As seen in Table 9, the ethanol production total cost was 6888 Yuan/t if ethanol was the single production. Given the conversion efficiency of corn stover, only hexoses were converted to ethanol, the yield was 143.75 kg/t DM. While the ethanol yield of co-fermentation of pentose and hexose in this paper was 202.75 kg/t DM. The improved conversion efficiencies of pentose resulted in 41.0% increase of ethanol yield.
The materials cost account for 52.1% of total cost, including 25.41% corn stover costs and 21.78% enzyme cost. Due to the multi-products within the industrial project, the corn stover costs would be shared with CNG and LPCM. As mentioned above, the ethanol yield was 202.75 kg/t DM corn stover, and the content of glucan and xylan within corn stover accounted for 60% (DM), while 30% for lignin. Therefore, the corn stover costs per ton ethanol were shared in ethanol, LPCM and CNG, for 60%, 30% and 10%, respectively, which resulted in the reduction of the feedstock cost of ethanol by 19.4%. The corresponding ethanol cost was reduced to 5571.6 Yuan/t after the cost was shared by LPCM and CNG. In conclusion, the low cost of feedstock, simple and integrated conversion process, and multi-products production contribute to the competiveness of this industrial ethanol production process.
4. Conclusion
Lignocellulosic bioethanol is an attractive alternative for renewable energy. However, there are still some challenges hampering its commercialization. The breakthrough of key technologies on pretreatment, hydrolysis and fermentation will make lignocellulosic bioethanol more promising. The recalcitrance was deconstructed using selective-fractionation technology, by which activating and improving the biotransformation performance of components suitable for enzymatic hydrolysis. Both pentose and hexose were simultaneously converted into bioethanol, increasing the yield of ethanol by 41% compared with that only hexose converted. Pre-hydrolysis for 24 h reduces the viscosity and increases the solid loading to 20% in industrial scale. The maximum ethanol yield reached 4.15% with SSCF for 48 h, which was 72.3% of the theoretical yield. Meanwhile, the fermentation residues were converted into high-valued products. Based on the integrated technologies, an efficient bioprocess was integrated and many side products were economic exploited, thus a large-scale commercial production of lignocellulosic bioethanol was realized, which may provide the guidance of large-scale commercial production of lignocellulosic bioethanol.