Process including a carbonation step

Abstract

The invention relates to a process for the removal of contaminants from a liquor, the process comprising: introducing a metal or ammonium hydroxide into the liquor; introducing the liquor into a reaction vessel; bubbling a carbon dioxide gas comprising at least 25% carbon dioxide through the liquor within the reaction vessel; and separating the precipitate formed by the carbonation of the metal hydroxide from the liquor, the precipitate comprising at least some of the contaminants from the liquor; wherein, on average, the liquor is resident within the reaction vessel for a period of no more than about 60 minutes. The invention also relates to a process for the removal of contaminants from a liquor, the process comprising: introducing a metal or ammonium hydroxide into the liquor and bubbling a carbon dioxide gas comprising at least 25% carbon dioxide through the liquor to fom1 a precipitate by carbonation in a period of no more than about 60 minutes. The carbonation processes may be included in sugar refining or water softening and/or decontamination processes. A use of a carbon dioxide gas comprising at least 25% carbon dioxide in a carbonation process for removing contaminants from a hydroxide-treated liquor is also provided, wherein the process forms a precipitate in period of no more than about 60 minutes.

1 . A process for the removal of contaminants from a liquor, the process comprising:
 introducing a metal or ammonium hydroxide into the liquor;   introducing the liquor into a reaction vessel;   bubbling a carbon dioxide gas comprising at least 50% to 100% carbon dioxide through the liquor within the reaction vessel; and separating the precipitate formed by the carbonatation of the metal or ammonium hydroxide from the liquor, the precipitate comprising at least some of the contaminants from the liquor;   wherein, on average, the residence time is no more than about 60 minutes and wherein the size of the precipitate is controlled by altering the pH of the liquor in the reaction vessel.   
     
     
         2 . A process as claimed in  claim 1 , wherein the size of the precipitate is further controlled by altering the residence time of the liquor in the reaction vessel. 
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . A process as claimed in  claim 1 , wherein flow rate of carbon dioxide gas into the reaction vessel is controlled by monitoring the pH of the liquor. 
     
     
         6 . (canceled) 
     
     
         7 . A process as claimed in  claim 1 , wherein the pH of the liquor within the reaction vessel is from about 3 to about 12. 
     
     
         8 . (canceled) 
     
     
         9 . A process as claimed in  claim 1 , wherein the residence time is controlled by one or more of: (i) the flow rate of the liquor into the reaction vessel; (ii) the working volume of the reaction vessel and its associated pipework; and (iii) the amount of liquor being recycled into the reaction vessel. 
     
     
         10 . A process as claimed in  claim 1 , wherein the pH of the liquor in the reaction vessel is controlled by recycling a portion of the liquor into the reaction vessel. 
     
     
         11 . A process as claimed in  claim 1 , wherein the precipitate is separated from the liquor when it reaches a size of at least about 5 μm. 
     
     
         12 . (canceled) 
     
     
         13 . A process as claimed in  claim 1 , wherein the flow rate of the liquor into the reaction vessel is up to about 120 m 3 /h. 
     
     
         14 . A process as claimed in  claim 1 , wherein the carbon dioxide gas comprises at least about 99% carbon dioxide. 
     
     
         15 . A process as claimed in  claim 1 , wherein the carbon dioxide gas bubbled into the liquor is recycled and reintroduced into the reaction vessel, optionally in combination with fresh carbon dioxide gas. 
     
     
         16 . A process as claimed in  claim 15 , wherein at least 85% of the carbon dioxide bubbled through the liquor is either used in the carbonatation reaction or is recycled. 
     
     
         17 . A process as claimed in  claim 1 , wherein the metal hydroxide is calcium hydroxide. 
     
     
         18 . A process as claimed in  claim 1 , wherein the precipitate formed by the carbonatation of the metal hydroxide is separated from the liquor by filtration. 
     
     
         19 . A process for the removal of contaminants from a liquor, the process comprising: introducing a metal or ammonium hydroxide into the liquor and bubbling a carbon dioxide gas comprising from 50% to 100% carbon dioxide through the liquor to form a precipitate by carbonatation in a period of no more than about 60 minutes wherein the size of the precipitate is controlled by altering the pH of the liquor in the reaction vessel. 
     
     
         20 . (canceled) 
     
     
         21 . A process as claimed in either  claim 19 , wherein the size of the precipitate is further controlled by altering the residence time of the liquor in the reaction vessel. 
     
     
         22 . A process as claimed in either  claim 19 , wherein the carbonatation process takes place in a single reaction vessel. 
     
     
         23 . A sugar refining process comprising a process as claimed in  claim 1 . 
     
     
         24 . A water softening or decontamination process comprising a process as claimed in  claim 1 . 
     
     
         25 . Use of a carbon dioxide gas comprising at least 50% to 100% carbon dioxide in a carbonatation process for removing contaminants from a hydroxide-treated liquor, wherein the process forms a precipitate in a period of no more than about 60 minutes and wherein the size of the precipitate is further controlled by altering the pH of the liquor in the reaction vessel. 
     
     
         26 . Use of a carbon dioxide gas as claimed in  claim 25 , wherein the size of the precipitate is further controlled by altering the residence time of the liquor in the reaction vessel.