2025 AIChE Annual Meeting

(584ck) Establishing Reaction Kinetics for LiAlH4 Vapor Hydrolysis

Authors

Matthew J. Kale, University of California, Riverside
William Knaeble, University of California at Berkeley
Anthony Dixon, Worcester Polytechnic Institute
Andrew Teixeira, Worcester Polytechnic Institute
Complex Metal hydrides such as alanates (NaAlH4, KAlH4, LiAlH4) and borohydrides (NaBH4, LiBH4, KBH4) have gained interest among researchers due to their high gravimetric and volumetric energy densities, demonstrating the potential of meeting the on-board hydrogen energy targets set by the U.S. Department of Energy. To further increase their hydrogen production potential, alanates and borohydrides can also undergo hydrolysis, effectively compounding the production with gas phase water splitting. While the liquid phase hydrolysis of alanates is well-studied for most alanates, the low-temperature gas-solid hydrolysis of LiAlH4 remains relatively unexplored and presents a unique challenge with the convolution of several kinetic steps and phase transition.

This research is focused on vapor hydrolysis of LiAlH4 in a Zero Length Column (ZLC) reactor to investigate the reaction kinetics and the influence of water vapor exposure on the efficiency of hydrogen release kinetics. The results demonstrate stoichiometric water consumption and hydrogen release that aligns with the reaction 2LiAlH4 + 10H2O -> 8H2 + LiAl2(OH)6.OH.2H2O + LiOH, showing that the evolved hydrogen comes from liberating both the framework and water-bound hydrogen. The rate expression is not an elementary rate order but rather expressed dependence on both solid and vapor reactants, r = k.mαLiAlH4.PβH2O where α = 1 and β =0.57 with rate constant and activation energy of 0.0963 mol.s.kg-1.57.m-2 and 24.7 kJ/mol respectively. The mechanism evaluation is supported by ex situ XRD, XPS and in situ DRIFTS and Raman spectroscopy that reveal the dominance of the double layered hydroxide hydration product. This study aims to provide insight that can help to optimize reaction conditions for maximum hydrogen yield.