Process for the vapor-phase thermal cracking of dicyclopentadiene and a process for the manufacture of high purity dicyclopentadiene

A process for manufacturing high purity dicyclopentadiene from C.sub.5 fractions obtained in thermal cracking of petroleum comprising the steps of:

• A. heating a C.sub.5 fraction to dimerize cyclopentadiene contained in said C.sub.5 fraction;
• B. distilling off unreacted C.sub.5 components from the effluent of step A to obtain crude dicyclopentadiene having a dicyclopentadine concentration of 70% by weight or more;
• C. thermally cracking, in a vapor-phase process, a mixture of said crude dicyclopentadiene and water and/or steam in a cracking tube or tubes under cracking conditions comprising a temperature ranging between about 250.degree. C. and 450.degree. C., wherein the mixing ratio of said crude dicyclopentadiene and said water and/or steam is between about 5 and 230 parts by weight of water and/or steam for each 100 parts by weight of said crude dicyclopentadiene, with the residence time of said mixture in said cracking tube or tubes being between about 0.3 and 5 seconds calculated as gaseous state of said mixture under the cracking conditions used and the direction of flow of said mixture passing through said cracking tube or tubes is constantly maintained downward;
• D. cooling the effluent of step C to liquify water and heavy components contained in the effluent of step C, separating and removing the liquified water and heavy components from a gas consisting substantially of cyclopentadiene, further cooling the gas to liquify the cyclopentadiene and recovering the liquified cyclopentadiene;
• E. redimerizing said cyclopentadiene obtained from step D;
• F. distilling the effluent of step E to remove light components as overhead;
• G. fractionating the bottom fraction of step F to recover purified dicyclopentadiene as the overhead fraction;
• and
• H. recycling the heavy fraction obtained as the bottom fraction of step G to said step C, to said step B, or to said step A.