Molecular sieve abstract
A process for a shape selective hydrocarbon conversion such as
toluene disproportionation, involves contacting a reaction stream
under conversion conditions with a catalytic molecular sieve which
has been preselectivated by agglomerating with an organosilicon
compound. The invention also includes a method for agglomeration-preselectivation
and the shape selective catalyst which results from the agglomeration
preselectivation.
Molecular sieve claims
What is claimed is:
1. A process for a shape selective hydrocarbon conversion comprises
contacting a reaction stream comprising hydrocarbon under conversion
conditions, with a catalytic molecular sieve which has been pre-selectivated
by agglomerating a mixture comprising crystalline molecular sieve
material and organosilicon compound.
2. The process of claim 1 wherein the shape selective hydrocarbon
conversion is selected from a group consisting of dewaxing of paraffins,
isomerization of alkylaromatics, oligomerization of olefins, transalkylation
of aromatics, alkylation of aromatics, conversion of oxygenates
to hydrocarbons, rearrangement of oxygenates and conversion of paraffins
and olefins to aromatics.
3. The process of claim 1 wherein the conversion conditions comprise
a temperature of from about 100.degree. C. to about 760.degree.
C., a pressure of about 0.1 atmosphere to about 100 atmospheres,
a weight hourly space velocity of from about 0.08 hr.sup.-1 to about
200 hr.sup.-1 and a hydrogen/hydrocarbon molar ratio of from about
0 to about 100.
4. The process of claim 1 wherein the shape selective hydrocarbon
conversion is toluene disproportionation.
5. The process of claim 1 wherein the molecular sieve has a Constraint
Index from about 1 to about 12.
6. The process of claim 1 wherein after being pre-selectivated
the molecular sieve is ion exchanged to contain ions selected from
a group consisting of hydrogen, hydrogen precursor, metals of Periodic
Table Group VIII and combinations thereof.
7. The process of claim 1 wherein the mixture comprising crystalline
molecular sieve material and organosilicon compound further comprises
a matrix material.
8. The process of claim 7 wherein the matrix material comprises
amorphous silica.
9. The process of claim 1 wherein the organosilicon compound is
selected from a group consisting of silicones, silanes, alkoxysilanes,
siloxanes and polysiloxanes.
10. The process of claim 9 wherein the organosilicon compound is
added to the mixture in an aqueous form selected from a group consisting
of solutions, aerosols, emulsions and surfactant-stabilized emulsions.
11. The process of claim 10 wherein the surfactant-stabilized aqueous
emulsion includes a surfactant which is a polyoxyethylene-octylphenol
ether.
12. The process of claim 9 wherein the organosilicon compound is
a polysiloxane.
13. The process of claim 12 wherein the polysiloxane is phenylmethylpolysiloxane.
14. A process for disproportionation of toluene into p-xylene comprising:
contacting a reaction stream comprising toluene under toluene disproportionation
conditions with a catalytic molecular sieve which has been pre-selectivated
by agglomerating a mixture comprising crystalline molecular sieve
material and an organosilicon compound.
15. The process of claim 14 wherein said catalytic molecular sieve
comprises a Constraint Index of about 1 to 12 and said reaction
conditions comprise a temperature of about 350.degree. C. to about
540.degree. C., a pressure of from about atmospheric to about 5000
psig, a WHSV of from about 0.1 to about 20 and a hydrogen to hydrocarbon
molar ratio of from about 0.1 to about 20.
16. The process of claim 14 wherein after being pre-selectivated
the molecular sieve is ion exchanged to contain ions selected from
a group consisting of hydrogen, hydrogen precursor, metals of Periodic
Table Group VIII and combinations thereof.
17. The process of claim 14 wherein the mixture comprising crystalline
molecular sieve material and organosilicon compound further comprises
a matrix material.
18. The process of claim 17 wherein the matrix material comprises
amorphous silica.
19. The process of claim 14 wherein the organosilicon compound
is selected from a group consisting of silicones, silanes, alkoxysilanes,
siloxanes and polysiloxanes.
20. The process of claim 14 wherein the organosilicon compound
is added to the mixture in an aqueous form selected from a group
consisting of solutions, aerosols, emulsions and surfactant-stabilized
emulsions.
21. The process of claim 20 wherein the surfactant-stabilized aqueous
emulsion includes a surfactant which is a polyoxyethylene-octylphenol
ether.
22. The process of claim 14 wherein the organosilicon compound
is a polysiloxane.
23. The process of claim 22 wherein the polysiloxane is phenylmethylpolysiloxane.
24. The process of claim 14 wherein the reaction stream further
comprises a second silicon-containing compound which is a high efficiency
para-xylene selectivating agent.
25. The process of claim 24 wherein the high efficiency para-xylene
selectivating agent comprises a silicone compound.
26. The process of claim 25 wherein the silicone compound comprises
a mixture of phenylmethylsilicone and dimethylsilicone.
27. The process of claim 25 wherein the reaction stream comprises
at least 80 wt. % of toluene and at least 0.1 wt. % silicone.
28. The process of claim 25 wherein the silicone compound is fed
with the reaction stream for at least one hour.
29. The process of claim 24 wherein the contacting provides a single
pass para-xylene product purity, relative to all xylene products
of at least 90 wt. % with at least about 15 wt. % toluene conversion.
Molecular sieve description
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to copending U.S. patent applications
Ser. Nos. 850104 and 850105 both filed Mar. 12 1992 which are
herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a process for shape selective
hydrocarbon conversions such as the regioselective production of
para-substituted compounds, e.g. para-xylene, over an agglomeration-preselectivated
catalyst, a catalyst so selectivated and the method of agglomeration-preselectivating
the catalyst. In a toluene disproportionation process, feedstock
containing toluene and which may include a high efficiency para-xylene
selectivating agent is fed over an agglomeration-preselectivated
catalytic molecular sieve.
2. Description of the Prior Art
The term shape-selective catalysis describes unexpected catalytic
selectivities in zeolites. The principles behind shape selective
catalysis have been reviewed extensively, e.g. by N. Y. Chen, W.
E. Garwood and F. G. Dwyer, "Shape Selective Catalysis in Industrial
Applications, 36 Marcel Dekker, Inc. (1989). Within a zeolite pore,
hydrocarbon conversion reactions such as paraffin isomerization,
olefin skeletal or double bond isomerization, oligomerization and
aromatic disproportionation, alkylation or transalkylation reactions
are governed by constraints imposed by the channel size. Reactant
selectivity occurs when a fraction of the feedstock is too large
to enter the zeolite pores to react; while product selectivity occurs
when some of the products cannot leave the zeolite channels. Product
distributions can also be altered by transition state selectivity
in which certain reactions cannot occur because the reaction transition
state is too large to form within the zeolite pores or cages. Another
type of selectivity results from configurational diffusion where
the dimensions of the molecule approach that of the zeolite pore
system. A small change in dimensions of the molecule or the zeolite
pore can result in large diffusion changes leading to different
product distributions. This type of shape selective catalysis is
demonstrated, for example, in toluene selective disproportionation
to p-xylene.
The para-xylene may be produced by methylation of toluene over
a catalyst under conversion conditions. Examples are the reaction
of toluene with methanol as described by Chen et al., J. Amer. Chem.
Sec. 1979 101 6783 and toluene disproportionation, as described
by Pines in "The Chemistry of Catalytic Hydrocarbon Conversions",
Academic Press, N.Y., 1981 p. 72. Such methods typically result
in the production of a mixture including para-xylene, ortho-xylene,
and meta-xylene. Depending upon the para-selectivity of the catalyst
and the reaction conditions, different percentages of para-xylene
are obtained. The yield, i.e., the amount of feedstock actually
converted to xylene, is also affected by the catalyst and the reaction
conditions.
Previously known toluene methylation reactions typically provide
many by-products such as those indicated in the following formula:
Thermodynamic Equilibria for Toluene Conversion to the Products
Indicated
Non-MTPX ##STR1##
One method for increasing para-selectivity of zeolite catalysts
is to modify the catalyst by treatment with "selectivating
agents". Various silicon compounds have been used to modify
catalysts to improve selectivity in hydrocarbon conversion processes.
For example, U.S. Pat. Nos. 4145315 4127616 and 4090981
describe the use of a silicone compound dissolved in an organic
solvent to treat a zeolite. U.S. Pat. Nos. 4465886 and 4477583
describe the use of an aqueous emulsion of a silicone to treat a
zeolite. U.S. Pat. Nos. 4950835 and 4927979 describe the use
of alkoxysilanes carried by gases or organic solvents to treat a
zeolite. U.S. Pat. Nos. 4100215 and 3698157 describe the use
of silanes in hydrocarbons, e.g., pyridine, ethers, to treat a zeolite.
Such modification methods are known in the art to be carried out
after agglomeration of the zeolite. But there has been no suggestion
to silicon-modify zeolites during agglomeration.
Some of these catalyst modification procedures, for example, U.S.
Pat. Nos. 4477583 and 4127616 have been successful in obtaining
para-selectivity, i.e., para-xylene/all xylenes, of greater than
about 90% but with commercially unacceptable toluene conversions
of only about 10%, resulting in a yield of not greater than about
9%, i.e., 10%.times.90%. Such processes also produce significant
quantities of ortho-xylene and meta-xylene thereby necessitating
expensive separation processes in order to separate the para-xylene
from the other isomers.
Typical separation procedures comprise costly fractional crystallization
and adsorptive separation of para-xylene from other xylene isomers
which are customarily recycled. Xylene isomerization units are then
required for additional conversion of the recycled xylene isomers
into an equilibrium mixture comprising para-xylene.
Those skilled in the art appreciate that the expense of the separation
process is proportional to the degree of separation required. Therefore,
significant cost savings are achieved by increasing selectivity
to the para-isomer while maintaining commercially acceptable conversion
levels.
It is, therefore, highly desirable to provide a regioselective
process over a para-selective catalyst for the production of para-xylene
from toluene while maintaining commercially acceptable toluene conversion
levels. It is also highly desirable to provide an efficient and
economical method for preselectivating the catalyst.
SUMMARY OF THE INVENTION
The invention is a process for shape selective hydrocarbon conversions
such as the regioselective production of para-xylene. A reaction
stream containing toluene is disproportionated over a catalytic
molecular sieve which has been preselectivated by agglomeration
with an organosilicon compound. Reaction conditions in the toluene
disproportionation process over the preselectivated catalyst can
provide a single pass para-xylene product, relative to all C.sub.8
products, of at least about 90% and at least 15% toluene conversion.
The invention is also a method for modifying a molecular sieve
catalyst having a Constraint Index of 1-12 by providing a mixture
of molecular sieve crystals, optional binder material and organosilicon
compound, subjecting the mixture to agglomeration and calcining
the resulting agglomerate. The catalyst may be subsequently contacted
with a mixture of a high-efficiency, para-xylene trim selectivating
agent and substituted aromatic at reaction conditions for converting
toluene to xylene to produce a twice selectivated catalyst. The
molecular sieve thus treated has greatly enhanced para-selectivity.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is useful in shape selective hydrocarbon
conversion processes such as in converting various aromatics of
C.sub.6-12 e.g., toluene and benzene, to commercially useful para-substituted
benzenes, such as para-xylene.
Molecular sieves to be used in the process of the invention include
intermediate pore zeolites. Such medium pore zeolites are considered
to have a Constraint Index from about 1 to about 12. The method
by which Constraint Index is determined is described fully in U.S.
Pat. No. 4016218 incorporated herein by reference. Molecular
sieves which conform to the specified values of Constraint Index
for intermediate pore zeolites include ZSM-5 ZSM-11 ZSM-5/ZSM-11
intermediate, ZSM-12 ZSM-21 ZSM-22 ZSM-23 ZSM-35 ZSM-38 ZSM-48
ZSM-50 MCM-22 and Zeolite Beta which are described, for example,
in U.S. Pat. Nos. 3702886 and Re. No. 29949 3709979 3832449
4046859 4556447 4076842 4016245 4229424 4397827
4954325 3308069 Re. 28341 and EP 127399 to which reference
is made for details of these molecular sieves. These zeolites may
be produced with differing silica:alumina ratios ranging from 12:1
upwards. Preferred molecular sieves include ZSM-5 ZSM-11 ZSM-12
ZSM-35 ZSM-38 and MCM-22. Particularly preferred is ZSM-5.
In the invention, the catalyst preferably has a silica-alumina
ratio less than 100 preferably about 20-80 and an alpha value greater
than 100 for example about 150-2000.
The activity of a zeolite is an important consideration in acid-type
catalysis such as toluene disproportionation. Silicious zeolites
may be considered to contain SiO.sub.4 -tetrahedra. Substitution
for the tetravalent element by a trivalent element such as aluminum
produces a negative charge which must be balanced. If this is done
by a proton, the material is acidic and active. The activity of
zeolite catalysts has been described in terms of its Alpha Value.
The Alpha Value is an approximate indication of the catalytic cracking
activity of the catalyst compared to a standard catalyst and it
gives the relative rate constant (rate of normal hexane conversion
per volume of catalyst per unit time.) It is based on the activity
of the amorphous silica-alumina cracking catalyst taken as an Alpha
of 1 (Rate Constant=0.016 sec.sup.-1). The Alpha Test is described
in U.S. Pat. No. 3354078 and in The Journal of Catalysis, Vol.
4 pp. 522-529 (August 1965): Vol. 6 p. 278 (1966); and Vol. 61
p. 395 (1980), each incorporated herein by reference as to that
description. It is noted that intrinsic rate constants for many
acid-catalyzed reactions are proportional to the Alpha Value for
a particular crystalline silicate catalyst (see "The Active
Site of Acidic Aluminosilicate Catalysts," Nature, Vol. 309
No. 5959 pp. 589-591 Jun. 14 1984). The experimental conditions
of the test used herein include a constant temperature of 538.degree.
C. and a variable flow rate as described in detail in the Journal
of Catalysis, Vol. 61 p. 395.
In the synthesis of zeolites, a reaction mixture is prepared generally
containing an oxide of silicon, optionally an aluminum source, a
templating agent which is an organic nitrogen containing compound,
and an alkaline aqueous medium.
The silicon oxide can be supplied from known sources such as silicates,
silica hydrosol, precipitated silica hydrosol, precipitated silica,
e.g. Hi-Sil, silica gel, silicic acid. The aluminum oxide may be
provided as only an impurity in another reactant, e.g., the silica
source.
The sources of organic nitrogen-containing cations, depending,
of course, on the particular zeolite product to result from crystallization
from the reaction mixture, may be primary, secondary or tertiary
amines or quaternary ammonium compounds. Non-limiting examples of
quaternary ammonium compounds include salts of tetramethylammonium,
tetraethylammonium, tetrapropylammonium, tetrabutylammonium, diethylammonium,
triethylammonium, dibenzylammonium, dibenzyldimethylammonium, dibenzyldiethylammonium,
benzyltrimethylammonium and chlorine. Non-limiting examples of amines
useful herein include the compounds of trimethylamine, triethylamine,
tripropylamine, ethylenediamine, propanediamine, butanediamine,
pentanediamine, hexanediamine, methylamine, ethylamine, propylamine,
butylamine, diamethylamine, diethylamine, dipropylamine, benzylamine,
aniline, pyridine, piperidine and pyrrolidine.
The sources of alkali or alkaline earth metal oxide may be, for
example, sodium, lithium, calcium, magnesium, cesium or potassium
hydroxides, halides (e.g. chlorides, and bromides), sulfates, nitrates,
acetates, silicates, aluminates, phosphates and salts of carboxylic
acids.
After crystallization of the zeolite, the organic cations are generally
removed by calcination or other methods known in the art, and alkali
or alkaline earth metals are generally removed, often by intermediate
formation of ammonium ion exchange and calcination of the ammonium
form to yield the hydrogen form.
After crystallization, zeolite crystals to be used in commercial
processes are generally formed into agglomerates for improved strength
and resistance to attrition. Various methods are used to agglomerate
zeolite crystals. These methods include, for example, extrusion
into pellets or beads, spray-drying into fluidizable microspheres,
or by hot pressing the zeolite crystals into agglomerates.
The powder form of the crystals can be shaped into a wide variety
of particle sizes. Generally speaking, the particles have been shaped
into granules, or beads, or a molded product, such as an extrudate
having particles size sufficient to pass through a 2 mesh (Tyler)
screen and be retained on a 300 mesh (Tyler) screen. In cases where
the catalyst is molded, such as by extrusion, the crystals can be
extruded before drying or partially dried and then extruded.
In the present invention a silicon-modified zeolite molecular sieve
catalyst is prepared by mixing zeolite crystals with an organosilicon
compound and optionally a binder material, and agglomerating the
mixture, followed by calcination of the agglomerate. Zeolite crystals
may be introduced into the mixture in as-synthesized form, and the
organic template and alkali or alkaline earth metal ions remaining
in the zeolite structure from the crystallization reaction mixture
may be removed by methods known in the art after the crystals are
agglomerated.
The organosilicon compound is added to the mixture in an aqueous
form, for example, as an emulsion which may be surfactant stabilized,
as a solution, or as an aerosol. Useful surfactants include, for
example, ethers of polyoxyethylene-octylphenols.
The organosilicon compounds include silanes such as alkylsilanes,
arylsilanes, alkyarylsilanes, alkoxysilanes, aryloxysilanes, oxyethylenesilanes,
alkyaryloxysilanes, siloxanes and polysiloxanes with alkyl and/or
aryl and/or glycol groups. Alkyl is intended to include 1 to 12
carbons. Aryl is intended to include 6 to 10 carbons. The organosilicon
compounds also include the silicone compounds described below which
may also be used in trim selectivation. Preferred are siloxanes
such as phenylmethylpolysiloxane.
For the shape selective hydrocarbon conversion process of this
invention, the suitable molecular sieve may be agglomerated or extruded
in combination with a support or binder material such as, for example,
a porous inorganic oxide support or a clay binder. While the preferred
binder is silica, other non-limiting examples of such binder materials
include alumina, zirconia, magnesia, thoria, titania, boria and
combinations thereof, generally in the form of dried inorganic oxide
gels or gelatinous precipitates. Suitable clay materials include,
by way of example, bentonite and kieselguhr. The relative proportion
of suitable crystalline molecular sieve to the total composition
of catalyst and binder or support may be about 30 to about 90 percent
by weight and is preferably about 50-80 percent by weight of the
composition. The composition may be in the form of an extrudate,
beads, pellets (tablets) or fluidizable microspheres.
Shape Selective Conversions
Molecular sieves which are selectivation agglomerated in accordance
with the invention are generally useful as catalysts in shape selective
hydrocarbon conversion processes including cracking reactions involving
dewaxing of hydrocarbon feedstocks; isomerization of alkylaromatics;
oligomerization of olefins to form gasoline, distillate, lube oils
or chemicals; transalkylation of aromatics; alkylation of aromatics;
conversion of oxygenates to hydrocarbons, rearrangement of oxygenates,
and conversion of light paraffins and olefins to aromatics.
Dewaxing
The subject catalysts have good cracking and hydrocracking activity
and may be used to convert paraffins from high to low molecular
weight substances in dewaxing processes. The catalysts of the invention
may be used in processes such as those described, for example, in
U.S. Pat. Nos. 3700585 Re. 28398 3968024 and 4181598 which
are incorporated herein by reference. The term dewaxing means the
removal of those hydrocarbons which will readily solidify (waxes)
from petroleum stocks. Hydrocarbon feeds which can be treated include
lubricating oil stocks as well as those which have a freeze point
or pour point problem, i.e., petroleum stocks boiling above 350.degree.
F. The dewaxing can be carried out at either cracking or hydrocracking
conditions.
In U.S. Pat. No. 3700585 and Re. 28398 to Chen et al., typical
cracking conditions include a liquid hourly space velocity (LHSV)
between about 0.5 and 200 a temperature between about 288.degree.
C. (550.degree. F.) and 590.degree. C. (1100.degree. F.), a pressure
between about subatmospheric and several hundred atmospheres over
ZSM-5 type catalysts. Typical hydrocracking conditions include a
liquid hourly space velocity between about 0.1 and 10 a temperature
between about 340.degree. C. (650.degree. F.) and 538.degree. (1000.degree.
F.), a pressure between about 100 and 3000 psig, and a hydrogen
to hydrocarbon mole ratio between about one and 20. U.S. Pat. No.
3968024 describes similar conversions using ZSM-5 of small crystal
size. U.S. Pat. No. 4181598 describes shape selective cracking
to produce lubes.
Isomerization of alkylaromatics
The modified catalysts of the invention are also advantageously
used in the isomerization of alkylaromatics in conversion reactions
of the type described, for example, in U.S. Pat. Nos. 3856872
3856873 Re. 30157 4101595 4101597 4312790 Re. 31919
and 4224141 which are herein incorporated by reference.
In U.S. Pat. No. 3856872 to Morrison, there is described a process
for converting C.sub.8 aromatics xylene and ethylbenzene to para-xylene
(octafining) at a temperature of 550.degree. F. (288.degree. C.)
to 900.degree. F. (482.degree. C.), a pressure of 150 to 300 psig,
and a liquid hour space velocity (LHSV) of 1 to 200 over an acid
form catalyst containing metal such as platinum or nickel and hydrogen.
In U.S. Pat. No. 3856873 to Burress, mixtures of C.sub.8 aromatic
hydrocarbons are isomerized to para-xylene by contact in vapor phase
with zeolite at a temperature of 500.degree. F. (260.degree. C.)
to 1000.degree. F. (538.degree. C.), a pressure of 0 (atmospheric)
to 1000 psig, and a WHSV of 0.5 to 250 with no added hydrogen.
The catalyst is an acid ZSM-5 ZSM-12 or ZSM-21.
U.S. Pat. No. 4101595 to Chen et al. describes the production
of para-xylene from aromatics of 8 to 10 carbons over a dual function
catalyst with a shape selective acid catalyzed step at a temperature
of 650.degree. F. (343.degree. C.) to 1000.degree. F. (538.degree.
C.), a pressure of 50 to 500 psig, a LHSV of 0.1 to 100 and a molar
ratio of hydrogen/hydrocarbon of 0.1 to 15. The acid form catalyst
has a Constraint Index of 1 to 12 a silica/alumina ratio of at
least 12 a crystal density of not less than 1.6 g/cc, may be pre-coked,
and includes Group VIII noble metal.
In U.S. Pat. No. 4101597 to Breckenridge, a C.sub.8 feed is first
isomerized at 550.degree. F. (288.degree. C.) to 700.degree. F.
(371.degree. C.) over a zeolite having a Constraint Index of 1 to
12 a silica/alumina ratio of at least 12 and containing a metal
having a hydrogenation/dehydrogenation function. A C.sup.9+ fraction
produced during isomerization of C.sub.8 is separated from the other
isomerization products, blended with hydrogen and toluene and contacted
with a porous, acidic catalyst such as ZSM-5 at 750.degree. (399.degree.
C.) to 900.degree. V (482.degree. C.). The catalyst has a Constraint
Index of 1 to 12 a silica/alumina ratio of at least 12 and a metal
providing hydrogenation/dehydrogenation function.
In U.S. Pat. No. 4224141 to Morrison, C.sub.8 aromatics are isomerized
to benzene, toluene and xylenes over a ZSM-5 which is reduced in
activity by dilution with inert matrix, steaming or thermal treatment,
very high silica/alumina ratio, base exchange with alkali metal,
coking or the like. The conversion is at a temperature of 800.degree.
F. (427.degree. C.) to 1000.degree. F. (538.degree. C.) in a low
pressure isomerization unit at a pressure only sufficient to overcome
pressure drop through downstream processing equipment, e.g. below
100 psig, and a WHSV of 1 to 200.
In U.S. Pat. No. 4312790 and Re. 31919 to Butter et al., a zeolite
is incorporated with noble metal subsequent to zeolite crystallization
but prior to catalyst extrusion. The catalyst is used for xylene
isomerization at a temperature of 500.degree. F. (260.degree. C.)
to 1000.degree. F. (540.degree. C.), a pressure between 50 and 1000
psig, a WHSV of 1 to 50 and a hydrogen/hydrocarbon mole ratio of
1 to 20.
Conversion of Oxygenates to Hydrocarbons
U.S. Pat. No. 4476330 to Kerr et al. which is herein incorporated
by reference describes the conversion of aliphatic oxygenates to
a higher molecular weight compound by contacting with a zeolite
having a silica/alumina ratio substantially greater than 10 at a
temperature of 70.degree. F. (21.degree. C.) to 1400.degree. F.
(760.degree. C.). The feeds include lower aliphatic organic oxygenates
up to C.sub.6 acetals, ketals, acid halides, alcohols, carboxylic
acids, aldehydes, acid anhydrides, epoxides, ethers, esters, hemiacetals,
gem diols, hydroxy acids, ketones, ketenes, lactones, peracids,
peroxides, sugars, and especially alcohols, ethers, and esters.
Oligomerization of olefins
The modified catalysts of the invention are advantageously used
in the oligomerization of olefins to form gasoline, distillate,
lube oils or chemicals in conversion reactions of the type described,
for example, in U.S. Pat. Nos. 4517399 4520221 4547609 and
4547613 which are herein incorporated by reference.
U.S. Pat. No. 4 517399 to Chester et al. describes the conversion
of olefins of 3 to 18 carbons, e.g. propylene, to high viscosity,
low pour point lubricating oils by contact with ZSM-5 type zeolites
having large crystals of at least two microns. The conversion conditions
include a temperature of 350.degree. F. (177.degree. C.) to 650.degree.
F. (343.degree. C.) a pressure of 100 to 5000 psig, and a WHSV of
0.1 to 10.
U.S. Pat. No. 4520221 to Chen describes the polymerization of
olefins to 2 to 8 carbons, e.g. propylene, butylene, to high viscosity
lubes, e.g. linear hydrocarbons, over highly siliceous, acidic ZSM-5
type catalysts with surface acidity inactivated by treatment with
base, e.g. bulky amines with a cross-section larger than about 5
Angstroms. The conversion involves a one or two stage process with
the polymerization of lower olefins to linear materials, e.g. at
about 200.degree. C. over a surface poisoned zeolite, and oligomerization
of the product over a modified or unmodified catalyst at a temperature
of 50.degree.-75.degree. C. lower than the first stage, e.g. 150.degree.
C. Therefore, the temperatures range from 25.degree. C. to 400.degree.
C., with a pressure of atmospheric to 1500 psi and a WHSV of 0.04
to 1.0.
U.S. Pat. No. 4547609 to Dessau describes a two stage process
whereby in the first stage, light olefins of 2 to 6 carbons are
oligomerized to gasoline and distillate liquids including aliphatics
of 10 to 20 carbons over a zeolite having a crystal size greater
than 0.5 micron at conditions including a temperature of 500.degree.
F. (260.degree. C.) or higher, e.g. a range of 500.degree. F. (260.degree.
C.) to 800.degree. F. (437.degree. C.), a pressure of atmospheric
to 2000 psig and a WHSV of 0.1 to 20. In the second stage, the distillage
fraction is converted to high viscosity lubes by contact with a
zeolite of smaller crystal size under milder conditions of a temperature
about 200.degree. F. (100.degree. C.) to 500.degree. F. (260.degree.
C.), a pressure of atmospheric to 650 psig, and a WHSV less than
one.
U.S. Pat. No. 4547613 to Garwood et al. describes converting
olefins of 2 to 16 carbons to high viscosity lube oil. A ZSM-5 type
catalyst is pre-conditioned by contact with light olefins of 2 to
16 carbons, e.g. propylene at 400.degree. F. (204.degree. C.) to
1000.degree. F. (538.degree. C.), at a pressure of 0 to 100 psig
for 1 to 70 hours. Conversion conditions include a temperature of
350.degree. F. (177.degree. C.) to 650.degree. F. (343.degree. C.),
a pressure of 400 to 5000 psig and a WHSV of 0.1 to 10. The lube
fractions may be subjected to a hydrogenation step to stabilize.
Conversion of aromatics to dialkyl-substituted benzene
The modified zeolite catalysts of the invention are advantageously
used in the conversion of aromatics compounds to provide dialkyl-substituted
benzene products which are highly enriched in the para-dialkyl substituted
benzene isomer. Conversion reactions of this type include aromatics
alkylation, transalkylation and disproportionation. Aromatics alkylations
in which the catalysts of the invention can be used are described,
for example, in U.S. Pat. Nos. 3755483 4086287 4117024 and
4117026 which are herein incorporated by reference.
As described in U.S. Pat. No. 3755483 to Burress, aromatic hydrocarbons
such as benzenes, naphthalenes, anthracenes and substituted derivatives
thereof, e.g. toluene and xylene, may be alkylkated with alkylating
agents such as olefins ethylene, propylene, dodecene, and formaldehyde,
alkyl halides, and alkyl alcohols with 1 to 24 carbons under vapor
phase conditions including a reactor inlet temperature up to about
900.degree. F. (482.degree. C.), with a reactor bed temperature
up to about 1050.degree. F. (566.degree. C.), at a pressure of about
atmospheric to about 3000 psig, a ratio of aromatic/alkylating agent
of about 1:1 to about 20:1 and a WHSV of 20 to 3000 over ZSM-12.
As described in U.S. Pat. No. 4086287 to Kaeding et al., monoalkylbenzenes
having alkyls of 1-2 carbons, such as toluene and ethylbenzene,
may be ethylated to produce a para-ethyl derivative, e.g. para-ethyltoluene
at a temperature of from about 250.degree. C. to about 600.degree.
C., a pressure of 0.1 atmospheres to 100 atmospheres, a weight hourly
space velocity (WHSV) of 0.1 to 100 and a ratio of feed/ethylating
agent of 1 to 10 over a catalyst having an acid activity, i.e.,
alpha, of 2 to 5000 modified by precoking or combining with oxides
of phosphorus, boron or antimony to attain a catalyst with a xylene
sorption capacity greater than 1 g/100 g of zeolite and an ortho-xylene
sorption time for 30% of said capacity of greater than 10 minutes,
where sorption capacity and sorption time are measured at 120.degree.
C. and a xylene pressure of 4.5.+-.0.8 mm of mercury.
U.S. Pat. No. 4117024 to Kaeding describes a process for the
ethylation of toluene or ethylbenzene to produce p-ethyltoluene
at a temperature of 350.degree. C. to 550.degree. C., a critical
pressure of greater than one atmosphere and less than 400 psig,
with hydrogen/ethylene ratio of 0.5 to 10 to reduce aging of the
catalyst. The zeolite described in U.S. Pat. No. 4117024 has a
crystal size greater then one micron, and is modified as the catalyst
in U.S. Pat. No. 4086287 to attain the sorption capacity described
in U.S. Pat. No. 4086287.
U.S. Pat. No. 4117026 to Haag and Olsen describes the production
of para-dialkyl benzenes having alkyls of 1 to 4 carbons under conditions
which vary according to the feed. When the feed includes monoalkyl
substituted benzenes having an alkyl of 1 to 4 carbons, olefins
of 2 to 15 or paraffins of 3 to 60 carbons or mixtures thereof,
conversion conditions include a temperature of 250.degree. C. to
750.degree., a pressure of 0.1 to 100 atmospheres and a WHSV of
0.1 to 2000. For the disproportionation of toluene, the conditions
include a temperature of 400.degree. C. to 700.degree. C., a pressure
of 1 to 100 atmospheres, and an a WHSV of 1-50. When the feed includes
olefins of 2 to 15 carbons including cyclic olefins, the conversion
conditions include a temperature of 300.degree. C. to 700.degree.
C., a pressure of 1 to 100 atmospheres and a WHSV of 1 to 1000.
When the feed includes paraffins of 3 to 60 carbons, conditions
include a temperature of 300.degree. C. to 700.degree. C., a pressure
of 1 to 100 atmospheres and a WHSV of 0.1 to 100. However for lower
paraffins of 3 to 5 carbons, the temperature should be above 400.degree.
C. When the feed includes mixed aromatics such as ethylbenzene and
toluene, and also optionally olefins of 2 to 20 carbons or paraffins
of 5 to 25 carbons, conversion conditions include a temperature
of 250.degree. C. to 500.degree. C. and a pressure greater than
200 psig. In the absence of added aromatics, the olefins and higher
paraffins are more reactive and require lower severity of operations,
e.g. a temperature of 250.degree. C. to 600.degree. C. preferable
300.degree.-550.degree. C. The catalyst described in U.S. Pat. No.
4117026 is modified as in U.S. Pat. No. 4086287.
Conversion of light paraffins and olefins to aromatics
The modified catalysts of the invention may also be used in the
conversion of light paraffins and olefins to aromatics in processes
of the type described, for example, in U.S. Pat. Nos. 3760024
and 3756942 which are herein incorporated by reference.
U.S. Pat. No. 3760024 to Cattanach describes a process for the
conversion of paraffins of 2 to 4 carbons and/or olefins to aromatics
of 6 to 10 carbons over a ZSM-5 type catalyst with or without hydrogenation/dehydrogenation
component. Conversion conditions include a temperature of 100.degree.
C. to 650.degree. C., a pressure of 0 to 1000 psig, a WHSV of 0.1
to 500 and a hydrogen/hydrocarbon ratio of 0 to 20.
U.S. Pat. No. 3756942 to Cattanach describes the conversion of
paraffins, olefins and naphthenes to aromatics over ZSM-5 type catalysts.
If the feed contains at least 35 wt. % olefins, conversion is at
650.degree. F. (363.degree. C.) to 1400.degree. F. (760.degree.
C.). If the feed contains less than 35 wt. % olefins, the temperature
is 900.degree. F. (482.degree. C.) to 1400.degree. F. (760.degree.
C.) with the absence of substantial added hydrogen. For both types
of feed, the pressure is atmospheric to 35 atmospheres and the WHSV
1 to 15.
Pyridine synthesis
The modified catalysts of the invention are also advantageously
used in the synthesis of pyridine. Pyridine bases may be produced
through the reactions of aldehydes and ketones with ammonia. The
reaction of acetaldehyde with ammonia in the presence of heterogenous
catalysts at about 350.degree. C. to about 550.degree. C. yields
2-and 4-methylpyridine. Acetaldehyde, formaldehyde and ammonia react
to yield pyridine and 3-methylpyridine. Pyridine synthesis is described,
for example, in U.S. Pat. No. 4220783 to Chang et al. and U.S.
Pat. No. 4675410 to Feitler which are herein incorporated by reference.
Caprolactam synthesis
Caprolactam is used in the commercial production of nylon. The
cyclohexanone precursor of caprolactam is produced from benzene
by phenol dehydrogenation or cyclohexane oxidation over a catalyst
containing palladium in liquid or vapor phase. Caprolactam may be
produced by Beckmann rearrangement of cyclohexane oxime over acid
catalysts including zeolites. The synthesis of caprolactam is described,
for example, in U.S. Pat. No. 4359421 which is herein incorporated
by reference.
Therefore, the modified catalysts of the present invention are
suitable for use in a variety of shape selective hydrocarbon conversion
processes including as non-limiting examples, cracking hydrocarbons
with reaction conditions including a temperature of from about 300.degree.
C. to about 700.degree. C., a pressure of from about 0.1 atmosphere
(bar) to about 30 atmospheres and a weight hourly space velocity
of from about 0 1 hr.sup.-1 to about 20 hr.sup.-1 ; dehydrogenating
hydrocarbon compounds with reaction conditions including a temperature
of from about 300.degree. C. to about 700.degree. C., a pressure
of from about 0.1 atmosphere to about 10 atmospheres and a weight
hourly space velocity of from about 0.1 to about 20; converting
paraffins to aromatics with reaction conditions including a temperature
of from about 300.degree. C. to about 700.degree. C., a pressure
of from about 0.1 atmosphere to about 60 atmospheres, a weight hourly
space velocity of from about 0.5 to about 400 and a hydrogen/hydrocarbon
mole ratio of from about 0 to about 20: converting olefins to aromatics,
e.g. benzene, toluene and xylene, with reaction conditions including
a temperature of from about 0.1 atmosphere to about 60 atmospheres,
a weight hourly space velocity of from about 0.5 to about 400 and
a hydrogen/hydrocarbon mole ratio of from about 0 to about 20: converting
alcohols, e.g. methanol, or ethers, e.g. dimethylether, or mixtures
thereof to hydrocarbons including olefins and/or aromatics with
reaction conditions including a temperature of from about 275.degree.
C. to about 600.degree. C., a pressure of from about 0.5 atmosphere
to about 50 atmospheres and a liquid hourly space velocity of from
about 0.5 to 100; isomerizing xylene feedstock components with reaction
conditions including a temperature of from about 230.degree. C.
to about 510.degree. C., a pressure of from about 3 atmospheres
to about 35 atmospheres, a weight hourly space velocity of from
about 0.1 to about 200 and a hydrogen/hydrocarbon mole ratio of
from about 0 to about 100; disproportionating toluene with reaction
conditions including a temperature of from about 200.degree. C.
to about 760.degree. C., a pressure from about atmospheric to about
60 atmospheres and a weight hourly space velocity of from about
0.08 to about 20; alkylating aromatic hydrocarbons, e.g. benzene
and alkylbenzenes in the presence of an alkylating agent, e.g. olefins,
formaldehyde, alkyl halides and alcohols, with reaction conditions
including a temperature of from about 250.degree. C. to about 500.degree.
C., a pressure of from about atmospheric to about 200 atmospheres,
a weight hourly space velocity of from about 2 to about 2000 and
an aromatic hydrocarbon/alkylating agent mole ratio of from about
1/1 to about 20/1; and transalkylkating aromatic hydrocarbons in
the presence of polyalkylaromatic hydrocarbons with reaction conditions
including a temperature of from about 340.degree. C. to about 500.degree.
C., a pressure of from about atmospheric to about 200 atmospheres,
a weight hourly space velocity of from about 10 to about 1000 and
an aromatic hydrocarbon/polyalkylaromatic hydrocarbon mole ratio
of from about 1/1 to about 16/1.
In general, therefore, catalytic conversion conditions over a catalyst
comprising the modified zeolite include a temperature of from about
100.degree. C. to about 760.degree. C., a pressure of from about
0.1 atmosphere (bar) to about 200 atmospheres (bar), a weight hourly
space velocity of from about 0.08 hr.sup.-1 to about 2000 hr.sup.-1
and a hydrogen/organic, e.g. hydrocarbon compound of from 0 to about
100.
Toluene Disproportionation
Toluene Disproportionation will be used as a representative shape
selective conversion. Reaction conditions in the toluene disproportionation
contemplated herein include temperatures ranging from about 100.degree.
C. to about 600.degree. C., preferably from about 300.degree. C.
to about 500.degree. C.; pressures ranging from about 0 to about
2000 psig, preferably from about 15 to about 800 psig; a mole ratio
of hydrogen to hydrocarbons from about 0 (i.e. no hydrogen is present)
to about 10 preferably from about 1 to about 4; at a weight hourly
space velocity (WHSV) from about 0.1 to about 100 hr.sup.-1 preferably
from about 0.1 to about 10 hr.sup.-1.
Normally a single pass conversion of a toluene stream results in
a product stream which includes dimethylbenzenes having alkyl groups
at all locations, i.e., ortho-, meta-, and para-xylenes. Furthermore,
the xylenes are known to proceed in a reaction which produces unwanted
ethylbenzenes (EB) by the following reaction: ##STR2##
Previously, the purity of p-xylene with respect to all of the C.sub.8
products in a single pass has been limited to less than 90% when
isomerization is permitted. This efficiency is reduced somewhat
by the production of ethylbenzene.
The present invention, however, provides high efficiency conversion
which reduces production of ortho- and meta-isomers to the benefit
of the desired para-isomer. The resulting product stream contains
greater than a 90% purity of para-xylene. For example, the ortho-xylene
isomer can be reduced to not more than about 0.5% of the total xylenes
content while the meta-xylene isomer can be reduced to less than
about 5% of the total xylene content. Moreover, when the reaction
system is properly treated, such as by deposition of platinum on
the molecular sieve, the presence of ethylbenzene can be reduced
to less than about 0.3% of the C.sub.8 product.
As explained in greater detail herein, the present invention provides
a method for obtaining para-xylene at conversion rates of at least
about 15%, preferably at least about 20-25%, and with para-xylene
purity of greater than 90%, preferably at least 95%, and most preferably
about 99%.
Therefore higher para-xylene purity can be attained at commercially
acceptable conversion rates than with previously disclosed processes.
The present invention thus allows for a significant reduction in
process costs previously associated with the separation of unwanted
by-products. Toluene disproportionation processes of the prior art
typically require expensive secondary and tertiary treatment procedures
in order to obtain these efficiencies.
The present invention includes the regioselective conversion of
toluene to para-xylene by methylating toluene in a reaction stream
containing a toluene feed with a trim selectivated catalytic molecular
sieve which has been pre-selectivated as described above with conversion
reaction conditions to provide a single pass, para-xylene purity
of at least about 90% based on the C.sub.8 products. The trim selectivation
methods are described below. As used herein, the term "para-xylene
purity" means the percentage of para-xylene in all of the C.sub.8
products which include ethylbenzene, para-xylene, ortho-xylene,
and meta-xylene. Those skilled in the art will appreciate that the
proximity of the boiling points of these C.sub.8 products necessitates
more expensive separation processes whereas para-xylene may be more
readily separated from other components in the product stream such
as benzene, toluene, and para-ethyltoluene.
As used herein, the term "xylene-conversion product"
indicates the total amount of xylenes resulting from the disproportionation
reaction. The word "para-xylene" in this term is not intended
to limit the scope of the present invention to the production of
xylenes since other para-substituted aromatics may be produced.
In a preferred embodiment, the invention also includes a method
for the regioselective production of para-xylene by passing a reaction
stream which contains an aromatic feedstock, e.g., toluene, in a
single pass, over a trim-selectivated catalytic molecular sieve,
which is pre-selectivated, the single pass in the presence of hydrogen
at reaction conditions suitable to provide para-xylene purity of
greater than about 90%. The product stream may also include small
amounts of ortho- and meta-xylene and trace amounts of impurities
such as ethylbenzene.
The toluene may be fed simultaneously with a high-efficiency selectivating
agent and hydrogen at reaction conditions until the desired p-xylene
selectivity, e.g., 90% or 95%, is attained, whereupon the feed of
selectivating agent is discontinued. This co-feeding of selectivating
agent with toluene will be termed "trim selectivation".
Reaction conditions for this trim-selectivation step generally include
a temperature of about 350.degree.-540.degree. C. and a pressure
of about atmospheric--5000 psig. The feed is provided to the system
at a rate of about 0.1-20 WHSV. The hydrogen is fed at a hydrogen
to hydrocarbon molar ratio of about 0.1-20.
The high efficiency para-xylene selectivating agent for trim selectivation
preferably comprises a silicon containing compound discussed in
greater detail below. For example, organic silicons such as phenylmethyl
silicone, dimethyl silicone, and mixtures thereof are suitable.
According to one embodiment of the present invention, a silicone
containing phenylmethylsilicone and dimethylsilicone groups in a
ratio of about 1:1 is co-fed to the system, while the other components,
e.g., toluene and hydrogen, are fed in the amounts set forth above.
The high-efficiency para-xylene selectivating agent is fed in an
amount of about 0.1%-50% of the toluene according to this preferred
embodiment. Depending upon the percentage of selectivating agent
used, the trim selectivation will preferably last for about 50-300
hours, most preferably less than 170 hrs.
The catalyst is modified by ex situ pre-selectivation during agglomeration
by mixing zeolite with an organosilicon compound, followed by agglomeration
of the mixture, then calcination of the agglomerate. The mixture
may also include binder material. After pre-selectivation, the catalytic
molecular sieves for the present invention are preferably converted
to the hydrogen and optionally, a Group VIII metal form. The crystal
size of zeolites used herein is preferably greater than 0.1 micron.
Subsequently the preselectivated agglomerate may be trim selectivated
with a high efficiency para-xylene selectivating agent.
As used herein, the term "high efficiency, p-xylene selectivating
agent" as used for trim selectivation is used to indicate substances
which will increase the para-selectivity of a catalytic molecular
sieve to the stated levels while maintaining commercially acceptable
toluene to xylene conversion levels. Such substances include, for
example, organic silicon compounds such as phenylmethyl silicone,
dimethylsilicone, and blends thereof which have been found to be
suitable.
The trim selectivation of the catalyst is preferably performed
with a silicone containing compound. An example of silicone compounds
which can be used in the present invention can be characterized
by the general formula: ##STR3## where R.sub.1 is hydrogen, fluorine,
hydroxy, alkyl, aryl, alkylaryl or fluoro-alkyl. The hydrocarbon
substituents generally contain from 1 to 10 carbon atoms and preferably
are methyl or ethyl groups. R.sub.2 is selected from the same group
as R.sub.1 and n is an integer of at least 2 and generally in the
range of 3 to 1000. The molecular weight of the silicone compound
employed is generally between about 80 and about 20000 and preferably
within the approximate range of 150 to 10000. Representative silicone
compounds include dimethylsilicone, diethylsilicone, phenylmethylsilicone,
methylhydrogensilicone, ethylhydrogensilicone, phenylhydrogensilicone,
methylethylsilicone, phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone,
ethyltrifluoropropysilicone, polydimethylsilicone, tetrachlorophenylmethyl
silicone, tetrachlorophenylethyl silicone, tetrachlorophenylhydrogen
silicone, tetrachlorophenylphenyl silicone, methylvinylsilicone
and ethylvinylsilicone. The silicone compound need not be linear
but may be cyclic as for example hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,
hexaphenylcyclotrisiloxane and octaphenylcyclotetrasiloxane. Mixtures
of these compounds may also be used as well as silicones with other
functional groups. Other silicon-containing compounds, such as silanes
and siloxanes, may also be utilized.
Preferably, the kinetic diameters of the high efficiency, p-xylene
trim selectivating agent and the selectivating silicon compounds
added during zeolite agglomeration are larger than the zeolite pore
diameter, in order to avoid reducing the internal activity of the
catalyst.
Before trim-selectivation, the catalyst is pre-selectivated during,
for example, extrusion, and a silicon compound is deposited on the
external surface of the molecular sieve catalyst.
Following deposition of the silicon-containing compound in pre-selectivation,
the catalyst is calcined. For example, the catalyst may be calcined
in an oxygen-containing atmosphere, preferably air, at a rate of
0.2.degree. to 5.degree. C./minute to a temperature greater 300.degree.
C. but below a temperature at which the crystallinity of the zeolite
is adversely affected. Generally, such temperature will be below
600.degree. C. Preferably the temperature of calcination is within
the approximate range of 350.degree. to 550.degree. C. The product
is maintained at the calcination temperature usually for 1 to 24
hours.
While not wishing to be bound by theory, it is believed that the
advantages of the present invention are obtained by rendering acid
sites on the external surfaces of the catalyst substantially inaccessible
to reactants while increasing catalyst tortuosity. Acid sites existing
on the external surface of the catalyst are believed to isomerize
the para-xylene exiting the catalyst pores back to an equilibrium
level with the other two isomers thereby reducing the amount of
para-xylene in the xylenes to only about 24%. By reducing the availability
of these acid sites to the para-xylene exiting the pores of the
catalyst, the relatively high level of para-xylene can be maintained.
It is believed that the high-efficiency, p-xylene selectivity agents
of the present invention block or otherwise render these external
acid sites unavailable to the para-xylene by chemically modifying
said sites.
In line with this theory, it is also believed that the presence
of hydrogen in the reaction zone during the trim selectivation is
important in order to maintain the desired high yields of para-xylene
when a silicone compound is used as the high-efficiency para-xylene
selectivating agent. The importance of the hydrogen may be reduced
in alternative embodiments by using a high efficiency para-xylene
selectivating agent comprising silane or some other compound which
effectively renders the isomerizing acid sites on the external surface
of the catalyst inaccessible.
The invention may utilize a high efficiency para-xylene selectivating
agent which includes a silicon compound wherein the silicon compound
is introduced by co-feeding, for example, at least one silicon compound
with the toluene feedstock over a conversion catalyst at reaction
conditions until the desired degree of selectivation is achieved,
at which time the feed of selectivating agent may be discontinued.
The toluene feedstock preferably includes about 50% to 100% toluene,
more preferably at least about 80% toluene in the toluene feedstock.
Other compounds such as benzene, xylenes, and trimethylbenzene may
also be present in the toluene feedstock without adversely affecting
the present invention.
The toluene feedstock may also be dried, if desired, in a manner
which will minimize moisture entering the reaction zone. Methods
known in the art suitable for drying the toluene charge for the
present process are numerous. These methods include percolation
through any suitable desiccant, for example, silica gel, activated
alumina, molecular sieves or other suitable substances, or the use
of liquid charge dryers.
Operating conditions employed in the improved process of the present
invention may be adjusted to affect the para-selectivity and toluene
conversion rate. Such conditions include the temperature, pressure,
space velocity, molar ratio of the reactants, and the hydrogen to
hydrocarbon mole ratio. One preferred embodiment of the present
invention includes contacting a catalytic molecular sieve with a
toluene feedstock which includes a silicone compound under conditions
for effecting vapor-phase disproportionation. Conditions effective
for accomplishing the high para-selectivity and acceptable toluene
disproportionation conversion rates include a reactor inlet temperature
of about 350.degree.-540.degree. C., preferably greater than about
400.degree. C., a pressure of about atmospheric--5000 psig, preferably
about 100 to 1000 psig, a WHSV of about 0.1-20 preferably about
2-4 and a hydrogen to hydrocarbon mole ratio of about 0.1-20 preferably
about 2-4. This process may be conducted in either batch or fluid
bed operation with attendant benefits of either operation readily
obtainable.
The effluent is separated and distilled to remove the desired product,
i.e., para-xylene, plus other by-products.
The catalyst may be further modified in order to reduce the amount
of undesirable by-products, particularly ethylbenzene. The state
of the art is such that the reactor effluent from standard toluene
disproportionation typically contains about 0.5% ethylbenzene by-product.
Upon distillation of the reaction products, the level of ethylbenzene
in the C.sub.8 fraction often increases to about 3-4 percent. This
level of ethylbenzene is unacceptable for polymer grade p-xylene
since ethylbenzene in the C.sub.8 product, if not removed, degrades
the quality of fibers ultimately produced from the p-xylene product.
Consequently, ethylbenzene content must be kept low. The specification
for ethylbenzene in the C.sub.8 product has been determined by industry
to be less than 0.3%. Ethylbenzene can be substantially removed
by isomerization or by superfractionation processes. Removal of
the ethylbenzene by conventional isomerization would be impractical
with the present invention since the xylene stream, which includes
greater than 90% para-xylene, would be concurrently isomerized to
equilibrium xylenes reducing the amount of para-xylene in this xylene
stream to about 24%. It is known in the art that the alternative
procedure of removing the ethylbenzene by superfractionation is
extremely expensive.
In order to avoid the need for downstream ethylbenzene removal,
the level of ethylbenzene by-product is advantageously reduced by
incorporating a hydrogenation-dehydrogenation function in the catalyst,
such as by addition of a metal compound such as platinum. While
platinum is the preferred metal, other metals such as palladium,
nickel, copper, cobalt, molybdenum, rhodium, ruthenium, silver,
gold, mercury, osmium, iron, zinc, cadmium, and mixtures thereof
may be utilized. The metal may be added by cation exchange, in amounts
of about 0.01-2%, typically about 0.5%. The metal must be able to
enter the pores of the catalyst in order to survive a subsequent
calcination step. For example, a platinum modified catalyst can
be prepared by first adding the catalyst to a solution of ammonium
nitrate in order to convert the catalyst to the ammonium form. The
catalyst is subsequently contacted with an aqueous solution of tetraamine
platinum(II) nitrate or tetraamine platinum(II) chloride. The metallic
compound advantageously enters the pores of the catalyst. The catalyst
can then be filtered, washed with water and calcined at temperatures
of about 250.degree. to 500.degree. C.
By the present process, toluene can be converted to aromatic concentrates
of high value, e.g., about 99% para-xylene based on all C.sub.8
products. In a typical embodiment of the present process, optimum
toluene conversion is found to be about 20-25 weight percent with
a para-xylene purity of about 90-99%.
The following non-limiting examples illustrate the invention:
EXAMPLE 1
To 15.57 g distilled water in a 150 cc beaker was added 1.01 g
50% sodium hydroxide solution and 2.20 g dimethyl silicon modified
with oxyethylene groups to render it water soluble to 38C.degree.
. To this solution was added a mixture of 10.85 g as-synthesized
ZSM-5 and 5.85 g hydrated amorphous silica with stirring. The resultant
dry paste was extruded using a hand extruder to give well-formed
1/16 inch extrudate. Drying at 120.degree. C. for two hours gave
12.91 g product.
EXAMPLE 2
To 15.58 g distilled water in a 150 cc beaker was added 1.03 g
50% sodium hydroxide solution and a mixture of 4.06 g phenylmethylpolysiloxane
and 0.79 g iso-Octylphenoxypolyethoxyethanol surfactant to form
an emulsion. To this emulsion was added a mixture of 10.85 g as-synthesized
ZSM-5 and 5.85 g hydrated amorphous silica (HiSil, PPG Industries,
Inc.) with stirring. The resultant dry paste was extruded using
a hand extruder to give well-formed 1/16 inch extrudate. Drying
at 120.degree. C. for two hours gave 13.49 g product. |