| Vermiculite is a kind of multilayer structure magnesium aluminum silicate mineral. In China, the reserves of vermiculite are very abundant. Xinjiang Yuli vermiculite is the largest vermiculite ore deposits in China, and its total geological reserves ranks second in the world. At same time, vermiculite possesses the properties of large cation exchange adsorption, good mechanical insulation, special expansion and other excellent property. However, vermiculite is applied only in low value field, such as agriculture, construction, environmental protection etc. In this manuscript, we modified vermiculite by the methods of expansion, acid treatment, carbon coating etc. And the modified vermiculite was used as catalyst support for acetylene hydrochlorination. Meanwhile, vermiculite-based porous Si O2 and Si C layer material were prepared by the template of layered vermiculite. The leap from natural minerals to advanced functional materials of vermiculite successfully came true, which improved the utilization value of Xinjiang Yuli vermiculite. Details of the experiment were summarized as follows:(1) In order to make up the disadvantage of easy to sublimate and poor abrasion performance of the Hg Cl2/active carbon catalysts, we used the Hg Cl2-supported modified vermiculite as the catalyst for acetylene hydrochlorination, due to the vermiculite was easy to be modified and had the high mechanical strength. In order to improve the stability of acetylene conversion of the Hg Cl2 / vermiculite catalyst for acetylene hydrochlorination, we modified the vermiculite supports by expanded, chitosan mixed, additives added, acid treatment, carbon mixed, carbon coated and silicon carbide modification, respectively. The results showed that the modified catalysts achieved good catalytic activity. The initial conversions of acetylene were above 90% and the selectivity of vinyl chloride were above 95%. The stability of the modified catalysts modified by expanded, chitosan mixed, additives added, acid treatment were bad, the life time of the above 90% conversions of acetylene was under 200 min. The modified catalysts modified by carbon mixed, carbon coated and silicon carbide modification possessed acetylene conversion of above 91% for 600 min, and the highest conversion rate was up to 98.89%. The catalytic performance is comparable to the activated carbon supported catalyst. The vermiculite based Si C catalysts possessed acetylene conversion of above 85.8% for 400 min. And the highest conversion rate was up to 96.9%. The catalytic performance is good.(2) The reasons for the poor stability of the catalyst were the composition of Si O2 in vermiculite, poor thermal stability, poor electric and thermal conductivity of supports, carbon deposition.etc. Wherein the composition of Si O2 in vermiculite was the main factors of the catalyst deactivation. It provided a reference for improving catalyst life time.(3) The vermiculite with layered structure was used as templates for the synthesizing of new mutilayered functional materials. The porous mutilayered silica was prepared by a facil one-step mixed acid leaching method. The Si O2 content was more than 99%. Its pore size distributed in the region of 1.81 nm, the maximum specific surface area was 505 m2/g, the pore volume was 0.406 cm3/g, and the thickness of thin layer was 5.5 nm. Mutilayered β-Si C was prepared by the microwave method and the low temperature magnesium magnesiothermic reduction method using the porous mutilayered silica as template. In the microwave method, the optimum preparation conditions were as follows: the mass ratio of Si O2:C was 5:3, the reaction temperature was 1500 oC, the reaction time was 2 h. The morphology characterization showed that the β-Si C was a multilayered structure with micropore in each layer,with the specific surface area of 153.8 m2/g. In the low temperature magnesium magnesiothermic reduction method, the optimum preparation conditions were as follows: the mole ratio of Si O2:C:Mg was 1:2:4, the reaction temperature was 600 oC, the reaction time was 5 h. which could prepare mutilayered elemental silicon. The β-Si C material also showed a multi-layer layered structure with larger pore size. and its specific surface area was up to 131.6 m2/g. |
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