Comparison of Gas and Liquid Propylene Polymerization Technique – Hydrogen Effect on Thermal,Rheological, and Morphological Properties of PP

Summary: A comparison of PP qualities, which are produced with two different polymerization techniques–gas phase(GP) and liquid pool (LP)–under precise control of the polymerization temperature (70 °C) and pressure (GP = 25 bar, LP < 60 bar) using identical Ziegler‐Natta catalyst (TiCl₄/phthalate/MgCl₂ + TEA/silane), is presented. A series of homopolymer PP in a wide MW range from 100 000 to 1 600 000 g · mol^?1 was polymerized. During polymerization all samples were characterized exactly by their Rp‐profil. The effect of hydrogen on the initial reaction rate and on MW and MWD was analyzed on the basis of this so‐called kinetic fingerprint. The results showed that the polymerization rate reached a maximum for LP, of about 150 kg · g_cat^?1 · h^?1, in contrast to GP with a maximum of R_p,₀ = 45 kg · g_cat^?1 · h^?1. Analysis was carried out by means of GPC, SEM, DSC, platte‐platte rheometer, and WAXS. The results first showed that the MWD of LP PP is narrower (PD ～ 6.8) than for the GP PP (PD ～ 8), polymerized in two steps. An SEM study of the powder particle shows the typical dent surface morphology of polymers using Ziegler‐Natta catalysts for polymerization. WAXS and DSC analysis demonstrated that almost only the α‐modification of crystalline structure exists and that the crystallinity becomes considerably higher after solidification from melt. Furthermore, it was found that the crystallite size distribution depends on the polymerization technique. Rheological studies indicate that GP PP behaves more elastically. To summarize, it is shown that PP produced with the LP polymerization technique is more homogenous and of high quality.

Particle geometry of gas phase and liquid pool polymerized PP powder observed by SEM (PP‐L0).     

Oxydehydrogenation of propane over Mg-V-Sb-oxide catalysts. II. Reaction kinetics and mechanism

Recently we reported that Mg₄V₂Sb₂O_x is selective for propane andn-butane Oxydehydrogenation at low hydrocarbon conversion, and that propane is oxidized in parallel reactions to propylene and CO_x. We report now on the kinetics of propane and propylene oxidations over this catalyst. The partial oxidations of propane and propylene and zero-order in oxygen, whereas deep oxidations of both hydrocarbons are half-order. This difference in reaction order indicates that different forms of reactive oxygen are involved in the partial and deep oxidation reactions. Presumably, nucleophilic lattice oxygen partakes in the partial oxidation, while electrophilic dissociatively adsorbed oxygen is involved in deep oxidation. A single activated surface adsorbed state of the hydrocarbons is thought to be involved in both the partial and deep oxidation reactions. An interpretation of the observed reaction kinetics in context of the Mg₄V₂Sb₂O_x solid state chemistry, and the partial oxidation literature in general, suggests that selective oxydehydrogenation of propane occurs on isolated (Sb-O-V-O-Sb) sites, deep oxidation on multiple vicinal vanadium sites (Sb-O-V-O-V-O-Sb), and partial oxidation of propylene to acrolein on subsurface V-promoted antimony sites (Sb-O-Sb). Therefore, unproved selectivity of desired intermediates (propylene/acrolein) should be achieved by further lowering the vanadium concentration and/or through key solid state positioning of the vanadium in the catalyst lattice. Alternatively, selective doping to electronically decrease the electrophilicity of the waste forming sites and its appended oxygen should also help depress the waste forming reaction channels in favor of the desired partial oxidation channels. Finally it is anticipated that higher useful product yields would be attained with a compositionally optimized Mg-V-Sb-oxide catalyst by opting for a more stable, isolatable intermediate, e.g., acrylonitrile, by reacting propane in the presence of ammonia and oxygen (air) over this catalyst.     

Racial microaggressions and the power to define reality.

Replies to comments by T. E. Schnacht (see record 2008-05553-009), K. R. Thomas (see record 2008-05553-010), R. S. Harris Jr. (see record 2008-05553-011), and R. Goodstein (see record 2008-05553-012), on the current authors' original article (see record 2007-07130-001) which discusses racial microaggressions. The reactions by three of the four respondents to our article on racial microaggressions illustrate nicely the invisible nature of aversive racism and how well-intentioned Whites often dismiss, negate, and minimize the experiential reality of People of Color (POC). For too long POC have not had the opportunity or power to express their points of view. For too long their worldviews have been diminished, negated, or considered invalid. For too long they have been told that their perceptions are incorrect, that there are other logical and rational reasons for the actions of others (especially on racial issues), and that their assertions have no empirical validity. These latter responses are clearly evident in the comments by Schacht (2008), Thomas (2008), and Harris (2008), who continue to question the racial realities of POC using a number of false analogies, surface arguments, and flawed reasoning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of age on detection of emotional information.

Age differences were examined in affective processing, in the context of a visual search task. Young and older adults were faster to detect high arousal images compared with low arousal and neutral items. Younger adults were faster to detect positive high arousal targets compared with other categories. In contrast, older adults exhibited an overall detection advantage for emotional images compared with neutral images. Together, these findings suggest that older adults do not display valence-based effects on affective processing at relatively automatic stages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Space-bandwidth conditions for efficient phase-shifting digital holographic microscopy

Microscopy by holographic means is attractive because it permits true three-dimensional (3D) visualization and 3D display of the objects. We investigate the necessary condition on the object size and spatial bandwidth for complete 3D microscopic imaging with phase-shifting digital holography with various common arrangements. The cases for which a Fresnel holographic arrangement is sufficient and those for which object magnification is necessary are defined. Limitations set by digital sensors are analyzed in the Wigner domain. The trade-offs between the various holographic arrangements in terms of conditions on the object size and bandwidth, recording conditions required for complete representation, and complexity are discussed.     

Photoactivation of CdSe/ZnS quantum dots embedded in silica colloids

A study of the influence of the local environment on the light-induced luminescence enhancement of CdSe/ZnS quantum dots (QD) embedded in silica colloids that are dispersed in various solvents is presented. The photoluminescence of the embedded QD is enhanced up to a factor of ten upon photoactivation by ultraviolet or visible light. This enhancement is strongly dependent on the local environment. The thickness-dependent permeability of the silica shell covering the QD controls the influence of the solvent on the QD. If foreign ions are present the activation state is stabilized after termination of the activation, whereas in their absence the process is partially reversible. A new qualitative model for the photoactivation of QD in various environments is developed. It comprises light-induced passivation and subsequent oxidation processes. The embedded QD also retain their fluorescence quantum yield inside living cells. Moreover, they can be activated for many hours in living cells by laser radiation in the visible regime.     

Accumulation of organotin compounds and mercury in harbour porpoises (Phocoena phocoena) from the Danish waters and West Greenland

The concentrations of butyltin (summation operatorBT=TBT+DBT+MBT) and mercury (Hg) were determined in the liver of 35 harbour porpoises (Phocoena phocoena), which were found dead along the coastlines or caught as by-catch in the Danish North Sea and the Inner Danish waters. In addition, three harbour porpoises hunted in West Greenland were analysed. High levels of butyltin and mercury, within the range of 68-4605 mg BT/kg ww and 0.22-92 mg Hg/kg ww, were found in the liver of the Danish harbour porpoises and both substances tend to accumulate with age. The levels in the harbour porpoise from West Greenland were 2.0-18 mg BT/kg ww and 6.3-6.9 mg Hg/kg ww, respectively. The concentrations of butyltin and mercury were both found to be higher in stranded than in by-caught harbour porpoises but only the butyltin concentration was significantly higher in stranded porpoises in the age group 1-5 years. These substances are suspected of inducing adverse effects on immune and endocrine systems in mammals and they may thereby pose a threat to the animals. This study suggests that organotin compounds are also important, when assessing the risks of contaminants on the health and viability of harbour porpoises in Danish waters.     

Standing on the shoulders of giants. Science, politics and trust: a parliamentary life. By Jeremy Bray, edited by Elizabeth Bray

Book Review

Standing on the shoulders of giants. Science, politics and trust: a parliamentary life. By Jeremy Bray, edited by Elizabeth Bray Elizabeth Bray, 2004, ISBN 0-9546922-0-9, £12 pbk, 302 pp     

Longitudinal and cross-cultural validation of the belief-discrepancy reasoning construct.

Conducted 2 studies to validate the construct of belief-discrepancy reasoning, or the judgments people make about others who disagree with them. In Study 1, 83 1st, 4th, 7th, and 10th graders were assessed and then retested 1 yr later. Assessment was conducted with an objective, standardized forced-choice scale of belief discrepancy. Ss heard a recording of a dilemma as well as a peer's solution, one that contradicted the S's. Longitudinal trends were significant. The trends supported a 4-stage sequence of level 0 (not understanding that one can judge a disagreeing other), Level 1 (intolerance toward the other), Level 2 (total open-mindedness toward the other), and Level 3 (a willingness to judge the other as good or bad with more information about the other's belief). There was a faster rate of growth for the children (Grades 1 and 4) than for the adolescents (Grades 7 and 10). In Study 2, 34 4th and 7th graders from Kinshasa, Zaire were administered a belief-discrepancy scale. There were significant differences between the grades favoring the 7th graders. Implications for belief-discrepancy reasoning development are discussed. Results support the theory that the intolerance construct is developmental and has stagelike features. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An efficient external sorting with minimal space requirement

An efficient external sorting algorithm with minimal space requirement is presented in this article. The average number of passes over the data is approximately 1 +Ln(N + 1)/4B, whereN is the number of records in the file to be sorted, andB is the buffer size. The external storage requirement is only the file itself, no additional disk space is required. The internal storage requirement is four buffers: two for input, and two for output. The buffer size can be adjusted to the available memory space. A stack of size log₂ N is also required.This work was partially supported by a fellowship and grant from Western Michigan University.