Reaction system and process for preparing polymethoxy dimethyl ether

A process for continuously preparing polymethoxy dimethyl ether with an aqueous formaldehyde solution or paraformaldehyde as raw material, which comprises the following steps:

• 1) optionally, concentrating an aqueous formaldehyde solution of 37˜40 wt. % to obtain a concentrated formaldehyde having a concentration of 50˜80 wt. % under the conditions of 50˜90° C. and a gauge pressure of −0.1˜−0.05 MPa in a formaldehyde concentrator;
• 2) optionally, feeding the concentrated formaldehyde obtained from step 1) into a vacuum drier, and obtaining paraformaldehyde by polymerization under the conditions of 60˜80° C. and a gauge pressure of −0.1˜−0.05 MPa;
• 3) subjecting the concentrated formaldehyde from step 1), the paraformaldehyde from step 2) or paraformaldehyde added directly from the exterior to a continuous acetalization reaction with methanol in the presence a functionalized acidic ionic liquid as a catalyst in an acetalization reactor, so as to form a reaction effluent liquid comprising polymethoxy dimethyl ether DMM1-8, water, unreacted raw materials and the catalyst;
• and
• 4) extracting the reaction effluent liquid obtained from step 3) with an extraction agent to give a light phase and a heavy phase in a product-separating unit, wherein the light phase comprises the extraction agent, DMM1-8, part of methanol and formaldehyde, and the heavy phase comprises the catalyst and an aqueous formaldehyde solution;
• separating the recycled material comprising formaldehyde, methanol and DMM1-2, the extraction agent and the desired product DMM3-8 by rectifying the light phase;
• feeding the recycled material back to an acetalization reactor;
• feeding the extraction agent back to an extraction tower for reuse;
• and flowing the heavy phase into a catalyst-regenerating unit from the tower bottom.