WO2000034305A1

WO2000034305A1 - Isolation and purification of sterols from neutrals fraction of tall oil pitch by dual decantation crystallization

Info

Publication number: WO2000034305A1
Application number: PCT/US1999/014137
Authority: WO
Inventors: Philip L. Robinson; Thomas J. Cuff; Julian E. Parker, Iii
Original assignee: Westvaco Corporation
Priority date: 1998-12-07
Filing date: 1999-07-12
Publication date: 2000-06-15
Also published as: AU4958599A; AR019781A1

Abstract

Isolation of the sterol component of a sterol-rich fraction of saponified tall oil pitch is disclosed. Sterol isolation is accomplished by deriving from the tall oil pitch a sterolrich fraction in a hydrocarbon (preferably heptane) phase at a relatively high temperature (preferably greater than 50 °C) to which small amounts of an alcohol solvent, preferably methanol, is added. To the hydrocarbon/alcohol/sterols solution is then added water (preferably of a temperature of at least 25 °C, and more preferably, 60-70 °C) to result in the formation fo two separate phases. The lower water/alcohol phase is decanted, after which additional water at high temperature (preferably 60°-70 °C) is again added to the remaining hydrocarbon phase to result again in an upper hydrocarbon phase and a lower water phase. Upon the decantation of the lower water phase, the remaining upper hydrocarbon phase is cooled to facilitate crystallization of sterols. The sterol crystals are isolated by filtration and then washed with hydrocarbon solvent to result in high yield and high purity.

Description

ISOLATION AND PURIFICATION OF STEROLS FROM NEUTRALS FRACTION OF TALL OIL PITCH BY DUAL DECANTATION CRYSTALLIZATION

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

CTO and Crude Sulfate Turpentine (CST) are major, renewable, chemical raw materials obtained from the kraft (sulfate) pulping of various coniferous trees. Coniferous trees, especially pine, contain resin acids in the free form, long chain fatty acids, and volatile terpenes. These materials, which are a major part of the wood extractives, are released from the wood during the kraft pulping process.

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. On concentration of the spent pulping liquor, the sodium soap of these mixed acids rise to the surface and can be skimmed off. This material is referred to as "soap skimmings" or "tall oil soap." 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 de-pitched 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 β-sitosterol. It is known, however, that an accepted process to obtain these sterols is 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 specially 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 sistosterol from tall oil pitch have become 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:

Patent No. Inventor Title

US 2,499,430 Vogel et al. "Obtaining Sterols of High Purity" US 2,530,809 Christenson et al. "Fractionation of Tall Oil"

US 2,530,810 Christensen, et al. "Separation of Unsaponifiable Matter from Tall Oil Residue"

US 2,547,208 Hasselstrora et al. "Method for the Refining of Tall Oil

Residue" S 2,715,638 Albrecht et al. "Production of Sterols from Tall Oil

Pitch" Patent No. Inventor Title US 2,835,682 Steiner et al. "Sterol Recovery Process" US 2,866,781 Chase et al. "Separating Non-acids from Soap Stocks" US 2,866,797 Berry et al. "Improved Process of Isolating Sterols" US 3,840,570 Julian et al. "Process for Preparing Sterols from Tall Oil Pitch"

US 3,879,431 Clark et al. "Purification of Sterols by Distillation"

US 3,965,085 Holmbom et al. "Method for Refining of Soaps Using Solvent Extraction"

US 4,044,031 Johansson et al. "Process for the Separation of Sterols"

US 4,124,607 Beaton et al. "Preparation of Sterol Substrates for Bioconversion"

US 4,420,427 Hamunen "Process for the Separation of sterols or Mixtures of Sterols"

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

US 4,496,478 Kulka ni et al. "Process for Separating Unsaponifiables from Fatty and Rosin Acids"

US 4,524,024 Hughes "Processes of Recovering Fatty Acids and Sterols from Tall Oil Pitch"

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

US 4,935,168 Sjoberg et al. "Process for the Preparation of Alcohols"

US 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 . Recently, it was discovered that sterols could be isolated from the solvent extraction neutrals mixture from a tall oil pitch fraction using a single decantation precipitation process (described in commonly-owned U.S . Application Serial No. 09/115, 002, filed on July 14, 1998 ) . Briefly, in the single decantation precipitation process, the partially concentrated (20-50% solids) solvent extraction neutrals are washed with aqueous methanol, phase separated, and cooled to 20-30°C. Next, water is added to precipitate sterols from the hydrocarbon phase, still at 20-30°C. Unfortunately, this often results in precipitating very small crystals, which can present filtration difficulties, as the small crystals are filtered during the sterol isolation step. It is anticipated that generation of larger crystals not only would improve sterol filterability, but improve sterol yields and purity as well.

Therefore, it is an object of this invention to provide a method for recovering the solvent-extracted or distilled neutral fraction of saponified tall oil pitch and isolating a high percentage of the sterol component thereof, by treating the neutral fraction to isolate therefrom sterol crystals of enhanced size to result in improved sterol yields and purity.

SUMMARY OF THE INVENTION

The above-stated objects of the invention are achieved by isolating the sterol component of a sterol-rich fraction of saponified tall oil pitch, such as the neutrals fraction, via the invention dual decantation- crystallization. The first step in the invention sterol isolation process is accomplished by obtaining the sterol-rich fraction from the tall oil pitch fraction. Then the sterol-rich phase, in a hydrocarbon (preferably heptane) , is blended with an alcohol solvent, preferably methanol, at elevated temperatures (e.g., above 25°C, preferably in a range of 60-70°C) . To the hydrocarbon/alcohol/sterols solution is added small amounts of water; after which the hydrocarbon/alcohol/sterols/water solution is allowed to separate into a hydrocarbon phase, containing the sterols, and an alcohol/water phase (in which remain the alcohol-soluble impurities) , which latter phase is decanted away. Again, at the elevated temperature range, water is added, with agitation, to the remaining sterol-containing hydrocarbon phase. This mixture is allowed to separate into a hydrocarbon phase, containing the sterols, and a water/alcohol phase (with water soluble impurities) , and the latter phase is decanted away. The washed mixture is allowed to cool slowly to about 20-30°C and receives a final injection of alcohol to aid in the purification of sterol crystal which form. Finally, the sterol crystals are recovered by solid-liquid separation.

BRIEF DESCRIPTION OF THE DRAWING

The Figure represents a flow diagram of the claimed process of isolation and purification of sterols from solvent-extracted neutrals of saponified tall oil pitch by dual decantation- crystallization, as described herein.

DESCRIPTION OF THE PREFERRED EMBODIMENT (S. The invention dual decantation crystallization process of recovering sterols from a solution of extracted, or distilled, tall oil pitch fraction rich in sterols, such as a neutrals fraction, is accomplished by, first, extracting the sterol-rich fraction from the tall oil pitch fraction. Then the obtained sterol-rich phase, in a hydrocarbon, selected from the group consisting of straight- and branched-chain hydrocarbons with from 5 to 12 carbons (preferably heptane), is blended with a first "wash" alcohol solvent, preferably methanol. To the hydrocarbon/alcohol/sterols solution is added small amounts of a first "wash" water; after which the hydrocarbon/alcohol/sterols/water solution is allowed to separate into an upper hydrocarbon phase, containing the sterols, and a lower alcohol/water phase (in which remain the alcohol-soluble impurities), which latter phase is decanted away. (In an alternative embodiment, the initial "washing" of the hydrocarbon/neutrals solution is accomplished with an aqueous alcohol solution (i.e., first wash alcohol and first wash water combined).) The first wash step transfers extracted impurities from the hydrocarbon phase into the alcohol phase. At an elevated temperature range (60°-70°C), a second "wash" water is added, with agitation, to the remaining sterol- containing hydrocarbon phase to remove additional impurities, and the mixture is allowed to separate into an upper hydrocarbon phase and a lower water phase. Upon decantation of the water phase, the hydrocarbon phase is allowed to cool (to about 20- 30°C) and, preferably, receives a final injection of alcohol to aid in the purification of sterol crystals which form upon cooling. The sterol crystals are recovered by solid-liquid separation, and, finally, the crystals are washed. The invention is further described by the following examples. Example 1

In a first quarter fractional factorial, Plackett-Burman designed experiment for the invention dual decantation crystallization process, 16 experimental runs were conducted with six center points, giving a total of 22 randomized runs. Both wash steps (the first was with alcohol and water combined) were done at 60-65°C. All else was done according to the general procedure given above. Table I shows the variables and ranges employed.

TABLE I Variables and Ranges

(^a) Parts refers to the relative weight ratio of the variable to the amount of neutrals used in the experiment.

(^b) Agitation rate refers to the rate of agitation of the organic phase during crystallization. The results from each run in this example are given in Table II .

TABLE II

Yield and purity values ranged from 28-74% and 77-94%, respectively. The mean and standard deviation for the six center point runs were 70.0 ±2.6% for mass yield, 58.9 ±3.2% for sterol yield, and 84.1 ±2.3% for sterol purity. None of the variables significantly affected the mass yield or sterol yield; however, the final temperature and 1st wash water content affected sterol purity and wax alcohol contamination, with the higher temperature and lower 1st wash water loading favored for both. The R-squared values indicate the model explained 68% of the variability in the mass yield, and 64% of the variability in the sterol yield. The R-squared values for purity and wax alcohol content were better (80 and 86% respectively) .

Example 2

This example also was a quarter fractional factorial Plackett-Burman design with 16 experimental runs and six center points, giving a total of 22 randomized runs. Again, both wash steps were done at 60-65°C (also, first wash was "combined") . All else was done according to the general procedure given above, except that a small amount of methanol was injected into the heptane phase after the final water wash and before the slow cooling crystallization step. Again, the purpose of adding methanol to the heptane phase prior to crystallization was to replace the methanol extracted into the water phase during the second (water) wash stage with vigorous agitation. This methanol inhibits co-crystallization of wax alcohols with concentrations will be needed during crystallization.

Table III shows the variables and ranges employed. Notice that the injected methanol was added as a variable in place of the agitation rate, which was held constant at 262 rad/s (250 rpm) for this set of experiments. Also, the final crystallization temperatures and crystallization times were adjusted based on proposed operations of a plant crystallizer.

TABLE III Variables and Ranges

(^a) Parts refers to the relative weight ratio of the variable to the amount of neutrals used in the experiment. The results from each run in the second experimental design are given in Table IV.

TABLE IV

Yields and purities ranged from 21-69% and 94-98%, respectively. The mean and standard deviation for the six center point runs were 44.3 ± 2.9% for mass yield, 42.7 ± 2.9% for sterol yield, 96.5 ± 0.6% for sterol purity, and 0% for wax alcohol. Lower heptane loadings, methanol loadings, and final temperatures gave increased yields, while higher heptane and lower 1st wash water loadings gave better purities. None of the variables affected wax alcohol contaminations once the crystallization methanol was included in the procedure. R- squared values for this experiment were higher than the previous experiment. The model explained 91% of the variability in the mass and sterol yields, approximately 80% of the variability in the purity, and 84% in the wax alcohol content.

As anticipated, the addition of a small amount of methanol prior to the crystallization step suppressed co-crystallization of wax alcohols with sterols. The best experiment in this example (run 3) gave near 65% yield and 95% purity. In general, however, problems were encountered with low yields, which likely resulted from poor phase separation. Several conditions gave no phase separation at all during the methanol/water wash step, and in these instances, the procedure mimics the single decantation crystallization (SDC) process (as disclosed in commonly owned U.S. patent application Serial No. 09/187,448, filed on November 6, 1998) . The reason for poor phase separation is thought to be a low wash water volume relative to the methanol content. Two experiments in this example (runs 3 and 12) had crystals form at high temperatures after the water addition. The reason for this is unclear. In any case, these conditions gave 64-65% sterol yield and 95-96% purity.

Example 3

This example is a half fractional, factorial Plackett- Burman design. Here, 16 experimental runs were coupled with four center points to give a total of 20 randomized experiments. In this example, the wash step was performed by mixing the neutrals in heptane with methanol at 65°C. The mixture was allowed to cool to 25°C, and water was added with agitation for 10 minutes. The agitation was stopped, the mixture was allowed to settle for 15 minutes, and the lower methanol/water phase was removed. The heptane phase was heated back to 60-65°C, and the experiment proceeded with the second water wash and methanol injection as in Example 2.

In order to define operating conditions with improved results, the variables and ranges were adjusted to values close to the best conditions based on the results of Example 2. These variables and ranges are given in Table IV. In each experiment, the agitation rate during crystallization was 78.5 rad/s (75 rpm) and the crystallization time was one hour. TABLE V Variables and Ranges

'^•' Parts refers to the relative weight ratio of the variable to the amount of neutrals used in the experiment.

The results from each run in this example are given in Table VI.

TABLE VI

Yields and purities ranged from 43-73% and 93-98%, respectively. The mean and standard deviation for the center points were 50.6 ± 2.9% for mass yield, 48.3 ±2.5% for sterol yield, 95.5 ±0.9% for purity, and 0% for wax alcohol. None of the variables in the third experiment had a significant effect on yield or purity, while heptane and first wash water significantly affected wax alcohol contamination. Higher heptane and lower first wash water loadings reduced wax alcohol contaminations. R-squared values indicate that the model as fitted explains 88% of the variability in mass yield, sterol yield, and non-elutables . The R-squared values for purity and wax alcohol content were 91% and 96% respectively.

One condition (run 8) had crystals in the organic phase after the methanol wash but before the first decantation. Similar experiments with identical heptane and methanol loadings, but less wash water, did not have crystallization problems. This suggests that higher water loadings in the methanol wash step may lead to premature sterol crystallization with the more concentrated neutrals solutions. Several of the experiments with low heptane and high methanol loadings had small amounts of black insoluble material in the neutrals solution before the 2^nd water wash step. There were no problems with sterol purities, however, after extensive washing on the Buchner funnel .

It can be seen from the above, the subject matter of the invention is: (1) A method for the isolation of sterols from sulfate pulping process tall oil pitch comprising the steps of:

(a) separating a sterol-rich fraction from a saponified tall oil pitch;

(b) blending a hydrocarbon solution of the sterol-rich fraction with a first wash alcohol solvent at a temperature greater than the crystallization temperature of sterol to produce a hydrocarbon/sterols/alcohol solution;

(c) adding a first wash water to the hydrocarbon/sterols/alcohol solution to result in a first upper hydrocarbon phase and a lower alcohol/water phase;

(d) removing the first lower alcohol/water phase;

(e) adding water of a temperature higher than the hydrocarbon phase to said hydrocarbon phase to produce a second upper hydrocarbon phase and a lower water phase;

(f) removing the lower water phase;

(g) the remaining hydrocarbon phase is allowed to cool to a final temperature range from about 20°C to about 40°C to produce sterol crystals; and

(h) the sterol crystals are recovered from the cooled solution.

(2) the method of (1) wherein the sterol-rich fraction 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 12 carbons;

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

(5) the method of (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, iso-propanol, and mixtures thereof;

(7) the method of claim 1 wherein the temperature in step (b) is at least 25°C;

(8) the method of claim 1 wherein the temperature in step (b) is at least 60°C;

(9) the method of claim 1 wherein the temperature in step (e) is at least 60°C;

(10) the method of claim 1 further comprising washing the recovered sterol crystals with a hydrocarbon solvent to obtain a high yield of sterols of high purity;

(11) the method of claim 10 wherein the sterol yield is at least 60% and the sterol purity is at least 92%;

(12) the method of claim 11 wherein the sterol yield is at least 65% and the sterol purity is at least 92%/;

(13) the method of claim 12 wherein the sterol yield is at least 70% and the sterol purity is at least 95%/;

(14) the method of claim 2 wherein the sterol-rich fraction is a neutrals fraction derived by solvent extraction; and (15) the method of claim 1 wherein steps (b) and (c) are combined by the first wash alcohol with the first wash water.

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 sulfate pulping process tall oil pitch comprising the steps of:

(a) separating a sterol-rich fraction from a saponified tall oil pitch;

(d) removing the first lower alcohol/water phase;

(f) removing the lower water phase;

(h) the sterol crystals are recovered from the cooled solution.

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 12 carbons.

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

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, iso-propanol, and mixtures thereof.

7. The method of claim 1 wherein the temperature in step (b) is at least 25°C.

8. The method of claim 1 wherein the temperature in step (b) is at least 60°C.

9. The method of claim 1 wherein the temperature in step (e) is at least 60°C.

10. The method of claim 1 further comprising washing the recovered sterol crystals of step (h) with a hydrocarbon solvent to obtain a high yield of sterols of high purity.

11. The method of claim 10 wherein the sterol yield is at least 60% and the sterol purity is at least 92%.

12. The method of claim 11 wherein the sterol yield is at least 65% and the sterol purity is at least 92%/.

13. The method of claim 12 wherein the sterol yield is at least 70% and the sterol purity is at least 95%/; and

14. The method of claim 2 wherein the sterol-rich fraction is a neutrals fraction derived by solvent extraction.

15. The method of claim 1 wherein steps (a) and (b) are combined by the first wash alcohol with the first wash water.