DE1227426B - Coated filter aid - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

BOId

German KL: 12 d- 25/01

Number; 1227 426

File number: D 43805 VII b / 12 d

Filing date: March 5, 1964

Opening day: October 27, 1966

The invention relates to coated filter aid based on a particulate material with an electronegatively charged surface, which is at least partially covered with a high molecular weight material is covered.

The filter aid materials according to the invention can be selected from a wide variety of substances which are generally used in particulate form for filtration purposes. These Filter hoppy materials are commonly referred to as anionic filter aids and are through Electronegatively charged surfaces are marked. Filter aid materials are generally used in Form a precoat applied on a filter screen, or they become a liquid suspension added as a collector for suspended material before the introduction of the suspension into the filter chamber.

From the German patents 594561 and 694 528 was already the use of fine distribution ao tem or colloidal silver on a ceramic material or fabric as a carrier for disinfection known aqueous liquids. However, this method has the disadvantage that only very low flow rates are possible, colloidal SiI-ber is very expensive and a complete disinfection is not possible at all.

From the United States patent specification 2 247 711 was already 'a process for the disinfection of liquids using solid particles coated with aliphatic amines, their hydrocarbon residue has at least 6 carbon atoms is known. This procedure already made it possible a significant increase in flow rates and the avoidance of expensive silver, one However, complete disinfection was also not possible in this way.

According to the invention, an improvement in the filtering speed and filtering efficiency is achieved Use of a coated filter aid achieved in that the coating material of a water-soluble polymer consists in which a large number of cationic groups on each polymer molecule is bound, namely primary, secondary or tertiary amino, aziridine, quaternary ammonium and sulfonium groups. Good results are achieved if the coated filter aid is 0.01 to 0.5 percent by weight of the polymer contains.

Particularly effective filter aids according to the invention are those in which the cationic Polymer coating a polyalkylene polyamine with an average molecular weight of at least Coated filter aid

Applicant:

The Dow Chemical Company,

Midland, me. (V. St. A.)

Representative:

Dipl.-Ing. F. Weickmann,

Dr.-Ing. A. Weickmann,

Dipl.-Ing. H. Weickmann

and Dipl.-Phys. Dr. K. Fincke, patent attorneys,

Munich 27, Möhlstr. 22nd

Named as inventor:

Kenneth Walter Guebert,

Johnnie dee Laman,

Irby Cullen Jones,

all Lake Jackson, Tex. (V. St. A.)

Claimed priority;

V. St v. America March 7, 1963 (263 417),
of February 7, 1964 (343 207)

contains. The cationic polymer coating advantageously contains an alkylenimine polymer, for example an ethylene imine polymer.

It is believed that the filter aid material according to the invention is not only used as an enhancement agent acts on the surface of the filter medium, but also as a collector for the suspended material, which, due to its degree of dispersion, allows passage through many of the known filter media permitted. The filter aid according to the invention is particularly useful for removing inorganic, organic substances Substances or a mixture thereof from a suspension and is particularly valuable for the removal of microorganisms from liquid media.

The filter aid according to the invention is well suited for removing suspended material from liquid Media, such as water, aqueous solutions, hydrophilic solvents or solutions, and from gaseous media such as air.

The coated filter aids according to the invention are advantageously characterized by high filtration speeds, effective filtration, i.e.

609 708/246

3 4

low turbidity of the filtrate, and long-lasting in the liquids that go through the filter bed, the filtration insert out. Due to a periodic presence of negatively charged particles to attract adding during the filtration of small amounts and to hold on. In order to filter this phenomenon of the "elekder-coated filter aid for liquids that are captured by Irish" particularly effectively, there is a further rise 5, it is necessary to choose a cationic, organic period of use for the filtration of the liquid polymer, the freely available. Compared to untreated filter aids, there are cationic sites on the outer side of the overlay with the coated filter aids according to the educated filter aid particles,
The cationic unit suitable for this purpose, longer periods of operation between polymers generally represent relatively cleaning and / or replacement of the filter aid material, linear polymers which, if at all, only represent one rials and it will have a higher percentage of low crosslinking and preferably achieve a rate of removal of the rather high particle-derived ratio of cationic charge haze from the filtered liquids. places to have molecular weight. As before-

The coated filter aid media in accordance with the provisions of the above, these polymers must be free to find possess numerous cationic sites that have joinable cationic sites after the for attracting and holding particles bonded to the anionic type filter aid stand. This "electrical capture" removal was designed to make the removal of a negative surface load free for contamination with a higher flow velocity mechanism acts in addition to the less ao diness of the contaminated liquids physical trapping mechanism (from arbors than with the untreated filter aid untreated filter aids) which is obviously possible.

due to the relatively thin cationic polyelectrolyte- cationic organic polymers, which are used for

Surface coating that is applied to the treated filter turn during the treatment of filter aids from

help is available, is not worsened. 25 anionic type are particularly effective to the

The stronger and more effective removal of coated filter aid materials according to the Erfin clouding agents, those obtained by the freely available manure are those obtained by polycationic Make the coated filter aids merization of an alkylenimine, z. B. ethyleneimine, becomes possible enables the use of filter aid particles to form an alkyleneimine polymer with larger diameters than they were in the 30 poses, and those made by a congeneral are possible if the mechanical densationsreaktion of a dihaloalkane with a Capture solely for the removal of haze polyalkylene polyamine such as ethylene dichloride substances responsible for the filtration of liquids and triethylenetetraamine, with the formation of polywords is. By using larger alkylene polyamines of higher molecular weight Filter aid particles result in larger »filtration- 35 were produced. Such polymers have a channels «, the increased filtration speeds a comparatively high ratio of cationic and prolonged filtration periods of operation charge sites to molecular weight and are water under while maintaining an effective soluble, making them aqueous solutions of the desired Allow removal of the opacifying substances. The concentration for use in enrobing coated filter aid materials according to the invention form the filter aid of the anionic type. Even though dung are made from filter aid particles from the anionic these polymers are normally water soluble, Type with an electronegatively charged surface, they form an adhesive coating on the filter, by creating a slurry of the filter aid, which does not escape through contact with water is removed in an aqueous solution of the cationic.

Polymers is prepared or by the in part 45 It is preferably a concentration between In some form, the filter aid material is about 5 and 30 percent by weight of the cationic Spray the dilute aqueous polymer solution around polyelectrolytes in the aqueous solution when moved will. To the treatment in the expenditure as a stock solution for the spray treatment of the slurry or spray closes normal- anionic type filter aid applied. References the dehydration and drying of the thinner solutions obtained have a lower viscosity coated filter aid. However, it can and are easier to use, however it arises the coating treatment immediately after the use, thereby a supply of more water to the Use the coated filter aid beforehand, where- filter aid. The water interferes with the formation of the In the case of the moist, coated particles, then, the filter aid is not simply coated, but that can be done be placed on a filter pad. 55 additional weight due to that in the overdrawn

A concentration of 1 to 15 percent by weight of retained water is undesirable the polymer in aqueous solution will be preferred. If a filter aid slurry treatment For slurry treatment or spray treatment as a process used is polymer congestion the anionic filter aid is used. About centering of the slurry is not critical. Many 0.05 to 0.5 percent by weight of the coated filter 60 particulate types of filter aids, aid products consist of the polyelectrolyte, such as diatomaceous earth, require large amounts of which forms an adherent surface layer, water to form a slurry. In the on the filter aid by the attraction of this case is the use of a solution with oppositely charged materials is bound. At 0.2 percent by weight or less of the polymer the formation of this coating is only very beneficial. More concentrated solutions can do one small part of the cationic sites result from the excess of polymers to be added, tion effect neutralized, with numerous free merely to achieve sufficient liquid available cationic sites remain to reach that of a slurry. This over-

excess polymer is lost when the coated filter aid is washed or during the Filtering operation, if the coated material is not washed, thus increasing the cost or contamination of the filtrate results.

Polymer concentrations of less than 0.2 percent by weight, for example in the area of 0.01 weight percent can be used in the slurry if desired. Self Even more dilute solutions can be used, but this involves handling large quantities of liquid relative to the weight of the coated filter aid, as a polymer coating from about 0.1 to 0.2 percent by weight based on the weight of the coated filter aid, generally is preferred.

example 1

The effectiveness of untreated filter aids 10 (FIG. 1) coated with polyelectrolytes 11 for removing opaque substances was investigated in the following manner. A spherical clay was used to produce contaminated water containing 444 parts per million (hereinafter referred to as ppm) opacifiers as determined by optical measurements. Aliquots of this cloudy water were then passed through 30 g amounts of either untreated diatomaceous earth (DE) or inventive coated diatomaceous earth, which was enclosed in a vertical cylinder on a sieve pad made of nickel with a mesh size of 0.075 mm (200 mesh) , was included. The filter aid formed a bed of uniform depth across the 102 cm ² cross-sectional area of the cylinder. A constant pressure of 400 mm Hg was maintained during the filtration.

The results of some such tests are summarized in Table I below. split (1) refers to the filter aid (DE or DE with a coating of 0.1 percent by weight of the listed Polymers) and column (2) shows the turbidity of the drain. In all cases there was a specific one Amount in untreated DE mixed with the feed to allow faster filtration of a Total amount of 11.3 liters of contaminated water through the 30 g filter aid, which prevents the Filters made to achieve.

Table I.

(D (2)

Untreated diatomaceous earth (DE)

0.1 weight percent 81.2 ppm

DE coated with ethylene imine polymers
(Molecular weight greater than about
100,000) 2.7 ppm

DE, covered with polyethylene polyamine
(Molecular weight greater than about
100,000) 4.7 ppm

DE, coated with polyvinylbenzyl tri-

methylammonium chloride 8.2 ppm

A similarly advantageous increase in the removal of the opacifying substances can be seen when sand, activated carbon, Carbon, paper filter paste, fuller's earth and asbestos treated with the listed polymers so that a coated filter aid with 0.1 percent by weight of the polyelectrolyte results.

Example 2

The procedure of Example 1 was followed, with the exception that the filtration was ended when more than 45 minutes were required to filter 11 cloudy feed. If DE with polyethyleneimine (hereinafter referred to as PEI) or polyethylene polyamine polymers (hereinafter PEPA designated) had been treated to a filter aid with a coating of 0.1 percent by weight To give polymers, about 2.4 times the liquid filtrate was obtained before the rate dropped to 45 minutes per liter than when untreated DE was applied.

Such cationic organic polymers which have the greatest number of freely available cationic sites result if they are used as a filter aid cover

ao are preferred for use in the method of the invention. The relative Numbers of such freely available cationic sites on a coated filter aid can easily can be determined according to the procedure outlined below, which is an »index« of the number such places results. The indices determined by this method are related to the Duration of the filtering operation and the removal of turbidity in order to ensure the effectiveness of cationic polymers for use in coating anionic type filter aids.

Procedure A

A high molecular weight anionic polyelectrolyte (a material corresponding to a copolymer of 30 mole percent sodium acrylate and 70 mole percent acrylamide, having a molecular weight of about 2,000,000) was ^{prepared using C 1} * to enable trace technology to be used in analytical determinations. This polymer exhibited a molecular weight sufficiently high to yield molecules in close proximity to the size of the anionic load bearing contaminants such as are generally present in contaminated liquids which are subjected to filtration through filter aid beds for clarification and purification. Due to the size of this polymer molecule, its conversion was only ensured with the freely available cationic sites of the filter aid coated with the polyelectrolyte, as they are present in the same way in colloidal or suspended anionic impurities that normally occur in practical applications of filter aids. The stock solution of the peeled polyacrylamide was made to contain 10 parts per million polymer.

A quantity of 10 ml of a 1 weight percent aqueous solution of the polyethylene polyamine polymer (molecular weight about 200,000) was diluted to 500 ml and used to slurry 100 g of DE filter aid (surface area = 4 m ² / g; mean particle size = 23.8 microns). This slurry was held for 30 minutes using a paddle stirrer at 100 rpm to keep the DE in suspension. The slurry was

7 8

drained on a nutsche, with deionized wear of the reciprocal values of the speed

Slurried water and drained the filtration (ordinate) compared to the diameter as above

sert to remove any excess of polymer- cut volume of the filtrate (abscissa) within

nen. This washing and dewatering stage was to be maintained for a defined period of time,

repeated twice, and the coated DE with 5 was determined according to the following, by FIG. 3 elucidation

a coating of 0.1 weight percent polymer! determined procedure.

30 g DE was then dried on stepped containers at normal laboratories. Five aliquots of the same supply with 5 g per 3.79 1 suspended ball of this dried, coated filter aid (0.25, 10 oily clay (kaolinite silica) as impurities 0.50, 0.75, 1.0 and 1.5 g) were used separately with each and 2.5 g each 3.79 1 DE with 0.2 percent by weight 5 ml portions of the parent polyethylene polyamine coating listed above. The filtration solution of the anionic polyacrylate to be drawn up was carried out under constant pressure, and the amide was reslurried for 15 minutes. It. the filterability _{index (C y} ) was made from using a multi-blade stirrer made of rust - running the line of values as in FIG. 3, free steel applied at 100 rpm to slow down in the higher values of C _v , which indicate more rapid equilibrium adsorption conditions, were used for filter aids that maintain. A centrifugal joint of lower filter aid coated with polyelectrolytes with lower indexes of the An-speed was used to separate the excess number of freely available cationic sites and the liquid, 20 were obtained. This can be seen in Fig. 4, where the which was then decanted and analyzed using the filterability index (ordinate) versus the indi-dilution counting technique in liquid dex the number of free cationic sites. Each sample was counted ten times, plotting the average count per minute (cpm) of polyelectrolytes used to coat DE. In FIGS. 4 and 5, explained below, the concentration (ppm) of the poly-25 to be drawn up had that which was related to the acrylamide. The polyethylene polyamine used values obtained are graphed in the drawing (PEPA) having a molecular weight greater than 100,000. The weight (in grams) of the coated material unless otherwise stated. Similarly, the filter medium (adsorbent) per gram adsorbed, the polyethyleneimine has a molecular weight greater than the anionic polymer (adsorbate) was applied against the 30 than 100,000. The applied quaternary ammonium reciprocal value of the equilibrium concentration of the salt consisted of an alkyltrimethylammonium anionic polymer. This curve of chloride and a dialkyldimethylammonium chloride corresponds to the well-known "Langmuir adsorption theory, with the alkyl chains having 8 to 18 carbon atoms" and is contained up to zero adsorbate concentration. The extrapolated by the letters TMVB. The reciprocal value of this value of the 35 points given on the figures represent a zero adsorption denotes the grams of adsorbed a copolymer of acrylamide and vinylbenzyl polymers per gram of coated filter medium of trimethylammonium chloride-coated DE.
or grams of adsorbate per gram of adsorbent. In the case of the index of the number of freely available cationic polymers, the reciprocal value of this charge point is related to the effective zero value, the weight in grams of the adsorbed speed of the removal of opacifiers in the anionic polymer per gram of the poly- Fig. 5, where the turbidity of the filtrate (original ethylene polyamine coated DE, this value lent turbidity of the feed = 444 ppm, optical index for the number of freely available measurements) is plotted in ppm on the ordinate cationic points, which are 0.1 weight and the cationic charge index is shown as the abscissa on percent polyethylene polyamine coated filter-45. The type and amount of coating on the medium are available. F i g. 2 explains that DE filter aid is indicated at each point
the above procedure, where an index = 0.820

for the number of freely available cationic sites Example 3
on the product. This index corresponds to

Number of grams of adsorbed adsorbate per 50 A large number of bacteria have been used

Grams of adsorbent at one solution concentration contamination of samples of sterile water

of the adsorbate from zero. used, and these samples were then

This index of the number of freely available cation-separated filter media is used to determine their suitability

shear points can be determined for each as a filter aid coating removal of these microorganisms,

applied material at any given concentration 55 culture broths from an age of 24 hours of

tration and also with different concentrations of Escherichia coli, Staphylococcus albus and aureus,

Any excess α- and γ-hemolytic Streptococci and Aerobacter present in the final product

Zugsmaterials are obtained. To those on these aerogenes were called microorganisms in these

Way applied for various cationic organic poly experiments. 1 ml of a test culture was

electrolytes or other materials that are added to excess 60 to 100 ml of sterile distilled water and

filter aid media have been used, total plate counts of the number of

obtained indexes with the filtration properties which organisms were produced by

to put in relation, a »filterability serial dilutions were made,

index «is set up in the following way. The inoculated samples were then quickly taken

. , 65 vacuum filtered through sterile suction filters, which a

Method B contained filter bed from DE, which with (1) a

The "filterability indices", which are graded as ethyleneimine polymers or (2) aluminum hydroxide

can be defined by lines that were covered by. For comparison, an uncomfortable

ίο

trade DE filter bed used. The coated DE was made by using the polymer as a about 15 weight percent aqueous solution was sprayed onto the DE. The other polymer coatings were applied by the slurry method described above. The ones with aluminum hydroxide coated filter aid was prepared by using an aqueous slurry of DE, Aluminum sulfate and anhydrous soda made, stirred for 15 minutes on the slurry The filter pad was deposited and washed with water to remove the excess material.

The coated filter aid contained about 2 weight

percent aluminum hydroxide. The bacteriological

Comparative counts of inflow and outflow are in 15 untreated sand

Filters were used to determine the total bacterial population. Otherwise identical An untreated sand and sand coated with aluminum hydroxide were tried Applied for comparison purposes. Table III below gives a comparison of the values obtained.

Table III

Filter medium

listed in Table II below.
Table II

Micro Count the bacteria after DE organism per milliliter Filtration Filter aid before the 210,000 E. coli Filtration 0 Untreated E. coli 310,000 88,000 0.2VoPEIO) S. albus 17,000 0 Untreated S. albus 130,000 60 0.2 «/ ο PEI (i) S. albus 76,000 0 2% Al (OH) ₃ «-Strepto 7,300 0.2% PEI (i) coccus 5,000 0 Aerobacter 0.2 »/ ο PEI (i) aerogenes 490,000 0 Aerobacter 1.0 poly aerogenes 50,000 acet- idine ( ² )

Untreated sand

Coated with Al (OH) ₃

Sand ....'

Sand covered with PEI

Bacteria count per milliliter

before filtration

80,000 86,000

19,000 82,000

after filtration

69,000 50,000

C ¹ ) PEI = ethyleneimine polymer.
( ² ) Polyazetidine = polymeric N, N-diethyl-3-hydroxyazetidine.

Again, the importance of the experiments lies in the need for the bacteria to be completely removed must be because, even if relatively small numbers in the filtrate by the aluminum hydroxide covered sand pass over, this due to the rapid growth to a reconstruction of the bacterial population.

Complete removal of intestinal parasites by filtering through 0.6 mm sand coated using the same procedure outlined above at a rapid rate of filtration was also achieved. Endoameba histolytica, Endolimax nina and Enterobius vermicularia were used to inoculate a sterile water inlet. The total removal of such microorganisms was achieved at flow rates of 7.61 per minute per 0.09 m ^{2 of} filter area.

35

40

Example 5

The removal of microorganisms from a

Although the great variety of fluids coated with inorganic matter was made with DE

DE a marked reduction in the number of bacteria with a coating of 0.2 percent by weight PEI than

showed make the great growth rate- filter medium shown. Beer with 400 microorganisms the presence of the bacteria was also very much 45 per milliliter at a rate of

low-number bacteria impossible if a sterile 1 l / minute through a suction filter No. 2 with a

Sequence is desired. 0.63 cm thick layer of the coated filter aid

with complete removal of the microorganisms

Example 4 i _tr t _he. I _n a similar manner, with 130,000 micro sand from the filtration rate of about 0.5 mm transit 50 organisms per milliliter contaminated kerosene was sterimesser lisiert for 12 hours in an aqueous by 0,5gewichtsprozentigen filter aid through this coated PEI solution to the Soaked setting of balance. Any excess PEI was then washed with deionized water
washed off and a column 45.7 cm high 55
this treated sand was placed in a vertical glass tube 91.4 cm with a diameter of 2.5 cm. The entire device was autoclaved before addition
of the coated sand sterilized. The sand was converted to 60 volumes of coated diatomaceous earth at 0.2% by backwashing with sterile water to weight percent PEI in 100 ml of a standard nutrient flow condition and then left to settle at 0, 5, 10 or 20 weight percent, where 2.5 cm Water slurried above the sand horse serum. Any such levels were available. The feed consisted of 700 ml of slurry, through a filter paper in sterile water, which was inoculated with Escherichia coli suction filter to form a filter bed, and was at a gravity speed and parts of the hydrate were in the usual density of 30 ml filtered per minute. Serial dilution tissue culture of ox kidney tissue beneath the water before the filtrate and after looking. There was no evidence of toxicity from the

609 708/246

medium was passed, with no ineffectiveness or clogging of the filter medium occurred.

Example 6

The following experiment was conducted to determine the effectiveness of the present removal method of virus organisms from liquids. In a number of approaches, 10.0 g

like filtrates versus tissue cultures were observed. Immediately after the nutrient medium had been filtered to form the filter bed, 100 ml of a suspension of the infectious ox rhinotracheitis virus, hereinafter referred to as IBR, were passed through the filter bed. Serial dilutions of the filtrate from each filter bed were inoculated into tubes containing cultures of common ox kidney cells. The cultures were then incubated under favorable growth conditions and observed for the development of the characteristic cytopathological effects indicative of the presence of IBR virus. The suspension of IBR virus used as the starting material was tissue culture swabs of the virus collected to give 500 ml of a suspension having a value of 10 ^s x ⁵ tissue culture infectious doses - 50%, hereinafter referred _{to as TCID 50} , of the IBR virus to 0.2 ml. This value can be determined from the dilution at which a cytopathogenic effect is observed in 50% of the culture tubes inoculated with this dilution. No cytopathogenic effect resulted from the values of the tests carried out when corresponding tests were carried out with the filtrates from the beds with coated filter aid, which had been prepared from slurries with a content of 0, 5, 10 and 20 percent by weight horse serum.

Example 7

The effectiveness of the process for removing microorganisms from commercially available dry cleaning agents was investigated by adding a tetrachlorethylene-water solution in the weight ratio was inoculated 1: 1 with different bacteria and then the contaminated solution through 40 g of DE with a coating of 0.2 weight percent PEI was filtered. It became a nutsche No. 2 used. The dilution of the dry cleaning solvent was necessary because 100% Tetrachlorethylene is toxic to the bacteria used. The coated DE was made by spray treatment of DE with an aqueous solution of PEI. The suspension of the test organisms in tetrachlorethylene water was filtered and the bacteria present before and after the filtration were determined according to standard plate counts. After 20 hours of incubation at 37 ° C, the Bacterial count listed in Table IV below as the number of bacteria per milliliter obtain.

Table IV
Bacteria / ml

Untreated after
Fil With! after
Fil CCl ₂ CCl ₂ -H ₂ O- DE tration PEI tration suspension before the
Fil 8000 coated DE 0 tration 3000 before the
Fil 0 A. aerogenes 16,000 2000 tration 0 S. aureus 17,000 14,000 B. subtilis 19,000 8,000 20,000

55

60

Example 8

The capacity of DE treated with PEI to remove microorganisms from air by Filtration was demonstrated by using a dry filter medium made from PEI coated to produce a Filter aid consisted of spray-treated DE with 0.02 percent by weight PEI, into a suction filter No. 2 with a No. 2 Whatman filter paper used as a base for the coated filter aid became. This filter was then placed on a nitrocellulose ester membrane filter using a pierced rubber stopper tied together. The system was placed under vacuum and the flow rate set to 600 l / hour. After completion of a filtration batch, the membrane filter (pore size 0.45 micron) was cultured on a standard agar and counted the microorganisms. The results in relation to the at different time intervals Total bacteria and fungi present are listed in Table V below.

Table V

Filter medium Time
Minutes Bacteria-
Fungi
count No .' 15th 24 No 30th 42 No 60 63 Untreated DE 15th
30th
60 13th
29
54 Untreated DE 15th
30th
60 0
0
0 Untreated DE With 0.2 percent by weight
PEI coating on DE
With 0.2 percent by weight
PEI coating on DE
With 0.2 percent by weight
PEI coating on DE

Example 9

The following experiment was carried out to determine the effectiveness of the filter aid coating in preventing the growth of microorganisms in the filter bed.

Diatomaceous earth was mixed with an aqueous solution of 0.2 percent by weight of the polyalkylene polyamine slurried according to Example 1 with an average molecular weight of 400 and about 0.54 cm deep filter bed formed in a normal suction filter. The funnel was fitted with a 500 ml filter flask connected, which contained 100 ml of sterile nutrient broth and successive portions of one Water heavily contaminated with bacteria was passed through the coated filter medium in the course of 3 days filtered. Any cloudiness that appeared in the nutrient broth was an indication of bacterial growth, in this case due to bacterial leakage, since the initial system was sterile and the only one The broth could be accessed through the filter medium. The coated filter aid removed all bacteria from the contaminated solution to be filtered. An untreated filter bed from DE was used for comparison. The result

Nits are listed in Table VI below.

Table VI

Time
hours

16
24
48
72

Untreated DE

visible growth
visible growth
visible growth
visible growth

Claims (4)

Claims: Exaggerated DE no growth no growth no growth no growth 1. Coated filter aid based on a particulate material with an electronegative charged surface, preferably diatomaceous earth, perlite, activated carbon, sand, asbestos, Cellulose pulp and fuller's earth, its surfaces are at least partially coated with a high molecular weight material, characterized in that that the coating material consists of a water-soluble polymer in which on each polymer molecule has a large number of cationic shear groups is bound, namely primary, secondary or tertiary amino, aziridine, quaternary Ammonium and sulfonium groups. 2. Coated filter aid according to claim 1, characterized in that the cationic Polymer coating a polyalkylene polyamine having an average molecular weight of contains at least 1000. 3. Coated filter aid according to claim 2, characterized in that the cationic Polymer coating contains an alkylenimine polymer. 4. Coated filter aid according to claim 2 or 3, characterized in that the cationic Polymer consists of an ethylene imine polymer. Considered publications: German Patent Nos. 594 561, 694 528; U.S. Patent No. 2247,711; "Chemische Rundschau", Bern, 1962, No. 14, pp. 393/394; F. Helfferich, "Ion Exchange", Vol. I, p. 44, Verlag Chemie GmbH Weinheim / Bergstr., 1959. 1 sheet of drawings 609 708/246 10.66 © Bundesdruckerei Berlin