MXPA06010494A - Filter media - Google Patents

Abstract

The invention concerns carbon block filter media for use in gravity fed filters comprising powder activated carbon (PAC) having a particle size distribution such that 95 wt%of the particles pass through 50 mesh and not more than 13%passes through 200 mesh, and a binder material having a Melt Flow Rate (MFR) of less than 5 g/10 min. The invention also provides water filters and a process for the preparation of a carbon block filter medium. The invention finally provides a process for the purification of water whereby the water under the influence of gravity is passed first through a washable or replaceable sediment filter for removing fine dust and other particulates above 3µm and thereafter through a carbon block filter medium comprising PAC and binder material.

Description

FILTER MEDIUM FIELD OF THE INVENTION The present invention relates to a carbon block filter medium for use in filtration units fed by gravity to filter particulate contaminants including microorganisms such as cysts, bacteria and viruses from a liquid, as well as for the removal of contaminants. chemicals, while at the same time maintaining high flow rates.

BACKGROUND AND PREVIOUS TECHNIQUE Fluids, such as liquids or gases, usually contain contaminants, which include particulates, chemicals, and organisms. In liquids such as water, especially drinking water, it is desirable to remove harmful contaminants before consumption in order to maintain proper hygiene and safety conditions for good health maintenance. Several different methods are known for water filtration and various devices and apparatuses have been designed and are commercially available. These methods and devices vary depending on whether the application is for industrial use or for home use. The water treatment for home use is basically aimed at providing safe drinking water. Methods and devices normally used at home for water treatment can be classified based on whether water is available under pressure, such as the high water head from an upper tank, or if water is available in small quantities, such as a few liters, in which case the available pressure is close to gravity. The filtration of water in the first case is classified under in-line systems, which have the advantage that the pressure of the water flow drives the filtration, and consequently usually does not face problems of reaching the desired flow velocity while supplying the basic need for effective filtration. Water filtration in the latter case is classified under self-contained systems, which process the water in batches under low gravity heads. It is a challenge to ensure the necessary removal of unwanted contaminants by filtration under such a low gravity head, at the time that the desired high flow rate is ensured. In this way, when filters designed for in-line systems are applied to gravity-fed systems they fail to produce the desired flow rates consistently over time, and often clog after a few liters pass, leading to the need for replacement or cleaning. Thus, it has been a real challenge to provide an effective filtration medium for self-contained systems, which would on the one hand provide the desired flow rate and at the same time supply the much-required removal of particulate contaminants including biological contaminants, such as protozoa such as crisptosporidium and even smaller organisms such as bacteria and viruses, as well as dissolved chemicals such as chlorine, organic and pesticide residues. Normally, a self-contained system for domestic application has a top and bottom chamber separated by a filter cartridge, where the water to be treated is emptied into the upper chamber and allowed to flow by gravity through the cartridge to the storage room. the lower chamber. The water treated in the lower chamber can be dispensed for consumption as and when desired. In such filter cartridges, the use of activated carbon is known to remove the bad smell and taste of water, as well as chlorine and other reactive chemicals. The use of ion exchange resin to remove metal and other ions from water is also known. It is also known to have gravity-fed water filters for domestic use, such as the decanter filter, in which water enters the filter element through a series of small perforations in the wider upper part of a shaped filter. trapezoid and flows through the filter to the narrower bottom in the process through a porous bed of loose absorbents. Such gravity flow gravity filters, like other gravity filters, have some inherent limitations to achieve effective flow rates, because water is required to pass through a deep bed of absorbent particles and water pressure is low in such systems, unlike systems in line, which have the advantage of high pressure and thus reach high flow rates. Attempts to increase the flow velocity in gravity fed systems by using larger particulates, lead to slower adsorption kinetics and thus, effective filtration loss. Conversely, the use of relatively small particles leads to greater flow restriction. US5505892 describes a process for manufacturing a filter unit made as a molded absorbent element permeable to gases and liquids, comprising (i) mixing granules of absorbent medium and a granular organic thermoplastic binder medium, (ii) placing in a mold and compressing it, ( iii) heating to a temperature of about 330 to 350 ° C until partial coking of the binding medium occurs, and (iv) cooling. The publication describes the use of granular type carbon, that is, granule size from 2 mm to 3 mm. EP 0345381 (American Cyanamid, 1989) discloses a filter structure for use in the purification of a liquid comprising activated carbon particles trapped within a porous plastic matrix, wherein the size of the activated carbon particles is 5-150. μm. The extremely fine carbon particles are bonded with thermoplastic binding agents of sizes substantially greater than on average, the particle size of the activated carbon particles. The activated carbon particles are evenly distributed through the porous plastic matrix structure.

The prior art discloses filter units comprising carbon particles of either very high granularity or very fine carbon powder, and would not be suitable for meeting the high demands of separation of microparticles, especially micro-organisms, from filtered water under low gravity head, while consistently maintaining the desired high flow throughput. US4753728 (Amway 1988) discloses a carbon particle filter comprising carbon particles attached to a filter block by a polymeric material of low melt index, having a melt index of less than 1 gram per 10 minutes, as determined by ASTM D1238 at 190 ° C and 15 kilograms of charge, whereby said polymeric material will stick to elevated temperatures, without becoming sufficiently liquid to substantially wet the carbon particles. The prior art does not provide the desired high flow velocity of water under gravity flow conditions, over a long period while consistently removing the desired contaminants to be removed. In this way, it has been a challenge to provide filters fed by gravity, which have effective flow rates and at the same time the desired filtering capacity and acceptable kinetics of adsorption.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides carbon block filter media comprising activated carbon powder of a selected particle size distribution and binder material having selected melt flow characteristics and specified particle size distribution. The filter media has been designed to have a desired particle size distribution profile across the bed height. The inventors have also developed an improved process for preparing the above filter medium. Thus, an object of the present invention is to provide filtration media for use in gravity fed filtration units, which provide the desired particulate removal including microorganisms such as cysts, bacteria and viruses, while giving the desired flow rate . In this way, the filter medium provides effective filtration leading to up to 99.9% removal of even chlorine-resistant cysts, such as cryptospodium parvum and Giardia Lamblia, which are in the size range of 3 to 6 μm and others microorganisms such as bacteria, which have size in the rang from 1 to 0.1 μm with a removal efficiency of more than 99.99% and even smaller organisms such as virus up to 99% removal, without affecting the flow rate. Additionally, the filter medium provides chemical removal including pesticides and odor removal. Another object of the invention is to provide a process for preparing the filter medium indicated above. Additionally, an object of the invention is to provide a process for purifying water using the filter medium indicated above.

DETAILED DESCRIPTION OF THE INVENTION In one aspect, the invention provides carbon block filter media for use in gravity fed filters, comprising: (a) activated carbon powder (PAC) having a particle size distribution, so that 95% by weight of the particles pass through 50 mesh and no more than 13% passes through 200 mesh, and (b) a binder material having a melt flow rate (MFR) of less than 5 g / 10 minutes. Preferably, 95% of the PAC particles also pass through 60 mesh. In addition, preferably no more than 12% passes through 200 mesh. Through their height, the particle size distribution in the medium of carbon block filter is preferably not uniform and it is preferred that 55 to 80% by weight of the PAC particles in the 100 to 200 mesh particle size range be located at 50% by volume of the medium. carbon block filter. It is further preferred that the carbon block filter medium has 55 to 95% by weight of the PAC particles in the smaller size range than 200 mesh, located at 50% lower volume of the carbon block filter medium. In another aspect, the invention provides water filters for use in gravity fed water filtration equipment comprising: (a) a washable or replaceable sediment filter to remove fine dust and other particulates above 3 μm, (b) a carbon block filter medium comprising the PAC and the binder material as described herein; (c) a base plate with a hole for the water outlet, to which the carbon block is attached; (d) a housing or cover to hold the entire filter as an integral unit. The cover or housing preferably is separable. In still another aspect, the invention provides a process for the preparation of a carbon block filter medium comprising the steps of (a) intimately mixing powdered activated carbon (PAC) having a particle size distribution, so that 95% by weight of the particles pass through 50 mesh and no more than 13% pass through 200 mesh with binder material, having a melt flow rate (MFR) of less than 5 in a mixer (b) compacting the mixture in a vibratory compactor (c) further compacting the mixture in a mold of desired shape and size by applying a pressure of no more than 20 kg / cm2 (d) heating the mold to a selected temperature (e) cooling the mold and release the carbon block from the mold. The PAC is preferably prepared from carbon sources selected from bituminous coal, coconut shell, wood or petroleum pitch. The surface area of the PAC is preferably above 500 m2 / g, more preferably exceeds 1000 m2 / g. The particle size of the PAC is selected so that 95% by weight of the particles pass through 50 mesh, preferably 60 mesh, and on the other hand no more than 13%, preferably no more than 12%, more preferably no more than 10% pass through 200 mesh. Preferably, the PAC has a size uniformity coefficient of less than 2, or more preferably less than 1.5, a carbon tetrachloride number exceeding 50%, more preferably, it exceeds 60%. The PAC preferably has a higher iodine number than 800, more preferably greater than 1000. As noted above, the carbon block filter means preferably has a particle size distribution profile across its height. It is preferred that the PAC particles are distributed across the height of the carbon block, such that 55 to 80% by weight, preferably 55 to 70% by weight of the PAC particles in the particle size range of 100 to 200 mesh is present in 50% by volume below the carbon block filter medium. It is also preferred that the PAC particles are distributed across the height of the carbon block, such that 55 to 95%, more preferably 60 to 95% of the PAC particles in the particle size range less than 200 mesh. it is present in the 50% lower volume of the carbon block filter medium. The bulk density of the binder material used in the invention is preferably not more than 2.5 g / cm 3, more preferably < 0.6 g / cm3, even more preferably < 0.5 g / cm3, very preferably < 0.25 g / cm3.

The binder material is selected to have a melt flow rate (MFR) of less than 5 g / 10 minutes, preferably less than 2 g / 10 minutes, more preferably less than 1 g / 10 min. The binder material preferably has a particle size distribution similar to that of the PAC, but the amount of particles passing a 200 mesh preferably is less than 40% by weight, more preferably less than 30% by weight. Preferably, the particle size distribution of the binder is substantially the same as that of the PAC. The Melt flow rate (MFR) is measured using the test of ASTM D 1238 (ISO 1 133). The test measures the flow of a molten polymer through an extrusion plastometer under specific temperature and load conditions. The extrusion plastometer consists of a vertical cylinder with a small die of 2 mm in the bottom and a removable piston in the upper part. A load of material is placed in the cylinder and is preheated for several minutes. The piston is placed on top of the molten polymer and its weight forces the polymer through the die and onto a collection plate. The time interval for the test varies from 15 seconds to 15 minutes, in order to accommodate the different viscosities of plastics. The temperatures used are 190, 220, 250 and 300 ° C (428, 482 and 572 ° F). The loads used are 1 .2, 5, 10 and 15 kg. For the present invention, the tests are made at 190 ° C to 15 kg load. The amount of polymer collected after a specific interval is weighed and normalized to the number of grams that had been extruded in 10 minutes: the melt flow rate is expressed in grams per reference time. The binder material is preferably a thermoplastic polymer having a MFR value described above. Suitable examples include ultra high molecular weight polymer, dpreference, polyethylene or polypropylene, which have these low MFR values. The molecular weight of preference is in the range of 106 to 1 09. Binders of this class are commercially available under the trade names HOSTALEN (from Tycona GmbH), GUR, Sunfine (from Asahi), Hizex (from Mitsubishi) and from Brasken Corp (Brazil). Other suitable binders include LDPE sold as Lupolen (from Basel Polyolefins) and LLDPE from Qunos (Australia). The proportion of the binder material to the PAC particles by weight is preferably chosen between 1: 1 and 1: 10, more preferably between 1: 2 and 1: 6. The carbon block filter medium described before the invention are capable of removing chemical contaminants and more importantly at least 99.9% of cysts, such as Giardia Lamblia, Cryptospordirium Parvum and Entamoeba Histolica, 99.99% of bacteria and 99% of virus without significantly affecting the flow velocity. Unlike the filter means of the prior art, the filter medium of the present invention does not require washing and reversing the flow discharge at regular intervals to ensure high flow rates. However, reversing the discharge can be done under running water or reverse the carbon block within the gravity filter device to cause a minor improvement. By means of the above filtration medium of the invention, it is possible to achieve an average water flow rate, from a height starting at 200 mm to 50 mm, under the gravity of 100-300 ml / min, preferably 120-200 ml / min, without compromising the removal requirements of particulate matter including microorganisms and chemical contaminants. The water filters according to the invention comprise a carbon block filter means of the invention. Water filters also comprise a sediment filter, which can be washable or replaceable and preferably is a woven or nonwoven fabric, more preferably a nonwoven fabric having micropores. This sediment filter is used as a pre-filter and has a suitable pore size to retain particles, generally above 3 μm. The sediment filter can be washed and rinsed under flowing running water or by using a small amount (0.1 -10 g / l) of gender wash detergent in water. This use of the sediment filter facilitates a broad and extensive application of the carbon block filter medium of the invention by preventing the filter medium from becoming clogged with sediment.

According to a preferred embodiment of the invention, the carbon block filter medium is attached to a base plate with a hole for the water outlet and additionally comprises a separable cover. The base plate is made of plastic, such as polypropylene, polyethylene, ABS, SAN. The separable cover is preferably also made of: polypropylene, polyethylene, ABS, SAN.

The filter medium can be of any desired shape and size. Suitable shapes include a flat circular disk of low thickness, a low-thickness square disk, a low-height tapered flat disk, a cylinder, a solid cone, a hollow cone, a solid or hollow hemisphere, etc. It is further preferred to include a bed of granular adsorbent particles in said water filter, so that the water to be filtered passes through said bed of granular adsorbent particles before passing through the carbon block filter medium. The granular adsorbent particles are preferably granular activated carbon. The granular adsorbent particles preferably have a particle size in the range of 200 to 5000 μm, more preferably 200 to 2000 μm, most preferably 500 to 1500 μm. Thus, according to a preferred aspect of the invention, a water filter is provided for use in gravity-fed applications, comprising: (a) a washable or replaceable sediment filter to remove fine dust and other particulates by above 3 μm; (b) a bed of granular adsorbent particles; (c) a carbon block filter medium comprising the PAC and the binder material as described herein; (d) a base plate with a water outlet hole, to which the carbon block is attached; (e) a cover or housing to hold the entire filter as an integral unit. Preferably, the bed of granular absorbent particles is provided in order to allow a quick and easy replacement of the particles, either by providing them in a separate housing which can be removed, and if it is desired to empty and fill with a new load. of particles, and readjusted again, or in a housing attached to the sediment filter to be removed and replaced with the sediment filter, or combined in a housing with the carbon block filter medium. The inclusion of the granular adsorbent particles in the water filter allows the filtration of a significantly greater amount of inlet water over a prolonged period, thereby ensuring a more efficient utilization of the carbon block filter medium of the invention. Additionally, granular adsorbent particles in the water filter allow effective filtration of highly contaminated water containing high amounts of fine particles such as dust and dissolved impurities such as iron and aluminum salts. As noted above, the invention also provides a process for the preparation of carbon block filter media, comprising the steps of intimately mixing PAC with binder material in a mixer, compacting the mixture in a vibratory compactor, further compacting the mixture in a mold, heat the mold, cool the mold and release the carbon block from the mold. For the step of mixing the PAC and the binder material, any low-cut mixer that does not significantly alter the particle size distribution is suitable, such as a mixer with blunt propeller blades, ribbon mixer, rotary mixer.

The mixing is performed to prepare a uniform mixture of the PAC and the binder material is preferably carried out for at least 15 minutes, more preferably 20 to 60 minutes. The compaction of the mixture is carried out in a vibratory compactor to obtain the profile of desired particle size distribution through the height of the carbon block. The vibratory compaction is preferably performed on a vibrator having a frequency in the range of 30 to 100 Hz. This process step is preferably carried out for a period of at least one minute, more preferably for 3 to 30 minutes. The compacted mass is then placed in a mold of pre-selected size and shape and subjected to a pressure of not more than 20 kg / cm2, preferably not more than 10 kg / cm2. The pressure is preferably applied using either a hydraulic press or pneumatic press, more preferably a hydraulic press. The mold is made from aluminum, cast iron, steel or any suitable material capable of withstanding temperatures exceeding 400 ° C. A mold release agis preferably coated on the interior surface of the mold. The mold release agis preferably selected from either silicone oil, aluminum foil or any other commercially available mold release aghaving little or no adsorption on the activated carbon or the binder material. The mold is then heated to a temperature of 150 to 400 ° C, preferably in the range of 180 to 320 ° C, depending on the binder material used. The mold is kept hot for a period of more than 60 minutes, preferably between 90 and 300 minutes depending on the size and shape of the mold, and sufficient to ensure uniform heating of the contents of the mold. The mold is preferably heated in a furnace, such as a convection forced-gas, forced-air, non-convection oven. The mold is then cooled and the carbon block released from the mold. Finally, the invention provides a process for the purification of water, whereby water under the influence of gravity is first passed through a washable or replaceable sediment filter to remove fine dust and other particulates above 3 μm and subsequently, through a carbon block filter means comprising PAC and binder material, as described hereinbefore. Preferably, the water is also passed through a bed of granular adsorbent particles as described hereinabove, between passing through the sediment filter and the carbon block filter medium. The initial pressure before entering the sediment filter is preferably no more than 3000 mmm of water column, more preferably when much 1000 mm of water column, most preferably does not exceed 500 mm of water column. The details of the invention, its objectives and advantages are explained below in more detail in the non-limiting examples: EXAMPLES Example 1: A carbon block was prepared by taking 100 grams of Active Carbon PAC (India) and 30 grams of ultra high molecular weight polyethylene with MFR ~ 0 and bulk density of 0.22 g / cm3 from Asahi (Japan) . The PAC had 6.5% by weight of the particles passing the 200 mesh and 98% of the particles passing through 50 mesh. The powders were mixed in a ribbon mixer for 30 minutes and transferred to a mold. The mold was then vibrated on a vibrator for 5 minutes and then subjected to a hydraulic pressure of 10 kg / cm2. The mold was then heated to 260 ° C for 150 minutes and then cooled.

Comparative Example A: A carbon block was prepared as for Example 1, except that the ligand used was HDPE from Sri Lanka, having an MFR of 25..

The two previous sample carbon blocks were subjected to water filtration under a 75 mm gravity head.

The characteristics of filtration and flow velocity over time are summarized in Table 1. The removal efficiency of microorganisms is measured using the test procedure summarized below in Table 1.

Table 1 The data in Table 1 indicate that the carbon block filter medium according to the invention (Example 1) provides efficiency l- > of very high microorganism removal, while providing a consistently high flow velocity under head conditions by gravity.

Procedure to determine the efficiency of removal of cysts: 0 The test of capacity and efficiency of removal of cysts was measured using 3-micron fluorescent microspheres and was carried out using the following procedure: Materials 5 Feeding water: 1.23 x 105 microspheres per liter of BIS / simple water. (See preparation section), filter housing chamber, vacuum pump, filter assembly, filter discs 0.45 μ Millipore (47 mm), Tween 80, glass material: conical flasks (250 ml), measuring cylinders (100 ml), pipette (1 ml), fluorescent microscope.

Preparation: A suspension of concentrated fluorescent polymer microspheres was used (catalog No. G0300, having reportedly 7.4 x 108 microspheres / ml with each microsphere having an average diameter of 3 microns, standard deviation of 0.1 miera, from Duke Scientific, Palo Alto, CA 94303, US). 10 μl of the above solution + 10 μl of Tween 80 + 9.98 ml of distilled water were taken. The mother preparation was vortexed for 10 min to ensure uniform distribution of the microspheres. Tween 80 was used as dispersant, (as for the ANSI / NSF protocol 53-2001). It is important to use the stock solution with 5 days of preparation (as for ANSI / NSF protocol 53-2001). The feed water was prepared by adding 1 ml of the stock solution to 6 liters of simle water. This resulted in a microsphere concentration of 1.23 x 105 particles / l.

Procedure: Escarpia: 1. Transfer 6 I of feed water into the upper filter mounting chamber. 2. Collect 100 ml of feedwater as input sample. 3. Collect 5 liters of the filtrate as 5 samples of one liter each (marked 1 to 5 in the attached report format).

Analysis of the scarp filtrate 1. 100 ml of each collected sample was used and passed through the Millipore 0.45 μ filter disc using the filter assembly and the vacuum pump. 2. Each filtered disc was allowed to air dry for at least 5 hours under ambient conditions. 3. The microspheres were then counted on each disc filtered at 40X magnification using a fluorescent microscope, (as for EPA-ICR method 814-B-95-003 chapter 6) as follows: 4. Count 20 fields randomly encompassing all the disk. Ensure an opening of at least 4 fields between each counted field. The removal efficiency is calculated as follows: Log of reduction (X) = log ((740000/6) / (M * 4000)) where M is average of the average of microspheres per field observed in 5 fractions (of 100 ml each) ), collected during each cycle of scarp. Because M is based on an average of 20 fields counted randomly (with the filter disk having 400 fields), M x 400 gives the total microspheres collected for each disk (100 ml). M x 4000 gives the total microspheres on an L of water collected. % removal = 100 (1 - (1/10? X)) Procedure for preparing a bacterial sample: The model organism chosen for the test was E. coli. The following are required for the bacteriological test: m-Endo or MacConkeys's agar or VRBA (DIFCO), water buffer APHA, tryptone saline solution, or PBS, trypticase and Agar soy broth (DIFCO), deionized water, millipore membrane filters Sterile 0.22 and 0.45 μ with filter holders and sterile forceps and syringes. Other requirements for both bacterial and viral tests: RO water, dechlorinated municipal water, CaCI2 grade AR, MgCI2, CaSO4, MgSO, NaHCO3, Na2CO3, NaOH, freshly prepared sodium hypochlorite (1% solution with 10000 ppm average chlorine), bottles, pipettes, pH meters, TDS, conductivity and turbidity.

Procedure: 1. The test organisms were washed and suspended in buffered saline with tryptone / phosphate before addition to the test water. 2. The culture is to be passed once every 24 hours in TSB for two successive days and incubated at 37 ° C. 3. On the third day, 0.1 ml of a 24-hour culture will be added to fresh TSB, stirred and incubated for more than 24 hours at 37 ° C. 4. The resulting suspension will be centrifuged for 10 minutes at 3000 rpm.

. The supernatant is discarded and the cells are washed three times with tryptone or sterile PBS and suspended in PBS. 6. The final concentration for immediate use (~ 5 x 106 cfu / 100 ml in the challenge water) is to be determined spectrophotometrically. 7. In addition, the actual account will be determined by the TSA / MacKonkey license plate account.

Procedure for preparing virus sample: MS2 culture The host strain used is E coli ATCC 15597. The host strain medium is prepared using tryptone (10 g), yeast extract (8 g), NaCl (8 g), distilled water ( 1 liter) and agar (15 g). The sample is filtered, sterilized and aseptically added to the sterile medium. The growth conditions are maintained at 37 ° C and in aerobic and stationary conditions.

Procedure for quantification of MS2: 1. Prepare an ATCC broth culture that actively grows from the MS2 host upon inoculation in 25 ml of the medium under static and aerobic conditions for 24 hours at 37 ° C. 2. Empty the basal agar plates with Escherichia medium agar and keep them at 37 ° C. 3. Dilute serially to 10"12 in the steps of 1: 10. 4. For each dilution pipette 1 ml of the virus sample into the sugar tube with 3 ml of soft agar maintained at 60 ° C and then add 250 ml of host culture.

. Mix and empty to base agar and transfer to plates and allow it to set for one hour before incubating for 24 hours at 37 ° C. 6. Count the number of plates observed on each plate against dark background. 7. Calculate the number of viruses in pfu / ml.

Comparative Example B An experiment was performed for Example 1, except that the vibratory compaction step was not performed. The data on the efficiency of microbial removal are given in Table 2.

Table 2 The data in Table 2 indicate that the carbon block prepared using the process according to the invention (Example 1), which ensures a particle size distribution profile across the block height, provides a removal of greatly improved microorganism as compared to that prepared by the prior art process. (Comparative example B).

Water filter 1: Water filter 1 was prepared as shown in Figure 1. The water filter as for Figure 1 comprises a sediment filter (SF), a carbon block filter (CB) medium prepared as for Example 1, which is adhered to a base plate (BP).

Water filter 2: Water filter 2 was prepared as shown in Figure 2. The water filter as for Figure 2 comprises a sediment filter (SF), a carbon block filter (CB) medium prepared as for Example 1, which was adhered to a base plate (BP). The space between the carbon block filter medium and the sediment filter is filled with granular activated carbon (GAP) with a particle size in the range of 500 to 1500 μm.

Examples 2 and 3: A water test was prepared having 15 mg / l of fine Arizona test powder and additionally 0.47 ppm of dissolved aluminum cations and 0.4 ppm of dissolved iron cations. This test water was filtered through the water filters of Figure 1 (Example 2) and Figure 2 (Example 3) with a constant head of 160 mm. The flow rates obtained over an extended period of use of the filters are summarized in Table 3. The acceptable quality of filtered water was obtained with both filters.

Table 3 The data in Table 3 indicate that the high-throughput flow rates of filtered water obtained with the use of the water filter comprising the carbon block filter medium according to the invention (Figure 1). The increased water flow rate was obtained with the use of the water filter according to the preferred aspect of the invention, which comprises granular adsorbent particles and the carbon block (Figure 2).

Examples 4 and 5: Highly contaminated torture test water was prepared having 130 mg per liter of Arizona fine test powder and additionally 4.7 ppm of dissolved aluminum cations and 4 ppm of dissolved iron cations. This test water was filtered through the water filters of Figure 1 and Figure 2 with a constant head of 160 mm. The flow rates obtained over an extended period of use of the filters are summarized in Table 4. The acceptable quality of filtered water was obtained with both filters.

Table 4 Examples 6 to 10 Additional experiments were conducted to determine the particle size distribution obtained through the height of the carbon block using the process of the invention. Five PAC samples were taken fulfilling the specification according to the invention and were subjected to vibration in a vibratory compactor for 5 minutes at 50 Hz. 50% in the upper volume of the sample and 50% in the lower volume of the samples they were separated and each sample was then sieved separately on a 200 mesh screen. Oversized weights and fractions below dimensioning were measured. The data are presented in Table 5.

Table 5 Note: The fines in the table above is the fraction having a particle size smaller than 200 mesh.

In all the samples of examples 6 to 10, the percentage of fines passing 200 mesh, which was 50% lower volume of the carbon block was in the range of 55 to 95% by weight of the total fines passing the 200 mesh. It was found that all these samples provide good carbon blocks as for the invention. Representative photographs (x150 magnification) of the upper and lower surface of the block are shown in Figures 3 and 4 respectively. The photographs clearly indicate the different particle size distributions obtained as a result of the vibratory compaction process step. In this way, the invention provides carbon block filter means, a process for preparing the same, water filters that can be prepared using such carbon blocks and a process for purifying water using the carbon blocks.

Claims (10)

1 . A carbon block filter means for use in gravity fed filters, comprising powdered activated carbon (PAC) and a binder material, wherein: (a) the PAC has such a particle size distribution, that the % by weight of the particles passes through 50 mesh and no more than 13% by weight passes through 200 mesh, and (b) the binder material has a melt flow rate (MFR) of less than 5 (in g / 10 min) and, (c) 55 to 80% by weight of the PAC particles in the 100 to 200 mesh particle size range is located at 50% in the lower volume of the filter medium.

2. A filter medium as claimed in claim 1, wherein 55 to 95% by weight of the PAC particles in the size range smaller than 200 mesh is located at 50% by volume less than filter.

3. A filter medium as claimed in any of claims 1 and 2, wherein the MFR of the binder material is less than 2.

4. A filter medium as claimed in claim 3, wherein the MFR of the material binder is less than 1.

5. A filter medium as claimed in any of the preceding claims, wherein the binder material has a bulk density less than 2.5 g / cm3.

6. A filter medium as claimed in any of the preceding claims, wherein the proportion of the binder material to PAC is in the range of 1.1 to 1: 10.

7. A filter medium as claimed in claim 6, wherein the proportion of binder material to PAC is in the range of 1: 2 to 1: 6

8. A filter medium as claimed in any preceding claim, wherein the binder means is selected from ultra high molecular weight polyethylene or polypropylene.

9. A filter medium as claimed in claim 8, wherein the molecular weight of the binder material is in the range of 106 to 109.

10. A water filter for use in water filtration equipment fed by gravity, which comprises: (a) a washable or replaceable sediment filter to remove fine dand other particulates generally above 3 microns, (b) a carbon block filter medium comprising the PAC and the binder material as claimed in any of the preceding claims, (c) a base plate with a water outlet orifice, to which the carbon block is attached; (d) a detachable housing or cover to hold the entire filter as an integral unit. eleven . A water filter as claimed in claim 10, wherein the water filter comprises a bed of granular adsorbent particles, so that the water to be filtered passes through said bed of granular absorbent particles before passing through the water. said carbon block filter. 12. A water filter as claimed in claim 1, wherein the granular absorbent particles are granular activated carbon. 13. A water filter as claimed in any of claims 11 or 12, wherein the granular adsorbent particles have a particle size in the range of 500 to 1500 μm. 14. A process for the preparation of a carbon block filter medium, comprising the steps of: (a) intimately mixing the activated carbon powder (PAC), which has a particle size distribution such that 95% by weight the particles pass through 50 mesh and no more than 13% pass through 200 mesh with binder material, having a melt flow rate (MFR) of less than 5 in a mixer; (b) compacting the mixture in a vibratory compactor; (c) further compacting the mixture in a mold of desired shape and size by applying a pressure of not more than 20 kg / cm2; (d) heating the mold to a selected temperature; (e) cool the mold and release the carbon block from the mold. 15. A process for the preparation of a carbon block filter medium as claimed in claim 14, where the mixture is compacted in the mold by applying a pressure of no more than 12 kg / cm2. 16. A process for the preparation of a carbon block filter medium as claimed in any of claims 14 or 15, wherein the mixing is done for a period of at least 15 minutes. 17. A process for the preparation of a carbon block filter medium, as claimed in any of claims 14 to 16, wherein the vibration compaction is performed for at least 1 minute at a frequency of at least 30 Hz 18. A process for the preparation of a carbon block filter medium, as claimed in any of claims 14 to 17, wherein the mold is heated to a temperature of 150 to 400 ° C. 19. A process for the preparation of a carbon block filter medium as claimed in claim 18, wherein the mold is heated to a temperature of 180 to 320 ° C. 20. A process for purification of water, whereby water under the influence of gravity, is first passed through a washable or replaceable sediment filter to remove fine dust and other particulates above 3 μm and subsequently to through a carbon block filter means comprising PAC and binder material as described in any of claims 1-9. twenty-one . A process as claimed in claim 20, wherein between the passage through the sediment filter and the carbon block filter medium, the water also passes through a bed of granular adsorbent particles.