Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OE THE INVENTION
The present invention relates to a method for reducing an oxidized
platinum ca-talyst used in hydrocarbon conversion processes.
Catalysts containing platinum are well kno~m for a variety of uses.
Conventionally, the metal is dispersed on a porous, refractory support, such
as alumina, silica, or the like. An acidic function is often supplied by the
support, e.g., a silica-alumina mixture, or by addition of a halogen, such as
fluorine or chlorine, -to the catalyst.
Platinum catalysts are used in such hydrocarbon con-version pro-
cesses as naphtha reforming, isomerization of C4-C6 paraffins, aromatics
alkylation, dealkylation and disproportionation, isomerization of alkylaromat-
ics, hydrogenation and dehydrogenation. I-t is well known that a high platinum
surface area is an important catalyst property. Various methods have been
proposed foY providing high platinum surface areas in initial preparation or
regeneration of these catalysts.
In addition to the platinum, the refractory support, and a halogen,
if used, platinum catalysts often include one or more promoters. One partic-
ularly effective catalyst, which has found use in naphtha reforming, includes
platinum, rhenium and halogen on an alumina support. Such a catalyst is de-
scribed, for example, in United States Patent 3,415,737.
Platinum catalysts usually become deactivated after a period of
cataly-tic use. In hydrocarbon conversion operations, the catalysts -typically
become fouled with a refrac-tory carbonaceous ma-terial termed coke. It is
knowm to regenerate a deactiva-ted catalyst by burning the coke off it at an
elevated temperature. In addition tP burning off coke, various other steps
are often employed in regenerating pla-tinum catalysts, such as high temper-
a-ture oxidation of the metal, ~alogen treatment, steaming, reduction wi-th
hydrogen, etc.
A typical procedure used in -the in-situ regeneration of a platinum
catalyst after it has become deactivated by use in a naphtha reforming
process may, for example, include: (1) burning -the coke off -the ca-talyst in
several stages using increasingly higher temperatures be-tween about 700F and
1100 F or higher, with successively higher molecular oxygen concentra-tions in
-the regenerating atmosphere; (2) halogen treatment of the catalys-t at a tem-
perature of 700F -to 1100 F to redisperse platinum and to adjust the halogen
concentration in the catalyst to a desired level; and (3) treatmen-t of the
catalyst with hydrogen a-t a temperature of 700F to 1100F to remove oxygen -
from -the catalyst and to reduce the oxidized platinum in -the catalyst to its
elemental form. One or more of such steps can also be used for activating
10 fresh platinum catalysts in-situ prior to use in a hydrocarbon conversion
system.
The various regeneration steps noted above, as well as fresh cat-
alyst activation steps, are normally accomplished at temperatures in the range
from 700F to 1100F, usually 800F or higher. There have been, however, some
suggestions in the art for accomplishing one or more of the activation or re-
generation steps after or during a temperature reduction, or at a temperature
below the conventional 700F minimum. For example, United Sta-tes Patent
3,617,523 discloses oxida-tion of a platinum group me-tal catalyst at a temper-
ature of 500-700F in a sulfur-contaminated hydroconversion unit to avoid
20 sulfur contamination of the catalyst. United States Patent 2,968,631 dis-
closes regeneration of an isomerization catalyst including platinum and nickel
on a silica-alumina support by oxidation at 880-1000F, cooling to 800F in
nitrogen, and reduction in hydrogen at 800F. United S-ta-tes Patent 3,937,660
discloses regeneration of an iridium-co-ntaining catalyst by oxidation of the
catalys-t at 572-1112 F, purging at below 752F, and reduction with hydrogen
a-t between 392F and 1022F. United Sta-tes Pa-tent 2,879,232 discloses oxida-
tion of a platinum group metal catalys-t at 750-1200F, rapia cooling of the
catalyst to below 860F, and reduction of the catalyst with hydrogen. United
Sta-tes Patents 2,856,349 and 2~856,350 disclose regeneration of a platinum
30 catalyst by oxidation at a temperature of 900-1050 F, cooling the ca-talyst to
. .
r~4
a temperature of 800-9ooF in the presence of oxygen, and then reducing the
catalyst with hydrogen.
In a typical regeneration operation, most of the hydrocarbons in
the conversion system are removed by purging or burn:ing. However, some
traces of hydrocarbons almost invariably remain in relatively inaccessible
locations in the hydrocarbon conversion system, even after high temperature
oxida-tion of the catalyst bed, purging with inert gas and evacuation of the
conversion system.
If a platinum-containing catalyst, in which at least a portion of
the platinum is combined with oxygen, is exposed to an inert or reducing at-
mosphere (as by an inert gas purge~ system evacuation or hydrogen reduction)
at the elevated temperatures (above 700F) normally used for platinum catalyst
regeneration, it has been found that -trace hydrocarbons in the conversion sys-
-tem react with the combined oxygen and pla-tinum, forming a very refractory
carbon deposit on -the ca-talyst and reducing the pla-tinum. This, in turn, re-
sults in an undesirable loss in the platinum surface area in the catalyst,
and generally severely decreases the activity and selectivity of the catalyst.
This reaction and its harmful effect are herein referred to as "hydrocarbon
reduction" of the catalyst as distinguished from hydrogen reduction of the
catalyst. Likewise, during normal hydrogen reduction of oxidized platinum in
a catalyst, using hydrogen at conven-tional hydrogen reduction temperatures
above 700 F, any traces of hydrocarbons in the hydrogen gas used for reduc-tion
can react with the oxidized platinum before hydrogen reduction has taken
place, causing the same loss of surface area, selectivity and activity by hy-
drocarbon reduction. For this reason, it has been necessary to employ sub-
stantially pure, electrolytically generated hydrogen for hydrogen reduction
of platinum-containing cataIysts to avoid deleterious hydrocarbon reduction
of the platinum in the catalys-t. Electrolytic hydrogen is quite expensive as
compared -to manufactured hydrogen available from normal pe-troleu~ refinery
sources such as naphtha reformers or hydrogen plants, sometimes being referred
to as "plant" hydrogen. It would be highly desirable to subs-titu-te plant
hydrogen for electrolytic hydrogen f`or hydrogen reduction of the catalyst in
catalyst activation or regeneration procedures, except that plan-t hydrogen is
invariably con-taminated with at least some amount of hydrocarbons. Attempts
have been made to remove hydrocarbons from COnVerSiOrl systems by one or more
evacuations of the internal gases~ followed by repressuring -the system. It
would be desirable to eliminate the necessity for such expensive and diffi-
cultly carried-out evacuation procedures in activating and regeneratlng a
platinum catalyst. The method of the presen-t invention provides a solution
to the foregoing problems.
SUMMARY OF THE INVENTION
In one embodiment the present invention relates to an improvement ~`
in a process for hydrogen -treating a platinum oxide component in a cata]ys-t
including the platinum oxide component and a refractory inorganic oxide com-
ponent, which comprises: maintaining the catalys-t at a tempera-ture below
700F whenever the catalyst, in the presence of a hydrocarbon, is in con-tact
with a gaseous atmosphere including less than 0.1 volume percent molecular
oxygen un-til subs-tantially all -the platinum oxide in the catalyst is reacted
with hydrogen to form elemental platinum.
In another embodiment, the present invention relates to a method
for regenerating a catalyst including a platinum component and a refractory
inorganic oxide component in~-situ in a hydrocarbon conversion system af-ter
coke has been deposited on the catalyst by use of the catalyst in the system,
which comprises the s-teps of: (a~ burning coke off the catalyst and forming
platinum oxide in the cataLyst by contacting the catalyst with molecuIar ox-
ygen at a temperature above 700F; (b) lowering the tempera-ture of -the result-ing platinum oxide-containing catalyst to below 700 F in the presence of a
gaseous atmosphere including at least 0.1 volume percent molecular oxygen;
~c) removing substantially all molecular oxygen from contact with the catalyst
at a temperature below 700F; and (d) reacting substantially al~L the platinum
oxide with hydrogen to form elemental platinum by contac-ting the catalyst
with a hydrogen-containing gas at a temperature below 700F.
In a still fur-ther embodimen-t, the present invention relates -to a
method for reducing a catalyst with hydrogen in a hycLrocarbon conversion sys-
tem, the catalyst including 0.01-10 weight percent platinum in associa-tion
with a refractory support, when oxygen is combined with at least a portion of
the platinum, comprising the steps of: ~a) heating the ca-talyst to a temper-
ature above 700 F in the presence of a molecular oxygen-containing gas;
(b) lowering the -temperature of the catalyst to below 700F in the presence
of a gaseous atmosphere including more than 0.1 volume percent molecular ox-
ygen; and (c) maintaining the temperature of the catalyst below 700CF and re-
moving combined oxygen from the catalyst by contacting catalyst with molecular
hydrogen.
I have found that the possibility of deleterious hydrocarbon reduc-
tion of a platinum catalyst can be vir-tually eliminated, regardless of the
presence of traces, or even fairly large amoun-ts, of hydrocarbons in the gas-
eous atmosphere in contact with the catalyst, by carrying oitt hydrogen reauc
tion of the platinum catalyst according to the present invention. By main-
taining the temperature of a platinum oxide-containing catalys-t ~elow 700 F
whenever the catalyst is in contact with a nonoxidizing atmosphere, the plat-
inum remains in the form of the oxide, and does not undergo -the harmful hy-
drocarbon reduction reaction to any substan-tial extent. When an oxidizing
atmosphere is present, any hydrocarbons con-tacting the catalyst are oxidized
or are burned off -the platinum surface of the catalyst if they become deposit-
ed thereon. When the temperature is below 700 F, the catalyst can be safely
exposed to hydrocarbons in an inert atmosphere, such as a nitrogen-rich gas,
or in a reducing atmosphere, such as hydrogen. Thus, combined oxygen in the
catalyst can be removed by reducing the platinum oxide with hydrogen even when
the hydrogen utilized is contaminated with hydrocarbons, as long as the tem-
perature is below 700 F. This hydrogen reduction may be accomplished without
`i :'` .
.
the danger of undesirab]e hydrocarbon reduction of the catalyst, therebyeliminating one of the severe problems in the in-situ activation and regener-
ation of platinum catalyst. Hydrocarbon-contaminated plan-t hydrogen (manu-
factured hydrogen) may accordingly be used in the in~situ hydrogen reduction
of platinum catalyst, as opposed to the pure, electrolytic hydrogen which was
necessarily used in conven-tional regeneration and activation operations.
Moreover, the need for several evacua-tions and repressurizations of a conver-
sion unlt, in order to remove trace hydrocarbons from the gaseous atmosphere
in the unit, is likewise elimina-ted by the practice of the present invention.
The present invention allows platinum ca-talyst to be reduced with
hydrogen during regeneration or preliminary activation in-situ in a hydro-
carbon-contaminated conversion uni-t, while providing a high platinum surface
area in the catalyst and providing a highly active and selec-tive catalyst
after activa-tion of fresh ca-talyst or regenera-tion of used catalyst. Other
obJects, embodiments and advantages of -the present invention will be apparen-t
from the following detailed description of the invention.
DETAILED DESCRIPTIO~ OF THE I~VE~TIO~
The catalysts which can be treated by -this invention are those con-
taining platinum. The ca-talyst includes between abou-t 0.01-5 weight percent
platinum, preferably be-tween about 0.1-3 weight percent platinum. The pres-
en-t method may also be used in an analogous manner, with or without modifica-
tion, for hydrogen reduction of catalysts containing Group VIII metals other
than platinum, particularly palladium or iridium.
The platinum is disposed on a porous, refractory carrier. The car-
rier ma-terial may, for example, be a porous, inorganic oxide having a relat-
ively high surface area, e.g., from 50~-500 m /g. Suitable carriers include
alumina, silica, naturally occurring or synthetic crystalline or amorphous
aluminosilicates, magnesia, silica-magnesia~ zirconia, silica-zi-rconia, mix-
tures of any two or more of the above-men-tioned materials and similar mate-
ri ~ s. Those skilled in the art will recognize that various refractory
.'
-- 6 --
D4~
inorganic oxide supports are suitable for use and that the preferred type ofrefractory support employed in a given pla-tinum ca-talyst is generally dic-
tated or suggested by the type of hydrocarbon conversion process in which
the catalyst is -to be used.
A particularly suitable refrac-tory suppor-t for use in catalysts em-
ployed in ca-talytic naphtha reforming is alumina. A preferred alumina car-
rier may be prepared by treating an alpha-alumina monohydrate with a mono-
basic acid, neutralizing the acid with a nitrogen base such as ammonia, shap-
ing the resulting mass into a desired par-ticle form, and then drying and
calcining. The platinum may be combined with the support in an~ conventionàl
manner, such as by aqueous impregnation o* the particles of the carrier with
a solution of the metal. Likewise, the me-tal may be combined wi-th the cat
alyst by cogellation of the metal from a solution along wi-th a solution of
the refractory metal. In the case of alumina, the carrier is preferably
~ol~med in-to particles of relatively small size, for example, by extruda-tion,
and the particles are then calcined prior to impregnation of the pla-tim~m.
In addition to the refractory carrier and the platinum, i-t may be
desirable to include a halogen in the catalyst. Preferred halogens are chlo-
rine and fluorine, especially chlorine. Mixtures of halogens may also be
used. The halogen may be present in an amount between 0.1 and lO weight per-
cent of the weight of the total ca-talyst, with an amount of halogen between
0.5 and 3 weight percen-t being preferred when the catalyst is used in naphtha
reforming. The halogen may be added to -the catalyst in any conventional man-
ner, e.g.~ during forma-tion of the refractory carrier, by impregnation of the
carrier, or by sublimation of a suitable halogen compound, such as aluminum
chloride, onto the catalyst.
q'he catalyst may con-tain other metals. Specific met~ls which are
effective promoters for platinum include iridium, zinc, germanium, tin, lead
and rhenium. The promoters may be presen-t in an amount be-tween 0.~1 and 5
weight percent of the catalyst, with about 0.1-3 weight percent being the
1~
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pre-ferred range for promoter metals. The promoter me-tals may be added to the
carrier in any conventional manner, as by impregnation prior -to the impregna-
tion of the platinum, impregnation along with the platinum, or impregnation
after the platinum. Promo-ter metals may also be added -to -the ca-talyst, e.g.,
by cogellation with a solution of a precursor of the re-fractory oxide used in
forming the support. A particularly preferred catalyst for use with the
present inven-tion is one containing 0.1-1 weight percent pla-tinum, 0.1-1
weight percent rhenium, and 0.1-5 weight percent chloride in associa-tion with
an alumina carrier. Preferably, the catalyst is prepared by coimpregnation
of the platinum, rheni~un, and chloride onto extruded and calcined particles
of the alumina, after which the catalyst is dried and calcined.
The present invention can be used in activa-ting or conditioning
ei-ther a fresh catalys-t or a ¢at~lyst which has been previously employed in a
hydrocarbon conversion operation and is being regenerated for reuse. The
presen-t invention is preferably used during in-si-tu treatmen-t of the catalyst
in a hydrocarbon conversion unit, since the potential problem of hydrocarbon
reduc-tion of the oxidized platinum in the catalyst is particularly serious
during in-situ catalyst activation and regeneration in a commerical conversion
system. The present invention is particularly preferred for use in in-situ
activation and regeneration of a catalyst employed in a naph-tha reforming
system or similar hydrocarbon hydroconversion system in which a hydrocarbon
charge stream and hydrogen are mixed, heated to the desired conversion temper-
a-ture, and then contacted wi-th catalyst in a series of one or more reactors.
The effluent ~rom the last reactor is cooled, and the hydrogen is then separ-
ated from the hydrocarbons and at least partially recycled. Various hydro-
conversion systems of this type are well ~nown to those skilled in the art,
as are methods for in-situ regeneration of platinum-containing catalys-t in
such systems.
The presen-t invention is used prior to and durlng hydroeen reduction
of a catalyst when oxygen is combined with at least a portion of -the platinum
~ :?~.
.-- .
4'74
in the catalyst. ~he form of combination of oxygen with the platinum can in-
clude either an oxide of all or a subs-tantial portion of -the platinum contain-
ed in the catalyst, or else the chemisorption of oxygen on the surface of the
platinum, so that the combined oxygen is only associa-ted with the surface
atoms of platinum in the catalyst, forming a surface layer of platinum oxide.
The oxygen can also be combined with the platinum both by chemisorption and by
substantial non-surface pla-tinum oxide forma-tion. Platinum which has been ox-
idized either by substantial subsurface oxide formation or by surface chemi-
sorption is subject to the problem of hydrocarbon reduc-tion, so that the
present me-thod is effective with platinum after either type of oxidation, or
both. Combined oxygen is oxygen bound in the catalyst either as non-surface
pla-tinum oxide or by surface chemisorption to form a platinum oxide surface
layer.
If the ca-talyst is fresh, the reaction of -the platinu~ w:ith oxygen
takes place simply by con-tacting a molecular oxygen-containing gas with the
cataIyst at a temperature of 100-1000F for a short period of time. When it
:... .
is desired to oxidize the platinum in the catalyst, the concentration of ox-
ygen in the gas used should be greater than 0.1 volume percent and preferably
greater -than 1 volume percent.
If the catalyst has previously been used for conversion of hydro-
carbons, the catalyst typically becomes contaminated with a substantial amount
of coke before it is necessary to regenerate it. In such cases, it is desir-
able to burn the coke off the catalyst as a first step. This may be accom-
plished by contacting the catalyst with an oxygen-containing gas a-t a temper-
a-ture of above 700 F, preferably above 800F, until heat evolution from the
ca-talyst and/or oxygen consumption during passage of an oxygen-containing gas
in contact with the catalyst have dropped to a low level, indicating that
practically all coke in the catalyst has been burned. When the coke content
.
in the catalyst has dropped to a low level~ e.g., less than 0.1 weight per-
cen-t, the coke is sufficiently removed, and platinum in the catalyst is
_ g _
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D47~L
simultaneously oxidized. The oxida-tion or coke burnoff treatment used in
catalyst regeneration may include tne use of successively higher oxygen con-
centrations and successively higher temperatures, although it is preferred
not to exceed a maximum tem-perature of about 950-1000F during coke burn-off.
The pressure employed in carrying out the coke burn-off is not cri-tical.
Eigher total pressures, and higher oxygen partial pressures~ result in more
rapid coke burn-off and more rapid oxidation of the platinum in the catalys-t.
Thus, the total pressure and oxygen partial pressure may be adjus-ted in order
to facilitate more rapid or less rapid coke burn-of-f to insure that maximum
desirable temperatures are no-t exceeded.
Optionally, the catalyst may be subjected -to a halogen treatment
during regeneration, preferably after completion of coke burn-off and plat-
inum oxidation. The halogenation temperatures is from 700F to 1000F. The
halogen may, for example, be contacted wi-th the catalyst in the form of an
organic chloride vapor which is passed in contact with the catalyst in a gas~
eous atmosphere containing a-t least 0.1 volume percent oxygen, preferably at
least 1 volume percent oxygen. Such a halogen treatment may aid in dispers-
ing or redispersing platinum on the refractory support, providing an increased
surface area for the catalytic metal in the ca-talyst. The halogen treatment
may also be performed in the presence o-f nitrogen, steam, etc., if desired,
in addition to -the molecular oxygen.
When -the platinum has been regenerated by high temperature oxida-
tion, and optionally halogen treatment, a-t a -temperature above 700F, -the tem-
perature of the catalyst is lowered to preferably to below 600CF bu-t above
300F, and particularly preferably to between 450F and 550F, while the cat-
alyst is kept in the presence of an oxidizing atmosphe~re, retainlng combined
oxygen in the catalyst in the platinum oxide. The molecular oxygen concen-
tration in the gaseous atmosphere in contact with the oxidized catalys-t is
carefully controlled during adjustment of the temperature so that the atmos-
phere ~s at least 0.1 ~olume percent molecular ox~ygen, and preferably between
-- 10 --
~l
7~
1 and 10 volume percent molecular oxygen, and particularly preferably between2 and 5 volume percent molecular oxygen. By main-taining an oxidizing atmo-
sphere, as specified, during adjustment of the temperature of the catalyst to
below 700F, but preferably above 300F, platinum in the ca-talyst is main-
tained in an oxidized state, and trace hydrocarbons present in the regenera-
tion gases contacting the catalyst do not react with the oxidized platinum in
an undesirable hydrocarbon reduction reaction. If a small amount of hydro-
carbon reacts with any platinum oxide during adjustment of the temperature,
the pla-tinum thereby reduced is immediately reoxidized to platinum oxide by
contact with oxygen in the oxidizing atmosphere surrounding -the catalyst.
Accordingly, the platinum surface area, achieved during preparation of the
fresh catalyst or during regeneration by coke burn-off-platinum oxida-tion,
and optional halogen trea-tment, is maintained at a high level. In catalyst
regeneration procedures, the pressure of the gaseous atmosphere in con-tact
with the catalyst during adJustment of the temperature after oxida-tion and
halogenation) of the catalyst is not critical. When the temperature of the
catalyst is lowered af-ter coke burn-off and platinum oxidation at an elevated
tempera;ture above 700F in an in-situ regeneration operation, then i-t may be
convenient to depressurize the conversion sys-tem a-t the same time as -the tem-
pera-ture of the catalyst is being lowered. ~he tempera-ture of the ca-talyst
thus preferably adjusted to below 700 F, preferably below 600F but above
300F, and particularly preferably be-tween 1~50F and 550F, in -the presence
of the oxidizing atmosphere.
When platinum has been oxygen treated a-t a temperature above 700F,
after the temperature of the catalyst has been adjusted to within the spec-
ified range in an oxidizing atmosphere, the platinum in the catalyst is
hydrogen reduced. Combined oxygen present in the catalyst, including either
chemisorbed oxygen forming a surface layer of platinum oxide or oxygen in the
form of a substantial amoun-t of non-surface platinum oxide, is removed from
the platinum in the catalyst by contacting the catalyst with molecular
-- 11 --
?47~
hydrogen, forming water vapor and elemental platinum. Before the hydrogen is
introduced into the atmosphere in con-tact with the catalyst, the concentra-
tion of molecular oxygen in the atmosphere should be lowered, i~ necessary,
at least below the level at which explosive combination of hydrogen and ox-
ygen would occur. Preferably the oxygen concentration in the gaseous atmo-
sphere is lowered to below 0.1 volume percent, i.e., substantially all un~
combined molecular oxygen is removed from contact with the catalyst. Molec-
ular oxygen in the atmosphere in contact with the catalyst may be removed
from contact with the catalyst by purging the system with an inert gas, such
as nitrogen, by evacuation of the system, or by any other conventional pro-
cedure. Preferably the catalyst is purged with inert gas, as by passing an
inert gas continuously across the catalyst until the amount of ~olecular
oxygen present in the inert gas after contac-t with the catalyst is below 0.1
volume percent.
When the amount of molecular oxygen in contact with the ca-talyst is
sufficiently low~ the catalyst is con-tacted with a molecular hydrogen-con-
taining gas. The hydrogen-containing gas may be pure hydrogen or a mixture
of hydrogen with one or more of inert or relatively inert gases, such as
nitrogen or steam. According to the invention, the hydrogen used in the re-
duction operation need not be electrolytic hydrogen, as found necessary inprior art regeneration operations. Electrolytic hydrogen has previously been
used in regeneration because hydrogen from more economical sources i.e., man-
ufac-tured hydrogen, is contaminated with hydrocarbons. When hydrocarbon-con-
taminated hydrogen has been used for reducing a platinum catalyst, the hydro-
carbon contaminants have reacted with oxidized p'atinum in the catalyst, re-
sulting in a severe loss of platinum surface area and in lower catalyst activ-
ity and selectivity when the catalyst is placed on stream. I have found that,
when the temperature of the catalyst is below 700F, preferably below 600F
but above 300 F, and particularly preferably between 1~50F and 550F, the
catalyst is not subject to undesirable hydrocarbon reduction in the absence
,
- 12 -
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of -the molecular oxygen-containing gases. The deleterious effects of hydro-
carbon reduction of oxidized platinum in -the ca-talyst are not encountered
when the present invention is employed in catalyst activation, even when the
catalyst is contacted with fairly substantial concentrations of hydrocarbon
contaminants in any nonoxidizing atmosphere used in the system, such as purge
gases, reducing gases, or even in vacuums in evacuated catalyst-holding ves-
sels. Various steps conventionally taken to remove trace hydrocarbons from
conversion systems during conventional regeneration or activation operations
to avoid hydrocarbon reduction of the platinum can also be eliminated from
the regeneration procedures used when the method of the present invention is
employed. Thus, a series of pressurizations and evacuations to remove hydro-
carbons need not be carried out when the present method is used during ac-tiv-
ation of fresh catalyst or regeneration.
The hydrogen content of the gas used to remove the combined oxygen
from the catalyst and to reduce the platinum oxide to elemental platinum may,
if desired, be increased from a low initial pressure or partial pressure up to
a higher level such as the pressure desired in carrying out the hydroconver-
sion process in w~hich the catalyst is used. The chemically combined oxygen in
the catalyst may fairly readily be removed from the catalyst by treatment in
the specified te~perature range with a gas including at least 2 volume percent
hydrogen. In any case, a hydrogen partial pressure of at least 0.3 psi should
be used. The required duration of the hydrogen reduction treatment may be
measured by determining the water content of the hydrogen-containing gas after
it has been contacted with the catalyst. When a $ubstantial amount of water
is no~longer evolved from the catalyst by reaction of hydrogen and oxygen,
then the combined oxygen has been substantially all removed from the catalyst
and~the plat1num ln the ca-talyst has been substantially all reduced to~elem-
ental platinum, so that undesirable hydrocarbon reduction of the platinum in
the catalyst~will not occur, even at higher temperatures. The hydrogen reduc-
tion treatment is performed while the tempera-ture of the cstalyst~i~s maintained
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below 700F, preferably below 600F but above 300F, and particularly pref-
erably between 450F and 550F. Thereafter, the catalys-t is preferably main-
tained in contact with a hydrogen-containing atmosphere until the catalyst
is to be used in a hydrocarbon conversion operation.
EXAMPLE 1
Tests were undertaken -to demonstrate the conditions at which hydro-
carbon reduction of platinum oxide in a catalyst took place, and to demonstrate
the deleterious effect of hydrocarbon reduction on the platinum surface area
of a catalyst. A catalyst containing 0.3 weight percent platinum on an alum-
ina carrier was reduced by heating in hydrogen at 1000 F for one hour. Oneportion of the reduced catalyst was oxidized slightly by being exposed to air
at room temperature. This por-tion was labeled Catalyst A. Another portion
of the catalyst was substantially oxidized by being calcined in air at 900F
and was labeled Catalyst B. Nitrogen was saturated a-t 70F with a reformed
Arabian naphtha. The nitrogen used was substantially oxygen-free. The
hydrocarbon-saturated nitrogen was contacted with samples of Catalysts A and
B at various temperatures, as shown in Table I, each test being undertaken for
one hour. In each test, the nitrogen was passed over the sample of the cat- -
alyst, with the catalyst and gas being maintained at the temperature shown.
Thereafter, the carbon content and platinum surface area (by CO chemisorp-
tion) of each sample were measured and folmd to be as shown in ~able I.
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o o
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o CO
V o ~ ,.
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o CU .. ~, .,
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The results set forth in Table I show -tha-t -the platinum surface
area in the catalyst samples decreased subs-tantially as the temperature of
naphtha-saturated nitrogen treatment was increased. A-t 800 and 900 F, the
pla-tinum surface area was decreased -to a very low level. There was a good
correlation be-tween the carbon content of each sample and the loss of plat-
inum surface area in each sample. The relative loss of platinum surface area
was much larger for the catalyst samples which had been substantially oxid-
ized at 900 F than for the samples which had been reduced and simply exposed
to room temperature air. It was noted that the loss of platinum surface area
was extremely severe considering the extremely small amounts of carbon which
were deposited on each of the samples in comparison with the loss of plat-
inum surface area normally observed in catalysts after much larger amounts of
carbon deposition in normal naphtha reforming with the same catal.yst. Thus,
the type of carbon deposition on the catalyst which took place in -the inert
n:itrogen atmosphere tests was felt to be particularly dele-terious -to -the ca-t-
alyst, and to be at least partially a different -type of carbon inactivation
than is observed with coke normally deposited on a catalyst in hydrocarbon
hydroconversion operations.
EXAMPLE 2
In a preferred embodiment, the me-thod of the present invention was
employed during an in-situ regeneration of a catalyst in a commercial naphtha
reforming uni-t after the ca-talys-t had become substantially deactivated by usein naphtha reforming in the system. The ca-talys-t contained about 0.3 weight
perceNt pla-tinum, about 0.3 weight percent rhenium and about o.8 weight per-
cen-t chloride and had an alumina carrier. Prior -to regeneration the catalys-t
contai.ned about 10 wt.% coke and had a low platinum surface area (typically
2-5 micromo1s per gram C0 chemisorption) due both to growth of metal par-
ticles and to deposition of carbonaceous material. In carrying out the re-
generation, the flow of naphtha feed into the unit was discontinued. The
platinurn in -the catalyst was oxidi~ed and carbonaceous materials were burned
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.
7'~
off the catalyst by use of successively higher concentra-tions of oxygen a-t
suecessively higher temperatures above 700 F. Carbon tetraehloride was then
injeeted into the circulating gases -to adjust the ehlorlde eoncentration in
the catalyst at a temperature above 700F. According to the invention, the
tempera-ture of the eireulating oxidizing atmosphere and the catalyst was then
adjusted to 500 F. The catalyst was cooled in the presence of an oxidizing
atmosphere consisting of 2-3 volume percent molecular oxygen in ni-trogen at a
total pressure of 100 psig. After the catalyst temperature had reached 500F,
the pressure in the unit was redueed to 50 psig, and the unit was substantial-
ly purged of moleeular oxygen by passing nitrogen through the unit. When -the
moleeular oxygen eoncentration was less than 0.3 volume percen-t, -the catalyst
was redueed by passing hydrogen through t~e unit to remove eombined oxygen
from the platinum oxide in the ea-talyst and reduee the platinum to elemental
platinum. The hydrogen emplo~ed in the reduetion was inexpensive plan-t hy-
drogen obtained ~rom a naphtha reformer. It contained a subs-tantial concen-
tration of light hydrocarbons sueh as methane and ethane. The surfaee area
of the eatalyst was measured af-ter the hydrogen reduetion treatment and was
found to give 13.1 mieromols per gram in a C0 chemisorption test. This indi-
eated a very satisfaetory catalyst regeneration in ter~s of restoration o~
the platinum surfaee area o~ the eatalyst. When the eatalyst was returned to
on-stream use in naphtha reforming, it was ~ound to be highly aetive and se-
leetive, fur-ther indieating that the regener~tion was sueeessful and that hy-
droearbon reduction o~ the eatalyst had not taken plaee during the regenera-
tion operation.
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