A model is built to describe the dynamic trajectories of the xylene soluble fraction (XS) in an industrial bulk propylene polymerization process. Emphasis is given to the coupling between the XS dynamics and the reactor liquid bleed policy. It is shown that cocatalyst recirculation can affect the dynamics of the cocatalyst/donor ratio and consequently the dynamics of XS during polymerization. Simulation results indicate that the effect of the reactor liquid bleed operation and of the cocatalyst/donor ratio upon the XS trajectories can be minimized if PI controllers are designed to control the propane concentration and to increase the speed of the cocatalyst/donor transitions. Finally, it is shown that the model is able to reproduce the dynamic XS profile obtained during a large XS transition at plant site.
The paper presents experimental data obtained in the study of liquid–liquid partition equilibriums in biphasic system in order to optimize the process of transport through bulk liquid membranes (triphasic partition systems). The partition equilibriums of some nitrophenols using chloroform as extraction solvent and membranary solvent, respectively, were studied. The influence of the pH on the partition equilibriums was investigated. The repartition constants and the pKa values of the studied nitrophenols were calculated. Nitrophenols were transferred in triphasic system from a feed phase with pH 2, through a chloroform liquid membrane, into a receiving phase with pH 12, with efficiencies over 90%. 相似文献
Abstract The high-pressure crystal structures of the compounds UX, where X = N, P, As and Sb, have been studied using X-ray diffraction in the pressure range up to about 60 GPa Rhornbohedral distortions are observed for UN and Up above 29 GPa and lO GPa, respectively. In Up a further transformation to an orthorhombic phase occurs at 28 GPa. UAs and USb transform to the CsCl structure at 20 GPa and 9 GPa, respectively. The latter transformations show a considerable hysteresis when the pressure is released. The scaling behaviour of the bulk modulus has been studied. It is confirmed that a log-log plot of bulk modulus versus specific volume for the cubic phases gives a straight line with a slope near ? 5/3. 相似文献
Near-normal incident infrared reflectivity spectra of a
(001) YVO4 single crystal have been measured at different
temperatures in the frequency region between 100 and 6000 cm-1.
The reflectivity spectra are analyzed with the factorized form of
the dielectric function, and the dielectric properties and optical
conductivity of the YVO4 crystal are obtained. From the TO/LO
splitting, effective charges at different temperatures are
calculated to study the ionicity of YVO4. The internal modes
of the VO43- ion and the external modes of the Y(VO4) lattice
are compared with SiO44- in zircon and with other rare-earth vanadates. 相似文献
Summary The theory of the RPA optical response of a solid has been generalized in order to take into account also the possible presence
of spatially nonlocal potentials in the Hamiltonian. Explicit expressions for first- and second-order susceptibilities are
given in the new framework. The expressions obtained depend on the matrix elements of operators of the form of a commutator
of a component of the position operatorr and an operator that commutes with the lattice translations. The problem of the evaluation of these matrix elements is solved
in a simple manner by introducing an auxiliary, periodic position operator,XXXr. In such a way a general formulation is obtained that preserves the gauge invariance. As an application of the new theory,
the second harmonic generation (SHG) from a semiconductor in a simple two-band model has been studied. The differences between
our correct gauge-invariant results and those obtained in the usual local approximation is an indication of a slow convergence
of the expressions obtained in the local approximation. 相似文献
The optical reflectivity as a function of temperature of the title compound for x=0, 5 and 12 has been measured over a broad spectral range from 4 meV up to 12 eV. Our findings suggest a very anisotropic dynamics
of the charge excitation spectrum when measuring along or perpendicular to the ladders. Moreover, a metal-insulator transition
develops at low temperatures, leading to a suppression of Drude spectral weight in the far and mid-infrared spectral range.
We identify this behaviour as a consequence of the localization effects for small Ca substitution, and of the possible formation
of a charge density wave condensate for large Ca substitution.
Received: 18 June 1998 /
Accepted: 17 July 1998 相似文献
The effect of bulk magnetic susceptibility (BMS) on solid state NMR spectra of paramagnetic compounds was investigated theoretically and experimentally. The BMS shift was calculated for cylindrical and spherocylinderical containers with some ratios of the lengthLand the diameterD. The results show the best resolution can be obtained by using a long cylindrical sample container withL/D> 10 and by exciting only the region near the center of the container. The effect of the random orientations and distributions of crystallites in a powder sample was also calculated according to a model proposed by Schwerket al.[J. Magn. Reson. A119, 157 (1996)] with removing the Fermi contact term from their model. Static and the magic-angle spinning13C NMR spectra were recorded on two paramagnetic compounds of Ln(C2D5SO4)3· 8H2O where Ln = Pr, Yb. The modified theory predicts the BMS broadening of the experimental spectra very well. 相似文献