Method for Producing Polyoxymethylene Dimethyl Ethers

A method for producing polyoxymethylene dimethyl ethers from dimethoxymethane and paraformaldehyde in a fluidized bed reactor with solid acid as catalyst, the method comprising the steps of:

• (1) synthetic reaction unit:
• feeding dimethoxymethane and paraformaldehyde into a fluidized bed reactor, the dimethoxymethane and paraformaldehyde contact with solid acid catalyst and react, and produce reaction mixture of PODEk, wherein k is an integer bigger than 1;
• (2) product separation unit:
• including pre-rectification, extractive rectification and vacuum rectification;
• during the pre-rectification, the reaction mixture from the fluidized bed reactor is fed into a pre-rectifying column and separated into overhead fraction dimethoxymethane, side-draw fraction PODE2 and heavy fraction comprising PODEn>2, unconverted formaldehyde and by-products, wherein a portion of overhead fraction dimethoxymethaneis is recycled into the fluidized bed reactor and the left is refluxed into the pre-rectifying column;
• the side-draw fraction PODE2 is recycled into the fluidized bed reactor;
• during the extractive rectification, the heavy fraction comprising PODEn>2 is fed into top of an extractive rectifying column and contact with extraction solvent;
• the unconverted formaldehyde and by-products enter the extract phase;
• and the extract phase is regenerated for separation of the extraction solvent and the unconverted formaldehyde for recycling,
• during the vacuum rectification, raffinate phase is fed into the vacuum rectifying column and separated into overhead fraction PODE3˜m and heavy fraction PODE(m+1)˜n, PODE3˜m are target components, wherein m is an integer bigger than 3, and determined by actual demand, and n is an integer bigger than m+1.