Process for recycling solvent and drying sodium salts of fatty acids and rosin acids from crude tall oil

Abstract

The present invention is directed to a method for recycling solvent and drying sodium salts of fatty acids and rosin acids obtained from crude tall oil. 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 subjected to a drying step wherein the alcohol is evaporated from the mixture and the salts are dried and recovered. The salts are useful for example for removal of extractives in pulp production or can be acidulated to produce high acid number tall oil.

Description

[0001] PROCESS FOR RECYCLING SOLVENT AND DRYING SODIUM SALTS OF FATTY ACIDS AND ROSIN ACIDS FROM CRUDE TALL OIL

[0002] Field of the invention

[0003] The present invention is directed to a method for recycling solvent and drying 5 sodium salts of fatty acids and rosin acids obtained from crude tall oil. 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 subjected to a drying step wherein the alcohol is evaporated from the mixture and the salts are dried and recovered. The salts 10 are useful for example for removal of extractives in pulp production or can be acidulated to produce high acid number tall oil.

[0004] Background

[0005] 15 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).

[0006] 20 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.

[0007] The separated soap comprises extractives, water, lignin, inorganic compounds, fibers and some black liquor. The fatty and rosin acids of crude 25 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

[0008] 30 unsaponifiables. 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.

[0009] 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.

[0010] 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.

[0011] 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. 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] There is a need to improve the processes for the handling of the fractions obtained from the methods for separating CTO.

[0016] Summary of the invention

[0017] 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 , can efficiently be processed to recycle solvent and simultaneously dry the sodium salts to facilitate further processing of the salts. The mixture of sodium salts of fatty acids and rosin acids in methanol, which is a neutral depleted fraction obtained in the process disclosed in WO 2022 / 269449 A1 , is foaming and becomes sticky upon concentration and is therefore difficult to handle. The present inventors surprisingly found that it is possible to process the mixture of sodium salts of fatty acids and rosin acids in methanol to obtain the sodium salts of fatty acids and rosin acids in solid, free-flowing powder form and at the same time recover the alcohol selected from methanol, ethanol and / or iso-propanol. Obtaining a free-flowing powder conveniently allows for high throughput industrial processing applications.

[0018] Thus, the present invention is directed to a process for recycling solvent and drying sodium salts of fatty acids and rosin acids obtained from crude tall oil, comprising the steps of a) providing a mixture comprising sodium salts of fatty acids and rosin acids and an alcohol selected from methanol, ethanol and / or isopropanol; b) subjecting the mixture from step a) to a drying step wherein the alcohol selected from methanol, ethanol and / or iso-propanol is evaporated from the mixture; and c) recovering the evaporated alcohol selected from methanol, ethanol and / or iso-propanol and recovering dried sodium salts of fatty acids and rosin acids, wherein the sodium salts of fatty acids and rosin acids in solid form has a content of volatiles of less than 6 wt-%, measured using thermogravi metric analysis at 150°C.

[0019] The evaporated alcohol selected from methanol, ethanol and / or iso-propanol can be recycled to a process for separating CTO into one neutral fraction and one neutral depleted fraction as disclosed in WO 2022 / 269449 A1. The present invention is also directed to the sodium salts of fatty acids and rosin acids in solid form recovered in step c) of the process of the present invention and to the use thereof.

[0020] Detailed description

[0021] 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.

[0022] 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 rosin acids.

[0023] Thus, when crude tall oil is treated according to WO 2022 / 269449 A1 , it is preferably treated as follows:

[0024] - providing a mixture comprising crude tall oil and alcohol selected from methanol, ethanol and / or iso-propanol;

[0025] - 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;

[0026] - 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.

[0027] The first fraction recovered is a neutral fraction. The neutral fraction comprises components generally described as unsaponifiables. The neutral fraction comprises phytosterols.

[0028] 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 rosin acids.

[0029] The present invention is directed to processing of the neutral depleted fraction that comprises components such as sodium salts of fatty acids and rosin acids. The neutral depleted fraction, which is a mixture comprising sodium salts of fatty acids and 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 rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol is provided in the form of a solution in step a).

[0030] The combined amount of fatty acids and rosin acid salts in the mixture provided in step a) is preferably 10-50 wt-%, such as 10-40 wt-%. The solid content of the mixture is preferably 10-50 wt-%, such as 10-40 wt-%. Of the solids, preferably 40-70% by weight is fatty acid salts and 20-50% by weight is rosin acid salts. Preferably, less than 5% by weight of the solids are other solids than fatty acid salts or rosin acid salts. The amount of alcohol selected from methanol, ethanol and / or iso-propanol in the mixture provided in step a) is preferably 50-95 wt-%, such as 60-95 wt-%.

[0031] The alcohol selected from methanol, ethanol and / or iso-propanol is preferably methanol.

[0032] Step b) of the process according to the present invention is a drying step wherein the alcohol selected from methanol, ethanol and / or iso-propanol is evaporated from the mixture from step a). The drying step is preferably carried out in a thin film dryer or a thin film evaporator. Preferably, the thin- film evaporator is a horizontal thin film evaporator. In some embodiments, the thin film evaporator is orientated at an angle between or between about 0° to 90° such as at or about at 5°, 10°, 15°, 30°, 45°, 60°, 75°, 80°, 85°, or any range of values there between, wherein 0° corresponds to the thin film evaporator being oriented straight down, toward the Earth’s center of mass and 180° corresponds to the heated thin film evaporator being oriented straight up, away from the Earth’s center of mass. In some embodiments, the thin film evaporator system comprises a feed pump to direct the feed solution (the mixture comprising sodium salts of fatty acids and rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol) into the thin film evaporator. In some embodiments, the thin film evaporator system comprises a hot oil jacketed, counter-current horizontal thin film evaporator. In some embodiments, the thin film evaporator system comprises condenser for solvent collection. In some embodiments, the thin film evaporator system comprises a vacuum pump. In some embodiments, the thin film evaporator system comprises a mass flow meter for inert gas sparge. In some embodiments, the thin film evaporator system comprises a bottom solid discharge valve. In some embodiments, the thin film evaporator system comprises a control system. In some embodiments, the control system is configured to maintain a thin film temperature, pressure, inert gas sparge, or feed rate, or combinations thereof of the thin film evaporator system. In some embodiments, the feed solution is introduced into the heated thin film evaporator having a thin film temperature between 100-180°C. In some embodiments, the feed is pre-heated to 100-150°C using an external heat exchanger before being introduced into the heated thin film evaporator. In some embodiments, the thin film evaporator is operated between 500 mbar and atmospheric pressure.

[0033] Preferably, the drying is preferably carried out using a horizontal heated kneader-dryer with rotating shafts. A heated kneader-dryer is a form of thin film dryer and operates according to a thin film evaporation principle. In a heated kneader-dryer mixing, heating, and evaporation is carried out simultaneously. Typically, the heated kneader-dryer has one or more rotating shafts, such as two rotating shafts, carrying out the kneading of the material subjected to drying. The temperature in the heated kneader-dryer is preferably in the range of from 100°C to 180°C, such as in a range of from 100°C to 170°C or from 100°C to 160°C. Preferably, nitrogen purge is used, to obtain an inert environment in the heated kneader-dryer. Preferably, the pressure in the heated kneader-dryer is between 500 mbar and atmospheric pressure. When the process according to the present uses a horizontal heated kneader-dryer in step b), the mixture of step a) is introduced into the heated dryer in one end. Preferably, the mixture of step a) is pre-heated to 100-150°C in an external heat exchange before being introduced into the heated dryer. The alcohol selected from methanol, ethanol and / or isopropanol will be evaporated along the length of the dryer and the heated kneader shafts will provide good heat transfer and break apart the sticky, pasty material to ensure evaporation of the alcohol selected from methanol, ethanol and / or iso-propanol until the salts have dried into a free-flowing granular powder. The granular, dry powder then exits the kneader-dryer in the other end through a chute or solid dispensing system. Preferably, an inert environment is used when the granular, dry powder exits the kneader-dryer, i.e. the dry powder is collected in an inert environment, optionally under vacuum. When the powder has cooled to a temperature of about 80-90°C or lower, the powder can be removed from the inert environment. It has been found that these conditions improve yield and avoid degradation of the product. Preferably, the kneader-dryer and the internal single or double shafts are heated to ensure good heat transfer. The evaporated alcohol selected from methanol, ethanol and / or iso-propanol preferably exits the dryer through vapor outlets on the top side and is then condensed in an external condenser and collected for purification and recycling in the process disclosed in WO 2022 / 269449 A1. The dryer can operate under atmospheric pressure or under vacuum and the internal volume can be purged with an inert gas to prevent flammable vapors being formed. Preferably, nitrogen purge is used, to obtain an inert environment in the heated kneader-dryer. Additionally, the temperature of the mixture of step a) can be between ambient temperature and 100 °C. Preferably, the mixture of step a) is pre-heated to 50-90 °C.

[0034] It has been found that by using the process according to the present invention, the sodium salts of fatty acids and rosin acids in solid form having a content of volatiles of less than 6 wt-%, measured using a TGA at 150 °C, can be isolated and recovered as free-flowing powder or granules. The amount of volatiles is determined thermogravimetrically, by measuring the weight reduction upon heating to 150°C. Preferably, the content of volatiles is less than 5 wt-%, more preferably less than 4 wt-%. The particles of the powder or granules have a particle size distribution wherein D90 is less than 10mm, determined gravimetrically using sieve trays. Advantageously, the method of the present invention provides sodium salts of fatty acids and rosin acids in solid form, more specifically in free-flowing form. In the context of the present invention, free-flowing means that the particles do not stick together and do not form aggregates.

[0035] The sodium salts of fatty acids and rosin acids in solid form can be converted to high-quality tall oil using methods known in the art. For example, the sodium salts of fatty acids and rosin acids in solid form can be mixed with water and sulphuric acid and heated to produce high acid number tall oil. The sodium salts of fatty acids and rosin acids in solid form can also be used in application areas in which rosin soap is traditionally used, for example to remove extractives in methods for pulp production. The sodium salts of fatty acids and rosin acids in solid form can also be converted into free fatty acids or derivatives thereof for example according to the method of US2016 / 0201010A1. In this method, free or bound fatty acid molecules are released from glycerides by thermal hydrolysis followed by acidulation of soaps using carbon dioxide. Distillation is the final step for the production of high quality fatty acids and rosin. Water soluble organics and carbonate salts can also be recovered.

[0036] The process according to the present invention may be carried out as a batch process or continuously. When a horizontal heated kneader-dryer is used in step b) of the process of the present invention, the process is preferably carried out continuously.

[0037] Example

[0038] Example 1

[0039] A mixture comprising sodium salts of fatty acids and rosin acids and methanol was provided. The mixture was a neutral depleted fraction obtained in the process disclosed in WO 2022 / 269449 A1.

[0040] The mixture was charged to a horizontal heated kneader-dryer with rotating shafts, in which a vacuum pressure of 500 mbar was applied and the temperature was 120°C. The batch kneader-dryer was equipped with a vapor outlet with a condenser but with no solid outlet. After continuously feeding the kneader-dryer for approximately 3 hours, and continuously allowing the vapors to be condensed in the external condenser, a free-flowing powder was recovered. The free-flowing powder was subjected to thermogravimetric analysis at 150°C and it was found that the amount of volatiles was 5.8 wt-%. The free-flowing powder was analyzed using NMR and it was found that the amount of fatty acid salts was 58.5%, the amount of rosin acid salts was 38.1 % and the amount of other components was 3.4%.

[0041] The off gas from the heated kneader-dryer was condensed and methanol was recovered as condensate.

[0042] Example 2

[0043] A mixture comprising sodium salts of fatty acids and rosin acids and methanol was provided. The mixture was a neutral depleted fraction obtained in the process disclosed in WO 2022 / 269449 A1.

[0044] The mixture was charged to a horizontal heated batch kneader-dryer with rotating shafts operating under atmospheric conditions and the temperature was 150°C. The batch kneader-dryer was equipped with a vapor outlet with a condenser but with no solid outlet. After continuously feeding the kneaderdryer for approximately 3 hours and continuously allowing the vapors to be condensed in the external condenser, a free-flowing powder was recovered. The free-flowing powder was subjected to thermogravimetric analysis at 150°C and it was found that the amount of volatiles was 3.9 wt-%. The free- flowing powder was analyzed using NMR and it was found that the amount of fatty acid salts was 60.6%, the amount of rosin acid salts was 36.1 % and the amount of other components was 3.3%.

[0045] The off gas from the heated kneader-dryer was condensed and methanol was recovered as condensate.

[0046] Example 3

[0047] The following experiments were conducted in a heated, continuous kneaderdryer in the following steps:

[0048] 1. Preheating of the equipment from 170 to 190 °C using a circulating hot-oil system. 2. Evacuation and / or inertization of the kneader with nitrogen to run under vacuum or atmospheric, inert conditions

[0049] 3. Pumping the feed solution from feed vessel to the heat exchanger

[0050] 4. Heating the feed solution to 130 °C

[0051] 5. Feeding the heated feed solution through a side flange into the kneader

[0052] 6. Evaporating the solvent through the vapor outlet in the top of the kneader, condensing and collection using an external condenser / solvent collection system

[0053] 7. Discharge of the dried granular soap via the front plate, with an adjustable wear height for adjusting the fill level

[0054] The temperature inside the kneader was measured at three positions along the length of the kneader, feed inlet (T prod inlet), middle (T prod middle), product outlet (T prod outlet).

[0055] The moisture content of the dried product was measured using an infrared solid content measurement oven (T=110 °C, 20 min) 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 recycling solvent and drying sodium salts of fatty acids and rosin acids obtained from crude tall oil comprising the steps of a) providing a mixture comprising sodium salts of fatty acids and rosin acids and an alcohol selected from methanol, ethanol and / or iso-propanol; b) subjecting the mixture from step a) to a drying step wherein the alcohol selected from methanol, ethanol and / or isopropanol is evaporated from the mixture; and c) recovering the evaporated alcohol selected from methanol, ethanol and / or iso-propanol and recovering dried sodium salts of fatty acids and rosin acids, wherein the sodium salts of fatty acids and rosin acids in solid form has a content of volatiles of less than 6 wt-%, measured using thermogravimetric analysis at 150°C.

2. A process according to claim 1 , wherein step b) is carried out in a thin film dryer or thin film evaporator.

3. A process according to claim 2, wherein step b) is carried out in a horizontal thin film dryer or horizontal thin film evaporator.

4. A process according to any one of claims 1-3, wherein step b) is carried out in a heated kneader-dryer.

5. A process according to any one of claims 1-4, wherein the temperature during the drying in step b) is in a range of from 100°C to 180°C.

6. A process according to any one of claims 1-5, which is carried out continuously.

7. A process according to any one of claims 1-6, wherein step b) is carried out under inert conditions.

8. A composition of dried sodium salts of fatty acids and rosin acids obtainable through the process of any one of claims 1-6.

9. A composition comprising dried sodium salts of fatty acids and rosin acids, wherein the amount of fatty acid salts is 40-70% by weight and the amount of rosin acid salts is 20-50% by weight and wherein the composition has a content of volatiles of less than 6 wt-%, measured using thermogravimetric analysis at 150°C.

10. A composition according to claim 9, wherein the dried sodium salts of fatty acids and rosin acids are in powder form.

11. A composition according to claim 10, wherein the particles of the powder have a particle size distribution wherein D90 is less than 10 mm, determined gravimetrically using sieve trays.

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