Biodiesel is a promising alternative, and renewable, fuel. As its production increases, so does production of the principle co-product, crude glycerol. The effective utilization of crude glycerol will contribute to the viability of biodiesel. In this review, composition and quality factors of crude glycerol are discussed. The value-added utilization opportunities of crude glycerol are reviewed. The majority of crude glycerol is used as feedstock for production of other value-added chemicals, followed by animal feeds.

The demand for efficient utilization of biomass induces a detailed analysis of the fundamental chemical structures of biomass, especially the complex structures of lignin polymers, which have long been recognized for their negative impact on biorefinery. Traditionally, it has been attempted to reveal the complicated and heterogeneous structure of lignin by a series of chemical analyses, such as thioacidolysis (TA), nitrobenzene oxidation (NBO), and derivatization followed by reductive cleavage (DFRC). Recent advances in nuclear magnetic resonance (NMR) technology undoubtedly have made solution-state NMR become the most widely used technique in structural characterization of lignin due to its versatility in illustrating structural features and structural transformations of lignin polymers. As one of the most promising diagnostic tools, NMR provides unambiguous evidence for specific structures as well as quantitative structural information. The recent advances in two-dimensional solution-state NMR techniques for structural analysis of lignin in isolated and whole cell wall states (in situ), as well as their applications are reviewed.

A low-cost and green biorefinery will increase the economy and revenue from lignocellulosic biomass. Herein, a biomass-derived deep eutectic solvent (DES) pretreatment was developed to deconstruct the recalcitrant structure of Eucalyptus for further cellulose enzymatic hydrolysis and lignin valorization. The DES consisted of biomass-derived chemicals (lactic acid and choline chloride). The results showed that DES pretreatment resulted in notable removal of hemicelluloses and lignin, and drastically reduced “biomass recalcitrance”. Under the optimum conditions (DES ratio: 10 : 1, temperature: 110 °C, time: 6 h), the glucose yield by enzymatic hydrolysis reached 94.3%, which was significantly enhanced 9.8 times compared to that of the original biomass without DES pretreatment. The state-of-the-art analysis indicated that the regenerated lignin exhibited well-preserved structures (i.e., β-O-4, β–β linkages) without contaminated carbohydrates, and it had a relatively low and homogeneous molecular weight. All these structural characteristics suggested that lignin has great potential application in its conversion into bio-based chemicals and materials. Besides, it is urgent to develop low-cost recycled DESs as green solvents for sustainable biomass pretreatment. The lifetime and recyclability experiment of the DES solution showed that the recovery yield of the DES was at least 90% and the fundamental structural properties of the recycled DES were almost unchanged throughout the recycling cycles. More importantly, the pretreatment efficiency (delignification and enzymatic saccharification) was still largely maintained after the recycling process. Overall, this work demonstrated that biomass pretreatment with the recycled DES was promising for a low-cost biorefinery to achieve an efficient fractionation of lignocellulosic biomass into fermentable glucose and high-quality lignin with tailored chemical structures.