Biorefinery of sweet sorghum stem

Sweet sorghum has been considered as a viable energy crop for alcohol fuel production. This review discloses a novel approach for the biorefining of sweet sorghum stem to produce multiple valuable products, such as ethanol, butanol and wood plastic composites. Sweet sorghum stem has a high concentration of soluble sugars in its juice, which can be fermented to produce ethanol by Saccharomyces cerevisiae. In order to obtain high ethanol yield and fermentation rates, concentrated juice with an initial total sugar concentration of 300gL−1 was fermented. The maximum ethanol concentration after 54h reached 140gL−1 with a yield of 0.49g ethanol per g consumed sugar, which is 97% of the theoretical value. Sweet sorghum bagasse, obtained from juice squeezing, was pretreated by acetic acid to hydrolyze 80–90% of the contained hemicelluloses. Using this hydrolysate as raw material (total sugar 55gL−1), 19.21gL−1 total solvent (butanol 9.34g, ethanol 2.5g, and acetone 7.36g) was produced by Clostridium acetobutylicum. The residual bagasse after pretreatment was extruded with PLA in a twin-screw extruder to produce a final product having a PLA: fiber ratio of 2:1, a tensile strength of 49.5M and a flexible strength of 65MPa. This product has potential use for applications where truly biodegradable materials are required. This strategy for sustainability is crucial for the industrialization of biofuels from sweet sorghum.