Abstract:
A process and a system for cracking dicyclopentadiene are disclosed pursuant to the process preheated dicyclopentadiene is introduced into a heated transfer fluid sufficiently below the transfer fluid surface to accomplish substantially complete conversion of said dicyclopentadiene to monomeric cyclopentadiene vapor.

Description:
This is a continuation of application Ser. No. 07/569,657, filed Aug. 20, 1990, now abandoned. 
    
    
     This invention relates to the thermal decomposition of dicyclopentadiene, C 10  H 12 , to produce cyclopentadiene monomer, C 5  H 6 . 
     BACKGROUND OF THE INVENTION 
     Various dicyclopentadiene cracking methods are known. The dissociation to the monomer is a monomolecular reaction. The cracking can be accomplished by distilling dicyclopentadiene under atmospheric pressure. Dicyclopentadiene boils at 170° C. It cracks at a rate of 36% per hour at 170° C. Monomer is obtained by maintaining the top temperature of the fractionating column at 41°-42° C. 
     Another procedure involves adding dicyclopentadiene to a hot liquid, e.g., a high boiling oil at 250°-260° C. The resulting vapors are fractionated to remove refluxing uncracked dimer and entrained liquid. A commercial procedure entails vapor phase cracking at 350°-400° C. See, generally, &#34;Cyclopentadiene and Dicyclopentadiene&#34;, Kirk-Othmer: Encyclopedia of Chemical Technology, Vol. 7 , 3d Ed., p. 424 (1979); and U.S. Pat. Nos. 2,453,044; 2,490,866; 3,007,978; 3,544,644; 3,719,718 and 4,048,242. 
     SUMMARY OF THE INVENTION 
     Increasing temperature increases the rate of the dicyclopentadiene cracking reaction. At temperatures above 100° C., cyclopentadiene reacts with dicyclopentadiene to form tri, tetra and higher cyclopentadiene polymers. This and other undesirable side reactions are to be avoided if high yields of cyclopentadiene monomer are to be obtained. 
     This invention provides an improved dicyclopentadiene cracking process which entails rapidly heating the dimer in a heat transfer fluid to the cracking temperature in the absence of the monomer and rapidly removing the cyclopentadiene monomer vapor from the heat transfer fluid prior to condensation to the liquid state. The invention also includes a dicyclopentadiene cracking apparatus or system. Optimum embodiments of the invention provide for about 98-100% conversion of dicyclopentadiene to monomer at about 97-100% purity. 
    
    
     DESCRIPTION OF THE FIGURE 
     FIG. 1 depicts the dicyclopentadiene system of the invention. Some details of the method are set forth on the figure. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the process embodiment of the invention includes introducing dicyclopentadiene in the liquid state into an agitated heat transfer medium maintained at a temperature effective to convert dicyclopentadiene to cyclopentadiene monomer. The dicyclopentadiene is introduced at a point sufficiently below the surface thereof to insure substantially complete conversion to monomeric cyclopentadiene vapor within the heat transfer fluid. The heat transfer fluid is agitated to achieve efficient monomeric cracking and escape of the cyclopentadiene monomer vapor from the heat transfer fluid surface. 
     The dicyclopentadiene is preheated for conversion from the normal solid state at room temperature to the liquid state prior to introduction below the surface of the heat transfer fluid. The dicyclopentadiene may be preheated to a temperature from about 32° C. to about 170° C., preferably from about 42° C. to about 150° C. 
     Any inert heat transfer fluid boiling above the cracking temperature of dicyclopentadiene may be utilized. Suitable heat transfer fluids include molten diphenylether, molten diphenylmethane, molten decalin, molten tetralin, and Dowtherm™. The heat transfer fluid is appropriately maintained at a temperature of from about 230° C. to about 350° C., preferably from about 230° C. to about 260° C. 
     As specifically illustrated by FIG. 1, dicyclopentadiene is transferred from supply 1 by metering pump 2 at a temperature above 50° C. into a preheater 3. In the system of the invention, the preheater is optional. Any means for providing cyclopentadiene in the liquid state may be used. As shown in FIG. 1, the preheater processes dicyclopentadiene at a temperature of about 150° C., which is then passed into a reactor 4 containing a heat transfer fluid 5, such as molten diphenylether, diphenylmethane, decalin, tetralin or Dowtherm™, maintained at a temperature of about 230° C. to 260° C. by electric heater elements 6. The heat transfer fluid is agitated by rotation of the agitator shaft 7, which is provided with blades 8. 
     The monomeric cyclopentadiene is removed from the reactor 4 at a temperature of about 230° C. to 250° C. through the conduit 7 which is provided with a first condensor 8 and with a mist eliminator packing 9 positioned near the top of the first condensor. The temperature of the condensate which exits from the condenser is about 45° C. The condensate passes through a second condensor 10, maintained at a temperature of about 0° C. to about 20° C., and thence into a chilled receiver 11, where it is maintained at 0° C. to 20° C. under an inert, e.g., nitrogen atmosphere. 
     In an actual experiment conducted under the conditions described and illustrated by FIG. 1, 1600 pounds of 97% pure dicyclopentadiene was pumped into the reactor--which contained about 7 gallons of molten diphenylether. Approximately 1568 pounds of 99% cyclopentadiene monomer was received in the chilled receiver. 
     After completion of the cracking reaction, the volume of the heat transfer fluid was still 7 gallons and its viscosity at 35° C. was about the same as that of fresh diphenylether, thus indicating negligible formation of high cyclopentadiene polymers during the cracking reaction.