Title:
Rectifying column
United States Patent 2317101


Abstract:
It is the object of my invention to produce a rectifying column of improved performance characteristics. More specifically, that object is to produce a rectifying column which will give close rectification without requiring excessive height of column; which maintains its effectiveness with...



Inventors:
Lecky, Herbert S.
Application Number:
US34425440A
Publication Date:
04/20/1943
Filing Date:
07/06/1940
Assignee:
PURDUE RESEARCH FOUNDATION
Primary Class:
Other Classes:
202/158, 261/95, 261/DIG.72, 422/609, 422/610, 422/648
International Classes:
G01N25/14
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Description:

It is the object of my invention to produce a rectifying column of improved performance characteristics. More specifically, that object is to produce a rectifying column which will give close rectification without requiring excessive height of column; which maintains its effectiveness with Increasing reflux rate until well toward the flooding point, as measured in the number of equivalent theoretical plates per foot; which has a high through-put; which has a very small H. E. T. P. (height equivalent to a theoretical plate); and which is relatively inexpensive to make.

In carrying out my invention, I provide in the column a helical permeable packing. This helical permeable packing may be of various forms.

Among those forms are a helix of wire screen, desirably a fine gauze; a helix formed by a wrapping of a close-wound helical wire spring; and a helix of textile fabric, suitably supported in the helical form, as for instance a hollow tubular fabric held tubular by an inserted helical spring and wound in helical form to produce the helical permeable packing.

This helical permeable packing has several advantages. It provides a continuous helical passage for the upwardly moving vapor. At the same time it provides the same continuous helical passage for the downwardly moving reflux.

It permits that reflux to permeate the meshes of the permeable packing, and so to form a film which on both its sides is exposed to the vapor.

In consequence, there is evaporation from and condensation upon the surface of the reflux on both the upper and lower sides of the helical permeable packing.

The accompanying drawing illustrates my invention: Fig. 1 is a sectional diagrammatic view, partly broken away, showing a rectifying column embodying my invention in a simple form; Fig. 2 is a plan view of a screen-washer which I may use for building up a screen helix; Fig. 3 is a side elevation of the screen-washer of Fig. 2, sprung apart into helical form, and showing in dotted lines fragments of associated similarly sprung-apart screen-washers to indicate the manner of assembly to make the complete screen helix; Fig. 4 is a plan view of a screen-washer similar to Fig. 2, but with an edge binding of metallic foil to reduce leakage around the edge; Pig. 5 is an enlarged fragmentary section, in partial elevation, of a multiple column, consisting of several coaxial annular columns of different diameters, with each column provided with its own helical-screen packing; Fig. 6 is an enlarged fragmentary dead-section on the line 6-6 of Fig. 5, with the screen helix provided with inner and outer bindings of metallic foil; Fig. 7 is a transverse section of a modified form of column in process of manufacture, showing a central tube with a projecting helical row of pins on which a permeable packing is being woven out of wire; Fig. 8 is a fragmentary front elevation of the central tube of Fig. 7, with its helical row of pins; Fig. 9 is a view similar to Fig. 7, but with the hellcal permeable packing consisting of a ribbon of textile or gauze interlaced on the helical row of pins; Fig. 10 is a fragmentary vertical section through a column in which the packing is a helical tube of fabric, such as a tubular shoestring, having within the fabric tube a helical spring which is wound with the shoestring into the larger helix of the packing; Fig. 11 is a fragmentary vertical dead-section of a modified form of screen-washer similar to that of Figs. 2, 3, and 4 but with the inner and outer angularly bent edge portions to reduce edge leakage in the column; and Fig. 12 is a transverse section through a column having a bundle of rectifying tubes.

The main structural features of the rectifying column, apart from the packing, may be of any usual or desired construction. One effective design of column is shown in Fig. 1. At the bottom there is a still-chamber 15, which contains the liquid 16 to be rectified, and which may be heated '- in any suitable way, for instance by a burner 17 as shown. The lower end of the column 21 is conveniently set directly in the mouth of the still-chamber 15. A vapor chamber 22 is located above the column 21; and if it is separat*:: able from the column, as it may be, the vapor-inlet tube 23 with which it is provided at the bottom has a close-fitting joint 24 with the upper end of the column. A thermometer well 25 is usually provided at the top of the vapor chamber 22, for receiving a thermometer 26. The vapor chamber 22, as shown, has an oblique downward outlet tube 27, provided with a stopcock 28; and the entrance to that tube 27 lies below the lower end of an oblique condenser 29, the upper end of which may be connected by a discharge tube 30 to a drip vent 31 to which the outlet tube 27 also leads. The condenser 29 has a suitable cooling jacket 32, in the usual manner of condensers; and the rectifying column 21 may have a vacuum jacket 33, surrounded if desired by an electrical heating coil 34. As so far described, the structure is more or less conventional, and may be varied along any conventional or desired lines.

The rectifying column may have a single rectifying tube 40, as is shown in Fig. 1; or may have 2 2,317,1 a plurality of rectifying tubes, for example either arranged in a bundle of tubes 40 as is shown in Fig. 12 or as a group of coaxial tubes 41, 42, and 43-as is illustrated in Fig. 5. The tube 40, or each tube 40, or the central tube 41, is provided with an axial rod (or closed-end tube) 44.

Within the tube 40, or each tube 40, or within each of the tubes 41, 42, and 43, I place my new helical permeable packing 50. This packing is located between the inner surface of the tube 10 within which it lies and the outer surface of the next adjacent cylinder within such tube, whether that next adjacent surface be of the axial rod (or closed-end tube) 44 or one of the inner tubes 42 or 41. According to my present preferences, 15 the helical permeable packing is most conveniently made of wire screen, desirably a fine gauze, made of wires or films of a material which is not attacked, or at most not too rapidly attacked, by the fluids which come in contact with it in the 20 rectifying process.

A simple way of making the helix of screen is to make first a series of screen-washers 51, as is shown in Fig. 2, having a suitable outer diameter to fit closely within the tube which'is to receive it (the tube 40, 41, 42, or 43) and a suitable inner diameter to fit closely upon the cylinder member which it surrounds (the tube 42, the tube 41, or the central rod 44). The screen-washer 51 is cut along a radial line 52, to make a split-visher; 30 and the split-washer is spread out into the form of a single-turn helix as is illustrated in Fig. 3.

The helical packing is produced by putting together a series of these single-turn helixes, end to end, and suitably fastening together the adjacent 3 ends of the several single-turn helixes, as by overlapping such adjacent ends and spot-welding them together. In this way, a multiple-turn helix of any desired length and number of turnsmay be built up. The number of turns may be as 40 many as several hundred, and the length may be many feet; the number of theoretical plates increases in substantial proportion to the length.

If desired, two or more helixes may be interthreaded together, as is done for the screen 45 helixes immediately within the tubes 42 and 43 in Fig. 5, to make a multiple helix in which each individual helix has a thread-pitch which is a multiple of the distance between the adjacent screen layers. 50 The helix 50, whether it be a single helix as is shown in the tube 40 of Fig. 1 and the tub s 41 of Fig. 5, or a multiple helix as shown within the tubes 42 and 43 of Fig. 5, is then mounted in place within the tube which is to receive it (the 55 tube 40, 41, 42, or 43) and around the next inward cylindrical surface (the rod 44, or the tube 41 or 42 as the case may be). The helical screen should have a tight joint with both cylindrical surfaces which it abuts-the inner surface of the 60 tube surrounding it and the outer surface of the cylinder which it surrounds. This is in order to prevent leakage past the edges of the helical screen. This tight joint, which need not be absolutely tight although it is desirable to have it 6E .as tight as possible, may be obtained in many ways. In one way, the glass tubes associated with any helix may be heated to the softening point, to produce a flowing of the glass around the helix edges. Instead of or in addition, the wash- 7( ers 51 may be provided with a binding 53 of metal foil, crimped in place on the washers. This metal-foil binding may, if desired be provided on only the outer edge of the screen-washer, as is illustrated in Fig. 4, or on both edges as is illus- 7 trated in Fig. 6. The metal-foil binding hugs the adjacent glass wall and materially reduces leakage. Alternatively, the washer 51 may be cupped, if desired only at its edges, as is shown in Fig. 11, to provide oblique flanges 54 which press resiliently against the adjacent glass walls (the relative diameters being properly selected) to reduce the edge leakage of fluid around the edges of the helixes.

Instead of building up the helix 50 of screenwashers 51, whether with or without the binding 53 or the oblique flanges 54, I may construct the helix in place. One way of doing this is shown in Figs. 7, 8, and 9. There the rod or tube 44 which the helical permeable packing is to surround is provided with a number of outwardly projecting radial pins 60, arranged on that rod or tube 44 in a helix as is clear from Fig. 8. The helical permeable packing is built on these helically arranged pins 60, as by circularly interweaving wires or threads 61 on such pins, as is shown in Fig. 7. Instead of the wires or threads 61 of Fig. 7, I may interweave on the pins 60 a flat ribbon 62 of woven or matted material, such as cotton.

The helix thus formed on the central rod or tube 44 has the surrounding tube placed over it, with a tight fit; and in case the helix is built up of wires or other non-inflammable material the tightness of the fit may be augmented by heating that surrounding tube sufficiently to soften the glass and let it contract on the helix.

Another variation is shown in Fig. 10. Here a tubular fabric member 65, such as a tubular shoestring in small columns, is wound helically on the central rod or tube 44, and surrounded by the next outer tube 40. The hollow tubular fabric member 65 may be held distended by having with it a wire helix 66, which is wrapped with the fabric member around the central rod or tube. 44. If desired, and if the helix 66 is close wound so that it forms in itself a permeable member, that helix may be wound around the central rod or tube 4' alone, without the covering of fabric 65; although I prefer that that covering of fabric 65 be used.

In operation, the liquid to be rectified is placed in the still-chamber 15, and suitably heated to produce evaporation of its contents. The vapors rise through the column 21, which may be heated; travel in the helical path or paths provided by the helical permeable packing or packings; and condense in the condenser 29. There may be one helical path, as in Fig. 1, or several parallel helical paths, as in Figs. 5 and 12. The condensate or reflux tends to run backward along the same general helical path or paths in which the vapors are ascending, and wet and permeate the helical permeable packing or packings. Thus the reflux and the vapors are in contact, and there .is a constant interchange of material between the vapor state and the liquid state as is common in rectifying columns. But with my helical permeable packing, this interchanging of phase between the vapor state and the liquid state occurs Son both surfaces of the helical permeable packing, the upper and lower surfaces in Fig. 5 for instance, and the liquid not only flows down the helical path but to some extent permeates the meshes of the permeable packing. By reason of 0 this close contact of the vapor with the reflux on both sides of it in the vapor passageway, (he continuous interchanging of phase is facilitated, and made more effective to produce the ├Żesired rectification; for there is a most intimate contact between the counter currents of ascendink vapor and descending liquid (reflux). In other words, because the liquid wets the wire screen or other helical permeable packing, and exposes a liquid surface at both sides of such packing, there are two surfaces of liquid-phase contact, in a long path for both the liquid and the vapor to travel for a relatively short length of the complete column.

The vapor which finally passes out at the top of the column 21 passes into the vapor chamber 22, and is condensed in the condenser 29, and drawn off by way of the drip vent 31, by which the take-off and hence the ratio of takeoff to reflux are controlled. Very close cuts may be obtained. The boiling points of the several cuts are determined by the thermometer 26.

My improved column has the unexpected property that its effectiveness as measured in H. E. T. P. is maintained with increasing reflux rate until close to the flooding point. This is a desirable and distinguishing feature; because most types of rectifying columns are more efficient at lower vapor velocities, so that for their efficiency it is necessary to keep the reflux rate or through-put relatively low.

Combined with this maintenance of effectiveness at high reflux rate, my improved column also has a very small hold-up-that is, it has a very small quantity of liquid in the column in operation, so that sharp separation between cuts is obtainable.

Further, there is a very low pressure-drop in my column, for the pressure at the bottom is very little higher than at the top.

My column has the further desirable feature that it can be constructed to have increased height efficiency at the expense of through-put or increased through-put at the expense of height efficiency by placing the turns of the helixes closer together or farther apart, as may be desired.

I claim as my invention: 1. In a rectifying column having means for connecting the lower part to a still-chamber and the upper part to a condenser, a helical permeable member for supporting a film of reflux liquid which by reason of the permeability of said helical permeable member is exposed over both its upper and lower sides to vapor ascending in a helical path provided by said helical permeable member, and means for closing the inner and outer sides of said helical path.

2. In a rectifying column having an impermeable tubular shell of which the lower part is provided with means for admitting vapor and for emitting liquid and the upper part is provided with means for emitting vapor and admitting reflux liquid, a helical permeable packing fitting within said shell and contiguous with the inner surface of said shell, and means for closing the inner side of that helical path, said helical permeable packing consisting of a helix of wire screen and engaging said shell and said closing means in a manner which substantially prevents short-circuiting flow of liquid between adjacent turns of said helical path.

3. In a rectifying column having an impermeable tubular shell of which the lower part is provided with means for admitting vapor and for emitting liquid and the upper part is provided with means for emitting vapor and admitting reflux liquid, a helical permeable packing fitting within said shell and contiguous with the inner surface of said shell, and means for 'asing the inner side of that helical path, said .,Jical permeable packing consisting of a helix of textile fabric and engaging said shell and said closing means in a manner which substantially prevents short-circuiting flow of liquid between adjacent turns of said helical path.

HERBERT S. LECKY.

CERTIFICATE OF CORRECTION.

Patent No. 2,317,101. April 20, 1945.

HERBERT S. LECEY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 8, for "with" read --within--; and that the said Letters Patent should be read with this correction therein that the samemay conform to the record of the case in the.Patent Office.

Signed and sealed this 1st day of June, A. D. 1945.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.