PATENT
Process for converting a heavy feed using a catalytic
cracking unit and a step for selective hydrogenation of the gasoline obtained
from catalytic cracking (IFP Energies Nouvelles)
Publication number
US20130211161 A1
Publication type
Application
Application number
US 13/767,072
Publication date
Aug 15, 2013
Inventors
Frédéric FEUGNET, Francois Hugues, Natacha Touchais, Hugues Dulot, Annick
Pucci,
Original Assignee
IFP Energies Nouvelles
Abstract
The present invention describes a process for
converting a heavy feed which is flexible for the production of propylene,
gasoline and middle distillate.
The process uses a catalytic cracking unit and a
unit for the oligomerization of C4 to C9 olefins. The process of the invention
includes selective hydrogenation of the unrefined gasoline cut obtained from
the catalytic cracking unit and separation between a light gasoline cut and a
heavy gasoline cut, the light gasoline being directed to the oligomerization
unit.
Description
FIELD OF THE INVENTION
The invention relates to a process for converting a heavy hydrocarbon feed
exhibiting great flexibility for the production of middle distillate, gasoline
and propylene.
The process of the present invention uses a catalytic cracking unit (FCC).
Generally, such catalytic cracking units are optimized with a view to the production
of light products: liquefied gas (or LPG), light olefins and gasoline, in order
to satisfy the needs of either the market for polymers obtained from the
polymerization of light olefins or gasoline consumption requirements in the
automotive industry.
Currently, given the substantial increase in the use of diesel in the
automotive industry, the demand for products of the middle distillate type has
increased substantially.
As a consequence, another mode of operation of the catalytic cracking unit has
been developed, with a view to orientating production towards middle
distillates.
The flexibility in and improvement to yields as regards one or other of the
three products are accomplished by adding an oligomerization unit treating C4
to C9 olefins obtained from FCC or from other additional sources such as the
coking unit, visbreaking unit, the unit for converting methanol into olefins or
any other process for converting alcohols into olefins, steam cracking or
indeed the Fischer-Tropsch synthesis unit, or from the paraffin dehydrogenation
unit, used alone or as a mixture.
A description of coking, visbreaking and steam cracking units can be found in
the reference work “Raffinage et génie chimique” [Refining and chemical
engineering] by P Wuithier, published by Technip.
The oligomerization unit requires a purification step in order to reduce the
quantity of nitrogen-containing compounds, which are poisonous to the reaction.
The dienes and sulphur-containing compounds present in the oligomerization
feed, which are inhibitors or poisonous to the reaction, are generally not
reduced in that purification step and have a negative impact on the cycle
period of the catalyst.
The present invention essentially consists of adding a step for selective
hydrogenation of the gasoline leaving the FCC (i.e. upstream of the
oligomerization unit), which can be used to limit the quantity of those
inhibitors and thus increase the cycle period of the oligomerization catalyst
without altering the distribution of the desired products.
EXAMINATION OF THE PRIOR ART
Patent application FR 2 935 377 concerns a process for converting a hydrocarbon
feed termed a heavy feed with a view to the co-production of propylene and of
gasoline with a minimum yield. The process of that invention comprises at least
two reaction steps, a first, catalytic cracking step and a second step for the
oligomerization of C3 and C4 olefins or C4 olefins or C4 and C5 olefins from
the catalytic cracking step.
The process of the cited patent can be used to carry out two types of
production, corresponding to two distinct working modes:
• ◦a “maxi propylene” mode, corresponding to maximum production of propylene
while keeping the gasoline yield to a minimum, or even slightly increased
compared to the potential yield from the catalytic cracking unit alone; or
◦a “maxi gasoline” mode, corresponding to maximum production of gasoline
without the production of propylene.
In that patent, only C3, C4 and C5 olefins are mentioned.
Application FR 10/04585 describes a process for converting a heavy feed that
can be used to improve the selectivity for middle distillate. The process uses
a catalytic cracking unit followed by one or more units for the oligomerization
of olefins containing 2 to 9 carbon atoms in order, preferably, to produce an
additional middle distillate cut. The light portion of the oligomerizate
produced, which cannot be incorporated into the middle distillate cut, is
recycled to the FCC for cracking into light olefins which return to the
oligomerization units as a supplement to the olefins of the feed in order,
preferably, to form heavy oligomerizates which can be incorporated into the
middle distillate cut.
In that application, the oligomerized C2 to C9 cut is constituted by a portion
of the FCC products without carrying out any other processes before
oligomerization.
Patent FR 2 797 639 B1 describes a process for the production of gasoline with
a low sulphur content, comprising a step for selective hydrogenation of
diolefins and optionally at least one step aimed at increasing the molecular
weight of the light sulphur-containing products present in the gasoline. The
cited patent describes separating the gasoline into two fractions: light
gasoline and heavy gasoline, and can be used to produce low sulphur gasolines.
Patent FR 2 895 416 B1 describes a catalytic system that can be used to carry
out joint selective hydrogenation of polyunsaturated compounds into
monounsaturated compounds contained in the gasolines, as well as to make light
sulphur-containing compounds heavier by reaction with the unsaturated
compounds.
In the cited patents, the intended aim is to obtain a gasoline without
substantial loss of octane number and with a low sulphur content, with the
gasoline entering the fuel pool.
In the context of the present invention, using a selective hydrogenation unit
on the gasoline cut obtained from the catalytic cracking unit before separating
the light gasoline and the heavy gasoline means that a light C5-C9 gasoline cut
can be obtained with a reduced quantity of diolefins and also of sulphur, which
can be sent directly to the final purification unit (reduction of
nitrogen-containing compounds) preceding the oligomerization unit. By using it
this way, the cycle period for the oligomerization catalysts is significantly
improved without altering the distribution of the desired products.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 represents a layout of the process of the invention. The dashed lines
represent the optional supplies or recycles. The notations assigned to the
units are introduced in the remainder of the text.
BRIEF DESCRIPTION OF THE INVENTION
The invention consists in a process for converting a heavy hydrocarbon feed
with great flexibility for the production of middle distillate, gasoline and
propylene, using a catalytic cracking unit (FCC) followed by a unit for the
selective hydrogenation (SHU) of the gasoline obtained from the FCC unit.
The gasoline obtained from the catalytic cracking unit has an end point that
differs depending on whether a maxi gasoline or a maxi distillate mode is
desired.
• ◦for the maxi gasoline mode, the ex FCC gasoline is preferentially defined as
C5-220° C.;
◦for the maxi distillate mode, the ex FCC mode is preferentially defined as
C5-150° C.
This distinction is important since, given the flexibility of the process, it
is essential to keep in mind the definition of the FCC outlet gas which should
be taken into account in each case.
The process of the invention may also function in accordance with a “maxi
propylene” mode, which is compatible with any end point of the gasoline in the
range 150° C. to 220° C. This “maxi propylene” mode is essentially obtained by
the operating conditions of the catalytic cracking unit (known as “high
severity” conditions) and by using a catalyst incorporating a certain
proportion of ZSM-5 zeolite.
Free Full Text Source: http://www.google.com/patents/US20130211161
Showing posts with label IFP. Show all posts
Showing posts with label IFP. Show all posts
Wednesday, October 2, 2013
Process For The Production Of Middle Distillate From A Conventional Heavy Feedstock Including A Step For Selective Hydrogenation Of The Ex Fcc Hco Cut (IFP Energies Nouvelles)
PATENT
Process For The Production Of Middle Distillate From A Conventional Heavy Feedstock Including A Step For Selective Hydrogenation Of The Ex Fcc Hco Cut (IFP Energies Nouvelles)
United States Patent Application 20130137907
Inventors:
Feugnet, Frederic (Lyon, FR)
Hudebine, Damien (Lyon, FR)
Roux, Romain (Rueil Malmaison, FR)
Application Number:
13/683134
Publication Date:
05/30/2013
Assignee:
IFP Energies Nouvelles (Rueil-Malmaison Cedex, FR)
Abstract:
The present invention describes a process for the conversion of a heavy feedstock for improving the production and selectivity for middle distillate, said process using a catalytic cracking unit followed by a unit for selective hydrogenation of the heavy distillate cut (HCO) or any other cut rich in triaromatic compounds before recycling it to the FCC reaction zone in order to maximize the middle distillate cut.
FIELD OF THE INVENTION
The present invention relates to a process for the conversion of a heavy hydrocarbon feedstock with improved selectivity for middle distillate. More precisely, the process of the present invention can be used to co-produce gasoline in a reduced yield, and to improve the production of middle distillate by at least 2% by weight with respect to the feedstock, which is highly significant having regard to the tonnages involved in the process.
Historically, catalytic cracking units, known by the abbreviation FCC (fluid catalytic cracking), are optimized for the production of light products—liquefied gas (or LPG), light olefins and gasoline—in order to satisfy the polymer market or the requirements of gasoline consumption in the automobile market.
In that type of function, the production of gas oil bases remains limited.
Currently, because of huge increases in the use of diesel on the automobile market, the demand for gas oil type products has increased greatly. As a consequence, it is becoming ever more necessary to orientate refinery production towards the production of gas oil bases and to limit the production of gasoline. Since FCC units, which are present in almost half of refineries, are on the one hand the principal source of gasoline and on the other hand a major source of light olefins, it is imperative to be able to convert them into units favouring the production of gas oils. The skilled person encapsulates this trend by using the term “maxi LCO mode FCC”, where LCO in this case designates the middle distillate cut, i.e. a cut with a distillation range in the range 220° C. to 360° C.
The process of the present invention can be used 1) to improve the production of gas oil bases in fluidized bed catalytic cracking units, 2) limit the production of heavy cuts that are difficult to upcycle, and also 3) limit the production of gasoline, since this cut is not wanted for maxi LCO mode running.
The present invention essentially consists of a concatenation of a FCC unit with one or more units for the selective hydrogenation of the heavy distillate cut (HCO) produced in the FCC, or any other cut which is rich in triaromatic compounds obtained, for example, from visbreaking, coking, “H-oil” units or the Pygas cut from a steam cracking unit.
This heavy distillate cut is selectively hydrotreated in order to minimize the proportion of triaromatics, while maximizing the ratio of diaromatics to monoaromatics. It is then recycled to the reaction zone of the FCC in order to significantly increase the yield of middle distillate (LCO) and also the selectivity of that cut with respect to gasoline while limiting the production of additional coke.
In the context of the present invention, the “middle distillate” cut (LCO) has a distillation range in the range 220° C. to 360° C.
The FCC process can be used to convert heavy hydrocarbon feedstocks with an initial boiling point which is generally more than 340° C. into lighter hydrocarbon fractions, in particular a gasoline cut, by cracking molecules of the heavy feedstock in the presence of an acid catalyst. FCC also produces liquefied petroleum gas (LPG) in large quantities with high olefins contents.
The process of the present invention may also generally be presented as a process for the production of middle distillate with an improvement of the selectivity for middle distillate over gasoline.
The present invention employs a catalytic cracking unit followed by one or more units for selective hydrogenation of the heavy distillate cut with a distillation range in the range 320° C. to 490° C. and primarily composed of triaromatics. This cut is usually denoted (HCO), an abbreviation which we shall retain in the text below.
The selective hydrogenation unit may also treat any other cut which is rich in triaromatic compounds obtained, for example, from visbreaking, coking, an H-oil unit or the Pygas cut from a steam cracking unit.
The process of the invention essentially consists of a concatenation of a catalytic cracking unit and one or more hydrotreatment units which selectively treat the HCO cut, with a recycle of the hydrotreated HCO cut to the catalytic cracking unit, as well as fine-tuning the hydrotreatment operating conditions in order to selectively transform the triaromatics of the feedstock for the unit into diaromatics, while maximizing the diaromatics to monoaromatics ratio. When recycled to the FCC reaction zone, the selectively hydrotreated HCO cut can be used to very significantly improve the selectivity for middle distillate of the process as well as limit the additional production of gasoline and coke.
The present invention is compatible with all catalytic cracking reactor technologies, whether it is gas-solid upflow technology or downflow technology.
The catalytic cracking unit employed in the present process may be classified into a number of modes, with a single reactor or a plurality of reactors, each reactor being able to operate in upflow or in downflow mode.
In the case of a plurality of selective hydrogenation units associated with the catalytic cracking unit, they can be arranged in series or in parallel.
EXAMINATION OF THE PRIOR ART
The prior art teaches recycling the cut known as the heavy distillate (HCO) to the reaction zone of the FCC, but not recycling said selectively hydrotreated cut with a view to maximizing middle distillate formation. One essential difference of the present invention over the prior art process cited above pertains precisely to the selective nature of the hydrogenation and to fine-tuning its operating conditions.
Patent FR 10/04 585 describes a process for the conversion of a heavy feedstock that can be used to improve the selectivity for middle distillate by using a catalytic cracking unit followed by one or more olefin oligomerization units in order to preferentially produce an additional middle distillate cut.
The present invention consists of a concatenation of a catalytic cracking unit (FCC) and one or more units for the selective hydrogenation of heavy distillate in order to significantly improve the production of middle distillate and at the same time to improve the selectivity for middle distillate over gasoline while at the same time limiting the formation of additional coke.
BRIEF DESCRIPTION OF THE INVENTION
The invention concerns a process for the conversion of a “heavy” hydrocarbon feedstock, i.e. constituted by hydrocarbons with a boiling point of more than approximately 340° C., with a view to improving the production of middle distillate and of reducing the production of gasoline.
The term “middle distillate”, denoted LCO, means a cut with a distillation range in the range 220° C. to 360° C.
The term “gasoline” means the cut with a distillation range of 70° C. to 150° C.
The process of the invention comprises at least two reaction steps, a first catalytic cracking step to process a heavy hydrocarbon feedstock such as a vacuum distillate or an atmospheric residue, or even in some cases a vacuum residue, and a second step for selective hydrogenation of the heavy distillate cut resulting from FCC, denoted HCO, alone or as a mixture with any other cut which is rich in triaromatic compounds obtained, for example, from visbreaking, coking, “H-oil” type units or the Pygas cut from a steam cracking unit.
The selective nature of the hydrogenation of the heavy distillate cut (HCO) can be used to limit the formation of monoaromatics which increase production of the gasoline cut after cracking in the FCC riser, the gasoline cut not being wanted in the maxi LCO operational mode, which is precisely the mode employed in the present invention.
The transformation of triaromatics can be employed to produce diaromatics which are vital to the production of LCO, but also to limit the formation of coke, a major product of these compounds after passing through the FCC. In the end, selective hydrogenation of the heavy distillate cut (HCO) can be used to substantially improve the middle distillate (LCO) to gasoline selectivity compared with a recycle of that cut to the FCC without hydrotreatment or with conventional hydrotreatment.
In the remainder of the text, the terms “hydrotreatment” and “selective hydrogenation” should be considered to be synonymous. Thus, both “hydrotreated HCO cut” and “selectively hydrogenated HCO cut” will be employed interchangeably.
The process of the invention can be used to satisfy two objectives:
• ◦upcycle the heavy distillate cut (HCO) or any cut which is rich in triaromatics, limiting the production of additional coke thereby;
◦increase the production of middle distillate (LCO) at the same time as the middle distillate to gasoline selectivity.
The middle distillate cut (LCO) corresponds to a hydrocarbon cut with a distillation range in the range 220° C. to 360° C.
The primary aim of upgrading the heavy distillate cut (HCO) produced in the FCC or any cut which is rich in triaromatics is achieved by sending that cut to one or more hydrogenation units in order to reduce its triaromatics content, coke precursors, and heavy compounds that cannot be upgraded after recycling to the FCC reaction zone.
The second aim in improving the production of middle distillate (LCO) and the middle distillate to gasoline selectivity is obtained by fine-tuning the operating conditions for the selective hydrogenation of the ex FCC HCO cut in order to selectively transform the triaromatic compounds into diaromatics, middle distillate precursors, while minimizing the production of monoaromatics, which are gasoline precursors.
The heavy hydrocarbon feedstock is cracked in a fluidized bed catalytic cracking reactor in the presence of a cracking catalyst.
The heavy distillate cut (HCO) or any other cut which is rich in triaromatic compounds is selectively hydrotreated in the presence of a hydrotreatment catalyst composed of one or more metals from group VIB, preferably molybdenum or tungsten, usually associated with one or more metals from group VIII, preferably nickel or cobalt, deposited on an amorphous mineral support, preferably alumina, silica, silica-alumina, magnesia, clays and mixtures of at least two of these elements.
The support may also comprise other compounds, for example, such as oxides selected from the group formed by boron oxide, zirconia, titanium oxide and phosphoric anhydride. The catalyst may be fresh, partially coked or regenerated.
It is possible, for example, to use a catalyst comprising 1% to 10% by weight of nickel, preferably 1% to 5% by weight of nickel (expressed as nickel oxide, NiO) associated with 1% to 30% by weight of molybdenum, preferably 5% to 20% by weight of molybdenum (expressed as molybdenum oxide, MoO3) on an alumina support.
The hydrotreated heavy distillate fraction from selective hydrogenation is cracked with the same cracking catalyst, separately or as a mixture with the heavy hydrocarbon feedstock.
The effluents from catalytically cracking the two feedstocks are sent to a common fractionation zone and the catalyst used for cracking the two feedstocks is regenerated in a common regeneration zone.
As will be disclosed in the next paragraph, the catalytic cracking unit may be classified into a number of modes, with a single reactor processing the heavy hydrocarbon feedstock and the selectively hydrotreated heavy distillate (hydrotreated HCO), or two reactors, one processing the heavy hydrocarbon feedstock, and the other the selectively hydrotreated heavy distillate (hydrotreated HCO).
In addition, each reactor may operate in upflow or downflow mode.
In the case of a plurality of selective hydrotreatment units associated with the catalytic cracking unit, they may be arranged in series or in parallel.
Free Full Text Source: http://www.freepatentsonline.com/y2013/0137907.html
Process For The Production Of Middle Distillate From A Conventional Heavy Feedstock Including A Step For Selective Hydrogenation Of The Ex Fcc Hco Cut (IFP Energies Nouvelles)
United States Patent Application 20130137907
Inventors:
Feugnet, Frederic (Lyon, FR)
Hudebine, Damien (Lyon, FR)
Roux, Romain (Rueil Malmaison, FR)
Application Number:
13/683134
Publication Date:
05/30/2013
Assignee:
IFP Energies Nouvelles (Rueil-Malmaison Cedex, FR)
Abstract:
The present invention describes a process for the conversion of a heavy feedstock for improving the production and selectivity for middle distillate, said process using a catalytic cracking unit followed by a unit for selective hydrogenation of the heavy distillate cut (HCO) or any other cut rich in triaromatic compounds before recycling it to the FCC reaction zone in order to maximize the middle distillate cut.
FIELD OF THE INVENTION
The present invention relates to a process for the conversion of a heavy hydrocarbon feedstock with improved selectivity for middle distillate. More precisely, the process of the present invention can be used to co-produce gasoline in a reduced yield, and to improve the production of middle distillate by at least 2% by weight with respect to the feedstock, which is highly significant having regard to the tonnages involved in the process.
Historically, catalytic cracking units, known by the abbreviation FCC (fluid catalytic cracking), are optimized for the production of light products—liquefied gas (or LPG), light olefins and gasoline—in order to satisfy the polymer market or the requirements of gasoline consumption in the automobile market.
In that type of function, the production of gas oil bases remains limited.
Currently, because of huge increases in the use of diesel on the automobile market, the demand for gas oil type products has increased greatly. As a consequence, it is becoming ever more necessary to orientate refinery production towards the production of gas oil bases and to limit the production of gasoline. Since FCC units, which are present in almost half of refineries, are on the one hand the principal source of gasoline and on the other hand a major source of light olefins, it is imperative to be able to convert them into units favouring the production of gas oils. The skilled person encapsulates this trend by using the term “maxi LCO mode FCC”, where LCO in this case designates the middle distillate cut, i.e. a cut with a distillation range in the range 220° C. to 360° C.
The process of the present invention can be used 1) to improve the production of gas oil bases in fluidized bed catalytic cracking units, 2) limit the production of heavy cuts that are difficult to upcycle, and also 3) limit the production of gasoline, since this cut is not wanted for maxi LCO mode running.
The present invention essentially consists of a concatenation of a FCC unit with one or more units for the selective hydrogenation of the heavy distillate cut (HCO) produced in the FCC, or any other cut which is rich in triaromatic compounds obtained, for example, from visbreaking, coking, “H-oil” units or the Pygas cut from a steam cracking unit.
This heavy distillate cut is selectively hydrotreated in order to minimize the proportion of triaromatics, while maximizing the ratio of diaromatics to monoaromatics. It is then recycled to the reaction zone of the FCC in order to significantly increase the yield of middle distillate (LCO) and also the selectivity of that cut with respect to gasoline while limiting the production of additional coke.
In the context of the present invention, the “middle distillate” cut (LCO) has a distillation range in the range 220° C. to 360° C.
The FCC process can be used to convert heavy hydrocarbon feedstocks with an initial boiling point which is generally more than 340° C. into lighter hydrocarbon fractions, in particular a gasoline cut, by cracking molecules of the heavy feedstock in the presence of an acid catalyst. FCC also produces liquefied petroleum gas (LPG) in large quantities with high olefins contents.
The process of the present invention may also generally be presented as a process for the production of middle distillate with an improvement of the selectivity for middle distillate over gasoline.
The present invention employs a catalytic cracking unit followed by one or more units for selective hydrogenation of the heavy distillate cut with a distillation range in the range 320° C. to 490° C. and primarily composed of triaromatics. This cut is usually denoted (HCO), an abbreviation which we shall retain in the text below.
The selective hydrogenation unit may also treat any other cut which is rich in triaromatic compounds obtained, for example, from visbreaking, coking, an H-oil unit or the Pygas cut from a steam cracking unit.
The process of the invention essentially consists of a concatenation of a catalytic cracking unit and one or more hydrotreatment units which selectively treat the HCO cut, with a recycle of the hydrotreated HCO cut to the catalytic cracking unit, as well as fine-tuning the hydrotreatment operating conditions in order to selectively transform the triaromatics of the feedstock for the unit into diaromatics, while maximizing the diaromatics to monoaromatics ratio. When recycled to the FCC reaction zone, the selectively hydrotreated HCO cut can be used to very significantly improve the selectivity for middle distillate of the process as well as limit the additional production of gasoline and coke.
The present invention is compatible with all catalytic cracking reactor technologies, whether it is gas-solid upflow technology or downflow technology.
The catalytic cracking unit employed in the present process may be classified into a number of modes, with a single reactor or a plurality of reactors, each reactor being able to operate in upflow or in downflow mode.
In the case of a plurality of selective hydrogenation units associated with the catalytic cracking unit, they can be arranged in series or in parallel.
EXAMINATION OF THE PRIOR ART
The prior art teaches recycling the cut known as the heavy distillate (HCO) to the reaction zone of the FCC, but not recycling said selectively hydrotreated cut with a view to maximizing middle distillate formation. One essential difference of the present invention over the prior art process cited above pertains precisely to the selective nature of the hydrogenation and to fine-tuning its operating conditions.
Patent FR 10/04 585 describes a process for the conversion of a heavy feedstock that can be used to improve the selectivity for middle distillate by using a catalytic cracking unit followed by one or more olefin oligomerization units in order to preferentially produce an additional middle distillate cut.
The present invention consists of a concatenation of a catalytic cracking unit (FCC) and one or more units for the selective hydrogenation of heavy distillate in order to significantly improve the production of middle distillate and at the same time to improve the selectivity for middle distillate over gasoline while at the same time limiting the formation of additional coke.
BRIEF DESCRIPTION OF THE INVENTION
The invention concerns a process for the conversion of a “heavy” hydrocarbon feedstock, i.e. constituted by hydrocarbons with a boiling point of more than approximately 340° C., with a view to improving the production of middle distillate and of reducing the production of gasoline.
The term “middle distillate”, denoted LCO, means a cut with a distillation range in the range 220° C. to 360° C.
The term “gasoline” means the cut with a distillation range of 70° C. to 150° C.
The process of the invention comprises at least two reaction steps, a first catalytic cracking step to process a heavy hydrocarbon feedstock such as a vacuum distillate or an atmospheric residue, or even in some cases a vacuum residue, and a second step for selective hydrogenation of the heavy distillate cut resulting from FCC, denoted HCO, alone or as a mixture with any other cut which is rich in triaromatic compounds obtained, for example, from visbreaking, coking, “H-oil” type units or the Pygas cut from a steam cracking unit.
The selective nature of the hydrogenation of the heavy distillate cut (HCO) can be used to limit the formation of monoaromatics which increase production of the gasoline cut after cracking in the FCC riser, the gasoline cut not being wanted in the maxi LCO operational mode, which is precisely the mode employed in the present invention.
The transformation of triaromatics can be employed to produce diaromatics which are vital to the production of LCO, but also to limit the formation of coke, a major product of these compounds after passing through the FCC. In the end, selective hydrogenation of the heavy distillate cut (HCO) can be used to substantially improve the middle distillate (LCO) to gasoline selectivity compared with a recycle of that cut to the FCC without hydrotreatment or with conventional hydrotreatment.
In the remainder of the text, the terms “hydrotreatment” and “selective hydrogenation” should be considered to be synonymous. Thus, both “hydrotreated HCO cut” and “selectively hydrogenated HCO cut” will be employed interchangeably.
The process of the invention can be used to satisfy two objectives:
• ◦upcycle the heavy distillate cut (HCO) or any cut which is rich in triaromatics, limiting the production of additional coke thereby;
◦increase the production of middle distillate (LCO) at the same time as the middle distillate to gasoline selectivity.
The middle distillate cut (LCO) corresponds to a hydrocarbon cut with a distillation range in the range 220° C. to 360° C.
The primary aim of upgrading the heavy distillate cut (HCO) produced in the FCC or any cut which is rich in triaromatics is achieved by sending that cut to one or more hydrogenation units in order to reduce its triaromatics content, coke precursors, and heavy compounds that cannot be upgraded after recycling to the FCC reaction zone.
The second aim in improving the production of middle distillate (LCO) and the middle distillate to gasoline selectivity is obtained by fine-tuning the operating conditions for the selective hydrogenation of the ex FCC HCO cut in order to selectively transform the triaromatic compounds into diaromatics, middle distillate precursors, while minimizing the production of monoaromatics, which are gasoline precursors.
The heavy hydrocarbon feedstock is cracked in a fluidized bed catalytic cracking reactor in the presence of a cracking catalyst.
The heavy distillate cut (HCO) or any other cut which is rich in triaromatic compounds is selectively hydrotreated in the presence of a hydrotreatment catalyst composed of one or more metals from group VIB, preferably molybdenum or tungsten, usually associated with one or more metals from group VIII, preferably nickel or cobalt, deposited on an amorphous mineral support, preferably alumina, silica, silica-alumina, magnesia, clays and mixtures of at least two of these elements.
The support may also comprise other compounds, for example, such as oxides selected from the group formed by boron oxide, zirconia, titanium oxide and phosphoric anhydride. The catalyst may be fresh, partially coked or regenerated.
It is possible, for example, to use a catalyst comprising 1% to 10% by weight of nickel, preferably 1% to 5% by weight of nickel (expressed as nickel oxide, NiO) associated with 1% to 30% by weight of molybdenum, preferably 5% to 20% by weight of molybdenum (expressed as molybdenum oxide, MoO3) on an alumina support.
The hydrotreated heavy distillate fraction from selective hydrogenation is cracked with the same cracking catalyst, separately or as a mixture with the heavy hydrocarbon feedstock.
The effluents from catalytically cracking the two feedstocks are sent to a common fractionation zone and the catalyst used for cracking the two feedstocks is regenerated in a common regeneration zone.
As will be disclosed in the next paragraph, the catalytic cracking unit may be classified into a number of modes, with a single reactor processing the heavy hydrocarbon feedstock and the selectively hydrotreated heavy distillate (hydrotreated HCO), or two reactors, one processing the heavy hydrocarbon feedstock, and the other the selectively hydrotreated heavy distillate (hydrotreated HCO).
In addition, each reactor may operate in upflow or downflow mode.
In the case of a plurality of selective hydrotreatment units associated with the catalytic cracking unit, they may be arranged in series or in parallel.
Free Full Text Source: http://www.freepatentsonline.com/y2013/0137907.html
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