Direct Production of Propene from the Thermolysis of Poly(beta-hydroxybutyrate) (PHB). An Experimental and DFT Investigation

Heidi Pilath, Ashutosh Mittal, David Robichaud, David Johnson, Jared Clark, William Michener

Research output: Contribution to journalArticlepeer-review

15 Scopus Citations


We demonstrate a synthetic route toward the production of propene directly from poly(β-hydroxybutyrate) (PHB), the most common of a wide range of high-molecular-mass microbial polyhydroxyalkanoates. Propene, a major commercial hydrocarbon, was obtained from the depolymerization of PHB and subsequent decarboxylation of the crotonic acid monomer in good yields (up to 75 mol %). The energetics of PHB depolymerization and the gas-phase decarboxylation of crotonic acid were also studied using density functional theory (DFT). The average activation energy for the cleavage of the R′C(O)O-R linkage is calculated to be 163.9 ± 7.0 kJ mol-1. Intramolecular, autoacceleration effects regarding the depolymerization of PHB, as suggested in some literature accounts, arising from the formation of crotonyl and carboxyl functional groups in the products could not be confirmed by the results of DFT and microkinetic modeling. DFT results, however, suggest that intermolecular catalysis involving terminal carboxyl groups may accelerate PHB depolymerization. Activation energies for this process were estimated to be about 20 kJ mol-1 lower than that for the noncatalyzed ester cleavage, 144.3 ± 6.4 kJ mol-1. DFT calculations predict the decarboxylation of crotonic acid to follow second-order kinetics with an activation energy of 147.5 ± 6.3 kJ mol-1, consistent with that measured experimentally, 146.9 kJ mol-1. Microkinetic modeling of the PHB to propene overall reaction predicts decarboxylation of crotonic acid to be the rate-limiting step, consistent with experimental observations. The results also indicate that improvements made to enhance the isomerization of crotonic acid to vinylacetic acid will improve the direct conversion of PHB to propene.

Original languageAmerican English
Pages (from-to)332-345
Number of pages14
JournalJournal of Physical Chemistry A
Issue number3
StatePublished - 28 Jan 2016

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.

NREL Publication Number

  • NREL/JA-2700-63606


  • crotonic acid
  • decarboxylation
  • depolymerization
  • kinetics
  • modeling
  • polyhydroxyalkanoates
  • polyhydroxybutyrate
  • propene
  • propylene


Dive into the research topics of 'Direct Production of Propene from the Thermolysis of Poly(beta-hydroxybutyrate) (PHB). An Experimental and DFT Investigation'. Together they form a unique fingerprint.

Cite this