Papers by Keyword: Alkali Metal

Abstract: The washing solution of Zhundong coal is a multi-ions mixed system, and the extraction reactions of the alkali and alkaline earth metal ions in the water washing solution with polymer material of dicyclohexyl-18-crown-6 were investigated. The results show that the content of Na in the washing solution is highest, followed by K. Dicyclohexyl-18-crown-6 has better extraction rate of K due to the diameter of K has the same size with the hole diameter of dicyclohexyl-18-crown-6, which enables it could effectively separate Na and K, while did not cause excessive pollution of aqueous solution. Alkali and alkaline earth metal ions were extracted by dicyclohexyl-18-crown-6 in the form of 1:1. Improving the concentration of dicyclohexyl-18- crown-6 in organic phase could effectively enhance the extraction rate. It is not conducive to the extraction reaction by increasing temperature, as the extraction reaction is exothermic.

Abstract: The photoluminescence properties of pristine adamantane molecule have been calculated by time-dependent density functional theory (TD-DFT) within the hybrid functional level. This study aims to investigate the luminescence properties of the pristine adamantane molecule and its functionalized with neutral and ion of alkali metal to form C₁₀H_16-nX_n structure (where X is Li, Li⁺, Na and Na⁺ atoms, n=1). The electronic gap of the pristine adamantane (7.15 eV) is too wide, leading to an insulator property. While all the functionalized adamantanes exhibit semiconducting behavior. The absorption and emission energies of the original structure are 6.51 eV and 5.63 eV, respectively which are in good agreement with experimental results. The pure adamantane exhibits a broad photoluminescence peak in the ultraviolet region (UV). The Stokes shift of the transition between vertical and emission is 0.88 eV which agrees well with the previous work that measures the Stokes shift of 0.7 eV. The modification of adamantane indicates that the absorption and emission gaps substantially decreases. Substituting with alkali metal causes the photoluminescence onset can be shifted from the UV to the near-IR region. These results suggest that pure and the alkali metal functionalized adamantane molecules are promoting as candidate materials for the opto-electronic applications in the ultraviolet to infrared spectral regions.

Abstract: Alkali metal (Cs/Li/Na) adsorption on (5, 5) and (9, 0) single-walled carbon nanotubes (CNTs) with a capped edge had been investigated by first-principles calculations. Our calculations are performed within density functional theory (DFT) under the generalized gradient approximation (GGA) of Perdew, Burke, and Ernzerhof (PBE).For the indefective (5, 5)/(9, 0) CNT, adsorption energy ordering of the alkali-metal adatoms is Cs>Li>Na so that the Cs adsorption was energetically favored with respect to the Li/Na adatom. However, the adsorption energy ordering of the alkali-metal adatoms for the defective (5, 5) CNT was Li>Cs>Na. Therefore, separation selectivity for alkali metals could be actualized using the capped single-walled carbon nanotubes. The (5, 5)/(9, 0) P-CNT adsorbed Cs atoms preferentially, while the (5, 5)/(9, 0) defective CNT (D-CNT) adsorbed Li atoms advantageously.

Abstract: Zhundong coal has a huge proved reserve and many excellent properties. However, the alkali metal content in Zhundong coal is distinctly high, which can accelerate the deactivation of De-NO_x SCR catalysts. Using solution impregnation method, the effect of operation conditions on activity of SCR catalysts before and after poisoned by sodium was experimentally investigated. The results show that the NO reduction ratio raises with the increase of NH₃/NO ratio. Longer residence time results in higher NO reduction ratio. Compared with catalyst poisoned by NaCl, residence time presents less influence on activity of fresh catalyst in 250-400 ^oC, which is beneficial for De-NO_x process. Both O₂ and NO concentration have no apparent influence on NO reduction ratio.

Abstract: Zhundong coal has a huge proved reserve and many excellent properties. However, the alkali metal content in Zhundong coal is apparently high, which can accelerate the deactivation of De-NO_x SCR catalysts. In the present study, the effect of alkali metal deposition on activity of SCR catalysts through solution impregnation method was experimentally investigated. The results indicate that alkali metal deposition on the catalyst surface significantly deactivates the capacity of SCR catalysts. NaOH presents the most intense poisonousness. The catalytic effect on NO reduction reduces with the increase of alkali metal content on catalyst surfaces. In addition, potassium establishes more obvious poisonousness on SCR catalyst than sodium. There is interaction effect between sodium and potassium on deactivating the SCR catalyst.

Abstract: The impacts of operation parameters on agglomeration characteristics during biomass gasification in fluidized bed were studied experimentally in a 0.02MWt CFB gasifier using cotton stalk pellet as fuel. The experimental results indicated that among the temperature range (600 °C-800 °C), bed agglomeration would occur after a period running with sand, high alumina bauxite or periclase as the bed material, and potassium gathered on the surface of bed materials. In the process of the fluidized-bed gasification of biomass, air velocity affected the degree of bed agglomeration, and the agglomeration problem in return valve was more serious than that in main bed.

Abstract: Alkali niobate lead-free piezoelectric ceramics with nominal compositions [(Na_0.52K_0.48)_{0.94+ x}Li_0.06-x](Nb_0.94Sb_0.06)O₃ ((NK)_xLNS) were prepared by normal sintering. Crystalline phase, piezoelectric properties and sintering behavior of (NK)_xLNS ceramics were investigated with a special emphasis on the influence of alkli metal content. The x-ray diffraction patterns and the corresponding calculation of lattice parameters indicated that a phase transition from tetragonal to orthorhombic symmetry occurs as x=0.01, resulting in enhanced piezoelectric constant and planar electromechanical coupling coefficient of 266 pC/N and 38.5%, respectively. With x=0.01, the ceramics sintered at 1050 C show higher density and better electrical properties. Our results indicate the importance of sintering temperature and elaborate compositional control for enhancing piezoelectric properties in niobate-based ceramics.

Abstract: A theoretical model consisting of 5 energy levels, with the three upper states coherently excited, was proposed to analyze the coherent characteristics of atomic wave packets using perturbative theory. Pump-probe technique was implemented to detect coupled difference frequency four-wave mixing processes for studying the coherent characteristics of Rb atomic wave packets. Quantum beats were extracted the time domain signal by Fourier transform. Moreover, the variation of quantum beats was gained by time-dependent Fourier transform. The results show that the coherent characteristics of alkali metal atomic wave packets are closely related to quantum beats embedded in the time delayed four-wave mixing signal. Theoretical results are consistent with experimental observations, possessing potential applications in multi-channel information encoding and decoding.

Abstract: As one kind of renewable energy, bio-energy attracts more and more scholars’ attention due to its good ignition, combustion characteristics and zero CO2 release during bio-energy combustion process, alkali metals’ emission could cause fouling, slagging, high temperature corrosion and ultra-fine particulate matter emission, which hazard equipment safety and human healthy. In this paper, the release characteristics of alkali metals during the combustion process of rice straw (RS) and sawdust (SD) was studied by the chemical desperation disposal method and in a vertical thermal balance furnace. Also, the concept of alkali metals’ release ratio was introduced. The Results indicated that increasing the combustion temperature leads to a bigger alkali metals’ release ratio. At the same temperature, the alkali metals release ratio of unwashed biomass is the largest, the acid-washed biomass is the smallest, and the water-washed biomass is in between them. Meanwhile, the existing forms of alkali metals cause different effect to the release ratio, i.e. the ionic form alkali metals release most greatly, the organic form smaller and the other forms the smallest.

Abstract: The effects of sewage sludge on combustion of loading alkali metal pulverized coal is carried out by thermogravimetric analysis (TGA). The result shows sewage sludge decreases initial release temperature and ignition temperature of volatile matter(VM) during the combustion of loading alkali metal pulverized coal. The combustion of fixed carbon in coal was promoted by the metal material in sludge when the sludge mixing ratio(SMA) was lower than 20% or inhibited because of the cover of sludge ash when SMA was higher than 40%. Comparison of stacking curves of sludge and measured curves of loading alkali metal coal, finds that: (1) there is no effect between sludge and coal, for the volatilization of water and small molecule substance, the combustion characteristic curves are superimposed in both experimental curves; (2) the co-combustion is interactional and interrestricted continuous change process, can't direct obtain from superimposition of curves, for the combustion of VM and fixed carbon. While SMA is lower than 20%, the samples have good combustion characteristic than pure coal.