Abstract: Process for preparing high-concentration gaseous formaldehyde having a molar CH2O:H2O ratio of ?0.6 from an aqueous formaldehyde solution by evaporation of at least part of the solution, in which the aqueous formaldehyde solution is heated to a vaporization temperature T and the gas phase formed is taken off, wherein the evaporation temperature T obeys the relationship: T[° C.]?T?min[° C.] where T?min(c)=A+B×(c/100)+C×(c/100)2+D×(c/100)3 and A=+68.759, B=+124.77, C=?12.851, D=?10.095, where c is the instantaneous CH2O content of the aqueous formaldehyde solution during the evaporation in percent by weight and is from 20 to 99% by weight.

Abstract: Method of stabilizing high-concentration formaldehyde solutions having a CH2O content of >70% by weight against precipitation of solids, which comprises heating the high-concentration formaldehyde solution at a heating rate of at least 5° C./min to a temperature of from 80° C. to 200° C. immediately after it has been prepared and storing it at a temperature in this range.

Abstract: Method of stabilizing high-concentration formaldehyde solutions having a CH2O content of >70% by weight against precipitation of solids, which comprises heating the high-concentration formaldehyde solution at a heating rate of at least 5° C./min to a temperature of from 80° C. to 200° C. immediately after it has been prepared and storing it at a temperature in this range.