Molecular sieve abstract
A boron-containing molecular sieve having the CHA crystal structure
and comprising (1) silicon oxide and (2) boron oxide or a combination
of boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium
oxide and mixtures thereof is prepared using a quaternary ammonium
cation derived from 1-adamantamine, 3-quinuclidinol or 2-exo-aminonorbornane
as structure directing agent. The molecular sieve can be used for
gas separation or in catalysts to prepare methylamine or dimethylamine,
to convert oxygenates (e.g., methanol) to light olefins, or for
the reduction of oxides of nitrogen n a gas stream (e.g., automotive
exhaust).
Molecular sieve claims
1. A process for the production of light olefins from a feedstock
comprising an oxygenate or mixture of oxygenates, the process comprising
reacting the feedstock at effective conditions over a catalyst comprising
boron-containing molecular sieve having the CHA crystal structure
and comprising (1) silicon oxide and (2) boron oxide or a combination
of boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium
oxide and mixtures thereof.
2. The process of claim 1 wherein the light olefins are ethylene,
propylene, butylene or mixtures thereof.
3. The process of claim 2 wherein the light olefin is ethylene.
4. The process of claim 1 wherein the oxygenate is methanol, dimethyl
ether or a mixture thereof.
5. The process of claim 4 wherein the oxygenate is methanol.
6. The process of claim 1 wherein oxide (2) is more than 50% boron
oxide on a molar basis.
Molecular sieve description
[0001] This application claims benefit under 35 USC 119 of Provisional
Application 60/632007 filed Nov. 30 2004.
BACKGROUND
[0002] Chabazite, which has the crystal structure designated "CHA",
is a natural zeolite with the approximate formula Ca.sub.6Al.sub.12Si.sub.24O.sub.72.
Synthetic forms of chabazite are described in "Zeolite Molecular
Sieves" by D. W. Breck, published in 1973 by John Wiley &
Sons. The synthetic forms reported by Breck are: zeolite "K-G",
described in J. Chem. Soc., p. 2822 (1956), Barrer et al.; zeolite
D, described in British Patent No. 868846 (1961); and zeolite R,
described in U.S. Pat. No. 3030181 issued Apr. 17 1962 to Milton
et al. Chabazite is also discussed in "Atlas of Zeolite Structure
Types" (1978) by W. H. Meier and D. H. Olson.
[0003] The K-G zeolite material reported in the J. Chem. Soc. Article
by Barrer et al. is a potassium form having a silica:alumina mole
ratio (referred to herein as "SAR") of 2.3:1 to 4.15:1.
Zeolite D reported in British Patent No. 868846 is a sodium-potassium
form having a SAR of 4.5:1 to 4.9:1. Zeolite R reported in U.S.
Pat. No. 3030181 is a sodium form which has a SAR of 3.45:1 to
3.65:1.
[0004] Citation No. 93:66052y in Volume 93 (1980) of Chemical Abstracts
concerns a Russian language article by Tsitsishrili et al. in Soobsch.
Akad. Nauk. Gruz. SSR 1980 97(3) 621-4. This article teaches that
the presence of tetramethylammonium ions in a reaction mixture containing
K.sub.2O--Na.sub.2O--SiO.sub.2--Al.sub.2O.sub.3--H.sub.2O promotes
the crystallization of chabazite. The zeolite obtained by the crystallization
procedure has a SAR of 4.23.
[0005] The molecular sieve designated SSZ-13 which has the CHA
crystal structure, is disclosed in U.S. Pat. No. 4544538 issued
Oct. 1 1985 to Zones. SSZ-13 is prepared from nitrogen-containing
cations derived from 1-adamantamine, 3-quinuclidinol and 2-exo-aminonorbornane.
Zones discloses that the SSZ-13 of U.S. Pat. No. 4544538 has a
composition, as-synthesized and in the anhydrous state, in terms
of mole ratios of oxides as follows:
[0006] (0.5 to 1.4)R.sub.2O : (0 to 0.5)M.sub.2O : W.sub.2O.sub.3
: (greater than 5)YO.sub.2 wherein M is an alkali metal cation,
W is selected from aluminum, gallium and mixtures thereof, Y is
selected from silicon, germanium and mixtures thereof, and R is
an organic cation. U.S. Pat. No. 4544538 does not, however, disclose
boron-containing SSZ-13.
[0007] U.S. Pat. No. 6709644 issued Mar. 23 2004 to Zones et
al., discloses zeolites having the CHA crystal structure and having
small crystallite sizes. It does not, however, disclose a CHA zeolite
containing boron. It is disclosed that the zeolite can be used for
separation of gasses (e.g., separating carbon dioxide from natural
gas), and in catalysts used for the reduction of oxides of nitrogen
in a gas stream (e.g., automotive exhaust), converting lower alcohols
and other oxygenated hydrocarbons to liquid products, and for producing
dimethylamine.
SUMMARY OF THE INVENTION
[0008] The present invention relates to a process for the production
of light olefins comprising olefins having from 2 to 4 carbon atoms
per molecule from an oxygenate feedstock. The process comprises
passing the oxygenate feedstock to an oxygenate conversion zone
containing a molecular sieve catalyst to produce a light olefin
stream.
[0009] Thus, in accordance with the present invention there is
provided a process for the production of light olefins from a feedstock
comprising an oxygenate or mixture of oxygenates, the process comprising
reacting the feedstock at effective conditions over a catalyst comprising
boron-containing molecular sieve having the CHA crystal structure
and comprising (1) silicon oxide and (2) boron oxide or a combination
of boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium
oxide and mixtures thereof.
DETAILED DESCRIPTION
[0010] The present invention relates to molecular sieves having
the CHA crystal structure and containing boron in their crystal
framework.
[0011] Boron-containing CHA molecular sieves can be suitably prepared
from an aqueous reaction mixture containing sources of sources of
an oxide of silicon; sources of boron oxide or a combination of
boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium
oxide and mixtures thereof; optionally sources of an alkali metal
or alkaline earth metal oxide; and a cation derived from 1-adamantamine,
3-quinuclidinol or 2-exo-aminonorbornane. The mixture should have
a composition in terms of mole ratios falling within the ranges
shown in Table A below: TABLE-US-00001 TABLE A YO.sub.2/W.sub.aO.sub.b
.sup. >2-2000 OH--/YO.sub.2 0.2-0.45 Q/YO.sub.2 0.2-0.45 M.sub.2/nO/YO.sub.2
0-0.25 H.sub.2O/YO.sub.2 22-80
wherein Y is silicon,; W is boron or a combination of boron and
aluminum, iron, titanium, gallium and mixtures thereof; M is an
alkali metal or alkaline earth metal; n is the valence of M (i.e.,
1 or 2) and Q is a quaternary ammonium cation derived from 1-adamantamine,
3-quinuclidinol or 2-exo-aminonorbornane (commonly known as a structure
directing agent or "SDA").
[0012] The quaternary ammonium cation derived from 1-adamantamine
can be a N,N,N-trialkyl-1-adamantammonium cation which has the formula:
where R.sup.1 R.sup.2 and R.sup.3 are each independently a lower
alkyl, for example methyl. The cation is associated with an anion,
A.sup.-, which is not detrimental to the formation of the molecular
sieve. Representative of such anions include halogens, such as fluoride,
chloride, bromide and iodide; hydroxide; acetate; sulfate and carboxylate.
Hydroxide is the preferred anion. It may be beneficial to ion exchange,
for example, a halide for hydroxide ion, thereby reducing or eliminating
the alkali metal or alkaline earth metal hydroxide required.
[0013] The quaternary ammonium cation derived from 3-quinuclidinol
can have the formula: where R.sup.1 R.sup.2 R.sup.3 and A are
as defined above.
[0014] The quaternary ammonium cation derived from 2-exo-aminonorbornane
can have the formula: where R.sup.1 R.sup.2 R.sup.3 and A are
as defined above.
[0015] The reaction mixture is prepared using standard molecular
sieve preparation techniques. Typical sources of silicon oxide include
fumed silica, silicates, silica hydrogel, silicic acid, colloidal
silica, tetra-alkyl orthosilicates, and silica hydroxides. Sources
of boron oxide include borosilicate glasses and other reactive boron
compounds. These include borates, boric acid and borate esters.
Typical sources of aluminum oxide include aluminates, alumina, hydrated
aluminum hydroxides, and aluminum compounds such as AlCl.sub.3 and
Al.sub.2(SO.sub.4).sub.3. Sources of other oxides are analogous
to those for silicon oxide, boron oxide and aluminum oxide.
[0016] It has been found that seeding the reaction mixture with
CHA crystals both directs and accelerates the crystallization, as
well as minimizing the formation of undesired contaminants. In order
to produce pure phase boron-containing CHA crystals, seeding may
be required. When seeds are used, they can be used in an amount
that is about 2-3 weight percent based on the weight of YO.sub.2.
[0017] The reaction mixture is maintained at an elevated temperature
until CHA crystals are formed. The temperatures during the hydrothermal
crystallization step are typically maintained from about 120.degree.
C. to about 160.degree. C. It has been found that a temperature
below 160.degree. C., e.g., about 120.degree. C. to about 140.degree.
C., is useful for producing boron-containing CHA crystals without
the formation of secondary crystal phases.
[0018] The crystallization period is typically greater than 1 day
and preferably from about 3 days to about 7 days. The hydrothermal
crystallization is conducted under pressure and usually in an autoclave
so that the reaction mixture is subject to autogenous pressure.
The reaction mixture can be stirred, such as by rotating the reaction
vessel, during crystallization.
[0019] Once the boron-containing CHA crystals have formed, the
solid product is separated from the reaction mixture by standard
mechanical separation techniques such as filtration. The crystals
are water-washed and then dried, e.g., at 90.degree. C. to 150.degree.
C. for from 8 to 24 hours, to obtain the as-synthesized crystals.
The drying step can be performed at atmospheric or subatmospheric
pressures.
[0020] The boron-containing CHA molecular sieve has a composition,
as-synthesized and in the anhydrous state, in terms of mole ratios
of oxides as indicated in Table B below:
As-Synthesized Boron-Containing CHA Composition
[0021] TABLE-US-00002 TABLE B YO.sub.2/W.sub.cO.sub.d 20-2000
M.sub.2/nO/YO.sub.2 0-0.03 Q/YO.sub.2 0.02-0.05
where Y, W, M, n and Q are as defined above.
[0022] The boron-containing CHA molecular sieves, as-synthesized,
have a crystalline structure whose X-ray powder diffraction ("XRD")
pattern shows the following characteristic lines: TABLE-US-00003
TABLE I As-Synthesized Boron-Containing CHA XRD 2 Theta.sup.(a)
d-spacing (Angstroms) Relative Intensity.sup.(b) 9.68 9.13 S 14.17
6.25 M 16.41 5.40 VS 17.94 4.94 M 21.13 4.20 VS 25.21 3.53 VS 26.61
3.35 W-M 31.11 2.87 M 31.42 2.84 M 31.59 2.83 M .sup.(a).+-.0.10
.sup.(b)The X-ray patterns provided are based on a relative intensity
scale in which the strongest line in the X-ray pattern is assigned
a value of 100: W(weak) is less than 20; M(medium) is between 20
and 40; S(strong) is between 40 and 60; VS(very strong) is greater
than 60.
[0023] Table IA below shows the X-ray powder diffraction lines
for as-synthesized boron-containing CHA including actual relative
intensities. TABLE-US-00004 TABLE IA As-Synthesized Boron-Containing
CHA XRD 2 Theta.sup.(a) d-spacing (Angstroms) Relative Intensity
(%) 9.68 9.13 55.2 13.21 6.70 5.4 14.17 6.25 33.5 16.41 5.40 81.3
17.94 4.94 32.6 19.43 4.56 6.8 21.13 4.20 100 22.35 3.97 15.8 23.00
3.86 10.1 23.57 3.77 5.1 25.21 3.53 78.4 26.61 3.35 20.2 28.37 3.14
6.0 28.57 3.12 4.4 30.27 2.95 3.9 31.11 2.87 29.8 31.42 2.84 38.3
31.59 2.83 26.5 32.27 2.77 1.4 33.15 2.70 3.0 33.93 2.64 4.7 35.44
2.53 3.9 35.84 2.50 1.2 36.55 2.46 10.9 39.40 2.29 1.8 40.02 2.25
1.3 40.44 2.23 1.0 40.73 2.21 6.0 .sup.(a).+-.0.10
[0024] After calcination, the boron-containing CHA molecular sieves
have a crystalline structure whose X-ray powder diffraction pattern
include the characteristic lines shown in Table II: TABLE-US-00005
TABLE II Calcined Boron-Containing CHA XRD 2 Theta.sup.(a) d-spacing
(Angstroms) Relative Intensity 9.74 9.07 VS 13.12 6.74 M 14.47 6.12
W 16.38 5.41 W 18.85 4.78 M 21.07 4.21 M 25.98 3.43 W 26.46 3.37
W 31.30 2.86 W 32.15 2.78 W .sup.(a).+-.0.10
[0025] Table IIA below shows the X-ray powder diffraction lines
for calcined boron-containing CHA including actual relative intensities.
TABLE-US-00006 TABLE IIA Calcined Boron-Containing CHA XRD 2 Theta.sup.(a)
d-spacing (Angstroms) Relative Intensity (%) 9.74 9.07 100 13.12
6.74 29.5 14.47 6.12 4.6 16.38 5.41 14.2 18.85 4.78 22.1 19.60 4.53
2.2 21.07 4.21 32.9 22.84 3.89 2.2 23.68 3.75 0.8 25.98 3.43 13.1
26.46 3.37 8.7 28.27 3.15 1.3 29.24 3.05 1.6 30.32 2.95 1.7 31.30
2.86 14.4 32.15 2.78 9.0 32.56 2.75 0.2 35.26 2.54 2.4 .sup.(a).+-.0.15
[0026] The X-ray powder diffraction patterns 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 Theta where Theta is the Bragg angle, were read from the spectrometer
chart. From these measured values, the relative intensities, 100.times.I/lo,
where lo is the intensity of the strongest line or peak, and d,
the interplanar spacing in Angstroms corresponding to the recorded
lines, can be calculated.
[0027] Variations in the diffraction pattern can result from variations
in the mole ratio of oxides from sample to sample. The molecular
sieve produced by exchanging the metal or other cations present
in the molecular sieve with various other cations yields a similar
diffraction pattern, although there can be shifts in interplanar
spacing as well as variations in relative intensity. Calcination
can also cause shifts in the X-ray diffraction pattern. Also, the
symmetry can change based on the relative amounts of boron and aluminum
in the crystal structure. Notwithstanding these perturbations, the
basic crystal lattice structure remains unchanged.
[0028] The present invention comprises a process for catalytic
conversion of a feedstock comprising one or more oxygenates comprising
alcohols and ethers to a hydrocarbon product containing light olefins,
i.e., C.sub.2 C.sub.3 and/or C.sub.4 olefins. The feedstock is
contacted with the molecular sieve of the present invention at effective
process conditions to produce light olefins.
[0029] The term "oxygenate" as used herein designates
compounds such as alcohols, ethers and mixtures thereof. Examples
of oxygenates include, but are not limited to, methanol and dimethyl
ether.
[0030] The process of the present invention may be conducted in
the presence of one or more diluents which may be present in the
oxygenate feed in an amount between about 1 and about 99 molar percent,
based on the total number of moles of all feed and diluent components.
Diluents include, but are not limited to, helium, argon, nitrogen,
carbon monoxide, carbon dioxide, hydrogen, water, paraffins, hydrocarbons
(such as methane and the like), aromatic compounds, or mixtures
thereof. U.S. Pat. Nos. 4861938 and 4677242 which are incorporated
by reference herein in their entirety, emphasize the use of a diluent
to maintain catalyst selectivity toward the production of light
olefins, particularly ethylene.
[0031] The oxygenate conversion is preferably conducted in the
vapor phase such that the oxygenate feedstock is contacted in a
vapor phase in a reaction zone with the molecular sieve of this
invention at effective process conditions to produce hydrocarbons,
i.e., an effective temperature, pressure, weight hourly space velocity
(WHSV) and, optionally, an effective amount of diluent. The process
is conducted for a period of time sufficient to produce the desired
light olefins. In general, the residence time employed to produce
the desired product can vary from seconds to a number of hours.
It will be readily appreciated that the residence time will be determined
to a significant extent by the reaction temperature, the molecular
sieve catalyst, the WHSV, the phase (liquid or vapor) and process
design characteristics. The oxygenate feedstock flow rate affects
olefin production. Increasing the feedstock flow rate increases
WHSV and enhances the formation of olefin production relative to
paraffin production. However, the enhanced olefin production relative
to paraffin production is offset by a diminished conversion of oxygenate
to hydrocarbons.
[0032] The oxygenate conversion process is effectively carried
out over a wide range of pressures, including autogenous pressures.
At pressures between about 0.01 atmospheres (0.1 kPa) and about
1000 atmospheres (101.3 kPa), the formation of light olefins will
be affected although the optimum amount of product will not necessarily
be formed at all pressures. The preferred pressure is between about
0.01 atmospheres (0.1 kPa) and about 100 atmospheres (10.13 kPa).
More preferably, the pressure will range from about 1 to about 10
atmospheres (101.3 kPa to 1.013 Mpa). The pressures referred to
herein are exclusive of the diluent, if any, that is present and
refer to the partial pressure of the feedstock as it relates to
oxygenate compounds.
[0033] The temperature which may be employed in the oxygenate conversion
process may vary over a wide range depending, at least in part,
on the molecular sieve catalyst. In general, the process can be
conducted at an effective temperature between about 200.degree.
C. and about 700.degree. C. At the lower end of the temperature
range, and thus generally at a lower rate of reaction, the formation
of the desired light olefins may become low. At the upper end of
the range, the process may not form an optimum amount of light olefins
and catalyst deactivation may be rapid.
[0034] The molecular sieve catalyst preferably is incorporated
into solid particles in which the catalyst is present in an amount
effective to promote the desired conversion of oxygenates to light
olefins. In one aspect, the solid particles comprise a catalytically
effective amount of the catalyst and at least one matrix material
selected from the group consisting of binder materials, filler materials
and mixtures thereof to provide a desired property or properties,
e.g., desired catalyst dilution, mechanical strength and the like
to the solid particles. Such matrix materials are often, to some
extent, porous in nature and may or may not be effective to promote
the desired reaction. Filler and binder materials include, for example,
synthetic and naturally occurring substances such as metal oxides,
clays, silicas, aluminas, silica-aluminas, silica-magnesias, silica-zirconias,
silica-thorias and the like. If matrix materials are included in
the catalyst composition, the molecular sieve preferably comprises
about 1 to 99%, more preferably about 5 to 90%, and still more preferably
about 10 to 80% by weight of the total composition. |