Formaldehyde process flow chart

Formaldehyde is a popular chemical product with wide application, simple production process and sufficient supply of raw materials. It is the backbone of the downstream product tree of methanol. The annual output of the world is about 25 million tons, and about 30% of methanol is used to produce formaldehyde. However, formaldehyde is a low-concentration aqueous solution, which is not convenient for long-distance transportation from an economic point of view, so factories are generally set up near major consumer markets, and import and export trade is also rare. Methanol oxidation and direct oxidation of natural gas are mainly used in industry:

1. methanol oxidation method: at 600~700℃, methanol, air and water are directly oxidized by silver catalyst or copper, vanadium pentoxide and other catalysts to generate formaldehyde, which is absorbed by water to obtain formaldehyde solution;

The overall reaction is exothermic, but 50~60% of formaldehyde is generated by oxidation, and the rest is generated by hydrogen reaction. The by-products are carbon monoxide and carbon dioxide, methyl formate and formic acid. The conversion rate of methanol is 80%, and the yield is 85%~90% based on methanol. This method has mature technology and high yield, and is widely used by domestic and foreign manufacturers.

2. Natural gas oxidation method: At 600-680℃, the mixture of natural gas and air is directly oxidized by oxide catalysts such as iron and molybdenum to generate formaldehyde, which is absorbed by water to obtain formaldehyde solution.

3. Introduce copper or silver catalyst into methanol steam at 300℃ to dehydrogenate methanol. Formaldehyde gas absorbs 36% ~ 40% of water, which is formaldehyde solution. The commercial formaldehyde solution is distilled to remove impurities, and methanol is added to obtain reagent formaldehyde solution.

4. Dimethyl ether oxidation method: dimethyl ether, a by-product of methanol synthesis from syngas under high pressure, is used as raw material and metal oxide is used as catalyst for oxidation.

5. Dehydrogenation of methanol: anhydrous formaldehyde can be obtained by direct dehydrogenation of methanol, and hydrogen is a by-product. This method is an attractive method to prepare formaldehyde. The key to its progress lies in the improvement of the performance of process catalysts.

6. Mix the gasified methanol, air and steam after alkali washing according to the volume ratio of1:1.8 ~ 2.0: 0.8 ~1.0, and heat to115 ~/20℃.

After the reaction, the reactants are quickly cooled to 80-85℃, absorbed by water, then unreacted methanol is distilled off, the kettle liquid is treated with anion exchange resin, an appropriate amount of polymerization inhibitor is added to the obtained formaldehyde solution, and the finished product is obtained by stirring and mixing.