| 1. |
- de Reijer, Guido J.L. 1997
(författare)
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Catalyst Design for the Valorisation of Biomass-derived Furans into Aromatics
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Anno 2023, mankind must strive towards a more sustainable chemical industry; one that does not solely rely on fossil fuels but also utilises renewable feedstocks such as biomass. Biomass can be catalytically converted into commodity chemicals such as aromatics, through intermediates like furans. Aromatics serve as building blocks for everyday materials. In this work, the conversion of one type of furans, 2,5-dimethylfuran, was studied at elevated temperatures in a flow reactor by using a selection of microporous, acidic catalysts. The effluent gas stream was analysed with Fourier-transform infrared spectroscopy and mass spectrometry. Zeolitic catalysts with the MFI-framework were synthesised bottom-up through hydrothermal synthesis, with aluminium or gallium substituted in their framework. Structural analysis was performed comprising X-ray fluorescence, X-ray diffraction, physisorption, thermogravimetric analysis, scanning electron microscopy, and acidity analysis by NH3-TPD. Both aluminium and gallium-substituted zeolites were active for converting 2,5-dimethylfuran into aromatics, of which Ga-MFI displayed superior benzene production and catalyst lifetime. Catalyst deactivation was caused by the loss of strong and extra-framework acid sites due to the coking. After deactivation towards aromatics, the intermediate products formed on weak acid sites such as 2,4-dimethylfuran, were detected as the main products. It was found that an increase in gallium content increases catalytic activity until a limit of Si/Ga=13 was reached, at which the synthesis of the catalyst also yielded an inactive, amorphous phase. Increasing the crystallisation duration enabled approaching this limit and forming phase-pure MFI zeolite with a Si/Ga ratio of Si/Ga=17. Mesopores were introduced to the catalyst to improve the mass transfer of reactants and products. Even though the total production of aromatics and the catalyst lifetime remained unchanged, its number of acid sites was halved implying that each acid site was able to produce twice as many aromatics.
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| 2. |
- Han, Joonsoo, 1990
(författare)
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NH3-SCR chemistry for NOx abatement: Influence of zeolite support on N2O formation & phosphorus species addition.
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different lattice arrangements of Si, Al, and O atoms result in a variety of pore dimensions and zeolite channel network systems, giving rise to different physicochemical environments inside the catalyst cage. The objective of the thesis work was to understand the influence of zeolite topology on NH3-assisted SCR chemistry over CHA, MFI, and BEA frameworks, on the formation of N2O and the addition of phosphorus species to attain fundamental insight into NOx emission control. A variety of characterization techniques and mechanistic experimental protocols were used to examine Cu2+ ions coordinated with 1Al and 2Al in frameworks, denoted as Z2Cu and ZCuOH, respectively. Catalytic activity tests were performed to investigate the influence of ammonium nitrate (AN)-forming N2O and phosphorus species on DeNOx performance over the Cu-impregnated CHA, MFI, and BEA. In Paper I, ammonium nitrate (AN) formation and decomposition were thoroughly investigated to see the effect of zeolite topology, copper species, and water vapor on the N2O formation in NH3 SCR of NOx at low temperatures. Three different Cu/zeolites (CHA, MFI, and BEA) were used, and these were compared with H/zeolites as the reference. H2 temperature programmed reduction and in-situ IR spectroscopy suggest that the CHA framework structure is more favorable than MFI and BEA to form AN inside the catalyst cage. AN formation was enhanced in the presence of Cu ions over the Cu/zeolites. Catalyst activity tests demonstrated that Cu/CHA has a potential for uncontrolled N2O emission in transient conditions despite it shows lower N2O formation over standard and fast SCR reaction due to a highly stabilized AN inside the catalyst cage at low temperatures. This indicates pros and cons of AN stability over CHA in NH3-SCR systems. The critical effect of water vapor on AN formation and decomposition was found. The water vapor causes the cleavage of Cu dimers into Cu2+-OH groups, which are responsible for NO oxidation forming NO+ and surface nitrates. Thus, it results in the formation of fewer surface nitrates, leading to less AN and less N2O formation in wet conditions. In Paper II, phosphorus poisoning of different zeolite topologies was investigated. Fresh Cu/zeolites (CHA, MFI, and BEA) were used as the reference, and these were compared with P-poisoned Cu/zeolites. X-ray powder diffraction (XRD) revealed that the MFI framework was vulnerable to phosphorus species attack, resulting in the deformation of the framework structure. A variety of phosphorus species, such as PO-3, PO3- 4, and P2O5 populations, were observed over Cu/zeolites with Xray photoelectron spectroscopy. Transient response methodologies suggest that ZCuOH sites were significantly poisoned by PO-3 and PO3- 4 over Cu/CHA. Accordingly, a promoted or deteriorated redox feature of Cu ions (i.e., Z2Cu and ZCuOH) was suggested. A significant drop in catalytic activity was demonstrated over Cu/MFI in catalytic activity tests. It is suggested that MFI framework deformation, such as pore-blockage, local expansion, and cracking, impedes the mobility of Cu+(NH3)2 complexes at low temperatures under standard SCR conditions. Consequently, we hypothesize that MFI framework degradation hinders the formation of NH3-solvated Cu dimer complexes, which are responsible for O2 activation.
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| 3. |
- Matyskin, Artem, 1989
(författare)
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On the solubility of radium sulfate and carbonate
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Radium is one of the most toxic elements and its concentration in different human activities and migration from man-made wastes provokes a strong interest in environmental science. To be able to model the migration process, reliable experimental thermodynamic data of radium compounds are needed.In this work details of the safe radium source disassembly which were previously used in brachytherapy are described and different methods for conversion of RaSO4 into aqueous solution are reviewed. The method of choice included three cycles of RaSO4 heating in 1.5 M Na2CO3 up to 85 ºC, cooling and subsequent removal of supernatant. X-ray diffraction studies showed that the method allows the synthesis of amorphous RaCO3, which can be dissolved in mineral acid. Gamma spectrometric measurements showed that most of the initial RaSO4 was converted into solution and that 7 ± 1 % of the initial 210Pb was co-precipitated with RaCO3. Synthesized RaCO3 was dissolved in HCl to prepare a radium stock solution. The radium stock solution was used to determine the solubility of pure RaSO4 and RaCO3 from oversaturation using Na2SO4 and Na2CO3 as a source of sulfate and carbonate ions. The solubility was determined at 25.1 ºC as a function of ionic strength using NaCl media. The concentration of radium was measured by gamma spectrometry after separation of the aqueous phase from the solid phase using ultracentrifugation. The extended specific ion interaction theory was used to extrapolate solubility product constants to zero ionic strength (log10 Ksp° = -10.16 ± 0.05 for RaSO4 and log10 Ksp° = -7.73 ± 0.56 for RaCO3) and to calculate ion interaction coefficients.A comparison of the shapes of the radium solubility curves for both anions with the shapes of corresponding barium solubility curves demonstrates the similarity of the behaviour of radium and barium salts in saline solutions. It can be supposed that due to the similarity of the radium and barium effective ionic radii, and the same charge, these ions undergo similar specific ion interactions in NaCl media.
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| 4. |
- Olsson, Susanna, 1977-
(författare)
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Environmental assessment of municipal solid waste incinerator bottom ash in road constructions
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There are several incentives for using bottom ash from municipal solid waste incineration (MSWI bottom ash) as a construction material, such as for road construction. These incentives include decreased disposal of material on landfills and a reduced amount of raw material extracted for road building purposes. However, one of the main obstacles to utilising the material is uncertainties regarding its environmental properties. The overall objective of this thesis is to describe the potential environmental impacts of utilising MSWI bottom ash in constructions and to improve the tools for environmental assessments. An environmental systems analysis (ESA) approach based on a life cycle perspective was outlined and used in a case study, with the aim of describing the differences in resource use and emissions that can be expected if crushed rock in the sub-base of a road in the Stockholm region in Sweden were to be substituted by MSWI bottom ash. The whole life cycle of the road was taken into account and the alternative disposal of the bottom ash was included. It was found that the studied alternatives would cause different types of potential environmental impact; whereas the conventional alternative with only crushed rock in the road’s sub-base would lead to larger use of energy and natural resources, the alternative with MSWI bottom ash in the sub-base would lead to larger contaminant leaching. It was concluded that a life cycle approach is needed in order to include both resource use and emissions in the comparison between the two alternative scenarios. The leaching of metals turned out to be the most important environmental aspect for the comparison and in particular the difference in copper (Cu) leaching was shown to be large. However, a large amount of Cu may not pose an environmental threat if the Cu is strongly bound to dissolved organic carbon (DOC). In order to improve the basis for toxicity estimates and environmental risk assessments, and thereby provide better input values for ESAs, the speciation of Cu to DOC in MSWI bottom ash leachate was studied. It was found that Cu to a large extent was bound to DOC, which is consistent with previous research. The results also suggest that the hydrophilic fraction of the MSWI bottom ash DOC is important for Cu complexation and that the pH-dependence for Cu complexation to MSWI bottom ash DOC is smaller than for natural DOC. This implies that models calibrated for natural DOC may give inconsistent simulations of Cu-DOC complexation in MSWI bottom ash leachate.
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| 5. |
- García, Indiana, 1966-
(författare)
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Removal of natural organic matter by enhanced coagulation in Nicaragua
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The existence of trihalomethanes (THMs) in a drinking water plant of Nicaragua has been investigated in order to see whether the concentration exceeded the maximum contaminant level recommended by the environmental protection agency of the United States (USEPA) and the Nicaragua guidelines. The influence of pH, temperature, chlorine dose and contact time on the formation of THMs were studied. The contents of organic matter measured by surrogate parameters such as total organic carbon, dissolved organic carbon, ultraviolet absorbance and specific ultraviolet absorbance were also determined in order to show which type of organic matter is most reactive with chlorine to form THMs. Models developed by other researchers to predict the formation of trihalomethanes were tested to see whether they can be used to estimate the trihalomethane concentration. In addition, empirical models were development to predict the THM concentration of the drinking water plant analysed. The raw water was treated by conventional and enhanced coagulation and these processes were compared with regard to the removal of natural organic matter (NOM). The significance of the results was assessed using statistic procedures. The average concentration of THMs found at the facility is below the USEPA and Nicaragua guideline values. Nevertheless the maximum contaminant level set by USEPA is sometimes exceeded in the rainy season when the raw water is rich in humic substances. Comparison between the water treated by conventional and enhanced coagulation shows that enhanced coagulation considerably diminished the trihalomethane formation and the value after enhanced coagulation never exceeded the guidelines. This is because enhanced coagulation considerably decreases the organic matter due to the high coagulant dose applied. The study of the trihalomethane formation when varying pH, time, temperature and chlorine dose using water treated by conventional and enhanced coagulation showed that higher doses of chlorine, higher pH, higher temperature and a longer time increases the formation of THMs. However, combinations of two and three factors are the opposite. The predicted THM formation equations cannot be used for the water at this facility, since the results shown that the measured THM differs significantly from the THM concentration predicted. Two empirical models were developed from the data for enhanced coagulation, using linear and non-linear regression. These models were tested using the database obtained with conventional coagulation. The non-linear model was shown to be able to predict the formation of THMs in the Boaco drinking water plant.
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| 6. |
- Malnes, Daniel
(författare)
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Contaminants of Emerging Concern in Swedish Freshwater Environments: Sources, Occurrence, and Impacts
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Contaminants of emerging concern (CECs) is one of several reasons for the deterioration of surface water quality globally, even though the CECs occur in trace concentrations. This thesis produced new CEC data through a oneyear field study for substances which occur in Sweden’s three largest lakes and their associated rivers. The purpose was to investigate mass flows and seasonal variations of CECs, as well as estimate the potential ecotoxicological hazard posed by the CECs’ occurrence. It was found that numerous CECs occurred in all examined rivers, and that a continuous influx of CECs with suspected hazardous properties into the lakes occurred. Total mass loads of the investigated CECs were estimated from 0.51 to 5.6 kg/day in the influx to the lakes, and from 0.12 to 4.3 kg/day in the outflux from the lakes. Seasonal variations were observed in the aquatic environment for both individual and groups of CECs. This could be due to variations in consumption and environmental conditions. Some of the seasonal variations were being reported for the first time in the academic literature. Many of the CECs were suspected to have the combination of the hazardous properties of persistency, mobility, and toxicity (PMT). Of the 71 CECs detected far from any suspected input into the lakes, 20 had previously been suspected of having PMT properties. Within the remaining 51 CECs, multiple others also had suspected PMT properties. The thesis suggests that CECs with suspected PMT properties should be analysed closer with respect to these properties.
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| 7. |
- Rydh Stenström, Jenny
(författare)
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Mixture toxicity of pesticides and biological effects in agricultural streams : field and laboratory studies
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to examine pesticide mixture toxicity and its effects on aquatic biota in agricultural streams. This was accomplished by (1) calculating the ΣTUs for algae and Daphnia magna and a pesticide toxicity index (PTI) based on water quality standards (WQS) for long-term monitoring data (2002-2010), (2) by performing algal inhibition tests with Pseudokirchneriella subcapitata, using both collected in situ water samples and reconstituted water spiked with field-observed pesticide mixtures, and (3) by studying seasonal changes in macroinvertebrate and diatom communities during 2008 in four agricultural streams and determine a set of community-based metrics such as species richness, diversity, ASPT, SPEAR and IPS. Partial Least Squares (PLS) regression was used to analyse community changes. Long-term data showed that collected stream water samples had peaks of estimated pesticide toxicity, mainly due to herbicides though insecticides and fungicides also contributed. ∑TUalgae, based on weekly average concentrations, exceeded 0.1 on 28 out of 902 occasions, and 8 of these were higher than 0.2. Only one or a few pesticides contributed to a major part of estimated mixture toxicity in the streams. The algal growth inhibition studies in spiked water showed negative effects at pesticide concentrations corresponding to those found in stream water samples, indicating that pesticide effects on algae occur under in situ conditions. The field study also showed effects of pesticides, suggesting diatom diversity as a sensitive indicator of pesticide effects. Macroinvertebrate community changes were primarily explained by physiochemical conditions, though some non-insect invertebrates decreased (Asellus aquaticus) or increased (Oligochaeta) with pesticide exposure. Somewhat surprisingly, the SPEARpesticides index, specifically developed to detect pesticide effects of macro-invertebrate communities in streams, was not related to pesticide toxicity. The SPEAR index may need to be modified to better fit to Swedish conditions. A combination of chemical and biological monitoring is needed to increase our understanding of the relationship between pesticide stress and the biological diversity of agricultural streams. Specific endpoints and analysis methods are also needed to separate effects of pesticides from effects of other stressors.
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| 8. |
- Filipovic, Marko, 1985-
(författare)
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Mass balance of perfluoroalkyl acids in the Baltic Sea
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Perfluoroalkyl acids (PFAAs) are man-made chemicals. Their unique properties make them beneficial for a wide range of industrial and consumer applications, such as constituents in fire fighting foams, hydraulic oils and food packaging materials.PFAAs have shown to be highly persistent in the environment, and the toxicological potential of long chain PFAA homologues is of a concern. International regulation and voluntary actions by the industry have been implemented and led to reduced primary emissions of PFAAs to the environment. However, the concentrations of some PFAAs in e.g. birds from the Baltic Sea are still very high and of ecotoxicological concern. Measures to reduce the PFAA contamination require an understanding of the sources and how the PFAAs are being transported in the environment.In this licentiate thesis a mass balance was assembled for perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA) and perfluorooctane sulfonic acid (PFOS) in the Baltic Sea. A one-box model was used including the input pathways river inflow, atmospheric deposition, wastewater discharges and inflow from the North Sea via the Danish Straits, while the loss processes considered were sediment burial, transformation of the chemicals and outflow to the North Sea via the Danish Straits. Additionally, the inventories of the four target PFAAs in the Baltic Sea were estimated. Both chemical fluxes and inventories were estimated using recently published monitoring data (2005-2010).In order to obtain a detailed perspective on the current knowledge regarding PFAAs in the Baltic Sea, challenges and uncertainties in data selection were discussed for the most dominant input pathways. This included WWTP emissions and calculation of emission factors (EFs), atmospheric deposition and riverine inflow.River inflow and atmospheric deposition were the dominant inputs, while wastewater treatment plant (WWTP) effluents made a minor contribution. The input to the Baltic Sea exceeded the output for all 4 PFAAs, suggesting that inputs were higher during 2005-2010 than during the previous 20 years despite efforts to reduce emissions of PFAAs. Comparing the difference between PFAA input and output with the PFAA inventory, the doubling time for the concentration in the Baltic Sea was estimated to be 8-94 yr for PFHxA, 12-16 yr for PFOA, 3-5 yr for PFDA and 4 yr for PFOS. The surplus of the input can be an effect of retention and delayed release of PFAAs from atmospheric deposition in the soils and groundwater of the watershed.The licentiate thesis contributes to a holistic understanding of the major input and output pathways and inventories of PFAAs in the Baltic Sea. Furthermore, it points out current knowledge gaps in our understanding of sources and fate of PFAAs in the aquatic environment.
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| 9. |
- Newton, Seth
(författare)
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Legacy persistent organic pollutants and chemicals of emerging concern in Sweden : from indoor environments to remote areas
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bulk atmospheric deposition samples were taken every two months for a year in 2009-2010 at two sites in northern Sweden and analyzed for a suite of legacy and emerging persistent organic chemicals including legacy organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and novel flame retardants (NFRs). To further investigate the urban occurrence and contribution to remote contamination of flame retardants, indoor air, ventilation system air, and dust were sampled in several microenvironments in Stockholm during the winter of 2012 for analysis of PBDEs, isomer-specific hexabromocyclododecane (HBCDD), and NFRs. Outdoor air and soil samples were also sampled around the same time period for analysis of the same compounds. Five emerging pollutants were detected in atmospheric deposition: the current-use pesticides trifluralin and chlorothalonil; and the NFRs 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), 1,2-bis(tribromophenoxy)ethane (BTBPE), and Dechlorane Plus (DP). A decrease in the fraction of the anti isomer of DP was observed at the more remote site, indicating isomer-selective degradation or isomerization during long range atmospheric transport. The more remote site also received more total deposition of organic pollutants despite its receiving less precipitation. Although PBDEs and emerging organic pollutants were detected, the bulk of the deposition consisted of PCBs and hexachlorocyclohexanes (HCHs) at both sites. Several NFRs were identified in indoor and ventilation air samples including TBECH, pentabromotoluene (PBT), hexabromobenzene (HBB), 1,2-bis(pentabromodiphenyl)ethane (DBDPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EHTBB), and bis(2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate (TBPH). There was no significant difference between concentrations of contaminants in ventilation system air and indoor air indicating that the flame retardants included in this study reach the outdoor environment via ventilation systems. Dust and outdoor air samples have only been analyzed for HBCDDs so far. HBCDD concentrations in apartments, offices, and schools were lower than reported concentrations for other countries in similar microenvironments. However, an enrichment of α-HBCDD compared to γ-HBCDD was observed in dust taken from near treated products in stores when compared to dust taken directly from those products. Very low concentrations of HBCDDs were detected in outdoor air.
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| 10. |
- Åberg, Annika, 1975-
(författare)
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Fate and exposure assessment of PCDD/Fs at contaminated sites
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzo-furans (PCDFs) belong to the most toxic compounds known to science and they are defined as Persistent Organic Pollutants (POPs) under the Stock-holm Convention. The general human exposure to PCDD/Fs is primarily through dietary intake. The importance of contaminated sites as secondary PCDD/F sources (i.e. sources that once received its contamination from a primary source) are getting increased attention. To be able to assess the risks for human exposure at PCDD/F contaminated sites, the environmen-tal distribution of PCDD/Fs and the potential mobilization between dif-ferent environmental media (e.g. food chain transfer) must be known. The primary aim of the work presented in this thesis was to investigate human exposure pathways associated with PCDD/F contaminated sites by combining field measurements and modeling. Site specific field measurements were made at a PCDD/F contaminated site in Sweden and multimedia modeling scenarios were evaluated against site specific data and national reference data. The results show that the congener distributions in exposure media affected by contaminated soil may differ significantly from the distribu-tions found in media from reference locations. Higher chlorinated PCDD/Fs may be transferred into food chains where they contribute to a large fraction of the toxic equivalent concentration (TEQ). Ingestion of locally produced animal food may be an important exposure pathway al-ready at low or moderate PCDD/F soil concentrations. However, the con-gener composition of the source is critical for the exposure. The signifi-cance of the individual exposure routes varies depending on e.g. the spatial distribution and magnitude of the soil contamination, the pro-perties of the exposure media and the human behavior. Multimedia mo-deling can be used in risk assessments as long as model algorithms and model parameters are representative for the superhydrophobic properties of PCDD/Fs. However, selection of physical-chemical PCDD/F properties is a challenge due to large variation in reported values. For some proper-ties, data is scattered or completely lacking
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