Extraction processes are widely used in biorefinery applications to recover target products from biomass, and their comprehensive evaluation is key to improving their economic and environmental sustainability. This paper applies a systematic methodology that combines a rigorous process design, techno-economic analysis, and life cycle assessment to evaluate the sustainability performance of solvent extraction-based processes, with a focus on downstream activities. The methodology, which consists of seven iterative steps that combine process simulation and economic and environmental sustainability assessment tools, is demonstrated using a biodiesel production process from algae biomass, with hexane as the lipid extraction solvent. The minimum biodiesel selling price is estimated at U.S. $8.95 per U.S. gal, using the discounted cash flow rate of return. This is 3.5 times the average price of fossil diesel, mostly due to the cost of algae biomass and lipid recovery capacity of the solvent. Eighteen environmental impact categories are estimated from cradle to grave using the ReCiPe v1.1 method. For example, the climate change and primary energy demand are calculated at 95 g CO2 eq./MJ and 1.52 MJ/MJ biodiesel, which are 5 and 24% higher compared to fossil diesel, respectively. Lipid extraction is identified as the hotspot of the downstream processing stages for all impact categories (52–97%) and an opportunity for improving the overall sustainability performance of algae biodiesel, e.g., solvent selection. These findings provide a benchmark for future improvements to biodiesel production from algae biomass, with focus on the interactions between biomass and the solvent, e.g., phase equilibrium thermodynamics.

Lipid extraction and biodiesel production from algae biomass rely on volatile organic solvents obtained from fossil resources such as hexane, whose use involves high energy consumption for recovery and negative environmental impacts due to their volatile and hazardous nature. This study presents a technoeconomic and environmental analysis of using alternative lipid extraction solvents in algae biodiesel production in an effort to understand how they may affect the performance of the process. Lipid recovery (LR), minimum biodiesel selling price (MBSP), solvent intensity (SI), energy intensity (EI), and water consumption (WC) are considered here as performance indicators at process and downstream processing levels. The studied solvents are limonene, ethyl tert-butyl ether (ETBE), and cyclohexane, which were screened in a previous study by the authors, and hexane for reference. The assessment is carried out using data sourced from the literature (upstream processing), while downstream processing data is generated in this study using the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) method and process simulation tools in the absence of experimental data for the solvents. The results indicate that while there is no single candidate solvent that outperforms hexane in every criteria considered here, ETBE and limonene are promising alternative solvents for lipid extraction and should be explored further. For example, ETBE presented the highest LR (95.5%) and lowest MBSP (8.58 $/US gal), while limonene has a SI that is 35% lower than hexane. In terms of EI and WC, ETBE is the best performing solvent after hexane with a 4% difference. The MBSP of ETBE is still around 3.5 times the selling price of fossil diesel, and further efforts to improving the economic viability of algae biodiesel production are still needed. Besides from decreasing algae biomass costs (upstream processing), other improvement opportunities worth exploring in downstream processing includes alternative cell disruption technologies, as this is the most energy intensive stage in lipid extraction. While the use of biobased and less hazardous solvents can help improve the environmental performance of downstream processing in algae biodiesel production, it is recommended that their environmental impacts are quantified on a life cycle basis, i.e., solvent production and disposal.

Volatile organic solvents derived from fossil resources are typically used in extraction processes, but this usually involves high energy consumption for solvent recovery and negative environmental impacts due to solvents’ hazardous, volatile, and flammable nature. This study presents a systematic approach to solvent screening, using molecular and process simulation techniques, data analysis, and classification methods applying technoeconomic, environmental, and safety criteria. This methodology is demonstrated for lipid extraction from wet algae biomass in biofuel production. First, relevant thermodynamic equilibrium data are predicted with the Conductor-like screening model for real solvents (COSMO-RS) method. The resulting solvents are clustered according to their partition coefficient and selectivity toward the target solute and then screened further, considering their physicochemical properties and health, safety, and environmental (HSE) performance. Finally, the lipid extraction process is simulated in Aspen Plus using all screened solvents to obtain technical, economic, and environmental performance data. Out of 88 initial candidates, cyclohexane, limonene, and ethyl tert-butyl ether are identified as potential alternatives to the benchmark solvent, hexane. While these solvents tend to be more expensive and their recovery is more energy-intensive (higher boiling points) compared to hexane, they have a higher selectivity toward lipids, thus reducing the solvent intensity of the process, and are less volatile and nonhazardous according to the HSE classification. This methodology can be applied to other extraction process applications or implemented at early stages in the process design to evaluate technoeconomic, environmental, and safety trade-offs when considering and selecting more sustainable alternatives to fossil-derived solvents.

No abstract

One important step toward the commercialization of microbial-derived colorants is the reproducibility of the cultivation stage in bench-scale bioreactors as well as improving the hydrodynamic design in bioreactors. Aiming to address these technical barriers, Talaromyces amestolkiae was cultivated in a 4 L stirred-tank bioreactor using two types of impellers (Rushton turbine (RT) and Elephant ear (EE) impellers) and aeration modes (cascading and constant airflow) to assess their effects on red colorant production. The results showed that EE under constant airflow (4.0 L min–1) promoted the maximum red colorant formation (28.7 UA500nm), thus improving the reproducibility of the process. The volumetric oxygen transfer coefficient of culture broth was correlated to cell morphology, which was a result of the impeller geometry of EE through the shear conditions impacting the fungi cells. The hairy pellet morphology favored nutrient and oxygen uptake and allowed an improvement in the colorant’s synthesis. Life cycle assessment was also carried out to identify opportunities for improving the best process design from an environmental sustainability perspective. For example, the total climate change and primary energy demand were estimated at 31.11 kg CO2 eq./g red colorant and 830.7 MJ/g red colorant, respectively, with the cultivation stage contributing with 65 and 63% of these impacts. The electricity consumption was identified as the main hotspot in this stage, a trend that was observed across all other impact categories. This can be improved by optimizing cultivation lengths combined with the use of low carbon electricity sources. These findings ensure a step forward toward the scaling-up at the industrial scale of the T. amestolkiae cultivation for the production of bio-based colorants in an environmentally sustainable way.