An antiscalant is a chemical or pre-treatment chemical that prevents the formation of scale, or crystallized mineral salts, commonly used in water purification systems, pipelines and cooling tower applications. Antiscalants are also known as scale inhibitor agents. Scale formation occurs when the concentration of dissolved salts in water exceeds their solubility limits, leading to the precipitation of these salts onto surfaces as hard deposits. Antiscalants dissolve the substances accumulated near the membrane surface and reduce the rate of fouling. They play a crucial role in preventing scale formation, thus improving the efficiency and longevity of industrial equipment and processes.

Common ingredients

Antiscalants could be broadly classified into 3 main categories: phosphorus based AS, synthetic polymeric AS and natural green AS. Common active ingredients include

phosphonates In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups, where R is an organic group (alkyl, aryl). If R is hydrogen then the compound is a dialkyl phosphite, which is a different functional gr ...

polyphosphates A polyphosphate is a salt or ester of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic (also called, ring) structures. In biology, the ...

polymers A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, b ...

aminophosphonate Aminophosphonates are organophosphorus compounds with the formula (RO)2P(O)CH2NR2. These compounds are structural analogues of amino acids in which a carboxylic moiety is replaced by phosphonic acid or related groups. Acting as antagonists of am ...

s and organic acids. Antiscalants typically contain a combination of active ingredients that interfere with the crystallization process of scale-forming salts. Phosphorus-based antiscalants has the largest application use globally and they can be further classified into phosphorus-based and phosphonate-based AS. Green antiscalants usually contain natural polymers such as

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...

and are recently being more widely investigated due to discharge requirements. Polymer-based AS are synthetic polymers that have functional groups like

carboxylic In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl group (e. ...

acid groups, acrylic acid, sulfonic acid, and phosphonic acid groups. Common global suppliers of antiscalants include Kurita Water Industries, Avista, Nalco, and

Veolia Veolia Environnement S.A., branded as Veolia, is a French transnational company with activities in three main service and utility areas traditionally managed by public authorities – water management, waste management and energy services. In ...

Chemistry and mechanism

These compounds work by various mechanisms such as suppression of crystallization, dispersion and crystal distortion.

Suppression of crystallization

Antiscalants contain molecules that can complex with metal ions present in the water, preventing them from participating in scale formation reactions. Phosphonates and polyphosphates are particularly effective in sequestering

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

, and other metal ions.

Dispersion

Antiscalants may also work by dispersing small-scale particles, preventing them from agglomerating and forming larger, more problematic deposits. Polymers are often used for their dispersing properties.

Crystal modification

Some antiscalants alter the crystal structure of scale-forming salts, making them less likely to adhere to surfaces and form stubborn deposits. At a submicroscopic level, these soft non-adherent scales with antiscalant use would appear distorted, more oval in shape and less compact.

Applications

Reverse osmosis and desalination

reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane, semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distribu ...

(RO) and

desalination Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is Soil salinity control, soil desalination. This is important for agric ...

plants, antiscalants are vital for preventing scale formation on membrane surfaces. Scaling can severely impair the efficiency of these processes and lead to increased maintenance costs. Antiscalants help maintain optimal performance and prolong the lifespan of membranes. Scales form in the RO or desalination plants occurs when the ionic product of sparingly dissolved salts in the concentrated flow equals or exceeds its solubility product. The extent and degree of scaling phenomena are determined not only by the

supersaturation In physical chemistry, supersaturation occurs with a solution (chemistry), solution when the concentration of a solute exceeds the concentration specified by the value of solubility at Solubility equilibrium, equilibrium. Most commonly the term ...

conditions that occurred, but also by the precipitation kinetics.

Water treatment

Scale deposition in

boilers A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central ...

can reduce heat transfer efficiency and increase energy consumption. Antiscalants are added to

boiler feedwater Boiler feedwater is the water which is supplied to a boiler. The feed water is put into the steam drum from a feed pump. In the steam drum the feed water is then turned into steam from the heat. After the steam is used, it is then dumped to the ...

to prevent scale formation on heat transfer surfaces, piping, and other boiler components.

Water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, ...

plants can use antiscalants to maintain filtration.

Cooling water systems

Industrial cooling water systems are susceptible to scale formation due to high temperatures and concentrations of dissolved minerals. Antiscalants help mitigate scale deposition in cooling towers, heat exchangers, and condensers, preserving their efficiency and reducing the need for maintenance.

Mining and oil and gas industry

Antiscalants are used in mining operations and oil & gas production to prevent scale deposition in pipelines, drilling equipment, and processing facilities. Scaling in these industries can lead to decreased flow rates, equipment damage, and production downtime. Preventing the formation of scale from blocking or hindering fluid flow through pipelines, valves, and pumps used in oil production and processing. Oilfield scaling is the

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

and accumulation of insoluble crystals (salts) from a mixture of incompatible

aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in wat ...

phases in oil processing systems.

References

{{reflist Industrial water treatment