Process for preparing essentially formic acid-free N-alkyl-N′-methylalkyleneureas

A process for preparing an N-alkyl-N′-methylalkyleneurea of the formula

• with R1=H or CH3, R2=CH3 and x=0, wherein the N-alkyl-N′-methylalkyleneurea has a formic acid content of less than 0.1%,
• by reacting an alkyleneurea with monomeric or polymerized formaldehyde in the presence of formic acid to obtain a reaction mixture comprising the N-alkyl-N′-methylalkyleneurea and formic acid, which process comprises
• feeding the reaction mixture to the upper region of a distillation column,
• distilling the reaction mixture in the column, and removing the N-alkyl-N′-methylalkyleneurea as a gas from the lower region of the column,
• wherein the pressure in the upper region of the column is set at a higher level than in the lower region of the column, and the difference in pressure between the upper and lower regions of the column is from 20 to 40 mbar, and
• the temperature in the lower region of the column is set at a higher level than in the upper region of the column, with the difference in temperature between the upper and lower regions of the column being from 80° C. to 150° C., whereby a mixture of formic acid and water is firstly distilled off.