Molecular sieve abstract
A process for the catalyzed conversion of wet acetylene-containing
streams to an essentially aromatic product rich in aromatic compounds,
particularly benzene, toluene and styrenes using a promoted catalyst
composition made by incorporating a major amount of a HAMS-1B crystalline
borosilicate molecular sieve composited in an inorganic matrix with
a minor amount of a zinc compound and calcining the result to form
a promoted catalyst composition containing supported zinc oxide.
Molecular sieve claims
What is claimed is:
1. A process for the conversion of a wet acetylene-containing stream
to a product rich in the aromatics benzene, toluene, and xylene,
comprising contacting said stream under conversion conditions with
a promoted catalyst composition comprising a minor amount of zinc
ion incorporated in a major amount of a catalyst composition consisting
of a HAMS-1B crystalline, borosilicate molecular sieve composited
in an inorganic matrix.
2. The process of claim 1 wherein said wet acetylene-containing
stream contains at least one of methane, carbon monoxide, carbon
dioxide, oxygen, nitrogen, hydrogen, and methanol and up to about
fifty (50) mol percent of acetylene and up to about fifty (50) mol
percent of water.
3. The process of claim 2 wherein said minor amount of zinc ion
lies between about one-half (0.5) and about ten (10) weight percent
of said promoted catalyst composition.
4. The process of claim 3 wherein said inorganic matrix is alumina,
silica-alumina or silica.
5. The process of claim 3 wherein said inorganic matrix is alumina.
6. The process of claim 5 wherein the amount of said HAMS-1B crystalline,
borosilicate molecular sieve in said catalyst composition lies between
about 20 and about 80 weight percent.
7. The process of claim 5 wherein said minor amount of zinc ion
lies between about one-half (0.5) and about five (5) weight percent.
8. The process of claim 6 wherein said minor amount of zinc ion
lies between about one-half and about five (5) weight percent.
9. A process for the conversion of a wet acetylene-containing stream
containing at least one of methane, carbon monoxide, carbon dioxide,
nitrogen, hydrogen and methanol, comprising contacting said stream
under conversion conditions with a promoted catalyst composition
comprising between about one-half and about five (5) weight percent
of zinc ion incorporated in a catalyst composition consisting of
a HAMS-1B crystalline, borosilicate sieve composited in gamma-alumina.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to an improved process for converting wet
acetylene-containing streams primarily to aromatics using a zinc-promoted,
crystalline borosilicate molecular sieve catalyst composition and,
more particularly, to an improved process for converting wet, impure,
acetylene-containing streams to a product rich in aromatics, particularly
benzene, toluene, and xylenes, using a promoted catalyst composition
made by incorporating a major amount of a HAMS-1B crystalline borosilicate
molecular sieve composited in an inorganic support with a minor
amount of a zinc compound and calcining the result to form a promoted
material containing supported zinc, essentially in the form of the
oxide.
Methane (natural gas) is expected to become a significant feedstock
for the production of fuels and chemicals importantly because of
the large amounts that become available in crude oil production.
Proven technology exists to convert methane by (1) methane pyrolysis
to form ethylene-acetylene mixtures or primarily acetylene, and
(2) partial oxidation to mixtures of gases containing 5-10 mol percent
of acetylene. Other gases which may be present in the products of
either the partial oxidation or pyrolysis technique are hydrogen,
oxygen, nitrogen, water, carbon monoxide, carbon dioxide, methane,
ethane, propane, and the like. For example, a typical output stream
from a methane pyrolysis plant contains acetylene, hydrogen, methane,
ethylene, carbon monoxide, carbon dioxide, nitrogen, and higher
acetylenes. Catalysts which can effectively convert acetylene to
useful liquid products, particularly aromatics, in the presence
of these other gases are relatively few. The value of such catalysts
lies in their ability to directly convert methane to hydrocarbon
transportation fuels without going through oxygenated intermediates.
Zirconia-alumina was recently discovered to be such a catalyst.
However, at vapor pressures of water of about half that of the acetylene
or greater in the feed stream, the products obtained over zirconia-alumina
contain a wide range of aliphatic and aromatic oxygenates. See U.S.
Pat. No. 4585897.
Another catalyst which has been used is based on unsupported zeolites
with a crystal framework structure similar to the crystalline aluminosilicates
of the ZSM-5 family. High silica/alumina ratio crystalline aluminosilicates
are preferred. See U.S. Pat. No. 4424401 and J. Catalysis (1983)
80 207. While the latter publications give examples which employ
the molecular sieve in the hydrogen form, H-ZSM, the sodium-exchanged
form is also mentioned. Other catalysts suggested for acetylene
conversion in these publications are crystalline aluminosilicates
containing small amounts of Periodic Groups I-VIII metal ions in
the crystal lattice. Several examples are shown in support of this
latter claim, but they all employ an uncharacterized iron-containing
ZSM-5 sieve. While three of the catalysts described give conversions
of about 80 to 90% most of the other conversion results are much
lower, less than 70% at 400.degree. C. It is also probable that
the conversion generally drops off sharply with time as shown in
Examples 19-20 with coking the probable cause of this loss of activity.
Most importantly, the sieves employed are used unsupported.
Most catalysts for converting acetylene to aromatics are very sensitive
to even trace amounts of water and oxygen. For example, U.S. Pat.
No. 4009219 teaches that acetylene is converted to benzene in
99+% yield by a catalyst consisting of 0.2% potassium chromate on
silica-alumina. This catalyst rapidly deactivates in the presence
of water. V. O. Reikhsfeld and K. L. Makovetskii in Russian Chemical
Reviews (1966) 35 510-523 cite many examples of organometallic
and Ziegler-Natta type catalysts which have also been employed,
but these too decompose on exposure to air, water, or both.
Now it has been found that by incorporating a small amount of a
zinc compound into a supported HAMS-1B crystalline, borosilicate
molecular sieve and calcining, supported zinc-promoted catalyst
compositions can be made which show considerably enhanced conversions
of a wet acetylene-containing stream to aromatics, particularly
benzene, toluene and xylenes, even in the presence of one or more
impurities such as hydrogen, oxygen, nitrogen, carbon dioxide, carbon
monoxide, organic oxygenates and hydrocarbons such as methane, etc.
Such a process could provide the basis for the direct upgrading
of such acetylene-containing streams to hydrocarbon products useful,
for example, in the transportation fuels industry.
SUMMARY OF THE INVENTION
Described herein is a process for the conversion of a wet acetylene-containing
stream to a product rich in benzene, toluene, and xylene comprising
contacting said stream under conversion conditions with a promoted
catalyst composition comprising a minor amount of zinc ion in a
major amount of a catalyst composition consisting of a HAMS-1B crystalline,
borosilicate molecular sieve composited in an inorganic matrix.
DETAILED DESCRIPTION OF THE INVENTION
The acetylene feed to the conversion reaction of the instant invention
is a wet acetylene-containing stream or more commonly a wet, impure,
acetylene-containing stream diluted with one or more of a lower
alcohol, a lower aldehyde, a lower ketone, other similar oxygen-containing
materials, hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide,
methane, ethane, propane and the like. The exact composition of
the feed stream will depend upon the source but generally contains
between about 1 to about 90 mol percent acetylene, more preferably
between about 5 and 25 mol percent of acetylene, and up to about
90 mol percent of impurities such as those mentioned above. In general,
the acetylene feed contains at least about 1 mol percent of water.
Preferably, the feed contains at least as much water as acetylene
and, more preferably, more water than acetylene on a molar basis.
It is believed that more water than acetylene in the stream has
little effect on conversion to aromatics and that less water than
acetylene in the stream leads to a lower conversion of the acetylene
to aromatics because of coking.
The catalyst compositions of the present invention are promoted
with zinc ion, thought to be essentially in its oxide form, incorporated
in a catalyst composition which is a HAMS-1B crystalline, borosilicate
molecular sieve, the hydrogen form of the AMS-1B crystalline, borosilicate
molecular sieve, composited in an inorganic matrix. The preparation
and support of such sieves and procedures of their support are detailed
below.
As said above, incorporated in the catalyst compositions, for example,
by impregnation, is zinc ion thought to be mostly, if not all, in
the form of the oxide after the catalyst composition (molecular
sieve plus support) is calcined. Such compounds as zinc nitrate,
acetate and other water-soluble salts whose anions decompose on
heating are useful for this purpose. The zinc compound can be incorporated
using it dissolved in an aqueous solution, and thereafter the incorporated
catalyst composition is heated sufficiently to decompose the compound
yielding zinc ion essentially in the oxide form. A preferred method
of incorporation uses the incipient wetness technique by which a
zinc compound-containing solution is added to the solid catalyst
composition until the porous solid is saturated and the solid surface
appears wet. In general, the amount of zinc contained in the promoted
catalyst composition lies between one-half (0.5) and about ten (10)
percent by weight, more preferably between about one-half (0.5)
and about eight (8) percent by weight, and most preferably between
about one-half (0.5) and about five (5) weight percent; all percents
here are given as weight percent zinc, calculated as the oxide,
and calculated on the total weight of the promoted catalyst composition.
The reaction is desirably carried out in a fixed bed reactor although
an ebullated, slurry, fluidized bed, or other type of reactor can
be useful, too, with appropriate changes in the reactor conditions
and possibly the physical makeup of the catalyst compositions as
can be understood by one skilled in the art.
The conversion is desirably carried out in the temperature range
from about 300.degree. C. to about 500.degree. C., more preferably
between about 300.degree. C. and about 400.degree. C. Although the
reaction can be carried out at near atmospheric pressure, elevated
pressure from about atmospheric to about 600 psig, more preferably
from about atmospheric to about 50 psig, is desirable. In a fixed
bed reactor, the WHSV desirably varies from about 0.1 to about 100
more preferably from about 1 to 10. In other than fixed bed reactors,
space velocities will be different as may be understood by one skilled
in the art.
Some of the catalyst compositions used in this invention are based
on AMS-1B crystalline, borosilicate molecular sieve, which is described
in U.S. Pat. Nos. 4268420 4269813 and 4285919 and Published
European Patent Application No. 68796 all incorporated herein
by reference, AMS-1B crystalline borosilicate generally can be characterized
by the X-ray pattern listed in Table A and by the composition formula:
wherein M is at least one cation, n is the valence of the cation,
y is between 4 and about 600 and z is between 0 and about 160.
More specifically, the material useful in the present invention
is prepared by mixing a base, a boron oxide source, and an organic
template compound in water (preferably distilled or deionized).
The order of addition usually is not critical although a typical
procedure is to dissolve base and boric acid in water and then add
the template compound. Generally, the silicon oxide compound is
added with intensive mixing such as that performed in a Waring Blender
and the resulting slurry is transferred to a closed crystalline
vessel for a suitable time. After crystallization, the resulting
crystalline product can be filtered, washed with water, dried, and
calcined.
During preparation, acidic conditions should be avoided. When alkali
metal hydroxides are used, the values of the OH.sup.- /SiO.sub.2
shown above should furnish a pH of the system that broadly falls
within the range of about 9 to about 13.5. Advantageously, the pH
of the reaction system falls within the range of about 10.5 to about
11.5 and most preferably between about 10.8 to about 11.2.
Examples of oxides of silicon useful in this invention include
silicic acid, sodium silicate, tetraalkyl silicates and Ludox, a
stabilized polymer of silicic acid manufactured by E.I. DuPont de
Nemours & Co. Typically, the oxide of boron source is boric
acid although equivalent species can be used such as sodium borate
and other boron-containing compounds.
Cations useful in formation of AMS-1B crystalline borosilicate
include alkali metal and alkaline earth metal cations such as sodium,
potassium, lithium, calcium and magnesium. Ammonium cations may
be used alone or in conjunction with such metal cations. Since basic
conditions are required for crystallization of the molecular sieve
of this invention, the source of such cation usually is a hydroxide
such as sodium hydroxide. Alternatively, AMS-1B can be prepared
directly in the hydrogen form by replacing such metal cation hydroxides
with an organic base such as ethylenediamine as described in Published
European Application No. 68796.
Organic templates useful in preparing AMS-1B crystalline borosilicate
include alkylammonium cations or precursors thereof such as tetraalkylammonium
compounds, especially tetra-n-propylammonium compounds. A useful
organic template is tetra-n-propylammonium bromide. Diamines, such
as hexamethylenediamine, can be used.
In a more detailed description of a typical preparation of this
invention, suitable quantities of sodium hydroxide and boric acid
(H.sub.3 BO.sub.3) are dissolved in distilled or deionized water
followed by addition of the organic template. The pH may be adjusted
between about 11.0ij 0.2 using a compatible acid or base such as
sodium bisulfate or sodium hydroxide. After sufficient quantities
of a silica source such as a silicic acid polymer (Ludox) are added
with intensive mixing, preferably the pH is again checked and adjusted
to a range of about 11.0 ij 0.2.
Alternatively, AMS-1B crystalline, borosilicate molecular sieve
can be prepared by crystallizing a mixture of sources for an oxide
of silicon, an oxide of boron, an alkyl ammonium compound and ethylenediamine
such that the initial reactant molar ratios of water to silica range
from about 5 to about 25 preferably about 5 to about 20 and most
preferably from about 10 to about 15. In addition, preferably molar
ratios for initial reactant silica to oxide of boron range from
about 4 to about 150 more preferably from about 5 to about 80 and
most preferably from about 5 to about 20. The molar ratio of ethylenediamine
to silicon oxide should be above about 0.05 typically below 5
preferably between about 0.1 and about 1.0 and most preferably between
about 0.2 and 0.5. The molar ratio of alkylammonium compound, such
as tetra-n-propylammonium bromide, to silicon oxide can range from
0 to about 1 or above, typically above about 0.005 preferably about
0.01 to about 0.1 more preferably about 0.01 to about 0.1 and most
preferably about 0.2 to about 0.05.
The resulting slurry is transferred to a closed crystallization
vessel and reacted usually at a pressure at least the vapor pressure
of water for a time sufficient to permit crystallization which usually
is about 0.25 to about 20 days, typically is about one to about
ten days and preferably is about one to about seven days, at a temperature
ranging from about 100.degree. C. to about 250.degree. C., preferably
about 125.degree. C. to about 200.degree. C. The crystallizing material
can be stirred or agitated as in a rocker bomb. Preferably, the
crystallization temperature is maintained below the decomposition
temperature of the organic template compound. Especially preferred
conditions are crystallizing at about 165.degree. C. for about five
to about seven days. Samples of material can be removed during crystallization
to check the degree of crystallization and determine the optimum
crystallization time.
The crystalline material formed can be separated and recovered
by well-known means such as filtration with aqueous washing. This
material can be mildly dried for anywhere from a few hours to a
few days at varying temperatures, typically about 50.degree. C.-225.degree.
C., to form a dry cake which can then be crushed to a powder or
to small particles and extruded, pelletized, or made into forms
suitable for its intended use. Typically, materials prepared after
mild drying contain the organic template compound and water of hydration
within the solid mass, and a subsequent activation or calcination
procedure is necessary, if it is desired to remove this material
from the final product. Typically, mildly dried product is calcined
at temperatures ranging from about 260.degree. C. to about 850.degree.
C. and preferably about 425.degree. C. to about 600.degree. C. Extreme
calcination temperatures or prolonged crystallization times may
prove detrimental to the crystal structure or may totally destroy
it. Generally, there is no need to raise the calcination temperature
beyond about 600.degree. C. in order to remove organic material
from the originally formed crystalline material. Typically, the
molecular sieve material is dried in a forced draft oven at 165.degree.
C. for about 16 hours and is then calcined in air in a manner such
that the temperature of about 540.degree. C. is reached. Calcination
at this temperature usually is continued for about 4 to 6 hours.
The AMS-1B crystalline borosilicate, useful in this invention in
its hydrogen form, HAMS-1B, is admixed with or incorporated within
various binders or matrix materials depending upon the intended
process use. The crystalline borosilicate can be combined with active
or inactive materials, synthetic or naturally-occurring zeolites,
as well as inorganic materials which would be useful for binding
the borosilicate. Well-known materials include silica, silica-alumina,
alumina, magnesia, titania, zirconia, alumina sols, hydrated alumina,
clays such as bentonite or kaolin, or other binders well-known in
the art. Typically, the borosilicate is incorporated within a matrix
by blending with a sol of the matrix material and gelling the resulting
mixture. Also, solid particles of the borosilicate and matrix material
can be physically admixed. Typically, such borosilicate compositions
can be pelletized or extruded into useful shapes. The crystalline,
borosilicate content can vary anywhere from a few up to 100 wt.
% of the total composition. Catalytic compositions can contain about
0.1 wt. % to about 100 wt. % crystalline borosilicate material and
preferably contain about 10 wt. % to about 95 wt. % of such material
and most preferably contain about 20 wt. % to about 80 wt. % of
such material.
Catalytic compositions comprising the crystalline borosilicate
material of this invention and a suitable matrix material can be
formed by adding a finely-divided, crystalline borosilicate and
a catalytically active metal compound to an aqueous sol or gel of
the matrix material. The resulting mixture is thoroughly blended
and gelled typically by adding a material such as ammonium hydroxide.
The resulting gel can be dried and calcined to form a composition
in which the crystalline borosilicate and catalytically active metal
compound are distributed throughout the matrix material.
The following Examples will serve to illustrate certain embodiments
of the herein disclosed invention. These Examples should not, however,
be construed as limiting the scope of the novel invention as there
are many variations which may be made thereon without departing
from the spirit of the disclosed invention, as those of skill in
the art will recognize.
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