Lignin-based thermo-sensitive hydrogel for selective recovery of butanol from dilute solution

Currently, biorefinery industry with biobutanol as product are firmly established in China. Corncobs are usually used as feedstock for Acetone–butanol–ethanol (ABE) fermentation. Cellulose and hemicellulose in corncobs could be used as raw materials for fermentation through enzymatic hydrolysis, but the lignin as a by-product has not been effectively used. Meanwhile, the low concentration of biobutanol in fermentation broth leads to high-energy consumption for separation. In this study, lignin obtained from corncobs was found to be a good material to prepare thermo-sensitive hydrogel for biobutanol enrichment, which has high adsorption capacity and unique desorption performance. By free radical polymerization, the excellent lignin-grafted-poly(N,N-diethylacrylamide) hydrogel (LGD) was successfully prepared. The adsorption capacity of LGD for butanol (544.22 mg g−1) was two times and five times as much as lignin and poly(N,N-diethylacrylamide) (PDEAAm), respectively. The adsorbed saturated hydrogel could first remove a large amount of free water at 50 °C to reduce the energy consumed for free water vaporization. Further thermal desorption at 120 °C yielded a concentrated desorption solution with a concentration of 118.74 g L−1, which could significantly reduce the energy consumption of subsequent distillation. The aromatic ring and hydrophobic chain in lignin proved to be effective sites for butanol adsorption. PDEAAm not only promoted the effective exposure of adsorption sites on lignin, but also increased the adsorption rate significantly by forming a pore structure. With its high adsorption capacity, fast adsorption rate, and low energy consumption for desorption, the lignin-based thermo-sensitive hydrogels show good prospects for the enrichment of low-concentration biofuels obtained through biological fermentation. It also opens up a new way for efficient and full-component utilization of corncobs.