Increasing the Equilibrium Yield of Oxidative Dehydrogenation with CO2 by Secondary Reactions

Oxidative dehydrogenation with carbon dioxide as an oxidant at low temperatures is strongly limited by its thermodynamic equilibrium. It is be shown that the equilibrium yield of the desired olefin can significantly be increased utilizing side reactions. This does not necessarily require the addition of another reactant, since this reactant can be formed in situ from the starting alkane. This effect allows for a decrease of the reaction temperature as well as the overall heat demand of the reaction. As a consequence, the exergy demand of the reaction system is reduced substantially.     

Enzymatic degradation of hyperbranched polyesters

In this work, the enzyme‐catalyzed degradation of hyperbranched polyesters (HBPEs) was investigated. Enzymatic degradation experiments were performed in a phosphate buffer in the presence of the lipases Candida cylindracea, Pseudomonas cepacia, Novozym 388, Amano CE, Lipomod 34P, and Cal‐B, whereas control experiments were performed in the same system without lipases. The extent of polymer degradation was determined by quantification of the released free fatty acids by gas chromatography. The influence of the alkane chain length and the number of alkane chain end groups on the lipase‐catalyzed hydrolysis of esterified HBPEs was investigated systematically. It was found that the increase in the alkane chain length of the end groups diminished the enzymatic degradation of the polymer, whereas the number of end groups had no influence on the degradation rate. The effect of temperature on the rate of degradation was also described. Surface morphological changes that occurred during the degradation were assessed with reflected electron microscopy. The changes in the crystallinity of the polymers after they were subjected to degradation were qualitatively determined with differential scanning calorimetry through the quantification of the enthalpy of melting. The enthalpy of melting of one HBPE sample increased from 79 to 90 and 94 J/g with and without the action of Lipomod 34P, respectively, in 7 days, showing the changes in the crystallinity of the polymer. The results prove that modified HBPEs are an important new class of biodegradable materials with a predictable degradation mechanism, and the degradation can be adjusted on the basis of the molecular engineering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Vorausberechnung von Flüssig/Flüssig-Gleichgewichten

Calculation of liquid/liquid equilibrium . The knowledge of phase equilibrium is of great importance in the design of extraction processes. A few years ago, the engineer had to rely on empirical and semi-empirical methods, whilst today the calculation of multicomponent systems can be performed with models based on molecular thermodynamics. In this survey, sources of data, principles of calculation, and methods for the determination of multicomponent liquid/liquid equilibria are presented. Results and accuracy of recent methods are compared.     

Widely tunable complex-coupled distributed feedback laser with photonic Crystal mirrors and integrated optical amplifier

We report the development of a current-controlled widely tunable laser diode based on InP with photonic crystal mirrors and an integrated amplifier section for stabilized power output. The laser consists of three longitudinally coupled ridge waveguide cavities that are coupled through photonic crystal mirror segments. A laterally defined binary superimposed grating provides complex-coupled distributed feedback into two of the laser cavities. The wavelength can be switched over a range of 26 nm. Through adjustment of the current into a third amplifier section, the output power can be stabilized over the tuning range of the laser.     

Establishing the Usability of a Virtual Training System for Assembly Operations within the Automotive Industry

Virtual training systems deliver training within a virtual environment (VE) using virtual reality (VR) or augmented reality (AR) technologies. However, to be fully accepted as a valid tool for training within the automotive industry, evidence is required on the ability of these systems to deliver effective and efficient training to the relevant users. This paper aims to investigate the effectiveness and efficiency of the first prototype of the virtual training system (VTS) developed within the VISTRA (Virtual Simulation and Training of Assembly and Service Processes in Digital Factories) project (FP7‐ICT‐285176), using real end users from the OPEL automotive plant in Rüsselsheim, Germany. Two separate and independent studies were employed that used objective and subjective methods of investigation to establish performance and usability measures. The objective results show that virtual training was effective in reducing error during task performance when compared to traditional training. The subjective results concluded that the opinions of the participants were mainly positive concerning the overall use of the VTS for assembly operation training; however, a number of issues were highlighted and reported to the developers for further advancement of the system.     

Synchrotron X-ray tomography for investigations of water distribution in polymer electrolyte membrane fuel cells

Synchrotron X-ray tomography is used to visualize the water distribution in gas diffusion layers (GDL) and flow field channels of a polymer electrolyte membrane fuel cell (PEMFC) subsequent to operation. An experimental setup with a high spatial resolution of down to 10 μm is applied to investigate fundamental aspects of liquid water formations in the GDL substrate as well as the formation of water agglomerates in the flow field channels. Detailed analyses of water distribution regarding the GDL depth profile and the dependence of current density on the water amount in the GDL substrate are addressed. Visualizations of water droplets and wetting layer formations in the flow field channels are shown. The three-dimensional insight by means of this quasi in situ tomography allows for a better understanding of PEMFC water management at steady state operation conditions. The effect of membrane swelling as function of current density is pointed out. Results can serve as an essential input to create and verify flow field simulation outputs and single-phase models.     

Measuring device for synchrotron X-ray imaging and first results of high temperature polymer electrolyte membrane fuel cells

In this paper, a measurement cell for recording synchrotron X-ray images of low and high temperature PEM fuel cells is described. The experimental setup allows for recording of cross-sectional images, as well as for radiograms in through-plane direction, with limited signal degradation. First results on H₃PO₄ concentration and distribution as a function of the operating conditions are presented.This basic cell design is optimized for liquid water detection. To visualize water in an operating cell the energy of the synchrotron X-ray beam has been chosen in a range between 7 and 30 keV where high resolution images can be obtained. The cell design is described in detail, and references to results obtained with LT-PEMFC applications focusing on liquid water evolution are given. For HT-PEMFC applications, the method of synchrotron X-ray imaging can provide an insight on electrolyte concentration and distribution. These investigations show that significant information can be collected on electrolyte distribution and concentration as a function of operating parameters such as temperature, media utilization and humidification degree. First results for the dependence of electrolyte distribution on operating conditions are presented.     

Nachweis und Verfolgung von Membran‐Fouling

Membrane fouling is a negative contamination effect: compounds in the feed solution settle on the membrane surface or in the pores, limiting the efficiency and separation performance of the membranes. This effect occurs for different membrane types such as reverse osmosis, ultra‐, nano‐ and microfiltration membranes. A method is presented how membrane fouling can be identified and tracked based on the zeta potential calculated from flow measurements.