Biorefining of ethanol and methane from NaOH pretreated poplar residues: Mass balance and energy flow analyses

Poplar, a crucial player in lignocellulosic biofuel production worldwide, can be divided into five types. The feedstock variability would significantly impact the scale-up and commercialization of biofuel technologies from poplar. To date, few studies were found comparing ethanol and biogas production from different types of poplar. This study compared the conversion efficiency of NaOH pretreated five types of poplar residues to ethanol and biogas under three biological conversion processes (namely ethanol fermentation process, anaerobic digestion (AD) process, and cascading ethanol fermentation and AD process); the flow of mass, carbon, nitrogen and energy were also analyzed by material flow analysis. 48.4-60.1 % of theoretical ethanol yield, and the specific methane yield of 201 +/- 11.0-270 +/- 3.40 mL/g volatile solids were obtained under the co-production process, with the highest yield from Populus trichocarpa (N2). These results showed that the co-production process (cascading ethanol fermentation and AD process) of poplar N2 outperformed ethanol fermentation and AD in terms of energy conversion efficiency, which was 121 % and 42.9 % higher than the ethanol fermentation process and AD process, respectively. Mass and energy balance analysis showed that under the co-production process, 158 g ethanol and 103 g methane could be obtained from 1 kg pretreated poplar N2, corresponding to a total energy output of 9.5 MJ, with an energy conversion efficiency of 54.3 %. This study may provide new insights into the breeding of new poplar species for the current biorefinery process.

Automated summary

Poplar, a crucial player in lignocellulosic biofuel production worldwide, can be divided into five types. This study compared the conversion efficiency of different types of poplar residues to ethanol and biogas and found that the co-production process of cascading ethanol fermentation and anaerobic digestion outperformed ethanol fermentation and anaerobic digestion in terms of energy conversion efficiency.