PREPARATION OF INVERSE EMULSION POLYMERS

FIELD OF THE INV ENTION

This invention pertains to water-in-oii emulsion polymerization. More particularly, the invention pertains to an environmentally friendly, oil phase system used for making water-in-oii emulsion polymers.

BACKGROUND

Inverse emulsion polymerization is a process that produces high molecular weight, water- soluble polymer in a convenient package for application. In the process an aqueous monomer solution is emulsified within an inert hydrocarbon phase containing surfactants that promote water-in-oi! ("w/o") emulsions. The resulting droplets are polymerized yielding polymer particles that are dispersed throughout the hydrocarbon phase and stabilized by surfactant

Over time various emulsification systems have been discovered and utilized. In

U.S. Patent No. 3,284,393, Yanderhofi ami Wiley espouse the use of conventional w/o emulsifiers such as, sorbitan monooleate, sorbitan monostearate, hexadecyl sodium phthalate, cety! or stearyl sodium phtha!te, and metal soaps.

U.S. Patent No. 3,826,771, to Anderson and Prisque, also teaches the use of conventional w/o emulsifiers, showing the use of sorbitan monostearate in all of the examples.

U.S. Patent No. 4,024,097, to S!ovinsky and Hurlock, introduced partially esterified lower Ν,Ν'-dialkanol substituted fatty amides, salts of fatty tertiary amines, quaternary salts of fatty tertiary amines, alkali metal salts, and aJkyl or alkyl aryi sulfates and sulfonates as w/o emulsifiers that yielded lattices with smaller particle size distributions and improved storage stability.

In U.S. Patent No. 4, 147,681, to Lim et a!., w/o emulsifiers with a HLB of at least 7 were used and many examples were cited. Lim and U.S. Patent No. 4,672,090, to Chan, made use of a system comprising a polyoxyethylene derivative of a sorbitan ester, sorbitan monooleate, and alkano!amide.

In U.S. Patent No. 4, 906 JO ϊ , to Clark, an inverse emulsion system utilizing

polyoxyethylene sorbitol esters, polyoxyethylene fatty alcohols with a HLB of 7-9, and glyeendes was revealed.

U.S. Patent No. 5,206,316, to Chuang, revealed the use ofnonionic oil-soluble surfactant and a compound selected from, N-alkyl lactams, and an alkylated polymer of a N-vinyl lactam. With this Six mind, It was desired to create an environmentally friendly oil phase system useful for making in verse emulsion polymers. The adopted definition of environmentally friendly are the rules that govern offshore chemical use in the North Sea. The environmental impact of a chemical is defined by three tests: bioaccumulation, biodegradation and toxicity. In. order for a chemical to be used without restriction offshore in the North Sea it .must satisfy two of the following three criteria;

1. Biodegradation must be greater than 60%, if less than 20% it is automatically

marked for substitution.

2. Bioaccumulation as measured by octanol/water partitioning coefficient (log

Po/w) must be below 3 (or have a molecular weight >700).

3. Toxicity to the most sensitive marine species (typically Skeietonema) must be

greater than LC50 or EC50 of 10 ppm.

One of the most popular and conventional w/o emulsifiers, sorbitan monooleate, does not pass the biodegradation and bioaccumulation protocols tbat govern offshore chemical use in the North Sea. For the initial assessment procedure, one must use marine biodegradation data as outlined in Organization for Economic Cooperation and Development, Procedure OECD 306 or BODIS. Sorbitan monooleate has a BODIS result of 32%, which coupled with log P > 3 prevents sorbitan monooleate from passing the test. Other governing bodies allow the use of other types of biodegradation data such as the OECD 301 series (freshwater) to prove a chemical's non-harm to the environment, but not for use in offshore applications. This prompted an investigation into other w/o surfactant systems that could be used to produce inverse emulsion polymers.

Lecithin is well known as an emulslfler and has been used in w/o emulsion technology in explosives. A number of publications illustrate this application including U.S. Patent

Nos. 3,535,174; 4,308,081 ; 4,357, 184; 4,473,418; 4,507, 161 ; and 4,602,970. Of particular interest. U.S. Patent Nos. 4,943,389 and 5,008,037 indicate that lecithin can be an inferior emulsifier for w/o emulsions. The patents teach that lecithin can be made into a better w/o emulsifier after subjection to a thermal process. Although inverse emulsions using lecithin are well known in the literature, not all inverse emulsions can go through the polymerization process and provide usable product.

Accordingly, there is a need for an environmentally friendly, oil. phase system used, for making water~in~oil emulsion polymers. Desirably, the oil phase system is biodegradable according to current environmental standards. More desirably, the oil phase system is comprised of substances recognized worldwide as generally safe for use.

SU MMA R Y OF THE INVENTION

The present invention is directed toward a water-in-oil emulsion composition. The composition comprises an aqueous phase, an organic solvent, and lecithin. Additionally, the composition may optionally comprise a nonionic surfactant, and the nonionic surfactant may comprise at least one polyoxyethylene derivative of a sorbitan ester.

The present invention is alternately directed toward a water-in-oil dispersion composition.

The composition results from a polymerization. The composition comprises a polymer phase, an organic phase, at least one initiator, and an inverting phase. The polymer phase is created from a monomer phase. The polymer phase may further comprise water, an inorganic salt, and a polymer created from at least one water soluble ethylenically unsaturated monomer. The organic phase may further comprise at least one hydrophobic solvent and lecithin. The at least one water soluble ethylenically unsaturated monomer may comprise at least one of an acrylic monomer and an acrylamide monomer. The inverting surfactant may he added after the polymer phase is created from the monomer phase. The organic phase of the water-in-oil emulsion composition may additionally comprise a polyoxyethylene derivative of a sorbitan ester.

The present invention is alternately directed toward a method for producing a water-in-oil polymer dispersion. The method comprises emulsifying an aqueous monomer solution in an organic phase, and polymerizing the aqueous monomer emulsion. The emulsifying forms an aqueous monomer emulsion. The polymerizing forms the water-in-oil polymer dispersion. The at least one monomer comprises at least one of an acrylic monomer and an acryiamide monomer, and the organic phase comprises lecithin and an organic liquid. The organic phase may additionally comprise a polyoxyethylene derivative of a sorbitan ester.

These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. DETAILED DESCRIPTION OF THE INVENTION

While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment widi the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.

It should be further understood that the title of this section of this specification, namely, "Detailed Description of the Invention," relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein.

An embodiment of the present invention is an environmentally friendly oil phase system comprising an organic solvent and lecithin. The immiscible organic solvent can be a

hydrocarbon solvent that is aliphatic or at least one oil derived from one or more natural products, and are at least 60% biodegradable after 28 days as determined by the Organization for Economic Cooperation and Development, Procedure OBCD 306, its text incorporated by reference. One or more non-ionic surfactants may be used, A preferred non-ionic surfactant is comprised of polyoxyethylene derivatives of a sorbitan ester that have a HLB of 9---I0.

It is important to define some of the nomenclature used within this disclosure, A monomer phase within a hydrocarbon solvent Is an inverse emulsion because such a composition is a liquid dispersed within another liquid. During polymerization, the liquid droplets become solid particles that are dispersed within the hydrocarbon solvent, creating a dispersion. Formally, a dispersion is solid particles dispersed within another phase. Acknowledgement of difference between an emulsion and a dispersion is important when dealing with the invention at hand.

The final component is lecithin, which can be obtained from sources such as soybean lecithin. The United States Food and Drug Administration has given lecithin the status of

Generally Recognized As Safe f'GRAS"), and the European body OSPAR that governs offshore chemical use in the North-East Atlantic has given lecithin the status of Poses Little Or NO Risk ("PLONOR"). chemicals with PLONOR status are inherently acceptable for use in the North Se.

Inverse emulsion polymers can be created with lecithin and the polyoxyethylene derivative of a sorbitan ester dispersion system. Evidence of the environmentally friendly oil phase system is shown in Table 1 , which shows the environmental profile for an aliphatic hydrocarbon solvent and two surfactants that can be used in the dispersion system.

In an embodiment, the organic solvent may be an aliphatic hydrocarbon. The aliphatic hydrocarbon may be derived from a natural product.

In. an embodiment, the organic solvent may he a fatty ester, The fatty ester may be derived from a natural product

In an embodiment _s the organic solvent may be at least 60% biodegradable after 28 days.

In an embodiment, the polyoxyethylene derivative may have a hydrophilic-iipophilic balance within the range from about 9 to about 10.

In an embodiment, the lecithin has not been subject to a thermal process.

In an embodiment, the aqueous phase is selected from at least one of a brine solution, an acid solution, a water soluble polymer solution, a gel, and a solid,

The polymer created by the invention may be anionic, cationic, nonionie, amphoteric, or a betaine-coiitaining polymer.

There are several envisioned uses for the invention. First the invention, may be used to produce inverse emulsion polymers thai could be used as friction (drag) reducers during pressure pumping operations, or an acid geilant in a crude oil recovery process. As an acid gellant, the invention could be used to produce stable gelled acid, and as a friction reducer when applied in low doses to fluids in turbulent flow, The invention could improve acid fracturing by allowing deeper penetration of the acid. The invention may be used as a hydrate inhibitor, as a clay stabilizing agent, or as a de-emuistfier. The invention may also improve pressure pumping by suppressing turbulent flow and minimizing the energy loss between the fluid and its

surroundings. The invention may be particularly useful in the treatment of a subterranean formation of an oil production operation and/or a gas production operation, i.e., those

applications that attempt to pump crude oil to the surface at steady state. Background information related to the aforementioned applications can be found in U.S. Patent Application Publication No. 2010/0056399, paragraphs [0048]- [0079], which are hereby incorporated by reference, Another use of the invention involves Its use as an environmentally friendly acid emulsifier. The emulsion would act to retard the action of acid, on acid-soluble formation rock, again typically found in the crude oil recovery process. Because the invention is environmentally friendly, its user would be less of a threat to the environment than perhaps other emulsifiers.

Several other envisioned uses of the invention include its use as an environmentally friendly dispersion system useful for the preparation or packaging of friction reducer, a scale inhibitor, or a hydrate inhibitor, depending on a particular application.

The following examples are meant to be illustrative and not limit the invention,

EXAMPLES

General Procedure:

The following is a general procedure for the preparation of a sodium 2-acryiamido-2- methyl-l -propanesulfonaie and aerylamlde copolymer. The continuous phase is prepared by dissolving the emulsifying surfactants in the hydrocarbon solvent. The dispersed phase is prepared by dissolving sodium or ammonium chloride in aerylamide and water, 2-Acrylamido- 2-methyl-1-propanesulfonic acid sodium salt solution is then added to the monomer phase followed by tetrasodiura ethylenediarainetetraacetate. After all of the solids are dissolved, the monomer phase is added to the oil phase and the emulsion is formed with adequate mixing. Typically a 1 kg emulsion is subjected to 60 seconds of mixing with a high shear rotor/stator laboratory mixer set at 5000 rpm. After the high shear mixing, the initiators are added and the system mixed with overhead stirring at 650 rpm while purging nitrogen, I ^' he reaction begins at around 43°C and is run isothermaliy for approximately 3 hours. At the end of three hours, the temperature is increased to 70 °C for one hour to lower residual monomer levels. After cooling to approximately 38-40 °C, the inverting surfactant is added to help the dispersion break when it is dispersed into an aqueous solution.

Table II below illustrates the formulation for this example prepared by following the general procedure outlined above. The resulting latex had a bulk viscosity of 693 cP when measured as Brookfield viscosity at room temperature with a #2 spindle at 30 rpm. The viscosity of an inverted 1% product solution in synthetic Nalco water was 277 eP using the same technique. The reduced specific viscosity ("RSV'') of a 450 ppm polymer solution in 1 -molar sodium nitrate was 20.3 dL/g using an Ubbelohde viscometer and the equation RSV ^» (l/e)[t/te - 1 ] where c - concentration, t« = time of flow for solvent, and t = time of flow for polymer solution.

Example 2:

Table ill below illustrates the formulation for this example prepared by following the general procedure outlined above, except adding the post-treatment chemicals indicated in the table. The resulting latex had a bulk viscosity of 494 cP when measured as Brookfield viscosity at room temperature with a #2 spindle at 30 rpm. The viscosity of an inverted 1 % product solution in Sugar Land, Texas, tap water was 238 cP using the same technique. The reduced specific viscosity of a 450 ppm polymer solution in 1 -molar sodium nitrate was 19.9 dL/g,

Example 3:

Table IV below illustrates the formulation for this example prepared by following the general procedure outlined above, except adding the post-treatment chemicals indicated in the table, ^" The resulting latex had a bulk viscosity of 1200 cP when measured as Brookfield viscosity at room temperature with a #3 spindle at 30 rpm. The viscosity of an inverted 1% product solution in synthetic Nalco water was 254 cP when measured as Brookfield viscosity at room temperature with a #2 spindle at 30 rpm. The reduced specific viscosity of a 450 ppm polymer solution in 1 -molar sodium nitrate was 17.5 dL/g.

All patents referred, to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure.

In the present disclosure, the words "a" or "an" are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall where appropriate, include the singular.

From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention, it is to be understood that no limitation with respect to the illustrated specific embodiments or examples is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.