Diss. (sammanfattning) Luleå : Luleå tekniska univ., 2004. / Härtill 7 uppsatser.

Thesis (B.A.)--Haverford College, Dept. of Computer Science, 2002. / Title from caption. Includes bibliographical references.

Thesis (Ph.D.) - University of St Andrews, October 2009.

No description available.

The rational design and synthesis of organic templates for the synthesis of new microporous materials has resulted in the production of five new materials, three of which are known to be microporous, the other two being better described as being open framework materials. The first three microporous materials are named STA-1, -2 and -3 (for St. Andrews) and have structural compositions of the form MgxAl1-xPO4 x/n Rn+.yH2O (Mg0.18Al0.82PO4.R0.094-0.22H2O, as determined by EDX for STA-1). The fourth novel microporous solid is a boron aluminophosphate (BAlPO) and the fifth an aluminophosphate solid containing its organic template intact. All of the new materials were synthesised following a systematic study over a wide range of templates including 5 homologous series designed specifically to be used as templates in the production of alumino-silicates and -phosphates. The structure of the first two magnesium aluminophosphates (STA-1, STA-2) to be solved by single microcrystal diffraction at the ESRF at Grenoble on crystals approximately 30 x 30 x 30 mum in size is described. The in situ location of the template was determined directly from x-ray diffraction in the second of these materials and has formed part of a combined experimental and computational study into template location within novel frameworks. The study shows how the encapsulation of the template is directly responsible for the similarity in pore architecture between MAPO-56 and STA- 2 (which co-crystallise) since the template adopts the same orientation in both materials Polymeric / oligomeric templates have also formed part of this study. These templates are shown to influence the phase, crystallinity, particle size and catalytic performance of the product magnesio-aluminophosphate MAPO-31. Computer modelling has also been utilised to interpret the experimental data obtained from the systematic study on the use of polymeric templates. The in situ synthesis and subsequent encapsulation of two coordination complexes inside the supercage of zeolite-Y, including the 3-methyl-1,3,5,8,12- pentaazacyclotetradecane macrocycle is also described.

No description available.

No description available.

The feasibility of separating piperylene (1,3-pentadiene) from a mixture of five-carbon olefins and diolefins with Linde 5A Molecular Sieves was investigated. Olefins and especially diolefins are very reactive and tend to polymerize on the highly polar adsorptive surface thereby clogging the pores of themolecular sieve. It is believed that the acid sites within the zeolite cages catalyze this polymerization reaction and that poisoning of these sites by adsorption of a nitrogenous base (ethylenediamine, dimethylamine or ammonia) or hydrogen sulfide inhibits the formation of polymers. Two criteria were used in the evaluation of the polymerization inhibitors tested. First, a series of consecutive runs (adsorption, purge, and desorption cycle) were made with the pretreated molecular sieves. The adsorption capacity (grams adsorbate/grams of molecular sieve) and percent desorption of adsorbate (grams desorbed adsorbate/grams adsorbate) were plotted to determine the relative amount of polymer buildup on the molecular sieve with the various candidate polymerization inhibitors. Secondly, the desorbed adsorbate (product) collected from a cold trap during the desorption step was analyzed by gas chromatography and the product quality, with respect to 1,3-pentadiene, was determined. Dimethylamine was found to be the best polymerization inhibitor of those tested when evaluated in this manner.

Piperylene concentrate is a complex mixture of 5-carbon unsaturates. The major components are trans-1,3-pentadiene and cyclopentene. The object of this work is to form a product high in cyclopentene and a product high in the pentadienes, through the use of 13X zeolite molecular sives. Separation by molecular sieves is difficult because of the tendency of trans and cis pentadience to polymerize o the sieve and to thus decrease the adsorptive capacity of the sieve. Nitrogenous bases (dimethylamine, pyridine, and piperidine) were used in an attempt to neutralize any acid sites on the sieve. Dealumination by EDTA was used to decrease the number of electron deficient aluminum cations. cation exchange with iron, copper, potassium, and barium were used in an attempt to decrease polymerization. Silylation, esterification, and methylation were attempted to decrease the number of polymerization sites. The degree of polymerization inhibition achieved by the different treatment procedures was determined by a comparison of adsorptive capacity (g adsorbate/g sieve) and by percent desorption ((g recovered adsorbate/g adsorbate) X 100). The copper exchanged 13X sieve showed very high initial adsorptive capacity at 0.42 g adsorbate/g sieve and the highest percent desorption at nearly 100% for the first two runs. The methylated and silylated 13X sieves showed high adsorptive capacity but low percent desorption.

High levels of vibration are essential for the proper operation of vibrating screens. However, this motion imparts high dynamic loads on their support structures leading to premature failure or costly construction. Various methods exist for the attenuation of these forces, but they require undesirable addition of weight to the screen assembly, which can be as much as 130% of the screen mass. More appropriate methods are pendulum, hydraulic and liquid inertia vibration absorbers. These devices can provide similar isolation at only a fraction of the weight increase of current screen isolation methods. The liquid inertia vibration absorber's unique properties make it ideal for the attenuation of screen forces, as this study will show. A mathematical model describing the motion for the vibration absorber was derived. This led to an equation describing the force transmissibility, which was used to show which parameters influence the absorber's performance. The model was extended to take into account the effect of conical port inlets/outlets, which were used to reduce the viscous damping. The effect of viscous damping was quantified using computational fluid dynamics. The mathematical model was used to show how an optimal set of parameters could be found. Two design procedures were developed for the vibration absorber and were then used to design an experimental absorber. The experimental absorber was used to validate the mathematical model. Several practical considerations for the design were discussed and solutions suggested. The stiffness of the absorber was estimated using finite element modelling. Two elastomeric springs of different hardnesses were fitted to the absorber. The softer spring achieved a transmissibility of 16% by 42 Hz. The main stumbling block in reducing the transmissibility even further is the reduction of the damping. The experience gained from the experimental absorber was used to suggest how an absorber could be applied to a screen. An absorber isolating at 12.5 Hz was designed for this purpose. A theoretical design study investigated two possible configurations of absorber fitment. When the absorber was fitted directly to the screen the force transmitted was reduced 7.2 times. Fitting the absorber to the sub-frame gave similar transmissibility results to that of a screen fitted with a sub-frame only, but the mass ratio was only 15%. The outcome of this study is a thorough understanding of liquid inertia vibration absorbers as well as a procedure for their optimal design. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted