triethanolamine borate synthesis: Adding trimethyl borate into the reaction bottle62.7g (0.6mol), 74.6g (0.5mol) of triethanolamine and 300g of toluene are slowly heated to reflux for 1 hour at room temperature, then distillate is distilled out under normal pressure (65-100°C) while reaction is carried out, sampling is carried out by GC detection, after the reaction is finished, reduced pressure concentration is carried out until no liquid distillation is carried out, acetonitrile is added for recrystallization, filtration and drying are carried out, 68g of white solid is obtained, HPLC (high performance liquid chromatography) is 98.8%, and the yield is 86.6%.