US2218240A

US2218240A - Vacuum distillation

Info

Publication number: US2218240A
Application number: US187454A
Authority: US
Inventors: Kenneth C D Hickman
Original assignee: Distillation Products Inc
Current assignee: Distillation Products Inc
Priority date: 1938-01-28
Filing date: 1938-01-28
Publication date: 1940-10-15
Anticipated expiration: 1957-10-15
Also published as: FR849596A; GB524439A; GB524390A

Description

Get. 15, 1940. c HlCKMAN 2,218,246

VACUUM DISTILLATION Filed Jan. 28, 1958 4 Shets-Sheet 1 FINAL DIS T/LLA TE IVDISTILLED RES/DUE 50 1 cawbmsnrs L RES/DUE CONDENSATE RES/DUE Hennflh CD; Hickman INVENTOR ATTORNEYS ct. 15, 1940. g D, H|KMAN 2,218,240

VACUUM DISTILLATION Filed Jan. 28, 1938 4 Sheets-Sheet '2 Kenneth CDLHickman INVENTOR W. M BY @a/MMM ATTORNEYS K. c. D. HICKMAN 2,218,240

VACUUM DISTILLATION Filed Jan. 28, 1958 4 Sheet s-Sheet s COOLING 2 mg. 7A LT mm m T. 1v M m w 4 m w n 5 m r 5 M i N m c M m. 4 m W m 1 E w n W 0 n Y m C e B u H H 6. .Q i Q 4 6 2 J 2 0 1/ 2 E B F. 0 00 W 5 6% m M g B. Q6 D N 0; 4/ 0 Z w M J (M w Al k y Oct. 15, 1940.

VACUUM DISTILLA'IIION Filed Jan. 28, 1958 4 Sheets-Sheet 4 Kenneth CDHickman INVENTOR W W BY WW ATTORIXEYS Patented Oct. 15, 1940 PATENT OFFICE 2,218,240 VACUUM DISTIILATION Kenneth C. D. Hickman, Rochester, N. Y., assignor, by mesne assignments, to Distillation Products, Inc., Rochester, N. Y., a corporation of Delaware Application January 28, 1938, Serial No. 187,454

5 Claims.

This invention relates to improved method and means for fractionating under high vacuum conditions and particularly high vacuum conditions wherein the evaporating and condensing surfaces are separated by substantially unconstricted space.

It is known that the constituents of a mixture can be separated by high vacuum, short path or molecular distillation. Due to the fact that the vapors must be immediately condensed, interchange of heat and constituents between vapor and condensate as ordinarily practiced is impossible. For this reason, no fractionation=takes place and it has been calculated that the best degree of separation of constituents possible by these types of distillation is about equal to one theoretical plate. In commercial practice, it is even less. This low capacity for separation is a decided shortcoming.

This invention has for its object to overcome the above difliculties of high vacuum, unob- 'structed path distillations. Another object is to provide means whereby improved fractionation or separation of constituents is possible under high vacuum, short path or molecular distillation conditions. A further object is to provide short path, vacuum distillation apparatus which permits repeated redistillations without great loss of decomposable substances. Other objects will become apparent from the following description.

In the following examples and description, I have set forth several of the preferred embodiments of my invention, but it is to be understood that they are given for the purposes of illustration and not as limitations thereof.

In the accompanying drawings, I have illustrated apparatus embodying the principles of my invention, wherein like numbers refer to like parts and wherein:

Fig. 1 is a horizontal section of a preferred type of fractionating still in which circulation of distilland over each vaporizing plate is caused by centrifugal force;

Fig. 2 is a detail of the scooping means shown in Fig. 1 for removing liquid from the turned edge or surface of each of the rotating plates;

Fig. 3 is a detail drawing of the scraper or scoop device illustrated in Fig. l for removing liquid from the opposite surface of each of the plates;

Fig. 4 is an elevation in section of a gravity still embodying the principles of my invention;

Fig. 5 illustrates in diagrammatic form an alternative type of gravity flow column;

Fig. 6 is a fragmentary section in elevation of a modified method of disposing the centrifugal plates of the apparatus illustrated in Fig. 1;

Fig. 7 is a horizontal section of a centrifugal plate provided with an alternative method of removing liquid residues; 5

Fig. 8 is a fragmentary section in elevation of the device illustrated in Fig. '7; 1

Fig. 9 is a perspective view showing in detailthe construction of themoving scraper of Fig. 7, and;

Figs. 10, 11 and 12 are diagrammatic sectional elevations illustrating alternative methods of collecting liquids from the surfaces of the centrifugal still plates.

Referring to Fig. 1, numeral 2 designates a cylindrical casing provided with

end plates

3 and 6 and with conduit 5 which connects to high vacuum pumps (not shown). A shaft 6 is located in the center of the casing 2 and is housed at one end in bearing I and at the other by a packed bearing 8. The external end of the shaft extending through bearing 8 is provided with a drive pulley 9. Upon shaft 6 are rigidly mounted a plurality of spaced plates II), II, I2, I3, I4, I5, I6 and I I. Plates I0, I2, I4 and I6 are vaporizing plates and are, therefore, provided with means for heating their surfaces, which comprises a heat radiating element 23 and a reflector 24. It will be noted that these vaporizing plates progressively decrease in area and, preferably, in a geometric ratio for reasons which will be explained below. Plates II, I3, I5 and I! serve as condensing plates and are cooled by circulation of liquid over their top surfaces. It will be noted that each of the plates is provided with an inwardly turned edge. Cooling fluid originally introduced onto the center of the condensing plates is, when the shaft 6 is rotated, thrown into the gutter formed by the turned edge-of each plate and is picked up by scoop 25. Due to the inertia 4o of the liquid and/or the action of pumps I8, it is caused to flow into conduit 26 through cooling coil 21 and back through conduit 28 to the center of the cooling plate. Substantially the same ac tion takes place with each condensing plate. These plates are also provided with

removal devices

29, 30, 3| and 32 located at the periphery of their other or opposite surface, which serve to collect and remove liquid which is condensed upon the surface and is thrown to the periphery by centrifugal force.

Each of the vaporizing plates Ill, I2, I4 and I6 are provided with a

scoop

33, 34, 35 and 36, respectively, which remove liquid from the turned edge gutter. Scoop 33 is connected to conduit 31 5 through which undistilled residue is'withdrawn from the st111..-"Scoop 34 connects to conduit 38 which 15.111 tum,- connected to conduit as 'by which material to be distilled is introduced onto the center of heated plate, I8. Scoop 29 connects to conduit 46 and scoop 35 of plate I4 connects to conduit 41. These conduits and 41 joint to conduit 48which serves to deliver liquid flowing therefrom onto the center of plate I2. Scoop 38 of condensing plate I3 is connected to conduit 49 and scoop 36 of vaporizing plate I6 is connected to conduit 58 and both of these conduits are connected to conduit 5| which serves to convey the liquid flowing therefrom onto the center surface of plate I4. Scoop 3| which removes liquid from the condensing surface I5 is connected to conduit 52 which serves to deliver the liquid onto the central surface of vaporizing plate I6. Scoop 32 is connected to conduit 53 by which the final fraction is removed from the still.

In Fig. 2 is illustrated the specific construction of the liquid removing scoop, such as 25, which removes liquid from the turned edge gutters of the condensing plates, such as plate I5. Numeral 25 designates the pointed scoop constructed from a small conduit, the point of which may be in close proximity to the surface of turned edge 62 or may actually touch it. The open part of the point faces in a direction opposite to that in which the plate is rotated and it is connected to a conduit 26 which serves to convey the removed liquid away from the scoop. The removing

devices

33, 34, 35 and 36 are constructed in the same manner.

Referring to Fig. 3, which illustrates another specific method of removing liquid from the surfaces of the plates, and in particular condensate from a condensing plate such as I5, numeral 3| designates a rectangular hollow conduit which may lightly touch the surface of plate I5. The rectangular conduit is constricted at the closed end not in contact with the plate and is connected to a conduit 52 by which liquid forced into rectangular element 3I is conveyed away. The open end of the rectangular element faces in a direction opposite to that in which the plate is caused to rotate.

Referring to Fig. 4, numeral 88 designates a cylindrical still casing having a substantially greater length than diameter. It is provided with a flange 8I at the top and a gutter 82 and a withdrawal conduit 83 at its base. A second cylindrical element 84 slightly shorter and somewhat smaller in diameter is located inside the main casing 88 and concentric therewith. This central element is carried by an integral flange 85 which rests upon the packing or sealing material 86 placed upon flared edge 8I of element 68. Element 84 is divided into a plurality of

zones

81, 88, 89 and 88, each of which can be maintained at a separate and distinct temperature by. an electrical heating element located inside the cylinder (not shown). The boundaries of each of these zones is approximately indicated by the horizontal distributing

devices

9I, 82, 93 and 84 which may be made of gauze loosely attached to the surface of element 84 and which serve to evenly spread-liquid over the heated surface in order to obtain a thin film for efficient vaporization. A'series-of annular gutters I88, I8I, I82 are formed in the walls of the main still casing 88. Gutter I88 is approximately level with the bottom portion of zone 88, gutter IN is approximately level with the bottom ofzone 89 and gutter I82 is approximately level with the lowest portion of zone 98.

I03. Gutter 82 is connected-to a Conduit I84 I85 up onto the distributing element 92.

'The' e m' i c t fthe-w m main. e16?" I ments 88. and is evacuated tothe required d gree mps'mot shown; connected to conduit pump I81 which serves to deliver'liquid collecting therein up onto distributing device 93. Gutter I8I connects to conduit I88 provided with pump I89 which serves to deliver liquid collected therein onto distributing device 94. Gutter I82 is connected to conduit II8 through which the final fraction is withdrawn from the still. A conduit III serves to deliver the liquid to be distilled to the distributing element 9I.

Referring to Fig. 5, which is substantially the same as the apparatus of Fig. 4, except for the heating zones, numeral 88' designates a cylindrical still casing provided with evacuating conduit I83 and condensate collecting gutters 82', I88, I8I' and I82. Numerals 81, 88', 89' and 98' designate superimposed sections of a vaporizing column corresponding to

sections

81, 88, 89 and 98 of Fig. 4.

Referring to Fig. 6, numerals I28 and I22 designate condenser plates, the upper and lower surfaces of which are provided with turned edges to form gutters I24, I26, I28 and I38. Numerals I32 and I34 designate evaporating surfaces provided with gutters I36 and I38 respectively. Numeral I48 designates a branched conduit which serves to remove condensate from the gutters I24 and I26. Numeral I42 designates a branched conduit by which distilland is introduced onto and removed from evaporating plates I32 and I34. Numerals I46, I48, I58 and I52 designate conduits for introducing cooling fluid onto and removing it from condensing plates I28 and I22. Numeral I54 designates a radiant heater disposed between evaporating plates I32 and I34.

Referring to Figs. 7, 8 and 9, numeral I68 designates a plurality of lugs integral with still casing 2 and I62 similar lugs supporting an adjustable gutter ring I64 which is in close proximity to the periphery of the centrifugal plate I66. The ring is split at I68 so that the clearance between it and the periphery of I66 can be adjusted. A conduit I18 communicates with the gutter. The center of plate I66 is raised at I12 and into the depression a stationary collar "I is placed so as to leave a slight clearance at I14. The collar is shaped so as to form a reservoir I16 which communicates with conduit I18. Numeral I88 designates a cleft scraper, the head of which is the same shape'as the inside of the gutter ring I64 and the cleft portion of which extends over and into a slot formed in the periphery of plate I66.

Referring to Fig. 10, numeral 288 designates a horizontal shaft to which is fixed a vertical vaporizing or condensing plate 282, the periphery of which extends into gutter I84 provided with inwardly turned edges I86.

Referring to Figs. 11 and 12, numeral 228 designates an approximately vertical shaft to which is fixed a plurality of

plates

222 and 224, either or both of which may be condensing or vaporizing plates. Numeral 226 designates a gutter into which the periphery of plate 224 extends 'and which is so constructed that the slit opening 228 is near the top portion thereof.

In operating the apparatus of Fig. 1, power is applied to pulley 9 and the shaft 6 and the various vaporizing and condensing plates are caused to rotate at a fairly high speed. The vacuum pumps connected to conduit! are put into operation and cooling liquid which has a low vapor pressure such, for instance, as a low vapor pressure hydrocarbon or glyceride is introduced into the cooling coils 21 or onto the surface of the cooled condensing plates II, I3, I5 and I1. During rotation, the cooling fluid flows through conduit 28 onto the center of each cooling plate. It is then caused to flow to the curved edge of that plate by centrifugal force. In passing over the surface of the plate, which is preferably of heatconducting material, cooling of the plate takes place and the cooling liquid is warmed. This slightly warmed liquid is removed from the turned edge by scoop 25 and, due to the inertia of the liquid, and/or the action of pump I8, it is forced through the external cooling coils 21 and is returned to the center of the plate by way of conduit 28. Each of the condensing, plates is, therefore, automatically cooled'as long as the centrifugal elements are caused to rotate. v

Liquid to be distilled and fractionated is introduced through conduit 39. The liquid flows to the center of vaporizing plate I0 and is'thrown to the turned edge at the periphery thereof by centrifugal force while in the form of a thin film. A portion of the opposite surface of each of the condensing plates is exposedto the heat-radiating element 23, the heat of which is also reflected against the plate by reflector 24. As the plate rotatesover this element, it is heated to distilling temperature, which may be regulated by the temperature of the element 23 and by the extent or area of the plate which is exposed to such radiation. In passing over the surface of plate I0 in the form of a thin film, vaporization of molecules in the high vacuum which exists throughout the system takes place. These molecules pass to the cool condensing-surface II and are condensed thereon. The distance between the vaporizing and condensing surface'is preferably small and under molecular conditions should be less than about the mean free path of the distilling molecules. Liquid condensed on the surface of plate II is thrown to the periphery where it is picked up by scoop 29. The force of gravity as well as the inertia of the liquid as it flows into this scoop causes it to continue to flow up through conduit 46 and into conduit 48 from which it is allowed to flow onto the center of vaporizing surface I2. This plate is preferably heated to a somewhat lower temperature than plate I0, the difference depending mainly upon the material distilled and the particular fraction removed. The liquid flowing from conduit 48 is caused to pass over the surface of vaporizing plate I2 and vaporized molecules are condensed upon the under surface of condensing plate I3. Undistilled residue from plate I2 is removed by scoop 34 and is forced by way of conduit 38 into conduit 39 where it is mixed with the initial material to be distilled. Condensate on plate I3 is thrown by centrifugal force into-removing device 30 from which it is forced to flow through conduit 49 into conduit 5I which delivers it onto the center of vaporizing surface I4, which is heated to a somewhat lower temperature than plate I2. The liquid is thrown as a thin film over this surface and undistilled residue collects inthe turned edge and is removed by a scoop 35 and delivered by way of conduit 41 into conduit 48 where it is mixed with the condensate removed from plate II. Molecules vaporized from plate I I condense upon the condensing plate I5 and are thrown by centrifugal force to scoop, 3| and flow thence into conduit '52 which delivers i-t-onto the center surface of vaporizing plate I0, which ispreferably at a temperature slightly lower than plate I4. On this plate, the final fraction vaporizes and is condensed upon plate I! and is removed therefrom by scoop 32 and conduit 53. Undistilled residue \ollecting in the turned edge of plate I6 is removed by scoop 36 and flows through conduit 50 into conduit 5| where it is mixed with condensate removed'from condensing plate I3.

The apparatus of Fig. 1 is simple to construct,

but it has the disadvantage that considerable heat loss takes place, since the cool condensing surfaces are alternate to the heated evaporating surfaces. Fig. ,6 illustrates the same apparatus,

in which the plates having the same function are mounted in pairs so that these losses are reduced to one-half or less. Liquid to be distilled is introduced onto evaporating plates I32 and I34 by conduit I42. Heating of the plates is caused by 154. Undistilled residue is removed by conduit I. Condensing plates I22 and I20 are cooled by fiuid introduced.- thereon by conduits I46 and I48. "Condensate is removed from both by conduit I40. Thefour plates effect a removal of 1 fraction.- of twice the volume of a pair of plates of Fig. 1. A fractionating still capable of removihg several fractions is constructed by mounting several units identical to that of Fig. 5 on one shaft and connecting them together as in Fig. 1.

The removal scoops shown in Figs. 2 and 3 can be usedon either of the surfaces. In some cases small amounts are not removed and the periphery can be equipped with a gutter. A col-' lecting device is shown in Figs. 7, 8 and 9 which 'efiiciently operates as the sole removing device place. During rotation, element I scrapes the liquid from the gutter and throws it into the conduit I10 which conveys it to any desired point.

In Figs. 10, 11 and 12, liquid from the revolving plate is received in a gutter from which it is withdrawn by a suitably located conduit. In Fig. 10, the plate 202 is vertical and the liquid in the gutter is prevented from dropping out by turned edges I06. In Fig. 11, the plate is horizontal. Splashing of liquid in the gutter is prevented by placing the slit at the top so that the plate is substantially out of contact with the body of liquid in the gutter. In Fig. 12 the shaft and plate assembly of Fig. 11 is mounted at an angle to increase the rate of fiow of liquid in the gutter to the lowest point at which the withdrawal conduit is located. I

During operation of the apparatus illustrated in Fig. 4, conduit I03 is connected to the high vacuum pumps (not shown).r Liquid to be distilled is introduced into distributing device SI by way of conduit III. The liquid is evenly distributed in the form of a thin film and flows down.

the walls of element 84 at the zone 01. This zone is heated to a temperature appropriate for removing the desired fraction. Undistilled residue fiows from the lowest pointof element into withdrawal conduit 83. Molecules vaporized from vaporizing zone 81 are condensedupon the and I00. The condensate .flowsdown the walls into the gutter 82 and-is withdrawn therefrom by conduit I04 and pump- I05 and delivered to distributing device v9,2 which evenly distributes it over the surface of zone 88 which is preferably heated to a lower temperature than zone 81.

The liquid flows over the heated wallsof 84 at zone 08 and vaporized constituents are condensed upon the walls of casing 80 in the area between gutters I00 and IOI. Condensate flows down the walls into gutter I00 and is removed therefrom by conduit I00 and pump I01 and delivered onto distributing device 93. This liquid then flows over zone 89 heated to a somewhat lower temperature and vapors removed at that zoneare collected in gutter IOI and delivered to distributing device 94 by way of conduit I08 and pump I09. The liquid then flows over zone 90, heated to'a still lower temperature where a final fraction is distilled which is collected in gutter I02 and is removed from the still by way of conduit H0.

In Fig. 5, distilland is introduced onto the top of vaporizing segment 90'. Undistilled residue flows to the horizontal portion at the base thereof where it collects and is redistributed onto the next segment 89' and so forth. This construction. results in more efficient distribution of distilland, as a thin film onto the vaporizing surfaces, and also has the advantage of increasing the clearance for removal of gas through conduit I03.

It will be apparent that the apparatus illustrated in the various figures can be considerably modified without departing from the spirit or scope of my invention. For instance, the number of vaporizing and condensing zones or plates can be varied greatly to suit the particular substance in question or degree of fractionation required. It is preferable to have the zones progressively decrease in area and according to some geometric ratio, such as /2; 1; /8 or 1; A; ,6,etc. Otherwise, considerable difiiculty and inconvenience is encountered in trying to regulate the successive zones so as to give only the required extent of distillation. Complete distillation on each zone might result in the absence of careful and constant control and no fractionation would, therefore, take place. The scoops for removing the liquid from the centrifugal surface can be constructed in a variety of forms other than those illustrated. It will be apparent that the scoop of Fig. 3 will vary in width according to the speed of rotation and that it should be as wide as the distance of travel of the liquid for each rotation. Otherwise, two or more scoops should be employed. When vertical rotating plates are used, such as used in Figure 10, the scoop should be located at the top of the plate, since the liquid removed can then flow by gravity to any-. point in the still. In this manner, the centrifugal liquid must obviously have a low vapor pressure -When separating a particular fraction, some of the volatile constituents which should havebeen first removed are still coming over, some;of' the heavier constituents which should waituntil later have started to come-over and some of the def sired components which should be distilling, fail to do sobecause they have gone to the wrong fractions. Accordingly, to obtain all of any one constituent, a very much larger fraction must be secured as a first fraction. On a second distillation, the desired constituent canbe concentrated further by distilling a large portion of the first fraction, the amount distilled being necessarily less than in the first step. This is more or less automatically controlled by varying the sizes of the plates as previously explained. The size of the fractions and the plates may vary according to various geometric decrements of which diminution by halving is probably the most useful. It is obvious that with such repeated distillations, thermal decomposition will be great and it is for this reason that the centrifugal apparatus is of such value for this purpose.

It will be apparent that the apparatus of Fig. 1 can be employed with several similar units in series, or that each pair of condensing and evaporating centrifugal plates can be a separate unit. Also, other obvious methods of recycling or mixing in order to concentrate a particular fraction can be practiced. For instance, if it is desired to concentrate a heavy fraction instead of a light one, the material to be distilled is passed successively over a series of evaporating plates at successively higher temperatures, distillate from each section is passed in a reverse direction, or to the next lowest temperature evaporating plate and the desired heavy fraction is withdrawn at one of the higher temperature plates after the removal of components of low volatility is substantially complete. The centrifugal plates are rotated at a speed such as to give the desired heating period. Speeds of between 250 and 30,000 R. P. M. will most generally be employed.

The invention permits an unlimited degree of fractionation, depending only upon the units employed. In order to increase the utility of such a fi'actionating still, it can be employed in connection with a reservoir for residue which can be recycled through or over the still surfaces. After all of one fraction has been recovered by continued recycling, the temperatures of the units can be adjusted for removal of a second fraction and the contents of the reservoir again recirculated through the still until all of that fraction has been recovered. Such operation permits one still to separate an unlimited number of components and to fractionate each component to a degree corresponding to the number of temperature or distilling zones in the still. The use of such a reservoir and the principles of recycling are more fully disclosed in my copending application No. 75,163, filed April 18, 1936.

The invention is applicable to high vacuum, distillation processes in general and particularly those in which the vaporizing and condensing plates are separated by unconstricted space. Such processes are well known in the art., It is advantageous in most distillations to have the condensing and evaporating surfaces separated by rather short distances, usually of less than about 1 foot. When distilling under molecular conditions, this distance is less than about the mean free path and usually about to 6 inches.

The pressure of residual gas in the space between the surfaces should be maintained at a suitable low value. When distilling under molecular conditions, the pressure should be about .1 mm. or less and preferably less than about .01 mm. such as .005 to .001 mm. I also contemplate employing high saturation distillation, such as described in my copending application No. 174,491, filed November 3, 1937. When operating in this manner, the vaporizing surface is maintained at a temperature sufliciently high to give a vapor stream of the distillate having a pressure of less than about 1 mm. of mercury, but of such density that the molecules of vapor travel more than five times their mean free path in passing to the condensing surface, and the pressure of residual gas is maintained lower than the pressure of the distilling molecules betweenthe two surfaces.

It is evident that my invention is not limited to the treatment of particular materials and that it is of general use for distilling organic substances which are distillable under high vacuum distillation conditions. Examples are the recovery of low or intermediate fractions from high boiling hydrocarbons and the distillation of animal and vegetable oils such as linseed, soy bean, cod liver, etc. oils to recover unsaturated glycerides, sterols or vitamin fractions.

In addition to the many advantages pointed out above, the apparatus of Fig. 1 has the distinct advantage that pumps for circulating fractions or cooling fluid are not required. The apparatus of Fig. 4- has the advantage that only distillate must be pumped. Both types are furthermore compact and easy to regulate and operate by a single set of controlling operations. The gravity column is excellent for most substances but with extremely thermal sensitive compounds the repeated and prolonged heating under gravity fiow conditions causes more or less decomposition. Due to the rapid heating in the centrifugal still of Fig. 1 such substances can be fractionated and refractionated without loss. It is to be noted that this is a result which has long been desired but which heretofore has not been possible.

What I claim is:

1. Apparatus for the separation of constituents of a mixture distillable under high vacuum, unobstructed path conditions which comprises in combination a series of pairs of closely adjacent rotatable surfaces, one of each pair being provided with a heater and adapted to serve as an evaporating surface and the other of each pair being adapted to be cooled and serve as a condensing surface, means for conveying condensate onto the evaporating surfaces in succession, and means for conveying undistilled residue onto the evaporating surfaces in reverse succession;

2. Apparatus for the separation of constituents of a mixture which is distillable under high vacuum, short path conditions, which comprises in combination a series of pairs of rotatable surfaces, one of each pair being provided with a heater and adapted to serve as an evaporatin surface and the other of each pair being pro-' vided with cooling means and adapted to serve as a condensing surface, means for maintaining a high vacuum between each pair of surfaces, means for collecting undistilled residue from each evaporating surface except the last of the series and passing it in succession over each evaporating surface of the series, a conduit for withdrawing undistilled residue from the last evaporating surface of the series, means for collecting condensate from each condensing surface and passof the series, but in an opposite direction to that in which undistilled residue is passed, means for introducing material to be distilled onto one of the evaporating surfaces and means for withdrawing, a final distillate from at least one plate which is remote in the series from the evaporating surface upon which the material to be distilled is introduced.

3. Apparatus for the separation of constituents of a mixture which is distillable under molecular distillation conditions which comprises in combination a series of closely adjacent pairs of rotatable surfaces, one of each pair being provided with a heater and adapted to serve as an evaporating surface and the other of each pair being provided with cooling means and adapted to serve as a condensing surface, means for maintaining a high vacuum between each pair of surfaces, a conduit for introducing material to be distilled onto the first of the series of evaporating surfaces, means for conveying condensate from each condensing surface, except the last to the evaporating surface of the next pair of the series,-

means for conveying undistilled residue from each evaporating plate, except the first, to the next evaporating'plate of the series, but in a succession reverse to that in which condensate is passed, means for removing undistilled residue from'the first evaporating plate and means for removing distillate from the last condensing plate.

4. Apparatus for the separation of constituents of a mixture distillable under high vacuum, short path distillation conditions. which comprises in combination a series of closely adjacent pairs of rotatable surfaces, one of each pair being provided with a heater and adapted to serve as an evaporating surface, these surfaces progressively decreasing insize from one end of the series to the other and the other surface of each pair being provided with cooling means and adapted to serve as a condensing surface, means for maintaining a high vacuum between each pair of surfaces, a conduit for introducingmaterial to be distilled onto the first and largest of the series of evaporating plates, means for withdrawing undistilled residue from this plate, means for conveying condensate from each condensing surface, except the last, to the next smallest evaporating surface of the next pair of plates, means for conveying undistilled residue from each evaporating plate to the next largest of the evaporating plates and means for collecting and withdrawing condensate from the condensing surface opposite the last and smallest evaporating surface.

5. Apparatus for the separation of constituents of a mixture distillable under high vacuum, short path distillation conditions which comprises in combination a series of pairs of closely adjacent rotatable surfaces, one of each pair being provided wltha heater and adapted to serve as an evaporating surface and the other of each pair being adapted to be cooled and serve as a condensing surface, conduits for conveying condensate onto the evaporating surfaces in succession and means for conveying undistilled residue onto the evaporating surfaces in reverse succession, the evaporating surfaces progressively decreasing in surface area according to a geometric ratio and in the same order as that in which condensate is passed thereover.

- KENNETH C. D. HICKMAN.