Sodium hypochlorite pH. Other directions of use. When was sodium hypochlorite discovered?

The results of determining the main indicators of the quality of the studied solutions are given in table.4.

2.2. Determination of the rate of decomposition of HCN solutions

Determination of the decomposition rate of hypochlorite solutions was determined in two ways:

1. At room temperature (for samples No. 1 and 2). At the same time, one sample of each HCN sample was stored in natural conditions (during the day - in the light), and the second sample was constantly in the dark.
2. At a temperature of 55 ° C (test speed). In this case, the duration of the test is 7 hours. Corresponds to the duration of storage in the dark equal to 1 year.

The results of determining the rate of decomposition of HCN solutions at room temperature are given in Table 5. Data on the rate of decomposition of HCN solutions of all three samples at a temperature of 55 ° C are given in Table 6. Unfortunately, the tests of sample No. 3 were terminated prematurely (a power outage due to an accident at an electrical distribution substation). However, the data obtained made it possible to calculate the percentage of HCN No. 3 solution for a test period of 3 hours, that is, about 4 months of storage at room temperature (the data are given in Table 4 in brackets).

Table 5. Experimental data on the decomposition rate of sodium hypochlorite at room temperature Table 5. Experimental data on the decomposition rate of sodium hypochlorite at room temperature

Table 6. Data on the rate of decomposition of sodium hypochlorite at a temperature of 55 ° C

Assessment of the initial quality of the imported HCN solution

The assessment of the initial content of active chlorine (AC) and sodium chloride in the imported HCHN solution was carried out on the basis of the following considerations:

1. According to the customer, a batch of sodium hypochlorite arrived from abroad at the end of July this year. Considering that for some, maybe a short time, the product was in the manufacturer's warehouse and transported, then as of the time of measurements (05.09.01) the total time of its storage and transportation was approximately equal to 60 days.
2. According to the results of the two-week stability tests given in the table, it was assumed that the loss of active chlorine over these 60 days was on average 120-109,65 \u003d 0.69 g / dm 3 per day.

   (average value for storage in the light and in the dark).

3. From these considerations, the initial content of active chlorine in the imported product was calculated, equal to
   120 + 0.69 * 60 \u003d 161.4 g / dm 3

Assuming that the decomposition of sodium hypochlorite occurs mainly by the reaction

2NaClO -2NaCl+O2

it is possible to estimate the initial content of sodium chloride in the initial HCN solution from the following considerations. For 1 g-mol of NaClO (74.5), its decomposition yields 1 g-mol of sodium chloride (58.5). Thus, the conversion factor is 0.785. Hence, the initial content of sodium chloride in the product is 179-0.785*0.69*74.5/51.5*60=179-47=132 g/dm 3

The values ​​obtained are close to the values ​​of active chlorine and sodium chloride in a sodium hypochlorite solution prepared at OAO Skoropuskovsky Pilot Plant (see Table 4).

DISCUSSION OF THE OBTAINED RESULTS

Comparison of the quality of the studied HCN solutions

First of all, the sharp difference between the samples of solutions No. 1 and No. 2 in appearance attracts attention. The light yellow imported product accordingly has a high light transmission coefficient (98%), and the product manufactured by Sintez OJSC, which is a slightly transparent liquid of dark red color, has a light transmission coefficient of 31%. As follows from the data given in Table 4, this is directly related to the content of iron in solutions. According to (2), the maximum allowable iron content in HCN solutions should not exceed 0.005 mg/dm requirements for sodium hypochlorite as a chemical product having high service properties.

Sodium hypochlorite solution manufactured by SOZ OJSC (sample No. 3) according to this indicator close to imported: color - light yellow, light transmission coefficient - 88%. The iron content in this solution is 0.0047 mg/dm 3 , which meets the requirements given in (d). The presence of iron in the HCN solution reduces its stability. This, in particular, is evidenced by the data on the rates of decomposition of the investigated solutions of HCN, given in Table. 5 and 6. Their values ​​for samples No. 1 and 3 are significantly lower than for sample No. 2, but very close to each other. From this we can make an unambiguous conclusion that the requirements for HCN solutions according to (3) are significantly inferior to the requirements for the service properties of solutions required by the industry and are based on the capabilities of technologies adopted at manufacturing enterprises. former USSR and were known to be at a low level.

The initial content of active chlorine in the samples of HCN solutions No. 1 and 3 is less than in sample No. 2. The content of sodium chloride in them corresponds to the stoichiometric. At the same time, in sample No. 2, in which the content of active chlorine is approximately 1.16 times greater than in samples No. 1 and 3, the content of sodium chloride is 1.21 times higher than the stoichiometric ratio (177 g / dm 3 instead of 146 g / dm 3), which additionally indicates a low level of production culture, in particular, the lack of control over the temperature level of the technological process.

Thus, we can conclude that sodium hypochlorite, manufactured at POPs using the technology of the DiL Prospecten company (sample No. 3), is practically similar to the imported product _ sodium hypochlorite from the Bayer company (Germany). Moreover, despite the absence of special preservative additives, sodium hypochlorite (sample No. 3) is more stable than the German one and its guaranteed shelf life exceeds the German one by two to three months.

Research group

GOSNII "Chlorproekt"

Structural formula

Molecular weight: 74.442

Sodium hypochlorite(sodium hypochlorous acid) - NaOCl, inorganic compound, sodium salt of hypochlorous acid. The trivial (historical) name of an aqueous solution of salt is "Labarrac water" or "javel water". The compound in the free state is very unstable, usually used as a relatively stable NaOCl 5H2O pentahydrate or an aqueous solution, which has a characteristic pungent chlorine odor and is highly corrosive. The compound is a strong oxidizing agent, contains 95.2% active chlorine. It has antiseptic and disinfectant action. It is used as a household and industrial bleach and disinfectant, a water purification and disinfection agent, an oxidizing agent for some industrial chemical production processes. As a bactericidal and sterilizing agent, it is used in medicine, food industry and agriculture. According to The 100 Most Important Chemical Compounds (Greenwood Press, 2007), sodium hypochlorite is one of the 100 most important chemical compounds.

Discovery history

Chlorine was discovered in 1774 by the Swedish chemist Carl Wilhelm Scheele. After 11 years in 1785 (according to other sources - in 1787), another chemist, the Frenchman Claude Louis Berthollet, discovered that an aqueous solution of this gas (see equation (1)) has bleaching properties:

Cl+H 2 O=HCl+HOCl

The small Parisian enterprise Societé Javel, opened in 1778 on the banks of the Seine and headed by Leonard Alban, adapted Berthollet's discovery to industrial conditions and began to produce bleaching liquid by dissolving chlorine gas in water. However, the resulting product was very unstable, so the process was modified in 1787. Chlorine was passed through an aqueous solution of potash (potassium carbonate), resulting in a stable product with high bleaching properties. Alban called it "Eau de Javel" ("javel water"). The new product became instantly popular in France and England due to its ease of transportation and storage.

In 1820, the French pharmacist Antoine Labarraque replaced potash with cheaper caustic soda (sodium hydroxide). The resulting sodium hypochlorite solution was named "Eau de Labarraque" ("Labarraque water"). It became widely used for bleaching and disinfection.

Despite the fact that the disinfecting properties of hypochlorite were discovered in the first half of the 19th century, its use for the disinfection of drinking water and wastewater treatment began only at the end of the century. The first water purification systems were opened in 1893 in Hamburg; In the United States, the first plant for the production of purified drinking water appeared in 1908 in Jersey City.

Physical properties

Anhydrous sodium hypochlorite is an unstable colorless crystalline substance.

Elemental composition: Na (30.9%), Cl (47.6%), O (21.5%).

Very soluble in water: 53.4 g in 100 grams of water (130 g per 100 g of water at 50 °C).

The compound has three crystalline hydrates:

• monohydrate NaOCl H 2 O - extremely unstable, decomposes above 60 ° C, at higher temperatures - with an explosion
• NaOCl 2.5H 2 O - more stable, melts at 57.5 °C.

NaOCl 5H 2 O pentahydrate - the most stable form, is a pale greenish-yellow (technical quality - white) rhombic crystals (a = 0.808 nm, b = 1.606 nm, c = 0.533 nm, Z = 4). Non-hygroscopic, highly soluble in water (in g / 100 grams of water, in terms of anhydrous salt): 26 (-10 ° C), 29.5 (0 ° C), 38 (10 ° C), 82 (25 ° C), 100 (30°C). In the air, it blurs, turning into a liquid state, due to rapid decomposition. Melting point: 24.4 °C (according to other sources: 18 °C), decomposes when heated (30-50 °C).

Density of an aqueous solution of sodium hypochlorite at 18 °C:

Freezing point of aqueous solutions of sodium hypochlorite of various concentrations:

Thermodynamic characteristics of sodium hypochlorite in an infinitely dilute aqueous solution:

• standard enthalpy of formation, ΔHo 298: −350.4 kJ/mol;
• standard Gibbs energy, ΔGo 298: −298.7 kJ/mol.

Chemical properties

Decomposition and disproportionation Sodium hypochlorite is an unstable compound that easily decomposes with the release of oxygen. Spontaneous decomposition occurs slowly even at room temperature: in 40 days, pentahydrate (NaOCl · 5H 2 O) loses 30% of active chlorine. At a temperature of 70 °C, the decomposition of anhydrous hypochlorite proceeds with an explosion. When heated, a disproportionation reaction occurs in parallel.

Hydrolysis and decomposition in aqueous solutions

Dissolving in water, sodium hypochlorite dissociates into ions. Since hypochlorous acid (HOCl) is very weak (pKa = 7.537), the hypochlorite ion undergoes hydrolysis in an aqueous medium.

It is the presence of hypochlorous acid in aqueous solutions of sodium hypochlorite that explains its strong disinfecting and bleaching properties. Aqueous solutions of sodium hypochlorite are unstable and decompose over time even at normal temperatures (0.085% per day). Decay accelerates illumination, heavy metal ions and chlorides alkali metals; on the contrary, magnesium sulfate, orthoboric acid, silicate and sodium hydroxide slow down the process; in this case, solutions with a strongly alkaline medium (pH > 11) are the most stable.

Oxidizing properties

An aqueous solution of sodium hypochlorite is a strong oxidizing agent that enters into numerous reactions with various reducing agents, regardless of the acid-base nature of the medium.

Identification

Among the qualitative analytical reactions to hypochlorite ion, one can note the precipitation of a brown precipitate of metahydroxide when the test sample is added at room temperature to an alkaline solution of monovalent thallium salt (detection limit 0.5 µg of hypochlorite).

Another option is a starch iodo reaction in a strongly acidic medium and a color reaction with 4,4'-tor n, n'-dioxytriphenylmethane in the presence of potassium bromate. common method quantitative analysis sodium hypochlorite in solution is a potentiometric analysis by adding the analyzed solution to the standard solution (MDA) or the method of reducing the concentration of the analyzed solution by adding it to the standard solution (MBA) using a bromine-ion-selective electrode (Br-ISE). A titrimetric method using potassium iodide (indirect iodometry) is also used.

Corrosion

Sodium hypochlorite has a fairly strong corrosive effect on various materials, as evidenced by the data below:

Physiological and environmental effects

NaOCl is one of the best known agents, exhibiting strong antibacterial activity due to the hypochlorite ion. It kills microorganisms very quickly and already at very low concentrations. The highest bactericidal ability of hypochlorite is manifested in a neutral environment, when the concentrations of HClO and hypochlorite anions ClO− are approximately equal (see subsection "Hydrolysis and decomposition in aqueous solutions"). The decomposition of hypochlorite is accompanied by the formation of a number of active particles and, in particular, singlet oxygen, which has a high biocidal effect. The resulting particles take part in the destruction of microorganisms, interacting with biopolymers in their structure that are capable of oxidation. Research has established that this process is similar to what occurs naturally in all higher organisms. Some human cells (neutrophils, hepatocytes, etc.) synthesize hypochlorous acid and associated highly active radicals to fight microorganisms and foreign substances. Yeast-like fungi that cause candidiasis, Candida albicans, die in vitro within 30 seconds when exposed to a 5.0-0.5% NaOCl solution; at a concentration of the active substance below 0.05%, they show stability 24 hours after exposure. Enterococci are more resistant to the action of sodium hypochlorite. For example, pathogenic Enterococcus faecalis dies 30 seconds after treatment with a 5.25% solution and 30 minutes after treatment with a 0.5% solution. Gram-negative anaerobic bacteria such as Porphyromonas gingivalis, Porphyromonas endodontalis and Prevotella intermedia die within 15 seconds after treatment with 5.0-0.5% NaOCl solution. Despite the high biocidal activity of sodium hypochlorite, it should be borne in mind that some potentially dangerous protozoa, such as giardiasis or cryptosporidiosis pathogens, are resistant to its action. High oxidizing properties sodium hypochlorite allow it to be successfully used to neutralize various toxins. The table below shows the results of toxin inactivation during 30-minute exposure to various concentrations of NaOCl (“+” - the toxin was inactivated; “-” - the toxin remained active). Sodium hypochlorite can have harmful effects on the human body. NaOCl solutions can be hazardous by inhalation due to the possibility of releasing toxic chlorine (irritant and asphyxiant). Direct contact with hypochlorite in the eyes, especially at high concentrations, can cause chemical burns and even lead to partial or complete loss of vision. Household bleaches based on NaOCl can cause skin irritation, while industrial bleaches can lead to serious ulcers and tissue death. Ingestion of dilute solutions (3-6%) of sodium hypochlorite usually leads only to irritation of the esophagus and sometimes acidosis, while concentrated solutions can cause quite serious damage, up to perforation of the gastrointestinal tract. Despite its high chemical activity, the safety of sodium hypochlorite for humans has been documented by studies by poison control centers in North America and Europe, which show that the substance at working concentrations does not carry any serious health effects after unintentional ingestion or contact with the skin. It is also confirmed that sodium hypochlorite is not mutagenic, carcinogenic and teratogenic, as well as a skin allergen. The International Agency for Research on Cancer has concluded that drinking water treated with NaOCl does not contain human carcinogens.

Oral toxicity of the compound:

• Mice: LD 50(English) LD 50) = 5800 mg/kg;
• Human (women): minimum known toxic dose eng. (English) TD Lo) = 1000 mg/kg.

Intravenous toxicity of the compound:

• Human: minimum known toxic dose TD Lo) = 45 mg/kg.

During normal household use, sodium hypochlorite breaks down in the environment into table salt, water and oxygen. Other substances may be formed in small quantities. According to the Swedish Institute for Environmental Research, sodium hypochlorite is unlikely to create environmental issues when used in the recommended order and quantities. Sodium hypochlorite poses no fire hazard.

industrial production

World production

Estimating the world volume of sodium hypochlorite production presents a certain difficulty due to the fact that a significant part of it is produced by the electrochemical method according to the “in situ” principle, that is, at the place of its direct consumption (we are talking about the use of the compound for disinfection and water treatment). As of 2005, the estimated global production of NaOCl was about 1 million tons, with almost half of this volume used for domestic use and the other half for industrial use.

Overview of industrial production methods

The outstanding bleaching and disinfecting properties of sodium hypochlorite led to an intensive growth in its consumption, which in turn gave an impetus to the creation of large-scale industrial production.

In modern industry, there are two main methods for the production of sodium hypochlorite:

• chemical method - chlorination of aqueous solutions of sodium hydroxide;
• electrochemical method - electrolysis of an aqueous solution of sodium chloride.

Application

Overview of areas of use

Sodium hypochlorite is the undisputed leader among hypochlorites of other metals of industrial importance, occupying 91% of the world market. Almost 9% remains for calcium hypochlorite, potassium and lithium hypochlorites have insignificant volumes of use.

The entire wide range of use of sodium hypochlorite can be divided into three conditional groups:

• use for domestic purposes;
• use for industrial purposes;
• use in medicine.

Domestic use includes:

• use as a means for disinfection and antibacterial treatment;
• use for bleaching fabrics;
• chemical dissolution of sanitary deposits.

Industrial uses include:

• industrial bleaching of fabric, wood pulp and some other products;
• industrial disinfection and sanitation;
• purification and disinfection of drinking water for public water supply systems;
• cleaning and disinfection of industrial effluents;
• chemical production.

According to IHS experts, about 67% of all sodium hypochlorite is used as bleach and 33% for disinfection and cleaning needs, with the latter trending upward. The most common area of ​​industrial use of hypochlorite (60%) is the disinfection of industrial and domestic wastewater. The overall global growth in industrial consumption of NaOCl in 2012-2017 is estimated at 2.5% annually. Growth in global demand for sodium hypochlorite for domestic use in 2012-2017 is estimated at about 2% annually.

Application in household chemicals

Sodium hypochlorite finds wide application in household chemicals and is included as an active ingredient in numerous products intended for bleaching, cleaning and disinfecting various surfaces and materials. In the US, approximately 80% of all hypochlorite used by households is for household bleaching. Usually, solutions with a concentration in the range of 3 to 6% hypochlorite are used in everyday life. The commercial availability and high efficiency of the active substance determines its widespread use by various manufacturing companies, where sodium hypochlorite or products based on it are produced under various trademarks.

Application in medicine

The use of sodium hypochlorite for wound disinfection was first proposed no later than 1915. In modern medical practice, antiseptic solutions of sodium hypochlorite are used mainly for external and topical use as an antiviral, antifungal and bactericidal agent in the treatment of skin, mucous membranes and wounds. Hypochlorite is active against many gram-positive and gram-negative bacteria, most pathogenic fungi, viruses and protozoa, although its effectiveness is reduced in the presence of blood or its components. The low cost and availability of sodium hypochlorite makes it an important ingredient in maintaining high hygiene standards throughout the world. This is especially true in developing countries where the use of NaOCl has become a critical factor in stopping cholera, dysentery, typhoid fever and other aquatic biotic diseases. For example, with a cholera outbreak in countries Latin America and the Caribbean at the end of the 20th century, sodium hypochlorite was able to minimize morbidity and mortality, as reported at the Tropical Diseases Symposium held under the auspices of the Pasteur Institute. For medical purposes in Russia, sodium hypochlorite is used as a 0.06% solution for intracavitary and external use, as well as an injection solution. In surgical practice, it is used for the treatment, washing or drainage of surgical wounds and intraoperative sanitation of the pleural cavity with purulent lesions; in obstetrics and gynecology - for perioperative treatment of the vagina, treatment of bartholinitis, colpitis, trichomoniasis, chlamydia, endometritis, adnexitis, etc.; in otorhinolaryngology - for rinsing the nose and throat, instillation into the ear canal; in dermatology - for wet dressings, lotions, compresses for various types infections. In dental practice, sodium hypochlorite is most widely used as an antiseptic irrigation solution (NaOCl concentration 0.5-5.25%) in endodontics. The popularity of NaOCl is determined by the general availability and cheapness of the solution, as well as the bactericidal and antiviral effect against such dangerous viruses as HIV, rotavirus, herpes virus, hepatitis A and B viruses. There is evidence of the use of sodium hypochlorite for the treatment of viral hepatitis: it has a wide range of antiviral, detoxifying and antioxidant effects. NaOCl solutions can be used to sterilize some medical devices, patient care items, dishes, linen, toys, rooms, hard furniture, sanitary equipment. Due to its high corrosivity, hypochlorite is not used for metal appliances and tools. We also note the use of sodium hypochlorite solutions in veterinary medicine: they are used for disinfection of livestock buildings.

Industrial Application

Application as an industrial bleach

The use of sodium hypochlorite as a bleach is one of the priority areas industrial use along with disinfection and purification of drinking water. The world market in this segment alone exceeds 4 million tons. Usually, for industrial needs, bleach is used aqueous solutions NaOCl, containing 10-12% of the active substance. Sodium hypochlorite is widely used as a bleach and stain remover in the textile industry and industrial laundries and dry cleaners. It can be safely used on many types of fabrics including cotton, polyester, nylon, acetate, linen, viscose and more. It is very effective in removing soil and a wide range of stains including blood, coffee, grass, mustard, red wine, etc. Sodium hypochlorite is also used in the pulp and paper industry for wood pulp bleaching. NaOCl bleaching usually follows a chlorination step and is one of the wood chemical processing steps used to achieve high pulp whiteness. Processing of fibrous semi-finished products is carried out in special hypochlorite bleaching towers in an alkaline environment (pH 8-9), temperature 35-40 °C, for 2-3 hours. During this process, lignin is oxidized and chlorinated, as well as the destruction of the chromophore groups of organic molecules.

Use as an industrial disinfectant

The widespread use of sodium hypochlorite as an industrial disinfectant is associated primarily with the following areas:

• disinfection of drinking water before it is supplied to the distribution systems of urban water supply;
• disinfection and algaecidal water treatment of swimming pools and ponds;
• treatment of domestic and industrial waste water, purification from organic and inorganic impurities;
• in brewing, winemaking, dairy industry - disinfection of systems, pipelines, tanks;
• fungicidal and bactericidal treatment of grain;
• disinfection of water of fishery reservoirs;
• disinfection of technical premises.

Hypochlorite as a disinfectant is included in some automated in-line dishwashing products and some other liquid synthetic detergents. Industrial disinfectants and bleach solutions are available from many manufacturers under various brand names.

Use for water disinfection

Oxidative disinfection with the help of chlorine and its derivatives is perhaps the most common practical method of water disinfection, the beginning of the mass use of which by many countries Western Europe, USA and Russia dates back to the first quarter of the 20th century.

The use of sodium hypochlorite as a disinfectant instead of chlorine is promising and has a number of significant advantages:

• the reagent can be synthesized by the electrochemical method directly at the place of use from readily available table salt;
• the necessary indicators of the quality of drinking water and water for hydraulic structures can be achieved due to a smaller amount of active chlorine;
• the concentration of carcinogenic organochlorine impurities in water after treatment is significantly less;
• replacement of chlorine with sodium hypochlorite improves environmental situation and hygiene safety: [p. 36].
• hypochlorite has a wider range of biocidal action on various types of microorganisms with less toxicity;

For domestic water treatment purposes, dilute sodium hypochlorite solutions are used: the typical concentration of active chlorine in them is 0.2-2 mg/l versus 1-16 mg/l for chlorine gas. Dilution of industrial solutions to a working concentration is carried out directly on site.

Also from a technical point of view, taking into account the condition of use in the Russian Federation, experts note:

• a significantly higher degree of safety of the reagent production technology;
• relative safety of storage and transportation to the place of use;
• loyal safety requirements when working with the substance and its solutions at the facilities;
• non-subordination of water disinfection technology with hypochlorite to Rostekhnadzor of the Russian Federation.

The use of sodium hypochlorite for water disinfection in Russia is becoming increasingly popular and is being actively introduced into practice by the leading industrial centers of the country. So, at the end of 2009, in Lyubertsy, the construction of a plant for the production of NaOCl with a capacity of 50 thousand tons / year for the needs of the Moscow municipal economy began. The Moscow government decided to transfer the water disinfection systems of Moscow water treatment plants from liquid chlorine to sodium hypochlorite (since 2012). The sodium hypochlorite plant will be commissioned in 2015.

Hydrazine production

Sodium hypochlorite is used in the so-called Raschig Process (eng. Raschig Process, oxidation of ammonia with hypochlorite) - the main industrial method for obtaining hydrazine, discovered by the German chemist Friedrich Raschig in 1907. The chemistry of the process is as follows: in the first stage, ammonia is oxidized to chloramine, which then reacts with ammonia, forming hydrazine itself.

Other uses

Among other areas of use of sodium hypochlorite, we note:

• in industrial organic synthesis or hydrometallurgical production for the degassing of toxic liquid and gaseous wastes containing hydrogen cyanide or cyanides;
• oxidizer for wastewater treatment industrial enterprises from impurities of hydrogen sulfide, inorganic hydrosulfides, sulfur compounds, phenols, etc.;
• in electrochemical industries as an etchant for germanium and gallium arsenide;
• V analytical chemistry as a reagent for the photometric determination of bromide ion;
• in the food and pharmaceutical industries for the production of food modified starch;
• in the military as a means for degassing chemical warfare agents such as mustard gas, Lewisite, sarin and V-gases.