Resumo em Inglês:

Utilization of biodegradable polymers for controlled drug delivery has gained immense attention in the pharmaceutical and medical device industry to administer various drugs, proteins and other bio-molecules both systematically and locally to cure several diseases. The efficacy and toxicity of this local therapeutics depends upon drug release kinetics, which will further decide drug deposition, distribution, and retention at the target site. Drug Eluting Stent (DES) presently possesses clinical importance as an alternative to Coronary Artery Bypass Grafting due to the ease of the procedure and comparable safety and efficacy. Many models have been developed to describe the drug delivery from polymeric carriers based on the different mechanisms which control the release phenomenon from DES. Advanced characterization techniques facilitate an understanding of the complexities behind design and related drug release behavior of drug eluting stents, which aids in the development of improved future drug eluting systems. This review discusses different drug release mechanisms, engineering principles, mathematical models and current trends that are proposed for drug-polymer coated medical devices such as cardiovascular stents and different analytical methods currently utilized to probe diverse characteristics of drug eluting devices.

Resumo em Inglês:

Recent developments in nanotechnologies have helped to benchmark carbon nanotubes (CNTs) as one of the most studied nanomaterials. By taking advantages of CNTs extraordinary physical, chemical and electronic properties, a wide variety of applications has been proposed in various engineering fields. In this short review, the contribution of CNTs is addressed in terms of sustainable environment and green technologies perspective, such as waste water treatment, air pollution monitoring, biotechnologies, renewable energy technologies, supercapacitors and green nanocomposites. Consideration of CNTs for large scale application from the aspect of cost and potential hazards are also discussed. Based on the literature studied, CNTs pose a great potential as a promising material for application in various environmental fields.

Resumo em Inglês:

This study examined the mass transfer performance in a pulsed perforated-plate extraction column with diameter of 50 mm using two different liquid systems. Mass transfer coefficients have been interpreted in terms of the axial diffusion model. The effects of pulsation intensity and dispersed and continuous phase velocities on the mass transfer performance have been investigated. Three different operating regimes, namely mixer-settler, transition, and emulsion regimes, were observed when the input energy was changed. Effective diffusivity is substituted for molecular diffusivity in the Gröber equation for prediction of dispersed phase overall mass transfer coefficients. A single correlation is derived in terms of Reynolds number, Eötvös number and dispersed phase holdup for prediction of the enhancement factor in all operating regimes. The prediction of overall mass transfer coefficients from the presented model is in good agreement with experimental results.

Resumo em Inglês:

In order to characterize the gas-liquid parameters of a down-flow jet loop reactor, experiments were carried out to study the gas holdup, bubble sizes and their distribution, mass transfer area and mass transfer coefficient. The experiments were performed in the bubbly flow regime because of its stability and uniformity. Analysis of experimental data showed an unambiguous relationship between gas holdup, bubble size, bubble size distribution and interfacial area. It has also been found that gas holdup and interfacial area is a strong function of slip velocity. The variation of interfacial area and mass transfer coefficient were also analyzed and expressed as a function of operational and geometric parameters.

Resumo em Inglês:

Fluid dynamics simulations were applied for evaluating the suspension of particles in stirred vessels. The spatial distribution of particles throughout the vessel was characterized by a single parameter, here called the suspension quality (s). Based on simulation results, a semi-empirical correlation was developed that correlated the suspension quality with the vessel geometry and solid and fluid properties, including a large variety of conditions, such as vessel and impeller diameters, impeller clearances, rotational speeds, particle densities and sizes. Comparison of the model with experimental data from the literature (Bohnet and Niesmak, 1980) suggests that the model can be extended to systems with different impeller geometries by adjustment of one single empirical parameter. The model can be used in the design of stirred vessels for the identification of the rotation speeds necessary to promote a specified suspension quality.

Resumo em Inglês:

An optimization problem regarding water removal in the press section of a paper machine is considered in this work. The proposed model tries to minimize a cost function comprising the replacement of the felts in the press section, the cost of energy to operate the press and the cost of energy in the drying section, while satisfying the constraints of water mass balance in the process. The model is classified as a mixed-integer nonlinear program (MINLP) in which the most important decisions are: a) the sequence of paper to produce or when to produce the paper; b) the need to exchange the felts; and c) when to exchange the felts. Numerical examples are presented to illustrate the performance of the model.

Resumo em Inglês:

The adsorption of reactive turquoise blue QG dye on commercial activated carbon was investigated in a batch reactor to obtain isotherm and kinetic data under different experimental conditions. The adsorbent was characterized by a FTIR method to analyze surface area and pH PZC and to identify functional groups. Experiments were conducted to obtain equilibrium data at 30°C, with the pH effect being assayed in the range of 2 to 8. Experiments were then carried out under the optimal pH condition for dye removal to obtain equilibrium data at 30°C, 45°C and 60°C. Adsorption isotherm models were used to correlate the equilibrium data. Maximum dye removal capacity was observed at a pH of 2 and temperature of 30°C. The kinetic experiments were carried out at a pH of 2 and at three different temperatures: 30°C, 45°C and 60°C. Pseudo-second-order models were used to describe the kinetics of dye adsorption.

Resumo em Inglês:

The adsorption characteristics of cadmium and nickel onto expanded perlite from aqueous solution have been investigated with respect to changes in pH of solution, adsorbent dosage, contact time and temperature of the solution. The maximum removal efficiency of Cd (II) is 88.8% at pH 6 and exposure to 10 g/L expanded perlite, while for Ni (II), it is 93.3% at the same pH and exposure to 8 g/L adsorbent. For the adsorption of both metals, the Freundlich isotherm model fitted the equilibrium data better than the Langmuir isotherm model. Experimental data are also evaluated in terms of kinetic characteristics of adsorption and it was found that the adsorption process for both metal ions follows well pseudo-second-order kinetics. Thermodynamic functions, the change of free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of adsorption are also calculated for each metal ion. The results show that the adsorption of these metal ions on expanded perlite is feasible and exothermic at 20-50°C.

Resumo em Inglês:

Enterococcus faecium, a lactic acid bacterium (LAB), was evaluated for its ability to remove copper(II) ions from water. The effects of the pH, contact time, initial concentration of copper(II) ions, and temperature on the biosorption rate and capacity were studied. The initial concentrations of copper(II) ions used to determine the maximum amount of biosorbed copper(II) ions onto lyophilised lactic acid bacterium varied from 25 mg L-1 to 500 mg L-1. Maximum biosorption capacities were attained at pH 5.0 and 6.0. Temperature variation between 20°C and 40°C did not affect the biosorption capacity of the bacterial biomass. The highest copper(II) ion removal capacity was 106.4 mg per g dry biomass. The correlation regression coefficients show that the biosorption process can be well defined by the Freundlich equation. The change in biosorption capacity with time was found to fit a pseudo-second-order equation.

Resumo em Inglês:

In this work, a study on the role of the long-range term of excess Gibbs energy models in the modeling of aqueous systems containing polymers and salts is presented. Four different approaches on how to account for the presence of polymer in the long-range term were considered, and simulations were conducted considering aqueous solutions of three different salts. The analysis of water activity curves showed that, in all cases, a liquid-phase separation may be introduced by the sole presence of the polymer in the long-range term, regardless of how it is taken into account. The results lead to the conclusion that there is no single exact solution for this problem, and that any kind of approach may introduce inconsistencies.

Resumo em Inglês:

The hydrophobicity of zeolite was achieved by a method of hydrothermal synthesis combined with acid treatment for the enhancement of CO2 absorption. The influence of zeolite before and after modification on the absorption of CO2 in three kinds of solvents (water, cyclohexane and soy bean oil) was investigated and many different effects were observed. In aqueous solution, modified zeolite showed a very remarkable enhancement with a maximum enhancement factor of 2.2 for a ratio of SiO2 and Al2O3 equal to 86. However, no measurable enhancement effect was found in cyclohexane solution by adding modified zeolite, although unmodified zeolite showed a weak increase in the absorption rate. In soybean oil, almost no change in CO2 absorption was obtained for both unmodified and modified zeolites. These results indicate that the particles with an enhancement effect for CO2 absorption rate need to have two properties, hydrophobicity and a high adsorption capacity for the solute. For predicting the enhancement factor of CO2 absorption by solid particles, a three-dimensional heterogeneous microcosmic mass transfer model was developed, in which the influence of several parameters and the interaction between particles were mainly considered. The results predicted by the present model show good conformity to experimental data, indicating that the model is rational and applicable for the enhancement process of CO2 absorption by modified zeolite particles.

Resumo em Inglês:

The ability of nano-silversol-coated activated carbon (NSSCAC) to adsorb Pb2+ from aqueous solution has been investigated through batch experiments. The adsorption of lead onto NSSCAC has been found to depend on adsorbent dose, initial concentration and contact time. The experiments were carried out at natural solution pH. Equilibrium data fitted well with the Langmuir model and Freundlich model with a maximum adsorption capacity of 23.81 mg of Pb/g of NSSCAC. The experiments showed that the highest removal rate was 92.42% for Pb2+ under optimal conditions. The sorption of Pb2+ on NSSCAC was rapid during the first 30 min and the equilibrium attained within 60 min. The kinetic processes of Pb2+ adsorption on NSSCAC were described by applying pseudo-first-order and pseudo-second-order kinetic models. The kinetic data for the adsorption process obeyed a pseudo-second-order kinetic model, suggesting that the adsorption process is chemisorption. The NSSCAC investigated in this study showed good potential for the removal of Pb2+ from aqueous solution.

Resumo em Inglês:

The adsorption behavior of rice husk for cadmium ions from aqueous solutions has been investigated as a function of appropriate equilibrium time, adsorbent dose, temperature, adsorbate concentrations and pH in a batch system. Studies showed that the pH of aqueous solutions affected cadmium removal with the result that removal efficiency increased with increasing solution pH. The maximum adsorption was 98.65% at solution pH 6, contact time 60 min and initial concentration of 25 mg/L. The experimental data were analysed by the Langmuir, Freundlich and Temkin models of adsorption. The characteristic parameters for each isotherm and related correlation coefficients have been determined. Thermodynamic parameters such as<img src="/img/revistas/bjce/v27n2/a13text1.jpg">, <img src="/img/revistas/bjce/v27n2/a13text2.jpg"> and <img src="/img/revistas/bjce/v27n2/a13text3.jpg">have also been evaluated and it has been found that the sorption process was feasible, spontaneous and exothermic in nature. The kinetics of the sorption were analysed using the pseudo-first order and pseudo-second order kinetic models. Kinetic parameters, rate constants, equilibrium sorption capacities and related correlation coefficients for each kinetic model were calculated and discussed. It was shown that the adsorption of cadmium could be described by the pseudo-second order equation, suggesting that the adsorption process is presumably a chemisorption. The rice husk investigated in this study showed good potential for the removal of cadmium from aqueous solutions. The goal for this work is to develop inexpensive, highly available, effective metal ion adsorbents from natural waste as alternative to existing commercial adsorbents.

Resumo em Inglês:

Solid waste (SW) from a biodiesel plant has been successfully used for the removal of the hazardous cationic water soluble dye - methylene blue (MB) - from an aqueous phase. Batch adsorption studies were carried out by monitoring the pH, amount of adsorbent, initial dye concentration and contact time. Attempts have also been made to monitor the adsorption process through Langmuir, Freundlich, Temkin and D-R adsorption isotherm models. Relevant thermodynamic parameters were calculated and it was found that the adsorption process was exothermic and feasible at low temperatures. The nature and randomness of the adsorption process was determined by calculating the thermodynamic parameters such as Gibbs free energy (∆Gº), change in entropy (∆Sº) and heat of adsorption (∆Hº). The kinetics of the adsorption indicates that the process is pseudo-second-order and also reveals the involvement of bulk diffusion and intraparticle diffusion mechanisms.