This invention relates to self-inverting water—in-oil emulsions of water-soluble polymers wherein emulsions, invert, immediately upon the addition of sufficient water. This invention also relates to processes for preparing such emulsions.

Various water-soluble polymers such as poly- acrylaπride and copolymers: of acrylamide with other monomers are well— nown to be effective flocculants for many substrates including, for example, sewage, cellu- losic fibers and fines, for retention and freeness, metal or treatment, plating waste, and coal tailings, Suchr polymers are also known, to exhibit superior thickening properties; when the polymers are dissolved in agueous- media. Particularly well-known for this purpose are the anionic carboxamide polymers such as acr lamide/acrylic- acid copolymers, including those prepared by hydrolysis of polyacrylamide. Such poly¬ mers _* are very useful as fluid mobility control agents in enhanced oil recovery processes.

In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymer in a water-in-oil emulsion wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, as well as a method for preparing them, are described in U.S. Patent 3,284,393 to Vanderhoff et al. Unfortunately for many applications, these emulsions do not invert, as readily as desired. In order to accelerate the inversion rate of such emulsions, it has been a common practice, e.g., as shown in U.S. Patent-

No. RE 28,474, to add a water-soluble surfactant just prior to inversion. While the addition of an inverting surfactant in this manner does increase the rate of inversion, the resulting emulsions often do not exhibit the activity or ability to pass through porous struc¬ tures (so-called screen factor or filterability) that is desired for fluid mobility control agents. More importantly, it is found that such practices are gener¬ ally not satisfactory when it is necessary to invert the emulsion in aqueous medium containing dissolved salts as is often the case for enhanced oil recovery practices.

In view of the foregoing deficiencies of conventional emulsions and methods for inverting them, it is highly desirable to provide a self-inverting water-in-oil emulsion that will invert quickly into an aqueous medium that may contain significant quantities of dissolved salts. It is also desirable to provide an

emulsion that has a reduced oil content and increased polymer solids.

The present invention is a self-inverting, stable water-in-oil emulsion comprising (1) a discontinu- ous aqueous phase containing a water-soluble polymer which discontinuous phase is dispersed in (2) a continu¬ ous oil phase wherein the emulsion contains an inverting amount of an inverting surfactant and an emulsifying amount of a water-in-oil emulsifier, characterized in that the emulsion is prepared by polymerizing a water- -in-oil emulsion onomeric precursor of a water-soluble monomer containing a portion of the inverting surfactant and adding the remainder of the inverting surfactant to the resultant water-in-oil emulsion of water-soluble polymer subsequent to polymerization, the portion added prior to the completion of polymerization being sufficient to increase the degree of inversion when the emulsion is. inverted into a continuous, aqueous phase but less than that which destabilizes the monomeric precursor or the emulsion of the polymer- An inverting amount of an inverting surfactant is. an amount such that the water- in-oil emulsion will, invert in a reasonably short period of time when the emulsion is combined with sufficient water. In the emulsion of this invention, it is critical that (1) at least a portion of the inverting surfactant be added at some point prior to the completion of polymerization and (2) at least a portion of the inverting surfactant be added to the emulsion after polymerization, but prior to inversion.

In another aspect, the present invention is a process for preparing the aforementioned emulsion which comprises (1) forming a stable water-in-oil emulsion

monomeric precursor containing at least one water-soluble monomer in the aqueous phase which is dispersed in a continuous oil phase, said emulsion containing an emulsifying amount of a water-in-oil emulsifier and an inverting amount of an inverting surfactant; (2) subject¬ ing the monomeric precursor to conditions sufficient to polymerize the monomer; characterized by (3) adding subsequent to the polymerization, an additional amount of an inverting surfactant to the resultant water-in-oil emulsion of water-soluble polymer sufficient to increase the portion added prior to the completion of polymeriza¬ tion being sufficient to increase the degree of inversion when the emulsion is inverted into a continuous aqueous phase but less than that which destabilizes the monomeric precursor or the emulsion of the polymer. Surprisingly, it is found that, by having a portion of the inverting surfactant present in the monomeric precursor prior to polymerization and by adding an additional portion of the inverting surfactant to the emulsion subsequent to polymerization, an emulsion is obtained which is superior to emulsions obtained by either adding all of the inverting surfactant to the monomeric precursor prior tα polymerization or by adding all of the inverting -- surfactant to the emulsion subsequent to the polymeriza- t±on. The emulsions of this invention are superior to conventional emulsions in that they have increased polymer solids, reduced oil content, lower bulk viscos¬ ity and less inverting surfactant than is employed in conventional emulsions- These emulsions, although self-inverting upon the addition of water, are stable in that they can be stored for long periods of time and/or can undergo several freeze-thaw cycles without irreversible coagulation or precipitation. Most surpris¬ ing is the ability of such emulsions to invert readily

into aqueous media containing substantial quantities, e.g., from 6.0001 to 20 weight percent, of dissolved salts which are commonly present in subterranean brines.

In addition to their utility as drilling muds, fracturing fluids, and fluid mobility control agents in oil recovery methods, the emulsions of the present invention are also useful as flocculating agents for sewages, industrial wastes, mining streams such as coal slurries and mining effluents, gas thick- eners for coating formulations and as additives for the manufacture of paper.

The present invention is practiced in the preparation of water-in-oil emulsions of any water- soluble polymer.- Such emulsions are those wherein the dispersed phase is an aqueous phase having dissolved therein a water-soluble polymer and the continuous oil phase is a water—immiscible inert organic liquid. The ratiα of the aqueous phase to the oil phase is suitably any ratio that permits the formation of a water-in-oil emulsion. Preferably, however, based on the total weight of the water—in-oil emulsion, the- disperse phase constitutes from 50 tα 90, more preferably from 65 to 80, weight percent of the emulsion. The continuous oil phase preferably constitutes from 10 to 50, more prefer- ably from 20 to 35, weight percent of the emulsion.

For the purposes of this invention, the water-soluble polymer contained in the aqueous phase of the emulsion is one which forms a thermodynamically stable mixture when combined with water. These mix- tures form spontaneously and include true solutions in which the individual polymer molecules are dispersed as

well as micellular or colloidal solutions wherein the polymer molecules are aggregated to some extent but wherein such aggregates are no larger than colloidal size. . Accordingly, the water-soluble polymers are generally homopolymers and copolymers of water-soluble ethylenically unsaturated monomers.

Suitable water-soluble monomers include those that are sufficiently water-soluble to form at least a 10 weight percent solution when dissolved in water and readily undergo addition polymerization to form polymers that are water-soluble. Exemplary water-soluble mono¬ mers include ethylenically unsaturated amides such as acrylamide, methacrylamide and fumaramide; their N-substituted derivatives such as 2-acrylamide-2— methylpropane sulfonic acid (AMPS), N-(dimethylamino- methyl)acrylamide as well as N-(trimethylammoniuinmethyl)- acrylamide chloride and N-(trimeth lammoniumpropyl)- ethacrylamide chloride; ethylenically unsaturated carboxylic acids such as acrylic, acid, methacrylic acid, itaconic acid and fumaric acid. Ethylenically unsaturated quaternary ammonium compounds such as vinylbenzyl trimethyl ammonium chloride, sulfoalkyl esters of unsaturated carboxylic acids such as 2-sulfo— ethyl methacrylate; ami oalkyl esters of unsaturated carboxylic ^* acids such as 2-aminoethyl methacrylate and 2-(N,N-dimethylamino)ethyl methacrylate as well as the quaternized derivatives thereof such as acryloylethyl trimethyl ammonium: chloride; vinyl amines such as vinyl pyridine and vinyl morpholine, diallyl amines and diallyl ammonium compounds such as diallyl dimethyl ammonium chloride; vinyl heterocyclic amides such as vinyl pyrrolidone; vinylaryl sulfonates such as vinyl¬ benzyl sulfonate as well as the salts of the foregoing

monomers. Of the foregoing water-soluble monomers, acrylamide- and combinations of acrylamide and acrylic .acid are preferred. Acrylamide and combinations thereof with up to 50-mole percent of other water-soluble monomers, based on total water-soluble monomer, are more preferred. Most preferred are polymers wherein the water-soluble monomer is acrylamide and a mixture of from 60 to 99 mole percent of acrylamide with from 1 to 40 mole percent of other water-soluble monomers.

The molecular weight of the water-soluble polymer is not particularly critical and may vary over a wide range from 1 to 25 million. Preferred polymers have weight average molecular weight in the range from 2 to 10 million.

The water-immiscible oil phase of the emul¬ sion generally comprises at least one inert hydrophobic liquid.. Usually such liquid is an organic liquid such as a liquid hydrocarbon or substituted hydrocarbon- Preferred organic liquids are the halogenated hydro— carbons such as, for example, perchloroethylene and methylene chloride as well as liquid hydrocarbon having from: to IS carbons per molecule including aromatic- and aliphatic hydrocarbons and mixtures thereof, for example, benzene, xylene, toluene, mineral oils, liquid paraffins such as kerosene and naptha. Of the foregoing organic liquids, the hydrocarbons are the more preferred, with aliphatic hydrocarbons being most preferred.

In general, the water-in-oil emulsions of the present invention are prepared by following the general procedure described in the prior art as exemplified in U.S. Patent Nos. 3,284,393; 3,624,019 and 3,734,873.

In such methods, an aqueous solution of water-soluble, ethylenically unsaturated monomer(s) is dispersed in the inert hydrophobic organic liquid containing a -sufficient amount-of a water-in-oil emulsifying agent to form a water-in-oil emulsion of the water-soluble monomer (monomeric precursor). At some point prior to or during the polymerization of such monomer, an invert¬ ing surfactant is incorporated in an amount that is sufficient to increase the degree of inversion of the emulsion of the water-soluble polymer when the emulsion is subjected to inverting conditions, provided that the amount of the inverting surfactant is less than that which destabilizes the monomeric precursor or the emulsion of the polymer. In accordance with this invention, the initial portion of inverting surfactant may be added to the monomeric precursor, or it may be added to the aqueous phase or oil phase prior to forma¬ tion of the monomeric precursor so long as it is present in the monomeric precursor prior to the completion of polymerization. By "degree of inversion" is meant the percentage of polymer ^" that completely dissolves in the aqueous phase upon inversion based on the total polymer that could dissolve. By "destabilizing the emulsion" is meant that the monomeric precursor or the water-iή- -oil emulsion of water-soluble polymer separates into two phases having a single interface or inverts into an oil—iπ-water emulsion. Preferably, the amount of inverting surfactant that is added prior to polymeri¬ zation is in the range from 0.05 to 5 percent based on monomer weight, most preferably from 0.2 to 2 weight percent. The resulting stable water-in-oil emulsion of monomer is then heated under free-radical forming conditions in order to polymerize the monomer in the dispersed phase to form a water-in-oil emulsion of the

water-soluble polymer. Subsequent to polymerization and prior to inversion, this water-in-oil emulsion is combined with additional inverting surfactant which may or may not be the same as the inverting surfactant added prior to polymerization. This post-added invert¬ ing surfactant is added in an amount sufficient to cause inversion when the water-in-oil emulsion is combined with sufficient water to form a continuous aqueous phase. Preferably, such post-added amount of invertin surfactant is in the range from 0.5 to 10, most preferably from 3 to 7, weight percent based on the weight of the polymer-

Emulsifiers suitably employed for purposes of emulsifying the aqueous phase containing the water- soluble monomer in the organic liquid are those emulsi¬ fiers that promote the formation and stabilization of water—in-oil emulsions. Normally such emulsifiers have a hydrophilic-lipophilic balance (HLB) in the range front Z tσ 9*, most preferably from 3 to 6. Preferably, the emulsifying agent is sorbitan monooleate, the reaction product of oleic acid with isopropanolamide or a mixture thereof. Other suitable emulsifying agents include hexadecyl sodium phthalate, decyl sodium phtha- late, octadecyl sodium phthalate, sorbitan monooleate, sorbitan stearate, glycerine mono- or distearate and combinations of such emulsifying agents. Generally, the emulsifier is used in amounts sufficient to provide the desired water-in-oil emulsion. This amount is normally in the range from 0.1 to 20, preferably from 3 to 5, weight percent based on the weight of monomer.

Inverting surfactants suitably employed in the practice of this invention are generally those that

promote the formation of oil-in-water emulsions or dispersions when the water-in-oil emulsion is combined with sufficient water to form a continuous aqueous phase. Generally, such inverting surfactants are water-soluble compounds having an HLB in the range from 6.5 to 20, preferably from 10 to 14. Examples of such inverting surfactants include nonionic, anionic, cationic or amphoteric surfactants with nonionic surfactants being preferred.

Preferred nonionic surfactants include

(1) alkyl polyethyleneoxy compounds such as alkyl polyethyleneoxy alcohol represented by the formula:

wherein R is £■ - ■ ^a - ⁱ - ^l y^' ^E0 -is ethyleneoxy and n is a number from 1 to 10 and (2) nonionic surfactants such as the reaction products of ethylene oxide or mixtures of ethylene oxide and higher alkylene oxide with active hydrogen compounds such as phenols, alcohols, carboxylic acids and amines, e.g., alkylphenoxyethyleneoxy alcohols and alkylphenoxy polyethyleneoxy alcohols.

Also suitable are anionic compounds repre¬ sented by the formula:

R-X

wherein R is as defined hereinbefore and X is SO,H, ^C0 2 ^{H 0:r P} °3 ^{Ξ and} * salts thereof. Examples include long chain carboxylates such as potassium oleate, sodium laurate, potassium stearate, potassium caprolate and sodium palmatate; alkali metal alkylbenzene sulfonates

such as sodium nonylbenzene sulfonate and potassium dodecylbenzene sulfonate; alkali metal alkyl sulfates such as sodium dodecyl sulfate and alkali metal dialkyl sulfosuccinates such as sodium dihexyl sulfosuccinate and sodium dioctyl sulfosuccinate; salts of resin acids such as abietic acid and dihydroabietic acid.

^" Also suitable are cationic surfactants such as alkyl ammonium or quaternary ammonium salts, e.g., dodecyl ammonium hydrochloride, and dodecyl trimethyl quaternary ammonium chloride, and ethoxylated fatty amines. Other suitable surfactants are described in McCutcheon ¹ Detergents and Emulsifiers, North American Edition, 1980 Annual. Also included in the aforemen¬ tioned surfactants are oligomeric and polymerizable surfactants described at pages 319-322 of Black!ey,

Emulsion Polymerization, Halsted Press (1975). Examples of such oligomers include ammonium and alkali metal salts of functionalized oligomers sold by Uniroyal Chemical under the trade name "Polywet" and copolymers of acrylonitrile and acrylic acid having molecular weights less than 2000 which are prepared in the presence of chain terminating agents such as n-octyl_. mercaptan. Examples of polymerizable surfactants include sodium salts of 9- and lθ-(acryloylamido)- stearic acid..

Of the foregoing surfactants, the nonionic types are preferred, with ethoxylated alkyl phenols and ethoxylated fatty alcohols being most preferred.

As mentioned hereinbefore, polymerization of the water-in-oil emulsion of the water-soluble monomers is advantageously effected under conventional conditions

such as described in U.S. Patent No. 3,284,393. Normally such polymerization is practiced in the pres¬ ence of a polymerization initiator capable of generat¬ ing free-radicals. Preferably, this free-radical initiator is employed in amounts from 0.01 to 0.1 weight percent of initiator based on the monomers. Exemplary polymerization initiators include the inor¬ ganic persulfates such as potassium persulfate, ammo¬ nium persulfate and sodium persulfate, azo catalysts such as azobisisobutyronitrile and dimethylazoisobuty- rate; organic peroxygen compounds such as benzyl peroxide, t-butylperoxide, diisopropylbenzene hydroperoxide and t-butyl hydroperoxide. Of these initiators, the organic types such as t-butyl hydroperoxide are preferred. In addition to the aforementioned ingredients, the emulsion polymerization recipe optionally includes chain transfer agents, chelating agents, buffers and salts.

The emulsions of this invention are self- inverting in that they invert readily when dispersed into water without adding additional inverting surfac¬ tant. They are particularly effective for inversion into aqueous media containing from 0.001 to 10, espe¬ cially from 0.Q5 to 5, weight percent of dissolved salts such, as sodium chloride, calcium chloride, or magnesium chloride that are normally present in subter¬ ranean brines.

The following examples are given to illustrate the invention and should not be construed as limiting its scope. Unless otherwise indicated, all parts and percentages are by weight. ^" —

Examples 1 to 12 and Comparative Runs A to D

For Example 1, a water-in-oil emulsion of an acrylamide/acrylic acid copolymer was prepared by dissolving 125 g of acrylamide and 54 g of acrylic acid in 100 g of water. The pH of the resulting aqueous solution was adjusted to 6.5 by the addition of a 50 percent aqueous solution of NaOH. To .this solution was added 0.04 g of the pentasodium salt of diethylene- triaminepentaacetic acid and 2 g of a polyethylene glycol ether of a secondary alcohol sold by Union Carbide under the trade name Tergitol 15-S-9. The total weight of this aqueous phase was adjusted to 490 g by the addition of water. This aqueous phase was then dispersed in an oil phase which contains 182 g of liquid hydrocarbon, 4 g of isopropanolamide of oleic acid and 4 g of sorbitan monooleate. The resulting emulsion was placed into a liter glass resin kettle equipped with a stirrer, a nitrogen sparger, a thermom¬ eter, a water bath and gas exit. The kettle containing the emulsion was sparged with nitrogen for about 1 hour to remove oxygen. The emulsion was then subjected to polymerization conditions as described in U.S. Patent No, 3,284,393 to form a water-in-oil emulsion of ac_ryla_nu.de/acrylic acid copolymer. After polymeri- zation,. 90 g of an aqueous solution of 16 g of a ₂ C0 ₃ was added to the water-in-oil emulsion. To this emul¬ sion was then added 7 g of Tergitol 15-S-9 (inverting surfactant) with stirring. The resulting emulsion was then tested for invertibility by the following procedure.

To a 473 ml bottle equipped with a three- bladed stirrer was added 300 g of an aqueous solution containing 3 percent NaCl and 0.05 percent CaCl ₂ . A 1.5 g portion of the aforementioned emulsion was then

rapidly added to the bottle while stirring the solution at 400 rpm for 30 minutes. The viscosity of the resul¬ tant solution was measured using a Brookfield RVT viscometer using a No. 1 spindle and operating at 20 rpm and 25°C.

Examples 2 through 12 were prepared using different amounts of inverting surfactants and different inverting surfactants in accordance with the foregoing procedure. These emulsions were also tested for inverti- bility. The results of these tests are reported in Table I.

For purposes of comparison, Comparative Runs A through D were prepared following the foregoing procedure except that all of the inverting surfactant was added subsequent to polymerization. These emul¬ sions were similarly tested for invertibility. The results are reported in Table I.

TABLE ϊ

Examples and

Compara¬ Pj:e-A4ded (2) Post-A4de4 (3) tive ¹ EmμlεfifW (1) Su f cta t Surf ctant Inverti- Runs Type Amt, % Type Amt, % Type Amt, % bility (4), %

IPO 2 15-S-9 * 15-S-9 2,5 51 SMO 2

A IΓQ 2 Q 15-S-9 3.5 34

SMO 2

2 IPO 2 .5-S-9 1 ^• 15-S-9 4.0 65 SMO 2

B IPO 3 0 "15-S-9 5.0 20

SMO 2

3 IPO 2 15-S-9 1 DN-14 2.0 77

SMO 2

C IPO 2 0 DN-14 3.5 <5 SMO 2

4 IPO 2 15-S-9 1 DN-14 4.0 >90 SMO 2

D IPO 2 0 Dl-14 6.0 58 SMO 2

5 IPO 2 15-S-9 0.2 Dfl-14 4.8 74 SMO 2

TABLE I (cont'4)

Pj:e-A44e4 (2) Post-A 4e4 (3)

Emulε fier (I) Surfactant Surfactant I verti- .

Example Type Amt, % Type Amt. % Type Amt _f % ability (4), %

6 IPO 2 15-S-9 0.5 m- 4.5 82

SMO 2

7 IPO 2 +5-S-9 2.0 ^* PN-14 3.0 96 SMO 2 a IPO 2 15-S-5 1 DN-14 4.0 >90 SMO 2

9 IPO 2 15-S-7 1 DN-14 4.0 >90 SMO 2

10 IPO 2 15-S-12 I DN-14 4.0 60 SMO 2

11 IPO 2 STO I . DN-14 4.0 47 SMO 2

12 IPO 2 DN-14 0.5 DN-14 4.0 >90 SMO 2

TABLE Ϊ (cont'4)

(I) Weight percent of w ter-in-oϋ emulsifier based o tota,l monomers wherein;

IPO - isopropanoiamide of oleic acid SMQ - so bi an mo oole t

(2) Weight percent based on total monomers of inverting surfactant added to the water-in-oil emulsion prior to polymerization wherein;

15-S-9 - Tergitol .J.5-S-9 (HLB = 13.5)

D1M4 - alkyl polyether alcohol (Triton DN-14 sold by Rohm and Haas)

15-S-5 - polyethylene glycol ether of secondary alcohol (HLB = 10.5) (TergitQi 15-S-5 sold by Union Carbide)

-j.5_S-7 - polyethylene glycol ether of secondary alcohol (HLB = 12.1) (Tergitol 15-S-7 sold by Union Carbide)

15-S-12 - polyethylene glycol ether of secondary alcohol (HLB = 14.5) (Tergitol 15-S-12 sold by Union Carbide)

STO Sorbitan trioleate having 20 units of polyoxyethylene (HLB = 11)

(3) Weight percent based on total monomers added to the water-in-oil emulsion after polymerization wherein 15-S-9 and D.fcf-14 are as defined in (2).

TABLE I (cont'd)

(4) invertibility is 4e e mine from the following equ tio : invertibiiity = % in ersion η sample - η blank η max, - η blank x 100

Wherein η sample is the prookfiel4 viscosity of the sample as determined by the procedure describe4 hereinbefore, q blank is the Brookfield viscosity of the aqueous solution containing 3 percent NaCl and 0.05 per¬ cent CaCl ₂ an40 ^max - i ^s ^e Brookfield viscosity of a control sample. This control sample is prepared by (I) adding 0.15 percent of polymer in emulsion form to deionized water containing 0.15 percent of inverting surfactant that is post-added in the preparation of the particular sample (η sample), (2) stirring the control sample at 400 rpm for 30 minutec as described hereinbefore and (3) adding 3 percent NaCl and 0.15 percent CaCl ₂ . In each case viscosity is measured soon after preparation and then after standing overnight. In Examples 1-12, the viscosities develop more rapidly and to higher values when compared to η max. In Comparative Runs A-D, the viscosities do not fully develop when compared to the values for η max.

w

As evidenced by the data of Table I, Examples 1-4 in which a part of the inverting surfac¬ tant was added prior to polymerization invert to a greater degree (percent of inversion) than when the entire amount of the inverting surfactant was added after polymerization as in Comparative Runs A-D.