Process for the preparation of phenothiazine granules having improved properties

Abstract

A process for the preparation of phenothiazine granules having a narrow particle size distribution, phenothiazine having a purity of at least 98% in liquid form being forced through a means provided with holes and a frequency being applied to the liquid phenothiazine and the liquid phenothiazine emerging through the holes entering a cooling medium having a temperature in the range of from −196 to =120° C. so that the liquid phenothiazine drops thus produced are brought to a temperature below the melting point and said drops are, if required, further solidified in a downstream cooling zone.

1 . A process for the preparation of phenothiazine granules having a narrow particle size distribution, phenothiazine having a purity of at least 98% in liquid form being forced through a means provided with holes and a frequency being applied to the liquid phenothiazine and the liquid phenothiazine emerging through the holes entering a cooling medium having a temperature in the range of from −196 to +120° C. so that the liquid phenothiazine drops thus produced are brought to a temperature below the melting point and said drops are, if required, further solidified in a downstream cooling zone.  
   
   
       2 . The process as claimed in  claim 1 , wherein the means provided with holes is a die plate.  
   
   
       3 . The process as claimed in at least one of the preceding claims, wherein the cooling medium has a temperature in the range of from −40 to +100° C.  
   
   
       4 . The process as claimed in at least one of the preceding claims, wherein the cooling medium used is nitrogen or air.  
   
   
       5 . The process as claimed in at least one of the preceding claims, wherein the cooling medium used is cooled air or cooled inert gas having a temperature in the range of from −40 to +100° C.  
   
   
       6 . The process as claimed in at least one of the preceding claims, wherein the phenothiazine granules prepared have a particle size distribution in the range of from 300 to 3 000 μm, the volume fraction thereof being at least 90%, based on the total volume.  
   
   
       7 . The process as claimed in at least one of the preceding claims, wherein the fine particle fraction having particles of <300 μm is less than 3%, in particular less than 2%.  
   
   
       8 . The process as claimed in at least one of the preceding claims, wherein any fine particle fractions or coarse particle fractions formed are removed by suitable methods.  
   
   
       9 . The process as claimed in at least one of the preceding claims, wherein the bulk density of the phenothiazine granules obtained is in the range of from 720 to 780 kg/m 3 .  
   
   
       10 . The process as claimed in at least one of the preceding claims, wherein the dissolution rate, in acrylic acid, of phenothiazine granules having a particle size fraction in the range of from 1 000 to 1 400 μm up to reaching a concentration of 1.5% is from 5 to 14 minutes.  
   
   
       11 . Phenothiazine granules having a narrow particle size distribution, obtainable by a process of one or more of  claims 1  to  10 .  
   
   
       12 . The use of phenothiazine granules having a narrow particle size distribution as claimed in  claim 11  as additives in oils and lubricants, as a polymerization inhibitor or stabilizer or as pesticides in agriculture.