Aramid polymerization method using carbon dioxide as solvent

Abstract

Disclosed herein is a method for aramid polymerization using carbon dioxide as a solvent, comprising reacting phenylenediamine with benzenedicarbonyl dichloride, wherein an acid-binding agent is added to the reaction system, and liquid carbon dioxide and/or a supercritical carbon dioxide fluid is used as a reaction solvent. The method of the present application is environmentally friendly, saves resources, has low cost, and is safe for production and suitable for industrial production. The polycondensate obtained in the present application has a controllable molecular weight, a good product quality, and an intrinsic viscosity ηinh of 8-9 dl/g. The yield in the aramid condensation stage can reach 98%, and the recovery rate of the aramid condensation solvent is higher than 90%.

1 . A method for aramid polymerization using carbon dioxide as a solvent, comprising
 reacting phenylenediamine with benzenedicarbonyl dichloride,   wherein an acid-binding agent is added to the reaction system, and liquid carbon dioxide, a supercritical carbon dioxide fluid, or both, is used as a reaction solvent.   
     
     
         2 . The method according to  claim 1 , wherein when the liquid carbon dioxide is used as a reaction solvent, the reaction temperature is lower than the critical temperature of CO 2  and higher than the triple-point temperature of CO 2 , and
 during the reaction, a pressure at which the carbon dioxide is maintained in a liquid state at the reaction temperature is maintained.   
     
     
         3 . The method according to  claim 1 , wherein when supercritical carbon dioxide fluid is used as a reaction solvent, the reaction environment is maintained above the critical temperature and the critical pressure of CO 2 , the reaction temperature is higher than 31.1° C., and the reaction pressure is greater than 7.29 MPa. 
     
     
         4 . The method according to  claim 1 , wherein when supercritical carbon dioxide fluid is used as a reaction solvent, the reaction temperature is between 31.1 and 120° C., and the pressure is between 7.29 and 50 MPa. 
     
     
         5 . The method according to  claim 1 , wherein the process using liquid carbon dioxide and supercritical carbon dioxide fluid as reaction solvents, further comprising
 initially controlling the carbon dioxide in a liquid state; then the carbon dioxide becomes supercritical when the heat released from the reaction of phenylenediamine with benzenedicarbonyl dichloride increases the temperature of the solution to exceed the critical temperature of carbon dioxide, and the pressure is also greater than the critical pressure, and continuing to complete the reaction in the supercritical state.   
     
     
         6 . The method according to  claim 1 , wherein molar ratio of the phenylenediamine to the benzenedicarbonyl dichloride is (0.95-1.0):(0.95-1.0). 
     
     
         7 . The method according to  claim 1 , wherein the amount of the acid-binding agent used is 0.95-1.2 times the theoretical stoichiometric amount required to neutralize the generated hydrogen chloride. 
     
     
         8 . The method according to  claim 1 , wherein the acid-binding agent is an organic base, an inorganic base or both. 
     
     
         9 . The method according to  claim 8 , wherein the acid-binding agent is a mixture of the organic base and the inorganic base. 
     
     
         10 . The method according to  claim 9 , wherein when the acid-binding agent is a mixture of the organic base and the inorganic base, the amount of the organic base used is 10-80% of the total amount sufficient to neutralize the generated hydrogen chloride. 
     
     
         11 . The method according to  claim 9 , wherein the inorganic base in the acid-binding agent is an alkali metal, alkaline earth metal carbonate, bicarbonate, or a combination thereof. 
     
     
         12 . The method according to  claim 1 , wherein the phenylenediamine and the benzenedicarbonyl dichloride are separately dissolved in the solvent to prepare a solution containing phenylenediamine and a solution containing benzenedicarbonyl dichloride. 
     
     
         13 . The method according to  claim 12 , wherein the acid-binding agent and the phenylenediamine are co-dissolved in the solvent to prepare a mixture liquid containing acid-binding agent-phenylenediamine-solvent; and
 then the mixture liquid of the acid-binding agent-phenylenediamine-solvent is reacted with the solution containing benzenedicarbonyl dichloride.   
     
     
         14 . The method according to  claim 12 , wherein when the solution containing phenylenediamine is prepared, the amount of the solvent used is 5-50 times the mass of the phenylenediamine; and when the solution containing benzenedicarbonyl dichloride is prepared, the amount of the solvent used is 5-50 times the mass of the benzenedicarbonyl dichloride. 
     
     
         15 . The method according to  claim 1 , wherein the molar ratio of the phenylenediamine to the benzenedicarbonyl dichloride is 1:1. 
     
     
         16 . The method according to  claim 1 , wherein the amount of the acid-binding agent used is 1.01-1.1 times the theoretical stoichiometric amount required to neutralize the generated hydrogen chloride. 
     
     
         17 . The method according to  claim 9 , wherein when the acid-binding agent is a mixture of the organic base and the inorganic base, the amount of the organic base used is 30-60% of the total amount sufficient to neutralize the generated hydrogen chloride.