Coeficientes de atividade a diluição infinita aplicados ao estudo da poluição aquática

Abstract

A correction to the modified UNTFAC model (GMEHLING et al. (1993)) is presented for the calculation of infinite dilution activity coefficient, for values above 100, common for hydrophobics Chemicals in water, that can present y® of the order of 108. Data of y® are specially important in environmental calculations, because distribution of long-lived Chemicals in the environment can be guessed knowing only two quantities: its vapor pressure and its infinite dilution activity coefficient. Also, for the design of separation equipments (for example, distillation columns and absorption towers) and for the removal of Chemical poluttants of diluted Solutions, the infinite diluition activity coefficients exactly provide big utility information, as it is the case of getting binary parameters for the model of the excess Gibbs energy for liquid phase. In this work, a correction for the combinatorial part of the modified UNIFAC model (GMEHLING et al. (1993)) was achieved through the inclusion of hydrophobics parameters for selected groups, that were adjusted through experimental values of y® from the literature. These parameters were introduced to take into account hydrophofics effects. The model with the proposed correction was used to calculate/predict y°° for a number of chlorinated hydrocarbons (the most common contaminant found at hazardous waste sites), n-alkanes, ketones and esteres. The calculated values were compared with experimental data and with estimated data using original UNIFAC (FREDENSLUND et al. (1975)) and modified UNIFAC (GMEHLING et al. (1993)). Data of solubility in water for some chlorinated hydrocarbons were also calculated, using the model, and compared with experimental values. The results gotten through the present model are in good accordance with the experimental data. The total mean relative deviation for mixtures of chlorinated hydrocarbons and water, n-alkanes and water, ketones and water, esteres and water were about 4,5% - 4,4% - 7,1% - 1,5% respectively and the total mean absolute deviation for data of solubility for chlorinated hydrocarbons was about 5 . 10"4.