US005221520A United States Patent (19) 11) Patent Number: 5,221,520 Cornwell (45. Date of Patent: Jun. 22, 1993

54 APPARATUS FOR TREATING INDOOR AIR 4,925,631 5/1990 Harwood, Jr. et al...... 55/387 X (75 Inventor: James H. Cornwell, Raleigh, N.C. Primary Examiner-Robert J. Warden o Assistant Examiner-E. Leigh Dawson

73) Assignee: Stils oy St. y stific Attorney, Agent, or Firm-White & Case (21) Appl. No.: 965,212 57) ABSTRACT (22 Filed: Oct. 23, 1992 Apparatus for purifying indoor air comprises a blower for circulating air through a duct and removing parti Related U.S. Application Data cles and neutralizing a number of harmful gases through 62)62 5Division of Ser. No. 766,713,' ' Sep.'P' 27,' '1991, Pat.' No' adrocarbons process of atmolecular ambient catalytic temperatures. cracking Preferably, of heavy hythe w w 1 was apparatus includes a series of treatment elements includ (51) Int. C...... A619/16 ing an ozone generator for producing a oxidator gas, a 52 U.S. C...... 422/122; 422/4; bio-mass collector, a filter coated with zeolite and sur 422/120, 55/387: 55/PIG. 30 face modified hopcalite for removal of CO and NO. (58) Field of Search ...... 422/122, 4, 120, 111; compounds, a filter coated with calcium carbonate for 55/DIG. 30,387 removing carbon dioxide and hydrohalic compounds, a 56 References Cited filter coated with zeolite for solvents such as MEK and adsorbing water, and one or more filters for removing U.S. PATENT DOCUMENTS particulates in the air stream. The filters thus remove 2: y 3. E. Jr. .. 35, s: particulates and neutralize a number of harmful gases 4,315,4,325,921 4/1982 AikenOurke et et al. al...... that may be present in indoor air.o 4,551.304 11/1985 Hölter et al...... 422/122 X 4,687,640 9/1987 Schillaci...... 422/120 3 Claims, 2 Drawing Sheets

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FFF 2 FG.2 5,221,520 1 2 tamination from outside the buildings was indicated by APPARATUS FOR TREATING INDOOR AIR 11%. Microbiological contamination was attributed to approximately 5% of the problems in these studies. 3% This application is a divisional of application Ser. No. of the cases were attributed to fabrics, wall treatments, 07/766,713, filed on Sep. 27, 1991, now U.S. Pat. No. formaldehyde emissions from wall treatments, hang 5,186,903. ings, carpets, materials, fiber materials, polyester, fab FIELD OF INVENTION rics, etc. Roughly 12% of the problems of the investiga The present invention relates to products for purify tion were undetermined. w ing indoor air. O Inadequate Ventilation BACKGROUND OF THE INVENTION In 52% of NIOSH investigations, the building venti A number of factors have contributed to the growing lation was determined to be inadequate. In evaluating problem of air contamination in commercial, industrial, building ventilation, ASHRAE standards are normally and residential buildings. For energy conservation, new 5. used for comparison. ASHRAE standard 62-1981 enti buildings are being built to be very tight, that is, to tled "Ventilation for Acceptable Indoor Air Quality", minimize infiltration of outside air into the building, and and ASHRAE standard 55-1981 entitled “Thermal En minimize the release of air from the building to the vironmental Conditions for Human Occupancy" are outside except as controlled by the building heating, both used for evaluation purposes. Some of the ventila ventilating, and air conditioning (HVAC) system. Addi 20 tion problems commonly encountered include an insuf. tionally, for energy conservation reasons, building own ficient supply of fresh outdoor air, poor air distribution ers often operate the HVAC systems in a manner that or mixing, which causes stratification, drafts, and pres will minimize the induction of fresh air in very hot and sure differentials between office space; temperature and very cold weather. Meanwhile, buildings house an in humidity extremes or fluctuations, which sometimes are creasing amount of equipment, furniture, and building 25 materials, as well as chemicals used to clean and main caused by poor air distribution or faulty thermostats: tain the building and its contents, which contaminate and air filtration problems caused by a faulty or no the air within the building. Insufficient replacement of maintenance ventilation systems. In many cases, the stale air with fresh air, combined with the release of ventilation problems are created or compounded by contaminants into the building air, results in what is certain energy conservation measures applied in the sometimes called the "tight building syndrome'. The operation of the ventilation system. These including air in buildings with "tight building syndrome' has been reducing or eliminating fresh outdoor air, reducing found to contain, among other substances, hydrocar infiltration and exfiltration, lowering thermostat set bons, both methane and non-methane, formaldehydes, tings in winter, raising them in summer, elimination of aldehydes, acrolein, nitrous oxide, carbon monoxide, 35 humidification systems; and early afternoon shutdown hydrogen sulfide, ammonia, and hydrogen cyanide. The with late morning start-up of emission systems. air frequently contains, as well, a high level of particu lates, e.g., mold spores, pollen, and dust, which serve as Inside Contamination vehicles to carry microbiological contaminants, as the Contamination generated by sources inside the office particulate filters commonly used in the HVAC systems space is a major problem identified in 17% of the inves are not very effective, and are often not properly main tigations. Copier machines, computers, and other office tained. equipment are often found to be a significant source of . NIOSH studies and investigations have been under indoor contamination, ranging from ozone to polymers, taken relative to indoor air quality. Investigations have acrolein, hydrogen cyanides, and materials from the been conducted in private and government sector office 45 inks and dyes used in the printing process. Examples of buildings, as well as in schools, colleges, and health care this type of problem include methyl alcohol from spirit facilities. The symptoms and health complaints reported duplicators, butyl methacrylate from signature ma by the workers and occupants of the buildings have chines, and ammonia and acetate from blueprint copi been diverse, and not specific to any particular medical ers. Other inside contamination encountered includes diagnosis or readily associated with a causative agent. A 50 typical spectrum of symptoms has included headaches, exposure to pesticides, such as chlordane, which were varying degrees of itching and burning eyes, irritation improperly applied, dermatitis from boiler additives, of the skin, including rashes, sinus problems, dry and such as diethyl ethanolamine, etc., improperly diluted irritated throats, and other respiratory irritations. The cleanly agents, such as rug shampoos, tobacco smoke, work place environment has been implicated, by virtue 55 and other gasses common to cafeterias and laboratories, of the fact that symptoms normally disappear on week and other sources which leak into other air handler ends, when people are away from the office. At times acS. these symptoms have been severe enough to result in Contaminants from inside or outside the office space, missed work, lost time, reassignment, and even termina or the building fabric, are essentially chemical contami tion. This has caused increased anxiety among workers, nants. Many times odors are associated with some of and often times has made the investigation in these areas these contaminants, which aid in source identification. difficult and frustrating. In most cases, these chemical contaminants have been Although some of these episodes may be multi-fac measured at levels above ambient (or normal) back torial, most of the studies have been classified by the ground but far below any existing occupational criteria. primary types of problems found. In recently reported 65 Even though these levels are below the evaluation crite investigations, inadequate ventilation was determined ria, they are still at sufficient levels to create at times to be the cause in 52% of the investigative cases. Con discomfort and disfunction for the employees and work tamination inside the building resulted in 17% . Con ers in these environments. 5,221,520 3 4. adverse health effects are experienced, or allow the Outside Contamination environment to become annoyingly uncomfortable to Contamination from sources outside the office space the office workers. is the major problem identified in 1% of the NIOSH While not previously mentioned, tobacco smoke is investigations. Problems due to motor vehicle exhaust, also a major contributor to indoor air quality problems. boiler gases, and previously exhausted air are essentially Tobacco smoke contains several hundred toxic sub caused by the re-entrainment of outside air. This is stances, the more important of which are carbon non usually the result of improperly locating exhaust and oxide, nitrogen dioxide, hydrogen cyanide, hydrocar intake vents and periodic changes in wind conditions. bons, ammonia, benzene, hydrogen sulfide, benso-A- Other outside contaminants include contaminants from O pyrene, tars, and nicotine. Tobacco smoke can irritate construction or renovation projects such as asphalt, the respiratory system and, in allergic and asthmatic solvents, and dusts; also gasoline fumes invading the persons, often results in wheezing, coughing, eye and basement and/or sewage systems can sometimes be a nasal irritation, sneezing, and other related sinus prob problem, and these are usually caused by gasoline leaks lems. People who wear contact lenses often complain of from ruptured, underground tanks at nearby service 5 burning, itching, and tearing eyes from cigarette smoke. stations. One of the most common sources of outside The ASHRAE ventilation guidelines for smoking areas contamination has been vehicle exhaust fumes from recognized the need to provide additional ventilation parking garages being drawn into building systems. (fresh outside air) to maintain air quality. Outside contaminations which are introduced into in Extensive research and study from various industrial door environments are the result of proximity to intake 20 and regulatory groups has transpired relative to in Wents. provement of indoor air quality. Recommended actions pertain to cleaning, maintenance, and control proce Microbiological Contamination dures, i.e., increased building ventilation and re-aeration 5% of NIOSH investigations have involved some or oxygenation. It is clear that these measures address type of microbiological contamination. Even though 25 only some of the causes of poor air, and would produce this is not a common cause of office problems, it can only moderate improvements in the quality of the air. result in a potentially severe health hazard known as To achieve even these modest improvements would be hypersensitivity pneumatosis. This respiratory problem very labor intensive, subject to production scheduling, can be caused by bacteria, fungi, protozoa, and micro and add to both overhead and operating costs. bial products that may originate from ventilation system 30 There are presently known various types of filters components. A similar condition, known as humidifier that may be used in HVAC recirculation systems to fever, most commonly reported in Europe, is also the remove particulate matter from polluted air streams. It result of microbiological contamination in systems. In would be desirable to remove harmful gaseous pollut the investigations, microbiological contamination has ants as well in indoor air treatment and other applica commonly resulted from water damage to carpets or 35 tions. It would also be desirable to provide a system for furnishings, or standing water inventilation systems and removal of such gaseous pollutants that operates at or cooling coil areas. near room temperature. Further, it would be desirable Although a variety of disorders, hypersensitivity, to provide a system that utilizes one or more filters, pneumatosis, humidifier fever, allergic rhinitis, conjevi containing catalyst materials, which could be used in a tis, can result from microbiological exposure, the room or building air recirculation system to remove NIOSH studies did not generally document these disor both harnful gaseous pollutants and particulates. ders on the basis of medical or epidemiological data. There are various types of known oxidation catalysts However, even if visible, microbial growth cannot be for treatment of organic compounds. Catalytic convert directly related to health complaints reported, it is a ers used in automobiles, for example, employ catalysts problem that needs to be addressed and corrected. 45 of noble metals for conversion of hydrocarbons, carbon monoxide, and nitrous oxide. Such catalysts are rela Building Fabric Contamination tively high in cost, and moreover have a relatively high Contamination from building material products is the light off temperature, and thus require that the passing major problem in 3% of the investigations. Formalde gas stream be maintained at a relatively high tempera hyde can offgas from ureaformaldehyde, foam insula 50 ture. Aside from the cost of the catalyst materials, the tion, particle board, and some glues and adhesives com elevated temperatures required make such catalysts monly used in construction. Building fabric problems unsuitable for most air treatment applications (e.g., in encountered include dermatitis resulting from fibrous air conditioning systems) and unsuitable for use on typi glass erosion in lined ventilating ducts, various organic cal filter materials. solvents from glues and adhesives, and acetic acid, used 55 There are several catalysts that are effective on cer as a curing agent in silicone caulking. w tain types of harmful gases at room temperature. These include zeolite, calcium carbonate, and hopcalite, Conclusion which is a copper/manganese compound. The major problems identified in indoor air quality Zeolite (cobalt oxide) is known to be an effective investigations can be placed into three general catego absorbent of solvents such as MEK, Toluene, etc. Cal ries, listed by decreasing frequency: cium carbonate is effective in absorption of carbon 1. inadequate ventilation dioxide (CO2). Hopcal is used in gas masks for convert 2. chemical contamination ing carbon monoxide into carbon dioxide (CO2). 3. microbiological contamination. While these catalysts would counteract a number of Inadequate ventilation is the single largest problem 65 the harmful gases which may be present in indoor air, seen in tight building syndromes. Although varied, they are not generally suitable for use in HVAC sys these ventilation problems can allow a build-up of any tems. Conventional hopcalite is moisture sensitive, and contaminants in the occupied space to the point that the moisture (humidity) normally present in indoor air 5,221,520 5 6 would eventually deactivate the catalytic properties of as an oxidation, reduction, reactant source. "Allotropic the material. Oxygen" O3 is well known as an effective oxidizer. Also, hopcalite is sold in granular pellets for use in a When O3 is generated on a continuous basis and in packed bed form. Zeolite is generally in 5-50 micron sufficient concentrations, it can be utilized in a titrated powder form. Calcium carbonate is also generally ac reaction, to oxidize and reduce heavy molecular weight quired in micron powder form. In HVAC systems, it hydrocarbons. Laboratory experiments have demon would be preferable to use these materials as filter coat strated the ability of O3 to oxidize compounds such as ings due to the pressure drop that can result from forc formaldehyde and ammonia as well as its ability to be ing a moving air stream through a packed bed. These used as an antimicrobial agent. One of the major prob materials are not generally useable as filter coatings, O lems of using O3 for this purpose is that when quantities however. Conventional hopcalite, for example, is not of ozone O3 sufficient to cause these reactions are gener suitable for wash coat formulations, in that its catalytic ated, the excess ozone that is generated becomes a properties are deactivated when mixed in a slurry. health hazard. Another, more recent, concern is radon. Radon is a The present invention includes apparatus for remov radioactive gas which seeps up through the ground and 15 ing hydrocarbon components, such as formaldehyde can become trapped inside of buildings. When allowed and ammonia, from an air stream utilizing a gas phase to accumulate and remain above certain levels, radon is oxidator such as ozone, but in which the ozone is con believed to create significant long term health risks. The tained inside the treatment apparatus rather than being EPA has set a limit of 4 pCi/1 (picoCuries per liter of discharged. The gas phase oxidator is generated in suffi air) as the maximum average annual level of radon gas 20 cient quantities to oxidize and reduce formaldehyde and to which persons should be exposed. Above this limit, ammonia catalytically. However, following this step remedial measures need to be taken. Presently, the any unreacted O3 reduction reactant is removed in a methods known for reducing indoor radon levels in second catalytic reaction, preferably using a surface volve entry prevention, such as sealing off basements, modified hopcalite, which is marketed by the assignee which is only partly effective; increasing ventilation 25 of the present application under the mark "ML-114''. A from outside air, which is undesirable from the stand simplified reaction scheme for formaldehyde is listed point of energy conservation; and removal of gas from below: the soil under and the building, which can be expensive. It would thus be desirable to develop other methods for reducing indoor radon levels. 30 SUMMARY OF THE INVENTION The present invention relates to a method and appara tus for the treatment of polluted indoor air. In particu 2O3 CATit lar, an air treatment system according to the present 35 invention includes one or more filters for removing The final reaction by-products of room temperature particulate matter, and catalyst materials for removing catalysis of formaldehyde are thus H2O and CO2. gaseous substances such as carbon monoxide and ozone The gas phase oxidator removes ammonia in a similar at room temperature. Preferably, the system combines manner, as explained by the following: the use of a gas phase oxidator and a solid phase cata lyst, and has the ability to bring about ambient tempera ture oxidation catalysis for the following hydrocarbon groups or formulas: methane hydrocarbons, non methane hydrocarbons, and halogenated hydrocarbons. NH; SH:o -- N2 A system according to the present invention, in addi 45 tion to removing particulates and harmful gases, prefer 2O3 itCAT s ably also reduces the levels of CO2, and increases the levels of O2, in the air stream. The ozone is used as a catalytic agent to oxidize and More particularly, apparatus according to the inven reduce the ammonia component and the modified hop tion includes a duct and a blower or other means for 50 calite ML-114 is used as a catalyst to decompose the circulating air through the duct. At least one filter is ozone. Utilizing this method of two stage catalytic re disposed in the duct, which filter is constituted prefera duction the by-products of these reactions are CO2 and bly by a fibrous filter material and is impregnated with H2O vapor with low level oxygen production. a catalyst compound of the type composed of at least In a preferred embodiment, a bio-mass collector is two mechanically mixed elements forming active cata 55 disposed downstream of the ozone generator. The bio lyst sites at the boundaries of such elements. Moreover, mass collector has a ceramic structure with a highly the catalyst material has been surface modified by irra amorphous surface designed to collect the bio-mass diation at an energy level sufficient to cause molecular residue of the destroyed microbes. dispersion of at least one of the elements and thereby Downstream of the bio-mass collector, a first filter, increase the number of active sites. coated with a combination of surface-modified hopca The filter preferably comprises a non-woven polyes lite and zeolite, is disposed downstream of the ozone ter material wash coated with the catalyst compound. generator and acts to remove the O3 and oxidize carbon The preferred catalyst compound comprises a surface monoxide (CO). A second filter element, coated with modified hopcalite. calcium carbonate, is disposed downstream of the hop In the preferred embodiment, the apparatus prefera 65 calite filter and acts to remove CO2 from the air stream. bly includes a plurality of other components disposed in A third filter element is coated with zeolite and dis the air passage. An ozone or "allotropic oxygen" gener posed downstream of the first filter element to remove ator is disposed in the path of incoming air, and serves halogenated hydrocarbons (hydrohalic acids), such as 5,221,520 7 8 HCl, and water vapor. A pre-filter thereafter removes An ozone generator 20 is disposed in the path of the larger particles in the air stream. Finally, an absolute incoming air, immediately downstream of the inlet vent filter, e.g. a HEPA filter, is disposed downstream of the 12, with a pair of diffusion plates 21, 22 disposed on other filters for removing fine particulates present in the either side of the generator. By way of example, ozone airstream. generator may be in the form of a glass tube surrounded Each of the catalyst-coated filter elements may be a by aluminum scrim. A capacitance field of sufficient fibrous filter material, e.g. non-woven polyester. Alter strength, e.g., 5000 volts, is established between the natively, one or more of the catalytic substances may be glass and aluminum, to set up a continuously discharg carried on a ceramic filter or metal substrate, which is ing capacitance field (without corona discharge). Ozone wash coated with the catalyst. In some cases it may be O generators as described above, or optionally also using desired to use the granulated material in a metal filter mercury, are well known and need not be described tray. In an exemplary embodiment, the hopcalite and further here. zeolite coated filters are fibrous filters wash coated with The diffusion plates 21, 22 act to create turbulence in the catalyst formulation, whereas the calcium carbonate the passing air stream, to enhance the mixing of ozone coated filter is a honeycomb ceramic. In addition to 15 with the polluted air. Each plate is provided with a their catalytic function, these filters also act as mechani plurality of holes, the number and size of which will cal filters to screen out larger particulates. depend upon the flow rate and acceptable pressure Apparatus according to the invention provides cata drop. Preferably, the diffusion plate 21, upstream of the lytic oxidation of hydrocarbons, carbon monoxide, and ozone generator 20, contains larger holes than the other harmful compounds, at room temperature. It pref. 20 downstream plate 22. By way of example, for flow rates erably functions as an air circulation system and utilizes in the range of about 1500-2000 cfm, plate 21 may be replaceable filter cartridges which can be readily re given holes of inch, whereas plate 22 may be given moved from the apparatus and replaced. holes of inch diameter. A filter material according to the invention is prefera Downstream of the ozone generator 20, a plurality of bly formed by grinding the catalyst to a predetermined 25 filter elements 24, 26, 28, 30, 32, 34 are disposed in the particle size, suspending the catalyst in a wash coat path of the moving air. Filter 24 is a bio-mass collector, formulation, and applying the wash coat formulation to for example a 400 cells per inch expanded ceramic foam the surface of a non-woven polyester carrier. Various cordierite of a known type. The known cordierite is methods can be used to apply the formulation, such as preferably etched with ascetic acid to enhance its ab immersion and spraying. Alternatively, surface modi 30 sorption capability. fied catalyst may be applied by impregnating the carrier Filter 26 is preferably a non-woven polyester fibrous with a binder containing a catalyst dispersion. filter (45% ASHRAE filter) which is surface coated It has been found that, when used in environments with a combination of hopcalite (copper manganese), containing accumulations of radon gas, the present ap 35 that has been surface modified as described below, and paratus can produce significant reductions in the level zeolite (cobalt oxide). Filter 28 is preferably a honey of the gas, in particular the harmful radon daughters. comb ceramic which has a coating of calcium carbon UV radiation emitted by the ozone generator in the ate. Filter 30 is preferably also a non-woven polyester present apparatus has the effect of accelerating the rate filter material (65% ASHRAE filter), which is surface of decay of radon or its daughters which are entrained coated with zeolite. Filter 32 is a mechanical pre-filter, in the air stream passing through the unit. As a result, which may be of any known suitable type, for screening radon daughters are converted to their ultimate decay larger particles. Finally, filter 34 is preferably a scrub product, lead 206. In tests of the apparatus in the base ber filter, e.g., a HEPA filter, for removing fine air- . ment of a single family home experiencing relatively borne particulates. high levels of radon concentration, a unit according to 45 Preferably, the filter materials in elements 24-34 are the invention achieved an 89% reduction in the average carried in cartridges or other such frames, which side radon daughter concentration. Preferably, for such into receptacles in the apparatus housing, so that they applications an additional filter is provided in the unit, can periodically be removed and replaced. Because the prior to the HEPA filter, for collecting the decay prod order of catalysis will affect the operations of the appa ucts of radon, i.e., lead 206. This filter may be in the 50 ratus, it is preferable that the respective filter cartridges form of alumina beads which are soaked in a 2-5% and the receptacles be designed so that a respective solution of acetic acid. cartridge is inserted in the proper location. For a better understanding of the invention, reference In operation, air is drawn into the inlet vent 12 by is made to the following detailed description of the blower 14. Hydrocarbons are removed in a two step preferred embodiments, taken in conjunction with the 55 process. First, the air is brought into contact with ozone drawings accompanying the application. generated by the ozone generator 20. Ozone is gener ated at a sufficient rate to set up a spontaneous titrated BRIEF DESCRIPTION OF THE DRAWINGS oxidation reduction reaction. By way of example, in the FIG. 1 is a schematic view of an apparatus according case of flow rates on the order of 1500-2000 cfm, the to the preferred embodiment of the invention; and 60 allotropic oxygen generator continuously produces FIG. 2 is a schematic view of a modified apparatus. 4.187 grams per hour of O3. Diffuser 21 acts to create sufficient turbulence to ensure that the oxygen is evenly DETALED DESCRIPTION OF THE mixed in the air stream. As a result, hydrocarbons (am PREFERRED EMBODIMENTS monia and formaldehyde) are reduced to water (H2O) Referring to FIG. 1, an air cleaning system includes a 65 and carbon dioxide (CO2). At the same time, microbio housing 10 with inlet vents 12 and a blower 14 having logical contaminants, bacteria, microbes, and items such an outlet 16 for discharging air. An interior duct pas as mold are also instantly destroyed by contact with the sage 18 connects the inlet vents 12 and blower 14. allotropic oxygen. 5,221,520 10 The airstream then enters the bio-mass collector 24, calite/lithium), e.g., in an amount of approximately 3% containing a highly amorphous surface, which collects by weight (relative to the weight of the hopcalite), in the bio-mass residue of the destroyed microbes. order to control the rate of the forward reaction of the The air, now free of high and low molecular weight exotherm. Lanthanum may also be added in a fractional hydrocarbons, but still containing excess ozone, enters aOt. filter 26, which contains a catalyst destructive to ozone Processes for forming a non-woven polyester filter (e.g., surface modified hopcalite and zeolite), thus elimi material impregnated with a hopcalite catalyst will now nating it. Filter 26 also acts to convert carbon monoxide be described. to carbon dioxide. The airstream, now containing the by-products of the 10 Catalyst Chemical Composition prior reactions, including O2, CO2 and H2O, passes In a preferred embodiment, catalytic impregnation is through filter 28, which is coated with calcium carbon effected using a modified hopcalite Type 21215 material ate and thereby absorbs CO2 and captures H2O. in a low temperature wash coat application. In the case Next, the air passes through filter 30 containing zeo of filter 26, the hopicalite is combined with zeolite. The lite, which acts to remove solvent vapors and water. 15 hopcalite is surface-modified as described above, Filter 32 is a 65% ASHRAE particle filter, which through an electrochemical plasma activation process. removes larger particles from the airstream. Finally, a The fractions of the metal oxides in this outer coating HEPA filter 34 removes small particles, down to about layer are approximately as follows: manganese dioxide 0.3 micron in size. The purified air is then exhausted (0.75); copper (II) oxide (0.15); and cobalt (II & III) through outlet 16. 20 oxide (0.10). The outer coating layer is applied in an The apparatus according to FIG. 2 is the same as that amount such that the outer coating layer constitutes shown in FIG. 1, except that it contains a lead trapping approximately 30% by weight of the total weight of the filter 31 upstream of the HEPA filter 34. As previously discussed, the apparatus according to the present inven catalyst and support medium (e.g., non-woven fiber). tion has the effect of acting on radon daughters, to 25 Catalyst Wash Coat Formulation accelerate its decay into lead. In certain applications, There are a number of formulations and processes therefore, i.e., where the air to be treated contains any that may be used to provide sufficient catalytic support significant amount of radon, elemental lead can be pro requirements. The preferred approach is to first coat the duced during the operation of the air treatment appara polyester non-woven substrate with an alumina wash tus. The purpose of filter 31 is to remove the lead from 30 coat in an aqueous salt solution. Then, using a slurry of the air stream, and at the same time do so before it finely ground hopcalite (5-20 microns), mixed with the reaches the HEPA filter 34, since it would tend to clog cobalt (II & III) oxide, and an appropriate binder, a such filter. thick layer is deposited on the media. After the wash Surface modified hopcalite is marketed by the North coat is applied to the substrate, the catalytic coated Carolina Center For Scientific Research, 2000 Aerial 35 substrate is dipped in a dilute solution of ethyl alcohol Center Parkway, Suite 115, Morrisville, N.C. 27560. It and water containing 5% by weight chloroplantic acid. is prepared starting with conventional hopcalite, which The substrate is then removed and dried in air at is sold by the Callery Chemical Companies, Callery, Pa. 150-200 degrees Fahrenheit, and then heated in a The hopicalite is subjected to a chemical plasma reaction 300-350 degrees Fahrenheit oven for at least 5-7 min process of sufficient field strength to cause sputtering utes. Preferably, the carrier temperature should not of-the copper, which process is described more fully in exceed 300 degrees Fahrenheit. The process of deposit U.S. application Ser. No. 07/766,713, U.S. Pat. No. ing the modified hopcalite is repeated until a level of 5, 186,903 filed concurrently herewith, the relevant dis 30% by weight of wash coat has been reach. It should closure of which is incorporated by reference herein. be noted that the copper manganese, or hopcalite, wash Hopcalite which has been surface modified in such a 45 coating deposition process can be substituted by either a manner (which is referred to throughout this specifica spraying operation or a dip-coating operation. tion as "surface modified hopcalite') is converted to an More particularly, in the preferred approach, hopca MnO6 catalyst and has a marked increase in the num lite catalyst type 21215, available from Callery Chemi ber of active catalytic sites. Not only does such a mate cal Company in Callery, Pa., is ground in water to a rial possess characteristically improve catalytic proper SO powder form having solder-mean diameter of between ties, but unlike conventional hopcalite it is significantly 2 and 4 microns and irradiated. A typical slurry compo more impervious to moisture and may be utilized in sition using the catalytic powder is listed below. processes such as wash coating without losing its cata lytic effectiveness. Horror-remainiana-a- To further increase the moisture resistance of the 55 Catalyst 21215 powder 100 parts by weight Kelzan 0.2 parts by weight modified hopcalite, lithium nitrate and/or lithium hy Binder 6 parts by weight droxide is added to the hopcalite. By way of example, Cobalt II and nitrate hexahydrate 10 parts by weight lithium may be added to the hopcalite in an amount of Deionized water 55 parts by weight approximately 15% prior to irradiation. When air flow, r acetic acid 75 parts by weight and particularly moist or damp air, is directed over the 60 -msm-reamineralaureau-allele catalytic surface, the moisture and carbon dioxide react exothermally with the lithium, producing localized The binders can be selected from, but not limited to, heat. This surface heat acts to keep the catalyst dried a silicon resin solvent, a monobasic phosphate or a col out and impervious to the moisture contained in the air loidal silica material. The preferred binder is one that stream. Because the heat is localized, it is desirable to 65 requires a processing temperature of less than 300 de ensure a homogeneous distribution of the lithium grees Fahrenheit. throughout the catalyst. Preferably also, yttrium is The slurry is deposited onto the non-woven material added to the slurry (i.e., after irradiation of the hop by dipping and air drying at 100-120 degrees Fahren 5,221,520 11 12 heit, until a 30% by weight of the 21215 catalyst coat is be applied in a slurry similar to that proposed earlier for achieved (i.e., the coating constitutes 30% of the total the 21215 mixture. weight of the catalyst and non-woven material sub Another method by which the catalytic material can strate). Other slurry compositions can be substituted, be applied onto the non-woven media is by first spray providing an adherent 30% by weight of the catalyst ing a tackifier coat of a variety of adhesives onto the coating to be deposited. In addition, a 4% by weight of non-woven media, and then applying the catalytic ma the cobalt II & III oxide is applied as part of the coating. terial in a granular, or pelletized, form. This can be provided as a solution, as listed in the table The foregoing examples describe wash coat formula above, or it can be added to the slurry in a powder form. tions for applying a hopcalite/zeolite mixture to a non Once coated, the non-woven media is cured in a gas O woven fibrous carrier. In place of the hopicalite-zeolite fired or other-heated oven. It may be necessary to fire coating on filter 26, it is possible to use hopcalite alone. the coating after each dipping operation to ensure the The same formulations may be utilized to apply hopca coating does not spall. lite alone to filter 26, to apply hopcalite containing In an alternative approach, the non-woven material is lithium and yttrium (with or without zeolite) to filter 26, soaked in a salt solution containing the respective met 15 to apply zeolite to filter 30, and to wash coat calcium als, and then fired to convert the deposited salts to the carbonate onto ceramic filter 28. corresponding oxides. Prior to soaking the non-woven In use, the dwell time through the catalytic filter is to substrate in the metal salt solution referred to above, the be within the range of 90-120 milliseconds. It has been pieces are soaked in a saturated solution of ammonia and found to be important to provide sufficient dwell time in water for approximately 5-15 minutes, then damp dried 20 order to promote mass transfer and catalytic oxidation in air at room temperature. Following pre-treatment of of compounds such as carbon monoxide. Longer dwell the non-woven carriers, the non-woven carriers are times than the minimums above, are, of course, required soaked for at least a 5 minute period in the salt solution, for a larger volumetric air flow rate. This undesirably then air dried at 100-120 degrees Fahrenheit. When the 25 increases the size of the apparatus. On the other hand, soaking and the drying are completed, the non-woven larger-than-required catalytic surface areas will have media is heated to approximately 280-300 degrees Fahr longer life between service and replacement. The par enheit in a reducing atmosphere until all the salts have ticulate filter, which is also impregnated with the cata decomposed. A change in weight does not occur. lyst, is comprised of a polyester non-woven media in A preferred solution for soaking the substrate is as 30 ranges of 4.5 denier up to 200 denier. The purpose of the follows: deionized water or acetic acid, 100 parts by dual catalytic infiltration system is to provide particu weight; manganese II and nitrate X hydrate, 50 parts by late removal efficiencies in the range of 40-65%; at the weight; copper II nitrate trihydrate, 50 parts by weight; same time, provide a high efficiency (60-85%) removal and zinc nitrate hexahydrate, 30 parts by weight. of carbon monoxide as a result of the copper manganese After the non-woven media, impregnated by the cata 35 impregnation. The service life of the catalytic filter is lyst, is soaked for at least 5-15 minutes, and air dried at determined by the clogging or particulate capture rate 100-120 degrees Fahrenheit, the substrates are heated in of the material. a reducing atmosphere to a sufficient temperature and The amount of catalyst and the type of binder used for a sufficient time to allow the decomposition of the for an application depends upon several factors. How salts. The process of soaking in the ammonia solution, these are selected can be described generally with refer and then in the above salt solution, followed by drying, ence to the catalytic mechanisms that occur in the reac is repeated as necessary, in order to obtain the required tion process. 30% by weight (the weight percent is the total catalyst The behavior of a gas-phase heterogeneous catalyst and support). This can also be accomplished by increas in an operating environment is influenced by three ing the load factors and modifying the wash coat formu 45 transport phenomena, which will be described with lation. This can be accomplished by soaking the carrier reference to a catalyst bed model. As the gas, or con in the solution given below: taminant passes through the interstices of the catalyst granulated bed, the gas flows around the exterior of the deionized water 100 parts by weight 50 catalyst pellet. If a reaction ensues, a concentration manganese II and 50 parts by weight gradient, and possibly a temperature gradient, Will nitrate X hydrate develop between the inlet and outlet of the control copper II nitrate trihydrate 50 parts by weight device, or filter media substrate. This is called axial zinc nitrate hexahydrate 30 parts by weight gradient. Also, concentrations in temperature gradients 55 can arise between the center of the substrate and the After soaking the substrate in the solution, for 5-15 walls of the substrate, which is known as a radial gradi minutes, the substrate is removed and dried in air at ent. These gradients will, in turn, generate inductive approximately 110 degrees Fahrenheit. When dry the and diffusive heat and mass transfer phenomena, re substrate is purged, then heated to 280-300 degrees ferred to as interreactor transport. Fahrenheit in a reducing atmosphere. The substrate is Because the flow rate at the surface of the catalyst maintained at temperature in the reducing atmosphere pellet is zero, a thin stagnant film will surround the for a sufficient time and to allow the salts to decompose. pellet or granule. The chemical reaction takes place The process of soaking, drying, and firing is repeated within the pellet. There will be a concentration, and until between 10-15% by weight of the support has possibly a temperature gradient, between the pellet and been deposited. An alternative process for the mixture 65 the flowing gas. The gradient crosses the boundary of copper manganese and zinc oxide can be applied as a layer between the pellet and the gas bulk. Heat and mass slurry to the substrate carrier. The oxides in the ratio of transfer across this boundary layer is called interphase 10 parts of copper II oxide to 6 parts of zinc oxide can transport. 5,221,520 13 14 In addition, if a chemical reaction occurs, heat and walls before being released. Knudsen's Diffusion has mass transfer will take place inside the porous pellet. been correlated in the following equation: This is known as intra-pellet transport. The following description of these phenomena begin with the interior of the catalyst and range outward. where Epis activation energy; Pis pressure. Pore diam Intra-pellet regime eters and gas concentrations that fall between those of Mass transport resistance inside a porous catalyst Fick's diffusion and Knudsen's Diffusion, i.e. a transi reduces the overall reaction rate with respect to the tion region, may exist because the inverse of the diffu intrinsic rate. Intra-pellet heat transport resistance in 10 sion constant is analogous to the resistance to the diffu creases the overall rate of exothermic reactions and sion. The two modes of the diffusion can be combined in increases the rate of endothermic reactions. However, the transition region to an effective diffusivity (D) for the physical characteristics of the catalyst are such that, a component. in actual service, the intra-pellet concentration gradient is far more influential than the intra-pellet temperature 15 h/Defii-l/Dk + 1/Dni d gradient. where Defi is the effective diffusivity of component i in Pore Diffusion a multi-component mixture (cm/s); Dk is the Knudsen diffusion coefficient; and Dni is the diffusivity of com Porous catalysts can provide up to hundreds of ponent i in a multicomponent mixture. square meters of reactive surface per gram of pellet. 20 Reactants diffuse through the pores to the active sur Temperature Gradient face and reactions occur. Products then diffuse out Intra-pellet heat conduction will be slow compared through the pores to the surface of the pellet. Gener to the rate of heat generated by the reaction (exother ally, the minute, irregularly shaped pores branch and 25 mic) and can create a temperature gradient in a catalyst connect in a fairly random manner. Because pore geom pellet. The gradient, if significant, can affect reaction etry is not well understood or classified, its character rate via the following development: ization remains partly empirical. Magnitude of this internal temperature gradient is If the mean free path of the diffusing molecule is examined using the fast, highly exothermic SO2 oxida much smaller than the pore diameter, i.e., the molecules 30 tion reaction as an example (example only). The maxi collide with each other more frequently than with the mum temperature gradient possible within the pellet has pore walls, the diffusive transport mode is called Fick's been estimated as follows: diffusion. For binary gas mixtures inside relatively large pores, the molar flux of binary gas mixture in pores of a cata 35 lyst (Ji, the rate of diffusion in the direction "z") is where TM is the maximum catalyst temperature; T is proportional to the concentration gradient in the direc the catalyst surface temperature; AH is the heat of reac tion of diffusion. The proportional concentration gradi tion; Defi is the effective diffusivity of component i in a ent is: multicomponent mixture; k is the thermal conductivity of the catalyst pellet; and Ci is the concentration gradi ent of component i at the catalyst surface. Boundary conditions pertinent to the intra-pellet where Dis Fick's Binary Diffusion Coefficient of com mass and heat transfer are: ponent "i" and component "j"; Ci is the concentration of component i at the catalyst surface (g-moles/cm), 45 kg(Ci-Ci)= Deff (dCi/dz);-pas DefiC"/d and z is distance in the direction of diffusion. Fick's Binary Diffusion Coefficient, in cm2/second, is corre lated at: where kg is the gas mass-transfer coefficient; Ci is the concentration of component i at the catalyst surface; D 0.001858 3/2(M + M)/MFM)1/2 C'i is the concentration of component i at the catalyst = -Pond H surface; hg is the gas heat transfer coefficient; T is the bulk gas temperature; Tsis the catalyst surface tempera where Mi and Mare the molecular weights of compo ture; and ks is the thermal conductivity of the catalyst nents i (manganese) and j (copper), respectively, the 55 pellet. constant 0001858 is a diffusive constant based upon The calculation of Fick's coefficient, the proportional temperature, P is total pressure in atmospheres, or is concentration gradient (Knudsen's Diffusion), and the the square of the constant force applied to the catalyst temperature gradient, will indicate the expected dwell surface, and Dis the integral rate of collision of the gas time and capture rate, Depending upon the particular molecules in contact with the catalyst surface. rate of air flow and concentration of contaminant gases If the mean free path of the diffusing molecules is to be neutralized, the amount of desired surface area of greater than pore diameter, i.e. relatively low gas den catalyst can be determined. sity, small pore size causes the molecules to bump into First the mass transport resistance is determined for the pore walls more frequently than into each other. surface modified hopicalite, as well as hopcalite in The transport is known as Knudsen's Diffusion. The 65 which lithium has been added. This can be accom diffusing molecules are adsorbed and desorbed in a plished using Fick's diffusion equation (J). After yt random direction, i.e. the molecules do not bounce off trium has been added, the total thermal conductivity the walls like billiard balls, but momentarily stick to the (Knudsen's diffusion) of the catalyst mix can be deter 5,221,520 15 16 mined using Knudsen's diffusion equation. Then, the trium thus acts as a thermal limit switch to maintain the catalyst volume (Vibed) can be determined using the exothermic reaction and at the same time not allow a following equation: thermal runaway condition to develop which would decomose the catalyst. The result is a very low tempera Ved=60 QCOM/SV ture oxidation reaction and a very effective low temper ature catalyst. where QCOM is the flow rate of the gas stream (standard In a preferred embodiment, lithium in an amount of cubic feet per minute (SCFM)) and SV is the space 15% by weight of the modified hopcalite is employed, velocity of the gas as it travels through the catalyst and added to the hopcalite prior to irradiation. The carrier (which is a function of the open area of the O catalyst bed, Ji and Knudsen's diffusion). amount of lithium may adjusted dependent upon the For example, in a typical system calculation of the calculated values of Fick's coefficient and the propor mass transport resistance and thermal conductivity may tional concentration gradient, Knudsen's Diffusion, and indicate a desirable maximum space velocity of 10,000 the temperature gradient. Yttrium in a ratio of 3% by cubic feet/hour, in order to allow sufficient (minimum) 5 weight of the modified hopcalite and lithium is prefera dwell time for optimum conversion. If the design flow bly used and adjusted as desired. rate of the gas is 2500 CFM, then the catalyst area The foregoing represents a description of the pre would equal 15 cubic feet. If a smaller amount of cata ferred embodiments of the invention. Variations and lyst were to be used, for example, 5 cubic feet, the ve modifications of the foregoing may be employed with locity over the catalyst surface would increase to 30,000 20 out departing from the inventive concepts disclosed CFH and the removal efficiency would decrease typi herein. For example, an additional hopcalite coated cally from about 99% to less than 90%. filter may be utilized, downstream of the hopcalite-zeo The dwell time and capture rate are increased by the lite filter to act as a last stage scrubber for CO and addition of lithium, in the form of lithium nitrate or hydrohalic compounds such as HCl. In addition, while lithium hydroxide, which will affect the mass transport 25 the filter material for removing lead was described as resistance of the catalyst surface. It has been found that operating in an air stream, a similar filter, i.e., of alumina lithium reacts with carbon dioxide and water and heats beads etched with acetic acid, may also be used in water the catalyst. This has the effect of heating the catalyst to remove lead. Also, a surface modified catalyst ac toward the light off temperature, which will increase cording to the invention may be applied to an appropri the catalytic action, and also keeping the copper-man 30 ate carrier for use in water, and has proven effective in ganese active sites dry. removing hydrogen peroxide. All such modifications Similarly, the capture rate may be slowed down by and variations are intended to be within the scope of the the addition of yttrium, which affects the pore diffusion, invention as defined in the following claims. to the wash coating formulation. I claim: More particularly, the addition of lithium to the cata 35 1. A method of molecular catalytic cracking of heavy lyst enhances and improves the mass transfer resistance hydrocarbons at ambient temperatures, comprising the and thus the binary diffusion coefficient of the catalyst steps of introducing ozone into an air stream for react material (which can be calculated by Fick's equation). ing with ammonia and formaldehyde; and directing the This is due to the fact that lithium gives off a high exo airstream and ozone through a catalyst compound com therm when in contact with carbon dioxide and water posed of at least two mechanically mixed Periodic table vapors. This exotherm serves to surface heat the cata elements of the type forming active catalyst sites at the lyst heat mass transfer. When an emission component boundaries of such Periodic table elements, in which the such as acetone is catalytically oxidized, the by prod catalyst compound has been surface modified by irradi ucts are CO2 and H2O which, in turn, contact the lith ation at an energy level sufficient to cause molecular ium and generate additional exothermic heat. 45 dispersion of at least one of the Periodic table elements The exothermic reaction of lithium tends to increase and increase the number of active sites. temperature at the reaction sites. The addition of yt 2. A method according to claim 1, wherein said cata trium, which turns into a superconductor at elevated lyst compound is surface coated on a filter material. temperatures, acts to thermally stabilize the carrier and 3. A method according to claim 2, wherein said cata prevent excess build up of heat, which could otherwise 50 lyst compound comprises hopcalite. cause thermal decomposition of the catalyst. The yt

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