Cyclic process for the production of taurine from alkali isethionate

Abstract

A cyclic process is disclosed for the production of taurine from alkali isethionate in a high overall yield by continuously converting the byproducts of the ammonolysis reaction, sodium ditaurinate and sodium tritaurinate, to sodium taurinate. Sodium sulfate and residual taurine in the crystallization mother liquor are efficiently separated by converting taurine into a highly soluble form of sodium taurinate or ammonium taurinate while selectively crystallizing sodium sulfate.

What is claimed is: 
     
       1. A cyclic process for the production of taurine from alkali isethionate, comprising,
 (a) adding an excess of ammonia to a solution of alkali isethionate and subjecting the solution to ammonolysis reaction in the presence of one or more catalysts to yield a mixture of alkali taurinate, alkali ditaurinate, alkali tritaurinate, and unreacted alkali isethionate;   (b) recovering the excess ammonia from (a) and neutralizing the solution with sulfuric acid to obtain a crystalline suspension of taurine in a solution of alkali sulfate, alkali ditaurinate, alkali tritaurinate, and alkali isethionate;   (c) separating taurine from (b) to provide a mother liquor   (d) adjusting the pH of the mother liquor to basic to convert taurine present in the mother liquor to alkali taurinate and prevent the crystallization of taurine, and removing alkali sulfate from the mother liquor by performing evaporative crystallization and cooling crystallization through solid-liquid separation;   (e) returning the mother liquor of (d) to (a) for further ammonolysis of alkali ditaurinate, alkali tritaurinate, and unreacted alkali isethionate.   
     
     
       2. The process according to  claim 1 , wherein the mother liquor containing alkali ditaurinate, and alkali tritaurinate is mixed with a new batch of alkali isethionate to inhibit the formation of alkali ditaurinate and alkali tritaurinate and to convert alkali ditaurinate and alkali tritaurinate to alkali taurinate during the ammonolysis. 
     
     
       3. The process according to  claim 2 , wherein alkali ditaurinate and alkali tritaurinate in the returning mother liquor are converted to di-alkali ditaurinate and tri-alkali tritaurinate by adding alkali hydroxide during the ammonolysis. 
     
     
       4. The process according to  claim 1 , wherein the one or more catalysts for the ammonolysis are comprised of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, sodium sulfate, sodium sulfite, potassium sulfate, or potassium sulfite. 
     
     
       5. The process according to  claim 1 , wherein the overall yield is greater than 85%. 
     
     
       6. The process according to  claim 1 , wherein the overall yield is greater than 90%. 
     
     
       7. The process according to  claim 1 , wherein the overall yield is greater than 95%, to nearly quantitative. 
     
     
       8. The process according to  claim 1 , wherein alkali metals are lithium, sodium, and potassium. 
     
     
       9. A cyclic process for the production of taurine from alkali isethionate in an overall molar yield of at least 85% on the basis of alkali isethionate, comprising,
 (a) adding excess ammonia to a solution comprised of alkali isethionate and subjecting the solution to ammonolysis in the presence of at least one catalyst to yield a mixture of alkali taurinate, dialkali ditaurinate, trialkali tritaurinate, and unreacted alkali isethionate;   (b) removing excess ammonia from the solution of step (a) and neutralizing the solution with sulfuric acid to form a crystalline suspension of taurine in a solution comprised of alkali sulfate, alkali ditaurinate, alkali tritaurinate, and unreacted alkali isethionate;   (c) recovering taurine by means of solid-liquid separation to obtain a mother liquor solution comprised of alkali ditaurinate, alkali tritaurinate, unreacted alkali isethionate, and unrecovered taurine;   (d) adjusting the pH of the mother liquor solution to basic with an alkali hydroxide wherein the molar amount of the alkali hydroxide is at least equal to the molar amount of the total taurinates in the mother liquor solution comprised of the alkali ditaurinate and alkali tritaurinate, so as to convert the taurine in the mother liquor solution to alkali taurinate and prevent the crystallization of taurine, and removing the alkali sulfate from the mother liquor solution by performing evaporative and cooling crystallization by means of solid-liquid separation; and   (e) returning the mother liquor solution of step (d) to step (a) and performing steps (a), (b), (c), and (d).   
     
     
       10. The process according to claim 9, wherein the mother liquor solution of the step (d) is mixed with a new batch of alkali isethionate. 
     
     
       11. The process according to claim 9, wherein the catalyst for the ammonolysis is selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, sodium sulfate, sodium sulfite, potassium sulfate, and potassium sulfite. 
     
     
       12. The process according to claim 9, wherein the overall molar yield of the taurine from the alkali isethionate is greater than 85%. 
     
     
       13. The process according to claim 9, wherein the overall molar yield of the taurine from the alkali isethionate is greater than 90%. 
     
     
       14. The process according to claim 9, wherein the overall molar yield of the taurine from the alkali isethionate is greater than 95%, to nearly quantitative. 
     
     
       15. The process according to claim 9, wherein the alkali is lithium, sodium, or potassium.