| Sodium sulphate-hydrogen peroxide-sodium chloride adduct (4Na2SO4 2H2O2 NaCl) with 9.79% of H2O2 by mass is a new-type of neutral assistant for synthetic detergents. In the clathrate structure of this adduct, the molecule of H2O2 are incorporated in a cage formed by sulphate-oxygen atoms. There is no uniform coordination for Nah ions in adduct. For 9 Na+ ions in the molecule of the adduct, each of 8 Na+ ions is surrounded in a distorted octahedron formed by 5 oxygen atoms and 1 choride ion and another Na+ ion is surrounded in a tetragonal prism formed by oxygen atoms.An experimental scheme based on orthonomalization method was designed and used to optimize the processing conditions for the adduct of 4Na2SO4 2H2O2 NaCl. The experimental results indicated that a high quality of adduct can be achieved when 8 g Na2SO4 and 8 g NaCl were added and stirred into 25 ml H2O2 solution with 30% H2O2 by mass and the whole solution was then stirred for one hour reaction at a temperature of 283 K. In this case, further analyses showed that the final product has a high stability, the concentration of H2O2 in the product is 9.71% by mass and the crystals in the product have a prismatic structure. The experimental results also indicated that a theoretical value of 9.79% H2O2 in the final product can be achieved if 9.5 g Na2S04 and 2-8 g NaCl were added into 25 ml H2O2 solution with 30% H2O2 by mass. However, the concentration of H2O2 in the final product will decrease below the theoretical value if more than 8 g NaCl was added into the same solution. The experimental results further illustrated that the reaction time will increase if Na2SO4 was first added into the H2O2 solution. Therefore, for anefficiency of the processing system and a high production of the adduct, NaCl should be added into the H2O2 solution before adding Na2SO4Thermal analysis was further carried to determine the decomposition temperature of the prepared adduct of 4Na2SO4 2H202 NaCl using both TG-DTG and DSC techniques. The analysis showed that the decomposition temperatures of the product measured by TG-DTG and DSC were 437.4 K and 462.65 K, respectively. Both measured values agree well with the data from the literatures, which are 433 K and 453 K, respectively.The measured TG-DTG curve further illustrated that the decomposition process of 4Na2SO4 2H202 NaCl is very complex. The decomposition process can be divided into two stages: (1) linear part, which is from 407.5 K to 423.95 K in the DTG curve and (2) characteristic curve part, which is from 423.95 K to 449.85 K. During the first stage, the weight loss of 4Na2SO4 2H2O2 NaCl is slow. However, at a temperature of 423.95 K, the weight of the product decreases significantly and the second decomposition begins. The weight loss rate reaches its maximum value at 436.95 K and the decomposition proceeds until the temperature of the product reaches 449.85 K.The decomposition mechanism of 4Na2SO4 2H2O2 NaCl was investigated using main curve method. The results indicate that the decomposition is controlled by the formation and growth of nuclei. The experimental data was further correlated by the Avrami-Erofe'ev equation to model the kinetic process of the decomposition, which is expressed as:The kinetic parameters in the Avrami-Erofe'ev equation were obtained byusing differential, integral and maximum decomposition rate methods, respectively. The parameters were further optimized by the nuclei formation -diffusion model to determine the apparent activation energy and pre-exponent. The Avrami-Erofe'ev equation with two kinetic parameters calculated by differential method cannot predict the decomposition process of the adduct very well. However, the equations with the parameters calculated by integration and optimization methods can achieve a good prediction. With those methods, the apparent activation energy and pre-exponent are determined as:The activity energy determined by the maximum decomposition rate was 1.739xl05 J-mol-1, which is close to the value achieved by the integration... |
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