Continuous process for crystallizing nitroguanidine

Abstract

A continuous process for forming spheroidal high bulk density nitroguanidine crystals from an aqueous solution of nitroguanidine which contains methylcellulose and partially hydrolyzed poly(vinyl alcohol) as crystal habit modifiers. A saturated aqueous solution of nitroguanidine is formed at a temperature T1 where 70 DEG C.</=T1</=100 DEG C. and crystallization occurs at a lower temperature T2 where 20 DEG C.</=T1-T2</=50 DEG C.

What is claimed is: 
     
       1. A continuous process for recrystallizing nitroguanidine comprising the following steps in order: (1) forming a saturated aqueous nitroguanidine solution at a constant temperature T 1  which is in the range of from about 70° C. to about 100° C. wherein the solution also contains from 0.5 to 2.0 weight percent of methylcellulose and from 0.5 to 2.0 weight percent of a partially hydrolyzed poly(vinyl alcohol);   (2) feeding the solution formed in step (1) into a crystallizer containing a saturated aqueous solution of nitroguanidine which is maintained at a constant temperature of T 2  wherein 20° C.≦T 1  -T 2  ≦50° C. and wherein the methylcellulose and partially hydrolyzed poly(vinyl alcohol) concentrations are the same as in the feed solution;   (3) separating the product spheroidal or ovate nitroguanidine crystals from the supernatant aqueous nitroguanidine solution; and   (4) recycling the separated supernatant aqueous nitroguanidine solution to be used again in step (1).   
     
     
       2. The process of claim wherein the solution in the crystalizer in step (2) is continuously agitated. 
     
     
       3. The process of claim 1 wherein 80° C.≦T 1  ≦100° C. 
     
     
       4. The process of claim 3 wherein 30° C.≦T 1  -T 2  ≦40° C. 
     
     
       5. The process of claim 1 wherein 30° C.≦T 1  -T 2  ≦40° C. 
     
     
       6. The process of claim 1 wherein the concentration of methylcellulose in the aqueous nitroguanidine solutions is from 0.5 to 1.0 percent by weight. 
     
     
       7. The process of claim 6 wherein the concentration of partially hydrolyzed poly(vinyl alcohol) in the aqueous nitroguanidine solutions is from 0.5 to 1.0 percent by weight. 
     
     
       8. The process of claim 1 wherein the concentration of partially hydrolyzed poly(vinyl alcohol) in the aqueous nitroguanidine solutions is from 0.5 to 1.0 percent by weight.