RESUMO

Simulation and rigorous design of industrial dryers combine a large number of models, which feed three fundamental balances: (1) mass; (2) energy; and (3) quantity of movement of the material through the dryer. Many of these models represent physical phenomena affecting the three balances at the same time, which makes these calculations extremely complex, hence, accurate models are essential. The hypothesis that the kinetic stage of drying of any material culminates in the thermodynamic moisture equilibrium between solid and drying gas has been in effect for many years. However, recent findings show that there is a transition stage between the kinetic stage and the thermodynamic equilibrium, which, experimentally, looks like an equilibrium. The beginning of this transition stage or dynamic pseudo-equilibrium stage would mark the end of the drying kinetics models, which has been named as the dynamic pseudo-equilibrium moisture contents (Xdpe). The non-observance of this phenomenon presupposes a model limited in its prediction capacity, especially in the last stages of drying and even more so at low drying temperatures. As a consequence, sizes of industrial dryers could be underestimated during the simulation and rigorous design process, or underestimate drying times, in batch dryers. On the other hand, the optimal conditions may never be found, during the optimization of existing industrial drying processes. The objective of this work is to present the procedure to determine Xdpe, during the experimental determination of drying curves of any material. Likewise, to propose the practical moisture ratio, which uses Xdpe, instead of the equilibrium moisture, to be used in the modeling of the drying kinetics.•The drying process is divided into three stages: kinetic, transition, and equilibrium.•The dynamic pseudo-equilibrium moisture content divides the kinetic and the transition stages.•The practical moisture ratio should be used in rigorous industrial dryer design calculations.

RESUMO

Electrochemically assisted photocatalysis (by electronic drainage) is a highly promising method for disinfection of water. In this research, the efficiency of photolytic oxidation using UV-A radiation and electrochemically assisted photocatalysis (with electric potential of 1.5 V) was studied by using electrodes prepared by thermal treatment and doped with silver, for inactivation of Escherichia coli and Staphylococcus aureus. The Chick-Watson microorganism inactivation model was applied and the electrical energy consumption of the process was calculated. It was observed no significant inactivation of microorganisms when UV-A light or electric potential were applied separately. However, the electrochemically assisted photocatalytic process, with Ag-doped electrode completely inactivated the microbial population after 10 (E. coli) and 60 min (S. aureus). The best performing non-doped electrodes achieved 52.74% (E. coli) and 44.09% (S. aureus) inactivation rates after 60 min. Thus, electrochemically assisted photocatalytic activity was not only effective for the inactivation of microorganisms, but also notably low on electrical energy consumption during the treatment due to small current and low electric potential applied.

Assuntos

RESUMO

In the present study, pressure mediated microanalysis (PMMA), a fast, convenient and efficient capillary electrophoresis (CE) method was developed for studying enzyme kinetics of tyrosinase and inhibition kinetics of kojic acid, a model inhibitor of tyrosinase. The enzymatic reaction conditions and CE conditions were optimized in order to obtain high enzyme activity and short analysis time. By PMMA, only the product could be detected at 475 nm, and no voltage was applied to separate the product from the reaction mixture thus greatly simplifying the optimization procedure. The spectrophotometric assay and electrophoretically mediated microanalysis (EMMA) were also performed to validate the developed method. With the present method, the Michaelis-Menten constant (Km) was calculated to be 1.347 mM for tyrosinase. The inhibition constant of kojic acid to free tyrosinase (KI) and kojic acid to tyrosinase/L-DOPA complex (KIS) were calculated to be 36.64 and 74.35 µM, respectively, and the half-maximal inhibitory concentration (IC50) was determined to be 46.64 µM for kojic acid. The developed method is fast and convenient for studying enzyme kinetics, inhibition kinetics and further screening enzyme inhibitors.

Assuntos