Chlorine dioxide bleaching of soda-anthraquinone jute pulp to a very high brightness.
Bleaching of soda-anthraquinone jute pulp by chlorine dioxide (ClO2) was studied to reach a target brightness of above 88% for the purpose of using less bleaching chemicals. The performance of either chlorine dioxide or peroxide in the final bleaching to boost brightness was also studied. The experimental results revealed that the final brightness depended on ClO2 charge in the Do and D1 stages. The brightness reversion was lower when the final stage brightening was done by peroxide. The use of Mg(OH)2 in the D1 and D2 stages improved the final brightness due to the formation of less chlorate and chlorite during the Mg(OH)2- based ClO2 brightening stages. The strength properties of pulp bleached by peroxide in the final stage was slightly better than that from ClO2 as the final ClO2 bleaching stage.
Chlorine Dioxide Bleaching
Chlorine dioxide bleaching is a well-proven technology which today is universally used in the pulp industry. Chlorine dioxide is a very strong oxidizing agent and preserves pulp strength while giving high and stable brightness. It is also very effective in particle elimination. Chlorine dioxide does not react extensively with carbohydrates, although some oxidation of cellulose does take place, so there is very little pulp strength deterioration in chlorine dioxide. The viscosity loss in chlorine dioxide bleaching stages is found to be very low, but under aggressive conditions, some carbohydrate degradation may take place. Chlorine dioxide is an unusual chemical compound because it has a single unpaired electron and thus is a free radical. At ambient temperature it is an unstable gas that explodes if compressed. It cannot be transported safely and therefore must be manufactured at the site where it is used. As soon as it is formed, it is dissolved in chilled water to form a dilute solution, generally 8–12 grams per liter at 5–10 °C. It is a multipurpose bleaching agent and is efficient in both delignification and brightening of pulp by reducing or eliminating residual lignin content without significant carbohydrate losses and by reducing chromophores in pulp. It has the capability to decolorize dirt specks, which makes it a most efficient bleaching agent. Kraft pulp could not be bleached to high brightness (90% ISO) before chlorine dioxide came into use in the mid-1940s. Substitution of chlorine dioxide for chlorine in a bleaching sequence reduces the AOX level in the bleaching filtrates, and it also changes the nature of the organochlorines formed during bleaching. Some additives are found to increase the efficiency of chlorine dioxide bleaching. A 2.5 kg/t charge of formaldehyde saved 10.8 kg of chlorine dioxide per ton of pulp when the target final ISO brightness was 89.2%, without detrimentally affecting effluent and pulp strength properties. A close examination of the performance of the process shows that about two-thirds of the chlorine dioxide is wasted in useless side reactions. This fact represents one major challenge facing the lignin chemists and the equipment suppliers. Several process modifications are proposed to minimize this problem. Moreover, today ozone represents a serious alternative to chlorine dioxide. For many reasons the replacement of some chlorine dioxide by ozone should be beneficial not only to the delignification rate but also to the brightness development .
Impact of acetaldehyde‐ and pyruvic acid‐bound sulphur dioxide on wine lactic acid bacteria
Aims:  To investigate the impact of acetaldehyde‐ and pyruvic acid‐bound sulphur dioxide on wine lactic acid bacteria (LAB).