Processes for preparing tri- and tetraoxymethylene glycol dimethyl ether (POMDME.sub.n=3,4) include feeding a reaction mixture of an aqueous formaldehyde solution and methanol into a reactive evaporator and separating into a first low boiler fraction and a first high boiler fraction, recycling the first high boiler fraction into the reactor, feeding the first low boiler fraction into a first distillation column and separating into a second low boiler fraction and a second high boiler fraction, recycling the second high boiler fraction into the reactive evaporator, feeding the second low boiler fraction into a second distillation column and separating into a third low boiler fraction and a third high boiler fraction, feeding the third high boiler fraction into a phase separation apparatus and separating into an aqueous phase and an organic phase, and feeding the organic phase into a third distillation column and separating into a low and high boiler fractions.