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The field of gas metrology is dealing with the development and improvement of gas analytical methods, as well as production of highly accurate primary reference standards. These are prepared at national metrological institutes (NMI) and represent the highest national level of traceability. Used for certification of secondary standards provided by specialty gas distributors these are very important for a high number of industrial sectors, which have to proof traceability due to legal or regulatory affairs, e.g., natural gas suppliers. Thus, improvements in the production and certification of these mixtures will have a direct influence on gas industry.
Due to its direct correlation to the number of spins within active sample volume quantitative NMR spectroscopy (qNMR) is a highly promising method with absolute comparison abilities in complex systems. Especially for liquefied petroleum gases (LPG) it has the ability of studying the unmodified sample at same conditions like in the cylinder. In contrast to gas chromatography no preparation steps and no changes like evaporation of the sample are necessary.
In this work we show the most recent results of our investigations on highly accurate LPG mixtures provided in constant-pressure piston cylinders. A dynamic pressure-resistant setup allows for sampling and circulation of the samples to ensure a homogeneous withdrawal from the cylinder. This is presented on examples of a commercial multicomponent LPG mixture obtained from specialty gas distributor, as well as two cylinders from the key comparison CCQM-K119 at highest level of international metrology.
During the last years quantitative NMR spectroscopy has become a general method for solving complex problems in science and industry. The opportunity of a calibration-free quantification, related to a simple counting of the nuclear spins in the active volume of the spectrometer represents a key advantage comparing to other analytical techniques. With modern NMR systems detection limits in the lower ppm range on a molar basis are accessible in a reasonable time period, which makes it a promising method for purity assessment, as well as applications in metrological research. First experiments showed that qNMR is suitable for gas analysis with respect to components used for production of primary reference gas mixtures. For this a laboratory setup for high-pressure NMR experiments up to 20 MPa (2900 psi) in fluid and gas phase was built and tested.
In this work we show the determination of the composition of high precision mixtures, consisting of liquid and liquefied hydrocarbons commonly supplied in floating piston cylinders. Therefore an experimental setup was developed allowing sampling, as well as circulation of the mixture within a high-pressure NMR tube by using a concentric tubing assembly. Additionally, a piston-cylinder pressure cell was designed and manufactured allowing wide-range volume displacement. Mainly intended for density variation within supercritical fluid experiments, it can also function as a compression element for further increasing of gas-pressure in the system. Equipped with liquid thermostat and a motor-powered screw drive unit it is designed to operate at pressure levels up to 60 MPa (8700 psi) and temperatures up to 130 °C.
Process monitoring of an intensified continuous production unit with compact NMR spectroscopy
(2016)
Monitoring chemical reactions is the key to chemical process control. Today, mainly optical online methods are applied. NMR spectroscopy has a high potential for direct loop process control. Compact NMR instruments based on permanent magnets are robust and relatively inexpensive analyzers, which feature advantages like low cost, low maintenance, ease of use, and cryogen-free operation. Instruments for online NMR measurements equipped with a flow-through cell, possessing a good signal-to-noise-ratio, sufficient robustness, and meeting the requirements for integration into industrial plants (i.e., explosion safety and fully automated data analysis) are currently not available off the rack. Recently, promising benchtop NMR instruments with acceptable performance came to market and process integrated sensors developed on basis of such laboratory instruments are on their way.
Intensified continuous processes are in focus of current research. Compared to traditional batch processes, these are giving admittance to new and difficult to produce compounds, leading to better product uniformity, and dras-tically reducing the consumption of raw materials and energy. Flexible (modular) chemical plants can produce different products using the same equipment with short down-times between campaigns, and quick introduction of new products to the market. Typically, such plants have smaller scale than big size facilities for production of basic chemicals but are still capable to produce kilograms to tons of specialty products each day. Such flexible (modular) plants can be provided in the size of 20 ft freight containers and represent a promising approach by their ability of easy transfer to production sites as well as the possibility of increasing production capacity by a simple numbering-up-approach.
However, full automation is a prerequisite to realize such benefits of intensified continuous production. In continu-ous flow processes steady automated measurements and tight closed-loop control of the product quality are mandatory. If these are not available, there is a huge risk of producing large amounts of out-of-spec (OOS) prod-ucts. This is addressed in the European Union’s Research Project CONSENS (Integrated Control and Sensing) by development and integration of smart sensor modules for process monitoring and control within such modular plant setups.
Process monitoring of an intensified continuous production unit with compact NMR spectroscopy
(2017)
Monitoring chemical reactions is the key to chemical process control. Today, mainly optical online methods are applied. NMR spectroscopy has a high potential for direct loop process control. Compact NMR instruments based on permanent magnets are robust and inexpensive analysers, which feature advantages like low maintenance, ease of use, and cryogen-free operation. Instruments for online NMR measurements equipped with a flow-through cell, possessing a good signal-to-noise-ratio, robustness, and meeting the requirements for integration into industrial plants (i.e., explosion safety and fully automated data analysis) are currently not available off the rack.
Intensified continuous processes are in focus of current research. Flexible (modular) chemical plants can produce different products using the same equipment with short down-times between campaigns and quick introduction of new products to the market. In continuous flow processes online sensor data and tight closed-loop control of the product quality are mandatory. Otherwise there is a huge risk of producing large amounts of out-of-spec (OOS) products. This is addressed in the European Union’s Research Project CONSENS by development and integration of smart sensor modules for process monitoring and control within such modular plant setups.
The presented NMR module is provided in an explosion proof housing with a module size of 57 x 57 x 85 cm and involves a compact 43.5 MHz NMR spectrometer together with an acquisition unit and a programmable logic controller for automated data preparation (phasing, baseline correction) and evaluation. Indirect Hard Modeling (IHM) was selected for data analysis of the low-field NMR spectra. A set-up for monitoring continuous reactions in a thermostated 1/8” tubular reactor using automated syringe pumps was used to validate the IHM models by using high-field NMR spectroscopy as analytical reference method.
Online-NMR- und -Raman-Spektroskopie – Kombination von PAT-Methoden für mehr Prozessverständnis
(2020)
Die Verbesserung des Prozessverständnisses ist eine notwendige Voraussetzung für die Anwendung von Konzepten wie „Industrial Internet of Things (IIoT)“ oder „Industrie 4.0“. Online-Methoden der Prozessanalytik (PAT) ermöglichen die direkte Verfolgung der ablaufenden Reaktionen innerhalb chemischer und pharmazeutischer Produktionsschritte und können somit einen wichtigen Beitrag für die Entwicklung von neuen, innovativen Prozessführungsstrategien liefern.
Während die Online-Raman-Spektroskopie bereits erfolgreich im industriellen Umfeld zum Einsatz kommt, ist der Entwicklungsstand für die Online-Niederfeld-NMR-Spektroskopie bislang noch nicht ausreichend für einen routinemäßigen Einsatz innerhalb industrieller Produktionsumgebungen. Der hohe Informationsgehalt der NMR-Daten in Verbindung mit einem geringen Kalibrieraufwand macht die Methode sehr interessant für moderne Konzepte flexibler Produktionsanlagen für die Herstellung vieler unterschiedlicher Produkte in wechselnden Kampagnen. Speziell in modularen Produktionskonzepten kann so die Rüstzeit der Prozessanalytik deutlich verkürzt werden.
Am Beispiel der heterogen katalysierten Hydrogenierung von 2-Butin-1,4-diol wird der Einsatz der Kombination von Online-NMR und -Raman-Spektroskopie demonstriert. Dieser Prozessschritt aus der industriellen Synthese des Lösungsmittels Tetrahydrofuran verläuft über ein Zwischenprodukt, welches konkurrierende Reaktionspfade aufweist. Die Kombination von Informationen aus der PAT, sowie von klassischen Prozessgrößen, wie Druck, Temperatur und Durchfluss in einem hoch automatisierten Aufbau erleichtert die Entwicklung und Erprobung von neuen Konzepten für die Prozessführung.