One‐Pot Catalytic Conversion of Poly(3‐hydroxybutyrate) to Propylene at 240 °C

Abstract

Poly(3-hydroxybutyrate) (PHB), a renewable feedstock from microorganisms, was a good resource for propylene production by a simple one-pot reaction. The reaction was catalyzed by triruthenium dodecacarbonyl (TD) at relatively mild temperature (240°C), and the yield and selectivity of propylene reached 22.9 wt% and 46.8%, respectively. A small part of hydrocarbon oils reached 9 wt% was also obtained, which contained 79.1 wt% of carbon and 12.3 wt% of hydrogen, with a theoretical high heating value of 41.2 MJ/kg. Poly(3-hydroxybutyrate) (PHB) [(C 4 H 6 O 2 ) n ], a material accumulated in a variety of microorganisms, is one kind of renewable aliphatic biomass. [1,2] PHB has been regarded as a potential material for the production of valuable compounds, e. g., crotonic acid (CA) and propylene, due to its special structural property and renewability. [3,4] Propylene, the second most important starting product in petrochemical industry, has been widely used for production of valuable chemicals, including polypropylene, propylene oxide, acrylonitrile, etc. [5][6][7] Recently, propylene from biomass has attained much more attention for the production of gasoline through oligomerization of olefins. [8,9] The conventional pathways of PHB conversion usually require high temperature (see Figure 1). The direct production of propylene from PHB by a conventional non-catalytic pyrolysis is not advocated, due to a low yield even at high temperature (> 300°C, Figure 1-1). [10][11][12] Propylene with a yield of 23.4 wt% can be also obtained from PHB through hydrothermal reforming. However, the temperature of the hydrothermal reforming was still high (370°C, Figure 1-2), [13] and heating the huge reaction solvent water to high temperature also increased the energy input. Catalytic pyrolysis at mild temperature is a promising way to save energy input, and the key is to develop an effective catalyst. Triruthenium dodecacarbonyl (TD) is an environmental-friendly catalyst, owing to its acid-free, non-corrosive and non-toxic characteristics, [14,15] and it was found that TD is active in the catalytic decarboxylation of long-chain fatty acid from plant oil. [16,17] In this work, TD was applied for the catalytic depolymerization of PHB, with the aim to obtain propylene at relatively mild temperature (240°C).Since no former information was reported on what is the lowest temperature or temperature range that the TD can catalytically depolymerize PHB, comprehensive thermal analysis (TG, DTG and DSC) of PHB, TD, and PHB-TD mixture were conducted (see Figure 2). Both the TG and DTG curves showed that the decomposition of TD begins at about 245°C, and therefore the highest catalytic pyrolysis temperature should be less than 245°C. PHB is a polyester with high crystallinity, which melted at around 180°C, according to the endothermic peak by the DSC curve at Figure 2B. This means that the reaction was changed from solid-solid contacting reaction to liquidphase involved reaction (solid-liquid or homogeneous phase) when the temperature was above 18...

Recovery Techniques Enabling Circular Chemistry from Wastewater

“…Depolymerization of PHA can be achieved by hydrolysis, alcoholysis, and thermolysis, resulting in 2-hydroxyalkanoic acids, 2-hydroxyalkanoic esters, and 2-alkenoic acids, respectively. So far, production of trans-crotonic acid (referred to as crotonic acid) and cis-crotonic acid (referred to as isocrotonic acid) [14,16,[104][105][106][107], methyl acrylate [108], methyl crotonate [108,109], propylene [110][111][112], 3-hydroxybutyric acid [16,104], methyl 3-hydroxybutanoate [113], cyclic and linear oligomers [114], and hydrocarbon oil [115] from PHB depolymerization have been reported. PHBV is the main biopolymer that can be obtained by MMC, and during the thermal breakdown of PHBV, crotonic acid and 2-pentenoic acid are the main products [116].…”

Tailored recycling chemicals and fuels from poly‐3‐hydroxybutyrate: A review

“…5(a)). 51 PHB is an excellent feedstock for propylene production via hydrothermal reforming 52 or pyrolysis with a triruthenium dodecacarbonyl (Ru 3 (CO) 12 ) catalyst, 53 and the yield of PHB from both processes can reach 23% with 47% selectivity (Fig. 5(b)).…”

“…It should be noted that ~9 wt% of hydrocarbon oils with a high heating value of 41.2 MJ kg −1 can be obtained along with the production of propylene through catalytic pyrolysis at 240°C. 53 The disadvantages of these two processes, however, include (i) they require expensive Ru 3 (CO) 12 and the release of CO in the catalytic pyrolysis 53 and (ii) high reaction pressure (>25 MPa) in the hydrothermal reforming owing to the existence of water at high temperatures (e.g. 370°C).…”