WO2018009762A1

WO2018009762A1 - Venturi method of low pressure recycling of co2

Info

Publication number: WO2018009762A1
Application number: PCT/US2017/041048
Authority: WO
Inventors: Glenn CHESNEY
Original assignee: Waters Technologies Corporation
Priority date: 2016-07-07
Filing date: 2017-07-07
Publication date: 2018-01-11

Abstract

Return loops for recovery/recycling components for highly-compressible fluid chromatography systems providing for reintroduction of the recovered highly-compressible fluid into a recycler, introduction being achieved by creating an introduction point at a venturi device for the return highly-compressible fluid flow into the return loop and to the recycler.

Description

VENTURI METHOD OF LOW PRESSURE RECYCLING OF C02

RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application No. 62/359,361, filed July 7, 2016, and entitled "Venturi Method of Low Pressure Recycling of C02", the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention generally relates to devices and methods for recovery/recycling systems within or connected to chromatography systems.

BACKGROUND

[0003] Highly-compressible fluid chromatography uses a solvent that includes a fluid (e.g., carbon dioxide, Freon, etc.) that is in a gaseous state at ambient/room temperature and pressure. For use in the chromatography system, the highly-compressible fluid is maintained in a liquid or supercritical fluid state. Typically, highly-compressible fluid chromatography involves a fluid that experiences significant density changes over small changes in pressure and temperature at conventional operating conditions. Although highly-compressible fluid chromatography may be carried out with several different compounds, in the current document carbon dioxide (C0₂) will be used as the reference compound as it is the most commonly employed.

[0004] In addition to C0₂, a liquid organic co-solvent (alternatively called a modifier) may be included in the solvent mixture. A common co-solvent is methanol. Examples of other co-solvents include acetonitrile and alcohols such as ethanol and isopropanol. The C0₂ and co-solvent (if any) mixture is maintained at a pressure and temperature where the mixture remains as a substantially homogeneous, single phase.

[0005] Some chromatography systems are capable of reusing C0₂. Reusing C0₂ may be cost effective and environmentally friendly. In order to reuse C0₂, a recovery/recycling system may be added to the chromatography system. The recovery/recycling system may receive the solvent mixture, including C0₂ and other components, such as co-solvents, sample, wash solvents, or contaminates, and may then separate out the C0₂ for reuse by the system. [0006] The present disclosure relates to systems and methods that provide for introduction of a return flowstream of C0₂ from a purification process (e.g. , gas-liquid separators) into a recycler unit within a C0₂ recovery/recycling system, where the recycler unit operates at a higher pressure than the purification process.

SUMMARY

[0007] The systems and methods of the current disclosure provide for a return loop within a recovery/recycling system that may be used in a chromatography system. The present technology includes the recycler unit and is able to accept the addition of compressible fluid at an introduction point at a lower pressure than the pressure at which the recycler unit operates. The systems and methods use one or more compressible fluid flowstreams and venturi devices.

[0008] In an embodiment, the present disclosure relates to a device for introducing a compressible fluid return flowstream into a recycler. The device includes (a) a return loop (including the recycler and a first venturi device), and (b) an introduction point at a throat of the first venturi device and in fluid communication with the compressible fluid return flowstream. The compressible fluid can be carbon dioxide. The device can additionally include a second venturi device. In addition to the second venturi device, the device can include a splitter and a coupler, wherein the splitter divides the flowstream between the first venturi device and the second venturi device, and the coupler receives the flowstream from both the first venturi device and the second venturi device. In some embodiments, the return loop can additionally include a pump located downstream of the recycler and upstream of the first venturi device. In certain embodiments, the return loop can additionally include a first heat exchanger located upstream of the first venturi device, and a second heat exchanger located downstream of the first venturi device and upstream of the recycler inlet. The first venturi device can have an exit cone and an entry cone such that the exit cone can be about 1.5 and 3 times longer than the entry cone. The first venturi device can have an inlet diameter and an outlet diameter where the inlet diameter can be approximately equal to the outlet diameter. The inlet diameter can be about 2 and 3 times larger than the diameter of the throat. The inlet diameter and the outlet diameter can each be about 0.25 mm and 2 mm.

[0009] In an embodiment, the present disclosure relates to a method for introducing a compressible fluid return flowstream into a recycler. The method includes: pressurizing a return loop from the recycler, through a venturi device, and returning to the recycler, and introducing the compressible fluid flowstream into the return loop at the venturi device.

[0010] In an embodiment, the present disclosure relates to a method for introducing a carbon dioxide return flowstream into a recycler system. The method includes: providing a carbon dioxide motive flowstream to a venturi device; providing the carbon dioxide return flowstream to the venturi device at an introduction point in the throat of the venturi device; permitting the carbon dioxide motive flowstream and the carbon dioxide return flowstream to mix to create a combined carbon dioxide flowstream; and introducing the combined carbon dioxide flowstream to the recycler. The method can additionally include the step of heating the carbon dioxide motive flowstream before introduction to the venturi device at a temperature sufficient to achieve gas phase within the heated portion of the carbon dioxide motive flowstream. The method can additionally include the step of cooling the combined carbon dioxide flowstream before introduction to the recycler to a temperature sufficient to achieve liquid phase within the cooled portion of the combined carbon dioxide flowstream. The carbon dioxide return flowstream can have a pressure below 600 psi. The carbon dioxide return flowstream can have a pressure below 400 psi. The carbon dioxide return flowstream can have a pressure below 300 psi. The carbon dioxide return flowstream can have a pressure below 200 psi.

[0011] In an embodiment, the present disclosure relates to a method for introducing a carbon dioxide return flowstream into a recycler system. The method includes: providing a first carbon dioxide motive flowstream to a first venturi device and a second carbon dioxide motive flowstream to a second venturi device; providing a first portion of the carbon dioxide flowstream to the first venturi device at an introduction point in the throat of the first venturi device, and a second portion of the carbon dioxide return flowstream to the second venturi device at an introduction point in the throat of the second venturi device; permitting the first carbon dioxide motive flowstream to mix with the first portion of the carbon dioxide return flowstream to create a first combined carbon dioxide flowstream and permitting the second carbon dioxide motive flowstream to mix with the second portion of the carbon dioxide return flowstream to create a second combined carbon dioxide flowstream; and returning the first combined carbon dioxide flowstream and the second combined carbon dioxide flowstream to the recycler. The method can additionally include using a third carbon dioxide motive flowstream feeding a third venturi device to accept a third portion of the carbon dioxide return flowstream and form a third combined carbon dioxide flowstream.

[0012] In an embodiment, the present disclosure relates to a fluid recovery system for a chromatography system including a plurality of gas-liquid separators; a recycler; a return loop, fed by and returned to the recycler; and a venturi device, arranged so that a primary flowpath through the venturi device is a segment of the return loop and a secondary flowpath is fed from the one or more gas-liquid separators. The return loop can additionally include a first heat exchanger upstream of the venturi device and a second heat exchanger downstream of the venturi device. The fluid recovery system can include a second venturi device.

[0013] Embodiments of the present technology allow purification processes within a chromatography system (e.g. , gas liquid separators) to feed a return flowstream from the purification system to a recycler while operating at a lower pressure than the pressure at which the recycler unit operates. By permitting a low pressure return flowstream, the present technology permits the purification system (e.g., GLS) to operate at lower pressure while continuing to feed the recycler operating at a higher pressure. By operating at a lower pressure, the purification process may achieve increased efficiency and increased purity of the purified compressible fluid. Further, the present technology can be implemented without requiring an additional pump if the return loop is pressurized by the recycler or by another pump already used in the system. Separately, the venturi device described herein may be more robust than a pump, which may be especially appreciated in the present application where the variation in pressure at the introduction point could cause wear.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0015] FIG. 1 schematically illustrates a prior art recycling system for a chromatography system;

[0016] FIG. 2 schematically illustrates a recycler outfitted with a return loop according to an embodiment of the present technology; [0017] FIG. 3 schematically illustrates a return loop according to an embodiment of the present technology;

[0018] FIG. 4 schematically illustrates another return loop according to an embodiment of the present technology;

[0019] FIG. 5 schematically illustrates a venturi device usable in embodiments of the present technology;

[0020] FIG. 6 schematically illustrates another venturi device showing terminology used herein to describe various dimensions;

[0021] FIG. 7 schematically illustrates a return loop according to an embodiment of the present technology having two venturi devices; and

[0022] FIG. 8 illustrates a method of operating a return loop to a recycler according to an embodiment of the present technology.

DETAILED DESCRIPTION

[0023] Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non- limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

[0024] In recovery/recycling systems for C0₂-based chromatography, the purification process may use phase changes to separate the C0₂ from other components. While embodiments of the present technology may be useful for any purification system that operates at a low pressure (that is, a lower pressure than the recycler unit), a gas-liquid separator (GLS) will be used to demonstrate how the return loop may function within the system. In a GLS, the co-solvent and sample will tend to precipitate out of the mixture, and can be removed from the separator separately from the C0₂. By using a series of GLSs, progressively more of the co-solvent and sample may be removed from the mixture. The separation may be improved by providing a lower pressure in each successive GLS. Moreover, the mixture may flow unassisted to each successive GLS if a pressure gradient is maintained such that the pressure decreases through each successive GLS.

[0025] Operating the recovery/recycling system may require tight control over characteristics of the mixture including temperature, pressure, flowrate etc. If these conditions are not maintained correctly, the substantially homogeneous, single-phase mixture may be lost. If the single phase is lost, the system may experience precipitation or crashing- out of the less-volatile components (e.g. , organic co-solvents), or rapid, uncontrolled expansion of the C0₂. These conditions may obstruct or damage system components and may require cleaning and repair of the system.

[0026] The lowest operating pressure within the recovery/recycling system may be limited by the pressure at which the recycler operates. This limitation may arise where the relative pressures determine the ability of the recycler unit to accept a return flowstream (e.g. , C0₂) from a GLS unassisted. For example, in prior art system 100 as depicted in FIG. 1, mobile phase flow may be drawn from holding vessel 110 by pump 120 and introduced to injector, column, detector 130. Downstream of injector, column, detector 130 the mobile phase flow may be delivered to collection vessel 140 and thereafter to GLS 150 which feeds recycler 170. Injector, column, detector 130 may operate at about 3000 psi. Recycler 170 may operate at about 800 psi. The return flowstream 155 provided from GLS 150 may be cooled by heat exchanger 160 to about 11 °C to transition to the liquid phase, and may then be supplied to the recycler. In order to achieve flow from GLS 150 to recycler 170, the pressure in GLS 150 will generally need to be higher than the pressure in recycler 170. In this example, due to the operating pressure of recycler 170, a pressure of about 800 psi or more may be required in GLS 150 to permit unassisted flow to recycler 170. This presents a range between about 3000 psi (the pressure of the chromatography system) and about 800 psi (the pressure of the recovery system) at which the GLS(s) may operate. Lower pressures in a GLS, however, may be desirable in order to obtain better separation and greater purity of the C0₂.

[0027] For example, one or more GLSs may operate at pressures as low as about 75, 100, 200, or 300 psi. The use of a lower pressure may increase the degree to which C0₂ converts to the gas phase in a GLS, which may increase the efficiency of the purification process by decreasing the ability of the C0₂ to hold the other components of the mixture (such as organic co-solvent) in solution. These pressures may be lower than the operating pressure of a typical recycler unit.

[0028] In a system with a GLS operating at these pressures, unassisted solvent flow as in FIG. 1, from GLS 150 to recycler 170, is not possible. The present technology achieves solvent flow, from, e.g., a GLS to a recycler, provides for this flow by establishing a second flowstream of highly-compressible fluid (e.g. , C0₂)— herein called a motive flowstream— feeding a venturi device, or more than one venturi device. The venturi device creates an introduction point for the return flowstream from the GLS, which permits flow from the GLS to the recycler.

[0029] The placement of an embodiment of the present technology within a chromatography system is depicted in FIG. 2, which shows return loop 205 within chromatography system 200. Return loop 205 has the ability to provide return flowstream 255 to recycler 260 through the use of venturi device 290 and motive flowstream 295, from recycler 260. Chromatography system 200 is shown with three GLSs: GLS 250, GLS 251, and GLS 252; but is otherwise comparable to chromatography system 100, with the addition of return loop 205. That is, chromatography system 200 includes holding vessel 210, pump 220, injector, column, detector 230, and collection vessel 240. In system 200, GLS 252 can provide a gas phase return flowstream 255 to venturi device 290. Venturi device 290 may accept return flowstream 255 and ultimately supply it to recycler 260, even though recycler 260 operates at a higher pressure than GLS 252.

[0030] The movement of the motive flowstream within a venturi device, and particularly changes in velocity of the motive flowstream caused by the shape of the venturi device, gives rise to the venturi effect. The venturi effect creates a low-pressure area at the point at which the velocity of the motive flowstream is greatest. For example, the venturi effect underlies the laboratory-type water aspirator of the sort which is attached to a water tap and used to draw a vacuum. In a water aspirator, the motive flowstream is the water, traveling through the aspirator. The shape of the aspirator— narrowing from the inlet— creates a low-pressure area within the column of flowing water at the point where the water column is narrowest (and velocity is greatest). This low-pressure area generates the vacuum. [0031] In venturi device 290, motive flowstream 295 is formed of a highly- compressible fluid (e.g. , CO₂) provided by recycler 260. As motive flowstream 295 passes through venturi device 290, it creates a low-pressure introduction point which draws return flowstream 255 from GLS 252. Motive flowstream 295 and return flowstream 255 mix within venturi device 290 to provide combined flowstream 297, which is ultimately returned to recycler 260. Combined flowstream 297 may then be prepared by recycler 260 both to be returned to holding vessel 210 for use in injector, column, detector 230, and to provide additional portions of motive flowstream 295.

[0032] In general, return loop components include: a recycler, a motive flowstream, and a venturi device. The return loop may optionally including a pump and one or more heat exchangers. In particular, a pump may be used where a recycler lacks the capability to provide a pressurized flowstream. A heat exchanger may be used to change the phase of the flowstreams within the return loop between liquid and gas. In an embodiment, two heat exchangers may be provided, one before the venturi device so that the motive flowstream is provided as a gas, and one before the recycler so that the combined flowstream enters the recycler as a liquid. Chromatography system 200 depicts these optional features as pump 270, heat exchanger 282 and heat exchanger 284. The operation of chromatography system 200 is described in further detail below.

[0033] Prior to entering the return loop 205, the flowstream is purified to separate liquids from the flowstream which passed through the injector, column, and detector 230. In general, one or more GLS devices are used for purification.

[0034] A gas-liquid separator (GLS) may include a chamber into which the mixture to be separated is introduced and which permits exit of gasses and liquids separately. Within the chamber, liquid co-solvent, sample, and any other liquid component may be permitted to precipitate from the mixture and may be removed from the chamber, while the remaining mixture exits to a subsequent chamber or component of the system. Ideally, all of the co- solvent and sample portion would precipitate and be removed, leaving only C0₂ for transfer to the next component of the system, such as the recycler. In practice, the mixture may retain some portion of co-solvent and sample, particularly if the C0₂ remains at least partially in fluid form. Reducing the pressure of the GLS may encourage increased conversion of C0₂ to the gas phase and improve the separation of the C0₂ from the co-solvent and sample. Increasing the number of GLSs may also provide better purification. [0035] For example, a first GLS may operate at about 3000 psi, a second GLS may operate at about 1800 psi, and a third GLS may operate at about 100 psi. Decreasing pressure permits unassisted flow to each consecutive (lower pressure) GLS, and increases removal of co-solvent and sample from the mixture. The pressure of the last GLS, relative to the recycler, determines whether flow from that GLS to the recycler may be unassisted or whether some other device, such as a pump, or the return loop of the present technology, is required to provide solvent flow to the recycler.

[0036] Turning to the features of the return loop (which is downstream of the GLS), they are minimally a recycler, a motive flowstream, and a venturi device. The recycler is a unit which treats the highly-compressible fluid, such as C0₂, to provide it in a form usable by the system, and which provides such fluid to the collection vessel.

[0037] The motive flowstream is a flowstream of highly-compressible fluid provided from the recycler. For a C0₂-based system, the motive flowstream would be C0₂. The motive flowstream may have the same level of purity as is provided by the recycler for use within the chromatography column.

[0038] The venturi device receives the motive flowstream (higher pressure) and the return flowstream (lower pressure) and mixes them. The characteristics of the venturi device, such as venturi device 290, are described in detail below.

[0039] The return loop may additionally incorporate optional components to maintain or change the phase of the flowstreams. The system may include a pump. The pump may be any pump capable of pressurizing a highly-compressible fluid flow within the return loop, e.g. , a gear pump. Where used, the pump may be capable of achieving a pressure comparable to that at which the recycler operates. The pump used within the return loop may not need to produce the pressures achieved by a pump used to pressurize the chromatography column. For example, the return loop pump, i.e., pump 270 of FIG. 2, may not be required to achieve comparably high pressures as pump 220, which pressurizes injector, column, detector 230.

[0040] The return loop system may also incorporate a first heat exchanger downstream of the pump (e.g. , pump 270) which may heat the motive flowstream to cause a liquid-to-gas phase change of the flowstream such that the flowstream is a gas when provided to the venturi device. This combined flowstream may then be cooled by the second heat exchanger to return to the recycler in the liquid phase. Other than within the venturi device, the pressure in the return loop may be approximately similar throughout. The term "heat exchanger" is used herein to refer to a device which may controllably change the temperature of a flowstream passing through the device. The heat exchanger may be a heat exchanger able to increase or decrease the temperature of the flowstream. The heat exchanger may also be a device able to increase, but not decrease, the temperature of the flowstream (e.g. , an inline heater), or may be a device able to decrease, but not increase, the temperature of the flowstream (e.g. , an in-line cooler).

[0041] The connections between the components of the return loop and between the venturi device and the chromatography system may be any type of connection maintaining an air-tight seal between the components. For example, the connections may be made by tubing, by directly connecting the components (such as by use of a zero-volume connector), or a combination of both types of connections. Where tubing is used, the tubing may be metal or plastic tubing, such as copper, stainless steel, PEEK or PETE. The tubing may have a diameter (or cross-sectional length) of about 2 mm, 1.75 mm, 1.5 mm, 1.25 mm, 1 mm, 0.9 mm, 0.8 mm, 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm, 0.05 mm, or about 0.025 mm. The tubing can have a circular cross-sectional shape, or some other shape, such as an elliptical, square, oval, or rectangular cross-sectional shape.

[0042] Returning to the venturi device, the principal features of the device are an entry cone, a throat, and an exit cone. The venturi device may be further understood by reference to venturi device 500 of FIG. 5. Venturi device 500 includes entry cone 510, throat 520, and exit cone 530, arranged such that the narrow portion of entry cone 510 meets one end of throat 520, and the narrow portion of exit cone 530 meets the other end of throat 520. In an embodiment, the entry cone, throat, and exit cone are each symmetrical if rotated about major axis 560 of the device (i.e. , the axis running through the center of the device in the primary (i.e. motive) flowstream). Each of the entry cone and the exit cone may be a truncated right circular cone, having the plane of the base parallel the opposite plane and being hollow and open at either end. The entry and exit cones may alternatively be described as a right circular frustum, open at both bases and hollow between. As shown in FIG. 5, entry cone 510 and exit cone 530 have approximately the same length. In other embodiments, the two components may have different lengths, for example, the exit cone may be longer than the entry cone. The throat may be a hollow right cylinder with a diameter matching the diameter of the cone bases. The throat diameter may be constant over the length of the throat. The throat segment additionally includes an introduction point which is an inlet through which the secondary (i.e. , return) flowstream may be introduced into the venturi device and mixed with the motive flowstream to create a combined flowstream. This feature is shown as introduction point 525.

[0043] In some embodiments, the inlet diameter and the outlet diameter may be the same. Alternatively, in some embodiments, the inlet diameter and the outlet diameter may be different. In particular, using a larger diameter for an outlet than for a corresponding inlet may accommodate embodiments in which addition of the return flow causes a significant increase in the quantity of material exiting the venturi. Alternatively, in other embodiments, such difference may not be significant, and/or may be accommodated otherwise, e.g., by compression of the combined flowstream, or by a faster flow rate on the exit side. Varying inlet and outlet diameter may assist in achieving the desired pressure variation.

[0044] In operation, a motive flowstream is provided along the major axis of the venturi device. As the cross-sectional area is reduced along the entry cone, the velocity of the motive flowstream will increase (within the regime in which mass flow is conserved, as is relevant here). Higher velocity corresponds to reduced pressure. Within the venturi device, the area of low pressure occurs at the throat. Thus, an inlet at the throat creates an introduction point where the motive flowstream pressure is substantially reduced and the return flowstream may be introduced. In embodiments of the present invention, the motive flowstream may be provided by the recycler in liquid phase, then changed by other system components (e.g. , a heat exchanger) to the gas phase before introduction to the venturi device. This permits mixing of the motive flowstream and return flowstream while both are gases. Additionally, operation of the venturi device with a gas motive flowstream may increase the performance of the venturi device.

[0045] The motive, return, and combined flowstreams are depicted with respect to venturi device 500 of FIG. 5. Flowstream 540 is the motive flowstream entering entry cone 510 of venturi device 500. Return flowstream 550 is introduced at inlet 525 and mixes with flowstream 540 to form flowstream 545, which is the combined flowstream. Flowstream 545 then leaves exit cone 530, and can then flow to a recycler.

[0046] The venturi device may be made of a material selected from: metals and alloys (e.g. aluminum, titanium, steel, stainless steel, bronze, brass); and plastics (e.g. , high density polyethylene (HDPE), low density polyethylene (LDPE), polyethylene terephthalate (PETE), polypropylene (PP), polycarbonate (PC), polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), nylons).

[0047] The venturi device may be made by any method, including, e.g. , casting, machining, molding, and additive manufacturing or printing. For example, the venturi device may be formed by casting or molding, in the form described above, in one or more pieces. Alternatively, the device may be machined from a solid piece of material, by removing the figure of the venturi device as described above, from the solid piece. That is, the relevant shape is defined by the interior surfaces of the device with which the flowstreams are in contact. Provided that the walls of the device are sufficiently thick as to ensure structural integrity of the device, the thickness and exterior dimensions may be any convenient dimensions.

[0048] In an embodiment, the entry cone, throat, and exit cone may each be separate pieces. Such a system may be designed with various sizes and shapes of each of the entry cone, throat, and exit cone, which may be interchangeable and which may be selected to create a venturi device with desired dimensions. Such assemblies are available from Vaccon Vacuum Products, Medway, Massachusetts under the trade name Vaccon(TM) Venturi Vacuum Cartridge Assembly.

[0049] Dimensions of the venturi device may be determined based upon the amount of material to be recycled, the sizes of existing system components, and the pressure change required. FIG. 6 depicts venturi device 600 showing terminology useful in referring to the dimensions of venturi devices in the present document. Namely: major axis 601, inlet diameter 602, entry cone length 603, entry angle 604, throat diameter 605, throat length 606, exit cone length 607, exit angle 608, outlet diameter 609, and inlet 625. Inlet 625 constitutes a low pressure introduction point at the throat of the venturi device. For example, the dimensions to be used in the venturi device in order to achieve an adequate volumetric flow within both the motive flowstream supplied by the recycler, and at the throat of the venturi may be determined using a mass flow equation and volumetric flow equations. The mass flow equation may be of the form: Eqn. 1

where C is the discharge coefficient, Y is the expansion factor, A₂ is the cross sectional area at the throat, Pi is the pressure at the inlet, P₂ is the pressure at the throat, Di is the diameter at the pump, D₂ is the diameter at the throat, γι is the product of the gas density (p) and acceleration due to gravity (g), and m is the mass flow.

[0050] The volumetric flow equations may be:

Eqn. 2

Eqn. 3 m

P2

where qi is the volumetric flow supplied by the recycler, pi is the density supplied by the recycler, q₂ is the volumetric flow at the throat and p₂ is the density at the throat. Where the recycler provides the motive flowstream as a fluid, pi may be the C0₂ fluid density and Pi may be the pressure at which the recycler operates. Where the flow at the throat is a gas, p₂ may be the C0₂ gas density and P₂ may be the pressure at which the GLS operates, or less.

[0051] Certain geometric relationships may assist in the determination of the dimensions of the venturi device, for example:

Eqn. 4

(Inlet Dia.—Throat Dia. )

Entry Cone Length =

2 x Tan (Entry Angle) Eqn. 5

(Outlet Dia. -Throat Dia. )

Exit Cone Length =

2 x Tan (Exit Angle) and, in the case where the inlet diameter equals the outlet diameter:

Eqn. 6

Exit Cone Length Tan(Entry Angle)

Entry Cone Length Tan (Exit Angle)

[0052] Some embodiments may include more than one venturi device, for example the embodiment depicted in FIG. 7, with venturi devices 790 and 792. While not wishing to be bound by theory, it is expected that such embodiments may be particularly beneficial at very high flow rates, as the flow rate for an embodiment with two venturi devices may be approximately twice the flow rate required for a one venturi system, and so forth. For example, while an embodiment with a single venturi device may have a flow rate of about 1200 g/min in the motive flowstream, a comparable embodiment having two venturi devices may have a flow rate of about 2400 g/min.

[0053] Now turning to FIG. 2, shown is an embodiment of a system outfitted with a return loop 205 for recycling C0₂ for reuse. In particular, FIG. 2 shows return loop 205 as a component of system 200. Return loop 205 includes recycler 260, pump 270, heat exchanger 282 upstream of venturi device 290, which is upstream of heat exchanger 284, which feeds recycler 260. System 200 also includes holding vessel 210, which holds a highly- compressible fluid supply, pump 220, injector, column, detector 230, collection vessel 240 downstream of injector, column, detector 230, and the GLS devices, GLS 250, GLS 251, and GLS 252.

[0054] In operation, and using C0₂ as the highly-compressible fluid, chromatography system 200 may manage its C0₂ supply to recycle and reuse the C0₂ after it passes through the chromatography system. Initially, C0₂ will be supplied through use of pump 220 from holding vessel 210 to injector, column, detector 230. After the analytic or preparatory separation is completed by injector, column, detector 230, the remaining mixture may be delivered to collection vessel 240, which in turn feeds GLS 250, which feeds GLS 251, which feeds GLS 252 for purification or separation of the C0₂. The separated C0₂ (from GLS 252) is fed into return loop 205 at venturi device 290. Meanwhile, within return loop 205, pump 270 pressurizes a C0₂ flow from recycler 270 through heat exchanger 282 to venturi device 290 then to heat exchanger 284 and back to recycler 260. Once C0₂ is supplied back to recycler 260, recycler 260 can begin to return C0₂ to holding vessel 210 for use in injector, column, detector 230.

[0055] For example, recycler 260 may operate at about 800 psi. To maintain a predominately liquid phase at this pressure, the temperature may be maintained at about 15- 17 °C. GLS 252 may operate at about 125 psi. By establishing a vacuum at the venturi throat, the current technology permits introducing the C0₂ gas from GLS 252 (at about 125 psi) to recycler 260 (at about 800 psi) through venturi device 290. In system 200, a heat exchanger similar to heat exchanger 160 of FIG. 1 is not required because GLS 250 may supply a gas phase return flowstream to venturi device 290. The conversion to liquid phase may then be made by heat exchanger 284.

[0056] While FIG. 2 shows return loop 205 within the context of a chromatography system, FIG. 3 depicts only a return loop 300 according to an embodiment of the present disclosure, which has recycler 360, motive flowstream 395, and venturi device 390. Recycler 360 establishes a motive flowstream to venturi device 390 where motive flowstream 395 mixes with return flowstream 355 from the chromatography system (e.g., from a GLS). The mixture of motive flowstream 395 and return flowstream 355 creates combined flowstream 397. Combined flowstream 397 flows from venturi device 390 to recycler 360. Recycler 360 may then supply a fully or partially recycled flowstream 365 to the chromatography system (e.g., to a holding vessel, pump, or injector).

[0057] The incorporation of various additional optional features is illustrated by return loop 400 of FIG. 4. These features permit system 400 to control the phase of the motive flowstream in different parts of system 400. System 400 includes pump 470, which is downstream of recycler 460. Pump 470 pressurizes motive flowstream 495 from recycler 460 to heat exchanger 482, which may be a liquid phase flowstream. Heat exchanger 482, which may be e.g., an in-line heater, may then heat motive flowstream 495 sufficiently to convert motive flowstream 495 from liquid phase to gas phase. For example, at about 800 psi, this temperature corresponds to about 60 °C. Motive flowstream 495 is then provided to venturi device 490. Movement of motive flowstream 495 through venturi device 490 creates a low-pressure introduction point which may accept return flowstream 455 from the chromatography system. Return flowstream 455 may also be a gas.

[0058] Within venturi device 490, motive flowstream 495 and return flowstream 455 may mix, forming combined flowstream 497. Combined flowstream 497 may also be a gas. Combined flowstream 497 may flow to heat exchanger 484. Heat exchanger 484 may cool combined flowstream 497 to convert combined flowstream 497 from gas phase to liquid phase. For example, at 800 psi, this temperature may correspond to about 15-17 °C. This liquid combined flowstream 497 may be returned to recycler 460. Recycler 460 may prepare and treat the combined flowstream to feed the chromatography system flowstream 465.

[0059] The present technology may also include more than one venturi device, as shown in return loop 700 of FIG. 7. Return loop 700 features venturi device 790 and venturi device 792. As shown, motive flowstream 795 from recycler 760 feeds both venturi device 790 and venturi device 792. This may be accomplished, e.g. , by providing a splitter upstream of the venturi devices or by establishing two separate motive flowstreams from the recycler. Return loop 700 includes splitter 707. Both venturi devices are fed return flowstream 755 from a chromatography system. Within each of venturi device 790 and venturi device 792, motive flowstream 795 and return flowstream 755 mix to form combined flowstream 797. Combined flowstream 797 may be united at a coupler and supplied to recycler 760, or the combined flowstream 797 may be returned in two distinct portions to recycler 760. Return loop 700 includes coupler 708. In a similar way, a return loop could feature three or more venturi devices. In a system with more than one venturi device, the return loop may be capable of controllably dividing flow between the venturi devices, for example to operate with fewer than the total number of venturi devices if such capacity, or pressure, is not required.

[0060] FIG. 8 shows method 800 according to an embodiment of the present technology. Step 810 calls for pressurizing a motive flow from the recycler. The recycler itself may generate the pressurized flow, or a pump may be included within the system in order to achieve this function. Step 820 calls for supplying the motive flowstream in the gas phase to the primary inlet of a venturi device. The primary inlet is the inlet of the entry cone which permits flow along the major axis of the venturi device. The gas phase may be achieved by heating the motive flowstream using a heat exchanger. Step 830 calls for supplying the return flowstream to the secondary inlet at the throat of the venturi device. The return flowstream is the flowstream from the purification system, such as a C0₂ flowstream. Step 840 calls for allowing the motive flowstream and return flowstream to mix in the venturi device to create a combined flowstream. Step 850 calls for return of the combined flowstream to the recycler in the fluid phase. The fluid phase may be achieved by cooling the flowstream using a heat exchanger.

[0061] One of ordinary skill in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

CLAIMS What is claimed is:

1. A device for introducing a compressible fluid return flowstream into a recycler, the device comprising:

(a) a return loop, the return loop comprising the recycler and a first venturi device, and

(b) an introduction point at a throat of the first venturi device and in fluid communication with the compressible fluid return flowstream.

2. The device of claim 1, wherein the compressible fluid is carbon dioxide.

3. The device of claim 1, wherein the device additionally comprises a second venturi device.

4. The device of claim 3, wherein the device additionally comprises a splitter and a coupler, wherein the splitter divides the flowstream between the first venturi device and the second venturi device, and the coupler receives the flowstream from both the first venturi device and the second venturi device.

5. The device of claim 1, the return loop additionally comprising a pump located downstream of the recycler and upstream of the first venturi device.

6. The device of claim 1, the return loop additionally comprising a first heat exchanger located upstream of the first venturi device, and a second heat exchanger located downstream of the first venturi device and upstream of the recycler inlet.

7. The device of claim 1, wherein the first venturi device has an exit cone and an entry cone and wherein the exit cone is between about 1.5 and 3 times longer than the entry cone.

8. The device of claim 1, wherein the first venturi device has an inlet diameter and an outlet diameter and wherein the inlet diameter is approximately equal to the outlet diameter.

9. The device of claim 8, wherein the inlet diameter is about 2 to about 3 times larger than the diameter of the throat.

10. The device of claim 8 wherein the inlet diameter and the outlet diameter are each about 0.25 mm to about 2 mm.

11. A method for introducing a compressible fluid return flowstream into a recycler, the method comprising: pressurizing a return loop from the recycler, through a venturi device, and returning to the recycler, and introducing the compressible fluid flowstream into the return loop at the venturi device.

12. A method for introducing a carbon dioxide return flowstream into a recycler system, the method comprising: providing a carbon dioxide motive flowstream to a venturi device; providing the carbon dioxide return flowstream to the venturi device at an introduction point in a throat of the venturi device; permitting the carbon dioxide motive flowstream and the carbon dioxide return flowstream to mix to create a combined carbon dioxide flowstream; and introducing the combined carbon dioxide flowstream to the recycler.

13. The method of claim 12, additionally comprising the step of heating the carbon dioxide motive flowstream before introduction to the venturi device to a temperature sufficient to achieve gas phase within the heated portion of the carbon dioxide motive flowstream.

14. The method of claim 12, additionally comprising the step of cooling the combined carbon dioxide flowstream before introduction to the recycler to a temperature sufficient to achieve liquid phase within the cooled portion of the combined carbon dioxide flowstream.

15. The method of claim 12 wherein the carbon dioxide return flowstream has a pressure below about 600 psi.

16. The method of claim 12 wherein the carbon dioxide return flowstream has a pressure below about 400 psi.

17. The method of claim 12 wherein the carbon dioxide return flowstream has a pressure below about 300 psi.

18. The method of claim 12 wherein the carbon dioxide return flowstream has a pressure below about 200 psi.

19. A method for introducing a carbon dioxide return flowstream into a recycler system, the method comprising: providing a first carbon dioxide motive flowstream to a first venturi device and a second carbon dioxide motive flowstream to a second venturi device; providing a first portion of the carbon dioxide return flowstream to the first venturi device at an introduction point in the throat of the first venturi device, and a second portion of the carbon dioxide return flowstream to the second venturi device at an introduction point in the throat of the second venturi device; permitting the first carbon dioxide motive flowstream to mix with the first portion of the carbon dioxide return flowstream to create a first combined carbon dioxide flowstream and permitting the second carbon dioxide motive flowstream to mix with the second portion of the carbon dioxide return flowstream to create a second combined carbon dioxide flowstream; and returning the first combined carbon dioxide flowstream and the second combined carbon dioxide flowstream to the recycler.

20. The method of claim 19, additionally comprising using a third carbon dioxide motive flowstream feeding a third venturi device to accept a third portion of the carbon dioxide return flowstream and form a third combined carbon dioxide flowstream.

21. A fluid recovery system for a chromatography system comprising: a plurality of gas-liquid separators; a recycler; a return loop, fed by and returned to the recycler; and a venturi device, arranged so that a primary flowpath through the venturi device is a segment of the return loop and a secondary flowpath is fed from the one or more gas-liquid separators.

22. The fluid recovery system of claim 21, wherein the return loop additionally comprises a first heat exchanger upstream of the venturi device and a second heat exchanger downstream of the venturi device.

23. The fluid recovery system of claim 21, additionally comprising a second venturi device.