[Overview]
Methanol is an organic compound and the simplest alcohol. Methanol is light, highly volatile, colorless, flammable and toxic. Usually used as solvent, antifreeze, fuel or neutralizer. It is widely used in the production of medicines, pesticides, dyes, coatings, plastics, synthetic fibers, synthetic rubber, etc., and is also used in solvents and industrial and civil fuels.
[Physical and Chemical Properties]
Appearance: Colorless liquid Density: 0.7918 g/cm3 Melting point: –97°C (176 K) Boiling point: 64.7°C (337.8 K) Solubility in water: Completely miscible with water pKa: ~15.5 Viscosity: 0.59 mPa·s , 20℃ Molecular dipole moment: 1.69 D (gaseous) Chemical properties: Methanol is a medium flash point liquid, flammable, and burns without flame; its vapor can form an explosive mixture with air, and when exposed to open flames, there is a danger of combustion and explosion at high temperatures; Molten acid, perchloric acid, etc. react violently and may cause an explosion.
[Preparation method]
1. High-pressure method: Syngas is produced under high temperature (340~420℃) and high pressure (30~50MPa), using zinc-chromium oxide as catalyst. It has large production capacity and high single-pass conversion rate. However, the high-pressure method has many disadvantages, such as high synthesis pressure and temperature, large equipment investment and operating costs, complex operation, difficult to control temperature and pressure, many by-products, and large loss of raw materials.
Figure 1 shows the process flow of methanol synthesis by high pressure method
2. Low-pressure method is to use synthetic odor raw materials at low pressure (5MPa) and a temperature of about 275°C, and use copper-based catalysts to synthesize methanol. The characteristics of the low-pressure method are high selectivity, few impurities in crude methanol, and high quality of refined methanol.
Figure 2 shows the process flow of methanol synthesis by low pressure method
3. Medium pressure method uses synthesis gas as raw material, operating pressure is 10-27MPa, temperature is 235-275°C, and the catalyst is a copper-based catalyst. This method is characterized by large processing capacity, large equipment, and large floor space.
Figure 3 shows the process flow of methanol synthesis by medium pressure method
[Toxicological effects]
Methanol is mainly absorbed through the respiratory tract and gastrointestinal tract, and can also be partially absorbed through the skin. After methanol is absorbed into the body, it can be quickly distributed in various tissues of the body. Among them, the content in cerebrospinal fluid, blood, bile and urine is the highest, the aqueous humor and vitreous humor are also high, and the content in bone marrow and adipose tissue is the lowest. Methanol is metabolized in the liver and is first oxidized to formaldehyde and then to formic acid through alcohol dehydrogenation and formaldehyde dehydrogenation. This product is slowly oxidized in the body, only 1/7 of ethanol, and is excreted slowly, with obvious accumulation effect. Methanol that has not been oxidized is excreted through the respiratory tract and kidneys, and part of it is slowly excreted through the gastrointestinal tract. The vast majority of cases of acute poisoning are caused by mistakenly ingesting fake wine mixed with methanol. Oral administration of 5 to 10 ml to a person can cause severe poisoning; oral administration of 15 ml at one time, or a cumulative total of 124 to 164 ml in divided doses within 2 days, can cause blindness. 30ml is the minimum lethal dose for adults. A small number of poisoning occurs through respiratory inhalation and skin absorption. Humans may be poisoned if exposed to air with a methanol concentration of 39-65g/m3 for 30-60 minutes.
The main damaged target organs after acute methanol poisoning are the central nervous system, optic nerve and retina. Methanol acts on the nervous system, has a significant anesthetic effect, and can cause cerebral edema. It has a special selective effect on the optic nerve and retina, which can easily cause optic nerve atrophy and lead to blindness. It is generally believed that the toxicity of methanol is caused by itself and its metabolites. It was previously believed that the toxic effects were mainly caused by the metabolite formaldehyde. Formaldehyde can inhibit the oxidative phosphorylation process of the retina, preventing the synthesis of ATP in the membrane, causing cell degeneration, and finally causing optic nerve atrophy. Recent studies have shown that formaldehyde is quickly metabolized into formic acid, and metabolic acidosis and eye damage caused by acute poisoning are mainly related to the formic acid content. Methanol inhibits certain oxidase systems in the body, inhibits the aerobic decomposition of sugar, causes the accumulation of lactic acid and other organic acids and formic acid, and causes acidosis. Formic acid causes plasma transport disorders by inhibiting cytochrome oxidase, leading to toxic optic neuropathy. Lactate can be produced by formic acid-induced inhibition of mitochondrial respiration and tissue hypoxia. The accumulation of formic acid, lactic acid, etc. causes metabolic acidosis.
【Purpose】
Methanol is widely used in the production of medicines, pesticides, dyes, coatings, plastics, synthetic fibers, synthetic rubber, etc., and is also used in solvents and industrial and civil fuels. Methanol is also sometimes used in higher molecular structures. For example, using modified kaolin as a catalyst, we can dehydrate methanol to produce dimethyl ether. Based on the catalytic role of kaolin in similar environments and the rich methane environment at the beginning of the earth, scientists have deduced that the generation of life on earth may have started with methanol. Used in the manufacture of formaldehyde, cellulose, methylation reactions, antifreeze, extraction agents, rubber accelerators, solvents for dyes, resins, artificial leather, paint films, cellophane, spray paint, etc., and paint and pigment removers. Intermediates for organic synthesis, etc. It can also be used as fuel and welding��.
[Application]
1. Methanol oxidation to formaldehyde Methanol is directly oxidized to formaldehyde in the presence of high temperature, pumice silver, catalyst or other solid catalysts. At present, more than 40% of methanol at home and abroad is used to make formaldehyde, which is then used to synthesize resins, plastics and other chemical raw materials. Polyacetal is an engineering plastic with excellent performance and has a wide range of uses. Formaldehyde is also used to produce nearly a hundred downstream products such as butanediol and methenamine.
2. Ammoniation of methanol to produce methylamine. Mix methanol and ammonia in a certain proportion, and synthesize them using activated alumina as a catalyst at 370~420℃ and 5.0~20.0MPa pressure to produce monomethylamine and dimethylamine. The mixture of amine and trimethylamine can be distilled to obtain mono, di or trimethylamine products. Mono-, di- and trimethylamine are used in pesticides, medicines, dyes or as organic raw material intermediates.
3. Methanol carbonylation to produce acetic acid. Methanol and carbon monoxide are carbonylated to produce acetic acid under low pressure. The total amount accounts for more than 50% of the world’s acetic acid production capacity.
4. Methanol esterification can produce various ester compounds.
5. The mixed catalytic reaction of methanol, chlorine and hydrogen generates mono-, di- and trichloromethane, and even carbon tetrachloride. Methyl chloride can be used as a raw material for organic silicon compounds and fluorine-containing resins. It is also an important methylating agent used in the production of methyl cellulose, quaternary ammonium chemicals, etc. Methylene chloride is used in paint removers, aerosols, pharmaceutical raw materials and silicon wafer production. Trichloromethane can be used to produce HCFC-22 as a refrigerant, or further processed to produce products such as tetrafluoroethylene. It can be used as an organic solvent, an extractant, and as an intermediate for dyes and drugs. Tetrachloromethane can be used to produce F-11, F-12, etc.
6. Methanol can be dehydrated to produce dimethyl ether in the presence of metal silicon-alumina catalyst or ZSM-5 molecular sieve.
7. Methanol dehydrogenation to produce methyl formate. Methyl formate is a raw material for organic synthesis and can be used to make formamide, dimethylformamide, etc. Formamide is a raw material for medicines, spices, and dyes. It can also be used as a paper treatment agent, a softener in the fiber industry, and a polar solvent for organic synthesis. Dimethylformamide is an important organic chemical raw material and an excellent solvent. It can be used as a gas absorbent, pesticide, polyurethane synthetic leather, polyacrylonitrile spinning and butadiene extraction and other fields.
8. Methyl tert-butyl ether (MTBE) from formic acid. MTBE has better blending properties than bactericidal preservatives. Considering both environmental protection and engine operation, MTBE is considered the best improver for gasoline. MTBE is listed as one of the 50 basic chemical products in the world. Each ton of MTBE requires approximately It consumes 0.4 tons of methanol, so it is expected to become a large market for methanol consumption in the future.
9. Methanol is used as fuel. Mixing zinc sulfide with methanol into gasoline has been legalized in North America and Western Europe. In my country, Sichuan Province has introduced local standards for M15 this year. All-methanol vehicles have been successfully developed in Shanxi Province and are being fully piloted in Shanxi Province. All-methanol vehicles have begun production in batches and are planned to be promoted in Shanxi and Anhui provinces.
10. Other methyl microorganisms ferment to produce methanol protein. In addition, it can also be used as a paint inhibitor, rust remover, etc.
