Note: Descriptions are shown in the official language in which they were submitted.
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"CATALYTIC COMPOSITE FOR CO~VERSIO~ OF UYDROCARBONS"
FIELD OF TWE I~VENTION
The present invention is directed toward a novel catalytic com-
posite for the conversion of hydrocarbons and especially for effecting
the dehydrocyclization of aliphatic hydrocarbons to aromatics. More par-
ticularly, the novel catalytic composite enables the conversion of
C6-plus paraffins to their corresponding aromatics with a high degree of
selectivity thereby enabling the facile production of large quantities
of aromatics.
In the past it has become the practice to effect conversion of
` aliphatic hydrocarbons to aromatics by means of the well-known catalytic
reforming process. In catalytic reforming a hydrocarbonaceous feedstock,
typically a petroleum naphtha fraction, is contacted with a Group VIII-
containing catalytic composite to produce a product reformate of increased
aromatics content. The naphtha fraction is~typically a full boiling
range fraction having an initial boiling point of from lO to about 38-C
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boiling range naphtha contains significant amounts of C6-plus paraffinic
hydrocarbons and C6-plus naphthenic hydrocarbons. As is well known these
parafflnic and naphthenic hydrocarbons are converted to aromatics by
means~of multifarious reaction mechanisms. These mechanisms include de-
" ~ ~20 ~ ~; hydrogenat10n, dehydrocyclization, isomerization followed by dehydrogena-
tion. Naphthenic hydrocarbons are converted to aromatics by dehydrogena-
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~ tion. Paraffinic hydrocarbons may be converted to the desired aromatics
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by dehydrocycl;zation and may also undergo isomerization. Accordingly
then, it is apparent that the number of reactions taking place in a
catalytic reforming zone are numerous and, therefore, the typical re-
forl,ling catalyst must be capable of effecting numerous reactions to be
considered usable in a commercially feasible reaction system.
Because of the complexity and number of reaction mechanisms
ongoing in catalytic reforming, it has become a recent practice to
attempt to develop highly specific catalysts tailored ~o convert only
specific reaction species to aromatics. Such catalysts offer advantages
over the typical reforming catalyst which must be capable of taking part
in numerous reaction mechanisms. In view of this, ongoing work has been
directed toward producing a catalyst for the conversion of paraffinic
hydrocarbons, particularly having six carbon atoms or more, to the cor-
responding aromatic hydrocarbon. Such a catalyst can be expected to be
much more specific with respect to the final product compounds, result-
ing in fewer undesirable side reactions such as hydrocracking. As can
be appreciated by those of ordinary skill in the art, increased produc-
tion of aromatics is desirable. The increased aromatic content of gaso-
lines, a result of lead phase down, as well as demands in the petrochem-
ical industry make C6-C8 aromatics highly desirable products. It is,
therefore, very advantageous to have a catalytic composition which is
highly selective for the conversion of less valuable C6-plus paraffins
to the more valuable C6-plus aromatics.
OBJECTS AND EMBODIMENTS
It is, therefore, a principal object of our invention to pro-
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vide a catalytic composite, and a method of making and using the same
for the conversion of hydrocarbons. A corollary objective is to pro-
vide a process for the conversion of C6-plus paraffinic hydrocarbons,
especially C6-C8 paraffinic hydrocarbons, to their corresponding aro-
matics.
Accordingly, a broad embodiment of the present invention is
directed toward a catalytic composite comprising a nonacidic zeolite,
catalytically effective amounts of a Group VIII metal componen~, and
a silica support matrix derived by a high pH gelation of an alkali
metal silicate sol.
An alternative broad embodiment of the present invention is
a hydrocarbon conversion process characterized in that it comprises
contacting at hydrocarbon conversion conditions, a hydrocarbon charge
stock with a catalytic composite comprising a nonacidic zeolite, cata-
1~ lytically effective amounts of a Group VIII metal component, and a
silica support matrix derived by a high pH gelation of an alkali metal
silicate.
A further embodiment of the present invention comprises a
method of preparing a catalytic composite comprising compositing a
Group VIII metal component, a nonacidic zeolite, and a silica support
matrix derived by a high pH gelation of an alkali metal silicate.
These as well as other objects and embodiments will become
evident from the following, more detailed description of the present
invention.
BACKGROUND OF THE INYENTION
Aluminosilicates containing alkali metals are well known in
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the art. For example, U.S. Patent 3,013,986, issued December 19, 1968,
discloses an alkali metal loaded L-zeolite. In particular this reference
indicates that the potassium or the potassium/sodium form of the L-zeo-
lite are the preferred starting materials for the alkali metal-loaded
L-zeolite. The reference teaches that a dehydrated molecular sieve may
be contacted with alkali metal vapors to produce an alkali metal-loaded
molecular sieve wherein the alkali metal is contained within the inte-
rior of the zeolitic molecular sieve. The reference, however, does not
disclose a catalytic composite comprising a nonacidic zeolite, catalyti-
cally effective amounts of Group VIII metal component, and a silica sup-
port matrix derived by a high pH gelation of an alkali metal silicate
sol. Moreover, the reference does not disclose that such a composite
would have any use as a hydrocarbon conversion catalyst.
U.S. Patent 3,376,215, issued April 2, 1968, discloses a hy-
drocarbon conversion catalyst comprising a cocatalytic solid support
containing a Group VIII metal which support comprises (1) an adsorbent
refractory inorganic oxide and (2) a mordenite structure zeolite having
deposited thereon about 10 to about 1000 ppm by weight, based on zeo-
lite, of a metal selected from the class of alkali metals, alkaline
earth metals and mixtures thereof. This reference teaches that the
support comprising a mordenite form zeolite and a refractory oxide be
cocatalytic. The reference does teach that the cocatalytic refractory
oxide may be a silica gel, or silica-alumina; however, the reference
does emphasize that alumina is the preferred refractory oxide. More-
; 25 over, the only examples of refractory supports derived by gelation are
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alumina supports derived from alumina sols, well known to be ac~dic,
with gelation be;ng effected by neutralization with ammonia. Accord-
ingly, thi~ reference does not disclose the catalyt;c composite of
the present invention. Firstly, the nonacidic zeolite of the prese~t
invention cannot be considered catalyt;c for the reaction of interest.
Rather, it is believed that the nonacidic zeolite acts to modify the
catalytic Group VIII metal component of the catalytic composite and not
to accelerate the dehydrocyclization reaction. Secondly, there is no
disclosure of use of a silica support matrix derived by a high pH gela-
tion of an alkali metal silicate sol. The reference is completely
silent as to the source of silica gel cocatalytic support disclosed
therein. Nor is there disclosure of the surprising and unexpected re-
sults to be obtained by use of the composite of the instant invention.
U.S. Patent 3,755,486, issued August 28, 1973, discloses a
process for dehydrocyclizing C6-C10 hydrocarbons having at least a
C6 backbone using an Li, Na, or K zeolite X or Y or faujasite impreg-
nated with 0.3 to 1.4% platinum. This reference, however, fails to
disclose the advantages to be derived by utilizing a catalytic com-
posite comprising a nonacidic zeolite, a Group VIII metal component,
and a silica support matrix derived by a high pH gelation of an alkali
metal silicate. Likewise, U.S. Patent 3,819,507~ issued June 25, 1974,
and U.S. Patent 3,832,414, issued August 27, 1974, while disclosing
processes similar to that of U.S. Patent 3,755,486 both fail to teach
the use and advantages to be derived by such use of a catalyst in ac-
cordance with the invention.
U.S. Patent 4,140,320, issued August 1, 1978, discloses a
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process for dehydrocyclizing aliphatic hydrocarbons utilizing a type
L-zeolite having exchangeable cations of which at least 90% are alkali
metal ions selected from the group consisting of ions of sodium, lith-
;um, potassium, rubidium and cesium and containing at least one metal
selected from the group which consists of metals of Group VIII, tin,
and germanium. This reference fails to disclose the catalytic com-
posite of the present invention in that it does not disclose a bound
catalyst system wherein the support matrix is derived by a high pH
gelation of an alkali metal silicate sol. U.S. Patent 4,417,083,
issued November 22, 1983, discloses a process for dehydrocyclization
utilizing a substantially nonacidic zeolite having a pore d;ameter
larger than 6.5 A and containing at least one metal selected from the
group consisting of platinum, rhenium, iridium, tin and germanium.
Additionally, the catalyst contains sulfur and alkaline cations. How-
ever, in this reference there is no disclosure of a catalyst having a
silica support matrix wherein the matrix is derived from a high pH gel-
ation of an alkali metal silicate sol.
U.S. Patent 4,416,806, issued November 22, 1983, discloses
yet another paraffin dehydrocyclization catalyst comprising platinum,
rhenium as a carbonyl, and sulfur on a zeolitic crystalline alumino-
silicate compensated in more than 90% by alkaline cations and having
a pore diameter of more than 6.5 Angstroms. This reference too fails
to disclose a catalytic composition for dehydrocyclization in accor-
dance with the invention. The reference does contain a broad disclo-
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sure of use of alumina or clay binders but does not disclose a binder
even remotely 1ike that of the invention.
Recent U.S. Patent 4,430,200, issued February 7, 1984, dis-
closes a hydrocarbon conversion catalyst comprising a high silica
zeolite such as mordenite or zeolite Y which has been base exchanged
with an alkali metal. This reference does teach a silica support ma-
trix but not one comparable to that of the invention which is derived
by a high pH gelation of an alkali metal silicate sol. Moreover, the
reference merely discloses the use of the prior art catalyst in a
cracking process and not a dehydrocyclization process.
Recent U.S. Patent 4,448,891, issued May 15, 1984, discloses
a dehydrocyclization catalyst comprising an L-zeolite which has been
soaked in an alkali solution having a pH of at least 11 for a time and
at a temperature effective to increase the period of time over which
the catalytic activity of the catalyst is maintained. Additionally,
the catalyst contains a Group VIII metal. However, the reference fails
to disclose use of a support matrix like that of the instant invention.
In summary then, the art has not recognized a catalytic com-
posite for the conversion of hydrocarbons, especially the dehydrocycli-
zation of C6-plus paraffins to aromatics, comprising a nonacidic zeo-
lite, catalytically effective amounts of a Group VIII metal component,
and a silica support matrix derived by a high pH gelation of an alkali
metal silicate sol. Moreover, the art has not recognized the attendant
advantages to be derived from such a novel catalyst and use thereof.
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DETAILED DESCRIPTION OF THE INVENTION
To reiterate briefly the present invention relates to a cata-
lytic composite comprising a nonacidic zeolite, cata1ytically effective
amounts of a Group VIII metal component, and a silica support matrix
derived by a high pH gelation of an alkali metal silicate sol. Addi-
tionally, the invention has particular utility as a catalyst for the
dehydrocyclization of C6-plus paraffins, especially C6-ClO paraffins.
As heretofore indicated it is an essential feature of the
catalyst of the present invention that lt comprise a nonacidic zeolite.
By "nonacidic zeolite" it is to be understood that it is meant that the
zeolite has substantially all of its cationic sites of exchange occupied
by nonhydrogen cationic species. Preferably, such cationic species will
comprise the alkali metal cations although other cationic species may be
present. Irrespective of the actual cationic species present in the
sites of exchange, the nonacidic zeolite in the present invention has
substantially all of the cationic sites occupied by nonhydrogen cations
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thereby rendering the zeolite substantially fully cationic exchanged
and nonacidic. Many means are well known in the art for arriving at a
` substantially fully cationic exchanged zeolite and thus they need not
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be elaborated herein. The nonacidic zeolite of the present invention
acts to modify the catalytic Group VIII metal and is substantially in-
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~ ` ert in the reaction. Hence, the nonacidic zeolite support of the pres-
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ent invention ls noncatatytic and an essential feature of the present
invention is that it be such.
Typical of the nonacidic zeolites which may be utilized in the
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present invention are X-zeollte, Y-zeolite and mordenite. Especially
preferred in application of the present invention is L-zeolite. Of
course, all of these zeolites must be in nonacidic form as defined
above and, therefore, the cationic exchangeable sites are substantially
fully cationic exchanged with nonhydrogen cationic species. As also
indicated above, typically the cations occupying the cationic exchange-
able sites will comprise one or more of the alkali metals including
lithium, sodium, potassium, rubidium and cesium. Accordingly then,
the nonacidic zeolite of the present invention may comprise the sodium
o forms of X-zeolite, Y-zeolite, or mordenite. An especially preferred
nonacidic zeolite for application in the present invention is the po-
tassium form of L-zeolite. It should also be understood, however,
that the nonacidic zeolite of the invention may contain more than one
type of the alkali metal cation at the cationic exchangeable sites,
for example, sodium and potassium.
Irrespective of the particular nonacidic zeolite utilized,
the catalyst of the present invention also comprises catalytically
effective amounts of a Group VIII metal component, including cataly-
tically effective amounts of nickel component, rhodium component,
palladium component, iridium component, platinum component or mix-
tures thereof. Especially preferred among the Group VIII metal com-
ponents is a platinum component. It is believed that in order for
the Group VIII metal component to achieve greatest catalytic effec-
tiveness it should be supported on the nonacidic zeolite as opposed
to the silica support matrix. Accordingly, it is preferred that the
Group VIII metal component be substantially supported on the non-
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acidic zeolite. The Group VIII metal component may be deposited on
the nonacid;c zeol;te by any su;table means known in the art. For
example, a platinum component may be impregnated into the nonacidic
zeolite from an appropriate solution such as a dilute chloroplatinic
acid solution and thereafter the nonacidic zeolite, having platinum
supported thereon, may be bound in the silica support matrix. Alter-
natively, the Group VIII metal component may be deposited on the non-
acidic zeolite by means of ion exchange in which case some of the
cationic exchange sites of the nonacidic zeolite will contain Group
VIII metal cat;ons. After ion exchange the Group VIII metal may be
subject to a low temperature oxidation prior to any reduct;on step.
Thereafter the nonacidic zeolite supporting the Group VIII metal com-
ponent may be bound in the silica support matrix. As shall be ex-
plained more fully hereinafter the nonacidic zeolite may also first
be bound in the silica support matrix and thereafter the Group VIII
metal component may be selectively composited with the zeolite and
support matrix, preferably in any manner which will result in the
selective deposition of the Group VIII metal component on the non-
acidic zeolite.
Irrespective of the exact method of depositing the Group
VIII metal component, any catalytically effective amount of Group VIII
metal component may be employed. The optimum Group VIII metal compo-
; nent content will depend generally on which Group YIII metal component
is utilized in the catalyst of the invention. However, generally from
about 0.01 to about 5.0 wt. % of the Group VIII metal component based
on the weight of the zeolite, Group YIII metal component, and silica
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support matrix may be advantageously deposited on the zeolite.
It should further be understood that best results are achieved
when the Group VIII metal component is highly dispersed on the nonacidic
zeolite. The Group VIII metal component is most effective in a reduced
state. Any suitable means may be employed for reducing the Group VIII
metal component and many are well known in the art. For example, after
deposition on the nonacidic zeolite the Group VIII metal component may
be subjected to contact with a suitable reducing agent, such as hydro-
gen, at an elevated temperature for a period of time.
In addition to comprising a Group VIII metal component it is
contemplated in the present invent;on, that the catalyst thereof may
contain other metal components well known to have catalyst modifying
properties. Such metal components include components of rhenium, tin,
cobalt, indium, gallium, lead, zinc, uranium, thallium, dysprosium,
and germanium, etc. Incorporation of such metal components have proven
beneficial in catalytic reforming as promoters and/or extenders. Ac-
cordingly, it is within the scope of the present invention that cata-
lytically effective amounts of such modifiers may be beneficially in-
corporated into the catalyst of the present invention improving its
performance.
Irrespective of the particular Group VIII metal component and
catalytic modifiers composited with the catalytic composition of the
present invention, a further essential feature of the invention is a
silica support matrix derived from a high pH gelation of an alkali
; 25 metal silicate sol. Silica support matrices are well known in the art.
Such support matrices have found wide use in the petroleum and petro-
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chemical industries. In particular, they have been used to bind molec-
ùlar sieves for numerous separation and catalytic processes. However,
as will be further explained hereinafter the silica support matrix of
the pres~nt invention, being derived from a high pH gelation of an
alkali metal silicate sol, results in surprising and unexpected bene-
fits in the present invention.
As is well known in the art the use of a silica support matrix
may enhance the physical strength of a catalyst. Accordingly, by bind-
ing the nonacidic zeolite in the silica support matrix a catalyst of
enhanced physical strength may be obtained. Additionally, bind;ng the
nonacidic zeolite allows formation of shapes suitable for use in cata-
lytic conversion processes. For example, by use of the silica support
the catalyst of the instant invention may be formulated into spheres.
The use of spheres is well known to be advantageous in various applica-
tions. In particular, when the catalyst of the instant invention is
emplaced within a continuously moving bed system, a spherical shape
enhances the ability of the catalyst to move easily through the reac-
tion zones. Of course, other shapes may be employed where advantageous.
Accordingly, the catalyst of the instant invention may be formed into
the shape of an extrudate, saddle, etc. Irrespective of the particular
shape of the silica support matrix, sufficient nonacidic zeolite and
silica support matrix should be employed in the catalyst of the inven-
tion such that the catalytic composition comprises from about 25 to 75
wt. X nonacidic zeolite based on the weight of the zeolite and support
matrix. A composite comprising about 50 wt. X nonacidic zeolite based
on the weight of the zeolite and support matrix is preferred. Addition-
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ally, the nonacidic zeolite crystallites should be evenly distributed
throughout the sil;ca support matr;x. Such uniform d;stribution of
the nonacidic zeolite imparts improved particle strength characteris-
tics and reaction properties to the catalytic composite.
Another essential feature of the present invention is that
the silica support matrix be derived from a high pH gelation of an al-
kali metal silicate sol. It is to be understood that as used therein
the term high pH gelation means that said gelation is effected at a
pH of 7 or more. This high pH gelation results in two distinct bene-
fits. First the high pH gelation allows incorporation of the nonacidic
zeolite into the alkali metal silicate sol prior to gelling the support
matrix without fear of loss of crystallinity. As is known zeolites tend
to be sensitive to the pH of their environment. Accordingly, zeolites
dispersed in an acidified sol may lose crystallinity during gelation.
This disadvantage is overcome by the high pH gelation utilized in the
invention to derive the silica support matrix. Since a most facile means
of preparing the catalyst of the present invention is to disperse the
nonacidic zeolite in an alkali metal silicate sol prior to gelation, the
high pH environment of the gelation avoids the attendant possibility of
loss of zeolite in the preparation of the catalytic composite of the in-
vention. The high pH gelation also avoids the introduction of acid sites
into the nonacidic zeolite. Introduction of such sites would cause the
zeolite to promote undesirable side reactions such as cracking, etc.
The second advantage of der;ving the silica support matrix from
a high pH gelation of an alkali metal silicate sol is that it results in
a finished catalytic composite having surprising and unexpected selec-
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tivity for the production of aromatic hydrocarbons from C6-plus paraffins.
Although it is not fully understood, it is believed that the high pH gel-
ation of the soluble alkali metal silicate results in a silica support
matrix with increased interaction between the nonacidic zeolite and the
silica of the support matrix. This interact;on apparently results in a
modification of the Group VIII metal component such that the overall se-
lectivity of the catalyst for the production of aromatics from C6-plus
paraffins is enhanced. Accordingly then, deriving the silica support
matrix from the high pH gelation of an alkali metal silicate not only
allows facile preparation of the final catalytic composi~e but also re-
sults in a catalytic composite of surprisingly high selectivity for the
production of C6-plus aromatics.
As is well known in the art, alkali metal silicate sols may be
used as precursors for silica support matrices. Waterglass (sodium sil-
icate) has often been used as a precursor for support matrices. Addition-
ally, there are various means known for effecting high pH gelation. How-
ever, the preferred alkali metal silicate and high pH gelation technique
is that set forth in U.S. Patent No. 4,537,866, issued
August 27, 1985. In
this preferred method a lithium silicate sol is caused to gel by heating
the sol to a temperature of about 70C or more. Thereafter, the gelled
lithium silicate sol is subjected to a washing step to remove lithium
therefrom thereby causing the gel to set. The lithium silicate sols em-
ployable in the present invention will have SiO2/Li20 molar ratios of
up to about 25:1. Especially preferred lithium silicates arethose having
SiO21Li20 molar ratios of from about 4:1 to about 8:1. These lithium sili-
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cate sols will all have a pH in excess of about 7 with the preferred lith-
ium silicate sols having a pH of from about lO to about ll. Since the
lith;um silicate sols may be gelled by heating without the need of adjust-
ing the pH with a gelling agent (typically an acid), it is possible to
effect a high pH gelation as defined herein. Accordingly then, in making
the catalytic composite of the present invention by the mRthod set forth
in previously referred to U.S. Patent No. 4,537,866, the nonacidic zeolite
is dispersed in the lithium silicate sol. Shaped particles of the lithium
silicate sol are thereafter formed. The shaped particles are then heated
to a temperature in excess of about 70C thereby causing the shaped parti-
cles to form gels. Thereafter, the lithium silicate gels containing non-
acidic zeolite are subjected to a washing step to remove lithium therefrom.
This washing step causes the gels to set.
As will be recognized by those having ordinary skill in the art,
many methods may be employed in forming the shaped particles of nonacidic
zeolite containing lithium silicate sol. These include extrusion, pilling,
molding, etc. Of all the many well known methods. the particularly pre-
ferred method of forming the shaped particles of the present invention is
the oil-drop method. In the oil-drop method particles of sol are formed
as droplets. Typically, these droplets are formed by passing the sol
through suitable orifices or from a rotating disc. The droplets then fall
into a suspending medium typically oil. As the droplets pass through the
oil suspending medium they take on a spheroidal form. The diameter of the
spheroidal particles may be controlled by adjusting the diameter of the
orifices from which the droplets flow and/or the vibrational rate of the
dropping head. As the nonacidic zeolite containing sol droplets pass
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through the suspending medium, they are heated to a temperature of about
70C or more thereby causing the sol to gel. The gelled particles are
then collected, aged and subjected to a washing step to remove lithium
therefrom. Accordingly then, there results a nonacidic zeolite bound
within a silica support matrix derived by a high pH gelation of an alkali
metal silicate with the preferred alkali metal silicate being lithium
silicate.
As heretofore indicated, it is preferred that the nonacidic
zeo1ite be composited with the silica support matrix and thereafter be
composited with the Group VIII metal component. Moreover, as was indi-
cated, it is preferred that the Group VIII metal component be supported
substantially on the nonacidic zeolite. Of course, any suitable means
of achieving these preferred steps may be utilized in the invention.
However, a particularly preferred method is the u~e of a selective ion
exchange procedure whereby the Group VIII metal component is deposited
substantially on the nonacidic zeolite as opposed to the silica support
matrix.
The selective deposition of platinum on the nonacidic zeolite
as opposed to the silica support matrix may be achieved by controlling
the pH of the exchange solution at a value less than 8. The silica sup-
port matrix is known to be a cation exchanger at a pH greater than about
8. By way of contrast the zeolite ion exchange capacity is not pH depen-
dent. Thus, when the Group VIII metal component is to be deposited by
means of ion exchange with an ion exchange solution having a pH of greater
than ~bout 8, thère will be a tendency for the Group VIII metal component
to be deposited both on the silica support matrix and the nonacidic zeo-
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lite. However, at pH values of less than 8 the silica support matrix loses
its cation exchange potential. Thus, by utilizing a cation exchange solu-
tion having a pH of less than about 8, will result in the Group VIII metal
component being deposited substantially selectively on the nonacidic zeo-
lite alone. It is particularly preferred that the pH of the cation exchangesolution be maintained at a pH in the range of from about 4 to about 8.
This will result in the selective deposition of the Group VIII metal compo-
nent on the nonacidic zeolite as opposed to the silica support matrix.
Irrespective of its exact method of preparation, the catalytic
composition of the present invention has particular utility as a hydrocar-
bon conversion catalyst. Accordingly, a hydrocarbon charge stock is con-
tacted at hydrocarbon conversion conditions with the catalytic composite
of the present invention. A wide range of hydrocarbon conversion condi-
tions may be employed and will depend upon the particular charge stock and
reaction to be effected; Generally, these conditions include a temperature
of about 0 to about 816-C, a pressure of from atmospheric to about 100
atmospheres, a liquid hourly space velocity (calculated on the basis of
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equivalent liquid volume of the charge stock contacted with the catalyst
per hour divided by the volume of conversion zone containing catalyst)
20 ~ of about 0.2 hr. 1 to lS hr. 1. Furthermore, hydrocarbon conversion con-ditions may include the presence of a diluent such as hydrogen. When such
is the case the hydrogen to hydrocarbon mole ratio may be from about O.S:l
:
to about 30:1.
A particularly preferred application of the catalyst of the
present invention is its use as a dehydrocyclization catalyst and in
~ particular for the dehydrocyclization of C6-C8 nonaromatic hydrocarbons.
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Accordingly, a hydrocarbon charge stock comprising C6-C8 nonaromatic hy-
drocarbons is contacted with the catalyst of the present ;nvention at
dehydrocyclization conditions. Dehydrocyclization conditions include
a pressure of from about 0 to about 6895 kPag with the pre~erred
pressure being from about 0 to about 4137 kPag, a temperature of
from about ~27 to about 649C, and a liquid hourly space velocity of
frum about 0.1 hr. 1 to about 10 hr. 1. Preferably, hydrogen may be
employed as a diluent. When present, hydrogen may be circulated at a
rate of from about 0.1 to about 10 moles of hydrogen per mole of hydro-
carbon.
According to the present invention a hydrocarbon charge stock
is contacted with the catalyst of the present invention in a hydrocarbon
conversion zone. This contacting may be accomplished by using the cata-
lyst in a fixed-bed system, a moving-bed system, a fluidized-bed system,
or ;n a batch-type operat;on. The hydrocarbon charge stock and, if de-
sired, a hydrogen-rich gas as diluent are typically preheated by any
su;table heating means to the desired reaction temperature and then are
passed into a conversion zone containing the catalyst of the invention.
It is, of course, understood that the conversion zone may be one or
more separate reactors with suitable means therebetween to ensure that
the desired conversion temperature ;s maintained at the entrance to
each reactor. It is also important to know that the reactants may be
contacted with the catalyst bed in either upward, downward, or radial-
flow fashion w;th the latter being preferred. In addition the reactants
may be in the l;quid phase, a mixed liquid-vapor phase, or a vapor phase
when they contact the catalyst. Best results are obtained when the re-
actants are in the vapor phase.
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In the case where the catalyst of the present ~nvention ;s em-
ployed in a dehydrocyclization process, the dehydrocyclization system
will comprise a reaction zone containing the catalyst of the present in-
vention. As indicated heretofore, the catalyst may be u~lized within the
reaction zone as a fixed-bed system, a moving-bed system, a fluidized-bed
system, or in a batch-type operation; however, in view of the operational
advantages well recognized in the art it is preferred to utilize the cat-
alyst of the present invention in a moving-bed system. In such a system
the reaction zone may be one or more separate reactors with heating means
therebetween to compensate for the endothermic nature of the dehydrocycli-
; zation reaction that takes place in each catalyst bed. The hydrocarbon
feedstream, preferably comprising C6-C8 nonaromatic hydrocarbons, is
contacted with the moving catalyst in the reaction zone to effect the
dehydrocyclycization thereof.
After contact with the catalyst of the present invention the
hydrocarbon charge stock having undergone dehydrocyclization is with-
; drawn as an effluent stream from the reaction zone and passed through a
cooling means to a separation zone. In the separation zone the effluent
may be separated into various constituents depending upon the desired
products. When hydrogen is utilized as a diluent in the reaction zone
,,
the separation zone will typically comprise a vapor-liquid equilibrium
separation zone and a fractionation zone. A hydrogen-rich gas is sepa-
rated from a high octane liquid product containing aromatics generated
within the dehydrocyclization zone. After separation at least a portion
of the hydrogen-rich gas may be recycled back to the reaction zone as
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diluent. The balance of the hydrogen-rich gas may be recovered for use
elsewhere. The high octane liquid product comprising aromatics may then
be passed to a fractionation zone to separate aromatics from the uncon-
verted constituents of the charge stock. These unconverted constituents
may then be passed back to the reaction zone for processing or to other
processes for utilization elsewhere.
A wide range of hydrocarbon charge stocks may be employed in
the process of the present invention. The exact charge stock utilized
will, of course, depend on the precise use of the catalyst. Typically,
hydrocarbon charge stocks which may be used in the present invention will
contain naphthenes and paraffins, although in some cases aromatics and
olefins may be present. Accordingly, the class of charge stocks which
may be utilized includes straight-run naphthas, natural naphthas, syn-
thetic naphthas, and the like. Alternatively, straight-run and cracked
naphthas may also be used to advantage. The naphtha charge stock may be
a full-boiling range naphtha having an initial boiling point of from
about 10 to about ~6C and an end boiling point within the range of
from about 163 to 219C, or^may be a selected fraction thereof. It
is preferred that the charge stocks employed in the present invention
be treated by conventional catalytic pretreatment methods such as hydro-
refining, hydrotreating, hydrodesulfurization, etc., to remove substan-
tially all sulfurous, nitrogenous and water-yielding contaminants there-
from.
When the catalyst of the present invention is utilized as a
-20-
.
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lZ69090
dehydrocyclization catalyst it is preferred that the charge stock sub-
stantially comprise paraffins. This, of course, is a result of the
fact that the purpose of a dehydrocyclization process is to convert
paraffins to aromatics. Because of the value of C6-C8 aromatics it is
additionally preferred that the hydrocarbon charge stock comprise C6-C8
paraffins. However, notwithstanding this preference the hydrocarbon
charge stock may comprise naphthenes, aromatics, and olefins in addi-
tion to C6-C8 paraffins.
In order to more fully demonstrate the attendant advantages
arising from the present invention the following examples are set forth.
It is to be understood that the following is by way of example only and
is not intended as an undue limitation on t h ot h rwise broad scope of
~- the present invention.
It should be understood that t here are three parameters use-
ful in evaluating hydrocarbon conversion catalyst performance, and in
particular in evaluating and comparing dehydrocyclization catalysts.
The first is "activity" which is a measure of the catalyst's ability
~ to convert reactants at a specified set of reaction conditions. The
; second catalyst performance criteria is "selectivity" which is an in-
dication of the catalyst's ability to produce a high yield of the de-
sired product. The third parameter is "stabitity" which is a measure
of the catalyst's ability to maintain its activity and selectivity
over time. In the appended examples the criteria which will be of
interest is catalyst selectivity. For purposes of the following, the
catalyst of the invention is exemplified as a dehydrocyclization cata-
.
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lyst and the measure of catalyst selectivity is the converslon of the
paraffin reactants to aromatics.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are plots of catalyst selectivity for the pro-
duction of aromatics as a function of time. In Figure 1 the performance
data for two catalysts are depicted therein, Catalyst A, not of the in-
vention, and Catalyst B, not of the invention. Figure 2 contains the
results of testing Catalyst C of the invention and Catalyst D, not of
the invention.
EXAMPLE I
A first catalyst comprising a silica-bound nonacidic zeolite
was prepared. However, in this instance the silica support matrix was
not derived from a high pH gelation procedure. For this catalyst the
nonacidic zeolite comprised a potassium exchanged L-zeolite. The cata-
lyst was prepared by admixing L-zeolite and a colloidal silica sol in
such quantities that the finished composite comprised 10 wt. % silica
and 90 wt. % L-zeolite based on the weight of the silica and L-zeolite.
The mixture was evaporated to dryness, ground, and extruded using
about 5% polyvinyl alcohol as an extrusion aid. The extrudates were
then calcined at 500C. The calcined extrudates were then subjected
to ion exchange step in order to deposit platinum thereon. An ion
exchange solution comprising Pt(NH3)4C12/KCl was utilized. Thereafter
the extrudates were subjected to an oxidation and reduction step at
350C. The finished catalyst comprised 0.877 wt. % platinum. This
12690~0
catalyst was designated Catalyst A. Althou~h bound in a support matrix
comprising silica, because the support matrix of Catalyst A was not de-
rived by a high pH gelation of an alkali metal silicate procedure, Cat-
alyst A was not in accordance with the invention.
EXAMPLE II
A second catalyst was prepared in this example. This catalyst
comprised an unbound L-zeolite in potassium form. The unbound L-zeolite
was subjected to an ion exchange step substantially as set forth in
Example I in order to deposit a platinum component thereon. After de-
position of the platinum component the unbound L-zeolite was given an
oxidation treatment in air at about 350C and thereafter a reduction
step in hydrogen at about 350C. The finished catalyst contained 0.657
wt. % platinum. This catalyst was designated Catalyst B and was not in
accordance with the invention.
EXAMPLE III
In this example Catalysts A and B were subjected to a test
proceture to determine their relative performance as dehydrocyclization
catalysts. The tests were conducted in a pilot plant comprising a re-
action zone in which the catalyst to be tested was emplaced. The condi-
tions within the reaction zone were a pressure of 690 kPag, a 1.0 hr.~
liquid hourly space velocity, and a 500C reaction inlet temperature.
- 20 Sufficient hydrogen was admixed w;th the charge stock prior to contact
~ with the catalyst to produce a hydrogen to hydrocarbon molar ratio of
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10.0:1Ø The feedstock was a blend of iso C6 + iso C7 ~ normal C
normal C7 paraffins with a small amount of alkylcyclopentanes.
The hydrocarbon feedstock was contacted with the catalyst em-
placed within the reaction zone and the reaction zone effluent was ana-
lyzed. The results of the data collected in test;ng both Catalysts A
and B in this test are set forth in Figure 1. Figure 1 is a graphical
representation of the catalyst selectivity for the production of aro-
matics as a function of time measured in periods of 6 hours. For the
purposes of this example, selectivity is defined as the grams of aro-
matics produced per gram of feed converted, multiplied by 100. As can
be seen from Figure 1, Catalyst B with the exception of Period 3 ex-
hibited higher selectivities for the production of aromatics than did
Catalyst A. Accordingly, the unbound L-zeolite containing a platinum
component supported thereon exhibited better selectivity for the pro-
duction of aromatics than did a catalyst comprising a platinum compo-
nent, an L-zeolite bound within a silica support matrix.
EXAMPLE IV
In this example a catalyst was made in accordance with the
invention. About 300 9 of L-zeolite in potassium form was ball-milled
for about 2 hours with 1382 9 of a lithium silicate sol in which the
SiO2/Li20 was 6 and the pH of the sol was about 10.5. The sol was then
dispersed as droplets into an oil suspending medium. Therein the sol
droplets were gelled at a temperature of about 100C. The gel spheres
-24-
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lZ69090
were then aged in the oil for about 2 hours at a temperature in the
range of from about 100 to 150C and a pressure of about 552 k~ag~
Thereafter the aged spheres were washed with 14 liters of 0.15 molar
KCl solution at about 95C for 2 hours to remove lithium therefrom.
The spheres were then dried at 95C. After drying the spheres were
gradually heated over a 6 hour period to 610C. The spheres were
then calcined in dry air for 2 hours at 610C. The result;ng spheres
comprised a potassium form L-zeolite bound in a silica support matrix
der~vedfrom a high pH gelation of an alkali metal silicate sol. The
composition was 50 wt. ~ L-zeolite and 50 wt. % silica.
The calcined spheres were then subjected to an ion exchange
step in order to deposit a platinum component substantially on the
L-zeolite. The ion exchange solution comprised a 0.030 molar
Pt(NH3)4C12/0.90 molar KCl solution maintained at a pH below 8. As
indicated heretofore by maintaining the pH below 8, it is possible to
deposit substantially all of the platinum on the L-zeolite. The cat-
alyst was then water washed and dried at a temperature of about 95C.
After drying the catalyst was-oxidized at a temperature of 350C and
reduced in a hydrogen stream at a temperature of about 350C. The
resulting catalyst comprised 0.786 wt. X platinum. This catalyst,
in accordance with the invention, was designated Catalyst C.
EXAMPLE V
; ~ An unbound nonacidic zeolite catalyst was prepared substan-
,~
tially as set forth in Example 11 above. ln this example, however,
the catalyst contained about 0.8%2 wt. % platinum on a potassium
25-
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form L-zeolite. Accordingly, the catalyst was substantially the same
as Catalyst B of Example II; however, the catalyst in this example con-
tained more platinum component. The catalyst made in this example was
designated Catalyst D.
EXAMPLE VI
In order to determine the relative performance as dehydrocy-
clization catalysts of a catalyst made in accordance with the invention
and a catalyst comprising an unbound L-zeolite containing platinum,
Catalysts C and D were subjected to a test. The test was carried out
in a p~lot plant substantially the same as that utilized to test Catalysts
A and B in Example III above. However, in this instance a different
testing procedure was utilized. The conditions employed during this
test of Catalysts C and D were a reaction zone inlet temperature of
500C, a 1.0 hr. 1 liquid hourly space ~elocity, and a reaction zone
pressure of 345 kPag. Hydrogen was admixed with the hydrocarbon charge
stock prior to contact with the catalysts. Sufficient hydrogen on a
once through basis was used to provide a 5:1 ratio of moles of hydrogen
to moles of hydrocarbon charge stock. The procedure followed in test-
ing was to first contact the catalyst with charge stock at a reaction
zone temperature of 410C. The 410C reaction zone inlet temperature
was maintained for a period of 7 hours. Thereafter the reaction zone
inlet temperature was increased to 500C over a 3 hour period. The
500C temperature was then maintained over a 12 hour test interval
during which the reaction zone effluent was analyzed by the on-line
~ gas chromatograph each hour.
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-26-
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The charge stock utilized in this example had the following
analysis:
C3/C4/Cs paraffin5 0.4 wt. %
C6 paraffins 69.5 wt. %
C6 naphthenes 0.7 wt. %
C7 paraffins 21.4 wt. %
C7 naphthenes 8.0 wt. %
Total100.0 wt. %
The results from the test are set forth in Figure ~. For pur-
poses of Figure 2 in the following discussion, selectivity has the same
definition as that given in Example III above. Surprisingly and unex-
pectedly, it can be seen from the data in Figure 2 that the catalyst of
the invention exhibited a much higher selectivity for the production of
aromatics than did the unbound L-zeolite and platinum catalyst. As will
1~ be noted from the data in Figure 1, this is contrary to the result ob-
served in Example III above. In Example III above the unbound L-zeolite
and platinum catalyst performed better than the silica bound, L-zeolite
and platinum catalyst. However, in this example the silica bound L-zeo-
lite and platinum catalyst exhibited higher selectivity for the produc-
tion of aromatics than did the unbound L-zeolite and platinum catalyst.
It can, therefore, be concluded that the surprising and unexpected re-
sults achieved by means of the invention result from the fact that the
silica support matrix of Catalyst C was derived by a high pH gelation
of an alkali metal silicate sol. Catalyst A, a silica bound L-zeolite
690gO
catalyst containing platinum, did not exhib;t superior selectivity in
comparison to unbound L-zeolite catalyst containing platinum. The dif-
ference in the relat;ve selectiv;t;es exh;bited in this example and in
Example III cannot be attributed to the varying platinum levels in that
;n each case the unbound catalyst contained more platinum on a weight
percent basis than did the bound catalyst. As indicated heretofore, the
nonacid;c zeol;te ;s noncatalytic and merely acts to modify the Group
VIII metal component which is the catalytic element in the system.
Although it is not fully understood why binding the platinum
containing nonacidic zeolite in a s;lica support matrix derived from a
h;gh pH gelation of an alkali metal silicate sol results in improved
selectivity, it is believed that interaction resulting from the high
pH gelation conditions between the silica of the support matrix and the
zeolite further modifies the platinum component catalytic function. This
further modification results in an improved selectivity for the conver-
sion of paraffins to aromatic compounds.
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