Pervaporation from a dense membrane: roles of permeant-membrane interactions, Kelvin effect, and membrane swelling

Dense polymeric membranes with extremely small pores in the form of free volume are used widely in the pervaporative separation of liquid mixtures. The membrane permeation of a component followed by its vaporization on the opposite face is governed by the solubility and downstream pressure. We measured the evaporative flux of pure methanol and 2-propanol using dense membranes with different free volumes and different affinities (wettabilities and solubilities) for the permeant. Interestingly, the evaporative flux for different membranes vanished substantially (10-75%) below the equilibrium vapor pressure in the bulk. The discrepancy was larger for a smaller pore size and for more wettable membranes (higher positive spreading coefficients). This observation, which cannot be explained by the existing (mostly solution-diffusion type) models ofpervaporation, suggests an important role for the membrane-permeant interactions in nanopores that can lower the equilibrium vapor pressure. The pore sizes, as estimated from the positron annihilation, ranged from 0.2 to 0.6 nm for the dry membranes. Solubilities of methanol in different composite membranes were estimated from the Flory-Huggins theory. The interaction parameter was obtained from the surface properties measured by the contact angle goniometry in conjunction with the acid-base theory of polar surface interactions. For the membranes examined, the increase in the "wet" pore volume due to membrane swelling correlates almost linearly with the solubility of methanol in these membranes. Indeed, the observations are found to be consistent with the lowering of the equilibrium vapor pressure on the basis of the Kelvin equation. Thus, a higher solubility or selectivity of a membrane also implies stronger permeant-membrane interactions and a greater retention of the permeant by the membrane, thus decreasing its evaporative flux. This observation has important implications for the interpretation of existing experiments and in the separation of liquid mixtures by pervaporation.     

碱金属钾对Ni基催化剂纤维素水蒸气气化活性的影响

采用两段式催化气化方式研究了生物质热解气化过程中碱金属的挥发对Ni基催化剂活性的影响。实验结果表明,负载K盐的纤维素水蒸气催化气化过程中,K挥发后会在催化剂表面沉积,而少量K的存在和表面沉积不但能够提高镍基催化剂的抗积炭能力,而且有助于提高其催化活性,产生更多的氢气。然而纤维素中K的浓度过大,将会抑制Ni基催化剂的效果;K在催化剂上的沉积随催化剂循环次数的增加而增加,K的含量愈高,对催化剂的抑制效果愈明显,从而缩短了催化剂的使用寿命。     

Thin films of semiconducting lithium ferrite produced by pulsed laser deposition

Thin films of lithium ferrite (Li_0.5Fe_2.5O₄) have been deposited on (0 0 1) Al₂O₃ by pulsed laser deposition, with substrate deposition temperatures ranging between 500 and 800 °C, and oxygen pressures between 1 × 10⁻¹ and 4 × 10⁻⁷ mbar. X-ray diffraction shows that films grow with a (1 1 1) orientation. Conversion electron Mössbauer spectra for the high-pressure films show a single sextet with a hyperfine field of 49 T, while the low-pressure films show two sextets with hyperfine fields of 47 and 49 T. The spectra also reveal paramagnetic ferric iron in both types of films. Magnetization measurements of the films show a saturation magnetization of between 1.7 and 3.1μ_B per formula unit and a coercivity of between 10 and 44 mT. The films prepared under the lower oxygen pressures are semiconducting with resistivities of 2 × 10⁻² to 8 × 10⁻² Ω cm. They exhibit an anomalous Hall effect with p-type conduction at 175 K.     

Eucleanal A and B:Two new napthalene derivatives from Euclea divinorum

Two new naphthalene derivatives named eucleanal A and B（1 and 2） were isolated from Euclea divinorum.The structures of the new compounds were elucidated by detailed spectroscopic analysis such as ¹H,¹³C NMR,COSY,HMQC,HMBC and HREIMS mass spectrometry.     

Phase-alternated compositeπ/2 pulses for solid state quadrupole echo NMR spectroscopy

Phase-alternated compositeπ/2 pulses have been constructed for spinI=1 to overcome quadrupole interaction effects in solid state nuclear magnetic resonance (NMR) spectroscopy. Magnus expansion approach is used to design these sequences in a manner similar to the NMR coherent averaging theory. It is inferred that the symmetric phase-alternated compositeπ/2 pulses reported here are quite successful in producing quadrupole echo free from phase distortions. This effectiveness of the present composite pulses is due to the fact that most of them are of shorter durations as compared to the ones reported in literature. In this theoretical procedure, irreducible spherical tensor operator formalism is employed to simplify the complexity involved in the evaluation of Magnus expansion terms. It has been argued in this paper that compositeπ/2 pulse sequences for this purpose can also be derived from the broadband inversionπ pulses which are designed to compensate electric field gradient (efg) inhomogeneity in spinI=1 nuclear quadrupole resonance (NQR) spectroscopy.     

Fabrication and photoresponse of n-$$\hbox {WS}_{2}/$$p-V$$_{0.25}$$0.25W$$_{0.75}$$0.75Se$$_{2}$$2 van der Waals heterojunction

Excitation functions for \(\alpha \)-induced reactions on natural vanadium were measured in the energy range up to 20 MeV. The stacked-foil activation technique was used. The experimental results were compared with the theoretical calculations using EMPIRE-3.1, EMPIRE-3.2.2 and TENDL 2015, and with earlier experimental results. Thick target yields were calculated for the production of \(^{54}\hbox {Mn}\) and for the associated impurity \(^{52}\hbox {Mn}\).     

用于EAST上低杂波平行波数测量的磁探针设计与测试

针对EAST上2.45GHz低杂波,完成了低杂波平行波数测量磁探针的设计、仿真与测试。利用有限元仿真软件COMSOL Multiphysics 5.2对磁探针尺寸进行仿真优化,确定了单匝环、矩形缝以及陶瓷片厚度等影响磁探针耦合性能的关键尺寸。测试结果表明,该磁探针对2.45GHz低杂波有良好的耦合性能和鉴别波极化的能力,与仿真结果一致。研究结果为EAST装置上低杂波平行波数测量诊断系统的建立提供重要的参考依据,从而为进一步开展高密度低杂波电流驱动实验研究提供必要的实验数据。     

Normal- and Reversed-Phase Thin-Layer Chromatography of Amino Acids on Unconventional Supports with Mixed Mobile Phases Containing Dimethyl Sulfoxide

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of twenty-four amino acids has been studied on untreated and on triaryl phosphate (TAP)-impregnated...     

On a tensor-analogue of the Schur product

We consider the tensorial Schur product \(R \circ ^\otimes S = [r_{ij} \otimes s_{ij}]\) for \(R \in M_n(\mathcal {A}), S\in M_n(\mathcal {B}),\) with \(\mathcal {A}, \mathcal {B}~\text{ unital }~ C^*\)-algebras, verify that such a ‘tensorial Schur product’ of positive operators is again positive, and then use this fact to prove (an apparently marginally more general version of) the classical result of Choi that a linear map \(\phi :M_n \rightarrow M_d\) is completely positive if and only if \([\phi (E_{ij})] \in M_n(M_d)^+\), where of course \(\{E_{ij}:1 \le i,j \le n\}\) denotes the usual system of matrix units in \(M_n (:= M_n(\mathbb C))\). We also discuss some other corollaries of the main result.