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Productos quimicos para el tratamiento de agua

Para el tratamiento quimico de agua una gran variedad de productos quimicos se pueden aplicar. A continuación, los diferentes tipos de productos quimicos para el tratamiento de agua están resumidos.
Proveedor:

Avista   

GE        

Ropur      

Algicidas

Alguicidas son productos químicos que matan a algas, tanto a las azules como a las verdes, cuando se añaden al agua. Algunos ejemplos son sulfato de cobre , sales de hierro, sales de amina de colofonia y cloruro de benzalconio. Alguicidas son eficaces contra las algas, pero no son muy útil para las floraciones de algas por razones medioambientales.
El problema con la mayoria de las alguicidas es que matan a todas las algas presentes, pero no eliminan las toxinas que son liberadas por las algas antes de morir.

Antiespumantes

La espuma es una masa de burbujas creadas cuando ciertos tipos de gases se dispersan en un líquido. Las películas fuertes de liquido que rodean las burbujas forman grandes volúmenes de espuma no productiva.
La causa de la espuma es un estudio complicado en la química física, pero ya sabemos que su existencia plantea serios problemas tanto en la operación de los procesos industriales como en la calidad de los productos terminados. Cuando no se mantiene bajo control, la espuma puede reducir la capacidad del equipo y aumentar la duracion y costes de los procesos.
Las mezclas de antiespumantes contienen aceites combinados con pequeñas cantidades de sílice. Descomponen la espuma gracias a dos propiedades de la silicona: incompatibilidad con sistemas acuosos y facilidad de propagacion. Los compuestos antiespumantes están disponibles ya sea como polvo o como una emulsión del producto puro.


Polvo
Los antiespumantes en polvo cubren un grupo de productos basados en polidimetilsiloxano modificado. Los productos varían en sus propiedades basicas, pero como grupo introducen excelentes propiedades antiespumantes en una amplia gama de aplicaciones y condiciones. Los antiespumantes son químicamente inertes y no reaccionan con el medio en el que se elimina la espuma.
Son inodoro, insípido, no volátiles, no tóxicos y los materiales no se corroen. El unico inconveniente de el producto en polvo es que no se puede utilizar en soluciones acuosas.

Emulsiones
Las emulsiones antiespumantes son emulsiones acuosas de fluidos de polidimetilsiloxano. Tienen las mismas propiedades que la forma de polvo, la unica diferencia es que tambien se pueden aplicar en soluciones acuosas.

Biocidas

Véase desinfectantes

Información detallada sobre biocides tambien esta disponible aqui.

Productos quimicos para agua de caldera

Productos químicos para agua de caldera incluyen todas las sustancias químicas que se utilizan en las siguentes aplicaciones:
· Captación de Oxígeno;
· Inhibición de incrustación;
· Inhibición de corrosión;
· Antiespumantes;
· Control de alcalinidad.

Coagulants

Cuando se refiere a coagulantes, los iones positivos con valencia alta son preferidos. Generalmente se aplican aluminio y hierro, aluminio como Al2(SO4)3- (aluin) y hierro, ya sea como FeCl o Fe2(SO4)3-. Tambien se puede aplicar la forma relativamente barata de FeSO4, a condicion de que se oxida a Fe3+ durante la aireación.
La coagulación depende mucho de la dosis de los coagulantes, el pH y las concentraciones de los coloides. Para ajustar los niveles de pH Ca(OH) se aplica como co-floculante. Las dosis varían generalmente entre 10 y 90 mg Fe3+/ L, pero cuando hay sales presentes se debe aplicar una dosis mas alta.

Inhibidores de corrosión

La corrosión es un termino general que indica la conversión de un metal en un compuesto soluble.
La corrosión puede causar fallos en las zonas criticas de sistemas de calderas, deposición de productos de corroción en zonas criticas de intercambio de calor y perdida de eficiencia global.
Esto es la razon por la que inhibidores de corroción se aplican a menudo. Inhibidores son productos químicos que reaccionan con una superficie metálica, dando un cierto nivel de protección a la superficie. Inhibidores trabajan a menudo mediante la adsorción de si mismos sobre la superficie metálica, protegiendo la superficie metálica a tráves de la formación de una película delgada. 

Hay cinco tipos diferentes de inhibidores de corrosión. Estos son:
1) Passivity inhibitors (passivators). These cause a shift of the corrosion potential, forcing the metallic surface into the passive range. Examples of passivity inhibitors are oxidizing anions, such as chromate, nitrite and nitrate and non-oxidizing ions such as phosphate and molybdate. These inhibitors are the most effective and consequently the most widely used.
2) Cathodic inhibitors. Some cathodic inhibitors, such as compounds of arsenic and antimony, work by making the recombination and discharge of hydrogen more difficult. Other cathodic inhibitors, ions such as calcium, zinc or magnesium, may be precipitated as oxides to form a protective layer on the metal.
3) Organic inhibitors. These affect the entire surface of a corroding metal when present in certain concentration. Organic inhibitors protect the metal by forming a hydrophobic film on the metal surface. Organic inhibitors will be adsorbed according to the ionic charge of the inhibitor and the charge on the surface.
4) Precipitation inducing inhibitors. These are compounds that cause the formation of precipitates on the surface of the metal, thereby providing a protective film.
The most common inhibitors of this category are silicates and phosphates.
5) Volatile Corrosion Inhibitors (VCI). These are compounds transported in a closed environment to the site of corrosion by volatilisation from a source. Examples are morpholine and hydrazine and volatile solids such as salts of dicyclohexylamine, cyclohexylamine and hexamethylene-amine. On contact with the metal surface, the vapour of these salts condenses and is hydrolysed by moist, to liberate protective ions.

Disinfectants

Disinfectants kill present unwanted microrganisms in water. There are various different types of disinfectants:
· Chlorine (dose 2-10 mg/L)
· Chlorine dioxide
· Ozone
· Hypochlorite

Chlorine dioxide disinfection
ClO2 is used principally as a primary disinfectant for surface waters with odor and taste problems. It is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. ClO2 penetrates the bacterial cell wall and reacts with vital amino acids in the cytoplasm of the cell to kill the organisms. The by-product of this reaction is chlorite.
Chlorine dioxide disinfects according to the same principle as chlorine, however, as opposed to chlorine, chlorine dioxide has no harmful effects on human health.

Hypochlorite disinfection
Hypochlorite is aplied in the same way as chlorine dioxide and chlorine. Hypo chlorination is a disinfection method that is not used widely anymore, since an environmental agency proved that the Hypochlorite for disinfection in water was the cause of bromate consistence in water.

Ozone disinfection
Ozone is a very strong oxidation medium, with a remarkably short life span. It consists of oxygen molecules with an extra O-atom, to form O3. When ozone comes in contact with odour, bacteria or viruses the extra O-atom breaks them down directly, by means of oxidation. The third O-atom of the ozone molecules is than lost and only oxygen will remain.

Disinfectants can be used in various industries. Ozone is used in the pharmaceutical industry, for drinking water preparation, for treatment of process water, for preparation of ultra-pure water and for surface disinfection.
Chlorine dioxide is used primarily for drinking water preparation and disinfection of piping.

Every disinfection technique has its specific advantages and its own application area. In the table below some of the advantages and disadvantages are shown:

Technology Environmentally friendly Byproducts Effectivity Investment Operational costs Fluids Surfaces
Ozone

+

+

++

-

+

++

++

UV

++

++

+

+/-

++

+

++

Chlorine dioxide

+/-

+/-

++

++

+

++

--

Chlorine gas

--

--

-

+

++

+/-

--

Hypochlorite

--

--

-

+

++

+/-

--

Flocculants

To promote the formation of flocs in water that contains suspended solids polymer flocculants (polyelectrolytes) are applied to promote bonds formation between particles. These polymers have a very specific effect, dependent upon their charges, their molar weight and their molecular degree of ramification. The polymers are water-soluble and their molar weight varies between 105 and 106 g/ mol.
There can be several charges on one flocculent. There are cationic polymers, based on nitrogen, anionic polymers, based on carboxylate ions and polyampholytes, which carry both positive and negative charges.

Neutralizing agents (alkalinity control)

In order to neutralize acids and basics we use either sodium hydroxide solution (NaOH), calcium carbonate, or lime suspension (Ca(OH)2) to increase pH levels. We use diluted sulphuric acid (H2SO4) or diluted hydrochloric acid (HCl) to decline pH levels. The dose of neutralizing agents depends upon the pH of the water in a reaction basin. Neutralization reactions cause a rise in temperature.

Oxidants

Chemical oxidation processes use (chemical) oxidants to reduce COD/BOD levels, and to remove both organic and oxidisable inorganic components. The processes can completely oxidise organic materials to carbon dioxide and water, although it is often not necessary to operate the processes to this level of treatment
A wide variety of oxidation chemicals are available. Examples are:
· Hydrogen peroxide;
· Ozone;
· Combined ozone & peroxide;
· Oxygen.

Hydrogen peroxide
Hydrogen peroxide is widely used thanks to its properties; it is a safe, effective, powerful and versatile oxidant. The main applications of H2O2 are oxidation to aid odour control and corrosion control, organic oxidation, metal oxidation and toxicity oxidation. The most difficult pollutants to oxidize may require H2O2 to be activated with catalysts such as iron, copper, manganese or other transition metal compounds.

Ozone
Ozone cannot only be applied as a disinfectant; it can also aid the removal of contaminants from water by means of oxidation. Ozone then purifies water by breaking up organic contaminants and converting inorganic contaminants to an insoluble form that can then be filtered out. The Ozone system can remove up to twenty-five contaminants.
Chemicals that can be oxidized with ozone are:
· Absorbable organic halogens;
· Nitrite;
· Iron;
· Manganese;
· Cyanide;
· Pesticides;
· Nitrogen oxides;
· Odorous substances;
· Chlorinated hydrocarbons;
· PCB's.

Oxygen
Oxygen can also be applied as an oxidant, for instance to realize the oxidation of iron and manganese. The reactions that occur during oxidation by oxygen are usually quite similar.
These are the reactions of the oxidation of iron and manganese with oxygen:
2 Fe2+ + O2 + 2 OH- -> Fe2O3 + H2O
2 Mn2+ + O2 + 4 OH- -> 2 MnO2 + 2 H2O

Oxygen scavengers

Oxygen scavenging means preventing oxygen from introducing oxidation reactions. Most of the naturally occurring organics have a slightly negative charge. Due to that they can absorb oxygen molecules, because these carry a slightly positive charge, to prevent oxidation reactions from taking place in water and other liquids.
Oxygen scavengers include both volatile products, such as hydrazine (N2H4) or other organic products like carbohydrazine, hydroquinone, diethylhydroxyethanol, methylethylketoxime, but also non-volatile salts, such as sodium sulphite (Na2SO3) and other inorganic compounds, or derivatives thereof. The salts often contain catalysing compounds to increase the rate of reaction with dissolved oxygen, for instance cobalt chloride.

pH conditioners

Municipal water is often pH-adjusted, in order to prevent corrosion from pipes and to prevent dissolution of lead into water supplies. During water treatment pH adjustments may also be required. The pH is brought up or down through addition of basics or acids. An example of lowering the pH is the addition of hydrogen chloride, in case of a basic liquid. An example of bringing up the pH is the addition of natrium hydroxide, in case of an acidic liquid.
The pH will be converted to approximately seven to seven and a half, after addition of certain concentrations of acids or basics. The concentration of the substance and the kind of substance that is added, depend upon the necessary decrease or increase of the pH.

Resin cleaners

Ion exchange resins need to be regenerated after application, after that, they can be reused. But every time the ion exchangers are used serious fouling takes place. The contaminants that enter the resins will not be removed through regeneration; therefore resins need cleaning with certain chemicals.
Chemicals that are used are for instance sodium chloride, potassium chloride, citric acid and chlorine dioxide.
Chlorine dioxide cleansing serves the removal of organic contaminants on ion exchange resins. Prior to every cleaning treatment resins should be regenerated. After that, in case chlorine dioxide is used, 500 ppm of chlorine dioxide in solution is passed through the resin bed and oxidises the contaminants.

Scale inhibitors

Scale is the precipitate that forms on surfaces in contact with water as a result of the precipitation of normally soluble solids that become insoluble as temperature increases. Some examples of scale are calcium carbonate, calcium sulphate, and calcium silicate.
Scale inhibitors are surface-active negatively charged polymers. As minerals exceed their solubility's and begin to merge, the polymers become attached. The structure for crystallisation is disrupted and the formation of scale is prevented. The particles of scale combined with the inhibitor will than be dispersed and remain in suspension.
Examples of scale inhibitors are phosphate esters, phosphoric acid and solutions of low molecular weight polyacrylic acid.

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