Neuman Solange de Resende

Modeling and optimization of the combined carbon dioxide reforming and partial oxidation of natural gas

The optimization of the combined carbon dioxide reforming and partial methane oxidation over a 1% Pt/-Al2O3 catalyst was studied in order to produce synthesis gas with hydrogen/carbon monoxide ratio close to 1, for applications in metallurgical and polycarbonates processes and for production of oxygenated compounds and hydrocarbons. The study was performed with the help of experimental design and two mathematical modeling approaches: empirical and phenomenological. Empirical polynomial models were employed to analyze the effects of the process variables on the response factors and the final correlation coefficients obtained were above 95%. The phenomenological model was obtained from individual mass balances and the obtained correlation coefficients were above 95% for CH4 and N2, 90% for CO2 and H2O and near 70% for H2 and CO. The empirical modeling approach was found to be more efficient, simpler and led to better results than those obtained with the phenomenological model approach. Therefore, the empirical modeling was used for optimization of the process operation conditions. At an oxygen/methane ratio of 0.55 gmol/gmol and temperature of 950 ◦ C, optimized process conditions were obtained with complete methane conversion, maximum carbon monoxide selectivity of 43% and minimum hydrogen/carbon monoxide ratio of 1.3, in absence of water.

Analysis of experimental errors in catalytic tests for production of synthesis gas

The proper determination of experimental errors in catalytic processes may be very important because experimental errors can exert a major impact upon the analysis of experimental results. For this reason, the influence of temperature upon the experimental errors observed during the combined carbon dioxide reforming and partial oxidation of methane over Pt/-Al2O3 is studied here. It is shown that fluctuations of output stream compositions may decrease more than one order of magnitude as reactor temperature increases in the range from 600 to 1100 ◦ C during catalytic tests. Additionally, it is shown that the covariance matrix of composition measurements is not diagonal, as usually assumed, and may change very significantly with the experimental conditions. Therefore, experimental errors should not be regarded as constant and covariance matrices should not be assumed to be diagonal a priori for kinetic model building and parameter estimation. It is also shown that the covariance matrix may contain significant amount of information about the reaction mechanism, which can be used for model building and interpretation of kinetic experiments. Particularly, it is shown that the actual experimental error may be much smaller than usually obtained when covariance terms are neglected and that fluctuation of catalyst activity may concentrate most of the experimental fluctuations observed experimentally.

Nanostructured screen-printed electrodes based on titanate nanowires for biosensing applications

This work demonstrates the successful modification of screen-printed electrodes using functionalized titanate nanowires for producing a peroxide biosensor. Titanate nanowires were synthesized by the hydrothermal method and characterized using physico-chemical techniques. The surface of the nanowires was modified with (3-aminopropyl)trimethoxysilane and glutaraldehyde to immobilize horseradish peroxidase through covalent bound, obtaining a surface coverage of 1.62mg of enzyme/m2. The surface of screen-printed carbon electrodes was modified with peroxidase-containing nanowires. Cyclic voltammetry and chronoamperometry were employed to study the electrochemical properties of the nanostructured electrode. A low hydrogen peroxide reduction potential around -0.98V (vs Ag, pH7.0) was observed, with linear response in the range of 40 to 560μmolL-1, detection limit of 10.7μmolL-1 and good stability. Reproducibility relative standard deviation was as low as 4.7%. For repeatability, deviation was 3.3%.

Modelling of Hg0 Removal from Gaseous Streams and its Fixation in Hydroxyapatite-Based Adsorbents Modified with Copper Sulphide

In this work, a mathematical model of a fixed-bed process for elemental mercury removal from gaseous streams is proposed. Advective and diffusive processes were taken into account in the macroscopic mass balance along the bed, and diffusive process was considered in the microscopic mass balance inside the adsorbent particle in which the adsorption process occurs. In addition, a chemical reaction term was used to represent the mercury fixation by the adsorbent. The proposed model was implemented in the Environment for Modelling, Simulation and Optimization dynamic simulator. Model parameters were estimated based on experimental breakthrough curves, by minimizing the least-square function. The model satisfactorily described two experimental breakthrough curves of mercury removal using adsorbents with different preparation methods, both with high mercury fixation capacity. The proposed mathematical model was also able to consistently describe the mercury concentrations in the bed and in the particle.

Activity of Horseradish Peroxidase Adsorbed onto Titanate Nanowires

Immobilization of horseradish peroxidase (HRP) onto titanate nanowires (TNWs) was investigated using different strategies. TNWs were synthesized by a hydrothermal method and characterized by scanning electron microscopy, X-ray diffraction, nitrogen physisorption (77K) and Fourier transform infrared spectroscopy. Free HRP was stable and active in a wide range of pH with optimal activity at 7.0. The Km of HRP with 4-aminoantipyrine and H2O2 as substrate was 0.77 ± 0.25 mmol l−1. Immobilization strategies studied were non-specific adsorption and covalent coupling through amine groups. Adsorption isotherms were well fitted by the Langmuir–Freundlich model. The coverage of TNWs containing HRP adsorbed by covalent coupling was 1.56 mg HRP m−2 and the residual enzymatic activity was approximately 40%. The enzymatic activity of free HRP and immobilized HRP was monitored as a function of storing time. The results confirm that the enzyme is firmly attached to the TNW surface through covalent binding, constituting a very promising platform for a variety of applications such as in biosensing.

Synthesis and characterization of titanium oxide monolayer

The structural evolution of titanium oxy-hydroxide overlayers was studied for 3% and 6%TiO2/Al2O3, prepared by grafting the γ-Al2O3 support at different temperature of calcination. Results showed that during calcination the oxy-hydroxide is dehydrated at around 550 K; the γ -Al2O3 support hinders the crystallization of TiO2 anatase structure. The titanium oxide is well dispersed on the alumina surface, as confirmed by TEM and XPS data. UV-visible results showed that dried materials have small polymerization degree. A linear correlation is proposed between the position of Ti charge transfer band and the number of titanium atoms in the second coordination sfhere of titanium. This leads to the model that polymeric units [Ti(OR)4]n are grafted without modification on the support; but after calcination, linear or cyclic chains of edge-sharing TiO6 octahedra are linked to the support.