I N D U S T R I A L A N D ENGINE.ERING CHEMISTRY
October 15, 1931
377
Improved Gauze-Plate Laboratory Rectifying Column’ S. Palkin BUREAUOP CHEMISTRY AND SOILS,WASHINGTON, D. C.
An improved gauze-plate column is described which was needed, one which, for ANY attempts have possesses the advantages of simplicity of construction high reflux ratio, is capable of been made to devise laboratory rectifying and resistance to flooding, and has been found parhandling comparatively large columns comparable to the ticularly well adapted for vacuum fractionation. columns of vapor without unb u b b l i n g - p l a t e t y p e freData in the form of graphs are given indicating the due tendency to flooding. auentlg used in the industry. character of fractionation obtainable with this column. A structural feature essential for the efficient operation As a rule such columns for laboratory use require somewhat elaborate glassblowing. A of bubbling columns in general is an adequate mechanism for device of this type which is simple in construction would doubt- the rapid transfer of reflux liquid down from plate to plate, less find extensive use in laboratories. In this paper such a in order to provide each with an appropriate scrubbing column, involving a minimum of glassblowingand structurally medium for the progressive enrichment of the ascending vapors in terms of the more volatile constituent. simple otherwise, is described. Dupont (2) describes a two-meter plate column similar to An interesting evolution in the development of the bubbling column is evidenced in the literature, ranging from the earlier that of Young and Thomas which he has found effective in forms such as the Glinsky, Le Bel-Henninger, Brown, Young the fractionation of turpentine. This device embodies simplicity of construction, since the internal mechanism consists only of a series of glass trap tubes hung in wire-gauze plates (inverted cup-shaped), the latter being held in the straight glass column tube by friction. The wire gauze automatically provides an effective means for producing intimate contact of descending liquid with ascending vapors. Experience in this laboratory with the Dupont column has shown, however, that the trap tubes (Figure 1, a) do not TRAP TUBE function dependably. “Blowing” of vapors through these tubes with consequent flooding of compartments occurs, necessitating frequent interruption. Careful observation has shown also that a portion of the reflux liquid in its course from trap tube to plate below finds -;TI. its way directly into the opening of the next lower tube 3= without forming a part of the pool of scrubbing medium of that plate, thus rendering the reflux partly ineffective. SCREEN
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-
110
6
105
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FRACTIONATION OF BENZOL-TOLUOL MIXTURE
(50- 50) FIG. 2
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100
HOOK TUBE
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FIG. 1
COLUMN
TUBE
SHOWING STAGGERED POSITION O f TRAP TUBES.
and Thomas (6, 7 ) , Taylor and Snyder (S), to the more recently improved bubbling cap-plate types described by Bruun (1). No attempt will be made in this paper to enter into any discussion of the relative merits and comparative effectiveness of bubbling columns ( 1 , J ) as against the packed form, evaporator, spiral ( 5 ) , and others. This subject has been treated in standard works (7) and in numerous publications (5). The preferred type of fractionating device will depend t o a large extent on the particular work for which it is to be used. In this laboratory an efficient means for the fractional distillation in vacuum of a complex mixture such as turpentine 1 Received May 6, 1931. Present& before the Division of Agricultural and Food Chemistry a t the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931.
70L
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100
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300
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400
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500
VOLUME, CC.
A Bruun column ( I ) , fifteen-plat6 available in this laboratory, although found to be a very effective fractionating device, also showed a tendency to flood when distilling in vacuum,2but much less so than the Dupont apparatus. A simple modification of the Dupont and Young and Thomas columns through the use of an improved trap tube, shown in Figure 1, has been found to overcome completely the 1 An improved form of this column has recently been developed by the same author, Bureau of Standards, unpublished.
ANALYTICAL EDI TI0N
378
difficulties encountered in the former and to function with complete smoothness and dependability. Their straight testtube form also permits a superimposed arrangement in staggered positions right and left rather than directly over each other, an arrangement not possible with the hook-form tube (Figure 1, a) of the Dupont apparatus. Since the integral parts, the wire-gauze plate and the glass trap tubes, can be easily made with ordinary laboratory facilities, construction of a long column is a relatively simple matter. IONATION OF BETA PINENE
Vol. 3, No. 4
OPERATION OF COLUMN-AS a rule the trap tubes prime themselves after a few minutes of running the column “total reflux.” This may also be expedited by allowing one or two of the spaces between the plates in the upper part of the column to.flood and then effecting a return of the condensed liquid by varying the pressure when distilling in vacuum, by blowing into the apparatus for a moment when distilling a t atmospheric pressure, or by rapidly cooling the distillation flask with an air blast. Test distillations were made, at atmospheric pressure, of a mixture of benzene and toluene, and a t reduced pressure of a mixture of alpha and beta pinene from turpentine with: ( a ) Bruun column, 15-plate and approximately 125 cm. long and 2 cm. external diameter. ( 6 ) Dupont column, 30-plate and approximately 190 cm. long and 2.5 cm. external diameter. (c) Improved gauze-plate column here described, 15-plate and approximately 110 cm. long and 2.5 cm. external diameter.
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B -30
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c -15 PLATE”WIRL GAUZE”COLUMN IMPROVED-X--
500 GMS OF SAMPLE USED IN A h B
PER CENT OF SAMPLE
The same mixtures were used in the respective columns a, b, and c in equal volumes (500 grams) except in the case of the alpha-beta pinene mixture for column e, where only enough of the sample remained to run 300 grams. The reflux ratio was oontrolled by an automatic reflux regulator (8a) in the Bruun apparatus, and by means of a stopcock in the other columns. All the columns were provided with thermal insulation, and the pressure was controlled with a pressure regulator when fractionating in vacuum. The results of these runs are shown graphically in Figures 2 and 3.
Construction of Apparatus TRAPTUBES-The simple glass manipulation involved in their construction may be expedited by proceeding in the following order: A small Pyrex test tube (stock size, 3 X 3/8inch, or 7.62 X 0.95 cm.) is used for the outer tube, and is made funnel-shaped a t the top and a hole made a t the point indicated. The inner tube, made funnel-shaped at the top and cut to length, is then simply fused in position, leaning, by rotating in the flame. The outer tube is then made to proper length by drawing off the lower end, leaving the tip at an angle as indicated. The volume of liquid in the reservoir portion of the trap tube, when primed, is calculated to provide sufficient head in the inner tube to insure against passage of vapors through it. WIRE-GAUZE PLATES--?JiCkel wire screen, 40-mesh, was found very serviceable in turpentine-oil fractionation. A form for pressing the screen into shape may be prepared by drilling a hole in a block of wood or metal, the diameter of the hole being about 1 or 2 mm. greater than the inside diameter of the column tube. The wire screen is cut into disks and pressed into the form with a metal plunger. The cupshaped gauze plate is then trimmed to leave an even shoulder about 1 cm. high. A hole, the diameter of which is very slightly less than the outer diameter of the trap tube, is made with a round file. Distortions of the plate are eliminated by reshaping. The outer diameter of the gauze plates should be somewhat larger (1 to 2 mm.) than the inside diameter of the column tube, so that they may be held in position by friction. ASSEMBLY OF CoLum-The gauze plates, each with its trap tube, are inserted in the straight column tube in such a way that the trap tubes have the lower ends (the tips) touching the side of column tube and arranged in a staggered position as indicated in Figure 1. This will direct the flow of reflux liquid from each successive trap tube away from the top opening of the next lower trap tube. A long stick, provided with a metal or glass tube having an inside diameter sufficient to surround the trap tube loosely, has been found convenient for placing the units in position as illustrated.
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PLATE COLUMN OF 32 PLATES FIG 4 1
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4W 600 800 1000 1ZW 1400 WEIGHT OF SAMPLE IN GRAMS
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The data shown in Figure 4 were obtained with a 32-plate gauze-plate column of type c on a sample of turpentine which contained G l per cent alpha pinene, 34 per cent beta pinene, and the remainder “tailings.” Composition data for the alpha-beta pinene mixtures were computed from optical rotations of the fractions by the method of Darmois and Dupont (2). These results indicate in a measure the degree of fractionation obtainable by the respective columns. However, in the absence of automatic control of the reflux ratio for the gauzeplate columns, and in view of structural differences in diameter, column length, etc., as indicated above, these results cannot be regarded as exact measures of the relative effectiveness of the respective columns. Literature Cited (1) Brnun, IND. Exo. CHEM.,Anal. Ed,1, 212, Fig. 7 (1929). (2) Dupont, Chime znduslrie, 8, 555 (1922). (3) Hill and Ferris, I N D .END.CHEM, 19, 379 (1927). (4) Marshall and Sutherland, Ibid., 19, 735 (1927). (5) Midgely, Ibid., Anal. E d , 1, 88 (1929). (6) Rittmann and Dean, J. IND.ENG CHEM.,7, 185 (1915). (7) Young, “Distillation Principles and Processes,” Chap. XI, Macmillan, London, 1922.
