I.lbs.Cochin cocoanut oil26Stearic acid165Caustic potash lye, 50° B.69Glycerine C. P.76Water38II.lbs.Cochin cocoanut oil18Stearic acid73Caustic potash lye, 39° B.54Glycerine33Water27III.lbs.Cochin cocoanut oil18Stearic acid73Caustic potash lye, 39° B.54Glycerine20Water40andlbs.Stearic acid60Glycerine C. P.85Water165Sodium carbonate50Borax1
To make a shaving cream by Formula I or II, the cocoanut oil and glycerine are first put into a suitable mixing apparatus or crutcher, and heated to 120° F. A part or all the potash lye is then added and the cocoanut oilsaponified. The rest of the potash lye and the water are then added, and with the mixer running the stearic acid, previously melted in a lead-lined or enameled vessel, is then poured in in a stream and the mass stirred until smooth, care being exercised not to aerate it too much. The cream is then tested for alkalinity, the best method being by that described under shaving soap, in which the sample is dissolved in alcohol. Because of the large quantity of water present, phenolphthalein is unsatisfactory, as dissociation of the soap may show a pink indication in spite of the fact the mass is on the acid side. For a quick method of testing the bite on the tongue is a satisfactory criterion. If a cooled sample bites the tongue more stearic acid is added until there is a 3% excess of this. When the proper neutralization has taken place the cream is perfumed and framed in a special frame, or it may be allowed to cool in the mixer and perfumed the next day. When cool the cream is strained, or put through an ointment mill, after which it is ready to fill into tubes.
The procedure for the first part of Formula III is the same as that just given. The second part of the formula is made the same as a vanishing cream for toilet purposes. To make this, first melt the stearic acid as already directed. Dissolve the sodium carbonate and borax in water and when dissolved add the glycerine and stir. Then heat this solution to about 100°-120° F. and while stirring in a suitable mixing machine into which this solution has been poured after being heated, or better still in which it has been heated by dry steam, add the stearic acid. Continue mixing until smooth and then allow to cool, or run into frames to cool.
When the shaving cream and vanishing cream are both cool, they are mixed in the proportion of one of the former to two of the latter. It is claimed that in thusmaking a shaving cream a smoother product is obtained, although it may be said that the vanishing cream is merely a soft soap and the ultimate result is the same as though the various ingredients were added in one operation, rather than making two separate products and then mixing them, thereby considerably increasing the cost of manufacture.
Pumice and sand are at times added to soap to aid in the removal of dirt in cleansing the hands. In some cases these soaps are made in the form of a cake, in others they are sold in cans in the form of a paste.
A hand paste is usually made by merely dissolving ordinary tallow base in two or three times its weight of hot water and mixing in the desired quantity of pumice or sand and in some instances adding a little glycerine to keep it soft or a solvent of some kind for grease. It may also be made by directly incorporating any of these in a potash soap.
A cold made or semi-boiled cocoanut or palm kernel oil soap is the base used to add the pumice or sand to in making a cake soap of this sort. The following formulae serve as a guide for these soaps.
I.Palm Kernel or Ceylon Cocoanut Oil705lbs.Pumice (Powdered)281"Soda Lye, 38° B.378"II.Cocoanut Oil100"Soda Lye, 38° B.55"Water6"Silver Sand (fine)60"
To proceed place the oil in a crutcher and heat to 140° F. Sift in the pumice and mix thoroughly. The lye is then added which causes a curdling of the grain. The stirring is continued until the grain closes and the soap is smooth, after which the desired perfume is added and the soap dropped into a frame and crutched by hand. When the soap is set, it is slabbed, cut into cakes, dried slightly and pressed.
Liquid soaps are merely solutions of a potash soap, usually cocoanut oil soap, although corn oil is used to make a cheap soap. One of the difficulties encountered in liquid soap is to keep it clear. At a low temperature a sediment is often formed, but this can be overcome by the use of sugar and filtering the soap through a filter press at a low temperature. In order to prevent the soap from freezing, it is necessary to lower the freezing point by the addition of glycerine or alcohol.
To make liquid soap by any of the formulae given below, the oil is first run into a jacketed kettle with a stirring device, and heated to about 120° F. The potash lye is then added and the oil saponified. When the saponification takes place, especially when cocoanut oil is used, the mass swells rapidly and may foam over the sides of the kettle unless water is used to check this, or a kettle of about four to five times the capacity of the total charge of soap is used. When the saponification has occurred, the sugar, borax and glycerine are added, the water run in and the mixture stirred until the soap is thoroughly dissolved. Heat aids materially in dissolving the soap. The soap is then allowed to cool and if color or perfume is to be added this is stirred in, after which the soap is cooled and filtered or else run directly into barrels.
Tallow is not suitable for making a clear liquid soap since it is too high in stearine which when formed into the stearate makes an opaque solution. The formulae herewith given have been found to give good practical results.
I.lbs.Cocoanut oil130Caustic potash lye, 28° B.135Sugar72Borax2Water267II.lbs.Corn oil130Caustic potash lye, 26° B.135Sugar72Borax2Water267III.lbs.Cocoanut oil100Caustic potash lye, 28° B.102Glycerine100Sugar70Water833
Formulae I and II contain about 20 per cent. fatty acids. It is possible, of course, to either increase or decrease the percentage of fatty acid by varying the amount of water. The water used in making liquid soaps, of course, should be soft, for hard water forms insoluble soaps which precipitate and cause a sediment.
While the introduction of the hydrogenation of oils is a decided advance in the production of suitable cheaper oils for soap making, comparatively little hardened oil is employed for soap making in America up to the present time. In Europe, however, considerable advance has been made by the use of such oils for manufacturing soap therefrom and a number of plants turn out large quantities of hydrogenated oils for soap making as well as for edible purposes. Recently a company has been formed in this country for hardening oils and it is very probable that the future will see this material extensively used in our own country, as these appear to be the one present hope of the soap manufacturer as a check on the ever increasing cost of fats and oils now used in making soap.
It is an unfortunate condition that hydrogenated oils produced abroad are sold under names which give absolutely no indication as to the oil which has been hardened. The softer and cheaper oils like fish oil, linseed oil, cottonseed oil, etc., are generally hardened for soap manufacture to different degrees of hardness. While it is impossible to definitely state just what products as Candelite, Talgol, Krutolin or several other coined names of hardened oils are, various investigators have experimented with them as to their adaptability for producing toilet soaps and found that suitable toilet soaps may be made from them. While many objections were at first met with concerning soaps made from these products, as to their unsatisfactory saponification, the poor lathering quality of the soaps and their odor and consequent difficulty in perfuming, the results of most investigators along these lines indicate that these in many cases were due to prejudice against or unfamiliarity with handling oils of this type for soap making.
In manufacturing soap from hardened oils it is usuallynecessary to incorporate with the charge lard, tallow, tallow oil or some other soft oil of this nature. Satisfactory bases for toilet soaps, made as boiled settled soap by the use of Talgol (undoubtedly hardened fish oil), are said to be made by the formulae[10]below.
I.Tallow45partsTalgol40"Cocoanut Oil15"II.Cocoanut Oil (Ceylon)6"Tallow12"Talgol, Extra12"
The method of boiling a soap of this type does not differ materially from that of making settled tallow soap base. The soap itself has a different odor than a straight tallow base, but is said to make a very satisfactory soap for milling and to be of good appearance.
Satisfactory transparent soaps are made from the hardened oil Candelite, which replaces the tallow in transparent soap formulae such as have already been given in the section under "Transparent Soaps." The method of manufacturing a soap by the use of this product varies in no way from the usual method employed for making these soaps.
Since hydrogenated oils are high in stearine, their use in shaving soaps is a decided advantage. It has previously been pointed out that potassium stearate forms an ideal lather for shaving, and in the hydrogenating process the olein is converted to stearine. Thus a hardenedoil is advantageous in a shaving soap. As an example of a cold made soap for shaving the following may be taken.[11]
Talgol Extra50 lbs.Cocoanut Oil10 "Lard10 "Soda Lye, 38° B.20 "Potash Lye, 37° B.21 "
This soap may be made in a crutcher by the method generally used in making soap by the cold process.
Soap is a very important product to every branch of the textile industry. For woolen fabrics it is used for scouring, fulling and throwing the wool; in the silk industry it is necessary for degumming the raw silk, as well as for dyeing; in the cotton mills it is used to finish cotton cloth and to some extent in bleaching; it is, furthermore, employed in a number of ways in the manufacture of linen. Large quantities of soap are thus consumed in an industry of so great an extent and the requirements necessitate different soaps for the different operations. We will, therefore, consider these in detail.
The soaps used to scour wool and for fulling the woven cloth are usually made as cheaply as possible. They are, however, generally pure soaps, as filling material such as sodium silicate does not readily rinse out of the wool and if used at all must be added very sparingly. Both cold made and boiled settled soaps are made for this purpose. The soap is generally sold in barrels, hence is run directly to these from the crutcher or soap kettle. As cold made soaps the following serve for wool scouring or fulling.
I.Palm Oil200 lbs.Bone Grease460 "Soda Lye, 36° B.357 "Water113 "Soda Ash50 "Citronella2 "II.Palm Oil (Calabar, unbleached)155 "House Grease360 "Soda Lye, 36° B.324 "Water268 "Sodium Silicate83 "III.House Grease185 "Palm Oil (unbleached)309 "Soda Lye, 36° B.309 "Water391 "Soda Ash70 "Sodium Silicate60 "Corn Starch10 "
These soaps are made in a crutcher by the usual process for cold-made soaps, crutched until smooth, dropped into a barrel and crutched by hand the next day or just before cooling.
As a settled soap for these operations the following charge is typical:
Palm Oil34partsCottonseed foots or its equivalent in fatty acids33"Rosin10"House Grease23"
The method of boiling such a soap is the same as for any settled soap up to the strengthening change. When this stage is reached, sufficient lye is added to strengthen the kettle strongly. It is then boiled down with closed steam on salt brine or "pickle" until a sample of the lye taken from the bottom stands at 16°-22° B. The soap is then run into barrels and after standing therein for a day is hand crutched until cool to prevent streaking of the soap.
Besides a soap of this type a settled tallow chip soap is used.
Soaps for wool throwing are sometimes made from olive oil foots but these are often objected to because of the sulphur-like odor conveyed to the cloth due to the method by which this oil is extracted with carbon disulphide. A potash soap hardened somewhat with soda is also used. As a formula for a suitable soap of this type this may be given.
Olive Oil Foots12 partsCorn Oil46 "House Grease20 "Soda Lye, 36° B.3 "Potassium Carbonate (dry)5-3/4 "Potassium Hydrate (solid)23 "
This soap is made as a "run" soap by the general directions already given for a soap thus made. The kettle is boiled with open and closed steam, adding water very slowly and aiming to obtain a 220-225 per cent. yield or fatty acid content of the finished soap of 46 per cent. When the soap is finished a sample cooled on a plate of glass should be neither slippery or short, but should string slightly. The finished soap is run directly into barrels.
A soap for wool throwing by the semi-boiled process may be made from olive oil foots in a crutcher thus:
Olive Oil Foots600 lbs.Potash Lye, 20° B.660 "
The oil is heated to 180° F., the lye added and the mass stirred until it bunches, when it is dropped into barrels.
For the finishing of worsted cloth soaps high in cocoanut oil or palm kernel oil are preferred. These soaps are finished very neutral, being made as settled soaps, but given an extra wash change after strengthening strongly. They are then finished as usual and run into barrels. If framed too hot, the high percentage of cocoanut oil causes mottling, which is prevented by crutching by hand until the temperature of the soap is 140°-145° F. Some typical charges, all of which are saponified with soda lye, follow:
I.Palm Kernel Oil60 partsCorn Oil40 "II.Palm Kernel Oil30 "Red Oil (single pressed)70 "III.Red Oil33-1/3 "Corn Oil33-1/3 "Cocoanut Oil or Palm Kernel Oil33-1/3 "
Soap is used to a very large extent in silk mills, both fordegumming the raw silk and in silk dyeing. Raw silk consists of the true silk fibre known as fibroin and a gummy coating, sericin, which dulls the lustre of the silk unless removed. For this purpose a slightly alkaline olive oil foots soap is best adapted, although palm oil and peanut oil soaps are sometimes used, as well as soaps made from a combination of house grease to the extent of 30 per cent., together with red oil or straight olein soaps, both of which are artificially colored green. In using house grease, if 30 per cent. is exceeded in combination with red oil, the titer is raised to such an extent that the soap does not readily rinse from the silk nor dissolve readily. They are also not advisable because they impart a disagreeable odor to the silk.
To make a soap for this purpose from olive oil foots it is made as a settled soap, care being taken to thoroughly boil the mass on the saponification change in the closed state to assure proper saponification. The kettle is usually grained with lye and given a good wash change to remove the excess strength. The change previous to the finish should not be too heavy or too large a nigre results. The lighter the grain is, the better the finished kettle is. A yield of 150 per cent. is usually obtained. This soap is generally run to a frame, slabbed upon cooling and packed directly into wooden cases.
For silk dyeing the above soap is suitable, although any well-made soap of good odor and not rancid is useable. While soap alone is often used in the bath for silk dyeing, certain dyestuffs require the addition of acetic or sulphuric acid, which sets free the fatty acids. If these be of bad odor it is taken up by the silk and is difficult to remove. The most generally used soaps are the just mentioned olive foots soap or a soap made from a good grade red oil.
Both kinds are extensively used.
In the manufacture of cotton goods, as compared to the wool and silk industries, very much less soap is used and it is only applied to the finished fabric either to clean the cloth preparatory to dyeing or to aid in dyeing with certain colors. It is also used in calico printing. For cleansing the cloth ordinary chip soap is suitable although a more alkaline soap finished as a curd soap is an advantage in that the free alkali contained therein aids in removing the dirt and has no harmful effect on the cotton. For dyeing cotton goods or to brighten certain colors after dyeing an olive oil foots soap is most generally employed. In calico printing soap is used to wash and clear the cloth after printing. A soap for this purpose should be easily soluble in water and contain no free alkali, rosin or filler. The best soaps for use in calico printing are either an olive oil foots soap or an olein soap.
While sulphonated oils are not used to any great extent in the manufacture of soap, they are used very largely in the dyeing and printing of turkey and alizarine reds on cotton as well as other colors. Just what action these oils have is not known. Turkey red oil or sulphonated castor oil is the best known sulphonated oil.
The process of making these oils is simple. The equipment necessary is a wooden tank or barrel of suitable capacity, approximately two and a half times the amount of oil to be treated. There are furthermore required other tanks or vessels to hold the solutions used such as caustic soda, ammonia and acid. The tank to be used for the preparation of sulphonated oil should be provided with a valve at the bottom of the tank and a gauge to measure the quantity of liquid therein.
The process is carried out as follows:
Three hundred pounds of castor oil are placed in the tank and 80 pounds at 66 deg. B. sulphuric acid are weighed out in another vessel. The acid is run into the tank containing the oil in a very thin stream while the oil is well stirred. At no time should the temperature exceed 40 deg. C. This operation should consume at least an hour and stirring should be continued half an hour longer to insure the thorough mixing of the oil with the acid. The mass is then allowed to settle for 24 hours, after which 40 gallons of water are added and the mixture stirred until it has a uniform creamy color indicating no dark streaks. This mixing process should be carefully carried out and when completed allowed to settle 36 hours. At this point the mass will have separated into two layers, the lower layer consisting of a water solution of acid and the upper layer of oil. The former is run out through the valve located at the bottom of the tank. Another wash may now be given or dispensed with as desired. In this wash the addition of salt or sodium sulphate at the rate of 1-1/2 pounds per gallon of water is advisable. A 24 deg. B. caustic soda solution is prepared and added slowly to the acidified oil with constant stirring. The mass first turns creamy, then becomes streaked, increasing in streaks as the caustic solution is poured in, and finally becomes clear and transparent. Water is now added to bring the volume to 75 gallons. The oil is now milky in appearance, but the addition of a little more soda solution restores the transparency.
In some cases ammonia is used in addition to caustic soda in neutralizing the oil. Three-fourths of the amount of caustic soda required to complete the neutralization is first added and then the neutralization is completed with a one to one liquid ammonia and water solution.
FOOTNOTES:[9]Seifensieder Ztg., 40, 47, 1266 (1913).[10]Seifensieder Ztg. (1913), p. 334 and 338." " (1912), p. 1229 and 1257.[11]Seifensieder Ztg. (1912), p. 954.
[9]Seifensieder Ztg., 40, 47, 1266 (1913).
[9]Seifensieder Ztg., 40, 47, 1266 (1913).
[10]Seifensieder Ztg. (1913), p. 334 and 338." " (1912), p. 1229 and 1257.
[10]Seifensieder Ztg. (1913), p. 334 and 338." " (1912), p. 1229 and 1257.
[11]Seifensieder Ztg. (1912), p. 954.
[11]Seifensieder Ztg. (1912), p. 954.
The recovery of glycerine is very closely allied with the soap-making industry, because glycerine is the very valuable by-product obtained in the saponification of oils and fats. No soap plant is, therefore, fully equipped unless it has some method whereby the glycerine is recovered and the importance of recovering this product cannot be too strongly emphasized.
It has already been pointed out that neutral fats or the glycerides are a combination of fatty acid with glycerine. These are split apart in the process of saponification. While by the termsaponificationas used in soap making it is inferred that this is the combination of caustic alkalis with the fatty acids to form soap, this term is by no means limited to this method of saponification, as there are various other methods of saponifying a fat. The chemical definition of saponification is the conversion of an ester, of which glycerides are merely a certain type, into an alcohol and an acid or a salt of this acid. Thus, if we use caustic alkali as our saponifying agent for a fat or oil, we obtain the sodium or potassium salt of the higher fatty acids or soap and the alcohol, glycerine. On the other hand, if we use a mineral acid as the saponifying agent, we obtain the fatty acids themselves in addition to glycerine. While the former is by far the most generally employed for making soap, other processes consist in saponifying the fats by some method other than caustic alkalis and then converting the fatty acids into soap by either neutralizing them with sodium or potassium carbonate or hydrate.
It is important to again point out here that fats and oilsdevelop free fatty acid of themselves and that the development of this acid represents a loss in glycerine. The selection of an oil or fat for soap making should therefore to a large extent be judged as to its adaptability by the free fatty acid content, as the higher this content is, the greater is the loss in the glycerine eventually obtained. Glycerine often represents the only profit to a soap manufacturer. It is indeed necessary to determine the percentage of free fatty acid before purchasing a lot of stock to be made into soap.
In taking up the question of glycerine recovery we will consider the various methods thus:
1. Where the glycerine is obtained from spent lye by saponifying the fats or oils with caustic alkali.
2. Where the glycerine is obtained by saponifying the fats or oils by some other method than the above, of which there are the following:
(a) Twitchell process.(b) Saponification by lime in autoclave.(c) Saponification by acid.(d) Saponification by water in autoclave.(e) Fermentative (Enzymes).(f) Krebitz process.
The spent lye obtained from the glycerine changes in making soap varies greatly, the quality depending upon the stock saponified and the soap maker's care in handling the operation. No two lyes run exactly alike as to proportion of the various ingredients, although they are all similar in containing the same substances either in solution or suspension. Spent lye is a water solution of mainly glycerine, free alkali either as caustic alkali or carbonate and salt, including sodium sulfate, but furthermore contains some soap and albuminous matter either in solution orsuspension. Upon standing in the storage tank the greater part of the soap usually separates when the lye cools. In order to assure the greatest economical yield of glycerine by saponifying a fat with caustic soda it is necessary to obtain a proportion of three parts of water to every part of fat made into soap. Test runs have shown that this is the proper proportion and that it is not economical to greatly exceed this amount, and if a much less proportion is used the full yield of glycerine is not obtained.
The spent lyes contain varying amounts of glycerine, the first change being richest in glycerine content, and this being reduced in the subsequent changes. If the lyes always run high in glycerine it is an indication that it is not all being obtained. The usual percentage is from 0.5% to 5% or even more, although the average is somewhere around 2% to 3%. The lye as it comes from the kettle should not contain any more than 0.5% to 0.6% of free alkali calculated as sodium carbonate, Na2CO3. If the proportion is higher than this, it shows that the saponification has been conducted with too high a proportion of alkali, a condition which should be corrected in the kettle room. An excess of free alkali does not interfere to any great extent with the successful recovery of the glycerine, but is a waste of both alkali and the acid used in neutralizing this. It is, therefore, more economical to run a strong lye over fresh stock and neutralize the alkali thus, rather than treating the lye for glycerine recovery.
Before the spent lye can be run into the evaporator it is necessary to remove the albuminous impurities and soap and to neutralize the excess alkali to between exactly neutral and 0.02% alkalinity. The lye should never be fed into the evaporator in the acid condition.
In order to treat the spent lyes for evaporation, they are first allowed to cool in the storage tank, after which anysoap which may have separated is skimmed off and returned to the soap kettle. This lye is then pumped to the treatment tank, an ordinary tank equipped with some method of agitating the liquor, either by a mechanical stirrer, steam blower or compressed air, until it is about two feet from the top.
After the lye has been skimmed off it is thoroughly agitated and a sample taken. The amount of lye in the tank is then calculated. Spent lye is about 1.09 times heavier than water, or weighs about 9 pounds to the gallon. While the sample is being tested for alkalinity it is advisable to add sulfate of alumina, which may be dissolving while the sample is being titrated. This substance should be added in the proportion of anywhere from 6 to 14 pounds per thousand pounds of lye, depending upon the amount of impurities contained therein. For a clean lye six pounds per thousand is sufficient, but for an impure lye a greater quantity is necessary. The sulfate of alumina used should be free from arsenic and sulfides and should contain a minimum amount of grit (silica), as grit reduces the life of the pump valves. This may be estimated with sufficient accuracy by rubbing the filtered-off portions, insoluble in water between the fingers and a plate of glass. The object of adding the sulfate of alumina is to transform the soap contained in the lye into the insoluble aluminum soaps, and at the same time to coagulate the albuminous impurities. It must be remembered that the sulfate of alumina is added only for the fresh lye put into the tank. Thus if there were 10,000 pounds of lye in the treating tank when the fresh lye was run in, and 50,000 pounds when the tank is filled, adding nine pounds of sulfate of alumina per thousand of lye, only 360 pounds would be added or enough for 40,000 pounds. Sulfate of alumina neutralizes one-third of its weight of caustic.
To determine the alkali in the sample, 10 cubic centimeters are pipetted into a beaker, a little distilled water added, then 3 or 4 drops of phenolphthalein indicator. From a burette, quarter normal (N/4) sulfuric acid is added until the pink color is just discharged. When this point is reached 4 to 5 c. c. more of acid are added and the solution is boiled to expel the carbon dioxide. Should the solution turn pink, it is necessary to add more acid. After having boiled for 3 to 4 minutes, N/4 caustic soda is added until the pink color just returns and the amount of caustic soda used is read on the burette. The difference between the number of cubic centimeters of N/4 sulfuric acid and N/4 caustic soda gives the amount of alkali in the sample. By using a 10 c. c. sample and N/4 sulfuric acid and N/4 caustic soda each c. c. obtained by the difference of these two solutions is equal to one-tenth of one per cent. (0.1%) of the total alkali in the lye. As an example, say we first used 7.7 c. c. of N/4 sulfuric acid to just discharge the pink, then added 4 c. c. more, or 11.7 c. c. in total. After boiling it required 5.3 c. c. to bring back a slight pink, the total alkalinity would be 11.7 c. c. - 5.3 c. c. = 6.4 c. c., or 0.64% total alkali in the lye in terms of caustic soda. If there were 40,000 pounds of lye to be treated then we should have to neutralize:
40,000 × .0064 = 256 lbs. alkali. Since sulfate of alumina neutralizes one-third of its weight in caustic, and there are say 9 lbs. of this added per thousand pounds of lye we would add
40,000 × 9 = 360 lbs. of sulfate of alumina. This would neutralize 360 × 1/3 = 120 lbs of alkali. There are then 256 - 120 = 136 lbs. of alkali still to be neutralized. If 60° B. sulfuric acid is used it requires about 1.54 lbs. of acid to one pound of caustic. Therefore to neutralize the caustic soda remaining it requires:
136 × 1.54 = 209.44 lbs. 60° B. sulfuric acid to neutralize the total alkali in the 40,000 pounds of spent lye.
The acid is added and the lye well stirred, after which another sample is taken and again titrated as before. From this titration the amount of acid to be added is again calculated and more acid is added if necessary. Should too much acid have been added, caustic soda solution is added until the lye is between exactly neutral and 0.02% alkaline. The filtered lyes at this stage have a slight yellowish cast.
To be sure that the lyes are treated correctly the precipitation test is advisable. To carry this out filter about 50 c. c. of the treated lye and divide into two portions in a test tube. To one portion add ammonia drop by drop. If a cloudiness develops upon shaking, more alkali is added to the lye in the tank. To the other portion add a few drops of 1 to 5 sulfuric acid and shake the test tube. If a precipitate develops or the solution clouds, more acid is needed. When the lyes are treated right no cloudiness should develop either upon adding ammonia or the dilute acid.
The properly treated lye is then run through the filter press while slightly warm and the filtered lye is fed to the evaporator from the filtered lye tank. The lye coming from the filter press should be clear and have a slight yellowish cast. As the pressure increases it is necessary to clean the press or some of the press cake will pass through the cloths. Where sodium silicate is used as a filler, the silicate scrap should never be returned to the soap kettle until the glycerine lyes have been withdrawn. This practice of some soapmakers is to be strongly censured, as it causes decided difficulty in filtering the lye, since during the treatment of the lye, free silicic acid in colloidal form is produced by the decomposition of the sodium silicate by acid. This often prevents filtering the treated lye even atexcess pressure and at its best retards the filtering.
As to the filter press cake, this may be best thrown away in a small factory. Where, however, the output of glycerine is very large it pays to recover both the fatty acids and alumina in the press cakes.
In some cases, especially when the lyes are very dirty and the total residue in the crude glycerine runs high, for which there is a penalty usually attached, a double filtration of the lye is advisable. This is carried out by first making the lye slightly acid in reaction by the addition of alum and acid, then filtering. This filtered lye is then neutralized to the proper point with caustic, as already described, and passed through the filter press again.
While in the method of treating the lyes as given sulfuric acid is used for neutralizing, some operators prefer to use hydrochloric acid, as this forms sodium chloride or common salt, whereas sulfuric acid forms sodium sulfate, having 3/5 the graining power of salt, which eventually renders the salt useless for graining the soap, as the percentage of sodium sulfate increases in the salt. When the salt contains 25 per cent. sodium sulfate it is advisable to throw it away. Sulfuric acid, however, is considerably cheaper than hydrochloric and this more than compensates the necessity of having to eventually reject the recovered salt. It may here also be mentioned that recovered salt contains 5-7 per cent. glycerine which should be washed out in the evaporator before it is thrown away. The following tables give the approximate theoretical amounts of acids of various strengths required to neutralize one pound of caustic soda:
For 1 pound of caustic soda—
3.25lbs.18° B.hydrochloric(muriatic)acidarerequired.2.92"20° B."""""2.58"22° B."""""
For 1 pound of caustic soda—
1.93lbs.50° B.sulphuricacidarerequired.1.54"60° B.""""1.28"66° B.""""
It is, of course, feasible to neutralize the spent lye without first determining the causticity by titrating a sample and this is often the case. The operator under such conditions first adds the sulfate of alumina, then the acid, using litmus paper as his indicator. Comparatively, this method of treatment is much slower and not as positive, as the amount of acid or alkali to be added is at all times uncertain, for in the foaming of the lyes their action on litmus is misleading.
After the lye has been filtered to the filtered lye tank it is fed to the evaporator, the method of operation of which varies somewhat with different styles or makes. When it first enters the evaporator the lye is about 11°-12° B. After boiling the density will gradually rise to 27° B. and remain at this gravity for some time and during which time most of the salt is dropped out in the salt filter. As the lye concentrates the gravity gradually rises to 28°-30° B., which is half crude glycerine and contains about 60 per cent. glycerine. Some operators carry the evaporation to this point and accumulate a quantity of half crude before going on to crude. After half crude is obtained the temperature on the evaporator increases, the vacuum increases and the pressure on the condensation drain goes up (using the same amount of live steam). As the liquor grows heavier the amount of evaporation is less, and less steam is required necessitating the regulation of the steam pressure on the drum. When a temperature of 210° F. on the evaporator, with 26 or more inches vacuum on the pump is arrived at, the crude stage has been reached and the liquor now contains about 80 per cent. glycerine in which shape it isusually sold by soap manufacturers. A greater concentration requires more intricate apparatus. After settling a day in the crude tank it is drummed.
Crude glycerine (about 80 per cent. glycerol) free from salt is 33° B., or has a specific gravity of 1.3. A sample boiled in an open dish boils at a temperature of 155° C. or over.
The Twitchell process of saponification consists of causing an almost complete cleavage of fats and oils by the use of the Twitchell reagent or saponifier, a sulfo-aromatic compound. This is made by the action of concentrated sulfuric acid upon a solution of oleic acid or stearic acid in an aromatic hydrocarbon. From 0.5 per cent. to 3 per cent. of the reagent is added and saponification takes place from 12-48 hours by heating in a current of live steam. The reaction is usually accelerated by the presence of a few per cent. of free fatty acids as a starter. Recently the Twitchell double reagent has been introduced through which it is claimed that better colored fatty acids are obtained and the glycerine is free from ash.
The advantages claimed for the Twitchell process as outlined by Joslin[12]are as follows:
1. All the glycerine is separated from the stock before entering the kettle, preventing loss of glycerine in the soap and removing glycerine from spent lye.
2. The liquors contain 15-20 per cent. glycerine whereas spent lyes contain but 3-5 per cent. necessitating less evaporation and consequently being more economical in steam, labor and time.
3. No salt is obtained in the liquors which makes the evaporation cheaper and removes the cause of corrosion ofthe evaporator; also saves the glycerine retained by the salt.
4. The glycerine liquors are purer and thus the treatment of the lyes is cheaper and simpler and the evaporation less difficult.
5. The glycerine can readily be evaporated to 90 per cent. crude rather than 80 per cent. crude, thus saving drums, labor in handling and freight. The glycerine furthermore receives a higher rating and price, being known as saponification crude which develops no glycols in refining it.
6. The fatty acids obtained by the Twitchell saponifier may be converted into soap by carbonates, thus saving cost in alkali.
7. There is a decrease in the odor of many strong smelling stocks.
8. The glycerine may be obtained from half boiled and cold made soaps as well as soft (potash) soaps.
While the advantages thus outlined are of decided value in the employment of the Twitchell process, the one great disadvantage is that the fatty acids obtained are rather dark in color and are not satisfactorily employed for the making of a soap where whiteness of color is desired.
To carry out the process the previously heated oil or fat to be saponified is run into a lead lined tank. As greases and tallow often contain impurities a preliminary treatment with sulfuric acid is necessary. For a grease 1.25 per cent. of half water and half 66° B. sulfuric acid is the approximate amount. The undiluted 66° B. acid should never be added directly, as the grease would be charred by this. The grease should be agitated by steam after the required percentage of acid, calculated on the weight of the grease, has been added. The wash lye coming off should be 7°-10° B. on a good clean grease or 15°-22° B. on cotton oil or a poor grease. As has beenstated the grease is heated before the acid is added or the condensation of the steam necessitates the addition of more acid. After having boiled for 1-2 hours the grease is allowed to settle for 12 hours and run off through a swivel pipe.
After the grease has been washed, as just explained, and settled, it is pumped into a covered wooden tank containing an open brass coil. Some of the second lye from a previous run is usually left in this tank and the grease pumped into this. The amount of this lye should be about one-third to one-half the weight of the grease so that there is about 60 per cent. by weight of grease in the tank after 24 hours boiling. Where occasions arise when there is no second lye about 50 per cent. by weight of distilled water to the amount of grease is run into the tank to replace the lye. The saponifier is then added through a glass or granite ware funnel after the contents of the tank have been brought to a boil. If the boiling is to be continued 48 hours, 1 per cent. of saponifier is added. For 24 hours boiling add 1.5 per cent. The boiling is continued for 24-48 hours allowing 18 inches for boiling room or the grease will boil over.
After boiling has continued the required length of time the mass is settled and the glycerine water is drawn off to the treatment tank. Should a permanent emulsion have formed, due to adding too great an amount of saponifier, a little sulfuric acid (0.1 per cent.-0.3 per cent.) will readily break this. During the time this is being done the space between the grease and the cover on the tank is kept filled with steam as contact with the air darkens the fatty acids.
To the grease remaining in the tank distilled water (condensed water from steam coils) to one-half its volume is added and the boiling continued 12-24 hours. The greaseis then settled and the clear grease run off through a swivel pipe. A layer of emulsion usually forms between the clear grease and lye so that it may easily be determined when the grease has all been run off. To prevent discoloration of the fatty acids it is necessary to neutralize the lye with barium carbonate. The amount of this to be added depends upon the percentage of saponifier used. About 1/10 the weight of saponifier is the right amount. The barium carbonate is added through the funnel at the top of the tank mixed with a little water and the lye tested until it is neutral to methyl orange indicator. When the fatty acids are thus treated they will not darken upon exposure to the air when run off.
Fresh grease is now pumped into the lye or water remaining in the tank and the process repeated.
The glycerine water or first lye is run to the treatment tank, the fat skimmed off and neutralized with lime until it shows pink with phenolphthalein, after having been thoroughly boiled with steam. About 0.25 per cent. lime is the proper amount to add. The mixture is then allowed to settle and the supernatant mixture drawn off and run to the glycerine evaporator feed tank. The lime which holds considerable glycerine is filtered and the liquor added to the other. The evaporation is carried out in two stages. The glycerine water is first evaporated to about 60 per cent. glycerol, then dropped into a settling tank to settle out the calcium sulfate. The clear liquor is then evaporated to crude (about 90 per cent. glycerine) and the sediment filtered and also evaporated to crude.
As to the amount of saponifier to use on various stocks, this is best determined by experiment as to how high a percentage gives dark colored fatty acids. For good stock such as clean tallow, prime cottonseed oil, corn oil, cocoanut oil and stock of this kind 0.75 per cent. saponifieris sufficient. For poorer grades of tallow, house grease, poor cottonseed oil, etc., 1 per cent. saponifier is required and for poorer grade greases higher percentages. The percentage of fatty acids developed varies in various stocks, and also varies with the care that the operation is carried out, but is usually between 85 per cent.-95 per cent. Due to the water taken up in the saponification process there is a yield of about 103 pounds of fatty acids and glycerine for 100 pounds of fat.
The Twitchell reagent has undoubtedly caused a decided advance in the saponification of fats and oils and has been of great value to the soap manufacturer, because with a small expenditure it is possible to compete with the much more expensive equipment necessary for autoclave saponification. The drawback, however, has been that the reagent imparted a dark color to the fatty acids obtained, due to decomposition products forming when the reagent is made, and hence is not suitable for use in soaps where whiteness of color is desired.
There have recently been two new reagents introduced which act as catalyzers in splitting fats, just as the Twitchell reagent acts, but the fatty acids produced by the cleavage are of good color. The saponification, furthermore, takes place more rapidly. These are the Pfeilring reagent and Kontact reagent.
The Pfeilring reagent is very similar to the Twitchell reagent, being made from hydrogenated castor oil and naphthalene by sulfonation with concentrated sulfuric acid. It is manufactured in Germany and is being extensively used in that country with good success.
The Kontact or Petroff reagent, discovered by Petroff in Russia, is made from sulfonated mineral oils. Until very recently it has only been manufactured in Europe, but now that it has been found possible to obtain the proper mineralconstituent from American petroleum, it is being manufactured in this country, and it is very probable that it will replace the Twitchell reagent because of the advantages derived by using it, as compared to the old Twitchell reagent.
The method and equipment necessary for employing either the Pfeilring or Kontact reagents is exactly the same as in using the Twitchell process.
While the introduction of the Twitchell process to a great extent replaced the autoclave method of saponification for obtaining fatty acids for soap making, the autoclave method is also used. This process consists in heating the previously purified fat or oil in the presence of lime and water, or water only, for several hours, which causes a splitting of the glycerides into fatty acids and glycerine. The advantage of autoclave saponification over the Twitchell process is that a greater cleavage of the fats and oils results in less time and at a slightly less expense. The glycerine thus obtained is also purer and of better color than that obtained by Twitchelling the fats.
An autoclave or digestor consists of a strongly constructed, closed cylindrical tank, usually made of copper, and is so built as to resist internal pressure. The digestor is usually 3 to 5 feet in diameter and from 18 to 25 feet high. It may be set up horizontally or vertically and is covered with an asbestos jacket to retain the heat. Various inlets and outlets for the fats, steam, etc., as well as a pressure gauge and safety valve are also a necessary part of the equipment.
The saponification in an autoclave is usually carried out by introducing the fats into the autoclave with a percentageof lime, magnesia or zinc oxide, together with water. If the fats contain any great amount of impurities, it is first necessary to purify them either by a treatment with weak sulfuric acid, as described under the Twitchell process, or by boiling them up with brine and settling out the impurities from the hot fat.
To charge the autoclave a partial vacuum is created therein by condensation of steam just before running the purified oil in from an elevated tank. The required quantity of unslaked lime, 2 to 4 per cent. of the weight of the fat, is run in with the molten fat, together with 30 per cent. to 50 per cent. of water. While 8.7 per cent. lime is theoretically required, practice has shown that 2 per cent. to 4 per cent. is sufficient. The digestor, having been charged and adjusted, steam is turned on and a pressure of 8 to 10 atmospheres maintained thereon for a period of six to ten hours. Samples of the fat are taken at various intervals and the percentage of free fatty acids determined. When the saponification is completed the contents of the autoclave are removed, usually by blowing out the digestor into a wooden settling tank, or by first running off the glycerine water and then blowing out the lime, soap and fatty acids. The mass discharged from the digestor separates into two layers, the upper consisting of a mixture of lime soap or "rock" and fatty acids, and the lower layer contains the glycerine or "sweet" water. The glycerine water is first run off through a clearing tank or oil separator, if this has not been done directly from the autoclave, and the mass remaining washed once or twice more with water to remove any glycerine still retained by the lime soap. The calculated amount of sulfuric acid to decompose the lime "rock" is then added, and the mass agitated until the fatty acids contained therein are entirely set free. Another small wash is then given and the washwater added to the glycerine water already run off. The glycerine water is neutralized with lime, filtered and concentrated as in the Twitchell process.
Due to the difficulties of working the autoclave saponification with lime, decomposing the large amount of lime soap obtained and dealing with much gypsum formed thereby which collects as a sediment and necessitates cleaning the tanks, other substances are used to replace lime. Magnesia, about 2 per cent. of the weight of the fat, is used and gives better results than lime. One-half to 1 per cent. of zinc oxide of the weight of the fat is even better adapted and is now being extensively employed for this purpose. In using zinc oxide it is possible to recover the zinc salts and use them over again in the digestor, which makes the process as cheap to work as with lime, with far more satisfactory results.
While it is possible to saponify fats and oils in an autoclave with the addition of acid to the fat, unless a specially-constructed digestor is built, the action of the acid on the metal from which the autoclave is constructed prohibits its use. The acid saponification is therefore carried out by another method.
The method of procedure for acid saponification, therefore, is to first purify the fats with dilute acid as already described. The purified, hot or warm, dry fat is then run to a specially-built acidifier or a lead-lined tank and from 4 per cent. to 6 per cent. of concentrated sulfuric acid added to the fat, depending upon its character, the degree of saponification required, temperature and time of saponification. A temperature of 110 degrees C. is maintained and the mass mixed from four to six hours. The tank is then allowed to settle out the tar formed during the saponification,and the fatty acids run off to another tank and boiled up about three times with one-third the amount of water. The water thus obtained contains the glycerine, and after neutralization is concentrated.
While lime or a similar substance is ordinarily used to aid in splitting fats in an autoclave, the old water process is still used. This is a convenient, though slower and more dangerous method, of producing the hydrolysis of the glyceride, as well as the simplest in that fatty acids and glycerine in a water solution are obtained. The method consists in merely charging the autoclave with fats and adding about 30 per cent. to 40 per cent. of their weight of water, depending on the amount of free fatty acid and subjecting the charge to a pressure of 150 to 300 pounds, until the splitting has taken place. This is a much higher pressure than when lime is used and therefore a very strong autoclave is required. Since fatty acids and pure glycerine water are obtained no subsequent treatment of the finished charge is necessary except separating the glycerine water and giving the fatty acids a wash with water to remove all the glycerine from them.
In discussing the causes of rancidity of oils and fats it was pointed out that the initial splitting of these is due to enzymes, organized ferments. In the seeds of the castor oil plant, especially in the protoplasm of the seed, the enzyme which has the property of causing hydrolysis of the glycerides is found. The ferment from the seeds of the castor oil plant is now extracted and used upon a commercial basis for splitting fats.
The equipment necessary to carry out this method ofsaponification is a round, iron, lead-lined tank with a conical bottom, preferably about twice as long as it is wide. Open and closed steam coils are also necessary in the tank.
The oils are first heated and run into this tank. The right temperature to heat these to is about 1 degree to 2 degrees above their solidification point. For liquid oils 23 degrees C. is the proper heat as under 20 degrees C. the cleavage takes place slowly. Fats titering 44 degrees C. or above must be brought down in titer by mixing with them oils of a lower titer as the ferment or enzyme is killed at about 45 degrees C. and thus loses its power of splitting. It is also necessary to have the fat in the liquid state or the ferment does not act. The proper temperature must be maintained with dry steam.
It is, of course, necessary to add water, which may be any kind desired, condensed, water from steam coils, well, city, etc. From 30 per cent. to 40 per cent., on the average 35 per cent. of water is added, as the amount necessary is regulated so as to not dilute the glycerine water unnecessarily. To increase the hydrolysis a catalyzer, some neutral salt, usually manganese sulfate is added in the proportion of 0.15 per cent. appears to vary directly as the saponification number of the fat or oil. The approximate percentages of fermentive substance to be added to various oils and fats follow: