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排序方式: 共有138条查询结果,搜索用时 0 毫秒
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Rongbin Qi Yujun Wang Jiding Li Changwei Zhao Shenlin Zhu 《Journal of membrane science》2006,280(1-2):545-552
Worldwide concerns over environment have stimulated increasing interest both in academic and industry for deep desulfurization of gasoline. Polydimethylsiloxane (PDMS) composite membrane was used to separate the binary and multicomponent alkane/thiophene mixtures by pervaporation. Effect of carbon number and concentration of alkane, and of feed temperature, on the separation efficiency of alkane/thiophene mixtures was investigated experimentally. Experimental results of binary mixtures indicated that the total fluxes for different alkane/thiophene mixtures decrease with increase of carbon number in the alkanes. Corresponding activation energies of permeation for alkanes in PDMS membrane increase with increase of carbon number in the alkanes. Differences of molecular size and structure of the alkanes lead to various selectivities thereof within PDMS membrane. In addition, the permeability and activation energy of thiophene in various systems differ from each other due to coupling effect which should be taken into consideration when dealing with multicomponent systems. Pervaporation results of ternary systems indicated that, the increase of content of lighter alkane in feed would result in a larger total flux, but a smaller selectivity to thiophene simultaneously. A quaternary system, the mixture of n-heptane, n-octane, n-nonane and thiophene, was employed to simulate the desulfurization process of gasoline. With the membrane having a PDMS layer of 11 μm, the total flux was measured to be about 1.65 kg/m2 h, with the corresponding enrichment factor of thiophene 3.9 at 30 °C. 相似文献
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Grand canonical Monte Carlo and configurational bias Monte Carlo techniques were employed to simulate the adsorption of binary mixtures of butane isomers and quaternary mixtures in nine zeolites at 300 K. For binary mixtures the results show there is a critical pore size, which is 10-membered-ring about 5.6 Å. The channel sizes of BEA, ISV, MOR and CFI are larger than this critical pore size, they prefer i-butane than n-butane, whereas TON with smaller channel size than critical pore size prefers n-butane than i-butane, but its selectivity decreases with pressure increasing. MFI, MEL and TER prefer i-butane than n-butane at low pressure, but with pressure increasing, the selectivity is reversed. BOG prefers i-butane than n-butane but the selectivity decreased with pressure increasing. It demonstrates that the adsorption and selectivity are controlled by both pore size and pore structure. The n-butane–i-butane–n-pentane–2-methylbutane quaternary mixtures adsorbed in these nine zeolites were studied, and the results show alkane chain length dependence at low pressure, but the adsorption is controlled by pore size and structure with pressure increasing in all the zeolites except for TON and BOG. 相似文献
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信息拓扑指数与烷烃分子热力学性质的关系 总被引:13,自引:0,他引:13
Two topological information indices were constructed based on Randic and Wiener indices, and the values of topological information indices for 85 alkanes were calculated. The thermodynamic properties such as the standard enthalpies of formation, the standard entropies and the standard free energies of formation for these alkanes were also correlated with these topological and information indices. It is found that the thermodynamic properties calculated for both gaseous and liquid states of the 85 alkanes are in excellent agreement with the experimental values through the regression analysis. 相似文献
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Micrometric BN powders used as catalyst support: influence of the precursor on the properties of the BN ceramic 总被引:1,自引:0,他引:1
Thin powders and foams of boron nitride have been prepared from molecular precursors for use as noble metal supports in the catalytic conversion of methane. Different precursors originating from borazines have been tested. The best results were obtained using a precursor derived from trichloroborazine (TCB) which, after reacting with ammonia at room temperature and then thermolyzing up to 1800°C, led to BN powders with a specific area of more than 300 m2 g−1 and a micrometric spherical texture. Comparable results were obtained using polyborazylene under similar conditions. Aminoborazine-derived precursors did not yield such high specific area ceramics but the BN microstructure resembled a foam with a crystallized skin and amorphous internal part. These differences were related to the chemical mechanism of the conversion of the precursor into BN. Polyhaloborazines and polyborazines yielded BN through gas-solid reactions whereas aminoborazine polymers could be kept waxy up to high temperatures, which favored the glassy foam. Catalysts composed of BN support and platinum have been prepared using two routes: from a mixture of precursor or by impregnation of a BN powder leading to very different catalysts. 相似文献
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根据化合物形成过程中价电子能量变化与生成焓之间的关系, 推导出烷烃的生成焓和电离能之间的关系. 以21个烷烃化合物为模型将实验测定的电离能与标准生成焓进行直接关联, 证实了模型方程的适用性, 所得回归方程的相关系数达到0.9999, 估算值与实验值之间的标准偏差仅为0.03 eV. 同时还利用实验测定的标准生成焓对一系列烷烃的电离能作了预测. 相似文献
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Feng Zhang Li Pan Juhee Choi Vikram Mehar John T. Diulus Aravind Asthagiri Jason F. Weaver 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(47):14113-14117
Achieving selective C H bond cleavage is critical for developing catalytic processes that transform small alkanes to value‐added products. The present study clarifies the molecular‐level origin for an exceptionally strong preference for propane to dissociate on the crystalline PdO(101) surface via primary C H bond cleavage. Using reflection absorption infrared spectroscopy (RAIRS) and density functional theory (DFT) calculations, we show that adsorbed propane σ‐complexes preferentially adopt geometries on PdO(101) in which only primary C H bonds datively interact with the surface Pd atoms at low propane coverages and are thus activated under typical catalytic reaction conditions. We show that a propane molecule achieves maximum stability on PdO(101) by adopting a bidentate geometry in which a H Pd dative bond forms at each CH3 group. These results demonstrate that structural registry between the molecule and surface can strongly influence the selectivity of a metal oxide surface in activating alkane C H bonds. 相似文献
10.
X.-T. Mu Y.-S. Ouyang L.-M. Pei Z.-X. Peng S.-Q. Shao S.-M. Wang H. Xiong Y. Xiao Q.-Y. Yang 《Materials Today Chemistry》2022
Adsorptive separation of C2H6 from C2H4 by adsorbents is an energy-efficient and promising method to boost the polymer grades C2H4 production. However, that C2H6 and C2H4 display very similar physical properties, making their separation extremely challenging. In this work, by regulating the pore environment in a family of chitosan-based carbon materials (C-CTS-1, C-CTS-2, C-CTS-4, and C-CTS-6)- we target ultrahigh C2H6 uptake and C2H6/C2H4 separation, which exceeds most benchmark carbon materials. Explicitly, the C2H6 uptake of C-CTS-2 (166 cm3/g at 100 kPa and 298 K) has the second-highest adsorption capacity among all the porous materials. In addition, C-CTS-2 gives C2H6/C2H4 selectivity of 1.75 toward a 1:15 mixture of C2H6/C2H4. Notably, the adsorption enthalpies for C2H6 in C-CTS-2 are low (21.3 kJ/mol), which will facilitate regeneration in mild conditions. Furthermore, C2H6/C2H4 separation performance was confirmed by binary breakthrough experiments. Under different ethane/ethylene ratios, C-CTS-X extracts a low ethane concentration from an ethane/ethylene mixture and produces high-purity C2H4 in one step. Spectroscopic measurement and diffraction analysis provide critical insight into the adsorption/separation mechanism. The nitrogen functional groups on the surface play a vital role in improving C2H6/C2H4 selectivity, and the adsorption capacities depend on the pore size and micropore volume. Moreover, these robust porous materials exhibit outstanding stability (up to 800 °C) and can be easily prepared on a large scale (kg) at a low cost (~$26 per kg), which is very significant for potential industrial applications. 相似文献