Method for acidulation

Abstract

The present invention is directed to a method for acidulation of tall oil soap in an alcohol selected from methanol, ethanol and / or iso-propanol. In the method according to the present invention, a mixture comprising sodium salts of fatty acids and rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol is acidulated using carbon dioxide.

Description

[0001] METHOD FOR ACIDULATION

[0002] Field of the invention

[0003] The present invention is directed to a method for acidulation of tall oil soap in an alcohol selected from methanol, ethanol and / or iso-propanol. In the method according to the present invention, a mixture comprising sodium salts of fatty acids and rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol is acidulated using carbon dioxide.

[0004] Background

[0005] During production of Kraft pulp, black liquor is formed and removed from the produced pulp. The removed black liquor comprises soap which needs to be separated from the black liquor since the soap comprises valuable wood extractives. The black liquor is concentrated by evaporation and the black liquor soap is skimmed off and acidulated to make crude tall oil (CTO). Another reason to separate the soap from the black liquor is that the soap may cause problems during subsequent treatment steps of the black liquor.

[0006] The separated soap comprises extractives, water, lignin, inorganic compounds, fibers and some black liquor. The fatty and rosin acids of crude tall oil (CTO) are in the form of sodium salts in the soap. The amount of each component in the soap depends on the raw material, as well as seasonal variations thereof, used pulping process and on the process in which the soap is separated from the black liquor, i.e. the soap skimming process. The CTO is mainly composed of fatty acids (TOFA), rosin acids (TOR) and unsaponifiables.

[0007] Crude tall oil is a valuable raw material and it is important to recover as much of the crude tall oil from the soap as possible. Crude tall oil can be used as a raw material for various chemicals and other products, e.g. biodiesel or detergents.

[0008] It is possible to isolate CTO from the soap by addition of an acid to the soap at certain temperature. After mixing of the soap and the added acid, tall oil is formed and it then separates into three major phases due to density differences of the phases; a CTO phase, a lignin phase and a spent acid phase, also referred to as brine. The lignin and spent acid phase are rejects in the CTO production and they need to be separated well from the CTO phase during the recovery of the CTO.

[0009] The amount of acid needed to separate the optimal amount of CTO from the soap depends on the quality of the soap, e.g. the CTO content, the water content, the fiber amount, the lignin content and / or the black liquor content. Today it is common to measure the density of the soap, and the pH and density of the spent acid as a measure of the amount of acid and water that needs to be added to separate the optimal amount of the CTO from the soap These measurements are done online, and the needed amount of acid and water is thereafter adjusted, i.e. feedback control.

[0010] Traditionally, CTO is fractionated using vacuum distillation to fractions like heads (low boiling compounds), fatty acids, rosin acids, and pitch (distillation residue). Also, due to similar boiling points of fatty and rosin acids, a middle fraction can be collected to prevent contamination of fatty and rosin acid fractions. During the distillation of CTO at high temperature alcohols from the neutral compounds (unsaponifiables) are esterified with carboxylic acids resulting in lower yield of the free acid fractions and increase in the lower value pitch fraction. Furthermore, thermal decomposition of compounds may occur during high temperature distillation.

[0011] As described above, the CTO can be used for production of several different products. Alternatively, the CTO could be first separated into unsaponifiables and high acid number tall oil. The high acid number tall oil can be further separated into rosin acids and fatty acids. The unsaponifiables fraction comprises i.a. phytosterols.

[0012] Phytosterols have several uses, including the use as food additives and as precursors for steroids. Several methods have been reported for the isolation of sterols from tall oil soap, such as the extraction of tall oil soap with a variety of organic solvents.

[0013] Currently, phytosterols are commercially produced from tall oil pitch. Due to the ester formation during distillation, phytosterol esters must be hydrolyzed if production of free phytosterols is targeted. This requires additional process steps.

[0014] WO 2022 / 269449 A1 discloses a process to more efficiently separate CTO into a neutral fraction and a neutral depleted fraction. The neutral fraction mainly comprises components generally described as unsaponifiables. The neutral depleted fraction mainly comprises components such as sodium salts of fatty acids and rosin acids.

[0015] WO 2024 / 134454 A1 discloses a further process to more efficiently separate CTO into a neutral fraction and a neutral depleted fraction. The neutral fraction mainly comprises components generally described as unsaponifiables. The neutral depleted fraction mainly comprises components such as sodium salts of fatty acids and rosin acids. In the process two strongly basic anion exchange resins are used to efficiently separate fractions from the crude tall oil.

[0016] US 3,901 ,869 discloses a process for recovery of fatty acids and rosin acids from tall oil soap by acidification, using carbon dioxide, of the tall oil soap, in the presence of from 75% to 200% by weight of water per part of tall oil soap.

[0017] US 5,283,319 discloses a process for recycling of carbon dioxide used in high pressure tall oil soap acidulation processes. There is a need to improve the processes for the handling of soap and tall oil and the fractions obtained from the methods for separating CTO.

[0018] Summary of the invention

[0019] It has surprisingly been found that a mixture of sodium salts of fatty acids and rosin acids in an alcohol selected from methanol, ethanol and / or iso-propanol, which is a neutral depleted fraction obtained in the process disclosed in WO 2022 / 269449 A1 or WO 2024 / 134454 A1 , can efficiently be processed to free fatty acids and free rosin acids, without the use of sulphuric acid. The mixture of sodium salts of fatty acids and rosin acids in an alcohol selected from methanol, ethanol and / or iso-propanol, which is a neutral depleted fraction preferably obtained according to the process disclosed in WO 2022 / 269449 A1 or WO 2024 / 134454 A1 , is foaming and becomes sticky upon concentration and is therefore difficult to handle. The present inventors surprisingly found that it is possible to efficiently process the mixture of sodium salts of fatty acids and rosin acids in an alcohol selected from methanol, ethanol and / or iso-propanol to obtain free fatty acids and free rosin acids by acidulation according to the present invention. It was found that acidulation could be carried out by adding carbon dioxide to the mixture, even in the presence of the alcohol, thereby generating a free fatty acid and free rosin acid mixture. Advantageously, the mixture of sodium salts of fatty acids and rosin acids in an alcohol selected from methanol, ethanol and / or isopropanol is in the form of a solution.

[0020] In the context of the present invention, free fatty acids are individual fatty acid molecules that are not esterified with an alcohol such as methanol, ethanol and / or isopropanol. Examples of such free fatty acids are linoleic acid, oleic acid and pinolenic acid. In the context of the present invention, free rosin acids are rosin acids that are not chemically bonded to any other element. Examples of a free rosin acid are abietic acid, dehydroabietic acid, palustric acid and pimaric acid.

[0021] Thus, the present invention is directed to a process for preparing a free fatty acid and free rosin acid mixture from sodium salts of fatty acids and sodium salts of rosin acids, comprising the steps of a) providing a mixture comprising sodium salts of fatty acids and sodium salts of rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol; b) subjecting the mixture from step a) to acidulation wherein carbon dioxide is mixed into the mixture of step a); and c) recovering a free fatty acid and free rosin acid mixture.

[0022] The present invention is also directed to a composition comprising the free fatty acids and free rosin acids recovered in step c) of the process of the present invention and to the use thereof.

[0023] Detailed description

[0024] During production of Kraft pulp, black liquor is formed and removed from the produced pulp. The removed black liquor comprises soap which needs to be separated from the black liquor since the soap comprises valuable raw materials. The water from the black liquor is then evaporated and the black liquor soap is skimmed off and acidulated to make crude tall oil. Crude tall oil can thus originate from pulping of softwood, hardwood or mixtures thereof.

[0025] The crude tall oil can be treated according to WO 2022 / 269449 A1 , wherein a process to more efficiently separate CTO into one neutral fraction and one neutral depleted fraction is disclosed. The neutral fraction mainly comprises components generally described as unsaponifiables. The neutral depleted fraction mainly comprises components such as sodium salts of fatty acids and sodium salts of rosin acids.

[0026] Thus, when crude tall oil is treated according to WO 2022 / 269449 A1 , it is preferably treated as follows:

[0027] - providing a mixture comprising crude tall oil and alcohol selected from methanol, ethanol and / or iso-propanol;

[0028] - optionally bringing the mixture comprising crude tall oil and an alcohol selected from methanol, ethanol and / or iso-propanol into contact with a strong acid cationic exchange resin;

[0029] - bringing the mixture comprising crude tall oil and an alcohol selected from methanol, ethanol and / or iso-propanol into contact with a strongly basic anion exchange resin; and o recovering at least a first fraction which comprises at least one component; o releasing acidic components that have adhered to the strongly basic anion exchange resin from the strongly basic anion exchange resin, preferably by addition of a mixture comprising sodium hydroxide and an alcohol selected from methanol, ethanol and / or iso-propanol; and o recovering a second fraction which comprises at least one component.

[0030] The first fraction recovered is a neutral fraction. The neutral fraction comprises components generally described as unsaponifiables. The neutral fraction comprises phytosterols.

[0031] The second fraction recovered is the soap fraction, which can also be described as a neutral depleted fraction. The neutral depleted fraction comprises components such as sodium salts of fatty acids and sodium salts of rosin acids, originating from tall oil. The amount of neutrals can be determined by saponifying all acids using potassium hydroxide in ethanol and water and then extracting out all unsaponified compounds from the soap in ethanol / water using hexane. The amount of unsaponifiables or neutrals is then determined gravimetrically after evaporation of the hexane. Standard method ISO 18609. Thus, the sodium salts of fatty acids and sodium salts of rosin acids is a mixture of sodium salts of fatty acids and sodium salts of rosin acids and can also be described as neutral depleted tall oil soap.

[0032] The present invention is directed to processing of the neutral depleted fraction that comprises components such as sodium salts of fatty acids and sodium salts of rosin acids. The neutral depleted fraction, which is a mixture comprising sodium salts of fatty acids and sodium salts of rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol, is provided in step a) of the process of the present invention. Preferably, the mixture comprising sodium salts of fatty acids and sodium salts of rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol is provided in the form of a solution in step a). In one embodiment, the neutral depleted fraction is pre-concentrated in an evaporator before being provided in step a) of the method of the present invention.

[0033] The combined amount of fatty acids and rosin acid sodium salts in the mixture provided in step a) is preferably 10-50 wt-%. The solid content of the mixture is preferably 10-50 wt-%. The solid content is determined by evaporation to dryness and weighing the solid residue. Of the solids, preferably 45-70% by weight is fatty acid salts and 25-50% by weight is rosin acid salts. Preferably, less than 5% by weight of the organic part of the solids are other neutral organic compounds than fatty acid salts and / or rosin acid salts.

[0034] The amount of alcohol selected from methanol, ethanol and / or iso-propanol in the mixture provided in step a) is preferably 50-95 wt-%.

[0035] The alcohol selected from methanol, ethanol and / or iso-propanol is preferably methanol. The combined amount of fatty acids and rosin acid salts in the mixture provided in step a) is preferably 30-50 wt-%. This concentration may for example apply when a pre-concentration has been carried out using an evaporator, as discussed above.

[0036] Step b) of the process according to the present invention is an acidulation step using carbon dioxide. Carbon dioxide is added to the mixture from step a). The carbon dioxide is preferably pressurized gaseous carbon dioxide.

[0037] In the method according to the present invention the carbon dioxide acidulation can be carried out directly on the mixture comprising sodium salts of fatty acids and sodium salts of rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol, either in the presence of a low amount of water or in the presence of a high amount of water. In the presence of a high amount of water, such as if the ratio of water to an alcohol, selected from methanol, ethanol and / or iso-propanol, is in a range of 0.2:1 to 9:1 or in a range of 0.2:1 to 3:1 on a weight basis, the driving force in the acidulation of sodium salts of fatty acids and sodium salts of rosin acids is the formation of two separate phases; an oil phase with the valuable free fatty acids and free rosin acids and a water phase where the formed NaHCOs ends up. The phases can then be separated, and the NaHCOs-containing water phase is handled separately. However, when the mixture used in step a) contains a low amount of water, such as if the ratio of water to an alcohol, selected from methanol, ethanol and / or iso-propanol, is in a range of 0.02:1 to 0.2:1 on a weight basis, the formed free fatty acids and free rosin acids are soluble in the alcohol (such as methanol) and no phase separation occurs. Instead, the driving force for the acid-base equilibrium reaction is the low solubility of the formed NaHCOs in the alcohol (1) and alcohol-tall oil mixture and the increased solubility of carbon dioxide in alcohol (2), compared to water (Ellingboe J.L., Runnels J. H., Journal of Chemical and Engineering Data, 11 (1966), 323-324). The NaHCOs will precipitate and allow for more carbon dioxide to be dissolved in the solution. An equimolar amount of water is the minimum amount of water needed as proton source (carbonic acid) in the protonation step.

[0038] Reaction formula:

[0039] RCO2Na + CO2+ H2O RCO2H + NaHCOs

[0040] This reaction can take place in a similar way as with carbon dioxide acidulation in water.

[0041] Thus, in the method according to the present invention, at least an equimolar amount of water needs to be present during the acidulation step b), but the carbon dioxide acidulation can be carried out directly on the mixture comprising sodium salts of fatty acids and sodium salts of rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol, when said minimum amount of water is present.

[0042] Thus, in one embodiment of the present invention the amount of water in the mixture provided in step a) is in a range of from 0.2:1 to 9:1 or in a range of from 0.2:1 to 3:1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or iso-propanol to form a bi-phasic mixture after the acidulation step.

[0043] In another embodiment of the present invention the amount of water in the mixture provided in step a) is in a range of from 0.02:1 to 0.2:1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or iso-propanol to form a mono-phasic mixture after the acidulation step.

[0044] Step b) is carried out in a reactor, wherein the mixture is preferably agitated. The reactor can for example be a batch reactor or a continuous stirred tank reactor. In step b) the temperature of the mixture is preferably in a range of from 20°C to 90°C, such as from 20°C to 80°C or from 20°C to 60°C or from 30°C to 60°C. In step b) the reactor in which the acidulation is carried out is preferably pressurized with carbon dioxide to a pressure in a range of from 1 bar(g) to 50 bar(g), such as from 2 bar(g) to 50 bar(g). The flow of carbon dioxide can be adjusted to achieve and maintain a pressure in this range.

[0045] In step c) a free fatty and rosin acid mixture is recovered. If the amount of water in the mixture provided in step a) was in a range of from 0.02:1 to 0.2:1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or iso-propanol and a mono-phasic mixture is obtained, the recovery and separation of the precipitated NaHCOs can be carried out by pumping out the contents of the reactor and passing the pumped-out mixture through a solid-liquid separation device, such as a continuous filter, such as a candle filter or continuous pressure filter or any other continuous filtration device or a separation device using centrifugal forces such as a centrifuge or a hydrocyclone. Alternatively, NaHCOs can be removed by settling, whereby the NaHCOs settles at the bottom of the reactor or an external settling tank and is subsequently removed. Preferably, such solid-liquid separation or settling takes place at elevated pressure and temperature since NaHCOs solubility decreases with increased temperature. After the removal of the NaHCOs, the methanol can be evaporated and recovered providing a free fatty and rosin acid mixture.

[0046] In step c), if the amount of water in the mixture provided in step a) was in a range of from 0.2: 1 to 9: 1 or in a range of from 0.2: 1 to 3: 1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or iso-propanol, phase separation can be carried out such that an acidulated phase, comprising free fatty and rosin acids, can be separated from a brine phase, for example using a decanter centrifuge. If needed, the acidulation step b) can be repeated until a sufficiently or fully acidulated product, i.e. free fatty and rosin acid mixture, is obtained. In one embodiment, a recovery step is employed wherein any unreacted carbon dioxide is separated from the products recovered in step c) and recycled for subsequent use. Several carbon dioxide recovery methods are known in the art. In one embodiment, un-reacted carbon dioxide can be separated from the products recovered in step c) by using a flash separation technique.

[0047] If the amount of water in the mixture provided in step a) was in a range of from 0.2:1 to 9:1 or in a range of from 0.2:1 to 3:1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or isopropanol, water soluble organics and carbonate salts can also be recovered from the process according to the present invention. The spent brine and alcohol selected from methanol, ethanol and / or iso-propanol can be sent to solvent recovery. Remaining NaHCOs-containing water phase can be used for example as sodium make-up in a pulp mill.

[0048] The process according to the present invention may be carried out as a batch process or continuously.

[0049] Thus, sodium salts of fatty acids and sodium salts of rosin acids can thus be converted into free fatty and rosin acid mixture, i.e. to high-quality tall oil, i.e. high acid number tall oil according to the present invention. The free fatty and rosin acid mixture may be subjected to drying, depitching and optionally a fractionation distillation. Distillation is the final step for the production of separated high-quality fatty acids and rosin streams.

[0050] Thus, the present invention is also directed to a composition comprising free fatty acids and free rosin acids, wherein the amount of free fatty acids is 45- 70% by weight and the amount of free rosin acid is 25-50% by weight and the amount of salts of free fatty acids and salts of rosin acids of less than 5 wt-%.

[0051] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be affected without departing from the spirit and scope of the invention.

Claims

Claims1. A process for preparing a free fatty acid and free rosin acid mixture from sodium salts of fatty acids and sodium salts of rosin acids comprising the steps of a) providing a mixture comprising sodium salts of fatty acids and sodium salts of rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol; b) subjecting the mixture from step a) to acidulation wherein carbon dioxide is mixed into the mixture of step a); and c) recovering a free fatty acid and free rosin acid mixture.

2. A process according to claim 1 , wherein the combined amount of fatty acids and rosin acid salts in the mixture provided in step a) is 30-50 wt-%.

3. A process according to claim 1 or 2, wherein the solid content of the mixture provided in step a) is 10-50 wt-%.

4. A process according to any one of claims 1-3, wherein the amount of water in the mixture provided in step a) is in a range of from 0.2:1 to 9:1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or iso-propanol.

5. A process according to claim 4, wherein the amount of water in the mixture provided in step a) is in a range of from 0.2:1 to 3:1 on a weight basis relative to the amount of the alcohol, selected from methanol, ethanol and / or iso-propanol.

6. A process according to any one of claims 1-5, wherein the alcohol selected from methanol, ethanol and / or iso-propanol is methanol.

7. A process according to any one of claims 1-6, which is carried out continuously.

8. A process according to any one of claims 1-7, wherein step b) is carried out under pressure in a range of from 2 to 50 bar(g).

9. A process according to any one of claims 1-8, wherein the temperature of the mixture in step b) is in a range of from 20°C to 90°C.

10. A composition of free fatty acids and rosin acids obtainable through the process of any one of claims 1-9.

11. A composition comprising free fatty acids and free rosin acids, wherein the amount of free fatty acids is 45-70% by weight and the amount of free rosin acids is 25-50% by weight and the amount of salts of fatty acids and salts rosin acids is less than 5 wt-%.