Method of synthesizing diglycerol tetranitrate, and solid rocket motor propellant containing the same

Abstract

Diglyercol tetranitrate is an energetic nitrate ester plasticizer having no freezing point, making the nitrate ester plasticizer especially suited for use in solid rocket motor propellants that are subjected to low temperature storage and operational environments, which can reach as low as −54° C. in temperature. In order to avoid problems associated with fume-off that characterize the conventional synthesis method of making diglycerol tetranitrate, synthesis is performed in a medium including a mixed acid phase and an inert organic phase. The mixed acid phase contains, as ingredients, at least one nitronium ion source and at least one acid having sufficient strength to generate nitronium ions from the nitronium ion source. The nitronium ions in the mixed acid nitrate diglycerol to form diglycerol tetranitrate, which is then received into the organic liquid. The organic liquid, which preferably is a chlorocarbon such as dichloromethane, is insoluble with diglycerol but soluble with diglycerol tetranitrate. The inert organic phase is then treated to neutralize any acid contained in the inert organic phase, and the diglycerol tetranitrate is separated from the inert organic phase.

What is claimed is:  
     
         1 . A method of synthesizing diglycerol tetranitrate, comprising: 
 forming a nitrating medium comprising a mixed acid phase and an inert organic phase, the mixed acid phase comprising, as ingredients, at least one nitronium ion source and at least one acid having sufficient strength to generate nitronium ions from the nitronium ion source, the inert organic phase comprising at least one organic liquid in which diglycerol is insoluble yet in which diglycerol tetranitrate is soluble;    combining the nitrating medium with diglycerol and nitrating the diglycerol in the mixed acid phase to form diglycerol tetranitrate, which is received into the inert organic phase;    separating the inert organic phase having the diglycerol tetranitrate dissolved therein from the mixed acid phase; and    recovering the diglycerol tetranitrate from the inert organic phase.    
     
     
         2 . The method of  claim 1 , further comprising neutralizing any of the acid or nitronium ion source present in the inert organic phase subsequent to said separating of the inert organic phase from the mixed acid phase.  
     
     
         3 . The method of  claim 1 , wherein the nitronium ion source comprises nitric acid and further wherein the acid comprises sulfuric acid.  
     
     
         4 . The method of  claim 3 , wherein a molar ratio of the nitronium ion source to the diglycerol is at least 4:1 and not greater than about 8:1.  
     
     
         5 . The method of  claim 3 , wherein a weight ratio of the nitric and sulfuric acids to water in the mixed acid phase is from about 100:0 to about 80:20.  
     
     
         6 . The method of  claim 3 , wherein the organic liquid comprises at least one organic chlorocarbon.  
     
     
         7 . The method of  claim 6 , wherein the chlorocarbon is dichloromethane.  
     
     
         8 . The method of  claim 3 , wherein a weight ratio of the inert organic phase to the diglycerol tetranitrate is preferably at least 1:1.  
     
     
         9 . The method of  claim 3 , wherein said nitrating of the diglycerol further comprises maintaining the nitrating medium in a range of from about 5° C. to about 20° C.  
     
     
         10 . The method of  claim 3 , further comprising neutralizing any of the acid or nitronium ion source present in the inert organic phase subsequent to said separating of the inert organic phase from the mixed acid phase.  
     
     
         11 . A rocket motor assembly comprising a rocket motor case, a solid propellant grain loaded in the rocket motor case, and a nozzle in operative association with the rocket motor case to receive and discharge combustion products generated upon ignition of the solid propellant grain, the solid propellant grain comprising diglycerol tetranitrate plasticizer.  
     
     
         12 . The rocket motor assembly of  claim 11 , wherein the diglycerol tetranitrate plasticizer is synthesizing by a method comprising: 
 forming a nitrating medium comprising a mixed acid phase and an inert organic phase, the mixed acid phase comprising, as ingredients, at least one nitronium ion source and at least one acid having sufficient strength to generate nitronium ions from the nitronium ion source, the inert organic phase comprising at least one organic liquid in which diglycerol is insoluble yet in which diglycerol tetranitrate is soluble;    combining the nitrating medium with diglycerol and nitrating the diglycerol in the mixed acid phase to form diglycerol tetranitrate, which is received into the inert organic phase;    separating the inert organic phase having the diglycerol tetranitrate dissolved therein from the mixed acid phase; and    recovering the diglycerol tetranitrate from the inert organic phase.