Continuous process for the industrial manufacture of dimethoxyethanal

Abstract

Process for the continuous preparation of dimethoxy ethanal (DME) in which a 70% by weight of an aqueous solution of glyoxal is continuously reacted with 8 to 12 moles of methanol/mole of glyoxal in the presence of a cation exchange resin, then the reaction solution obtained is subjected to an initial distillation, at atmospheric pressure, in order to recover more than 90% of the unreacted methanol, which is recycled, then to a second distillation under a pressure of less than 10.+-.2 kPa in order to isolate an aqueous mixture containing the greater part of DME and 1,1,2,2-tetramethoxyethane (TME) formed. This mixture, after dilution with water (molar ratio of water/TME 29.+-.4), is subjected to a distillation under a pressure of less than 19 kPa in order to remove from the top fraction an aqueous mixture containing more than 98.5% of the TME present and to also obtain an aqueous solution of DME having a purity greater than 98.5%, and that, at the same time as these operations, the aqueous mixture containing the TME as well as the bottom fraction of the distillation produced from the distillation column of aqueous mixture containing the greater part of DME and TME, is treated continuously while warm, in the presence of a cation exchange resin, in order to obtain a water-methanol-glyoxal mixture, the methanol of which is evaporated off and recycled with the methanol recovered previously, before recycling half of it with the starting aqueous glyoxal solution after having been concentrated and recycling half with the aqueous mixture containing the TME.