Global warming is believed to be caused by the extensive emission of greenhouse gases, such as carbon dioxide, into the atmosphere by combustion of fossil fuels, such as coal, oil and natural gas.To reduce the emission of carbon dioxide and hence avoid global warming, alternative fuels derived from renewable resources are desired. Another reason for the worldwide interest in finding alternative fuels is that the reserves of the fossile fuels are limited and the oil and gas resources will eventually run out.Biogas and natural gas are interesting alternatives with no or at least reduced emission of fossil carbon dioxide to the atmosphere as compared to coal and oil. Both gases mainly consist of methane (60–95%) but may also contain a large fraction of carbon dioxide and water. Removal of carbon dioxide and water from biogas and natural gas is of great importance mainly to lower the transportation costs and to increase the heat value of the gas. The most commonly used separation technique is amine absorption. This is an expensive and complex process and alternative techniques are desired. Zeolites are an interesting alternative due to their great potential both as selective adsorbents and membranes. Due to the unique pore structure zeolites are capable of separating species in a mixture based on the molecule size and adsorption properties. Since water, carbon dioxide and methane all have a molecular size smaller than the pore size of the zeolite ZSM-5 studied in the present work, the molecules can enter and adsorb in the pores and hence the separation is based on adsorption rather than size.In the present work, the single component adsorption of water, carbon dioxide and methane in zeolite ZSM-5 was studied using in-situ Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and the method was successfully further used to study multicomponent adsorption in zeolites.For single gas adsorption experiments, recorded infrared spectra of adsorbed water, carbon dioxide and methane showed characteristic well separated bands for each gas. Adsorbed concentrations of water, carbon dioxide and methane were determined from the recorded infrared spectra. For single gas experiments, the Langmuir model was fitted to the adsorption isotherms and the model matched the experimental data very well. The fitted Langmuir parameters obtained in the present work showed good agreement with values reported in the literature.For multicomponent adsorption experiments, the Ideal Adsorbed Solution Theory (IAST) was used to predict the adsorbed concentrations of water, carbon dioxide and methane using the single component adsorption isotherm parameters as input. The IAST accurately predicted the adsorbed concentrations of both carbon dioxide and methane when adsorbed from binary mixtures. Internary mixtures, also including water, the IAST accurately predicted the adsorbed concentration of methane, however it severely underestimated the adsorbed concentration of carbon dioxide.The latter is probably an effect of a non-ideal behavior of carbon dioxide in the presence of water.The CO2/CH4 adsorption selectivity was determined for various gas compositions and temperatures showing a general increase in the selectivity with decreasing temperature, which is related to the higher heat of adsorption of carbon dioxide. This indicates that the separation of carbon dioxide from biogas and natural gas should be more efficient at lower temperatures. Compared to the literature, the selectivity observed in the present work is relatively high indicating that low silica Na-ZSN-5 may be an effective membrane material.

The common European Energy and Climate policy states that in 2020 the share of biofuels for inland transports should be 10 %. Such a stipulation calls for a commercially sustainable biofuel production. A promising route for Sweden is biofuel production via gasification of black liquor, which could replace about 25 % of the current Swedish consumption of transportation fuel. The main components in the gas produced by black liquor gasification are H2, CO, CO2, N2, CH4 and H2S, which has been reported in previous work. In the present work, trace components in synthesis gas produced via black liquor gasification have been characterized, since trace components could influence the subsequent fuel synthesis. Of the trace components, the most abundant ones were benzene at an average concentration of about 60 ppm, followed by COS, with an average concentration of about 50 ppm. In addition, low amounts (i.e. a few ppm), of C2-hydrocarbons were observed in the gas. No tars were observed in the gas, but tars were observed in some deposits at pipe walls. The concentration of particles in the synthesis gas was very low; < 0.1 mg/Nm3. Submicron particles were comprised of elements such as C, O, Na, Si, S, Cl, K, and Ca, and these particles probably originated from black liquor. Larger particles were comprised mainly of Fe, S and Ni and were probably the result of corrosion of steel in the plant pipe-work. Synthesis gas was also purified by passing beds of active carbon and zinc oxide, mixed with hydrogen gas from cylinders and in the present work, for the first time, catalytically converted to methanol using bench scale equipment during 45 hours in total. The space time yield of methanol produced at a pressure of 25 bar was 0.16-0.19 g methanol/ (g catalyst h) and comparable results were obtained using synthesis gas from gas cylinders with pure gas. The spent catalyst, exposed to gas from the gasifier, was slightly enriched in Ca and Na at the inlet of the reactor and in B and Ni at the outlet of the reactor. Ca, Na and B probably stem from black liquor whereas Ni probably originates from the stainless steel in the equipment. A slight deactivation of the catalyst exposed to gas from the gasifier was identified but it was not possible to reveal the origin of the deactivation. However, the surface area and mesoporosity of the catalyst was reduced. As expected, the produced methanol also contained water and traces of hydrocarbons up to C4, ethanol and dimethyl ether. In summary, this work has shown that the synthesis gas produced by gasification of black liquor is pure and that methanol synthesis from the gas is quite feasible.

Zeolite membranes exhibiting high flux and high selectivity are of major interest for potential future applications. In order to achieve high flux and high selectivity, the zeolite film must be thin (< 1 µm) and free from flow-through defects. The development of thin defect free zeolite membranes requires powerful tools for characterization of flow-through defects in the membranes. Permporometry is one of the most straightforward and powerful techniques for characterization of flow-through pores in ceramic membranes. In permporometry, the flow of a non-condensable gas, e.g., helium, through the membrane is monitored as a function of the activity of a strongly adsorbing compound, e.g., hydrocarbon.In the present work, MFI membranes prepared by a seeding method were characterized by permporometry using helium as the non-condensable gas and n-hexane or benzene as the adsorbing compound. In order to appreciate permporometry data, the membranes were also characterized by scanning electron microscopy (SEM), single gas permeation and separation experiments. The permporometry data were then compared to the SEM morphology of the membranes, permeances of different probe molecules and membrane separation performance.In order to determine the conditions of the permporometry experiment leading to blocking of zeolite pores, a model describing helium transport in the zeolite pores in the presence of n-hexane or benzene was developed. The model is based on percolation theory and knowledge of the adsorption isotherms and adsorption sites for n-hexane and benzene in the zeolite pores. Parameters needed in the model were estimated by Density Functional Theory (DFT) using a Local-Density Approximation (LDA), the most sophisticated theory yet applied to this system. Based on the permporometry data, it was demonstrated that the model could adequately describe helium transport in zeolite pores in the presence of the hydrocarbons.The sensitivity of the permporometry technique towards the defect size has been improved considerably. It was revealed that high quality MFI membranes prepared in the present work contained mainly micropore defects which are most like the defects in the zeolite crystal lattice (intracrystalline defects).The work has shown how permporometry data could be used to estimate the area distribution of the flow-through defects in the membranes. The results on the defect distribution were corroborated by the SEM observations and the separation experiments. The width of cracks, including support cracks, and open grain boundaries observed by SEM was in excellent agreement with the defect width estimated from permporometry data. A straightforward correlation was observed between separation data and permporometry data, i.e. membranes of higher quality according to permporometry analysis exhibited greater separation performance. Also, the permeance of molecules diffusing through defects in the membrane in the separation experiment was found to scale with the permeance of helium through the defects measured in the permporometry experiment. In addition, this work showed that single gas permeance ratios could not detect slight variations in the membrane quality. For membranes with similar however slightly different amount of defects, the ratios are mainly affected by the membrane thickness and support morphology.To summarise, the present work demonstrates that permporometry data adequately reflect membrane quality and that permporometry is a very powerful technique for MFI membrane characterization.

Cryogenic scanning electron microscopy (cryo-SEM), image analysis (IA) of SEM micrographs and X-ray microtomography (XMT) were used to obtain new information about the morphology of iron ore green pellets in this work. Cryo-SEM and freeze fracturing was used to observe entrapped air bubbles and arrangement of particles around the bubbles and in the matrix of wet green pellets. The observations of samples prepared by plunge and unidirectional freezing indicate that unidirectional freezing facilitates the observation of entrapped bubbles with minimum formation of artifacts, whereas plunge freezing enables observation of the degree of water filling at the outer surface of wet pellets with minimum amount of artifacts. It was also observed in the wet pellets that the size of the water domains in the matrix is quite small and the finer grains are mixed with coarser grains resulting in a denser matrix, whereas no fine grains were observed in the vicinity of the air bubbles. Two types of pellets prepared with and without addition of extra flotation reagent prior to balling were studied using IA and XMT. IA of scanning electron micrographs of epoxy impregnated pellets was used to separate bubble porosity from packing porosity and to quantify the former. The individual SEM micrographs acquired by a backscattered electron detector were reconstructed to provide the entire two-dimensional (2D) sections of the pellets. The 2D data obtained by IA were unfolded to three-dimensional (3D) by stereology and relatively good agreement with XMT data was observed. The size and amount of air bubbles could be quantified with both techniques. The addition of extra flotation reagent was found to increase the number of entrapped air bubbles and slightly decrease the median bubble diameter. The additional entrapped air bubbles due to the addition of extra flotation reagent was shown to be responsible for the difference in total porosity observed by mercury porosimetry between the two types of pellets. Mercury intrusion porosimetry (MIP) is shown in this work to produce inappropriate results with regard to the porosity due to bubble entrapment, it only provides values for total porosity and the throat size distribution of the porosity. In summary, this work has shown that cryo-SEM, IA of SEM micrographs and XMT are powerful and very useful methods for characterization of the morphology of iron ore green pellets.

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. / Godkänd; 2004; 20070126 (ysko)

In this study, well defined ZSM-5 films were prepared on monoliths, ceramic foams, alumina beads, glass beads and crushed quartz glass by further refinement of a method originally developed at the division of Chemical Technology, Luleå University of Technology. The supports were seeded with silicalite-1 seeds and hydrothermally treated, either at 75 °C or at 150 °C in a single or several steps. By adding sodium to the solution the aluminum concentration increased in the zeolite, which is beneficial for catalytic activity. Consequently, films with different Si/Al ratios could be prepared. The film thickness could be controlled from 110 nm to 9000 nm. Short hydrothermal treatments and use of multi-step synthesis was utilized to prevent excessive bulk crystallization and ultrasound treatment was beneficial in order to remove sedimented crystals on top of the zeolite films. The choice of support material and its influence on the performance of thin ZSM-5 film catalysts was examined by testing the reactivity of the zeolite- coated materials in two reactions; para-xylene isomerization and triisopropylbenzene cracking. ZSM-5 films with a thickness of 150, 350, 800 and 2300 nm, respectively, were prepared on alumina beads and quartz glass. Based upon the zeolite content, the films on quartz glass were much more active for para-xylene isomerization and for cracking of triisopropylbenzene, which is attributed to poisoning of the films on alumina due to impurities in the support. Model parameters were fitted to experimental results. The simulations indicated that thicker films contained a higher fraction of defects, which may be caused by open grain boundaries and cracks. These defects explain higher xylene diffusivities and higher triisopropylbenzene cracking activity for thicker films. As expected, thicker films possessed higher diffusion resistance than thin films despite the higher fraction of defects. The present work has given substantial and valuable fundamental understanding of the performance of thin molecular sieve film catalysts. These findings will be beneficial for development of materials that may be used in novel industrial applications. / Godkänd; 2003; 20070216 (ysko)

Traditionally the reactor is recognised as the `heart' of a chemical process system and hence the focus on this part of the system is usually quite detailed. Steam reforming, however, due to the `building block' nature of its reaction products is unusual and generally is perceived as a `utility' to other reaction processes and hence the focus is drawn " towards the 'main' reaction processes of the system. Additionally as a `mature' process, steam reforming is often treated as sufficiently defined for the requirements within the overall chemical process. For both primary and secondary steam reformers several models of varying complexity were developed which allowed assessment of issues raised about previous models and model improvements; drawing on the advancements in modelling that have not only allowed the possibility of increasing the scope of simulations but also increased confidence in the simulation results. Despite the complex nature of the steam reforming systems, a surprisingly simplistic model is demonstrated to perform well, however, to improve on existing designs and maximise the capability of current designs it is shown that more complex models are required. After model development the natural course is to optimisation. This is a powerful tool which must be used carefully as significant issues remain around its employment. Despite the remaining concerns, some simple optimisation cases showed the potential of the models developed in this work and although not exhaustive demonstrated the benefits of optimisation.

Traditionally the reactor is recognised as the `heart' of a chemical process system and hence the focus on this part of the system is usually quite detailed. Steam reforming, however, due to the `building block' nature of its reaction products is unusual and generally is perceived as a `utility' to other reaction processes and hence the focus is drawn " towards the 'main' reaction processes of the system. Additionally as a `mature' process, steam reforming is often treated as sufficiently defined for the requirements within the overall chemical process. For both primary and secondary steam reformers several models of varying complexity were developed which allowed assessment of issues raised about previous models and model improvements; drawing on the advancements in modelling that have not only allowed the possibility of increasing the scope of simulations but also increased confidence in the simulation results. Despite the complex nature of the steam reforming systems, a surprisingly simplistic model is demonstrated to perform well, however, to improve on existing designs and maximise the capability of current designs it is shown that more complex models are required. After model development the natural course is to optimisation. This is a powerful tool which must be used carefully as significant issues remain around its employment. Despite the remaining concerns, some simple optimisation cases showed the potential of the models developed in this work and although not exhaustive demonstrated the benefits of optimisation.

Cu-In, Cu-Al and Cu-In-Al metallic precursor layers were deposited using radio-frequency magnetron sputtering and selenised to produce thin films of CuInSe2 (CIS), CuAlSe2 (CAS) and CuIn1-xAlxSe2 (CIAS), respectively. The selenisation stage of this 2-stage process was carried out in a tube furnace (TF) or a rapid thermal processor (RTP) in the presence of elemental Se, either deposited on top of the precursor film or provided from an external source in the chamber, in order to fabricate the chalcopyrite material. The aim was to produce single phase, device quality CIS, CAS and CIAS for use as an absorber layer material in thin film photovoltaic solar cells. Profilometry performed on the as-deposited Cu-In-Al metallic precursors showed an important increase in surface roughness compared to the Cu-In and Cu-Al precursors. This was found to be due to the preferential formation of Cu9(In,Al)4, which stoichiometry led the excess In to form island-shaped In phases at the surface of the bulk, while only Cu2In and CuIn2 formed in Cu-In precursors. Regarding the selenisation, temperatures ranging from 250°C to 550°C were used, and the resulting samples were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GD-OES). Thin films of single phase CIS and CAS were successfully produced with energy band gaps of 0.99 eV and 2.68 eV, respectively. However the incorporation of Al proved to be difficult. The results showed that no incorporation of the Al into the chalcopyrite lattice was achieved in the samples selenised in the RTP, which was believed to be due to the oxidation of the element Al into amorphous Al2O3. In the tube furnace, possibly due to lower levels of oxidation, incorporation occurred more readily but Al and In segregated towards the back and front of the layer, respectively. The causes of the segregation were studied and solutions to avoid it developed, resulting under certain conditions in successful production of CuIn1-xAlxSe2. Samples were tested in a photoelectrochemical cell and showed (apparent) external quantum efficiency values comparable to a CuInSe2 (CIS) sample used as a standard.

The use of solar thermal energy to drive both large and small scale power generation units is one of the prospective solutions to meet the dramatic increase in the global energy demand and tackle the environmental problems caused by fossil fuels. New energy conversion technologies need to be developed or improved in order to enhance their performance in conversion of renewable energy. The Organic Rankine Cycle (ORC) is considered as one of the most promising technologies in the field of small and medium scale combined heat and power (CHP) systems due to its ability to efficiently recover low-grade heat sources such as solar energy. This technology is especially in demand in isolated areas where connection to the grid is not a viable option. The present research provides thermodynamic performance evaluation and economic assessment for a small-scale (10 kW) hybrid solar/biomass ORC power system to operate in the UK climate conditions. This system consists of two circuits, namely organic fluid circuit and solar heating circuit in which thermal energy is provided by an array of solar evacuated tube collectors (ETCs) with heat pipes. A biomass boiler is also integrated to compensate for solar energy intermittence. A dynamic model for the hybrid ORC power system has been developed to simulate and predict the system behaviour over a day-long period for different annual seasons. In the thermodynamic investigation, an overall thermodynamic mathematical model of the proposed power system has been developed. The calculation model of the ORC plant consists of a number of control volumes and in each volume the mass and energy conservation equations are used to describe energy transfer processes. The set of equations were solved numerically using a toolbox called Thermolib which works in the MATLAB/Simulink® environment. The numerical results obtained on the performance of the ORC plant were validated against the theoretical and experimental data available in the open literature. The predicted results were in very good agreement with the data published in the literature. The comparison demonstrated that the developed simulation model of the ORC plant accurately predicts its performance with a maximum deviation of less than 7%. The developed mathematical model then has been used to carry out the parametric analysis to investigate the effect of different operating conditions on the system performance. The economic analysis has been performed with the use of equipment costing technique to estimate the system’s total capital investment cost. This approach is based on the individual costing correlation of each component in the system, considering all the direct and indirect costs of the proposed components. The system cost calculations have been conducted for a range of operating parameters and different working fluids for a fixed value of net power output. At the final stage of the research, a thermo-economic optimization procedure has been developed using Genetic Algorithm (GA) approach for selection of the rational set of design parameters and operating conditions for optimum system performance.