| 摘要 |
A process for preparing tri- and tetraoxymethylene glycol dimethyl ether (POMDMEn=3,4) by reacting formaldehyde with methanol and subsequently working up the reaction mixture by distillation is disclosed, wherein the process comprises the steps of: (a) feeding aqueous formaldehyde solution and methanol into a reactor and reacting to give a mixture a comprising formaldehyde, water, methylene glycol (MG), polyoxymethylene glycols (MGn>1), methanol, hemiformals (HF), methylal (POMDMEn=1) and polyoxymethylene glycol dimethyl ethers (POMDMEn>1); (b) feeding the reaction mixture a into a first distillation column and separating into a low boiler fraction b1 and a high boiler fraction b2 comprising formaldehyde, water, methanol, polyoxymethylene glycols, hemiformals and polyoxymethylene glycol dimethyl ethers (POMDMEn>1); (c) feeding the high boiler fraction b2 into a second distillation column and separating into a low boiler fraction c1 comprising formaldehyde, water, methylene glycol, polyoxymethylene glycols, methanol, hemiformals, di-, tri- and tetraoxymethylene glycol dimethyl ether (POMDMEn=2,3,4) and a high boiler fraction c2 comprising polyoxymethylene glycols, high-boiling hemiformals (HFn>1) and high-boiling polyoxymethylene glycol dimethyl ethers (POMDMEn>4); (d) feeding the low boiler fraction c1 and, if appropriate, one or more recycle streams composed of formaldehyde, water, methylene glycol and polyoxymethylene glycols into a third distillation column and separating into a low boiler fraction d1 comprising formaldehyde, water, methanol, polyoxymethylene glycols, hemiformals and dioxymethylene glycol dimethyl ether (POMDMEn=2), and a high boiler fraction d2 substantially consisting of formaldehyde, water, methylene glycol, polyoxymethylene glycols, tri- and tetraoxymethylene glycol dimethyl ether (POMDMEn=3,4); (e) feeding the high boiler fraction d2 into a phase separation apparatus and separating into an aqueous phase e1 substantially consisting of formaldehyde, water, methylene glycol and polyoxymethylene glycols, and an organic phase e2 comprising tri- and tetraoxymethylene glycol dimethyl ether (POMDMEn=3,4); (f) feeding the organic phase e2 into a fourth distillation column and separating into a low boiler fraction f1 substantially consisting of formaldehyde, water, methylene glycol and polyoxymethylene glycols, and a high boiler fraction f2 substantially consisting of tri- and tetraoxymethylene glycol dimethyl ether (POMDMEn=3,4).
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