Advancing the Compositional Analysis of Olefin Polymerization Catalysts with High-Throughput Fluorescence Microscopy

To optimize the performance of supported olefin polymerization catalysts, novel methodologies are required to evaluate the composition, structure, and morphology of both pristine and prepolymerized samples in a resource-efficient, high-throughput manner. Here, we report on a unique combination of laboratory-based confocal fluorescence microscopy and advanced image processing that allowed us to quantitatively assess support fragmentation in a large number of autofluorescent metallocene-based catalyst particles. Using this approach, significant inter- and intraparticle heterogeneities were detected and quantified in a representative number of prepolymerized catalyst particles (2D: ≥135, 3D: 40). The heterogeneity that was observed over several stages of slurry-phase ethylene polymerization (10 bar) is primarily attributed to the catalyst particles' diverse support structures and to the inhomogeneities in the metallocene distribution. From a mechanistic point of view, the 2D and 3D analyses revealed extensive contributions from a layer-by-layer fragmentation mechanism in synergy with a less pronounced sectioning mechanism. A significant number of catalyst particles were also found to display limited support fragmentation at the onset of the reaction (i.e., at lower polymer yields). This delay in activity or "dormancy" is believed to contribute to a broadening of the particle size distribution during the early stages of polymerization. 2D and 3D catalyst screening via confocal fluorescence microscopy represents an accessible and fast approach to characterize the structure of heterogeneous catalysts and assess the distribution of their fluorescent components and reaction products. The automation of both image segmentation and postprocessing with machine learning can yield a powerful diagnostic tool for future research as well as quality control on industrial catalysts

Elucidating the Sectioning Fragmentation Mechanism in Silica-Supported Olefin Polymerization Catalysts with Laboratory-Based X-Ray and Electron Microscopy

Strict morphological control over growing polymer particles is an indispensable requirement in many catalytic olefin polymerization processes. In catalysts with mechanically stronger supports, e. g., polymerization-grade silicas, the emergence of extensive cracks via the sectioning fragmentation mechanism requires severe stress build-up in the polymerizing catalyst particle. Here, we report on three factors that influence the degree of sectioning in silica-supported olefin polymerization catalysts. Laboratory-based X-ray nano-computed tomography (nanoCT) and focused ion beam-scanning electron microscopy (FIB-SEM) were employed to study catalyst particle morphology and crack propagation in two showcase catalyst systems, i.e., a zirconocene-based catalyst (i.e., Zr/MAO/SiO2, with Zr=2,2’-biphenylene-bis-2-indenyl zirconium dichloride and MAO=methylaluminoxane) and a Ziegler-Natta catalyst (i.e., TiCl4/MgCl2/SiO2), during slurry-phase ethylene polymerization. The absence of extensive macropores in some of the catalysts’ larger constituent silica granulates, a sufficient accessibility of the catalyst particle interior at reaction onset, and a high initial polymerization rate were found to favor the occurrence of the sectioning pathway at different length scales. While sectioning is beneficial for reducing diffusion limitations, its appearance in mechanically stronger catalyst supports can indicate a suboptimal support structure or unfavourable reaction conditions

Effects of Digested Onion Extracts on Intestinal Gene Expression: An Interspecies Comparison Using Different Intestine Models.

Human intestinal tissue samples are barely accessible to study potential health benefits of nutritional compounds. Numbers of animals used in animal trials, however, need to be minimalized. Therefore, we explored the applicability of in vitro (human Caco-2 cells) and ex vivo intestine models (rat precision cut intestine slices and the pig in-situ small intestinal segment perfusion (SISP) technique) to study the effect of food compounds. In vitro digested yellow (YOd) and white onion extracts (WOd) were used as model food compounds and transcriptomics was applied to obtain more insight into which extent mode of actions depend on the model. The three intestine models shared 9,140 genes which were used to compare the responses to digested onions between the models. Unsupervised clustering analysis showed that genes up- or down-regulated by WOd in human Caco-2 cells and rat intestine slices were similarly regulated by YOd, indicating comparable modes of action for the two onion species. Highly variable responses to onion were found in the pig SISP model. By focussing only on genes with significant differential expression, in combination with a fold change > 1.5, 15 genes showed similar onion-induced expression in human Caco-2 cells and rat intestine slices and 2 overlapping genes were found between the human Caco-2 and pig SISP model. Pathway analyses revealed that mainly processes related to oxidative stress, and especially the Keap1-Nrf2 pathway, were affected by onions in all three models. Our data fit with previous in vivo studies showing that the beneficial effects of onions are mostly linked to their antioxidant properties. Taken together, our data indicate that each of the in vitro and ex vivo intestine models used in this study, taking into account their limitations, can be used to determine modes of action of nutritional compounds and can thereby reduce the number of animals used in conventional nutritional intervention studies

Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts

Kinetics-based differences in the early stage fragmentation of two structurally analogous silica-supported hafnocene- and zirconocene-based catalysts were observed during gas-phase ethylene polymerization at low pressures. A combination of focused ion beam-scanning electron microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy (IR PiFM) revealed notable differences in the distribution of the support, polymer, and composite phases between the two catalyst materials. By means of time-resolved probe molecule infrared spectroscopy, correlations between this divergence in morphology and the kinetic behavior of the catalysts' active sites were established. The rate of polymer formation, a property that is inherently related to a catalyst's kinetics and the applied reaction conditions, ultimately governs mass transfer and thus the degree of homogeneity achieved during support fragmentation. In the absence of strong mass transfer limitations, a layer-by-layer mechanism dominates at the level of the individual catalyst support domains under the given experimental conditions

Silica-magnesium-titanium Ziegler–Natta catalysts. Part II. Properties of the active sites and fragmentation behaviour

In this work, which follows Part I that is dedicated to the precatalyst, we investigate the electronic properties and the accessibility of the Ti active sites in a highly active silica-supported Ziegler–Natta catalyst for industrial polyethylene production, applying a multi-scale, multi-technique approach. Complementary electronic spectroscopies (i.e. Ti K-edge XANES, Ti L2,3-edge NEXAFS and DR UV–Vis-NIR) reveal the coexistence of several titanium phases, whose relative amount depends on the concentration of the alkyl aluminum activator. In addition to β-TiCl3-like clusters and monomeric Ti(IV) sites, which are already present in the precatalyst, isolated Ti(III) sites and α-TiCl3-like clusters are formed in the presence of the activator. Two families of alkylated Ti(III) sites characterized by a different electron density are detected by IR spectroscopy of adsorbed CO, and two types of Ti-acyl species are formed upon CO insertion into the Ti-alkyl bond, characterized by a different extent of η2-coordination. The whole set of data suggests that TiCl3 clusters are preferentially formed at the exterior of the catalyst particles, likely as a consequence of Ti(III) mobility in the presence of strong Lewis acids, in most cases hampering the spectroscopic detection of isolated Ti(III) sites. In contrast, only monomeric Ti(III) sites are formed at the interior of the catalyst particles, characterized by a high electron density evocative of the presence of electron donors in the close proximity (e.g. aluminum alkoxide by-products). These sites are less accessible because of diffusion limitations, and only become visible by surface-sensitive spectroscopic methods (such as Ti L2,3-edge TEY-NEXAFS) upon the fragmentation of the catalyst particles

X-ray nanotomography uncovers morphological heterogeneity in a polymerization catalyst at multiple reaction stages

During olefin polymerization on supported catalysts, the controlledmorphological evolution of the catalyst particle is vital for ensuringoptimal product properties and high catalyst activity. We employednon-destructive hard X-ray holotomography to quantitatively assessthe 3D morphology of multiple silica-supported hafnocene-basedcatalyst particles during the early stages of gas-phase ethylene polymerization.Image processing and pore network modeling revealedclear variations in the dimensions and interconnectivity of pristineparticles’ macropore networks. This, together with apparent differencesin the fragmentation behavior of pre-polymerized particles,suggests that the reactivity and morphological evolution of individualparticles are largely dictated by their unique support and porespace architectures. By minimizing the structural heterogeneityamong pristine catalyst particles, more uniform particle morphologiesmay be obtained. Significant polymerization activity,observed in the particles’ interiors, further implies that appropriatepolymerization conditions and catalyst kinetics can guarantee sufficientlyhigh particle accessibilities and thus more homogeneoussupport fragmentation

Substituted bis-2-indenyl metallocene compounds

The present invention provides a compound according to formula (I): (I) wherein: • R2 is a bridging moiety containing at least one sp2 hybridised carbon atom; • each R4, R4', R7 and R7' are hydrogen or moieties comprising 1-10 carbon atoms, wherein each R4, R4', R7 and R7' are the same; • each R5, R5', R6 and R6' are moieties comprising 1-10 carbon atoms, wherein each R5, R5', R6 and R6' are the same; and • Z is a moiety selected from ZrX2, HfX2, or TiX2, wherein X is selected from the group of halogens, alkyls, aryls and aralkyls. Such compound allows for the preparation of catalyst systems that provide improved olefin reactivity, such as ethylene reactivity, increased molecular weight in olefin polymerisation, such as increased Mw in ethylene polymerisation, and increased comonomer incorporation in copolymerisation reactions of olefins, such as in copolymerisation reactions of ethylene with 1- hexene

1,2-PHENYLENE BRIDGED 1-INDENYL-2-INDENYL METALLOCENE COMPLEXES FOR OLEFIN POLYMERIZATION

The invention relates to a metallocene complex according to formula (I), (I) wherein R1 and R2 are independently selected from H, an alkyl or an aryl group, wherein R3 is a C1 -C10 alkyl group, wherein R' is selected from H, an alkyl group, an aryl group and wherein different R' substituents can be connected to form a ring structure and wherein B is a 1,2 phenylene bridging moiety, which can be optionally substituted, wherein Mt is selected from Ti, Zr and Hf, X is an anionic ligand, z is the number of X groups and equals the valence of Mt minus 2. The invention also relates to a catalyst comprising the reaction product of the metallocene complex and a cocatalyst. Further the invention relates to a (co)polymerisation process of olefinic monomers

Correction to “Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts”

Figure 1 in the original paper shows d-acetonitrile molecules with four bonds between the N and C atoms. This has been corrected here. new figure to demonstrate a direct correlation between the point spectra and IR maps that were recorded on the given particle cross-section. The main text was adapted as follows: Point spectra, recorded of PE- (i.e., A1 and B1 in Figure 5) and silica-rich regions (i.e., A2 and B2 in Figure 5) as well as reference materials (Figures S10.S12), further helped to assign the imaged phases. A correction to the Supporting Information, section S4.B, was made to reflect that all data were recorded in PiF and not PiFM mode: Atomic force microscopy (AFM) topography images, IR maps and IR point spectra were recorded in dynamic noncontact PiF mode (60 accumulations, 500 ms pixel dwell time, 1 cm.1 spectral resolution) using NCHR Au-coated cantilevers (force constant: 40 N/m). The iFM labels in Figures S7.S9 (Supporting Information) were changed to PiF. Furthermore, the methodology for recording an IR map at a specific wavenumber was described in more detail, both in the Supporting Information and in the main text: Prior to acquiring an IR map at a specific wavenumber, a preliminary low-resolution scan was performed. A point spectrum was then taken in the mapped area to determine the wavenumber of the targeted vibrational band (i.e., the wavenumber at which the band has its maximum intensity). The IR PiFM maps were recorded in noncontact mode26 (amplitude ratio set point of 80%, attractive van der Waals force regime; Table S3) at characteristic wavenumbers for the Si.O stretching vibration46,47 (maps recorded at single wavenumbers in the range of 1050.1030 cm.1, (Si.O), Figure 4) and the symmetric C.H bending vibration of the methylene group37.39 (maps recorded at single wavenumbers in the range of 1472.1460 cm-1, (C.H), Figure 4)