Abstract
Poplar NE222 (Populus deltoides Bartr. ex Marsh × P. nigra L.) wood chips were pretreated in a 390 L pilot-scale rotating wood-pulping digester using a dilute sulfite solution of approximately pH 1.8 at 160°C for 40 min for bioconversion to ethanol and lignosulfonate (LS). An estimated combined hydrolysis factor (CHF) of 3.3 was used to scale the pretreatment temperature and time from laboratory bench scale experiments, which balanced sugar yield and inhibitor formation to facilitate high titer ethanol production through fermentation using S. cerevisiae YRH400 without detoxification. A terminal ethanol titer of 43.6 g L-1 with a yield of 247 L tonne wood-1 was achieved at total solids loading of 20%. The relatively low ethanol yield compared with yield from SPORL-pretreated softwoods was due to inefficient utilization of xylose. The LS from SPORL has a substantially higher phenolic group (Ph-OH) content although it is less sulfonated and has a lower molecular weight than a purified commercial softwood LS, and therefore has potential for certain commercial markets and future novel applications through further processing.
Highlights
Biomass from short rotation woody crops has been considered a viable feedstock for producing biofuels and bioproducts using the forest biorefinery concept to reduce our reliance on fossil fuel, mitigate climate change, and stimulate rural economic development (Zhu and Pan, 2010; Zalesny et al, 2011)
Building upon the success of SPORL, we demonstrated SPORL optimization for bioconversion of a poplar wood in laboratory bench scale (1 L) experiments using a combined hydrolysis factor (CHF) to control pretreatment severity at CHF ≈ 2, which allowed us to successfully achieve high titer (>40 g L−1) ethanol production without detoxification using an engineered Saccharomyces cerevisiae (Zhang et al, 2015)
The compounding effect of fermentation inhibition from acetic acid and furans was managed by balancing sugar yield with inhibitor formation using a CHF as a pretreatment severity measure
Summary
Biomass from short rotation woody crops has been considered a viable feedstock for producing biofuels and bioproducts using the forest biorefinery concept to reduce our reliance on fossil fuel, mitigate climate change, and stimulate rural economic development (Zhu and Pan, 2010; Zalesny et al, 2011). Achieving high titer biofuel production from poplar woods remains a challenge; because, the chemical pretreatment step required for removing the recalcitrance of poplars for efficient enzymatic saccharification often produces inhibitors that cause difficulties in downstream processing. The cell wall of poplar woods are highly acetylated (Gille and Pauly, 2012) to result in high concentration of acetic acid in the pretreatment hydrolyzate to substantially inhibit yeast fermentation (Palmqvist and Hahn-Hagerdal, 2000; Klinke et al, 2004; Tian et al, 2011). The compounding inhibition effect of acetic acid with furans and aromatics (Palmqvist et al, 1999) made fermentative cellulosic ethanol production from poplar woods more challenging than from softwoods. Reported studies were limited to using washed solids alone or at low solid loadings when pretreatment hydrolyzate (spent liquor) was used to avoid fermentation difficulties without detoxification (Zhu et al, 2011; Kim et al, 2013; Kundu et al, 2014)
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