INDUSTRIAL A I D EUGINEERISG CHEMISTRY
86
standard plunger and for sufficient total weight to continue experiments as far as the yield point and beyond.
The Gel Factor The importance of a higher expression for gel strength waa first suggested by Sheppard in terms of the torsional elasticity of the gel (9). The dope of the load-versus-penetration characteribtic alone, as indicated by one point on this slope (the Blooiii figure) is not indicatire alone of the gel strength of gelatin. What is indicative of gel strength is the total work nece>saiy before the final break in the jelly occurs. It is proper. therefore, to determine this gel factor in teiiny of the area of the triangle included between the load-versubpenetration curve and the abscissa. This total area O.IK (Figure 6) is then
A
= ‘/z
the breaking load X penetration (gram per cm.)
I n this specific instance the gel factor, J , would equal x 294 X 0.75 = 110.6 (gram per cm.). This result, niultiplied by a numerical constant, C, can be compared with the expression for proof resiliency, as suggested by Sheppard iii terms of the torsional elasticity of a standard jelly cast. The term “gel factor” was suggested by the writer in 1935 in order to avoid confusion with the term “jelly strength” which in comnion use today is assumed to be proportionate to the Bloom number only (6). For industrial control tests as well as for research ~\~Orli, it has been found more accurate to determine the value of
VOL. 10, NO. 2
gelatin in terms of the gel factor. It is entirely possible ttJ have a high gel factor despite a low Bloom number and vice versa. \$‘hat seems to be most characteristic for gelatin ic. the amount of total work necessary before the final break in the jelly occurs, and not the amount of load to produce one haphazardly taken penetration depth. Tests should represent ronditions that are actually of primary importance for the product, and not necessarily certain points that are conI enient for a limited number of producers. It is, of course, easily possible to attach a different plungei Iiead of conical, needle-shaped, hall, 01 otliei desirable form. In this manner the apparatus lends itself also to penetrometer iiieawrements, such as those deicrihed by T d z , Culpepper, Jloon, and hleyers ( 2 ) ,
Literature Cited DeBeaukelaer, F. L., Powell, J. R., and Rahlmann, E. F., Isi). EXG.CHEM., Anal. Ed., 2, 348 (1930). Liita, J. hl., Culpepper. C. W., Moon, H. H., and Meyers, D. T., Canning A g e , 1 4 , 4 0 4 , 414, 428 (1933) : Canner, 77, 14 (19331. Saxl. I. J., Electronics (January, 1937). Saxl, I. J., Melliand Teztilber., 19, 47-8 (1938). Saxl, I. J., Physics, 7, 62-6 (1936). Saxl, I. J., Te.rtile Research, 8, 5-14 (1937). Sheppard, S. E., “Gelatin in Photography,” p . 217, New York, D. Van Nostrand Co., 1923. Sheppard, S. E., and Elliott, F. A . . J . Optical SOC.4 m . , 9, 181-4 (1924).
Sheppard, S . E., and Sweet,
,S.
d . , IND.ENQ.CHEM.,15, 571
(1923).
Sheppard,
S.E., Sweet, S. P., and Henedict, A . J., J . -47n. f ‘ h e t n .
Soc., 44, 1857 (1922).
Discontinuous Fractional Extraction Apparatus Utilizing Reflux H . E. HERSH, K. A. VARTERESSIGV. R . A . RUSK, AND &I. R . FEUSKE The Pennsylbania State College, State College, Pa.
Solvent-extraction processes are very useful in effecting the separation of complex liquid mixtures by physical means. This is especially true if reflux conditions and countercurrent contacting of the phases are employed. In this way, the sharpness of the separation is better and the segregation of the components more complete. This paper describes a suitable small-scale
F
OR several years this laboratory has devoted some efforts
to the development of the fundamentals of estraction, to the design of efficient estraction equipment, and to the application of these in the field of solvent refining of petroleum products (3,5,10-13). This paper describes a discontinuous fractional extraction apparatus, developed in this laboratory, that is novel in design and satisfactory in operation. It is particularly valuable in the analysis of lubricating oils where a given batch of material must be resolved into its component parts. The results of such analyses will be given in subsequent papers.
Principles of Design Aside from auxiliary equipment for the control of temperatures and of rates of flow, the apparatus consists of three
batrh-extraction proress ulilizing reflux for conditions where the solvent is either lighter or heavier than the liquid undergoing treatment. The apparatus is shown to be reproducible, efficient, and practically selfoperating. It permits the separation of a liquid mixture by solvents into as many fractions as desired. iliain sections: a leaching section, a countercurrent cotitacting section, and a reflux-producing section. The solvent is continuously introduced to the leaching section where the batch of oil to be solvent-fractionated is charged. There, a portion of the oil goes into solution, forming a solvent phase which separates because of density diffpi ence and flows into the contacting section. I n general, the dissolved portion of the oil will contain the constituents of the charge in proportions that are in the order of their solubilities in the solvent and of their amounts in the charge. From the contacting section the solvent phase passes into a still where i t is stripped of part or all the solvent The resulting oil phase is returned to the contacting section where it flows countercurrent to the solvent phase; in this section the oil and solvent phases interact, with the result that the solvent phase becomes I
FEBRUARY 15. 1938
ANALYTICAL EDITIOS
richer while the oil phase becomes poorer in the more soluble constituents. The oil phase returns to the leaching section and mixes with the remainder of the charge ready for further leaching. The solvent phase proceeds to the still, is stripped of solvent, and the resulting oil phase is returned as reflux. The repetition of this operation concentrates the more soluble constituents of the charge in the reflux-producing section. This concentrate is then removed as product and the operation is repeated on the remainder of the charge, thus dividing it into as many portions as desired.
TABLEI. COMPARIBON OF BATCHREFLUXEXTRACTIOSS TO DETERMINE EFFECT OF AMOUNTOF CHARQE ON SHARPKESS OF SEPAR.4TION
[Temperature of extraction = 77' F. (2.5' C.). liters per hour.] 1-Gallon Chargei 4 Liters) Over-all RaffinProperty of Oil oil Extract ate Weight % of charge 100 15.2 82.6 Viscosity a t 210' F. Centistokes 5.83 7.49 5.56
--
Solvent (acetone) rate
=
6.0
-5-Gallon
charge--^. (20 Litern) Over-all Raffiiioil Extract ate 100 5.92
81.1
17.2 9.35
5.t;l
Savhnlt . ~ ~. " ~
seconds 44.5 Viscosity a t inno -R . Centistokes 39.44 Saybolt 183.7 Eeconds Kinematic viscosity index 98 Gravity,c.l.P.I.30.2 Specific gravity a t 60' F. 0.875 Viscosity-gravity constant 0.820 -
_
49.7
43.7
44.8
56.1
40.31
152.0
43 8
I
84.35 388 20 21.4
34.68 161.9
187.7
110 32.1
99 30.2
34 29 100, e
702 -27 17.6
113
3:j.n
0.925
0.86;
0.876
0.949
0 800
0.875
0.809
0.820
0.900
0 804
87
vent phaqe will still contain appieciable amounts of the less soluble constituents. It is therefore desirable to separate the latter and to replace them with the more soluble constituents. This is the function of the countercurrent contacting section. I n this section the oil phase formed in the refluxproducing section and the solvent phase formed in the leaching section flow countercurrently. I n a properly designed column, a t each cross section the oil phase comes in contact with a solvent phase that is poorer in the more qoluble constituents than required by the equilibrium relations. This induces interaction between the phases, with the result that the ratio of the more soluble constituents to that of tlie less soluble constituents increases in the solvent phaqe and decreases in the oil phase. Other factors being the same, the extent of interaction will depend on the interfacial area between the two phases. I n order to increase this area as much as practicable, various means may be employed. Of these, the use of spray nozzle or of packing to divide the refluxed oil into small globules is the more comnion. I n batch extraction, where both the viscosity and the amount of refluxed oil vary with time, tlieuse of packing is simpler. It has an additional advantage over the use of spray nozzles in that if there is any tendency for the oil globules to coalesce, the packing tends to divide them again. The advantages of using a packing material in the extraction tower, also when the oil formed the continuous phase, were shoivn by Rushton (9). Table I1 presents data showing the effect of various packings on the quality of approximately 15 per cent extract from a given oil. Of the packings inveatigated, 0.25-inch carbon rings gave the better result., yielding an extract with a viscosity of 407 Saybolt seconds at 100" F. (37.8' C.) and a viscosityindexof 19, while S o . 15 iron jack-chain or a 3.00 RIonarch spray nozzle gave less efficient iesults, yielding an extract with a viscody of around 340 Saybolt second8 at 100" F. and a viscosity index of 33. The differences, however, are small, and the advantage to be gained by using one packing instead of another is slight as compared with the effect of other factors, such as the amount of charge (see Table I). It should be noted that the per cent of the charge held up in the contacting section may be different for different packings, and therefore in batch runs the effect of holdup will be combined with those of the other characteristics of the packing, such as shape, size, etc. Semicontinuous rtiw where, after steady conditions are established, the extract and raffinate are remored and replaced with aiiother batch of the same quality charge without removing the holdup in the system, and this process is repeated until the successive extracts and raffinates do not change in coniposition and amount ant1 add up to thoqe of the charge, may be used instead. Experiments using a 1-gallon (4-liter) charge 4iow that tliia condition is approached after three successive batvh runs.. Table I11 giyes data ohtaine(l in this manner. I t is evident that, although the
LEACHIXG SECTION.The purpose of this section is to bring the solvent into intimate contact with the entire charge in order to produce continuously differential amounts of solvent phase in substantial equilibrium x i t h the oil phase. Thi. may be approached in practice by forcing the solvent into tlie charge of oil through spray nozzles that atomize the solvent, and by otherwise keeping the charge reasonably well agitated. I n addition to providing intimate solvent-oil contact and proper mixing, the leaching section for batch operation mubt be large enough so that the holdup of oil in the column may be small compared with the charge. Keeping other Variables constant, the effect of the amount of charge is shown in Table I. Sharpness of separation increased appreciably when a 5gallon (20-liter) replaced a 1-gallon (4-liter) charge. On the average, 16 per cent separation yielded an extract with a viscosity of 702 Saybolt seconds a t 100" F. (37.8' C.) and a viscosity index of -27 in the case of the 5-gallon charge, as against an extract of 389 Saybolt seconds a t 100" F. and a vivosity index of f 2 0 in the case of the 1-gallon charge. In this and the following tables the original oil had substantially the properties as given in Table 1T'-i. e., i t waq a neutral oil of about 100 viscosity index. I n all this work v i s c o s i t i e s were determined in modified Ostwald viscometers (2, 4) and conversion from TABLE 11. COYPARISOS OF BATCH REFLUXEXTRACTIONS T O DETER31tNE F:FFECT O F TYPEO F P A C K I X G O S SHARPNESS O F SEP.IRATIO?r' kinematic viscosity to Saybolt seconds and calculation of kinematic viscosity acetone. Teniperatule of est:.avtion = 77' F. ~ ' 3 ' C.". Charge = I Kalloil ;4 liters).] [Solvent ___ P a ? k i u g - - - - - indexes were made from experimental None. 3.00 No. 15 relations (6, 8). G r a v i t i e s were de-/,-inch '/r-inch 3/s-inch '/i-inch Monarch iron glass porcelain carbon 'pray jackcarbon termined with hydronieters ( I ) and the Property of 011 I ings rings rings lings nozzle chain viscosity-gravity c o n s t a n t was calcuE x t r a c t , neight % of charge 14.7 14.6 139 1.3.6 15.1 14 7 viscosity a t 210' F.: l a t e d b y t h e m e t h o d of H i l l a n d Centistokes i.G2 i.48 7 3; 7.21 7.16 7.14 Coats ( 7 ) . Saybolt seconds 50.1 49.7 49 3 48.8 48.6 48 6 Viscosity a t 100' F.: C O U N T E R C U R R E N T CONTACTISG SECCentistokes 88 4 84.5 80 8 76 0 74 2 73 3 TION. Even in the ideal case where Saybolt seconds 407 389 373 330 342 339 Kinematic viscosity index 19 '4 30 33 20 34 the solvent d if f e r e n t i a 11y dissolves 22 16 Holdup, weight % of charge 37 e; 15 17 out of the c h a r g e p o r t i o n s of oil in 10.4 ti6 r 4 Solvent rate, liters per hour 9 9 6.5 6 5 e q u il i b r i u n i concentrations, the ao1-
-
~
88
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t'OL. 10, NO. 2
FIGURE 1 packings are in general ratrd as in the batch runs, reversals in rating are also found. These are beliered to be due to the disappearance of the holdup effect and to the difficultv - of getting strictly steady conditions. A point that is significant in connection with the semicontinuous runs is that better separation is obtained when compared with the batch runs, using the same packing and extracting the same percentage from a given oil. Thus, using 0.25-inch carbon ring packing and extracting approximately 15 per cent, the semicontinuous method gave an extract of 584 Saybolt seconds a t 100" F. (37.8" C.) and a viscosity index of - 18, compared with an extract of 407 Saybolt seconds a t 100" F. and a viscosity index of +I9 obtained when using the batch method. Finally, for a giren per cent extract. higher viscosity and lower viscosity index may not always b e i n sharper separation even though the solvent and charging stock used are identical. However, with the part'icular solvent-oil sy&m and
the per cent extraction employed in these experiments, such anassumptioniswell justified. TABLE
Iv.
PROPERTIES O F OIL USED IN P .4CKISG INVESTIG.ITIOS
Gravity, O A . P. I. Specific gravity a t 60' F. Viscosity a t 100' F.: Centistokes Saybolt seconds Viscosity a t 210' F.: Centistokes Saybolt setonds Flash point, F. Fire point, F. Pour point, F. Color Conridson A. S.carbon T. hl. residue, Kinematic viscosity index
30.8 0.872 38 55 179.6 5.80
44.4 425 (218OC.1 490 (254' C.) 2 ,5 ( - 4 0 C.) A
p e r cent
6.01 101
Table IT' gives inspection data on the oil used in all the experiments on inrestigating the effectof packing. REFLUX-PRODUCISG SECTION.Here, the solvent phase leaving the countercurrent contacting section 's stripped TABLE 111. COiVPARISOh' OF SEMICOSTIKLTOTY ITEFLUX EXTR.lCTIoXS TO DETERMINE of its solvent to produce an oil phase. EFFECTOF TYPEOF PACKING OX SH.4RPNESS OF SEPARATION [Solrent = acetone. Teniperature of extraction = 7 7 O F. (23O C,). Charge = 1 pallon ( 4 liters). The is returned to leachS u m b e r of charges = 3.1 ing section while the oil phase flows Packing Sone, 3.00 x , ~1.5. to the c o n t a c t i n g section. Other iron Monarch '/a-inch Vs-inch l/X-inch a/s-inch glass jackOf p r o d u c i n g reflux! such Its carbon carbon porcelain sprayProperty of Oil sings sings rings nozzle rings rhain cooling or adding precipitating agents, Extract, weight % of charge 15.j 15.1 11.3 15.7 15.0 15.0 etc., may be used, if desired, in place Viscosity a t 210' F.: Centistokes 8.64 8.53 8.44 8.25 8.26 8.10 of distillation. Vacuum or p r e s s u r e Saybolt seconds 53.6 53.3 52.9 52.2 52.2 51.7 may be applied to the system to keep Viscosity a t 100' F.: Centistokes 126.7 123.7 118.2 111.6 109.2 106.0 within the desired temperature range, Baybolt seconds 884 571 546 514 503 489 depending on the solvent employed. Kinematic viscosity index - 18 -1: -11 -7 -1 - .> Solvent rate, liters per hour 6.5 ,. 5 6.4 6.5 6.5 Ti6 Varteressian and Fenske ( l a ) have o u t l i n e d t h e factors that must in
-
FEBRV.413\- 15, 1938
ATALYTICAL EDITIOS
89
general be considered for the proper use of reflux. Ordi100" I;. (3T.8" C.) viscosities of tlie extract, raffinate, and narily, when the refluxed oil phase meets the solvent phase holdup were 1136,187.4, and 925 daybolt seconds. respectively. I t is obvious that good separation was ohtained. in the contacting section, two processes take place: (1) the solvent phase dissolves the more soluble constituents of I n order to establish definitely the effect of reflux on the the refluxed oil; (2) the less soluble constituents of the oil in nature of separat'ion, an oil was fractionally extracted :into the solvent phase are precipitated. With lubricating oils, approximately 5 per cent' cuts under itlentical conditions with the constituents of which differ considerably from each other and without the use of reflux. A detailed discussion of the rein solubility, the first of t'he ah0T-e processes may become presults obtained viith swli procedures will be presented later. dominating. Table V, however, is inclucled here, to show the differences in A third process that niay take place, especially with oil the cuts obtained a t various stages of tlie extraction, both mith charges of high aromatic content, is that the refluxed oil phase and without reflux. The procedure described with the entirely dissolves in the solvent phase. The solution thus heading "no reflux" is analogous t o simple distillation, while formed, being different in density from the solvent phase in "reflux" signifies a procedure analogoils to fractional distillation under total reflux, in both capes the soinlilt, acetone, the contacting section, tends to flow countercurrent to it. When it reaches a region in the contacting section where the taking the place of heat. The superiority of separation ~vlien utilizing reflux is strikcontents of the saturated solvent phase are more paraffinic, the two solutions of different densities interact and precipitate ing. For instance, when cut d i; coinpared with cut B, it is out small globules of a paraffinic oil phase. In one inst'ance, obvious that during the first stages of rstrsction reflux has T-ery using a 10-foot (3-meter) glass column, and an oil charge having a viscosity index Of l4 and a 10oo F. (37.8" c.) TABLEV. COMPARISON OF BATCHEXTRACTIOXS, WITH ASD WITHOUT REFLUX,TO viscosity of 468.5 Saybolt seconds, a DETERMINE EFFECTO F REFLUXO S SH.4RPNEsS O F SEPARATION reflux oil phase was first observed in {Temperature of extraction = 770 F. (260 c.). C h a r i e = 5 gallons (20 liters). Solvent (acetone) rate = 5.g liters per hour (0 tu 20% extracted); 10.0 liters per hour (20 t o 100% extracted).] the column at a point 3.5 feet (107 cm.) Cut A , 0 t o 670, Cut B , 40,tu 4870, Cut C, 90 t? l O Q % Over-.ill Approximate Approximate Approximate from the point of i n t r o d u c t i o n of Property of Oil Oil Reflux N o reflux Reflus S o reflux Reflux No reflux reflux. Under such conditions of exViscosity at 210° F.: traction, the 16 per cent extract had a Centistokes 5.93 8.84 7.09 4.78 5.51 8.29 7.33 Saybolt seconds 44.8 54.3 48.4 11 3 43.5 i3.4 49.2 viscosity index of -79 and the 48 per Viscositv ac 100° F.: cent raffinate a viscosity i n d e x of Centistoires 39.86 142.2 64.78 2i.08 35.47 X.48 47.84 Saybolt seconds 299 4 183.6 128.1 165.4 261.0 222.0 656,O 98. The remainder of the charge (36 Kinematic viscosity index --H7 f113 +lo2 101 -. +124 +I23 C 60 Grayity, A . P. I. 30 2 16.0 23.3 32.9 30.9 per cent) m-as held up in the column; 33.8 34.1 Specific gravity a t 60' F. 0.87.51 0.9141 0.9693 0.860i 0.8713 0,8560 0.8548 its viscosity index was -48. The solViscosity-gravity constant 0 820 0 863 0 809 0.817 0.915 0.790 0.790 \-ent used was acetone a t 20" C. The O
INDUSTRIAI~ASD ENGINEERING CHEMISTRY
90
appreciably aided in the separation of the highly viscous components of low viscosity index from those having lower viscosities and higher viscosity indexes, whereas straight extraction has only partially succeeded in doing so. Again, comparing cut B with cut C, it is noticed that during the last stages of extraction: reflux has made possible a better separation of the more viscous from the less viscous of the high viscosity index constituents, than has straight extraction.
-4pparatus and Procedure Figures 1 and 2 present discontinuous fractional extraction equipments using solvelit's lighter and heavier, respectively, than the charging stock. Only the unit in Figure 1, for the lighter solvents, will be discussed in detail because it was the one used in obtaining the results reported here. The design and operat,ion of the unit for heavier solvent,s will then be obvious. ?'lie leaching section consists of a cylindrical steel contairirr 1 foot (30.5 cm.) in diameter and 10 inches (25.4 cm.) high,
with a capacit.y of approximately 5 gallons (20 liters), with provisions for introducing and withdrawing its contents. Tno openings are provided at the loxver end of the cont'ainer where spray nozzles (No. 3, Type F-27, purchased from t'he Monarcli Manufacturing Works, Inc., Philadelphia, Pa.) for introducing the solvent are fitted at such angles to each other as to tend to give the contents of the container a slight rotary or swirling motion. The solvent, before reaching the nozzles, is pumped through a steel coil located inside the leaching section for the purpose of ensuring a temperature substantially the same as that of the oil charge. A pressure gage and a strainer are in3erted in the line. The leaching drum is heated electrically to the desired constant temperature by means of resistance w-ire wound around it and a bimetallic regulator-relay system. A thermometer is inserted directly inside the drum. The countercurrent contacting section consists of a 15-foot (&&meter) length of No. 16 B. & S. gage seamless steel pipe 2 inches (5 cm.) in outside diameter, having a capacity of 2.11 gallons (8.10 liters). Two small lugs, brazed on the inside of the pipe at the bot.tom of the tower hold a ring having several cross wires to support the packing material in the column. In order to maintain the desired temperature in the tower, the latter is jacketed with a seamless steel pipe 3 inches (7.5 cm.) in outside diameter, for circulating wrtter in the annular space. I t will be noticed that provision is made, through proper piping, to introduce the water at the top end of the tower, so that countercurrent cooling is possible for extract'ion using a temperature gradient in t,he conhcting section. Thermometers are inserted at the entrance and exit of water to the jacket.
TABLE\'I.
\rARI.4TION
O F REFRACTIVE INDEX O F WITH TIME
REFLUXO I L
of extraction 77O F. (2.5' C,). Charge gallon (4 liters). olvent (acetone) rate = 5.5 litera per hour. Weight per cent extracted 2.1 kTemperature = 1
=
=
Elapsed Time0
Oil Rate from Still
Hour8
C'c./hoiLr
0: 6 7 1.67 2.67 3.67 4.67
360 456 582 870 925 948
a
Refractive Index of Reflux, n%o
Total Solvent rsed Life78
1.5143 1.5150 1.5199 1.5230 1.5230 1.5231
11.4 16.8 22.2 27.6 33.0 38.4
Measured from time reflux occurred.
TABLE VII. VARIATION OF REFRACTIVE INDEX OF REFLUX OIL WITH OTHERPROPERTIES [Temperature of extraction = 77' F. ( 2 5 " C.). Charge = 1 gallon (4 liter*]. Solvent (acetone) rate = 5.5 liters per hour.] Run Time of Weight Refractive Yiscosity Viscosity No. Run Percent Index, n'$ at looo F. Index Hours Saybolt Sac.
-4 6
1 3 5 8
1.97 2.02
2.10 2.07
1.5151 1.6215 1.5230 1.5226
348 418 476 467
33 11 -1 1
VOL. 10, NO. 2
.4 specially fabricated Pyrex glass top permits detection of entrainment of oil in the upward-flowing solvent phase. It is 1 foot (30.5 cm.) long and 3 inches (7.5 cm.) in diameter except at the bottom for a length of about 3 inches (7.5 cm.), where it, is reduced to a 2-inch (5-cm.) diameter and flanged to the 2-inch tower. The top of the glass pipe is closed with a steel plate fastened with a flange. This plate contains an overflow line leading to the still for stripping the solvent, and a second line for introducing reflux, centered wit,hin the glass pipe, the tip of which extends to within 2 inches (5 cm.) of the bottom of the glass section. The constant-temperature water supplied to the tower jacket, as well as to the solvent and reflux oil inlet jackets, is obtained h y running tap water through a copper coil inserted in a .sater bath. Electric immersion heaters and a mercury regulator-relay system give satisfactory control of temperature. The reflux-producingsection consists of a still made of a %foot (91.5-cm.) length of square Shelby steel tube, 3 inches (7.5 cm.) in outside diameter, jacketed with a 5-inch (12.5-cm.) standard steel pipe, with suitable openings for introducing steam into the annular space. The still is inclined, and an inlet is provided at the upper end and an outlet, for the nonvolatile liquid at the Ion-er end; both inlet and outlet lines have traps to prevent the escape of vapors. The vapor line is a 1.5-inch standard steel pipe, brazed to the 3-inch tube at an angle, and leads directly t,o a condenser which consists merely of a continuation of the vapor line set at a right angle and containing a coil of 0.3125-inch (8mm.) copper tubing through which the cooling water flows. A siphon-counter, placed beneath the discharge end of the condenser, permits measurement of the condensate rate of flow into the solvent reservoir. The oil line from the still leads into a graduated extract reservoir. Both reservoirs are directly connected each to a piston-type Hills-McCanna proportioning pump driven by a Janette 1 ) s h. p., 1750 r. p. m., motor and speed reducer having a 56 to 1 gear ratio. The extract reservoir contains a level-control device (not shown in drawing) which enables t,he pump to adjust it's stroke automatically according to the rate at lyhich the oil floi5-s into the reservoir from the still, so that a constant, predetermined amount of oil is held in the reservoir and reflux is adjusted according to the solubility of the cut'. The unit is very simple to operate. The oil t,o be solventfractionated is charged in the leaching section and the solvent in olvent reservoir. After adjusting water rates and tempera, the solvent pump is started at, the desired rate, and the control in the extract reservoir is set to give the desired amount of extract cut. After the solvent phase reaches the top of the tower, it overflows into the st,ill. The solvent from the still flows to the solvent reservoir, while the oil phase accumulates in the extract reservoir. 4 s this oil phase reaches a predetermined volume (say, 5 per cent of the charge) the oil pump is allowed to send reflux to the top of the tower at a rate equal to the inflow of oil phase to the reservoir. This operation is simply continued until steady condition8 of extract rate and quality are obtained. The time required for the establishment of steady conditions will depend on the rate of throughput, the per cent extracted, the packing employed, the temperature of extraction, and the oil and solvent used. When steady conditions are established, the extract reservoir is emptied and another cut is obtained in a similar manner. This is repeated until a desired percentage of the charge is divided into the desired number of extraction cuts. At the completion of the run the contents of the leaching section and the countercurrent contacting section are pumped to the still through a line in the bottom of the leaching section. Solvent is then recirculated through the apparatus until the last traces of oil have been washed from the packing and lines. The apparatus is finally drained in preparation for another run.
In order to follow the course of extraction and to find the time a t which steady conditions have been established, it is desirable to follow some property of the oil, the measurement of which is simple and does not require a large sample. Refractive index is found satisfactory for this purpose. Table VI presents data on the variation with time of the refractive index of the oil from the still. It is evident that, under the conditions of the experiment somewhere between 2 and 3 hours from the time reflux occurred, steady conditions were established. It is of course to be granted that two samples of a complex solution (such as a lubricating oil cut) that have a single property (such as refractive index) in common may not necessarily be identical in other properties. However, usicg a given oil and a given solvent, and ext'racting out a given percentage, the
FEBRUARY 15, 1938
AN.4LYTICAL EDITION
establishment of any one property of the cut usually defines, within a narrow range, the rest of the properties a t least for practical purposes. The data in Table VII, for instance, show that as the refractive index of the extract becomes constant, so do also its viscosities and viscosity indexes. They represent different runs of different durations, and not only show that there is no need to carry on the run beyond a t most 5 hours, but also that by simply following the refractive index of the reflux oil it is possible to predict the constancy of quality of the extract.
Acknowledgment The authors xish to acknowledge the help of J. A . Pollock in testing the packing materials, and of H. S. Smith in some of the extraction experiments. This work was made possible by funds contributed partly by the Pennsylvania Grade Crude Oil Association, and this assistance is greatly appreciated.
91
Literature Cited Am. Soc. Testing Materials, Designation D287-37, Standards on Petroleuni Products and Lubricants, 1937. .Im. SOC. Testing Materials, Designation D445-37T, Method R , Standards on Petroleum Products and Lubricants, 1937. Cannon, M. R., and Fenske, M. R . , IND. EXQ.CHEM.,28, 1035 (.1936). Cannon, hI. R . , and Fenske, hf. R., Oil Gas J . , 33, No. 47, 52 (1935); Ibid., 34, KO.47, 45 (1936). Hersh, R. E., ,Vat. Petroleum Sews, 28, No. 45, 30 (1936). Hersh, R. E., Fisher, E. K.. and Fenske, M . R., ISD. EXQ. CHEX,27, 1441 (1935). Hill, J. B., and Coats, H. B., Ibid., 20, 641 (1928). hloCluer, IT. B., and Fenske, M. R., Ibid., 24, 1371 (1932). Rushton, J. H., Ibid., 29, 308 (1937). Varteressian, K. A . , Ph.D. dissertation, The Pennsylvania State College, 1935. Varteressian, K. -4.. and Fenskr, 51. R . , IND.ENO. CHEM.,28, 928 11936). Ibid., 28, 1353 (1936). Ibid., 29, 270 (1937). R E C E I V E DOi toher 28, 1937.
Fused Magnesia Crucibles E. P. BARRETT k h W. ~ F. HOLBROOK Blast Furnace Studies Section, JIetallurgical Dirision, Rurcau of 11iiies, 1linneapolis. 3Iinn.
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0 MATTER is of greater importance nor of more con-
cern to the metallurgist and to the operator of a hightemperature furnace than the kind, life, and use of the refractory that forms the melting chamber.
Melting Point The melting point of a refractory material does not tletermine the temperature to which a charge in the crucible may be safely heated. The manner of heating is very iniportant. Kanolt (6) states that magnesium oxide heated under reduced pressure (0.5 to 1.0 em. of mercury) volatilizeconipletely before it melts. When heated a t atmospheric pressure in contact with carbon, magnesium oxide rolatilizes rapidly a t temperatures above 2000" C. If the metal withill the crucible is heated directly by induction in the high-fiequency induction furnace the metal is always hotter than the crucible, whereas if the metal is heated indirectly by conduction of the heat through the wall of the crucible the crucible is always as hot as, if not hotter than, the metal within it Slight amounts of impurities such as bonding materials useti in forming the crucibles may lower the softening point of the crucibles by several hundred degrees below the melting point of the pure refractory material. Roller and Rittenberg (8) found that fused magnesia crucibles fired to approximately 2600" C. in a high-frequency induction furnace sometimes bulged a t the base. They state: This illustrates that there is a region of crucible flow a t high temperatures rather than a sudden melting down."
Reactions of Fused Magnesia with Carbon Swanger and Caldwell (12) suggest that graphite molds Le used in forming the crucibles, since magnesium oxide does not form carbides and the crucibles can be heated to 1800" C. in the molds in which they were formed. Kanolt (6) found that magnesium oxide when heated a t atmospheric pressure in contact with carbon volatilized rapidly a t temperatures above 2000" C. Roller and Rittenberg (8) reported that
dense fuineb were evolved when iiiagiiesium oxide was heated in (*ontact with carbon a t temperatures of ahout 2500" C.
Methods of Making Small Crucibles Processes for the manufacture of magnesia crucibles have been described by Burgess and Aston ( I ) , Cain, Schranim, and Cleaves (Z), Yensen (14),Fergerson (S),and Watts ( I S ) . Mehl (7') states: "In all of these processes the purified magnesium oxide was first shrunk by heating to a temperature near 1600" C., then ground and pressed into a mold under high pressure, and finally heated to a temperature a t which sintering occurs, with consequent roliesioii of the rather coarse particles of magnesium oxide." Nehl mixed a thick sirup of diellac in absolute alculivl with the calcined c. P. magnesia and packed the mixture into a braes mold. The core and then the base were removed, and the crucible was dried for several hours in a brisk current of air. The crucible was then removed from the mold and dried for several hours in an air oven at 100' to 130" C. The dried crucible v a s fired in an electric furnace. Jordan, Patterson, and Phelps (6) found that, commercial fused magnesium oxide was not pure enough for preparing crucibles for w e in melting pure metals. Since the chemical reagent grade of unfused magnesium oxide shrinks a great deal xhen heated to 1600" C. it is necessary to calcine it before wing it to form crucibles. They moistened < 100-mesh calcined oxide nith a 2 per cent solution of MgC12.6H20,tamped the mixture into a graphite mold, and fired in the mold at 1600' to 1800" C. The crucibles were very hard and dense and had an almost porcelainlike body or texture. The apparent specific gravity of such crucibles was ahout 3.5. They found that the addition of about 15 per cent of a mixture of equal parts of 100- and 200mesh purified white zirconium silicate incwased the strength of magnesia crucibles. Zirconium silicate often contain* phosphorus. Schuette (10) tamped
