Processes for the electrolysis of alkali metal chloride brines

Abstract

Processes are described which include: (a) providing an initial crude alkali metal chloride brine; (b) mixing the initial crude brine with a recirculated brine to form a process brine steam; (c) subjecting the process brine stream to electrolysis to form chlorine gas and an electrolyzed weak brine; and (d) subjecting the electrolyzed weak brine to a post-electrolysis salt enrichment comprising (i) diverting a substream of the electrolyzed weak brine at a post-electrolysis diversion point; (ii) removing water from the substream; (iii) crystallizing salt present in the substream; (iv) separating the crystallized salt from the substream; and (v) introducing the separated salt into the electrolyzed weak brine to form the recirculated brine.

1 . A process comprising: 
 (a) providing an initial crude alkali metal chloride brine;    (b) mixing the initial crude brine with a recirculated brine to form a process brine steam;    (c) subjecting the process brine stream to electrolysis to form chlorine gas and an electrolyzed weak brine; and    (d) subjecting the electrolyzed weak brine to a post-electrolysis salt enrichment comprising (i) diverting a substream of the electrolyzed weak brine at a post-electrolysis diversion point; (ii) removing water from the substream; (iii) crystallizing salt present in the substream; (iv) separating the crystallized salt from the substream; and (v) introducing the separated salt into the electrolyzed weak brine to form the recirculated brine.    
     
     
         2 . The process according to  claim 1 , further comprising a purification selected from the group consisting of purifying the initial brine, purifying the process brine stream, and combinations thereof.  
     
     
         3 . The process according to  claim 2 , wherein the purification comprises precipitating one or more ions selected from the group consisting of Ca, Mg, Fe, Al and mixtures thereof from one or both of the initial brine and the process brine stream; and 
 filtering out the precipitated ions.    
     
     
         4 . The process according to  claim 1 , further comprising subjecting the process brine stream to a purification comprising precipitating one or more ions selected from the group consisting of Ca, Mg, Fe, Al and mixtures thereof; filtering out the precipitated ions; and passing the filtered process brine stream over an ion exchange resin.  
     
     
         5 . The process according to  claim 1 , further comprising purifying the initial brine and purifying the process brine stream.  
     
     
         6 . The process according to  claim 5 , wherein purifying the initial brine comprises precipitating one or more ions selected from the group consisting of Ca, Mg, Fe, Al and mixtures thereof from the initial brine and filtering out the precipitated ions; and wherein purifying the process brine stream comprises precipitating one or more ions selected from the group consisting of Ca, Mg, Fe, Al and mixtures thereof; filtering out the precipitated ions; and passing the filtered process brine stream over an ion exchange resin.  
     
     
         7 . The process according to  claim 1 , further comprising removing at least a portion of any residual chlorine present in the electrolyzed weak brine prior to the salt enrichment.  
     
     
         8 . The process according to  claim 7 , wherein removing at least a portion of any residual chlorine comprises stripping the portion of residual chlorine under a reduced pressure.  
     
     
         9 . The process according to  claim 2 , further comprising removing at least a portion of any residual chlorine present in the electrolyzed weak brine prior to the salt enrichment.  
     
     
         10 . The process according to  claim 5 , further comprising removing at least a portion of any residual chlorine present in the electrolyzed weak brine prior to the salt enrichment.  
     
     
         11 . The process according to  claim 1 , wherein the substream of the electrolyzed weak brine is diverted at a weight ratio of the substream to a remainder of the electrolyzed weak brine of 1:1 to 1:20.  
     
     
         12 . The process according to  claim 1 , further comprising subjecting the initial crude brine to a pre-electrolysis salt enrichment comprising (i) diverting a substream of the initial crude brine at a pre-electrolysis diversion point; (ii) removing water from the substream; (iii) crystallizing salt present in the substream; (iv) separating the crystallized salt from the substream; and (v) reintroducing the separated salt into one or both of the initial crude brine after the pre-electrolysis diversion point and the mixing of the initial crude brine and the recirculated brine.  
     
     
         13 . The process according to  claim 12 , wherein the substream of the initial crude brine is diverted at a weight ratio of the substream to a remainder of the initial crude brine of 5:1 to 1:5.  
     
     
         14 . The process according to  claim 1 , wherein the alkali metal chloride comprises sodium chloride.  
     
     
         15 . The process according to  claim 1 , wherein the electrolysis is selected from membrane electrolysis, diaphragm electrolysis and amalgam electrolysis.  
     
     
         16 . The process according to  claim 1 , wherein the initial crude brine has an alkali metal chloride concentration of at least 14 wt. %.  
     
     
         17 . The process according to  claim 1 , wherein the separated salt is reintroduced at a reintroduction point after the post-electrolysis diversion point.  
     
     
         18 . The process according to  claim 1 , wherein the separated salt is divided into two or more portions and one of the two or more portions is reintroduced at a first reintroduction point after the post-electrolysis diversion point, and another of the two or more portions is reintroduced at a second reintroduction point before the post-electrolysis diversion point.  
     
     
         19 . A process comprising: 
 (a) providing an initial crude sodium chloride brine having a sodium chloride concentration of at least 14 wt. %;    (b) precipitating one or more ions selected from the group consisting of Ca, Mg, Fe, Al and mixtures thereof from the initial brine and filtering out the precipitated ions to form a pre-purified crude brine;    (c) mixing the pre-purified crude brine with a recirculated brine to form a process brine steam;    (d) precipitating one or more ions selected from the group consisting of Ca, Mg, Fe, Al and mixtures thereof from the process brine stream; filtering out the precipitated ions; and passing the filtered process brine stream over an ion exchange resin;    (e) subjecting the filtered, ion-exchanged process brine stream to electrolysis to form chlorine gas and an electrolyzed weak brine;    (f) removing at least a portion of any residual chlorine from the electrolyzed weak brine; and    (g) subjecting the electrolyzed weak brine to a post-electrolysis salt enrichment comprising (i) diverting a substream of the electrolyzed weak brine at a post-electrolysis diversion point; (ii) removing water from the substream; (iii) crystallizing salt present in the substream; (iv) separating the crystallized salt from the substream; and (v) introducing the separated salt into the electrolyzed weak brine to form the recirculated brine.    
     
     
         20 . The process according to  claim 19 , further comprising subjecting the pre-purified crude brine to a pre-electrolysis salt enrichment comprising (i) diverting a substream of the pre-purified crude brine at a pre-electrolysis diversion point; (ii) removing water from the substream; (iii) crystallizing salt present in the substream; (iv) separating the crystallized salt from the substream; and (v) reintroducing the separated salt into one or both of the pre-purified crude brine after the pre-electrolysis diversion point and the mixing of the pre-purified crude brine and the recirculated brine.