Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/68—Treatment of water, waste water, or sewage by addition of specified substances, e.g. trace elements, for ameliorating potable water
  • C02F1/681—Treatment of water, waste water, or sewage by addition of specified substances, e.g. trace elements, for ameliorating potable water by addition of solid materials for removing an oily layer on water
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
  • B01D17/02—Separation of non-miscible liquids
  • B01D17/0202—Separation of non-miscible liquids by ab- or adsorption
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
  • C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them

Definitions

• This invention generally relates to a method for separating hydrophobic liquids from a substantially polar solution and is particularly applicable to removing liquid hydrocarbons from contaminated bodies of water.
• detergents are often used as a rapid and cost efficient way to disperse hydrophobic liquids in an aqueous environment.
• the detergents employed for such tasks often contain large amounts of phosphorus and are highly toxic to any aquatic life in the area. This is especially true when the contaminated body of water is a relatively closed system such as a lake or stream.
• the dispersion of the petroleum based products may result in increased toxicity over a far greater range than a relatively coherent slick.
• the formation of detergent-hydrocarbon complexes may actually facilitate the entry of the oil into the ecosystem and concentrate it in the flora and fauna of the stressed area.
• the burning or sinking of the hydrocarbon contaminant can also increase the toxic impact of the material on living organisms. Besides being difficult to start in an aquatic environment, burning leaves behind large amounts of unreacted residue. In addition, the uncontrolled combustion of the petroleum products is likely to result in substantial amounts of air pollution. Conversely, sinking the oil may result in its extended preservation. To sink the oil, a nucleating agent is introduced which produces tar like agglomerations of hydrocarbons that settle to the sea floor. Often the sea floor environment is poor in oxygen which retards the further degradation of the agglomerated hydrocarbon. If the oil sinks to a shallow, well oxygenated sea floor, fragile ecosystems such as reefs or kelp beds are likely to be irreparably damaged.
• Floating agglomerates allow the absorbent and associated hydrocarbon to be physically collected without picking up large volumes of water. Accordingly, effective absorbents should primarily absorb the contaminating hydrocarbon and not the water. In other words the best materials for these applications are both oleophilic and hydrophobic.
• absorbent materials which have been proposed for removing oil from water are wood chips, sawdust, certain clays, sulphur compounds, polymeric substances, cellulosic materials and many others.
• most of the absorbents used for such tasks are not salvageable or reusable and are intended to be destroyed or discarded along with the sorbed oil.
• one of the major drawbacks to the use of these materials is the prohibitive cost inherent in the preparation and utilization of a non- recyclable sorbent.
• non-recyclable absorbents are often limited by the properties of the material. For example certain absorbent materials have been reported to generate a charge when contacted with liquid hydrophobic compounds. The presence of these charged materials in the proximity of the combustible gases given off by volatile components of a spill can easily lead to catastrophic explosions. Further many absorbents are ineffective in extreme environmental conditions where the absorption rate and capacity of the material may be severely limited. Still other problems are brought about by the alteration of the absorbent under adverse conditions. Many materials possess limited hydrophobic characteristics or rapidly lose them when exposed to environmental conditions and preferably absorb water rather than the contaminating hydrocarbon. Even when the hydrocarbon is initially absorbed by the selected material, electrostatic interactions and environmental equilibration often allow the compounds to separate before the agglomerates can be collected and treated.
• hydrophobic adsorbent materials have been applied to bodies of water contaminated with hydrocarbons.
• Hydrophobic adsorbent materials differ from absorbent materials in that they distribute any associated liquid hydrocarbons in a film over the surface of the adsorbing particle.
• absorption involves the uptake of the liquid hydrocarbon into the body of the solid absorbent and is closely related to the porous structure of the absorbent material.
• adsorbent materials include plastic fibers, fine sands, clays, solid inorganic compounds, hydrophobic polymers and treated natural fibers.
• peat fibers, coconut husk, cotton fibers, jute, or wool may be coated with hydrophobic materials such as rubber or paraffin to provide a floating adsorbent.
• hydrophobic materials such as rubber or paraffin to provide a floating adsorbent.
• coated fiber adsorbents generally involve labor intensive fabrication techniques and relatively sophisticated production facilities. Further such adsorbents are usually non-recyclable, often making them prohibitively expensive to employ.
• other adsorbents such as hydrophobic polymers or plastic fibers may be too expensive for routine utilization and, if not easily biodegradable, may actually increase the adverse environmental impact.
• adsorbents such as inorganic materials, fine clay or sand often cause the floating oil to sink thereby rendering it unrecoverable.
• absorbents used for hydrocarbon removal suffer many of the same limitations as absorbents used for hydrocarbon removal. Among these limitations are ineffective hydrophobicity, limited retention times and lower efficiency under environmentally extreme conditions.
• activated carbon may provide an efficient adsorbent of liquid hydrocarbons in an aqueous environment.
• Activated carbon is the collective name for a group of porous carbons which usually contain small amounts of chemically bonded hydrogen and oxygen. In general they are manufactured either by the treatment of carbon with gases or by carbonization of carbonaceous materials with simultaneous activation by chemical treatment. The resultant carbon is usually in the form of small crystallites having dimensions considerably smaller than those observed in natural graphite. Adsorption properties of such carbon materials are generally related to the amount of inner surface area.
• U.S. Patent 3,891,574 discloses a sphere of carbon which consists of a porous shell enclosing an empty space.
• the activated carbon particle is obtained by coating a core material with the carbon and subsequently removing the core through thermal decomposition. This process reportedly forms a heliosphere having a bulk density of approximately 275 g/1 which has activated surfaces on both the interior and exterior surface.
• the disclosure teaches that the resultant material may be used to adsorb crude oil. Yet, in addition to being fairly heavy, the material has a relatively low loading capacity of approximately 1.5 times its weight after extended exposure to the oil.
• the process of the present invention which provides a method by which hydrophobic liquids may be separated and removed from polar solutions.
• the present invention is successful in overcoming the problems associated with the prior art methods for removing petroleum based products from aqueous solutions. While the disclosed process is useful for all such separations, it may advantageously be used to clean up and remove spills of liquid hydrocarbons such as oil from natural bodies of water in an ecologically sound and cost efficient manner. The materials used in the process may be recycled repeatedly thereby reducing the costs and the amount of material necessary for the effective separation of the contaminating liquid. Moreover, the hydrophobic liquid recovered using this method may be processed and employed as originally intended thus eliminating waste disposal problems.
• the present invention is directed to a process for removing a hydrophobic liquid from a liquid contaminated therewith, comprising: contacting a liquid contaminated with a hydrophobic liquid with a plurality of expanded graphite particles; forming an agglomerate resulting from adsorption of said hydrophobic liquid by said plurality of expanded graphite particles; and removing said agglomerate from the contaminated liquid.
• the process further comprises recovering the hydrophobic liquid and the expanded graphite particles from the agglomerates following their removal from the contaminated liquid.
• the present invention advantageously allows the recovery and eventual reuse of the hydrophobic liquid as well as the expanded graphite particles. This separation may be accomplished in a number of ways including the application of physical forces and the use of chemical agents. For instance, it is possible to remove the hydrophobic liquid from the agglomerates through the use of centrifugal force or mechanical pressing. Chemically, the use of selected surfactants will disrupt the adsorption forces between the hydrophobic liquid and the expanded graphite particles. Whichever method is chosen, the recovered hydrophobic liquid may be treated to remove any harmful impurities and used in its normal capacity.
• the expanded graphite particles can be reactivated through exposure to elevated temperatures. This application of heat, whether by direct combustion or other means, removes any residue of the hydrophobic liquid and regenerates the binding ability of the expanded graphite particles. It is important to note that the hydrophobic liquid does not have to be separated from the expanded graphite prior to its reactivation by heat. Regardless of whether the contaminating liquid is recovered for later use, the expanded graphite may be reactivated and reused.
• hydrophobic liquids which may be separated from polar solvents using the present invention include, but are not limited to, gasoline, kerosene, fuel oil, crude oil, paraffinic oils, xylenes, toluene, styrene, alkylbenzenes, naphthas, liquid organic polymers, vegetable oils and the like.
• the present invention is particularly useful for removing hydrophobic liquids from natural bodies of water
• the process may be practiced on any volume of fluid in any configuration.
• the fluid containing the hydrophobic liquid may be found in, but is not limited to, an area of ocean, bay, river, lake, a fluid ditch, holding tank, separation column, oil tanker compartment, oil transportation compartment, process stream, aquifer, or reservoir.
• the composition of the fluid separated from which the hydrophobic liquid is to be separated is irrelevant provided that it is substantially polar in nature.
• Exemplary fluids include fresh water as well as aqueous solutions such as brine or sea water.
• the expanded graphite particles used as the sorbent in the instant invention are highly porous in nature with a large amount of surface area per unit weight. These materials are well known and used in the manufacture of highly conductive ductile items, thermal insulation tape, compounds with a high specific surface, catalysts, packing, electrothermal elements, fillers and protective coverings. Expanded graphite particles are generally derived from oxidized forms of graphite through intercalation and thermal impact. During the production process, expanded graphite particles with various fill densities are derived depending on the degree of oxidation, the intercoolant used, and the physical parameters employed during the graphite expansion.
• the unexpanded graphite particles are placed into an acid solution containing a strong oxidizing agent such as potassium dichromate, nitric acid or ammonium persulfate (K 2 Cr 2 0 7 , HN0 3 , (NH 4 ) 2 S 2 0 8 ) .
• a strong oxidizing agent such as potassium dichromate, nitric acid or ammonium persulfate (K 2 Cr 2 0 7 , HN0 3 , (NH 4 ) 2 S 2 0 8 ) .
• K 2 Cr 2 0 7 , HN0 3 , (NH 4 ) 2 S 2 0 8 ammonium persulfate
• the resultant particles are hydrophobic in nature.
• the amount of expanded graphite applied to the contaminated area is between 0.1 % and 10 % of the weight of the hydrophobic liquid.
• the amount of particulate matter distributed depends on the exact bulk density of the expanded graphite, but is preferably on the order of 0.5% to 5% of the weight of the hydrophobic liquid.
• the expanded graphite particles are preferably in a dry, finely divided state which may be easily dispersed, they may be combined with a suitable non-reactive liquid carrier.
• the method used to apply the expanded graphite particles is not critical and may be accomplished using techniques well known in the art. For instance the dispersal of the expanded graphite in the contaminated area may be achieved simply by casting the particulate matter on the contaminated surface.
• the expanded graphite may be applied from a ship or aircraft, such as by using pressure guns, fans or spraying apparatus. Any method resulting in the substantial dispersion of the expanded graphite particles within the vicinity of the hydrophobic liquid can be used in the present invention.
• hydrophobic liquids such as oil floating on the surface of water they rapidly form cohesive, buoyant agglomerates.
• These semi-solid agglomerates generally have average dimensions on the order of 8 mm or larger and are sturdy enough to be collected using mechanical processes. That is, the mechanical strength of the cohesive agglomerates is such that they are generally not disrupted when subjected to mechanical collecting operations.
• mechanical collecting means include, but are not limited to, paddle collectors, water porous conveyor belts, screens, raking devices, floating fences and nets having mesh sizes less than the average diameter of the agglomerates being collected.
• Any means capable of separating the solid agglomerate from the polar liquid body is suitable for use in the present invention.
• the means used to collect the formed agglomerates may depend on their average size as well as other factors such as weather conditions or the condition of the body of water.
• Fig. 1 is a longitudinal sectional view of a multichamber furnace used to expand the substantially dried intercalated graphite particles.
• Fig. 2 is a photograph of unexpanded intercalated graphite particles magnified 1000X having a 50 ⁇ m scale bar at the bottom center.
• Fig. 3 is a photograph of expanded graphite particles magnified 1000X having a 50 ⁇ m scale bar at the bottom center.
• the process of the present invention is applicable to the removal of any hydrophobic liquid from a substantially polar environment.
• Use of expanded graphite particles in the disclosed process advantageously allows the recovery and subsequent treatment of the separated hydrophobic liquid as well as the regeneration of the graphite adsorbent.
• the present invention is highly suitable for separation or purification applications in manufacturing or laboratory settings.
• one of the most significant applications of the present invention is the removal of contaminating hydrocarbons from bodies of water. Consequently, while the following exemplary embodiments are discussed within such a framework, this should in no way limit the applications of the present invention.
• a process has been discovered for effectively and inexpensively separating hydrophobic liquids from a substantially polar medium.
• the process includes dispersing expanded graphite particles in the vicinity of a hydrophobic liquid; allowing the graphite particles to contact the hydrophobic liquid, thereby forming cohesive buoyant agglomerates; and physically collecting and removing the agglomerates from the polar medium.
• a hydrophobic liquid separation costs are dramatically lowered.
• the ability to easily and inexpensively regenerate the adsorption capacity of the expanded graphite particles allows their reuse, further lowering material costs.
• intercalation compounds are formed by inserting extra atoms or molecules into a host structure, without disrupting the chemical bonds of the host material.
• Carbon atoms in graphite are located at. the points of a hexagonal lattice and kept in place through relatively strong covalent bonds.
• the hexagonal lattices are displaced relative to each other and held in place by weaker Van Der Waals forces.
• the lower bond energy between the lattices and packing defects make the graphite particles susceptible to the insertion of foreign materials.
• graphite powder is heat treated in the presence of a gaseous or liquid agent. The pressure at which actual intercalation begins is dependent on the polarity and the structural disorder of the graphite. Expansion to well over 100 times their original particle size may be realized.
• the fabrication of the expanded graphite particles used in the present invention involves the thermal shock of previously formed intercalated graphite compounds.
• the process of oxidizing and expanding graphite has been previously described in the literature.
• the production of the desired intercalated graphite starts with highly ordered graphite flakes which having stack heights of at least 75 nm.
• Precursor flakes are usually treated with an oxidizing agent, such as mixtures of sulfuric acid and nitric acid to yield an intercalation compound.
• an oxidizing agent such as mixtures of sulfuric acid and nitric acid to yield an intercalation compound.
• Other oxidizing agents such as K 2 Cr 2 0 7 , Kmno 4 , or (NH 4 ) 2 S 2 0 8 may also be used.
• the volume of the oxidizing solution used is not critical as long as it is sufficient to suspend the particulate mass and ensure effective intercalation. Large industrial processing may require relatively greater volumes or extended mixing times.
• the temperature may be elevated between 50°C and 100°C to increase the rate of oxidation. After the desired intercalated graphite is formed, the particles are thoroughly rinsed in water and then rapidly heated to approximately 1000°C. This heating, which results in further expansion, is generally performed in an electrical furnace allowing substantial amounts of expanded particles to be produced.
• the degree of expansion is significantly influenced by the temperature of the heat transfer medium and the concentration of the intercalants added to the sulfuric acid. When ammonium persulfate is added to the sulfuric acid the degree of expansion drops in comparison to the use of potassium dichromate. Accordingly, oxidizing mixtures of sulfuric acid and potassium dichromate are preferred for large scale fabrication of expanded graphite because of the explosive character of mixtures of graphite with H 2 S0 4 and HN0 3 .
• the bulk densities of the expanded graphite may vary. Such properties are important in that they correspond to the adsorption capacity of the expanded graphite. More specifically the lower the bulk density, the higher the specific surface area will be, and, therefore, the higher the adsorption capacity for petroleum products. Moreover, at very low bulk densities of about 0.3 - 0.5 g/1 the critical wettability angle may reach 180 degrees, which is manifested as an enhancement of the hydrophobic properties of the material. Like other graphite compounds these expanded graphite particles are resistant to temperature, aging, and most corrosive media in addition to possessing a relatively low coefficient of friction of about 0.08-0.1.
• the following exemplary process may be used to produce expanded graphite particles suitable for use in the present invention.
• EXAMPLE I The starting material used for the production of these particles was large-flake graphite obtained from the Zaval'evskiy deposit located in Russia. After crushing, grinding and flotation beneficiation, a concentrate was obtained containing up to 10% gangue. From this precursor material various grades of graphite were produced differing only in their concentration of gangue. These include crucible graphite, pencil graphite, battery graphite, cast graphite, and scrap graphite. Tests have demonstrated that all graphites are oxidized identically and the surface of the expanded product changes little with the different graphite varieties.
• the expanded graphite obtained from crucible type graphite with an ash content of approximately 7% contained particles of measuring 0.2-1.0 mm and floccules measuring approximately 30-40 mm.
• the expanded material fabricated from scrap graphite had particles and floccules exhibiting roughly the same proportions.
• the degree of expansion, estimated based on the bulk density, reaches 270-290, which is explained not only by the expansion of the particles themselves, but also by the increasing porosity of the outer layer. Microscopic examination of the samples show that the surface of the tubes feature projections indicative of the convoluted macrostructure of the expanded graphite.
• Example II and the data shown in Table II indicate the impact of process parameters on the production of highly adsorptive graphite particles particularly useful in the present invention.
• the expansion of the intercalated graphite takes place in a multichamber furnace 12.
• Initially cold gas air, nitrogen
• the heated gas is then injected tangentially through a pipe 32 into a mixing chamber 16 having a protective casing and located at one end of the cylindrical chamber 18.
• Partially dried, oxidized graphite is simultaneously fed by a screw motor 14 into the mixing chamber 16 at rates determined by the size of the apparatus.
• the hot gas medium is mixed with the oxidized graphite in the mixing chamber 16 and the resulting downward flow is directed into a tube-like cavity of one or more silicon carbide heaters 20.
• the heaters 20 are insulated on their exterior 22 and run through the length of the cylindrical chamber 18. Within the heater cavity the gaseous suspension of intercalated graphite was rapidly heated to between 1350°C and 1500°C undergoing partial expansion. The mixture of hot gases and partially expanded graphite particles were then fed into a rarefaction chamber 24 adjacent to the cylindrical chamber 18 at the end opposite the mixing chamber 16. Here the graphite expands further due to the substantial pressure differential created by the 10-20 fold expansion of gas into the volume of the rarefaction chamber 24. The gaseous products were then removed through a lattice 26 and outlet port 34 while the expanded graphite is injected into a storage vessel 28.
• Expanded graphite with different bulk densities was obtained depending on the operating mode and the structural features of the unit.
• varying the pressure change due to the ratio of the inner diameter of the rarefaction chamber to the inner diameter of the heating cavity had a dramatic effect on the bulk density of the finished expanded graphite.
• the preferred bulk densities for adsorbing hydrophobic liquids range from approximately 0.3 g/1 to 2.0 g/1.
• Example II demonstrates that these processing parameters can be adjusted to consistently produce expanded graphite having bulk densities particularly suitable for use in the present invention. The results of varying these parameters are shown in Table II.
• Figs. 2 and 3 show that process described in Example II transformed intercalated graphite flakes into expanded graphite exhibiting a highly porous structure. Cursory observation shows the increased surface area and convoluted exterior of the expanded material in Fig. 3 contrast sharply with the smooth regular surface of the unexpanded graphite of Fig. 2. More specifically, Fig. 3 shows a sample of expanded graphite particles obtained using the procedure described in Example II while Fig. 2 shows the same sample prior to expansion. Both images have been magnified 1000X and scale bars are provided to give some idea of the size of the individual flakes.
• the expanded graphite may be stored in a dried state or formulated with a non-reactive carrier liquid.
• the storage and post production handling of the expanded graphite is dependant on the ultimate use of the material. For instance in large shipboard operations it may be more convenient to handle the carbon as a liquified slurry or suspension. Conversely, for small, immediate applications of the expanded particles it may be more convenient to directly apply substantially dry powdered material by hand.
• the method of application is not critical for the separation of the hydrophobic liquid from the polar medium and may be done in any convenient manner.
• the dispersement of the expanded graphite particles may be accomplished from land, the deck of a ship or from the air depending on the size and nature of the separation desired. For example, a large oil slick may be contained most efficiently by dispersing the expanded graphite over an extensive area from the air.
• the lightweight particulates may be dropped directly from the aircraft or mixed with a liquid carrier and applied using cropdusting techniques. Other mechanical distribution means such as commercially available spray guns or spreaders may also be used. For smaller bodies of water such as holding tanks or drainage ditches which are easily accessible and have a well defined area the application of the expanded graphite may be readily accomplished without mechanical assistance.
• Example III serves to further illustrate the highly beneficial characteristics of the present invention.
• the regeneration of the particles may be accomplished through the simple heating or combustion of the material in any suitable apparatus.
• Table III indicates that particles which had been loaded with hydrophobic material and regenerated ten times were as efficient in removing hydrocarbons from the water as unused particles. While the amount of hydrocarbon contamination was slightly higher on the tenth pass this was most likely due to the larger mesh size used to remove the agglomerates. This unexpected regeneration capability greatly reduces the amount of material necessary to remove a given amount of hydrophobic liquid with a corresponding reduction in cost.
• the amount of material required is already relatively low. More preferably the amount of expanded carbon dispersed will be less than 5% of the weight of the hydrophobic liquid.
• Example III obtained excellent results repeatedly using expanded graphite equivalent to 1.5% of the weight of the hydrophobic liquid. While slightly higher amounts may be necessary to obtain the same results under adverse conditions or when the bulk density of the expanded graphite is somewhat higher, the adsorptive capacity of the particles ensures that effective remediation may be accomplished using small amounts of material. This greatly simplifies the logistics and expenses involved in the removal of hydrophobic contaminants especially from relatively inaccessible areas.
• the removal of the hydrophobic liquid may easily be accomplished through the application of physical force or chemical compounds.
• the agglomerated material could be spun in an industrial centrifuge or mechanically pressed to separate the liquid hydrocarbon or adsorbed organic material.
• the agglomerated material could be exposed to a surfactant or detergent causing the release of the hydrophobic liquid by altering the surface properties of the expanded graphite particles.
• Both chemical or physical separation processes will provide relatively high recovery of the hydrophobic liquid.
• the portion recovered from the expanded graphite will be relatively free of contaminating polar material. This selective separation may be easily exploited for manufacturing processes or laboratory procedures. Additionally the recovery of the hydrophobic material will not interfere with the subsequent regeneration of the expanded carbon particles.
• Example III also illustrates the rapid formation of cohesive floating agglomerates composed of expanded graphite particles and the hydrophobic material.
• floating indicates that the agglomerates have a density less than the surrounding polar medium. For pure water this would translate to a density of less than one while in sea water it may be slightly higher.
• the agglomerates tend to form in a relatively short time following the contact of effective amounts of expanded graphite with the hydrophobic material. For instance the agglomerates were completely formed and of sufficient mechanical strength to remove after thirty seconds in Example III.
• the speed of agglomerate formation is highly dependant on the contact rate between the expanded carbon particles and the hydrophobic liquid.
• this contact rate depends on such factors as the efficiency of particle dispersion, degree of agitation, concentration of hydrophobic liquid and physical parameters such as temperature and medium composition.
• the efficiency of particle dispersion In open bodies of water the natural action of wind and waves will increase the agitation and contact rate up to a point. Beyond this the rough water may tend to interfere with the attractive forces of the materials and break up forming agglomerates.
• the temperature of the water or the presence of salt may effect surface properties of the hydrophobic liquid or carbon particles and alter the agglomerate formation time.
• the same parameters can also effect agglomerate size and cohesiveness.
• any agglomerates strong enough to be mechanically collected and separated from the surrounding liquid are suitable.
• the agglomerates attained an average size of 8 mm and were cohesive enough to collect using a mesh adsorbent trap.
• the increase in the mesh size of the adsorbent trap did little to reduce the effectiveness of the treatment and facilitated the collection of the agglomerates.
• the collection of the agglomerates from the surface of the polar liquid is preferably accomplished when the surrounding medium is allowed to drain away before the agglomerates are stored. Accordingly the preferred collecting means are porous such as screens, nets and the like. While mesh sizes less than 12 mm are preferred, the actual equipment used will depend on agglomerate dimensions and absolute volume.

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• 1992
  • 1992-10-14 RU RU92000506/26A patent/RU2050329C1/ru not_active IP Right Cessation
• 1993
  • 1993-10-04 CA CA 2147143 patent/CA2147143A1/en not_active Abandoned
  • 1993-10-04 EP EP93924292A patent/EP0664769A4/de not_active Withdrawn
  • 1993-10-04 WO PCT/US1993/009404 patent/WO1994008902A1/en not_active Application Discontinuation
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