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There are two contrasting opinions on the stratigraphic and palaeogeographic distribution of the relatively rare trace fossil Ophiomorpha irregulaire: 1) the trace is mostly restricted to the Upper Cretaceous of the Western Interior Seaway, or 2) it has a post-Palaeozoic record and a worldwide geographic distribution. In this study we document the finding of O. irregulaire in Upper Cretaceous turbidites of the Alta Vista Formation, southern Patagonia, providing additional evidence on the morphology and composition of its pelletal masses, the ethology of its producer and the palaeogeographical and palaeoenvironmental distribution of the trace fossil. The burrow walls are lined with dark mud and their elongate, spiky pellets are formed by a sand core that is also lined with mud. The association with typical fodinichnia, such as Halopoa, Spirophyton, and Zoophycos and the common presence of O. irregulaire in sediments with abundant plant detritus, suggest that the producer was a deposit feeder. Crosscutting relationships and occurrences at several levels within thick-bedded turbidites, suggest a relatively deep tier emplacement of the trace. The finding of the trace in the Southern Hemisphere supports its envisaged worldwide palaeogeographic distribution

A new high-latitude record of the trace fossil Macaronichnus segregatis degiberti is documented from the lower Miocene Punta Basilica beds, Tierra del Fuego, which were previously considered to be ...

Los depósitos marinos del Mioceno temprano en Tierra del Fuego albergan un grupo de gasterópodos struthiolaridos que se destacan por su alta variabilidad morfológica. Desde finales del siglo 19 se interpretó que esta variabilidad reflejaba (1) un grupo de especies altamente diversificado en rápida evolución o (2) una única especie plástica caracterizada por una amplia variabilidad intraespecífica. El estudio morfológico de más de 100 ejemplares del género Perissodonta Martens recolectados en las formaciones fueguinas Carmen silva, Viamonte e Irigoyen indica que parámetros significativos, como la forma del caparazón, la longitud de la espira y el número de ornamentaciones espirales y axiales (líneas espirales finas, cordones, tubérculos) varían continuamente dentro de una amplia gama de valores, favoreciendo una única especie plástica. Los especímenes topotipo de Perissodonta ameghinoi (Ihering), recolectados de la Formación Monte León del Mioceno temprano en la Patagonia, muestran una plasticidad de caracteres similar. Además, material de topotipo reciente de Perissodonta georgiana strebel de las Islas Georgias del sur, una especie considerada sinónimo muy cercano o junior del genotipo de la especie P. mirabilis (smith), indica un grado similar de plasticidad. En consecuencia, los struthiolaridos fueguinos asignados previamente a Perissodonta ameghinoi; P. fueguina (Ihering) o P. densestriata (Ihering) se refieren en este trabajo a P. ameghinoi, un gasterópodo struthiolarido restringido al Mioceno temprano en Tierra del Fuego y Patagonia. The early Miocene marine deposits in Tierra del Fuego bear a group of struthiolariid gastropods that stand out for their high morphological variability. since the end of the 19th century this variability was interpreted as reflecting (1) a highly diversified rapidly evolving group of species or (2) a single, plastic species characterized by ample intraspecific variability. The morphological study of more than 100 specimens of the Fuegian struthiolariid genus Perissodonta Martens collected in the Carmen silva, Viamonte, and Irigoyen formations indicate that significant parameters, such as shell shape, spire length and number of spiral and axial sculptures (cords, threads, tubercles) vary continuously within an ample range of values, favoring a single, plastic species. Topotype specimens of Perissodonta ameghinoi (Ihering), collected from the early Miocene Monte León Formation in Patagonia, show similar plasticity of characters. Furthermore, recent topotype material of Perissodonta georgiana strebel from Islas Georgias del sur, a species considered very close or junior synonym of the genotype species P. mirabilis (smith), indicates a similar degree of plasticity. Accordingly, the Fuegian struthiolariids previously assigned to Perissodonta ameghinoi; P. fueguina (Ihering); or P. densestriata (Ihering) are here referred to P. ameghinoi, a struthiolariid gastropod restricted to the early Miocene in Tierra del Fuego and Patagonia. Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina

Tide-influenced deposits of the Pennsylvanian Rock Lake Shale Member, Stanton Formation, Missouri and Kansas (U.S.A.), contain well-preserved evidence of the burrowing activities of protobranch bivalves, including locomotion (Protovirgularia) and locomotion-resting (Protovirgularia-Lockeia) trace fossils. Protovirgularia shows three distinct morphotypes, the morphological variability of which was controlled by external factors such as substrate conditions, toponomy, and undertrack deficiency. Extreme morphological modifications of Protovirgularia and/or Lockeia, represented by irregular bilobate structures, probably result from erosion and subsequent partial passive filling of the original biogenic structures. In addition, very well-preserved trace fossils showing intergradation of a fan-shaped cluster of ridges with Protovirgularia-Lockeia structures are interpreted as a compound biogenic structure that represents locomotion, resting, and feeding activities of burrowing protobranch bivalves. Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Mangano, Maria Gabriela. University of Saskatchewan; Canadá Fil: Buatois, Luis Alberto. University of Saskatchewan; Canadá Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Maples, Christopher G.. University of Missouri; Estados Unidos

The present work deals with the study of estradiol permeation in chitosan membranes. A fractional factorial design was built for the determination of the main factors affecting estradiol permeation. The independent factors analysed were: concentration of chitosan, concentration of cross-linking agent, cross-linking time and thermal treatment. It was found that concentration of chitosan and cross-linking time significantly affected the response. The effects of thermal treatment and concentration of cross-linking agent were not significant. An optimization process based on response surface methodology was carried out in order to develop a statistical model which describes the relationship between active independent variables and estradiol flux. This model can be used to find out a combination of factor levels during response optimization. Possible options for response optimization are to maximize, minimize or move towards a target value. Fil: Mengatto, Luciano Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico Para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico Para la Industria Química; Argentina Fil: Luna, Julio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico Para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico Para la Industria Química; Argentina

Polymeric membranes with skin-mimetic permeability properties appear as attractive models for use in the development of transdermal drug delivery systems. These membranes can be placed in contact with the transdermal system and simulate the skin barrier. In the current work, statistical experimental design was implemented for preparation of the optimized chitosan membrane to mimic human epidermis. For this purpose, an optimization process based on response surface methodology was carried out in order to determine the best combination of independent factors for membrane preparation. The independent factors analyzed were concentration of chitosan, concentration of cross-linking agent, and cross-linking time. The optimized membrane successfully simulated the cumulative amount of estradiol released per unit time for human epidermis. In addition, the optimized membrane was evaluated for the development of an estradiol delivery system. This in vitro technology may offer an alternative methodology for the development of transdermal delivery systems.

A mathematical modeling of controlled release of drug from torus-shaped single-layer devices is presented. Analytical solutions based on the pseudo-steady state approximation are derived. The reliability and usefulness of the model are ascertained by comparison of the simulation results with matrix-type vaginal ring experimental release data reported in the literature. A good agreement between the model prediction and the experimental data is observed. An analysis of the effect of the variation in torus design parameters on the solute release is also presented. The model is applicable only to torus-shaped single-layer systems wherein the initial load of drug is higher than its solubility in the polymer.

A series of new N-acetylated non-ionic and cationic gemini surfactants (3a–f) having dimeric structures derived from primary and tertiary amines with variably long tails (C8–C12–C18) were synthesized. In addition, N-acetylated monomeric analogues 6a and 6b were prepared and their antifungal potency and surface properties were also determined. Critical micelle concentration (CMC), effectiveness of surface tension reduction (cCMC), surface excess concentration (C), and area per molecule at the interface (A) were also determined and the resulting values indicate that the cationic series is characterized by good surface-active and self-aggregation properties. For the first time, all surfactants were tested to evaluate their antifungal properties using the method for the broth macrodilution test (M27-A2, NCCLS). Four microbial strains were used to perform the study: Candida parapsilosis (ATCC 22019), C. albicans (ATCC 64548), and a wild-type strain of C. parasilosis and Saccharomyces cerevisiae (ATCC 9763). The antimicrobial activity was measured by yeast growth inhibition expressed as minimum inhibitory concentration (MIC) values. Results were compared to those obtained for their monomeric analogues and for a commercially available reference compound (Fluconazole). Gemini 3b, 3e and 3f were found to be the most potent compounds. The results show S. cerevisiae as the most sensitive strain. In contrast, the wild strain of C. parapsilosis was resistant. Fil: Murguia, Marcelo Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Machuca, Laura Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Lura, Maria Cristina Enriqueta. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Cátedra de Microbiología General; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

The kinetics of the hydrogenation and cis/trans isomerization of methyl oleate on a Ni/a-Al2O3 catalyst was studied in the absence of mass-transport limitation, at 398K=T=443Kand370kPa = PH2 = 650 kPa. On the basis of the Horiuti–Polanyi mechanism, involving a sigma half-hydrogenated surface intermediate, a kinetic model was derived in the framework provided by the Langmuir–Hinshelwood–Hougen–Watson formalism, using the advanced concept of semi-competitive adsorption. The classical LHHW rate equations for competitive and non-competitive adsorption between the hydrogen and large organic species were matched as asymptotic cases. Statistical results clearly demonstrated the inadequacy of the model approaching non-competitive adsorption to describe the experimental data, but the residual sum of squares between experimental data and model predictions was insufficient to discriminate between the kinetic models based on competitive and semi-competitive adsorption. However, the model considering semi-competitive adsorption gave additional indication that the adsorbed molecules of cis- and trans-methyl oleate could cover up to eleven surface sites, which is in excellent agreement with a rough estimate from primary molecular modeling. This feature seems to be the most fascinating result, since it is factual and unattainable from the classical LHHW approaches. Results and distinctive features characterizing this advanced approach are highlighted. Some insights to improve parameter estimation and adsorption model discrimination are also pointed out. Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

On the basis of kinetic modeling, this study provides some insight into the hydrogenation kinetics of avermectins B1a and B1b (Avi, i = B1a and B1b) with the in situ formed Wilkinson's catalyst from the dinuclear chloro-bridged Rh(I) complex [RhCl(COD)]2 (COD = 1,5-cyclo-octadiene) and triphenylphosphine (Ph3P). More significantly, this paper is the first attempt to derive describing kinetic models. The kinetic behavior was studied in a temperature range of 313–343 K, at a hydrogen pressure of 275.7 kN m−2. A significant induction period strongly dependent on the temperature was noticed during the in situ generation of the catalytic species. After improving a previous kinetic model describing Wilkinson's hydrogenation catalytic cycle, kinetic models for the in situ synthesis of the catalytic species were developed on the basis of reaction pathways assuming that the COD ligand replacement occurs via substitution by PPh3 or via reductive elimination of COE (COE = cyclo-octene). Estimates of the kinetic parameters characterizing both reaction routes were uncoupled from those of the catalytic cycle steps. Among the rival kinetic models tested, a simple model featuring the PPh3 insertion in the bidentate COD ligand as rate determining step (RDS) and the competitive replacement of the COD ligand by both PPh3 and Avi proved fair enough to describe the synthesis process in the presence of these macrocyclic lactones. A very high activation barrier characterizes the in situ synthesis of the catalytic complexes, and the presence of avermectins in the reaction medium interferes with the course of the catalytic species synthesis due to the formation of too stable intermediate complexes. From these observations, high reaction temperature and the absence of avermectins in the synthesis medium of the species responsible for the catalysis are two necessary conditions for improving the performance of this catalytic hydrogenation system.

A kinetic study of the homogeneous catalytic hydrogenation of avermectins is reported for a series of isosteric p-substituted arylphosphines as ligands. The activity of the rhodium complexes formed in situ from [RhCl(COD)]2 increased with increasing the electron-donor capacity of the P(p-XC6H4)3: P(p-ClC6H4)3 < P(C6H5)3 < P(p-CH3C6H4)3 < P(p-OCH3C6H4)3. As expected, this trend was also observed when using preformed complexes thereof. Linear correlations based on Hammett and Kabachnik treatments are provided as useful tools to guide the exploration work towards improved [RhCl(COD)]2/P(p-XC6H4)3 catalytic systems. Fil: Zgolicz, Patricia Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

A versatile approach for solving the design equations of dissolution/diffusion-controlled drug release from planar, cylindrical and spherical matrix systems is provided, as an extension of a previously validated approach for planar geometry. The original set of differential mass balance equations is cast into an equivalent system of integral equations by generating appropriate Green’s functions. Mathematical features common to the matrix geometry, drug diffusion process, and boundary layer resistance are imbedded in Green’s functions, and thus separated from specific aspects arising from the drug dissolution process. This avoids repetitive computational effort when analyzing different drug dissolution rates. The solution for the perfect sink condition is given as a special case. Another singular feature is related to the friendly manipulation of a broad variety of spatially non-uniform drug loading, including size distribution of solid drug particles. Composite matrices consisting of multi-layers of equal diffusivity, including membranes, can be numerically simulated solving a concise dissolution–diffusion integral equation, coupled to the integral equations governing the variable surface area of the dissolving drug particles. This is made within a unique framework and without introducing extra difficulties or adjustments in the programming from one matrix architecture to another. The reliability of the approach presented is ascertained by comparing the results with existing analytical and numerical solutions for special cases, and also by matching, as asymptotic case, the numerical solution of the diffusion equation with a continuum dissolution source described by the Noyes–Whitney equation. An iterative routine, combined with the topological concept of homotopy, is used to improve the numerical performance. Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

The kinetics of the hydrogenation of methyl oleate on a Ni/alpha-Al2O3 catalyst was studied in the absence of mass-transport limitation, at 398=T=443K and 3.7=PH2 =6.5 bar. The kinetic modeling was performed on the basis of elementary step mechanisms involving different regimes of competition between hydrogen and methyl oleate. Admitting a distinction between occupied-sites and covered-sites by the large molecule of methyl oleate, a rigorous proposal was made to link the seemingly separate kinetic models corresponding to the extreme modes of competitive and non-competitive adsorption, without having to draw the common distinction between two types of surface sites. General rate equations were formulated without expressing opinion a priori on whether the adsorption regime is competitive or non-competitive. Then, typical LHHW rate equations for both extreme adsorption regimes were straightforwardly derived as special cases. Statistical results demonstrated the inadequacy of the models approaching non-competitive adsorption to describe the experimental data but results did not allow a definite discrimination between rival models with competitive and semi-competitive adsorption. A mechanistic model featuring dissociative adsorption of hydrogen, molecule of methyl oleate interacting with a single atom of Ni, and second insertion of hydrogen as RDS, proved to be the best candidate to describe the experimental data satisfactorily with physically reasonable parameters. As a distinctive feature, the model considering semi-competitive adsorption gave additional indication that the adsorbed molecule of methyl oleate could cover up to seven surface sites. From this finding, the semi-competitive model seems to be more realistic than the competitive one. Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

A new approach for modeling the drug release from planar polymeric systems containing slowly dissolving drugs is presented. A distinctive feature of the proposed approach relates to the mathematical description of the drug above solubility. The drug remaining solid in the matrix is envisaged like a delta function-type dissolution sources releasing drug according to the Noyes–Whitney equation. Dissolution sources are inventoried in a unique mass balance equation governing the simultaneous dissolution and diffusion processes. This approach explicitly avoids solving multiple mass balances for the interwoven regions of solid and dissolved drugs, and makes easier the numerical solution. Another singular characteristic is related with the friendly manipulation of a broad variety of non-uniform drug loading, including particles size distributions. To make the numerical treatment versatile, the mathematical solution is expressed in terms of integral equations suitable to be numerically solved by a simple iterative scheme. The reliability of the mathematical and numerical procedures is ascertained by comparison of the simulation results with experimental and numerical data existing in the literature, and also matching, as asymptotic case, the solution of the diffusion equation with a continuum dissolution source described by the Noyes–Whitney equation. The versatility of the method to treat different architectures resembling multilayer laminate polymeric systems is shown.

A convenient procedure for the synthesis of bis-quaternary ammonium salts from long-chain alkyldimethylamines and epichlorohydrin is studied. An improved preparation of bis-quaternary ammonium salts from N,N-dimethyloctylamine, N,N-dimethyldodecylamine or N,N-dimethyloleylamine, their amine hydrochlorides, and epichlorohydrin can be achieved by carrying out the reaction in an aqueous micellar medium. The amine hydrochlorides are used as functional surfactants to produce the self-micellization and solubilization of reactants. The formation of micelles is a necessary condition for a successful quaternization. Comparison of the quaternization performance in ethanol, ethanol/water mixtures, and aqueous micellar medium leads to the conclusion that this micellar-improved synthesis enables easier and cheaper access to bis-quaternary ammonium salts by avoiding the formation of the mono-quaternary ammonium salts as intermediates, and by using water as solvent under mild reaction conditions. Mechanistic aspects of the quaternization reaction in micellized medium are also suggested. Fil: Ricci, Claudia Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Luna, Julio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

Aqueous micellar systems proved to be an excellent reaction medium for the selective synthesis of bis-quaternary ammonium salts 5a-c from epichlorohydrin 2 and long-chain alkyldimethylamines 1a-c, in the presence of the corresponding amine chlorohydrates 3a-c as functional surfactants. Unlike alcohol or alcohol-water mixtures as reaction medium, mono-quaternary ammonium salts 4a-c were formed, if any, in very small amounts under micellar conditions, allowing a more direct and rapid access to these quaternary ammonium gemini surfactants. Fil: Ricci, Claudia Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Luna, Julio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

A comparison of liquid-liquid and solid-liquid PTC for the selective synthesis of diglycidyl ether from protected pentaerythritol and epichlorohydrin is presented. Solid-liquid PTC was found to be more useful than liquid-liquid PTC because the use of water or other solvents can be avoided and higher yields and selectivity are achieved. It was proved that etherification takes place in the solid phase-organic phase system even in the absence of the phase-transfer catalyst. However, the use of tetrabutylammonium bisulfate as catalyst is essential due to its crucial effect on the enhancement of the rate of etherification and on the improvement of the selectivity to diglycidyl ether, which is higher than 98%.

An approach for solving the hollow fiber bioreactor design equations is presented. The original set of differential mass balance equations is cast into an equivalent system of integral equations by generating the appropriate Green’s functions. Mathematical features common to all hollow fiber bioreactors (HFBRs) operating with laminar flow are imbedded in the corresponding Green’s functions on the lumen side, and thus separated from specific aspects arising from mass transport through the permeable wall. On the spongy matrix side, the appropriate Green’s functions are expressed in terms of the mass transfer properties without involving any chemical kinetic parameters; this avoids repetitive computational effort when treating different reaction kinetics. The derived integral equations are numerically solved on an appropriately transformed coordinate system. The numerical method is well suited for problems where steep gradients of concentration cause an inaccurate numerical integration and low rates of convergence if the equations are solved with a uniform rectangular grid on the original coordinate system. The effectiveness of the proposed approach for the simulation of HFBRs with power-law, Michaelis–Menten and zero-order kinetics is demonstrated. The method is readily extendible to treat problems with chemical kinetics described by any arbitrary functional form.

The simulation of the complex polychlorination of methane in a non-isothermal photoreactor with laminar flow regime shows the usefulness of the integral equations deduced in Part I of this contribution. Improved iterative schemes for numerical solution have been implemented by using the particular equations proposed for species having slow, very fast and instantaneous reaction regimes. From such integral equations, in a mathematically consistent form, deviations in the fields of predicted concentrations with and without the application of the local steady-state approximation for homogeneous reactions involving atomic and free radical species have been obtained. Similarly the fields of predicted concentrations applying the usual assumption of negligible wall reactions for the same highly reactive intermediate species has been compared with the reaction mechanisms that includes the wall reactions. A comprehensive analysis of the validity of these simplifying assumptions is presented.

Design equations for non-isothermal Laminar Flow Tubular Reactors (LFTRs) with homogeneous and heterogeneous - at the reactor wall - reactions with arbitrary kinetic equations have been satisfactorily treated transforming the original P.D.E. problem into a system of integral equations. The kernels of the integral operators are related to an eigenvalue problem which does not depend on the kinetic equations; this avoids repetitive computational effort in the treating of different reaction kinetics. To render a more efficient numerical treatment and according to the governing reaction rate regime, modified expressions of the general solution were obtained was follows: (i) a solution with kernels depending only on the diffusion and convective times was obtained for a low reaction regime; (ii) another solution with kernels including the reaction lime, besides the diffusion and convective ones, was necessary for a fast reaction regime and (iii) the local quasi-steady-state approximation was obtained as limiting...

The potential of iron(II)-catalysed reactions the synthesis of α-aryl and α-alkyl thioacetylamides from acetylthiomides is reported. Iron(II) ion efficiently catalyses reactions of iodobenzene 1a or 1-iodoadamantane 1b with N -thioacetylmorpholine anion 2 in DMSO. Ferrous bromide amounts in the 0.6–1.6 mol% range are large enough to reach yields of 86% of α-phenil- N -thioacetylmorpholine 3a and 65% of α-(1-adamanthyl)- N -thioacetyl-morpholine 3b . These catalytic reactions are more easily handled than photoinduced reactions, and provide a useful route to the synthesis of α-aryl and α-alkyl thioacetylamides from acetylthiomides without the need for special photochemical devices. A possible reaction pathway is suggested for the iron(II)-catalysed process involving iron-thioamide enolate complexes.

A kinetic model to represent the time evolution of a photocatalytic reaction is presented. It can be applied for reacting systems having the following characteristics: (i) the catalyst is a suspension (in water) of fine particles of titanium dioxide, (ii) the substrate is a hydrocarbon compound amenable to hydroxyl radical attack for the initiation of an oxidative reaction, (iii) the catalyst activation is produced by radiation energy in the near ultraviolet range (300 nm ≤ λ ≤ 400 nm), (iv) oxygen is always present in the reacting medium, and (v) there are no mass transport limitations. The model is based on Turchi and Ollis (J. Catal.122, 178 (1990)) proposed reaction sequence. The described formulation incorporates a precise and detailed evaluation of the radiation energy absorption effects. With this purpose the kinetic model is used in conjunction with a specially developed experimental device (Cabreraet al.,Ind. Eng. Chem. Res.33, 3031 (1994); Alfanoet al.,Ind. Eng. Chem. Res.34, 488 (1995)) for which a one-dimensional–one-directional radiation and reactor model has been derived and validated. The model provides an explicit formulation for the radiation-absorbed effects that comprises in a single equation the cases of low and high irradiating conditions. The whole kinetic model development has been applied to the photodegradation of trichloroethylene in water, and it is the subject of a companion paper. Using this approach, reliable intrinsic kinetic data can be obtained.

Fine-grained sandstones and siltstones of Late Cretaceous to Eocene age in Antarctica and Tierra del Fuego yield an association of well-known shallow-marine trace fossils. Among them stick out complex spreite burrows, which are formally described as Euflabella n. igen. and subdivided into five ichnospecies with different burrowing programs and occurrences. As shown by concentrations of diatoms, radiolarians, foraminifers, and calcispheres in particular backfill lamellae, the unknown trace makers lived on fresh detritus from the surface as well as the burrowed sediment. In some ichnospecies, vertical sections show that the spreite is three-dimensionally meandering in upward direction and that upper laminae tend to rework the upper backfill of the folds underneath. This could mean a second harvest, after cultivated bacteria had time to ferment refractory sediment components, which the metazoan trace maker had been unable to digest before. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Cientificas; Argentina; Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Cientificas; Argentina

Precise kinetic studies of photocatalytic reactions in solid catalyst water suspensions require the accurate description of the radiation fieldlight distributioninside the reactor. Solution of the radiative transport equation (RTE) inside the reaction is one of the best ways of accessing to such information. For solving this equation, a minimum of two parameters (the absorption and scattering coefficients) and one scattering spatial distribution function (the phase function) are needed. These attributes are directly associated with the optical behavior of the reacting system and are not independent of catalysts more conventional properties. A complete report on the physical and optical characteristics of titanium dioxide particulate suspensions in water is presented. Results were obtained for six different commercially available powders. The investigated parameters were (i) size of elementary particles, (ii) size of particle aggregates in water suspensions, (iii) specific surface area, (iv) spectral extin...

During the past 10 years increasing attention has been paid to heterogeneous photochemical systems, considering their eventual uses not only in industrial synthesis of chemical products but mainly in their applications related to solid photocatalyzed reactions particularly addressed to photodegradation of air and water polluted streams. The radiation field in a planar participating and reacting medium was studied. A one-dimensional model with azimuthal symmetry was employed to investigate radiation absorption and scattering phenomena in the reaction space. The mathematical model was solved numerically, and the results were compared with experimental data obtained in a perfectly mixed, isothermal, batch reactor with recycle. Inside the reactor the well-known oxalic acid homogeneous photodecomposition was conducted and scattering was artificially produced by addition of different amounts of small particles of silica that are chemically inert and transparent to radiation in the investigated wavelength range. Model predictions and experiments have good agreement. They demonstrate that scattering in a well-stirred system always produces a decrease in the volume-averaged reaction rate when compared with a purely absorbing system. According to the relative magnitude of the absorption and scattering contributions, there are cases where radiation losses produced by scattering may bring about a significant reduction in the ratemore » of the homogeneous reaction.« less

A model for heterogeneous (solid-fluid) photochemical reactors, previously developed and validated experimentally, has been used to investigate the effects produced by absorption and scattering on different variables associated with the reactor performance. With this purpose a parametric study was conducted analyzing the effects engendered by changes in the scattering inert center concentration, scattering center characteristics, and radiation absorbing species concentration on the following properties of the heterogeneous system: (i) spatial and directional distribution of radiation intensities, (ii) local volumetric rate of energy absorption, (iii) reactor volume averaged rate of reaction for a simple reaction occurring in the fluid phase, and (iv) radiation absorption efficiency inside the reactor. The effect of adopting different models of the scattering phase function for computing the radiative transfer equation was also studied. Operating conditions under which scattering effects may be significant were defined. It was found that there exist combinations of the optical parameters where addition of inert scattering centers may reduce the rate of reaction in as much as 50%.

In the past decade an increasing interest in photocatalytic kinetic studies has been observed, particularly related to promising remediation processes for air and water pollution. Normally, the reacting system includes a suspended solid semiconductor and one or two fluid phases. One of the major problems lies in the difficulties associated with the proper evaluation of the absorbed radiant energy due to the unavoidable system heterogeneities that produce light scattering. A novel form of reactor, combined with a radiation distribution model, has been used to evaluate the volumetric rate of energy absorption during the photocatalytic oxidation of trichloroethylene in water using a suspension of titanium dioxide. All the required information to solve the radiative transfer equation in a one-dimensional photocatalytic reactor is obtained either from radiation theory or from specially designed experiments. The proposed approach permits a correct description of the radiation field inside the heterogeneous reactor and, consequently, a precise accounting of the absorbed photons. The quantum yield concept is revisited to propose an appropriate and equivalent property for solid photocatalyzed systems. Afterward, the reactor and the model were used to evaluate heterogeneous-system quantum efficiencies.

The internal structure and growth direction of well-preserved Tasselia ordamensis specimens from the Upper Cretaceous–Cenozoic of Antarctica and Tierra del Fuego are not compatible with its current interpretation as a domichnion/equilibrichnium trace fossil. Accordingly, its functional morphology and the likely ethology of the producer are revised. Tasselia is a protrusive structure composed of a lined inner tube surrounded by vertically stacked sediment disks and ending in a basal chamber. Each disk has two domains of active burrow fills. The micritic, outer burrow fill domain consists of radial petaloid elements containing abundant radiolaria, calcispherules, diatoms and plant debris. This domain was formed by excavation due to deposit feeding; thereby non-ingested particles remained in the chamber and ingested particles passed through the gut to the sediment surface. Microfossil-rich material was collected at the sediment surface, placed in the feeding chamber, and rearranged within the petaloid elements probably after pulsed delivery of organic matter. The wineglass-shaped inner burrow fill domain is enriched in coarser particles and its petaloid elements crosscut the outer burrow fill domain. This domain probably functioned as “culturing compartment” for bacteria and its secondary reworking implies some form of ‘gardening’ and feeding on these bacterial populations at depth. The concentric striae on the organic-lined inner tube and the vertically stacked series of sediment-disks suggest maldanid polychaetes as the producers of T. ordamensis. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Analytical solutions based on the pseudo-steady state approximation (PSSA) were derived for the case of controlled dispersed-drug release from erodible and non-erodible planar matrices, through a membrane, and taking into account the existence of a diffusion boundary layer and a finite release medium. The solutions can be applied to a broad range of situations from drug release into finite or infinite medium, from erodible or non-erodible matrices, in the presence or absence of a membrane, and in the presence or absence of a stagnant liquid layer. The prediction is accurate for the cases in which the initial drug load is higher than the drug solubility in the polymer (e.g. A/Cs mayor o igual a 3) till the entire dispersed drug is dissolved. The dependence on the release kinetics with different parameters was simulated and provides a theoretical platform for the design of dispersed drug release devices. Fil: Helbling, Ignacio Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Ibarra, Juan Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Luna, Julio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo Jose Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

Chitosan membranes were obtained by a casting/solvent evaporation method and cross-linking with sodium tripolyphosphate. The effect of cross-linking time was studied and the cross-linked membranes were characterized with respect to equilibrium water content, sodium content, IR spectroscopy and permeability to a model drug (Estradiol). Sodium content increased with increasing cross-linking time. Equilibrium water content was higher in the membrane with the lowest cross-linking time. This membrane also showed a higher flux of Estradiol compared with the other which exhibited an increment in equilibrium water content and flux of Estradiol with the increase in cross-linking duration. These dissimilar results could be explained by a significant correlation between the hydrophilicity of the membrane and the hydrophobicity of Estradiol. Fil: Mengatto, Luciano Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Luna, Julio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

A model for the photochlorination of methyl chloride in the liquid phase was developed, with numerical solution and experimental verification. The reaction was carried out under pressure, using carbon tetrachloride as a solvent with polychromatic radiation in a nonisothermal tubular reactor. Momentum, thermal energy, mass and photon balances were established rigorously and solved numerically. Reaction constants were taken from the known reaction mechanistic kinetics in the gas phase. Theoretical results agreed well with bench-scale experiments performed inside an elliptical reflector in the prediction of both reactant conversion and product selectivities. The validated model was used to show the existence of significant temperature and concentration gradients inside the reactor, both in the radial and in the axial directions.

Kinetic studies of the catalytic hydrogenation of vegetable oils and fatty acid methyl esters in liquid-phase are commonly performed in the framework of the Langmuir-Hinshelwood-Hougen-Watson (LHHW) formalism using the competitive and non-competitive adsorption models, which are certainly extreme. Based on the advanced concepts of multicentered adsorption and semi-competitive adsorption, mechanistic kinetic models including a distinction between occupiedsites and covered-sites by the large molecules of FAMEs were formulated without expressing an opinion a priori on whether the adsorption regime is competitive or non- competitive. The theoretical basis of the advanced kinetic modeling is described and successfully applied to three application examples of increasing complexity, including: (a) the hydrogenation of methyl oleate without cis-trans isomerization distinction, (b) the cis-trans isomerization and hydrogenation of the methyl oleate, and (c) the methyl linoleate hydrogenation including the cis-trans isomerization of the methyl oleate. The kinetic studies were carried out using a Ni/-Al2O3, at 398, 413, 428 and 443 K, under isobaric conditions at hydrogen pressures of 370, 510, and 650 kPa, in the absence of mass-transport limitation. After model discrimination based on statistical analysis and taking into account the physical meaning of the estimated parameters, semi-competitive adsorption models were found to be more realistic than the classical LHHW competitive and non-competitive ones, mainly because they give additional information indicating that the adsorbed molecules of methyl linoleate and methyl oleate could cover up to 12 and 7 surface sites, respectively. These values are in adequate agreement with those expected from a rough computational simulation and seem to be the most interesting result, since they are factual and unattainable from the classical LHHW approaches.-Al2O3, at 398, 413, 428 and 443 K, under isobaric conditions at hydrogen pressures of 370, 510, and 650 kPa, in the absence of mass-transport limitation. After model discrimination based on statistical analysis and taking into account the physical meaning of the estimated parameters, semi-competitive adsorption models were found to be more realistic than the classical LHHW competitive and non-competitive ones, mainly because they give additional information indicating that the adsorbed molecules of methyl linoleate and methyl oleate could cover up to 12 and 7 surface sites, respectively. These values are in adequate agreement with those expected from a rough computational simulation and seem to be the most interesting result, since they are factual and unattainable from the classical LHHW approaches. Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

The photochlorination of methane employing nitrogen as an inert diluent is studied in a continuous flow, tubular, non-isothermal, bench-scale, polychromatic, photoreactor with particular emphasis on selectivities. An extremely high sensitivity to some of the values of the employed specific rate constants is found, particularly when an accurate prediction of selectivities is being sought. Using this verified reactor model, the effect of the output power and output spectral distribution of the radiation energy fed to the photoreactor upon the reaction yield and selectivities is also studied.

The kinetics of the hydrogenation of avermectins B1a and B1b catalyzed by RhCl(Ph3P)3 complexes was studied in a temperature range of 298–328 K at 275.7 kN m2, using catalyst loading in the range of 0.75–7.25 wt.% with respect to the avermectins in toluene solution. The effects on the hydrogenation rate of the catalyst, avermectins, and hydrogen concentrations were determined under complete induction time suppression and without catalyst deactivation. Rate equations were developed for various kinetic schemes on the basis of the main steps suggested by Wilkinson for simple olefin hydrogenation and fitted to the experimental data. A statistical analysis of regression using three plausible mechanisms of reaction allows a discussion on the adequacy of the models to approach the observed half-order reaction with respect to the catalyst loading and first-order to avermectins and hydrogen concentrations. A reaction mechanism featuring non-extensive simple dissociation of the catalyst precursor and reaction pathway along the hydride route with the rate-determining olefin coordination step proved fair enough to describe the hydrogenation of this macrocyclic lactone. The physical reasonability of the equilibrium and kinetic parameters was also discussed. Fil: Zgolicz, Patricia Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

New anionic oligomeric (tetrameric) surfactants with different spacing architecture based on dioxane rings were synthesized, and their surface-active properties were studied. The synthesis of these compounds involves a three-step procedure comprising tetraglycidyl ethers as key intermediates for connecting four amphiphilic moieties. Critical aggregation concentration (CAC), surface tension at the CAC (γCAC), ability of these compounds to lower surface tension by 0.02 N/m (C20 and pC20), estimated values of the surface area occupied by the surfactant headgroups (a), and packing parameter (P) values are reported at 20 and 40 °C. The molecular architecture of these compounds influences strongly the values of these physicochemical parameters. It was found that the ability of these compounds to lower surface tension is good, but the high relative propensity to form aggregates is their distinctive feature. This ability of aggregation is favored as the number of dioxane rings in the spacer group increases and the spacer group is less flexible. Fil: Murguia, Marcelo Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Cabrera, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Guastavino, Javier Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Grau, Ricardo José Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

Quantum efficiencies of the photocatalytic decomposition of trichloroethylene employing a suspension of titanium dioxide in water and polychromatic radiation have been investigated. Aldrich, Degussa P25 and Hombikat 100 titanium dioxides were studied using an approach that permits the correct evaluation of the true absorbed UV radiation. Computed results using initial reaction rates show that differences in efficiencies among the different varieties of titanium dioxides are not very dramatic. However, reaction conversion after several hours of identical operating conditions favors the use of the Aldrich catalyst. Quantum efficiencies show an important dependence with the initial reactant concentration, the irradiation intensity and the catalyst loading. Under some operating conditions, quantum efficiencies as high as 50 % were measured.

A kinetic model to represent the intrinsic reaction kinetics of the decomposition of trichloroethylene in water, employing suspended titanium dioxide catalytic particles is presented. The catalyst activation was produced bjy radiation energy in the near ultraviolet range (300 nm s λ

An annular flow photoreactor for the direct photolysis of 2,4-dichlorophenoxyacetic acid has been developed, mathematically modeled and experimentally verified in a bench scale apparatus. The model employs a very simple kinetic equation that was previously obtained in a well stirred tank, batch laboratory reactor. Reasonably good agreement has been obtained between model predictions and experimental results. The observed errors are mainly due to the fact that the kinetics of this very complex reaction have been modeled in terms of just one single concentration.

The intrinsic kinetics of the photochemical decomposition of 2,4-dichlorophenoxyacetic acid in aqueous solution has been studied using light of 253.7 nm. Experiments were carried out in a well stirred batch reactor irradiated from its bottom by means of a tubular lamp and a parabolic reflector. Results were analyzed in terms of a very simple kinetic expression. Absorbed radiation effects were duly quantified by means of a one-dimensional radiation field model. This approach incorporates a variable absorption coefficient that is a function of the 2,4-D conversion. The decomposition kinetics can be properly represented with a point valued equation of the following form: RD, λ = − Φ D,λ e λ (y).