Economic determinants on the implementation of a Eucalyptus wood biorefinery producing biofuels, energy and high added-value compounds

The economic impact of different potentially scalable process improvements was here assessed for the first time in the specific context of a Eucalyptus wood biorefinery producing biofuels, high-value chemicals and energy. The base case scenario referring to bioethanol as the only product was clearly unviable, which mostly resulted from the high cost of cellulases and heat transfer utilities and the moderate final ethanol titers. By supplementing cheese whey to eucalyptus wood hydrolysis, ethanol production increased 51% leading to a notable improvement on the NPV, from −14.4 to −3.4 M$. Similarly, when an additional section was included for the recovery of XOS present in the autohydrolysis liquor, the operating costs raised 36% but annual revenues increased around 5 M$, resulting in a very solid NPV of 18.9 M$. Internally burning the final stillage led to savings of 98% on low-pressure steam consumption and an additional electricity revenue, both contributing to a more economic scenario. One final scenario consisted on the simultaneous integration of all process variations, referring to a complex facility producing not only ethanol but also XOS and energy. This integrated process provided the best economic output, which was translated on a noticeable reduction of the minimum ethanol selling price from 4.88 $/gal (Base case) to 0.76 $/gal, and thus confirming the critical role of adopting biorefinery schemes for an economic utilization of lignocellulosic materials.