Method for manufacturing methanol

Hydrogen can be used to synthesize methanol, which is one of the main raw materials in organic chemical industry and an important petrochemical product, with low production cost and wide applications. Its main application can be used to produce formaldehyde, followed by dimethyl terephthalate (DMT), methyl methacrylate (MMA), methylamine, polyvinyl alcohol, methyl chloride, acetic acid and so on. In addition, methanol can also be used as solvent and fuel. Hydrogen can also be produced if necessary. In the early days, methanol was made by dry distillation of wood, but this method was almost eliminated after the opening of the synthesis method. In the early days, methanol was made from coal. After World War II, natural gas, refineries and light oil were developed as raw materials. The coal law has declined. Only coal is cheap, and it is still used near the steel-making industrial zone. The reaction formula of methanol synthesis is as follows: increasing pressure and decreasing temperature in the main reaction are beneficial to the main reaction to produce methanol. In the early synthesis method, carbon dioxide was removed before the reaction in order to prevent equipment corrosion. Later, it was found that carbon dioxide can also be used as raw material, so it is not necessary to remove carbon dioxide first. The key to methanol synthesis is pressure. In the past, low pressure was developed by high pressure method, and the pressure was above 300 atmospheres. 1966. Later, the medium-pressure method was developed, the pressure was about 200 atmospheres, and the pressure (atm) and temperature (℃) were 300 ~ 600. The medium-pressure method for Cr-Zn catalyst/the low-pressure method for Kloc-0/05 ~ 300 225 ~ 270 Cr-Al catalyst was 40~60 200~300 Cu-Zn catalyst with high conversion rate. However, in order to achieve high pressure, reciprocating compressors need to consume more energy. The low-pressure method can use centrifugal compressor, which consumes less energy and has a smaller economic scale, and can also use synthetic gas with high hydrogen content. Centrifugal compressor can also be used in the middle pressure method, which does not need to add carbon dioxide like the low pressure method, which improves the shortcomings of the low pressure method. The synthesis tower is a vertical shell-and-tube type, in which the catalyst is filled and the outside is cooled by boiling water. It can also be a packed tower, so that cold raw materials can be introduced at many positions in the tower to control the reaction temperature. The compressed feed gas is mixed with the circulating unreacted gas, and enters the synthesis tower after heat exchange with the reaction product gas, and reacts through the catalyst bed. After the reaction product gas is cooled by heat exchange, methanol is condensed, separated by separator, gas circulation and mixed with raw material gas. Crude methanol synthesized by this condensation contains impurities. Generally, the impurities in methanol synthesized by low pressure method are less than those in methanol synthesized by high pressure method. Impurities in crude methanol can be divided into three categories except water, namely, low-boiling compounds, ethanol and high-boiling compounds. The further refining steps, operation and design of crude methanol vary with the synthesis method and finished product specifications. If the purity of the finished product is low, single tower distillation can be used. When the purity requirement is high, double tower distillation can be used. When the purity of finished products is high, three-tower distillation is more suitable. In double-tower distillation, impurities with low boiling point, such as dimethylbenzene, are discharged from the top of the first tower, and higher alcohols with high boiling point are discharged from the bottom of the second tower, and high-purity methanol is obtained from the top of the tower.