Nuclear Magnetic Resonance Investigation of the Fractionation of Water–Ethanol Mixtures with Cellulose and Its Cross-Linked Biopolymer Forms

Abstract

Cellulose (CE) was cross-linked with epichlorohydrin (EPI) at variable compositions, and the fractionation properties were investigated in binary water–ethanol (W–E) solutions, including the pure solvent systems. The relative uptake of each solvent was measured using quantitative ¹H nuclear magnetic resonance (qNMR) spectroscopy. This study highlights the utility of qNMR as a rapid screening method for estimation of solvent selective fractionation in binary mixtures. The uptake properties of CE–EPI cross-linked polymers with ethanol and water were well-described using the Sips isotherm model. Modeling shows that the monolayer surface coverage (<i>Q</i>_m) of ethanol and water onto the polymer materials covers a range (1.13–2.44 g/g) of values with heterogeneous adsorption behavior, in agreement with the Sips exponential fitting parameter (<i>n</i>_s ≠ 1). The CE–EPI adsorbents display unique fractionation with water and ethanol from binary solutions, as evidenced by the relative selectivity (<i>R</i>_selectivity) value in binary W–E solvent systems. The <i>R</i>_selectivity [<i>Q</i>_m(W)/<i>Q</i>_m(E)] values at saturative conditions varied (from 1.10 to 2.03) and further illustrate that CE materials display molecular selective solvent fractionation in binary W–E solutions. This study provides a greater molecular level understanding for the adsorptive uptake properties of CE that are relevant to developing CE-based adsorbent technology for the fractionation of biofuels and related chemical separations