(2022) Journal of CO₂ Utilization_Recovery of lactic acid from biodegradable straw waste through a CO₂-assisted thermochemical process

Kim S., Lee H.S., Yang W., Kwon E.E., Lee J.

(Elsevier Ltd) Journal of CO2 Utilization ISSN: 22129820 Vol.64 Issue. Article No.102164 DOI: 10.1016/j.jcou.2022.102164

Although biodegradable straws are widely used, they are often unsuitable for disposal in open environments and cannot be recycled in the same manner as conventional plastic straws. Hence, an effective disposal method needs to be developed. Herein, the thermochemical conversion of biodegradable straws made mostly of polylactic acid (PLA) was considered, and the effects of CO₂ on the characteristics of thermochemical products produced from biodegradable straws were explored. The thermochemical conversion of the biodegradable straw in CO₂ atmosphere yielded more non-condensable gases than the thermochemical conversion in N₂ owing to an enhanced thermal cracking of volatiles at 800 °C. At temperatures > 600 °C in CO₂, the reverse water-gas shift reaction considerably increased the CO selectivity. Using CO₂ in the thermochemical conversion decreased yields of char and wax, which was attributed to CO₂ enhancing thermal cracking of volatiles evolved during the thermochemical conversion and C-H and O-H bonds present in the feedstock. The CO₂ thermal agent promoted the cleavage of the polymeric bond of PLA to produce up to 14-fold more lactic acid (the monomer of PLA) than that produced with N₂ agent, while it suppressed radical reactions to produce fewer phenyls and polycyclic aromatic hydrocarbons. Thermochemical treatment in a CO₂ environment has a significant feature of upcycling biodegradable plastic waste, such as biodegradable straws. © 2022 Elsevier Ltd.

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Government of Republic of Korea ( Ministry of Science and ICT ) (No. 2020R1C1C1003225 and 2021R1A4A1031357 ).