Apparatus and process for electrodialysis of salts

A process for converting an incoming feed of a salt of a monovalent cation and a low molecular weight monovalent weak acid anion into an acidified product stream reduced in its monovalent cation content, said process comprising the steps of:

• subjecting the feed to nanofiltration to obtain a filtrate having a total divalent metal content which is less than about 25 parts per million;
• passing the filtrate through a salt/acid compartment of a two compartment electrodialysis cell containing at least a bipolar membrane and a cation membrane, said bipolar membrane having a cation side and an anion side, said salt/acid compartment being located between said cation selective side of the bipolar membrane and a cation membrane, the other of said two compartments being a base compartment coupled in a base loop;
• supplying a liquid including water to the base compartment of the cell, said base compartment being located between said anion side of the bipolar membrane and a cation membrane;
• passing a direct current through the electrodialysis cell for causing an acidification of the feed salt and the concurrent transport of the monovalent cation to the base loop;
• producing a base product through a combination of the transported cation with a hydroxyl ion generated by the bipolar membrane in the base loop;
• maintaining a pH in the base loop in the range of 7 to about 13.5;
• and
• withdrawing the acidified feed and the base products.

A process for converting an incoming feed stream of a salt with a monovalent cation and a low molecular weight monovalent anion into an acid product stream and a base product stream, said process comprising the steps of:

• (a) subjecting the incoming feed stream to nanofiltration so as to obtain a filtrate having a total divalent metal content which is less than about 25 parts per million;
• (b) passing the filtrate of step (a) through a salt compartment of a three compartment electrodialysis cell containing at least a bipolar membrane, a cation membrane, and an anion membrane, said bipolar membrane having a cation side and an anion side, said salt compartment being located between the cation membrane and the anion membrane, the other two compartments of said three electrodialysis cell being an acid cell, and a base cell coupled in a base loop;
• said acid compartment being located between said cation side of the bipolar membrane and the anion membrane and said base compartment being located between said anion selective side of the bipolar membrane and a cation membrane;
• (c) supplying a liquid including water to the acid and base compartment of the cell;
• (d) passing a direct current through the electrodialysis cell for causing a conversion of at least a portion of the feed salt into its acid and base components;
• (e) maintaining a pH in the base loop in the range of 7 to about 13.5;
• and
• (f) withdrawing the feed depleted in its salt content, the acid and the base product.

A process for converting an incoming feed of a salt of a monovalent cation and a weak acid anion into an acidified product stream which is reduced in its monovalent cation content, said process comprising the steps of:

• (a) obtaining an input feedstream which is freed of suspended solids;
• (b) passing the feed of step (a) through a salt/acid compartment of a two compartment electrodialysis cell containing at least a bipolar membrane and two cation membranes, said bipolar membrane having a cation side and an anion side, said salt/acid compartment being located between said cation side of the bipolar membrane and one of said cation membranes, the other of said two compartments being a base compartment coupled in a base loop, said base compartment being located between said anion side of the bipolar membrane and the other of said cation membranes;
• (c) supplying a liquid including water to the base compartment of the cell, said base compartment having an output stream in communication with an ion exchange column in said base loop, said column being packed with a material capable of removing multivalent cations that may enter the base loop;
• (d) passing a direct current through the electrodialysis cell for causing an acidification of the feed salt and a concurrent transport of monovalent cations to the base loop;
• (e) producing a base product through a combination of the transported cation with a hydroxyl ion generated by the bipolar membrane in the base loop;
• and
• (f) withdrawing the acidified feed and the base product.

A process for converting an incoming feed of a salt of a weak base monovalent cation and an anion into a basified product stream which is reduced in its anion content, said process comprising the steps of:

• (a) obtaining a feed which is free of suspended solids;
• (b) passing the feed through a salt/base compartment of a two compartment electrodialysis cell containing at least a bipolar membrane and an anion membrane, said bipolar membrane having a cation selective side and an anion selective side, said salt/base compartment being located between said anion selective side of the bipolar membrane and an anion membrane;
• said salt/base compartment being coupled in a base loop, the other of said two compartments being an acid compartment, said salt/base compartment being in communication with an ion exchange column capable of removing the multivalent cations that may enter the acid loop;
• (c) supplying a liquid including water to the acid compartment of the cell, said acid compartment being located between said cation selective side of the bipolar membrane and an anion membrane;
• (d) passing a direct current through the electrodialysis cell for causing a basification of the feed salt and a concurrent transport of the anion to the acid loop;
• (e) producing an acid product through a combination of the transported anion with a hydrogen ion generated by the bipolar membrane in the acid loop;
• and
• (f) withdrawing the basified feed and the acid product.

A process for converting an incoming feed of a salt of a monovalent cation and an anion into an acid product stream and a base product stream, said process comprising the steps of:

• (a) obtaining a feed which is free of suspended solids;
• (b) passing the filtrate of step (a) through a salt compartment of a three compartment electrodialysis cell containing at least a bipolar membrane, a cation membrane, and an anion membrane, said bipolar membrane having a cation selective side and an anion selective side, said salt compartment being located between the cation membrane and the anion membrane, the other two of said three compartments being an acid compartment and a base compartment coupled with their respective acid and base loops;
• (c) supplying a liquid including water to the acid and base compartment of the cell, said acid compartment being located between said cation selective side of the bipolar membrane and said anion membrane, said base compartment being located between said anion selective side of the bipolar membrane and said cation membrane, said base compartment being in communication with an ion exchange column packed with a material capable of removing multivalent cations that may enter the loop;
• (d) passing a direct current through the electrodialysis cell for causing a conversion of at least a portion of the feed salt to its acid and base components;
• and
• (e) withdrawing the feed depleted in its salt content, the acid, and the base product.

A process for the production of organic acid, said process comprising the steps of:

• (a) fermentation of a suitable substrate to generate a feed stream of a monovalent salt of the organic acid;
• (b) filtering said fermentation feed to remove solids suspended therein;
• (c) supplying the filtered fermentation feed of step (b) to an acid compartment;
• (d) supplying a liquid including water to a base compartment, said acid compartment and said base compartment together forming a two compartment cation cell apparatus, said apparatus having an ion exchange column in communication with the base compartment;
• (e) passing a direct current through the two compartment cation cell for producing the organic acid and a base product;
• and
• (f) withdrawing said organic acid and base products.

A process for recovering sulfur dioxide from gases, said process comprising:

• (a) absorbing from a feed stream selected from a group consisting of a sulfite or hydroxide containing a solution of a monovalent cation for forming a mixture of bisulfite and sulfite;
• (b) dividing a solution derived in step (a) into two parts and feeding one of said divided parts into a salt/acid loop and feeding the second of said parts into a base loop of a two compartment cation cell;
• (c) transporting said part in said base loop through an ion exchange column packed with a material capable of removing multivalent cations that may enter the base loop;
• (d) passing a direct current through said feed stream to convert the bisulfite/sulfite values to sulfur dioxide in the salt/acid loop and concurrently producing a sulfite rich alkaline solution in the base loop;
• and
• (e) withdrawing the said acid and base products from said feed stream after it is processed through.

A process for the production sodium alkali from impure sodium mineral sources, said process comprising the steps of:

• (a) filtering a sodium mineral feed solution to remove insoluble materials;
• (b) acidifying a portion of the feed of step (a) with a portion of an acid product from a two compartment cation electrodialysis cell, the two compartment cell having an acid compartment and a base compartment in communication with an ion exchange column packed with a material for removing multivalent cations that may enter the base compartment;
• (c) separating carbon dioxide formed in steps (a) and (b) and forwarding salt comprising an anion of acid to the acid compartment of the electrodialysis cell;
• (d) feeding a liquid including water to the base compartment in order to regulate the concentration of the base produced;
• and
• (e) withdrawing acid and base products produced by said process.

A process for producing monovalent organic acid, said process comprising the steps of:

• (a) fermenting a substrate to generate a salt solution of an organic acid;
• (b) subjecting the salt solution of step (a) to nanofiltration to reduce its divalent metals content to a level below approximately 25 ppm;
• (c) supplying the nanofiltered salt solution of step (b) to an acid compartment of a two compartment cation cell and supplying a liquid including water to a base compartment of said two compartment cation cell;
• (d) passing a direct current through the two compartment cation cell for producing an organic acid and a base product;
• and
• (e) withdrawing said organic acid and base products as an output of said process.

A process for producing organic acid, said process comprising the steps of:

• (a) fermenting a substrate to generate a salt solution of organic acid;
• (b) subjecting the salt solution of step (a) to nanofiltration to reduce its divalent metals content to below a predetermined level;
• (c) supplying the nanofiltered salt solution of step (b) to an acid compartment of an electrodialysis cell and supplying a liquid including water to a base compartment of said cell, said base compartment having an ion exchange column in communication with a base loop of the cell, said ion exchange column capable of removing the multivalent cation entering the loop;
• (d) passing a direct current through the cell for producing an organic acid and a base product;
• and
• (e) withdrawing said organic acid and base products as an output of said process.