Method for recovering crude tall oil

Abstract

The present invention relates to a method for recovering crude tall oil from a soap which method comprises the steps of: determining a correlation between the crude tall oil content and the water content of the soap, determining an amount of acid and water needed in order to separate an optimal amount of crude tall oil from the soap dependent on the crude tall oil content of the soap, measuring the water content of the soap, adding the optimal amount of acid and water to the soap, mixing the added acid and water with the soap whereby an acidulated soap is formed and the crude tall oil is separated and recovering the separated crude tall oil from the acidulated soap.

Claims

1. A method for recovering crude tall oil from a soap comprising the steps of: (a) determining a correlation between the crude tall oil content and a water content of the soap by measuring the crude tall oil content of samples of the soap containing different water content, (b) determining an amount of acid and water needed in order to separate an optimal amount of crude tall oil from the soap dependent on the crude tall oil content of the soap by adding different amounts of acid and water to samples of soaps having different crude tall oil content and identifying the amount of acid and water providing the highest amount of recovered crude tall oil for a given crude tall oil content, (c) measuring a water content of the soap, (d) determining the crude tall oil content of the soap from the water content measured in step (c) and the correlation determined in step (a), (e) determining an optimal amount of acid and water for the crude oil content determined in step (d) based on the amount of acid and water identified in step (b) as providing the highest amount of recovered crude tall oil, (f) adding the optimal amount of acid and water to the soap, (g) mixing the added optimal amount of acid and water with the soap whereby acidulated soap is formed and crude tall oil is separated from a lignin phase and a spent acid phase, and (h) recovering the separated crude tall oil from the acidulated soap.

2. The method according to claim 1 wherein the water content is measured on-line on a soap flow.

3. The method according to claim 1, wherein a pH of the spent acid D fraction of the acidulated soap after addition of the acid and water in step (g) is less than 5.

4. The method according to claim 1, wherein a temperature of the D acidulated soap in step (g) is between 80 to 102 C.

5. The method according to claim 1, wherein step (g) is followed by D a retention time before entering the recovery step (h).

6. The method according to claim 1, wherein the acid added in step (f) is a strong acid.

7. The method according to claim 6, wherein the acid added in step (f) is sulfuric acid which is added in an amount of between 120 to 300 kg/t crude tall oil.

8. The method according claim 1, wherein a hydrodynamic separator, centrifugal separator or decanter type processes are used for the recovery of the separated crude tall oil in step (h).

9. The method according to claim 1, wherein the water content of said soap measured in step (b) is between 25 to 55 wt-%.

10. The method according to claim 1, wherein step (a) also comprises the step of measuring a black liquor content of the soap and adjusting the black liquor content to 3 to 30 volume %.

11. The method according to claim 1, wherein the water content of said soap measured in step (c) is between 32 to 44 wt-%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Shows the correlation between the soap density and the CTO content of the soap at 25 C.

(2) FIG. 2. Shows the correlation between the soap density and the black liquor content of the soap at 25 C.

(3) FIG. 3. Shows the correlation between the dry content and the CTO content of the soap at 25 C.

(4) FIG. 4. Shows the correlation between the dry content and the black liquor content of the soap at 25 C.

(5) FIG. 5. Shows the amount of separated CTO when the end pH of the spent acid is changed by charging different acid amounts to the soap.

(6) FIG. 6. Shows the amount of separated CTO at different total acid concentrations when the end pH of the spent acid is constant.

(7) FIG. 7. Shows the CTO separation rate depending on the water content of the soap.

(8) FIG. 8. Shows the CTO recovery when the optimal amount of acid has been added.

(9) FIG. 9. Shows the CTO recovery when a non-optimal amount of acid and water has been added.

EXAMPLES

(10) The soap samples used in the experimental part as shown in FIGS. 1, 2, 3 and 4 were collected between June and July 2011 and the soap sample showed in FIGS. 5 and 6 was collected in June 2013 and the soap sample showed in FIG. 7 was collected in November 2013. All samples were collected from a soap acidulation process at a kraft pulp mill directly before the soap acidulation.

(11) The origin of the soap used in FIGS. 1, 2, 3 and 4 was from a kraft pulping process using approximately 60% birch and 40% softwood (mainly pine). Fatty acid content was 44 m-%, resin acid content was 24 m-% (GC composition). The origin of the soap used in FIGS. 5, 6 and 7 was also from a kraft pulping process using approximately 60% birch and 40% softwood (mainly pine).

(12) The dry content of the soap was measured using the method SCAN-N 22:77 and the water content was calculated as described in the definition above for all the samples of FIGS. 1, 2, 3, 4, 5, 6 and 7. The black liquor content in the soap was measured by centrifugation (based on method of an accredited laboratory).

(13) The CTO content in soap of FIGS. 3, 4, 5 and 6 has been measured by method PCTM7 (Pulp Chemicals Association, 1996). The CTO content of the soap samples for FIG. 7 was analyzed using PCA-7.

Example 1. Prior Art ProcessDensity Measurements

(14) Based on laboratory analysis, the black liquor content in soap does not correlate linear with the measured soap density as illustrated in FIG. 1.

(15) Furthermore, the soap density does also not correlate linearly with the CTO content in soap as shown in FIG. 2.

(16) The results shown in FIGS. 1 and 2 demonstrate that the changes in soap quality cannot be controlled only based on density measurements. If density is used as the only control parameter for the addition of acid and water, the CTO losses increases due to the inaccuracy of the control. Consequently, the required acid and water amount for optimal CTO separation and recovery cannot be adequately adjusted only based on density measurements.

Example 2. Correlation Between the Dry Content and the CTO Content and Between the Dry Content and the Black Liquor Content

(17) FIG. 3 shows the correlation between the dry content of the soap and the CTO content of the soap at 25 C.

(18) FIG. 4 shows the correlation between the dry content of soap and the black liquor content in soap at 25 C.

(19) Both correlation lines, as shown in FIG. 3 and FIG. 4, are soap and/or mill specific and depend on the soap composition of the specific soap.

(20) The soap dry content correlates linearly with the CTO content in the soap as well as with the black liquor content of soap as can be seen in FIGS. 3 and 4. Consequently, once the correlation line is determined it is possible to measure the water content of the soap and then to know the CTO content and the black liquor content of the soap.

Example 3. Separation of Crude Tall Oil from the Soap

(21) The amount of crude tall oil that is separated and recovered from the soap depends on the amount of acid added during the acidulation step. This can be seen in FIG. 5.

(22) From FIG. 5 it can clearly be seen that the amount of acid added to the soap separates different amounts of CTO from the soap. The acidulation of the soap was performed with different acid charges in order to obtain different pH of the spent acids after the retention time. The retention time for these tests were 2 hours.

(23) The amount of crude tall oil that is separated and recovered from the soap depends on the acid concentration, i.e. the amount of water added during the acidulation step. This can be seen from FIG. 6.

(24) From FIG. 6 it can clearly be seen that the amount of water mixed to the soap separates different amounts of CTO from the soap when the pH of the spent acid after the retention time is kept constant. The retention time for these tests were 2 hours.

Example 4. Separation of Crude Tall Oil Dependent on the Water Content

(25) 410 l soap samples were collected from the same soap. Each soap sample was mixed with black liquor in order to obtain different water contents of the soaps. The different water contents of the samples were; 33% by weight, 36% by weight, 41% by weight and 47% by weight.

(26) To each soap sample 40 wt-% sulphuric acid was added and mixed with the soap in order to form acidulated soap. The end pH of the spent acid fraction was3 and the temperature during the acidulation was 98 C. The acidulated soap was thereafter poured into a measurement glass and the CTO separation was measured volumetrically as a function of time. The temperature of the soap during the retention time was 95 C.

(27) The result can be seen in FIG. 7 and it is evident that the amount of acid added to the soap in order to achieve good separation of CTO at a reasonable time clearly depends on the water content of the soap.

Example 5. Illustration of Changed Water Content of a Soap

(28) FIGS. 8 and 9 show an illustrative example of what happens when the water content of a soap changes but the amount of acid and water added to the soap is unchanged.

(29) To 1 kg of soap the same amount of acid and water is added. The water content of the soap shown in FIG. 8 is 35 wt-% and the water content of the soap shown in FIG. 9 is 45 wt-%. In FIG. 8 the optimal amount of the CTO of the soap is separated and recovered, i.e. the amount of acid and water added to the soap with a water content of 35 wt-% is thus optimal. However, in FIG. 9, not all of the present CTO is separated and recovered. Consequently, it is very important to monitor the water content of the soap in order to be able to separate all CTO present in the soap.

(30) It should be understood that the embodiments given in the description and in the examples above are for illustrative purposes only, and that various changes and modifications are possible within the scope of the invention.