Microwave-assisted extraction of lignin from coconut coir using deep eutectic solvents and its valorization to aromatics

Lignin is a rich renewable source of aromatics present in lignocellulosic biomass (LCB). The extraction of lignin from the intricate LCB network is a challenging task for successful commercialization of sustainable biorefineries. In the present study, a series of choline chloride (ChCl)-carboxylic acid based deep eutectic solvents (DESs) were used for the extraction of lignin from coconut coir under microwave irradiation. Among the synthesized DESs, ChCl: lactic acid (LA) (1:4) gave the highest lignin yield of 82% with >95% purity. Interestingly, the severity factor (H factor) for the pretreatment process was found to be a significantly lower (55.5) as compared to reported studies due to efficient microwave heating. Moreover, the DES showed good recyclability for four recycle runs thus making it a promising candidate for the delignification of LCB. Finally, the extracted lignin was converted to aromatics via catalytic transfer hydrogenation (CTH) using Ru/C and isopropanol as in-situ hydrogen donor.

Automated summary

In this study, deep eutectic solvents (DESs) based on choline chloride and carboxylic acid were successfully used to extract lignin from coconut coir under microwave irradiation, yielding 82% lignin with >95% purity. The severity factor for the pretreatment process was significantly lower, thanks to efficient microwave heating. The extracted lignin was converted to aromatics via catalytic transfer hydrogenation, showing promising results for the delignification of lignocellulosic biomass.