Kathleen F. Haigh

The sugar yield achieved during pretreatment of lignocelluloses has an impact on the economic outcome of biorefineries. Chemical and physiochemical pretreatment methods were evaluated and compared to determine the most favorable pretreatment method for the commercial co‐production of succinic acid and electricity in a sugarcane lignocellulosic biorefinery. Nine methods were identified and simulated in Aspen Plus®. All the pretreatment methods were profitable except organosolv and wet oxidation. Steam explosion (STEX), sulfur dioxide (SO₂), catalyzed STEX, and ammonia fibre expansion (AFEX™) resulted in the highest succinic acid yields, with 45.7, 43.5 and 33.4 kg succinic acid per 100 tonnes of dry feedstock, respectively, and they are recommended for commercial application. However, due to the high cost of enzymatic hydrolysis (46.23 million US$), the AFEX™ pretreatment method was the most expensive scenario at 385.7 million US$ total capital cost with an internal rate of return (IRR) of 22.81%. This may be compared with 384.2 million US$ for STEX pretreatment, which resulted in the most profitable biorefinery scenario with an IRR of 28.04%. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

This study investigates whether a biorefinery, annexed to an existing sugar mill and co‐producing succinic acid, polyhydroxybutyrate (PHB), and electricity from sugarcane bagasse and trash lignocelluloses, will be a viable investment opportunity for existing sugarcane mills. Four scenarios were simulated in Aspen Plus® and were included in the economic analysis. Scenario A involved the production of PHB and electricity; Scenario B the production of PHB, succinic acid, and electricity; Scenario C the production of succinic acid and electricity; and Scenario D involved the production of electricity only. The most favorable configuration was found for Scenario B where PHB was produced from 25% of the fermentable glucose stream, and succinic acid from the hemicellulose hydrolysate together with 75% of the glucose, resulting in an internal rate of return (IRR) of 24.1% with a net present value of US$477.2 million. Alternatively, Scenario D could be selected if low capital (130.1 million US$) and operational costs (US$13.2 million) are desired, although weak returns (IRR 10.3% and net present value of US$6.08 million) were observed for an electricity price of 0.08 US$ kWh⁻¹. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

Six conceptual process scenarios for the production of biobutanol from lignocellulosic biomass through acetone‐butanol‐ethanol (ABE) fermentation, using reported data on process performances, were developed with ASPEN Plus® V8.2 software. The six scenarios covered three fermentation strategies, i.e. batch separate hydrolysis and fermentation (SHF), continuous SHF, and batch simultaneous saccharification and fermentation (SSF) integrated with gas stripping (GS). The two downstream processing options considered were double‐effect distillation (DD) and liquid‐liquid extraction and distillation (LLE&D). It was found that the SSF‐GS/DD scenario was the most energy efficient with a liquid fuel efficiency of 24% and an overall efficiency of 31%. This was also the scenario with the best economic outcome, with an internal rate of return (IRR) of 15% and net present value (NPV) of US$387 million. The SSF‐GS/DD scenario was compared to a similar molasses process, based on the product flow rates, and it was found that the molasses process was more energy efficient with a gross energy value (GEV) of 23 MJ kg¹ butanol compared to −117 MJ kg¹ butanol for the lignocellulosic process. In addition, the molasses‐based process was more profitable with an IRR of 36% compared to 21%. However, the energy requirements for the molasses process were supplied from fossil fuels, whereas for the lignocellulose processes a portion of the feedstock was diverted to provide process energy. Improved environmental performance is therefore associated with the lignocellulosic process. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Driven by a range of sustainability challenges, e.g. climate change, resource depletion and expanding populations, a circular bioeconomy is emerging and expected to evolve progressively in the coming decades. South Africa along with other BRICS countries (Brazil, Russia, India and China) represents the emerging bioeconomy and contributes significantly to global sugar market. In our research, South Africa is used as a case study to demonstrate the sustainable design for the future biorefineries annexed to existing sugar industry. Detailed techno-economic evaluation and Life Cycle Assessment (LCA) were applied to model alternative routes for converting sugarcane residues (bagasse and trash) to selected biofuel and/or biochemicals (ethanol, ethanol and lactic acid, ethanol and furfural, butanol, methanol and Fischer–Tropsch synthesis, with co-production of surplus electricity) in an energy self-sufficient biorefinery system. Economic assessment indicated that methanol synthesis with an internal rate of return (IRR) of 16.7% and ethanol–lactic acid co-production (20.5%) met the minimum investment criteria of 15%, while the latter had the lowest sensitivity to market price amongst all the scenarios. LCA results demonstrated that sugarcane cultivation was the most significant contributor to environmental impacts in all of the scenarios, other than the furfural production scenario in which a key step, a biphasic process with tetrahydrofuran solvent, had the most significant contribution. Overall, the thermochemical routes presented environmental advantages over biochemical pathways on most of the impact categories, except for acidification and eutrophication. Of the investigated scenarios, furfural production delivered the inferior environmental performance, while methanol production performed best due to its low reagent consumption. The combined techno-economic and environmental assessments identified the performance-limiting steps in the 2G biorefinery design for sugarcane industry and highlighted the technology development opportunities under circular bioeconomy context.