WO2013121220A1

WO2013121220A1 - Ionic liquid separations

Info

Publication number: WO2013121220A1
Application number: PCT/GB2013/050374
Authority: WO
Inventors: Martyn Earle; Kenneth Seddon
Original assignee: The Queen's University Of Belfast
Priority date: 2012-02-16
Filing date: 2013-02-15
Publication date: 2013-08-22
Also published as: GB201202707D0

Abstract

A process for the separation of inorganic compounds comprises centrifugal partitioning of at least one inorganic compound between a mobile liquid phase and an immiscible stationary liquid phase. At least one of the mobile liquid phase and the stationary liquid phase comprises or consists of an ionic liquid. A rotary coil centrifuge for counter current chromatography and a liquid-liquid chromatography or liquid-liquid extraction apparatus may be used in the process.

Description

Ionic Liquid Separations

This invention relates to the use of ionic liquids in processes for separating inorganic compounds which rely on the partitioning of the compounds between immiscible liquid phases. This invention also relates to chromatography apparatus and to extraction apparatus and, more particularly to such apparatus comprising an ionic liquid as well as one or more inorganic compounds to be separated.

Extraction and chromatography apparatus include, inter alia types of apparatus referred to in the art as liquid-liquid chromatographs or hydrodynamic counter current chromatographs or hydrostatic counter current chromatographs (also referred to as centrifugal partition chromatographs).

Many of the ways that chemical compounds can be separated for analytical or bulk purification purposes rely on the way in which different compounds partition between immiscible substances (for example a liquid and a solid, a gas and a solid, a gas and a liquid, or two immiscible liquids). In one form this may involve the simple extraction of a substance from one liquid phase into a second liquid phase that is immiscible with the first, or the adsorption of a substance from a liquid or gas onto a solid material. In another form, chromatographic techniques enable the separation of two or more chemical compounds by reliance on differences in the extent to which they partition between immiscible substances.

In general, chromatographic separations are based on the distribution of compounds between a fluid termed the "mobile phase" and another substance termed the "stationary phase". For example, in liquid chromatography, a mobile liquid phase passes over a stationary phase in the form of a packed bed of a finely divided particulate solid, such as silica. In gas chromatography, a gaseous mobile phase, such as helium or nitrogen, passes over a liquid stationary phase (usually supported on an inert solid). As the mobile phase is passed over or through the stationary phase, differential partitioning of compounds between the mobile and stationary phase occurs. Compounds that partition towards the stationary phase travel through along the flow path of the chromatographic apparatus more slowly than those which partition towards the mobile phase. As a result, different compounds elute from the chromatographic apparatus at different rates, and can be collected as discrete fractions. The degree to which a compound partitions between the mobile and stationary phases is quantified as the partition coefficient. For the purposes of the present invention, the partition coefficient of a compound is defined as the ratio of the concentration of the compound in the mobile phase to the concentration of the compound in the stationary phase at a defined temperature and pressure.

Counter-current extraction and counter-current chromatography (also referred to as CCC or liquid-liquid chromatography) are separation techniques in which compounds partition between a biphasic mixture comprising a liquid stationary phase and a liquid mobile phase. Compounds in this system exchange between the liquid stationary phase and the liquid mobile phase and the relative partition coefficients of different compounds control the speed with which they elute from the CCC column. Typically these liquid- liquid separation techniques rely on a density difference between the liquid phases to maintain the stationary liquid phase in position by physical means. Usually a centrifuge is used for this purpose.

There is some confusion of the nomenclature in liquid-liquid chromatography. Historically the phrase counter-current-chromatography, CCC was used to mean liquid-liquid chromatography. The name CCC implies that liquids move in opposite directions. Typically however, in many cases referred to as CCC only one phase is actually mobile. Thus, there may not actually be any counter-current flow in CCC. The phrase centrifugal partition chromatography (CPC) has also been used. In general, the phrase CPC refers to sun-centric rotational liquid-liquid chromatography. Planetary centrifuge systems are often referred to as hydrodynamic CCC. Sun-centric systems may be referred to as hydrostatic CCC. The efficiency of chromatographic separations is improved by ensuring that the partitioning of each of the compounds to be separated is as close to the equilibrium partition coefficient as possible. In the context of liquid chromatography, this is usually achieved by the use of an extremely finely divided solid phase in order to maximise the interactions between the compounds to be separated and the mobile and stationary phases. In liquid-liquid chromatography, a similar effect has been obtained by the use of High Speed Counter-Current Chromatography (HSCCC), which is sometimes called Hydrodynamic CCC or High-Performance CCC.

HSCCC, sometimes called high-speed counter-current chromatography (HSCCC) or high-performance counter-current chromatography and general CCC typically employs "columns" wound as coils onto the rotors of a planetary centrifuge. Such apparatus typically comprises a coil of inert tubing carried on a bobbin, which spins on its own axis whilst the bobbin as a whole rotates eccentrically (orbits) about some other (main) axis. The spinning rotation of the coil about its own axis can be thought of as planetary rotation whilst the rotation of the coil as a whole can be thought of as an orbit about the main axis - hence the name, planetary centrifuge. This motion is particularly advantageous because it provides periodic variations in the centripetal acceleration of fluids carried in the coil. These variations provide a cycle comprising two stages: (1 ) a mixing stage during which centripetal acceleration is comparatively low; and (2) a centrifugation stage during which centripetal acceleration is comparatively much higher. The shear stresses, tensile stresses and pressure variations to which fluids are subjected by planetary centrifuges vary rapidly between these two extremes and this has the advantage of providing speedy and efficient mixing and separation in biphasic liquid-liquid systems. As the liquid phases move through the column a series of mixing and separating zones are set up in the column. The term "ionic liquid" as used herein refers to a liquid that is capable of being produced by melting a salt, and when so produced consists solely of ions. An ionic liquid may be formed from a homogeneous substance comprising one species of cation and one species of anion, or it can be composed of more than one species of cation and/or more than one species of anion. Thus, an ionic liquid may be composed of more than one species of cation and one species of anion. An ionic liquid may further be composed of one species of cation, and one or more species of anion. Still further, an ionic liquid may be composed of more than one species of cation and more than one species of anion.

The term "ionic liquid" includes compounds having both high melting points and compounds having low melting points, for example at or below room temperature. Thus, many ionic liquids have melting points below 200 °C, particularly below 100 °C, around room temperature (15 to 30 °C), or even below 0 °C. Ionic liquids having melting points below around 30 °C are commonly referred to as "room temperature ionic liquids" and are often derived from organic salts having nitrogen-containing heterocyclic cations, such as imidazolium and pyridinium-based cations. In room temperature ionic liquids, the structures of the cation and anion prevent the formation of an ordered crystalline structure and therefore the salt is liquid at room temperature.

Ionic liquids are most widely known as solvents due to favourable properties including negligible vapour pressure, temperature stability, low flammability and recyclability. Due to the vast number of anion/cation combinations that are available it is possible to fine- tune the physical properties of the ionic liquid (e.g. melting point, density, viscosity, and miscibility with water or organic solvents) to suit the requirements of a particular application.

There is limited teaching in the art with regard to the use of ionic liquids in liquid-liquid separations. Previous work in this area by Berthod et al ( A new class of solvents for CCC: The Room Temperature Ionic Liquids, Journal of Liquid Chromatography and Related Technologies, 2003, 26:9-10, 1493-1508) has investigated the use of ionic liquids in liquid-liquid systems for the separation of organic compounds, specifically substituted benzenes. The use of such systems for the separation of inorganic compounds has not been considered. It would be expected in such systems that the combination of the cations and anions of the ionic liquid together with inorganic compounds, which may also comprise cationic and anionic components, would lead to an extremely complex mixture and thus extreme difficulties in obtaining effective separations. However, the present inventors have surprisingly found that ionic liquids are extremely effective media for the partitioning of inorganic compounds.

The investigations of Berthod further suffered from difficulties due to the viscosity of the ionic liquid phase. More specifically, it was found that it is not possible to use ionic liquids where they comprise more than 45%, of the total content of the hydrodynamic or hydrostatic CCC liquid system. The highest ratio of ionic liquid reported in the literature to date is a system comprising 45/10/45 water/acetonitrile/[1 -butyl-3- methylimidazolium][PF6] (also known as [Bmim][PF6]) (Solvent systems for counter current chromatography: An aqueous two phase liquid system based on room temperature ionic liquid - Alain Berthod, Journal of Chromatography A, 1151 (2007) 65- 73; Use of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate in counter current chromatography - Alain Berthod, Anal. Bioanal. Chem., (2004), 380, 168-177). The reason given for the use of these dilute systems is the need to limit the viscosity of the liquid phases to a few centipoise at most. More recent work by the same authors also makes clear the prejudice that ionic liquids cannot be used directly in any practical hydrodynamic or hydrostatic counter current chromatography system. The prejudice in the art that it is simply the viscosity of ionic liquids that give rise to problems in hydrodynamic or hydrostatic CCC have meant that attempts to address the problem have focussed solely on diluting the ionic liquid to reduce viscosity. However, where neutral solvents are present beyond certain critical levels, solutions comprising ionic liquid may lose most or substantially all of the particular benefits of ionic liquid chromatographic media. Reports suggest that in H₂0/ACN/[Bmim][PF6] systems a ratio of 40/20/40 is preferred, and attempts to use higher ratios of ionic liquid cause the liquid- liquid separation apparatus to fail. In such dilute mixtures, ionic liquids tend not to behave as ionic liquids at all and more closely resemble salts in solution.

The present inventors have now found that, not only are ionic liquids highly effective media for the separation of inorganic compounds, but that ionic liquids can be used in amounts well in excess of the upper limit proposed by Berthod. By avoiding the need to dilute ionic liquids to obtain a viscosity reduction, the processes of the present invention benefit from the unique structural and electronic properties of ionic liquids. More specifically, by appropriate configuration of coil bore size and coil length and coil tubing materials (such as, stainless steel, titanium etc) and by operational control of the rotation parameters of a rotary planet centrifuge, it is possible to employ ionic liquids in practical counter current chromatography systems. Examples of the invention include systems in which one phase of the liquid system is mobile and another phase is stationary. Examples of the invention also include systems in which two phases are mobile. Mobile phases may flow in different directions. Examples of the invention include hydrodynamic and hydrostatic CCC machines, planetary and sun-centric centrifuges, CCC and CPC and other forms of liquid-liquid chromatography instrumentation. Some examples include liquid systems comprising over 46% by weight, for example over 50 wt% of ionic liquid.

In a first aspect, the present invention provides a process for the separation of inorganic compounds comprising centrifugal partitioning of at least one inorganic compound between a mobile liquid phase and an immiscible stationary liquid phase, wherein at least one of the mobile liquid phase and the stationary liquid phase comprises or consists of an ionic liquid, and wherein the total ionic liquid content of the mobile and stationary phases is 15 wt% or greater. As used herein, the term "centrifugal partitioning" is used to refer to separation processes in which inorganic compounds partition between a mobile liquid phase and a stationary liquid phase under centrifugation. Preferably, the centrifugal partitioning involves passing the mobile liquid phase along a coiled flow path containing the stationary liquid phase wherein the coiled flow path is mounted on a centrifuge such that it rotates about its own axis. Most preferably, the coiled flow path is mounted on a planetary centrifuge as described above.

The term "centrifugal partitioning" is used herein to refer both to extraction processes and chromatography processes.

Thus, in some embodiments, the process of the present invention may be used for the liquid-liquid extraction of one or more inorganic compounds from the mobile liquid phase into the stationary liquid phase, or alternatively from the stationary liquid phase into the mobile liquid phase. Preferably, the process is used to extract one or more inorganic compounds from the mobile liquid phase into the stationary liquid phase.

In other embodiments, the process of the present invention may be used for the chromatographic separation of two or more inorganic compounds based on a difference in the partition coefficients of the compounds.

The ionic liquids used in accordance with the present invention may be defined by the empirical formula:

[Cat⁺][X^"] wherein [Cat⁺] refers to one or more cationic species; and

[X^"] refers to one or more anionic species.

In accordance with the present invention, [Cat⁺] preferably comprises a cationic species selected from: ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1 ,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, /so-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, /so-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, /so-thiadiazolium, thiazinium, thiazolium, iso- thiazolium, thiophenium, thiuronium, triazinium, triazolium, /so-triazolium, and uronium. More preferably, [Cat⁺] has a formula selected from:

wherein: R^a, R^b, R°, R^d, R^e, R^f and R⁹ are each independently selected from hydrogen, a Ci to C₂o, straight chain or branched alkyl group (preferably

Ci to Cio straight chain or branched alkyl),, a C₃ to C₈ cycloalkyl group, or a C₆ to Cio aryl group, or any two of R^b, R°, R^d, R^e and R^f attached to adjacent carbon atoms form a methylene chain -(CH₂)_q- wherein q is from 3 to 6; and wherein said alkyl, cycloalkyi or aryl groups or said methylene chain are unsubstituted or may be substituted by one to three groups selected from: Ci to C₆ alkoxy, C₂ to C12 alkoxyalkoxy, C₃ to C₈ cycloalkyi, C₆ to C10 aryl, C₇ to Cio alkaryl, C₇ to C10 aralkyl, -CN, -OH, -SH, -N0₂, -F, -C0₂R^x, -OC(0)R^x, -C(0)R^x, -C(0)NR^yR^z, or -NR^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl.

In this embodiment of the invention, [Cat⁺] preferably comprises a cation selected from:

wherein: R^a, R^b, R°, R^d, R^e, R^f, and R⁹ are as defined above. Still more preferably, [Cat⁺] preferably comprises a cation selected from:

wherein: R^a, R^b, R°, R^d and R⁹ are as defined above.

Preferably, [Cat⁺] comprises a cation selected from:

wherein: R^a and R⁹ are as defined above. Most preferably, [Cat⁺] comprises a cation having the formula:

wherein: R^a and R⁹ are as defined above.

Specific examples of preferred nitrogen-containing aromatic heterocyclic cations that may be used according to the present invention include:

emim [bmim] [MeOC₂mim]

H₃C- -(CH₂)₉CH₃

[hmim] [C₈mim] [C₁₀mim]

In another preferred embodiment of the invention, [Cat⁺] comprises a saturated heterocyclic cation selected from cyclic ammonium, 1 ,4-diazabicyclo[2.2.2]octanium, morpholinium, cyclic phosphonium, piperazinium, piperidinium, quinuclidinium, and cyclic sulfonium.

More preferably, [Cat⁺] comprises a saturated heterocyclic cation selected from:

wherein: R^a, R^b, R°, R^d, R^e, R^f, and R⁹ are as defined above.

Still more preferably, [Cat⁺] comprises a saturated heterocyclic cation selected from

and is most preferably:

wherein: R^a, R^b, R°, R^d, R^e and R⁹ are as defined above. In the aromatic and saturated heterocyclic cations described above, R^a is preferably selected from Ci to C₂o, linear or branched, alkyl, more preferably C₂ to Ci₅ linear or branched alkyl, still more preferably, C₂ to C12 linear or branched alkyl, and most preferably C₂ to C10 linear or branched alkyl. Further examples include wherein R^a is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n- heptadecyl and n-octadecyl.

In the cations comprising an R⁹ group, R⁹ is preferably selected from Ci to Ci₀ linear or branched alkyl, more preferably, Ci to C₅ linear or branched alkyl, and most preferably R⁹ is a methyl group.

In the cations comprising both an R^a and an R⁹ group, R^a and R⁹ are each preferably independently selected from Ci to C₂₀, linear or branched, alkyl, and one of R^a and R⁹ may also be hydrogen. More preferably, one of R^a and R⁹ may be selected from C₂ to Ci5 linear or branched alkyl, still more preferably, C₂ to Ci₂ linear or branched alkyl, and most preferably C₂ to Ci₀ linear or branched alkyl, and the other one of R^a and R⁹ may be selected from Ci to Ci₀ linear or branched alkyl, more preferably, Ci to C₅ linear or branched alkyl, and most preferably a methyl group.

In further preferred embodiments, R^b, R°, R^d, R^e, and R^f are independently selected from hydrogen and Ci to C₅ linear or branched alkyl, and more preferably R^b, R°, R^d, R^e, and R^f are each hydrogen.

In another preferred embodiment of the invention, [Cat⁺] comprises an acyclic cation selected from:

[N(R^a)(R^b)(R°)(R^d)]⁺, [P(R^a)(R^b)(R°)(R^d)]⁺, and [S(R^a)(R^b)(R°)]⁺, wherein: R^a, R^b, R°, and R^d are each independently selected from a Ci to C₂₀, straight chain or branched alkyl group, a C₃ to C₈ cycloalkyl group, or a C₆ to Cio aryl group; and wherein said alkyl, cycloalkyl or aryl groups are unsubstituted or may be substituted by one to three groups selected from: Ci to C₆ alkoxy, C₂ to Ci₂ alkoxyalkoxy, C₃ to C₈ cycloalkyl, C₆ to Cio aryl, C₇ to Cio alkaryl, C₇ to Cio aralkyl, -CN, -OH, -SH, -N0₂, -F, -C0₂R^x, -OC(0)R^x, -C(0)R^x, -C(0)NR^yR^z, or -R^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl and wherein one of R^a, R^b, R°, and R^d may also be hydrogen.

More preferably, [Cat⁺] comprises a cation selected from:

[N(R^a)(R^b)(R°)(R^d)]⁺, [P(R^a)(R^b)(R°)(R^d)]⁺, wherein: R^a, R^b, R°, and R^d as defined above.

In the acyclic cations defined above, R^a is preferably selected from Ci to C₂o, linear or branched, alkyl, more preferably C₂ to Ci₆ linear or branched alkyl, and most preferably C₄ to Ci4 linear or branched alkyl. Further examples include wherein R^a is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n- undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl and n-octadecyl.

In the acyclic cations defined above, R^b, R° and R^d are preferably independently selected from Ci to Cio linear or branched alkyl, more preferably, Ci to C₅ linear or branched alkyl.

Preferably two of R^b, R° and R^d, and more preferably each of R^b, R° and R^d, are selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl and n-hexyl.

Still more preferably, two of R^b, R° and R^d, and more preferably each of R^b, R° and R^d, are n-butyl or n-hexyl.

In one embodiment, R^a, R^b, R° and R^d are the same, and may be selected from any of the possibilities disclosed above. By way of example, R^a, R^b, R° and R^d may all be ethyl, n-propyl, n-butyl or n-hexyl.

In accordance with the present invention, [X^"] may comprise an anion selected from halides, sulphates, sulfonates, sulfonimides, phosphates, phosphonates, carboxylates, CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^".

More preferably, [X^"] comprises an anion selected from F^", CI^", Br^", I^", S0₄ ^2", R¹OS0₂0^", R²S0₂0^", (R²S0₂)₂N^", P0₄ ^3", R¹OP0₃ ^2", (R¹0)₂P0₂ ^", [R²P0₃]^2", R¹C0₂ ^", CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^", wherein: R¹ and R² are independently selected from the group consisting of C1-C10 alkyl, C₆ aryl, C1-C10 alkyl(C₆)aryl, and C₆ aryl(Ci-Ci₀)alkyl each of which may optionally be substituted by one or more groups selected from: -F, -CI, -Br, -I, Ci to C₆ alkoxy, C₃ to C₈ cycloalkyl, C₆ to C10 aryl, C₇ to C10 alkaryl, C₇ to C10 aralkyl, -CN, -OH, -SH, -N0₂, -C0₂R^x, -OC(0)R^x,

-C(0)R^x, -C(0)NR^yR^z, or -NR^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl, and wherein R² may also be fluorine.

Still more preferably, [X^"] comprises an anion selected from CI^", Br^", I^", S0₄ ^2", FS0₂0^", CF₃S0₂0^" (also referred to herein as triflate or OTf), CH₃S0₂0^", CH₃CH₂S0₂0^", 4- methylbenzene sulfonate (also referred to herein as tosylate or OTs^"), (CF₃S0₂)₂N^" (also referred to herein as bistriflimide or NTf₂ ^"), P0₄ ^3", HC0₂ ^", CH₃C0₂ ^", CF₃C0₂ ^", CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^".

Most preferably, [X^"] comprises an anion selected from CI^", Br^", CF₃S0₂0^", CH₃S0₂0^", (CF₃S0₂)₂N^", CH₃C0₂ ^", CF₃C0₂ ^", CN^", N0₃ ^", BF₄ ^" and PF₆ ^". For example the anion may be selected from CI^", Br^", OTf, NTf₂ ^", CH₃C0₂ ^", or CF₃C0₂ ^".

In further embodiments, [X^"] may comprise an amino acid anion. As used herein, the term "amino acid anions" refers to conjugate anions of naturally occurring amino acids as well as synthetic amino acids. Amino acid anions which may be used according to the present invention include alaninate, argininate, asparaginate, aspartate (as the monoanion and the dianion), cysteinate, cystinate (i,e, the disulfide linked dimer of cysteine, as the monoanion and the dianion) glutamate (as the monoanion and the dianion), glycinate, histidinate, isoleucinate, leucinate, lysinate, methioninate, phenylalaninate, prolinate, serinate, threoninate, tryptophanate, tyrosinate, valinate, and taurinate.

Preferred amino acid anions which may be used as the ionic liquid anion in the process of the invention include serinate, prolinate, histidinate, threoninate, valinate, asparaginate, lysinate taurinate, and cystinate.

In view of the foregoing disclosure, it will be appreciated that the present invention is not limited to ionic liquids comprising cations and anions having only a single charge. Thus, the formula [Cat⁺][X^"] is intended to encompass ionic liquids comprising, for example, doubly, triply and quadruply charged cations and/or anions. The relative stoichiometric amounts of [Cat⁺] and [X^"] in the ionic liquid are therefore not fixed, but can vary to take account of cations and anions with multiple charges. For example, the formula [Cat⁺][X^"] should be understood to include ionic liquid species having the formulae [Cat⁺]₂[X^2"]; [Cat²⁺][X^"]₂; [Cat²⁺][X^2"]; [Cat⁺]₃[X^3"]; [Cat³⁺][X^"]₃ and so on.

The ionic liquids used in accordance with the above aspects of the present invention are liquid at the operating temperature of the centrifugal partitioning process. Thus, the ionic liquids preferably have a melting point of 50 °C or less, more preferably 40 °C or less, more preferably 30 °C or less, still more preferably 25 °C or less, still more preferably 20 °C or less, and most preferably 15 °C or less, for instance 10 °C or less or 5 °C or less.

The ionic liquid preferably has a viscosity at 20 °C of 1000 cP or less, more preferably 500 cP or less, still more preferably 200 cP or less, and most preferably 100 cP or less.

The ionic liquid may have a viscosity at 20 °C of at least 1 cP, for example the ionic liquid may have a viscosity at 20 °C of at least 5 cP, such as at least 10 cP, at least 20 cP, at least 30 cP, at least 40 cP, at least 50 cP, at least 60 cP, at least 70 cP, at least 80 cP, at least 90 cP or at least 100 cP.

As noted above, the ionic liquid may be used as the stationary phase or the mobile phase. The other one of the stationary phase and the mobile phase may comprise one or more solvents which form a biphasic mixture with the ionic liquid phase and which are preferably selected from organic solvents and water.

The choice of solvent used depends on the compounds to be separated or extracted and the type of ionic liquid phase used. Examples of solvents which may be used as the other liquid phase include:

i. hydrocarbon solvents, such as n-pentane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, benzene, toluene, xylenes, and mixtures of hydrocarbons such as petroleum ether (for instance the fractions boiling in the range 40 to 120 °C);

ii. chlorinated hydrocarbon solvents, such as dichloromethane, chloroform, trichloroethylene, 1 ,2-dichloroethane, and 1 , 1 , 1 -trichloroethane; iii. ethers, such as diethyl ether, di-iso-propyl ether, methyl-tert-butyl ether, and tetrahydrofuran;

iv. esters, such as ethyl acetate and butyl acetate;

v. alcohols, such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, 5 iso-butanol, sec-butanol, tert-butanol and n-octanol;

vi. ketones, such as acetone and 2-butanone;

vii. other solvents, such as acetonitrile, acetic acid, dimethylformamide, and dimethylsulfoxide;

viii. water; and

10 ix. aqueous salt solutions, such as salt solutions comprising a phosphate anion and/or a potassium cation.

Mixtures of two or more of the above solvents may also be used in accordance with the present invention. Mixtures of three or more of the above solvents may also be used.

Preferred solvents include n-hexane, n-heptane, cyclohexane, dichloromethane, 15 chloroform, methyl-tert-butyl ether, ethyl acetate, methanol ethanol, n-propanol, iso- propanol, n-butanol, iso-butanol, acetone, acetonitrile, acetic acid, dimethylformamide, dimethylsulfoxide, water, and mixtures thereof.

Particularly preferred solvents include methanol ethanol, n-propanol, iso-propanol, n- butanol, iso-butanol, acetone, acetonitrile, acetic acid, dimethylformamide, 20 dimethylsulfoxide, water, and mixtures thereof.

In accordance with the present invention, it is most preferred that an ionic liquid is used as the stationary phase and a non-ionic liquid solvent is used as the mobile phase.

As noted above, the total ionic liquid content of the mobile and stationary phases is 15 wt% or greater. Preferably, the total ionic liquid content of the mobile and stationary 25 phases is 20 wt% or greater, more preferably 25 wt% or greater, more preferably 30 wt% or greater, and most preferably 40 wt% or greater.

In further preferred embodiments, the total ionic liquid content of the mobile and stationary phases is 46 wt% or greater, more preferably 50 wt% or greater, more preferably 55 wt% or greater, still more preferably 60 wt% or greater, and most preferably 30 65 wt% or greater. The total ionic liquid content of the mobile and stationary phases is preferably less than 80 wt%, more preferably less than 75 wt%, and most preferably less than 70 wt%.

Where the process of the present invention is used for liquid-liquid extraction of one or more inorganic compounds from the mobile liquid phase into the stationary liquid phase, the one or more inorganic compounds preferably have a partition coefficient that is 1.0 or less, more preferably 0.5 or less, more preferably 0.1 or less, still more preferably 0.05 or less, and most preferably 0.01 or less.

Where the process of the present invention is used for liquid chromatographic separation of two or more inorganic compounds, each of the compounds to be separated preferably has a partition coefficient in the range of from 0.1 to 10, more preferably in the range of from 0.2 to 5, still more preferably in the range of from 0.3 to 3, still more preferably in the range of from 0.4 to 2.5, and most preferably in the range of from 0.5 to 2.

Most preferably, the partition coefficients of the inorganic compounds to be separated differ by at least 0.05, more preferably by at least 0.1 , more preferably by at least 0.2, still more preferably by at least 0.3, still more preferably by at least 0.4, and most preferably by at least 0.5. Where the difference in partition coefficients of the inorganic compounds to be separated is small, it is generally preferred to use an increased flow path length in the liquid-liquid chromatography process.

The factors to be considered when selecting the mobile and stationary phases are directly analogous to those involved when selecting the phases for other types of chromatographic separations, such as HPLC, and depend largely on the polarity of the compounds to be separated. The selection of suitable solvent systems for the separation and extraction of chemical compounds falls within the routine tasks of the skilled person. Thus, where the partition coefficients are too high, the mobile phase may be modified so as to reduce the solubility of the compounds in the mobile phase. For instance, the solvent used as the mobile phase may be changed, or a mixture of solvents may be used to tailor the solubility of the compounds in the mobile phase. Alternatively, the stationary phase may be modified so as to increase the solubility of the compounds to be separated in the stationary phase. The converse applies where the partition coefficient is too low. One advantage of the present invention is that the polarity of the ionic liquid phase can readily be modified due to the wide range of ionic liquids that are available, such that the partition coefficients can be carefully tailored to optimise separation and extraction processes. For instance, the use of long chain alkyl groups as quaternising groups on the ionic liquid cation reduces the polarity of the ionic liquid and thus increases the solubility of non-polar compounds in the ionic liquid phase. The use of shorter chain alkyl groups on the ionic liquid cation and/or polar substituents on the ionic cation increases the solubility of polar compounds in the ionic liquid phase.

In some aspects of the invention, the retention of the stationary phase in the coil may be calibrated as a function of the mobile phase flow rate at a given temperature and coil rotational speed. It will be appreciated that as the flow rate increases or the rotational speed of the centrifuge is reduced, the tendency of the mobile phase to drive the stationary phase from the coil is increased. The use of calibration curves can therefore provide a useful means of rapidly identifying suitable operating conditions for a particular combination of stationary and mobile phases so as to maintain the required amount of ionic liquid in the coil during operation.

The mobile phase and/or the stationary phase may be at room temperature during the process of the present invention. In a preferred embodiment, the phase containing the ionic liquid is heated. More preferably, both the mobile phase and the stationary phase are heated. The mobile phase and/or the stationary phase may be heated to a temperature of at least 30 °C, such as at least 35 °C, and preferably at least 40 °C. Without wishing to be bound by any theory, it is believed that the higher temperates enhance separation and/or extraction by reducing the extent to which the ionic liquid sticks to the apparatus. The process of the present invention may be applied to the separation and/or extraction of a wide range of different inorganic compounds, with the only practical limitation being that the compound can partition between a stationary liquid phase and a mobile liquid phase, wherein at least one of the stationary and mobile liquid phases comprises or consists of an ionic liquid. In preferred embodiments, the process may be used to separate or extract metal salts. In principle, the process of the present invention may be used to separate or extract salts of any of the metals in the periodic table, but is particularly applicable to the separation or extraction of salts of the alkali metals, the alkaline earth metals and the transition metals.

In preferred embodiments, the process of the present invention is used to separate two or more salts of any of the metals in the periodic table, more preferably two or more salts of the alkali metals, the alkaline earth metals and the transition metals.

In further preferred embodiments, the process of the present invention is used to separate three or more salts of any of the metals in the periodic table, more preferably three or more salts of the alkali metals, the alkaline earth metals and the transition metals. Examples of salts which may be separated according to the process of the present invention include those containing metal cations selected from Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr^2*, Ba²⁺, Sc³⁺, Ti³⁺, Ti⁴⁺, V²⁺, Cr^2*, Cr³⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu⁺, Cu²⁺, and Zn²⁺.

It is preferred that the each of the metal salts has the same anion. It is still more preferred that each of the metal salts has the same anion as the ionic liquid. In this way, it is possible to avoid possible metathesis of the salts during separation which could potentially lead to a complex mixture of products.

In preferred embodiments, the metal salt may be paired with one or more anions selected from halides, sulphates, sulfonates, sulfonimides, phosphates, phosphonates, carboxylates, CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^".

More preferably, the metal salt may comprise an anion selected from F^", CI^", Br^", I^", S0₄ ^2", R¹OS0₂0^", R²S0₂0^", (R²S0₂)₂N^", P0₄ ^3", R¹OP0₃ ^2", (R¹0)₂P0₂ ^", [R²P0₃]^2", R¹C0₂ ^", CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^", wherein: R¹ and R² are independently selected from the group consisting of C1 -C10 alkyl, C₆ aryl, C1 -C10 alkyl(C₆)aryl, and C₆ aryl(Ci -Ci₀)alkyl each of which may optionally be substituted by one or more groups selected from: -F, -CI, -Br, -I, Ci to C₆ alkoxy, C₃ to C₈ cycloalkyl, C₆ to C10 aryl, C₇ to C10 alkaryl, C₇ to C10 aralkyl, -CN, -OH, -SH, -N0₂, -C0₂R^x, -OC(0)R^x, -C(0)R^x, -C(0)NR^yR^z, or -NR^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl, and wherein R² may also be fluorine.

Still more preferably, the metal salt may comprise an anion selected from CI^", Br^", I^", S0₄ ^2", FS0₂0^", OTf, CH3SO2O^", CH3CH2SO2O^", OTs^", NTf₂ ^", P0₄ ^3", HC0₂ ^", CH₃C0₂ ^", CF3CO2^", CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^".

Most preferably, the metal salt comprises an anion selected from CI^", Br^", I^", S0₄ ^2", P0₄ ^3", HC0₂ ^", CH3CO2^", CF3CO2^", CN^", and N0₃ ^".

Examples of salts which may be separated in accordance with the present invention include LiCI, LiBr, Lil, Li₂S0₄, NaCI, NaBr, Nal, Na₂S0₄, KCI, KBr, Kl, K₂S0₄, MgCI₂, MgBr₂, Mgl₂, MgS0₄, CaCI₂, CaBr₂, Cal₂, CaS0₄, ScCI₃, ScBr₃, TiCI₃, VCI₂, CrCI₂, CrCI₃, MnCI₂, MnBr₂, Mnl₂, MnS0₄, FeCI₂, FeBr₂, Fel₂, FeS0₄, FeCI₃, FeBr₃, Fel₃, Fe₂(S0₄)₂, C0CI2, CoBr₂, Col₂, Co₂S0₄, NiCI₂, NiBr₂, Nil₂, Ni₂S0₄, CuCI, CuBr, Cul, Cu₂S0₄, CuCI₂, CuBr₂, Cul₂, ZnCI₂, ZnBr₂, Znl₂ and ZnS0₄. In a further aspect, the present invention provides the use of an ionic liquid as the stationary phase or the mobile phase in a process for the separation of inorganic compounds by centrifugal partitioning as defined above, wherein the total ionic liquid content of the mobile and stationary phases is 15 wt% or greater, 20 wt% or greater, more preferably 25 wt% or greater, more preferably 30 wt% or greater, and most preferably 40 wt% or greater.

In further preferred embodiments, the total ionic liquid content of the mobile and stationary phases is 46 wt% or greater preferably 50 wt% or greater, more preferably 55 wt% or greater, more preferably 60 wt% or greater and most preferably 65 wt% or greater. In accordance with this aspect of the invention, the ionic liquid is preferably as defined above.

In a further aspect there is provided a rotary coil centrifuge for counter current chromatography comprising:

a rotary bobbin configured to spin about a spin axis of the bobbin and to orbit a principal rotary axis of the centrifuge; a fluid line carried by the bobbin to provide a column for counter current chromatography wherein the fluid line is coiled so that it orbits of the spinning bobbin about the orbit axis provide planetary motion of the coil which includes a separating interval, and a mixing interval during which the centripetal acceleration of a part of the coil at closest approach to the orbit axis is relatively lower than the centripetal acceleration of the part of the coil most distant from the sun axis during the separating interval, a rotary drive operable to drive the bobbin in a rotary motion having a spin angular frequency of rotation about the spin axis and a principal frequency of rotation about the principal axis selected such that the linear acceleration of the part of the coil during the mixing phase is at least 2 G and less than 100 G and the linear acceleration of the part of the coil during the separating phase is not more than 500 G; and

a liquid system in the fluid line comprising an ionic liquid in an amount of 15 wt% or greater, preferably 20 wt% or greater, more preferably 25 wt% or greater, more preferably 30 wt% or greater, and most preferably 40 wt% or greater, and further comprising one or more inorganic compounds to be separated.

In a further preferred embodiment, the liquid system in the fluid line may comprise an ionic liquid in an amount of 46 wt% or greater, more preferably 50 wt% or greater, more preferably 55 wt% or greater, still more preferably 60 wt% or greater, and most preferably 65 wt% or greater, and further comprises one or more inorganic compounds to be separated.

In some examples the linear acceleration during the mixing phase is at least 5G. In some cases it is not more than 75G. These examples have the advantage that shear thickening induced effects in the ionic liquid do not cause blockages in the fluid lines. In some cases the linear acceleration of the part of the coil during the separating phase is not more than 300 G, in some cases it is at least 10G. In some cases it is at least 50G. In some possibilities it is not more than 200G. These types of apparatus have the advantage that, although ionic liquids may exhibit unpredictable behaviour in response to changes in shear stress, the selected ranges of linear acceleration during the mixing and separating phases enable the use of majority ionic liquid systems without the viscous effects which generate damaging back pressures. 1. Preferably the rotary drive is configured to rotate the bobbin at a frequency of at least 1000 rpm and preferably less than 5000rpm. Preferably the rotary drive is configured to rotate the bobbin at a frequency of at least 1200 rpm and preferably less than 3000rpm. Preferably the rotary drive is configured to rotate the bobbin at a frequency of at least 1400 rpm and preferably less than 2000rpm. Preferably the rotary drive is configured to rotate the bobbin at rotate the bobbin at a frequency of at least 1450 rpm and preferably less than 5 1900rpm. Typically the principal frequency of rotation about the principal axis (orbit frequency) is half the bobbin frequency. In some embodiments described herein a rotation controller is configured to control rotation of a centrifuge rotor to provide these same rotation frequencies.

In accordance with this aspect of the invention, the liquid system preferably comprises0 one or more ionic liquids as described above as well as the one or more inorganic compounds to be separated. The spin radius of the coil is preferably at least 45mm and it may preferably be less than 100 mm. The spin radius of the coil may preferably be at least 50mm and it may preferably be less than 90 mm. The spin radius of the coil is preferably at least 55mm and it may preferably be less than 90 mm. A preferable range is5 between 60.5mm and 83mm.

The orbit radius of the bobbin about the principal axis of the centrifuge is preferably at least 80mm; preferably at least 90mm; preferably at least 95mm. The orbit radius of the bobbin about the principal axis of the centrifuge is preferably less than 250mm; preferably less than 150mm; preferably less than 1 10mm. One preferable range is0 between 90mm and 100mm, e.g. 97.5mm.

The β value, e.g. the ratio of the spin radius of the coil to the orbit radius is preferably at least 0.4 and preferably less than 2. Preferably the β value is at least 0.5. Preferably the β value is at least 0.6. Preferably the β value is less than 1.5. Preferably the β value is less than 1.2. Preferably the β value is less than 1.0, or less than 0.9. One preferable5 range is between 0.62 and 0.85.

The ionic liquid can be present in a concentration of 46 wt% or greater of the chromatographic liquid system, preferably 50 wt% or greater of the chromatographic liquid system, preferably 55 wt% or greater, more preferably 60 wt%, and most preferably 65 wt% or greater of the chromatographic liquid system. In these cases the orbit radius0 may be least 5 mm and less than 9000 mm. Some examples have an orbit radius of at least 50mm. For example these may be less than 1 metre. It has been found that, although subject to rapid changes in pressure, tensile stress and shear stress, CCC coils having these parameters enable the use of higher ratios of ionic liquids.

In some cases, the coil may be arranged on the bobbin so that the ratio of the spin radius of the coil to the orbit radius of the bobbin about the principal axis of the centrifuge, β, is more than 0.3 and less than 2. This and other possibilities have the advantage of enabling the safe use of ionic liquids in CCC because efficient mixing is achieved during the mixing interval without applying shear stresses that may give rise to shear thickening.

In some of these particular examples the ratio, β, is less than 1.8 whilst the liquid system may have a viscosity of at least 5 centipoise. The bore diameter of the fluid line is preferably 0.2 to 200 mm whilst the diameter of the coil on the bobbin is 5 to 9000 mm. The ionic liquid carried in the fluid line may undergo a transition from a highly shear stressed state, during the mixing phase (where a high degree of turbulence would exist in a Newtonian fluid) to a state in which a shear-thickened liquid (analogous to a solid), would be under a high degree of tensile stress, e.g. during the separating interval. This combination of coil parameters provide a transition between these states which appears not to cause the unpredictable fluid dynamic effects which may generate excessive back pressures.

In some examples the ratio, β, is at least 0.5 whilst the liquid system may have a viscosity of less than 100 centipoise. These examples have the advantage that the advantageous chromatographic properties of ionic liquids can be exploited in coils of practical, useful, dimensions without the disadvantages reported by other work in this field.

In some cases the liquid system further comprises at least one solvent selected from the list consisting of:

ii. chlorinated hydrocarbon solvents, such as dichloromethane, chloroform, trichloroethylene, 1 ,2-dichloroethane, and 1 , 1 , 1 -trichloroethane;

iii. ethers, such as diethyl ether, di-iso-propyl ether, methyl-tert-butyl ether, and tetrahydrofuran; iv. esters, such as ethyl acetate and butyl acetate;

v. alcohols, such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol and n-octanol;

vi. ketones, such as acetone and 2-butanone;

viii. water; and

ix. aqueous salt solutions, such as salt solutions comprising a phosphate anion and/or a potassium cation. Mixtures of two or more of the above solvents may also be used in accordance with the present invention.

Preferred solvents include n-hexane, n-heptane, cyclohexane, dichloromethane, chloroform, methyl-tert-butyl ether, ethyl acetate, methanol ethanol, n-propanol, iso- propanol, n-butanol, iso-butanol, acetone, acetonitrile, acetic acid, dimethylformamide, dimethylsulfoxide, water, and mixtures thereof.

Particularly preferred solvents include methanol ethanol, n-propanol, iso-propanol, n- butanol, iso-butanol, acetone, acetonitrile, acetic acid, dimethylformamide, dimethylsulfoxide, water, and mixtures thereof.

In some examples the apparatus comprises a rotation controller operable to control the speed of rotation of the rotary bobbin about the orbit axis of the centrifuge at an angular velocity selected based on at least one of the internal radius of the fluid line, the density of the chromatographic medium and the viscosity of the chromatographic medium.

In some examples the apparatus comprises a pressure control means arranged to apply and/or limit pressure in the fluid line to a selected fluid pressure selected based on the density and/or viscosity of the chromatographic medium.

In some examples the pressure control means is operable to control the flow of fluid in the line such that the backpressure in the line does not exceed 1600 psi. In some cases the maximum pressure may be selected based on the burst pressure of the flying leads (fluid lines which supply the coils). In some embodiments the pressure control means comprises the rotation controller and controlling the pressure comprises controlling the speed of rotation so that fluid pressure in the fluid line does not exceed the burst pressure. The flying leads may comprise PTFE, PEEK, stainless steel or titanium. The burst pressure may be at least 1000 psi, although in some cases the burst pressure is at least 1600psi. In some cases the burst pressure is at least 2000psi. In one possibility there is provided a rotary coil centrifuge comprising: a fluid line configured to provide a column for counter current chromatography and coupled to a rotary bobbin of the centrifuge; a flow control means operable to control the flow of fluid in the line such that the backpressure in the line does not exceed the limiting pressure of the flying leads, limited to 1000 psi, or the coil tubing, which could be PTFE, PEEK, stainless steel or titanium tubing and can have a breaking stress of up to 12,000 psi. In some cases polymer tubing used for the coil may have a burst pressure/breaking stress of up to 200 psi.

In one possibility there is provided a rotary coil centrifuge comprising: a fluid line configured to provide a column for counter current chromatography and coupled to a rotary bobbin of the centrifuge wherein the internal diameter of the fluid line is at least 0.2 mm and less than 200 mm and the breaking stress of the fluid line is at least the limiting pressure of the flying leads (see above), e.g. 1000 psi. Where stronger materials such as stainless steel or titanium are used this pressure may be up to 12,000 psi.

There is also provided a counter current chromatography machine comprising: a rotary planet coil centrifuge having a fluid line configured to provide a column for counter current chromatography and coupled to a rotary bobbin of the centrifuge, wherein the rotary bobbin is configured to spin about a spin axis and to orbit a principal axis of the centrifuge to provide a planetary motion; a rotary drive operable to drive the bobbin in a rotary motion having a spin angular frequency of rotation about the spin axis and a principal frequency of rotation about the principal axis; a controllable fluid supply means operable to provide a fluid into the fluid line at a selected pressure; a controller configured to control at least one of the rotary drive and the fluid supply means such that the fluid pressure in the fluid line does not exceed a selected threshold pressure.

In an aspect there is provided a liquid-liquid chromatography or liquid-liquid extraction apparatus comprising: a first duct for channelling a flow of a liquid comprising an ionic liquid, the first duct being carried on a centrifuge rotor arranged to provide cyclic variations in the centripetal acceleration of the first duct so that the liquid flowing in the first duct is mixed and separated in accordance with the cyclic variations in centripetal acceleration; a pump coupled to the first duct to provide a flow of liquid into the first duct; a flow controller adapted to control the flow of liquid from the pump into the first duct; a rotation controller configured to control rotation of the centrifuge rotor and thereby the centripetal acceleration of the fluid in the first duct; a second duct coupled between a stationary mounting and the centrifuge rotor, and arranged to carry the flow of liquid to the first duct to join with the first duct at a joint coupled to the centrifuge rotor, the second duct being flexible and having an internal cross section selected to match the internal cross section of the first duct so that the pressure drop per unit length at the joining point is less than or equal to the pressure drop per unit length along the first duct and the second duct.

Preferably the flow controller comprises an injection valve, which may be controlled by a computer or other control logic, and/or based on a pressure sensor measurement. In some examples the apparatus comprises the liquid and the liquid comprises at least 50% by weight of the ionic liquid, which may be selected from anyone described herein. These and other examples have the advantage that fluid pressure is substantially continuous along the liquid ducts to inhibit the creation of bottlenecks in the liquid system which has been found to enable the use of ionic liquids in concentrations that have not previously been usable.

The flow controller may be configured to control the flow of a liquid comprising an ionic liquid into the first duct, so that a selected fraction of the capacity of the first duct is filled with the liquid, and the rotation controller and the flow controller may be configured so that, once the selected fraction has been filled with the liquid, the rotor is rotated for a time interval during which no further flow of liquid is provided into the first duct. This has the advantage that the liquid in the duct is able to reach an equilibrium state which has been found to enable the use of ionic liquids in amounts exceeding 50% by weight of the total liquid in a centrifuge.

The rotation controller may be configured to rotate the rotor at a constant rate during this time interval prior to introduction of further fluid. Further advantageously, the flow controller can be controlled to provide a second liquid into the first duct after the time interval has elapsed. This second liquid typically comprises a solvent having a substantially lower viscosity than the first liquid. The second duct may be arranged so that the pressure drop per unit length along the second duct is less than the pressure drop per unit length along the first duct. In some possibilities at least one of the flow controller and the rotation controller are configured to control a respective one of the rotation of the centrifuge and the flow of liquid into the centrifuge so that the liquid pressure in the first duct does not exceed 1600psi. This has the advantage that continuous operation of the apparatus can be ensured without the ionic liquids causing pressure/shear thickening induced blockages in the ducts. In some cases the centrifuge comprises a rotary planet centrifuge and the first duct is carried on a rotary bobbin configured to spin about a spin axis of the bobbin and to orbit a principal rotary axis of the centrifuge. The first duct may be provided by a fluid line that is coiled so that orbits of the spinning bobbin about the orbit axis provide planetary motion of the coiled line. Preferably orbits of the bobbin provide a separating interval, and a mixing interval, during which the centripetal acceleration of a part of the coil at closest approach to the orbit axis is relatively lower than the centripetal acceleration of the part of the coil most distant from the orbit axis during the separating interval, thereby providing the cyclic variations in the centripetal acceleration.

In an aspect there is provided a rotary planet centrifuge comprising: a body, and a rotary bobbin mounted to the body and configured to spin about a spin axis of the bobbin and to orbit a principal rotary axis of the centrifuge, a first duct carried on the rotary bobbin and arranged such that, in use, orbits of the bobbin about the orbit axis provide planetary motion of the duct as the bobbin spins about its spin axis, a second duct coupled to the first duct for fluid to flow therebetween, wherein the internal cross section of the first duct is different from the internal cross section of the second duct, and the centrifuge comprises a coupling duct having a tapered internal cross section arranged to couple fluid between the first duct and the second duct.

The coupling duct may comprise a first mouth having an internal cross section selected for coupling to the first duct. The internal cross section of the first mouth may be the same as the internal cross section of the first duct. The coupling duct may comprise a second mouth having an internal cross section selected for coupling to the second duct. The internal cross section of the second mouth may be the same as the internal cross section of the second duct. The coupling duct can be arranged to provide fluid flow along the first duct through the first mouth, along the coupling duct, through the second mouth, and along the second duct, to provide fluidic coupling between the first duct and the second duct.

The internal cross section of the first duct may be greater than the internal diameter of the second duct. The tapered coupling may be arranged to provide a continuous transition in internal cross section between the ducts. The first duct may be provided by a fluid line that is coiled. Preferably orbits of the bobbin provide a separating interval, and a mixing interval, during which the centripetal acceleration of a part of the coil at closest approach to the orbit axis is relatively lower than the centripetal acceleration of the part of the coil most distant from the orbit axis during the separating interval, thereby providing the cyclic variations in the centripetal acceleration.

The internal surface of the first duct may comprise a material that does not comprise fluorine, preferably the internal surface of the first duct does not comprise PTFE. The internal surface of the first duct may comprise PEEK, or a metal such as steel or titanium.

In an aspect there is provided a rotary planet centrifuge comprising: a body, and a rotary bobbin mounted to the body and configured to spin about a spin axis of the bobbin and to orbit a principal rotary axis of the centrifuge, a first duct carried on the rotary bobbin and arranged such that, in use, orbits of the bobbin about the orbit axis provide planetary motion of the duct as the bobbin spins about its spin axis, wherein the internal surface of the first duct comprises a material selected from the list comprising: a material that does not comprise fluorine; PEEK; a metal; steel; and titanium. This may enable the use of ionic liquids in separations because the inventors in the present case have appreciated that ionic liquids adhere to materials which comprise fluorine thereby blocking the ducts and preventing operation of the centrifuge. Specific embodiments of the invention will now be described, by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a counter current chromatography machine; and,

Figure 2 shows a schematic drawing of a rotary coil planet centrifuge;

Figure 2B shows an arrangement for the flying leads of a rotary coil planet centrifuge such as that shown in Figure 2; Figure 3 shows a configuration of fluid flow into and out from a centrifuge;

Figure 4 shows a schematic drawing of a system in accordance with Figure 1 ;

Figure 5 shows calibration curves for stationary phase retention as a function of mobile phase flow rate, temperature and rotational frequency;

Figure 6 shows experimental data from the separation of CuCI₂, NiCI₂ and CoCI₂ using a CCC machine at 30 °C;

Figure 7 shows experimental data from the separation of CuCI₂, NiCI₂ and CoCI₂ using a CCC machine at 38 °C; and

Figure 8 shows experimental data from the separation of CuCI₂, NiCI₂ and CoCI₂ using a CCC machine at 46 °C. In Figure 1 a CCC machine comprises a liquid reservoir 104 comprising a source of the mobile phases, a liquid reservoir 106 comprising a source of the stationary phase, and a supply of pressurised gas 102. A pump 1 10 couples the mobile phase fluid from its reservoir 104 into an upstream inlet valve 1 12. A second pump 108 couples the stationary phase fluid from its reservoir 106 in to the same valve 1 12. The pressurised gas 102 is coupled to the valve 1 12 by a gas line.

The upstream valve 1 12 is coupled to a CCC centrifuge 1 by an injection valve 1 14 which controls the injection of fluids into the centrifuge 1. A fluid line 1 15 couples the injection valve 1 14 to coils on the rotor of the centrifuge. The fluid output from the centrifuge drains into a downstream valve 116. The down stream valve 1 16 is coupled to a waste fluid sump 122 and to a detector 1 18 by a fluid line 1 17. A fraction collector 129 may also be coupled to the fluid line for collecting selected fraction(s) of the liquids which elute from the centrifuge. The fraction collector 129 is operable to select particular fractions from material eluted from the centrifuge based on a signal from the detector 1 18. In this way the fraction collector can be configured to collect particular fractions of interest (as sensed by detector 1 18) whilst the rest of the eluted liquids are dumped.

An inlet pressure sensor 126 is arranged for sensing the pressure in the fluid line upstream of the injection valve 1 14, between the injection valve 1 14 and the upstream valve 1 12. An outlet pressure sensor 127 is provided at an outlet of the centrifuge 1 to sense the fluid pressure in the line 117, upstream of the downstream valve 116.

A computer 120 is coupled to the detector 1 18 to receive measurement data from the detector. The pressure sensors 126 and 127 are coupled to the computer 120 to provide pressure measurements of the inlet and outlet pressure of the centrifuge. The computer 120 is also coupled to control the pumps 108, 1 10, the valves 1 12, 1 14, 1 16 and the rotation speed of the centrifuge 1.

The computer 120 is configured to control the flow rate of liquids into/out from the centrifuge 1 based on the pressure sensed by the sensors 126, 127 and so that the fluid pressure at the inlet of the centrifuge does not exceed a selected threshold pressure. The threshold is selected based on at least one of: the rotation speed of the centrifuge; the pump flow rates; the viscosity of at least one of the phases of the liquid system; the pressure rating of the fluid lines on the centrifuge and/or the lines and fittings that couple the fluids to or from the centrifuge. The computer 120 is also configured to control the flow of fluids from the pumps 108, 1 10. Where the reservoir 104 includes more than one reservoir of fluid, the pump 108 includes a selector valve which is operable to select between these reservoirs of fluid to control the composition of the liquid from that reservoir. This enables computer control of the composition, and hence density and viscosity of the mobile phase. In addition to control of the pumps, controlling the flow rate of liquids into/out from the centrifuge 1 can be achieved by opening/closing the injection valve 1 14. Control can also be achieved by controlling the outlet valve 1 16. The computer 120 is configured to control the outlet pressure of the centrifuge (e.g. via valve 1 16) based on the pressure sensed at the injection valve by pressure sensor 126. The pumps 1 10, 108 are operable to provide flow rates of between from 0ml per minute and 1 litre per minute. The fluid pressure provided by the pumps is controllable in the range between 10 psi (6.895x10⁴ Pa) and 6000 psi (4.137x10⁷ Pa).

The upstream valves include solvent selection valve 1 12 and injection valve 1 14, are solenoid actuated valves. The upstream valve 1 12 comprises a multiport selector valve operable to couple one of a plurality of fluid inputs to a single fluid output.

The down stream valve 1 16 is substantially similar to the upstream solvent stream- switching valve and provides a 3-way selector valve to allow outflow from the centrifuge to be diverted to the waste or fraction collector, and/or to the detector. In overview, the CCC machine of Figure 1 operates as follows. The computer 120 controls the upstream valve 1 12 to couple the pumps 108, 1 10 to the columns (coils) of the centrifuge 1. The computer 120 then controls the pump 108 to prime the centrifuge 1 by filling the columns (coils) with the stationary phase fluid from the reservoir. The computer 120 then controls the centrifuge 1 to begin to rotate at a selected speed. The computer 120 is configured to control the centrifuge so that it rotates at a selected speed before it controls the pump 1 10 to begin the flow of mobile phase into the coil. In addition, the computer is configured to sense the temperature of the coils (e.g. using a temperature sensor such as a thermocouple) to determine that the operating temperature of the coils is within a selected temperature range before it controls the pump 1 10 to begin flow of the mobile phase into the centrifuge coil.

Once the computer 120 has determined that the rotation of the coil has stabilised and the temperature is within the selected range, it controls the pump 1 10 to deliver the mobile phase into the column through the upstream valve 1 12. The computer 120 then controls the upstream valve 1 12, the injection valve 1 14 and the pump 1 10 to control the flow of the mobile phase into the centrifuge 1 from the reservoir 104.

The computer 120 stores a look up table in memory which provides a relationship between rotation speed and mobile phase flow rate. Based on this relationship, the computer 120 controls the pump 1 10 and the rotation speed of the centrifuge 1 so that the flow rate of the mobile phase depends on the rotation speed of the centrifuge. As the mobile phase elutes from the coils of the centrifuge 1 it flows into the down stream valve 1 16, which is controlled to couple the eluted liquid into either the waste sump 122 or the detector 1 18. The detector 1 18 performs analytical measurements on the eluted fluid and communicates measurement data to the computer system 120.

5 Manually or under computer control the contents of the coil, stationary phase plus mobile phase and retained targets plus matrix, may be extruded by either stopping rotation or by pumping stationary phase or by switching to pump stationary phase while rotation continues. This action both enables the system to be ready for subsequent injections, and enables all materials injected onto the CCC coil to be collected, from solvent front 10 (non retained) to infinitely retained (had coil not been extruded) components.

The apparatus of Figure 1 comprises a single liquid reservoir 104 comprising a single source of the mobile phase liquid. However, there may be a number of such reservoirs and each of these reservoirs may comprise one or more liquid components of the mobile phase. Also, the liquid reservoir 106 may comprise a plurality of separate liquid 15 reservoirs and each reservoir may comprise one or more liquid components of the stationary phase. Although the pressured gas system may be used to blow liquid out of the coil the use of gas, and the presence of a gas system at all is optional, it need not be included.

At the outset of a process, e.g. a chromatography, separation or extraction process, the 20 fluids in the reservoirs 104, 106 contain target components in their start matrices to be separated. The components to be separated may be in either the upper phase or the lower phase. In some cases components to be separated may be present in both the upper and lower phases.

The down stream valve 116 is described as coupled to a waste fluid sump 122 a detector 25 1 18 and a fraction collector. In some cases one or more of these components may be omitted, or they may be provided in series, for example the fraction collector may be arranged so that fluid flows into the fraction collector after the detector. The fraction collector 129 may be controlled by the computer 120, for example based on a signal from the detector 1 18, to collect one or more fractions of interest. Although a fully computer controlled system has been described one or more functions may be manually controlled. In some examples a degree of computer control is provided and facility for manual control of some parameters can also be included. In some examples, process parameters which are computer controlled may also be controlled manually. In these examples the manual control typically takes precedence (overrides) the computer control. In these cases, where manually selected parameters influence other parameters in the system the computer 120 may be configured to adjust other operating parameters of the system to compensate, for example where an operator manually selects a particular flow rate for one of the two phases the computer 120 may be configured to adjust one or more parameters selected from the list comprising: the pump pressure applied to that phase of the liquid system; the pump pressure applied to a second, different, phase of the liquid system; rotation speed of the centrifuge; the percentage by weight of a component in that phase of the liquid system, for example to modify viscosity and/or density of that phase; the percentage by weight of a component in a second, different, phase of the liquid system, for example to modify viscosity and/or density of that second, different, phase.

The computer 120 may be a suitably programmed general purpose computer having appropriate input/output couplings for controlling the centrifuge or a dedicated processor may be provided, such as a dedicated DSP or FPGA. In some examples a dedicated (e.g. specifically designed) Human Machine Interface, HMI, unit is included.

The inlet pressure sensor 126 and outlet pressure sensor 127 are both optional. In some examples only one of these two pressure sensors may be present. In some cases no pressure sensor is present at all. In addition, or as an alternative, a human readable pressure gauge may be provided at the inlet and/or the outlets. Feedback control of the pumps based on sensed pressure data is described however in some systems this computer control can be provided manually by an operator monitoring an indication of pressure (e.g. from a pressure gauge) and trimming the pump flow rate(s) based on that monitoring. In some cases no feedback control is provided and the system runs using selected pressure, rotation speed and flow rate values. The computer 120 may not be configured to control the characteristics of fluids from the reservoirs. For example the reservoirs 104 and 106 may both comprise a single reservoir and the only control necessary may be the selection of a pumping rate and/or pressure. However either or both of the reservoirs 104 and 106 may include more than one reservoir of fluid as described above with specific reference to Figure 1. Where one of the reservoirs 104, 106 includes separate sub-reservoirs of different fluids the pump 5 coupled to that reservoir includes a selector valve which is operable to select between those sub-reservoirs. A selector valve may be solenoid actuated or controlled by a pneumatic or hydraulic system. The use of such selector valves means that, in addition to being able to control the composition of the mobile/stationary phase the computer may be operable to select the use of an entirely different liquid for use as a particular phase.

10 Controlling the flow rate of liquids into/out from the centrifuge 1 by opening/closing the injection valve 1 14 is optional. Although control may also be achieved by controlling the outlet valve 1 16 this too is not essential and the may be controlled by other means. Although the computer 120 may be configured to control the outlet pressure of the centrifuge (e.g. via valve 1 16) based on the pressure sensed at the injection valve by

15 pressure sensor 126 other configurations are possible, for example control may be provided based on the pressure difference sensed between the two pressure sensors 126 and 127, or from the pressure sensed at the outlet. In some cases the computer is configured to control the valve at the inlet based on the pressure at the outlet.

The computer 120 can be configured to control the speed and direction of rotation of the 20 centrifuge 1 (e.g. via control of a motor in the centrifuge) and is operable to start and stop rotation of the centrifuge 1. In some examples temperature sensors and other safety features such as leak detectors are coupled to the computer 120 and/or are arranged to provide visible or audible alert signals in response to a sensed safety condition such as the detection of a leak, sensing that the temperature has exceeded a selected level or 25 sensing that the rotation of the centrifuge has become unbalanced. In some examples the computer is configured to control the rotation of the centrifuge based on one or more of these safety parameters.

The pumps 1 10, 108 may be any type of typical laboratory scale pump and may be operable to provide fluid flows in the following ranges: 0 ml/min to 10 ml/min; 0 ml/min to 30 50 ml/min; 0 ml/min to 100 ml/min; 0 ml/min to 250 ml/min, 0 ml/min to 500 ml/min; and 0 ml/min to 1000 ml/min. The apparatus may be scaled up to process large volumes, in which case the pumps 1 10, 108 are selected to provide flows from as low as 10ml per minute up to 10Olitre/min, for example pumps rated for between 0 to 10 litres/min and 0 to 100 litres/min; laboratory scale pumps may also be used in larger volume processes. For these larger scale processes, the pumps 1 10, 108 may be operable to provide pressures of up to 10 psi or up to 3000psi.

The pumps 1 10, 108 may be manually controlled or may be controlled by an external computer or HMI. The pumps may be configured to provide controlled (e.g. variable) flow rate or to provide a constant flow rate with internal feed back loops to monitor flow and/or backpressure in the centrifuge coils to ensure operation with selected limits. The pumps can be configured to operate as multiple sets, e.g. to ration flows from one or more sources to allow defined mixing of liquids from multiple reservoirs. This has the advantage that pre-existing biphasic mixes do not always require pre-mixing and isocratic delivery. The pumps may be configured to pre-mix biphasic solvents and/or to vary the ratios of the solvents in the mixture so that the concentrations vary with time in a step-wise, linear or non-linear way.

The mobile phase may be a single solvent (isocratic elution) or two or more solvents may be provided and their relative compositions may change in a step, linear or non-linear manner (gradient elution).

The upstream valve 1 12 and injection valve 1 14, are described as being under computer control but may also be controlled manually. The particular arrangement of valves shown in Figure 1 may be varied, the valves may not be arranged in the configuration shown. For example, an upstream valve may be configured to the inlet of a pump to different solvent reservoirs. The pressure rating of the valves is preferably selected to match (or exceed) the pressure rating of the system in which they are used. In the case of the injection valve, the injection volume may be determined based on the volume of the sample loop. Although the valves are described as being solenoid actuated, this is optional and other types of valve may be used. For example the valves may be hydraulically or pneumatically controlled and/or manual control may be used. The down stream valve 1 16 may also be solenoid actuated controlled hydraulically, pneumatically or manually. The down stream valve is described as being a 3-way selector valve but other arrangements are possible. The example of Figure 1 indicates that fluid is pumped into the centrifuge from one end of the coils and elutes passively from the other. As will be appreciated, this is merely schematic and other configurations may be used, for example one phase of the liquid system (and/or a component thereof) may be pumped back into the coil from an opposite end to the other phase.

The computer 120 may be configured to control the rotation speed of the centrifuge based on the sensed pressure and may comprise a look up table which relates sensed pressure to a speed of rotation to enable the rotation speed to be selected based on the sensed pressure. This has the advantage of enabling on-the fly control of backpressure in the centrifuge coils without the need for complex calculations. In some cases, rather than using a look up table a calculating function (e.g. a subroutine) is provided to calculate the rotation speed based on the sensed pressure. This has the advantage of enabling more flexible and/or finely resolved control than a look up table approach. Other look up tables and/or functions/subroutines may also be used. For example the computer 120 may store a look up table of sensed pressure and pump pressure so that the computer can control the pressure provided by one or more of the pumps based on a sensed pressure measurement. The valves may be controlled in a similar way. However, the usage of such look up tables and/or the use of any computer control is optional and the system may be manually controlled or controlled to operate according to a pre- selected set of conditions. The pre-selected set of conditions may be determined from a calibration experiment.

The computer 120 may also be configured to control the pump 1 10 and the rotation speed of the centrifuge 1 so that the flow rate of the mobile phase depends on the rotation speed of the centrifuge. This is optional but, if this control is provided the control of mobile phase flow rate based on rotation speed may be provided based on a stored look up table. In these cases the computer 120 may index into the look up table using a sensed or desired mobile phase flow rate and retrieve a corresponding rotation speed based on that flow rate. Having retrieved the rotation speed value the computer 120 is configured to control rotation of the centrifuge so that it rotates at the selected speed. Conversely, where a particular rotation speed is desired, the computer 120 may index into the look up table using a sensed or desired rotation speed and retrieve a corresponding flow rate value from the look up table based on that rotation speed. This has the advantage that specific centripetal forces (and so specific mixing /settling conditions) can be applied for a selected flow rate.

In some cases the computer stores a look up table of critical limits or shut-off values such as pressure and/temperature limits. In these cases the computer is configured to determine that a critical value has been reached or exceeded and to shut off or decrease at least one of the pump pressure and or the rotation of the centrifuge. In some cases the computer 120 is configured to sound an audible and/or visual warning in the event that the sensed pressure and/or temperature reaches a selected percentage of a critical value. In the examples and embodiments described above control is provided by the computer 120, and this may be a suitably programmed general purpose computer. It will, of course, be understood that one or more computing apparatus may be used and that such computing apparatus may or may not be physically separated. In addition, it may be possible to implement the described examples and embodiments by use of hard-wired circuitry and one or more digital signal processors (DSPs), for example.

The functionality ascribed to the computer 120 need not necessarily be provided by one physical entity. As an example, the pumps 108, 1 10 may include the pressure sensing functionality 126 and may be configured to control their output pressure and/or flow rate in the manner described above. Connections indicated as being wired in Figure 1 may be wireless and, for example communicated using a wi-fi protocol such as IEEE802.1 1 n. In some cases, rather than multiple individual connections a single control BUS or loom may be used. In addition, the configuration of the computer 120 may where appropriate be provided by hard-wired elements, software elements or firmware elements or any combination of these. To initiate operation the computer 120 may control the pump 108 to prime the centrifuge 1 by filling the columns (coils) with the stationary phase fluid from the reservoir and the centrifuge 1 may then be controlled to begin to rotate at a selected speed. Different modes of operation are possible. Filling can be carried out after rotation has begun, or rotation may commence when the coil is part filled. If the coil is filled "on stop" (e.g. beginning filling when the coil is stationary) the CCC will ramp up to a selected speed in an appropriate manner, for example linearly. The computer of Figure 1 is configured to control the flow of mobile phase via pumps 108, 1 10 however flow from one or both of these pumps need not be adjustable/controllable. In some cases only one pump is present. In some cases the pumping rate/pressure is selected based on a calibration and held constant or varied according to a selected time-pressure profile.

The injection valve 1 14 need not comprise a sensor, a pressure sensor may be provided elsewhere in the apparatus and fluid coupled to sense pressure in the liquid system. Indeed, in some cases the pressure sensor is optional, particularly where the pumping rate/rotation speed is preselected based on a calibration so that sensing the inlet pressure (or other pressure in the system) is optional.

Figure 2 shows a schematic drawing of a rotary coil planet centrifuge 1 of a CCC machine such as that shown in Figure 1. The rotary planet centrifuge comprises an arm 2, which supports at least two bobbins 10, 20 equidistantly spaced about either side of a central axis 18. Each bobbin 10, 20 is carried on the arm by a bearing 4 which enables the bobbin 20 to rotate about the bobbin axis 22. The bobbins 10, 20 may be driven by a planetary gear arrangement or other rotary drive coupling such that as the bobbins.

The bobbins 10, 20 each carry a coiled fluid line 14, which provides the chromatography column for the chromatographic analysis. The fluid line comprises stainless steel and has an internal diameter of 3.7 mm. The wall thickness of the coil is 0.5mm. Other examples of working coil parameters are provided in the examples described below.

The fluid line 14 wound on the bobbin is 23.83m long wound in 52 turns and has a total internal capacity of 236 ml. The walls of the fluid line have a breaking stress of at least 200psi. The fluid line 14 is coupled to at each end (upstream valve 1 14 and downstream valve 1 16) to a flexible fluid line (also called a lead, flexible lead or flying lead), provides a flow path for fluid of the liquid system into/out from the coiled fluid line 14 of the centrifuge. The flexible leads and the coil are arranged to provide a substantially constant change of gauge pressure per unit length along the flow path. In this way bottle necks along the line are avoided which inhibits damaging pressure build ups. One way to achieve this is to provide a flexible leads 16 (flying leads) having a bore size that is matched to the bore size of the coil. It will be appreciated that the drawing of Figure 2 merely shows a schematic arrangement of the flying leads 16 in which for clarity only a single lead is indicated, typically flying leads will be provided in similar configurations at the outlet and inlets of each coil 14. Figure 3 shows one way to arrange the flying leads going into and out from the coils/bobbins.

To manage the backpressure in the fluid lines, as described above with reference to Figure 1 , the computer 120 of Figure 1 is configured to control the flow into the fluid line 14 of mobile phase via pumps 108, 1 10 and/or the speed of rotation of the CCC machine (Figure 1 ). The injection valve 1 14 in Figure 1 is configured to provide offline filling of a sample loop and the computer 120 is configured to switches this sample loop into the stream of liquid flowing into the CCC. In the arrangement of Figure 2 there is no centre shaft, the rotor plates are held apart by spacers. The coils are wound in a mirrored configuration so that the flying leads come in through either side of the housing. The flying leads then go through one rotor plate and loop into the bobbin shaft with connectors on side of bobbin.

An example of this configuration is shown in Figure 2B. The fluid line which provides the coil and/or the flying leads may be configured to resist high back pressure. The coil tubing and/or the flying leads may comprise stainless steel or titanium and may have an internal diameter between 0.5mm and 100 mm. The wall thickness of the tubing is selected based on the tube material and the required pressure ratings, for example the tubes may have a breaking stress of at least 1000psi. More robust tubes may be used, in line with the examples of bursting pressure of the flying leads recited above.

The material of the coil tubing and/or the flying leads may be selected to be inert to the target, matrix and biphasic solvent system being tested

The coil may comprise at least 20 and preferably over 50 winds around the bobbin. The total internal volume of the fluid line on the centrifuge bobbin is dependent on the coil internal diameter and the length of the coil. Thus the linear extent of the coil tubing is determined by the bobbin diameter.

Typical coil volume for a 1 mm internal diameter coil is at least 20ml. Typical coil volume for a 2mm internal diameter coil is at least 100ml. Typical coil volume for 3 to 4mm internal diameter coil is at least 200ml. The breaking stress of the coils is sufficient to contain an internal pressure of up to 1000psi, or up to 1600psi, preferably at least 2000psi, in some case as much as 12,000psi.

The flying leads may have different internal diameters for different flow rates. The choice of internal diameter and outer diameter depends on the ionic liquid system and the length of coil. A typical laboratory scale PTFE flying lead would have 0.5mm internal diameter and 1.68mm outer diameter. The use of PEEK tubing is preferred in some examples.

Coils having different internal diameters maybe used and the flow rate of the mobile phase selected accordingly, for example, where the coil fluid lines have an internal diameter of 1 mm the flow rate of the mobile phase is between 0.1 ml per minute and at least 2ml per minute. Where the coil fluid lines have an internal diameter of 2mm the flow rate of the mobile phase is between 1 ml per minute and at least 20ml per minute, and where the coil fluid lines have an internal diameter of 10mm the flow rate of the mobile phase is between 3ml per minute and at least 500ml per minute. Coils on the bobbin may be wound in a single layer or in multiple layers, where the outer layers have a larger winding radius than the inner layers. Multiple coils can be wound side by side or one on top of the other (e.g. having different winding diameter) to suit the application. Accordingly the winds of the coil on the outer layer experience higher centripetal acceleration than those of smaller winding radius. Although rotation control may be performed in response to a sensed pressure, particular liquid systems may also be characterised in advance (e.g. by calibration experiments or by a simulation) so that the relationship between rotation speed and backpressure can be predicted. Other flow control means may be used, for example the bore diameter of a fluid coupling to the coil, or the coil itself may be choked or relaxed to modify fluid flow. In some cases the computer does not monitor the pressure and the internal diameter of the coil is selected to prevent the backpressure from exceeding a selected threshold level.

The rotary planet centrifuge of Figure 2 comprises at least two bobbins in a mirrored configuration but in some cases only one bobbin with a counter balance may be used. Other configurations may have 3 or more bobbins. The bobbins of Figure 2 are equidistantly spaced about either side of a central axis 18 but in some cases one bobbin may be further from the central (orbit) axis than the other. This has the advantage of providing varying conditions of centripetal acceleration within a single centrifuge. The bobbins 10, 20 of Figure 2 are driven by a planetary gear arrangement so that they execute two complete revolutions (spins) for each orbit of the central axis. Other gear ratios may be used, for example higher multiples of the orbit frequency or non-integer multiples may be used so that the spinning of the bobbins is not synchronous with the orbit of the bobbin about the central (orbit) axis. The rotation of the bobbins need not be driven by a planetary gear arrangement, and any rotary drive coupling may be used. In some cases the spin (rotation speed) of the bobbin is controlled independently of the orbit of the bobbin about the central (orbit) axis.

Although the fluid line 14 has been described as a tube it need not have circular cross section. In the example above the fluid line comprises stainless steel but other materials may be used such as titanium, and polymers such as PEEK, or other polymers capable of withstanding the pressures recited herein. The fluid line 14 in the example of Figure 2 has a bore size of between 0.2mm and 5 mm, but other bore sizes may be used depending on the viscosities of the liquids that make up the liquid system, and at least one of (a) the centrifuge rotation speed (orbit frequency) and (b) the spin frequency of the bobbin, (c) the ratio of the radius of the coil on the bobbin to the orbit radius of the bobbin on the centrifuge.

The coil fluid line on the bobbin is coupled at the tail end to a source of mobile phase for the liquid system and, at the head end to sink by at least one flexible lead adapted to couple a supply of fluid into and/or out from the fluid line whilst, in use, the bobbin rotates and in which the at least one flexible lead has a breaking stress of at least. The flexible lead(s) provide a flow path for fluid of the liquid system in/out of the centrifuge. These leads can be arranged to provide a substantially constant change of gauge pressure per unit length along the flow path.

Figure 2B illustrates a configuration such as might be applied to the centrifuge of Figure 1 and Figure 2. A plurality of coils, 700, 702, 704 are arranged in series to provide a liquid flow path through the centrifuge. The coils 700, 702, 704 are arranged so that the tail end of one coil 700 is coupled to the head end of the second coil 702 and the tail end of the second coil 702 is coupled to the head end of the third coil 704 (or head and tail may be reversed for whole assemblage to suit which biphasic solvent is being utilised). At the connection between the first coil 700 and the second coil 702 a tap valve 708 is provided through which "stationary" (or lower) phase of the liquid system can be introduced to the coils. At the connection between the second coil 702 and the third coil 704 a tap valve 706 is provided through which a mobile (or upper) phase of the liquid system is introduced to the coils. In this configuration, in use, the mobile upper phase elutes from the head end of the first coil and the stationary phase will elute from the tail end of the third coil so that the components of the liquid system can be collected. Each coil comprises a helical tube of internal diameter 2.1 mm and length 36.02m. The coil winding has 76 full turns and the capacity of the coil is 133ml. The tube comprises PEEK.

In operation the stationary phase is pumped into tap valve 708 to prime the centrifuge coils. The tap valve 708 is then closed. Rotation of the centrifuge is started at an initial rate of 70rpm and ramped up linearly until a rotation speed of 500rpm is reached. On reaching operational rotation speed the mobile phase is pumped into the coils through the tap valve 706 as the coil rotates. Some analytes in the mobile phase are carried out of the centrifuge with the lower phase through the tail end 716 of the centrifuge coil 704. The mobile phase from which some analytes have been removed elutes from the centrifuge via the head end 714 of the first coil 700.

The configuration of Figure 2B may be applied in the centrifuges of Figure 1 and Figure 2 or in other arrangements. The coils may all be carried on the same bobbin or they may be carried on different bobbins of the same centrifuge. In some cases one or more of the bobbins of the liquid system depicted in Figure 2B may be on separate centrifuges so, for example one centrifuge per bobbin may be used.

In Figure 2B, three mutually similar coils, 700, 702, 704 are used however it may be advantageous to use coils of differing lengths and/or bore sizes. In some cases a single coil may comprise two or more tubes in parallel. These parallel tubes may be of the same length and bore size (internal diameter) or they may be different. Figure 3 shows an example centrifuge in which the coil 14 comprises a plurality of coils 1 , individually labelled Coil 1 , Coil 2, Coil 3 and Coil 4. A side view of the centrifuge is also provided. A first bobbin 10 carries Coil 1 and Coil 2 which are wound adjacent to and axially offset from each other on the first bobbin 10. A second bobbin 20 carries Coil 3 and Coil 4 which are wound adjacent to and axially offset from each other on the second bobbin 20. The configuration of Figure 3 is otherwise similar to that depicted in Figure 2 and like reference numerals are used to indicate like elements.

A line 210 couples a supply of a liquid system 200 into the coils 14. The line 200 is coupled to a flying lead (flexible fluid line) 224 by a fluid coupling 218. The flexible fluid line 224 couples the fluid coupling 218 to Coil 1 of the coils 14. The line 200 is coupled to a second flying lead (flexible fluid line) 225 by a fluid coupling 216. The flexible fluid line 225 couples the fluid coupling 218 to Coil 2 of the coils 14.

The line 200 is coupled to a third flying lead (flexible fluid line) 226 by a fluid coupling 214. The flexible fluid line 226 couples the fluid coupling 214 to Coil 3 of the coils 14. The line 200 is coupled to a fourth flying lead (flexible fluid line) 228 by a fluid coupling 212. The flexible fluid line 228 couples the fluid coupling 212 to Coil 4 of the coils 14. The fluid couplings 212, 214, 216, 218 may provide injection valves, such as injection valves 1 14 in Figure 1. Thus a single supply of a liquid system may be provided to a plurality of coils.

Figure 4 indicates parts of a configuration such as that described above with reference to Figure 1. In Figure 4 and Figure 1 like reference numerals are used to indicate like elements.

Examples

To illustrate the foregoing there now follow a number of non-limiting examples. The following disclosure should in no way be considered to limit the description, statements of invention and claims provided elsewhere herein. To the extent that the following examples imply that any feature is essential this is only a statement that those features are relevant to the particular example being described.

Example 1 - Coil Parameters

A CCC machine such as described above with reference to Figure 1 to Figure 2B was fitted with 4 coils of different length and diameter as shown in Table 1. Table 1 , The dimensions of the coils in the IL prep machine.

Coil 1 is intended for analytic scale separations and small scale testing, where the amount of ionic liquid needed is of the order of 15-20 ml.

Coil 2 is intended for small scale preparative separations using approximately 150 ml of ionic liquid.

Coil 3 is a longer version of coil 1 and is intended analytical separations where the distribution coefficient differences in the two liquid phases is small. This coil is the most likely to develop large backpressures. Coil 4 is for preparative separations on the scale of 10 to 50 g in one shot. It also gives information on how the separation performs when scaled up.

The spin radius of the coil is between 60.5 to 83mm and the orbit radius of the bobbin about the principal axis of the centrifuge is 97.5mm, giving a β value of 0.62 to 0.85. The machine has been tested at 1000 psi (69 Bar) at full speed for several 48 hour periods. No evidence of leakage or failing components was observed during this test. This demonstrates that far higher pressures that most other liquid-liquid extraction or HSCCC can be carried out. The machine is configured to operate with internal pressures of up to 1600 psi (1 10 Bar) and thus is able to work with supercritical carbon dioxide as the mobile phase.

The 12 cm³ coil is intended to be used where the quantity of ionic liquid is small. It can be used to test separations and extractions.

The 34 cm³ coil is for analytical type separations and has the best resolution of all the coils. The 133 cm³ coil is for general, small preparative scale separations of several grams of material. Most separations carried out so far use this coil due to its good resolution and low backpressures.

The 236 cm³ coil is for testing scale up of separation processes, as it will allow much faster flow rates and is the least affected coil by frictional interactions with the coil walls.

Table 2. The flow velocities and relative flow rates of the 4 coils in the IL-Prep machine

The four coils behave differently in separations. The two 1 .0 mm diameter coils have the highest flow velocities at a given flow rate. These appear to be dominated by capillary forces and wetting properties of the liquids used and can behave differently when compared with the larger diameter coils. The ability of a coil to separate two compounds depends on the length to diameter ratio of the coil and so coil 3 gives the best separation performance of those tested. The amount of compounds that can be separated depends in part on the amount of stationary phase in the coil. The greater the diameter of the coil, then the faster the mobile phase can be pumped. For similar amounts of phase retention, the 3.7 mm diameter coil can be pumped 13.7 times faster.

Example 2 - Phase Retention

A series of calibration experiments were conducted using the CCC machine of Example 1 to examine the effect of coil rotation speed and mobile phase flow rate on the equilibrium retention of the stationary phase. Coil 2 was filled with 1 -dodecyl-3- methylimidazolium bistriflimide ([Ci₂mim][NTf₂]) and then a hexane mobile phase was pumped into the coil. The retention of the stationary phase as a function of temperature, coil rotation speed and hexane flow rate is shown in Figure 5. In accordance with the present invention, it is desirable to operate the machine such that the phase retention remains above 50%, for instance above 60%.

Example 3 - General Procedure for Partitioning Experiments

Partitioning experiments were conducted using a CCC machine as described in Example 1. The apparatus is operated with a bobbin rotation speed of 865 rpm and a principal frequency of rotation about the principal axis of 865 rpm.

The partition coefficients of the compounds to be separated or extracted are determined. As noted above, for chromatographic separations, the liquid phases are selected such that each of the compounds to be separated preferably has a partition coefficient in the range of from 0.1 to 10, more preferably in the range of from 0.2 to 5. Partition coefficients of 0.5 to 0.1 or less require larger amounts of the mobile phase to be used, but can provide better separation.

When used in chromatographic mode, the sample of compounds to be separated is introduced to the upstream inlet as a narrow band, eluted through the apparatus under a continuous flow of the mobile phase, and fractions of eluent are collected.

All separations are conducted at room temperature unless stated otherwise.

Example 4 - Separation of transition metal salts

Coil 2 of the CCC machine of Example 1 was charged with a biphasic mixture of water as the mobile phase and a mixture of trihexyl(tetradecyl)phosphonium chloride ([Pe.e.e.ul.CI]) and dichloromethane as the stationary phase, in a ratio of waterdichloromethane: ionic liquid of 1 :1 :1 by volume.

A mixture of CuCI₂ 1.5 g and CoCI₂ 1.5 g dissolved in water 5.0 mL was introduced into the column inlet and eluted through the column using water as the mobile phase at a flow rate of 2 mL/min. 5 mL fractions were collected at the column outlet and the virtually complete separation of CuCI₂ and CoCI₂ could be observed as the separation of red fractions (containing CoCI₂) and blue fractions (containing CuCI₂) separated by virtually colourless fractions (containing neither CoCI₂ nor CuCI₂ in significant quantities). This separation gave excellent results, although it is noted that the copper and cobalt aqueous solutions make the mobile water phase denser than the ionic phase. This flips the mobile phase with the stationary phase in part of the coil and causes some bleeding of ionic liquid from the coil. This can be solved by using a denser ionic phase or carrying out the separation with the phase's densities in an opposite manner to this separation, and with the flow reversed.

Example 5 - Separation of transition metal salts

Coil 2 of the CCC machine of Example 1 was charged with a biphasic mixture of water as the mobile phase and a mixture of trihexyl(tetradecyl)phosphonium chloride ([Pe.e.e.ul.CI]) and ethyl acetate as the stationary phase, in a ratio of water: ethyl acetate:ionic liquid of 1 :1 :1 by volume. The use of ethyl acetate in the ionic liquid phase reduces the density of this phase such that the mobile phase water is the denser phase. Consequently, the process is carried out in the reverse direction.

A mixture of CuCI₂ 1.0 g, CoCI₂ 1.0 g and NiCI₂ 1.0 g dissolved in water 5 ml_ was introduced into the column inlet and eluted through the column in the reverse direction using water as the mobile phase at a flow rate of 2 mL/min. 5 ml_ fractions were collected at the column outlet and the virtually complete separation of all three salts could be observed as the separation of green fractions (containing NiCI₂), red fractions (containing CoCI₂) and blue fractions (containing CuCI₂) separated by virtually colourless fractions (containing neither CoCI₂ nor CuCI₂ in signficant quantities).

It was found that separation of this mixture of salts could be improved still further by the addition of ca. 1.6 wt% concentrated HCI to the aqueous mobile phase. This reduces the partition coefficients for all three metals, such that the retention of each by the stationary phase is increased and the elution of each metal is proportionately increased. In practical terms, this means that the elution of the metals is delayed and is spread across a larger number of fractions.

The separation was carried out in reversed-mode, wherein the flow of the mobile phase was from head to tail. The separation produced complete separation of the three metals. The experiment was repeated with the addition of 5 ml c.HCI (aq) to the mobile water phase (300 ml). This has the effect of pushing all three metal ions into the ionic phase, which has the effect of retarding the elution time of the metal ions.

Example 6 - Separation of transition metal salts

A biphasic mixture was formed by mixing water, trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14_[CI]), ethyl acetate and acetone, in a ratio of watenethyl acetate:acetone:ionic liquid of 5:1.25:1.25:3 by volume. The aqueous phase was the denser phase.

A CCC machine was heated to 30 °C and set to rotate at 865 RPM. Coil 2 of the CCC machine, with dimensions as specified in Example 1 , was charged with the ionic phase pumped head to tail (reverse mode). The lighter ionic phase was pumped into the coil, followed by the aqueous phase at 2.0 mL/min followed by 3.0 mL/min. The amount of displaced ionic phase was measured in a measuring cylinder. This gave phase retention figures of 67.7 % at 2mL/min and 61.7 % at 3.0 mL/min.

After the coil had stabilised, 2 ml_ of a mixture of CuCI₂.2H₂0 1.0 g, CoCI₂ 1.0 g and NiCI₂.2H₂0 1.0 g dissolved in water 6 ml_ was transferred to the injection coil and introduced into the machine. The aqueous phase was pumped at 1.0 mL/min. The separation was measured by UV-Vis spectroscopy, recording the absorbance at 400 nm (nickel signal), 460 nm, 520 nm (cobalt signal) and 800 nm (copper signal). The data for the metal salts is shown in Figure 6.

The experiment was repeated with the CCC machine heated to 38°C and 46 °C. Experimental data obtained from separation of the metal salts at 38°C and at 46 °C are shown in Figures 7 and 8, respectively.

The results demonstrate that the best separation occurred during the experiment conducted at 46 °C, suggesting that high temperatures and lower viscosities favour good separations in a reduced time period and sharper peaks.

Claims

1. A process for the separation of inorganic compounds comprising centrifugal partitioning of at least one inorganic compound between a mobile liquid phase and an immiscible stationary liquid phase, wherein at least one of the mobile liquid phase and the stationary liquid phase comprises or consists of an ionic liquid, and wherein the total ionic liquid content of the mobile and stationary phases is 15 wt% or greater.

2. A process according to Claim 1 , wherein said process comprises passing the mobile liquid phase along a coiled flow path containing the stationary liquid phase wherein the coiled flow path is mounted on a centrifuge such that it rotates about its own axis.

3. A process according to Claim 2, wherein the coiled flow path is mounted on a planetary centrifuge.

4. A process according to any one of the preceding claims, wherein the process is used for the liquid-liquid extraction of one or more inorganic compounds from the mobile liquid phase into the stationary liquid phase, or from the stationary liquid phase into the mobile liquid phase.

5. A process according to Claim 4, wherein the partition coefficient of the one or more inorganic compounds is 1 or less, preferably 0.5 or less, more preferably 0.1 or less, still more preferably 0.05 or less and most preferably 0.01 or less.

6. A process according to any one of Claims 1 to 3, wherein the process is used for the chromatographic separation of two or more inorganic compounds.

7. A process according to Claim 6, wherein each of the two or more inorganic compounds has a partition coefficient in the range of from 0.1 to 10, more preferably in the range of from 0.2 to 5, still more preferably in the range of from 0.3 to 3, still more preferably in the range of from 0.4 to 2.5, and most preferably in the range of from 0.5 to 2.

8. A process according to Claim 6 or Claim 7, wherein the partition coefficients of the two or more inorganic compounds differ by at least 0.05, more preferably by at least 0.1 , more preferably by at least 0.2, still more preferably by at least 0.3, still more preferably by at least 0.4, and most preferably by at least 0.5.

A process according to any one of the preceding claims, wherein the ionic liquid is defined by the empirical formula:

[Cat⁺][X^"]

wherein [Cat⁺] refers to one or more cationic species; and

[X^"] refers to one or more anionic species.

A process according to Claim 9, wherein [Cat⁺] comprises a cationic species selected from: ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1 ,4-diazabicyclo[2.2.2]octanium, diazabicyclo- undecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, /so-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, /so-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, /so-thiadiazolium, thiazinium, thiazolium, iso- thiazolium, thiophenium, thiuronium, triazinium, triazolium, /so-triazolium, and uronium.

A process according to Claim 10, wherein [Cat⁺] comprises a cation selected from:

wherein: R^a, R^b, R°, R^d, R^e, R^f and R⁹ are each independently selected from hydrogen, a Ci to C₂o, straight chain or branched alkyl group, a C₃ to C₈ cycloalkyl group, or a C₆ to Ci₀ aryl group, or any two of R^b, R°, R^d, R^e and R^f attached to adjacent carbon atoms form a methylene chain -(CH₂)_q- wherein q is from 3 to 6; and wherein said alkyl, cycloalkyl or aryl groups or said methylene chain are unsubstituted or may be substituted by one to three groups selected from: Ci to C₆ alkoxy, C₂ to Ci₂ alkoxyalkoxy, C₃ to C₈ cycloalkyl, C₆ to Ci₀ aryl, C₇ to Ci₀ alkaryl, C₇ to Ci₀ aralkyl, -CN, -OH, -SH, -N0₂, -F, -C0₂R^x, -OC(0)R^x, -C(0)R^x, -C(0)NR^yR^z, or -NR^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl.

12. A process according to Claim 1 1 , wherein [Cat⁺] comprises a cation selected from:

wherein: R^a, R^b, R°, R^d, R^e, R^f, and R⁹ are as defined in Claim 11.

13. A process according to Claim 10, wherein [Cat⁺] comprises a saturated heterocyclic cation selected from:

wherein: R^a, R^b, R°, R^d, R^e, R^f, and R⁹ are as defined in Claim 11.

A process according to Claim 10, wherein [Cat⁺] comprises an acyclic cation selected from:

[N(R^a)(R^b)(R°)(R^d)]⁺, [P(R^a)(R^b)(R°)(R^d)]⁺, and [S(R^a)(R^b)(R°)]⁺,

wherein: R^a, R^b, R°, and R^d are each independently selected from a Ci to C₂o, straight chain or branched alkyl group, a C₃ to C₈ cycloalkyl group, or a C₆ to C10 aryl group; and wherein said alkyl, cycloalkyl or aryl groups are unsubstituted or may be substituted by one to three groups selected from: Ci to C₆ alkoxy, C₂ to C12 alkoxyalkoxy, C₃ to C₈ cycloalkyl, C₆ to C10 aryl, C₇ to C10 alkaryl, C₇ to C10 aralkyl, -CN, -OH, -SH, -N0₂, -F, -C0₂R^x, -OC(0)R^x, -C(0)R^x, -C(0)NR^yR^z, or -R^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl and wherein one of R^a, R^b, R°, and R^d may also be hydrogen.

A process according to Claim 14, wherein [Cat⁺] comprises a cation selected from:

[N(R^a)(R^b)(R°)(R^d)]⁺, [P(R^a)(R^b)(R°)(R^d)]⁺,

wherein: R^a, R^b, R°, and R^d as defined in Claim 14.

A process according to any one of Claims 9 to 15, wherein [X^"] comprises an anion selected from halides, sulphates, sulfonates, sulfonimides, phosphates, phosphonates, carboxylates, CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^". A process according to Claim 16, wherein [X^"] comprises an anion selected from F, CI^", Br^", I^", S0₄ ^2", R¹OS0₂0^", R²S0₂0^", (R²S0₂)₂N^", P0₄ ^3", R¹OP0₃ ^2", (R¹0)₂P0₂ ^", [R²P0₃]^2", R¹C0₂ ^", CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^",

wherein R¹ and R² are independently selected from the group consisting of C1-C10 alkyl, C₆ aryl, C1-C10 alkyl(C₆)aryl, and C₆ aryl(Ci-Ci₀)alkyl each of which may optionally be substituted by one or more groups selected from: -F, -CI, -Br, -I, Ci to C₆ alkoxy, C₃ to C₈ cycloalkyl, C₆ to C10 aryl, C₇ to C10 alkaryl, C₇ to C10 aralkyl, -CN, -OH, -SH, -N0₂, -C0₂R^x, -OC(0)R^x, -C(0)R^x, -C(0)NR^yR^z, or -NR^yR^z, wherein R^x, R^y and R^z are independently selected from hydrogen or Ci to C₆ alkyl, and wherein R² may also be fluorine.

A process according to Claim 17, wherein [X^"] comprises an anion selected from CI^", Br^", I^", S0₄ ^2", FS0₂0^", CF₃S0₂0^", CH₃S0₂0^", CH₃CH₂S0₂0^", TsO^", (CF₃S0₂)₂N^", P0₄ ^3", HC0₂ ^", CH₃C0₂ ^", CF₃C0₂ ^", CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^".

A process according to any one of Claims 9 to 15, wherein [X^"] comprises an amino acid anion.

A process according to any one of the preceding claims, wherein the ionic liquid has a melting point of 50 °C or less, more preferably 40 °C or less, more preferably 30 °C or less, still more preferably 25 °C or less, still more preferably 20 °C or less, and most preferably 15 °C or less, for instance 10 °C or less or 5 °C or less.

A process according to any one of the preceding claims, wherein the ionic liquid has a viscosity at 20 °C of 1000 cP or less, more preferably 500 cP or less, still more preferably 200 cP or less, and most preferably 100 cP or less.

A process according to any one of the preceding claims wherein at least one of the stationary phase and the mobile phase comprises a solvent which is immiscible with the ionic liquid phase and which is selected from:

i. hydrocarbon solvents, such as n-pentane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, benzene, toluene, xylenes, and mixtures of hydrocarbons such as petroleum ether (for instance the fractions boiling in the range 40 to 120 °C); ii. chlorinated hydrocarbon solvents, such as dichloromethane, chloroform, trichloroethylene, 1 ,2-dichloroethane, and 1 , 1 , 1 -trichloroethane;

iii. ethers, such as diethyl ether, di-iso-propyl ether, methyl-tert-butyl ether, and tetrahydrofuran;

5 iv. esters, such as ethyl acetate and butyl acetate;

vi. ketones, such as acetone and 2-butanone;

vii. other solvents, such as acetonitrile, acetic acid, dimethylformamide, and 10 dimethylsulfoxide;

viii. water; and

ix. aqueous salt solutions, such as salt solutions comprising a phosphate anion and/or a potassium cation,

and mixtures thereof.

15 23. A process according to Claim 22, wherein the solvent is selected from n-hexane, n-heptane, cyclohexane, dichloromethane, chloroform, methyl-tert-butyl ether, ethyl acetate, methanol ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, acetonitrile, water, and mixtures thereof.

24. A process according to any one of the preceding claims, wherein the total ionic 20 liquid content of the mobile and stationary phases is 20 wt% or greater, more preferably 25 wt% or greater, more preferably 30 wt% or greater, and most preferably 40 wt% or greater.

25. A process according to Claim 24, wherein the total ionic liquid content of the mobile and stationary phases is 46 wt% or greater, more preferably 50 wt% or

25 greater, more preferably 55 wt% or greater, still more preferably 60 wt% or greater, and most preferably 65 wt% or greater.

26. A process according to any one of the preceding claims, when used to separate or extract one or more metal salts.

27. A process according to Claim 26, when used to separate two or more salts of any 30 of the metals in the periodic table, more preferably two or more salts of the alkali metals, the alkaline earth metals and the transition metals.

28. A process according to Claim 27, when used to separate three or more salts of any of the metals in the periodic table, more preferably three or more salts of the alkali metals, the alkaline earth metals and the transition metals.

29. A process according to any one of Claims 26 to 28, wherein at least one salt 5 comprises a metal cation selected from Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr^2*,

Ba²⁺, Sc³⁺, Ti³⁺, Ti⁴⁺, V²⁺, Cr^2*, Cr³⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu⁺, Cu²⁺, and Zn²⁺.

30. A process according to any one of Claims 26 to 29, wherein at least one salt comprises an anion selected from halides, sulphates, sulfonates, sulfonimides,

10 phosphates, phosphonates, carboxylates, CN^", N0₃ ^", N0₂ ^", BF₄ ^" and PF₆ ^".

31. Use of an ionic liquid as the stationary phase or the mobile phase in a process for the separation of inorganic compounds by centrifugal partitioning as defined in any one of claims 1 to 30, wherein the total ionic liquid content of the mobile and stationary phases is 15 wt% or greater.

15 32. A rotary coil centrifuge for counter current chromatography comprising:

a rotary bobbin configured to spin about a spin axis of the bobbin and to orbit a principal rotary axis of the centrifuge;

a fluid line carried by the bobbin to provide a column for counter current chromatography wherein the fluid line is coiled so that it orbits of the spinning

20 bobbin about the orbit axis provide planetary motion of the coil which includes a separating interval, and a mixing interval during which the centripetal acceleration of a part of the coil at closest approach to the orbit axis is relatively lower than the centripetal acceleration of the part of the coil most distant from the sun axis during the separating interval, a rotary drive operable to drive the bobbin in a rotary

25 motion having a spin angular frequency of rotation about the spin axis and a principal frequency of rotation about the principal axis selected such that the linear acceleration of the part of the coil during the mixing phase is at least 2 G and less than 100 G and the linear acceleration of the part of the coil during the separating phase is not more than 500 G; and

30 a liquid system in the fluid line comprising an ionic liquid in an amount of 15 wt% or greater, preferably 20 wt% or greater, more preferably 25 wt% or greater, more preferably 30 wt% or greater, and most preferably 40 wt% or greater, and further comprising one or more inorganic compounds to be separated.

A liquid-liquid chromatography or liquid-liquid extraction apparatus comprising: a first duct for containing a flow of ionic liquid, the first duct being carried on a centrifuge rotor arranged to provide cyclic variations in the centripetal acceleration of the first duct so that a fluid flowing in the first duct is mixed and separated in accordance with the cyclic variations in centripetal acceleration;

a pump coupled to the first duct to provide a flow of liquid into the first duct;

a flow controller adapted to control the flow of liquid from the pump into the first duct;

a rotation controller configured to control rotation of the centrifuge rotor and thereby the centripetal acceleration of the fluid in the first duct;

a second duct coupled between a stationary mounting and the centrifuge rotor, and arranged to carry the flow of liquid to the first duct to join with the first duct at a joint coupled to the centrifuge rotor, the second duct being flexible and having an internal cross section selected to match the internal cross section of the first duct so that the pressure drop per unit length at the joining point is less than or equal to the pressure drop per unit length along the first duct and the second duct.

The apparatus of claim 33 in which the flow controller is configured to control the flow of a liquid comprising an ionic liquid into the first duct, so that a selected fraction of the capacity of the first duct is filled with the liquid, and the rotation controller and the flow controller are configured so that, once the selected fraction has been filled with the liquid, the rotor is rotated for a selected time interval during which no further flow of liquid is provided into the first duct.

The apparatus of claim 34 in which the rotation controller is configured to rotate the rotor at a constant rate during the selected time interval.

The apparatus of claim 35 in which the flow controller is configured to provide a second liquid into the first duct after the selected time interval has elapsed.

The apparatus of claim 36 in which the second liquid comprises a solvent having a substantially lower viscosity than the first liquid. The apparatus of any of claims 33 to 37 in which the second duct is arranged so that the pressure drop per unit length along the second duct is less than the pressure drop per unit length along the first duct.

The apparatus of any of claims 33 to 38 wherein at least one of the flow controller and the rotation controller are configured to control a respective one of the rotation of the centrifuge and the flow of liquid into the centrifuge so that the liquid pressure in the first duct does not exceed 1600psi.

The apparatus of any of claims 33 to 39 wherein the centrifuge comprises a rotary planet centrifuge and the first duct is carried on a rotary bobbin configured to spin about a spin axis of the bobbin and to orbit a principal rotary axis of the centrifuge.

The apparatus of claim 40 wherein the first duct is provided by a fluid line that is coiled so that orbits of the spinning bobbin about the orbit axis provide planetary motion of the coiled line.

The apparatus of claim 41 in which orbits of the bobbin provide a separating interval, and a mixing interval, during which the centripetal acceleration of a part of the coil at closest approach to the orbit axis is relatively lower than the centripetal acceleration of the part of the coil most distant from the orbit axis during the separating interval, thereby providing the cyclic variations in the centripetal acceleration.

The apparatus of claim 41 or 42 comprising a rotary drive operable to drive the bobbin in a rotary motion having a spin angular frequency of rotation about the spin axis and a principal frequency of rotation about the orbit axis selected such that the linear acceleration of the part of the coil during the mixing phase is at least 2G and less than 100G and the linear acceleration of the part of the coil during the separating phase is not more than 500G.

The apparatus of any of claims 33 to 43 comprising the first liquid in one of the first duct and the second duct, wherein the liquid comprises at least 46% by weight of ionic liquid.