Mehanizmi, reakcije in kinetika katalitskega razklopa boranov do vodika

Drobež, Katja (author), Skalar, Tina (mentor)

Zaradi porasta svetovne populacije in vedno večjega števila tehnologij, se povečuje poraba energije. Ta se večinoma pridobiva iz fosilnih goriv, katerih viri pa so omejeni, hkrati pa njihova uporaba negativno vpliva na okolje. Z željo po zmanjšanju segrevanja ozračja se raziskujejo alternativni viri energije, ki so čisti in obnovljivi. Možna alternativa je vodik, ki bi med drugim lahko zamenjal uporabo nafte pri avtomobilih. Vodik je lahek in najbolj razširjen element v naravi, brez vonja, barve, ni toksičen in ne povzroča emisij CO2. Ker ima nizko volumensko energijsko gostoto, je za njegovo praktično uporabo potreben velik volumen. Zaradi omejenosti prostora v aplikacijah ga je potrebno shranjevati utekočinjenega pod visokim tlakom. V ta namen se odkrivajo in razvijajo materiali, ki bi omogočali njegovo shranjevanje. Eden izmed takšnih je AB, ki vsebuje 19,6 mas. % vodika, ki ga lahko sprošča pri segrevanju. To naj bi se dogajalo v treh stopnjah, kar sem pri magistrski nalogi spremljala s termičnimi analizami (TG, DTA, QMS). Hkrati sem z enakimi metodami ugotavljala vplive pretoka, segrevalne hitrosti in dodatka katalizatorja na termično razgradnjo AB-ja do vodika. Ugotovila sem, da uporabljen pretok prepihovalnega plina vzorca na razpad ne vpliva opazno. Pri primerjavi dveh različnih pretokov, 50 in 100 mL/min, so bila temperaturna območja izhajanja plinastih fragmentov in opaznih padcev TG krivulj skoraj enaka. Poleg tega pretok ni vplival niti na velikost spremembe mase v posameznih padcih. Vpliv segrevalne hitrosti sem ugotavljala s primerjavo treh vzorcev AB-ja, podvrženih različnim temperaturnim programom, hitrosti segrevanja 1, 5 in 10 K/min. Hitrost ponovno ni vplivala na izgubo mase v posameznih stopnjah. Vplivala pa je na temperaturna območja sprememb mas in izhajanja vodika. Z višanjem segrevalne hitrosti so se dvigale tudi temperature, pri katerih je prišlo do razgradnje AB-ja. Na koncu sem primerjala tudi vpliv dodanega katalizatorja, 5 % Ni/C, na potek termičnega razpada AB-ja. To sem naredila s primerjavo vzorcev s tremi različnimi deleži dodanega katalizatorja, z 0,20 in 40 mas. % glede na AB. Dodan katalizator ni bistveno vplival na temperaturna območja vidnih stopenj izgub mas vzorcev, vplival pa je na spremembo mase vzorcev. Z višanjem deleža Ni/C sta se spremembi mas v posameznih stopnjah razgradnje manjšali. Primerjava QMS krivulj pa je pokazala, da naj bi se izhajanje vodika začelo pri nižjih temperaturah ob povečevanju prisotnega katalizatorja. Poleg tega je katalizator vizualno vplival na AB. Pri vzorcih z 20 in 40 mas. % Ni/C se AB-ju ni opazno povečal volumen, medtem ko se pri vzorcu le z AB-jem je. S pomočjo literature in pridobljenih rezultatov termičnih analiz sklepam, da AB pri segrevanju razpada po polimerni poti. Ta v prvi stopnji vodi do nastanka poliamino borana, v drugi do poliimino borana, ki lahko nato vodi do nastanka borazina, ali borovega nitrida, tega pa pri nobeni izmed meritev nisem zaznala.

• Language: Slovenian
• Keywords: Vodik, amonijev boran, termična razgradnja.
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2022
• PID: 20.500.12556/RUL-140524
• COBISS.SI-ID: 130987779
• Publication date in RUL: 15.09.2022

Secondary language

• Language: English
• Title: Mechanisms, reactions and kinetics of catalytic decomposition of boranes to hydrogen

Abstract

Due to growth of the world’s population and the increasing number of technologies, the consumption of energy is increasing. It is mostly obtained from fossil fuels whose sources are limited. Furthermore, their use affects the environment in a negative way. Alternative energy sources, pure and renewable, are being explored because of the desire to limit global warming. A possible alternative is hydrogen which could substitute oil in cars. Hydrogen is a light element and the most common in nature, odourless, colourless, non-toxic and does not cause CO2 emissions. Due to its low volumetric energy density, its practical use demands great volume. Therefore, it needs to be stored liquid under great pressure, so materials are being discovered and developed to enable its storage. One of them is AB containing 19,6 weight % of hydrogen which can be discharged at heating. The procedure is supposed to run in three stages. This is the subject matter of the degree and has been researched with the help of thermal analysis (TG, DTA, QMS). The same methods have been used to measure the effects of flow, heating rate and the use of catalyst on thermal decomposition of AB to hydrogen. Research has shown that the flow of flushing gas sample does not affect disintegration in a great deal. When comparing two flows, namely 50 and 100 mL/min, the temperature ranges of gas fragmentation and substantial falls at TG curves were almost identical. Furthermore, the flow did not affect the size of mass change at a specific fall. The impact of heating rate has been established by comparing three AB samples, subject to various temperature programmes, namely the heating rate of 1, 5 and 10 K/min. The rate did not affect the mass loss in a specific stage. On the other hand, it did affect temperature ranges of mass change and hydrogen emission in a specific stage. By increasing heating range, the temperature when AB decomposition started, increased as well. Finally, the impact of catalyst (5 % Ni/C) on thermal decomposition of AB has been investigated by comparing samples with three different shares of catalyst added, namely 0, 20 and 40 weight % according to AB. The use of catalyst did not greatly affect temperature ranges of mass loss in samples. However, it did affect the change of mass in samples. By increasing the share of Ni/C, the change of mass in specific stages of decomposition decreased. Comparing QMS curves revealed that hydrogen emission started at lower temperature when increasing the use of catalyst. What is more, the catalyst visually affected AB. In samples with 20 and 40 weight % of Ni/C, the AB’s volume did not greatly enlarge, whereas in sample without the catalyst, the volume of AB enlarged. Taking into consideration thermal analysis results and data from literature, it has been concluded that AB when heated is decomposed in a polymeric way which in the first stage leads to poly(aminoborane) creation, in the second stage to poly(iminoborane) creation and can afterwards lead to creation of borazine or even boron nitride. However, this has not occurred in any of the measures.

• Keywords: Hydrogen, ammonia borane, thermal decomposition.