Patent Description:
The Kraft process in the paper pulping industry produces black liquor soap (BLS), which contains sulfur. The presence of sulfur compounds in BLS-derived materials such as in tall oil and tall oil derived products can limit the scope of their end use applications, for example due to malodor. Sulfur impurities are known to act as noble metal catalyst poisoners, can have a detrimental impact on catalytic hydrogenation and disproportionation reactions and can contribute to corrosion. There is a need for industrial applicable, cost-effective and safe BLS desulfurization processes.

The prior art BLS desulfurization processes have been carried in the presence of aqueous hydrogen peroxide (H<NUM>O<NUM>) solution and concentrated caustic soda in the presence of brine (NaCl). As a result of oxidative desulfurization methods, sulfides are oxidized into more polar sulfoxides and sulfones, but such methods can also lead to concomitant detrimental oxidation of sensitive tall oil components such as abietic acid and linoleic acid and can lead to excessive foaming due to oxidant decomposition and release of oxygen gas.

The acidulation of BLS into CTO with sulfuric acid results in the formation of Na<NUM>SO<NUM>. In current paper mills, the recovery boiler is an essential section to recover the inorganic sodium salts NaOH and Na<NUM>S in order to render the Kraft paper pulping process economical viable. During such a recycling process, the presence of halogen ions like in brine (NaCl) is undesirable and can deteriorate the chemical recycling process, e.g., formation of tenacious deposits in recovery boilers. In the acidulation or refinery process, the halogen atoms might react with tall oil components, which may lead to a covalent incorporation of halogen atoms into tall oil and its refined products.

<CIT> discloses process for recovering isomerized fatty acids and/or rosin acid comprising the steps of subjecting a tall oil skimming soap or a tall oil soap in a thin film evaporator so as to evaporate and remove water and low-boiling unsaponifiable matter; adding an alkali to the thus obtained crude soap in an amount of <NUM> to <NUM> times the amount required to saponify the saponifiables in said tall oil skimming soap or tall oil soap at <NUM> to <NUM> over a period of <NUM> minutes to <NUM> hours, thereby simultaneously decomposing esters of rosin acid and fatty acids with sterols and other alcohols and isomerizing nonconjugated double bond containing fatty acids to conjugated fatty acids; and then subjecting the saponification product to acid decomposition and then to distillation to obtain the desired isomerized fatty acids and/or rosin acid. There is still a need for better BLS desulfurization processes resulting in low sulfur content, negligible halogen content, a low color, improved odor properties, e.g., low odor intensity and low odor hedonic tone. In particular, as part of a sustainable process wherein applied chemicals can be recycled.

The present invention relates to a method of purifying black liquor soap (BLS) from sulfur compounds as specified in claim <NUM>. In one aspect, the disclosure provides a method of purifying black liquor soap (BLS) from sulfur compounds by: subjecting the BLS to one or more extractions with of an aqueous alkaline solution comprising <NUM>-<NUM> mol/L of inorganic base, the inorganic base is selected from the group consisting of NaOH, LiOH, KOH and any combination thereof, the weight ratio of the applied aqueous alkaline solution/black liquor soap mixture is greater than <NUM>/<NUM> and less than <NUM>/<NUM>; optionally heating the BLS in an inert atmosphere or in a vacuum at a temperature in the range of <NUM> to <NUM>, wherein the alkaline solution is substantially free from brine, sulfate salts or carbonate salts, and wherein the total solids sulfur content of the BLS is reduced by at least <NUM> % and wherein the purified BLS has a chloride content of less than <NUM> ppm.

In yet another aspect, the disclosure provides crude tall oil compositions purified from sulfur, dehydrated crude tall oil compositions purified from sulfur, depitched crude tall oil compositions purified from sulfur and depitched crude tall oil distillation fractions purified from sulfur, including tall oil rosin (TOR), tall oil fatty acid (TOFA), distilled tall oil (DTO) and tall oil pitch (TOP), and chemical compositions derived therefrom, which compositions are resulting from successive acidulation, dewatering, depitching and subsequent fractionations and chemical reactions of the obtained BLS compositions purified from sulfur, according to the desulfurization methods herein.

The following terms will be used throughout the specification and will have the following meanings.

"Substantially free" is used herein to describe an alkaline solution, comprising inorganic base such as NaOH, LiOH or KOH that contains less than <NUM>%, preferably less than <NUM>%, more preferably less than <NUM>% by weight of brine, sulfate salts, or carbonate salts.

In one aspect, the disclosure provides a method of purifying black liquor soap from sulfur by means of one or more extractions with an aqueous alkaline solution substantially free from brine, sulfate salts or carbonate salts.

Black Liquor Soap (BLS) Feedstock: Black liquor, from which tall oil is obtained, is an aqueous solution separated from the cellulosic portions of wood in the manufacture of paper pulp by alkaline processes. It typically contains fatty acid soaps, resin soaps (rosin acid sodium salts), , and unsaponifiable organic compounds. The fatty acids are predominantly oleic and linoleic acids with small quantities of linolenic, stearic and palmitic acid. The rosin acids are monocarboxylic diterpene acids having a general formula C<NUM>H<NUM>O<NUM>. The predominant rosin acids are abietic and dehydroabietic acid.

When the black liquor from the Kraft process is concentrated, a large proportion of the soap will separate and can be collected by skimming it from the concentrated black liquor surface. BLS in general contains <NUM>-<NUM> wt. % of entrained water and has a sulfur content which typically ranges from <NUM>-<NUM> ppm, and a total solids sulfur content which typically ranges from <NUM>-<NUM> ppm.

Method for Purifying BLS: The BLS is purified for the removal of sulfur by being brought into contact with an aqueous alkaline solution comprising an inorganic base, via contact methods and equipment known in the art.

The contact with the aqueous alkaline solution is for any period of time of at least <NUM> minute, at least <NUM> minutes, at least <NUM> minutes, at least <NUM> minutes, and at least <NUM> hrs. The contact can be either con-current or countercurrent, or via a non-dispersive or dispersive method. The dispersive method can be via mixing tanks, vessels, static mixers, etc. The non-dispersive method can be via contactors.

The inorganic base is selected from the group consisting of NaOH, LiOH, KOH, and mixtures thereof. The aqueous alkaline solution is substantially free of brine, sulfate salts or carbonate salts, containing the inorganic base at a concentration of <NUM> - <NUM> mol/L, or <NUM> - <NUM> mol/L, or <NUM> - <NUM> mol/L, or <NUM> - <NUM> mol/L, or <NUM> - <NUM> mol/L, or <NUM> - <NUM> mol/L, or at least <NUM> mol/L of inorganic base. An aqueous <NUM>-<NUM> mol/L NaOH solution contains <NUM>-<NUM> wt.

Optionally, the aqueous alkaline solution comprises <NUM> to <NUM> wt. % of hydrogen peroxide, or alternatively <NUM> to <NUM> wt. % of hydrogen peroxide. The optional hydrogen peroxide can be added in doses of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> wt. Optionally, an anti-foaming agent can be added in BLS treatments which are conducted in the presence of hydrogen peroxide. An example is Antifoam A Concentrate defoamer (Merck).

The resulting black liquor soap phase is separated from the aqueous alkaline phase by known separation methods such as filtration, decantation or centrifugation and collected. The weight ratios of the applied aqueous alkaline solution/black liquor soap mixtures range from <NUM>/<NUM> to <NUM>/<NUM>, or at least <NUM>/<NUM> to <NUM>/<NUM>, or from <NUM>/<NUM> to <NUM>/<NUM>, or from <NUM>/<NUM> to <NUM>/<NUM>. The extraction processes can be any of batch, continuous, and combinations thereof.

In embodiments, the mixture of black liquor soap and aqueous alkaline solution is heated in an inert atmosphere or in a vacuum, wherein at elevated temperatures, e.g., from <NUM> to <NUM>, volatile impurities including but not limited to sulfur containing impurities are evaporated. The process step can be followed with one or more extractions of the resulting black liquor soap composition with an aqueous NaOH solution. In general, the applied vacuum can range from <NUM> mbar to <NUM> mbar, or <NUM> mbar to <NUM> mbar, or from <NUM> mbar to <NUM> mbar. The inert atmosphere is argon, neon, helium, krypton, xenon, steam, hydrocarbons like methane, carbon monoxide, hydrogen, and nitrogen gas.

First at <NUM>, the entrained water in BLS is evaporated and subsequently at more elevated temperatures, volatile impurities including but not limited to sulfur containing impurities are evaporated. Under these conditions, GC analyses data show that the main chemical composition had not substantially changed. For example, the relative total amount of abietadienoic acids (e.g., abietic acid, levopimaric acid, neoabietic acid and palustric acid) does not substantially change after <NUM> hour heating of BLS at <NUM> in an oven under a nitrogen atmosphere. In addition, the relative total amount of abietadienoic acids as compared to the relative amounts of dehydroabietic acid and dihydroabietic acids does not substantially change at this temperature or below.

At heating temperatures higher than <NUM>, GC analyses data show that the main chemical composition changes for some of the chemical components, for example, the relative total amount of some fatty acids such as linoleic acid and conjugated linoleic acids decreases and the relative amounts of the rosin acids dehydroabietic acid and dihydroabietic acids increases at the expense of the relative total amount of abietadienoic acids. Fatty acid thermal dimerization reactions and rosin acid disproportionation reactions can account for some of the observed differences in chemical composition by applying BLS heating temperatures higher than <NUM>.

The BLS can also be purified by means of heating black liquor soap in an atmosphere like air, which contains a substantial amount of oxygen, for a resulting BLS with decreased sulfur content but generally with a darker color.

In embodiments, the process steps can be repeated and after each extraction, the resulting black liquor soap phase is separated from the aqueous phase, and subsequently collected. After the last extraction, the resulting black liquor soap is optionally neutralized with an acid to adjust the pH to between <NUM> and <NUM>.

Properties: In embodiments, the BLS treated by the methods described herein has a total solids sulfur content reduced by at least any of <NUM>%, <NUM> %, <NUM>%, and <NUM>%. In one example, the purified BLS has its total solids sulfur content reduced to any of less than <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, and less than <NUM> ppm. The resulting crude tall oil product prepared from the purified BLS has a final solids sulfur content of less than <NUM> ppm, <NUM> ppm, <NUM> ppm, and less than <NUM> ppm. The depitched tall oil product in one embodiment has a total sulfur content of less than any of <NUM> ppm, <NUM> ppm, <NUM> ppm, and <NUM> ppm.

The depitched tall oil product has a color of any of less than <NUM> Gardner, <NUM> Gardner, and <NUM> Gardner.

With the purification process employing an alkaline solution substantially free from brine, sulfate salts or carbonate salts, the purified BLS is characterized as being substantially free of chloride content. In embodiments, the Cl- content is < <NUM>,<NUM> ppm, or < <NUM> ppm, or < <NUM> ppm, or < <NUM> ppm, or < <NUM> ppm, or < <NUM> ppm, or < <NUM> ppm.

End-use Applications / Products made from Desulfurized BLS: The desulfurized / purified BLS is particularly suitable for making tall oil fractions with reduced sulfur contents.

Upon acidification of the desulfurized / purified BLS with an acid such as sulfuric acid, crude tall oil (CTO) is obtained. The crude tall oil (CTO) can be dewatered and depitched in vacuum such as by short path evaporation to give a depitched crude tall oil fraction and tall oil pitch (TOP) fraction. Depitched crude tall oil can be further fractionated by fractional vacuum distillation to obtain tall oil fatty acid (TOFA), distilled tall oil (DTO), and tall oil rosin (TOR) fractions. These compositions are resulting from successive acidulation, dewatering, depitching and subsequent fractionations and chemical reactions of the purified BLS compositions.

In addition to having a reduced sulfur content, products obtained from the purified BLS composition exhibit features such as improved color, color stability, and improved odor properties such as reduced odor intensity and ameliorated odor hedonic tone properties. Light color and color stability are important characteristics for commercial acceptance of these tall oil fractions. Tall oil fatty acids, which consist primarily of oleic and linoleic acids, and tall oil fatty acid derivatives are typically used in alkyd coating, surfactant and emulsifier applications. Tall oil rosin derivatives, particularly esters of polyols such as glycerol and pentaerythritol, are used in products such as adhesives, lacquers and varnishes where a light colored product that retains its color under normal conditions of use is required.

In embodiments, desulfurized compositions derived from purified BLS, and desulfurized TOFA compositions prepared therefrom include TOFA amides, TOFA diamides, TOFA dimer, TOFA dimer derived polyamides, TOFA monomer and hydrogenated TOFA derivatives such as isostearic acid and stearic acid.

In embodiments, compositions prepared from the purified BLS include disproportionated tall oil rosin, hydrogenated tall oil rosin and tall oil rosin esters, including disproportionated tall oil rosin esters and hydrogenated tall oil rosin esters. Rosin esters are derived from one or more TORs and one or more polyhydric alcohols having <NUM> - <NUM> carbon atoms and having <NUM>-<NUM> average hydroxyl functionality, including ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, <NUM>,<NUM>'-isopropyl-idenedicyclohexanol, <NUM>,<NUM>-cyclohexanedimethanol, <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>,<NUM>-cyclobutanediol, <NUM>,<NUM>-bis(hydroxymethyl)tricyclo[<NUM>. <NUM><NUM>,<NUM>]decane, glycerol, diglycerol, polyglycerol, polyglycerol-<NUM>, polyglycerol-<NUM>, polyglycerol-<NUM>, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol, tripentaerythritol, mannitol, sorbitol, and xylitol. Optionally, one or more catalysts and color reducing agents can be applied during the rosin ester preparation. Non-limiting examples of esterification catalysts are Irganox® <NUM>, ZnO and MgO. Non-limiting examples of color reducing agents are <NUM>-fluorenone and xanthone. In embodiments, the tall oil rosin composition has a sulfur content < <NUM> ppm, or < <NUM> ppm, or < <NUM> ppm. In embodiments, the tall oil rosin ester composition has a color of < <NUM> Gardner, or < <NUM> Gardner.

Other embodiments include one or more polyhydric alcohols having <NUM> to <NUM> carbon atoms and having <NUM> to <NUM> average hydroxyl functionality alcohol, and optionally more than <NUM> up to <NUM> wt. % of all reactants of one or more dicarboxylic acid functional organic compounds. In embodiments, the desulfurized compositions derived from the desulfurized TOR compositions are oligoesters which are derived from one or more TORs, one or more TOFAs, one or more polyhydric alcohols, and optionally with up to <NUM> wt. % of all reactants of one or more dicarboxylic acid functional organic compounds. Other embodiments of desulfurized compositions resulting from the purified BLS include oligoesters and TOP esters, originating from a chemical reaction of TOP with one or more polyhydric alcohols having <NUM> to <NUM> carbon atoms and having <NUM> to <NUM> average hydroxyl functionality, and optionally more than <NUM> up to <NUM> wt. % of all reactants of one or more dicarboxylic acid functional organic compounds.

EXAMPLES: The examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.

Sulfur content (expressed as parts per million or ppm) can be measured according to ASTM D5453-<NUM>. Sulfur content can also be determined by Inductively Coupled Plasma with optical emission spectroscopy (ICP-OES) spectrometry or Inductively Coupled Plasma with mass spectrometry (ICP-MS).

Total chloride content (sum of Cl and chloride (Cl-), expressed as ppm) can be determined by sample combustion of an aliquot of accurately weighed sample, typically between <NUM> and <NUM>, in an oxygen bomb charged with <NUM>-<NUM> atmospheres of oxygen which is fired, whereafter the combustion gases are absorbed in a known volume of reducing solution (<NUM>% hydrogen peroxide). Measurement of chloride content in the resulting solution is performed by means of suppressed ion chromatography detection method, which is based on ASTM D <NUM>: Standard Test Method for Anions in Water by Chemically Suppressed Ion Chromatography. Instrument: Dionex Model DX500 chromatograph. Column: Dionex® IonPac® AS9-SC 4x250 mm. Eluent: <NUM> Na2CO3: <NUM> NaHCO3. Sample introduction: Auto injection (Hitachi Model AS7200). Determination: Conductivity detection/linear regression.

Gardner color can be measured according to ASTM D1544-<NUM> (<NUM>).

Rosin acid and tall oil fatty acid content in crude tall oil and its fractionation products can be determined according to ASTM D5974-<NUM> (<NUM>).

In examples to convert the BLS composition into the corresponding CTO composition, a sample (<NUM>) and <NUM> 2N potassium hydroxide (KOH) in ethanol were added to tall oil in a high pressure microwave reaction vessel. The sample was saponified in a microwave for <NUM> minutes at <NUM>. Upon completion of the microwave-assisted saponification, the reaction mixture was transferred to a separatory funnel, and dilute hydrochloric acid was added to reduce the pH value to < <NUM> to convert the rosin and/or fatty acid soaps to rosin and/or fatty acids. The resulting rosin acids were isolated by way of diethyl ether extraction. Upon removal of the diethyl ether solvent, the rosin acids were derivatized and analyzed according to ASTM D5974-<NUM> (<NUM>).

Oven heating experiments were conducted in a nitrogen atmosphere unless indicated otherwise. Oven heating rates amounted to approximately <NUM>/hour. One hour heating at the given oven temperature was applied unless indicated otherwise. BLS water content was derived by either determining the weight (mass) difference between aqueous BLS starting material and obtained BLS after heating to <NUM> in an oven under N<NUM> for <NUM> hour, or by applying an electronic moisture analyzer. If M1 is the weight of the initial (wet) BLS sample and M2 the weight following drying, the BLS total solids content is expressed as a ratio of weights obtained before and after the drying process and is expressed as M2/M1.

BLS total solids sulfur content (abbreviated as TSSC, expressed in ppm) can be calculated by dividing the sulfur content value of the wet BLS by the BLS total solids content. For example, BLS A, having a sulfur content of <NUM> ppm and water content of <NUM> wt%, has a BLS total solids content of <NUM> - <NUM> = <NUM> and a calculated BLS total solids sulfur content (TSSC) value of <NUM>/<NUM> = <NUM> ppm.

In the examples, three BLS materials were applied: BLS A: S content <NUM> ppm, water content <NUM> weight%; BLS B: S content <NUM> ppm, water content <NUM> wt. %; BLS C: S content <NUM> ppm, water content <NUM> wt. %, and <NUM> ppm total chloride content.

In the tables, weight percent is wt. %; hour: hr. ; minute: min; gram: g; liter: L; nitrogen: N<NUM>; room temperature: R. ; sulfur: S; aqueous: aq.

Example <NUM>. BLS A (<NUM>) was heated in an oven at <NUM> in N<NUM> atmosphere during which the formed water vapor was allowed to escape. After <NUM> hr. heating, sample was cooled to R. The formed anhydrous solid BLS showed S content of <NUM> ppm.

Examples <NUM>-<NUM>. An analogous procedure as described in Example <NUM> was executed with varying applied oven temperatures. Results and conditions are provided in Table <NUM>. Since the entrained water in BLS has evaporated during the oven heating, resulting purified BLS sulfur content values equal the calculated TSSC values in examples <NUM>-<NUM>.

Example <NUM>. <NUM> BLS B was added to a flask, equipped with thermocouple, N<NUM> gas inlet and outlet, mechanical stirrer and dropping funnel. A heating mantle was applied. NaOH (<NUM> wt. % NaOH, specific gravity (<NUM>/<NUM>) <NUM>, <NUM> mol NaOH/L) was slowly added during <NUM> by a dropping funnel to the stirred mixture at <NUM>. After the addition, the mixture was stirred for one hour. NaOH layer was allowed to separate from the BLS layer during <NUM> at <NUM> and separated from the upper BLS layer. The collected BLS fraction showed S content of <NUM> ppm.

Example <NUM>. The BLS material formed in example <NUM> was extracted twice according to procedure of example <NUM> to provide purified BLS having S content of <NUM> ppm.

Example <NUM>. <NUM> BLS A was extracted according to the procedure of example <NUM> with two modifications: A) a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH:BLS was applied, and B) the BLS layer after the extraction was separated by centrifugation (<NUM> rpm for <NUM>). This extraction procedure was repeated twice. The obtained BLS fraction after the third extraction showed S content of <NUM> ppm. The calculated BLS total solids sulfur content (TSSC) value amounted to <NUM>/<NUM> = <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with two modifications: A) a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH:BLS was applied and, B) a temperature of <NUM> was applied. The obtained BLS fraction after the third extraction showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted but with <NUM> and at <NUM>, with two consecutive extractions. The BLS fraction after the second extraction showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with <NUM> BLS with the following three modifications: A) a <NUM>:<NUM> weight ratio of <NUM> % aq. NaOH:BLS was applied, B) a temperature of <NUM> was applied, and C) one extraction was performed. The collected BLS fraction showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with BLS C with the following modification: a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH:BLS was applied. The collected BLS fraction showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with BLS C with two modifications: A) a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH, <NUM> mol NaOH:BLS was applied, and B) one extraction was performed. <NUM> BLS was extracted. The collected BLS fraction (<NUM>) showed S content of <NUM> ppm, and less than <NUM> ppm total chloride content.

Example <NUM>. The procedure of example <NUM> was conducted with one modification: a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH, <NUM> mol NaOH:BLS was applied. The collected BLS fraction showed S content of <NUM> ppm.

Example <NUM>. BLS obtained analogously to the procedure of example <NUM> was heated as described in example <NUM>. The resulting BLS showed S content of <NUM> ppm.

Example <NUM>. BLS obtained analogously to the procedure of example <NUM> was heated analogously to the procedure of example <NUM> but at <NUM> instead of <NUM>. The resulting anhydrous BLS showed S content of <NUM> ppm.

Example <NUM>. BLS obtained analogously to the procedure of example <NUM> was heated analogously to the procedure of example <NUM> but at <NUM>. The resulting anhydrous BLS showed S content of <NUM> ppm.

Example <NUM>. BLS obtained analogously to the procedure of example <NUM> was heated analogously to the procedure of example <NUM>, but at <NUM>, followed by heating for <NUM> hr. in vacuum (<NUM> mbar) at <NUM>. The resulting BLS showed S content of <NUM> ppm.

Example <NUM>. BLS obtained analogously to the procedure of example <NUM> was heated for <NUM> hr. in vacuum (<NUM>) mbar at <NUM>. The resulting anhydrous BLS showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with one modification: A) a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH:BLS was applied. The collected BLS was heated analogously to the procedure of example <NUM> but at <NUM>. The resulting anhydrous BLS showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with a modification: a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH (<NUM> mol NaOH/L):BLS was applied. The obtained BLS layer was heated analogously to the procedure of example <NUM> but at <NUM>. The obtained BLS showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was conducted with a modifications: a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH (<NUM> mol NaOH/L):BLS was applied. The resulting anhydrous BLS showed S content of <NUM> ppm.

Example <NUM>. The obtained BLS in example <NUM> was heated analogously to the procedure of example <NUM> but at <NUM>. The resulting BLS showed S content of <NUM> ppm.

Example <NUM>. The obtained BLS in example <NUM> was heated analogously to the procedure of example <NUM>. The resulting BLS showed S content of <NUM> ppm.

Example <NUM>. To <NUM> of the obtained anhydrous BLS in example <NUM> was added <NUM> water. To the resulting mixture was added <NUM> of <NUM> wt. Extraction was performed analogously to the procedure of example <NUM> with the following modification: a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH:BLS was applied. The obtained BLS after the extraction showed S content of <NUM> ppm.

Example <NUM>. Purified BLS material (having less than <NUM> ppm total chloride content and S content of <NUM> ppm, TSSC value <NUM> ppm) obtained from BLS C, analogously to the procedure of example <NUM> by applying <NUM> wt. NaOH instead of <NUM> wt. NaOH, was subsequently adjusted to pH = <NUM> with <NUM> wt. H<NUM>SO<NUM>. The resulting BLS was heated to <NUM> for <NUM> hr. analogously to the procedure described in example <NUM>. A <NUM> wt. % portion of water was added to the obtained anhydrous BLS.

The resulting mixture was acidulated to CTO. The BLS was heated to <NUM>. H<NUM>SO<NUM> was slowly added by a dropping funnel to the BLS until a pH value of <NUM> was obtained. The resulting mixture was subjected to collect the CTO phase and wash with water. The resulting CTO showing S content of <NUM> ppm was depitched in a wiped film evaporator at a pressure of <NUM> Hg, at <NUM>, by applying a feed rate of <NUM>/min. A depitched CTO fraction showed S content <NUM> ppm, Antek method, S content <NUM> ppm, ICP-OES, color <NUM> Gardner, and a tall oil pitch fraction showed S content <NUM> ppm, Antek method; S content <NUM> ppm, ICP-OES method were obtained.

Example <NUM>. BLS C was heated analogously to the procedure of example <NUM> but with applied oven temperature of <NUM>. Part of the formed BLS (<NUM>) was dissolved in water (<NUM>). The resulting mixture was extracted with <NUM> of <NUM> wt. NaOH analogously to the procedure of example <NUM>. The resulting BLS showed S content of <NUM> ppm (TSSC value <NUM> ppm) and was subsequently acidulated into CTO analogously to the procedure of example <NUM>. The S content of the obtained CTO amounted to <NUM> ppm.

Example <NUM> (Comparative). BLS C was acidulated analogously to the procedure of example <NUM> to give CTO having an S content of <NUM> ppm.

Example <NUM> (Comparative). BLS B was acidulated to CTO and depitched analogously to the procedure of example <NUM>. A depitched tall oil fraction (S content <NUM> ppm, Antek method, S content <NUM> ppm, ICP-OES, color <NUM> Gardner) and a tall oil pitch fraction (S content <NUM> ppm, Antek method; S content <NUM> ppm, ICP-OES) were obtained.

Example <NUM>. Solution A was prepared by dissolving NaOH (<NUM>) and H<NUM>O<NUM> (<NUM> of a <NUM> wt. solution) in water (<NUM>). BLS A was extracted at <NUM> with <NUM> of solution A slowly added by using a dropping funnel and rapid stirring (<NUM> rpm) to control foaming. After the addition, the resulting mixture was kept at <NUM> for <NUM> without stirring, subsequently heated up to <NUM> and thereafter stirred for <NUM> hr. (<NUM> rpm). The resulting BLS layer was separated from the mixture by centrifugation. The collected BLS fraction showed S content of <NUM> ppm.

Example <NUM>. The procedure of example <NUM> was executed with the following modification: A) a <NUM>:<NUM> weight ratio of <NUM> wt. NaOH:BLS was applied starting with <NUM> BLS A. The collected BLS fraction after the third extraction showed S content of <NUM> ppm and a water content of <NUM> wt.

Example <NUM>. Purified BLS material obtained from BLS C, analogously to the procedure of example <NUM> by applying <NUM> wt. NaOH instead of <NUM> wt. NaOH, was subsequently heated to <NUM> for <NUM> hr. analogously to the procedure described in example <NUM>. The obtained anhydrous BLS showed S content of <NUM> ppm.

Example <NUM>. Solution B was prepared by dissolving NaOH (<NUM>) and H<NUM>O<NUM> (<NUM> of a <NUM> wt. solution) in water (<NUM>). Antifoam A Concentrate (<NUM>) (Merck) was added to BLS B (<NUM>). The resulting BLS was treated at <NUM> with <NUM> of solution B which was slowly added (dropping funnel) under rapid stirring (<NUM> rpm). The resulting mixture was slowly heated to <NUM> and stirred for <NUM>. The resulting BLS layer was separated from the mixture by centrifugation (<NUM> rpm for <NUM>) and showed S content of <NUM> ppm. Subsequent acidulation analogously to the procedure of example <NUM> gave CTO having S content of <NUM> ppm. <NUM> of the obtained CTO was dehydrated at <NUM> mbar at <NUM> prior to depitching. Depitching was performed by vacuum distillation (conditions: <NUM> mbar, <NUM>-<NUM>, <NUM> distillation bridge height) which gave a depitched CTO distillate (<NUM>, S content <NUM> ppm) and a tall oil pitch residue (S content <NUM> ppm).

Claim 1:
A method of purifying black liquor soap (BLS) from sulfur compounds , the method comprising:
subjecting the BLS to one or more extractions with an aqueous alkaline solution containing less than <NUM>% by weight of brine, sulfate salts and carbonate salts as well as comprising <NUM>-<NUM> mol/L of an inorganic base, wherein the inorganic base is selected from the group consisting of NaOH, LiOH, KOH and any combination thereof, the weight ratio of the applied aqueous alkaline solution/BLS is greater than <NUM>/<NUM> and less than <NUM>/<NUM>, wherein after each extraction, the resulting BLS phase is separated from the aqueous phase; and subsequently collected as purified BLS;
wherein the purified BLS has a total solids sulfur content which is reduced by at least <NUM> %, and a chloride content of less than <NUM> ppm.