Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~973~2
This invention relates to a catalyst comprising a porous carbon
particulate support formed from carbon black spheres in packed relationship
and a carbon binder, and, carried thereon, at least one activator. ~lore
particularly, this invention relates to porous carbon catalysts of controlled
pore size distribution and to improved catalytic processes employing same.
This application is divided from applicant's copending Canadian
application, Serial No. 246,462 filed on February 24th 1976. Application
Serial No. 246,462 is directed to a porous carbon particulate comprising
carbon black spheres in packed relationship and a carbon binder, said spheres
having a particulate size in the rang~ of about 80 to 5000 angstrom units and
said particulate having pore size distribution exhibiting peaks at a pore
raclius in excess of 10 angstrom units. Furthermore Application Serial No.
246,462 is directed to a process for preparing porous carbon particulates as
hereinbefore defined which comprises uniformly admixing carbon hlack spheres
having diameters in the range from about 80 to about 5,000 angs*rom units with
carbonizable binder in a volatile mixing medium, forming the mixture into
shaped particulates, removing said mixing medium by volatilization, and
carbonizing said binder.
Carbons containing macropores can be useful as catalyst supports,
20 particularly where large reactant molecules, such as those in the pharmaceutic-
al and petroleum industries are involved. For example, such a carbon particle
activated with a noble metal such as platinum or rhodium, could be used for
catalyzing hydrogenation reactions of molecules containing several benzene
rings.
; Porous carbons 'nave been obtained in the prior art by activation of
a suitable material, such as coal- or wood charcoal, with oxidizing agents.
These oxidizing agents, e.g. 2~ CO2, steam, and the like, react away portions
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of the carbon, leaving behind pores. Carbons with controlled pore size
distribution cannot be made by this procedure since new pores are continuously
formed while existing pores are constantly enlarged. This results in a wide
range of pore sizes, including many small pores, i.e. well below 20 angstrom
units, as activation is continued. Thus, it has been difficult to obtain
porous carbons containing predominantly transitional pores (diameter 20-200
angstrom units~ as well as carbons having a narrow range of specific pore
sizes.
In addition to the problem of controlling pore size distribution in
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prior art carbons, the reacting away of carbon to provide pores creates
additional problems. When large pores are desired in the carb~n, ~he reacting
away of the carbon weakens the mechanical strength of the final structure.
The reacting away of carbon increases the percent of ash present on the residu-
al carbon and ash contents of 5-lO weight percent are normal.
Thus, there continues to exist the need for substantially pure car-
bon structures that have desirable levels of porosity or controlled pore
size distribution and are free of or improved with respect to deficiencies
of the prior art carbons. Such a development would fill a long-felt need
in the art and provide a notable advance in the art.
Accordingly, the present invention is directed to providing a catalyst
comprising an activator carried on a porous carbon structure having pores
of controlled size distribution.
In accordance with the present invention there is provided a catalyst
comprising a pOTOUS carbon particulate support comprising carbon black spheres
and a carbon binder, said spheres having a particle size in the range of about
80 to 5000 angstrom units and said particulate having a pore size distribut-
ion exhibiting peaks at a pore radius in excess of 10 angstrom units and,
carried on said support, an effective amount of an activator. Preferably,
the particula~e will have a composltion of at least 99 weight percent carbon.
In preferred embodiments, the carbon particulate will exhibit pore volume in
tke range of about 0.2 to 1.0 cubic centime~ers per gram with pore size dis-
tribution showing-peaks at a radius of at least 10 angstrom units and
~ fre~uently showing peaks at several values of pore radius and, more preferably,
-~ will have a pore volume of at least 0.4-1.0 cubic centimeters per gram. Pre-
ferred carbon particulates will have a pore size distribution exhibiting peaks
in the range of radii of about 10-250, more preferably 40-100, angstrom units.
:
In accordance with the present invention, there is also provided
a process for the cataly~tic reduction of 6-hydroxy hydronaphthacenes so as to
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form the cor-responding 6-deoxy derivative thereof which comprises reducing
a polar solvent solution of a 6-hydroxy hydronaphthacene with hydrogen in
the presence of the catalyst composition as defined above until about one mole
of hydrogen has been absorbed for each mole of starting material used, and
recovering the 6-deoxy derivative so formed. In still another preferred
embodiment, the support will contain less than 1 weight percent of ash.
In yet another preferred embodimen~, the carbon black spheres used to prepare
the support have an average diameter in the range of 80-300 angstrom units.
In another aspect, the present invention also provides a process
for the catalytic reduction of 2,4-dinitrotoluene to 2,4-diaminotoluene which
comprises reducing a polar solvent solution of 2,4-dinitrotoluene with hydro-
gen in the presence of the catalyst composition as defined above until the
corresponding 2,4-diaminotoluene is formed and recovering the 2,4-diamino-
toluene so formed.
In accordance with the present invention, pores of the carbon partic-
ulate are formed by packing together of suitable carbon black spheres and bind-
iDg the spheres together in packed relationship with a carbon binder. The use
of the carbon binder allows the carbon particulate to-possess improved
mechanical strength. When the carbon black spheres packed and bonded together
are of substantially the same size and relatively small, a narrow range of pore
size distribution will arise and the particulate will possess good mechanical
strength. The particular range of pore sizes~and distribution thereof will
vary with particle size of the carbon black spheres selected and the variations
which occur within a designated size. Thus, if larger carbon black spheres
are used, the interstitial space or pores will be larger, while the use of
spheres of varying diameter will result in a wide range of pore sizes.
The present inven-tion, by use of the carbon binder, provides, carbon
particulates of good mechanical strength in conjunction with large pore sizes.
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In prior art carbon structures, when large pores are desired, extensive
oxidation is necessary to provide the pores and the loss of carbon thus
occasioned greatly weakens the rasulting structure.
The carbon particulates in the present invention will, in preferred
embodiments, have a large surface area resulting from pores in the transitional
range, i.e. 20 to 200 angstrom units, and from macropores, i.e. pores greater
than about 200, for example about 250, angstrom units. The number of pores
in the transi~ional and macropore range will be much greater than can be
achieved by the prior art procedures.
Since the carbon black spheres used in the fabrication of carbon
particulates of the present invention are of a high state of purity, the
resulting `particulates will be much purer than prior art carbon structure
obtained by the conventional oxidation procedures. Normally the prior art
structures contain from 5-10 weight percent of ash. In addition, since the
carbon particulates of the present invention are prepared without the use of
oxidizing agents to react away carbon, the carbon particulates of the present
invention will contain considerably less surface oxygen-containing groups
than the conventional carbon structures.
Carbon blacks are formed by the thermal decomposition of gaseous and
liquid hydrocarbons. Two main manufacturing processes are employed. In the
c~annel process, carbon black is collected by impingement of small, natural
gas difusion flames on cool channel iron surfaces. ~y al~ering the size of
the burner tip and its distance from the channel surface, the particle size
of the carbon black can be Yari~d.
The furnace combustion process, which currently produces the greater
amount of carbon black~ uses larger diffusion flames to combust natural gas
and/or liquid hydrocarbons in firebrick-lined furnaces. Carbon black with con-
siderably larger p Fticle size than channel black can be produced.
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Carbon particles useful in the present invention may be of a-ny shape
that can be packed and bonded together to provide particulates which have
the desired porosity. Particularly suitable are available carbon blacks
made by the above processes, which generally have an average diameter from about
80 to 5000 angstrom units and a porosity that varies with the specific pre-
parative method employed. These carbon blacks are revealed by electron
photomicrographs to consist of ultimate particles which appear to be essenti-
ally, spherical. For convenience, therefore, in the present application
and claims, the carbon black particles are referred to as spheres but it is
to be understood that the present invention is inclusive of other shapes,
such as oval-shapes, round-corned squares, rectangles, triangles, and
the like as long as such particles upon packing and bonding give rise to
the porosity desired.
Carbon black spheres useful in the present invention may be selected
from any that are commercially available. Selection is based on the
porosity and pore size distribution desired in the carbon particulate to
be provided in accordanc-é with the present~invention. When small pores of a
narrow pore size distribution are desired, car~on black spheres of small
particle size and narrow variation in particle size are selected. When
large pores are desired, carbon black spheres of large particle size are
selected. When a wide range of pore sizes are desired, mixtures of carbon
black spheres varying particle sizes are selected. It is to be noted that
large carbon black spheres can provide a wide range of pore size distribution
as ~ell as large pores.
In addition to the carbon black spheres, it is also necessary to
employ a binder for the spheres that are to become arranged in packed relation-
ship. The binder is a substance which when heat-treated in an inert or non-
oxidizing atmosphere yields a high proport on of carbon. Generally, a carbon
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yield greater than about 20 weight yield is desirable when heat-treatment
is carried out at 600C. in an atmosphere of nitrogen. Carbon yield is
the weight of carbon residue derived by the weight of starting material and
multiplied by 100. Materials which meet this qualification include polymers
such as poly(~urfuryl alcohol), polyacrylonitrile; resins such as phenol-
formaldehyde, phenol-benzaldehyde; and certain natural materials such as
coal tar pitch. Preferably the binder will be a thermosetting resin . Enough
binder is required to hold the carbon structure together after carbonization
of the binder. Normal ratios of carbon black spheres to binder will be
from about 10:1 to 01:1, preferably 5:1 to -1:1, on a weight basis based on
the amounts of materials employed prior to heat-treatment to carbonize the
binder.
It is also necessary to employ a mixing medium to provide intimate mix-
ing of the binder and the carbon black spheres. Preferably the mixing medium
will be a solvent for ~he binder but it is possible to employ the binder in
emulsified or dispersed form in the mixing medium. The mixing medium should
be volatile enough so that gentle heating ~100-150C.) will effect volatiliza-
tion and eliminate the possibilities that the mixing medium will interfere with
or take part in carbonization of the binder. Suitable mixing media include
acetone, methyl isobutyl ketone and other ketones, benzene, pyridine, water
and the like. The-amount of mix mg medium should be enough to ensure intimate
mixing and may vary widely. Generally the amount of mixing medium will be
such as to provida the binder as about a 5 ~o 50 weight percent solution
or emulsion, preferably about l0 to 20 weight percant solution.
Once the carbon black spheres, ~he binder and the mixing medium are
selected and intimately admixed and the resulting composition is processed so
as to pack the carbon black particles into a suitable structure. Such
processing may involve extrusion, pelletizing, pilling, tabletizing and such
oth~r forms of molding as are conventionally employed in forming structured
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particles. It is also possible to employ rolling mills andflakers to provide
a formed structure of packed carbon particles although such procedures do not
usually form uniform par~icles as in the case of molding. It is generally
preferred to employ extrusion to obtain the carbon structure. The carbon
structure thus obtained is referred to as a "green body". The green body
is subjected to carbon zation at elevated temperature in an inert or non-
-oxidizing atmosphere so as to convert the binder to carbon. The resulting
carbon structure may be utilized in the form obtained or it may be subdivided
by crushing or grinding, if desired, If can also be further modified by
treatment with an oxidizing agent, if desired, although it is generally pre-
ferable to take advantage of the desirable properties achieved in the absence
of oxidation of the carbon structure.
As has been indicated, the carbon structure in the present invention
can be prepared in a wide variety of pore volume and pore size distribùtion.
In particular embodiments, ~he carbon structures will have a larger surface
area in the large pore region than previously available carbons, the large
pores occurring in a narrow size range, if desired. Such a carbon structure
is very useful as a selective adsorbent when large molecules are to be ad-
sorbed. ~his type of carbon, by virtue of its method o~`preparat~n will also
have a much lower ash content ~impurity level) than conventional oxidized
carbons.
~ he catalyst of the present invention comprises the carbon support
described and, carried thereon, an effective amount of an activator. The
actlvator and amount thereof employed will depend upon the particular reaction
to be catalyzed and the rela~ive effectiveness of the ac~ivator in the react-
ion. There are numerous reactions that are effectively catalyzed by supported
activators and many wherein carbon is a useful support. In general, any
catalyst composition based on a carbon support which is known to be useful
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in the prior art will be advantageously prepared using the carbon support of
the pr0sent invention because of the greater proportion of pores of larger
radii of the present supports and the attendant reduction in wasted catalyst
material, especially where large reactant molecules are involved. Thus,
no new teachings as to activators or amounts thereof are necessary since
the present invention contemplates conventional activators on an improved car-
bon support in the conventional reactions.
The catalys~ compositions of the present invention exhibit improved
activity in conjunction with hydrogenation reactions and are illustrated in
this type of reaction. Particularly effective activators in this type of
reac~ion are the platinum met~lsJ which include ruthenium, rhodium, palladium,
osmi-um,- iridî~m, and!platinum. Effective amounts may range from about a
thousandth to about 10 ~eight percent or more, depending upon the reaction
m volved and the metal employed. In such reactions, activator usage and amounts
will conform to conventional teachings with improved activity being obtained
by use of the support of the present invention. Preferred reactions are
in the reduction of 6-hydroxy hydronaphthacenes, as described in United States
; Patent 3,019,260, issued January 30, 1962 to McCormick et al. and related com-
pounds. Another preferred reaction is in the reduction of 2,4-dinitrotoluene
and related compounds to the corresponding diamines.
; It is also known that catalysts based on carbon supports are useful
in hydrodesulfurizatlon of petroleum residua.~ In such reactions, a combinat-
ion of an activator and promoter are generally employed. The activator is
generally selected from molybdenum and tungsten and the promoter from
cobalt and nickel with the metals being in the form of their sulfides in use.
The invention may be ~urther understood by re~erences to Figure 1
which shows comparative pore size distribution of various carbons and Figure 2
which shows comparative effectiveness of catalysts prepared using as substrates
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carbon particulates of the present invention and typical prior art carbon
particulat~.
The invention is more fully illustrated by the examples which follow
wherein all parts and percentages are by weight unless otherwise specified.
In the examples which follow, reference is made to certain physical
properties of the particulate supports obtained. These properties are obtained
in accordance with conventional methods employed in the art of catalyst supports.
Pore volume may be obtained by mercury penetration or water adsorp-
kion. The latter is a preferred method because it is easily performed and
has an accuracy of - 10%, In the wa~er adsorption procedure, a small
quantity of support (1-2 grams) is weighed into a glass dish. Water is slow-
ly poured onto the support until no more is adsorbed. Excess droplets are care-
fully removed by blotting and a reweighing is made. Assuming that one gram
of water occupies one cubic centimeter, the pore volume is calculated from
the initial and final weights of the support.
Surface area is measured by a low temperature nitrogen adsorption
technique which is reported in J. Am. Chem. Soc., 60, 309 ~1938), with
; modifications as reported in Anal. Chem. 30, ~1958) and Anal. Chem., 34,
1150 (1962).
Comparative Exam~le A
Into 12 milli iters of water were added 13 grams of carbon black
spheres having an average particle diameter of 120 angstrom units and a sur-
face area of 850 square meters per gram. After hand mixing, the resulting
composition was extruded through a hole of 1/16 inch diameter using a piston-
type extruder operating at a pressure of 2000 pounds per square inch gauge.
The resulting ext~udates were dried in air at 110C. and then hea~ed in
flowing nitrogen at 600C. for 1 hour. The product was obtained in the form
of cylindrical pellets. Properties are given in Table I.
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Example 1
A furfuryl alcohol polymer was prepared by mixing 2D0 milliliters
of water, and 1 milliliter of concentrated H2S04. The mixture was heated
at 90C. for 10 minutes. The dark polymer obtained was washed twice with
water and then stored in a closed bottle.
In 100 ml. of acetone was dissolved 10 grams of the furfuryl alcohol
polymer thus prepared. The resulting solution was added to 40 grams of car-
bon black spheres having an average particle diameter of 850 square meters per
gram. Th`e resulting composition was thoroughly mixed using a *Sunbeam Mix-
master. The mixture was then extruded through a hole of 1/16 inch diameter
using a piston-type extruder operating at 800-2000 pounds per square inch
gauge.
The resulting extrudates were heated overnight at 110C. to volatil-
ize all of the acetone present and then carbonized in a tube furnace under
flowing N2. A temperature of 600C. was reached in about 1 hour and held
for 1 hour. The extrudatss were then cooled to room temperature under
flowing nitrogen. The product was obtained in the form of cylindrical pellets.
Properties are also given in Table I.
Example 2
The procedure of Example 1 was repeated in every essen~ial detail
except that 20 grams of a commerical phenol-formaldshyde resin was substituted
for the furfuryl alcohol polymer of Example 1 and the extrusion pressure was
2400 psig. Propertics of the resulting pellets are also given in Table I.
*Trademark
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Table I
Properties of Carbon Particulates
Binder Pore Crush
Example Binder Amount* Volume** Strength***
Comp. A None 0 1.00 1;2
1 Poly~furfuryl 25 0.99 5.4
alcohol)
2 Phenol-formal- 50 0.62 7.7
dehyde resin
Notes: *Weight % based on weight of carbon black
**Cubic Centimeters per gram
***Pounds -
Table I illustrates the impor~ance of the binder in obtaining improved
particulate strength. It can be seen that use of 25% binder resulted in
a 4.5 fold increase in strength with essentially no loss in pore volume. Use
of higher amounts of binder results in further increases in strength but
results in lower pore volumes. Thus, if lower pore vol~nes can be tolerated,
higher binder usage may be desirable.
Example 3
~ In 75 ml. of acetone were dissolved 7.5 grams of poly~furfuryl alcohol)
; prepared~as in Example 1. To ~his solution were added 30 grams of the carbon
black spherés as used in Example 1. Ater thorough mixing, the resulting
composition was extruded as in Example 1 using 250-500 psig extrusion pressure.
The extrudates were dried overnight and then carbonized as in Example 1.
Properties of the resulting pellets are given in Table II and Figure 1.
~Comparative Example B
; For comparison purposes, a commerical available carbon prepared by
oxidation of carbon was selected. This carbon is sold under the tradename
Darco Granular and was in the form of grains 12 x 20 mesh. Properties are
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also given in Table II and Figure 1.
Comparative Example C
For comparative purposes, another commercially available carbon
prepared by oxidation of carbon was selected. This carbon is sold under the
tradename *Columbia Type L and was in the form of grains 12 x 20 mesh.
Properties are also shown in Table II and Figure 1.
Table II
Properties of Carbon Parti~ulates
Pore Surface Crush
Example Volume*Area** Strength***
3 0~92 530 3.1
Comp. B 1.07 580 2.3
Comp. C 0.86 1235 5.7
Notes: *cc/gram
**M2/gram
***lbs.
In Figure 1 are shown the pore size distribution for the carbons
of Example 3, Comparative Example B, and Comparative Example C as obtained
by mercure porosity ~ ee Orr, C., Powder Technol 3, 117 ~1969-70)~ . In
the figure, the change in pore volume with respect to the change in the natural
logarithm of the pore radius is plotted against the logarithm to the base 10
of the pore radius. As can be seen by thè figure, the pore size distribution
curves illustrate the major diference of carbon particulates of the present
invention, which have many ~more pores in the region of radii of 40-100
angstrom units while many of the pores o ~he comparative carbons are too small
to be measured by mercury penetration.
In these examples, a series of carbon particulates were prepared
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following the procedure of Example 3 in every essential detail except that
carbon black spheres of different particle sizes were employed in separate
preparations. Proper~ies of the carbon black spheres employed and of the
resulting carbon particulates are given in Table III.
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It can be seen from Table III that the physical properties of the
catalyst particulates of the present invention may be varied by varying the
size of the carbon black spheres or the ratio of spheres to binder. It is evi-
; dent that the pore size of the carbon particulates can be shifted toward
larger sizes by using carbon black spheres of larger average particle size.
Example 8
In this example a catalyst was prepared by depositing rhodium metalon catalyst particulates prepared in accordance with Example 3.
In 20 ml. of water were dissolved 3.7~ grams of RhC13.3H2O and the
resulting solution was added to 180 ml. of dimethylformamide in a 500 ml.
bottle. To the mixture was added 10.5 grams of catalyst particulate of Example
3 and the mixture was hydrogenated at 50 psig using a Parr shaker to deposit
rhodium metal on the carbon particulates. l~hen H2 uptake was complete, the
catalyst was filtered and washed with water, and stored in an approximately
50% water-wet state.
Comparative Example D
In this example a catalyst was prepared by depositing rhodium
metal on commercially available caTbon particulates prepared by conventional
oxidation procedures to provide porosity.
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The procedure of Example 8 was followed in all essential details
;~ except that the carbon particulates were those commercially available under
the tradename *Norit SGX.
Example 9
In this example, the catalysts prepared in Example S and Comparative
Example D were evaluated in the process of catalytic reduction of 6-hydroxy
hydronaphthacenes, as described in United States Patent No. 3,019,26Q, issued
:
January 30, 1962 to McCormic~ et al. For testing, catalysts were prepared
as in Example 8 except that the amount of RhC12.3H20 was varied so that
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catalysts wcre obtaincd i~hich contained either 6% metal or 12% metal based
on the total ~eight of the catalyst composition. The catalyst was added
in the amount of 0.003 or 0.006 troy ounces of rhodium metal depending on
whetller the catalyst contained 6 or 12~ metal, respectively to 40 ml. of
methyl cellosolve*and reduced at 35C. for 1 hour and 40 psig hydrogen pres-
sure using a Parr shaker. A solution containing 6-demethyltetracycline dis-
solved in mcthyl cellosolve was then added to provide a concentration of 60
grams per liter of 6-demethyltetracycline. The solution was then hydrogenated
at 35C. for 1 hour and 40 psig. hydrogen pressure. After 1 hour of reduction,
samples were taken for analysis and concen~rations of reactant and product,
6-demethyl-6-deoxytetracycline. Results are given in Table IV.
Table IV
Catalytic Reduction of 6-Demethyltetracycline
CatalystRhodium Conversion Selec~ivity To
of ~%)* % After 6-Demethyl ~-
Exam~le 1 I-lour Deoxytetracycline
Comp. D 6 45 0.80
9 6 57 0.88
Comp. D 12 55 0.81
9 12 66 0.84
* Percent based on total of catalysts composition
The data of Table IV sho~ that catalysts prepared using as carriers
the carbon particulates of the present invention provide both a greater activity
and greater selectivity than similar catalysts prepared using conventional
carbon supports. Note that the catalyst of the invention is more active
at ~% metal than the comparative catalyst at 12% metal. It is believed
that the superior results achieved by catalysts prepared by use of carbon
particulates of the present invention is due primarily to the increased number
of pores in the 50-200 angstrom units range of pore radii since these pores
*Trademark for ethylene glycol monomethyl ester.
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would be large enough to allow unrestricted entry of the large r~actan* mole-
cules.
Example 10
Using the carbon particulate prepared in accordance with Example 3,
a catalyst was prepared.
To 100 ml. of water was added 0.17 gram of PdC12 (60% Pd) and then
4.0 ml. of 10% aqueous HCl was added. The composition was stirred for
about 40 minutes to dissolve the PdC12. To the solution was then added 4.9
grams of the carbon particulates of Example 3 in a particle size of 40 x 60
mesh and an additional 15 minutes of stirring was effected. The pH of
the mixture was raised to 9.5-10.5 by the addition of 2M NaOH. The pH
was maintained for 15 minutes by dropwise addition of NaOH as necessary.
A total of 2.5-3.0 ml. of caustic was required. The catalyst was -then
separated by filtration and washed with 300 ml. of water. The water-white
filtrate indicated that all of the palladium was taken up by the carbon. The
~; catalyst was bottled and stored in a state of 50% water-wet. Before use,
an aliquot was dried 30 minutes at 125C. to determine its actual wetness.
Comparative Example E
The procedure of Example 10 was followed in ~very material detail
: :
except that in place of the carbon particulate prepared in accordance with
Example 3, there was substituted the carbon particulate of Comparative Example
C in a particle si~e of 40 x 60 mesh.
Example 11
; In this example, the catalysts prepared in Example 10 and Comparative
~; Example E were evaluated in the process o catalytic reduction of 2,4-dinitroto-
;~ luene.
: .
In a mixtu~e o~ 10 ml. of water and 60 ml. of isopropanol in a 500
ml. Parr bottle was dissolved O.~.I gram ~0.005 mole~ of 2,4-dinitrotoluene.
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Enough catalyst in the 50% water-wet state was added to provide 0.20 gram o~
catalyst on a dry basis, the catalyst corresponding to 2% Pd on carbon.
~he bottle was attached to the Parr hydrogenator and flushed 3 times with
hydrogen. It was then pressurized with hydrogen to 40 psig and isolated.
Shaking of the bottle was carried out and the extent of reaction was followed
by noting the hydrogen-pressure drop on the gauge. ~he reaction bottle was
maintained at 35 - 0.5C. using a thermostated water jacket. Results of the
reactions are shown in Figure 2.
From Figure 2 it can be seen that the reaction is complete in
approximately 45 minutes when the catalyst prepared in accordance with
Example 10 is employed. On the other hand, when the catalyst prepared in accord-
ance with Comparative Bxample E is employed a reaction time of approximately
115 minutes is required. Again, it appears that the superior results obtained
with the catalysts of the invention is due primarily to the wide pores it
contains and to the smaller mass transfer limitations imposed thereby.
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