Alkyl amine borane production and dehydrogenation characteristics

Hydrogen can be used as an environmentally friendly energy carrier. However if it is going to be used as a synthetic fuel there will be some difficulties such as production, storage, reliability and cost. One of the safe options for transportation and storage of hydrogen is chemical storage. In recent years, from boron compounds amine boranes have attracted attention as a hydrogen storage material. The first step out of two for this study was laboratory-scale synthesis studies of n-butylamine borane (NBAB), tert-butylamine borane (TBAB) and ethylenediamine bisborane (EDABB) were parametrically investigated. For the second part of the study, catalytic and non-catalytic dehydrogenation studies of synthesized amine boranes were carried out. The synthesis variables were sodium borohydride concentration, temperature and reaction time and their effect on the production yield and purity were studied. Apart from these variables, solvent type, ambient pH and reactant stoichiometric ratios were also investigated. The best results in synthesis studies as follows 97% purity, 70.4% production efficiency for NBAB at 32.5 °C, 0.15 M SBH/THF (tetrahydrofuran), 2.5 h time, 97% purity 75.1% production efficiency for TBAB at 25 °C, pH 5, nAmin/nSBH 1, 4 h time and 90% purity, 82.5% production efficiency for EDABB at 25 °C, 0.1 M SBH/THF, 4 h time. In the second stage of this study, different dehydrogenation methods including catalytic hydrolysis, thermolysis of NBAB, thermohydrolysis of TBAB and dehydrogenation of EDABB have been applied. Ethylenediamine solvent, which is an ionic solvent different from water and is the main compound of our reagent, was used for dehydrogenation studies of EDABB. Ni-Zr-B-O (40% Ni, 60% Zr by mass) and Pd-Ni-Zr-B-O (5% Pd, 38% Ni and 57% Zr by mass) catalysts were prepared for catalytic dehydrogenation studies by using chemical precipitation and impregnation methods. The hydrolysis of 0.2% by mass amine borane made with 0.05 g Pd-Ni-Zr-B-O catalyst at 55 °C having 98% hydrogen production efficiency in 185 s for TBAB and 99% hydrogen production efficiency in 215 s for EDABB were achieved. Kinetic analyzes were made as a result of the catalytic hydrolysis of TBAB and EDABB. The reaction was determined to be zero order for both catalysts and amine boranes. Moreover, activation energies, enthalpies and entropies of TBAB and EDABB were also calculated for the hydrolysis. In hydrolysis studies with Pd-Ni-Zr-B-O catalyst, activation energies were found as 28.0 kJ.mol-1 and 27.04 kJ.mol-1 for TBAB and EDABB respectively. FTIR, XRD and 11B NMR analyzes were performed to determine the structures and characteristics of the synthesized amine borane compounds. The characteristic and morphological properties of the catalysts used in catalytic studies were investigated by XRD, XPS, multi-point BET and SEM-EDX analyses.