WO1998014265A1

WO1998014265A1 - Method for manufacturing molded carbon filters

Info

Publication number: WO1998014265A1
Application number: PCT/US1997/017708
Authority: WO
Inventors: Paul Kelley
Original assignee: Honeywell Inc.
Priority date: 1996-10-01
Filing date: 1997-10-01
Publication date: 1998-04-09

Abstract

A method for manufacturing molded carbon water filter blocks includes the steps of supplying carbon powder or granules, a thermoplastic polymeric binder, and an additive (in form of a redox material, anionic resin beads or powder or slowly soluble phosphate beads) through computer-controlled conveyors to individual weigh bins. Each of these materials is weighed in preestablished proportions; and when the appropriate amount of material is present in each of the weigh bins, they are emptied into a mixer. The carbon, binder and additives are thoroughly mixed and then supplied to a second weigh bin, which then is emptied into a mold. The mold is moved through a conveyor oven to cause the binder to bind the mixture of carbon, binder and additive together. After the mold is removed from the oven, it is compressed under pressure until it cools to a temperature below the melting temperature of the binder. The filter block then is removed from the mold.

Description

METHOD FOR MANUFACTURING MOLDED CARBON FILTERS

BACKGROUND Throughout the world, there is increasing need to purify drinking water at the point of consumption. This is particularly true in undeveloped countries, where the drinking water supply is highly contaminated. Even in highly developed nations, however, increasing amounts of manmade contaminants are found-in drinking water. While in developed nations drinking water generally is chemically purified prior to delivery to consumers, even the chemicals used in the purification process, primarily chlorine, generally are considered undesirable. Consequently, the provision of water filters at the point of consumption, which remove natural and manmade contaminants as well as "purifying" chemicals from the water, are becoming increasingly popular.

In some of the most effective point-of-use water purification systems, contaminants are removed by adsorbing or absorbing them by use of a sorbent bed through which the water is passed. Effective sorbent beds typically are made of activated carbon material. An effective form of such filters is to shape carbon particles and a binder into pressed carbon blocks. These blocks then may be used in axial flow or radial flow filters. If a radial flow filter configuration is used, the block typically is formed around a porous plastic sleeve located in the core, which keeps the charcoal from flaking off into the water exiting the block. For axial flow filters, a similar porous plastic disk or retainer is located at the exit end of the block.

A double shell filter in the form of such carbon block is disclosed in the United States patent to VanderBilt No. 4,859,386. This filter includes an inner shell of bonded 80 to 400 U.S. mesh screen carbon particles and an outer shell of bonded 20 to 80 mesh screen carbon particles. The inner and outer shells are bonded internally to each other, with the two shells forming a filter which exhibits improved water flow characteristics.

In some operating environments, it has been found that contamination of the sorbent bed may take place through the growth of microorganisms which produce undesirable byproducts., The U.S. patent to Kirnbauer No. 5,443,735 discloses a pressed carbon filter bound together with a polymer adhesive. In addition, brass particles are dispersed throughout the filter to inhibit the growth of microorganisms in the filter; so that the water effluent is substantially free of such microorganisms. The manner in which these brass particles are dispersed in the carbon medium during manufacturing is described as having the particles "blended in with the carbon particles" or present in a separate slurry for a "dipped" filter construction. Three other patents which recognize the desirability of mixing brass particles and carbon together in a water filter are the U.S. patents to Iana Nos. 5,122,272 and 5,167,819 and the U.S. patent to Heligman No. 5,411,661. None of these three patents, however, is directed to a pressed carbon block type of construction where the particles are immobilized relative to one another in the filter. The carbon granules and the brass granules are not bonded together in these filters.

The U.S. patents to Wilkinson No. 5,149 and VonMedlin No. 5,269,919 are directed to three-stage filters where the different stages have different filter elements in them. The filter devices of each of these patents employ one filter section filled with a brass particle filtering material, a second filter section filled with activated carbon, and a third section comprising either a biocidal filter or an acid ion exchange. It should be noted that the filter elements are not combined together as a single filter medium mixture, but that three separate stages, using different filter media, are employed in these patents.

Other patents which disclose the desirability of using either pressed carbon block filtration or brass particle filtration are the U.S. patents to Goodwin Nos. 5,092,993 and

5,277,802 (brass particle) and the U.S. patent to Heligman No. 5,017.286. A different filter is disclosed in the U.S. patent to Sutera No. 5,405,526, which discloses an activated carbon/silver filter. A problem which exists in the manufacture of pressed carbon block filters, particularly filters which incorporate other elements or additives, such as the brass particles of the

Kirnbauer patent No. 5,443,735, is that of maintaining a uniform dispersion of the additive particles throughout the finely powdered carbon during the manufacturing stages and ultimate use of such filters. When a pressed carbon block filter of the type disclosed in Kirnbauer is manufactured, the heavier brass particles tend to "settle down" in the carbon mixer prior to the bonding together of all of the particles during manufacture. The Kirnbauer patent does not disclose the manufacturing steps for ensuring a uniform dispersion of the brass particles during manufacture. The three-stage filters of the VonMedlin and Wilkinson described above do not have such a problem of maintaining uniform dispersion; but these multiple-stage filters do not exhibit the improved filtration advantages of pressed carbon block filters.

It is desirable to provide a carbon block filter which may be accurately and efficiently manufactured with a uniform dispersement of additives throughout the carbon in the finished filter, and which overcomes the disadvantages of the prior art noted above.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved method of manufacturing a fluid filter.

It is another object of this invention to provide an improved method of manufacturing a carbon block filter.

It is an additional object of this invention to provide an improved method of manufacturing a carbon block filter having additives dispersed throughout the block.

It is a further object of this invention to provide an improved automated method of manufacturing a carbon block filter with additives uniformly dispersed throughout the finished filter element for enhancing specific filtering characteristics cf the finished product. In accordance with a preferred embodiment of the invention, a method for manufacturing molded carbon block filters includes the steps of supplying predetermined amounts of carbon powder or granules having a size in a range of 20 x 50 to 80 x 400 U.S. mesh screen, a thermoplastic binder, and an additive selected to impart particular characteristics to the finished filter. The carbon, binder and additive are mixed to produce a homogenous mixture. A predetermined weight of mixture is supplied to a mold. The mold then is moved on a conveyor through a temperature controlled oven to melt the binder and adhere it to the carbon and the additive. When the mold exits the oven, the filter mixture in the mold is compressed until the mold cools to a temperature which is lower than the melting temperature of the binder. The filter then is removed from the mold. This operation is effected on a continuous basis; so that molds are continuously moving through the oven immediately after they are filled, which takes place immediately after the mixing of the ingredients to produce a homogeneous mixture.

BRIEF DESCRIPTION OF THE DRAWING The sole figure of the drawing is a block diagram of a process and system according to a preferred embodiment of the invention.

DETAILED DESCRIPTION Reference now should be made to the drawing, which discloses the apparatus and process used to produce improved molded carbon blocks for fluid filters. As illustrated in the drawing, the method commences with the various raw materials for the production of molded carbon blocks placed in bulk storage bins. These bins are shown in the drawing as a carbon bin 10, a binder bin 12 and an additive bin 14.

The carbon which is placed in the bin 10 is carbon powder 20 x 50 to 80 x 400 U.S. mesh screen, with no more than 17% carbon fines and no more than 8% ash. The moisture level of this carbon is controlled to be between 4% and 6%. The carbon is commercially available and suitable carbon powder or granules are BARNABY SUTCLIFF 3025, CALGON CAREON TOG, CALGON CARBON TOG/C, and AMERICAN NORITT DARCO. While all of these carbon powders may be used in applicant's manufacturing process, the most preferred is BARNABY SUTCLIFF 80 x

325 U.S. mesh screen powdered bituminous coal.

For the binder placed in the storage bin 12, a thermoplastic binder, which preferably is a polymeric plastic, is used. Preferred binders are high or ultra-high molecular weight, high density polyethylene. The ultra high high molecular weight is selected to provide restricted flow properties of the melted material, which is important in the uniform bonding of the finished product. Suitable binders are produced by the HOEST CELANESE CO. and are identified as UHMW-PE GUR 2122, NB6O81 or GUR 4022 PE,A LDPE, such as HA1684, HX1681, or HA1681. For the method described here, the preferred binder is GUR 4022. The binder is added in powder form in a mesh size comparable to the mesh size of the carbon powder stored in the bin 10.

The third bin 14 is filled with the particular additive which is to be added to the binder and carbon supplied from the bins 10 and 12. For example, the bin 14 may be filled with brass powder, again selected have a mesh size in the range of the mesh size of the carbon particles; although the brass powder may have a mesh size which is half that of the smallest carbon particles to a size which is approximately double that of the largest carbon particles. It is important, however, that the brass particles be comparable in size to the carbon particles for the most effective utilization in the filter to be produced by the method and system shown in the drawing. A type of brass which has been found to be particularly effective is sold under the trademark KDF manufactured by Zinc Corporation of America. KDF is a mixture of copper and zinc in a formulation which is suitable for water filtration systems. This material is a reduction/oxidation (redox) material, which has been found to be effective in removing chlorine or magnesium permeate from water passing through a filter employing KDF.

Other materials which alternatively may be used in the additive bin 14, or which may be employed in additional additive bins to be added in parallel to the material shown in the bins 10, 12 and 14, are a nitrate reduction resin in the form of strong based anionic beads or powder. Suitable anionic resins are PUR LITE-NITREX A-520 nitrate removal resin, IONAC ASB IP/HP, IONAC A-554, IONAC SR-8 or IONAC SR-7 manufactured by SYBRON CHEMICALS. Additional resins are MITSUBISHI CHEMICAL RDA 416, DIAION RESIN, and RESIN-TECH ABD 15. Of these, the most preferred is SYBRON CHEMICAL'S SR-7, with SYBRON CHEMICAL'S A554 the next most preferred. All of these resins, however, are suitable for use in nitrate reduction in a completed filter.

In the manufacturing process to be described, the anionic resin must be used in dry form. This resin typically is received from the manufacturer as a slurry. In order to prepare the resin for use in the prescribed method, the resin is placed in stainless steel plates and heated for a sufficient period of time to dehydrate the resin beads. The moisture content of the resin, as it is received from the manufacturer, typically is about 42% by weight; and it dehydrated to less than 3% by weight before being placed in the additive bin 14.

A third additive, which may be used either in place of the additives described above or in conjunction with either or both of them, is a slowly-soluble polyphosphate

(slo-phos). Slo-phos may be employed in the carbon block filter for scale prevention, corrosion inhibition, and iron control. The size of the slo-phos beads is also selected to be within the mesh size of carbon placed in the bin 10.

Irrespective of the particular additive which has been placed in the bin 14, the system and the method which are shown in the drawing operate in the same general manner. The operation of the system is controlled by a central control computer 24, which operates three flat worm gear conveyors 16, 18 and 20. These are connected, respectively, to the storage bins 10, 12 and 14 to deliver controlled portions of the contents in each of the storage bins 10, 12 and 14, which are desired for inclusion in the filter to be manufactured by the process. The conveyors 16, 18 and 20 preferably are horizontal auger type conveyors; and the computer 24 controls the rate of operation of these conveyors to coordinate that operation to deliver the desired amounts of carbon, binder and additive to corresponding weigh bins 26, 28 and 30 required for the composition of the filter being manufactured by the system.

For example, the binder supplied by the conveyor 18 from the storage bin 12 is added as a percentage of the total weight of the mixture, and is selected to be not less than five percent nor more than twenty-six percent of the total weight of the three elements (carbon, binder and additive) used to form filter being manufactured. The amount of binder which is used depends upon the type and particle size of the carbon used, with smaller amounts of binder being used for larger carbon particle sizes. The amount of additive also is weighed in the weigh bin 30 as a percentage of the total amount of material used to produce the finished filter. For example, if anionic resin beads are employed, the resin is added in an amount not exceeding seventy percent of the total weight of the finished carbon block, but not less than ten percent by volume of the block. For anionic resin beads, an optimum amount is approximately fifty percent by volume. The determination of the weight required to produce this volume is made empirically; and once this determination is made, the program of the computer 24 selects the appropriate amount in the weigh bin 30 to produce the desired result in the end product.

For SLO-PHOS, a suitable range of material has been found to be between twenty percent and sixty percent; by weight, of the finished carbon block which is being manufactured. For KDF, since the brass is significantly heavier by volume and the carbon, the percentage by weight of KDF material, when this is the additive supplied from the bin 14, is typically between ten percent and twenty percent of the total weight of the filter mixture.

Once the control computer 24 has been programmed with the appropriate weight of each of the three materials, namely carbon, binder and additive, which are required to produce a single filter, the conveyors 16, 18 and 20 are operated until the appropriate percentages, by weight, of these materials are supplied to respective weigh bins 26, 28 and 30. These weigh bins send signals back to the computer control 24, which then terminates operation of the various conveyors 16, 18 and 20 when the desired weight of each of the materials for the finished filter block (typically 1" x 3", to 5" x 20" in size) is present in the bins. At this time, bins 26, 28 and 30 are opened and the material in them is delivered to a mixer 32.

The mixer 32 may be any suitable mixer. A satisfactory mixer used in the production of commercial products by the method disclosed here is a McGUIRE computer-controlled Series 400 mixer/blender/dispenser unit manufactured by McGUIRE PROCESSING EQUIPMENT CO.

The materials supplied from the weigh bins 26, 28 and 30 are mixed in the mixer 32 for a set period of time, empirically determined, which may range from a time between one minute and 30 minutes. This depends both on the type of additive supplied from the bin 14 and also on the particular size of the filter being manufactured. Obviously, a small filter requires less material than a large filter, and therefore requires less mixing time to ensure a homogenous mixture is produced. After the mixing operation, the material is dumped into a second weigh bin 34, which is similar to the weigh bins 26, 28 and 30. The material is held in the weigh bin 34 until it is needed and a signal is also supplied back to the control computer 24 to ensure that the proper total weight of material for the particular filter being manufactured is present. If it is not, an adjustment is made and additional material is supplied, as needed, in the correct proportions, from the bins 10, 12 and 14 in the manner described previously, with this additional material then being supplied to the weigh bin 34.

The next step is to empty the weigh bin 34 under the control of the computer 24 into a mold 36. The mold 36 typically is an open topped cylindrical mold of the type commonly used in the manufacture of carbon block filters. Immediately after the mold 36 is filled, it is placed on the conveyor of a conveyor oven 38. This is a speed controlled conveyor, immediately moving the mold 36 into the oven 38 where the temperature is controlled to heat the mixture to melt the binder; so that it adheres to the carbon and additive particles in the mixture. A typical temperature range for accomplishing this with high density and ultra-high density polyethylene binders is between 180° Celsius and 225° Celsius. The conveyor typically operates to keep the molds 36 in the heat chamber of the oven for a period of time between seven minutes and forty-five minutes. This time is dependent upon the size of the particular mold 36 and, to some extent, upon the type of binder which is used.

After the mold has exited the conveyor oven 38, the next step in the manufacturing process is to compact the carbon block mixture in the mold. This is effected by applying compression to the material in the mold through a piston which has an outside diameter approximately the same as the inside diameter of the mold in which the material is being processed. For the various mixtures which have been described above, a pressure of not more than 50 PSI (pounds per square inch) and not less than 10 PSI is applied for a time period of between three minutes to fifteen minutes (depending upon the density desired or the length and type of filter being manufactured). This compaction causes the binder, which is heated to its melting point in the conveyor oven 38, to adhere to as many of the carbon fines as possible. The pressure is maintained until the mold is cooled down to between 70° Celsius and 110° Celsius, with a preferred temperature being approximately 90° Celsius. At these lower temperatures, the binder solidifies to hold the entire filter mixture together in a block form. The next step after the compaction step is to remove the pressure, and then remove the formed carbon block filter from the mold. Following this step at 42, the mold is cored (if it already was not made with a hollow center around a plastic core), wrapped, and finished for utilization at the core and wrap stage 44.

Following the general process outlined above in the system/flow chart diagram of the drawing, carbon block filters incorporating the various additives described above have been constructed, as described in the following examples: EXAMPLE 1

The general process was used to produce a molded carbon block filter containing brass articles of KDF uniformly dispersed throughout. To produce this carbon block, a mixture of 70% by weight of carbon powder 80 x 325 U.S. mesh screen (BARNABY SUTCLIFF 3025), 20% by weight GUR 4022 binder, and 10% by weight of KDF powder was processed according to the general process described above. The mixture was blended for 5.25 minutes. The conveyor oven 38 was a thirty-six foot long three (3) zone controlled oven; and the temperature was set at 175° Celsius. The conveyor of the oven 38 was run at a speed to keep molds in the heat chamber of the oven for 27 minutes. After molding, the product in the mold was compacted using 60 PSI of pressure for 11 minutes. This was for a cylindrical mold size 2.6" x 9.75".

EXAMPLE 2 A carbon block designed for nitrogen reduction was manufactured using BARNABY SUTCLIFF 3025 carbon powder 80 x 325 U.S. mesh screen, comprising 40%) by weight of the total mixture. A polypropylene binder GUR 4022 comprising

20%) of total weight of the finished product was added, along with anionic resin powder (CYBRON SR-7) in the amount of 40% by weight of the total mixture. The mixture was blended for five minutes and then placed in a mold of the proper size for the filter. The mold was placed on a conveyor set for a 2.5-feet- per-minute run and run through a thirty-six foot long three (3) zone controlled oven at a temperature of 190° Celsius. This was for a cylindrical mold size 4.25" x 9.5".

After the mold was removed from the oven, it was placed in a compaction device using spacer rings and a pneumatic cylinder and compressed to desired size at a pressure of 80 pounds of pressure for a time period of 7.5 minutes. After the mold cooled to a temperature of 90° Celsius, the compression pressure was released and the filter block was removed from the mold.

EXAMPLE 3 A carbon block water filter was manufactured in accordance with the general process mentioned above, in which the additive was in the form of slowly soluble polyphosphate beads (SLO-PHOS). In the manufacture of this filter, the carbon powder was BARNABY SUTCLIFF 3025 80 x 400 U.S. mesh screen, with less than 17% carbon fines and less than 3% ash. The binder was GUR 2122. The percentages by weight of the ingredients were carbon 40 percent, binder 10 percent, and SLO-PHOS 50 percent of a total weight of 14.812 ounces to produce a cylindrical mold of 2.6" x 9.75". The SLO-PHOS particles were at a size of 20 x 5O U.S. mesh screen.

The three materials, in the amounts listed, were transferred to the mixer and were blended for a period of fifteen minutes. After mixing, the material was supplied to a mold, which was moved through a conveyorized heat controlled oven (a thirty-six foot long three (3) zone controlled oven). The oven temperature was 170° Celsius and the mold was moved on the conveyor at a rate of 2.5 feet per minute. After leaving the oven conveyor, the mold was compacted using spacer rings and an air cylinder using 40 pounds of pressure for 12 minutes. The mold cooled to a temperature between 70° and

80° Celsius; and the pressed carbon block with SLO-PHOS additive dispersed throughout the block, was ejected from the mold.

The foregoing description of the preferred embodiment of the invention and the specific examples of various carbon block compositions should be considered as illustrative and not as limiting. Various changes and modifications will occur to those skilled in the art for performing substantially the same function, in substantially the same way, to achieve substantially the same result, without departing from the true scope of the invention as defined in the appended claims.

Claims

1. A method for manufacturing molded carbon filters including the steps of: supplying predetermined amounts of carbon powder or granules having a size in a range of 20 x 50 to 80 x 400 U.S. MESCHSCREEN, a thermoplastic binder, and an additive selected to impart particular characteristics to the finished filter; mixing said carbon, binder and additive to provide a homogeneous mixture; supplying a predetermined amount of said mixed carbon, binder and additive to a mold for said filter; moving said mold through a temperature controlled oven at a predetermined rate to cause said binder to melt and adhere to said carbon and to said additive; removing said mold from said oven; compressing said filter in said mold at a pressure of between 7 pounds to

60 pounds pressure until said filter in said mold cools to a predetermined temperature less than the melting temperature of said binder; and removing said filter from said mold.

2. The method according to Claim 1 wherein said thermoplastic binder is a polymeric binder and said additive is a redox material.

3. The method according to Claim 2 wherein the moisture level of the carbon is between 4 percent and 6 percent by weight and wherein said mixture includes between 5 percent and 26 percent, by weight, of binder and between 10 percent and 20 percent, by weight, of redox material additive.

4. The method according to Claim 3 wherein the melting temperature of said binder is between 180° Celsius and 225° Celsius with said mold moving through said oven for a time period between 7 minutes and 34 minutes.

5. The method according to Claim 4 wherein said step of supplying predetermined amounts of carbon, binder and additive is effected by moving said material from storage bins to said mixer using flat auger conveyors, with said material first being supplied to weigh bins for individually weighing the amounts of said carbon, binder and additive prior to supplying these materials to a mixer, where the step of mixing the carbon, binder and additive is effected, and the step of moving said mold through said temperature controlled oven is effected by placing said mold on a conveyor passing through said oven set to a temperature selected to heat said binder to the melting point.

6. The method according to Claim 5 wherein the operation of said conveyors and said weighing step are controlled by a computer system.

7. The method according to Claim I wherein the moisture level of the carbon is between 4 percent and 6 percent by weight and wherein said mixture includes between 5 percent and 26 percent, by weight, of binder and between 10 percent and 20 percent, by weight, of redox material additive.

8. The method according to Claim 1 wherein the melting temperature of said binder is between 1800 Celsius and 2250 Celsius with said mold moving through said oven for a time period between 7 minutes and 34 minutes.

9. The method according to Claim 1 wherein said step of supplying predetermined amounts of carbon, binder and additive is effected by moving said material from storage bins to said mixer using flat auger conveyors, with said material first being supplied to weigh bins for individually weighing the amounts of said carbon, binder and additive prior to supplying these materials to a mixer where the step of mixing the carbon, binder and additive is effected, and the step of moving said mold through said temperature controlled oven is effected by placing said mold on a conveyor passing through said oven set to a temperature selected to heat said binder to the melting point.

10. The method according to Claim 9 wherein the operation of said conveyors and said weighing step are controlled by a computer system.

11. The method according to Claim I wherein said additive comprises anionic resin beads in an amount less than 70 percent of the total weight of said filter, but not less than 10 percent by volume of said filter, with said resin being supplied in a dry form with a moisture content of less than 3 percent by weight.

12. The method according to Claim 11 wherein the melting temperature of said binder is between 180° Celsius and 225° Celsius with said mold moving through said oven for a time period between 7 minutes and 34 minutes.

13. The method according to Claim 12 wherein said step of supplying predetermined amounts of carbon, binder and additive is effected by moving said material from storage bins to said mixer using flat auger conveyors, with said material first being supplied to weigh bins for individually weighing the amounts of said carbon, binder and additive prior to supplying these materials to a mixer where the step of mixing the carbon, binder and additive is effected, and the step of moving said mold through said temperature controlled oven is effected by placing said mold on a conveyor passing through said oven set to a temperature selected to heat said binder to the melting point.

14. The method according to Claim 13 wherein the operation of said conveyors and said weighing step are controlled by a computer system.

15. The method according to Claim 1 wherein said additive is slowly soluble polyphosphate beads in an amount of 10 percent to 50 percent, by weight, of the mixture.

16. The method according to Claim 15 wherein the slowly soluble polyphosphate beads have a size selected to dissolve at a rate of 0.5 to 5.0 PPM in the filter.

17. The method according to Claim 16 wherein said step of supplying predetermined amounts of carbon, binder and additive is effected by moving said material from storage bins to said mixer using flat auger conveyors, with said material first being supplied to weigh bins for individually weighing the amounts of said carbon, binder and additive prior to supplying these materials to a mixer where the step of mixing the carbon, binder and additive is effected, and the step of moving said mold through said temperature controlled oven is effected by placing said mold on a conveyor passing through said oven set to a temperature selected to heat said binder to the melting point.

18. The method according to Claim 17 wherein the operation of said conveyors and said weighing step are controlled by a computer system.