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Development of Raman spectroscopy methods for the study of chemical kinetics in hydrogenation and degradation reactions

le, Daphne LU (2017) KEML16 20161
Department of Chemistry
Abstract
Hydrogenation is a universal reaction, which is widely used in industry and academy. However, the reaction is not easy to be studied in extreme conditions such as high temperature and high pressure. On top of that, using Raman spectroscopy to observe the reaction is not so customary. Due to these aspects, the experiment was carried out. During the working process, the degradation reaction was also observed to try whether the technique could apply to all type reactions. Raman spectroscopy is a powerful method, which has a better resolution than such as infrared spectroscopy that can provide complete information about molecule structure of a compound. Therefore, the method is a suitable technique when several compounds studied.

Our work... (More)
Hydrogenation is a universal reaction, which is widely used in industry and academy. However, the reaction is not easy to be studied in extreme conditions such as high temperature and high pressure. On top of that, using Raman spectroscopy to observe the reaction is not so customary. Due to these aspects, the experiment was carried out. During the working process, the degradation reaction was also observed to try whether the technique could apply to all type reactions. Raman spectroscopy is a powerful method, which has a better resolution than such as infrared spectroscopy that can provide complete information about molecule structure of a compound. Therefore, the method is a suitable technique when several compounds studied.

Our work was based on Raman spectroscopy in-situ to develop methods to study the kinetics of two chemical reactions: hydrogenation under high-pressure and degradation. The method was used to monitor the change in intensity of the significant peaks with time and it would be applicable to all substrates.

Before the hydrogenation reaction under high-pressure was studied, several fluorescence-tests for acetonphenone (reactant), phenathroline and pyridon (ligands), iron (acac)3 (catalyst) dissolved in different solvents were acquired to make sure that significant signals of the reaction could be detected and monitored by Raman spectroscopy. The results showed that fluorescence came from two ligands: pyridon and phenanthroline. However, it was possible to detect the signal of the carbonyl group from reactant, acetonphenone. Based on the promising results, the reaction hydrogenation kinetics of acetonphenone into phenanthroline in ACN, in the presence of iron (acac)3, and K2CO3 under high pressure (100 bars) and high temperature (110°C) could be studied by in-situ Raman spectroscopy. Unfortunately, the seals of the studying high-pressure vessel were destroyed by the solvent and the experiment had to be stopped.

The degradations of beta-carotene, ascorbic-acid and quercetin by exposure to light at room temperature were studied. At the wavelength 532 nm that used in the experiment, all three compounds emitted fluorescence. The relevant signal corresponding to the degradation of beta-carotene could be detected but not monitored due to fluorescence. Whereas, no signals from ascorbic acid and quercetin could be found because fluorescence caused a high base line and all the signals were overlapped by it. The experiments therefore could not be continued further.

Due to fluorescence and the destroyed seals, the degradation and hydrogenation, respective could not be studied further. Raman spectroscopy is a suitable method for hydrogenation reaction because the obtained spectrum can show complete information of a compound. However, it does not work so efficiently in degradation reaction. Otherwise, the method would be developed and validated by using well-known hydrogenation and degradation reactions.

Keywords: Raman spectroscopy, chemical kinetics, hydrogenation under high-pressure, degradation, beta-carotene, ascorbic acid, quercetin. (Less)
Popular Abstract (Swedish)
När vi påstår att en reaktion är snabb, vad är det exakt vi menar? För att förenkla saken, en snabb reaktion betyder att omvandlingen från reaktant till produkt sker inom ett kort tidsintervall. En explosion är ett exempel på en snabb reaktion. Motsatt är en långsam reaktion som produkten genereras över en längre tidsperiod, exempelvis vid korrosion. Hastighet av reaktion kan studeras genom att kontrollera förändringen i koncentration av antingen reaktanten eller produkten med tiden. Beroende på vilken del av reaktionen som studeras, substratkonsumtion eller produktbildning, kan hastigheten av processen uppträda efter ett mönster. Detta kallas för kinetik. Målet är att med hjälp av Ramanspektroskopi utveckla en metod för att studera... (More)
När vi påstår att en reaktion är snabb, vad är det exakt vi menar? För att förenkla saken, en snabb reaktion betyder att omvandlingen från reaktant till produkt sker inom ett kort tidsintervall. En explosion är ett exempel på en snabb reaktion. Motsatt är en långsam reaktion som produkten genereras över en längre tidsperiod, exempelvis vid korrosion. Hastighet av reaktion kan studeras genom att kontrollera förändringen i koncentration av antingen reaktanten eller produkten med tiden. Beroende på vilken del av reaktionen som studeras, substratkonsumtion eller produktbildning, kan hastigheten av processen uppträda efter ett mönster. Detta kallas för kinetik. Målet är att med hjälp av Ramanspektroskopi utveckla en metod för att studera kinetiken av två kemiska reaktioner: hydrogenering av omättade föreningar och självnedbrytning av naturprodukter. I ett sådant arbete är det viktigt att kunna identifiera de karakteristiska signaler som skulle kunna användas för en kinetisk undersökning. En utmaning som fås under arbetsgången är att kunna bevisa om detektionsgränsen (LOD) och kvantifieringsgränsen (LOQ) i den använda tekniken är tillräckligt bra för att kunna utföra studien. De två gränserna påverkas av provtyp och Raman-instrument. Instrumenten består av en ljuskälla, här användes en grön laser med våglängden 532 nm, en detektor och en Charged Coupled Device (CCD) kamera.

Första reaktionen som studerades var hydrogenering. Hydrogenering är en kemisk reaktion där väteatomer adderar till en förening som har dubbel eller trippel bindningar i närvaro av en katalysator. Hydrogenering är en viktig reaktion med applikationer både inom industri och akademi. I detta arbete studeras omvandlingen av reaktanten, acetonfenon till produkten, 1 - fenylethanol i närvaro av en komplex av katalysator i metall saltet, järn (accac)3 och en ligand. Reaktionen observeras vid 110℃, med trycket mellan 100 och 200 bar och i närvaro av vätgas (H2). Innan kinetiken av hela reaktionen undersöktes, utfördes tester med olika lösningsmedel och metalljoner för att optimera reaktionen. Den optimerade reaktionen användes vidare för att studera kinetiken i en högtrycksreaktor. Ett problem med materialet av trycksisoleringen uppstod vid reaktionsgång samt tiden som krävdes för att upphetta reaktionen till 110℃ var för lång.

Andra reaktionen är molekylärnedbrytning. Beta-karoten (vitamin A), askorbinsyra (vitamin C) och quercetin är naturligt förekommande föreningar som har antioxidativa egenskaper. Under återvinningsprocessen från naturliga källor kan molekylerna brytas ner av ljus och luft. Syftet är att studera hur föreningarna bryts ner under belysning av en halogenlampa vid rumstemperatur. Experimenten utfördes under enkla förhållanden där proverna förvarades i transparenta vialer och utsattes för en vanlig halogenlampa. På grund av dessa betingelser blev resultatet inte som förväntat. Inga signifikanta signaler kunde detekteras i askorbinsyra och quercetin. En relevant signal av beta-karoten identifierades och kunde användas för att studera kinetiken. Experimenten kunde inte utvecklas vidare eftersom tiden för den fullständiga nedbrytningen skulle ta upp till 200 timmar. (Less)
Please use this url to cite or link to this publication:
author
le, Daphne LU
supervisor
organization
course
KEML16 20161
year
type
M2 - Bachelor Degree
subject
keywords
Raman spectroscopy, chemical kinetics, hydrogenation under high-pressure, degradation, beta-carotene, ascorbic acid, quercetin, analytical chemistry, analytisk kemi
language
English
id
8905051
date added to LUP
2018-02-01 11:43:40
date last changed
2018-02-01 11:43:40
@misc{8905051,
  abstract     = {Hydrogenation is a universal reaction, which is widely used in industry and academy. However, the reaction is not easy to be studied in extreme conditions such as high temperature and high pressure. On top of that, using Raman spectroscopy to observe the reaction is not so customary. Due to these aspects, the experiment was carried out. During the working process, the degradation reaction was also observed to try whether the technique could apply to all type reactions. Raman spectroscopy is a powerful method, which has a better resolution than such as infrared spectroscopy that can provide complete information about molecule structure of a compound. Therefore, the method is a suitable technique when several compounds studied. 

Our work was based on Raman spectroscopy in-situ to develop methods to study the kinetics of two chemical reactions: hydrogenation under high-pressure and degradation. The method was used to monitor the change in intensity of the significant peaks with time and it would be applicable to all substrates. 

Before the hydrogenation reaction under high-pressure was studied, several fluorescence-tests for acetonphenone (reactant), phenathroline and pyridon (ligands), iron (acac)3 (catalyst) dissolved in different solvents were acquired to make sure that significant signals of the reaction could be detected and monitored by Raman spectroscopy. The results showed that fluorescence came from two ligands: pyridon and phenanthroline. However, it was possible to detect the signal of the carbonyl group from reactant, acetonphenone. Based on the promising results, the reaction hydrogenation kinetics of acetonphenone into phenanthroline in ACN, in the presence of iron (acac)3, and K2CO3 under high pressure (100 bars) and high temperature (110°C) could be studied by in-situ Raman spectroscopy. Unfortunately, the seals of the studying high-pressure vessel were destroyed by the solvent and the experiment had to be stopped. 

The degradations of beta-carotene, ascorbic-acid and quercetin by exposure to light at room temperature were studied. At the wavelength 532 nm that used in the experiment, all three compounds emitted fluorescence. The relevant signal corresponding to the degradation of beta-carotene could be detected but not monitored due to fluorescence. Whereas, no signals from ascorbic acid and quercetin could be found because fluorescence caused a high base line and all the signals were overlapped by it. The experiments therefore could not be continued further. 
 
Due to fluorescence and the destroyed seals, the degradation and hydrogenation, respective could not be studied further. Raman spectroscopy is a suitable method for hydrogenation reaction because the obtained spectrum can show complete information of a compound. However, it does not work so efficiently in degradation reaction. Otherwise, the method would be developed and validated by using well-known hydrogenation and degradation reactions.

Keywords: Raman spectroscopy, chemical kinetics, hydrogenation under high-pressure, degradation, beta-carotene, ascorbic acid, quercetin.},
  author       = {le, Daphne},
  keyword      = {Raman spectroscopy,chemical kinetics,hydrogenation under high-pressure,degradation,beta-carotene,ascorbic acid,quercetin,analytical chemistry,analytisk kemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Development of Raman spectroscopy methods for the study of chemical kinetics in hydrogenation and degradation reactions},
  year         = {2017},
}