Decolorization of amines
The present invention provides methods that are used to decolorize compositions containing one or more amines in the presence of one or more weak acids. Significantly, the weak acids, particularly organic acids such as glacial acetic acid, when used in combination with a heat treatment produce dramatically less by-products than do the stronger mineral acids, making heat treatments and subsequent separation techniques more effective while producing less waste. In some modes of practice, the weak acids do not need to be neutralized, eliminating neutralizing steps and waste streams associated with neutralization. Low color products can be obtained easily at very high yield as a consequence.
1. A method of reducing color of a composition including one or more amines, comprising the steps of:
(a) providing the composition, wherein the composition has an initial color;
(b) heat treating the composition in the presence of at least one weak acid for a period in the range from about 3 minutes to about 150 hours; wherein the weak acid has a pKa of at least about 1 and is selected from a carboxlic acid, a dicarboxylic acid, an anhydride of a dicarboxylic acid, and combinations of these; and
(c) after heat treating, using at least a separation technique to recover at least a portion of the amines from the heat treated composition in a manner such that the recovered portion has less color relative to the initial color, wherein the separation technique is selected from distillation, extraction, chromatography, and combinations of these.
2. The method of claim 1 , further comprising the step of monitoring the progress of the heat treatment said monitoring compressing sampling the heat treated composition, distilling the sample, and checking color of an overhead product obtained from distilling the sample.
3. The method of claim 1 , wherein step (a) comprises providing a amine composition having a color in the range from about 400 APHA to about 5000 APHA.
4. The method of claim 1 , wherein the amine composition comprises linear triethylenetetramine and/or a congener thereof.
5. The method of claim 1 , wherein the at least one weak acid comprises acetic acid.
6. The method of claim 1 , wherein the at least one weak acid comprises glacial acetic acid.
7. The method of claim 1 , wherein the at least one weak acid has a pKa of at least about 2.
8. The method of claim 1 , wherein the at least one weak acid has a pKa of at least about 4.
9. The method of claim 1 , wherein heat treating occurs in the presence of an amount of weak acid(s) in the range from about 0.1 and 5 parts of the at least one weak acid per 100 parts of the amine composition.
10. The method of claim 1 , wherein heat treating occurs for at least one hour.
11. The method of claim 1 , wherein heat treating occurs for at least 24 hours.
12. The method of claim 1 , wherein the heat treating occurs at a temperature in the range from about 70° C. to about 100° C.
13. The method of claim 1 , wherein the heat treating occurs at a temperature in the range from about 100° C. to about 130° C.
14. The method of claim 1 , wherein the heat treating occurs at a temperature in the range from about 130° C. to about 160° C.
15. The method of claim 1 , wherein the heat treating occurs at a temperature in the range from about 160° C. to about 200° C.
16. The method of claim 1 , wherein the color of the recovered amine composition is less than 150 API-IA.
17. The method of claim 1 , wherein the color of the recovered amine composition is less than 50 APHA.
18. A method of reducing color of a composition including one or more amines, comprising the steps of:
(a) providing the composition, wherein the composition has an initial color;
(b) heat treating the composition in the presence of at least one weak acid for a period in the range from about 3 minutes to about 150 hours; wherein the weak acid comprises boric acid; and
(c) after heat treating, using at least a separation technique to recover at least a portion of the amines from the heat treated composition in a manner such that the recovered portion has less color relative to the initial color, wherein the separation technique is selected from distillation, extraction, chromatography, and combinations of these.