Rigorous Calculation of Greenhouse Gases (GHG) in Sustainable <scp>l</scp>-lactic Acid Production from Lignocellulosic Biomass based on Advanced Biorefinery Processing Technology

Utilizing lignocellulosic biomass to produce high-purity l-lactic acid as the monomer of poly(lactic acid) (PLA) is an important pathway for reducing greenhouse gas (GHG) emissions. This study developed an Aspen Plus simulation model and a life-cycle assessment model for producing high-purity l-lactic acid using corn stover feedstock based on thermodynamic principles and experimental data. An advanced dry biorefinery technology is selected as the process platform because of its high conversion performance, close to the dry milling of corn, as well as the significantly reduced energy consumption and wastewater generation. The GHG emissions of corn stover during the growth period are not considered due to its agricultural waste property and to prevent double counting from corn. Full evaporation of wastewater is used to provide process water and steam supplies, considering the weak infrastructure for wastewater treatment and the freshwater supply in agricultural regions. The rigorous calculations show that producing one metric ton of purified l-lactic acid consumes 2.87 ton of corn stover as carbohydrate feedstock, 219.3 kWh of electricity, and 2.98 ton of fresh water for process use with the generation of 1.24 ton of wastewater. No external heat energy input is needed, because the lignin residue combustion provides sufficient heat energy for process use. Based on the detailed data, the calculated GHG emissions for producing one kg l-lactic acid by dry biorefining of corn stover is 0.618 kg CO2 equiv which is only 18% of that produced by dry milling of corn. This study provides an important sustainability basis and decision-making support for biobased plastic implementation.