Sodium borohydride production with trimethyl borate

The aim of this study is to produce sodium borohydride which is an advantageous alkali metal borohydride for storage of hydrogen. The study was carried out in two parts: The first part includes trimethyl borate production and the second part includes sodium borohydride production with trimethyl borate produced in the first part.In the first part, trimethyl borate was produced by using constant amounts of boric acid and calcium chloride in all experiments, but methanol amount was changed between 160-360 ml. The operation temperatures were investigated in four ranges (44-53,5ºC, 53,5-56ºC, 56-62ºC and 62-65ºC) and the samples produced at the different temperature ranges were analyzed to determine trimethyl borate contents by using the method of B2O3 analysis with hydrochloric acid (wet analysis). The same samples were analyzed to determine the functional groups by using FTIR spectrophotometer. Furthermore, the trimethyl borate-methanol azeotrope was purified using calcium chloride and the purified trimethyl borate was obtained. This sample was analyzed by using a gas chromatograph, UV spectrophotometer and FTIR spectrophotometer. According to these methods, trimethyl borate purity was determined as 99,8 % by gas chromatography and 99,99 wt % by UV spectrophotometer. In the last step of trimethyl borate production, recycling of calcium chloride used in the trimethyl borate production experiments for removal of water was investigated. According to this experiment, 23,77 wt % of calcium chloride could be recycled.In the second section, the sodium borohydride was produced by sodium hydride and trimethyl borate in paraffinic oil at different temperatures (206-274°C) and at high argon pressures (330-690 psi). The samples produced at different operating conditions were analyzed to determine the sodium borohydride contents by using the methods of B2O3 analysis with hydrochloric acid (solid analysis) and electrochemical analysis. According to these methods, the efficiency of the sodium borohydride production changed between 49,9-83,5 %. The optimum sodium borohydride production conditions were determined as 240°C, 483 psi, 120 minute and 20 % sodium hydride concentration. Finally, trimethyl borate-methanol azeotrope was used instead of purified trimethyl borate and it is observed that the pressure of the reaction increased in dangerous way with great difficulty to control. Besides, the efficiency of sodium borohydride production was 57 % with trimethyl borate-methanol azeotrope. According to these results, it was concluded that there was no advantage of using trimethyl borate-methanol azeotrope instead of pure sodium borohydride.