USOO6806396 B2 (12) United States Patent (10) Patent No.: US 6,806,396 B2 Gelblum et al. (45) Date of Patent: Oct. 19, 2004 (54) DISPOSAL OF FLUOROFORM (HFC-23) (52) U.S. Cl. ....................... 570/237; 570/153; 570/159; 570/170; 570/171; 570/216; 570/257; 570/261 (75) Inventors: Peter Gideon Gelblum, Philadelphia, PA (US); Velliyur Nott Mallikarjuna (58) Field of Search ................................. 570/237, 153, Rao, Wilmington, DE (US); Charles 570/159, 170, 171,216, 257, 261 Joseph Noelke, Wilmington, DE (US); Norman Herron, Newark, DE (US) (56) References Cited (73) Assignee: E. I. du Pont de Nemours and U.S. PATENT DOCUMENTS Company, Wilmington, DE (US) 3,009,966 A 11/1961 Hauptschein et al. 3,202.720 A 8/1965 Hauptschein et al. (*) Notice: Subject to any disclaimer, the term of this 5,516,947 A 5/1996 Manogue et al. patent is extended or adjusted under 35 6,025,532 A 2/2000 Sage et al. U.S.C. 154(b) by 134 days. FOREIGN PATENT DOCUMENTS (21) Appl. No.: 10/320,143 GB 1076699 7/1967 (22) Filed: Dec. 16, 2002 WO 96/29296 2/1996 (65) Prior Publication Data Primary Examiner Elvis O. Price US 2003/0166981 A1 Sep. 4, 2003 (57) ABSTRACT Related U.S. Application Data The present invention relates to the co-pyrolysis of fluoro 60) ProvisionalrOVISIOnal application No.NO. 60/341,640,O4U, filedIlled on Dec.Lec. 1818, form and chlorodifluoromethane to form a mixture of useful 2001. fluoroolefin and Saturated HFCs, notably, tetrafluoroethyl (51) Int. Cl." ......................... C07C 17/26; CO7C 17/38; ene and hexafluoropropylene and CFCHF and CO7C 21/00; CO7C 21/02; CO7C 21/19; CFCHFCF, respectively. C07C 21/22; CO7C 17/02; CO7C 17/04; C07C 17/08; CO7C 21/18 14 Claims, No Drawings US 6,806,396 B2 1 2 DISPOSAL OF FLUOROFORM (HFC-23) Washing could also limit the ultimate reaction product to saturated HFC compounds. In the Examples the reactor is This application claims the benefit of Provisional Appli quartz. Quartz reacts with hydrogen fluoride, a probable cation No. 60/341,640, filed Dec. 18, 2001. intermediate in the pyrolysis reaction of HFC-23 and HCFC 22. The elements of hydrogen fluoride are part of the process BACKGROUND OF THE INVENTION according to the present invention and its consumption in Side reactions, as with quartz, would lead to a reduction in 1. Field of the Invention the production of Saturated hydrofluorocarbons. This invention relates to the disposal of CHF. Another reference disclosing the auxiliary use of fluoro 2. Description of Related Art form in a pyrolysis reaction is U.S. patent application Ser. Fluoroform (CHF, HFC-23) is a by-product of the reac No. 09/878,540, filed Jun. 11, 2001 (U.S. patent application tion of HF with trichloromethane to form chlorodifluo Publication Ser. No. 2002/0032356-A), which discloses the romethane (CHF.Cl, HCFC-22), which is the primary pyrolysis of HCFC-22 in a gold-lined reactor to direct the source of perfluoroolefin, such as tetrafluoroethylene (TFE). 15 synthesis reaction to the formation of the fluoroolefins TFE The fluoroform by-product constitutes less than about 3 wt and HFP, without forming significant amounts of PFIB. The % of the HCFC-22 formed, but because annual production Examples disclose the co-pyrolysis of HCFC-22 and HCFC of HCFC-22 is large worldwide, the amount of fluoroform 124 (CFCHFCI) to favor the formation of HFP over TFE. by-product made amounts to Several millions of pounds per The possibility of fluoroform (CHF) being present with the HCFC-22 is also disclosed as a recycle gas in the reactor year. The fluoroform by-product either has to be used or has System, the fluoroform thereby being the major component to be Subject to disposal. fed to the reactor, indicating that the fluoroform is acting as U.S. Pat. No. 3,009,966 discloses that fluoroform is an inert carrier in the pyrolysis process, as would be thermally inert (col. 1, I. 13–14), but nevertheless finds a use expected from the relatively low pyrolysis temperatures and for the fluoroform as a source of TFE and hexafluoropro 25 short contact times disclosed. Such use of fluoroform is not pylene (HFP) by pyrolysis of the fluoroform at temperatures an effective way to dispose of fluoroform. of 700–1090° C., with temperatures of 1000° C. and higher The problem remains of finding an economically accept being required to obtain conversions of at least 50% for the able use for the fluoroform by-product so that it does not fluoroform at contact (pyrolysis times) of 0.1-0.12 sec. have to be incinerated. (Tables 1 and 2). The higher yields of HFP are accompanied by increasing amounts of perfluoroisobutylene (PFIB), BRIEF SUMMARY OF THE INVENTION which is toxic. Even at lower pyrolysis temperatures, the The present invention Solves this problem by consuming yields of PFIB can be quite high. U.S. Pat. No. 6,025,532 fluoroform (HFC-23) to economically produce useful prod discloses the pyrolysis of fluoroform to a mixture of HF, 35 uct by co-pyrolyzing the fluoroform with chlorodifluo TFE and HFP at a temperature of at least 700° C., but romethane (HCFC-22) at a temperature in the range of about actually at 1000 C. at a contact time of 32 milliseconds 625-800° C., preferably about 690–775° C. and contact time (Examples), followed by contacting the mixture with a of less than two Seconds, and obtaining as a result thereof a fluorination catalyst to obtain HFC-125 (CFCHF) and/or product mixture of useful Saturated and unsaturated HFC-227ea (CFCHFCF). The high temperature required 40 compounds, i.e. at least three compounds Selected from the for pyrolyzing fluoroform at short contact times has limited group consisting of pentafluoroethane (CFCHF, HFC the use of fluoroform by-product, whereby excess fluoro 125), heptafluoropropane (CFCHFCF, HFC-227ea), TFE, form has been available, which to avoid venting to the and HFP, respectively. The process can be carried out by atmosphere has been disposed of by incineration. 45 feeding the mixture of reactants (HCFC-22 and HFC-23) Several references disclose the use of fluoroform in an through a reaction Zone, the Surface of which is metal, auxiliary pyrolysis role. WO 96/292.96 discloses the preferably gold, to minimize the formation of perfluor co-pyrolysis of HCFC-22 with fluoroalkane to form prima oisobutylene by-product in the pyrolysis reaction. rily large molecule fluoroalkanes. In particular, the reference Unexpectedly, the HFC-23 pyrolyzes at the relatively low discloses this reaction being carried out wherein the fluo 50 temperature of the co-pyrolysis reaction in Short contact roalkane co-reactant is fluoroform and the pyrolysis tem times to produce a high yield, e.g. at least 80%, of the perature is 700° C. and the contact time is 10 seconds, to above-mentioned useful products and little to no detectable obtain 100% conversion of the HCFC-22, with the result PFIB. Apparently, the presence of the HCFC-22 in the being a 60% yield of pentafluoroethane (Example 1). The 55 pyrolysis reaction reduces the reaction (decomposition) tem disadvantage of this process, besides the extraordinarily perature of the HFC-23 so that the latter is consumed in the long contact time, is that 40% of the yield is apparently not pyrolysis reaction. Typically at least 4 parts by weight of useful product. It is impractical to attempt to dispose of HFC-23 is consumed for each 100 parts by weight of HFC-23 by consuming it in a process which produces Such HCFC-22 Such that the amount of HFC-23 consumed is a high yield of by-product which itself needs disposal. 60 greater than the amount produced as by product during the Example 1 also reports that perfluoropropene is formed, manufacture of HCFC-22. without quantifying its amount, which is characteristic of The function of the fluoroform in the present invention is reporting trace amounts detectable in the gas phase chro to increase the amount of useful Saturated two- and three matography analysis used. The Examples of this reference 65 carbon atom compounds, CFCHF (HFC-125) and are conducted with an aqueous alkaline wash of the pyroly CFCHFCF (HFC-227ea), along with production of TFE sis reaction mixture to eliminate the HCl co-produced. The and HFP. US 6,806,396 B2 3 4 DETAILED DESCRIPTION OF THE structural integrity to the reactor. Inconel(R) and Hastelloy(R) INVENTION are nickel alloys Suitable for use as Supporting materials for The pyrolysis reaction in the present invention is carried the gold lining of the reactors (see for example U.S. Pat. No. out by continuous feeding of the co-reactants to a pyrolysis 5,516,947). Other thermally conductive supporting materi reactor and continuously withdrawing the resultant mixture als can be used. Thermal conductivity enables the reactor to of reaction products and unreacted reactants from the reac be externally heated to provide the interior temperature tor. Pyrolysis reactors generally comprise three Zones: a) a necessary for the pyrolysis reaction. It is desirable that the preheat Zone, in which reactants are brought close to the Supporting material be metallurgically bonded to the gold reaction temperature; b) a reaction Zone, in which reactants lining for the best heat transfer. By a metallurgical bond is reach reaction temperature and are at least partially meant a bond in which atoms of the metals in the Supporting pyrolyzed, and products and any by-products form; c) a material and the gold lining interdiffuse, that is, diffuse quench Zone, in which the Stream exiting the reaction Zone among each other about the bonded interface.