Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process in the
separation of solid catalyst particles suspended in
liquid.
It is customary, in process technology, ta carry
out reactions between sas and liquid or one or more
substances dissolved in liquid with the aid of cata-
lytically active solid substances present in liquids.
Examples of such reactions are hydrogenation, oxidation
and halogenation~ The catalyst may be in the form of
a fixed bed through which the liquid passes, or a sus-
pension of particles which t by the application of energy,
are held freely suspended in the lîquid. The suspension
catalyst offers certain advantages, such as being suc
cessively renewable in continuous processes. In several
cases, the dispersed catalyst retains its activity for
a considerable period of time, and if the reaction is
to proceed continuously, the catalyst must therefore
be retained in or constantly recycled to the reaction
chamber through which the liquid passes. This can ~e
accomplished by wi~hdrawing the finally reacted liquid .
through a filter retaining the catalyst particlesO
In general, the instantaneous filtrate flow through
a filter is directly proportional to the ilter surface
and the pressure drop across said surface and inversely
proportional to the viscosity of the liquidl the total
amount of deposit on the filter surface, and a constant
which depends on the permeability of the deposit.
- . It is already known tha~ a filter surface can be
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instantaneously freed from deposits by so-called back-
washing, implying that liquid is pressed through the
filter in a direction opposite to that of the normal
iltrate fLow. U.S. patent specification 2,990,238 teach-
es backwashing with the aid of a piston or diaphragm
pump which in one stroke direction exhausts filtrate
and in the other stroke direction presses a part of
~he filtrate back through the filterc
As will appear from Fig. 1 of the said U.S. patent
specification, only half the available time is utilised
for the withdrawal of filtratet regardless of the pump
stroke frequency which is given as 1 500 strokes per
minute. Furthermore, it appears that the backflow should
amount to 20-70% of the amount of filtrate exhausted,
and this results in a further coxresponding reduction
of the product flow. According to this procedure, the
backwashing flow cannot be greater than the filtrate
flow.-
German patent specification 1,542,089 shows a filterarrangement for use in con~inuous hydrogena~ion. The
filtrate is led out through a stationary centrifugal
pump. When the pump is started, iltrate is pressed
back through the filter. Hydrogenation is carried out
by the circulation of llquid and hydrogen gas dispersed
in the llquid, the flow rate according Example 1 being
0.7-2.8 m~s. The fllter is placed laterally of the cir-
culation flow, for which reason the flow rate during
filtratlon will approach zero at the filter top. Accord-
ing to the description, backwashing can be effectedfor a few seconds. The concentration of solid particles
is given as 1-5 g/1 in the Examples,
British patent specification gS9,583 discloses
the hydrogenation of a liquid consisting of alkyl anthra-
quinone dissolved in organic solvents, This hydrogenation
is a partial process in the well-known anthraquinone
process for the production of hydr,ogen peroxide. The
hydrogenation catalyst susp~nded in the solution is
retained on a filter which is periodically backwashed
with the aid of a pump. No further information about
the backwashing and the catalyst is given.
German patent specification 1,272 t 292 exemplifies
the same hydrogsnation process~ The filter medium employed
is a porous solid carbon material. The anthraquinone
solution contains as catalyst 0.07% by weight palladium
black. The particle size of the catalyst is 0.01-1 ~m.
The filtrate flow is 0.46 m3 per hour and m2 of filter
surface. According to the description~ the carbon fil
ter is to be backwashed for 3-10 s at intervals of
20-30 min.
For the hydroyenation comprised by the anthraquinone
process, use is made, in addition to palladium black J
also of Raney nickel or, for example, palladium provided
on a so-called carrier, usually a ceramic materialO
These suspension catalysts are used in concentrations
higher than 5 g per litre of llquid, and the average
particle size is greater than 1 ~m.
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The use of such catalysts has made the dischar~e
of product liquid through filters so difficult that
the catalyst separation in some cases has been carried
out by means of hydrocyclones and/or centrifuges.
The present invention provides a process in the
separation of solid particles suspended in liquid, such
as Raney nickel, said particles being catalytically
active in continuous chemical processes, such as the
hydrogenation process cornprised by the anthraquinone
process in the production of hydrogen peroxide, more
than 75% of said particles hasving a particle size greater
than 1 ~m, and said particles being present in a con-
centration which~ on an average, is maintained above
5 g per litre of liquid, the liquid containing the reac~
tion product being caused, after passage of a reaction
chamber, to pass through one or more filters, the solid
paxticles thus retained on the filter surfaces being
,
released by periodic backwashing and then resuspended
in the reaction chamber. The process of the invention
is characterised ln that backwashing is carried out
with an amount of 11quld which is greater than the amount
of liquid that can be enclosed within the filter or
filters, and in that the specific backwashing flow through
the filter or filters is so adapted that it will be
greater than the specific filtrate flow throuyh the
filter or filters during the first 20 seconds after
backwashing ~ ~
The process o~ the present invention makes it pos-
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136~9
sible to obtain, under long-time continuous conditions,
an effective specific amount of filtrate which is greater
than 0.5 m3 per hour and m2 of filter surface; also
when the catalyst concentration is greater than 5 g
per litre of liquid and/or the deposit on the filter
has low permeability.
The deposit on ~he filter constitutes not only
an obstruction; it also serves as a filter intercept
ing those particles which otherwise could have passed
through the pores in the fixed filter. During each back-
washing, the filter surface is exposed for such penetra-
tion. In view hereof, and in order to obtain maximum
discharge of the product flow, it has pro~ed to be most
advantageous to effect backwashing at intervals from
1/3 minute to twenty minutes, depending upon the con-
centration of solid particles in the liquid and the
permeability of the deposit.
Backwashing is intended not only to wash off the
outer deposit on the filter surface, but also, if pos-
sible, to wash back any particles ~hat may have pene-
trated into the pore system of the filter medium.
To this end~ the backwashing according to the in-
vention must be carried out with an amount of liquid
which is greater than the one enclosed in the filter
medium, preferably 2-10 times greater than this amount.
Furthermore, the speciflc backwashing flow must be great-
er than the specific filtrate flow during the first
twenty seconds after backwashing. It has also proved
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to be advantageous to impart to the filter surfaces
facing the reaction chamber a movement adjacent said
filter surfaces which, on an average, is greater than
0.1 m/s.
Preferably, more than 75% of the catalyst particles
have a particle size greater than 1 um.
The invention will be explained in greater detail
below, reference being had to the following Examples
and the accompanying drawing.
EXAM~LE 1 (for comparison3
Fig~ 1 illustrates the filtration run during hydro-
genation of anthraquinone derivatives dissolved in or-
gan~c solvents. The solution contained 110 g/l of sus-
pended Raney nickel having a particle size of from about
1 ~m up to 0.5 mm, more than 75% of said particles hav-
ing a particle siæe greater than 1 ~m. Th~ filter medium
consisted of sintered particles of acidproof steeL. The
material thickness was 2 mm, and the porssity amount-
ed to about 40~. Maximum pore width was 8 ~m~
Before the fil~ration run, the pore system of the
. .
filter medium had been chemically cleaned~ Through appli-
cation of mechanlcal energy, a turbulent flow ra~e which,
on an average~ was greater than 0 1 m/s, was imparted
to the solution at the filter surface~ Backwashing was
carried out for 6 seconds, and the filtrat~ flow was
then shut down for altogether 12 seconds. Backwashing
was carried out at intervals of 10 minutes.
After deduction of the hydrogenated solution back-
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washed through the filter, the average filtrate flow
during each 10-min. period was about 1.3 m3 per m2 of
filter surface and hour. After continuous operation
for ten days, the effective filter flow was less than
1.0 m3tm2. The hydrogenation formed part of the anthra-
quinone process for the production of hydrogen peroxide.
EXAM
Fig. 2 illustrates the filtra~ion run under the
same conditions as in Example 1. Backwashing was car-
ried out for 2 seconds during each minute. The average
effective filtrate flow was 2.25 m3/m2/hour~ After con-
tinuous operation for 60 days the e~fective filtrate
flow was about 2.1 m3/m2/houx.
.
