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Theoretical Investigation of the Zeolite Hydrolysis under Realistic Conditions
Jin, Mengting ; Grajciar, Lukáš (advisor) ; Chizallet, Céline (referee) ; Piskorz, Witold (referee)
Zeolites are one of the most widely used and one of the most industrially important materials. They are utilized in a variety of commercial applications, particularly in heterogeneous catalysis, adsorption/separations applications and as ion exchangers. Zeolites are stable when exposed to water or water vapor at ambient conditions and exhibit high thermal stability. However, zeolites can be partially or even fully hydrolyzed under certain conditions. This hydrolytic instability of zeolites can be considered both a major problem in some applications and a useful means to tune catalyst properties in the others. However, the thorough studies of the hydrolytic mechanisms under realistic conditions (high water loading, alkaline conditions, high heteroatom concentrations, etc.) and employing realistic models (dynamical simulation of ab initio accuracy) is mostly lacking. This dissertation uses the ab initio calculations to systematically study the hydrolysis mechanism of zeolites under realistic conditions, including: (1) hydrolysis mechanism of germanosilicate zeolite UTL, (2) hydrolysis of siliceous zeolite CHA under alkaline conditions, and (3) identification of the nature of framework-associated Al(Oh) species in aluminosilicate zeolite CHA under wet conditions. The main results obtained are as...
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Templating as a new method of creating and modifying the porous texture of polyacetylene networks
Sokol, Jiří ; Sedláček, Jan (advisor) ; Balcar, Hynek (referee)
A new method of introducing permanent micropores into hyper-cross-linked polyacetylene networks has been developed. The method used a combination of polyacetylene chemistry and Schiff base chemistry. Through the coordination chain-growth polymerization of monomers with polymerizable ethynyl groups, a wide series of homopolymer and copolymer networks with rigid polyene main chains interconnected by arylene links was prepared. The networks carried substituents of the predominantly aromatic Schiff-base-type in the pendant groups. With increasing content and volume of these substituents the specific surface area of the networks decreased. The networks with a high content of Schiff-base-type substituents were non-porous. The prepared networks were subsequently hydrolyzed under the conditions optimized in this diploma thesis. The hydrolysis led to a highly efficient cleavage of the Schiff base methanimine linkages and to the removal of the cleaved low molecular weight aromatic amine and aldehyde segments from the networks. In this way, new functional groups were generated in the networks, either CH=O or NH2. The hydrolytic modification had a fundamental effect on the texture parameters of the networks. The modification of the originally microporous networks mostly led to an increase in the specific...
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Measurement of viscosity of suspensions during wheat bran processing
Koukal, Jan ; Slavíková, Zuzana (referee) ; Pořízka, Jaromír (advisor)
This bachelor thesis deals with the assessment of the viscosity evolution of wheat bran suspension during alkaline hydrolysis. Wheat bran is a widely produced low-cost by-product of the milling industry. Due to its composition, bran is a suitable substrate for biorefining and involvement in the circular economy. However, during processing, viscosity development occurs, which greatly affects the energy requirements for processing. The temporal evolution of viscosity during alkaline hydrolysis was determined using a rotational rheometer at constant shear rate. Viscosity was assessed as a function of NaOH concentration, temperature and bran ration. Furthermore, the evolution of viscosity was measured during alkaline extraction of proteins. The highest viscosity was measured in a 0.2 M NaOH system at 30 °C with a bran to hydroxide ratio of 1:10. Its value was 0.991 ± 0.010 Pa.s. Based on the theoretical part and the data obtained from rheological measurements, the design of a stirred reactor for wheat bran processing on an industrial scale was carried out. It is a vertical cylindrical vessel with a total volume of 10 m3. The vessel is equipped with three Chemineer HE-3 hydrofoil impellers mounted on a vertical shaft. The power input of the agitator was calculated at 2.8 kW and compared to a conventional 4-blade, 45-degree pitched blade turbine, the chosen design was four times more efficient.
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Preparation and characterization of packaging films based on beta-keratin
Měšťánková, Zuzana ; Mikulíková, Renata (referee) ; Kovalčík, Adriána (advisor)
This diploma thesis deals with keratin isolation from poultry feather waste and preparation of keratin-polymers composite films utilizing isolated keratin. The main goal was to isolate keratin from poultry feathers by hydrolysis and compare yield of diverse hydrolysis types. The most efficient was hydrolysis using 0.5% sodium hydroxide with yield 480 g of keratin per 1 kg of chicken feathers. Structure, morphology and thermal properties of isolated keratin was analyzed. Comparison with protein molecular weight standard it was revealed that hydrolysis cleaved keratin to macromolecules smaller than 15 kDa. Scan electron microscopy showed that size of lyophilized keratin particles was in the order tens of µm and had an irregular shape. Further, composite films based on isolated -keratin and other polymers were prepared. Thermal analysis showed, the addition of keratin significantly reduced the thermal stability of composite films. Analyses revealed that Polyvinyl alcohol composite films reached the best mechanical properties. For example, an addition of 0.25 g of keratin per 1 g of polyvinyl alcohol increased the tensile elongation by up to 68.9%. Moreover, the film based on chitosan and keratin had antibacterial properties. The results demonstrate that it is able to efficiently isolate keratin from poultry feather waste by alkaline hydrolysis and isolated keratin can be utilized to prepare potentially applicable keratin-polymers composite films.
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Theoretical investigation of water-zeolite interactions under steaming conditions
Benešová, Tereza ; Heard, Christopher James (advisor) ; Fišer, Jiří (referee)
The thesis is focused on theoretical study of hydrolysis and isotopic oxygen exchange in zeolite chabazite under steaming conditions. The theoretical study was performed by the methods of computational chemistry, namely density functional theory. Reactions of water with zeolites were investigated within the periodic model with chabazite supercell consisting of 36 Si/Al tetrahedra. Reactivity was investigated for one or two water molecules corresponding to the conditions relevant to high-temperature steaming. Relevant mechanisms of isotopic oxygen exchange were found and their competitiveness with hydrolysis was discussed.
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Biochemical aspects of study and restoration of aged paintings
Hradilová, Iveta ; Hudeček, Jiří (advisor) ; Smrček, Stanislav (referee)
Every part of a work of art is changing in the course of time. Even simultaneously in its creation, when tempera or oil paint used dry up. Already this process can be considered as a biochemical change in the material. The main goal of a submitted bachelor's thesis is to compile recent knowledge about resins and protein media used in works of art, to describe their composition and, in particular to evaluate the changes they undergo in time after their application on canvas, wooden or metal surfaces and paper to their irrecoverable destruction. In addition, biological degradation of these substances by several species of bacteria, yeasts and fungi is discussed in the last part of this work. Key words: resins, terpenoids, protein media, degradation, oxidation, hydrolysis (In Czech)
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Isolation of pure aminoacids from wheat bran
Sloupová, Klára ; Diviš, Pavel (referee) ; Pořízka, Jaromír (advisor)
Wheat bran is a promising material containing a wide range of useful components, including proteins. In addition, it is produced in significant volumes. Currently, wheat bran is used for the production of energy by combustion and for feed purposes. Gradually, new methods of valorization of this material are being sought. One of the possibilities of using wheat bran is the isolation of proteins, hydrolysis, and separation of selected amino acids. This diploma thesis deals with this issue, it is focused on the recovery of arginine and leucine from a protein isolate. Proteins were extracted from wheat bran by changing the pH. Thanks to the subsequent lyophilization a protein isolate was gained. Prior to hydrolysis of the resulting isolate, a stability test of arginine and leucine amino acid standards was first performed, to which various hydrolysis methods were applied. Acid hydrolysis using a mineralizer, which was applied to the protein isolate, was proved to be the most effective. This was followed by the derivatization of the hydrolysates with OPA and analysis of the resulting hydrolysates by high-performance liquid chromatography with UV-VIS detection. Then, suitable adsorption and desorption conditions were optimized. It was found that the time dependence does not affect the amount of adsorbed material on the sorbent. Therefore, an application time of 15 minutes was chosen. While optimizing the amount of used standard, it was found that the optimal weight was 0.25 g of sorbent. The selected conditions were applied to the protein hydrolyzate. Two fractions were obtained by the separation of selected amino acids due to the change in the pH of the citrate buffer. After the application of this procedure, 0.26 g of arginine and 0.82 g of leucine were obtained from one kilogram after evaporation. From evaporation two, 1.01 g of arginine and 0.25 g of leucine were obtained after evaporation.
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Extraction of arabinoxylans from wheat bran
Koblasová, Dana ; Kouřilová, Xenie (referee) ; Diviš, Pavel (advisor)
This diploma thesis is focused on the use of wheat bran as a raw material for extraction of arabinoxylans. Wheat bran is a waste product of mill processing of wheat into flour and is mainly used as a livestock feed. However, the amount of bran produced significantly exceeds its consumption as feed, which opens up space for research into their further use. Polysaccharides such as cellulose, hemicelluloses and lignin are mainly present in the bran. The most common type of hemicelluloses are arabinoxylans, which form the main structural component of wheat bran. Alkaline extraction disrupts hydrogen and covalent bonds and releases polysaccharides of various molar weights from the crosslinked cell wall structure. Hydrolysis is required to obtain arabinose and xylose. Trifluoroacetic acid was chosen for the hydrolysis. The acid breaks down glycosidic bonds of the poly- and oligosaccharides to give the corresponding monosaccharides. The experiments made during this thesis have shown that the yield of multi stage extraction is twice as high as the yield of single stage extraction. Hydrolysis of the solid fractions after alkaline extraction revealed that a relatively large amount of arabinoxylans and other carbohydrates still remain bound in the complex matrix of the bran cell wall. Thus, alkaline extraction alone may not be the best option for obtaining arabinoxylans on a larger scale, or process optimization must be considered. Extraction with the addition of hydrogen peroxide appears to be effective for large-scale extraction processes.
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Theoretical Study of Influence of Silanol Nest Defects on Hydrolysis of Zeolite Chabazite
Vacek, Jaroslav ; Grajciar, Lukáš (advisor) ; Fišer, Jiří (referee)
This thesis is focused on theoretical study of influence of the silanol nest defects on the hydrolysis of zeolite Chabazite under harsh steaming conditions. The motivation of the thesis was a recent experiment proving that the silanol nest defect enhances the hydrolysis of a zeolite. The harsh steaming conditions have been chosen as some important technological processes involving zeolites require high temperatures and have water vapour present. The study was performed by using density functional theory calculations. To investigate the influence of the defect two models were used a reference pristine model and a defected model containing the silanol nest defect. The two models were pure siliceous Chabazite periodical models with supercell containing 36 and 35 Si tetrahedra respectively. A multi-step hydrolysis leading to detachment of a Si(OH)4 cluster from the zeolite, known as total desilication, was calculated for the two models. Multiple possible paths of the hydrolysis were discovered, compared and discussed on both models. Both the most favourable hydrolysis paths of the two model as well as their arithmetic means were compared. The experimentally set expectations that a silanol nest defect enhances the hydrolysis of the zeolite have been met.
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Theoretical investigation of water-zeolite interactions under steaming conditions
Benešová, Tereza ; Heard, Christopher James (advisor) ; Fišer, Jiří (referee)
The thesis is focused on theoretical study of hydrolysis and isotopic oxygen exchange in zeolite chabazite under steaming conditions. The theoretical study was performed by the methods of computational chemistry, namely density functional theory. Reactions of water with zeolites were investigated within the periodic model with chabazite supercell consisting of 36 Si/Al tetrahedra. Reactivity was investigated for one or two water molecules corresponding to the conditions relevant to high-temperature steaming. Relevant mechanisms of isotopic oxygen exchange were found and their competitiveness with hydrolysis was discussed.
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