Low molecular weight phosphorus-containing polyacrylic acids and use thereof as scale inhibitors in water-carrying systems

Abstract

The invention relates to an aqueous solution of acrylic acid polymers, obtainable by polymerization of acrylic acid in feed mode with peroxodisulfate as initiator in the presence of hypophosphite in water as solvent, wherein (i) water and optionally one or more ethylenically unsaturated comonomers are initially charged, and (ii) acrylic acid in acidic, unneutralized form, optionally one or more ethylenically unsaturated comonomers, aqueous peroxodisulfate solution and aqueous hypophosphite solution are added continuously, and (iii) a base is added on completion of the acrylic acid feed to the aqueous solution, wherein the comonomer content does not exceed 30% by weight, based on total monomer content.

1 . A process for producing an aqueous solution of an acrylic acid polymer by polymerization of acrylic acid in feed mode with peroxodisulfate as initiator in the presence of hypophosphite in water as solvent, wherein:
 (i) water and optionally one or more ethylenically unsaturated comonomers are initially charged, and   (ii) acrylic acid in acidic, unneutralized form, optionally one or more ethylenically unsaturated comonomers, aqueous peroxodisulfate solution and aqueous hypophosphite solution are added continuously, and   (iii) a base is added on completion of the acrylic acid feed to the aqueous solution,   wherein the comonomer content does not exceed 30% by weight, based on total monomer content.   
     
     
         2 - 10 . (canceled) 
     
     
         11 . The process according to  claim 1 , wherein the polymerization is carried out under an inert gas atmosphere. 
     
     
         12 . A method, comprising adding an aqueous solution of an acrylic acid polymer to a water carrying system,
 wherein the aqueous solution of the acrylic acid polymer is obtained by polymerization of acrylic acid in feed mode with peroxodisulfate as initiator in the presence of hypophosphite in water as solvent, wherein:   (i) water and optionally one or more ethylenically unsaturated comonomers are initially charged, and   (ii) acrylic acid in acidic, unneutralized form, optionally one or more ethylenically unsaturated comonomers, aqueous peroxodisulfate solution and aqueous hypophosphite solution are added continuously, and   (iii) a base is added on completion of the acrylic acid feed to the aqueous solution,   and wherein the comonomer content does not exceed 30% by weight, based on total monomer content.   
     
     
         13 . The method according to  claim 12 , wherein said method is a method for inhibiting calcium sulfate scale deposits. 
     
     
         14 . The method according to  claim 12 , wherein said method is a method for inhibiting scale deposits in seawater desalination plants, cooling water systems and boiler feed water systems. 
     
     
         15 . A method, comprising adding an acrylic acid polymer to a water carrying system, wherein the acrylic acid polymer is obtained by polymerization of acrylic acid in feed mode with peroxodisulfate as initiator in the presence of hypophosphite in water as solvent, wherein:
 (i) water and optionally one or more ethylenically unsaturated comonomers are initially charged, and   (ii) acrylic acid in acidic, unneutralized form, optionally one or more ethylenically unsaturated comonomers, aqueous peroxodisulfate solution and aqueous hypophosphite solution are added continuously, and   (iii) a base is added on completion of the acrylic acid feed to the aqueous solution,   and wherein the comonomer content does not exceed 30% by weight, based on total monomer content.   
     
     
         16 . The method according to  claim 15 , wherein said method is a method for inhibiting calcium sulfate scale deposits. 
     
     
         17 . The method according to  claim 15 , wherein said method is a method for inhibiting scale deposits in seawater desalination plants, cooling water systems and boiler feed water systems. 
     
     
         18 . The process according to  claim 1 , wherein the acrylic acid polymer has a weight average molecular weight ranging from 1000 to 2500 g/mol and wherein at most 8% of phosphorous contained in said acrylic acid polymer is present in the form of phosphinate and/or phosphonate groups bound at a polymer chain end. 
     
     
         19 . The process according to  claim 1 , wherein the weight average molecular weight of the acrylic acid polymer ranges from 1200 to 2500 g/mol. 
     
     
         20 . The process according to  claim 1 , wherein the M w /M n  polydispersity index of the acrylic polymer is ≦2.5. 
     
     
         21 . The process according to  claim 1 , wherein the acrylic acid polymer is an acrylic acid homopolymer. 
     
     
         22 . The process according to  claim 1 , wherein the acrylic acid polymer is an acrylic acid copolymer comprising up to 30% by weight, based on all ethylenically unsaturated monomers, of one or more ethylenically unsaturated comonomers selected from the group consisting of methacrylic acid, maleic acid, maleic anhydride, vinylsulfonic acid, allylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid, as polymerized units.