Reactor design and operation for gas-phase ethylene polymerization using ziegler-natta catalysts

A well-instrumented, semi-batch reactor has been constructed for studying the gas-phase polymerization of ethylene using solid Ziegler—Natta type catalysts. This reactor can be operated over the entire range of temperatures and pressures used in the commercial production of linear low, and high density polyethylenes. Successful operation of the reactor depends on careful control of the reaction temperature which in turn is mainly dependent on the total rate of polymerization. If this rate is too large, then the reaction temperature increases uncontrollably (thermal runaway) until catalyst deactivation occurs when melting polymer encapsulates the catalyst particles. Operating conditions are described which resulted in precise and reproducible kinetic measurements for a δ-TiCl₃ δ 1/3AlCl₃ catalyst (Stauffer AA Type 2.1) with diethylaluminum chloride (DEAC) as the co-catalyst. This system displayed first-order kinetic behavior over the temperature range 20 to 90°C with an activation energy of 32.6 kJ/mol.     

Effect of pretreatment and adsorption conditions on gas adsorption by supported metal catalysts

The influence of pretreatment and adsorption conditions on the adsorption of oxygen and hydrogen on supported Pt and Rh catalysts has been studied. It has been found that reduction conditions (temperature and time) and subsequent out gassing conditions influence the amount of gas adsorbed. Oxygen and hydrogen uptakes measured in a static system were significantly different than those measured in a dynamic system. Reproducible adsorption uptakes can be obtained by careful control of pretreatment and adsorption conditions.     

The oxidation of ethylene over a supported platinum catalyst

The complete oxidation of ethylene over a 0.3% Pt/Al₂O₃ catalyst, at ethylene concentration of ≤ 1.0 mol/m³ and oxygen concentrations of 0.16 to 8.6 mol/m³, was studied in a recycle reactor at temperatures of 362 to 472 K. The activity of the catalyst was influenced by pretreatment and reaction conditions causing fluctuations in rate measurements. Nevertheless, a simple rate function, r =Ae^?E/RT[O₂]/[C₂H₄], fitted the data as well as more complicated rate functions.     

CuIn1 − xGaxSe2 photovoltaic devices for tandem solar cell application

CuIn_1 − xGa_xSe₂ (CIGS) solar cells show a good spectral response in a wide range of the solar spectrum and the bandgap of CIGS can be adjusted from 1.0 eV to 1.7 eV by increasing the gallium-to-indium ratio of the absorber. While the bandgaps of Ga-rich CIGS or CGS devices make them suitable for top or intermediate cells, the In rich CIGS or CIS devices are well suited to be used as bottom cells in tandem solar cells. The photocurrent can be adapted to the desired value for current matching in tandem cells by changing the composition of CIGS which influences the absorption characteristics. Therefore, CIGS layers with different [Ga]/[In + Ga] ratios were grown on Mo and ZnO:Al coated glass substrates. The grain size, composition of the layers, and morphology strongly depend on the Ga content. Layers with Ga rich composition exhibit smaller grain size and poor photovoltaic performance. The current densities of CIGS solar cells on ZnO:Al/glass varied from 29 mA cm^− 2 to 13 mA cm^− 2 depending on the Ga content, and 13.5% efficient cells were achieved using a low temperature process (450 °C). However, Ga-rich solar cells exhibit lower transmission than dye sensitized solar cells (DSC). Prospects of tandem solar cells combining a DSC with CIGS are presented.     

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

The effects of support friability (Φ) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2‐L reactor operated in the semibatch gas‐phase mode at 80°C and 1.4 MPa. Φ of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support Φ as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)^?1 h^?1 for low‐Φ catalysts to 10–20 t of PE (mol of Zr)^?1 h^?1 for moderate‐Φ catalysts and up to 100 t of PE (mol of Zr)^?1 h^?1 for the high‐Φ catalysts. The presence of 1‐hexene and propylene comonomers increased the activity of the low‐Φ catalysts by up to 20‐fold and 50‐fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1‐hexene was less than 3‐fold for the moderate‐Φ catalysts, whereas the high‐Φ catalysts showed little activity enhancement. Sometimes, 1‐hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different Φ's. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 514–527, 2007     

Influence of high growth rates on evaporated Cu(In,Ga)Se2 layers and solar cells

Thin film solar cells based on polycrystalline Cu(In,Ga)Se₂ were prepared by elemental co‐evaporation using modified three‐stage processes on soda lime glass substrates at a low substrate temperature of 450°C intended for application on polyimide foils. The growth rates in the different stages of the growth process were varied, and it was observed that the final composition profile and structural quality of the film are mainly determined by the growth rate in the third stage. Application of high growth rates in the second stage was found to have no significant impact on layer morphology and gallium grading profile, which was confirmed by scanning electron microscopy, secondary ion mass spectroscopy, and x‐ray diffraction measurements. On the other hand, scanning electron microscopy cross sections revealed that high growth rates in the third stage lead to a fine‐grained structure toward the surface as well as smaller grains toward the back contact. Secondary ion mass spectroscopy and x‐ray diffraction measurements of such layers revealed a pronounced gallium grading profile, while Raman spectroscopy showed strong occurrence of group III‐rich phases in the near‐surface region. The final device performance was found to deteriorate by about 10% relative to the baseline process efficiency when growth rates of up to 500 nm min⁻¹ were applied in the second stage or 600 nm min⁻¹ in the third stage. Copyright © 2011 John Wiley & Sons, Ltd.     

Modification of the three-stage evaporation process for CuIn1−xGaxSe2 absorber deposition

CuIn_1−xGa_xSe₂ absorbers for highest efficiency state-of-the-art solar cells are generally deposited by a sequential three-stage coevaporation process from elemental sources. We investigated the influence of the maximum copper concentration used during processing in the second stage of the growth process. The impact on the Ga grading in the deposited layer was measured by SIMS. The position and slope of the Ga grading profiles were optimized for high efficiency solar cells. Effects on the phases found in the absorber layer were investigated by Raman spectroscopy. The recorded spectra show the formation of a group III rich phase in layers grown at high maximum Cu contents. Best PV parameters were achieved for solar cells developed with absorbers grown with [Cu]/[In + Ga] = 1.05 at the end of the 2nd stage.     

Separation of mono- and di-saccharide derivatives by high-resolution gas chromatography

Summary The gas chromatographic analysis of NaBH₄-reduced monosaccharide mixtures (either trimethylsilylated or acetylated) and NaBH₄-reduced trimethylsilylated disaccharide mixtures in open tubular glass capillary columns is described. Complete separations of the investigated monosaccharides can be achieved if the same separation column and the appropriate method of derivatization are used. Kovats' retention indices of the derivatives are determined and their experimental repeatability is discussed.

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Hochauflösende gaschromatographische Trennung von Mono- und Disaccharidderivaten

Zusammenfassung Die gaschromatographische Analyse NaBH₄-reduzierter und entweder trimethylsilylierter oder acetylierter Monosaccharidmischungen und NaBH₄-reduzierter trimethylsilylierter Disaccharidmischungen in Glascapillartrennsäulen wird beschrieben. Es wird gezeigt, daß bei Anwendung der geeigneten Derivatisierungsmethode vollständige Trennungen der untersuchten Monosaccharide in derselben Trennsäule erzielt werden können. Die Retentionsindizes nach Kovats werden bestimmt und ihre experimentelle Reproduzierbarkeit diskutiert.