| 1. |
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| 2. |
- Gavrilovic, Ljubisa, et al.
(författare)
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Influence of potassium species on Co based Fischer-Tropsch-catalyst.
- 2016
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Konferensbidrag (refereegranskat)abstract
- 1. IntroductionThe purpose of this work is better understanding of the alkali influence on Co-based F-T catalyst. Since potassium is one of the elements that can be present in syngas from biomass[1], one of the questions is how potassium species affect the Co catalyst. From previous work it has been shown that alkali species act as poisons, thus deactivating catalysts[2]. Most previous work in this group[3][4] and by others[5] has concerned Co catalysts that were exposed to potassium species by incipient wetness impregnation, which is essentially different from the real behaviour during the gasification process where the species will mainly be in the vapor phase. In the present work we study potassium influence on a Co-based catalyst, using aerosol technology as a new method for potassium deposition on the Co surface. 2. Experimental4 different potassium salts were deposited using aerosol deposition on 20%Co/0.5%Re/γAl2O3. The amount of potassium salts deposited were determined using ICP analysis. Potassium salts were chosen from studies of the gases from biomass gasification[6]. These are K2SO4, KCl, KNO3 and K2CO3. KNO3 will be reduced to KOH during biomass gasification, but since in these experiments temperature was not so high and there was no H2/CO, most likely KNO3 will be deposited as such on the Co surface.BET N2 adsorption, H2 chemisorption, temperature programmed reduction (TPR) were used to characterize all the poisoned catalysts.Fischer Tropsch activity and selectivity measurements were performed at the in house build set-up, at 210°C, 20 bar and at H2:CO ratio of 2.1. The GHSV was consistently varied to maintain comparable CO conversion levels between 20-50%. A detailed description of the setup and procedures can be found elsewhere[3]. 3. ResultsThe potassium species were deposited using aerosol technology in the apparatus shown in Fig. 1. Potassium salts are dissolved in deionized water and the solution is placed inside the atomizer, which produces aerosol particles. Nitrogen is used as a carrier gas which forces aerosol particles in the reactor direction. Before entering the reactor, the gas mixture carrying the aerosol is passing the impaction vessel to remove large particles. The catalyst bed is placed in the middle of the reactor, which can be heated up to 800°C. The generated aerosol particles were physically characterized according to their electrical mobility using a scanning mobility particle sizer (SMPS) consisting of a differential mobility analyser (DMA) and a condensation particle counter (CPC)[7]. The three target concentrations of potassium salts, 200 ppm, 800 ppm and 4000 ppm, were monitored by the above-mentioned instruments.Results from characterization by elemental analysis, H2 chemisorption, BET surface area, TPR together with the results from the Fischer Tropsch synthesis i.e. CO conversion, selectivity, and activity will be compared with the same catalyst without any poison and also with previous results obtained from solution impregnation of the same poisons[8][3][9].4. DiscussionThe purpose of the work is to study how this procedure of poisoning Co catalyst with aerosol particles will affect catalyst performances during Fischer Tropsch reaction. Previous similar work on Ni catalyst in the SCR reaction using aerosol technology as a method of deposition, has proven loss in metallic surface area, decreasing of metal dispersion and severe reduction in the catalytic activity [7]. The idea is to develop a technique to transfer potassium species, and potentially other relevant impurities, in vapor phase to the catalyst surface. This new approach can to a great extent simulate behaviour during the real industrial process. The aerosol could better represent in situ poisoning and therefore give a more realistic picture of the effect of potassium. This knowledge will be useful for designing new BTL processes. 5. ConclusionAerosol technology was used as a new method for depositing potassium salts on the Co surface. Poisoned catalysts were tested in Fischer Tropsch synthesis reactor together with elemental analysis. Results are compared to the reference catalyst and with previous work which use IWI as poisoning method. 6. References[1] A. Norheim, D. Lindberg, J. E. Hustad, and R. Backman, Energy and Fuels, (2009)[2] E. S. Wangen, A. Osatiashtiani, and E. A. Blekkan, Top. Catal., (2011)[3] C. M. Balonek, A. H. Lillebø, S. Rane, E. Rytter, L. D. Schmidt, and A. Holmen, Catal. Letters, (2010)[4] E. A. Blekkan, A. Holmen, S. Vada, Acta Chem. Scand., (1993)[5] J. Gaube and H. F. Klein, Appl. Catal. A Gen., (126–132, 2008)[6] H. M. Westberg, M. Byström, and B. Leckner, Energy and Fuels, (18–28, 2003)[7] S. Albertazzi, F. Basile, J. Brandin, J. Einvall, G. Fornasari, C. Hulteberg, M. Sanati, F. Trifirò, and A. Vaccari, Biomass and Bioenergy, (2008)[8] A. H. Lillebø, E. Patanou, J. Yang, E. A. Blekkan, and A. Holmen, in Catalysis Today, (2013)[9] E. Patanou, A. H. Lillebø, J. Yang, D. Chen, A. Holmen, and E. A. Blekkan, Ind. Eng. Chem. Res., (2014)[10] J. Einvall, S. Albertazzi, C. Hulteberg, A. Malik, F. Basile, A. C. Larsson, J. Brandin, and M. Sanati, Energy and Fuels, (2007)
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| 3. |
- Holmén, Anders, 1967, et al.
(författare)
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Assignment of electronic transition moment directions of adenine from linear dichroism measurements
- 1997
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 119:50, s. 12240-12250
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Tidskriftsartikel (refereegranskat)abstract
- The electronic spectra of a series of adenine derivatives have been investigated with respect to the number of electronic transitions, their intensities, and transition moments. The experimental work includes linear dichroism (LD) measurements on samples partially oriented in stretched polymer poly(vinyl alcohol) films, fluorescence anisotropy (FA), and: magnetic circular dichroism (MCD). The UV spectra of both 7-methyladenine (7MA) and 9-methyladenine (9MA) are resolved into contributions from five pi --> pi* transitions (I-V). Their polarizations relative to the C-4-C-5 axis are for 7MA +45 degrees (I, 36 600 cm(-1)), -16 degrees (II, 39 500 cm(-1)), -28 degrees (III, 42 600 cm(-1)), +76 degrees (IV 45 800 cm(-1)) and similar to-29 degrees (V, similar to 47 700 cm(-1)); and for 9MA +66 degrees (I, 36 700 cm(-1)), +19 degrees (II, 38 820 cm(-1)), -15 degrees (III, 43 400 cm(-1)), -21 degrees (IV, 46 800 cm(-1)), and similar to-64 degrees (V, similar to 48 320 cm(-1)). The experimental results are correlated with results from semiempirical INDO/S and ab initio CIS/6-31G(d) and CASPT2 molecular orbital calculations. The transition moments are found to be conserved when the adenine amino group has been substituted with either one or two methyl groups. In addition, LD and MCD spectra for 6-(dimethylamino)-9-ethylpurine, which is soluble in nonpolar solvents, have been measured in stretched polyethylene film and cyclohexane, respectively. The results indicate that the electronic transition moments of the 9-substituted adenine chromophore are essentially the same in a polar and a nonpolar solvent. On the basis of the. results,for 7MA and 9MA, the reduced LD and absorption spectra of adenine are analyzed in terms of contributions from the 7-H and 9-H tautomers of adenine. By comparison with theoretical and experimental results for purine and 2-aminopurine regarding the position of the lowest n --> pi* transition, we are able to confidently position the lowest n --> pi* transition in 9MA very close to the lowest pi --> pi* transition. The proximity of the first (1)n pi* and (1) pi pi* states in adenine might be related to the efficient nonradiative deactivation of the lowest excited (1) pi pi* state.
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| 4. |
- Holmén, Anders, 1967, et al.
(författare)
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Ir Transition Moments of 1,3-Dimethyluracil - Linear Dichroism Measurements and Ab-Initio Calculations
- 1994
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Ingår i: Journal of Physical Chemistry. - 0022-3654. ; 98:19, s. 4998-5009
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Tidskriftsartikel (refereegranskat)abstract
- The vibrational transition moment directions of 1,3-dimethyluracil (DMU), 1,3-dimethyluracil-5-d (DMU-5-d), and 1,3-dimethyluracil-6-d (DMU-6-d) have been determined from measurements of polarized IR spectra on samples partially aligned in stretched poly(vinyl alcohol) and by ab initio calculations at the HF/6-31G* level of approximation. The agreement between experiments and theory is good. IR spectra of DMU, DMU-5-d, and DMU-6-d in KBr and in D2O form, together with the calculated spectra and the IR polarizations, the basis for some reassignments. Special attention is paid to the double-bond region, where the high-frequency carbonyl stretching mode is assigned to an in-phase vibration of the C4O and the C2O. This vibration is polarized in a direction almost bisecting the angle between the two carbonyl bonds, in agreement with an in-phase assignment. The low-frequency mode is the out-of-phase vibration of the two carbonyl groups, and it is consequently polarized perpendicular to the high-frequency mode. In order to determine the orientation axis of DMU in the polymer matrix, the UV linear dichroism (LD) spectrum was measured and the polarizations of the electronic transitions were estimated from a semiempirical self-consistent reaction field (SCRF) calculation including solvent effects. The combined information from IR LD and UV LD shows that the molecular orientation axis in the stretched film experiment is parallel to the first pi --> pi* transition in DMU.
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| 5. |
- Locke, Adam E, et al.
(författare)
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Genetic studies of body mass index yield new insights for obesity biology.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 197-401
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (P < 5 × 10(-8)), 56 of which are novel. Five loci demonstrate clear evidence of several independent association signals, and many loci have significant effects on other metabolic phenotypes. The 97 loci account for ∼2.7% of BMI variation, and genome-wide estimates suggest that common variation accounts for >20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
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| 6. |
- Rydén, Magnus, 1975, et al.
(författare)
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Novel oxygen-carrier materials for chemical-looping combustion and chemical-looping reforming; LaxSr1─xFeyCo1─yO3─δ perovskites and mixed-metal oxides of NiO, Fe2O3 and Mn3O4
- 2008
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Ingår i: International Journal of Greenhouse Gas Control. - 1750-5836. ; 2:1, s. 21-36
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Tidskriftsartikel (refereegranskat)abstract
- Solid oxygen-carrier materials for chemical-looping applications have been examined by reduction with CH4 and oxidation with air in a fixed-bed quartz reactor at 900ºC. Four perovskite materials, three metal-oxide materials and four metal-oxide mixtures have been studied. It was found that LaxSr1─xFeO3─δ perovskites provided very high selectivity towards CO/H2 and should be well suited for chemical-looping reforming. Substituting La for Sr was found to increase the oxygen capacity of these materials, but reduced the selectivity towards CO/H2 and the reactivity with CH4. La0.5Sr0.5Fe0.5Co0.5O3─δ was found to be feasible for chemical-looping combustion applications. NiO/MgAl2O4 propagated formation of solid carbon, likely due to the catalytic properties of metallic Ni. Fe2O3/MgAl2O4 had properties that made it interesting both for chemical-looping combustion and chemical-looping reforming. Adding 1% NiO particles to a bed of Fe2O3-particles increased both reactivity with CH4 and selectivity towards CO/H2 for reforming applications. Mn3O4/MgZrO2 was found to be suitable for chemical-looping combustion applications, but it could not be verified that adding NiO produced any positive effects.
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| 7. |
- Shungin, Dmitry, et al.
(författare)
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New genetic loci link adipose and insulin biology to body fat distribution.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 187-378
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Tidskriftsartikel (refereegranskat)abstract
- Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms.
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| 8. |
- Almquist-Tangen, Gerd, et al.
(författare)
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Influence of neighbourhood purchasing power on breastfeeding at four months of age : a Swedish population-based cohort study
- 2013
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Ingår i: BMC Public Health. - London : BioMed Central. - 1471-2458. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Parental socioeconomic status (SES) is an important determinant in child health, influencing beneficial factors such as breastfeeding. A better understanding of the influence of neighbourhood-level SES measures, relating to spatial determinants, might lead to targeted actions to promote breastfeeding during infancy.METHODS: A cross-sectional study analysis the association between breastfeeding at four months of age and neighbourhood purchasing power, taking account of individual-level variables including maternal age, smoking and parental level of education. Data were obtained from a prospective population- based cohort study recruited from birth in 2007-2008 in the Halland region, southwestern Sweden. Questionnaire data on the individual-level variables and the outcome variable of breastfeeding at four months (yes/no) were used (n=2,407). Each mother was geo-coded with respect to her residential parish (there are 61 parishes in the region) and then stratified by parish-level household purchasing power. It emerged that four neighbourhood characteristics were reasonable to use, viz. <10%, 10-19%, 20-29% and ≥ 30% of the resident families with low purchasing power.RESULTS: The proportion of mothers not breastfeeding at four months of age showed a highly significant trend across the neighbourhood strata (p=0.00004): from 16.3% (< 10% with low purchasing power) to 29.4% (≥ 30% with low purchasing power), yielding an OR of 2.24 (95% confidence interval: 1.45-3.16). After adjusting for the individual-level variables, the corresponding OR=1.63 (1.07-2.56) was significant and the trend across the strata was still evident (p=0.05). A multi-level analysis estimated that, in the neighbourhoods with ≥ 30% of the families with low purchasing power, 20% more mothers than expected, taking account of the individual-level factors, reported no breastfeeding at four months of age (≥ 95% posterior probability of an elevated observed-to-expected ratio).CONCLUSION: The neighbourhood purchasing power provided a spatial determinant of low numbers of mothers breastfeeding at four months of age, which could be relevant to consider for targeted actions. The elevated observed-to-expected ratio in the neighbourhoods with the lowest purchasing power points toward a possible contextual influence. © 2013 Almquist-Tangen et al.; licensee BioMed Central Ltd.
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| 9. |
- Andersson, Robert
(författare)
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Catalytic conversion of syngas to higher alcohols over MoS2-based catalysts
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis concerns catalytic conversion of syngas (H2+ CO) into a blend of methanol and higher alcohols, an attractive way of producing fuels and chemicals. This route has the potential to reduce the oil dependence in the transport sector and, with the use of biomass for the syngas generation, produce CO2-neutral fuels.Alkali promoted MoS2-based catalysts show a high selectivity to higher alcohols, while at the same time being coke resistant, sulfur tolerant and displaying high water-gas shift activity. This makes this type of catalyst especially suitable for being used with syngas derived from biomass or coal which typically has a low H2/CO-ratio.This thesis discusses various important aspects of higher alcohol synthesis using MoS2-based catalysts and is a summary of four scientific papers. The first part of the thesis gives an introduction to how syngas can be produced and converted into different fuels and chemicals. It is followed by an overview of higher alcohol synthesis and a description of MoS2-based catalysts. The topic alcohol for use in internal combustion engines ends the first part of the thesis.In the second part, the experimental part, the preparation of the MoS2-based catalysts and the characterization of them are handled. After describing the high-pressure alcohol reactor setup, the development of an on-line gas chromatographic system for higher alcohol synthesis with MoS2 catalysts is covered (Paper I). This method makes activity and selectivity studies of higher alcohol synthesis catalysts more accurate and detailed but also faster and easier. Virtually all products are very well separated and the established carbon material balance over the reactor closed well under all tested conditions. The method of trace level sulfur analysis is additionally described.Then the effect of operating conditions, space velocity and temperature on product distribution is highlighted (Paper II). It is shown that product selectivity is closely correlated with the CO conversion level and why it is difficult to combine both a high single pass conversion and high alcohol selectivity over this catalyst type. Correlations between formed products and formation pathways are additionally described and discussed. The CO2 pressure in the reactor increases as the CO conversion increases, however, CO2 influence on formation rates and product distribution is to a great extent unclear. By using a CO2-containing syngas feed the effect of CO2 was studied (Paper III).An often emphasized asset of MoS2-based catalysts is their sulfur tolerance. However, the use of sulfur-containing feed and/or catalyst potentially can lead to incorporation of unwanted organic sulfur compounds in the product. The last topic in this thesis covers the sulfur compounds produced and how their quantity is changed when the feed syngas contains H2S (Paper IV). The effect on catalyst activity and selectivity in the presence of H2S in the feed is also covered.
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| 10. |
- Bakhtiary-Davijany, Hamidreza, et al.
(författare)
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Analysis of External and Internal Mass Transfer at Low Reynolds Numbers in a Multiple-Slit Packed Bed Microstructured Reactor for Synthesis of Methanol from Syngas
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 51:42, s. 13574-13579
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of mass transfer limitations in an integrated micro packed bed reactor-heat exchanger (IMPBRHE) for methanol synthesis was experimentally investigated. Experiments were performed with three different particle size distributions (50-200 mu m) of a Cu-based catalyst at 80 bar and 215-270 degrees C. Negligible effects of pore diffusion limitations on the performance of the reactor under methanol synthesis conditions for catalyst particle diameters up to 125 mu m were found. Due to a very low Reynolds numbers (similar to 1) and dominance of molecular diffusion, variation of the total pressure was applied as a suitable technique to alter the diffusivities of reactants in the gas mixture by dilution, while keeping the reactant flow and partial pressure constant. No significant change in the CO conversion was observed in the temperature range 235-255 degrees C, pressure range 50-90 bar, and for reactant contact times of 105-308 ms.g/mL. The same procedure was applied to a laboratory. fixed bed reactor with similar results. Possible heat transfer effects associated with the dilution were shown to be negligible. We therefore conclude that both reactor systems operate in the absence of external mass transfer limitations.
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