José Roberto Nunhez

Effect of immobilized cells in calcium alginate beads in alcoholic fermentation

Saccharomyces cerevisiae cells were immobilized in calcium alginate and chitosan-covered calcium alginate beads and studied in the fermentation of glucose and sucrose for ethanol production. The batch fermentations were carried out in an orbital shaker and assessed by monitoring the concentration of substrate and product with HPLC. Cell immobilization in calcium alginate beads and chitosan-covered calcium alginate beads allowed reuse of the beads in eight sequential fermentation cycles of 10 h each. The final concentration of ethanol using free cells was 40 g L-1 and the yields using glucose and sucrose as carbon sources were 78% and 74.3%, respectively. For immobilized cells in calcium alginate beads, the final ethanol concentration from glucose was 32.9 ± 1.7 g L-1 with a 64.5 ± 3.4% yield, while the final ethanol concentration from sucrose was 33.5 ± 4.6 g L-1 with a 64.5 ± 8.6% yield. For immobilized cells in chitosan-covered calcium alginate beads, the ethanol concentration from glucose was 30.7 ± 1.4 g L-1 with a 61.1 ± 2.8% yield, while the final ethanol concentration from sucrose was 31.8 ± 6.9 g L-1 with a 62.1 ± 12.8% yield. The immobilized cells allowed eight 10 h sequential reuse cycles to be carried out with stable final ethanol concentrations. In addition, there was no need to use antibiotics and no contamination was observed. After the eighth cycle, there was a significant rupture of the beads making them inappropriate for reuse.

Three-dimensional modeling of fluid catalytic cracking industrial riser flow and reactions

Abstract A three-dimensional and two-phase flow model to predict the dynamic behavior of a fluid catalytic cracking (FCC) industrial reactor was developed in this work. The study took into account heat transfer and chemical reactions. A four-lump model was proposed to represent the catalytic cracking reactions in which the heavy oil (gas oil) is converted into gasoline and light hydrocarbon gases. Gas acceleration inside the reactor due to molar expansion and a model to describe undesirable catalyst deactivation by coke deposition on its surface were also considered. An Eulerian description of the phases was used to represent the two-phase flow. A commercial CFD code (Ansys CFX version 11.0) was used to obtain the numerical data. Appropriate functions were implemented inside the CFX code to model the heterogeneous kinetics and catalyst deactivation. Results show nonuniform tendencies inside the reactor, emphasizing the importance of using three-dimensional models in FCC process predictions.

Software para modelagem de dispersão de efluentes em rios

This work presents a three-dimensional model for the dispersion of effluents in rivers using Computational Fluid Dynamics (CFD) techniques. There are several models in the literature, some of which even analyze complex flows. They are however restricted to small river sections. The main contribution of this work is that it proposes a new software capable of predicting the dispersion of effluents in very large open channels. The model is very fast, an unusual feature of CFD models. Due to this, it is possible to predict the dispersion of substances in long sections of rivers with some kilometers in extension. Moreover, multiple emissions can be analyzed by the model, allowing its use as a predictive tool to analyze and guide management decisions on future industrial installations near rivers. Results for the dispersion of an inert emission in a river near Campinas (Brazil) were used to validate the model.

A simple two-dimensional method for orthogonal and nonorthogonal grid generation

Abstract This work presents a new and simple formulation of a two-dimensional grid generation method that uses a special cubic spline algorithm developed to generate the analytical representation of arbitrary boundaries for two-dimensional domains. These cubic spline functions used for the fitting of points belonging to a boundary are special because they are generated based on a procedure that minimizes the length of the cubic spline functions defining the boundary. This avoids unwarranted inflection points common to cubic spline functions. Since the piecewise spline functions are cubic, they can easily accommodate contours of any shape, giving an analytical representation for the boundaries. The streamlines are constructed based on the boundaries generated by the spline model and the potential lines are built using the orthogonality principle. This mesh-generating model was developed for a two-dimensional two-phase computational fluid dynamic (CFD) model to study oil spills. The model, however, can be extended to three dimensions and some comments are presented in Section 3.