bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive Hydrogen Content: A Tool to Predict FCC Yields
Authors: Mariaca-Dominguez Ernesto , Rodríguez-Salomón Silvano , Yescas Rafael Maya
Published: October 2005

Fluid Catalytic Cracking is a process conceived to produce gasoline as the main product. Feed stocks to the process are vacuum gas oils (VGO) showing boiling point ranges typically between 343°C and 538°C. Since these boiling range cut points are usually fixed, the carbon number range of encountered hydrocarbons is approximately constant and this is also true for the relative amounts of paraffins, naphthenes and aromatics, regardless of changes from feed to feed. Under FCC reaction conditions, each of the above hydrocarbon groups exhibit different crackability. In order to explain the existing relationship between feed composition and yields and quality of end products, it is necessary to establish the effect of composition and operational conditions on cracking behavior of feedstocks, expressed in terms of a relation between some specific properties, or as in our case, by its Reactive Hydrogen Content (RHC). Therefore, yields should then be dependent on three factors, RHC value, as a measure of feed quality, catalysts and applied operational conditions. In this work, a RHC for a series of feeds of known composition is determined and correlated to conversion and yields obtained under different operational conditions, using the same catalyst. The resulting correlations are then applied to unknown feeds with the RHC being calculated from physical properties, and yields.
Detection and Modeling of the Core-Annulus Transition in Industrial and Pilot Plant Risers
Authors: Briens Lauren , Briens Cedric , Nevicato David , Bernard Jean René
Published: October 2005

The core-annulus structure is essential to the modeling and optimization of riser reactors such as used in Fluid Catalytic Cracking. This paper presents results of measurements taken with various probes in a pilot plant and in an industrial riser. The instantaneous probe signals were analyzed with sophisticated signal analysis methods based on the detection of cycles and the determination of the correlation dimension.In a pilot plant riser, a core-annulus structure was identified with optical and momentum probe measurements. Cycle analysis of the optical probe measurements showed that the annulus was unstable: its thickness fluctuated with an average cycle time of 0.3 s. There were waves at the core-annulus boundary. In an industrial riser, a similar core-annulus structure could be identified with temperature and momentum probe measurements. Local temperature measurements are much easier to perform in an industrial riser than momentum probe measurements but can provide, with cycle analysis, the location of the core-annulus transition. Analysis of the momentum probe and temperature signals showed that the thickness of the wavy transition layer between core and annulus was about the same in the pilot plant and the industrial riser, meaning that the relative range of fluctuations in annulus thickness was much smaller in the larger industrial riser.A model was developed to predict the time-averaged transition between core and annulus. This model, which had been successfully used to predict the annulus thickness in dilute-phase vertical pneumatic transport lines, assumes that the annulus thickness is such that the riser pressure drop is minimized. Measurements and model predictions were in good agreement.
Kinetics and Equilibrium of Cadmium Biosorption by Yeast Cells S. cerevisiae and K. fragilis
Authors: Hadi Bashar , Margaritis Argyrios , Berruti Franco , Bergougnou Maurice
Published: October 2005

The biosorption of cadmium metal ions by Saccharomyces cerevisiae and Kluyveromyces fragilis yeast cells was studied under various operating conditions in a batch system using shaker flasks and a 2-L double draft tube fluidized bioreactor system. The effects of key parameters such as solution pH, initial metal concentration, biosorbent concentration, and age of the biosorbent cells were investigated. The experiments were carried out at room temperature and pH values of 3.5, 4.5 and 5.0. Three biosorbent yeast cells concentrations (2.5, 5.0 and 7.5 g dry wt./L) were employed with aqueous solutions having initial cadmium concentrations of 50, 100 and 200 mg/L. The solution pH was found to play a critical role in the biosorption process and the metal uptake increased with an increase in pH value. The optimum pH was found to be 5.0. Also, increasing the metal concentration and decreasing the biosorbent concentration increased the final metal uptake per unit cell mass. At a sufficiently high cadmium concentration of 200 mg/L, the effect of initial metal concentration became the dominant factor, since the metal uptake became constant with respect to the initial metal concentration, regardless of pH value. The results showed that the effect of biosorbent concentration on metal uptake was less significant than those of the cadmium concentration and the pH. It was also found that the younger the yeast biosorbent, the higher the metal uptake capacity. Generally, the cadmium uptake was found to take place rapidly, whereby almost 90% uptake occurred within the first five minutes of exposure. The equilibrium of cadmium biosorption was investigated under the same operating conditions. The Langmuir and the Freundlich adsorption isotherms were used to fit the experimental data. However, both of these conventional adsorption models did not fit the experimental data accurately. The maximum uptake capacity was estimated to be close to 35 and 40 mg Cd/g DW cell for S. cerevisiae and K. fragilis, respectively at a pH value of 5.0.
The CREC Fluidized Riser Simulator. Characterization of Mixing Patterns
Authors: Ginsburg Jason M , Pekediz Ahmet , de Lasa Hugo Ignacio
Published: October 2005

The CREC Riser Simulator Reactor is a new laboratory scale unit that was invented at CREC-UWO (de Lasa, 1991). It was specially designed for catalyst testing and kinetic modeling under the conditions of riser and downer reactors. Preliminary work on mixing patterns in the Riser Simulator was already effected by our group using a helium tracer and a constant temperature hot wire anemometer (Pekediz et al, 1993) with both of these devices placed in the outer reactor annulus. However and given the possible ambiguity of the mixing patterns established with these data, helium tracer was injected in the present study into the central catalyst basket, while velocity measurements were effected in the outer annulus. This methodology allowed the definition of effective gas mixing time and gas superficial velocities at various reactor pressures and impeller speeds with increased confidence. This study found that gas mixing times corresponding to high gas recirculation rates in a CREC Riser Simulator occur over impeller rotational speeds ranging from 3000-6000 rpm and total reactor pressures ranging from 1-5 atm. With this end, gas mixing patterns in a Riser Simulator represent a well mixed unit, and thus, the importance of the Riser Simulator can be realized in the context of its potential use for gas-solid reaction kinetics.
Hydrodynamic Modeling of CFB Risers and Downers
Authors: Bolkan Yasemin , Berruti Franco , Zhu Jesse , Milne Bruce
Published: October 2005

Making best use of the Circulating Fluidized Bed (CFB) hydrodynamics is crucial in order to attain optimal yield and selectivity of desirable products in such reactors. While the conventional CFB riser has been proven to be highly effective for fast gas-solid reaction systems, the CFB downer promises further improvements over the CFB riser, due to its more uniform flow and better controlled fluid-solid contact times. To obtain a better understanding of both reactors, individual hydrodynamic models are developed for a downer and a riser. Both hydrodynamic models incorporate parameters that have not been investigated in depth so far. For example, empirical correlations have been developed to estimate the agglomeration within downers and the slip velocity in risers.The simulation results of both models are verified using experimental data that has been collected using a state-of-the-art riser/downer pair. The comparison of downer and riser model predictions reveals that downers operate at higher particle velocities and under more dilute conditions than risers and may therefore be better suited for fast chemical reactions that are run under dilute conditions. The benefit of downers may be extended if the higher solids holdups observed in risers can be attained through improvements in recycling and feeding particles into the downer. Most of the catalyst particles that the feed gas contacts in the downer are at their highest activity levels since the particles move slightly faster than the gas phase due to gravitational effects. Also, in case of catalytic reactions where over-cracking is an issue, the narrow residence time distribution in downers allows for better reaction control that leads to higher rates of desirable products. Therefore, at similar solids concentrations, downers are expected to outperform risers for catalytic reactions.
Kinetics of Synthesis of Perfumery Grade p-tert-Butylcyclohexyl Acetate Over Ion Exchange Resin Catalyst
Authors: Yadav Ganapati D. , Murkute Ambareesh D.
Published: October 2005

Esterification reactions are conventionally carried out by using homogeneous acids on industrial scale and only a few heterogeneous catalysts are reported. Esters represent an imperative class of aroma compounds. They often possess fruity odors and are widely used by the food and fragrance industries. In view of stringent environmental concern the use of heterogeneous catalysts is now heavily pursued. In order to develop environmentally benign process, the present work hinges on importance of Amberlyst-15 (an ion exchange resin) in the esterification of p-tert-butylcyclohexanol (PTBCH) with acetic acid to get p-tert-butylcyclohexyl acetate (PTBCHA) including kinetics of the reaction. PTBCHA has a sweet, almost creamy-woody odour with a soft-floral undertone. PTBCHA is expensive and is widely used in perfumery industry. The effects of various parameters on rate of reaction were studied in detail and a model was developed for an intrinsically kinetically controlled reaction which is free from either intra-particle diffusion or external mass transfer resistance. The catalyst is reusable without loss of activity. Esterification of PTBCH was also carried with propionic acid, isobutyric acid, pentanoic acid and hexanoic acid to study the effect of chain length and also because of their commercial significance.
A 3D Model of Combustion in Large-Scale Circulating Fluidized Bed Boilers
Authors: Luecke Karsten , Hartge Ernst-Ulrich , Werther Joachim
Published: October 2005

In a circulating fluidized bed (CFB) combustor the reacting solids are locally fed into the combustion chamber. These reactants have to be dispersed across the reactor's cross-sectional area. Since the rate of mixing is limited this leads to a mal-distribution of the reactants and to locally varying reaction conditions. In order to describe the influence of mixing a three-dimensional model of the combustion chamber is suggested. The model is divided into three sub-topics. First, the flow structure in terms of local gas and solids velocities and solids volume concentrations is described. Second, mixing of the solids and the gas phase is quantified by defining dispersion coefficients, and finally the combustion process itself, i.e. the reaction kinetics, is modelled. The model was validated against data from measurements in the large-scale combustor of Chalmers University of Technology in Göteborg/Sweden. Insufficient fuel mixing generated mal-distributions of locally released volatiles, which were the basis for the uneven reactants distribution at steady-state. In the case of two-stage operation, the injected secondary air did not reach immediately the reactor's center but was slowly mixed with the main gas flow. The concentration gradients hardly vanish before the exit of the combustion chamber.
Granular Flows and Gas Fluidization
Authors: Campbell Charles S.
Published: October 2005

This presentation examines the roles that granular flow theory might play in the modeling the solid-phase stresses in fluidized beds. It begins with a discussion of the historical limiting cases of quasistatic and rapid-flow regimes. It then reviews the elastic granular theories that unify those two regimes. Finally, it shows that measurements of solid-phase pressures cannot be explained by commonly used rapid-flow theories, and most likely lie in the elastic flow regimes.
Elastic Granular Flows
Authors: Campbell Charles S
Published: October 2005

Large scale landslide simulations provided the surprising result that the effective friction coefficient (the ratio of shear to normal forces at the base of the slide) increased with the shear rate. This might possibly explain the effect of slide volume on the runout of large landslides, but it also indicates that landslides operated in an entirely new and unexplored flow regime.Previously, granular flows had been divided into (1) the slow, quasistatic regime, in which the effective friction coefficient is taken to be a material property and thus constant, and (2) the fast, rapid-flow regime, where the particles interact collisionally, but which scales in such a way that the effective friction coefficient is independent of the shear rate. Both indicate that the effective friction coefficient is independent of the shear rate. Consequently the landslides operated in a separate intermediate regime.This talk will discuss detailed computer simulation studies into this intermediate regime and into the transitions between regimes. In this way, it is possible to draw the entire flowmap connecting the quasistatic and rapid-flow regimes. The key was to include the elastic properties of the solid material in the set of rheological parameters; in effect this put solid properties into the rheology of granular solids, properties that were unnecessary in previous theories as a result of the plasticity and kinetic theory formalisms on which quasistatic and rapid-flow theories are respectively based. Granular flows are then divided into two broad categories, the Elastic Regimes, in which the particles are locked in force chains and interact elastically over long duration contact with their neighbors and the Inertial regimes, where the particles have broken free of the force chains. The Elastic regimes can be further subdivided into the Elastic-Quasistatic regime (the old quasistatic regime) and the Elastic-Inertial regime. The Elastic-Inertial regime is the new regime observed in the landslide simulations, in which the inertially induced stresses are significant compared to the elastically induced stresses. The Inertial regime can also be sub-divided into an Inertial-Non-Collisional where the stresses scale inertially, but the particles interact through long duration contacts, and the Inertial-Collisional or the old rapid-flow regime.Finally, it will be shown that Stress-Controlled flows are rheologically different from Controlled-Volume flows. Physically, there is a range of dense concentrations (solid volume fractions between 0.5 and 0.6) in which it is possible to form force chains and thus to demonstrate elastically. But there are conditions under which force chains do not form at the same average concentrations. (In other words it is possible for the material to exhibit two different states at the same concentration.) By forcing the material to support an applied loads across force chains, Stress-Controlled flows generally behave elastically through this range of concentrations under the same conditions where Controlled-Volume flows behave inertially.
Numerical and Experimental Studies of Air Bubbles Coalescence in a Quiescent Water Column
Authors: Martinez Jean-Michel , Chesneau Xavier , Zeghmati Belkacem
Published: October 2005

Numerical and experimental studies of the dynamics of bubbles coalescence is reported. The numerical method based on the PLIC-VOF method and our advection and surface tension algorithms has been applied to analyse the effect of surface tension and convective terms of the Navier-Stokes equations on air bubbles' coalescence in a quiescent water column. Experimental and numerical results show a mechanical attraction between both bubbles' interface before the coalescence. We analyse the effect of the type of discretization of the convective terms of the Navier-Stokes equations on the shape of bubble after the coalescence phenomenon. Numerical results are in agreement with the images of bubbles' coalescence of our experimental device recorded by a camera. Somes images show obviousness bubbles' coalescence caracterized by an intense liquid jet within the following bubble.
Application of CFD Modelling Technique in Engineering Calculations of Three-Phase Flow Hydrodynamics in a Jet-Loop Reactor
Authors: Szafran Roman G. , Kmiec Andrzej
Published: October 2005

The hydrodynamics of a down flow jet-loop reactor with a gas-liquid-solid three-phase system in semi-industrial scale were investigated. The Eulerian-Eulerian modelling approach was applied to predict flow behaviour in the reactor. A commercially available, control-volume-based code FLUENT 6.1 was chosen to carry out the computer simulations. In order to reduce computational times and required system resources, the 2D axisymmetric segregated solver was chosen. The influence of different k-e turbulence models, as well as, different types of meshes on velocity profiles in each phase was analyzed. The unstructured mesh reduces discrepancies on the axis of symmetry caused by the axisymmetric solver and is more accurate. The prediction error of the water circulation rate ratio for a gas-liquid system was only 3.6 % and about 15 % for gas-liquid-solid system. Unfortunately the gas hold-up was not predicted properly.
Alternative Designs for Fixed Bed Catalytic Reactors
Authors: de Morais Edvaldo Rodrigo , de Toledo Eduardo Coselli Vasco , Filho Rubens Maciel , Wolf Maciel Maria Regina
Published: October 2005

The scope of this paper is to explore the benefits of both conventional operation design co-current and counter-current, to propose a new alternative design for fixed bed catalytic reactor. Steady state and dynamic behavior were considered in the analysis. Additionally for the steady state, a study on the possible alternatives for the patterns of cooling fluid was also realized, searching for an efficient refrigeration, as well as, minimum energy cost, for the fixed bed catalytic reactor. These new alternative designs consist of using the main advantages of both conventional configurations in an unique design. The results show that the proposed alternative design for fixed bed catalytic reactor has considerable advance compared to conventional system.
Hydrogenation of Citral Over Ni on Monolith
Authors: Aumo Jeannette , Mikkola Jyri-Pekka , Bernechea Jose , Salmi Tapio , Murzin Dmitry
Published: October 2005

Citral was hydrogenated over Ni on alumina wash-coated cordierite monoliths in a screw impeller batch reactor. The prepared catalyst was characterized by means of nitrogen adsorption (BET), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The performance of the monolith reactor configuration at different temperatures and pressures was compared. Reasonable reaction rate was obtained even after 18 consecutive experiments without regeneration of the catalyst. At temperatures up to 80°C and 5 bar pressure the selectivity to citronellal was ca. 93 %. Increasing the temperature to 100°C decreased the selectivity of citronellal to 65 %. At 100°C and 40 bar pressure the selectivity of citronellal was diminished to 1.4 % due to the formation of the fully hydrogenated product 3,7-dimethyloctanol with a selectivity of 93 %.
Glucose Diffusion on Support for Solid State Fermentation and its Influence on Tannase Production Profiles
Authors: Cerda Montalvo Maria Luisa , Esquivel Juan Carlos Contreras , Herrera Raul Rodriguez , Aguilar Cristobal N
Published: October 2005

In this study, catabolic repression of tannase in solid-state culture of Aspergillus niger Aa-20 on polyurethane foam was investigated considering the diffusion of a repressor molecule as the main responsible factor. The fundamental hypothesis considers that if repressor molecule uptake rate is higher than repressor molecule diffusion rate on solid matrix, the catabolic repression phenomenon will be minimized. Results showed that addition of low glucose concentrations enhanced the extracellular and intracellular tannase activities (from 5.8 to 6.6 and from 0.96 to 1.76 IU). Besides the glucose uptake rate was higher (1.23 x 10-5 cm2/seg) than glucose diffusion rate on solid matrix (2.8 x 10-6 cm2/seg). On the contrary results at high glucose concentrations, showed that when extracellular tannase activity decreased from 6.6 to 1.87 IU, while intracellular tannase activity was not affected; and under these conditions the glucose diffusion rate governed the process. A particular behaviour was obtained in the repression ratio and the glucose uptake rate/glucose diffusion rate ratio, which permitted to know the sensitivity degree of the culture system, according to the glucose amount added. Substrate diffusion in solid-state culture can be a key factor in its capacity to minimize the catabolic repression of hydrolytic fungal enzymes.
iso-Amyl Acetate Synthesis by Catalytic Distillation
Authors: Saha B , Teo H T R , Alqahtani A
Published: October 2005

With ever-growing environmental concerns, petrochemical and fine chemical industries face an omnipresent issue in recovering dilute acetic acid from its aqueous solutions. Catalytic distillation holds an ascendancy over conventional physical separation methods such as distillation and extraction. Distillation is associated with the high costs involved in vaporising the more volatile water that exists in high proportions and possesses a high latent heat of vaporisation. Extraction is limited in view of the distribution of the components in the reacting system. The implementation of catalytic distillation reduces capital and operating costs, and allows for a wider range of operating conditions. Catalytic distillation is receiving increasing attention and holds a huge potential for the recovery of acetic acid. Through the application of catalytic distillation via the reaction of acetic acid with iso-amyl alcohol, a useful ester in the form of iso-amyl acetate could be produced.In the present work towards further process development, the synthesis of iso-amyl acetate via reactive distillation is studied using Katamax® catalyst packing in the catalytic reactive section. The reactive distillation experiments were carried out at laboratory scale in a 50 mm diameter column with a catalytic packing section of 1 m and non-reactive packed enriching and stripping sections of about 1 m each. A cation exchange resin catalyst, Purolite® CT-175, was used. The experiments were conducted with the aim of achieving an optimum column configuration as well as process conditions for the synthesis of iso-amyl acetate in a reactive distillation column (RDC). Several variants of the RDC set-up e.g. total feed mole ratio, reflux ratio, location of feed points, reflux configuration and acid concentrations were explored for the recovery of dilute acetic acid and to achieve a high purity value added product, iso-amyl acetate.
Compact Direct Methanol Fuel Cells for Portable Applications: A Modeling Study
Authors: Specchia Stefania , Icardi Ugo A. , Specchia Vito , Saracco Guido
Published: October 2005

Consumers demand for portable audio/video/ICT devices has driven the development of advanced power technologies in recent years. Fuel cells are a clean technology with low emissions levels, able to work with renewable fuels and capable, in a next future, to replace conventional power systems meeting the targets of the Kyoto Protocol for a society based on sustainable energy systems. Within such a perspective, the objective of the European project MOREPOWER (Compact direct methanol fuel cells for portable applications) is to develop a low cost, low temperature, portable Direct Methanol Fuel Cell (DMFC; nominal power 250 W) of compact construction and modular design for the potential market area of weather stations, medical devices, signal units, gas sensors and security cameras. This investigation is focused on a conceptual study of the DMFC system carried out in the Matlab/Simulink platform. Two different DMFC configurations were devised in which alternative components arrangements along the methanol recycle line are considered. Based on a number of simulations, the system configuration characterized by a gas-liquid separator for carbon dioxide removal placed upstream the radiator for heat removal shows the most promising results, thanks to an easier design and operability of the radiator itself.
A Reverse Flow Catalytic Membrane Reactor for the Production of Syngas: An Experimental Study
Authors: Smit J. , Bekink G.J. , van Sint Annaland M. , Kuipers J.A.M.
Published: October 2005

In this paper experimental results are presented for a demonstration unit of a recently proposed novel integrated reactor concept (Smit et. al., 2005) for the partial oxidation of natural gas to syngas (POM), namely a Reverse Flow Catalytic Membrane Reactor (RFCMR). Natural gas has great potential as a feedstock for the production of liquid fuels via the Gas-To-Liquid (GTL) process, but this process has not found widespread application yet, mainly due to the large costs associated with cryogenic air separation and complex heat integration. In conventional GTL processes excess O2 (20-40 %) is used together with preheating of the feed (250-400 °C). The O2 consumption and heat integration cost can be reduced substantially by integrating the recuperative heat exchange inside the POM reactor using the reverse flow concept. The RFCMR concept basically consists of two fixed bed compartments (e.g. in a shell-and-tube configuration) separated by a porous membrane (or filter), through which the O2 is fed distributively to the syngas compartment, thereby avoiding possibly explosive feed mixtures and hot spots. Furthermore, the flow directions of the gas streams are periodically alternated. A small amount of CH4 is combusted in the O2 compartment to create the trapezoidal temperature profile. Also some steam is added to the O2 feed to keep the center of the reactor isothermal.To demonstrate the RFCMR concept an experimental set-up was constructed with a single shell-and-tube design, from which axial temperature profiles and the composition of the produced syngas could be measured. This set-up was first operated as a conventional reverse flow reactor and it was found that radial heat losses have a major influence on the axial temperature profiles as expected, but that suitable temperature profiles could be established. Subsequently, the demonstration unit was operated as a reverse flow catalytic membrane reactor. Syngas with high CO (93 %) and H2 (96 %) selectivities with high CH4 (85 %) conversions was produced from undiluted CH4 feed. These selectivities are higher than the typically encountered values of 90 % in industrial practice, because of the lower O2/CH4 ratio, and could be improved even further by going to higher temperatures, but this was not possible in this study due to mechanical constraints. The temperature plateau was flat in the center of the reactor and no hot spots were observed. The experiments have clearly demonstrated the potential of the RFCMR concept for energy efficient production of syngas.
Experimental and Model Based Study of the Hydrogenation of Acrolein to Allyl Alcohol
Authors: Hamel Christof , Bron Michael , Claus Peter , Seidel-Morgenstern Andreas
Published: October 2005

The hydrogenation of acrolein was investigated experimentally in a fixed-bed reactor (FBR) using several classical and a newly developed hydrogenation catalyst. The aim was to evaluate selectivity and yield with respect to the desired product allyl alcohol. The kinetics of the two main parallel reactions of acrolein hydrogenation were quantified for a supported silver catalyst which offered the highest performance. In a second part the reaction kinetics identified were used in a theoretical study applying a simplified isothermal 1D reactor model in order to analyse the hydrogenation of acrolein performed in single- and multi-stage packed bed membrane reactors (PBMR). The goal of the simulations was to evaluate the potential of dosing one reactant in a distributed manner using one or several membrane reactor stages. The results achieved indicate that the membrane reactor concept possesses the potential to provide improved yields of allyl alcohol compared to conventional co-feed fixed-bed operation.
Kinetics Study on Heterogeneous Catalytic Wet Air Oxidation of Phenol using Copper/Activated Carbon Catalyst
Authors: Wu Qiang , Hu Xijun , Yue Po Lock
Published: October 2005

Heterogeneous kinetics of catalytic wet air oxidation (CWAO) of phenol was studied using copper supported on activated carbon as the catalyst and oxygen as the oxidant. Both mass transfer effect and deactivation of catalyst can affect the kinetics measurement. To eliminate the mass transfer barriers, the study was conducted in a stirred tank batch reactor using catalysts of very small particle size. In order to prevent the catalyst deactivation caused by copper leaching from the support, saturated pH buffer solution was added into the reaction system and the initial phenol and catalyst concentrations were reduced. A mathematic model was proposed following the Langmuir-Hinshelwood mechanism to simulate the reaction kinetics. It is believed through simulation that the dissolved oxygen is adsorbed by the catalyst in molecular form which subsequently starts to degrade phenol on the catalyst surface. Both reaction rate constant and activation energy were determined for a temperature range of 140 - 160 oC and an oxygen partial pressure range of 0.4 - 1.6 MPa. The proposed mechanism and kinetic model were found to be in good agreement with experimental results.
Catalytic Gasification of Biomass in a CREC Fluidized Riser Simulator
Authors: Ginsburg Jason , de Lasa Hugo Ignacio
Published: October 2005

Gasification of biomass is an environmentally important technology that may contribute to fulfill requirements set by the Kyoto protocol. Biomass can be converted into a vast array of chemical products and fuel, and can be utilized to produce power/electricity. However, a major limitation of biomass gasification is the resultant tars and particulate matter that potentially destroy downstream process equipment, harm the environment, and hinder economic efficiency. This study considers the catalytic steam gasification of waste-wood, with the catalyst being fluidizable nickel/a-alumina. Experiments are conducted in the CREC Riser Simulator Reactor, at temperatures between 800°C - 850°C, near atmospheric pressures, and reaction times over 10 seconds. Experimental results suggest that catalytic steam gasification of biomass is a versatile process; with a considerable amount of H2 being produced at steam/biomass feed ratios above 0.3kg/kg daf. It is also found that the catalyst effectively converts tars to permanent gases at temperatures ranging from 800°C - 850°C and for steam/biomass feed ratio ranging from 0.17  0.58kg/kg daf, with the carbon conversion being above 90% in all cases. An equilibrium model from the literature is developed and modified, and then considered to analyze the experimental data. At 800°C and steam/biomass ratios from 0.17  0.42kg/kg daf, the H2/CO product ratio is estimated accurately by the equilibrium model. However, product lump compositions are estimated with less accuracy, which provides support to the need of a non-equilibrium model to fully explain the inter-conversion of gaseous species following biomass catalytic gasification.
Acceleration of Chemical Reactions Using a Supercritical Water Microreaction System
Authors: Sato Masahiro , Ikushima Yutaka , Hatakeda Kiyotaka , Ikeshoji Tamio
Published: October 2005

Water is an environmentally friendly chemical species that can be employed either as catalyst or as reactant. The use of water has attracted much interest for many acid-catalyzed organic syntheses. These reactions have been studied under hot water conditions with maximum formation of ions. Under these circumstances, long reaction times are required to obtain suitable yields however with poor selectivities given the influence of side reactions. The microreaction system of the present study can heat up a substrate solution very quickly from ambient conditions to the supercritical water state (scH2O) and can then quench rapidly the same solution to sufficiently low temperatures. This allows epsilon-caprolactam production with close to 100% selectivity and 80% yield in a acid free reaction system in less than 1-second reaction time. To justify these results, first principle molecular dynamics calculations and in situ IR measurements are employed as they can be applied to the structural and electronic properties of water in the near critical point region. Close to the critical point at low fluid densities, small clusters, mainly dimers and trimers, are the dominant features with no H-bonds expected. The significant reduction of H-bond strength in H2O, peculiar to near the critical point, leads to the activation of protons or H3O+. Hence, in the scH2O microreaction system, the acidic properties of H2O at the supercritical state are considered as the likely pathway promoter which prevents the hydrolysis and the pyrolysis of cyclohexanone-oxime as well as the pyrolysis of epsilon-caprolactam. It is also observed that dilute acids at supercritical conditions further enhance the epsilon-caprolactam process with close to 100% yield and 100% selectivity.
Direct Synthesis of Dimethyl Ether From (H2+CO) and (H2+CO2) Feeds. Effect of Feed Composition
Authors: Ereña Javier , Garoña Raúl , Arandes José M. , Aguayo Andrés T. , Bilbao Javier
Published: October 2005

The effects of feed composition on the conversion of CO and CO2, selectivity to DME, yield of DME and product distribution are studied in the synthesis of DME from syngas and from (H2+CO2) in a single reaction step using the bifunctional catalysts CuO-ZnO-Al2O3/gamma-Al2O3 and CuO-ZnO-Al2O3/NaHZSM-5. For feeds made up of H2 and CO, the maximum conversion levels of CO, yield of DME and selectivity to DME obtained with both catalysts are very similar, close to 95 %, 75 % and 80 %, respectively, although the catalyst CuO-ZnO-Al2O3/gamma-Al2O3 requires a higher H2/CO ratio. For the feeds made up of H2 and CO2, the catalyst based on NaHZSM-5 zeolite (moderately acid function) performs better due to the fact that higher water content in the reaction medium leads to its adsorption on the Lewis acid sites of gamma-Al2O3 and limits the transformation capacity of methanol to DME.
Kinetics of Adiponitrile Hydrogenation Over Rhodium-Alumina Catalysts
Authors: Di Felice Renzo , Bottino Aldo , Capannelli Gustavo , Comite Antonio , Di Felice Tommaso
Published: October 2005

The catalytic hydrogenation of adiponitrile is generally carried out industrially at high temperature and pressure over Ni-Raney catalysts, which have the disadvantages of possessing low mechanical resistance and of being pyrophoric. In this work adiponitrile was hydrogenated in a three phase stirred slurry reactor using rhodium over alumina powder as a catalyst instead. Catalysts were prepared with a ion exchange technique by contacting 100 micron alumina powder with a solution of hydrate rhodium cloride for 36 h. The reaction runs were conducted in a 100 cc vessel at a pressure of 3 MPa and temperatures of 72  92 °C varying the initial concentration of adiponitrile. A variety of series-parallel reactions took place when adiponitrile was contacted with hydrogen in our reactor. Attention was concentrated on hexamethylenediamine, the final product, and on aminocapronitrile, a very interesting intermediate which could be used subsequently for caprolactam production (and from this the direct synthesis of nylon). Samples were withdrawn from the reactor at fixed interval of time and analysed with a gas-chromatograph so that time dependency of reactant conversion and product selectivity could be determined. The results showed the expected qualitative behaviour: adiponitrile conversion increased with time, as did the hexamethylenediamine selectivity, whereas aminocapronitrile selectivity showed a clear maximum and then decreased to negligible values. The Chemical reaction engineering approach was used and proved sufficient to describe quantitatively the observed kinetic behaviour of the reactor.
Nanofiber Generation of Gelatin–Hydroxyapatite Biomimetics for Guided Tissue Regeneration
Authors: Kim H.‐W. , Song J.‐H. , Kim H.‐E.
Published: October 2005

The development of biomimetic bone matrices is one of the major goals in the bone‐regeneration and tissue‐engineering fields. Nanocomposites consisting of a natural polymer and hydroxyapatite (HA) nanocrystals, which mimic the human bone matrix, are thus regarded as promising bone regenerative materials. Herein, we developed a biomimetic nanocomposite with a novel nanofibrous structure by employing an electrospinning (ES) method. The HA precipitate/gelatin matrix nanocomposites are lyophilized and dissolved in an organic solvent, and then electrospun under controlled conditions. With this process, we can successfully generate a continuous fiber with a diameter of the order of hundreds of nanometers. The internal structure of the nanofiber features a typical nanocomposite, i.e., HA nanocrystals well distributed within a gelatin matrix. These nanocomposite fibers improve the bone‐derived cellular activity significantly when compared to the pure gelatin equivalent. This method of generating a nanofiber of the biomimetic nanocomposite was effective in producing a biomedical membrane with a composition gradient, which is potentially applicable in the field of guided tissue regeneration (GTR).
Studies on Simulated Ageing of Paper by Photochemical Degradation
Authors: Campanella Luigi , Battilotti Massimo , Costanza Cecilia
Published: October 2005

The study of the ageing of two paper types was performed on monitoring it during a simulated process by means of the measure of the photocatalytic degradation of the paper cellulose. Such evaluation was possible due to the combined responses of a photosensor based on titanium dioxide in suspension, of an enzymatic biosensor based on superoxide dismutase (SOD), of a specific conductivity sensor and of an enzymatic biosensor based on glucose oxidase.
Headspace Solid Phase Micro Extraction GC‐ECD Determination of Volatile Organic Chlorinated Hydrocarbons in Soils
Authors: Pastore Paolo , Favaro Gabriella , Badocco Denis , Lavagnini Irma
Published: October 2005

Soil samples were suspended in a suitable aqueous solvent and a solid phase microextraction (SPME) fibre was used to sample the headspace (HS) for five volatile chlorinated compounds (VOX). Their determination was made by GC‐ECD technique in the splitless mode. Preliminary studies on the effects of methanol and of the sand/clay ratio on the fibre extraction were made. Four experimental factors, namely, extraction time, extraction temperature, pH and NaCl %, able to affect distribution of the analytes among the four different phases, were varied in suitable ranges. A multivariate approach applied to the face centred cube (FCC) experimental design, was used to try to optimise the overall sample response. The suitable set of factors found for the determination of chloroform, 1,2‐dichloroethane, trichloroethylene, 1,1,2‐trichloroethane, 1,1,2,2‐tetrachloroethane, was a compromise among the relevant optimal factor sets of the single analytes. Detection limits of 0.003 ng, 0,022 ng, 0,001 ng, 0,015 ng and 0,002 ng were found respectively for the five cited analytes. The method was successfully used to determine the analyte contents in two real soils sampled in an industrial area.
Composition of Aqueous Solutions Containing Sodium Glycocholate and Glycodeoxycholate
Authors: Bottari Emilio , Festa Maria Rosa
Published: October 2005

Composition and existence range of aggregates formed by sodium glycocholate and glycodeoxycholate contemporary present in aqueous micellar and premicellar solutions were investigated. Solubility measurements of lead (II) glycocholate and glycodeoxycholate give analytical concentration of lead (II) and glycocholate and glycodeoxycholate, respectively. Electromotive force measurements provide the free concentration of hydrogen, sodium and lead (II) ions. Experimental data obtained at 25 °C and at three different concentrations of N(CH3)4Cl, used as a constant ionic medium, can be explained by assuming the presence of aggregates of different composition depending on the reagent and ionic medium concentrations. Next to two species containing only glycocholate or glycodeoxycholate, the presence of aggregates formed with the contemporary participation of both bile anions in different ratios was assumed. Species with the hydrogen ion participation are not present in appreciable quantity in the investigated concentration range. As expected, the size of aggregates increases by increasing reagent and ionic medium concentration. Most of the species can be explained with a “core + link” mechanism, where all the glycocholate aggregation numbers are even, while those of glycodeoxycholate are always multiple of three. Analogy and difference with aggregates formed by the two bile anions separately are discussed.
A Method for Risk Assessment for Three Contaminated Sites in Northern Italy
Authors: Critto Andrea , Nadal Nadia , Carlon Claudio , Marcomini Antonio
Published: October 2005

A stepwise human health risk assessment procedure carried out using American Society for Testing and Materials methodology was applied to three contaminated sites located in northern Italy: an uncontrolled landfill, an abandoned industrial site and an industrial waste contaminated land. Two different tiers of analysis were performed by means of the analytical model RBCA Tool Kit and the numerical model API‐DSS, respectively. The latter was applied according to both a deterministic and a probabilistic risk analysis. The comparison of the two approaches highlighted the great benefit provided by probabilistic analysis for the risk assessment based on site specific parameters and more complex models, in particular for groundwater exposure route. Finally, the risk‐based site specific target levels were compared to the generic regulatory threshold limits fixed by the Italian regulation. The comparison showed the regulatory limits generally too restrictive for non‐carcinogenic substances but less protective for carcinogenic chemicals, outlining the need of a site‐specific risk assessment especially for carcinogenic substances.
Direct Gravimetric Measurements of the Mass of the Antarctic Aerosol Collected by High Volume Sampler: PM10 Summer Seasonal Variation at Terra Nova Bay
Authors: Truzzi Cristina , Lambertucci Luca , Illuminati Silvia , Annibaldi Anna , Scarponi Giuseppe
Published: October 2005

An on‐site procedure was set up for direct gravimetric measurement of the mass of aerosol collected using high volume impactors (aerodynamic size cut point of 10 μm, PM10); this knowledge has hitherto been unavailable. Using a computerized microbalance in a clean chemistry laboratory, under controlled temperature (±0.5 °C) and relative humidity (±1 %), continuous, long time filter mass measurements (hours) were carried out before and after exposure, after a 48 h minimun equilibration at the laboratory conditions. The effect of the electrostatic charge was exhausted in 30‐60 min, after which stable measurements were obtained. Measurements of filters exposed for 7‐11 days (1.13 m3 min−1) in a coastal site near Terra Nova Bay (December 2000 – February 2001), gave results for aerosol mass in the order of 10‐20 mg (SD ∼2 mg), corresponding to atmospheric concentrations of 0.52‐1.27 μg m−3. Data show a seasonal behaviour in the PM10 content with an increase during December – early January, followed by a net decrease. The above results compare well with estimates obtained from proxy data for the Antarctic Peninsula (0.30 μg m−3), the Ronne Ice Shelf (1.49 μg m−3), and the South Pole (0.18 μg m−3, summer 1974‐1975, and 0.37 μg m−3, average summer seasons 1975‐ 1976 and 1977‐1978), and from direct gravimetric measurements recently obtained from medium volume samplers at McMurdo station (downwind 3.39 μg m−3, upwind 4.15 μg m−3) and at King George Island (2.5 μg m−3, summer, particle diameter <20 μm). This finding opens the way to the direct measurement of the chemical composition of the Antarctic aerosol and, in turn, to a better knowledge of the snow/air relationships as required for the reconstruction of the chemical composition of past atmospheres from deep ice core data.
Luminescent Determination of Automobile Petrol in Hexane Solutions
Authors: Chukova Oksana , Krut Olexander , Nedilko Sergiy , Sakun Vadim , Scherbatskyi Vasyl
Published: October 2005

The work deals with the problem of determination of automobile petrol of various octane numbers and petroleum contamination of some objects on the basis of analysis of photoluminescence spectra of automobile petrol samples. For this purpose steady state luminescence properties of samples of automobile petrol of different types being in sale were measured. Samples of automobile petrol diluted in hexane were prepared and their luminescence spectra were measured at room and liquid nitrogen temperatures of samples. We constructed concentration dependences of luminescence intensity of both wide band luminescence of liquid solutions obtained at room temperature and peak intensities of luminescence lines of quasi linear spectra of solutions frozen at 77 K. Possibility to use luminescence method for analysis of petrol pollutions on some objects is illustrated by results of investigation of pine‐wood pieces contaminated by automobile petrol.
The Metal Flux: A Preparative Tool for the Exploration of Intermetallic Compounds
Authors: Kanatzidis Mercouri G. , Pöttgen Rainer , Jeitschko Wolfgang
Published: October 2005

This review highlights the use and great potential of liquid metals as exotic and powerful solvents (i.e. fluxes) for the synthesis of intermetallic phases. The results presented demonstrate that considerable advances in the discovery of novel and complex phases are achievable utilizing molten metals as solvents. A wide cross‐section of examples of flux‐grown intermetallic phases and related solids are discussed and a brief history of the origins of flux chemistry is given. The most commonly used metal fluxes are surveyed and where possible, the underlying principal reasons that make the flux reaction work are discussed.
Cover Picture: Mass Spectrometric Profiling of Intact Biological Tissue by Using Desorption Electrospray Ionization (Angew. Chem. Int. Ed. 43/2005)
Authors: Wiseman Justin M. , Puolitaival Satu M. , Takáts Zoltán , Cooks R. Graham , Caprioli Richard M.
Published: October 2005

Desorption electrospray ionization is applied to the mass spectrometric profiling of phospholipids. In their Communication on page 7094 ff., R. G. Cooks, R. M. Caprioli, and co‐workers report the rapid analysis of untreated biological tissues, including the tumor region of liver tissue. The impact of charged liquid microdroplets on liver tissue in air and the release of lipids and other molecules as ions for analysis is illustrated in the cover picture (prepared by Z. Ouyang, J. Wiseman, and R. Shreve).