WO2016032841A1

WO2016032841A1 - Water-soluble cationic copolymers useful as additives for oil field applications

Info

Publication number: WO2016032841A1
Application number: PCT/US2015/046049
Authority: WO
Inventors: Hongwei SHEN; Disha JAIN; Kurt J. MAGNI; Ralph C. Even; Wen-Shiue YOUNG
Original assignee: Dow Global Technologies Llc; Rohm And Haas Company
Priority date: 2014-08-26
Filing date: 2015-08-20
Publication date: 2016-03-03
Also published as: AR102335A1

Abstract

Oil-water dispersions and emulsions derived from petroleum industry operations are demulsified and clarified using cationic copolymer clarifier composition. Said cationic copolymer comprises the polymerization product of (i) a (meth)acrylate monomer and (ii) a cationic monomer.

Description

WATER-SOLUBLE CATIONIC COPOLYMERS USEFUL AS ADDITIVES FOR OIL

FIELD APPLICATIONS

FIELD OF THE INVENTION

The present invention relates to cationic copolymers, in particularly water-soluble cationic copolymers, and use thereof, for the separation of oil and water phases in emulsions and dispersions, in particular, oil field produced waste waters. BACKGROUND OF THE INVENTION

As oil field reservoirs age and become depleted, one method to increase oil production is to maintain the pressure in the formation by injecting water or steam into the formation. The water or steam forces the oil out of the formation and to the surface. This method for sustaining oil production is referred to as secondary oil recovery. Secondary recovering is one of the most widely used recovery methods.

In secondary oil recovery, the produced fluids include the injected water emulsified with the oil. In order for the oil to be sold, it must first be separated from the water. The oil separation process is, however, not totally efficient. Some amount (200-10,000 ppm) of oil remains emulsified in the produced water. It is this waste water which is of concern. The produced water must be treated in some manner to remove and collect the residual oil before discharge.

The emulsified oil in the produced water is typically present in the range of several hundred to tens of thousands of ppm. It is critical to remove this residual oil not only from an economic standpoint of selling the oil, but also from an environmental standpoint. The United States Environmental Protection Agency has placed tight restrictions on total oil and grease (TOG) limits for water that is to be discharged into public drinking water supplies or into open bodies of water. In addition to the governmental regulations, the residual oil must be removed in order to maintain a clean source of water or steam for reinjection into the underground formation. Failure to do so would result in eventual plugging of the formation and decreased production.

Cationic polymers are used as clarifiers in oil field produced water, see

USP 5,021,167, as opacifiers in home and personal care compositions, see USP 8,192,504 and US Publications 2008/0216978 and 2013/0259812, and for use in waste water disposal and paper making, see USP 5,006,590.

There exists a strong desire in the oil recovery industry to identify new materials for use as oil-in-water clarifiers. The water-soluble cationic polymers of the present invention and use thereof, offer a new solution for the treatment of oil-in-water emulsions, in particular, oil field produced waste waters.

SUMMARY OF THE INVENTION

The present invention is a cationic copolymer, preferably a water-soluble cationic copolymer comprising the polymerization product of

(i) a (meth)acrylate monomer having the following structure:

wherein R is hydrogen or a methyl group and

R¹ is an alkylene group of 1 to 8 carbon atoms, preferably alkylene group of 1 or 2 carbon atoms

and

(ii) a cationic monomer having the following structure:

wherein R' is hydrogen or a methyl group,

A is an oxygen atom or NH, preferably an oxygen atom, R² is an alkylene group of 2 to 6 carbon atoms, preferably an alkylene group of 2 carbon atoms,

and

X^" is an anionic counter ion, preferably CI^".

In one embodiment of the present invention, for the cationic copolymer described herein above each R is hydrogen, R^]and R² are both an alkylene group of two carbon atoms, A is an oxygen atom, and X^" is CI^".

In one embodiment of the present invention, the cationic copolymer described herein above is polymerized by a solution polymerization process or an emulsion polymerization process.

In one embodiment of the present invention, the cationic copolymer described herein above is prepared by a polymerization process initiated using a catalyst or initiation agent.

In one embodiment of the present invention, the amount of cationic monomer subunit is present in the cationic copolymer described herein above in an amount of from 40 percent to 60 percent by weight of copolymer.

In one embodiment of the present invention, the cationic copolymer described herein above has a weight average molecular weight of from 50,000 to 10,000,000 daltons.

Another embodiment of the present invention is a method of separating oil and water in an oil- water emulsion from an oil field produced water, the method comprising the steps of treating the oil-containing water with an effective amount, preferably from 1 ppm to 10,000 ppm, of the cationic copolymer described herein above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photograph showing oil-in-water emulsions treated with water-soluble cationic copolymers of the present invention compared to an oil- in-water emulsion with no clarifier.

DETAILED DESCRIPTION OF THE INVENTION

A "polymer," as used herein and as defined by FW Billmeyer, JR. in Textbook of Polymer Science, second edition, 1971, is a relatively large molecule made up of the reaction products of smaller chemical repeat units. Polymers may have structures that are linear, branched, star shaped, looped, hyperbranched, crosslinked, or a combination thereof; polymers may have a single type of repeat unit ("homopolymers") or they may have more than one type of repeat unit ("copolymers"). Copolymers may have the various types of repeat units arranged randomly, in sequence, in blocks, in other arrangements, or in any mixture or combination thereof. Chemicals that react with each other to form the repeat units of a polymer are known herein as "monomers," and a polymer is said herein to be made of, or comprise, "polymerized units" of the monomers that reacted to form the repeat units. The chemical reaction or reactions in which monomers react to become polymerized units of a polymer, whether a homopolymer or any type of copolymer, are known herein as "polymerizing" or "polymerization."

A copolymer comprises two or more monomers, for example it may comprise two, three, four, five, six, or more monomers. However, if a copolymer is described as

"consisting of two monomers (for example monomers A and B), the copolymer is made up of only the two monomers (i.e., A and B). In other words, the phrase "a copolymer consisting of the polymerization product of monomers A and B" means that the copolymer is made up of only the monomeric subunits of A and B.

Alternatively, if a copolymer is described as consisting of three monomers selected from monomers A, B, C, D, E, and F, the copolymer is made up of any selection of only three monomers from the group of A, B, C, D, E, and F, for example A, B, and C; or A, C, and D; or A, C, and E; etc.

In all of the compositions herein the weight percentages will always total 100 percent. Thus, the percentages stated hereinbelow to describe the proportions of the various monomeric components in the polymer are all based on the total weight of the polymer, with the total being 100 percent.

As used herein, the prefix "(meth)acrylate" means "methacrylate or acrylate." The term "petroleum industry operations," as used herein, includes, but not is limited to, activities and processes for exploration, production, refining and chemical processing of hydrocarbons including, but not limited to, crude oil, gas and their derivatives. For example, exploration often involves the initial drilling of wells wherein drilling fluid, or drilling mud, which is typically a mixture of liquid and gaseous fluids and solids, is used as lubricant and heat sink. Suitable dispersants are helpful to stabilize such mud to a homogenous composition. Production operations include, but are not limited to, pumping large quantities of water into the ground, as described above, which commensurately generates large quantities of "formation water," an oil-in- water dispersion or emulsion. Breaking of such emulsions with additives to remove and recover oil from the produced water is a common and beneficial practice. Oil refining processes, for example, include but are not limited to, the removal of inorganic solids and salts (referred to as "desalting") from produced oil. Desalting operations produce oil in water mixtures which require clarification and/or demulsifying prior to discharge or reuse. Lastly, chemical processing in the petroleum industry includes many various activities such as, for example, without limitation, production of ethylene by fractionation which involves water quench operations. The quench operations of ethylene manufacturing generate quench waters containing heavy, middle and light hydrocarbons and, therefore, require demulsifying and/or clarification. Persons of ordinary skill in the art will readily recognize the many various operations performed in the petroleum industry to which the present invention is reasonably applicable and the invention is intended to include all such applications.

The term "oil-water emulsion," as used herein, includes dispersions even where a stable emulsion does not exist and also includes water-in-oil emulsions and oil-in-water emulsions, as well as multiple emulsions, such as water-in-oil-in-water. Oil is the continuous, or external, phase in water-in-oil emulsions. For oil-in-water emulsions, the continuous, or external, phase is water.

Endpoints of ranges are considered to be definite and are recognized to incorporate within their tolerance other values within the knowledge of persons of ordinary skill in the art, including, but not limited to, those which are insignificantly different from the respective endpoint as related to this invention (in other words, endpoints are to be construed to incorporate values "about" or "close" or "near" to each respective endpoint). The range and ratio limits, recited herein, are combinable. For example, if ranges of 1-20 and 5-15 are recited for a particular parameter, it is understood that ranges of 1-5, 1-15, 5- 20, or 15-20 are also contemplated and encompassed thereby.

The present invention provides a water-soluble cationic water clarifying composition and a method for use thereof to separate oil and water phases of an oil-water dispersion or emulsion derived from petroleum industry operations. The clarifying composition of the present invention is a copolymer comprising the polymerization product of a (meth)acrylate monomer and a cationic monomer.

Suitable (meth)acrylate monomers have the following structure:

wherein R is hydrogen or a methyl group

and

R¹ is an alkylene group of 1 to 8 carbon atoms, preferably an alkylene group of 1 to 4 carbon atoms, more preferably an alkylene group of 1 or 2 carbon atoms.

Suitable cationic monomers have the following structure:

wherein R' is hydrogen or a methyl group,

A is an oxygen atom or NH, preferably an oxygen atom,

R² is an alkylene group of 2 to 6 carbon atoms, preferably an alkylene group having 2 to 4 carbon atoms, more preferably an alkylene group having 2 carbon atoms,

and

X^" is an anionic counter ion, preferably CI^".

In one embodiment of the present invention, the clarifying water-soluble cationic copolymer composition is a copolymer comprising the polymerization product of (i) a (meth)acrylate monomer and (ii) a cationic monomer wherein the combination the

(meth)acrylate monomer and a cationic monomer subunits comprise equal to or less than 95 weight percent by weight of the total copolymer, preferably equal to or less than 90 weight percent, more preferably equal to or less than 80 weight percent, more preferably equal to or less than 70 weight percent, and more preferably equal to or less than 50 weight percent by weight of the total copolymer. In one embodiment of the present invention, the clarifying water-soluble cationic copolymer composition is a copolymer comprising the polymerization product of (i) from 30 to 70 weight percent a (meth)acrylate monomer preferably ethyl acrylate, methyl acrylate, or methyl methacrylate and (ii) from 70 to 30 weight percent of a cationic monomer.

In one embodiment of the present invention, the clarifying water-soluble cationic copolymer composition is a copolymer comprising the polymerization product of (i) from 10 to 50 weight percent a (meth)acrylate monomer preferably butyl acrylate or 2- ethylhexyl acrylate and (ii) from 50 to 90 weight percent of a cationic monomer.

In one embodiment of the present invention the clarifying water-soluble cationic copolymer composition is a copolymer consisting of the polymerization product of (i) one (meth)acrylate monomer and (ii) one cationic monomer, in other words a water-soluble cationic copolymer made up of only 2 monomer subunits, (i) and (ii).

The comonomers are polymerized in water under conditions sufficient to prepare a copolymer, but copolymers of this invention can be prepared with any technique that is known to one of ordinary skill in the art of preparing polymers and copolymers. Methods used to synthesize copolymers include, but are not limited to: emulsion polymerization, microemulsion polymerization, miniemulsion polymerization, inverse emulsion polymerization, solution polymerization, precipitation polymerization, dispersion polymerization, suspension polymerization, and neat and/or bulk polymerization. In one embodiment, the preferred process is solution and emulsion polymerization.

In the preparation of aqueous copolymers by both solution and emulsion polymerization, distinctions are generally made between batch, semibatch, and continuous processes, and different methods of adding the monomers to the reaction vessel are described. For example, in a semibatch process the monomer mixture or emulsion is prepared in a separate batching vessel and the mixture or emulsion is passed continuously into a polymerization reactor, where it is polymerized. According to a general procedure for a semibatch process, the feed stream may comprise all of the ingredients used, such as monomers, water, and additives, with the aqueous monomer mixture or emulsion being prepared in a separate batching vessel, referred to as the feed tank.

In other embodiments of the invention, the copolymer is prepared by a continuous process or a batch process. In a continuous process, the monomers are admixed and fed continuously into the reactor, while in a batch process, the monomers are admixed and reacted without the further addition of monomer. Any method of polymerization may be used with the present invention.

The copolymer may be prepared using a catalyst or, in the alternative, the copolymer may be prepared using thermal energy to initiate polymerization. Any method of catalyzing and/or initiating polymerization of an aqueous dispersion of monomers having one or more polymerizable double bonds may be used with the present invention. For example, the monomers may be heated to from about 30°C to about 95 °C to initiate polymerization, or may be conducted at room temperature with the proper initiating system.

When the copolymer is prepared using a catalyst, in one embodiment a free-radical catalyst is used. Suitable free-radical polymerization initiators include all those which are capable of setting off a free-radical polymerization. They may comprise either peroxides, e.g., alkali metal peroxodisulfates or organic peroxides, or azo compounds. Use may also be made of combined systems which are composed of at least one organic or inorganic reductant and at least one peroxide and/or hydroperoxide, an example being tert-butyl hydroperoxide with the sodium salt of hydroxymethanesulfonic acid or hydrogen peroxide with ascorbic acid.

Combined catalyst systems may be used which include a small amount of a metal compound which is soluble in the polymerization medium and whose metallic component is able to exist in a plurality of valence states, e.g., ascorbic acid/iron(II) sulfate/hydrogen peroxide, in which in many cases the ascorbic acid may be replaced by the sodium salt of hydroxymethanesulfonic acid, sodium sulfite, sodium hydrogen sulfite or sodium bisulfite and the hydrogen peroxide by tert-butyl hydroperoxide or alkali peroxodisulfates and/or ammonium peroxodisulfate. Preferred initiators are the ammonium or alkali metal salts of peroxosulfates or peroxodisulfates, especially sodium or potassium peroxodisulfate, and V- 50 (2,2'-azobis(2-methylpropionamidine) dihydrochloride), an azo initiator.

Additives may be used to prepare the copolymers of the invention. One class of additives which may be useful with the present invention is electrolytes such as salts and polyelectrolytes. Typical salts include chloride, acetate, sulfate, phosphate salts but not limited to the listed ones. Polyelectrolytes include poly(sodium acrylate), poly(sodium styrene sulfonate), but not limited to them. These substances are commonly used in amounts of up to 20 percent by weight in some embodiments, from 0.5 to 15 percent by weight, in other embodiments, and from 0.5 to 10 percent by weight in still other embodiments of the invention, based on the weight of the solvent.

Exemplary protective colloids include polyvinyl alcohols, cellulose derivatives, or copolymers based on vinylpyrrolidone. Suitable emulsifiers are, in particular, anionic and nonionic emulsifiers, such as ethoxylated mono-, di- and trialkylphenols, ethoxylates of long chain alkanols, alkali metal salts and ammonium salts of alkyl sulfates, of sulfuric monoesters with ethoxylated alkanols and ethoxylated alkylphenols, of alkylsulfonic acids and of alkylarylsulfonic acids.

Nonionic emulsifiers which can be used include arylaliphatic or aliphatic nonionic emulsifiers, examples being ethoxylated mono-, di- and trialkylphenols (degree of ethoxylation: from 3 to 50, alkyl radical: C4-C1₀), ethoxylates of long-chain alcohols (degree of ethoxylation: from 3 to 50, alkyl radical: C8-C36), and also polyethylene

oxide/polypropylene oxide block copolymers.

Suitable cationic emulsifiers for use with the present invention include quaternary ammonium halides, e.g., trimethylcetylammonium chloride, methyltrioctylammonium chloride, benzyltriethylammonium chloride, or quaternary compounds of N— (C₆- C2o)alkyl)pyridines, N— (C6-C₂o)alkyl morpholines or N— (C6-C₂o)alkyl imidazoles, e.g., N- laurylpyridinium chloride.

The copolymers of the invention may also be prepared in other solvents besides water. Any solvent known to be useful to those of ordinary skill in the art of preparing polymer and copolymers may be used. Examples of such solvents include organic solvents, but are not limited to: polyvinylpyrrolidone, N-methyl-2-pyrrolidinone (also called N- methyl-2-pyrrolidone), 2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, lactic acid, methanol, ethanol, tetrahydrofuran, isopropanol, 3-pentanol, n-propanol, glycerol, butylene glycol (butanediol), ethylene glycol, propylene glycol, mono- and diacylated

monoglycerides (such as glyceryl caprylate), dimethyl isosorbide, acetone,

dimethylformamide, 1,4-dioxane, polyethylene glycol (for example, PEG4, PEG-8, PEG-9,

PEG-12, PEG-14, PEG-16, PEG-120, PEG-75, PEG-150) polyethylene glycol esters

(examples such as PEG4 dilaurate, PEG- 20 dilaurate, PEG-6 isostearate, PEG-8 palmitostearate, PEG-150 palmitostearate), polyethylene glycol sorbitans (such as PEG-20 sorbitan isostearate), polyethylene glycol monoalkyl ethers (examples such as PEG-3 dimethyl ether, PEG4 dimethyl ether), polypropylene glycol (PPG), polypropylene alginate,

PPG-10 butanediol, PPG-10 methyl glucose ether, PPG-20 methyl glucose ether, PPG-15 stearyl ether, propylene glycol dicaprylate/dicaprate, propylene glycol laurate. Other solvents include saturated aliphatic hydrocarbons such as butane, pentane, hexane and heptane; saturated cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; monoolefins such as 1-butene and 2-butene; aromatic hydrocarbons such as benzene and toluene; halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene, 1,2-dichloroethane, chlorobenzene, bromobenzene and chlorotoluene.

In the copolymers of the present invention the cationic monomer subunit can comprise from 1 percent to 90 percent by weight of the copolymer, preferably from 10 percent to 90 percent, more preferably from 30 percent to 70 percent, most preferably from 40 percent to 60 percent by weight of the copolymer.

The copolymers of the present invention may have a weight average molecular weight (Mw) in the range of 50,000 to 10,000,000 daltons. In one embodiment, the copolymer may have a weight average molecular weight (Mw) in the range of 50,000 to 2,000,000 daltons. In still another embodiment, the copolymer may have a weight average molecular weight (Mw) in the range of 75,000 to 1,000,000 daltons.

The copolymers of the present invention are particularly useful in production fluid demulsification and water clarification and flocculation. For the purposes of this invention, a production fluid is the often multiphase admixture of hydrocarbons, water, soluble inorganic materials and particulate matter produced from an oil and gas well. The copolymers of the present invention may be used, optionally in combination with other additives, to treat production fluid downhole, at the surface in a separator, or even downstream from the production well to facilitate the separation of the hydrocarbon from the water in the production fluid to produce a hydrocarbon phase that can be efficiently and cost effectively transferred and refined. In another embodiment, the copolymers of the present invention may be used down hole in conjunction with, for example, a descaler, to penetrate and break emulsions in the producing formation to facilitate the flow of hydrocarbons into an oil well bore. The copolymers of the present invention may be used in any way known to those of ordinary skill in the art of producing oil and gas to be useful.

An effective amount of the copolymer of the present invention useful for clarification of emulsified oil from an oil field produced water is from 1 to 10,000 ppm and preferably from 5 to 500 ppm, more preferably from 5 to 200 ppm.

In clarification applications, the copolymers of the present invention may be used to clarify process or waste water. In one embodiment, the copolymers of the present invention are admixed with waste water to produce a floe which can then be separated from the water using a separator device. In another embodiment, the copolymers of the present invention may be added to process water to reduce turbidity. The copolymers of the present invention maybe used in any way known to those of ordinary skill in the art of treating process and waste water to be useful.

The copolymers of the present invention may be used in the form of a copolymer solution or preferably a copolymer emulsion. In one embodiment, the copolymers are prepared by emulsion polymerization with additives such as salts. The resultant polymer emulsion may be used without additional treatment or modification as both a demulsifier and clarifier/flocculant agent. The copolymer emulsion is prepared by addition of certain dosage of salts and once the salt concentration is reduced with dilution by waste or produced water the emulsion copolymer will be soluble in the treated waste or produced water.

A preferred embodiment of the present invention is a method of separating oil and water in an oil- water emulsion from an oil field produced water, the method comprising the steps of treating the oil-containing water with an effective amount of a water-soluble cationic copolymer of the present invention.

EXAMPLES

A description of the raw materials used in the Examples is as follows, all chemicals are available from Sigma Aldrich unless otherwise noted.

TERGITOL 15-S-40 is a 70 weight percent aqueous solution of

polyethylene glycol (41) trimethylnonyl ether available from the Dow Chemical Company,

PG is propylene glycol,

EG is ethylene glycol,

EA is ethyl acrylate,

EDTA is ethylenediaminetetraacetic acid,

IAA is D-isoascorbic acid IAA,

t-BHP is tert-butyl hydroxyl peroxide

t-AHP is tert-amyl hydroxyl peroxide, and

ADAMQUAT™ BZ80 (BZ80) is 80 weight percent 2-(acryloxy)-N-benzyl-N,N- dimethylethanaminium chloride available from Whyte Chemicals Limited.

Solution polymerization. The polymers are synthesized via a shot polymerization process using free radical mechanisms. A 500 mL 4-neck round bottom flask coupled with thermocouple, overhead stir and cooling condenser is used for polymer synthesis. A heating mantel is used to control reaction temperature. A fixed amount of de-ionized water, PG or EG, TERGITOL 15-S-40, EA, BZ80, EDTA, and ferrous sulfate are charged to the reactor. After the temperature reaches the target, a controlled dosage of initial initiator or redox package is added and temperature is held for four hours. After the four-hour

polymerization, a second dosage of initiator or redox package is used to reduce the amount of non-reacted monomers down to ppm levels. After additional one-hour hold at temperature, the reactor is cooled to near room temperature before taking the solution polymer out of the reactor for analysis and performance tests.

Example 1

The synthesis process is a solution polymerization using the following reagents: 58.7 grams of de-ionized water, 99 grams of PG, 2.1 grams of TERGITOL 15-S-40, 15 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution.. All reactants are charged into the reaction flask. The temperature is set to 70 + 1°C. The first redox package includes 1.2 grams of 0.5 weight percent of reducing agent IAA and 1.2 grams of 0.5 weight percent t- BHP aqueous solutions. The second redox set for reducing unreacted monomers includes 5 grams of 0.5 weight percent of IAA aqueous solution and 5 grams of 0.5 weight percent t- BHP aqueous solution.

Example 2

The reaction flask is charged with 45.5 grams of de-ionized water, 90 grams of EG, 22.3 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution. The temperature is set to 60 + 1°C. The first redox package includes 0.6 grams of 0.5 weight percent of reducing agent IAA and 0.6 grams of 0.5 weight percent t-BHP aqueous solution. The second redox dosage for reducing unreacted monomers is the same as in Example 1.

Example 3

The reaction flask is charged with 138.6 grams of de-ionized water, 26.4 grams of EG, 2.1 grams of TERGITOL 15-S-40, 15 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution. The temperature is set to 70 + 1°C. The first redox package includes 1.2 grams of 0.5 weight percent of reducing agent IAA and 1.2 grams of 0.5 weight percent t-BHP aqueous solution. The second redox dosage for reducing unreacted monomers is the same as in Example 1.

Example 4

The reaction flask is charged with 94.1 grams of de- ionized water, 71 grams of EG, 2.1 grams of TERGITOL 15-S-40, 15 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution. The temperature is set to 70 + 1°C. The first redox package includes 1.2 grams of 0.5 weight percent of reducing agent IAA and 1.2 grams of 0.5 weight percent t-BHP aqueous solution. The second redox dosage for reducing unreacted monomers is the same as in Example 1. Emulsion polymerization. The polymers are synthesized via a shot polymerization process using free radical mechanisms. A 500 mL 4-neck round bottom flask coupled with thermocouple, an overhead stirring and a cooling condenser is used for polymer synthesis. A heating mantel is used to control reaction temperature. Fixed amount of de-ionized water, additives (such as sodium sulfate) to induce insolubility of cationic monomers and oligomers and thus the emulsion process, TERGITOL 15-S-40, ethyl acrylate, BZ80, EDTA, and ferrous sulfate are charged to the reactor. After the temperature reaches the target, a controlled dosage of initial initiator or redox package is added and temperature is held for four hours. After the four-hour polymerization, a second dosage of initial initiator or redox package is used to reduce the amount of non-reacted monomers down to ppm levels. After additional one-hour hold at temperature, the reactor is cooled to near room temperature before taking the emulsion polymer out of reactor for analysis and performance tests. Example 5

The synthesis process is an emulsion polymerization using the following reagents: 139.9 grams of de-ionized water, 8.2 grams of sodium sulfate, 2.1 grams of TERGITOL™ 15-S-40, 15 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution. All reactants are charged in the reaction flask. The temperature is set to 50 + 1°C. EDTA, 6 grams of 0.5 weight percent of reducing agent IAA, and 6 grams of 0.5 weight percent t-BHP aqueous solutions are added at once and at temperature. The second dosage for reducing unreacted monomers includes 5 grams of 0.5 weight percent of IAA aqueous solution and 5 grams of 0.5 weight percent t-BHP aqueous solution.

Example 6

The reaction flask is charged with 128.2 grams of de-ionized water, 24.8 grams of sodium sulfate, 2.1 grams of TERGITOL 15-S-40, 15 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution. The temperature is set to 60 + 1°C. The first redox package includes 3.6 grams of 0.5 weight percent of reducing agent IAA and 3.6 grams of 0.5 weight percent t-BHP aqueous solutions. The second redox dosage for reducing unreacted monomers is the same as in Example 5.

Example 7

The reaction flask is charged with 128.2 grams of de-ionized water, 6.6 grams of sodium chloride, 2.1 grams of TERGITOL 15-S-40, 15 grams of EA, 18.8 grams of BZ80, plus 2 grams of 0.1 weight percent EDTA solution and 2 grams of 0.1 weight percent ferrous sulfate solution. The temperature is set to 60 + 1°C. The first redox package includes 3.6 grams of 0.5 weight percent of reducing agent IAA and 3.6 grams of 0.5 weight percent tert-amyl hydroxyl peroxide (t-AHP) aqueous solutions. The second redox dosage for reducing unreacted monomers is the same as in Example 5.

Example 8

The reaction flask is charged with 102.4 grams of de-ionized water, 10.7 grams of sodium sulfate, 51.9 grams of EG, 2.1 grams of TERGITOL 15-S-40, 15 grams of EA, and 18.8 grams of BZ80. All reactants are charged in the reaction flask. The temperature is set to 70 + 1°C. The first redox package includes 1.2 grams of 0.5 weight percent of reducing agent IAA and 1.2 grams of 0.5 weight percent t-BHP aqueous solutions. The second redox dosage for reducing unreacted monomers is the same as in Example 5.

The compositions and polymerization parameters for Examples 1 to 8 are summarized in Table 1.

The following characterizations are performed on Examples 1 to 8: Molecular weight and chemical composition of the water-soluble cationic copolymer are determined using size-exclusion chromatography with on-line UV absorbance and multi-angle light scattering detections (SEC-UV-MALS). The polymer separation is carried out on a column set that consists of TSKgel G6000PWxl-CP, G5000PWxl-CP, and G3000PWxl-CP using 100 mM ammonium formate (NH₄OFA) at pH 3 as the mobile phase at 1 ml/min flow rate. All samples were diluted in 100 mM ammonium formate (NH₄OFA) at pH 3 at a concentration of about 2 mg/mL, shaken overnight on a mechanical shaker and filtered using 0.45 μιη PVDF filters prior to the analysis. The injection volume is 100 μΕ. The SEC-UV-MALS system is calibrated using a narrow 45 kg/mol PEO standard, and the UV absorbance signal was recorded at 254 nm wavelength.

A typical process for calculating water soluble copolymer molecular weight and chemical composition is described as follows. A trace amount of ADAMQUAT BZ80 monomer could be hydrolyzed and produced equal mole of acrylic acid (AA) and benzyldimethyl(2-hydroxyethyl)ammonium chloride (BHAC), the hydrolysis level must be known prior to the calculation of copolymer molecular weight. The amount of BHAC is estimated using its peak area in the UV chromatogram and the standard prepared from commercial BHAC. It is assumed that all AA goes into the copolymer backbone. The amount of ADAMQUAT BZ80 monomer in the copolymer backbone is calculation from the copolymer UV peak area. The UV extinction coefficient used for this calculation is obtained from the UV chromatograms of known samples (determined by NMR). The dRI peak area (from differential refractometer) of the copolymer is contributed from ethyl acrylate (EA), ADAMQUAT BZ80, and AA. As the amount of ADAMQUAT BZ80 and AA are known from the UV chromatogram, the amount of EA can be calculated. The refractive index increment, dn/dc, values used are 0.114 mL/g for EA, 0.161 mL/g for ADAMQUAT BZ80, and 0.093 mL/g for AA. The dn/dc of the copolymer is calculated using the weight- average value of the dn/dc of three monomers on the copolymer backbone. The water-soluble fraction of the sample is obtained using the dRI peak area of copolymer, the copolymer dn/dc, and prepared sample concentration. The copolymer dn/dc is then used for absolute molecular weight calculation using the online multi-angle light scattering signals. The results are summarized in Table 1.

Table 1

Examples are tested for their clarification ability to resolve oil-in- water emulsions in 3 different test conditions in either synthetic produced water or fresh produced water. The results are summarized in Table 2.

Method 1

A synthetic produced oil-in-water emulsion is prepared by adding 250 μΕ of 2 weight percent aqueous NaOH solution to 650 mL of DI water and then mixing in 6.5 mL of mid-gravity Middle Eastern crude oil for about 10 seconds under high shear (12,000 rpm). Continue the agitation of the synthetic produced oil-in-water emulsion for a further 2 minutes under high shear of 12,000 rpm. The resultant synthetic produced oil-in-water emulsion has a pH of about 8.5. 100 ml of these emulsions are added quickly to 6 ounce clear glass bottles and inverted several times to coat the bottles with emulsified oils. The individual bottles are dosed with Examples 1, 5, 6 and 7 at a final dosage of 50 ppm. A bottle without any treated chemical is chosen as the blank. The bottles are agitated 50 times by hand. Observations such as water clarity is depicted as either positive or negative, where positive in water clarity ratings indicates that emulsions are clear to near clear (i.e., Ex. 1 and Ex. 6) and negative in water clarity ratings refers that the emulsions are not cleared, (i.e., the blank), see FIG. 1. Method 2

For each test, a 6 ounce clear glass bottle is filled with 100 mL fresh produced water (from Field 1) and inverted several times to coat the bottles with emulsified oils. The individual bottles are dosed with Examples 1 to 8 at a final dosage of 50 ppm. A bottle without any treatment chemical is chosen as the blank. The bottles are agitated 100 times by hand. Observations such as water clarity are depicted as either positive or negative, as those defined in Method 1. Method 3

For each test, a 6 ounce clear glass bottle is filled with 100 mL fresh produced water (from Field 2) kept at 146° F and inverted several times to coat the bottles with emulsified oils. The individual bottles are dosed with Examples 1 to 8 at dosages between 100-400 ppm. A bottle without any treatment chemical is chosen as the blank. The bottles are agitated 200 times by hand. Observations such as water clarity are depicted as either positive or negative, as those defined in Method 1.

Table 2

FIG. 1 shows the results for Example 1, Example 6, and the blank following treatment according to Method 1.

Claims

claimed is:

A cationic copolymer comprising the polymerization product of

i a (meth)acrylate monomer having the following structure:

wherein R is hydrogen or a methyl group

and

R¹ is an alkylene group of 1 to 8 carbon atoms,

and

ii a cationic monomer having the following structure:

wherein R' is hydrogen or a methyl group,

A is an oxygen atom or NH,

R² is an alkylene group of 2 to 6 carbon atoms,

and

X^" is an anionic counter ion.

2. The cationic copolymer of Claim 1 wherein R is hydrogen or methyl, R' is hydrogen or methyl, R¹ is an alkylene group of 1 or 2 carbons, R² is an alkylene group two carbon atoms, A is an oxygen atom, and X^" is CI^".

3. The cationic copolymer of Claim 1 wherein the polymerization conditions comprise a solution polymerization process or an emulsion polymerization process.

4. The cationic copolymer of Claim 1 wherein the copolymer is prepared by a polymerization process initiated using a catalyst or initiation agent.

5. The cationic copolymer of Claim 1 wherein the cationic monomer subunit is present in an amount of from 40 percent to 60 percent by weight of the copolymer.

6. The cationic copolymer of Claim 1 wherein the copolymer has a weight average molecular weight of from 50,000 to 10,000,000 daltons.

7. A method of separating oil and water in an oil-water emulsion from an oil field produced water, the method comprising the steps of treating the oil-containing water with an effective amount of a cationic copolymer comprising the polymerization product of i a (meth)acrylate monomer having the following structure:

wherein R is hydrogen or a methyl group

and

R¹ is an alkylene group of 1 to 8 carbon atoms,

and

ii a cationic monomer having the following structure:

wherein R' is hydrogen or a methyl group,

A is an oxygen atom or NH,

R² is an alkylene group of 2 to 6 carbon atoms,

and

X^" is an anionic counter ion.

8. The process of Claim 7 wherein R is hydrogen or methyl, R' is hydrogen or methyl, R¹ is an alkylene group of 1 or 2 carbons, R² is an alkylene group two carbon atoms, A is an oxygen atom, and X^" is CI^".

9. The process of Claim 7 wherein the cationic copolymer is used in an amount of from 1 ppm to 10,000 ppm.