Perfluorinated emulsifiers, production

Production and Fate of Perfluorinated Emulsifiers in the Past Industrial production of PFOS and PFOA is predominantly based on electrochemical fluorination (EOF) of hydrocarbon precursors followed by hydrolysis of the acid fluoride and salt formation [7, 20] (Scheme 21.2). 

The Daikin product may be produced by the addition of 1,2-epoxy hexafluoro-propane (HFPO) to carbonylfluoride [66] and conversion of resulting acid fluoride to the ammonium salt [67] (Scheme 21.11). Alternatively partially/perfluorinated emulsifiers based on tetrafluorooxetane were described [68]. 

Similar to other fluoropolymers and fluoroelasto-mers, such as PTFE, FEP, PFA, etc., low-level perfluorinated surfactants or chemicals, such as ammonium perfluoro-octanoate (APFO), etc. may be used in some fluoropolymer production as an emulsifier. These perfluorinated compounds are mostly extremely stable, degrade slowly, and therefore persist in the environment. These surfactants have varying ecotoxicity profiles, and users should contact their supplier for a more detailed ecotox information for their particular product.Industrial efforts are being made to reduce or even eliminate the use of such perfluorinated surfactants in their products and/or manufacturing processes. 

Suspension and emulsion polymers have been prepared. In the case of emulsion polymers, the choice of surfactant is particularly critical. Salts of perfluorinated heptanoic or octanoic acids have been found suitable [6], although the products frequently are somewhat off-white. Higher yields of polymer and excellent color were obtained when salts of perfluoroalkylpropyla-mines served as emulsifiers. Even these materials, the patent implies, lead to slurries of polymer in the aqueous medium rather than to reasonably stable latices [36]. 

Recovery/Removal and Recycling of Perfluorinated Acids from Fluoropolymers and Industrial Waste Streams In the last decade of the twentieth century, PFOS and PFOA as well as other fluorinated substances came under scrutiny because they are environmentally persistent and potentially bioaccumulative. Analytical developments resulted in the detection of these substances widespread in the environment [28]. Triggered by these environmental concerns, as well as by the high price of the fluorinated emulsifiers, methods were developed which allowed effective recovery and recycling of fluorinated emulsifiers from these industrial production processes. 

Following these selection criteria, a large number of potential emulsifiers was synthesized and tested. Finally, a monohydrofluorocarboxylic acid ammonium salt, internally referred to as ADONA, was selected. ADONA is based on a readily available perfluorinated vinyl ether. Several different production routes for ADONA are available. The first synthesis [59] starts with the addition of methanol to the vinyl ether under radical conditions. The resulting alcohol is oxidized to the carboxylic acid [59,60]. After reaction with methanol, the resulting ester is separated and purified. Finally, the ester is converted to ADONA (Scheme 21.7). 

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