US3832411A - Method for the depolymerization of polytetrafluoroethylene - Google Patents

Method for the depolymerization of polytetrafluoroethylene Download PDF

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Publication number
US3832411A
US3832411A US00111963A US11196371A US3832411A US 3832411 A US3832411 A US 3832411A US 00111963 A US00111963 A US 00111963A US 11196371 A US11196371 A US 11196371A US 3832411 A US3832411 A US 3832411A
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Prior art keywords
steam
tetrafluoroethylene
temperature
polytetrafluoroethylene
pyrolysis
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US00111963A
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English (en)
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B Arkles
R Bonnett
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Zeneca Inc
Liquid Nitrogen Processing Corp
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Liquid Nitrogen Processing Corp
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Priority to US00111963A priority Critical patent/US3832411A/en
Priority to FR7128299A priority patent/FR2124212B1/fr
Priority to GB61872A priority patent/GB1361341A/en
Priority to IT67211/72A priority patent/IT948929B/it
Priority to DE2204141A priority patent/DE2204141B2/de
Priority to JP47010620A priority patent/JPS5238525B1/ja
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Publication of US3832411A publication Critical patent/US3832411A/en
Assigned to LNP CORPORATION, A CORP OF DE reassignment LNP CORPORATION, A CORP OF DE ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: BEATRICE COMPANIES, INC.
Assigned to ICI AMERICAS INC. reassignment ICI AMERICAS INC. MERGER (SEE DOCUMENT FOR DETAILS). EFFECTIVE DECEMBER 29, 1986 Assignors: ARBCO ELECTRONICS INC., ATLAS CHEMICAL INDUSTRIES, INC., CA, ATLAS CHEMICAL INDUSTRIES, OR., ATLAS CHEMICAL INDUSTRIES, RI, ATLAS CHEMICAL INDUSTRIES, TX (MERGED INTO), CONVERTERS INK CO., ICI SPECIALTY CHEMICALS INC., IMPERIAL OIL AND GREASE CO., KATALCO CORPORATION, LNP CORPORATION, PERMUTHANE INC., POLYVINYL CHEMICALS INC., STAHL CHEMICALS INC., THORO SYSTEM PRODUCTS, INC.
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C17/00—Preparation of halogenated hydrocarbons
    • C07C17/361—Preparation of halogenated hydrocarbons by reactions involving a decrease in the number of carbon atoms
    • C07C17/367—Preparation of halogenated hydrocarbons by reactions involving a decrease in the number of carbon atoms by depolymerisation

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  • ABSTRACT High yield monomeric tetrafluoroethylene may be recovered from polytetrafluoroethylene and polytetrafluoroethylene composites by pyrolyzing the polymer in the presence of high temperature steam.
  • the steam acts as a condensable carrier gas for the low molecular weight pyrolysis products and should be present in an amount such that the mole ratio of steam to pyrolysis products is at least one to one.
  • the steam also acts as a means for heating the polymer to the necessary decomposition temperatures.
  • the present invention relates to the production of low molecular weight fluorine-containing compounds by depolymerizing polymeric tetrafluoroethylene. More particularly, the invention is directed to a method of recovering monomeric tetrafluoroethylene from polymeric tetrafluoroethylene by pyrolysis using the controlled presence of high temperature steam.
  • polytetrafluoroethylene generally referred to as polytetrafluoroethylene, TFE fluorocarbon polymer or PTFE
  • TFE fluorocarbon polymer PTFE
  • the pyrolysis products are a mixture of many compounds including -TFE monomer, hexafluoropropene (C F octafluorocyclobutane (C F and other gaseous and liquid perfluorinated products having relatively low boiling points.
  • C F hexafluoropropene
  • C F and other gaseous and liquid perfluorinated products having relatively low boiling points When pyrolysis is conducted at near atmospheric pressures these products usually contain considerably less than 50 percent of the monomer, and consequently the mixture is of little commercial value.
  • the difficulty arises because: (1) materials capable of withstanding the high temperature and corrosive pyrolysis conditions generally have poor strength and rigidity at the high temperatures involved; (2) the use of vacuum precludes convective heat supply to the polymer and thus restricts the supply of en'- ergy necessary for pyrolysis to conduction and radiation from the surface of the vessel; and (3) polytetrafluoroethylene itself has very poor heat-transfer properties.
  • the net result is that the maximum diameter of a vacuum-pyrolysis vessel is generally limited to about 10 inches, and the batch of polymer to be pyrolyzed is generally restricted to a relatively small weight.
  • vacuum pyrolysis offers the probability of haz ardous introduction of air into the pyrolyzate stream. As a result, to the best of our knowledge no important commercial depolymerization of polytetrafluoroethylene in vacuum has been accomplished.
  • Scrap or waste polytetrafluoroethylene is an attractive source of monomer tetrafluoroethylene from several standpoints.
  • the production of monomer tetrafluoroethylene by depolymerization of the polymer represents a substantial cost saving compared to the synthesis of the monomer from usual refrigerant gas sources.
  • a substantial difficulty encountered in producing polytetrafluoroethylene is the presence of by-product difluoroethylene and trifluoroethylene with the crude monomer tetrafluoroethylene made from CHCIF or CHF These impurities are generally removed by slow and costly methods.
  • monomer from the depolymerization of polytetrafluoroethylene has substantially reduced portions of these products.
  • the objects of this invention are achieved by heating polymeric tetrafluoroethylene to temperatures above the decomposition temperature of the polymer in the presence of high temperature steam under such conditions that the mole ratio of steam to off-gas decomposition products is at least one to one.
  • the off-gas products are collected after condensing the steam.
  • FIG. 1 is a simplified representation of an apparatus which may be used in the present invention according to Example 1.
  • FIG. 2 is a simplified representation of an apparatus which may be used for processing larger quantities according to the method of the present invention.
  • the process of the present invention depends in large part upon the role of steam as a diluent and carrier gas for the tetrafluoroethylene monomer, which is the predominant product of the decomposition of the polymer.
  • the commercial feasibility of the present invention depends upon the fact that high temperature steam may conveniently be used to conduct sufficient heat to the polytetrafluoroethylene to decompose the material.
  • the decomposition at this temperature'only proceeds at a rate on the order of percent per hour. It is not until considerably above the polymer first-order transition temperature (approximately 625 F) that substantial decomposition is observed. That is, the polytetrafluoroethylene should be heated to a temperature of between about 780 F and l,400 F, and preferably between about 800 F and I,IOO F. Good results may be achieved when the temperature of the steam impinging upon the polymer melt is between 950 F and l,800 F.
  • the specific temperature of the steam supplied to the polymer tetrafluoroethylene mass may be varied over a large range, the flow rate of steam required will be largely dependent on the temperature of the steam. This is due to the fact that the depolymerization rate is increased by increased interface temperature of the polymer under pyrolysis. Therefore, as the temperature is raised, the mass-rate of steam must be increased in order to adequately dilute the tetrafluoroethylene monomer which is forming at a more rapid rate, and thereby minimize the tendency of free-radical difluoromethylene groups to trimerize or polymerize. In other words, to maintain a high degree of TFE monomer yield, it is prudent to dilute free-radical interaction by maintaining an adequate steam flow rate. In general, the higher the temperature, the more steam required to maintain uniform yield.
  • An easy way to accomplish uniform yield is to maintain a constant mole ratio of steam to off-gas decomposition products. It has been found that a minimum mole ratio of steam to decomposition products of about four to one is required to maintain a high level of monomer yield. Mole ratios of as low as about one to one still produce good levels of monomer'yield as well as increased yields of other low molecular weight fluorinecontaining compounds. At lower mole ratios, monomer tetrafluoroethylene concentration is low, and the amount of solid sublimate as well as other decomposition by-products is increased. On the other hand, at extremely high mole ratios, it is possible to produce almost pure monomer tetrafluoroethylene. A mole ratio of steam to decomposition products of between about ten to one and forty to one is preferable. There is apparently no upper limit on the amount of steam which may be used or the maximum temperature of the steam. However, economic considerations render higher temperatures and amounts impractical.
  • the reaction vessel 10 should be made of a material which is able to withstand the high temperatures and corrosive byproducts of the pyrolysis reaction.
  • An optimum material is platinum lined high temperature stainless steel.
  • lnconel a trademark for alloys of nickel and chromium
  • Monel metal a trademark for alloys of predominantly nickel and copper
  • the high temperature steam used in the process of the present invention may be produced either outside or within the reaction vessel.
  • Super-heated steam, steam or water enters the vessel 10 through inlet tube 12 at the side of the vessel near the bottom. Inlet tube 12 extends approximately to the center of the vessel.
  • the tube. may be made of stainless steel, for example.
  • the vessel 10 In order to produce the steam or maintain or raise the temperature of the steam, the vessel 10 is provided with gas burners 14. In addition, the sides and top of the vessel are provided with suitable insulation 16.
  • the batch 18 of material. to be pyrolyzed is supported by a porous surface 20 which may be made of a heavy gaugescreen or a perforated metal plate.
  • the porous surface 20 is in turn supported by a replaceable tripod 22, which is positioned over the steam inlet tube 12.
  • the screen or perforated metal plate which forms the porous surface 20 not only serves as a support for batch 18, but also conducts heat to the batch to further the decomposition. Since typically encountered PTFE melt does not usually flow until it reaches a temperature of about 850 F or more, flowing of the melt through the holes of the screen or perforated plate is not a major problem. In fact, the melt produces a stalactite effect, and the hotter steam'beneath the screen or plate decomposes the polymer before the drips of 'melt can hit the bottom of the vessel. Nevertheless, the holes in the screen or plate should be sufficiently small to prevent particles of the solid polymer from falling through. For example, two overlapped layers of 14 mesh screen have been found to be quite suitable, whereas 8 mesh screen or inch drilled holes in a steel plate were usually'too large.
  • screen 24 which may suitably bemade of 14 mesh stainless steel.
  • the screen 24 inhibits the blowing off of any solid raw-material with the steam and decomposition gases, as well as reducing sublimate formation.
  • the reduction of sublimation is important since the condensation of the sublimate tends to block the exit gas lines.
  • sublimate formation may also be reduced or substantially eliminated by using higher mole ratios of steam.
  • the steam After passing through .and around the porous supporting surface 20 and the batch 18, the steam carries the gaseous pyrolysis products away from the polymer mass and out of the vessel 10 through effluent gas outlet 26, which may suitably be stainless steel tubing. It is good practice to position the effluent outlet 26 below the vessel opening 28, since gasketing capable of withstanding the depolymerization temperatures and corrosive conditions (i.e., hydrofluoric acid) is generally not available.
  • the efiluent gas outlet 26 may suitably be positioned about 2 inches above the batch 18 and 6 inches below the vessel opening 28.
  • the lid 30 of the vessel may be gasketed with polytetrafluoroethylene, provided enough of the heat supplied to the bottom of the vessel is removed through effluent outlet 26 to keep the gasket temperature below about 500 F.
  • the vessel may be suitably provided with thermocouples 32, in wells 33 positioned in the lid 30 and the bottom 34 of vessel 10, for example, to determine the respective temperatures of the batch l8 and the steam below the batch.
  • the vessel may also be provided with appropriate flowmeters (not shown) at the inlet tube 12 and/or outlet 26 to read the amounts of steam and pyrolyzate passing through the system.
  • This apparatus may be of any EXAMPLE I This example was performed in the apparatus which is illustrated in the simplified representation of FIG. 1 of the accompanying drawings.
  • a 100 gram sample 40 of unfilled polytetrafluoroethylene resin was wrapped in stainless steel screening 42 and placed one foot from the end of a 3% foot long stainless steel tube 44 having a diameter of one inch.
  • the 2 foot length of tubing 44 prior to the polytetrafluoroethylene sample 40 was wrapped with heating bands 46.
  • the end 48 was reduced to A inch diameter stainless steel tubing 52 which ran for 3 feet, acting as an air condenser, which in turn was connected to a rubber tube 54 which led to a small filter flask 56 for dropping out the water 58 condensed from the steam.
  • Filter flask 56 was provided with a product gas outlet 60 which led to a collection flask 62.
  • Collection flask 62 was immersed in a dry ice-acetone bath 63 for condensation of the decomposition gases.
  • EXAMPLE 111 One kilogram of unsintered scrap PT FE containing 25 percent fiber glass and pigmentation was pyrolyzed in the same vessel as Example ll with l,l00 F steam flowing at a rate of 12-15 grams per minute. Over a one half hour period, 250 grams of the material was pyrolyzed. The mole ratio of steam to off gas products was approximately 10 to l. The composition of the product gases was QB, 10% C F and 4% C F EXAMPLE IV A pyrolysis run was made in the same vessel as Example I! using sintered, unfilled scrap PT FE.
  • EXAMPLE V A l kilogram sample of PT F E material was pyrolyzed in the apparatus of Example II with l,l00 F steam flowing at 20-25 grams per minute.
  • the PTF E material employed consisted of whole and broken sintered billets filled with bronze, carbon, molybdenum disulfide and some pigmentation. Over a minute period the sample was pyrolyzed completely and produced a monomer tetrafluoroethylene yield (based on gases) of 70-85 percent. Sublimate formation was reduced with thishigh steam flow to about 5 percent of the total solids.
  • Example VI The pyrolysis vessel of Example II was charged with 7 pounds of flake reprocess grade (scrap and turnings of PTFE put through a grinder to make uniform size sintered particles) polytetrafiuoroethylene. Steam having a temperature ranging between 1,100 F and l,200 F was introduced at a rate of 35-40 grams per minute. The pressure measured at the bottom of the polymer melt was 5-8 psi during equilibrium pyrolysis conditions. The flow of off gases was measured after condensation of the steam, drying of the products and condensation of products heavier than TF E. The TF E gas was produced at about 2,200 cc per minute (approximately 10 grams per minute). This represented a mole ratio of steam to off gas products of approximately 20 to l. The analysis of the effluent gases indicated 90-95 percent monomer tetrafluoroethylene.
  • the utility of the present invention is apparent when compared to previous processes which either yield extremely low concentrations of desirable pyrolysis products or have limited commercial success because of restricted capacity.
  • the process of this invention offers a highly available feed stock for the production of tetrafluoroethylene polymer and fluorine containing compounds of various molecular weights.
  • the invention can recycle scrap polytetrafluoroethylene in virtually any form, including scrap lathe-turnings and other machine scrap, unsintered or sintered tape and sheet trimmings, discarded finished parts, and other unfilled or composite forms.
  • Polytetrafluoroethylene composites may include, for example, mixtures of PTFE with fiber glass, bronze, carbon and other inert materials.
  • a method of producing tetrafluoroethylene monomer by pyrolysis of polymeric tetrafluoroethylene comprising the steps of heating polymeric tetrafluoroethylene to a temperature of at least about 780 F. at a pressure of at least atmospheric pressure and in the presence of high temperature steam, said steam being present in an amount such that the mole ratio of steam to pyrolysis products is at least about 4 to l, condensing the steam from the mixture of pyrolysis products of the polymeric tetrafluoroethylene and collecting the resulting pyrolysis products.
  • a method for depolymerizing polymeric tetrafluoroethylene by pyrolysis comprising heating polymeric tetrafluoroethylene at a pressure of at least atmospheric pressure and in the presence of high temperature steam sufficient to heat said polymeric tetrafluoroethylene to a temperature of at least about 780 F., said steam being present in an amount such that the mole ratio of steam to pyrolysis products is at least about 4 to l, condensing the steam from the mixture of pyrolysis products, and collecting the resulting pyrolysis products.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
  • Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
US00111963A 1971-02-02 1971-02-02 Method for the depolymerization of polytetrafluoroethylene Expired - Lifetime US3832411A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US00111963A US3832411A (en) 1971-02-02 1971-02-02 Method for the depolymerization of polytetrafluoroethylene
FR7128299A FR2124212B1 (it) 1971-02-02 1971-08-02
GB61872A GB1361341A (en) 1971-02-02 1972-01-06 Method for the depolymerisation of polytetrafluoroethylene
IT67211/72A IT948929B (it) 1971-02-02 1972-01-25 Procedimento per la depolimerizza zione del politetrafluoroetilene
DE2204141A DE2204141B2 (de) 1971-02-02 1972-01-28 Verfahren zur Herstellung von Tetrafl uoräthy len
JP47010620A JPS5238525B1 (it) 1971-02-02 1972-01-31

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US00111963A US3832411A (en) 1971-02-02 1971-02-02 Method for the depolymerization of polytetrafluoroethylene

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JP (1) JPS5238525B1 (it)
DE (1) DE2204141B2 (it)
FR (1) FR2124212B1 (it)
GB (1) GB1361341A (it)
IT (1) IT948929B (it)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4128589A (en) * 1977-06-22 1978-12-05 Hughes Aircraft Company Generation of CF4 from Teflon for reactive atmosphere processing and growth of metal fluorides
US5432259A (en) * 1993-10-06 1995-07-11 Hoechst Aktiengesellschaft Process for the preparation of fluorinated monomers
WO1995032170A1 (fr) * 1994-05-19 1995-11-30 Nauchno-Vnedrencheskaya Firma 'polikom, Ink.' Procede d'obtention d'un monomere par decomposition pyrolitique d'un polymere et son dispositif de mise en ×uvre
US20040112758A1 (en) * 2002-12-16 2004-06-17 Bauer Gerald L Process for manufacturing fluoroolefins
EP1481957A1 (en) * 2002-03-01 2004-12-01 Daikin Industries, Ltd. Process for producing fluoromonomer
US20110184214A1 (en) * 2008-10-01 2011-07-28 Klaus Hintzer Process of making fluoroolefins by thermal decomposition of fluorinated materials
RU2469056C1 (ru) * 2011-06-16 2012-12-10 Государственное образовательное учреждение высшего профессионального образования "Национальный исследовательский Томский политехнический университет" Способ получения композиционного материала на основе политетрафторэтилена и диоксида кремния
RU2497846C1 (ru) * 2012-04-24 2013-11-10 Федеральное государственное бюджетное учреждение науки Байкальский институт природопользования Сибирского отделения Российской академии наук (БИП СО РАН) Способ утилизации отходов политетрафторэтилена
RU2656488C1 (ru) * 2017-05-03 2018-06-05 Общество с ограниченной ответственностью "Малое инновационное предприятие "Байкальский научный центр прочности" Способ утилизации отходов политетрафторэтилена
WO2021130626A1 (en) 2019-12-23 2021-07-01 3M Innovative Properties Company Process of making fluoroolefins by thermal decomposition of fluorinated ionomers

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2394581A (en) * 1943-10-04 1946-02-12 Kinetic Chemicals Inc Pyrolysis of tetrafluoroethylene polymer
US2406153A (en) * 1944-06-23 1946-08-20 Du Pont Depolymerization of polymeric tetrafluoroethylene
DE1003700B (de) * 1954-07-30 1957-03-07 Hoechst Ag Verfahren zur Herstellung von niedermolekularen Fluorchlorkohlenstoffen fluessiger oder wachsartiger Konsistenz
GB960309A (en) * 1962-01-24 1964-06-10 Ici Ltd Production of tetrafluoroethylene
US3284169A (en) * 1962-02-21 1966-11-08 Thiokol Chemical Corp Reactor equipment for the production of tetrafluoroethylene

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2394581A (en) * 1943-10-04 1946-02-12 Kinetic Chemicals Inc Pyrolysis of tetrafluoroethylene polymer
US2406153A (en) * 1944-06-23 1946-08-20 Du Pont Depolymerization of polymeric tetrafluoroethylene
DE1003700B (de) * 1954-07-30 1957-03-07 Hoechst Ag Verfahren zur Herstellung von niedermolekularen Fluorchlorkohlenstoffen fluessiger oder wachsartiger Konsistenz
GB960309A (en) * 1962-01-24 1964-06-10 Ici Ltd Production of tetrafluoroethylene
US3284169A (en) * 1962-02-21 1966-11-08 Thiokol Chemical Corp Reactor equipment for the production of tetrafluoroethylene

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4128589A (en) * 1977-06-22 1978-12-05 Hughes Aircraft Company Generation of CF4 from Teflon for reactive atmosphere processing and growth of metal fluorides
US5432259A (en) * 1993-10-06 1995-07-11 Hoechst Aktiengesellschaft Process for the preparation of fluorinated monomers
WO1995032170A1 (fr) * 1994-05-19 1995-11-30 Nauchno-Vnedrencheskaya Firma 'polikom, Ink.' Procede d'obtention d'un monomere par decomposition pyrolitique d'un polymere et son dispositif de mise en ×uvre
EP1481957A4 (en) * 2002-03-01 2006-05-24 Daikin Ind Ltd PROCESS FOR THE PREPARATION OF FLUOROMONOMER
US7317071B2 (en) * 2002-03-01 2008-01-08 Daikin Industries, Ltd. Process for producing fluoromonomer
EP1481957A1 (en) * 2002-03-01 2004-12-01 Daikin Industries, Ltd. Process for producing fluoromonomer
US20060020106A1 (en) * 2002-03-01 2006-01-26 Daikin Industries, Ltd. Process for producing fluoromonomer
US20050240067A1 (en) * 2002-12-16 2005-10-27 3M Innovative Properties Company Process for manufacturing fluoroolefins
US20040112758A1 (en) * 2002-12-16 2004-06-17 Bauer Gerald L Process for manufacturing fluoroolefins
US7250540B2 (en) 2002-12-16 2007-07-31 3M Innovative Properties Company Process for manufacturing fluoroolefins
US6919015B2 (en) 2002-12-16 2005-07-19 3M Innovative Properties Company Process for manufacturing fluoroolefins
US20110184214A1 (en) * 2008-10-01 2011-07-28 Klaus Hintzer Process of making fluoroolefins by thermal decomposition of fluorinated materials
US8344190B2 (en) 2008-10-01 2013-01-01 3M Innovative Properties Company Process of making fluoroolefins by thermal decomposition of fluorinated materials
RU2469056C1 (ru) * 2011-06-16 2012-12-10 Государственное образовательное учреждение высшего профессионального образования "Национальный исследовательский Томский политехнический университет" Способ получения композиционного материала на основе политетрафторэтилена и диоксида кремния
RU2497846C1 (ru) * 2012-04-24 2013-11-10 Федеральное государственное бюджетное учреждение науки Байкальский институт природопользования Сибирского отделения Российской академии наук (БИП СО РАН) Способ утилизации отходов политетрафторэтилена
RU2656488C1 (ru) * 2017-05-03 2018-06-05 Общество с ограниченной ответственностью "Малое инновационное предприятие "Байкальский научный центр прочности" Способ утилизации отходов политетрафторэтилена
WO2021130626A1 (en) 2019-12-23 2021-07-01 3M Innovative Properties Company Process of making fluoroolefins by thermal decomposition of fluorinated ionomers

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Publication number Publication date
DE2204141A1 (de) 1972-08-17
IT948929B (it) 1973-06-11
JPS5238525B1 (it) 1977-09-29
FR2124212A1 (it) 1972-09-22
GB1361341A (en) 1974-07-24
DE2204141B2 (de) 1974-05-30
FR2124212B1 (it) 1973-11-23

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Owner name: LNP CORPORATION, 412 KING STREET, MALVERN, PA 1935

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