US3803114A

US3803114A - Process for producing unsaponifiablesfree tall oil products

Info

Publication number: US3803114A
Application number: US00233449A
Authority: US
Inventors: D Redford; D Mitchell; F Greebe
Original assignee: ST Regis Paper Co
Current assignee: ST Regis Paper Co
Priority date: 1972-03-10
Filing date: 1972-03-10
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09

Abstract

CRUDE SOAP SKIMMINGS, FROM THE KRAFT PLUP PROCESS, ARE UP-GRADED BY REMOVING CONTAINED UNSAPONIFIABLES, THIS IS DONE BY ADMIXING THE SKIMMINGS WITH WATER AND A DEEMULSIFYING ALCOHOL (E.G. METHANOL), CLARIFYING THE MIXTURE, AND CONTAINING THE CLARIFIED SOLUTION WITH A HYDROCARBON (E.G. HEPTANE) WHEREBY THE UNSAPONIFIABLES ARE EDTREATED INTO THE HYDROCARBO PHASE. THE COMPOSITION OF THE EXTRACTION FEED IS CONTROLLED TO ENSURE THAT SUBSTANTIALLY ALL THE UNSAPONIFIABLES ARE EXTRACTED WHILE ONLY A VERY SMALL AMOUNT OF THE SOAPS REPORT IN THE HYDROCARBON PHASE. THE RAFFINATE IS THEN DISTILLED TO RECOVER THE ALCOHOL.

Description

A ril 9, 1914 PROCESS FOR PRODU Filed March 10, 1972 CLARIFICATION SOLVENT ALCOHOL RECOVERY BY ALKALINE DISTILLATION 16 Sheets-Sheet 1 SOAPS SKIMMINGS CON AINABLE UNSAPONIFIABLES HYDROCARBON CONTAINING SOLIDS AND SOME UNSAPON l FIAB LE5 EXTRACTION o CONTAINING ALL UNSAPONIFIABL REMAI MN 6 CLARIFIED SOAPS SOLUTION (SOAPS SKIMMINGS WATER+ALCOHOL+ UNSAPONIFIABLES) DE'EMULSIFYING ALCOHOL e. g. METHANOL e.q. h- HEP ANE TO EXTRACT SOME UNSAPONIFIA BLES AND REMOVE SOLIDS HYDROCARBON SOLVENT EXTRACTION CO LUMN UNSAPONIFIAB LES (COUNTER CURRENT) HYDROCARBON 0.0. h- HEPTANE CLARIFIED UNSAPONIFIABLES FREE SOAPS SOLUTION (SOAPS SKIMMINGS WATER+ ALCOHOL) PRE- HEAT TO VAPORIZE FEED DISTILLATION COLUMN CLARIFIED, UNSAPONIF'IABLES FREE SOAPS SOLUTION (SOAPS SKIMMINGS+ WATER) April 9, 1974 L, MlTCHELL ET AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS 16 Sheets-Sheet 3 Filed March 10, 1972 HEPTANE MAN /\/\/W mum/ Av. FEED um; 4/ vAv THANOL TER April 9, 1974 D, MlTCHELL ET AL 3,803,114

ALL 011,

PROCESS FOR PRODUCING JNSAPONIFIABLES-FREE T Filed March 10, 1972 wwwww wI April 9, 1974 D. 1.. MITCHELL ETAL PROCESS FOR PRODUCING UNSAPONIPIABLES -FRI1FL FALL ()II, PRODUCT? Filed March 10, 1972 l6 Sheets-Sheet b April 9, 1974 MlTCHELL ET AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL, OIL PRODUCTS Filed March 10, 1972 1G Sheets-Sheet 6 YAVA AYAY

AYAYAYA AYAVAYAVA AYAVAYAVAYA AYAYWA I FEED use Y PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed Maich 10, 1972 April D. 1.. MITCHELL ETA!- 16 Sheets-Sheet April 9, 1974 D, MlTcHELL ET AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed Harsh 10, 1972 15 Sheets-Sheet 6 April 9, 1974 L, M|TCHELL E'TAL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed Hatch 10, 1972 16 Sheets-Sheet J:-

AYAYAYA AVA AYAY

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FEED LINE METHANOL WATER A April 1974 D. L. MITCHELL ETAL PROCESS. FOR PRODUCING UNSAPC-NIFIABLES-FREE TALL OIL PRODUCTS Filed March 10, 1972 l6 Sheets-Sheet 10 zomm uomorx Q April 9, 1974 0. L. MITCHELL ET u. 3,803,114

PROCESS FOR PRODUCING UNSAONlFIABLES-}-'REE TALL OIL PRODUCTS Filed March 10, 1972 16 Sheets-Sheet 11 FEED LINE METHANOL +WATER A April 9, 1974 D. L. MITCHELL ET AL 3,803,114

PROCESS FOR YRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed March 10, 1972 1,6 Sheets-

Sheet

12 ,6 Weight Froc'ion Soups '0 Upper Phase vs Hydrocarbon Concentration in System I I I I l I I I I I I I I lncubclmr Manual Mixing Tumine Mixing I4 20% Solids in Stock Solufion 19% Solids in Stock Solution 3 9 g I X o O I I I I I I I I I I I I I I 10 4O 10 2O 30 4O 50 6O 96 Hydrocarbon in System A ril 9, 1974 rrc ET AL 3,803,114

PROCESS F R PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed March 10, 1972 1G Sheets-Sheet 15 gJE-J- l l I l I l l l 1 I l I Ex'r cf Phase Composi'ion (Turbine Mixing) \3 H 5 10 d 5 X l l l l l l l l l I l l 1 2 3 4 5 6 7 8 9 10 H 12 13 14 I5 I W? 96 Solids in Ex'mct Phase April 9, 1974 L, MlTCHELL ETAL 3,803,114 PROCESS FOR PRODUCING UN SAPONIFIABLES-FRBE TALL OIL PRODUCTS Filed March 10, 1972 L6 Sheets-Sheet 14 FI QJEE.

ExIrOCi Phase Composi'ion (Turbine Mixing I 2 3 4 8 9 I0 \1 l2 I3 14 Wt Unsuponifiables in Extract Phase April 9, 1974 MlTCHELL ETAL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREJE TALL OIL PRODUCTS Filed March 10, 1972 16 Sheets-Sheet 15 I gJfi-l.

Exlrdd Phase Conposiflon (Equilibrium,

34% Stock Solids (Symbol o) 20% Stock Solids (Symba! o 20% Stock Solids (Symbol I) 41% smk Solids (Symbol O =-'-='1'- 20% Sum Solids (Symbol') l l l l l I l I l I l l l l I 2 3 4 5 6 7 8 9 I0 H I2 13 14 I5 WI Unsuponifiubles in Extract Phaso April 9, 1974 D. L. MITCHELL EI'AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed March 10, 1972 16 Sheets-Sheet l6 glf-E.

Y T I F T I' l l I l I l I I Extruc' Phase Composi'ion l3 (Equilibrium) 34% Stock Solids (Symbol 0) 4 20% Stock Solids (Symbol Q 3 I l l l l J l l l l l l l l I 2 3 4 5 6 7 8 9 10 H 2 l3 H W! Solids in Extract Phase nited States Patent (3" US. Cl. 26097.7 1 Claim ABSTRACT OF THE DISCLOSURE Crude soap skimmings, from the Kraft pulp process, are upgraded by removing contained unsaponifiables. This is done by admixing the skimmings with water and a deemulsifying alcohol (e.g. methanol), clarifying the mixture, and containing the clarified solution with a hydrocarbon (e.g. heptane) whereby the unsaponifiables are extracted into the hydrocarbon phase. The composition of the extraction feed is controlled to ensure that substantially all the unsaponifiables are extracted while only a very small amount of the soaps report in the hydrocarbon phase. The rafiinate is then distilled to recover the alcohol.

BACKGROUND OF THE INVENTION This invention relates to a process for producing upgraded soap solution from Kraft pulp process soap skimmings. The enriched solution contains fatty and resin acid soaps, but has had the normally present unsaponifiables content substantially removed during processing. The product solution finds use as a high quality feed-stock from which crude and refined tall oil products can be made.

Soap skimmings are a by-product of the well known Kraft process. This process is used to produce wood pulp from woods which contain resinous constituents known as wood extractives. Woods especially abundant in these extractives are the various species of pine, balsam, cedar, larch and some species of spruce and hemlock.

The Kraft (or sulphate) process involves cooking wood chips. This is done at elevated temperature and pressure in dilute alkaline liquors which contain sodium hydroxide and sodium sulphide as the active ingredients. Cooking efiects cellular breakdown and dissolution of the lignin, wood extractives and hemicelluloses. Additionally, it renders the cellulose in a dispersed, fibrous form which can be separated by filtration. The spent cooking liquor (known as black liquor) is separated and concentrated to a solids content suitable for combustion in a recovery furnace (about 60-70% soluble solids). Concentration is carried out by passing the black liquor through a series of multiple-efiect evaporators. After several stages (30% soluble solids content), a portion of the solids, known as crude sulphate soaps, becomes insoluble. At this point, the black liquor is transferred to a holding tank and these soaps are skimmed oil? and recovered. The skimmings consist of a mixture of solids material (50-70%) associated with an entrained liquid portion (30-50%).

.The soap skimmings when diluted with water give a product which usually comprises:

as solids:

suspended fibres insoluble sodium salts (organic and inorganic) some lignin in solution:

Water some lignin fatty and resin acid sodium soaps unsaponifiables odor bodies (such as 'mercaptans and disulphides) color bodies (principally sodium soaps of oxidized resin acids and oxidized unsaponifiables) ICC Typical soap skimmings from Alberta, Canada and North American west coast mills would have the compositions given in Table 'I.

TABLE I [Composition of soap skimmings] Percent by weight Alberta West coast Constituent Sodium salts of fatty and resin acids Unsaponifiables 10 15 Moisture and low molecular weight volatiles 35-40 37 Lignin, cellulose, inorganic salts 7-12 10 The soap skimmings are usually treated to produce crude tall oil; this product may be further refined to produce the distilled fractions of tall oil.

The first step in this treatment involves reacting the skimmings with sulphuric acid. Hydrogen ions substitute for the sodium ions to convert the soaps to fatty and resin acids. The products of acidulation separate into three layers in a batch reactor. The top layer is referred to as the crude tall oil layer. Its main constituents comprise fatty acids, resin acids, unsaponifiables and esters. Small amounts of suspended solids and water are also present in this layer. The second or intermediate layer is called the lignin layer. It contains the bulk of the lignin and insoluble non-soap solids which were originally present in the skimmings. The bottom layer is mainly made up of sodium sulphate and water.

The crude tall oil is drawn off and can be sold as such or can be further refined by fractional distillation. Typical compositions of northern (made from woods grown in Canada and the northern United States) and southern (made from woods grown in the southern United States) crude tall oils are shown in Table IL TABLE II [Analysis and characteristics of northern and southern tall oils] Acid number -135 -175 It will be noted that tall oils are characterized by their acid number. This is simply a quantitative measure of the concentration of constituents present in the oil that possess acidic groups. More specifically, it is the number of milligrams of KOH required to neutralize one gram of the oil.

The crude tall oil is a dark brown, viscous, opaque liquid possessing an offensive odor. The dark color originates from traces of occluded black liquir and oxidized resin acids. Insoluble inorganic salts and short lengths of cellulose fibre product the opacity. (The Gardner Number serves as an industry measure of the color qualities of the material.) Kraft sulphurous products, hydrogen sulphide, organic sulphides and disulphides generate the unpleasant odor.

In this crude state, the applications of crude tall oil are limited to uses where color and odor are not very important. In addition to the limited applicability of the crude tall oils in general, northern crude tall oil suffers from an even greater disadvantage of applicability because of the proportionately higher unsaponifiables content; these constituents produce a plasticizing effect on certain formulations using crude tall oil.

For most applications, it is necessary to upgrade the crude tall oil. This is done by substantially eliminating color and odor bodies and also by separating the blend of acids into concentrated fractions of which fatty and resin acids constitute the products of economic importance. Upgrading is normally done by distillation.

Distillation involves flashing the crude tall oil at 160- 260 C. and at a pressure of 1-10 mm. Hg. The volatile constituents are vaporized and leave behind a residue. The residue contains the occluded fibres, insoluble salts, suspended solids and lignin. In an idealized distillation, starting with a feed stock of low unsaponifiables content, the vapors would be fractionated into six product streams as follows:

(1) Gases (water, sulphides, disulphides);

(2) Heads (low molecular weight (C16) fatty acids and unsaponifiables);

(3) A main fatty acid fraction (C18 chain acids);

(4) A distilled tall oil fraction (C20 chain acids blended with some C20 ring acids);

(5) A resin acid fraction (C20 ring acids); and

(6) Pitch, containing esters, sterols and polymerization products.

It should be noted that the prior art distillation is carried out under acidic conditions.

Through these operations, the bulk of the undesirable insoluble suspended solids present in the soap skimmings have been removed. Additional insoluble suspended solids generated by the acidulation process have been further removed during acidulation or during the subsequent operation of flashing the crude tall oil prior to fractional distillation.

Returning again to Table II, it will be seen that the main dilference, in terms of chemical composition, between the northern and southern crude tall oils is the amount of contained unsaponifiables. It is apparent that the extent of unsaponifiables content is governed by the species and geographic origin of the wood involved.

Unsaponifiables can be generally described as a class of organic compounds which do not contain a saponifiable group (such as carboxyl, thiolate or sulphonate). More specifically, FIG. 2 shows a breakdown of the unsaponifiables contained in a typical Alberta soap skimmings. These compounds can be divided into three general groups:

(1) High molecular weight alcohols such as diterpene (C20) alcohols, linear (C20-C26) alcohols and sterols;

(2) Diterpene aldehydes and ketones; and

(3) Hhydrocarbons and triterpenes.

It will be noted that approximately As of the unsaponifiables are made up of a complex combination of alcohols.

In comparison, tall oils originating from the southern United States differ in their unsaponifiables constituent composition both in kind and degree. Their major unsaponifiable constituents are the sterols and hydrocarbons; diterpene alcohols and diterpene aldehydes and ketones are not present as major constituents. The substantially decreased content of diterpene alcohols, aldehydes and ketones results in considerably different distillation characteristics and distillation products.

The presence of unsaponifiables is undesirable in both crude and refined tall oil products. This is particularly a problem when large amounts of unsaponifiables are present, as in the case of northern feeds. In the case of crude, tall oil, unsaponifiables dilute the acid content resulting in products of low acid number. In the case of using northern crude tall oils for distillation feed-stock, various problems result in the distillation step and in the color quality and acid number of the distilled products. These characteristics may affect the marketability of northern crude tall oil destined for distillation feed-stock.

The tall oil industry has adapted itself to getting along with products having small amounts of unsaponifiables; however, it penalizes or refuses to use high unsaponifiables content products such as are obtained from northern woods.

The following examples will illustrate the difficulties in using northern crude tall oil either as a crude product or as a feed-stock for a distillation operation.

In limited operations, crude tall oil may be used as an ingredient in inexpensive, low quality paint, particularly where dark colored products are not considered a disadvantage. Such formulations are usually based on the acid number or acid content of the crude tall oil. It is common for paint manufacturers to require crude tall oil having an acid number greater than a typical northern crude tall oil will only have an acid number of about 130.

The major proportion of available crude tall oil is utilized in subsequent refining processes of which fractional distillation is the most important and the most common. Northern crude tall oils are considered poor feed-stocks for such refining operations because of their contained unsaponifiables constituents. These tall oils have unsatisfactory distillation yields and the quality of the distillates is inferior to that produced by southern tall oils, particularly with respect to unsaponifiables content in distillants. These disadvantages come about in two ways. Firstly, the acids and hydroxyl containing unsaponifiables (alcohols) react with each other, particularly at elevated temperatures, to form esters. Most of these esters have sufiiciently high molecular weights to be non-volatile and report in the pitch fraction during distillation and are subsequently lost. The acid content of the esters is also, of course, lost. Secondly, during distillation of northern tall oils the more volatile unsaponifiables compounds tend to be carried over with the acid fraction because the vapor pressures of the diterpene alcohols and aldehydes are very close to those of the fatty acids and resin acids. In this respect, the distillation characteristics differ from the southern tall oils. As a result, the volatile diterpene alcohols and aldehydes dilute or contaminate the separate acid streams, thus defeating, to some extent, the purpose of the distillation. Since ester formation is time dependent, the distiller could increase the distillation temperature and feed rate through the tower to reduce the esterification. However, in doing so, he will increase the carry-over of volatile unsaponifiables into the acid fractions. Consequently the distilled products will be substantially contaminated with non-acid constituents which may penalize the value of the products.

These problems facing the distiller are so serious that many northern crude tall oils cannot be fractionated on a paying basis because of the yields obtained and also because of the quality of the distillation products derived.

To sum up the foregoing, a northern pulp manufacturer produces a soap skimmings product which has an undesirably high unsaponifiables content. He suffers penalties if he sells the product in crude tall oil form. He finds that the fractionation procedures, which were originally developed for southern-type materials, are not usually applicable to his product.

One answer to all of these problems would be to remove the unsaponifiables from the soap skimmings.

Unsaponifiables have hydrophobic properties and are soluble in certain organic solvents. It had long been suspected that low molecular weight hydrocarbons, such as hexane and heptane, could be used to extract them from aqueous solutions. The unsaponifiables are preferentially soluble in the hydrocarbons and they, in turn, are substantially immiscible in the soap solution. However, there was a serious problem which prevented useful application of this knowledge. When the aqueous soap solution and the hydrocarbon were mixed together, they would form a very stable emulsion.

The problem of emulsification was solved by Christenson and Gloyer. Their solution was described in US. Pat. No. 2,530,809. Basically, they taught that certain alcohols would act as de-emulsifiers if provided in a water-soap skimmings-hydrocarbon system. They also taught operative ranges of composition which, if observed, would result in rapid phase separation. In other words, if water, soap skimmings, alcohol and hydrocarbon were shaken up together, the unsaponifiables would be extracted by the hydrocarbon and, when the mixture was allowed to stand, the components would quickly separate into a lower phase, consisting mainly of soap-water-alcohol, and an upper phase consisting mainly of hydrocarbon and unsaponifiables. They further taught that the quantities of sodium soaps which did become dissolved in the upper phase could be removed by a subsequent operation of washing with water.

The process taught by Christenson and Gloyer was directed to the recovery of unsaponifiables as a source of sterols, useful in the drug industry. Although the patentees recognized that the removal of unsaponifiables would enhance acid yields from soap skimmings, they did not teach an industrially operative process for accom' plishing this end.

The present invention is a process.

SUMMARY OF THE INVENTION directed to providing such It is an object of this invention to provide a process for removing substantially all of the unsaponifiables and insoluble, non-soap solids from soap skimmings to produce a purified soap solution. The product solution should be a high quality feed-stock. Crude tall oil and distilled products made from it should be substantially free of unsaponifiables and should be characterized by high acid numbers and improved color characteristics.

It is another object to provide a process, the practice of which will result in improved yields of fatty and resin acids, in the form of distillation products, from soap skimmings.

It is another object to provide a soaps upgrading process, involving solvent extraction of unsaponifiables and alcohol recovery, which is carried out under alkaline conditions.

It is another object to provide a soaps upgrading process involving solvent extraction of unsaponifiables wherein washing of the extract fraction to recover dissolved soaps is not necessary.

It is another object to provide a soaps upgrading process, involving separation of suspended solids and sterols, wherein the solids and sterols are recovered in the form of a filter cake. This cake forms a preferable feedstock for the production of phytosterols.

It is another object to provide a soaps upgrading process involving separation of undissolved solids wherein these solids are recovered as a hydrocarbon-wetted fioc under two phase formation which minimizes emulsion formation and recovers an extractable portion in undegraded form.

It is another object to provide a soaps upgrading process, involving alcohol recovery by distillation, which is conducted in a manner to avoid foaming, fouling and plugging in the distillation column.

These and other objects of the invention will be apparent from consideration of the following specification and appended drawings.

'In accordance with the invention, the following steps and limitations are employed:

Firstly, crude soap skimmings are admixed with water and a de-emulsifying alcohol to form a mixture comprising a soap solution, dissolved unsaponifiables and undissolved solids.

Secondly, the mixture is preferably treated to remove substantially all its undissolved solids. This may be done by mixing the mixture with hydrocarbon and allowing the product to settle to form an upper hydrocarbon phase and a lower soap solution phase. The undissolved solids report in the hydrocarbon phase as a hydrocarbon-wetted fioc layer. This phase can be drawn off to leave a clarified soap solution.

Thirdly, the clarified soap solution is contacted with sufiicient hydrocarbon to extract substantially all the unsaponifiables present therein.

Suitable alcohols and hydrocarbons are known from the prior art. We have found methanol, ethanol, n-propanol and isopropanol and mixtures thereof particularly suitable as the de-emulsifying alcohol. Methanol is preferred. Hexane, heptane and petroleum cuts containing one or both of them as major constituents are particularly suitable for use as the hydrocarbon solvent. 'Heptane is preferred. These hydrocarbons are solvents for the unsaponifiables, are stable in alkaline conditions and are substantially immiscible in the soap solution.

The composition of the soap solution fed into the extraction vessel, the extent of dilution therein with hydrocarbon and the composition of the distillation feed will preferably be controlled by the following limitations:

(a) Two phase separation of the soap solution and hydrocarbon must take place relatively quickly. This can be tested by placing a representative mixture in a laboratory separation funnel, shaking it manually for 10 minutes and allowing it to stand. If substantially complete separation occurs within 6 minutes the composition meets this requirement. UJS. Pat. No. 2,530,809 teaches systems in accordance with this requirement;

(b) The dissolved solids content in the extraction feed should be restricted to minimize retention of unsaponifiables in the rafiinate phase. In other words, dissolved solids content should be less than a predetermined maximum amount. This maximum amount is that amount which will result in a raffinate having an exhaustively extracted acid number of 174, as arrived at by the following test:

Dilute a sample of the feed with hydrocarbon in the proportion which is to be used in the process; shake this mixture in a laboratory separation funnel to reach a single stage equilibration; draw olf the hydrocarbon phase; repeat the procedure to take a total of six cross-current extractions. If the acid number of the raffinate phase is equal to or greater than about 174, then the dissolved solids content in the clarified soap solution is equal to or less than the preferred maximum permissible amount;

(0) The extraction feed composition and hydrocarbon dilution should be selected to ensure that the extract stream from the decanter and/or extraction vessel contains less than about 5.5% by weight dissolved solids;

(d) The ratio of dry, unsaponifiables-free solids to Water in the feed to the distillation tower should be greater than about 3:7 so as to help prevent uncontrollable foam ing therein.

Fourthly, the rafiinate is distilled, preferably under alkaline conditions, to recover alcohol. The end product soap solution is substantially free of unsaponifiables and undissolved solids. It comprises a high quality feed-stock which may be acidulated to make superior crude tall oil.

Now, a number of the foregoing features require amplification:

Clarification of the soap solution prior to solvent extraction is important to the process. If the undissolved solids are not removed, plugging and fouling of the extraction tower, alcohol recovery tower and heat exchangers will occur. Additionally, clarification aids subsequent acidulation by removing a portion of the solids which would appear at the intermediate acidulation layer.

Exercising control-of the dissolved solids in the extraction feed is a preferred feature. We have found that a high solids content results in large amounts of unsaponifiables being retained in the rafiinate. By restricting solids content, a raffinate can be produced which, when acidulated, will have a desirable acid number (such as 174 or greater). The raffinate should have an acid number greater than about 174, otherwise the process is impractical.

Exercising control of the amount of solids dissolved in the extract phase is another preferred feature. This is done by carefully choosing the extraction feed composition. If the solids content in the extract phase is kept below about 5.5 percent by weight, dissolution of soaps in that phase is kept to a negligible amount. If the solids content is allowed to exceed 5.5%, substantial dissolution of soaps in that phase will begin to take place. As a result, soap recoveries will decrease. Reclaiming of the lost soaps from the extract phase may then become an undesirable necessity.

Alkaline distillation of the clarified soap solution to recover alcohol is another preferred feature. We have found that foaming, which is the main stumbling block to distilling a soap solution, can be operatively controlled in a simple fashion. This is done by maintaining a minimum dry, unsaponifiables-free solids to water ratio in the feed to the distillation tower and by minimizing vapor velocities in the stripping section by pre-concentrating the distillation feed. These antifoaming measures are preferred features of the process.

Distillation is preferably carried out under alkaline conditions to avoid secondary recovery problems. If the soap solution is acidulated before alcohol recovery, dissolved lignins in the system become insoluble. These lignins cause serious fouling problems in the alcohol recovery tower and associated heat exchangers. The undissolved lignin would, therefore, have to be removed from the system before distillation. This lignin contains en trapped tall oil, alcohol and hydrocarbon. It would be necessary to salvage these by secondary recovery. In addition, noxious gases such as H 8, CO and mercaptans would be generated during acidulation. They may also appear in the distillation column. These gases are corrosive and may require use of special construction materials. Additionally, they have to be vented from the acidulation and distillation column. This results in a concomitant loss of alcohol and hydrocarbon which may have to be reclaimed by secondary recovery.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a flow diagram of the process;

FIG. 2 is a schematic representation of the constituents which makeup the unsaponifiables in an Alberta soap skimmings;

FIG. 3 is a triangular coordinate phase diagram based on the data of Table 3A;

FIG. 4 is a triangular coordinate phase diagram based on the data of Table 4A;

FIG. 5 is a triangular coordinate phase diagram based on the data of Table 5A;

FIG. 6 is a triangular coordinate phase diagram based on the data of Table 6A;

FIG. 7 is a triangular coordinate phase diagram based on the data of Table 7A;

FIG. 8 is a triangular coordinate phase diagram based on the data of Table 8A;

FIG. 9 is a triangular coordinate phase diagram based on the data of Table 9A;

FIG. 10 is a triangular coordinate phase diagram based on the data of Table 10A;

FIG. 11 is a triangular coordinate phase diagram based on the data of Table 11A;

FIG. 12 is a plot showing the changes in amount of soaps which go to the upper phase during extractions with varying amounts of hydrocarbon. Three hydrocarbons were used: heptane (-x-xcurve), ISO-200 F. refinery fraction (O-. curve), and 190-210 F. refinery fraction (-I curve). High shear mixing was used;

FIG. 12 -1 plots percent solids in the extract phase against the weight ratio of the unsaponifiables in the extract phase and the soap in the extract phase;

FIG. 12-2 is the same as FIG. 12-1 except that percent unsaponifiables in the extract phase is plotted. All the FIG. 12 curves are based on the data of Table 12A;

FIGS. 13, 13-1 and 13-2 are similar to FIGS. 12, 12-1 and 12-2 except that manual mixing was used. These figures are based on the data of Tables 13A, 13B and 13C.

8 DESCRIPTION OF THE PREFERRED EMBODIMENT The above mentioned limitations can be best under stood and justified using triangular phase diagrams.

In our phase diagrams, we have plotted alcohol plus water, hydrocarbon and dry total solids. The semi-circular curve on each diagram divides the system into those compositions which would exist as a single phase (above the curve) from those compositions which would separate into two phases (beneath the curve). The curves have been developed by equilibrating a sample of a particular composition in a separatory funnel. The mixture was allowed to stand for 30 minutes and the extract and rafiinate phases were subsequently analyzed. The compositions of the rafiinate phases were plotted to provide the left hand side of the phase curve while the compositions of the extract phases were plotted to develop the right hand side. The line joining the rafiinate, mixture and extract composition points is referred to as a tieline.

In FIG. 10, point D represents a composition of solids, hydrocarbon and aqueous alcohol phases in the mixture. This mixture separates into the two phases identified as points I and I on the phase diagram curve. A tie-line joins points I, D and I. The compositions of the two phases given by I and J represents the equilibrium composition of the two phase mixture. For example, if a system represented by point D contains 14% dry solids, 36% methanol-water and 50% by weight hydrocarbon, then the composition of the rafiinate phase would be expressed as that given by point I on the phase diagram. This composition is solids 23%, methanol-water 67% and hydrocarbon 10%. The composition of the extract phase is given by point I on the phase diagram. This point has the following composition: solids 4%, methanol-water 1.5% and hydrocarbon 94.5%.

Not all compositions described under the phase diagram curve will give desirable systems for our process. As mentioned, systems which do not contain sufficient solids in the rafiinate phase have a tendency to foam during subsequent alcohol recovery. Therefore a certain minimum solids content is desirable for operation of the alcohol recovery tower. Also, solids content in the system has a bearing on the degree to which the unsaponifiables are extracted during a multi-stage extraction operation. It has been found that systems containing a high solids content give extracted soaps which still contain some unsaponifiables. These soaps, upon acidulation. give undesirably low acid numbers. Turning now to the extract phase, we have also found that soap losses to that phase depend upon the percentage solids dissolved in it. Soap losses through solution into the extract phase are kept to a minimum when the solids content of the extract phase is kept below 5.5% by weight.

FIG. 10 has two portions of the curve darkened in with a thick, black line.

In accordance with the invention, in order to meet the requirements of the over-all process, any system (that 1s, composition of soaps, alcohol-water and hydrocar- 'bon), when shaken in a separatory funnel to reach single stage equilibration, should have a tie-line whose ends lie in those portions of the curve described by the thick black lines. In other words, the composition of the raffinate phase, after single stage equilibrium, should be defined by any composition given by the thick black segment on the left hand portion of the diagram. Similarly, the composition of the extract phase, after single stage equilibrium, should be described by a composition given by the thick black line appearing at the right hand side of the diagram. All other tie lines that intersect the phase diagram at locations other than those given by the thick black lines will not give the preferred operating characteristics in the overall process.