Method for preparing highly pure m-pentadiene through acetonitrile process

The invention relates to a method for preparing highly pure m-pentadiene through an acetonitrile process. The method comprises the following steps: carrying out thermal polymerization on an m-pentadiene concentrate obtained in the ethylene cracking C5 separation process through a thermal polymerization kettle, allowing the thermal polymerized concentrate into a heavy component removal tower in order to remove dicyclopentadiene, allowing the material obtained from the tower top to enter a light component removal tower in order to remove light components, allowing the material obtained from the tower bottom to enter a primary extraction rectifying tower in order to carry out extracting separation, allowing the material based on m-pentadiene and an extractant from the tower bottom to enter a primary stripping tower to carry out stripping rectification, allowing the material obtained from the tower top to enter a secondary extraction rectifying tower in order to rectify, and allowing crude m-pentadiene obtained from the tower top to enter a water washing tower to remove acetonitrile and water in order to obtain m-pentadiene with high purity of above 98% and generate dicyclopentadiene with the purity of above 60%. A two stage extraction and two stage washing process is adopted, so impurities in m-pentadiene can be well removed, and the method has the advantages of simple process, high yield and purity, and easy industrialized production.