CA1119105A - Filter and method of making same - Google Patents
Filter and method of making sameInfo
- Publication number
- CA1119105A CA1119105A CA000322321A CA322321A CA1119105A CA 1119105 A CA1119105 A CA 1119105A CA 000322321 A CA000322321 A CA 000322321A CA 322321 A CA322321 A CA 322321A CA 1119105 A CA1119105 A CA 1119105A
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- Canada
- Prior art keywords
- filter
- filter aid
- particulate
- sheet
- cationic resin
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
A filter media sheet comprising fine particulate and a self-bonding matrix of cellulose fiber, the surfaces of at least one of which are modified with a polyamido-polyamine epichlorhydrin cationic resin, the matrix incorporating beaten cellulose fiber to provide a Canadian Standard Freeness of less than 600 ml.
A filter media sheet comprising fine particulate and a self-bonding matrix of cellulose fiber, the surfaces of at least one of which are modified with a polyamido-polyamine epichlorhydrin cationic resin, the matrix incorporating beaten cellulose fiber to provide a Canadian Standard Freeness of less than 600 ml.
Description
`. -- ` 1119~05 1 FILT~R AND METHOD OF MAKING SA~E
B~KG~nU~JD OF THE INVENTION
.
This invention relates to fil-tration and, more p~r-ticularly, to the removal of submicron contaminants from aque-5 OU5 ~ystems, utilizing filter media sheet comprising highl~els of particulate filter aids.
The filtration of fine particle size contaminant~
from fluids has been accomplished by the use of various porous ilter media through which the contaminated fluid is passed.
To flmction as a filter, the media must allow the fluid, com-monly water, throush, while holding back the particulate cont2minant. This holding back of the contaminant is accom-plished by virtue of the operation, within the porous media, of one or both of two distinctly different filtration mecha-15ni~ms, namely (1) mechanical straining and t2) electrokineticparticle capture. In ~echa~ical straining, a particle is rer,loved ~y physical entrapmont when it attempts to pass through a pore smaller than itself. In the case of the electroli;inetic capture mechanisms, the particle coll~ides with a surrace face within ~he porous filter media and is retained on the surrace by short rang2 attrac.ive forces.
With the exception of microporous polymeric ~bran2s, the po-ous filter media known to the art as being suit~ble for the filtration of fine particle size contaminants are comprised ~50f fiber-fiber or fiber-particulate mixtures formed dynamically into shect by vacuum felting from an aqueous slurry and then ~uhseque~tly drying the finished sheet. In those fibrous filter .aedia that depend upon mechanical straining to hold back par-ticulate contaminants, it is necessary that the pore si~e of 30the filter medium be smaller than the particle ~ize of the ~`
contaminant to be removed from the fluid. For removal of fine, submicronic contaminant particles by mechanical straining, the filter media need have correspondingly fine pores. Since the pore size of such a sheet is determined predominantly by the size and morphology of the materials used to form the sheet, it is necessary that one or more of the component materials be of a very small size, such as small diameter fibers. See, for example, any of the Pall U.S. Patents 3,158,532; 3,238,056;
3,246,767; 3,353,682 or 3,573,158.
As the size of the contaminants sought to be removed by filtration decreases, especially into the submicron range, the difficulty and expense of providing suitably dimensioned fiber structures for optimum filtration by mechanical straining increases. Accordingly, there is considerable interest in the use of fine particulates such as diatomaceous earth.
However, for such materials it is necessary to provide a matrix in order to present a coherent handleable structure for commerce and industry. Thus, at least one of the component materials in the sheet is a long,self-bonding structural fiber, to give the sheet sufficient structural integrity in both the wet "as formed" and in the final dried condition, to allow handling during processing and suitability for the intended end use. Unrefined cellulose fibers such as wood pulp, cotton, cellulose acetate or rayon are commonly used. These fibers are typically relatively large, with commercially available diameters in the range of six to sixty micrometers. Wood pulp, most often used because of its low relative cost, has fiber diameters ranging from fifteen to twenty-five micrometers, and fiber lengths of about 0.85 to about 6.5 mm.
, Filter media sheets are conveniently formed by vacuum felting from an aqueous slurry of the component material.
The vacuum felting is performed on a foraminous surface, normally a woven wire mesh which, in practice, may vary from 50 mesh to 200 mesh, with mesh openings ranging from 280 micrometers to 70 micrometers respectively. Finer meshes are unsuitable because of clogging problems and/or structural inadequacy.
The size of the openings in the foraminous vacuum felting surface, and the pore size of the cellulose fiber matrix of the formed sheet, are quite large in comparison to some or all of the dimensions of the fine fiber or particulate components required to produce the desired submicronic filter media sheet. Retention of such fine components during the vacuum formation of the filter media sheet is difficult, and imposes severe constraints on the choice of such materials, the specific details of the process utilized to form the filter media sheet, and, most important, upon the level of filtration performance that may be attained. Fine fibers, whose length may be large in comparison to their diameter, present less of a problem and tend to be retained reasonably well. Fine particulates, on the other hand, tend to show very poor retention during sheet formation.
Flocculation with polymeric retention aids, or coagulation has been used as a means of improving retention of fine particulates, in effecting the grouping of particles to offer an effective large dimension. However, filter sheet prepared from a well-flocculated slurry will have a broad particle size distribution, with small pores occurring inside the flocs, and large pores occurring between the flocs.
The existence of these larger pores will limit the ability ll~t91(~S
of the filter media sheet to remove fine contaminants. The use of flocculation to achieve high retention in filter media ~- is therefore somewhat counterproductive.
It is, of course, possible to apply hydrodynamic shear forces, breaking up the flocs, and further charge modify until the system assumes a stable disperse form. This does achieve a relatively uniform sheet of narrow pore size distri-bution. However, the retention of the particulates in such a system is very low, leading to concomitant reduction of filtration efficiency.
In addition to controlling the dispersion character-istics (and therefore the porosity of the sheet) and providing wet strength, charge modifiers are employed to control the zeta potential of the sheet constituents and maximize perform-ance in the electrokinetic capture of small charged contamin-ants. In practice, cationic charge modifiers are employed since most naturally occurring contaminant surfaces are anionic at fluid pH of practical interest. A preferred ,~ charge modifier is a melamine-formaldehyde colloid disclosed ~s for filter sheets in U.S. Patents 4,007,113-4.
t Generally, filter media employing charge modified .J
elements are utilized without further treatment after media formation. However, where treatment of biological liquids is contemplated the filter media are commonly subjected to saniti-zation or sterilization procedures under stringent conditions, e.g., relatively high temperatures and pressures, and these conditions can effect some diminution of performance with certain charge modified media or increase extractables beyond allowable limits. This phenomenon, although not entirely under-stood, may be attributable to loss of or degradation of the resin itself, or the charge functionality from the system through chemical or physical action. In any event, it appears to be specific to the choice of resin. In particular, the melamine-formaldehyde colloid modified system is incapable of satisfac-torily resisting autoclaving or hot water flush conditions, '. ~
': ' ' ~ ' ~1~91~5 losing significant amounts of charge, thus limiting its effective life. This charge modifier, being of low molecular -. weight, also is limited in respect of the amount of change modification which can be achieved in its use. Substitutes to meet these limitations are of particular interest.
It is accordingly an object of the present inven-tion to provide charge modified filter media sheets of enhanced filtration performance, especially for the removal of submicron contaminants from aqueous systems at high effi-ciency.
Another object is to afford a filter media sheet comprising a high level of fine particulates.
A still further object is the provision of sanitiz-' able or sterilizable filter media resisting degradation in such treatment and retaining sufficient charge potential to effectuate enhanced electrokinetic capture of small charged contaminants.
According to the above objects, from abroad aspect, ; the present invention provides a filter media sheet compris-,, " 20 ing fine particulate and a self-bonding matrix of cellulose fiber, the surfaces of at least one of which are modified with a polyamido-polyamine epichlorhydrin cationic resin.
The matrix ~ncorporates beaten cellulose fiber to provide a Canadian Standard Freeness of less than 600 ml.
According to a further broad aspect of the present invention there is provided a method for the preparation of filter media sheets adapted for the removal of electronega-tive submicron contaminants from contaminated liquids. The ; method comprises forming a filter sheet from fine particulate ,, ' 30 and a cellulose pulp system as a self-bonding matrix, the surfaces of at least one of the particulate and the pulp being modified with a polyamido-polyamine epichlorhydrin cationic resin. The pulp system incorporates beaten pulp to provide a Canadian Standard Freeness for the system of 100 to 600 ml.
-, .
ill9i~5 - 5a -According to a still further broad aspect of the present invention there is provided a particulate filter aid coated with a sufficient amount of polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
According to a still further broad aspect of the present invention there is provided a method for the removal of submicron contaminants from a fluid comprising passing the contaminated fluid through afilter bed comprised of a particulate filter aid coated with a sufficient amount of a polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
These and other objects are achieved in the practice of the present invention as described hereinafter.
GE~ERAL DESCRIPTION OF THE INVENTIO~
i In accordance with the present invention, charge modified filter media sheets are prepared utilizing in sheet s incorporating beaten cellulose fibers, usually a moderately to highly beaten pulp, to provide a fiber system having a Canadian Standard Freeness of 100-600 ml preferably 200-300 ml or less. The provision of shorter or more fibrillated fiber permits the retention of fine particulates ranging in the preferred embodiments upwards of 50 percent up to 70 -percent or more by weight of the sheet.
- The charge modifier selectiuely employed for the preparation of sanitizable or sterilizable filter media is a polyamido-polyamine epichlorhydrin cationic resin which resists degradation in such treatment and retains sufficient D
as positive charge potential to effectuate enhanced electrokinetic capture of small negatively charged contaminants. Thus, sterilizable filter media may be formed which are non-toxic, exhibit less than 1.5~ extractables, and are efficacious in use despite autoclaving conditions of e.g., 130C. under 15 lb.
pressure for 1 hour or hot water flushing at 180F. for 1 hour at a flow rate of 225 cc/min. Surprisingly, such filter media also afford remarkably improved performance in the filtration of intermediate (5-8) to high pH liquids, as compared to melamine-formaldehyde cationic colloid charge modified systems.
The filter media sheet, preferably formed by vacuum felting of a cationically disperse aqueous slurry comprising beaten cellulose fibers and fine particulate shows a uniform, high porosity, and fine pore size structure with excellent filtration and flow characteristics.
It will be appreciated that the high particulate retentions achieved in accordance with the invention are all the more remarkable when the total amount of cellulose fiber available to act as à matrix is considered. Thus, in the preferred embodiments, the cellulose pulp may comprise as little s as 10-20% of the total sheet weight.
Relatively high levels of particulate retention (up to about 45 percent by weight) have been achieved in the filtration arts, but only at the expense of an unacceptably high pressure drop due to the tight construction employed. The filter media sheets of the present invention, on the other hand, may be constructed in such manner to evidence low differential pressure drops, e.g., less than 4.0 psid, even at 70% loadings.
Combinations of fibers of various dimension for filters are known,as shown, for example in U.S. 2,144,781;
B~KG~nU~JD OF THE INVENTION
.
This invention relates to fil-tration and, more p~r-ticularly, to the removal of submicron contaminants from aque-5 OU5 ~ystems, utilizing filter media sheet comprising highl~els of particulate filter aids.
The filtration of fine particle size contaminant~
from fluids has been accomplished by the use of various porous ilter media through which the contaminated fluid is passed.
To flmction as a filter, the media must allow the fluid, com-monly water, throush, while holding back the particulate cont2minant. This holding back of the contaminant is accom-plished by virtue of the operation, within the porous media, of one or both of two distinctly different filtration mecha-15ni~ms, namely (1) mechanical straining and t2) electrokineticparticle capture. In ~echa~ical straining, a particle is rer,loved ~y physical entrapmont when it attempts to pass through a pore smaller than itself. In the case of the electroli;inetic capture mechanisms, the particle coll~ides with a surrace face within ~he porous filter media and is retained on the surrace by short rang2 attrac.ive forces.
With the exception of microporous polymeric ~bran2s, the po-ous filter media known to the art as being suit~ble for the filtration of fine particle size contaminants are comprised ~50f fiber-fiber or fiber-particulate mixtures formed dynamically into shect by vacuum felting from an aqueous slurry and then ~uhseque~tly drying the finished sheet. In those fibrous filter .aedia that depend upon mechanical straining to hold back par-ticulate contaminants, it is necessary that the pore si~e of 30the filter medium be smaller than the particle ~ize of the ~`
contaminant to be removed from the fluid. For removal of fine, submicronic contaminant particles by mechanical straining, the filter media need have correspondingly fine pores. Since the pore size of such a sheet is determined predominantly by the size and morphology of the materials used to form the sheet, it is necessary that one or more of the component materials be of a very small size, such as small diameter fibers. See, for example, any of the Pall U.S. Patents 3,158,532; 3,238,056;
3,246,767; 3,353,682 or 3,573,158.
As the size of the contaminants sought to be removed by filtration decreases, especially into the submicron range, the difficulty and expense of providing suitably dimensioned fiber structures for optimum filtration by mechanical straining increases. Accordingly, there is considerable interest in the use of fine particulates such as diatomaceous earth.
However, for such materials it is necessary to provide a matrix in order to present a coherent handleable structure for commerce and industry. Thus, at least one of the component materials in the sheet is a long,self-bonding structural fiber, to give the sheet sufficient structural integrity in both the wet "as formed" and in the final dried condition, to allow handling during processing and suitability for the intended end use. Unrefined cellulose fibers such as wood pulp, cotton, cellulose acetate or rayon are commonly used. These fibers are typically relatively large, with commercially available diameters in the range of six to sixty micrometers. Wood pulp, most often used because of its low relative cost, has fiber diameters ranging from fifteen to twenty-five micrometers, and fiber lengths of about 0.85 to about 6.5 mm.
, Filter media sheets are conveniently formed by vacuum felting from an aqueous slurry of the component material.
The vacuum felting is performed on a foraminous surface, normally a woven wire mesh which, in practice, may vary from 50 mesh to 200 mesh, with mesh openings ranging from 280 micrometers to 70 micrometers respectively. Finer meshes are unsuitable because of clogging problems and/or structural inadequacy.
The size of the openings in the foraminous vacuum felting surface, and the pore size of the cellulose fiber matrix of the formed sheet, are quite large in comparison to some or all of the dimensions of the fine fiber or particulate components required to produce the desired submicronic filter media sheet. Retention of such fine components during the vacuum formation of the filter media sheet is difficult, and imposes severe constraints on the choice of such materials, the specific details of the process utilized to form the filter media sheet, and, most important, upon the level of filtration performance that may be attained. Fine fibers, whose length may be large in comparison to their diameter, present less of a problem and tend to be retained reasonably well. Fine particulates, on the other hand, tend to show very poor retention during sheet formation.
Flocculation with polymeric retention aids, or coagulation has been used as a means of improving retention of fine particulates, in effecting the grouping of particles to offer an effective large dimension. However, filter sheet prepared from a well-flocculated slurry will have a broad particle size distribution, with small pores occurring inside the flocs, and large pores occurring between the flocs.
The existence of these larger pores will limit the ability ll~t91(~S
of the filter media sheet to remove fine contaminants. The use of flocculation to achieve high retention in filter media ~- is therefore somewhat counterproductive.
It is, of course, possible to apply hydrodynamic shear forces, breaking up the flocs, and further charge modify until the system assumes a stable disperse form. This does achieve a relatively uniform sheet of narrow pore size distri-bution. However, the retention of the particulates in such a system is very low, leading to concomitant reduction of filtration efficiency.
In addition to controlling the dispersion character-istics (and therefore the porosity of the sheet) and providing wet strength, charge modifiers are employed to control the zeta potential of the sheet constituents and maximize perform-ance in the electrokinetic capture of small charged contamin-ants. In practice, cationic charge modifiers are employed since most naturally occurring contaminant surfaces are anionic at fluid pH of practical interest. A preferred ,~ charge modifier is a melamine-formaldehyde colloid disclosed ~s for filter sheets in U.S. Patents 4,007,113-4.
t Generally, filter media employing charge modified .J
elements are utilized without further treatment after media formation. However, where treatment of biological liquids is contemplated the filter media are commonly subjected to saniti-zation or sterilization procedures under stringent conditions, e.g., relatively high temperatures and pressures, and these conditions can effect some diminution of performance with certain charge modified media or increase extractables beyond allowable limits. This phenomenon, although not entirely under-stood, may be attributable to loss of or degradation of the resin itself, or the charge functionality from the system through chemical or physical action. In any event, it appears to be specific to the choice of resin. In particular, the melamine-formaldehyde colloid modified system is incapable of satisfac-torily resisting autoclaving or hot water flush conditions, '. ~
': ' ' ~ ' ~1~91~5 losing significant amounts of charge, thus limiting its effective life. This charge modifier, being of low molecular -. weight, also is limited in respect of the amount of change modification which can be achieved in its use. Substitutes to meet these limitations are of particular interest.
It is accordingly an object of the present inven-tion to provide charge modified filter media sheets of enhanced filtration performance, especially for the removal of submicron contaminants from aqueous systems at high effi-ciency.
Another object is to afford a filter media sheet comprising a high level of fine particulates.
A still further object is the provision of sanitiz-' able or sterilizable filter media resisting degradation in such treatment and retaining sufficient charge potential to effectuate enhanced electrokinetic capture of small charged contaminants.
According to the above objects, from abroad aspect, ; the present invention provides a filter media sheet compris-,, " 20 ing fine particulate and a self-bonding matrix of cellulose fiber, the surfaces of at least one of which are modified with a polyamido-polyamine epichlorhydrin cationic resin.
The matrix ~ncorporates beaten cellulose fiber to provide a Canadian Standard Freeness of less than 600 ml.
According to a further broad aspect of the present invention there is provided a method for the preparation of filter media sheets adapted for the removal of electronega-tive submicron contaminants from contaminated liquids. The ; method comprises forming a filter sheet from fine particulate ,, ' 30 and a cellulose pulp system as a self-bonding matrix, the surfaces of at least one of the particulate and the pulp being modified with a polyamido-polyamine epichlorhydrin cationic resin. The pulp system incorporates beaten pulp to provide a Canadian Standard Freeness for the system of 100 to 600 ml.
-, .
ill9i~5 - 5a -According to a still further broad aspect of the present invention there is provided a particulate filter aid coated with a sufficient amount of polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
According to a still further broad aspect of the present invention there is provided a method for the removal of submicron contaminants from a fluid comprising passing the contaminated fluid through afilter bed comprised of a particulate filter aid coated with a sufficient amount of a polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
These and other objects are achieved in the practice of the present invention as described hereinafter.
GE~ERAL DESCRIPTION OF THE INVENTIO~
i In accordance with the present invention, charge modified filter media sheets are prepared utilizing in sheet s incorporating beaten cellulose fibers, usually a moderately to highly beaten pulp, to provide a fiber system having a Canadian Standard Freeness of 100-600 ml preferably 200-300 ml or less. The provision of shorter or more fibrillated fiber permits the retention of fine particulates ranging in the preferred embodiments upwards of 50 percent up to 70 -percent or more by weight of the sheet.
- The charge modifier selectiuely employed for the preparation of sanitizable or sterilizable filter media is a polyamido-polyamine epichlorhydrin cationic resin which resists degradation in such treatment and retains sufficient D
as positive charge potential to effectuate enhanced electrokinetic capture of small negatively charged contaminants. Thus, sterilizable filter media may be formed which are non-toxic, exhibit less than 1.5~ extractables, and are efficacious in use despite autoclaving conditions of e.g., 130C. under 15 lb.
pressure for 1 hour or hot water flushing at 180F. for 1 hour at a flow rate of 225 cc/min. Surprisingly, such filter media also afford remarkably improved performance in the filtration of intermediate (5-8) to high pH liquids, as compared to melamine-formaldehyde cationic colloid charge modified systems.
The filter media sheet, preferably formed by vacuum felting of a cationically disperse aqueous slurry comprising beaten cellulose fibers and fine particulate shows a uniform, high porosity, and fine pore size structure with excellent filtration and flow characteristics.
It will be appreciated that the high particulate retentions achieved in accordance with the invention are all the more remarkable when the total amount of cellulose fiber available to act as à matrix is considered. Thus, in the preferred embodiments, the cellulose pulp may comprise as little s as 10-20% of the total sheet weight.
Relatively high levels of particulate retention (up to about 45 percent by weight) have been achieved in the filtration arts, but only at the expense of an unacceptably high pressure drop due to the tight construction employed. The filter media sheets of the present invention, on the other hand, may be constructed in such manner to evidence low differential pressure drops, e.g., less than 4.0 psid, even at 70% loadings.
Combinations of fibers of various dimension for filters are known,as shown, for example in U.S. 2,144,781;
2,372,437; 2,708,982; or 3,034,981 and retention of ion exchange resins is shown in relations to pulp freeness in U.S. 2,955,067.
_7_ ..
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is further illustrated by the accompanying drawings, in which:
Figure 1 is a graph of normalized streaming potential vs. time, comparing equilibrium flush out curves for a prior art filter sheet, and a filter sheet manufactured in accordance with the invention.
Figures 2 and 3 are graphs of normalized streaming potential and effluent turbidity vs. time, comparing monodis-perse latex contaminant challenge tests for a prior art filter sheet, and a filter sheet manufactured in accordance with the invention.
Figure 4 is a graph of normalized streaming potential vs. time, comparing equilibrium flush out curves for a prior art filter sheet with filter sheet manufactured in~accordance with the invention, in the as-is or untreated form, as autoclaved, and hot water flushed.
DETAILED DESCRIPTION OF THE INVENTION
The filter media sheets of the invention are prepared from cationically modified filter elements, usually in the form of a cationically disperse aqueous slurry comprising cellulose fiber and optimized levéls of fine particulate such as diatomaceous earth or perlite. The filter elements may be cationically modified in the slurry and the sheet prepared dynamically by vacuum felting and drying, or the filter elements may be pretreated and formed into sheet media. A
special feature of the invention is the provision of filter media sheet in which the level of particulate retained is enhanced as compared to sheet prepared conventionally.
The state of refinement of a wood pulp fiber is determined by means of a "freeness" test in which measurement , *91~S
as the flow rate through a forming pad of the fibers on a standard screen is determined, most commonly utilizing the "Canadian Standard Freeness Tester." In this method, the quantity which is measured is the volume of water (expressed in ml.) which overflows from a receiver containing an orifice outlet at the bottom. The Canadian Standard Freeness measure-ments are employed in the present specification. Coarse unbeaten wood pulp fibers produce high drainage rates into the receiver from the screen resulting in large overflow volumes, and hence record a high freeness. Typical wood pulps show Canadian Standard Freeness values ranging from +400 ml. to +800 ml. In paper or filter media manufacture, such pulps may be subject to mechanical refining processes such as beating, which tends to cut and/or fibrillate the cellulose fibers. Such beaten fibers exhibit slower drainage rate, and, therefore, lower freeness.
In accordance with the present invention, such beaten pulp is employed in the self-bonding matrix for the filter media. The Canadian Standard Freeness of the pulp system will vary with pulp selection, and may be reflective of varying states of subdivision or refinement, as where different pulps or differently beaten pulps are combined for sheet formation, but the beaten pulp will be employed to provide a composite or average value ordinarily ranging from 100 to 600 ml., with lower values e.g., 200-300 ml. or less being preferred for higher solids retention.
The wood pulp may comprise as little as 10 percent by weight with up to 20 to 30 percent, by weight of the total, being preferred to provide filter media sheet with structural characteristics suitable for industrial filtration applications.
` 11~9105 g 1 Performance is enhanced by maximizing the amount of fine particulate in the filter media sheet. While as little as 10 percent of a fine particulate will result in noticeable improvement in filtration performance of either 5~ype of media, optimum performance is achieved by u~ilizing the maximum amount of fine particulate. For industrial `
filtration, structural characteristics suggest a practicable maximum of about 70 percent by weight. Of course, for less demanding applications, somewhat higher levels will be possi-ble. Generally, levels of 50-70 percent by weight are employed.
There are various types of fine anionic particulates that are suitable for the intended purpose, including diatoma-ceous earth, perlite, talc, silica gel, polymeric particulates such as those produced by emulsion or suspension polymerization, e.g., polystyrene, polyacryla~es, poly(vinyl acetate), poly-ethylene, ~or o.her such materials as described in Emulsions and Emulsion Technology, Lissant, Kenneth J., Marcel Dekker, 1974) activ~ted carbon, molecular sieves, clay, etc. Function-20 ally, the fine particulate should have a specific surface areain excess of one square meter/gram and/or particle diameters of less than 10 microns. In a brDad sense, any fine particu-late may be suitable (such as ~.~. Filter Cel, Standard Super Cel*, Celite 512,* Hydro Super Cel*, Speed Plus*and Speedflow~
25 Dicalite 215*and Dicalite 416*and Dicalite 436~ and may be evaluated by techniques well-known to the art. From the standpoint of size, morphology, cost, fluid compatibility and general performance characteristics, the finer grades o' diatomaceous earth and perlite filter aids exhibiting
_7_ ..
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is further illustrated by the accompanying drawings, in which:
Figure 1 is a graph of normalized streaming potential vs. time, comparing equilibrium flush out curves for a prior art filter sheet, and a filter sheet manufactured in accordance with the invention.
Figures 2 and 3 are graphs of normalized streaming potential and effluent turbidity vs. time, comparing monodis-perse latex contaminant challenge tests for a prior art filter sheet, and a filter sheet manufactured in accordance with the invention.
Figure 4 is a graph of normalized streaming potential vs. time, comparing equilibrium flush out curves for a prior art filter sheet with filter sheet manufactured in~accordance with the invention, in the as-is or untreated form, as autoclaved, and hot water flushed.
DETAILED DESCRIPTION OF THE INVENTION
The filter media sheets of the invention are prepared from cationically modified filter elements, usually in the form of a cationically disperse aqueous slurry comprising cellulose fiber and optimized levéls of fine particulate such as diatomaceous earth or perlite. The filter elements may be cationically modified in the slurry and the sheet prepared dynamically by vacuum felting and drying, or the filter elements may be pretreated and formed into sheet media. A
special feature of the invention is the provision of filter media sheet in which the level of particulate retained is enhanced as compared to sheet prepared conventionally.
The state of refinement of a wood pulp fiber is determined by means of a "freeness" test in which measurement , *91~S
as the flow rate through a forming pad of the fibers on a standard screen is determined, most commonly utilizing the "Canadian Standard Freeness Tester." In this method, the quantity which is measured is the volume of water (expressed in ml.) which overflows from a receiver containing an orifice outlet at the bottom. The Canadian Standard Freeness measure-ments are employed in the present specification. Coarse unbeaten wood pulp fibers produce high drainage rates into the receiver from the screen resulting in large overflow volumes, and hence record a high freeness. Typical wood pulps show Canadian Standard Freeness values ranging from +400 ml. to +800 ml. In paper or filter media manufacture, such pulps may be subject to mechanical refining processes such as beating, which tends to cut and/or fibrillate the cellulose fibers. Such beaten fibers exhibit slower drainage rate, and, therefore, lower freeness.
In accordance with the present invention, such beaten pulp is employed in the self-bonding matrix for the filter media. The Canadian Standard Freeness of the pulp system will vary with pulp selection, and may be reflective of varying states of subdivision or refinement, as where different pulps or differently beaten pulps are combined for sheet formation, but the beaten pulp will be employed to provide a composite or average value ordinarily ranging from 100 to 600 ml., with lower values e.g., 200-300 ml. or less being preferred for higher solids retention.
The wood pulp may comprise as little as 10 percent by weight with up to 20 to 30 percent, by weight of the total, being preferred to provide filter media sheet with structural characteristics suitable for industrial filtration applications.
` 11~9105 g 1 Performance is enhanced by maximizing the amount of fine particulate in the filter media sheet. While as little as 10 percent of a fine particulate will result in noticeable improvement in filtration performance of either 5~ype of media, optimum performance is achieved by u~ilizing the maximum amount of fine particulate. For industrial `
filtration, structural characteristics suggest a practicable maximum of about 70 percent by weight. Of course, for less demanding applications, somewhat higher levels will be possi-ble. Generally, levels of 50-70 percent by weight are employed.
There are various types of fine anionic particulates that are suitable for the intended purpose, including diatoma-ceous earth, perlite, talc, silica gel, polymeric particulates such as those produced by emulsion or suspension polymerization, e.g., polystyrene, polyacryla~es, poly(vinyl acetate), poly-ethylene, ~or o.her such materials as described in Emulsions and Emulsion Technology, Lissant, Kenneth J., Marcel Dekker, 1974) activ~ted carbon, molecular sieves, clay, etc. Function-20 ally, the fine particulate should have a specific surface areain excess of one square meter/gram and/or particle diameters of less than 10 microns. In a brDad sense, any fine particu-late may be suitable (such as ~.~. Filter Cel, Standard Super Cel*, Celite 512,* Hydro Super Cel*, Speed Plus*and Speedflow~
25 Dicalite 215*and Dicalite 416*and Dicalite 436~ and may be evaluated by techniques well-known to the art. From the standpoint of size, morphology, cost, fluid compatibility and general performance characteristics, the finer grades o' diatomaceous earth and perlite filter aids exhibiting
3 ~ mean particle size of less than 5 microns are preferred. In many cases, mixtures of more than 35 * Registered Trademarks . ~
.
91~S
1 one type of fine particulate such as diatomaceous earth/perlite for example, in proportion by weight of from about 80/20 to 20/80 give be~ter filtration performance or better cost/perfor-mance characteristics than that achieved by the use of any ` 5 single type by itself. Similarly, mixtures in all proportions of relatively coarse and fine particulates, e.g., 50/5~ parts by weight of 10 ~nd 5 micron diameter particulates may be used.
Suitable polyamido-polyamine epichlorhydrin cationic resins are those of U.S. Patents 2,926,116; 2,926,154; 3,224,935;
lO 3,332,901 ana 3,382,096 and may be produced by reacting a dicarboxylic acid with a poly-am-ne dim2r to form a water soluble polymer s~hich is further reacted with epichlorhydrin. The dimer unit may have the general formula:
2~ 1(CH2)2-NH]X(CH2)2-NH2 where x is an integer of 1 to 7, and the dicarboxylic acid ~ay be aromatic or aliphatic such as adipic, azelaic, digly-colic, oxalic or malonic acids. The cationic charge is s 20 induced through the amine function in tertiary or quaternized ; configuration. Other suitable charge modifying resins, employ-ing a heterocyclic dicarboxylic acid reactant are disclosed in U.S. Patent 3,761,350. The poly2mido-polyamine epichlorhydrin cationic resins are available commercially, as Polycup 1884*, 25 2002 or S2064 (Hercules); Cascamide Resin pR-420 (Bordon); or Nopcob~nd 35*(Nopco).
In paper production, where cationic charge modifiers are sometimes used, the objective is reduction of charge to approximately the isoelectric point to maximize efficiency 3 in interfelting of fiber. For filtration, maximum charge ifi desired to enhance removal of charged particles by * Registered Trademarks ' i~
.
'.'--` lil9~05 electrokinetic mechanisms. In the present case the surface charge of at least one of the negatively charged filter elements i.e., cellulose and particulate is reduced to render the surface less electronegative and optionally (and preferably) reversed by the deposition of sufficient cationic charge modifier to render the surface electropositive, to provide at least certain electropositive regions or sites within the filter sheet. In order to accomplish charge reversal, of course, one proceeds through the isoelectric point, and then positive charge buildup is accomplished to the maximum practical level.
The amount of charge modifier employed in the present ~ -invention is thus preferably that sufficient to at least provide a cationically disperse system i.e., a system in which no visible flocculation occurs at ambient conditions in the absence of applied hydrodynamic shear forces. The system therefore comprises essentially discrete fiber/particulate elements exhibiting a positive charge or zeta potential relatively uniformly or homogeneously distributed in and throughout the aqueous medium. The specific level will, of course, vary with the system and the modifier selected but will be readily determined by one skilled in the art. For example, the inflectionipoint on a plot of particulate retention vs. amount of charge modifier approximates the minimum level for better performance. Thus a 2 percent level is appropriate for a polyamido-polyamine epichlorhydrin resin.
Although additional modifier may be employed to advantage where desired, this level represents the best balance on a cost/performance basis. Premodified filter elements e.g., particulate precoated with charge modifier may of course be incorporated in any manner into filter sheets with similar results, and where a cationically disperse slurry is not employed, charge modification will be commensurately reduced by control of modifier levels.
The charge modification effected is demonstrable in measurements of surface zeta potential, and in improved filtration efficiency for negatively charged particles in liquid systems.
The slurry of pulp and particulates is formed in any suitable manner. The sequence of adding these components to water to form the initial slurry appears to be relatively unimportant. The consistency of the slurry will represent the highest possible for a practical suspension of the components, usually about 4 percent. The system is subjected to hydrodynamic shear forces as by a bladed mixer, and the charge modifier is then added to the slurry.
The shear level is not critical i.e., any otherwise suitable shear rate or shear stress may be employed having regard for available equipment, preferred processing times etc., but is selected and employed simply to break up the flocs and maintain the system in a dispersed condition during treatment. Of course, upon the formation of a cationically disperse slurry, the system is free of floc formation even in the absence of applièd shear.
After charge modification, the slurry is diluted with additional water to the proper consistency required for vacuum felting sheet formation, ordinarily 0.5 to 2~ percent, depending upon the type of equipment used to form the sheet, in a manner known to the artisan. The slurry is formed into a sheet and oven dried in standard manner. The performance of the sheet is related to the drying parameters and optimized conditions may reflect energy considerations or desired thermal history consistent with minimization of unnecessary exposure to elevated temperatures, especiallyas the decomposition or scorch point for the system is approached.
In accordance with a preferred embodiment of the invention, filter media sheets are formed from filter elements, i.e., particulate and a self-bonding matrix of cellulose pulp at least one of which is charge modified, the pulp being a system incorporating beaten pulp to provide a Canadian Standard Freeness of up to 600 ml., preferably less than 300 ml. e.g., 100-200 ml. the charge modifier consisting of a polyamido-polyamine epichlorhydrin cationic resin, and being applied in a proportion to reduce electronegativity of the surface, preferably to achieve charge reversal beyond the isoelectric point, e.g., to an add-on level of about 2% by weight. Filter media sheets so prepared may be autoclaved, hot water flushed or otherwise treated at elevated temperature to sanitize or sterilize the structure. In addition to having special utility for the filtration of biological liquids, these sheets also may be employed for filtration without flush out delay, as ions present in the structure have been removed during the sanitization or sterilization procedure.
The performance benefits of the polyamido-polyamine epichlorhydrin cationic resin may be seen dramatically illustrated in the drawings, representing the results of testing conducted as described in Examples VI and VII. The resin of the invention retains high charge and contaminant removal capacity and has longer effective life than the melamine-formaldehyde cationic colloid of U.S. Patent No.
.
91~S
1 one type of fine particulate such as diatomaceous earth/perlite for example, in proportion by weight of from about 80/20 to 20/80 give be~ter filtration performance or better cost/perfor-mance characteristics than that achieved by the use of any ` 5 single type by itself. Similarly, mixtures in all proportions of relatively coarse and fine particulates, e.g., 50/5~ parts by weight of 10 ~nd 5 micron diameter particulates may be used.
Suitable polyamido-polyamine epichlorhydrin cationic resins are those of U.S. Patents 2,926,116; 2,926,154; 3,224,935;
lO 3,332,901 ana 3,382,096 and may be produced by reacting a dicarboxylic acid with a poly-am-ne dim2r to form a water soluble polymer s~hich is further reacted with epichlorhydrin. The dimer unit may have the general formula:
2~ 1(CH2)2-NH]X(CH2)2-NH2 where x is an integer of 1 to 7, and the dicarboxylic acid ~ay be aromatic or aliphatic such as adipic, azelaic, digly-colic, oxalic or malonic acids. The cationic charge is s 20 induced through the amine function in tertiary or quaternized ; configuration. Other suitable charge modifying resins, employ-ing a heterocyclic dicarboxylic acid reactant are disclosed in U.S. Patent 3,761,350. The poly2mido-polyamine epichlorhydrin cationic resins are available commercially, as Polycup 1884*, 25 2002 or S2064 (Hercules); Cascamide Resin pR-420 (Bordon); or Nopcob~nd 35*(Nopco).
In paper production, where cationic charge modifiers are sometimes used, the objective is reduction of charge to approximately the isoelectric point to maximize efficiency 3 in interfelting of fiber. For filtration, maximum charge ifi desired to enhance removal of charged particles by * Registered Trademarks ' i~
.
'.'--` lil9~05 electrokinetic mechanisms. In the present case the surface charge of at least one of the negatively charged filter elements i.e., cellulose and particulate is reduced to render the surface less electronegative and optionally (and preferably) reversed by the deposition of sufficient cationic charge modifier to render the surface electropositive, to provide at least certain electropositive regions or sites within the filter sheet. In order to accomplish charge reversal, of course, one proceeds through the isoelectric point, and then positive charge buildup is accomplished to the maximum practical level.
The amount of charge modifier employed in the present ~ -invention is thus preferably that sufficient to at least provide a cationically disperse system i.e., a system in which no visible flocculation occurs at ambient conditions in the absence of applied hydrodynamic shear forces. The system therefore comprises essentially discrete fiber/particulate elements exhibiting a positive charge or zeta potential relatively uniformly or homogeneously distributed in and throughout the aqueous medium. The specific level will, of course, vary with the system and the modifier selected but will be readily determined by one skilled in the art. For example, the inflectionipoint on a plot of particulate retention vs. amount of charge modifier approximates the minimum level for better performance. Thus a 2 percent level is appropriate for a polyamido-polyamine epichlorhydrin resin.
Although additional modifier may be employed to advantage where desired, this level represents the best balance on a cost/performance basis. Premodified filter elements e.g., particulate precoated with charge modifier may of course be incorporated in any manner into filter sheets with similar results, and where a cationically disperse slurry is not employed, charge modification will be commensurately reduced by control of modifier levels.
The charge modification effected is demonstrable in measurements of surface zeta potential, and in improved filtration efficiency for negatively charged particles in liquid systems.
The slurry of pulp and particulates is formed in any suitable manner. The sequence of adding these components to water to form the initial slurry appears to be relatively unimportant. The consistency of the slurry will represent the highest possible for a practical suspension of the components, usually about 4 percent. The system is subjected to hydrodynamic shear forces as by a bladed mixer, and the charge modifier is then added to the slurry.
The shear level is not critical i.e., any otherwise suitable shear rate or shear stress may be employed having regard for available equipment, preferred processing times etc., but is selected and employed simply to break up the flocs and maintain the system in a dispersed condition during treatment. Of course, upon the formation of a cationically disperse slurry, the system is free of floc formation even in the absence of applièd shear.
After charge modification, the slurry is diluted with additional water to the proper consistency required for vacuum felting sheet formation, ordinarily 0.5 to 2~ percent, depending upon the type of equipment used to form the sheet, in a manner known to the artisan. The slurry is formed into a sheet and oven dried in standard manner. The performance of the sheet is related to the drying parameters and optimized conditions may reflect energy considerations or desired thermal history consistent with minimization of unnecessary exposure to elevated temperatures, especiallyas the decomposition or scorch point for the system is approached.
In accordance with a preferred embodiment of the invention, filter media sheets are formed from filter elements, i.e., particulate and a self-bonding matrix of cellulose pulp at least one of which is charge modified, the pulp being a system incorporating beaten pulp to provide a Canadian Standard Freeness of up to 600 ml., preferably less than 300 ml. e.g., 100-200 ml. the charge modifier consisting of a polyamido-polyamine epichlorhydrin cationic resin, and being applied in a proportion to reduce electronegativity of the surface, preferably to achieve charge reversal beyond the isoelectric point, e.g., to an add-on level of about 2% by weight. Filter media sheets so prepared may be autoclaved, hot water flushed or otherwise treated at elevated temperature to sanitize or sterilize the structure. In addition to having special utility for the filtration of biological liquids, these sheets also may be employed for filtration without flush out delay, as ions present in the structure have been removed during the sanitization or sterilization procedure.
The performance benefits of the polyamido-polyamine epichlorhydrin cationic resin may be seen dramatically illustrated in the drawings, representing the results of testing conducted as described in Examples VI and VII. The resin of the invention retains high charge and contaminant removal capacity and has longer effective life than the melamine-formaldehyde cationic colloid of U.S. Patent No.
4,007,113.
The filter media sheets may be subjected to standard-ized testing reflecting performance in use, represented herein by the following:
1 ~ilt~ation EfEiciency Test In this test, contaminated fluid of a specified turbidity is drawn through the test filter media by a constant vacuum under standard conditions, effluent turbidity measured
The filter media sheets may be subjected to standard-ized testing reflecting performance in use, represented herein by the following:
1 ~ilt~ation EfEiciency Test In this test, contaminated fluid of a specified turbidity is drawn through the test filter media by a constant vacuum under standard conditions, effluent turbidity measured
5 (using a E~ach model 2100~ Turbidimeter~ and expressed as p~rcent filtration efficiency when compared to the inlet turbidity, calculated as Efficiency = Turbidity In -. Test Turbidity Out Turbidity In contaminant is Hyplar*(produced by Grumbacher) a polydisperse acrylic latex produced by emulsion polymerization and compris-ing colloidal polymer particles ranging from 0.05 to 1.0 micron.
Contaminant le~el is 25-200 NTU (Nephalometric Turbidity Units) in distilled water, at pH 6.5-7Ø Filter sheet is cut into 57 ~m dia. discs, and then placed in a Millipore*47 mm vacuum 5 filter holder. 100 ml. of the prepared contaminant dispPrsion i5 then filtered through the disc using a 23 in. Hg vacuum.
Membrane Protection Test i In this test, contaminated fluid is pumped under ~tandard conditions through test filter media and a mambrane in series at a constant flow rate, and differential pressure with time recorded. The time or total volume of flow passed at a defined pressure increase is a measure of the life of the prefilter, and interrelates satisfactorily with perfor-mance in use. Typically, a 47 mm. 0.22 micron membrane is -employed ~t a flow rate of 225 ml./min. Test contaminant is the same Hyplar*polydisperse acrylic latex referred to above.
Contaminant level is 5-50 ~TU ~Hach Turbidimeter* Model 2100A).
The test is continued until the differential pressure across - either the membrane or the test filter paid exceeds 5-10 psid.
3 Membrane protection times of less than a few minutes indicates no practically useful effect.
* Registered Trademarks .
.. . .
Oil Flow Test As a measure of the porosity of the filter media she~ts, 100 ssu oil is pumped through the sample sheet until a differential pressure drop of 5 psid is attained, at which point the flow rate (ml./min.) is recorded.
Normalized Streaming Potential The measurement of streaming potential is a conventional means of determining zeta potential i.e., the electric potential excess of the surface, and the surrounding fluid to the hydrodynamic shear plane, over the bulk potential of the fluid.
In the present test, streaming potential values are determined, and normalized for differing pressure drop in the media being tested, expressing the results in units of millivolts per foot of water. The filter media is evaluated by flushing out the filter media with water until the measured streaming potential achieves a relatively stable maximum value. At this point, the filter media has ceased to contribute any significant ionic species to the water, i.e., the inlet resistivity equals the outlet resistivity.
The filter media test cell is based on the design of Oulman, et al. JAWWA 56:915 (1964~. It is constructed from Lucite having an effective area of 3.14 square inches (2"
diameter) and is equipped with platinum black electrodes.
Water and mercury manometers are used to measure the pressure drop across the media being evaluated. Streaming potential values (by convention, of opposite sign to the zeta potential and the surface charge) are measured with a high impedance volt meter. The influent and effluent resistance are monitored with conductivity flow cells (cell constant = 0.02/cm) using a resistance bridge.
Upon the attainment of equilibrium streaming poten-tial (i.e., after flush out) contaminant challenge tests `~ 9105 may be performed in the same system, using an aqueous dispersion of a single size monodisperse latex, while measuring the 90 light scattering intensity (selected for high relative sensitivity for particle diameters in the 0.1 to l.0 micrometer range) of the influent and effluent streams, providing a quantitative determination of the filtration efficiency of the filter media. Effluent turbidity is measured using a Moniteck Turbidity Meter.
Inlet turbidity is selected to range from 15 to 20 NTU, using a Dow Diagnostics 0.109 micrometer emulsion polymer-ized polystyrene latex dispersion, and flow rate is maintained relatively constant. The tests above are -described in more detail in a paper presented at the 71st Annual AICHE meeting (1978): "Measuring the Electrokinetic Properties of Charged Filter Media", Knight et al.
In the following examples which further illustrate this invention; proportions are by weight, basPd upon total pulp and particulate, excluding charge modifier.
.
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.
ll~9~Q~
1 EX~lPLE I
A series of filter sheets were prepared utilizing ~e~erhauser Coho Kraft pulp, beaten to the levels indicated below, and Grefco Dicalite 416*Perlite* havincJ a mean particle 5 size of 3.9 microns.
The charge modifier emoloyed in these runs was cationic polyamine-polyamide epichlorhydrin resin ~lercules Polycup 1884* about 100000 mol. wgt.; about 150A particle SiZe~, The total input weight (bone dry basis) of the component materials was 80 grams, exclusive of charge ~odifier. A constan~ proportion of pulp (30 percent by weight, or 24 grams) and particulate 570 percen~ by wei~ht, or 56 grams) ~as maintained. The components were added to 15 water in a 1 liter polyethylene buc~et, with strong agita-tion, to form an aqueous slurry at two percent consistency, and the charge madifier added. (The system was subjected to hydrodynamic shear by action of a Hei-Dolph stirrer (Pol~science Inc.), having 4 propeller blades, rotating at 20 about 700 rpm on settiny 2.~ The slurr~ was subsequently diluted to 0.5 percent consistency and vacuum ~elted into a sheet rangin~ from about .160 to .200 inch thickness (depending upon retQntion) in a nine inch by twelve inch hand sheet apparatus utilizing a 100 mesh screen. The sheet 25 was subsequently removed, dried in a static ov~n at 350~F.
until constant weight was achieved, and the final weight recorded. Comparison o the final sheet weight with the total input material weight allowed determination of total solids reten~ion in the sheet. Filter sheets were subjected 3~ So filtration (membrane protection) and oil flow tests, as described above. Results are set forth in Table I.
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`~ -As will be seen from the above reported testing, ~ samples which were not charge modified evidenced - essentially no membrane protection. Solids retention improved with reduced average CSF of the pulp system employed. Failure in the systems of lowest freeness was by pad plugging, with little increase in membrane pressure drop.
~119105 EXAMPLE II
A series of runs were conducted in the manner of Example I, employing as the particulate Grefco Perlite 426, having a mean particle size of 4.2 microns, and a constant (2%) level of Hercules 1884 charge modifier. Results are set forth in Table II.
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~l91~S
EXAMPLE III
A. Particulate filter aid was precoated in an aqueous slurry at a 2.5% consistency with the below indicated levels of hercules 1884 charge modifier over a contact time of about 15 minutes, isolated, drained and dried at 2500F. for 30 minutes.
The treated particulate filter material was slurried in 100 ml. of water and filtered through a porous fritted glass holder base in a Millipore 47 mm.
vacuum filter holder, until a 1/4 inch thick cake was formed, and filtration efficiency tests were then performed. Results are set forth in Table III.
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The improvement in filtration performance with charge modification is dramatic, especially with the larger particulates.
' EXAMPLE III
B. An aqueous slurry of the precoated particulate prepared as set forth above is alternatively formed into a filter sheet comprising 30 percent by weight beaten pulp as a matrix, and dried. The pulp system employed exhibited a freeness of 130 C.S.F. Membrane protection -' : tests were performed, with the results set forth in Table IV. ~
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C. A preformed sheet comprising a 130 C.S.F.
pulp system (30~ by weight) and Perlite 416 particulate was treated with Hercules 1884 resin (2% solids), dried and cured. In filtration tests, membrane protection time was 6 . 5 minutes, and failure was by pad plugging at 5 psid.
, . A
1 EX~IPLE IV
A. In the manner of Example III A, mechanically defibered cellulose (Solka*floc) was precoated with Hercules 1884 cationic resin, dried and cured formed into a filter : 5 cake, and tested for filtration efficiency. The results are set forth in Ta~le V, as follows.
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- EXAMPLE IV
B. A ~ilter sheet was formed from a slurry consisting of 30% untreated cellulose pulp and 70%
pretreated defibered cellulose from Example IV A, and tested as described in Example III B, with the results set forth in Table VI, as follows.
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J 5u~ æ u, L'~ L') L') EXAMPLE V
In a manner similar to Example I, filter media were prepared employing 70~ particulate and 30% pulp, and as the particulate Grefco Dicalite 215 Diatomaceous earth, the system being surface modified with 2~ Hercules Polycup 1884 cationic resin. The pulp system was varied to reflect the presence of more highly beaten pulp and solids retention increased commensurately from 49.3~ to 80.0~ by weight.
- 1~191~5 -32~
In this Example, the performance of a prior art melamine-formaldehyde cationic colloid (Parez 607) charge modified filter media sheet (see U.S. Patent 4,007,113) was 5 cor,pared to filter media sheet charge modified with a poly-amido-polyamine epichlorhydrin cationic resin (Hercules Polycup 1884~ in accordance with the invention.
A. Filter media sheets were prepared containing 70% by weight of a cellulose pulp system (C.S.F. 130) and lO 30% by weight of a 50/50 admixture of diatomaceous earth and perlite and were each formed in identical manner by pre-paring a cationically disperse aqueous slurry, vacuum felting and oven drying, except that optimized charge modifier levels ~7% for Parez 607*, and 2% for Hercules 1834) and drying 15 conditions were employed.
Employing test conditions detailed above, nor~alized streaming potential values were determined over time, and equilibrium flush out curves plotted for the respective filter media, compared in Figure 1. As will be seen, the prior art 20 (melamine-formaldehyde) media exhi~its an anomolous flush-out curve, peaking out ~ery rapidly and then slowly decaying with timz. The media sheet prepared in accordance with the inven-tion exhibited an increasingly negative normalized streaming potential which stabilized at a high equilibrium value 25 indicative of a high positive surface charge.
B. The same filter media were then challer.ged with contaminated liquid (0.109 micron Dow Diagnostics latex dispersion; 5.5 pH), and filtration efficiency and normalized streaming potential plotted against time in Figures 2 and 3 3~ comparing respectively the prior art (melamine-formaldehyde cationic colloid) system (Figure 2)-with the polyamido-polyamine epichlorhydrin modified media of the invention (Figure 3). The negatively charged latex particles are, * Registered Trademarks ~910S
initially, essentially quantitatively removed by electro-kinetic capture and adsorption. The normalized streaming potential decays linearly from a negative value, through zero, and then asymptoti~ally approaches a positive value. As the streaming potential approaches and passes through zero, the effluent turbidity starts to decay (breakthrough). This increase continues until the effluent turbidity asymptotically approaches the inlet turbidity indicating that all of the latex is passing through the filter media.
The filter media sheet of the invention (Figure 3) retained its filtration performance significantly longer than that of the prior art filter (Figure 2).
11~910~ .
EXAMPLE VII
In this Example, a further performance comparison was made between filter media sheet of the invention and that of the prior art (melamine-formaldehyde) in the as-is or untreated condition, and as autoclaved and hot water flushed, the latter treatments being adapted to sanitize or sterilize the filter media sheet for use in conjunction with biological liquids.
A. Filter sheets were prepared and tested in identical manner to that set forth in Example VIB, except that in addition to the as-is or untreated material, additional filter media sheets were prepared which were respectively treated under autoclaving conditions (130C under 15 lb. pressure for one hour) or hot water flush conditions (180 F. for 1 hour at a flow rate of 225 cc/min.). The results of comparison streaming potential testing is set forth graphically in Figure 4.
As will be seen, the prior art (melamine-formalde-hyde) modified filter media lost its positive charge under either of the conditions required for sanitization or sterilization; whereas the polyamido-polyamine epichlor-hydrin cationic resin modified sheets not only retained effectiveness but indicated superior performance under the stringent conditions employed.
B. The as-is or untreated and autoclaved filter media sheets prepared as in part A, above, were additionally subjected to comparison membrane protection tests, (inlet turbidity 50 NTU, 0.2 micron membrane, flow rate 225 ml/min.) with results set forth in Table VII as follows:
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~119105 As will be seen from the above data, the respectively charge modified systems responded competitively in the as-is condition to this test, with failure occurring by membrane plugging in the case of the prior art system, and by pad plugging in the case of the system of the invention; however, when autoclaved, membrane protection time deteriorated markedly for the prior art system.
'Biological liquids' as that term is employed in the specification and claims, is a liquid system which is derived from or amenable to use with living organisms, and ordinarily handled and processed under sanitary or sterile conditions, therefore requiring sanitized or sterilized media for filtration. Included are isotonic solutions for i.m. or i.v.
administration, solutions designed for administration per os, as well as solutions for topical use, biological wastes or other body fluids which may comprise filterable bodies such as impurities, e.g., bacteria, viruses or pyrogems which are desirably isolated or separated for examination or disposal by immobilization or fixation upon or entrapment within filter media.
Filter media sheets in accordance with the invention may be employed alone or in combination with other such media to treat pharmaceuticals such as antibiotics, saline solutions, dextrose solutions, vaccines, blood plasma, serums, sterile water or eye washes; beverages, such as cordials, gin, vodka, -beer, scotch, whisky, sweet and dry wines, champagne or brandy;
cosmetics such as mouthwash, perfor~, shampoo, hair tonic, face cream or shaving lotion; food products such as vinegar, vegetable oils, extracts, syrups, fruit juices, make-up water or cooking oils; chemicals such as antiseptics, insecticides, photographic solutions, electroplating solutions, cleaning ~1~9~0S
~37-1 ccmpoundsr solvan~ purification and lubricating oils; and the l.iXe for retention of submicronic particles, removal of bacterial contaminants and resolution oE colloidal hazes.
- - "
. . .
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- "
Contaminant le~el is 25-200 NTU (Nephalometric Turbidity Units) in distilled water, at pH 6.5-7Ø Filter sheet is cut into 57 ~m dia. discs, and then placed in a Millipore*47 mm vacuum 5 filter holder. 100 ml. of the prepared contaminant dispPrsion i5 then filtered through the disc using a 23 in. Hg vacuum.
Membrane Protection Test i In this test, contaminated fluid is pumped under ~tandard conditions through test filter media and a mambrane in series at a constant flow rate, and differential pressure with time recorded. The time or total volume of flow passed at a defined pressure increase is a measure of the life of the prefilter, and interrelates satisfactorily with perfor-mance in use. Typically, a 47 mm. 0.22 micron membrane is -employed ~t a flow rate of 225 ml./min. Test contaminant is the same Hyplar*polydisperse acrylic latex referred to above.
Contaminant level is 5-50 ~TU ~Hach Turbidimeter* Model 2100A).
The test is continued until the differential pressure across - either the membrane or the test filter paid exceeds 5-10 psid.
3 Membrane protection times of less than a few minutes indicates no practically useful effect.
* Registered Trademarks .
.. . .
Oil Flow Test As a measure of the porosity of the filter media she~ts, 100 ssu oil is pumped through the sample sheet until a differential pressure drop of 5 psid is attained, at which point the flow rate (ml./min.) is recorded.
Normalized Streaming Potential The measurement of streaming potential is a conventional means of determining zeta potential i.e., the electric potential excess of the surface, and the surrounding fluid to the hydrodynamic shear plane, over the bulk potential of the fluid.
In the present test, streaming potential values are determined, and normalized for differing pressure drop in the media being tested, expressing the results in units of millivolts per foot of water. The filter media is evaluated by flushing out the filter media with water until the measured streaming potential achieves a relatively stable maximum value. At this point, the filter media has ceased to contribute any significant ionic species to the water, i.e., the inlet resistivity equals the outlet resistivity.
The filter media test cell is based on the design of Oulman, et al. JAWWA 56:915 (1964~. It is constructed from Lucite having an effective area of 3.14 square inches (2"
diameter) and is equipped with platinum black electrodes.
Water and mercury manometers are used to measure the pressure drop across the media being evaluated. Streaming potential values (by convention, of opposite sign to the zeta potential and the surface charge) are measured with a high impedance volt meter. The influent and effluent resistance are monitored with conductivity flow cells (cell constant = 0.02/cm) using a resistance bridge.
Upon the attainment of equilibrium streaming poten-tial (i.e., after flush out) contaminant challenge tests `~ 9105 may be performed in the same system, using an aqueous dispersion of a single size monodisperse latex, while measuring the 90 light scattering intensity (selected for high relative sensitivity for particle diameters in the 0.1 to l.0 micrometer range) of the influent and effluent streams, providing a quantitative determination of the filtration efficiency of the filter media. Effluent turbidity is measured using a Moniteck Turbidity Meter.
Inlet turbidity is selected to range from 15 to 20 NTU, using a Dow Diagnostics 0.109 micrometer emulsion polymer-ized polystyrene latex dispersion, and flow rate is maintained relatively constant. The tests above are -described in more detail in a paper presented at the 71st Annual AICHE meeting (1978): "Measuring the Electrokinetic Properties of Charged Filter Media", Knight et al.
In the following examples which further illustrate this invention; proportions are by weight, basPd upon total pulp and particulate, excluding charge modifier.
.
,- .: -, ~ .
.
ll~9~Q~
1 EX~lPLE I
A series of filter sheets were prepared utilizing ~e~erhauser Coho Kraft pulp, beaten to the levels indicated below, and Grefco Dicalite 416*Perlite* havincJ a mean particle 5 size of 3.9 microns.
The charge modifier emoloyed in these runs was cationic polyamine-polyamide epichlorhydrin resin ~lercules Polycup 1884* about 100000 mol. wgt.; about 150A particle SiZe~, The total input weight (bone dry basis) of the component materials was 80 grams, exclusive of charge ~odifier. A constan~ proportion of pulp (30 percent by weight, or 24 grams) and particulate 570 percen~ by wei~ht, or 56 grams) ~as maintained. The components were added to 15 water in a 1 liter polyethylene buc~et, with strong agita-tion, to form an aqueous slurry at two percent consistency, and the charge madifier added. (The system was subjected to hydrodynamic shear by action of a Hei-Dolph stirrer (Pol~science Inc.), having 4 propeller blades, rotating at 20 about 700 rpm on settiny 2.~ The slurr~ was subsequently diluted to 0.5 percent consistency and vacuum ~elted into a sheet rangin~ from about .160 to .200 inch thickness (depending upon retQntion) in a nine inch by twelve inch hand sheet apparatus utilizing a 100 mesh screen. The sheet 25 was subsequently removed, dried in a static ov~n at 350~F.
until constant weight was achieved, and the final weight recorded. Comparison o the final sheet weight with the total input material weight allowed determination of total solids reten~ion in the sheet. Filter sheets were subjected 3~ So filtration (membrane protection) and oil flow tests, as described above. Results are set forth in Table I.
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`~ -As will be seen from the above reported testing, ~ samples which were not charge modified evidenced - essentially no membrane protection. Solids retention improved with reduced average CSF of the pulp system employed. Failure in the systems of lowest freeness was by pad plugging, with little increase in membrane pressure drop.
~119105 EXAMPLE II
A series of runs were conducted in the manner of Example I, employing as the particulate Grefco Perlite 426, having a mean particle size of 4.2 microns, and a constant (2%) level of Hercules 1884 charge modifier. Results are set forth in Table II.
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EXAMPLE III
A. Particulate filter aid was precoated in an aqueous slurry at a 2.5% consistency with the below indicated levels of hercules 1884 charge modifier over a contact time of about 15 minutes, isolated, drained and dried at 2500F. for 30 minutes.
The treated particulate filter material was slurried in 100 ml. of water and filtered through a porous fritted glass holder base in a Millipore 47 mm.
vacuum filter holder, until a 1/4 inch thick cake was formed, and filtration efficiency tests were then performed. Results are set forth in Table III.
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The improvement in filtration performance with charge modification is dramatic, especially with the larger particulates.
' EXAMPLE III
B. An aqueous slurry of the precoated particulate prepared as set forth above is alternatively formed into a filter sheet comprising 30 percent by weight beaten pulp as a matrix, and dried. The pulp system employed exhibited a freeness of 130 C.S.F. Membrane protection -' : tests were performed, with the results set forth in Table IV. ~
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C. A preformed sheet comprising a 130 C.S.F.
pulp system (30~ by weight) and Perlite 416 particulate was treated with Hercules 1884 resin (2% solids), dried and cured. In filtration tests, membrane protection time was 6 . 5 minutes, and failure was by pad plugging at 5 psid.
, . A
1 EX~IPLE IV
A. In the manner of Example III A, mechanically defibered cellulose (Solka*floc) was precoated with Hercules 1884 cationic resin, dried and cured formed into a filter : 5 cake, and tested for filtration efficiency. The results are set forth in Ta~le V, as follows.
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- EXAMPLE IV
B. A ~ilter sheet was formed from a slurry consisting of 30% untreated cellulose pulp and 70%
pretreated defibered cellulose from Example IV A, and tested as described in Example III B, with the results set forth in Table VI, as follows.
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J 5u~ æ u, L'~ L') L') EXAMPLE V
In a manner similar to Example I, filter media were prepared employing 70~ particulate and 30% pulp, and as the particulate Grefco Dicalite 215 Diatomaceous earth, the system being surface modified with 2~ Hercules Polycup 1884 cationic resin. The pulp system was varied to reflect the presence of more highly beaten pulp and solids retention increased commensurately from 49.3~ to 80.0~ by weight.
- 1~191~5 -32~
In this Example, the performance of a prior art melamine-formaldehyde cationic colloid (Parez 607) charge modified filter media sheet (see U.S. Patent 4,007,113) was 5 cor,pared to filter media sheet charge modified with a poly-amido-polyamine epichlorhydrin cationic resin (Hercules Polycup 1884~ in accordance with the invention.
A. Filter media sheets were prepared containing 70% by weight of a cellulose pulp system (C.S.F. 130) and lO 30% by weight of a 50/50 admixture of diatomaceous earth and perlite and were each formed in identical manner by pre-paring a cationically disperse aqueous slurry, vacuum felting and oven drying, except that optimized charge modifier levels ~7% for Parez 607*, and 2% for Hercules 1834) and drying 15 conditions were employed.
Employing test conditions detailed above, nor~alized streaming potential values were determined over time, and equilibrium flush out curves plotted for the respective filter media, compared in Figure 1. As will be seen, the prior art 20 (melamine-formaldehyde) media exhi~its an anomolous flush-out curve, peaking out ~ery rapidly and then slowly decaying with timz. The media sheet prepared in accordance with the inven-tion exhibited an increasingly negative normalized streaming potential which stabilized at a high equilibrium value 25 indicative of a high positive surface charge.
B. The same filter media were then challer.ged with contaminated liquid (0.109 micron Dow Diagnostics latex dispersion; 5.5 pH), and filtration efficiency and normalized streaming potential plotted against time in Figures 2 and 3 3~ comparing respectively the prior art (melamine-formaldehyde cationic colloid) system (Figure 2)-with the polyamido-polyamine epichlorhydrin modified media of the invention (Figure 3). The negatively charged latex particles are, * Registered Trademarks ~910S
initially, essentially quantitatively removed by electro-kinetic capture and adsorption. The normalized streaming potential decays linearly from a negative value, through zero, and then asymptoti~ally approaches a positive value. As the streaming potential approaches and passes through zero, the effluent turbidity starts to decay (breakthrough). This increase continues until the effluent turbidity asymptotically approaches the inlet turbidity indicating that all of the latex is passing through the filter media.
The filter media sheet of the invention (Figure 3) retained its filtration performance significantly longer than that of the prior art filter (Figure 2).
11~910~ .
EXAMPLE VII
In this Example, a further performance comparison was made between filter media sheet of the invention and that of the prior art (melamine-formaldehyde) in the as-is or untreated condition, and as autoclaved and hot water flushed, the latter treatments being adapted to sanitize or sterilize the filter media sheet for use in conjunction with biological liquids.
A. Filter sheets were prepared and tested in identical manner to that set forth in Example VIB, except that in addition to the as-is or untreated material, additional filter media sheets were prepared which were respectively treated under autoclaving conditions (130C under 15 lb. pressure for one hour) or hot water flush conditions (180 F. for 1 hour at a flow rate of 225 cc/min.). The results of comparison streaming potential testing is set forth graphically in Figure 4.
As will be seen, the prior art (melamine-formalde-hyde) modified filter media lost its positive charge under either of the conditions required for sanitization or sterilization; whereas the polyamido-polyamine epichlor-hydrin cationic resin modified sheets not only retained effectiveness but indicated superior performance under the stringent conditions employed.
B. The as-is or untreated and autoclaved filter media sheets prepared as in part A, above, were additionally subjected to comparison membrane protection tests, (inlet turbidity 50 NTU, 0.2 micron membrane, flow rate 225 ml/min.) with results set forth in Table VII as follows:
~119105 1.
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~119105 As will be seen from the above data, the respectively charge modified systems responded competitively in the as-is condition to this test, with failure occurring by membrane plugging in the case of the prior art system, and by pad plugging in the case of the system of the invention; however, when autoclaved, membrane protection time deteriorated markedly for the prior art system.
'Biological liquids' as that term is employed in the specification and claims, is a liquid system which is derived from or amenable to use with living organisms, and ordinarily handled and processed under sanitary or sterile conditions, therefore requiring sanitized or sterilized media for filtration. Included are isotonic solutions for i.m. or i.v.
administration, solutions designed for administration per os, as well as solutions for topical use, biological wastes or other body fluids which may comprise filterable bodies such as impurities, e.g., bacteria, viruses or pyrogems which are desirably isolated or separated for examination or disposal by immobilization or fixation upon or entrapment within filter media.
Filter media sheets in accordance with the invention may be employed alone or in combination with other such media to treat pharmaceuticals such as antibiotics, saline solutions, dextrose solutions, vaccines, blood plasma, serums, sterile water or eye washes; beverages, such as cordials, gin, vodka, -beer, scotch, whisky, sweet and dry wines, champagne or brandy;
cosmetics such as mouthwash, perfor~, shampoo, hair tonic, face cream or shaving lotion; food products such as vinegar, vegetable oils, extracts, syrups, fruit juices, make-up water or cooking oils; chemicals such as antiseptics, insecticides, photographic solutions, electroplating solutions, cleaning ~1~9~0S
~37-1 ccmpoundsr solvan~ purification and lubricating oils; and the l.iXe for retention of submicronic particles, removal of bacterial contaminants and resolution oE colloidal hazes.
- - "
. . .
3~ :
- "
Claims (26)
1. A filter media sheet comprising fine particulate and a self-bonding matrix of cellulose fiber, the surfaces of at least one of which are modified with a polyamido-polyamine epichlorhydrin cationic resin, the matrix incorporating beaten cellulose fiber to provide a Canadian Standard Freeness of less than 600 ml.
2. The filter media sheet of claim 1, comprising sufficient cationic resin to provide a positive zeta potential to at least one of said fiber and said particulate.
3. The filter media sheet of claim 1, comprising from about 1 to about 3 percent by weight of said cationic resin.
4. The filter of claim 1, wherein said fine particulate comprises at least 50 percent by weight of diatomaceous earth.
5. The filter of claim 1, wherein said fine particulate comprises an admixture of diatomaceous earth and perlite.
6. The filter of claim 1, wherein said fine particulate exhibits an average particulate dimension of less than about 10 microns.
7. A method for the preparation of filter media sheets adapted for the removal of electronegative submicron contaminants from contaminated liquids comprising forming a filter sheet from fine particulate and a cellulose pulp system as a self-bonding matrix, the surfaces of at least one of said particulate and said pulp being modified with a polyamido-polyamine epichlorhydrin cationic resin, said pulp system incorporating beaten pulp to provide a Canadian Standard Freeness for said system of 100 to 600 ml.
8. The method of claim 7, further including the step of sanitizing or sterilizing said sheet.
9. The method of claim 8 wherein the sheet is autoclaved.
10. The method of claim 8 the sheet is hot water flushed.
11. A method of removal of submicron contami-nants from biological fluids comprising passing the contaminated fluid through a sanitized or sterilized filter sheet comprising particulate material and a self-bonding matrix consisting of a cellulose pulp system, at least one of which is surface modified with a polyamido-polyamine epichlorhydrin cationic resin, the cellulose pulp system incorporating beaten pulp to provide a matrix having a Canadian Standard Freeness of less than 600 ml.
12. In a filter for the removal of submicron contami-nants from liquids comprising a sheet vacuum felted from a cationically disperse aqueous slurry of cellulose pulp and fine particulate, the improvement which comprises forming the filter sheet from a slurry comprising beaten pulp to provide a Canadian Standard Freeness of 100 to 600 ml., the surfaces of said particulate and said cellulose pulp being modified by treatment with a polyamido-polyamine epichlorhydrin cationic resin to exhibit a positive zeta potential.
13. Particulate filter aid coated with a sufficient amount of a polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
14. Particulate diatomaceous earth filter aid coated with a sufficient amount of a polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
15. Particulate perlite filter aid coated with sufficient amount of a polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositve.
16. Defibered cellulose filter aid coated with a sufficient amount of a polyamido-polyamine epichlorhydrin cationic resin to render the anionic surface of the filter aid electropositive.
17. The filter aid as claimed in claim 13, 14 or 15 wherein the filter aid exhibits an average particulate dimension of less than about 10 microns.
18. The filter aid as claimed in claim 13, 14 or 15 wherein the filter aid exhibits an average particulate dimension of less than about 5 microns.
19. The filter aid as claimed in claim 13, 14 or 15 wherein the filter aid exhibits a specific area in excess of one square meter/gram.
20. A filter bed comprised of the filter aid of claim 13, 14 or 15.
21. A method for the removal of submicron contaminants from a fluid comprising passing the contaminated fluid through a filter bed comprised of the filter aid of claim 13, 14 or 15.
22. The filter aid as claimed in claim 16 wherein the filter aid exhibits an average particulate dimension of less than about 10 microns.
23. The filter aid as claimed in claim 16 wherein the filter aid exhibits an average particulate dimension of less than about 5 microns.
24. The filter aid as claimed in claim 16 wherein the filter aid exhibits a specific area in excess of one square meter/gram.
25. A filter bed comprised of the filter aid of claim 16.
26. A method for the removal of submicron contami-nants from a fluid comprising passing the contaminated fluid through a filter bed comprised of the filter aid of claim 16.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1371679A | 1979-02-21 | 1979-02-21 | |
| US13,716 | 1979-02-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1119105A true CA1119105A (en) | 1982-03-02 |
Family
ID=21761355
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000322321A Expired CA1119105A (en) | 1979-02-21 | 1979-02-26 | Filter and method of making same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1119105A (en) |
-
1979
- 1979-02-26 CA CA000322321A patent/CA1119105A/en not_active Expired
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