PREPARATION OF AQUEOUS SOLUTION OF FORMALDEHYDE

PURPOSE:To obtain the titled aqueous solution with a low methanol content, by feeding a specific excess amount of water from the top of an absorption column in absorbing a product gas obtained by oxidative dehydrogenation of methanol in water, taking out the above-mentioned excess amount as a side stream, and adding the resultant aqueous solution to a raw material gas. CONSTITUTION:A raw material gas containing methanol, air and steam is catalytically reacted on a silver catalyst to give a reaction product gas, which is if necessary recovered in a boiler and then introduced from the bottom of an absorption column. Water in the total amount, required for diluting the product formaldehyde solution, and corresponding to steam to be added to the raw material gas as absorbing water is added thereto from the top of the column, and an aqueous solution having a composition of 0.1-3.0wt% methanol concentration and 0.1-1.0wt% formaldehyde concentration in an amount corresponding to the steam for the raw material gas is taken out of a point near the upper tray of the absorption column and added to the raw material gas to afford a solution in 37-60wt% formaldehyde concentration from the bottom of the column. The aimed product with 0.5-1.0wt% methanol content is obtained under conditions of 1.6-1.8 molar ratio of air to methanol.