with effluents from feedstock conversion processes from renewable materials mentioned above.

The correlations of the crystal disappearance point (CP) and/or the cloud point (CP) as a function of the normal paraffin content nC16 and nC18 are all valid for the kerosene and diesel fractions without distinction between these two types of fractions.

Analytical method

Step a) of simulated distillation measurement

The analytical method according to the present invention comprises a step a) of measuring a DS of the hydrocarbon cut by the ASTM D2887 method.

ASTM D2887 is a gas chromatography (GC) method with a flame ionization detector (FID). The sample, diluted in carbon disulfide (CS ₂ ), is injected into a gas chromatograph equipped with an on-column injector and a metal capillary column with a nonpolar stationary phase. The compounds are eluted with helium as a carrier gas according to their boiling point and detected with a flame ionization detector. The detector signal is processed by a computer equipped with acquisition software and a chromatogram is obtained. The boiling point corresponding to each % m/m of eluted product is calculated from a calibration curve ( ) obtained by injecting a mixture of normal paraffins whose boiling points cover the boiling temperature range of the sample. Calculations are performed by software using the parameters defined in the method. The results are usually expressed as a curve of boiling temperature versus the percentage of mass of sample eluted, integrated DS curve ( ), obtained by cumulative integration of the chromatogram ( ).

Step b) Calculation of the yield of the diesel and/or kerosene fraction

The analytical method according to the present invention comprises a step b) of calculating the yield of the diesel and/or kerosene fraction in the hydrocarbon cut using the result of the DS.

“Kerosene fraction” means a fraction comprising hydrocarbon compounds boiling at 150°C to 280°C.

The term “diesel” fraction means a fraction comprising hydrocarbon compounds boiling at 250°C to 370°C.

The term “yield of the diesel and/or kerosene fraction” therefore means the weight percentage of hydrocarbon compounds boiling at 250°C to 370°C and/or hydrocarbon compounds boiling at 150°C to 280°C within the hydrocarbon cut, relative to the total weight of the hydrocarbon cut.

The yield of the diesel and/or kerosene fraction is advantageously calculated using the integrated DS curve ( ) obtained with the ASTM D2887 method which presents the boiling temperature relative to the weight percentage of eluted hydrocarbon cut sample.

Step c) of calculation of the nC18 and/or nC16 content in the hydrocarbon fraction

The analytical method according to the present invention comprises a step c) of calculating the nC18 and/or nC16 content in the hydrocarbon cut via the integration of the peaks of the chromatogram obtained by the DS.

Advantageously, the nC18 and/or nC16 content in the hydrocarbon cut is calculated by valley-to-valley integration of the peaks of the chromatogram which correspond to n-hexadecane and n-octadecane ( ). The identification of the n-hexadecane and n-octadecane peaks is carried out using the calibration curve which gives the relationship between the retention time of the capillary column and the boiling temperature of the n-paraffins. The nC16 and nC18 contents in the hydrocarbon cut are the percentages of the area of the nC16 and nC18 peaks relative to the total area of all peaks on the chromatogram.

Step d) calculation of the nC18 and/or nC16 content in the diesel and/or kerosene fraction

The analytical method according to the present invention comprises a step d) of calculating the nC18 and/or nC16 content in the diesel and/or kerosene fraction using the results of steps b) and c).

Normal paraffin nC16 has a boiling point of 287°C. Depending on the quality of fractionation of the hydrocarbon feedstock, a portion of nC16 is carried over into the kerosene fraction comprising hydrocarbon compounds boiling at 150°C to 280°C due to cross-referencing.

The percentage of nC16 entrained in the kerosene fraction is advantageously calculated using an efficiency function, varying from 0 to 1, derived from the Fenske equation as follows:

With :

X _nC16 : The percentage of nC16 entrained in the kerosene fraction

T _cut : Temperature, in Kelvin, of the final cutting point of the kerosene fraction

T _eb,nC16 : Boiling temperature of normal paraffin nC16

N _Fe : Fenske number equivalent to the number of theoretical plates of a distillation column with total reflux operation

For example, for a Fenske number of 12.4 and a kerosene fraction of 150-280°C, the fraction of nC16 entrained in the kerosene fraction is 0.16.

Preferably, the nC16 content in the kerosene fraction is determined using the following equation:

With X the percentage of nC16 entrained in the kerosene fraction.

As for the diesel fraction comprising hydrocarbon compounds boiling at 250°C to 370°C, 100% of normal paraffin nC18 (whose boiling temperature is 317°C) is contained in the diesel fraction.

Preferably, the nC18 content in the diesel fraction is determined using the following equation:

Step e) of calculating the PT and/or the FP

The analytical method according to the present invention comprises a step e) of calculating the PT and/or the FP from the following equations:

with x _w,nC18 the n-octadecane content in the diesel fraction;

with x _w,nC16 the n-hexadecane content in the kerosene fraction.

For example, for a diesel fraction containing 4% by weight of nC18, the value x _w,nC18 is 0.04.

List of figures

There shows the evolution of kerosene FP temperature as a function of nC16 content. The kerosene FP temperature was measured by the automated standard method ASTM D5972. The nC16 content was obtained by measuring a DS of the sample and estimating the nC16 content in the cut using the DS results.

There shows the evolution of diesel PT as a function of the normal nC18 content. Diesel PT was measured by the ISO 3015 standard method. The nC18 content was obtained by measuring a DS of the sample and estimating the n-octadecane content in the cut using the DS results.

The hydrocarbon cut samples are obtained from different types of processes: hydrotreatment, hydrocracking and hydroconversion, with different feedstocks such as: diesel fuel mixtures with lipid feedstocks, vacuum distillate mixtures with lipid feedstocks, lipid feedstocks alone and fossil feedstocks alone.

The figures show that the kerosene FP is well correlated with the nC16 content and the diesel PT is well correlated with the nC18 content regardless of the type of process and the type of feedstocks according to the equations of step e) of the analytical method according to the present invention.

There shows a simulated distillation calibration curve giving the relationship between the retention time of the capillary column and the boiling temperature of n-paraffins. This allows the identification of the peaks in the chromatogram corresponding to nC16 and nC18.

There shows an integrated DS curve showing the boiling point versus the mass percentage of eluted sample. This curve is obtained using the calibration curve and the results of the chromatogram obtained in DS. It allows the calculation of the yield of the diesel and/or kerosene fraction in the hydrocarbon cut.

There shows a chromatogram obtained under DS conditions presenting the signal intensity as a function of the retention time. This chromatogram makes it possible in particular to establish the integrated DS curve and to calculate the nC16 and/or nC18 content in the hydrocarbon cut.

There shows the valley-to-valley integration of the nC18 peak in the DS chromatogram of the allowing the calculation of the nC18 content in the hydrocarbon fraction.

EXAMPLES

The examples below show the use of the analytical method according to the invention, compared with the use of the correlation given by the Da Costa method according to the prior art to predict the cloud point and the crystal disappearance point of the diesel and kerosene fractions, respectively, for 4 samples below from different feeds and different processes. These two methods are compared with the experimental measurement values, which are FP and PT analyses of the kerosene and diesel fractions obtained by distillation of the total liquid effluent.

Sample 1: Effluent obtained following a hydrotreatment process of a fossil diesel feedstock comprising compounds having a boiling point between 150 and 370°C mixed with 30% rapeseed oil, for the production of low sulfur diesel, on a NiMo/Al ₂ O ₃ hydrotreatment catalyst.

Sample 2: Effluent obtained following a hydrotreatment process of a fossil vacuum distillate feedstock comprising compounds with a boiling point between 370 and 540°C mixed with 10% animal fat, on a NiMo/Al ₂ O ₃ hydrotreatment catalyst, at high pressure. This process is a pretreatment before the catalytic cracking step, which has the objective of producing light products (LPG, gasoline and kerosene) with a low sulfur content.

Sample 3: Effluent obtained following a process for treating a fossil vacuum distillate feedstock comprising compounds having a boiling point between 370 and 540°C mixed with 20% animal fat, said treatment comprising a sequence of a hydrotreatment step (on NiMo/Al catalyst)₂O₃) followed by a hydrocracking step (on NiMo/zeolite zeolite catalyst). This process aims to produce high-quality middle distillates (diesel and kerosene).

Sample 4: Effluent obtained following a process for treating a fossil vacuum distillate feedstock comprising compounds having a boiling point between 370 and 540°C mixed with 20% animal fat, said treatment comprising a hydrotreatment step (on NiMo/Al catalyst)₂O₃) followed by a hydrocracking step (on NiMo/zeolite zeolite catalyst), and followed by a dewaxing step on an industrially commercialized dewaxing catalyst (NiO catalyst supported on a ZSM-5 zeolite). The objective of this process is the production of high-quality middle distillates (diesel and kerosene), in which the diesel cut is dewaxed to meet the cold property specification of winter diesel (cloud point less than or equal to -5°C).

Example 1 : Prediction of PT and FP by the analytical method according to the invention

For each sample 1, 2, 3 and 4, the analysis method according to the invention (steps a) to e)) is used to predict the PT of the diesel fractions and the FP of the kerosene fractions from different processes. The Fenske number used to calculate the percentage of nC16 entrained in the kerosene fraction is 12.4.

Table 1 shows the values of nC16 and nC18 contents in the total liquid effluents, in the kerosene and diesel fractions, and the kerosene FP and diesel PT obtained by the analytical method according to the invention.

Example 2 ( comparative ) :Kerosene FP and diesel PT prediction by the prior art Da Costa method.

According to the study carried out by Da Costa, the FP of kerosene and the PT of diesel are correlated with the properties of the feedstocks and the operating conditions of the hydrotreatment and hydrocracking processes. These correlations were constructed from the experimental data obtained in the pilot tests and in the industrial hydrotreatment and hydrocracking units.

The FP of kerosene is estimated by the correlation below:

with :

d154 _charge : density at 15°C of the charge entering the process (g/ml)

DS50 _charge : temperature at 50% distilled from the charge according to simulated distillation (°C)

DS95 _charge : temperature at 95% distilled from the charge according to simulated distillation (°C)

HDN: the rate of elimination of nitrogen compounds at the outlet of the hydrotreatment stage (%)

DS05 _kero : temperature at 5% distilled from the kerosene fraction according to the simulated distillation (°C)

DS50 _kero : temperature at 50% distilled kerosene fraction according to simulated distillation (°C)

DS95 _kero : temperature at 95% distilled kerosene fraction according to simulated distillation (°C)

ppH2: partial pressure of hydrogen at the process outlet (bars)

X ₃₇₀ : conversion of the fraction comprising compounds boiling above 370°C (%)

And with a1, a2, …, a10 are parameters obtained by data modeling:

a1 = -36.97

a2 = -151.19

a3 = 0.061

a4 = -0.0082

a5 = -0.097

a6 = -0.045

a7 = 0.024

a8 = 0.366

a9 = 0.045

a10 = -0.042

The diesel PT is estimated by the correlation below:

with :

X ₃₇₀ : conversion of the fraction comprising compounds boiling above 370°C (%)

[N] _charge : the total nitrogen content in the process input charge (ppm)

DS95 _diesel : temperature at 95% distilled from the diesel fraction according to simulated distillation (°C)

And with b1, b2, b3 and b4 are constants obtained by data modeling:

b1 = 142.47

b2 = -0.276

b3 = 0.009

b4 = 0.335

The Table presents the properties of the loads and the operating conditions allowing to estimate the FP of kerosene and the PT of diesel by the comparative method according to the prior art Da Costa.

The reference values are the measured kerosene FP and diesel PT, i.e. the total liquid effluents were distilled to recover the kerosene and diesel fractions. The kerosene FP is measured according to the ASTM D5972 standard method and the diesel PT is measured according to the ISO 3015 standard method.

Conclusion: The results (Table 1 below) show that the FP and PT obtained by the analytical method of the invention are very close to the experimentally measured values. Conversely, the FP and PT predicted by the comparative method according to the prior art Da Costa are very far from the experimental values. The analytical method according to the invention can therefore be used to very quickly obtain the FP and PT reliably without the need for distillation of the total liquid effluents from hydrocarbon feedstock refining processes partly comprising compounds from renewable material.

Sample Unit 1 2 3 4 Total pressure MPa 8 14 14 14 Density at 15°C charge g/ml 0.8791 0.9262 0.9262 0.9262 DS50 charging °C 317.6 493.2 493.2 493.2 DS95 charging °C 613.9 610.4 610.4 610.4 Nitrogen content in the feed Ppm 122 1065 1065 1065 Partial pressure of hydrogen MPa 7.18 13.39 12.18 12.41 Nitrogen removal rate (NDR) % 99.52 99.0 99.2 99.2 Conversion of the 370°C+ total cut % 80.9 26.1 86.4 80.0 DS05 of distilled kerosene fraction °C 173.4 204.1 152.1 148.9 DS50 of distilled kerosene fraction °C 238.8 253.5 212.0 208.3 DS95 of distilled kerosene fraction °C 275.7 276.8 273.3 271.6 DS95 Distilled Diesel Fraction °C 379.3 392.4 358.8 361.1 Measured values of distilled kerosene and diesel fractions Kerosene FP 150-280°C measured °C -51 -15 -43.5 -48.3 Diesel PT 250-370°C measured °C 3 13 0 -5 Values estimated by the Da Costa prior art comparative method (non-compliant) Kerosene FP 150-280°C °C -66.2 -58.0 -61.1 -61.3 Diesel PT 250-370°C °C -36 -9 -36 -34 Values estimated by the analytical method according to the invention (compliant) % nC16 in total effluent by DS %weight 1.5 2.4 2.3 1.6 % nC18 in total effluent by DS %weight 11.3 6.7 4.5 2.6 % kerosene 150-280°C in total liquid effluent by DS %weight 36.7 4.5 32.4 37.4 % diesel 250-370°C in total liquid effluent by DS %weight 69.7 22.3 36.9 30.1 % nC16 in kerosene %weight 0.7 8.5 1.1 0.7 % nC18 in diesel %weight 16.2 30.0 12.2 8.5 Kerosene FP 150-280°C °C -50.1 -16.2 -43.7 -49.2 Diesel PT 250-370°C °C 3 11 -1 -6

(HDT = Hydrotreatment; HCK = Hydrocracking; DSV = Vacuum Distillate; HDW = Hydrodewaxing)

Claims (5)

Analytical method for determining the cold properties of a hydrocarbon fraction partly comprising compounds derived from renewable material, and comprising a diesel and/or kerosene fraction, said method comprising the following steps:
a) Measurement of a Simulated Distillation of the hydrocarbon cut by the ASTM D2887 method;
b) Calculation of the yield of the diesel and/or kerosene fraction in the hydrocarbon cut using the result of the Simulated Distillation;
c) Calculation of the nC18 and/or nC16 content in the hydrocarbon cut via the integration of the peaks of the chromatogram obtained by Simulated Distillation;
(d) Calculation of the nC18 and/or nC16 content in the diesel and/or kerosene fraction using the results of steps (b) and (c);
e) Calculation of the cloud point and/or disappearance point of the crystals from the following equations:

with x _w,nC18 the nC18 content in the diesel fraction;

with x _w,nC16 the nC16 content in the kerosene fraction. The method of claim 1, wherein the hydrocarbon fraction has an initial boiling temperature greater than 100°C and a final boiling temperature less than 420°C according to the simulated distillation method ASTM D2887. Method according to any one of the preceding claims, in which the hydrocarbon cut is obtained from refining processes such as hydrotreatment, hydrocracking, hydroisomerization, hydroconversion, using feedstocks from renewable materials mixed with fossil petroleum feedstocks with at least 1% of feedstocks from renewable materials. Method according to claim 3, in which the feedstocks from renewable materials are chosen from vegetable oils, animal fats, fish fats, effluents from Fischer-Tropsch conversion rich in paraffinic compounds, or a mixture thereof. A method according to claim 3 or 4, wherein the fossil petroleum feedstocks are feedstocks having an initial boiling point greater than or equal to 120°C and a final boiling point less than or equal to 600°C.