Preparation And Properties Of Catalysts For Anthraquinone Hydrogenation And Catalysts For Anthraquinone Degradation Products Regeneration

Hydrogenation peroxide ?H₂O₂? is an important inorganic chemical product, which is widely used in papermaking, spinning, chemical synthesis, environment protection and other fields. The application areas of hydrogenation peroxide becomes wider and the demand continues to increase. Commercially, H₂O₂ is mainly produced by anthraquinone hydrogenation. The process are the following steps:2-ethylanthraquinone ?EAQ? is catalytically hydrogenated to 2-ethylanthrahydroquinone ?EAQH₂? and 2-ethyltetrahydroanthrahydroquinone ?H₄EAQH₂?, and then oxidized by oxygen, which generates EAQ and hydrogenation peroxide, Both EAQ and 2-ethyletrahydroanthraquinone ?H₄EAQ? are called as "active quinones". However, in the process of hydrogenation and oxidation, some anthraquinone molecules structure underwent change, generating anthraquinone degradation products which cannot be oxidized by O2 to generate H₂O₂, threatening the quality of hydrogen peroxide products. Commercially, supported Pd catalysts and Raney Ni catalysts are the most frequently used hydrogenation catalysts in the anthraquinone process. Supported Pd catalysts exhibit high hydrogenation activity and selectivity in this process. However, the precious metal Pd is expensive and scarce; Raney Ni catalysts have been fallen into disuse because of noticeably deteriorates owing to a trace amount of hydrogen peroxide in the working solution, ignitable characteristic and dangerous handing. Thus, it is highly desirable to develop a new approach to obtain non-precious metal catalysts which exhibit highly activity and selectivity simultaneously.We prepared a series of Ni/Al₂O₃ catalysts using NiAl-CO₃-layered double hydroxides ?NiAl-LDHs? with different Ni/Al molar ratio ?2:1-4:1? as precursors and discussed the influence of reduction temperature and Ni/Al ratio on the catalytic performance in the hydrogenation of anthraquinone. The experiment results show that Ni/Al₂O₃-2:1 catalyst reduced at 500 ? shows the highest anthraquinone hydrogenation activity, with the increase of Ni/Al molar ratio, the hydrogenation efficiencies of Ni/Al₂O₃ catalysts reveal a trend of gradual decrease. Moreover, Ni/Al₂O₃-2:1 catalysts modified by different promoters ?Fe, La and Zr? were prepared and studied the influence of promoters on the structure and catalytic performance of Ni/Al₂O₃ catalysts. The catalytic results show that promoters modified Ni/Al₂O₃ catalysts show higher hydrogenation activity and preferable selectivity, furthermore, La modified Ni/Al₂O₃ catalyst shows the highest hydrogenation activity and selectivity. Superior activity can be attributed to the smaller Ni particle size and higher Ni dispersion, preferable selectivity can be ascribed to the electronic effect of promoters, resulting in electron-rich Ni and weakening the adsorption of anthraquinone hydrogenation products. Furthermore, different amount of La modified Ni/Al₂O₃-2:1 catalysts were prepared using the same method and showed higher hydrogenation activity. When the La loading is 2%, the hydrogenation activity increases by 20.7%and shows preferable selectivity compared with Ni/Al₂O₃-2:1 catalyst. However, higher La loading is harmful to the hydrogenation efficiency because some surface nickel active centers could be covered by La oxides.In industrial production, NaOH/y-Al₂O₃ catalyst prepared by impregnation is widely used for anthraquinone degradation products regeneration. However, the present NaOH/y-Al₂O₃ catalyst has very short lifetime and loss active component seriously. A series of CaAl-NO₃-LDHs precursors were synthesized in situ on the surface of spherical y-Al₂O₃ and then CaAl-MMO/y-Al₂O₃ ?MMO:mixed metal oxides? solid base catalysts were prepared through the calcination of CaAl-NO₃-LDHs. Crystal structure, Micro morphology, specific surface area, and surface basicity of CaAl-MMO/y-Al₂O₃ catalysts were characterized by means of XRD, SEM, BET and CO2-TPD. The CaAl-MMO/y-Al₂O₃ catalysts were used to regenerate anthraquinone degradation products in the anthraquinone method, the experiment results show that when CaO loading was 20 wt%, compared with 0.20-CaO/y-Al₂O₃ catalysts prepared by impregnation, the anthraquinone regeneration performance of CaAl-MMO/y-Al₂O₃ catalyst increased by 77%.