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- Arora, Prakhar, 1987
(author)
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Deactivation of Catalysts and Reaction Kinetics for Upgrading of Renewable Oils
- 2019
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Doctoral thesis (other academic/artistic)abstract
- The transport sector is one of the main contributors of greenhouse gas emissions in the world. Advanced biofuels from renewable oils can play a decisive role in reducing carbon emissions from the transport sector. Advanced biofuels from waste streams like tall oil, used cooking oil etc. can lower the CO2 emissions in a range of up to 90% making our future and society more sustainable. Catalytic hydrodeoxygenation (HDO) is a process in which oxygen is selectively removed from renewable oils to produce advanced biofuels. These biofuels are drop-in hydrocarbons which can substitute fossil-based fuels without infrastructure or vehicle changes. This thesis focuses on aspects of catalyst deactivation and reaction kinetics during the production of such biofuels via HDO reactions. Renewable oils can be sourced from varied streams like tall oil (paper industry residue), animal fats, used cooking oil etc. due to which their composition and innate contaminants can vary significantly. Phosphorus, alkali metals like potassium or sodium, iron, silicon, chlorides etc. are some of the common poisons present in renewable feedstocks which can cause catalyst deactivation during the upgrading process. In the first section of this thesis, the influence of iron (Fe), phosphorus (from phospholipid) and potassium (K) as poisons during HDO of fatty acids over molybdenum based sulfided catalysts was investigated. A range of concentration of poisons was evaluated to show that these poisons severely impacted the activity of catalysts. A change in selectivity was also seen, which is an important parameter to consider during the industrial production of biofuels. Different characterization techniques were employed to study the poison distribution on catalyst samples from lab experiments as well as from a refinery. It was suggested that Fe deposits preferentially near Ni-rich sites which deteriorated the ability of these catalysts to create active sites i.e. via sulfur vacancies. However, phosphorus resulted in irreversible phase transformation of the support to aluminum phosphate (AlPO4) which resulted in catalyst deactivation via pore blockage. In the comparative experiments, with spherical catalyst particles (1.8 mm), the Fe caused the strongest deactivation among P and K, based on the quantity added to feed oil. Although, considering the decrease in surface area per unit of deposited element after the experiment, then P caused the most deactivation. It was concluded that Fe deposited mostly near to the outer surface irrespective of concentration while P and K penetrated deeper in catalyst particles such that the distribution profile was dependent on the concentration. Reaction kinetics of HDO of fatty acids provides critical knowledge which could be applied at the refining scale in process design and optimization. The activity and selectivity of NiMo catalyst during HDO of stearic acid was studied by varying reaction conditions like temperature, pressure, feed concentration and batch-reactor stirring rate and using intermediates like octadecanal and octadecanol. A deeper understanding of the reaction scheme and selectivities was developed based on the experimental results. A Langmuir–Hinshelwood-type mechanism was used to develop a kinetic model which well-predicted the changes in selectivities at varying reaction conditions.
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| 2. |
- Arora, Prakhar, 1987, et al.
(author)
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Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
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Journal article (peer-reviewed)abstract
- The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.
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| 3. |
- Salam, Muhammad Abdus, 1983, et al.
(author)
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NiMoS on alumina-USY zeolites for hydrotreating lignin dimers: Effect of support acidity and cleavage of C-C bonds
- 2019
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In: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 4:1, s. 149-163
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Journal article (peer-reviewed)abstract
- NiMoS on alumina, USY and mixed alumina-USY supports was studied in a batch reactor to assess the effect of support acidity in valorizing lignin dimers by hydrodeoxygenation (HDO). The reactivity of α-O-4 (benzyl phenyl ether), β-O-4 (2-phenethyl phenyl ether) and 5-5′ (2,2′-dihydroxybiphenyl) linkages was investigated in dodecane at 593 K and a H2 pressure of 5 MPa. A relatively fast rate of hydrogenolysis of the sp3 hybridized etheric bonds was observed for the catalyst supported on the mixed support. With the α-O-4 linkage, the USY supported catalyst selectively yielded deoxygenated aromatics including BTX products with fewer residual C-C dimers. For the β-O-4 linkage, analogous trends have been observed but with more aromatics. Interestingly, with 5-5′ linkages the catalyst on USY and mixed supports can break the C-C linkages without producing other intermediate C-C dimer byproducts. The results show high hydrocracking and isomerization activities of the catalyst supported on USY and mixed supports. This is consistent with XRD, Raman, XPS and TEM measurements, where enhanced dispersion of the active phase was observed. However, hydrogenation activity on the USY support is reduced to a significant degree which results in a large amount of benzene compared to NiMoS-Al2O3 that produces mostly cyclohexane. In addition, elemental analysis revealed that carbon deposition is higher on the USY-based catalyst compared to the alumina-based catalyst owing to its higher acidity. However, the potential for superior C-C bond cleavage on NiMoS-USY opens the possibility to valorize technical lignin in biorefinery processes.
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| 4. |
- Wang, Aiyong, 1989, et al.
(author)
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Investigation of the robust hydrothermal stability of Cu/LTA for NH3-SCR reaction
- 2019
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 246, s. 242-253
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Journal article (peer-reviewed)abstract
- Recently copper ion-exchanged LTA zeolites were proved to be robust for NH3-SCR reaction. In this study, Cu/LTA catalysts with Si/Al = 15 and Cu/Al = 0.4 were synthesized via incipient wetness impregnation (IWI) method, following degreening/hydrothermal aging at different temperatures (750, 800, 850, 900 °C), and used to catalyze standard SCR, fast SCR and NH3/NO oxidation reactions. Catalysts were characterized with surface area/pore volume, powder X-Ray diffraction (XRD), nuclear magnetic resonance (NMR), H2-temperature programmed reduction (H2-TPR) and in situ Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS). Through the BET surface areas, XRD and NMR results, it can be found that the framework structure stability of Cu/LTA catalysts during hydrothermal aging was outstanding, even after harsh aging at 900 °C. Moreover, various Cu species, including Z-Cu2+, Z-[Cu(OH)]+ and CuOx clusters, were quantified for Cu/LTA catalysts hydrothermally aged under various temperatures with H2-TPR and in situ DRIFTS. An imperative finding in this study is the exceptional hydrothermal stability of [Cu(OH)]+ and the gradual conversions of both Cu2+ and CuOx clusters to [Cu(OH)]+ with increasing aging temperature. It is worth noting that this phenomenon is exactly the opposite of Cu/SSZ-13. As it is known from the literature (Song et al., 2017), the formation of CuOx not only decreases the selectivity of NOx conversion, but also can cause deterioration of zeolite structure, since the ion-exchanged copper stabilizes the zeolite. This may also explain why the hydrothermal stability of Cu/LTA samples is outstanding.
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