Neutralization Process

Abstract

The invention relates to a neutralization process in which at least one ethylenically unsaturated carboxylic acid is preneutralized at least partly with a base, wherein the preneutralized solution is divided into at least two part-solutions and at least one part-solution is aftertreated so as to form part-solutions with different degree of neutralization and/or solids content, and also to an apparatus for carrying out the process.

1 . A neutralization process in which at least one ethylenically unsaturated carboxylic acid in solution is preneutralized at least partly with a base, optionally with addition of water, which comprises dividing the preneutralized solution into at least two part-solutions, at least one part-solution being aftertreated to form part-solutions with a different degree of neutralization and/or solids content. 
   
   
       2 . The process according to  claim 1 , wherein the degree of neutralization of the preneutralized solution is increased by adding base. 
   
   
       3 . The process according to  claim 1 , wherein a degree of neutralization of the preneutralized solution is lowered by adding ethylenically unsaturated carboxylic acid. 
   
   
       4 . The process according to  claim 1 , wherein the solids content of the preneutralized solution is lowered by adding water. 
   
   
       5 . The process according to  claim 1 , wherein the aftertreatment is carried out continuously. 
   
   
       6 . The process according to  claim 1 , wherein the preneutralization is carried out continuously. 
   
   
       7 . The process according to  claim 1 , wherein the base is aqueous alkali. 
   
   
       8 . The process according to  claim 6 , wherein the preneutralized solution is recycled partly into the preneutralization. 
   
   
       9 . The process according to  claim 8 , wherein between 25 and 95% of the preneutralized solution is recycled. 
   
   
       10 . The process according to  claim 8 , wherein the recycled preneutralized solution, in the preneutralization, is admixed successively with base and ethylenically unsaturated carboxylic acid. 
   
   
       11 . The process according to  claim 8 , wherein the recycled preneutralized solution, in the preneutralization, is admixed successively with water, bases and ethylenically unsaturated carboxylic acid. 
   
   
       12 . The process according to  claim 7 , wherein the ethylenically unsaturated carboxylic acid has a temperature of from 15 to 25° C. and/or the aqueous alkali has an alkali content of less than 25% by weight and a temperature of from 15 to 30° C. or the aqueous alkali has an alkali content of at least 25% by weight and a temperature of from 30 to 50° C. and/or, if used, the water has a temperature of from 15 to 30° C. 
   
   
       13 . The process according to  claim 1 , wherein at least one metering point for base, ethylenically unsaturated carboxylic acid, and, optional water is designed as a Venturi tube. 
   
   
       14 . The process according to  claim 7 , wherein the aqueous alkali is a sodium hydroxide solution and/or the ethylenically unsaturated carboxylic acid is acrylic acid. 
   
   
       15 . A process for preparing water-absorbing polymers, comprising a neutralization process according to  claim 1 . 
   
   
       16 . An apparatus for continuous neutralization, comprising
 i) a ring line R,   ii) at least one first inlet Z 1  into the ring line R,   iii) at least one second inlet Z 2  into the ring line R,   iv) at least one heat exchanger W in the ring line R, the heat exchanger W being disposed beyond the inlets Z 1  and Z 2  in a flow direction,   v) at least two outlets A n  from the ring line R, the outlets A n  being disposed beyond the heat exchanger W in the flow direction,   vi) at least one inlet ZX n1  and/or ZX n3  in at least one outlet A n ,   vii) a pump P, and   viii) optionally, a vessel B between the heat exchanger W and the outlets A n .   
   
   
       17 . The apparatus according to  claim 16 , wherein the ring line R and/or at least one of the outlets A n  is designed as a Venturi tube at the opening of at least one inlet Z 1 , Z 2 , ZX n1 , or ZX n3.    
   
   
       18 . The process according to  claim 1  wherein the aftertreatment is carried out simultaneously and the preneutralization is carried out continuously. 
   
   
       19 . The process according to  claim 18  wherein the preneutralization solution is recycled partly into the preneutralization.