Extraction of Furfural and Furfural/5-Hydroxymethylfurfural from Mixed Lignocellulosic Biomass-Derived Feedstocks

We present a combined in
silico and experimental
study on the extraction of furfural and 5-hydroxymethylfurfural (HMF)
in aqueous–organic biphasic systems. We predict the liquid–liquid
equilibria and furfural/HMF partition coefficients of over 2200 water-organic
biphasic systems using the multiscale COSMO-RS model and measure experimentally
single-component (furfural) and mixture (furfural and HMF) partition
coefficients at room and dehydration reaction-relevant temperatures
in 28 solvents. We find the experimental data to be within a factor
of 2 from the COSMO-RS predictions. Even though furfural and HMF have
chemical similarity, the slight differences in molecular structure
render the separation of furfural easier by the supply of more solvents
of higher partition coefficient for extraction. We leverage this molecular
difference and experimentally demonstrate that with an additional
extraction step, using dichloromethane or toluene, we can selectively
extract furfural from furfural-HMF mixtures, which can coexist in
lignocellulosic biomass dehydration products, despite their partition
coefficients being generally correlated. We complement solvent selection
criteria for biphasic lignocellulosic biomass processes with a simple
mass balance extraction model for determining volume ratios in multistage
extraction. Finally, the molecular nature of the preferential furfural
extraction is rationalized using COSMO-RS σ-profile analysis.