| 1. |
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Chalmers Environmental Initiative Progress Report 2001
- 2001
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Editorial collection (peer-reviewed)abstract
- The Board of the Chalmers University of TechnologyFoundation decided in 1999 to invest SEK 100million in a strategic investment in the environmentwith a special focus on environmental systems analysis.This investment was entitled The ChalmersEnvironmental Initiative (CEI). Through thisenvironmental initiative Chalmers has acquired aprominent international position within environmentalsystems analysis.CEI is the result of the active research and educationthat has taken place at Chalmers over the past 10years. A broad base in combination with leadingedge technology presented the opportunity to createa very strong research programme based oninteraction between the various schools at Chalmers.As CEI is integrated into undergraduate anddoctoral programmes at Chalmers, engineers,architects and doctoral students have access, withinthe framework of their studies, to research-basedenvironmental education with a focus on asustainable society. CEI also co-operates with otherparties, such as industry, politicians, various organisationsand the general public, as a further means ofcontributing to sustainable development in society.Within CEI, seven new professors have beenappointed within the following areas:Management for SustainabilityRolf Wolff, 1 June 2000Environmental Systems TechnologyAnne-Marie Tillman, 1 September 2000Sustainable Industrial MetabolismChristian Azar, 1 September 2000Global Environmental MeasurementsDonal Murtagh, 1 November 2000Green ChemistryWilliam J. Frederick Jr, 1 August 2001Sustainable Energy SystemsFilip Johnsson, preliminary 1 October 2001Design for Sustainable Urban DevelopmentVacant: interviews during April 2001The four professors appointed in 2000 are presentedin this report as well as their declaration of intentfor the next few years. At present, the CEI professorsare involved with approximately 40 universities,institutes and industrial partners in the form ofproject co-operation and joint publications. The fourprofessors have the greater proportion of theirenvironmental research funded through externalgrants, compared to CEI. The proportion of facultyfunds and other internal Chalmers funds is at presentvery low. A summary of the financing structureis also included in this report.During 2001, various forms of co-operation wereinitiated between the professors, such as joint projectplans, doctoral students, courses and graduateschools. During autumn 2001, a residential seminaris planned for discussions within CEI as well as anopen presentation of the project and the professors.This major in-house focus on environmental researchhas attracted attention externally and contributedto the opening up of new potential in combinationwith increased expectations. Since May 1, 2000,Chalmers has been a member of the Alliance forGlobal Sustainability (AGS), an association of someof the world’s foremost universities in theenvironmental field. AGS and other platforms formthe basis for international research collaboration.CEI and other environmental activities have led tospin-off effects and contributed to increased interestin Chalmers as an environmental university.Chalmers and Göteborg University were, forexample, jointly awarded the King Carl XVI Gustafvisiting professorship in environmental science for2001-2002 and Margot Wallström received anhonorary doctorate from Chalmers in 2001. A largenumber of well-known environmental researchershave also visited Chalmers to take part inconferences and seminars, including the winners ofthe Volvo Environmental Award for 2000 and thewinner of the City of Göteborg InternationalEnvironmental Award for 2000.
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| 2. |
- Wang, Zeng, et al.
(author)
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Zeolite coated ATR crystals for new applications in FTIR-ATR spectroscopy
- 2004
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In: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :24, s. 2888-2889
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Journal article (peer-reviewed)abstract
- Thin silicalite-1 films were grown on ATR crystals and used for detection of low amounts of organic molecules in a gas flow by FTIR spectroscopy.
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| 3. |
- Mamontov, Eugen, 1955, et al.
(author)
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High-Dimensional Nonlinear Diffusion Stochastic Pprocesses. Modelling for Engineering Applications
- 2001
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Book (other academic/artistic)abstract
- This book is the first one devoted to high-dimensional (or large-scale) diffusion stochastic processes (DSPs) with nonlinear coefficients. These processes are closely associated with nonlinear Ito's stochastic ordinary differential equations (ISODEs) and with the space-discretized versions of nonlinear Ito's stochastic partial integro-differential equations. The latter models include Ito's stochastic partial differential equations (ISPDEs). The book presents the new analytical treatment which can serve as the basis of a combined, analytical-numerical approach to greater computational efficiency in engineering problems. A few examples discussed in the book include: the high-dimensional DSPs described with the ISODE systems for semiconductor circuits; the nonrandom model for stochastic resonance (and other noise-induced phenomena) in high-dimensional DSPs; the modification of the well-known stochastic-adaptive-interpolation method by means of bases of function spaces; ISPDEs as the tool to consistently model non-Markov phenomena; the ISPDE system for semiconductor devices; the corresponding classification of charge transport in macroscale, mesoscale and microscale semiconductor regions based on the wave-diffusion equation; the fully time-domain nonlinear-friction aware analytical model for the velocity covariance of particle of uniform fluid, simple or dispersed; the specific time-domain analytics for the long, non-exponential "tails" of the velocity in case of the hard-sphere fluid. These examples demonstrate not only the capabilities of the developed techniques but also emphasize the usefulness of the complex-system-related approaches to solve some problems which have not been solved with the traditional, statistical-physics methods yet. From this veiwpoint, the book can be regarded as a kind of complement to such books as "Introduction to the Physics of Complex Systems. The Mesoscopic Approach to Fluctuations, Nonlinearity and Self-Organization" by Serra, Andretta, Compiani and Zanarini, "Stochastic Dynamical Systems. Concepts, Numerical Methods, Data Analysis" and "Statistical Physics: An Advanced Approach with Applications" by Honerkamp which deal with physics of complex systems, some of the corresponding analysis methods and an innovative, stochastics-based vision of theoretical physics. To facilitate the reading by nonmathematicians, the introductory chapter outlines the basic notions and results of theory of Markov and diffusion stochastic processes without involving the measure-theoretical approach. This presentation is based on probability densities commonly used in engineering and applied sciences.
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| 4. |
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| 5. |
- Malkoch, Michael, et al.
(author)
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Synthesis and characterization of 2,2-bis(methylol)propionic acid dendrimers with different cores and terminal groups
- 2004
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In: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 42:7, s. 1758-1767
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Journal article (peer-reviewed)abstract
- Three sets of aliphatic polyester dendrimers based on 2,2-bis(methylol)propionic acid (bis-MPA) were synthesized. Two of the sets had benzylidene terminal groups and either a trimethylolpropane or triphenolic core moiety. The last set had acetonide terminal groups and a triphenolic core moiety. Benzylidene-[G#1]-anhydride and acetonide-[G#1] -anhydride were used as the reactive building blocks in the construction of all dendrimers. The large excess of building blocks used in the coupling reactions initially resulted in considerable material loss. This waste was eliminated through the development of a recycling method. H-1 and C-13 NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis were used to verify the purity of all compounds. Size exclusion chromatography (SEC) was used, as well as MALDI-TOF, for molecular weight determinations. The SEC measurements were conducted with a universal calibration method and an online right-angle laser light scattering detector. Measured dendrimer molecular weights were close to their theoretical molar masses. Observations were also made of the hydrodynamic radius and intrinsic viscosity for the different dendrimers.
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| 6. |
- Bengtsson, Cecilia, 1974, et al.
(author)
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Co-ordination of pinch technology and the MIND method : applied to a Swedish board mill
- 2002
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In: Applied Thermal Engineering. - 1359-4311 .- 1873-5606. ; 22:2, s. 133-144
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Journal article (peer-reviewed)abstract
- By combining the pinch technology and the MIND method, it is possible to identify beneficial and energy-efficient measures in a complex industrial energy system. By tackling a problem on the two different aggregation levels, the result is thoroughly evaluated and durable measures are achieved. The strength of the combination of methods is elucidated in a case study where a Scandinavian pulp and paper mill is analysed. The studied problem concerns pre-evaporation of effluents in a board mill using excess heat. Different alternatives are evaluated, taking into account economic, technical and practicable constraints. The results show that it is cost-effective to pre-evaporate the effluent using excess heat in the studied mill.
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| 7. |
- Fritzson, Anna, 1977, et al.
(author)
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Energy conservation in the food industry using process integration - Methodologies and case study
- 2003
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In: ICEF-2003 International Conference Engineering and Food.
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Conference paper (other academic/artistic)abstract
- Increased sales of ready-made meals mean that the environmental impacts of the households are changed and the degree of processing in industry is increased, Process integration methods are briefly presented and partly used in this study to identify parts of the process in a Swedishslaughterhouse and meat processing plant where there is a potential to save energy. Several areas where heat savings are possible are identified.
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| 8. |
- Fridell, Erik, 1963, et al.
(author)
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Model studies of NOx storage and sulphur deactivation of NOx storage catalysts
- 2001
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In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 133-137
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Journal article (peer-reviewed)abstract
- The storage of NOx under lean conditions in model NOx storage catalysts as well as the deactivation by sulphur have been studied. We find that NO2 plays an important role in the storage mechanism as an oxidising agent. Two different mechanisms for this are discussed: the formation of surface peroxides and the oxidation of nitrites to nitrates, FTIR studies show that NOx is stored as surface nitrates, The sulphur deactivation is found to be more severe when SO2 is added during the rich phase than when SO2 is added during the lean period. FTIR shows the formation of bulk sulphates both under lean and rich conditions.
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| 9. |
- Lindgren, M., et al.
(author)
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Styrene emissions from the spray-up and vacuum injection processes - A quantitative comparison
- 2002
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In: AIHAJ - Journal of Occupational and Environmental Hygiene. - : Informa UK Limited. - 1529-8663 .- 2163-3711. ; 63:2, s. 184-189
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Journal article (peer-reviewed)abstract
- Styrene emissions were studied during manufacturing of two identical glass-fiber reinforced plastic boats by two different manufacturing methods. The manufacturing methods were spray-up, which is an open method, and vacuum injection, which is a closed method. Changing the manufacturing process from an open method to a closed method decreased the styrene evaporation dramatically in this particular case. By using vacuum injection, the styrene emission during the laminate application was reduced by 98% compared with the styrene emission during laminate application by spray-up. Gel coat application by spraying will remain a major source for styrene emissions. The greatest environmental benefit is achieved with closed manufacturing methods when products without gel coat are made. The whole manufacturing process can then be performed in a closed system virtually free from emissions.
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| 10. |
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| 11. |
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| 12. |
- Yao, Yiming, 1957, et al.
(author)
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Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part I: The silicon substrate/nanotube film interface
- 2004
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In: Journal of Materials Science: Materials in Electronics. ; 15:8, s. 533-543
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Journal article (other academic/artistic)abstract
- The interface between the silicon substrate and a carbon nanotube film grown by thermal CVD with acetylene (C2H2) and hydrogen at 750 or 900 °C has been characterized by high resolution and analytical transmission electron microscopy, including electron spectroscopic imaging. Silicon (0 0 2) substrates coated with a thin (2.8 nm) iron film were heat treated in the CVD furnace at the deposition temperature in a mixture of flowing argon and hydrogen whereby nanosized particles of (Fe,Si)3O4 formed. These particles were reduced to catalytic iron silicides with the α–(Fe, Si), α2–Fe2Si and α1–Fe2Si structures during CVD at 900 °C, and multi-wall carbon nanotubes grew from supported particles via a base-growth mechanism. A limited number of intermediate iron carbides, hexagonal and orthorhombic Fe7C3, were also present on the substrate surface after CVD at 900 °C. The reduction of the preformed (Fe, Si)3O4 particles during thermal CVD at 750 °C was accompanied by disintegration leading to the formation of a number of smaller (
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| 13. |
- Carlsson, Per-Anders, 1972, et al.
(author)
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Periodic control for improved low-temperature catalytic activity
- 2001
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In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 343-347
-
Journal article (peer-reviewed)abstract
- The influence of transient changes in the gas composition on the low-temperature activity of a commercial three-way catalyst and a Pt/Al2O3 model catalyst has been studied. By introducing well-controlled periodic O2 pulses to simple gas mixtures of CO or C3H6 (in N2), a substantial improvement of the low temperature oxidation activity was observed for both catalysts. The reason for low activity at low temperatures is normally attributed to self-poisoning by CO or hydrocarbons. The improved catalytic performance observed here is suggested to origin from the transients causing a surface reactant composition that is favourable for the reaction rate.
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| 14. |
- Engström, V., et al.
(author)
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The effect of seed size on the growth of silicalite-1 films on gold surfaces
- 2000
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In: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 38:1, s. 51-60
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Journal article (peer-reviewed)abstract
- Silicalite-1 films grown on gold surfaces seeded with colloidal crystals with a size of 60, 165 and 320 nm were investigated by reflection–absorption infrared spectroscopy, scanning electron microscopy and X-ray diffraction in order to follow up the formation of nano-scale defects and to determine the optimal synthesis conditions for preparation of silicalite-1 films with a low concentration of defects. Using 60-nm-sized colloidal crystals, the seeding method was capable of producing silicalite-1 films with low concentrations of defects and with thicknesses ranging from 100 to 300 nm, which are predominantly oriented with the a-axis perpendicular to the surface. Hydrothermal treatment times of the 60-nm-seeded surfaces longer than 36 h as well as the seeding with 165 or 320 nm colloidal crystals substantially enhanced the formation of defects in the films.
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| 15. |
- Eriksson, Håkan, 1973, et al.
(author)
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Potential for increased electricity production at an integrated pulp and paper mill with black liquor gasification
- 2001
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In: Proceedings of the 2001 TAPPI Engineering/Finishing and Converting Conference and Trade Fair, San Antonio, 16-20 September 2001. - 1930657838 ; , s. 411-426
-
Conference paper (peer-reviewed)abstract
- A number of ongoing efforts aim at reducing greenhouse gas emissions from industrial energy systems. This can be achieved through increased biofuel usage. Biofuels are however a limited resource, and their usage must therefore be as efficient as possible. The objective of this study was to identify pulp and paper mill powerhouse configurations with maximal electricity production from a given limited amount of biofuel (black liquor and conventional wood fuels). The configurations investigated include black liquor gasification and conventional Tomlinson recovery boiler systems. The study is based upon a detailed model of the mill's chemical recovery island and a simplified model of the remainder of the mill. In order to satisfy the mill's heat balance, extra biofuel must be imported for most of the configurations considered. The configuration with the highest on-site electricity production (96 MW) includes biofuel gasification and firing in a gas turbine combined cycle unit. However, if biofuel is assumed a limited resource, importing biomass to the mill implies that less biofuel is available for other competing users. The net global electric power production is shown to decrease from 96 MW to 41 MW for the same powerhouse configuration when performance is evaluated in a global perspective.
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| 16. |
- Carlsson, Per-Anders, 1972, et al.
(author)
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Low-temperature CO oxidation over a Pt/Al2O3 monolith catalyst investigated by step-response experiments and simulations
- 2004
-
In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30/31:1-4, s. 375-381
-
Journal article (peer-reviewed)abstract
- The ignitionextinction processes for CO oxidation over a Pt/Al2O3 monolith catalyst have been studied by flow-reactor experiments and simulations. The study was performed by stepwise changes of the inlet O2 concentration ranging 020 vol% while the CO concentration and the inlet gas temperature were kept constant at 1.0 vol% and 423 K, respectively. Several features observed experimentally are qualitatively simulated with our model: (i) the ignition of the CO oxidation demands 8.0vol% O2 (ii) corresponding to a catalyst ignition temperature of 433 K (due to the exothermicity of the reaction) and (iii) occurs in the rear part of the monolith where (iv) a local reaction zone is formed which (v) moves towards the reactor inlet as a function of time on stream. Additionally, the simulations show first order kinetic phase transitions, i.e. rapid adsorbate concentration changes, where the catalyst surface is predominantly CO covered in the low reactive state and almost completely oxygen covered in the high reactive state. For the ignition process the kinetic phase transition occurs after the actual catalytic ignition. However, the extinction process is more difficult to simulate dynamically without changing the model parameters for O2 adsorption in the low and high reactive state, respectively. The influence of diffusion limitations and the role of formation of a less reactive Pt state under oxidising conditions is discussed.
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| 17. |
- Svedberg, Pernilla, 1974, et al.
(author)
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Influence of the storage material on the storage of NOx at low temperatures
- 2004
-
In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30/31:1-4, s. 199-206
-
Journal article (peer-reviewed)abstract
- The NOx storage performance at low temperature (100-200°C) has been studied for model NOx storage catalysts. The catalysts were prepared by sequentially depositing support, metal oxide and platinum on ceramic monoliths. The support material consisted of acidic aluminium silicate, alumina or basic aluminium magnesium oxide, and the added metal oxide was either ceria or barium oxide. The NOx conversion was evaluated under net-oxidising conditions with transients between lean and rich gas composition and the NOx storage performance was studied by isothermal adsorption of NO2 followed by temperature programmed desorption of adsorbed species. The maximum in NOx storage capacity was observed at 100°C for all samples studied. The Pt/BaO/Al2O3 catalyst stored about twice the amount of NO x compared with the Pt/Al2O3 and Pt/CeO2/Al2O3 samples. The storage capacity increased with increasing basicity of the support material, i.e. Pt/Al2O3·SiO2
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| 18. |
- Wallin, Mikaela, 1975, et al.
(author)
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Selective catalytic reduction of NOx over H-ZSM-5 under lean conditions using transient NH3 supply
- 2004
-
In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30/31:1-4, s. 107-113
-
Journal article (peer-reviewed)abstract
- The selective catalytic reduction (SCR) of NO x over zeolite H-ZSM-5 with ammonia was investigated using in situ FTIR spectroscopy and flow reactor measurements. The adsorption of ammonia and the reaction between NO x , O2 and either pre-adsorbed ammonia or transiently supplied ammonia were investigated for either NO or equimolar amounts of NO and NO2. With transient ammonia supply the total NO reduction increased and the selectivity to N2O formation decreased compared to continuous supply. The FTIR experiments revealed that NO x reacts with ammonia adsorbed on Brønsted acid sites as NH4 + ions. These experiments further indicated that adsorbed -NO2 is formed during the SCR reaction over H-ZSM-5.
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| 19. |
- Junior, Vasco, 1963, et al.
(author)
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Integrated environment health and safety model for glass plant design
- 2004
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In: proceeding of the 4th international symposium on Occupational Safety and Hygiene, February 19-20 2004- Porto, Portugal. - 9729564671 ; , s. 133-144
-
Conference paper (peer-reviewed)abstract
- Abstract:The integration of environment, health and safety principles in process design constitutes a major challenge. The lack of appropriate methodologies for conducting effective risk assessment at early stage of process design and the inability of bringing together different types of expertise in the design practice are, among others, the most relevant limiting factors.In this study, a systematic, structured approach to risk assessment is adopted. A model for a high-temperature process, which encompasses the formulation of Environment, Safety and Health Problem as part of engineering process, has been developed.The model requirements are the availability at a very early stage of a statement of the project, plant process specifications and pertinent chemical or engineering data. The Hazard Identification and Environmental Aspects Identification in the production process are initially implemented at a component level. Afterwards, the identification is carried out at a process section level, following the process mapping approach. Risk assessment is then applied to the entire plant. Subsequently, process improvement options are established and evaluated. The last stage encompasses a systematic evaluation of risks and environmental impacts against a set of control options and the choice of the best glass plant design option.
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| 20. |
- Wik, Torsten, 1968, et al.
(author)
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Model based control of external carbon dose rate in a full-scale predenitrification system
- 2004
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In: Water Intelligens Online, IWA Publishing.
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Journal article (peer-reviewed)abstract
- In wastewater treatment plants (WWTPs) with biological nitrogen removal it is commonthat large amounts of an easily biodegradable carbon source have to be added for completedenitrification. At the Rya WWTP in Göteborg, which is a predenitrification system with postnitrifyingtrickling filters (NTFs) in the recirculation stream, this occurs during periods of loworganic loads and after nitrate chock loads after flooding and back washing of the NTFs. In thisstudy, this costly control problem is regarded as an uncertain dynamic system. A model based feedforward loop, using biased information about the recirculated nitrate flow is combined with a robustPI feed back controller that applies large stability margins and ensures that these are fulfilled for alllikely operating points of the system. Different feed forward strategies to deal with possible overdosagedue to lack of past information in periods when full denitrification has occurred withoutexternal carbon, are assessed by simulation. After evaluation of the controllers by simulation usinga simplified activated sludge model a controller was implemented at Rya WWTP with good results.
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| 21. |
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| 22. |
- Alkasrawi, Malek
(author)
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Development of Simultaneous Saccharification and Fermentation for Production of Ethanol from Softwood
- 2004
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with the development of simultaneous saccharification and fermentation (SSF) in order to improve the economy of the softwood-to-ethanol process. The effect of process stream recirculation on ethanol production from steam-pretreated softwood based on SSF was investigated for two process cases. In the first case, part of the stillage stream after distillation was recycled and in the second case the liquid after SSF was recycled. The aim was to minimize the energy demand in the distillation of the fermentation broth and in the evaporation of the stillage, as well as the use of fresh water. It was possible to replace of 60% of the fresh water by recirculation of stillage, while maintaining the ethanol yield. This would result in a reduction in the ethanol production cost of 17%. In the second case, where the stream after SSF was recirculated, up to 40% of the fresh water could be replaced without affecting the final ethanol yield, which would result in a 12% reduction in the estimated production cost. Recirculation of the condensates from the evaporation step to SSF could be employed to replace all the fresh water without affecting the ethanol yield. This will make it possible to further reduce the use of fresh water and thereby reduce the volume of wastewater. Increased water-insoluble material (WIM) content in SSF often gives rise to severe inhibition of yeast metabolism due to the increased concentration of toxic compounds formed in the pretreatment step. One way to overcome this problem is to adapt the baker’s yeast to the increased amount of inhibitors in SSF by cultivating it on steam pretreatment hydrolysate. The WIM load was increased from 5 to 8% while maintaining the ethanol yield when the adapted yeast was used in SSF. This could result in a lowering of the production cost by 19%. In order to increase the WIM further, SSF was run in fed-batch mode, using the adapted yeast. Fed-batch SSF with up to10% WIM had no effect on the ethanol yield. A combination of high WIM in fed-batch SSF and recirculation of the process stream will definitely reduce the ethanol production cost. The effect of adding detergent to SSF was investigated using Tween-20, a non-ionic detergent. Tween-20 at 2.5 g/L increased the ethanol yield in SSF by 8%, and could be used to reduce the amount of cellulases required by 50% while maintaining the ethanol yield.
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| 23. |
- Junior, Vasco, 1963, et al.
(author)
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Cost effective waste minimisation approach to specialty glass making
- 2004
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In: proceeding of “waste Management, Emissions & Recycling in the Metallurgical & Chemical Process Industries, 18 – 19 March 2004, Mintek, Randburg – South Africa. ; , s. 33-45
-
Conference paper (peer-reviewed)abstract
- Abstract:A cleaner glass melting process has been developed through a prevention-oriented approach to minimizing waste at its generation source. Waste minimization principles have been combined with environmental, technical and safety requirements in a formal process design framework. The applied methodology comprises the positive identification of waste generation activities, waste segregation and quantification. The process design is evaluated in terms of the impact produced by the applied waste minimization options. In addition to material and energy assessment, the process validation is extended to include an analysis of the financial effort required for a reasonable waste management strategy. The evaluated parameters, including the financial indicators, point out that a glass melting plant developed through the usage of the applied methodology meets the required parameters of cost-effectiveness and reliability.
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| 24. |
- Andersson, Charlotte
(author)
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Properties of molecular sieve membranes
- 2004
-
Licentiate thesis (other academic/artistic)abstract
- Zeolites are crystalline aluminosilicates with molecular sieving properties and are widely used in industry for catalysis, sorption and ion-exchange applications. Zeolite membranes are commercially interesting since this technology may be employed for continuous separation of molecules under severe conditions. MFI zeolite has suitable pore diameter for many applications and relatively high thermal and chemical stability. Zeolite films in membranes must be thin, to obtain a high flux and free from defects for high selectivity. Many parameters are affecting the properties of zeolite films and in this thesis some of them are investigated. MFI zeolite membranes were prepared using seed crystals and hydrothermal synthesis and characterized with scanning electron microscopy, single gas permeation measurements, porosimetry and separation experiments. Membranes grown in one or several steps with seeding in-between the synthesis steps were compared. It was observed that membranes comprised of small crystals and consequently high concentration of grain boundaries had low separation performance. Grain boundaries could also be opened by extensive rinsing, which reduced membrane quality. The influence of the calcination rate on the performance of zeolite membranes of a particular type was also studied. It was demonstrated that the calcination rate does not affect the membrane quality.
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| 25. |
- Andersson, Charlotte, et al.
(author)
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Silicalite-1 membranes with small crystal size
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 626-631
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Conference paper (peer-reviewed)abstract
- Silicalite-1 membranes with small crystal size were prepared using a multiseeding method, where the support was repeatedly seeded and exposed to a short hydrothermal treatment up to five times. The film were characterized using SEM, single gas permeation, porosimetry and mixture separation experiment Films with three or four layers were of high quality i.e with minor defects according to the porosimetry experiments but showed poor separation of binary mixtures. This result may be attributed to the small crystal size and/or large amount of grain boundaries in the films.
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| 26. |
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| 27. |
- Creaser, Derek, et al.
(author)
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Kinetic modelling of oxygen dependence in oxidative dehydrogenation of propane
- 2000
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In: Canadian Journal of Chemical Engineering. - : Wiley. - 0008-4034 .- 1939-019X. ; 78:1, s. 182-193
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Journal article (peer-reviewed)abstract
- Several Mars-Van Krevelen-type redox kinetic models were developed for the catalytic oxidative dehydrogenation of propane and examined for their ability to predict high propene yields at low oxygen/propane feed ratios. The intent in this study was to use modelling as a means of extracting further mechanistic insight from experimental data rather than to identify the best model. Thus, a conventional redox model with a consecutive reaction mechanism and a single pathway for the production of carbon oxides predicts higher propene selectivity but only at the expense of low propane conversion. Experimental data indicated, however, that even at the same propane conversion, propene selectivity increased as the oxygen partial pressure was lowered. Models that successfully describe the data had an additional carbon oxide production path involving the reaction of propane with deeply oxidizing surface oxygen species. Kinetic models and experimental data examined do not fully resolve how these deeply oxidizing surface oxygen species are formed. However, they do reflect the accepted view that lattice oxygen selectively produces propene whereas more weakly bound surface adsorbed oxygen reacts to completely oxidize propane.
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| 28. |
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| 29. |
- Edin, M., et al.
(author)
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Hot melt adhesion of liner sized with alkylketene dimer
- 2002
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In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 17:4, s. 395-400
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Journal article (peer-reviewed)abstract
- The effect of the sizing agent alkylketene dimer (AKD) on hot melt adhesive joint strength was studied. By varying the amount of AKD added, and varying the degrees of beating and calendering, sheets with different surface energies, surface structures, and strength properties, were obtained. The sheets were adhesively bonded using a commercial packaging machine, and the adhesive joints were tested in T-peel and creep tests. Contact angles, water absorptivity, delamination strength, density, and surface roughness were measured to study the way in which the addition of AKD, beating, and calendering influence these paper properties. The results indicate that neither sizing with AKD nor calendering or beating have any pronounced effect on the adhesive joint strength, at least not under the conditions used. Most of the differences observed are within the limits of the experimental error. The greatest influence on the joint strength was observed when samples had been stored at low temperature.
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| 30. |
- Fridell, Erik, 1963, et al.
(author)
-
Platinum oxidation and sulphur deactivation in NOx storage catalysts
- 2004
-
In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 143-146
-
Journal article (peer-reviewed)abstract
- Flow reactor experiments and X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the importance of platinum oxide formation on Pt/BaO/Al2O3 NOx storage catalysts during reactions conditions. The reaction studied was NO(g) + 1/2 O-2(g) NO2 (g). During NO2 exposure of the catalyst the NO2 dissociation rate decreased during the reaction. This activity decrease with time was also studied with XPS and it was found to be due to platinum oxide formation. The influence of sulphur exposure conditions on the performance of the NOx storage catalysts was studied by exposing the samples to lean and/or rich gas mixtures, simulating the conditions in a mixed lean application, containing SO2 The main results show that all samples are sensitive to sulphur and that the deactivation proceeds faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. Additionally, the influence of the noble metals present in the catalysts was investigated regarding sulphur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable to retain high performance of the catalyst under SO2 exposure and subsequent regeneration. Finally, the behaviour of micro-fabricated model NOx storage catalysts was studied as a function of temperature and gas composition with area-resolved XPS. These model catalysts consisted of a thin film of Pt deposited on one-half of a BaCO3 pellet. It was found that the combination of SO2 and O-2 resulted in migration of Pt on the BaCO3 support up to one mm away from the Pt/BaCO3 interface.
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| 31. |
- Fridell, Erik, 1963, et al.
(author)
-
The Mechanism for NOx Storage
- 2000
-
In: Catalysis Letters. - 1572-879X .- 1011-372X. ; 66:1-2, s. 71-74
-
Journal article (peer-reviewed)abstract
- The mechanisms for storing of NOx in platinum-barium-alumina catalysts during lean-rich transients are investigated. Oxidation of NO to NO2 is found to be an important step. NO2 is found to be important for oxidation of the catalyst or of nitrites to form nitrates. NOx is then stored in the form of surface nitrates. FTIR studies show no formation of bulk nitrates in these experiments.
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| 32. |
- Grahn, Mattias
(author)
-
Development of a novel zeolite coated ATR-FTIR sensor
- 2004
-
Licentiate thesis (other academic/artistic)abstract
- Thin zeolite films have great potential in several novel application areas such as: structured catalysts, membranes and sensors. To fully exploit the advantages of these films it is of great importance to determine the properties of the films. A powerful technique for studies of phenomena at surfaces or in thin films is FTIR/ATR-spectroscopy (Fourier Transform Infra Red / Attenuated Total Reflection). Furthermore, thin zeolite films may be utilized for enhanced selectivity and sensitivity for this technique. In this work films with a thickness of 200 nm of the zeolites ZSM-5 and silicalite-1 were grown on ZnSe, ZnS, ZrO2, Si and Ge ATR elements using a method that had been developed previously. The coated elements were evaluated in a gas sensor application by comparing the sensitivity for a hydrocarbon of zeolite-coated elements versus a standard 10 cm gas cell. The sensitivity was approximately 85 times higher for the coated elements compared to the gas cell at low hydrocarbon concentration. The response time was investigated by exposing the coated element to a step increase of an analyte and recording the response as a function of time. The response was relatively fast, equilibrium was achieved after approximately 250 s, but already after a few seconds a strong signal could be detected. The coated elements were also used to determine single gas adsorption isotherms. The systems studied were n-hexane/silicalite-1 and p-xylene/silicalite-1. Adsorption isotherms determined at varying temperatures were typical for microporous materials. Capillary condensation was observed at higher concentration of the adsorbent. Henry constants and heats of adsorption determined from low-pressure data agreed well with previously reported data in the literature.
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| 33. |
- Harvey, Simon, 1965, et al.
(author)
-
Sustainable solutions for handling wastewater treatment sludge - A chemical engineering education case study
- 2004
-
In: Proceedings, International Conference on Engineering Education for Sustainable Development EESD2004. October 27-29, 2004. Barcelona, Spain.
-
Conference paper (other academic/artistic)abstract
- The Environmentally Sustainable Process Technology international Masters program at Chalmers University of Technology in Göteborg, Sweden, aims to provide students with the knowledge and skills necessary to improve and develop processes that are environmentally sustainable as well as economically sound. The program includes courses in core chemical engineering as well as applied environmental engineering areas. The social development aspects of sustainability for the chemical process industry are also taken up, i.e. how a process interacts with the surrounding world, including rules and regulations, public acceptance, risk, political aspects, etc. The Case Study project course is a key feature of the program, in which the knowledge acquired in the programs core course subject areas are used to solve an industrially relevant process engineering problem. The problem analysis and assessment of the proposed solution focus on various aspects of sustainability, including economical viabilityenvironmental impact and waste minimisation. This paper presents the results of a case study project that investigated the possible implementation of a SCWO (SuperCritical Water Oxidation) process plant for treatment of sludge from a Wastewater Treatment Plant in the Göteborg area. The project was related to a broader ongoing project GÖTEBORG 2050 that aims at generating long-term and sustainable future visions to be used for planning purposes in the City of Göteborg area. The paper aims at illustrating how chemical engineering education can introduce students to using process engineering methods and tools to identify sustainable solutions for e.g. energy planning and waste treatment problems. The Göteborg 2050 project provides a context for the students to relate to, thus facilitating for them to adopt the holistic attitude necessary for sustainable development.
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| 34. |
- Hedlund, Jonas, et al.
(author)
-
A masking technique for high quality MFI membranes
- 2003
-
In: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 222:1-2, s. 163-179
-
Journal article (peer-reviewed)abstract
- A procedure for the preparation of high quality zeolite membranes was developed. This procedure relies on a masking approach that fills all support pores with wax while leaving the top surface free for deposition of the zeolite film, thus, protecting the support from the synthesis mixture. Zeolite films of different thickness were grown on masked and non-masked supports using a seeded growth method. The zeolite-coated supports were calcined in order to remove the wax from the support and the template molecules from the zeolite. The membranes were characterized by SEM, XRD, single gas and multi-component permeation measurements. Support masking reduces the zeolite membrane thickness and the width of the cracks in the zeolite film. Thicker films, especially those prepared without masking, are defective. Masked membranes with a film thickness of 500 nm show no cracks or pinholes. These membranes have a H2 permeance of 220×10−7 mol/(s m2 Pa), an n-butane permeance of 9.8×10−7 mol/(s m2 Pa) and an n-butane/iso-butane separation factor of 9.0 at 25 °C. The separation factor for a mixture of n-hexane/2,2-dimethyl-butane was 227 at 400 °C and the n-hexane permeance was 5.6×10−7 mol/(s m2 Pa). The p-xylene permeance was 2.7×10−7 mol/(s m2 Pa) and the para/ortho separation factor was 17 at 400 °C for a mixture of xylenes.
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| 35. |
- Hedlund, Jonas
(author)
-
Control of the preferred orientation in MFI films synthesized by seeding
- 2000
-
In: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 7:4, s. 455-464
-
Journal article (peer-reviewed)abstract
- Single crystal silicon and quartz wafers were seeded with colloidal TPA-silicate-1 crystals. Hydrothermal treatment of the seeded substrates was used to grow dense MFI films. The preferred orientation of the crystals constituting the films as a function of the amount and size of seeds, film thickness and hydrothermal treatment conditions was investigated. In thin films, most of the crystalline material was found to be oriented with the b-axes close to perpendicular to the substrate surface. In thick films, the a- or c-axes were close to perpendicular to the substrate surface depending on the conditions used for hydrothermal treatment. The seed size and amount was found to affect the rate of change in preferred orientation as a function of film thickness. A film growth mechanism which is able to explain the experimental results is proposed
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| 36. |
- Hedlund, Jonas, et al.
(author)
-
Factors affecting the performance of MFI membranes
- 2004
-
In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 640-646
-
Conference paper (peer-reviewed)abstract
- Thin MFI membranes with varying morphology have been prepared using high flux alumina supports using all advanced synthesis procedure employing support masking and seeding. Evaluation of membrane quality by physical characterization and permeation measurements revealed a number of factors affecting the membrane performance. In the present work, the effects of film thickness, support type, preferred orientation and calcination rate are discussed. Some quality criteria for zeolite membranes are also debated and the porosimetry technique is discussed.
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| 37. |
- Hedlund, Jonas, et al.
(author)
-
High-flux MFI membranes
- 2002
-
In: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 52:3, s. 179-189
-
Journal article (peer-reviewed)abstract
- The synthesis and evaluation of high performance MFI-type membranes is described. These systems exhibit fluxes that are one to two orders of magnitude higher than previous literature reports, with comparable selectivities, when tested for various single component gases and for mixtures of C4, C6 and xylene isomers.These materials are the result of a rational fabrication approach targeting ultra-thin, defect-free MFI films on open supports by using a two-step support masking technique and a monolayer of colloidal nucleation seeds, followed by in situ hydrothermal growth, producing a defect-free film with a thickness of 0.5 μm. Reproducibility of the membrane preparation was excellent.
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| 38. |
- Hedlund, Jonas, et al.
(author)
-
Synthetis of nanosized offretite crystals
- 2001
-
In: Zeolites and mesoporous materials at the dawn of the 21st century. - Amsterdam : Elsevier. - 0444502386 ; , s. 187-
-
Conference paper (peer-reviewed)
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| 39. |
- Hedlund, Jonas, et al.
(author)
-
The synthesis and testing of thin film ZSM-5 catalysts
- 2004
-
In: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 59:13, s. 2647-2657
-
Journal article (peer-reviewed)abstract
- The synthesis and catalytic testing of thin ZSM-5 films on glass and alumina beads is described. The thickness of the ZSM-5 films was controlled to 150, 350, 800 and 2300 nm. The samples were characterised by SEM, gas adsorption and p-xylene isomerisation and 1,3,5-tri-isopropyl benzene cracking test reactions. A reaction–diffusion model adequately described the p-xylene isomerisation data. Estimates of model parameters were obtained by fitting the model to the experimental data. In both cases, the reaction rate constant increased with increasing film thickness. The xylene reaction data showed that secondary reaction products increased as expected with increasing diffusion limitations, but the increase was less than that predicted by the variation of thickness only. The trends in the reaction data could be explained by more defects in the thicker films and/or partial poisoning of the zeolite by mobile support cations in thinner films and/or orientation effects.
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| 40. |
- Jareman, Fredrik, et al.
(author)
-
Effects of aluminum content on the separation properties of MFI membranes
- 2003
-
In: Separation and Purification Technology. - 1383-5866 .- 1873-3794. ; 32:1-3, s. 159-163
-
Journal article (peer-reviewed)abstract
- MFI membranes with almost identical film thickness and defect distribution but different Si/Al ratio were evaluated by separation of butane and hexane isomers. Film thickness was evaluated by SEM and defect distribution by porosimetry. When the temperature was varied, the membranes showed similar separation trends for butanes, but clear differences were observed for hexane separation. The hexane separation factor varied with temperature for the silicalite-1 membrane but was constant for the ZSM-5 membrane. It is believed that this difference may be a result of differences in adsorption properties.
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| 41. |
- Jareman, Fredrik
(author)
-
MFI-molecular sieve membranes : synthesis, characterization and modelling
- 2002
-
Licentiate thesis (other academic/artistic)abstract
- 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.
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| 42. |
- Jareman, Fredrik, et al.
(author)
-
Modelling of single gas permeation in real MFI membranes
- 2004
-
In: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 236:1-2, s. 81-89
-
Journal article (peer-reviewed)abstract
- A novel permeation model for flow through defects and zeolite pores in real MFI membranes, also accounting for substrate effects has been developed. Defect distributions for two types of MFI membranes were determined from porosimetry data using the model, which incorporated the Horvath Kawazoe (micropores) or the Kelvin equation (mesopores). The narrowest (1.08 nm) and also most common defects were found to be separated with a distance of 10–40 μm according to the model. Diffusion coefficients for hydrogen, helium, nitrogen and SF6 in the zeolite were further determined from single gas permeation data using the model using the independently determined defect distribution. The coefficients are consistent with values previously reported in the literature.
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| 43. |
- Jareman, Fredrik
(author)
-
Properties and modeling of MFI membranes
- 2004
-
Doctoral thesis (other academic/artistic)abstract
- The permeation properties of thin (<2µm) film MFI molecular sieve membranes have been studied in the present work and a model has been developed. The synthesis of such materials has been studied to a smaller extent. The films have been grown on graded a-alumina microfiltration filters using a seeding method. Scanning electron microscopy and x-ray diffraction were used in addition to permeation measurements for characterization of the materials. In particular, a simple and unique model describing single component permeation was developed. The model is a combination of simple and basic equations for permeation and adsorption. The important defect distribution of the membrane and the properties of the support are measured in separate experiments. The model is unique since it is accounting for the effect of defects and support on the permeation properties. The model can adequately describe the performance of various MFI membranes. The model indicates mass transfer limitations of the supports that strongly affect, for instance, permeance ratios. It was also found that these ratios are dependent on crystallographic orientation, film thickness and experimental conditions in addition to the amount of defects. Permeance ratios can thus only be used to compare membranes with similar morphology and tested under similar conditions. It was found that defects formed in thicker films. Membranes prepared on masked substrates were of higher quality than membranes prepared on unmasked substrates. MFI membranes with low and varying aluminum content with similar material properties, such as defect distribution and thickness, were evaluated with multi-component hydrocarbon isomers permeation. The silicalite-1 membrane showed a minimum in separation selectivity between two C6 isomers whereas the ZSM5 membrane showed an almost constant selectivity, independent of temperature, but with lower permeances. The effect of the calcination rate on the membrane quality was investigated for silicalite-1 membranes. Based on a number of permeation characterization techniques, the membrane quality was independent of the calcination rate. It was found that the permeation properties of membranes comprised of small crystals in several layers were different from membranes comprised of one layer of larger crystals, although the quality of the membranes was similar. ZSM-5 membranes with high aluminum content showed catalytic conversion of ethanol into diethylether and ethylene under simultaneous separation of the ethanol / water azeotrope
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| 44. |
- Lassinantti-Gualtieri, Magdalena, et al.
(author)
-
Accurate measurement of the thermal expansion of MFI zeolite membranes by in situ HTXRPD
- 2004
-
In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 703-709
-
Conference paper (peer-reviewed)abstract
- Template removal by calcination of MFI type membranes is often accompanied by crack formation. The thermal behavior of MFI type membranes, synthesized with and without masking, was studied to understand the mechanism. Masking prevents growth of zeolite in the interior of the Support during membrane synthesis. Rietveld refinements of powder diffraction data collected in situ at high temperature allowed to accurately determine the change in thermal expansion of the MFI film and the porous alpha-alumina support. During heating, a relatively large contraction of the cell volume during template removal occurred in the zeolite powder and in the film of the membrane prepared with masking. The much smaller decrease in the non-masked sample indicates that this membrane is under stress during heating and as a consequence, cracks are formed. The stress imposed in the membrane prepared without masking may be due to the opposite thermal behavior of the Substrate in combination with strong bonds between the membrane and the support.
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| 45. |
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| 46. |
- Lassinantti, Magdalena, et al.
(author)
-
Faujasite-type films synthesized by seeding
- 2000
-
In: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 38:1, s. 25-34
-
Journal article (peer-reviewed)abstract
- Thin and continuous Faujasite-type films were synthesized on α-alumina wafers using a seeding technique. Surface modified wafers were seeded with colloidal zeolite Y crystals prior to film growth in a synthesis mixture. The effects of hydrothermal treatment on film thickness, morphology and preferred orientation of the crystals constituting the film were investigated using scanning electron microscopy and X-ray diffraction. During hydrothermal treatment a precipitate formed rapidly, leaving an almost clear solution in the upper part of the reactor. Experiments at 60–100°C were performed with the sample placed in the upper part of the synthesis solution. An increase in the film growth rate with increasing temperature was observed. Adsorbed seeds were shown to be oriented with the {1 1 1} pyramid, parallel to the substrate surface. A change in the orientation with film growth was noted, probably due to the attachment of secondary crystals to the growing film surface. In one experimental series, film growth was effected at the bottom of the tube at 100°C. Faster film growth and multilayered films were obtained. A decrease in the film thickness after prolonged hydrothermal treatment was observed in all experimental series. This is probably due to the dissolution of the film and formation of zeolite P in the synthesis solution. The thicknesses of the films synthesized in this work are in the range of 150–2700 nm. The films are promising candidates for use in membrane applications.
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| 47. |
- Lassinantti, Magdalena, et al.
(author)
-
Preparation and evaluation of thin ZSM-5 membranes synthesized in the absence of organic template molecules
- 2001
-
In: Catalysis Today. - 0920-5861 .- 1873-4308. ; 67:1-3, s. 109-119
-
Journal article (peer-reviewed)abstract
- Porous α-alumina supports with a pore size of 100 nm were seeded with colloidal TPA-silicalite-1 crystals with a size of 120 nm. The seeded supports were calcined and treated in a synthesis solution free from organic template molecules to form ZSM-5 films on the supports. According to SEM images, the films were about 2 μm thick and no defects could be found on the as-synthesized membranes. Single gas permeation data was collected and good quality membranes (defined as having a non-detectable permeance of SF6 after drying at 100°C) were further evaluated using binary/ternary gas mixtures. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Water was selectively separated from a helium-diluted vaporized water/ethanol azeotrope with a maximum selectivity of 12.4.
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| 48. |
- Lassinantti, Magdalena
(author)
-
Synthesis, characterization and properties of zeolite films and membranes
- 2001
-
Licentiate thesis (other academic/artistic)abstract
- 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.
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| 49. |
- Li, Qinghua
(author)
-
Colloidal zeolites : from nucleation to zoned films by seeded growth
- 2002
-
Doctoral thesis (other academic/artistic)abstract
- The work presented in this thesis concerns the investigation of nucleation kinetics for colloidal zeolites, especially the determination of the nucleation period during crystallization. It also concerns the use of colloidal TPA-silicalite-1 for the preparation of zoned MFI films. A novel method, a two-stage varying-temperature procedure, involving starting a crystallization at a certain temperature, and then rapidly changing temperature at some point during the crystallization, was developed for the investigation of nucleation kinetics of colloidal zeolites. As the duration of the crystallization at the initial temperature was extended, the ultimate crystal size and crystal concentration varied until they were approximately equal to those obtained for a complete synthesis at the initial temperature. At this point, the nucleation stage during the crystallization was completed. For the synthesis of colloidal TPA-silicalite- 1, the nucleation process occurred over a substantial period of time, extending over the induction period, but was completed before crystal growth was detected, independent of aging time and silica source. For the synthesis of colloidal zeolite Y, the nucleation and crystal growth processes occurred simultaneously and the nucleation period was significantly longer than the induction period. The two-stage varying-temperature synthesis procedure was used to synthesize particularly small colloidal crystals of TPA-silicalite-1 with a high yield for short synthesis time. In addition, midsynthesis addition of sodium after the nucleation of zeolite Y produced pure colloidal zeolite Y with slightly larger crystals (less than 110 nm) and a high yield. Colloidal TPA-silicalite-1 crystals with a size of 60 nm were used as seeds to prepare different types of zoned MFI films on various substrates by a two- step crystallization method. In the first step a type of MFI film was synthesized on the seeded substrate by hydrothermal treatment. In the second step crystallization of another type of MFI film was achieved by further hydrothermal treatment. The structural configuration of the films was characterized by SEM, EDS, XRD and TEM techniques. The channel continuity at the interface between two different layers depended on both the composition and synthesis conditions used and the order of the layers in the film.
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| 50. |
- Li, Qinghua
(author)
-
Crystallization of colloidal TPA-silicalite-1 by a two-stage varying-temperature synthesis
- 2000
-
Licentiate thesis (other academic/artistic)abstract
- 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.
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