A mixed complex soap based grease composition and method for preparation thereof

Abstract

The present invention relates to a mixed complex soap based grease composition comprising a lubricating base oil; a saponifiable material; a metal oxide; an alkali/alkaline metal hydroxide; and a complexing acid. The present invention also discloses a single-step, open kettle, energy-efficient process which gives smooth textured zinc-alkali/alkaline earth metal mixed complex grease composition with relatively low thickener content while still maintaining desired consistency. The zinc-alkali/alkaline earth metal mixed complex grease composition is tailor made to have dropping point in a range of 180° C. to 300° C. comparable to lithium and lithium complex grease composition, have inherent oxidation stability, extreme pressure, anti-wear properties, and water resistance properties. The zinc-alkali/alkaline earth metal mixed complex grease composition shows excellent additive response good mechanical stability, low temperature properties, pumpability, and corrosion resistance.

We claim: 
     
         1 . A zinc-alkali/alkaline earth metal mixed complex grease composition, comprising:
 i) a base oil;   ii) a saponifiable material;   iii) zinc oxide or zinc hydroxide;   iv) an oxide or hydroxide of an alkali or alkaline earth metal;   v) a complexing acid; and   vi) optionally, a performance additive.   
     
     
         2 . The grease composition as claimed in  claim 1 , wherein the base oil is having viscosity in a range of ISO VG 2 to 3200 or a mixture thereof; wherein the base oil is selected from mineral base oils of API groups I-III, synthetic base oils of API group IV, ester base oil, paraffinic base oil, naphthenic base oil, and re-refined base oil; wherein the synthetic base oil is selected from polyalphaolefins (PAO), polyalkyl glycol (PAG), polyol esters, diesters and alkylated aromatics. 
     
     
         3 . The grease composition as claimed in  claim 1 , wherein the base oil is present in a range of 65.0-90.0 wt %; the saponifiable material is present in a range of 8.0-18.0 wt %; the oxide and hydroxide of an alkali and alkaline earth metal is present in a range of 0.20-3.0 wt %; the complexing acid is present in a range of 1.0-5.0 wt %; and the performance additive is present in a range of 0.01-3 wt %. 
     
     
         4 . The grease composition as claimed in  claim 1 , wherein the saponifiable material is a fatty acid selected from 12-hydroxy stearic acid, stearic acid, oleic acid or a mixture thereof; wherein the oxide or hydroxide of an alkali or alkaline earth metal is selected from sodium hydroxide, calcium oxide, calcium hydroxide, hydrated lime, lithium hydroxide, or lithium hydroxide monohydrate; and wherein the complexing acid is a dicarboxylic acid having C3 to C10 selected from malonic acid (C3), succinic acid (C4), glutaric acid (C5), adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9) or sebacic acid (C10); and wherein the performance additive is selected from rust and corrosion inhibitor, metal deactivator, metal passivator, antioxidant, pressure additive, polymer, tackifier, dye, chemical marker, fragrance imparter, anti-wear additive or a combination thereof. 
     
     
         5 . An open kettle single step process for preparing zinc-alkali/alkaline earth metal mixed complex grease composition, the process comprising:
 a) mixing a saponifiable material to a base oil to form a mixture;   b) adding a complexing acid, a zinc oxide and an aqueous solution of oxide or hydroxide of an alkali or alkaline earth metal to the mixture obtained in step a);   c) heating and dehydrating the mixture obtained in step b) with continuous stirring to obtain a solid mass;   d) adding base oil to the solid mass obtained in step c) to form a mixture;   e) cooling the mixture obtained in step d) and optionally adding a performance additive; and   f) homogenizing the mixture obtained in step e) to obtain the mixed complex grease composition.   
     
     
         6 . The process as claimed in  claim 5 , wherein the mixing of step a) is performed at temperature in a range of 25 to 80° C. 
     
     
         7 . The process as claimed in  claim 5 , wherein the heating in step c) is performed in three consecutive steps in a sequence of specified steps, the steps comprising:
 i) heating at temperature in a range of 90-100° C. for 1 hour;   ii) heating at temperature in a range of 130-140° C. for next 1 hour; and   iii) heating at temperature in a range of 165-175° C. for another next 0.5 to 1.0 hours   
     
     
         8 . The process as claimed in  claim 5 , wherein the base oil has viscosity in a range of ISO VG 2 to 3200 or a mixture thereof; wherein the base oil is selected from API group I-III mineral base oils, synthetic base oils of API group IV, ester base oil, paraffinic base oil, naphthenic base oil, and re-refined base oil; wherein the synthetic base oil is selected from polyalphaolefins (PAO), polyalkyl glycol (PAG), polyol esters, diesters and alkylated aromatics. 
     
     
         9 . The process as claimed in  claim 5 , wherein the saponifiable material is a fatty acid selected from 12-hydroxy stearic acid, stearic acid, oleic acid or a mixture thereof; wherein the complexing acid is a dicarboxylic acid having C3 to C10 selected from malonic acid (C3), succinic acid (C4), glutaric acid (C5), adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9) or sebacic acid (C10); wherein the oxide or hydroxide of an alkali or alkaline earth metal is selected from sodium hydroxide, calcium oxide, calcium hydroxide, hydrated lime, lithium hydroxide, or lithium hydroxide monohydrate; and wherein the performance additive is selected from rust and corrosion inhibitor, metal deactivator, metal passivator, antioxidant, pressure additive, polymer, tackifier, dye, chemical marker, fragrance imparter, anti-wear additive or a combination thereof. 
     
     
         10 . The process as claimed in  claim 5 , wherein the base oil is present in a range of 65.0-90.0 wt %; the saponifiable material is present in a range of 8.0-18.0 wt %; the oxide and hydroxide of an alkali and alkaline earth metal is present in a range of 0.20-3.0 wt %; the complexing acid is present in a range of 1.0-5.0 wt %; and the performance additive is present in a range of 0.01-3 wt %.