WO2004061160A1 - Process for manufacturing fluoroolefins - Google Patents
Process for manufacturing fluoroolefins Download PDFInfo
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- WO2004061160A1 WO2004061160A1 PCT/US2003/036577 US0336577W WO2004061160A1 WO 2004061160 A1 WO2004061160 A1 WO 2004061160A1 US 0336577 W US0336577 W US 0336577W WO 2004061160 A1 WO2004061160 A1 WO 2004061160A1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/23—Preparation of halogenated hydrocarbons by dehalogenation
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/26—Preparation of halogenated hydrocarbons by reactions involving an increase in the number of carbon atoms in the skeleton
- C07C17/263—Preparation of halogenated hydrocarbons by reactions involving an increase in the number of carbon atoms in the skeleton by condensation reactions
- C07C17/269—Preparation of halogenated hydrocarbons by reactions involving an increase in the number of carbon atoms in the skeleton by condensation reactions of only halogenated hydrocarbons
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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
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C21/00—Acyclic unsaturated compounds containing halogen atoms
- C07C21/02—Acyclic unsaturated compounds containing halogen atoms containing carbon-to-carbon double bonds
- C07C21/18—Acyclic unsaturated compounds containing halogen atoms containing carbon-to-carbon double bonds containing fluorine
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C21/00—Acyclic unsaturated compounds containing halogen atoms
- C07C21/02—Acyclic unsaturated compounds containing halogen atoms containing carbon-to-carbon double bonds
- C07C21/18—Acyclic unsaturated compounds containing halogen atoms containing carbon-to-carbon double bonds containing fluorine
- C07C21/185—Acyclic unsaturated compounds containing halogen atoms containing carbon-to-carbon double bonds containing fluorine tetrafluorethene
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B3/00—Electrolytic production of organic compounds
- C25B3/20—Processes
- C25B3/27—Halogenation
- C25B3/28—Fluorination
Definitions
- This invention relates to a process for manufacturing fluoroolefins.
- Tetrafl oroethylene (TFE) and hexafluoropropylene (HFP) are widely used as monomers in the manufacture of plastic and elastomeric fluoropolymers. See, for example, J. Scheirs in Modern Fluoropolymers, Wiley, 1996.
- the worldwide consumption of TFE exceeds 10 5 tons/year.
- HFP is used as a comonomer to manufacture thermoplastic and elastomeric fluoropolymers and as starting material for making hexafluoropropene oxide (HFPO).
- HFPO hexafluoropropene oxide
- the worldwide consumption is estimated to be 30,000 tons/year.
- TFE and HFP There are several known methods for manufacturing TFE and HFP.
- the high temperature (600°C to 1000°C) pyrolysis of CHC1F 2 yields TFE and HFP in high yields.
- R-22 This process produces equimolar amounts of aqueous hydrochloric acid and considerable amounts of partially fluorinated and chlorinated compounds, which are difficult to separate from TFE to obtain polymerization grade TFE (U.S. Patent No. 4,898,645).
- aqueous hydrochloric acid For the aqueous hydrochloric acid, industrial applications are generally sought that can use the aqueous hydrochloric acid.
- the fluorinated and other side products have to be incinerated through thermal oxidizers, which is another costly process and produces high amounts of CO 2 .
- U.S. Patent No. 5,611,896 describes a process where elemental fluorine is reacted with carbon to produce CF 4 , which is converted to TFE in a plasma torch in the presence of carbon. Unreacted CF is fed back to the plasma.
- this technology is advantageously "closed-loop" which means emissions to the environment are minimal. But this process is hardly economically viable due to the use of costly elemental fluorine and the high-energy consumption involved.
- a further method described in the art involves reacting TFE and/or HFP with ethylene and then fluorinating the cyclobutanes by electrochemical fluorination (ECF).
- ECF electrochemical fluorination
- This perfluoro- cyclobutane product is then pyrolyzed using conventional pyrolizing techniques as described for example in EP 455,399 including the references cited therein and WO 00/75092.
- Any byproducts formed in the ECF process are separated off and are not further used in accordance with the teaching of WO 00/75092. Accordingly, substantial waste material is produced with this process, which causes an environmental burden and makes the process economically less attractive.
- the process requires the use of TFE as one of the starting compounds, which creates an additional economical disadvantage as part of the TFE produced is needed to produce further TFE.
- U.S. Patent No. 3,081,245 discloses a process for preparing TFE that comprises feeding a saturated perfluorocarbon to a continuous electric arc, passing the emerging gaseous product through a carbon bed at a temperature of 2700°C to 2000°C and quenching the resulting gaseous product mixture to less than 500°C in less than one second.
- EP 371,747 discloses a process for making TFE by heating in the presence of a gas selected from Ar, HF, CO, CF 4j and CO 2 at a temperature of at least 2000°K a C 2 to Cio compound containing fluorine and hydrogen in which the F to H ratio is greater than or equal to 1 and the F to C ratio is greater than or equal to 1. Heating is carried out with a Direct Current
- TFE Another chlorine-free process for making TFE is disclosed in GB 766 324 by pyrolyzing a fluorocarbon with at least 3 carbons per molecule. Pyrolyzing occurs at a temperature of at least 1500°C preferably generated in an electric arc. The side products of the pyrolysis are fed back in the pyrolysis furnace after the separation of TFE.
- the fluorocarbons to be pyrolyzed are obtained from exhaustive fluorination of petroleum fractions using elemental fluorine, which renders the process economically unattractive.
- Still another chlorine-free process to make TFE is disclosed in WO 01 58841-A1 where gaseous or liquid fluorocarbons are pyrolyzed via DC plasma.
- Another chlorine-free process to make TFE is described in WO 01/58584-A2.
- Gaseous, liquid, and solid perfluorocarbons, particularly perfluoropolymers, are pyrolyzed via inductive heating.
- TFE may have an efficient yield (overall yield preferably is higher than 90% based on a hydrocarbon feed) and may eliminate a hydrochloric acid waste stream.
- the process of the present invention may also produce HFP and can thus be used to make both TFE and HFP if desired.
- the process generally involves less separation efforts to purify TFE, can be designed in a cost efficient manner, and can be designed as a so-called closed-loop in which no or very low amounts of waste material is created. This closed-loop process is environmentally advantageous.
- the present invention provides a process for manufacturing tetrafluoroethylene and/or hexafluoropropylene comprising:
- the pyrolysis of step (c) is carried out in the presence of carbon.
- This allows for the conversion of perfluorinated compounds that have a high F to C ratio such as CF 4 and C 2 F 6 .
- These compounds are typically present in an off-gas stream of the ECF cell and can in accordance with an embodiment of the present invention be separated therefrom and thus pyrolyzed in the presence of carbon.
- the pyrolysis may proceed with a DC plasma or through inductive heating and is preferably carried out in the presence of carbon.
- the pyrolysis may be carried out at a temperature of at least 500 °C, generally from 500°C to 3000°C (inclusive), typically between 700°C and 3000°C (inclusive), or between 900°C and 1500°C (inclusive).
- Fig. 1 shows schematically one embodiment of the inventive process as a closed-loop.
- a hydrocarbon feedstock is electrochemically fluorinated in an ECF cell (10).
- the lower boiling fluorocarbons are separated (11) from the off-gas, mainly hydrogen, stream 10a, and optionally further separated into perfluorinated compounds to be fed in the pyrolysis furnace (20), stream 1 la, and partially fluorinated compounds to be fed back to the ECF cell (10), stream 1 lb.
- the higher boiling fluorinated chemical compounds are separated from the ECF effluent or so-called brine of the ECF cell (12), stream 10b.
- fluorinated compounds are further separated in perfluorinated compounds to be fed as the perfluorinated feed material in the pyrolysis furnace (20) and partially fluorinated compounds that are fed back to the ECF cell (10), stream 12b.
- the perfluorinated compounds of stream 11a and 12a are pyrolyzed at temperatures of 500°C to 3000°C in a pyrolysis chamber (20) and quenched.
- the quenched gases, stream 20a are subjected to distillation (30) yielding TFE and optionally HFP, and undesired by-products, which are fed back to the pyrolysis furnace (20), stream 30b.
- Fig. 2 shows another embodiment of the present invention.
- the stream 30b of Fig. 1 is now fed into a DC plasma furnace (40), stream 30c.
- the quenched pyrolyzed gases are fed back to the distillation (30), stream 40a, to recover TFE and optionally HFP therefrom.
- all or part of the perfluorinated compounds from the off-gas stream 10a of the ECF cell may be fed in the DC plasma furnace (40), as carrier gases (stream lie).
- the present invention provides a process for manufacturing tetrafluoroethylene and/or hexafluoropropylene.
- the process involves perfluorinating a starting material using electrochemical fluorination and then feeding the perfluorinated material into a pyrolysis furnace to yield TFE and optionally HFP.
- the process of the present invention is preferably designed as a closed-loop process where all perfluorinated compounds can be converted into fluoroolefins and all undesired byproducts (e.g., C-H containing/partially fluorinated materials) can be recycled until completion. This reduces the process cost and fluorinated compounds in waste streams.
- the process of the present invention is environmentally responsible.
- a variety of hydrocarbons linear, branched, saturated, unsaturated
- the perfluorinated ECF effluent is fed into the pyrolysis and the partially fluorinated materials are fed back to the ECF cell.
- partially fluorinated materials that are fed back to the ECF cell are generally referred to as starting materials.
- desired TFE and/or HFP is produced. Any perfluorinated waste products can be recycled and again be subjected to pyrolysis.
- the pyrolysis is preferably carried out in the presence of carbon. Inductive heating is advantageously used but also DC plasma can be used. When inductive heating is used, the pyrolysis can proceed at a temperature of at least 500°C and not more than 3000°C. Any partially fluorinated compounds in the waste streams can be re-fed into the ECF cell.
- the present invention requires less separation efforts than processes known in the art especially during the separation and purification of TFE. This reduces the costs involved. The capital and energy costs are less because simple distillation is involved (fewer columns) versus R-22 pyrolysis.
- the process of the present invention may be economically feasible even at a smaller volume scale (e.g., 1000 tons/year) than the processes known in the art, and thus may require less capital expenditure.
- TFE cannot be efficiently transported because of its instability. Therefore, TFE is typically converted to a polymer or further processed prior to transport. Thus, it is advantageous to be able to produce TFE at the site where the end polymer is produced. Because the process of the present invention is economically feasible at low volume production, the TFE can be readily produced at the site where the end polymer is made.
- Fluorinated refers to chemical compounds having at least one carbon-bonded hydrogen replaced by a fluorine, and specifically includes perfluorinated compounds and partially fluorinated compounds, i.e., compounds that have C-F and C-H bonds in the molecule.
- Perfluorinated compounds refers to chemical compounds where essentially all carbon- bonded hydrogens have been replaced by fluorines, although typically some residual hydride will be present in a perfluorinated composition; e.g., preferably less than 2 weight % perfluorinated product.
- Fig. 1 One embodiment of the process of the present invention is set forth in Fig. 1.
- HF and starting material are fed into the ECF cell 10.
- the ECF effluent 10b is then fed to the separation process 12 and the off-gas from the ECF cell 10a is fed to a membrane process 11.
- the membrane process separates the off-gas 10a, partially fluorinated compounds 1 lb, and perfluorinated compounds 11a.
- the partially fluorinated compounds are returned to the ECF cell for further processing.
- the off-gas (H 2 ) may be vented or used for energy production.
- the ECF effluent 10b is separated 12 and the desired perfluorinated compound 12a and the perfluorinated compounds 1 la are fed to the pyrolysis furnace 20.
- the product mixture 20a is then fed into the separation process 30, which typically is a simple distillation.
- the desired products TFE and/or HFP are separated out (30a).
- the undesirable fluorine- containing products 30b are returned to the pyrolysis furnace for further processing.
- perfluorinated compounds lie from the off-gas 10a and the perfluorinated compounds from the distillation 30 (stream 30c) are subjected to a DC plasma (40).
- the reaction mixture of the DC plasma is quenched and then fed into the separation process 30 (stream 40a).
- All of the off-gas perfluorinated compounds may be fed into the DC plasma (stream lie) in which case stream 11a will not be present or only part thereof may be fed into the DC plasma such that both streams 11a and lie co-exist.
- stream 40a may be used or alternatively co-exist with stream 30b.
- the starting material can be a gas, a liquid, or a mixture thereof.
- the starting material generally comprises linear or branched hydrocarbon compounds, partially fluorinated linear or branched hydrocarbon compounds or mixtures thereof.
- the linear or branched hydrocarbon compound generally consists of carbon and hydrogen but hydrocarbon compounds having one or more substituents such as hydroxy, amino groups, carboxy groups, sulphonic acid groups and amide groups are within the scope of the term 'hydrocarbon compound' as used in this invention.
- the starting material will be substantially free of chlorine, bromme, or iodine containing materials as these create undesirable waste material.
- Substantially free means that the starting material is either free of or contains a material in amount of not more than 1 or 2% by weight relative to the total weight of starting material.
- the starting material may contain cyclic compounds, such as cyclic hydrocarbons in admixture with the linear or branched (partially fluorinated) hydrocarbon compounds.
- the process provides for the use of mixtures of compounds as the starting material and these mixtures may be complex in that they contain a large variety of different compounds.
- the hydrocarbon compound may comprise saturated and unsaturated compounds including olefins and aromatic compounds such as benzene, toluene, or xylene.
- Examples of especially preferred starting materials include butane, pentane, hexane, heptane, and octane.
- Examples of preferred readily available starting materials include methane and hydrocarbons up to Cio and mixtures thereof, and mixtures of hydrocarbons with olefins (e.g., isobutylene, etc.).
- a particular hydrocarbon starting material includes crude oil and petroleum fractions, so-called distillation cuts originating from refining of crude oil and from making olefins such as ethylene and propylene.
- the boiling point of these petroleum fractions is not more than 200°C, and more preferably not more than 150°C or 100°C.
- the gaseous starting material has a boiling point of at least -50°C and is easy to liquefy, e.g., propane (b.p. -42°C), propene (b.p. - 47°C), butane (b.p. 0°C), butene (b.p. -6°C), isobutylene (b.p. -7°C).
- propane b.p. -42°C
- propene b.p. - 47°C
- butane b.p. 0°C
- butene b.p. -6°C
- isobutylene b.p. -7°C
- any electrochemical fluorination process can be used to perfluorinate the starting material.
- the Simons electrochemical fluorination process the interrupted current process (see WO Publication 98/50603), the bipolar flow cell (see U.S. Patent No. 5,322,597), the SOLUTIA EHD process, and the like, may be used.
- the Simons electrochemical fluorination (Simons ECF) process was commercialized initially in the 1950s by Minnesota Mining and Manufacturing Company. This ECF process comprises passing a direct electric current through an electrolyte, (i.e., a mixture of fluorinatable organic starting compound, liquid anhydrous hydrogen fluoride, and perhaps a conductivity additive), to produce the desired fluorinated compound or fluorochemical.
- Simons ECF cells typically utilize a monopolar electrode assembly, i.e., electrodes connected in parallel through electrode posts to a source of direct current at a low voltage (e.g., four to eight volts).
- Simons ECF cells are generally undivided, single-compartment cells, i.e., the cells typically do not contain anode or cathode compartments separated by a membrane or diaphragm.
- the Simons ECF process is disclosed in U.S. Patent No. 2,519,983 (Simons) and is also described in some detail by J. Burdon and J. C. Tatlow in Advances in Fluorine Chemistry (M. Stacey, J. C. Tatlow, and A. G. Sharpe, editors) Volume 1, pages 129-37, Buttersworths Scientific Publications, London (1960); by W. V. Childs, L. Christensen, F. W. Klink, and C. F. Kolpin in Organic Electrochemistry (H.
- Simons ECF can be carried out essentially as follows.
- a starting material and an optional conductivity additive are dispersed or dissolved in anhydrous hydrogen fluoride to form an electrolytic "reaction solution.”
- One or more anodes and one or more cathodes are placed in the reaction solution and an electric potential (voltage) is established between the anode(s) and cathode(s), causing electric current to flow between the cathode and anode, through the reaction solution, and resulting in an oxidation reaction (primarily fluorination, i.e., replacement of one or more carbon-bonded hydrogens with carbon-bonded fluorines) at the anode, and a reduction reaction (primarily hydrogen evolution) at the cathode.
- oxidation reaction primarily fluorination, i.e., replacement of one or more carbon-bonded hydrogens with carbon-bonded fluorines
- electrical current refers to electric current in the conventional meaning of the phrase, the flow of electrons, and also refers to the flow of positively or negatively charged chemical species (ions).
- the Simons ECF process is well known, and the subject of numerous technical publications.
- An early patent describing the Simons ECF process is U.S. Patent No. 2,519,983 (Simons), which contains a drawing of a Simons cell and its appurtenances.
- a description and photograph of laboratory and pilot plant-scale electrochemical fluorination cells suitable for practicing the Simons ECF process appear at pages 416-418 of Vol. 1 of "Fluorine Chemistry," edited by J.H. Simons, published in 1950 by Academic Press, Inc., New York.
- United States Patent Numbers 5,322,597 (Childs et al.) and 5,387,323 (Minday et al.) each refer to the Simons ECF process and Simons ECF cell.
- the Simons ECF process is practiced with a constant current passed through the electrolyte; i.e., a constant voltage and constant current flow. See for example W.N. Childs, et al., Anodic Fluorination in Organic Electrochemistry, H. Lund and M. Baizer eds., Marcel Dekker Inc., New York, 1991.
- the current passing through the electrolyte causes one or more of the hydrogens of the starting material to be to replaced by fluorine.
- Flow cells comprise a set (one of each), stack, or series of anodes and cathodes, where reaction solution is caused to flow over the surfaces of the anodes and cathodes using forced circulation.
- These types of flow cells are generally referred to as monopolar flow cells (having a single anode and a single cathode, optionally in the form of more than a single plate, as with a conventional electrochemical fluorination cell), and, bipolar flow cells (having a series of anodes and cathodes).
- U.S. Patent No. 5,322,597 (Childs et al.) incorporated by reference herein more recently describes the practice in a bipolar flow cell of an electrochemical fluorination process comprising passing by forced convection a liquid mixture comprising anhydrous hydrogen fluoride and fluorinatable organic compound at a temperature and a pressure where a substantially continuous liquid phase is maintained between the electrodes of a bipolar electrode stack.
- the bipolar electrode stack comprises a plurality of substantially parallel, spaced-apart electrodes made of an electrically conductive material, e.g., nickel, which is essentially inert to anhydrous hydrogen fluoride and when used as an anode, is active for electrochemical fluorination.
- the electrodes of the stack are arranged in either a series or a series-parallel electrical configuration.
- the bipolar electrode stack has an applied voltage difference that produces a direct current that can cause the production of fluorinated organic compound.
- Solutia EHD electrohydrodimerization
- a reaction solution is prepared that comprises hydrogen fluoride and a starting material.
- the hydrogen fluoride is preferably anhydrous hydrogen fluoride, meaning that it contains at most only a minor amount of water, e.g., less than about 1 weight percent (wt%) water, preferably less than about 0.1 weight percent water.
- the reaction solution within the ECF cell includes an electrolyte phase comprising HF and an amount of starting material dissolved therein.
- the starting material is preferably to some degree soluble or dispersible in liquid hydrogen fluoride. Gaseous starting materials can be bubbled through the hydrogen fluoride to prepare the reaction solution, or charged to the cell under pressure. Solid or liquid starting materials can be dissolved or dispersed in the hydrogen fluoride. Starting materials that are relatively less soluble in hydrogen fluoride can be introduced to the cell as a solute dissolved in a fluorochemical fluid.
- reaction solution is exposed to reaction conditions (e.g., temperature, pressure, electric voltage, electric current, and power) sufficient to cause fluorination of the starting material.
- reaction conditions e.g., temperature, pressure, electric voltage, electric current, and power
- Reaction conditions chosen for a particular fluorination process depend on factors such as the size and construction of the ECF cell, the composition of the reaction solution, the presence or absence of a conductivity additive, flow rate, etc.
- the reaction temperature can be any temperature that allows a useful degree of fluorination of the starting material.
- the temperature may depend on the factors discussed in the preceding paragraph, as well as the solubility of the starting material and the physical state of the starting material or the fluorinated product.
- the electricity passed through the reaction solution can be any amount that will result in fluorination of the starting material.
- the current is preferably insufficient to cause excessive fragmentation of the starting material or to cause the liberation of fluorine gas during fluorination.
- the ECF effluent can be separated using conventional techniques such as distillation.
- the desired perfluorinated compounds are then fed to the pyrolysis.
- the insufficiently fluorinated compounds are returned to the ECF cell for perfluorination.
- the amounts of partially fluorinated materials in the feed to the pyrolysis preferably is less than 10 weight percent, more preferably less than 5 weight percent, and most preferably less than 2 weight percent.
- the ECF cell may have one or more membrane systems to capture the off-gas.
- the off-gas is hydrogen (H 2 ).
- Some fluorine-containing compounds i.e., perfluorinated and non-perfluorinated compounds
- a membrane process can be used to capture the partially fluorinated and perfluorinated compounds and then the partially fluorinated compounds can be fed back into the ECF cell.
- Membranes separate gases by the principle of selective permeation across the membrane wall.
- the rate of permeation of each gas is determined by its solubility in the membrane material and the rate of diffusion through the molecular free volume in the membrane wall. Gases that exhibit high solubility in the membrane and gases that are small in molecular size, permeate faster than larger, less soluble gases.
- the output from the ECF process includes a large volume of hydrogen, perfluorinated product, and partially fluorinated materials.
- the membrane process separates the hydrogen from the fluorinated species by allowing the smaller, more soluble hydrogen to pass through the membrane while concentrating the fluorinated material (permeate).
- the desire is to recover greater than 99% of the fluorinated materials at greater than 99.9% purity ( « 1% H2).
- Suitable membranes are commercially available.
- One commercially available membrane is the MEDALTM Gas-separation membrane available from Air Liquide, Houston, TX. (See also U.S. Patent Numbers 5,858,065; 5,919,285; 5,814,127; and 5,759,237.)
- cryogenic distillation process may be used to separate the off-gas (H 2 ).
- catalytic "cold combustion" of H 2 by metals (e.g., platinum) in the presence of O 2 can be used.
- Pyrolysis is defined as subjecting perfluorinated materials obtained from the ECF, streams 11a and 12 a, to temperatures above 500 °C thereby heat cracking the perfluorinated materials e.g., in a pyrolysis furnace ((20), Fig. 1).
- the perfluorinated compounds can be fed in the furnace as gases mostly under sub-atmospheric pressure. The perfluorinated compounds fragment under these conditions prevailingly into difluoro carbenes
- the so obtained hot "reaction mixture” is subsequently quenched, i.e., rapid cooling to below 400 °C, generally below 300°C and preferably below 100°C typically within less than a second, preferably in less than 0.1 seconds.
- Cooling rates of 10 - 10 5 K/sec may be used. , These high cooling rates can be achieved either by conducting the hot reaction mixture through a bundle of pipes which are externally cooled or by injecting a coolant in the reaction mixture.
- the latter technology is also called wet quenching, the former dry quenching.
- Cold gases or liquids, like liquid perfluorinated carbons or water can be used as coolant.
- the efficiency of the quench process generally controls the selectivity of TFE. The higher the cooling rate the higher the selectivity and the less coking. Coking is formation of carbon arising via disproportionation of
- Heating of the pyrolysis chamber can be achieved from external sources, like electric power or superheated steam.
- the pyrolysis is carried out at a temperature of at least 500°C to not more than 3000°C.
- a modern technology is inductive heating via microwaves. The needed powerful microwave generators are commercially available. Frequencies are usually at about 50 to 3000 kHz. Temperature is typically in the range of 600 to 3000°C, for example 700°C to 2500°C.
- Inductive heating via microwaves is described in WO 95/21126, U.S. Patent No. 5,110,996, WO 00/75092-A1, and WO 01/58584-A2.
- the pyrolysis proceeds in the presence of carbon.
- carbon may be provided as a heat packing material.
- the use of carbon is particularly advantageous to convert CF 4 , C 2 F 6 and other perfluorinated compounds where the ratio fluorine atoms to carbon atoms is significantly greater than 2, e.g., greater than 2.5 or 2.1, to TFE. These compounds cannot be readily converted to TFE in absence of carbon because of stoichiometric constraints.
- the needed temperature to convert these perfluorinated compounds into TFE in the presence of carbon can be readily achieved with inductive heating.
- Another method for pyrolysis is the Direct Current (DC) Plasma technology as described for example in U.S. Patent No. 5,611,896 incorporated by reference herein.
- a carrier gas is needed to maintain the flame between the electrodes. Flame temperature may exceed 10000°K.
- the DC plasma pyrolysis is also conducted in the presence of carbon.
- CF 4 is a carrier gas
- the CF 4 is also converted to TFE in addition to other perfluorinated compounds that have a lower fluorine to carbon ratio.
- Carbon may be provided for in the DC plasma pyrolysis through injection of powdery carbon or by operating "self consuming" carbon electrodes.
- the hot reaction mixture resulting in the DC plasma can be quenched as described above to obtain TFE and/or HFP at high selectivities.
- Plasma technology is, for example, covered in "Fluorine Reactions in Plasma" by Barry Bronfm, MIT PRESS, Mass. (1967).
- a further suitable DC plasma installation is described for example in WO 01/00156.
- pyrolysis at a temperature of not more than 3000°C e.g., via inductive heating is used to pyrolyze perfluorinated compounds originating from the ECF effluent ( Figure 2, stream 12a) and a DC plasma is used to pyrolyze perfluorinated compounds originating from the ECF off-gas (stream lie) and distillation (stream 30c).
- each of these pyrolysis is conducted in the presence of carbon.
- the process or part of it can be either batch or continuous.
- the ECF cell can produce a perfluorinated effluent that is fed batchwise to the pyrolysis, or the ECF cell can produce a perfluorinated effluent that is continuously fed into the pyrolysis. With either method, the process can be designed as a closed-loop.
- TFE and F ⁇ FP are isolated from the quenched mixture of gases, streams 20a and 40a, via distillation (30).
- the mixture typically contains, TFE, HFP, perfluoroisobutylene (PFIB), and saturated perfluoroalkanes like CF 4 , C 2 F 6 , or octafluorocyclobutane.
- PFIB perfluoroisobutylene
- saturated perfluoroalkanes like CF 4 , C 2 F 6 , or octafluorocyclobutane.
- chlorine hydrogen and chlorine containing chemical compounds are virtually absent. This renders the separation of TFE and HFP via distillation relatively simple in comparison to the R-22 process even when TFE is to be used in a subsequent polymerization to produce PTFE.
- the process of the present invention can yield polymerization grade TFE with only few distillation columns; essentially only 2 columns are needed to separate the "low boiling” components like CF 4 , C 2 F 6 , eye. C 4 F 8 from the high boiling components like PFIB.
- the distillation cuts of these side products are fed back to pyrolysis e.g., stream 30b, Fig. 1 to a low temperature pyrolysis using inductive heating, or in another embodiment of the present invention to a DC plasma furnace (40), stream 30c, Fig. 2.
- a 1-liter electrochemical fluorination cell of the type described in U.S. Patent No. 2,567,011, equipped with 2 overhead condensers having a nickel anode with a surface area of 0.037 m 2 was charged with 1000 grams C 6 F ⁇ 4 , 40 grams of dimethyldisulfide, 40 grams of octane and 200 grams of anhydrous HF.
- the cell was operated at 45 °C and 2 bar.
- Voltage was between 5-6 Volts, current density about 1500 A/m 2 .
- Voltage was reduced for 4 seconds to less than 4 Volts causing the current to fall to essentially zero after each 80 seconds ("intermitted current").
- Octane was continuously fed to the cell to maintain its concentration in the circulating fluorochemical phase at about 5 wt%. Circulation rate was varied from 0.3 to 1 cell volume/hour with an external pump without an observably distinct effect on the fluorination rates.
- the experiment was run for 500 hours. Intermittently, a portion of the fluorochemical phase was removed, the perfluoroalkanes were separated, partially stored and partially recycled back to the ECF cell. HF was replenished according to current consumption. The off-gas containing 1.1 volume % of fluorocarbons were stored in a vessel at 8 bar and subjected to the Membrane Process set forth in Example 2 below.
- perfluoroalkanes were analyzed via gas chromatography for perfluoro octane. The yield of which was 15 wt%. The other products are lower fluoroalkanes fragmented down up to CF 4 . Current efficiency was about 95 %.
- Example 1 The off-gas stream emanating from the ECF cell behind the overhead condensers at the run of Example 1 contained about 1.7 volume % of perfluorinated alkanes. Typical composition is shown in Table 1.
- the off-gas stream was washed with aqueous NaOH solution, filtered to remove any liquid and solid particles compressed to 8 bar and fed to a 2-stage membrane system consisting of a polyimide, asymmetric composite hollow fiber membrane.
- a MEDALTM Gas separation process from Air Liquide, Houston, Texas, according to Example 4 of U.S. Patent No. 5,814.127 was used.
- the output of the 2 nd membrane module yielded 99.9 % fluorocarbon with less than 0.1 % H 2 , the composition of which is given in Table 2.
- the "waste-stream" contained 99.7 % hydrogen.
- the recovered fluorocarbons can be directly used as carrier gas at the DC plasma pyrolysis and also as feedstock for the inductive heating pyrolysis.
- Table 4 gives the results of the fluorocarbon mixture as recovered from the off-gas (Example 2). No additional CF 4 as used as carrier gas. Table 4: DC plasma pyrolysis of fluorocarbon mixture from off-gas
- Example 6 The same installation as in Example 4 was used to investigate the converting of CF 4 to TFE and HFP. Results are given in Table 6. CF was fed into the installation at a flow-rate of 2 kg/hr at varying temperatures of the heating packing material (graphite). The same quenching as in Example 4 was practiced. Results are given in Table 6. Table 6: Pyrolysis of CF 4 ; flow rate 2 kg/hr
- Table 6 illustrates that CF 4 can be converted to TFE and HFP at reasonable rates. The yield for these monomers suffers from decreasing quenching rates at higher pyrolysis temperatures.
Abstract
Description
Claims
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EP03783545.1A EP1573088B1 (en) | 2002-12-16 | 2003-11-14 | Process for manufacturing fluoroolefins |
JP2004565003A JP2006509831A (en) | 2002-12-16 | 2003-11-14 | Method for producing fluoroolefin |
AU2003290961A AU2003290961A1 (en) | 2002-12-16 | 2003-11-14 | Process for manufacturing fluoroolefins |
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US10/320,796 US6919015B2 (en) | 2002-12-16 | 2002-12-16 | Process for manufacturing fluoroolefins |
US10/320,796 | 2002-12-16 |
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US (2) | US6919015B2 (en) |
EP (1) | EP1573088B1 (en) |
JP (1) | JP2006509831A (en) |
CN (1) | CN1726308A (en) |
AU (1) | AU2003290961A1 (en) |
RU (1) | RU2005114348A (en) |
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Cited By (1)
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WO2012012113A1 (en) | 2010-06-30 | 2012-01-26 | 3M Innovative Properties Company | Process for manufacturing perfluoroolefins by pyrolysis of perfluorocarbons in the presence of hydrogen |
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WO2012012113A1 (en) | 2010-06-30 | 2012-01-26 | 3M Innovative Properties Company | Process for manufacturing perfluoroolefins by pyrolysis of perfluorocarbons in the presence of hydrogen |
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JP2006509831A (en) | 2006-03-23 |
US20050240067A1 (en) | 2005-10-27 |
US6919015B2 (en) | 2005-07-19 |
US7250540B2 (en) | 2007-07-31 |
CN1726308A (en) | 2006-01-25 |
US20040112758A1 (en) | 2004-06-17 |
ZA200505678B (en) | 2007-02-28 |
EP1573088A1 (en) | 2005-09-14 |
AU2003290961A1 (en) | 2004-07-29 |
EP1573088B1 (en) | 2015-03-11 |
RU2005114348A (en) | 2006-01-20 |
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