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The Cycloheptatriene-Norcaradiene EquilibriumPikulik, Ivan Ignac 01 1900 (has links)
<p> The effect of a C-7 substituent on the position of the cycloheptatriene/
norcaradiene equilibrium has been investigated. For this purpose a series of monosubstituted cycloheptatrienes was prepared in which the C-7 substituent was a carbonium ion grouping. From the spectral properties of these systems, it has been concluded that proportion of the norcaradiene valence tautomer present increases as the electron withdrawing ability of the carbonium ion substituent is enhanced.</p> <p> From a comparison of the pmr spectra of 7-norcaradienylmethyl cations with suitable model systems it is suggested that these norcaradienes are aromatic and that they support an induced diamagnetic ring current when in a magnetic field. It would appear that this type of cyclic delocalization is enhanced by the presence of an electron defficient substituent at C-7 of a norcaradiene and possible reasons
for this are discussed.</p> <p> The 7-norcaradienylmethyl cations underwent a thermal isomerization to give benzenoid materials at relatively low temperatures. A mechanism for this rearrangement has been proposed and the implication of these results to the general pathways involved in the rearrangements of the C8H9+ family of cations discussed.</p> <p> Several synthetic routes to 9-substituted-3,4-homotropylidenes were investigated. A number of new compounds were isolated and a new synthetic approach to this class of compounds is suggested.</p> <p> Diamagnetic susceptibility exaltations of a series of substituted
cycloheptatrienes were determined and used as a criterion of aromaticity. It was concluded that cycloheptatrienes are best regarded as homoaromatic molecules. Moreover it would appear that the substantial diamagnetic susceptibility exaltations observed with these compounds are related to the bulk of a C-7 substituent. One neutral norcaradiene was examined by this technique and was found to be nonaromatic.</p> / Thesis / Doctor of Philosophy (PhD)
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Structural, Spectroscopic, and Kinetic Investigation of Modified Photochromic Ruthenium Sulfoxide ComplexesMalizia, Jason Patrick 02 May 2014 (has links)
No description available.
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Investigating Linkage Isomerization in Sulfoxide Complexes of Ruthenium and OsmiumMockus, Nicholas V. January 2007 (has links)
No description available.
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Spectroscopic and Kinetic Characterization of Photochromic Ruthenium Chelating Sulfoxide ComplexesMcClure, Beth Anne January 2010 (has links)
No description available.
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Reaction of meta-diisopropylbenzene on acid molecular sieves and synthesis of zeolites by a vapor phase transport methodKim, Man-Hoe 20 October 2005 (has links)
Meta-diisopropylbenzene is reacted with propylene over the acid form of the molecular sieves SAPO-5, mordenite, offretite, beta, hexagonal and cubic faujasite (hex and FAU), L, SAPO-37, and an amorphous silica-alumina at temperatures around 463 K in a flow-type fixed-bed reactor. A small amount of cracking is observed. The main reactions of meta-diisopropylbenzene are isomerization and alkylation. This alkylation is proposed as a new test reaction to characterize the effective size of the voids in larger pore (12 T-atom rings or above) molecular sieves by measuring the amount ratio of formed 1,3,5- to 1,2,4-triisopropylbenzene. In most cases, this ratio increases with the increasing effective void size of the molecular sieves in the order: SAPO-5 < mordenite < offretite < beta < hex ≈ FAU < L < SAPO-37 < amorphous silica-alumina. Since samples with the FAU topology show lower selectivities to 1,3,5-triisopropylbenzene than the mesoporous, amorphous silica-alumina, pore curvature has an influence on alkylation selectivity even for voids of 13 A size. / Ph. D.
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Synthesis, characterization, and kinetics of isomerization, C-H and P-C bond activation for unsaturated diphosphine-coordinated triosmium carbonyl clusters.Wu, Guanmin 05 1900 (has links)
Substitution of MeCN ligands in the activated cluster Os3(CO)10(MeCN)2 by the unsaturated diphosphine ligands (Z)-Ph2PCH=CHPPh2 (cDPPEn) or 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) proceeds rapidly at room temperature to furnish the ligand-bridged cluster 1,2-Os3(CO)10(P-P) (P-P represents cDPPEn or bpcd). Heating 1,2-Os3(CO)10(P-P) leads to the formation of the thermodynamically more stable chelating isomer 1,1-Os3(CO)10(P-P). Each compound of Os3(CO)10(P-P) has been characterized by x-ray diffraction, IR, 31P NMR and 1H NMR. Ligand isomerization kinetics have been investigated by UV-VIS and 31P NMR (for cDPPEn) or 1H NMR (for bpcd) spectroscopies. The isomerization mechanism is discussed based on the activation parameters and CO inhibition (for cDPPEn) or ligand trapping experiments (for bpcd). Thermolysis of 1,1-Os3(CO)10(bpcd) in refluxing toluene gives the hydrido cluster HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] and the benzyne cluster HOs3(CO)8(μ3-C6H4)[μ2,η1-PPhC=C(PPh2)C(O)CH2C(O)]. Photolysis of 1,1-Os3(CO)10(bpcd) using near UV light affords HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] as the sole product. HOs3(CO)8(μ3-C6H4)[μ2,η1-PPhC=C(PPh2)C(O)CH2C(O)] has been characterized in solution by IR and NMR spectroscopies. Furthermore its molecular structure has been determined by X-ray crystallography. Reversible C-H bond formation in HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] is demonstrated by ligand trapping studies to give 1,1-Os3(CO)9L(bpcd) (where L = CO, phosphine) via the unsaturated intermediate 1,1-Os3(CO)9(bpcd). The kinetics for reductive coupling in HOs3(CO)9[γ-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] and DOs3(CO)9[μ-(PPh2-d10)C=C{P(Ph-d5)(C6D4)}C(O)CH2C(O)] in the presence of PPh3 give rise to a kH/kD value of 0.88, whose magnitude supports the existence of a preequilibrium involving the hydride(deuteride) cluster and a transient arene-bound Os3 species that precedes the rate-limiting formation of 1,1-Os3(CO)9(bpcd). Strong proof for the proposed hydride(deuteride)/arene preequilibrium has been obtained from photochemical studies employing the isotopically labeled cluster 1,1-Os3(CO)10(bpcd-d4ortho), whose bpcd phenyl groups each contain one ortho hydrogen and deuterium atom. Equilibrium and kinetic isotope effects in the orthometallation step has been determined by 1H NMR in photochemical studies. Kinetics for the transformation from HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)CH2C(O)] to HOs3(CO)8(μ3-C6H4)[μ2,η1-PPhC=C(PPh2)C(O)CH2C(O)] has been studied by UV-VIS spectroscopy for which the mechanism is discussed.
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Characterization and optimization of an extractor-type catalytic membrane reactor for meta-xylene isomerization over Pt-HZSM-5 catalystDaramola, Michael Olawale 12 1900 (has links)
Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Future chemical production is faced with a challenge of limited material and energy
resources. However, process intensification might play a significant role to alleviating this
problem. Vision of process intensification through multifunctional reactors has stimulated
research on membrane-based reactive separation processes, in which membrane separation
and catalytic reaction occur simultaneously in one unit. These processes are rather attractive
applications because they are potentially compact, less capital intensive, and have lower
processing costs than traditional processes. Moreover, they often enhance the selectivity and
yield of the target product.
For about three decades, there has been a great evolution in p-Xylene production
technology, with many equipment improvements being instituted in the industry. Typically,
these improvements bring economic as well as processing advantages to the producers. Such
developments are vital, as the capital costs for process equipment to produce and separate
p-Xylene from xylene isomers, especially into high purity p-Xylene, still remain very high.
However, with numerous advantages of membrane-based reactive separation processes
compared to the conventional processes, the research focus has been channelled toward
application of MFI-type zeolite membranes for in situ separation and isomerization of xylene
in extractor-type catalytic membrane reactors. To contribute to this research line, this study
has focused on characterization and optimization of an extractor-type catalytic membrane
reactor (e-CMR) equipped with a nanocomposite MFI-alumina membrane as separation unit
for m-Xylene isomerization over Pt-HZSM-5 catalyst.
Nanocomposite MFI-alumina zeolite membranes (tubes and hollow fibres) used in
this study were prepared via a so-called “hydrothermal pore-plugging synthesis technique”
developed by Dalmon and his group more than a decade ago. In this concept, MFI material is
grown by 'pore-plugging' direct hydrothermal synthesis in a porous matrix rather than forming
thin films on top of the support. The advantages of this type of architecture over conventional
film-like zeolite membranes include: (i) minimization of the effect of thermal expansion
mismatch between the support and the zeolite, (ii) easy to scale-up, and (iii) easy module
assembly, because the separative layer (zeolite crystals) are embedded within the pores of the
ceramic support, reducing the effects of abrasion and thermal shocks. After membrane
synthesis, the membrane quality and separation performance of these membranes were
evaluated through single gas permeation (H2), binary gas separation (n-butane/H2) and ternary
vapour mixture of xylene isomers using the vapour permeation (VP) method with p-Xylene as
the target product. After evaluating the xylene isomer separation performance of the membranes, the membranes were used in extractor-type catalytic membrane reactors to carry
out m-Xylene isomerization over Pt-HZSM-5 catalyst with p-Xylene as the target product.
This dissertation has shown that nanocomposite MFI-alumina membrane tubes and
hollow fibre membranes were selective to p-Xylene from xylene isomers. The dissertation
also reports for the first time in open literature the excellent xylene separation performance of
nanocomposite MFI-alumina membrane tubes at higher xylene loading (or vapour pressure).
Unlike their film-like counterparts, the membranes still maintain increased selectivity to p-
Xylene at higher xylene vapour pressures without showing a drastic decrease in selectivity.
This outstanding property makes it a promising choice for pervaporation applications where
concentration profile is usually a major problem at higher loading of xylene.
With the use of nanocomposite MFI-alumina hollow fibre membranes, this research
has demonstrated that membrane configuration and effective membrane wall thickness play a
prominent role in enhancing cross membrane flux. Results presented in the study show, for
the first time in open literature, that nanocomposite MFI-alumina hollow fibre membrane
could enhance p-Xylene fluxes during the separation of ternary vapour mixture of xylene due
to the smaller effective wall thickness of the membrane (membrane thickness <1 μm) when
compared to conventional randomly oriented MFI zeolite films (membrane thickness >3 μm).
During xylene isomers separation with nanocomposite hollow fibre membrane, about 30%
increase in p-Xylene flux was obtained compared to the membrane tubes, operated under the
same conditions. Additionally, hollow fibres offer the added advantage of membrane surfaceto-
volume ratios as high as 3000 m2/m3 compared to conventional membrane tubes. Using
this type of system could be instrumental in reducing both the size and cost of permeating
modules for future xylene separation processes. However, obtaining high quality
nanocomposite MFI-alumina membrane fibres is subject to the availability of high quality
fibre supports.
Regarding the application of nanocomposite MFI-alumina membrane tubes as
extractor-type catalytic membrane reactors (referred to as extractor-type zeolite catalytic
membrane reactor (e-ZCMR) in this study) for m-Xylene isomerization over Pt-HZSM-5, the
results presented in this study further substantiate and confirm the potentials of e-ZCMRs
over conventional fixed-bed reactors (FBRs). In the combined mode (products in the
permeate plus products in the retentate), the e-ZCMR displayed 16-18% increase in p-Xylene
yield compared to an equivalent fixed-bed reactor operated at the same operating conditions.
On the basis of the high p-Xylene-to-o-Xylene (p/o) and p-Xylene-to-m-Xylene (p/m)
separation factors offered by the membranes, p-Xylene compositions in the permeate-only
mode (products in the permeate stream) in the range 95%-100% were obtained in the
e-ZCMR. When a defect-free nanocomposite MFI-alumina membrane tube with p-Xylene-too-
Xylene (p/o) separation factor >400 was used, ultra pure p-Xylene with p-Xylene purity approaching 100% in the permeate-only mode was obtained. Moreover, the e-ZCMR
displayed 100% para-selectivity in the permeate-only mode throughout the temperatures
tested. This is not possible with conventional film-like MFI-type zeolite membranes.
Therefore, the application of nanocomposite MFI-alumina membranes in extractor-type
catalytic membrane reactors could catalyse the development of energy-efficient
membrane-based process for the production of high purity p-Xylene.
Furthermore, in this dissertation, a report on modelling and sensitivity analysis of an
e-ZCMR equipped with a nanocomposite MFI-alumina membrane tube as separation unit for
m-Xylene isomerization over Pt-HZSM-5 catalyst is presented. The model output is in fair
agreement with the experimental results with percentage errors (absolute) of 17%, 29%,
0.05% and 19.5% for p-Xylene yield in combined mode, p-Xylene selectivity in combined
mode, p-Xylene selectivity in permeate-only mode and m-Xylene conversion, respectively.
Therefore, the model is adequate to explain the behaviour of e-ZCMR during m-Xylene
isomerization over Pt-HZSM-5 catalyst. The model is also adaptable to e-ZCMRs of different
configurations such as hollow fibre MFI-alumina membrane-based e-ZCMRs. To gain more
insight into the behaviour of the model to small changes in certain design parameters,
sensitivity analysis was performed on the model. As expected, the sensitivity analysis
revealed that intrinsic property of membrane (porosity, tortuosity), membrane effective
thickness and reactor size (indicated with reactor internal diameter) play a significant role on
the performance of e-ZCMR during p-Xylene production from the mixed xylenes.
MFI-alumina zeolite membranes with optimized parameters such as membrane porosity,
membrane tortuosity, and membrane effective wall thickness might enhance transport of
p-Xylene through the membrane and thus resulting in higher p-Xylene flux through the
membrane. This eventually would translate into an increase in p-Xylene yield in
permeate-only mode. As far as it could be ascertained, this is the first report in open literature
on modelling study with sensitivity analysis of e-ZCMR equipped with nanocomposite
MFI-alumina membrane tubes as separation unit for m-Xylene isomerization over Pt-HZSM-
5 catalyst.
In addition, the results of this study have confirmed previous research efforts
reported on the application of extractor-type catalytic membrane reactors, having MFI-type
membranes as separation units, for p-Xylene production via m-Xylene isomerization over a
suitable catalyst. Also, new ideas were developed, tested and proposed that now provide a
solid basis for further scale-up and techno-economical studies. Such studies are necessary to
evaluate the competitiveness of the technology with the traditional processes for the
production of high purity p-Xylene from mixed xylene.
In summary, the encouraging results, as documented in this dissertation and also
communicated to researchers in the area of membrane-based reactive separation (in the form of four peer-reviewed international scientific publications and four conference proceedings),
could provide a platform for developing a scaled-up membrane-based energy-efficient
industrial process for producing high purity p-Xylene through isomerization. / AFRIKAANSE OPSOMMING: Die produksie van chemiese stowwe word belemmer deur die uitdaging van beperkte
materiaal- en energiebronne. Prosesuitbreiding kan egter ‘n noemenswaardige rol in die
verligting van hierdie probleem speel. Die moontlike gebruik van multi-funksionele reaktore
in prosesuitbreiding het navorsing in membraan-gebaseerde reaktiewe skeidingsprosesse
(waar membraanskeiding en die katalitiese reaksie gelyktydig in ‘n enkele eenheid plaasvind)
aangemoedig. Hierdie prosesse is aantreklik omdat hulle potensieel kompak en minder
kapitaal-intensief is en ook teen laer koste as tradisionele prosesse bedryf kan word. Dit is ook
dikwels die geval dat die multi-funksionele reaktor die selektiwiteit en opbrengs van die
gewenste produk verhoog.
In die afgelope drie dekades was daar ’n sterk verandering in die tegnologie wat
gebruik word in die produksie van p-Xileen, met vele verbeterings aan nuwe toerusting wat in
die nywerheid in bedryf gestel is. Hierdie verbeteringe hou gewoonlik ekonomiese-, sowel as
bedryfsvoordele vir die produsente in. Ontwikkelings in hierdie veld is noodsaaklik aangesien
die kapitale uitgawes vir die toerusting om p-Xileen, veral baie suiwer p-Xileen, van
xileenpolimere te produseer en te skei, steeds baie hoog is. Met talle voordele gekoppel aan
membraangebaseerde reaktiewe skeidingsprosesse in vergelyking met normale prosesse, is
die navorsing egter gekanaliseer na die gebruik van MFI-tipe zeolietmembrane vir die in-situ
skeiding en isomerisasie van xileen in ekstraksie-tipe katalitiese membraanreaktore. As
bydrae tot hierdie navorsingsveld het hierdie studie op die karakterisering en optimering van
‘n ekstraksie-tipe katalitiese membraanreaktor (e-KMR), toegerus met ’n nanosaamgestelde
MFI-alumina membraan as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid
van ‘n Pt-HZSM-5 katalis, gefokus.
Nanosaamgestelde MFI-alumina zeolietmembrane (buise en hol vesels) wat in hierdie
studie gebruik is, is voorberei deur die sogenaamde “hidrotermiese porie-sperring sintese
tegniek” wat meer as ‘n dekade gelede ontwikkel is deur Dalmon en sy groep. In hierdie
tegniek word MFI-materiaal gekweek deur direkte hidrotermiese sintese in ‘n poreuse
matriks, eerder as die vorming van dun films bo-op die ondersteuningsbasis. Die voordele van
hierdie ontwerp bo dié van die konvensionele filmagtige zeolietmembrane sluit in: (i)
minimering van die effek van termiese uitsetting op die gaping tussen die ondersteuningsbasis
en die zeoliet, (ii) die gemak van opskalering, en (iii) die gemak waarmee die modules
aanmekaar gesit kan word, omdat die skeidingslaag (zeolietkristalle) binne die porieë van die
keramiek-ondersteuningsbasis geleë is, wat die effek van erodering en termiese skok
verminder. Ná die membraansintese is die membraankwaliteit en skeidingsvermoë geevalueer
deur enkel-gas-deurdringing (H2), binêre-gas-skeiding (n-butaan/H2), en ternêre dampmengsel van xileen-isomere deur die gebruik van die damp-deurdringingsmetode met
p-Xileen as die teikenproduk.
Hierdie tesis het gewys dat nanosaamgestelde MFI-alumina membraanbuise en hol
vesel membrane selektief was ten opsigte van p-Xileen vanuit xileen-isomere. Die tesis doen
ook, vir die eerste keer in die oop literatuur verslag, oor die uitstekende p-Xileen skeidingsvermoë
van nanosaamgestelde MFI-alumina buise by hoër xileenladings (of dampdrukke).
Anders as hulle filmagtige eweknieë het die membrane steeds hul verhoogde selektiwiteit vir
p-Xileen by hoër dampdrukke behou, sonder ‘n merkbare verlaging in die selektiwiteit.
Hierdie merkwaardige eienskap maak dit ‘n belowende keuse vir pervaporasie toepassings,
waar die konsentrasieprofiel (as gevolg van hoër xileenladings) gewoonlik ’n noemenswaardige
probleem is.
Met die gebruik van nanosaamgestelde MFI-alumina membrane het hierdie navorsing
gewys dat membraankonfigurasie en –wanddikte ‘n prominente rol speel in die verbetering
van vloei oor die membraan. Resultate wat in die studie voorgelê word, wys, vir die eerste
keer in oop literatuur, dat hol vesel nanosaamgestelde MFI-alumina membrane die deurvloei
van p-Xileen kan verbeter gedurende die skeiding van ternêre dampmengsels van xileen, as
gevolg van die kleiner effektiewe wanddikte van die membraan (<1 μm) wanneer dit vergelyk
word met konvensionele kansgewys-geörienteerde MFI-zeoliet films met ‘n membraandikte
van >3 μm. Tydens die skeiding van xileen-isomere met nanosaamgestelde hol vesel
membrane is ‘n verbetering van ongeveer 30 % in die deurvloei van p-xileen verkry,
vergeleke met membraanbuise, by identiese bedryfstoestande. Hol vesels bied ook die verdere
voordeel van oppervlak-tot-volume verhoudings van so hoog as 3000 m2/m3 vergeleke met
konvensionele membraanbuise. Die gebruik van hierdie tipe sisteem kan deurslaggewend
wees in die vermindering van die grootte en koste van deurlatingseenhede in toekomstige
xileen-skeidingsprosesse. Die vervaardiging van hoë-kwaliteit nanosaamgestelde MFIalumina
membraanvesels is egter onderworpe aan die beskikbaarheid van hoë-kwaliteit
vessel-ondersteuningsbasisse.
Wat die gebruik van nanosaamgestelde MFI-alumina membraanbuise as ekstraksietipe
katalitiese membraanreaktore betref (ekstraksie-tipe zeoliet katalitiese membraanreaktor,
of e-ZKMR in hierdie studie) vir m-Xileen isomerisasie in die teenwoordigheid Pt-HZSM-5,
bevestig die resultate die potensiaal van e-ZKM reaktore bo konvensionele vaste-bed reaktore
(VBR). In die gekombineerde verstelling (met produkte in die permeaat sowel as die
retentaat) toon die e-ZKMR ‘n 16 – 18% verbetering in die opbrengs van p-Xileen vergeleke
met ‘n ekwivalente VBR by dieselfde bedryfskondisies. Gegrond op die hoë p-Xileen-tot-o-
Xileen (p/o) en p-Xileen-tot-m-Xileen (p/m) skeidingsfaktore wat deur die membraan gebied
word, is p-Xileen-samestellings in die slegs-permeaat verstelling (produkte in die
permeaatstroom) van tussen 95 en 100% in die e-ZKMR verkry. Toe ‘n defek-vrye nanosaamgestelde MFI-alumina membraanbuis met ‘n (p/o) skeidingsfaktor van >400 gebruik
is, is p-Xileen met ‘n suiwerheid na aan 100% in die slegs-permeaat verstelling verkry. Die
e-ZKMR het ook 100% para-selektiwiteit in die slegs-permeaat verstelling getoon by alle
toets-temperature, iets wat onmoontlik is met gewone filmagtige MFI-tipe zeolietmembrane.
Om hierdie rede is dit moontlik dat die gebruik van MFI-alumina membrane in ekstraksie-tipe
katalitiese membraanreaktore die ontwikkeling van energie-doeltreffende membraangebaseerde
prosesse vir die produksie van suiwer p-Xileen kan bevorder.
Verder word daar in hierdie tesis verslag gedoen oor die modelering en
sensitiwiteitsanalise van ‘n e-ZKMR wat toegerus is met ‘n nanosaamgestelde MFI-alumina
membraanbuis as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n
Pt-HZSM-5 katalis. Die model-uitsette is redelik in ooreenstemming met eksperimentele
resultate met absolute fout-persentasies van 17, 27, 0.05 en 19.5 % vir die p-Xileen opbrengs
in die gekombineerde verstelling, p-Xileen selektiwiteit in die gekombineerde verstelling,
p-Xileen selektiwiteit in die slegs-permeaat verstelling en m-Xileen omsetting,
onderskeidelik. Om hierdie rede kan die model die gedrag van ‘n e-ZKMR verduidelik tydens
die m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis. Die model kan
ook aangepas word na e-ZKM reaktore met verskillende konfigurasies, soos hol vesel MFIalumina
membraan-gebaseerde e-ZKMRe. Om meer insig te kry in die gedrag van die model
op klein veranderinge in sekere ontwerpparameters, is ‘n sensitiwiteitsanalise op die model
uitgevoer. Soos verwag, het die sensitiwiteitsanalise gewys dat die intrinsieke eienskappe van
die membraan (porositeit, tortuositeit), die effektiewe van membraandikte en die
reaktorgrootte (gemeet as die interne deursnit van die reaktor) ‘n noemenswaardige rol speel
in die gedrag van die e-ZKMR gedurende p-Xileen produksie vanuit gemengde xilene.
MFI-alumina zeolietmembrane met geoptimeerde parameters soos membraanporositeit,
-tortuositeit, en –wanddikte mag dalk die oordrag van p-Xileen deur die membraan
bevorder en sodoende ‘n hoër vloei van p-Xileen oor die membraan bewerkstellig. Dit sal
uiteindelik lei tot ‘n verhoging in die opbrengs van p-Xileen in die slegs-permeaat verstelling.
So ver dit vasgestel kon word, is hierdie die eerste verslag in die oop literatuur wat die
modelering en sensitiwiteitsanalise van ‘n e-ZKMR, toegerus met nanosaamgestelde MFIalumina
membraanbuise as skeidingseenheid vir m-Xileen isomerisasie in die
teenwoordigheid van ‘n Pt-HZSM katalis, aanspreek.
Verder ondersteun die resultate van hierdie studie vorige navorsingspogings op die
gebruik van e-KMRe, met MFI-tipe membrane as skeidingseenhede, vir die produksie van
p-Xileen deur middel van m-Xileen isomerisasie in die teenwoordigheid van ‘n geskikte
katalis. Verder is nuwe idees ontwikkel, getoets en voorgestel wat dien as ’n stewige basis vir
verdere opskalering- en tegno-ekonomiese studies. Sodanige studies is nodig om die
vatbaarheid van die tegnologie relatief tot die tradisionele prosesse te bepaal. Ter opsomming, die bemoedigende resultate, soos in die tesis gedokumenteer (en ook
gepubliseer in vier ewe-knie beoordeelde internasionale wetenskaplike joernale en vier
konferensiestukke), kan as ‘n platform dien vir die ontwikkeling van ’n opgeskaleerde
membraan-gebaseerde energie-doeltreffende nywerheidsproses vir die produksie van suiwer
p-Xileen deur middel van isomerisasie.
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Using Molecular Dynamics to Elucidate the Mechanism of CyclophilinMcGowan, Lauren 09 May 2014 (has links)
Cyclophilins are ubiquitous enzymes that are involved in protein folding, signal transduction, viral proliferation, oncogenesis, and regulation of the immune system. Cyclophilin A is the prototype of the cyclophilin family. We use molecular dynamics to describe the catalytic mechanism of cyclophilin A in full atomistic detail by sampling critical points along the reaction coordinate, and use accelerated molecular dynamics to sample cis-trans interconversions. At these critical points, we analyze the conformational space sampled by the active site, flexibility of the enzyme backbone, and modulation of binding interactions.We use Kramer’s rate theory to determine how diffusion and free energy contribute to lowering the activation energy of prolyl isomerization. We also find preferential binding modes of several cyclophiln A inhibitors, and compare the conformational space sampled by inhibited cyclophilin A to the conformational space sampled during wild-type interactions. We also analyze the mechanism of the next family member cyclophilin B in order to probe differences in enzyme dynamics and intermolecular interactions that could possibly be exploited in isoform-specific drug design. Our results indicate that cyclophilin proceeds by a conformational selection binding mechanism that manipulates substrate sterics, electrostatic interactions, and multiple reaction timescales in order to speed up reaction rate. Conformational space sampled by cyclophilin when inhibited and when undergoing wild-type interactions share significant similarity. Cyclophilins A and B do have notable differences in enzyme dynamics, due to variation in intramolecular interactions that arise from variation in primary structures. This work demonstrates how computational methods can be used to clarify catalytic mechanisms.
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Solution isomerization of commercial C2-symmetric metallocene catalystsSoltan, Omar 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / This study concerns the investigation of the isomerization of different
metallocene catalysts in solution, and the effects thereof on the microstructure
of polypropylenes prepared with these catalysts.
Two C2 symmetric ansa metallocenes, ethylene-bis(indenyl) zirconium
dichloride (EI) and dimethylsilyl-bis(2-methyl benzoindenyl) zirconium
dichloride (MBI) were exposed, in solution, to both sunlight and UV radiation.
The rac-meso isomerization of these catalysts were followed by 1H NMR
spectroscopy. The reaching of a photostationary state is described, as well as
the effect of isomerization of these catalysts in solution on the polymerization
of propylene.
Results show that metallocene structure has an effect on the isomerization
rate and photostationary state. Results also show that the wavelength of light
plays a role in the isomerization process.
Effects on stereochemistry and molecular weight of the formed polymer as
well as the catalyst activity is described and discussed. In addition the effect
of activating the catalysts with MAO before exposure to light is discussed.
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A study on the reversible photo-induced isomerisation of platinum(II) and palladium(II) complexes of the N,N-dialkyl-N’-acyl(aroyl)thioureas with reversed-phase HPLC separation from related rhodium(III), ruthenium(III) and iridium(III) complexesNkabyo, Henry Ane 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: See item for full text / AFRIKAANSE OPSOMMING: Sien item vir volteks
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