Process for preparing polyoxymethylene dimethyl ethers from formaldehyde and methanol in aqueous solutions

Process for preparing polyoxymethylene dimethyl ethers having ≥3 oxymethylene units (OMEn≥3), comprising the steps:

• (i) introduction of formaldehyde, methanol and water into a reactor R and reaction to give a reaction mixture containing formaldehyde, water, methylene glycol, polyoxymethylene glycols, methanol, hemiformals, methylal (OMEn=1) and polyoxymethylene dimethyl ethers (OMEn>1);
• and
• (ii) introduction of the reaction mixture into a reactive distillation column K1 having a feedpoint, a bottom offtake, and an overhead offtake and separation into a low boiler fraction F1 containing formaldehyde, water, methylene glycol, polyoxymethylene glycols, methanol, hemiformals, methylal (OMEn=1) and polyoxymethylene dimethyl ethers having from 2 to 3 oxymethylene units (OMEn=2-3) and a high boiler fraction F2 containing essentially polyoxymethylene dimethyl ethers having more than two oxymethylene units (OMEn≥3), wherein the high boiler fraction F2 contains at least 90% by weight of polyoxymethylene di-methyl ethers having more than 2 oxymethylene units (OMEn≥3), wherein the ratio of a volume of the liquid in the region between feedpoint and bottom offtake including any side reactors present and the bottom to the volume flow of the bottom offtake stream in the reactive distillation column K1 is at least 10 min, wherein the low boiler fraction F1 and the high boiler fraction F2 are withdrawn from the reactive distillation column K1.