Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-04-02
2001-03-06
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S685000
Reexamination Certificate
active
06198009
ABSTRACT:
The present invention relates to a perfluoropropylvinylether (FPVE) purification process. More particularly to a FPVE purification process of recovered FPVE from a fluoropolymer synthesis, which allows the reuse of FPVE in polymerization processes.
Fluoropolymer polymerization processes are known that use this monomer with the aim to improve the base characteristics of the polymer. For instance in tetrafluoroethylene (TFE), or ethylene/(E) TFE and/or CTFE (chlorotrifluoroethylene) polymers.
The FPVE reactivity is such that the amount of unreacted monomer after its use in a copolymerization process varies according to the polymer synthesis. Specifically its reactivity depends on the monomers involved, the pressure, the temperature, additives, solvents, chain transfer agents, etc., used in the synthesis
The usual separation by distillation of unreacted monomers in polymerization does not always allow the recovery of the monomer free from residual substances used in the synthesis, for instance chain transfer agents, solvents or various additives, being this the case of FPVE. This situation becomes more critical when azeotropic compositions are formed between FPVE and undesired substances present in the polymerization process. For instance, in FPVE modified ECTFE copolymers where chloroform and/or methylcyclopentane and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) are present, distilled FPVE still contains solvent and chain transfer agents as impurities. Therefore the use of distilled FPVE limits the synthesis of materials containing very high molecular weight fractions. As known, this high molecular weight fraction imparts excellent mechanical properties at elevated temperatures as shown by high stress at break values which determine the thermal rating of the material. Consequently, the use of distilled FPVE for the synthesis of high performance ECTFE's is not possible.
More generally the presence of impurities in FPVE does not allow the monomer reuse in fluoropolymer synthesis. In this case its disposal is required leading to an unavoidable environmental impact. Besides, it is known in the art that the synthesis of FPVE is complex and therefore its efficient use is always recommended.
Therefore the need was felt to develop a purification process of FPVE to reduce the impurities such as solvents and chain transfer agents in order to allow the FPVE reuse in fluorinated polymers syntheses.
The Applicant has surprisingly and unexpectedly found a perfluoropropylvinylether (FPVE) purification process that consists in treating a FPVE phase containing contaminants with C
1
-C
10
alcohols or mixtures thereof. C
1
-C
5
alcohols or their mixtures are preferred. The more preferred are methanol and propanol.
The FPVE purification process according to the present invention is a treatment comprising one or more extractions or washings between liquid phases or liquid and gaseous phases.
When more extractions are carried out on the same FPVE solution to be treated, the subsequent extractions can be carried out with a fresh extracting phase or by recycling the extracting phase used in the first or previous treatments. More specifically the purification process is carried out by one or more extractions by using fresh alcohols or by recycling the alcohols already used in the previous extractions.
The ratio between the extracting phase and the FPVE phase to be purified varies according to the desired purity. Typically, when the starting contaminants amount is low the ratio between the extracting phase and the FPVE phase value is about 1:20 by weight, preferably 1:10 by weight. When the starting contaminants amount is at high levels the ratio between the extracting phase and the FPVE phase values is about 20:1 by weight, preferably 10:1 by weight.
The process of the invention is particularly suitable for the purification of unreacted FPVE, when its conversion in polymerization is lower than 80%. This is the case of the FPVE modified ECTFE polymerization.
As a matter of fact the FPVE modified ECTFE copolymers characterized by their high viscosity combined with excellent mechanical properties and processability, are synthesized by using practically no chain transfer agent at the beginning of the polymerization, but adding later to the reactor the chain transfer agent.
At the end of the polymerization there is a high amount of unreacted FPVE containing chain transfer agents. In order to recycle the FPVE it is necessary to clean it from the chain transfer agents. These chain transfer agents can be generally hydrogenated and/or halogenated compounds, e.g., methylcyclopentane, and chloroform which are substantially eliminated from the recovered FPVE using the purification process of the present invention.
The FPVE purification process of the invention can also be advantageously used when, as impurities, one or more polymerization solvents are present in general in an amount higher than 10% by weight in the recvovered FPVE. This leads to a change of the molar concentration ratios between the monomers in the reaction medium. The variations of molar ratio values between the monomers influence the monomer composition of the final product. An example of that is the purification of FPVE from CFC-113, solvent widely used in the fluoropolymer synthesis.
The purification process of the invention can be carried out by liquid-liquid or liquid-gas extraction either by a continuous process, or a semi-batch or a batch process. The liquid extracting phase is preferred.
The extracting agents used in the FPVE purification process of the invention are environmentally safe (low toxicity, easy disposal), non corrosive and they have a high extraction efficiency.
For extraction efficiency (or yield) of the alcohols it is meant the variation, normalized to hundred, of the percentage of the contaminants amount present in recovered FPVE that is to be purified, before and after the treatment:
initial wt % contaminants−final % wt % contaminants.100
initial wt % contaminants
The FPVE purification treatment can be also carried out with an extracting phase formed of a mixture of the above alcohols and H
2
O. In this case a lowered extraction efficiency makes it necessary to conduct a greater number of washings relative to the use of pure alcohols.
It has been found by the Applicant that the FPVE purification process of the present invention can be applied for purifying a FPVE solution containing hydrogenated, halogenated and perhalogenated saturated or unsaturated residual substances.
The following examples are given to merely illustrate the invention but they are not limitative to the scope of the invention.
REFERENCES:
patent: 4042634 (1977-08-01), Cope et al.
patent: 5239055 (1993-08-01), Abe et al.
patent: 5352785 (1994-10-01), Herzberg et al.
patent: 5618894 (1997-04-01), DeSimone et al.
patent: 0 451 851 A1 (1991-10-01), None
Abusleme Julio A.
Blanke John W.
Arent Fox Kintner Plotkin & Kahn
Ausimont S.p.A.
Keys Rosalynd
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