U.S. patent application number 10/457018 was filed with the patent office on 2004-02-26 for process for producing hydrocarbons with low sulphur and nitrogen contents.
This patent application is currently assigned to Institute Francais du Petrole. Invention is credited to Debuisschert, Quentin, Marchal-George, Nathalie, Nocca, Jean-Luc, Picard, Florent, Uzio, Denis.
Application Number | 20040035752 10/457018 |
Document ID | / |
Family ID | 29433349 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040035752 |
Kind Code |
A1 |
Marchal-George, Nathalie ;
et al. |
February 26, 2004 |
Process for producing hydrocarbons with low sulphur and nitrogen
contents
Abstract
A process for desulphurizing a gasoline feed comprising at least
150 ppm by weight of sulphur-containing compounds using a
hydrodesulphurization catalyst is characterized in that said feed
undergoes prior denitrogenation treatment under conditions such
that the amount of nitrogen-containing compounds present in said
feed when it is brought into contact with said
hydrodesulphurization catalyst does not exceed 150 ppm by
weight.
Inventors: |
Marchal-George, Nathalie;
(Saint Genis Laval, FR) ; Picard, Florent; (Saint
Symphorien D'Ozon, FR) ; Uzio, Denis; (Marly Le Roi,
FR) ; Debuisschert, Quentin; (Rueil Malmaison,
FR) ; Nocca, Jean-Luc; (Houston, TX) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
Institute Francais du
Petrole
Rueil Malmaison Cedex
FR
|
Family ID: |
29433349 |
Appl. No.: |
10/457018 |
Filed: |
June 9, 2003 |
Current U.S.
Class: |
208/211 ;
208/210 |
Current CPC
Class: |
C10G 67/06 20130101 |
Class at
Publication: |
208/211 ;
208/210 |
International
Class: |
C10G 065/04; C10G
065/06; C10G 045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2002 |
FR |
02/07.054 |
Claims
1. A process for desulphurizing a gasoline feed comprising at least
150 ppm by weight of sulphur-containing compounds using a
hydrodesulphurization catalyst, characterized in that said feed
undergoes prior denitrogenation treatment under conditions such
that the amount of nitrogen-containing compounds present in said
feed when it is brought into contact with said
hydrodesulphurization catalyst does not exceed 150 ppm by
weight.
2. A process according to claim 1, in which said denitrogenation
treatment is carried out immediately prior to said contact.
3. A process according to claim 1, in which at least one step
selected from the group constituted by: a) selective hydrogenation
of the dienes contained in the feed; b) transformation of light
sulphur-containing compounds contained in the feed; c) separation
of said feed into at least two fractions including: a light
fraction containing a minor portion of the sulphur-containing
compounds; a heavy fraction containing a major portion of the
sulphur-containing compounds; is carried out between said
denitrogenation treatment (step d)) and said contact with the
hydrodesulphurization catalyst (step e) and possibly step f))
4. A process according to claim 3, in which said contact is made
with at least the heavy fraction from step c).
5. A process according to claim 2, in which at least one step
selected from the group constituted by: a) selective hydrogenation
of the dienes contained in the feed; b) transformation of light
sulphur-containing compounds contained in the feed; c) separation
of said feed into at least two fractions including: a light
fraction containing a minor portion of the sulphur-containing
compounds; a heavy fraction containing a major portion of the
sulphur-containing compounds; is carried out prior to said
denitrogenation temperature (step d)).
6. A process according to claim 5, in which contact with the
hydrodesulphurization catalyst is made with at least the heavy
fraction from step c).
7. A process according to one of the preceding claims, in which
said contact is made in at least two steps e) and f).
8. A process according to one of the preceding claims, in which
said hydrodesulphurization catalyst comprises at least one element
from group VII of the periodic table.
9. A process according to one of the preceding claims, in which
said hydrodesulphurization catalyst comprises at least one element
from group VIB of the periodic table.
10. A process according to claim 8 or claim 9, in which said
catalyst comprises at least one element from group VIII of the
periodic table selected from the group constituted by nickel and
cobalt, and at least one group VIB element selected from the group
constituted by molybdenum and tungsten.
11. A process according to one of the preceding claims, in which
said contact is made at a temperature in the range 250.degree. C.
to 350.degree. C., a pressure in the range 1 to 3 MPa, an hourly
space velocity in the range 1 h.sup.-1 to 10 h.sup.-1, and a
H.sub.2/HC ratio in the range 50 l/l to 500 l/l.
12. Application of the process according to one of the preceding
claims, to gasoline from catalytic cracking or from cokefaction of
a heavy hydrocarbon feed or from steam cracking.
Description
[0001] The present invention relates to a process for producing
hydrocarbons with a low sulphur content. Said hydrocarbon fraction
contains an olefin fraction that generally exceeds 5% by weight,
usually 10% by weight, a sulphur content of more than 100 ppm by
weight and a nitrogen content of more than 20 ppm by weight. The
process allows all of a gasoline cut containing sulphur to be
upgraded, reducing the sulphur content of said gasoline cut to very
low levels, without reducing the gasoline yield, and minimizing the
reduction in the octane number during said process. The invention
is of particular application when the gasoline to be treated is a
cracked gasoline containing more than 300 ppm by weight or more
than 500 ppm by weight of sulphur, and a nitrogen content that is
generally more than 50 ppm by weight, or more than 100 ppm by
weight, preferably more than 150 ppm by weight, or 200 ppm by
weight or more.
[0002] Future regulations regarding vehicle fuels will require a
substantial reduction in the sulphur content of those fuels, in
particular gasoline. That reduction is particularly aimed at
limiting the sulphur dioxide content and the nitrogen content in
particular in vehicle exhausts. Current specifications regarding
sulphur contents are of the order of 150 ppm by weight and will be
reduced in the future to below 10 ppm via a limit of 30 ppm by
weight. The change in the sulphur content specifications
necessitates the development of novel processes for severe
desulphurization of gasoline.
[0003] The principal sources of sulphur in gasoline bases are
cracked gasolines, principally the gasoline fraction deriving from
a process for catalytic cracking of a residue from atmospheric
distillation or vacuum distillation of crude oil. The gasoline
fraction derived from catalytic cracking, which represents an
average of 40% of gasoline bases, contributes more than 90% of the
sulphur in that gasoline. As a result, the production of low
sulphur gasoline requires a step for desulphurizing catalytically
cracked gasoline. That desulphurization is conventionally achieved
by one or more steps for bringing the sulphur-containing compounds
contained in said gas into contact with a gas that is rich in
hydrogen in a hydrodesulphurization process.
[0004] Further, the octane number of said gasolines is very closely
linked to their olefin content. Preserving the octane number of
said gasolines thus necessitates limiting reactions transforming
olefins to paraffins, which reactions are inherent to
hydrodesulphurization processes.
[0005] When the gasoline is desulphurized conventionally, the
olefin saturation reactions occurring in parallel with the
reactions transforming sulphur-containing compounds into H.sub.2S
lead to a substantial octane number drop. Within the context of
restriction to sulphur specifications in gasoline, such processes
result in severe drops in octane number. A variety of solutions
have been proposed to selectively eliminate the sulphur-containing
compounds from the gasoline by limiting undesirable olefin
hydrogenation reactions, generally determined by the skilled person
as the degree of olefin saturation at the reactor outlet. However,
the impact of nitrogen-containing compounds on the activity and/or
selectivity of gasoline hydrodesulphurization catalysts is
practically unknown.
[0006] However, in the case of hydrotreating middle distillates
(gas oil and kerosene), the presence of nitrogen-containing
compounds is known to inhibit hydrodesulphurization reactions. As
an example, a process for producing middle distillates with a low
sulphur content has been proposed, comprising a step for
eliminating basic nitrogen before the hydrotreatment step (Proc Int
Conf Stab Handl Liq Fuels, 7.sup.th Meeting, 2000, Vol 1, 153-163).
This step for eliminating basic nitrogen is stated to be necessary
to obtaining high degress of desulphurization. However, the
technical problems posed by gasoline hydrodesulphurization appear
to differ from those posed by hydrodesulphurization of middle
distillates, in particular due to difficulties inherent to the
presence of unsaturated compounds in gasolines and to the specific
problem of the loss of octane number described above.
[0007] In the particular case of gasoline, U.S. Pat. No. 6,120,679
describes, in contrast, a method for preparing
hydrodesulphurization catalysts based on a step for pre-treating
the catalysts with a nitrogen-containing compound (pyridine).
[0008] Studies carried out by the Applicant concerning the present
application have demonstrated that the presence of nitrogen in a
substantial quantity, i.e., in amounts higher than those previously
described, have a non negligible effect on the activity of the
gasoline hydrodesulphurization catalyst and in particular, the
presence of basic nitrogen-containing compounds such as pyridine
beyond a certain threshold degrades not only the activity but also
the selectivity of the hydrodesulphurization catalysts. In
particular, the Applicant has discovered that eliminating certain
proportions of said nitrogen-containing compounds has a very
substantial effect on the decomposition of sulphur-containing
compounds by the catalyst, but a relatively limited effect on the
hydrogenation of unsaturated compounds. In one possible application
of the present invention, for the same degree of saturation of
olefins at the reactor outlet and for the same operating
temperature for the hydrodesulphurization reactor, it is possible
to increase the catalyst activity by prior reduction in the
nitrogen-containing compounds present in the gas. In a further
application of the present invention, eliminating basic
nitrogen-containing compounds prior to hydrodesulphurization can
limit the degree of olefin saturation for a fixed sulphur content
at the reactor outlet. The present invention is thus of particular
application to the treatment of gasoline cuts with a high
nitrogen-containing compound content.
[0009] In general, the present invention relates to a process that
can achieve at least one of the following advantages and preferably
all simultaneously:
[0010] satisfy future specifications on vehicle gasoline, i.e.,
sulphur contents of the order of 50 ppm or less than 10 ppm
depending on the State;
[0011] limit the nitrogen content in the gasoline;
[0012] control olefin hydrogenation processes during said
process;
[0013] thereby limit the octane number loss linked to
hydrodesulphurization processes;
[0014] maximize the service life of hydrodesulphurization catalysts
by employing hydrodesulphurization reactors at lower
temperatures.
[0015] In summary, the present desulphurization process proposes a
solution to obtaining high degrees of desulphurization while
limiting the octane number loss due to olefin hydrogenation. This
results in the production of a low sulphur gasoline with a high
octane number.
[0016] The present invention provides a process for desulphurizing
a gasoline feed comprising at least 150 ppm by weight of
sulphur-containing compounds using a hydrodesulphurization
catalyst, characterized in that said feed undergoes prior
denitrogenation treatment under conditions such that the amount of
nitrogen-containing compounds present in said feed when it is
brought into contact with said hydrodesulphurization catalyst does
not exceed 150 ppm by weight.
[0017] In one possible implementation of the invention, the
denitrogenation treatment is carried out immediately prior to said
contact (hydrodesulphurization).
[0018] In a first implementation, for example when said treatment
is carried out immediately prior to said contact (step e) and
possibly f)), at least one step selected from the group constituted
by:
[0019] a) selective hydrogenation of the dienes contained in the
feed;
[0020] b) transformation of light sulphur-containing compounds
contained in the feed;
[0021] c) separation of said feed into at least two fractions
including:
[0022] a light fraction containing a minor portion of the
sulphur-containing compounds;
[0023] a heavy fraction containing a major portion of the
sulphur-containing compounds;
[0024] is carried out prior to said denitrogenation temperature
(step d)).
[0025] Advantageously, said contact (step e) and possibly step f))
is preferably carried out with at least the heavy fraction from
step c).
[0026] In an alternative implementation, at least one step selected
from the group constituted by:
[0027] a) selective hydrogenation of the dienes contained in the
feed;
[0028] b) transformation of light sulphur-containing compounds
contained in the feed;
[0029] c) separation of said feed into at least two fractions
including:
[0030] a light fraction containing a minor portion of
sulphur-containing compounds;
[0031] a heavy fraction containing a major portion of the
sulphur-containing compounds;
[0032] is carried out between said denitrogenation treatment (step
d)) and said contact (step e) and possibly step f)).
[0033] Advantageously, said contact (hydrodesulphurization) is
preferably carried out with at least said heavy fraction from step
c).
[0034] Preferably, said contact is made in at least two steps e)
and f), regardless of the envisaged implementation.
[0035] In general, said hydrodesulphurization catalyst comprises at
least one element from group VIII of the periodic table, and
advantageously, said hydrodesulphurization catalyst comprises at
least one element from group VIB of the periodic table.
[0036] Preferably, said group VIII element is selected from the
group constituted by nickel and cobalt and said at least one group
VIB element is selected from the group constituted by molybdenum
and tungsten.
[0037] The conditions for said contact are generally as follows: a
temperature in the range 200.degree. C. to 450.degree. C., a
pressure in the range 1 to 3 MPa, an hourly space velocity in the
range 1 h.sup.-1 to 10 h.sup.-1, and a H.sub.2/HC ratio (ratio of
hydrogen to hydrocarbons, expressed in litres per litre) in the
range 50 l/l to 500 l/l.
[0038] The present process can advantageously be applied to
gasoline from catalytic cracking or from cokefaction of a heavy
hydrocarbon feed or from steam cracking.
[0039] The invention will be better understood from the following
description of an implementation given purely by way of
illustration and which is not in any way limiting.
[0040] In a preferred but not obligatory implementation of the
invention, the feed to be desulphurized is optionally pre-treated
in a concatenation of reactors for selective diolefin hydrogenation
(step a) and for rendering light-sulphur-containing compounds
heavier (step b)). The feed that has optionally been pre-treated is
then distilled and fractionated into at least two cuts (step c)): a
light gasoline that is depleted in sulphur and rich in olefins, and
a heavy gasoline that is rich in sulphur and depleted in olefins.
The light fraction from the three preceding steps generally
contains less than 100 ppm of sulphur, preferably less than 50 ppm
of sulphur, and highly preferably, less than 20 ppm of sulphur, and
in general does not need subsequent treatment prior to its
incorporation as a gasoline base. The heavy fraction from the three
preceding steps, which contains the major portion of the sulphur,
is treated using the process of the present invention. This
preferred implementation has the advantage of further minimizing
the octane number loss as light olefins containing 5 carbon atoms,
which are readily hydrogenated, are not sent to the
hydrodesulphurization section.
[0041] Step a) is optional and is principally intended to eliminate
the diolefins present in the gasoline. This step can maximize the
service life of catalysts used in the downstream steps. Steps b)
and c) are also optional, but if they are carried out prior to step
e), they can minimize the overall octane number loss in the
process.
[0042] Denitrogenation step d) is carried out before contact with
the hydrodesulphurization catalyst (steps e) and/or f)) or before
at least one of steps a), b) and/or c), so that the amount of
nitrogen-containing compounds does not exceed 150 ppm (expressed by
weight), preferably 125 ppm, more preferably 100 ppm.
[0043] The process of the invention comprises at least the two
steps d) and e). Step d) corresponds to a step for at least partial
elimination of the nitrogen contained in the gasoline; step e)
corresponds to a step for hydrotreatment of the pre-treated
gasoline.
[0044] In general, the experimental conditions of these
pre-treatment, denitrogenation or hydrodesulphurisation steps a) to
f) are as follows:
[0045] 1) Selective Hydrogenation (Step a)):
[0046] This optional pre-treatment step for the gasoline to be
desulphurized is intended to at least partially eliminate the
diolefins present in the gasoline. Diene hydrogenation is an
optional but advantageous step, which can eliminate the vast
majority of the dienes present in the cut to be treated prior to
hydrotreatment. Diolefins are precursors to gums, which polymerise
in the hydrotreatment reactors and limit their service life.
[0047] This step generally takes place in the presence of a
catalyst comprising at least one group VIII metal, preferably
selected from the group constituted by platinum, palladium and
nickel, and a support. As an example, it is possible to use a
catalyst containing 1% to 20% by weight of nickel deposited on an
inert support such as alumina, silica, silica-alumina, a nickel
aluminate or a support containing at least 50% alumina. This
catalyst operates at a pressure of 0.4 to 5 MPa, at a temperature
of 50.degree. C. to 250.degree. C., with an hourly space velocity
of the liquid of 1 h.sup.-1 to 10 h.sup.-1. A further group VIB
metal such as molybdenum or tungsten can be combined therewith to
form a bimetallic catalyst. This group VIB metal, if combined with
a group VIII metal, will be deposited in an amount of 1% by weight
to 20% by weight.
[0048] As to the operating conditions, usually, we operate under
pressure in the presence of a quantity of hydrogen that is in
slight excess with respect to the stoichiometric value necessary to
hydrogenate the diolefins. The hydrogen and the feed to be treated
are injected as upflows or downflows into a reactor, preferably
with a fixed catalyst bed. The temperature is most generally in the
range 50.degree. C. to 300.degree. C., preferably in the range
80.degree. C. to 250.degree. C., more preferably in the range
120.degree. C. to 210.degree. C.
[0049] Most generally, the pressure is 0.4 to 5 MPa, preferably
more than 1 MPa. An advantageous pressure is in the range 1 to 4
MPa, limits included.
[0050] Under these conditions, the space velocity is of the order
of 1 h.sup.-1 to 12 h.sup.-1, preferably of the order of 4 h.sup.-1
to 10 h.sup.-1.
[0051] The light fraction of the catalytically cracked gasoline cut
can contain up to a few % by weight of diolefins. After
hydrogenation, the diolefins content is reduced to less than 3000
ppm, or less than 2500 ppm and more preferably less than 1500 ppm.
In some cases, a content of less than 500 ppm can be achieved. The
diene content after selective hydrogenation can even be reduced to
less than 250 ppm.
[0052] Concomitantly with the selective diolefin hydrogenation
reaction, the external double bond of the olefins leads to the
formation of internal olefins. This isomerization results in the
formation of olefins that are more resistant to saturation with
hydrogen and to s slight increase in octane number (or a
compensation in octane number due to the slight olefin loss). This
is due to the fact that internal olefins have an octane number that
is generally higher than that of terminal olefins.
[0053] In one implementation of the invention, the diene
hydrogenation step is carried out in a catalytic hydrogenation
reactor that comprises a catalytic reaction zone preferably
traversed by the entire feed and by the quantity of hydrogen
necessary to carry out the desired reactions.
[0054] Certain nitrogen-containing compounds are also transformed
during this step. This is the case, for example, with slightly
basic nitriles which, through hydrogenation, are transformed into
amines which are more basic.
[0055] 2) Transformation of Light Sulphur-Containing Compounds
(Step b)):
[0056] This optional step consists of transforming light saturated
sulphur-containing compounds, i.e., compounds with a boiling point
that is lower than that of thiophene, into saturated
sulphur-containing compounds with a boiling point that is higher
than that of thiophene. Said light sulphur-containing compounds are
typically mercaptans containing 1 to 5 carbon atoms, CS.sub.2 and
sulphides containing 2 to 4 carbon atoms. This transformation is
preferably carried out over a catalyst comprising at least one
group VIII element (groups 8, 9 and 10 of the new periodic table)
on an alumina, silica or silica-alumina or nickel aluminate type
support. The choice of catalyst is made so as to promote the
reaction between light mercaptans and olefins, which results in
mercaptans or sulphides with boiling points that are higher than
thiophene.
[0057] This optional step can possibly be carried at the same time
as step a), in the same reaction bed and with the same catalyst. As
an example, it may be particularly advantageous to operate, during
the diolefin hydrogenation, under conditions such that at least a
portion of the mercaptans are transformed.
[0058] In this case, the temperatures are generally in the range
100.degree. C. to 300.degree. C., preferably in the range
150.degree. C. to 250.degree. C. The H.sub.2/feed ratio is adjusted
to between 1 and 20 litres per litre, preferably to between 3 and
15 litres per litre. The space velocity is generally in the range 1
h.sup.-1 to 10 h.sup.-1, preferably in the range 2 h.sup.-1 to 6
h.sup.-1, and the pressure is in the range 0.5 to 5 MPa, preferably
in the range 1 to 3 MPa.
[0059] The nitrogen-containing compounds present in the gas are
also partially rendered heavier during this step. The inventors
have discovered that the nitrogen-containing compounds present in
the IP (initial point) fraction -60.degree. C. were transformed
into heavier nitrogen-containing compounds with a boiling point of
more than 60.degree. C. Thus, step b) renders possible separation
of a portion of the nitrogen-containing compounds from the
IP-60.degree. C. fraction.
[0060] 3) Separation of Gasoline into at Least Two Fractions (Step
c)):
[0061] This optional step, carried out after steps a) and b), can
produce a light desulphurized gasoline, generally containing less
than 5 ppm of mercaptans. During this sep, the gasoline is
fractionated into at least two fractions:
[0062] a light fraction containing a limited residual sulphur
content, preferably less than about 50 ppm, more preferably less
than about 20 ppm, highly preferably less than about 10 ppm, and
which enables said cut to be used without carrying out (an)other
treatment(s) aimed at reducing the sulphur content; this light
fraction is generally depleted in light nitrogen-containing
compounds;
[0063] a heavy fraction in which the major portion of the sulphur
initially present in the feed i.e., all of the sulphur which is not
found in the light gasoline, is concentrated.
[0064] Said separation is preferably carried out using a
conventional distillation column. This fractionation column can
separate a light fraction of the gasoline containing a small
fraction of sulphur from a heavy fraction preferably containing the
major portion of the sulphur initially present in the initial
gasoline.
[0065] The light gasoline obtained following separation generally
contains at least all of the olefins containing five carbon atoms,
preferably compounds containing five carbon atoms and at least 20%
of olefins containing six carbon atoms. Generally, this light
fraction obtained after steps a) and b) has a low sulphur content,
i.e., it is not in general necessary to treat the light cut before
using it as a fuel.
[0066] 4) Elimination of Nitrogen from Gasoline: Step d):
[0067] The nitrogen-containing compounds present in gasoline are
principally from the following families: nitrites, amines,
pyrroles, pyridines and anilines. These compounds are generally
present in the gasoline in an amount of 20 to 400 ppm. Most of
these compounds are basic; thus, they can be eliminated by
separation in an acidic medium. The step for eliminating nitrogen
from the gasoline can thus consist of washing the gasoline with an
aqueous solution containing an acid compound. Examples of acids
that can be cited are phosphoric acid, sulphuric acid, hydrochloric
acid and formic acid. Any type of acid that is soluble in water and
has sufficient acidity to protonate nitrogen can be used for this
operation. This operation is carried out by bringing the gasoline
to be treated into contact with the acid, for example in a washing
column. The washing conditions are optimized so that the gasoline
that is recovered contains less than 150 ppm of nitrogen,
preferably less than 100 ppm by weight, and more preferably less
than 50 ppm of nitrogen, or less than 20 ppm.
[0068] Step d) can also be accomplished by treating the gasoline on
a solid with a sufficient Lewis or Bronsted acidity to fix the
nitrogen-containing compounds. Examples of solids that can be used
are ion exchange resins, strong acids on mineral supports such as
phosphoric acid on silica, or silica aluminas in the zeolitic or
amorphous form. This list is only given by way of illustration, and
the scope of the present invention encompasses the use of any other
known technique for eliminating all or a portion of the
nitrogen-containing compounds present in a hydrocarbon fraction.
The gasoline traverses a guard mass that is in general use in a
fixed bed, the basic nitrogen-containing compounds are protonated
and become fixed on the mass. Once saturated, the mass can be
regenerated, or more simply, replaced with a fresh mass.
[0069] The choice of mass, its length of use and the operating
conditions are optimized so that the gasoline produced during step
d) contains less than 150 ppm of nitrogen, or 100 ppm of nitrogen,
preferably less than 50 ppm of nitrogen, more preferably less than
20 ppm of nitrogen. In a further implementation, the choice of
mass, its service life and the operating conditions are optimized
so that at least 50%, preferably 70% and more preferably at least
90% of the nitrogen-containing compounds are eliminated during this
step.
[0070] In an advantageous implementation of the invention, step a)
is carried out before step d). Certain nitrogen-containing
compounds such as nitrites are transformed during step a) to form
the corresponding amines. The observed reaction is as follows:
CH.sub.3--CH.sub.2--CN+2H.sub.2.fwdarw.CH.sub.3--CH.sub.2--CH.sub.2--NH.su-
b.2
[0071] As amines are more basic than nitrites, their extraction
during step d) will be facilitated.
[0072] Step d) can also include separation, generally by
distillation, of the gasoline to be treated. The basic compounds
present in the cracked gasoline are concentrated in the heavy
fraction of the gasoline. Said heavy fraction is eliminated by
distillation, and can thus at least partially eliminate the basic
nitrogen-containing compounds. In this case, step d), which
consists of distillation, produces at least two fractions:
[0073] the light fraction, which concentrates the olefins and which
is depleted in nitrogen;
[0074] the heavy fraction, which concentrates the basic nitrogen
and the aromatics and which is depleted in olefins.
[0075] 5) Gasoline Hydrodesulphurization: Step e)
[0076] The hydrodesulphurization step (step e)) consists of passing
the gas to be treated, in the presence of hydrogen, over a
hydrodesulphurization catalyst at a temperature in the range
200.degree. C. to 350.degree. C., preferably in the range
250.degree. C. to 320.degree. C. and at a pressure in the range 1
to 3 MPa, preferably in the range 1.5 to 2.5 MPa. The liquid space
velocity is generally in the range 1 h.sup.-1 to 10 h.sup.-1,
preferably in the range 2 h.sup.-1 to 5 h.sup.-1; the H.sub.2/HC
ratio is 50 litres/litre (l/l) to 500 l/l, preferably in the range
100 l/l to 450 l/l, and more preferably in the range 150 l/l to 400
l/l. The H.sub.2/HC ratio is the ratio between the hydrogen flow
rate at 1 atmosphere and at 0.degree. C. and the hydrocarbon flow
rate. Under these conditions, the reaction takes place in the gas
phase. The operating conditions during this step are adjusted as a
function of the characteristics of the feed to be treated, to
accomplish the desired degree of desulphurization. The effluents
from said hydrodesulphurization step are partially desulphurized
gasoline, residual hydrogen and the H.sub.2 S produced by
decomposition of the sulphur-containing compounds.
[0077] The catalysts used during step e) comprise at least one
group VIII element and/or at least one group VIB element on a
suitable support.
[0078] The amount of group VIII metal, expressed as the oxide, is
generally in the range from 0.5% to 15% by weight, preferably in
the range 1% to 10% by weight. The amount of group VIB metal is
generally in the range 1.5% to 60% by weight, preferably in the
range 3% to 50% by weight.
[0079] The group VIII element, when present, is preferably cobalt,
and the group VIB element, when present, is generally molybdenum or
tungsten. The catalyst support is normally a porous solid such as
an alumina, a silica-alumina, or other porous solids, such as
magnesia, silica or titanium oxide, used alone or as a mixture with
alumina or silica-alumina. To minimize hydrogenation of the olefins
present in the heavy gasoline, it is preferable to use a catalyst
in which the density of the molybdenum, expressed as the % by
weight of MoO.sub.3 per unit surface area, is more than 0.07 and
preferably more than 0.10. The catalyst of the invention preferably
has a specific surface area of less than 200 m.sup.2/g, more
preferably less than 180 m.sup.2/g, and highly preferably less than
150 m.sup.2/g.
[0080] The catalyst used is preferably in an at least partially
sulphurized form. The sulphur or sulphur-containing compound can be
introduced ex situ, i.e., outside the reactor in which the process
of the invention is carried out, or in situ, i.e., in the reactor
used for the process of the invention. Sulphurization consists of
passing a feed containing at least one sulphur-containing compound,
which once decomposed fixes sulphur on the catalyst. This feed can
be gaseous or liquid, for example hydrogen containing H.sub.2S, or
a liquid containing at least one sulphur-containing compound.
[0081] 6) Gasoline Hydrodesulphurization: Step f)
[0082] Hydrodesulphurization step e) can be followed by a
supplemental step aimed at improving the final degree of
desulphurization. This step is compulsory after step e) and can be
carried out with or without intermediate H.sub.2S elimination. Step
f) comprises at least one step for decomposing saturated
sulphur-containing compounds deriving from step e). Said
sulphur-containing compounds are transformed into H.sub.2S over a
catalyst and under conditions such that the olefins are only very
slightly hydrogenated. The degree of hydrogenation (saturation) of
olefins in this step is generally less than 20%, and preferably
less than 10%.
[0083] This hydrodesulphurization step (step f)) generally consists
of passing the gasoline to be treated, in the presence of hydrogen,
over a hydrodesulphurization catalyst, at a temperature in the
range 250.degree. C. to 450.degree. C., preferably in the range
300.degree. C. to 360.degree. C. and at a pressure in the range 1
to 3 MPa, preferably in the range 1.5 to 2.5 MPa. The liquid space
velocity is generally in the range 1 h.sup.-1 to 10 h.sup.-1,
preferably in the range 1 h.sup.-1 to 5 h.sup.-1; the H.sub.2/HC
ratio is in the range 50 litres/litre (l/l) to 500 l/l, preferably
in the range 100 l/l to 450 l/l, and more preferably in the range
150 l/l to 400 l/l. Under these conditions, the reaction takes
place in the gas phase. The operating conditions during this step
are thus adjusted as a function of the characteristics of the feed
to be treated in order to reach the desired degree of
desulphurization.
[0084] The catalyst used during step e) comprises at least one
group VII element selected from the group constituted by nickel,
cobalt, iron, molybdenum and tungsten.
[0085] The amount of group VIII metal, expressed as the oxide, is
generally in the range 1% to 60% by weight, preferably in the range
1% to 40% by weight.
[0086] The catalyst support is normally a porous solid such as an
alumina, a silica-alumina or other porous solids such as magnesia,
silica or titanium oxide, used alone or as a mixture with alumina
or silica-alumina. The catalyst of the invention preferably has a
specific surface area in the range 25 to 350 m.sup.2/g.
[0087] The catalyst is preferably at least partially in the
sulphurized form. The sulphur or a sulphur-containing compound can
be introduced ex situ, i.e., outside the reactor in which the
process of the invention is carried out, or in situ, i.e., in the
reactor used for the process of the invention. Sulphurization
consists of passing a feed containing at least one
sulphur-containing compound, which once decomposed fixes sulphur on
the catalyst. This feed can be gaseous or liquid, for example
hydrogen containing H.sub.2S, or a liquid containing at least one
sulphur-containing compound.
[0088] The importance and advantages of the present invention will
be demonstrated by comparing Example 1 in accordance with the prior
art with Example 2, in accordance with the invention.
EXAMPLE 1
[0089] (Prior Art)
[0090] Example 1 concerns a desulphurization process with no
preliminary nitrogen elimination.
[0091] A hydrodesulphurization catalyst A was obtained by
impregnating a transition alumina in the form of beads with a
specific surface area of 130 m.sup.2/g and with a pore volume of
1.04 ml/g, with an aqueous solution containing molybdenum and
cobalt in the form of ammonium heptamolybdate and cobalt nitrate.
The catalyst was then dried and calcined in air at 500.degree. C.
the amount of cobalt and molybdenum in this sample was 3% of CoO
and 10% of MoO.sub.3.
[0092] 100 ml of catalyst A was placed in a hydrodesulphurization
tube reactor using a fixed bed. The catalyst was initially
sulphurized by treatment for 4 hours at a pressure of 3.4 MPa at
350.degree. C., in contact with a feed constituted by 2% of sulphur
in the form of dimethyldisulphide in n-heptane.
[0093] The treated feed was a catalytically cracked gasoline with
an initial boiling point of 50.degree. C. and an end point of
225.degree. C. The sulphur content was 1450 ppm by weight and its
bromine index (BrI) was 69 g/100 g. This gasoline had a nitrogen
content of 180 ppm of nitrogen including 165 ppm of basic nitrogen
(the term "basic nitrogen" means the nitrogen included in compounds
comprising a nitrogen-containing group with a basic nature). The
total nitrogen was assayed using American standard method ASTM
4629, and the basic nitrogen was assayed using ASTM 4739.
[0094] This feed was treated over catalyst A, at a pressure of 2
MPa, a H.sub.2/HC ratio of 300 l/l and a HSV of 2 h.sup.-1. Table 1
shows the influence of temperature on the degress of olefin
desulphurization and saturation.
1TABLE 1 Sulphur content BrI of in desulphurized Degree of
desulphurized Degree of olefin Temperature gasoline
desulphurization gasoline saturation (.degree. C.) (ppm by weight)
(HDS-%) (g/100 g) (HDO-%) 280 292 79.9 49.2 28.7 290 165 88.6 45.6
33.9 300 108 92.6 38.97 43.6
[0095] In this example, it appears to be difficult to achieve low
sulphur contents in the effluents for this feed. At 300.degree. C.,
the sulphur content in the effluent was more than 100 ppm for a
degree of olefin saturation of close to 44%.
EXAMPLE 2
[0096] In Accordance with the Invention
[0097] Example 2 was carried out in accordance with the invention,
i.e., most of the basic nitrogen-containing compounds were
eliminated during an acid washing step carried out prior to
desulphurization.
[0098] The feed that was treated was the same as that of Example 1.
This gasoline contained 180 ppm of nitrogen, including 165 ppm of
basic nitrogen. 50 kg of this gasoline was mixed, in a batch
reactor, with 100 kg of a 10% by weight concentrated sulphuric acid
solution in distilled water. The mixture was stirred for 15 minutes
then allowed to settle. The aqueous phase in the lower portion of
the reactor was drawn off. The remaining gasoline was washed with
50 kg of distilled water. After settling, the water was separated
from the gasoline.
[0099] An analysis showed that the gasoline produced had a nitrogen
content of 12 ppm, including 0 ppm of basic nitrogen.
[0100] The reactor used in Example 1 was charged with fresh
catalyst A and sulphurized using the same procedure as that
described in Example 1.
[0101] This feed was treated over catalyst A, at a pressure of 2
MPa, a H.sub.2/HC ratio of 300 l/l and a HSV of 2 h.sup.-1. The
operating conditions applied in Example 2 were identical to the
operating conditions of Example 1. Table 2 shows the influence of
temperature on the degrees of olefin desulphurization and
saturation.
2TABLE 2 Sulphur content BrI of in desulphurized Degree of
desulphurized Degree of olefin Temperature gasoline
desulphurization gasoline saturation o (.degree. C.) (ppm by
weight) (HDS-%) (g/100 g) (HDO-%) 280 160 89.0 48.2 30.1 290 97
93.3 43.1 37.5 300 59 95.9 37.4 45.8
[0102] Under the same operating conditions, the degree of
desulphurization achieved in the process of the invention was
higher than that of Example 1. In contrast, the degrees of olefin
saturation were comparable. This means that a desulphurization
process carried out in accordance with the invention can increase
the selectivity of the catalyst used: the loss of olefins and thus
the octane number (measured at constant degree of desulphurization)
are lower when the gasoline is at least partially freed from
nitrogen-containing compounds before desulphurization than when
treated directly.
[0103] The reduction in the amount of nitrogen in the gasoline
prior to hydrodesulphurization also causes a substantial
improvement in catalyst activity. This increase can, for example,
minimize deactivation phenomena and maximize the service life of
hydrodesulphurization catalysts by using lower operating
temperatures.
[0104] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0105] The entire disclosures of all applications, patents and
publications, cited herein and of corresponding French application
No. 02/07.054, filed Jun. 7, 2002 are incorporated by reference
herein.
[0106] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *