CA1137671A - Ultrafiltration process for the concentration of polymeric latices - Google Patents
Ultrafiltration process for the concentration of polymeric laticesInfo
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- CA1137671A CA1137671A CA000252892A CA252892A CA1137671A CA 1137671 A CA1137671 A CA 1137671A CA 000252892 A CA000252892 A CA 000252892A CA 252892 A CA252892 A CA 252892A CA 1137671 A CA1137671 A CA 1137671A
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- latex
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- membrane
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Abstract
ABSTRACT OF THE DISCLOSURE
In a process for the concentration of an aqueous polymeric latex, which latex comprises polymeric particles dispersed in an aqueous phase by a semipermeable membrane process, such as an ultrafiltration process and which latex is subject to destabiliza-tion, the improvement which comprises: adding to the latex a sufficient amount of a compatible surfactant to stabilize the latex and to maintain the dispersion of the polymeric particles in the aqueous phase of the latex during the concentration of the latex in a semipermeable membrane process.
In a process for the concentration of an aqueous polymeric latex, which latex comprises polymeric particles dispersed in an aqueous phase by a semipermeable membrane process, such as an ultrafiltration process and which latex is subject to destabiliza-tion, the improvement which comprises: adding to the latex a sufficient amount of a compatible surfactant to stabilize the latex and to maintain the dispersion of the polymeric particles in the aqueous phase of the latex during the concentration of the latex in a semipermeable membrane process.
Description
~13'7~
Semipermeable membrane devices, and in particular semi-permeable ultrafiltration membrane devices, have been employed to concentrate or separate polymeric emulsions or latices Such latices typically comprise solid polymeric particles dispersed in water or a water-alcohol or other liquid phase. Often such latices contain a surfactant material which has been added during the manufacturing process to aisperse the polymeric particles in the liquid phase. Typical latices would include, but not be limited to: styrene-butadiene latices, poly-vinyl-chloride latices and the like.
Past commercial attempts to concentrate such latices through the removal of a portion of the liquid phase after manu-facture from a permeate zone of a semipermeable membrane device have not been successful. Such lack of success has been due in part to the inability of the semipermeable membranes to maintain the initially or originally high flux rates during the separation or concentration process. Quite often the flux rates rapidly diminish with time to an unsatisfactory or very low flux value, and, therefore, require, such as described in U.S. Patent
Semipermeable membrane devices, and in particular semi-permeable ultrafiltration membrane devices, have been employed to concentrate or separate polymeric emulsions or latices Such latices typically comprise solid polymeric particles dispersed in water or a water-alcohol or other liquid phase. Often such latices contain a surfactant material which has been added during the manufacturing process to aisperse the polymeric particles in the liquid phase. Typical latices would include, but not be limited to: styrene-butadiene latices, poly-vinyl-chloride latices and the like.
Past commercial attempts to concentrate such latices through the removal of a portion of the liquid phase after manu-facture from a permeate zone of a semipermeable membrane device have not been successful. Such lack of success has been due in part to the inability of the semipermeable membranes to maintain the initially or originally high flux rates during the separation or concentration process. Quite often the flux rates rapidly diminish with time to an unsatisfactory or very low flux value, and, therefore, require, such as described in U.S. Patent
2~ 3,956,114, Joseph Del Pico, issued May 11, 1976, the periodic employment of a solvent in order to help maintain or restore such original flux value. Thus, it is desirable to provide a rapid, simple, and inexpensive process which will permit the concentration of polymeric latices in a semipermeable membrane process, such as a low-pressure, ultrafiltration process, and for such process to operate in a commercially satisfactory and continuous manner without severe flux degradation.
My invention relates to an improved process for the concentration or separation of polymeric latices, and in parti-cular, my invention concerns an improved process forstabilizing a polymeric cl~. - 3 -.J.
latex during a concentration process by ultrafiltration through the addition of surfactant to the latex to stabilize the latex and thereby maintain acceptable flux rates during the concen-tration process~
I have found -that, by adding surfactants, particularly anionic and nonionic surfactants, to polymer latices prior to or during the concentration or separation process of the latices with a semipermeable membrane, the latices are stabilized and good flux rates are maintained. I believe that the addition of the surfactants to the polymer latices provides for adsorption .~ on the surface of the latex particles or electrical boundary layers, which prevent or retard the polymer particles from coalescing during the semipermeable membrane process.
~he invention relates to an improvement in a process for the concentration or separation of an aqueous polymeric ~ latex, which comprises polymer particles dispersed in an aqueous-i liquid phase, by a semipermeable membrane which permits the passage of th~ liquid phase and r~tains the pol~mer particles.
The improvement comprises adding to the latex an amount of a 2Q co.mpatible surfactant effective to stabilize the latex contact-ing the semi-permeable membrane to maintain the dispersion of the polymer particles in the liquid phase during the con-centration or separation, said surfactant forming polymer-surfactant particles thereby preventing the formation of coagulum from the latex and degradation of the flux rate of the process, the polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through the membrane. In particular the amount of surfactant may be in excess of the amount of surfactant which may be lost through the semi-permeable membrane during concentration or separation.
r~ - 4 - .
~3~7~
The concentration and/or separation of a polymer latex is carried out by introducing the latex into the feed zone of a semi-permeable membrane device, wherein a feed zone is separated from a permeate zone through the employment of a particular semi-permeable membrane. The semi-permeable membrane device may comprise one or more reinforced tubes, such as a braided tube having a semi-permeable membrane parti-cularly of cellulose acetate or other membrane material, on the inside or the outside of the tube, or may comprise a spiral-type module device, such as described, for example, in U.S. Patents 3,367,504, 3,386,5~3 3,397,790, and
My invention relates to an improved process for the concentration or separation of polymeric latices, and in parti-cular, my invention concerns an improved process forstabilizing a polymeric cl~. - 3 -.J.
latex during a concentration process by ultrafiltration through the addition of surfactant to the latex to stabilize the latex and thereby maintain acceptable flux rates during the concen-tration process~
I have found -that, by adding surfactants, particularly anionic and nonionic surfactants, to polymer latices prior to or during the concentration or separation process of the latices with a semipermeable membrane, the latices are stabilized and good flux rates are maintained. I believe that the addition of the surfactants to the polymer latices provides for adsorption .~ on the surface of the latex particles or electrical boundary layers, which prevent or retard the polymer particles from coalescing during the semipermeable membrane process.
~he invention relates to an improvement in a process for the concentration or separation of an aqueous polymeric ~ latex, which comprises polymer particles dispersed in an aqueous-i liquid phase, by a semipermeable membrane which permits the passage of th~ liquid phase and r~tains the pol~mer particles.
The improvement comprises adding to the latex an amount of a 2Q co.mpatible surfactant effective to stabilize the latex contact-ing the semi-permeable membrane to maintain the dispersion of the polymer particles in the liquid phase during the con-centration or separation, said surfactant forming polymer-surfactant particles thereby preventing the formation of coagulum from the latex and degradation of the flux rate of the process, the polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through the membrane. In particular the amount of surfactant may be in excess of the amount of surfactant which may be lost through the semi-permeable membrane during concentration or separation.
r~ - 4 - .
~3~7~
The concentration and/or separation of a polymer latex is carried out by introducing the latex into the feed zone of a semi-permeable membrane device, wherein a feed zone is separated from a permeate zone through the employment of a particular semi-permeable membrane. The semi-permeable membrane device may comprise one or more reinforced tubes, such as a braided tube having a semi-permeable membrane parti-cularly of cellulose acetate or other membrane material, on the inside or the outside of the tube, or may comprise a spiral-type module device, such as described, for example, in U.S. Patents 3,367,504, 3,386,5~3 3,397,790, and
3,417,870.
-- Typically, polymer latices are separated or concentrated in an ultrafiltration, rather than a reverse osmosis process, wherein the pressures employed are about 10 to 200 psi, for e~ampl~, 20 to 100 psi. The temperatures employed in such proce~;ses may vary, depending upon the viscosity of the latex to be con-centrated, the flux rate of the membrane and other factors, but typically range - 4a -.~
~ 3~
from about 70 to 180F, for example, 90 to 140 F. In the process, the latex is introduced into one end of the feed zone of the semi-permeable membrane device, and a concentrated latex is removed from the other end of the feed zone and a portion of the liquid phase,typically water and low-molecular weight salts,are removed from the permeate zone. The concentration process may be directed to sending the latex through one or more semipermeable membrane devices in a series, or more typically, the latex is introduced by a pump ~nto the feedzone of the semipermeable membrane, and the concentrated fraction recycled, employing the same pump or another pump, back to the introductory feed zone portion of the device, while the permeate fraction comprising the liquid phase, typically water with low-molecular-weight materials~ and often containing some of the surfactant in the latex is removed from the permeate zone.
I have found that in the process of concentrating a latex mechanical shear is placed on the latex, since the latex is pumped about in a typical ultraf;ltrat:;on system and that this mechanical shear force contribute~ to the destabilization of ~he latex and the formation of coagulum which reduces flux rate.
Further, the ultrafiltration semipermeable membrane process re-moves the liquid-water phase and some surfactant and their salts in the polymer latex which contributes further to destabilization of the latex. When the latex destabilizes, then coagulum; that is, aggregates of latex polymeric particles, coagulate and dest-abilization of the latex occurs, resulting in fouling of the mem-brane surface and pores with reduced flux rates resulting.
Thus, many polymeric latices are unstable in the presence of the high-mechanical shear required to pump the latex into the feed zone, and to recyle the processed latex back into the feed zone of the semipermeable membrane device. The mechanical shear that is developed in the seals and impellers of the high-volume centri~uga pumps; that ls, pumps that have relat~vely low shear and high volume, are employed in pumping latices through ultrafiltration an _ 5 -.3~6~
reverse-osmosis systems. Such pumps are an opened-face impeller~
while pumps which have a closed-face impeller or gear pumps or pumps that have close tolerances are not employed in pumping latices9 since such pumps tend to destabilize rapidly the latices.
Furthermore, diaphragm pumps, although they produce a pulsating f1OW, are not normally used, except with an accumulator which evens out the flow rate.
Another pump recommended for use with an ultrafiltra~ion process for the separation of a latex is a low-shear screw pump which has large tolerances. Thus, for example, low-shear screw pumps with large tolerances and centri~ugal pumps with an opened-face impeller are used in ultra~iltration processes for the con-centration of polymeric latices, while other pumps9 which place a much higher mechanical shear on the late~, are not recommended, since otherwise very large uneconomical amounts of surfactant may be required to stabilize the latex.
However, regardless of what pumps are used, quite often the latex becomes unstable, eYen though the latex may contain surfac-tants added usually during the manufacturing o~ poly~erization process of ~he latex. Addition of these surfac~ants added during manufacturing often provides for only a low order of stability.
The use o~ additlonal surfactants, as required in my process, often is not necessary under normal conditions, because the latex is not subject to a high shear or other factors such as concentra-tion polymerization layers employed or found in an ultrafiltrationprocess.
In addition, I have found that latices which are to be con-centrated in a semipermeable separation process are often unstable at the concentrations found in the polarization concentration laye formed adjacent the semipermeable membranes employed in the ultra-filtration and reverse-osmQsis devices. Since there is a hi~her concentration of polymer particles in the polarization layer ad-jacent the membrane skin, this concentration is often sufficient , l ~37~7~
during the process to effect also the destabilization of the l~tex, Thus, tha higher temperatures~ the higher concentration of the polarîzation layer and the greater shear caused by the pumps and the pumpi ng processes dur;ng the ultrafiltration process cause a more frequent and energetic collision of the macro-mol ecules of the polymer particles, and thus lead to a greater tendency of coa-gulation of the particles and destabili~ation of the latex, which coagulation results in fouling of the membrane and reduction in flux rate.
I have found that destabilization of the latex during a mem-brane separation process may be avoided, prevented or at least considerably reduced along with the r~sulting coagulum from the d~stab~lized latex, by employing additional and minor amounts of a surfactant to the latices prior to or durlng the concentration process. The amount of the surfactant to be added may vary, dependiny upon the particular polymeric latices to be employed and the conditions under which the process is to be operated, but typically may comprise about 0.05 to 2.0% o~ the surfactant based on the weight of the polymer in the latices, for example, from 2Q about 0.1 to about 1.0% such as 0.4 to 0.8%. The su~factant may be added in a continuous manner into the latex prior to pumping or during recyle, or where a batch process is used~ the surfactant may be added to and mixed with the batch of the latex to be con-centrated prior to separation and concentration. Where a portion of the surfactant is removed with the liquid phase from the permeate zone, it may be ~ound necessary to add additional sur-factant during the recycling of the concentrated fraction back to the feed zone, to maintain the desired concentration level of the latex to prevent destabilization.
The amount of surfactant required to stabilize the latex l¦during a particular process may be determined by carrying out 767~
I .
the particular process under similar temperature and pressure conditions with the desired pump9 e~ther in a pil~ plant or in la commercial unit and continually adding smaller incremental amounts of surfactant to reach and determine the minimum con~
centration ~evel required for stabilization of the latex under the commercial operating condi~ons to be employed. Another method for determining-the amount of surfactant to be employed is to test the latex by mixing the latex in a blender while adding incremental amounts of surfactant, and observing for coagulum under the high shear blending conditions. Such a test is a typical test for mechanical stability of latices, as set forth in ASTM D 1076-73 (Test No. 16).
My process will be described in reference to particular po1y-meric latices; however, my process is useful with a wide variety ; 15 of polymeric latices, such as natural latex, butyl rubber, nitrile rubber~ ethylene-propylene copolymers and terpolyme~s, homo and copolymers of diene polymers like butadiene-styrene copoly-mers~ as well as terpolymers with acrylonitrile, acrylate latex, polyvinyl alcohol and polyvinyl-acetate emulsions, homo and ~0 copolymers of vinyl-halides like polyvinyl-chloride and vinyl chloride-vinyl acetate copolymers and other polymeric emulsions and latex compositions where it is desired to concentrate the latex to a higher concentration value. My process is particularl applicable to vinyl-chloride polymer latices~ such as polyvinyl-chloride latex or a vinyl~chloride~vinyl-acetate Jatex and the like and natural rubber latex since such latices tend generally to be relatively unstable as compared to styrene-butadiene rubber latices.
The polymeric latices may be concentra~ed typically up to as hlgh as 70% conc~ntration. For example, with polyvinyl-chloride and vinyl-halide/vinyl-acetate copolymer emulsions, the latex L3~67~
is usually manufactured at about 25 to 35% polymer, and is con-centrated up to 50 to 60%~ Styrene-butadiene rubber latices are oFten concentrated from about 10 to 20%; for example, 15%, up to 45 to 60% concentration levels, o~ higher if desired. My process may also be employed on waste streams which contain a polymeric latex where it is desired to concentrate the latex from a ~ery low value; for example, less than 1%~ up to 20%, and~ thereafter9 to mix the concentrated fraction recovered with other latex concentra-tion ~or further concentration to a higher level. ThPrPfore, in the concentration processes for polymeric latices, the feed stream may range from very low amounts (as low as 0.1 to about 1%) to concentration levels of 55 to 75% or higher. Where very high concentrations occur, the polymer often becomes viscous, so that a hi~her temperature must be employed in the ultrafiltration process and when such occurs, often additional amounts of surfactant are required in order to prevent destabilization of the latices due to the morP energetic polymer molecules a~; the higher temperature process levels.
The surfactants useful in my process and to be added to the polymeric lat;ces encompass a wide variety of surfactants and surfactant-functioning materials. Any material may be used as a urfactant in my process as I use the term which stabilizes the polymeric latices under the membrane concentration layer condi-tiuns and high-~shear pumping conditions of the process. Typically the surfactant should be compatib~e with the polymer latices; that is, not lead to an electrical imbalance, for example, adding an anionic surfactant to a cationic stabilized latex, and preferably the surfactant employed is the same surfactant or same type or class as used by the manufacturer in the latex~ and more particu-larly, the use of nonionic surfactants is preferred, It isrecognized that s~me latices are sold as unstable-type latices and are compounded in this manner so that they may be used for a particular process. However, such latices are not of the type useful in ultrafiltration processes and are not generally used in such processes, due to such compounded and intentional destabi-lization of the latices.
The polymeric latices are usually prepared by polymerization of the monomer in an aqueous medium in the presence of a suit-able polymerization catalyst to provide a latex of lO to 60%
total solids. The aqueous medium may be surfactant-free or it ¦may contain a surfactant or a surfactant may be added later in the process.
Suitable surfactants used in latex manufacture and useful in my process include organic su1fates and sulfonates, such as sodium lauryl sulfate, but are not limited to: ammonium lauryl sulfate, the alkali-metal and ammonium salts of sulfonated petroleum or paraffin oils, the sodium salts of aromatic sulfonic acidsS such as the sodium salt of naphthalene sulfonic acids, the sodium salts of dodecane-l-sulfonic acid, octadiene-l-sulfonic acid, etc.; aralkyl sulfonates, such as sodium isopropyl benzene sulfonate, sodium dodecyl benzene sulfonate and sodium isobutyl naphthalene sulfonatea alkali-metal and ammonium salts of sul-fonated discarboxylic acid esters and amides, such as sodium dioct l sulfosuccinate, sodium octadecyl sulfo succinamate and the like and others.
Cationic surfactants, such as the salts of strong inorganic acids and organic bases3 containin~ long carbon chains, for exampl , lauryl amine hydrochloride, the hydrochloride of diethylaminooctyl decylamine, trimethyl cetyl ammonium bromide, dodecyl trimethyl ammonium bromide, the diethyl cyclohexylamine salt of cetyl sulfon c ester and others may be used. One preferred class, however, is the anionic surfactants such as the alkali~metal and ammonium salt L37~73~
of aromatic sulfonic acids, aralkyl sulfonates and long-chain ~kyl sulfates. Suitable anionic surfactants would comprise sodium lauryl sulfate, ethoxylated sodium sulfo succinate~ and alkylaryl polyether sulfates.
In addition to the above and other polar or ionic emulsifiers, and surfactants, another most preferred class which may be used, singly or in combination with one or more of the foregoing types of surfactants, includesthe so-called "nonionic" surfactants, such as the polyether alcohols prepared by condensing ethylene or pro-pylene oxide with higher alcohols, the fatty alkylol-amine con-densates, the digylcol esters of lauric~ oleic and stearic acids and others. Specific nonionic surfactants include C8-Cg alkyl phenoxy polyetho~y ethanols or propanols containing from about 20 to 100 ethoxy or pr~xy groups like tertiary octyl and nonylphenoxy polyethoxy ethanols.
My invention will be described for the propose of illus~ration only in connection with the concentration of certain polymeric latices; however, it is recognized ancl within the sp~rit and scope of my inventi~n that Yarious changes, modifications and alteration may be made without departing from the spirit and scope of my in vention.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows an illustrated schematic process of an ultra f~ltration device employed for the concentration of a polymeric lat~x employing my invention.
DESCRIPT~ON OF THE EMBODIMENTS
The drawing shows an ultrafiltration device and process in which a polymeric latex 10 is placed in a batch container 12, and a surfactant 16 added and mixed by a mixer 14 with the polymeric latex. The polymeric latex 10 with the additional surfactant is withdrawn from the container 12 through line 18 and through a 3'76 ;'~
centrifugal opened-face impeller highovolume pump 20 into an ultra f~ltration membrane device 22 comprising for example a module with a plurality of tubes having a semipermeable membrane coated on the inside diameter of the reinforced tubes or a spiral module ultra-filtration membrane device, for example, with a cellulose-acetate semipermeable membrane.
A permeate fraction 34 is removed from line 24 from the permea e zone, the permeate fraction comprising the liquid phase, prima~ly water, plus also some low-molecular-weight salts if present in the lU ori~nal polymeric latex 10, and also small amounts of surfactants in some cases. The concentrated latex is removed from the other end of the feed zone through line 28 and is recycled through line 30 to be reintroduced into the semipermeable membrane device 22 unt~l the desired level of concentration is obtained, and then the concentrated latex 32 is removed continuously through line 26.
Add;tional surfactant 36 is shown introduced into the recycle line 0 to maintain the surfactant level~ The drawing illustrates a typical batch process for the concentration of a manufactured atex. Of course, where desired, rather than employing a single emipermeable membrane unit 22~ a series of such units may be mployed, with the latex progressively concentrated as it passes hrough each membrane device.
Example 1.
A polyvinyl-chlorlde latex having a solids content of about
-- Typically, polymer latices are separated or concentrated in an ultrafiltration, rather than a reverse osmosis process, wherein the pressures employed are about 10 to 200 psi, for e~ampl~, 20 to 100 psi. The temperatures employed in such proce~;ses may vary, depending upon the viscosity of the latex to be con-centrated, the flux rate of the membrane and other factors, but typically range - 4a -.~
~ 3~
from about 70 to 180F, for example, 90 to 140 F. In the process, the latex is introduced into one end of the feed zone of the semi-permeable membrane device, and a concentrated latex is removed from the other end of the feed zone and a portion of the liquid phase,typically water and low-molecular weight salts,are removed from the permeate zone. The concentration process may be directed to sending the latex through one or more semipermeable membrane devices in a series, or more typically, the latex is introduced by a pump ~nto the feedzone of the semipermeable membrane, and the concentrated fraction recycled, employing the same pump or another pump, back to the introductory feed zone portion of the device, while the permeate fraction comprising the liquid phase, typically water with low-molecular-weight materials~ and often containing some of the surfactant in the latex is removed from the permeate zone.
I have found that in the process of concentrating a latex mechanical shear is placed on the latex, since the latex is pumped about in a typical ultraf;ltrat:;on system and that this mechanical shear force contribute~ to the destabilization of ~he latex and the formation of coagulum which reduces flux rate.
Further, the ultrafiltration semipermeable membrane process re-moves the liquid-water phase and some surfactant and their salts in the polymer latex which contributes further to destabilization of the latex. When the latex destabilizes, then coagulum; that is, aggregates of latex polymeric particles, coagulate and dest-abilization of the latex occurs, resulting in fouling of the mem-brane surface and pores with reduced flux rates resulting.
Thus, many polymeric latices are unstable in the presence of the high-mechanical shear required to pump the latex into the feed zone, and to recyle the processed latex back into the feed zone of the semipermeable membrane device. The mechanical shear that is developed in the seals and impellers of the high-volume centri~uga pumps; that ls, pumps that have relat~vely low shear and high volume, are employed in pumping latices through ultrafiltration an _ 5 -.3~6~
reverse-osmosis systems. Such pumps are an opened-face impeller~
while pumps which have a closed-face impeller or gear pumps or pumps that have close tolerances are not employed in pumping latices9 since such pumps tend to destabilize rapidly the latices.
Furthermore, diaphragm pumps, although they produce a pulsating f1OW, are not normally used, except with an accumulator which evens out the flow rate.
Another pump recommended for use with an ultrafiltra~ion process for the separation of a latex is a low-shear screw pump which has large tolerances. Thus, for example, low-shear screw pumps with large tolerances and centri~ugal pumps with an opened-face impeller are used in ultra~iltration processes for the con-centration of polymeric latices, while other pumps9 which place a much higher mechanical shear on the late~, are not recommended, since otherwise very large uneconomical amounts of surfactant may be required to stabilize the latex.
However, regardless of what pumps are used, quite often the latex becomes unstable, eYen though the latex may contain surfac-tants added usually during the manufacturing o~ poly~erization process of ~he latex. Addition of these surfac~ants added during manufacturing often provides for only a low order of stability.
The use o~ additlonal surfactants, as required in my process, often is not necessary under normal conditions, because the latex is not subject to a high shear or other factors such as concentra-tion polymerization layers employed or found in an ultrafiltrationprocess.
In addition, I have found that latices which are to be con-centrated in a semipermeable separation process are often unstable at the concentrations found in the polarization concentration laye formed adjacent the semipermeable membranes employed in the ultra-filtration and reverse-osmQsis devices. Since there is a hi~her concentration of polymer particles in the polarization layer ad-jacent the membrane skin, this concentration is often sufficient , l ~37~7~
during the process to effect also the destabilization of the l~tex, Thus, tha higher temperatures~ the higher concentration of the polarîzation layer and the greater shear caused by the pumps and the pumpi ng processes dur;ng the ultrafiltration process cause a more frequent and energetic collision of the macro-mol ecules of the polymer particles, and thus lead to a greater tendency of coa-gulation of the particles and destabili~ation of the latex, which coagulation results in fouling of the membrane and reduction in flux rate.
I have found that destabilization of the latex during a mem-brane separation process may be avoided, prevented or at least considerably reduced along with the r~sulting coagulum from the d~stab~lized latex, by employing additional and minor amounts of a surfactant to the latices prior to or durlng the concentration process. The amount of the surfactant to be added may vary, dependiny upon the particular polymeric latices to be employed and the conditions under which the process is to be operated, but typically may comprise about 0.05 to 2.0% o~ the surfactant based on the weight of the polymer in the latices, for example, from 2Q about 0.1 to about 1.0% such as 0.4 to 0.8%. The su~factant may be added in a continuous manner into the latex prior to pumping or during recyle, or where a batch process is used~ the surfactant may be added to and mixed with the batch of the latex to be con-centrated prior to separation and concentration. Where a portion of the surfactant is removed with the liquid phase from the permeate zone, it may be ~ound necessary to add additional sur-factant during the recycling of the concentrated fraction back to the feed zone, to maintain the desired concentration level of the latex to prevent destabilization.
The amount of surfactant required to stabilize the latex l¦during a particular process may be determined by carrying out 767~
I .
the particular process under similar temperature and pressure conditions with the desired pump9 e~ther in a pil~ plant or in la commercial unit and continually adding smaller incremental amounts of surfactant to reach and determine the minimum con~
centration ~evel required for stabilization of the latex under the commercial operating condi~ons to be employed. Another method for determining-the amount of surfactant to be employed is to test the latex by mixing the latex in a blender while adding incremental amounts of surfactant, and observing for coagulum under the high shear blending conditions. Such a test is a typical test for mechanical stability of latices, as set forth in ASTM D 1076-73 (Test No. 16).
My process will be described in reference to particular po1y-meric latices; however, my process is useful with a wide variety ; 15 of polymeric latices, such as natural latex, butyl rubber, nitrile rubber~ ethylene-propylene copolymers and terpolyme~s, homo and copolymers of diene polymers like butadiene-styrene copoly-mers~ as well as terpolymers with acrylonitrile, acrylate latex, polyvinyl alcohol and polyvinyl-acetate emulsions, homo and ~0 copolymers of vinyl-halides like polyvinyl-chloride and vinyl chloride-vinyl acetate copolymers and other polymeric emulsions and latex compositions where it is desired to concentrate the latex to a higher concentration value. My process is particularl applicable to vinyl-chloride polymer latices~ such as polyvinyl-chloride latex or a vinyl~chloride~vinyl-acetate Jatex and the like and natural rubber latex since such latices tend generally to be relatively unstable as compared to styrene-butadiene rubber latices.
The polymeric latices may be concentra~ed typically up to as hlgh as 70% conc~ntration. For example, with polyvinyl-chloride and vinyl-halide/vinyl-acetate copolymer emulsions, the latex L3~67~
is usually manufactured at about 25 to 35% polymer, and is con-centrated up to 50 to 60%~ Styrene-butadiene rubber latices are oFten concentrated from about 10 to 20%; for example, 15%, up to 45 to 60% concentration levels, o~ higher if desired. My process may also be employed on waste streams which contain a polymeric latex where it is desired to concentrate the latex from a ~ery low value; for example, less than 1%~ up to 20%, and~ thereafter9 to mix the concentrated fraction recovered with other latex concentra-tion ~or further concentration to a higher level. ThPrPfore, in the concentration processes for polymeric latices, the feed stream may range from very low amounts (as low as 0.1 to about 1%) to concentration levels of 55 to 75% or higher. Where very high concentrations occur, the polymer often becomes viscous, so that a hi~her temperature must be employed in the ultrafiltration process and when such occurs, often additional amounts of surfactant are required in order to prevent destabilization of the latices due to the morP energetic polymer molecules a~; the higher temperature process levels.
The surfactants useful in my process and to be added to the polymeric lat;ces encompass a wide variety of surfactants and surfactant-functioning materials. Any material may be used as a urfactant in my process as I use the term which stabilizes the polymeric latices under the membrane concentration layer condi-tiuns and high-~shear pumping conditions of the process. Typically the surfactant should be compatib~e with the polymer latices; that is, not lead to an electrical imbalance, for example, adding an anionic surfactant to a cationic stabilized latex, and preferably the surfactant employed is the same surfactant or same type or class as used by the manufacturer in the latex~ and more particu-larly, the use of nonionic surfactants is preferred, It isrecognized that s~me latices are sold as unstable-type latices and are compounded in this manner so that they may be used for a particular process. However, such latices are not of the type useful in ultrafiltration processes and are not generally used in such processes, due to such compounded and intentional destabi-lization of the latices.
The polymeric latices are usually prepared by polymerization of the monomer in an aqueous medium in the presence of a suit-able polymerization catalyst to provide a latex of lO to 60%
total solids. The aqueous medium may be surfactant-free or it ¦may contain a surfactant or a surfactant may be added later in the process.
Suitable surfactants used in latex manufacture and useful in my process include organic su1fates and sulfonates, such as sodium lauryl sulfate, but are not limited to: ammonium lauryl sulfate, the alkali-metal and ammonium salts of sulfonated petroleum or paraffin oils, the sodium salts of aromatic sulfonic acidsS such as the sodium salt of naphthalene sulfonic acids, the sodium salts of dodecane-l-sulfonic acid, octadiene-l-sulfonic acid, etc.; aralkyl sulfonates, such as sodium isopropyl benzene sulfonate, sodium dodecyl benzene sulfonate and sodium isobutyl naphthalene sulfonatea alkali-metal and ammonium salts of sul-fonated discarboxylic acid esters and amides, such as sodium dioct l sulfosuccinate, sodium octadecyl sulfo succinamate and the like and others.
Cationic surfactants, such as the salts of strong inorganic acids and organic bases3 containin~ long carbon chains, for exampl , lauryl amine hydrochloride, the hydrochloride of diethylaminooctyl decylamine, trimethyl cetyl ammonium bromide, dodecyl trimethyl ammonium bromide, the diethyl cyclohexylamine salt of cetyl sulfon c ester and others may be used. One preferred class, however, is the anionic surfactants such as the alkali~metal and ammonium salt L37~73~
of aromatic sulfonic acids, aralkyl sulfonates and long-chain ~kyl sulfates. Suitable anionic surfactants would comprise sodium lauryl sulfate, ethoxylated sodium sulfo succinate~ and alkylaryl polyether sulfates.
In addition to the above and other polar or ionic emulsifiers, and surfactants, another most preferred class which may be used, singly or in combination with one or more of the foregoing types of surfactants, includesthe so-called "nonionic" surfactants, such as the polyether alcohols prepared by condensing ethylene or pro-pylene oxide with higher alcohols, the fatty alkylol-amine con-densates, the digylcol esters of lauric~ oleic and stearic acids and others. Specific nonionic surfactants include C8-Cg alkyl phenoxy polyetho~y ethanols or propanols containing from about 20 to 100 ethoxy or pr~xy groups like tertiary octyl and nonylphenoxy polyethoxy ethanols.
My invention will be described for the propose of illus~ration only in connection with the concentration of certain polymeric latices; however, it is recognized ancl within the sp~rit and scope of my inventi~n that Yarious changes, modifications and alteration may be made without departing from the spirit and scope of my in vention.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows an illustrated schematic process of an ultra f~ltration device employed for the concentration of a polymeric lat~x employing my invention.
DESCRIPT~ON OF THE EMBODIMENTS
The drawing shows an ultrafiltration device and process in which a polymeric latex 10 is placed in a batch container 12, and a surfactant 16 added and mixed by a mixer 14 with the polymeric latex. The polymeric latex 10 with the additional surfactant is withdrawn from the container 12 through line 18 and through a 3'76 ;'~
centrifugal opened-face impeller highovolume pump 20 into an ultra f~ltration membrane device 22 comprising for example a module with a plurality of tubes having a semipermeable membrane coated on the inside diameter of the reinforced tubes or a spiral module ultra-filtration membrane device, for example, with a cellulose-acetate semipermeable membrane.
A permeate fraction 34 is removed from line 24 from the permea e zone, the permeate fraction comprising the liquid phase, prima~ly water, plus also some low-molecular-weight salts if present in the lU ori~nal polymeric latex 10, and also small amounts of surfactants in some cases. The concentrated latex is removed from the other end of the feed zone through line 28 and is recycled through line 30 to be reintroduced into the semipermeable membrane device 22 unt~l the desired level of concentration is obtained, and then the concentrated latex 32 is removed continuously through line 26.
Add;tional surfactant 36 is shown introduced into the recycle line 0 to maintain the surfactant level~ The drawing illustrates a typical batch process for the concentration of a manufactured atex. Of course, where desired, rather than employing a single emipermeable membrane unit 22~ a series of such units may be mployed, with the latex progressively concentrated as it passes hrough each membrane device.
Example 1.
A polyvinyl-chlorlde latex having a solids content of about
4.5% was introduced into an ultrafiltrat~on process as set forth n the drawing, and it was found that the centrifugal pump could nly run for approximately two hours at 2600 rpm before the latex oagulated, The addition of an anionic or a nonionic surfactan~
o the polyvinyl-chloride latex, at approximately 0.4% of the eight of the polymer, permitted the latex to be run in the ltrafiltration process and to be concentrated to approximately 3~G79~
64% solids without difficulty. One surfactant employed was Tergitol 7, an anionic surfactant similar to the surfac~ant em-ployed by the manufacturer in stabilizing the polyvinyl-chloride latex during manufacture. Tergitol 7 is a trademark of Union Carbide Corp. to identify a sodium sulfonate derivative of 1, 9-dlethyltridecanol-6 A nonionic surfactant Triton X-100, an alkylaryl polyether alcohol, which is a ~rademark of Rohm & Haas C~o., was also added and found to be satisfactory.
~e~.
~ A poly~inyl-chloride emulsion of a different manufacturer, the Example 1, having about 30% solids 9 when placed in an ultrafiltra-tion system of the type described, and could not be pumped at all without destabilization oF the latex and formation of coagulum.
The addition of between 5 and 50 m1 per gallon of an anionic sur-lS factant of the same type as employed by the manufacturer to the latex provided additional stability and permitted the latex to be concentrated in the ultraf~ltrat;ion process.
Example 3 .
A 50%-solids styrene-butadiene rubber latex of about 50%-solid 2Q was diluted to 0.~% solids, and run w;th both tubular and spiral ultrafiltration membrane devices. After several hours of running at a steady state, as the temperature increased from 15 to 35C, the process flux dropped from 60 to 10 gfd for the tubes (gallons per square foot of membrane per day). The add;tion of about 5X
- 25 of a nonionic surfactant Triton X-100, based on the polymer weight, at a rate of 14 ml to 15 gallons of a latex pre~ented the process flux of the tubes and the spiral membrane from decreasing with time. After addition of the surfactant the flux of the membrane was then approximately 200 gfd at 50C.
Thus 9 the addition of surfactants to polymer latices prior to ¦or during the process of ultrafiltration stabilized the latices 3'767~
~and prevented coagulum from forming and decre~sing the flux rate.
¦The addition of surfactant also prevented pump fai7ure9 which failure often occurs by virtue of the coagulant plu~ging up the l seals in the internal portion of the pump. ~ly process provides S la rapid, simple and an effective means to overcome the difficultie ¦of the prior art and to permit the commercial concentration and ¦seperation of polymeric latices.
o the polyvinyl-chloride latex, at approximately 0.4% of the eight of the polymer, permitted the latex to be run in the ltrafiltration process and to be concentrated to approximately 3~G79~
64% solids without difficulty. One surfactant employed was Tergitol 7, an anionic surfactant similar to the surfac~ant em-ployed by the manufacturer in stabilizing the polyvinyl-chloride latex during manufacture. Tergitol 7 is a trademark of Union Carbide Corp. to identify a sodium sulfonate derivative of 1, 9-dlethyltridecanol-6 A nonionic surfactant Triton X-100, an alkylaryl polyether alcohol, which is a ~rademark of Rohm & Haas C~o., was also added and found to be satisfactory.
~e~.
~ A poly~inyl-chloride emulsion of a different manufacturer, the Example 1, having about 30% solids 9 when placed in an ultrafiltra-tion system of the type described, and could not be pumped at all without destabilization oF the latex and formation of coagulum.
The addition of between 5 and 50 m1 per gallon of an anionic sur-lS factant of the same type as employed by the manufacturer to the latex provided additional stability and permitted the latex to be concentrated in the ultraf~ltrat;ion process.
Example 3 .
A 50%-solids styrene-butadiene rubber latex of about 50%-solid 2Q was diluted to 0.~% solids, and run w;th both tubular and spiral ultrafiltration membrane devices. After several hours of running at a steady state, as the temperature increased from 15 to 35C, the process flux dropped from 60 to 10 gfd for the tubes (gallons per square foot of membrane per day). The add;tion of about 5X
- 25 of a nonionic surfactant Triton X-100, based on the polymer weight, at a rate of 14 ml to 15 gallons of a latex pre~ented the process flux of the tubes and the spiral membrane from decreasing with time. After addition of the surfactant the flux of the membrane was then approximately 200 gfd at 50C.
Thus 9 the addition of surfactants to polymer latices prior to ¦or during the process of ultrafiltration stabilized the latices 3'767~
~and prevented coagulum from forming and decre~sing the flux rate.
¦The addition of surfactant also prevented pump fai7ure9 which failure often occurs by virtue of the coagulant plu~ging up the l seals in the internal portion of the pump. ~ly process provides S la rapid, simple and an effective means to overcome the difficultie ¦of the prior art and to permit the commercial concentration and ¦seperation of polymeric latices.
Claims (22)
1. In a process for the concentration or separation of an aqueous polymeric latex, which comprises polymer particles dispersed in an aqueous-liquid phase, by a semi-permeable membrane which permits the passage of the liquid phase and retains the polymer particles, the improvement which comprises:
adding to the latex an amount of a compatible surfactant effective to stabilize the latex contacting the semi-permeable membrane to maintain the dispersion of the polymer particles in the liquid phase during the concentration or separation, said surfactant-forming polymer-surfactant particles with the polymer particles, thereby preventing the formation of coagulum from the latex and the degradation of the flux rate of the process, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane.
adding to the latex an amount of a compatible surfactant effective to stabilize the latex contacting the semi-permeable membrane to maintain the dispersion of the polymer particles in the liquid phase during the concentration or separation, said surfactant-forming polymer-surfactant particles with the polymer particles, thereby preventing the formation of coagulum from the latex and the degradation of the flux rate of the process, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane.
2. The process of claim l, which includes adding about 0.05 to 2.0 weight percent of the surfactant based on the weight of the polymer in the latex.
3. The process of claim l, wherein the process is an ultrafiltration process carried out at a pressure of about 10 to 200 psi.
4. The process of claim 1, wherein the process is an ultrafiltration process carried out at a temperature of from about 70 to 180°F.
5. The process of claim l, wherein the latex is a vinylchloride resin, a styrene-butadiene or a natural rubber latex.
6. The process of claim 1, wherein the latex contains from about 0.1 to 2% by weight polymer, and is concentrated to about 10 to 20%.
7. The process of claim 1, wherein the latex contains from about 20 to 40% by weight polymer, and is concentrated to about 45 to 70%.
8. The process of claim 1, wherein the latex contains a surfactant and the surfactant added is the same surfactant as in the latex.
9. The process of claim 1, wherein the surfactant is an anionic or a nonionic surfactant.
10. The process of claim 1, wherein the surfactant is an anionic surfactant which comprises a water-soluble salt of a long-chain alcohol sulfate.
11. The process of claim 1, wherien the surfactant is a nonionic surfactant which comprises an alkylaryl polyether alcohol.
12. The process of claim 1, wherein the latex is introduced into contact with the semipermeable membrane by an opened-face impeller centrifugal pump.
13. The process of claim 1, which includes adding the surfactant to a batch of the latex prior to concentration and separation and pumping the latex into contact with the semi-permeable membrane.
14. The process of claim 1, wherein the latex is with-drawn from and recirculated into contact with the semi-permeable membrane until the desired concentration level is obtained.
15. The process of claim 1, wherein the semipermeable membrane is disposed in an ultrafiltration apparatus con-taining tubes to support the membrane or in a spiral module apparatus.
16. The process of claim 1, which includes adding surfactant continuously to the latex.
17. In a process for the concentration or separation of an aqueous polymeric latex, which comprises polymer particles dispersed in an aqueous liquid phase, by an ultrafiltration semipermeable membrane process wherein the membrane permits the passage of the liquid phase and retains the polymer particles, the improvement which comprises:
a) providing a latex selected from the group of polymers consisting of vinylchloride, butadiene-styrene and natural rubber, which latex, under the process con-ditions of the ultrafiltration process, becomes destabilized;
b) adding to the latex from about 0.05 to 2.0 weight percent, based on the polymer of the latex, of an anionic or nonionic surfactant prior to concentration or separation in the ultrafiltration process to stabilize the latex, said surfactant forming polymer-surfactant particles with the polymer particles, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane;
c) pumping the stabilized latex into the inlet of a feed zone of an ultrafiltration membrane device;
d) withdrawing a permeate fraction from the permeate zone of the ultrafiltration device;
e) withdrawing a concentrated latex from the feed zone and recycling by pumping at least a portion of the concentrated latex to the inlet of the feed zone; and f) recovering a concentrated latex from the feed zone.
a) providing a latex selected from the group of polymers consisting of vinylchloride, butadiene-styrene and natural rubber, which latex, under the process con-ditions of the ultrafiltration process, becomes destabilized;
b) adding to the latex from about 0.05 to 2.0 weight percent, based on the polymer of the latex, of an anionic or nonionic surfactant prior to concentration or separation in the ultrafiltration process to stabilize the latex, said surfactant forming polymer-surfactant particles with the polymer particles, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane;
c) pumping the stabilized latex into the inlet of a feed zone of an ultrafiltration membrane device;
d) withdrawing a permeate fraction from the permeate zone of the ultrafiltration device;
e) withdrawing a concentrated latex from the feed zone and recycling by pumping at least a portion of the concentrated latex to the inlet of the feed zone; and f) recovering a concentrated latex from the feed zone.
18. In a process for the concentration or separation of an aqueous polymeric latex, which comprises polymer particles dispersed in an aqueous-liquid phase, by an ultrafiltration semi-permeable membrane which permits the passage of the liquid phase and retains the polymer particles, in which said latex destabilizes and forms coagulum during said concentration or separation to reduce the flux rate the improvement which comprises:
adding to the latex about 0.05 to 2.0% by weight percent, based on the weight of polymer in the latex of a compatible surfactant effective to stabilize the latex pumped into contact with the semi-permeable membrane to maintain the dispersion of the polymer particles in the liquid phase during the concentration or separation, said surfactant forming polymer-surfactant particles with polymer particles, thereby preventing the formation of coagulum from the latex and the degradation of the flux rate of the process, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane, said concentration or separation being carried out at a pressure of about 10 to 200 psi, and at a temperature of from about 70 to 180°F.
adding to the latex about 0.05 to 2.0% by weight percent, based on the weight of polymer in the latex of a compatible surfactant effective to stabilize the latex pumped into contact with the semi-permeable membrane to maintain the dispersion of the polymer particles in the liquid phase during the concentration or separation, said surfactant forming polymer-surfactant particles with polymer particles, thereby preventing the formation of coagulum from the latex and the degradation of the flux rate of the process, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane, said concentration or separation being carried out at a pressure of about 10 to 200 psi, and at a temperature of from about 70 to 180°F.
19. In a process for the concentration or separation of an aqueous polymeric latex, which comprises polymer particles dispersed in an aqueous-liquid phase, by an ultrafiltration semi-permeable membrane which permits the passage of the liquid phase and retains the polymer particles, in which said latex destabilizes and forms coagulum during said concentration or separation to reduce the flux rate, the improvement which comprises:
pumping and recycling the latex into contact with said membrane and adding to the latex during said pumping and recycling, an amount of a compatible surfactant effective to stabilize the latex so pumped and recycled to maintain the dispersion of the polymer particles in the liquid phase during said concentration or separation, said surfactant forming polymer-surfactant particles with the polymer particles, thereby preventing the formation of coagulum from the latex and the degradation of the flux rate of the process, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane.
pumping and recycling the latex into contact with said membrane and adding to the latex during said pumping and recycling, an amount of a compatible surfactant effective to stabilize the latex so pumped and recycled to maintain the dispersion of the polymer particles in the liquid phase during said concentration or separation, said surfactant forming polymer-surfactant particles with the polymer particles, thereby preventing the formation of coagulum from the latex and the degradation of the flux rate of the process, said polymer-surfactant particles having dimensions such that a substantial portion thereof do not pass through said membrane.
20. The process of claim 19, which includes adding about 0.05 to 2.0 weight percent of the surfactant based on the weight of the polymer in the latex, said process being carried out at a pressure of about 10 to 200 psi, and a temperature of from about 70 to 180°F.
21. The process of claim 1, wherein said surfactant is an organic surfactant.
22. The process of claim 1, wherein the amount of surfactant added to the latex is in excess of the amount of surfactant which may be lost through the semi-permeable membrane during concentration or separation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000252892A CA1137671A (en) | 1976-05-19 | 1976-05-19 | Ultrafiltration process for the concentration of polymeric latices |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000252892A CA1137671A (en) | 1976-05-19 | 1976-05-19 | Ultrafiltration process for the concentration of polymeric latices |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1137671A true CA1137671A (en) | 1982-12-14 |
Family
ID=4105999
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000252892A Expired CA1137671A (en) | 1976-05-19 | 1976-05-19 | Ultrafiltration process for the concentration of polymeric latices |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1137671A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016004526A1 (en) * | 2014-07-07 | 2016-01-14 | Lanxess Inc. | Ultrafiltration of polyisoolefin copolymers |
| WO2016095018A1 (en) * | 2014-12-19 | 2016-06-23 | Lanxess Inc. | Ultrafiltration of polyisoolefin copolymers and polyisoolefin copolymers with reduced oligomer content |
-
1976
- 1976-05-19 CA CA000252892A patent/CA1137671A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016004526A1 (en) * | 2014-07-07 | 2016-01-14 | Lanxess Inc. | Ultrafiltration of polyisoolefin copolymers |
| WO2016095018A1 (en) * | 2014-12-19 | 2016-06-23 | Lanxess Inc. | Ultrafiltration of polyisoolefin copolymers and polyisoolefin copolymers with reduced oligomer content |
| US10766974B2 (en) | 2014-12-19 | 2020-09-08 | Arlanxeo Singapore Pte. Ltd. | Ultrafiltration of polyisoolefin copolymers and polyisoolefin copolymers with reduced oligomer content |
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