Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2000-04-03
2001-08-21
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S209000, C507S211000, C536S020000, C536S055300
Reexamination Certificate
active
06277792
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the modification of chitosan to produce viscosifiers (thickeners, gellants) for aqueous liquids, and to viscosified aqueous fluids containing such modified chitosans dispersed therein.
BACKGROUND OF THE INVENTION
Many viscosifiers for, and methods of, increasing the viscosity of aqueous liquids are known. Such viscosifiers may be so-called water-soluble polymers such as biopolymers, gums, cellulose derivatives, alginates, and other polysaccharides or polysaccharide derivatives, and various synthetic polymers. Representative polymers are set forth in the book “Handbook of Water Soluble Gums and Resins,” Robert L. Davidson, Ed., 1980.
Noticeably absent from this book is any mention of chitosan or derivatives thereof.
Viscoelastic fluids are characterized as having a rheological profile which is shear thinning, having a high viscosity at extremely low shear rates and a low viscosity at high shear rates. Thus such fluids are pseudoplastic having a high yield stress.
This type of rheology is produced by hydrating in the fluid certain water soluble polymers. These polymers presently known are biopolymers, i.e., microbially produced polysaccharides or heteropolysaccharides, and are well known in the art.
There is a need for fluids which exhibit a high low shear rate viscosity which are shear thinning.
Chitosan is a partially or fully deacetylated form of chitin, a naturally occurring polysaccharide. Structurally, chitin is a polysaccharide consisting of beta-(1→4)2-acetamido-2-deoxy-D-glucose units, some of which are deacetylated. The degree of deacetylation usually varies between 8 and 15 percent, but depends on the species from which the chitin is obtained, and the method used for isolation and purification.
Chitin is not one polymer with a fixed stoichiometry, but a class of polymers of N-acetylglucosamine with different crystal structures and degrees of deacetylation, and with fairly large variability from species to species. The polysaccharide obtained by more extensive deacetylation of chitin is chitosan.
Like chitin, chitosan is a generic term for a group of polymers of acetylglucosamine, but with a degree of deactylation of between 50 and 100 percent. Chitosan is the beta-(1-4)-polysaccharide of D-glucosamine, and is structurally similar to cellulose, except that the C-2 hydroxyl group in cellulose is substituted with a primary amine group in chitosan. The large number of free amine groups (pKa=6.3) makes chitosan a polymeric weak base. Both chitin and chitosan are insoluble in water, dilute aqueous bases, and most organic solvents. However, unlike chitin, chitosan is soluble in dilute aqueous acids, usually carboxylic acids, as the chitosonium salt. Solubility in dilute aqueous acid is therefore a simple way to distinguish chitin from chitosan.
Chitosan is unique in that it is a polysaccharide containing primary amine groups. Chitosan forms water-soluble salts with many organic and inorganic acids.
It is known to prepare chitosan derivatives by attaching various groups to one or more hydroxyl groups of the chitosan, as in various cellulose derivatives, and/or in attaching various groups to the primary amino group of chitosan. Thus it is disclosed in Hall and Yalpani U.S. Pat. No. 4,424,346 that chitosan can be reacted with various aldehydes by Schiff base formation with the primary amino group. The reaction is conducted in the presence of a reducing agent, specifically sodium cyanoborohydride, to reduce the imino group formed to a secondary amino group, i.e., the chitosan undergoes reductive alkylation. Among the aldehyde reactants are aldose or ketose sugars, or sugars oxidizable or hydrolyzable to aldoses or ketoses, for example, glucose, galactose, arabinose, xylose, N-acetylglucosamine, lactose, cellobiose, maltose, and melibiose. Example 5 specifically discloses the reductive alkylation of chitosan with lactose at weight ratios of lactose/chitosan of 2.4 (Product A), 3.0 (Product B, Product C), and 6.0 (Product D), to form products having the group—NHR′ therein, where R′ is an aldose or ketose residue. When the reaction was carried out in the absence of the sodium cyanoborohydride reducing agent at a weight ratio of lactose/chitosan of 8.0, the resulting product was minimally reacted with a degree of substitution of only 0.1. The reactions were carried out at room temperature. A paper which discusses the preparation and characteristics of the chitosan derivatives set forth in the Hall et al. U.S. Pat. No. 4,424,346 is “Some Chemical and Analytical Aspects of Polysaccharide Modifications. 3. Formation of Branched-Chain, Soluble Chitosan Derivatives,” M. Yalpani and L. D. Hall, MACROMOLECULES 1984, 17, 272-281. These chitosan derivatives are disclosed to offer a wide range of solubility, gelling and compatibility properties.
SUMMARY OF THE INVENTION
I have now determined that acidic viscous fluids having enhanced low shear rate viscosity (hereinafter sometimes referred to as ELSRV) can be prepared by dispersing in aqueous liquids certain acidic chitosan-containing concentrates (hereinafter sometimes referred to as ACCC).
The ACCC are prepared by reacting acidic chitosan salts in aqueous solution with an aldehyde group-containing chemical modifier (hereinafter sometimes referred to as AGCCM) at an elevated temperature wherein the concentration of chitosan in the acidic solution and the reaction time at the elevated temperature are sufficient to produce a semi-solid gel.
The preferred AGCCM are aldose or ketose sugars, or sugars oxidizable or hydrolyzable to aldoses or ketoses, such as glucose, galactose, arabinose, xylose, N-acetylglucoamine, lactose, cellobiose, maltose, and melibiose, or oligomers of the monosaccharides thereof containing from two to ten combined sugar units, of the same or different monosaccharides.
Preferably the concentration of chitosan in the ACCC is at least about 5 ppb (1.43 w/v %), the AGCCM to chitosan weight ratio is greater than about 0.5, and the reaction temperature is greater than about 140° F. (60° C.).
It is an object of this invention to provide a process for the preparation of acidic chitosan-containing concentrates which are efficient thickeners (viscosifiers, gellants) for compatible aqueous liquids to provide aqueous liquids having an elevated low shear rate viscosity.
It is another object of this invention to provide acidic chitosan-containing concentrates which are efficient thickeners (viscosifiers, gellants) for compatible aqueous liquids to provide aqueous liquids having an elevated low shear rate viscosity.
It is still another object to provide aqueous liquids which exhibit an elevated low shear rate viscosity having dispersed in a compatible aqueous liquid the acidic chitosan-containing concentrates of this invention.
These and other objects of the invention will be apparent to one skilled in the art upon reading the specification and claims hereof.
While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof will hereinafter be described in detail and shown by way of example. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.
The compositions can comprise, consist essentially of, or consist of the stated materials. The method can comprise, consist essentially of, or consist of the stated steps with the stated materials.
PREFERRED EMBODIMENTS OF THE INVENTION
The chitosans useful in the present invention will have at least 50% of their amino groups deacetylated, i.e., the degree of deacetylation is at least 50%, preferably at least 70%, and most preferably from about 85% to about 100%.
One aspect of the invention is to prepare aqueous pseudoplastic fluids having a Brookfield 0.5 rpm viscosity (hereinafter sometimes referred to as “low shear rate viscosity” or “LSRV”) of
House Roy F.
Tucker Philip
Venture Innovations, Inc.
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