Liquid purification or separation – Processes – Preventing – decreasing – or delaying precipitation,...
Reexamination Certificate
2002-03-21
2003-11-04
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Preventing, decreasing, or delaying precipitation,...
C134S003000, C134S022140, C134S041000, C252S180000
Reexamination Certificate
active
06641740
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods and compositions for sequestering metal ions in solution, and to methods and compositions for combating metal compound deposits. Of particular interest (but not the exclusive interest) is the prevention of the deleterious effects associated with compounds of alkaline earth metals. Calcium salts, for example calcium carbonate, and magnesium salts form particularly prevalent salt deposits commonly known as scale or lime scale, which is troublesome in itself and which provides sites for concentrations of soils and bacterial growth. Calcium and magnesium ions in aqueous solution are responsible for “hard” water, in which it is difficult to form a lather with soap or detergent, and which may then form an unpleasant scum. Of course, it is from hard water that scale forms.
Known calcium ion sequestrants, acting as water softeners, include sodium carbonate, sodium citrate, and phosphates, including sodium acid pyrophosphate, sodium polyphosphate, trisodium phosphate, tetrasodium pyrophosphate and sodium tripolyphosphate. Many such sequestrants have certain limitations on how they can be used, for example within a certain pH range only, some give rise to undesirable effluents, and some are corrosive to metals.
It would be desirable to employ a composition which can act as an effective sequestrant, acting as a water softener, without having one or more of the problems of known sequestrants, as mentioned above.
Known scale removers typically employ mineral acids, for example hydrochloric acid. They must be employed with some care and may represent an environmental hazard, and be corrosive to metals.
It would be desirable to employ a composition which can effectively combat solid metal compound deposits, for example scale, without incurring one or more of the problems of known compounds, as mentioned above.
BRIEF SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention there is provided a method of combating metal species carried by or deposited from water, the method comprising the delivery to an environment in which the metal species are present of a composition comprising an algin.
The term “combating” may include the treatment of a metal compound already present as a solid deposit, or the treatment of the said environment to prevent or hinder the deposition of such a compound from solution, or both. Thus, the treatment could be one of deposit removal, and/or water purification and/or water softening.
The term “metal species” includes ions in solution and deposits of metal compounds, including metal oxides and, especially, metal salts.
Algins may be found in and isolated from various organisms, in particular from algae belonging to the order Phaeophyceae and soil bacteria such as
Azotobacter vinelandii
and
Azotobacter crococcum
and from several strains of Pseudomonas bacteria. Common algal sources of algins include
Laminaria digitata, Ecklonia maxima, Macrocystis pyrifera, Lessonia nigrescens, Ascophyllum nodosum, Laminaria japonica, Durvillea antartica, Durvillea potatorum
and, especially,
Laminaria hyperborea.
Alginic acid is a linear hetero-polysaccharide comprising units of &bgr;-D-mannuronic acid and &agr;-L-guluronic acid. Alginic acid may comprise homopolymeric sequences of mannuronic acid, homopolymeric sequences of guluronic acid, and mixed sequences of mannuronic acid and guluronic acid units.
Alginic acid itself is effective in the method of the present invention in combating metal species. Salts of alginic acid used in the method of the present invention may include alkali metal salts, for example sodium and potassium salts, and ammonium and alkanolamine salts. Alkali metal salts are of particular interest.
The term “algins” as used herein includes alginic acid and salts of alginic acid, irrespective of the relative proportion of mannuronic and guluronic units, and is intended to include glycolated or alkoxylated derivatives, especially those derivatized with propylene glycol. However, preferred compounds are not alkoxylated or glycolated. Guluronic acid-rich alginic acid and guluronic acid-rich salts of alginic acid are of particular interest. Preferred compounds have at least about 50%, more preferably about 55-99%, most preferably about 60-80% of guluronic units (by weight), the balance being mannuronic units. For guidance on production of algins very high in guluronic units the reader is referred to International Patent Application Publication WO 98/51710.
DETAILED DESCRIPTION OF THE INVENTION
We have found particularly good results, notably in removing metal compound deposits, using methods which employ algins and an acid (by which we mean a non-alginic acid, when said algin is alginic acid). Particularly preferred are methods which employ a salt of alginic acid, preferably an alkali metal alginate, and an acid.
In such compositions said acid could (except when said algin is itself alginic acid) be alginic acid. However good results may be obtained using a salt of alginic acid and an acid which is not alginic acid. Suitably, such an acid is an organic acid, preferably a carboxylic acid, preferably one having a plurality of carboxylic groups, for example citric acid, or gluconic acid. Preferably the algin can dissolve in water before the pH is substantially reduced. Gluconic acid can be produced by cleavage of glucono delta lactone in the presence of water. This takes place slowly and offers the possibility of a dry mix of ingredients, including the algin and glucono delta lactone (or other suitable lactone, splitting in the presence of water to form an acid, preferably once the algin has dissolved). Alternatively, the acid could be a mineral acid, for example hydrochloric acid, preferably present in low concentration, and preferably added after the algin has dissolved. Preferably, a non-alginic acid employed in this invention is substantially odorless.
While an acid could be employed in a method of combating a metal species before or after a salt of alginic acid is employed, preferably both such compounds are used at the same time. To this end, a treatment composition may comprise both such compounds in admixture, preferably in an aqueous composition.
Very good results may be obtained, notably in methods of removing metal salt deposits, when the algin is sodium alginate. Especially preferred, however, is potassium alginate. Potassium alginate appears from our tests to be relatively easy to incorporate in stable solutions and to be highly effective in removal of deposits of metal compounds.
Especially preferred for use in methods of water softening is an alginic acid, preferably as the sole algin present.
Preferably, the pH of an aqueous composition comprising an algin is in a range of about 2-12, preferably about 3-11.
Preferably, the pH of an aqueous composition comprising an algin and an acid is less than about 7, preferably about 2-6, and most preferably about 3-5. Preferably, the pH of the composition is in excess of the pKa value of the algin. As noted above, we have found that formation of a stable solution is most easily achieved when the algin is mixed in (preferably dissolved in) water, which is then acidified by an acid.
On the alkaline side, we have obtained good results at pH values in a range of about 8.5-11, especially about 9-10.5, as would be found in dishwashing machines.
A composition used in the method could be provided in a solid form, for example a powder or granules, which is applied directly to a metal compound deposit to be combated or to a substrate on which the deposit could form, or added to water with which the deposit or a said substrate is in contact, or which otherwise contains deleterious or potentially deleterious metal ions. It could be a tablet to be added to, for example, a cistern of a lavatory. Preferably, however, the composition is provided in a liquid form, preferably as an aqueous composition. The in-use composition will suitably be made by dilution of a concentrate, for example a powder, granules or tablet; or a gel or liqu
Cornelius Gay Joyce
Jolliffe Ian Gordon
McKechnie Malcolm Tom
Onsoyen Edvar Jarle
Akin Gump Strauss Hauer & Feld L.L.P.
Hruskoci Peter A.
Reckitt Benckiser (UK) Limited
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