WO2000004038A1

WO2000004038A1 - Isolation and purification of sterols from neutrals fraction of tall oil pitch by direct precipitation

Info

Publication number: WO2000004038A1
Application number: PCT/US1999/014134
Authority: WO
Inventors: Raymond S. Vicente; Thomas J. Cuff; Philip L. Robinson; Jane F. Byrne
Original assignee: Westvaco Corporation
Priority date: 1998-07-14
Filing date: 1999-07-12
Publication date: 2000-01-27
Also published as: AU4958299A; AR019779A1

Abstract

Sterols from the neutrals fraction of tall oil pitch are disclosed to be isolated and purified by a process of a liquid-liquid extraction where the hydrocarbon extraction stream is washed with an aqueous methanol solution to remove methanol-soluble impurities. The hydrocarbon/methanol/neutrals solution is allowed to cool to from about 25-40 °C, and water is then added, with agitation, to facilitate crystallization of sterols, which crystals are recovered by filtering.

Description

ISOLATION AND PURIFICATION OF STEROLS FROM NEUTRALS FRACTION OF TALL OIL PITCH BY DIRECT PRECIPITATION

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is related to methods of isolating and purifying the valuable constituents from Crude Tall Oil (CTO) recovered from the black liquor residue of wood pulping processes, primarily used in making paper. More particularly, the present invention is related to methods of extraction of valuable constituents from the neutrals fraction of CTO. Most particularly, the present invention is related to methods of isolation and purification of extracted or distilled constituents of the neutrals fraction of CTO which, upon said purification and subsequent modification, are useful as a dietary supplement in foods to reduce cholesterol levels in humans .

Description of Related Art

It has long been appreciated that the black liquor residue from wood pulping contains valuable chemicals, which make up the CTO, with various industrial applications. The black liquor contains the soaps of rosin and fatty acids, as well as sodium lignate and the spent cooking chemicals for reuse. The CTO is recovered by partially evaporating the black liquor, for concentration purposes, and then skimming off the tall oil soaps which float to the top of a skimming tank. The soap skimmings are converted to CTO by reaction with sulfuric acid and then separated from the simultaneously- formed spent acid by batch cooking, continuous centrifuging, or continuous decanting. The CTO is normally divided into various fractions by distillation which first extracts the pitch (or bottoms) . The depitched CTO is then separated into fractions of heads, tall oil rosin (TOR) , tall oil fatty acids (TOFA) , and distilled tall oil (DTO) . A major ingredient of the neutral fraction of CTO, concentrated in the pitch fraction thereof, is a class of compounds known as sterols, including sitosterol . It is known, however, that a better place to obtain these sterols is via solvent extraction of tall oil soap, which is done commercially in Scandinavia.

Recently, U.S. Patent No. 5,502,045 disclosed the use (by ingestion) of a β-sitostanol fatty acid ester for reducing serum cholesterol level. The patent's assignee, Raisio, a Finnish manufacturer of foodstuffs, grain, and specialty chemicals, has developed a cholesterol-reducing margarine called Benecol^®. The active ingredient (in cholesterol reduction) in Benecol^* is the claimed fat-soluble stanol ester which prevents cholesterol from being absorbed into the human digestive system. The stanol ester is produced from plant-derived sterols (phytosterols) via hydrogenation and trans-esterification reactions. Cholesterol reductions (LDL and HDL) of 10-15% are common for individuals with diets containing Benecol^* . Therefore , the value of recovering plant -derived sterols has become enhanced and the particular problems associated with recovering sitosterol from tall oil pitch worthy of investigation . A viable commercial process must achieve a high percent recovery of neutrals and/or sterols (greater than 70% recovery is preferable) and achieve high final sterol purity (higher than 95% is desirable) . Past attempts to extract neutrals/sterols from one or more fractions of CTO are reported in the following patents :

u.s. Inventor Title

NOS

2,499,430 Vogel et al "Obtaining Sterols of High Purity" 2,530,809 Chπstenson et al "Fractionation of Tall Oil* 2,530,810 Chnstensen, et al "Separation of Unsapomflable from Tall Oil Residue" 2,547,208 Hasselstrom et al "Method for the Refining of Tall Oil Residue" 2,715,638 Albrecht et al "Production of Sterols from Tall Oil Pitch" 2,835,682 Sterner et al "Sterol Recovery Process* 2,866,781 Chase et al "Separating Non-acids from Soap Stocks" 2,866,797 Berry et al "improved Process of Isolating 3,840,570 Julian et al "Process for Preparing Sterols Tall Oil Pitch" 3,879,431 Clark et al "Puri ication of Sterols by Distillation" 3,965,085 Holrabom et al "Method for Refining of Soaps Using Solvent Extraction" 4,044,031 Johansson et al "Process for the Separation of Sterols" 4,124,607 Beaton et al "Preparation of Sterol Substates for Bioconversion^* 4,153,622 Lammin ari et al "Process for the Recovery of Beta-Sitosterol" 4,420,427 Hamunen "Process for the Separation of Sterols or Mixtures of Sterols" 4,422,974 Hamunen "Process for the Purification of Beta- Isolated from the Unsapomflables from the Cellulose Process"

4,422,966 Ame "Separation of Neutrals from Tall Oil Soaps"

4,496,478 Kulkarm et al "Process for Separating Unsapomflables from Fatty and Rosin Acids"

4,524,024 Hughes "Processes of Recovering Fatty Acid Sterols from Tall Oil Pitch"

4,849,112 Barder et al "Adsorption Separation of Sterols from Tall Oil Pitch with Carbon Adsorbent"

4,935,168 S]δberg et al "Process for the Preparation of Alcohols*

5, 097,012 Thies et al "Solvent Extraction of Fatty Acid Stream with Liquid Water and Elevated Temperatures and Pressures" These approaches have failed to provide both a high percent recovery of neutrals and/or sterols and a high final sterol purity. It is an object of this invention, therefore, to provide a method for recovering the single-solvent extracted or distilled neutral fraction of saponified tall oil pitch and isolating a high percentage of the sterol component thereof. It is a further object of this invention to obtain the isolated sterols at a high purity.

SUMMARY OF THE INVENTION

The above-stated objects of the invention are achieved by isolating the sterol component of the neutrals fraction of saponified tall oil pitch. The isolation is accomplished by a liquid-liquid extraction from the neutrals where an alcohol solvent, preferably methanol, is added to the hydrocarbon extraction stream. The hydrocarbon/alcohol/neutrals solution is allowed to cool to about 20-35°C and water is added, with agitation, to facilitate crystallization of sterols. The alcohol-soluble impurities remain in the aqueous-alcohol solution.

BRIEF DESCRIPTION OF THE DRAWING (S)

The Figure represents a flow diagram of the claimed process of isolation and purification of sterols from the neutrals fraction of tall oil pitch by direct precipitation. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention direct precipitation involves precipitating sterols from a solution of extracted, or distilled, tall oil pitch neutrals in a hydrocarbon solvent, preferably heptane, and an alcohol solvent, preferably methanol, by adding water (at a temperature of about 20-35°C) with agitation. Yields average 75% based on the weight of sterols recovered, divided by the available sterols in the neutrals. Purities are in the 92-98% range, with negligible contamination by wax alcohols. The ratio of heptane to methanol (10:1) appears to be crucial in obtaining pure sterols .

In a preferred embodiment of the invention process, the first step involves dissolving concentrated (solventless) single-solvent extraction neutrals of a tall oil pitch fraction in a mixture of heptane and methanol in a ratio between 2 and 5 parts hydrocarbon and 0.1 to 0.5 parts methanol to 1 part neutrals. (For the purposes of the following examples, solventless single-solvent extraction neutrals are prepared in the laboratory; but, in actual plant operation, the neutrals remain in residual heptane from the flash vessel following the single-solvent extraction operation. A temperature of 50-60°C is sufficient to dissolve the neutrals in the lab.) Next, the mixture is allowed to cool to 20-35°C and water (1 part) is added with agitation to precipitate the sterols. Finally, the sterol precipitate is vacuum filtered and washed with heptane (1-2 parts) . The most consistent results were obtained with 3.5 parts heptane, 0.35 parts methanol, and 1 part neutrals. Sterol yields and purities from the direct precipitation are given in Table I.

TABLE I

Sterol Crystallization Data for Single Decantation Precipitation (SDP) Process

The methanol appears to affect purity when the water addition is kept constant. At heptane/methanol ratios above or below 10:1, purities were below 90%. For example, at a heptane/methanol ratio of 50:1 (entry 9) , the sterol purity was near 64%, and the filter cake appeared dark brown. At a heptane/methanol ratio of 5:1 (entry 1), the sterol purity was near 89%, and again, the filter cake was contaminated with a brown impurity. Wax alcohol contamination increases from near zero to 1.2% and then to 3.2% as the heptane/methanol ratio increases from 10:1 to 20:1 (entry 8) and then to 50:1 (entry 9) . At heptane/methanol ratios of 10:1, there appears to be 2- 3% other elutants and approximately 4-6% non-eluting impurity. The non-eluting impurity likely could be removed by more efficient washing of the sterol filter cake. Further work is necessary to better define the nature of the impurities and the methods for removing them.

In another set of experiments, the direct precipitation process proceeds as follows. Again, the dry (solventless) neutrals are dissolved into a refluxing mixture of heptane and methanol. The heptane is at ratios between two and five parts heptane to one part single-solvent extraction neutrals, and the methanol is 0.2 to 0.5 parts to one part neutrals. The mixture of heptane, methanol, and neutrals is then allowed to cool to the final precipitation temperature, and at the specified agitation rate, water (0.5 to 1.5 parts) is added to precipitate the sterols. This mixture is held stirring for the specified agitation time. Finally, the sterol granules that precipitate are filtered from the two liquid phases and the solid is washed with an additional two parts heptane on the Buchner f nnel. The sterols are then dried, weighed, and analyzed for mass yield, sterol yield, and sterol purity. Again, the key variables listed in the general procedure above are the heptane content, methanol content, crystallization water content , crystallization temperature, crystallization agitation time, and crystallization agitation rate. The high, low, and center point values are listed for each variable in Table II.

TABLE II

Ranges for Variables in Single Decantation Precipitation (SDP) Process

(a) Parts refers to the relative weight ratio of the variable to the amount of neutrals used in the experiment. For example, experiments performed with the high heptane value were run with five parts heptane to one part neutrals.

The results from Examples 10-31 of the direct precipitation process are given in Table III. The mass yields range from 0 to 100%; sterol yields range from 0 to 82.9%; and the purities range from 0 to 96.1%. Again, one experiment (Example 14) produced an emulsion that did not settle well, therefore, a very low sterol yield was obtained. This run had high heptane, high methanol, and high crystallization water conditions, which led to problems. The center point in the design was replicated six times to give an assessment of the reproducibility of the experiment. The mean and standard deviation for the six center point experiments were 78.3 ± 2.4% for mass yield, 73.2 ± 2.9% for sterol yield, and 93.6 ± 3.6% for sterol purity.

Mean and standard deviation center po nts - 18.412.4 93.613.6 13.212.9

Mass Yield - grams recovered/available sterols Sterol Yield - mass yield x purity Neutrals Source ( 33 4% stetols) The subject matter of the invention is:

(1) A method for the isolation of sterols from the neutrals fraction of tall oil pitch comprising the steps of:

(a) dissolving said dry neutrals by heating with a hydrocarbon solvent in a ratio of two to five parts hydrocarbon solvent to one part neutrals;

(b) blending the hydrocarbon solution of neutrals with a 1- 4:0.1-0.5 mixture, respectively, of an alcohol solvent and water at a temperature from about 50 °C to about 60 °C;

(c) the blended solution is cooled to a final crystallization temperature from about 20°C to about 40°C;

(d) upon reaching said final crystallization temperature, an equal part of water is added with agitation to precipitate sterol granules; and

(e) the sterol granules are recovered by filtering;

(2) The method of (1) wherein the extraction neutrals of tall oil pitch are derived by a process selected from the group consisting of solvent extraction and distillation;

(3) The method of (1) wherein the hydrocarbon solvent is selected from the group consisting of straight- and branched- chain hydrocarbons with from 5 to 10 carbons;

(4) The method of (3) wherein the hydrocarbon solvent is selected from the group consisting of pentane, hexane, heptane, and iso-octane;

(5) The method of (1) wherein the alcohol solvent is an aliphatic alcohol; and (6) The method of claim 5 wherein the alcohol solvent is selected from the group of aliphatic alcohols consisting of methanol, ethanol, butanol, and iso-propanol .

(7) A method for the isolation of sterols from a hydrocarbon solution of tall oil pitch neutrals comprising the steps of:

(a) blending the hydrocarbon solution of neutrals with a 1- 4:0.1-0.5 mixture, respectively, of an alcohol solvent and water at a temperature from about 50°C to about 60 °C;

(b) the blended solution is cooled to a final crystallization temperature from about 20°C to about 40°C;

(c) upon reaching said final crystallization temperature, an equal part of water is added with agitation precipitate sterol granules; and

(d) the sterol granules are recovered by filtering.

Modifications to this invention will occur to those skilled in the art. Therefore, it is to be understood that this invention is not necessarily limited to the particular embodiments disclosed; rather, it is intended to cover all modifications which are within the true spirit and scope of this invention, as disclosed and claimed herein.

Claims

What is claimed is:

1. A method for the isolation of sterols from the neutrals fraction of tall oil pitch comprising the steps of:

(b) blending the hydrocarbon solution of neutrals with a 1- 4:0.1-0.5 mixture, respectively, of an alcohol solvent and water at a temperature from about 50┬░C to about 60 ┬░C;

(c) the blended solution is cooled to a final crystallization temperature from about 20┬░C to about 40┬░C;

(d) upon reaching said final crystallization temperature, an equal part of water is added with agitation precipitate sterol granules; and

(e) the sterol granules are recovered by filtering.

2. The method of claim 1 wherein the extraction neutrals of tall oil pitch are derived by a process selected from the group consisting of solvent extraction and distillation.

3. The method of claim 1 wherein the hydrocarbon solvent is selected from the group consisting of straight- and branched- chain hydrocarbons with from 5 to 10 carbons.

4. The method of claim 3 wherein the hydrocarbon solvent is selected from the group consisting of pentane, hexane, heptane, and iso-octane.

5. The method of claim 1 wherein the alcohol solvent is an aliphatic alcohol.

6. The method of claim 5 wherein the alcohol solvent is selected from the group of aliphatic alcohols consisting of methanol, ethanol , butanol, and iso-propanol .

7. A method for the isolation of sterols from a hydrocarbon solution of tall oil pitch neutrals comprising the steps of :

(a) blending the hydrocarbon solution of neutrals with a 1- 4:0.1-0.5 mixture, respectively, of an alcohol solvent and water at a temperature from about 50┬░C to about 60 ┬░C;

(b) the blended solution is cooled to a final crystallization temperature from about 20┬░C to about 40┬░C;

(d) the sterol granules are recovered by filtering.