University, Diss., 2004--Bonn.

Proefschrift Rijksuniversiteit Groningen. / Datum laatste controle: 03-06-1997. Auteursnaam op omslag: Hans Hektor. Lit.opg. - Met een samenvatting in het Nederlands.

No description available.

No description available.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 281-284).

No description available.

M.Tech. / Clinoptilolite possesses acid and base properties, and is hydrothermally stable at high temperatures. It can be reactivated by simple oxidation, and is highly selective due to its unique-shape selectivity. It is also not harmful to the environment and it has shown benefits to soil as well (Mumpton,1977). An initial study of the reactions of methanol amination was done using both natural local and synthetic clinoptilolites. Characterization of each was done before and after modification using XRD, TPD and BET analysis. The BET analysis showed an increase in the surface area and pore diameter of both the natural and synthetic types after acid treatment and calcination. Most interesting of all was the large increase in surface area, where the natural type increased from 16 to 36.7 m 2/g after acid treatment and the synthetic type increased almost 13 times, from 2 to 27.7 m2/g after acid treatment. This effect had a strong influence on the selectivity of methylamines by allowing a larger surface area to be in contact with the feed reagents. The XRD of the treated and untreated natural and synthetic clinoptilolite were compared and discussed. The catalytic properties of zeolites depend on the treatment of clinoptilolite, and the characteristic peaks of natural and the acid treated form can be identified in the XRD plots.The TPD analyses showed that there were two acid sites associated with the clinoptilolite; one weak and one strong. The synthetic clinoptilolite weak acid site also showed a much lower ammonia uptake, than the natural clinoptilolite weak acid site. Clinoptilolite was shown to be successful as a catalyst for the production of dimethylamine with high selectivity. This was attributed to a transition state shape selectivity associated with the clinoptilolite channels. The natural clinoptilolite displayed good selectivities at 400°C and a 5:1 ratio of methanol to ammonia, and gave a high conversion of > 90% ammonia to amines. The synthetic clinoptilolite gave better conversions and lower TMA selectivity than the natural clinoptilolite over a large range of feed ratios and temperatures. This included conversions of over 90% for most ratios (at 400 and 450°C). The natural clinoptilolite gave better results than those obtained using the amorphous clinoptilolite, which is currently used in industry. For example, low TMA selectivity was observed when a ratio of 5:1 or greater (methanol to ammonia) was used. The TMA selectivity is still far lower than the thermodynamic equilibrium selectivities obtained without a catalyst (62%). The catalyst lifetime has been shown to deteriorate with time.

The methanol extract of Helichrisum pedunculatum was screened for antimicrobial activity up to a concentration of 5 mg/ml using the agar dilution technique. A number of test bacterial isolates, comprising both Gram negative and Gram positive organisms were susceptible to the crude extract of the plant. The minimum inhibitory concentrations (MICs) of the extract ranged between 1 and 5 mg/ml for the susceptible organisms. The MICs of the selected antibiotics, chloramphenicol and penicillin, ranged between 2 and 4 mg/L, and 2 and 32 mg/L respectively against Bacillus cereus, Proteus vulgaris and Staphylococcus aureus OKOH1. Bactericidal activity was determined by the time kill assay. The methanol extract of the plant was not bactericidal at 1 × MIC for B. cereus, P. vulgaris and Staph. aureus OKOH1. At 2 × MIC the extract was bacteriostatic against B. cereus but bactericidal against P. vulgaris and Staph. aureus OKOH1. Combination studies were done at 1/2 × MIC, 1 × MIC and 2 × MIC of the plant extract with 1 × MIC of the antibiotics. Combinations of the plant extract and chloramphenicol resulted in mostly indifferent interactions against P. vulgaris and Staph. aureus OKOH1 but synergistic interactions at higher concentration of the plant extract for B. cereus. Penicillin combinations gave synergistic interactions at lower concentrations of the plant for P.vulgaris and Staph. aureus OKOH1 but was mostly indifferent for B. cereus.

The photocyclization and photosolvolysis of a series of hydroxy-substituted biaryl methanols [special characters omitted] have been studied. The proposed mechanism involves deprotonation of the HOAr moiety and heterolytic cleavage of the C-O bond of the hydroxymethyl group [special characters omitted] in the first excited singlet state (S1), to give biaryl quinone methide intermediates, which subsequently cyclize to the corresponding chromene product and/or react with solvent to give the solvolysis product. The formation of these quinone methide intermediates is facilitated by the excited state planarization and the subsequent charge polarization (negative charge transferred from the HOAr ring into the [special characters omitted] ring) of the biaryl. Although both of these processes are influenced by steric and electronic factors, the latter turns out to have a more significant effect on reaction efficiency. When the geometry of the molecule goes from a twisted conformation to a more planar form, the molecule becomes more conjugated and thus gains delocalization energy. This energy is generally larger for the planarization in the S1 state than in the ground state. When it is large enough to overcome the steric repulsion for twisting, biaryls can planarize efficiently in the excited state, which is true for most biphenyl systems. However, it is shown that the deprotonated forms [special characters omitted] of these biaryls have an even larger driving force for S1 planarization than the neutral forms [special characters omitted]. Thus, biaryls with naphthalene ring(s) joined at the 1-position which do not planarize efficiently in the neutral form can still reach a more planar geometry after adiabatic deprotonation of the phenolic hydroxy group in S1. That is, the photocyclization of these molecules proceeds via initial adiabatic deprotonation from the twisted S1 state, followed by twisting (to the planar form) and subsequent charge polarization which expels the hydroxy group at the benzylic position [special characters omitted], to give the required quinone methide intermediate. The o,o'-biaryl quinone methides derived from the o,o'-substituted biaryl methanols are very short-lived due to rapid intramolecular ring closure and are therefore not detectable by nanosecond laser flash photolysis. The o,p’- and p,p'-biphenyl quinone methides, however, do not cyclize and as expected, are readily observable by nanosecond laser flash photolysis. When the benzylic hydroxy group is replaced by other leaving groups, the reaction can be used, in principle, as a photodeprotecting reaction and also to photogenerate acid. These and other results of the Thesis have uncovered many interesting mechanistic details of this new class of reaction and hence have increased our general knowledge of the excited state behavior of aromatic molecules. / Graduate

No / Comparison of optimal operation between conventional batch reactive distillation column (CBRD) and middle-vessel batch reactive column (MVBRD) for the production of lactic acid via hydrolysis of methyl lactate has not been considered in the past. Therefore, it is the main focus in this work. A dynamic optimization problem incorporating a process model is formulated to minimize the batch time subject to constraints on the amount and purity of lactic acid. Control variables (reflux ratio or/and a reboil ratio) are treated as a piecewise constant. Optimization results indicate that MVBRD is more effective than CBRD in terms of saving in batch time which can be as high as of 20 %.