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.
733
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
73-1
T H E J O U R N A L O F i.'iDS7STRIA L A N D E S G Z ~ V E E R I N GC H E M I S T R Y
found difficult t o make this vacuum chamber absolutely tight so a petcock was soldered on and frequently t h e vacuum was attained again b y means of t h e pump. This trough saved considerable cost in CO: and alcohol. preventing t h e former from being melted b y the heat in t h e room t o a considerable extent and 'enabling one t o collect all of t h e alcohol after t h e determination b y allowing t h e COS t o vaporize off. 111-The P?OS, which soon ceased t o be active in respect t o water vapor, necessitated cutting t h e tube leading from this bulb and connecting the two pieces by means of rubber tubing. I n this way fresh P 2 0 s a n d glass wool could be easily inserted. Several other points of operation may be of interest. A n ordinary Gerylr vacuum p u m p , single stroke, was used and found effective. I t might be well t o state t h e well-knovn method of making C02-snow economically. A cylinder containing j o lbs. C 0 2 a t high pressure is inverted t o an angle of about 4j O and the snow which issues forth when t h e valve is opened quite Ti-ide is caught in a canvas bag about 1 2 X 18 in. in size. The snow keeps vel1 in a cardboard box, I t was found t h a t more constant results were obtained by bringing the bulb up t o room temperature after immersion in the freezing mixture. by means of inserting it in water for I O min. I. more careful control of the temperature can thus be maintained. Although this article is intended only t o give certain suggestions for t h e operation of Burrell and Robertson's apparatus it might be of interest t o show some results obtained with it using coke-oven gas, t o supplement the results obtained a t t h e Bureau of Mines on Pittsburgh illuminating gas.
Yol. 8,No. 8
series) there appears t o be little ltnown and with reason as its composition varies in different plants. With an actual recovery during the period of one month of 2 . 2 0 gals. per net ton of coal carbonized of benzol toluol solvent naphtha, t h e average of many results determined b y this apparatus indicated an amount equal t o 1.70 gals. per ton coal or 2 2 . 7 per cent lorn. The recovered hydrocarbons in practice consisted in t h e following:
+
+
HYDROCARBON: 90Y0 Benzol Per cent recovered..
.,.,
67.5
Crude Toluol 29.3
Solvent A-aphtha 13.2
This would seem t o indicate t h a t all of the benzol, part of the toluol and little if a n y of t h e solvent naphtha C.: but was condensed a t the temperature of -78" this is merely a suggestion as it has not been as yet thoroughly investigated. In conclusion i t might be added t h a t this method is more difficult of operation t h a n it appears. The apparatus is delicate and t h e conditions as stated above must be rigidly adhered t o in order to obtain consistent checks. As a method for determining benzol scrubber efficiency i t is of some value; as a method of absolute determination of benzol, toluol and solrent naphtha it is of doubtful value, giving results apparently 24 per cent lower t h a n those obtained in actual practice. Furthermore, the operation of the method requires a man skilled in handling such apparatus. LABORATORY OF
& C O A L PRODCCTS CHATTANOOGA, TENXESSBE
CHATTANOOGA G A S
COMPANY
AN AUTOMATIC PIPETTE] By XLEXAXDERLOWY
Received March 28, 1916 Gas d (dup!icates) Bar. pressure, m m . , , . , . . . , . . 742 . 0 742.0 Partial press. benzol vapors.. . . 5,4 5.2 Per cent benzol in gas.. . . . . , . , 0,729 0.702
Gas B (duplicates) 741.0 541.0 1.8 1.9 0.243 0.256
These are typical determinations made b y this machine. Benzol scrubber efficiency does not call for absolute benzol determinations, comparative results before a n d after scrubber being sufficient. Therefore it is not necessary t o have t h e manometer. as carefully leveled as otherwise. Efficiency of scrubbers with t h e above results averaged would be determined zhus:
The extreme results on the above tests would indicate 66.7 and 6 3 . 7 per cent efficiencies, which is as good as can be expected with this apparatus. The resulL using this method as a determination of absolute benzol, toluol and solvent naphtha is somewhat lower t h a n t h a t obtained b y absorption methods and averaged 2 4 per cent less t h a n the amount obtained in actual practice. Benzol it is kcon-n has a sufficiently low vapor pressure at --78" C. t o assert t h a t it is completely condensed; about toluol there appears t o be some doubt, and about solvenx naphtha < amixture of xylol and higher homologues of the benzene
Fig. I shows the entire pipette with t h e modified stopcock adaptable t o any given volume. Fig. z shows the position of the stopcock while t h e liquid is being drawn up. Line A B is the mark of graduation. H shows the chamber below stopcock and G t h e chamber above the stopcock. F is a cylindrical bore through the stopcock connecting chambers I; and H during the process of suction. E is a cylindrical bore ending back of F a t an angle of 9 0 ' . of which C is a continuation and ends a t a slight elevation a t D. Fig. 3 shon-s t h e position of stopcock after it has been turned clocltrvise 90' t o t h a t shown in Fig. z. D shows place closed by thumb. In this position channel C is connected with chamber H through opening E . I n this position channel G is shut off from channel H . TT'ith suction applied a t end of chamber G (Fig. 2 ) . the !iquid is drawn u p through chamber H until it just passes t h e graduated mark A B . The t h u m b is then placed on D so as t o close opening D air--tight.. The stop-cock is then rotated clockwise through 90' thus bringing opening E (the continuation of tube C and D ) t o line of graduation A B and directly in contact with the upper opening of chamber ZI. The t h u m b is then released. -air pressure now forces the exact 1
Patent applied for
