Compositions – Water-softening or purifying or scale-inhibiting agents – Plant or organic material containing
Reexamination Certificate
2001-06-11
2003-11-04
Yoon, Tae H. (Department: 1714)
Compositions
Water-softening or purifying or scale-inhibiting agents
Plant or organic material containing
C252S181000, C252S175000, C524S807000, C526S287000
Reexamination Certificate
active
06641754
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of inhibiting corrosion and controlling the formation and deposition of scale imparting compounds in aqueous systems such as cooling, boiler and gas scrubbing systems. The novel polymeric compositions which are useful in accordance with the present invention comprise water-soluble or water-dispersible copolymers of ethylenically unsaturated monomers with sulfate, phosphate, phosphite or carboxylic terminated polyalkylene oxide allyl ethers.
BACKGROUND OF THE INVENTION
The problems of corrosion and scale formation and the attendant effects have troubled water systems for years. For instance, scale tends to accumulate on internal walls of various water systems, such as boiler and cooling systems, and thereby materially lessen the operational efficiency of the system.
Deposits in lines, heat exchange equipment, etc., may originate from several causes. For example, precipitation of calcium carbonate, calcium sulfate and calcium phosphate in the water system leads to an accumulation of these scale-imparting compounds along or around the metals' surfaces which water circulating through the system. In this manner, heat transfer functions of the particular system are severely impeded.
Corrosion, on the other hand, is a degradative electrochemical reaction of a metal with its environment. Simply stated, it is the reversion of refined metals to their natural state. For example, iron ore is iron oxide. Iron ore is refined into steel. When steel corrodes, it forms iron oxide which, if unattended, may result in failure or destruction of the metal, causing the particular water system to shut down until the necessary repairs can be made.
Typically, in cooling water systems, the formation of calcium sulfate, calcium phosphate and calcium carbonate, among others, has proven deleterious to the overall efficiency of the cooling water system. Recently, due to the popularity of cooling treatments using high levels of orthophosphate to promote passivation of the metal surfaces in contact with the system water, it has become critically important to control calcium phosphate crystallization so that relatively high levels of orthophosphate may be maintained in the system to achieve the desired passivation without resulting in fouling or impeded heat transfer functions which would normally be caused by calcium phosphate deposition.
Silica (SiO
2
) is present in most natural waters. When these waters are cycled in a cooling tower, the silica level increases and often a level is reached where precipitation of a silica species occurs. Sometimes the precipitation proceeds by the polymerization of silica itself, resulting in a silica gel. For this to occur, a relatively high SiO
2
concentration is required, usually greater than approximately 200 ppm. However, when certain cations are present, silica species can precipitate at much lower concentrations. Cations that promote silica precipitation include, but are not limited to, Al
3+
, Mg
2+
, Zn
2+
and Fe
3+
. Aluminum is very insoluble in water and readily precipitates under cooling water conditions. When aluminum gets into a cooling system (such as by carryover) it can cause serious precipitation problems. One such problem is the precipitation of phosphate species which may be present as a corrosion inhibitor. Such precipitates can be problematic due to both deposition and corrosion effects.
Although steam generating systems are somewhat different from cooling systems, they share a common problem in regard to deposit formation.
As detailed in the Betz Handbook of Industrial Water Conditioning, 9
th
Edition, 1991, Betz Laboratories Inc., Trevose, Pa., Pages 96-104, the formation of scale and sludge deposits on boiler heating surfaces is a serious problem encountered in steam generation. Although current industrial steam producing systems make use of sophisticated external treatments of the boiler feedwater, e.g., coagulation, filtration, softening of water prior to its feed into the boiler system, these operations are only moderately effective. In all cases, external treatment does not in itself provide adequate treatment since muds, sludge and hardness-imparting ions escape the treatment, and eventually are introduced into the steam generating system.
In addition to the problems caused by mud, sludge or silt, the industry has also had to contend with boiler scale. Although external treatment is utilized specifically in an attempt to remove calcium and magnesium from the feedwater, scale formation due to residual hardness, i.e., calcium and magnesium salts, is always experienced. Accordingly, internal treatment, i.e., treatment of the water fed to the system, is necessary to prevent, reduce and/or retard formation of scale imparting compounds and their resultant deposition. In addition to carbonates of magnesium and calcium being a problem as regards scale, having high concentrations of phosphate, sulfate and silicate ions either occurring naturally or added for other purposes cause problems since calcium and magnesium, and any iron or copper present, react and deposit as boiler scale. As is obvious, the deposition of scale on the structural parts of a steam generating system causes poorer circulation and lower heat transfer capacity, resulting in an overall loss in efficiency.
RELATED ART
U.S. Pat. No. 4,471,100 to Tsubakimoto et al. discloses a copolymer consisting of maleic acid and polyalkyleneglycol monoallyl ether repeat units useful as a dispersant for cement and paint and as a scale inhibitor for calcium carbonate.
U.S. Pat. Nos. 5,180,498; 5,292,379; and 5,391,238 to Chen et al., disclose copolymers of acrylic acid and polyethyleneglycol allyl ether for boiler water treatment and metal pretreating applications.
U.S. Pat. No. 5,362,324 describes terpolymers of (meth)acrylic acid and polyethyleneglycol-monomethylether-(meth)acrylate and polypropyleneglycol di(meth)acrylate for superplasticizer applications. U.S. Pat. No. 5,661,206 and EP448717 disclose similar technology but using diepoxy based compounds as crosslinking agents. Japanese Patents 93660, 226757 and 212152 disclose acrylic acid terpolymers with sodium methallylsulfonate and methoxy polyethylene glycol-monomethacrylate for superplasticizer applications.
U.S. Pat. No. 5,575,920 to Freese et al. discloses terpolymers of acrylic acid, allyloxy-2-hydroxypropylsulfonic ester (AHPS) and polyethyleneglycol allyl ether for cooling water treatment as calcium phosphate inhibitors.
U.S. Pat. No. 3,875,202 to Steckler discloses polymerizable ammonium and alkali metal salts of sulfated monoethylenically unsaturated alcohols of from 3 to 12 carbon atoms and of the alkenoxylated adducts of such alcohols. The polymerizable monomers are useful as co-polymerizable surfactants for self-stabilizing latexes and as comonomers in the copolymerization with other monomers in the preparation of co- or ter-polymeric films and fibers, especially as receptors for basic dyes and to build in anti-static properties. Monomers such as vinyl chloride, ethyl acrylate, 2-ethylhexyl acrylate, vinyl acetate and N-methyl acrylamide are disclosed in the patent to be copolymerizable with the ammonium salt of sulfated monoethylenically unsaturated alcohols. The copolymers disclosed are not water-soluble.
U.S. Pat. No. 5,705,665 to Ichinohe et al. relates to organic silicon compounds having as one of the components ethoxylated allyl alcohol with alkali metal salt of sulfonate group in the molecule. The resulting compound is useful as a surface treating agent and modifier for inorganic material. The copolymers disclosed are not water-soluble or dispersible.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, it has been surprisingly discovered that water-soluble or water dispersible polymers, which contain pendant functional groups are effective in controlling the formation and deposition of mineral deposits and in inhibiting corrosion in various aqueous systems. The novel polymers useful in the present invention
Buentello Kristin E.
Chen Fu
Kaechelin Julie A.
Kessler Stephen M.
Kolson Natalie A.
BetzDearborn Inc.
Boyd Steven D.
Yoon Tae H.
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