BACKGROUND OF THE INVENTION

The present invention relates to treating aqueous systems to prevent or remediate problems of mineral scale deposition and buildup. Fields of expected application include, without limitation, water treatment, industrial aqueous systems treatment, cooling water systems, boiler operation, thermal and reverse osmosis desalination activities, gas and oilfield operations, municipal and wastewater treatment, pulp and paper processes, and detergent/cleaning applications.

Various types of contaminants in an aqueous system under a variety of conditions can cause problems such as corrosion, microbiological contamination, or mineral scaling, in which contaminants precipitate out of solution in the system and form undesirable scale deposits on system surfaces. Of particular interest to the present invention is the challenge of scale management. Polymer mediated scale control techniques historically involve a variety of mechanisms that are generally known in the art, including, for example, threshold inhibition, sequestration, chelation, stabilization, particulate dispersion, and crystal habit modification. These mechanisms are discussed and defined below.

Threshold inhibition involves extending the solubility of an otherwise insoluble salt beyond normal saturation limits using an additive which functions at sub-stoichiometric levels. This sub-stoichiometric functionality differentiates treatment additives such as polymers and phosphonates from materials that function according to strict stoichiometric ratios such as Ethylenediaminetetraacetic acid (EDTA). Threshold inhibition is often a temporary effect. For example, if uninhibited water takes 60 seconds to begin precipitating calcium carbonate in a given set of conditions (such as pH, temperature, concentrations of calcium and carbonate, etc.), the same water may be treated to extend this time to one hour through a threshold inhibition additive. The extent and duration of threshold inhibition may be related to a variety of factors or conditions, including without limitation the driving forces for precipitation (pH, temperature, concentrations of scale-forming ions, etc.), the particular efficacy of a selected threshold inhibition additive, other water impurities (dissolved or suspended), rate of water concentration or evaporation, and frequency of additive dosage.

Sequestration can be another important function of treatment additives, particularly of many polymers and phosphonates. Sequestration is the complexation of a metal ion such that the ion does not retain its original reactive properties. Unlike threshold inhibition, sequestration does not connote either stoichiometry or specific functionality. Some phosphonate or polymer additives commonly used for mineral scale control can sequester ions such as calcium, magnesium, and barium, preventing them from forming insoluble complexes with compounds such as carbonate and sulfate.

A chelate is a coordination compound in which a central metal ion such as Ca2+is attached by coordinate links to two or more non-metal atoms in the same molecule, called ligands. Thus, a chelating agent is an additive that links to a metal ion at two or more points within the agent molecule. In practice, polymers such as polycarboxylates and sulfonated copolymers act as chelating agents with most multi-valent ions due to the multiple binding sites along the polymer's backbone. In common usage, chelation further implies a more permanent or substantive relationship between the ion and the ligand and refers to stoichiometric relationships between the metal ion and the ligand.

Stabilization may refer to two distinct mechanisms. In colloidal stabilization, precipitation in a fluid (such as water) occurs, but the polymer additive prevents agglomeration of particles larger than one micron in size. These particles are thus stabilized via electrostatic interactions with the polymer and remain suspended throughout the water phase. These sub-micron particles are typically invisible to the naked eye. A notable exception to this is stabilized iron particles, which can be visible due to the orange-brown color associated with most oxidized (Fe3+) iron complexes. Colloidal stabilization can fail due to physical or chemical changes in the fluid that result in particulate agglomeration beyond one micron in size and bulk settling of the precipitate. The alternate usage of “stabilization” is as a synonym for sequestration, where a coordination complex between a polymer additive and soluble ions, or surface interaction between polymer and forming crystal lattices, occurs, preventing precipitation.

Particulate dispersion is a suspension of particulates in an aqueous solution. Particulate dispersion involves a mixture of finely divided particles, called the internal phase (often of colloidal size), being distributed in a continuous medium, called the external phase. These can be inorganic (e.g., calcium carbonate), organic (e.g., biomass), or a mixture of the two. Polymer composition and molecular weight (Mw) are key determinants in deriving functionality for effective particulate dispersion.

The final mechanism discussed here in relation to scale control is crystal habit modification. A crystal habit is defined as the normal size and shape of a precipitated substance in a given set of environmental conditions.FIGS. 1A through 1Eillustrate simplistically a formation process of crystals such as calcium carbonate, and the crystals' subsequent deposition onto surfaces. The formation of crystals such as calcium carbonate and their subsequent deposition onto surfaces follow a process, simplified here for clarity, of nucleation (illustrated inFIG. 1A), lattice formation and propagation (illustrated inFIG. 1B), bulk precipitation (illustrated inFIG. 1C), and surface deposition (illustrated inFIGS. 1D & 1E). Modification of crystal habit involves introducing a “poison” or contaminating additive that disrupts normal lattice formation. This, in turn, yields crystals tending either to re-dissolve or to precipitate in abnormal forms that deviate from the substance's untreated crystal habit. This effect tends to reduce cohesion of the crystals to each other (dispersion) and adhesion of crystals to system surfaces (scaling).

Although the general mechanisms described above are known and, to some degree, understood in the art of treating aqueous systems, the exact functionality of treatment additives often is not. In practice, various polymer additives often are viewed as single-purpose. In application, threshold inhibition is often prioritized as the most important scale control mechanism, to the relative neglect of other mechanisms. By focusing more precisely on additive functionalities, it is possible to take advantage of interrelationships among these scale control mechanisms, and improvements can be achieved in the art of treating aqueous systems.

An object of the invention is to achieve improved treatment of aqueous systems by re-prioritizing the scale treatment mechanisms targeted. A further object is to prepare a substantially poly-maleic additive through in-situ formation of maleic acid copolymer so that mono-carboxylic acids, non-ionic functional groups, and terminal hydroxyl groups are also formed during polymerization. Improved treatments may then be applied to aqueous systems to achieve various improvements in scale prevention or remediation.

BRIEF SUMMARY OF THE INVENTION

In a basic embodiment of the invention, a method is described to prioritize crystal habit modification in selecting a treatment additive for aqueous systems. In further illustrative embodiments, polymer materials are specified which exhibit improved crystal habit modification properties and other advantages. Also, methods are specified for preparing and applying improved polymer additives to prevent, reduce, or remediate scale formation or precipitation in aqueous systems.

