Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROPYLENE VIA METHANOL OVER ALUMINOSILICATE CATALYST
Field of the invention
The invention relates to the synthesis of high silica aluminosilicate catalyst
for methanol conversion reaction to light olefins. More particularly, the
invention relates to method for synthesis of H-ZSM-5 catalyst for methanol
conversion to light olefins especially propylene.
Background of the invention
Zeolite molecular sieve catalysts are one of the most versatile catalysts ever
found in this technology. Zeolite is three-dimensional, crystalline compounds,
which are built from A104 and Si04 tetrahedral. It exhibits such properties as
being a shape-selective catalyst with unusual catalytic properties, high
thermal
stability and high quality of ion-exchanging, so that, zeolites have dedicated
numerous technical applications, for example they are used as sorbents, ion-
exchangers, separation medias and pollution control agents in the petroleum,
chemical and process industries.
Catalysts based on crystalline aluminosilicates which are prepared from a
source of aluminum, a source of silicon, a source of alkali, a template and
water, Depending on the composition of the starting mixture, the size of the
primary crystallites is 1 micron or less. Commercially important zeolites,
such
as ZSM-5 and beta, can be produced under "hydrothermal" conditions, in
which a silicon source, an aluminum source, optionally an organic template
and a mineralizer (for example, alkali metal hydroxides or fluorides or HF)
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were converted at more than 100 C. under pressure in the pH range between 4
and 14. Hydrothermal syntheses of zeolites with a Si/Al atomic ratio of more
than 20, for example, pentasil, are run in autoclaves at temperatures that are
generally higher than 130 C., for example, at 180.degree (Accordance with
U.S. Pat. No. 3,702,886, U.S. Pat. No. 6645461 and U.S. Pat. No. 6054113).
Methanol conversion is one of the promising and indirect processes in
reducing natural gas resources to valuable products such as polymers. In
which, the methanol-to-olefins conversion is noticeable process by scientists
in
recent years which is performed on an acidic molecular sieve catalyst bed.
Production of methanol conversion catalysts based on crystalline
aluminosilicates is known from DE-A-28 22 725. The diameter of the primary
crystallites is 1 m and more. According to West German Patent No. DE
2,405,909, the catalysts for hydrocarbon conversion are prepared on the basis
of zeolites of the ZSM-5 type, the mean diameters of the primary crystallites
being in the range from 0.05 to 0.1 micron.
According to DE-A-29 35 123. ZSM-5 or ZSM-11 zeolites are prepared,
using ammonium hydroxide and an alcohol as template, in which the presence
of nuclei is characteristic. The zeolites are used as cracking and
hydrocracking
catalysts and as catalysts for isomerization and dewaxing.
A method for production of large flat-structured crystals of zeolites of the
pentasil type from Si02 and a compound of one or more trivalent elements, like
Al, B, Fe, Ga, Cr, in amine-containing solutions is known from DE-A-35 37
459, characterized by the fact that highly dispersed Si02, prepared by burning
of a silicon chloride compound, is used as starting material. The zeolites are
used for conversion of organic compounds, especially for conversion of
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methanol to hydrocarbons containing lower olefins and aromatics. The
obtained zeolites are not agglomerated.
European Patent No. EP- 123,449 describes a process for converting alcohol
or ethers into olefins, using steam-treated zeolite catalysts; the latter have
a
crystal size of less than 1 micron and can be incorporated into a matrix.
Clays,
silica and/or metal oxides are mentioned as matrix materials.
U.S. Pat. No. 4,206,085 relates to hydrocarbon conversion catalysts based
on zeolites and a matrix material, for increasing the abrasion resistance. The
matrix material used is alumina from pseudoboehmite, and Si02 from
ammonium polysilicate or silica sol. The preferred zeolite is of the faujasite
type. There are no data on the size of the zeolite crystals.
U.S. Pat. No. 5063187 concerns catalyst based on crystalline
aluminosilicates of the pentasil type, having an Si/Al atomic ratio of at
least 10,
has the structure of primary crystallites of a mean diameter of at least 0.1
micron and at most 0.9 micron.
Summary of the invention
The present invention relates to catalysts based on crystalline
aluminosilicate of the pentasil type having a Si02/A1z03 molar ratio at least
270. These catalysts have an increased activity and selectivity in methanol
conversion process to light olefins, in particular in methanol conversion to
propylene (MTP). These catalysts are defined by a structure of crystallites of
a
mean diameter of at least about 1 m and at most 12 gm, the BET surface area
from 300 about to 350 m2/g, total pore volume about to 0.15 to about 0.4cm3/g
and the average pore diameter at least 2 and at most 20 nm.
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The families of crystalline aluminosilicate zeolite known as the ZSM-5
type are more particularly describe in U.S. Pat. No. 3,702,886, the disclosure
of
which is incorporated herein by reference. These crystalline aluminosilicates
are characterized by a silica/alumina mole ratio of greater than 5 and more
precisely in the anhydrous state by the general formula:
0.9 ::L 0.2 M2/õO : A1203 : 5-300 Si02
Where M is selected from the group consisting of a mixture of alkali metal
cations and organo ammonium cations, particularly a mixture of sodium and
tetraalkylammonium cations, the groups of which preferably contain 2 to 5
carbon atoms. The term "anhydrous" as used in the above context means that
molecular water is not include in the formula. In a more specific embodiment,
the mole ratio of Si02 to A1203 in the above formula is 5-100 and preferably
15-100.
The original cations can be replaced in accordance with techniques well
known in the art, at least in part, by ion exchange with other cations.
Preferred
replacing cations include alkylammonium cations, metal ions, ammonium ions,
hydrogen ions and mixtures of the same. Particularly preferred cations are
those which render the zeolite catalytically active. These include hydrogen,
rare earth metals, aluminum, metals of Groups II and VIII of the Periodic
Table
and manganese. Also desired are zeolites which are thermally treated products
of the foregoing, said thermal treatment consisting of heating the ZSM-5 type
zeolite in the desired particular cation from at a temperature of at least 700
F.
Members of the family of ZSM-5 zeolites possess a definite distinguishing
crystalline structure whose X-ray diffraction pattern shows the following
significant lines:
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Interplanar spacing d(A): Relative intensity
11.1 0.2 s.
10.0 0.2 s.
7.4 0.15 w.
7.1 0.15 w.
6.3 0.1 w.
6.04 0.1 w.
5.97 0.1 w.
5.56 0.1 w.
5.01 0.1 w.
4.60 0.08 w.
4.25 0.08 w.
3.85 0.07 V.S.
3.71 0.05 s.
3.04 0.03 w.
2.99f0.02 w.
2.94 0.02 w.
The values were determined by standard techniques. The radiation was the
K-alpha doublet of copper, and a scintillation counter spectrometer with a
strip
chart pen recorder was used. The peak heights, I, and the positions as a
function of 2 times theta, where theta is the Bragg angle, were read from the
spectrometer chart. From these, the relative intensities, 100 I/lo, where I0
is the
intensity of the strongest line or peak, and d (obs.), the interplanar spacing
in
A, corresponding to the recorded lines, were calculated. In the above
tabulation, the relative intensities are given in terms of the symbols s=
strong,
w= weak and vs = very strong.
Zeolite ZSM-5 as the catalyst for use in the hydrocarbon conversion
reactions described herein can be suitably prepared from sodium aluminate as a
source of aluminum, silicic acid as a source of silicon and
tetrapropylammonium compounds (for example tetrapropylammonium
hydroxide) as a source of template and sodium hydroxide.
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Detailed description of the Invention
In the catalyst of this invention, the crystallites have a mean diameter of at
least about 1 micron and at most 12 micron. Preferably, the mean diameter of
the crystallites is in the range from 4 to 8 micron. The pure catalyst
(without
binder) determines the BET surface area from 350 to 400m2/g, the total pore
volume between 0.15 and 0.4 cm3/g, and the pore diameter have preferably, a
diameter of 2-20 nm.
The catalyst according to the invention is obtainable preferably in the
following manner:
(a) In an aqueous reaction batch containing a source of aluminum, sodium
hydroxide, a source of tetrapropylammonium template, and a source of silicon
alumimosilicate gel is produced at room temperature and converted to a
crystalline aluminosilicate under atmospheric pressure in a PTFE lined vessel.
(b) The crystallites are separated from the aqueous reaction medium, dried,
washed with ionized water and subjected to an appropriate calcination process.
(c) The product from stage (b) is reacted in an aqueous medium with an
ammonium salt on heating in a manner that described in U.S. Pat. No. 4,
447,669 for the purpose of exchanging the sodium ions with hydrogen ions.
(d) The product from stage (c) is mixed with an amorphous silica -alumina
binder; and
(e) The product from stage (d) is subjected to a final calcination.
The catalyst according to the invention is obtainable is explained in more
detail below:
In stage (a), an aqueous reaction batch containing a source of silicon (for
example silicic acid), a source of aluminum (for example sodium aluminate),
sodium hydroxide and a template of tetrapropylammonium compound (for
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example tetrapropylammonium hydroxide) is first prepared. The proportions
by weight between the source of silicon and the source are aluminum is
selected such that the crystalline aluminosilicates having a Si02/A1203 mole
ratio of at least 250 to about 500 are obtained. An alkaline alumimosilicate
gel
(synthesis gel) is produced from the reaction batch at room temperature and is
transformed to alumimosilicate crystallites under a mild temperature from 80
to
105 C under atmospheric condition in an stainless steel fitted with a
polytetrafluoroethylene (PTFE) inner lining for a duration of 15 days.
Preferred
templates are tetrapropylammonium hydroxide and bromide (TPAOH and
TPABr). The aqueous reaction batch of stage (a) has preferably by a pH value
from 10.5 to 13.5.
In stage (b) the product crystallites are separated by filtration. The
intermediate calcination can be completed in an oxidizing atmosphere at about
500 to 550 C.
In stage (c) the product from stage (b) is reacted in an aqueous medium with
ammonium nitrate on heating in a manner that described in U.S. Pat. No. 4,
447,669. The Na form of zeolite is added to 1M solution of ammonium nitrate.
The mixture is stirred at a temperature 60 C for 4 hours. The product is
recovered by filtration. This operation is renewed third times. The product is
then dried and then calcined in air at 650 C for 3 hours.
In stage (d) the product from stage (c) is mixed with the amorphous
alumimosilicate binder composed 65% of A1203 and 35% of Si02 in a manner
that described in U.S. Pat. No. 4,616,098. The extrudates are dried at I10 C
for 16 hours and calcined at 550 C for 12 hours.
The end product thus obtained can be used in methanol conversion
processes for the production of light olefins, especially for propylene.
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Example 1
This example illustrates the preparation of zeolite ZSM-5. 5.886 grams
NaA1O2 (comp.: 53 wt. percent A1203, 44.5 wt. percent Na20, 2.5 wt. percent
H20) partially dissolved in 62.700 ml. 0.178N sodium hydroxide by vigorous
stirring. There was slowly added 388.941 grams of TPAOH (tetra-n-
propylammonium hydroxide, 40 vol%, Merck) as a template. 527.850 grams
silicic acid (Si02Ø5H20) was added to above mixture under vigorous stirring
at about 500 rpm. After about 60 minutes with stirring, the pH of reaction
mixture was adjusted about 10 values by sulfuric acid addition. The resulted
mixture had the following composition: 7.650 mole Si02, 0.0306 mol A1203,
0.260 mole Na20, 0.765 mole (CH3CH2CH2)4NOH, 153 mole H20. The
mixture was placed in a PTFE lined vessel and heated at 1050 C, at atmospheric
pressure for 5 days under reflux with stirring about 100 rpm. The resultant
solid product was cooled to room temperature, removed, washed with 80 liter
H20. The product was then dried overnight at 105 C. A portion of this product
was subjected to X-ray analysis and identified as ZSM-5 phase with
amorphous phase. The product was then calcined in air at 550 C for 10 hours.
Example 2
This example illustrates the preparation of zeolite ZSM-5. 4.264 grams
NaAlO2 (comp.: 53 wt. percent A1203, 44.5 wt. percent Na20, 2.5 wt. percent
H20) partially dissolved in 2490.140 ml. 0.189 N sodium hydroxide by
vigorous stirring. There was slowly added 395.04 grams of TPAOH as a
template. 536.130 grams silicic acid was added to above mixture under
vigorous stirring at about 500 rpm. After about 60 minutes with stirring, the
pH
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of reaction mixture was adjusted about 10 values by sulfuric acid addition.
The
resulted mixture had the following composition: 7.770 mole Si02, .0222 mol
A1203, 0.266 mole Na20, 0.777 mole (CH3CH2CH2)4NOH, 155.400 mole H20.
The mixture was placed in a PTFE lined vessel and heated at 105 C, at
atmospheric pressure for 10 days under reflux with stirring about 100 rpm.
The resultant solid product was cooled to room temperature, removed, washed
with enough distilled water. The product was then dried overnight at 105 C. A
portion of this product was subjected to X-ray analysis and identified pure
ZSM-5 phase that had a degree of crystallinity of 100%, the BET surface area
319.86 m2/g, total pore volume 0.167 cm3/g, the average pore radius 10.44
angstrom and crystallite size between 1-12 m.
The product was then calcined in air at 550 C for 10 hours. The analysis
results of product are indicated in table I.
Example 3:
This example illustrates the preparation of zeolite ZSM-5. 3.019 grams
NaA1O2 (comp.: 53 wt. percent A1203, 44.5 wt. percent Na20, 2.5 wt. percent
H20) partially dissolved in 2515.810 ml. 0.195N sodium hydroxide by
vigorous stirring. There was slowly added 395.04 grams of TPAOH solution as
a template. 541.650 grams silicic acid was added to above mixture under
vigorous stirring at about 500 rpm. After about 60 minutes with stirring, the
pH
of reaction mixture was adjusted about 10 values by sulfuric acid addition.
The
resulted mixture had the following composition: 7.85 mole Si02, 0.0 16 mol
A1203, 0.267 mole Na20, 0.785 mole (CH3CH2CH2)4NOH, 157 mole H20. The
mixture was placed in a PTFE lined vessel and heated at 105 C, at atmospheric
pressure for 15 days under reflux with stirring about 100 rpm. The resultant
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solid product was cooled to room temperature, removed, washed with 80 liter
H20. The product was then dried overnight at 105 C. A portion of this product
was subjected to X-ray analysis and identified of ZSM-5 phase and quartz
phase. The product was then calcined in air at 550 C for 10 hours. The
analysis results of product are indicated in table I.
TABLE I
Example
1 2 3
Time (day) 5 10 15
Temperature ( C) 105 105 105
Reaction composition, moles
SiO2 250 350 500
A1~O3 1 1 1
NazO 8.50 12 17
(CH3CH2CH2)4NOH 25 35 50
Product, weight percent in the H-form
zeolite (calcined 550 C)
Na20 0.076 0.067 0.051
A1,03 0.625 0.491 0.313
Si02 99.34 99.50 99.41
Total as oxides 100.04 100.05 99.77
SiO2/A1ZO3 270 344 540
Na2O/A1203 0.200 0.224 0.268
Product phase ZSM-5+Arnorph Pure ZSM-5 ZSM-5+Quartz
Application Example:
The catalyst conversion of methanol to light olefins especially propylene
over HZSM-5 catalyst (Catalyst of example 2) with Si021A1203 molar ratio of
344 was performed in a fixed-bed stainless steel reactor (1 inch I.D.). For
methanol conversion, 300 grams of shaped catalyst was placed between two
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beds of alumina balls with the same dimension of the catalyst. Prior to
introducing methanol feed, the catalyst was heated under flow of nitrogen (100
ml/min) at 550oC during 12 hours. Typical test of catalyst was experienced in
condition of a pressure of latm. (1.04 bar), temperature of 460 3oC, WHSV of
lh-1, with a feed of 50% methanol in water. The conversion of methanol was
defined as:
X= noCH3OH - (nCH3OH+2nDME) x 100%
noCH3OH
Wherein X is the conversion, noCH3OH is the moles of methanol fed to
the reactor per unit time, nCH3OH is the moles of unreacted methanol leaving
the reactor per unit time, nDME is the moles of dimethyl ether leaving the
reactor per unit time. That is, the moles of dimethyl ether are treated as
equivalent moles to unreacted methanol, not as a reaction product.
Distribution
of hydrocarbons and oxygen products are shown in table II.
TABLE II
TOS(h) 100 200 300 400 500
Hydrocarbon Distribution (mole %)
CH4 0.69 1.24 0.83 1.31 1.42
C2H4 15.11 12.94 14.57 9.00 8.78
C2H6 0.25 0.18 0.26 0.12 0.12
C3H6 37.54 41.47 43.02 44.30 43.07
CzHg 3.17 2.00 2.80 1.07 0.96
DME 0.01 0.00 0.27 0.00 0.01
TOTAL C4= 25.55 26.56 26.49 27.82 24.50
n-Butane 2.20 2.46 1.93 2.93 1.43
iso-Butane 2.03 2.42 2.03 2.65 3.25
C5 hydrocarbons 3.66 2.24 2.56 3.17 3.79
C6 hydrocarbons 1.87 1.54 0.94 1.78 3.13
C7 hydrocarbons 1.12 1.05 0.59 1.07 1.91
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Benzene 0.20 0.12 0.04 0.05 0.12
Toluene 1.49 1.09 0.40 0.54 1.07
p,m,o-Xyelenes 3.01 2.32 0.96 1.75 3.11
Tri methyl benzene 0.50 0.55 0.32 0.50 1.10
C8 hydrocarbons 0.47 0.46 0.28 0.48 0.81
C9+ hydrocarbons 0.58 0.69 0.42 0.41 0.48
CO2 0.22 0.44 0.98 0.50 0.03
CO 0.09 0.09 0.09 0.08 0.08
MeOH (unreacted) 0.09 0.00 0.03 0.12 0.38
Acetone 0.15 0.15 0.06 0.10 0.19
1-Propanol 0.00 0.00 0.01 0.02 0.03
Oxygenates 0.00 0.00 0.11 0.22 0.24
Total 100.00 100.00 100.00 100.00 100.00
%Conversion 99.90 100.00 99.20 99.93 99.73
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