On-line NMR monitoring of chemical processes [Elektronische Ressource] / Qingxia Gong

Qgong

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2010
• Nombre de lectures: 27
• Langue: Deutsch
• Poids de l'ouvrage: 3 Mo

Extrait

On-line NMR Monitoring of Chemical Processes



Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der RWTH
Aachen University zur Erlangung des akademischen Grades einer Doktorin der
Naturwissenschaften genehmigte Dissertation








vorgelegt von
Qingxia Gong
aus Zhejiang, Volksrepublik China



Berichter: Universitätsprofessor Dr. Dr. h.c. Bernhard Blümich
Prof. Dr. Jürgen Klankermayer


Tag der mündlichen Prüfung: 10.12.2010


Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar.
Contents

1 Introduction ......................................................................................................................... 1

2 Biphasic ionic liquid/CO systems studied by NMR ........................................................ 5 2
2.1 Introduction .................................................................................................................. 5
2.2 Experimental ................................................................................................................ 7
2.2.1 Sample preparation............................................................................................ 7
2.2.2 High-pressure NMR measurements .................................................................. 8
2.3 Results and discussion.................................................................................................. 9
2.3.1 CO impacts on ILs ........................................................................................... 9 2
2.3.2 H impacts on the biphasic IL/CO systems.................................................... 15 2 2
2.4 Conclusions ................................................................................................................ 23

3 On-line monitoring of hydrogenation with supported ionic liquid phase (SILP)
1catalysts by H PHIP-NMR ................................................................................................... 25
3.1 Introduction 25
3.2 Experimental .............................................................................................................. 26
3.2.1 Sample preparation.......................................................................................... 26
3.2.2 PHIP NMR measurements .............................................................................. 27
3.3 Results and discussion................................................................................................ 28
13.3.1 Propene hydrogenation monitored by PHIP enhanced H NMR spectroscopy
.................................................................................................................................. 28
3.3.2 Propene hydrogenation monitored by PHIP enhanced NMR imaging ........... 41
3.4 Conclusions ................................................................................................................ 46

4 Improvement of low-field NMR sensitivity by PHIP..................................................... 47
4.1 Introduction 47
4.2 Experimental .............................................................................................................. 49
4.2.1 Sample preparation.......................................................................................... 49
14.2.2 H NMR measurements................................................................................... 49
4.3 Results and discussion................................................................................................ 51
14.3.1 PHIP enhanced H NMR spectroscopy ........................................................... 51
14.3.2 NH-PHIP enhanced .................................................... 57
4.3 Conclusions ................................................................................................................ 63
i
5 Micromixer performances monitored by mobile NMR................................................. 65
5.1 Introduction ................................................................................................................ 65
5.2 Experimental .............................................................................................................. 68
5.3 Results and discussion................................................................................................ 69
5.3.1 Miscible system studied by NMR spectroscopy ............................................. 69
5.3.2 Immiscible system studied by NMR imaging................................................. 79
5.4 Conclusions 90

6 Summary and outlook....................................................................................................... 93

References ............................................................................................................................... 95
ii
1 Introduction
Nuclear Magnetic Resonance (NMR) is a well-established analytical method widely used
in many different research areas and its use is still expanding. NMR is the most
imformation-rich analytical tool for structural and conformational analysis of molecules in
chemistry, biology, medicine, and material science. On the basis of the techniques
involved in the material characterization such as spectroscopy, relaxometry and diffusion,
NMR parameters like chemical shift, nuclear spin relaxation times, dipolar couplings, and
self-diffusion coefficients can be measured to reveal the fundamental properties of the
analytes. NMR has a great advantage over other analytical methods in producing images
contrasted by different NMR parameters. The NMR images are usually contrasted by
material density. Diffusive and coherent molecular motions can be displayed in a non-
invasive fashion. Variations in molecular order and orientation can be converted to image
contrast too. Chemical composition can be imaged by analysing signal intensities at
different chemical shifts of the object.
Low-field NMR is a technique which receives increasing attention in research and
technology. Low-field NMR uses inexpensive permanent magnets and can be made
mobile. With the development of a novel shim strategy based on the use of movable
permanent magnet blocks, high-resolution spectroscopy and imaging are possible by
portable NMR. The use of low-field NMR promises new applications in well-logging, in
the chemical and material sciences, for analysis of objects of heritage culture, and for food
1quality control which are prohibited by or difficult to perform with high-field machines .
Para-hydrogen induced polarization (PHIP) combined with NMR spectroscopy has
developed into a powerful tool to provide profound insight into the reaction mechanisms
2-19of the catalytic hydrogenation . PHIP produces a dramatic NMR signal enhancement
and thus enable the detection of reaction intermediates and products even if they are
present at low concentrations. As prerequisites for the PHIP effect to occur, the two
hydrogen atoms in a para-hydrogen molecule must be transferred as a pair to non-
equivalent positions upon their addition to a substrate, and the spin-lattice relaxation times
4,10,19of these atoms must be longer than the duration of the catalytic cycle . Two
experimental PHIP procedures are described in the literature: PASADENA (para-
hydrogen and synthesis allow dramatically enhanced nuclear alignment) and ALTADENA
4-6,8,10,19(adiabatic longitudinal transport after dissociation engenders nuclear alignment).
PASADENA experiments are conducted at high field inside the NMR magnet where the
1Chapter 1. Introduction
two polarized protons give rise to anti-phase multiplets in the NMR spectra of reaction
products. In the ALTADENA experiments, the para-hydrogenation reaction is performed
at low field outside the NMR magnet followed by an adiabatic transfer of the
hydrogenated product to the high magnetic field. The ALTADENA spectrum is generally
distinguished by characteristic emission and absorption patterns. It is important to note
that the ALTADENA method not only produces strong non-thermal polarization, but also
leads to the formation of long-lived coherent spin states at low field, in which singlet-state
character still exists and the hyperpolarization is stored for much longer time than the
longitudinal relaxation time.
Recently, an alternative approach to generate PHIP sensitized materials based on
reversible interactions with para-hydrogen which is known as NH-PHIP has been
15,16,20developed . This method involves a temporary association of a substrate and a para-
hydrogen molecule via a suitable transition metal based host, the spontaneous polarization
transfer from parahydrogen derived hydride ligands to the bound substrate via scalar
coupling at low magnetic field, and the fast dissociation of the magnetically labelled
substrate. This process results in the production of non-hydrogenative parahydrogen
induced polarization and is achieved without any chemical modification of the substrate.
This work focuses on providing reliable information details for the optimization of
chemical processes with the use of different aspects of NMR. Due to the non-invasive
nature of t