FR2858981A1 - PROCESS FOR TREATING AN INTERMEDIATE FRACTION FROM VAPOCRACKING EFFLUENTS - Google Patents

Abstract

Process for the treatment of steam cracking effluents, comprising: - the separation of an intermediate fraction comprising gasoline, - a hydrotreatment of this intermediate fraction in an HD1 unit, - a fractionation of the HD1 effluent, to produce a C5 cut and a C6 + cut, - a fractionation of the C6 + cut, to produce a C6-C8 cut and a C9 + cut, - a hydrotreatment of the C6-C8 cut, - a hydrotreatment of the C9 + cut to saturate at least 20% aromatics with excess hydrogen, and obtain a solvent, or a kerosene, or diesel, or domestic fuel cut.

Description

1 2858981

  The present invention relates to a process for treating hydrocarbon steam cracking effluents. The steam cracking process is a well-known petrochemical process, which is the basis of the production of the major intermediates, in particular ethylene and propylene. Steam cracking produces, in addition to ethylene and propylene, significant quantities of less valuable co-products, especially aromatic pyrolysis gasoline, which is found in significant quantities when cracking propane or butane, and even more so. when you crack naphtha or diesel.

  The crude pyrolysis gasoline is often hydrotreated in two stages, with intermediate fractionation to typically produce a C5 cut, a C6-C7-C8 cut, and a C9 + cut.

  By definition, a section Cn is a section consisting essentially of hydrocarbons with n carbon atoms, and a Cn + section is a section composed essentially of hydrocarbons with at least n carbon atoms.

  The C5 cut is generally recycled to the steam cracker, the C6-C7-C8 cut, subsequently denoted C6-C8 (essentially composed of hydrocarbons with 6, 7 or 8 carbon atoms), used as a base for producing aromatics , and the C9 + cut used as a motor gasoline base. The entire C5 + or C6 + cut can also be used as a motor gasoline base, after having undergone a first hydrolysis of dedienization (selective hydrogenation). Typically, the hydrotreatments carried out on the fractions that may contain aromatics are made by preserving these aromatics as much as possible, the content of which is hardly modified. This technical philosophy results from the following facts: - Either a C6-C8 cut used as a base for the production of aromatics is produced, and it is obviously advantageous to preserve these aromatics as much as possible, - or a C6-C8 cut is produced , or C5 +, or C6 + used as a gasoline base, and it is also necessary to preserve as much aromatics as possible to maximize the octane number of gasoline.

  Pyrolysis gasolines, moreover, typically have high sulfur contents, in particular that of the C9 + cut, which is often of the order of 300 ppm 2 weight. However, this sulfur content becomes incompatible with the evolution of standards on the maximum sulfur content of gasoline which tends to fall below 50 ppm, or 30 ppm or 10 ppm weight.

  The high sulfur content of the pyrolysis gasolines therefore poses a delicate technical problem for the steam cracking industry, for the valorization of these species.

  Three approaches are currently being implemented or envisaged to deal with this situation, in particular for existing steam crackers: 1) Modify the two existing hydrotreating units to greatly increase desulphurisation. Suitable desulphurisation catalysts exist, the most commonly used catalysts being mainly based on nickel and molybdenum, or nickel and tungsten or cobalt and molybdenum, supported on alumina.

  2) add a third unit of final desulfurization on the fraction sold as gasoline.

  These two routes lead to significant additional investments, with no gain on the valuation of products, which remain fuel bases of rather poor quality. In addition, the extensive desulphurization is accompanied by a limited reduction of the aromatics content, which is sought to minimize, but which remains unfavorable for the octane number of gasoline, and therefore its valuation. It is also accompanied by a certain reduction in olefins, which is also unfavorable for the octane number of gasoline, and therefore its recovery. The high level of desulphurization will therefore lead to a loss of valuation, compared to the current situation.

  3) yield the gasoline fraction as produced to an oil refinery which will achieve final desulphurization. This option leads to a significant reduction in the price of gasoline thus sold.

  The object of the invention is to find a technically simple solution to the aforementioned problem, and this by requiring a minimum or no modification of existing units, and allowing a high valuation of products.

  To this end, the invention proposes a process for the treatment of hydrocarbon steam cracking effluents, comprising: a) the separation of these effluents to produce in particular an intermediate fraction comprising the greater part at least (that is to say At least 50% by weight) of the pyrolysis gasoline contained in those effluents and composed in its major part at least of hydrocarbons having at least 5 carbon atoms and a final boiling point of less than 310 ° C, (b) a first hydrotreatment of this intermediate fraction in a unit HD1, c) a fractionation of at least a portion of the effluent of the unit HD1, to produce a C5 cut and a C6 + cut, d) a fractionation of a at least part of the C6 + cut, to produce a C6-C8 cut and a C9 + cut, e) a second hydrotreatment of at least a portion of the C6-C8 cut in an HD2 unit to produce a hydrotreated C6-C8 cut , f) a third hydrotreatment of a tank comprising at least a portion of the C9 + cut, and optionally at least a portion of the C6-C8 cut or hydrotreated C6-C8 cut, in an HD3 unit to saturate at least 20%, usually at least 25%, and typically at least 35% by volume of the aromatics included in the feed of the unit HD3 with, in part or preferably all of the excess hydrogen produced by said steam-cracking. It is then possible to produce at the output of HD3 at least one final product from the group consisting of: solvents comprising less than 5% volume of aromatics, kerosene or diesel cuts, or heating oil, or bases for the manufacture of these products . The products in this group have a high valuation, which is not related to the maintenance of a high content of aromatics and olefins, unlike gasoline for which the octane number, related to the content of aromatics and olefins, is an essential parameter. It is therefore possible to obtain high value products without penalty for the reduction of aromatics and olefins, whatever the desired level of desulphurization. On the contrary, the reduction in particular of the aromatics content increases the quality of the products under consideration (purity of the solvents, smoke point of kerosene, cetane number of diesel fuels, combustion capacity of domestic fuel oil).

  Preferably, the feed rate of the unit HD3, and / or the degree of saturation of the aromatics in this unit, are limited so that the hydrogen consumption in HD3 is less than or equal to the quantity of excess hydrogen produced. by steam-cracking, and the hydrogen feeding HD3 (and preferably hydrogen feeding HD1, HD2 and HD3) is provided in full by this excess hydrogen.

  The invention thus makes it possible, by departing from the conventional technical philosophy of preserving the aromatics of the pyrolysis gasoline, to use the excess hydrogen of the steam cracker to change the spectrum of co-products of the steam cracker, and to produce a or several new products of high recovery, which are no longer gasoline, and which eliminate the technical problem related to the amount of sulfur contained in the pyrolysis gasoline.

  In particular, it is possible to produce, at the outlet of HD3, a solvent or a solvent base having at least 60% by volume of naphthenes, at most 5%, and preferably at most 30% by volume of aromatics, and at most 10 ppm by weight of sulfur. It is also possible to produce, at the outlet of HD3, a kerosene or a light gas oil or a kerosene or diesel base, having less than 30%, or less than 20% of aromatics, at most 300 ppm by weight of sulfur, and an interval distillate (ASTM) within the range of [120 C-310 C]. It is also possible to produce a domestic fuel of aromatic content generally less than 50% by volume, or at 30% by volume or even at 20% by volume, with a sulfur content typically of less than 300 ppm by weight, typically having an ASTM distillation range. within the range [120 C-310 C].

  Preferably, the unit HD3 uses at least one catalyst comprising platinum and palladium deposited on a support. It has indeed been found that such catalysts, used in the refinery, but not in the steam-cracking industry, prove to be effective and compatible with the specific compounds present in the pyrolysis gasolines.

  In a particularly advantageous manner, the unit HD3 uses at least one catalyst comprising from 0.1 to 0.30% by weight of platinum, and from 0.2 to 1% and preferably from 0.4 to 0.7% by weight. palladium, deposited on a fluorinated alumina, comprising from 1 to 5% by weight of fluorine. This catalyst makes it possible to operate at high hourly space velocities (VVH), notably comprised between 1 and 6 on these charges of pyrolysis gasolines. Optionally, a conventional catalyst, for example LD 145, a NiMo (nickel / molybdenum) catalyst marketed by Axens, can optionally be optionally used in the guard bed or in the first reactor in the same unit HD3. Finally, it is possible, particularly when the production of deflavored solvents is not sought, to use conventional hydrorefining catalysts, for example of the Ni-Mo, Co-Mo type (for example the CoMo HR406, HR306C type catalysts ( sold by Axens) with a NiMo LD145 type catalyst guard bed (marketed by Axens) or a catalyst which is at least partially saturating the olefins, for example a CoMo type hydrosulfurization catalyst on a guard bed, can also be used in a guard bed. For example, at least 70%, or at least 90%, or at least 95% by weight or more of the olefins present in the feedstock of HD3 can be saturated, for example, the residual olefin content of the products derived from HD 3, according to the invention. , in particular solvent, or kerosene, or diesel, or domestic fuel, or base of one of these products, can be reduced to less than 5% by weight, or preferably less than 1% by weight, or very preferably less than 0.5% by weight, v substantially zero.

  According to a variant of the invention, explained below, the intermediate fraction produced in step a), and the charge of the unit HD3 are not limited to the pyrolysis gasoline, and may have an ASTM endpoint. between 230 and 310 C, and preferably between 250 and 280 C.

  The invention will be explained more specifically in the description of FIGS. 1 and 2.

  Figure 1 shows the main part of an installation according to the method of the invention, this main part representing the pyrolysis gasoline treatment plant, or the intermediate fraction comprising pyrolysis gasoline. The upstream part allowing the primary fractionation of the steam cracking effluents is not represented. Figure 1 is also a simplified representation, 6 2858981 comprising hydrotreating units which have not been detailed (including the possible recycling of hydrotreated feedstock, and hydrogen additions are not shown).

  FIG. 2 represents a more detailed representation of a hydrotreatment unit 5 of the installation of FIG. 1.

  According to FIG. 1, the feedstock, also called the intermediate fraction, according to the invention, is supplied by line 1 and treated in a hydrotreating unit HD1 to carry out in particular a prior dedenization. The dediénisée charge circulates by the line 2 and is fractionated in a distillation column 3 in a fraction C5 circulating by the line 4, typically recycled to steam-cracking, and a C6 + cut flowing through the line 5. This C6 + cut is fractionated in the column of distillation 6 in a C6-C8 fraction (C6-C7-C8), feeding via line 7 a second hydrotreating unit HD2 which performs a thorough desulfurization of the C6-C8 cut, and a deep conversion of olefins. For example, an LD 265 type catalyst marketed by Axens can be used. The treated C6-C8 cut discharged via line 9 can have, for example, less than 1 ppm by weight of sulfur and less than 50 ppm by weight of olefins. It is generally sought to minimize the loss of aromatics in the unit HD2, to maximize their subsequent recovery. The C9 + cut leaving the bottom of the column 6 via the line 8 then feeds a third hydrotreating unit HD3 to produce a desulfurized cut with a low aromatic content evacuated via the line 11. The cut produced is, according to the invention, typically either a kerosene or a diesel fuel (or a base of kerosene or diesel fuel), the aromatic content of which is less than 30% by volume, generally less than 20% by volume, ie a solvent or a solvent base, with an aromatic content of less than 5% volume. When the cut produced is a solvent (or solvent base), it may optionally comprise substantial amounts of C6-C8 hydrocarbons also fed to the unit HD3 via the line 10. The cut produced at the output of HD3 can also be a domestic fuel, or a domestic fuel oil base, typically less than 50% aromatic content, usually less than 30% volume, or even less than 20% volume.

  According to FIG. 2, showing in greater detail the hydrotreating unit HD3, the C9 + cut fed by the line 8 is supplemented with a recycled fraction of hydrotreated product, circulating in the line 8f, and a current hydrogen-rich recycle gas flowing in line 8c. This stream comprises makeup hydrogen fed by a line not shown. The overall stream from the mixture then feeds the hydrotreating reactor R3. The effluent of R3 circulates in the line 8a or it is cooled by means not shown, and enters the separator tank S3. The gas separated in S3 is mainly recycled via line 8c, a fraction being purged by line 8d. The liquid product from S3 circulates in line 8b, to be partially recycled by line 8e and partially discharged via line 11. The hydrotreated product discharged via line 11, which can typically be a solvent, or a cut or base of kerosene or diesel fuel or domestic fuel, is typically stabilized (in means not shown) before storage, to remove light fractions and H2S. Part of the recycled liquid in the line 8e is injected inter-beds in the reactor R3, as a quenching liquid.

  According to the invention, the unit HD3 comprises at least one catalyst making it possible to very efficiently achieve, in a single unit, the desired sulfur and aromatic specifications.

  According to one of the variants of the invention, the catalyst of the unit HD3 comprises in particular at least one platinum / palladium catalyst bed on a fluorinated alumina support. The support may be composed essentially of gamma-alumina and comprise from 1 to 10, preferably from 1 to 7, and very preferably from 3 to 5% by weight of fluorine. The unit HD3 may therefore comprise such a fluorinated alumina support catalyst, arranged in one or more beds, and optionally a first bed or guard bed with a conventional Ni / Mo type catalyst acting pretreatment.

  This platinum / palladium catalyst may preferably comprise between 0.10 and 0.30%, preferably between 0.15 and 0.30%, and very preferably between 0.20 and 0.30% by weight of platinum. as well as generally from 0.2 to 1.0%, and preferably from 0.4 to 0.7% by weight of palladium. The molar ratio of palladium to platinum may especially be between 3 and 8, preferably between 3.5 and 6.

  According to another variant of the invention, the end point of the treated section is modified and increased with respect to a conventional section of pyrolysis gasoline, the end point of which is often between 205 and 220.degree. In this variant of the invention, the final cut of the treated fraction may be higher because the C 9 + cut is then typically intended to be converted into products other than gasoline. Indeed, some solvents, as well as kerosene, diesel or domestic fuel fractions, may have final distillation points (ASTM distillation) greater than 220 ° C.

  The treated fraction may therefore be a long fraction going beyond petrol, having a final point of distillation greater than 220 ° C., for example between 230 ° C. and 310 ° C., in particular between 240 ° C. and 280 ° C. This can be obtained by modifying during the fractionation of the steam cracking effluents in the primary distillation, the cutting point between the gasoline fraction and the fuel fraction of pyrolysis, to leave fractions boiling above about 220 ° C. in the so-called "gasoline" fraction, which becomes intermediate fraction "gasoline + middle distillate".

  It is therefore possible to reduce from 5 to 50%, and often from 10 to 40%, the amount of pyrolysis fuel produced. This is interesting when cracking naphtha or condensates, and even more when cracking heavier loads.

  The process according to the invention thus makes it possible to produce, in particular, one or more of the following products: a solvent (or a solvent base) of ASTM distillation interval typically comprised within, approximately, the interval [ 65 C-250 C], or the range [90 C-240 C] or the range [130 C-230 C], very low aromatics, generally less than 5% by volume, or 3 % volume or even 1% volume, sulfur content typically less than 10 ppm by weight, or even 5 ppm or even 1 ppm.

  a kerosene or a gas oil (or a kerosene or diesel base) of ASTM distillation range typically within the range [120 C-310 C], or the range [130 C- 280 C], or in the range [140 C-250 C], of very low aromatics, generally less than 30% by volume, or even 20% by volume, with a sulfur content of typically less than 300 ppm weight, in particular less than 50 ppm by weight, or even less than 10 ppm by weight, - a domestic fuel (or a heating oil base), of ASTM distillation range typically comprised within the range [120 C-310 C], or the range [130 C-280 C], or the range [140 C-250 C], of aromatics generally less than 50% by volume, or 30% by volume or even 20 % volume, sulfur content typically less than 300 ppm weight, especially less than 50 ppm weight.

  These products are intended for explicit uses and are therefore neither gasoline bases, nor products intended to be sold to be transformed into gasoline bases, for example by complementary desulfurization. This new production requires an investment, but allows to have new and important outlets, for high recovery products, for which a significant reduction of the aromatics and olefins content does not present disadvantages, and is even desirable, and can typically be obtained through the excess hydrogen of the steam cracker.

EXAMPLES:

  The following examples explain, in a non-limiting manner, catalysts and operating conditions that can be used in the process according to the invention: EXAMPLE 1 Processed feedstock: Steam-cracking effluents of naphtha are fractionated in a plant for treating these effluents, including distillation. primary, to produce in particular a pyrolysis gasoline cut, comprising the C5 cut and heavier hydrocarbons to an ASTM endpoint of 210 C.

  This cut is the "intermediate fraction" of the process according to the invention, and has the following characteristics: Distillation range ASTM: 20 - 219 C Density: 0.82 2858981 Sulfur content: 400 ppm weight Composition (% wt): mono - aromatics: 65% di-aromatics: 1% di-olefins (dienic compounds): 15% mono-olefins: 6% saturated compounds: balance.

  This pyrolysis gasoline feedstock is treated according to the process scheme described in FIG. 1. The feed fed to the hydrotreating unit HD3 is the C9 + feed, without C6 / C8 cutting input from HD2, the line 10 not being used.

  Catalyst and operating conditions of the first hydrotreating unit HD1: Catalyst: palladium on alumina catalyst, comprising 0.30% by weight of palladium.

  The catalyst is placed in two beds in a reactor, with a device for injecting a fluid intended in particular to cool the reaction mixture between the two beds.

  Reactor outlet temperature: 110 C reactor outlet pressure: 3.0 MPa 20 VVH (hourly space velocity): 2.4 h-1 Hydrogen content (total reactor inlet gas): 90 Nm3 of hydrogen / m3 of feedstock. The unused gas is separated and sent as an add-on to the second unit HD2.

  Recycle rate of the feedstock: 2 (two volumes of hydrotreated product leaving HD1 are recycled for a volume of fresh feed supplied with HD1, to limit the increase in temperature due to the exothermicity of the reaction).

  Catalyst and operating conditions of the second HD2 hydrotreatment unit 2858981 Catalyst: 2 catalyst beds are used. The first bed contains a catalyst of the Ni / Mo type on alumina: LD 145, marketed by AXENS. The second bed contains a catalyst of Co / Mo type on alumina: HR 306 C, sold by AXENS.

  Reactor outlet temperature: 300 C Reactor output pressure 2.5 MPa VVH (hourly space velocity): 2 h-1 Additional hydrogen rate: 40 Nm3 / m3 load, hydrogen recycle rate 400 Nm3 / m3 gas No intermediate cooling is performed.

  Catalyst and operating conditions of the third hydrotreatment unit HD3: Advanced treatment of the HD3 feed is carried out to obtain in a single step a very low aromatic content cut having the specifications of a commercial solvent.

  The loading of HD3 has the following composition: Distillation range ASTM: 145-218 ° C. Density: 0.9 Sulfur content: 500 ppm by weight Composition: 53% by weight aromatics including 3% diaromatics, 35% olefins the rest being saturated compounds.

  Catalyst: platinum / palladium on fluorinated alumina, containing% by weight: 0.2% platinum; 0.4% palladium; 1.1% chlorine; 4.0% of fluorine.

  Methods for the preparation of platinum / palladium catalysts on fluorinated alumina are described in European Patent Application EP 1 099 477 A1.

  Reactor inlet temperature: 290 C, Reactor outlet temperature: 330 C, Reactor outlet pressure: 4.0 MPa VVH: 2 h-1 12 2858981 Recycling rate of hydrogen including make-up hydrogen ( total gas rich in hydrogen: inlet + quenching): 400 Nm3 / m3 of charge of unit HD3.

  Recycling rate of the unit: 5 (recycling of liquid effluent in mass ratio relative to the load). 90% of the recycle is mixed with the feed, and 10% is injected in inter-catalytic beds to adjust the thermal profile. The recycling of liquid is in fact made necessary by the heat released during the hydrogenation.

  The results after hydrotreatment in the unit HD3 are as follows: A solvent with an aromatic content equal to 5% by volume and a distillation range of 143-208 C.

  Sulfur content of the solvent: <10 ppm by weight. EXAMPLE 2 Example 1 is repeated, but with a long charge, end point ASTM 250 C. This is obtained by modifying the operating parameters of the treatment of the steam cracking effluents, so that the fractionation leaves with the pyrolysis gasoline fractions. a little heavier than gasoline.

  In particular, it is possible to use a slightly higher temperature in the primary fractionation tower and / or to increase the stripping a little.

  We can then increase the C9 + fraction feeding HD3, and use, with the same catalyst, milder conditions than in Example 1, in particular: Reactor inlet temperature: 290 C, reactor outlet temperature: 330 C, Reactor outlet pressure: 4.0 MPa VVH: 4 h -1 Recycle hydrogen content including make-up hydrogen (hydrogen-rich total gas: inlet + quench): 400 Nm 3 / m3 of unit charge HD3.

  Recycling rate (recycling of liquid effluent with the load and between beds in order to adjust the thermal profile): 3 en masse, of which 0.45 in inter-beds.

  The results after hydrotreating in unit HD3 are as follows: Aromatic content of the product obtained: 19.5% by volume.

  Distillation range ASTM: 144 - 241 C Sulfur content: <10 ppm by weight.

  It is thus possible to obtain a base of kerosene, diesel fuel or domestic fuel, and to reduce the production of pyrolysis fuel.

  The invention may also use other hydrotreatment catalysts, and / or other operating conditions, or other characteristics not described but obvious to those skilled in the art.

Claims (10)

  A process for treating hydrocarbon steam cracking effluents, comprising: a) separating said effluents to produce an intermediate fraction comprising at least the major part of the pyrolysis gasoline included in these effluents, and composed for its most of compounds having at least 5 carbon atoms and a final boiling point of less than 310 ° C, b) a first hydrotreatment of this intermediate fraction in a unit HD1, c) a fractionation of at least a part of the effluent of the unit HD1, to produce a C5 cut and a C6 + cut, d) a fractionation of at least a portion of the C6 + cut, to produce a C6-C8 cut and a C9 + cut, e) a second hydrotreatment at least a portion of the C6-C8 cut in a unit HD2 to produce a hydrotreated C6-C8 cut; f) a third hydrotreatment of a filler comprising at least a portion of the C9 + cut, and optionally a portion thereof; at least of the C6-C cut 8 or the hydrotreated C6-C8 cut, in an HD3 unit to saturate at least 20% by volume of the aromatics included in the feed of the unit HD3 with, in part or in full, the excess hydrogen produced by said steam-cracking, and producing at the output of HD3 at least one final product from the group consisting of solvents comprising less than 5% of aromatics, kerosene or diesel cuts, or domestic fuel, or bases for the manufacture of these products.   2. The method of claim 1 wherein limiting the feed rate of the unit HD3, and / or the degree of saturation of aromatics in this unit, so that the hydrogen consumption in HD3 is less than or equal to the amount excess hydrogen produced by the steam cracking, and that the hydrogen feeding HD3 is provided in full by this excess hydrogen.   3. Method according to one of claims 1 and 2, wherein there is produced at the outlet of HD3 a solvent or a solvent base having at least 60% by volume of naphthenes, at most 5% by volume of aromatics, and at most ppm weight of sulfur.   4. Method according to one of claims 1 and 2, wherein is produced at the output of HD3 kerosene or a gas oil or a base of kerosene or gas oil having less than 30% aromatic volume, at most 300 ppm weight of sulfur, and an ASTM distillation range within the range [120 C-310 C].   5. Method according to one of claims 1 and 2, wherein is produced at the output of HD3 a domestic fuel or a home heating oil base having less than 50% by volume of aromatics, at most 300 ppm by weight of sulfur, and a ASTM distillation range in the range [120 C-310 C].   6. Method according to one of claims 1 to 6, wherein the HD3 unit uses at least one catalyst comprising platinum and palladium deposited on a support.   7. Process according to claim 6, in which the unit HD3 uses at least one catalyst comprising 0.10 to 0.30% by weight of platinum and 0.2 to 1% by weight of palladium deposited on a fluorinated alumina. comprising from 1 to 5% by weight of fluorine.   8. The process according to one of claims 1 to 6, wherein the intermediate fraction produced in step a), and the feed of unit HD3 have an ASTM end point between 230 and 310 ° C.   9. Method according to one of the preceding claims, wherein said final product has an olefin content of less than 1% by weight.   16 2858981 10. Final product of the group consisting of solvents containing less than 5% aromatics, kerosene, diesel or domestic fuel cuts, or bases for the manufacture of these products, the final product having been obtained by the process   according to one of claims 1 to 9.