Aminolytic depolymerization of poly(ethylene terephthalate) waste in a microwave reactor

The aminolytic depolymerization of poly(ethylene terephthalate) (PET) taken from waste soft‐drink bottles, under microwave irradiation, is proposed as a recycling method with possible substantial energy savings. The reaction was carried out with ethanolamine and without the use of any other catalyst in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. Experiments under constant temperature or microwave power were carried out for several time periods. The main product, bis(2‐hydroxyethyl) terephthalamide, was identified from Fourier transform infrared (FTIR) spectra and DSC measurements. It was found that PET depolymerization is favoured by increasing temperature, time and microwave power. The average molecular weight of the PET residues, determined using viscosity measurements, was found to decrease with the percentage of PET degradation, indicating a random chain scission mechanism to some extent. From a simple kinetic model, the activation energy of the reaction was evaluated. Complete depolymerization was found to occur in less than 5 min when the irradiation power applied was 100 W or the temperature was 260 °C. These results support the use of microwave‐assisted aminolytic degradation as a very beneficial method for the recycling of PET wastes. Copyright © 2010 Society of Chemical Industry     

Electrochemical enhancement of solar photocatalysis: degradation of endocrine disruptor bisphenol-A on Ti/TiO2 films

The photoelectrocatalytic oxidation over immobilized Ti/TiO₂ films in the presence of simulated solar light was investigated for the degradation of bisphenol-A (BPA) in water. The catalyst, consisting of 75:25 anatase:rutile, was prepared by a sol-gel method and characterized by cyclic voltammetry, X-ray diffraction and scanning electron microscopy. Experiments were conducted to assess the effect of applied current (0.02-0.32 mA/cm²), TiO₂ loading (1.3-9.2 mg), BPA concentration (120-820 μg/L), initial solution pH (1 and 7.5) and the aqueous matrix (pure water and treated effluent) on BPA photoelectrocatalytic degradation which was monitored by high performance liquid chromatography equipped with a fluorescence detector. The reaction was favored at anodic currents up to 0.04 mA/cm² and lower substrate concentrations, but it was hindered by the presence of residual organic matter and radical scavengers (e.g. bicarbonates) in treated effluents. Moreover, a pseudo-first order kinetic model could fit the experimental data well with the apparent reaction constant taking values between 2.9 and 32.4 10⁻³/min. The degradation of BPA by pure photocatalysis or electrochemical oxidation alone was also studied leading to partial substrate removal. In all cases, the contribution of applied potential to photocatalytic degradation was synergistic with the photocatalytic efficiency increasing between 24% and 97% possibly due to a more efficient separation and utilization of the photogenerated charge carriers. The effect of photoelectrocatalysis on the ecotoxic and estrogenic properties of BPA was also evaluated measuring the bioluminescence inhibition of Vibrio fischeri and performing the yeast estrogen screening assay, respectively.     

Evaluation of notional nozzle approaches for CFD simulations of free-shear under-expanded hydrogen jets

Several approaches are usually applied for modelling the source of high pressure under-expanded jets, ranging from the computationally expensive resolution of the jet's shock structure to simple formulae (pseudo-source or notional nozzle approaches). However, the assumptions made in each approach introduce inaccuracies in the CFD calculations. The objective of this work was twofold; to compare and evaluate the performance of both selected notional nozzle approaches and turbulence models with experimental results of free-shear high momentum H₂ round jets. The experimental data covered horizontal H₂ releases issuing from small nozzles (0.25–1 mm diameter). Three two-equation turbulence models were chosen for the simulations, the popular standard k-ε, the Shear Stress Transport (SST) and the baseline (BSL) k-ω model together with five notional nozzle approaches. The numerical results were presented in a systematic way in order to make general conclusions on the performance of both the approaches and models.     

High-level customization framework for application-specific NoC architectures

Network-on-Chip (NoC) has been recognized as the new paradigm to interconnect and organize a high number of cores. NoCs address global communication issues in System-on-Chips (SoC) involving communication-centric design and implementation of scalable communication structures evolving application-specific NoC design as a key challenge to modern SoC design. In this paper we present a SystemC customization framework and methodology for automatic design and evaluation of regular and irregular NoC architectures. The presented framework also supports application-specific optimization techniques such as priority assignment, node clustering and buffer sizing. Experimental results show that generated regular NoC architectures achieve an average of 5.5 % lower communication-cost compared to other regular NoC designs while irregular NoCs proved to achieve on average 4.5×higher throughput and 40 % network delay reduction compared to regular mesh topologies. In addition, employing a buffer sizing algorithm we achieve a reduction in network’s power consumption by an average of 45 % for both regular and irregular NoC design flow.     

Life-cycle cost optimal design of passive dissipative devices

The cost-effective performance of structures under natural hazards such as earthquakes and hurricanes has long been recognized to be an important topic in the design of civil engineering systems. A realistic comprehensive treatment of such a design requires proper integration of (i) methodologies for treating the uncertainties related to natural hazards and to the structural behavior over the entire life-cycle of the building, (ii) tools for evaluating the performance using socioeconomic criteria, as well as (iii) algorithms appropriate for stochastic analysis and optimization. A systematic probabilistic framework is presented here for detailed estimation and optimization of the life-cycle cost of engineering systems. This framework is a general one but the application of interest here is the design of passive dissipative devices for seismic risk mitigation. A comprehensive methodology is initially presented for earthquake loss estimation; this methodology uses the nonlinear time-history response of the structure under a given excitation to estimate the damage in a detailed, component level. A realistic probabilistic model is then presented for describing the ground motion time history for future earthquake excitations. In this setting, the life-cycle cost is uncertain and can be quantified by its expected value over the space of the uncertain parameters for the structural and excitation models. Because of the complexity of these models, calculation of this expected value is performed using stochastic simulation techniques. This approach, though, involves an unavoidable estimation error and significant computational cost, features which make efficient design optimization challenging. A highly efficient framework, consisting of two stages, is discussed for this stochastic optimization. An illustrative example is presented that shows the efficiency of the proposed methodology; it considers the seismic retrofitting of a four-story non-ductile reinforced-concrete building with viscous dampers.     

Effectiveness factor of fast (Fe3+/Fe2+), moderate (Cl2/Cl?) and slow (O2/H2O) redox couples using IrO2-based electrodes of different loading

The effectiveness factor, E _f, (fraction of the electrode surface that participates effectively in the investigated reaction) of fast (Fe³⁺/Fe²⁺), moderate (Cl₂/Cl⁻) and slow (O₂/H₂O) redox couples has been estimated using IrO₂-based electrodes with different loading. The method of choice was linear sweep voltammetry (measurement of the anodic peak current) for the Fe³⁺/Fe²⁺ redox couple and steady-state polarization (determination of the exchange current) for the O₂ and Cl₂ evolution reactions. The results have shown that the effectiveness factor depends strongly on the kinetics of the investigated redox reaction. For the Fe³⁺/Fe²⁺ redox couple, effectiveness factors close to zero (max 4%) have been obtained contrary to the O₂ evolution reaction where effectiveness factors close to 100% can be achieved, all being independent of IrO₂ loading. For the Cl₂ evolution reaction, intermediate values of the effectiveness factor have been found and they decrease strongly, from 100% down to about 60%, with increasing loading.     

An efficient framework for optimal robust stochastic system design using stochastic simulation

The knowledge about a planned system in engineering design applications is never complete. Often, a probabilistic quantification of the uncertainty arising from this missing information is warranted in order to efficiently incorporate our partial knowledge about the system and its environment into their respective models. This leads to a robust stochastic design framework where probabilistic models of excitation uncertainties and system modeling uncertainties can be introduced; the design objective is then typically related to the expected value of a system performance measure, such as reliability or expected life-cycle cost. For complex system models, this expected value can rarely be evaluated analytically and so it is often calculated using stochastic simulation techniques, which involve an estimation error and significant computational cost. An efficient framework, consisting of two stages, is presented here for the optimization in such robust stochastic design problems. The first stage implements a novel approach, called stochastic subset optimization (SSO), for iteratively identifying a subset of the original design space that has high plausibility of containing the optimal design variables. The second stage adopts some other stochastic optimization algorithm to pinpoint the optimal design variables within that subset. The focus is primarily on the theory and implementation issues for SSO but also on topics related to the combination of the two different stages for overall enhanced efficiency. An illustrative example is presented that shows the efficiency of the proposed methodology; it considers the optimization of the reliability of a base-isolated structure considering future near-fault ground motions.