bluuebunny/crossref_metadata_2025 huggingface dataset:
NOx Emission in In-line Low-NOx Calciners - A Theoretical Study
Authors: Iliuta Ion , Iliuta Maria
Published: October 2005

Abstract - The present contribution is a continuation of our endeavor in developing mathematical models for In-Line Low-NOx calciners. The objective of the present work is to obtain new information about NO formation and reduction in In-Line Low-NOx calciners. So, the influence of the air combustion mixing into the main flow, limestone feed position, limestone feed ratio in the reducing zone, air combustion temperature and fuel type on the level of NO emission in the in-line low-NOx calciners was investigated. The analysis was carried out using a heterogeneous mathematical model based on non-isothermal diffusion-reaction models for char combustion and limestone calcination. The mixing in the oxidizing zone was modeled using a modified Zwietering approach, which supposes that combustion air is gradually mixed into the sub-stoichiometric suspension leaving the reducing zone. The analysis shows that the mixing rate of oxygen into the main flow determines different local oxygen concentrations and different char-N oxidation rates in the oxidizing zone which in turn affect the level of NO emission. The change of limestone feed position in the oxidizing zone modifies very much the temperature in the region up to the feed level and thereby the NO emission. In the case of bituminous coal, changing the limestone feed ratio in the reducing zone corresponds to an insignificant modification of the NO concentration. The increase of the air combustion temperature has a negative influence on NO emission.
Eulerian/Eulerian CFD Simulation of a Cold Flowing FCC Riser
Authors: Hansen Kim G , Ibsen Claus H , Solberg Tron , Hjertager Bjørn H
Published: October 2005

A computational fluid dynamics simulation, CFD, of a cold flowing riser fluidized with FCC catalysts has been performed. The computations are performed using a 3D multiphase computational fluid dynamics code with a Eulerian description of both gas and particle phase. The turbulent motion of the particulate phase is modelled using the kinetic theory for granular flow, and the gas phase turbulence is modelled using a Sub-Grid-Scale model. The complex inlet geometry is approximated using multiple inlet patches. The results were submitted to a blind-test in connection to the 10th international workshop on two-phase flow prediction held in Merseburg, Germany, 2002. The results are validated against experimental findings of particle mass flux across the riser and pressure profile along the riser. The calculations show good agreement with experimental findings of both mass flux and pressure profile, but further improvements are proposed and investigated. A parameter study shows that mesh refinement, choice of particle diameter and choice of drag model are crucial when simulating FCC riser flow.
Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene
Authors: Sung Dae Jin , Moon Dong Ju , Lee Yong Jun , Hong Suk-In
Published: October 2005

Difluorochloromethane (CHClF2, R22) has been used as a refrigerant for air conditioners and a raw material for the manufacturing of fluorinated compounds such as tetrafluoroethylene (C2F4, TFE), and hexafluoropyropylene (C3F6, HFP). TFE has been produced by the pyrolysis of chlorofluoroparaffins especially, R22, in the temperature ranges of 750 - 950 °C. To improve the relatively poor yield of TFE, the catalytic pyrolysis of R22 over activated carbon supported Cu-based catalysts was investigated. The catalytic activities over the prepared catalysts were compared with those of a non-catalytic pyrolysis reaction. Alteration of reactivity as a function of reaction time was also observed. At 650 °C and 700 °C, the yield for TFE over 10wt% Cu/A.C catalyst was higher than that in the non-catalytic pyrolysis. Reduced Cu catalysts were more active than CuO catalysts and the selectivity of HFP increased with increasing the amount of Cu loading in Cu/A.C catalysts. It was found that the reduced Cu catalyst was undergoing surface modification during the pyrolysis of R22 due to the reaction of Cu/A.C catalyst with hydrogen fluoride produced during the catalytic pyrolysis. The fresh catalysts and catalysts after the reaction were characterized by XRD and EDS. The metal fluoride formed during the pyrolysis was either CaAlF5 or Ca2AlF7, or their mixture
Combating Deactivation in Methane Non-Oxidative Dehydrocyclization via Hydrogen Feed Pulsing
Authors: Iliuta Maria , Iliuta Ion , Grandjean Bernard , Larachi Faical
Published: October 2005

The non-oxidative dehydrocyclization of methane was carried out over RuMo/HZSM-5 catalyst in a fixed-bed catalytic reactor between 873 and 973 K. The catalyst, prepared by incipient wetness co-impregnation, was highly selective towards benzene production. The formation and deposition of low-H/C carbonaceous species was found to be more important at high temperatures and high methane space velocities. Intermittent hydrogenation of the catalyst by periodically switching from CH4 stream to pure hydrogen in the feedstream contributed significantly to the regeneration of active sites through hydrogenation of the carbonaceous species. Coke removal from the catalyst during H2 exposure was confirmed through temperature programmed oxidation and mass spectrometry analyses of spent catalyst. Alternating sequences of dehydrocyclization and hydrogenation under moderate and high feed flow rates resulted in improving catalyst stability due to efficient reduction of coke formation. These results might suggest an option for maintaining relatively high catalyst activity towards benzene production for prolonged reaction times.
Radial Profiles of Particle Velocity in a Large Scale CFB Downer
Authors: Qian Zhen , Zhang Minghui , Yu Hao , Wei Fei
Published: October 2005

Radial profiles of particle velocity in a large scale (418 mm I.D.) downward Circulating Fluidized Bed (CFB downer) were obtained via a Laser Doppler Velocimetry (LDV) system. Results show that particle velocity is gradually increasing along the radial direction and there exists a peak value in the near wall region. Such unique radial profile shape can be explained by the solids accumulating trend in the near wall region of the downer. Experiment results in this large scale downer are also compared with those obtained by other researchers in small scale units so as to investigate the scale-up effect on the radial particle velocity distribution in the downer.
A Simulation Model for the Growth of Engineered Cartilage on Polymeric Scaffolds
Authors: Pisu Massimo , Lai Nicola , Cincotti Alberto , Delogu Francesco , Cao Giacomo
Published: October 2005

A mathematical model to simulate the growth of engineered cartilage on polymeric scaffold performed in rotating bioreactors has been developed. The model, based upon the material balance for the nutrient species (oxygen) and the primary extra-cellular matrix product (GAG), accounts for population balances to simulate cell proliferation and its distribution within the polymeric scaffold. A comparison between model results and literature experimental data in terms of GAG contents and its distribution within the tissue construct has been performed. All model parameters are taken from the literature except for the constant of the time rate of mass change appearing in the proposed population balance which has been adjusted to reproduce the experimental data concerning the tissue culture performed at 80 mm Hg of oxygen partial pressure. The predictive capability of the model has been also demonstrated by comparison with experimental data obtained for a different value of oxygen partial pressure (40 mm Hg).
A Mechanistic Model for the Water Gas Shift Reaction Over Commercial Catalysts Containing CuO/ZnO
Authors: Mann Ronald F. , Amphlett John C. , Peppley Brant , Thurgood Chris P.
Published: October 2005

The water gas shift (WGS) and reverse water gas shift (RWGS) reactions are important in a great number of chemical processes where the adjustment of the relative amounts of CO2, CO and H2 is important. So-called "low temperature shift", LTS, catalysts, normally operating in the temperature range 175 to 325oC, have been commonly based on CuO/ZnO although Al2O3 is normally also present in commercial catalysts. Such LTS catalysts have also been almost universally used in the past two or three decades to promote the methanol-steam reforming reaction for the production of hydrogen. The general application for such hydrogen has been as the feed to a fuel cell.Our group has done extensive work in developing understanding of this methanol-steam reforming (MSR) process with one of the major objectives being development of the ability to predict CO production rates for a variety of process conditions. It is now generally agreed that the WGS/RWGS reactions play a significant role in determining the composition of the product gas leaving the reformer. Since most of our interest has been in PEM fuel cells, for which CO is a serious anode poison, much of our MSR work has been directed to the development of mechanistic reaction models which can be used to design processes with minimum CO yield. Two publications (Peppley et al, 1999a and 1999b) summarize our proposed MSR reaction model, a key feature of which is a proposed mechanistic WGS/RWGS model.The paper demonstrates the application of this WGS/RWGS model to kinetic data for feeds such as CO+H2O, CO2+ H2, and simulated reformate, H2/CO2/CO/H2O, mixtures. Test pressures were at or near atmospheric. Results are presented for two commercial catalysts- one a CuO/ZnO and the other a CuO/ZnO/Al2O3 formulation. The thermodynamic consistency of the kinetic results is discussed.
Some Aspects of the Hydrodynamics of Bubble Columns
Authors: Wild Gabriel , Poncin Souhila , Li Huai-Zhi , Olmos Eric
Published: October 2005

Bubble columns have been the object of much attention these last 20 years; it has become a kind of benchmarking reactor for both advanced measuring techniques and for CFD. However, the classical approaches are still of interest, and improving these reactors is still a field of research. In the present article, first some reminders on classical approaches of bubble columns and airlift reactors are presented with recent applications, then the different aspects of CFD as applied to bubble columns are presented, then highlights on some features specific to non-Newtonian fluids are given, finally some attempts to improve bubble columns are presented.
Optimization of Steam Reformers: Heat Flux Distribution and Carbon Formation
Authors: Piña Juliana , Bucalá Verónica , Borio Daniel Oscar
Published: October 2005

Optimal heat flux distributions along the axial position of steam reformer tubes are analyzed, aiming to maximize the outlet methane conversion without violating the upper bounds specified for the tube skin temperature, Tw(z) and the local heat flux, Q(z). The possible occurrence of the carbon deposition phenomenon is considered as an additional constraint in the optimization problem by means of a kinetic criterion which accounts for the rate of carbon formation (rC,net).The problem of finding the axial heat flux profile that leads to maximum methane conversion (or minimum tube skin temperature for specified production) without violating the upper limits imposed for Tw(z), Q(z) and rC,net is in principle a complex optimization process. In this work, a relatively simple semi-analytical method, that requires only iterative reactor simulations, is proposed.At conditions of fresh catalyst and for operations with typical feed compositions and temperatures, the carbon formation constraint is not active. For low values of the maximum allowable local heat flux (Qall), the optimal heating policies are monotonically increasing Tw(z) trajectories. Conversely, for higher Qall values the optimal Tw(z) shows an initial increase in the first tube section followed by an isothermal section. Decreasing axial wall temperature profiles or Tw(z) curves with maximum are clearly not optimal.When the catalyst is strongly deactivated, the optimal manipulation of Q(z), or Tw(z), is an appropriate procedure to achieve carbon free conditions. As this heating policy consists basically in reducing the firing in the top section of the reformer tube, it leads to unavoidable production losses.The shape of the catalyst activity axial profile has a considerable influence on the risk of carbon formation. Increasing activity distributions (similar to those found when sulfur poisoning takes place) may result in severe carbon formation in the reformer top. An optimal control of the heat input can contribute to minimize this practical operation problem.
Memory Based Local Learning: Application to Process Engineering Problems
Authors: Kulkarni Abhijit J. , Patil Sanjay Vasant , Jayaraman Valadi K. , Kulkarni Bhaskar D.
Published: October 2005

Linear and nonlinear regression problems are very common in different fields of science and engineering. A number of different methods to provide accurate input/output relationship have been proposed in the literature. Lazy learning is a recently introduced nonparametric regression technique that employs a memory based local learning approach. Employment of (i) local weighted regression for parametric identification and (ii) PRESS statistic to assess a local model for structural identification, are the two unique features of Lazy learning. The method attempts to fit the training data in a region around the location of the query point by locally interpolating the relevant neighboring points based on distance measure. This is particularly useful when limited number of input/output pairs are available and an accurate prediction is required. Being a memory based technique, it does not require separate training, which greatly enhances the speed of implementation. Moreover the method is less susceptible to noise contamination. All these features are illustrated with one benchmark multivariate statistical example and three important chemical engineering examples comprising boiling point prediction of aliphatic hydrocarbons using quantitative structural property relations, system identification for a continuous stirred tank reactor in which an exothermal irreversible reaction between sodium thiosulfate and hydrogen peroxide occurs and a fermentation process for polyol production. The performance of the proposed method is compared with some of the state-of-art approaches.
Phase Mixing Modeling in Multiphase Reactors Containing Gas Bubble: a Review.
Authors: Lefebvre Sylvain , Chaouki Jamal , Guy Christophe
Published: October 2005

Multiphase reactors are often used as petrochemical, biological and pharmaceutical reactors. Understanding the mixing mechanism responsible for phase mixing is necessary for modeling purposes. Phase mixing may considerably affect reactor performance. In the literature, each phase mixing was often described by the Axial Dispersion Model (ADM), without physical justification. Some authors doubted the validity of the ADM and that it could represent the mixing of the phases and instead proposed other models. Also, some authors studied the fundamental mechanism responsible for phase mixing. For conversion and selectivity prediction purposes, the use of more complex phenomenological phase mixing models is essential when the kinetics are rapid and the interfacial mass transfer is limited. Many literature reviews concerning multiphase reactors have been published. These reviews, however, discuss phase mixing modeling based on the ADM and do not deal with the other phase mixing models. The aim of this work is to review the literature on phase mixing modeling, based on a mechanistic approach, for three kinds of multiphase reactors: the bubble column (solid free), slurry bubble column (small/light particles) and three phase fluidized bed (large/heavy particles) reactors. The common feature of these reactors is the presence of gas bubbles, which considerably influence the phase hydrodynamic. Hence, a mixing model proposed for one of these reactors may be conceptually representative of the mixing of the two others.
Industrial Applications of Reactive Distillation: Recent Trends
Authors: Hiwale Rameshwar S , Bhate Nitin V , Mahajan Yogesh S , Mahajani Sanjay M.
Published: October 2005

Last few years have seen a dramatic rise in the number of applications of reactive distillation (RD). This useful technology is now being applied for any scale of operation- from manufacture of fine chemicals to that of bulk chemicals. This article reviews the very recent applications and serves as a supplement for the exhaustive review on this subject by Sharma and Mahajani (2003). It not only furnishes the information on the ongoing research in the existing applications but also elaborates the newly discovered applications such as manufacture of phenol, linear alkyl benzene, carbonates, chlorosilane derivatives and chiral chemicals. Multiple reactions in RD, failure of RD in some cases and new RD configurations to increase the overall yields are some of the additional aspects being covered.
Optimization of Flow Shear Stress Through a Network of Capillary Fibers With the Use of CFD
Authors: Dasilva Arthur , Heran Marc , Sinfort Carol , Grasmick Alain
Published: October 2005

As hydrodynamics conditions govern membrane fouling, simulations with a Computational Fluid Dynamics software were run to establish optimal design of membrane network. First, simulation through one cylinder was used to calibrate model by comparing the separation angle of experiments executed by Sucker & Brauer (1975) and the separation angle of simulations. Moreover, streamlines profile were compared for different Reynolds numbers. Intermediate or turbulent flow (Red = 600) imposed the choice of turbulence models. It is proved that the standard model, k-epsilon, is not well adapted to simulate the flow around a curved body. The SST-k-omega model resulted in better simulations. Geometry and boundary conditions were taken as common used (Newman and Dirichlet). Once the model was calibrated, simulations were run with a bundle of capillary fibers (membrane network). Velocity, velocity gradient, and friction coefficient were used to define optimal design according to experimental results.
Reactor Operating Strategy and Secondary Nucleation in Emulsion Polymerization
Authors: Zeaiter Joseph , Romagnoli Jose , Gomes Vincent G
Published: October 2005

Particle formation is a key step in emulsion polymerization reactions and has been the subject of extensive investigations in the past few decades. The main aim of this work was to investigate, both theoretically and experimentally, the conditions for secondary nucleation and particle evolution in batch and semi-batch emulsion polymerization. The effects of variation in monomer and emulsifier concentration in the feed, the distribution between the charge and the feed, temperature and the emulsion feed rate on polystyrene particle size distribution were investigated both theoretically and experimentally. The population balance and kinetic models developed were employed for predicting the product attributes for a range of reactor operating conditions. The sets of nonlinear algebraic and integro-differential evolution equations were solved efficiently for this work.Monomer and surfactant feed rates were found to have significant effects on the growth of polymer particles and consequently on the particle size. Different particle sizes and distributions were obtained using the same procedure with variable operating mode. A semi-batch reactor with variable monomer emulsion feed can produce latexes with variable polydispersity. A high initial rate of particle formation could lead to reduction in secondary nucleation and hence to the formation of a mono-modal PSD. This can be achieved by using high initiator and emulsifier concentrations in the feed, a high temperature, or a low monomer concentration in the charge. A low initial rate of nucleation increases the possibility of secondary nucleation and the formation of a bimodal PSD. The evolution of a bimodal PSD requires secondary nucleation after primary nucleation occurs.
Horizontal Penetration of Gas-Liquid Spray Jets in Gas-Solid Fluidized Beds
Authors: Ariyapadi Siva , Berruti Franco , Briens Cedric , McMillan Jennifer , Zhou David
Published: October 2005

A new method has been developed to predict the horizontal jet penetration of gas-liquid sprays injected into gas-solid fluidized beds. The technique involves combining a theoretical model to predict the momentum flux of two-phase sprays with the Benjelloun et al. (1995) correlation for gas jets. Following this treatment, a generalized version of the jet penetration correlation has been developed, which includes the effect of nozzle geometry. The correlation predictions are in very good agreement with the experimental data for a wide range of nozzle geometries, nozzle scales, and jet fluids.
Gas-Liquid-Solid Fluidization: Perspectives
Authors: Fan L.-S.
Published: October 2005

Gas-liquid-solid (three-phase) fluidization systems encompass a variety of operating modes of gas, liquid and solid phases with solids in suspended states. Commercial or large-scale operations using three-phase fluidization systems are prevalent for physical, chemical, petrochemical, electrochemical and biological processings. This presentation highlights recent advances in this field with a specific focus on subjects concerning particle-particle interaction, liquid turbulence, particle-evaporative liquid droplet interaction, flow structure, high pressure effects, and computational fluid dynamics (CFD).
Optimal Non-isothermal Reactor Network for Van de Vusse Reaction
Authors: Waghmare Ravindra S , Moharir Arun S
Published: October 2005

For complex reactions the optimal reactor networks can involve several reactors operating at various temperature profiles. The often-reported strategy of optimizing parameters of a heuristically predetermined reactor system (Super-structure Approach) falls short of obtaining true solution due to the presence of multiple local optima. Attainable set method gives Global optimum but requires study of each reaction scheme in depth. Here one such study using phase-plane analysis (instead of convexity based analysis) is reported for finding globally optimal non-isothermal reactor network for van de Vusse reaction (A -> B -> C, 2A -> D, objective is to maximize yield of B). Compared to two-reactor networks proposed earlier, it is found that up to 5 reactors (CSTR with/without bypass of feed, Isothermal PFR, Non-isothermal PFR, CSTR, Isothermal PFR) may be required to get the highest yield of the desired intermediate. The proposed method involves only elementary calculus. The detailed solution algorithm has been described using analogy with highways. Three cases with the values of reaction constants reported in the literature have been solved.
Hydrogenation of Acetylene: Kinetic Studies and Reactor Modeling
Authors: Mostoufi Navid , Ghoorchian Ali , Sotudeh-Gharebagh Rahmat
Published: October 2005

The kinetics of acetylene hydrogenation has been studied in a fixed bed reactor of a commercial Pd/Al2O3 catalyst. The experiments were carried out at 30, 50 and 70 ºC with various feed compositions at atmospheric pressure. The experiments were repeated at 70 ºC in the presence of the used catalyst to determine the effect of the catalyst deactivation where the corresponding deactivation rate constant was determined in order to predict the activity of the catalyst during each run. Two well known kinetic models were used for a nearly similar catalyst to predict the experimental data of this work and none of them were found satisfactory. A new model was then proposed to fit the experimental data. The hydrogenation reactor was also simulated at industrial operating conditions with the proposed kinetics for both plug and dispersion flows. The results of these simulations were almost close to each other in most cases.
Optimal Operation of Semi-Batch Processes with a Single Reaction
Authors: Palanki Srinivas , Vemuri Jyothy
Published: October 2005

In a large number of industrial semi-batch reactor applications, a single reaction takes place in the reactor and the operational objective is to compute the optimal feed rate of reactants and the optimal batch temperature that optimizes an objective function at the end of a fixed batch time. In this work, it is shown that the optimal operating policy can be split into several time intervals. Analytical expressions for the optimal input are developed for each interval. Parametric uncertainty is handled by implementing this strategy in closed-loop. This methodology is illustrated via simulation of two semi-batch reactor applications.
CFD Simulation of Heat Transfer in a Circular Channel: Effect of the Pe Number
Authors: Donsi' Francesco , Di Benedetto Almerinda , Marra Francesco S , Russo Gennaro
Published: October 2005

The numerical investigation of interphase heat transfer in a circular channel under laminar flow regime at different values of the Pe number is performed by means of a 2D mathematical axisymmetric model in which energy equations are coupled to the Navier-Stokes equations. The constant wall heat flux and constant wall temperature cases are simulated at different values of the Pe number. Results show that the heat transfer efficiency in both cases is strongly influenced by the back-diffusion even at very high values of Pe (Pe > 700). This behaviour is shown to be the result of the coupling between the interphase heat transport phenomena and the fluid flow. New correlations are hence derived to take into account the effect of back-diffusion on heat transfer.
Production of iso-Amyl Acetate: Heterogeneous Kinetics and Techno-feasibility Evaluation for Catalytic Distillation
Authors: Saha B. , Alqahtani A. , Teo H.T.R.
Published: October 2005

Esterification reactions are typically equilibrium limited, and face challenges with product purification. They are carried out commercially using either large excess of one of the reactants, or by removing one of the products continuously in a reactive distillation column (RDC). In the present work, we studied the kinetics of esterification reactions of dilute acetic acid with iso-amyl alcohol to produce a value added ester (iso-amyl acetate) using ion-exchange resins, Purolite® CT-175 and CT-275 as catalysts in a batch reactor. The effect of agitation speed, catalyst particle size, reaction temperature, acetic acid concentration, acetic acid to iso-amyl alcohol molar ratio and catalyst loadings were investigated to optimise the reaction conditions. The non-ideality of each species in the reacting mixture was accounted for by using the activity coefficient via the use of the UNIFAC group contribution method. The kinetic data were correlated with Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (E-R) models. The detailed kinetic data and a reliable rate expression for the esterification of acetic acid with an aliphatic alcohol (iso-amyl alcohol) would be useful for the simulation and design of an RDC for removing dilute acetic acid from aqueous streams. Another objective of this work was to evaluate the techno-feasibility of this operation through a systematic procedure of residue curve map (RCM). RCM gives a design engineer an idea of the existence of any separation boundaries imposed by the singular points corresponding to the reactive or kinetic azeotropes and thereby provide an insight into the feasibility of the desired operation. In the present study, RCM was generated for the quaternary system (acetic acid - iso-amyl alcohol - iso-amyl acetate - water) under different conditions to work out the feasibility of the operation. This map also suggests possible column sequencing or configurations to achieve a desired duty in an RDC.
Modeling of Solid Acid Catalyzed Alkylation Reactors
Authors: Ramaswamy R. C. , Ramachandran P. A. , Dudukovic M. P.
Published: October 2005

The current solid acid catalyst based alkylation processes suffer from rapid deactivation of the catalysts which is affected by the shape and size of the catalysts, reactor configuration and the reactants feeding pattern. In this work, the deactivation of the solid acid catalysts in alkylation of iso-butane with butene and the reactor performance are studied using the multi-scale mathematical models. A pseudo-steady state catalyst pellet level model, incorporating the alkylation and deactivation kinetics, is coupled to the transient model of back mixed reactor configurations like a single CSTR and CSTR-in-series. The effects of catalyst shape, initial acid strength of the catalyst, paraffin-to-olefin feed ratio on the conversion of the olefin, on the yield of alkylates and on the time required for complete deactivation of the catalyst are investigated. The role of the size of the catalyst particles on the types of deactivation mechanism is elucidated. The effect of contacting pattern of iso-butane and butene in the reactor on the catalyst life and on the alkylate yield is also presented.
Redox Stabilization Effect of TiO2 in Co3O4 as Oxygen Carrier for the Production of Hydrogen through POX and Chemical Looping Processes
Authors: De los Rios Thelma , Lardizabal Gutierrez Daniel , Collins Martínez Virginia , López Ortiz Alejandro
Published: October 2005

Novel proposed processes for H2 production and energy generation such as partial oxidation of hydrocarbons (POX-MeO) and chemical looping process (CLP), respectively require the use of solid oxides as oxygen carriers. In POX-MeO the required oxygen for the partial oxidation of methane is provided by a transition metal oxide (MeO). First, H2 is produced through CH4+MeO = CO+H2+Me. Secondly, Me is re-oxidized through Me+O2 = MeO to regenerate the oxygen carrier. In the CL process, CH4 is being completely oxidized through CH2 + MeO = CO2 + H2O + Me producing heat and CO2 ready for sequestration. Finally, Me is re-oxidized using air to regenerate the Me back to MeO. In both processes the regenerated MeO is sent back to the initial step to result in a cyclic operation. Continuous exposure of MeO to Redox cycles frequently produces sinterization and MeO stabilization is needed to avoid loss of activity. The objective of this study is to investigate the stabilization effect of TiO2 in Co3O4 during Redox cycles to be used as an oxygen carrier using CoxTiOy type spinnels. Characterization of the synthesized samples included XRD, TPR, and SEM. Co2TiO4 and CoTiO3 spinnels were synthesized by solid state reaction. TGA and TPR Redox performance cycles of Co3O4 produced sintering, while results using a Co2TiO4 spinnel structure suggest a strong stabilization effect of TiO2 on Co. Ten Redox cycles using H2 and CH4 as reducing agents and a mixture of O2/N2 as oxidizer resulted in fixation of Co to TiO2 avoiding sintering.
An Approximate Analytical Solution for the Diffusion and Reaction Problem in a Catalyst Pellet in the Presence of Coke Formation
Authors: Morales-Cabrera Miguel A , Marroquin O. , Viveros Tomás , Ochoa-Tapia J.A.
Published: October 2005

An approximate solution for the problem of diffusion-reaction in an isothermal catalyst pellet when coke deposition occurs was developed. The approximation is based on the linearization of reaction terms, producing analytical expressions to evaluate concentration profiles inside the pellet and the effectiveness factor. The approximate solution can be extended to any form of reaction rate functionalities for the main and coking reactions. Coke formation from reactants (parallel coking) or products (consecutive coking) and deactivation functions dependent on the coke content are considered in pellets with slab, cylindrical and spherical geometry.In this work, first-order kinetics for the main and coking reactions and linear and exponential deactivation functions were evaluated. The approximate predictions of the concentration profiles and the effectiveness factors were compared with results obtained by the complete numerical solution. A good agreement was found for both parallel and consecutive coking, including the cases when low and high intra pellet diffusion resistances are present.
The Applicability Of Activities In Kinetic Expressions: a More Fundamental Approach To Represent the Kinetics Of the System CO2-OH- In Terms Of Activities
Authors: Haubrock Jens , Hogendoorn J. A. , Versteeg Geert F.
Published: October 2005

In this paper the applicability of using activities instead of concentrations in kinetic expressions has been investigated using the reaction of CO2 with various hydroxide solutions as a model system. For this system it is known that when the reaction rate constant is based on the use of concentrations in the kinetic expression, this "constant" depends both on the counter ion in the solution and the ionic strength. Using the data of Pohorecki, it could be revealed that the use of activities reduces the influence of the ionic strength on the derived rate constant to a very large extent. Hence the kinetic constant using the activity based approach seems much more like a real constant than the "constant" using the traditional kinetic expression using concentrations. Besides this, the absolute values of the rate constants for the three different counter-ions also moved closely together. This points out that applying one fixed rate constant, independent of the counter-ion or the ionic strength, might be sufficient for describing the reaction rate in the studied system. A large advantage of using activities in kinetic expressions is that the fundamental description of kinetics and thermodynamics is consistent which each other so that at equilibrium the net reaction rate (based on the kinetic expression) is indeed zero.
Supramolecular Ordered Organic Thin Films for Nonlinear Optical and Optoelectronic Applications
Authors: Khan R. U. A. , Kwon O‐P. , Tapponnier A. , Rashid A. N. , Günter P.
Published: October 2005

For second‐order nonlinear optics, a supramolecularly ordered non‐centrosymmetric structure is required. Additionally, well‐ordered organic semiconducting thin films possess superior electronic properties compared to their amorphous counterparts. Herein, we firstly highlight that the design of nonlinear molecules and their functionalization for good molecular orientation (e.g., H‐bonding) is an important method in which to induce supramolecular ordering during subsequent growth. Secondly, we demonstrate a range of growth strategies (e.g., oblique‐incidence molecular beam deposition, hot‐wall deposition) for the growth of molecularly ordered thin films. Thirdly, we discuss various organic supramolecularly ordered material systems (4‐[trans(pyridin‐4‐ylvinyl)] benzoic acid, 5‐bromo‐5′‐formyl‐2,2′‐bithiophene‐4‐nitrophenyl hydrazone, tris(8‐hydroxyquinoline) aluminum) and observe the effects of molecular orientation on their nonlinear optical and optoelectronic properties.
Core–Shell Zeolite Microcomposites
Authors: Bouizi Y. , Diaz I. , Rouleau L. , Valtchev V. P.
Published: October 2005

Core–shell zeolite composites possessing a core and a shell of different zeolite structure types have been synthesized. A characteristic feature of the obtained composites is the relatively large single‐crystal core and the very thin polycrystalline shell. The incompatibility between the core crystals and the zeolite precursor mixture yielding the shell layer has been circumvented by the adsorption of nanoseeds on the core surface, which induced the crystallization of the shell. The pretreated core crystals are subsequently subjected to a continuous growth in a zeolite precursor mixture. The feasibility of this synthetic approach has been exemplified by the preparation of core–shell β‐zeolite–silicalite‐1 composites. The synthesized composites have been characterized using X‐ray diffraction, high‐resolution transmission electron microscopy, and scanning electron microscopy. The integrity of the shell layer has been tested via N2‐adsorption measurements on materials comprising a calcined core (β‐zeolite) and a non‐calcined tetrapropylammonium (TPA)‐containing shell, the latter being non‐permeable for the N2 molecules. These measurements have shown that 86 % of the β‐zeolite crystals are covered with a defect‐free TPA–silicalite‐1 shell after a single hydrothermal treatment, while after three consecutive crystallization steps this value reaches 99 %. The shell integrity of the calcined composite has been studied by the adsorption of butane, toluene, and 1,3,5‐trimethylbenzene, which confirmed the superior performance of the triple‐shell composites.
Enhancement of Hydrolysis through the Formation of Mixed Hetero‐Metal Species: Dioxouranium(VI) – Cadmium(II) Mixtures
Authors: Crea Francesco , Milea Demetrio , Sammartano Silvio
Published: October 2005

In order to continue the investigation on the formation of hetero‐metal polynuclear hydrolytic species, in this paper we report some results (at I = 0.16 mol L−1 in NaNO3, at t = 25 °C by potentiometry, ISE‐H+, glass electrode) on the hydrolysis of several mixtures (in different ratios) of the dioxouranium(VI) and cadmium(II) cations. The same experimental and calculation procedure of previously investigated systems was followed, and all measurements were performed by two different operators, using completely independent instruments and reagents. Many different speciation models were considered in the calculations, and a simple statistical analysis of obtained results was proposed too. UO22+ and Cd2+ form two heterometal polynuclear hydrolytic species, namely UO2Cd(OH)3+ and (UO2)2Cd(OH)42+, with logβpqr = −3.25 ± 0.25 and ‐13.75 ± 0.10, respectively. The formation of heterometal hydrolytic species is thermodynamically favored with respect to the homo‐metal ones, and causes an enhancement of the percentage of hydrolyzed metal cations; comparisons with previously studied systems reveal that the hydrolytic behavior of UO22+ / Cd2+ mixtures is more similar to that observed for UO22+ / Cu2+ than for UO22+ / (C2H5)2Sn2+, and the tendency to form hetero polynuclear hydrolytic species with dioxouranium(VI) by other cations follows the trend (C2H5)2Sn2+ > Cu2+ ≥ Cd2+.
Water Quality of Two Glacial Alpine Italian Lakes
Authors: Zelano Vincenzo , Zambrotta Maria , Defilippi Albino , Torazzo Annamaria
Published: October 2005

The purpose of this study was to characterize, in a period of one year, two glacial lakes, Alice and Meugliano, located in an alpine reservoir on the basis of physical and chemical features. The two lakes show two periods of mixing: one in the spring and one in the autumn, so can be classified as dimictic lakes 1. They are characterized by pH, alkalinity, low conductivity and and quite dilute ionic concentrations. With regard to nutrients, most nitrogen occurred in the nitric form in the superficial layers. During the period of thermal stratification, in the anoxic layer NO3− decreases and NH4+ increases, confirming the activity of the anaerobic denitrificant bacteria. Total and soluble phosphorus levels show homogeneity during the cold period at different depths, while with stratification concentrations increase in the hypolimnium and metalimnium. In both lakes there is an inverse correlation between transparency and chlorophyll a. To evaluate the trophic state the conventional criteria of Nurnberg 2 and four lake trophic indices (TSIs) are used 3,4. Both evaluations suggest that the two lakes are eutrophic, with worse conditions in Alice. Deviations of the trophic states, based on the relation between TSIs 5,6, indicate that factors other than phosphorous limit the algal biomass, and that nonalgal particles influence light attenuation.
Molecularly Imprinted Polymer for Monocrotophos and its Binding Characteristics for Organophosphorus Pesticides
Authors: Zhu Xiaolan , Yang Jun , Su Qingde , Cai Jibao , Gao Yun
Published: October 2005

In this study, molecular imprinting was used to develop a method based on noncovalent interaction for the synthesis of a monocrotophos‐specific polymer. The selective binding characteristics of the template polymer were evaluated by 1H NMR study. The result was consistent with the existence of multi‐molecular complexes formed by hydrogen‐bonding interactions. Batch rebinding studies in acetonitrile were undertaken to quantitatively evaluate the affinity of the polymer for monocrotophos. The experimental binding isotherms were fitted to the Freundlich isotherm and the total number of binding sites of the polymer can be calculated to be 4.046μmolg−1. The induced affinity and selectivity by imprinting were examined chromatographically. The polymer gave more than 15 times longer retention for monocrotophos than the nonimprinted polymer with the same chemical composition. Other organophosphorus pesticides under study were eluted close to the void volume on the polymer column.
A Simple and Rapid Spectrophotometric Method for Determination of Ultra Trace Amounts of Thallium(III) with 4‐(4′‐N,N‐Dimethylaminophenyl) Urazole as a New Reagent
Authors: Rezaei Behzad , Mallakpour Shadpour , Khalili Honieh , Rafiee Zahra
Published: October 2005

A simple and selective spectrophotometric method is proposed for the determination of ultra trace amounts of Tl(III). The reported method is based on the oxidation of 4‐(4′‐N,N‐dimethylaminophenyl)urazole (DAPU) to the corresponding triazolinedione (TAD) by Tl(III) at pH 4.0. The reaction was monitored spectrophotometrically by measuring the increasing color of TAD compound at 514 nm by the fixed‐time method. At a given time of 2.0 min at 30 °C, the working range of calibration was 5.0 × 10−8 ‐ 2.0 × 10−5 M Tl(III) and detection limit of 5.0 × 10−8 M was obtained. The influences of pH, reagent concentration, ionic strength and temperature were studied. The effect of diverse ions on the determination of Tl(III) by the proposed method was also investigated. Thallium in real samples was determined by this method, with satisfactory results.
Preclinical Huntington's disease: Compensatory brain responses during learning
Authors: Feigin Andrew , Ghilardi Maria‐Felice , Huang Chaorui , Ma Yilong , Carbon Maren , Guttman Mark , Paulsen Jane S. , Ghez Claude P. , Eidelberg David
Published: October 2005

Motor sequence learning is abnormal in presymptomatic Huntington's disease (p‐HD). The neural substrates underlying this early manifestation of HD are poorly understood. To study the mechanism of this cognitive abnormality in p‐HD, we used positron emission tomography to record brain activity during motor sequence learning in these subjects. Eleven p‐HD subjects (age, 45.8 ± 11.0 years; CAG repeat length, 41.6 ± 1.8) and 11 age‐matched control subjects (age, 45.3 ± 13.4 years) underwent H215O positron emission tomography while performing a set of kinematically controlled motor sequence learning and execution tasks. Differences in regional brain activation responses between groups and conditions were assessed. In addition, we identified discrete regions in which learning‐related activity correlated with performance. We found that sequence learning was impaired in p‐HD subjects despite normal motor performance. In p‐HD, activation responses during learning were abnormally increased in the left mediodorsal thalamus and orbitofrontal cortex (OFC; BA 11/47). Impaired learning performance in these subjects was associated with increased activation responses in the precuneus (BA 18/31). These data suggest that enhanced activation of thalamocortical pathways during motor learning can compensate for caudate degeneration in p‐HD. Nonetheless, this mechanism may not be sufficient to sustain a normal level of task performance, even during the presymptomatic stage of the disease. Ann Neurol 2006
Noradrenergic modulation of space exploration in visual neglect
Authors: Malhotra Paresh A. , Parton Andrew D. , Greenwood Richard , Husain Masud
Published: October 2005

Visual neglect after stroke is often associated with a failure to explore contralesional space. Here, we show that guanfacine, a noradrenergic agonist that modulates dorsolateral prefrontal cortex, improves leftward space exploration in selected right‐hemisphere patients with neglect. The positive effects of guanfacine were associated with extended ability to maintain attention on task. The results suggest that neuropharmacological targeting of intact frontal areas might be one way to enhance cognitive function after damage to posterior brain regions in selected individuals. Ann Neurol 2005
Metallische Schmelzen – Reaktionsmedien zur Präparation intermetallischer Verbindungen
Authors: Kanatzidis Mercouri G. , Pöttgen Rainer , Jeitschko Wolfgang
Published: October 2005

Ziel dieses Aufsatzes ist es, die Vorzüge von flüssigen Metallen als Lösungsmittel bei der Synthese intermetallischer und ähnlich zusammengesetzter Verbindungen aufzuzeigen. Eine Vielzahl neuer Phasen mit zum Teil ungewöhnlichen Zusammensetzungen wurde in den letzten Jahren auf diese Weise erstmals hergestellt. Nach einem kurzen historischen Überblick werden die vorteilhaften Eigenschaften der eingesetzten Metallschmelzen (Flussmittel, Flux) für die Synthese eines breiten Spektrums von Verbindungen besprochen.
Conformational behavior of temporin A and temporin L in aqueous solution: A computational/experimental study
Authors: D'Abramo M. , Rinaldi A. C. , Bozzi A. , Amadei A. , Mignogna G. , Di Nola A. , Aschi M.
Published: October 2005

Molecular dynamics (MD) simulations and circular dichroism (CD) experiments were carried out on aqueous temporin A and L, two short peptides belonging to an interesting class of natural substances known to be active mainly against Gram‐positive/negative bacteria and fungi. Experimental results indicate the higher propensity of temporin L, with respect to temporin A, in forming α‐helical structures. These results were revisited by long‐timescale MD simulations, in which their α‐helical propensity was investigated in the absence of trifluoroethanol. Results clearly show the higher stability of α‐helix conformations in temporin L; moreover, an interestingly strong mechanical analogy emerges since both temporins show the same residue interval (from 7 to 10) as the most energetically accessible for α‐helix formation. Such studies provide some intriguing structural and mechanical evidence that may help in better understanding and rationalizing the conformational behaviour of temporins in water solution and, ultimately, the inner principles of their microbial targets selectivity and mechanism of action at the level of cell membranes. © 2005 Wiley Periodicals, Inc. Biopolymers 81: 215–224, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Numerical Simulation of the Effect of Solvent Viscosity on the Motions of a β‐Peptide Heptamer
Authors: Gee Peter J. , van Gunsteren Wilfred F.
Published: October 2005

This report examines the effect of a decrease in solvent viscosity on the simulated folding behaviour of a β‐peptide heptamer in methanol. Simulations of the molecular dynamics of the heptamer H‐β3‐HVal‐β3‐HAla‐β3‐HLeu‐(S,S)‐β3‐HAla(αMe)‐β3‐HVal‐β3‐HAla‐β3‐HLeu‐OH in methanol, with an explicit representation of the methanol molecules, were performed for 80 ns at various solvent viscosities. The simulations indicate that at a solvent viscosity of one third of that of methanol, only the dynamic aspects of the folding process are altered, and that the rate of folding is increased. At a viscosity of one tenth of that of methanol, insufficient statistics are obtained within the 80 ns period. We suggest that 80 ns is an insufficient time to reach conformational equilibrium at very low viscosity because the dependence of the folding rate of a β‐peptide on solvent viscosity has two regimes; a result that was observed in another computational study for α‐peptides.