MXPA00011838A - Method for recovering fluorinated alkanoic acids from waste waters - Google Patents

Abstract

The invention relates to a method for recovering fluorinated emulsifying agent acids from waste waters, characterized in that the finely dispersed solids in the waste water are stabilized with a nonionic or cationic surfactant or an analogous acting surface active substance, the fluorinated emulsifying agent acids are subsequently bonded on an anion exchange resin and the fluorinated emulsifying agent acids are eluted from the latter.

Description

PROCEDURE FOR THE RECOVERY OF FLUORATED ALCOHOLIC ACIDS OF RESIDUAL WATER DESCRIPTION 5 DESCRIPTIVE MEMORY In the polymerization of fluorinated monomers in dispersion water, fluorinated alkanoic acids are used as emulsifiers, because they do not have telogenic properties. In particular, it is use of salts, preferably alkali metal or ammonium salts, of alkanocarboxylic acids or perfluorinated alkanesulfonic acids or partially fluorinated These compounds are prepared by electrofluorination or by telomerization of fluorinated monomers, which is expensive. Therefore, there have been many attempts to recover these valuable wastewater materials.

US-A-5 442 097 describes a process for the recovery of fluorinated carboxylic acids in usable form from initial materials contaminated. In this procedure, the carboxylic acid fluoride, if necessary, is released from these materials in an aqueous medium using a sufficiently strong acid, the fluorinated carboxylic acid is reacted with a suitable alcohol, and the ester formed is distilled. The material Initially, it can be a polymerization liquor, in particular an emulsion polymerization in which the fluoropolymer is prepared in the form of colloidal particles with the help of relatively high amounts of emulsifier. This procedure has proved useful, but requires a certain concentration of fluorinated carboxylic acid in the initial material. DE-A-20 44 986 describes a process for the recovery of perfluorocarboxylic acids from diluted solution, wherein the diluted solution of the perfluorocarboxylic acids is brought into contact with anion with a weak base anion exchange resin, and the perfluorocarboxylic acid present in the solution is thus adsorbed to the anion exchange resin, the anion exchange resin is eluted with an aqueous ammonium solution, and the adsorbed perfluorocarboxylic acid is thus transferred to the eluent, and the acid is finally isolated from the eluate. However, complete elution requires relatively large amounts of dilute ammonium solution, and this procedure requires a lot of time. These disadvantages are overcome by the method known from US-A-4 282 162 for the elution of fluorinated emulsifying acids adsorbed on basic anion exchangers, in which the elution of the fluorinated emulsifier acid adsorbed from the anion exchanger is carried out using a mixture of dilute mineral acid and an organic solvent. In this process, the ion exchange resin is regenerated at the same time using the acid. It has been found that the aforementioned process presents problems in industrial practice when, in particular, the processed waste water contains very small solids which in ^ J ^^ J ^ the past were not recognized or at least not recognized as a problem. In this case, the apparatus containing the anion exchange resin clogs with these solids more or less rapidly, which becomes remarkable as a result of increased flow resistance and reduced performance. Upstream filters or commonly used fritted materials are not effective here. It has also been found that these difficulties are caused by the small solids that are being trapped in relatively stable colloidal suspension by the emulsifying acids. When these acids are removed from the system by the anion exchange resin, this relatively stable dispersion is destroyed and the solid precipitates, and clogs the ion exchange resin. It was also found that the performance of the process known from US-A-4 282 162 can be considerably improved and waste water containing small solids can also be made suitable if the dispersion of the solids in the waste water is stabilized by the addition of an active non-ionic or cationic surfactant (surfactant) before the wastewater comes into contact with the anion exchanger. The nonionic or cationic surfactants are not bound by the 20 anion exchanger. A) Yes, the invention provides a process for the recovery of fluorinated emulsifying acids from wastewater, which includes the stabilization of solids that are finely dispersed in the water - * - • - * - * * »*» * - > * > - * - • > a * - residual by means of a nonionic or cationic surfactant, or a surface active substance having an analogous effect and subsequently, the binding of the fluorinated emulsifying acids with an anion exchange resin and the elution of the fluorinated emulsifying acids this. The wastewater suitable for treatment is process waste water in which surface-active fluorinated alkanoic acids are present. The process is particularly suitable for residual water from the polymerization of fluorinated monomers by the emulsion method, wherein the fluorinated monomer is converted in the presence of a relatively high concentration of fluorinated emulsifying acid, and with moderate mixing in a finely divided polymer the which is finely dispersed, in colloidal form, and in which the latex obtained is coagulated, for example, by intensive agitation, after the desired concentration of the solids has been reached, so that the polymer is precipitated as a fine powder . It has been found that in the known treatment, especially the relatively low molecular weight polymer material is the one causing difficulties; the adverse effect of these low molecular weight polymers becomes particularly noticeable when the polymerization process leads to a broad molecular weight distribution. Also in the case of this "difficult" water, the method of the invention shows its capabilities. It is also known to remove solids before the waste water is brought into contact with the ion exchange resin (German patent application 198 24 614.5 of June 2, 1998, under the title "Verfahren zur Rückgewinnung von fluorierten Alkansáuren aus Abwássern "). However, this has the disadvantage of a high expense in terms of apparatus for the removal of solids, and the amount of auxiliary chemicals that must be added (for example, lime milk, aluminum salts, flocculants). Particularly, at low concentrations of solids the complete elimination of the colloidal material requires relatively large amounts of chemicals, which are removed again only to a limited extent in the removal of solids. In the process of the invention, the expense in terms of apparatuses and chemical substances is considerably reduced, because the addition of small amounts of a preferably readily biodegradable surfactant is sufficient to stabilize the colloids and ensure trouble-free operation of the exchanger. The adsorption of the emulsifying acids in the ion exchange resins can be carried out in a manner known per se. Suitable resins are, in particular, strong base anion exchange resins such as those obtainable, for example, under the trade names ® AMBERLITE IRA-402, AMBERJET 4200 (both from Rohm &Haas), © PUROLITE A845 (Purolite GmbH ) or ® LEWATIT MP-500 (Bayer AG). The adsorption can be carried out in a manner known per se, with the ion exchange resins placed in the usual apparatuses, . . ,. . .. "..,. »,,,, Such as tubes or columns through which the wastewater flows. The emulsification of the binding emulsifying acids is also carried out in a well known manner with preference given to the method described in US-A-4 282 162. Suitable methods for isolating the emulsifying acids in high purity, required for their use in polymerization are , for example, those described in US-A-5 442 097 mentioned above, or that described in US-A-5 312 935, in which first the eluted material is substantially free of water and then treated with oxidizing agents. The residual water remaining after the adsorption of the emulsifying acids is treated in a known manner, depending on the content of other materials. The invention is illustrated by the following examples. Examples 1 to 4 and comparative example. The initial material used is wastewater from the copolymerization of tetrafluoroethylene and perfluoro (n-propylvinyl ether) in which the ammonium salt of n- and iso-perfluorooctanoic acid (PFOA) is used as an emulsifier. The concentration of PFOA is 750 mg / l. In a stirred vessel, 1000 g of this liquor is mixed with 0.1 g of non-ionic surfactant ®TRITON X-100 Rohm & amp;; Haas, p-octylphenol ethoxylate, CAS No. 9002-93-1) or ®GENAPOL UD 088 (Hoechst AG, fatty alcohol polyglycol ether) and stirred. Approximately 50 ml of an ion exchange resin ^^^ ^ a m Lk of strong base (®AMBERLITE IRA-402, Rohm &Haas, styreivinylbenzene type, anion: chloride, gel, total capacity: 1.3 eq / l, overall density: 710 g / l) are placed in a cylindrical glass column (length: 25 cm, diameter: 16 mm) provided with a glass frit and rinsed with water. To add the ion exchanger, the solution is pumped up through the bed by a pump. The water leaving the column is collected as a plurality of samples, and the concentration of PFOA is determined. The pressure drop on the bed of the ion exchanger is measured by means of a pressure gauge. The water leaving the column is collected as a plurality of samples and the concentration of PFOA is determined. The loading experiment without addition of surfactant (comparative example) had to be stopped because the pressure drop increased above 1 bar / m, as a result of the precipitated polymer, and the resin showed a significant conglutination.

EXAMPLE 5 150 ml of an elution solution were mixed from methanol, concentrated sulfuric acid (96%) and water (proportions by weight: 5 89%, 7%, 4%). The column of the ion exchanger, after being charged, was first rinsed with 100 ml of water to remove the remaining residual water from the column. The elution solution was then passed through the column at a linear velocity of 0.5 m / h and collected. The column was finally rinsed with another 50 ml of water. The elution solution 10 contains approximately 95% of the emulsifier solution in the waste water used. riui-ri-tiilf-ltt-iÉ-fM- ^^ Ui ^ -a

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the recovery of fluorinated emulsifying acids from waste water, which includes the stabilization of the solids that are finely dispersed in the waste water, by means of a surfactant or a surface active substance, and subsequently the binding of Fluorinated emulsifying acids with an anion exchange resin, and the elution of the fluorinated emulsifying acids thereof.

2. The process according to claim 1, further characterized by using waste water from the polymerization of fluorinated monomers.

3. The process according to claim 1 or 2, further characterized in that the material that can be converted into solids is precipitated.

4. The process according to one or more of the preceding claims, further characterized in that the anion exchange resin used is a strong base anion exchange resin.

5. The method according to one or more of the preceding claims, further characterized in that the elution is carried out using a mixture of dilute mineral acid and an organic solvent. g ^ g ^ -