Inhibition of temperature runaway phenomenon in the Sabatier process using bed dilution structure: LBM-DEM simulation

The Sabatier process is promising for carbon dioxide utilization and energy storage. However, the serious problem that limits more comprehensive industrial applications is catalyst deactivation due to the temperature runaway phenomenon. The inert particle dilution approach, including the mixing dilution method and layered dilution method is applied to solve this problem. Based on the lattice kinetic scheme-lattice Boltzmann method (LKS-LBM), the effects of three parameters in bed dilution structure reconstructed by the discrete element method (DEM) on temperature distribution and carbon conversion rate were discussed, so as to investigate the relationship between packing structure and temperature distribution. Furthermore, numerical results indicated that an optimal bed dilution structure, which not only can control the peak temperature below the critical temperature to avoid coking and sintering of catalyst, but also can improve the conversion rate by almost 18% compared with the structure without dilution under the same circumstance.     

Characterization of Surface-Oxidized Phase in Silicon Nitride and Silicon Oxynitride Powders by X-ray Photoelectron Spectroscopy

Surface-oxidized phases on α-silicon nitride, β-silicon nitride, and silicon oxynitride powders were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (XAES). The spectra of Si2 p XPS and Si( KLL ) XAES were measured precisely and were deconvoluted into some separate peaks, which correspond to each parent phase, a SiO x N y , oxidized phase, a nonstoichiometric SiN x . nitride phase, and a satellite peak of the parent phase, by the least-squares method. The Auger parameter (AP) was calculated for each phase using the Si2 p XPS and Si( KLL ) XAES data, and the average chemical compositions of the oxidized phases in each sample were evaluated from the AP data. The chemical compositions of these phases were between those of silica and silicon oxynitride and varied among the samples, but were usually close to SiO₂. Average thicknesses of the surface-oxidized phases were estimated to be 0.1–0.8 nm from the peak area ratio of the oxidized phase against the parent phase of the XAES spectra, assuming a continuous surface layer model.     

比表面积与入口气体分压对热解炭微观结构影响的数值模拟研究

本研究在炭/炭复合材料热解炭基体织构形成与转化的模型基础上, 基于石墨微晶片层的表面结构特点, 建立了蜂窝结构的热解炭沉积表面几何模型, 并运用Monte Carlo方法模拟了在等温等压化学气相渗透(CVI)过程中热解炭基体沉积的动力学过程, 研究了预制体比表面积(A_S/V_R)和入口气体分压对热解炭微观结构的影响。通过数值模拟并结合已公开发表的实验结果发现, 在CVI工艺过程中一定的压力条件下, 通过控制A_S/V_R可以获得不同织构的热解炭, 预制体的A_S/V_R存在两个临界值, 靠近反应器入口处的临界值为1.45 m^-1和8.9 mm^-1, 靠近反应器出口处的临界值为0.3 mm^-1, 当A_S/V_R处于这两个临界值之间时, 系统主要沉积高织构热解炭; 在同一A_S/V_R且压强小于30 kPa的条件下, 通过控制反应气体压强的值也可以得到不同织构的热解炭, 并且压强也存在一个临界值, 当压强大于这个临界值时, 系统主要沉积高织构热解炭。     

Kinetics of surface reactions in carbon deposition from light hydrocarbons

Carbon deposition from ethene, ethine and propene as a function of pressure was studied at various temperatures and two different surface area/volume ratios. Deposition rates as a function of pressure of all hydrocarbons indicate Langmuir-Hinshelwood kinetics which suggests that the deposition process is controlled by the heterogeneous surface reactions (growth mechanism). These kinetics are favored at decreasing reactivity (C₃H₆>C₂H₂>C₂H₄), decreasing temperature and residence time as well as increasing surface area/volume ratio. A linear rate increase at high pressures suggests that carbon is additionally or preferentially deposited by aromatic condensation reactions between polycyclic aromatic hydrocarbons large enough to be physisorbed or condensed on the substrate surface (nucleation mechanism). The results completely agree with earlier results obtained with methane.     

High-throughput screening of improved protease inhibitors using a yeast cell surface display system and a yeast cell chip

Protease-targeted inhibitors have been promising pharmaceuticals. Here, we combined a yeast cell surface display system with a yeast cell chip for the high-throughput screening of protease inhibitors, and succeeded in improving the activity of a protease inhibitor.     

Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen

The molecular weight of asphaltenes has been a controversy for several decades. In recent years, several techniques have converged on the size of the fused ring system; indicating that chromophores in virgin crude oil asphaltenes typically have 4-10 fused rings. Consequently, the molecular weight debate is equivalent to determining whether asphaltenes are monomeric (one fused-ring system per molecule) or whether they are polymeric. Time-resolved fluorescence depolarization (FD) is employed here to interrogate the absolute size of asphaltene molecules and to determine the relation of the size of the fused ring system to that of the corresponding molecule. Coal, petroleum and bitumen asphaltenes are compared. Molecular size of coal asphaltenes obtained here by FD-determined rotational diffusion match closely with Taylor-dispersion-derived translational diffusion measurements with UV absorption [1]. Coal asphaltenes are smaller than petroleum asphaltenes. N-methyl pyrrolidinone (NMP) soluble and insoluble fractions are examined. NMP soluble and insoluble fractions of asphaltenes are monomeric. It is suggested that the ‘giant’ asphaltene molecules reported from SEC studies using NMP as the eluting solvent may actually be the expected flocs of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results.     

Mechanism of decomposition of aromatics over charcoal and necessary condition for maintaining its activity

Decomposition of mono- to tetra-aromatics over charcoal was investigated under conditions such as temperature; 700–900 °C, inlet concentrations of aromatics, steam and H₂; 7.5–15 g/Nm³, 0–15.5 vol% and 0–15.5 vol%, respectively, gas residence time within charcoal bed; 0.2 s, particle size of charcoal; 1.3–2.4 mm. The charcoal, with an initial surface area of 740 m²/g, was active enough to decompose naphthalene completely even at 750 °C. Aromatics with more rings per molecule were decomposed more rapidly. The aromatics were decomposed over the charcoal by coking rather than direct steam reforming irrespective of temperature and steam/H₂ concentrations. The coking, i.e., carbon deposition from the aromatics, caused loss of micropores and thereby activity of the charcoal, while steam gasification of the charcoal/coke formed or regenerated micropores. Relationship between the overall rate of carbon deposition by the coking and gas formation by the gasification within the charcoal bed showed that progress of the gasification at a rate equivalent with or greater than that of the carbon deposition was necessary for maintaining the activity of the charcoal.