Net hydrogen off-gas from the continuous catalyst regeneration type catalytic reforming process (CCR process) contains inorganic chlorides. In order to prevent potential problems such as corrosion in the downstream processes, such chlorides are commonly removed by using fixed-bed chloride traps. We have extensively investigated the chloride removal properties of various materials for the chloride traps and have developed effective and practical zinc oxide based chloride traps. Firstly, we found that net hydrogen off-gas from the CCR process contains not only inorganic chlorides but also organic chlorides. Secondly, we found that the widely used activated alumina based chloride traps have the major disadvantages of formation of organic chlorides from inorganic chlorides on the surface and leakage of the organic chlorides to the downstream processes. These organic chlorides may be decomposed by heating and may cause corrosion in the downstream processes. Conversely, we found that zinc oxide based chloride traps have high potential to remove both inorganic chlorides and organic chlorides through the presumptive mechanism that organic chlorides are converted into inorganic chlorides on the surface and are then trapped by reaction with zinc oxide. However, zinc oxide based chloride traps have problems with pellet breakage and pressure drop buildup due to the deliquescence of zinc chloride derived from the reactions of chloride compounds and zinc oxide. To solve these problems, the chemical and physical properties have been improved by appropriate reduction of zinc oxide content and increase of pore volume with addition of porous inorganic materials to increase the contribution of zinc oxide inside pellets to chlorine removal and to enhance zinc chloride retention capacity. Consequently, we developed a new zinc oxide chloride based chloride trap, JCL-1. Demonstration tests of the JCL-1 showed stable operation with effective removal of both inorganic chlorides and organic chlorides without pressure drop buildup or pellet breakage.
Adsorption structure and electronic structure of ethylene on Pt 3 Ti(001) and PtTi 3 (001) intermetallic compounds surfaces are studied in terms of density functional calculations. In both intermetallic compounds, adsorption energy of bridge and hollow sites are larger than that of the atop sites. Moreover, obtained adsorption energy and the C-C separations at most sites on both intermetallic compounds are larger than those reported for Pt(111). Analyzing the surface LDOSs, it turns out that the bimodal density of states made by the occupied Pt d-states and unoccupied Ti d-states are effectively interact with the HOMO and LUMO of ethylene, which are bonding and anti-bonding states of the ³-bond between carbon atoms, and then leading the elongated C-C bond and large adsorption energy. Larger adsorption energy at bridge and hollow sites is also understood in the same way. Although we found out the possibility that the bimodal density of states realized in intermetallic compounds composed of early and late transition metals is effective for molecular dissociation reaction generally, no clear evidence indicating the experimentally reported higher catalytic activity of Pt 3 Ti than PtTi 3 and Pt in the ethylene hydrogenation is obtained in this study.
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