Giane Gonçalves Lenzi

Molecular Orientation of a Nematic Between Concentric Cylinders: Weak Anchoring Situation

The molecular orientation of a nematic sample limited by two concentric cylinders is theoretically investigated. The surfaces are assumed as having an inhomogeneous distribution of easy directions. The results are found in the one-constant approximation, in the presence of an external electric field, for weak anchoring of the molecules at the surfaces. In order to validate our approximations, the analytical results are compared with the ones obtained by numerically solving the non-linear bulk differential equation for the tilt angle profile subjected to non-linearized boundary conditions. We show that the agreement improves as the extrapolation length increases.

Simulation Studies of Steam Reforming of Methane using Ni-Al2O3 Catalysts

This paper reports the results of reforming methane into synthesis gas using industrial Ni-Al2O3 catalyst (75% NiO wt.) and Ni-Al2O3 produced by the sol gel method (8% Ni wt.). A mathematical investigation on the performance of a one-dimensional model of catalytic conventional fixed-bed reactor was developed and implemented for the process. The results indicated that the industrial catalyst favored the water gas shift (WGS) reaction increasing CO2 production. However in temperatures of 773 and 973 K the yield (H2/CH4,reacted) was more efficient for the sol-gel catalyst. This result is possibly due to the different characteristics as specific surface area and temperature reduction. The model validation for the adjustment parameters U and a1 was more efficient for temperature profiles (2% error) than for mole fraction (10% error).

Comparision of photocatalysis and photolysis processes for arsenic oxidation in water

The oxidation of As(III) to As(V) in aqueous solution was evaluated using heterogeneous photocatalysis and photolysis. The influence of TiO2 as catalyst in different crystalline (rutile, anatase) and commercial forms was evaluated in a batch reactor and an insignificant difference was observed between them. The process by photocatalysis reached up to 97% As(III) oxidation and no significant difference was observed comparing to results obtained by photolysis. The photolysis experiments (UV radiation only), also carried out in a batch system, showed a high oxidation rate of As(III) (90% in 20min). The influence of different matrices (well water, river water and public water supply) were evaluated. Additionally, the effect of As(V) concentration, generated during the oxidation process, was studied. Continuous photolysis experiments using only UV radiation were performed, resulting in a high As(III) oxidation rate. Using a flow rate of 5mLmin-1 and an initial concentration of As(III) 200µgL-1, gave an oxidation percentage of As(III) of up to 72%, showing a simple and economical alternative to the oxidation step of As(III) to As(V) in the treatment of water contaminated with arsenic.

BIOSSORPTION OF Pb(II) BY URUCUM SHELLS (Bixa orellana) IN AQUEOUS SOLUTIONS: KINETIC, EQUILIBRIUM AND THERMODYNAMIC STUDY

This study describes the application of new and low cost biosorbent, shells of urucum (Bixa Orellana), for removal of lead ions (Pb(II)) from water solution. The urucum shells were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Batch adsorption experiments were performed in order to evaluate the effect of pH, agitation speed, adsorbent dosage, contact time, temperature, presence of interfering ions and matrix effect on the adsorption of process. The kinetics of biosorption followed pseudo-second-order model. Langmuir and Freundlich isotherm models were applied to describe the biosorption of Pb(II) by urucum shells. The Langmuir model showed better fit and the estimated biosorption capacity was 43.6 mg g-1. The negative Gibbs free energy, ΔG°, confirms the spontaneous nature and positive value of enthalpy, ΔH°, the endothermic character of the process. Furthermore, we also performed an evaluation of matrix and others ions effect on the biosorption process.

Biosorption and Diffusion Modeling of Pb(II) by Malt Bagasse

The removal of Pb(II) from water by biosorption processes onto malt bagasse was investigated and the kinetic and thermodynamic parameters were obtained; additionally a diffusion modeling was proposed. The characterization of malt bagasse was performed by FTIR and SEM/EDS. The experiments were conducted in batch system and an experimental design based response surface methodology was applied for agitation speed and pH optimization. The kinetics of biosorption followed pseudo-second-order model and the temperature of the process affected the biosorption capacity. Isotherm models of Langmuir, Freundlich, and Elovich were applied and the Langmuir model showed better fit and the estimated biosorption capacity was 29.1 mg g−1. The negative values obtained for and positive values of confirm, respectively, the spontaneous and endothermic nature of the process. The diffusion modeling was performed based on experiments in the absence of agitation to investigate the influence of the biosorbent on the sorption process of Pb(II) ions.