Coated activated carbon for contaminant removal from a fluid stream

Abstract

Product attrition by dusting of granular and shaped activated carbons is disclosed to be reduced significantly, or essentially eliminated, by the application of a thin, continuous polymer coating on the granular or shaped activated carbon, without a reduction in adsorption velocity or capacity of the activated carbon when used in fluid stream filters for removing contaminants. The avoidance of carbon dust leads to improved fluid stream filter performance in contaminant removal.

Description

[0001] This application is a continuation-in-part application of Ser. No. 09/448,934 titled “Coated Activated Carbon,” by L. H. Hiltzik, E. D. Tolles, and D. R. B. Walker, filed on Nov. 23, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to activated carbon pellets and activated granules with improved dusting characteristics for contaminant removal from water. In particular, this invention relates to activated carbons susceptible to dust attrition due to abrasion where dusting can result in loss of product and often cause other problems related to its use in contaminant removal from drinking water.

[0004] 2. Description of Related Art (Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

[0005] Active carbon long has been used for removal of impurities and recovery of useful substances from liquid and gas fluid streams because of its high adsorptive capacity. Generally, “activation” refers to any of the various processes by which the pore structure is enhanced. Typical commercial activated carbon products exhibit a surface area (as measured by nitrogen adsorption as used in the B.E.T. model) of at least 300 m2/g. For the purposes of this disclosure, the terms “active carbon” and “activated carbon” are used interchangeably. Typical activation processes involve treatment of carbon sources, such as resin wastes, coal, coal coke, petroleum coke, lignites, polymeric materials, and lignocellulosic materials including pulp and paper, residues from pulp production, wood (like wood chips, sawdust, and wood flour), nut shell (like almond shell and coconut shell), kernel, and fruit pits (like olive and cherry stones) either thermally (with an oxidizing gas) or chemically (usually with phosphoric acid or metal salts, such as zinc chloride).

[0006] Chemical activation of wood-based carbon with phosphoric acid (H3PO4) is disclosed in U.S. Pat. No. Re. 31,093 to improve the carbon's decolorizing and gas adsorbing abilities. Also, U.S. Pat. No. 5,162,286 teaches phosphoric acid activation of wood-based material which is particularly dense and which contains a relatively high (30%) lignin content, such as nut shell, fruit stone, and kernel. Phosphoric acid activation of lignocellulose material also is taught in U.S. Pat. No. 5,204,310 as a step in preparing carbons of high activity and high density.

[0007] Also, U.S. Pat. No. 4,769,359 teaches producing active carbon by treating coal cokes and chars, brown coals or lignites with a mixture of NaOH and KOH and heating to at least 500EC in and inert atmosphere. U.S. Pat. No. 5,102,855 discloses making high surface area activated carbon by treating newspapers and cotton linters with phosphoric acid or ammonium phosphate. Coal-type pitch is used as a precursor to prepare active carbon by treating with NaOH and/or KOH in U.S. Pat. No. 5,143,889.

[0008] Once the activated carbon product is prepared, however, it may be subject to some degradation before and during its use. Abrading during materials handling and actual use of such activated carbon results in loss of material in the form of dust. Such “dusting” of the product is a function of its relative hardness and its shape, as well as how it is handled in the plant-in moving it into and out of plant inventory, in loading for transport and in off-loading by the receiver, and in how it is handled by the receiver to place the product into use. In certain applications, where the activated carbon is subject to constant vibration or erosion, product degradation by dusting continues through the life of the product.

[0009] The hardness of an activated carbon material is primarily a function of the hardness of the precursor material, such as a typical coal-based activated carbon being harder than a typical wood-based activated carbon. The shape of granular activated carbon also is a function of the shape of the precursor material. The irregularity of shape of granular activated carbon, i.e., the availability of multiple sharp edges and corners, contributes to the dusting problem. Of course, relative hardness and shape of the activated carbon are both subject to modification. For example, U.S. Pat. Nos. 4,677,086, 5,324,703, and 5,538,932 teach methods for making pelleted products of high density from lignocellulosic precursors. Also, U.S. Pat. No. 5,039,651 teaches a method of producing shaped activated carbon from cellulosic and starch precursors in the form of “tablets, plates, pellets, briquettes, or the like.” Further, U.S. Pat. No. 4,221,695 discloses making an “Adsorbent for Artificial Organs” in the form of beads by mixing and dissolving petroleum pitch with an aromatic compound and a polymer or copolymer of a chain hydrocarbon, dispersing the resultant mixture in water giving rise to beads, and subjecting these beads to a series of treatments of removing of the aromatic hydrocarbon, infusibilizing, carbonizing, and finally activating.

[0010] Despite these and other methods of affecting activated carbon hardness and shape, however, product dusting continues to be a problem in certain applications. For example, in U.S. Pat. No. 4,221,695, noted above, the patentees describe conventional beads of a petroleum pitch-based activated carbon intended for use as the adsorbent in artificial organs through which the blood is directly infused that are not perfectly free from carbon dust. They observe that some dust steals its way into the materials in the course of the preparation of the activated carbon, and some dust forms when molded beads are subjected to washing and other treatments. The patentees reflected conventional wisdom in noting that the application of a film-forming substance to the surface of the adsorbent “is nothing to be desired,” because the applied substance acts to reduce the adsorption velocity of the matters to be adsorbed on the adsorbent and limit the molecular size of such matters being adsorbed.

[0011] Subsequently, however, in U.S. Pat. No. 4,476,169, the patentees describe a multi-layer glass window wherein vapor between the glass sheets is adsorbed by a combination of a granular zeolite with granular activated carbon having its surface coated with 1-20 wt % synthetic resin latex. The coating of the activated carbon is described as greatly inhibiting the occurrence of dust without substantially reducing the absorptive power of activated carbon for an organic solvent.

[0012] The present invention relates to the discovery that activated carbon, granular or pelletized, can be coated to reduce dust that is a nuisance in contaminant removal from fluid streams, and particularly in point-of-use (POU) water treatment applications. A coating can be applied that causes no significant decrease in performance for POU water filter applications, as measured by chlorine removal performance. Additionally, activated carbon can be colored by applying pigment and binder to either coated or uncoated activated carbon. Insoluble pigments, rather than soluble dyes, are preferred since soluble dyes are adsorbed by activated carbon yielding a black product that leaches color afterwards as the dye desorbs. Colored coatings may also be used to provide a functional indicator to show when a carbon filter is spent. Colored coatings can be applied for aesthetic purposes, such as for carafe type filters, so that the activated carbon is not black. Different colors can provide an effective means of differentiating between different activated carbon grades, such as grades for chlorine removal and grades for chlorinamine removal. Also, color can be used to identify the year of manufacture, quality assurance, and/or brand identification. For example, a water filter manufacturer could demand a red activated carbon filter media to assure that some other manufacturer's activated carbon is not used in its place.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a graphical representation of the initial dust values of polymer coated, shaped activated carbons of various sources, as well as the effect of the polymer coating on their respective initial dust values, as reported in Table III.

[0014] FIG. 2 is a graphical representation of the dust rate values of polymer coated, shaped activated carbons of various sources, as well as the effect of the polymer coating on their respective dust rate values, as reported in Table III.

[0015] FIG. 3 is a graphical representation of the fines content as a function of polyethylene coating content

[0016] FIG. 4 is a graphical representation of chlorine removal by 2% polyethylene coated and uncoated 10×20 mesh activated carbon.

SUMMARY OF THE INVENTION

[0017] It has been discovered that product attrition by dusting of granular and shaped activated carbons can, in fact, be reduced significantly, or essentially eliminated, by the application of a thin, continuous polymer coating on the granular or shaped activated carbon, without a reduction in adsorption velocity or capacity of the activated POU carbon contaminant removal filters. The avoidance of attrited carbon dust leads to improved chlorine removal performance in water filtration.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0018] Manufacturers of filters used to remove contaminants from fluid streams often direct users to flush carbon filters of dust before a filter is put into service. Dust issues have led some manufacturers to use carbon blocks instead of granular carbon. Ideally, a coated carbon would not require flushing and would have the same adsorptive and/or removal performance as an uncoated carbon. Filter manufacturers may even accept a slight reduction in performance in exchange for reduction of dust. Chlorine removal (from water) testing shows that significant dust reduction is possible with little to no loss in chlorine removal efficacy.

[0019] A method is disclosed based on applying a visible polymer coating on the finished product and then removing any residual dust. The product is considered dust free, as shown by an “initial dust” value of ≦0.3 mg/dL and a “dust rate” value of ≦0.01 mg/min/dL, both below the detection limits of the standard dust attrition test. The product is “essentially” dust free, as shown by a “dust rate” value of ≦0.06 mg/min/dL, a detectable value but dramatically lower than the dust rate of uncoated activated carbon and, as noted in the tables which follow in the examples below, is the highest dust rate value of the invention-treated activated carbons. The retention of butane adsorption and working capacity properties are an important feature of the coated pellets. As shown in the examples below, the coated pellets retained 94-100% of the uncoated pellet butane activity and 88-100% of the uncoated pellet butane working capacity (BWC). For example, the invention coated shaped and granular activated carbon will have a butane activity of greater than 15 g/100 g, preferably greater than 25 g/100 g, more preferably greater than 35 g/100 g, even more preferably greater than 45 g/100 g, even more preferably greater than 55 g/100 g, even more preferably greater than 65 g/100 g, and most preferably greater than 75 g/100 g. Also, the invention coated shaped and granular activated carbon will have a butane working capacity greater than 9.0 g/dL, preferably greater than 10.0 g/dL, more preferably greater than 11.0 g/dL, even more preferably greater than 12.0 g/dL, even more preferably greater than 13.0 g/dL, even more preferably greater than 14.0 g/dL, and most preferably greater than 15.0 g/dL.

[0020] An additional feature is that this coating provides the pellets with a glossy and attractive appearance that calls attention to product cleanliness. The glossy nature of the coating results from the film-forming nature of the polymer and the emulsion form by which it is applied to the pellets. An added facility, and possible benefit, provided by the invention composition and process is achieved by the natural color of the coating material or by the addition of coloring agents, such as pigments and optical brighteners, to the polymer emulsion. In particular, distinct carbon products may be identified through color-coding. The color-coding may relate to product application, plant origination, customer designation, or any designation desired.

[0021] The difference in appearance between the invention emulsion coated glossy pellets and previous dispersion-coated pellets is due to the different forms of the polymers used in applying the coatings. The particle sizes of emulsions are smaller than dispersions, therefore emulsions form continuous films due to the effects of capillary forces when dried of the carrier liquid. Dispersions do not form continuous films by drying, and they leave behind discrete (i.e., noncontinuous) polymer particles similar in size to the originally dispersed particles. The continuous, emulsion-applied polymer film, on the other hand, provides a glossy appearance, coating integrity, pellet dust reduction, and hydrophobicity that a dispersion-applied, non-continuous film does not.

[0022] Also, it should be noted that while the polymer film resulting from the application of the polymer emulsion onto the shaped or granular carbon is a continuous film, it may be porous or non-porous, depending on the irregularity of surface shape of the carbon material. The appearance of a porous continuous film occurs more often on the more irregular shaped granular activated carbons than on shaped activated carbons.

[0023] A variety of colored carbons can be prepared by choosing the proper combination of pigments for addition to the polymer emulsion and the emulsion application methods, as taught in the foregoing examples, in order to attain the desired color, plus obtain the desired benefits of the coating.

[0024] The process for essentially eliminating dust attrition of activated carbon material by coating the activated carbon material comprising the steps of:

[0025] (a) spraying an emulsion of the polymer onto exposed surfaces of the activated carbon material while it is in a state of turbulence at a processing temperature above ambient temperature; and

[0026] (b) drying the coated activated carbon material.

[0027] The process may optionally include an initial step of preheating the active carbon material to above ambient temperature. The process may include multiple repetitions of steps (a) and (b). Also, the process of the claimed invention may comprise a further step

[0028] (c) de-dusting the dried coated activated carbon material by removing any residual dust therefrom.

[0029] As those skilled in the art appreciate, various processing conditions are generally interdependent, such as processing time and processing temperature. These operating conditions as well may depend on the nature of the carbon material to be coated (shaped or granular, coal-based or lignocellulosic-based, etc.) and the coating material (relative volatility, viscosity, etc.). Thus, the temperature range for coating application and coating drying steps may range from just below ambient of about 50° F., up to about 280° F. (138° C.), and the processing time may take from about 1 minute to about 12 hours. For most combinations of shaped or granular active carbon material and coating material, a preferred operating temperature range for the coating and drying steps is from about 70° F. (21° C.) to about 250° F. (121° C.) for from about 5 minutes to about 6 hours.

[0030] The turbulent state of the active carbon material can be induced by various known means. For example, the carbon material, in granular or shaped (usually pellet) form, may be placed in a rotary tumbler, in a mixing device, or on a fluidized bed. While it is critical that the active carbon material be in a kinetic, rather than static, state when the coating material is applied to assure relative even coating on the surface area of the active carbon material, it is not critical how the kinetic state is achieved.

[0031] The coating materials useful in the claimed invention are those capable of forming a continuous film. In particular, polymers, copolymers, and polymer blends that are suitable coating materials include: polyolefins, such as polyethylene, polypropylene, polyisobutylene, polystyrene, polyisoprene, polychloroprene, poly-4-methyl-1-pentene, polybutadiene, and polybutene; polyacrylics, such as polyacrylates, polymethyl methacrylate, polybutylmethacrylate, polymethacrylates, and polyacrylic acid; halogen-substituted alkanes, such as polytetrafluoroethylene, trifluoroethylene, vinyl fluoride, fluorvinylidene, fluorobutylene, and fluoropropylene; and other polymers including polyurethane, polyethylene terephthalate, styrene butadiene, modified polybutadiene, epoxies, modified alkyds, polyesters, starches, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl acetate, cellulose acetate, cellulose nitrate, cellulose tri acetate, cellulose acetate, phthalate, cellulose propionate morpholinobutyrate, hydroxypropylmethyl cellulose, ethylene vinyl acetate, acrylic copolymers, polysulfones, polyether sulfones, polyethers, polyethylene, glycols, polyimines, polybutylene, polyvinyl ethers, polyvinyl esters, polyalkylsulfides, polyarylsulfides, lignosulfonates, polyacrylamide, cyanoacryl ate, polyamides, polyimides, polysiloxanes, methacrylonitrile, polyacrylonitrile, polyvinyl pyridine, polyvinyl benzene, polyvinyl acetate, polyvinyl pyrrolidene, polyvinyl butyral, polyvinyl alcohol, polyvinyl chloride, polyvinyl formaldehyde, polyformaldehyde, polycarbonates, and polyvinylidene chloride.

[0032] The shaped or granular active carbon material of the invention described herein may be derived from any known active carbon precursors including coal, lignocellulosic materials, including pulp and paper, residues from pulp production, wood (like wood chips, sawdust, and wood flour), nut shell (like almond shell and coconut shell), kernel, and fruit pits (like olive and cherry stones), petroleum, bone, and blood.

[0033] Gas and vapor phase streams of commercial importance that can be treated with activated carbon include: air, helium, neon, argon, krypton, xenon, hydrogen, oxygen, nitrogen, methane, natural gas, ethane, ethylene, propane, propylene, carbon dioxide, syngas, carbon monoxide, ammonia, chlorofluorocarbons, chlorofluorohydrocarbons, sulfur hexafluoride and vapor spaces in contact with volatile organic compounds, such as fuel tanks of all sizes.

[0034] Liquid streams of commercial importance that are treated with activated carbon include: process water, drinking water, solutions of sugars or carbohydrates such as high fructose corn syrup, solutions obtained during the processing of sugar cane and sugar beets, fruit juices, wine, beer, malt beverages, distilled spirits such as whiskey, bourbon, vodka, scotch, and gin, petroleum distillates such as gasoline, diesel fuel, jet fuel, fuel oil and lubricating oil, propanediol, ethylene glycol, propylene glycol, lactic acid, acetic acid, citric acid, phosphoric acid, vegetable oil, glycerin, and wastewater effluents.

[0035] The following list of contaminants are among those subject to removal by the present method in the treatment of gas and vapor phase streams: acetaldehyde, acetamide, acetone, acetonitrile, acrolein, acrylamide, acrylic acid, acrylonitrile, allyl chloride, ammonia, benzene, benzotrichloride, bromoform, 1,3-butadiene, butane, carbon disulfide, carbon tetrachloride, carbonyl sulfide, chlorine, chloroacetic acid, chlorobenzene, chloroform, chloroprene, o-cresol, m-cresol, p-cresol, cumene, cyclohexane, cyclohexanone, diazomethane, 1,4-dichlorobenzene, 1,3-dichloropropene, diethanolamine, N,N-dimethylaniline, N,N-dimethylformamide, N,N-dimethylacetamide, 1,1-dimethylhydrazine, dimethyl sulfate, 1,4-dioxane, epichlorohydrin, 1,2-epoxybutane, ethyl acrylate, ethylbenzene, ethyl carbamate, ethyl chloride, ethylene dibromide, ethylene dichloride, ethylene glycol, ethyleneimine, ethylene oxide, ethylene thiourea, ethylene dichloride, formaldehyde, gasoline vapor, hexachloroethane, hexane, hydrazine, hydrochloric acid, hydrogen fluoride, hydrogen sulfide, malodor compounds, mercaptans, mercury, methanol, methyl bromide, methyl chloride, methyl chloroform, methyl ethyl ketone, methyl hydrazine, methyl iodide, methyl isobutyl ketone, methyl methacrylate, methyl tert-butyl ether, methylene chloride, N-methyl pyrrolidinone, naphthalene, nitrobenzene, phenol, phosgene, phosphine, propylene dichloride, propylene oxide, 1,2-propyleneimine, styrene, styrene oxide, sulfur dixoide, toluene, 1,2,4-trichlorobenzene, 1,1,2-trichloroethane, trichloroethylene, triethylamine, vinyl acetate, vinyl bromide, vinyl chloride, vinylidene chloride, xylenes mixed isomers, o-xylene, m-xylene, p-xylene, and glycol ethers.

[0036] The following list of compounds are those which may be removed by the present method from liquid fluid streams: alachlor, asbestos, atrazine, bad and/or objectionable taste and odor compounds, barium, benzene, cadmium, carbofuran, carbon tetrachloride, chlordane, chloramine, chlorine, chloroform, chlorobenzene, chromium-hexavalent, chromium-trivalent, color bodies, copper, 2,4-D, dibromochloroprane, o-dichlorobenzene, p-dichlorobenzene, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloro ethylene, trans-1,2-dichloroethylene, 1,2-dichloropropane, dinoseb, endrin, ethylbenzene, ethylene dibromide, fluoride, geosmin, heptachlor (H-34 or Heptox), heptachlor epoxide, hexachlorocyclopentadiene, lead, lindane, mercury, methoxychlor, methyl tert-butyl ether (MTBE), MIB, nitrate, nitrite, pentachlorophenol, polychlorinated biphenyls (PCBs), radon, selenium, simazine, styrene, 2,4,5-TP (silvex), tetrachloroethylene, toluene, toxaphene, 1,2,4-trichlorobenzene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, TTHM, xylenes mixed isomers, o-xylene, m-xylene, and p-xylene.

[0037] The following examples describe the method and properties of materials that have been treated.

EXAMPLE 1

[0038] Two types of coatings were applied to pellets of Westvaco Corporation BAX 1100 activated carbon that provided dust free carbons: a high-density polyethylene (ChemCor polyethylene emulsion Poly Emulsion 325N35) and aminoethylaminopropylpolysiloxane (General Electric silicone emulsion SM2059). Other polymers, including polypropylene and polystyrene, may be employed as alternative coating materials. Coating properties, such as abrasion resistance, permeability, and porosity, may also be further enhanced for a particular class of polymer by selecting materials with different molecular weight, density, particle size, and/or degree of cross-linking.

[0039] The activated carbon pellets were coated by tumbling in a rotating cylinder and initially heated to 250° F. (121° C.) using a hot air gun. An emulsion of the polymer was then sprayed on the carbon in successive doses as the activated carbon was maintained at about 150° F. (66° C.) under the hot air flow. (The emulsion of the polyethylene solution was 3.5 wt % solids. The emulsion of the polysiloxane solution was 3.9 wt % solids.) The coated activated carbon was then dried overnight at 220° F. (105° C.). After drying, any residual dust on the pellet exterior was removed by applying the vibration and airflow treatment of the first 10-20 minutes of the dust attrition test (described below). The final coated product has a shiny, smooth appearance, compared with the (lull exterior of the uncoated material.

[0040] Table I compares the dusting attrition properties for the uncoated and coated pellets. Data for a baseline sample using only de-ionized water for the spray are also included to prove the importance of the polymer coating on the change in dust properties. Dust attrition rates were measured with the two-point method in a 30-minute test (described below). 1 TABLE I Coating Initial Dust Loading Dust Rate AD Sample ID (wt %) (mg/dL) (mg/min/dL) (g/mL) Uncoated1 0.361 11.4 0.69 0.353 11.4 0.69 0.357 Polyethylene Emulsion Run 1A 2.92 0.00 0.00 0.361 Run 1B 1.63 0.00 0.00 0.356 Silicone 3.44 0.00 0.00 0.349 Emulsion Run 2 1Same sample, duplicate measurements-to obtain representative average reading. 2Derived as average of wet-basis weight gain (1.0 wt %) and emulsion weight used (4.8 wt %). 3Derived as average of wet-basis weight gain (0.5 wt %) and emulsion weight used (2.8 wt %). 4Derived as average of wet-basis weight gain (0.9 wt %) and emulsion weight used (5.8 wt %).

[0041] Initial dust and dust rate values were measured by a modified, 3-filter version of the “Standard Test Method for Dusting Attrition of Granular Carbon” (ASTM D5159-91). A 1.0 dL sample of carbon is placed on a screen with 0.250 mm openings in a test cell holder and is subjected to vibration of 40 m/s/s RMS acceleration and downward air flow of 7 L/min for a 10 minute interval. A glass fiber filter, placed below the sample screen, collects dust from the sample. The vibration and airflow step is conducted three times with three different filters. The dust rate is calculated by the following equation:

Dust Rate (mg/min/dL), DR=0.0732 w3

[0042] where w3 is the milligram weight gain of the third filter.

[0043] The dust rate from this equation is within a standard deviation of ±13% of the dust rate obtained by the standard ASTM procedure that uses filter weight data from three additional 10 minute test intervals.

[0044] The initial dust is calculated as the milligram weight gain for the first filter, w1, minus the amount of dust attrited within 10 minutes (10 ×DR):

Initial Dust (mg/dL)=w1−10 DR.

[0045] Note that the weight gain of the second filter, w2, is not directly applied in these calculations. However, the w2 value has utility in confirming whether dust rate detection limits have been reached for a sample by showing a zero or negative weight gain.

[0046] The inherent error in dust rate is ±0.01 mg/dL by a partial differential error analysis of its equation for calculation and the 0.1 mg readability of the four decimal place gram balance required in the procedure. Likewise, the inherent error in initial dust is ±0.3 mg/dL. Therefore, the non-detect dust rate value would be 0.01 mg/min/dL and the initial dust value would be 0.3 mg/dL.

[0047] Compared with the reduction of initial dust, the sharp reduction in dust rate is the more important feature of the coated shaped or granular activated carbon materials. By definition, a dust rate of 0.01 &mgr;g/min/dL or less means that initial dust was removed within the attrition test to the detection limits of the test, and demonstrates that initial dust would be likewise readily removed by other means. Alternatively, complete removal of initial dust without a sharp reduction in dust rate is perceived as being comparatively less useful since dust would be expected to readily reappear upon exposure of the sample to inter-particle motion from vibration, agitation or other motive force acting thereon.

[0048] The data in Example 1 show that, as a result of the polymer coatings, the treated samples show initial dust and dust rate values in the non-detect range.

EXAMPLE 2

[0049] Further tests show that similarly coated activated carbon pellets (Westvaco Corporation BAX 1500) exhibit increased abrasion resistance, as measured by a standard pellet hardness test (CTC Procedure 960-130), which is a modified version of ASTM D3802-79 (ball pan hardness). The pellet hardness test involves shaking the sample (2 mm extruded carbon pellets) in a Ro-Tap Sieve Shaking Machine with stainless steel balls (10 of ¾ inch diameter and 20 of ½ inch diameter) and measuring the amount of pellet breakage in terms of the change in mean particle size of particles collected in a special pan at the bottom of an equivalent 6 (full height) high sieve nest (consisting of #6, #8, #10, #12, #14, #18, and #60). Step 1: a standard sieve analysis is performed on 100 grams of sample material and the fractions of material on each sieve is weighed. Step 2: then the fractions are combined in the special pan with the 30 steel balls, and the special pan is shaken on the Ro-Tap for 20 minutes, after which the shaken sample is poured onto the top sieve of the sieve nest. Repeat steps 1 and 2, except the Ro-Tap time for step 2 is 10 minutes. Calculate the average particle size. The strength values are determined by dividing the mean particle diameter after grinding by the initial mean particle diameter and multiplying the quotient by 100.

[0050] One coated sample (“Run 3A”) was as a composite of 10 replicate preparations using the polymer application method of Example 1. Another coated sample (“Run 3B”) was prepared differently. A larger, 2-ft diameter rotating cylinder with lifters was used, and the samples were initially heated by indirect- and direct-fired burners rather than direct hot air flow. No de-dusting step was applied.

[0051] Table II compares the hardness, butane and dust attrition properties for the uncoated and coated pellets. Dust data were measured by a three-filter test method. 2 TABLE II Coating Initial Sample Loading Pellet AD Dust Dust Rate ID (wt %) Hardness (g/mL) (mg/dL) (mg/min/dL) Uncoated — 68.6 0.295 3.2 0.22 Coated Run 3A 3.3 99.9 0.304 0.9 0.01 Run 3B1 2.6 100.0 0.298 1.8 0.03

[0052] 2 Different preparation method vs. Run 3A, plus no de-dusting step employed to remove initial dust.

[0053] The demonstration of increased hardness was made with 2 mm diameter BAX 1500 pellets of 68.6 hardness before coating. Pellets coated with about 1-3 wt % polyethylene have hardnesses of 99.9-100.0, indicating no change in mean particle size in the test.

EXAMPLE 3

[0054] To show that the coating process of dust attrition reduction or elimination is applicable to a variety of commercial activated carbons, samples of a shaped commercial coal-based activated carbon (Kuraray 3GX) and a shaped commercial olive pit-based activated carbon pellets (Norit CNR 115) were coated with polyethylene (9.0 wt % emulsion solids) and compared with a similarly coated shaped commercial wood-based activated carbon (Westvaco Corporation BAX 1500). The polymer coating has the same benefits as previously shown with wood-based BAX 1100 and BAX 1500 pellets for reducing dust without significant effect on key properties.

[0055] The coatings were applied by the previously described method of Example 1. A de-dusting step was not applied prior to analyses. The polymer loadings (coating wt. %) were determined by heating samples to 932° F. (500° C.) and measuring the amount of volatilized components with a hydrocarbon analyzer calibrated with carbons of known polyethylene content.

[0056] The results are shown in Table III and FIGS. 1, 2, and 3. 3 TABLE III Measured Initial Dust Loading AD Dust Rate Sample ID (wt %) (g/mL) (mg/dL) (mg/min/dL) 2 mm wood-based Uncoated* — 0.282 2.24 0.15 — 0.283 3.31 0.11 average: 0.283 2.78 0.13 Coated Run 4A 0.4 0.279 1.42 0.06 Run 4B 1.1 0.282 0.81 0.03 Run 4C 2.4 0.288 0.28 0.02 2.8 mm coal-based Uncoated* — 0.326 — 0.323 6.76 0.53 average: 0.325 6.76 0.53 Coated Run 5A 0.7 0.328 3.00 0.00 Run 5B 1.5 0.334 0.70 0.00 Run 5C 2.8 0.337 0.00 0.00 2 mm olive pit-based Uncoated — 0.355 5.7 0.22 Coated Run 6A 0.7 0.347 1.24 0.04 Run 6B 1.4 0.353 0.23 0.01 Run 6C 2.4 0.356 1.60 0.00 *Same sample, duplicate measurements-to obtain representative average reading.

[0057] Compared with their respective uncoated base carbons, initial dust and dust rate are sharply reduced.

EXAMPLE 4

[0058] Acrylic copolymer is another example of an active carbon coating material, in addition to the previously cited polyethylene and silicone materials, in the present invention. BAX 1100 and BAX 1500 active carbon pellets were coated in the lab with JONREZ7 E-2062, an acrylic copolymer salt solution produced by Westvaco Corporation.

[0059] The coatings were applied by the previously described method of Example 1. After evaluating the properties of two samples of uncoated BAX 1500, two samples of the same BAX 1500 plant production were coated with a 9.0 wt % solids acrylic copolymer emulsion. Similarly, after measuring the properties of a sample of uncoated BAX 1100, a sample of the same BAX 1100 plant production was coated with a 6.0 wt % solids acrylic copolymer emulsion. A de-dusting step was not applied prior to analyzing the coated products. The coating loading on BAX 1500 was determined by heating samples to 932° F. (500° C.) and measuring the amount of volatilized components with a hydrocarbon analyzer calibrated with carbons of known acrylic copolymer content. The coating loading on BAX 1100 was derived from the wet-basis weight gain of the coated sample and the amount of applied emulsion spray. The acrylic copolymer coating has the same benefits as previously shown with polyethylene and silicone for reducing dust, as shown in Table IV. 4 TABLE IV Initial Dust Coating AD Dust Rate Sample ID (wt %) (g/mL) (mg/dL) (mg/min/dL) Uncoated — 0.282 2.24 0.15 BAX 15001 — 0.283 3.31 0.11 0.283 2.78 0.13 average: Coated with Acrylic Copolymer Run 7A 1.62 0.277 1.93 0.01 Run 7B 3.42 0.283 1.30 0.00 Uncoated — 0.361 BAX 11003 — 0.353 11.40 0.69 average: 0.357 11.40 0.69 Coated with Acrylic 4.34 0.352 1.02 0.00 Copolymer Run 8 1Noted as Uncoated wood-based samples in Table III 2Measured by hydrocarbon analyzer method 3Noted as “Uncoated” sample in Table I 4Average of 1.0 and 7.7 wt % (from wet-basis weight gain and emulsion solids sprayed, respectively)

[0060] The data show that a 1.6 wt % polymer coating on the BAX 1500 shaped active carbon essentially eliminated dusting. Even more surprising is that a 3.4 wt % coating on the same active carbon material achieved total elimination of dusting. Also, a 4.3 wt % coating of the BAX 1100 shaped active carbon achieved a total elimination of dusting.

[0061] As the polyethylene coating on 10×20 mesh RGC was increased, the amount of dust that transferred from the carbon to water decreased from 24.3 mg/dL to 0.5 mg/dL, as shown in FIG. 1. The concentration of dust in water was quantified by measuring the transmittance at a wavelength of 440 nm with a spectrophotometer. A calibration between transmittance and dust concentration was made using water slurries containing a known concentration of carbon fines. Carbon fines used were formed by spex milling RGC for one minute. FIG. 3 data are listed in Table V. 5 TABLE V Color, Composition, and Fines Properties of Coated Wood-based Carbon Samples Polyethylene Pigment Fines Carbon Pigment Content Content Content Color Identification wt % wt % mg/dL Black(a) none 0 none 24.3 Black none 0.5 none 16.3 Black none 1 none 7 Black none 2 none 3.2 Black none 4 none 1.2 Black none 6 none 0.5 Silver Afflair 119 Polar White (b) 3.5 2 3.9 Blue-grey DuPont TI-Pure Titanium Dioxide 3.3 3 2.8 Silver-grey Afflair 103 Rutile Silver (b) 1.8 1 10.7 Silver-grey Afflair 111 Rutile Fine Silver 1.8 1 3.9 Gold Afflair 500 Bronze (b) 3.5 2.7 3.9 Red Afflair 502 Red Bronze b 5 2.7 1.6, 3.2 Silver Afflair 119 Polar White (b), 6.8 5 3.9, 6.4 DuPont TI-Pure Titanium Dioxide Silver Afflair 119 Polar White (b) 3.5 2.7 3.6 Yellow Afflair 351 Sunny Gold (b) 3.5 2.7 4.3 Red Afflair 502 Red Bronze (b) 3.5 2.7 11.3 Yellow Afflair 205 Rutile Platinum Gold (b) 3.5 2.7 7.3 Green Afflair 235 Rutile Green (b) 3.5 2.7 6.8 Purple Afflair 219 Rutile Lilac (b) 3.5 2.7 6.9 Silver Afflair 111 Rutile Fine Silver (b) 3.5 2.7 2.7 (a) Parent carbon (RGC carbon, available from MeadWestvaco Corporation) coated as subsequent samples. (b) Manufactured by EM Industries.

[0062] Uncoated wood-based activated carbon and the same carbon materials coated with 2% polyethylene had little to no difference in chlorine removal performance as shown in FIG. 4. The 2% coated carbon had fines of 3.2 mg/dL, compared to the 24.3 mg/dL of the uncoated carbon. After each carbon treated 425 gallons of water, chlorine removal by the uncoated and coated carbon remained above 95%. Two columns, 12 inches long and 1 inch in diameter containing 50 grams of 10×20 mesh carbon, were tested simultaneously at flow rates of 500 ml/min. Bleach (6% solution of sodium hypochlorite) was injected at a rate of 1 ml/hr into deionized water to create a feed having about 1 ppm free chlorine. Deionized water was used to avoid forming chloramines, which results when bleach is added to tap water containing nitrogen compounds.

[0063] Color change features could be incorporated into carbon coatings to indicate when adsorptive capacity is spent so filters are used more efficiently. Manufacturers' recommendations for changing POU filters are usually based on either a time period of use or a volume of water treated. On-line monitoring of the effluent concentration of the filter requires electronic components that are not economically suitable for POU applications. With either the time or volumetric basis for changeout, it is difficult for users to change their filters when their capacity has been used to maximum benefit. When filters are changed with some adsorptive capacity remaining, then users incur added expense. When filters are changed after they are saturated, breakthrough one or more components has likely occurred. Both cases of added expense and breakthrough are undesirable to carbon filter users. A color-changing indicator that provides a more precise method identifying when filters should be replaced is therefore useful.

[0064] When a new carbon filter is put on-line, the concentration of a component targeted for adsorption will be low in the vicinity of the original “fresh” coating since it will be adsorbed by the activated carbon. As the activated carbon becomes saturated at the feed end of the filter, the concentration of the adsorbate in the water surrounding the “fresh” coating will increase. With a coating designed to undergo a color change triggered by the increase in concentration, a second “spent” color will develop in the filter bed. The “spent” color will develop at the feed end and move towards the product end of the filter. For example, a pigment in the coating could become bleached by free chlorine present in municipal drinking water. The opposite could occur as well, as many colorless compounds exist that can be oxidized by chlorine into chromophores. The user would replace the filter when the entire length of the filter changed from the fresh to the spent color, confident that the filter's maximum useful life has been obtained. Either the “spent” or “fresh” color could be colorless or clear. The color indicating compound could be added as a pigment to the coating or as a reactive chemical group grafted onto the coating polymer.

[0065] Thus, the subject matter of the applicants' invention is:

[0066] (1) A method for capturing chlorine from a fluid stream containing same by routing said stream through a filter comprising an activated carbon material having its surface coated with a continuous film of a polymer, said polymer film being operable for essentially eliminating attrition of the activated carbon material resulting from dusting;

[0067] (2) the method of (1) wherein the activated carbon material is coated by:

[0068] (a) spraying an emulsion of the polymer onto exposed surfaces of the activated carbon material while it is in a state of turbulence at a processing temperature above ambient temperature; and

[0069] (b) drying the coated activated carbon material at above ambient temperature.

[0070] While the preferred embodiments of the present invention have been described, it should be understood that various changes, adaptations, and modifications may be made thereto without departing from the spirit of the invention and the scope of the appended claims. It should be understood, therefore, that the invention is not to be limited to minor details of the illustrated invention shown in preferred embodiment and the figures and that variations in such minor details will be apparent to one skilled in the art. The claims, therefore, are to be accorded a range of equivalents commensurate in scope with the advances made over the art.

Claims

1. A method for capturing contaminants from a fluid stream containing same by routing said stream through a filter comprising an activated carbon material having its surface coated with a continuous film of a polymer, said polymer film being operable for essentially eliminating attrition of the activated carbon material resulting from dusting.

2. A method for capturing chlorine from a fluid stream containing same by routing said stream through a filter comprised of a polymer-coated activated carbon prepared by coating the activated carbon material according to the steps of:

(a) spraying an emulsion of the polymer onto exposed surfaces of the activated carbon material while it is in a state of turbulence at a processing temperature above ambient temperature; and

(b) drying the coated activated carbon material at above ambient temperature.

3. The method of claim 2 comprising a further step

(c) de-dusting the dry coated activated carbon material by removing any residual dust therefrom.

4. The method of claim 3 further comprising an initial step of heating the active carbon material at above ambient temperature.

5. The method of claim 3 wherein the processing temperature is maintained from 50° F. (10° C.) to 280° F. (138° C.) for from about 1 minute to about 12 hours.

6. The method of claim 5 wherein the processing temperature is maintained from about 70° F. (21° C.) to about 250° C. (121° C.) for from about 5 minutes to about 6 hours.

7. The method of claim 1 wherein the polymer is selected from the group consisting of.polyethylene, polypropylene, polyisobutylene, polystyrene, polyisoprene, polychloroprene, poly-4-methyl-1-pentene, polybutadiene, polybutene, polyacrylate, polymethyl methacrylate, polybutylmethacrylate, polymethacrylates, polyacrylic acid, polytetrafluoroethylene, trifluoroethylene, vinyl fluoride, fluorvinylidene, fluorobutylene, fluoropropylene, polyurethane, polyethylene terephthalate, styrene butadiene, modified polybutadiene, epoxies, modified alkyds, polyesters, starches, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl acetate, cellulose acetate, cellulose nitrate, cellulose triacetate, cellulose acetate, phthalate, cellulose propionate morpholinobutyrate, hydroxypropylmethyl cellulose, ethylene vinyl acetate, acrylic polymers and copolymers, polysulfones, polyether sulfones, polyethers, polyethylene, glycols, polyimines, polybutylene, polyvinyl ethers, polyvinyl esters, polyalkylsulfides, polyarylsulfides, lignosulfonates, polyacrylamide, cyanoacrylate, polyamides, polyimides, polysiloxanes, methacrylonitrile, polyacrylonitrile, polyvinyl pyridine, polyvinyl benzene, polyvinyl acetate, polyvinyl pyrrolidene, polyvinyl butyral, polyvinyl alcohol, polyvinyl chloride, polyvinyl formaldehyde, polyformaldehyde, polycarbonates, and polyvinylidene chloride.

8. The method of claim 7 wherein the polymer is selected from the group consisting of acrylic polymer and polyethylene.

9. The method of claim 1 wherein the active carbon material is derived from a member of the group consisting of coal, lignocellulosic materials, petroleum, bone, and blood.

10. The method of claim 9 wherein the lignocellulosic materials are selected from the group consisting of including pulp, paper, residues from pulp production, wood chips, sawdust, wood flour, nut shell, kernel, and fruit pits.

11. The method of claim 2 wherein the polymer is selected from the group consisting of polyethylene, polypropylene, polyisobutylene, polystyrene, polyisoprene, polychloroprene, poly-4-methyl-1-pentene, polybutadiene, polybutene, polyacrylate, polymethyl methacrylate, polybutylmethacrylate, polymethacrylates, polyacrylic acid, polytetrafluoroethylene, trifluoroethylene, vinyl fluoride, fluorvinylidene, fluorobutylene, fluoropropylene, polyurethane, polyethylene terephthalate, styrene butadiene, modified polybutadiene, epoxies, modified alkyds, polyesters, starches, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl acetate, cellulose acetate, cellulose nitrate, cellulose triacetate, cellulose acetate, phthalate, cellulose propionate morpholinobutyrate, hydroxypropylmethyl cellulose, ethylene vinyl acetate, acrylic polymers and copolymers, polysulfones, polyether sulfones, polyethers, polyethylene, glycols, polyimines, polybutylene, polyvinyl ethers, polyvinyl esters, polyalkylsulfides, polyarylsulfides, lignosulfonates, polyacrylamide, cyanoacrylate, polyamides, polyimides, polysiloxanes, methacrylonitrile, polyacrylonitrile, polyvinyl pyridine, polyvinyl benzene, polyvinyl acetate, polyvinyl pyrrolidene, polyvinyl butyral, polyvinyl alcohol, polyvinyl chloride, polyvinyl formaldehyde, polyformaldehyde, polycarbonates, and polyvinylidene chloride.

12. The method of claim 11 wherein the polymer is selected from the group consisting of polysiloxane, acrylic copolymer and polyethylene.

13. The method of claim 1 wherein the active carbon material is derived from a member of the group consisting of coal, lignocellulosic materials, petroleum, bone, and blood.

14. The method of claim 20 wherein the lignocellulosic materials are selected from the group consisting of including pulp, paper, residues from pulp production, wood chips, sawdust, wood flour, nut shell, kernel, and fruit pits.

15. The method of claim 2 wherein a color pigment is added to the polymer emulsion to produce a colored carbon material.

16. The method of claim 1 wherein the fluid stream is selected from the group consisting of liquid streams and gaseous and vapor streams.

17. The method of claim 16 wherein the fluid stream is liquid and the contaminants are selected from the group consisting of alachlor, asbestos, atrazine, bad and/or objectionable taste and odor compounds, barium, benzene, cadmium, carbofuran, carbon tetrachloride, chlordane, chloramine, chlorine, chloroform, chlorobenzene, chromium-hexavalent, chromium-trivalent, color bodies, copper, 2,4-D, dibromochloroprane, o-dichlorobenzene, p-dichlorobenzene, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, 1,2-dichloropropane, dinoseb, endrin, ethylbenzene, ethylene dibromide, fluoride, geosmin, heptachlor (H-34 or Heptox), heptachlor epoxide, hexachlorocyclopentadiene, lead, lindane, mercury, methoxychlor, methyl tert-butyl ether (MTBE), MIB, nitrate, nitrite, pentachlorophenol, polychlorinated biphenyls (PCBs), radon, selenium, simazine, styrene, 2,4,5-TP (silvex), tetrachloroethylene, toluene, toxaphene, 1,2,4-trichlorobenzene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, TTHM, xylenes mixed isomers, o-xylene, m-xylene, and p-xylene.

18. The method of claim 1 wherein the fluid stream is selected from the group consisting of gaseous and vapor streams.

19. The method of claim 18 wherein the fluid stream includes gaseous and vapor streams and the contaminants are selected from the group consisting of acetaldehyde, acetamide, acetone, acetonitrile, acrolein, acrylamide, acrylic acid, acrylonitrile, allyl chloride, ammonia, benzene, benzotrichloride, bromoform, 1,3-butadiene, butane, carbon disulfide, carbon tetrachloride, carbonyl sulfide, chlorine, chloroacetic acid, chlorobenzene, chloroform, chloroprene, o-cresol, m-cresol, p-cresol, cumene, cyclohexane, cyclohexanone, diazomethane, 1,4-dichlorobenzene, 1,3-dichloropropene, diethanolamine, N,N-dimethylaniline, N,N-dimethyl formamide, N,N-dimethylacetamide, 1,1-dimethylhydrazine, dimethyl sulfate, 1,4-dioxane, epichlorohydrin, 1,2-epoxybutane, ethyl acrylate, ethylbenzene, ethyl carbamate, ethyl chloride, ethylene dibromide, ethylene dichloride, ethylene glycol, ethyleneimine, ethylene oxide, ethylene thiourea, ethylene dichloride, formaldehyde, gasoline vapor, hexachloroethane, hexane, hydrazine, hydrochloric acid, hydrogen fluoride, hydrogen sulfide, malodor compounds, mercaptans, mercury, methanol, methyl bromide, methyl chloride, methyl chloroform, methyl ethyl ketone, methyl hydrazine, methyl iodide, methyl isobutyl ketone, methyl methacrylate, methyl tert-butyl ether, methylene chloride, N-methyl pyrrolidinone, naphthalene, nitrobenzene, phenol, phosgene, phosphine, propylene dichloride, propylene oxide, 1,2-propyleneimine, styrene, styrene oxide, sulfur dixoide, toluene, 1,2,4-trichlorobenzene, 1,1,2-trichloroethane, trichloroethylene, triethylamine, vinyl acetate, vinyl bromide, vinyl chloride, vinylidene chloride, xylenes mixed isomers, o-xylene, m-xylene, p-xylene, and glycol ethers.