1. Catalytic hydro(deoxy)genation of furfural and modelling of its reaction kinetics : dissertationRok Šivec, 2024, doctoral dissertation Abstract: In recent decades, there has been a growing interest in producing biofuels and biochemicals from renewable sources. Furfural stands as one of the ligno(hemi)cellulosic biomass derived platform chemical, which can be transformed into numerous value-added products.
The goal of this PhD was to systematically study hydrotreatment reactions of furfural under varying operating conditions and to gain insights into the reaction mechanism and kinetics. An extensive experimental and computational study of hydrogenation, hydrodeoxygenation, oligomerisation and etherification of furfural in a three-phase batch reactor was performed. The goals were divided into three consecutive objectives.
In the first part, hydrotreatment of furfural over Pd/C catalyst under various reaction conditions, including the solvent selection (solventless conditions, tetrahydrofuran, isopropanol), atmosphere (nitrogen, hydrogen), temperature (100–200 °C), pressure (25–75 bar) and stirring speed, was studied. A reaction pathway network and a micro-kinetic model were developed, incorporating thermodynamics (hydrogen solubility), mass transfer, adsorption, desorption, and surface reactions. These phenomena and their contribution to the surface coverages, TOF’s and global reaction rates were studied. The hydrogen presence on the catalyst surface was found to influence the main reaction pathway, leading to ring, aldehyde group or full hydrogenation.
In the second part, various monometallic catalysts (Pd/C, Pt/C, Re/C, Ru/C, Rh/C, Ni/C, Cu/C) were tested at 100 -200 °C with 60 bar of hydrogen and tetrahydrofuran as solvent. A generalized reaction pathway network was developed. H2 temperature-programmed reduction (H2-TPR) and CO temperature-programmed desorption (CO-TPD) were conducted, and a regression analysis of the results was subsequently performed by numerical modelling and optimisation. The obtained adsorption and desorption kinetic parameters for active metallic sites were further used in a generalized micro-kinetic model, applicable to all tested catalysts. Pd/C exhibited high activity and non-selective hydrogenation of furfural, while other catalysts showed selective aldehyde group hydrogenation followed by deoxygenation, consistent with density functional theory (DFT) calculations. Ru/C uniquely produced 2 methyltetrahydrofuran and ring-opening products at 200 °C. In silico optimization of reaction conditions for promising catalysts ((Pd/C, Pt/C, Re/C, Ni/C) aimed to maximize the yield of the target product.
In the third part, the influence of support on catalytic activity was studied. Hydrotreatment of furfural over Pd/Al2O3, Pd/SiO2, Ru/Al2O3, Ru/SiO2, Ni/Al2O3, and Ni/SiO2 was performed between 150 - 200 °C, using 60 bar of hydrogen and tetrahydrofuran as solvent. The strength and rate of adsorption and desorption to/from acidic, metallic and interface site structures were determined, using H2-TPR, CO-TPD and NH3-TPD and subsequent regression analysis of the results by numerical modelling and optimisation. The resulting parameters were sequentially used in the generalized micro-kinetic model to quantify the contribution of the active metal (Ni, Pd, or Ru), support (Al2O3 or SiO2), interphase sites and their relationship on catalyst activity and selectivity. Evaluation of morphological and structural characteristics, adsorption/desorption and intrinsic reaction kinetics has indicated that the coverage of acidic sites (on alumina or silica) facilitated yielding ring hydrogenation and inhibited deoxygenation, decarbonylation and cyclic compound opening. The rates for aromatics or aldehyde functional groups were, nonetheless, affected in a different order.
The used and developed methods and findings of this PhD offer useful guidelines for transforming furfural into high-value chemicals through catalytic hydrotreatment, with significant implications for future research and industrial applications.
Keywords: lignocellulosic biomass, furfural, catalytic hydrogenation, micro-kinetic mass transfer model, reaction kinetics, first-principle methods, furfuryl alcohol, tetrahydrofurfuryl alcoholv, dissertations
Published in RUNG: 08.11.2024; Views: 327; Downloads: 5
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4. Chemistry of the iron-chlorine thermochemical cycle for hydrogen production utilizing industrial waste heatMatjaž Valant, Uroš Luin, 2024, original scientific article Abstract: This research presents an inventive thermochemical cycle that utilizes a reaction between iron and HCl acid for hydrogen production. The reaction occurs spontaneously at room temperature, yielding hydrogen and a FeCl2 solution as a by-product. Exploring the thermal decomposition of the FeCl2 by-product revealed that, at conditions suitable for utilization of low-temperature industrial waste heat (250 °C), chlorine gas formation can be circumvented. Instead, the resulting by-product is HCl, which is readily soluble in water, facilitating direct reuse in subsequent cycles. The utilization of low-temperature industrial heat not only optimizes resource utilization and reduces operational costs but also aligns with environmentally sustainable production processes. From the kinetic studies the activation energy was calculated to be 45 kJ/mol and kinetics curves were constructed. They showed significant kinetics at room temperature and above but rapid decrease towards lower temperatures. This is important to consider during real-scale technology optimization. The theoretical overall energy efficiency of the cycle, with 100% and 70% heat recuperation, was calculated at 68.8% and 44.8%, respectively. In practical implementation, considering the efficiency of DRI iron reduction technology and free waste heat utilization, the cycle achieved a 41.7% efficiency. Beyond its energy storage capabilities, the Iron-chlorine cycle addresses safety concerns associated with large-scale hydrogen storage, eliminating self-discharge, reducing land usage, and employing cost-effective storage materials. This technology not only facilitates seasonal energy storage but also establishes solid-state energy reserves, making it suitable for balancing grid demands during winter months using excess renewable energy accumulated in the summer.
Keywords: chemical cycles, hydrogen production, thermal decomposition, reaction kinetics, iron, chlorine
Published in RUNG: 12.01.2024; Views: 1962; Downloads: 43
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5. Preparation of porous [alpha]-Fe[sub]2O[sub]3 thin films for efficient photoelectrocatalytic degradation of basic blue 41 dyeManel Machreki, Takwa Chouki, Mitja Martelanc, Lorena Butinar, Branka Mozetič Vodopivec, Saim Emin, 2021, original scientific article Abstract: A novel method was developed for the preparation of porous hematite (α-Fe2O3) thin films. First, a solution containing iron precursor was spin-coated on fluorine-doped tin oxide substrate and later short heat-treated at 750 °C. The prepared α-Fe2O3 thin films were applied as dual-function catalyst in photoelectrochemical (PEC) water oxidation and textile dye degradation studies. For the first time, α-Fe2O3 thin films were used in efficient PEC degradation of a textile dye (Basic Blue 41 – B41) using in-situ generated reactive chlorine species. In comparison with photocatalytic and electrocatalytic approaches, the PEC technique allows faster degradation of B41 dye at an applied bias potential of 1.5 V versus reversible hydrogen electrode and under visible light illumination. In the presence of Cl− using the PEC approach the degradation of B41 reaches 99.8%. High-performance liquid chromatography coupled with UV–VIS system confirmed the degradation of B41 dye using PEC. Gas-chromatography coupled to mass spectrometry was used to study the by-products obtained during PEC degradation. Chemical oxygen demand analyses confirmed that the mineralization level of B41 is in the order of 68%. The α-Fe2O3 films developed in this study give a higher level of PEC degradation efficiency compared to other iron oxide-based systems.
Keywords: thin films, photoelectrocatalysis, kinetics, visible light, degradation, textile dye
Published in RUNG: 10.05.2021; Views: 3417; Downloads: 13
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6. Water reveals non-Arrhenius kinetics in protein folding experimentsArtem Badasyan, 2020, published scientific conference contribution abstract (invited lecture) Abstract: Statistical theories describe systems in equilibrium, and cannot be used to study kinetics. However, the theo-
ries are based on coarse-grained parameters, that include assumptions regarding the underlying kinetics. If
such assumptions are incorrect, the theoretical expressions, used to process the experimental data, will not
fit. I report on one such case we have met within the application of Zimm-Bragg [1] theory to process folding
experiments, and discuss the reasons and consequences.
Studies of relaxation phenomena in glass-forming liquids by default account for the shift in temperature by
some value, corresponding to the glass formation temperature, .In particular, temperature
shift
appears in hydrated proteins because of the presence of partially glassy states giving rise to
non-
Arrhenius relaxation times log τ ~ [2].
A phenomenological approach was suggested
by Adam and Gibbs as early as in 1965 to describe
the sudden increase of viscosity and the slowing down of the collective modes in super-cooled liquids as the
temperature is approaching[3]. The key idea of Adam-Gibbs theory was to consider the supercooled liquid
as a set of clusters (cooperatively rearranging regions) of different sizes that change with temperature,
giving rise to the shift in re-
laxation time. The temperature shift factor is present in many theories
describing properties of water.
Thus, Truskett and Dill had to include the Adamm-Gibbs temperature
shift into their simple analytical model of water to achieve the agreement with experimental data on the tem-
perature dependence of self-diffusion coefficient [4]. Later, Schiro and Weik have summarised recent in vitro
and in silico experimental results regarding the role of hydration water in the onset of protein structural dy-
namics, and have reported the presence of super-Arrhenius relaxation region above the ”protein dynamic
transition” temperature [4]. Recently, Mallamace et al have used the Adam-Gibbs theory in their NMR meas-
urements of protein folding-unfolding in water [4] and to rationalise the complicated pressure-temperature
diagrams in these glass-forming systems.
Motivated by the considerations above, and taking into account the
relationship between the
unimolecular rate of folding in water and the relaxation time 45 , we
introduce the
tem-
perature shift into the formulas used to fit experimental data on hydrated polypeptides.
By doing so we resolve the paradox and complete the new method of processing the Circular Dichroism ex-
perimental data on protein folding
Keywords: water, protein folding, non-Arrhenius kinetics
Published in RUNG: 20.07.2020; Views: 3507; Downloads: 117
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7. KINETICS OF CELLULOSE DEGRADATION STUDIED USING SIZE EXCLUSION CHROMATOGRAPHYAneta Balažic Fabjan, 2016, master's thesis Abstract: For more than five centuries, paper has been the predominant carrier of information and numerous medieval manuscripts bear witness of its durability. However, increasing demand for paper led to several changes in its production in the 19th century. High quality rag fibres were replaced by inferior wood-originating ones. Acid manufacturing technology was introduced which, due to its simplicity and low cost, continued to be used until the end of the 20th century. Inherently stable paper rapidly degrades in the presence of acids and its decay is further promoted by the poor storage conditions and environmental pollutants. As a result, the amount of degraded paper in libraries, archives and museums is reaching enormous proportions. In order to prolong the usable time of the vast quantities of original materials, paper collections may be deacidified and/or stored at lower temperatures. While preservation options are known, lack of the competent comparative studies leaves collection keepers hesitant of their use. The introductory part of the project is focused on development of analytical methodologies and model materials, representative of historical acid paper. As uniqueness and inherent value of cellulose-based cultural heritage limits the use of analytical methodologies to the non-destructive or micro-destructive ones. A new methodology for determination of the condition of paper was developed. The analytical technique-size exclusion chromatography for the first time allows us to reproducible determine the condition of paper which contains a significant amount of wood derived lignin. A few fibres suffice for the analysis, which renders the methodology suitable for characterisation of historical materials. The results of the research will represent the effect of deacidification processes with use of micro destructive analytical methodologies. As written word is all what we have for our legacy from generation to generation, evaluating preservation strategies for decaying collections, safekeeping and long term access to the endangered written cultural heritage is one of the most important facts.
Keywords: paper, size exclusion chromatography, kinetics, deacidification process
Published in RUNG: 02.09.2016; Views: 7323; Downloads: 287
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8. Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbentMina Jovanovic, Iztok Arčon, Janez Kovač, Nataša Novak Tušar, Bojana Obradovic, Nevenka Rajić, 2016, original scientific article Abstract: In this study the uptake capacity of Mn(II) ions by zeolite A beads was investigated for different initial Mn concentration (100e400 mg Mn dm^-3) in batch mode at 25e55 C. The obtained adsorption capacity varying from 30 to 50 mg Mn g^-1 demonstrated a high affinity of zeolite A towards Mn(II) present in solutions. Kinetic studies indicated the intra-particle diffusion as the rate limiting step up to 45 C with apparent diffusivities in the range (1.2e2.0) x 10^-13 m2 s^-1 and the activation energy of 21.9 kJ mol^-1, which implies strong interactions between the zeolite A and Mn ions. At 55 C ion-exchange became the rate limiting step. The adsorption isotherms were studied at 25 C showing that the Mn adsorption is the best described by the Langmuir model suggesting a homogenous zeolite surface. XPS analysis of the Mnloaded beads showed that there is no surface accumulation of Mn but an almost uniform Mn distribution inside zeolite A, whereas XANES and EXAFS suggested that the adsorption of Mn(II) was followed by the Mn(II) oxidation and oxide formation. Regeneration of the spent zeolite was examined in 8 adsorption/desorption cycles by a chelating Na2EDTA in a fluidized column. It has been found that zeolite A beads could be reused for at least 4 cycles with satisfactory Mn(II) adsorption efficiencies of about 70%.
Keywords: Zeolite A
Manganese
Adsorption kinetics
EXAFS/XANES
XPS
Published in RUNG: 01.04.2016; Views: 6148; Downloads: 0
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