| abstract |
Process for preparing high-concentration formaldehyde solutions having a CH 2 O content of ≧50% by weight from an aqueous formaldehyde solution having a lower CH 2 O content by evaporation of part of this solution (partial evaporation), in which the aqueous formaldehyde solution is heated to an evaporation temperature T at which the gas phase becomes enriched in water relative to the liquid phase and the gas phase formed is taken off continuously or discontinuously, wherein the evaporation temperature T obeys the relationship: n nT[° C.]<T max [° C.]n n where T max (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, n where c is the instantaneous CH 2 O content of the aqueous formaldehyde solution during the evaporation in percent by weight and is from 20 to 99% by weight. |