US2899450A - Method of caustic recovery in soap manufacture - Google Patents

Description

Aug. 11, 1959 R. v. OWEN ETAL 2,899,450

METHOD OF CAUSTIC RECOVERY IN SOAP MANUFACTURE Filed Dec. 6,. 1955 E v i s Sheets-Sheet 1 m vm ro/ss I Roma. Vmqm-r Dw'an NORMAN Austn'r Hum- CAMPDELL,BRUMBAUGH, FREE no Grows:

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Aug. 11, 1959 R. v. OWEN ETAL 2,899,450

METHOD OF CAUSTIQ RECOVERY IN SOAP MANUFACTURE Filed Dec. 6. 1955 3 Sheets-Sheet 2 /Nl//Y7OR$ RONALD \lmcan'r wen Noam/ N ALBERT HURT CAMPBELL, BauMBAuGI-l, FRE AND QRAVB Aflav-neqs Aug. 11,1959 R. v. OWEN ET AL METHOD OF CAUSTIC RECOVERY IN SOAP MANUFACTURE Filed Dec. 6. i955 3 Sheets-Sheet 3 M. 1 "a t u w A w r? RR N is Mm NW A um "FR 0 RN m m A c nite States Pate METHOD OF CAUSTIC RECOVERY IN SOAP MANUFACTURE Ronald Vincent Owen, Sale, and Norman Albert Hurt, Lymm, England, assignors to Lever Brothers Company, New York, N.Y., a corporation of Maine Application December 6, 1955, Serial No. 551,449

Claims priority, application Great Britain December 8, 1954 8 Claims. (Cl. 260-418) This invention relates to improvements in the manufacture of soap, and in particular to neutralizing the free caustic alkali in crude lye formed in soap-making processes.

In the manufacture of soap, alkali such as caustic soda is generally employed to saponify vegetable and animal oils, hereinafter referred to as fatty oils. saponification of the fatty oils results in a mixture of crude soap and aqueous liquor containing glycerine, any unreacted fatty oil and caustic alkali as well as colouring matter and other impurities. This mixture of crude soap and aqueous liquor is generally washed, for example with an aqueous solution of brine, and then allowed to settle into an upper layer of grained soap and a lower aqueous layer, the lye. A number of successive washes may be applied, and each of the resultant settled lyes withdrawn from the system. Besides brine (or other electrolyte used in washing the crude soap), glycerine and some dissolved soap, the lye also contains impurities washed out of the soap and free caustic alkali present from the saponification stage. The concentration of free caustic alkali in the spent lye may vary according to the degree of control exercised in the soap-making process. For example, spent lye from a continuous soap-making process may contain a greater proportion of caustic alkali than spent lye from a batch process. In continuous soap-making processes, it may be practicable, for reasons of economy of space and time, to employ a greater excess of caustic alkali. In a batch process, in which more time may be available, completion of the saponification reaction may be obtained with a relatively slight excess of caustic alkali.

It has been the practice to neutralize the free alkali in the lye by agitating the spent lye with acid oils, that is fatty oils containing a high proportion of free fatty acid. The alkali reacts readily with the fatty acids to form soap, but does not react, or only reacts to an insignificant degree, with the glycerides (the neutral oil) of the acid oil. For this reason it has been necessary in such a process of spent lye neutralisation to employ a large bulk of material, a substantial amount of which was never utilised in the process. A

The soap formed by neutralising spent lye with acid oils is generally of a poor quality containing most of the colouring matter and other impurities present in the lye. The acid oils may be part of the charge undergoing saponification in a soap-making process. When substantially all the free fatty acids in the acid oils have reacted with the free alkali in the spent lye, the resultant mixture of soap, glycerides and any remaining free fatty acid, after separation from the lye and removal, as best possible, of impurities and colouring matter contained in this mixture, is usually returned to the soap-making process.

It has now been found that glycerides in fatty oils will react readily with free caustic alkali in spent lye under conditions of vigorous and sustained agitation, yielding a soap of satisfactory quality.

Accordingly, the present invention provides a process of neutralising the free caustic alkali in spent lye from Patented Aug.. 11, 1959 a soap-making process, in which a stream of the spent lye is mixed with a stream of fatty oil containing free fatty acid, if any, in an amount insufficient to neutralise all the free caustic alkali in the lye, and the resultant mixture is vigorously agitated, and the vigorous agitation is continued until substantially all the free caustic alkali has reacted with the glycerides in the fatty oil.

Suitable amounts of soap aid a saponification reaction between glycerides and free caustic alkali by promoting more intimate contact between the reactants. Although spent lye from a soap-making process always contains some soap, it has been found advantageous in the present process to increase the concentration of soap. Accordingly, it is preferred to add an additional amount of soap to the reactants of the present process. The additional amount of soap may be added to either the lye or the fatty oil, but preferably it is added to a mixture of these two reactants. V

The soapto be added may be grained soap from a soapmaking process, or it may be part of the soap formed during the process of the invention. Soap from any other source, such as neat soap or soap chips, may also be added. Generally, the electrolyte content of the lye is such that the additional soap added to the process is present in a finely grained condition.

According to the present invention it is preferred to use for the neutralisation of the caustic alkali in the spent lye a portion of the oil charge undergoing saponification in the soap-making process from which the lye derives. The oil charge may be any glyceride oil, or it may contain free fatty acids, for example, as in most commercial oils used for soap-making; acid oils resulting from the splitting by mineral acid of soapstock formed in the alkali refining of oils may also be used. Saponification of the oil proceeds after some of the free alkali has been neutralised by any free fatty acid present in the oil.

The rate of saponification differs for different oils. Also, the total reaction time for a given quantity of oil and alkali varies inversely with the temperature, .and to some extent with the intensity of agitation which is used during the process, but in general will not'exceed 3 hours. The agitation must, however, always be sufliciently intense to provide for intimate mixing of the reactants. Under optimum conditions only minutes or less are required to carry the process to completion. It may, therefore, be preferable to reduce the space/time requirements of the reaction by providing the most intense agitation that can be applied economically.

For most fatty oils a temperature of reaction in the range of 90 to C. is preferred. Good results have been obtained at temperatures of C. and higher. At temperatures lower than 85 C. the process may become uneconomic as the rate of reaction slows down. When using lye directly from a soap-making process, it is preferred, so as to conserve heat, to carry out the process of the invention as soon as possible after separating washed soap from the lye.

The time of reaction may be reduced by using an excess of the fatty oil over the stoichiometric proportion required for the reaction to proceed to substantial completion, preferably an excess of at least 10% by weight, based on the weight of free caustic alkali in the lye;

The process of the invention is suitable for working in conjunction with a batch or a continuous process of soap-making. It is particularly adapted for use with the latter because the crude spent lyes obtained from a continuous soap-making process canbe used to saponify continuously both the fatty acids and the glycerides in a part of the fat charge being fed to sucha process.

Yielding relatively pure material, the process of the invention, when carriedout in'conjunction with a continuous soap-making process, therefore allows nearly completely saponified material to be directly fed back into the saponification stage of the soap-making process. This is a great advance over the conventional methods, Where a much larger bulk of ,onlypartly saponified material had to be cleanedfbefore being incorporated in othersoaps.

.For economic working it is preferred to agitate the exhausted spent lye from the process of the invention,

.that. is lyein which the'free caustic alkalihas been neutralised, with a small proportion of acid oil. The acid oil facilitates the substantial removal of any dissolved soap from the exhausted spent lyefrom which it separates after the agitation as a soap/ oil emulsion. A batch of acid oil may be usedto treat successive .quantitiesof exhausted spent lye until the batch of oil itself becomes saturated with soap. After saturation the oil may be cleaned, and then the clean soap or soap/oilemulsion may be added to the soap-making process. This soap extraction step may be carried out in a continuous .man-

her, and in this case a'batch of acidoilis-preferably recycled until it becomes saturated with soap washed out from the exhausted spent lye. At this stage, any free alkalinity in the exhaustedspent lye due to, for example, sodium carbonate, may also be neutralised by the free fatty acids in the acid oil.

The invention will now be described with reference to the accompanying drawings in which:

Fig. 1 shows diagrammatically an arrangement of apparatus for carrying out the invention,

Fig. 2 shows diagrammatically another arrangement of apparatus for carrying out theinvention,

Fig. 3 shows diagrammatically yet another arrangement of apparatus for carrying out the invention, and

Fig. 4 shows a cross section on the line IVIV of Fig. 1.

Referring to Fig. l, a vessel 1, fitted with a weir 2, is provided with three supply conduits 3, 4 and 5. The vessell is connected by conduit 6 to the bottom of the first of three vessels 7a, 7b and 70, each fitted respectively with a pair of vertical baflles 8a, 8b and'8c, and a pair of impellers 9a, 9b and 9c on vertical shafts110a, 10b and 100, driven by motors 11a, 11b and 11c. Conduits 12a and 12b,.provided with vents 13a and 13b to prevent syphoning, connect respectively the top of vessels 7a-and 7b withthe bottom of vessels 7b and 7c. The vessels are arranged stepwise so that liquid can flow under the influence of gravity from the top of one vessel to the bottom of the next. Vessel 7c is provided with a recessed compartment 14, in which rides a float 15. This -float is coupled by lever arms 16a and 16b to a butterfly valve 17, located in the suction conduit 18. ofpump "19. Conduit 18 is connected-to the top of vessel 70.

A delivery conduit20 of pump 19 terminates in a distributing manifold 21 located within a settling 'vessel 22. This vessel 22 may be of any suitable shape including that l of a shallow tray. It is fitted with means for controlling automatically the lye and soap outflows, the means consisting of a float 23 adapted to be supported by the lye at the interface of the lye and the soap. The float has an upper guide rod 24 passing loosely, between stops 25, through a guide 26. A lower. guide rod 27 passes through a lye outlet orifice and collar 28. Near its lower end guide rod 27 carries a small inverted cone 29 adapted to ride in the lye outlet orifice and collar 28. This lye outlet orifice and collar 28 communicates with a conduit 30 which is provided with a vent 31,- terminating, as

shown, above the level of the soap in the settling vessel 22 to prevent vortex formation impeding the smooth movement of theifloat 23. Near the top of vessel 22, and

on. the side opposite the .distributing manifold 21, a slot 32 is'provided toacLas a weir. 4A gutter 33 surrounds slot.32 and is provided with a short slot 34 which is in .turn surrounded by a short gutter 35. The arrangement .of slots and'gutters is further illustrated in Fig. 4, which shows a cross section on. theline IV-.IV of. Fig, 1. A

vertical partition 36 divides gutter 35 into two equally sized compartments, and slot 34 into two halves. A plate 37 is movable by means, not shown, in a lower horizontal slide 38 and an upper horizontal slide, not shown, the slides being located respectively below and above the slot 34. One of the compartments in gutter 35 communicates with vessel 1 through conduit 5. The other compartment communicates with the saponification vessel of a soapmaking process (not shown) through conduit 39.

The operation of the above described arrangement is as follows:

Crude spent lye from a soap-making process enters vessel 1 through conduit 4 below the level of the contents of-the vessel to prevent foaming. Fatty oil, the flow of which is adjusted inthe correct proportions according to the feed rate and the alkalinity of the lye, enters through conduit 3. A portion ofthe soap formed during the process is returned through conduit 5 to increase the speed of the reaction. The mixture of lye,

oil and soap passes over baffle 2 and then under the influence of gravity through conduit 6 to the bottom of vessel 7a. The shafts 10a, 10b and in vessels 7a, 7b and 7c are driven at speeds of about 1,000 revolutions per minute by motors 11a, 11b and lie respectively. After passage under the influence of gravity through each of the three vessels by way of conduits 12a and 12b respectively, the mixture, in which substantially all the free caustic alkali has reacted with the fatty oil, is passed through conduit 18 to pump-19. The float/lever arm and butterfly valve arrangement denoted by 15 to 17 controls the pump section and maintains the level of the reacted mixture in vessel '70 at a constant height above the inlet of conduit 18, thus avoiding an intake of airinto the system The mixture is finally pumped through conduit 20 and distributing manifold 21 to the settling vessel '22, settlingtherein into an upper layer of aqueous soap and a lower layer of spent lye. The float 23 and the cone'29 within vessel 22 rise or fall with changes in the level of the soap/ lye interface, thus opening or closing the orifice in collar 28, and keeping constant, within certain limits, the level of the soap/lye interface. The exhausted spent lye passes out of vessel 22 through conduit 30 and is then treated with acid oil to extract dissolved soap. The soap from the upper layer spills through slot 32 into gutter 33, and thence through slot 34. By adjusting the position of plate 37 the proportions of soap being recycled to the lye neutralisation process through conduit-Sand to the saponification stage of the soap-making process through conduit 39 may be controlled.

In practice, forexample, vessels 7a, 7b and 70, each of 500 to 1,000 kgm. capacity, are suitable for continuously neutralising hot spent lye supplied direct from a continuous soap-making plant at the rate of 1,000 to 1,500 kgm. per hour. The contents of each vessel are preferably agitated by impellers rotating at up to 1,000 revolutions per minute. However, a variety of agitators may be employed. For example, comparatively large paddles being rotated at 100 revolutions per minute, or less, may be used if suitable horizontal baflles are also provided. The spent lye from a soap-making process, that is, the lye used in the present process, usually has a free alkali content of from 0.5% to 1.0%, but lower or higher contents of up to 2 or 3% may be found. The exhausted spent lye contains only about 0.02 to 0.05% of free alkali after treatment with commercial fatty oils containing as little as 1% of free fatty acids. The rate at which the soap from settling vessel 22 is recycled to vessel 1 is preferably approximately equal to that at which fresh soap is produced by the process.

The following examples illustrate the invention when carried outwith the arrangement of apparatus shown in Fig. l,

Example 1 Fatty oil charge: 3 parts of tallow, 1 part of palm kernel oil, bleached by treatment with fullers earth. Characteristics of fatty oil charge:

Free alkalinity of lye expressed as percent weight per weight (sodium oxide) Na O:

Initial crude lye 0.64

Lye from vessel 7a 0.30

Lye from vessel 7b 0.11

Lye from vessel 70 0.04

Example 2 Fatty oil charge: 3 parts of tallow, 1 part of palm oil, 1 part of palm kernel oil, bleached by treatment with fullers earth.

Characteristics of fatty oil charge:

Free fatty acid (as oleic acid) percent 1.39

Moisture do 0.5

Saponification equivalent 274.8 Flow rates:

Crude lye kilogrammes per hour 1520 Fatty oil do 80.3

Soap recycled from process do 36.6

Free alkalinity of lye expressed as percent weight per weight (sodium oxide) Na Oz Initial crude lye 0.49

Lye from vessel 7a 0.24'

Lye from vessel 7b 0.09

Lye from vessel 7c 0.04

Example 3 Fatty oil charge (percent by weight):

70% tallow 15% soft acid oils 15% palm kernel acid oil Characteristics of fatty oil charge:

Free fatty acid (as oleic acid) percent 22.0

Moisture do 0.7

saponification equivalent 265.5 Flow rates:

Crude lye kilogrammes per hour 1015 Fatty oil do 60.9

Soap recycled from process do 27.4

Free alkalinity of lye expressed as percent weight per weight (sodium oxide) Na O:

Initial crude lye 0.56 Lye from vessel 7a 0.12 Lye from vessel 7b 0.05 Lye from vessel 70 0.02

In an alternative arrangement shown diagrammatically in Fig. 2, a single cylindrical vessel 40 is divided into four compartments, namely compartments 41a, 41b and 410, which correspond to vessels 7a, 7b and 7c in Fig. 1, and a settling compartment 42. Each of the partitions dividing the compartments 41a, 41b and 410 have an aperture provided to allow the reaction mixture to pass from one compartment to the next. The aperture in the partition between compartment 41c and compartment 42 is in communication with a conduit and manifold distributor 43. In each of the compartments 41a, 41b and 410, impellers carried on inclined shafts 44a, 44b and 440, as shown, are driven by electric motors 45a, 45b and 450, respectively. Baffles may be provided in each of the three compartments, if desired. The vessel 1, arrangement of gutters 33 and 35, slots 32 and 34, appropriate conduits and slides, and parts within the settling compartment 42, are similar to those described in connection with Figs. 1 and 4. The pump 19 is, however, arranged between the Vessel 1 and compartment 41a, that is, in conduit 6 and not conduit 20 of Fig. 1, which is dispensed with. In the present arrangement, the conduit 30 is partly, and collar 28 is wholly, within the compartment 410.

The operation of the arrangement of apparatus shown in Fig. 2 is very similar to that shown in Fig. 1. However, instead of the reaction mixture passing through saponification vessels 7a, 7b and 70 under the influence of gravity, it is progressively forced upwards, by pump 19, from compartment 41a to 41b to 410, and thence through the manifold distributor 43 into settling compartment 42. The presence of the manifold distributor ensures quiescent conditions in the settling compartment.

The rate of saponification may be increased by having a preponderance of one or other of the reactants at the beginning and the end of the reaction. This is the principle which underlies the arrangement of apparatus shown in Fig. 3. Referring to Fig. 3, two cylindrical vessels 46 and 47 are provided With compartments 48a and 49a, and 48b and 49b respectively. Compartments 48a and 48b are provided with impellers on shafts 50a and 50b and motors 51a and 51b, respectively. Compartments 49a and 491) are provided with the arrangement of float, orifice and collar, and manifold distributor described in connection with the settling vessel 22 of Fig. 1. As in Fig. 1 a conduit 3 supplies spent lye to a vessel 1 which is provided with a weir 2. Vessel 1 is connected by a conduit 6 to the bottom of compartment 48a of vessel 46. Compartment 49a is provided with the same arrangement of gutters, plate and slots as is the vessel 22 of Fig. 1. It is also provided with conduits 5 and 39. Conduit 5 empties into a sump tank 52, fitted with a float and butterfly valve arrangement similar to that fitted to vessel 7c in Fig. 1. A conduit 53, which is connected to the variable orifice and collar in the bottom of compartment 49a also empties into sump tank 52. Butterfly valve 17 is on a conduit 54, which includes pump 19. Conduit 54 connectssump tank 52 with a vessel 55, similar to vessel 1, and fitted with a weir 56. A conduit 4 supplies fresh oil to vessel 55. A conduit 57 connects the bottom of vessel 55 to the bottom of compartment 48b of vessel 47. Compartment 4% of vessel 47 is provided with a gutter 58 for receiving material from the top of the compartment. A conduit 59 from gutter 58 feeds vessel 1.

The operation of the arrangement shown in Fig. 3 is as follows:

Crude lye is passed to vessel 1 through conduit 3, where it is mixed with partly saponified material, obtained in a manner described below, from compartment 49b of vessel 47. The mixture, which contains an excess of lye, passes under the influence of gravity through conduit 6 to compartment 48a of vessel 46. saponification of the fatty oil proceeds to completion in this compartment. Soap and partly spent lye separate in compartment 49a of vessel 46. The soap flows into gutter 33 and then divides into two streams in the manner described previously. One stream of the soap is conveyed, through conduit 39, to the saponification stage of a conventional soap-making process. The other stream is recycled to the present process through conduit 5 to sump tank 52. The partly spent lye is conveyed through conduit 53 also to sump tank 52, and the resultant mixture of partly spent lye and soap is pumped through conduit 54 by pump 19 to vessel 55. Fatty oil is added to vessel 55 through conduit 4 and the mixture, now containing an excess of fatty oil, flows under the influence of gravity into compartment 48b of vessel 47 through conduit 57. In this compartment the free caustic alkali in the partly spent lye is substantially neutralised. The mixture containing the exhausted spent lye passes into compartment 49b where it sepa 7 rates into .two layers. Thebottorn layer, exhausted spent lye, passes out of the system through conduit 30 so that it may be treated, preferably continuously, with acid oil, to removeanydissolved soap. The top layer,

containing partly saponified oil, flows into gutter 58 and through conduit 59 to vessel 1, where it meets fresh crude lye. The above described cycle of operation then recommences.

We claim:

1. A process of neutralizing the freecaustic .alkaliin spent lye from a soap-making process the free caustic alkali content of said spent lye being ,not greater than 3%, comprising mixing a stream of, the spent lye with a stream of fatty oil, the amountof fatty o il fed into the stream of the spent .lye being stoichiometrically at least 10% in excess of the amount of free alkali in the spent lye, vigorously agitating the resultant mixture at a temperature in the range of from 90 to 100 C. and continuing the vigorous agitation within said temperature range until substantially all the free caustic alkali has been reacted with the glycerides in the fattyoil, separating the exhausted spent lye from the saponified oil, and separately discharging the exhausted spent lye and saponified oil.

2. A process of neutralizing the free caustic alkali in spent lye from a soap-making process, the free caustic alkali content of said spent lye being not greater than 3%, comprising mixing a stream of the spent lye with a stream of fatty oil, the amount of fatty oil fed into the stream of spent lye being stoichiometrically at least 10% in excess of the amount of free alkali in the spent lye, adding soap to catalyze the reaction of the free caustic alkali with the glycerides in the fatty oil, vigorously agitating the resulting mixture at a temperature .in the range from 90 to 100 C. and continuing the .vigorous agitation within said temperature range until substantially all the free caustic alkali has reacted with the glycerides in the fatty oil, separating the exhausted spent lye from the saponified oil, and separately discharging the exhausted spent lye and saponified oil.

3. A process of neutralizing the free caustic alkali in spent lye from a soap-making process, thefree caustic alkali content of said spent lye being not greater than 3%, comprising mixing a stream of the spent lye with a stream of fatty oil, the amount of fatty oil fed into the stream of spent lye being stoichiometrically at least 10% in excess of the amount of free alkali in the spent lye, passing the mixed stream of spent lye and oil in the presence of grained out soap through a reaction vessel maintained at a temperature in the range of 90 to 100 C. in which vigorous agitation is provided, at a rate to accomplish the required neutralization during the passage of the mixture of lye and oil through the reaction vessel,

separating the exhausted spent lye from .the saponified oil and continuously and separately discharging the exhausted spent lye and saponified oil.

4. A process of neutralizing the free caustic alkali in the -free caustic alkali-'in the lye, vigorously agitating the resulting mixture and continuingithe vigorous agitation until the fatty oil is fully saponified, continuously separatingthe spent lye from the saponified oil, the free caustic alkali content of said spent -lye being not greater than 3%, continuously and separately discharging .the saponified-oil and-the spent lye, -mixing a stream -.of the spent lye with the stream of fatty oil, the amountof fatty oil fed into the stream of spent lye being stoichiometrically at least 10% in excess of the amountof free caustic alkali in the spent lye, vigorouslyagitating the resulting mixture at a-temperature in the range of to v C. and continuing the -vigorous agitation within said temperature range until substantially all the free caustic alkali has reacted with the glycerides in .the fatty oil, separating the exhausted spent lye from the saponified oil and separately discharging the exhausted spent lye and saponified oil.

5. A process of neutralizing the free caustic alkali in spent lye from a soap-making process, the free caustic alkali content of said spent lye being not greater than 3%, comprising mixing a stream of the spent lye with a stream of fatty oil, the amount of fatty oil fed into the stream of the lye being stoichiometrically at least 10% in excess of the amount of free alkali in the spent lye, adding soap to catalyze the reaction of the free caustic alkali with the glycerides in the fatty oil, vigorously agitating the resulting mixture at a temperature in the range of from 90 to 100 C., and continuing the vigorous agitation within said temperature range until substantially all the free caustic alkali has reacted with the glycerides in the fatty oil, separating the exhausted spent lye from the saponified oil, separately discharging the saponified oil and the exhausted spent lye, and extracting from the exhausted spent lye dissolved soap by treatment with a small amount of acid oil.

6. The process according to claim 1 in which the free caustic alkali content of the spent lye is from 0.5% to 1.0%.

7. A process according to claim 2, in which the added soap is a recycled part of the soap formed during the process.

8. A process according to claim 5, in which a small amount of acid oil is used to treat successive quantities of the exhausted spent lye until the amount of acid oil is saturated with soap.

References vCited in the file of this patent UNITED STATES PATENTS 2,232,544 Lorenz Feb. 18, 1941 2,300,750 Scott Nov. 3, 1942 2,727,915 Palmquist Dec. 20, 1955 OTHER REFERENCES Davidsohn et al.: Soap Manufacture, vol. 1 (copyright 1953), pp. 344-345.

Claims (1)

1. A PROCESS OF NEUTRALIZING THE FREE CAUSTIC ALKALI IN SPENT LYE FROM A SOAP-MAKING PROCEES, THE FREE CAUSTIC ALKALI CONTENT OF SAID SPENT LYE BEING NOT GREATER THAN 3%, COMPRISING MIXING A STREAM OF THE SPENT LYE WITH A STREAM OF FATTY OIL, THE AMOUNT OF FATTY OIL FED INTO THE STREAM OF THE SPENT LYE BEING STOICHIOMETRICALLY AT LEAST 10% IN EXCESS OF THE AMOUNT OF FREE ALKALI IN THE SPENT LYE, VIGOROUSLY AGITATING THE RESULTANT MIXTURE AT A TEMPERATURE IN THE RANGE OF FROM 90 TO 100* C. AND CONTINUING THE VIGOROUS AGITATION WITHIN SAID TEMPERATURE RANGE UNTIL SUBSTANTIALLY ALL THE FREE CAUSTIC ALKALI HAS BEEN REACTED WITH THE GLYCERIDES IN THE FATTY OIL, SEPARATING THE EXHAUSTED SPENT LYE FROM THE SAPONIFIED OIL, AND SEPARATELY DISCHARGING THE EXHAUSTED SPENT LYE AND SAPONIFIED OIL.

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