Process for recovering crude tall oil

1. A process which comprises:

(a) acidulating a crude tall oil soap stream to produce crude tall oil and a spent acid stream that comprises spent acid, lignin, and entrained crude tall oil;

(b) subjecting the spent acid stream to dissolved gas flotation to separate a lignin phase comprising lignin and entrained crude tall oil from a clarified spent acid stream;

(c) causticizing the lignin phase to convert the entrained crude tall oil to a recovered tall oil soap and generate an aqueous phase comprising dissolved lignates;

(d) isolating the recovered crude tall oil soap; and

(e) optionally reacidulating the recovered crude tall oil soap to produce crude tall oil;

wherein step (b) is performed in the presence of dissolved gas bubbles having an average diameter less than 1 μm.

2. The process of claim 1 wherein dissolved air flotation is used in step (b).

3. The process of claim 1 wherein the pH of the clarified spent acid stream is adjusted to be within the range of 10-13, and the resulting alkaline brine is used to wash black liquor soap.

4. A continuous process of claim 1 .

5. The process of claim 1 wherein step (b) is performed at a temperature greater than or equal to 50° C.

6. The process of claim 1 wherein step (b) is performed at a temperature within the range of 50° C. to 90° C.

7. The process of claim 1 wherein step (b) is performed at a temperature within the range of 60° C. to 80° C.

8. The process of claim 1 wherein step (b) is performed at a pH within the range of 4.0 to 5.0.

9. The process of claim 1 wherein step (b) is performed at a pH within the range of 4.1 to 4.5.

10. The process of claim 1 wherein the difference in specific gravities between the lignin phase and the clarified spent acid stream is less than or equal to 0.002 g/cm3.

11. The process of claim 1 wherein step (b) is performed in the presence of an organic coagulant.

12. The process of claim 1 wherein step (b) is performed in the presence of a polyacrylamide flocculant.

13. The process of claim 1 , using apparatus for recovering crude tall oil soap or crude tall oil, comprising:

(a) a crude tall oil acidulation unit;

(b) a dissolved gas flotation unit;

(c) a causticizing unit; and

(d) a soap separation unit;

wherein the dissolved gas flotation unit is configured to accept from the acidulation unit a spent acid stream comprising spent acid, lignin, and entrained crude tall oil, and is configured to discharge a clarified spent acid phase and a lignin phase comprising lignin and entrained crude tall oil; and

wherein the causticizing unit is configured to accept a base stream and the lignin phase, and to discharge to the soap separation unit a recovered crude tall oil soap and an aqueous phase comprising dissolved lignates.

14. The process of claim 1 , wherein the spent acid stream obtained by step (a) comprises:

(a) a lignin phase comprising the lignin and the entrained crude tall oil; and

(b) a clarified spent acid phase comprising the spent acid;

wherein the lignin phase comprises at least 5 wt. % or more of the entrained crude tall oil, and

wherein the lignin phase further comprises at least 10 wt. % of the spent acid stream.

15. The process of claim 1 , for preparing a crude tall oil soap composition comprising:

(a) crude tall oil soap obtained from Kraft paper mill black liquor; and

(b) crude tall oil soap recovered from a lignin phase of crude tall oil spent acid.

16. The process of claim 1 , for preparing a crude tall oil composition comprising:

(a) crude tall oil obtained from acidulated Kraft paper mill black liquor soap; and

(b) crude tall oil recovered from a lignin phase of a crude tall oil spent acid.