Formaldehyde, chemical formula HCHO or CH₂O, molecular weight 30.03, also known as antaldehyde. Colorless, irritating to human eyes and nose. The relative density of gas is 1.067 (air = 1), and the density of liquid is 0.815g / cm³ (-20 ° C). Melting point -92 ° C, boiling point -19.5 ° C. Soluble in water and ethanol. The concentration of the aqueous solution is up to 55%, usually 40%. It is called formaldehyde, commonly known as formalin, and it is a colorless liquid with irritating odor.

It has strong reducing ability, especially in alkaline solution. It can burn, vapor and air form explosive mixture, the explosion limit is 7% -73% (volume). The ignition point is about 300 ° C.

It can be produced by the dehydrogenation or oxidation of methanol under the catalysis of metals such as silver and copper. It can also be separated from the oxidation products of hydrocarbons. It can be used as raw materials for phenolic resin, urea resin, vinylon, urotropine, pentaerythritol, dyes, pesticides and disinfectants.

Industrial formaldehyde solution generally contains 37% formaldehyde and 15% methanol as a polymerization inhibitor with a boiling point of 101 ° C.

On October 27, 2017, in the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization, formaldehyde was placed in the list of carcinogens.

Application area

chemical industry

Used in the production of polyoxymethylene (POM) [3]. Generally, the formaldehyde solution (55%) needs to be concentrated to more than 75%, and the first polymerization reaction is carried out to generate paraformaldehyde. Then, paraformaldehyde is used as a reaction monomer, and an appropriate amount of dioxane is used as a comonomer to carry out In the second polymerization step, a long-chain polyoxymethylene is obtained, and the reaction is ended by adding a terminator (carboxylic acid, etc.) and closing the chain ends. After finishing processing, polyacetal plastic particles are finally obtained.

POM is also called "Saigang", because of its excellent performance, it has been widely used in many industrial fields such as industrial machinery, automobile manufacturing, electronics and electrical appliances. With the development of technology, the performance of POM is still further improved. DuPont of the United States, Polyplastics of Japan, China Bluestar Group, Shenhua Group, and Yuntianhua Group have actively invested in research in this field. The entire POM industry will have a lot of room for development in the future. .

Wood industry

It is used to produce urea-formaldehyde resin and phenol-formaldehyde resin. Urea-formaldehyde resin is formed by reacting formaldehyde and urea in a certain molar ratio. Formaldehyde and phenol are mixed and reacted in a certain molar ratio to form a phenolic resin. The irreplaceable position of formaldehyde in the wood processing industry is being replaced by MDI glue.

Textile industry

For the production of clothing fabrics, in order to achieve the functions of anti-wrinkle, anti-shrink, flame retardant, etc., or to maintain the durability of printing and dyeing, or to improve the feel, formaldehyde needs to be added to the auxiliary. More formaldehyde printing and dyeing additives are pure cotton textiles, because pure cotton textiles are easy to wrinkle, using formaldehyde-containing additives can improve the stiffness of cotton. Textiles containing formaldehyde will gradually release free formaldehyde during people's wearing and using, causing respiratory tract inflammation and skin inflammation through human respiratory tract and skin contact, and also irritating the eyes. Formaldehyde can cause allergies and can also cause cancer. Manufacturers use formaldehyde-containing dyeing auxiliaries, especially some manufacturers use low-cost auxiliaries with high formaldehyde content to reduce costs, which is very harmful to the human body.

Antiseptic solution

A 35% to 40% formaldehyde aqueous solution is commonly known as formalin. It has antiseptic and antiseptic properties and can be used to soak biological specimens and disinfect seeds. However, it is easy to make specimens brittle due to denaturation of proteins.

The main reason that formaldehyde has antiseptic and antiseptic properties is that formaldehyde can react with amino groups on proteins of organisms (including bacteria).

Removal method

Ventilation method

Through the circulation of indoor air, the content of harmful substances in the indoor air can be reduced, thereby reducing the harm of such substances to the human body. In winter, people often close doors and windows, and indoor and outdoor air cannot circulate. Not only the formaldehyde content in indoor air will increase, but radon will continue to accumulate, even reaching high concentrations.

Advantages: good effect, no cost.

Disadvantages: It takes a long time, and it usually takes more than three years to remove formaldehyde.

Governance Misunderstanding

1.Remove formaldehyde with water, vinegar, and black tea

Many people on Amethyst said that because formaldehyde is soluble in water, you can put more water basins at home to absorb formaldehyde, or use vinegar or black tea to soak water. The fact that formaldehyde is easily soluble in water, alcohols and ethers is the fact that free formaldehyde in the air will dissolve into it after encountering water during exercise, which is similar to the adsorption principle of activated carbon. The contact area of a basin of water and air is only the size of a basin, and the specific surface area of the pores in 1 gram of activated carbon can be as large as a football field. Even if you put a hundred pots of water in the room, in fact, the adsorption effect will not be much stronger than a small package of activated carbon. So using water, black tea, vinegar and other methods to adsorb formaldehyde is obviously unrealistic. The release of formaldehyde is closely related to the indoor temperature and humidity. As the temperature in the air increases, the amount of formaldehyde release will greatly increase. The experimental results show that when the relative humidity in the air increases by 10%, the indoor formaldehyde emission will increase by about 5%.

2.Purify the air with plants

During this process, the plants themselves will also be injured, and many plants will be injured in severe environments with formaldehyde, and they may even die. Among them, wood sorrel is particularly sensitive. As long as it is thrown in an environment with a formaldehyde concentration of 0.1 mg / m3 and left for 3 hours, 95% of the leaves will be injured (calculated by area ratio). Also, as the formaldehyde concentration increases, the rate of injury is faster. They can only last for 3 hours in an environment with a formaldehyde concentration of 0.4 mg / m3, and then the entire leaf turns yellow-brown and loses water and wilts, becoming hay.

3.Adsorb formaldehyde with fruits such as oranges and pineapples

This is a method that many people like to use in the past, it can be said that it is a folk soil method. Many folk methods are a summary of long-term life experience, and are truths tested by time and practice. But this method is completely ridiculous. CCTV's "Is It Real" column of the Financial Channel once broadcast a program that removes formaldehyde from grapefruit peels and pineapples? The experiment was performed deliberately in the program. The experimental results show that in the same sealed bin, the formaldehyde content of the experimental bin in which the grapefruit peel is placed is ten times that of the blank bin. After the grapefruit husk was put in, the temperature of the experimental chamber increased, and the amount of formaldehyde released greatly increased. Grapefruit peel, pineapple, etc. not only cannot remove formaldehyde, but also increase the indoor formaldehyde content. In the past, the reason why many people think that after using grapefruit peel and pineapple, the interior decoration tastes less, because the taste of fruit masks the smell of formaldehyde.

Process flow

Almost all industries use carbon monoxide and carbon dioxide pressurized catalytic hydrogenation to synthesize methanol. Typical processes include raw gas production, raw gas purification, methanol synthesis, and crude methanol rectification.

Natural gas, naphtha, heavy oil, coal and its processed products (coke, coke oven gas), acetylene tail gas, etc. can all be used as raw materials for the production of methanol synthesis gas. The steam conversion of natural gas and naphtha requires complex structures and high cost. It is carried out in a reforming furnace. The reforming furnace is provided with a radiant chamber and a convection chamber to perform hydrocarbon vapor conversion reaction in the presence of a high temperature and a catalyst. Partial oxidation of heavy oil needs to be performed in a high temperature gasification furnace. When solid fuel is used as a raw material, intermittent gas can be used Gasification or continuous gasification of water and gas. The intermittent gasification method uses air and steam as gasification agents, and separates the blowing and gas-making stages. Continuous gasification uses oxygen and steam as gasification agents, and the process continues.

Various catalysts used in methanol production, such as natural gas and naphtha vapor conversion catalysts, and methanol synthesis catalysts are susceptible to sulfide poisoning and lose their activity, and sulfides must be removed. Gas desulfurization methods can be divided into two categories, one The type is dry desulfurization, and the other is wet desulfurization. Dry desulfurization equipment is simple, but due to the slow reaction rate, the equipment is relatively large. Wet desulfurization can be divided into three types: physical absorption method, chemical absorption method and direct oxidation method.

The synthesis of methanol is carried out in the presence of high temperature, high pressure, and catalyst, which is a typical composite gas-solid phase catalytic reaction process. With the continuous development of methanol synthesis catalyst technology, the general trend is to develop from high pressure to low and medium pressure.

Crude methanol contains impurities such as water, higher alcohols, ethers, and ketones, which need to be refined. The refining process includes rectification and chemical treatment. Chemical treatment mainly uses alkali to destroy impurities that are difficult to separate during the rectification process and adjusts the pH. It removes volatile components, such as dimethyl ether, and difficult-to-volatile components, such as ethanol higher alcohol, water, etc.

The three methods and differences of high pressure method, medium pressure method and low pressure method are briefly described below.

High pressure method

The high-pressure process generally refers to the process of synthesizing methanol at a high temperature and pressure of 300-400 ° C and 30 MPa using zinc-chromium catalyst. Since the first successful synthesis of methanol by this method in 1923, it has almost 50 years. This method is used in the production of synthetic methanol, and there are only certain differences in design.For example, there are two main types of heat transfer methods in the methanol synthesis tower: cold tube continuous heat exchange and cold shock multi-stage heat exchange. The gas flow has axial and radial or a mixture of both, and there are processes that produce by-product steam and non-by-product steam. In recent years, China has developed synthesis on copper-based catalysts at 25-27 MPa pressure. Methanol technology, the methanol content in the outlet gas is about 4%, and the reaction temperature is 230-290 ° C.

Medium pressure method

The medium pressure method is further developed based on the research of the low pressure method. Due to the low operating pressure of the low pressure method, the equipment volume is quite large, which is not conducive to the large-scale production of methanol. Therefore, the medium pressure method for methanol synthesis with a pressure of about 10 MPa was developed. It can more effectively reduce the cost of building a plant and the cost of methanol production. For example, ICI has successfully researched a 51-2 copper-based catalyst whose chemical composition and activity are similar to those of a low-pressure synthesis catalyst 51-1, except that the crystal structure of the catalyst is different. The manufacturing cost is more expensive than the 51-1 type. Because this catalyst can also maintain a long life under higher pressure, it is possible for ICI to increase the original synthesis pressure of 5MPa to 10MPa. The synthesis tower used and low pressure The same method is also a four-stage cold shock type, and its process and equipment are similar to the low-pressure method.

Low pressure method

The ICl low-pressure methanol method was successfully researched by the British company ICl in 1966, thereby breaking the monopoly of the high-pressure method for methanol synthesis. This is a major change in the methanol production process. It uses a 51-1 copper-based catalyst. The synthesis pressure is 5 MPa. The synthesis tower used in the ICl method is a hot wall multi-stage cold shock type with a simple structure. A diamond-shaped cold shock gas distributor is installed on the upper part of each stage of the catalyst layer to allow the cold shock gas to enter the catalyst layer uniformly to adjust the interior of the tower. The types of low-pressure synthesis towers include the tube-bundled by-product steam synthesis tower of the Federal German company Lurgi and the three-phase methanol synthesis system of the American Electric Research Institute. In the 1970s, the Sichuan Vinylon Plant of the Ministry of Light Industry of China introduced it from the French company Speichim. A 300-ton-day low-pressure methanol plant using acetylene tail gas as a raw material (UK ICI patented technology) was introduced. In the 1980s, the second chemical fertilizer plant of Qilu Petrochemical Company introduced a low-pressure methanol synthesis plant from Federal German Lurge Company.