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T H E J O U R N A L O F I j V D L ’ S T R I A L A N D EdVGISEERI;VG C H E M I S T R Y
Vol. 8 , No. 8
LABORATORY AND PLANT COMMENTS ON THE KREBITZ PROCESS OF SOAPMAKING AND GLYCEROL RECOVERY’
t o 1 2 hrs., it has t h e appearance of a solid porous mass which is still sufficiently warm and soft t o allow digging By G. A . WRISLEY out t h e lime soap. This lime soap is dropped through Received M a y 5 , 19 16 a trap door in the bottom of t h e t a n k into a hopper T h e process of soapmaking by boiling fats and oils and then t o the mill where it is ground t o the size of (glycerides) with caustic soda is, in general, considered fine corn meal. the most practical process since it yields soaps of uniWith the lime and water there will result between formly good quality, color and hardness, and a t the I j:ooo and 16,000 lbs. of lime soap from ~ 0 , 0 0 0lbs. same time a good amount of glycerol m a y be recovered of f a t and oil. The finely ground soap is carried on b y comparatively simple means. The yield of glycerol a conveyor and allowed t o fall loosely into a circular, from the soap lye runs from 60 t o 80 per cent of t h e hopper-shaped tower. a capacity of about 2 j,ooo-tothl amount formed b y t h e saponification of t h e fats 30,000 lbs. being necessary. Four washes, about 4 0 , 0 0 0 and oils. The loss depends upon t h e few or many lbs. of water, are required t o leach out t h e glycerol washes t h a t t h e soap receives. However. it seems from such a batch. The first wash d a t e r contains t h a t no matter how careful one is t o make t h e washes I O t o 1 2 per cent of glycerol, and is sent t o t h e glycerin and changes on the soap, there is always some glycerol, works. The second. third, and fourth waters are I I ’ ~ t o I per cent, left in t h e soap. I t has also been p u t on a fresh batch, only the last wash being made demonstrated t h a t in evaporating down waste lyes Kith fresh water. I n this way, there is no cause for and handling so much salt which cannot be perfectly evaporating glycerin water contsining less t h a n I O dried and freed from glycerol, t h a t there is recovered per cent of glycerol. When t h e plant is working satisbut about 90 per cent of t h e glycerol t h a t is in the soap factorily the water evaporated averages I j per cent of lye. Hence even after t h e glycerol is in t h e soap glycerol. lye, there is a loss in its recovery. After the glycerol has been obtained, t h e lime soap With the continually advancing price of fats, oils, is carried by a conveyor and introduced slowly into and other raw materials, it is becoming more neces- t h e soap kettle containing a boiling solution of soda sary for t h e soap manufacturer t o obtain a large glycerol ash. After the lime has been replaced by t h e soda, yield; in fact it is essential t h a t he should recover all a stage which can be noticed b y the nonappearance the glycerol liberated by t h e saponification. Then, of small lumps on t h e paddle, a small amount of caustic too, the grade of fats and oils obtainable for soapmaking soda is added, and shortly after the soap is salted out. is lower, because of increased utilization of the better The contents of the kettle are allowed t o rest, when grades for edible purposes, so t h a t t h e soap manufac- CaCOa settles out a t t h e bottom as a heavy sludge, turer must strive t o produce a good quality soap from and the soap gathers on top, a salt solution containing a poorer grade of material. an excess of alkali forming a n intermediate layer. The Krebitz process, here discussed, offers t h e possiAlthough Krebitz claims t h a t the lime sludge will bility of recovering the theoretical yield of glycerol, settle out and occlude or entangle but 4 t o 7 per cent while a t the same time t h e caustic lime exercises some of soap, it has been impossible, so far, t o prevent the purifying action, especially in the case of a low-grade occlusion of less t h a n 9 t o 1 2 per cent of soap. Of material. T h e Allen B. Wrisley Company, of Chicago, course, this soap must be recovered. At first this is t h e first in this country t o work this process on a constituted quite a serious problem, because the lime large scale with good results. sludge could not be filtered without leaving 2 t o 3 The Krebitz process is based on two simple chemical per cent of soap in the lime cake. Atternpts t o wash reactions: out the soap b y a series of washings and filtration were unsuccessful, because so much soap was present as t o ( I ) 2C3Hb(GgH3602)3 3Ca(OH)2 = 3Ca(ClsH3502)2 zC3H5(OH13 fill up the pores of the filter cloth. making filtration ( 2 ) Ca(ClgH3bOz)g Na2C03 = zC18H3602Na CaC03 slow and unsatisfactory. Attempts t o boil u p the I n practice a batch of 10,000lbs. of fat and oil may be sludge with a little mater and resalt out the soap were conveniently handled, I n a rather shallow t a n k unsuccessful. because on salting out, the lime sludge settled t o the bottom carrying most of the soap with 1 2 0 0 t o 1400 lbs. of lime are slaked with 3 ; o o t o 4500 lbs. of water, and the mass is heated, if necessary, t o it again. By continued experiment, it was found t h a t about 70’ C. Then t h e fat and oil are run in n-hile the addition of enough water with heat and vigorous the entire mass is stirred vigorously. With live steam agitation caused t h e soap t o go into solution, and on the mass is heated up slowly t o 9 0 - 9 2 ~ C , . and taking allowing the mass t o settle the lime sludge, occluding about one-haf hour t o gain t h a t temperature, v i t h b u t 3 t o j per cent of soap, went t o t h e bottom, the constant stirring, a thorough emulsion is obtained. soap rose t o the top, and could be pumped off and SO The vessel is then covered t o prevent loss of heat. recovered. The lime sludge could t,hen be easily Two or three hours after corering the mass is likely t o filtered, and only I t o I . j per cent of soap is lost in the boil and swell considerably. After it has stood 8 lime cake. This loss, though small, may perhaps still be reduced. Presented before t h e 52nd Meeting of t h e American Chemical Society, The quality and color of the finished soap obtained Urbana-Champaign, April 18-2 I , 1916.
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Aug., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
b y the Krebitz process compares favorably with t h e soap produced by any other process. The amount of lime found in t h e finished soap depends on t h e number of washes or changes made in t h e kettle. Usually there was never less than' 0 . 2 per cent of lime and it may r u n as high as 0.5 t o 0.7 per cent lime. The process, however, claims t h a t only a few thousandths of one per cent should remain in t h e finished soap. At the present time a yield of about 95 per cent glycerol is being obtained b y this process. This, compared t o t h e yield of 60 t o 80 per cent obtained b y the recovery of glycerol from t h e soap lye in t h e case of soapmaking b y boiling the glycerides withcauctic soda, would give t h e Krebitz process a decided advantage. Moreover, we must recall t h a t soap lyes contain a t best b u t j t o 8 per cent glycerol, depending on t h e way in which t h e changes of soap lye are worked u p , and at t h e same time hold in solution much common salt, some caustic soda, soda ash, and organic impurities; whereas t h e Krebitz waters contain 1 2 t o 15 per cent glycerol and are comparatively free from impurities, thereby making purification more simple and giving less water t o handle and evaporate. Soda ash is cheaper t h a n caustic soda, and since soda ash is used in place of caustic soda another material saving is made. Without doubt. t h e Krebitz process would be preferred a t this time, because of the high price of glycerol, b u t were glycerol I j t o 2 0 cents per lb. instead of jj t o 60 cents per lb. there might be a shadow of doubt as t o whether it would be preferred t o the soap-lye process taking into consideration t h e manifold operations prior t o t h e soapmaking proper, and t h e work necessary t o recover all the entangled soap from t h e lime sludge. 5872 KINA AVENUE
NORWOOD P A R K , CHICAGO
THE DETERMINATION OF BENZOL IN COKE-OVEN GAS BY BURRELL'S VAPOR APPARATUS By LOUISC WHITON Received April 18, 1916
T h e method for determining benzol and its homologues in gas as proposed b y t h e Laboratory of Gas Investigations, U.S. Bureau of Mines,' has been tried in this laboratory with a view t o determining the efficiency of benzol scrubbers utilizing coke-oven gas. The extraction of benzol, toluol and solvent naphtha has become a t once such a profitable and important addition t o a by-product coke. oven's equipment t h a t a rapid method of determination of scrubber efficiency seems imperative. The customary method of absorption of t h e vapors requires from 1 2 t o 24 hrs. time and in this period many dollars worth of benzol and toluol may be lost, due t o faulty operation of the scrubbers. Furthermore, especially when starting u p a plant, conditions m a y have automatically been improved, without the operator's knowledge, toward t h e end of t h e test, which would mean t h a t a change in operation as indicated b y t h e test would perhaps be a disadvantage rather t h a n otherwise. The method as described in THIS J O U R X X L did THISJOURNAL, I
(1915). 669.
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not give t h e details of operation, which are extremely essential if accuracy is t o be expected when determining such small traces of benzol vapors as are contained in debenzolized coke-oven gas. Briefly, t h e apparatus as described b y Burrell and Robertson, of t h e Bureau of Mines, consists essentially of a bulb about 6 in. long with a slight constriction in t h e center. The upper portion of the bulb contains glass wool mixed with phosphorus pentoxide t o extract all t h e moisture from t h e gas. Connected with this bulb is a mercury manometer a n d an entry and exit t u b e with a ground glass 3-way cock. The air is first evacuated b y means of a vacuum pump, t h e gas t o be tested is sucked in and t h e 3-way cock turned when t h e gas is under barometric pressure. The entire bulb is then placed in liquid air or in a mixture of COz-snow mixed t o a consistency of slush with alcohol or acetone. I t is allowed t o remain there I O min., t h e temperature being approximately -78' C. The benzol freezes out a t this temperature and t h e COz, 02,CO, HB,CH,, Nz, and CzH4,which have a high vapor pressure a t this temperature, are evacuated b y means of the vacuum pump, t h e cock turned t o seal t h e system and t h e apparatus brought u p t o room temperature. The partial pressure of t h e benzol vapor is registered on t h e manometer and this result divided b y t h e barometric pressure times I O O indicates t h e per cent benzol. There were several difficulties which had t o be overcome in order t o t e r m t h e above a practical method for commercial work. I-The readings on t h e manometer ranged from I O mm. for benzolized gas t o I mm. for debenzolized gas. With a n ordinary manometer it is difficult t o read much closer t h a n I mm., which was beyond an allowable error. a-In a vertical position it was impossible t o surround t h e apparatus with t h e COS-alcohol slush with economy in t h e use of t h e material which withal, as a commercial proposition, is expensive. 3-The Pz05in t h e glass wool soon ceased t o be a good dehydrator and with t h e suggested construction of t h e apparatus it was impossible t o charge it again with P20s. These difficulties were overcome t o a certain extent in t h e following manner: I-The mercury manometer was connected by means of a short, heavy piece of rubber tubing and was placed a t a I O t o I slant, i. e., I O on the hypothenuse t o I of altitude. This was placed on a firm gauge stand and leveled with spirit levels both ways. T h e gauge then gave a reading ten times t h e actual pressure. Thus it was possible t o determine the pressure within 0.1mm. which was sufficiently accurate. 11-The bulb was laid horizontally in a trough with a notch a t t h e end through which t h e stem of t h e apparatus could pass. I n this position i t could be more easily surrounded with carbon dioxide slush without danger of breakage of t h e bulb and with greater economy in respect t o t h e slush. This trough was 8 in. long, 2 ' 1 2 in. deep and 21/2 in. wide, with a hinged cover and double walls w:th the air evacuated. I t was
