No description available.

Silica supported chromium oxide catalysts, known as Phillips catalysts, are used in the production of over 40% of the world's high-density polyethylene. The original catalyst comprised CrO(_3) impregnated onto silica. Due to the carcinogenic nature of chromium(VI), chromium(m) catalyst precursors which are oxidised during calcination are now preferred. Two such precursors have been employed throughout the studies reported in this thesis; one is prepared by the aqueous impregnation of a silica support with basic chromium(in) acetate, whilst the other comprises a dry-blended mixture of chromium(m) acetylacetonate with silica. Calcination of the two precursors has been studied using a combination of temperature-programmed quadrupole mass spectrometry and infrared spectroscopy. The chromium(III) acetylacetonate precursor is postulated to disperse near its melting point and react via an acetate intermediate. Both precursors may therefore be expected to produce the same catalyst following calcination. The study of subsequent CO reduction of these calcined catalysts by quadrupole mass spectrometry supports this observation. The reduction is found to proceed via a Langmuir-Hinshelwood mechanism, both precursors demonstrating the same behaviour. Activation energies for the catalyst reduction have been determined from the corresponding Arrhenius plots. Quadrupole mass spectrometry techniques have identified 1-hexene production during the early stages of polymerization using the CO reduced catalysts. This indicates the formation of a chromacyclopentane intermediate species which may also be involved in the mitiation of polymerization. The continuous fragmentation of the catalyst support and polymer growth have been investigated using contact mode and phase-imaging atomic force microscopy. Non-equilibrium plasma oxidation of the two catalyst precursors has been studied by quadrupole mass spectrometry. An active catalyst is obtained from the chromium(m) acetate catalyst, however the dry-blended chromium(in) acetylacetonate precursor is unable to achieve the dispersion required, and the oxidised species are inactive for ethylene polymerization.

No description available.

Diss. Stockholm : Karol. inst.

Thesis (Ph.D.)--Virginia Commonwealth University, 2008. / Title from title-page of electronic thesis. Prepared for: Dept. of Medicinal Chemistry. Bibliography: leaves 95-108

Thesis (Ph.D.)--Virginia Commonwealth University, 2008. / Prepared for: Dept. of Medicinal Chemistry. Bibliography: leaves 95-108. Available online via the Internet.

A bacterial additives treatment experiment was conducted to assess the microbial and biochemical changes in stored swine manure. Nitrate salt was added to a slurry of swine waste collected from a waste storage pit to identify the effects of varying levels of nitrate upon the microbial community and the resulting metabolic changes. This research was an attempt to reduce the formation of odorous sulfur-containing compounds and to increase the formation of odorless nitrogen gas by manipulating the metabolic pathways in anaerobic decomposition of the organic matter within manure. Sulfide production from swine wastewater was reduced approximately 45 percent with the addition of 1500 mg/l or more of nitrate to the wastewater.

No description available.

No description available.

Thesis (Ph. D.)--Ohio University, June, 2004. / Includes bibliographical references (leaves 128-139).