Cyclic process for producing taurine
There is disclosed a process for producing taurine from ammonium isethionate by the ammonolysis of alkali isethionate in the presence of alkali ditaurinate or alkali tritaurinate, or their mixture, to inhibit the formation of byproducts and to continuously convert the byproducts of the ammonolysis reaction to alkali taurinate. Alkali taurinate is reacted with ammonium isethionate to obtain taurine and to regenerate alkali isethionate. The production yield is increased to from 90% to nearly quantitative. The ammonolysis reaction is catalyzed by alkali salts of hydroxide, sulfate, sulfite, phosphate, or carbonate.
1. A cyclic process for producing taurine from ammonium isethionate, comprising:
(a) adding ammonia to a solution of a mixture of alkali isethionate, alkali ditaurinate, and alkali tritaurinate, and subjecting the solution to an ammonolysis reaction in the presence of one or a combination of two or more catalysts to yield a mixture of alkali taurinate, alkali ditaurinate, and alkali tritaurinate;
(b) adding ammonium isethionate to the solution of (a) before or after removal of ammonia to yield alkali isethionate and ammonium taurinate;
(c) decomposing ammonium taurinate by heating and removing ammonia from (b) to obtain a crystalline suspension of taurine in a solution of alkali isethionate, alkali ditaurinate, and alkali tritaurinate; then
(d) separating taurine by means of solid-liquid separation and to provide a mother liquor containing a mixture of alkali isethionate, alkali ditaurinate, and alkali tritaurinate;
(e) returning the mother liquor of (d) to (a) for further ammonolysis reaction.
2. The process according to claim 1 , wherein ammonium taurinate is decomposed to taurine by heating from 75° C. to 150° C.
3. The process according to claim 1 , wherein ammonia released in step (c) from the thermal decomposition of ammonium taurinate is removed from solution under reduced, normal, or increased pressure.
4. The process according to claim 1 , wherein the basic solution of reacting ammonium isethionate with alkali taurinates in step (c) becomes neutral in a pH range of 6 to 8 after thermal decomposition and ammonia removal.
5. The process according to claim 1 , wherein the amount of ammonium isethionate in relation to alkali taurinates in the ammonolysis solution of step (c) is from 0.1 to 10 on the molar basis.
6. The process according to claim 1 , wherein the yield of taurine from ammonium isethioante is from 90% to nearly quantitative.
7. The process according to claim 1 , wherein the taurine product of step (d) does not contain alkali sulfate or alkali halide as impurities.
8. The process according to claim 1 , wherein one or a combination of two or more catalysts for the ammonolysis reaction is selected from the alkali salts of hydroxide, carbonate, sulfate, sulfite, phosphate, nitrate, or carboxylate.
9. The process according to claim 1 , wherein the alkali taurinate, alkali ditaurinate and alkali tritaurinate are lithium, sodium, or potassium salts thereof.