Resumo em Inglês:

The influence of oxygen supply rate on the growth and the production of both ethanol and acetaldehyde by the aerotolerant fermentative bacterium Z. mobilis is discussed in this work. The results showed similar values of cell mass yield (0.043 g/g) for the five different levels of initial volumetric oxygen transfer coefficient (K La) studied. The maximum specific growth rate (µx,m.) under anaerobic conditions was higher than those found in aerated runs. Anaerobic cultivation resulted in the best ethanol yield (0.38 g/g). For initial K La values of 62, 94, and 118 h-1, ethanol yields were 0.10, 0.12, and 0.09 g/g, respectively, whereas for K La of 30 h-1, an intermediate value (0.24 g/g) was achieved. Under anaerobiosis, no acetaldehyde was produced. With initial K La values of 62, 94, and 118 h-1, acetaldehyde yields were similar (0.12 to 0.17 g/g), and for K La of 30 h-1 only 0.07 gram of acetaldehyde was formed per gram of glucose. Although increasing values for the maximal specific acetaldehyde formation rate were calculated as K La was increased, our results showed that the presence of an excess of dissolved oxygen throughout fermentation is enough to provide appropriate conditions for the production of acetaldehyde by Z. mobilis.

Resumo em Inglês:

In this work, SO2 was treated by reaction with dolomite limestone (24 µm) in a fluidized bed reactor composed of 500-590 µm sand particles. The influence of operating temperature (500, 600, 700 and 800ºC), superficial gas velocity (0.8, 1.0 and 1.2 m/s) and Ca/S molar ratio (1, 2 and 3) on SO2 removal efficiency for an inlet concentration of 1000 ppm was examined. Removal of the pollutant was found to be dependent on temperature and Ca/S molar ratio, particularly at 700 and 800ºC. A maximum removal of 76% was achieved at a velocity of 0.8 m/s, a temperature of 800°C and a Ca/S of 3. The main residence time of the powder particles was determined by integrating normalized gas concentration curves as a function of time; the values found ranged from 4.1 to 14.4 min. It was concluded that the reactor operated in bubbling fluidization under every operational condition.

Resumo em Inglês:

The transformation of methylcyclohexane at 723 K over on a USHY sample and on an FCC catalyst composed of 30% USHY and 70% matrix containing 25% Al2O3 was studied. With both samples, C2-C7 alkenes and alkanes, cyclopentane and methylcyclopentane (cracking products), dimethylcyclopentanes and ethylcyclopentane (isomers) and aromatics appeared as primary products. The activity and selectivity of fresh samples as well as the influence of coke deposits on porosity and selectivity are discussed.

Resumo em Inglês:

Stirred Tank Reactors are extensively used in chemical industries. When they are used for highly exothermic reactions, jackets or coils are employed for heat removal. Internal coils can be either helical or axial and they considerably affect the flow inside the reactor because they impose an additional resistance to flow circulation. The aim of this work is to show that the design of vessels cooled by helical coils can be further improved. The design of these reactors follows very much the geometry proposed by Oldshue and Gretton (1954), and some minor modifications in the coil arrangements are likely to improve internal circulation inside these vessels mainly in the region between coils and wall of the vessel. Results show a gain in performance when small alterations are made specially in the shape of the coil arrangement.

Resumo em Inglês:

This experimental work presents the optimization results of obtaining a high indium concentration solution and minimum iron poisoning by solvent extraction with D2EHPA solubilized in isoparaffin and exxsol. The variables studied in the extraction step were D2EHPA concentration, acidity of the aqueous phase and time of contact between phases. Different hydrochloric and sulfuric acid concentrations were studied for the stripping step. The optimum experimental conditions resulted in a solution with 99% indium extraction and less than 4% iron. The construction of a McCabe-Thiele diagram indicated two theoretical countercurrent stages for indium extraction and at least six stages for indium stripping. Finally, the influence of associated metals found in typical sulfate leach liquors from zinc plants was studied. Under the experimental conditions for maximum indium extraction, 96% indium extraction was obtained, iron extraction was about 4% and no Ga, Cu and Zn were co-extracted.

Resumo em Inglês:

Some physical characteristics of cassava starch extruded using a single-screw extruder, varying acid concentration, feed moisture content and barrel temperature were evaluated using surface response methodology. The combined effects of different concentrations of sulphuric acid and extruder parameters provided unique physical functionality to the extruded cassava starch. Product hardness and torque value was highly significant for three variables. The addition of sulphuric acid (0.06N) during extrusion cooking gave the highest values for expansion and softness of the extruded samples. The highest torque values (60-70 Nm) were for the samples extruded at the lowest moisture content, while the lowest torque values (23.0-26.0 Nm) were for the samples extruded at the highest values of feed moisture and barrel temperature.

Resumo em Inglês:

In this work, a bentonite clay from Mendoza, Argentina was activated with H2SO4 (4 and 8 N) at 90ºC for 2 and 3.5 hours. Under these conditions several cations were removed from the octahedral sheet (Mg, Al, and Fe) and the DTA-TGA curves of the solids obtained after treatment were modified. Treatment time and acid concentration increased the degree of destruction of the bentonite structure. Activated samples were tested in order to verify their capacity to bleach soybean oil and were compared to a standard commercial bleaching clay. Treated samples are more efficient in bleaching than the standard.

Resumo em Inglês:

The postmortem catabolism of adenosine triphosphate (ATP) in cold-stored adductor muscles from scallops (Zygochlamys patagónica) was studied. Changes in the pH of stored muscles were also studied. The ATP content increased for a short time after death and afterwards decreased up to 24 hr of storage. Thereafter, the nucleotide level remained unchanged up to the end of storage. The ADP content slightly decreased up to 48 hr and after that remained unchanged. The AMP slowly accumulated to around 15% of the total nucleotide concentration when the ATP decreased. Small amounts of IMP were detected in all samples. Conversely, adenosine (Ado) was not detected. Inosine (HxR) increased slightly after 48 hr of storage and hypoxanthine (Hx) increased significantly after 24 hr. The 260/250 absorbance ratio of muscle extracts and the pH of stored muscles fell sharply up to 24 hr and then decreased slowly up to the end of storage. The hypoxanthine concentration and the 260/250 absorbance ratio could be reliable indicators of storage age in adductor muscles from scallops.

Resumo em Inglês:

Muscles and different proteins obtained from scallops (Chlamys tehuelchus and Zygochlamys patagonica) were analyzed. In both species of scallop, the thermograms of striated and smooth muscles showed two endothermic transitions. The Tmax values corresponding to striated and smooth muscles from C. tehuelchus were 53.2, 79.0ºC and 52.7, 78.0 ºC, respectively. The Tmax corresponding to striated and smooth muscles of Z. patagonica were 55.0, 79.2ºC and 54.7, 78.7ºC, respectively. No significant differences were observed between the thermal transitions of myofibrils and actomyosin of both types of muscles from both species of scallop. Irrespective of the species, the thermal stability decreased when the pH of the muscles was increased. The increase in ionic strength greatly affected Tmax, the deltaH total and the deltaH of the first transition. A significant decrease in deltaH total and deltaH corresponding to both transitions was observed, particularly in the striated muscles of Zygochlamys patagonica. These results indicate a major sensitivity of the adductor muscles of Zygochlamys to changes in the chemical environment.

Resumo em Inglês:

Desulfurization of the gases from coal combustion was studied, using limestone (marble) as the sorbent in a fluidized-bed reactor. The kinetic parameter, k, was measured by analyzing the reduction in SO2 emissions in relation to time when a batch of limestone was introduced directly into the combustor chamber. The influence of sorbent composition and particle size was also studied. The CaO content in the limestone was more important than the MgO content. Sorbent particle size showed a strong influence on the reaction time and efficiency of desulfurization. The results of this work prove that marble type is very important in the choice of sorbent for a desulfurization process. A magnesian limestone showed a better performance than a dolomite. Therefore, the magnesian limestone is more efficient for a shorter particle residence time, which is characteristic of the bubbling fluidized bed.

Resumo em Inglês:

This work addresses the influence of a prepolymerization system on the behavior of the fluidized bed reactor used for polyethylene production. Its influence on the polymer's physicochemical characteristics and production was also studied. The results indicate that the use of prepolymerized catalyst particles results in milder temperatures in the fluidized bed reactor, thus avoiding the formation of hot spots, melting of the polymer particle and reactor shutdown. Productivity can be enhanced depending on the operational conditions used in the prepolymerization reactor.

Resumo em Inglês:

The simulated moving bed (SMB) is potentially an economical method for the separation and purification of natural products because it is a continuous processes and can achieve higher productivity, higher product recovery, and higher purity than batch chromatographic processes. Despite the advantages of SMB, one of the challenges is to specify its zone flow rates and switching time. In this case it is possible to use the standing wave analysis. In this method, in a binary system, when certain concentration waves are confined to specific zones, high product purity and yield can be assured. Appropriate zone flow rates, zone lengths and step time are chosen to achieve standing waves. In this study the effects of selectivity on yield, throughput, solvent consumption, port switching time, and product purity for a binary system are analyzed. The results show that for a given selectivity the maximum throughput decreases with increasing yield, while solvent consumption and port switching time increase with increasing yield. To achieve the same purity and yield, a system with higher selectivity has a higher throughput and lower solvent consumption.

Resumo em Inglês:

In this paper, the modeling of the mass transfer process in packed-bed reactors is presented and takes into account dispersion in the main fluid phase, internal diffusion of the reactant in the pores of the catalyst, and surface reaction inside the catalyst. The method of volume averaging is applied to obtain the governing equation for use on a small scale. The local mass equilibrium is assumed for obtaining the one-equation model for use on a large scale. The closure problems are developed subject to the length-scale constraints and the model of a spatially periodic porous medium. The expressions for effective diffusivity, hydrodynamic dispersion, total dispersion and the Darcy's law permeability tensors are presented. Solution of the set of final equations permits the variations of velocity and concentration of the chemical species along the packed-bed reactors to be obtained.

Resumo em Inglês:

Continuity and momentum equations applied to the entrance region of an axial, incompressible, isothermal, laminar and steady flow of a power-law fluid in a concentric annulus, were solved by a finite difference implicit method. The Newtonian case was solved used for validation of the method and then compared to reported results. For the non-Newtonian case a pseudoplastic power-law model was assumed and the equations were transformed to obtain a pseudo-Newtonian system which enabled its solution using the same technique as that used for the Newtonian case. Comparison of the results for entrance length and pressure drop with those available in the literature showed a qualitative similarity, but significant quantitative differences. This can be attributed to the differences in entrance geometries and the definition of asymptotic entrance length.