JPS61246142A - Collection of fluorine-base surfactant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides reusable, highly pure perfluorinated or substantially perfluorinated anionic surfactants.
It consists of methods for recovery in high yields even when present at relatively low concentrations from solution in aqueous media. Such solutions are often obtained in the production of fluoropolymers, such as tetrafluoroethylene polymers, by aqueous processes.

Fluorinated surfactants are widely used in the production of fluoropolymers (and copolymers) in aqueous media. They are primarily used in the production of fluoropolymer dispersions and dried solid polymers derived therefrom, but they are described, for example, in U.S. Pat.
．． Tetrafluoroethylene (
It is also commonly used in the production of slurry- (so-called granule-) type polymers, as described for the polymerization of TFE). The main classes of commonly used fluorinated surfactants are usually ammonium salts (APFO).
) in the form of perfluoroalkanoates, especially perfluorooctanoates, but even alkali metal salts and the corresponding free acids can be used.

Although these fluorinated surfactants are of wood value, their recovery is difficult due to their relatively low concentration in the used polymerization medium. Furthermore, since the surfactants consist of molecules with more or less pronounced polar and non-polar parts, they can generally be used for their separation, such as by liquid-liquid extraction. It tends to "crosslink" immiscible media. Furthermore, the surfactants have a pronounced and generally undesirable foaming tendency, especially in aqueous media.

Despite these drawbacks, the difficulty of disposing of the used reaction mixture by acceptable means
Recovery of the surfactants is desirable.

Avoiding complex techniques such as ion exchange to perform the separation of surfactants by using common inexpensive inorganic reagents and simple organic solvents, and adjusting the media and conditions, especially the pH level, appropriately. It would be desirable to provide a method for recovering such surfactants that selectively overcomes foaming and can be carried out at atmospheric pressure and ambient temperature.

The gist of the invention is that a) formula % formula % c in which Rf is a saturated perfluorinated linear or methyl-branched alkylene group having 5 to 10 carbon atoms, and X is hydrogen; , fluorine or chlorine, and M is a member of the group consisting of H, ammonium or potassium metal. is 1-16 alkyl, carbon number is 6-10
is an aryl or aralkyl having 7 to 11 carbon atoms, with the proviso that the total number of carbon atoms in R1 and R2 is at least 15, and A is an anion. Produces fluoroalkanoic acid quaternary ammonium salts.

b) contacting the resulting mixture produced in a) with a chlorinated hydrocarbon liquid to extract the salt from the aqueous mixture; C) separating the salt from the chlorinated hydrocarbon liquid; and d) separating. adding acidified water to the prepared salt and subjecting the resulting mixture to steam distillation to distill off the fluoroalkanoic acid, and e) collecting the fluoroalkanoic acid distillate.

This is a method for recovering fluoroalkanoic acid from an aqueous medium.

The present invention primarily relates to the recovery of fluoroalkanoic acids or salts from aqueous solutions or mixtures containing them by reaction with quaternary ammonium compounds and subsequent extraction.

Representative examples of quaternary ammonium compounds that can be used in the present invention include di-n-decyldimethylammonium chloride, hexadecyltrimethylammonium chloride, n
-tetradecylbenzyldimethylammonium chloride, n-octyldodecyldimethylammonium chloride, and the like. Hexadecyltrimethylammonium chloride is preferred. Similar bromides can also be used. The particular anion of the quaternary ammonium compound is not critical so long as it does not interfere with the formation of the salt formed by the interaction of the quaternary ammonium cation with the fluoroalkanoate anion.

A very attractive feature regarding the use of these quaternary ammonium cations in reactions with fluoroalkanoate anions is that no substantial excess of cation is required over the stoichiometric requirement. ,
That is, the reaction is relatively quantitative at room temperature even in aqueous solution. The quaternary ammonium compound is simply added to the aqueous mixture. If desired, the aqueous mixture can be acidified prior to the extraction step, preferably using a mineral acid.

The extraction step is simply carried out by adding a chlorinated hydrocarbon liquid (liquid at normal room temperature, i.e. about 22° C.), such as di- or trichloromethane, and stirring briefly at room temperature. The quaternary ammonium salt mass migrates into the chlorinated hydrocarbon organic layer.

The resulting quaternary ammonium fluoroalkanoate (hereinafter referred to as "quaternary ammonium salt") is free from other components of the reaction (which includes inorganic ammonium salts such as ammonium chloride) during the extraction process. separated into Inorganic salts remain primarily in the aqueous liquid. moreover,
When the system is stirred during extraction, there is no noticeable tendency to foaming, especially when carrying out the acidification described above.

The advantage of this extraction step is that it allows control of the presence of fluoropolymer in the feed stream, as often occurs in aqueous streams obtained in the production of fluoropolymers. Even if such a polymer is colloidally dispersed, as is often the case, it does not substantially interfere with the extraction process, as it tends to coagulate during extraction and can be easily filtered off. .

Separation of the quaternary ammonium salt from the chlorinated hydrocarbon is carried out by evaporating the chlorinated hydrocarbon.

If the quaternary ammonium salt is isolated in dry solid form or in a relatively concentrated solution in an extractant solution,
Recovery of the fluoroalkanoic acid is carried out by steam distillation. - double distillation is sufficient, but for the highest purity two consecutive distillations in the presence of strong aqueous sulfuric acid (for final purification an oxidizing agent such as K 2 Cr 20 y) is used. It is preferable to perform the second test with additional presence of the compound. - If two distillation steps are carried out, whether double or double distillation is carried out, neutralization of the distillate with ammonium hydroxide will result in ammonium fluoroalkanoic acid salts. , a distillate acidification step can be carried out to effect concentration of fluoroalkanoic acids in the first distillate. decomposing the quaternary ammonium salt by distillation to produce an aqueous fluoroalkanoic acid in the distillate;
It was unexpected that quaternary ammonium cations would remain in the distillation vessel (along with the aqueous sulfuric acid solution).

Even low amounts of fluoroalkanoic acids or their salts can be effectively recovered. A recovery of approximately 95% is obtained at a relatively low concentration of 170 ppm by weight. In general, the lower the fluoroalkanoate concentration, the better to minimize the loss of extractant (such as through evaporation) to avoid that the cost of the extractant exceeds the value of the surfactant recovered. Much attention should be paid.

Distillation from aqueous sulfuric acid generally proceeds without the disadvantages caused by the foaming tendency of fluoroalkanoic acids.

The foaming problem is the last part of fluoroalkanoic acid (about 5%)
It appears that the liquid does not begin to become a real liquid until it leaves the distillation vessel.

The present invention primarily focuses on (either in the form of ammonium or alkali metal salts or the corresponding free acids)
Although this invention relates to the recovery of fluoroalkanoate surfactants, and in particular fluorooctanoic acid, other perfluoroalkanoates include perfluorohexane and the present invention is not limited to this type. Acid acid (C-6
) or perfluorohebutanoate (C-7) surfactants, or perfluorononanoate (C-9) or perfluorodecanoate (C-10) surfactants. They may be linear or branched, and in the C-9 and C-10 forms give relatively high boiling points resulting in desirable high concentrations of fluorocarbon acids in the distillate. In order to achieve this, the relatively low volatility of the corresponding free acids may require relatively high aqueous sulfuric acid concentrations in the double water door vapor distillation stages used for recovery and purification.

Similarly, one method of the present invention may be applied to a compound other than fluorine, such as in the above-mentioned compounds in which a hydrogen or chlorine atom replaces a fluorine atom at the omega position, as in hydro(per)fluorononanoate surfactants. It is also applicable to fluorine-based surfactants in which some atom(s) are present.

Step a) 15 ml ammonium perfluorooctanoate (MN,
Commercially available by 3M Company, Cent Ball
Fluorad (Fluorad JFC-143) 0.
12.7 ml of hexadecyltrimethylammonium bromide (reagent grade, J, T from Phillips Barbe, New Chassis) in a 1% aqueous solution (at room temperature)
, commercially available from Baker Chemical Company) was added. The amounts of the two reagents used were stoichiometrically equivalent on a 1:1 mole basis.

Step b) 10 ml portions of the resulting solution (contained in a 125 ml squib type glass separation funnel) contain 66 mg c7) M sulfuric acid and 210
After adding 1 ml of an aqueous solution containing 100 mg of sodium dihydrogen phosphate-hydrate buffer, a 5 ml portion of trichloromethane was added. The contents of the funnel were shaken vigorously for 2 minutes. A negligible amount of stable foam was formed.

Step C) After a precipitation period of about 45 minutes, the lower layer (which was colorless and almost transparent) was removed. After evaporation of the extract at room temperature in a stream of nitrogen, a white solid residue remained consisting of perfluorooctanoic acid hexadecyltrimethylammonium salt.

Steps d) and e) A quantity of 4.29 g of the dried perfluorooctanoic acid hexadecyltrimethylammonium salt extract obtained as described above is charged into a glass distillation apparatus together with 20 ml (28 g) of 50% by weight aqueous sulfuric acid solution. did. Distillation is started and continued several times in which demineralized water is distilled until the volume of distillate (consisting of a gel-like slurry of slightly impure fluorooctanoic acid in water) reaches between approximately 2 and 4 ml. Portions approximately equal to the volume of distillate were added to the vessel.

(The purpose of these additions is that the non-volatile sulfuric acid becomes much more concentrated than its original value, resulting in a possible increase in boiling point and in the distillate undesirable impurities containing C-H bonds. Foaming in the distillation vessel was not a problem for the most part, but it did tend to occur when boiling resumed after water was added to the distillation solution. At that point care had to be taken to avoid foam migration into the condenser and distillate.

Example 2 A gaseous waste stream produced in the production of a 1 L tetrafluoroethylene/hexafluoropropylene copolymer was used. The gas was the vapor released from the drying of a wet coagulated polymer synthesized using ammonium perfluorooctanoate as a dispersant in an aqueous medium. It was passed through a water flapper and the water in the flapper fluid was used here. The vapor was analyzed to contain 0.017% ammonium perfluorooctanoate by weight. 2000m1
This solution, which has a partial pH of about 5, is further acidified using a 50% by weight aqueous sulfuric acid solution to a pH of about 2, and then a 1=1 stoichiometric equivalent of o, ioo in a concentration of % by weight of hexane. Treated with an aqueous solution of decyltrimethylammonium chloride.

Step b) The resulting solution was extracted with dichloromethane at room temperature in a 3000 ml squib type glass separating funnel. Extraction in two (successive) stages, each 200 m
Two extracts were carried out using 1 extractant and kept on the side for 30 minutes after a 2 minute shaking period after each removal. A total of 8 liters of flapper fluid was treated in this manner.

Step C) The solid recovered was white and had a somewhat spiral consistency. - The amount of solid hexadecyltrimethylammonium fluoroctanoate recovered after evaporation of the solvent from the combined first stage dichloromethane extracts was about 75% less than that from the combined second stage extracts. % more, the total amount corresponding to an overall yield of about 95% of theory.

Steps d) and e) A 0.815 g portion of the (combined) recovered solid was subjected to a simple distillation at atmospheric pressure in the presence of 20 ml (27.7 g) of 50% by weight aqueous sulfuric acid solution. 95% in the distillate before the contents of the distillation flask begin to foam to the extent that migration into the condenser and into the distillate may occur.
of perfluorooctanoic acid was recovered. The distillate consisted of mobile, somewhat gel-like, slightly impure perfluorooctanoic acid at a concentration of approximately 10% by weight in water.

Steam distillation in the presence of a non-volatile mineral acid and an oxidizing agent such as potassium dichromate produced more pure perfluorooctanoic acid.

For the analytical measurement of ammonium perfluorooctanoate (APFO), the Encyclopedia of Industrial Chemical Analysis (Encyclopedia of Industrial Chemical Analysis)
a of Industrial Chemistry
al AnalysisS), volume 1, pages 339-40,
A highly sensitive colorimetric extraction process as described in Interscience Haflishers, New York, NY (1971) was used. The method uses cationic blue dyes such as methylene blue or azure (A
zure) A) to produce an extractable blue complex with an absorption peak in the visible range at about 635 nm. To obtain peak absorption values in the range between 0 and 1, use an appropriate sample diluent and
A “control” correction was applied. In cases where possible sources of interference are present (e.g. cationic surfactants such as quaternary ammonium salts), the sample is first steam distilled in the presence of a dilute aqueous phosphoric acid solution at atmospheric pressure. APFO
were separated (in corresponding steps) into distillate fractions and the colorimetric process abbreviated above was applied to the distillate in the first order. Distillation was continued until the level of APFO produced was insignificant.

Claims (1)

[Claims] 1.a) Formula X-Rf-COOM [wherein Rf is a saturated perfluorinated linear or methyl-branched alkylene group having 5 to 10 carbon atoms; , X is a member of the group consisting of hydrogen, fluorine or chlorine, and M is a member of the group consisting of H, ammonium or potassium metal. , tables, etc.▼ [In the formula, each R is an alkyl having 1 to 16 carbon atoms, and 6 to 10 carbon atoms.
is an aryl or aralkyl having 7 to 11 carbon atoms, with the proviso that the total number of carbon atoms in R_1 and R_2 is at least 15, and A is an anion] producing a fluoroalkanoic acid quaternary ammonium salt; b) contacting the produced mixture prepared in a) with a chlorinated hydrocarbon liquid to extract the salt from the aqueous mixture; and c) chlorinating the salt. d) adding acidified water to the separated salt and subjecting the resulting mixture to steam distillation to distill the fluoroalkanoic acid; and e) collecting the fluoroalkanoic acid distillate. A method for recovering fluoroalkanoic acids from an aqueous medium, comprising: 2. The method according to claim 1, wherein the perfluoroalkanoic acid is perfluorooctanoic acid. 3. The method according to claim 1, wherein the chlorinated hydrocarbon is dichloromethane or trichloromethane. 4. Claims 1, 2 or 3, wherein the aqueous medium is a used polymerization medium resulting from the production of fluoropolymers.
The method described in section.