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Synthesis and Characterization of Ultramicroporous Zeolitic Membranes for Hydrogen SeparationZheng, Zhenkun 22 September 2008 (has links)
No description available.
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Quantifying Defects in Zeolites and Zeolite MembranesHammond, Karl Daniel 01 February 2010 (has links)
Zeolites are crystalline aluminosilicates that are frequently used as catalysts to transform chemical feedstocks into more useful materials in a size- or shape-selective fashion; they are one of the earliest forms of nanotechnology. Zeolites can also be used, especially in the form of zeolite membranes (layers of zeolite on a support), to separate mixtures based on the size of the molecules. Recent advances have also created the possibility of using zeolites as alkaline catalysts, in addition to their traditional applications as acid catalysts and catalytic supports. Transport and catalysis in zeolites are greatly affected by physical and chemical defects. Such defects can be undesirable (in the case of zeolite membranes), or desirable (in the case of nitrogen-doped alkaline zeolites). Studying zeolites at the relevant length scales requires indirect experimental methods such as vapor adsorption or atomic-scale modeling such as electronic structure calculations. This dissertation explores both experimental and theoretical characterization of zeolites and zeolite membranes. Physical defects, important in membrane permeation, are studied using physical adsorption experiments and models of membrane transport. The results indicate that zeolite membranes can be modeled as a zeolite powder on top of a support—a “supported powder,” so to speak—for the purposes of adsorption. Mesoporosity that might be expected based on permeation and confocal microscopy measurements is not observed. Chemical defects—substitutions of nitrogen for oxygen—are studied using quantum mechanical models that predict spectroscopic properties. These models provide a method for simulating the 29Si NMR spectra of nitrogendefected zeolites. They also demonstrate that nitrogen substitutes into the zeolite framework (not just on the surface) under the proper reaction conditions. The results of these studies will be valuable to experimentalists and theorists alike in our efforts to understand the versatile and complicated materials that are zeolites.
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TOWARDS COMMERCIALIZABLE FEATURED ZEOLITES - MESOPOROUS PARTICLES, NANOPARTICLES AND BENDABLE ZEOLITE MEMBRANESWang, Bo January 2016 (has links)
No description available.
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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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Synthesis Of Low Silica/alumina Zeolite Membranes In A Flow SystemAkbay, Sezin 01 September 2007 (has links) (PDF)
Zeolite A-type membranes are usually synthesized from hydrogels and rarely
synthesized from clear solutions mostly in batch systems. Few studies were carried
out using semi-continuous systems for zeolite A membrane synthesis. Zeolite A
membranes are mainly used in pervaporation processes for separation of water from
water/organic mixtures because of their hydrophilic property.
In this study, zeolite A membranes were synthesized on -alumina supports from a
clear solution with a molar composition of 49Na2O: 1Al2O: 5SiO2: 980H2O.
Synthesis was done both in a batch system and in a flow system in which solution
was circulated through the support under atmospheric pressure. Effects of synthesis
temperature, time, flow rate and seeding on membrane formation were investigated.
The membranes were characterized by X-ray diffraction (XRD), scanning electron
microscopy (SEM), single gas permeation measurements and pervaporation tests.
In batch system, pure zeolite A membranes having cubic form of zeolite A was
obtained for the syntheses carried out at 60° / C for 24 h and 80° / C for 8 h.
Thicknesses of the membranes synthesized at 80° / C and 60° / C were about 2 µ / m and
4 µ / m, respectively. N2 permeances were 2*10-8 mol/m2sPa and 8*10-8 mol/m2sPa
for of the membranes synthesized in the batch system at 60° / C and 80° / C,
respectively. When synthesis was carried out in flow system pure and continuous
zeolite A membranes were obtained for all conditions. Membranes synthesized at
60° / C and 80° / C had thicknesses of about 1.5 and 2 µ / m, respectively. Lower N2
permeations were obtained for the membranes synthesized in flow system. It was
observed that flow rate and seeding did not significantly affect the thickness of the
membrane layer. The membranes synthesized in this study are significantly thinner
than the membranes reported in the literature. Single gas permeation tests at 25° / C
for the membranes showed that comparable membranes with the ones in literature
were obtained in this study. For a double layer membrane synthesized in flow
system at 80° / C for 8h separation factor about 3700 was obtained for the separation
of 92:8 (wt.%) ethanol/water mixture at 45° / C.
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Pervaporation Of Ethanol/water Mixtures By Zeolite A Membranes Synthesized In Batch And Flow Systems(arican) Yuksel, Berna 01 January 2011 (has links) (PDF)
Zeolite A membranes have great potential in pervaporation separation of ethanol/water mixtures with high flux and selectivity. Zeolite membranes usually synthesized from hydrogels in batch systems. In recent years, zeolite membranes are prepared in semicontinuous, continuous and recirculating flow systems to allow the synthesis of zeolite membranes with enlarged surface areas and to overcome the limitations of batch system at industrial level production.
The purpose of this study is to develop a synthesis method for the preparation of good quality zeolite A membranes in a recirculated flow system from hydrogels and to test the separation performance of the synthesized membranes by pervaporation of ethanol/water mixture. In this context, three different experimental synthesis parameters were investigated with zeolite A membranes synthesized in batch system. These parameters were the composition of the starting synthesis hydrogel, silica source and the seeding technique. Syntheses were carried out using hydrogels at atmospheric pressure and at 95 ° / C. The membranes were characterized by X-ray diffraction, scanning electron microscopy and pervaporation of 90 wt% ethanol-10 wt% water mixtures.
v
Pure zeolite A membranes were synthesized both in batch and flow systems. The membranes synthesized in batch system have fluxes around 0.2-0.3 kg/m2h and selectivities in the range of 10-100. Membranes with higher selectivities were obtained in batch system by using waterglass as silica source, seeding by dip-coating wiping method, and with a batch composition of 3.4Na2O:Al2O3:2SiO2:155H2O. The membranes prepared in flow system have higher pervaporation performances than the ones prepared in batch system in considering both flux and the selectivity. Fluxes were around 0.3-3.7 kg/m2h and selectivities were in the range of 102-104 for the membranes prepared in flow system which are comparable with the data reported in literature for batch and flow systems.
A high quality zeolite A membrane was also synthesized from 3.4Na2O:Al2O3:2SiO2:200H2O hydrogel at 95 ° / C for 17 hours in flow system. Pervaporation flux of this membrane was 1.2 kg/m2h with a selectivity > / 25,000 at 50° / C. Although the synthesis method is resulted with high quality membrane, reproducibility of the synthesis method is poor and it should be improved.
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Synthesis and Modification of MFI-Type Zeolite Membranes for High Temperature Hydrogen Separation and Water Gas Shift Membrane ReactionsTang, Zhong 06 December 2010 (has links)
No description available.
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Gas separation of steam and hydrogen mixtures using an α-alumina-Alumina supported NaA membrane / by S. MoodleyMoodley, Shawn January 2007 (has links)
Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.
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Synthesis Of Zeolite Membranes In Flow SystemOnder, Aylin 01 October 2012 (has links) (PDF)
Zeolite membranes are formed as a thin zeolitic layer on the supports. They are usually synthesized by hydrothermal methods in batch systems. In this study, MFI and SAPO-34 type zeolite membranes were produced on macroporous tubular alumina supports in a recirculating flow system at elevated temperatures for the first time in the literature. During the synthesis, the synthesis mixture is flown between the reservoir and the membrane module which includes the support material.
The synthesis temperatures were 180° / C and 220° / C, and the corresponding system pressures were approximately 20 and 30 bars for MFI and SAPO-34, respectively. The CH4 and n-C4H10 single gas permeances were measured through MFI membranes and the performance of membranes was investigated in the separation of equimolar CH4/n-C4H10 mixtures. The best MFI membrane had a CH4 single gas permeance of 1.45x10-6 mol/m2-s-Pa and CH4/n-C4H10 ideal selectivity of 35 at 25oC. The membranes preferentially permeated n-C4H10 in the separation of mixtures. The n-C4H10/CH4 separation selectivity was 43.6 with a total permeance of approximately 0.8x10-6 mol/m2-s-Pa at 25oC.
The ideal selectivities of CO2/CH4 of SAPO-34 membrane synthesized in stagnant medium were 227, and > / 1000 at 220 and 200oC, respectively. Formation of amorphous structure and the additional secondary phases (impurities) were observed on SAPO-34 membranes synthesized in recirculating flow system. The results showed that it is possible to produce SAPO-34 and high quality MFI membranes by a recirculating flow system operating at elevated temperature.
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Dehydration Of Aqueous Aprotic Solvent Mixtures By PervaporationSarialp, Gokhan 01 February 2012 (has links) (PDF)
Aprotic solvents are organic solvents which do not easily react with a substance dissolved in it and they do not exchange protons despite of their high ion and polar group dissolving power. Therefore, this characteristic property makes aprotic solvents very suitable intermediates in many industries producing pharmaceuticals, textile auxiliaries, plasticizers, stabilizers, adhesives and ink. Dehydration of these mixtures and recirculation of valuable materials are substantial issues in industrial applications. The conventional method for recovery of aprotic solvents has been distillation, which requires excessive amount of energy to achieve desired recovery. Hydrophilic pervaporation, which is a membrane based dehydration method with low energy consumption, may become an alternative. Because of high dissolving power of aprotic solvents only inorganic membranes can be employed for this application.
In this study three types of inorganic membranes (NaA zeolite, optimized silica and HybSi) were employed. Main objective of this studys to investigate effect of membrane type and various operationg parameters (feed composition at a range of 50-5% and temperature at a range of 50-100oC) on pervaporative dehydration of aprotic solvents / dimethylacetamide, dimethylformamide and n-methylpyrrolidone. During the experiments, feed samples were analyzed with Karl Fischer Titration Method / permeate samples were analyzed with Gas Chromatography.
Experiments showed that proper dehydration of aqueous aprotic solvent mixtures was succeded with all three membranes investigated. In the target feed water content range (50 to 20%wt), permeate water contents were higher than 98%wt which was quite acceptable for all membranes. Moreover, NaA zeolite membrane performed higher fluxes than optimized silica and HybSi in composition range of 50 to 15% water at 50oC. It was also observed that HybSi membrane had higher fluxes and permeate water contents than optimized silica membrane for all solvents. On the other hand, the rates of decrease in permeate fluxes changed depending on the type of solvent for optimized silica and HybSi membranes. With both membranes, permeate flux of dimethylformamide decreased much slower than that of n-methylpyyrolidone. Furthermore, the results showed that permeate fluxes of HybSi membrane increased with increasing operation temperature due to the change of solvent activity in mixture. In addition, an Arrhenious type equation was used to describe changes in fluxes with changing temperature. It was also found that activation energy of water for diffusion through HybSi membrane was calculated as 8980 cal/mol.
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