Synergies Between the Distillation of First- and Second-Generation Sugarcane Ethanol for Sustainable Biofuel Production

This work investigated synergies for improved energy efficiency between integrated first- (1G) and second-generation (2G) sugarcane ethanol distillation, an energy-intensive unit operation, especially for stand-alone 2G ethanol. For this investigation, integrated and separated 1G2G distillation simulations were conducted using Aspen Plus v.10 assuming a dilute 2G fermentation beer with titer varying from 5 to 40 g/L. The results were then assessed in heating energy demand savings for distillation, and it was measured the potential of saved bagasse (boiler fuel) for valorization in either electricity or 2G ethanol. A life cycle assessment was also performed for a consequential approach to carbon emission reductions from energy savings. As our main result, distillation integration can maintain the heat demand of a stand-alone 1G mill, regardless of the 2G ethanol beer titer. This means energy savings between 9 and 15% in total ethanol heat demand, and between 46 and 92% in 2G ethanol heat demand. The savings are due to the reflux ratio associated with 2G ethanol distillation becoming close to the host 1G distillation process. However, although the energy savings may result in economic gains, not assessed in this study, by using saved bagasse for either electricity (between 0.14 and 0.23 MJElectricity/kgEthanol) or 2G ethanol production (between 6.8 and 4.1 g2G Ethanol/kgEthanol), the boiler fuel savings do not significantly decrease carbon emissions of ethanol production (less than 1%). Nonetheless, the lower energy demand has the potential to debottleneck the operational cost challenge of distillation for 2G ethanol production without associated trade-offs.