Dimethyl carbonate (DMC) is actually recognized as an environmentally benign chemical because of its negligible ecotoxicity and low bioaccumulation and persistence. The diffusion of DMC as safe chemical necessarily implies a clean and safe route for its production, such as the base-catalyzed transesterification reaction with methanol of alkylene carbonates. Until now few bases were reported to be effective as heterogeneous catalysts under mild conditions (low temperature and atmospheric pressure). Therefore inorganic salts, namely, Na 3 PO 4 and Na 2 CO 3 , were selected because of their basic properties and their negligible ecotoxicity. Using Na 3 PO 4 as catalyst, the equilibrium yield for the reaction ethylene carbonate f DMC is reached in about 1 h at atmospheric pressure and at a temperature above 50 °C, while in the case of the propylene carbonate f DMC reaction, the equilibrium yield is difficult to reach, because the kinetics of this reaction are 5 times slower than those of the EC f DMC reaction. Both reactions can be well represented with first-order kinetics and present a similar activation energy, suggesting a diffusional rate-determining step. The quite different frequency factors suggest that the PC f DMC reaction is slow because of steric factors.
There is growing interest in processing and utilizing the red mud by-product of the Bayer process for alumina extraction from bauxite. This interest stems largely from the environmental impacts associated with red mud and the storage costs involved. Furthermore, complete utilization of the raw materials, in this case bauxite, meets an ecological concept while ensuring raw material conservation. To prepare this article, the authors perused approximately 100 patents and articles in order to provide a concise description of the methods of storing red mud and its uses as a flocculant or construction material and in other minor applications. Special attention has been given to the methods developed for recovering metals contained in the red mud.
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