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Quantitative online nuclear magnetic resonance (NMR) spectroscopy was used to study the species distribution in solutions of carbon dioxide (CO2) in aqueous N-methyldiethanolamine (MDEA), and MDEA + piperazine (PIP). The mass fraction of MDEA in the unloaded ternary solution was 0.2, 0.3, and 0.4 g/g. In quaternary solutions, the mass fraction of MDEA was 0.3 g/g, and that of PIP was 0.1 g/g. The temperature ranged from 293 K to 333 K, and the overall CO2 loading was up to 1.4 molCO2 /molamine. For the measurements, a special apparatus was used that allowed the mixtures to be prepared gravimetrically and applied pressures up to 25 bar to keep the CO2 in solution. It was coupled to a 400 MHz NMR spectrometer by heated capillaries. Using both 1H and 13C NMR spectroscopy, quantitative information on the concentrations of the following species was obtained: amines, carbamates, bicarbonate, and CO2. Because of the fast proton transfer between molecular and protonated amines, only the sum of their concentrations can be determined. Furthermore, a byproduct was observed and quantified. The experimental data were used to develop a thermodynamic model of the studied electrolyte solutions, based on the extended Pitzer G E-model. In the model development, vapor−liquid equilibrium (VLE) data from the literature also were included. The model describes both the species distribution and the VLE of the studied mixtures. The properties of the quaternary system are predicted from information on the subsystems.

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Quantitative 13 C NMR spectroscopy was used to investigate the complex chemical equilibria in ternary liquid mixtures of formaldehyde-water-methanol at temperatures between 298 and 383 K. In these mixtures, formaldehyde is predominantly bound in methylene glycol, poly-(oxymethylene) glycols, hemiformal, and poly(oxymethylene) hemiformals, which are formed by a series of oligomerization reactions. The present study is the first in which data on the species distribution in the studied technically important ternary system is reported. It complements previous work in which the focus was on the binary systems formaldehyde-water and formaldehyde-methanol. It also extends the temperature range in which data are available, which was previously limited by the fact that all experiments were carried out in batch cells under ambient pressure. In the present experimental study, a pressurized NMR flow cell was used for the first time. The results from the present study were obtained independently in two different laboratories with different NMR techniques and instruments. Details on the experimental procedures are presented. A comparison of the two data sets shows excellent agreement. The experimental results are compared to predictions from a recently published physicochemical model that aims at the description of vapor-liquid equilibria in the studied mixtures. The results suggest that some model parameters should be revised if the model is to be applied to quantitatively predict liquid-phase compositions (e.g., the distribution of formaldehyde to different species) in the studied ternary system.

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Monitoring specific chemical properties is the key to chemical process control. Today, mainly optical online methods are applied, which require time- and cost-intensive calibration effort. NMR spectroscopy, with its advantage being a direct comparison method without need for calibration, has a high potential for enabling closed-loop process control while exhibiting short set-up times. Compact NMR instruments make NMR spectroscopy accessible in industrial and rough environments for process monitoring and advanced process control strategies. We present a fully automated data analysis approach which is completely based on physically motivated spectral models as first principles information (indirect hard modeling-IHM) and applied it to a given pharmaceutical lithiation reaction in the framework of the European Union's Horizon 2020 project CONSENS. Online low-field NMR (LF NMR) data was analyzed by IHM with low calibration effort, compared to a multivariate PLS-R (partial least squares regression) approach, and both validated using online high-field NMR (HF NMR) spectroscopy. Graphical abstract NMR sensor module for monitoring of the aromatic coupling of 1-fluoro-2-nitrobenzene (FNB) with aniline to 2-nitrodiphenylamine (NDPA) using lithium-bis(trimethylsilyl) amide (Li-HMDS) in continuous operation. Online 43.5 MHz low-field NMR (LF) was compared to 500 MHz high-field NMR spectroscopy (HF) as reference method.