(12) United States Patent
`Tapscott
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 6,300,378 B1
`Oct. 9, 2001
`
`US006300378B1
`
`(54) TROPODEGRADABLE BROMINE-
`CONTAINING HALOCARBON ADDITIVES
`TO DECREASE FLAMMABILITY OF
`REFRIGERANTS FOAM BLOWING AGENTS
`SOLVENTS AEROSOL PROPELLANTS AND
`STERILANTS
`
`(75)
`
`Inventor: Robert E. Tapscott, Albuquerque, NM
`(US)
`
`(73) Assignee: University of New Mexico
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/049,787
`
`(22)
`
`Filed:
`
`Mar. 27, 1998
`
`FOREIGN PATENT DOCUMENTS
`
`1 112 051
`1 106 737
`1 195 279
`0286610
`0453949
`0778085
`1252822
`
`8/1961 (DE).
`12/1961 (DE).
`6/1965 (DE).
`12/1988 (EP).
`10/1991 (EP).
`6/1997 (EP).
`11/1971 (GB).
`OTHER PUBLICATIONS
`
`Ullman’s Encyclopedia of Industrial Chem, 5”“ Ed. (1989),
`vol. 413, 447-457.
`Patent Abstracts of Japan entry for Japanese Laid Open
`Patent Publication No. 58—180452 to Kawasaki KK dated
`Oct. 21, 1983.
`Patent Abstracts of Japan entry for Japanese Laid Open
`Patent Publication No. 59-51235 to Kawasaki KK dated
`Mar. 24, 1984.
`
`Related U.S. Application Data
`
`* cited by examiner
`
`(63)
`
`(30)
`
`Continuati0n—in—part of application No. 08/720,112, filed on
`Sep. 27, 1996, now Pat. No. 5,900,185.
`
`Foreign Application Priority Data
`
`Primary Examiner—S. Mark Clardy
`Assistant Examiner—Alton Pryor
`(74) Attorney, Agent, or Firm—Robert W. Becker &
`Associates
`
`Mar. 28, 1997
`
`(EP)
`
`............................................... .. 97870044
`
`(57)
`
`ABSTRACT
`
`A set of tropodegradable chemical additives to decrease the
`flammability of normally flammable refrigerants,
`foam
`blowing agents, cleaning solvents, aerosol propellants, and
`sterilants is disclosed. The additives are characterized by
`high efficiency and short atmospheric lifetimes. The latter
`property is essential and results in a low ozone depletion
`potential (ODP) and a low global warming potential (GWP).
`The additives are bromine-containing alkenes, bromine-
`containing alcohols, bromine-containing ethers with at least
`one hydrogen atom (preferably adjacent
`to the oxygen
`atom), bromine-containing amines with at least one hydro-
`gen atom (preferably adjacent
`to the nitrogen atom),
`bromine-containing carbonyl compounds, bromine-
`containing aromatics, and/or bromine-containing non-
`fluorinated alkanes.
`
`16 Claims, 1 Drawing Sheet
`
`(51)
`
`Int. Cl.7 ............................ .. C09K 5/00; A01N 29/00
`
`(52) U.S. Cl.
`
`.............................. .. 514/743; 252/67; 252/68
`
`(58) Field of Search ................................... .. 514/102, 743,
`514/744, 746, 747, 751, 757, 760, 761;
`252/67, 68
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`....................... .. 23/207
`12/1960 Darbee et al.
`2,966,397
`.... .. 423/588
`12/1975 Kirchner et al.
`3,923,967
`. . . . .. 423/588
`12/1976 Vaughan . . . . . . . . . .
`3,998,937
`4,238,551 * 12/1980 Lal et al.
`........................... .. 428/660
`4,374,820
`2/1983 Guenter .............................. .. 423/588
`5,399,333
`3/1995 Kato et al.
`......................... .. 423/588
`
`
`
`Page 1 of 9
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`Arkema Exhibit 1017
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`Arkema Exhibit 1017
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`Page 1 of 9
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`

`
`U.S. Patent
`
`Oct. 9, 2001
`
`US 6,300,378 B1
`
`Evaporator \
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`Low-Pressure
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`Side
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` ][
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`V 4
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`\- Expansion
`Valve
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`/ Condenser
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`High-Pressure
`Side
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`US 6,300,378 B1
`
`1
`TROPODEGRADABLE BROMINE-
`CONTAINING HALOCARBON ADDITIVES
`TO DECREASE FLAMMABILITY OF
`REFRIGERANTS FOAM BLOWING AGENTS
`SOLVENTS AEROSOL PROPELLANTS AND
`STERILANTS
`
`This appln is a CIP of Ser. No. 08/720,112 filed Sep. 27,
`1996 now U.S. Pat. No. 5,900,185.
`FIELD OF THE INVENTION
`
`The invention described and claimed herein is generally
`related to bromine-containing halocarbon additives used to
`decrease or eliminate the flammability of refrigerants, foam
`blowing agents, cleaning agents (solvents), aerosol
`propellants, and sterilants. Specific and novel to this inven-
`tion are the combined properties of these additives: (1) The
`halocarbon additives claimed are destroyed or otherwise
`removed rapidly by natural processes in the earth’s tropo-
`sphere and thus have short atmospheric lifetimes, low ozone
`depletion potentials (ODPs), and low global warming poten-
`tials (GWPs). (2) These additives are chemically active
`flammability reducing agents and do not operate merely by
`dilution of a flammable substance with a nonflammable
`
`substance. In this document, I refer to atmospheric lifetimes,
`ODPs, and GWPs as “global environmental properties”
`since they determine the potential environmental impact on
`the earth as a whole rather than just one area. The additives
`claimed are called “tropodegradable” since they are
`removed rapidly from the earth’s troposphere.
`BACKGROUND
`
`Flammability and Explosivity
`It is important at this point to briefly discuss what is meant
`by flammability and explosivity. Materials used in the appli-
`cations of interest here (refrigeration,
`foam blowing,
`solvents, aerosol propulsion, and sterilization) are liquids or
`gases. In many cases, they are stored in one form and used
`in another or they are present in both forms during use.
`When flammable liquids burn, combustion actually occurs
`in the vapor phase, which is formed above the surface of the
`liquid by evaporation of the liquid. When flammable gases
`or vapor from evaporated flammable liquids are allowed to
`mix with air,
`the mixture can be explosive.
`(In this
`document,
`I use the terms “vapor” and “gas” as
`synonymous.) In fact, for the materials of interest here,
`explosions are just rapid combustion in the gaseous state.
`Explosions are often termed “deflagrations” if the combus-
`tion is relatively slow and as “detonations” if it is extremely
`fast. Thus “burning,” “combustion,” “explosion,”
`“deflagration,” and “detonation” all involve a rapid oxida-
`tion and differ primarily in the rapidity of the process and the
`results (explosions are often highly destructive). For the
`materials of interest here, flammability is often determined
`by introducing the material as a gas or as a vapor from an
`evaporated liquid into a container with air or oxygen and
`determining whether deflagration occurs. Thus, throughout
`this document,
`I use the term “flammable” to indicate
`whether combustion can occur without regard for whether
`the combustion occurs in the vapor phase above the liquid/
`vapor interface of a liquid or as a deflagration or explosion
`in a gas/air mixture. Halocarbons
`The broad class of halocarbons consists of all molecules
`
`containing carbon and one or more of the following halogen
`atoms:
`fluorine, chlorine, bromine, and/or
`iodine.
`Halocarbons, as the term is used here, may also contain other
`chemical features such as hydrogen, oxygen, and/or nitrogen
`atoms; carbon-to-carbon multiple bonds; and aromatic rings.
`
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`Due to their generally low toxicities and low or non-
`existent flammability, one family of halocarbons—the chlo-
`rofluorocarbons (CFCs), which contain only carbon,
`chlorine, and fluorine atoms—has been used for many years
`in a variety of applications. Refrigerants
`Air conditioning, refrigerating, and heat pump appliances
`transfer heat from one area to another. In vapor compression
`systems, a chemical or mixture of chemicals, the refrigerant
`or “working fluid”, is compressed in one area (the high-
`pressure side), where heat is given off, and then allowed to
`expand in a second area (the low-pressure side), where heat
`is taken up. In most cases, the working fluid condenses in the
`high pressure area and then evaporates in the low pressure
`area. A schematic of a typical refrigeration system is shown
`in FIG. 1.
`
`CFCs have been the refrigerants of choice in many air
`conditioning, refrigerating, and heat pump appliances. Thus,
`CFC-12 (See Halocarbon Nomenclature, Center for Global
`Environmental Technologies, New Mexico Engineering
`Research Institute, The University of New Mexico,
`Albuquerque, N. Mex., Revised September 1997 for a
`discussion of this “halocarbon number” and other halocar-
`
`bon nomenclature), also known as R-12 or dichlorodifluo-
`romethane (CCl2F2), has been a widely used medium-
`pressure refrigerant
`for commercial and residential
`refrigeration, medium-pressure centrifugal chillers, and
`automobile air conditioners. CFC-11 (R-11,
`trichlorofluoromethane, CCl3F) has been widely used in
`low-pressure centrifugal chillers, and CFC-114 (R-114, 1,2-
`dichloro-1,1,2,2-tetrafluoroethane, CCIFZCCIFZ) is widely
`used by the U.S. Navy for centrifugal chillers. Other CFCs
`have also been used as refrigerants, either pure or in mix-
`tures
`
`Foam Blowing Agents
`insulation,
`The manufacture of plastic foams for
`cushioning, and packaging foams requires the use of gas or
`volatile liquid blowing agents to create bubbles or cells.
`CFC-11, CFC-12, CFC-113 (1,1,2-trichloro-1,2,2-
`trifluoroethane, CCl2FCCIF2), and CFC-114 have been used
`as blowing agents in the manufacture of foam plastic prod-
`ucts. In addition to their remarkably low toxicities and lack
`of flammability, CFCs provide plastic closed-cell foams
`with excellent insulating ability and generally have good
`materials compatibility.
`Solvents
`
`CFC-113 has been widely used as a solvent in metals,
`electronic, and precision cleaning and/or decreasing. In this
`application,
`in addition to acceptable toxicities and low
`flammability, rapid evaporation is desired. Rapid evapora-
`tion decreases or eliminates energy consumption for drying
`cleaned parts. All CFCs in common use evaporate rapidly.
`CFCs and related materials have also been used for disso-
`
`lution of solutes (dissolving) in many applications including
`aerosol sprays.
`Aerosol Propellants and Sterilants
`CFCs have also been used as aerosol propellants though
`this use is decreasing and is nearly absent in some areas of
`the world, and a mixture of CFC-12 and ethylene oxide
`(C2H4O) is used for gas sterilization of medical equipment
`and devices. Ethylene oxide is the actual sterilant; CFC-12
`is added only to decrease the ethylene oxide flammability. It
`is estimated that in 1989, 95 percent of all U.S. hospitals
`used an ethylene oxide/CFC-12 mixture as a sterilant.
`Global Environmental Problems
`
`CFCs and many other halocarbons, have come to be
`recognized as serious global environmental threats due to
`their ability to cause stratospheric ozone depletion and
`
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`US 6,300,378 B1
`
`3
`global warming and their significant atmospheric lifetime.
`The ozone depletion and global warming impact of chemi-
`cals such as these is measured by the ozone depletion
`potential (ODP) and global warming potential (GWP). ODP
`and GWP give the relative ability of a chemical to deplete
`stratospheric ozone or to cause global warming on a per-
`pound-released basis. ODP and GWP are usually calculated
`relative to a reference compound (usually CFC-11 for ODP
`and either CFC-11 or carbon dioxide for GWP) and are
`usually calculated based on a release at the earth’s surface.
`It is important to note that ODP and GWP values must be
`calculated by computer models; they cannot be measured.
`As models, theory, and input parameters change, the calcu-
`lated values vary. For that reason, many different values of
`ODP and GWP are often found in the literature for the same
`
`the calculation results are very
`compound. Nevertheless,
`accurate in predicting which compounds are highly detri-
`mental to ozone depletion or global warming, which are only
`moderately detrimental, and which have very low or essen-
`tially zero impacts.
`Despite the wide utility of CFCs, their production has
`been severely restricted due to concerns about stratospheric
`ozone depletion. In fact, under the Montreal Protocol, an
`international treaty enacted in 1987 and amended in 1990,
`1992, and 1995, the production of CFCs was phased out in
`all industrialized nations at the end of 1995. Moreover, the
`production of certain other halocarbon chemicals has also
`been halted. Thus,
`the production of methyl chloroform
`(1,1,1-trichloroethane, CH3CCl3), which like CFC-113 has
`been widely employed both as a solvent in cleaning appli-
`cations and as a foam blowing agent, was also ended at the
`end of 1995 in industrialized countries.
`
`Replacements and Proposed Replacements for Ozone
`Depleting Chemicals
`Among the earliest chemicals proposed as replacements
`for CFCs and methyl chloroform were the hydrochlorofluo-
`rocarbons (HCFCs). These compounds contain hydrogen in
`addition to carbon, fluorine, and chlorine. The hydrogen
`atoms in the HCFCs react with hydroxyl free radicals, which
`are normal constituents of the earth’s atmosphere, and this
`reaction decreases the atmospheric lifetime of HCFCs rela-
`tive to CFCs. This decrease in atmospheric lifetime limits
`the amounts of HCFCs that reach the stratosphere to deplete
`ozone.
`
`HCFC-22 (chlorodifluoromethane, CHCIF2) has long
`been the standard refrigerant for home air conditioners;
`however, HCFCs are now being promoted as CFC replace-
`ments in a number of other applications. For example,
`HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane, CHCl2CF3)
`is now widely used as a replacement for CFC-11 in low-
`pressure centrifugal chillers and, along with HCFC-141b
`(1,1-dichloro-1-fluoroethane, CH3CCl2F) and HCFC-124
`(2-chloro-1,1,1,2-tetrafluoroethane, CHCIFCF3), as a foam
`blowing agent. HCFCs such as a mixture of the two isomers
`HCFC-225 ca (3,3-dichloro-1,1,1,2,2-pentafluoropropane,
`CHCl2CF2CF3) and HCFC-225 cb (1,3-dichloro-1,1,2,2,3-
`pentafluoropropane, CHCIFCF2CCIF2) are also being used
`for cleaning. Unfortunately,
`the atmospheric destruction
`process for HCFCs is insufficiently efficient to prevent all of
`a chemical from reaching the stratosphere. Thus, HCFCs
`exhibit a low, but significant, ODP. For that reason, HCFCs
`are scheduled for eventual phaseout under the amended
`Montreal Protocol.
`
`Much research has gone on to find replacements for the
`CFCs, HCFCs, and methyl chloroform. Hydrofluorocarbons
`(HFCs), which contain only hydrogen, fluorine, and carbon,
`and perfluorocarbons (PFCs or FCs), which contain only
`
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`fluorine and carbon, are being commercialized as replace-
`ment chemicals in a number of applications. Since these
`materials contain no chlorine, bromine, or iodine (required,
`in most cases,
`if a compound is to exhibit significant
`stratospheric ozone depletion), they have a nominally zero
`ODP. (Here, I use the word “nominally” since calculations
`have shown an exceedingly small ODP for some of these
`materials.) However, HFCs and PFCs have very long atmo-
`spheric lifetimes and contribute to global warming. In fact,
`many PFCs have atmospheric lifetimes of several thousand
`years, compared with a few years for most HCFCs and a few
`hundred years for most CFCs. Moreover, a number of HFCs
`and HCFCs are flammable. When present as gases in volume
`containing oxygen (for instance, when the refrigerant leaks
`into a room), explosions can occur. Many new refrigerants—
`1,1-difluoroethane (HFC-152a, CH3CHF2), difluo-
`romethane (HFC-32, CH2F2),1,1,1-trifluoroethane (HFC-
`143a, CH3CF3),1,1-dichloro-1-fluoroethane (HCFC-141b,
`CH3CCl2F), and 1-chloro-1,1-difluoroethane (HCFC-142b,
`CH3CCIF2)—are flammable and/or explosive, at least under
`some conditions. (It should be noted, that HCFC-141b and
`HCFC-142b are less flammable than the other alternatives
`listed and, in fact, are stated to be nonflammable in some
`sources. Both of these compounds do, however, have upper
`and lower flammability limits and HCFC-142b is classified
`as flammable in refrigeration standards issued by the Ameri-
`can Society of Heating, Refrigerating and Air-Conditioning
`Engineers, which gives no classification for HCFC-141b).
`This list of flammable HFC and HCFC refrigerants includes
`some of the most energy-efficient refrigerants, particularly
`HFC-152a and HFC-32. Flammable refrigerants are often
`mixed with nonflammable refrigerants to produce lower
`flammability or nonflammable refrigerant blends for
`commercialization, and a large number of such blends are
`now being marketed.
`In this document,
`I use the term
`“dilution” to indicate all non-chemical (i.e., “physical”)
`means by which a nonflammable component reduces flam-
`mability (e.g., dilution of oxygen and heat absorption).
`Reduction of flammability primarily by dilution is less than
`satisfactory, however, since a large amount of nonflammable
`refrigerant must often be added to a flammable refrigerant to
`obtain a nonflammable blend, and this often produces less
`than optimal properties.
`Many non-halocarbons are being commercialized or seri-
`ously considered as CFC replacements. The use of hydro-
`carbon refrigerants such as propane (CH3CH2CH3, R-290),
`isobutane [CH3CH (CH3)CH3, R600a], and propylene
`(CH2=CHCH3, R-1270) is increasing in many parts of the
`world. These materials are highly energy-efficient and have
`excellent global environmental properties (low atmospheric
`lifetimes, low GWPs, and zero ODPs); however, they are
`also highly flammable, and this has limited their use in many
`countries and in many applications. In some cases, these
`hydrocarbons are being blended with nonflammable refrig-
`erants (as is being done for flammable HFCs and HCFCs);
`however,
`this often reduces the energy efficiency and
`increases the global environmental
`impact. Ammonia
`(NH3), a highly energy-efficient refrigerant that has been
`used for many years, has a zero ODP and a very low
`atmospheric lifetime and GWP; however, its flammability is
`coming under increasing scrutiny. Blends of ammonia with
`HFCs are now being considered to decrease the flammability
`problem.
`The hydrocarbon cyclopentane (C5H10) is now used to
`blow refrigerator insulating foams in some parts of the
`world, and hydrocarbons such as n-pentane
`(CH3CH2CH2CH2CH3),
`isopentane [(CH3)2CHCH2CH3],
`
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`US 6,300,378 B1
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`5
`
`n-butane (CH3CH2CH2CH3), and isobutane have long been
`used in the production of extruded polystyrene foam sheet
`products. However,
`these hydrocarbons are flammable.
`Other flammable chemicals being considered or being used
`as blowing agents are HCFC-141b, HFC-152a,
`2-chloropropane (CH3CHClCH3), and acetone [CH3C(O)
`CH3]. Conversion from CFC and methyl chloroform to
`flammable blowing agents will entail significant capital
`investment to ensure worker safety. There is also concern
`about the ability of foams blown with flammable blowing
`agents to meet code requirements and safety standards.
`No solvent that is equivalent to CFC-113 and methyl
`chloroform in toxicity and safety; has a low ODP, GWP, and
`atmospheric lifetime; and is an effective and easily evapo-
`rated cleaner has been identified (Tapscott, R. E., and
`Skaggs, S. R., Identification 0fAlternatives to CFC-113 for
`Solvent Cleaning, NASA White Sands Test Facility, Las
`Cruces, N. Mex., September 1994). A number of new
`chemicals—e.g., monochlorotoluenes, benzotrifluorides,
`volatile methyl siloxanes (VMSs), and terpenes—that are
`being considered or that are now used as solvents have very
`good global environmental and solvent properties but are
`flammable, and this flammability limits their use. There will
`also be increasing use of flammable chemicals long used as
`solvents-alcohols, petroleum distillates and other
`hydrocarbons, ethers, esters, and ketones.
`A number of flammable materials are being used or
`considered for use as aerosol propellants. Among these are
`the hydrocarbons n-butane (CH3CH2CH2CH3),
`isobutane
`[(CH3)2CHCH3], and propane (CH3CH2CH3); dimethyl
`ether (CH3OCH3); siloxanes; HFC-152a; HCFC-141b; and
`HCFC-142b.
`
`Flammable materials have been used in the past as
`refrigerants, foam blowing agents, cleaning solvents, and
`aerosol propellants; however,
`the number of applications
`and usage are increasing due to the production bans on
`CFCs. Moreover, as regulations on HFCs and HCFCs
`increase,
`there will be increasing pressure to use
`hydrocarbons, petroleum distillates, ethers, and other highly
`flammable materials.
`
`Solution to Flammability Problems
`The applicability of many of the most useful substitutes or
`potential substitutes for CFCs in refrigeration,
`foam
`blowing, cleaning, aerosol propulsion, and chemical steril-
`ization is severely limited by concerns about flammability.
`As noted earlier, in some cases, blending of nonflammable
`materials whose mode of action is primarily dilution with
`flammable materials has allowed the production of nonflam-
`mable or low-flammability products; however, this course of
`action has been less than satisfactory due to the large amount
`of nonflammable components needed in many cases. What
`I claim here is the use of highly effective additives to
`decrease or eliminate flammability of normally flammable
`refrigerants, foam blowing agents, cleaning solvents, aerosol
`propellants, and sterilants. The action of these additives is
`not due solely to dilution, as in existing and proposed blends
`with nonflammable components;
`these additives also act
`chemically to actually suppress flammability. Such additives
`can be used in relatively low amounts and, therefore, have
`a decreased influence on the characteristics of the principal
`component or components. The mode of action is described
`immediately below.
`Bromine- and iodine-containing compounds disrupt the
`free-radical chain reactions that maintain combustion. This
`
`disruption is a highly effective “chemical” mechanism for
`fire suppression, as opposed to the primarily “physical” (i.e.,
`“dilution”) mechanisms of cooling and smothering provided
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`by nonflammable components used to obtain many nonflam-
`mable refrigerant and other blends. Iodides, though useful in
`direct fire protection technologies, appear to have too high
`a toxicity and too low a stability for serious consideration as
`additives in the specific applications discussed here.
`Bromine-containing compounds, such as the halon fire
`extinguishing agents, are also highly effective chemical fire
`suppressants. However, bromine-containing compounds in
`the specific chemical forms used today as fire extinguishing
`agents (bromochlorofluoro- and bromofluoroalkanes) have
`high ODPs because of their long atmospheric lifetimes, and
`their production has been banned in industrialized nations.
`Moreover, production of the one (briefly) commercialized
`bromine-containing halon replacement CHBrF2 (HBFC-
`22B1) has now also been banned in industrialized nations
`under the Montreal Protocol along with all other hydrobro-
`mofluorocarbons (HBFCs). In this case, the presence of a
`hydrogen atom in the molecule (without other features
`described in the present disclosure) was insufficient
`to
`achieve the hoped-for low atmospheric lifetime. In fact,
`none of the many halon substitute technologies now being
`commercialized contain bromine due to the concern about
`
`their expected high ODP. It should be noted that once they
`enter the stratosphere, bromine-containing compounds are
`about 40 times more destructive to stratospheric ozone than
`are chlorine-containing compounds (Solomon, S., and
`Albritton, D. L., “Time-Dependent Ozone Depletion Poten-
`tials for Short- and Long-Term Forecasts,” Nature, Vol. 357,
`pp. 33—37, 7 May 1992).
`There is, however, a solution to the problem of strato-
`spheric ozone depletion by bromine-containing compounds.
`If chemical features that promote extremely rapid atmo-
`spheric removal are incorporated into the compounds, insuf-
`ficient amounts of the materials will reach the stratosphere
`to cause significant stratospheric ozone depletion. Thus, the
`compounds will have exceptionally low ODPs, even though
`they contain bromine, which is normally a strong ozone
`depleter. In fact, the resulting short atmospheric lifetimes
`will also result in low GWPs. Using this concept, I have (1)
`examined mechanisms for removal of compounds from the
`atmosphere, (2) determined chemical features that could
`enhance the various removal processes, and (3) carried out
`calculations to estimate the atmospheric lifetimes. This
`three-step process has allowed us to invent several families
`of bromine-containing halocarbons that have very short
`atmospheric lifetimes. Moreover, my calculations and esti-
`mation methods indicated that these compounds had much
`shorter atmospheric lifetimes than I had expected and that
`these very short atmospheric lifetimes resulted in very low
`estimated ODPs. I then discovered that such compounds can
`be used as additives to normally flammable materials pro-
`posed or used in the following five applications covered by
`this disclosure:
`
`1. Refrigeration
`2. Foam Blowing
`3. Cleaning, Degreasing, and Solute Dissolution
`4. Aerosol Propulsion
`5. Sterilization
`
`the following
`Thus, pursuant to the present invention,
`seven groups of compounds having short tropospheric life-
`times and correspondingly low ODPs and GWPs, but also
`having chemical features (specifically, bromine) that pro-
`mote effectiveness to reduce flammability have been arrived
`at. These families are the
`
`1. Bromine-Containing Alkenes
`2. Bromine-Containing Alcohols
`3. Bromine-Containing Ethers
`
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`US 6,300,378 B1
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`7
`4. Bromine-Containing Amines
`5. Bromine-Containing Carbonyl Compounds
`6. Bromine-Containing Aromatics
`7. Bromine-Containing Non-Fluorinated Alkanes
`Accordingly, it is the object of the present invention to
`provide bromine-containing additives that act chemically to
`reduce the flammability of refrigerants,
`foam blowing
`agents, cleaning agents, aerosol propellants, and chemical
`sterilants and that are rapidly destroyed or removed by
`natural processes in the troposphere. I refer to such additives
`as “tropodegradable.” As a result of the rapid degradation in
`the troposphere or removal from the troposphere, the addi-
`tives will have very short atmospheric lifetimes, low ozone
`depletion potentials, and low global warming potentials. My
`criterion is that the estimated atmospheric lifetime be on the
`order of days or weeks, giving ODPs and GWPs that
`approach zero (probably less than 0.02 ODP) for a ground-
`level release. Note that I do not consider materials such as
`
`HCFCs, HFCs, and HBFCs to be “tropodegradable” as
`defined here, even though such chemicals are partially
`destroyed in the troposphere. The destruction processes are
`relatively inefficient compared to those for the additives
`claimed here, and HCFCs, HFCs, and HBFCs normally have
`atmospheric lifetimes of years to hundreds of years.
`
`BRIEF DESCRIPTION OF FIGURE
`
`FIG. 1: A schematic of a typical refrigeration system.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides tropodegradable bromine-
`containing halocarbons that can be used as additives to
`reduce or eliminate the flammability of normally flammable
`refrigerants,
`foam blowing agents, solvents, aerosol
`propellants, and sterilants and/or that can be used to provide
`nonflammable or low-flammability refrigerant, foam blow-
`ing agent, solvent, aerosol propellant, and sterilant and
`sterilant mixtures. These compounds in accordance with the
`invention have the characteristics of high effectiveness for
`flammability reduction, but have short atmospheric lifetimes
`(on the order of days or weeks) resulting in low ODPs and
`GWPs. These chemicals are of seven classes: (1) bromine-
`containing alkenes, (2) bromine-containing alcohols, (3)
`bromine-containing ethers, (4) bromine-containing amines,
`(5) bromine-containing carbonyl compounds, (6) bromine-
`containing aromatics, and (7) bromine-containing non-
`fluorinated alkanes. In general, to reduce hepatotoxicity and
`flammability, such compounds, with the exception of the
`bromine-containing alkanes, will be at least partially fluori-
`nated. The compounds may also contain chlorine, but should
`contain no iodine. To obtain the desired low atmospheric
`lifetimes, the amines and ethers preferably contain at least
`one hydrogen atom attached to a carbon atom adjacent to
`nitrogen or oxygen. The prediction of atmospheric lifetimes
`for these additives is described below.
`
`Four primary processes exist for removal of organic
`molecules from the troposphere: (1) reaction with tropo-
`spheric hydroxyl free radicals; (2) photolysis; (3) physical
`removal; and (4) reaction with tropospheric ozone.
`Hydroxyl free radicals
`are found naturally in the
`earth’s troposphere. These free radicals react with atmo-
`spheric pollutants or other atmospheric compounds that
`contain hydrogen atoms within their molecules or that are
`unsaturated. Unsaturated compounds include compounds
`containing carbon-carbon double bonds (e.g., C=C) and
`aromatic compounds such as benzene. HCFCs, HFCs, and
`HBFCs have hydrogen atoms within their molecules and,
`
`8
`therefore, react with tropospheric hydroxyl free radicals.
`However, this reaction is relatively ineflicient for the HCFCs
`and HFCs, many of which are in use today, and for the
`HBFCs, whose production has now been banned, giving
`them relatively long atmospheric lifetimes. I have realized,
`however,
`that hydrogen atoms on carbon atoms that are
`adjacent to oxygen or nitrogen atoms are more susceptible to
`reaction with tropospheric hydroxyl free radicals than they
`would otherwise be. Thus amines [compounds containing a
`nitrogen atom, N, attached to three groups to give the
`characteristic structure N(R)(R‘)(R“), where the R, R‘, and
`R“ groups are organic substituents or hydrogen atoms] and
`ethers (compounds containing an oxygen atom, O, attached
`to two organic groups R and R'to give the characteristic
`structure R—O—R‘) react relatively quickly with tropo-
`spheric hydroxyl free radicals as long as the molecules
`contain one or more hydrogen atoms attached to carbon
`atoms adjacent to the nitrogen or oxygen atoms. My recent
`work indicates that this may be true even when the hydrogen
`atoms occupy other positions in amine and ether molecules.
`I have calculated estimated lifetimes of less than one year for
`many hydrofluoroamines
`and hydrofluoroethers
`(HFEs). Moreover,
`I estimate that the replacement of a
`fluorine atom with a bromine atom in these materials will
`
`decrease the lifetime by approximately a factor of ten due,
`at least in part, to enhanced photolysis (see below). Using
`this reasoning, I have estimated atmospheric lifetimes as
`short as 11 days for some hydrobromofluoroamines (HBAs)
`and hydrobromofluoroethers (HBFEs). Using a limited
`amount of data,
`I estimate that for bromine-containing
`compounds, each 10 years increase in atmospheric lifetime
`increases the ODP by approximately 2. Thus, I estimate a
`minimum ODP of around 0.006 for some HBFAs and
`HBFEs. I also note that nonfluorinated amines and ethers,
`though of slightly less interest, would have even shorter
`atmospheric lifetimes and lower ODPs. Estimations using
`the same type of calculations show that alcohols
`[compounds containing the structural feature HOC(R)(R‘)
`(R“), where the R, R‘, and R“groups are organic substituents
`or hydrogen atoms] also react rapidly with hydroxyl free
`radicals when they contain a hydrogen atom on a carbon
`atom adjacent to the OH group characteristic of alcohols.
`However, a more important atmospheric removal process
`(rainout, see below) exists for many alcohols.
`I have also calculated that many non-fluorine-containing
`bromoalkanes will have very short atmospheric lifetimes
`due to reaction with tropospheric hydroxyl free radicals. For
`example, using published rate constants for reaction of
`hydroxyl free radicals with related compounds and reason-
`ing similar to that described above, I estimate an atmo-
`spheric lifetime of approximately four weeks and an ODP of
`0.017 for 1-bromopropane (CH2BrCH2CH3). Of some inter-
`est is that these values should decrease as the carbon chain
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`length increases. Thus, the ODP and atmospheric lifetime of,
`for example, 1-bromobutane (CH2BrCH2CH2CH3), should
`be even shorter.
`
`60
`
`65
`
`Unsaturated compounds such as alkenes [compounds
`containing the structural
`feature (R)(R‘)C=C(R“)(R‘"),
`where the R, R‘, R“, and R‘" groups are organic substituents,
`chlorine, bromine, fluorine, or hydrogen atoms] and aromat-
`ics (compounds containing a benzene, C6, ring or related
`structural features) react very rapidly with tropospheric
`hydroxyl free radicals. I estimate lifetimes on the order of a
`few days for these types of compounds with correspondingly
`low ODPs for bromine-containing derivatives.
`in a
`Some compounds are broken down by sunlight
`process known as photolysis, and my estimations show that
`
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`US 6,300,378 B1
`
`9
`this is likely to be an effective tropospheric removal process
`for carbonyl compounds [compounds containing a group
`(R)(R')C=O, where R and R'are any substituents). Such
`carbonyl compounds include aldehydes [(R)(H)C=O,
`where R is an alkyl or aryl group], ketones [(R)(R‘)C=O,
`where R and R'are alkyl or aryl groups], and esters [(RO)
`(R‘)C=O, where R and R‘