عدد المساهمات : 3514
تاريخ التسجيل : 15/09/2009
العمر : 49
الموقع : مصر
|موضوع: البيروكسيد السبت أكتوبر 30, 2010 2:31 pm|| |
the characteristics of hydrogen peroxide
Peroxide is a chemical compound that contains the peroxide ion (O22-).
The peroxide ion consists of a single bond between two oxygen atoms: (O-O)2-. It is a strong oxidiser.
Hydrogen peroxide has the chemical formula H2O2 and the following structural formula:
The hydrogen peroxide molecule contains one extra oxygen atom, compared to the more stable water molecule. The bond between the two oxygen atoms, the so-called peroxide bond, is broken while two H-O radicals are formed. These radicals quickly react with other substances, while new radicals are formed and a chain reaction takes place. Hydrogen peroxide solutions look like water and can be dissolved in water unrestrainedly. At high concentrations these solutions give off an irritating, acidic smell. Hydrogen peroxide is inflammable. At low temperatures it becomes solid. The amount of hydrogen peroxide in the solution is expressed in weight percentage. For water treatment, concentrations of 35 or 50 % hydrogen peroxide are used.
Hydrogen peroxide is used for different applications, because it is very selective. By changing the reaction conditions (temperature, pH, dose, reaction time and the addition of a catalyser), hydrogen peroxide will attack different pollutions.
Corrosiveness of hydrogen peroxide
The corrosiveness of process water due to hydrogen peroxide depends on the amount of dissolved oxygen that is produced. Oxygen corrodes iron-containing metals. The amount of iron and the pH are a greater influence on corrosiveness than the concentration of hydrogen peroxide is.
hydrogen peroxide dosed
Most hydrogen peroxide applications consist of hydrogen peroxide injection into flowing water. No other chemicals or equipment are required. This application is used to control biological growth, to add oxygen, to remove chlorine residues and to oxidize sulphides, sulphites, metals and other easily oxidized materials. The suitability of hydrogen peroxide for these applications is influenced by pH, temperature and reaction time.
Catalytic hydrogen peroxide
Pollutions that are not easily oxidized, require hydrogen peroxide activation by catalysers (iron, manganese or other metalloids). These catalysers can also be used to enhance hydrogen peroxide reactions, which would otherwise take hours or days.
advanced oxidation processes
Advanced oxidation processes are a new development in the field of hydrogen peroxide disinfection. These processes produce reactive oxygen radicals, without the interference of metal catalysers. Examples are the combination of hydrogen peroxide with ozone (peroxone) or Ultra Violet Light. The result of these methods is far-reaching oxidation of difficultly degradable substances, without the production of residues or sludge. These methods are used worldwide for groundwater treatment, for drinking water and process water treatment and for organic matter disinfection and removal from industrial wastewater.
hydrogen peroxide disinfection work
Among other applications, hydrogen peroxide is used as a disinfectant. It is used to treat inflammation of the gums and to disinfect (drinking) water. It is also used to combat excessive microbial growth in water systems and cooling towers.
In the United States, hydrogen peroxide is used more and more frequently to treat individual water supplies. It is used to prevent the formation of colors, tastes, corrosion and scaling by pollution degradation (iron, manganese, sulphates) and micro-organism degradation. Hydrogen peroxide reacts very fast. It will than disintegrate into hydrogen and water, without the formation of byproducts. This increases the amount of oxygen in water.
The disinfection mechanism of hydrogen peroxide is based on the release of free oxygen radicals:
H2O2 → H2O + O2
Pollutions are decomposed by free oxygen radicals, and only water remains. Free radicals have both oxidising and disinfecting abilities. Hydrogen peroxide eliminates proteins through oxidation.
Peroxides such as hydrogen peroxide (H2O2), perborate, peroxiphosphate and persulphate, are good disinfectants and oxidisers. In general these can adequately remove micro-organisms. However, these peroxides are very unstable.
Perborates are very toxic. Peracetic acid (PAA) is a strong acid. It can be very agressive in its pure form. Stabilised persulphates can be used to replace chlorine for waste water treatment.
hydrogen peroxide used for drinking water disinfection
hydrogen peroxide was first used for drinking water disinfection in Eastern Europe. It is known for its high oxidative and biocidal efficiency. Hydrogen peroxide has not been used often for drinking water disinfection, but it's popularity seems to increase. It is often used combined with ozone, silver orUV.
hydrogen peroxide used for swimming pool disinfection
The application of peroxides for disinfection and water treatment are limited. Recently, more stable forms have been developed, which can be used for application in swimming pools.
Hydrogen peroxide disinfection requires a high dose. The main disadvantage is the small disinfecting and oxidising ability of hydrogen peroxide at active concentrations (tens of milligrams per litre), which are required for swimming pool disinfection. Another problem is the quick decomposition of hydrogen peroxide in water and the presence of oxygen radicals. Through stabilizer addition, the decomposition of hydrogen peroxide is delayed and the disinfection ability can be maintained.
Compared with chlorine, bromine, ozone and other disinfectants, hydrogen peroxide is not a very powerful disinfectant. Swimming pools disinfection by hydrogen peroxide is not allowed, unless it is used in combination with other disinfectants (UV, ozone, silver salts or ammonia quart salts). Hydrogen peroxide improves the disinfection ability of other disinfectants.
hydrogen peroxide be used for cooling tower water disinfection
Hydrogen peroxide can be used for cooling tower water disinfection, when it is combined with other disinfectants. Peracetic acid (CH3COOH, PAA) can also be used for cooling tower water disinfection.
hydrogen peroxide remove chlorine
Hydrogen peroxide can be used for dechlorination, in other words to remove residual chlorine. Residual chlorine forms corrosive acids when it is oxidised by air or condensates on process systems.
When chlorine reacts with hydrogen peroxide, hydrogen peroxide falls apart into water and oxygen. Chlorine gas hydrolyses into hypochlorous acid (HOCl), which subsequently ionises into hypochlorite ions (OCl).
Cl2 + HOCl + H+ + Cl
HOCl + H+ + Cl
After tha, hydrogen peroxide reacts with hypochlorite:
OCl- + H2O2 (g) -> Cl- + H2O + O2
The reaction between hydrogen peroxide and hypochlorite takes place very quickly. Other organic and inorganic substances cannot react with hypochlorite.
the advantages and disadvantages of hydrogen peroxide use
Contrary to other chemical substances, hydrogen peroxide does not produce residues or gasses. Safety depends on the applied concentration, because hydrogen peroxide is completely water soluble.
Hydrogen peroxide is a powerful oxidizer. It reacts with a variety of substances. It is therefore diluted during transport, as a safety measure. However, for hydrogen peroxide disinfection, high concentrations are required.
Hydrogen peroxide slowly decomposes into water and oxygen. An elevation of temperature and the presence of pollutions enhance this process.
The concentration of hydrogen peroxide in a solution slowly decreases. This is caused by the following reaction:
2 H2O2 → 2 H2O + O2
This is a redox reaction. Hydrogen molecules partly function as reductors and partly as oxidizers.
hydrogen peroxide efficient
The efficiency of hydrogen peroxide depends on several factors, such as pH, catalysers, temperature, peroxide concentration and reaction time.