Note: Descriptions are shown in the official language in which they were submitted.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-1-
TITLE OF THE INVENTION
HYBRID CATALYSTS FOR THE DEEP CATALYTIC
CRACKING OF PETROLEUM NAPHTHAS AND OTHER HYDROCARBON
FEEDSTOCKS
FIELD OF THE INVENTION
The present invention relates to catalysts that are used in
the deep catalytic cracking (DCC) of petroleum naphthas and other
hydrocarbon feedstocks.
BACKGROUND OF THE INVENTION
Steam-cracking of light paraffins (ethane, ~ propane and
butane, obtained mainly by extraction from various natural gas sources) and
of naphthas and other heavier petroleum cuts, produces:
i) primarily ethylene and propylene;
ii) secondarily, depending on the feedstock employed, a C4 cut rich in
butadienes and a C5+ cut with a high content of aromatics,
particularly benzene; and thirdly
iii) hydrogen.
The feedstocks of choice are ethane and LPG for the
U.S.A. and naphthas and gas oils for Europe. However, in recent years, the
situation has dramatically changed with the U.S.A. moving towards the
utilization of heavier hydrocarbon feedstocks. It is worth noting that steam
cracking is one of the core processes in the petrochemical industry with a
worldwide production of ca. 100 million metric tons/year of ethylene and
propylene.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
_2_
Steam cracking is a thermal cracking reaction performed at
high temperatures and in the presence of steam, a diluent which is coifed
with the hydrocarbon stream. The reaction temperature ranges from 700
°C
to 900 °C according to the type of feedstock treated (the longer the
hydrocarbon molecular structure, the lower the temperature of cracking),
while the residence time ranges from a few seconds to a fraction of second.
Steam cracking is a well-established technology. However,
it suffers from many drawbacks:
lack of flexibility in the product selectivity, mostly in the yield of
propylene, which needs to be increased in order to respond to the
increasing demand of the market.
ii) significant production of fuel oil which contains heavy hydrocarbons
such as heavy alkylaromatics and even polyalkylaromatics. It is
known that the latter products are precursors of « coke ». Coking is a
serious problem in the steam cracking technology, which decreases
the energy efficiency and requires non-easy decoking procedures for
reactors.
iii) in order to achieve a high conversion, a high operational severity is
currently used which consists mainly of using high reaction
temperatures and, the recycle of some gaseous paraffinic products.
A process aiming at upgrading the products of propane
steam cracking was developed more than twelve years ago [1]. This
process consisted of adding a small catalytic reactor to the conventional
steam cracker of propane. The catalyst used was based on the ZSM5
zeolite, modified with AI and Cr [2]. Significant increases in the yield of
ethylene and aromatics were obtained.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-3-
A new process, consisting of using two reactors in
sequence, was recently developed [3,4]. The first reactor (I) contains a
mildly active but robust catalyst, and the second reactor (II) is loaded with
a
ZSM5 zeolite based catalyst, preferably of the hybrid configuration.
Variations of the temperature of reactor I, and the textural properties,
and/or
the surface composition of the catalyst of reactor (II), are used to increase
the conversion and to vary the product distribution, namely the
ethylene/propylene ratio.
Although such a process is of great industrial interest, the
use of two reactors, which may be heated separately, represents a
significant challenge in terms of technology and investment. Therefore, to
change the previous two-reaction-zone technology into a one-reaction-zone
technology, hybrid catalysts capable of expressing several functions [5]
have been proposed. Such hybrid catalysts contain a microporous
component such as a ZSM-5 zeolite or a pentasil-type silicalite, a
mesoporous silica-alumina co-catalyst into which is incorporated aluminum
oxide, .chromium oxide or a mixture of aluminum and chromium oxides, and
an inorganic binder such as bentonite clay.
There thus remains a need to develop hybrid catalysts
useful in one-reaction zone technology, for the deep catalytic cracking of
petroleum naphthas and other hydrocarbon feedstocks.
The present invention seeks to meet these and other
needs.
SUMMARY OF THE INVENTION
The present invention relates to new hybrid catalysts
useful in a one-reaction-zone system, and which show higher conversion
CA 02473751 2005-08-15
-t4_
and product selectivity (ethylene and propylene) as compared to the
presently available hybrid catalysts.
The present invention relates to new hybrid catalysts
allowing for selectively deep catalytic cracking (DCC) of petroleum naphthas
and other hydrocarbon feedstocks.
The present invention further relates to a hybrid catalyst
for use in deep catalytic cracking of hydrocarbon feedstocks to selectively
produce light olefins, the hybrid catalyst comprising a microporous catalyst
component, a mesoporous catalyst component and an inorganic binder. In a
specific embodiment of this invention, the weight ratio of microporous to
mesoporous catalyst component ranges from 0.25 to 4Ø In a more specific
embodiment, this weight ratio is about 1.5. In other embodiments of the
present invention, the binder is bentonite clay and is present in a proportion
of 9 to 25 wt.% based on the total weight of the hybrid catalyst. In other
embodiments of this invention, zirconium oxide is present in the hybrid
catalyst in a proportion of 1.5 to 4.0 wt.% based on the total weight of the
hybrid catalyst.
In addition, the present invention relates to new hybrid
catalysts having the following chemical composition (in terms of oxides and
excluding the inorganic binder):
a Si02 . b M203., c Mo03
wherein "M" is AI, Ce and La, and wherein the values of "a", "b" and "c" are
defined as follows (with respect to the final hybrid catalyst:
a=0-95wt%
CA 02473751 2005-08-15
-4b-
b+c= 5-15wt%
c/b (molar ratio) = 0.5 - 1.5
Further scope and applicability will become apparent from
the detailed description given hereinafter. It should be understood however,
that this detailed description, while indicating preferred embodiments of the
invention, is given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will become
apparent to those skilled in the art.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-5-
DETAILED DESCRIPTION OF' THE INVENTION
The present invention relates to new hybrid catalysts which
are advantageously used in the deep catalytic cracking of petroleum
naphthas and other hydrocarbon feedstocks (including light parafins),~ for
the selective production of light olefins, namely ethylene, propylene and
butenes, more particularly isobutene. BTX aromatics, mainly benzene, are
also produced in significant amounts.
The concept leading to the preparation of the hybrid
catalysts of the present invention is based on the hybrid catalyst
configuration [2]. This configuration takes advantage of the possibility of
transferring the reaction intermediates, during the catalytic reaction, from
the microporous component to the mesoporous component, using an effect
that is due to the pore continuum [2].
In a preferred embodiment, the present invention provides
for the following results:
i) in terms of catalyst performance relative to steam cracking:
a) higher combined yields of ethylene and propylene products;
b) production of insignificant amounts of fuel oil (it is worth noting
that these heavy hydrocarbons, in particular polyalkylaromatics
and others, are produced in very significant amounts when using
the current steam cracking technology);
c) production of dramatically reduced amounts of methane;
d) on-stream stability of the hybrid catalysts exceeds 6 hours;
e) total recovery of the catalyst's activity and selectivity, following
regeneration;
f) no need for reduction of the fresh catalyst or the regenerated
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-6-
catalyst, even tough some induction period (a few minutes) is
reported for all the runs; and
g) no apparent damage of the catalyst's surface (surface area) and
no changes in the chemical composition are observed even after
multiple « reaction/regeneration » cycles.
ii) in terms of the technology being used by the catalysts of the present
invention:
a) only one catalyst is loaded into a reactor, which may have a very
simple tubular configuration;
b) the reaction temperature is reduced by more than 120°C as
compared to the .temperature for steam cracking, implying
significant energy savings;
c) the catalysts are regenerated « in-situ », by exposure to air at a
temperature ranging from about 550°C to about 590°C for a few
hours;
d) the on-stream stability, and the relative ease of regeneration of
the catalysts of the present invention, provide for the use of a
simple reactor configuration: a dual system of tubular reactors
(one in working conditions and the other in regeneration phase);
e) the production of carbon dioxide and other related volatile oxides
during the regeneration phase is significantly reduced since the
carbonaceous deposits on the catalyst of the present invention
are much less important than those found on the walls of the
currently used steam-cracking reactors, meaning that when using
the catalyst of the present invention, the production of
environmentally harmful gasses ("green house gasses" such as
carbon dioxide, methane, etc.) is substantially reduced.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-7-
In a further preferred embodiment, the hybrid catalysts
comprise:
a) a microporous crystalline silicate having slightly acidic properties,
similar to the ammonium-treated pentasil-type silicalite;
b) a mesoporous alumina-silica having slightly acidic properties and
having a large surface area, into which may be incorporated
aluminum oxide, molybdenum oxide or a mixture of aluminum
and molybdenum oxides;
c) an inorganic (essentially catalytically inert) binder, such as
bentonite clay.
In yet a further preferred embodiment, the hybrid catalysts
of the present invention comprise:
a) a microporous component having isolated acidic active centers,
dispersed in a subnanometric channel network;
b) a mesoporous co-catalyst component whose surface exhibits
Bronsted acid sites;
c) an inert binder whose role is to embed in its rigid matrix, the
micron-sized particles of the two catalytic components, in order
to favor the transfer of reacting molecules.
Since steam cracking remains the driving force for the total
conversion of the feed, the presence of steam as well as relatively high
reaction temperatures (ca. 700°C) are required. Both catalyst
components
should therefore show high thermal stability under harsh reaction
conditions.
PROCEDURE FOR CATALYST PREPARATION
1. REFERENCE CATALYSTS:
CA 02473751 2005-08-15
-8-
H-ZSM5 zeolite catalyst (herein referred to as HZSMS):
This catalyst (Zeocat~ PZ-2/50, H-form, 1/16 " extrudates)
was purchased from Chemie Uetikon AG (Switzerland), and contains ca. 20
wt % of an unknown binder. Prior to catalytic testing, it was activated
overnight in air at 700°C. Its main physical properties are:
surface area = 389 m2/g;
microporosity = 177 m2/g; and
Si/AI = ca. 50.
Silica-alumina catalyst (SiAI) (herein referred to as SiAI):
This catalyst was obtained by extrusion of silica-alumina
(Aldrich, support grade 135, Si02 = 86 wt %, AI203 = 13 wt %, surface area
= 455 m2/g, average pore size = 6.5 nm) with bentonite clay (Spectrum
Products) as follows: The silica-alumina was carefully mixed with bentonite,
(stirring an hour under dry conditions) which was used as binder (15 wt %).
Water was then added dropwise until a malleable paste was obtained. The
resulting extrudate was dried overnight in air at 120°C, and was then
activated at 500°C for 3 hours and finally at 750°C for 2 hours.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
_g_
H-silicalite catalyst (HSiI) (herein referred to as H-Sil):
75 g of silicalite (UOP, MHSZ-420, SiO~ = 99.8 wt %, Si/AI
> 300) was immersed in 500 ml of a solution of ammonium chloride (10 wt
%). The suspension was left at room temperature for 12 hours while being
continuously stirred. It was then left to settle and filtrated. The so-
obtained
solid was once again immersed in a solution of ammonium chloride (500
ml). The repeated ion-exchange operation was carried out for another 12
hours. The solid was filtered out, washed with distilled water, and dried
overnight in air at 120°C. The solid was finally activated at
500°C for 3
hours. The resulting material is herein referred to as HSiI (powder).
The final catalyst extrudates were obtained by extrusion
with bentonite (15 wt %), followed by overnight drying at 120°C, and
air
activation at 500°C for 3 hours and finally at 750°C for another
5 hours.
2. HYBRID CATALYSTS CAT IVa:
The Cat IVa hybrid catalysts were prepared by admixing (x)
g of SiAI (pure silica-alumina) with (y) g of H-Sil (powder), wherein x + y =
10, with x varying from 3 to 6. The solid mixture was then extrudated with
bentonite clay (15 wt %). The resulting extrudates were first dried overnight
in air at 120°C, followed by activation at 500°C for 3 hours,
and finally by
activation at 750° C for 2 hours. These catalysts are herein referred
to as
HYBa~), Y being the weight percent of HSiI (powder) in the initial solid
mixture.
3. HYBRID CATALYSTS CAT IVb:
The Cat IVb hybrid catalysts were prepared by admixing (x)
g of Cocat (co-catalyst) with (y) g of H-Sil (powder). The solid mixture was
then extrudated with bentonite clay (1.5 g). The resulting extrudates were
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-10-
first dried overnight in air at 120°C, followed by activation at
500°C for 3
hours, and finally by activation at 750°C for 2 hours.
The hybrid catalysts of this series were obtained using
solid mixtures having the following compositions:
(Mo-0): x = 5.0 g of Mo-0 Cocat; y = 5.0 g of HSiI
(MoAI-1 ): x = 5.0 g of MoAI-1 Cocat; y = 5.0 g of HSiI
(MoAI-2): x = 5.0 g of MoAI-2 Cocat; y = 5.0 g of H-Sil
(MoAI-3): x = 5.0 g of MoAI-3 Cocat; y = 5.0 g of HSiI
(MoAI-4): x = 5.0 g of MoAI-4 Cocat; y = 5.0 g of HSiI
(AI-0): x = 5.0 g of AI-0 Cocat; y = 5.0 g of HSiI
(MoAI-31 ): x = 4.5 g of MoAI-3 Cocat; y = 5.5 g of HSiI
(MoAI-32): x = 4.0 g of MoAI-3 Cocat; y = 6.0 g of HSiI
(MoAI-33): x = 3.0 g of MoAI-3 Cocat; y = 7.0 g of HSiI
Preparation of the co-catalyst herein referred to as Cocat:
The co-catalysts were obtained by incorporating
molybdenum (oxide), aluminum (oxide), or a mixture thereof, into the silica-
alumina in accordance with the following procedures:
Co-catalyst for the Mo-O sample:
A solution of 0.64 g of ammonium molybdate,
(NH4)6Mo~024.4H20 (ACS reagent, Anachemia) in 8.0 ml of distilled water,
was impregnated into 5.0 g of silica-alumina (total amount of Mo03
incorporated = 3.6 mmol). The resulting solid was slowly dried on a hot
plate, followed by overnight drying at 120°C. It was then activated at
250°C
for 2 hours and finally at 500°C for another 2 hours.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-11-
Co-catalyst for the AI-0 sample:
A solution of 3.14 g of aluminum nitrate, AI(N03)3.9H2O
(Fisher Sc. Company) in 8.0 ml of distilled water, was impregnated into 5.0
g of silica-alumina (total amount of AI203 incorporated = 4.2 mmol). The
resulting solid was slowly dried on a hot plate, followed by overnight drying
at 120°C. It was then activated at 250°C for 2 hours and finally
at 500°C for
another 2 hours.
Co-catalysts for the MoAI samples:
A solution of (x) g of aluminum nitrate and (y) g of
ammonium molybdate in 8.0 ml of distilled water, was impregnated into 5.0
g of silica-alumina. The resulting solid was slowly dried on a hot plate,
followed by overnight drying at 120°C. It was then activated at
250°C for 2
hours and finally at 500°C for another 2 hours.
(x) and (y) as mentioned above had the following values:
MoAI-1 sample: (x) = 1.60 g; (y) = 0.45 g; Mo03/AI203 molar ratio = 1.3;
total amount incorporated = 4.6 mmol.
MoAI-2 sample: (x) = 3.23 g; (y) = 0.46 g; Mo03/AI203 molar ratio = 0.65;
total amount incorporated = 6.0 mmol.
MoAI-3 sample: (x) = 2.27 g; (y) = 0.51 g, Mo03/AI203 molar ratio = 1.0;
total amount incorporated = 5.9 mmol.
MoAI-4 sample: (x) = 3.21 g; (y) = 0.75 g, Mo03/AI203 molar ratio = 1.0;
total amount incorporated = 8.5 mmol. ,
4. HYBRID CATALYSTS CAT IVY:
The Cat IV° hybrid catalysts were prepared by admixing (x)
g of pure silica-alumina, or MoAI-3 Cocat with (y) g of H-DSiI. The solid
CA 02473751 2005-08-15
-12-
mixture was then extrudated with bentonite clay (1.5 g). The resulting
extrudates were first dried overnight in air overnight at 120°C,
followed by
activation at 500°C for 3 hours, and finally by activation at
750°C for 2
hours.
The hybrid catalysts were obtained using solid mixtures
having the following compositions:
(SiAI-1 ): 5.0 g of pure silica-alumina; 5.0 g of H-DSiI
(MoAI-3D): 4.0 g of MoAI-3 co-catalyst; 6.0 g of H-DSiI
Preparation of the desilicated silicalite herein referred to as H-DSiI:
26.0 g of silicalite were added to Teflon~ beaker
containing 260 ml of a 0.6 mol/L sodium carbonate solution, in accordance
with the desilication method previously developed [6,7j. The suspension
was heated to 80°C for 1.5 hours while moderately stirring. it was then
filtered and the solid so-obtained was placed in a beaker containing 260 ml
of distilled water. The suspension was heated to 80°C for 0.5 hours
while
moderately stirring. The solid was recovered by filtration, washed with
distilled water and finally dried overnight in air at 120°C. The
resulting solid
material was immersed in a solution of ammonium chloride (180 ml; 10 wt.
%). The resulting suspension was left at room temperature for a period of
12 hours, while being continuously stirred. It was then left to settle and
filtered. The so-obtained solid was again immersed in an ammonium
chloride solution (180 ml; 10 wt. %). The new ion-exchange operation was
carried for a period of 12 hours. The solid was filtrated out, washed with
distilled water, dried overnight in air at 120°C, and finally activated
at 500°C
for 3 hours. The resulting material is herein referred to as H-DSiI (powder).
_r~ _..a~ .~..._.~..~.~,.~. r__.___Y...~_._.... .... ,..~ .~,.~~,."....,~~~,
CA 02473751 2005-08-15
-13-
Preaaration of (MoAI-32)b and (MoAI-D3)b
8.2 g of (MoAI-32) and (MoAI-3D) extrudates were each
impregnated with 6 ml of zirconyl nitrate, obtained by dissolving 1.40 g of
Zr0(N03)2.4H20 (Aldrich Company) in 12 ml of distilled water. The resulting
materials were slowly dried on a hot plate, followed by overnight drying at
120°C. The catalyst samples, herein referred to as (MoAI-32)b and (MoAI-
D3)b respectively, were obtained by activation in air at 500°C for 2
hours
followed by activation at 750°C for another 2 hours.
5. HYBRID CATALYSTS USED FOR TESTING WITH ULTRAMAR
LIGHT NAPHTHA:
Microporous component
Preparation of silicalite in acidic form, herein referred to as the H-Sil
catal st
225.0 g of silicalite (UOP, HISIV-3000 powder, Si/AI >
200), dried overnight at 120°C, was placed in a beaker containing 1500
ml
of an ammonium chloride solution prepared by dissolving 150 g of
ammonium chloride in 1500 ml of water (ca. 10 wt %). The suspension was
stirred at room temperature for 24 hours. It was then left to settle and
filtered. The so-obtained solid was again immersed in a fresh ammonium
chloride solution and stirred at room temperature for 24 hours. The solid
was filtered out, washed with distilled water (1000 ml), and dried overnight
at 120°C. The solid was finally activated in air at 550°C for 3
hours.
ZSM-5 zeolite catalyst (HZ)
This catalyst (Zeocat~ PZ-2/100H, powder, Si/AI = 100,
acidic form) was purchased from Zeochem-Uetikon. It was dried overnight
at 120°C.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-14-
Co-catalyst 1
100.0 g of silica-alumina (Aldrich, support grade 135),
dried overnight at 120°C was impregnated with a suspension obtained by
vigorously mixing solutions A and B (homogeneous suspension having a
yellow-pink color).
Solution A: 16.9 g of ammonium molybdate (ACS reagent, Anachemia)
dissolved in distilled water (100m1);
Solution B: 5.3 g of cerium (III) nitrate hexahydrate (Aldrich) dissolved in
distilled water (80 ml).
The resulting solid material was left at room temperature
for 0.5 hours, dried overnight in air at 120°C, and activated at
550°C for 3
hours.
Co-catalyst 2
g of zirconium(IV) oxide (Zr02, Aldrich), dried overnight
15 at 120°C, was impregnated with a suspension obtained by vigorously
mixing
solutions A and B (homogeneous suspension of a white color).
Solution A: 3.4 g of ammonium molybdate (ACS reagent, Anachemia)
dissolved in distilled water (10 ml);
Solution B: 1.2 g of lanthanum (III) nitrate hydrate (Aldrich) dissolved in
20 distilled water (16 ml).
The resulting solid material was left at room temperature
for 0.5 hours, dried overnight in air at 120°C, and activated at
550°C for 3
hours.
Hybrid Catalyst DC 1
The DC 1 hybrid catalyst was prepared by extruding zeolite
HZ with Co-catalyst 1 as follows:
5.0 g of HZ, 3.1 g of co-catalyst 1, and 2.0 g of bentonite
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-15-
(Aldrich, dried overnight at 120°C) were placed in a mortar and
thoroughly
crushed-mixed. Water was then added until a malleable paste was
obtained. The resulting solid was dried overnight in air at 120°C, and
finally
activated in air at 650°C for 3 hours. Before use, the so-obtained
solid was
cut into short extrudates of a few millimeters in length.
Hybrid Catalyst DC 2
The DC 2 hybrid catalyst was prepared by extrusion and
activation at high temperatures as was described for Catalyst DC 1. The
initial composition consisted of 5.0 g of HSiI, 3.1 g of co-catalyst 1 and 2.0
g
of bentonite (Aldrich, dried overnight at 120°C).
Hybrid catalyst DC 3
The DC 3 hybrid catalyst was prepared by extrusion and
activation at high temperatures as was described for Catalyst DC 1. The
initial composition consisted of 3.1 g of HSiI, 5.0 g of co-catalyst 2, and
2.0
g of bentonite (Aldrich, dried overnight at 120°C).
Hybrid catalyst DC 4
The DC 4 hybrid catalyst was prepared by extrusion and
activation at high temperatures as was described for Catalyst DC 1. The
initial composition consisted of 9.6 g of co-catalyst 2, 2.4 g of bentonite
(Aldrich, dried overnight at 120°C).
EXPERIMENTAL SET-UP
Experiments were perFormed using a Lindberg tubular
furnace, coupled to a Lindberg type 818 temperature control unit. The
reactor vessel consisted of a quartz tube 95 cm in length and 2 cm in
diameter. The temperature of the catalyst bed (6.5 cm in length) was
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-16-
measured using a thermocouple placed in a quartz thermowell, which was
positioned exactly in the middle of the catalyst bed.
TESTING PROCEDURE
Liquids, namely n-hexane (or n-octane) and water, were
injected into a vaporizer using a double-syringe infusion pump and using
nitrogen as the carrier gas. The water/n-hexane ratio was monitored using
syringes of different diameters. In the vaporizer, the carrier gas was mixed
with n-hexane (or n-octane) vapors and steam. The gaseous stream was
then sent into a tubular reactor which contained the catalyst extrudates
previously prepared. The products were analyzed by gas chromatography
using a PONA capillary column for liquid phases and a GS-alumina capillary
column for gaseous products.
The testing conditions were as follows:
Weight of catalyst: 7.5 g;
W.H.S.V.: 0.6 h-~;
Water/n-paraffin weight 0.71;
ratio:
Reaction temperature: 715-735C;
Nitrogen flow-rate: ca. 11.5
ml/min;
Duration of a run: 4-5 hours.
Testing procedure using the Ultramar light naphtha
The light naphtha was obtained from Ultramar Co.
(Quebec, Canada) and has the following characteristics:
Density: 0.65 g/ml;
Composition (wt %): paraffins: 48.1;
isoparaffins: 34.5;
naphthenes: 13.7;
aromatics: 3.7.
Experiments were performed using a Lindberg triple zone
series tubular furnace, coupled to a Lindberg control unit capable of
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-17-
individually regulating, the temperature of each zone. The reactor vessel
consisted of a quartz tube 95 cm in length and 2 cm in diameter.
Zone 1 (ca. 15 cm in length), located at the reactor inlet,
and heated at T1 was packed with quartz granules (void volume = 0.45
ml/ml, such that the volume heated at T1 is about 22 ml).
Zone 3 (catalyst be of ca. 7 cm in length), located at the
reactor outlet, and heated at T3 was packed with catalyst extrudates.
Several thermocouples were used to control the
temperature of these zones. Zone 2, which is sandwiched between Zones 1.
and 3, was used as a cooling zone, because temperature T1 was always
set slightly higher than temperature T3.
The testing conditions are as follows:
Weight of catalyst: 6.5 g;
Flow-rate of water: 3.3 g / hour;
Flow-rate of light naphtha: 10 ml/hour;
Water/naphtha weight ratio: 0.5;
Weight hourly space velocity (W.H.S.V.), for catalyst of zone 3: 1.51 h-~;
Residence time (estimated), for Zone 1: ca. 3.6 s.
Each run starts with the pumping of water (for 15 min) before introducing
the naphtha feed into the vaporizing flask.
Duration of a run: 5 hours;
Reaction temperature: T1 = 720-735°C;
T3 (catalyst bed) = 640°C.
Decoking (regeneration): air (flow-rate 40 ml/min) at 500°C
overnight.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-18-
RESULTS AND DISCUSSION
Table 1 shows that the parent ZSM-5 zeolite (column # 2)
produces less "ethylene + propylene" than the current steam cracking
process (column # 1 ). As expected, the propylene and aromatics yield, as
well as the yield of light paraffins is high. Since the reaction temperature
is
lower, methane production is also much lower. However, the H-ZSM5
catalyst is considerably on-stream unstable, due to its narrow pore network
(coking). It is also unstable over several reaction-regeneration cycles, due
to a gradual structural collapse upon the joint action of high reaction
temperature and steam.
Table 1 also reports that steam-cracking (no catalyst or
with bentonite extrudates, which are assumed to be catalytically inert) of n-
hexane and n-octane (two paraffins used as model molecules for petroleum
naphthas), results in lower conversion when tested under the DCC
conditions of the present invention. However, the ethylene/propylene weight
ratio is significantly higher while the combined production of ethylene and
propylene is puite similar to (with n-hexane feed) or higher than (with n-
octane feed) that of the naphtha steam-cracking (columns # 3-7 versus
column # 1 ). It is worth noting that the production of methane, and the
coking rate (which produces carbon oxides during the regeneration phase
with air), is much lower.
Considering the catalytic data of the reference catalysts
reported in Table 2:
(a) the silicalite catalyst, HSiI (column 1, Table 2), is
slightly more active than the steam-cracking carried out under the same
reaction conditions (columns # 3 and 6). The production of methane by the
H-Sil catalyst is also significantly lower;
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-19-
(b) the silica-alumina catalyst (column # 6, Table 2) is
significantly more active than the HSiI catalyst (column # 1, Table 2).
However, it yields significantly higher amounts of methane and aromatics,
while the combined production of ethylene and propylene is much lower.
(c) the hybrid catalysts show a conversion level that is
situated in between those of the HSiI and the SiAI catalysts (columns # 2-5).
More importantly, the combined production of ethylene and propylene is
significantly higher when compared to the reference catalysts, while the
yields in aromatics and in methane did not change when compared to the
HSiI catalyst. This clearly indicates that there exists a synergistic effect
between the two catalyst components during the conversion of n-hexane.
Table 3 shows that the incorporation of Mo03 or AI203 , or
a mixture of these two species, onto the co-catalyst surface (silica-alumina),
significantly increases both the total conversion of n-hexane and the
combined yield of ethylene and propylene. It is remarkable that the
production of methane does not change significantly. The highest combined
production of ethylene and propylene was obtained with a (Mo03/AI203)
molar ratio of 1.0 (columns # 4 and 5, Table 3).
Table 4 shows that varying the relative percentages of the
two catalyst components, induces changes in the product spectrum. The
best performance, in terms of combined production of ethylene and
propylene, is obtained with the MoAI-32 hybrid catalyst, i.e. the co-catalyst
with a Mo03/AI203 molar ratio equal to 1.0 and a HSiI/co-catalyst weight
ratio of 60/40 (column # 6 versus columns # 2 and 7 of Table 4 and column
# 4 of Table 3).
Desilication of the silicalite results in slightly more acidic
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-20-
materials (HDSiI) which when incorporated into a hybrid catalyst lead to a
combined production of ethylene and propylene that is not significantly
lower than the analogous hybrid catalyst prepared with HSiI (column # 3 of
Table 5 versus column # 6 of Table 4), while the yield in methane is
extremely low because of the considerably lower reaction temperature.
The incorporation of Zr02 into the final catalyst extrudates
mechanically strengthens them without changing their catalytic properties
(column # 4,versus column # 3, all of Table 5).
Results obtained using Ultramar light naphtha
~ The catalytic performance of the DC 1 and DC 2 hybrid
catalysts are reported in Table 6. Columns 1 and 2 of Table 6 allow for a
comparison between the DC 1 and DC 2 hybrid catalysts, which differ only
by the microporous component used in their preparation. The catalytic
performances are very similar under essentially identical reaction
conditions. Hybrid catalyst DC 1 is actually slightly more active than hybrid
catalyst DC 2, due to a slightly higher surface acidity, which depends on the
silica/alumina ratio. This small difference only has a small affect on the
overall catalytic behavior of the hybrid catalyst. Columns 3 to 7 of Table 6,
show the stability of the DC 2 hybrid catalyst over several cycles of "run
followed by regeneration". It is worth noting that the temperature T1 was
increased by 5 degrees Celcius with respect to that of the run illustrated in
column 2. It thus appears thus that when using a slightly higher cracking
temperature, the ethylene and the aromatics yield increase significantly.
The production of methane is unfortunately also higher.
The results reported in columns 3-7 of Table 6 indicate that
the DC 2 hybrid catalyst is very stable over several testing cycles (reaction
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-21-
followed by regeneration), as is evidenced by the high reproducibility of the
yield data. It is believed that this catalyst stability stems from the
stability of
the co-catalyst surface. Ln fact, it is well known that molybdenum oxide is
quite unstable at high temperatures and in the presence of water. The
conversion, therefore, of this oxide into stable cerium molybdate, enhances
the co-catalyst stability.
The catalytic performance of the DC 2, DC 3 and DC 4
catalysts are reported in Table 7. As can be seen from Table 7, T1 was set
at 735°C and T2 at 640°C. Higher cracking temperatures again
result in
higher yields of ethylene and aromatics, as be observed by comparing
column #1 (DC 2) of Table 7 with columns 3-7 of Table 6.
The main difference between hybrid catalyst DC 3 (column
#2 of Table 7) and hybrid catalyst DC 2 (column # 1, Table 6) resides in the
acidity and the composition of the co-catalyst surface. More specifically,
these differences are inherent to both the acidic support (zirconia versus
silica-alumina), and the stabilizing species used (lanthanum versus cerium).
Zirconia is known to be slightly more acidic than silica-alumina. Zirconia,
however, has a smaller surface area than silica alumina (ca. 50 m2/g versus
ca. 400 m2/g). Lanthanum species are said to be less aromatizing than
cerium species, even though lanthanum, like cerium, promotes the
formation of stable lanthanum molybdate. The combined effect of these
changes leads to a higher combined yield of ethylene and propylene, and a
lower production of aromatics. However, the butadiene yield is much higher
(column 2 versus column 1, both of Table 7) because of a reduced
consumption of butadiene resulting from cracking in zone 1, which is due to
the reduced aromatization effect of lanthanum.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-22-
The catalytic data of hybrid catalyst DC 4, in which the
microporous component is totally absent, are reported in column #3 of
Table 7. While the combined yield of ethylene and propylene is quite high,
the yield of butadiene is ~ also much higher. This result suggests that the
microporous component (zeolite or acidic silicalite) of hybrid catalysts DC 1
or DC 2 contributes more to the conversion of butadiene into aromatics than
into light olefins. The new co-catalysts DC 3 and DC 4 ensure a much lower
production of the greenhouse gas methane as compared to co-catalyst DC
2 (columns # 2 and 3 versus column # 1, all of Table 7).
The present reactor configuration having two reaction
zones, i.e. a zone for partial steam-cracking (Zone 1 ) and a zone for
catalytic conversion (Zone 3), anticipates potential industrial applications.
In
fact, only minor changes are required to incorporate the process of the
present invention into existing steam-cracking technology. An existing
steam-cracker can be used as Zone 1 (obviously using operating conditions
close to those reported for the present invention), while Zone 3 can be
incorporated into a steam-cracking plant as a fixed (or fluidized) bed
catalytic reactor. All remaining sections of the steam-cracking plant remain
unchanged. The present technology can be used for improving the current
steam-cracking of hydrocarbons (light paraffins, naphthas, heavier
feedstocks) with little capital investme4nts.
It is worth to dwell on the following aspects of the hybrid
catalysts of the present invention:
a) the concept of "pore continuum" applies to hybrid catalysts where
enhancements in activity and selectivity for the production of
desired olefinic products (ethylene and propylene) can be
reasonably attributed to an "easier communication" between the
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-23-
two catalyst components;
b) any intervention on the co-catalyst's surface, e.g. the incorporation
of metal oxides such as V205, or the incorporation of mixtures of
metal oxides such as Cr203 / AI2O3, Mo03 / AI203 , W03 / AI203,
Re20~ / AI203, capable of developing mild Bronsted surface acidity
[7], has a significant effect on the conversion and product
selectivity;
c) stronger effects on the conversion and product selectivity are
obtained even with a limited increase in the Bronsted surface
acidity of the microporous component. This can be ascribed to a
narrower pore size of the molecular sieve component of the hybrid
catalyst, which induces a slower diffusion of the reacting molecules,
favoring their adsorption (onto the active sites) / reaction / and
desorption;
d) there is always an optimum (in terms of product selectivity) weight
ratio of microporous component to mesoporous co-catalyst
component;
e) an "organic matrix embedding the two types of ~ particles i.e.
mesoporous co-catalyst component and microporous component,
fixes their respective position;
f) the incorporation of zirconium species into the final catalyst
extrudates mechanically strengthens them without significantly
changing their catalytic performance.
The hybrid catalysts of the present invention are not only
very stable .on-stream, but they are also readily regenerated in-situ by
heating the reactor overnight in air to ca. 550°C. The emissions of
carbon
oxides during the regeneration phase are reduced by at least 90 % with
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-24-
respect to those observed using a current steam-cracking reactor. Low
emissions of carbon oxides (regeneration phase) and low production of
methane (methane and carbon dioxide being known "green-house gases")
implies that deep catalytic cracking, using the hybrid catalysts of the
present
invention, represents a much "cleaner" process. The yields of methane
reported for the hybrid catalysts of the present are reduced by more than
50%, as compared to those observed during steam-cracking (Table 1,
column #1 ).
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-25-
TABLE 1: Reference data of steam-cracking and catalytic cracking performed in
deep
catalytic cracking conditions.
Column 1 2 3 5 6
# 4 7
Process STEAM DEEP
CRACKING CATALYTIC
CRACKING
Feed Medium-rangen-hexane n-octanen-hexane n-octane
naphtha
Catal / H-ZSM5 / ! bentonite
st extrudates
Process Industrial
high
conditionsseverity
T= 850C
650C 735C 735C 725C 735C 735C
R = 0.71 0.71 0.71 0.71 0.71
0.36
a b b b b b
Yields
(wt.%)
ethylene 33.6 21.1 29.6 36.0 27.0 29.3 35.4
propylene15.6 23.5 20.6 21.6 20.6 21.2 22.0
butadiene4.5 0.0 3.1 3.8 3.3 3.1 3.6
butenes 3.7 6.4 4.7 5.5 5.7 5.6 5.8
aromatics11.9 14.1 2.1 2.8 0.5 0.8 3.7
Non-aromatics6.8 3.3 4.5 5.5 3.2 3.7 5.5
Fuel oil 4.7 trace 0.2 0.0 0.0 0.0 2.3
(C9+)
Methane 17.2 7.2 10.4 8.7 9.3 9.7 8.0
Other 0.5 23.0 4.3 7.9 4.0 4.2 8.6
light
parafins
Conversion98.5 98.6 79.5 91.8 72.9 77.7 92.8
(wt. %
)
Ethylene 49.2 44.6 50.2 57.6 47.5 50.5 57.4
+
Propylene
Ethylene/2.2 0.9 1.4 1.7 1.3 1.4 1.6
Propylene
Light 57.9 51.0 58.1 66.9 55.9 59.2 66.7
olefins
and diolefins
Notes On-stream ~ Very
and unstable stable
Remarks
R = H20/hydrocarbon feed ratio (by weight)
Weight hourly space velocity: a = 0.3-0.4 h-' and b = 0.6 h-~ .
At T = 850 °C and R = 0.71, the steam-cracking of n-hexane gave similar
product yields.
However, rapid coking of the reactor walls with a consequent rapid activity
decay (steady
increase of methane production) were observed.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-26-
TABLE 2: Performance of the CAT IVa, hybrid catalysts of the present invention
(feed = n-hexane, T = 735 o C, R = 0.71 )
Column # 1 2 3 4 5 6
Catalyst Hsil HYBa HYBa HYBa HYBa SiAI
(70) (60) (50) (40)
Conversion (wt 86.0 91.1 91.5 86.4 88.9 92.1
%)
Product yields
(wt%)
Ethylene 27.3 27.3 26.7 27.2 26.7 22.7
Propylene 24.3 28.2 28.8 28.5 28.0 21.4
Butadiene 2.0 1.1 1.0 0.9 1.1 0.9
n-Butenes 3.6 3.1 3.4 3.5 3.2 3.2
Isobutene 2.7 2.4 2.6 2.7 2.4 2.5
Aromatics 4.8 4.8 5.3 4.2 3.9 8.4
Non-aromatics 3.4 1.9 1.9 1.6 1.7 2.2
(C5-C8)
Fuel oil (C9+) 0.5 0.3 0.3 0.2 0.0 0.1
Methane 8.3 8.5 8.3 8.9 8.6 15.4
Other light 9.3 13.6 13.2 12.6 13.3 15.4
paraffins
Ethylene + Propylene51.6 55.5 55.5 55.7 54.7 44.1
Ethylene/Propylene1.1 1.0 0.9 0.9 0.9 1.1
C2-C4 olefins 59.7 62.0 62.5 62.7 61.3 50.6
&
diolefins
Remarles: high
on-stream
stability
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
TABLE 3: Performance of the CAT IVb, hybrid catalysts of the present invention
(feed = n-
hexane, T = 735 o C, R = 0.71 )
Column # 1 2 3 4 5 6
Catalyst Mo-0 MoAI-1 MoAI-2 MoAI-3 MoAI-4 AI-0
Conversion 94.0 96.2 96.0 95.9 97.2 93.7
(wt %)
Product yields
(wto/u)
Ethylene 27.4 27.3 28.3 28.8 30.1 28.1
Propylene 30.6 30.1 29.8 30.6 28.8 29.0
Butadiene 1.4 1.3 1.2 1.3 1.3 1.3
n-Butenes 2.6 2.2 2.4 1.9 2.1 2.9
Isobutene 2.1 1.8 2.0 2.1 1.8
Aromatics 5.4 7.9 8.0 6.8 8.4 5.3
Non-aromatics1.3 1.5 1.8 1.8 1.8 2.1
(C5-C8)
Fuel oil (C9+)0.1 0.3 0.3 0.1 0.3 0.3
Methane 9.2 8.3 8.5 8.8 9.4 8.9
Other light 13.9 15.4 13.7 13.7 13.2 13.4
paraffins
Ethylene + 58.0 57.4 58.1 59.4 58.9 57.1.
Propylene
Ethylene/Propylene0.9 0.9 0.9 0.9 1.0 1.0
C2-C4 olefins64.1 62.7 63.7 64.6 64.1 63.6
&
diolefins
Remarks: high
on-stream
stability
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
_~$_
TABLE 4: Performance of the CAT fVb, hybrid catalysts of the present invention
(R = 0.71 )
Column 1 2 5 6 7
# 3 4
Catal MoAI-31 MoAI-32 MoAI-33
st
Temperature725 735 725 735 725 735 735
(~ C)
Feed n-hexanen-hexanen-octanen-octanen-hexanen-hexanen-hexane
Conversion93.9 97.3 98.2 98.9 93.7 97.2 96.4
(VYt
%)
Product
yields
(wt~/a)
Ethylene24.5 28.6 26.6 29.5 24.6 30.5 28.5
Propylene32.3 30.2 32.2 30.6 31.7 29.3 29.9
'
Butadiene1.3 1.2 1.6 1.9 1.3 1.2 1.2
n-Butenes2.8 2.3 4.1 3.4 3.0 2.2 2.4
Isobutene2.4 2.3 3.4 3.0 2.5 1.8 2.0
Aromatics6.6 7.9 9.1 7.7 6.9 8.0 8.2
Non-aromatics1.5 1.6 2.6 3.0 1.9 1.6 1.7
(Cs-Cs)
Fuel 0.2 0.3 0.0 0.2 0.2 0.2 0.3
oil
(C9+)
Methane 8.3 8.7 6.8 8.6 7.7 8.9 8.2
Other 13.9 14.5 11.7 11.0 14.0 13.6 14.1
light
paraffins
Ethylene56.8 58.8 58.8 60.1 56.3 59.8 58.4
+ ~
Propylene
Ethylene/prop0.8 0.9 0.8 1.0 0.8 1.0 0.9
ylene
Cz-CQ 63.3 64.1 67.9 68.4 63.1 64.8 64.0
olefins ~
& diolefins
Remarks High
: on-stream
stability
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-29-
TABLE 5: Performance of the CAT IVc hybrid catalysts of the present invention
(R =
0.71 )
Column # 1 2 3
Catalyst (SIAI-1 ) (SIAI-1 ) (MoAI-3D)
Temperature (C) 735 725 715
Feed n-hexane n-hexane n-hexane
Conversion (wt 96.7 90.3 93.5
%)
Product yields
(wt%)
Ethylene 28.0 25.5 22.8
Propylene 28.4 28.8 31.5
Butadiene 1.0 1.2 0.9
n-Butenes 2.2 3.4 ~3.5
Isobutene 1.8 2.7 1.6
Aromatics 7.6 5.5 7.8
Non-aromatics 1.5 1.7 1.5
(C5-C8)
Fuel oil (C9+) 0.0 0.2 0.1
Methane 10.4 8.2 7.2
Other light paraffins15.8 13.2 16.7
Ethylene + Propylene56.4 54.3 54.2
Ethylene/Propylene1.0 0.9 0.7
C2-C4 olefins 61.4 61.4 60.2
&
diolefins
Remarks: acceptable
on-stream
stability
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-30-
Table 6: Performance of CAT IVY hybrid catalyst using light naphtha feed
1 2 3 4 5 6 7
Catalyst DC 1 DC
2
Temperature 720 725
1 (C)
Temperature 640
3 (C)
Product Yield
(wt.%)
Methane 13.8 12.7 16.5 17.2 16.1 16.1 15.7
Ethylene 23.8 23.6 25.5 25.2 25.6 25.2 25.7
Propylene 22.3 22.1 21.8 21.5 21.8 21.3 21.8
Butadiene 0.2 0.2 0.2 0.2 0.2 0.2 0.2
BTX aromatics 9.2 8.8 10.2 10.6 10.0 9.6 10.1
Heavy hydrocarbons0.3 0.3 0.5 0.4 0.4 0.4 0.4
Ethylene + 46.1 45.7 47.3 46.7 47.4 46.5 47.5
Propylene
Table 7: Performance of CAT IVY hybrid catalyst using light naphtha feed
1 2 3
Catalyst DC 2 DC 3 DC 4
Temperature 735
1 (C)
Temperature 640
3 (C)
Product Yield
(wt.%)
Methane 15.0 12.8 12.7
Ethylene 27.8 29.3 29.1
Propylene 21.0 21.4 20.9
Butadiene 0.2 1.1 2.3
BTX aromatics12.7 10.2 8.2
Heavy hydrocarbons0.6 0.7 0.4
Ethylene + 48.8 50.7 50.0
Propylene
Although the present invention has been described hereinabove by way of
preferred embodiments thereof, it can be modified without departing from
the spirit and nature of the subject invention as defined in the appended
claims.
CA 02473751 2004-07-19
WO 03/064039 PCT/CA03/00105
-31-
REFERENCES
1. R. Le Van Mao; U.S. Patent 4,732,881 (March 22, 1988)
2. R. Le Van Mao; Hybrid catalysts containing a microporous zeolite
and mesoporous co-catalyst forming a pore continuum for a better
desorption of reaction products; Microporous and Mesoporous
Materials 28 (1999), 9-17.
3. R. Le Van Mao; Selective Deep Cracking of Petroleum Naphthas and
other Hydrocarbon Feedstocks for the Production of Light Olefins
and Aromatics; U.S. patent application.
4. R. Le Van Mao, S. MeJancon, C. Gauthier-Campbell, and P.
Kletniecks; Catalysis Letters 73 (2l4), (2001 ), 181.
5. R. Le Van Mao; Selective Deep Cracking of Petroleum Naphthas and
other Hydrocarbon Feedstocks for the Production of Light Olefins
and Aromatics; U.S. patent application.
6. R. Le Van Mao, S. Xiao, A. Ramsaran, and J. Yao; J. Materials
Chemistry, 4(4) (1994), 605.
7. R. Le Van Mao, S. T. Le, D. Ohayon, F. Caillibot, L. Gelebart and G.
Denes; Zeolites, 19 (1997), 270-278.
8. H. H. Kung, Transition metal oxides: Surface Chemistry and
Catalysis, Studies in surFace science and catalysis, Vol. 45, Elsevier
(Amsterdam) (1989), p72-90.
