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Changes in the global bulk and local structures, of three different barium compounds (BaZrO3, BaF2, and BaFCl),were induced by mechanical milling and followed using X-ray powder diffraction (PXRD), subsequent microstructure analysis, and 137Ba solid state NMR spectroscopy. Harder materials like BaZrO3 experience significantly higher structural changes upon milling than softer materials like BaF2. Moreover, soft materials with layered structures, like BaFCl, show a pronounced structural change during the milling process. By combining PXRD and solid state NMR, detailed information on the changes to the global and local structures were obtained, which are of interest for mechanochemical synthesis, mechanically treated catalysts or ionic conductors.
Fenton-like processes using persulfate for oxidative water treatment and contaminant removal can be enhanced by the addition of redox-active biochar, which accelerates the reduction of Fe(III) to Fe(II) and increases the yield of reactive species that react with organic contaminants. However, available data on the formation of non-radical or radical species in the biochar/Fe(III)/persulfate system are inconsistent, which limits the evaluation of treatment efficiency and applicability in different water matrices. Based on competition kinetics calculations, we employed different scavengers and probe compounds to systematically evaluate the effect of chloride in presence of organic matter on the formation of major reactive species in the biochar/Fe(III)/persulfate system for the transformation of the model compound N,N‑diethyl-m-toluamide (DEET) at pH 2.5. We show that the transformation of methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2) cannot serve as a reliable indicator for Fe(IV), as previously suggested, because sulfate radicals also induce PMSO2 formation. Although the formation of Fe(IV) cannot be completely excluded, sulfate radicals were identified as the major reactive species in the biochar/Fe(III)/persulfate system in pure water. In the presence of dissolved organic matter, low chloride concentrations (0.1 mM) shifted the major reactive species likely to hydroxyl radicals. Higher chloride concentrations (1 mM), as present in a mining-impacted acidic surface water, resulted in the formation of another reactive species, possibly Cl2•−, and efficient DEET degradation. To tailor the application of this oxidation process, the water matrix must be considered as a decisive factor for reactive species formation and contaminant removal.
We present a versatile and simple method using electrochemistry for the exclusive functionalization of the edge of a graphene monolayer with metal nanoparticles or polymeric amino groups. The attachment of metal nanoparticles allows us to exploit surface-enhanced Raman scattering to characterize the chemistry of both the pristine and the functionalized graphene edge. For the pristine patterned graphene edge, we observe the typical edge-related modes, while for the functionalized graphene edge we identify the chemical structure of the functional layer by vibrational fingerprinting. The ability to obtain single selectively functionalized graphene edges routinely on an insulating substrate opens an avenue for exploring the effect of edge chemistry on graphene properties systematically.
The use of proton-transfer-reaction mass spectrometry (PTR-MS) for the determination of formaldehyde, ammonia and volatile sulfur organic compounds is described and suggestions are made for the application of stationary PTR-MS in a test laboratory. One advantage of PTR-MS compared to TD-GC-MS (thermal desorption gas chromatography mass spectrome-try) is the faster online measurement. Another advantage is the simultaneous determination of formaldehyde, ammonia, very volatile organic compounds (VVOC) and volatile organic com-pounds (VOC) which normally needs four different kinds of sampling. Coupling the PTR-MS with (multiple) air sample canisters or (multiple) emission test chambers would enable a quick analysis of indoor air and material emissions.
The CCQM-K148.a comparison was coordinated by the BIPM on behalf of the CCQM Organic Analysis Working Group for NMIs and DIs which provide measurement services in organic analysis under the CIPM MRA. It was undertaken as a "Track A" comparison within the OAWG strategic plan. CCQM-K148.a demonstrates capabilities for assigning the mass fraction content of a solid organic compound having moderate molecular complexity, where the compound has a molar mass in the range (75 - 500) g/mol and is non-polar (pKow < −2), when present as the primary organic component in a neat organic solid and where the mass fraction content of the primary component in the material is in excess of 950 mg/g.
Participants were required to report the mass fraction of Bisphenol A present in one supplied unit of the comparison material. Participants using a mass balance method for the assignment were also required to report their assignments of the impurity components present in the material. Methods used by the seventeen participating NMIs or DIs were predominantly based on either stand-alone mass balance (summation of impurities) or qNMR approaches, or the combination of data obtained using both methods. The results obtained using thermal methods based on freezing-point depression methods were also reported by a limited number of participants. There was excellent agreement between assignments obtained using all three approaches to assign the BPA content.
The assignment of the values for the mass fraction content of BPA consistent with the KCRV was achieved by most of the comparison participants with an associated relative standard uncertainty in the assigned value in the range (0.1 - 0.5)%.
Exploratory analysis of hyperspectral FTIR data obtained from environmental microplastics samples
(2020)
Hyperspectral imaging of environmental samples with infrared microscopes is one of the preferred methods to find and characterize microplastics. Particles can be quantified in terms of number, size and size distribution. Their shape can be studied and the substances can be identified. Interpretation of the collected spectra is a typical problem encountered during the analysis. The image datasets are large and contain spectra of countless particles of natural and synthetic origin. To supplement existing Analysis pipelines, exploratory multivariate data analysis was tested on two independent datasets. Dimensionality reduction with principal component analysis (PCA) and uniform manifold approximation and projection (UMAP) was used as a core concept. It allowed for improved visual accessibility of the data and created a chemical two-dimensional image of the sample. Spectra belonging to particles could be separated from blank spectra, reducing the amount of data significantly. Selected spectra were further studied, also applying PCA and UMAP. Groups of similar spectra were identified by cluster analysis using k-means, density based, and interactive manual clustering. Most clusters could be assigned to chemical species based on reference spectra. While the results support findings obtained with a ‘targeted analysis’ based on automated library search, exploratory analysis points the attention towards the group of unidientified spectra that remained and are otherwise easily overlooked.
Working towards a comprehensive understanding of introduction pathways, number, and fate of micro¬plastics in the environment, suitable analytical methods are a precondition. Micro-spectroscopic methods are probably the most widely used techniques. Besides their ability to measure single spectra of a particle or fiber, most modern FTIR- and Raman microscopes are also capable of two-dimensional imaging. This is very appealing to microplastics research because it allows to simultaneously characterize the analytes chemically as well as their size (distribution) and shape.
Two-dimensional imaging on extensive sample areas with FTIR-micros¬copes is facilitated by focal plane array (FPA) detectors resulting in large data sets comprised of up to several million spectra. With numbers too large for manual inspection of each individual spectrum, automated data evaluation is inevitable. Identifying different polymers based on the comparison with known reference spectra (library search) has proven to be a suitable approach. For that purpose, FTIR-spectra of common plastics can be collected to create an individual reference library.
To Supplement this ‘targeted analysis’, looking for known substances via library search, an exploratory approach was tested. Principal component analysis (PCA) proved to be a helpful tool to drastically reduce the size of the data set while maintaining the significant information. Subsequently, cluster analysis was used to find groups of similar spectra. Spectra found in different clusters could be assigned to different polymer types. The variation observed within clusters gives a hint on chemical variability of microplastics of the same polymer found in the sample. Spectra labeled according to the respective cluster/polymer type were used to build a classification model which allowed to quickly predict the polymer type based on the FTIR spectrum. Classification was tested on a second, independent data set and results were compared to the spectral library search procedure.
In der Prozessindustrie findet die optische Spektroskopie (z. B. NIR- und Raman-Spektroskopie) als Online-Analytik zunehmend Anwendung zur Überwachung che-mischer Qualitäts¬attribute in der Produktion. Ihr ganzes Potential entfalten die Methoden aber meist nur in Kombination mit einer aufwendigen, multivariaten Kalibrierung. Diese muss alle relevanten Zustände des Systems abdecken und bedarf einer geeigneten Referenz¬analytik. Moderne instrumentelle Analysengeräte weisen eine hohe Empfind¬lich¬keit und Robustheit auf, sind aber dennoch stark von Fehler und Variabilität der Probennahme beeinflusst, was sich auf die Richtigkeit und Qualität des multivariaten Modells auswirkt.
Diese Probleme lassen sich verringern, indem die Referenzanalytik ebenfalls online erfolgt. Eine mögliche Lösung stellt die hochauflösende NMR-Spektroskopie als quanti¬tative Online-Referenzanalytik dar. Insbesondere kom¬pakte NMR-Spektrometer auf Basis von Permanent¬magneten sind für diesen Zweck geeignet. Ausschlusskriterien für herkömmlicher NMR-Systeme, wie der große Wartungs-aufwand (Kryotechnik) und der Platz¬bedarf, werden damit vermieden.
Im Rahmen des EU-Projekts CONSENS wurde die Nutzung einer Online-Referenz¬analytik mit NMR-Spektroskopie am Beispiel einer industriellen Pilotanlage erfolgreich realisiert. Untersuchungsgegenstand war die kontinuierliche Synthese eines Aus¬gangsstoffs für die pharmazeutische Industrie. Die enthaltenen metallorganischen Verbindungen sind für die bisher genutzte HPLC Analytik unzu-gänglich und die Analyse ausgewählter Proben erfolgte nach dem Quenchen der Lösung oft mit einem großen zeitlichen Abstand zur Probennahme. Konzen-trationswerte auf Basis von Online-NMR-Spektren standen hingegen mit einer zeitlichen Auflösung von drei Spektren pro Minute über den gesamten Reaktionsverlauf hinweg zur Verfügung. Außerdem konnten durch die NMR-Spektroskopie intermediär auftretende Spezies erstmal quantitativ bestimmt und diese Daten für die Kalibrierung eines NIR-Spektrometers genutzt werden.
µ-FTIR spectroscopy is a widely used technique in microplastics research. It allows to simultaneously characterize the material of the small particles, fibers or fragments, and to specify their size distribution and shape. Modern detectors offer the possibility to perform two-dimensional imaging of the sample providing detailed information. However, datasets are often too large for manual evaluation calling for automated microplastic identification. Library search based on the comparison with known reference spectra has been proposed to solve this problem.
To supplement this ‘targeted analysis’, an exploratory approach was tested. Principal component analysis (PCA) was used to drastically reduce the size of the data set while maintaining the significant information. Groups of similar spectra in the prepared data set were identified with cluster analysis. Members of different clusters could be assigned to different polymer types whereas the variation observed within a cluster gives a hint on the chemical variability of microplastics of the same type. Spectra labeled according to the respective cluster can be used for supervised learning. The obtained classification was tested on an independent data set and results were compared to the spectral library search approach.
Der Vortrag zeigt aktuelle Entwicklungen und Betätigungsfelder des Fachbereichs Prozessanalytik zum Thema Automation in der Analytik. Dies Umfasst die Laborautomation am Beispiel der Probenpräparation für die Röntgenfluoreszenzanalyse und moderne Synthesekonzepte in der organischen Chemie. Außerdem wird die Rolle der Prozessanalytik in der kontinuierlichen Produktion thematisier. Als Anschauungsgegenstand dienen die Überwachung einer Hydroformylierung mittels Raman- und NMR-Spektroskopie und der Einsatz eines NMR-Sensors in einer modularen Produktionsanlage im Pilotmaßstab.