Avaliação hidrodinâmica e transferência de massa em uma coluna de absorção recheada para o sistema acetona-água

Abstract

The present study relates hydrodynamic data and analysis of the mass transfer behavior in a gas absorption column with glass Raschig ring type packing. The hydrodynamics of a packed column is understood as all the behavior of the flow of phases inside it, with the various varieties of phase flow rates, stirring speeds and even the geometry of the system. Thus, the intention was to study the application of absorption column for the treatment of gases, such as volatile organic compounds, describing the pressure drop and parameter definitions for this application. In the initial experimental set, the analyses were made by a liquid-gas system (water-air), using the correlations based on the literature for the dry bed test, and for the wet bed, following the Prahl's (1970) method, where 5 values of water flow rate were tested in the range from 0.72 L/min to 1.41 L/min, while the air flow rates, in this step, were based on the same ones that had been used in the dry bed tests, totaling 45 experiments. Once the hydrodynamic procedure was finished, the mass transfer process was started, and it was possible to find experimental regions, from the response surface methodology (RSM), used to evaluate the factors that influence the response variable of acetone concentration in water. For this second experimental group, related to mass transfer, a fractional statistical planning was used with three more repetitions in the central point (CP), totaling 19 experiments, counting as parameters the light phase flow rate (Qd), the heavy phase flow rate (Qc), temperature (T) and time (t), considered as independent variables. With the hydrodynamics performed, the optimal operational conditions for the system were determined, such as liquid and gas phase inlet flow rates, and head losses. Three operating regions were found, as well as the critical operating point, where the pressure difference in the column stabilizes. Also obtained were the flood point and the loading point situated between 3.0 and 4.0 L/min of the molar air flow rates. Finally, an empirical model was developed in order to correlate the column pressure drop with the operational parameters. With this model, it was noticed an average decrease of errors of 15%, when comparing results by the method of Prahl (1970) used. After the mass transfer procedure, and carrying out the experimental planning, MSR brought fundamental information that helped in the understanding of the absorption process, as an example of the significant profile of the interaction of the variables Qd and Qc, presenting a greater leap, in comparison to the other combinations.With the studied MSR two other empirical equations were developed, now aimed at finding values of acetone concentration in water and acetone removal rate.Thus, compiling the information obtained by the hydrodynamic study along with the data obtained in the mass transfer, served as a behavioral database for the column, thus making it possible to develop two new empirical equations, as well as to prove the effectiveness of the analysis methods exposed in the literature based on the comparison of results. This study brought an opportunity for continuity to the gas treatment project, as planned in the research general project.