Scielo RSS http://bibliotecadigital.uns.edu.ar/rss.php?pid=0327-079320020022&lang=en vol. 32 num. 2 lang. en http://bibliotecadigital.uns.edu.ar/img/en/fbpelogp.gif http://bibliotecadigital.uns.edu.ar http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200001&lng=en&nrm=iso&tlng=en Copolymers of furfuryl methacrylate (M) with N-vinyl-2-pyrrolidone (P) were prepared by free radical copolymerization in DMF solution at 50°C, using 2,2'-azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both monomers were calculated according to the general copolymerization equation using the Fineman-Röss and Kelen-Tüdos linearization methods, as well as the Tidwell-Mortimer non linear least-squares treatment and the Monte Carlo random method. The values of the reactivity ratios calculated using the first methodology were rM = 3.92 and rP = 0.004. Similar results were obtained by both, the Monte Carlo and the non-linear least square techniques that certified the precision of the proposed method. The microstructure of copolymer chains based on the first order Markov statistics is described. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200002&lng=en&nrm=iso&tlng=en A catalytic oxidation process of traces of SO2 to SO3 for the treatment of dust-free flue-gas from power stations and some special waste incinerators has been developed. The catalyst was prepared by impregnation of platinum precursors on alumina/silicates-based material. The behavior of this industrial sized honeycombtype catalyst was studied at lab and pilotplant scale. The evolution of SO2 conversion and some physico-chemical properties of the catalyst with time in operation were examined. The 7-8 wt.% of sulfate deposition on the fresh catalyst had no influence on the catalytic activity at steady state conditions. The catalyst showed SO2 to SO3 conversion value of 80-90 vol.% operating at a temperature of 450ºC and space velocities of 3000-6150 h-1 (NTP). http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200003&lng=en&nrm=iso&tlng=en Four silica samples were evaluated as supports in the hydroformylation of oct-1-ene by Supported Aqueous Phase Catalysis (SAPC) using [Rh2(µ-StBu)2(CO)2(TPPTS)2] and [Rh(COD)Cl]2/TPPTS as catalysts. Adsorption studies of the [Rh(COD)Cl]2/TPPTS complex from aqueous solutions on the supports were carried out at 25 °C. The isotherms obtained were correlated by several models, among which the Fowler-Guggenheim/Jovanovic-Freundlich equation was found to be the most satisfactory. The influence of the nature of catalytic complex and of the methods for supporting the catalyst on the silica conversion was also studied. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200004&lng=en&nrm=iso&tlng=en This paper deals with the possibility of reducing carbon content by heat treatment in reactive atmospheres in order to improve plastic deformations properties of steel sheets. The heat treatment involves a decarburation annealing after a cold rolling, as opposed to the traditional process that performs the heat treatment in non-reactive atmospheres. Some of the most relevant variables were studied. For this, commercial hot rolling steel sheets were cold rolled with different grades of cold reduction (60%, 70% and 80%). The recrystallization temperature and the decarburation kinetics were determined by heat treatments performed at temperatures varying between 600 and 700ºC, for variable lengths of time up to 2 hours. The grain size evolution was monitored by metallography. In order to analyse the plastic properties of the treated sheets, the n and r coefficients were obtained by tension tests and the sheet texture was determined by X-ray diffraction. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200005&lng=en&nrm=iso&tlng=en The kinetics of the gas-phase isomerization of β-pinene over an acid-activated bentonite clay has been investigated in a fixed-bed continuous flow reactor, at atmospheric pressure between 58 and 90 oC. The major isomers produced were camphene, α-pinene and limonene. The reaction rates of β-pinene conversion and the apparent activation energy were determined. The kinetics of β-pinene isomerization was described by zero-order kinetics with an activation energy of 30-35 kJ/mol for the major products formed. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200006&lng=en&nrm=iso&tlng=en A new interpretation to the kinetics of iron oxide direct reduction, based on the influence of probability of activation of the reaction on the "flux of transformation", is presented in this paper. This interpretation is applied to justify a new process of direct reduction of iron oxides, by using carbon as the only reactant. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200007&lng=en&nrm=iso&tlng=en A model that predicts isothermal alkali diffusion and reaction with acetyl groups in moist wood chips was derived and approximated. System parameters were estimated from unsteady-state experimental data. Simulation results reinforce the idea that the diffusion effect is not fully exploited in pulping processes. Traditionally, digestion is conducted at high temperature, where delignification reaction kinetics is enhanced and the reaction effect is predominant. This approach is being reviewed by modern industry since energy and environmental savings associated with low temperature operation might compensate for high-yield productivity. The concentration of alkali at the center of the chip is a measure of the completeness of wood deacetylation, which translates into the aptitude of the final product for pulping purposes. This concentration is predicted here from the solution to a pair of coupled ODE's. Since alternatives combining both low and high-temperature processes are being studied, the results in this paper provide basic data for optimization analysis. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200008&lng=en&nrm=iso&tlng=en In this work, an alternative procedure to retrofit an industrial plant is proposed, based on a new heat exchanger network (HEN) synthesis and evolution algorithm. The idea is to consider the retrofitting as a grassroots design, but with match constrains accounted for during the synthesis. First, a lower bound for the HEN total annual cost (TAC) is determined and a new HEN is synthesized. A comparison between this HEN and the actual one is performed to search for structural similarities, forming the set of match constrains. Then, a new HEN keeping those similarities is proposed. The comparison among the three HENs indicate the recommended structural modifications. A Case Study is considered. Results show a reduction on the TAC, indicating the actual HEN is poorly integrated and a retrofit can be performed without many changes on the structure. The automatic HEN synthesis and evolution are performed using the software AtHENS, http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200009&lng=en&nrm=iso&tlng=en The three-dimensional pore model, that characterizes solid materials prepared by aggregating and coalescing spherical microparticles, is used to evaluate the role of structural and transport parameters in a catalytic system of parallel - consecutive first order reactions. The selection of the optimum catalyst structure (porosity), which leads to maximum reaction rates, is illustrated. The effects of intermediate product external concentration and the influence of a non-uniform catalytic activity distribution inside the pellet are also presented. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200110&lng=en&nrm=iso&tlng=en Chemical induced separation is used in a number of instances to accomplish difficult separations; however, there is a lack of information in the literature. In the present work, a fuzzy heuristic system for separation sequence synthesis using chemical induced separation is constructed. The construction of the present rule based system is based on the previous work of Huang and Fan (1990) in which knowledge-based system has been applied to physically induced separation sequence synthesis. Although the methodology proposed here, involves the use of declarative and procedural knowledge the emphasis is done on selection and sequence of chemical induced separation. A simple example is included to illustrate the procedure. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200111&lng=en&nrm=iso&tlng=en The physical characterization of solids, mainly the surface area measurement and the pore size distribution determination by means of nitrogen adsorption and mercury porosimetry, respectively, might be a matter of controversy in the case of materials that can suffer important structural changes between 77K and their operation temperatures (room or higher), or whose pore structure may be damaged due to the mercury intrusion. The goal of this work is to identify changes in the physical structure of solids when they are exposed to temperatures similar to those used in conventional thermal pretreatments, when they are used as catalysts, by means of mass transfer coefficient measurements. Our working hypothesis is that, if structural changes occur, these should be easily detected via noticeable changes in the mass transfer coefficient for a selected adsorbate. The calculation of relaxation constants, which characterize the transport of cyclohexane through the hybrid materials is carried out by modeling the experimental data corresponding to the transient state of the adsorption tests. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200112&lng=en&nrm=iso&tlng=en Power consumption of unsteadily forward-reverse rotating multiple impellers, a new cross type of impellers with four delta blades (CDs), was experimentally studied in an unbaffled agitation vessel containing water with a liquid heigh t-to-diameter ratio of 2. The effect of clearance on the power number of forward-reverse rotating double and triple CDs was compared with that of udidinationally rotating disk turbine impellers with six flat blades (Dls) in the baffled vesseL The result was discussed in relation to the difference in bulk flow pattern between the unbaffled vessel with CDs and the baffled vessel with Dls, The study also revealed that the value of power consumption for the forward-reverse rotating multiple CDs in the unbaffled vessel can be evaluated as the value for the single CD system multiplied by the number of impeller stages over a wide range of impeller clearances. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200113&lng=en&nrm=iso&tlng=en The main aim of this work is the development of mathematical models of aerobic batch fermentations for its use in estimation and control algorithms. Most batch fermentation models are empirical and simple, and do not provide interrelationships between state variables and measurements. In this work such interrelationships are obtained from mass and energy balances of the fermentation components. Since aerobic fermentations with formation of a single metabolite exhibit three degrees of freedom, three independent kinetic equations are necessary to build the state space model. Test results on the batch fermentation of xanthan gum are presented. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200114&lng=en&nrm=iso&tlng=en A spent clay from the oil refining industry was recycled through an extraction process using organic solvents for removal of residual oil, followed by reactivation through heat treatment. The solvents used showed the following order in the efficiency of oil extraction: methylethylketone> acetone > petroleum ether @ hexane. The bleaching efficiency of regenerated clay samples for soybean oil was determined spectrophotometrically in the visible region. For comparison of the bleaching experiments, a sample of virgin commercial clay was used. Results showed that extraction process, using just solvent, is insufficient to recover the bleaching power of the spent clay, needing then a further high temperature treatment. The bleaching power of the regenerated clay is dependent of temperature and time of calcination. The regenerated clay samples presented a similar bleaching efficiency for soybean oil comparable to a virgin commercial clay utilized as reference. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932002002200115&lng=en&nrm=iso&tlng=en Morganella morganii, the most histaminogenic bacteria in chilean mackerel, was isolated and used to study the effect of temperature on h istamine production in this fish. Growth and histamine production rates at different initial pH (4.0, 5.5, 6.0, 7.0) and temperatures (10, 15, 20, 30 °C) were studied in batch cultures of M. morganii in a synthetic medium (TSBH- 2% histidine). An Arrhenius- type relationship between growth rate and temperature was found; its activation energy was 88.49 kJ mol-1. Bacterial growth and histamine formation were negligible below pH 5.0. The Leudeking-Piret expression for product formation rate was used; the α parameter was not significantly different at 30, 20 and 15 °C and its average value was 0.1 [mg histamine (mg cell)-1]. Assuming an initial protein content of 188 g (kg fish)-1, a level of 500 mg histamine (kg fish)-1 would be produced after 43 h at 15 °C or after 24 h at 20 °C. The prediction of histamine level at different temperatures can be used as a strategy of catch management.