Microwave Process for Preparing Stable Metal Oxide Dispersions

Abstract

Microwave irradiation is used to prepare stable dispersions of small particle metal oxides, such as magnesium oxide and calcium oxide, from a composition prepared from a mixture comprising an oxide, hydroxide or carbonate of the metal, a carrier, a sulfonic or carboxylic acid dispersant, and typically a low MW carboxylic acid and water. Dispersions with an average particle size of one micron or less, often from 1-100 nm, are typically obtained.

What is claimed: 
     
         1 . A process for preparing a stable, free flowing overbased metal oxide dispersion, wherein
 a) 5-80% of a metal hydroxide, metal oxide or metal carbonate   b) 2-15% of a sulfonate or carboxylate dispersant   c) 10-70% of a high boiling hydrocarbon carrier selected from mineral oils, alkylated benzenes, oligomers or polymers of alpha olefins, polycyclic aromatics, alkylated derivatives of polycyclic aromatics and waxes,   d) 0-10% of a C 1-5  carboxylic acid,   e) 0%-30% water   
       and
 f) 0-60% of an organic solvent having a boiling point of less than 280° C., 
 wherein the percentages are by weight based on the total weight of the mixture, are combined to form a preliminary dispersion, which is subjected to microwave irradiation to yield after irradiation a metal oxide dispersion with average particle size of less than 1 micron. 
 
     
     
         2 . The process according to  claim 1  wherein the metal of the hydroxide, oxide or carbonate is selected from Li, Na, K, Cs, Mg, Ca, and Ba. 
     
     
         3 . The process according to  claim 2  wherein the metal of the hydroxide, oxide or carbonate is selected from Mg, Ca, and Ba. 
     
     
         4 . The process according to  claim 3  wherein the metal of the hydroxide, oxide or carbonate is Mg. 
     
     
         5 . The process according to  claim 1 ,  2 ,  3 ,  4  or  5  wherein the sulfonate or carboxylate dispersant is an alkylarylsulfonate or alkylaryl carboxylate dispersant. 
     
     
         6 . The process according to  claim 5  wherein
 a) 5-50% of a metal hydroxide, metal oxide or metal carbonate 
 b) 2-15% of a sulfonate or carboxylate dispersant 
 c) 10-70% of a high boiling hydrocarbon carrier selected from mineral oils, alkylated benzenes, oligomers or polymers of alpha olefins, polycyclic aromatics, alkylated derivatives of polycyclic aromatics and waxes, 
 d) 0-10% of a C 1-5  carboxylic acid, 
 e) 0%-30% water 
 and 
 f) 0-60% of an organic solvent, 
 are combined and heated to temperatures of from about 85° C. to about 220° C. for from about 0.25 to about 5 hours, 
 and volatiles are removed by distillation to form the preliminary dispersion which is then subjected to microwave irradiation. 
 
     
     
         7 . The process according to  claim 6  wherein
 a) 5-40%, typically a metal hydroxide, metal oxide or metal carbonate 
 b) 3-7% of an alkylbenzene sulfonic acid dispersant, 
 c) 10-70% of a high boiling hydrocarbon carrier, 
 d) 1-7% of a C 1-5  carboxylic acid, 
 e) 8%-30% water 
 and 
 f) 10-60%, of an organic solvent with a boiling point of from about 80° C. to about 210° C., are combined, heated and distilled to remove volatiles to form the preliminary dispersion. 
 
     
     
         8 . The process according to  claim 7  wherein the metal hydroxide, metal oxide or metal carbonate is magnesium oxide or magnesium hydroxide, the C 1-5  carboxylic acid is acetic acid, and the organic solvent is xylene or mesitylene and the metal oxide dispersion formed is a magnesium oxide dispersion with an average particle size of less than 1 micron. 
     
     
         9 . The process according to  claim 8  wherein the metal oxide dispersion formed is a magnesium oxide dispersion with an average particle size of from about 1 nm to about 100 nm. 
     
     
         10 . A magnesium oxide dispersion obtained by the process according to  claim 1 . 
     
     
         11 . A lubricant or fuel composition comprising the magnesium oxide dispersion according to any of  claims 1  to  10 . 
     
     
         12 . The composition according to  claim 11  wherein the lubricant or fuel is petroleum based.