Patent ID: 7700809

Claim:
A process for preparing tri- and tetraoxymethylene glycol dimethyl ether (POMDME n=3,4 ) by reacting formaldehyde with methanol and subsequently working up the reaction mixture by distillation, comprising the steps of: a) feeding an aqueous formaldehyde solution having a formaldehyde concentration of from 20 to 60% by weight and methanol into a reactor and reacting to give a mixture a comprising formaldehyde, water, methylene glycol (MG), polyoxymethylene glycols (MG n>1 ), methanol, hemiformals (HF), methylal (POMDME n=1 ) and polyoxymethylene glycol dimethyl ethers (POMDME n >1 ); b) feeding the reaction mixture a into a first distillation column and separating it into a low boiler fraction b 1 comprising formaldehyde, water, methylene glycol, methanol, methylal and dioxymethylene glycol dimethyl ethers (POMDME n=2 ), and a high boiler fraction b 2 comprising formaldehyde, water, methanol, polyoxymethylene glycols, hemiformals and polyoxymethylene glycol dimethyl ethers (POMDME n>1 ); c) feeding the high boiler fraction b 2 into a second distillation column and separating it into a low boiler fraction c 1 comprising formaldehyde, water, methylene glycol, polyoxymethylene glycols, methanol, hemiformals, di-, tri- and tetraoxymethylene glycol dimethyl ether (POMDME n=2,3,4 ), and a high boiler fraction c 2 comprising polyoxymethylene glycols, high-boiling hemiformals (HF n>1 ) and high-boiling polyoxymethylene glycol dimethyl ethers (POMDME n>4 ); d) feeding the low boiler fraction c 1 and, if appropriate, one or more recycle streams composed of formaldehyde, water, methylene glycol and polyoxymethylene glycols into a third distillation column and separating it into a low boiler fraction d 1 comprising formaldehyde, water, methanol, polyoxymethylene glycols, hemiformals and dioxymethylene glycol dimethyl ether (POMDME n=2 ), and a high boiler fraction d 2 substantially consisting of formaldehyde, water, methylene glycol, polyoxymethylene glycols, tri- and tetraoxymethylene glycol dimethyl ether (POMDME n=3,4 ); e) feeding the high boiler fraction d 2 into a phase separation apparatus and separating it into an aqueous phase e 1 substantially consisting of formaldehyde, water, methylene glycol and polyoxymethylene glycols, and an organic phase e 2 comprising tri- and tetraoxymethylene glycol dimethyl ether (POMDME n=3,4 ); f) feeding the organic phase e 2 into a fourth distillation column and separating it into a low boiler fraction f 1 substantially consisting of formaldehyde, water, methylene glycol and polyoxymethylene glycols, and a high boiler fraction f 2 substantially consisting of tri- and tetraoxymethylene glycol dimethyl ether (POMDME n=3,4 ); and g) optionally feeding the aqueous phase e 1 into a fifth distillation column and separating it into a low boiler fraction g 1 substantially consisting of formaldehyde, water, methylene glycol and polyoxymethylene glycols, and a high boiler fraction substantially consisting of water.