Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ ~6~39~
BACKGPOUND OF THE INVENTION
Field of the Invention
This invention relates to novel species of crystalline silicates
containing chromia and methods for preparing same. These compositions are
useful as catalysts for hydrocarbon processes, particularly in dewaxing
operations and olefin production.
Prior Art
Molecular sieve crystalline zeolites are aluminosilicates comprised
of a rigid three-dimensional framework of SiO4 and A104 tetrahedra joined
by common oxygen atoms. The inclusion of aluminum atoms in the framework
produces a deficiency in electrical charge which must be locally neutralized
by the presence of additional positive ions within the structure. In
natural zeolites and many of the synthetic zeolites, these ions are
normally alkali metal or alkaline earth cations which are quite mobile
and readily exchanged in varying degrees by conventional techniques for
other cations. The cations occupy channels and interconnected voids
provided by the framework geometry.
United States Patent No. 3,702,886 discloses a new family of
crystalline zeolites, designated as ZSM-5. The ZSM-5-type zeolites have
a composition expressed in mol ratios of oxide as follows:
o~g+o~2M2/no:w2o3 5-looyo2 zH2o
wherein M is at least one cation, n is the valence thereof, W is
either aluminum or gallium, Y is either silicon or germanium, and z
is between O and 40. Members of the ZSM-5 family are disclosed to
possess a random powder of X-ray diffraction pattern having the following
--1--
~L~6.'.'~
significant lines:
TABLE 1
Inter lanar Spacin d(A)- Relative Intensity
P g
11.1 + 0.2 s.
10.0 + 0.2 s.
7.4 + 0.15 w.
7.1 + 0.15 w.
6.3 ~ O.I w.
6.04)
+ 0.1 w.
5.97)
5.56 + 0.1 w
5.01 + 0.1 w.
4.60 + 0.08 w.
4.25 + 0.08 w.
3.85 + 0.07 v.s.
3.71 + 0.05 s.
3.04 + 0.03 w.
2.99 + 0.02 w.
2.94 + 0.02 w.
The above values were determined by conventional techniques
described in the patent.
The patent teaches that ZSM-5-type zeolites are prepared by
hydrothermally crystallizing a reaction mixture of tetrapropylammonium
hydroxide, sodium oxide and an oxide of aluminum or gallium and an oxide
of silicon or germanium.
United States Patent No. 3,941,871 discloses a crystalline metal
10 organosilicate having the composition~ in its anhydrous state, as follows:
~L6.53~2
0-9+0-2 LxR2o+(l-x)M2/no~ oo5Al2o3 >lsio2
wherein M is a metal, o~her than a metal of Group IIIA, n is the valence
thereof, R is an alkylammoniu~l radical and x is between 0 and 1. The
disclosed compositions are synthesized by hydrothermally crystallizing a
reaction mixture of alkylammonium oxides, sodium oxides, water and oxides
of a metal other than Group IIIA. Alumina appears in the product in small
quantities due to reactant impurities and/or the equipment used in the
synthesis. Random X-ray powder diffraction analysis shows the following
significant lines:
TABLE 2
Interplanar Spacing d(A): Relative Intensity
11.1 ~ 0.2 s.
10.0 + 0.2 s.
7.4 i 0.15 w.
7.1 + 0.15 w.
6.3 + 0.1 w.
6.04)
+ 0.1 w.
5.97)
5.56 + 0.1 w.
5.01 + 0.1 w.
4/7- + /08 w.
4.25 + 0.08 w.
3~85 + 0.07 v.s.
3.71 i 0.05 s.
3.04 ~ 0.03 w.
2.99 + 0.02- w.
2.94 + 0.02 w.
United States Patent No. 4,061,724 discloses a crystalline silica,
denominated as "silicalite". Silicalite is prepared by
~6~
01 hydrothermal crystallization of a reaction mixture
containing water, silica and an alkylonium compound such
as tetraethylammonium hydroxide, tetrapropylammonium
hydroxide, or the salts corresponding thereto, such as
05 tetrapropylammonium bromide. Silicalite, after calci-
nation in air at 600C for one hour~ exhi~its the
following X-ray diffraction pattern:
TABLE
: ~-A Relative Intensity
11.1 0.2 v.s.
~:: 10.0 1 0.2 v.s.
.
~: 3.85 ~ 0.07 v.s.
3.~2 ~ 0.07 5
3.76 ~ 0.05 s
: 3.72 0.05 s
Table:4 presents the results of an X-ray
::: 20 diffraction analysis of a silicalite composition after
calcination containing 51.9 mols of SiO2 per mol of
: tetrapropylammonium oxide:
~: 25
'
~.~6~53~
01 TABLE 4
Relative Relative
d-A Intensity d-A Intensity
05
11.1 100 4.35 5
10.02 64 4.25 7
9.73 16 4.08 3
8.99 1 4.00 3
8.04 0.5 3.8559
7.42 1 3.8232
7.06 0.5 3.7424
6.68 5 3.71. 27
6.35 9 306412
5.98 14 3 590.5
5.70 7 3.483
5.57 8 3.445
5.36 2 3.3411
5.11 2 3.307
5.01 4 3.253
4.98 5 ~ 3.170.5
4.86 0.5 3.130.5
4.60 3 3.055
4.44 0.5 2.9810
All of the above compositions have a pore
diameter of approximately 6 Angstroms and are individually
useful in certain hydrocarbon processing applications.
However, ZSM-5-type aluminosilicates are "overly" active
in hydrocracking services, for example, in cracking normal
paraffins from a feedstock for dewaxing purposes. This
high activity results in high gas production and low
liquid yields. Silicalite per se, in contrast, is much
less active and is used primarily as an absorbent for oil
from oil-water mixtures.
~6.53~L~
It is, therefore~ an object of the present invention
to provide a novel composition which is useful for dewaxing feed-
stocks with high liquid yields 3 for the production of olefins,
and for other hydrocarbon conversion processes.
FIGURE
The figure illustrates the ESCA spectra for chromium
in the CZ~ chromia silicates of the present invention and in
silicalite impregnated with chromium obtained in Example 5.
SUMMARY OF THE ~NVENTIO
The present invention provides novel crystalline
chromia silicates which have a silica:chromia ratio, in terms
of mol ratios of oxides of greater than about 20:1, and a random
powder X-ray diffraction pattern characterized by the
diffraction lines of Table 5.
TABLE 5
Interplanar Spacing,
d-A ReIativ:e Intensity
11.1 + 0.2 v.s.
10.0 + 0.2 v.s.
3-85 + 0.07 v.s.
3.82 + 0.07 s.
3-76 + 0.05 s.
3-72 + 0.05 s.
The present invention also provides a process for
hydrocarbon conversion which comprises contacting a hydrocarbon
charge under conversion conditions with the chromia silicate as
catalyst metioned above.
The present invention further provides a process for
preparing crystalline chromia silicate mentioned above, which
process comprises: hydrothermally crystallizing a reaction
mixture containing a quaternary alkylammonium oxide, an oxide
- 6 -
5~
of an alkali metal from the group of alkali metals consisting of
lithium, sodium, potassium or mixtures thereof, chromium oxide
and silica; said reaction mixture having a composition expressed
in terms of mols of oxides as follows:
R20:aM~O:bCr203:Csio2:dH2o~
wherein R20 is a ~uaternary alkylammonium oxide, M is an alkali
metal selected from the group of alkali metals consisting of
lithium, sodium, potassium or mixtures thereof, a is greater
than C but less than 5, c is in the range 1-100, c/b is greater
than 12, and d is in the range 70~500.
- 6a -
~ ,~
- ~ ~L6~
01 The chromia silicates, hereinafter referred to as CZM,
have a composition, expressed in the anhydrous state in
terms of mols of oxides which comprises:
05 R2O:aM20:bCr2O3 cs~io2
wherein R2O is a quaternary alkylammonium oxide, prefer-
ably tetrapropylammonium oxide, M is an alkali metal
selected from the group of alkali metals consisting of
lithium, sodium, potassium or mixtures thereof, preferably
sodium, a is between 0 and 1.5, c is greater than or equal
to 12, and c/b is greater than 20. The ratio c/b will
normally range between 20 and 3000, and is preferably in
the range of 50 to 1000. Said chromia silicate exhibits
:~ 15 the random powder X-ray diffraction lines shown in Table
6.
~; .
:;:
~ : 25
:
--8--
01 TABLE 6
Interplanar Spacing 2e Normaliæed
d (An~strom) (Doubled Bragg angle) Intensities
0511.2 i .2 7.90 100
10.05 ~ .12 8.80 70
9.75 ~ .11 9O07 17
8.99 i .09 9.84
7.44 ~ .06 11.90
6.71 + .05 13.20 7
6.36 ~ .05 13.92 11
105.99 i .04 1~.78 14
5.71 i .04 15.53 7
5.57 ~ .04 15.91 10
5.36 + .03 16.54 3
5.14 + .03 17.25
5.02 03 17.65 5
154.98 l .03 17.81 5
4.61 ~ .02 19.25 4
4.36 + .02 20.37 5
4.25 ~ .02 20.88 8
4.08 02 21.78 2
.01 .02 22.18 3
3.86 ~ .02 23.07 52
203.82 i .02 23.29 32
`~ 3.75 ~ .02 23.73 17
3.72~+ .02 23.73 ' 26
; 3.65 + .02 24.40 12
3.60 i .01 24.76 2
- 3.48 ~ .01 25.58 2
3.44 ~ .01 25.88 4
253.40 1 .01 26.24
3.35 ~ .01 26.60 3
3.31 ~ ~01 26.95 6
3.25 ~ .01 27.43 2
3.05 + .01 29.28 4
2.9g i .01 29.90 9
302.96 + .01 30.22
The X-ray diffraction patterns were obtained by
standard diffractometer methods using a copper target X-
ray tube, a graphite crystal monochromator set to select
1~6S3~.~
01 ~he K-alpha doublet radiation of copper, and a propor-
tional counter tube operating to selectively measure the
reflected K-alpha doublet radiation. The patterns were
recorded with a strip chart recorder and the diffraction
05 peak intensities normalized to a scale of 0 to 100. The
interplanar spacings, d (measured in angstroms), corre-
sponding to the recorded diffraction peaks were
calculated.
The crysta~line chromia silicate is prepared by
; 10 ~lydrothermally crystallizing an aqueous reaction mixture
containing quaternary alkylammonium oxide, chromium oxide,
silica and an oxide of an alkali metal from the group of
alkali metals consisting of lithium, sodium, potassium or
~ mixtures thereof, preferably sodium.
; 15 The reaction mixture preferably has a composi-
tion expressed in terms of mols of oxides, as follows:
O aM2O:bCr2O3:C~iO2:dH2O
; 20 wherein a i5 greater than 0 but less than S, c is in the
range 1 to 100, the ratio c/b is greater than 12 but less
than 800, and d is in the range, 70-500. Preferably, a is
in the range O.OS to 1, c is in the range 2-20, the ratio
c/b is in the range 30 to 600 and d is in the range 100 to
300. Hydrothermal crystallization is preferably conducted
at a temperature in the range of 100 to 200C, more
preferably at 125 to 175C, and still more preferably at
150C. The crystallization is conveniently conducted at
the autogenous pressure of the reaction mixture.
CZM is useful as a hydrocarbon processing
catalyst and ls particularly useful in dewaxing operations
and olefin production.
In such processes, a hydrocarbon charge, such as
a reformate, is contacted ~ith C~M catalyst under conver-
sion conditions.
i ~_61,;;,3~ -
--10--
01 Normal paraffins in the reformate are cracked
and yield substantial quantities of ole~ins, even in the
presence of hydrogen.
Preferably, the reformate is contacted with the
05 CZM catalyst in the presence of hydrogen at a hydrogen
partial pressure in the range of 10 to 27 atmospheres and
at a temperature in the range of 450 to 510C. These
conversion conditions permit the catalyst to be placed to
receive the entire reformer effluent either in a separate
vessel following the reformer unit or as a layered bed of
c~atalyst in the last reformer reactor. A liquid hourly
space velocity in the range of 0.5 to 3 should preferably
be maintained.
The CZM catalyst of the present invention may be
used with or without a matrix or binder. If a matrix is
used, the CZM may be conventionally bound therewith in a
weight ratio of catalyst to matrix of from about 95:5 to
100. The matrix in such cases should comprise substan-
tially nonacidic materials such as alumina or silica. A
preferred binder is alumina which may be peptized,comulled with the catalyst, and extruded.
: DETAILED DESCRIPTION OF PREFERRED E~BODIMENTS
The chromia silicates of the present invention
comprise crystalline structures identiEied by random
powder X-ray diffraction pa~terns similar to those
patterns exhibited by ZSM-5 aluminosilicates and silica-
e. In the present invention, the chromia must bepresent in the reaction mixture during hydrothermal
crystallization. The mol ratio of silica to chromia in
the product composition is greater than 20 and is prefer-
ably in the range 50 to 1000.
CZM may be hydrothermally crystallized from areaction mixture containing appropriate sources of
chromium, silicon and sodium oxides, water, and quaternary
3~
alkylammonium cations having the formula (R4N)~ in whlch R represents an
alkyl group containing 1 to 4 carbon atoms.
Preferably R is an ethyl, propyl or normal butyl alkyl group,
especially propyl. Illustrative compounds which supply the derived cation
in solution, include tetraethylammonium hydroxide, tetrapropylammonium
hydroxide, tetrabutylammonium hydroxide, and the salts corresponding to
these hydroxides, such as the chloride, bromide and iodide salts.
Suitable sources of silica for the reaction mixture include alkali
metal silicates, such as sodium silicate solution, as well as reactive forms
10 of the silica sols, silica gels and fumed silicas. Silica sols, such as
the commercially available, Ludox* brand silica sol which contains 30%
SiO2 by weight, are especially preEerred. Since alumina will be readily
incorporated into the crystalline lattice, care should be taken to minimize
the sources of alumina impurities. Commercially available silica sols
typically contain 500 to 700 ppm A1203, and at least a portion of the alumina
will appear in the final product.
Generally, sodium, potassium or lithium may be added to the reaction
mixture in the form of hydroxides or the corresponding salts thereof.
Alkali metal silicates may also provide all or a portion of the required
metals in addition to serving as a source of silica. Pre~erred reaction
sources include sodium hydroxide, sodium nitrate and sodium silicate
solution or water glass.
Chromium sources include soluble chromium salts such as chromium
chloride, chromium sulfates, and chromium nitrates, the nitrates being
especially preferred. The chromium silicates in the present invention are
preferably crystallized from a basic reaction mixture having a pH in the
range from 10 to 13. To obtain a mixture in this pH range, it may be
necessary, depending upon the source of
*Trade Mark
--11--
~L~ti~3~
:
-12-
01 reactants, to raise the pH by adding additional base to
the mixture te.g. ammonium hydroxide or alkali metal
hydroxides) or to lo~er the pH into the desired range
using an acid (e.g. mineral acids). Sodium, lithium or
05 potassium hydroxides are particularly useful in adjusting
the pH upwards since the alkali metals are also required
as reactants in the crystallization process.
The reaction mixture should preferably comprise,
in terms of ratios of mols of oxides, 0.05 to 5 mols of
sodium, potassium or lithium oxide, i to 100 mols of SiO2,
70 to 500 mols of water and a ratio of mols of silica to
mols of chromia equal to or greater than 12 for each mol.
Preferred reaction mixtures have from 0.05 to 1 mol of
sodium, potassium or lithium oxide, preferably sodium
oxide, 2 to 20 mols of silica, 100 to 300 mols of water
and a ratio of mols of silica to mols of chromia in the
range 30 to 600.
After the reaction mixture is prepared, the
mixture is heated to a temperature in the range 100 to
200C, preferably 125 to 175C, and more preferably at a
temperature of 150C, and maintained at said temperature
and at autogenous pressure until the hydrated forms of CZM
; are formed~ Crystalline hydrated CZ~I will normally form
and precipitate from the reaction mixture within 6 hours
to 6 days, and normally within 48 hours. The product
crystals are separated from the mother liquor, such as by
cooling to room temperature, filtering and washing. Low
sodium or dehydrated forms of the product may be prepared
by conventional techniques from the synthesized crystals.
The following examples are provided to more
fully illustrate the nature of the invention.
EXAMPLE 1
A reaction solution was prepared by dissolving
47.9 grams of tetrapropylammonium bromide in 35 ml of
water and adding to the solution 7.2 grams of sodium
;3 ~l6~
-13-
01 hydroxide dissolved in 30 ml. of water. 8 grams of
Cr(NO3)3.3H2O dissolved in 20 ml of water and 116 grams of
Ludox brand t30 weight percent SiO2) silica 501 were added
to the TPA BR-NaOH mixture with rapid stirring. The total
05 reaction mixture was autoclaved in an open Teflon bottle
at a temperature of 150C and at autogenous pressure for
48 hours. At the end of the hydrothermal crystallization
period, the product crystals were flltered from the solu-.
tion and washed with water. The crystals were dried over-
night at 121C and then calcined for 8 hours at 450C.
They had the X-ray diffraction pattern shown in Table 6
and had a composition in terms of mols of oxide as
0~6Na2O:Cr2O3: 280SiO2 after washing with aqueous N~4NO3.
EXAMPLE 2
2.3 grams of sodium nitrate dissolved in 10 ml
of water and 5.5 grams o Cr(NO3)3.9H2O dissolved in 10 ml
~; o water were sequentially added to 100 grams of a 25
~eight percent solution of tetrapropylammonium hydroxid~
with rapid stirring. 80 grams of Ludox brand (30 weight
percent SiO2) silica sol were added to the above solution
and the total mixture was placed in an autoclave main-
; tained at 144C for two days at the solution vapor
pressure. The product crystals were filtered from the
solution and recovered, exchanged with ammonium nitrate,
water-washed, dried at 121C overnight, and calcined for 8
hours at 450C. X-ray analysis revealed the diffraction
pattern shown in Table 6, above.
The crystals had a composition expressed in
terms of mol oxides as follows:
o.5Na2o:cr2o3:66sio2
,
EXAMPLE 3
In testing the CZM catalyst, a sample of the
chromia silicate/ prepared in accordance with Example 2,
\
6'3~ ~
-14-
01 was mixed with a binder (peptized Ziegler alumina-Catapal)
in a weight ratio of 1 to 1, extruded, exchanged with
ammonium acetate, dried, and calcined at 450C for 8
hours. The exchange and calcination were repeated twice.
S The non-alumina portion of the catalyst had a composition,
expressed in terms of mol oxides, as follows:
0.01Na2OoCr2O3:225SiO2.
A 385C-~ isosplitter bottoms feedstock, having a
pour point of ~33C was passed over the catalyst with
hydrogen at a pressure of 68 atmospheres, a temperature of
350C and a liquid hourly space velocity of 2. Hydrogen
feed to the reactors was maintained at 17.8 liters per
liter of feed~ Under these conditions a 370C+ product
yield of 83.8 weight percent, having a pour point of -30C
was obtained. For comparison purposes, a similar test was
conducted using the same weight ratio of silicalite,
prepared in accordance with U.S. Patent No. 4,061,724, to
Catapal binderO However, in order to obtain a comparable
C4+ product, an operating temperature of 406C was
required, thus dramatically demonstrating the greater
activity of the chromia silicate over the prior art.
EXAMPLE 4
A series of experiments were performed to
examine the activity of CZM, silicalite, and silicalite
impregnated with chromium after synthesis using
Cr(NO3)3.9H2O and standard techniques.
The CZM catalyst was prepared as follows: The
sieve of Example 2 was exchanged five times with 25%
ammonium acetate solution at 80C, water-washed, dried
overnight at 121C, and calcined at 450C for 8 hours.
The exchange, drying, and calcination was repeated.
Silicalite was prepared using the techniques of
U.S. 4,061,724. The catalyst was prepared by exchanging
~3 ~ ~
silicalite four times with 20% ammonium nitrate solution at 80C, water-
washing, drying overnight at 121C, and calcining at 450C for 8 hours.
The chromium impregnated silicalite was prepared by impregnating
the above catalyst with a solution of Cr~N03)3.9H2() by the pore-fill method.
The catalyst was dried overnight at 121C, and calcined at 450C for 8
hours.
Inspections of the three catalysts are given in Table 7.
TABLE 7
Al~ppm) ~a(ppm? Cr(wt %)
CZM 380 <50 0.56
Silicalite 400 ~50 0
Silicalite impregnated with 400 100 0.5
chromium
The catalysts were bound with Catapal* alumina, extruded, dried,
and calcined 8 hours at 450 C. Samples of each were placed in porcelain
crucibles in a calcination pot and treated at 1400 F with a 100% steam
atmosphere.
Steamed and unsteamed catalyst samples were then tested in a
"pulse decane crack-lng test" to determine their cracking activity. The
test prodecure was as follows: 0.1-0.5g of catalyst were mixed with lg of
acid-washed and neutralized alundum and packed in a 3/16" stainless steel
reactor tube with the remaining space filled with alundum. The reactor
contents were calcined for one hour at 450C. The reactor was then placed
in a clam-shell furnace and the reactor outlet connected to the inlet of a
gas chromatograph. The inlet was connected to the carrier gas line of the
GC, Helium was passed through the system at 30 cc/min. 0.04 Microliter
*Trade Mark
-15-
3~
pulses of n-decane were in~ected through a septum above the reactor and
reaction products were determined by standard GC analysis. Blank runs
with alundum* showed no conversion under the experimental conditlons, nor
did a 100% Catapal*alumina catalyst.
A pseudo-first-order, cracking rate constant, k, was calculated
using the formula
K= 1 ln - 1
A l-x
where A is the weight of zeolite in grams and x is the fractional conversion
to products boiling below decane.
Table 8 shows the resulting values of the ln of k as a function
of steaming time at 1400F.
TABLE 8
Ln k a~ter steaming at 1400 F
0 hrs. 6 hrs. 24 hrs.
CZM >O -1.85 -2.70
Silicalite -1~40 -3.00 -4.35
Silicalite impregnated with >0 -2.65 -4.20
chromium
With no steaming, both chromium containing catalysts were very
active. After 6 hours steaming, CZM was about three times as active as
silicalite, while the chromium-impregnated silicalite was only about 1.4
times as active. After 24 hours steaming, CZM was five times as active as
siIicalite, while the silicalite impregnated with chromium had only slightly
improved activity. These data illustrate the significantly different
catalytic
*Trade Mark
-16-
~ 3~653~l~
01 activity obtained by the CZM chromia silicates from low
alumina silicates which have and have not been impregnated
with chromium.
EXAMPLE 5
05 ESCA Analysis of Cr Silicalites
A series of tests were performed to show the
differences between the chromium in CZM chromia silicates
and in silicalite impregnated with chromium.
Samples of CZM and chromium impregnated sili-
calite prepared as in Example 4 (but unsteamed) were
examined in a Hewlett-Packard 5950A ESCA (Electron
Spectroscopy for Chemical Analysis) Spectrometer. The
samples were not bound in a composite. Both samples were
powders and were mounted in the spectrometer by dusting
them onto double-sided sticky tape. Al K~ radiation that
had keen passed through a monochromator was employed as
the excitation source, 2 eV electrons from an electron
flood gun with an emission setting of 0.3 mAmp were used
to compensate for sample charging effects. The pressure
in the spectrometer durinq analysis was about 2xlO 8
torr, For chromium a 50 eV window with 256 points was
scanned, while for silicon, carbon and oxygen 20 eV
windows with 256 points were scanned. The various windows
were scanned several times and then signal averaged to
obtain good signal-to-noise ratios and resolution. The
anaIyzer was caIibrated by setting the Au(4f 7/2) binding
energy (BE) at 34.0~0.1 eV. After accounting for the
sample charging effects the Cr(2p3/2) BE ~as 2 eV lower in
CZM than in chromium impregnated silicalite, while the
Si(2p) and O(ls) BE's of the two samples were the same
within experimental accuracy (~O.leV). The Figure shows
the difference in the Cr(2p) lines for CZM and chromium
impregnated silicalite. The large difference in Cr BE's
3~
-18-
01 indicates that the ch~omium, surprisingly, is in different
oxidation states in the two samples.
Visual inspection of the CZM and the chromium
impregnated silicalite gives further evidence of differ-
05 ences between the samples. After the calcination step ofthe preparation (450C; 8 hr)~ the CZM sample was light
green in color while the chromium impregnated silicalite
was yellow. This shows the increased stability of the
chromium in the CZM chromia 9 il icate as compared to the
chromium impregnated silicalite.
The synthetic chromia silicates can be used as
synthesized or can be thermally treated (calcined).
Usually, it is desirable to remove al~ali metal cation by
ion exchange and replace it with hydrogen, ammonium, or
any desired metal ion. The chromia silicate can be used
; in intimate combination with hydrogenating components,
such as tungsten, vanadium, molybdenum, rhenium, nickel,
cobalt, chromium, manganese, or a noble metal, such as
palladium or platinum, for those applications in which a
hydrogenation-dehydrogenation function is desired.
Typ;ical metal cations can include rare earth, Group IIA
and Group VIII metals, as well as their mixtures; cations
of metals such as rare earth, Mn, Ca, Mg, Zn, Cd, Pt, Pd,
Ni, Co, Ti, Al, Sn, Fe and Co are particularly preferred.
The hydrogen, ammonium and metal components can
be exchanged into the chromia silicate. The chromia
silicate can also be impregnated with the metals, or, the
metals can be physically intimately admixed with the
chromia silicate using standard methods ~nown to the art.
Typical ion exchange techniques involve contac-
ting the synthetic chromia silicate ~ith a solution
containing salt of the desired replacing cation or cat-
ions. Although a wide variety of salts can be employed,
chlorides and other halides, nitrates, and sulfates are
particularly preferred. Representa~ive ion-exchange
:~6S3~
--19--
01 techniques are disclosed in a wide variety of patents
including U.S. Patent Nos. 3,1~0,2~9 3,140,251; and
3,140,253. Ion-exchange can ta~e place either before or
after the zeolite is calcined.
05 Following contact with the salt solution of the
desired replacing cation, the chromia silicate is
typically washed with water and dried at a temperature
ranging from 65C to about 315C. After washing, it can
be calcined in air or inert gas at temperatures ranging
from about 200C to 820C for periods of time ranging from
1 to 48 hours, or more, to produce a catalytically-active
product especially useful in hydrocarbon conversion
processes.
Regardless of the cations present in the
synthesized form of the chromia silicate, the spatial
arrangement of the atoms which form the basic crystal
lattice remains essentially unchanged. The exchange of
cations has little, if any, effect on the lattice
structures
The chromia silicates can be manufactured into a
wide variety of physical forms. Generally speaking, they
can be in the form of a powder~ a granule, or a molded
product, such as extrudate having particle size suf~icient
to pass through a 2-mesh (Tyler) screen and be retained on
a 400-mesh (Tyler) screen. In cases where the catalvst is
molded, such as by extrusion with an organic binder, the
chromia silicate can be extruded before drying, or, dried
or partially dried and then extruded.
The chromia silicate can be composited with
other materials resistant to the temperatures and other
conditions employed in organic conversion processes. Such
matrix materials include active and inactive materials and
synthetic or naturally occurring zeolites as well as inor-
ganic materials such as clays, silica and metal oxides.
The latter may be either naturally occurring or in the
.
. . .
;i.53 ;a~
-20-
01 form of gelatinous precipitates, sols or gels including
mixtures of silica and metal oxides. Use of a material in
conjunction with the synthetic chromia silicate, i.e.,
combined therewith, which is active, tends to improve the
05 conversion and selectivity of the catalyst in certain
organic conversion processes. Inactive materials suitably
serve as diluents to control the amount of conversion in a
given process so that products can be obtained econom
ically without employing other meàns for controlling the
rate of reaction. The chromia silicates can be incorpo-
rated into naturally occurring clays, e.g., bentonite and
kaolin. These materials, i.e., clays~ oxides, etc.,
function, in part, as binders for the catalyst. It is
desirable to provide a catalyst having good crush
strength, because in petroleum refining the catalyst is
often subjected to rough handling. This tends to brea~
the catalyst down into powder-like materials which cause -
problems in processing.
Naturally occurring clays which can be com-
posited~with the chromia silicates of this invention
include the montmorillonite and kaolin families, which
~families include the sub-bentonites, and the kaolins
commonly known as Dixie, McNamee, Georgia and Florida
clays or others in which the main mineral constituent is
halloysite, kaolinite, dickite, nacrite, or anauxite.
~ Fibrous clays such as sepiolite and attapulgite can also
;~ be used as supports. Such clays can be used in the raw
state as originally mined or initially subjected to
calcination, acid treatment or chemical modification.
In addition to the foregoing materials, the
chromia silicate can be composited with porous matrix
materials and mixtures of matrix materials such as silica,
alumina, titania, magnesia, silica alumina, silica-
magnesia, silica-zirconia, silica-thoria, silica-beryllia,
silica-titan~a, titania-zirconia as ~ell as ternary
'
~653~2
-21-
01 compositions such as silica-alumina-thoria, silica-
alumina-zirconia, silica-alumina-magnesia and silica-
magnesia-zirconia. The matrix can be in the form of a
cogel.
05 The chromia silicates can also be composited
with other zeolites such as synthetic and natural
faujasites, erionites, and mordenites (e.g. X and Y).
They can also be composited with synthetic zeolites.
The relative proportions of the crystalline
chromia silicates of this invention and the inorganic
oxide gel matrix can vary ~7idely. The chromia silicate
content can range from about 1 to about 90 percent by
weight but is more usually in the range of about 2 to
about 50 percent by weight of the composite.
Chromia silicates are useful in hydrocarbon
conversion reactions. Hydrocarbon conversion reactions
; ~ ~ are chemical and catalytic processes in which carbon~
containing compounds are changed to different carbon-
containing compounds. Examples of hydrocarbon conversion
reactions include catalytic cracking, hydrocracking, and
olefin and aromatics formation reactions. The catalysts
are useful in other petroleum refining and hydrocarbon
conversion reactions such as isomerizing n-paraffins and
naphthenes, polymerizing and oligomerizing olefinic or
acetylenic compounds such as isobutylene and butene-l,
reforming, alkylating, isomerizing polyalkyl substituted
aromatics te.g., ortho xylene) r and disproportionating
aromatics (e.g.~ tolueneJ to provide a mixture of benzene,
xylenes and higher methylbenzenes.
Thé chromia silicates can be used in processing
hydrocarbonaceous feedstocks. Hydrocarbonaceous feed-
stocks contain carbon compounds and can be from many
different sources, e.g., virgin petroleum fractions,
recycle petroleum fractions, shale oil, liquefied coal,
tar sand oil, and in general any carbon containing ~luid
~L~6~3~
01 susceptible to zeolitic catalytic reactions. Depending on
the type of processing the hydrocarbonaceous feed is to
undergo, the feed can be metal-containing or without
metalsj it can also have high or low nitrogen or sulfur
05 impurities. It can be appreciated, however, that in
general the processing will be more efficient (and the
catalyst more active) the lower the nitrogen content of
the feedstock.
The conversion of hydrocarbonaceous feeds can
take place in any convenient mode, for example, in
fluidized bed, moving bed, or fixed bed reactors depending
on the types of process desired. The formulation of the
~ ~ catalyst particles will vary depending on the conversion
;~ process and method of operation.
lS Using chromia silicates containing hydrogenation
components, heavy petroleum residual stocks, cyclic
stocks, and other hydrocrackable charge stocks can be
~; hydrocracked at temperatures from 300C to 525C using
molar ratios of hydrogen to hydrocarbon charge from 1 to
100~ The pressure can vary from 10 to 5000 psig and the
liquid hourly space velocity from 0.1 to 30. For these
purposes, the chromia silicates can be composited with
mixtures of inorganic oxide supports as well as with
faujasites such as X and Y.
The chromia silicates can be used for catalytic
cracking using ~emperatures from about 260C to 625C~
pressures from subatmospheric to several hundred atmos-
pheres, and other standard conditions.
Chromia silicates can be used to dewax hydrocar-
bonaceous feeds by selectively removing straight chain and
slightly branched chain paraffins. The process conditions
can be ~hose of hydrodewaxing - a mild hydrocracking, or
they can be at lower pressures in the absence of hydrogen.
Dewaxing produces significant amounts of olefins from the
cracked paraffins.
;i53~
-23-
01 Chromia silicates can also be used in reforming
reactions using temperatures from 360C to 600C, pres-
sures from atmospheric to 500 psig, and liquid hourly
space velocities from 0.1 to 20. The hydrogen to
S hydrocarbon mol ratio can be generally from 1 to 20.
The catalyst can also be used to hydroisomerize
normal paraffins, when provided with a hydrogenation
component, e.g., platinum. Hydroisomerization is
yenerally carried out at temperatures from 200C to 375C,
and liquid hourly space velocities from 0.01 and 5. The
hydrogen to hydrocarbon mol ratio is from 1:1 and 5:1.
Additionally, the catalyst can be used to isomerize
olefins using temperatures from 140C to 320C.
Other reactions which can be accomplished
employing the catalyst of this invention containing a
metal, e.g., platinum, include hydrogenation-dehydrogena-
tion reactions, denitrogenation and desulfurization
raactions.
Chromia silicates can be used in hydrocarbon
conversion reactions with active or inactive supports~
wi~h organic or inorganic binders, and with and without
added metals These reactions are well known to the art
as are ~he reaction conditions.
~ ::
.
