[0001] The present invention concerns a process in accordance with the preamble of claim
1 for refining oil.
[0002] According to a process of the present kind, a charge containing in particular light
olefins is oligomerized in the presence of a zeolite catalyst in order to prepare
a diesel fuel product.
[0003] The catalyst ZSM-5 is widely used in the oil industry. It is employed, for instance,
as an additive or promoter for cracking catalysts (FCC), in the preparation of synthetic
gasoline (MTG), for converting propane and butane to aromatic compounds (Cyclar) and
for selective hydrocracking of n-paraffines (M-forming and Dewaxing). It is further
known that zeolites and particularly the ZSM-5 catalyze alkylation of aromatic hydrocarbons
and oligomerization of olefines. By the last-mentioned process it is possible to prepare
mixtures containing abundant C
11+ hydrocarbons from light olefines, said mixtures yielding products of the diesel fuel
type upon hydrogenation.
[0004] The benefits of the ZSM-5 zeolite as a catalyst in oil refining primarily stem from
its form selectivity and its lower rate of coke formation in comparison to other zeolites.
[0005] The lattice structure of zeolites is formed by silicon and aluminium cations tetrahedrically
joined together by oxygen bridges. Since the charge of silicon in a zeolite is +4
whereas the aluminium is three-coordinate, a third cation is needed for balancing
the lower positive charge of aluminium in comparison to silicon. The balancing cation
may, for instance, be a sodium, potassium or hydrogen ion. Conventionally the ZSM-5
comprises a sodium cation as a balancing ion at the ion exchange site. Since the ZSM-5
zeolite in this form is not catalytically active, the sodium ion has to be at least
partially exchanged for a hydrogen ion, whereby acidic sites are formed on the zeolite,
which catalyze some of the typical oil refining reactions.
[0006] Of the many patents which deal with the preparation of conventional ZSM-5 zeolites
reference may be made to, in particular, the U.S. Patent Specification No. 3,702,886.
[0007] It is known in the art that, in addition to the alkaline metal cations mentioned
above, other basic cations, such as Ca, Cs, Sr and Ba, may be incorporated into the
zeolites by ion exchange. By means of the ion exchange it is possible to improve the
catalytic properties of the zeolite. Thus, it has been discovered that the calcium
ion improves the stability of the zeolite catalyst in connection with conversion of
methanol to gasoline. U.S. Patent Specification No. 4,675,460 teaches the use of a
Ca-modified ZSM-5 zeolite catalyst in a process wherein light olefins first are oligomerized
in the presence of a ZSM catalyst modified with Ca (or by another basic cation) for
preparing products of the gasoline class, which then are oligomerized by means of
a Friedel Crafts-type catalyst to provide gas oils.
[0008] The present invention is based on the surprising observation that by using a Ca modified
ZSM-5 zeolite as a oligomerization catalyst for light olefins, a product mixture is
obtained whose cetane number after hydrogenation is higher than that of a product
mixture prepared in the presence of an unmodified ZSM-5 zeolite.
[0009] According to the invention, there is provided a process for preparing a diesel fuel
fraction comprising the steps of
- preoligomerizing a charge containing light C2 - C6 olefins in the presence of a Ca modified ZSM-5 zeolite catalyst containing a minimum
of 0.01 %wt. of Ca, in order to produce a product stream which contains 10 to 95 %wt
C5+ olefins,
- oligomerizing the preoligomerized charge in the presence of a Ca modified ZSM-5 zeolite
catalyst containing a minimum of 0.01 %wt of Ca, in order to prepare a product composition
which at least partially consists of C8+ hydrocarbons, and
- hydrogenating the product composition thus obtained to prepare a diesel fuel fraction
with a high cetane number that boils in the range from 200 to 320°C.
[0010] Considerable benefits are obtained by means of the invention. Thus, by using a Ca
modified ZSM-5 zeolite it is possible substantially to raise the cetane number of
the hydrogenated diesel product obtained from oligomerization of light olefins. As
the working examples below will show, the engine cetane number of a hydrogenated diesel
product prepared by using an unmodified catalyst is in the range from 45 to 47, whereas
the use of a Ca modified catalyst raises the cetane number to above 50. This makes
it possible substantially to decrease or even entirely to eliminate the need for the
additives conventionally used for increasing the cetane number.
[0011] In particular, it should be noticed that the improvement of the diesel fuel quality
cannot be attributed to an increase of the avarage molecular size. The experiments
below were carried out in such a way that the avarage carbon number of the product
obtained by a Ca modified zeolite catalyst was lower or at the most as high as that
of the reference product obtained by an unmodified catalyst.
[0012] In the following, the invention will be examined by means of a detailed description
and some working examples.
A. Catalyst preparation
[0013] The base zeolite of the Ca modified catalyst used in the present invention may be
prepared as described in, for instance, the U.S. Patent Specification No. 3,702,886.
It is required that, for the oligomerization of hydrocarbons, the size of the pores
of the base zeolite are optimal as regards the form selectivity of the zeolite. Upon
distillation the hydrocarbons obtained will yield high quality diesel fuels or isoparaffinic
solvents, for instance. The ratio of Si to Al of the base zeolite and at the same
time also of the Ca modified zeolite is preferably less than 400, in particular it
is in the range from about 30 to 200.
[0014] The Ca ion exchange is carried out by using a zeolite, which is in H
+ form. It is not decisive whether the zeolite has been converted into the H
+ form already during the synthesis or by ion exchange after the synthesis. There might
be small amounts, preferably less than 1000 ppm, of Na present in the zeolite.
[0015] The Ca ion exchange may be performed in liquid or in solid phase. Typically it is
carried out by using aqueous calcium salts. The technology used is widely known. The
salts may be selected from the group comprising chlorides, nitrates, sulfates and
acetates. According to a preferred embodiment of the present invention the Ca ion
is exchanged to the zeolite from a calcium acetate solution. The amount of calcium
in the solution in relation to the zeolite depends to a large extent on the zeolite
used and is typically in the range from 1 to 10 000 µmol Ca
2+/g zeolite, preferably 5 to 2000 µmol Ca
2+/g zeolite. The molarity of the calcium acetate solution is generally in the range
from 0.005 to 1 M, preferably 0.05 to 0.5 M.
[0016] The ion exchange is carried out under stirring at a temperature in the range from
25 to 100 °C, preferably at 40 to 90 °C. The duration of the ion exchange is 0.1 to
4 h, preferably 0.5 to 2 h. The ion exchange zeolite is washed with hot water. The
sample is dried at 100 to 120 °C over night. Calcination is carried out at 500 °C
for 3 h. Calcination may be performed in air, vacuum or in an inert gas atmosphere.
[0017] After drying and calcination the amount of ion exchanged or impregnated calcium is
0.01 to 1.0 % wt, preferably 0.05 to 0.5 % wt. Too high amounts of calcium may impair
the activity of the catalysts. However, if the concentration of calcium is within
the ranges indicated above, calcium does not lessen the zeolite activity. On the contrary,
in some cases calcium may even improve said activity.
[0018] When the zeolite has been ion exchanged by Ca and then calcined, it may be used as
the active part of the catalyst. Because the catalyst generally is required to have
certain physical, thermal and mechanical properties, the zeolite is mixed with a carrier
which is inert as far as the reaction is concerned. The carrier may also, on some
occasions, have catalytical properties. Typically the carrier is selected from the
group comprising clays, silicates, aluminas and other metal oxides. These may be naturally
occurring or synthetical. The carrier may also comprise a mixture of several metal
oxides. Different organic and inorganic adjuvents and binders, such as methyl cellulose,
may be employed for the preparation of the catalyst. The particle size of the catalyst
depends on the type and diameter of the reactor. Thus, in the case of micro reactors,
catalysts with particles sizes in the range from 0.149 to 0.350 mm were used in the
examples. Test runs were also carried out in larger reactors, the catalyst particle
sizes being in the ranges from 0.35 to 1.0 mm or from 1.0 to 2.0 mm. The catalyst
amounts charged into the micro reactors typically varied between 2 and 20 g and those
used in the larger reactors between 50 and 200 g.
B. Oligomerization
[0019] In the present invention a Ca modified ZSM-5 zeolite is used as a catalyst for oligomerization
of light C
2 - C
6 olefines, preferably of n-butene, to provide C
5 - C
22 hydrocarbons. The products of the reaction are typically comprised of mixtures of
branched olefines. There are no aromatic hydrocarbons present in the products or,
possibly, their concentration is less than 0.2 % wt. By distillation gasoline, kerosine
and diesel fractions can be separated from the oligomerization product. For the purposes
of the present invention, the term "diesel fraction" designates a fraction boiling
in the range from 200 ° to 320 °C. It should be pointed out that several different
solvent fractions containing branched paraffines may further be separated from the
oligomerization product by distillation.
[0020] Oligomerization was carried out at a temperature in the range from 160 ° to 350 °C,
preferably in the range from 200 ° to 310 °C and at a pressure in the range from 1
to 150 bar, preferably from 10 to 80 bar. It has been found out that an increase of
the pressure promotes the reaction. However, since high pressures place severe requirements
on the reactor design, is is not preferred to use pressures in excess of 150 bar.
The conversion rate can be raised by increasing the temperature. Too high temperature
may lead to too much cracking and aromatization reactions instead of oligomerization.
The flow rates depend on the oligomerization reactor. Typically the weight hourly
space velocity (WHSV) is in the range from 0.5 to 10, preferably from about 1 to 5
in a conventional tubular reactor. The flow rates and the temperature may also be
changed during the reaction to provide an even degree of conversion.
[0021] Ca modification of the ZSM-5 catalyst will increase the cetane number of the hydrogenated
diesel fraction in comparison to a corresponding product prepared by using unmodified
catalyst by at least 2 units, generally from about 45 to about 50. The cetane number
mentioned in the examples below have been determined as engine cetane numbers.
[0022] In connection with the present invention it has been discovered that products of
diesel fuel type with a high cetane number may be prepared at high yields by using
Ca modified zeolite catalyst in a process wherein a charge mainly comprising light
olefins is contacted at least twice with said zeolite. By way of an example, the process
according to the invention is carried out by first preoligomerizing olefine feed in
the presence of a Ca modified zeolite in order to increase the proportion of the C
8+ fraction, the actual oligomerization being carried out subsequently. Alternatively
the oligomerization product may be fed a second time through the same catalyst bed
to increase the yield of the diesel product. In this respect, the invention differs
from the prior art represented by the U.S. Patent Specification No. 4,675,460 which
requires that the product obtained from a first oligomerization step be alkylated
in the presence of a Friedel-Crafts-catalyst to obtain products of diesel fuel type.
[0023] According to one preferred embodiment, the process according to the invention is
carried out in a plurality of successive reactors, which all contain the same kind
of Ca modified zeolite catalyst.
[0024] By means of process embodiments comprising circulation of the products or employment
of several successive oligomerization reactors, the first oligomerization step of
the C
4 fraction will produce a product stream which contains 10 to 90 % wt, preferably 40
to 80 % wt C
5 + olefins. In this case, the product stream will contain at least some, generally
about 5 to 50 % wt C
8+-components and also C
11+ fractions will be present (in amounts ranging from about 5 to 25 %). Thus, the last-mentioned
components will be formed already during the first oligomerization stage, and their
relative amounts will increase when the mixture is contacted again with the catalyst.
[0025] The product mixture of oligomerization is hydrogenated in a manner knwon
per se, for instance, by hydrogen in the presence of a nickel catalyst to form a diesel
fuel product.
[0026] It should also be noticed that even if the test result presented below have been
obtained in laboratory reactors charged with almost 100 % olefins, the process will
work also on industrial scale with charges whose olefin content lies in the range
from 20 to 100 %, usually from about 30 to 95 %.
[0027] The paraffines, if any, contained in the feed stream do not to any large extent impair
the oligomerization reaction.
[0028] The product prepared by the invention may be used as such as a diesel fuel or it
may be mixed with conventional straight-run distillation fractions.
[0029] Next, the invention will be examined in more detail by means of working examples.
Example 1
Preparation of a Ca modified zeolite catalyst
[0030] A ZSM-5 zeolite was prepared according to the method described in the U.S. Patent
Specification No. 3,702,886. Na-ZSM-5 was ion exchanged three times with a NH
4NO
3 (3 M) solution while stirring. 15 g of the ammonium nitrate solution were used for
each g of the zeolite. The duration of one ion exchange step was 1.5 h. The temperature
of the ion exchange solution was 80 °C. After the ion exchanges the zeolite was washed
with 100 ml hot water/1 g zeolite. The ion exchanged zeolite was dried at 110 °C over
night, and subsequently calcined at a temperature of 540 °C for 3 hours.
[0031] After the above-described ion exchanges with ammonium nitrate the zeolite was subjected
to Ca ion exchange. An ion exchange solution was prepared by mixing 100 ml of a calcium
acetate solution (1 M) with 900 ml of water. 50 g of zeolite were mixed with the solution.
During the ion exchange the solution was continuously stirred. The temperature of
the solution was 80 °C and the time of the ion exchange 1 hour. After the ion exchange
the zeolite was washed with 100 g hot water for each gram of zeolite. Subsequently
the zeolite was dried at 110 °C. Calcination was carried out at 500 °C for 3 hours.
After the ion exchange the calcium content of the zeolite was 0.24 % wt.
The zeolite was admixed with 35 % wt of SiO
2 carrier (Silica gel, Ludox AS-40). After the addition of the carrier the catalyst
was dried and calcined at 540 °C for 3 h. The catalyst was screened to a particle
size of 1.0 to 2.0 mm.
Example 2
Preparation of a Ca modified zeolite catalyst
[0032] The preparation of the zeolite and the ion exchange with the NH
4NO
3 solution were carried out as described in example 1. The Ca ion exchange solution
was prepared by mixing 25 ml of a calcium acetate solution (1 M) with 975 ml of water.
50 g of zeolite were admixed with the solution. The ion exchange was carried out as
described in example 1. The Ca concentration of the zeolite was after the ion exchange
0.092 % wt. The carrier was added in the same way as in example 1.
Example 3 (comparative)
The use of an unmodified zeolite catalyst for oligomerization; the properties of the
diesel fuel fraction
[0033] 200 g of catalyst was charged into a tubular steel reactor whose diameter was 30
mm. The catalyst particle size was in the range from 1.0 to 2.0. First 1-butene was
fed through the catalyst bed. Then, in order to increase the yield of diesel fractions,
the product obtained was fed a second time through the same catalyst. The composition
of the liquid feed was C
4 = 42.2 %, C
8 = 42.4 %, C
11+ = 11.3 %, C
5+C
6+C
7+C
9+C
10 = 4.1 %
Test conditions |
|
Reactor temperature (°C) |
240 - 280 |
Pressure (bar) |
50 |
WHSV (h-1) |
1 |
Catalyst |
unmodified ZSM-5 |
[0034] The product was collected in a cooled vessel. The product was distilled with the
following cut points:
Distillation fraction: |
|
IBP - 30 °C |
total gases |
30 - 180 °C |
gasoline |
180 - 200 °C |
kerosine |
200 - 285 °C |
diesel |
285 - FBP |
bottoms |
[0035] The yield of the diesel fraction was 23.1 %. The diesel fraction was hydrogenated
before analyzing its product properties. The engine cetane number of the diesel fraction
(IBP 200 °C, FBP 285 °C) was
45. The avarage carbon number was 13.25. The remaining data of the product analysis
were as follows:
Product analysis |
|
Density (15 °C, kg/m3) |
778.2 |
Bromine number |
0.3 |
Viscosity (mm2/s, 20 °C) |
2.08 |
Cloud point (°C) |
<-50 |
Pour point (°C) |
<-50 |
Filterability (°C) |
<-50 |
Example 4 (comparative)
Properties of a diesel fraction distilled with different cut points
[0036] The product obtained from the tubular reactor of example 3 was distilled with different
cut points.
[0037] The product was collected in a cooled vessel. The product was distilled with the
following cut points.
Distillation fractions: |
|
IBP - 30 °C |
total gases |
30 - 180 °C |
gasoline |
180 - 200 °C |
kerosine |
200 - 315 °C |
diesel |
315 - FBP |
bottoms |
[0038] The yield of the diesel fraction was 23.1 %. The diesel fraction was hydrogenated
before analysing is for its product properties. The engine cetane number of the diesel
fraction (IBP 200 °C, FBP 315 °C) was
46. The avarage carbon number was 13.45. The other data of the product analysis:
Product analysis |
|
Density (15 °C, kg/m3) |
798.8 |
Bromine number |
0.4 |
Viscosity (mm2/s, 20 °C) |
2.60 |
Cloud point (°C) |
<-50 |
Pour point (°C) |
<-50 |
Filterability (°C) |
<-50 |
Example 5
The use of a Ca modified zeolite in oligomerization; the properties of the diesel
fuel fraction
[0039] 200 g of the catalyst were charged into a tubular steel reactor whose diameter was
30 mm. The catalyst particle sizes were in the range from 1.0 to 2.0 mm. First, 1-butene
was fed through the catalyst bed. Thereafter, in order to increase the diesel yield,
the product obtained was fed once more through the same catalyst bed. The composition
of the liquid feed was C
4 = 43.9 %, C
8 = 40.6 %, C
11+ = 11.2 %, C
5+C
6+C
7+C
9+C
10 = 4.3 %
Test conditions: |
|
Reactor temperature (°C) |
240 - 270 |
Pressure (bar) |
50 |
WHSV (h-1) |
1 |
Catalyst |
Ca modified ZSM-5 |
[0040] The product was collected in a cooled vessel. The product was distilled according
to the following cut points.
Distillation fractions |
|
IBP - 30 °C |
total gases |
30 - 180 °C |
gasoline |
180 - 200 °C |
kerosine |
200 - 318 °C |
diesel |
318 - FBP |
bottoms |
[0041] The yield of the diesel fraction was 23.4 %. The diesel fraction was hydrogenated
before analysing it for its product properties. The engine cetane number (IBP 200
°C, FBP 318 °C) was
50. The avarage carbon number was 13.10. The other data of the product analysis were:
Product analysis |
|
Density (15 °C, kg/m3) |
783.6 |
Bromine number |
1.8 |
Viscosity (mm2/s, 20 °C) |
2.74 |
Cloud point (°C) |
<-50 |
Pour point (°C) |
<-50 |
Filterability (°C) |
<-50 |
Example 6 (comparative)
The use of an unmodified zeolite catalyst in oligomerization; the properties of the
diesel fuel fraction
[0042] 50 g of the catalyst were charged into a tubular steel reactor whose diameter was
30 mm. The catalyst particle sizes were in the range from 0.5 to 1.0 mm. First, 1-butene
was fed through the catalyst bed. In order to increase the diesel yield, the product
obtained was fed still another time through the same catalyst. The composition of
the liquid feed was C
4 = 55.0 %, C
8 = 33.2 %, C
11+ = 9.3 %, C
5+C
6+C
7+C
9+C
10 = 2.5 %
Test conditions: |
|
Reactor temperature (°C) |
210 - 235 |
Pressure (bar) |
50 |
WHSV (h-1) |
10-3 |
Catalyst |
unmodified ZSM-5 |
[0043] The product was collected in a cooled vessel. The product was distilled with the
following cut points:
Distillation |
|
IBP - 30 °C |
total gases |
30 - 180 °C |
gasoline |
180 - 200 °C |
kerosine |
200 - 317 °C |
diesel |
317 - FBP |
bottoms |
[0044] The yield of the diesel fraction was 37 %. The diesel fraction was hydrogenated before
analyzing it for its product properties. The engine cetane number of the diesel fraction
(IBP 200 °C, FBP 318 °C) was
46. The avarage carbon number was 13.23. The other data of the product analysis were
the following:
Product analysis |
|
Density (15 °C, kg/m3) |
784.4 |
Bromine number |
0.4 |
Viscosity (mm2/s, 20 °C) |
2.68 |
Cloud point (°C) |
<-50 |
Pour point (°C) |
<-50 |
Filterability (°C) |
<-50 |
Example 7 (comparative)
The properties of a diesel fraction distilled with different cut points
[0045] The product obtained from the tubular reactor of example 6 was distilled with different
cut points.
[0046] The product was distilled with the following cut points.
Distillation fractions |
|
IBP - 30 °C |
total gases |
30 - 180 °C |
gasoline |
180 - 205 °C |
kerosine |
205 - 318 °C |
diesel |
318 - FBP |
bottoms |
[0047] The yield of the diesel fraction was 31.7 %. The diesel fraction was hydrogenated
before analyzing it for its product properties. The engine cetane number of the diesel
fraction (IBP 205 °C, FBP 318 °C) was
47. The avarage carbon number was 13.61. The other data of the product analysis were
the following:
Product analysis |
|
Density (15 °C, kg/m3) |
788.9 |
Bromine number |
1.4 |
Viscosity (mm2/s, 20 °C) |
2.75 |
Cloud point (°C) |
<-50 |
Pour point (°C) |
<-50 |
Filterability (°C) |
<-50 |
Example 8
The use of a modified zeolite catalyst in oligomerization; the properties of the diesel
fuel fraction
[0048] 50 g of catalyst were fed into a tubular steel reactor, the diameter of the tubes
being 30 mm. The catalyst particle size was 0.35 to 1.0 mm. First, 1-butene was fed
through the catalyst bed. In order to increase the yield of diesel oil, the product
obtained was fed still another time through the same catalyst. The composition of
the liquid feed was C
4 = 56.1 %, C
8 = 34.3 %, C
11+ = 6.8 %, C
5+C
6+C
7+C
9+C
10 = 2.8 %.
Experimental conditions: |
|
Reactor temperature (°C) |
260 - 305 |
Pressure (bar |
50 |
WHSV (h-1) |
8-2 |
Catalyst |
Ca modified ZSM-5 |
[0049] The product was collected in a cooled vessel. The product was distilled with the
following
Distillation fractions: |
|
IBP - 30 °C |
light gas |
30 - 180 °C |
gasoline |
180 - 200 °C |
kerosine |
200 - 317 °C |
diesel |
317 - FBP |
bottoms |
[0050] The yield of the diesel fraction was 41 %. It was hydrogenated before analyzing its
product properties. The engine cetane number of the diesel fraction (IBP 200 °C, FBP
317 °C) was
50. The avarage carbon number was 13.32. The other results obtained by product analysis
were:
Product analysis |
|
Density (15 °C, kg/m3) |
774.4 |
Bromine number |
1.2 |
Viscosity (mm2/s, 20 °C) |
2.64 |
Cloud point (°C) |
<-50 |
Pour point (°C) |
<-50 |
Filterability (°C) |
<-50 |
1. A process for preparing a diesel fuel fraction comprising the steps of
- preoligomerizing a charge containing light C2 - C6 olefins in the presence of a Ca modified ZSM-5 zeolite catalyst containing a minimum
of 0.01 %wt. of Ca, in order to produce a product stream which contains 10 to 95 %wt
C5+ olefins,
- oligomerizing the preoligomerized charge in the presence of a Ca modified ZSM-5
zeolite catalyst containing a minimum of 0.01 %wt of Ca, in order to prepare a product
composition which at least partially consists of C8+ hydrocarbons, and
- hydrogenating the product composition thus obtained to prepare a diesel fuel fraction
with a high cetane number that boils in the range from 200 to 320°C.
2. A process as claimed in claim 1, in which a diesel fuel fraction is prepared having
a cetane number higher than 47, preferably higher than 49.
3. A process as claimed in claim 1 or claim 2, in which a Ca modified ZSM-5 zeolite is
used having a ratio of Si to Al less than 400, preferably in the range from 30 to
200.
4. A process as claimed in any one of claims 1 to 3, in which a Ca modified ZSM-5 zeolite
is used containing from 0.01 to 1.0% wt, preferably 0.05 to 0.5 % wt, of ion exchanged
calcium.
5. A process as claimed in any one of the preceding claims, in which the oligomerization
is carried out at a temperature in the range from 160 to 350°C, preferably at 200
to 310°C, and at a pressure in the range from 1 to 150 bar, preferably at 10 to 80
bar.
6. A process as claimed in any one of the preceding claims, in which the charge for the
preoligomerizing step contains 20 to 100 % wt, preferably 30 to 95 % wt, olefins.
7. A process as claimed in any one of the preceding claims, wherein the preoligomerized
charge of the oligomerizing step comprises a hydrocarbon fraction with 40 to 80 %
wt C5+ olefins.
8. A process as claimed in claim 7, in which the preoligomerized charge contains at least
some, preferably 5 to 50 % wt. C8+ olefins.
9. A process as claimed in claim 1, in which the catalysts used in the preoligomerizing
and the oligomerizing steps are the same as each other.
10. A process as claimed in any one of the preceding claims, in which the charge for the
oligomerizing step is obtained by combining a part of the product composition of the
oligomerizing step with fresh feed containing light olefins.
11. A process as claimed in claim 1, in which the oligomerization is carried out in a
reactor to which a part of the product composition of the oligomerization is recirculated
and combined with fresh feed of light olefins.
12. A process as claimed in claim 1, in which the oligomerization is carried out in at
least two successive reactors, the following reactor also being fed with the reaction
composition of the previous reactor and each reactor using a Ca modified ZSM zeolite
as catalyst.
1. Verfahren zur Herstellung einer Dieseltreibstoff-Fraktion, umfassend die Stufen:
Voroligomerisierung von einer Beschickung mit leichten C2- bis C6- Olefinen in Gegenwart von einem mit Calcium modifizierten ZSM-5-Zeolith-Katalysator
mit einem Minimalgehalt an Calcium von 0,01 Gew.-% zur Bildung eines Produktstroms,
der 10 bis 95 Gew.-% an C5+- Olefinen enthält,
Oligomerisierung der voroligomerisierten Beschickung in Gegenwart von einem mit Calcium
modifizierten ZSM-5-Zeolith-Katalysator mit einem Minimalgehalt an Calcium von 0,01
Gew.-% zur Bildung einer Produktmischung, die mindestens teilweise aus C8+- Kohlenwasserstoffen besteht, und
Hydrierung der so erhaltenen Produktmischung zur Bildung einer Dieseltreibstoff-Fraktion,
die eine hohe Cetanzahl aufweist und im Bereich von 200 bis 320 ° C siedet.
2. Verfahren gemäß Anspruch 1,
bei dem eine Dieseltreibstoff-Fraktion hergestellt wird, die eine Cetanzahl höher
als 47, vorzugsweise höher als 49 aufweist.
3. Verfahren gemäß Anspruch 1 oder 2,
wobei ein calciummodifizierter ZSM-5-Zeolith verwendet wird, in dem ein Verhältnis
von Si : Al von weniger als 400, vorzugsweise im Bereich von 30 bis 200 vorliegt.
4. Verfahren gemäß einem jeden der Ansprüche 1 bis 3,
wobei ein calciummodifizierter ZSM-5-Zeolith verwendet wird, der vermittels Ionenaustausch
Calcium in einer Menge von 0,01 bis 1,0 Gew.-%, vorzugsweise 0,05 bis 0,5 Gew.-%,
enthält.
5. Verfahren gemäß einem jeden der vorangehenden Ansprüche,
wobei die Oligomerisierung bei einer Temperatur im Bereich von 160 bis 350 °C, vorzugsweise
bei 200 bis 310 °C, und bei einem Druck im Bereich von 1 bis 150 bar, vorzugsweise
bei 10 bis 80 bar, durchgeführt wird.
6. Verfahren gemäß einem jeden der vorangehenden Ansprüche,
wobei die Beschickung für die Voroligomerisierungsstufe 20 bis 100 Gew.-%, vorzugsweise
30 bis 95 Gew.-% an Olefinen enthält.
7. Verfahren gemäß einem jeden der vorangehenden Ansprüche,
wobei die voroligomerisierte Beschickung für die Oligomerisierungsstufe eine Kohlenwasserstoff-Fraktion
mit 40 bis 80 Gew.-% an C5+- Olefinen umfaßt.
8. Verfahren gemäß Anspruch 7,
wobei die voroligomerisierte Beschickung mindestens einige, vorzugsweise 5 bis 50
Gew.-% an C8+- Olefinen enthält.
9. Verfahren gemäß Anspruch 1,
wobei die Katalysatoren, die in der Voroligomerisierungsstufe und in der Oligomerisierungsstufe
verwendet werden, dieselben sind.
10. Verfahren gemäß einem jeden der vorangehenden Ansprüche,
wobei die Beschickung für die Oligomerisierungsstufe durch Kombinieren von einem Teil
der Produktmischung aus der Oligomerisierungsstufe mit einer leichte Olefine enthaltenden
frischen Einspeisung erhalten wird.
11. Verfahren gemäß Anspruch 1,
wobei die Oligomerisierung in einem Reaktor durchgeführt wird, in dem ein Teil von
der Produktmischung aus der Oligomerisierung rezirkuliert und mit frisch eingespeisten
leichten Olefinen kombiniert wird.
12. Verfahren gemäß Anspruch 1,
wobei die Oligomerisierung in mindestens zwei aufeinanderfolgenden Reaktoren durchgeführt,
der nachfolgende Reaktor mit der Reaktionsmischung aus dem vorangehenden Reaktor gespeist
und in jedem Reaktor ein mit Calcium modifizierter ZSM-Zeolith als Katalysator verwendet
wird.
1. Procédé pour la préparation d'une fraction de carburant diesel, comprenant les étapes
de :
- préoligomérisation d'une charge contenant des oléfines légères en C2-6 en présence d'un catalyseur à base de zéolite ZSM-5 modifiée par du Ca contenant
un minimum de 0,01% en poids de Ca, pour produire un courant de produits qui contient
10 à 95% en poids d'oléfines en C5+,
- oligomérisation de la charge préoligomérisée en présence d'un catalyseur à base
de zéolite ZSM-5 modifiée par du Ca contenant un minimum de 0,01% en poids de Ca,
pour préparer une composition de produits qui consiste au moins partiellement en hydrocarbures
en C8+, et
- hydrogénation de la composition de produits ainsi obtenue pour préparer une fraction
de carburant diesel qui bout dans la gamme de 200 à 320°C.
2. Procédé suivant la revendication 1, dans lequel il est préparé une fraction de carburant
diesel ayant un indice de cétane supérieur à 47, de préférence supérieur à 49.
3. Procédé suivant les revendications 1 ou 2, dans lequel il est utilisé une zéolite
ZSM-5 modifiée par du calcium ayant un rapport de Si à Al inférieur à 400, de préférence
compris dans la gamme de 30 à 200.
4. Procédé suivant l'une quelconque des revendications 1 à 3, dans lequel il est utilisé
une zéolite ZSM-5 modifiée par du calcium contenant de 0,01 à 1,0% en poids, de préférence
de 0,05 à 0,5% en poids de calcium introduit par exchange d'ion.
5. Procédé suivant l'une quelconque des revendications précédentes, dans lequel l'oligomérisation
est conduite à une température comprise dans la gamme de 160 à 350°C, de préférence
dans la gamme de 200 à 310°C et à une pression comprise dans la gamme de 1 à 150 bar,
de préférence de 10 à 80 bar.
6. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la charge
pour l'étape de préoligomérisation contient 20 à 100% en poids, de préférence 30 à
95% en poids d'oléfines.
7. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la charge
préoligomérisée de l'étape d'oligomérisation comprend une fraction hydrocarbonée ayant
40 à 80% en poids d'oléfines en C5+.
8. Procédé suivant la revendication 7, dans lequel la charge préoligomérisée contient
au moins un peu d'oléfines en C5+, de préférence de 5 à 50% en poids de celles-ci.
9. Procédé suivant la revendication 1, dans lequel les catalyseurs utilisés dans l'étape
de préoligomérisation et dans l'étape d'oligomérisation sont les mêmes.
10. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la charge
pour l'étape d'oligomérisation est obtenue par combinaison d'une partie de la composition
de produits de l'étape d'oligomérisation avec une charge d'alimentation fraîche contenant
des oléfines légères.
11. Procédé suivant la revendication 1, dans lequel l'oligomérisation est conduite dans
un réacteur dans lequel une partie de la composition de produits de l'oligomérisation
est remise en circulation et combinée avec une charge d'alimentation fraîche d'oléfines
légères.
12. Procédé suivant la revendication 1, dans lequel l'oligomérisation est conduite dans
au moins deux réacteurs successifs, le réacteur suivant étant aussi alimenté avec
la composition réactionnelle du réacteur précédent et chaque réacteur utilisant une
zéolite ZSM modifiée par du Ca comme catalyseur.