Patent Publication Number: US-2022229024-A1

Title: Liquid carbon dioxide supply device and supercritical fluid apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a liquid carbon dioxide sending supply device and a supercritical fluid apparatus. 
     BACKGROUND ART 
     In a supercritical fluid apparatus such as a supercritical fluid chromatograph (SFC) or a supercritical fluid extraction device (SFE), a sample is analyzed or sorted with a supercritical fluid used as a mobile phase. For example, in an SFC described in Patent Document 1, liquid carbon dioxide is supplied as a mobile phase to a mobile phase flow path by a liquid sending pump. Further, a sample is injected into the mobile phase flow path by a sample injector. 
     The mobile phase and the sample pass through a separation column arranged in the mobile phase flow path. Here, the pressure in the mobile phase flow path is kept by a back-pressure valve and the temperature of the separation column is kept by a column oven such that the mobile phase is in a supercritical state at least in the separation column. The sample is separated into sample components by passing through the separation column and detected by a detector. 
     [Patent Document 1] JP 2016-173343 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the supercritical fluid extraction device, a flow path for carbon dioxide is cooled to keep carbon dioxide a liquid phase. In a case where the volume of liquid carbon dioxide is large, a chiller is generally used to cool the flow path. However, the chiller is relatively large and is often installed on the floor. Therefore, an installation space for the chiller is large, so that the size of the supercritical fluid apparatus is increased. Further, because a pipe is cooled indirectly with use of a refrigerant such as water, the temperature of liquid carbon dioxide cannot be controlled stably. In this case, the flow rate of liquid carbon dioxide becomes unstable since density of liquid carbon dioxide becomes unstable. 
     An object of the present invention is to provide a liquid carbon dioxide sending supply device and a supercritical fluid apparatus that can supply liquid carbon dioxide at a stable flow rate while an increase in size of the liquid carbon dioxide sending supply device and the supercritical fluid apparatus is suppressed. 
     Solution to Problem 
     An aspect according to the present invention relates to a liquid carbon dioxide supply device that supplies liquid carbon dioxide to a supercritical fluid apparatus including a separation column and includes first and second flow paths, a compressor that circulates a first refrigerant through the first flow path such that a refrigerant cycle is repeated, a heat exchanger that exchanges heat between the first flow path and the second flow path, and a pump that supplies liquid carbon dioxide flowing through the second flow path to the separation column. 
     Advantageous Effects of Invention 
     The present invention enables supply of liquid carbon dioxide at a stable flow rate while an increase in size of a liquid carbon dioxide sending supply device and a supercritical fluid apparatus is suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of a supercritical fluid apparatus according to one embodiment of the present invention. 
         FIG. 2  is a diagram showing the configuration of a liquid carbon dioxide supply device of  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (1) Configuration of Supercritical Fluid Apparatus 
     A liquid carbon dioxide sending supply device and a supercritical fluid apparatus according to embodiments of the present invention will be described below in detail with reference to the drawings.  FIG. 1  is a diagram showing the configuration of the supercritical fluid apparatus according to one embodiment of the present invention. As shown in  FIG. 1 , the supercritical fluid apparatus  200  is a supercritical fluid chromatograph (SFC) and includes the liquid carbon dioxide supply device  100 , a modifier supply device  110 , a mixer  120 , a sample supplier  130 , a separation column  140 , a detector  150 , a back-pressure valve  160  and a controller  170 . 
     Bottles  201 ,  202  are provided in the supercritical fluid apparatus  200 . Liquid carbon dioxide that is cooled to about 5° C., for example, is stored as a mobile phase in the bottle  201 . The liquid carbon dioxide supply device  100  pumps the liquid carbon dioxide stored in the bottle  201  while cooling the liquid carbon dioxide. Details of the liquid carbon dioxide supply device  100  will be described below. 
     A modifier such as an organic solvent is stored as a mobile phase in the bottle  202 . The modifier supply device  110  is a liquid sending pump, for example, and pumps the modifier stored in the bottle  202 . The mixer  120  is a gradient mixer, for example, and supplies the mobile phases that have been respectively pumped by the liquid carbon dioxide supply device  100  and the modifier supply device  110  while mixing the mobile phases at a predetermined ratio. 
     The sample supplier  130  is an injector, for example, and introduces a sample to be analyzed into the separation column  140  together with a mobile phase supplied by the mixer  120 . The separation column  140  is contained in a column oven (not shown) and heated to a predetermined temperature (about 40° C. in the present example) such that liquid carbon dioxide in the introduced mobile phase is put in a supercritical state. The separation column  140  separates the introduced sample into components according to differences in chemical property or composition. 
     The detector  150  is an absorbance detector, for example, and detects components into which the sample has been separated by the separation column  140 . A result of detection by the detector  150  is used to generate a supercritical fluid chromatogram representing the relationship between a retention time of each component and a detection intensity, for example. The back-pressure valve  160  keeps the pressure applied to the mobile phase in the flow path at a value equal to or larger than a critical pressure of liquid carbon dioxide (8 MPa, for example) such that the liquid carbon dioxide in the mobile phase is put in a supercritical state at least in the separation column  140 . 
     The controller  170  includes a CPU (Central Processing Unit) and a memory, or a microcomputer or the like and controls the operation of each of the liquid carbon dioxide supply device  100 , the modifier supply device  110 , the mixer  120 , the sample supplier  130 , the separation column  140  (the column oven), the detector  150  and the back-pressure valve  160 . Further, in a case where a sorting device such as a fraction collector is provided at a position farther downward than the back-pressure valve  160 , the controller  170  further controls the operation of the sorting device based on a result of detection by the detector  150 . The controller  170  may be provided in the back-pressure valve  160 . 
     (2) Configuration of Liquid Carbon Dioxide Supply Device 
       FIG. 2  is a diagram showing the configuration of the liquid carbon dioxide supply device  100  of  FIG. 1 . As shown in  FIG. 2 , the liquid carbon dioxide supply device  100  includes a cooler  10  and a pump  20 . Further, flow paths  1 ,  2 ,  3  are provided in the liquid carbon dioxide supply device  100 . Each of the flow paths  1  to  3  is a pipe, for example. The flow paths  1  to  3  are examples of first to third flow paths, respectively. In the following description, in the flow paths  2 ,  3 , the direction in which liquid carbon dioxide or a refrigerant flows is defined as downstream, and its opposite direction is defined as upstream. 
     The cooler  10  includes a heat exchanger  11 , a compressor  12 , a storage  13  and a liquid sender  14 . The heat exchanger  11  includes a block  11   a  and a metallic material  11   b . The block  11   a  is constituted by four side surfaces, an upper surface and a bottom surface formed of sheets of metal and has a cuboid shape. Parts of the respective flow paths  1 ,  2 ,  3  are contained in the block  11   a . The metallic material  11   b  includes tin, for example, and the block  11  a is filled with the melted metallic material  11   b . Thus, the gaps among the flow paths  1 ,  2 ,  3  are filled with the metallic material  11   b  in the block  11   a.    
     The both ends of the flow path  1  are drawn out from the block  11   a  and connected to the compressor  12 . The compressor  12  circulates a refrigerant such as fluorocarbon 407C (R-407C) through the flow path  1  such that a refrigerant cycle is repeated. Thus, the inside of the block  11   a  is cooled. In the present example, the flow path  1  is provided while being wound in a coil shape in the block  11   a . Therefore, even in a case where the sufficiently long flow path  1  is used, the block  11   a  is kept compact. Thus, it is possible to sufficiently cool the inside of the block  11   a  by using the sufficiently long flow path  1 . 
     The flow path  2  connects the bottle  201  and the mixer  120  to each other. The heat exchanger  11  and the pump  20  are provided in this order from an upstream portion toward a downstream portion in the flow path  2 . In the block  11   a , heat is exchanged between the flow path  1  and the flow path  2  through the metallic material  11   b . Thus, the liquid carbon dioxide supplied from the bottle  201  to the mixer  120  is cooled. In the present example, the flow path  2  is provided in the block  11   a  in a meander-shape. Therefore, the length of the portion of the flow path  2  provided in the block  11   a  can be increased. Therefore, the liquid carbon dioxide can be cooled sufficiently. 
     The storage  13  is a bottle, for example, and stores a refrigerant such as ethylene glycol having a concentration of 60%. The liquid sender  14  is a diaphragm pump, for example, and pumps the refrigerant stored in the storage  13  to the pump  20  through the flow path  3 . The heat exchanger  11  is provided in the portion of the flow path  3  between the liquid sender  14  and the pump  20 . In the block  11   a , heat is exchanged between the flow path  1  and the flow path  3  through the metallic material  11   b . Thus, the refrigerant supplied from the liquid sender  14  to the pump  20  is cooled. The refrigerant supplied to the pump  20  is returned to the storage  13  through the flow path  3 . 
     In the present example, the pump  20  is a parallel plunger pump and includes two pump heads  21 ,  22 . In the pump  20 , the flow path  2  includes main flow paths  2   a ,  2   b  and branch flow paths  2   c ,  2   d . The main flow paths  2   a ,  2   b  are respectively connected to the cooler  10  and the mixer  120 . The branch flow paths  2   c ,  2   d  are arranged in parallel with each other as two flow paths into which each of the main flow paths  2   a ,  2   b  is branched. The pump heads  21 ,  22  are respectively provided in the branch flow paths  2   c ,  2   d  and alternately pumps the liquid carbon dioxide stored in the bottle  201  to the mixer  120  through the cooler  10 . 
     Further, in the pump  20 , the flow path  3  includes main flow paths  3   a ,  3   b  and branch flow paths  3   c ,  3   d . The main flow paths  3   a ,  3   b  are respectively connected to the heat exchanger  11  and the storage  13  of the cooler  10 . The branch flow paths  3   c ,  3   d  are arranged to be in parallel with each other as two flow paths into which each of the main flow paths  3   a ,  3   b  is branched, and are respectively attached to the surfaces of the pump heads  21 ,  22 . A refrigerant supplied from the heat exchanger  11  through the main flow path  3   a  flows through the branch flow paths  3   c ,  3   d . Thus, the pump heads  21 ,  22  are cooled. The refrigerant that has flown through the branch flow paths  3   c ,  3   d  is returned to the storage  13  through the main flow path  3   b.    
     (3) Operation of Controller 
     With the above-mentioned cooling mechanism, in the heat exchanger  11 , the flow path  1  is cooled to about −30° C., for example, and each of the flow paths  2 ,  3 , is cooled to about −10° C. On the other hand, the temperature of the liquid carbon dioxide flowing through the flow path  2  is preferably another value (about 5° C. in the present example). Further, the temperatures of the pump heads  21 ,  22  are preferably another value (about 5° C. in the present example). 
     As such, heaters  15 ,  16  are respectively attached to downstream portions of the flow paths  2 ,  3  drawn out from the block  11   a . The heaters  15 ,  16  are examples of first and second heaters, respectively. Further, at a position farther downward than the heater  15 , a temperature sensor  4  is attached to the surface of the flow path  2 . Further, temperature sensors  5 ,  6  are respectively attached to the surfaces of the pump heads  21 ,  22 . Each of the temperature sensors  4  to  6  includes a thermistor, for example. The temperature sensor  4  is an example of a first temperature sensor, and the temperature sensors  5 ,  6  are examples of a second temperature sensor. The operations of the heaters  15 ,  16  are controlled independently from the controller  170  of  FIG. 1 . 
     Specifically, the operation of the heater  15  is controlled such that a temperature detected by the temperature sensor  4  is a desired temperature. Here, because the temperature sensor  4  is directly attached to the surface of the flow path  2 , the temperature of liquid carbon dioxide flowing through the flow path  2  is detected accurately as a temperature of the flow path  2 . Therefore, with the above-mentioned control, the temperature of liquid carbon dioxide flowing through the flow path  2  can be kept at a desired temperature. The temperature sensor  4  may be fixed to the flow path  2  by a conductive tape or a conductive adhesive having a high heat transfer property. In this case, the temperature of the flow path  2  can be detected with higher accuracy. 
     Similarly, the operation of the heater  16  is controlled such that the temperatures detected by the temperature sensors  5 ,  6  are desired temperatures. Thus, the temperatures of the pump heads  21 ,  22  can be maintained at desired temperatures. The temperature sensors  5 ,  6  may be directly attached to the surfaces of the branch flow paths  3   c ,  3   d , and the temperatures of the pump heads  21 ,  22  may be respectively detected as temperatures of the branch flow paths  3   c ,  3   d.    
     (4) Effects 
     In the supercritical fluid apparatus  200  according to the present embodiment, because a chiller is not required in order to cool the flow path  2 , an increase in size of the liquid carbon dioxide supply device  100  is suppressed. In this case, the liquid carbon dioxide supply device  100  does not have to be installed on the floor and can be placed on a table. Therefore, a large space can be ensured in the supercritical fluid apparatus  200 , and this can save space. 
     Further, the flow path  2  can be directly cooled without use of a refrigerant such as water. Therefore, the temperature of liquid carbon dioxide is stabilized, so that density of the liquid carbon dioxide is stabilized. As a result, it is possible to supply liquid carbon dioxide at a stable flow rate while suppressing an increase in size of the liquid carbon dioxide supply device  100  and the supercritical fluid apparatus  200 . 
     Further, the flow path  2  is heated by the heater  15  based on a temperature detected by the temperature sensor  4 . Here, because the temperature sensor  4  is directly attached to the surface of the flow path  2 , the temperature of the flow path  2  can be detected with high accuracy as a temperature of liquid carbon dioxide flowing through the flow path  2 . Therefore, the temperature of liquid carbon dioxide can be adjusted easily to a desired temperature. Thus, liquid carbon dioxide can be supplied at a more stable flow rate. 
     Further, in a case where the flow rate of liquid carbon dioxide is small, the temperature of liquid carbon dioxide is likely to change due to an effect of outside air in a portion of the flow path  2  from the heat exchanger  11  to the pump  20 . Even in this case, heat is exchanged by the heat exchanger  11  between the flow path  1  and the flow path  3 . Further, the temperature of the flow path  3  is adjusted by the heater  16  to a desired temperature based on temperatures of the pump heads  21 ,  22  respectively detected by the temperature sensors  5 ,  6 . Thus, the pump heads  21 ,  22  are cooled to desired temperatures through a refrigerant flowing through the flow path  3 . As a result, the temperature of liquid carbon dioxide supplied by the pump  20  can be stabilized more sufficiently. 
     (5) Other Embodiments 
     (a) While the cooler  10  is configured to be capable of cooling the pump heads  21 ,  22  of the pump  20  in the above-mentioned embodiment, the embodiment is not limited to this. In a case where the temperatures of the pump heads  21 ,  22  are sufficiently stable or a case where the temperatures of the pump heads  21 ,  22  are adjusted by another temperature adjustment device, the cooler  10  does not have to be configured to be capable of cooling the pump heads  21 ,  22  of the pump  20 . 
     (b) While the heater  15  is attached to a downstream portion of the flow path  2  drawn out from the block  11   a  in the above-mentioned embodiment, the embodiment is not limited to this. The heater  15  may be attached to an upstream portion of the flow path  2  drawn out from the block  11   a . Even in this case, the temperature sensor  4  is attached to the flow path  2  at a position farther downstream than the heat exchanger  11  and the heater  15 . 
     While the heater  16  is similarly attached to a downstream portion of the flow path  3  drawn out from the block  11   a , the embodiment is not limited to this. The heater  16  may be attached to an upstream portion of the flow path  3  drawn out from the block  11   a.    
     Further, in a case where liquid carbon dioxide flowing through the flow path  2  is cooled by the heat exchanger  11  to a desired temperature, the heater  15  does not have to be attached to the flow path  2 . In a case where the pump heads  21 ,  22  are cooled to a desired temperature by the heat exchanger  11 , the heater  16  does not have to be attached to the flow path  3 . 
     (c) While the supercritical fluid apparatus  200  is configured as an SFC in the above-mentioned embodiment, the embodiment is not limited to this. The supercritical fluid apparatus  200  may be configured as a supercritical fluid extraction device (SFE). Alternatively, the supercritical fluid apparatus  200  may be configured as an SFC-MS in which a mass spectrometer (MS) is provided instead of the detector  150 . 
     (Aspects) 
     (Item 1) A liquid carbon dioxide supply device according to one aspect that supplies liquid carbon dioxide to a supercritical fluid apparatus including a separation column, may include first and second flow paths, a compressor that circulates a first refrigerant through the first flow path such that a refrigerant cycle is repeated, a heat exchanger that exchanges heat between the first flow path and the second flow path, and a pump that supplies liquid carbon dioxide flowing through the second flow path to the separation column. 
     In this liquid carbon dioxide supply device, the first refrigerant is circulated through the first flow path by the compressor such that the refrigerant cycle is repeated. In this case, in the heat exchanger, heat is exchanged between the first flow path and the second flow path, and the second flow path is cooled. Therefore, the liquid carbon dioxide flowing through the second flow path is cooled. The liquid carbon dioxide cooled in the second flow path is supplied to the separation column of the supercritical fluid apparatus by the pump. 
     With this configuration, because it is not necessary to use a chiller to cool the second flow path, an increase in size of the liquid carbon dioxide supply device is suppressed. Further, it is possible to cool the second flow path directly without using a refrigerant such as water. Therefore, the temperature of liquid carbon dioxide is stabilized, so that density of the liquid carbon dioxide is stabilized. As a result, it is possible to supply liquid carbon dioxide at a stable flow rate while suppressing an increase in size of the liquid carbon dioxide supply device. 
     (Item 2) The liquid carbon dioxide supply device according to item 1, wherein the heat exchanger may include a block having an inner space that contains part of the first flow path and part of the second flow path, and a metallic material that fills the inner space of the block to fill in a gap between the first flow path and the second flow path. 
     In this case, heat can be exchanged efficiently between the first flow path and the second flow path through the metallic material. 
     (Item 3) The liquid carbon dioxide supply device according to item 1 or 2, may further include a first heater that heats the second flow path. 
     In this case, it is possible to easily keep the temperature in the second flow path at a desired temperature by heating the second flow path. Thus, the temperature of the liquid carbon dioxide flowing through the second flow path can be kept at a desired temperature. 
     (Item 4) The liquid carbon dioxide supply device according to item 3, may further include a first temperature sensor that is attached to the second flow path at a position farther downstream than the heat exchanger and the first heater and detects a temperature in the second flow path. 
     In this case, because the first temperature sensor is attached to the second flow path, the temperature of the second flow path can be detected with high accuracy as a temperature of the liquid carbon dioxide flowing through the second flow path. Therefore, the temperature of the liquid carbon dioxide flowing through the second flow path can be easily adjusted by the first heater based on a detected temperature. Thus, the liquid carbon dioxide can be supplied at a more stable flow rate. 
     (Item 5) The liquid carbon dioxide supply device according to item 1 or 2, may further include a third flow path in which a second refrigerant circulates, wherein the heat exchanger may further exchange heat between the first flow path and the third flow path, and the pump may include a pump head to which part of the third flow path is attached. 
     In a case where the flow rate of liquid carbon dioxide is small, the temperature of liquid carbon dioxide is likely to change due to an effect of outside air in the portion of the second flow path from the heat exchanger to the pump. Even in this case, with the above-mentioned configuration, the pump head is cooled by the third flow path. Thus, the temperature of liquid carbon dioxide supplied by the pump can be stabilized more sufficiently. 
     (Item 6) The liquid carbon dioxide supply device according to item 5, may further include a second heater that heats the third flow path. 
     In this case, it is possible to easily keep the temperature of the third flow path at a desired temperature by heating the third flow path. Thus, the temperature of the pump head can be kept at a desired temperature through the second refrigerant flowing through the third flow path. As a result, the temperature of liquid carbon dioxide supplied by the pump can be kept at a desired temperature. 
     (Item 7) The liquid carbon dioxide supply device according to item 6 may further include a second temperature sensor that detects a temperature of the pump head. 
     In this case, the temperature of the third flow path can be easily adjusted by the second heater based on a temperature detected by the second temperature sensor. 
     (Item 8) A supercritical fluid apparatus according to another aspect may include a separation column, the liquid carbon dioxide supply device according to claim  4  that supplies liquid carbon dioxide to the separation column, and a controller that controls an operation of the first heater such that a temperature detected by the first temperature sensor of the liquid carbon dioxide device is a preset temperature. 
     In this supercritical fluid apparatus, the operation of the first heater is controlled by the controller such that the temperature detected by the first temperature sensor of the above-mentioned liquid carbon dioxide supply device is a preset temperature. Thus, the temperature of liquid carbon dioxide flowing through the second flow path is kept at a desired temperature. With this configuration, it is possible to supply liquid carbon dioxide to the separation column at a stable flow rate while suppressing an increase in size of the liquid carbon dioxide supply device.