Kinetic Investigation of the Pyrolysis of Isobutyric Anhydride and Isobutyric Acid

Low-carbon
ketenes are produced by the pyrolysis of corresponding
anhydrides or acids. In this work, the pyrolysis experiments of isobutyric
anhydride (IBAN) and isobutyric acid (IBA) were carried out to investigate
the pyrolysis kinetics. Results showed that the pyrolysis temperature
of IBA is far higher than that of IBAN, and dimethylketene (DMK, the
main product) selectivity during IBA pyrolysis is much lower than
that during IBAN pyrolysis. Furthermore, compared with the four-centered
transition state of acid pyrolysis, a more stable six-centered transition
state of anhydride pyrolysis was obtained by computational chemistry,
which is the reason for the lower pyrolysis temperature of anhydrides.
The reaction network of IBAN pyrolysis and the corresponding kinetics
were discussed as well. Finally, the effect of different functional
groups (methyl, vinyl, and ethynyl groups) on the activation energies
of anhydride pyrolysis was investigated, providing references for
low-carbon anhydride pyrolysis.