Showing papers by "DECHEMA published in 2018"

Methanogens: biochemical background and biotechnological applications.

Abstract: Since fossil sources for fuel and platform chemicals will become limited in the near future, it is important to develop new concepts for energy supply and production of basic reagents for chemical industry. One alternative to crude oil and fossil natural gas could be the biological conversion of CO2 or small organic molecules to methane via methanogenic archaea. This process has been known from biogas plants, but recently, new insights into the methanogenic metabolism, technical optimizations and new technology combinations were gained, which would allow moving beyond the mere conversion of biomass. In biogas plants, steps have been undertaken to increase yield and purity of the biogas, such as addition of hydrogen or metal granulate. Furthermore, the integration of electrodes led to the development of microbial electrosynthesis (MES). The idea behind this technique is to use CO2 and electrical power to generate methane via the microbial metabolism. This review summarizes the biochemical and metabolic background of methanogenesis as well as the latest technical applications of methanogens. As a result, it shall give a sufficient overview over the topic to both, biologists and engineers handling biological or bioelectrochemical methanogenesis.

Microbial Cell Factories for the Production of Terpenoid Flavor and Fragrance Compounds

Abstract: Terpenoid flavor and fragrance compounds are of high interest to the aroma industry. Microbial production offers an alternative sustainable access to the desired terpenoids independent of natural sources. Genetically engineered microorganisms can be used to synthesize terpenoids from cheap and renewable resources. Due to its modular architecture, terpenoid biosynthesis is especially well suited for the microbial cell factory concept: a platform host engineered for a high flux toward the central C5 prenyl diphosphate precursors enables the production of a broad range of target terpenoids just by varying the pathway modules converting the C5 intermediates to the product of interest. In this review typical terpenoid flavor and fragrance compounds marketed or under development by biotech and aroma companies are given, and the specificities of the aroma market are discussed. The main part of this work focuses on key strategies and recent advances to engineer microbes to become efficient terpenoid producers.

CO2 to Terpenes: Autotrophic and Electroautotrophic α-Humulene Production with Cupriavidus necator.

Abstract: We show that CO2 can be converted by an engineered "Knallgas" bacterium (Cupriavidus necator) into the terpene α-humulene. Heterologous expression of the mevalonate pathway and α-humulene synthase resulted in the production of approximately 10 mg α-humulene per gram cell dry mass (CDW) under heterotrophic conditions. This first example of chemolithoautotrophic production of a terpene from carbon dioxide, hydrogen, and oxygen is a promising starting point for the production of different high-value terpene compounds from abundant and simple raw materials. Furthermore, the production system was used to produce 17 mg α-humulene per gram CDW from CO2 and electrical energy in microbial electrosynthesis (MES) mode. Given that the system can convert CO2 by using electrical energy from solar energy, it opens a new route to artificial photosynthetic systems.

An extensive study about influence of the carbon support morphology on Pt activity and stability for oxygen reduction reaction

Abstract: Several commercial carbons were tested with respect to their thermal stability and electrochemical activity as Pt catalyst support for oxygen reduction reaction (ORR). TGA analysis revealed that carbons with low BET surface such as graphite nanoparticles (GNP500, 100 m² g−1) are less prone to degradation than ordered mesoporous carbon (OMC, 1000 m²g−1). Moreover, high Pt loading favored considerably carbon oxidation rate in air. Best results in terms of activity for ORR and stability during electrochemical accelerated degradation tests (ADT) were yielded by Pt/GNP500 and Pt/OMC, respectively. High graphitization level and mesoporous surface structure of carbon were found to be determinant for sustainable Pt stability. Addition of certain amount of PTFE to Nafion as binder in gas diffusion electrode (GDE) catalyst layer clearly improved electrochemical surface area (ECSA) retention. Comparative identical location TEM images of electrochemically-aged Pt on Vulcan and OMC demonstrated positive influence of mesoporous carbon surface on immobilization of catalyst particles and consequently on ECSA retention. After 10,000 ADT cycles, ECSA retention was close to 30% for Pt/OMC compared to about 1% for Pt/Vulcan. This was due to dramatic increase of Pt particle size on Vulcan support up to 40 nm compared to about 15 nm for Pt on OMC.

Surface modification of Ti 13Nb 13Zr by plasma electrolytic oxidation

Abstract: Titania coatings were produced on Ti 13Zr 13Nb by a unipolar pulsed DC plasma electrolytic oxidation (PEO) process in an electrolyte containing 1 M H2SO4 + 0.1 M H3PO4. The samples were galvanostatically anodized under a constant charge-carrier density of 63 C cm− 2 and current-densities reaching from 14 mA cm− 2 up to 700 mA cm− 2. Both a constant current mode and a unipolar pulsed mode with a duty-cycle of 50% and frequencies of 1 Hz to 50 Hz were performed. The surface layers were characterized by scanning electron microscopy (SEM/EDX), X-ray diffraction (XRD) and nanoindentation. Titanium oxide coatings with a thickness of several micrometers and a porous structure could be generated. The coatings morphology was evaluated. It can be shown that the porosity can be reduced with increasing frequency. The coatings consist of anatase and rutile, the phase composition of the coatings can be adjusted by the PEO current density. The corrosion resistance of the layers was tested in a simulated body fluid (SBF) with the addition of 0.1 M H2O2 by open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). EIS data fitting indicates a composed layer structure of an outer porous layer and an inner barrier layer. Higher current densities during the PEO process formed thicker coatings, which consequently resulted in lower corrosion currents. The addition of zirconia nanoparticles into the electrolyte increased the surface hardness to an average value of 12.8 GPa, compared to that of an untreated sample (4.1 GPa) and PEO samples without particle addition (8.5 GPa).

Heterologous expression of 2-methylisoborneol / 2 methylenebornane biosynthesis genes in Escherichia coli yields novel C11-terpenes.

Abstract: The structural diversity of terpenoids is limited by the isoprene rule which states that all primary terpene synthase products derive from methyl-branched building blocks with five carbon atoms. With this study we discover a broad spectrum of novel terpenoids with eleven carbon atoms as byproducts of bacterial 2-methylisoborneol or 2-methylenebornane synthases. Both enzymes use 2-methyl-GPP as substrate, which is synthesized from GPP by the action of a methyltransferase. We used E. coli strains that heterologously produce different C11-terpene synthases together with the GPP methyltransferase and the mevalonate pathway enzymes. With this de novo approach, 35 different C11-terpenes could be produced. In addition to eleven known compounds, it was possible to detect 24 novel C11-terpenes which have not yet been described as terpene synthase products. Four of them, 3,4-dimethylcumene, 2-methylborneol and the two diastereomers of 2-methylcitronellol could be identified. Furthermore, we showed that an E. coli strain expressing the GPP-methyltransferase can produce the C16-terpene 6-methylfarnesol which indicates the condensation of 2-methyl-GPP and IPP to 6-methyl-FPP by the E. coli FPP-synthase. Our study demonstrates the broad range of unusual terpenes accessible by expression of GPP-methyltransferases and C11-terpene synthases in E. coli and provides an extended mechanism for C11-terpene synthases.

Reactors for Microbial Electrobiotechnology

Abstract: From the first electromicrobial experiment to a sophisticated microbial electrochemical process – it all takes place in a reactor. Whereas the reactor design and materials used strongly influence the obtained results, there are no common platforms for MES reactors. This is a critical convention gap, as cross-comparison and benchmarking among MES as well as MES vs. conventional biotechnological processes is needed. Only knowledge driven engineering of MES reactors will pave the way to application and commercialization. In this chapter we first assess the requirements on reactors to be used for bioelectrochemical systems as well as potential losses caused by the reactor design. Subsequently, we compile the main types and designs of reactors used for MES so far, starting from simple H-cells to stirred tank reactors. We conclude with a discussion on the weaknesses and strengths of the existing types of reactors for bioelectrochemical systems that are scored on design criteria and draw conclusions for the future engineering of MES reactors.

Fast Microwave-Assisted Hydrothermal Synthesis of Pure Layered δ-MnO2 for Multivalent Ion Intercalation

Abstract: This work reports on the synthesis of layered manganese oxides (δ-MnO2) and their possible application as cathode intercalation materials in Al-ion and Zn-ion batteries. By using a one-pot microwave-assisted synthesis route in 1.6 M KOH (MnVII:MnII = 0.33), a pure layered δ-MnO2 birnessite phase without any hausmannite traces was obtained after only a 14 h reaction time period at 110 °C. Attempts to enhance crystallinity level of as-prepared birnessite through increasing of reaction time up to 96 h in 1.6 M KOH failed and led to decreases in crystallinity and the emergence of an additional hausmannite phase. The influence of MnII:OH− ratio (1:2 to 1:10) on phase crystallinity and hausmannite phase formation for 96 h reaction time was investigated as well. By increasing alkalinity of the reaction mixture up to 2.5 M KOH, a slight increase in crystallinity of birnessite phase was achieved, but hausmannite formation couldn’t be inhibited as hoped. The as-prepared layered δ-MnO2 powder material was spray-coated on a carbon paper and tested in laboratory cells with Al or Zn as active materials. The Al-ion tests were carried out in EMIMCl/AlCl3 while the Zn-Ion experiments were performed in water containing choline acetate (ChAcO) or a ZnSO4 solution. Best performance in terms of capacity was yielded in the Zn-ion cell (200 mWh g−1 for 20 cycles) compared to about 3 mAh g−1 for the Al-ion cell. The poor activity of the latter system was attributed to low dissociation rate of tetrachloroaluminate ions (AlCl4−) in the EMIMCl/AlCl3 mixture into positive Al complexes which are needed for charge compensation of the oxide-based cathode during the discharge step.

Corrosion testing of diffusion-coated steel in molten salt for concentrated solar power tower systems

Abstract: In the course of energy transition the development of sustainable technologies for power generation providing base load supply is of particular importance In comparison to photovoltaics concentrated solar power (CSP) Systems have great potential to fulfil this requirement by the use of thermal storage systems utilizing molten salt mixtures as heat transfer fluids For this purpose, molten nitrates are frequently discussed due to their beneficial thermal and physical properties as well as high operation temperatures In order to protect the piping system from degradation, coatings can be applied on the surface of the employed materials, which are commonly steels or Ni-based alloys The goal is to achieve cost reduction to ensure an even more competitive position of the CSP technology with respect to other renewable sources on the market In this study, the corrosion behavior of coated and uncoated ferritic-martensitic steels of type T91 and VM12 in molten salt (mixture of NaNO3 and KNO3) has been investigated under isothermal conditions The diffusion coatings are based on potentially protective elements such as Al, Si or Cr and were applied on the steels either by pack cementation or slurry deposition Characterization of the samples was conducted by means of optical microscope and EPMA in order to gain a deeper understanding of the occurring corrosion mechanisms and for the purpose of lifetime analysis

Grafted iron(III) ions significantly enhance NO2 oxidation rate and selectivity of TiO2 for photocatalytic NOx abatement

Abstract: Semiconductor photocatalysis could be an effective means to combat nitrogen oxides (NOx) based air pollution through mineralisation of NOx to nitrate. However, most of the typically TiO2-based catalysts employed show a much higher reactivity towards NO than NO2, leading to an accumulation of this unwanted and toxic intermediate. By grafting the photocatalyst with small amounts (≤0.1 at%) of isolated iron(III) ions, the reactivity towards NO2 is increased by the factor of 9, bringing it up to par with the NO-reactivity and alleviating the problem with intermediate accumulation. Consequently, the observed selectivity of the reaction is dramatically increased from less than 40% to more than 90%. The paper also discusses possible mechanisms for this very beneficial behavior.

Characterization of a membrane-separated and a membrane-less electrobioreactor for bioelectrochemical syntheses.

Abstract: Bioelectrochemical systems (BESs) have the potential to contribute to the energy revolution driven by the new bio-economy. Until recently, simple reactor designs with minimal process analytics have been used. In recent years, assemblies to host electrodes in bioreactors have been developed resulting in so-called "electrobioreactors." Bioreactors are scalable, well-mixed, controlled, and therefore widely used in biotechnology and adding an electrode extends the possibilities to investigate bioelectrochemical production processes in a standard system. In this work, two assemblies enabling a separated and non-separated electrochemical operation, respectively, are designed and extensively characterized. Electrochemical losses over the electrolyte and the membrane were comparable to H-cells, the bioelectrochemical standard reaction system. An effect of the electrochemical measurements on pH measurements was observed if the potential is outside the range of -1,000 to +600 mV versus Ag/AgCl. Electrobiotechnological characterization of the two assemblies was done using Shewanella oneidensis as an electroactive model organism. Current production over time was improved by a separation of anodic and cathodic chamber by a Nafion® membrane. The developed electrobioreactor was used for a scale-up of the anaerobic bioelectrochemical production of organic acids and lysine from glucose using an engineered Corynebacterium glutamicum. Comparison to a small-scale custom-made electrobioreactor indicates that anodic electro-fermentation of lysine and organic acids might not be limited by the BES setup but by the biocatalysis of the cells.

The DaNa2.0 Knowledge Base Nanomaterials—An Important Measure Accompanying Nanomaterials Development

Abstract: Nanotechnology is closely related to the tailored manufacturing of nanomaterials for a huge variety of applications. However, such applications with newly developed materials are also a reason for concern. The DaNa2.0 project provides information and support for these issues on the web in condensed and easy-to-understand wording. Thus, a key challenge in the field of advanced materials safety research is access to correct and reliable studies and validated results. For nanomaterials, there is currently a continuously increasing amount of publications on toxicological issues, but criteria to evaluate the quality of these studies are necessary to use them e.g., for regulatory purposes. DaNa2.0 discusses scientific results regarding 26 nanomaterials based on actual literature that has been selected after careful evaluation following a literature criteria checklist. This checklist is publicly available, along with a selection of standardized operating protocols (SOPs) established by different projects. The spectrum of information is rounded off by further articles concerning basics or crosscutting topics in nanosafety research. This article is intended to give an overview on DaNa2.0 activities to support reliable toxicity testing and science communication alike.

Improving the selectivity of photocatalytic NOx abatement through improved O2 reduction pathways using Ti0.909W0.091O2Nx semiconductor nanoparticles: from characterisation to photocatalytic performance

Abstract: In this paper, we provide detailed insight into the electronic–crystallographic–structural relationship for Ti0.909W0.091O2Nx semiconductor nanoparticles, explaining the mutual electronic and magnetic influence of the photoinduced stable N- and W-based paramagnetic centers, their involvement in the photoinduced charge-carrier trapping, and their role in improving the nitrate selectivity of the photocatalytic oxidation of NOx to nitrates. In particular, reduced tungsten species in various crystallographic environments within the anatase host lattice were observed as playing a fundamental role in the storage and stabilization of photogenerated electrons. Here, we show how these reduced centers can catalyze multielectron transfer events without the need for rare and expensive platinum-group metals (PGMs). This allows for the versatile and elegant configuration of redox potentials. As a result, electron-transfer processes that are kinetically inaccessible with metal oxides such as TiO2 can now be accessed, en...

Environmental Screening of Electrode Materials for a Rechargeable Aluminum Battery with an AlCl3/EMIMCl Electrolyte

Abstract: Recently, rechargeable aluminum batteries have received much attention due to their low cost, easy operation, and high safety. As the research into rechargeable aluminum batteries with a room-temperature ionic liquid electrolyte is relatively new, research efforts have focused on finding suitable electrode materials. An understanding of the environmental aspects of electrode materials is essential to make informed and conscious decisions in aluminum battery development. The purpose of this study was to evaluate and compare the relative environmental performance of electrode material candidates for rechargeable aluminum batteries with an AlCl3/EMIMCl (1-ethyl-3-methylimidazolium chloride) room-temperature ionic liquid electrolyte. To this end, we used a lifecycle environmental screening framework to evaluate 12 candidate electrode materials. We found that all of the studied materials are associated with one or more drawbacks and therefore do not represent a “silver bullet” for the aluminum battery. Even so, some materials appeared more promising than others did. We also found that aluminum battery technology is likely to face some of the same environmental challenges as Li-ion technology but also offers an opportunity to avoid others. The insights provided here can aid aluminum battery development in an environmentally sustainable direction.

ToF-SIMS Study on the Initial Stages of the Halogen Effect in the Oxidation of TiAl Alloys

Abstract: Intermetallic titanium aluminide samples implanted with fluorine using plasma immersion ion implantation were investigated after high-temperature exposure for short times at 500 and 900 °C in air by ToF-SIMS as a surface analytical method. The ToF-SIMS method was applied in order to obtain information regarding the location of fluorine with respect to the oxide layer formed and the substrate after ion implantation and after high-temperature exposure, respectively. The aim of the present work was to obtain further insight into the mechanisms active during the initial stages of oxidation. The scale structure in the initial oxidation phase consists of titanium and aluminum oxides/fluorides/oxyfluorides. The arrangement of their layered structure can be interpreted according to their thermodynamic stabilities in the partial pressure gradient of oxygen over the scale and according to the metal activities and the presence of fluorine at the metal/scale interface.

Strengthened Cr-Si-base alloys for high temperature applications

Abstract: The microstructural development of Cr Si alloys with Cr ≥ 89 at.% has been studied. As well as silicon, up to 2 at.% germanium, molybdenum, and platinum were used as alloying elements. All alloys consist of only two phases, Crss and A15. The phase fraction of primary A15 precipitates present in the arc melted condition and fine secondary A15 precipitates formed after a heat treatment (100 h at 1200 °C) were determined. EPMA and SEM measurements show that the alloying elements partition in different ways: Molybdenum is homogeneously dissolved in both phases, while platinum, germanium, and silicon predominantly act as A15 phase formers. Additionally, molybdenum refines the A15 precipitates, germanium increases the amount of secondary precipitates, and platinum coarsens the microstructure. The lattice parameters of both phases were determined using XRD. The results were found to be in accordance to the elemental partitioning behavior of the constituent phases and can be correlated to the respective covalent atomic radii of the respective alloying element. Microhardness measurements confirmed the alloy's ability of precipitation hardening. Using nanohardness measurements the A15 phase was found to be around 18GPa harder compared to Crss offering a way to design mechanical properties depending on alloying element additions, A15 phase fraction, and distribution.

Effect of Pressure on Metal Dusting Initiation on Alloy 800H and Alloy 600 in CO-rich Syngas

Abstract: The effect of pressure on metal dusting initiation was studied by exposing conventional alloys 600 and 800H in CO-rich syngas atmosphere (H2, CO, CO2, CH4, H2O) at ambient and 18 bar total system pressure and 620 °C for 250 h. It was verified that, at constant temperature, increasing the total system pressure increases both oxygen partial pressure (pO2) and carbon activity (a C), simultaneously. Both samples exposed at ambient pressure showed very thin oxide scale formation and no sign of metal dusting. By contrast, samples exposed in the high-pressure experiment showed severe mass loss by metal dusting attack. Iron- and chromium-rich oxides and carbides were found as corrosion products. The distinct pressure-dependent behavior was discussed by considering both thermodynamic and kinetic aspects with respect to the protective oxide formation and pit initiation.

Biorefineries: A Short Introduction.

Abstract: The terms bioeconomy and biorefineries are used for a variety of processes and developments. This short introduction is intended to provide a delimitation and clarification of the terminology as well as a classification of current biorefinery concepts. The basic process diagrams of the most important biorefinery types are shown.