PROCESS FOR PRODUCING FLUOROPOLYMERS USING 2-ALKOXYACETATE SURFACTANTS
20220081494 · 2022-03-17
Inventors
- Bhuvanesh GUPTA (New Delhi, IN)
- Bishwajit Santosh Bhattacharya (Noida, IN)
- Rajeev Chauhan (Noida, IN)
- Jitendra Kumar Rathour (Noida, IN)
- Gaurav Kumar (Noida, IN)
- Chetna Verma (New Delhi, IN)
Cpc classification
International classification
Abstract
The present invention relates to a process for the polymerization of fluoromonomers in an aqueous medium, said process comprising the steps of: forming an aqueous emulsion comprising a 2-Alkoxy acetate surfactant and fluoromonomer in a reactor; and initiating polymerization of said fluoromonomer by adding an initiator into the reaction mixture. Preferably, the surfactant used in the instant process is either Sodium 2-[(2-hexyldecyl)oxy] acetate or Sodium-2-dodecyloxyacetate.
Claims
1. A process for preparing a fluoropolymer in an aqueous medium, comprising: (a) forming an aqueous emulsion comprising a 2-Alkoxy acetate surfactant and a fluoromonomer in a reactor; and (b) initiating polymerization of said fluoromonomer by adding an initiator.
2. The process as claimed in claim 1, wherein step (a) comprises the steps of: i. adding deionized water and optionally paraffin wax into the reactor; ii. adding the 2-Alkoxy acetate surfactant in one shot into the reactor; and iii. adding fluoromonomer into the reactor and agitating the reaction mixture.
3. The process as claimed in claim 1, wherein step (b) comprises adding the initiator in one shot into the reactor.
4. The process as claimed in claim 1, wherein the 2-Alkoxy acetate surfactant has a structure of R—O—CH.sub.3—COOM, wherein R is a hydrocarbon group, and M is a monovalent cation selected from the group consisting of hydrogen ions, alkali metal ions, and ammonium ions.
5. The process as claimed in claim 4, wherein R is an alkyl group containing 6 to 21 carbon atoms.
6. The process as claimed in claim 4, wherein M is selected from the group consisting of potassium, sodium and ammonium.
7. The process as claimed in claim 1, wherein the 2-Alkoxy acetate surfactant is represented by formula 1. ##STR00004##
8. The process as claimed in claim 1, wherein the 2-Alkoxy acetate surfactant is represented by formula 2. ##STR00005##
9. The process as claimed in claim 1, wherein the aqueous emulsion comprises an initiator, for initiating the polymerization process, the initiator being selected from the group consisting of Ammonium Persulphate (APS), Disuccinic Acid Peroxide (DSAP) and combinations thereof.
10. The process as claimed in claim 2, wherein the aqueous emulsion comprises stabilizing agents such as paraffin wax.
11. The process as claimed in claim 1, wherein the reaction temperature is in the range of 20 to 160° C., preferably 60 to 130° C., and more preferably 75 to 95° C.
12. The process as claimed in claim 1, wherein the reaction pressure ranges from 2 to 200 bar.
13. The process as claimed in claim 1, wherein the reaction pressure is 24 bar.
14. The process as claimed in claim 1, wherein the reaction mixture is agitated at 50 rpm.
15. The process as claimed in claim 1, wherein the concentration of the surfactant in the reaction mixture ranges from 1000 to 7000 ppm, and preferably 3000 to 4000 ppm.
16. The process as claimed in claim 1, wherein the concentration of the surfactant in the reaction mixture is 3125 ppm.
17. The process as claimed in claim 3, wherein the concentration of the initiator ranges from 50 to 2000 ppm, preferably from 50 to 400 ppm and more preferably from 150 to 400 ppm.
18. The process as claimed in claim 1, wherein the solid content of the fluoropolymer ranges from 15 to 25% and more preferably from 18 to 25%.
19. The process as claimed in claim 1, wherein the particle size of the fluoropolymer ranges from 180 nm to 240 nm.
20. The process as claimed in claim 1, wherein the reaction time ranges from 60 to 160 minutes.
21. The process as claimed in claim 1, wherein the fluoromonomer is selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, perfluoropropylvinylether, perfluorobutylethylene and combinations thereof.
Description
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0036]
DETAILED DESCRIPTION OF THE INVENTION
[0037] Discussed below are some representative embodiments of the present invention. The invention in its broader aspects is not limited to the specific details and representative methods. Illustrative examples are described in this section in connection with the embodiments and methods provided.
[0038] It is to be noted that, as used in the specification, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a mixture of two or more compounds. It should also be noted that the term “‘or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0039] The expression of various quantities in terms of “%” or “% w/w” means the percentage by weight of the total solution or composition unless otherwise specified.
[0040] The present invention, in all its aspects, is described in detail as follows:
[0041] The present invention relates to a process for preparing a fluoropolymer in an aqueous medium, comprising: [0042] (a) forming an aqueous emulsion comprising a 2-Alkoxy acetate surfactant and fluoromonomer in a reactor or reaction vessel; and [0043] (b) initiating polymerization of said fluoromonomer by adding an initiator.
[0044] Surfactant
[0045] The term “surfactant” means a type of molecule which has both hydrophobic and hydrophilic, portions, which allows it to stabilize and disperse hydrophobic molecules and aggregates of hydrophobic molecules in aqueous systems. A preferred group of surfactants for fluoropolymer synthesis according to the embodiments of the present invention includes non-fluorinated carboxylate surfactants, more preferably 2-Alkoxy acetate surfactants. The 2-Alkoxy acetate surfactant has a structure of R—O—CH.sub.3—COOM, wherein R is a hydrocarbon group, M is a monovalent cation selected from the group consisting of hydrogen ions, alkali metal ions, and ammonium ions. More preferably, R is an alkyl group containing 6 to 21 carbon atoms. Preferably, M can be potassium, sodium or ammonium. In a particularly preferred embodiment, the 2-alkoxy acetate surfactant is represented by the formula 1. Compound of formula 1 is also known by the chemical name-Sodium-2-[(2-hexyldecyl)oxy] acetate.
##STR00002##
[0046] In another particularly preferred embodiment, the 2-alkoxy acetate surfactant is represented by the formula 2. Compound of formula 2, is also known by the chemical name Sodium-2-dodecylacetate.
##STR00003##
[0047] Fluoromonomers
[0048] The term “fluoromonomer” or the expression “fluorinated monomer” means a polymerizable alkene which contains at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group attached to the double bond of the alkene that undergoes polymerization. The term “fluoropolymer” means a polymer formed by the polymerization of at least one fluoromonomer, and it is inclusive of homopolymers, copolymers, terpolymers and higher polymers. Specific examples of suitable fluoromonomers include, without limitation, vinyl fluoride, vinylidine fluoride (VDF), 1-fluoro-1-chloro-ethylene, perfluoropropylvinylether, trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropene (HFP), chlorotrifluoroethylene (CTFE), 1-chloro-2,2-difluoroethylene, perfluoromethyl vinylether (PMVE), etc. Preferably, the fluoromonomer is tetrafluoroethylene (TFE) and the fluoropolymer obtained as a result of the polymerization reaction is polytetrafluoroethylene (PTFE).
[0049] The aqueous emulsion comprises an initiator for initiating the polymerization process.
[0050] Initiators
[0051] The term “initiator” and the expressions “radical initiator” and “free radical initiator” refer to a chemical that is capable of providing a source of free radicals, either induced spontaneously, or by exposure to heat or light. Examples of suitable initiators include peroxides, peroxydicarbonates and azo compounds. “Initiators” also includes redox systems useful in providing a source of free radicals. The term “radical” and the expression “free radical” refer to a chemical species that contains at least one unpaired electron. The radical initiator is added to the reaction mixture in an amount sufficient to initiate and maintain the polymerization reaction rate. Preferably, the addition of the initiator into the reaction vessel or reactor is carried out in one shot. The radical initiator may comprise a persulfate salt, such as sodium persulfate, potassium persulfate, or ammonium persulfate. Alternatively, the radical initiator may comprise a redox system. “Redox system” is understood by a person skilled in the art to mean a system comprising an oxidizing agent, a reducing agent and optionally, a promoter as an electron transfer medium. In a preferred embodiment, the radical initiator is either Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS), Potassium Persulfate (KPS) or combinations thereof.
[0052] Polymerization Conditions
[0053] The process parameters for carrying out the polymerization of the fluoromonomers in accordance with the present invention, illustrated in
[0054] The pressure used for polymerization may vary from 2-200 bar, depending on the reaction equipment, the initiator system, and the monomer selection. In a preferred embodiment the reaction is carried out at a pressure of 24 bar.
[0055] The polymerization occurs under stirring or agitation. The stirring may be constant, or may be varied to optimize process conditions during the course of the polymerization. In one embodiment, both multiple stirring speeds and multiple temperatures are used for controlling the reaction.
[0056] According to an embodiment of the process of the invention referring to
[0057] Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reaction vessel. Preferably, the solid content ranges from 15 to 25%, and more preferably from 18 to 25%. The particle size of the fluoropolymer particles ranges from 180 nm to 240 nm.
[0058] The present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those of skill in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following example are on a weight basis, and all reagents used in the example were obtained or are available from the chemical suppliers.
[0059] The following example illustrates the basic methodology and versatility of the present invention.
Example 1
[0060] The polymerization process was carried out in a 150 L horizontal reactor, with six blade agitator. 96 L of de-ionized water, and 4 kg of paraffin wax were added into the reactor. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant, molecule of formula 1, also known as Sodium 2-[(2-hexyldecyl)oxy] acetate, 3125 ppm, was added in one shot into the reactor. Thereafter, the addition of Tetrafluoroethylene (TFE) resulted in an increase in the pressure to 24 bar and the temperature was increased to 80 to 95° C. After attaining the aforesaid pressure and temperature, a solution comprising an initiator Ammonium Persulphate (APS), was added so that the final concentration of initiator in the reaction mixture was 275 ppm. Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reaction vessel. Examples 2 to 5 were also carried out in an identical manner and the ingredients and reaction parameters of Examples 1 to 5 are illustrated in Table 1 below. The latex particle size of the polymer was determined by—Dynamic Laser light scattering for analysis of particle size using a Nano particle Analyzer—HORIBA SZ-100. Although example 1 pertains to the polymerization of tetrafluoroethylene, the process may be applied to any monomer selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, perfluoropropylvinylether, perfluorobutylethylene and combinations thereof. All parameters were derived in accordance with ASTM D 4895.
TABLE-US-00001 TABLE 1 Ingredients/ Reaction Parameters Units Example-1 Example-2 Example-3 Example-4 Example-5 Di-Ionized Water Kg 96 96 96 96 96 Wax Kg 4 4 4 4 4 02 Content in the ppm ≤10 ≤10 ≤10 ≤10 ≤10 System Agitation RPM 50 50 50 50 50 Reaction Pressure Bar 24 24 24 24 24 Non-fluorinated ppm 3125 3125 3125 3125 3125 surfactant Total APS ppm 275 200 200 300 400 Succinic Acid g 32.62 32.62 32.62 32.62 32.62 Reaction Start ° C. 80 91 85 90 90 Temperature Total Kg 24 24 24 24 24 Tetrafluoroethylene (TFE)consumption Reaction End ° C. 85.12 80.20 81.67 80.15 80.62 Temperature Total Reaction min 80 75 70 75 66 Time Latex % 20.56 21.58 22.67 22.15 22.00 Concentration Latex Particle size nm 225.2 203 215 210 206 pH 3.01 3.52 3.88 3.75 3.12 Solid Content % 22.48 20.31 21.66 22.15 22.69 Standard Specific 2.185 2.176 2.189 2.178 2.189 Gravity Tensile Strength psi 25.16 26.11 27.23 25.98 25.97 Elongation % 241.4 240.2 268.1 278.2 231.3 Melting Point ° C. 341.76 341.73 343.05 343.51 344.09
Example 6
[0061] The polymerization process was carried out in a 150 L reactor. 96 L of de-ionized water, and 4 kg of paraffin wax were added into the reactor. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant, molecule of formula 2, also known as Sodium Salt of 2-dodecyloxyacetic acid (Sodium-2-dodecyloxyacetate), 3125 ppm, was added in one shot into the reactor. Thereafter, the addition of Tetrafluoroethylene (TFE) resulted in an increase in the pressure to 24 bar and the temperature was increased to 80 to 95° C. After attaining the aforesaid pressure and temperature, a solution comprising an initiator, Disuccinic Acid Peroxide (DSAP), was added so that the final concentration of initiator in the reaction mixture was 156 ppm. Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reaction vessel. Examples 7 to 9 were also carried out in an identical manner and the ingredients and reaction parameters of Examples 6 to 9 are illustrated in Table 2 below. Although example 6 pertains to the polymerization of tetrafluoroethylene, the process may be applied to any monomer selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, perfluoropropylvinylether, perfluorobutylethylene and combinations thereof.
TABLE-US-00002 TABLE 2 Ingredients/ Reaction Parameters Units Example-6 Example-7 Example-8 Example-9 De-ionized water kg 96 96 96 96 Wax kg 4 4 4 4 O.sub.2 content in the ppm ≤10 ≤10 ≤10 ≤10 system Agitation rpm 50 50 50 50 Reaction pressure bar 24 24 24 24 Non-fluorinated ppm 3125 3125 3125 3125 surfactant Total DSAP ppm 156 187 187 187 Succinic acid g 32.62 32.62 32.62 32.62 Polymerization Reaction Start ° C. 82.04 84.12 83.71 83.5 Temperature Total tetrafluoroethylene kg 24 24 24 23 (TFE) consumption Reaction end ° C. 81.51 90.62 89.94 90.06 temperature Total Reaction Time min 75 131 157 156 Latex Concentration % 21.40 22.48 20.84 20.43 Latex particle size (LPS) nm 226.3 203.1 228.3 217.8 pH 3.25 3.22 3.30 3.25 Solid Content % 21.46 22.52 20.90 20.53 Standard Specific 2.193 2.181 2.181 2.182 Gravity (SSG) Tensile strength psi 25.09 27.93 29.71 26.20 Elongation % 230.1 246.3 267.0 233.7 Melting Point (° C.) 343.54 343.69 342.7 342.51
[0062] The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.
Example 10
[0063] The polymerization process was carried out in a 150 L reactor. 83 L of de-ionized water with 160 PPM of sodium pyro-phosphate as a buffer is added to the reactor. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant, molecule of formula 1, also known as Sodium Salt of 2-dodecyloxyacetic acid (Sodium-2-dodecyloxyacetate), 4200 ppm, was added in one shot into the reactor. Thereafter, the addition of 2.4 kg Tetrafluoroethylene (TFE), 5.4 kg Hexafluoropropylene (HFP) and 60 g perfluoropropylvinyl ether (PPVE) resulted in an increase in the pressure to 22 bar and the temperature was increased to 90° C. After attaining the aforesaid pressure and temperature, a solution comprising initiators Potassium persulfate and ammonium persulfate (1% solution), was added at a starting rate rate of 15 ml/min, gradually reduced to 6 ml/min. 29 PPM ethane gas was added as chain transfer agent after the reaction kicks off as indicated by a pressure drop of 0.5 bar. Upon completion of the polymerization reaction after metering of 27.1 kg TFE and 2.4 kg HFP in 400 minutes, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure. The resulting polymer latex had a solid content of 27% by weight with a primary particle size of 234.2 nm. The latex particle size of the polymer was determined by—Dynamic Laser light scattering for analysis of particle size using a Nano particle Analyzer—HORIBA SZ-100. The resulting polymer powder after coagulation had the following properties: MFR (Melt Flow Rate): 26 g/10 min (372° C.; 5 kg load); Melting Temperature: 280.6° C.; Enthalpy: 27.6 J/g. All properties were derived in accordance with ASTM D 2116.
Example 11
[0064] The polymerization process was carried out in a 150 L reactor. 77 L of de-ionized water with 135 PPM of sodium pyro-phosphate as a buffer is added to the reactor. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant, molecule of formula 1, also known as Sodium Salt of 2-dodecyloxyacetic acid (Sodium-2-dodecyloxyacetate), 4500 ppm, was added in one shot into the reactor. Thereafter, the addition of 1.3 kg Tetrafluoroethylene (TFE) and 5.0 kg Hexafluoropropylene (HFP) resulted in an increase in the pressure to 22 bar and the temperature was increased to 94° C. After attaining the aforesaid pressure and temperature, a solution comprising initiators Potassium persulfate and ammonium persulfate (1% solution), was added at a starting rate of 15 ml/min, and gradually reduced to 9 ml/min. 59 PPM ethane gas was added as chain transfer agent after the reaction kicks off as indicated by a pressure drop of 0.5 bar. Upon completion of the polymerization reaction, after metering of 27.10 kg TFE and 2.94 kg HFP in 430 minutes, the reactor was brought to ambient temperature and the residual unreacted monomer was vented to atmospheric pressure. The resulting polymer latex had a solid content of 29% by weight with a primary particle size of 235.2 nm. The latex particle size of the polymer was determined by—Dynamic Laser light scattering for analysis of particle size using a Nano particle Analyzer—HORIBA SZ-100. The resulting polymer powder after coagulation had the following properties: MFR: 24 g/10 min (372° C.; 5 kg load); Melting Temperature: 284.3° C.; Enthalpy: 24.1 J/g. All properties were derived in accordance with ASTM D 2116.
[0065] The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.