Thesis (M. Phil.)--University of Hong Kong, 2008.

The objective of the research described in this dissertation was the search for optimum ligand-metal complex combination that would facilitate the contrathermodynamic isomerisation of internal olefins. To this end a variety of ligands where synthesised and subsequently tested, firstly for their ability to isomerise alpha olefins and secondly their ability to isomerise internal olefins. Due to the lack of information obtainable from literature about catalytic isomerisation of olefins, the general reaction parameters had to be investigated. Various factors that could play a role in the isomerisation of olefins where investigated and these included the effect that solvents have on the isomerisation as well as the possibility of metalhydride formation. The possible formation of metal-hydrides was tested by adding a variety of acids and also the addition of hydrogen gas to the solution. All of these factors played an important role in the subsequent isomerisation of alkenes and valuable data could be obtained from these experiments. Solvents were found to have an effect on the isomerisation, but a trend could not be established. The effect of added acid was more pronounced and a correlation between acid strength and isomerisation could be established. It was also found that hydrogen gas added to the reaction mixture generally increased the reactivity of the metal catalysts and some experiments were done to optimise the use of hydrogen in these reactions. The use of commercially available ligands for the isomerisation reaction was also investigated and gave a broad indication of possible active ligands. After these initial reactions and information gathered from literature, it was decided to synthesise a set of di-imine ligands and also a set of bis-phisphite ligands. Due to tautomerism of the di-imines to the corresponding enamines, a set of enamine/imine ligands was synthesised and tested with two rhodium and two palladium catalysts. The synthesis of bis-phosphite ligands was initially problematic, but ideal conditions were found and a set of bis-phosphite ligands was synthesised and tested. Results obtained from the testing of both the enamine/imine lignds as well as the bisiii phosphite ligands were of value and a great many trends could be observed. Many of these observations had correlations to either the electronic nature of the various ligands as well as that of the metal centre. The testing of a set of palladium(II) metallocycles also gave an insight into the electronic properties necessary for the successful isomerisation of olefins. These electronic properties are always a combination of ligand and metal centre effects and thus a fine balance must be struck between these two factors. As a final conclusion to the work that was performed, internal olefins were subjected to tandem isomerisation-hydroformylation reactions using some of the more active metal-ligand systems. Internal olefins were isomerised and hydroformylated in the same reaction vessel to afford branched and linear aldehydes. In these reactions, it was proved that isomerisation as a primary reaction could be coupled to a secondary reaction and be of use in industry and further research in this field might prove to be of some value. / Prof. D.B.G. Williams

P-xylene is one of the highly influential commodities in the petrochemical industry. It is used to make 90% of the world’s third largest plastic production, polyethylene terephthalate (PET). With a continuously increasing demand, the current technology’s high energy intensity has become a growing concern. Membrane separation technology is a potential low-energy alternative. Polymeric membranes were investigated in a pervaporation experiment to separate xylene isomers. Polymers of intrinsic microporosity (PIMs) as well as polyimides (PIM-PI), including thermally cross-linked PIM-1, PIM-6FDA-OH and thermally-rearranged PIM-6FDA-OH were investigated as potential candidates. Although they exhibited extremely high permeability to xylenes, selectivity towards p-xylene was poor. This was attributed to the polymers low chemical resistance which was apparent in their strong tendency to swell in xylenes. Consequently, a perfluoro-polymer, Teflon AF 2400, with a high chemical resistance was tested, which resulted in a slightly improved selectivity. A super acid sulfonated perfluoro-polymer (Nafion-H) was used as reactive membrane for xylenes isomerization. The membrane exhibited high catalytic activity, resulting in 19.5% p-xylene yield at 75ᵒC compared to 20% p-xylene yield at 450ᵒC in commercial fixed bed reactors. Nafion-H membrane outperforms the commercial technology with significant energy savings.

Cellulose, a major constituent of biomass, is a promising source of sustainable energy. A key step in the conversion of cellulose to a platform chemical is glucose isomerization to fructose. Sn-Beta zeolite catalyzes this reaction with high yield. The effect of methanol as a reaction medium on glucose transformations catalyzed by Sn-Beta has not been quantified. Here, density functional calculations are employed to elaborate on the effect of methanol medium, specifically to determine how reaction pathways and energy barriers are affected by methoxylation of Sn or Si groups at the active sites in Sn-Beta. Calculations suggest that the presence of the neighboring silanol group is necessary for glucose isomerization. If the silanol group is altered by methoxylation glucose epimerization is promoted and will likely occur. These results provide additional understanding of the active site of Sn-Beta for glucose transformations and are insightful for novel catalyst design and development.

<p> The Arrhenius equation for the ring opening isomerization of cyclopropylmethyl radicals (R•) to 3-buten-1-yl radicals (R•') for the 303-362 K temperature range was determined by thermolysis of cyclopropylmethyl [1-hydroxy-1-methylethyl] diazene in the presence of excess 1,1,3,3-tetra-methylisoindolin-2-yloxyl (Y•).</p> <p> Rate constants for coupling of R• with Y• were assumed to be proportional to diffusion controlled rate constants (kd) and rate constants (ki) for the isomerization were calculated from kd (corrected) and product ratios (RY/R'Y). The temperature dependence of ki, given by log(ki/s^-1) = (13.9 ± 0.4) - (7.6 ± 0.1)/θ, is significantly different from that determined by Ingold and co-workers by kinetic epr spectroscopy in the temperature range 128-153 K; log(ki/s^-1) = (11.34 ± 0.85) - (5.94 ± 0.57)/θ, where θ = 2.3 RT kcal mol^-1.</p> / Thesis / Master of Science (MSc)

<p> The single selective inversion recovery experiment, developed by Bain and Cramer, has been used with great success in elucidating the molecular dynamics of three systems.</p> <p> The isomerization of d,l bis(1-indenyl)dimethylsilane to its meso isomer proceeds through sequential [1,5]-suprafacial shifts; ΔH+ for the process was evaluated as 21.9 ± 0.5 kcal/mol. There is only one mechanism operating at a detectable rate below about 150°C. Below 100°C this process is too slow to be detected by DNMR, but it is readily followed by classical kinetics methods. Above 100°C, the isomerization may be followed by 1D selective inversion experiments. The isoindene intermediate is conveniently trapped as its double Diels-Alder adduct showing that the rearrangement occurs relatively rapidly on the chemical time-scale.</p> <p> The barrier to hindered rotation about the Mn - C(4) sigma bond in (n^1 -Cpp)Mn(CO)3(PEt3)2 was measured. The observed value of ΔH+ was 13.1 ± 0.2 kcal/mol. ΔS+ was determined to be -11.2 ± 0.7 eu. As the compound is thermally sensitive, it would have been impossible to use lineshape analysis to determine the barrier. 1D selective inversion recovery experiments were used.</p> <p> A combination of 13C NOESY, 13C single selective inversion, and 13C lineshape analysis experiments identified the exchange pathways and determined temperature-dependent rate constants for the N,N'-[dimethyl-(2,2'dithiobisacetyl)]ethylenediamine (DADS) system. DADS exists as five exchanging rotamers in solution. Two of the conformers are symmetric, with C2 symmetry (ZZ1 and ZZ2). The other three conformers are asymmetric, with one amide group cis and the other trans (ZE1, ZE2, ZE3).</p> <p> The NOESY experiments gave a site-to-site map of the exchange processes at several temperatures. At room temperature, ZE1 is exchanging with both ZE2 and ZE3, but there appears to be no exchange between ZE2 and ZE3. This process seems to occur via hindered rotation about the disulfide bond, with ΔH+ = 15.3 ± 0.4 kcal/mol, and ΔS+ = -6.3 ± 1.1 eu.</p> <p> At higher temperatures, ZZ1 and ZZ2 start to exchange with ZE1 via hindered rotation about the amide bonds. ΔH+ for the process was determined to be 19.8 ± 0.4 kcal/mol, and ΔS+ was found to be 0.7 ± 1.2 eu. The barrier agrees quite well with that measured for the uncyclized precursor to DADS. ΔH+ was found to be 19.3 ± 0.7 kcal/mol, while ΔS+ was determined to be 2.5 ± 2.1 eu.</p> / Thesis / Master of Science (MSc)

No description available.

Yes / Naphtha isomerization is an important issue in petroleum industries and it has to be a simple and cost effective technology for producing clean fuel with high gasoline octane number. In this work, based on real industrial data, a detailed process model is developed for an existing naphtha isomerization reactor of Baiji North Refinery (BNR) of Iraq which involves estimation of the kinetic parameters of the reactor. The optimal values of the kinetic parameters are estimated via minimizing the sum of squared errors between the predicted and the experimental data of BNR. Finally, a new isomerization process (named as AJAM process) is proposed and using the reactor model developed earlier, the reactor condition is optimized which maximizes the yield and research octane number (RON) of the reactor.

Fluorescence spectroscopy and imaging have a very broad spectrum of applicationswithin the life sciences, in particular for detection and characterization ofbiomolecular dynamics and interactions in different environments. This thesis comprisesprojects that strive to further expand the information content extracted fromthe detected fluorescence, leading to sensitive readout parameters for studies ofbiomolecular dynamics and interactions. Two major strategies are presented toachieve this aim. The first strategy is based on the expansion of the availablereadout parameters beyond the "traditional" fluorescence parameters: intensity,wavelength, polarization and fluorescence lifetime. The additional parameters arebased on blinking properties of fluorescent labels. In particular on transitions betweensinglet and triplet states, and transitions between the trans- and cis-isomersof fluorophores. Two publications in the thesis are based on this strategy (paperI and IV). The second strategy is based on the utilization of fluorescence intensityfluctuations in order to detect the oligomerization mechanisms of fluorescentlylabeled peptides and proteins. This strategy combines the intensity fluctuationanalysis and the readout of distance dependent energy transfer between fluorescentmolecules together with the correlation analysis of fluorescence from two labeledproteins emitting at different wavelengths. Another two publications presented inthe thesis are based on the second comprehensive strategy (papers II and III).The work presented in this thesis shows that the blinking kinetics of fluorescentlabels contain significant information that can be exploited by a combination of fluctuationsanalysis with distance dependent excitation energy transfer between thefluorescent molecules, or by analysis of fluorescence covariance between moleculesthat emit at different wavelengths. These fluorescence-based methods have a significantpotential for molecular interaction studies in the biomedical field. / <p>QC 20160527</p>

Chromatographic methods were used to determine the absolute values of cis-aconitic acid and trans-aconitic acid present in sugar cane factory processing streams and to determine the rates of isomerisation from the trans-aconitic acid to the cis-aconitic acid isomer. A reproducible, solid phase, ion exchange extraction method was developed to isolate the organic acids found in sugar factory process streams. The isolated acids were quantified using a dual ion-exclusion column, high performance liquid chromatographic method. To improve resolution of the acids, columns were maintained at different temperatures, whilst the combined use of both ultra-violet (UV) and refractive index detection proved useful in peak identification. Concentrations of the aconitic acid isomers were used to calculate the cis/trans aconitic acid isomer ratio occurring across the different processes found in a sugar cane factory. trans-Aconitic acid was found to be the predominant form present in the cane entering the factory. Analysis showed that isomerisation of the trans-aconitic acid to the cis-aconitic acid isomer occurred during processing. To understand and model this reaction, a reproducible experimental isomerisation method was developed making use of buffers to maintain pH conditions during experiments. A chromatographic analysis method, using ion-exclusion chromatography and UV detection, was developed to analyse the isomerisation reaction mixture. Chromatography was used in both an on-line and off-line mode for quantitation of the isomers. The method was used to study the isomerisation under conditions similar to those found in the factory. These included pH, temperature, ionic strength and the presence of monovalent and divalent cations found in sugar cane juices. It was shown that the isomerisation is a first order reversible reaction under the conditions studied. Temperature and pH were shown to be the important isomerisation variables. Temperature enhances the rate of isomerisation of the trans-aconitic isomer to the cis-aconitic acid isomer whilst pH affects the ultimate cis/trans aconitic acid ratio attained. Ionic strength was found to be a relatively unimportant factor. The presence of divalent and monovalent cations, at concentrations usually found in cane juice, was shown to have little effect on the rate of isomerisation. Activation parameters, including the activation energy (Ea), pre-exponential factor (log A), enthalpy (?H‡) and entropy of activation (?S‡), were calculated at each combination of buffer concentration and pH used in the experimental procedures. The values recorded are of a similar value to those reported for structurally similar compounds. cis-Aconitic acid was shown to undergo decarboxylation to itaconic acid. This occurred at low pH values and high temperatures. A detailed study was not undertaken since the conditions under which it occurs are considered extreme from the viewpoint of a sugar technologist. A model describing the equilibrium cis/trans aconitic acid isomer ratio was developed as a function of pH, temperature and time from the kinetic results. This was used to predict the equilibrium ratio for the aconitic acid isomers at the output of various processes in the sugar factory. Given the time, average pH and temperature the model can successfully predict the equilibrium ratio for the relevant process stream. / Thesis (M.Sc.)-University of Natal, Durban, 2000.