Deep eutectic solvents (DES) are intrinsically cheaper than many ionic liquids (ILs) due to low precursor cost, simple synthesis and improved recyclability. In comparison to ILs, DES research in biomass processing is still in its nascent stages. Meanwhile certain DESs can be as effective as ILs in fractionating lignocellulosic biomass. However, the lignin carbohydrate complex degradation mechanism in metal chloride DES (mDES), computational predictability of eutectic points, and mDES characteristics are not well understood. Also, understanding the structural and chemical properties of DES-processed lignin (DES-PL) will be critical for identifying possible valorization pathways for the DES-PL toward high-value products. This study aims to i) explore the pretreatment efficacy of mDES in releasing fermentable sugars, ii) characterize the lignin streams from mDES treated sorghum and further upgrade the extracted lignin to phenolic compounds, iii) predict the eutectic points for the transition metal DES and characterize its physicochemical properties. Results illustrate a glucose and xylose yield of 96.3 and 82.9 %, respectively using ethylene glycol:ZnCl2 (4:1) at 10% biomass loading. Molecular weight distribution of the lignin fraction was followed using gel permeation chromatography, while the products in the liquid fraction were identified and quantified using a GC-MS. Cleavage of the lignin inter-unit linkages was further investigated by H1C13 HSQC NMR to understand the fractionation mechanisms. Using a computational approach to calculate physicochemical properties of DES via PSRK-NRTL EoS and the solid:liquid boundaryof the ethylene glycol:ZnCl2 DES was investigated. The eutectic point was determined to exist at an ethylene glycol mole fraction of 0.88, while the freezing point at the eutectic point was determined to be 254.5 K. This is in reasonable agreement with an experimentally determined freezing point of 243.15 K. This study provides a mechanistic understanding of biomass fractionation and lignin depolymerization in mDES and explores catalytic upgrading of DES-PL to value-added products.

Metal chloride deep eutectic solvents for biomass fractionation: Experimental and computational approach

2019 Spring National Meeting

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