(195b) Separation of Complex Mixtures of Aromatic Isomers and Their Hydrogenated Derivates By Batch-Rectification

Liquid Organic Hydrogen Carriers (LOHCs) are aromatic compounds that allow storing renewable energy through a reversible catalytic hydrogenation reaction. This way it is possible to store and transport hydrogen safely with reasonable density and to overcome the limitations by its high volatility and low volumetric energy density.

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.