In recent years, with the development of coal chemical industry, the technology of using coal as raw material to synthesize methanol has matured, and domestic methanol production capacity has been growing rapidly. Methylal is one of the most important downstream products of methanol. It has excellent physical and chemical properties, such as good solubility, low boiling point, and good miscibility with water. It can be widely used in cosmetics, pharmaceuticals, automotive industry supplies, and pesticides. , rubber industry, paints and inks and other products.
Product features
Methyl is irritating to mucous membranes and has anesthetic effects. Inhaling steam can cause nose and throat irritation; inhalation of high concentrations can cause dizziness. Damage to eyes that may last for several days. Prolonged skin contact may cause skin dryness. Methylal can form potentially explosive peroxides when exposed to air or light. Methyl is mainly used in pesticides, refrigerants, low boiling point industrial solvents, etc. The industrial grade content is between 82-85%, and other impurities are methanol and formaldehyde. The theoretical oxygen content is 42%, but the actual oxygen content is higher. The measured calorific value is slightly higher than that of methanol, and the RON is very low. The domestic octane number testing machine cannot detect it. The imported CFR testing machine can detect it, but the detection process may damage the expensive CFR testing machine (the author has tested it). Almost no one knows its exact octane rating.
Preparation method
Using methanol and formaldehyde as raw materials, there are two main processes for producing methylal: liquid phase condensation method and reactive distillation method.
Liquid phase condensation method is a commonly used industrial method. Using inorganic acids (such as sulfuric acid, hydrochloric acid), Lewis acids (such as aluminum trichloride, ferric chloride, etc.) and heteropoly acids (such as silicotungstic acid, phosphotungstic acid) as catalysts, methanol and formaldehyde aqueous solutions react in the tube The acetal reaction occurs in the device, and each ton of methylal products produced consumes approximately 1.3 tons of formaldehyde aqueous solution and approximately 1.1 tons of industrial-grade methanol raw material. This method is simple to operate, and the reaction conditions are warm and thixotropic. However, a large amount of acidic organic wastewater containing formaldehyde is produced during production, which is difficult to treat and pollutes the environment. Therefore, this method has been gradually eliminated.
Reactive distillation has been widely used in industrial production and is the mainstream process for methylal production at home and abroad. Different from the liquid acid catalyst used in the liquid phase condensation method, the reactive distillation method uses solid acid catalysts (such as strongly acidic cation exchange resin, H-ZSM-5 molecular sieve, high silicon to aluminum ratio aluminum silicate-LZ40 molecular sieve, gamma zeolite Molecular sieves, etc.), the production process is similar to the liquid phase condensation method. Each production of 1 ton of 85% methylal requires about 1.0 t of formaldehyde aqueous solution and 6 tons of industrial-grade methanol raw material 0.8 diluent.
Compared with the liquid phase condensation method, this process replaces the acidic organic wastewater containing formaldehyde with low-concentration formaldehyde wastewater, resulting in a smaller amount of wastewater. It is often coupled with the methanol catalytic production process of formaldehyde. On the one hand, formaldehyde is the raw material for methylal production; on the other hand, the low-concentration formaldehyde wastewater generated in the methylal production process can be used as secondary absorption process water for gaseous formaldehyde.
The reaction flow diagram of the acetal reaction between methanol and formaldehyde to prepare methylal under the action of a catalyst is shown in Figure 1. Formaldehyde, the raw material of this process, is produced by oxidation of methanol, which better solves the problem of downstream utilization of methanol.
Figure 1 Simplified process flow chart for producing methylal by reactive distillation
Technical Highlights
1. Under reasonable process and equipment conditions, qualified methylal products can be obtained directly from the top of the tower;
2. Reaction and separation are carried out in the same equipment, which can save equipment costs and operating costs;
3. The reaction heat is directly used in the distillation process, which can reduce energy consumption;
4. Due to the concentration effect of distillation, the concentration requirements for the raw material formaldehyde are reduced. Formaldehyde aqueous solutions with a concentration of 7% to 38% can be used directly.
