Method for separating tall oil soap from black liquor and use of cationic polymer in separation of tall oil soap and black liquor

Abstract

A method for improving a separation of tall oil soap from black liquor in a tall oil soap separation phase, which comprises adding of a polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer into black liquor. The cationic epichlorohydrin-dimethylamine based polymer has a weight average molecular weight in the range of 1 500 – 500 000 g / mol. The cationic epichlorohydrin- dimethylamine based polymer may be further crosslinked with ethylenediamine (EDA). The polymer additive can be added to black liquor from pulping process prior to tall oil soap separation, and / or to a tall oil soap solution, which is achieved from separating tall oil soap from black liquor.

Description

[0001] METHOD FOR SEPARATING TALL OIL SOAP FROM BLACK LIQUOR AND USE OF CATIONIC POLYMER IN SEPARATION OF TALL OIL SOAP AND BLACK LIQUOR

[0002] Field of the invention

[0003] The present invention relates to a tall oil production, and particularly a method for separating tall oil soap from black liquor according to the claims presented below. The invention relates also to use of cationic polymer in a separation of tall oil soap and black liquor.

[0004] Background of the invention

[0005] Tall oil is a side product of Kraft pulp production. Tall oil is produced from tall oil soap, which is formed from wood extractives i.e. fatty acids and resin acids during alkaline cooking process. Soap, i.e. sodium salts of fatty and resin acids, dissolve into cooking liquor, also called as black liquor, and enters chemical recovery cycle. The density difference between soap particles and black liquor causes the soap particles to rise on the surface of black liquor. The majority of soap is separated from black liquor letting black liquor to settle in tanks for several hours (e.g. 5-10 h) at relatively high temperature (e.g. 95-105°C). The soap is collected from surface of the tanks. There is high interest in industry to make this process faster and more efficient.

[0006] Tall oil soap separation from black liquor is a complex phenomenon, which is affected by several factors. The main factors are found to be rising rate of soap particles, solubility of soap in black liquor, and other process related factors e.g. wood raw material, equipment and process design. Inefficient soap separation can cause operational challenges in pulp mill, such as increased scaling of evaporators in black liquor concentration and problems in recovery boiler control.

[0007] Summary of the Invention

[0008] It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art. It is an object of the present invention to improve a separation of tall oil soap and black liquor by using a polymer additive.

[0009] In order to achieve among others the objects presented above, the invention is characterized by what is presented in the characterizing parts of the enclosed independent claims.

[0010] Some preferred embodiments of the invention will be described in the other claims.

[0011] The embodiments and advantages mentioned in this text relate, where applicable, both to the polymer additive, the method as well as to the uses according to the invention, even though it is not always specifically mentioned.

[0012] A typical method according to the invention for separating tall oil soap from black liquor in a tall oil soap separation phase comprises

[0013] - adding a polymer additive comprising cationic epichlorohydrindimethylamine based polymer into black liquor , wherein the cationic epichlorohydrin-dimethylamine based polymer has a weight average molecular weight in the range of 1500 - 500 000 g / mol, determined by SEC method with PEO calibration, and wherein a dry matter content of the black liquor is in the range of 15 - 35 weight-%, calculated from the total amount of black liquor, and

[0014] - separating tall oil soap from the black liquor.

[0015] In a method according to the present invention a cationic epichlorohydrin- dimethylamine based polymer (poly-ECH-DMA) is added into black liquor in a tall oil separation for improving a separation of black liquor and tall oil soap from each other. It has been found that the addition of a polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer enhances the tall oil soap separation from black liquor, and thus more tall oil soap can be recovered from the black liquor in a certain period of time, before the black liquor is transferred to the recovery boiler. A polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer can also be used in separation of black liquor residues from tall oil soap after a tall oil soap separation phase, wherein the quality of the tall oil soap can be improved. The method according to the present invention enhances the tall oil soap separation and thus also increases the yield of tall oil. The separated tall oil soap can be conveyed further to crude tall oil production process.

[0016] According to the present invention, a polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer is used as an additive for improving a separation of tall oil soap and black liquor, wherein the cationic epichlorohydrin-dimethylamine based polymer has a weight average molecular weight in the range of 1500 - 500 000 g / mol, determined by SEC method with PEO calibration. Particularly, cationic epichlorohydrin- dimethylamine based polymer is used as an additive for improving tall oil soap separation from black liquor, wherein the polymer additive is added to black liquor prior to tall oil soap separation, and the cationic epichlorohydrin- dimethylamine based polymer has a weight average molecular weight in the range of 1500 - 500 000 g / mol, determined by SEC method with PEO calibration.

[0017] Epichlorohydrin-dimethylamine polymers (poly-ECH-DMAs) are high cationic polymers which are chemically stable for e.g. hydrolysis even at high alkaline pH, such as pH in a range of 10 - 14. High cationic polymer can grab soap molecules by poly-ion complexation and form a block in which more soap material can adsorb and thus improve soap separation. Poly-ECH-DMAs are formed by reaction of epichlorohydrin (ECH) and dimethylamine (DMA), which forms linear structure having fairly low weight average molecular weight (Mw), e.g. around 10 000 g / mol at maximum. In an embodiment according to the present invention, a crosslinking of poly-ECH-DMAs with ethylenediamine (EDA) is used for achieving polymers with higher molecular weight, wherein the polymer to be used is poly-ECH-DMA-EDA. Weight average molecular weight up to 500 000 - 600 000 g / mol can be achieved with EDA. However, crosslinking causes branching of the polymer and high branching level is assumed to cause steric hindrance, which may limit the amount of cationic charges, which can take part in polyion-complexation with soap molecules. Positively charged quaternary amines of the polymer can be used to collect soap particles. It has been observed that too high crosslinking of poly-ECH-DMA-EDA may decrease soap separation efficiency as well as too low weight average molecular weight of linear poly-ECH-DMA. Now, it has been found the most efficient polymers, as characterised by the weight average molecular weight, for use in improving a separation of tall oil soap and black liquor.

[0018] Further, the epichlorohydrin-dimethylamine based polymers are one of the cheapest cationic polymers in cost vs. polymer charge comparison. Therefore, the present invention also provides a cost-efficient method for improving a separation of tall oil separation and black liquor.

[0019] Description of the drawings

[0020] The invention will be described in more detail with reference to appended drawings, in which

[0021] Fig. 1 show a simplified process chart and addition points of a polymer additive comprising epichlorohydrin-dimethylamine based polymer, according to some embodiments of the present invention. Addition points for a polymer additive according to the present invention are illustrated by arrows A and B in the chart. A polymer additive can also be added at point C illustrated in the chart.

[0022] Fig.2 shows instability index as function of time, relating to Example 2. Instability index gained its maximum value fastest with the low molecular weight polyamine.

[0023] Detailed description of the invention

[0024] According to the present invention, a polymer additive comprising or consisting of a cationic epichlorohydrin-dimethylamine based polymer is used in improving a separation of tall oil soap and black liquor. Particularly, a polymer additive comprising or consisting of a cationic epichlorohydrin- dimethylamine based polymer is used in improving tall oil soap separation from black liquor in a tall oil separation.

[0025] According to an embodiment of the present invention an epichlorohydrin- dimethylamine based polymer can be linear epichlorohydrin-dimethylamine copolymer, denoted as poly-ECH-DMA. According to another embodiment of the present invention, the cationic epichlorohydrin-dimethylamine based polymer is crosslinked with ethylenediamine (EDA) for increasing the molecular weight of the polymer, wherein a cationic epichlorohydrin- dimethylamine based polymer is poly(dimethylamine-co-epichlorohydrin-co- ethylenediamine), denoted as poly-ECH-DMA-EDA. According to an embodiment of the present invention, the cationic epichlorohydrin- dimethylamine based polymer is thus selected from the group consisting of poly-ECH-DMA and / or poly-ECH-DMA-EDA. In an embodiment according to the present invention, a polymer additive comprises or consists of poly-ECH- DMA and / or poly-ECH-DMA-EDA.

[0026] According to the present invention, a weight average molecular weight (Mw) of linear or crosslinked epichlorohydrin-dimethylamine based polymer is preferably in the range of 1 500 - 500 000 g / mol, more preferably 2 000 - 400 000 g / mol, and even more preferably 3 000 - 300 000 g / mol, determined by SEC method with PEO calibration.

[0027] In an embodiment of the present invention, the cationic epichlorohydrin- dimethylamine based polymer has a mol ratio of epichlorohydrin to amine groups in the range of 0.9: 1 - 1 :1.1 , preferably in the range of 0.95:1 - 1 :1.05, for achieving the desired cationicity and molecular weight of the polymer.

[0028] According to the present invention, an epichlorohydrin-dimethylamine based polymer has high cationicity. In a typical embodiment according to the present invention, the charge density of the cationic epichlorohydrin- dimethylamine based polymer, such as poly-ECH-DMA or poly-ECH-DMA- EDA, is over 6.8 meq / g, typically over 7.0 meq / g, and more typically about 7.2 meq / g.

[0029] According to the present invention, a polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer is added to a black liquor from pulping process. A polymer additive can be used to improve tall oil soap separation from black liquor, wherein the polymer additive is typically added to black liquor prior to a tall oil separation. Tall oil soap achieved from the tall oil soap separation may contain residues of black liquor. Therefore, according to an embodiment of the present invention, a polymer additive can also be used to remove black liquor residues from tall oil soap, wherein the quality of the tall oil soap can be improved. In an embodiment of the present invention, a polymer additive comprising cationic epichlorohydrindimethylamine based polymer is also added to a tall oil soap solution, which is achieved from separating tall oil soap from black liquor.

[0030] According to the present invention the polymer additive is added to the black liquor prior to a tall oil soap separation. The polymer additive may be added to black liquor in a soap separation phase, or the polymer additive can be added to black liquor prior to a soap separation phase. In the present disclosure the tall oil separation phase refers to a process step where tall oil is separated from black liquor. According to the present invention, tall oil soap can be removed from black liquor in a separation phase before the black liquor is transferred to recovery boiler. The separation can be performed in various methods, e.g. by settling, by decanting, centrifugation and / or other means known in the art. According to an embodiment of the present invention, a method comprises at least one separation phase. Two or more separation phases may be arranged in parallel and / or in consecutively in the process. According to one preferred embodiment of the present invention, the separation of tall oil soap from black liquor is performed in at least one separation tank. The separation phase may be performed in one separation tank, or it may be performed in two or more separation tanks in parallel and / or in consecutively. The majority of tall oil soap can be separated from black liquor letting black liquor to settle in tanks for several hours, e.g. 5- 10 h at relatively high temperature, e.g. 95-105°C. The tall oil soap can be collected from surface of the tanks. Irrespective of the separation method(s) used in a separation phase, the present invention is based on it that a polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer is added to the black liquor prior to tall oil soap is separated from black liquor in a separation phase. A polymer additive comprising cationic epichlorohydrin-dimethylamine based polymer can be added to black liquor prior to a separation phase and / or into a separation phase.

[0031] Figure 1 illustrates the simplified process chart, where the possible addition points of a polymer additive comprising epichlorohydrin-dimethylamine based polymer are presented by arrows labelled as A, B, C. A polymer additive can be added as one, two or more additions points illustrated in Figure 1. According to an embodiment of the present invention, a polymer additive can be added to a weak black liquor tank and / or an intermediate black liquor tank, typically prior to tall oil soap separation, as illustrated by arrows A and B in Figure 1. In Figure 1 , black liquor from pulping process is conveyed firstly to a weak black liquor tank, where black liquor dry matter content is about 18

[0032] - 22 weight-%, calculated from the total amount of black liquor. After the weak black liquor tank, black liquor can be further conveyed to an intermediate black liquor tank, where black liquor dry matter content is about 30 - 35 weight-%, calculated from the total amount of black liquor. Tall oil soap is separated from black liquor in both tanks. The separated tall oil soap is further conveyed to tall oil soap handling and processing steps. Tall oil soap may comprise residues of black liquor, and hence a polymer additive comprising epichlorohydrin-dimethylamine based polymer may also be added to tall oil soap solution, which is achieved from separating tall oil soap from black liquor, as illustrated by arrow C in Figure 1. Black liquor residues from tall oil soap can be separated in similar manner as tall oil soap from black liquor.

[0033] According to an embodiment of the present invention, a dry matter content of black liquor, to which the polymer additive is added, is in the range of 15 - 35 weight-%, calculated from the total amount of black liquor. A pH of black liquor is alkaline, typically within the range of 10 to 14.

[0034] According to an embodiment of the invention, a method for separating tall oil soap from black liquor, comprises at least the following steps

[0035] - obtaining a black liquor from kraft pulping process,

[0036] - adding a polymer additive comprising an epichlorohydrin-dimethylamine based polymer into black liquor,

[0037] - separating tall oil soap from black liquor in a separation phase, and

[0038] - conveying the black liquor to a recovery boiler and the separated tall oil soap to tall oil production process.

[0039] Black liquor can be softwood or hardwood originated black liquor.

[0040] According to an embodiment of the invention, a method for separating black liquor residues from tall oil soap, comprises at least the following steps - obtaining a tall oil soap solution comprising a tall oil soap and black liquor residues from a tall oil soap separation phase,

[0041] - adding a polymer additive comprising an epichlorohydrin-dimethylamine based polymer into the tall oil soap solution,

[0042] - separating black liquor residues from tall oil soap in a separation phase, and

[0043] - conveying the tall oil soap to further soap handling and processing steps.

[0044] According to an embodiment of the invention, the polymer additive comprising an epichlorohydrin-dimethylamine based polymer is added in an amount of 50 - 800 g / ton of black liquor. Addition of the polymer additive can be performed by using conventional equipment know in the art. A polymer additive may be added as a single doses or multiple doses.

[0045] EXPERIMENTAL PART

[0046] Testing procedure and analyses

[0047] Soap separation tests were performed in a laboratory close to the pulp mill. Black liquor (BL) samples for the tests were obtained from a pulp mill. It is necessary to have fresh BL samples, with a temperature close to the processing temperature. Therefore, both softwood (SW) and hardwood (HW) BL samples, were collected from the mill each morning. The BL samples were stored in 5 L-canister in a styrofoam box for the transferring of the samples from the mill to the laboratory.

[0048] The experiments were made in 500-mL separation funnels. The BL and the chemical product, a dosage of 200 g / t of black liquor, were mixed in two measuring beakers by pouring the samples back and forth from one measuring beaker to the other. After mixing, the sample was poured into a separation funnel and placed in the heated oven at 95°C for 3 hours (SW samples) or for 2 hours (HW samples).

[0049] After the reaction time, pictures were taken of the soap layer found on the surface of BL sample in the separation funnel. Also, the soap layer thickness was measured by hand using a caliper and other observations were recorded. Around 100 mL BL samples were taken from each separation funnel bottom (sample A) and top (sample B) part for further analyses.

[0050] Samples from soap separation tests were analyzed with Lumifuge technology. Lumifuge is an analytical centrifuge that measures transmittance on-line during centrifugation. Samples were centrifuged for 2 hours at 25°C 2500 rpm and with 30 second sampling interval. Centrifugation enhances the separation process of a multicomponent sample, like soap and BL, according to their densities. The soap layer density is approximately 850 kg / m3and the BL density is approximately 1070 kg / m3, so the soap layer will move to the top of the centrifugal tube and BL to the bottom.

[0051] The wavelength was set at 880 nm (at NIR wavelength), which allows penetration through the very dark sample matrix. The transmitted light is measured across the full length of the sample and detected using a CCD- line. The phase separation of BL and soap layers causes changes in transmittance during centrifugation and based on the results, SEPView - software calculates instability index for the sample. Instability index values are between 0 and 1 with lower instability index values indicating better emulsion stability. Samples taken from the soap layer (sample B) should have a high instability index, indicating a high amount of soap. The samples were mixed carefully, and a small amount was carefully injected to the sample cell with a needle and syringe.

[0052] Example 1

[0053] The effect of low weight average molecular weight (Mw 1800 g / mol) linear polyamine and dispersing agent on soap separation from softwood black liquor was studied. Low Mw linear polyamine was poly-ECH-DMA. Dispersing agent was naphthalene sulfonate.

[0054] Testing procedure is described above.

[0055] From the results presented at Table 1 , it can be seen that when low molecular weight polyamine was added to the softwood black liquor, a higher thickness of soap layer was observed compared to the reference sample and to the trial point with dispersing agent addition. Reference sample was without any chemicals. When low Mw linear polyamine was used, the instability index determined using Lumifuge equipment was high indicating a high amount of soap.

[0056] Table 1 . Thickness of softwood soap layer, and instability indices of softwood soap layer.

[0057] Example 2

[0058] The effect of low weight average molecular weight (Mw 1800 g / mol) linear polyamine, high weight average molecular weight (Mw 305 000 g / mol) branched polyepiamine, and dispersing agent on the soap separation from the hardwood black liquor was studied. Low Mw linear polyamine was poly- ECH-DMA, high Mw branched polyepiamine was crosslinked poly-ECH- DMA-EDA. Dispersing agent was a mixture of naphthalene sulfonate and ethoxylates.

[0059] Testing procedure is described above, and it was the same as in Example 1 .

[0060] Significantly higher instability index was seen when low molecular weight polyamine was used compared to the high molecular weight branched polyepiamine and the reference (Table 2). High instability index indicates high soap amount.

[0061] Instability index gained its maximum value fastest with the low molecular weight polyamine (Fig. 2). This indicates better performance of low Mw polyamine in soap separation in comparison to the other trial points. Reference samples were without any chemicals.

[0062] Example 3

[0063] Low weight average molecular weight (Mw 1800 g / mol) linear polyamine, high weight average molecular weight (Mw 6500 g / mol) linear polyamine and high weight average molecular weight (Mw 305 000 g / mol) branched polyepiamine were tested in soap separation from softwood and hardwood black liquors. Low Mw linear polyamine and high Mw linear polyamine were poly-ECH-DMA, and high Mw branched polyepiamine was crosslinked poly- ECH-DMA-EDA.

[0064] The test procedure is described above, and it was the same as in Example 1.

[0065] According to the results presented at Tables 3 and 4, there was a clear increase in thickness of the soap layer, when polyamines according to the present invention were used. The thickness of the softwood soap layer was higher when linear polyamines were used compared to the reference samples and the sample in which high molecular weight branched polyepiamine was added. The thickness of both hardwood and softwood soap layer was the highest when linear high Mw polyamine was added to the black liquor. Instability indexes of the soaps were slightly higher when linear polyamines were used compared to the other samples. Reference samples were without any chemicals. Table 3. Thickness of softwood soap layers, and instability indices of softwood soap layers.

[0066] Table 4. Thickness of hardwood soap layers, and instability indices of hardwood soap layers.

[0067] Example 4 High weight average molecular weight (Mw 6500 g / mol) linear polyamine was added to the hardwood black liquor. The dosage of the polyamine was 200 g / t of black liquor, 500 g / t of black liquor and 800 g / t of black liquor. High Mw linear polyamine was poly-ECH-DMA.

[0068] The testing procedure is described above, and it was the same as in Example 1.

[0069] Thickness of the soap layer was the same as that of the Reference 1 , and higher than that of the Reference 2. Reference samples were without any chemicals.

[0070] Clearly higher instability index was seen when high molecular weight linear polyamine was added compared to the reference samples. Increase of instability index as a function of dose was also visible, as shown at Table 5.

[0071] Table 5. Thickness of hardwood soap layers, and instability indices of hardwood soap layers.

[0072] Example 5

[0073] In this Example, the separation of black liquor residues from tall oil soap was studied and further the effect of chemistry on crude tall oil yield was clarified. Various polyamines were added to tall oil soap. The dosage of the polyamines was 200 g / t. The polyamines used had different average molecular weights: 1800 g / mol, 17 000 g / mol and 305 000 g / mol. The branched polyamines having average molecular weights of 17 000 g / mol and 305 000 g / mol were crosslinked poly-ECH-DMA-EDAs. The polyamine having average molecular weight of 1800 g / mol was linear poly-ECH-DMA. The procedure of the experiment was as follows:

[0074] 1 ) The soap is heated to the reaction temperature 95 °C.

[0075] 2) The soap sample and the chemical product are mixed using a mixing blade in a beaker.

[0076] 3) The sample is poured into a measuring cylinder of 500 ml and a watch glass is put on the top of measuring cylinder.

[0077] 4) The measuring cylinder is placed in the heated oven at 95 °C for 3 hours.

[0078] 5) After the retention time the volume of various layers tall oil, lignin and water were detected. Then the crude tall oil yield from the incoming soap was calculated.

[0079] The results are presented at Table 6. The yield of crude tall oil (CTO) increased in comparison to reference sample. Reference sample was without any chemicals.

[0080] Table 6.

Claims

Claims1. A method for separating tall oil soap from black liquor in a tall oil soap separation phase, characterized in that the method comprises- adding a polymer additive comprising cationic epichlorohydrindimethylamine based polymer into black liquor, wherein the cationic epichlorohydrin-dimethylamine based polymer has a weight average molecular weight in the range of 1 500 - 500 000 g / mol, determined by SEC method with PEO calibration, and wherein a dry matter content of the black liquor is in the range of 15 - 35 weight-%, calculated from the total amount of black liquor, and- separating tall oil soap from the black liquor.

2. The method according to claim 1 , characterized in that the cationic epichlorohydrin-dimethylamine based polymer is further crosslinked with ethylenediamine (EDA).

3. The method according to claim 1 or 2, characterized in that a weight average molecular weight of the cationic epichlorohydrin-dimethylamine based polymer is preferably in the range of 2 000 - 400 000 g / mol, and more preferably 3 000 - 300 000 g / mol, determined by SEC method with PEO calibration.

4. The method according to any one of the preceding claims, characterized in that the cationic epichlorohydrin-dimethylamine based polymer has a mol ratio of epichlorohydrin to amine groups in the range of 0.9: 1 - 1 :1.1 , preferably in the range of 0.95: 1 - 1 :1.05.

5. The method according to any one of the preceding claims, characterized in that the charge density of the cationic epichlorohydrin-dimethylamine based polymer is over 6.8 meq / g, typically over 7.0 meq / g, and more typically about 7.2 meq / g.

6. The method according to any one of the preceding claims, characterized in that the polymer additive is added to the black liquor prior to a tall oil soap separation.

7. The method according to any one of the preceding claims, characterized in that the polymer additive is added to black liquor in a soap separation phase.

8. The method according to any one of the preceding claims, characterized in that the polymer additive is added to a weak black liquor tank and / or an intermediate black liquor tank in a soap separation phase.

9. The method according to any one of the preceding claims, characterized in that the polymer additive is added in an amount of 50 - 800 g / ton of black liquor.

10. The method according to any one of the preceding claims, characterized in that the polymer additive is further added to a tall oil soap solution, which is obtained from separating tall oil soap from black liquor.

11. Use of a polymer additive comprising cationic epichlorohydrindimethylamine based polymer as an additive for improving a separation of tall oil soap and black liquor, wherein the cationic epichlorohydrin-dimethylamine based polymer has a weight average molecular weight in the range of 1500 - 500 000 g / mol, determined by SEC method with PEO calibration, and wherein the polymer additive is added to black liquor in a tall oil soap separation phase, wherein a dry matter content of the black liquor is in the range of 15 - 35 weight-%, calculated from the total amount of black liquor.

12. The use according to claim 11 , characterized in that the cationic epichlorohydrin-dimethylamine based polymer is further crosslinked with ethylenediamine (EDA).

13. The use according to claim 11 or 12, characterized in that a weight average molecular weight of the cationic epichlorohydrin-dimethylamine based polymer is preferably in the range of 2 000 - 400 000 g / mol, and more preferably 3 000 - 300 000 g / mol, determined by SEC method with PEO calibration.

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