Desenvolvimento de um processo de taninos utilizando dióxido de enxofre (SO2) como alvejante.

Abstract

The industry of Acacia tannins mearnssi De Wild (black wattle) has found great difficulties, especially in the last four years , on the production of clarified tannins due to changes in the form of harvest and strip of the trees . The technologies of the mechanized striping of the trees provide higher productivity, lower cost and a better utilization of manpower , however , the largest crushing and comminution of the bark left this more susceptible to degradation and consequent darkening. Despite the industrial process of whitening tannins admittedly be efficient, it has no capability of bleaching on the concentrated extracts with very dark colors . Thus , the target of this study was to evaluate the bleaching of high tannin concentration (TAC) using sulfur dioxide as a bleach agent. The experiments were conducted under controlled experimental conditions, where was evaluated the influence of the temperature, the initial color of the TAC, reaction time, and the quantity of the bleaching agent. On the quality evaluating of the final product were considered the color parameters, ash content and iron content. Were made in total 40 experiments, and on 20 of these was tested tannin bleaching with addition of sulfur dioxide, 14 experiments with addition of sulfur dioxide and sodium metabisulfite and 6 laboratory trials by adding sodium metabisulphite to bleach the tannin . The use of metallic copper, metallic zinc and copper sulphate were tested as additives in some trials. The best bleaching results were obtained in tannin 7A, 7B, 8A and 8B tests, the condition of temperature of 90 ° C and four hours of reaction. 7A and 7B in tests (using SO2) decreased by 53%, while in 8A and 8B (with Na2S2O5) testing the reduction of the red color was in the range of 65% (better bleaching result of this study). In tests with SO2, the peak time of reduction of red color is observed in the first hour of reaction and after that time there is a decrease in bleaching, even with new additions of input, achieving color stability, but it is not clearing after this stability. The combination with sodium metabisulphite not improves the bleaching. For additives, zinc metal, unlike the metallic copper and copper sulfate, showed promising results regarding its use as a catalyst, which should be explored further trials in larger scale.