Method of Using Polymers of Amido-Sulfonic Acid Containing Monomers and Salts as Drilling Additive

The present invention relates to a method of utilizing high energy mechanical mixing to produce homopolymers and copolymers made from amido-sulfonic acid monomers or salts thereof. More specifically, the present invention relates to producing such polymers by utilizing a high final stage polymerization temperature as well as drying the polymer before any substantial cooling thereof.

U.S. Pat. No. 3,663,518 to Patzelt et al relates to a process for preparing acrylamide polymers by forming a solution of at least one monomer and a catalyst, preparing a thin film therefrom, heating said formed thin film to a temperature sufficient to initiate polymerization and initiating such polymerization and maintaining the polymerization temperature until the polymerization is essentially complete.

U.S. Pat. No. 3,732,193 to Svarz relates to a continuous polymerization process in which an aqueous solution of a water soluble unsaturated monomer is polymerized on a heated continuously moving belt to produce a dry thin film. The polymer is usually polyacrylamide.

U.S. Pat. No. 3,478,091 to Murfin et al relates to the preparation of 2-amido-2-alkenesulfonates by reacting a ketone having at least one hydrogen atom in each alpha position with a nitrile and a sulfuric acid.

U.S. Pat. No. 3,503,941 to Fleetwood relates to the production of dry acrylic polymers produced by polymerizing an aqueous solution of acrylic acid in a pressurized, heated reaction zone and subsequently extruding the polymer to yield a fibrous brittle ribbon.

U.S. Pat. No. 3,666,810 to Hoke relates to the preparation of N-3-aminoalkyl propionamides and to polymers thereof by reaction analogous N-3-oxohydrocarbon-substituted amides with an amine in the presence of a reducing agent.

U.S. Pat. No. 4,034,001 to Miller relates to the preparation of bis-amidoalkanesulfonic acids and salts thereof.

U.S. Pat. No. 4,138,539 to Landolt relates to a multi-step process for preparing a high molecular weight water soluble synthetic polymer in the form of a readily dissolved powder wherein water soluble ethylenically unsaturated monomers and an aqueous redox initiator system are utilized.

U.S. Pat. No. 4,208,329 to Smiley relates to the purification of acrylonitrile monomer by the removal of oxazole therefrom.

U.S. Pat. No. 4,283,517 to Perricone et al relates to a continuous process for solution polymerization of acrylamide by rapidly heating a single phase high solids aqueous solution of the monomers to polymerization initiation temperature immediately prior to depositing a uniform layer thereof, as well as a solution of a polymerization initiator, onto a moving surface wherein the surface of the reaction mixture is heated only if necessary to maintain the temperature of the polymerization from dropping substantially below the polymerization initiation temperature.

U.S. Pat. No. 4,293,427 to Lucas et al relates to utilizing a copolymer of an acrylamido alkyl sulfonic acid or alkali metal salt thereof and an acrylamide or N-alkyl acrylamide as an aqueous drilling fluid composition.

U.S. Pat. No. 4,309,329 to Lucas et al relates to a terpolymer consisting essentially of alkali metal acrylate units, hydroxyalkyl acrylate units and acrylamide as a filtration control agent in an aqueous drilling fluid.

U.S. Pat. No. 4,404,111 to Bi et al relates to an N,N-dimethylacrylamide/2-acrylamido-2-methyl-propane sulfonic acid copolymer.

U.S. Pat. No. 4,032,701 to Hughes relates to a continuous method for producing a dry, solid polyacrylamide by polymerization on a hot rotating disc.

British Patent No. 777,306 relates to a method of polymerizing acrylic acid salts by spraying an aqueous solution of one or more monomers thereof in the presence of an alkali metal or ammonium persulfate onto a heated gaseous medium.

An article relating to "Acrylamide Production Simplified" by Matsuda, Chemtech, May 19, 1977 pages 306-308 sets forth a catalytic hydration method for converting nitriles to amides.

An article relating to "Adiabatic Polymerization of Acrylamide Using a Persulfate-Bisulfite Redox Couple" by Polh et al, Journal of Applied Polymer Science, Vol 26, pages 611-618 (1980) sets forth the results of an investigation as to reaction rates under various conditions to establish the dependence of rate on monomer as well as initiator concentration.

Accordingly, it is an aspect of the present invention to provide a method for producing a homopolymer from amido-sulfonic acid or salt containing monomers. Similarly, another aspect relates to a method for producing copolymers from amido-sulfonic acid or salt containing monomers as well as vinyl comonomers containing a nitrogen and/or oxygen group therein. Solid polymers containing relatively low amounts of water therein are produced desirably via an aqueous solution in the presence of high energy mechanical mixing which polymers are desirably subjected to drying before any substantial cooling thereof.

The amido-sulfonic acid or salt containing monomers according to the present invention can be generally represented by the following formula: ##STR1##

wherein R.sup.1 is a hydrocarbyl group having from 1 to 11 carbon atoms. More specifically, R.sup.1 is an aliphatic or an olefinic group having from 1 to about 4 carbon atoms with a vinyl group being preferred. R.sup.2, R.sup.3 R.sup.4, and R.sup.5, independently, can be hydrogen or a hydrocarbyl with the proviso that the total number of carbon atoms is 8 or less. Desirably, R.sup.2 and R.sup.3, are hydrogen or a lower alkyl having from 1 to 8 carbon atoms. Preferably, R.sup.2 and R.sup.3 are methyl. Desirably R.sup.4 and R.sup.5, independently, are hydrogen or an alkyl having from 1 to 8 carbon atoms with hydrogen being preferred. M is H, an ammonium cation, a metal cation, or mixtures thereof. The metal cation can generally be any metal cation and desirably potassium, magnesium, calcium, lithium, iron, zinc, sodium and the like. Sodium and potassium are especially preferred. Typically, the monomers are utilized in the form of a salt. A highly desirable monomer for making either a homopolymer or a copolymer is 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof.

The storage of the amido-sulfonic acid or salt containing monomer as well as polymerization thereof generally occurs in the presence of a solvent. Water is the preferred solvent for the preparation of both homopolymers and copolymers of the amido-sulfonic acid or salt containing monomers because of the limited solubility of the monomers in most organic solvents. Other suitable but less desirable solvents include dimethylformamide, methanol, dimethylsulfoxide, and other polar solvents. The amount of the amido-sulfonic acid or salt containing monomer, or combinations of the various such different monomers in the solvent generally ranges from about 15% to about 100% by weight based upon the weight of the monomer and solvent. Generally, an amount is utilized which is less than the saturation weight amount of the monomer in the solvent. With regard to an aqueous solution, the amount of monomer is generally from about 40 to 70% by weight, desirably from about 40% to about the saturation point of the aqueous solution, preferably from about 50% to about the saturation point of the aqueous solution, more preferably from about 50% to about 60% and highly preferable from about 55% to about 60% by weight based upon the weight of said monomer and said aqueous solution. Such high amounts by weight of the monomer are desirable in that the polymerization thereof results in higher yields, higher molecular weight, better performance properties and is easier to handle.

According to the present invention, a wide variety of copolymers can be prepared utilizing suitable comonomers. Generally, the comonomer is such that the overall copolymer is soluble in the solvent and preferably soluble in water. Oftentimes, the comonomer itself is water soluble. The various comonomers generally contain a vinyl group as well as a nitrogen and/or an oxygen molecule therein. Thus, various acrylamides, various vinyl pyrrolidones, various vinyl caprolactams, various acrylates, various acrylonitriles, various maleic acids and maleic anhydrides, as well as various acrylic acids can be utilized. By the term "various" it is meant the different compounds, derivatives or salts thereof known to the art and to the literature. Considering the acrylamides, specific examples of monomers include methacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide dimethylaminopropylmethacrylamide, t-butylacrylamide, acrylamide, and the like. Examples of suitable pyrrolidones include N-vinylpyrrolidone and the like. Various caprolactams include N-vinylcaprolactam and the like. Suitable acrylates include t-butylacrylate, methylacrylate, dihydrodicyclopentadienyl acrylate, 4-butane diol monoacrylate, diethylaminoethylacrylate, methylmethacrylate, and the like. Examples of various acrylonitriles include acrylonitrile, chloroacrylonitrile, methacrylonitrile, and the like. Besides maleic anhydride or acid, various derivatives and salts thereof can be utilized. In addition to acrylic acid, various derivatives thereof can be utilized such as methacrylic acid, and the salts of these acids. Preferred comonomers of the present invention include N-vinylpyrrolidone, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamide, N-vinylcaprolactam, and t-butylacrylamide with N,N-dimethylacrylamide being highly preferred.

Desirably, the comonomers have good solubility in the solvent. Should the comonomer not have good solubility, it is then desirable to utilize a small portion of another solvent such as an alcohol, for example methanol, to render the comonomer soluble in the solvent such as water. The amount of comonomer utilized will generally vary depending upon the type of comonomer utilized as well as the type of copolymer desired. Generally, it will vary from about 0.1% to about 30% by weight, desirably from about 1% to about 15% and preferably from about 3% to about 8% by weight based upon the total weight of all of the monomers.

An important aspect of the present invention is the use of high energy mechanical mixing the polymerizing monomers regardless of whether a homopolymer or a copolymer is being made. In other words good mixing is desired. Various types of high energy mechanical mixing devices include a two roll mill, an extruder, a continuous mixer and the like. It is also contemplated that static mixers can also be utilized wherein high energy is imparted by a pump. Inasmuch as the polymerization mixture tends to be viscous and/or tacky, equipment which tends to be self-wiping is desired. Extruders are preferred since the comonomers and other additives can be fed to the feed hopper with a polymerized product being produced in a suitable strand, ribbon, or the like. A twin screw extruder is highly desirable in that it is self-cleaning, that is wipes itself free of any residual or viscous polymer.

During polymerization, the various monomers or comonomers are heated to a suitable polymerization temperature. Heating is generally gradual throughout the heating cycle regardless of the type of high energy mechanical mixing device utilized be it a two roll mill, an extruder, or the like. Should an extruder be utilized, the screw configuration is not important and thus generally any type of screw configuration can be utilized. Inasmuch as the polymerization reaction is exothermic, the reaction itself will contribute to the temperature increase. The rate of temperature increase is generally not critical and the various monomers and additives can be initially added at ambient temperature. Heat is gradually applied until a polymerization temperature is reached. In an extruder, various zones can be heated to produce a suitable polymerization reaction temperature as well as a final polymerization reaction temperature. For example, if a three heating zone extruder is utilized, the first zone can be heated to a temperature of approximately 90.degree. to 180.degree. F. , the second zone, a temperature of about 150.degree. to about 240.degree. F. with the third zone being heated to a temperature of from about 200.degree. to approximately 300.degree. F. It is to be understood however that many other types of heating zones or arrangements via an extrusion reaction can be utilized.

According to the present invention, it is an important aspect to utilize a high final stage polymerization temperature to facilitate drying of the polymer. Otherwise, it has been found that subsequent drying is difficult and the production of a suitable homopolymer or copolymer is reduced. That a high final stage polymerization temperature could be utilized was unexpected since it was thought that the molecular weight would be impaired or decreased. A desirable final polymerization temperature of a homopolymer or copolymer according to the present invention is from about 200.degree. F. to slightly below the degradation temperature of the lowest degrading monomer, desirably from about 220.degree. F. to just below said degradation temperature, preferably from about 230.degree. F. to about 300.degree. F. with a highly preferred temperature being from about 240.degree. F. to about 280.degree. F. By the term "slightly below the degradation temperature", it is meant from about 1.degree. F. to about 20.degree. F. of below said degradation temperature. By the "final polymerization temperature" it is meant the temperature at the end of the high energy mechanical mixing device which oftentimes is the exit temperature.

According to the present invention, a solid homo- or copolymer is produced. In addition to conducting the final or terminal polymerization step at a high temperature, it is important that the homo- or copolymer be substantially dried before any substantial reduction in temperature of the homo- or copolymer occurs. That is, the temperature of the homo- or copolymer should not be reduced to ambient and preferably is maintained at a temperature of at least 200.degree. F. and more preferably at least 240.degree. F. before it is subjected to drying. Although the homo- or copolymer can be maintained or stored at an elevated temperature, it is often desirable after polymerization to immediately commence drying thereof. Any conventional or common mode of drying can be utilized such as irradiation, for example, infrared, convection heat, and the like. Regardless of the high energy mechanical device utilized, in polymerizing the monomers, the homo- or copolymer is transferred to a suitable vessel to be dried. A desirable mode of drying is the transfer of the polymer as from an extruder, to a moving conveyor belt where, because of economic reasons, infrared heat can be utilized to remove the solvent. The drying temperature at standard conditions is from at least the boiling point of the solvent utilized to approximately 600.degree. F. In the preferred embodiment wherein water is utilized, the drying temperature is from about 212.degree. F. to about 600.degree. F., desirably from about 350.degree. F. to about 550.degree. F., and preferably from about 400.degree. F. to about 500.degree. F. Drying can also be achieved by applying a vacuum, without heat or with heat at temperatures of from ambient to those set forth above. Drying is continued until most of the solvent is removed. Desirably, the amount of solvent such as water remaining in the solid polymer is 20% or less, more desirably 10% or less and preferably 3% by weight or less. A dried product is very desirable because of commercial reasons such as ease of size reduction, ease of handling, inventory advantages and the like.

Generally, the polymerization is carried out in a basic medium wherein various polymerization aids can be utilized. Although initiators are often utilized, polymerization may be conducted without initiators as in the presence of an inert atmosphere, for example nitrogen. Moreover, polymerization can be carried out in an acidic medium and even without heat although heat is desirable. Generally, initiators are utilized in the aqueous system such as peroxides, persulfates, persulfate-sulfites, various redox systems and the like. Such initiators are well known to the art and to the literature. A preferred initiator is ammonium persulfate.

Another aspect of the present invention relates to utilizing a co-catalyst which is added only initially to the polymerization reaction and not throughout the entire reaction. Such initiators are generally well known to the art as well as to the literature. An example of such a preferred initiator is sodium meta-bisulfite. Inasmuch as such initiators tend to adversely affect the molecular weight of the polymer, they are not utilized in high amounts whenever high molecular weights are desired. The total amount of the initiator is generally from 0 to about 5 parts by weight per 100 parts by weight of monomer, desirably from about 0.05 to 0.5 parts and preferably from about 0.2 to about 0.3 parts by weight. As noted, the co-catalyst is only added at the onset of a polymerization process.

Generally, the approximate weight average molecular weight of the homopolymer or copolymer made according to the present invention will range from about 100,000 to about 9,000,000, desirably from about 500,000 to 6,000,000, and preferably from about 1,000,000 to about 3,000,000. Naturally, the molecular weight can be varied depending upon desired end product usage such as those set forth herein below. Once the homopolymer or copolymer has been produced and dried, it can be ground into a powder by any conventional grinding apparatus.

Polymers and copolymers produced according to the present invention are useful in many applications. For example, they can be utilized as dispersants in water to remove, inhibit, or control rust, scale or alluvian deposits, as polymeric surfactants in paints, as polymeric scintillators, as polymers for the construction of contact lenses, in cosmetics, as anti-fog optical coatings, as fluid thickeners in aqueous hydraulic fluids, and the like. Another desirable use is as a fluid loss agent utilized in oil wells to make an impermeable layer to seal the wall of a drill hole.

The invention will be better understood by reference to the following examples.

A monomer blend consisting of 3.0% weight N,N-dimethylacrylamide, 56.3% (wt) sodium 2-acrylamido-2-methylpropanesulfonate, and 40.7% (wt) water having a pH of 9.0-9.5 is fed to a 4-inch Baker Perkins twin-screw extruder at 70 lb/hr. Just prior to entering the extruder, the monmer feed is heated to 100.degree.-110.degree. F. An initiator solution consisting of 8.4% (wt) ammonium persulfate and 91.6% (wt) water is fed to the extruder at 1.3 lb/hr. Both the monomer solution and the initiator solution are fed to the front of the extruder. At startup, about 1.3 lbs/hour of a solution of 7.1% wt of sodium meta-bisulfite is added and gradually reduced to zero over a period of 30 minutes. The material temperature is monitored at 3 different locations in the extruder and at the extruder die. The material temperatures in the first third, second third, and final third of the extruder are 155.degree.-165.degree. F., 210.degree.-220.degree. F., and 225.degree.-235 .degree. F. The material temperature at the extruder die is 255.degree.-265.degree. F. Tempered water is fed to jackets on the extruder to maintain these temperatures. The residence time in the extruder is 3-5 minutes. The resulting polymer is extruded in the form of 3/8-inch diameter strands onto the belt of an infrared conveyor dryer. The polymer moves through the dryer at a rate of 1.75-1.85 feet/minute. In the dryer, the polymer is dried to a water content of 1-2% (wt). The polymer reaches a temperature of 450.degree.-500.degree. F. in the dryer. The residence time in the dryer is 8-12 minutes. At the end of the dryer, the polymer falls into a crusher where it is crushed to a suitable size. The copolymer produced is the desired product.

The procedure from Example 1 is repeated, except that the 8.4% initiator solution is fed to the extruder at a rate of 1.75 lb/hr. The material temperatures in the extruder and dryer remain as they are in Example 1. The copolymer produced is the desired product.

The procedure from Example 1 is repeated, except that the 8.4% (wt) initiator solution is fed to the extruder at a rate of 0.75 lb/hr. Except for the material temperature in the first third of the extruder, temperatures in the extruder and the dryer remain as they are in Example 1. The material temperature in the first third of the extruder is 175.degree.-185.degree. F. The copolymer produced is the desired product.

The procedure from Example 1 is repeated, except that a monomer blend consisting of 2.6% (wt) N,N-dimethylacrylamide, 48.7% (wt) sodium 2-acrylamido-2-methylpropanesulfonate, and 48.7% (wt) water is fed to the extruder at 80.9 lb/hr. The initiator solution concentration and feed rate are maintained as indicated in Example 1. The material temperatures in the first third, second third, and final third of the extruder are 140.degree.-150.degree. F., 200.degree.-210.degree. F., and 220.degree.-230.degree. F. The material temperature at the extruder die is 250.degree.-260.degree. F. In the dryer, the polymer is dried to a water content of 1-2% (wt). The copolymer produced is the desired product.

The procedure from Example 1 is repeated, except that a monomer solution consisting of 58% (wt) sodium 2-acrylamido-2-methylpropanesulfonate and 42% (wt) water is fed to the extruder at 70 lb/hr. An initiator solution consisting of 8.4% (wt) ammonium persulfate and 91.6% (wt) water is fed to the extruder at 0.8 lb/hr. The material temperature in the first third, second third, and final third of the extruder are 135.degree.-145.degree. F., 200.degree.-210.degree. F., and 200.degree.-210.degree. F. The material temperature at the extuder die is 200.degree.-210.degree. F. The resulting polymer is dried to a water content of 0-1% (wt). The final dried homopolymer has a weight-average molecular weight of 900,000.

While in accordance with the present invention, a best mode of preferred embodiment has been illustrated in detail, the invention is not limited thereto, but rather by the scope of the attached Claims.