Molecular sieve abstract
In a process for preparing a selectivated catalyst composition
useful in the disproportionation of toluene, a catalyst comprising
an acidic molecular sieve is contacted with a boron compound at
a temperature in excess of 500.degree. C.; and the resultant catalyst
is then contacted with a medium containing hydrogen ions to at least
partially restore the acid activity of the molecular sieve.
Molecular sieve claims
What is claimed is:
1. A process for preparing a selectivated catalyst composition
comprising the steps of: (a) contacting a catalyst comprising an
acidic molecular sieve with a boron compound at a temperature greater
than 500.degree. C.; and, (b) contacting the catalyst produced in
step (a) with a medium containing hydrogen ions to at least partially
restore the acid activity of the molecular sieve.
2. The process recited in claim 1 wherein the contacting step
(a) comprises impregnating the molecular sieve with the boron compound
and then heating the boron-impregnated catalyst to said temperature.
3. The process recited in claim 1 wherein said molecular sieve
has a Diffusion Parameter, D/r.sup.2 for 23-dimethylbutane of
less than 1000.times.10.sup.-6 sec.sup.-1 when measured at a temperature
of 120.degree. C. and a 23-dimethylbutane pressure of 60 torr.
4. The process recited in claim 1 wherein the contacting step
(a) is conducted at a temperature of about 650 to about 705.degree.
C.
5. The process recited in claim 1 wherein the molecular sieve
is an intermediate pore size molecular sieve.
6. The process recited in claim 1 wherein the contacting step
(a) is conducted in the presence of oxygen.
7. The process recited in claim 1 wherein the contacting step
(a) is conducted in the presence of air.
8. The process recited in claim 1 wherein the medium used in step
(b) is an aqueous medium.
9. The process recited in claim 1 wherein the medium used in step
(b) is water.
10. The process recited in claim 9 wherein said medium further
comprises a chelating agent.
11. The process recited in claim 2 wherein the contacting step
(a) is repeated at least two times.
12. The process recited in claim 2 wherein said catalyst is dried
prior to contacting the molecular sieve with the boron compound.
13. The process recited in claim 1 wherein said boron compound
is incorporated into said molecular sieve by extrusion or impregnation.
14. The process recited in claim 2 wherein said molecular sieve
is impregnated with the boron compound by: (i) contacting the molecular
sieve with the boron compound; (ii) mulling the product of step
(i); and (iii) extruding a mixture comprising water and the product
of step (ii) under conditions sufficient to form an extrudate.
15. The process recited in claim 5 wherein the molecular sieve
has a structure type selected from the group consisting of MWW,
MFI, MEL, MFS, MEI, MTW, EUO, MTT, HEU, FER, and TON.
16. The process recited in claim 15 wherein said molecular sieves
is a composition having the following molar relationship: X.sub.2O.sub.3::(n)Y0.sub.2
wherein X is a trivalent element such as aluminum, iron, boron,
and/or gallium and Y is a tetravalent element such as silicon, tin,
and/or germanium; and n has a value greater than 12.
17. The process recited in claim 16 wherein the molecular sieve
is an aluminosilicate zeolite.
18. The process recited in claim 5 wherein the molecular sieve
is selected from the group consisting of ZSM-5 ZSM-11 ZSM-12
ZSM-22 ZSM-23 ZSM-34 ZSM-35 ZSM-38 ZSM-48 ZSM-50 and ZSM-57.
19. The process recited in claim 18 wherein said catalyst further
comprises a hydrogenation/dehydrogenation component.
20. The process recited in claim 5 wherein said catalyst contains
at least about 0.01 percent by weight of boron.
21. The process recited in claim 18 wherein said catalyst has an
alpha value greater than 50.
22. The process recited in claim 21 wherein said catalyst has
an alpha value greater than 200.
23. The process recited in claim 20 wherein said boron compound
is selected from the group consisting of boric acid, trimethylborate,
boron hydride, boron oxide, boron sulfide, butylboron dimethoxide,
butylboronic acid, dimethylboric anhydride, hexamethylborazine,
phenylboric acid, triethylborane, tetramethylammonium borohydride,
triphenyl boron and allylborate.
24. The process recited in claim 1 wherein said catalyst further
comprises a binder.
25. The process recited in claim 24 wherein said binder is silica.
26. The process recited in claim 2 wherein the molecular sieve
is ZSM-5.
27. The process recited in claim 26 wherein the boron compound
is boric acid.
28. A process for shape selective hydrocarbon conversion comprising
contacting a reaction stream containing a hydrocarbon to be converted,
under conversion conditions, with a selectivated catalyst composition
prepared by a process comprising the steps of: (a) contacting a
catalyst comprising an acidic molecular sieve with a boron compound
at a temperature in excess of 500.degree. C.; and, (b) contacting
the catalyst produced in step (a) with a medium containing hydrogen
ions to at least partially restore the acid activity of the molecular
sieve.
29. The process recited in claim 28 wherein the contacting step
(a) comprises impregnating the molecular sieve with the boron compound
and then heating the boron-impregnated catalyst to said temperature.
30. The process recited in claim 29 wherein the contacting step
(a) is conducted at a temperature of about 650 to about 705.degree.
C.
31. The process recited in claim 28 wherein said molecular sieve
has a Diffusion Parameter, D/r.sup.2 for 23-dimethylbutane of
less than 1000.times.10.sup.-6 sec.sup.-1 when measured at a temperature
of 120.degree. C. and a 23-dimethylbutane pressure of 60 torr.
32. The process recited in claim 29 wherein the molecular sieve
is an intermediate pore size molecular sieve.
33. The process recited in claim 32 wherein the contacting step
(a) is conducted in the presence of oxygen.
34. The process recited in claim 32 wherein the contacting step
(a) is conducted in the presence of air.
35. The process recited in claim 32 wherein the medium used in
step (b) is an aqueous medium.
36. The process recited in claim 35 wherein the medium used in
step (b) is water.
37. The process recited in claim 36 wherein said medium further
comprises a chelating agent.
38. The process recited in claim 32 wherein the contacting step
(a) is repeated at least two times.
39. The process recited in claim 32 wherein said catalyst is dried
prior to contacting the molecular sieve with the boron compound.
40. The process recited in claim 32 wherein said boron compound
is incorporated into said molecular sieve by extrusion or impregnation.
41. The process recited in claim 32 wherein said molecular sieve
is impregnated with the boron compound by: (i) contacting the molecular
sieve with the boron compound; (ii) mulling the product of step
(i); and (iii) extruding a mixture comprising water and the product
of step (ii) under conditions sufficient to form an extrudate.
42. The process recited in claim 32 wherein the molecular sieve
has a structure type selected from the group consisting of MWW,
MFI, MEL, MFS, MEI, MTW, EUO, MTT, HEU, FER, and TON.
43. The process recited in claim 42 wherein the molecular sieve
is an aluminosilicate zeolite.
44. The process recited in claim 32 wherein the molecular sieve
is selected from the group consisting of ZSM-5 ZSM-11 ZSM-12
ZSM-22 ZSM-23 ZSM-34 ZSM-35 ZSM-38 ZSM-48 ZSM-50 and ZSM-57.
45. The process recited in claim 44 wherein said catalyst further
comprises a hydrogenation/dehydrogenation component.
46. The process recited in claim 44 wherein said catalyst contains
at least about 0.01 percent by weight of boron.
47. The process recited in claim 44 wherein said catalyst has
an alpha value greater than 50.
48. The process recited in claim 44 wherein said catalyst has
an alpha value greater than 200.
49. The process recited in claim 44 wherein said boron compound
is selected from the group consisting of boric acid, trimethylborate,
boron hydride, boron oxide, boron sulfide, butylboron dimethoxide,
butylboronic acid, dimethylboric anhydride, hexamethylborazine,
phenylboric acid, triethylborane, tetramethylammonium borohydride,
triphenyl boron and allylborate.
50. The process recited in claim 44 wherein said catalyst further
comprises a binder.
51. The process recited in claim 50 wherein said binder is silica.
52. The process recited in claim 29 wherein the molecular sieve
is ZSM-5.
53. The process recited in claim 49 wherein the boron compound
is boric acid.
54. The process recited in claim 32 wherein said conversion is
the conversion of non-aromatic compounds to aromatic compounds.
55. The process recited in claim 32 wherein said conversion is
the conversion of aromatic compounds to different aromatic compounds.
56. The process recited in claim 32 wherein the reaction stream
contains toluene and the shape selective hydrocarbon conversion
is the disproportionation of toluene to produce para-xylene.
57. The process recited in claim 56 wherein said process produces
at least about 80% paraxylene versus the other xylene isomers.
58. The process recited in claim 32 wherein the conversion conditions
comprise a temperature in the range of from about 350.degree. C.
to about 550.degree. C., at a pressure in the range of from about
1 atmosphere to about 5000 psig and at a weight hourly space velocity
of about 0.1 to about 20.
Molecular sieve description
FIELD OF THE INVENTION
[0001] The present invention relates to the selectivation of molecular
sieve catalysts and the use of the selectivated catalysts in shape
selective hydrocarbon conversion processes, such as the disproportionation
of toluene to para-xylene.
BACKGROUND OF THE INVENTION
[0002] Shape-selective catalysis is described, 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 pore of the
molecular sieve, hydrocarbon conversion reactions such as isomerization,
disproportionation, alkylation, and transalkylation of aromatics
are governed by constraints imposed by the pore size. Reactant selectivity
may occur when a fraction of the feedstock is too large to enter
the molecular sieve pores to react, while product selectivity may
occur when some of the products cannot leave the molecular sieve
pores. 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 molecular
sieve pores or cages.
[0003] Another type of selectivity results from configurational
constraints on diffusion where the dimensions of the molecule approach
that of the molecular sieve pore system. A small change in the dimensions
of the molecule or the molecular sieve pore can result in large
diffusion changes leading to different product distributions. This
type of shape-selective catalysis is demonstrated, for example,
in selective alkyl-substituted benzene disproportionation to para-dialkyl-substituted
benzene.
[0004] A representative para-dialkyl-substituted benzene is para-xylene.
Typical methods for the production of para-xylene include the methylation
of toluene and the disproportionation of toluene over a catalyst
under conversion conditions. Such methods may result in the production
of a mixture of the three xylene isomers, i.e., para-xylene, ortho-xylene,
and meta-xylene. Depending upon the degree of selectivity of the
catalyst for para-xylene (para-selectivity) and the reaction conditions,
different percentages of para-xylene are obtained. Of the xylene
isomers, i.e., ortho-, meta- and para-xylene, para-xylene is of
particular value as a large volume chemical intermediate in a number
of applications, such as the manufacture of terephthalic acid, which
is an intermediate in the manufacturer of polyester.
[0005] Various methods are known in the art for increasing the
para-selectivity of zeolite catalysts. One such method involves
selectivating the catalyst, e.g., ZSM-5 with a selectivating agent.
The term "selectivating agent" is used herein to indicate
substances which will increase the shape-selectivity (e.g., para-selectivity)
of the catalyst. For example, one technique, as disclosed in U.S.
Pat. No. 5243117 involves treating the catalyst with a selectivating
agent containing silicon. This technique usually requires several
sequential silicone treatments that can substantially increase the
cost of manufacturing the catalyst. Another technique, as disclosed
in U.S. Pat. No. 4097543 involves the selective disproportionation
of toluene in the presence of a catalyst comprising a molecular
sieve, e.g., ZSM-5 that contains a controlled amount of carbon
coke deposited on the catalyst. This technique requires on-stream
selectivation of the catalyst and further selectivations after regeneration
of the catalyst. Still another technique involves impregnating the
catalyst with oxides that are difficult to reduce, such as those
of magnesium, calcium, and/or phosphorus.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, there is provided
a process for preparing a selectivated catalyst. The process comprises:
(a) contacting a catalyst comprising an acidic molecular sieve with
a boron compound at a temperature greater than 500.degree. C.; and,
(b) contacting the catalyst of step (a) with a medium containing
hydrogen ions to at least partially restore the acid activity of
the molecular sieve.
[0007] In another embodiment, the present invention provides a
process for the conversion of organic compounds, e.g., hydrocarbons,
using the boron-selectivated catalyst prepared by the process described
above. Examples of conversion processes that find particular application
include the disproportionation of toluene, xylenes isomerization,
toluene alkylation with methanol, reformate alkylation with methanol,
ethylbenzene isomerization, ethylbenzene dealkylation, shape selective
reform, conversion of oxygenates to light olefins, and conversion
of oxygenates to aromatics.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The present invention concerns incorporating a boron compound
into a molecular sieve catalyst formulation, such as by extrusion
or impregnation, calcining the boron-containing molecular sieve
catalyst at a temperature greater than 500.degree. C., and then
contacting the catalyst with a medium containing hydrogen ions to
at least partially restore the acid activity of the molecular sieve.
[0009] The calcination is conducted at a temperature substantially
above the normal calcination temperatures used with molecular sieve
catalysts. Although not bound by any theory of operation, it is
believed that the high temperature calcination causes the boron
compound to react with the molecular sieve crystals from the outside
in to leave an amorphous boundary, e.g., coating, on the surface
of the crystals. It is also believed that longer calcination times
can increase the thickness of this boundary. Subsequent washing
of the coated molecular with a medium containing hydrogen ions is
believed to remove any unreacted boron compound, which could block
the pores, from the molecular sieve. In line with this theory, it
is believed that the resulting boundary forms an effective diffusion
barrier on the molecular sieve. Regardless of the theory proposed,
molecular sieves prepared by the process have one or more of the
improved properties which are disclosed herein.
[0010] The molecular sieve, which is subjected to the selectivation
treatment described herein, is preferably an intermediate pore size
molecular sieve. Such intermediate pore size molecular sieves usually
have a Constraint Index of between about 1 and about 12. A method
for determining Constraint Index is described in U.S. Pat. No. 4016218.
[0011] Intermediate pore size molecular sieves have a pore size
from about 5 to about 7 .ANG.. Examples of such molecular sieves
include MWW, MFI, MEL, MFS, MEI, MTW, EUO, MTT, HEU, FER, and TON
structure types. These materials are described in "Atlas of
Zeolite Framework Types", eds. Ch. Baerlocher, W. H. Meier,
and D. H. Olson, Elsevier, Fifth Edition, 2001 which is hereby
incorporated by reference. Examples of specific intermediate pore
size molecular sieves include ZSM-5 ZSM-11 ZSM-12 ZSM-22 ZSM-23
ZSM-34 ZSM-35 ZSM-38 ZSM-48 ZSM-50 and ZSM-57. The preferred
molecular sieve is ZSM-5.
[0012] The intermediate pore size molecular sieves will generally
be a composition having the following molar relationship:
X.sub.2O.sub.3::(n)Y0.sub.2
[0013] wherein X is a trivalent element such as aluminum, iron,
boron, and/or gallium and Y is a tetravalent element such as silicon,
tin, and/or germanium; and n has a value greater than 12 said value
being dependent upon the particular type of molecular sieve. When
the intermediate pore size molecular sieve has a MFI structure,
n is preferably greater than 10.
[0014] When the molecular sieve is an aluminosilicate zeolite,
the zeolite will generally have a silica to alumina mole ratio from
10:1 to 700:1 and preferably from 20:1 to 200:1.
[0015] When the molecular sieve is a gallosilicate molecular sieve,
the molecular sieve usually will be a composition having the following
molar relationship:
Ga.sub.2O.sub.3:ySiO.sub.2
[0016] wherein y is between about 20 and about 500. The molecular
sieve framework may contain only gallium and silicon atoms or may
also contain a combination of gallium, aluminum, and silicon.
[0017] Preferably, the molecular sieve is a metallosilicate, such
as an aluminosilicate, borosilicate, or gallosilicate.
[0018] The molecular sieve subjected to the selectivation treatment
described herein should have sufficient acidity to provide the catalyst
with the activity required for the contemplated organic compound,
e.g., hydrocarbon conversion process. An approximate indication
of the acid activity of a catalyst is its so-called "alpha
value". The alpha test is described in U.S. Pat. No. 3354078
and in the Journal of Catalysis, Vol. 4 522-529 (1965); Vol. 6
278 (1966); and Vol. 61 395 (1980), each incorporated herein by
reference to that description. The experimental conditions of the
alpha test preferably include a constant temperature of 538.degree.
C. and a variable flow rate as described in detail in the Journal
of Catalysis, Vol. 61 395 (1980). The present catalysts may have
an alpha value greater than 50 e.g., greater than 200 e.g., from
about 200 to about 1500.
[0019] The molecular sieve, which is subjected to the selectivation
treatment described herein, may be combined with a binder material
prior to contact with the boron compound. This binder material is
preferably an inert, non-alumina binder material, such as a silica
binder. Optionally, however, the molecular sieve may be selectivated
in the unbound state. Thus, one particular process for introducing
the boron compound into molecular sieve is by impregnation, in which
the bound or unbound-molecular sieve is allowed to contact a solution
of the boron compound in a solvent, such as water. Thereafter, the
solvent is removed, such as by evaporation, and the boron-containing
molecular sieve is heated to the desired calcination temperature.
[0020] An alternative process for contacting the molecular sieve
with the boron compound comprises the steps of mulling and then
extruding a mixture comprising water, the molecular sieve and a
boron compound under conditions sufficient to form an extrudate
having an intermediate green strength sufficient to resist attrition
during subsequent processing. The extruded mixture is then heated
to drive off the water and then react the molecular sieve with the
boron compound. If desired, the extruded mixture may undergo intermediate
processing, such as, for example, contacting the extruded mixture
with an aqueous solution comprising ammonium cations under conditions
sufficient to exchange cations in molecular sieve with ammonium
cations and calcining the ammonium exchanged extruded mixture under
conditions sufficient to generate the hydrogen form of said sieve.
[0021] Where the treating boron compound is a liquid, such compound
can be in solution in a solvent at the time contact with the molecular
sieve is effected. Any solvent relatively inert with respect to
the treating compound and the molecular sieve may be employed. Suitable
solvents include water and aliphatic, aromatic or alcoholic liquids.
Where the boron-containing compound is, for example, trimethylborate,
a hydrocarbon solvent such as n-octane may be employed. The boron-containing
compound may be used without a solvent, i.e., may be used as a neat
liquid.
[0022] In addition to the liquid phase contacting processes so
far described, the combination of the boron compound with the molecular
sieve can be conducted in the gaseous phase. Where the boron-containing
compound is in the gaseous phase, such as where gaseous diborane
is employed, the treating compound can be used by itself or can
be used in admixture with a gaseous diluent inert to the boron-containing
compound and the molecular sieve such as nitrogen or helium or with
an organic solvent, such as octane.
[0023] The catalyst may be preselectivated with boron by single
or multiple treatments with the boron compound, each treatment being
followed by calcination of the treated material in an oxygen containing
atmosphere, e.g., air. For example, the catalyst may be treated
at least twice, e.g., at least 3 times, e.g., from 4 to 6 times,
with a liquid medium comprising a liquid carrier and at least one
boron compound. The liquid carrier may be water, an organic liquid
or a combination of water and an organic liquid. Particularly, when
the liquid medium comprises an emulsion of the boron compound in
water, the liquid medium may also comprise an emulsifying agent,
such as a surfactant.
[0024] Representative boron-containing compounds, which can be
used in the selectivation process of the invention, include boric
acid, trimethylborate, boron hydride, boron oxide, boron sulfide,
butylboron dimethoxide, butylboronic acid, dimethylboric anhydride,
hexamethylborazine, phenylboric acid, triethylborane, tetramethylammonium
borohydride, triphenyl boron and allylborate. An embodiment of the
invention concerns using boric acid as the boron compound, because
of its low acidity and melt characteristics, i.e., boric acid (H.sub.3BO.sub.3)
at about 150.degree. C. forms boric oxide (B.sub.2O.sub.3), which
at about 500.degree. C. forms a molten phase.
[0025] Prior to contacting the molecular sieve with the boron-containing
compound, the catalyst may be dried. Drying can be effected in the
presence of air. Elevated temperatures may be employed. However,
the temperature should not be such that the crystal structure of
the molecular sieve is destroyed.
[0026] After contacting with the boron-containing compound, the
molecular sieve is calcined by heating to a temperature in excess
of 500.degree. C., typically from about 550 to about 800.degree.
C., such as at about 650 to about 705.degree. C. (1200 to 1300.degree.
F.). By heating at such temperatures, it is believed that the boron
compound reacts with the molecular sieve and, upon cooling and solidification,
partially blocks the pores of the molecular sieve, thereby creating
a diffusion barrier.
[0027] When the molecular sieve is preselectivated by a multiple
impregnation technique, the molecular sieve is heated after each
impregnation to remove the carrier. Following each or the final
impregnation, the molecular sieve may be heated at a rate of from
about 0.2.degree. C./minute to about 5.degree. C./minute to a temperature
greater than 500.degree. C., but below the temperature at which
the crystallinity of the molecular sieve is adversely affected.
The duration of calcination at the calcination temperature may be
from 1 to 24 hours, e.g., from 2 to 6 hours.
[0028] The impregnated molecular sieve may be calcined in an inert
or oxidizing atmosphere. An example of such an inert atmosphere
is a nitrogen, i.e., N.sub.2 atmosphere. An example of an oxidizing
atmosphere is an oxygen containing atmosphere, such as air. Calcination
may take place initially in an inert, e.g., N.sub.2 atmosphere,
followed by calcination in an oxygen containing atmosphere, such
as air or a mixture of air and N.sub.2. Calcination should be performed
in an atmosphere substantially free of water vapor to avoid undesirable
uncontrolled steaming of the molecular sieve. The molecular sieve
may be calcined once or more than once following each impregnation.
The various calcinations following each impregnation need not be
identical, but may vary with respect to the temperature, the rate
of temperature rise, the atmosphere and the duration of calcination.
[0029] Although the amount of boron incorporated with the molecular
sieve will vary, the molecular sieve will usually contain at least
about 0.01 percent by weight, and, preferably, at least about 0.5
percent, and most preferably at least 0.8 percent by weight of boron.
It is preferred that the amount of boron in the molecular sieve
be at least about 1 percent by weight when the same is combined
with a binder. The amount of boron can be as high as about 20 percent
by weight or more depending on the amount and type of binder present.
Preferably, the amount of boron added to the molecular sieve is
between about 3.0 and 12.0 percent by weight.
[0030] The amount of boron incorporated with the molecular sieve
by reaction with a boron-containing compound will depend upon several
factors. One of these is the reaction time, i.e. the time that the
molecular sieve and the boron-containing source are maintained in
contact with each other. With greater reaction times, all other
factors being equal, a greater amount of boron is incorporated with
the molecular sieve. Other factors upon which the amount of boron
incorporated with the molecular sieve is dependent include reaction
temperature, concentration of the treating compound in the reaction
mixture, the degree to which the molecular sieve has been dried
prior to reaction with the boron-containing compound, the conditions
of drying of the molecular sieve after reaction of the molecular
sieve with the treating compound, and the amount and type of binder
incorporated with the molecular sieve.
[0031] After selectivation with boron, the catalyst is contacted
with a medium containing hydrogen ions to at least partially restore
the acid activity of the molecular sieve. The medium employed is
conveniently an aqueous medium, such as water or an ammonium hydroxide
solution. Preferably, the medium will also contain a chelating agent,
such as oxalic acid. Alternatively, the catalyst can be subsequently
washed with an aqueous medium containing a chelating agent.
[0032] The present invention can impart distinct changes (4-6 orders
of magnitude) in diffusion characteristics of the molecular sieve
while it retains excellent acid activity. Diffusional resistance
for porous crystalline materials is typically reported as the Diffusion
Parameter, D/r.sup.2.times.10.sup.6 wherein D is the diffusion
coefficient (cm.sup.2/sec) and r is the crystal radius (cm). The
required diffusion parameters can be derived from sorption measurements
provided the assumption is made that the plane sheet model describes
the diffusion process. Thus for a given sorbate loading Q, the value
Q/Q.sub..infin., where Q.sub..infin. is the equilibrium sorbate
loading, is mathematically related to (Dt/r.sup.2).sup.1/2 where
t is the time (sec) required to reach the sorbate loading Q. Graphical
solutions for the plane sheet model are given by J. Crank in "The
Mathematics of Diffusion", Oxford University Press, Ely House,
London, 1967.
[0033] Preferably, the molecular sieve has a Diffusion Parameter,
D/r.sup.2 for 23-dimethylbutane of less than 1000.times.10.sup.-6
sec.sup.-1 when measured at a temperature of 120.degree. C. and
a 23-dimethylbutane pressure of 60 torr. Further, the selectivated
molecular sieve can show about 80% selectivity towards p-xylene
versus meta- and ortho-xylene in processing toluene. In addition,
the present invention provides a selectivation process, which is
permanent, inexpensive and environmentally benign.
[0034] The present invention provides a catalyst, which is particularly
useful in selective toluene disproportionation, because the catalyst
does not require any further modification or selectivation and gives
selectivities similar to silicon selectivated catalysts. Further,
the present invention provides a catalyst preparation method, which
requires fewer steps than a silicon selectivated catalyst, thus
providing significant efficiencies and cost savings for manufacture.
The present invention also provides a catalyst, which exhibits better
yield benefits as compared to a silicon selectivated catalyst, including
lower ethylbenzene and C.sub.9+ production. Longer process cycles
often result from lower C.sub.9+ yields in aromatics processes.
[0035] The present invention provides a catalyst which is useful
in other shape-selective processes such as xylene isomerization
and ethylbenzene hydrodealkylation, toluene alkylation with methanol,
reformate alkylation with methanol, reformate upgrading, p-ethyltoluene
synthesis, p-diethylbenzene synthesis, ethylbenzene isomerization
and shape selective reforming. The catalyst also exhibits properties
which make it useful in other processes including methanol conversion
(e.g., methanol to olefins), fluidized catalytic cracking, enhanced
naphtha cracking, pyridine synthesis, paraffin isomerization, lube
dewaxing, and cresol isomerization.
[0036] In practicing the desired conversion process it may be desirable
to combine the molecular sieve with another material resistant to
the temperatures and other conditions employed in the conversion
process. Such matrix materials include synthetic or naturally occurring
substances as well as inorganic materials such as clay, silica and/or
metal oxides. The latter may be either naturally occurring or in
the form of gelatinous precipitates or gels including mixtures of
silica and metal oxides. Naturally occurring clays which can be
composited with the modified molecular sieve include those of the
montmorillonite and kaolin families, which families include the
sub-bentonites and the kaolins commonly known as Dixie, McNamee-Georgia
and Florida clays or others in which the main mineral constituent
is halloysite, kaolinite, dickite, nacrite or anauxite. Such clays
can be used in the raw state as originally mined or initially subjected
to calcination, acid treatment or chemical modification.
[0037] In addition to the foregoing materials, the molecular sieve
employed herein may be composited with a porous matrix material,
such as alumina, silica-alumina, silica-magnesia, silica-zirconia,
silica-thoria, silica-berylia, silica-titania, as well as ternary
compositions, such as silica-alumina-thoria, silicia-alumina-zirconia,
silica-alumina-magnesia and silica-magnesia-zirconia. The matrix
may be in the form of a cogel. Further, the molecular sieve may
be composited with crystalline microporous molecular sieve material.
Examples of such materials are disclosed in U.S. Pat. No. 6008425
which is hereby incorporated by reference. The relative proportions
of molecular sieve and matrix material may vary widely with the
sieve content ranging from between about 1 to about 99 percent by
weight and more usually in the range of about 5 to about 80 percent
by weight of the composite.
[0038] Optionally, the present catalyst may contain a hydrogenation/dehydrogenation
component. Examples of such optional components include the oxide,
hydroxide or free metal (i.e., zero valent) forms of Group VIII
metals (i.e., Pt, Pd, Ir, Rh, Os, Ru, Ni, Co and Fe), Group IVA
metals (i.e., Sn and Pb), Group VA metals (i.e., Sb and Bi), and
Group VIIB metals (i.e., Mn, Tc and Re). Noble metals (i.e., Pt,
Pd, Ir, Rh, Os and Ru) are particular optional hydrogenation/dehydrogenation
components. Combinations of catalytic forms of such noble or non-noble
metal, such as combinations of Pt with Sn, may be used. The valence
state of the metal is preferably in a reduced valence state, e.g.,
when this component is in the form of an oxide or hydroxide. The
reduced valence state of this metal may be attained, in situ, during
the course of a reaction, when a reducing agent, such as hydrogen,
is included in the feed to the reaction. Preferably, the present
catalyst is free of noble metal.
[0039] The optional hydrogenation/dehydrogenation component may
be incorporated into the catalyst by methods known in the art, such
as ion exchange, impregnation or physical admixture. For example,
solutions of appropriate metal salts may be contacted with the remaining
catalyst components, either before or after selectivation of the
catalyst, under conditions sufficient to combine the respective
components. The metal containing salt is preferably water soluble.
Examples of such salts include chloroplatinic acid, tetrammine-platinum
complexes, platinum chloride, tin sulfate and tin chloride.
[0040] The amount of optional hydrogenation/dehydrogenation component
may be that amount which imparts or increases the catalytic ability
of the overall catalyst to catalytically hydrogenate or dehydrogenate
an organic compound under sufficient hydrogenation or dehydrogenation
conditions. This amount is referred to herein as a catalytic amount.
Quantitatively speaking, when the present catalyst comprises a noble
metal, it may comprise, for example, from about 0.001 to about 5
wt %, e.g., from about 0.1 to about 2 wt %, of the noble metal.
[0041] The conversion can take place in any convenient mode, for
example, in fluidized bed, moving bed, or fixed bed reactors depending
on the types of process desired.
[0042] The selectivated catalyst can be used for a wide variety
of organic, e.g., hydrocarbon, conversion processes. Exemplary processes
include processes where aromatic compounds are converted to different
aromatic compounds. Non-limiting examples of such processes include
the following:
[0043] (A) The isomerization of dialkyl substituted benzenes, e.g.,
xylenes. Typical reaction conditions including a temperature from
about 230.degree. C. to about 510.degree. C., a pressure of from
about 1 atmosphere to about 50 atmospheres, a weight hourly space
velocity of from about 0.1 hr.sup.-1 to about 200 hr.sup.-1 and
a hydrogen/hydrocarbon mole ratio of from 0 (no added hydrogen)
to about 100.
[0044] (B) The disproportionation of monoalkyl substituted benzenes,
e.g., disproportionation of toluene to benzene and xylenes. Typical
reaction conditions including a temperature of from about 200.degree.
C. to about 760.degree. C., a pressure of from about atmospheric
to about 60 atmospheres and a weight hourly space velocity of from
about 0.08 hr.sup.-1 to about 20 hr.sup.-1.
[0045] (C) The alkylation of aromatic compounds, e.g. benzene and
C.sub.7 and C.sub.8 alkylbenzenes, in the presence of an alkylating
agent, e.g., olefins, formaldehyde, alkyl halides, and oxygenates,
e.g., ethers, and alcohols. Typical reaction condition include 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 2 hr.sup.-1 to about
2000 hr.sup.-1 and an aromatic hydrocarbon/alkylating agent mole
ratio of from about 1/1 to about 20/1.
[0046] (D) The transalkylation of aromatic compounds in the presence
of polyalkylaromatic compounds. Typical reaction conditions include
a temperature of from about 340.degree. C. to about 600.degree.
C., a pressure of from about atmospheric to about 200 atmospheres,
a weight hourly space velocity of from about 10 hr.sup.-1 to about
1000 hr.sup.-1 and an aromatic hydrocarbon/polyalkylaromatic hydrocarbon
mole ratio of from about 1/1 to about 16/1.
[0047] (E) The dealkylation of alkylaromatic compounds. In the
case of ethylbenzene, the ethylbenzene can be converted to benzene
and ethane. Typical reaction conditions including a temperature
from about 230.degree. C. to about 510.degree. C., a pressure of
from about 1 atmosphere to about 50 atmospheres, a weight hourly
space velocity of from about 0.1 hr.sup.-1 to about 200 hr.sup.-1
and a hydrogen/hydrocarbon mole ratio of from 0 (no added hydrogen)
to about 100.
[0048] (F) The isomerization of ethylbenzene to form xylenes. Exemplary
conditions include a temperature from about 300.degree. C. to about
550.degree. C., a pressure of from about 50 to 500 psig, and a LHSV
of from about 1 to about 20.
[0049] (G) The isomerization of dialkylnaphthalene, e.g., dimethylnaphthalene,
to form a mixture of isomers. Of the dimethylnapthalene isomers,
26-dimethylnapthalene is a key intermediate in the production of
26-napthalenedicarboxylic acid, a valuable monomer for specialty
polyester manufacture. Typical reaction conditions including a temperature
from about 230.degree. C. to about 510.degree. C., a pressure of
from about 1 atmosphere to about 50 atmospheres, a weight hourly
space velocity of from about 0.1 hr.sup.-1 to about 200 hr.sup.-1
and a hydrogen/hydrocarbon mole ratio of from 0 (no added hydrogen)
to about 100.
[0050] (H) The disproportionation of mono-alkyl substituted naphthalenes,
e.g., disproportionation of mono-methyl naphthalene to dimethyl-naphthalene
and naphthalene.
[0051] Exemplary conversion processes also include processes where
non-aromatic compounds are converted to aromatic compounds. Non-limiting
examples of such processes include the following:
[0052] (A) The conversion of light paraffins to aromatics and olefins.
Typical reaction conditions include a temperature from about 375.degree.
C. to about 760.degree. C. and a pressure from about 10 to about
2000 psig.
[0053] (B) The conversion of light olefins to aromatics. Exemplary
reaction conditions include a temperature from about 175.degree.
C. to about 760.degree. C. and a pressure from about 100 to about
2000 psig
[0054] (C) The conversion of naphtha, e.g., C.sub.6-C.sub.10 and
similar mixtures to highly aromatic mixtures. Thus, normal and slightly
branched chained hydrocarbons, preferably having a boiling range
above about 40.degree. C., and less than about 200.degree. C., can
be converted to products having a substantial higher octane aromatics
content. Typical reactions include a temperature in the range of
from about 400.degree. C. to 600.degree. C., preferably 480.degree.
C. to 550.degree. C., a pressure in the range from atmospheric to
40 bar, and liquid hourly space velocities (LHSV) ranging from 0.1
to 15.
[0055] (D) The dehydrogenation of cycloaliphatics having 6 member
rings. Typical reaction conditions include a temperature of from
about 300.degree. C. to about 700.degree. C., a pressure of from
about 0.1 to about 10 atmospheres, a weight hourly space velocity
of from about 0.1 hr.sup.-1 to about 20 hr.sup.-1.
[0056] (E) The conversion of alcohols, e.g., methanol, or ethers,
dimethylether, or mixtures thereof to aromatics. Typical reaction
conditions include a temperature of from about 275.degree. C. to
about 600.degree. C., a pressure of from about 0.5 to about 50 atmospheres,
a LHSV of from about 0.5 hr.sup.-1 to about 50 hr.sup.-1. Examples
of such processes are disclosed in U.S. Pat. No. 4088706 which
is hereby incorporated by reference.
[0057] (F) The dehydration of alcohols to form aromatics, such
as the dehydration of cyclohexane-triol to form benzene.
[0058] In general, catalytic conversion conditions over the present
catalyst will 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.
[0059] The selectivated catalyst finds particular application in
the production of para-xylene via the catalytic disproportionation
of toluene. More particularly, this catalyst, under disproportionation
conditions, is capable of high conversions of toluene, while at
the same time producing a very high proportion of para-xylene among
the total of the xylene isomers. However, it will be understood
that this catalyst may also be used to catalyze other organic, especially
hydrocarbon, conversion reactions.
[0060] When the present catalyst is used in a toluene disproportionation
reaction, the reaction conditions may include a temperature of about
350.degree. C. to about 550.degree. C., a pressure of about atmospheric
to about 5000 psig, a toluene feed rate of about 0.1 to about 20
WHSV, and a hydrogen to toluene mole ratio of about 0.1 to about
20. The hydrogen cofeed serves to suppress catalyst aging, thereby
dramatically increasing the cycle length.
[0061] The liquid feedstock for the present toluene disproportionation
reaction may, optionally, include hydrocarbons other than toluene.
Such hydrocarbons include non-aromatic hydrocarbons, such as paraffins
and/or cycloparaffins. These non-aromatics may have boiling points
close to the boiling point of toluene, which is about 111.degree.
C. These non-aromatics are, therefore, difficult to remove from
toluene by distillation, and extraction techniques may be needed
to separate these toluene coboilers from toluene. The amount of
non-aromatics in the fresh feed may be from 0 wt. % to about 3 wt.
%, e.g., from about 0.2 wt. % to about 1.5 wt. %. It will also be
understood that commercial toluene disproportionation reactions
are run by recycling unconverted toluene. The amount of recycled
toluene in the feed to the reactor will vary on the amount of toluene
conversion per pass. For example, this feed may comprise from about
50 wt. % to about 85 wt. % of recycled toluene. As a result, difficult
to remove non-aromatic constituents (e.g., toluene coboilers) may
build up in the recycle stream. These toluene coboilers may eventually
comprise from about 2 wt. % to about 15 wt. % of the toluene recycle
stream. Thus, the total liquid feed to the present disproportionation
reactor may comprise both fresh (i.e., make-up) toluene and recycled
toluene, and this liquid feed may comprise from 0 wt. % to about
15 wt. % of non-aromatics.
[0062] When the present catalyst is used in an ethylbenzene disproportionation
reaction, the reaction conditions may include a temperature of about
200.degree. C. to about 600.degree. C., e.g., from about 350.degree.
C. to about 540.degree. C.; a pressure of from about atmospheric
to about 5000 psig, e.g., from about 100 to about 1000 psig; an
ethylbenzene feed rate of from about 0.1 WHSV to about 20 WHSV,
e.g., from about 2 WHSV to about 10 WHSV; and a hydrogen to ethylbenzene
mole ratio of from about 0.1 to about 20 e.g., from about 2 to
about 6.
[0063] The present catalysts may be used to convert paraffins from
high to low molecular weight hydrocarbons in a dewaxing process.
Examples of such dewaxing processes are disclosed in U.S. Pat. Nos.
3700585; Re. 28398; 3968024; and 4181598 the entire disclosures
of which are incorporated herein by reference. Hydrocarbon feeds
for dewaxing processes include petroleum stocks that have a freeze
point or pour point problem, e.g., petroleum stocks boiling above
350.degree. F. Lubricating oil stocks may be feedstocks to a dewaxing
process. The dewaxing may be carried out under either cracking or
hydrocracking conditions. Cracking conditions for dewaxing may 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. Hydrocracking conditions for dewaxing
may include a liquid hourly space velocity (LHSV) between about
0.1 and 10 a temperature between about 340.degree. C. (650.degree.
F.) and 538.degree. C. (1000.degree. F.), a pressure between about
100 and 3000 psig, and a hydrogen to hydrocarbon mole ratio between
about one and 20.
[0064] The present catalysts may be used to catalyze the conversion
of aliphatic oxygenates to higher molecular weight compounds, e.g.,
olefins. Such a conversion includes those described, for example,
in U.S. Pat. No. 4476330 the entire disclosure of which is incorporated
herein by reference.
[0065] The present catalysts may be used as catalysts in the oligomerization
of olefins to form gasoline, distillate, lube oils and/or chemicals.
Examples of such oligomerization processes are disclosed in U.S.
Pat. Nos. 4517399; 4520221; 4547609; and 4547613 the entire
disclosures of which are incorporated herein by reference.
[0066] The present catalysts may be used to catalyze the conversion
of olefins having from 3 to 18 carbon atoms, e.g., propylene, to
high viscosity, low pour point lubricating oils. Such a conversion
is described, for example, in U.S. Pat. No. 4517399 the entire
disclosure of which is incorporated herein by reference.
[0067] The present catalysts may be used for catalyzing the ethylation
of toluene or ethylbenzene to produce a para-ethyl derivative, e.g.,
para-ethyltoluene. Such a conversion is described, for example,
in U.S. Pat. No. 4086287 the entire disclosure of which is incorporated
herein by reference.
[0068] The present catalysts may be used as catalysts in the synthesis
of pyridine and substituted pyridines. Process conditions may be
selected from those disclosed in U.S. Pat. Nos. 4675410 and 4220783
the entire disclosures of which are incorporated herein by reference.
[0069] The present catalysts may be used as catalysts in the synthesis
of caprolactam by the Beckmann rearrangement of cyclohexane oxime.
Process conditions may be selected from those disclosed in U.S.
Pat. No. 4359421 the entire disclosures of which are incorporated
herein by reference.
[0070] The following examples illustrate the invention:
EXAMPLE 1
[0071] A catalyst base material comprising {fraction (1/16)}"
extrudates containing 90 wt % ZSM-5 crystal and 10 wt % SiO.sub.2
binder was impregnated to 2 wt % B.sub.2O.sub.3 from boric acid
and then dried at 120.degree. C. (250.degree. F.). Thereafter this
process of impregnation and drying was repeated 3 more times for
a total of 8 wt % B.sub.2O.sub.3 on base catalyst. The dried catalyst
was then calcined in flowing air at 700.degree. C. (1300.degree.
F.) for 18 hrs. The calcined catalyst was then washed with excess
deionized water for 4 days after which it was dried at 120.degree.
C. (250.degree. F.) and calcined in flowing air at 540.degree. C.
(1000.degree. F.) for 3 hrs.
[0072] The selectivated catalyst was characterized for its diffusive
properties using 23-dimethylbutane as the probe molecule at a temperature
of 120.degree. C. and a value of D/r.sup.2=48.times.10.sup.-6 m.sup.2/sec
was obtained. The catalyst was also characterized for its acid cracking
capability (alpha) at 540.degree. C. (1000.degree. F.) and an alpha
value of 130 was obtained. The hexane uptake on the catalyst was
measured at 48 mg/g.
EXAMPLE 2
[0073] 1.67 g of the selectivated catalyst of Example 1 was loaded
into a 0.375 inch internal diameter stainless steel cylindrical
reactor (with sand as inert packing material). The catalyst was
dried in nitrogen, heated up in hydrogen, and held at 400.degree.
C. for one hour prior to starting reagent flow. The reagent was
100% toluene. Total reactor effluent was vaporized then analyzed
by on-line gas chromatography. The results are given in the following
Table 1.
1 TABLE 1 Temperature, .degree. C. 400.8 399.6 440.4 441 Temperature,
.degree. F. 753.44 751.28 824.72 825.8 Pressure, psig 272 268 266
265 Liquid flowrate ml/hr 5.77 5.77 5.77 5.77 WHSV, hr-1 3.0 3.0
3.0 3.0 H.sub.2 flowrate cc/mm 22.3 22.3 22.3 22.3 H.sub.2/HC ratio
1.0 1.0 1.0 1.0 TOS, hr 2 4 6 8 Product Composition, Wt % C5- 0.30
0.34 0.81 0.96 Benzene 6.40 6.14 11.62 11.26 Toluene 84.34 84.92
74.15 74.30 Ethylbenzene 0.04 0.03 0.10 0.09 Para-xylene 7.62 7.20
10.68 10.93 Meta-xylene 0.71 0.70 1.81 1.77 Ortho-xylene 0.13 0.13
0.32 0.31 Total C.sub.9+ 0.47 0.54 0.51 0.38 Para-xylene selectivity,
% 90.1 89.8 83.4 84.0 Para-xylene purity, % 89.7 89.4 82.7 83.4
Toluene conversion, % 15.7 15.1 25.9 25.7 Benzene/xylene (molar)
1.03 1.04 1.23 1.18 Total xylenes 8.5 8.0 12.8 13.0 Temperature,
.degree. C. 440.6 440.2 439.9 439.9 457.6 457.7 461.8 Temperature,
.degree. F. 825.08 824.36 823.82 823.82 855.68 855.86 863.24 Pressure,
psig 264 264 263 262 262 274 275 Liquid flowrate ml/hr 5.77 5.77
5.77 5.77 5.77 5.77 5.77 WHSV, hr-1 3.0 3.0 3.0 3.0 3.0 3.0 3.0
H.sub.2 flowrate cc/mm 22.3 22.3 22.3 22.3 22.3 22.3 22.3 H.sub.2/HC
ratio 1.0 1.0 1.0 1.0 1.0 1.0 1.0 TOS, hr 10 12 14 16 18 20 22 Product
Comp, Wt % C5- 0.80 0.73 0.61 0.65 1.01 1.30 1.21 Benzene 10.66
10.59 10.38 9.87 12.23 12.70 12.98 Toluene 75.19 75.86 76.69 76.55
71.76 71.50 70.52 Ethylbenzene 0.08 0.08 0.08 0.08 0.12 0.12 0.13
Para-xylene 10.95 10.47 10.20 10.65 11.75 11.37 11.78 Meta-xylene
1.68 1.55 1.48 1.53 2.22 2.13 2.38 Ortho-xylene 0.30 0.28 0.26 0.27
0.39 0.37 0.41 Total C.sub.9+ 0.34 0.45 0.36 0.40 0.53 0.52 0.58
Para-xylene selectivity, % 84.7 85.1 85.4 85.5 81.9 81.9 80.8 Para-xylene
purity, % 84.2 84.6 84.9 85.0 81.2 81.2 80.1 Toluene conversion,
% 24.8 24.1 23.3 23.4 28.2 28.5 29.5 Benzene/xylene (mol.) 1.12
1.17 1.18 1.08 1.16 1.24 1.21 Total xylenes 12.9 12.3 11.9 12.5
14.3 13.9 14.6 Temperature, .degree. C. 462.2 462 462.4 462.1 462.1
462.4 462.3 Temperature, .degree. F. 863.96 863.6 864.32 863.78
863.78 864.32 864.14 Pressure, psig 273 272 267 268 266 266 265
Liquid flowrate ml/hr 5.77 5.77 5.77 5.77 5.77 5.77 5.77 WHSV, hr-1
3.0 3.0 3.0 3.0 3.0 3.0 3.0 H.sub.2 flowrate cc/mm 22.3 22.3 22.3
22.3 22.3 22.3 22.3 H.sub.2/HC ratio 1.0 1.0 1.0 1.0 1.0 1.0 1.0
TOS, hr 24 26 30 32 34 36 38 Product Camp, Wt % C5- 1.55 1.66 1.35
1.53 0.98 0.94 1.18 Benzene 13.31 13.15 13.07 12.81 12.66 12.11
12.45 Toluene 70.22 70.41 70.73 71.14 72.23 72.44 71.90 Ethylbenzene
0.13 0.12 0.12 0.11 0.11 0.11 0.11 Para-xylene 11.44 11.16 11.37
11.07 10.99 11.41 11.37 Meta-xylene 2.42 2.34 2.33 2.20 2.14 2.21
2.19 Ortho-xylene 0.42 0.41 0.41 0.38 0.37 0.38 0.38 Total C.sub.9+
0.52 0.75 0.63 0.76 0.52 0.40 0.41 Para-xylene selectivity 80.1
80.2 80.6 81.1 81.4 81.5 81.6 Para-xylene purity, % 79.4 79.6 79.9
80.4 80.8 80.8 80.9 Toluene conversion, % 29.8 29.6 29.3 28.9 27.8
27.6 28.1 Benzene/xylene (mol.) 1.27 1.29 1.26 1.27 1.27 1.18 1.21
Total xylenes 14.3 13.9 14.1 13.7 13.5 14.0 13.9
EXAMPLE 3 (COMPARATIVE)
[0074] A silica selectivated catalyst was prepared following the
procedure described in U.S. Pat. No. 5243117. The preparation
was carried out by adding HZSM-5/SiO.sub.2 extrudate to a solution
of dimethylphenyl polysiloxane (Dow 550) dissolved in an organic
solvent and subsequently calcining the selectivated catalyst. The
catalyst was treated with 3 additional silicon selectivation treatments
using substantially the same procedure.
[0075] The silica selectivated catalyst was characterized for its
diffusive properties using 23-dimethylbutane as the probe molecule
at a temperature of 120.degree. C. and a value of D/r.sup.2=143.times.10.sup.--
6 m.sup.2/sec was obtained. The catalyst was also characterized
for its acid cracking capability (alpha) at 540.degree. C. (1000.degree.
F.) and an alpha value of 280 was obtained. The hexane uptake on
the catalyst was measured at 62.6 mg/g.
[0076] The silica selectivated catalyst was tested for the disproportionation
of toluene in the same way as in Example 2 and the results, together
with those of the boron selectivated of Example 1 at similar toluene
conversion, are given in Table 2.
2 TABLE 2 Example 3 Example 1 Catalyst Temperature, .degree. C.
399 462 Temperature, .degree. F. 751 864 Pressure, psig 269 273
WHSV, hr-1 3.0 3.0 H.sub.2/HC ratio 1.0 1.0 TOS, hr 20 24 Product
Comp, Wt % C5- 0.78 1.55 Benzene 12.8 13.31 Toluene 70.03 70.22
Ethylbenzene 0.42 0.13 Para-xylene 13.4 11.44 Meta-xylene 1.48 2.42
Ortho-xylene 0.23 0.42 Total C.sub.9+ 0.86 0.52 Para-xylene selectivity
88.7 80.1 Toluene conversion, % 30.0 29.8 Benzene/xylene (mol.)
1.15 1.27 Total xylenes 15.1 14.3
[0077] It will be seen from Table 2 that, although the boron selectivated
catalyst required a higher temperature to achieve the same toluene
conversion as the silica selectivated catalyst, the yields of ethylbenzene
and C.sub.9+ compounds were expectedly lower with the boron selectivated
catalyst. |