Formaldehyde
Formaldehyde result from the exothermic oxidation and endothermic dehydrogenation of methanol. The reaction to produce formaldehyde can see on the below formula:
CH3OH + ½ O2 -----> CH2O + H2O ΔH = -156 kJ
CH3OH -----> CH2O + H2 ΔH = + 85 kJ
These two reaction occur simultaneously in commercial units in a balanced reaction, called auto thermal because the oxidative reaction furnishes the heat to cause the dehydrogenation to take place. About 50 to 60 percent of the formaldehyde is formed by the exothermic reaction. The oxidation requires 1.6 m3 of air per kilogram of methanol reacted, a ratio that is maintained when passing operate stream of these two material forward. Fresh and recycle methanol are vaporised, superheated, and passed into the methanol air mixer. Atmosphere air is purified, compressed and preheated to 54oC in a finned heat exchanger. The products leave the converter at 620oC and at 34 to 60 kPa absolute. The converter is a small water jacketed vessel containing the silver catalyst. About 65% of the methanol is converted per pass. The reactor effluent contains about 25% formaldehyde, which is absorbed with the excess methanol and piped to the make tank. The latter feeds the methanol column for separation of recycle methanol. The water intake adjusts the formaldehyde to 37% strength (marketed as formalin). The yield from the reaction is 85 to 90 percent. The catalyst is easily poisoned so stainless steel equipment must be used to protect the catalyst from metal contamination.
In 1982 about 2.2 x 108 t of 37% solution (formalin) was produced in the United States at a price of 19 to 20 cents per kilogram.
CH3OH + ½ O2 -----> CH2O + H2O ΔH = -156 kJ
CH3OH -----> CH2O + H2 ΔH = + 85 kJ
These two reaction occur simultaneously in commercial units in a balanced reaction, called auto thermal because the oxidative reaction furnishes the heat to cause the dehydrogenation to take place. About 50 to 60 percent of the formaldehyde is formed by the exothermic reaction. The oxidation requires 1.6 m3 of air per kilogram of methanol reacted, a ratio that is maintained when passing operate stream of these two material forward. Fresh and recycle methanol are vaporised, superheated, and passed into the methanol air mixer. Atmosphere air is purified, compressed and preheated to 54oC in a finned heat exchanger. The products leave the converter at 620oC and at 34 to 60 kPa absolute. The converter is a small water jacketed vessel containing the silver catalyst. About 65% of the methanol is converted per pass. The reactor effluent contains about 25% formaldehyde, which is absorbed with the excess methanol and piped to the make tank. The latter feeds the methanol column for separation of recycle methanol. The water intake adjusts the formaldehyde to 37% strength (marketed as formalin). The yield from the reaction is 85 to 90 percent. The catalyst is easily poisoned so stainless steel equipment must be used to protect the catalyst from metal contamination.
In 1982 about 2.2 x 108 t of 37% solution (formalin) was produced in the United States at a price of 19 to 20 cents per kilogram.
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