Liquid purification or separation – Processes – Separating
Reexamination Certificate
2002-02-19
2004-05-18
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Separating
C210S733000, C426S007000, C426S422000, C426S495000
Reexamination Certificate
active
06736981
ABSTRACT:
The present invention relates to the use of particulate, water-insoluble and scarcely swellable polymers based on ethylenically unsaturated monomers as filter aids for filtering aqueous liquids, and to novel particulate, water-insoluble and scarcely swellable copolymers.
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 aids 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 auxiliary layer on the filter surface. In precoat filtration, for example before the start of filtration, a filter aid precoat is applied to a support surface. 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 lexicon], 9th edition, Georg Thiemer Verlag Stuttgart, pp. 1357 ff. and C. Alt in Ullmann's Encyclopedia of Industrial Chemistry, 5th ed. on CD-ROM, “Filtration”, especially Chapter 4 “Deep-Bed Filtration” and Chapter 11 “Filter Aids” 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.
WO96/35497 and EP483099 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 177812 discloses highly crosslinked, scarcely swellable, pulverulent popcorn 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.
Furthermore, the filter aid should be inexpensive and producible as far as possible in a solvent-free manner.
We have found that this object is achieved, surprisingly, by particulate, water-insoluble and scarcely swellable polymers based on ethylenically unsaturated monomers, which polymers contain, copolymerized, at least 20% by weight, based on the total weight of monomers, of at least one &agr;,&bgr;-monoethylenically unsaturated monocarboxylic and/or dicarboxylic acid having from 3 to 6 carbons. The present invention therefore relates to the use of such polymers as filter aids for filtering aqueous liquids.
The polymers to be used inventively, despite their hydrophilicity which is due to the copolymerized acid monomers a), are virtually or completely water-insoluble and are not swollen by water, or are only swollen to a slight extent. The maximum degree of swelling Q
max
(H
2
O) is equivalent here to the maximum percent by weight of water that is maximally absorbed by one part by weight of polymer at room temperature. Generally, Q
max
(H
2
O) will not exceed 400%. Preferably, Q
max
(H
2
O) is less than 100%, and in particular less than 80%.
The low water solubility and water swellability of the polymers to be used inventively are achieved by a high degree of crosslinking or high crosslinking density of the polymer chains among one another.
The content of the ethylenically unsaturated carboxylic acids, hereinafter also monomers a), in the inventive polymers is generally from 20 to 100% by weight, or, in the presence of comonomers, up to 99.9% by weight, preferably from 25 to 95% by weight, in particular from 30 to 80% by weight, and particularly preferably from 40 to 70% by weight, in each case based on the total weight of the monomers constituting the polymer. Examples of ethylenically unsaturated carboxylic acids having from 3 to 6 carbons are acrylic acid, methacrylic acid and crotonic acid as monocarboxylic acids, and maleic acid, fumaric acid and itaconic acid as dicarboxylic acids. Preferably the polymers to be used inventively contain copolymerized acrylic acid and/or methacrylic acid, with polymers that contain copolymerized acrylic acid as monomer a) being particularly preferred.
Comonomers which come into consideration are in principle all monomers that can be copolymerized with the ethylenically unsaturated carboxylic acids. These include, in particular, derivatives of the ethylenically unsaturated carboxylic acids, for example their alkyl esters, their amides and their hydroxyalkyl esters, vinylaromatic monomers such as styrene and styrene derivatives, N-vinylamides and N-vinyl nitrogen heterocycles, and crosslinking monomers, that is to say a compound having at least 2 nonconjugated ethylenically, unsaturated double bonds.
The content of comonomers in the monomers constituting the polymer is, where present, generally in the range from 0.1 to 80% by weight, preferably from 5 to 75% by weight, in particular in the range from 20 to 70% by weight, and particularly preferably in the range from 30 to 60% by weight.
Examples of derivatives of ethylenically unsaturated carboxylic acids are: amides such as acrylamide, methacrylamide, alkyl esters preferably having from 1 to 18 carbons in the alkyl moiety, for example methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate and stearyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylat
Gomez Marcos
Meffert Helmut
Rock Tilman C
Sanner Axel
BASF - Aktiengesellschaft
Hruskoci Peter A.
Keil & Weinkauf
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