US2558624A

US2558624A - Decontaminating products from pyrolysis of chcif2

Info

Publication number: US2558624A
Application number: US22491A
Authority: US
Inventors: William S Murray
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1948-04-21
Filing date: 1948-04-21
Publication date: 1951-06-26
Anticipated expiration: 1968-06-26

Description

' Patented June 26, 1951 DECONTAMINATING PRODUCTS FROM PYROLYSIS 0F CHClF-z William S. Murray, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilming'ton, Dcl., a corporation of Delaware No Drawing. Application April 21, 1948, Serial No. 22,491

Claims.

This invention relates to decontaminating products obtained in the pyrolysis of CHClFa and particularly to rendering innocuous the toxic impurities present in the higher boiling products obtained in the pyrolysis of CHClFz.

Downing et al., in Patent 2,384,821 granted on September 18, 1945, and Park et al., in an article Synthesis of Tetrafluorcethylene, ap-

pearing on pages 354 to 358, inclusive, of In-' dustrial and Engineering Chemistry, vol. 39, No. 3, for March, 1947, disclose the pyrolysis of CHCIF'z at temperatures of from about 600 C. to about 1000 C. to produce C2F4 (tetrafluoroethylene) and higher boiling fluorinated products commonly referred to as high boilers. Upon removal of acids, the C2F4 and unreacted CHC1F2 from the pyrolysis mass, the high boilers" are obtained as a residue, amounting to about 20 pounds to about 35 pounds for every 100 pounds of 02F; produced, which boils above .4.0 0., generally in the range of from about 30 C. to about 200 C. Such residue is a mixture of highly fluorinated straight-chain and cyclic aliphatic compounds, the boiling points of the individual members thereof varying from about 30 C. to about 228 C. Over 97% of such high boiler residue is made up of such stable and non-toxic compounds as CHF2--CC1F2, cyclic ClFa and compounds of the series represented by the formula H(CF2)1.C1 wherein it varies from 3 to 14. Such residue, or mixture of higher boiling compounds, and the various fractions and components thereof will be hereinafter referred to, for convenience, as high boilers.

The high boiler residue or mixture is contaminated with from about 2% to about 3% of.

highly toxic compounds which are characterized by a pungent odor. These toxic compounds have not been positively identified and their chemical constitutions and structures have not been exactly determined. 'Theyare definitely known to be highly fluorinated organic compounds, at least some of which contain chlorine. They appear to contain a cyclic structure. The boiling points and tentatively assigned formulae of some of such toxic compounds are disclosed in the article by Park et al. hereinbefore referred to, and particularly in Table II' on page 358.

These toxic compounds render the vapors of the high boilers containing them so toxic on inhalation as to make extremely hazardous the handling of the material for any further desired processing or their disposal as waste materials. This is demonstrated by the fact that test rats, when exposed to air containing about 3% by volume of the contaminated high boilers for 15 minutes, died within an hour from severe.

hemorrhagic pulmonary edema. Such toxic compounds cannot be separated from the high boilers by fractional distillation, apparently because they form azeotropes with constituents of the high boilers, and appear in substantially. all fractions of the high boiler mixture obtained by fractional distillation.

It is an object of the present invention to provide an economical, efiicient, commercially practicable method for rendering the toxic compounds in the high boilers innocuous. other object is to provide a method of rendering the toxic compounds innocuous and removing them from the high boilers. Further objects are to advance the art. Still other objects will appear hereinafter. I

The above and other objects may be accomplished in accordance with my invention which comprises mixing at least 3% by weight of anhydrous ammonia with the pyrolysis products which boil in the range of from about -3D C. to about 228 0., obtained in the pyrolysis CHC1F2 at temperatures of from about 600 C. to about 1000 C., and which contain toxic impurities, in the liquid phase at temperaturesof from about C. to about 50 C., and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete. I have found that anhydrous ammonia reacts spontaneously and with the evolution of considerable heat with the impurities in the high boilers at temperatures as low as 75 C. to form innocuous brown compounds which are solid at ordinary temperatures and insoluble in the high boilers and in water, but which are fairly soluble in methanol. If it is desired to recover constituents of the high boilers, the ammonia reaction products may beseparated therefrom by filtration, fractional distillation, extraction with solvents or the like. If the "constituents of the high boilers are not to be recovered but are to be disposed of as waste, then the decontaminated material may be safely discarded as such. However, in such latter case, it will generally be preferred to mix the decontaminated material with methanol or other solvent for the ammonia reaction products or to carry out the decontamination in the presence of such solvent so as to facilitate the discharge of the decontaminated material from the reaction vessel and its subsequent disposal.

The high boilers, which are to be treated in accordance with my invention, may be the residue obtained after removal of the acidic con- An- I assess-4 stituents, the tetrafluoroethylene and any unreacted CHClFa. Alternatively, such residue may be subjected to one or more fractional distillations and then the treatment applied to each fraction which contains the toxic compounds.

At least about 3% by wei ht of anhydrous ammonia, based on the high boilers" treated, is required for reaction with the toxic compounds.

Preferably, an excess of ammonia, from about 5% to about by weight, is employed. Much larger excesses of ammonia can be used, if desired, but such larger excesses have the disadvantage of requiring larger equipment and the recovery of such larger amounts of ammonia. The liquid high boilers may be added to the liquid ammonia or the ammonia may be added to the high boilers.

The process has been carried out successfully at -75 C. and at 50 C. Preferably, it will be carried out at temperatures of from about C. to about 50 C. While reaction may be carried out at temperatures substantially above 50 C., such higher temperatures will be generally undesirable because of the high pressures that would be required to maintain the reaction in the liquid phase and to maintain the ammonia in effective contact with the "high boilers. Ammonia is somewhat soluble in the high boilers. Since the reaction takes place spontaneously upon mixing the liquids, pressure is without influence on the reaction and hence only such pressures as will maintain the reactants in contact in the liquid phase will be required. The reaction takes place in the liquid phase only. All efforts to decontaminate the high boilers in the vapor phase, even at temperatures as high as 500 0., were unsuccessful.-

Usually, where constituents of the high boilers are to be recovered, it will be preferred to employ substantially pure anhydrous ammonia. However, even where constituents of the high boilers are to be recovered, it will some times be found desirable to carry out the reaction in the presence of methanol or other, solvent for the ammonia and the reaction products. This serves to lower the ammonia pressure and to facilitate discharge of the decontaminated material from the reaction vessel and transportation to other apparatus for further processing. In order to effect reasonable solution of the reaction products, from about 3 to 6 gallons of methanol per 100 pounds of the high boilers (from about 19% to about 40% by weight) should be used. Larger amounts of methanol may be used, if desired. Aqueous solutions, including concentrated ammoniumhydroxide, are ineffective and hence the presence of any substantial amount of water must be avoided.

In order to more clearly illustrate my invention and preferred modes of carrying the same into effect, the following examples are given:

Example 1 a To 360 g. of high boiler residue in a 600 cc. steel cylinder was added 16 g. of anhydrous ammonia (4.25% by weight). After standing for 28 hours, a liquid phase sample was scrubbed by passing the vapor through water, dried with 09504 and tested on rats. After an 8 minute exposure period, the rats were killed and examined; their lungs showed slight congestion but no gross edema. A similar sample, taken after standing 28 days, produced only a slight discoloration and congestion when similarly tested. Another sample, treated with 3.1% by weight of ammonia for 50 hours, produced no gross pathol- 4 ogy. A sample of the untreated high boilers, scrubbed, dried and tested in the same manner as the ammonia treated ones, produced marked edema, areas of hemorrhage and general congestion. In all these tests, the air contained about 5% by volume of high boiler" vapor.

Example 2 To an evacuated 5 gallon steel autoclave equipped with brine cooling, plow type a tation, and the usual vapor and standpipe connections, etc., was added one gallon of methanol and 2 pounds of anhydrous ammonia. The pressure in the autoclave, at a liquid temperature of 4 0., was 8 p. s. i. a. A total of 24 pounds of toxic high boiler residue was then added at an average rate of 1 pound per minute. Within a half hour after the addition had been completed, the decontaminated liquid was sampled, scrubbed by passing the vapor through water, dilute sulfuric acid, and water again (to remove methanol and excess ammonia), dried with 02504 and later tested for toxicity. As a result of this ammonia treatment, the test rats, instead of suffering from severe pulmonary 'hemorrhagic edema. were found to be, for all practical purposes, perfectly normal after a 6 minute exposure to air containing 4% by volume of the decontaminated material.

It will be understood that the preceding examples are given for illustrative purposes solely and that my invention is not to be limited to the specific embodiments disclosed therein. Within the scope of this disclosure, as heretofore given, it will be evident that the proportions of reactants and solvent, the temperatures, pressures, order of steps, apparatus and the like may be varied as desired. Also, any desired fraction may be separated from the "high boiler residue and treated in accordance with the principles of my invention.

Since the most characteristic pr perty of highly fluorinated aliphatic compounds is their unusualstability and inertness to chemical reaction, it was wholly surprising to find that the toxic impurities in the high boilers" would react with ammonia and, particularly, so remarkably spontaneously. It was also quite surprising to find that the reaction would take place only in my invention provides a commercially practicable and economical process for decontaminating the high boilers."

I claim:

1. The process for decontaminating the pyrolysis products which boil in the range of from about 30 C. to about 228 0., obtained in the pyrolysis of CHCIF: at temperatures of from about 600 C. to about 1000 C., and which contain highly fluorinated organic toxic impurities,

which process comprises'mixing the pyrolysisproducts in the liquid phase at temperatures of from about --'75 C. to about 50 C. with at least 3% by weight of anhydrous ammonia, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

2. The process for decontaminating the pyrolysis products which boil in the range of from about -30 C. to about 228 C., obtained in the pyrolysis of CHClFz at temperatures of from about 600 C. to about 1000 C., and which contain highly fiuorinated organic toxic impurities, which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about -'75 C. to about 50 C. with from 3% to about 10% by weight of anhydrous ammonia, andmaintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantiallycomplete.

3. The process for decontaminating the pyrolysis products which boil in the range of from about 30 C. to about 228 C., obtained in the pyrolysis of CHClFz at temperatures of from about 600 C. to about 1000 C., and which contain highly fluorinated organic toxic impurities. which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about 75 C. to about 50" C. with from about to about by weight of anhydrous ammonia, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

4. The process for decontaminating the pyrolysis products which boil in the range from about 30 C. to about 228 C., obtained in the pyrolysis of CHClF2 at temperatures of from about 600 C. to about 1000 C., and which contain highly fiuorinated organic toxic impurities, which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about C. to about 50 C. with at least 3% by weight of anhydrous ammonia, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

5. The process for decontaminating the PV- rolysis products which boil in the range of from about 30 C. to about 228 C., obtained in the pyrolysis of CHClFz at temperatures of from about 600 C. to about 1000 C., and which contain highly fiuorinated organic toxic impurities,

which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about -20 C. to about 50 C. with from 3% to about 10% by weight of anhydrous ammonia, and maintaining the ammonia in ad-- mixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

6. The process for decontaminating the pyrolysis products which boil in the range of from about 30 C. to about 228 C., obtained in the pyrolysis of CHClFz at temperatures of from about 600 C. to about 1000 C., and which contain highly fluorinated organic toxic impurities, which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about -20 C. to about 50 C. with from about 5% to about 10% by weight of anhydrous ammonia, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

7. The process for decontaminating the pyrolysis products which boil in the range of from about -30" C. to about 228 C., obtained in the pyrolysis of CHClFz at temperatures of from about 600 C. to about 1000 C., and which contain highly fiuorinated organic toxic impurities, which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about 75" C. to about 50 C. with at least 3% by weight of substantially pure anhydrous ammonia, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

8. The process for decontaminating the pyrolysis products which boil in the rangeof from about -30 C. to about 223 C., obtained in the pyrolysis 'of CHClF2 at temperatures of from about 600 C. to about 1000 C., and which contain highly fiuorinated organic toxic impurities, which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about 20" C. to about 50 C. with from about 5% to about 10% by weight of substantially pure anhydrous ammonia, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

9. The process for decontaminating the pyrolysis products which boil in the range of from about 30 C. to about 228 C., obtained in the pyrolysis of CHClFz at temperatures 'of from about 600 C. to about 1000 C., and which contain highly fluorinated organic toxic impurities,

'which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about -75 C. to about 50 C. with at least 3% by weight of anhydrous ammonia dissolved in from about 19% to about 40% by weight of methanol based on the pyrolysis products, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

10. The process for decontaminating the pyrolysis products which boil in the range of from about 30 C. to about 228 C., obtained in the pyrolysis of CHClF2 at temperatures of from about 600 C. to about 1000 C., and which contain highly fiuorinated organic toxic impurities, which process comprises mixing the pyrolysis products in the liquid phase at temperatures of from about 20 C. to about 50 C. with from about 5% to about 10% by weight of anhydrous ammonia dissolved in from about 19% to about 40% by weight of methanol based. on the payrolysis products, and maintaining the ammonia in admixture with the liquid pyrolysis products under such conditions until reaction of the ammonia with the toxic impurities is substantially complete.

WILLIAM S. MURRAY.

Name Date Downing et al. Sept. 18, 1945 Number

Claims

1. THE PROCESS FOR DECONTAMINATING THE PYROLYSIS PRODUCTS WHICH BOIL IN THE RANGE OF FROM ABOUT -30* C. TO ABOUT 228* C., OBTAINED IN THE PYROLYSIS OF CHCIF2 AT TEMPERATURES OF FROM ABOUT 600* C. TO ABOUT 1000* C., AND WHICH CONTAIN HIGHLY FLUORINATED ORGANIC TOXIC IMPURITIES, WHICH PROCESS COMPRISES MIXING THE PYROLYSIS PRODUCTS IN THE LIQUID PHASE AT TEMPERATURES OF FROM ABOUT -75* C. TO ABOUT 50* C. WITH AT LEAST 3% BY WEIGHT OF ANHYDROUS AMMONIA, AND MAINTAINING THE AMMONIA IN ADMIXTURE WITH THE LIQUID PYROLYSIS PRODUCTS UNDER SUCH CONDITIONS UNTIL REACTION OF THE AMMONIA WITH THE TOXIC IMPURITIES IS SUBSTANTIALLY COMPLETE.