Compositions – Absorptive – or bindive – and chemically yieldive
Reexamination Certificate
1999-11-08
2001-01-23
Tucker, Philip (Department: 1712)
Compositions
Absorptive, or bindive, and chemically yieldive
C252S182350, C521S026000, C210S670000
Reexamination Certificate
active
06177027
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with improved iron-complexing or scavenging compositions in solid or liquid form which include Sn
+2
ion preferably derived from stannous chloride, as well as phos-acid(s) and alkali metal hexametaphosphate. The compositions of the invention can be used as a downhole well treatment or with sodium chloride to form a regenerating medium for cation exchange resins used in water softening systems.
2. Description of the Prior Art
Water softening systems have long been used in households and by industry to replace hardness cations such as calcium and magnesium with sodium ions. This is accomplished by passing an incoming water supply through a bed of sodium charged cation exchange resin beads or particles. As the water passes through the cation exchange resin bed, the incident hardness cations are exchanged for the sodium ions of the bed. In the course of time, the ion exchange resin bed becomes saturated with hardness cations removed from the incoming water, and it is necessary to recharge the bed by passing a brine solution primarily consisting of sodium chloride through the resin bed. This replenishes the bed with sodium ions and removes unwanted calcium, magnesium, or other ions previously removed from the water.
Over time, the exchange capacity of an ion exchange resin bed deteriorates as impurities in the incoming water collect in the resin bed and are not removed by periodic recharging. At some point, depending primarily on the characteristics of the incoming water supply, the resin bed becomes unacceptably “fouled,” i.e., the resin bed's capacity to soften water has been diminished to an extent that it must be specially treated to restore softening capacity.
Although a number of factors can lead to fouling of an ion exchange resin bed, perhaps the greatest single contributing factor is the presence of iron in an incoming water supply. Iron can exist in several valence states in water, the most common being the ferrous and ferric states. It is most desirable to maintain the iron in the ferrous state, inasmuch as ferrous iron can readily be removed during conventional resin bed regeneration. However, ferrous iron tends to become oxidized to the ferric state after being exchanged onto a resin bed, which makes its removal very difficult and can cause the resin beads to split.
Iron also presents significant problems in the context of oil well drilling operations. For example, excessive iron in oil well fluids can lead to the formation of viscous downhole emulsions which can block flow and significantly minimize oil production. Accordingly, oil well operators need to carefully monitor and to the extent possible inhibit the formation of viscous emulsions of this type.
SUMMARY OF THE INVENTION
The present invention overcomes the problems outlined above and provides novel products in the form of solids mixtures and aqueous dispersions which can be used as a part of cation exchange resin regenerating media or in the context of downhole well treatments. The compositions of the invention have the ability to complex or scavenge iron in its various valence forms, and broadly include Sn
+2
ion as well as phos-acid(s), i.e., an acid selected from the group consisting of phosphorous acid, phosphoric acid and mixtures thereof, where the phos-acid(s) can be in any form such as ortho-, meta- or polyphosphoric acids such as pyrophosphoric and more complex poly acids. The most preferred source of Sn
+2
ion is stannous chloride, SnCl
2
.
In addition, the compositions of the invention generally include an alkali metal hexametaphosphate such as sodium hexametaphosphate, and may also have therein minor amounts of EDTA. In the case of solids mixtures, anti-caking agents or other similar additives may be employed.
Broadly, the compositions of the invention contain from about 0.3-15% by weight Sn
+2
ion, which is generally derived from a corresponding salt such as a halide salt, particularly SnCl
2
. The phos-acid component is preferably phosphorous acid in the context of solid products and concentrated polyphosphoric acids for liquids. The phos-acid component is generally present at a level of from about 0.1-75% by weight; this solids preferably include from about 0.1-10% by weight acid, whereas the liquids have from about 0.1-75% by weight thereof. The hexametaphosphate is present at a level of from about 0.5-95% by weight; in solid products the preferred hexametaphosphate content is from about 50-95% by weight, whereas in liquids the level of use is from about 0.5-50% by weight.
The compositions of the invention can be used to form regenerating media for cation exchange resins. This involves mixing minor amounts of an Sn
+2
ion source and phos-acid(s) with a preponderant amount of sodium chloride. This can be done in the dry form or as a liquid. Alternately, the compositions of the invention can be used as an oil well treatment agent which involves introducing the aqueous dispersions directly into the oil well for the purpose of preventing or breaking the formation of viscous oil emulsions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As indicated, the present invention is directed to solid products and dispersions each containing Sn
+2
ion and phos-acid(s), as well as a regenerating medium for cation exchange resins and corresponding methods. For ease of understanding, the different aspects of the invention are described separately.
Solid Mixtures
The solid mixtures in accordance with the invention can be used as downhole well treatments or as a part of cation exchange regenerating media. The solids are preferably made up of a source of Sn
+2
ion (Sn
+2
ion present at a level of from about 0.3-15% by weight, more preferably from about 0.3-7% by weight) and an acid selected from the group consisting of phosphorous acid, phosphoric acid and mixtures thereof, most particularly phosphorous acid. Stannous chloride is preferably used at a level of from about 0.5-25% by weight, and more preferably at a level of from about 0.5-10% by weight. The acid component is used at a level of from about 0.1-10% by weight, and more preferably from about 0.25-5% by weight. The single most preferred acid is phosphorous acid, and a 1% by weight solution of the overall mixture in water at room temperature normally would have a pH in the range of about 3-4. The preferred compositions also include an alkali metal hexametaphosphate therein, especially sodium hexametaphosphate. The hexametaphosphate component is used at a level of from about 50-95% by weight, more preferably from about 90-95% by weight. The hexametaphosphate will usually change the pH of the compositions in water to about 4-5. EDTA can also be used in these compositions, generally at trace levels of up to about 1% by weight.
Aqueous Dispersions
In this form of the invention, respective quantities of Sn
+2
ion and phosphorous and/or phosphoric acid are dispersed in an aqueous medium, typically water, dilute acids or brines. Usually, hexametaphosphate is also present. The liquid dispersions find particular utility as downhole well treatments and as an additive adapted to be added to sodium chloride for the purpose of creating a regenerating medium for cation exchange resins.
In the case of downhole well treatments, the aqueous dispersions generally have from about 0.3-15% by weight Sn
+2
ion therein, more preferably from about 0.3-5% by weight Sn
+2
ion; SnCl
2
is the most preferred source of Sn
+2
ion, used at a level of from about 0.5-25% by weight, more preferably 0.5-7% by weight. The phos-acid(s) is present at a level of from about 0.1-75% by weight, more preferably from about 25-60% by weight. The most preferred phos-acid is concentrated polyphosphoric acid. The hexametaphosphate component is used at a level of from about 0.5-50% by weight, more preferably from about 1-25% by weight. EDTA if used is present at trace amounts of up to about 1% by weight. The pH of the dispersions
Wolf Beth Ann
Zaid Gene H.
Hovey Williams Timmons & Collins
JACAM Chemicals L.L.C.
Tucker Philip
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