Note: Descriptions are shown in the official language in which they were submitted.
105~)956
BACKGROUND OF THE INVENTION
1. Pield of the Invention
This invention relates to the well-known continuous
cyclic fluid catalytic cracking (FCC) of hydrocarbons wi-th a catalyst,
generally a catalyst containing a crystalline aluminosilicate zeolite
component, in the absence of added hydrogen to produce gasoline, which
cracking results in the for~ation on the catalyst particles of a
deposit of combustible hydrocarbons known as coke, and the spent catalyst
particles from the catalytic reactor are regenerated in a separate zone
by burning off sufficient coke to place the catalyst particles in a
condition suitable for recycling to the hydrocarbon conversion zone.
In particular the invention is concerned with a solid additive capable
of promoting combustion of carbon monoxide to carbon dioxide in FCC
regenerators wlthout appreciably affecting the ability of the catalyst
particles to catalyze the hydrocarbon conversion reaction in the
conversion zone.
, Present-day continuous cyclic FCC processes utilize
j fluidizable catalyst particles containing a crystalline zeolitic
aluminosilicate component (usually an ion-exchanged form of a synthetic
faujasite such as zeolite X or Y) and a porous inorganic oxide matrix.
I This type of catalyst must be regenerated to low carbon levels, typically
0.5% or less, to assure required activity and selectivity beEore the
catalyst particles can be recycled to a conversion zone. In most
regenerators, the combustible solids deposited on the spend solid catalyst
~; 25 - particles from the cracking zone are burned in a con*ined regeneration
one in the form of a fluidized bed which has a relatively high
concentration of catalyst particles (dense phase). A region of lower
solids concentration (light phase) ls maintained above the dense phase.
~A typical regeneration cycle is described in U. S. Patent 3,944,482
to Mitchell.
. ,~. :. -- 1 --
';
'~ ~
56
High residual concentrations of carbon monoxide in flue
gases from regenerators have been a problem since the inception of
catalytic cracking processes. The evolution of FCC has resulted in the
use of increasingly high temperatures in FCC regenerators in order to
achieve the required low carbon levels in the regenerated crystalline
aluminosilicate catalysts. Typically regenerators now operate at
temperatures in the range of 1100 to 1350F. and result in flue gases
having a CO2/CO ratio in the range of 1.5 to 0.8. The oxidation of
carbon monoxide is highly exothermic and can result in so-called
"carbon monoxide afterburning" which can take place in the dilute
catalyst phase, in the cyclones or in the f~ue gas lines. ~fterburning
has caused significant damage to plant equlpment. On the other hand,
unburned carbon monoxlde in atmosphere~vented flue gases represents a
loss of fuel value and ls ecologically undesirable.
Restrictions on the amount of carbon monoxide which can
be exhausted into the atmosphere and the need for efficient coke removal
from spent catalyst particles have stimulated several approaches to
the provlsion of means for achieving a balance between afterburning
and incomplete regeneration of spent fluid zeolitic catalysts.
It is well known that metal such as iron, nickel, vanadium
and copper can promote carbon monoxide combustion when present as
contamlnants in cracking feedstocks. ~arly in the development of
catalytic cracking and long prior to the introduction of crystalline
zeolitic aluminosilicate catalysts, it was proposed (U. S. 2,436,927
25- to Kassel) to prevent afterburning in fluldized catalytic cracking
processes by introducing a small amount of a carbon monoxide oxidiæing
catalyst. ~he proposed oxidant was an oxide of metals from the first
transition series. It was suggested to introduce such material either
as a component of the cracking catalyst or, preferably, as separate
3Q particles supported "on a suitable carrier." Such carrier was not
-- 2 --
gs6
described in the patent. Chromium oxide was proposed as an impregnant
for gel-type moving bed cracking catalysts in U. S. 3,647,860 to Plank
et al. This was also prior to the introduction of crystalline zeolitic
catalysts. Subsequently it was suggested to incorporate titanium in
; 5 cracking catalysts for improved carbon monoxide conversion but this
approach was directed to achieve only partial combustion of carbon
monoxide since regenerators available at that time were not capable of
withstanding the heat release resulting from full combustion.
U. S. 3,36~,136 to Chen suggested the use of a noble metal
- 10 such as platinum to promote carbon monoxide oxidation in a regenerator
of a FCC unit operated with a zeolitic aluminosilicate catalyst.
According to the teachings of the patent, the noble metal had to be
held wlthin the inner pore structure of a so-called "shape selective"
zeol:Lte, speciflcally a zeolite having pores large enough to allow
penetration of oxygen, carbon monoxide and carbon dioxide but too small
for molecules of gas-oil. In one preferred embodiment, the particles of
shape selective zeolite containing the oxygen promoter within the pores
were contained in the same particles which included both the larger pore
catalytically active zeolite and a conventional inorganic oxide matrix
component. For example, the two different zeolites, one including a
promoter such as platinum within the pores, were composited into unitary
particles with an lnorganic oxide matrix material. An alternative
I disclosed in the Chen patent invol~ed mixing the particles of sieve
; containing the oxidation promoter with particles of the zeolitic catalyst.
In a preferred embodiment of this alternative, the individual components
were of different particle size so that the oxidation component could
be withdrawn as well as added to the circulating catalyst mass to
alter the degree of carbon monoxide conversion. In all variations of
this technology, preparation of a costly small pore zeolitic component is
required and the oxidant will be present on a high surface a:rea support.
-- 3 --
'
According to the teachings of West German Application
DT 2444911, small amounts of metal or metallic elements of Period 5
and 6 of Group VIII of the Periodic Table or rhenium or compounds thereof
are simply added in amounts up to 50 p.p.m. to conventional FCC (or TCC)
catalysts to decrease the carbon monoxide content of flue gases, as
e~idenced by the improved CO2/C0 ra-tio of such gases, without appreciably
affecting the cracking properties of the catalysts. The metal component,
preferably a platinum compound, is introducecl into the catalyst by
impregnation or by ion exchange during any stage of catalyst manufacture,
or even after the catalyst particles are formed. According to the teachings
of the German patent application, the active cracking catalyst component
(zeolitic aluminosilicate) is preferably ion-exchanged with the metal and
the ion-exchanged material is composi~ed with the porous matrix to
produce catalyst partlcles. The German appllcatlon also dlscloses that
a sillcon-containing support or clay can be ion-exchanged or lmpregnated
wlth the metal but there is no explanation as to how this is accompllshed.
Based on illustrative examples, a reasonable interpretation is that the
exchanged support or clay is mixed with the catalytically active zeolite
component to form composite catalyst particles in which the metal
promoter and actlve æeollte are present in the same partlcles.
The patented techniques for preparlng a platlnum metal
promoted cracking catalyst leave something to be desired. Impregnation
or ion-exchange of the zeollte or the porous matrlx beEore composltlng
- the constituents can be used only in the production of those catalysts
in which the zeolite is formed separately from the matrix; for example,
catalysts prepared as described in U. S. 2,140,249 and U.S. 2,140,253
to Plank et al. When a finished catalyst is trea-ted, the entire tonnage
of catalyst must be processed. Similarly, the entire catalyst must
be treated with a metal when the catalyst particles are produced in SitU
from preforms, such as catalysts produced in accordance with the teachings
' .
-- 4
9s~
of U. S. 3,647,718 to Haden et al. By way of example, in Example 10
of the DT 2444911 application, a promoted FCC catalyst was prepared
containing 3 p.p.m. platinum by impregnating HFZ~20 zeolitic molecular
sieve catalyst with a solution of platinum-tris (ethylenediamine)
tetrachloride Eollowed by washing and drying. Using this technique on
a commercial basis, the production of 10,000 tons of metal-promoted
catalyst would require the use of about 35,000 tons of platinum solution
to add only 100 tons of platinum. This would necessitate a substantial
capital investment for equipment for impregnation, washing and drying.
Prior to our invention, the suggestion was made that the platinum
oxidation might be incorporated on a solid support material. Presumably,
a conventional high surface area gel-type catalyst was intended as the
support.
A general object of the lnvention is to provide -lmprovements
in prior art means for achieving controlled oxidation of carbon monoxide
in the regeneration zone of a cyclic FCC process.
THE INVENTION
The essence of the present invention resides in promoting
the combustion of carbon monoxide in a ~CC regenerator by the use of an
additive obtained by uniformly impregnating a small amount of solution
of a platinum compound on coherent fluidi.zable particles of kaolin clay
calclned to a substantially anhydrous condition and having a low surface
area (in the range of about 10 to 15 m2/g. as determ:Lned by the B.E.T.
nitrogen absorption method) and a total pore volume as determined by
nitrogen absorption in the range of about 0.02 to 0.04 cc./g., said
particles being free from a component having appreciable ability to
crack hydrocarbons. The amount of platinum compound present in the
particles is generally in the range of about 5 -to 150 p.p.m., most
` usually in the range of 50 to 100 p.p.m., expressed as platinum metal.
Another aspect of the invention comprises a cracking catalyst
- - 5 -
~s~gs6
for use in a cyclic FCC cracking process, the catalyst being a mixture
of a major weight percentage, preferably at least 90% by weight, of
particles of a conventional zeolitic aluminosilicate FCC catalyst and
a minor amount of separate particles of said platinum impregnated
microspheres of calcined clay, the latter being present in amount such
that the platinum content of the mixture is in the range of 1 to 50
p.p.m., preferably in the range of about 1 to 5 p.p.m.
Still another aspect of the invention comprises an
improvement in a conventional cyclic FCC process carried out in the
absence of added hydrogen. The improvement comprises the use of a
catalyst which is a mixture of fluidizable particles of a conventional
zeolitic catalyst and separate particles of the novel oxidation promoter
of the lnventlon, the mlxture being introduced into a cracking zone and
subsequently regenerated ln a separate regeneration zone by burning and
recycled into a crack-Lng zone. This embodiment of the invention is
especially adapted for use in cracking units in which essentially complete
combustion of carbon monoxide to carbon dioxlde is feasible. However,
the catalyst mixture may be useful in achieving partial controlled
combustion in units in which complete combustion is not feasible; for
example, in regenerators not capable af withstanding the high temperatures
resulting ~rom complete combustion.
The novel particulate promoter oE the invention has the
desirable properties o mechanical hardness (generally comparable to
that of quality FCC zeolitic catalyst particles) and it is readily
fluidized in conversion zones and in the regenerator. The base material
; for the promoter (calcined microspheres of kaolin clay) is relatively
inexpensive. The apparent bulk density of such promoter (0.9) is
similar to that of conventional equilibrium FCC catalysts and undesirable
segregation of the promoter during storing, shipment or use of a mixture
of the promoter and active FCC catalyst particles is minimized.
-- 6 --
-
3L~5~9S~
Processing advantages over pri~r art methods involving impregnation or
ion-exchange of the entire catalyst tonnage are sel~-evident. Only a
fraction of -the catalyst requires treatment and risks of platinum contamin-
ation and 105s of platinum are minimized. In marked contrast to the
separate promoter particles o~ the Chen patent (supra) which contain a
high surface area zeolitic component, the promoter particles of this in-
vention do not contain zeolite and they have a relatively low surface area.
An unexpected benefit of providing platinum-containing promoter
and cracking catalyst in di~feren-t particles, the promoter being impregnated
on calcined microspheres of kaolin clay, is that the mixture is frequently
more effective in promoting the oxidation of carbon monoxide to carbon
dioxide in a regenerator than would be the case if the same quantity of
platinum were impregnated on the particles of the active cracking catalyst.
D~SCRIPTION OF PREFERRED EMBODIMENTS
The microspheres of calcined kaolin clay used in the production
of the promoter particles are known in the art and are employed as a chemical
reactant wi~h a sodium hydroxide in the manufacture of ~luid zeolitic
cracking catalysts as described ln U. S. 3,647,718 to ~aden et al. In
practice of the instant invention, in contrast, the micr~spheres of calcined
kaolin clay are not used as a chemical reactant. Thus the chemical
composition of the microspheres of calcined clay used in practice of this
invention corresponds to that of a dehydrated kaolin clay. Typically, the
calcined microspheres analyze about 51% to 53% (wt.) SiO2, ~1 to ~5% A12O3,
and from O to 1% H20, the balance being minor amounts of indigenous
i~purities, notably iron, titanium and alkaline earth metals. Generally,
iron content (expressed as ~e2O3~ is about 1/2% by weight and titanium
(expressed as TiO2) is approximately 2%. It is reasonable to believe that
the metallic impurities in kaolin clay which are present in the microspheres
may contribute to the outstanding effectiveness of the platlnum impregnated
microspheres as a promoter for carbon monoxide oxidation.
--7--
;
:,
` . , : . , . ~: . " ' .
9~6
The microspheres are preferably produced by spray during an
aqueous suspension of kaolin clay. The term "kaolin clay" as used herein
embraces clays, the predominating mineral constituent of which is kaolinite,
halloyslte, nacrite, dickite, anauxite and mixtures thereof. Preferably a
fine particle size plastic hydrated clay, i.e!., a clay containing a
substantial amount of submicron size particles, is used in order to produce
microspheres having adequate mechanical strength.
To facilitate spray drying, the powdered hydrated clay is
preferably dispersed in water in the presence of a defloccuLIting agent
exemplified by sodium silicate of a sodium condensed phosphate salt such
as tetrasodium pyrophosphate. By employing a deflocculating agent, spray
drying may be carried out at higher solids levels and h æder products are
usually obtained. When a deElocculating agent is employed, slurries
containlng about 55 to 60% sollds may be prepared and these hlgh sollds
slurries are preferred to the ~O to 50% slurries which do not contain a
deflocculating agent.
Several procedures can be followed in mixing the ingredients
to form the slurry. One procedure, by way of example, is to dry blend the
finely divlded solids, add the water and then incorporate the deflocculating
agent. The components can be mechanically worked together or individually
to produce slurrles or deslred vlscosity characteristics.
Spray dryers wlth countercurrent, cocurrent or mixecl counter-
current and cocurrent flow of slurry and hot alr can be employed to produce
the~microspheres. The air may be heated electrically or by other indirect
means. Combustlon gases obtained by burning hydrocarbon fuel in alr can
be used.
Using a cocurrent dryer, air lnlet temperatures ~o 1200F.
ma~ be used when the clay feed is charged at a rate sufficient to produce
an air outlet temperature within the range of 250F. to 600F. At these
temperatures, free moisture is removed from ~he slurry ~ithout removing
_~_
., . . ~ ~ . . . .
9S6
water of hydration (water of crystallization) from the raw clay ln~redient.
; Dehydration of some or all of the r~w clay during spray drying is, however,
within the scope of the invention. The spray dryer discharge may be
fractionated to recover microspheres of desired parti,rle size. Typically
S particles having a diameter in the range of 20 to 150 microns are preferably
recovered for use in preparing the support for the platinum promoter.
While it is preferable in some cases to calcine the
microspheres at temperatures in the range of about 1600F. to 21C'~0F. in
order to produce particles of maximum hardness, it is possible to dehydrate
the microspheres by calcination at lower temperatures; for example,
temperatures in the range of 100F. to 1600F. 9 thereby converting the
clay into the material known as "metakaolin." After calcination the micro-
spheres should be cooled and fractlonated, if necessary, to recover the
portion which is in desired size range.
Pore volume of the microspheres will vary slightly with the
calcination temperature and duration of calcination. Pore size distribution
analysis of a representative sam~le obtained by nitrogen desorption indicates
that most of the pores have diameters in the range of 150 to 600 Angstrom
' units.
I 20 The surface area of the calcined microspheres is usually
within the range of lQ to 15 m2/g. as measured by the well-known B.E.T.
method using nitrogen ab~orptlon. It is noted that the surface areas of
commercial fluid zeolitic catalysts i,~ considerably higher, generally
exceeding values of 100 m2/g. as measured by ~he B.E.T. method.
Simple impregnation of the calcined microspheres with an
aqueous solution of a soluble platinum compound will su~fice to achieve
uniform deposition of the trace platlnum compound on the spray dried calcined
microspheres since these microspheres have adequate porosity for uniform
depositio~n of trace amoun~s of an i~ regnant. However, the porosity of
the calcined microspheres is sufficiently low to minimize coke deposition ln
'.' .
.! _9_
''i
i
S6
the cracking zone of a FCC unit.
The platinum compound may be one in which the platinum is in
the anion, such as for exa~ple chloroplatinic acid, or the platinum may
be in the cation, such as for example Pt (ethylene diamine) C14. During
impregnation, the microspheres should be agit:ated. Preferably the solution
of platinum compound is applied by means of a spray. Provided the platinum
compound is applied as an aqueous solution oi- sufficiently high concentration,
a drying step will be optional after impregnation. ~efore use or during
use, the platinum impregnated microspheres are contacted with hot air or
steam, possibly converting the platinum compound to an oxide. Any conventional
method for impre~nating platinum on inorganic support material may be used
and sources of platinum other than the specific materials mentioned above
may be ernployed. DT2444911 (supra), U. S. 3,840,514 to Haensel and ~. S.
2,971,904 to Gladrow et al set Eorth procedures that can be used. Such
procedures are modified when necessary to reduce the amount of impregnated
platinum to levels suitable for practice of this inventlon.
The amount of platinum deposited on the microspheres will
depend inter alia on the proportion of impregnated microspheres to be
blended with separate particles of active cracking catalyst and whether
complete or partial combustion of carbon monoxide is desi~ea. Generally,
; from 70 to 95 part~ by weight of catalytically active cracking catalyst
particles are mixed with 30 to 5 parts by weight o~ th~ platinum impregnated
microspheres. Preferably the platinum impregnated microspheres constitute
10% by weight or less of the total mixture since the presence of more than
10% of the promoter particles may result in an appreciable ascrease in ~he
cracking activity of the catalyst. Use of less than about 3 ~ 5% platinum
impregnated microspheres can result in difficulties in securing ~iform
blends. In general, the use of about 4 to 7% impregnated microspheres is
especially preferable.
The level of platinum in a blend of promoter particles and
.
--10--
S6
separate catalyst particles is usually in the range of 3 to 10 p.p.m.
(based on the total mixture) when full combustion is desired~ From 0.5 to
3 p.p.m. may be used for partial combustion. A suitab]e level of platinum
will vary with the design of a particular regeneration system.
In an illustrative example, microspheres of calcined kaolin
clay were produced using a fine particle si~e uncalcined paper coating grade
of hydrated Georgla kaolin clay as a starting material. The clay was formed
into a slurry of about 60% solids using tetrasodium pryophosphate in amount
of 0.5% of the clay weight as a deflocculating agent. The slurry was spray
dried and calcined at a temperature of about 1900F. ~o an essentially
- anhydrous condition. The calcined spray dried microspheres were screened
to recover a desired fraction which had the following particle size
dlstribution:
Tyler Screen Wt. %
15 ~100 1-2
-100 ~200 35-50
-200 +325 30-48
-325 16-18
Surface area was 12.8 m2/g. (B.E.T. method, using nitrogen as an absorbate).
Pore volume (nitrogen absorption) was 0.026 cc./gm.
j~ A 600 gram charge oE the microspheres was placed in a Teflon-
; coated 1-1/2 gallon can provided wfth flights. The can was ro~ated slowly
~35 r.p.m.) while an aqueous solution of chloroplatinum acid containing
400 p.p.m. Pt was sprayed as a fine mlst into the open drum. The concen-
tratlon and amount of impregnating solutlon were calculated to incorporate
60 p.p.m. of platinum on the support without increasing the L.O.I. (loss on
ignition as determined at 1800~F.) above 13.7%.
A sample of the impregnated microspheres calcined clay
(5 parts by weight~ was blended with particles o HFZ-2Q cracking catalyst
~95 parts by weight). The ml~ture (identified as Sample A) had a platinum
. .
~LalSi~1~51~
content of 3 p.p.m.
For purposes of comparison another sample of HFZ-20 cracking
catalyst was impregnated with the solution of chloroplatinic acid in
generally the same manner to provide a catalyst containing 3 p.p.m. Pt
except that the amount and concentration of chloroplatinic acid were
increased. The catalyst sample is identified as Sample B.
A sample of HFZ-20 without a promoter was identified as
Sample C. A typical sample of H~Z-20 analyzes 0.9% Na20, 37.0% SiO2,
59.3% SiO2, 2.4% TiO2, 0.61% Fe203 and 13.0% L.O.I. Surface area is
above 300 m2/g. before steaming.
Catalysts A, B and C were activated and aged by calcination
at 1400F. and 1500F. for 4 hours in an atmosphere of 100% steam and the
steamed catalysts were used in cracking gas-oil feedstock in a micro-
activity test unit. It was found that with the exception of a slight
increase in hydrogen make, catalysts A and B had substantially the same
activity and selectivity as catalyst C. Thus, the presence of platinum
did not materially affect the activity and selectivity of the HFZ-20 catalyst.
In order to determine whether the catalysts containing added
platinum (A and B) were capable of promoting the oxidation of carbon monoxide
to carbon dioxide, the following carbon monoxide conversion test was carried
out with samples of catalysts A, B, a~d C steamed at 1400F. for 4 hours
in an atmosphere of 100% steam.
To carry out the test, a fluidized bed of the sample was
brought to a temperature of 1215F. in the presence of helium and a gas
containing carbon dioxide (8%), carbon monoxide (4%) and oxygen (4%) was
iniected through the catalyst. A~ter a steady state was established, a
chromotograph was used to determine the CO2/C0 ratio in the effluent gas.
Catalysts A and B, both containing impregnated platinum, converted
essentially all of the carbon monoxide to carbon clioxide, while the control
(catalyst C) converted 25% of the carbon mono~ide. Thus, the carbon monoxide
-12-
~LOS0956
conversion test indicated that uncoked catalysts A and B were capable of
catalyzing carbon monoxide burning.
; To compare the effectiveness of platinum promoters during
regeneration, spent catalyst A was ~ixed with fresh catalyst A (steamed
at 1400F.? to provide a blend containing 0.65% coke. The same was done
wi~h catalysts B and C. To stimulate regeneration, a 3 to 4 gram sample
of each spent (coked) catalyst was fluidized and heated to 1215F. in a
hslium atmosphere. Air was then passed through the fluidized bed at-a
- constant flow rate of 215 cc./min. for 5 minutes to burn off the coke. The
gas was collected and the C02/CO ratio was determined by gas chromotography.
Results are summarized below in table form.
EFFECT OF PLATINUM ON REGEN~RATION
OF SPENT FCC CATALYST
C02/CO Ratio Upon
Sample Regeneration
i A - 95% HFZ-20 & 5% Pt impregnated 63
calcined microspheres of
kaolin clay, 3 p.p.m. Pt
B - HFZ-20 impregnated with 3 p.p.m. Pt 49
C - HPZ-20 - no Pt 1.3
Data for the regeneration test show that when catalysts A
and B were used to promote oxidation of carbon monoxide during conditions
stimulating regeneration of a coked catalyst, the catalyst of the invention
(catalyst A) was s-lgnificantly more effective than the catalyst containing
the same amount of platinum impregnated directly on the catalyst particles
(catatlys~ B~. As mentioned above, the data for the CO conversion test
; show that prior to coking, catalysts A and B were both capable of
` ~ catab zing fully the oxidation of carbon monoxide at 1215F. Since the
surface area of the calcined kaolin support for the platinum in catalyst A
is only about 13-~m2kg.while the surface area of the support for the
,~ 3Q platlnum in catalyst B is over 300 m2/ g. a reasonable explanation for
.;,
~ ~ -13-
il :
' t
~5~95~
the superiority of catalyst A is that less coke is present on the support
particles of catalyst A during regeneration with the result that the
platinum is accessible for a longer period during regeneration to burn
carbon monoxide. On the other hand, it is conceivable that the porous
microstructure (minus lO0 Angstrom pores) oE a æeolitiæed HFZ-20 microsphere
or conventional cracking catalyst is such that when the platinum is ion-
exchanged or impregnated thereon (in~o a zeolitiæed microsphere) the
platinum becomes less readily accessible and a diffusion controlled mechanism
may prevail, thus hindering burn-off of CO to CO2.
Results similar to those detailed above were realized when the
platinum impregnated microspheres were blended wlth other zeolitic cracking
catalysts containing a type Y zeolite component, lncluding catalysts
containing rare earth metals.
It is intended that the invention should not be limited to
the details of the examples but broadly as deflned in the appended claims.
-14-
