Nowadays, the need and interest for renewable sources of energy has increased. Biogas is a renewable source of energy that can be considered as a sustainable substitute for natural gas. Biogas is mainly composed of CH4 and CO2, and normally the CO2 content of the gas has to be reduced as it decreases the calorific value of the gas and it may also cause corrosion in pipes and other equipment. Most today’s technologies used for upgrading biogas have been adapted from upgrading of natural gas. However, these technologies are best suited for large scale operation; whereas, production of biogas is typically several orders of magnitude smaller. This leads to high costs for removal of CO2 from biogas and consequently, new efficient technologies for upgrading biogas should be developed. Membrane-based separations are generally considered as energy efficient and are suitable for a wide range in scale of production due to their modular design. Zeolite membranes have been singled out as especially attractive membranes for gas separations. In this work, we therefore study separation of CO2 from CH4 and H2 using zeolite MFI membranes.  The performance of a high-silica (Si/Al ca. 139) MFI membrane for CO2/CH4 separation was investigated in a wide temperature range i.e. 245 K to 300 K. The separation factor increased with decreasing temperatures as is typically the case for adsorption governed separations. The highest separation factor observed was about 10 at 245 K. The CO2 permeance was very high in the whole temperature studied, varying from ca. 60 × 10-7 mol s-1 m -2 Pa-1 at the lowest temperature to about 90 × 10-7 mol s-1 m -2 Pa-1 at the highest temperature studied. The CO2 permeance was higher than that reported previously in the open literature for this separation. Modeling of the experimental data revealed that the membrane performance was adversely affected by pressure drop over the support, whereas the effect of concentration polarization was small. Removing the former effect would improve both the permeance and selectivity of the membrane.  In order to investigate the impact of the aluminum content on the performance of MFI membranes for the CO2/CH4 separation, MFI membranes with different Si/Al ratios were prepared. Increasing the aluminum content makes the zeolite II more polar which should increase the CO2/CH4 adsorption selectivity. Again the effect of temperature on the performance was investigated by varying the temperature in a range almost similar as above. Altering the Si/Al ratio in MFI zeolite membranes indeed changed the separation performances. At the lower temperatures the separation performance increased with increasing aluminum content in the zeolite as a result of larger adsorption selectivity. However, as the temperature was decreased, the selectivity of the membrane with the highest aluminum content went through a maximum, whereas for the other membranes the selectivity continued to increase with decreasing temperature under the conditions studied. At the same time, the CO2 permeances were high for all membranes studied and for the membrane with the highest selectivity, the CO2 permeance increased from 65 × 10-7 to 100 × 10-7 mol s-1 m -2 Pa-1 with increasing temperature.  High-silica MFI membranes were also evaluated for CO2/H2 separation, which is critical for syngas purification and H2 production. The highest CO2 permeance at the feed pressure of 9 bar was about 78 × 10-7 mol s-1 m -2 Pa-1 at around 300 K, which is one or two order of magnitude higher than those reported previously in the literature. By decreasing the temperature, separation factor reached its highest value of 165 at 235 K.  In summary, zeolite membranes show great potential for CO2 separation from industrial gases, in particular for CO2 removal from synthesis gas. For the CO2/CH4 separation the selectivity of the MFI membranes should be improved or other frameworks relying on molecular sieving e.g. the CHA framework should be explored.

Alkylketene dimer, AKD, dispersions are used in the paper industry to obtain paper grades with a hydrophobic character i.e. resistance to sorption of water. AKD is used in neutral to alkaline internal sizing, pH in the interval of 6-9. AKD dispersions consist of wax particles emulsified in water. The particles are electrostatically and in most cases also sterically stabilized by cationic polyelectrolytes. The size of the particles is usually in the range of 0.5-2 µm in diameter. The idea of having cationic particles is that they are supposed to be deposited onto the negatively charged fiber surfaces, heterocoagulation. An increased usage of recycled pulp and a closure of the wet-end circuits of the paper machine will lead to increasing levels of dissolved and colloidal substances. These substances could be detrimental by affecting the AKD deposition onto the fiber material and the colloidal stability i.e. induce flocculation of sizing particles. Flocculation could lead to an inhomogeneous distribution of the sizing agent. The aims addressed in this thesis were the following: to investigate if high levels of shear, electrolyte concentration, anionic polymers and surfactants could affect the colloidal stability and induce flocculation of differently designed AKD dispersions to study the migration of AKD and the influence of extractives on the migration to study the sizing efficiency and retention using flocculated dispersions The colloidal stability of the dispersions was tested under shear by measuring the particle size distribution and the microelectrophoretic mobility. The migration of AKD through paper sheets with defined thickness and through paper sheets impregnated with extractives was analyzed with contact angle measurements on stored samples. The sizing efficiency of flocculated AKD was determined by measuring 60-second Cobb and contact angles on laboratory sheets. The retention of AKD was determined by quantitative analysis of the AKD content in the laboratory sheets using alkaline hydrolysis followed by solvent extraction and quantification with capillary gas chromatography. It was shown that anionic polymers and surfactants could seriously affect the colloidal stability of the dispersions, while shear and electrolyte concentration had a small influence. Dispersions with a high surface charge flocculates easier than dispersions with a low surface charge in process water from the wet-end of a linerboard paper machine. The flocculation rate is fast and occurs on the same time scale as deposition onto fines and fibers. The AKD agglomerates could be up to 30 µm in diameter even at high levels of shear. The AKD diffusion coefficient in paper sheets was estimated to be 10-11 m2/s at a temperature above the melting point of the wax. The results indicate that extractives do not interfere with the AKD migration. A reasonable explanation is that migration occurs via the vapor phase. It was also shown that sizing with flocculated AKD improved the sizing efficiency significantly due to increased retention. This clearly indicates that migration is efficient and that agglomerates can be used for internal sizing provided that the flocculation process is controlled. The conventional picture that the sizing agents must be very evenly distributed to achieve efficient sizing could, from the viewpoint of these results, be questioned. The process of sizing with pre-flocculated AKD dispersions is the subject of a patent application. Even if this thesis is focused on AKD dispersions, the obtained knowledge should be possible to transfer to other sizing systems. The emulsification process for rosin and ASA is based on the same principles as for AKD. / Godkänd; 2002; 20070222 (ysko)

This work concerns evaluation by permeation measurements and modeling of thin (<2µm) MFI molecular sieve membranes and, to a smaller extent, synthesis of such materials. The membranes have been synthesized on graded a-alumina microfiltration filters using The seed film method. Scanning electron microscopy and x-ray diffraction were used for characterization in addition to permeation measurements. Mathematical models describing membrane flux for real membranes and defect distributions were developed. Defect distributions were calculated from porosimetry data and were further used for prediction of single gas permeation characteristics for real membranes. The models confirm the experimental findings, with respect to ideal selectivities as a measurement of membrane quality. Membrane permeation simulations indicate increasing ideal selectivities, with increasing film thickness, for quotients containing SF6. Thereby a high quality membrane could possess low ideal selectivities. This finding was confirmed by comparing experimental data of several membranes with varying thickness. The correlation between multi component separation data and commonly used quality criteria was investigated. It was found that commonly used single gas permeation quotients (ideal selectivity) between light inorganic gases, especially those containing sulphurhexaflouride (SF6), is less appropriate for membrane quality measurement. The porosimetry experiment showed on the other hand a good agreement between experimental data and separation performance of the membranes, as expected. ZSM-5 membranes with low aluminum content and silicalite-1 membranes with similar material properties, such as defect distribution and thickness were evaluated with multi component hydrocarbon isomers permeation. The ZSM-5 membrane had lower permeances and a slightly better butane isomer separation performance than the silicalite-1 membrane. The latter membrane showed a minimum in separation selectivity between two C6 isomers whereas the ZSM-5 membrane showed an almost constant selectivity, independent of temperature, but with lower permeances. ZSM-5 membranes with a high aluminum content catalyzed the formation of diethylether and ethylen at temperatures exceeding 150°C from a water/ethanol mixture. The membrane separated a mixture of C4 isomers with good performance at elevated temperatures. However these membranes suffered from temperature instability problems. / Godkänd; 2002; 20070224 (ysko)

Molecular sieve films and colloidal particles may have great potential for further utilization in novel technological sophisticated applications such as structured catalysts, sensors and membranes. The work presented in this thesis concerns the synthesis molecular sieve films and the crystallization of zoned MFI materials for novel catalyst and sensor applications. The seeding method developed at the division has been modified for the preparation of MFI and FAU type films on a variety of steel substrates ranging from ordinary carbon steel to highly corrosion resistant stainless steel. The films were characterized by SEM, XRD and gas adsorption techniques. The results revealed that the type of steel did not affect the film morphology, the thickness or the preferred orientation of the crystals, whereas the thermal stability was dependent on the steel. Films on various stainless steel supports were stable during calcination, whereas films on carbon steel supports peeled off upon rinsing after calcination because a relatively thick magnetite/hematite film formed. Pre-calination of carbon steel improved the zeolite film stability upon calcination. Zoned MFI materials (colloidal zoned MFI crystals and zoned films) were synthesized in this work in order to improve the catalytic performance of MFI. A two-step crystallization method was developed to prepare zoned MFI materials, in which precursor ZSM-5 colloidal particles or film were grown in a silicalite-1 synthesis solution directly or after acid treatment. It was shown that zoned MFI materials did not form when the ZSM-5 surface had a high aluminum content. In this case, polycrystalline aggregates or a sandwich film formed due to secondary nucleation. After reducing the aluminum content to half by acid treatment of ZSM-5, secondary nucleation of new silicalite-1 crystals was inhibited and zoned MFI material was obtained. / Godkänd; 2003; 20070216 (ysko)

A novel synthesis method called a two-stage varying-temperature synthesis was developed for the investigation of kinetics and mechanism of the crystallization of discrete colloidal crystals of TPA-silicalite-1. Briefly, this method involves a rapid change in treatment temperature at some point during the crystallization. By extending the duration of the period at the initial synthesis temperature, the crystal concentration and final crystal size varied until they were approximately equal to those obtained for a complete synthesis at the initial temperature. At this point in the crystallization, it was concluded that the nucleation stage was completed. In the TPAOH-TEOS-H2O system, the nucleation was a continuous process and the rate of nucleation was initially high immediately after the start of hydrothermal treatment, but then exponentially declined throughout the nucleation period. In the TPAOH-SiO2-H2O-ethanol system, where SiO2 was colloidal amorphous silica, the nucleation was still a successive process, whereas the nucleation profile was more similar to that usually considered to occur during zeolite syntheses with an autocatalytic increase in the nucleation rate. When the synthesis conditions were identical, except for the silica source in the above two systems, the nucleation period for the TPAOH-SiO2-H2O-ethanol system was longer than that for the TPAOH-TEOS-H2O system. This was presumably due to the fact that the colloidal silica particles needed to depolymerize to reach a supersaturation concentration in order for nucleation and crystal growth to occur. Also, it was found that irrespective of silica sources, the vast majority of nucleation occurred during an induction period before linear crystal growth started. The two-stage synthesis method could also be used to produce particularly small colloidal crystals of TPA-siliclaite-1 with reduced synthesis times and high yields. Using this method involves starting a synthesis at a lower temperature and ending the synthesis at a higher temperature. After determining the nucleation stage, an elevated temperature can be used to accelerate the crystal growth and reach higher equilibrium yields controlled by the final temperature. The effects of temperature, dilution and alkalinity on the synthesis were studied to optimize syntheses. The effect of aging on the kinetics and mechanism for crystallization of colloidal TPA-silicalite-1 with varying silica source was also investigated with the two-stage synthesis procedure. With the TEOS silica source, aging for up to 15 days at room temperature had no significant effect on the nucleation and crystallization at a low synthesis temperature. Whereas with amorphous silica, aging caused the nucleation kinetics to become increasingly similar to those for syntheses with TEOS. Thus, with sufficient aging of more economical amorphous silica sources, the properties of the final products approached that with the more exotic TEOS silica source, viz., small colloidal crystals with a narrow crystal size distribution. / Godkänd; 2000; 20070318 (ysko)

The preparation of zeolite macrostructures in the form of bilayered hollow tubes and microspheres is presented. The bilayered hollow ZSM-5/silicalite-1 tubes were prepared using carbon fibers as a substrate. The surface of the fibers was modified and colloidal silicalite-1 seed crystals adsorbed. The fibers were then treated with a synthesis mixture yielding ZSM-5. After separation of the fiber/zeolite composites a second treatment resulting in the crystallization of silicalite-1 was performed. Finally, the carbon fibers were removed by calcination leaving hollow tubes. Silicalite-1 micropsheres were prepared using macroporous anion exchange resins as shape directing macro-templates. Resin beads were hydrothermally treated with a synthesis solution yielding silicalite-1 resulting in the crystallization of silicalite-1 in the pores of the resin. The resin was then removed by calcination leaving self-bonded silicalite-1 micropsheres identical in shape and size to the original resin beads. The zeolite macrostructures were extensively characterized using SEM, XRD, EDS-analysis, Raman spectroscopy, nitrogen adsorption and microhardness measurements. / Godkänd; 1999; 20070322 (ysko)

The solid state reaction between sodium tri-titanate and sodium carbonate, forming mainly sodium penta-titanate, was investigated. Experiments were carried out in a micro-differential reactor made of quartz glass at various temperatures between 800°C and 880°C and in a pilot fluidized bed reactor operated in a semi-batch mode. In the micro-differential reactor, basic kinetic data was obtained by measuring the release of carbon dioxide during the reaction. Different kinetic models were considered to describe the conversion, such as the Valensi-Carter model for diffusion controlled reaction rates and the phase-boundary model for first-order reaction kinetics. Furthermore, a model that included both diffusion in the solid material and the chemical kinetics was derived. This model described the experimental data obtained in the micro-differential reactor very well. Finally, rating models describing the conversion obtained in a fluidized bed and in an entrained flow reactor were developed. / Godkänd; 1999; 20070403 (ysko)

The work presented in this thesis was aimed to synthesize zeolite films in the absence of organic additives to avoid the potentially detrimental calcination procedure. Furthermore, the support surface was seeded with colloidal seed crystals prior to film growth. This technique has previously been used to prepare thin zeolite films. The films were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and gas permeation experiments. Films of three different types of zeolites were synthesized in this work; FAU-type zeolite, ZSM-5 and zeolite NaA. The thickness of the FAU-type zeolite films could be controlled by varying the synthesis temperature and duration. However, a maximum film thickness was found. Prolonged hydrothermal treatment caused the film thickness to decrease due to the transformation of FAU into zeolite P. The adsorbed seeds were oriented with the <111> pyramid parallel to the surface of the support. During growth, the crystals constituting the films became randomly oriented. The ZSM-5 films were tested as membranes for the separation of butane isomers. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Furthermore, the ZSM-5 membranes were found to be catalytically active, converting ethanol into diethylether and ethylene. The growth of silicious species into the porous support during zeolite NaA membrane synthesis was examined. Higher temperatures of synthesis resulted in relatively more growth into the porous support compared to the film growth on top of the support. By using a multi-step synthesis procedure at low temperature, thicker films with less growth into the support could be prepared. / Godkänd; 2001; 20070315 (ysko)

The main objective of this thesis was to acquire a better understanding of the mechanisms involved in the preparation of Silicalite-1 films in general and on gold surfaces in particular. Molecular sieve films on gold surfaces were prepared using the seed film method. The deficiency of negative charge on a gold surface in aqueous solution was overcome by a coupling agent (gamma-mercaptopropyltrimethoxysilane or sodium hydrosulfide). The resulting negatively charged surface was modified by a cationic polymer, facilitating the adsorption of negatively charged colloidal silicalite-1 seed crystals. The seed crystals were grown into a continuous molecular sieve film during hydrothermal treatment in synthesis solution. Reflection absorption infrared spectroscopy was found to be an excellent method to gain insight about the structures formed after each step in this preparation procedure. The recorded vibrational spectra were compared with vibrational modes calculated from the dynamic matrix of the clusters concidered. These comparisons showed that the organic coupling agent was oriented with the methylene chain perpendicular to the gold surface, the cationic polymer introduces disorder in the silane layer, the silanol groups predominantly form 6-membered puckered Si-O rings upon condensation and that linear defects in the films are formed during the hydrothermal treatment. The effects of seed size and hydrothermal treatment time on the formation of linear defects were investigated. / Godkänd; 1999; 20070320 (ysko)

The preparation of molecular sieve based catalysts in appropriate macroforms suitable for practical utilization is of great technological importance. This thesis is dedicated to the preparation of metal containing molecular sieve macrostructures (modified macrostructures). Modified molecular sieve macrostructures were prepared by the resin templating method. Firstly, molecular sieves were synthesized within the pore structure of macroporous anion exchange resin beads. After this step, a certain degree of ion exchange capacity is retained by the resin facilitating the secondary insertion of metal anions. Metal anionic species were ion exchanged into the resin-molecular sieve composites obtained in a following step. Finally, the resin was removed by calcination leaving behind self-bonded metal containing molecular sieve spheres with a shape and size similar to the original resin beads. V, W, Cr and Pd containing macrostructures were prepared by the method. Resin-silica composites, in which the structure of the silica was changed from amorphous to crystalline silicalite-1 were used for the preparation of the V and W spheres. The Cr and Pd containing spheres were prepared from resin-zeolite beta composites. The properties of the product spheres (metal content, crystallinity, morphology, nature of the metal species, etc.) were extensively characterized by atomic adsorption spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive, Raman and UV-vis spectroscopy, nitrogen adsorption and chemisorption measurements. The materials prepared are of interest for application mainly in the area of catalysis. / Godkänd; 2002; 20070222 (ysko)