WO1996023726A1 - Chemically impregnated zeolite and method for its production and use - Google Patents

Chemically impregnated zeolite and method for its production and use Download PDF

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Publication number
WO1996023726A1
WO1996023726A1 PCT/US1995/005493 US9505493W WO9623726A1 WO 1996023726 A1 WO1996023726 A1 WO 1996023726A1 US 9505493 W US9505493 W US 9505493W WO 9623726 A1 WO9623726 A1 WO 9623726A1
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Prior art keywords
impregnated
zeolite crystals
permanganate
manganese dioxide
zeolite
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PCT/US1995/005493
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French (fr)
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Fred Klatte
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Fred Klatte
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Priority to AU24332/95A priority Critical patent/AU2433295A/en
Publication of WO1996023726A1 publication Critical patent/WO1996023726A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/54—Nitrogen compounds
    • B01D53/58—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/72—Organic compounds not provided for in groups B01D53/48 - B01D53/70, e.g. hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
    • B01J20/16—Alumino-silicates
    • B01J20/18—Synthetic zeolitic molecular sieves
    • B01J20/186—Chemical treatments in view of modifying the properties of the sieve, e.g. increasing the stability or the activity, also decreasing the activity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/02—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
    • B01J8/04—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds the fluid passing successively through two or more beds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B11/00—Oxides or oxyacids of halogens; Salts thereof
    • C01B11/02—Oxides of chlorine
    • C01B11/022—Chlorine dioxide (ClO2)
    • C01B11/023—Preparation from chlorites or chlorates
    • C01B11/024—Preparation from chlorites or chlorates from chlorites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/10—Oxidants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/50—Inorganic acids
    • B01D2251/512—Phosphoric acid

Definitions

  • the invention relates to processes for producing chemically impregnated zeolite and coated, chemically impregnated zeolite, to the products of such processes, and to use of such products for absorbing a contaminant from a fluid.
  • a preferred embodiment of the invention is a process for chemically impregnating zeolite crystals with manganese dioxide, and then coating the impregnated zeolite crystals with a quaternary ammonium cation.
  • Zeolites are hydrated metal aluminosilicate compounds with well-defined (tetrahedral) crystalline structures. Because zeolite crystals (both natural and synthetic) have a porous structure with connected channels extending through them, they have been employed as molecular sieves for selectively absorbing molecules on the basis of size, shape, and polarity. Volumes packed with zeolite crystals (for example, small zeolite crystals chosen to have size in the range from 0.2 mm to several millimeters) have been employed in water and air (or other gas) filtration systems to selectively absorb contaminants from a flowing stream of water or gas.
  • zeolite does not function adequately as a molecular sieve for organic chemicals such as benzene, toluene, and xylene.
  • zeolite crystals have not been impregnated (throughout their volume) with permanganate.
  • permanganates are strong oxidizing agents, those skilled in the art have avoided exposing quaternary ammonium cations or salts to permanganates (to avoid violent reactions of the type predicted in the literature) . For this reason, it has not been proposed to treat a permanganate- impregnated substrate (such as permanganate- impregnated zeolite) with a quaternary ammonium cation or salt. Nor has it been proposed to treat a substrate impregnated with a QAC (quaternary ammonium cation) to permanganate.
  • QAC quaternary ammonium cation
  • zeolite crystals can readily be impregnated with a usefully high concentration of potassium permanganate.
  • the inventor has recognized that, under certain conditions, such permanganate-impregnated zeolite reacts too rapidly to be practically useful for some air filtration applications. For example, when air contaminated with 50 ppm of hydrogen sulfide is caused to flow (at a rate of 15 liters per minute) through a bed of the inventive permanganate- impregnated zeolite crystals (where the crystals have size about 0.25 inch x 0.125 inch, and the bed has volume of 75 cubic centimeters, and dimensions 1" (Id) x 6”), the crystals typically become saturated with hydrogen sulfide within about 48 hours.
  • the impregnated zeolite crystals usefully absorb hydrogen sulfide from air, the hydrogen sulfide absorption rate is significantly higher than can be achieved using conventional permanganate- impregnated alumina products, and is undesirably high for some applications.
  • Zeolite coated (but not impregnated) with manganese dioxide has been employed in water filtration systems to selectively absorb contaminants from a flowing stream of water, as described in U.S. Patent 4,581,219, issued April 8, 1986 to Imada, et al .
  • the invention is a process for producing zeolite crystals impregnated with manganese dioxide.
  • the product of such process is another embodiment of the invention.
  • Other embodiments of the invention are methods for using manganese dioxide-impregnated crystals to absorb contaminants from fluid (which may be either a liquid such as water or a gas such as air) .
  • One preferred technique for producing manganese dioxide-impregnated crystals is to flow a gas comprising (and preferably, consisting essentially of) one or more of hydrogen, nitrogen, ethylene, and formaldehyde through a bed of permanganate- impregnated zeolite crystals (preferably, with the crystals enclosed in a vessel or other container having a gas inlet and a gas outlet) .
  • the permanganate-impregnated zeolite crystals are caused to flow through a non-flowing volume of such gas.
  • the gas which flows through the permanganate-impregnated zeolite crystals comprises one or more of hydrogen, nitrogen, ethylene, formaldehyde, and other similar gases capable of reacting with permanganate to form manganese dioxide (but not H 2 S gas) .
  • the invention produces manganese dioxide-impregnated zeolite crystals from zeolite crystals impregnated with permanganate, in the following manner.
  • the permanganate-impregnated zeolite crystals e.g., crystals having a potassium permanganate content of about 4% and a moisture content of about 15%
  • filter fluid such as air or liquid water
  • a gas e.g., a contaminant gas
  • the crystals become “spent” due to chemical reaction with one or more of the listed gases in the fluid.
  • the inventor has recognized that each of the "spent" zeolite crystals is substantially uniformly impregnated with manganese dioxide throughout its volume.
  • permanganate used alone is intended to refer to any permanganate, including permanganate of potassium, sodium, magnesium, calcium, barium, or lithium.
  • the method of the invention includes the step of impregnating zeolite crystals with manganese dioxide and then coating the impregnated zeolite with a quaternary ammonium cation (QAC) or a permanganate.
  • QAC quaternary ammonium cation
  • the inventor has unexpectedly found that the coating acts as a protective agent for the impregnating substance in each crystal's interior. The presence of the coating allows regulated time release control of the impregnating substance, and thus permits a controlled diffusion (or absorption) rate in applications in which the coated, impregnated zeolite is employed to absorb contaminants from a fluid such as air or water.
  • An important aspect of the invention is that the characteristics of a QAC (or permanganate) coating on a zeolite crystal impregnated with manganese dioxide can be varied to control the reaction rate of the manganese dioxide within the zeolite. Such characteristics can be varied by changing the concentration of the coating solution employed to coat each impregnated zeolite crystal.
  • coated (or uncoated) manganese-dioxide impregnated zeolite can be used for any of a variety of molecular sieving applications, such as filtration of contaminants from fluid (e.g., air or water) .
  • fluid e.g., air or water
  • coated and uncoated crystals desirably matches specific environmental circumstances which can be calculated by analysis of the air, water, or other fluid to be treated.
  • Other embodiments are a process for producing zeolite crystals impregnated with phosphoric acid, phosphoric acid-impregnated zeolite crystals produced by such process, and methods for using phosphoric acid-impregnated crystals to absorb contaminants from fluid.
  • Figure 1 is a cross-sectional view of a zeolite crystal impregnated with permanganate.
  • Figure 2 is a cross-sectional view of the impregnated zeolite crystal of Fig. 1, after it has been coated with a QAC in accordance with the invention.
  • Figure 3 is a cross-sectional view of a zeolite crystal impregnated with manganese dioxide.
  • Figure 4 is a cross-sectional view of the impregnated zeolite crystal of Fig. 3, after it has been coated with a QAC in accordance with the invention.
  • Figure 5 is a cross-sectional view of a zeolite crystal impregnated with phosphoric acid.
  • the invention is a process for impregnating zeolite crystals (for example, crystals having size 0.125 inch x 0.10 inch, 0.25 inch x 0.125 inch, 0.125 inch x 0.50 inch, or 0.50 inch x 0.75 inch) with manganese dioxide, and the product of such process.
  • zeolite crystals for example, crystals having size 0.125 inch x 0.10 inch, 0.25 inch x 0.125 inch, 0.125 inch x 0.50 inch, or 0.50 inch x 0.75 inch
  • Preferred embodiments of such process employ, as input material, zeolite crystals uniformly impregnated with potassium permanganate, with a 4% potassium permanganate content and a 15% moisture content.
  • Such input material is preferably produced by a method including the steps of initially dehydrating the zeolite crystals to have about 5% moisture content, then mixing the dehydrated zeolite crystals with potassium permanganate crystals (preferably with a weight ratio P/T substantially equal to 4%, where P is the potassium permanganate weight and T is the total weight of the final product of the process) , then immersing the crystal mixture in (or spraying the mixture with) water at about 190° F, thoroughly mixing the resulting slurry, and then air drying the mixed slurry to produce potassium permanganate-impregnated zeolite crystals having about 15% moisture content.
  • potassium permanganate crystals preferably with a weight ratio P/T substantially equal to 4%, where P is the potassium permanganate weight and T is the total weight of the final product of the process
  • Fig. 1 represents one such impregnated crystal, having channels uniformly impregnated with potassium permanganate 2.
  • Variations on the method described above produce zeolite crystals uniformly impregnated with potassium permanganate, having a potassium permanganate content of X%, where X is greater than 4, and is preferably in the range from 8 to 10.
  • the dehydrated zeolite crystals are mixed with solid potassium permanganate with a weight ratio P/T substantially equal to X%, where P is the potassium permanganate weight and T is the total weight of the final product of the process.
  • permanganate other than potassium permanganate (such as permanganate of sodium, magnesium, calcium, barium, or lithium) is employed to impregnate the zeolite crystals.
  • zeolite crystals are immersed in (or sprayed with) aqueous potassium permanganate (having permanganate concentration in the range from about 10% to about 20%) , where the weight of aqueous potassium permanganate is about 10% of the weight of the final product of the process.
  • the crystals (after they are dried) will be uniformly impregnated with about a 1% concentration of potassium permanganate.
  • zeolite crystals are immersed in (or sprayed with) supersaturated aqueous potassium permanganate (having permanganate concentration of 20% or higher) at 190° F, where the weight of aqueous potassium permanganate is about 10% of the weight of the final product of the process.
  • the zeolite crystals (after they are dried) are uniformly impregnated with a concentration of potassium permanganate greater than
  • the desired concentration of potassium permanganate impregnated in zeolite crystals is in the range from about 1% to about 4% (or from about 1% to about 8% or 10%) .
  • permanganate- impregnated zeolite may have an activity rate too high or too low for some useful applications (i.e., its rate of absorption of contaminants may be too high, or too low, for some air or water filtration applications) .
  • the inventor has found that the rate at which permanganate-impregnated zeolite absorbs (or reacts with, or both absorbs and reacts with) selected contaminants can be controlled (and reduced or increased to a desired level) by applying a quaternary ammonium cation (QAC) coating to the permanganate-impregnated zeolite.
  • QAC quaternary ammonium cation
  • the inventor has also found that the rate at which QAC-impregnated zeolite absorbs selected contaminants can be controlled (and reduced or increased to a desired level) by applying a permanganate coating to the QAC- impregnated zeolite.
  • the inventive method uses zeolite which has first been impregnated with permanganate (preferably, potassium permanganate) and then coated with a QAC (preferably, cetyltrimethylammonium, although other QACs are suitable for certain applications) .
  • Fig. 2 represents one such impregnated crystal, whose channels contain QAC 4 in the region near the crystal's surface, and whose channels are impregnated with potassium permanganate 2A throughout the volume of the crystal inside the region containing QAC 4.
  • the invention uses zeolite which has been impregnated with a QAC (preferably, cetyltrimethylammonium) and then coated with permanganate (preferably, potassium permanganate) .
  • QAC preferably, cetyltrimethylammonium
  • permanganate preferably, potassium permanganate
  • Either type of coated, impregnated zeolite (or a mixture of both types of coated, impregnated zeolite, or a mixture of uncoated impregnated zeolite with coated, impregnated zeolite of either type) is useful for a variety of molecular sieving applications (such as filtration of contaminants from air or water) .
  • cetyltrimethylammonium entered the channels near each crystal's outer surface but the QAC did not penetrate farther into the interior of each crystal .
  • the weight ratio of liquid cetyltrimethylammonium chloride employed for coating permanganate-impregnated zeolite crystals should preferably (at least for most air filtration applications) satisfy the following relation: 0.1% ⁇ Q/T ⁇ 0.5%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process.
  • the activity rate of QAC-coated, potassium permanganate-impregnated zeolite depends on the concentration of the QAC solution with which the permanganate-impregnated zeolite is coated. Increasing the QAC concentration will decrease the activity rate.
  • the leaching rate of permanganate from within QAC-coated, impregnated zeolite is negligible if the weight ratio of the QAC coating is in the range from 1% to 2% (i.e., if the weight of liquid cetyltrimethylammonium chloride employed for coating permanganate-impregnated zeolite crystals satisfies the relation 1% ⁇ Q/T ⁇ 2%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) .
  • the optimum QAC coating weight ratio is in the range from 0.1% to 0.5% (i.e., the weight of liquid cetyltrimethylammonium chloride employed for coating the permanganate-impregnated zeolite crystals satisfies the relation 0.1% ⁇ Q/T ⁇ 0.5%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) .
  • the weight of liquid cetyltrimethylammonium chloride employed for the coating should satisfy the relation 1% ⁇ Q/T ⁇ 2%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) .
  • An optimal permanganate-impregnated zeolite product for absorbing (and/or reacting with) any of a wide variety of contaminants (or contaminant groups) from a fluid can be determined experimentally in the following manner.
  • Uncoated, QAC-impregnated zeolite crystals (preferably produced in the manner described below) are mixed in various ratios with QAC-coated, permanganate-impregnated zeolite crystals, and the contaminant absorption and/or reaction characteristics of each mixture studied. The mixture producing the best absorption and/or reaction characteristics is identified as the optimal mixture.
  • a preferred method for impregnating zeolite crystals with QAC to produce zeolite crystals uniformly impregnated with cetyltrimethylammonium cations includes the following steps: dehydrating the zeolite crystals to have about 5% moisture content, then immersing the dehydrated zeolite crystals in (or spraying the dehydrated crystals with) liquid cetyltrimethylammonium chloride (the cetyltrimethylammonium chloride weight is preferably in the range from 5% to 15% of the total weight of the final product of the process) and thoroughly mixing the resulting slurry, and finally air drying the mixed slurry to produce the cetyltrimethylammonium-impregnated zeolite crystals.
  • fifteen pounds of liquid QAC and 90 pounds of dehydrated (5% moisture) zeolite crystals are employed to produce each 100 pounds of such cetyltrimethylammonium-impregnated zeolite crystals.
  • the QAC in preferred embodiments of the invention is cetyltrimethylammonium
  • other QACs can be substituted for cetyltrimethylammonium in alternative embodiments.
  • the inventor has also unexpectedly observed that no obvious reaction resulted from immersion of cetyltrimethylammonium-impregnated zeolite in (or spraying of such impregnated zeolite with) aqueous potassium permanganate (where the weight of the potassium permanganate is in the range from 0.1% to 2% of the weight of the impregnated zeolite) .
  • the immersion (or spraying) solution results in application of a permanganate coating to each QAC-impregnated zeolite crystal (in the sense that permanganate enters the channels near each crystal's outer surface but permanganate does not penetrate farther into the interior of each crystal) .
  • the inventor has found that immersion of QAC- impregnated zeolite crystals in (or spraying of QAC- impregnated zeolite with) aqueous permanganate results in penetration of permanganate throughout the channels of each crystal (with permanganate displacing QAC from channels not only near each crystal's outer surface but also from channels deep within the interior of each crystal) .
  • potassium permanganate solution for coating QAC-impregnated zeolite crystals preferably (at least for many air filtration applications) includes a total weight of permanganate in the range from 0.1% to 0.5% of the weight of the final weight of the permanganate- coated, QAC-impregnated product of the process.
  • the activity rate of permanganate-coated, QAC- impregnated zeolite depends on the concentration of the permanganate solution with which the QAC- impregnated zeolite is coated. Increasing the permanganate concentration of the coating solution will decrease the activity rate (until the concentration is reached at which the permanganate penetrates through the entire volume of each zeolite crystal, displacing QAC impregnated throughout such volume) .
  • the optimum weight of permanganate in the coating solution is in the range from 0.1% to 0.5% of the final weight of the permanganat -coated, QAC-impregnated product of the process.
  • An optimal QAC-impregnated zeolite product for absorbing any of a wide variety of contaminants (or contaminant groups) from a fluid can be determined experimentally in the following manner. Uncoated, permanganate-impregnated zeolite crystals are mixed in various ratios with permanganate-coated, QAC-impregnated zeolite crystals, and the contaminant absorption characteristics of each mixture studied. The mixture producing the best absorption characteristics is identified as the optimal mixture.
  • the characteristics of a QAC (or permanganate) coating on a zeolite crystal impregnated with permanganate (or QAC) can be varied to control the reaction rate of the substance impregnated within the zeolite. Such characteristics can be varied by changing the concentration of the coating solution in which (or with which) the impregnated zeolite crystal is immersed (or sprayed) to form the coating.
  • One preferred technique for producing the inventive manganese dioxide-impregnated crystals is to flow a gas comprising one or more of hydrogen, nitrogen, ethylene, and formaldehyde through a bed of permanganate-impregnated zeolite crystals (preferably, with the crystals enclosed in a vessel or other container having a gas inlet and a gas outlet) .
  • the permanganate-impregnated zeolite crystals are caused to flow through a non- flowing volume of such gas.
  • the gas which flows through the permanganate-impregnated zeolite crystals comprises one or more of hydrogen, nitrogen, ethylene, formaldehyde, and other gases similar to these gases (but not H 2 S gas) .
  • the invention produces manganese dioxide-impregnated zeolite crystals from zeolite crystals impregnated with permanganate (with or without a QAC coating) in the following manner.
  • the permanganate-impregnated zeolite crystals e.g., crystals having a potassium permanganate content of about 4% and a moisture content of about 15%) are employed to filter fluid
  • each of the "spent" zeolite crystals is substantially uniformly impregnated with manganese dioxide throughout its volume.
  • permanganate-impregnated zeolite becomes impregnated with manganese dioxide (as it becomes "spent" when employed to filter air) is believed to be as follows. This example assumes that the zeolite is initially impregnated with potassium permanganate (KMn0 4 ) , and that the potassium permanganate-zeolite is employed to filter air contaminated with ethylene (C 2 H 4 ) . The following reaction is believed to explain the result that manganese dioxide forms in the pores throughout the volume of each zeolite crystal as it becomes "spent" (activated to Mn0 2 ) :
  • Fig. 3 represents a "spent" zeolite crystal produced according to the invention, having channels substantially uniformly impregnated with manganese dioxide 6 throughout the crystal's volume.
  • the manganese dioxide-impregnated zeolite crystals of the invention can be coated with a QAC (or with a permanganate) , e.g., as a result of any of the above-described coating operations.
  • Fig. 4 represents one such coated, impregnated crystal, whose channels contain QAC 8 in the region near the crystal's surface, and whose channels are impregnated with manganese dioxide 6A throughout the volume of the crystal inside the region containing QAC 8.
  • the presence of such a QAC coating allows regulated time release control of the impregnating manganese dioxide 6A (which is an oxidizing filtering agent) , and thus permits a controlled diffusion (or absorption) rate in applications in which QAC-coated, manganese dioxide-impregnated zeolite crystals are employed to absorb contaminants from a fluid (especially a liquid such as water) .
  • the characteristics of the QAC coating can be varied to control the reaction rate of the impregnating substance (manganese dioxide) within the zeolite crystals. Such characteristics can be varied by changing the concentration of the coating solution employed to coat the impregnated zeolite crystals.
  • the manganese dioxide-impregnated zeolite crystals, or QAC-coated, manganese dioxide- impregnated zeolite crystals of the invention can be used for a variety of molecular sieving applications, such as filtration of contaminants from fluid (especially liquid) .
  • Various combinations of such coated and uncoated crystals can be employed to match specific environmental circumstances which can be calculated by analysis of the fluid to be treated.
  • the fluid is caused to flow through a bed of the inventive manganese dioxide-impregnated zeolite crystals (coated or uncoated) , or the crystals are caused to flow through the fluid.
  • inventions are a process for producing zeolite crystals impregnated with phosphoric acid, phosphoric acid-impregnated zeolite crystals produced by such process, and methods for using phosphoric acid-impregnated crystals to absorb contaminants from fluid.
  • Zeolite crystals have some capacity to absorb NH 3 due to their cation exchange capacity.
  • the NH 3 absorption capacity is increased greatly (up to five times the NH 3 absorption capacity of non-impregnated zeolite crystals) .
  • the impregnation step is performed by immersing the zeolite in (or spraying the zeolite with) aqueous phosphoric acid.
  • the inventive method preferably includes the steps of: dehydrating the zeolite crystals until they have moisture content substantially below their initial moisture content (preferably until their moisture content is about 5%) , then immersing the dehydrated zeolite crystals in (or spraying the dehydrated crystals with) an aqueous solution of phosphoric acid at high temperature and thoroughly mixing the resulting slurry, and finally air drying the mixed slurry to produce impregnated zeolite crystals.
  • Fig. 5 represents one such impregnated crystal, having channels uniformly impregnated with phosphoric acid 10.
  • Phosphoric acid-impregnated zeolite crystals can be used to control NH 3 odor in fluids such as air (or liquid manure) .
  • the reaction for neutralizing NH 3 gas in such fluids is believed to be 2NH 3 + H 3 P0 4 --> (NH 4 ) 2 HP0 4 , where (NH 4 ) 2 HP0 4 has no odor.
  • beds of phosphoric acid- impregnated zeolite crystals can be used in animal confinement facilities to receive liquid animal wastes.
  • phosphoric acid-impregnated zeolite crystals can be used for such applications as in cat litter boxes and in stable "freshener" products for filtering air (or liquids) .

Abstract

A class of methods for impregnating zeolite crystals with one manganese dioxide and phosphoric acid, and the impregnated zeolite product of each such method. The manganese dioxide-impregnated zeolite (2A) is optionally coated with a quaternary ammonium cation (4) or a permanganate. In some embodiments, manganese dioxide-impregnated zeolite crystals are produced by flowing a fluid, containing at least one substance (such as ethylene gas) capable of reacting with permanganate to produce manganese dioxide, relative to permanganate-impregnated crystals. In some embodiments, manganese dioxide-impregnated zeolite crystals are produced by flowing a gas consisting essentially of one or more of hydrogen, nitrogen, ethylene, and formaldehyde (or a fluid contaminated with at least one such gas) through a bed of potassium permanganate-impregnated zeolite crystals.

Description

CHEMICALLY IMPREGNATED ZEOLITE AND METHOD FOR ITS PRODUCTION AND USE
Cross-Reference to Related Application The present application is a continuation-in- part of pending U.S. Patent Application Serial No. 08/150,438 filed November 10, 1993, which is a continuation-in-part of U.S. Patent Application Serial No. 07/975,680, issued as U.S. Patent 5,278,112 on January 11, 1994.
Field of the Invention
The invention relates to processes for producing chemically impregnated zeolite and coated, chemically impregnated zeolite, to the products of such processes, and to use of such products for absorbing a contaminant from a fluid. A preferred embodiment of the invention is a process for chemically impregnating zeolite crystals with manganese dioxide, and then coating the impregnated zeolite crystals with a quaternary ammonium cation.
Background of the Invention
Zeolites are hydrated metal aluminosilicate compounds with well-defined (tetrahedral) crystalline structures. Because zeolite crystals (both natural and synthetic) have a porous structure with connected channels extending through them, they have been employed as molecular sieves for selectively absorbing molecules on the basis of size, shape, and polarity. Volumes packed with zeolite crystals (for example, small zeolite crystals chosen to have size in the range from 0.2 mm to several millimeters) have been employed in water and air (or other gas) filtration systems to selectively absorb contaminants from a flowing stream of water or gas.
It has been proposed to treat zeolite crystals by impregnating them with quaternary ammonium cations (such as tetramethylammonium, tetraethylammoniu , hexadecyltrimethylammonium, dibenzyldimethylammonium, benzyltriethylammonium, and cetyltrimethylammonium) , to enhance the zeolite's capacity to absorb heavy metal, benzene, toluene, and xylene contaminants from water. See, for example, Cadena, et al . , "Treatment of Waters Contaminated with BTX and Heavy Metals Using Tailored Zeolites, " New Mexico Waste-management Education and Research Consortium Technical Completion Report for Project No. WERC-91-41 (February 1992) . If not impregnated with a quaternary ammonium cation (QAC) , zeolite does not function adequately as a molecular sieve for organic chemicals such as benzene, toluene, and xylene. It has also been proposed to impregnate an aqueous solution of permanganate (such as permanganate of potassium, sodium, magnesium, calcium, barium, or lithium) into pores of substrates such as silica gel, alumina, silica-alumina, activated bauxite, and activated clay. The resulting impregnated porous substrates have been employed for filtering and deodorizing air. See, for example, U.S. Patent 3,049,399, issued August 14, 1962, to Gamson, et al .
However, zeolite crystals have not been impregnated (throughout their volume) with permanganate.
Further, because permanganates are strong oxidizing agents, those skilled in the art have avoided exposing quaternary ammonium cations or salts to permanganates (to avoid violent reactions of the type predicted in the literature) . For this reason, it has not been proposed to treat a permanganate- impregnated substrate (such as permanganate- impregnated zeolite) with a quaternary ammonium cation or salt. Nor has it been proposed to treat a substrate impregnated with a QAC (quaternary ammonium cation) to permanganate.
The inventor has found that zeolite crystals can readily be impregnated with a usefully high concentration of potassium permanganate. However, the inventor has recognized that, under certain conditions, such permanganate-impregnated zeolite reacts too rapidly to be practically useful for some air filtration applications. For example, when air contaminated with 50 ppm of hydrogen sulfide is caused to flow (at a rate of 15 liters per minute) through a bed of the inventive permanganate- impregnated zeolite crystals (where the crystals have size about 0.25 inch x 0.125 inch, and the bed has volume of 75 cubic centimeters, and dimensions 1" (Id) x 6"), the crystals typically become saturated with hydrogen sulfide within about 48 hours. Although the impregnated zeolite crystals usefully absorb hydrogen sulfide from air, the hydrogen sulfide absorption rate is significantly higher than can be achieved using conventional permanganate- impregnated alumina products, and is undesirably high for some applications.
For both air (and other gas) and water filtration applications, it would be desirable to reduce the rate at which permanganate-impregnated zeolite absorbs selected contaminants, and to control such absorption rate. Similarly, it would be desirable to reduce the rate at which QAC-impregnated zeolite absorbs selected contaminants, and to control such absorption rate. However, until the present invention, it was not known how to achieve either of these objectives.
Zeolite coated (but not impregnated) with manganese dioxide has been employed in water filtration systems to selectively absorb contaminants from a flowing stream of water, as described in U.S. Patent 4,581,219, issued April 8, 1986 to Imada, et al . However, until the present invention, it was not known how to impregnate zeolite with manganese dioxide, or to employ zeolite impregnated with manganese dioxide in water or gas filtration systems to selectively absorb contaminants from a flowing stream of water or gas.
Summary of the Invention In one class of embodiments, the invention is a process for producing zeolite crystals impregnated with manganese dioxide. The product of such process is another embodiment of the invention. Other embodiments of the invention are methods for using manganese dioxide-impregnated crystals to absorb contaminants from fluid (which may be either a liquid such as water or a gas such as air) .
One preferred technique for producing manganese dioxide-impregnated crystals is to flow a gas comprising (and preferably, consisting essentially of) one or more of hydrogen, nitrogen, ethylene, and formaldehyde through a bed of permanganate- impregnated zeolite crystals (preferably, with the crystals enclosed in a vessel or other container having a gas inlet and a gas outlet) . Alternatively, the permanganate-impregnated zeolite crystals are caused to flow through a non-flowing volume of such gas. Also alternatively, the gas which flows through the permanganate-impregnated zeolite crystals comprises one or more of hydrogen, nitrogen, ethylene, formaldehyde, and other similar gases capable of reacting with permanganate to form manganese dioxide (but not H2S gas) .
In another preferred embodiment, the invention produces manganese dioxide-impregnated zeolite crystals from zeolite crystals impregnated with permanganate, in the following manner. The permanganate-impregnated zeolite crystals (e.g., crystals having a potassium permanganate content of about 4% and a moisture content of about 15%) are employed to filter fluid (such as air or liquid water) containing a gas (e.g., a contaminant gas) comprising one or more of hydrogen, nitrogen, ethylene, and formaldehyde. During the filtration step, the crystals become "spent" due to chemical reaction with one or more of the listed gases in the fluid. The inventor has recognized that each of the "spent" zeolite crystals is substantially uniformly impregnated with manganese dioxide throughout its volume.
Throughout the specification, including in the claims, the term "permanganate" used alone is intended to refer to any permanganate, including permanganate of potassium, sodium, magnesium, calcium, barium, or lithium.
In some preferred embodiments, the method of the invention includes the step of impregnating zeolite crystals with manganese dioxide and then coating the impregnated zeolite with a quaternary ammonium cation (QAC) or a permanganate. The inventor has unexpectedly found that the coating acts as a protective agent for the impregnating substance in each crystal's interior. The presence of the coating allows regulated time release control of the impregnating substance, and thus permits a controlled diffusion (or absorption) rate in applications in which the coated, impregnated zeolite is employed to absorb contaminants from a fluid such as air or water.
An important aspect of the invention is that the characteristics of a QAC (or permanganate) coating on a zeolite crystal impregnated with manganese dioxide can be varied to control the reaction rate of the manganese dioxide within the zeolite. Such characteristics can be varied by changing the concentration of the coating solution employed to coat each impregnated zeolite crystal.
Also in accordance with the invention, coated (or uncoated) manganese-dioxide impregnated zeolite, or a mixture of such coated and uncoated impregnated zeolite, can be used for any of a variety of molecular sieving applications, such as filtration of contaminants from fluid (e.g., air or water) . The appropriate combination of coated and uncoated crystals desirably matches specific environmental circumstances which can be calculated by analysis of the air, water, or other fluid to be treated.
Other embodiments are a process for producing zeolite crystals impregnated with phosphoric acid, phosphoric acid-impregnated zeolite crystals produced by such process, and methods for using phosphoric acid-impregnated crystals to absorb contaminants from fluid.
Brief Description of the Drawings
Figure 1 is a cross-sectional view of a zeolite crystal impregnated with permanganate.
Figure 2 is a cross-sectional view of the impregnated zeolite crystal of Fig. 1, after it has been coated with a QAC in accordance with the invention. Figure 3 is a cross-sectional view of a zeolite crystal impregnated with manganese dioxide.
Figure 4 is a cross-sectional view of the impregnated zeolite crystal of Fig. 3, after it has been coated with a QAC in accordance with the invention.
Figure 5 is a cross-sectional view of a zeolite crystal impregnated with phosphoric acid.
Detailed Description of the Preferred Embodiments In one class of embodiments, the invention is a process for impregnating zeolite crystals (for example, crystals having size 0.125 inch x 0.10 inch, 0.25 inch x 0.125 inch, 0.125 inch x 0.50 inch, or 0.50 inch x 0.75 inch) with manganese dioxide, and the product of such process. Preferred embodiments of such process employ, as input material, zeolite crystals uniformly impregnated with potassium permanganate, with a 4% potassium permanganate content and a 15% moisture content. Such input material is preferably produced by a method including the steps of initially dehydrating the zeolite crystals to have about 5% moisture content, then mixing the dehydrated zeolite crystals with potassium permanganate crystals (preferably with a weight ratio P/T substantially equal to 4%, where P is the potassium permanganate weight and T is the total weight of the final product of the process) , then immersing the crystal mixture in (or spraying the mixture with) water at about 190° F, thoroughly mixing the resulting slurry, and then air drying the mixed slurry to produce potassium permanganate-impregnated zeolite crystals having about 15% moisture content. Typically, the process employs four pounds of potassium permanganate and fifteen pounds of water for every 86 pounds of dehydrated (5% moisture) zeolite crystals, and this mixture (105 pounds) is dried to produce 100 pounds of permanganate- impregnated zeolite crystals having about 15% moisture content. Fig. 1 represents one such impregnated crystal, having channels uniformly impregnated with potassium permanganate 2.
Variations on the method described above produce zeolite crystals uniformly impregnated with potassium permanganate, having a potassium permanganate content of X%, where X is greater than 4, and is preferably in the range from 8 to 10. In such variations, the dehydrated zeolite crystals are mixed with solid potassium permanganate with a weight ratio P/T substantially equal to X%, where P is the potassium permanganate weight and T is the total weight of the final product of the process.
In variations on any of the above-described methods, permanganate other than potassium permanganate (such as permanganate of sodium, magnesium, calcium, barium, or lithium) is employed to impregnate the zeolite crystals.
In another variation on the described methods, zeolite crystals are immersed in (or sprayed with) aqueous potassium permanganate (having permanganate concentration in the range from about 10% to about 20%) , where the weight of aqueous potassium permanganate is about 10% of the weight of the final product of the process. The crystals (after they are dried) will be uniformly impregnated with about a 1% concentration of potassium permanganate.
In yet another variation on the described methods, zeolite crystals are immersed in (or sprayed with) supersaturated aqueous potassium permanganate (having permanganate concentration of 20% or higher) at 190° F, where the weight of aqueous potassium permanganate is about 10% of the weight of the final product of the process. The zeolite crystals (after they are dried) are uniformly impregnated with a concentration of potassium permanganate greater than
1 18- . For many applications (including air and water filtration applications) , the desired concentration of potassium permanganate impregnated in zeolite crystals is in the range from about 1% to about 4% (or from about 1% to about 8% or 10%) . However, as explained above, permanganate- impregnated zeolite may have an activity rate too high or too low for some useful applications (i.e., its rate of absorption of contaminants may be too high, or too low, for some air or water filtration applications) . The inventor has found that the rate at which permanganate-impregnated zeolite absorbs (or reacts with, or both absorbs and reacts with) selected contaminants can be controlled (and reduced or increased to a desired level) by applying a quaternary ammonium cation (QAC) coating to the permanganate-impregnated zeolite. The inventor has also found that the rate at which QAC-impregnated zeolite absorbs selected contaminants can be controlled (and reduced or increased to a desired level) by applying a permanganate coating to the QAC- impregnated zeolite.
Thus, in a first class of preferred embodiments, the inventive method uses zeolite which has first been impregnated with permanganate (preferably, potassium permanganate) and then coated with a QAC (preferably, cetyltrimethylammonium, although other QACs are suitable for certain applications) . Fig. 2 represents one such impregnated crystal, whose channels contain QAC 4 in the region near the crystal's surface, and whose channels are impregnated with potassium permanganate 2A throughout the volume of the crystal inside the region containing QAC 4.
In a second class of preferred embodiments, the invention uses zeolite which has been impregnated with a QAC (preferably, cetyltrimethylammonium) and then coated with permanganate (preferably, potassium permanganate) . Either type of coated, impregnated zeolite (or a mixture of both types of coated, impregnated zeolite, or a mixture of uncoated impregnated zeolite with coated, impregnated zeolite of either type) is useful for a variety of molecular sieving applications (such as filtration of contaminants from air or water) .
Development of the first class of preferred embodiments began with our unexpected observation that no obvious reaction resulted from immersion of potassium permanganate-impregnated zeolite in (or spraying of such impregnated zeolite with) liquid cetyltrimethylammonium chloride (with a weight ratio Q/T in the range from 0.1% to 5%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) . As a result of such immersion (or spraying) , a QAC coating was applied to each permanganate-impregnated zeolite crystal in the sense that the QAC
(cetyltrimethylammonium) entered the channels near each crystal's outer surface but the QAC did not penetrate farther into the interior of each crystal . From a practical point of view, the inventor has found that the weight ratio of liquid cetyltrimethylammonium chloride employed for coating permanganate-impregnated zeolite crystals should preferably (at least for most air filtration applications) satisfy the following relation: 0.1% < Q/T < 0.5%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process.
As a result of permanganate leaching studies on the inventive QAC-coated, potassium permanganate- impregnated zeolite crystals (in which the coated, permanganate-impregnated zeolite crystals were immersed in, or sprayed with, water and the permanganate concentration in the water measured over time) , the inventor determined that the QAC coating substantially slowed the permanganate leaching rate (and thus would substantially slow the expected activity rate, i.e., the rate at which the impregnated zeolite would absorb and/or react with contaminants such as organic chemicals) . This result was highly unexpected in view of the conventional belief that the presence of QAC would increase zeolite's absorption of organic chemicals (such as toluene) .
The inventor found that the activity rate of QAC-coated, potassium permanganate-impregnated zeolite depends on the concentration of the QAC solution with which the permanganate-impregnated zeolite is coated. Increasing the QAC concentration will decrease the activity rate. The inventor found that the leaching rate of permanganate from within QAC-coated, impregnated zeolite (and hence the expected activity rate) is negligible if the weight ratio of the QAC coating is in the range from 1% to 2% (i.e., if the weight of liquid cetyltrimethylammonium chloride employed for coating permanganate-impregnated zeolite crystals satisfies the relation 1% < Q/T < 2%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) . To produce QAC-coated, potassium permanganate- impregnated zeolite for most air filtration applications, the optimum QAC coating weight ratio is in the range from 0.1% to 0.5% (i.e., the weight of liquid cetyltrimethylammonium chloride employed for coating the permanganate-impregnated zeolite crystals satisfies the relation 0.1% < Q/T < 0.5%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) . However, for permanganate-impregnated zeolite crystals with a permanganate concentration greater than 4%, it may be desirable to employ a greater amount of QAC for the coating (i.e., the weight of liquid cetyltrimethylammonium chloride employed for the coating should satisfy the relation 1% < Q/T < 2%, where Q is the cetyltrimethylammonium chloride weight and T is the total weight of the final product of the process) .
An optimal permanganate-impregnated zeolite product for absorbing (and/or reacting with) any of a wide variety of contaminants (or contaminant groups) from a fluid (such as air or water) can be determined experimentally in the following manner. Uncoated, QAC-impregnated zeolite crystals (preferably produced in the manner described below) are mixed in various ratios with QAC-coated, permanganate-impregnated zeolite crystals, and the contaminant absorption and/or reaction characteristics of each mixture studied. The mixture producing the best absorption and/or reaction characteristics is identified as the optimal mixture. Since the QAC known as cetyltrimethylammonium is commercially available in aqueous form, impregnation of zeolite with this aqueous QAC product can be accomplished more easily than can impregnation of zeolite with potassium permanganate. A preferred method for impregnating zeolite crystals with QAC to produce zeolite crystals uniformly impregnated with cetyltrimethylammonium cations includes the following steps: dehydrating the zeolite crystals to have about 5% moisture content, then immersing the dehydrated zeolite crystals in (or spraying the dehydrated crystals with) liquid cetyltrimethylammonium chloride (the cetyltrimethylammonium chloride weight is preferably in the range from 5% to 15% of the total weight of the final product of the process) and thoroughly mixing the resulting slurry, and finally air drying the mixed slurry to produce the cetyltrimethylammonium-impregnated zeolite crystals. Typically, fifteen pounds of liquid QAC and 90 pounds of dehydrated (5% moisture) zeolite crystals are employed to produce each 100 pounds of such cetyltrimethylammonium-impregnated zeolite crystals.
Although the QAC in preferred embodiments of the invention is cetyltrimethylammonium, other QACs can be substituted for cetyltrimethylammonium in alternative embodiments. The inventor has also unexpectedly observed that no obvious reaction resulted from immersion of cetyltrimethylammonium-impregnated zeolite in (or spraying of such impregnated zeolite with) aqueous potassium permanganate (where the weight of the potassium permanganate is in the range from 0.1% to 2% of the weight of the impregnated zeolite) . Where the weight of the potassium permanganate in the immersing (or spraying) solution is in the range from 0.1% to 1% of the weight of the impregnated zeolite, the immersion (or spraying) results in application of a permanganate coating to each QAC-impregnated zeolite crystal (in the sense that permanganate enters the channels near each crystal's outer surface but permanganate does not penetrate farther into the interior of each crystal) . Where the weight of the permanganate in the immersing (or spraying) solution is above 1% of the weight of the impregnated zeolite, the inventor has found that immersion of QAC- impregnated zeolite crystals in (or spraying of QAC- impregnated zeolite with) aqueous permanganate results in penetration of permanganate throughout the channels of each crystal (with permanganate displacing QAC from channels not only near each crystal's outer surface but also from channels deep within the interior of each crystal) . From a practical point of view, potassium permanganate solution for coating QAC-impregnated zeolite crystals, preferably (at least for many air filtration applications) includes a total weight of permanganate in the range from 0.1% to 0.5% of the weight of the final weight of the permanganate- coated, QAC-impregnated product of the process.
As a result of permanganate leaching studies on potassium permanganate-coated, QAC-impregnated zeolite crystals (in which the coated, QAC- impregnated zeolite crystals were immersed in water and the QAC concentration in the water measured over time) , it has been determined that the permanganate coating substantially slowed the QAC leaching rate (and thus would substantially slow the expected activity rate, i.e., the rate at which the impregnated zeolite would absorb contaminants such as organic chemicals) .
The activity rate of permanganate-coated, QAC- impregnated zeolite depends on the concentration of the permanganate solution with which the QAC- impregnated zeolite is coated. Increasing the permanganate concentration of the coating solution will decrease the activity rate (until the concentration is reached at which the permanganate penetrates through the entire volume of each zeolite crystal, displacing QAC impregnated throughout such volume) . To produce potassium permanganate-coated, QAC-impregnated zeolite for most air filtration applications, the optimum weight of permanganate in the coating solution is in the range from 0.1% to 0.5% of the final weight of the permanganat -coated, QAC-impregnated product of the process.
An optimal QAC-impregnated zeolite product for absorbing any of a wide variety of contaminants (or contaminant groups) from a fluid (such as air or water) can be determined experimentally in the following manner. Uncoated, permanganate-impregnated zeolite crystals are mixed in various ratios with permanganate-coated, QAC-impregnated zeolite crystals, and the contaminant absorption characteristics of each mixture studied. The mixture producing the best absorption characteristics is identified as the optimal mixture.
It may also be useful to mix permanganate- coated, QAC-impregnated zeolite crystals with QAC- coated, permanganate-impregnated zeolite crystals.
The characteristics of a QAC (or permanganate) coating on a zeolite crystal impregnated with permanganate (or QAC) can be varied to control the reaction rate of the substance impregnated within the zeolite. Such characteristics can be varied by changing the concentration of the coating solution in which (or with which) the impregnated zeolite crystal is immersed (or sprayed) to form the coating.
Important aspects of the invention are methods for producing zeolite crystals impregnated with manganese dioxide, the product of such methods, and methods for using such manganese dioxide-impregnated zeolite crystals to absorb contaminants from fluid (especially liquids) . One preferred technique for producing the inventive manganese dioxide-impregnated crystals is to flow a gas comprising one or more of hydrogen, nitrogen, ethylene, and formaldehyde through a bed of permanganate-impregnated zeolite crystals (preferably, with the crystals enclosed in a vessel or other container having a gas inlet and a gas outlet) . Alternatively, the permanganate-impregnated zeolite crystals are caused to flow through a non- flowing volume of such gas. Also alternatively, the gas which flows through the permanganate-impregnated zeolite crystals comprises one or more of hydrogen, nitrogen, ethylene, formaldehyde, and other gases similar to these gases (but not H2S gas) .
In another preferred embodiment, the invention produces manganese dioxide-impregnated zeolite crystals from zeolite crystals impregnated with permanganate (with or without a QAC coating) in the following manner. The permanganate-impregnated zeolite crystals (e.g., crystals having a potassium permanganate content of about 4% and a moisture content of about 15%) are employed to filter fluid
(such as air or liquid water) containing a gas (e.g., a contaminant gas) comprising one or more of hydrogen, nitrogen, ethylene, and formaldehyde. The filtration can be performed either by flowing the fluid through the crystals or by flowing the crystals through the fluid. During the filtration step, the crystals eventually become "spent" due to chemical reaction with the fluid (including one or more of the listed gases in the fluid) . The inventor has recognized that each of the "spent" zeolite crystals is substantially uniformly impregnated with manganese dioxide throughout its volume.
One mechanism by which permanganate-impregnated zeolite becomes impregnated with manganese dioxide (as it becomes "spent" when employed to filter air) is believed to be as follows. This example assumes that the zeolite is initially impregnated with potassium permanganate (KMn04) , and that the potassium permanganate-zeolite is employed to filter air contaminated with ethylene (C2H4) . The following reaction is believed to explain the result that manganese dioxide forms in the pores throughout the volume of each zeolite crystal as it becomes "spent" (activated to Mn02) :
KMn04 +C2H4 --> KMn02 +C02 +H20. In a variation on the previous example, the air is contaminated with another oxidizable gas similar to ethylene, such as formaldehyde (HCHO) . In the latter case, the following reaction is believed to explain the result that manganese dioxide forms in the pores throughout the volume of each zeolite crystal as it becomes "spent" (activated to Mn02) : KMn04 +HCHO + H20 --> KOH + C02 + Mn02 +H20.
Fig. 3 represents a "spent" zeolite crystal produced according to the invention, having channels substantially uniformly impregnated with manganese dioxide 6 throughout the crystal's volume.
The manganese dioxide-impregnated zeolite crystals of the invention can be coated with a QAC (or with a permanganate) , e.g., as a result of any of the above-described coating operations. Fig. 4 represents one such coated, impregnated crystal, whose channels contain QAC 8 in the region near the crystal's surface, and whose channels are impregnated with manganese dioxide 6A throughout the volume of the crystal inside the region containing QAC 8. The presence of such a QAC coating allows regulated time release control of the impregnating manganese dioxide 6A (which is an oxidizing filtering agent) , and thus permits a controlled diffusion (or absorption) rate in applications in which QAC-coated, manganese dioxide-impregnated zeolite crystals are employed to absorb contaminants from a fluid (especially a liquid such as water) . The characteristics of the QAC coating can be varied to control the reaction rate of the impregnating substance (manganese dioxide) within the zeolite crystals. Such characteristics can be varied by changing the concentration of the coating solution employed to coat the impregnated zeolite crystals. The manganese dioxide-impregnated zeolite crystals, or QAC-coated, manganese dioxide- impregnated zeolite crystals of the invention, can be used for a variety of molecular sieving applications, such as filtration of contaminants from fluid (especially liquid) . Various combinations of such coated and uncoated crystals can be employed to match specific environmental circumstances which can be calculated by analysis of the fluid to be treated.
To perform fluid filtration, the fluid is caused to flow through a bed of the inventive manganese dioxide-impregnated zeolite crystals (coated or uncoated) , or the crystals are caused to flow through the fluid.
Other embodiments of the invention are a process for producing zeolite crystals impregnated with phosphoric acid, phosphoric acid-impregnated zeolite crystals produced by such process, and methods for using phosphoric acid-impregnated crystals to absorb contaminants from fluid. Zeolite crystals have some capacity to absorb NH3 due to their cation exchange capacity. By impregnating zeolite crystals uniformly throughout their volume with phosphoric acid (to cause the impregnated zeolite crystals to include from 1% to 10% phosphoric acid by weight) , the NH3 absorption capacity is increased greatly (up to five times the NH3 absorption capacity of non-impregnated zeolite crystals) .
Preferably, the impregnation step is performed by immersing the zeolite in (or spraying the zeolite with) aqueous phosphoric acid. The inventive method preferably includes the steps of: dehydrating the zeolite crystals until they have moisture content substantially below their initial moisture content (preferably until their moisture content is about 5%) , then immersing the dehydrated zeolite crystals in (or spraying the dehydrated crystals with) an aqueous solution of phosphoric acid at high temperature and thoroughly mixing the resulting slurry, and finally air drying the mixed slurry to produce impregnated zeolite crystals. Fig. 5 represents one such impregnated crystal, having channels uniformly impregnated with phosphoric acid 10.
Phosphoric acid-impregnated zeolite crystals can be used to control NH3 odor in fluids such as air (or liquid manure) . The reaction for neutralizing NH3 gas in such fluids is believed to be 2NH3 + H3P04 --> (NH4)2HP04 , where (NH4)2HP04 has no odor. We contemplate that beds of phosphoric acid- impregnated zeolite crystals can be used in animal confinement facilities to receive liquid animal wastes. Similarly, phosphoric acid-impregnated zeolite crystals can be used for such applications as in cat litter boxes and in stable "freshener" products for filtering air (or liquids) .
Various modifications and variations of the described method of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.

Claims

WHAT IS CLAIMED IS:
1. A method for absorbing a contaminant from a fluid, including the steps of:
(a) exposing manganese dioxide-impregnated zeolite crystals to the fluid, each of said manganese dioxide-impregnated zeolite crystals being substantially uniformly impregnated with manganese dioxide throughout its volume; and
(b) causing one of the fluid and the manganese dioxide-impregnated zeolite crystals to flow relative to another of the fluid and the manganese dioxide- impregnated zeolite crystals.
2. The method of claim 1, wherein step (b) includes the step of flowing the fluid relative to a stationary bed of the manganese dioxide-impregnated zeolite crystals.
3. The method of claim 1, also including the step of:
(c) before step (a) , causing a second fluid to flow relative to zeolite crystals impregnated with permanganate, thereby producing said manganese dioxide-impregnated zeolite crystals, where the second fluid contains a substance capable of reacting with permanganate to produce manganese dioxide.
4. The method of claim 3, wherein the substance is a member of the group consisting of hydrogen gas, nitrogen gas, ethylene gas, and formaldehyde gas.
5. The method of claim 3, wherein the substance is a mixture of at least two members of the group consisting of hydrogen gas, nitrogen gas, ethylene gas, and formaldehyde gas.
6. The method of claim 3, wherein the permanganate is potassium permanganate.
7. The method of claim 3, wherein said zeolite crystals impregnated with permanganate are coated with a quaternary ammonium cation.
8. A method for producing zeolite crystals impregnated with manganese dioxide, including the steps of:
(a) providing zeolite crystals impregnated with permanganate; and
(b) flowing a fluid, containing a substance capable of reacting with the permanganate to produce manganese dioxide, relative to said zeolite crystals impregnated with permanganate, thereby producing said zeolite crystals impregnated with manganese dioxide.
9. The method of claim 8, wherein the substance is a member of the group consisting of hydrogen gas, nitrogen gas, ethylene gas, and formaldehyde gas.
10. A zeolite crystal impregnated with manganese dioxide, produced as a result of the method of claim
9.
11. The method of claim 8, wherein the substance is a mixture of at least two members of the group consisting of hydrogen gas, nitrogen gas, ethylene gas, and formaldehyde gas.
12. The method of claim 8, wherein the permanganate is potassium permanganate.
13. A zeolite crystal impregnated with manganese dioxide, produced as a result of the method of claim 12.
14. The method of claim 8, also including the step of :
(c) after step (b) , coating said zeolite crystals impregnated with manganese dioxide with a quaternary ammonium cation.
15. A zeolite crystal impregnated with manganese dioxide and coated with said quaternary ammonium cation, produced as a result of the method of claim 14.
16. A zeolite crystal impregnated with manganese dioxide, produced as a result of the method of claim 8.
17. The method of claim 8, wherein said fluid consists essentially of a member of the group consisting of hydrogen gas, nitrogen gas, ethylene gas, and formaldehyde gas.
18. The method of claim 8, wherein said fluid consists essentially of a mixture of at least two members of the group consisting of hydrogen gas, nitrogen gas, ethylene gas, and formaldehyde gas.
19. A method for chemically impregnating zeolite crystals, including the steps of:
(a) dehydrating the zeolite crystals to substantially decrease their moisture content below their initial moisture content;
(b) after step (a) , adding aqueous phosphoric acid to the zeolite crystals; (c) after step (b) , drying the zeolite crystals to produce phosphoric acid-impregnated zeolite crystals .
20. A phosphoric acid-impregnated zeolite crystal produced by performing the method of claim 19.
21. A method for neutralizing a contaminant in a fluid, including the steps of:
(a) exposing phosphoric acid-impregnated zeolite crystals to the fluid, each of said phosphoric acid- impregnated zeolite crystals being substantially uniformly impregnated with phosphoric acid throughout its volume; and
(b) causing one of the fluid and the phosphoric acid-impregnated zeolite crystals to flow relative to another of the fluid and the phosphoric acid- impregnated zeolite crystals.
22. The method of claim 21, wherein step (b) includes the step of flowing the fluid relative to a stationary bed of the phosphoric acid-impregnated zeolite crystals.
23. The method of claim 21, wherein the contaminant is NH3.
24. The method of claim 23, wherein the fluid is liquid manure.
PCT/US1995/005493 1995-02-02 1995-05-03 Chemically impregnated zeolite and method for its production and use WO1996023726A1 (en)

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Cited By (3)

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GB2327048A (en) * 1997-07-09 1999-01-13 Secr Defence Adsorbent zeolite composition
WO2009029876A3 (en) * 2007-08-29 2009-04-23 Spectrasensors Inc Scrubber for reactive gasses
CN110124748A (en) * 2019-03-12 2019-08-16 武汉工程大学 A kind of preparation method and applications of melamino-formaldehyde foam support nanometer titanium dioxide manganese material

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US4581219A (en) * 1983-06-22 1986-04-08 Mitsui Mining & Smelting Co., Ltd. Method of making macroporous manganese dioxide
JPH02198629A (en) * 1989-01-25 1990-08-07 Toshiyuki Nakajima Adsorptive oxidizing agent
US5278112A (en) * 1992-11-13 1994-01-11 Fred Klatte Chemically impregnated zeolite and method for chemically impregnating and coating zeolite

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JPS571421A (en) * 1980-06-04 1982-01-06 Nippon Chem Ind Co Ltd:The Air cleaning agent
US4581219A (en) * 1983-06-22 1986-04-08 Mitsui Mining & Smelting Co., Ltd. Method of making macroporous manganese dioxide
JPH02198629A (en) * 1989-01-25 1990-08-07 Toshiyuki Nakajima Adsorptive oxidizing agent
US5278112A (en) * 1992-11-13 1994-01-11 Fred Klatte Chemically impregnated zeolite and method for chemically impregnating and coating zeolite

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2327048A (en) * 1997-07-09 1999-01-13 Secr Defence Adsorbent zeolite composition
GB2327048B (en) * 1997-07-09 2001-04-18 Secr Defence Adsorbent materials
WO2009029876A3 (en) * 2007-08-29 2009-04-23 Spectrasensors Inc Scrubber for reactive gasses
US7829046B2 (en) 2007-08-29 2010-11-09 Spectrasensors, Inc. Scrubber for reactive gases
AU2008292847B2 (en) * 2007-08-29 2012-04-12 Spectrasensors, Inc. Scrubber for reactive gasses
AU2008292847C1 (en) * 2007-08-29 2012-09-20 Spectrasensors, Inc. Scrubber for reactive gasses
CN110124748A (en) * 2019-03-12 2019-08-16 武汉工程大学 A kind of preparation method and applications of melamino-formaldehyde foam support nanometer titanium dioxide manganese material
CN110124748B (en) * 2019-03-12 2022-02-08 武汉工程大学 Preparation method and application of melamine formaldehyde foam loaded nano manganese dioxide material

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