Showing papers in "Chemical and Biochemical Engineering Quarterly in 2009"

Process Intensification through Microreactor Application

Abstract: A substantial amount of publications each year demonstrate how through the application of microprocess engineering significant benefits can be obtained concerning product yield, purity and time needed for chemical transformations, compared to the equivalent bulk reactions. Microreactors clearly hold the potential to revolutionize chemical synthesis, but scarce articles demonstrate specific suggestions for possible replacement of existent industrial processes. The focus of this review is to assess whether significant advances have been made for the implementation of microstructured devices into existent industrial processes or their complete replacement. The papers are reviewed in light of particular beneficial microreactor characteristics with potential for process intensification.

A Mini-Review on Greenness of Ionic Liquids

Abstract: Ionic liquids (ILs) have been considered as "green solvents" in many published works. However, recent research on their eco-toxicity and degradability has proven that some ILs are not as "green" as expected. In this review, the greenness of ILs was discussed in terms of their synthesis, eco-toxicity and degradability and their applications. Greenness of ILs depends not only on themselves but also on their synthesis and specific applications. For a chemical process where the IL is employed, its greenness should be assessed using the life cycle analysis method and compared with other alternative processes. The green process is much more important than the IL itself with respect to green chemistry, and more research should be made to improve the greenness of process employing ILs.

Antioxidant, Radical Scavenging and Antimicrobial Activities of Red Onion (Allium cepa L) Skin and Edible Part Extracts

Abstract: The antioxidant, radical scavenging and antimicrobial activities of extracts from skin and edible part of red onion have been investigated. Crude extracts of red onion were obtained separately with acetone, ethanol and mixtures of solvents with water. The amounts of isolated phenolic compounds and quercetin from onion skin were approximately 3 to 5 times higher as from the onion edible part. Antioxidant and radical scavenging activities of onion skin extracts were generally high, results were comparable to that of BHT. Extracts from onion edible part showed somewhat lower activity. Furthermore, high activity of skin extracts against bacteria Escherichia coli, Pseudomonas fluorescens and Bacillus cereus and fungi Aspergillus niger, Trichoderma viride and Penicillium cyclopium was observed. Antimicrobial activity of edible part extracts against tested microorganisms is generally lower, while for Escherichia coli no growth inhibition was observed.

Overview on Reactions with Multi-enzyme Systems

Abstract: Production of specialty chemicals and pharmaceuticals includes multi-step procedures that are still carried out in the traditional way: by isolating the intermediary product of each step and using it as a substrate for the next step, which is money and time consuming. These are also the procedures that require many chemicals, energy and labour. Over the last couple of decades scientists have been working on the new, integrated processes that require fewer resources and are more close to nature, as they produce less waste. These kinds of processes are discussed in this paper. The advantages of enzyme catalyzed reactions are well documented and numerous. Enzyme reactions are carried out at mild reaction conditions. The enzymes are enantioselective and stereoselective, which is important particularly for the pharmaceutical industry. By combining the action of different enzymes we can imitate the processes in the living cells and produce the desired compounds. Enzyme catalyzed reactions can also be combined with chemical reactions in one-pot chemo-enzymatic synthesis. The progress in the development of these reactions will be presented.

Studies on the Growth of Chlorella vulgaris in Culture Media with Different Carbon Sources

Abstract: Diminishing oil reserves, rising oil prices and a significant increase in atmospheric carbon dioxide levels have led to an increasing demand for alternative fuels. Microalgae have been suggested as a suitable means for fuel production because of their advantages related to higher growth rates, higher photosynthetic efficiency and higher biomass production, compared to other terrestrial energy crops. During photosynthesis, microalgae can fix carbon dioxide from different sources, including the atmosphere, industrial exhaust gases and soluble carbonate salts. To determine the most optimal conditions for the growth of Chlorella vulgaris in order to produce lipids that can be transformed into biodiesel fuel, different nutritional conditions were investigated. For this purpose, three media, namely Jaworski's medium, an enriched solution from modified Dual Solvay process and natural mineral water, were prepared and analyzed for biomass production, chlorophyll content and lipid content. The best growth resulted in an enriched solution from the modified Solvay process. This medium was diluted in different dilution ratios (1:100, 1:50, 1:10) and the best results were obtained in a medium diluted in a 1:10 ratio on the fifth day of culturing (3.72 · 10 6 cells mL -1 ; 4.98 μg mL -1 chlorophyll a).

The Effect of Enzymatic Treatments of Pulps on Fiber and Paper Properties

Abstract: Biotechnological treatment of pulps provides great potential for the reduction of energy consumption and greenhouse gas emissions. In the present work, the influence of different commercial cellulases and xylanases or their mixtures on the quality of different bleached kraft pulps was investigated. The effects of enzymes on reducing sugars release and changes in fiber length were assessed for 3 different eucalyptus pulps, for a pulp consisting of a mixture of hardwoods and for softwood pulp. Despite the extremely high enzyme concentrations used in this part of the study, almost no change in fiber length was observed for pulps treated with enzyme preparations alone, while all combinations of cellulases and xylanases resulted in significant changes in average fiber length, portion of fines and reducing sugars release. Besides, vessel cell deformation was observed as a consequence of all enzymes applications. Furthermore, physical and mechanical properties of laboratory sheets made with enzymatically treated pulps were evaluated for various refining conditions and compared to those of untreated pulps. Potential energy savings up to 17 % were achieved with enzyme treatment, but some decrease in pulp quality was also observed.

Process Intensification of Nicotinic Acid Production via Enzymatic Conversion using Reactive Extraction

Abstract: Nicotinic acid is widely used in the food, pharmaceutical and biochemical industries. Compared to chemical methods, enzymatic conversion of 3-cyanopyridine is an advantageous alternative for the production of nicotinic acid and nicotinamide. The separation of the product is complicated, owing to its high dilution rate in fermentation broth and high cost. Reactive liquid-liquid extraction by a suitable extractant system has been found to be a promising alternative to the other conventional separation techniques. This paper gives a state-of-the-art review for manufacturing processes (chemical and enzymatic) of nicotinic acid and nicotinamide. It also focuses on the most efficient separation technique, reactive extraction. Reactive extraction has advantages of less consumption of material and energy. It also avoids product inhibition and increases the separation selectivity.

Polypropylene-based Eco-composites Filled with Agricultural Rice Hulls Waste

Abstract: In this work the properties of rice-hull-filled polypropylene (PP) composites were investigated with the purpose of enhancing adhesion between the polymer and the filler through the addition of w = 5 % PP-grafted-MA (CA). Composites containing w = 20 and 30 % rice hulls (RH), as well as composites with a certain amount of PP matrix substituted with a coupling agent, were prepared by extrusion and compression moulding. The composites' mechanical properties were investigated through tensile and fracture tests at low and high strain rate, using the concept of linear elastic fracture mechanics. Introduction of rice hulls in the PP matrix resulted in a decreased stress at peak, together with increase of composites tensile modulus (E PP = 1013 MPa, E PP/RH (ξ = 0.70:0.30) = 1690 MPa) and modulus in flexure. Introduction of w = 5 % PP-g-MA caused 6 % and 12 % improvement in the composite tensile strength, respectively for the PP composites with w = 20 and 30 % rice hulls. Modulus in flexure for the composite PP/RH/CA (ξ = 0.65:0.30:0.05) reached E f = 1646 MPa, which was an improvement of 52 % when compared to pure polypropylene. K c and G c values were determined for PP and PP-based composites. Thermal stability of PP was slightly improved by adding rice hulls.

MINLP Synthesis of Processes for the Production of Biogas from Organic and Animal Waste

Abstract: This paper describes a superstructure approach for the synthesis of biogas processes simultaneously with the selection of different process background alternatives. The superstructure consists of anaerobic fermentation under thermophilic or mesophilic conditions, including options for a rendering plant, with different organic and animal wastes from either existing or new plants, different water supplies, wastewater treatments and biogas usage options. An aggregated mathematical model with an economic objective function, formulated as a mixed-integer nonlinear programming (MINLP) problem, was developed. An industrial case study was applied to an existing large-scale meat company, in order to describe the mathematical model and illustrate the MINLP synthesis approach. The optimal solution indicates that significant benefit can be obtained if biogas processes are selected simultaneously with the selection of different process background alternatives thus yielding the optimal integration of biogas processes with their background.

Experimental Determination of Surface Stress Changes in Electrochemical Systems - Possibilities and Pitfalls

Abstract: In the present paper, the different techniques used for the determination of changes of surface stress of solid electrodes, as well as the kind and quality of information that can be achieved using these methods are discussed. The most important methods are briefly reviewed and advantages/drawbacks highlighted. Special attention is paid to issues related to the use of the “bending beam” (“bending cantilever”, “laser beam deflection”, “wafer curvature”, etc.) methods. Recent development in these techniques has been introduced and discussed.

Electrochemical and Spectroscopic Study of Benzotriazole Films Formed on Copper, Copper-zinc Alloys and Zinc in Chloride Solution

Abstract: The formation of protective layers on copper, zinc and copper-zinc (Cu-10Zn and Cu-40Zn) alloys at open circuit potential in aerated, near neutral 0.5 M NaCl solution containing benzotriazole (BTA) was studied using potentiodynamic measurements, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The addition of benzotriazole affects the dissolution of the materials investigated. Benzotriazole, generally known as an inhibitor of copper corrosion, is also shown to be an efficient inhibitor for copper-zinc alloys and zinc metal. The effectiveness of inhibition depending on the type of materials was compared. X-ray photoelectron spectroscopic results showed that the surface layer formed on alloys in BTA-inhibited solution comprised both oxide and polymer components. The formation of Cu 2 O/Cu(I)-BTA on copper, mixed oxides/Zn(II)-BTA and Cu(I)-BTA on copper-zinc alloys and ZnO/Zn(II)-BTA polymer surface film on zinc provides an effective barrier against corrosion on materials investigated in chloride solution.

Modeling Growth of Cellulomonas cellulans NRRL B 4567 under Substrate Inhibition During Cellulase Production

Abstract: Cellulase production study was performed in shake flask and bioreactor system using Cellulomonas cellulans NRRL B 4567 for initial substrate concentration from γs 0 = 2 to 12 g L ―1 . The growth, substrate uptake profile and enzyme activity at different initial substrate concentrations were measured. The results inferred the presence of substrate inhibition kinetics. Various substrate inhibition models were tested and parameters were estimated, using non-linear regression analysis. Han-Levenspiel model was found to be the best fitted model for both shake flask and reactor study. The highest volumetric enzyme activity was observed at initial substrate concentration of γs 0 = 12 g L ―1 and 4 g L ―1 in shake flask and bioreactor respectively.

A Simple But Highly Selective Electrochemical Sensor for Dopamine

Abstract: A modified platinum electrode was fabricated by the electropolymerization of pyrrole using a sodium p-sulphonatocalix[6]arene as the supporting electrolyte. The modified electrode acts as a reasonably sensitive electrochemical sensor for dopamine giving a linear calibration curve in the range 0.075 – 1.00 mM dopamine. The sensor shows no ability to sense the common interferent ascorbic acid, therefore the concentration for dopamine can be directly sensed in a large excess of ascorbic acid with no need to make adjustments for the signal for ascorbic acid. Investigations are included to study the mode of sensing of the modified electrode.

Lentikat®-based Biocatalysts: Effective Tools for Inulin Hydrolysis

Abstract: A commercial inulinase preparation from Aspergillus niger was immobilized into polyvinyl alcohol hydrogel lenticular particles (Lentikats ® ) and into hemispheric-shaped capsules, both based on the use of LentiKat ® liquid. The characterization of the resulting biocatalysts, aiming at inulin hydrolysis to fructose, was performed, and the two methods of immobilization were compared. Temperature and pH profiles, as well as kinetic constants were determined, for both free and immobilized enzyme preparations. A broader-shaped curve was observed for the pH-activity profile when immobilized forms were compared to the free form. The apparent K M of inulinase increased roughly 2-fold upon immobilization in either form of the support particles, suggesting diffusion limitations of inulin inside the gel. Long-term operation with immobilized enzymes proved un-feasible above 55 °C, due to the lack of mechanical stability of the supports tested. When the temperature of incubation was lowered to 50 °C, the hemispheric form of the immobilized enzyme displayed considerable long-term operational stability, since it allowed 20 repeated, consecutive batch-mode runs, with a final decay in product yield of 20 %. When inulinase immobilized in Lentikats ® particles was used, the final decay in product yield was roughly 70 %.

Prediction of Dynamic Plasmid Production by Recombinant Escherichia coli Fed-Batch Cultivations with a Generalized Regression Neural Network

Abstract: A generalized regression neural network with external feedback was used to predict plasmid production in a fed-batch cultivation of recombinant Escherichia coli. The neural network was built out of the experimental data obtained on a few cultivations, of which the general strategy was based on an initial batch phase followed by an exponential feeding phase. The different cultivation conditions used resulted in significant differences in bacterial growth and plasmid production. The obtained model allows estimation of the experimental outputs (biomass, glucose, acetate and plasmid) based on the bioreactor starting conditions and the following on-line inputs: feeding rate, dissolved oxygen concentration and bioreactor stirring speed. Therefore, the proposed methodology presents a quick, simple and reliable way to perform on-line feedback prediction of the dynamic behaviour of the complex plasmid production process, based on simple on-line input data obtained directly from the bioreactor control unit and with few cultivation experiments for neural network learning.

Model-free Kinetics Analysis of Thermal Degradation of Polysiloxane Lubricant

Abstract: The object of this study was to investigate the thermal stability and degradation kinetics of polysiloxane material used as lubricant in the die casting process of aluminium alloys. The degradation of dried polysiloxane emulsion was studied by thermal gravimetric analysis (TGA) using nitrogen atmosphere. Several non-isothermal experiments at different heating rates and isothermal experiments were performed. The isoconversional kinetic analysis using the integral procedure was applied to the non-isothermal TGA results. The apparent activation energy was calculated by the Flynn-Wall-Ozawa method as a reliable way of determining the kinetics parameters. Based on the determined apparent activation energy isothermal degradation behavior of the lubricant at different temperatures was predicted. The efficiency of the predictions was verified and confirmed by isothermal TGA experiments.

Optimization of Carbon and Nitrogen Sources for L-asparaginase Production by Enterobacter aerogenes using Response Surface Methodology

Abstract: A full factorial central composite design (CCD) was applied to study various effects of sodium citrate, diammonium hydrogen phosphate (DAHP) and L -asparagine to determine the optimal concentration (y) of these compounds on L-asparaginase production by Enterobacter aerogenes MTCC 2823 under shake flask fermentation conditions. A second order polynomial model describing the relationship between the variables and the L-asparaginase activity was fitted in coded units of variables. The statistical reliability and significance of the model was validated by F-test for analysis of variance at higher R 2 value (R 2 = 0.871). The optimum estimated concentration of sodium citrate (X 1) , DAHP (X 2 ) and L-asparagine (X 3 ) was 18.76, 5.72 and 8.58 g L -1 respectively with maximum L-asparaginase activity of 19.129 IU mL -1 . The composite desirability of 98.38 % reveals the validity of the model and predicted values. The L-asparaginase activity was increased by 5.96 % than predicted activity, after optimization of carbon and nitrogen sources for L-asparaginase production by Enterobacter aerogenes MTCC 2823 using CCD.

Treatment of Landfill Leachate by H2O2 Promoted Wet Air Oxidation: COD-AOX Reduction, Biodegradability Enhancement and Comparison with a Fenton-type Oxidation

Abstract: Treatment experiments of a landfill leachate were performed by wet air oxidation (WAO) with the addition of H 2 O 2 (as free radical promoter), and a Fenton-type (at pH ≃7) process, in order to compare COD (chemical oxygen demand) and AOX (adsorbable organic halogen) reduction as well as biodegradability enhancement measured by OUR respirometric parameter The WAO reactions were performed in a batch reactor at various temperatures in the range of T = 430―500 K employing a concentration of c = 088 mol L -1 of H 2 O 2 The same H 2 O 2 concentration was used in the Fenton-type-pH ≃7 experimental session considering H 2 O 2 /Fe(II) mole ratios of 5, 10 and 15 Similar results were obtained in COD abatement but appreciably different performance in AOX removal and biodegradability enhancement was observed A comparison between the treatment trials brought to the evidence that Fenton-Type-pH ≃7 process has poor performance in biodegradability enhancement, diversely the H 2 O 2 promoted WAO get to better performances even at mild temperature This process could be considered as advantageous solution in landfill leachate pre-treatment when the main objectives are COD and AOX degradation together with the biodegradability enhancement for fmal treatment in common biological aerobic wastewater treatment plants

Hydrogen Peroxide Decomposition by Pyrite in the Presence of Fe(III)-ligands

Abstract: The decomposition of hydrogen peroxide (H2O2) by pyrite in the presence of Fe(III)-ligands (sulfosalicylate (SSAL), ethylenediaminetetraacetate (EDTA), and phosphate) has been investigated in aqueous acidic media (pH 1) at 25 °C. It was found that H2O2 decomposition by pyrite was inhibited by the presence of EDTA, SSAL and phosphate. On the other hand, pyrite oxidation by H2O2 does not seem to be affected by the presence of Fe(III)-ligands. The experimental results demonstrate that H2O2 decomposition in the presence of Fe(III)-ligands is catalyzed by pyrite surface (a heterogeneous process). This process is first order with respect to [H2O2]. It is expected that the rate-determining step of the reaction mechanism of H2O2 decomposition in the presence of Fe(III)-ligands is one of the following two reactions: FeHO2 2 Fe2 HO2 • Fe(OH)(HO2) Fe2 HO2 • HO– where denotes pyrite surface.

A Lumped Specific Heat Capacity Approach for Predicting the Non-stationary Thermal Profile of Coffee During Roasting

Abstract: Coffee undergoes numerous and relevant chemical and physical changes during roasting. These modifications lead to the development of those typical organoleptic properties of coffee, on which the acceptability of the product depends. The roasting process therefore, plays a central role within the coffee’s technological cycle. This crucial character of roasting has contributed to encouraging the continuous progress of the roasting industry incorporating the necessary scientific and technological research. However, due to the geometrical complexity and transformations undergone by coffee during roasting, the relationship between the heating mode and the material properties of coffee on the one hand and the non-stationary temperature profile within the bean on the other, are still far from being fully understood. In this presented work, a dynamic model is proposed for predicting the non-stationary thermal profile of coffee during roasting. The model is based on the assumption that the thermal effects occurring within the bean during roasting, such as moisture evaporation, can be approximately encompassed within a lumped together specific heat parameter. Using this hypothesis, it is possible to develop a mathematical model, which is quite simple in structure but still able to describe the two most important technological aspects, i.e. the evolution over time of the beans’ average temperature and internal thermal gradient.

Electrochemical and STM Study of α,ω-alkanedithiols Self-assembled Monolayers

Abstract: Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions containing ,-alkanedithiol, n-alkanethiol or mixed thiol/dithiol solutions, with 6, 9 and 10 carbon atoms in the alkyl chain, have been investigated. The amount of adsorbate and the SAM stability in alkaline medium is evaluated by reductive desorption of the prepared monolayers by cyclic voltammetry. An upright orientation of the dithiol self-assembled molecules and disulfide bonding at the SAM/solution interface are suggested by the higher reductive desorption charge of the dithiol monolayers (relative to thiol SAMs) for n = 6 and 9. The results show that an improvement on the stability of these dithiol SAMs is obtained by the presence of monothiols, resulting in mixed monolayers. Mixed SAMs prepared from longer alkane chain thiols, n = 10, allow to overcome the increased possibility of loop formation and therefore lower surface coverage is obtained for the 1,10-decanedithiol monolayers. Morphological characterisation of the modified electrodes is performed by scanning tunnelling microscopy (STM) ex situ, in air. Typical one atom deep thiol induced depressions are observed in the STM images of the dithiol and mixed SAMs.

Modelling of Continuous L-Malic Acid Production by Porcine Heart Fumarase and Fumarase in Yeast Cells

Abstract: Continuous production of L-malic acid will be presented in this paper.The fumarase isolated from porcine heart, fumarase in the permeabilized non-growing cells of baker’s yeast and Saccharomyces bayanus (UVAFERM BC) were used as biocatalysts.In the pro duction of L-malic acid with fumarase isolated from porcine hearts, there was no enzyme deactivation for a period of two days.At the average residence time of 4 hours, the conversion of about 80 % was achieved.Inactivation of the enzyme was observed using permeabilized cells.This inactivation is described as a reversible process.Conversion of about 50 % was achieved with the remaining enzyme activity.A mathematical model that describes the pro duction of L-malic acid, which contains the enzyme inactivation rate, was developed.Based on simulations, the used biocatalysts were compared.The results show that in the continuous production of L-malic acid, one milligram of purified enzyme corresponds to 68 g (wet weight) cells of Saccharomyces bayanus or 120 g (wet weight) cells of baker’s yeast.

Glucose Electrooxidation for Biofuel Cell Applications

Abstract: The kinetics of glucose electrooxidation on different catalysts has been studied at physiological conditions (pH 7 and 37 °C). Electrochemically activated rough gold, rough gold modified with a self-assembled monolayer (SAM) of cystamine and an enzymatic electrode based on a charge transfer complex (CTC) and glucose oxidase (GOx) have been tested. The influence of glucose concentration, electrode rotation rate and presence of oxygen has been investigated and the stability of the different catalysts has been evaluated. All parameters have been discussed in the context of the potential application of these catalysts in an implantable glucose/O 2 biofuel cell. Rough gold exhibits high activity with very low overpotential for glucose oxidation but its extreme instability and low oxygen tolerance make it inappropriate as potential anode in a biofuel cell. The CTC enzymatic electrode on the other side shows high activity for glucose oxidation, reasonably low overpotential and relatively high stability.

Studies on Transport of Carbonate Ions through a Supported Liquid Membrane

Abstract: The transport of carbonate ions through a supported liquid membrane in the presence and absence of carriers has been explored. The liquid membrane used was the combined liquid cation and anion exchangers in toluene immobilized in the porous polypropylene support. The permeability coefficient (P) of carbonate ions transport from the source to receiving through membrane phase has been estimated. The different experimental variables such as the concentration of carbonate ions in source phase, the concentration of Aliquat-336 (tricapryl(methyl)ammonium carbonate) and PC-88A (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) in membrane phase, alkali metal hydroxide concentration in receiving phase, and the stirring speed of the source phase and receiving phase have been explored. The stability of liquid membrane phase during the transport of carbonate ions from source phase to receiving phase was tested for 50 h. The enrichment factor for carbonate ion transport from the source to receiving phase was found to be higher at lower concentrations of carbonate ions in comparison with that of at higher concentrations. A model has been developed for the effective transport of carbonate ions through the cross section area of liquid membrane phase from source to receiving phase.

Linearizing Control Based on Adaptive Observer for Anaerobic Continuous Sulphate Reducing Bioreactors with Unknown Kinetics

Abstract: Anaerobic reactors are a typical example of processes that exhibit non-linear behavior and, also time varying parameters; hence their operation is known to be difficult to model and control. In contrast to modeling approaches, in practice linear controllers are widely employed for industrial processes because of their easy implementation and manipulation by plant operators; nevertheless linear approaches are not robust when the operating conditions change suddenly and/or strong disturbances are present. In order to introduce robust controllers to these processes, this paper addresses the tracking problem for the substrate (sulphate) control in a class of continuous bioreactors. An experimentally corroborated bioreactor model serves as benchmark problem for advanced non-linear analysis and control techniques; taking into account system non-linearities, stability and performance objectives over large operating regions. It is considered that, as it is common in practice, the rate of substrate consumption exhibits uncertainty. Results show that the proposed controller exhibits better dynamic performance than a classical Proportional-Integral control tuned using the methodology suggested by Internal Model Control.

Electrochemical and AFM Study of Corrosion Inhibition with Respect to Application Method

Abstract: The aim of this work was to investigate how the efficiency of a corrosion inhibitor and the mechanism of its inhibiting action depend on the inhibitor application method. Studies were performed on copper in 0.5 M NaCl solution for two imidazole derivatives. Studied compounds were either added to the corrosive solution or the inhibitor film was formed prior to immersion in the corrosive solution. The investigations were conducted by means of electrochemical methods and atomic force microscopy. The results obtained indicate that the method of inhibitor application may determine the mechanism of inhibition and the efficiency of an inhibitor. When the inhibitors were adsorbed on the metal surface from the organic solvent, they acted primarily as cathodic corrosion inhibitors. On the other hand, when they were added to the aqueous solution, both anodic and cathodic reaction rates slowed down. AFM studies have also confirmed changes in the inhibition mechanism due to the application method. All experimental methods have confirmed that the studied imidazole compounds can control the corrosion processes more efficiently when they are dissolved in a chloride solution than when used in nanolayers.

Corrosion Behavior of Composite Coatings Obtained by Electrolytic Codeposition of Copper with Al2O3 Nanoparticles

Abstract: Composite coatings of copper incorporating Al 2 O 3 nanoparticles electrodeposited on carbon steel were obtained and characterized. By using electrochemical methods such as open circuit potential (ocp) measurements, polarization curves and electrochemical impedance spectroscopy, the corrosion behavior of the Al 2 O 3 -copper nanocomposite coatings was examined. The corrosion parameters determined from the polarization curves recorded in Na 2 SO 4 solution (pH 3) indicate that the corrosion process on copper-Al 2 O 3 composite surface is slower than on pure copper. The impedance spectra recorded at the ocp showed in all cases an increase of the polarization resistance in time, which may be explained by the development of corrosion products on the electrode surface. Using a (2RC) equivalent electrical circuit, the process parameters were estimated by non-linear regression calculations with a Simplex method. The Al 2 O 3 particles embedded in the electroplated copper, increase the polarization resistance and decrease the corrosion rates as compared with electrodeposited pure copper. The electrochemical results were corroborated with those obtained by SEM and EDX investigations.

Amperometric Adhesion Signals of Liposomes, Cells and Droplets

Abstract: Individual soft microparticles (liposomes, living cells and organic droplets) in aqueous media are characterized by their adhesion signals using amperometry at the dropping mercury electrode. We confirmed that the general mechanism established for adhesion of hydrocarbon droplets and cells is valid as well for liposome adhesion within a wide range of surface charge densities. Incidents and shape of adhesion signals in liposome suspensions reflect liposome polydispersity, surface charge density and properties of phospholipid head group. Major distinction in adhesion behavior of liposomes when compared to organic droplets was identified as: (i) different values of critical interfacial tensions of adhesion at the positively and the negatively charged electrode, and (ii) appearance of signals revealing the specific interactions of phospholipid polar head groups with the electrode.

A Whole-cell Model to Simulate Mercuric Ion Reduction by E. coli under Stationary and Perturbed Conditions

Abstract: Gram-negative bacteria display mercury resistance conferred by the plasmid encoded mer operon. A genetic regulatory circuit (GRC), inducible by the presence of mercury compounds in the environment, allows controlling the expression of at least 6-7 mer genes producing enzymes responsible for the mercuric ions transport and reduction. In spite of extensive studies on bacterial toxic metal resistance, few and rather unstructured kinetic models have been proposed to characterize the process dynamics. This paper aims at proposing an extended dynamic model, of modular construction, to reproduce the characteristics of GRC controlling the mercury uptake and reduction process. The illustrated case study uses experimental data from literature collected on cultures of E. coli cells cloned with the plasmid R100 to increase the source of mer operon. The available information is used to fit the model parameters and to adjust the GRC properties. The pathway includes seven regulatory modules placed in an E. coli growing cell on which response to external perturbations is studied. The model, accounting for the variable cell volume under isotonic conditions, can reproduce the GRC dynamic control in connection with the cell content replication, and various cell behaviours such as mer gene expression amplification at low levels of external stimuli, or cell content 'ballast' effect when coping with stationary or dynamic perturbations.

Analysis of Modified Starch Adsorption Kinetics on Cellulose Fibers via the Modified Langmuir Adsorption Theory

Abstract: The kinetics of starch adsorption on cellulose fibers is one of the most important criteria regarding the efficient application of papermaking additives due to the continuous nature of paper production and the concomitant need to determine optimum residence times. This study presents an analysis of the kinetics of modified starch adsorption onto cellulose fibers via the application of the modified Langmuir adsorption theory (i.e. the collision theory). A model based on this theory was used to describe the kinetics of starch binding, and to obtain the adsorption rate constant under different process conditions, which closely correspond to the conditions commonly encountered in industrial production of paper and board. The model predictions were then correlated with the experimental data. The adsorption of modified starch was found to increase by increasing the fiber consistency, shear forces (via stirring frequency) and the refining degree of fibers. The results also demonstrate that, at least in the studied range of process variables, the modified Langmuir adsorption theory can be applied to describe the adsorption kinetics of modified starch on cellulose fibers.