WO2018065876A1

WO2018065876A1 - Process for separating unsaponifiables from tall oil soap

Info

Publication number: WO2018065876A1
Application number: PCT/IB2017/056060
Authority: WO
Inventors: Jari KAVAKKA; Heikki LOTTI
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2016-10-04
Filing date: 2017-10-02
Publication date: 2018-04-12
Anticipated expiration: 2019-04-04
Also published as: SE540491C2; SE1651300A1

Abstract

The present invention relates to a process for separating unsaponifiables from tall oil soap (TOS) using co-distillation. The invention also enables the production of tall oil with high acid number.

Description

PROCESS FOR SEPARATING UNSAPONIFIABLES FROM TALL OIL

SOAP

Field of the invention

Background Tall oil soap (TOS) is a by-product of the Kraft process. The soap consists mainly of sodium salts of fatty acids, sodium salts of diterpenic (rosin) acids, free fatty acids, free rosin acids and unsaponifiable neutral compounds such as fatty alcohols, sterols, steryl esters and waxes. The water content of neat soap is typically 25 to 45%, such as 30 to 35%. The pH of the soap is typically in the range of 1 1 to 13, arising from the presence of entrained black liquor. In industrial practice, soap is routinely acidulated with sulphuric acid to produce crude tall oil (CTO), an article of commerce.

Crude tall oil can be refined by distillation into heads, tall oil fatty acids (TOFA), tall oil rosin acids (TOR) and tall oil pitch (TOP) fractions. Distillation is done at low pressure and at high temperature which is somewhat detrimental to sterols. The sterols which survive the harsh distillation conditions are esterified with either rosin or fatty acids. Despite the loss of some sterols and the formation of sterol esters in the distillation phase the TOP is currently used as the primary source of pine based phytosterols.

Sterols, in particular 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. The general method involves the extraction of neat soap with a variety of organic solvents. The presence of entrained black liquor promotes and stabilizes the unwanted water-oil emulsion, which is known to be extremely difficult to break.

Consequently, the efficiency of solvent extraction of neat soap for the isolation of sterols is greatly reduced. Holmbom et al. teach in US Patent 3,965,085 the extraction of a mixture of acetone-water soap slurry, with a water-immiscible solvent such as hexane. The aqueous phase contains mainly sodium salts of fatty and resin acids. The organic phase contains mostly unsaponifiables including sterols. In US Patent 4,044,031 , Johansson et al. teach the dissolution of soap in a water-immiscible mixture comprising hexane and acetone, extraction of the water-immiscible phase with another solvent mixture comprising methanol, hexane, acetone and water, and isolation of sterols from the methanolic phase by evaporative crystallization. In US Patent 5,770,749, Kutney et al. teach the use of a mixture of ketones, hydrocarbons and water to extract sterols from soap. The hydrocarbon extract is further processed with methanol. However, the complexity of recovering the multi- component spent solvent is seen as problematic in these processes. Also, recycling highly water soluble solvents such as acetone and methanol from water mixtures is very complicated.

Further examples of methods of obtaining sterols are described in

US2005/0107582, WO2009/106696, CA2319230, US6297353, US6465665, US6462210, US7078544, US7087402 and US20020107168. The methods known in the art for separation of phytosterols and other neutral compounds from alkaline tall oil soap are generally complex and the methods using distillation suffer from the drawbacks of solidification of water depleted distillation residue and the distillate. There is thus a need for a more efficient method of obtaining phytosterols from tall oil soap. Summary of the invention

The present invention is directed to a process for separating unsaponifiables from tall oil soap using co-distillation, to produce tall oil with high acid number.

In a first step, a molecular solvent having a boiling point higher than 160°C and in which sterols are essentially insoluble is added to the soap and most or all the water of the soap is evaporated using e.g. a wipe-film evaporator or any other distillation technique applicable. Alternatively, water is distilled along the chosen molecular solvent. The water can be removed in

atmospheric or under reduced pressure. The molecular solvent can be e.g. ethylene glycol, propylene glycol, 1 ,3-propanediol, 1 ,3-butanediol, 1 ,4- butanediol, glycerol or a mixture thereof.

In a second step, after the water removal, the mixture is distilled, for example in atmospheric or under reduced pressure using e.g. a wipe-film evaporator or any other distillation technique applicable for the present mixture.

Phytosterols are co-distilled (the distillation temperature is below the boiling point of phytosterols) with the molecular solvent but are not soluble in the chosen solvent. When the distillate is collected and the distillate temperature is reduced, phytosterols are insoluble and can be isolated either by phase separation or after precipitation by sedimentation, filtration, centrifugation or any combination thereof. The phytosterol depleted distilled molecular solvent can be returned back to the distillation vessel or purified and recycled by further distillation.

The distillation condenser temperature can be controlled in order to avoid solidification of the phytosterols which could lead to clogging of the

condenser. The condenser temperature is chosen according to the molecular solvent used. Preferably, the chosen molecular solvent can perform as the crystallization solvent and produce high purity sterol mixture. Alternatively, the crude sterols can be purified using methods known in the art.

After the distillation of the unsaponifiables, most of the molecular solvent still present in the residue can be distilled off with remaining phytosterols and the distillation residue is acidified using the standard acid cooking in order to produce high acid number tall oil. The residual molecular solvent still present in the distillation residue dissolves into the water fraction and high quality tall oil can be separated using the standard procedure.

Thus, through the advanced distillation sequence presented herein, both isolation of phytosterols from tall oil soap and production of tall oil with high acid number can be achieved. Thus, the present invention is directed to a process for isolation of

phytosterols and/or other neutral compounds from tall oil soap using co- distillation wherein added molecular solvent is used to achieve the co- distillation of phytosterols, comprising the steps of: a) adding the molecular solvent having a boiling point higher than

160°C, and in which sterols are essentially insoluble at 25°C, to tall oil soap;

b) distilling the mixture obtained in step a) at a distillation temperature below the boiling point of phytosterols; and

c) collecting the distillate, reducing the temperature of the distillate and isolating the phytosterols and/or other neutral compounds.

The molecular solvent used in step a) is a solvent that is miscible with water. The molecular solvent used in step a) is a polar solvent.

In one embodiment of the invention, the molecular solvent used in step a) has a boiling point higher than 170°C, such as 180°C or 190°C or 195°C or 200°C or 205°C or 210°C or 215°C. In one embodiment of the invention, the molecular solvent is selected from ethylene glycol, propylene glycol, 1 ,3-propanediol, 1 ,3-butanediol, 1 ,4- butanediol, glycerol or a combination thereof. Further examples of groups of solvents from which a molecular solvent for use in step a) can be selected include sulfoxides, sulfones and ketones.

The term "essentially insoluble" as used herein means that the sterols concerned are only partly soluble, such as less than 1 % of the sterols being soluble in the molecular solvent or the sterols are completely insoluble in the molecular solvent concerned.

The distillation in step b) may be carried out in atmospheric pressure or under reduced pressure.

In one embodiment of the present invention, the distillation in step b) is carried out in a wiped film evaporator.

In one embodiment of the present invention, in or prior to step a), most or all water is removed from the tall oil soap before step b). In one embodiment, the water is removed by evaporation. The water can be removed at atmospheric or reduced pressure.

In one embodiment of the present invention, the process also comprises the step of acidulating the remaining tall oil soap from step c) and optionally washing the molecular solvent from the tall oil to obtain high acid number tall oil.

The optional washing in step d) is typically done with water.

One embodiment of the present invention is a distillation residue obtainable by the process according to the present invention. One embodiment of the present invention is tall oil having an acid number of at least 170, such as at least 175 or at least 180. The acid number can be determined using methods known in the art. One aspect of the present invention is tall oil is obtainable by the process according to the present invention.

Brief description of the figures Fig 1 : illustrates a process according to the present invention. The molecular solvent having a boiling point higher than 160°C, and in which sterols are essentially insoluble at 25°C, is added to tall oil soap (TOS). The mixture is distilled at a distillation temperature below the boiling point of phytosterols. The distillate is collected, the temperature of the distillate is reduced and the phytosterols and/or other neutral compounds are isolated. The figure also illustrates the step of acidulating the remaining tall oil soap.

Detailed description

The term "phytosterol" is intended to mean a sterol derived from plants and encompasses all plant sterols and the saturated forms of phytosterols thereof (i.e., phytostanols). Plant sterols fall into one of three categories: 4- desmethylsterols (lacking methyl groups); 4-monomethylsterols (one methyl group); and 4,4-dimethylsterols (two methyl groups) and include, but are not limited to, sitosterol (e.g., [alpha] and [beta] sitosterol), campesterol, stigmasterol, taraxasterol, and brassicasterol. The term "phytostanol" is intended to mean a saturated phytosterol and encompasses, but is not limited to, sitostanol (e.g., [alpha] and [beta] sitostanol), campestanol, stigmastanol, clionastanol, and brassicastanol. Phytosterols isolated by the methods of the invention may be quantified by any means known in the art. The phytosterol crystallization can be performed using methods known in the art, including cooling, concentration by removing some of the solvent by distillation, evaporation to dryness followed by introduction of a solvent or solvent mixture in which the phytosterols only dissolve at elevated

temperature followed by cooling or through seeding with phytosterol crystals.

The process according to the present invention may be carried out as a batch process or as a continuous process.

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 effected without departing from the spirit and scope of the invention.

Claims

A process for isolation of phytosterols and/or other neutral compounds from tall oil soap using co-distillation wherein added molecular solvent is used to achieve the co-distillation of phytosterols, comprising the steps of

a) adding the molecular solvent having a boiling point higher than 160°C, and in which sterols are essentially insoluble at 25°C, to tall oil soap;

b) distilling the mixture obtained in step a) at a distillation

temperature below the boiling point of phytosterols; and c) collecting the distillate, reducing the temperature of the

distillate and isolating the phytosterols and/or other neutral compounds.

A process according to claim 1 , wherein the molecular solvent in step a) is selected from ethylene glycol, propylene glycol, 1 ,3- propanediol, 1 ,3-butanediol, 1 ,4-butanediol, glycerol or a combination thereof.

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

A process according to any one of claims 1 -3, wherein, in or prior to step a), most or all water present in the tall oil soap is removed before step b).

A process according to claim 4, wherein the water is removed by evaporation at atmospheric or reduced pressure.

A process according to any one of claims 1 to 5, further comprising the step of d) acidulating the remaining tall oil soap from step c) and optionally washing the molecular solvent from the tall oil to obtain high acid number tall oil.

Distillation residue obtainable by the process according to any one of claims 1 to 6.

Tall oil having an acid number of at least 170.

Tall oil according to claim 8, having acid number of at least 180.

Tall oil obtainable by the process according to any one of claims 1 to 6.