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International audience; The acceleration of the development of ethylene oligomerization processes by homogeneous catalysis requires a complete characterization of the catalytic system. This work proposes to use segmented gas-liquid flow in microchannels to achieve high experimental throughput for catalyst testing. Gas-liquid flow was studied in order to validate the microreactor setup. Results showed that bubble and slug lengths vary linearly with the superficial velocities ratio following the Garstecki et al. model [21]. The impact of lateral feed in Taylor flow was explored to mimic the catalyst feed in an oligomerization test. The experiments showed that the volume of the liquid slugs increased proportionally to the additional flow rate, thereby suggesting that the majority of the liquid in the lateral feed is ultimately retained in the liquid slug. A study of mass transfer showed that the volumetric mass transfer coefficient is between 0.27 and 0.55 s−1. These values lead to a Hatta number < 0.5, thus confirming the possibility of conducting the ethylene oligomerization reaction in the chemical kinetic regime. Finally, an ethylene oligomerization test performed in the microreactor showed that the continuous microreactor system can be used for catalyst screening purpose.

International audience; Brought to life more than half a century ago and successfully applied for high-value petrochemical intermediates production, nickel-catalyzed olefin oligomerization is still a very dynamic topic, with many fundamental questions to address and industrial challenges to overcome. The unique and versatile reactivity of nickel enables the oligomerization of ethylene, propylene and butenes into a wide range of oligomers that are highly sought-after in numerous fields to be controlled. Interestingly, both homogeneous and heterogeneous nickel catalysts have been scrutinized and employed to do this. This rare specificity encouraged us to interlink them in this review so as to open up opportunities for further catalyst development and innovation. An in-depth understanding of the reaction mechanisms in play is essential to being able to fine-tune the selectivity and achieve efficiency in the rational design of novel catalytic systems. This review thus provides a complete overview of the subject, compiling the main fundamental/industrial milestones and remaining challenges facing homogeneous/heterogeneous approaches as well as emerging catalytic concepts, with a focus on the last 10 years.

International audience; The reactivity of a phenoxy-imine-ether system (FI)TiCl3/MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization product, 1-hexene (85 wt %, 520-450 kg1-hexene gTi-1 h-1) between 30 and 40 °C, to a moderate polyethylene formation (70-80 wt %, 60-70 kgpolyethylene gTi-1 h-1) at higher reaction temperature (T > 60 °C). Polymerization was investigated based on an original "polymer-to-catalyst" strategy aiming at identifying the active species responsible for this side reaction. Using DSC, SEC and high temperature 13 C NMR analyses, polyethylenes were found to exhibit high molar masses (> 10 5 g mol-1) and a low 1-hexene content (< 1 mol %) at any temperature. Kinetic studies support that trimerization and polymerization species are generated from the catalyst precursor at 40 °C but a parallel process may occur at higher temperature. The increase dispersity to 4.6 at 80 °C suggests a change from single to multisite catalysis. The poor comonomer incorporation ability of the active species is reminiscent of a molecular Ziegler Natta or a bulky postmetallocene catalyst.

International audience; Oligomerization applications still raise numerous issues regarding process optimization as well as new catalyst development. This requires an important testing capacity, which cannot be reached with standard tools and methods (typically stirred tank reactors) in a short time. Using microreactors, which generally allow fast analysis times, is expected to minimize liquid holdup and the duration of experiments. The reaction of interest is the two-phase dimerization of ethylene using a liquid catalyst that is converted into butenes (70-80%), hexenes (20-30%) and heavier products up to C12 (5-10%). Performing this reaction in a microreactor can be challenging as the gas-liquid segmented flow will evolve as a function of the residence time in the reactor, starting from high gas-liquid ratios and long bubbles at the entrance, to a complete disappearance of the gas phase at the outlet when the reactant is totally converted and dissolved in the liquid phase. In order to understand this evolving gas-liquid flow, a hydrodynamic study was conducted in a tubular microreactor (ID: 500 µm, length: 1 m) under the operating conditions of the oligomerization reaction (typically 45°C and 20 bar). A bubble train was generated by introducing ethylene (gas phase) and a solvent (liquid phase) in a T-junction. The injection of the liquid phase catalyst was mimicked by introducing the solvent in a second T-junction, downstream of the generation of the bubble train. The flow generation in the T-junction and the stability of the gas-liquid flow after the second liquid injection were firstly studied. Flow patterns and typical characteristics of the flow (bubble and slug length, bubble velocity, film thickness) were monitored using a camera and image processing techniques. Both the gas and liquid flow rates were varied in the range Q G = 0-500 NmL/h, Q L = 0.1-2 mL/h (corresponding to U G =XXX and UL xxx) in order to represent the evolution of gas-liquid ratio during the reaction and to cover the entire conversion range in our system.This detailed characterization of the flow allows identification of the operating range that is favorable, in terms of hydrodynamics, for the reaction and of the limits of operability of the system

This work presents the epoxidation of camphene employing methyltrioxorhenium(VII) (MTO) as catalyst. The effect of different factors on the formation of camphene oxide with respect to high yield and selectivity was investigated. First, the ratio camphene:MTO:pyrazole:H2O2 was studied in dichloromethane as solvent in order to determine the optimal condition. Moreover, the influence of the Lewis base adduct (tert-butylpyridine, 4,4'-dimethy1-2,2'-bypridine, imidazole or pyrazole) was investigated. The effect of an aqueous oxidant, namely H2O2 and a solid oxidant, namely urea hydrogen peroxide (UHP) was also examined. Finally, the solvent was varied from dichloromethane to chloroform, toluene and nitromethane. Based on the results the optimal conditions for the epoxidation of camphene using MTO as catalyst were determined. The molar ratio camphene:MTO:pyrazole: H2O2 of 100:0.5:10:110 in dichloromethane at room temperature leads after 3 h to 97

This report presents a study of the epoxidation of limonene employing methyltrioxorhenium (MTO) as catalyst. The influence of base ligands, namely t-butylpyridine, 4,4′-dimethyl-2,2′-bipyridine and pyrazole on the catalytic activity was investigated. The choice of the oxidant (H2O2 in water or H2O2 stabilized by urea) was also examined. The effect of the solvent has been studied in order to determine optimal conditions for the epoxidation of (+)-limonene. The best result was obtained when a molar ratio (+)-limonene:MTO:H2O2:t-butylpyridine of 100:0.5:10:150 was used at 25 °C in dichloromethane. 1,2-Limonene oxide was formed with 77% yield and 96% selectivity after 1 h with a TOF of ca. 900 h−1.

The epoxidation of α-pinene employing methyltrioxorhenium as catalyst is examined. The influence of mono- and bidentate Lewis basic additives (e.g. tbutylpyridine, 4,4′-dimethyl-2,2′-bipyridine, and Schiff-bases) is investigated. Additionally the impact of the oxidant (H2O2 in water or urea–hydrogen peroxide (UHP)) on the catalytic performance is studied. The effect of the solvent is also examined in order to determine the optimal conditions for the epoxidation of α-pinene. The best and straightforwardly applicable result is obtained when a ratio α-pinene:MTO:tbutylpyridine:UHP of 200:1:40:600 is applied at 0 °C in nitromethane. In this case, α-pinene oxide is formed with 95% yield after 3 h with a turnover frequency (TOF) of 610 h−1.