Note: Descriptions are shown in the official language in which they were submitted.
11,035
1 ~ 2~77
BACKGROUND OF THE INVENTION
This invention relates to an improved process
for hydrating olefins to form alcohols, and a catalyst
composition useful for such process. More particularly,
this invention relates to an olefin hydration process
utilizing a phosphoric acid catalyst capable of long-term
operation at a relatively high-level of catalytic activ-
ity.
Processes for reactmg olefins with water vapor
at elevated pressures to form alcohols in the presence of
suitable catalysts are ~ell-known in the art. The pre-
ferred catalysts for the reaction generally c~mprise
phosphoric acid impregnated upon a predominantly silic-
eous carrier or support material. Typical of such
support materials are the various forms of calcined
diatomaceous earth which essentially consist of diatoms
of silicon dioxide in intimate admixture with clay or
clay-like materials which serve as bonding agents for
the silica. U.S. Patent Nos. 2,960,477 and 3,704,329,
for example, are descriptive of such olefin hydration
processes.
Although phosphoric acid catalysts of the type
described above have gained general commercial acceptance,
they, nevertheless, have certain disadvantages relating,
primarily, to their relatively short opera~ing life.
This is due, in part, to the tendency of phosphoric acid
to "drool" during normal operation, namely, the aqueous
phosphoric acid tends to seep from the catalyst support
11,03
l~ Z7~7
and flow slowly through the catalyst bed. This adversely
affects the physical integrity of the support to the
extent that i~ begins to disintegrate and cake together
in a relatively short period of time during operation.
This has the effect of plugging up the bed of catalyst
support thereby increasing the pressure drop of the gases
flowing therethrough, decreasing the ef~ective contact
(or surface) area of the catalyst, and, in general,
reducing catalyst efficiency.
U.S. Patent No. 2,496,621, discloses a catalyst
preparation procedure wherein the catalyst support
material is calcined at a temperature in the range of
800-1400C. prior to ~mpregnation with the phosphoric
acid catalyst. This results in an independently strong
catalyst support capable of maintaining its physical
integrity for a relatively long period of time. Un-
fortunately, the catalyst is not sufficiently active to
provide the level of olefin csnversion required fox a
commercial hydration process.
Canadian Patent No. 1076095 describes an
olefin hydration process and catalyst wherein the cata-
lyst support is prepared from a mixture comprising from
about 50-70 (wt.) % diatomaceous earth, a~out 15-25 (wt.)
% bentonite and from about 5-35 (wt.) % of a combustible -
organic filler material, such mixture being calcined at
a temperature of from about 1200 to 1500F prior to im-
pregnation with phosphoric acid thereby forming a catalyst
~19035
2~7~
support capable of maintaining its physical integrity
over a long period of time under normal process operating
conditions. The calcined support is thenimpregna~ed with
phosphoric acid to form ~he suppor~ed hydration catalyst.
Canadian Patent No. 1076095 is also
directed to a process and catalyst wherein the
activity and operating life of the hydration
catalyst is enhanced by using a catalyst support
having a surface area greater than about 12 square
meters per gram.
The level of impurities in catalyst supports,
spec~fically, the concentration of iron and aluminum, has
heretofore gone unrecognized as an important operating
variable affec~ing the activity and operating life of an
olefin hydration catalyst. U.S. Patent No. 2,960,477
to Smith et al discloces an olefin hydration catalyst
comprising a catalyst support impregnated with phosphoric
acid, the support consisting of an admixture of diatom-
aceous earth and clay. The patentees note the fact that
` the presence of iron in the catalyst may promote olefin
cracking. Thus, iron i8 recognized in the art as an un-
des~rable element insofar as it promotes a side reaction
to the principal olefin hydration process. However, in
the absence of any guch side reaction, the presence of
iron would appear to have no adverse effect on the activ-
ity and oper~ting life of æn olefin hydration catalyst.
,
'
11~035
~g 27~
U.S. Patent No. 3,704,329 to Rindtorff et al
attempts to solve the characteristic problem of conven-
tional ealcined diatomaceous earth carriers impregnated
with phosphoric acid, namely, the dissolution of aluminum
oxide from the carrier. The patent is directed to the
use of a bentonite carrier material, normally used for
hydrogenation and dehydrogenation reactions, which is
pre-treated wlth acid to reduce the aluminum oxide content
of the material to about 10 percent or less and thereby
render it suitable for catalytic hydration o olefins.
The starting bentonite material preferably contains an
; aluminum oxide content as high as possible, (e.g., above 16
percent), the purpose of acid pre-treatment being prim-
arily to increase the surface area and pore volume of
the carrier material and, at the same time, improve its
resistance to eros~on by min~m~zing the dissolution of
al~minum oxide from the carrier during normal process
operation.
SUMMARY OF THE INVENTION
The present invention provides an improvement
of the olefin hydration process and catalyst described
in the aforementioned Canadian Patent No. 1076095.
The olefins are contacted with water vapor in the
presence of a supported hydration catalyst which is pre-
pared by forming a mixture of from about 50-70 (wt.) %
diatomaceous earth, from about 15-25 (wt.) % bentonite,
and from about 5-35 ~wt.) % of a combustible organic
filler material, and then calcining the resulting
. '
~ 3 ~3~
~1~27~
mixture at a temperature of from about 1200F to
1500F. Fo~lowing calcination and prior to im-
pregnation of the catalyst support with phosphoric acid,
the aluminum and iron content of the calcined catalyst
support is reduced to a value below about 2,25~/o~ by
weight, of the catalyst support. More precisely, the
collective concentration of aluminum and iron in the
finished catalyst (i.e., following impregnation with
phosphoric acid) is maintained below about 2.25%, by
weight, based on the acid-free catalyst support. The
allowable concentration of aluminum and iron in the
supported catalyst is t~erefore independent of the phos-
phoric acid "loading" of the finished catalyst, i.e.,
the weight fraction of H3P04 in the impregnated catalyst.
The present invention is predicated on the
discovery that the activity and operating life of the
olefin hydration catalysts described in Canadian
Patent No. 1076095 are materially enhanced by ~-
restricting the aluminum and iron content of the
supported hydration catalyst to below the above-
described upper limit. Removal of aluminum and iron impur-
~ties ~in the form of oxides) from the support material is
preferably carried out by contacting the support with a
mineral acid, such as phosphoric, hydrochloric or
sulphuric, at reaction conditions capable of reducing
; the concentration of the oxide impurities in the supportmaterial to the desired level. Thus, for example, a
~ B
11, 035
typical catalyst support containing about 1.5% iron and
3.8% aluminum may be effectively treated with 85 (wt.) %
H3P0~ at a temperature of from about 150C to 200C in a
sealed pressure vessel for a period of time of from about
8 to 15 hours to reduce the concentration of Al plus Fe
in the support to about 2%, by weight.
The removal of aluminum and iron from the
catalyst support to the low levels desired in accordance
with the invention cannot, in general, be accompl~shed
with sintered support materials. That is, the oxides of
aluminum and iron are not readily leached out of a
sintered catalyst support even aiter relatively long
periods of acid treabment at elevated temperatures.
Hence, as a practical matter, the present invention is
res~ricted to non-sintered catalyst supports. It shoul~
be noted, however, that the surface area of the catalyst
support is of no moment for purposes of the present inven-
tion and need not necessarily be above 12 meters2/gram,
the surface area defined by Canadian Patent No.
1076095. Although sintering of the support is
avoided by regulating calcination conditions in the furn-
ace so as to produce a surface area above 12 meters2lgramr
supports having surface areas below such value are
; not necessarily sintered and may be simply "under-
calcinedl', i.e., partially calcined support materials
containing unoxidized filler material The removal
of aluminum and iron impurities from such support
materials is within the scope of the present invention
~ ,
~ 77 11,035
DETAILED DESCRIP ION OF THE INVENTION
The composition of the catalyst support employed
in preparing the olefin hydration catalysts of the inven-
tion is from about 50-70 percent by weight, diatomaceous
earth, from about 15-25 percent by weight, bentonite and
from about 5-35 percent by weight, of a combustible
organic filler material, the above percentages referring
to the composition of the support prior to the calcina-
tion step. A preferred composition in terms of providing
an optimum balance of catalytic activity and mechanical
strength is about 62 (wt.) % diatomaceous earth, about
21 (wt.) % bentonite and about 18 (wt.) % filler material.
During calcination, the organic filler material is burned
out to provide a structure having sufficient porosity to
ensure an even coating of phosphoric acid throughout the
support during impregnation and to allow the reacting
gases to readily contact the internal active sites of
the support during operation. In general, the greater
the percentage of filler material in the support-forming
mixture, the greater the surface area of the calcined
support. It is generally desirable to have as high a
surface area as possible provided the mechanical
integrity of the supported catalyst and the ultim~te
catalyst life are not adversely affected.
11. 9 03~
~L:I~Z777
The combustible organic filler is preferably
cornmeal, but powdered combustible materials such as wood,
flour, starch, carbon black, and the like may also be used.
To attain the desired porosity, the size of the filler
materials admixed with the particles of diatomaceous earth
and bentonite should be within the range of about 500 to
2000 microns, and preferably about 1000 microns.
Diatomaceous earth, the main component of the
catalyst support, is a naturally occurring fonm of silicon
dioxide which serves to provide active sites for the form-
ation of the reactive acid film. ~n especially desirable
form of tiatomaceous earth is man~factured by Johns-Manville
Corporation and is designated as "Celite ~ FC" posRessing R .
surface area of 20-30 meters2/gram. This material has the
following average composition:
ComponentWeight Percent
SiO2 86.7
A12O3 3 3
Fe2O3 1.2
CaO 0.5
H2O, trace metal 8.3
oxides
Bentonite, having a preferred particle size
distribution such that about 90% of the particles are
below a size of about 74 microns, is admixed with the
diatomaceous earth to provide mechanical stren~th to
the catalyst ~upport. ~entonite is a hydrated silicate
having the following average composition:
~ .
~ ~ 2~7q~ 11,035
ComponentWeight P rcent
SiO2 49.0
A123 20.4
Fe2O3 4.1
CaO 1.8
H2O, trace metal 24.7 -
oxides
To prepare the catalyst support, diatomaceous
earth, bentonite and cornmeal, in the proportions recited
above, are admixed with water to form a paste which is
dried and then calcined to burn out the organic filler
and form a hardened support material, typically in the
form of a pellet about 1/8 to 1/4 inch in diameter. The
purpose of the drying step is to substantially reduce
tke moisture content of the pellet prior to calcination.
This is conveniently accomplished by conveying the pellets
over a belt-dryer at a temperature in the range of about
150-340~F. for a period of about 30 minutes. Calcination
may be effected at a temperature within the range of about
1200F to about 1500F depending somewhat upon the ~mount
of filler in the support; the lower the percentage of
filler material, the lower the desired temperature within
the stated range. For a support containing about 17 (wt.)
-i % or~anic iller, the preferred calcination temperature
is about 1350F. The time required for calcination in,
for exsmple, a rotary kiln wherein uniform heating is
provided may vary from about 10-30 minutes depending upon
the temperature employed.
11,035
~l~Z`777
Following calcination and prior to catalyst
impregnation, the support material is treated with an
acid solution to remove aluminum oxide and iron oxide
impurities to the low levels desired in accordance with
the invention. The acid treatment is conveniently
effected with any strong mineral acid; hydrochloric
acid (1:1, about lg.5 wt. %) or phosphoric acid
(85%, by weight) being preferred for this purpose. The
catalyst support pellets are preferably refluxed with
the acid for a period of from about 10-20 hours, or
alternatively, contacted with an acid, such as, 85%
phosphoric acid, at a temperature of from about 150-200C
in a sealed pressure vessel for a period of from about
8-15 hours. Following such acid treatment, the support
pellets are washed with water at 90~C for a period of
about 2 hours until the support material is free of acid.
Impregnation of the calcined support material
is carried out in an aqueous solution of phosphoric acid
containing from about 40 to 80 percent, by weight, of
phosphoric acid. The impregnation can be effected in any
; manner which will result in substantial saturation of the
support material with the acid catalyst. Typically, the
sup~ort material is soaked in an acid solution maintained
at a temperature of about 30C for a period of time of
from about 1/2 hour to 8 hours. Generally, a period of
about 2 hours will suffice. The saturated support mater-
ial is then freed of excess acid and dried at a tempera-
ture below 280C to prevent sintering of the support
material. Dryint is conveniently carried out at a
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~ .
l~$Z777 11,035
temperature of about 180~. The resulting impregnated
catalyst contains from about 30 to 60 percent, by weight,
- orthophosphoric acid based on the weight of the composite
structure, i.e., support material plus acid catalyst.
Lower olefins, such as, ethylene, propylene and
the butenes, may be directly hydrated to the corresponding
alcohols by reacting the olefin starting material with
water vapor in the presence of a catalyst in accordance
with the invention at a temperature within the range of
about 175 to 300C., a water vapor to olefin mole ratio
of about 0.3 to 1.0, and an operating pressure of about
350 to 12Q0 psig. Preferred operating conditions for
the conversion of, for example, ethylene to ethanol are
a temperature of about 270C., a water vapor to olefin
mole ratio of about 0.6, and a reaction pressure of about
1000 psig. Lower temperatures and higher pressures favor
high equilibrium yields. However, if temperatures are
- too low, reaction rates decrease, while unduly high
pressures result in relatively large amounts of polymeric
material in the reaction products. Higher water vapor to
olefin mole ratios result in improved conversion, but at
the expense of increased energy requirements for vapor-
ization.
The caicined catalyst supports prepared in accord-
ance with the following examples were found to contain
12
11,035
1~7 . . ,
iron and aluminum (prior to acid leaching) in the follow-
ing range of concentrations: 1.5 + .25 (wt.) % Fe, and
3.8 ~ .25 (wt.) % Al.
EXAMPLE 1
62 parts by weight of "Celite FC" diatomaceous
earth, 21 parts by weigh~ of bentonite (90% of the
particles being below a size of about 74 microns) and
17 parts by weight of cornmeal (1000 microns), were
admixed with water to form pellets, 5/32" in diameter.
The pellets were dried at a temperature of 350F for
30 minutes in a 3-stage belt-dryer to remove moisture
and then calcined in air for 40 minutes at 1350F. The
surface area of the support as determined by a one-point
BET nitrogen adsorption method was 13.5 m2/gm. Following
calcination, the support was leached by treating the -
pellets with 20~/o hydrochloric acid at 200F for 12 hours
to remave metallic impurities, then washed with water at
90C for 2 hours. The leached support pellets were then
dried at 350F for 1 hour and impregnated with 65 wt. %
phosphoric acid at 70F for 8 hours. The excess acid
was allowed to drain off and the catalyst pellets were
dried under lnert conditions at 350F for 32 hours. The
metal content of the finished catalyst as determined by
atomic absorption (expressed as a percentage of the
acld-free catalyst support) was as follows: 0.51 wt. %
iron and 2.16 wt. % aluminum (=2.67% total o iron plus
aluminum).
,
~ 13 ~ -
11,035
7q7
A gaseous mixture of ethylene and steam in a
molar ratio of 1.8:1 was passed through this supported
catalyst at the rate of 2000 SCFH per cuft of catalyst.
The reactor pressure was 1000 psig and the temperature
of the catalyst bed was maintained at 270C. After
100 hours of operation, ethanol production was 9.1 lbs.
per hour per ft3 of catalyst. At the end of 900 hours,
ethanol production declined to a value of 7.6.
EXAMPLE 2
Examples 2 and 3 demonstrate the improved
activity and catalytic life obtained when the concen-
tration of iron and aluminum in t~e supPort is reduced
to less than about 2.25 (wt.) %.
Support pellets from the same batch used in
Example 1 were subjected to a two-step acid leaching
operation. This comprised an initial treatment of the
support pellets with 20% HCl for 27 hours at 200F,
followed by refluxing with 20% HCl for 6 hours. This was
followed by the washing and drying steps described in
Example 1. Impregnation was then effected with 70%
phosphoric acid at 75F for 8 hours. The excess acid
was then drained and the pellets dried at 900F for
2 hours. The metal content of the catalyst on an acid-free
basis, as determined by atomic absorption,was as follows:
0.2~ (wt.) % Fe and 1.29 (wt.) % Al (a total of 1.55 (wt.) %
; of iron plus aluminum).
14
11,035
77~7
Steam and ethylene were passed through a bed of
the above-described catalyst under process conditions
described in Example 1. The initial ethanol production
of 9.1 lbs. per hour per cuft. of catalyst was unchanged
after 900 hours of operation.
EXAMPLE 3
Catalyst support pellets having the same com-
position disclosed in Example 1, were dried in a tunnel
dryer for 48 hours at a temperature of from about
350-400F. Calcination at 1350F for 30 minutes pro-
vided a sample with a surface area of 14.9 m2/gm. The
support pellets were thereafter leached by refluxing
with 20% HCl for 10 hours to remove metallic impurities.
The leached support was then washed and dried as in
Example 2. The pellets were thereafter impregnated with
70% phosphoric acid at 75F and then dried at 320F for
16 hours. The metal content of the catalyst on an acid-free
basis, as determined by atomic absorption,was as follows:
0.27 (wt.) % Fe and 1.75 (wt.) % Al (a total of 2.02
(wt.) % iron plus aluminum).
Steam and ethylene were passed through a bed
of this catalyst under process conditions described in
E~ample 1. The initial productivity (at the end of 100
hours) was 9.4 lbs. of ethanol per hour per ft.3 of
catalyst. At the end of 900 hours of operation the
ethanol production was essentially unchanged at 9.2.
-
11,035
~1();~7~77
EXAMPLE 4
This example demonstrates an alternate acidleaching procedure for effectively removing metals from
the support.
Catalyst support pellets having the same com-
position described in Example 1, were dried at 350F
for 40 minutes with a belt-dryer and calcined in air
at 1250F for 40 minutes. The surface area of the
support was 13.2 m2/gm. Following calcination, the
support was leached with 85% phosphoric acid for 10 hours
at 160C in a sealed pressure vessel, then washed with
water at 90C for 2 hours. The leached support was then
dried at 140C for 18 hours and impregnated with 62%
phosphoric acid at room temperature for 8 hours. The
excess acid was allowed to drain off and the catalyst
pellets were dried under inert conditions at 110C for
18 hours. The metal content of this catalyst on an
acid-free basis was found to be the following: 0.09 (wt.)%
iron and 0.57 (wt.) % aluminum (- 0.66 (wt.) % total iron
plus aluminum).
Ethylene hydration was carried out in accord-
ance with the procedure described in Example 1. The
catalyst activity was constant over gO0 hours of
operation resulting in a constant ethanol production
of 9.0 lbs. per hour per ft.3 of catalyst.
16
11,035
EXAMPLE 5
This example demonstrates the adverse effect
of sintering the catalyst support with regard to the
removal of metals from said support by acid treatment,
and the effect of the resulting high metal content on
catalyst life.
Catalyst support pellets of similar size and
composition to those described in Exampie 1 were dried
in accordance with the procedure disclosed in that Example,
but were calcined at a temperature of about 1400F for
40 minutes. The measured BET surface area of the support
was a relatively low 8.2 m2/gm. Acid leaching, impregna-
tion and final drying were then carried out as described in
Example 4. Although the leaching process was identical
to that described in Example 4, the resulting catalyst
had a high residual metal content. The metal content
of the catalyst (on an acid-free basis) as measured by
atomic absorption was as follows: 0.42 (wt.) % iron and
2.1 (wt.) % aluminum (- 2.52 (wt.) % total iron plus
alumi.num).
Steam and ethylene were passed through a bed of
the above-described catalyst as described in Example 1.
After 900 hours of operation, ethanol production declined
from an initial value of 9.1 lbs. per hour per ft.3 of
catalyst to about 7Ø
EXAMPLE 6
This example demonstrates that metal removal
may be accomplished in accordance with the invention
from low surface area support materials provided they
are not overcalcined ox sintered.
17
11,035
11~*777
Catalyst support pellets of similar size and
composition to those described in Example 1, were dried
in accordance with the procedure of that Example. The
pellets were calcined at 1350F for 32 minutes3 20% less
time than that employed in Example 1. This resulted in
black specks of unburned cornmeal remaining in the pellets
due to incomplete combustion. The surface area of the
support was a relatively low 9.3 m2/gm. Leaching, drying,
impregnation and final drying were carriecl out as in
Example 4. The metal content of the catalyst on an
acid-free basis, as measured by atomic absorption,was
as follows: 0.27 (wt.) % Fe and 1.22 (wt.) /0 Al (a
total of 1.49 (wt.) /O iron plus aluminum).
Ethylene hydration was carried out under the
process conditions described in Example 1. The ethanol
production rate remained invariant over 900 hours of
operation at 8.7 lbs. per hour per ft.3 of catalyst.
18
