Potential Liquid Organic Hydrogen Carrier Research Articles

Measurement of Hydrogen Solubility in Potential Liquid Organic Hydrogen Carriers

Liquid organic hydrogen carriers (LOHC) are potential compounds that can facilitate chemical energy storage and hydrogen logistics using reversible hydrogenation. For the process development, the physical solubility of hydrogen in potential LOHCs is required. In this work, solubility of hydrogen in the potential LOHC systems toluene/methylcyclohexane, N-ethylcarbazole/perhydro-N-ethylcarbazole, and dibenzyltoluene/perhydrodibenzyltoluene was measured using the static isochoric saturation method. The data were measured at low pressures up to 10 bar within the temperature range of (293 to 373) K. Hydrogen solubility in hydrogenated forms of the LOHCs was found to be higher compared to the dehydrogenated forms. Solubility in all substances increased with increasing temperature within the whole temperature range under consideration. The temperature dependency of the Henry coefficient of hydrogen in the solvents was correlated using the Benson and Krause correlation.

Hydrogen Storage: Thermochemical Studies of N-Alkylcarbazoles and Their Derivatives as a Potential Liquid Organic Hydrogen Carriers

Although N-ethylcarbazole is considered as a most promising potential liquid organic hydrogen carriers (LOHC) substance, a major drawback for stationary and particularly mobile applications is its high melting point of 343 K. Study of other possible N-alkylcarbazole-derivatives having lower melting points but keeping a high storage density is of practical importance. This contribution presents thermochemical properties (enthalpy of formation, enthalpy of vaporization, enthalpy of sublimation, and fusion enthalpy) for N-alkylcarbazoles (with alkyl = isopropyl, n-propyl, and n-butyl) derived from experiments in order to investigate the applicability of the carbazole derivatives as potential LOHCs. Additionally, high-level quantum chemical calculations were applied to determine molar enthalpies of formation of the gaseous carbazole derivatives and thus validated the experimental findings. Using a combination of the quantum-chemical calculations with vaporization enthalpy data measured in this work, the stand...

Experimental Study of Solubility of Water in Liquid Organic Hydrogen Carriers

Liquid organic hydrogen carriers (LOHC) are one of the potential candidates to assuage the problem of hydrogen storage. Prior to the storage step, hydrogen produced from electrolysis can contain a significant amount of water, which can lead to the formation of an undesired two-phase system in the LOHC storage tanks. In this work, solubility of water in potential liquid organic hydrogen carriers (toluene, dibenzyltoluene, and N-ethylcarbazol) in their hydrogenated and dehydrogenated forms as well as mixtures of these forms have been measured within the temperature range of (293 to 343) K. The solubility of water in LOHC materials is found to increase with temperature. This effect has been correlated using the Tsonopoulos and Wilson equation. Furthermore, various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy of dissolution were estimated based on the solubility data using the van’t Hoff equation.

Environmental and health impact assessment of Liquid Organic Hydrogen Carrier (LOHC) systems – challenges and preliminary results

This paper presents the first account on the ecotoxicological profile of some potential LOHC structures.

Dehydrogenation Mechanism of Liquid Organic Hydrogen Carriers: Dodecahydro‐N‐ethylcarbazole on Pd(111)

Dodecahydro-N-ethylcarbazole (H12-NEC) has been proposed as a potential liquid organic hydrogen carrier (LOHC) for chemical energy storage, as it combines both favourable physicochemical and thermodynamic properties. The design of optimised dehydrogenation catalysts for LOHC technology requires a detailed understanding of the reaction pathways and the microkinetics. Here, we investigate the dehydrogenation mechanism of H12-NEC on Pd(111) by using a surface-science approach under ultrahigh vacuum conditions. By combining infrared reflection-absorption spectroscopy, density functional theory calculations and X-ray photoelectron spectroscopy, surface intermediates and their stability are identified. We show that H12-NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of C-H bonds is observed within the five-membered ring. Rapid dehydrogenation occurs to octahydro-N-ethylcarbazole (H8-NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H8-NEC proceeds within the six-membered rings. Starting from clean Pd(111), C-N bond scission, an undesired side reaction, is observed above 350 K. By complementing surface spectroscopy, we present a temperature-programmed molecular beam experiment, which permits direct observation of dehydrogenation products in the gas phase during continuous dosing of the LOHC. We identify H8-NEC as the main product desorbing from Pd(111). The onset temperature for H8-NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H8-NEC is observed even above the temperature threshold for H8-NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure.

Thermodynamic Evaluation of Potential Organic Hydrogen Carriers

Thermodynamic Evaluation of Potential Organic Hydrogen Carriers

Homogeneous dehydrogenation of liquid organic hydrogen carriers catalyzed by an iridium PCP complex

The activity of the PCP pincer complex IrH2{C6H3-2,6-(OPBu(t)2)2)}, (3) as a catalyst for the dehydrogenation of the potential liquid organic hydrogen carriers: perhydro-dibenzofuran (4), perhydro-indole (5), N-methyl perhydro-indole (6), 4,4'-bipiperridine (7), 4-amino-methylpiperridine (8), and aminomethylcyclohexane (9) was investigated. Only low levels of dehydrogenation were achieved with 4 at 150 and 200 degrees C except in the presence a hydrogen acceptor, 3,3-dimethyl-1-butene (tbe). At temperatures above 150 degrees C, 3 showed high activity with 5 but only for the release of H2 across the C-N bond. Dehydrogenation of 6 at 150 degrees C was found to release up to 2.9 wt% H2, giving N-methyl tetrahydroindole in 92% yield, but only 7% N-methyl indole. However, efficient dehydrogenation of the aliphatic hydrogens occurred at 200 degrees C giving mixtures that approached a approximately 1:3 equilibrium between N-methyl indole and N-methyl tetrahydroindole at longer reaction times. The pincer catalyst was observed to be effective for the dehydrogenation of 7 and 8 at 200 degrees C but the products polymerize. The catalytic dehydrogenation of 9 was very efficient at 200 degrees C but gave primarily the undesired products dibenzylamine (68%), benzylidenebenzylamine (22%), ammonia and only minor amount of benzonitrile (10%). At 160 degrees C, 85% of the substrate was consumed after 24 h of heating but only a minor amount of cyclohexanecarbonitrile (2%) was detected with the major products being biscyclohexylmethylamine (45%) and cyclohexylmethyl-cyclohexylimine (38%). The nitrile yield is remarkably improved to 97% when the dehydrogenation was carried out at 160 degrees C in the presence of 10 mol% NaOBu(t) but heating the reaction mixtures containing the base to 200 degrees C resulted in the decomposition of the pincer catalyst.