System and method for continuously producing polyoxymethylene dimethyl ethers

A system for continuously producing polyoxymethylene dimethyl ethers, comprising:

• a polymerization reaction unit, comprising a polymerization reactor, an extraction column, and a rectification column, wherein a polymerization reaction takes place in the presence of a first acid ionic liquid as a catalyst by using formaldehyde as a reaction material in the polymerization reactor, a gas generated in the polymerization reactor enters the extraction column after condensation, followed by extraction by an extractant, and trioxymethylene is obtained through the rectification in the rectification column;
• an acetalation unit, comprising a single or multi-stage reactor and a gas phase condenser, wherein in the single or multi-stage reactor, the trioxymethylene obtained in the polymerization reaction unit is subjected to an acetalation reaction with methanol in the presence of a second acid ionic liquid catalyst resulting in crude polyoxymethylene dimethyl ethers (DMMn, n=1-8);
• a product separation unit, comprising an extraction column and a single or multi-stage rectification column connected to each other in series;
• wherein the crude DMMn is separated into a light phase and a heavy phase in the product separation unit, wherein the heavy phase contains the second acid ionic liquid catalyst and water, the light phase contains unreacted methanol and DMM1, trioxymethylene and DMM2, DMM3-8, and the extractant;
• and
• a catalyst regeneration unit, comprising a film separator, wherein the catalyst regeneration unit receives the heavy phase separated from the product separation unit, and the second acid ionic liquid catalyst in the heavy phase is recycled to the acetalation reaction unit after dehydration in the catalyst regeneration unit.