Synthesis of borohydride from saline compounds and its catalytic dehydrogenation

Today, the most important necessity of developing and developed countries is energy. Since the fossil energy resources are finite, it is inevitable to seek clean energy resources. Therefore, hydrogen is the most important and noteworthy energy resource which should be taken into account in the future. While there is no problem about production of hydrogen, there are still some problems are existing in the extent of its storage. The metal borohydrides have great significance to store hydrogen among chemical compounds.In this research, metal borohydrides (MBH4) were produced with mechanochemical method by means of reacting NaCl, KBO2 and LiBO2 with MgH2 and B2O3 at high energy infect reactor, having no high temperature and pressure, under inert (Ar) atmosphere and this has not been indicated in the literature yet. Solid phase reactions have been performed with different reaction times, 300, 600, 800 and 1000 minutes and different stoichiometric ratios, 0.65, 1, 1.3. Etilendiamine was used as a solvent for purification of the obtained mixture. The pure NaBH4, KBH4 and LiBH4 were produced and purified MBH4 and by-products was characterized with FT-IR and XRD analyses. Later, activated carbon-supported catalysts whose active center is CoI2 were developed in order to recovery of hydrogen from NaBH4 which has not been tried in the literature. H2 exit rate and strength of catalyses having 20 %, 30 %, 40 % and 45 % CoI2 are determined in dehydrogenation process. SEM-EDS and BET analyses were performed to determine surface characteristics and elemental contents of catalyses. Furthermore, physical strenght and cycle numbers of catalysts which were developed for dehydrogenation and having 20 %, 30 % and 40 % CoI2 were determined. Catalyst that contains 20 % CoI2 was deactivated after 28 experiments (attempts). While activation of 30 % CoI2 and 40 % CoI2 catalysts were continuing, the works were ended after 300 experiments in order to perform analyses. As 45 % CoI2 catalyst was showing dispersion and fracture into base solution in the beginning of studies, the experiments with 45 % CoI2 were not performed. The highest H2 exit rate was determined at 40 % CoI2 catalyst. The activation energies of NaBH4, KBH4 and LiBH4 was calculated by use of catalyst having 40 % CoI2 at 8 different temperatures ranging 20 ? 70 oC. As a result of kinetic studies performed with catalyst having 40 % CoI2 at 20 ? 70 oC, hydrogen exit rates of NaBH4, KBH4, and LiBH4 were identified as 111 - 917 ml/min.g(catalyst), 40.7 - 754.3 ml/min.g(catalyst), 12.7 - 653.9 ml/min.g(catalyst) respectively by means of CoI2 dehydrogenation process whose values are similar to literature data. In these studies, activation energy of NaBH4 was obtained as 36.63 kJ/mole which is lesser than the literature values of 50 kJ/mole. Also, zeroth-order reaction temperature at 20 ? 70 oC was obtained lower than the literature data. Moreover, lower activation energies for KBH4 and LiBH4 were obtained. zeroth-order reaction activation energy of KBH4 was calculated as 25.46 kJ/mole at low temperatures and its first-order reaction activation energy was calculated as 49.13 kJ/mole at high temperature. zeroth-order reaction activation energy of LiBH4 was determined as 53.16 kj/mole subsequently.