Sustainability assessment of succinic acid production technologies from biomass using metabolic engineering

Over the past few years, bio-succinic acid from renewable resources has gained increasing attention as a potential bio-derived platform chemical for the detergent/surfactant, ion chelator, food and pharmaceutical markets. Until now, much research was undertaken to lower the production costs of bio-succinic acid, however a multicriteria sustainability evaluation of established and upcoming production processes from a technical perspective is still lacking in the scientific literature. In this study, we combine metabolic engineering with the most mature technologies for the production of bio-succinic acid from sugar beet and lignocellulosic residues. Downstream technologies such as reactive extraction, electrodialysis and ion exchange are investigated together with different upstream technologies such as neutral pH level-, acidic- and high sugar fermentation including metabolically engineered E. coli strains. Different biorefinery concepts are evaluated considering technical, economic, environmental and process hazard aspects in order to gain a broad sustainability perspective of the technologies. The results reveal that energy integration is a key factor for biorefinery concepts in order to be economically reasonable and to achieve lower environmental impacts compared to the conventional production from non-renewable resources. It was found that metabolically engineered E. coli with resistance at the acidic pH level in the fermentation together with reactive extraction in the purification presents the most environmentally competitive technology. However, E. coli strains with resistance at high sugar concentrations together with reactive extraction are revealed to present the most economically competitive technology for the production of bio-succinic acid. Moreover, both technologies are flagged for higher process hazards and require the right measures to enhance process safety and mitigate environmental loads and worker exposure.

Amorphous Molybdenum Sulfide Films as Hydrogen Evolution Catalysts in Water

Daniel Andreas Merki

Molecular hydrogen is a promising candidate to replace fossil fuels as the energy carrier. Hydrogen does not exist in its molecular form on earth and must therefore be generated, starting from hydrogen-rich compounds. Water would be a renewable resource for hydrogen. It can be split into oxygen and hydrogen. Water splitting, however, needs electrical energy. If this energy is produced from renewable resources, such as solar or wind power, water splitting would be a sustainable and green process. One key step in water splitting is the reduction of protons to form hydrogen. To achieve a high efficiency in this reaction, catalysts are required. This dissertation is devoted to the development of hydrogen evolution catalysts that are made of earth-abundant and inexpensive materials. First, transition metal complexes of tetrathiotungstate and tetrathiomolybdate were studied as potential homogeneous catalysts for hydrogen evolution in organic or aqueous solutions (chapter 1). The redox activity of these complexes was investigated by cyclic voltammetry in the absence and presence of an acid in organic solutions. The first reduction peak of (Pr4N)2[Ni(MoS4)2] became more intense and was shifted to less negative potentials upon addition of an acid, e.g. p-cyanoanilinium tetrafluoroborate. This was considered as a sign for catalytic proton reduction. Electrolysis of a solution containing (Pr4N)2[Ni(MoS4)2] and an acid produced hydrogen. However, the complex turned out to be a precursor of the real catalytically active species, which was deposited on the working electrode’s surface during the electrochemical experiment. Consecutive cyclic voltammetric scans were found to be a good method to deposit the catalytically active film in a controllable manner from an aqueous solution of (Pr4N)2[Ni(MoS4)2]. Furthermore, a catalytically active film could be deposited from a solution of MoS42-, i.e. in the absence of Ni2+. Chapter 2 describes the investigation and characterization of films made using MoS42- as the precursor. The films consist of amorphous molybdenum sulfide. They are efficient hydrogen evolution catalysts in water. The films were characterized by XPS and electron microscopy. Whereas the pre-catalysts could be MoS3 or MoS2, the active form of the catalysts was identified as amorphous MoSx, with x close to 2. Significant geometric current densities were achieved at low overpotentials (e.g., ca. 15 mA/cm2 at η = 200 mV) using these catalysts. The catalysis was compatible with a wide range of pH values. The current efficiency for hydrogen production was quantitative. A Tafel slope of 39 mV/dec was observed, suggesting a rate-determining Heyrovsky step. The turnover frequency per active site was estimated.

EPFL2012

A computational framework for integration of lipidomics data into metabolic pathways

Noushin Hadadi, Vassily Hatzimanikatis, Marianne Seijo, Keng Cher Soh, Aikaterini Zisaki

Lipids are important compounds for human physiology and as renewable resources for fuels and chemicals. In lipid research, there is a big gap between the currently available pathway-level representations of lipids and lipid structure databases in which the number of compounds is expanding rapidly with high-throughput mass spectrometry methods. In this work, we introduce a computational approach to bridge this gap by making associations between metabolic pathways and the lipid structures discovered increasingly thorough lipidomics studies. Our approach, called NICELips (Network Integrated Computational Explorer for Lipidomics), is based on the formulation of generalized enzymatic reaction rules for lipid metabolism, and it employs the generalized rules to postulate novel pathways of lipid metabolism. It further integrates all discovered lipids in biological networks of enzymatic reactions that consist their biosynthesis and biodegradation pathways. We illustrate the utility of our approach through a case study of bis(monoacylglycero)phosphate (BMP), a biologically important glycerophospholipid with immature synthesis and catabolic route(s). Using NICELips, we were able to propose various synthesis and degradation pathways for this compound and several other lipids with unknown metabolism like BMP, and in addition several alternative novel biosynthesis and biodegradation pathways for lipids with known metabolism. NICELips has potential applications in designing therapeutic interventions for lipid-associated disorders and in the metabolic engineering of model organisms for improving the biobased production of lipid-derived fuels and chemicals.

Academic Press Inc Elsevier Science2014

Methodology for the identification of promising integrated biorefineries

Ayse Dilan Celebi

Steady increase in global energy consumption, greenhouse gas emissions, and depletion of fossil energy resources, together with increased attention towards sustainable development has prompted researchers to discover economical and environmentally competitive non-petroleum alternatives and biomass is considered to be one of the most promising renewable sources of energy and carbon of this matter to address the aforementioned issues within a biorefinery platform. A biorefinery is an integrated processing facility that converts biomass into transportation fuels, value-added chemicals, heat, and electricity via biochemical and thermochemical conversion routes. Integrated biorefineries are capable of mimicking petroleum refineries via application of advanced process synthesis methods including modeling, simulation, integration and optimization techniques. This thesis presents a comprehensive synthesis methodology for the integration of bioprocessing technologies in biorefineries by addressing techno-economic and environmental sustainability analysis. The proposed systematic design approach combines advanced process modeling approaches, process integration techniques, and multi-objective optimization algorithms to assess the performance of the overall system with respect to economic, environmental, and energetic indicators. The design strategy is applied based on different case studies. Results indicate that multi-product processes can yield significant cost and environmental benefits. Additionally, the integration of biochemical and catalytic processes with thermochemical conversion pathways results in increased carbon efficiency and economic and environmental competitiveness. Synergies between biorefineries and energy system are assessed by integrating industrial plants with a cogeneration system producing biofuels and process heat. In doing so, system efficiency is increased by coupling the proposed cogeneration system with carbon capture and sequestration (CCS) and power-to-gas technologies to store the renewable intermittent electricity in the form of biofuels. The results exhibit that through system expansion, integrated biorefinery systems allow us to imitate fossil refineries with a large spectrum of bio-based products. This further increases the resource efficiency while offering a promising solution to mitigate CO2 emissions and hence reaching the longer-term decarbonization target set by the Paris Agreement.