CA1073598A - Method of removing impurities from a liquid using a filter bed - Google Patents
Method of removing impurities from a liquid using a filter bedInfo
- Publication number
- CA1073598A CA1073598A CA228,529A CA228529A CA1073598A CA 1073598 A CA1073598 A CA 1073598A CA 228529 A CA228529 A CA 228529A CA 1073598 A CA1073598 A CA 1073598A
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- particles
- surface charge
- exchange resin
- filter bed
- resin particles
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- Treatment Of Liquids With Adsorbents In General (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Impurities are removed from a liquid by passing the liquid through an improved filter bed. The filter bed comprises a mixture of oppositely charged particles of filter aid material, the particles normally having a surface charge in aqueous solution. A portion of these particles are treated with a chemical compound to produce a surface charge that is opposite from the normal surface charge. These oppositely charged particles clump in aqueous suspension, and produce a filter bed which is capable of removing suspended particles with very high efficiency, while maintaining a relatively low pressure drop across the filter bed.
Impurities are removed from a liquid by passing the liquid through an improved filter bed. The filter bed comprises a mixture of oppositely charged particles of filter aid material, the particles normally having a surface charge in aqueous solution. A portion of these particles are treated with a chemical compound to produce a surface charge that is opposite from the normal surface charge. These oppositely charged particles clump in aqueous suspension, and produce a filter bed which is capable of removing suspended particles with very high efficiency, while maintaining a relatively low pressure drop across the filter bed.
Description
SPECI~ICATIO~
The present invention relates to an improved method for removing impurities from a liquid, and to an improved filter be~.
It has been found that the removal of suspended impurities from a liquid is enhanced by passing the liquid through a filter that has been precoated with a layer of ion exchange resin particles in the size range of 60 to 400 mesh. Such a method is described and claimed in U. S.
Patent No. 3,250,703, which is assigned to the assignee ¦ 10 of this application. It has further been found that the pressure drop across the bed of finely divided resin par-ticles may be reduced, while filtration efficiency is simultaneously increased, by employina a bed comprising a mixture of cation and anion exchange resin particles, this mixture comprising in the range of about 5 to 95~
cation exchange resin particles based on the weight of the mixture. The reduced pressure drop results from "clumping," which occurs when the particles are combined in aqueous suspension. This method is described and 20 claimed in U. S. Patent INo. 3,250,702, which is assigned to the assignee of this application.
As used herein, the term "bed" refers to a layer, such as a precoat layer, which has been deposited on a filter screen, a wound, annular filter cartridge, a film, a deep or shallow bed, or the like. Such a bed may ad- -vantageously be deposited on a tubular filter cartridge such as those described in U. S. Patent ~o. 3J 279,608, which is assigned to the assignee of this application.
- .
3S~
Although ion exchange resin mixtures form a highly efficient filtration system, the ion exhange resins are expensive, and, in many instances, ion exchange capacity is unnecessary.
That is, it is sometimes desired to employ a filter having a reduced pressure drop and increased efficiency solely for the removal of finely divided suspended particles ("crud") from liquids There are also instances where it is desirable to employ a non-ion-exchange resin overlay over the ion exchange resin itself. Such a method is particularly desirable when the liquid being filtered contains suspended particles which interfere with the ion exhange resin. For example, it has been found that iron contaminants have a tendency to cause cracking of ion exchange resin precoats, with a resultant loss in both filtration and ion exchange efficiency. If an overlay can be employed over the ion exchange resin in order to remove these contaminants from the liquid, the run length for the ion exchange resin can be greatly increased.
Generally, the present invention relates to a method for removing impurities from a liquid by passing the liquid through a filter bed which comprises a mixture of oppositely charged particles of filter aid material. The filter aid particles that are employed normally have a surface charge in aqueous solution, and a portion of the particles is treated with a chemical com-pound to produce a surface charge which is opposite to the normal surface charge. A mixture of oppositely charged particles (normal and reversed) is therefore produced, and the "clumping"
phenomenon is achieved without the need to employ expensive cation and anion exchange resin particles.
Thus, the invention contemplates a method for removing impurities from a liquid which comprises passing the liquid -107359~
throu~h a filter bed made up of a mixture of oppositely charged particles of filter aid materïal with the particles normally all having the same surface charge in aqueous solution, wherein a portion of the particles has been treated with a chemical compound that produces a surface charge opposite to the normal surface charge. The portion of the particles comprises from about 5 to about 95 percent of said particles hy weight.
The invention also provides an improved filter bed which comprises a mixture of oppositely charged particles of filter aid material. Again, these particles normally all have the same surface charge in aqueous solution, and a portion of the parti-cles is treated with a chemical compound to produce a surface charge opposite to the normal surface charge. The portion comprises from about 5 to about 95 percent of the particles by weight.
More specifically, it has been found that the phenomenon of "clumping" described in U. S. Patent No. 3,250,702, together with the advantageous reduced pressure drop and increased filtration efficiency of this phenomenon, can be achieved by combining particles of filter aid material which have been treated in a manner to produce an opposite charge on a portion of such particles. This opposite charge is produced by treating a portion of the particles with a chemical compound that pro-duces a surface charge opposite to the normal surface charge.
In order to produce the clumping phenomenon, it is necessary that a portion of the particles retain a charge which is the same as the normal surface charge. These particles may be untreated, or, desirably, may also be treated with chemical compounds in order to enhance the normal surface charge thereon.
It is well known in the art that many types of filter aid material normally carry a surface charge. By the term "filter aid material," applicant refers to those materials which are conventionally deposited on a filter screen or the like in order to aid in the filtration which is produced by the filter.
107359~
Most of such material are characterized by electronegatively charged s-urface. Such materials are well known in the art, and include diatomaceous earth, cellulose fibers, charcoal, expanded -perlite, asbestos fibers, etc. Cation exchange resin particles also have a negatïve surface charge, and may be employed as filter aid particles in accordance with the present invention.
Particularly preferred filter aid particles for use in accordance with the invention are cellulose fibers, which are available -commercially under the trade name "SOLKA-FLOC".
Although most filter aid materials normally have a negative surface char~e, some have a positive charge. Such particles include, for example, anion exhange resin particles. Such filter aid materials may also be empolyed in accordance with the present invention, wherein they are treated with a chemical compound in order to produce a positive surface charge on some of the part-icles, so that the clumping phenomenon is again achieved when oppositely charged particles are mixed.
A wide variety of chemical compounds may be empolyed in accordance with the present invention in order to produce a reverse surface charge on a portion of the particles. Such compounds must be miscible with water, and the compounds must have a plurality of charge sites. A plurality of charge sites is required in order that the compound form a bond with the filter aid material, and will have charge sites remaining to produce a surface charge that is the reverse of the normal surface charge.
When the filter aid particles normally have a negative surface charge, a cationic electrolyte-type compound is employed, preferably a cationic organic polyelectrolyte.
~ 3~9~
These cationic compounds form an electrical bond with the surface of the negatively charged filter aid material, producing a positive charge on the surface thereof.
Suitable non-polymeric cationic-type compounds include l-carboxymethyl pyridinium chloride and cetyl pyridinium chloride. Suitable cationic polyelectrolytes include linear polyelectrolytes characterized by little, if any, cross-linking. Many such polyelectrolytes are well known in the art, and include polyalkylene imines, polyalkylene polyamines, polyvinyl benzyl quaternary ammonium salts, polyvinyl benzyl tertiary amines, vinylbenzyl sufonium polymers, etc. Specific polymeric compounds that could be employed include, for example, poly (l-butyl-4-vinyl pyridinium bromide), and poly (1,2-dimethyl-5-vinyl pyridinium methyl sulfate). A particularly suitable cationic polyamine is one characterized by the repeating structure:
~2t H X
However, it should be understood that the above-mentioned specific compounds are not the only ones that can be utilized, as many cationic polyelectrolytes are well known in the art.
1~73S98 In the instance where the filter aid employed has an electropositively charged surface in aqueous solution, an anionic-type compound is employed in order to produce a reverse surface charge~ Again, the preferred compound is an anionic polyelectrolyte. Suita~le anionic compounds include polymeric acids such as polyacrylic acids, poly-sulfonic acids, etc.
As previously stated, it is frequently desirable to treat a filter aid material with both anionic and cationic polyelectrolytes in order to enhance the normal surface charge in accordance with the present invention. Thus, an electronegatively charged filter aid material, such as cellulose fibers, can be treated with a suitable chemical compound in order to produce a positive surace charge, and then with another chemical compound in order to again reverse the charge to the normal surface charge. However, this reversed charge is often stronger, and therefore capable of producing clumping characteristics that are superior to those produced when untreated material is employed.
The application of chemical compounds to the filter aids in order to produce a reverse surface charge is nor-mally carried out in aqueous suspension. In carrying out the preferred method, the filter aid material is simply suspended in water, and an adequate amount of chemical compound is added to produce the desired reverse surface charge. With high molecular weight polyelectrolytes (i.e., molecular weights in excess of 100,000), the point at which adequate electrolyte has been added can be determined by observing the filter aid material as the polyelectrolyte is added.
10735~8 Initially, clumping will be produced as the surface char~e of a portion of the particles is reversed, and this clump-ing will then disappear when a reversal of substantially all of the surface charge is observed. However, with lower molecular weight electrolytes, and even with some combinations of high molecular weight polyelectrolytes and filter aid material, no noticeable clumping is produced when the electrolyte is added. In those instances, an adequate amount of electrolyte must be determined from the results obtained when the treated particles are mixed with particles having an opposite ~urface charge.
In general, at least about 5% of the chemical compound, based upon the weight of the dry filter aid particles, is required. However, much larger amounts can be employed, as there is no detriment realized from the use of an excess amount of the surface charge reversal-producing compound.
Of course, the amount of compound required in a particular case depends upon many factors, including the nature of the particles being treated and the number of positive or negative sites that are available on the chemical compound being added.
As will be apparent from the foregoing, one method of carrying out the present invention when high molecular weight polyelectrolytes are employed is simply to add a polyelectrolyte which produces a reverse surface charge to an a~ueous suspension of filter aid particles. This compound is added in an amount sufficient to produce the desired clumping effect, indicating that the surface charge of a portion of the filter aid particles in suspension has been reversed, and that these particles have clumped with the remaining, untreated particles.
07359~
~ ore desirably, howe~er, the particles are first treated in aqueous suspension to produce a complete reversal of surface charge, and the suspension is then dewatered through well known techniques such as decanting, filtration, or a combination thereof. Thes-e particles are then combined in aqueous suspension w-ith particles having the normal surface charge. Ordinarily, this com~ination is performed in about a 50-50 proportion, although this proportion may be adjusted in order to produce the desired amount of clumping.
In general, clumping is produced in aqueGus suspensions containing anywhere from 5 to 95% of particles having the reversed surface charge.
In the most preferred embodiment of the invention, particles having a negative surface charge in aqueous suspension are treated with a cationic polyelectrolyte to produce a positive surface charge. The treated particles are dewatered and mixed in aqueous suspension with particles having an enhanced negative surface charge. This enhanced negative charge is produced by treating the particles in aqueous suspension with a cationic polyelectrolyte, dewater-ing the suspension, resuspending the particles in water, and treating them with an anionic polyelectrolyte. The suspension is again dewatered, and the treated particles are mixed in aqueous suspension with particles that have been treated with a cationic polyelectrolyte. It has been found that this method produces a high degree of clumping and a stable floc of filter aid material. Again, the clumping is performed in aqueous suspension, preferably with about a 50-50 mixture of positively and negati~ely charged polyelectrolytes, although the ratio may be varied anywhere 1~73598 from 5 to 95% positively charged ~ilter aid particles.
After clumping, the mixture may be dewatered and dried, and then resuspended in water when it is desired to precoat a filter to form a filter bed.
The following examples are intended to illustrate the present invention, and should not be construed as limitative, the scope of the invention being determined by the appended claims:
Example I
36g of cellulose fibers having an average length of 96 microns and an a~erage diameter of 17 microns was suspended in 1000 ~1 of water in a 1.0 liter beaker equipped with a magnetic stirrer. The stirrer was turned on to maintain the cellulose in suspension, and a water-soluble polyethylene polyamine was added slowly. The polyelectrolyte was added until a maximum amount of clumping was observed, which required about 8% polyelectrolyte, based on the dry weight of the cellulose fibers.
The slurry prepared as above was dewatered by filtration with a Buchner funnel and dried. This material could be resuspended in water precoated onto a filter, such as a tubular, nylon-wound filter element, to produce good filtration characteristics together with a lower pressure drop than would be produced with untreated cellulose fibers.
Example II
A suspension of 36g of anion exchange resin particles was suspended in 1000 ml of water, as in Example I. The particles were in the size range of 60-400 mesh, and were of the styrene-divinylbenzene copolymer type having quaternary ammonium active groups. The polymer was about 8~ cross-linked.
_9_ lQ73S9~3 A solution of polyacrylic acid ha~ing a concentration of 25% by weight and an average molecular weight of about 50,000-150,000 was added slowly to the suspension until maximum clumping was o~served, as in Example I. About 10%
polyacrylic acid, based upon the weight of the dry resin particles, was required.
The slurry was dewatered with a Buchner funnel and dried. This material could be resuspended in water and precoated onto a filter, such as a tubular, nylon-wound filter element, to produce good filtration characteristics, together with a lower pressure drop than would be produced with untreated cellulose fibers.
Example III
150 gallons of water were placed in a 250-gallon tank e~uippe~ with a mechanical stirrer. 30 pounds of cellulose fibers of the type employed in ~xample I were added, and the cellulose was suspended using the stirrer. 4 pounds of a polyamide cationic polyelectrolyte having a molecular weight in the range of 20,000 to 100,000. This polyamide is commercially available under the trade name "Betz 1175,"
sold by the Bet2 Company, Trevose, Pennsylvania. The suspension was then stirred for one hour to thoroughly mix the polyelectrolyte. The cellulose was then dewatered with a Buchner funnel.
Half of the treated cellulose was separated and transferred to a 500-gallon tank equipped with a mechanical stirrer and containing 150 gallons of water. The stirrer was started to resuspend the cellulose, and 8 pounds of an -aqueous solution of polyacrylic acid having a concentration of 25% b~ weight, and having an average molecular weight in the range of 50,000-150,000 was added. This polyacrylic acid ,, .
-10- .
~73598 solution is commercially available under the trade name "ACRYSOL" A-3 from Rohm & Haas Co., Philadelphia, Pennsylvania. The stirrer was run for 30 minutes to thoroughly coat the treated cellulose fibers to produce a negative surface charge. The suspension was dewatered using a Buchner funnel, and was reslurried in 300 gallons of water. The portion of the cellulose that was treated only with the polyamide was added, and mixed for ten minutes, and the mixture was then dewatered.
The foregoing mixture was suspended in water and coated on a nylon-wound tubular filter element. The material produced excellent iltration characteristics with a minimum o~ pressure drop.
EXample IV
A tubular, wound nylon filter element was precoated with a mixture of 75% cation exchange resin and 25~ anion exchange resin in the size range of about 60 to 400 mesh, as described in U.S. Patent No. 3,250,703. This ion exchange resin precoat was applied in an amount of 0.2 pound per square foot of filter element. A second coat of filter aid material prepared in accordance with Example III was then applied to the filter over the precoat of ion exchange resin particles in an amount of 0.06 pound per square foot. The filter cartridge was employed to filter liquid containing both ions and suspended particles containing iron contaminants. The coating of cellulose fibers over the ion exchange resin effectively removed the bulk of the iron contaminants, preventing the cracking of the ion exchange resin that would normally be observed.
lO~S~-3 Very little increase in pxessure drop was produced through the use o~ this overlay.
Obviously, many modifications and variations of the invention as hereinbefore set forth will occur to those skilled in the art, and it is intended to cover in the appended claims all such modifications and variations as fall within the true spirit and scope of the invention.
The present invention relates to an improved method for removing impurities from a liquid, and to an improved filter be~.
It has been found that the removal of suspended impurities from a liquid is enhanced by passing the liquid through a filter that has been precoated with a layer of ion exchange resin particles in the size range of 60 to 400 mesh. Such a method is described and claimed in U. S.
Patent No. 3,250,703, which is assigned to the assignee ¦ 10 of this application. It has further been found that the pressure drop across the bed of finely divided resin par-ticles may be reduced, while filtration efficiency is simultaneously increased, by employina a bed comprising a mixture of cation and anion exchange resin particles, this mixture comprising in the range of about 5 to 95~
cation exchange resin particles based on the weight of the mixture. The reduced pressure drop results from "clumping," which occurs when the particles are combined in aqueous suspension. This method is described and 20 claimed in U. S. Patent INo. 3,250,702, which is assigned to the assignee of this application.
As used herein, the term "bed" refers to a layer, such as a precoat layer, which has been deposited on a filter screen, a wound, annular filter cartridge, a film, a deep or shallow bed, or the like. Such a bed may ad- -vantageously be deposited on a tubular filter cartridge such as those described in U. S. Patent ~o. 3J 279,608, which is assigned to the assignee of this application.
- .
3S~
Although ion exchange resin mixtures form a highly efficient filtration system, the ion exhange resins are expensive, and, in many instances, ion exchange capacity is unnecessary.
That is, it is sometimes desired to employ a filter having a reduced pressure drop and increased efficiency solely for the removal of finely divided suspended particles ("crud") from liquids There are also instances where it is desirable to employ a non-ion-exchange resin overlay over the ion exchange resin itself. Such a method is particularly desirable when the liquid being filtered contains suspended particles which interfere with the ion exhange resin. For example, it has been found that iron contaminants have a tendency to cause cracking of ion exchange resin precoats, with a resultant loss in both filtration and ion exchange efficiency. If an overlay can be employed over the ion exchange resin in order to remove these contaminants from the liquid, the run length for the ion exchange resin can be greatly increased.
Generally, the present invention relates to a method for removing impurities from a liquid by passing the liquid through a filter bed which comprises a mixture of oppositely charged particles of filter aid material. The filter aid particles that are employed normally have a surface charge in aqueous solution, and a portion of the particles is treated with a chemical com-pound to produce a surface charge which is opposite to the normal surface charge. A mixture of oppositely charged particles (normal and reversed) is therefore produced, and the "clumping"
phenomenon is achieved without the need to employ expensive cation and anion exchange resin particles.
Thus, the invention contemplates a method for removing impurities from a liquid which comprises passing the liquid -107359~
throu~h a filter bed made up of a mixture of oppositely charged particles of filter aid materïal with the particles normally all having the same surface charge in aqueous solution, wherein a portion of the particles has been treated with a chemical compound that produces a surface charge opposite to the normal surface charge. The portion of the particles comprises from about 5 to about 95 percent of said particles hy weight.
The invention also provides an improved filter bed which comprises a mixture of oppositely charged particles of filter aid material. Again, these particles normally all have the same surface charge in aqueous solution, and a portion of the parti-cles is treated with a chemical compound to produce a surface charge opposite to the normal surface charge. The portion comprises from about 5 to about 95 percent of the particles by weight.
More specifically, it has been found that the phenomenon of "clumping" described in U. S. Patent No. 3,250,702, together with the advantageous reduced pressure drop and increased filtration efficiency of this phenomenon, can be achieved by combining particles of filter aid material which have been treated in a manner to produce an opposite charge on a portion of such particles. This opposite charge is produced by treating a portion of the particles with a chemical compound that pro-duces a surface charge opposite to the normal surface charge.
In order to produce the clumping phenomenon, it is necessary that a portion of the particles retain a charge which is the same as the normal surface charge. These particles may be untreated, or, desirably, may also be treated with chemical compounds in order to enhance the normal surface charge thereon.
It is well known in the art that many types of filter aid material normally carry a surface charge. By the term "filter aid material," applicant refers to those materials which are conventionally deposited on a filter screen or the like in order to aid in the filtration which is produced by the filter.
107359~
Most of such material are characterized by electronegatively charged s-urface. Such materials are well known in the art, and include diatomaceous earth, cellulose fibers, charcoal, expanded -perlite, asbestos fibers, etc. Cation exchange resin particles also have a negatïve surface charge, and may be employed as filter aid particles in accordance with the present invention.
Particularly preferred filter aid particles for use in accordance with the invention are cellulose fibers, which are available -commercially under the trade name "SOLKA-FLOC".
Although most filter aid materials normally have a negative surface char~e, some have a positive charge. Such particles include, for example, anion exhange resin particles. Such filter aid materials may also be empolyed in accordance with the present invention, wherein they are treated with a chemical compound in order to produce a positive surface charge on some of the part-icles, so that the clumping phenomenon is again achieved when oppositely charged particles are mixed.
A wide variety of chemical compounds may be empolyed in accordance with the present invention in order to produce a reverse surface charge on a portion of the particles. Such compounds must be miscible with water, and the compounds must have a plurality of charge sites. A plurality of charge sites is required in order that the compound form a bond with the filter aid material, and will have charge sites remaining to produce a surface charge that is the reverse of the normal surface charge.
When the filter aid particles normally have a negative surface charge, a cationic electrolyte-type compound is employed, preferably a cationic organic polyelectrolyte.
~ 3~9~
These cationic compounds form an electrical bond with the surface of the negatively charged filter aid material, producing a positive charge on the surface thereof.
Suitable non-polymeric cationic-type compounds include l-carboxymethyl pyridinium chloride and cetyl pyridinium chloride. Suitable cationic polyelectrolytes include linear polyelectrolytes characterized by little, if any, cross-linking. Many such polyelectrolytes are well known in the art, and include polyalkylene imines, polyalkylene polyamines, polyvinyl benzyl quaternary ammonium salts, polyvinyl benzyl tertiary amines, vinylbenzyl sufonium polymers, etc. Specific polymeric compounds that could be employed include, for example, poly (l-butyl-4-vinyl pyridinium bromide), and poly (1,2-dimethyl-5-vinyl pyridinium methyl sulfate). A particularly suitable cationic polyamine is one characterized by the repeating structure:
~2t H X
However, it should be understood that the above-mentioned specific compounds are not the only ones that can be utilized, as many cationic polyelectrolytes are well known in the art.
1~73S98 In the instance where the filter aid employed has an electropositively charged surface in aqueous solution, an anionic-type compound is employed in order to produce a reverse surface charge~ Again, the preferred compound is an anionic polyelectrolyte. Suita~le anionic compounds include polymeric acids such as polyacrylic acids, poly-sulfonic acids, etc.
As previously stated, it is frequently desirable to treat a filter aid material with both anionic and cationic polyelectrolytes in order to enhance the normal surface charge in accordance with the present invention. Thus, an electronegatively charged filter aid material, such as cellulose fibers, can be treated with a suitable chemical compound in order to produce a positive surace charge, and then with another chemical compound in order to again reverse the charge to the normal surface charge. However, this reversed charge is often stronger, and therefore capable of producing clumping characteristics that are superior to those produced when untreated material is employed.
The application of chemical compounds to the filter aids in order to produce a reverse surface charge is nor-mally carried out in aqueous suspension. In carrying out the preferred method, the filter aid material is simply suspended in water, and an adequate amount of chemical compound is added to produce the desired reverse surface charge. With high molecular weight polyelectrolytes (i.e., molecular weights in excess of 100,000), the point at which adequate electrolyte has been added can be determined by observing the filter aid material as the polyelectrolyte is added.
10735~8 Initially, clumping will be produced as the surface char~e of a portion of the particles is reversed, and this clump-ing will then disappear when a reversal of substantially all of the surface charge is observed. However, with lower molecular weight electrolytes, and even with some combinations of high molecular weight polyelectrolytes and filter aid material, no noticeable clumping is produced when the electrolyte is added. In those instances, an adequate amount of electrolyte must be determined from the results obtained when the treated particles are mixed with particles having an opposite ~urface charge.
In general, at least about 5% of the chemical compound, based upon the weight of the dry filter aid particles, is required. However, much larger amounts can be employed, as there is no detriment realized from the use of an excess amount of the surface charge reversal-producing compound.
Of course, the amount of compound required in a particular case depends upon many factors, including the nature of the particles being treated and the number of positive or negative sites that are available on the chemical compound being added.
As will be apparent from the foregoing, one method of carrying out the present invention when high molecular weight polyelectrolytes are employed is simply to add a polyelectrolyte which produces a reverse surface charge to an a~ueous suspension of filter aid particles. This compound is added in an amount sufficient to produce the desired clumping effect, indicating that the surface charge of a portion of the filter aid particles in suspension has been reversed, and that these particles have clumped with the remaining, untreated particles.
07359~
~ ore desirably, howe~er, the particles are first treated in aqueous suspension to produce a complete reversal of surface charge, and the suspension is then dewatered through well known techniques such as decanting, filtration, or a combination thereof. Thes-e particles are then combined in aqueous suspension w-ith particles having the normal surface charge. Ordinarily, this com~ination is performed in about a 50-50 proportion, although this proportion may be adjusted in order to produce the desired amount of clumping.
In general, clumping is produced in aqueGus suspensions containing anywhere from 5 to 95% of particles having the reversed surface charge.
In the most preferred embodiment of the invention, particles having a negative surface charge in aqueous suspension are treated with a cationic polyelectrolyte to produce a positive surface charge. The treated particles are dewatered and mixed in aqueous suspension with particles having an enhanced negative surface charge. This enhanced negative charge is produced by treating the particles in aqueous suspension with a cationic polyelectrolyte, dewater-ing the suspension, resuspending the particles in water, and treating them with an anionic polyelectrolyte. The suspension is again dewatered, and the treated particles are mixed in aqueous suspension with particles that have been treated with a cationic polyelectrolyte. It has been found that this method produces a high degree of clumping and a stable floc of filter aid material. Again, the clumping is performed in aqueous suspension, preferably with about a 50-50 mixture of positively and negati~ely charged polyelectrolytes, although the ratio may be varied anywhere 1~73598 from 5 to 95% positively charged ~ilter aid particles.
After clumping, the mixture may be dewatered and dried, and then resuspended in water when it is desired to precoat a filter to form a filter bed.
The following examples are intended to illustrate the present invention, and should not be construed as limitative, the scope of the invention being determined by the appended claims:
Example I
36g of cellulose fibers having an average length of 96 microns and an a~erage diameter of 17 microns was suspended in 1000 ~1 of water in a 1.0 liter beaker equipped with a magnetic stirrer. The stirrer was turned on to maintain the cellulose in suspension, and a water-soluble polyethylene polyamine was added slowly. The polyelectrolyte was added until a maximum amount of clumping was observed, which required about 8% polyelectrolyte, based on the dry weight of the cellulose fibers.
The slurry prepared as above was dewatered by filtration with a Buchner funnel and dried. This material could be resuspended in water precoated onto a filter, such as a tubular, nylon-wound filter element, to produce good filtration characteristics together with a lower pressure drop than would be produced with untreated cellulose fibers.
Example II
A suspension of 36g of anion exchange resin particles was suspended in 1000 ml of water, as in Example I. The particles were in the size range of 60-400 mesh, and were of the styrene-divinylbenzene copolymer type having quaternary ammonium active groups. The polymer was about 8~ cross-linked.
_9_ lQ73S9~3 A solution of polyacrylic acid ha~ing a concentration of 25% by weight and an average molecular weight of about 50,000-150,000 was added slowly to the suspension until maximum clumping was o~served, as in Example I. About 10%
polyacrylic acid, based upon the weight of the dry resin particles, was required.
The slurry was dewatered with a Buchner funnel and dried. This material could be resuspended in water and precoated onto a filter, such as a tubular, nylon-wound filter element, to produce good filtration characteristics, together with a lower pressure drop than would be produced with untreated cellulose fibers.
Example III
150 gallons of water were placed in a 250-gallon tank e~uippe~ with a mechanical stirrer. 30 pounds of cellulose fibers of the type employed in ~xample I were added, and the cellulose was suspended using the stirrer. 4 pounds of a polyamide cationic polyelectrolyte having a molecular weight in the range of 20,000 to 100,000. This polyamide is commercially available under the trade name "Betz 1175,"
sold by the Bet2 Company, Trevose, Pennsylvania. The suspension was then stirred for one hour to thoroughly mix the polyelectrolyte. The cellulose was then dewatered with a Buchner funnel.
Half of the treated cellulose was separated and transferred to a 500-gallon tank equipped with a mechanical stirrer and containing 150 gallons of water. The stirrer was started to resuspend the cellulose, and 8 pounds of an -aqueous solution of polyacrylic acid having a concentration of 25% b~ weight, and having an average molecular weight in the range of 50,000-150,000 was added. This polyacrylic acid ,, .
-10- .
~73598 solution is commercially available under the trade name "ACRYSOL" A-3 from Rohm & Haas Co., Philadelphia, Pennsylvania. The stirrer was run for 30 minutes to thoroughly coat the treated cellulose fibers to produce a negative surface charge. The suspension was dewatered using a Buchner funnel, and was reslurried in 300 gallons of water. The portion of the cellulose that was treated only with the polyamide was added, and mixed for ten minutes, and the mixture was then dewatered.
The foregoing mixture was suspended in water and coated on a nylon-wound tubular filter element. The material produced excellent iltration characteristics with a minimum o~ pressure drop.
EXample IV
A tubular, wound nylon filter element was precoated with a mixture of 75% cation exchange resin and 25~ anion exchange resin in the size range of about 60 to 400 mesh, as described in U.S. Patent No. 3,250,703. This ion exchange resin precoat was applied in an amount of 0.2 pound per square foot of filter element. A second coat of filter aid material prepared in accordance with Example III was then applied to the filter over the precoat of ion exchange resin particles in an amount of 0.06 pound per square foot. The filter cartridge was employed to filter liquid containing both ions and suspended particles containing iron contaminants. The coating of cellulose fibers over the ion exchange resin effectively removed the bulk of the iron contaminants, preventing the cracking of the ion exchange resin that would normally be observed.
lO~S~-3 Very little increase in pxessure drop was produced through the use o~ this overlay.
Obviously, many modifications and variations of the invention as hereinbefore set forth will occur to those skilled in the art, and it is intended to cover in the appended claims all such modifications and variations as fall within the true spirit and scope of the invention.
Claims (24)
1. A method for removing impurities from a liquid compri-sing: passing said liquid through a filter bed comprising a mix-ture of oppositely charged particles of filter aid material, said particles normally all having the same surface charge in aqueous solution, wherein a portion of said particles has been treated with a chemical compound that produces a surface charge opposite to said normal surface charge, said portion comprising from about 5 to about 95 percent of said particles by weight.
2. The method as defined in claim 1 wherein said particles normally have a negative surface charge.
3. The method as defined in claim 2 wherein said particles comprise cellulose fibers.
4. The method as defined in claim 2 wherein said particles comprise cation exchange resin particles in the size range of 60 to 400 mesh.
5. The method as defined in claim 1 wherein said chemical compound comprises a polyelectrolyte.
6. The method as defined in claim 1 further comprising the step of passing said liquid through a mixture of anion and cation exchange resin particles after passing said liquid through said filter aid material, said resin particles being in the size range of about 60 to 400 mesh, said cation exchange resin particles comprising about 5 to 95% by weight of the particles in said mix-ture.
7. The method as defined in claim 6 wherein said filter aid particles comprise cellulose fibers.
8. The method as defined in claim 7 wherein said chemical compound comprises a polyelectrolyte.
9. A method for removing impurities from a liquid compri-sing passing said liquid through a bed of oppositely charged particles of filter aid material, said particles normally all having a negative surface charge in aqueous solution, wherein a first portion of said particles has been treated in aqueous sus-pension with a cationic polyelectrolyte, and wherein a second portion of said particles has been treated in aqueous suspension with a cationic polyelectrolyte and then with an anionic poly-electrolyte, said first portion comprising from about 5 to 95 percent of said particles by weight.
10. The method as defined in claim 9 wherein said particles comprise cellulose fibers.
11. The method as defined in claim 9 wherein said particles comprise cation exchange resin particles.
12. The method as defined in claim 9 further comprising the step of passing said liquid through a mixture of anion and cation exchange resin particles after passing through said filter aid material, said resin particles being in the size range of about 60 to 400 mesh, said cation exchange resin particles comprising about 5 to 95% by weight of the particles in said mixture.
13. The method as defined in claim 12 wherein said particles comprise cellulose fibers.
14. An improved filter bed comprising a mixture of opposite-ly charged particles of filter aid material, said particles normally all having the same surface charge in aqueous solution, wherein a portion of said particles has been treated with a chemical compound that produces a surface charge opposite to said normal surface charge, said portion comprising from about 5 to abou 95 percent of said particles by weight.
15. The improved filter bed as defined in claim 14 wherein said particles normally have a negative surface charge.
16. The improved filter bed as defined in claim 15 wherein said particles comprise cellulose fibers.
17. The improved filter bed as defined in claim 15 wherein said particles comprise cation exchange resin particles.
18. The improved filter bed as defined in claim 14 wherein said chemical compound comprises a polyelectrolyte.
19. The improved filter bed as defined in claim 14 wherein said filter bed further comprises a layer of ion exchange resin particles beneath said filter aid material, said resin particles comprising a mixture of anion and cation exchange resin particles in the size range of about 60 to 400 mesh, said cation exchange resin particles comprising about 5 to 95% by weight of the particles in said mixture.
20. The improved filter bed as defined in claim 19 wherein said filter aid particles comprise cellulose fibers.
21. An improved filter bed comprising: a bed of oppositely charged particles of filter aid material, said particles normally all having a negative surface charge in aqueous solution, wherein a first portion of said particles has been treated in aqueous suspension with a cationic polyelectrolyte, and wherein a second portion of said particles has been treated in aqueous suspension with a catianic polyelectrolyte and then with an anionic poly-electrolyte, said first portion comprising from about 5 to about 95 percent of said particles by weight.
22. The improved filter bed as defined in claim 21 wherein said particles comprise cellulose fibers.
23. The improved filter bed as defined in claim 21 wherein said filter bed further comprises a layer of ion exchange resin particles beneath said filter aid material, said resin particles comprising a mixture of anion and cation exchange resin particles in the size range of about 60 to 400 mesh, said cation exchange resin particles comprising about 5 to 95% by weight of the particles in said mixture.
24. The improved filter bed as defined in claim 23 wherein said filter aid particles comprise cellulose fibers.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA228,529A CA1073598A (en) | 1975-06-04 | 1975-06-04 | Method of removing impurities from a liquid using a filter bed |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA228,529A CA1073598A (en) | 1975-06-04 | 1975-06-04 | Method of removing impurities from a liquid using a filter bed |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1073598A true CA1073598A (en) | 1980-03-11 |
Family
ID=4103243
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA228,529A Expired CA1073598A (en) | 1975-06-04 | 1975-06-04 | Method of removing impurities from a liquid using a filter bed |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1073598A (en) |
-
1975
- 1975-06-04 CA CA228,529A patent/CA1073598A/en not_active Expired
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