Kinetics of isoprene-maleic anhydride Diels-Alder reaction in supercritical carbon dioxide

The rate constants for the Diels-Alder reaction of isoprene with maleic anhydride in supercritical carbon dioxide were measured. The temperatures of the measurement were at 308.2, 313.2 and 318.2 K and the pressure range was from 7.5 to 14.1 MPa. A batch reactor used was connected to the Fourier transform infrared (FT-IR) spectroscopy, so that the amount of product can be measured without sampling. The concentrations of product were measured for about 30 to 40 hours at interval of several hours. The reaction rate constants were determined based on the second order reaction relationship. The reaction rate constants at high pressure region coincide with the literature data. The rate constants near the critical pressure of carbon dioxide are several times higher than those in high pressure region at each temperature. It is considered that reaction rate enhancement near the critical pressure is resulted from the local composition enhancement due to density fluctuation because molecular collision would be more frequently. The rate constants obtained were correlated using the transition-state theory coupled with a local composition model by using the Peng-Robinson (PR) equation of state. The correlated results showed a good agreement with the experimental results.