Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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H 1126
T~e present invention relates -to a process for the
manufacture of pul~erulent catalyst carriers o~ catalysts
for effec-ting reactions in a flow bed in liquid phase,
which comprises contacting the pulverulent catalyst
carrier or catalyst with an upwardly flowing liquid and
thereby freeing it from inhomogeneous particle-s contained
therein, in accordance with the principle of classifying
` 10 material in a medium flowing upwardly.
~: Further preferred features of -the process of the
present inven-tion provide
a) for the ca-tal.yst carrier or cataIyst to consis-t of
particles having a diameter within the range 20 and
2000 microns;
.~ b) for silica -to be used as the catalyst carrier;
c) for water to be used as the upwardly flowing liquid;
and
d) for the liquid to flow upwardly at a velocity at
least equal to the rate of produc-t discharge from a
sedimentation zone in effecting catalytic reactions
. in a flow bed in liquid phase.
-. German Patent Specification "Offenlegungsschrift"
2 053 115 describes a process for carrying out
. heterogeneous catalytic reactions continuously in liquid
phase in a flow bed, wherein a suspension o:E liquid star-
ting material and ca-talyst toge-ther with resulting
reaction product is continuously circulated, the reaction
, product is continuously separated from the catalys-t
;. 30 susper;sion in a separeting zone forming part of the
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liquid circulation conduit, and fresh starting material is added
continuously to the balance catalyst suspension.
The single drawing in this application illustrates
in side elevation the apparatus of German Patent Specification
2,053,115.
~ he process described in the said German specifica-
tion, comprises more particularly circulating continuously, in
accordance with the principle of an air-lift pump, a homogeneous
suspension of liquid starting material and fine particulate
catalyst together with resulting reaction product by the intro-
duction of a gas or vaporous material near the bottom of a reac-
tion zone 1, separating a portion of resulting reaction product
continuously from the suspension in a separating zone 2 designed
as an injector system, and supplying the suspension continuously
with an aliquot portion of fresh starting material, the velocity
of flow of the reaction product in separating zone 2 towards the
reaction product outlet 3 being smaller than the sedimentation
velocity of the catalyst in the suspension. The reaction product
discharged from the separating zone 2 can be delivered to a
filtering apparatus 4 (e.g. filter candles) and freed therein
from catalyst particles carried along therewith, and the catalyst
particles filtered off can be recycled to the reaction zone 1.
The principle underlying the continuous separation of a pure
liquid reaction product from a catalyst suspension is based on
the utilization of the difference in density between the catalyst
and reaction product within the separation zone 2, wherein flow
of material is substantially avoided, and on the utilization of
the suction effect produced by the injector system and being
directed downwardly, into recycle line 5.
We have now found that the use of a pulverulent
catalyst containing inhomogeneous particles is not absolutely
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satisfactory for the undisturbed operation of a flow bed or fluidized bed in
liquid phase. The term "inhomogeneous particles" as used herein means e.g.
uncompact hollow particles (spheroids) and more generally particles of which
the pore structure differs significantly from that of the bulk of the
particles. Such inhomogeneous particles have very minor dimensions. As a
result they can reasonably be assumed predominantly to form part of the
fines in a pulverulent catalyst, frequently to retain bubbles of airJ which
adhere thereto, and therefore to behave irregularly during sedimentation,
whereby the separation of crude liquid reaction product from the catalyst
suspension may be rendered very difficult.
This invention provides for a process for the manufacture of a
pulverulent silica catalyst carrier or silica carrier based catalyst, suit-
able for use in a liquid-phase fluidized bed reaction system wherein a liquid
product is separated from the catalyst particles by means of a sedimentation
zone from which the liquid product is removed, which comprises contacting the
pulverulent catalyst, or carrier, with an upwardly flowing liquid to separate
; from the catalyst or carrier inhomogeneous particles having a pore structure
differing significantly from the bulk of the particles contained therein, the
upward velocity of the flowing liquid being at least equal to the rate of
product discharge from the sedimentation zone in the reaction system in which
the catalyst, or carrier, is to be used.
The invention will now be exemplified with reference to the
hydrogenating dehalogenation of dichloroacetic acid to monochloroacetic acid
in contact with a palladium catalyst deposited on a SiO2-carrier. The
catalyst may be produced, for example, by the process described in German
published Specification "Offenlegungsschrift" 2 240 ~66, wherein a SiO2-carrier
is impregnated with a palladium salt which is successively reduced to metallic
; palladium. In view of the fact that chloroacetic acids are highly corrosive
material and that it is necessary
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to have a mechanically strong catalyst, it is highly desiràble
in this particular case that SiO2 be exclusively used as the
catalyst carrier and that it be prepared by a spray drying
process. Carrier material so made has a particle size between
20 and 300 microns and the sieve analysis (determined on a
specimen)
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indicated in Table 1 hereinafter.
It is possible for the carrier having the-above
particle size distribu-tion to be used for making (cf.
German published Specification 2 240 L~66) the ca-talyst,
and for -the catalyst so made to be used for -the
hydrogenating dehalogenation (cf. German published
Specifica-tion "Offenlegungsschrift" 2 053 115) of
dichloroacetic acid. A catalyst so made can be--~sed at a
rate of at most 15 kg per cubic meter of reaction chamber
(including the separation zone 2). If more catalyst is
used per cubic me-ter of reac-tion chamber, -the process
ceases to be reliable in operation. In this case, the
catalyst no longer set-tles in the separation zone 2. It
rather settles so rapidly in the filter candles 4 that
it is impossible for the standard operational conditions
to be main-tained. In o-ther words, i-t is the catalyst
quantity used per unit volume which critically de-termines
-the capacity of -the apparatus as the conversion rate
depends ex-tensively on -the Pd-metal surface available.
, 20 We have now unexpectedly found that considerably
; more catalyst can be used per cubic me-ter of reactor
volume substantially in -the absence of adverse effec-ts
on the flow bed, provided -that the catalys-t is freed from
fines contained in it. If -this is done, i-t is possible
for -the fluidized bed to be subs-tan-tially lmproved, in
respect of space/time-yield. Practice has shown that
~ commercial standard separation methods, such as
- sc~eening or air separa-tion, fail to yield ca-talysts or
catalyst carriers suitable for use in a flow bed or
fluidized hed in liguid phase. The opera-tive~less of a
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:~low bed is critically deter~ined not only by the
diameter but also by the density of ca-talyst particles
¦ and it~is unders-tandable therefore why -the above separation
methods cannot be used for making optimum ~low bed catalysts
for operation in liquid phase.
The present invention provides a simple process for
making a ca-talyst very suitable ~or use in a ~low bed in
liquid phase, wherein the catalyst carrier or catalyst
is contacted wi-th a liquid flowing upwardly and thereby
freed from inhomogeneous par-ticles 9 in accordance with
the principle of classifying material in a medium ~lowing
upwardly. By the selection of a suitable veloci-ty for the
upwardly flowing liq~id and by the provision of a satis-
factory difference in density between solid material
(catalyst carrier or catalyst) and suspension liquid, it
is possible by this invention to produce pulverulent
catalyst carriers or catalys-ts which present an op-timum
particle size distribution for effecting reactions in a
flow bed in liquid phase. This means in o-ther words that
~; 20 it is also possible ~or the water normally used as the
suspension liquid to be replaced 7 e.g. by an organic
liquid, to provide ~or more important differences in
density. On the other hand, it may be necessary for -the
; water to be replaced by another suspension medium, i~ the
water is likely -to extrac-t desirable catalyst constituen-ts
~rom -the catalyst which is to be classified. Needless to
say it is not possible -to iden-tify -the veloci-ty of flow
or di~ference ln density -to be selec-ted in each par-ti-
c~lar case. This, however, is easy -to determine by
experiment,by -those skilled in -the ar-t.
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EXA~PLE 1:
A tube 3.5 m high and 200 r~m wide was filled sub-
stantially halfwa~ its height with 54 l of a spray-dried
SiO2-carrier (unclassi~ied, cf. Table 1 for particle
size distribution). 35 l/h of water travelling at a
speed of 0.3 mm/sec. was introduced into the lower end
of the tube. The water travelled upwardly therein and
kept the en-tire catalys-t mass in suspension. Ohly
fractions of fines having a given size issued -through
the outle-t at the upper end of the -tube. Inhomogeneous
par-ticles ceased to be discharged after about 2 hours.
This was indicated by -the fac-t -that the issuing water
wasfree from carrier material. The discharged ma-terial
was filtered off and used again. The ma-terial which was
; retained in the tube was taken -therefrom through a
filtering appara-tus and a catalyst was made therefrom~
In the present Example, -the average result was 12 % of ~
fines and 88 % of' desirable carrier material having the
particle size distribu-tion indicated in Table 1
hereinafter.
EXAMPLE 2:
The appara-tus of Example 1 was supplied wi-th the
same quantity of carrier (54 l) but wi-th an increased
quantity of wa-ter (47 l/h) flowing upwardly -therein at
a speed increased to O.L~1 mm/sec. Inhomogeneous carrier
particles ceased to be discharged after about 2 hours.
The average resul-t obtained in the presen-t Exarnple,
- in which the water was caused -to -travel upwardl~ a-t
increased speed, was 18 % of fines and 82 % of desirable
~0 catal~st carrier having the par-ticle size distribution
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indicated in the f~llowing Table 1.
~ a b 1 e 1:
Diameter ofUnclassified Carrier Carrier
carrier carrier of Example 1 of Example 2
particles
~300 110.2 % 0.3 % 0~4 %
300 - 200 ,u 2 . 6 % 2 . 8 % 2 . 9 %
200 - 100 11 60 . 6 % 67 . 6 %7 2 . 3 %
100 - 63 11 -22 .-5 % -24 . O %- - 24 . 3 %
V . . . , ~
63 - 40 11 8.5 % 5.0 % o. 1 %
C40 Il 5.6% - o.3% o.o%
The starting materials used and the carriers
producéd in Examples1 and 2, respectively, were employed
in making Pd-catalysts by the process described in German
published Specification "Offenlegungsschrift" 2 240 566,
and the catalysts so made were used in -the hydrogena-ting
dehalogenation of dichloroacetic acid to monochloroacetic
acid in a fluidized bed in liquid phase (cf. German
published Specifica-tion "Offenlegungsschri.ft" 2 053 115).
The results obtained in identical devices wi-th -the use
of -three differen-t ca-talys-ts are indicated in the
following Table 2:
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h O h0 4~ ~ d ~ ~,1 h
h ~ d h ~ ,~ ~ 3 ~4
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o ~3 h h ~ ~ 8 ~ ~ ~
~ h S ~ ''~
R 'C) ~ O ~rl ~ ~ b~ .
O ~ l h O h O O ~ u~
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~ `s results from the da-ta indica-ted in -the above two
Tables, it is possible for -the pure monochloroacetic
acid yield ob-tainable per cubic meter of reactor volume
per hour in a fluidized bed in liquid phase -to be
improved considerably by the use of a catalys-t containing
lesser proportions of fines 9 i.e. a ca-talys-t classified
in a medium flowlng upwardly at; increased speed.
While it is generally advan-tageous in -the present
process to classify the catalyst carrier in an upwardly
flowing medium, it is naturally also possible for the
finished catalyst to be so classified. In this latter
case, the inhomogeneous catalyst par-ticles discharged,
-that are naturally more valuable than the carrier
par-ticles, are~ however, required to be discarded or
to be upgraded, e.g. to palladium. Needless to say this
does not add to the economy of the process.
