RU2601414C2 - Improved method of heavy raw material converting into middle distillates with preliminary treatment before supply to catalytic cracking plant - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to method of heavy raw material converting. Method of middle distillates producing from heavy raw material (1) of vacuum gas oil type or atmospheric distillation residues is successively carried out in 4 stages, containing: a) preliminary treatment (PRET) stage, which is carried out on hydrocracking or hydraulic processing plant, which enables to reduce amount of sulphur and nitrogen-containing impurities in raw material, as well as amount of diolefins, during which gasoline fraction C5-160 °C (3) is produced, middle distillate (4) first fraction with boiling point temperature range of 160-360 °C and part (5), called non-converted, which has essentially same boiling point temperature range, as initial heavy raw material, b) said non-converted part (5) catalytic cracking (FCC) stage, taken from preliminary treatment (PRET) stage, during which dry gases fraction (7) is produced used as fuel, fraction C3 (8), fraction C4 (9), gasoline fraction C5-160 °C (10) and second middle distillates fraction (11), wherein gasoline fraction (10) is supplied to cleaning (PUR) plant, c) oligomerization (OLG) stage, to which fraction C3 (8) is supplied, fraction C4 (9), taken from catalytic cracking plant, and gasoline fraction (10') from cleaning plant (PUR), and during which fraction C3/C4 (14) is produced, gasoline fraction C5-160 °C (15), which are added to gasoline pool, and third middle distillates fraction (16), which is supplied to hydraulic treatment (HDT) plant, d) complete hydrogenation (HDT) stage of middle distillates fraction (16) taken from oligomerization stage, to achieve compliance with requirements for commercially distributed gas oil.

EFFECT: higher selectivity by middle distillates compared to petrol and their increased yield.

9 cl, 10 tbl, 1 dwg, 2 ex

Description

FIELD OF THE INVENTION

The invention relates to the improvement of a method for the conversion of heavy hydrocarbons, providing an improved yield of middle distillates. More specifically, the method according to the present invention allows:

- increase the number of medium distillates compared to raw materials,

- significantly improve the selectivity for middle distillates compared to gasoline,

- to obtain fractions C3, C4 and light gasoline with a low amount of impurities, which gives a significant gain in respect of the cleaning steps required before the oligomerization steps, or in terms of the service life of the catalysts used in the oligomerization units.

These improvements are made possible through the use of a hydrotreatment or hydroconversion unit, called a pretreatment unit, upstream of the system, consisting of a catalytic cracking unit and an oligomerization unit connected in series.

Historically, catalytic cracking units called FCC (short for Fluid Catalytic Cracking, which means fluid catalytic cracking) have been optimized to produce light products: liquefied gases (or LPG in English), light olefins and gasoline to satisfy either the market demand for polymers obtained by the polymerization of light olefins, or the gasoline needs of a fleet.

With this mode of operation, the production of base gas oils remains limited. Currently, given the tendency for the car fleet to switch to diesel fuel, the demand for gas oil type products has increased. As a result, it is becoming increasingly necessary to reorient the production of oil refineries to middle distillates and improve the selectivity for middle distillates compared to gasoline.

Since FCC units, which are available at almost every second refinery, are, on the one hand, the main source of gasoline, and on the other hand, an important source of light olefins, it is extremely important to be able to convert these units into units that facilitate the production of medium distillates.

In the framework of the present invention, we are talking about a pre-treatment method, at a hydrotreating or hydroconversion unit, upstream of the catalytic cracking unit, in order to obtain a more capable of conversion feedstock, which allows to increase the final volume of production of middle distillates at the output of the FCC unit + oligomerization unit and improve middle distillate selectivity compared to gasoline.

Another objective of the present invention is to facilitate the purification of raw materials for the installation of oligomerization and, thus, increasing the duration of the catalytic cycle, having raw materials with fewer impurities such as nitrogen and sulfur. The pretreatment unit, which is located in the technological scheme prior to the FCC system and oligomerization, can be a hydroconversion or hydrotreatment unit for heavy feedstocks capable of carrying out any hydrotreating reactions, such as hydrodeazotization, hydrodesulfurization and hydrogenation of aromatic compounds, at high hydrogen pressure and in the presence of catalysts.

This method allows you to convert part of the heavy hydrocarbon feed, the initial boiling point of which is usually above 340 ° C, into gasoline and middle distillates at a partial pressure of hydrogen and hydrotreat the obtained fractions, as well as unconverted heavy hydrocarbon feed, which reduces the amount of impurities, in particular compounds nitrogen and sulfur.

The FCC process allows you to convert heavy hydrocarbon feeds, whose initial boiling point is usually above 340 ° C, into lighter hydrocarbon fractions, in particular the gasoline fraction, by cracking the heavy feed molecules in the presence of an acidic catalyst. With FCC, LPG (liquefied petroleum gas) with a high amount of olefins is also produced in significant quantities. In the present invention, the feed for the FCC consists of an unconverted fraction from a hydrotreatment unit.

The aim of the oligomerization process is to oligomerize C3-C12 olefins, which may consist of several separate fractions, such as the C3-C4 fraction and the gasoline fraction C5-220 ° C, preferably C5-160 ° C and even more preferably C5-120 ° C used individually or in a mixture to obtain a mixture of hydrocarbons containing monoolefins with the number of carbon atoms is preferably greater than or equal to 9.

Of the C4 olefins, oligomers are typically prepared with the number of carbon atoms generally less than or equal to 30 and for the most part from 8 to 20.

The present invention uses a special combination of sequentially arranged installations, which allows:

a) increase the total production of middle distillates,

b) improve middle distillate selectivity compared to gasoline, and

c) facilitate the purification of the oligomerization unit and increase the duration of the catalytic cycle, having raw materials with a reduced amount of impurities such as nitrogen, sulfur, and diolefins.

The invention essentially consists in placing the hydroprocessing or hydroconversion unit upstream of the catalytic cracking unit, which allows a general increase in the production of middle distillates.

This arrangement of the plants can also significantly increase the selectivity for middle distillates compared to gasoline.

Another effect of the invention is that it allows the formation of a gasoline fraction after catalytic cracking, in which the amount of impurities such as nitrogen and sulfur, as well as diolefins, is reduced.

The gasoline fraction purified in this way reduces the need for purification according to the scheme above oligomerization and increases the duration of the catalytic cycle.

The present invention is compatible with any catalytic cracking reactor technology, be it dense gas upstream technology (a riser reactor) or a downflow technology (a dropper or downer reactor in English).

The catalytic cracking unit used in the present method can be used in several versions: with a single reactor or several reactors, each reactor can be operated in an upstream or downstream mode.

If combined with a catalytic cracking unit, several oligomerization units should be connected in series or in parallel.

Prior art analysis

Patent application FR 2935377 relates to a method for the conversion of heavy hydrocarbons for the joint production of propylene and gasoline with a minimum yield. The method described in this patent includes at least two reaction steps: a first catalytic cracking step and a second oligomerization step of C3 and C4 olefins, or C4 olefins, or C4 and C5 olefins leaving the catalytic cracking. In some cases, a third reaction step for the selective hydrogenation of olefins may be necessary before oligomerization.

The method proposed in this invention allows for the implementation of two production modes:

- a mode called "maximum propylene", corresponding to the maximum production of propylene while maintaining a minimum gasoline yield and even slightly increased compared to the potential yield only from the catalytic cracking unit, or

- a mode called "maximum gasoline", corresponding to the maximum production of gasoline without producing propylene.

Patent WO 03/078547 describes a method for catalytic cracking of a feedstock having a boiling point of more than 350 ° C and a secondary, relatively light feedstock with a boiling point of less than 320 ° C, said secondary feedstock consisting of olefins with at least 8 carbon atoms obtained oligomerization of light olefins with 4 or 5 carbon atoms.

Patent WO 03/078364 describes a method for producing oligomers from C4 olefins, said oligomers later cracking in a catalytic cracking unit in order to maximize the production of propylene.

Patent application FR 11/01444 describes a method for the collaboration of catalytic cracking and an oligomerization unit.

This application describes a method for the conversion of heavy feedstocks, which allows to increase the selectivity for middle distillates. The method employs a catalytic cracking unit, behind which one or more olefin oligomerization units with the number of carbon atoms from C2 to C12 are installed, which makes it possible to preferably obtain an additional fraction of middle distillates. The light part of the obtained oligomers, which cannot be attributed to the middle distillate fraction, is partially returned

either to the oligomerization step for conversion to middle distillates by reaction with light olefins from the feed, as described in patent FR 2871167,

or to an FCC unit for cracking onto light olefins, which are returned to the oligomerization units in addition to the olefins from the feed, in order to preferably form heavy oligomers that can be included in the middle distillate fraction.

The present invention consists in a special sequence of application of three units, which allows to significantly increase the production of middle distillates, as well as to improve the selectivity for middle distillates compared to gasoline, i.e. selectivity, which is currently sought in the context of a reorientation of demand from gasoline to gas oil.

The sequence described in the present invention also allows to improve the efficiency and service life of the catalyst used in the oligomerization unit by obtaining a purified fraction of gasoline with FCC, with a reduced amount of impurities such as sulfur, nitrogen, and also diolefins, i.e. due to the gasoline fraction, which is then fed to the oligomerization unit for conversion to olefins with a higher molecular weight corresponding to the middle distillate fraction.

The sequence of processes according to the present invention consists in using a hydrotreating unit, such as a soft or deep hydrocracking unit (sold by AXENS under the trade name HyC or HyK-HP), or a fixed or fluidized bed hydrotreating unit (manufactured by AXENS under the trade name Hyvahl / Hoil _DC / Hoil _RC ), located upstream of the catalytic cracking unit (FCC), behind which there are one or more oligomerization units processing all or only a part of fractions C 3, C4 and all gasoline or light gasoline obtained at the FCC.

The synergistic effect achieved by combining the sequence of units proposed by the present invention allows to increase the total amount of middle distillates obtained in comparison with the simple system described in the prior art consisting of a catalytic cracking unit and an oligomerization unit.

The sequence of plants according to the present invention allows a very noticeable improvement in the selectivity for middle distillates compared to gasoline, as well as to obtain a fraction of gasoline sent to the refined oligomerization unit, which has an undeniable advantage in terms of catalyst efficiency and service life.

Brief Description of the Figures

FIG. 1 shows a diagram of a method according to the invention, in which the plants are indicated as follows:

PRET: preprocessing,

FCC: catalytic cracking,

PUR: purification unit before oligomerization,

OLG: indicated oligomerization unit and

HDT: hydrotreatment unit for middle distillate fraction leaving oligomerization.

SUMMARY OF THE INVENTION

The invention relates to a method for the conversion of heavy hydrocarbon feeds, that is, a fraction consisting of hydrocarbons with a boiling point above about 340 ° C, to increase the production volume of medium distillates, which are the basis for commercial gas oil.

The method according to the invention allows to achieve three goals:

1) increase the production of medium distillates due to

- the production of raw materials that are more capable of conversion at the FCC level, which is advantageous in that it leads to an increase in the production of C3, C4 olefins and light gasoline, which, after conversion in the oligomerization unit, allows to further obtain an average distillate,

- obtaining a middle distillate in the pre-treatment unit itself,

2) very significantly increase the selectivity for middle distillates compared with gasoline,

3) to limit the need for purification to oligomerization and increase the duration of the catalytic cycle by obtaining a fraction of catalytic cracking gasoline, which reduces the amount of impurities such as nitrogen and sulfur, as well as the number of diolefins.

The method according to the present invention can be defined as a method for producing a middle distillate from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues, in which 4 stages are carried out sequentially:

a) the pre-treatment stage (PRET), which is carried out at a hydrocracking or hydrotreating unit, which allows reducing the amount of sulfur-containing and nitrogen-containing impurities in the feedstock, as well as the number of diolefins, during which a gasoline fraction of C5-160 ° C is obtained (3), the first fraction of the average distillate (4) with a boiling range of 160-360 ° C and a portion (5) called unconverted, which has essentially the same boiling range as the starting heavy feed,

b) a catalytic cracking step (FCC) of said unconverted portion (5) taken from a pretreatment step (PRET), during which a fraction (7) of dry gases used as fuel is obtained, fraction C3 (8), fraction C4 (9 ), a C5-160 ° C gasoline fraction (10) and a second middle distillate fraction (11), the gasoline fraction (10) being fed to a purification unit (PUR),

c) an oligomerization step (OLG), to which fraction C3 (8), fraction C4 (9) taken from the catalytic cracking unit, and gasoline fraction (10 ′) from the purification unit (PUR) are fed, and during which fraction C3 is obtained / C4 (14), a gasoline fraction of C5-160 ° C (15), which are added to the gasoline pool, and a third middle distillate fraction (16), which is fed to the hydrotreatment unit (HDT),

d) a full hydrogenation step (HDT) of the middle distillate fraction (16) taken from the oligomerization step to achieve compliance with the requirements for commercially available gas oil.

According to one preferred embodiment of the method of the present invention, a pretreatment unit (PRET) is a mild hydrocracker operating under the following conditions:

- temperature from 350 ° C to 420 ° C,

- pressure from 8 to 12 MPa,

- VVH from 0.3 to 1 h ^-1 ,

-H ₂ / HC from 300 to 800 l / l,

- catalysts based on NiMo, NiCoMo, NiW.

According to another preferred embodiment of the method of the present invention, a pretreatment unit (PRET) is a hydrotreatment unit operating under the following conditions:

- temperature from 350 ° C to 420 ° C,

- pressure from 4 to 8 MPa,

- VVH from 0.5 to 2 h ^-1 ,

- H ₂ / HC from 150 to 200 l / l,

- catalysts based on NiMo, CoMo, NiCoMo.

According to one preferred embodiment of the method of the present invention, a catalytic cracking unit (FCC) operates under the following conditions:

- when catalytic cracking is carried out in a single upflow reactor, the reactor outlet temperature (ROT) is from 450 ° C to 650 ° C, preferably from 470 ° C to 620 ° C, and the C / O ratio is from 2 to 20, preferably from 4 to 15,

when the reactor is a downflow reactor, the reactor outlet temperature (ROT) is from 480 ° C to 650 ° C, and the C / O ratio is from 10 to 50, preferably from 10 to 30.

According to one preferred variant of the method of the present invention, the purification unit (PUR) of the FCC gasoline fraction is fractionated by distillation to obtain a light fraction depleted in nitrogen-containing compounds and / or an adsorption step on molecular sieves under the following conditions:

- temperature from 20 ° C to 50 ° C,

- pressure from 5 to 30 bar,

- VVH from 0.5 to 4 h ^-1 ,

molecular sieves, for example of the type NaX or NaY.

According to one preferred embodiment of the method of the present invention, the oligomerization unit (OLG) of gasoline with FCC operates under the following conditions:

- operating temperature from 100 ° C to 350 ° C, preferably from 150 ° C to 270 ° C,

- operating pressure from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, more preferably from 4 to 5 MPa,

- catalysts based on amorphous silicoaluminium or aluminosilicate or crystalline zeolite.

According to another preferred embodiment of the method of the present invention, the oligomerization unit (OLG) of gasoline with FCC operates under the following conditions:

- operating temperature from 180 ° C to 350 ° C, preferably from 200 ° C to 270 ° C,

- operating pressure from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, even more preferably from 4 to 5 MPa,

- catalysts based on crystallized zeolite in the case of distillate processing into diesel.

According to one preferred embodiment of the method of the present invention, the oligomerization unit (OLG) of gasoline with FCC operates under the following conditions:

- operating temperature from 60 ° C to 200 ° C, preferably from 80 ° C to 180 ° C,

- operating pressure from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, more preferably from 2 to 4 MPa,

- catalysts such as acidic organic resins.

According to one preferred embodiment of the method of the present invention, the gasoline fraction (15) obtained by oligomerization (OLG) is at least partially returned to the FCC in order to maximize the production of middle distillates.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, the total raw material to be pre-processed contains more than 50 mass. % hydrocarbons having a boiling point above 340 ° C, and often at least 80 vol.% compounds boiling above 340 ° C. Preferably, this typical feed has a boiling point above 340 ° C, even better above 370 ° C, i.e. 95% of the compounds in the feed have a boiling point above 340 ° C and, even better, above 370 ° C.

The nitrogen content in the processed hydrocarbon feed is usually more than 500 parts per million. Typically, the sulfur content is from 0.01 to 5 mass. %

The feed for the catalytic cracking unit corresponds to the unconverted portion of the feed for the pre-treatment unit. It usually contains more than 50 mass. % hydrocarbons with a boiling point above 340 ° C. This feed contains fewer impurities such as nitrogen or sulfur compounds than the feed to be hydrotreated and has a high hydrogen content, typically from 11 to 15%.

The gasoline fraction corresponds to a hydrocarbon fraction with a boiling range of from 50 ° C to 220 ° C, preferably from 50 ° C to 160 ° C.

The middle distillate fraction corresponds to a hydrocarbon fraction with a boiling range of 130 ° C to 380 ° C, preferably 150 ° C-370 ° C.

The slurry fraction (suspension) corresponds to a hydrocarbon fraction with a boiling point above 380 ° C, preferably above 360 ° C.

The specific conditions at various stages of the method according to the invention are described in more detail below.

1) Pre-processing step (PRET)

According to the invention, the pretreatment step can be carried out on a hydroprocessing unit for heavy raw materials in a fixed or fluidized bed or on a soft or deep hydrocracking unit carried out using hydroprocessing or hydrocracking catalysts, classically catalysts such as metal sulfides of groups VI and VIII on substrates such as aluminum oxide or aluminosilicate . Catalysts comprising zeolite in a support may also be provided. When the pretreatment reactions are carried out in a fixed bed under downward parallel flow conditions, the following operating conditions are usually selected: temperatures from 300 ° C to 450 ° C, preferably from 350 ° C to 430 ° C, total pressures from 30 to 300 bar, preferably from 50 to 180 bar, hourly space velocities from 0.1 to 10 h ^-1 , preferably from 0.3 to 5 h ^-1 and the ratio of hydrogen / hydrocarbons from 200 Nm ³ / m ³ to 4000 Nm ³ / m ³ , preferably from 300 to 2000 Nm ³ / m ³ .

These plants allow hydrosulphonation, hydrodeasotization, hydrodearomatization of raw materials and provide the transformation of part of the heavy raw materials into more valuable products. The degree of conversion is more significant for a hydroconversion unit than for a hydrotreatment unit.

Pretreatment is carried out in a catalytic process at high hydrogen pressure, in a fixed bed or in a fluidized bed, using hydroprocessing or hydrocracking catalysts.

The pre-treatment section contains at least one reaction zone containing at least one hydrotreating catalyst, preferably having a high activity with respect to hydrodesulphurization, hydrodeazotization and hydrogenation of aromatic compounds.

Pretreatment catalysts, also called hydrotreating, can be selected from catalysts commonly used in this field. The hydrotreating catalyst may preferably comprise a matrix of at least one hydrogenation-dehydrogenation element selected from the group consisting of elements of group VIB and group VIII of the periodic system.

The matrix may consist of such compounds (used individually or in a mixture) such as alumina, halogenated alumina, silica, aluminosilicate, clays (selected, for example, from natural clays such as kaolin or bentonite), magnesium oxide, titanium oxide , boron oxide, zirconium oxide, aluminum phosphates, titanium phosphates, zirconium phosphates, coal, aluminates. It is preferable to use matrices containing alumina in any form known to those skilled in the art, even more preferably aluminas, for example gamma alumina.

The hydrogenation-dehydrogenating element may be selected from the group consisting of base elements of group VIB and group VIII of the periodic system.

Preferably, the hydrogenation-dehydrogenation element is selected from the group consisting of molybdenum, tungsten, nickel and cobalt.

More preferably, the hydrogenation-dehydrogenation element contains at least one element of group VIB and at least one non-noble element of group VIII. This hydrogenating-dehydrogenating element may, for example, comprise a combination of at least one element of group VIII (Ni, Co) with at least one element of group VIB (Mo, W).

Preferably, the hydrotreating catalyst further comprises at least one alloying element deposited on said catalyst selected from the group consisting of phosphorus, boron and silicon. In particular, the hydrotreating catalyst may contain boron and / or silicon and, in addition, optionally phosphorus as alloying elements.

The content of boron, silicon, phosphorus is usually from 0.1 to 20 mass. %, preferably from 0.1 to 15 mass. %, more preferably 0.1-10 mass. %

The hydrotreating catalyst may preferably contain phosphorus.

This compound provides, among other things, two main advantages of a hydrotreating catalyst; the first advantage is the easier preparation of said catalyst, in particular during impregnation with a hydrogenating-dehydrogenating element, for example, solutions based on nickel and molybdenum.

A second advantage provided by this compound is an increase in hydrogenation activity of the catalyst.

In a preferred hydrotreating catalyst, the total concentration of metal oxides of groups VIB and VIII is from 2% (preferably 5%) to 40 mass. %, preferably from 3% (preferably 7%) to 30 mass. %, and the mass ratio of the metal (or metals) of group VIB to the metal (or metals) of group VIII, expressed in metal oxide, is from 20 to 1.25, preferably from 10 to 2.

The concentration of phosphorus oxide P ₂ O ₅ may be below 15 mass. %, preferably below 10 wt. % Preferred substrates are alumina or silica-alumina containing 5-95% SiO ₂ , used individually or in admixture with zeolite.

In another hydrotreating catalyst containing boron and / or silicon, preferably boron and silicon, the catalyst also contains, in mass. % of the total mass of the specified catalyst:

- from 1 to 99%, preferably from 10 to 98%, more preferably from 15 to 95% of at least one matrix,

- from 3 to 60%, preferably from 3 to 45%, more preferably from 3 to 30% of at least one metal of group VIB,

- optionally, from 0 to 30%, preferably from 0 to 25%, more preferably from 0 to 20% of at least one metal of group VIII,

- from 0.1 to 20%, preferably from 0.1 to 15%, more preferably from 0.1 to 10% boron and / or from 0.1 to 20%, preferably from 0.1 to 15%, more preferably from 0.1 to 10% silicon,

- optionally, from 0 to 20%, preferably from 0.1 to 15%, more preferably from 0.1 to 10% of phosphorus, and

- optionally, from 0 to 20%, preferably from 0.1 to 15%, more preferably from 0.1 to 10% of at least one element selected from group VIIA, for example fluorine.

Another hydrotreating catalyst contains:

- from 1 to 95 mass. % (% oxide) of at least one matrix, preferably alumina,

- from 5 to 40 mass. % (% oxide) of at least one base element from groups VIB and VIII,

- from 0 to 20%, preferably from 0.1 to 20 mass. % (% oxide) of at least one promoter selected from phosphorus, boron, silicon,

- from 0 to 20 mass. % (% oxide) of at least one element of group VIIB (e.g., manganese),

- from 0 to 20 mass. % (% oxide) of at least one element of group VIIA (e.g. fluorine, chlorine), and

- from 0 to 60 mass. % (% oxide) of at least one element of group VB (e.g., niobium).

Hydrotreating catalysts are generally preferred having the following molar ratios:

- the molar ratio of metals of group VIII to metals of group VIB from 0 to 1,

- when B is present, the molar ratio of B / metals of group VIB is from 0.01 to 3,

when Si is present, the molar ratio of Si / Group VIB metals is from 0.01 to 1.5,

- when P is present, the molar ratio of P / metals of group VIB is from 0.01 to 1, and

- when at least one element of group VIIA is present, the molar ratio of elements of group VIIA to metals of group VIB is from 0.01 to 2.

Particularly preferred hydrotreating catalysts are NiMo and / or NiW catalysts on alumina or aluminosilicate, as well as NiMo and / or NiW catalysts on alumina or aluminosilicate doped with at least one member of the atomic group consisting of phosphorus, boron, silicon and fluorine.

Applicants have also developed such catalysts. Call, for example, the catalysts described in patents FR 2904243, FR 2903979, EP 1892038.

In the case where a higher conversion is desired in the pretreatment step, hydrocracking catalysts are used. These hydrocracking catalysts must be bifunctional catalysts containing a hydrogenation phase so that aromatic compounds can be hydrogenated and an equilibrium between saturated compounds and the corresponding olefins can be achieved, and an acidic phase that promotes hydroisomerization and hydrocracking reactions.

The acid function is provided by substrates with large surfaces (usually 100-800 m ² / g), which have significant acidity, such as halogenated aluminum oxides (in particular chlorinated or fluorinated), combinations of boron and aluminum oxides, amorphous aluminosilicates and zeolites.

The hydrogenation function is introduced either by one or more metals of group VIII of the periodic system of elements, such as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, or by a combination of at least one metal of group VIB of the periodic system, such as molybdenum and tungsten, and at least one metal of group VIII.

The authors of the application have also developed a whole range of such catalysts. We call, for example, patents FR 2819430, FR 2846574, FR 2875417, FR 2863913, FR 2795341 and FR 2795342.

Among the catalysts suitable for use in the pretreatment unit (PRET) according to the invention, mention may be made of HR500 series catalysts (e.g. HR526, HR538, HR548, HR558, HR562, HR568 and HRK558), HDK700 (HDK766, HDK776, HDK786) or HYK700 ( HYK732, HYK752, HYK762, HYK742) manufactured by AXENS.

A flow separation unit and a pre-treatment unit typically include a primary separation of gas and liquid streams, a hydrogen recirculation section, and also distillation sections for fractionating different liquid fractions.

At the exit from the pretreatment stage (PRET), the obtained unconverted fraction contains significantly less sulfur and nitrogen compounds than if the raw materials were not subjected to the pretreatment step and has a higher hydrogen content. These factors can significantly reduce the amount of impurities that would be obtained in the streams leaving the FCC stage, which is further down the scheme.

2) Catalytic cracking step (FCC):

The catalytic cracking unit contains a reactor that can operate in upstream or downstream mode.

When catalytic cracking is carried out in a single upflow reactor, the reactor outlet temperature (ROT) is from 450 ° C to 650 ° C, preferably from 470 ° C to 620 ° C, and the C / O ratio is from 2 to 20, preferably from 4 to 15.

When the reactor is a downflow reactor, the outlet temperature of the reactor (ROT) is from 480 ° C to 650 ° C, and the C / O ratio is from 10 to 50.

The spent catalyst stream exiting the FCC reactor is separated from the cracked products in any gas-solid separation system known to the skilled person and regenerated in a special regeneration zone.

The stream from the catalytic cracking reactor is conducted to the fractionation zone to obtain several fractions, determined in accordance with the needs of the owners of the refinery.

According to the invention, the catalytic cracking catalyst consists of an alumina, silica or aluminosilicate matrix, with or without ultra-stable type Y zeolite distributed in this matrix.

You can also provide for the addition of additives based on zeolite ZSM5 in a content below 30 mass. % of the total amount of catalyst.

The catalyst in an FCC reactor typically consists of particles with an average diameter typically in the range of 40 to 140 microns, most often from 50 to 120 microns.

The catalytic cracking catalyst contains at least one suitable matrix, such as alumina, silica or silica-alumina, in the presence or absence of type Y zeolite distributed in this matrix.

The catalyst may further comprise at least one zeolite having shape selectivity of one of the following structural types: MEL (e.g., ZSM-11), MFI (e.g., ZSM-5), NES, EUO, FER, CHA (e.g. , SAPO-34), MFS, MWW. It may also contain one of the following zeolites: NU-85, NU-86, NU-88 and IM-5, which also have shape selectivity.

An advantage of these zeolites having shape selectivity is to obtain better propylene / isobutylene selectivity, i.e., a higher propylene / isobutylene ratio in cracked effluents.

The proportion of zeolite having shape selectivity of the total amount of zeolite may vary depending on the raw materials used and the structure of the desired products. Often used from 0.1% to 60%, preferably from 0.1% to 40%, in particular from 0.1 to 30 mass. % zeolite with selectivity in shape.

Zeolite or zeolites can be distributed in a matrix based on silicon oxide, aluminum oxide or aluminosilicate, and the proportion of zeolite (from all zeolites taken together) is often from 0.7 to 80 mass. %, preferably from 1 to 50 mass. %, even more preferably from 5 to 40 mass. % by weight of the catalyst.

In the case where several zeolites are used, they can be introduced into a single matrix or into several different matrices. The content of zeolite having a selectivity in form, from all zeolites below 30 mass. %

The catalyst used in the catalytic cracking reactor may consist of ultra-stable type Y zeolite dispersed in an alumina, silica or aluminosilicate matrix, to which an additive based on zeolite ZSM5 has been added, and the number of ZSM5 crystals is less than 30 mass. % of the total mass of the catalyst.

A catalytic cracking reactor (FCC) separation separation unit typically includes primary separation of the streams from the FCC, a gas compression and fractionation section, and a distillation section for fractionating various liquid fractions.

In some cases, the HCO fraction obtained at the FCC unit (shown as stream (17) in FIG. 1) can be returned to the pretreatment unit.

Catalytic cracking olefin fractions consisting of C3, C4 olefins and gasoline with a boiling point below 220 ° C, preferably below 160 ° C, which can be formed from several separate fractions, such as, for example, the C3 fraction and the gasoline fraction on one or more oligomerization units.

At the exit from this stage, the resulting gasoline fraction contains less sulfur and nitrogen compounds than would be if only FCC were carried out, while maintaining the equivalent olefin content.

These factors can reduce and even avoid purification immediately before the oligomerization step.

3) Cleaning step (PUR)

The gasoline fraction to be processed is fed to a purification unit that uses an adsorbent, such as molecular sieves (e.g., NaX or NaY type), operating under the following operating conditions:

- temperature from 20 ° C to 50 ° C,

- pressure from 5 to 30 bar,

- VVH from 0.5 to 4 h ^-1 .

Of the adsorbents suitable for use in a purification plant, metal oxides such as aluminum oxides, crystallized aluminosilicates, such as zeolites (often called molecular sieves), or mixtures of these compounds can be mentioned.

Of these compounds, molecular sieves based on a faujasite type zeolite are preferred. One example is NaX zeolite, for example, marketed by Axens under the name SBE 13X.

In some cases, simple fractionation may also provide a light fraction with a reduced amount of nitrogen compounds suitable for the oligomerization section.

4) Oligomerization Step (OLG)

The purpose of the oligomerization step is to oligomerize C3-C12 olefins, which can be formed from several separate fractions, such as the C3-C4 fraction and the C5-160 ° C gasoline fraction, individually or in a mixture, to obtain a hydrocarbon mixture containing monoolefins with the number of carbon atoms, preferably greater than or equal to 8.

As a rule, oligomers are obtained from C4 olefins, the number of carbon atoms in which is predominantly less than or equal to 30, and for the most part is from 8 to 20.

Oligomerization differs from polymerization by the addition of a limited number of molecules. The number of attachable molecules in the context of the invention is from 2 to 10, including borders, preferably from 2 to 5, even more preferably from 2 to 4.

However, oligomers may contain trace amounts of olefins, the degree of oligomerization of which is greater than 10. Most often, these trace amounts are less than 5 mass. % of the formed oligomers.

Oligomerization can be carried out in one or more stages, in one or more reactors, in parallel or in series, and on one or more catalysts.

The following description of the catalyst and operating conditions is applicable to any of the steps and / or to any reactors.

The solid oligomerization catalyst operating in the heterogeneous phase is selected from known prior art catalysts. The following describes in more detail specific conditions at different stages of the method according to the invention.

For oligomerization, acidic catalysts based on amorphous silicoaluminate or aluminosilicate, crystalline zeolite or resins are preferably used.

Of the resins, TA801 manufactured by AXENS is preferably selected.

The operating temperature is from 60 ° C to 200 ° C, preferably from 80 ° C to 180 ° C.

The operating pressure is from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, more preferably from 2 to 4 MPa.

Of the zeolites, it is preferable to select zeolites described in patent FR 2894850. The operating temperature is from 100 ° C to 350 ° C, preferably from 150 ° C to 270 ° C.

The operating pressure is from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, more preferably from 4 to 5 MPa.

A portion of the C5-220 ° C gasoline fraction obtained in the oligomerization unit, preferably light C5-160 ° C gasoline, can optionally be returned to the oligomerization reactor in order to increase the yield of middle distillates.

5) Final hydrogenation step (HPT)

At the final stage of hydrogenation (HDT), partially or fully sulfonated catalysts based on Ni, or NiMo, or CoMo, or NiCoMo and NiW supported on a substrate of the type of heat-resistant oxide (Al, Ti, Si) are used, possibly with one or more promoters ( F, P, Ca, Na).

The invention is explained in more detail using figure 1.

Feedstock (1) is introduced along with the supply of hydrogen (1b) to the pretreatment unit (PRET).

This treatment in the presence of hydrogen aims to convert olefins to alkanes; it can be implemented on any catalyst known to those skilled in the art and under appropriate operating conditions. In particular, Ni and Mo-based sulfonated catalysts such as HR 306, HR 406 or HR 506 manufactured by AXENS can be used. These catalysts operate in the gas phase, at a high temperature of 350-420 ° C and at a high hydrogen content.

Ni and S based catalysts can also be used and are preferred, for example, LD 241, 341 and 541 series catalysts manufactured by AXENS operating in the liquid phase and furthermore at low temperature (150-180 ° C).

From the pretreatment unit (PRET) are classically isolated, in order of increasing molecular weight:

- gasoline fraction (3),

- fraction of middle distillates (4),

- unconverted fraction (5).

So, fraction (5) is fed to a catalytic cracking unit (FCC), from which they are classically selected, in order of increasing molecular weight:

- fraction of dry gas (7), consisting of hydrogen (H ₂ ), methane and, possibly, ethane, ethylene,

- fraction C3 (8), consisting of hydrocarbon molecules containing 3 carbon atoms, enriched in propylene,

- fraction C4 (9), consisting of hydrocarbon molecules containing 4 carbon atoms, enriched with butenes,

- gasoline fraction (10),

- middle distillate fraction (11),

- fraction (12) called "slurry" (suspension), which is added to the fuel pool.

In some cases, the HCO fraction can be pumped out and returned to pre-treatment (2).

In this case, the gasoline fraction (10) is optionally purified in a purification unit (PUR).

The gasoline fraction (10 ′) thus purified is then supplied together with fractions (8) and (9) as feed to the oligomerization unit (OLG).

3 fractions were selected from this oligomerization unit (OLG):

- raffinate fraction (14), which corresponds to unconverted olefins and paraffins from fractions C3 (8) and C4 (9).

- gasoline fraction (15), which corresponds to the paraffins contained in fraction (10 ′), as well as part of the oligomers formed from fractions (8) and (9),

- middle distillate fraction corresponding to heavy oligomers formed from fractions (8), (9), (10 ').

The middle distillate fraction is fed to a hydrogenation unit (HDT) to meet commercial specifications.

EXAMPLES

Below are 2 examples to illustrate the improvement in the efficiency of the method according to the invention compared with the method corresponding to the prior art.

Example 1 (prior art): basic version of "FCC + oligomerization"

This first example is a basic variant and corresponds to the FCC unit with one upstream reactor, behind which the oligomerization unit is located.

The FCC unit has a capacity of 40,000 BPSD, that is 230 t / h (BPSD stands for "barrels per day"), which processes straight run vacuum gas oil ("straight run VGO"), that is, a fraction called vacuum gas oil coming directly from the vacuum gas oil unit distillation.

The catalytic cracking unit operates with a catalytic system consisting of aluminosilicate.

The main characteristics of the raw materials as well as the operating conditions in the FCC unit are presented in tables 1 and 2, respectively.

Table 1 Main characteristics of the VGO fraction Density at 15 ° C 0.9149 Nitrogen base mg / kg 417 Nitrogen % 0.127 Sulfur % 1.22 Hydrogen mass % 12.3

table 2 Operating conditions in the FCC installation according to example 1 Example 1 Plant productivity FCC, VGO fraction barrels / day 40,000 VGO fraction consumption t / h 230 Upstream reactor pressure bar hut 1.4

Upstream reactor outlet temperature ° C 550 Raw material preheating temperature ° C 220 The ratio of the mass flow rate of the catalyst and raw materials 6.2

For these conditions, the yields of products leaving the catalytic cracking unit are shown in Table 3, based on raw materials.

Table 3 The output from the catalytic cracking unit of example 1 mass % Exit with FCC, basic version dry gases 3.9 fraction C3 8.9 fraction C4 12.5 gasoline (PI-160 ° C) 36,4 heavy gasoline (160-220 ° C) 9.7 medium distillates (220-360 ° C) 15.7 "Slurry" (360 ° C +) 7.4 Coke 5.5 Total one hundred

The olefin content in gasoline PI-160 ° C is 47.6 mass. %, and the nitrogen content is 50 hours / million

The sulfur content is equal to 800 parts per million.

The C3 fraction, which consists mainly of propylene and propane, as well as the C4 fraction, which consists mainly of butenes and butane, as well as the gasoline fraction (PI-160 ° C), are then fed to the oligomerization unit.

Given the presence of sulfur and nitrogen, the purification section is placed according to the technological scheme before oligomerization. It consists of a mass of NaX molecular sieves that are in a fixed layer and operate at a temperature of 25 ° C, with one layer in operation and the other in regeneration.

The operating conditions in the purification and oligomerization unit are presented in table 4.

Table 4 Operating conditions in a purification and oligomerization unit Example 1 Raw material consumption (C3-160 ° C) t / h 133 Cleaning installation The number of molecular sieves NaX (purification) t 22.1 Oligomerization unit Temperature ° C 160-250 ^* Pressure bar hut fifty Amount of catalyst t 250 Catalyst IP 811 (Axens) ^{* the} temperature is gradually increased to maintain the activity of the catalyst

Under these conditions, the yields of products obtained from the catalytic cracking and oligomerization unit at the inlet of the catalytic cracking unit are shown in Table 5 below, based on the feed.

Table 5 The yields of the products formed in the system "catalytic cracking plus oligomerization" according to example 1 mass % Origin Example 1
State of the art dry gases Fcc 3.89

raffinate oligomerization 4.27 gasoline (PI-220 ° C) oligomerization and FCC 33.95 medium distillates (220-360 ° C) FCC and oligomerization 45.00 "Slurry" (360 ° C +) Fcc 7.40 coke Fcc 5.49 Total one hundred

The middle distillate fraction obtained after oligomerization is then hydrogenated, hydrogenation is carried out on a nickel sulfide catalyst (LD 541) at 160 ° C, at a hydrogen pressure of 50 bar, VVH 1.5 h ^-l and the ratio of the flow of hydrogen gas to the flow rate of liquid feed 100 Nl / l.

Thus, the implementation of fractions C3, C4 and gasoline for oligomerization can increase the yield of middle distillates by 29.3 mass. %

Example 2 (according to the invention): a combination of the sequence of the installation of soft hydrocracking and installation of FCC with the installation of oligomerization of olefins C3, C4 and gasoline

In Example 2, the FCC unit operates under the same conditions as described for Example 1, but this time the FCC unit is preceded by a soft hydrocracker unit, which is fed with the same raw materials as in Example 1, i.e. straight run VGO.

Operating conditions in the installation of soft hydrocracking are shown in table 6.

Table 6 Operating conditions in a soft hydrocracker, example 2 Soft hydrocracking unit Example 2 Raw material consumption VGO t / h 230

Temperature ° C 365 Vvh h ^-1 1,0 H2 / HC l / l 400 Pressure bar hut 70

For these conditions, the yields of products exiting mild hydrocracking are presented, calculated on raw materials, in table 7.

Table 7 The yields of products obtained on the installation of soft hydrocracking according to example 2 mass % Appointment gasoline (PI-220 ° C) 2.0 into products medium distillates (220-360 ° C) twenty into products hydrotreated VGP 78 at FCC Total one hundred

After catalytic cracking, the yields of products, based on the hydrotreated VGO fraction, change as shown in table 8 below.

Table 8 The yield after catalytic cracking according to example 2 mass % dry gases 2,37 fraction C3 9.92 fraction C4 14.23 gasoline (PI-160 ° C) 42.13 heavy gasoline (160-220 ° C) 10.15 medium distillates (220-360 ° C) 12.14 "Slurry" (360 ° C ⁺ ) 4.45 Coke 4.61 Total one hundred

The olefin content of gasoline PI-160 ° C ^- is equal to 44.0% and a nitrogen content of 20 pbw / mn. The sulfur content is 150 ppm.

The C3 fraction, consisting predominantly of propylene and propane, as well as the C4 fraction, consisting mainly of butenes and butane, and the gasoline fraction (PI-160 ° C) are then sent to the oligomerization unit.

The purification and oligomerization conditions are shown in table 9 below.

Table 9 Operating conditions in purification and oligomerization units Raw material consumption (C3-160 ° C) t / h 119 Cleaning installation The number of molecular sieves NaX t 8.8 Oligomerization unit Temperature ° C 160-250 ^* Pressure bar hut fifty Amount of catalyst Catalyst IP 811 (Axens) t 240 ^{* the} temperature is gradually increased to maintain the activity of the catalyst

The lowest amount of impurities (nitrogen and sulfur) in the feedstock allows very strongly, from 22.1 tons to 8.8 tons, to reduce the number of molecular sieves used in the purification unit, which is in the flow prior to the oligomerization unit.

Thus, the size of the molecular sieve purifier can be significantly reduced.

The product yields after the system "soft hydrocracking, catalytic cracking and oligomerization" of fractions C3 =, C4 =, gasoline, calculated on the raw materials included in the installation of soft hydrocracking, are shown in table 10.

Table 10 The product yields after the system "soft hydrocracking, catalytic cracking and oligomerization", according to example 2 mass % Origin Example 1
State of the art dry gases Fcc 1.85 raffinate oligomerization 4.40 gasoline (PI-220 ° C) soft hydrocracking and oligomerization 32.65 medium distillates (220-360 ° C) soft hydrocracking, FCC and oligomerization 54.03 "Slurry" (360 ° C +) Fcc 3.47 coke Fcc 3.60 Total one hundred

Then the middle distillate fraction is hydrogenated under conditions identical to those in Example 1.

The combination of the sequence of the soft hydrocracking unit (PRET) and the unit (FCC) with the oligomerization unit (OLG) significantly increases the amount of middle distillates obtained. In the basic version, this amount of medium distillate is 45.0 mass. % of FCC feedstock versus 54.03 mass. % in the configuration according to the present invention, that is, there is an increase of 9.03%.

As for the gasoline fraction, its content does not increase due to pre-treatment and even decreases by 1.30%, changing from 33.95 mass. % in the base case up to 32.65 mass. %

Thus, the selectivity for middle distillates compared to gasoline (the ratio of middle distillates / gasoline) improves, increasing from 1.32 to 1.65, that is, the relative increase is 25 mass. %, which is a significant improvement, given the changes in the fuel market.

Claims (9)

1. A method of producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues, in which 4 stages are carried out in series:
a) the pre-treatment stage (PRET), which is carried out at a hydrocracking or hydrotreating unit, which allows reducing the amount of sulfur-containing and nitrogen-containing impurities in the feedstock, as well as the number of diolefins, during which a gasoline fraction of C5-160 ° C is obtained (3), the first fraction of the average distillate (4) with a boiling range of 160-360 ° C and a portion (5) called unconverted, which has essentially the same boiling range as the initial heavy feed,
b) a catalytic cracking step (FCC) of said unconverted portion (5) taken from a pretreatment step (PRET), during which a fraction (7) of dry gases used as fuel is obtained, fraction C3 (8), fraction C4 (9 ), a C5-160 ° C gasoline fraction (10) and a second middle distillate fraction (11), the gasoline fraction (10) being fed to a purification unit (PUR),
c) an oligomerization step (OLG), to which fraction C3 (8), fraction C4 (9) taken from the catalytic cracking unit, and gasoline fraction (10 ') from the purification unit (PUR) are fed and during which fraction C3 / C4 (14), a gasoline fraction of C5-160 ° C (15), which are added to the gasoline pool, and a third middle distillate fraction (16), which is fed to the hydrotreatment unit (HDT),
d) a full hydrogenation step (HDT) of the middle distillate fraction (16) taken from the oligomerization step to achieve compliance with the requirements for commercially available gas oil. 2. A method of producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein the pretreatment unit (PRET) is a mild hydrocracker operating under the following conditions:
- temperature from 350 to 420 ° C,
- pressure from 8 to 12 MPa,
- VVH from 0.3 to 1 h ^-1 ,
- H ₂ / HC from 300 to 800 l / l,
- catalysts based on NiMo, NiCoMo, NiW. 3. A method for producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein the pretreatment unit (PRET) is a hydrotreatment unit operating under the following conditions:
- temperature from 350 to 420 ° C,
- pressure from 4 to 8 MPa,
- VVH from 0.5 to 2 h ^-1 ,
- H ₂ / HC from 150 to 200 l / l,
- catalysts based on NiMo, CoMo, NiCoMo. 4. A method for producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein the catalytic cracking unit (FCC) operates under the following conditions:
when catalytic cracking is carried out in a single upflow reactor, the outlet temperature of the reactor (ROT) is from 450 to 650 ° C, preferably from 470 to 620 ° C, and the C / O ratio is from 2 to 20, preferably from 4 to fifteen,
- when the reactor is a downflow reactor, the reactor outlet temperature (ROT) is from 480 to 650 ° C, and the C / O ratio is from 10 to 50, preferably from 10 to 30. 5. A method for producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein fractionation by fractionation is carried out by distillation in a purification unit (PUR) of a gasoline with FCC to obtain a light fraction depleted in nitrogen compounds, and / or an adsorption step on molecular sieves, under the following conditions:
- temperature from 20 to 50 ° C,
- pressure from 5 to 30 bar,
- VVH from 0.5 to 4 h ^-1 ,
- molecular sieves of the type NaX or NaY. 6. The method of producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein the oligomerization unit (OLG) of gasoline with FCC operates under the following conditions:
- operating temperature from 100 to 350 ° C, preferably from 150 to 270 ° C,
- operating pressure from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, more preferably from 4 to 5 MPa,
- catalysts based on amorphous silicoaluminate, or aluminosilicate, or crystalline zeolite. 7. The method for producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein the oligomerization unit (OLG) of gasoline with FCC operates under the following conditions:
- the operating temperature is from 180 to 350 ° C, preferably from 200 to 270 ° C,
- operating pressure from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, even more preferably from 4 to 5 MPa,
- catalysts based on crystallized zeolite in the case of distillate processing into diesel. 8. The method for producing medium distillates from heavy raw materials (1) such as vacuum gas oil or atmospheric distillation residues according to claim 1, wherein the oligomerization unit (OLG) of gasoline with FCC operates under the following conditions:
- operating temperature from 60 to 200 ° C, preferably from 80 to 180 ° C,
- operating pressure from 1 to 10 MPa (1 MPa = 10 ⁶ Pascal), preferably from 2 to 6 MPa, more preferably from 2 to 4 MPa
- catalysts such as acidic organic resins. 9. The method according to PP. 6-8, in which the gasoline fraction (15) obtained by oligomerization is at least partially returned to the FCC unit in order to maximize the productivity of middle distillates.

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