Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2002-10-01
2004-11-16
Drodge, Joseph (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S511000, C210S513000, C210S801000, C562S485000
Reexamination Certificate
active
06818132
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process and an apparatus for separating solids from a liquid phase.
The separation of solids from a liquid phase is a task which frequently has to be carried out in industry. An example which may be mentioned is the separation of aluminum hydroxide crystals from the basic mother liquor. In the separation, it is important to free the solid as completely as possible of the liquid phase without large amounts of dilute washing liquor being obtained.
A particular separation problem occurs when the liquid phase has to be separated virtually completely (>99%) from the solid. The liquid phase frequently contains nonvolatile components which have to be separated off. In this case, drying of the solid does not solve the separation problem. Rather, the solid needs to be washed without dilute washing liquors being obtained. This is the case in the preparation of some high-performance polymers in high-boiling solvents. The process of the invention is of particular relevance to polymers which are prepared in a high-boiling solvent with formation of salts or acids or bases which have to be neutralized subsequently. Examples of such processes are the preparation of polyaramides from diamines and diacid chlorides, of polycarbonates from diphenols or diphenoxides and phosgene, of polysulfones, polyether sulfones or polyether ketones from diphenoxides and dihalogenated aromatic hydrocarbons or the preparation of polyarylenesiloxanes from diaryldichlorosilanes and diphenoxides. In particular, the term high-performance polymers encompasses polyarylene sulfides.
In the preparation of poly(p-phenylene) sulfide (PPS), the polymer has to be freed of high-boiling N-methylpyrrolidone (NMP) and undissolved and dissolved by-products. The proportion of residual solvent (NMP) in the polymer should be less than 100 ppm. The generation of dilute NMP-containing washing liquors would require a high outlay for distillation and therefore has to be avoided.
According to the prior art, separation can be carried out by means of filtration and subsequent washing of the filter cake. However, substantial volumes of washing liquid are necessary to achieve virtually complete removal of the liquid phase from the solid and have to be worked up at considerable cost.
Vaporization of the solvent from the solid/liquid mixture, if appropriate at elevated temperature, is likewise known. In the case of high-boiling solvents such as NMP, this is time-consuming and costly. In addition, nonvolatile impurities remain in the PPS solid and have to be removed in a further process step.
SUMMARY OF THE INVENTION
From an economic point of view, carrying out the abovementioned separation task in a continuously operating separation apparatus continues to be of interest.
It is an object of the present invention to provide a process and an apparatus for separating solids from solid/liquid mixtures, with the liquid phase being separated off from the solid virtually completely without a large amount of dilute washing liquor being obtained.
The object of the present invention is achieved by the solid in a first liquid phase being brought into contact with a second liquid phase in countercurrent and the solid being transferred into the second liquid phase.
The process of the invention is carried out by bringing the solid in the first liquid phase into contact with a second liquid in countercurrent in an apparatus which has at least one solid/liquid inlet (
1
), at least one solid/liquid outlet (
4
), at least one liquid inlet (
3
) and at least one liquid outlet (
2
) (cf. FIG.
1
and FIG.
3
).
The solid in the first liquid phase is fed into the solid/liquid inlet (
1
). The second liquid phase is fed into the liquid inlet (
3
). The solid is almost completely discharged in the second liquid phase through the solid/liquid outlet (
4
). The first liquid phase is virtually completely discharged through the liquid outlet (
2
).
In the process of the invention, only small amounts of the first liquid phase are discharged together with the solid in the second liquid phase through the solid/liquid outlet (
4
). The proportion of first liquid phase, based on the second liquid phase, in the solid/liquid mixture discharged through the outlet (
4
) is less than 50% by weight, preferably less than 10% by weight and particularly preferably less than 1% by weight.
In the process of the invention, the first liquid phase is not greatly diluted with the second liquid phase. The proportion of second liquid phase, based on the first liquid phase, in the liquid discharged through the outlet (
2
) is less than 80% by weight, preferably less than 50% by weight, particularly preferably less than 30% by weight.
In general, only small amounts of solid are carried out in the liquid discharged through the outlet (
2
) in the process of the invention. This proportion of solid is, based on the solid introduced through the solid/liquid inlet (
1
), preferably less than 30% by weight, particularly preferably less than 10% by weight.
In the process of the invention, the solid travels through the apparatus by sedimentation under gravity. In a preferred embodiment of the invention, the solid of the solid/liquid mixture is sedimented at least once in an apparatus and the sedimented solid is washed in countercurrent with a second liquid phase.
In the process of the invention, the first liquid phase is preferably an organic solvent and the second liquid phase is preferably water. Organic solvents used are, for example, dipolar aprotic solvents, preferably NMP.
In the process of the invention, the first and second liquid phases are preferably miscible.
The solid can consist of one or more components. The main constituent of the solid is preferably a polymer such as a polyarylene sulfide, very particularly preferably PPS.
The process of the invention can also separate mixtures of solids it the constituents have different solubilities in the first and second liquid phases.
Preference is given to the main constituent of the solid dissolving neither in the first liquid phase nor in the second liquid phase. Secondary constituents of the solid or of the first liquid phase which are to be separated off preferably have a good solubility in the second liquid phase.
In a particularly preferred embodiment, a polymer which is to be separated off and to be purified, for example PPS, is insoluble in the first and second liquid phases under the conditions of the process of the invention, while the impurities to be removed, for example salt and high-boiling solvent, dissolve in the second liquid phase.
A particular advantage of the process of the invention is that it offers the opportunity of the separating off the solid continuously even at elevated temperature and under superatmospheric pressure.
In the process of the invention, the density of the solid is different from the density of the first liquid phase and of the second liquid phase.
The object is achieved by a process in which the apparatus of the process of the invention comprises at least one top section, at least one bottom section and at least one middle section having n sedimentation trays.
A first preferred embodiment of the invention is a process using an apparatus which has at least one sedimentation tray (ST) which comprises at least one sedimentation funnel having a sediment outlet, at least one flow zone and at least one supernatant liquid outlet.
The solid is sedimented on each sedimentation tray in the sedimentation funnel and washed in the flow zone. This is repeated sequentially in n stages. The sedimentation tray has a funnel-like construction and ends in a bottom outlet which represents the solid/liquid outlet. The top section has an inlet for the solid/liquid mixture which leads to the uppermost sedimentation tray. The top section also has an outlet for discharge of the supernatant liquid from the uppermost sedimentation tray.
The apparatus of the process of the invention makes it possible to separate the solid from the mixture in such a way that the propo
Haubs Michael
Wagener Reinhard
Connolly Bove & Lodge & Hutz LLP
Drodge Joseph
Ticona GmbH
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