Integrated nanoreactor system | EPFL Graph Search

This thesis describes a method that allows the production in parallel of nano-reactor systems whose function is controlled by a remote stimulus. The reactors comprise a nested system of lipid vesicles part of which release their content during a thermotropic phase transition. The integration of all components (substrate and enzyme for instance) in a single element eliminates the need for external manipulation/intervention and therefore renders this nanoscopic system entirely autonomous. The smallest attainable size for vesicles (diameter 20 nm, volume 10-21 L) puts a lower limit to the total volume of the device of about 10-18 L making it ideally suited for manipulating interacting partners at the single molecule level. The proof of principle of individual reactors immobilized on glass is first characterized using confocal microscopy and a fluorescent dye that reports dilution during the release. In a further step, enzymatic reactions were performed and recorded by fluorescence microscopy down to single vesicle level. Initial reaction rates were evaluated and compared between several containers showing a dependency with encapsulated substrate concentration. Using vesicles of several different lipid phase transition temperatures, the process was extended to perform 2 consecutive enzymatic reactions. In addition to confined enzymatic reactions, the system was characterized by fluorescence correlation spectroscopy providing the determination of the concentration of fluorophores and small vesicles incorporated inside individual larger containers. Combination of this method with vesicle microarray technology will permit the simultaneous observation and quantitative analysis of confined (bio)chemical reactions in millions of separated reactors and may find applications as high-throughput screening of single enzyme reaction system. The possibility to perform multiple consecutive biochemical reactions may permit to use this system as artificial cells.

Compact reactor for continuous multi-phase reactions

Martin Grasemann

The objective of this thesis is the development of a compact reactor for continuous three-phase reactions in single-pass configurations. The design is based on a bubble column reactor staged with layers of catalytic material. To make the reactor suitable for reactions with high adiabatic temperature rise such as highly exothermic hydrogenation reactions under solvent free conditions, work focuses on two different aspects of integrated reactor and catalyst design: Preparation and characterization of structured catalyst stages optimized for high intrinsic activity as well as for intense gas-liquid redistribution and mass transfer on each reactor stage Development of heat transfer equipment integrated in the staged bubble column for efficient, quasi continuous in-line removal of process heat. Chapter 3 is dedicated to the preparation and characterization of a structured catalyst for the use in a staged bubble column reactor. Sintered Metal Filters (SMF), a material consisting of metal fibers with a diameter of ~ 20 µm forming thin and highly porous sheets is chosen as support material. The fibers are coated with a 5wt% layer of ZnO grains, leaving the open structure of the SMF material intact. Monodispersed Pd nanoparticles as active phase are deposited on the ZnO surface layer with a total metal loading of 0.2wt%. The resulting Pd/ZnO/SMF catalyst shows high activity in the model hydrogenation reaction of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-butene-2-ol (MBE). Semi-batch autoclave hydrogenations show rates of up to 30 mol/molPds with target product (MBE) yields of up to 96.5%. Activity and selectivity of the Pd/ZnO/SMF catalyst are strongly influenced by Strong Metal Support Interaction (SMSI) between the ZnO support and the deposited Pd nanoparticles. XPS and XRD analysis show the formation of a PdZn alloy already under ambient conditions, decreasing the catalyst activity but, on the other hand, preventing strong catalyst deactivation. The formation of this alloy phase was observed under ambient conditions as well as low temperature reaction conditions, but can also be achieved by high temperature treatment of the catalyst in hydrogen atmosphere. The intrinsic kinetics of the MBY hydrogenation was studied in semi-batch experiments. First order towards hydrogen was found and a Langmuir-Hinshelwood kinetic model was developed, describing the experimental data reasonably well. Chapter 4 describes a compact heat exchange (HEX) element integrated in the SBCR. The cross flow heat exchanger design is based on vertical micro-slits of 0.3mm width, a breadth between 12mm and 40mm and 6mm length as reaction side channel geometry, ensuring a minimum of added reaction volume and small heat transfer distances. The single and two-phase heat transfer performance of the HEX element is studied considering the influence of gas and liquid superficial velocities as well as liquid properties. With one SMF layer placed at the HEX element entrance redispersing gas and liquid phase, heat transfer performance was observed to increase linearly with gas and liquid throughput. The maximum heat transfer performance per reaction volume was determined as ~ 0.5 MW/m3K, obtained for moderate gas and liquid superficial velocities. The hydrodynamics of a bubble column staged only with ZnO/SMF sheets show an narrow residence time distribution (RTD) and negligible backmixing through the catalyst layers. The RTD can be described accurately by a "tanks-in-series" model. The gas-liquid pressure drop through the SMF material is mainly governed by capillary effects and the gas velocity. A semi-empirical model is developed, combining both friction and surface tension effects and predicting the pressure drop through the SMF material with an accuracy of ±10%. In Chapter 5, the novel SBCR based on Pd/ZnO/SMF catalytic stages and the integrated micro-HEX elements are tested in the hydrogenation model reaction of MBY to MBE. The reaction in a loop setup comprising 5 HEX/catalyst stages is shown to be strongly influenced by external mass transfer, resulting in an observed catalyst effectiveness below 65%. Intense gas-liquid mass transfer in the SMF structure leads to high volumetric mass transfer coefficient in the staged bubble column of 1s-1 - 4s-1 and an observed reactor productivity of up to ~ 12000 kg/m3h. This signifies an increase of around two orders of magnitude compared to standard industrial semi-batch equipment. High catalyst densities in the reactor lead to high reactor productivity, but have a detrimental effect on product selectivity. The drop in product yield amounts up to 6% for high catalyst density, but can be decreased to only 0.5% if a 5mm distance ring is inserted between HEX stages to decrease the catalyst loading in the reactor.

EPFL2009

Single molecule detection and fluorescence correlation spectroscopy on surfaces

Kai Hassler

In this thesis a new approach for single molecule detection and analysis is explored. This approach is based on the combination of two well established methods, fluorescence correlation spectroscopy (FCS) and total internal reflection fluorescence microscopy (TIRFM). In contrast to most existing fluorescence spectroscopy techniques, the subject of primary interest in FCS is not the fluorescence intensity itself but the random intensity fluctuation around the mean value. Intensity fluctuations are induced by thermal noise in a minute observation volume, which is in classical FCS the confocal volume of a confocal microscope. E.g. FCS is commonly utilized to investigate diffusion. In this case, diffusing fluorescent molecules entering or leaving the observation volume cause intensity fluctuations, which are analyzed by calculating the temporal autocorrelation of the observed signal. The autocorrelation is a measure for the self-similarity of a signal and contains information about the average fluctuation strength and duration. The confocal observation volume, i.e. the measurement volume that is actually seen by the detector is approximately given by the product of the optical transfer function with the fluorescence exciting intensity distribution of a focused laser beam. To achieve a high signal-to-background ratio a small observation volume is absolutely essential, first of all because the background from e.g. scattered light increases with the size of the observation volume. Second, a small volume assures for a small average number of fluorophores inside the observation volume and therefore for a high fluctuation amplitude i.e. FCS signal. This thesis proposes and discusses an alternative to confocal FCS specially conceived for measurements on surface-bound molecular systems, such as biological receptors or immobilized enzymes. In contrast to confocal FCS, fluorescence is excited within an evanescent field generated by total internal reflection (TIR) of a laser beam at the interface between a microscope coverslip and the sample. This is achieved by focusing the laser beam off-axis at the back focal plane of a high NA oil-immersion objective. The collimated beam that emerges from the objective is incident at an oblique angle at the coverslip-sample interface and totally internal reflected. In contrast to confocal FCS, the generated observation volume is completely confined to the surface and background fluorescence as well as scattered light from the bulk is efficiently suppressed. Our method, called objective-type TIR-FCS in the following, features an increased collection efficiency compared to existing techniques that combine evanescent wave excitation and FCS. Existing techniques use total internal reflection on the surface of a prism to generate an evanescent field. This leads to a configuration where the choice of objectives is limited to air or water-immersion objectives. In our system we use a high NA oil-immersion objective, specially conceived for TIR applications, which collects light efficiently. The collection efficiency is further enhanced by a naturally occurring change of the emission properties of fluorophores close to interfaces between dielectric media. The presence of the interface favors emission into the optically denser medium so that about 60% of the emitted light can be collected. These factors, together with a reduced observation volume lead to a very sensitive method with a high potential for applications in single molecule detection and analysis. The performance of the proposed method was experimentally shown for measurements on molecules subject to Brownian motion and binding to modified coverslips. In particular, it was experimentally shown that objective-type TIR-FCS features high signal-to-background ratio on a single molecule level. In this thesis, concise derivations of analytical expressions for autocorrelation functions for diffusion and most important, the case of ligands reversibly binding to a single and localized binding site are presented. The derived model allows for the quantitative determination of binding rates for a single receptor. We strongly believe that the application of these results in the context of investigations of receptor-ligand binding kinetics will allow for deeper understanding of cellular signaling. Moreover, this thesis discusses the applicability of the proposed method in enzymology. Enzymes, as most proteins are subject to continuous changes of their structure or conformation. These conformational changes are correlated with the function of the enzyme. In the discussed example the enzyme catalyzes an oxidation where the product is fluorescent but the substrate is not. The function of the enzyme i.e. the recurring product formation leads to observable intensity fluctuations. Since function and conformational states are correlated, conformational fluctuations can be investigated by means of FCS as was already shown for confocal FCS. A technique closely related to FCS is fluorescence lifetime spectroscopy (where lifetime refers to the mean lifetime of the electronic excited state). Whereas in FCS the relaxation after random deviations from thermal equilibrium is investigated, relaxation of excited fluorophores towards their electronic ground-state is investigated in lifetime spectroscopy. The technique is used for e.g. discrimination between fluorophores with different lifetimes. Lifetime spectroscopy combined with imaging is used in many domains of life-science, including microarray reading and medical diagnostics. In preliminary work we developed a novel approach to perform lifetime imaging that is based on a multiplexing technique. The proposed method requires no mechanical scanning stage and only a single-point detector. Furthermore, noise is reduced under certain circumstances if the signal is low. Characteristics of this technique as well as advantages and disadvantages are shortly discussed.

EPFL2006

Hydrogénation sélective du 2-butyne-1,4-diol avec des catalyseurs de palladium supportés sur des matériaux filamenteux structurés

Eric Joannet

The principal objective of this thesis is the development of a palladium catalyst supported on woven fabrics of activated carbon fibers (ACF) for the reactions of hydrogenations in liquid phase and the design of multiphase reactors using the characteristics of these structures. This work was focused on Preparation, characterization and optimization of catalysts supported on the woven fabrics of activated carbon fibers; The intrinsic kinetics of the selective hydrogenation of 2-butylene-1,4-diol to 2-butyne-1,4-diol as model reaction; The comparison of the activity of our structured catalyst with that of commercial catalysts; Increase the catalyst concentration in the multiphase reactors with the design of a loop reactor containing a bubble column staged with the fiber fabrics supporting the catalyst, its characterization and the startup of this loop reactor which can operate in continuous or in batch mode. Chapter 4 presents the methods of manufacture of our palladium catalysts supported on woven structures of activated carbon fibers, their reproducibility and their homogeneous deposition. The characteristics of the support such as its handiness, its resistance to mechanical forces, the opening of its surface to liquid flow, its great specific surface area and its homogeneous distribution of micropores are defined there. The deposition of nanoparticules of active phase (0.5-5%mass) is characterized by metal surface obtained (280-87 m2/g), the dispersion of this surface (62.8-19.6%) and the average diameter of the nanoparticles (1.78-5.72 nm). The total degree of initial reduction (before reaction) was confirmed. Chapter 5 is devoted to the study of the reaction of selective hydrogenation of the 2-butyne-1,4-diol (B3) to 2-butylene-1,4-diol (B2) with a commercial palladium catalyst supported on activated carbon powder. A zero value even slightly negative was found for B3 partial order and equal to one for hydrogen. The activity obtained for this catalyst is large (37.1 mol(H2)/h gPd) but its initial selectivity is particularly low (SB3,0 = 76.8 %). Effect of support was tested and highlighted. Two supports (CaCO3 and Al2O3) gave reaction rates approximately half the size of those of the carbon support, but an initial selectivity close to 99 %. In chapter 6, selective hydrogenation in an autoclave with an agitator containing structured catalyst is tested. This reactor is first of all evaluated like a reactor working in kinetic mode for the selected reaction. Kinetics was studied and showed that the fibrous support does not change the orders of reaction compared to the commercial catalyst. Energy of activation of 30 kJ/mol was found in the studied configuration. A variation of the catalytic amount on woven structure was studied and gave a reaction rate of 19.4 (mol(H2)/h gPd) for an initial selectivity of 98 % for the best catalyst (Pd(2%)/ACF). The reuse of this catalyst with an in situ reactivation in hydrazine allowed a stabilization of the activity at 50% of the initial activity after four experiments. A constant Turn Over Frequency (TOF) for catalysts with high deposits (2-5%) was given. An increase in the TOF for the low deposits (0.5% and 1%) was found. This increase in the TOF agrees with a fall of the initial selectivity. The effect of several variables of the reaction such as pressure, temperature and pH of the solution were examined. Within the framework of the variation of pH an initial selectivity of 100% and selectivity during reaction remaining higher than 95% until a conversion of 90 % were obtained. This profit of selectivity was achieved only with the detriment to the reaction rate which decreased by a factor 2.5. Finally, experiments with even less harm to the environment were made without solvent thus allowing the avoidance of purification. The rate of hydrogenation in this configuration is very high (79.2 mol(H2)/(h gPd)). But in this configuration, this increase in activity is not done at the expense of the initial selectivity (98 %). In chapter 7, the increase in the catalyst concentration in the reactor was required for higher productivity. For that purpose, a new concept of reactor was studied. This new reactor is a loop reactor containing a bubble column staged with woven catalytical structure. The pressure drop, the emulsion crossing the bubble column and the RTD were characterized. The reactor, functioning in batch or continuous mode, was studied. The productivity in batch was improved by an order of magnitude due to the increase in the catalytic concentration. A unit worked during 50 hours continuously without deactivation of catalyst providing 160 g of B2 per hour (> 1 tons/year). The reaction led to a conversion of 85% with a selectivity of 96 %.

EPFL2005