Conc. formaldehyde soln. mfr. from dil. aq. soln. - by distn. in rectification column operating at reduced pressure in upper part and elevated pressure in boiler

摘要

Process for prodn. of conc. formaldehyde solns. by rectification of dil. aq. solns. is carried out using a rectification column operated under reduced pressure with a minimal drop in pressure in the upper part of the column, and under elevated pressure in the boiler. Pref. the pressure in the upper part of the column is 20-300 mm Hg and the fall in pressure in that part of the column is 3-100 mm Hg. Pref. the pressure in the boiler is 0.8-2.5 atmos. and the drop in pressure in the lower part of the column is 0.6-2.4 atmos.. A stabilising additive such as formic acid may be introduced into the middle or lower part of the column. An organic solvent which does not form an azeotrope with water, such as hydroxylated cpds. contg. at least 2 or 3 OH gps. or a mixt. of secondary prods. of high b.pt. obtd. in the synthesis of dimethyldioxane from isobutylene and formaldehyde, may also be introduced into the middle or lower part of the column to reduce the operating temp. Process is useful for the prodn. of stable conc. aq. formaldehyde solns. contg. 90-95 % HCHO, using boiler temps. of not more than 130 deg.C. Prods. are useful raw materials in liq. phase reactions such as the synthesis of 4,4-dimethyl- 1,3-dioxane, an intermediate in the prodn. of isoprene.