METHOD FOR SUSPENDING AND INTRODUCING SOLID MATTER IN A HIGH-PRESSURE PROCESS

PROCEDE POUR METTRE EN SUSPENSION ET INTRODUIRE DES SUBSTANCES SOLIDES DANS DES PROCESSUS HAUTE PRESSION

English Abstract

The invention relates to a method for suspending and introducing solid matter
in a high-pressure process, for example colorant pigments in a high-pressure
process, in which a supercritical fluid is used as the process medium and a
pressure in excess of 150 bar prevails. According to the invention, the
suspension of the solid matter takes place at a low-pressure in a completely
separate suspension method. In the latter, the solid matter is suspended or
partially dissolved in a non-critical, liquid gas. The pressure in said
suspension method is less than 90 % of the critical pressure of the liquid
gas. The suspension is introduced into the high-pressure process by means of a
pump.

French Abstract

La présente invention concerne un procédé pour mettre en suspension et introduire une substance solide dans un processus haute pression, par exemple des pigments colorés dans un processus haute pression dans lequel un liquide surcritique est utilisé comme substance de processus et une pression de plus de 150 bar règne. Selon l'invention, la mise en suspension de la substance solide est réalisée à basse pression au moyen d'un procédé de mise en suspension complètement séparé. Dans le cadre de ce procédé de mise en suspension, la substance solide est mise en suspension ou partiellement dissoute dans un gaz non critique liquéfié. La pression au cours de la mise en oeuvre de ce procédé vaut moins de 90 % de la pression critique du gaz liquéfié. L'introduction de la suspension dans le processus haute pression s'effectue au moyen d'une pompe.

Claims

5
Claims
1. Process for solids suspension and dosing of a granular, grain or powder
type of
solid material in a high-pressure process, using essentially a supercritical
fluid as
process fluid, the said process being a suspension step which is part of the
high-
pressure process and consisting of a suspension vessel and a device for
circulation
of the liquid as well as for feed and discharge operations,
- solid material and a fluid being fed to the suspension vessel and the said
fluid
being a liquefied gas,
- the solid material becoming suspended in the fluid with the aid of the
device for
agitating the liquid, thus keeping the solids in suspension,
characterised in that
- the pressure applied in the suspension step is < 90% of the critical
pressure of
the process fluid and in an advantageous variant < 60 bars, a gaseous phase
blanketing the liquid phase in the suspension vessel,
- and in a last step the suspension is conveyed by pump into the high-pressure
process.
2. Process according to Claim 1,
characterised in that the pressure in the suspension vessel is essentially
stabi-
lised during the feed cycle to the high-pressure process by admitting solids
free
gas.
3. Process according to one of the preceding Claims 1 or 2,
characterized in that the device for circulation of the fluid in the vessel is
an agi-
tator mounted in the vessel.
4. Process according to one of the preceding Claims 1 or 2,
characterized in that the device for agitating the liquid is a pump connected
to the
suspension vessel via an intake and delivery line and part of the suspension
in-
ventory being constantly circulated in a cycle.
5. Process according to one of the preceding Claims 1 to 4,
characterised in that the fluid in the suspension vessel is essentially
identical
chemically with the high-pressure process fluid.
6. Process according to one of the preceding Claims 1 to 5,
characterised in that further non-solid feedstock is added to the fluid, such
as H2O

6
or cyclic and acyclic short-chain hydrocarbons or short-chain alcohols,
aldehydes or
ketones as well as mixtures thereof.
7. Process according to one of the preceding Claims 1 to 6,
characterised in that the pressure applied in the suspension tank during the
feed
cycle to the high pressure process is maintained constant by adding gas in the
gaseous state.
8. Process according to one of the preceding Claims 1 to 7,
characterised in that the suspension is permanently stabilised during the
suspen-
sion feed cycle to the high-pressure process by means of the liquid agitating
de-
vice.
9. Process according to one of the preceding Claims 1 to 8,
characterised in that the input solid material is a fluid to be dissolved in
the high-
pressure process, such as colour pigments, bonding agents, bleaching agents,
aromatic fluids, scent extracts or mixtures thereof.
10. Process according to one of the preceding Claims 1 to 9,
characterised in that the suspension feed operation to the high-pressure
process
is run in a continuous mode during the vessel discharge cycle, the volume feed
rate
being either even or variable so that the concentration in the suspension
vessel is
essentially kept constant.
11. Process according to one of the preceding claims 1 to 10,
characterised in that the suspension stream is adjusted at the admixture to
the
high-pressure process in such a manner that the ratio of the volumetric
streams of
suspension and high-pressure fluid is 1 : 50 and in the ideal version .ltoreq.
1 : 100.

Description

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Process for solids suspension and dosing in a high-pressure process
[0001] The invention relates to a process for solids suspension and dosing in
a high-
pressure process, for example colour pigments in such a high-pressure process
using
a supercritical fluid as process fluid at a pressure of >150 bar. The solids
suspension
step takes place at low pressure in a completely separate suspension process.
The
solids undergo a suspension or partial dissolution in a non-critical and
liquefied gas.
Said suspension pressure is as low as <90 % of the critical pressure of the
liquefied
gas. The dosing of the solids suspension in the high-pressure process takes
place by
means of a pump.
[0002] Various state-of-the-art techniques and devices are known what solids
can be
feed during a high-pressure process. It is common practice to feed the solids
by means
of a feed hopper, feed tank or similar device, said devices being flooded with
the proc-
ess fluid so that the solids are entrained to enter the high-pressure process.
[0003] DE 199 28 405 describes a process for dyeing a textile substrate in the
pres-
ence of at least one supercritical fluid, including a dosing process in which
the required
quantity of powdered dyeing agent is divided into a multitude of small
batches, each
batch coming into contact with the supercritical fluid for that time necessary
for solids
dissolution or dispersion. The device described in the published document
provides for
an oscillating piston with a bearing on either side, the piston being placed
across the
stream and moved along the process line that contains the critical fluid. The
said piston
takes up a batch of solids through the first bore in the end position and in
the opposite
end position. This first bore is located in the main stream so that the solids
are re-
moved from the bore by the said fluid. At the other piston end, a second bore
is simul-
taneously filled or emptied, respectively.
[0004] The process and device according to DE 199 28 405 have the disadvantage
that the device must be rated and sized in accordance with the main process.
Further-
more, the bore emptied and located in the main stream is used to catch
supercritical
gas and moved into the filling position so that this section must either have
an equal or
higher pressure or a flashing cycle must each time be performed which would
inevita-
bly impair the filling process. Moreover it is in fact critical to cross a
high-pressure gas-
ket with the bores guided by the piston. After short operating periods there
will surely
be damage to the gasket material, i.e. leakage problems will occur.
(0005] WO 97/13915 describes a very common method of dosing solids in a
supercriti-
cal process. This process provides for a dye preparation vessel arranged in a
by-pass
of the main process stream. For removal of the solids the respective valves
are opened

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and the solids are entrained by a part stream of the main process fluid.
Hence, it is not
possible that uniform dosing or fine tuning of the dying agent feed be carried
out since
the mixture of solids and fluid is diluted by the process fluid taken in.
Moreover, all
components arranged in this process by-pass must satisfy the pressure and
tempera
s ture requirements of the main process.
[0006] A comparison with the suspension process optimised in accordance with
WO 97/13915 is described in patent US 6,261,326. In said process a dye
preparation
vessel is used for the dissolution or suspension of the dying agent, with the
aid of an
agitator or a pump to circulate a partial quantity of the solids. As stated in
the said
document, there is an almost critical fluid state in this preparation process
because the
latter is fed with supercritical fluid from the main process. As in the case
of the proc-
esses mentioned above, this preparation method also has a deficiency, i.e. it
must
meet the high-pressure requirements of the main process, which in this
particular case
is called treatment process. Moreover, solids dosing and input not shown in US
6,261,326 must be effected by a sophisticated hopper system or the solids feed
vessel
requires that the high pressure of the main process be met.
[0007] The aim of the invention, therefore, is to provide a solids suspension
and dosing
process that operates independently of the high-pressure cycle and with a
higher de-
gree of efficiency than that of the state-of-the-art processes.
[0008] The aim of the invention can be achieved by means of a suspension and
dosing
process for granulated or powdered solids to be fed to a high-pressure process
which
essentially uses a supercritical gas as process fluid. The said step
constitutes a solids
suspension stage of the high-pressure process and consists of a suspension
tank and
a device for liquid stirring, incl. the respective inlet and outlet lines.
[0009] When the process is implemented the first step provides for a
suspension tank
filled with solids and a fluid, the latter being a liquefied gas which is in a
non-critical
state.
[0010] In a second step, the solids become suspended in the fluid by means of
a liquid
agitating device and are kept in suspension. The liquid agitating device
should be an
agitator or a pump arranged on the outside of the suspension tank, said pump
being
connected to the vessel by an intake line and a delivery line and part of the
suspension
inventory being constantly circulated in a cycle.
[0011] The pressure in the suspension step should preferably be <90% of the
critical
pressure of the gas used, the ideal value being <60 bar so that a gaseous
phase is

~
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present above the liquid phase, the ideal value being <60 bar so that a
gaseous phase
is present above the liquid phase.
[0012] The last step is required to pump the suspension into the high-pressure
proc-
ess. Hence, the pump and its delivery line connected to the main process must
satisfy
the high-pressure process requirements. Any process equipment mounted on the
in-
take side of the pump merely needs comply with the lower standard.
[0013] An advantageous embodiment of the process according to the invention is
to
provide a fluid for the solids suspension which essentially is chemically
identical with
the process fluid of the high-pressure process.
[0014] To optimise the process further substances are added to the fluid. Said
sub-
stances are, for example, cyclic and acyclic short-chain hydrocarbons or
alcohols, al-
dehydes or ketones as well as H20 and mixtures thereof.
[0015] For the process according to the invention it is recommended that the
pressure
applied in the suspension tank during the dosing cycle of the solids
suspension into the
high-pressure process be maintained at a preferably constant level by topping
up with
gas in the gaseous state.
[0016] An ideal process variant, therefore, permits the feed of the solids
suspension
into the high-pressure process to take place continuously during the vessel
emptying
cycle and, additionally, the concentration of the solids in the fluid to be
maintained at a
constant level or at a variable value with the aid of the pump delivery. The
concentra-
tion in the suspension tank essentially remains constant during the emptying
cycle as
the top-up gas is not in the liquid phase but in the gaseous phase.
[0017] Another advantageous embodiment of the invention provides for solids
that are
soluable in the high-pressure process, such as colour pigments, bonding
agents,
bleaching agents, aromatic fluids or mixtures thereof. In this context the
invention also
bears an advantage to the extent that the solids - contrary to the start-of-
the-art tech-
nology - is merely suspended and that the specific soluability of the
respective feed-
stocks must not be met in the suspension stage. When the said feedstocks are
added
to the big volumetric streams of the main process, the said solids directly
dissolve on
account of the high concentrate rate.
[0018] Therefore, a beneficial embodiment of the invention is constituted by
the fact
that the suspension stream is adjusted at the admixture to the high-pressure
process in
such a manner that the ratio of the volumetric streams of suspension and high-
pressure fluid is 1 : 50 and in the ideal version it is <_ 1 : 100.

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[0019] The suspension stream which is very small compared to the main-process
volumetric stream, as a rule, has a negligible physical influence only on the
main proc-
ess.
[0020] The process according to the invention is illustrated on the basis of
the two
figures showing a typical process layout.
[0021] Figure 1 shows the suspension process using a pump to stir the liquid
and Fig-
ure 2 depicts the process using an agitator without external cycle.
[0022] According to Figure 1, suspension process (1) connected to the high-
pressure
process (4) via line (6) essentially consists of suspension tank (2) and pump
(3). Sus-
pension tank (2) is filled with liquefied gas via line (7) and with solids via
line (8). The
layout in Figure 1 shows that liquid inventory (2a) and gas inventory (2b)
form in sus-
pension tank (2). A part stream is withdrawn from the tank by means of suspen-
sion pump (9) via line (10) and recycled via line (11 ).
[0023] When suspension tank (2) is emptied the solids suspension is conveyed
via line (5) by means of pump (3) and via line (6) to high-pressure process
(4). It
becomes obvious that merely pump (3) and the delivery side of the pump, i.e.
line (6), must be rated for the pressures applied in high-pressure process
(4).
The remaining components of the suspension process must merely comply with
the requirements for pressures up to about 60 bar.
[0024] Figure 2 shows a further embodiment of the process, suspension tank (2)
being equipped with agitator (13) so that a suspension can be prepared and
kept stable.

Representative Drawing