Caracterização físico-química e modelagem estatística de diafragmas de células eletrolíticas utilizadas para produção de cloro-soda.

Abstract

In the chlor-alkali industry, the diaphragm technology is still known for being the one that most contributes in industrial production. With asbestos diaphragms, asbestos with polymer diaphragms, or non-asbestos diaphragm, the diaphragm is the major component of the electrolytic cell, being responsible for the operational security and for the process and energetic efficiency. Nevertheless, the way in which the diaphragm is manufactured did not suffer any significant change since the first diaphragm deposited on cathode of the electrolytic cell, around 1920. The most significant aspect of this work is the quantitative understanding of the influence of the effects that the variables involved in the process of deposition have over the performance of the diaphragm in operation. The major variables involved in this process that were considered in this work are: the specific weight of the diaphragm, the relation between the length of the asbestos fibers and the concentrations of NaCl, NaOH and the polymer. With the use of well known statistics techniques, through which we obtained a statistic mathematical model, it was possible to established quantitative relations between these variables and the parameters that characterize the diaphragm, such as the MacMullin number and permeability. The statistic model presented a correlation coefficient of approximately 100% of certainty. Following this, the parameters calculated with the help of the statistic model were applied to an existing mathematical model which was developed specifically for the electrolytic diaphragm cell. The mathematical model calculates the current efficiency and the concentration of NaOH produced in the catholyte of the cell. Therefore, it was possible to compare the calculated values of the current efficiency and the concentration of NaOH with the values measured in a group of 34 cells in operation in an industrial scale. The results show that, for the current efficiency, 75% of the measured data are in accordance to the data calculated in a range of ± 5% of certainty. For the concentration of NaOH, 74% of the measured data are in accordance to the data calculated in a range of ± 10% of certainty. Therefore, it was possible to establish relations between the variables involved in the process of deposition with the performance of the diaphragm in operation in an electrolytic cell an industrial scale.