Method for producing polyoxymethylene dimethyl ethers

A method for producing polyoxymethylene dimethyl ethers, the method comprising:

• conducting a synthetic reaction process including:
• feeding dimethoxymethane and paraformaldehyde into a fluidized bed reactor, and
• contacting the dimethoxymethane and paraformaldehyde with a solid acid catalyst to produce a reaction mixture of PODEk, wherein k is an integer bigger than 1;
• conducting a product separation process including:
• a pre-rectification, an extractive rectification and a vacuum rectification;
• during pre-rectification:
• feeding the reaction mixture from the fluidized bed reactor into a pre-rectifying column and separating the reaction mixture into an overhead fraction of dimethoxymethane, a side-draw fraction of PODE2 and a heavy fraction of PODEn>2, unconverted formaldehyde and by-products, recycling a first portion of the overhead fraction of dimethoxymethane into the fluidized bed reactor,
• refluxing a second portion of the overhead fraction of dimethoxymethane into the pre-rectifying column, and
• recycling the side-draw fraction of PODE2 into the fluidized bed reactor;
• during the extractive rectification:
• feeding the heavy fraction of PODEn>2 into the top of an extractive rectifying column,
• contacting the heavy fraction of PODEn>2 with an extraction solvent,
• entering the unconverted formaldehyde and by-products into an extract phase, and
• regenerating the extract phase to separate the extraction solvent and the unconverted formaldehyde for recycling;
• and
• during the vacuum rectification:
• feeding a raffinate phase from the bottom of the extractive rectifying column into the vacuum rectifying column, and
• separating the raffinate phase into an overhead fraction of PODE3˜m and a heavy fraction of PODE(m+1)˜n, wherein m is an integer bigger than 3 and n is an integer bigger than m+1.