Read Ebook: Soap-Making Manual A Practical Handbook on the Raw Materials Their Manipulation Analysis and Control in the Modern Soap Plant. by Thomssen Edgar George

Font size: 10 px 15 px 20 px 25 px 30 px 35 px

Background color: BlackWhiteGrayLight GrayDark GrayDim Gray

Text color: BlackWhiteGrayLight GrayDark GrayDim Gray

Apply/Save settings

Ebook has 724 lines and 47174 words, and 15 pages

ulfuric 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:

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is used as a filler, the silicate scrap should never be returned to the soap kettle until the glycerine lyes have been withdrawn.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 at excess 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--

For 1 pound of caustic soda--

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 . 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 is usually sold by soap manufacturers. A greater concentration requires more intricate apparatus. After settling a day in the crude tank it is drummed.

Crude glycerine 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.

TWITCHELL PROCESS.

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 are as follows:

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 been stated 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 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 to one-half its volume is added and the boiling continued 12-24 hours. The grease is 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 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. saponifier is 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 mineral constituent 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.

AUTOCLAVE SAPONIFICATION.

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.

LIME SAPONIFICATION.

The saponification in an autoclave is usually carried out by introducing the fats into the autoclave with a percentage of 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 wash water 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.

ACID SAPONIFICATION.

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.

AQUEOUS SAPONIFICATION.

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.

SPLITTING FATS WITH FERMENTS.

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 of saponification 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:

Cocoanut oil 8 % Palm Kernel oil 8 % Cottonseed oil 6-7 % Linseed oil 4-5 % Tallow oil 8-10%

The oil, water, manganese sulfate and ferment having been placed in the tank in the order named, the mixture is agitated with air for about a quarter of an hour to form an even emulsion, in which state the mass is kept by stirring occasionally with air while the saponification is taking place. A temperature is maintained a degree or two above the titer point of the fat with closed steam which may be aided by covering the tank for a period of 24 to 48 hours. The splitting takes place rapidly at first, then proceeds more slowly. In 24 hours 80 per cent. of the fats are split and in 48 hours 85 per cent. to 90 per cent.

When the cleavage has reached the desired point the mass is heated to 80 degrees-85 degrees C. with live or indirect steam while stirring with air. Then 0.1 per cent.-0.15 per cent of concentrated sulfuric acid diluted with water is added to break the emulsion. When the emulsion is broken the glycerine water is allowed to settle out and drawn off. The glycerine water contains 12 per cent. to 25 per cent. glycerine and contains manganese sulfate, sulfuric acid and albuminous matter. Through neutralization with lime at boiling temperature and filtration the impurities can almost all be removed after which the glycerine water may be fed to the evaporator. Should it be desired to overcome the trouble due to the gypsum formed in the glycerine, the lime treatment may be combined with a previous treatment of the glycerine water with barium hydrate to remove the sulfuric acid, then later oxalic acid to precipitate the lime.

The fatty acids obtained by splitting with ferments are of very good color and adaptable for soap making.

KREBITZ PROCESS.

The Krebitz process which has been used to some extent in Europe is based upon the conversion of the fat or oil into lime soap which is transformed into the soda soap by the addition of sodium carbonate. To carry out the process a convenient batch of, say, 10,000 pounds of fat or oil, is run into a shallow kettle containing 1,200 to 1,400 pounds of lime previously slaked with 3,700 to 4,500 pounds of water. The mass is slowly heated with live steam to almost boiling until an emulsion is obtained. The tank is then covered and allowed to stand about 12 hours. The lime soap thus formed is dropped from the tank into the hopper of a mill, finely ground and conveyed to a leeching tank. The glycerine is washed out and the glycerine water run to a tank for evaporation. The soap is then further washed and these washings are run to other tanks to be used over again to wash a fresh batch of soap. About 150,000 pounds of water will wash the soap made from 10,000 pounds of fat which makes between 15,000 and 16,000 pounds of soap. The first wash contains approximately 10 per cent. glycerine and under ordinary circumstances this only need be evaporated for glycerine recovery.

Share on: WhatsApp @Hash Facebook Tweet