WO2025262363A1

WO2025262363A1 - Method for separating water from co2 pre-acidified tall oil soap

Info

Publication number: WO2025262363A1
Application number: PCT/FI2025/050322
Authority: WO
Inventors: Leif ROBERTSÉN; Sanna LEHTO; Paula SONNÉ; Sari ASIKAINEN; Saara HANHIVAARA
Original assignee: Kemira Oyj
Current assignee: Kemira Oyj
Priority date: 2024-06-17
Filing date: 2025-06-16
Publication date: 2025-12-26
Anticipated expiration: 2026-12-17

Abstract

In tall oil production process, water is separated from a CO2 pre-acidified tall oil soap before the soap cooking phase. Method for improving a water separation from a CO2 pre-acidified tall oil soap comprises adding a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers, to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase. The synthetic polymer additive is a net cationic at pH 7 and has a weight average molecular weight of 1 500 000 – 10 000 000 g/mol.

Description

METHOD FOR SEPARATING WATER FROM CO2 PRE-ACIDIFIED TALL

OIL SOAP

Field of the invention

The present invention relates to a method for improving a separation of water from a CO2 pre-acidified tall oil soap in tall oil production process. The invention relates also to polymer additives for use in a production process of crude tall oil for improving the water separation from CO2 pre-acidified tall oil soap.

Background of the invention

Tall oil is a by-product obtained from kraft pulping process. 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 in pulp production. Tall oil soap is collected from pulp mills. Tall oil is produced from tall oil soap by acidification process, commonly executed with sulphuric acid at high temperature (e.g. 95-100°C). During acidification process, fatty and resin acids are released from their sodium salts and from crude tall oil (CTO) with unsaponified neutral compounds. The acidification splits the tall oil soap to different fractions, which can be separated from each other. The acidified tall oil soap separates into four layers: CTO containing oil phase on the top, brine containing water phase, lignin layer in the middle of the oil and water phases and solid calcium sulphate on the bottom. CTO can be collected and used in the pulp mill for energy or sold outside to be used for other purposes e.g. as chemicals.

Sulphuric acid (H2SO4), which is commonly used in acidifying of tall oil soap, increases the loading of sulphuric compounds in the pulp mill and in the environment. In order to decrease the amount of sulphuric acid in tall oil soap acidification process, tall oil soap can be pre-acidified by using carbon dioxide (CO2), whereby the pH of the tall oil soap is decreased from pH about 12-14 to pH about 8. After the CO2 pre-acidification, the tall oil soap is further acidified in the acidification process with sulphuric acid to form crude tall oil. The problem relating to the pre-acidification of tall oil soap with CO2 is that CO2 pre-acidification requires addition of water into the tall oil soap. However, water is unwanted component in the following soap acidification process since it increases acid consumption and may hinder separation of crude tall oil phase from an aqueous brine phase, and thus the yield of crude tall oil is decreased. Therefore, good quality tall oil soap for tall oil acidification process should not contain too much water. Currently, water is removed from CO2-preacidified tall oil soap e.g. by settling in a tank prior to the soap acidification process. However, there is still a need for improved methods to remove water from CO2 pre-acidified tall oil soap before it enters into the soap acidification process.

Summary of the Invention

It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art.

The object of the invention is to provide an improved method for separating water from CO2 pre-acidified tall oil soap in a production of crude tall oil, and hence also to improve the yield of the crude tall oil.

The object of the present invention is also to provide efficient polymer additives for use in crude tall oil production to enhance water and crude tall oil separation.

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.

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

The embodiments and advantages mentioned in this description relate, where applicable, both to the method as well as to the uses according to the invention, even though it is not always specifically mentioned. A typical method according to the present invention for improving a separation of water from a CO2 pre-acidified tall oil soap in tall oil production process comprises adding a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers, to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase, wherein the synthetic polymer additive is a net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol.

According to the present invention a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers, is used in a production process of crude tall oil for improving the separation of water from CO2 pre-acidified tall oil soap, wherein the synthetic polymer additive is net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol, and it is added to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase.

CO2 pre-acidification of tall oil soap is used to decrease acid consumption in an acidification process of tall oil soap, commonly executed with sulphuric acid at high temperature, also called as a cooking phase of tall oil soap. The tall oil soap typically has a pH between 10 and 12, often close to 12. However, it can be adjusted by acidulation with carbon dioxide and water, typically to a pH between 6.0 and 8.5, more typically a pH between 7 and 8. Water has to be added to tall oil soap in pre-acidification with CO2 and now it has been found that water separation from a CO2 pre-acidified tall oil soap prior to the cooking phase can be enhanced using a synthetic polymeric additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers, which synthetic polymeric additive is net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol, preferably 4 000 000 - 8 000 000 g/mol. In the method according to the invention, a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers is added into the CO2 preacidified tall oil soap prior to a water separation phase and/or in a water separation phase, which water separation phase is performed prior to conveying the CO2 pre-acidified tall oil soap to the cooking phase to form crude tall oil. In the present invention, it has also been observed that a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers according to the present invention improves the yield of crude tall oil after the cooking phase.

Figure 1 shows a simplified flow chart according to an embodiment of the process of treating tall oil soap to form crude tall oil. Addition points of the synthetic polymer additive according to the present invention are illustrated in the flow chart by arrows A, B and C.

Detailed description of the invention

In a method according to the present invention a CO2 pre-acidified tall oil soap is as a starting material. The method according to the present invention is a part of the tall oil production process.

Figure 1 shows a simplified flow chart according to an embodiment of the process of treating tall oil soap. Tall oil soap is at first pre-acidified in a pressurized CO2 reactor, where carbon dioxide (CO2) is fed together with water. CO2 reacts with the sodium in the tall oil soap forming sodium bicarbonate (NaHCOs). The reaction between CO2 and saponified fatty and resin acids can be described as follows:

R - COONa + CO2 + H2O -> R - COOH + NaCHOs

CO2 pre-acidified tall oil soap is obtained from the CO2 reactor, and water is removed from the CO2 pre-acidified tall oil soap in a water separation phase, where an aqueous phase comprising sodium bicarbonate (NaCHOs), also called an aqueous sodium bicarbonate brine is separated from the CO2 preacidified tall oil soap. Water removal is carried out prior to further acidification of the CO2 pre-acidified tall oil soap in a cooking phase with an acid, such as sulphuric acid to form a solution comprising crude tall oil.

Water separation phase can be carried out by allowing the tall oil phase and an aqueous sodium bicarbonate phase to separate into layers. Water separation phase after CO2 reactor can be performed e.g. in a separation tank. The tall oil phase obtained from the water separation phase comprises tall oil and unreacted tall oil soap, since tall oil soap cannot be fully converted into tall oil using only carbon dioxide for acidification, but the CO2 preacidified tall oil soap still contains a substantial portion of sodium soaps, R - COONa. Hence, the tall oil production process typically also includes a further acidification phase, also called as a cooking phase where the CO2 pre-acidified tall oil soap is acidified with acid, such as sulphuric acid (H2SO4) at high temperature (e.g. 95-100 °C) to form a solution comprising crude tall oil (CTO). After the cooking phase the CTO can be separated from the solution, e.g. by settling in a separation tank as illustrated in Figure 1. The acidification with sulphuric acid in a cooking phase splits the tall oil soap to two fractions, the upper fraction containing the crude tall oil with free fatty and resin acids (R-COOH) as well as neutral substances, and the lower fraction containing the used chemicals sodium sulphate (Na2SO4) and water, described as follows:

2R - COONa + H2SO4 2R - COOH + Na₂SO₄

According to the present invention, a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers is added to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase, wherein the synthetic polymer additive is a net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol. Addition points of the synthetic polymeric additive according to the present invention prior to a water separation phase and/or in a water separation phase are indicated in Figure 1 by arrows A and B. In Figure 1 the water separation phase is performed in at least one separation phase arranged between the CO2 reactor and the cooking phase. According to the present invention, a synthetic polymer additive is used to enhance water separation from the CO2 pre-acidified tall oil soap prior to a cooking phase following the water separation phase of the CO2 pre-acidified tall oil soap.

As also illustrated in Figure 1 , the method according to an embodiment of the present invention further comprises - conveying the CO2 acidified tall oil soap from the water separation phase to a cooking phase,

- acidifying the CO2 acidified tall oil soap in the cooking phase to form a solution comprising crude tall oil, and

- separating the crude tail oil (CTO) from the solution in a separation phase arranged after the cooking phase.

According to an embodiment of the present invention the synthetic polymer additive may further be added to the CO2 acidified tall oil soap after the water separation phase, prior to the cooking phase, as indicated by arrow C in Figure 1. It has been observed that a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers according to the present invention improves the yield of crude tall oil after the cooking phase and hence it is advantageous to add polymeric additive to the CO2 acidified tall oil soap also prior to the cooking phase.

According to the present invention, water removal from the CO2 acidified tall oil soap in water separation phase, prior to the cooking phase 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. Separation phases may be arranged in parallel and/or in consecutively in the process. According to one preferred embodiment of the present invention, the water separation phase, i.e. the separation of tall oil phase from an aqueous brine phase after CO2 acidification is performed in at least one separation tank. The water 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. Irrespective of the separation method(s) used in a water separation phase, the present invention is based on it that a synthetic polymer additive is added to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or it is added to at least one water separation phase for enhancing separation of an aqueous phase from the pre-acidified tall oil soap.

According to an embodiment of the invention, a method for separating water from CO2 pre-acidified tall oil soap in tall oil production process, comprises at least the following steps - obtaining a CO2 pre-acidified tall oil soap,

- adding a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers, to CO2 pre-acidified tall oil soap, wherein the synthetic polymer additive is a net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol,

- separating an aqueous phase from the CO2 pre-acidified tall oil soap in a water separation phase,

- conveying the CO2 acidified tall oil soap from the water separation phase to a cooking phase,

- separating the crude tail oil from the obtained solution.

The acidification of the CO2 pre-acidified tall oil soap in the cooking phase comprises an addition of an acid to the CO2 pre-acidified tall oil soap. The acid may comprise sulphuric acid or formic acid. Typically, the acid comprises sulphuric acid. In an embodiment the acid added to the cooking phase may comprise a waste acid from the chlorine dioxide plant, which comprises sulphuric acid.

The CO2 pre-acidified tall oil soap comprises tall oil soap and water. A pH of the CO2 pre-acidified tall oil soap is within the range of 6.0 - 8.5. In a typical embodiment according to the present invention, the CO2 pre-acidified tall oil soap comprises water and tall oil soap in a ratio of 0.5:1 - 2:1 , preferably 1 :1 - 2:1 , and more preferably about 1 :1. Water is added to tall oil soap in CO2 acidification.

According to the present invention, a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers is a net cationic. The net charge of the polymer additive is calculated as the sum of the charged groups present in the polymer.

According to the present invention, a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol, preferably 4 000 000 - 10 000 000 g/mol, more preferably 4 000 000 - 8 000 000 g/mol. In the present invention, it has been observed that when a weight average molecular weight of the polymer additive is > 1 500 000 g/mol and < 10 000 000 g/mol, it enhances the water separation from the CO2- preacidified tall oil soap compared to the polymer additive with higher weight average molecular weight. In this application the value “mass average molecular weight” is used to describe the magnitude of the polymer chain length. Mass average molecular weight values are calculated from intrinsic viscosity results measured in a known manner in 1 N NaCI at 25 °C by using an Ubbelohde capillary viscometer. The capillary selected is appropriate, and in the measurements of this application an Ubbelohde capillary viscometer with constant K=0.005228 was used. The average molecular weight is then calculated from intrinsic viscosity result in a known manner using Mark- Houwink equation [q]=K-Ma, where [q] is intrinsic viscosity, M molecular weight (g/mol), and K and a are parameters given in Polymer Handbook, Fourth Edition, Volume 2, Editors: J. Brandrup, E.H. Immergut and E.A. Grulke, John Wiley & Sons, Inc., USA, 1999, p. VII/11 for poly(acrylamide). Accordingly, value of parameter K is 0.0191 ml/g and value of parameter “a” is 0.71 . The average molecular weight range given for the parameters in used conditions is 490 000 - 3 200 000 g/mol, but the same parameters are used to describe the magnitude of molecular weight also outside this range. pH of the polymer solutions for intrinsic viscosity determination is adjusted to 2.7 by formic acid.

According to an embodiment of the invention, the synthetic polymer additive may comprise cationic and/or amphoteric polymer, preferably cationic and/or amphoteric polyacrylamide. The amphoteric polymer or amphoteric polyacrylamide denotes a polyacrylamide where both cationic and anionic groups are present in an aqueous solution at pH 7. According to an embodiment of the invention, the synthetic polymer additive comprises cationic polymer obtained by copolymerization of acrylamide or methacrylamide together with at least cationic monomers, and/or amphoteric polymer obtained by copolymerization of acrylamide or methacrylamide together at least both cationic and anionic monomers. The definition (meth)acrylamide denotes in the disclosure that polymer may comprise acrylamide or methacrylamide. Preferably synthetic polymer additive comprises cationic polymer which is obtained by copolymerisation of acrylamide together with cationic monomers, and/or amphoteric polymer which is obtained by copolymerisation of acrylamide together with at least both cationic and anionic monomers. According to one embodiment of the invention 10 - 90 %, preferably 30 - 90 %, more preferably 50 - 85 %, even more preferably 60 - 80 %, of the charged groups in the amphoteric polyacrylamide are cationic.

In an embodiment of the present invention, the synthetic polymer additive has cationicity of < 10 mol-%, calculated from the total amount of the monomers. According to an embodiment of the invention, the synthetic polymer additive has cationicity in the range of 5 - 10 mol-%, preferably 5 - 7 mol-%, calculated from the total amount of the monomers. In the present invention, it has been observed that the polymer additive with lower molecular weight and lower cationicity enhance the water separation from the CO2-preacidified tall oil soap compared to the polymer additive with higher weight average molecular weight and higher cationicity.

In an embodiment of the invention , the synthetic polymer additive comprises cationic monomers selected from the group consisting of 2- (dimethylamino)ethyl acrylate (ADAM), [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-CI), 2-(dimethylamino)ethyl acrylate benzylchloride, 2-(dimethylamino)ethyl acrylate dimethylsulphate, 2- dimethylaminoethyl methacrylate (MADAM), [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MADAM-CI), 2-dimethylaminoethyl methacrylate dimethylsulphate, [3-(acryloylamino)propyl] trimethylammonium chloride (APTAC), [3-(methacryloylamino)propyl] trimethylammonium chloride (MAPTAC) and diallyldimethylammonium chloride (DADMAC).

In an embodiment of the invention, the anionic monomers in the amphoteric polymer are selected from group consisting of unsaturated mono- or dicarboxylic acids, such as acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid or tiglic acid.

According to one preferable embodiment the synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers is a linear polyacrylamide. In other words, the polymer additive is unbranched and preferably not crosslinked. In the polymerisation the amount of cross-linker is less than 0.002 mol-%, preferably less than 0.0005 mol-%, more preferably less than 0.0001 mol-%. According to one embodiment the polymerisation is completely free of cross-linker. The synthetic polymer additive is produced by know methods in the art, e.g. by gel polymerisation.

A synthetic polymer additive is water-soluble. According to the present invention, a synthetic polymer additive may be dissolved into water and an aqueous solution of the polymer additive is added to the CO2 pre-acidified tall oil soap. The polymer content in the said aqueous solution may be 0.1 - 4 weight-%, preferably 0.3 - 3 weight-%, more preferably 0.5 - 2 weight-%.

According to an embodiment of the invention, the synthetic polymer additive is added in an amount of 100 - 1000 g (dry) /ton of the CO2 pre-acidified tall oil soap, and preferably 200 - 1000 g (dry) /ton of the CO2 pre-acidified tall oil soap. Addition of the polymer additive can be performed by using conventional equipment know in the art. A synthetic polymer additive may be added as a single doses or multiple doses. According to the present invention, it can be added to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase. If the addition is made both prior to a water separation phase and in a water separation phase, the addition amount is the sum of the additions.

EXPERIMENTAL

In this experiment, a synthetic polymer additive was used to enhance water separation from the CO2-preacidified tall oil soap sample.

The experiment was carried out at laboratory scale. The samples for the experiment were obtained from a pulp mill. The softwood tall oil soap sample was taken from the process after the CO2 pre-acidification stage before the addition of sulphuric acid.

The weight of the CO2-preacidified tall oil soap sample of 500 ml was determined. Same amount of the CO2-preacidified tall oil soap was added to each sample. pH of the samples was adjusted from 8.1 to 7.1-7.4 by adding sulphuric acid. Then an aqueous solution of the synthetic polymer additive (concentration 0.5 w-%) was added to the CO2-preacidified tall oil soap sample. The dosage of the synthetic polymer additive was 200 g (dry) /t of the CO2-preacidified tall oil soap. Reference sample was treated the same way, but without the addition of the synthetic polymer additive. Samples were poured into a 500 ml graduated cylinder and kept in an oven at 45 °C for 180 min for separating the soap oil and water layers from each other. The samples were taken from the soap oil layer and water layer for further analyses. Dry matter content and water content were determined from the soap oil layer. Dry matter content was determined by Karl Fischer titration. Total Organic Carbon (TOC) was determined from the water layer, according to the standard of SFS-EN 1484 using SHIMADZU TOC L analyser. The samples were filtered using filter of 30 pm before the TOC analysis.

In this experiment, the synthetic polymer additive was amphoteric polymer obtained by copolymerization of acrylamide with cationic and anionic monomers and having a molecular weight in the range of 4 000 000 - 8 000 000 g/mol and net cationicity of 5 mol-%, at pH 7.

The sample with the polymer additive addition showed a higher amount of water phase, as shown in Table 1. The water phase volume calculated from the total volume of the sample was 44.3 % in the reference and 51 .0 % in the sample where the polymer additive was added to the tall oil soap sample. In addition, the water layer was clearer than that in the reference by visual inspection, after 180 min retention time.

Compared to the reference sample, the sample treated with the synthetic polymer additive had also a lower TOC value (Table 1 ) in water layer, indicating that the tall oil soap content of the water phase is lower than that of the reference sample. This indicates that the synthetic polymer additive is performing well. Table 1. The results of Example 1 .

Example 2

In this experiment, synthetic polymer additives having various molecular weights and cationic charges were tested in water separation from CO2- preacidified tall oil soap.

The test procedure was the same as in Example 1 . Reference sample was without the addition of the synthetic polymer additive.

In this experiment, the synthetic polymer additives are as follows:

- cationic polymer obtained by copolymerization of acrylamide with cationic monomers and having a molecular weight in the range of 11 000 000 - 14 000 000 g/mol and cationicity of 5 mol-%, at pH 7

- cationic polymer obtained by copolymerization of acrylamide with cationic monomers and having a molecular weight in the range of 11 000 000 - 14 000 000 g/mol and cationicity of 20 mol-%, at pH 7,

- cationic polymer obtained by copolymerization of acrylamide with cationic monomers and having a molecular weight in the range of 11 000 000 - 14 000 000 g/mol and cationicity of 33 mol-%, at pH 7,

- amphoteric polymer obtained by copolymerization of acrylamide with cationic and anionic monomers and having a molecular weight in the range of 4 000 000 - 8 000 000 g/mol and net cationicity of 5 mol-%, at pH 7.

According to the results presented in Table 2, a higher phase volume of water layer and a higher dry matter content of the tall oil soap layer were observed in the sample treated with the polymer additive having molecular weight in the range of 4 000 000 - 8 000 000 g/mol and cationicity of 5 mol-% compared to the reference sample and the samples treated with the polymer additive having higher molecular weight and higher cationic charge. It can be concluded based on the results that the synthetic polymer additive with lower molecular weight and lower cationicity is enhancing the water separation from the CO2-preacidified tall oil soap sample.

Table 2. The results of Example 2.

Example 3

In this experiment, the effect of dosage amount of the synthetic polymer additive was studied on water separation from the CO2-preacidified tall oil soap sample. The polymer additive was cationic polymer obtained by copolymerization of acrylamide with cationic monomers and having low molecular weight (4 000 000 - 8 000 000 g/mol) and low cationic charge (7 mol-%, at pH 7). The following dosages of the synthetic polymer additive were tested: 50, 100, 200 and 600 g (dry) /t of the CO2-preacidified tall oil soap.

According to the results presented in Table 3, the polymer dosage of 50 g/t of the CO2-preacidified tall oil soap didn’t seem to enhance the water separation. When the dosage of the polymer additive was increased to 100 g/t or 200 g/t of the CO2-preacidified tall oil soap or even higher, 600 g/t of the CO2-preacidified tall oil soap, more water was separated from the CO2- preacidified tall oil soap when comparing to the other test points. With the higher dosage amounts, this was also seen as lower water content and higher dry matter content of tall oil soap layer compared to the reference sample.

Table 3. Results of Example 3.

Example 4

In this experiment cationic polymers having low molecular weight (4 000 000 - 8 000 000 g/mol) and low cationic charge (7 mol-%, at pH 7 and 5 mol-%, at pH 7) were tested in water separation from CO2-preacidified tall oil soap. After the water separation the tall oil soap sample received was further processed to obtain crude tall oil (CTO). The chemical products and dosages of those are shown in Table 4.

Table 4. Chemical product and dosages.

The test procedure for the water separation from CO2-preacidified tall oil soap was as in Example 1 . Reference sample was without the addition of the synthetic polymer additive.

After the water separation the tall oil soap was further processed as follows:

1 ) Tall oil soap sample (ca. 400 ml + water, 112 ml) was heated to 97 °C and then the sulphuric acid was added in small amounts. pH was measured during the acid addition. At pH of 2.5 the acid addition was stopped.

2) The sample was left to temperature of 97 °C for 30 minutes.

3) After the retention time the solution was transferred to a measuring cylinder and left to separate overnight at room temperature.

4) The amounts of tall oil, water, middle fraction (lignin) and precipitate were measured.

According to the results presented in Tables 5 and 6 the polymers having low molecular weight performed well when the dosage of the polymer was 600 g/t of tall oil soap. The water separation was enhanced shown as higher water phase volume and tall oil soap dry matter content (Table 5) and also the amount of produced tall oil was increased (Table 6). In addition, the quality of the produced tall oil was good, and all values were at the substantially same level as those of the reference samples, except the ash content was slightly higher than that of the reference when low molecular weight polymer of charge 7 mol-% (Table 7). Table 5. Results of Example 4, water separation from CO2-preacidified tall oil soap.

Table 6. Results Example 4, Crude tall oil production. Table 7. Quality of tall oil

Claims

1. Method for improving a separation of water from a CO2 pre-acidified tall oil soap in tall oil production process, characterized in that the method comprises adding a synthetic polymer additive obtained by copolymerization of (meth)acrylamide and at least cationic monomers, to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase, wherein the synthetic polymer additive is a net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol.

2. The method according to claim 1 , characterized in that the water separation phase is performed in at least one separation phase.

3. The method according to claim 1 or 2, characterized in that the method further comprises

- separating the crude tail oil from the solution.

4. The method according to claim 3, characterized in that the synthetic polymer additive is further added to the CO2 acidified tall oil soap after the water separation phase, prior to the cooking phase.

5. The method according to any one of the preceding claims, characterized in that a pH of the CO2 pre-acidified tall oil soap is within the range of 6.0 - 8.5.

6. The method according to any one of the preceding claims, characterized in that the CO2 pre-acidified tall oil soap comprises water and tall oil soap in a ratio of 0.5:1 - 2:1 , preferably 1 :1 - 2:1 , and more preferably about 1 :1.

7. The method according to any one of the preceding claims, characterized in that the synthetic polymer additive has a weight average molecular weight of 4 000 000 - 10 000 000 g/mol, preferably 4 000 000 - 8 000 000 g/mol.

8. The method according to any one of the preceding claims, characterized in that the synthetic polymer additive comprises cationic polymer obtained by copolymerization of (meth)acrylamide and at least cationic monomers, and/or amphoteric polymer obtained by copolymerization of (meth)acrylamide with at least cationic and anionic monomers.

9. The method according to any one of the preceding claims, characterized in that the synthetic polymer additive has cationicity of < 10 mol-%, calculated from the total amount of the monomers.

10. The method according to claim 7, characterized in that the synthetic polymer additive has cationicity in the range of 5 - 10 mol-%, preferably 5 - 7 mol-%, calculated from the total amount of the monomers.

11 . The method according to any one of the preceding claims, characterized in that the synthetic polymer additive comprises cationic monomers selected from the group consisting of 2-(dimethylamino)ethyl acrylate (ADAM), [2- (acryloyloxy)ethyl] trimethylammonium chloride (ADAM-CI), 2- (dimethylamino)ethyl acrylate benzylchloride, 2-(dimethylamino)ethyl acrylate dimethylsulphate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy)ethyl] trimethylammonium chloride (MADAM-CI), 2- dimethylaminoethyl methacrylate dimethylsulphate, [3-(acryloylamino)propyl] trimethylammonium chloride (APTAC), [3-(methacryloylamino)propyl] trimethylammonium chloride (MAPTAC) and diallyldimethylammonium chloride (DADMAC).

12. The method according to any one of the preceding claims 8-11 , characterized in that the anionic monomers in the amphoteric polymer are selected from the group consisting of unsaturated mono- or dicarboxylic acids, such as acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid or tiglic acid.

13. The method according to any one of the preceding claims, characterized in that the synthetic polymer additive is added in an amount of 100 - 1000 g (dry) /ton of the CO2 pre-acidified tall oil soap, and preferably 200 - 1000 g (dry) /ton of the CO2 pre-acidified tall oil soap.

14. Use of a synthetic polymer additive in a production process of tall oil for improving water separation from CO2 pre-acidified tall oil soap, wherein the synthetic polymer additive is obtained by copolymerization of (meth)acrylamide and at least cationic monomers, and the synthetic polymer additive is a net cationic at pH 7 and has a weight average molecular weight of 1 500 000 - 10 000 000 g/mol, and the synthetic polymer additive is added to the CO2 pre-acidified tall oil soap prior to a water separation phase and/or in a water separation phase.

15. Use according to claim 14, wherein the synthetic polymer additive is further added prior to the cooking phase following the water separation phase of the CO2 pre-acidified tall oil soap.