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Enantioselective resolution processes can be improved by integration of racemization. Applying environmentally friendly enzymatic racemization under mild conditions is in particular attractive. Owing to the variety of enzymes and the progress in enzyme engineering, suitable racemases can be found for many chiral systems. An amino acid racemase (AAR) from P. putida KT2440 is capable of processing a broad spectrum of amino acids at fast conversion rates. The focus of this study is the evaluation of the potential of integrating ARR immobilized on Purolite ECR 8309 to racemize L- or D-methionine (Met) within an enantioselective chromatographic resolution process. Racemization rates were studied for different temperatures, pH values, and fractions of organic co-solvents. The long-term stability of the immobilized enzyme at operating and storage conditions was found to be excellent and recyclability using water with up to 5 vol% ethanol at 20 °C could be demonstrated. Packed as an enzymatic fixed bed reactor, the immobilized AAR can be coupled with different resolution processes; for instance, with chromatography or with preferential crystallization. The performance of coupling it with enantioselective chromatography is estimated quantitatively, exploiting parametrized sub-models. To indicate the large potential of the AAR, racemization rates are finally given for lysine, arginine, serine, glutamine, and asparagine.

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Temperature control in heat exchangers in reacting and non-reacting flows is of great importance for process optimization. In this context, phosphor thermometry is a promising technique for remote planar temperature sensing. The thermometry technique is based on exciting a luminescent material by a laser pulse and analysing the subsequent phosphorescence signal. A particular interesting application is chemical hydrogen storage using liquid organic hydrogen carrier (LOHC) systems. The knowledge of temperature fields is of special interest for the characterisation and understanding of hydrogen release from the carrier liquid. We investigated the luminescence properties of the thermographic phosphor (Sr,Ca)SiAIN3:Eu2+ (“SCASN:Eu2+”) dispersed in different heat transfer fluids, in particular LOHC systems, using a newly developed calibration cell. As heat transfer fluids may be excited to fluorescence by the laser as well, their absorption and florescence behaviour is studied to develop an excitation and detection concept for thermometry. We found strong absorption of the heat transfer fluids from the UV range to a wavelength of about 400 nm. In addition, fluorescence signals were found in the visible wavelength range, which can interfere with the phosphor emissions. These fluorescence signals should therefore be circumvented by utilizing the different luminescence decay times in the chosen detection strategy. For thermometry, the SCASN:Eu2+ particles were excited by a laser sheet of a 532 nm Nd:YAG laser. A spectrometer and photomultiplier tube (PMT) were used to detect the emission spectrum and phosphorescence decay time. Two temperature evaluation strategies were applied, which are based on either the intensity ratio of two spectral emission regions (two-colour laser-induced phosphorescence) or the phosphorescence decay time. The results obtained show an applicable measurement range between 293 K and 598 K for the intensity ratio method with a maximum relative sensitivity of 0.12 % K-1 at 293 K. For the phosphorescence decay time method, the phosphor allows measurements between 423 K and 598 K with a maximum relative sensitivity of 0.56 % K-1 at 598 K.

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