• Energy Research

This work proposes a decision-making framework for the selection of processes and unit operations for lignocellulosic bioethanol production. Process alternatives are described by its capital and operating expenditures, its contribution to process yield and technological availability information. A case study in second generation ethanol production using Eucalyptus globulus as raw material is presented to test the developed process synthesis tool. Results indicate that production cost does not necessarily decrease when yield increases. Hence, optimal processes can be found at the inflexion point of total costs and yield. The developed process synthesis tool provides results with an affordable computational cost, existing optimization tools and an easy-to-upgrade description of the process alternatives. These features made this tool suitable for process screening when incomplete information regarding process alternatives is available.

Scheffersomyces stipitis is a yeast able to ferment pentoses to ethanol, unlike Saccharomyces cerevisiae, it does not present the so-called overflow phenomenon. Metabolic features characterizing the presence or not of this phenomenon have not been fully elucidated. This work proposes that genome-scale metabolic response to variations in NAD(H/(+)) availability characterizes fermentative behavior in both yeasts. Thus, differentiating features in S. stipitis and S. cerevisiae were determined analyzing growth sensitivity response to changes in available reducing capacity in relation to ethanol production capacity and overall metabolic flux span. Using genome-scale constraint-based metabolic models, phenotypic phase planes and shadow price analyses, an excess of available reducing capacity for growth was found in S. cerevisiae at every metabolic phenotype where growth is limited by oxygen uptake, while in S. stipitis this was observed only for a subset of those phenotypes. Moreover, by using flux variability analysis, an increased metabolic flux span was found in S. cerevisiae at growth limited by oxygen uptake, while in S. stipitis flux span was invariant. Therefore, each yeast can be characterized by a significantly different metabolic response and flux span when growth is limited by oxygen uptake, both features suggesting a higher metabolic flexibility in S. cerevisiae. By applying an optimization-based approach on the genome-scale models, three single reaction deletions were found to generate in S. stipitis the reducing capacity availability pattern found in S. cerevisiae, two of them correspond to reactions involved in the overflow phenomenon. These results show a close relationship between the growth sensitivity response given by the metabolic network and fermentative behavior.

Abstract Short rotation woody crops appear to be a promising option of biomass for bioethanol production. The traditional short rotation periods for Eucalyptus globulus vary between 8 and 12 years, however intensive forest management practices and genetic improvement have increased the productivity of plantations and reduced the rotation periods up to 5 years. This study aims to assess the potential environmental impacts associated with Chilean short rotation E. globulus plantations for bioenergy production from a Life Cycle Assessment perspective. Thus, for the first time it is presented a detailed life cycle inventory and environmental assessment of a forest system in Latin America. Forest operations carried out over a lifespan of 12 years, with rotation periods of 4 years, were divided into four phases: crop establishment, harvesting, hauling and logistics infrastructure. The managed life cycle inventory included forest site data from a representative plantation dedicated to Eucalyptus chips production for energy purposes, and the inventory of the fuels production in Chile was also determined to fulfil the information requirement. The environmental profile was analysed in terms of several impact categories: climate change, ozone depletion, terrestrial acidification, freshwater y marine eutrophication, photochemical oxidant formation, human toxicity, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity, water depletion and fossil fuel depletion. The harvesting phase was the main contributor to almost all the impact categories with contributing ratios higher than 56%. Within the harvesting phase, fertilisation and forwarding were the main processes responsible for derived environmental impacts. The results in terms of climate change and terrestrial acidification were compared with those reported for Eucalyptus biomass production in European countries. The comparison was performed considering the same system boundaries and functional unit. Differences identified were related to different forest management activities carried out as well as different biomass yields. The LCA study remarked those stages where the researchers need to improve the environmental performance. The results suggested that both fertiliser dosage and fuel consumption in forest activities should be optimised in order to decrease most effectively the global environmental impacts.

Clostridium beijerinckii population branches into metabolically diverse cell types in batch cultures. Here, we present a new kinetic model of C. beijerinckii's Acetone-Butanol-Ethanol fermentation that considers three cell types: producers of acids (acidogenic), consumer of acids and producers of solvents (solventogenic), and spores cells. The model accurately recapitulates batch culture data. Also, the model estimates cell type-specific kinetic parameters, which can be helpful to improve the operation of the ABE fermentation and give a framework to study acidogenic and solventogenic metabolic pathways. To exemplify the latter, we used a constraint-based model to study how the ABE pathways are used among acidogenic and solventogenic cell types. We found that among both cell types, glycolytic production of ATP and consumption of NAD+ varies widely during the fermentation, with their maximum production/consumption rates happening when acidogenic and solventogenic growth rates were at their highest. However, acidogenic cells use the ABE pathway to contribute with an extra 12.5% of the total production of ATP, whereas solventogenic cell types use the ABE pathway to supply more than 75% of the demand for NAD+, alternating between the production of lactate and butyrate, being both coupled to the production of NAD+.

Clostridium autoethanogenum can to convert waste gases (CO2, CO, H2) and xylose from hydrolyzed biomass into acetate, lactate, formate, ethanol and 2,3-butanediol, being a candidate for the transformation of waste streams of lignocellulosic biorefineries. Electro-fermentation (EF) modify the pattern of traditional fermentations resulting in improved product yields as has been shown when using Clostridium strains. The aim of this work was to evaluate the influence of pH on microbial growth and product distribution during fermentation and EF of xylose by C. autoethanogenum DSM10061. Fermentation and EF were carried out in a H-type reactor at three controlled pH: 5.0, 5.5 and 5.8, and at a fixed potential of -600 mV (versus Ag/AgCl) in the EF. The experiments showed that maximum biomass concentration increased as the pH increased in fermentation and EF. In accordance with maximum biomass reached, the highest substrate conversion was observed at pH 5.8 for both systems, with 76.80 % in fermentation and 96.18 % in EF. Moreover, the highest concentrations of acetic acid (1.41 ± 0.07 g L-1) and ethanol (1.45 ± 0.15 g L-1) were obtained at the end of cultures in the EF at pH 5.8. The production of lactic and formic acid decreased by the application of the external potential regardless of the pH value, reaching the lowest productivity at pH 5.8. In contrast, the specific productivity of acetic acid and ethanol was lower in both fermentation and EF at the lowest pH. Furthermore, the presence of 0.06 g L-1 of 2,3-butanediol was only detected in EF at pH 5.8. The results revealed that EF modulated microbial metabolism, which can be explained by a possible increased generation of NADP+/NADPH cofactors, which would redirect the metabolic pathway to more reduced products.

Gasoline is the second most consumed fuel in Chile, accounting for 34% of the total fuel consumption in transportation related activities in 2012. Chilean refineries process more than 97% of the total gasoline commercialized in the national market. When it comes to evaluating the environmental profile of a Chilean process or product, the analysis should consider the characteristics of the Chilean scenario for fuel production and use. Therefore, the identification of the environmental impacts of gasoline production turns to be very relevant for the determination of the associated environmental impacts. For this purpose, Life Cycle Assessment has been selected as a useful methodology to assess the ecological burdens derived from fuel-based systems. In this case study, five subsystems were considered under a "well-to-wheel" analysis: crude oil extraction, gasoline importation, refinery, gasoline storage and distribution/use. The distance of 1 km driven by a middle size passenger car was chosen as functional unit. Moreover, volume, economic and energy-based allocations were also considered in a further sensitivity analysis. According to the results, the main hotspots were the refining activities as well as the tailpipe emissions from car use. When detailing by impact category, climate change was mainly affected by the combustion emissions derived from the gasoline use and refining activities. Refinery was also remarkable in toxicity related categories due to heavy metals emissions. In ozone layer and mineral depletion, transport activities played an important role. Refinery was also predominant in photochemical oxidation and water depletion. In terms of terrestrial acidification and marine eutrophication, the combustion emissions from gasoline use accounted for large contributions. This study provides real inventory data for the Chilean case study and the environmental results give insight into their influence of the assessment of products and processes in the country. Moreover, they could be compared with production and distribution schemes in other regions.

AbstractThis work presents a comparative simulation study involving the techno‐economic and environmental assessment of lignocellulosic‐based small‐scale biorefineries, integrated with a piggery waste‐based anaerobic digestion platform (ADB), located in Portugal and Chile. Two main products are obtained: isobutene and xylo‐oligosaccharides (XOS). The bioproduction of isobutene using a genetically engineered organism (Escherichia coli), coupled with the removal and purification of high added‐value XOS, obtained after a feedstock hydrothermal pre‐treatment, was evaluated. Two lignocellulosic agricultural wastes were used: corn stover in the Portuguese case study and wheat straw in Chilean case study. Both processes were simulated using the Aspen Plus modeling software tool, while the Aspen Process Economic Analyzer was used to carry out the economic evaluation. The simulation results were validated with experimental data from the laboratory and the literature. An economic assessment was performed considering the different locations of both biorefineries. A life‐cycle analysis (LCA) was also applied to evaluate the differences in environmental impacts on both locations. The results showed that the isobutene / XOS biorefinery concept was economically viable in both Portugal and Chile, mainly due to the high market value of XOS. The biorefinery has lower production costs for isobutene and XOS (1 US$/kg of isobutene and 1.18 US$/kg of XOS) when located in Portugal, as compared with Chile (1.14 US$/kg of isobutene and 1.56 US$/kg of XOS). Conversely, it leads to less environmental impact when located in Chile: 48.8 kgCO2eq./GJisobutene, in comparison to 60.7 kgCO2eq./GJisobutene in Portugal. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

Abstract Energy conversion strategies based on lignocellulosic and industrial waste streams is considered a challenge in many countries producing huge quantities of biomass. The production of biogas as an energy vector has been gaining attention in the industry sector due to the energy policies for wastes managements or the feasibility of using the biogas for electricity and steam generation. An interesting feedstock alternative for the biogas production is milk whey, one of the main residues of the dairy industry. Additionally the potato stem generated in the harvest stage can be an attractive raw material for biogas production. Co-digestion is the combination of biodegradable raw materials to improve the balance of nutrients in anaerobic digestion. In this context, the characteristics of milk whey and potato stem are not enough to consider it as a good single substrate. However, the synergetic use of these two residues can represent an improvement in biogas production. The biogas production was calculated in Aspen Plus software using stoichiometric and kinetic models based on the experimental characterization of both materials. Through seven different scenarios: potato stem digestion, milk whey digestion and five co-digestion relations of both materials. Heat and electricity generation using biogas was analyzed. Then the generation of heat and electricity was simulated, where the economic profit was evaluated in terms of the production cost, capital cost, revenues and net present value. In terms of biogas production, the scenarios that involved high organic load were the best. For the economic assessment the raw material cost had the most influence over the total processing cost (80% approximately). However, even if energy is produced it is necessary to include the valorization of the digestate as biofertilizer in order that the different scenarios present economic viability.