Chapter 19: A Route from Biomass to Hydrocarbons via Depolymerization and Decarboxylation of Microbially Produced Polyhydroxybutyrate

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Abstract

There are many potential chemical intermediates that can be made by fermentation of sugars, and a variety of chemicals that could be made by growing organisms, such as fungi, on biomass. Virtually all of these intermediates require some form of chemical transformation before they are ready to be used as infrastructure-compatible transportation fuels. The route that has been examined in this work is the conversion of polyhydroxybutyrate (PHB) to propene that would be an intermediate to hydrocarbon fuels. This route appears promising, because there are several microorganisms that can be grown on sugars or even biomass that incorporate high levels of PHB (up to 80% of dry cell mass) as a form of energy storage molecule. Thermal breakdown of PHB proceeds via an intermediate carboxylic acid, which can then be decarboxylated to an alkene. Oligomerization of the alkene by well-known patented technologies would permit production of a range of hydrocarbon fuels from a carbohydrate derived intermediate. 2-Butenoic acid (crotonic acid (CA)), the depolymerization product from PHB, can be effectively decarboxylated to propene at molar yields approaching 80% using a relatively simple thermal treatment at 400°C for 15min. This objective has been accomplished by direct treatment of solid CA, without use of water or another solvent and without use of a catalyst. The pressures generated (about 180psi at the reaction temperature) are just due to the formation of the product gases, propene and CO2. Furthermore, PHB can be directly converted under the same conditions to propene in similar yields. In addition, Cupriavidus necator-containing PHB has been produced and used to test the direct conversion of PHB in bacterial cells. The yields (60-70molar%) of propene from whole cells were slightly lower than from CA or pure PHB, but still acceptable. Importantly, propene was obtained from whole cells, demonstrating that an expensive process step to isolate PHB from the cells was unnecessary for this process.

Original languageAmerican English
Title of host publicationDirect Microbial Conversion of Biomass to Advanced Biofuels
EditorsC. A. Eckert, Cong T. Trinh
PublisherElsevier
Pages383-394
Number of pages12
ISBN (Print)9780444595928
DOIs
StatePublished - 2015

Bibliographical note

Publisher Copyright:
© 2015 Elsevier B.V. All rights reserved.

NREL Publication Number

  • NREL/CH-2700-66113

Keywords

  • Fermentation
  • Hydrocarbons
  • PHA
  • PHB
  • Polyhydroxybutyrate

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