WO2016187177A1

WO2016187177A1 - Inverse emulsion polymerization process and surfactant composition used therefor

Info

Publication number: WO2016187177A1
Application number: PCT/US2016/032822
Authority: WO
Inventors: Jin Ming Zhang; Steven Qun Dong; Yong Quan DONG
Original assignee: Ecolab Usa Inc.
Priority date: 2015-05-19
Filing date: 2016-05-17
Publication date: 2016-11-24
Also published as: CN106279468A

Abstract

The invention relates to the technical field of the inverse emulsion polymerization, in particular to a surfactant composition used in the inverse emulsion polymerization, and to the inverse emulsion polymerization process using the composition as well as polymers prepared therefrom. The surfactant composition comprises at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

Description

INVERSE EMULSION POLYMERIZATION PROCESS AND SURFACTANT COMPOSITION USED THEREFOR

Cross-Reference to Related Application

This application claims priority to Chinese Patent Application Serial No.

201510255698.6 filed on May 19, 2015, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The disclosure relates to the technical field of inverse emulsion polymerization. In particular, the disclosure relates to a surfactant composition used in inverse emulsion polymerization and to an inverse emulsion polymerization process using the composition as well as polymers prepared therefrom. Background Art

High molecular weight cationic polymers, such as copolymers of acrylamide and dimethylaminoethyl acrylate methylammonium chloride (DMAEA.MCQ), are widely used in papermaking and water treatment processes. Polymer products of this type can be usually synthesized through free radical polymerization, wherein the inverse emulsion free radical polymerization (water-in-oil emulsion polymerization, hereinafter referred to as inverse emulsion polymerization) becomes more and more popular due to a series of advantages. In the inverse emulsion polymerization, an aqueous solution of water soluble monomers, such as acrylamide, as disperse phase and a water immiscible organic solvent as continuous phase form a water-in-oil emulsion under the action of a water-in-oil emulsifier or surfactant.

On one hand, the inverse emulsion polymerization process has numerous advantages, such as rapid polymerization, high molecular weight and narrow molecular weight distribution of the product, good product performances, moderate reaction temperature and fast heat transfer. In addition, by adding cationic monomers, it is possible to adjust the cationic degree of polymers thereby achieving the better flocculation effect. For example, US 3,284,393 describes an inverse emulsion polymerization process. In addition, for example, US 6,753,388 studies the influences of a chain transfer agent or a cros slinking agent on the properties of final products by adding it at different conversion stages during the inverse emulsion polymerization.

On the other hand, oil split usually occurs in the inverse emulsion polymerized products due to the thermodynamic instability. Because of the gravity difference between polymer particles and the oil phase, the polymer particles settle down to the bottom, while the oil phase forms the upper layer. Therefore, frequent mixing is required during storage and transportation, which requires additional equipment, energy and technology to prevent oil split.

Recently, certain polymeric surfactants, for example, a block polyester such as Hypermer B246, which is obtainable by the reaction of polyethylene oxide and long chain fatty acid, have been reported for preparing the stable inverse emulsion.

US 7,396,874 discloses a process for the synthesis of cationic or amphoteric acrylamide copolymers. In its examples, a surfactant system consisting of Hypermer B246 and Span 80 is employed. However, the resultant new products are inferior to the comparative polymers in terms of first pass ash retention of papermaking.

Therefore, it is necessary to further develop this kind of inverse emulsion polymerization, in particular inverse emulsion polymerization of acrylamide-based polymers, so as to improve the performance and stability.

Summary of the Invention

Therefore, one object of the present invention is to further improve the stability of the inverse emulsion polymerization. The polymer flocculants obtained from the improved inverse emulsion polymerization process of the present invention result in better ash retention when used for papermaking, especially higher first pass ash retention than the traditional Span-Tween emulsifier combinations.

The inventors of the present invention unexpectedly found that a composition comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester exhibit improved stability of the inverse emulsion polymerization. Herein and hereafter, the term "surfactant(s)" specifically refer to the emulsifiers used for emulsion polymerization.

Furthermore, the novel surfactant composition leads to a very low Brookfield viscosity (BFV) of the final polymer emulsion product. This means the composition according to the present invention can efficiently reduce the energy required for product transfer by pumping, in-situ diluting and mixing the emulsion polymer.

Therefore, a first aspect of the present invention relates to a surfactant composition useful for the inverse emulsion polymerization, comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids, and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

A second aspect of the present invention relates to an inverse emulsion

polymerization process, in which a surfactant composition is used, the surfactant composition comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

A third aspect of the present invention relates to polymers, especially

acrylamide-based polymers, prepared by the inverse emulsion polymerization process of the present invention.

Detailed Description of the Invention

The first aspect of the invention relates to a surfactant composition useful for the inverse emulsion polymerization, comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

In the surfactant composition of the present invention, it is advantageous when the types and proportions of various surfactants are selected such that the finally obtained HLB value (hydrophilic-lipophilic balance value) lies in the range of approximately from 5 to 8, preferably approximately from 6 to 8. If the HLB value is too high or too low, a substantial amount of gel will form during the polymerization and render the resultant emulsion unstable.

Within the scope of the present invention, the polymeric surfactant based on polyalkylene oxide and long chain fatty acids is a block polyester derived from a polyalkylene oxide e.g. polyethylene oxide and the long chain fatty acids, which may be diblock or triblock. For example, it may be prepared from polyethylene oxide of various molecular weights and the long chain fatty acids. Such products include, for example, some commercially available polymeric surfactants of Hypermer series. Herein, said long chain fatty acid may be e.g. linear or branched fatty acids with 8-30 or 8-22 carbon atoms.

Examples of such diblock and triblock polymeric surfactants include, but are not limited to, diblock and triblock copolymers based on polyester derivatives of fatty acids and polyoxyethylene (for example, Hypermer B246SF and B210 from Croda), as well as diblock and triblock copolymers based on polyoxyethylene and polyoxypropylene. Preferably, the diblock and triblock copolymers are based on polyester derivatives of fatty acids and polyoxyethylene. When a triblock surfactant is used, it is preferable that the triblock contains two hydrophobic regions and one hydrophilic region i.e.

hydrophobe-hydrophile-hydrophobe block.

In addition, the preferred number average molecular weight ranges from about 500 to about 10000, preferably from about 1000 to about 8000. Such surfactants include, for example, commercially available polymeric surfactants of Hypermer B series, such as Hypermer B210.

The inventors of the present invention have surprisingly found that the performance of the products prepared by inverse emulsion polymerization can be significantly improved if combining polymeric surfactants based on polyalkylene oxide and long chain fatty acids, in particular polyester surfactants based on fatty acids and

polyoxyethylene e.g. Hypermer B series, with surfactants based on polyoxyethylene sorbitan fatty acid ester such as Tween.

Within the scope of the present invention, the surfactants based on polyoxyethylene sorbitan fatty acid ester, for example, the products of Tween series, and their preparation processes are known to a person skilled in the art. The commercially available surfactant products can be used in the present invention.

By way of example, the surfactants based on polyoxyethylene sorbitan fatty acid ester can be represented by the following formula

wherein w+x+y+z = an integer of 15-25, especially 18-22 and in particular 20, and R represents a substituent of saturated or unsaturated long chain fatty acid, for example, a substituent of saturated or unsaturated fatty acid having about 10-25 carbon atoms, especially about 12-20 carbon atoms. Such long chain fatty acids include, for example, stearic acid (for example, commercially available Tween-61), oleic acid (for example, commercially available Tween-80 and Tween-81), lauric acid (for example,

commercially available Tween-20) and the like.

According to one specific embodiment of the present invention, the surfactant composition useful for the inverse emulsion polymerization comprises at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester. Advantageously, the weight ratio of the polymeric surfactant based on polyalkylene oxide and long chain fatty acids to the surfactant based on polyoxyethylene sorbitan fatty acid ester is in the range of about 1: 2 to 3: 1, preferably about 1: 1 to 5: 2. In case the weight ratio of the polymeric surfactant based on polyalkylene oxide and long chain fatty acids to the surfactant based on polyoxyethylene sorbitan fatty acid ester is less than 1 : 2, the emulsion tends to be unstable and oil split. In case this ratio exceeds 3: 1, the final use performance of the product may be dis advantageously affected.

In one embodiment, the surfactant composition can be a binary surfactant composition, namely, it consists of at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester as described above. For example, a combination of Hypermer B210 with Tween-61 is possible.

In another preferred embodiment, if the surfactant composition further comprises the surfactants based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol, i.e. the surfactant composition comprises at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids, at least one surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol as well as at least one surfactant based on polyoxyethylene sorbitan fatty acid ester, and especially if the surfactant composition is a ternary surfactant composition consisting of at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids, at least one surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol as well as at least one surfactant based on polyoxyethylene sorbitan fatty acid ester, the surfactant composition can further improve the performances, for example, a higher ash retention of the obtained emulsion polymer.

In this embodiment, said surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol is the copolyester prepared by the condensation reaction of the succinic anhydride having alkyl or alkenyl substituents as shown below and the polyalkylene glycol,

R— CH— CO

\

O

/

Cf¾— CO

where R is an alkyl or alkenyl chain with 8 to 18 carbon atoms, preferably 12 to 18 carbon atoms, or a saturated or unsaturated hydrocarbon substituent derived from a polymer chain of mono-olefin containing from 40 to 500 carbon atoms and preferably having a number average molecular weight of 600 to 1000.

When group R is an alkyl or alkenyl chain with 8 to 18 carbon atoms, this substituent can be derived from the aliphatic mono-olefin with 8 to 18 carbon atoms, such as nonene, decene, dodecene and octadecene. In one embodiment, R is dodecene. When group R is a saturated or unsaturated hydrocarbon substituent derived from a polymer chain of mono-olefin containing from 40 to 500 carbon atoms, such a polymer chain of mono-olefin include those obtained by polymerizing a mono-olefin with from 2 to 6 carbon atoms such as ethylene, propylene, butylene, isobutylene and any mixture thereof. Preferably, these polymer chains contain 40 to 500 carbon atoms. In some embodiments, (polyisobutylene) succinic anhydride containing from 50 to 200 carbon atoms in the alkenyl chain is preferred.

Said polyalkylene glycol has a number average molecular weight ranging from 200 to 20000, preferably 400 to 4000, more preferably 400 to 1000, and is soluble in water to the extent of at least 5% by weight at 25 °C. Such polyalkylene glycols may be, for example, polyethylene glycols, mixed poly(ethylene-propylene) glycols or mixed poly(ethylene-butylene) glycols, provided that they satisfy the molecular weight and water- solubility requirements hereinabove stated. In some embodiments, polyalkylene glycols are polyethylene glycols are preferred.

Therefore, a preferred surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol is the copolyester derived from (polyisobutylene) succinic anhydride and polyethylene glycol as described above, or the blend of this copolyester with other copolyesters derived from succinic anhydride having alkyl or alkenyl substituents containing 8 to 18 carbon atoms and polyethylene glycol. Preferably, said copolyester has a number average molecular weight ranging from 500 to 10000. Such surfactants include, e.g. the commercially available product Hypermer 2296.

The surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol as well as the succinic anhydride having alkyl or alkenyl substituents can be prepared by the skilled person according to the techniques and methods known in the art or referring to the content of e.g. US

4,256,605 which is incorporated by reference in its entirety into the instant specification.

In this embodiment, the weight ratio of the polymeric surfactant based on polyalkylene oxide and long chain fatty acids to the surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol is in the range of 1: 100 to 100: 1, preferably 1: 4 to 10: 1, more preferably 1: 2 to 7: 1. The proportion of the surfactant based on poly oxy ethylene sorbitan fatty acid ester is in the range of 1% to 70% by weight, preferably 20% to 65% by weight, e.g. 25% to 48% by weight, based on the total weight of the surfactant composition.

In the present invention, in the emulsion polymerization, the ratio of the total weight of the surfactants to the total weight of the polymerizing monomers is at least 1: 100, preferably at least 3: 100, more preferably at least 7: 100.

The second aspect of the invention relates to an inverse emulsion polymerization process, in which the surfactant composition as described above is employed. In particular, the surfactant composition can be the binary or ternary surfactant composition as described above.

Within the scope of the present invention, the inverse emulsion polymer or latex polymer as obtained by the inverse emulsion polymerization process of the present invention, relates to a water-in-oil polymer emulsion comprising a cationic, anionic or nonionic polymer, preferably a cationic polymer, in the aqueous phase, a hydrocarbon oil for the oil phase and water-in-oil emulsifying agents such as the surfactant composition as described above. The inverse emulsion polymers are then "inverted" or activated by releasing the polymer from the particles using shear, dilution and under the action of surfactant. With regard to the general description about the inverse emulsion

polymerization process, U.S. Pat. No. 3,734,873 may be referred to and it is incorporated herein in its entirety by reference. Representative preparations of inverse emulsion polymers are described in U.S. Pat. Nos. 2,982,749; 3,284,393; and 3,734,873. See also, "Mechanism, Kinetics and Modeling of the Inverse-Microsuspension

Homopolymerization of Acrylamide," Hunkeler, et al., Polymer (1989), 30(1), 127-42; and "Mechanism, Kinetics and Modeling of Inverse-Microsuspension Polymerization: 2. Copolymerization of Acrylamide with Quaternary Ammonium Cationic Monomers," Hunkler et al., Polymer (1991), 32(14), 2626-40.

The aqueous phase is prepared by mixing together in water the following: one or more water-soluble monomers, and any polymerization additives such as inorganic salts, chelants, pH buffers, and the like.

The oil phase is prepared by mixing together an inert hydrocarbon liquid with the surfactant composition according to the present invention. If necessary, the oil phase may need to be heated to ensure the formation of a homogeneous oil solution.

The oil phase is then charged into a reactor equipped with a stirrer, a thermocouple, a nitrogen purge tube, and a condenser. The aqueous phase is added to the reactor containing the oil phase with vigorous stirring to form an emulsion. The resulting emulsion is heated to the desired temperature, purged with nitrogen, and a free-radical initiator is added. The reaction mixture is stirred for several hours under a nitrogen atmosphere at the desired temperature. Upon completion of the reaction, the water-in-oil emulsion polymer is cooled to room temperature, where any desired post-polymerization additives, such as antioxidants may be added.

In the present invention, the monomers suitable for the inverse emulsion

polymerization principally can be selected by a person skilled in the art according to the various requirements, but acrylic compounds are preferred. For example, the inverse emulsion polymerization process can be used for the preparation of acrylamide-based polymers. Such acrylamide polymers can be used, for example, as flocculants in the pulp treatment. The monomers suitable for the inverse emulsion polymerization of the present invention can comprise for example acrylamide and/or methacrylamide as well as one or more compound(s) selected from the group consisting of diallyldimethylammonium chloride, dimethylaminoethyl acrylate methylammonium chloride,

acrylamidopropyltrimethylammonium chloride, dimethylaminoethyl methacrylate methyl chloride quaternary salt, methacrylamidopropyltrimethylammonium chloride, acrylic acid, sodium acrylate, ammonium acrylate, methacrylic acid, sodium methacrylate, and anmonium methacrylate. The most preferred is, for example, a copolymer of acrylamide and dimethylaminoethyl acrylate methylammonium chloride (DMAEA.MCQ).

In addition, in one preferred specific embodiment, the inverse emulsion

polymerization process of the present invention further comprises initiating

polymerization of monomers in emulsion under free radical polymerization conditions, and adding at least one structure modifier such as chain transfer agent in the polymer emulsion after at least 30% polymerization of the monomers has completed. Suitable chain transfer agents are selected from the group consisting of alcohols, sulfur compounds, carboxylic acids or salts thereof, phosphites and combination thereof. If, in the inverse emulsion polymerization process of the present invention, a chain transfer agent is added after at least 30%, preferably at least 50%, more preferably at least 70%, and especially at least 80% and, for example, 80-90% polymerization of the monomers has completed, the molecular weight of the obtained emulsion polymer can be further increased. The structure modifier such as chain transfer agent can be added in an amount of, for example, about 200 ppm in the emulsion.

Examples

The present invention is further illustrated by the following Examples, but not limited to these Examples.

Test methods

1. Reduced specific viscosity (RSV)

Within a series of polymer homologs which are substantially linear and well solvated,

"reduced specific viscosity (RSV)" measurements for dilute polymer solutions are an indication of polymer chain length and average molecular weight according to Paul J. Flory, in "Principles of polymer Chemistry", Cornell University Press, Ithaca, N.Y., ©1953, Chapter VII, "Determination of Molecular Weights", pp. 266-316. The RSV is measured at a given polymer concentration and temperature and calculated as follows:

RSV = [(r|/r|₀)-l]/c

η = viscosity of polymer solution

T|o = viscosity of solvent at the same temperature

c = concentration of polymer in solution.

The unit of concentration "c" is (g/100 ml or g/dl). Therefore, the unit of RSV is e.g. dl/g. In the instant application, 1.0 M sodium nitrate solution is used for measuring RSV, unless specified otherwise. The polymer concentration in this solvent is 0.045 g/dl. The

RSV is measured at 30°C. The viscosities η and η₀ are measured using a Cannon

Ubbelohde semimicro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a thermostatic bath adjusted to 30 ± 0.02°C. The inherent error in the RSV calculation is about 1 dl/g. When two polymer homologs within a series have similar RSV, that is an indication that they have similar molecular weights. 2. Brookfield viscosity

Bulk Brookfield viscosity (BFV) of emulsion is measured using Brookfield viscometer, No. 62 spindle at a rotating speed of 30 rpm.

3. Stability test

The procedure is described as follows: adding 60 g latex into Φ25 x 200 mm plugged glass tube, and storing it at room temperature for 90 days. Oil split is defined more than 1mm height from the interface of latex particles and oil phase to the upper surface of emulsion, measured by ruler from time to time during the storage. 4. Dynamic filtration test

A concentrated paper furnish from paper machine is diluted by the white water to get a paper pulp with solid content of about 1%. A dynamic filtration test instrument (Britt Jar) is used as testing apparatus. 500 ml of paper pulp is metered into a wide-necked jar of the testing apparatus, while simultaneously initiating the stirrer and timing. The rotation speed is controlled at 1000 rpm. After 10 seconds, a certain dosage of the polymer solution is added to the paper pulp. A further 10 second stirring later, 100 ml of filtrate is filtered and collected which is measured by weight method for the solid content and ash concentration. First pass retention (FPR) is calculated from solid contents of pulp and filtrate, and first pass ash retention (FPAR) is calculated from ash concentration of pulp and filtrate using the respective equation as follows:

FPR = (1 - solid% of filtrate/solid% of pulp) x 100%

FPAR = (1 - ash% of filtrate/ash% of pulp) x 100%

Raw materials

Hypermer B210, polymeric surfactant based on polyethylene oxide and long chain fatty acids, available from Croda,

Tween-61, surfactant based on polyoxyethylene sorbitan fatty acid ester, available from Croda, Hypermer 2296, copolymer based on poly(isobutylene) succinic anhydride (PIBSA) and polyethylene glycol, available from Croda.

Examples and Comparative Examples

1. Comparison among various surfactant (emulsifier) combinations

Example 1: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant (using a surfactant composition comprising Hypermer B210 and Tween-61 in weight ratio of 2: 1):

An aqueous phase was prepared by mixing under stirring to dissolve the following substances: 545.82 g of 49.4% aqueous acrylamide solution, 20.55 g of deionized water, 9.72 g of adipic acid, 14.73 g of urea. Then, 102.29 g of 80.2% aqueous solution of DMAEA.MCQ and 0.20 g of EDTA 4Na⁺ were added in the solution.

An oil phase was prepared by heating at 50°C a mixture of 257.78 g of paraffin oil,

19.85 g of Hypermer B210 and 9.61 g of Tween-61 until the emulsifiers were completely dissolved. The oil phase was charged into a 2 L reactor, and stirred at 800 rpm with keeping the temperature at 42°C. Then, the aqueous phase was slowly added into the oil phase, and stirred for 30 minutes to obtain a water-in-oil emulsion.

With stirring at 800 rpm, 0.200 g of AIBN and 0.026 g of AIVN were added into the obtained water-in-oil emulsion. After charging nitrogen, the reaction was carried out for about three hours at 42°C. When the conversion rate reached 80 - 85% (measured by densimeter), 0.44 g of 40% sodium metaphosphate was added. After further stirring for 15 minutes, the reaction continued for one hour at an elevated temperature of 70°C, followed by cooling to obtain a cationic polyacrylamide emulsion. The emulsion had a bulk Brookfield viscosity of 193.0 cp, and RSV of 32.4 dl/g.

Example 2: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant (using a surfactant composition comprising Hypermer B210 and Tween-61 in a weight ratio of 1: 1):

The procedure was the same as Example 1, except for using 14.46 g of Hypermer B210 and 15.06 g of Tween-61. The finally obtained emulsion had a bulk Brookfield viscosity of 540.9 cp, and RSV of 31.0 dl/g.

Example 3: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant (using a surfactant composition comprising Hypermer B210, Hypermer 2296 and

Tween-61 in a weight ratio of 1: 1: 1):

The procedure was the same as Example 1, except for using 10.00 g of Hypermer B210, 9.75 g of Hypermer 2296 and 9.71 g of Tween-61. The finally obtained emulsion had a bulk Brookfield viscosity of 265.9 cp, and RSV of 33.3 dl/g.

Example 4: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant (using a surfactant composition comprising Hypermer B210, Hypermer 2296 and

Tween-61 in a weight ratio of 6: 1: 3):

The procedure was the same as Example 1, except for using 17.00 g of Hypermer B210, 2.85 g of Hypermer 2296 and 9.61 g of Tween-61. The finally obtained emulsion had a bulk Brookfield viscosity of 204.0 cp, and RSV of 30.7 dl/g.

Example 5: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant

(using a surfactant composition comprising Hypermer B210, Hypermer 2296 and

Tween-61 in a weight ratio of 1: 2: 1.6):

The procedure was the same as Example 1, except for using 6.0 g of Hypermer B210, 13.85 g of Hypermer 2296 and 9.61 g of Tween-61. The finally obtained emulsion had a bulk Brookfield viscosity of 198.0 cp, and RSV of 27.7 dl/g.

Comparative Example 1: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant (using a traditional emulsifier combination comprising Span 80 and Tween-61 in a weight ratio of 1.8: 1)

The procedure was the same as Example 1, except using 18.92 g of Span 80 and 10.54 g of Tween-61. The finally obtained emulsion had a bulk Brookfield viscosity of 532.9 cp, and RSV of 27.4 dl/g. Much gel formed during the synthesis, the stability was poor, and oil split was observed after 2 days.

Comparative Example 2: Synthesis of 10 mol% cationic polyacrylamide emulsion flocculant (using a traditional emulsifier combination comprising Span 80 and Tween-61 in a weight ratio of 1 : 1.5) The procedure was the same as Example 1, except using 11.66 g of Span 80, and 17.77 g of Tween-61. The finally obtained emulsion had a bulk Brookfield viscosity of 530.9 cp, and RSV of 35.5 dl/g.

Comparative Example 3: Synthesis was performed with reference to Example 11 in the patent US 7,396,874 (using a surfactant combination of Hypermer B210 9.32 g and Span-80 4.66 g). The obtained emulsion had a RSV of 13.2 dl/g. Much gel formed during the synthesis, the emulsion was instable, and oil split was observed after 2 days.

Table 1 Stability test results of emulsions with various surfactant combinations:

2. Comparison on different additions of chain transfer agent

Example 6: No addition of CTA (using the surfactant composition as described in Example 1)

An aqueous phase was prepared by mixing under stirring to dissolve the following substances: 545.82 g of 49.4% aqueous acrylamide solution, 20.55 g of water, 9.72 g of adipic acid, 14.73 g of urea. Then, 102.29 g of 80.2% aqueous solution of

DMAEA.MCQ and 0.20 g of EDTA 4Na⁺ were added into the solution.

An oil phase was prepared by heating at 50°C a mixture of 257.78 g of paraffin oil, 19.85 g of Hypermer B210 and 9.61 g of Tween-61 until the emulsifiers were completely dissolved. The oil phase was added to a 2 L reactor, and stirred at 800 rpm with keeping the temperature at 42°C. Then, the aqueous phase was slowly added into the oil phase, and stirred for 30 minutes to obtain a water-in-oil emulsion.

With stirring at 800 rpm, 0.200 g of AIBN and 0.026 g of AIVN were added to the water-in-oil emulsion. After charging nitrogen, the reaction was carried out for about three hours at 42°C. When the conversion rate reached above 90% (measured by densimeter), the reaction continued for one hour at an elevated temperature of 70°C, followed by cooling to obtain a cationic polyacrylamide emulsion with RSV of 21.9 dl/g.

Example 7: Addition of CTA at a conversion rate of 50% (using the surfactant composition as described in Example 1)

The procedure was the same as Example 6, except that 0.44 g of 40% sodium hypophosphite (CTA) was added at a conversion rate of 50%; and after further stirring for 15 minutes, the reaction continued for one hour at an elevated temperature of 70°C, followed by cooling to obtain a cationic polyacrylamide emulsion with RSV of 23.8 dl/g.

Example 8: Addition of CTA at a conversion rate of 85% (using the surfactant composition as described in Example 1)

The procedure was the same as Example 7, except that CTA was added at a conversion rate of 85%. RSV of 31.6 dl/g.

Example 9: Addition of CTA at a conversion rate of 91% (using the surfactant composition as described in Example 1)

The procedure was the same as Example 7, except that CTA was added at a conversion rate of 91%. RSV of 25.5 dl/g.

Example 10: Addition of CTA at a conversion rate of 50% (using the surfactant composition as described in Example 4)

An aqueous phase was prepared by mixing under stirring to dissolve the following substances: 545.82 g of 49.4% aqueous acrylamide solution, 20.55 g of water, 9.72 g of adipic acid and 14.73 g of urea. Then, 102.29 g of 80.2% aqueous solution of

DMAEA.MCQ and 0.20 g of EDTA 4Na⁺ were added into the solution.

An oil phase was prepared by heating at 50°C a mixture of 257.78 g of paraffin oil, 17.00 g of Hypermer B210, 2.85 g of Hypermer 2296 and 9.61 g of Tween-61 until the emulsifiers were completely dissolved. The oil phase was added into a 2 L reactor, and stirred at 800 rpm with keeping the temperature at 42°C. Then, the aqueous phase was slowly added to the oil phase, and stirred for 30 minutes to obtain a water-in-oil emulsion.

With stirring at 800 rpm, 0.200 g of AIBN and 0.026 g of AIVN were added into the water-in-oil emulsion. After charging nitrogen, the reaction was carried out for about three hours at 42°C. When the conversion rate reached above 50% (measured by densimeter), 0.44 g of 40% sodium hypophosphite (CTA) was added. After further stirring for 15 minutes, the reaction continued for one hour at an elevated temperature of 70°C, followed by cooling to obtain a cationic polyacrylamide emulsion with RSV of 22.7 dl/g.

Example 11: Addition of CTA at a conversion rate of 90% (using the surfactant composition as described in Example 4)

The procedure was the same as Example 10, except that CTA was added at a conversion rate of 90%. RSV is 28.3 dl/g.

Example 12: Addition of CTA at a conversion rate of 50% (using the surfactant composition as described in Example 5)

The procedure was the same as Example 10, except that CTA was added at a conversion rate of 50%. RSV is 23.6 dl/g.

Example 13: Addition of CTA at a conversion rate of 90% (using the surfactant composition as described in Example 5)

The procedure was the same as Example 10, except that CTA was added at a conversion rate of 90%. RSV is 27.6 dl/g.

3. Ash retention performance test of inverse emulsion polymer

All emulsions are inverted prior to the performance test by adding fatty alcohol polyoxyethylene ether, wherein the emulsion and fatty alcohol polyoxyethylene ether were mixed in a ratio of approximately 100: 2 at room temperature for 20 minutes to obtain an inverted emulsion. The prepared polymer samples in above Examples and Comparative Examples were used. The pulp used in dynamic filtration test was 100% waste newspaper deinked pulp or corrugated board pulp. Table 2. Ash retention performance using 100% waste newspaper deinked pulp

"Blank" in table 2 and hereafter refers to test without polymer treatment and "ppm" means inverse emulsion sample addition weight per dry pulp weight. Table 3. Ash retention performance using corrugated board pulp

Claims

1. A surfactant composition useful for an inverse emulsion polymerization, comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

2. The surfactant composition according to Claim 1 , further comprising at least one surfactant based on a copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol.

3. The surfactant composition according to Claim 1 or 2, wherein the surfactant composition has an HLB value (hydrophilic-lipophilic balance value) in a range of approximately 5 to 8.

4. The surfactant composition according to any one of Claims 1 to 3, wherein the polymeric surfactant based on polyalkylene oxide and long chain fatty acids is diblock and triblock polyesters based on fatty acids and polyoxyethylene, having a number average molecular weight in a range of 500-10000.

5. The surfactant composition according to any one of Claims 1 to 4, wherein the polymeric surfactant based on polyalkylene oxide and long chain fatty acids is diblock and triblock copolymers based on polyester derivatives of fatty acids and

polyoxyethylene, diblock and triblock copolymers based on polyoxyethylene and polyoxypropylene, or any mixtures of the foregoing polymers.

6. The surfactant composition according to any one of Claims 1 to 5, wherein a weight ratio of the polymeric surfactant based on polyalkylene oxide and long chain fatty acids to the surfactant based on polyoxyethylene sorbitan fatty acid ester is in a range of 1 : 2 to 3: 1.

7. The surfactant composition according to any one of Claims 2 to 6, wherein a weight ratio of the polymeric surfactant based on polyalkylene oxide and long chain fatty acids to at least one surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol is in a range of 1: 100 to 100: 1.

8. The surfactant composition according to any one of Claims 2 to 7, wherein the proportion of the surfactant based on polyoxyethylene sorbitan fatty acid ester is in a range of 1% to 70% by weight, based on the total weight of the surfactant composition.

9. The surfactant composition according to any one of Claims 1 to 6, wherein the surfactant composition is a binary surfactant composition comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

10. The surfactant composition according to any one of Claims 2 to 6 and 8 to 9, wherein the surfactant composition is a ternary surfactant composition comprising at least one polymeric surfactant based on polyalkylene oxide and long chain fatty acids, at least one surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol and at least one surfactant based on polyoxyethylene sorbitan fatty acid ester.

11. The surfactant composition according to any one of Claims 2 to 10, wherein said at least one surfactant based on the copolyester derived from succinic anhydride having alkyl or alkenyl substituents and polyalkylene glycol is a copolyester derived from (polyisobutylene) succinic anhydride containing from 50 to 200 carbon atoms in the alkenyl chain and polyethylene glycol or a blend of the copolyester with one or more copolyesters derived from succinic anhydride having alkyl or alkenyl substituents containing 8 to 18 carbon atoms and polyethylene glycol.

12. An inverse emulsion polymerization process, wherein the surfactant composition according to any one of Claims 1 to 11 is employed.

13. The inverse emulsion polymerization process according to Claim 12, wherein the process is used for preparing acrylamide -based polymers.

14. The inverse emulsion polymerization process according to Claim 12 or 13, wherein the process further comprises initiating polymerization of monomers in emulsion under free radical polymerization conditions, and adding at least one structure modifier in the polymer emulsion after at least 30% polymerization of the monomers has completed.

15. The inverse emulsion polymerization process according to Claim 14, wherein said structure modifier is a chain transfer agent.

16. A polymer prepared by the inverse emulsion polymerization process according to any one of Claims 12 to 15.

17. The polymer according to Claim 16, wherein the polymer is an acrylamide -based polymer.