Formaldehyde is a very common hungry chemical with certain toxicity. Long-term exposure to formaldehyde is very harmful to human body. However, when the content does not exceed the standard, it can also help our daily life in many ways.
Formalin is widely used in agriculture, industry and medicine. In addition to being directly used as disinfection, sterilization and preservative, formaldehyde is mainly used in organic synthesis, synthetic materials, coatings, rubber, pesticides and other industries. Its derivatives mainly include paraformaldehyde, polyformaldehyde, phenolic resin, urea formaldehyde resin, amino resin Urotor products and polyols, etc. The wood-based panel industry is developed, and there is a great demand for formaldehyde. Formaldehyde has a wide range of uses. It is used in synthetic resin, surfactant, plastics, rubber, leather, papermaking, dyes, pharmaceuticals, pesticides, photographic films, explosives, building materials, disinfection, fumigation and anti-corrosion. It can be said that formaldehyde is a generalist in the chemical industry, but there must be a limit and standard for the use of anything, Once the use exceeds the standards and limits, it will bring disadvantages. In recent years, the output of formaldehyde in China has increased year by year, which is consistent with the development of China's textile industry and building materials industry. Because of its low price and broad market, formaldehyde will still be the darling of China's chemical industry for a long time in the future.
Formaldehyde is prepared by catalytic oxidation of methanol in industry. The mixture of methanol vapor and air is absorbed by water through silver catalyst at 600 ~ 700 °C to form formaldehyde and unactive methanol. After removing part of methanol from the solution, the aqueous solution of formaldehyde is obtained, which contains 40 % formaldehyde and 8 % ~ 10 % methanol. This aqueous solution is called ' formalin '.
In the preparation of formalin solution ( fixed solution or storage solution ), 37 – 40 % formalin solution should be used as solute. For example, when preparing 5 % solution, 5 mL and 95 mL distilled water of 37 – 40 % solution should be mixed, which is also a commonly used preparation method in the laboratory.
Formalin, put it in a well sealed plastic bottle in the shade. The storage temperature is related to the concentration of formaldehyde solution and can be calculated through the formula, that is, "storage temperature = (concentration value + 5) ℃", so the storage temperature is usually between 15 ° C and 25 ° C.
Formalin is stored in the refrigerator or at room temperature for a long time. White precipitates can be precipitated in the aqueous solution, that is, paraformaldehyde. If it is heated, it can become a liquid. Therefore, formalin is not suitable for refrigeration in the refrigerator, otherwise it is easy to agglomerate. For the aqueous solution with formalin content of 35% to 40% (generally 37%), 10% ~ 15% methanol is also added to prevent polymerization.