The production of zeolite membranes has developed over the last decade, and the membranes have been used extensively in pervaporation separation processes due to their resistance to chemical and thermal operating conditions. However, the conventional methods used in preparing anisotropic zeolite membranes, such as the secondary growth and in-situ crystallization methods, involve long and complex procedures that require the preparation of zeolite aluminosilicate gel prior to the fabrication process. Therefore, the aim of this study was to develop and test an easier, less expensive, and less time-consuming technique to fabricate different types of zeolite anisotropic membranes. Moreover, the fabrication of zeolite membranes using inexpensive kaolin raw materials taken straight out of the ground was taken into account and assessed. Within this framework, a novel technique of converting raw source alumina and silica, to a useful pure material of zeolite A was developed without any form of pre-treatment. Although this technique yielded a successful outcome in terms of the purity of the product, the later work conducted in fabricating membranes was focused on natural and commercial sources of zeolites rather than using the prepared products, to avoid the lengthy procedure. Anisotropic membranes of zeolite A, mordenite, and ZSM-5 were fabricated successfully using a simple, economical, and straight-forward technique. This technique made it possible to fabricate types of zeolite membranes that have been difficult to synthesise at the lab scale, where an anisotropic, clinoptilolite, thin membrane was fabricated for the first time in this study. All of the four membranes were subjected to different types of mixtures and provided promising results.

The separation characteristics of binary alcohol-water mixtures were studied overa wide range of feed concentration and temperature using polymeric and zeoliticpervaporation membranes. For the hydrophilic PVA membrane, the total flux (at 55 0C)for the ethanol-water system decreased from 0.45 to 0.05 kg/m2/hr as the feed ethanolconcentration was increased from 30 to 95 wt. %. The separation factor (water/ethanol)was found to increase by about 100 times for the same range of concentration. TheUNIQUAC theory was used to predict the activity of binary alcohol-water mixtures in thePVA membrane. The UNIQUAC theory successfully takes into account the nonidealitiespresent in the alcohol/water-PVA membrane system. The transport of waterand alcohol species through the PVA membrane was modeled using the UNIQUACtheory in conjunction with the conventional activity driving force model. Using themodel and the experimental pervaporation data, the diffusivity correlations andconcentration profiles for various species through the membrane were developed. Basedon the developed diffusivity correlations, the water and alcohol fluxes through the PVAmembrane were predicted at 80 ??C.Experiments were also conducted on the water selective zeolite (type NaA)membrane using various alcohol-water mixtures and with dimethylformamide-watermixture over a wide range of temperatures (25 to 70 ??C) and solvent concentrations (0 -100 wt. %). The total flux for the ethanol-water mixture was found to decrease from 2 to0.05 kg/m2/hr at 60 ??C as the feed ethanol concentration was increased from 0 to 100 wt.%. Both, the water to ethanol and water to isopropanol separation factors were observedto lie between 1000 and 5000 over a wide range of solvent concentrations. The Maxwell-Stefan theory was used to model the permeation of water through zeolite NaAmembranes. The precise micropore structure of the zeolite cage helps in a partialmolecular sieving of the large solvent molecules leading to high separation factors. Thezeolite membrane active layer may contain certain non-zeolitic interstitial pores withpreferential water sorption. A high degree of hydrophilicity of the zeolite membrane issuggested from a pure water sorption value of 0.6 gm/gm zeolite. The detailedinterpretation of this result, however, requires consideration of both true zeoliticmicrocavity uptake as well as interstitially held water between crystallites. The use ofpervaporation for volume reduction and solvent recovery applications in thepharmaceutical industry has been demonstrated.

No description available.

Nanoporous materials have attracted tremendous interest, investment and effort in research and development due to their potential applications in various areas such as membranes, catalysis, sensors, delivery, and micro devices. Controlling a nanoporous material’s microstructure is of great interest due to the strong influence on efficiency and performance. For particles, microstructure refers to particle size, shape, surface morphology, and composition. When discussing thin films, microstructure includes film thickness, crystal orientation and grain boundaries. In this respect, we focus to develop novel methods for the synthesis and characterization of nanoporous materials and their films, which are capable of controlling the microstructure of material. This dissertation is composed of two main sections and each explores the fabrication of a different nanoporous material: 1) A simple fabrication method for producing oriented MFI zeolite membranes with controlled thickness, orientation, and grain boundary; 2) A microfluidic synthesis of ordered mesoporous silica particles with controllable size, shape, surface morphology, and composition. The first section of this dissertation demonstrates a simple and commercially viable method termed the micro-tiles-and-mortar method to make continuous b-oriented MFI membranes with controlled membrane microstructure. This simple method allows for control of the thickness of the membrane by using plate-like seed crystals with different thicknesses along the b-axis (0.5 μm to 2.0 μm), as well as to manipulate the density and structure of grain boundaries. Microstructural effects of silicalite-1 membranes on the gas separation are investigated by measuring the permeation and separation for xylene isomers. In the second section of this dissertation, a new synthesis method for the ordered mesoporous silica particles with controllable microstructure is demonstrated. This novel method combines a microfluidic emulsification technique and nonaqueous inorganic synthesis with a diffusion-induced self-assembly (DISA). The systematic control of the particle microstructure such as size, shape, and surface morphology is shown by adjusting microfluidic conditions.

Zeolite membrane synthesis is conventionally carried out in batch systems. Recently, several attempts have been performed to synthesize zeolite membranes in flow systems which can allow preparation of membranes with large specific surface areas. Membranes synthesized in the recirculating flow system had comparable N2/SF6 and n- C4H10/i-C4H10 ideal selectivities with the membranes prepared in the batch system, indicating that good quality membranes can be produced by this method. The objective of this study is to separate organic/water mixtures by pervaporation by using MFI type membranes synthesized in the flow system. Effect of number of synthesis steps and synthesis method on the separation factor and flux was investigated. Membranes were synthesized from clear solutions with a molar composition of 80SiO2:16TPAOH:1536H2O at 95oC and atmospheric pressure. The synthesis solution was recirculated through the tubular alumina support with a flow rate of 6 ml/min for 72 h. The membranes were characterized by X-ray diffraction for phase identification and scanning electron microscopy for morphology determination. Single gas permeances of N2, H2, CH4, CO2, n-C4H10 and i-C4H10 were measured between 25 and 200oC. Mixtures of 5 wt% ethanol/water, 2-propanol/water and acetone/water were separated by pervaporation at different temperatures. The single gas permeances decreased with increasing temperature for weakly adsorbed gases. For n-C4H10 the permeance passed through a maximum and i-C4H10 permeance was nearly constant. For a membrane synthesized by two consecutive synthesis steps, the ideal selectivity for n-C4H10/i-C4H10 was 132 at 200oC. The selectivity in the pervaporation separation of ethanol-water mixture was 43 with a permeate flux of 0.2 kg/m2h at 25oC. With increasing temperature, selectivity decreased but the flux increased, the selectivity was 23 and the flux was 1.9 kg/m2h at 85oC. 2-propanol/water and acetone/water separation factors were 36 and 1024 with 0.2 and 0.1 kg/m2h fluxes, respectively. The separation factors and fluxes for membranes synthesized in the flow system were comparable with membranes synthesized in the batch system.

Zeolite membranes are considered to be a promising alternative to polymeric membranes and they have the potential to separate gases under harsh conditions. Silicalite-1 membranes in particular are easy to prepare and suitable for several industrial applications. In this research project, silicalite-1/ceramic composite membranes were prepared using the pore plugging hydrothermal synthesis method and supports with zirconium oxide and/or titanium oxide as active layers. The effect of the support’s pore size on the morphology and permeation performance of the prepared membranes was investigated using five supports with different active layer pore sizes in the range of 0.14 – 1.4 m. The prepared membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), electron diffraction spectrometer (EDS), single gas and binary gas mixtures permeation tests. The results confirmed the presence of a typical silicalite-1 zeolite structure with a high internal crystalline order grown inside the pores of the active layer of the supports, with a dense film covering most of the supports active layers. Silicalite-1 crystals in the prepared membranes were preferably oriented with either a- or b-axes perpendicular to the support surface. Single gas permeation results illustrated that the observed permeances were not directly related to the kinetic diameter of permeants. Instead, the transport of the studied gases through the prepared membranes occurred by adsorption followed by surface diffusion mechanism. Binary gas tests performed with CO2 and N2 mixtures showed that the prepared membranes were selective and very permeable with CO2/N2 permselectivities up to 30 and a CO2 permeances in the order of 10-6 mol m-2 Pa-1 s-1. A model was developed, based on Maxwell−Stefan equations and Extended Langmuir adsorption isotherm, to describe the transport of binary CO2 and N2 mixtures through the prepared silicalite-1 membranes. The model results showed that the exchange diffusivities (D12 and D21) were less dependent on the feed pressure and feed composition compared to the permeances and the permselectivities. Hence, they are more appropriate to characterize the intrinsic transport properties of the prepared silicalite-1 membranes.

MFI type zeolites, are the most widely studied zeolites for membrane separations. Conventionally, zeolite membranes are prepared in batch systems by hydrothermal synthesis in autoclaves. This method has several disadvantages for use in industrial scale for the synthesis of membranes with large areas and complex geometries that are commonly used in membrane modules. The objective of this study is to prepare MFI type zeolite membranes on tubular alumina supports in a continuous system where the synthesis solution is circulated through the tubular supports. Syntheses were carried out using clear solutions, at atmospheric pressure and at temperatures below 100&deg / C. The membranes were characterized by N2, SF6, n-butane and isobutane permeances, X-ray diffraction and scanning electron microscopy. A 2-&amp / #956 / m membrane was synthesized using the composition 80SiO2: 16TPAOH: 1536H2O at 95&deg / C in the continuous system. The membrane showed N2 permeance of 4.4 x 10-7 mol/m2.s.Pa and N2/SF6 selectivity of 11. The membrane synthesized in the batch system showed a N2 permeance of 3.4 x 10-7 mol/m2.s.Pa and a N2/SF6 selectivity of 27. Both membranes showed n-butane/isobutane mixture (50%-50%) selectivities of about 6 at temperatures of 150 and 200&deg / C. Among many zeolite membranes reported in literature, these membranes are one of the few zeolite membranes synthesized in a flow system and the first MFI type membranes synthesized in a continuous flow system with circulation of the synthesis solution. The permeances and selectivities of the membranes synthesized in the continuous system are comparable with the MFI type membranes synthesized in batch systems in literature.

Abstract The production of liquid transportation fuels such as bioethanol and more recently also biobutanol from renewable resources has received considerable attention. In the production of bio-based alcohols, the separation steps are expensive as the mixtures to be separated are dilute. As an energy-efficient separation technology, pervaporation is considered to be a potential process in biofuel purification. One of the main constraints in the commercialization of pervaporation has been low membrane fluxes, and the consequent high costs due to the high membrane area needed. In order to obtain high fluxes, the membranes should be as thin as possible. In this thesis, the performance of ultra-thin zeolite membranes in pervaporation was investigated. Binary ethanol/water and n-butanol/water mixtures were studied using both hydrophobic and hydrophilic zeolite membranes for alcohol concentration, as well as dehydration. The development of pervaporation membranes and processes has been mainly empirical. Process modeling, however, is an indispensable tool in process design. In this work, the pervaporation performance of the studied membranes was evaluated on the basis of experimental results in combination with mathematical modeling. Due to the low film thickness of the studied membranes, the fluxes were generally higher than reported earlier. Nevertheless, the evaluation in this work showed that the pervaporation performance of the ultra-thin membranes decreased due to flux limitation by membrane support. In this work, pervaporation was modeled by applying both a semi-empirical and a detailed Maxwell-Stefan based mass transfer model. The latter model considers explicitly both adsorption and diffusion, i.e. the phenomena involved in separation by pervaporation. The description of the support behavior was included in the models. Maxwell-Stefan formalism was applied in unary pervaporation for the determination of diffusivities in zeolite membranes. The models performed well within the range of experimental data. Additionally, a practical modeling approach was developed in this work to predict the temperature dependency of adsorption on zeolites. The developed approach can be utilized, e.g., in pervaporation modeling. Thus, this thesis provides knowledge of using ultra-thin zeolite membranes in the pervaporation of alcohol/water mixtures, and offers tools for pervaporation modeling. / Tiivistelmä Kiinnostus uusiutuvista raaka-aineista valmistettavia liikennepolttoaineita, kuten bioetanolia ja -butanolia, kohtaan lisääntyy koko ajan. Biopohjaisten alkoholien tuotannossa etenkin erotusvaiheet ovat kalliita, koska erotettavat liuokset ovat laimeita. Pervaporaatio on energiatehokas kalvoerotusmenetelmä ja sen vuoksi potentiaalinen osaprosessi biopolttoaineiden tuotantoon. Pervaporaation kaupallistamisen merkittävimpiä rajoitteita ovat olleet alhaiset ainevuot, jotka johtavat suureen kalvopinta-alan tarpeeseen ja näin ollen korkeisiin kustannuksiin. Korkean ainevuon saavuttamiseksi kalvojen tulisi olla mahdollisimman ohuita. Tässä väitöstyössä tutkittiin hyvin ohuiden zeoliittimembraanien suorituskykyä pervaporaatiossa. Kohteena olivat binääriset etanoli/vesi- ja n-butanoli/vesiseokset, joista väkevöitiin alkoholeja tai poistettiin vettä hydrofobisia ja hydrofiilisiä zeoliittimembraaneja käyttäen. Pervaporaatiossa käytettävien kalvojen ja pervaporaatiota hyödyntävien prosessien kehitystyö on ollut pääasiassa kokeellista. Prosessimallinnus on kuitenkin tärkeä työkalu prosessisuunnittelussa. Tässä työssä membraanien suorituskykyä pervaporaatiossa arvioitiin sekä kokeellisesti että mallinnuksen keinoin. Käytettyjen kalvojen ohuuden ansiosta tässä työssä saavutetut ainevuot olivat yleisesti ottaen korkeampia kuin aiemmin raportoiduilla membraaneilla. Ohuilla kalvoilla tukimateriaalin aiheuttama aineensiirron vastus oli kuitenkin merkittävä, alentaen membraanien suorituskykyä. Tässä työssä pervaporaatiota mallinnettiin käyttäen sekä puoliempiiristä että yksityiskohtaisempaa Maxwell-Stefan -pohjaista mallia. Jälkimmäisessä mallissa adsorptio ja diffuusio, eli ilmiöt joihin erotus pervaporaatiossa perustuu, otetaan eksplisiittisesti huomioon. Myös tukimateriaalin vaikutukset huomioitiin käytetyissä malleissa. Maxwell-Stefan -mallinnusta käytettiin puhtaiden komponenttien pervaporaatiossa zeoliittimembraanin diffuusiokertoimien määrittämiseksi. Käytettyjen mallien suorituskyky kokeellisella alueella oli hyvä. Tässä työssä kehitettiin lisäksi helppokäyttöinen menetelmä aineiden adsorptiokäyttäytymisen ennustamiseen zeoliiteissa eri lämpötiloissa. Kehitettyä menetelmää voidaan hyödyntää esimerkiksi pervaporaation mallinnuksessa. Kokonaisuudessaan väitöstyöstä saadaan tietoa ultraohuiden membraanien käytöstä pervaporaatiossa sekä työkaluja pervaporaation mallinnukseen.

Zeolite membranes are considered to be a promising alternative to polymeric membranes and they have the potential to separate gases under harsh conditions. Silicalite-1 membranes in particular are easy to prepare and suitable for several industrial applications. In this research project, silicalite-1/ceramic composite membranes were prepared using the pore plugging hydrothermal synthesis method and supports with zirconium oxide and/or titanium oxide as active layers. The effect of the support’s pore size on the morphology and permeation performance of the prepared membranes was investigated using five supports with different active layer pore sizes in the range of 0.14 – 1.4 m. The prepared membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), electron diffraction spectrometer (EDS), single gas and binary gas mixtures permeation tests. The results confirmed the presence of a typical silicalite-1 zeolite structure with a high internal crystalline order grown inside the pores of the active layer of the supports, with a dense film covering most of the supports active layers. Silicalite-1 crystals in the prepared membranes were preferably oriented with either a- or b-axes perpendicular to the support surface. Single gas permeation results illustrated that the observed permeances were not directly related to the kinetic diameter of permeants. Instead, the transport of the studied gases through the prepared membranes occurred by adsorption followed by surface diffusion mechanism. Binary gas tests performed with CO2 and N2 mixtures showed that the prepared membranes were selective and very permeable with CO2/N2 permselectivities up to 30 and a CO2 permeances in the order of 10-6 mol m-2 Pa-1 s-1. A model was developed, based on Maxwell−Stefan equations and Extended Langmuir adsorption isotherm, to describe the transport of binary CO2 and N2 mixtures through the prepared silicalite-1 membranes. The model results showed that the exchange diffusivities (D12 and D21) were less dependent on the feed pressure and feed composition compared to the permeances and the permselectivities. Hence, they are more appropriate to characterize the intrinsic transport properties of the prepared silicalite-1 membranes.

Zeolites and zeolite membranes are two important advanced chemical materials which are widely used in chemical processes. The manufacture of these materials usually involves the use of expensive chemicals. This study involves the use of Ahoko Nigerian kaolin (ANK) as precursor material for the development of zeolites and zeolite membranes. The synthesis of zeolite A, Y and ZSM-5 was successfully obtained following a sequence, collection of the raw clay from Nigeria, metakaolinization, dealumination and actual hydrothermal synthesis of the zeolites. Raw ANK was refined using sedimentation technique and about 97% kaolin was recovered from the raw sample. A novel metakaolinization technique was developed to convert kaolin into a reactive metastable phase. Amorphous metakaolin was obtained at a temperature of 600°C and exposure time of 10 min. This is a significant result because previous studies use higher temperatures and longer exposure times for the metakaolinization step. The metakaolin was used to prepare a number of different zeolites under various conditions. Highly crystalline zeolite A was obtained at an ageing time of 12 h, crystallization time of 6 h and crystallization temperature of 100oC. Zeolite Y was obtained at an ageing time of 3 h, crystallization time of 9 h and crystallization temperature of 100oC. Zeolite Y was also synthesised by using a dealuminated kaolin and highly crystallized zeolite Y with Si/Al ratio of 1.56 and BET surface area was obtained of 630 m2/g. ZSM-5 was synthesised using an ageing period of 36 h, crystallization time of 48 h and temperature of 140oC. The results obtained from zeolite powder synthesis from ANK were then used as guide to prepare supported zeolite films and membranes by a hydrothermal method. The effect of the support surface (stainless steel) was investigated using two synthesis methods namely modified in-situ and secondary (seeded) growth. Zeolite A, Y and ZSM-5 films were successfully prepared from ANK for the first time and on two modified supports, etched and oxidised. The zeolite films and membranes developed showed complete coverage on the two supports with the oxidised showing better adhesion and intergrowth. The separation performance of the three developed zeolite membrane was tested by pervaporation of water/ethanol mixture. The results of pervaporation of ethanol/water mixture showed that zeolite A membrane is highly selective towards water mainly because of hydrophilic properties occasioned by the high aluminium content. Zeolite Y membrane show a similar response when their separation performance was evaluated but with less selectivity because of reduced aluminium content. ZSM-5 showed selectivity towards ethanol because of it hydrophobicity allowing only ethanol to permeate. In all the zeolite membranes, the flux is lower in comparison to commercial zeolite membranes due mainly to the thickness of the zeolite layer. Oxidised support membranes showed better performance because of their better interaction between the oxide surface and the aluminosilicate gel. The results show that ANK can successfully be used to prepare zeolites and zeolite membrane.