Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1999-08-10
2002-03-12
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S360000, C528S363000, C528S373000, C528S374000, C528S332000, C525S418000, C525S420000, C252S175000
Reexamination Certificate
active
06355771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a modified polyaspartic acid, a method for the production thereof, and a metal corrosion inhibitor and a scale formation inhibitor which use the modified polyaspartic acid.
2. Description of the Related Art
Generally when a metal is used in an environment inhabited by water, such problems as the formation of scale and the corrosion of metal arise frequently.
Natural water contains calcium ions and magnesium ions in the form of dissolved hydrogen carbonates. These salts, when heated, give rise to scale which forms the cause for damage to a boiler, for example. In recent years, the practice of injecting sea water into an oil field has been in vogue for the purpose of increasing the production of crude oil. In this case, the scale which has carbonates and sulfates of alkaline earth metals such as calcium, strontium and barium as main components is formed by the mixture of oil field brine and sea water. The scale possibly poses the problem of blocking the oil well pipes. The scale inhibitor is used, depending on the situation, for the purpose of coping with these problems. The observance of the prevention of scale formation is important in the field of industrial production.
The corrosion of metal, which is another problem herein, is a very serious matter in the management of various facilities and devices which handle aqueous media. To this problem, generally the metal corrosion inhibitor is applied.
The mode of using the scale inhibitor and the metal corrosion inhibitor is known in two forms, i.e. the closed system and the open system. The feature of these inhibitors in the open system is important because it has direct bearing on conservation of the environment. As one example of the use of the scale inhibitor or metal corrosion inhibitor in the open system, it is cited the protection of oil well pipes in the extraction of crude oil. The scale inhibitor and the metal corrosion inhibitor are dissolved in water (sea water) and the water is injected by the water flooding method. The mixture of the oil field brine and the injected water (sea water) is discarded after the separation of the crude oil. In consequence of the growth of consciousness of the environmental protection in recent years, the desirability of ensuring safety of the scale inhibitor and the metal corrosion inhibitor and decreasing their load on the environment have come to compel enthusiastic recognition.
Among the chemical substances that are expected or used as the scale inhibitor and the metal corrosion inhibitor, is counted polyaspartic acid. The polyaspartic acid is regarded as one of the biodegradable materials. It is the polymer of aspartic acid that is one species of amino acid. This polymer discharges the function of preventing scale formation and inhibiting metal corrosion.
SUMMARY OF THE INVENTION
The polyaspartic acid is a hopeful biodegradable material and a useful scale inhibitor. It, however, shows poor activity in the prevention of metal corrosion. If it is enabled to enhance the activity thereof in the prevention of metal corrosion, it will further gain in usefulness. Besides this merit, the enhanced activity enjoys a decrease in the application rate and in the load on the environment and, therefore, proves advantageous from the viewpoint of the conservation of environment.
Heretofore, none of the cysteamine modified polyaspartic acids has a branched chain structure in the art (U.S. Pat. No. 4,363,797 and JP-A-6-248072). I have pursued an elaborate study with a view to imparting further advanced functionality to cysteamine modified polyaspartic acids. As a result, I have developed a method for the synthesis of novel cysteamine modified polyaspartic acids, such as those having a branched chain structure and those having numerous branched chain structures formed of one aspartic acid residue. I have discovered that these cysteamine modified polyaspartic acids exhibit a great ability to prevent metal corrosion and inhibit scale formation. The present invention has been perfected as a result. The term “branched chain structure” as used herein is meant to describe the fact that a polyaspartic acid has in the main chain thereof a side chain formed of at least one aspartic residue.
The cysteamine modified polyaspartic acids of this invention are clearly distinct from the conventional cysteamine modified polyaspartic acids devoid of a branched chain (branched chain structure) even in terms of physical constants such as the metal ion bonding force which are related to the molecular structure.
I have carried out an elaborate study in search of a method for the synthesis of modified polyaspartic acids. As a result, I have discovered a commercially practicable method for the synthesis of modified polyaspartic acids that fulfills the task mentioned above.
In accorrdance with the first aspect of this invention, it provides a modified polyaspartic acid characterized by containing a partial structure represented by the formula I:
at a molar ratio (I) in the range of not less than 1 to not more than 99, and at least one branched chain structure selected from the group consisting of the formulas II and III at a molar ratio (I) of not less than 1 to not more than 49:
wherein the term “molar ratio (I)” used herein means the ratio based on the number of moles (100) of a total aspartic residue of a polyaspartic acid, and Asp denotes an aspartic residue, n an integer of not less than 1 to not more than 25, and m an integer of not less than 2 to not more than 2n, M and M′ independently denote a hydrogen atom, an ammonium, or a metal, and (Asp)p denotes a branched chain.
In accordance with the second aspect of this invention, it provides a method for the production of a modified polyaspartic acid, characterized by comprising a step of adding a mercapto amine precursor, a mercapto amine, or a salt of mercapto amine to an anhydro polyaspartic acid and then allowing them to react with each other, wherein the term “mercapto amine” means HSCnHmNH
2
, n denoting an integer of not less than 1 to not more than 25 and m an integer of not less than 2 and not more than 2n.
In accordance with the third aspect of this invention, it provides a metal corrosion inhibitor incorporating therein the modified polyaspartic acid mentioned above.
In accordance with the fourth aspect of this invention, it provides a scale formation inhibitor incorporating therein the modified polyaspartic acid mentioned above.
The modified polyaspartic acid of this invention has a high metal ion bonding force owing to the characteristic of molecular structure thereof and, as a result, exhibits a higher ability as a scale formation inhibitor and a metal corrosion inhibitor than the conventional polyaspartic acids. Thus, it is expected to find utility as such inhibitors.
The objects, features, and advantages of this invention other than those set forth above will become clear from the following description of the preferred embodiments.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The term modified polyaspartic acid used herein also includes salts of modified polyaspartic acid. Counterions for modified polyaspartic acid include, but are not limited to, the alkaline and alkaline earth cations, some example of which are Na
+
, K
+
, Mg
++
, Ca
++
, Sr
++
, and NH
4
+
.
This invention concerns a modified polyaspartic acid containing a partial structure represented by the formula I:
at a molar ratio (I) in the range of not less than 1 to not more than 99, and at least one branched chain structure selected from the group consisting of the formulas II and III at a molar ratio (I) of not less than 1 to not more than 49:
wherein the term “molar ratio (I)” used herein means the ratio based on the number of moles (100) of a total aspartic residue of a modified polyaspartic acid, and Asp denotes an aspartic residue, n an integer of not less than 1 to not more than 25, and m an integer of not less than 2 to not more than 2n, M and M′ independ
Fish & Richardson P.C.
Hampton-Hightower P.
Nippon Shokubai Co. , Ltd.
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