Experimental Investigation of the Axial Liquid Holdup Profile in a Liquid Organic Hydrogen Carrier Dehydrogenation Reactor Using Densitometry

Abstract

In the dehydrogenation of perhydro benzyltoluene, one of the most promising liquid organic hydrogen carrier (LOHC) molecules, in a fixed-bed reactor, hydrogen release induces pronounced volumetric expansion and progressive evaporation of the carrier, leading to a transition from a liquid–solid to a gas–liquid–solid and finally to a gas–solid reaction system. Since the axial liquid holdup profile governs both heat transfer and catalyst stability, quantitative knowledge of the spatial distribution under reactive conditions is essential for process optimization and predictive reactor modeling. However, such data are not available for technically relevant LOHC systems. In the present study, the axially resolved liquid holdup is determined in operando in a fixed-bed LOHC dehydrogenation reactor over a wide range of reaction conditions using a non-destructive densitometric measurement technique. While a pronounced axial decrease in liquid holdup with increasing shell temperature was observed, all experimentally determined liquid holdup values significantly exceeded predictions based on bulk vapor–liquid equilibrium. This discrepancy is attributed to the increased capillary pressure in the pores resulting in condensation of LOHC within the pores. Based on the acquired experimental data, a first empirical correlation for the radially averaged local liquid holdup is proposed, thus providing a first quantitative basis for incorporating realistic liquid holdup profiles into multiphase LOHC reactor models.