(195b) Separation of Complex Mixtures of Aromatic Isomers and Their Hydrogenated Derivates By Batch-Rectification
Among others, benzyl toluene (H0-BT or Marlotherm LH®) is a promising LOHC with the ability to store up to 6.2 mass% hydrogen in its hydrogenated state (H12-BT) and to withstand even harsh conditions (>300 °C). However, BT is not a pure compound but a mixture of constitutional isomers dependent on the manufacturing process. Additionally, every isomer of H0-BT forms further stable intermediates (mostly isomers of H6-BT) and diastereomeres (of H12-BT) during the hydrogenation reaction. In total, more than 13 stable isomers could be detected in the reaction mixture, which makes the LOHC system a complex multicomponent mixture. The objective is to separate the multicomponent mixture to measure thermo-physical data and to perform further studies on the reaction mechanism.
In this contribution, a batch rectification processes, both in lab scale (2-250 ml) and pilot plant scale (5-20 l), are used to separate the isomeric mixture. Because of the isomers having almost equal vapor pressures, the distillation of this high boiling mixture is performed in a column with up to 40 separation stages and under vacuum conditions. First the H0-BT isomer mixture was distilled. To gain simplified mixtures of hydrogenated intermediates and diastereomeres a partial hydrogenation reaction is performed for each H0-BT isomer separately. The hydrogenated fractions are isolated as well. All separated fractions are analyzed by GC-MS.
The distillation routine presented in this contribution is part of a kinetic study defining a detailed hydrogenation reaction framework of the LOHC system. Pure isomers are used to calibrate a Raman Device to facilitate a non-invasive method for individual compound quantification during the LOHC hydrogenation reaction.