Reginaldo Guirardello

Preparative chromatography of xylanase using expanded bed adsorption

Expanded bed adsorption was used to purify a marketable xylanase often used in the kraft pulp bleaching process. Experiments in packed and expanded beds were carried out mainly to study the adsorption of xylanase on to a cationic adsorbent (Streamline SP) in the presence of cells. In order to study the presence of cells, a Bacillus pumilus mass (5% wet mass) was mixed with the enzyme extract and submitted to an expanded bed adsorption system. One xylanase was purified to homogeneity in the packed bed. However, the 5% cell content hampered purification.

Biosorption of binary mixtures of Cr(III) and Cu(II) ions by Sargassum sp

The adsorption of two metal ions, Cr(III) and Cu(II), in single-component and binary systems by Sargassum sp., a brown alga, was studied. Equilibrium batch sorption studies were carried out at 30oC and pH 3.5. Kinetic tests were done for a binary mixture (chromium + copper) for a contact time of 72 hours to guarantee that equilibrium was reached. The monocomponent equilibrium data obtained were analyzed using the Langmuir and Freundlich isotherms. The binary equilibrium data obtained were described using four Langmuir-type and Freundlich isotherms. The F-test showed a statistically significant fit for all binary isotherm models. The parameters for isotherms of the Langmuir-type were used to determine the affinity of one metal for the biosorbent in the presence of another metal. The chromium ion showed a greater affinity for Sargassum sp. than the copper ion.

Modelling of a slurry bubble column reactor applied to the hydroconversion of heavy oils

Abstract This work uses a computational fluid dynamics approach for the simulation of a slurry bubble column reactor, applied in the hydroconversion of heavy oils under severe temperature and pressure operating conditions. Simulations are carried out in two steps: first, the fluid dynamics is determined by the calculation of the pressure drop in the bed and the radial distribution of gas and slurry for the holdup, effective viscosity (dispersion) and velocity. Then a thermal cracking reaction is simulated and the oil conversion to lighter fractions such as gasoil, diesel, naphtha and gases in obtained. Results show the recirculation pattern in the reactor which leads to a high degree of backmixing in the slurry phase. Temperature and liquid residence time are found to have a great influence in the oil cracking conversion.

Phase stability analysis of liquid-liquid equilibrium with stochastic methods

Minimization of Gibbs free energy using activity coefficient models and nonlinear equation solution techniques is commonly applied to phase stability problems. However, when conventional techniques, such as the Newton-Raphson method, are employed, serious convergence problems may arise. Due to the existence of multiple solutions, several problems can be found in modeling liquid-liquid equilibrium of multicomponent systems, which are highly dependent on the initial guess. In this work phase stability analysis of liquid-liquid equilibrium is investigated using the NRTL model. For this purpose, two distinct stochastic numerical algorithms are employed to minimize the tangent plane distance of Gibbs free energy: a subdivision algorithm that can find all roots of nonlinear equations for liquid-liquid stability analysis and the Simulated Annealing method. Results obtained in this work for the two stochastic algorithms are compared with those of the Interval Newton method from the literature. Several different binary and multicomponent systems from the literature were successfully investigated.

Simultaneous calculation of chemical and phase equilibria using convexity analysis

Chemical and phase equilibria were considered for closed multicomponent reactive systems at: (a) constant pressure and temperature; (b) constant pressure and enthalpy. Equilibrium at constant P and T was found by minimization of G, while equilibrium at constant P and H was found by maximization of S or minimization of −S, all with respect to the number of moles of each component in each phase. Both cases could be handled as optimization problems, satisfying the restrictions imposed by mole or atom balances, and non-negativity of number of moles. Convexity analyses were carried out, and the conditions were found in order to guarantee global minimum, for one liquid phase, one gas phase, and a number of solid phases. The minimum point was then found either by analytical methods or by direct minimization methods. These strategies were tested for a number of cases, with good results.

Application of interval analysis for gibbs and helmholtz free energy global minimization in phase stability analysis

The tangent plane criterion has become important for a correct solution evaluation phase and chemical of equilibrium problem. This method, applicable to single and multiphase systems, is mainly used for a single equation of state modeling all phases involved. The present work is mainly concerned with the application of interval analysis methods for global energy minimization in high-pressure phase stability problems. Two approaches are applied: (i) the Gibbs free energy global minimization under conditions of constant temperature and pressure and (ii) the Helmholtz free energy density global minimization under conditions of constant temperature and volume. Five case studies, one ternary and four binary systems, are analyzed in connection with the Peng-Robinson equation of state (PREOS) model. Five more case studies, for the CO2 + trans-2-hexen-1-ol system at high pressures, are used to compare different methods of phase equilibrium calculation with the approach using interval analysis. Finally, a complex system, clove oil + CO2, is analyzed. The results indicate that the interval analysis method is robust and reliable for all the problems studied.

Oxidative reforming of methane for hydrogen and synthesis gas production: Thermodynamic equilibrium analysis

Abstract A thermodynamic analysis of methane oxidative reforming was carried out by Gibbs energy minimization (at constant pressure and temperature) and entropy maximization (at constant pressure and enthalpy) methods, to determine the equilibrium compositions and equilibrium temperatures, respectively. Both cases were treated as optimization problems (non-linear programming formulation). The GAMS® 23.1 software and the CONOPT2 solver were used in the resolution of the proposed problems. The hydrogen and syngas production were favored at high temperatures and low pressures, and thus the oxygen to methane molar ratio (O 2 /CH 4 ) was the dominant factor to control the composition of the product formed. For O 2 /CH 4 molar ratios higher than 0.5, the oxidative reforming of methane presented autothermal behavior in the case of either utilizing O 2 or air as oxidant agent, but oxidation reaction with air possessed the advantage of avoiding peak temperatures in the system, due to change in the heat capacity of the system caused by the addition of nitrogen. The calculated results were compared with previously published experimental and simulated data with a good agreement between them.

Modeling and simulation of a pseudo-three-phase slurry bubble column reactor applied to the process of petroleum hydrodesulfurization

Abstract This work presents a new CFD model for the hydrodesulfurization process in the petroleum industry. The new model considers the loss of effectiveness of the catalyst by coupling a model that considers the physical structure of the catalyst. The hydrodesulfurization process takes place in a pseudo-three-phase fluidized-bed slurry bubble column reactor with liquid and gas flowing upwards. This reactor presents a transient behavior for the catalytic effectiveness due to the obstruction of the catalyst pores, caused mainly by parallel reactions of hydrodemetalization acting on the catalyst. The emphasis of this work is the introduction of a kinetic model for the reactivity reduction of the catalyst inside slurry bubble column reactors. The hydrodynamic model is simple and adopts an Eulerian–Eulerian approach, where the momentum and mass conservation equations are used to describe the two-phase fluid dynamic fields. The k – ɛ model is used to account for turbulence. The kinetic model considers the reactions controlled by diffusion and occurring on the catalyst pores, which are obstructed along the process by the hydrodemetalization by-products. The model presented in this work allows for an assessment of the influence of the operational conditions of the reactor, such as liquid and gas feed velocities, as well as catalyst properties. The estimation of the yield of the process takes into account the transient activity of the catalyst.

Modeling vapor liquid equilibrium of ionic liquids + gas binary systems at high pressure with cubic equations of state

Ionic liquids (IL) have been described as novel environmentally benign solvents because of their remarkable characteristics. Numerous applications of these solvents continue to grow at an exponential rate. In this work, high pressure vapor liquid equilibria for 17 different IL + gas binary systems were modeled at different temperatures with Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state, combined with the van der Waals mixing rule with two binary interaction parameters (vdW-2). The experimental data were taken from the literature. The optimum binary interaction parameters were estimated by minimization of an objective function based on the average absolute relative deviation of liquid and vapor phases, using the modified Simplex algorithm. The solubilities of all gases studied in this work decrease as the temperature increases and increase with increasing pressure. The correlated results were highly satisfactory, with average absolute relative deviations of 2.10% and 2.25% for PR-vdW-2 and SRK-vdW-2, respectively.

A CFD model for pollutant dispersion in rivers

Studies have shown that humankind will experience a water shortage in the coming decades. It is therefore paramount to develop new techniques and models with a view to minimizing the impact of pollution. It is important to predict the environmental impact of new emissions in rivers, especially during periods of drought. Computational fluid dynamics (CFD) has proved to be an invaluable tool to develop models able to analyze in detail particle dispersion in rivers. However, since these models generate grids with thousands (even millions) of points to evaluate velocities and concentrations, they still require powerful machines. In this context, this work contributes by presenting a new three-dimensional model based on CFD techniques specifically developed to be fast, providing a significant improvement in performance. It is able to generate predictions in a couple of hours for a one-thousand-meter long section of river using Pentium IV computers. Commercial CFD packages would require weeks to solve the same problem. Another innovation inb this work is that a half channel with a constant elliptical cross section represents the river, so the Navier Stokes equations were derived for the elliptical system. Experimental data were obtained from REPLAN (PETROBRAS refining unit) on the Atibaia River in Sao Paulo, Brazil. The results show good agreement with experimental data.