Process for treating liquid

Abstract

A process for treating a liquid comprising subjecting a liquid containing, in solution, citric acid as well as a less desirable component having a similar molecular weight to citric acid, to nanofiltration in a filtration step. From the filtration step, a permeate in which the ratio of the concentration of the citric acid to that of the less desirable component is greater than the ratio of the concentration of the citric acid to that of the less desirable component in the solution, is obtained.

1 . A process for treating a liquid, which process comprises 
 subjecting a liquid containing, in solution, citric acid as well as a less desirable component having a molecular weight similar to that of citric acid, to nanofiltration in a filtration step;    obtaining, from the filtration step, a permeate in which the ratio of the concentration of the citric acid to that of the less desirable component is greater than the ratio of the concentration of the citric acid to that of the less desirable component in the solution; and    concentrating the permeate by subjecting it to crystallization without treating the permeate to remove the remaining less desirable component prior to the crystallization.    
     
     
         2 . A process according to  claim 1 , wherein the molecular weight of the less desirable component is within 20% of that of citric acid.  
     
     
         3 . A process according to  claim 2 , wherein the molecular weight of the less desirable component is within 10% of that of citric acid.  
     
     
         4 . A process of  claim 1 , wherein the molecular weight of the less desirable component is less than that of citric acid.  
     
     
         5 . A process according to  claim 4 , wherein the liquid is clarified citric acid fermentation broth so that the permeate is a purified citric acid solution, and the less desirable component is glucose and/or fructose.  
     
     
         6 . A process according to  claim 5 , wherein the filtration step is carried out at a concentration of the citric acid in the broth of 5% -30% by mass, and wherein the filtration is carried out at a temperature of 10° C.-100° C.  
     
     
         7 . A process according to  claim 5 , wherein the clarified citric acid fermentation broth is, before the filtration step, subjected to cation exchange to remove cations therefrom.  
     
     
         8 . A process according to  claim 5 , wherein the citric acid solution from the filtration step is purified by anion exchange and/or by contacting it with activated carbon.  
     
     
         9 . A process according to  claim 5 , which includes concentrating the purified citric acid solution by subjecting it to crystallization.  
     
     
         10 . A process according to  claim 9 , wherein the concentration is effected by passing the purified citric acid solution sequentially through an evaporator; a first crystallizer; a first centrifuge; optionally, a dissolution tank, a second crystallizer and a second centrifuge; and producing mother liquor in the first centrifuge and, when present, in the second centrifuge, with a portion of the mother liquor from the second centrifuge then being recycled to the first crystallizer, while the mother liquor from the first centrifuge is withdrawn.  
     
     
         11 . A process according to  claim 10 , which includes (i) recycling a portion of the mother liquor from the first centrifuge to upstream of the evaporator; and/or (ii) withdrawing at least a portion of the mother liquid from the first centrifuge as a liquid product; and/or (iii) drying and grating at least a portion of the mother liquor from the first centrifuge to obtain a solid citric acid/carbohydrate product; and/or (iv) treating at least a portion of the mother liquor from the first centrifuge, in a recovery step, to recover citric acid for recycle, or citrate salts as product.  
     
     
         12 . A process according to  claim 10 , which includes treating at least a portion of the mother liquid from the first centrifuge, in a recovery step, to recover citric acid, with the citric acid being recycled to upstream and/or downstream of the nanofiltration step, and with treatment in the recovery step comprising one of the following: calcium citrate precipitation by adding lime thereto and redissolving with sulfuric acid; solvent extraction of citric acid utilizing a suitable solvent, followed by re-extraction of citric acid from the solvent into water using concentration differences or heating; ion exchange using a resin which selectively adsorbs citric acid, followed by elution; or chromatography.  
     
     
         13 . A process according to  claim 12 , which includes (i) withdrawing at least a portion of the retentate from the filtration step as a liquid product, and/or (ii) drying or granulating at least a portion of the retentate from the filtration step to obtain a solid citric acid product, and/or (iii) treating at least a portion of the retentate from the filtration step in a citric acid recovery step.  
     
     
         14 . A process for treating a liquid, which process comprises 
 subjecting a liquid containing, in solution, citric acid as well as a less desirable component having a similar molecular weight to citric acid, to filtration in a filtration step;    obtaining, from the filtration step, a permeate in which the ratio of the concentration of the citric acid to that of the less desirable component is greater than the ratio of the concentration of the citric acid to that of the less desirable component in the solution;    concentrating the permeate by subjecting it to crystallization in at least one crystallizer, with citric acid crystals and mother liquor being produced in the crystallizer;    separating the citric acid crystals from the mother liquor;    treating at least a portion of the mother liquor to recover citric acid therefrom; and    recycling at least a portion of the recovered citric acid to upstream and/or down stream of the filtration step.    
     
     
         15 . A process according to  claim 14 , wherein the molecular weight of the less desirable component is within 20% of that of citric acid, and wherein the liquid is clarified citric acid fermentation broth so that the permeate is a purified citric acid solution, and the less desirable component is glucose and/or fructose.  
     
     
         16 . A process according to  claim 15 , wherein the filtration is nanofiltration.  
     
     
         17 . A process according to  claim 15 , wherein recovery of the citric acid is effected by means of chromatography.  
     
     
         18 . A process according to  claim 15 , wherein the molecular weight of the less desirable component is less than that of citric acid.  
     
     
         19 . A process for treating a liquid, which process comprises 
 subjecting a liquid containing, in solution, citric acid as well as a less desirable component having a molecular weight less than that of citric acid, to nanofiltration in a filtration step; and    obtaining, from the filtration step, a permeate in which the ratio of the concentration of the citric acid to that of the less desirable component is greater than the ratio of the concentration of the citric acid to that of the less desirable component in the solution.    
     
     
         20 . The process of  claim 19  wherein the less desirable component is glucose and/or fructose.