TECHNICAL FIELD This invention relates generally to continuous countercurrent devices for the separation of samples, and more particularly to an elution method and apparatus for continuous countercurrent chro atography of the type employing a rotating coiled tube, with gravimetric separa¬ tion means cooperating with said rotating tube.

BACKGROUND ART Various arrangements for countercurrent chromato- graphy have been developed to produce high efficiency solute partitioning in two-phase solvent systems. These systems generally use a stationary phase which is re¬ tained in the column while the mobile phase elutes through the system. In these prior systems, since the sample solution is introduced at the beginning of each operation, such systems are regarded as constituting batch separation techniques, and not continuous extraction processes.

However, continuous extraction processes necessitate "genuine" countercurrent flow, wherein two immiscible solvents move in opposite directions with respect to the separation column to allow continuous sample feedback and continuous enrichment and/or stripping of the ingre¬ dient or ingredients desired to be collected, present in a large quantity of liquid. Heretofore no satisfactory system for accomplishing this objective has been available.

The following prior U.S. patents illustrate the present state of the art:

Ito et al. 3,775,309

Ito et al. 4,040,742

Ito 4,051,025

Ito 4,058,460 SUMMARY OF THE INVENTION

In order to meet the above-described continuous-fl extraction requirement, the present invention employes the "genuine" countercurrent flow of two immiscible sol vents through a helical column to achieve high-efficien continuous solute extraction or partitioning. This extraction scheme will be useful not only in the separa tion of chemicals in research laboratories, but also in large-scale industrial applications, including reproces ing nuclear fuels and in eliminating hazardous pollutan from industrial waste water.

The principle employed is substantially as follows: When an end-closed coiled tube containing two . immiscible liquids is rotated in an acceleration field acting perpendicular to the axis of the coil, a dynamic equilibrium is established wherein the two liquids occ approximately equal volumes in each coil unit fromone end the coil (the head end) , and any excess of either phase remains at the other end of the coil (the tail end) . This dynamic equilibrium of the two phases enables a hi efficiency separation of solutes when the mobile phase eluted through the head end of the coiled tube. Both retention of the stationary phase and thorough mixing o the phases are attained in the coiled tube so as to separate solutes according to their partition coeffi- cients. For example, an efficiency of up to 10,000 theoretical plates has been achieved in the separation dinitrophenyl amino acids using the flow-through coil planet centrifuge technique.

In order to introduce "genuine" countercurrent flo through this rotating coiled tube, it is further necess to understand the following physical properties inheren in this dynamic equilibrium of two phases in the rotati coiled tube:

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1) It creates a linear pressure gradient from the head end to the tail end through the coiled tube. The maximum p ^c ressure difference Pmax can be calculated from the equation ^P max = ⁿ ( _H -P _L ⁾ 5 ^h where n denotes the number of coil units; p _L and p„ denote the densities of the lighter and heavier phases; g denotes the acceleration; and h denotes the helical diameter. Thus, if the two portions of the coil contain- i ⁿ g the two phases are connected with a tube, the liquids start to circulate through the newly created loop in a direction from the head to the tail end through the connecting tube.

2) When any amount of one phase is replaced by the other phase at any portion of the coil containing the two phases, the dynamic equilibrium is quickly reestablished by itself by "genuine" countercurrent flow of the two phases, i.e., forward movement of the former phase and backward movement of the latter phase. 3) There are two directions for introducing the flow through the entire length of the coiled tube. The head-tail elution with either phase results in retention of the other phase in the coiled tube, as described above. On the other hand, the tail-head elution with either phase elutes out both .phases until the entire column space is occupied by the same phase.

Accordingly, a main -object of the present invention is to provide an improved countercurrent chormatography system which overcomes the deficiencies and disadvantages of the previously-used systems employed in countercurrent chromatography.

A further object of the invention is to provide a novel and improved system for high-efficiency solute partitioning which employs countercurrent flow wherein two immiscible solvents move in opposite directions with respect to a separation column to allow continuous sample feeding and continuous collection of a desired ingredient or ingredients.

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A still further object of the invention is to pro¬ vide an improved method and apparatus for continuous-flo countercurrent chromatography of the type employing a rotating coiled tube, wherein separation and collection are affected by cooperation of gravimetric separation means with the rotating coiled tube, and wherein the out put flow may be selected to be either only the heavier phase or only the lighter phase of a two-phase mixture. A still further object of the invention is to pro- vide an improved continuous-flow countercurrent chromato graphy system which utlizes a rotating helical column to separate two phases of different densities and which fur ther utilizes pressure gradients derived from the differ ence in densities to produce a circulation aiding in the selective output of one or the other of the two phases. A still further object of the invention is to pro¬ vide an improved continuous-flow countercurrent chromato graphy system which employs a rotating helical column in a gravity field to separate two phases of different densities, which collects the two phases in a chamber at the head end of the column, which allows the lighter and heavier phases to become separated in said chamber, and which includes means to elute one or the other of sa two phases with high efficiency. . More general objects include providing for improved separation or extraction of components in a liquid; and providing a genuine countercurrent liquid-liquid separa¬ tion process and apparatus.

Further objects and advantages of the invention wil become apparent from the following description and claim and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic representation of a horizontal rotating coiled chromatography tube in a gra- vitational field, with inlet and outlet flow tube connections for two immiscible phases.

Figure 2 is a diagrammatic view showing a structura arrangement according to the present invention connected

to the head end of the chromatography tube of Figure 1 for eluting a desired phase.

Figure 3 is a diagrammatic view similar to Figure 2 but showing a modification of the structural arrangement. 5 Figure 4 is an enlarged vertical cross-sectional view taken longitudinally through the inner end portion of the elution pipe of Figure 3.

Figure 5 is a longitudinal cross-sectional view of a further modification of a chromatography column and head 10 end elution arrangement according to the present invention.

Figure 6 is a diagrammatic view of a further modified structural arrangement according to the present invention, using a shunt and settling chamber outside the rotating 15 part of the chromatography assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

On the basis of the above-described physical f ctors, there will now be considered the provision of "genuine" countercurrent flow through the rotating coiled chromato- 20 graphy tube.

Referring to the drawings, Figure 1 shows a rotating helically coiled tube 11 in an acceleration (gravitation) field g. The coiled tube 11 has ^' two pair ^' s of flow- connecting tubes, Ip and I to respectively feed and 25. collect phase I, and IIr_ and 11 C^., to respectively feed and collect phase II, where phases I and II are two immiscible' phases -in the rotating coiled tube 11. These flow- connecting tubes may be brought outside the rotating parts of the apparatus in a conventional manner with or 30 without the use of rotating seals, as will be presently discussed. The flow-connecting tubes may be provided with suitable control valves 12 to 15, as shown.

The flow-connecting tube II_ and I are located at the tail end of coiled tube 11 and the flow-connecting 35 tubes U _p and I _c are located at the head end.

Assume that the rotating coiled tube 11 contains phases I and II in a dynamic equilibrium state, with all valves 12 to 15 closed. It is then possible to introduce phase II through tube li _p and collect the same

through tube II _C by opening valves 14 and 12 to establis countercurrent flow of phase II through the coiled tube However, introduction of phase I through tube I„ to collect this phase exclusively at I-, is difficult becaus in this situation both phases will be eluted at tube I,,. This difficulty can be solved, however, by utilizing one of the following two possible methods:

1. Employ a selecting device at the head of the coiled tube 11 arranged such that only phase I is eluted through tube I .

2. Take out the mixture of phases I and II in suc a way that the ^' flow rate of phase I through tube I _c is equal to the feed rate of phase I through tube I _p while returning the eluted phase II into the coiled tube 11 through a loop established between tubes I_ and II_. Figures 2 to 5 show examples of head end phase- selecting devices utilizing the first of the above two methods.

Figures 2 and 3 illustrate the use of a hollow cylinder 16 which is connected to the head end of the coiled tube 11 and is mounted to rotate coaxially there¬ with, whereby the acceleration g acts perpendicularly to the axis of the cylinder. Two-phase mixture introduced from the head of coiled tube 11 into the cylinder 16 can then be separated by the acceleration field into two phases, the heavier phase being at the bottom and the lighter phase being at the top, with an interface at 17, as shown in Figure 2. These two phases remain substan¬ tially stationary relative to the acceleration field g, while the rotating cylinder moves relative to said two phases. Thus, if the input portion of collection tube I stays always in the lower part of the cylinder 16, this permits only the heavier phase to be eluted, and if the input portion of collection tube I _c stays always in the upper part of said cylinder, this permits only the light phase to be eluted through I .

The phase-selecting device of Figure 2 comprises a flexible tube 18 extending rotatably and sealingly throu the center of the circular end cylinder wall 19 and

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leading to collecting tube I _p . Flexible tube 18 has a weight (or float) 20 secured thereon close to its inner end. If the density of the element 20 is substantially greater than that of the heavier phase, it forces the inner end of tube 18 to be always positioned in the heavier phase, and if the density of element 20 is substantially less than that of the lighter phase, it acts as a float and forces the inner end of flexible tube 20 to stay always in the lighter phase. Thus, by suitable selection of the density of element 20, either the heavier or the lighter phase may be eluted at I_.

Figures 3 and 4 show another embodiment similar to Figure 2 wherein the .eluting tube Ip comprises a rigid pipe 21 extending rotatably and sealingly through the center of the cylinder end wall 19 and being provided with an end closure cap 22 threadedly engaged on a reduced end portion 23 of the pipe. Said reduced end portion is provided with a plurality of flow holes 24. An annular groove is thus defined between cap 22 and the shoulder 26 adjacent reduced portion 25. A ring member 27 is freely rotatably mounted on the pipe, said ring member having an inner annular retaining rib 28 _, which engages rotatably in said annular groove. The ring member is provided with a radial outlet tube _o 29 on which is mounted a weight (or float) 20 similar to that employed in Figure 2. Thus, the ring mem¬ ber 27 can freely rotate around the pipe 21 as a bearing, while permitting flow from the outlet tube 28 through the perforations 24 in the reduced pipe portion 23. The proper selection of the density of the weight or float element 20 biases the outlet tube 29 downwardly or upwardly in the rotating cylinder 16 to permit elution of the desired phase into collection tube I _r .

Another embodiment which is functionally generally similar to that of Figure 2 is illustrated in Figure 5, wherein the design of a coiled column with a cylinder is simplified by employing a cylindrical, elongated, precision-bore casing 30 inwhich is tightly secured a threaded rod 31 which is sufficiently shorter than the length of the casing so as to define a cylindrical space

32 at the head end of the helical column defined by the heli space 33 between the rod 31 and the inside surface of th casing 30. As in Figure 2, a flexible tube 18 may be employed, extending rotatably and sealingly through the center of end wall 34 of casing 30, with a weight or flo 20 secured on its inner end, to define the elution colle tion conduit I _p . Alternatively, the pipe 21, ring 27, radial tube 29, and weight or float 20 of Figures 3 and may be employed in the embodiment of Figure 5. Figure 6 shows an embodiment which employs the sec of the above-described possible methods, namely, which u a shunt and settling chamber outside the rotating part. Figure 6 shows the use of an arrangement which allows co tinuous countercurrent extraction by employing a shunt S between the flow tubes Ip and 11- and including a settl chamber 40. Phase mixture eluted through I _p first enter the settling chamber 40, where phase separation takes place in the gravitational field. Phase I (in this case the heavier phase) is removed from the bottom of the settling chamber through a flow regulator 41 at a rate equal to the feed rate of phase I through I _p . (If phase I is the lighter phase it is removed from the top portio of the settling chamber rather than from the bottom.) Then, in the case illustrated in Figure 6, phase II (in this case the lighter phase) separated in the chamber 4 spontaneously enters S and II to return into the coiled tube 11 due to the pressure difference between the points of connection of II- and I _p to coiled tube 11, as previ¬ ously described. Phase II pumped through U _p is mixed with the same phase entering through S and then enters t coiled tube 11, where it splits into two streams, one flowing toward the rail of the coiled tube 11 and eluted through I at the rate equal to the feed rate through Up, and the other flowing toward the head end of the coiled tube 11 to circulate through the loop defined by settling chamber 40 and shunt element S.

In operation of the apparatus, the entire space of the coiled tube 11 is first filled with the extraction phase (phase II) . Elimination of air bubbles from

coiled tube 11 can be completed by introducing the solvent from the tail into the rotating coiled tube. After closing valve 12 at IL, the sample phase (phase I) which contains solute or solutes to be extracted, is introduced through I _p , and a flow regulator employed on I _r is adjusted to elute the solvent at the same rate. When phase I starts to elute through I , the extraction phase . (phase II) is intro¬ duced through Up and the valve on IL is opened to elute the same phase. When the optimal conditions of flow rates and rotational speed are chosen, the steady "genuine" countercurrent flow will soon be attained in the portion of the coiled tube between the inlets of I _p and U _p .

Applicable flow rates of the two phases depend upon various factors such as: 1) column factor (internal diameter, helical dia¬ meter and length of the tube) ,

2) apparatus factor (acceleration field and rota¬ tional speed) , and

3) solvent factor (interfacial tension, viscosity, and density difference of the two phases)-, and should be determined by preliminary experiments.

Rotation of the coiled tube 11 with respect to the gravitational and/or centrifugal acceleration fields may be accomplished by conventional means, for example, as shown in U.S. patents 3,775,309; 4,051,025; and 4,058,460, above cited. All flow tubes of the rotating coiled tube 11 are brought to the outside of the rotary member of the apparatus either with or without the use of the rotating seals. U.S. patent 3,775,309 shows an arrangement provid- ing a rotating centrifugal force field without the use of rotating seals. U.S. patent 4,051,025 shows an arrange¬ ment including a slowing rotating coiled tube in the gravitational field. Although it requires two sets of rotating seals, it can be conventionally and economically adapted for large-scale industrial use. Likewise, the arrangement of U.S. patent 4,058,460 can utilize both gravitational and centrifugal acceleration fields without the use of rotating seals. Therefore, it is suitable for both small-scale laboratory use and large-scale industrial

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applications.

While certain specific embodiments of continuous countercurrent devices for the separation of samples, us a rotating chromatography column, have been disclosed in the foregoing description, it will be understood that various modifications within the scope of the invention may occur to those skilled in the art. Therefore it is intended that adaptations and modifications should and a intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

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