Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) Ashutosh Mittal, Heidi M. Pilath, and David K. Johnson Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401 Abstract Thermal depolymerization and decarboxylation of polyhydroxybutyrate to propene To transform biomass components into hydrocarbon fuels it is clear that there are two main in a flow-through reactor transformations that need to occur, i.e., deoxygenation and carbon chain extension. The Schematic of a flow-through reactor potential routes for decreasing the oxygen content of biomass intermediates include dehydration, hydrodeoxygenation and decarboxylation. One route that is examined here is the conversion of polyhydroxyalkanoates (PHA) to alkenes that would be intermediates to Reactor details: Coil ID: 0.3873 cm; hydrocarbon fuels. Thermal breakdown of PHA proceeds via an intermediate carboxylic acid, Length: 330 cm ; which can then be decarboxylated to an alkene. Oligomerization of alkenes by well-known Volume: 155 mL commercial technologies would permit production of a range of hydrocarbon fuels from a Residence time: 15.5 min carbohydrate derived intermediate. Moreover, polyhydroxybutyrate (PHB) can be produced in 150 μm Cupriavidus necator (formerly known as Ralstonia eutropha) and Alcaligenes eutrophus on a variety of carbon sources including glucose, fructose and glycerol with PHB accumulation reaching 75% of dry cell mass. We conducted thermal conversion of PHB and pure crotonic acid (CA), the intermediate carboxylic acid produced by thermal depolymerization of PHB, in a flow-through reactor. The results of initial experiments on the thermal conversion of CA showed that up to 75 mole% yields of propene could be achieved by optimizing the residence time and temperature of the reactor. Further experiments are being investigated to optimize the reactor parameters and enhance propene yields via thermal conversion of PHB. Chemical transformation of PHB to a hydrocarbon fuel H OH - - - Fermentation Depolymer Decarbox Oligomer HO - CH O ization ylation ization H 2CO2 3 CH3 O CH3 HO O - H CO2 H HO O OH n Gas (Propene and CO2) production in a flow-through experiment H OH OH n 2,500 120 ucose o rox u ra e ro on c c ro ene rocar ons Gl H P lyhyd yb ty t (PHB) C t i A id (CA) P p Hyd b Exp # 15 Exp # 15

2,000 Exp # 16 100 Exp # 16

Kinetics for the depolymerization of PHB and decarboxylation of 80 crotonic acid in a batch reactor 1,500 2.5 2.0 60 250C 400C 1,000

A 1.8 mL Volume, 40

234C B 375C mL/min Flowrate, Heat-up Reaction N2 Flush 217C 350C 500 2.0 1.6 20 200C 325C 1.4 0 0 0 20 40 60 80 0 20 40 60 80 1.5 1.2 Time, min Time, min 1.0 CA Conv)] PHB Conv.)] PHBConv.)] - - Propene and CO2 yields from decarboxylation of CA in flow-through experiments 1.0 0.8 Ln(1 Ln(1 [- [- 0.6

Reaction Unreacted Yield 0.5 0.4 Temp. ˚C CA

0.2

Flowrate

2

time, min Propene CO2 0.0 0.0 Residence N g % Coil 0 900 1800 2700 3600 4500 5400 0 1000 2000 3000 4000 5000 6000 Tube % % Time, s Time, s First-order reaction kinetics for (A) thermal depolymerization of PHB(B) decarboxylation of CA. 340 375 10 15.5 79.1 78.8 0.37 18.5 The straight lines represent linear fits to the experimental data 340 375 10 15.5 70.5 68.8 0.53 26.5 Arrhenius parameters and Propene and CO yields from batch experiments 2 375 375 10 15.5 60.2 61.6 0.73 36.5 E (kJ Temperature, Propene CO Yield A (s-1) a R2 Time, min 2 mol-1) °C Yield (%) (%) Conclusions PHB 65 22 ± 3 32 ± 5 1.6 × 1010 128.6 0.987 325 • This work has shown that in a batch reactor both the depolymerization of PHB to CA depolymerization 100 28 42 60 43 ± 4 58 ± 5 and the decarboxylation of CA can be described with first-order reaction kinetics. CA 350 • Decarboxylation is the rate limiting step; the CA decarboxylation rate is 500-900 times 1.65 × 108 140.2 0.964 90 51 ± 1 67 ± 0.4 decarboxylation 30 49 ± 2 59 ± 5 slower than the PHB depolymerization reaction depending on temperature. 375 • 60 64 ± 2 76 ± 4 Thermal decarboxylation of crotonic acid was achieved in a flow-through reactor. Arrhenius parameters for the conversion of PHB and • 10 50 ± 3 66 ± 3 Decarboxylation of crotonic acid in a flow-through reactor under optimized conditions crotonic acid through depolymerization and 400 resulted in greater than 75% yields of propene at 375˚C. decarboxylation, respectively. 15 64 ± 2 81 ± 8

Propene and CO2 yields from decarboxylation of CA

The information contained in this poster is subject to a government license. This work was supported by the Bioenergy Technology Office (BETO) 249th ACS National Meeting & Exposition of the U.S. Department of Energy March 22 – 26, 2015, Denver, Colorado Operated by the Alliance for Sustainable Energy, LLC NREL/PO-2700-63973 This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08-GO28308 with the National Renewable Energy Laboratory