Razvoj katalizatorjev za magnetno segrevano oksidacijo propena v propilen oksid z molekularnim kisikom

magistrsko delo

Katja Svetek (Author), Sašo Gyergyek (Mentor), Janvit Teržan (Co-mentor)

Abstract

Propilen oksid je komercialna kemikalija z velikim industrijskim pomenom. Metode za pridobivanje propilen oksida imajo dve glavni pomanjkljivosti – onesnaževanje okolja in visoke stroške proizvodnje. Začeli so razvijati nove metode, med drugim tehnologije pridobivanja propilen oksida z neposredno epoksidacijo ob prisotnosti molekularnega O2 kot oksidanta, s poudarkom na novih katalitskih sistemih. Težava ostaja pri kontroli nad selektivnostjo, saj je zaradi sorazmerno visoke temperature reakcijske mešanice težko preprečiti popolno oksidacijo propilena. Z uporabo magnetnih nanodelcev, bi lahko bistveno izboljšali selektivnost reakcije, saj se magnetni nanodelci zelo hitro segrejejo v izmeničnem magnetnem polju. Pri takšnih katalizatorjih se segreva zgolj katalizator, torej zgolj področje kjer se bo zgodila kemijska reakcija, reakcijska mešanica pa ostaja na sorazmerno nizki temperaturi. V magistrskem delu smo sintetizirali katalizatorje na osnovi Cu/CuO specij nanešenih na magnetne nanokompozite. Magnetni nanokompoziti so sestavljeni iz magnetnih nanodelcev železovega oksida porazdeljenega po oksidni matrici. Oksidne matrice iz Al2O3, TiO2 in ZrO2 smo pripravili s hidrolizo prekurzorjev (prekurzorji: aluminijev nitrid, raztopina titanilovega sulfata v žveplovi (VI) kislini in raztopina cirkonovega acetata) v koloidni suspenziji nanodelcev magnetnega železovega oksida. Magnetni nanokompozit, katerega matrica je Al2O3, smo kalcinirali pri 500 °C 1 uro. Magnetna nanokompozita, kjer je matrica TiO2 in ZrO2 pa smo kalcinirali pri 350 °C 3 ure. Nato smo Cu/CuO specije nanesli na površino nanokompozitov s hidrolizo raztopine Cu2+ in kalcinirali pri temperaturi 350 °C 3 ure. Nazadnje smo nanokompozite modificirali s kalijem in ponovno kalcinirali pri temperaturi 350 °C 3 ure. Nanokompozite smo okarakterizirali z uporabo presevne elektronske mikroskopije (TEM), merjenjem magnetnih lastnosti, določevanjem specifične površine, rentgensko praškovno difrakcijo (XRD), rentgensko fluorescenčno spektrometrijo (XRF), temperaturno programirane desorpcije s CO2 (TPD-CO2), pulzne oksidacije z N2O in opravili teste katalitske aktivnosti za kontinuirno oksidacijo propilena z molekularnim O2 v plinski fazi in magnetnim segrevanjem katalizatorja. Z uporabo metod smo ugotovili, da vsi katalizatorji vsebujejo magnetni železov oksid, izkazujejo sorazmerno visoko specifično površino (do 217,9 m2/g), razen katalizator kjer je matrica ZrO2 (19,6–25,8 m2/g). Kljub primerljivi nasičeni magnetizaciji in relativno homogeni porazdelitvi magnetnih nanodelcev znotraj matrice so pri enakih amplitudah magnetnega polja katalizatorji dosegli različne stacionarne temperature v toku reakcijske mešanice 18 ml/min. Vse dosežene temperature so bile nižje od 260 °C. Zaradi sorazmerno nizke dosežene temperature je bila stopnja konverzije propilena manjša od 1 %, željenega produkta propilen oksida pa nismo zaznali. Na podlagi izvedenih testov sklepamo, da je potrebno dodatno delo na tematiki (povečanje količine katalizatorja v nasutju za dosego višje temperature, povečati delež Cu/CuO, povečati delež promotorja, itd.), da bi lahko zanesljivo ovrgli ali potrdili hipotezo o izboljšanju selektivnosti zaradi specifičnega gretja katalizatorja.

Keywords

magnetni nanodelci;magnetno segrevanje;selektivna oksidacija;propilen oksid;magistrske naloge;

Data

Language:	Slovenian
Year of publishing:	2021
Typology:	2.09 - Master's Thesis
Organization:	UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher:	[K. Svetek]
UDC:	544.478+542.86(043.2)
COBISS:	96814851
Views:	281
Downloads:	49
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Development of catalysts for the magnetically heated oxidation of propylene to propylene oxide using molecular oxygen
Secondary abstract:	Propylene oxide is a commercial chemical of great industrial importance. Propylene oxide production methods have two main disadvantages, namely environmental pollution and high production costs. They began to develop new methods, among other technologies for the production of propylene oxide by direct epoxidation in the presence of molecular O2 as an oxidant, with an emphasis on new catalytic systems. The problem remains with selectivity control, as it is difficult to prevent total oxidation of propylene due to the relatively high temperature of the reaction mixture. The use of magnetic nanoparticles can improve the selectivity of these reactions, as magnetic nanoparticles heat-up very quickly when exposed to an alternating magnetic field. In this type of catalysts, only the catalyst is heated, i.e. only the area where the chemical reaction takes place and the reaction mixture remains at a relatively low temperature. In the master's thesis, we synthesized catalysts based on Cu/CuO species deposited on magnetic nanocomposites. Magnetic nanocomposites were composed of magnetic iron oxide nanoparticles distributed within an oxide matrix. Oxide matrices from either Al2O3, TiO2 or ZrO2 were prepared by hydrolysis of precursors (precursors: aluminium nitride, solution of titanyl sulfate in sulfuric (VI) acid and zirconium acetate solution) in a colloidal suspension of magnetic iron oxide nanoparticles. The magnetic nanocomposite with Al2O3 was calcined at 500 °C for 1 hour. The magnetic nanocomposites where the matrix was TiO2 or ZrO2, were calcined at 350 °C for 3 hours. Cu/CuO species were then deposited to the surface of the nanocomposites by hydrolysing a Cu2+ solution, followed by calcination at 350 °C for 3 hours. Finally, the nanocomposites were modified with potassium and re-calcined at 350 °C for 3 hours. Nanocomposites were characterized using transmission electron microscopy (TEM), measurement of magnetic properties, determination of specific surface area, X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), temperature programmed desorption of CO2 (TPD-CO2), N2O pulse oxidation and tested catalytic activity for the continuous oxidation of propylene with molecular O2 in the gas phase using magnetic heating of the catalyst. We found out that all catalysts contain magnetic iron oxide and show a relatively high specific surface area (up to 217,9 m2/g), except for the catalyst where the matrix is ZrO2 (19,6–25,8 m2/g). Despite comparable saturated magnetization and relatively homogeneous distribution of magnetic nanoparticles within the matrix, the catalysts reached different temperatures in the flow of the reaction (18 ml/min) at the same magnetic field amplitudes. All the temperatures we were able to reach were below 260 °C. Due to the relatively low temperature reached, the conversion of propylene was less than 1 %, and the desired product propylene oxide, was not detected. Based on the tests performed, we conclude that additional work on the topic (increasing the amount of catalyst to achieve a higher temperature, increasing the content of Cu/CuO, increasing the content of the promoter, etc.) is needed to reliably refute or confirm the hypothesis of improving selectivity due to specific heating of the catalysts.
Secondary keywords:	magnetic nanoparticles;magnetic heating;selective oxidation;propylene oxide;
Type (COBISS):	Master's thesis/paper
Thesis comment:	Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages:	1 spletni vir (1 datoteka PDF (IX, 36 f.))
ID:	13868125