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What is the Basic Principle of Silver Formaldehyde Preparation?

Dec. 08, 2020

As a Formaldehyde Production Plant, let me share with you.

The principle of silver-method formaldehyde reaction The silver-method formaldehyde mainly produces main reactions and side reactions. Among them, side reactions 3 and 4 have a certain influence on the yield of formaldehyde produced by the main reaction. The formation of CO2 mainly occurs in the catalyst layer, which is the product of parallel reactions; while CO and formic acid are mainly generated after leaving the catalyst layer, which is a series of reaction products of deep oxidation of formaldehyde. There is no effective method to prevent CO2; however, a series of side reactions of deep oxidation after leaving the catalyst layer can be controlled by rapidly cooling the reactants. For the reaction of methanol oxidation to formaldehyde, if molybdenum oxide alone is used as a catalyst, the reaction selectivity is good, but the conversion rate is too low. Only a catalyst made of Fe-Mo oxide in an appropriate ratio can achieve satisfactory results. 

Formaldehyde Production Silver Process

Formaldehyde Production Silver Process

The main technical reaction temperature of silver-method formaldehyde The iron-molybdenum catalyst has poor thermal conductivity and is not resistant to high temperatures. The reaction temperature must be strictly controlled. The process requires the operating temperature to be 20-40°C lower than the maximum allowable use temperature of the catalyst (ie the calcination temperature during preparation), that is, to operate below 380°C. When the temperature exceeds 480°C, the catalyst activity is destroyed. The methanol feed concentration is very sensitive to the effect of oxidation temperature. The absolute value of methanol concentration increases by 0.1%, and the reaction hot spot temperature increases by about 5°C. Therefore, the methanol concentration in the feed gas must be kept constant. When the temperature is lower, the conversion rate of methanol is lower, and the yield of formaldehyde is not high. As the temperature increases, both increase. Between 300°C and 360°C, the single-pass yield of formaldehyde can reach about 90%, but if the temperature is too high, the CO yield will increase, while the single-pass yield of formaldehyde will decrease. Therefore, the reaction temperature is chosen to be around 350°C.

The silver method formaldehyde raw material ratio technology is within a certain concentration range (3%-8%). The ratio of methanol in the air mixture has no significant effect on the yield of formaldehyde and CO. However, the operating concentration of methanol is too low and the production capacity is limited. . In industry, safe production is usually adopted at the highest value of the lower limit concentration of the methanol and air mixture explosion zone, that is, the operating concentration of methanol in the raw materials should generally be about 6% (volume). The oxidation reaction has the characteristics of high space velocity and large heat release. If a fluidized bed reactor is used, the operating concentration of methanol can be increased, and the production capacity can be greatly increased. The contact time has a very obvious impact on the product distribution. If the contact time is too short, The conversion rate is too low; as the contact time increases, the methanol conversion rate increases, and the formaldehyde yield also increases, but the yields of by-products CO and formic acid also increase, so the contact time cannot be too long in the operation [3]. That is, methanol is oxidized with excess air on the iron-molybdenum catalyst, which is suitable for high space velocity conditions.

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