Scielo RSS <![CDATA[Brazilian Journal of Chemical Engineering]]> vol. 17 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<STRONG>Liquid-liquid extraction of biomolecules in downstream processing - A review paper</STRONG>]]> Economic analysis shows that protein separation and purification are a very important aspect of biomolecules production and processing. This is particularly true for protein processing which, because of the complexity of the starting material, often requires many steps to reach the levels of purity required for medical and food applications. The separation specialists' task is to develop safe and simple processes to achieve products with a high level of purity. On a large scale, chromatography of proteins is not an easily applied method, although on a laboratory scale it is very effective and relatively simple. When it is scaled up, shortcomings such as discontinuity in the process, slow protein diffusion and large pressure drops in the system are seen. For these reasons a substantial research effort has been directed toward the use of aqueous two-phase systems (ATPSs) to replace the initial steps in protein purification and chromatography. This article reviews the chronology and main ATPS fundamentals and discuss the broader applications of this type of system in the extraction and separation of biomolecules. <![CDATA[<STRONG>Fluid dynamical considerations on heat exchanger networks</STRONG>]]> The synthesis and analysis of heat exchanger networks are issues of great industrial interest due to the possibilities of decreasing plant costs, through the reduction of the utilities consumption and/or the number of equipments, in a grassroot design or retrofitting an existent network. The present paper explores a new design algorithm based on the Total Annual Cost (TAC) optimization for a thermal equipment, with mean tubeside and shellside flow velocities constraints, studying also the influence of pumping cost in the network’s final cost. <![CDATA[<STRONG>Liquid-liquid extraction by reversed micelles in biotechnological processes</STRONG>]]> In biotechnology there is a need for new purification and concentration processes for biologically active compounds such as proteins, enzymes, nucleic acids, or cells that combine a high selectivity and biocompatibility with an easy scale-up. A liquid-liquid extraction with a reversed micellar phase might serve these purposes owing to its capacity to solubilize specific biomolecules from dilute aqueous solutions such as fermentation and cell culture media. Reversed micelles are aggregates of surfactant molecules containing an inner core of water molecules, dispersed in a continuous organic solvent medium. These reversed micelles are capable of selectively solubilizing polar compounds in an apolar solvent. This review gives an overview of liquid-liquid extraction by reversed micelles for a better understanding of this process. <![CDATA[<STRONG>Measurement of the electrostatic charge in airborne particles</STRONG>: <STRONG>I - development of the equipment and preliminary results</STRONG>]]> The design and construction of a equipment capable of measuring the electrostatic charges in aerosols, named the electrostatic charge classifier, were carried out. They were based on the concept of particle electromobility and the charge classifier was intended to classify the nature and the distribution of electrostatic charges as a function of particle size. The resulting piece of equipment is easy to dismount, which facilitates its cleaning and transport, and easy to operate. Early results indicate that the values of electrostatic charge measured on test particles are inside the range reported in the literature, indicating the adequacy of the technique utilized. <![CDATA[<STRONG>New robust stable MPC using linear matrix inequalities</STRONG>]]> This paper addresses the stability of Model Predictive Control (MPC) with output feedback. The proposed controller uses a new state-space formulation of the system, and the control problem is presented as an LMI optimization problem. The stability condition for the closed loop is included as a Lyapunov inequality. The resulting optimization problem becomes nonlinear with the inclusion of the stabilizing condition. A suboptimal solution is developed and the problem reduces to a pair of coupled LMI problems. An iterative solution that converges to a stable output feedback gain is proposed. A polytopic set of process models can be considered. A simulation example is included in the paper and shows that the proposed strategy eliminates the usual practice of enforcing robustness by detuning the MP controller. <![CDATA[<B>Preparation of silica with controlled pore sizes for enzyme immobilization</B>]]> A simple method for the preparation of silica with controlled pore size, for use as a support for the immobilization of enzymes, is described in this article. Using sodium silicate and hydrochloric acid, a microporous silica was obtained that was then submitted to a hydrothermal treatment, resulting in macroporous silica suitable for enzyme immobilization. Suitability of the macroporous silica as a support depends on the method chosen for its preparation, which will determine pore volume and the effect of hydrothermal treatment on pore size. The pore volume of the support was 0.8-0.9 cc/g and the average pore size, controlled by the hydrothermal treatment, was in the range of 16 to 75 nm. The enzyme amyloglucosidase was used for the immobilization studies. <![CDATA[<STRONG>Modelling and simulation of the hydrocracking of heavy oil fractions</STRONG>]]> This work presents a model to describe the behavior of the concentration of constituents of heavy fractions from petroleum during the hydrocracking process. An approximation based on pseudocomponents or lumps is adopted due to the complexity of the mixture. The system is modeled as an isothermal tubular reactor with an axial dispersion, where the hydrogen flows upward concurrently with the oil while the solid catalyst particles stay inside the reactor in an expanded bed regime. Simulations are carried out for different values of liquid superficial velocity, reactor length and degree of mixing (Peclet number). <![CDATA[<STRONG>On the acidity and/or basicity of USY zeolites after basic and acid treatment</STRONG>]]> The isopropanol decomposition reaction was used to evaluate the catalytic activity of ultrastable (USY) zeolites with different degrees of dealumination, treated in strongly alkaline medium at various temperatures and contact times. This treatment resulted in the reinsertion of non-framework aluminium, a result of the ultrastabilization process. The samples obtained were also submitted to an acid treatment, leaching the non-framework aluminium that had not been reinserted. The results obtained at 723K showed a large reduction in the acidic activity of the alkaline-treated zeolite, as the treatment conditions became more severe (the longer the treatment time or the higher the temperature, the higher the degree of dealumination). On the other hand, treated samples displayed some isopropanol dehydrogenation activity (basic sites). However, this activity was not very significant and did not depend on the alkaline treatment or ultrastabilization conditions used. The effect of reaction temperature and acid leaching on activity is also shown. <![CDATA[<STRONG>Influence of hydrothermal treatment on the acid and redox functions of a Ga/HZSM5 catalyst </STRONG>]]> After steaming at 530° C for 30 minutes and for 6 hours, a Ga/HZSM5 catalyst was characterized by three model reactions (meta-xylene isomerization, propane aromatization and methylcyclohexane transformation). The activity and selectivity of this catalyst were compared to those of a fresh Ga/HZSM5 catalyst. It was demonstrated that hydrothermal treatment provokes a significant decrease in the dehydrogenation activity of the gallium species and a small decrease in the protonic acidity of the catalyst. <![CDATA[<STRONG>A study of the desorption isotherms of lentils</STRONG>]]> The aim of this work was to analyze the main equilibrium equations used for grains to find the best way to represent the equilibrium conditions between lentil and air. The experimental study was based on the static method using saturated salt solutions. We developed criteria for distinguish between some existing equations used for grains. To distinguishing between these equations we explored some nonlinearity measures. The results obtained showed that the Halsey modified equation was the best model in terms of nonsignificance for bias and nonlinearity measures. <![CDATA[<STRONG>Effect of magnetic field on the crystallization of zinc sulfate</STRONG>]]> The effect of magnetic field on the crystallization of diamagnetic zinc sulfate was investigated in a series of controlled batch cooling experiments. Zinc sulfate solutions were exposed to magnetic fields of different intensities, up to a maximum of 0.7T. A clear influence of magnetic field on the following zinc sulfate crystallization parameters was found: an increase in saturation temperature, a decrease in metastable zone width, and an increase in growth rate and average crystal size. These effects were observed for the diamagnetic zinc sulfate, but not in similar, previously reported experiments for paramagnetic copper sulfate.