Process for the inhibition of scale

Abstract

The present invention is directed to an improved process for inhibiting calcium carbonate scaling in aqueous systems such as that employed in the kraft process for the production of wood pulp. Such an improved process is achieved by the addition to the system of at least one antiscalant comprising at least one monomer unit derived from the group consisting of 1,2-dihydroxy-3-butene, N-(hydroxymethyl) acrylamide, and N-(sulfomethyl) acrylamide, and at least one monomer unit derived from the group consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid, and salts thereof. The present invention further provides a novel class of polymer antiscalants which are polymers comprising a 1,2-dihydroxy-3-butene monomer unit and at least one monomer unit derived from the groups consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid, and salts thereof, with the proviso that said polymers do not contain the monomer unit —(CH 2 —CH═CH—CH 2 —O)—.

We claim:  
     
         1 . A process for treating an aqueous liquid having scale forming salts of calcium therein which comprises adding to said aqueous liquid a scale inhibiting amount of a polymeric antiscalant comprising: 
 (A) 1,2-dihydroxy-3-butene monomer units, and,    (B) at least one monomer unit derived from the group consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid, and salts thereof, with the proviso that said polymeric additive does not include the monomer unit —(CH 2 —CH═CH—CH 2 —O)—.    
     
     
         2 . The process of    claim 1    wherein said aqueous system is at a temperature in the range of from about 100° C. to about 200° C. and a pH in the range of from about 10 to about 14.  
     
     
         3 . The process of    claim 1    wherein said polymeric antiscalant has a weight average molecular weight in the range of from about 1,000 to about 100,000.  
     
     
         4 . The process of    claim 3    wherein said polymeric antiscalant is added to said aqueous system in an amount such there is provided from about 1 ppm to about 200 ppm of additive in the resulting treated aqueous system.  
     
     
         5 . The process of    claim 4    wherein said polymeric antiscalant is derived from a mixture of 1,2-dihydroxy-3-butene and either maleic acid, acrylic acid or a combination of maleic acid and acrylic acid.  
     
     
         6 . The process of    claim 5    wherein said 1,2-dihydroxy-3-butene monomer units are present in an amount in the range of from about 1 mole percent to about 50 mole percent.  
     
     
         7 . The process of    claim 5    wherein said polymeric antiscalant is a terpolymer of 1,2-dihydroxy-3-butene, maleic acid and acrylic acid.  
     
     
         8 . The process of    claim 5    wherein said polymeric antiscalant is a copolymer of 1,2-dihydroxy-3-butene and maleic acid.  
     
     
         9 . In a kraft process for the production of wood pulp which comprises the steps of digesting wood chips in a digesting zone, bleaching the resulting wood pulp in a bleaching zone, and concentrating the separated liquor from the digesting zone in an evaporation zone, the improvement which comprises adding to at least one of said digesting zone, bleaching zone and evaporation zone a polymeric antiscalant in an amount sufficient to inhibit the scale formation therein, said polymeric antiscalant comprising: 
 (A) at least one monomer unit derived from the group consisting of 1,2-dihydroxy-3-butene, N-(hydroxymethyl) acrylamide and N-(sulfomethyl) acrylamide and,    (B) at least one monomer unit derived from the group consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid, and salts thereof.    
     
     
         10 . The process of    claim 9    wherein said polymeric antiscalant is added to the digesting zone.  
     
     
         11 . The process of    claim 9    wherein said polymeric antiscalant is added to the bleaching zone.  
     
     
         12 . The process of    claim 9    wherein said polymeric antiscalant is added to the evaporation zone.  
     
     
         13 . The process of    claim 9    wherein said polymeric antiscalant has a weight average molecular weight in the range of from about 1,000 to about 100,000.  
     
     
         14 . The process of    claim 13    wherein said polymeric antiscalant is added in an amount in the range of from about 1 ppm to about 200 ppm.  
     
     
         15 . The process of    claim 14    wherein said polymeric antiscalant is derived from a mixture of N-(sulfomethyl) acrylamide and either maleic acid, acrylic acid or a combination of maleic acid and acrylic acid.  
     
     
         16 . The process of    claim 15    wherein said N-(sulfomethyl) acrylamide is present in an amount in the range of from about 1 mole percent to about 20 mole percent.  
     
     
         17 . The process of    claim 14    wherein said polymeric antiscalant is derived from a mixture of N-(hydroxymethyl) acrylamide and either maleic acid, acrylic acid or a combination of maleic acid and acrylic acid.  
     
     
         18 . The process of    claim 17    wherein said N-(hydroxymethyl) acrylamide is present in an amount in the range of from about 1 mole percent to about 50 mole percent.  
     
     
         19 . The process of    claim 14    wherein said polymeric antiscalant is derived from a mixture of 1,2-dihydroxy-3-butene and either maleic acid or a combination of maleic acid and acrylic acid.  
     
     
         20 . The process of    claim 19    wherein said 1,2-dihydroxy-3-butene monomer units are present in an amount in the range of from about 1 mole percent to about 50 mole percent.  
     
     
         21 . The process of    claim 19    wherein said polymeric antiscalant is a terpolymer of 1,2-dihydroxy-3-butene, maleic acid and acrylic acid.  
     
     
         22 . The process of    claim 19    wherein said polymeric antiscalant is a copolymer of 1,2-dihydroxy-3-butene and maleic acid.  
     
     
         23 . The process of    claim 21    wherein said terpolymer is 33.3 mole percent 1,2-dihydroxy-3-butene, 33.3 mole percent maleic acid and 33.3 mole percent acrylic acid.  
     
     
         24 . The process of    claim 22    wherein said copolymer is 50 mole percent 1,2-dihydroxy-3-butene and 50 mole percent maleic acid.  
     
     
         25 . Polymers comprising: 
 (A) 1,2-dihydroxy-3-butene monomer units and    (B) at least one monomer unit derived from the groups consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid, and salts thereof, with the proviso that said polymers do not contain the monomer unit   —(CH 2 —CH═CH—CH 2 —O)—.    
     
     
         26 . Polymers of    claim 25    having a weight average molecular weight in the range of from about 1,000 to about 100,000.  
     
     
         27 . Polymers of    claim 25    having a weight average molecular weight in the range of from about 1,000 to about 50,000.  
     
     
         28 . Polymers of    claim 25    wherein the mole percent of (A) is in the range of from about 1 to 50 percent of the total mole percent in the polymer.  
     
     
         29 . Polymers of    claim 25    wherein (B) is derived from maleic acid.  
     
     
         30 . Polymers of    claim 25    wherein (B) is a mixture of maleic acid and acrylic acid.  
     
     
         31 . A polymer of    claim 30    wherein the mole ratio of the terpolymer is 33.3:33.3:33.3.  
     
     
         32 . A polymer of    claim 29    wherein the mole ratio of the copolymer is 50:50.