System for Pumping a Compressible Liquid

Abstract

A system for pumping a compressible fluid, a chromatography system comprising the system for pumping a compressible fluid, and a chromatography method using the system for pumping a compressible fluid, the system for pumping a compressible fluid comprising at least two pumps including a first pump and a second pump, respective pump outlet lines of which are brought together in a connection piece and are guided out of this connection piece into a common outlet line, wherein the second pump is controllable by a control unit, wherein the control unit is operatively connected to a flowmeter and the pump output of the second pump is controllable as a function of the flow measurement by the control unit.

Claims

1. A system for pumping a compressible fluid, comprising at least two pumps including a first pump and a second pump, each pump having a pump outlet line, the respective pump outlet lines of which are brought together in a connection piece and are guided out of the connection piece into a common outlet line, wherein the second pump is controllable by a control unit, wherein the control unit is operatively connected to a flowmeter, and pump output of the second pump is controllable as a function of the flow measurement by the control unit.

2. The system according to claim 1, wherein the flowmeter is arranged in the common outlet line.

3. The system according to claim 1, wherein viewed in a direction of flow, a heat exchanger is provided in the common outlet line downstream of the connection piece and upstream of the flowmeter.

4. The system according to claim 1, wherein, viewed in the direction of flow, a pulsation damper is provided in the common outlet line downstream of the connection piece and upstream of the flowmeter.

5. The system according to claim 1, wherein the first pump and/or the second pump is a piston pump with two pistons.

6. The system according to claim 1, wherein, viewed in the direction of flow, a pressure measurement sensor is provided in the first pump outlet line between an outlet of the first pump and the connection piece, wherein the pressure measurement sensor is operatively connected to the control unit.

7. The system according to claim 1, wherein pump output of the first pump is higher than the pump output of the second pump.

8. A chromatography system comprising a system for pumping a compressible fluid according to claim 1.

9. The chromatography system according to claim 8 wherein, in addition to the system for pumping a compressible, the chromatography system comprises a third pump which is connected to a fluid reservoir for a second fluid.

10. The chromatography system according to claim 8, wherein the chromatography system includes a chromatography column and, downstream, viewed in a direction of flow, at least one backpressure regulator.

11. The chromatography system according to claim 10, wherein, viewed in the direction of flow, a gas-liquid separator is provided downstream of the backpressure regulator.

12. The chromatography system according to claim 8, wherein the chromatography system is controllable by a chromatography system controller and the chromatography system controller is operatively connected to or forms a unit with the control unit of the system for pumping a compressible fluid.

13. The chromatography system according to claim 8, wherein the chromatography system is formed as a supercritical fluid chromatography (SFC) system, wherein a chromatographic procedure with a solvent gradient is performable.

14. A method for performing a chromatographic procedure comprising using a chromatography system according to claim 8.

15. A set for converting a high pressure liquid chromatography (HPLC) system into a chromatography system according to claim 8 comprising at least one system for pumping a compressible fluid according to claim 1 and a gas-liquid separator.

16. The system according to claim 7, wherein the pump output of the first pump is at least twice the pump output of the second pump.

Description

[0089] In the following, preferred embodiments of the present invention shall be described by way of example with reference to four figures, without any restriction of the invention being intended. Therein:

[0090] FIG. 1 is a representation of a first embodiment of a system according to the invention for pumping a compressible fluid,

[0091] FIG. 2 is a representation of a second embodiment of a system according to the invention for pumping a compressible fluid,

[0092] FIG. 3 is a representation of a third embodiment of a system according to the invention for pumping a compressible fluid,

[0093] FIG. 4 is a schematic representation of a chromatography system with a system according to the invention for pumping a compressible fluid.

[0094] FIG. 1 describes a first embodiment of a system according to the invention for pumping a compressible fluid.

[0095] The system comprises two pumps, a first pump (10) and a second pump (20), the respective pump outlet lines (12, 22) of which are brought together in a connection piece (36) and guided out from said connection piece (36) into a common outlet line (40).

[0096] In the present embodiment, the pumps are connected to a reservoir (28), wherein the fluid line (30) via which a fluid is guided into the first pump (10) comprises a branch, such that the second pump (20) is correspondingly supplied with fluid via the fluid line (32).

[0097] The first pump (10) has two pistons (14, 16), the pump head of which in each case has cooling (15, 17). The second pump (20) likewise comprises two pistons (24, 26) which are in each case equipped with pump head cooling (25, 27). Pump head cooling is in particular expedient for maintaining the fluid in a liquid state since gas formation can be effectively prevented in this manner.

[0098] The fluid is guided into the outlet line (40) via the connection piece (36) which brings together the respective pump outlet lines (12, 22). The outlet line (40) in the present embodiment firstly comprises a pulsation damper (44) which can for example take the form of a relatively large vessel into and out of which the fluid is guided. In the present case are then arranged, viewed in the direction of flow, a heat exchanger (46) and a flowmeter (48).

[0099] The flowmeter (48) is connected to a control unit (50), by means of which the second pump (20) is controllable. In the present embodiment, the control unit (50) is connected via the control line (52) to the second pump (20) and via the measurement line (54) to the flowmeter (48).

[0100] The pump output of the second pump (20) is controllable by means of the control unit (50) as a function of flow measurement. In the control unit (50), a nominal flow rate is here preferably compared with an actual value thereof and the pump output of the second pump (20) correspondingly adapted to equalize the two values. Due to the compressibility of the fluid, for example of the liquid or supercritical carbon dioxide (CO.sub.2), the actual value is conventionally always lower than the nominal value, such that the pump output of the second pump (20) is always greater than or equal to zero.

[0101] In the present embodiment, the nominal value of the first pump (10) can be determined by means of the chromatography system controller (56), wherein a data line (58) provides a connection between the chromatography system controller (56) and the control unit (50), via which the control unit (50) receives the corresponding values. It is, however, obvious to a person skilled in the art that the chromatography system controller (56) and the control unit (50) can be designed as one item of equipment. The first pump (10) can be controlled by means of the chromatography system controller (56), wherein the corresponding connection is not shown for reasons of clarity.

[0102] In the present embodiment, the devices shown are in particular suitable for converting an existing HPLC system, wherein the control unit (50) is separate from the chromatography system controller (56). The second pump (20) is controlled in such a manner that any shortfall in the volume of fluid caused by compression of the compressible fluid and identified by the comparison between the nominal flow rate and actual flow rate is made up by means of the pump output from the second pump (20).

[0103] FIG. 2 shows a second embodiment of a system according to the invention for pumping a compressible fluid.

[0104] This embodiment likewise comprises two pumps, a first pump (10) and a second pump (20), wherein the respective pump outlet lines (12, 22) of which are brought together in a connection piece (36) and guided out from said connection piece (36) into a common outlet line (40). In the outlet line (40) is provided a flowmeter (48) which is connected to a control unit (50) by means of which the second pump (20) is controllable. In the present embodiment, the control unit (50) is connected via the control line (52) to the second pump (20) and via the measurement line (54) to the flowmeter (48).

[0105] The device shown in FIG. 2 thus corresponds in many details to the system shown in FIG. 1, wherein identical reference signs denote identical components, such that the explanations provided in respect of FIG. 1 also apply to the second embodiment.

[0106] The embodiment described in FIG. 2 in particular differs in that the nominal values of the flow rate of the first pump (10) are not provided by the chromatography system controller (56).

[0107] This nominal output therefore has to be determined by other methods. The corresponding flow rate of the first pump (10) is determined in the present embodiment on the basis of the frequency of the first pump (10). A pressure sensor, which is connected via measurement line (64) to control unit (50), is provided to this end in the outlet line (12) of the first pump (10). Pump frequency can be determined by measuring the pressure variations which accompany the piston stroke of a piston pump. Multiplying the pump frequency by the known swept volume provides the flow rate of the first pump (10) as a nominal value. A non-return valve (68) is provided in the outlet line (12) of the first pump (10) between the sensor, connected via the measurement line (64) to the control unit (50), and the connection piece (36) in order to improve measuring accuracy.

[0108] FIG. 3 shows a third embodiment of a system according to the invention for pumping a compressible fluid.

[0109] This embodiment likewise comprises two pumps, a first pump (10) and a second pump (20), wherein the respective pump outlet lines (12, 22) of which are brought together in a connection piece (36) and guided out from said connection piece (36) into a common outlet line (40). In the outlet line (40) is provided a flowmeter (48) which is connected to a control unit (50) by means of which the second pump (20) is controllable. In the present embodiment, the control unit (50) is connected via the control line (52) to the second pump (20) and via the measurement line (54) to the flowmeter (48).

[0110] The device shown in FIG. 3 therefore corresponds in many details to the systems shown in FIGS. 1 and 2, wherein identical reference signs denote identical components, such that the explanations provided in respect of FIGS. 1 and 2 also apply to the third embodiment.

[0111] The embodiment described in FIG. 3 in particular differs from the configuration described in FIG. 2 in that the system has a cooled fluid feed line. Cooling for the fluid (34) is accordingly provided between the reservoir (24) and the inlet lines to the first pump (10) and the second pump (20).

[0112] This configuration is in particular expedient for reservoirs in which the fluid is stored and supplied to the pumps under relatively low pressure. In the case of CO.sub.2, gas formation can occur if the reservoir has a pressure of 60 bar or below, such that corresponding cooling is expedient in order to keep the fluid in the liquid or supercritical state on supply to the pumps. Details with regard to the corresponding temperature or pressure are obtainable from the fluid's boiling point diagram.

[0113] FIG. 4 is a schematic representation of a chromatography system 100 with a system according to the invention for pumping a compressible fluid.

[0114] Such a system is described by way of example using supercritical CO.sub.2, wherein methanol is shown as an exemplary solvent. Obviously, systems in which other solvents, preferably organic solvents are applied, or other supercritical fluids are used, have a similar structure.

[0115] As shown in FIG. 4, the respective fluids are stored in reservoirs (102, 104) and supplied to the system with a system according to the invention for pumping a compressible fluid (106) or a pump (108). In particular, the gas subsequently used in a supercritical state is stored in a storage tank (102) and supplied to the further components of the system by means of a system according to the invention for pumping a compressible fluid (106). The solvent is provided in a storage tank (104) which is delivered by means of a pump (108) to the further components of the system. In the system 100 described here, a preparation stage (110, 112) is preferably provided in each fluid feed line, by means of which the fluids can be temperature controlled. Further, a leveling of the pressure fluctuations indicated by the pumps can also be provided. Accordingly, this preparation stage can be designed, for example, as a heat exchanger or as a pump. Depending on the configuration of system for pumping a compressible fluid (106), component (110) can be part of the system according to the invention (106). In the solvent line, an addition unit (114) can preferably be provided, for example an injector, by means of which a mixture to be segregated is introduced into the system (100) before the CO.sub.2 and the solvent are passed into a mixer (116) and from the latter to a chromatography column (118).

[0116] In the present system (100), two analysis units are arranged downstream of the chromatography column (118), wherein a sample discharge unit (120) is connected to a mass spectrometer (122) and a UV detector (124) is provided downstream of the sample discharge unit. The backpressure regulator (126) provided in the line maintains the particular pressure that is necessary for the fluid to remain in a supercritical state. Downstream of the backpressure regulator (126) is provided a heat exchanger (128) which prevents the aerosol from freezing during the expansion process. Subsequently, the aerosol is introduced into a gas-liquid separator (130) according to the invention, wherein the gas in the system is discharged via an outlet (132).

[0117] The liquid is introduced into a fraction collector (134) and fractionated therein. The solvent contained in the fractionated samples can be removed from the samples.

[0118] The features of the invention disclosed in the preceding description, as well as in the claims, figures and exemplary embodiments, can be essential both individually and in any combination for realizing the invention in its various embodiments.

[0119] Systems which allow the nominal flow rate of the first pump to be established by means of the chromatography system controller may accordingly also include cooling of the fluid between reservoir and pumps. The optional components, for example the pulsation damper or the heat exchanger, can furthermore, if present, also be arranged in different locations.