Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIXED BED CATALYST
FIELD O~ TE~E INVENTION
The present in~ention relates to a ~ixed bed
catalyst, and more particularly, to a fixed bed catalyst
which allows a fluid to pass therethrough without large
lesistance, and which produces and maintains a large con~act
area between the fluid and the catalyst, and fu~thermore,
when the fluid contains a gas and a liquid, between the gas
and ~he liquicl.
` BACKGROUND O~ THE INVENTION
Activated carbon has heretofoTe been used as a
catalyst support in a powdery or granular :Form. Furthermore,
acti~ated carbon powder o grains are solidified together
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wi-th ac-ti~r~ catalyst compo~en~s or components, which can be
~; 15 activated later,~by means of compression molding or the like
to produce a porous solid product si~ilar tD a sintered
metal. The porous solid product thus obtained has been used,
~or example, as an ~lectrode in a fuel cell.
These porous solid catalysts, howe~e~, produce
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large resis-tance when a flud is passed therethrough, and
cannot be used in a tubular reactor in~which a reaction is
carried out while ~lowing a ~luid over a long distance.
Thus, many d~f~:iculties have been encoun~ered in utilizing
such pOTOUS solid catalysts in other industrial applications.
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Catalytic reaction equipment generally used in the
chemical industry can be divided into a fixed bed reactor
and a fluidized bed reactor. Such a fixed bed reactor is
widely used in a gas pllase fixed bed reaction system, for
example, in hydrogenation reactions such as the production
of aniline from nitrobenzene and the production of cyclohexane
from benzene and, furthermore, in hydrogenation reactions in
petroleum refining. Also, hydro-desulfurization of heavy oil
is carried out in a liquid phase fixed bed reaction system.
The ixed bed reactor has the advantages that means
adapted to separate ~he catalyst ~rom the reaction product
is not needed~ and a reaction can be carried out at a high
catalyst concentration. In the fixed bed reaction equipment,
however, it is required that the catalyst be used in the form
of pellets prepared by solidifying the catalyst or in the
orm of coarse grains. This oten gives rise to problems
such as brealcage of the pelle~s or grains and a reduction in
activity which is caused by sinterlng o~ the surface of the
pellets or grains. Furthelmore, in employing these pellets
or grains, problems arise in tha~ the flow and diffusion of
a 1uid in the interior thereo are not smooth because of
their coarseness even though they are porous, and in that
since their surace areas as a particle are small, the
contact between gas and liquid is disadvantageously in-
suicient.
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A fluidized bed reactor is used in hydrogenation
of alkylanthraquinone for the production o hyd~ogen per-
oxide, hydrogenation o~ glucose for the production o
sorbitol, and so forth.
In the fluidized bed reactor, a finely dividea
catalyst can be used and, thereore, it has the advantage
that the contac~ between the catalyst and a fluid such as a
liquid and a gas can be enhanced. Furthermore, there is no
danger o the ca~alyst losing its activity by the accumula-
tion of heat due to the reaction in the catalyst grains.
The fluidized bed reactor~ however, requires means
to separate the catalyst from the reaction product, and this
separation is troublesome since the catalyst is in a inely
divided form. In particular, i~ a reaction is intended to
be ef~icien~ly carried out at a high catalyst concentration,
the separation of the catalyst will become more diicult
and -troublesome.
- ~ In o~der to overcome the above-described problems,
a method has been disclosed in U.S. Patent 4,182,919)~ in
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~ 20 whlch a ilter is employed to separate a catalyst in a
., reactor. This method, however, suffers from various problems
l such as blocking of the filter and ~everse-washing operation
`; o-f the filteri When a reaction product has a low boiling
point as in the production o cyclohexane~ ~he ca~alyst can
be separated ~rom ~he reaction product by withdrawing the
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reaction product from an upper portion o~ the reactor in a
gaseous form. In the production of reaction products having
a high boiling point, such as sorbitol, however, the above-
described method cannot be employed.
In a fluidized bed reactor using finely divided
catalysts the contact between fluids, i~e., gas and liquid,
is insufficient although the contact between the catalyst
and the fluid can be improved. Thus, the fluidized bed
reactor requires procedures consuming a large quantity of
energy, such as the use of vigorous stirring while introducing
a large amo~mk o~ gas in~o ~he liquid.
An object of the invention is to provide a ixed
bed catalyst which provides a large contact area between a
1uid and the catalyst, and which allows the 1uid to 10w
and di~fuse smoo~hly -therethrough although it is a catalyst
-for use in a ixed bed reactor.
Another object of the lnvention is to provide a
~ fixed~bed catalyst which increases the contact area between
; ~ a gas and a liqu~id.
Still another object of the invention is to
~provide a catalyst having a high activity.
SUMMARY 0~ THE IN~ENTION
~ In accordance with the present invention there is
provided a ~ixed bed ca~alyst comprising activated carbon
ibers and an ac~ive ca~alyst component or components
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deposited on the activated carbon fibers. The activated
carbon fibers are formed in a structure in which they are
intertwined with each other. The structure has a high space-
retention force such that a bulk density of 0.2 g/cm3 or
less at a compression load of at least 1 kg/cm2 is maintained.
DETAILED DESCRIPTION OF TH~ INVENTION
The fixed bed catalyst according to the present
invention is prepared by depositing an active catalyst
component or components on fibrous activated carbon or
activated carbon fibers having a large specific surface area
and high adsorptivity. These activated carbon -ibers are
prepared by subjecting carbon fibers obtained rom various
; materials, such as acryl fibers, cellulose fibers~ and pitch,
or flame-resistant fibers which have not yet been sufficiently
carbonized7 to an activation treatment, such as a steam
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treatment, to make them active and porous. The fibers are
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used in a bulky condition wherein the fibers are intertwined
with each other, e.g., in a felt-like form.
An activated carbon flber has stiffness as a single
yarn, i.e., indi~idual fiber, and a bulky aggregation of
such activated carbon fibers is characterized in that it can
resist a strong compression force and in that a low bulk
density is maintalned. Therefore, even if a fluid is passed
under pressure khrough -~his fixed bed catalyst, no appre-
ciable deformation will OCCUT and the bulkiness lS maintained.
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Thus, the fixed bed catalyst of the invention allows a fluidto pass therethrough withou~ large resistance. Furthermore,
since the spaces between fibers remain uncollapsed, a large
contact area between the fluid and the catalyst, and a large
contact area between a liquid wetting the fiber and a gas
are stably maintained.
Uniform deposition o an active catalyst component
or components on activated carbon fibers having a structure
such that they are intertwined with each other ~hereinater
this structure is re-Eerred ~o as a "felt structure") requires
techniques unlike ~hose employed for powdery or granular
activated carbon. Such techniques include a method in which
a liquid containing ~he catalyst component or components is
circulated rapidly in a felt of activated carbon fibers to
avoid~uneven adsorption of the catalyst9 a method in which
the specific catalyst component is chosen so as to achieve
slow adsorption thereof on the fibers, and a method in
which, with a gradual increase in temperature, compounds
which are sparingly adsorbed are converted into those which
are easily adsorbed.
Various techniques can be developed depending on
the type of the desired active catalyst component and pre-
ferred ones can be selected.
In charging the fixed bed catalyst of the invention
into a fixed bed reactor, it is preferred to pack felt sheets
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one UpOTI another into a reactor wi~h compressing since a
uniform fixed bed can be easily obtained.
By way of example, the relationship between
compression force and bulk density when felts comprising
activated carbon fibers having a single yarn diameter of
7 to 20 microns are packed, while compressing, in a cylinder
having a diameter of 2 cm is shown in Table 1. A low bulk
density is maintained at a fairly high compression force.
- Therefore, the structure remains unchanged also under the
pressure of the flow of the ~luid, allowing the liquid to
pass -therethrough smooth:ly, and main~ains an increased
con-tact area between the -fluid and the catalyst or between
the liquid wetting the fiber sur~ace and a gas. Thus, in
combination with the properties of the activated carbon that
produce a deposited ca~alyst having a high activi-ty, there
; can be obtained a ~ixed bed catalyst structure having a high
reaction activi-ty.
Table l
Compression Force ~ Bulk Density
~(kg/cm2) ~ (g/cm3)
1 0.08
2 0.10
4 0.12
8 0.16
12 0.20
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In order to determine the pressure loss when a
fluid is passed through a fixed bed having a bulk density
as shown in Table 1 above, water and air were passed through
the fixed bed at ~arious velocities. It has been found that
the pressure loss can be represented by the ollowing formula
~1)
QP = 0.9 x pl- (VL + 0.04 VG) ~1)
wherein
~ P is a pressure loss ~kg/cm2-m~,
p is a bulk de~si~y.(g/cm3),
V~ is the volume of water passing per unit area of
the inner cross sec~ion of the ixed bed (cm3/min-cm2), and
: YG is the volume o air passing per unit area of the
inner CTOSS section of ~he fixed bed ~cm31min cm2).
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lS : In general~ in ca.rrying out a reaction by the use o~
an~industrially employed reactar~column, it is preferred from
~; an~economic viewpoint that the~ helght of the column~is~about
:~ ~ m and the:residence time of a reaction solution is within
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lO hours. When the ~ixed bed catalyst of the invention~is
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charged tol.a~height of 5 m such that the bulk density lS
0.2 g/cm , and ~ liquid such.as water and a gas such as air
are passed through the above-prepared catalyst bed at rates
o~ 1 cm3/min-cm2 and 10 cm3/min cm2, respectively, the
residence time of ~he liquid is within 10 hours and the
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pressure loss resulting rom the flow of the 1uid is l kg/cm2
or less according to the above-described for~ula (I). Thus 7
in order that the fixed bed remain unchanged and maintain a
stable s-tructure, it is required that the fixed bed catalyst
structure have a strength such that it retains a bulk density
of 0.2 g/cm3 or less at a compression load of 1 kg/cm2. It
is important that the fixed bed catalyst structure must not
be deformed`by the flow pressure o~ fluid. Therefore, it is
preferred that the fixed bed catalyst structure has lower
bulk density at higher flow pressure of fluid. It can be
readily seen fTom Table 1 that the fixed bed catalyst of the
invention possesses such a strength.
When a fluid is passed through the fixed bed catalyst
o the invention, the fluid exhibits a flow very similar to
piston flow. This is supported by the ~act that even when
wa-ter~and air are passed ~here~hrough, there is observed a
s~arp pea~ in the residence tlme distrubution of the water.
This flow behavior indica~es ~ha~ TeveTse-mixing is reduced,
and is suitable for obtaining the desired product at~a hlgh
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~20 conversion. Depending on the type o~ reaction, substances to
: be reacted tend~to flow more slowly than the fluid by lts
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interaction with the acti~ated carbon. This is often preferred
in a practical operation.
In order to change the flow of a fluid in a fixed
bed of the catalys~ o the invention, or ~he flow of each o
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a gas and a liquid, other fillers such as wire mesh may be
incroporated into the fixed bed to form therein a plate-like
or spherical space. However, a fixed bed consisting of the
actiuated carbon fiber structure alone is preferred in that
it provides a most uniform piston ~low.
The activated carbon fibers employed in the present
invention exhibit stiffness sufficient to withstand compression
force as long as the single yarn diameter is at least 3 microns.
Furthermore~ when the single yarn diameter is 50 microns or
less, the brittleness of the fiber is such that i~ does not
cause a disadvantage. A commercially available activated
carbon felt usually comprises intertwined fibers having single
yarn diameters of several microns to several ten microns, and
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can be used satisfactorily in the invention. Moreover, its
specific surface area is about 1,000 m2/g which is nearly
equal to that of the usuat activated carbon, and its adsorption
properties are as high as that of the usual activated carbon.
Various activated carbon fibers are commercially
available and, there~ore, those fibers which exhibit the
optimum actlvity when used in comblnation with an active
catalyst component or components should be selected.
Various active catalyst components can be used in
the invention depending on the type of reaction for which the
ultimate activated carbon iber catalyst is used. Typical
examples of catalyst components which can be used include
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noble metals such as Pt, Pd, Rh, Ru, Os, and Ir, for which
activated carbon is favorably used as a support.
These active components are used singly or as a
mix~ure comprising two or more thereof to impregnate the
activated carbon fibers therewith, or are deposited on the
activated carbon fibers. The amount of the active component
being deposited, when the activated carbon ~iber structure
is used as a support, is generally from 0.01 to 10~ by weight,
as calculated as the metallic element, of the support, which
0 lS the same as the range conventionally employed.
The following examples and comparative examples are
given to illustrate the invention in greater detail although
the invention is not intended to be limited thereto.
EXAMPLE 1
lS An activated carbon fiber felt (:produced by Toho
Rayon Co., Ltd., containing 4 to 6% by weight of nitrogen)
was impregnated with an aqueous solution of a noble metal
chloride by circulating the aqueous solution therethrough.
After neutralizing with a 1 N aqueous caustic soda solution,
2a the felt was washed with water and~dried at 90C for 20
hours. Thereafter, the noble metal chloride was reduced in
a stream of hydrogen at 150C for 1 hour to prepare an
activated carbon fiber catalyst. Then, 6 g o -the catalyst
thws produced was charged into a stainless steel pipe having
2S a diameter of 2 cm and a length o 20 cm to form a fixed
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catalyst bed having a bulk density of 0.l0 g/cm3 at a compres-
sion load of 2 kg/cm2, through which a 1% aqueous solution of
acetone and hydrogen gas were passed downward at rates of
l00 ml/min and l NL/min, respectively, at an ordinary tempera-
ture and atmospheric pressure. In this way, a continuousreaction was per~ormed to convert acetone to isopropyl alcohol.
The resul~s are shown in Table 2.
Table 2
Noble Metal DepositedConversion ~)
l~ 5% Ru l00
2% Ru -~ 3% Pd 95
2~ Ru ~ 3~ Pt l00
3% Ru ~ 2% Rh lO0
5~ Rh 52
COMPARATIVE EXAMPLE 1
Powdery ac~ivated carbon ~Norit) and an aqueous
soIution o a noble me~al chloride were mixed and stirred~
neutralized with a l N aqueous caustic soda solution, ~iltered,
wasiled with water, and thereafter treated in the same manner
20 as in Example 1 to prepare a catalyst. Then, a 1% aqueous
solution o~ acetone containing 10% by weight of the catalyst
as prepared above was passed upward through a stainless steel
pipe having a diame~er of 2 cm and a length of 20 cm at a
rate o~ l00 ml/min, and in addition, hydrogen gas was passed
therethough at a ra~e of l NL/min at the inlet o the stainless
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steel pipe. At the outlet of the stainless steel pipe,
the liquid and gas were separated from each other immediately.
In this way, a continuous reaction was perormed to convert
acetone to isopropyl alcohol. The results are shown in
Table 3.
Table 3
Noble Metal Deposited COnVeTSiOn
5% Ru 32
2% Ru + 3% Pd 25
2~ Ru ~ 3% Pt 46
3~ Ru ~ 2% Rh 35
5~ Rh 15
EXAMPLE 2
A ibrous activated carbon felt ~produced from
cellulose fiber) was impregnated with an aqueous solution of
a noble me~al chloride and dried. The noble metal chlo~ide
was~ then reduced in a stream of hydrogen at 200C or~1 hour
to prepare a catalyst. Then, 4.5 g of the catalyst was
charged into a stalnless steel pipe having a diameter of
2 cm and a length of 20 cm to oTm~a ixed catalyst bed having
a bulk density o~ 0.08 g/cm3 at a compression load of 1 kg/cm3,
through which a 5% tert-butanol solution of phenylacetone and
hydrogen gas were passed downward at ra-tes of 10 ml/min and
1.5 NL/min~ respectively, at an ordinary temperature and
atmospheric pressure. In this way, a continuous reaction was
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performed to con~ert phenylacetone to methylbenzyl carbinol.
The results are shown in Table 4 below.
Table 4
Noble Metal DepositedConversion (~)
5~ Ru 93
S% Os 100
5% Pt 90
EXAMPLE 3
Twelve grams of a~ca-talyst comprising a fibrous
activated carbon elt (produced by Toyobo Co., Ltd.) with 5%
by weigh-t of Pd deposi~ed thereon was charged into a stainless
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steel pipe having a diameter of 2 cm and a length of 20 cm to
form a ixed catalyst bed having a bulk density of 0.19 g/cm
at a compression load of 12 kg/cm2, through which 150 ml ~ a
30% àqueous solu-tion o~ glucose~was circula~ed upward at a
~rate of 25 ml/min and air was passed upward at a rate of
; 0.8 NL/min. During the~reaction, the pH o the ~react~ion
solution was maintained at~ 9 to lO~with a 1 N aqueous~ caustic ~ ;
~ soda solutlon. In~this way,~a reaction was performed at an ~ ~ ~
-~ 20 ordinary temper~ture and atmospheric pressure, and the ~:
conversion of glucose to gluconic~acid was 59.1
EXAMPLE 4 -
Into a s~ainless steel pipe having a diameter oX
2 cm and a leng~h of 20 cm was charged 8.5 g o~ a catalyst
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comprising a fibrous activated carbon felt (produced by Toyobo
Co., Ltd.) with 4.7% by weight of Ru and 0.3% by weight of Pd
deposited thereon to form a fixed catalyst bed ha~ing a bulk
density of 0~14 g/cm3 at a compression load of 6 kg/cm2. Then,
140 ml of a 50% aqueous solution of glucose was circulated
downward in the stainless steel pipe at a rate of 8 ml/min
and hydrogen was passed downward therethrough at a rate of
2.0 N~/min. During the reaction, the pressure was maintained
at 7.5 kg/cm2 and the temperature at 120G. In this way, a
reaction was performed for 3 hours. Glucose was reduced to
sorbitol a~ a conversion of 100~.
COMPRATIVE EXAMPLE 2
A 100-ml autoclave provided with a stirrer was
charged with 4.25 g of a catalyst comprising powdery activated
carbon ~Norit) with 4.7~ by weight of Ru and 0.3~ by weight
of Pd deposited -~hereon~ and 70 ml of a 50% aqueous solution
of glucose. A reaction was performed while maintaining the
pressure at 7.5 kg/cm2 by introducing hydrogen and the
temperature at 120C, and while stirriDg for 3 hours. Glucose
was reduced to sorbitol at a conversion of 32~.
While the invention~has been described in detail and
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with reference to specific embodiment thereof, it will be
apparent to one skilled in the art that various changes and
modificatio~s can be made therein without departing from the
spirit and scope *hereof.
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