crease in the nonconducting volume of the cellulose fibers by swelling, Application of the Kozeny-Carman equation to permeability measurements indicates a n increase by swelling of about 100% in the volumes of fibers of cotton (9), high tenacity rayon, and dried bleached sulfite pulp, and much larger increases for undried bleached sulfite pulp (4). However, not all of the swollen volume, as found from fluid flow measurements, is unavailable for ion transport (3, 7 ) , so that the values assumed for z are not unreasonable. Further work investigating the variation of z with experimental conditions --e.g., in the presence of swelling agents such as thiourea (10)-is indicated.
is indebted to the Medical Research Council of Ireland for a maintenance grant.
NOMENCLATURE
A A‘ k
K K’ l
v VI
ACKNOWLEDGMENT
V, W,
The authors are grateful t o J. H. J. Poole, R. B. Elliott, and D. C. Pepper for advice and for the loan of equipment; to s. G. Mason for discussion and access to unpublished work; and to IT. Cocker for his constant support and encouragement. Robert Crawford
z 01
e p
cross-sectional area of column of solution (column l ) ,sq. cm. = cross-sectional area of column of solution dispersed solid (column 2), sq. cm. = specific conductance of solution, mho cm.-l = conductance of column 1, mhos = conductance of column 2, mhos = length of columns 1 and 2, cm. = original specific volume (before smelling) of dispersed solid ( = Vp/W,),ml. per gram = original volume of solution in columns 1 and 2, ml. = original volume of solid dispersed i i column 2, ml. = original weight of solid dispersed in column 2. erams = fractional incigase in nonconducting volume of dispersed solid from swelling = absorbance of solution by dispersed solid ( = V,/TY,), ml. per gram = void fraction of column 2 = obstructive factor of dispersed solid ( = K’/K) =
+
LITERATURE CITED
( I ) Balston, J. N., Talbot, B. E., “Guide
to Filter Paper and Ce,l,lulose Powder Chromatography, p. 20, H. Reeve Angel & Co., Ltd., London,
1952. (2) Biefer, G. J., Mason, S. G., Ph.D. thesis, RIcGill University, Liontreal, 1954. (3) Bikerman, J. J., J. Phys. Chem. 46. 724 (1942). ,(4) Carroll, M., Mason, S. G., Can. J . Technol. 30, 321 (1952). (5) Foster, A. B., Chem. and Ind. 1952, 1050. (6) Gallay, W., Tappi 33, 425 (1950). ( 7 ) Goring, D. A. I., Mason, S. G., Can. J. Research 28B, 307 (1950). (8) Kunkel, H. G., Tiselius, A , , J. Gen Physiol. 35, 89 (1951). (9) Mason, S. G , Tappi 33,403 (1950) (10) Ott, E., Spurlin, H. RI., Graflin, - - I
31. W., “Cellulose and Cellulose Derivatives,” Part I, p. 319, Interscience, New York, 1954. (11) Ibzd., p. 401. (12) Ibid., p. 430. (13) H. Reeve Angel & Co., Ltd., private communication. (14) Stamm, A. J., T a p p i 33,436 (1950). (15) Trautman, R., Kunkel, H. G., Ahstracts of Papers, 130th Meeting, ilCS, Atlantic City, S. J., September, 1956, p. 31. RECEIVED for review August 8, 1956. Accepted May 27, 1957.
Analytical Distillation in Miniature Columns Design and Testing of Teflon Spinning Band A. G. NERHEIM Research Department, Standard Oil Coo(Indiana), Whiting, Ind.
b To increase the efficiency of miniature spinning band columns, effects of band design were studied. A fourbladed Teflon band seems to offer the most advantages, Tests a t both total and partial reflux show that this band gives the high separating power of packed columns as well as the low pressure drop and small holdup inherent in band columns. Increased efficiency is probably caused by increasfd vaporliquid contacting and lower frictional heat a t high band speed.
I
improvements have been made in the design (3, 6,8, 10) and operation (IS) of laboratory fractionating columns. Selecting a column for a given fractionation often involves a choice between the greater number of plates in a packed column and the lower holdup of a spinning band column. Because of low holdup, the miniature spinning band column better separates small, complex samples ( 7 ) . Increasing K RECENT YEARS
1546
ANALYTICAL CHEMISTRY
the effectiveness of the band would add the advantage of more plates (11, 18). High band speeds increase column efficiency, probably by causing better vapor-liquid contacting ( 7 ) . On the other hand, heat of friction decreases efficiency and, hence, limits band speed. A band designed to give better contacting without generating excessive heat would greatly improve the column. The efficiency of the spinning band column has been increased by improving the design of the band and constructing it of Teflon. The effect of band design was studied by testing bands of different cross-sectional shapes in well-designed spinning band distillation equipment. A column containing a Teflon band of the most effective design was compared with conventional Hyper-Cal and spinning band columns (9) a t both total and partial reflux. TESTING OF BANDS
Bands of four different designs mere constructed of Teflon. This material
was chosen because it has a n exceedingly low coefficient of friction and is not wetted by hydrocarbons; however, it gives off toxic vapors at 550’ F. ( 8 ) and can be used only below this temperature. The four designs mere 5 mm. in diameter but differed in number of blades and width of blade edge, as shown in Table I. Each band was fabricated by stringing shaped Teflon sections with s e r r a t d blade edges on a stainless steel tube. Five bands were made, including two 90-cm. ones of the most promising design for further evaluation in a longer column. Performance characteristics-number of theoretical plates, pressure drop, and holdup-were determined a t total reflux as a function of band speed and throughput ( 7 ) ; detailed data vi11 be made available to those interested. Columna were also compared under actual operating conditions a t partial reflux. Throughput was estimated from reflux drop rate a t the condenser drip tips. Reflux was established before spinning the band because Teflon wiped off onto the dry column would reduce efficiency. At total reflux the test mixtures used
Figure 1. Effect of band design on performance TWO BLADES
Table 1.
Dimensions of Teflon Bands
Cross Section Area, Shape sq. cm.
0
0.B L
THROUGHPUT:
23 M L . / H R . I
I
0.4
I
I
Length, Cm.
0.10
0 92
23
0.09
0.92
23
g
0.08
0 92
20.5
@
0.10
0.92
90
/$=
0.10
0.64
90
4)
0.6
Blade Edge Width, Cm.
0.6
d 0.4 I
O"
1
1
THROUGHPUT: 9 ML./HR.
01 0
I
I
2000
I
band design on performance at optimum speed
6000
1.0-
5
EFFECT OF BAND DESIGN
I
I
5000
4000 B A N D SPEED, RPM.
3000
the second comparison, 40-ml. samples IT-ere used because the larger volume favors the Hyper-Cal column.
TWO
The effect of the number of blades as a function of band speed was studied n-ith the short bands. Figure 1 shows H.E.T.P. as a function of band speed at low and moderate throughputs. Optimum speed of rotation increases as the number of blades decreases:
BLADES
0.8
I-
w
I
0.4
1
0.2 0
I
I 5
0
10
I 15
I 20
25
T H ROUGH PUT, M L . / H R .
I6O THEORETICAL
PLATES
1
1
e),
l40k
-I
'.'.a,
120
,I
A-TEFLON BAND
6 0 1 ,
I
--, METAL
BAND I
40 12
1
[ P R E S S U R E DROP'
'
1
'
,," ,, ,/'HYPER-CAL
z
differed with the length of the band. For short bands a mixture of n-heptane I and methylcyclohexane was used (1, and plates produced in that part of the column not occupied by the band were subtracted before height equivalent t o a theoretical plate (H.E.T.P.) was calculated. For the long bands, because of the larger number of plates, a mixture of n-heptane and 2,2,4-triniethylpentane (6) v-as used. At partial reflux a five-component mixture of hydrocarbons ( 7 ) was used in comparing three 90-em. columns at a throughput of 16 nil. per hour and a 45 to 1 reflux ratio. A Teflon band column 5 mm. in diameter with a wide blade edge was compared with a similar metal band column and with a Hyper-Cal column 8 mm. in diameter. I n the first comparison 20-ml. samples were used because this volume is better separated by spinning band columns. I n
04 c--
METAL BAND
-- ----------
HYPER-CAL
4
Figure 3. Performance at total reflux and atmospheric pressure Dashed lines from Nerheim and Dinerstein (7)
Blades
Speed, R.P.M.
4 3 2
3500 4500 >5000
The tn-o-bladed band has the highest optimum speed because it generates less frictional heat, but it shows the smallest increase in efficiency with increasing band speed. The four-bladed band increases in efficiency most rapidly Kith increasing speed, possibly because more blades increases vapor-liquid contacting. I n Figure 2 the H.E.T.P. values for the bands are compared as a function of throughput a t optimum band speed. All of the Teflon bands are better than a two-bladed metal band ( 7 ) . The efficiency of the four-bladed band suffers least nith increasing throughput. Because it is the most efficient a t high throughputs, the four-bladed band seems the most practical. Hon-ever, the threebladed band is nearly as good, and may be desired for work a t lower throughputs. More than four blades would be impractical because of the small column diameter. The effect of the nidth of the blade edge was studied as a function of throughput using two four-bladed bands having edges 0.92 and 0.64 mm. wide. Results are shoxn in Table 11. Flood point was 480 nil. per hour for narrowedged blades and 120 for wide-edged blades. Both give about the same number of plates, but the lower pressure drop and higher flood point nith the narrower edge make it better for n ork a t reduced pressure. COMPARISON OF COLUMNS
0
l
0
20
,
I
,
,
,
40 60 THROUGHPUT, ML./HR.
/
BO
100
Results of comparing the three 90-em. columns a t total reflux are shon-n in VOL. 2 9 , NO. 10, OCTOBER 1957
e
1547
Figure 3. The Teflon band gives the most plates at low throughputs. The pressure drop and holdup with the Teflon band are lower than those of the Hyper-Cal but are slightly higher than those with the metal spinning band. Comparisons a t partial reflux of these columns are shown in Figure 4. The boiling point curve represents both distillations. The refractive index curves show that the Teflon band is equivalent to both reference columns.
1.X
Figure 4. Comparison of miniature columns
1.41
1.4E
8.
c
d 1.44 z
CONCLUSIONS
The higher efficiency of the Teflon band results from specific design features: more blades, larger band core, and more points of contact with the reflux on the column wall. These features cause better mixing, shorter vapor diffusion path, and smoother band rotation. I n addition, higher optimum band speeds are attained because the Teflon band causes little frictional heat. Use of a Teflon band incorporates all of the advantages of low pressure drop, small holdup, and a large number of plates in a single column. Hence, for many distillations the choice between packed and band columns is no longer necessary. The design principles evolved in the present study should also apply to columns of larger diameter. I n such columns more than four blades might further improve efficiency. LITERATURE CITED
(1) Beatty, H. A , Calingaert, George, I n d . Eng. Chem. 26, 504-8 (1934). (2) Chemical and Powder Products, Inc., Kew York, N. Y . , Bull. CP554, Sect. B (1955). (3) Donnell, C. K., Kennedy, R. M., I n d . Eng. Cliem. 42, 2327-32 (1950). (4) Fenske, XI. R., Ibid., 24, 482-5 (1932). (5) Griswold, John, Zbid., 35, 247-51 (1943).
W
? U
2
1.42
W
1.40
1.38
1.36 DISTILLATE. ML
Table II.
Effect of Blade Edge Width
Width a t Blade Edge, Mm.
ThroughPut, Ml./Hour
0.92
15 30 60
133 113 85
0.64
Plates
0.92
0.64
Pressure drop, rnm. Hg 140 114 85
0.37 0.49 0.75
Murray, K. E., J. Am. Oil Chemists’ SOC.28, 235 (1951).
Nerheim, A. G., Dinerstein, R. A., ANAL.‘CHEM.28, 1029 (1956). Piros, J. J., Glover, J. A., U.S. Patent 2,608,528 (Aug. 26, 1952); Chicago Section, ACS, One-Day Technical Meeting, Jan. 24, 1947. Podbielniak, Inc., Chicago, Ill., Bull. A-3 (1953).
Podbielniak, W. J., IND. ENG. CHEM., ANAL. ED. 13, 639-45 (1941).
0.31 0.39 0.66
0.92
0.64
Holdup, ml. 2.4 2.7 2.9
2.2 2.3 2.6
(11) W‘eissberger, A., “Technique of Organic Chemistry,” Vol. IV, p . 215-19, Interscience, New Yorf, 1951. (12) Ibid., pp. 229-31. (13) Winters, J. C., Dinerstein, R. A., ANAL. CHEM. 27, 546 (1955).
RECEIVED for review July 23) 1956. Accepted May 11, 1957. Divlsion of Petroleum chemistry, 130th Meeting, ACS, Atlantic City, N. J., September 1956.
p-ToIuenesuIfonic Acid Spot Plate Test for Steroids EMANUEL EPSTEIN, WILLIAM 0. MADDOCK, and A. J. BOYLE Departments o f Medicine and Chemistry, Wayne State Universify, Defroif 2,
A rapid, convenient color test for steroids avoids the charring often encountered with the use of sulfuric acid. p-Toluenesulfonic acid as a spot test reagent does not char steroids in the course of the test and yields colors which are frequently different and generally more intense than those produced by sulfuric acid. The spot test described appears to add another method of identifying steroids which 1548
ANALYTICAL CHEMISTRY
Mich.
is easy to control.
The resulting melt presents a more intense fluorescence than is exhibited by sulfuric acid.
G
ENERALIZED color tests for ster-
oids as analytical aids have been confined largely to sulfuric acid and antimony trichloride. The references t o these and similar reagents are too voluminous to be mentioned here. I n recent years a reaction involving
perchloric acid was submitted by Tauber ( 2 ) . This reagent yielded various colors for many types of steroids. The work reported involves p-toluenesulfonic acid as a convenient and definitive steroid reagent in a melt-spot test reaction. MATERIALS
Spot plate, porcelain, white.
