Liquid purification or separation – Processes – Separating
Reexamination Certificate
2001-12-19
2004-05-11
Popovics, Robert James (Department: 1724)
Liquid purification or separation
Processes
Separating
C210S193000
Reexamination Certificate
active
06733680
ABSTRACT:
The present invention relates to the use of particulate water-insoluble polymer preparations as filter aids for filtering aqueous liquids, and to a process for filtering aqueous liquids using these filter aids.
Separating solid-liquid mixtures by filtration is an important process step in many industrial production processes. In particular when aqueous liquids are filtered, filter aids are frequently used. Filter aids are particulate, for example granulated, pulverulent or fibrous substances which, depending on the type and amount of solids present in the liquid to be filtered, make it possible for a filter cake to build up or are intended to loosen this.
The action of the filter aid is based on developing capillaries in the filter cake which, firstly, are small enough to retain solids, but secondly are numerous enough in order to facilitate the outflow of the liquid phase. For this purpose the filter aid can be added to the suspension to be filtered (pulp) and/or the filter aid can be applied before the filtration as an auxilliary layer on the filter surface (filter cloth). In precoat filtration, for example before the start of filtration, a filter aid precoat is applied to a support surface (filter cloth). The filter aid is then added to the pulp, preferably continuously. During the filtration a loose filter cake of filter aid thus forms, which retains the pulp solids, so that the liquid dispersion medium can flow off as clear filtrate (see also “Roempp Chemielexikon” [Roempp's chemistry lexikon], 9th edition, Georg Thiemer Verlag Stuttgart, pp. 1357 ff. for the terms filter aid and filtration).
Obviously, the filter aids should be chemically inert and insoluble in the pulp to be filtered. In addition, under the action of pressure, they should not deform, so that the pores in the filter cake do not collapse. Furthermore, it is desirable that the filter aids can be regenerated.
The most customary filter aids, in addition to organic substances such as cellulose, wood charcoal and wood powder, comprise inorganic materials, in particular of silicate nature, such as kieselguhr, pearlites, diatomaceous earths and bentonites. However, these materials have the disadvantage that they cannot be regenerated and therefore must be disposed of.
In the drinks industry especially, there is a great requirement for filter aids for aqueous liquids, since fruit juice drinks and fermented beverages such as beer are frequently subjected to filtration. A filter aid frequently used in the drinks industry is kieselguhr. In the production of beer, for example, from 150 to 200 g of filter aid, in particular kieselguhr, are required per hl of beer. Since the filtering action of these filter aids decreases after a certain time, they must be removed and, in the case of the non-regenerable filter aids, disposed of, which obviously is associated with high costs. In addition, a carcinogenic action of the kieselguhr used in the drinks industry is currently a subject of discussion.
There has therefore been no lack of attempts to provide synthetic filter aids. U.S. Pat. No. 4,344,846, for example, describes the use of expanded polystyrene in precoat filtration.
WO 96/35497 and EP 48309 describe filter aids for precoat filtration which are based on spherical, incompressible polymers, for example polyvinylpyrrolidone or Nylon 11, which form a filter cake having a porosity in the range from 0.3 to 0.5.
EP-A 879629 describes filter aids which consist of a particulate or fibrous support and a hydrophobic coating applied thereon.
EP-A 177812 and EP-A 351363 disclose highly crosslinked, scarcely swellable, pulverulent polymers based on N-vinylpyrrolidone which can be used as filter aids.
DE-A 19920944 describes insoluble, scarcely swellable popcorn polymers based on styrene and N-vinyllactams. The use of these popcorn polymers as filter aids is proposed.
The synthetic filter aids based on polymers have an improved regenerability. However, their filtering action sometimes leaves something to be desired. Some of the synthetic filter aids are again less suitable for precoat filtration of aqueous liquids, since they do not sediment in water, or only sediment poorly.
It is an object of the present invention to provide filter aids for filtering aqueous liquids, which filter aids have a good filtering action and are suitable for precoat filtration. In addition, good regenerability of the filter aids is desired.
We have found that this object is achieved, surprisingly, by particulate polymer preparations that comprise a polymer P that is made up of hydrophilic and hydrophobic polymer segements.
The present invention therefore relates to the use of particulate water-insoluble polymer preparations comprising at least one polymer P that is essentially made up of hydrophilic polymer segments and hydrophobic polymer segments, as filter aids for filtering aqueous liquids, in particular for precoat filtration. The invention also relates to a process for filtering aqueous liquids using such polymer preparations, in particular a process which is carried out by the method of precoat filtration.
In the polymers P used according to the invention, the polymer particles essentially consist of hydrophilic polymer segments and hydrophobic polymer segments. Polymer segments are understood by those skilled in the art to be polymer chains or polymer substructures that are made up of a plurality, generally at least 10, preferably at least 20, preferred according to the invention at least 30, identical repeat units. Hydrophobic polymer segments are accordingly polymer substructures or polymer chains that are made up of a plurality of hydrophobic monomer building blocks that are linked to one another. Correspondingly, hydrophilic polymer segments are polymer chains or polymer substructures that are made up of a plurality of hydrophilic monomer building blocks as repeat units. The hydrophilic and hydrophobic polymer segments can be bound to one another by chemical bonds in the manner of a block polymer or grafted polymer. They can also be present as an intimate physical mixture in the polymer P used according to the invention. It is important solely that the individual polymer particles of the polymer P are made up both of hydrophilic and of hydrophobic polymer segments.
For the inventive water insolubility it is advantageous if the proportion by weight of hydrophilic polymer segments does not exceed that of the hydrophobic polymer segments. Generally, therefore, the weight ratio of hydrophilic polymer segments to hydrophobic polymer segments in the polymer P is in the range from 1:1 to 1:100, preferably in the range from 1:2 to 1:50, and particularly preferably in the range from 1:3 to 1:20.
Furthermore, it has proved to be expedient if the hydrophilic polymer segments are of nonionic nature, that is to say have less than 0.1 mol/kg of ionic or ionogenic groups such as carboxylate, sulfonate or amino groups. Particularly preferably, the hydrophilic polymer segments have no ionic or ionogenic groups.
Examples of nonionic hydrophilic polymer segments are those that are made up of ethylenically unsaturated monomers having a water solubility above 50 g/l (at 25° C., 1 bar), further polyvinylalcohol structures, and polyether chains. Examples of monomers having a water solubility above 50 g/l are methyl acrylate, acrylamide, methacrylamide, hydroxyalkyl acrylates and hydroxyalkyl methacrylates such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, N-vinylpyrrolidone, N-vinylcaprolactam, methyl vinyl ether and comparable monomers.
Preferred hydrophilic polymer segments have a polyether structure, in particular a poly-C
2
-C
4
-alkylene ether structure. Particularly preferably, the hydrophilic polymer segments are derived from polyethylene oxides, polypropylene oxides and/or polyethylene/polypropylene oxide block copolymers, for example block copolymers having a central polypropylene oxide segment and terminal polyethylene oxide segments.
It has further proved to be advantageous if th
Drohmann Christian
Kolter Karl
Sanner Axel
Schweikert Loni
Witteler Helmut
BASF - Aktiengesellschaft
Keil & Weinkauf
Popovics Robert James
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