Study On The Recovery Of Magnesium Chloride From The Waste Residue Of Triphenylphosphine Synthesis By Grignard Method

Triphenylphosphines(TPP)is an important ligand for homogeneous catalysts used in contemporary petrochemical and fine chemical production,such as the Wilkinson catalyst for the homogeneous catalytic hydrogenation of olefins and the witting reagent for fine chemicals It is not only widely used in petrochemicals and fine chemicals.Triphenylphosphine is also used in the pharmaceutical industry,organic synthesis,analysis and other fields.There are various methods for synthesizing triphenylphosphine.Among them,the triphenylphosphine produced by the Grignard method has been widely used in chemical production,but a large amount of magnesium-containing waste residues will be produced in the production process.The main components are by-products magnesium chloride and organic solvents.If it is directly discharged without treatment,it will waste resources on the one hand and cause pollution to the environment on the other hand.Therefore,we urgently need to find a way to convert waste residue into useful industrial magnesium chloride products.This experiment explores several separation and purification methods currently used in the industries: vacuum distillation,extraction separation,roasting,crystallization,and the integrated methods of vacuum distillation-crystallization.From the two aspects of separation effect and economic cost,the separation and treatment effect of the above five methods on waste residue were analyzed.The experimental results show that: Vacuum distillation and extraction cannot completely separate organic and inorganic salts,and roasting can separate organic and inorganic salts,but magnesium chloride is unstable and easily decomposes into magnesium oxide at high temperatures,which is not conducive to recovery.The magnesium chloride crystal obtained by the crystallization method has a high impurity content and poor solubility,which does not meet the standards of industrial magnesium chloride products.The integrated method of vacuum distillation-crystallization can effectively separate organic and inorganic salts and obtain industrial-grade magnesium chloride products.The TPP synthetic waste residue was treated by water immersion stirring,filtration separation,vacuum distillation,and cooling crystallization.The wasteresidue was characterized by infrared spectroscopy,and the presence of magnesium in the waste residue was determined by chemical selective dissolution.Through single-factor experiments and orthogonal experiments,the optimal process conditions were finally determined:the solid-liquid ratio of 1:20,the water immersion temperature of 75 ?,the stirring time of 30 min,slurry pH of 3,the distillation temperature of 125 ?,the distillation time is 4h,the crystallization temperature is30 ?,and the crystallization time is 2h.Finally,the recovery rate of magnesium chloride reached 81.6%.The magnesium chloride crystals separeted from the waste residue were tested according to international standard methods,all indicators reached industrial-grade magnesium chloride standards.