U.S. patent application number 10/398239 was filed with the patent office on 2004-03-18 for method for producing diesel fuel by moderate pressure hydrocracking.
Invention is credited to Benazzi, Eric, Billon, Alain, Duee, Didier, Gueret, Christophe, Marion, Pierre.
Application Number | 20040050753 10/398239 |
Document ID | / |
Family ID | 8855038 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040050753 |
Kind Code |
A1 |
Marion, Pierre ; et
al. |
March 18, 2004 |
Method for producing diesel fuel by moderate pressure
hydrocracking
Abstract
The invention concerns a process for moderate pressure
hydrocracking (i.e., at a hydrogen partial pressure of more than 70
bars and at most 100 bars) with a conversion of at least 80% by
volume, of a feed with a T.sub.5 temperature in the range
250.degree. C. to 400.degree. C. and a T.sub.95 temperature of at
most 470.degree. C. (T.sub.5 and T.sub.95 measured in accordance
with ASTM-D2887), to produce a diesel with a 95% distillation point
of less than 360.degree. C., a sulphur content of at most 50 ppm
and a cetane number of more than 51. The process operates with or
without a recycle of the liquid effluent. Highly advantageously, it
can be integrated into a refinery layout comprising catalytic
cracking. The invention also concerns a unit for carrying out said
process.
Inventors: |
Marion, Pierre; (Antony,
FR) ; Benazzi, Eric; (Chatou, FR) ; Duee,
Didier; (Eragny Sur Oise, FR) ; Gueret,
Christophe; (St Romain en Gal, FR) ; Billon,
Alain; (Le Vesinet, FR) |
Correspondence
Address: |
Millen White
Zelano & Branigan
Arlington Courthouse Plaza I
2200 Clarendon Boulevard Suite 1400
Arlington
VA
22201
US
|
Family ID: |
8855038 |
Appl. No.: |
10/398239 |
Filed: |
September 22, 2003 |
PCT Filed: |
September 28, 2001 |
PCT NO: |
PCT/FR01/03016 |
Current U.S.
Class: |
208/89 ;
208/111.3; 208/111.35; 208/254H |
Current CPC
Class: |
C10G 2400/04 20130101;
C10G 2300/202 20130101; C10G 2300/107 20130101; C10G 45/08
20130101; C10G 69/00 20130101; C10G 2300/1077 20130101; C10G
2300/4006 20130101; C10G 2300/301 20130101; C10G 69/04 20130101;
C10G 47/16 20130101; C10G 2300/307 20130101; C10G 2300/1074
20130101; C10L 1/08 20130101; C10G 65/00 20130101; C10G 2300/4012
20130101; C10G 45/12 20130101; C10G 65/12 20130101 |
Class at
Publication: |
208/089 ;
208/111.3; 208/111.35; 208/254.00H |
International
Class: |
C10G 065/12; C10G
047/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2000 |
FR |
00/12736 |
Claims
1. A process for producing a diesel having a 95% distillation point
of less than 360.degree. C., a sulphur content of at most 50 ppm
and a cetane number of more than 51, said process treating
hydrocarbon feeds with a Ts temperature in the range 250.degree. C.
to 400.degree. C. and a T.sub.95 temperature of at most 470.degree.
C., said process comprising hydrotreatment which produces an
effluent having an organic nitrogen content below 10 ppm followed
by moderate pressure hydrocracking with a hydrocracking catalyst
comprising at least one Y zeolite, at least one matrix and at least
one hydro-dehydrogenating function said hydrocracking being carried
out at a hydrogen partial pressure of more than 70 bars and at most
100 bars, at a temperature of at least 320.degree. C., with a
H.sub.2 feed volume ratio of at least 200 Ni/Ni, and at an hourly
space velocity of 0.15-7 h.sup.-1, the process being carried out
with a conversion of at least 80% by volume and the liquid effluent
obtained by hydrocracking being distilled to separate the
diesel.
2. A process according to claim 1, in which the conversion is at
least 95% by volume.
3. A process according to any one of the preceding claims, in which
the hydrocarbon feed has a T.sub.95 temperature in the range
390-430.degree. C.
4. A process according to any one of the preceding claims, in which
the hydrocarbon feed has a T.sub.5 temperature in the range
320.degree. C. to 370.degree. C.
5. A process according to any one of the preceding claims, in which
the hydrocarbon feed is selected from the group formed by heavy
atmospheric gas oils or light vacuum gas oils, light vacuum
distillates, mixtures of said feeds and mixtures of said feeds with
a diesel fraction.
6. A process according to any one of the preceding claims, in which
hydrotreatment and hydrocracking are carried out in the same
reactor and without intermediate separation of the gases produced
by hydrotreatment.
7. A process according to any one of the preceding claims, in with
the hydrocracking residue is recycled to the process after
purging.
8. A process according to any one of the preceding claims, in which
the diesel obtained has a 95% point of at most 340.degree. C., a
sulphur content of at least 10 ppm and a cetane number of at least
54.
9. A process according to any one of the preceding claims, in which
the hydrotreatment catalyst contains: 5% to 40% by weight of at
least one element from group VIB and non noble group VIII (%
oxide); 0-20% of at least one promoter element selected from
phosphorus, boron, silicon (% oxide) 0-20% of at least one group
VIIB element 0% of group VIIA element 0-60% of at least one group
VB element 0.1-95% of at least one matrix and the hydrocracking
catalyst contains 0.1-80% by weight of Y zeolite; 0.1-40% by weight
of at least one element from group VIB and group VIII (% oxide);
0.1-99.8% by weight of matrix (% oxide); 0-20% by weight of at
least one element selected from the group formed by P, B, Si (%
oxide) 0% by weight of group VIIA element 0-20% by weight of at
least one group VIIB element 0-60% by weight of at least one group
VB element.
10. A process according to any one of the preceding claims, in
while the feed with a T.sub.5 temperature of 250.degree. C. to
400.degree. C. and a T.sub.95 temperature of at most 470.degree. C.
is a light fraction from vacuum distillation of an atmospheric
residue.
11. A process according to claim 10, in which the vacuum
distillation also produces a vacuum residue with a boiling point of
at least 535.degree. C. and at least one heavy fraction located
between said light fraction and the residue, at least a portion of
said heavy fraction undergoing catalytic cracking.
12. A process according to any one of the preceding claims, in
which the hydrocarbon feed to be treated by moderate pressure
hydrocracking is a heavy atmospheric gas oil from atmospheric
distillation, the atmospheric residue boiling above said gas oil
being vacuum distilled to produce at least one heavy vacuum
distillate fraction that undergoes catalytic cracking and a vacuum
residue.
13. A process according to any one of the preceding claims, in
which the moderate pressure hydrocracking purge undergoes catalytic
cracking.
14. A process according to any one of the preceding claims in
which, before undergoing catalytic cracking, the heavy vacuum
distillate is hydrotreated under a hydrogen partial pressure of
25-90 bars, at a temperature of 350-430.degree. C., with a
conversion of at least 10% and less than 40% by volume, to products
boiling below 350.degree. C.
15. A process according to any one of the preceding claims, in
which the vacuum residue undergoes a treatment by a process
selected from the group formed by visbreaking, residue
hydroconversion, and coking processes.
16. A process for treatment of a crude hydrocarbonated feed,
comprising the following steps: atmospheric distillation of the
crude hydrocarbonated feed, producing at least one naphta fraction,
at least one kerosene fraction, at least one diesel fraction and an
atmospheric residue, vacuum distillation of the atmospheric residue
to separate at least one light distillate fraction, at least one
heavy distillate fraction and a vacuum residue, treatment of said
light fraction by the process according to any one of the claims 1
to 15 with production of hydrocracking residue, catalytic cracking
of at least one heavy fraction, optionally added with at least a
part of the hydrocracking residue.
17. A process for treatment of a crude hydrocarbonated feed,
comprising the following steps: atmospheric distillation of the
crude hydrocarbonated feed, producing at least one naphta fraction,
at least one kerosene fraction, at least one diesel fraction, a
heavy atmospheric gasoil and an atmospheric residue, vacuum
distillation of the atmospheric residue to separate at least one
heavy distillate fraction and a vacuum residue, treatment of said
heavy gasoil cut by the process according to any one of the claims
1 to 15 with production of hydrocracking residue, catalytic
cracking of at least one heavy fraction, optionally added with at
least a part of the hydrocracking residue.
18. A process according to claim 16 in which atmospheric
distillation also produces a heavy atmopsheric gasoil cut, said cut
being also treated with the said light fraction by the process
according to any one of the claims 1 to 15.
19. A process according to any one of the claims 16 to 18 also
comprising the treatment of vacuum residue by viscoreduction.
20. A unit for producing diesel, comprising: a column for
distilling a hydrocarbon feed to separate at least one fraction
with a T.sub.5 temperature in the range 250.degree. C. to
400.degree. C. and a T.sub.95 temperature of at most 470.degree.
C.; at least one zone for hydrotreating said feed or said fraction;
at least one zone for moderate pressure hydrocracking of said
reaction, said pressure being more than 70 bars and at most 100
bars; at least one zone for separating products to obtain a diesel
with a 95% distillation point of less than 360.degree. C., a
sulphur content of at most 50 ppm and a cetane number of more than
51.
21. A unit for producing diesel according to claim 20, from a crude
hydrocarbon feed, comprising: a column for atmospheric distillation
of said crude feed to separate at least naphtha, diesel and an
atmospheric residue; a vacuum distillation column to treat said
atmospheric residue, and to separate at least one vacuum distillate
and a vacuum residue; in which unit the atmospheric distillation
column or vacuum distillation column comprises at least one line
recovering a fraction with a T.sub.5 temperature in the range
250.degree. C. to 400.degree. C. and a T.sub.95 temperature of at
most 470.degree. C.; the unit also comprising at least one zone for
hydrotreating said fraction followed by at least one moderate
pressure hydrocracking zone and at least one zone for separating
products to obtain a diesel with a 95% distillation point of less
than 360.degree. C., a sulphur content of at most 50 ppm and a
cetane number of more than 51.
22. A unit according to claim 20 or claim 21, comprising a
hydrotreatment zone prior to the hydrocracking zone and located in
the same reactor.
23. A unit according to any one of claims 20 to 22, in which the
product separation zone separates a hydrocracking residue with a
boiling point of more than at least 535.degree. C. and comprises a
purge line for said residue and optionally a line for recycling
said purged residue towards the hydrocracking zone or reactor.
24. A unit according to any one of claims 20 to 23, comprising a
catalytic cracking zone for treating at least one vacuum distillate
fraction located between the fraction with a T.sub.95 temperature
of at most 470.degree. C. and the vacuum residue.
25. A unit according to any one of claims 20 to 24, comprising a
line supplying the purge to the catalytic cracking zone.
26. A unit according to any one of claims 20 to 25, comprising a
hydrotreatment zone prior to the catalytic cracking zone.
Description
[0001] The invention relates to a process with moderate pressure
hydrocracking, for the production of very high quality diesel in
high yields.
[0002] The invention also relates to
[0003] a process including said hydrocracking process and to a
catalytic cracking process, and to a unit for use in carrying out
the process.
[0004] The refining industry must now find refinery layouts that
can be adapted to the tightening of regulations regarding fuel
quality and which will be in force in Europe in 2005. The maximum
sulphur content in diesel will be at most 50 ppm. The 95%
distillation point (ASTM D-86) for diesel, currently 360.degree.
C., will probably be reduced, for example by 10.degree. C., which
for a refinery currently represents a reduction of 5% in the volume
of diesel produced. It is also envisaged that the existing
permitted quantities of polyaromatic compounds will be halved from
its existing 11% by weight. The cetane number will also be
increased to above 51, for example passing from its existing value
of 51 to 52.
[0005] At the same time, the demand for diesel is constantly
increasing; over the next decade, demand is expected to increase by
about 20%.
[0006] Distilling crude is not sufficient to cover diesel
production; diesel is currently produced by high pressure
hydrocracking processes (in general at least 120 bars hydrogen
partial pressure), treating heavy feeds that are feeds with a
T.sub.95 temperature that is usually of the order of at least
500.degree. C., T.sub.95 being the temperature of the 95% by volume
obtained by simulated distillation (ASTM-D28 87). Heavy compounds
are cracked into lighter compounds, a portion of which is in the
middle distillate cut (diesel and kerosine) of the hydrocracking
distillation. Such high pressure processes are conventional.
[0007] To satisfy the new standards, diesel from crude distillation
will have to undergo deep hydrodesulphurisation. Further, high
pressure hydrocracking is a solution that can be expensive. Thus, a
solution that is more advantageous has been sought that can also be
integrated into existing units to optimise the use of existing
refinery resources.
[0008] The process disclosed in the present application is a
hydrocracking process functioning at moderate temperatures (above
70 bars and at most 100 bars of hydrogen partial pressure) that can
directly produce diesel satisfying 2005 specifications from
relatively light feeds under more economical conditions than those
used in high pressure hydrocracking.
[0009] More precisely, the invention concerns a process for
producing a diesel having a 95% distillation point of less than
360.degree. C., a sulphur content of at most 50 ppm and a cetane
number of more than 51, said process treating hydrocarbon feeds
with a T.sub.5 temperature in the range 250.degree. C. to
400.degree. C. and a T.sub.95 temperature of at most 470.degree.
C., said process comprising hydrotreatment followed by
hydrocracking under a hydrogen partial pressure of more than 70
bars and at most 100 bars, at a temperature of at least 320.degree.
C., with a H.sub.2/feed volume ratio of at least 200 Nl/Nl, an
hourly space velocity of 0.15-7 h.sup.-1 and the process being
carried out with a conversion of at least 80% by volume and the
liquid effluent obtained by hydrocracking being distilled to
separate the diesel. Preferably, the distillation residue is
recycled to the process after purging.
[0010] Feeds, Hydrotreatment and Hydrocracking
[0011] The feeds treated in the process have a T.sub.5 point in the
range 250.degree. C. to 400.degree. C., preferably in the range
280.degree. C. to 370.degree. C. The point T.sub.5 represents the
temperature of the 5% by volume point obtained by simulated
distillation (ASTM-D28 87).
[0012] In general, the feeds have a T.sub.5 point in the range
320-400.degree. C. or in the range 320-370.degree. C. Highly
advantageously, a diesel fraction can be added to these feeds, for
example a heavy diesel from atmospheric crude distillation, which
usually has a T.sub.5 point of the order of at least 280.degree. C.
This heavy diesel fraction can also be obtained directly in the
atmospheric residue.
[0013] This arrangement (adding diesel) is particularly
advantageous. It allows a heavy portion of the diesel fraction,
which is charged with nitrogen-containing and sulphur-containing
compounds that are the most difficult to be hydrotreated, to be
treated by hydrotreatment followed by moderate pressure
hydrocracking. From then on, conventional hydrotreatment can be
used to treat the remaining diesel fraction, which needs no
expensive investment.
[0014] Further, by treating that heavy diesel portion in the
process of the invention, the heavy fraction is hydrodesulphurised
and at the same time its qualities are improved (cetane number
higher than that which would have been obtained by severe
hydrotreatment alone).
[0015] The feeds that can be used also have a T.sub.5 temperature
of at most 470.degree. C., preferably at most 450.degree. C., more
preferably in the range 390-430.degree. C., T.sub.95 representing
the temperature of the 95% point obtained by simulated distillation
(ASTM-D28 87).
[0016] Feeds that can be cited are light vacuum distillates, a
light fraction of a conventional vacuum gas oil (VGO) (for example,
the lightest half), heavy atmospheric gas oils (HGO), mixtures of
said feeds or mixtures of said feeds with at least one diesel
fraction, for example from crude distillation or from an FCC
(catalytic cracking) unit.
[0017] The sulphur contents of the treated hydrocarbon feeds are
generally 0.2% to 4% by weight, and the nitrogen contents are
100-3500 ppm by weight. Thus, they are generally hydrotreated
before being hydrocracked to reduce the organic nitrogen contents
(i.e., the nitrogen contained in organic molecules) to below 80
ppm, or preferably to below 50 ppm, more preferably to below 10
ppm, and the amounts of organic sulphur (i.e., sulphur contained in
organic molecules) to below 200 ppm, preferably below 50 ppm. These
hydrotreated feeds (clean feeds) can then undergo
hydrocracking.
[0018] The hydrotreatment conditions are generally:
[0019] pressure of 5-25 MPa, preferably with a hydrogen partial
pressure of more than 70 bars and at most 100 bars, preferably at
least 80 bars or at least 85 bars,
[0020] temperature of at least 320.degree. C., in general at least
350.degree. C. and at most 450.degree. C., usually at most
430.degree. C.,
[0021] H.sub.2/feed volume ratio of at least 100 N/l, usually
between 100-2000 Nl/l or 300-2000 Nl/l,
[0022] hourly space velocity of 0.1-10 h.sup.-1, preferably 0.15-7
h.sup.-1, advantageously 0.054 h.sup.-1.
[0023] The conversion achieved with hydrotreatment is generally at
least 40% by volume, and less than 40% of product boiling below
350.degree. C.
[0024] Hydrotreatment can be carried out either in a hydrocracking
reactor and in at least one bed preceding the first hydrocracking
catalyst bed, in the direction of feed flow, or in an independent
reactor preceding the hydrocracking reactor. There may or may not
be intermediate separation of the gases regenerated by
hydrotreatment. The first mode (same reactor) with no intermediate
separation is preferred. The process also includes an
implementation in which hydrotreatment is carried out in the
refinery a long way upstream of the hydrocracking step;
intermediate treatments can also be carried out.
[0025] At least a portion of the clean feed is brought into contact
with at least one hydrocracking catalyst in the presence of
hydrogen under the following operating conditions:
[0026] hydrogen partial pressure of more than 70 bars and at most
100 bars, preferably at least 80 bars or at least 85 bars;
[0027] temperature of at least 320.degree. C., in general at least
350.degree. C. and at most 450.degree. C., usually at most
430.degree. C.;
[0028] H.sub.2/feed volume ratio of at least 200 Nl/Nl, usually in
the range 300-2000 Nl/Nl;
[0029] hourly space velocity 0.15-7 h.sup.-1, preferably 0.054
h.sup.-1.
[0030] The process can function with or without a recycle of the
distillation residue of the hydrocracking residue (unconverted
fraction). When present, the recycle is made to the hydrocracking
reactor if it is separated from the hydrotreatment step, for
example, or to the feed entering the reactor where hydrotreatment
and hydrocracking are carried out.
[0031] Under these conditions, for the global process, the
conversion of products boiling below 350.degree. C. is at least 80%
by volume, more generally at least 90% by volume, or at least 95%
by volume.
[0032] Hydrotreatment Catalysts
[0033] Conventional catalysts can be used, which contain at least
one amorphous support and at least one hydrodehydrogenating element
(generally at least one element from groups VIB and non noble
elements from group VIII, and usually at least one element from
group VIB and at least one non noble element from group VIII).
[0034] Highly advantageously, a hydrotreatment catalyst comprises
at least one matrix, at least one hydrodehydrogenating element
selected from the group formed by elements from group VIB and from
group VIII of the periodic table, optionally at least one promoter
element deposited on the catalyst and selected from the group
formed by phosphorus, boron and silicon, optionally at least one
element from group VIIA (preferably chlorine, fluorine), and
optionally at least one element from group VIIB (preferably
manganese), and optionally at least one element from group VB
(preferably niobium).
[0035] In general, the hydrotreatment catalyst contains:
[0036] 5% to 40% by weight of at least one element from group VIB
and non noble group VIII (5 oxide);
[0037] 0-20% of at least one promoter element selected from
phosphorus, boron, silicon (% oxide), preferably 0.1-20%;
advantageously, boron and/or silicon are present, and optionally
phosphorus;
[0038] 0-20% of at least one group VIIB element (for example
manganese);
[0039] 0-20% of at least one group VIIA element (for example
fluorine, chlorine);
[0040] 0-60% of at least one group VB element (for example
niobium);
[0041] 0.1-95% of at least one matrix, preferably alumina.
[0042] Preferably, this catalyst contains boron and/or silicon as a
promoter element, optionally with additional phosphorus as the
other promoter element. The boron, silicon and phosphorus contents
are 0.1-20%, preferably 0.1-15%, more advantageously 0.1-10%.
[0043] Non limiting examples of matrices that can be used alone or
as mixture are alumina, halogenated alumina, silica,
silica-alumina, clays (for example natural clays such as kaolin or
bentonite), magnesia, titanium oxide, boron oxide, zirconia,
aluminium phosphates, titanium phosphates, zirconium phosphates,
charcoal, aluminates. Preferably, matrices containing alumina are
used, in forms known to the skilled person, more preferably
aluminas, for example gamma alumina.
[0044] The hydrodehydrogenating function is preferably provided by
at least one metal or compound of a metal from non noble group VIII
and VI, preferably selected from molybdenum, tungsten, nickel and
cobalt. Preferably, it is supplied by a combination of at least one
element from group VIII (Ni, Co) with at least one element from
group VIB (Mo, W).
[0045] This catalyst can advantageously contain phosphorus; in the
prior art, it is known that this compound endows hydrotreatment
catalysts with two advantages: ease of preparation in particular
when impregnating nickel and molybdenum solutions, and better
hydrogenation activity.
[0046] In a preferred catalyst, the total concentration of oxides
of metals from groups VI and VIII is in the range 5% to 40% by
weight, preferably in the range 7% to 30% by weight, and the weight
ratio, expressed as the ratio of metal oxide between the group VIB
metal (or metals) and the group VII metal (or metals) is preferably
in the range 20 to 1.25, more preferably in the range 10 to 2. The
concentration of phosphorous pentoxide P.sub.2O.sub.5 is less than
15% by weight, preferably 10% by weight.
[0047] A further preferred hydrotreatment catalyst that contains
boron and/or silicon (preferably boron and silicon) generally
comprises, as a % by weight with respect to the total catalyst
weight, at least one metal selected from the following groups and
in the following amounts:
[0048] 3% to 60%, preferably 3% to 45%, more preferably 3% to 30%
or at least one group VIB metal;
[0049] and optionally
[0050] to 30%, preferably 0 to 25%, more preferably 0 to 20% of at
least one group VIII metal;
[0051] the catalyst further comprising at least one support
selected from the following groups and in the following
amounts:
[0052] 0 to 99%, advantageously 0.1% to 99%, preferably 10% to 98%,
and more preferably 15% to 95%, of at least one amorphous or low
crystallinity matrix;
[0053] said catalyst being characterized in that it further
contains:
[0054] 0.1% to 20%, preferably 0.1% to 15%, more preferably 0.1% to
10% of boron and/or. 0.1% to 20%, preferably 0.1% to 15%, more
preferably 0.1% to 10% of silicon;
[0055] and optionally:
[0056] 0 to 20%, preferably 0.1% to 15%, more preferably 0.1% to
10% of phosphorus;
[0057] and preferably again;
[0058] 0 to 20%, preferably 0.1% to 15%, more preferably 0.1% to
10% by weight of at least one element selected from group VIIA,
preferably fluorine.
[0059] In general, formulae with the following atomic ratios are
preferred:
[0060] a group VIII metal/group VIB metal atomic ratio in the range
0 to 1;
[0061] a B/group VIB metal atomic ratio in the range 0.01 to 3;
[0062] an Si/group VIB metal atomic ration in the range 0.01 to
1.5;
[0063] a P/group VIB metal atomic ratio in the range 0.01 to 1;
[0064] a group VIIA element/group VIB metal atomic ratio in the
range 0.01 to 2.
[0065] Such a catalyst has a higher activity for hydrogenating
aromatic hydrocarbons and for hydrodenitrogenation and
hydrodesulphurisation than catalytic formulae containing no boron
and/or silicon, and also has a higher activity and selectivity for
hydrocracking than known catalytic formulae. The catalyst
containing boron and silicon is particularly advantageous. Without
wishing to be bound by a particular theory, it appears that the
particularly high catalytic activity with boron and silicon is due
to a reinforcement of the acidity of the catalyst by the joint
presence of boron and silicon in the matrix, which causes both an
improvement in the hydrogenating properties, hydrodesulphurisation
properties and hydrodenitrogenation properties, and an improvement
in the hydrocracking activity compared with catalysts normally used
in hydrorefining and hydroconversion reactions.
[0066] Preferred catalysts are NiMo and/or NiW on alumina type
catalysts, also NiMo and/or NiW on alumina type catalysts doped
with at least one element selected from the group formed by
phosphorus, boron, silicon and fluorine, or NiMo and/or NiW type
catalysts on silicaalumina, or on silica-alumina-titanium oxide
doped or otherwise by at least one element selected from the group
formed by phosphorus, boron, fluorine and silicon.
[0067] A further particularly advantageous catalyst (in particular
with an improved activity) for hydrotreatment comprises a partially
amorphous Y zeolite that will be described below in the
hydrocracking catalyst section.
[0068] Prior to injection of the feed, the catalysts used in the
process of the present invention preferably undergo a
sulphurisation treatment to at least partially transform the
metallic species to the sulphide prior to bringing them into
contact with the feed to be treated. This sulphurisation activation
treatment is well known to the skilled person and can be carried
out using any method that has been described in the literature,
either in-situ, i.e., in the reactor, or ex-situ.
[0069] A conventional sulphurisation method that is well known to
the skilled person consists of heating in the presence of hydrogen
sulphide (pure or, for example, in a stream of a hydrogen/hydrogen
sulphide mixture) at a temperature in the range 150.degree. C. to
800.degree. C., preferably in the range 250.degree. C. to
600.degree. C., generally in a traversed bed reaction zone.
[0070] Hydrocracking Catalysts
[0071] A preferred catalyst comprised at least one Y zeolite, at
least one matrix and at least one hydrodehydrogenating function.
Optionally, it can also contain at least one element selected from
boron, phosphorus and silicon, at least one group VIIA element (for
example chlorine, fluorine), at least one group VIIB element (for
example manganese), and at least one group VB element (for example
niobium).
[0072] The catalyst comprises at least one porous or low
crystallinity mineral oxide type matrix. Non limiting examples that
can be cited are aluminas, silicas, silica-aluminas, aluminates,
alumina-boron oxide, magnesia, silica-magnesia, zirconia, titanium
oxide and clay, used alone or as a mixture.
[0073] The hydrodehydrogenating function is generally provided by
at least one element from group VIB (for example molybdenum and/or
tungsten) and/or at least one non noble element from group VIII
(for example cobalt and/or nickel) of the periodic table. A
preferred catalyst essentially contains at least one group VI
metal, and/or at least one non noble group VIII metal, Y zeolite
and alumina. A more preferred catalyst essentially contains nickel,
molybdenum, Y zeolite and alumina.
[0074] The catalyst optionally comprises at least one element
selected from the group formed by boron, silicon and phosphorus.
Advantageously, the catalyst optionally comprises at least one
element from group VIIA, preferably chlorine or fluorine,
optionally at least one element from group VIIB (for example
manganese) and optionally at least one element from group VB (for
example niobium).
[0075] Boron, silicon and/or phosphorus can be in the matrix or the
zeolite or, as is preferable, deposited on the catalyst and thus
principally located on the matrix. A preferred catalyst contains B
and/or Si as a promoter element, preferably deposited in addition
to the phosphorus promoter. The quantities introduced are 0.1-20%
by weight of catalyst, calculated as the oxide.
[0076] The element introduced, in particular silicon, principally
located on the matrix of the support, can be characterized by
techniques such as a Castaing microprobe (distribution profile of
the various elements), transmission electron microscopy coupled to
X ray analysis of the catalyst components, or by producing a
distribution map of the elements present in the catalyst using an
electronic microprobe.
[0077] In general, a preferred hydrocracking catalyst
advantageously contains:
[0078] 0.1-80% by weight of Y zeolite;
[0079] 0.140% by weight of at least one element from group VIB and
group VIII (% oxide);
[0080] 0.1-99.8% by weight of matrix (% oxide);
[0081] 0-20% by weight of at least one element selected from the
group formed by P, B, Si (% oxide), preferably 0.1-20%;
[0082] 0-20% by weight of at least one group VIIA element,
preferably 0.1-20%;
[0083] 0-20% by weight of at least one group VIIB element,
preferably 0.1-20%;
[0084] 0-60% by weight of at least one group VB element, preferably
0.1-60%.
[0085] Regarding the silicon, the range 0-20% only includes the
added silicon and not that in the zeolite.
[0086] The zeolite can optionally be doped by metallic elements
such as metals from the rare earth series, in particular lanthanum
and cerium, or noble or non noble group VIII metals such as
platinum, palladium, ruthenium, rhodium, iridium, iron and other
metals such as manganese, zinc, magnesium.
[0087] Different Y zeolites can be used.
[0088] A particularly advantageous H-Y acid zeolite is
characterized by different specifications: a global
SiO.sub.2/Al.sub.2O.sub.3 mole ratio in the range about 6 to 70,
preferably in the range about 12 to 50; a sodium content of less
than 0.15% by weight, determined for the zeolite calcined at
1100.degree. C.; a lattice parameter in the range
24.58.times.10.sup.-10 m to 24.24.times.10.sup.-10 m, preferably in
the range 24.38.times.10.sup.-10 m to 24.26.times.10.sup.-10 m; a
CNa sodium ion take-up capacity, expressed as grams of Na per 100
grams of modified zeolite, neutralised then calcined, of more than
about 0.85; a specific surface area, determined using the BET
method, of more than about 400 m.sup.2/g, preferably more than 550
m.sup.2/g, a water vapour absorption capacity at 25.degree. C. for
a partial pressure of 2.6 torrs (i.e., 34.6 MPa), of more than
about 6%; and advantageously, the zeolite has a pore distribution,
determined by nitrogen physisorption, in the range 5% to 45%,
preferably in the range 5% to 40% of the total pore volume of the
zeolite contained in pores with a diameter located between
20.times.10.sup.-10 m to 80.times.10.sup.-10 m, and in the range 5%
to 45%, preferably in the range 5% to 40% of the total pore volume
of the zeolite contained in pores with a diameter of more that
80.times.10.sup.-10 m and generally less than 1000.times.10.sup.-10
m, the remainder of the pore volume being contained in pores with a
diameter of less than 20.times.10.sup.-1.sup.0 m.
[0089] A preferred catalyst using this type of zeolite comprises a
matrix, at least one dealuminated Y zeolite with a lattice
parameter in the range 2.424 nm to 2.455 nm, preferably in the
range 2.426 nm to 2.438 nm, a global SiO.sub.2/Al.sub.2O.sub.3 mole
ratio of more than 8, an amount of alkaline-earth metal or alkali
metal cations and/or rare earth cations such that the atomic ratio
(n.times.M.sup.n+)/Al is less than 0.8, preferably less than 0.5 or
0.1, a specific surface area determined by the BET method of more
than 400 m.sup.2/g, preferably more than 550 m.sup.2/g, and a water
adsorption capacity at 25.degree. C. for a P/P.sub.0 value of 0.2
of more than 6% by weight, said catalyst also comprising at least
one hydrodehydrogenating metal, and silicon deposited on the
catalyst.
[0090] In an advantageous implementation of the invention, a
catalyst comprising a partially amorphous Y zeolite is used for
hydrocracking.
[0091] The term "partially amorphous Y, zeolite" means a solid
with:
[0092] i/ a peak intensity that is less than 0.40, preferably less
than about 0.30;
[0093] ii/ a crystalline fraction, expressed with respect to a
reference Y zeolite in the sodium form (Na), which is less than
about 60%, preferably less than about 50%, and determined by X ray
diffraction.
[0094] Preferably, partially amorphous Y zeolites, solids forming
part of the composition of the catalyst of the invention, have at
least one (preferably all) of the following characteristics:
[0095] iii/ a global Si/Al ratio of more than 15, preferably more
than 20 and less than 150;
[0096] iv/ a framework Si/Al.sup.IV greater than or equal to the
global Si/Al;
[0097] v/ a pore volume of at least 0.20 ml/g of solid of which a
fraction, in the range 8% to 50%, is constituted by pores with a
diameter of at least 5 nm (nanometres), i.e., 50 .ANG.;
[0098] a specific surface area of 210-800 m.sup.2/g, preferably
250-750 m.sup.2/g, advantageously 300-600 m.sup.2/g.
[0099] The peak intensities and crystalline fractions are
determined by X ray diffraction, using a procedure derived from the
ASTM D3906-97 method "Determination of relative X-ray diffraction
intensities of faujasite-type-containing materials". Reference
should be made to this method for the general conditions of
application of the procedure, in particular for the preparation of
the samples and references.
[0100] A diffractogram is composed of characteristics lines from
the crystalline fraction of the sample and a background, caused
essentially by diffusion from the amorphous or microcrystalline
fraction of the sample (a weak diffusion signal can be linked to
the apparatus, air, sample carrier, etc). The peak intensity of a
zeolite is the ratio, within a pre-set angular zone (typically
8.degree. to 40.degree.-2.theta. when using the K.alpha. copper
curve (1=0.154 nm), of the area of the zeolite lines (peaks) over
the overall area of the diffractogram (peaks+background). This
peak/(peak+background) ratio is proportional to the quantity of
crystalline zeolite in the material. To estimate the crystalline
fraction of a Y zeolite sample, the peak intensity of the sample is
compared with that of a reference considered to be 100% crystalline
(for example NaY). The peak intensity of a perfectly crystalline
NaY zeolite is of the order of 0.55 to 0.60.
[0101] The peak intensity of a conventional USY zeolite is 0.45 to
0.55; its crystalline fraction with respect to a perfectly
crystalline NaY is 80% to 95%. The peak intensity of the solid used
in the present invention is less than 0.4, preferably less than
0.35. Its crystalline fraction is thus less than 70%, preferably
less than 60%.
[0102] The partially amorphous zeolites are prepared from
commercially available Y zeolites, i.e., generally with high
crystallinities (at least 80%) using dealumination techniques that
are in general use. More generally, it is possible to start from
zeolites with a crystalline fraction of at least 60%, or at least
70%.
[0103] Y zeolites generally used in hydrocracking catalysts are
produced by modifying commercially available Na-Y zeolite. This
modification can produce zeolites that are termed stabilised,
ultra-stabilised or dealuminated. This modification is carried out
by at least one of the dealumination techniques, for example by
hydrothermal treatment, or acid attack. Preferably, this
modification is carried out by combining three types of operations
that are known in the art: hydrothermal treatment, ion exchange and
acid attack.
[0104] A further particularly advantageous zeolite is a globally
non dealuminated and highly acidic zeolite.
[0105] The term "globally non dealuminated" means a Y zeolite
(structure type FAU, faujasite) in accordance with the nomenclature
developed in the "Atlas of zeolite structure types", W. M. Meier,
D. H. Olson and Ch. Baerlocher, 4 Revised edition, 1996, Elsevier.
The lattice parameter of this zeolite may be reduced by extracting
aluminium from the structure or framework during preparation but
the global SiO.sub.2/Al.sub.2O.sub.3 ratio is not changed as the
aluminium is not chemically extracted. Such a globally non
dealuminated zeolite thus has a silicon and aluminium composition,
expressed as the global SiO.sub.2/Al.sub.2O.sub.3 ratio, equivalent
to the starting non dealuminated Y zeolite. The values for the
other parameters (SiO.sub.2/Al.sub.2O.sub.3 ratio and lattice
parameter) are given below. This globally non dealuminated Y
zeolite can be in the hydrogen form or it can be at least partially
exchanged with metal cations, for example using cations of
alkaline-earth metals and/or cations of rare earth metals with
atomic number 57 to 71 inclusive. Preferably, a zeolite that is
depleted in rare earths and alkaline-earths is used, also for the
catalyst.
[0106] The globally non dealuminated Y zeolite generally has a
lattice parameter of more than 2.438 nm, a global
SiO.sub.2/Al.sub.2O.sub.3 of less than 8, a framework
SiO.sub.2/Al.sub.2O.sub.3 ratio of less than 21 and more than the
global SiO.sub.2/Al.sub.2O.sub.3 ratio. The globally non
dealuminated zeolite can be obtained by any treatment that does not
extract aluminium from the sample, such as steam treatment,
treatment with SiCl.sub.4, etc. . . .
[0107] A further type of advantageous catalyst for hydrocracking
contains in acidic amorphous oxide matrix of the alumina type doped
with phosphorus, a globally non dealuminated and highly acidic Y
zeolite and optionally, at least one element from group VIIA, in
particular fluorine.
[0108] The invention is not limited to the preferred Y zeolites
cited above, but other types of Y zeolites can be used in the
process.
[0109] Prior to injection of the feed, the catalyst undergoes a
sulphurisation treatment to transform at least a portion of the
metallic species into the sulphide prior to bringing them into
contact with the feed to be treated. This sulphurisation activation
treatment is well known to the skilled person and can be carried
out using any method that has been described in the literature,
either in-situ, i.e., in the reactor, or ex-situ.
[0110] A conventional sulphurisation method that is well known to
the skilled person consists of heating in the presence of hydrogen
sulphide (pure or, for example, in a stream of a hydrogen/hydrogen
sulphide mixture) at a temperature in the range 150.degree. C. to
800.degree. C., preferably in the range 250.degree. C. to
600.degree. C., generally in a traversed bed reaction zone.
[0111] When the hydrotreatment and hydrocracking catalysts are in
the same reactor or in two reactors with no intermediate
separation, they are sulphurised at the same time.
[0112] Product Separation
[0113] The liquid effluent from hydrocracking is then distilled to
separate a naphtha cut, a diesel cut, possibly a kerosine cut
(which can sometimes include at least a portion of the diesel cut),
light LPG gases. A liquid residue remains that can advantageously
be recycled to the process generally after purging.
[0114] Clearly, the hydrogen has also been separated from the
liquid effluent, which can subsequently be stripped before being
distilled.
[0115] Unexpectedly, it has been seen that with the process of the
invention, very high quality diesels are produced that satisfy
specifications and no further treatment (severe
hydrodesulphurisation, hydrogenation, etc. . . . ) is necessary to
improve its qualities.
[0116] The process can directly produce a diesel with a 95% by
volume distillation point of less than 360.degree. C., and
generally, this point is at most 350.degree. C., or even at most
340.degree. C., and has a sulphur content of at most 50 ppm,
generally at most 10 ppm, with a cetane number of at least 52 and
more generally at least 54, preferably with a polyaromatic compound
content of at most 6% and generally at most 1%, preferably a pour
point of less than -10.degree. C., preferably an aromatics content
of less than 15% by weight.
[0117] This process also produces a good quality kerosine with a
smoke point of more than 20 mm, preferably more than 22 mm, and
with a sulphur content of less than 50 ppm, preferably less than 10
ppm. At least a portion of the kerosine can optionally be sent to
the diesel pool, depending on the operator's requirements.
[0118] It is quite remarkable that such diesel quality can be
obtained without subsequent treatment and for a much lower
investment that high pressure hydrocracking, while enabling
upgrading of "light" refinery feeds such as existing gas oils
which, because of the tightening of specifications, are either in
excess or have to undergo subsequent severe treatments.
[0119] Regarding the yields of middle distillate (kerosine+diesel)
produced, these are at least 60% by volume, usually at least 65% by
volume. The other products formed are light LPG gases (representing
at most 10% by weight and more generally at most 5% by weight) and
naphtha (generally at least 20% by volume).
THE FIGURES
[0120] The process will now be described in brief with reference to
the Figures.
[0121] FIG. 1 shows an implementation of a moderate pressure
hydrocracking process.
[0122] FIGS. 2B, 2C, 3 and 4 show this process integrated into a
catalytic cracking unit, and FIG. 2A shows the prior art.
[0123] The moderate pressure hydrocracking process is shown in FIG.
1 The feed to be treated enters via line 1, and in the Figure, it
is added to the hydrocracking residue recycle via line 2 and
hydrogen via line 3. It passes through a heat exchanger 4 mixed
with recycled hydrogen supplied via line 5, then through a reheater
6 before being introduced into the moderate pressure hydrocracking
reactor (or zone) 7 optionally containing upstream hydrotreatment
zone(s).
[0124] Reactor 7 contains at least one catalytic bed 8 of at least
one hydrocracking catalyst. Preferably, it can contain at least one
hydrotreatment catalyst upstream of the first bed 8. The liquid
effluent from the reactor leaving via line 9 passes through
exchanger 4 then into a gas-liquid separator 10 separating
hydrogen, which is recycled to hydrocracking reactor 7 via line
5.
[0125] The separated liquid effluent leaving via line 11 is
preferably sent to a stripper 12 that separates naphtha and light
gases via line 13 and a resulting effluent leaving via line 14 is
distilled in atmospheric distillation column 15. This arrangement
schematically illustrates an embodiment of the distillation. Any
other known arrangement that results in separating the same
products would also be suitable.
[0126] This produces a diesel evacuated via line 16 and a residue
recycled to the hydrocracking reactor via line 2, apart from a
purge via line 17. Kerosine is optionally obtained.
[0127] The product separation zone separates a hydrocracking
residue with a boiling point of more than at least 535.degree. C.,
and comprises a line for purging said residue and optionally a line
for recycling said purged residue towards the hydrocracking zone or
reactor.
[0128] The figure does not show the compressors and utilities used,
which are known to the skilled person.
[0129] The hydrocracking process described here can advantageously
be integrated into the refinery into a catalytic cracking process
(generally FCC: fluidised bed catalytic cracking).
[0130] This results in a combined process producing both good
quality diesel and naphtha (for the production of gasoline).
[0131] The invention also concerns a unit for carrying out the
process described above. This unit comprises:
[0132] a column for distilling a hydrocarbon feed to separate at
least one fraction with a T.sub.5 temperature in the range
250.degree. C. to 400.degree. C. and a T.sub.95 temperature of at
most 470.degree. C.;
[0133] at least one zone for hydrotreating said feed or said
fraction;
[0134] at least one zone for moderate pressure hydrocracking of
said fraction, said pressure being more than 70 bars and at most
100 bars;
[0135] at least one zone for separating products to obtain a diesel
with a 95% distillation point of less than 360.degree. C., a
sulphur content of at most 50 ppm and a cetane number of more than
51.
[0136] In a particular implementation of the invention, shown
below, the unit comprises:
[0137] a column for atmospheric distillation of said crude feed to
separate at least naphtha, diesel and an atmospheric residue;
[0138] a vacuum distillation column to treat said atmospheric
residue, and to separate at least one vacuum distillate and a
vacuum residue;
[0139] in which unit the atmospheric distillation column or vacuum
distillation column comprises at least one line recovering a
fraction with a T.sub.5 temperature in the range 250.degree. C. to
400.degree. C. and a T.sub.95 temperature of at most 470.degree.
C.;
[0140] the unit also comprising at least one zone for hydrotreating
said fraction followed by at least one moderate pressure
hydrocracking zone and at least one zone for separating products to
obtain a diesel with a 95% distillation point of less than
360.degree. C., a sulphur content of at most 50 ppm and a cetane
number of more than 51.
[0141] For a better understanding of the invention and its
advantages, FIG. 2A shows the prior art and FIG. 2B shows the
invention, and the process of the invention will be described with
reference to the Figures.
[0142] FIG. 2A shows an existing unit. The crude hydrocarbon feed
(or crude oil) arriving via line 20 is distilled in an atmospheric
column 21. A naphtha fraction (line 22) (the term "a" in this
respect is taken to mean at least one), a fuel fraction (line 23)
and a diesel fraction (line 24) are separated.
[0143] The atmospheric residue leaving via line 25 is vacuum
distilled in vacuum distillation column 26. A vacuum distillate
(line 27) is separated and a vacuum residue remains (line 38).
[0144] Said vacuum distillate is sent to a catalytic cracking unit
28 (generally a fluidised bed) which produces, inter alia, naphtha
evacuated via line 29, a highly aromatic diesel type fraction
(light cycle oil LCO) evacuated via line 30, and a slurry or
residue leaving via line 31.
[0145] Usually, the vacuum residue is treated in a visbreaking unit
39 which, inter alia, produces naphtha (line 40) and diesel (line
41), both of low quality. Like the slurry, the visbreaking residue
(line 42) can only be used as fuel; a portion of the LCO can serve
to flush the fuel.
[0146] FIG. 2B shows the process and unit of the invention,
combining moderate pressure hydrocracking with catalytic
cracking.
[0147] The reference numerals of FIG. 2A are used, and the
visbreaker is not shown in order to simplify the figure, although
it is generally present in the unit.
[0148] In addition to the elements of the prior art (FIG. 2A), the
unit of the invention (FIG. 2B), comprises a moderate pressure
hydrocracking unit 32 that receives a light fraction from the
vacuum distillation step supplied via line 33.
[0149] Unit 32 comprises the moderate pressure hydrocracking
reactor(s) or zone(s) and the associated separating means to
separate, inter alia, a high quality diesel via line 34, a naphtha
via line 35 and the purge of the hydrocracking residue via line 36.
Normally, unit 32 also comprises a zone for hydrotreatment prior to
hydrocracking.
[0150] At least a portion of the hydrocracking residue can be sent
for catalytic cracking (unit 28) but this is not obligatory. The
purge from the hydrocracking unit is advantageously sent to unit
28.
[0151] The Figure does not show a recycle of the purged residue to
the hydrocracking zone or to the hydrocracking reactor also
comprising a hydrotreatment zone. Recycling and passage of the
purge to FCC can be carried out separately or together.
[0152] Within the context of the process of the invention, as
shown, for example, in FIG. 2B with FCC, the cut point for the
distilled diesel cut (line 24) during atmospheric distillation is
selected by the operator.
[0153] The atmospheric residue, which thus contains at least a
portion of the heavy atmospheric gas oil, is vacuum distilled into
at least one light fraction (distillate) and at least one heavy
fraction (distillate), and a vacuum residue remains.
[0154] Said light fraction to be treated by hydrocracking has a
T.sub.5 temperature that is in the range 250.degree. C. to
400.degree. C. and a T.sub.95 temperature that is at most
470.degree. C. It is a light vacuum gas oil (LVGO). The end point
is selected by the operator depending on the column that is
available and depending on the desired upgrading for the products.
Said light fraction has other characteristics of the hydrocarbon
feeds treated by the process of the invention and described
above.
[0155] In general, this light vacuum distillate treatment by
moderate pressure hydrocracking can be carried out when the
production and/or quality of the diesel is to be increased,
regardless of the type of reactor reserved for the heavy
distillate(s) and the residue from the vacuum distillation.
[0156] In a further implementation, instead of fractionating the
atmospheric residue into light and heavy fractions by vacuum
distillation and sending the light fraction(s) to the hydrocracking
step, the heavy gas oil cut with substantially the same T.sub.5 and
T.sub.95 temperatures as regards atmospheric distillation is taken
(if the type of column allows it). This mode is shown in FIG. 2C,
which shows the same reference numerals as for the preceding
figures and where the feed for unit 32 is an atmospheric gas oil
supplied via line 37. In this figure, line 33 no longer exists. In
this case, the atmospheric residue boiling above the heavy gas oil
is vacuum distilled, vacuum distillation also producing a residue
and at least one vacuum distillate, term the heavy distillate in
this case.
[0157] The vacuum distillation residue (line 38), which generally
has a T.sub.5 temperature of at least 535.degree. C., preferably at
least 550.degree. C., or even at least 565.degree. C. or
570.degree. C., can, for example, undergo visbreaking (shown in
FIG. 1) or residue hydroconversion or coking.
[0158] In all cases, at least one heavy vacuum distillation
fraction located between the light fraction with a T.sub.95
temperature of at most 470.degree. C., and the vacuum residue,
undergoes catalytic cracking.
[0159] FIG. 3 shows a unit and a process in which prior to said
cracking, the heavy fraction from vacuum distillation which
undergoes catalytic cracking undergoes hydrotreatment in a zone 43.
The reference numerals of the preceding figures are shown again
here.
[0160] This hydrotreatment prior to FCC is carried out in the
presence of at least one amorphous catalyst. All conventional
hydrotreatment catalysts can be used. Catalysts that can be cited
include those containing at least one non noble group VIII element
(for example Co, Ni) and at least one group VIB element (for
example M, W) deposited on a support preferably based on alumina or
silica-alumina. The particularity of this step resides in the
operating conditions: a hydrogen partial pressure between 25 and 90
bars, preferably less than 85 bars, or more preferably less than 80
bars, or even more preferably less than 70 bars, and a temperature
of 350-450.degree. C., preferably 370-430.degree. C. adjusted to
maintain a conversion of at least 10%, preferably less than 40% of
products boiling below 350.degree. C., preferably 15-30%.
[0161] This produces a naphtha (line 44) and a diesel (line 45) but
of medium quality and intended either for use as a domestic fuel or
to be sent to the diesel pool.
[0162] The hydrotreated effluent then passes into a catalytic
cracking unit 28.
[0163] FIG. 4 is a flowchart for an addition of heavy diesel
fraction to unit 32 in which moderate pressure hydrocracking is
carried out. In this implementation, an atmospheric distillate is
obtained, in addition to naphtha cuts (line 22), kerosine cuts
(line 23), a light LGO diesel fraction (line 46) and a heavy diesel
fraction HGO (line 47). This heavy diesel fraction is sent to unit
32 where it undergoes hydrotreatment then moderate pressure
hydrocracking.
[0164] The present application describes a process for producing
diesel and naphtha, diesel production being carried out by a
moderate pressure hydrocracking process as described above, and
naphtha production being essentially obtained by catalytic
cracking. Preferably, the hydrocracking purge is sent to the
catalytic cracking step.
[0165] We have described a preferred embodiment of this type of
process, but other embodiments and arrangements are possible that
will produce the same result.
[0166] To illustrate the advantage of the invention, we describe
below production from an existing refining scheme, and from an
existing scheme for producing diesel to 2005 specifications and
from a scheme of the invention. In the scheme of FIG. 2A (existing
specification 2000 scheme) to treat 10 Mt/yr of North Sea crude, we
have (scheme 1):
1 naphtha 3.17 Mt/yr jet fuel 0.73 Mt/yr diesel 2.32 Mt/yr domestic
fuel 1.5 Mt/yr
[0167] fuel from 565.degree. C.+ residue undergoing visbreaking:
1.42 Mt/yr of 40 cst fuel
[0168] (diluted by LCO and including slurry)
[0169] The diesel has a cetane number of 49 and the sulphur content
is 2100 ppm. To satisfy specifications, it has to undergo
conventional desulphurisation.
[0170] Without changing the refinery scheme, but with diesel
qualities to 2005 specifications (95% point taken at 340.degree.
C.), we have (scheme 2):
2 naphtha 3.32 Mt/yr jet fuel cut 0.82 Mt/yr diesel 2.13 Mt/yr
domestic fuel 1.36 Mt/yr 40 cst fuel from 565.degree. C. + residue
1.43 Mt/yr
[0171] The diesel has a cetane number of only 48 and thus has to
undergo extremely severe hydrodesulphurisation and hydrogenation
which cannot be achieved with existing units.
[0172] The naphtha pool should have a sulphur content of 270 ppm by
weight, which would necessitate severe subsequent treatments to
reduce it to 10-50 ppm by weight. To avoid expensive investment,
the naphtha fraction from FCC will be treated separately by severe
hydrodesulphurisation, with the disadvantage of reducing the octane
number. The other naphtha fractions (for example from the
visbreaker, crude distillation, etc. . . . ) will be sent to the
reforming step and possibly to an isomerisation unit prior to
hydrotreatment.
[0173] Adding a hydrotreatment step prior to catalytic cracking to
scheme 2 above (as shown in FIG. 3 but under hydrocracking)
produces the following (scheme 3):
3 naphtha 3.06 Mt/yr jet fuel 0.84 Mt/yr diesel 2.57 Mt/yr domestic
fuel 1.40 Mt/yr 40 cst fuel from 565.degree. C. + residue 1.36
Mt/yr
[0174] The cetane number of the diesel remains at about 48. The FCC
naphtha has a sulphur content of 15 ppm, and in the naphthene pool
the sulphur content can be reduced to as low as about 5.5 ppm,
without substantial loss of octane number.
[0175] With the preferred scheme 4 of the invention (FIG. 3)
including moderate pressure hydrocracking, we obtain (scheme
4):
4 naphtha 2.90 Mt/yr jet fuel 0.86 Mt/yr diesel 2.82 Mt/yr domestic
fuel 1.44 Mt/yr 40 cst fuel 1.34 Mt/yr
[0176] In this case, vacuum distillation separates out a light
fraction 350-410.degree. C., a heavy fraction 410-565.degree. C.
and a 565.degree. C+ residue.
[0177] In hydrocracking, conversion is almost complete
(.gtoreq.98%), the H.sub.2 consumption is 1.85% by weight, and the
pressure is 90 bars ppH.sub.2.
[0178] The diesel obtained is as follows:
5 95% point 340.degree. C. flash point >60.degree. C. cetane
number 56 sulphur content <10 ppm polyarmoatics <1% by
weight
[0179] A comparison of these figures shows the excellent quality of
the diesel obtained using a scheme of the invention, which quality
has never before been produced.
[0180] Compared with conventional hydrocracking, for the same
product qualities, we have saved 50 bars of hydrogen pressure,
which considerably reduces the costs.
[0181] In terms of productivity, the quantities of products are
similar to those of scheme 3 but in contrast, comparison with
scheme 2 (existing refinery but to 2005 specifications) shows
important gains, for the same quantity of crude oil, in:
6 diesel +32.4% kerosine 4.9%
[0182] We could also adjust the diesel/naphtha balance towards high
quality diesel, while reducing the 40 cst fuel production (-6.3%)
thus adapting the refinery to market needs. Further, the FCC unit
does not operate at full capacity, and so the operator can highly
advantageously introduce a supplemental feed that can be treated
under FCC (such as an atmospheric residue). This addition is
preferably made to the feed entering the vacuum distillation column
(dotted lines in FIG. 3).
* * * * *