Method for purification in a supercritical medium and associated device

Abstract

The invention relates to a purification method comprising the following steps: forming a solution comprising a solute (70) and a supercritical fluid; then separating the solute from the supercritical fluid. The method further comprises, after the step of forming the solution, a step of moving a flow (74) comprising the solution; and the step of separating the solute from the supercritical fluid comprises: - passing the flow through a filtration membrane (34), the membrane comprising a filtration surface (46) arranged substantially vertically; - retaining the solute (70) on the filtration surface, with the supercritical fluid passing through the filtration membrane; and - moving, using gravity, the retained solute to a collection receptacle (50) arranged beneath the filtration surface.

Description

[0001] DESCRIPTION

[0002] Supercritical purification process and associated device

[0003] The present invention relates to a purification method comprising the following steps: forming a solution comprising at least a first solute and a supercritical fluid; then separating the first solute and the supercritical fluid.

[0004] Supercritical fluids, particularly supercritical carbon dioxide (CO2), are commonly used to extract compounds from plant matrices. Supercritical CO2 is a solvent for non-polar or slightly polar compounds. Extracted products, particularly vegetable oils, are thus obtained with a high level of purity, without any trace of organic solvent.

[0005] However, products extracted by supercritical CO2 are frequently recovered by precipitation, during a step of expanding the CO2 to a gaseous state. Recycling the CO2 then requires a compression step, which is energy-intensive.

[0006] The recovery of products by supercritical membrane filtration eliminates the CO2 expansion step. Such supercritical membrane filtration is notably described for rice oil by Brunner et al., Auftrennung überkritischer Fluidgemische mithilfe von Hochdruckmembrane, Institut für Therm ische Verfahrenstechnik, Technische Universitàt Hamburg-Harburg, 2007.

[0007] D’autres exemples de filtrations membranaires en milieu supercritique sont notamment décrits dans les documents suivants : O. Akin, K. Araus, et F. Temelli, « Separation of lipid mixtures using a coupled supercritical CO2-membrane technology system », Separation and Purification Technology, vol. 156, p. 691-698, déc. 2015 ; T. Higashijima, H. Ohya, Y. Tsuchiya, H. Tokunaga, M. Aihara, et Y. Negishi, « Separation of supercritical fluid mixtrues of CO2 and petroleum components with an asymmetric polyimide membrane », Journal of Membrane Science, vol. 93, n° 2, p. 165-173, août 1994 ; S. J. Sarrade, G. M. Rios, et M. Cariés, « Supercritical CO2 extraction coupled with nanofiltration separation: Applications to natural products », Separation and Purification Technology, vol. 14, n° 1 , p. 19-25, août 1998 ; J. M. de Moura, L. A. Gonçalves, L. A. Sarmento, et J. C. C. Petrus, « Purification of structured lipids using SCCO2 and membrane process », Journal of Membrane Science, vol.299, n° 1-2, p. 138-145, 2007.

[0008] However, known supercritical membrane filtration processes are difficult to apply industrially. In particular, the retentate that accumulates on the filtration membranes ends up clogging them, reducing the flow rate passing through said membranes.

[0009] The aim of the present invention is to propose a purification process in a supercritical medium, allowing large-scale application at low energy cost.

[0010] To this end, the invention relates to a method of the aforementioned type, in which: the method further comprises, after the step of forming the solution, a step of moving a first flow comprising the solution; ; and the step of separating the first solute and the supercritical fluid comprises: passing said first flow through a first filtration membrane, said first membrane comprising a first filtration surface, arranged substantially vertically; retaining the first solute on said first filtration surface, the supercritical fluid passing through the first filtration membrane; and moving said retained first solute by gravity to a first recovery container, arranged vertically above said first filtration surface.

[0011] Such a process makes it possible in particular to drastically limit the clogging of the first filtration membrane.

[0012] According to other advantageous aspects of the invention, the method comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0013] - the supercritical fluid is supercritical carbon dioxide;

[0014] - the solution comprising at least the first solute and the supercritical fluid is single-phase;

[0015] - a concentration of the first solute in the first flow is greater than or equal to 90% of a saturation concentration of said first solute in the supercritical fluid;

[0016] - the concentration of the first solute in the first flow is greater than or equal to 95% of the saturation concentration of said first solute in the supercritical fluid;

[0017] - the supercritical fluid has a first pressure upstream of the first filtration membrane and a second pressure downstream of said first filtration membrane, the second pressure being less than or equal to the first pressure;

[0018] - after passing through the first filtration membrane, the supercritical fluid is subjected to a compression step up to a third pressure;

[0019] - a difference between the third pressure and the second pressure is less than 100 bars, preferably less than 70 bars;

[0020] - the solution further comprises a second solute; during the step of separating the first solute and the supercritical fluid, the second solute passes through the first filtration membrane with said supercritical fluid, to form a second flow; and the method then comprises a step of separating the second solute and the supercritical fluid, said step comprising: passing said second flow through a second filtration membrane, said second membrane comprising a second filtration surface, arranged substantially vertically; retaining the second solute on said second filtration surface, the supercritical fluid passing through the second filtration membrane; and moving by gravity said retained second solute, to a second recovery container, arranged vertically to said second filtration surface;

[0021] - a concentration of the second solute in the second flow is greater than or equal to 90% of a saturation concentration of said second solute in the supercritical fluid;

[0022] - the concentration of the second solute in the second flow is greater than or equal to 95% of the saturation concentration of said second solute in the supercritical fluid.

[0023] The invention further relates to a purification device for implementing a method as described above, said device comprising: a supercritical fluid circuit, said circuit forming a closed loop; and a solution apparatus, a separation module and a compressor, arranged on said supercritical fluid circuit; the solution apparatus being suitable for forming a solution of the first solute and the supercritical fluid; the separation module comprising: a conduit for circulating a first flow of supercritical fluid; a first filtration membrane, onto which the conduit opens, said first membrane comprising a first filtration surface arranged substantially vertically;and a first recovery container, arranged vertically above said first filtration surface and configured to allow movement by gravity, to said first recovery container, of a solute retained on said first filtration surface; the circulation conduit and the first filtration membrane being arranged on the supercritical fluid circuit.;

[0024] According to other advantageous aspects of the invention, the purification device comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0025] - the purification device further comprises a compartment and a valve, said valve being movable between open and closed positions, respectively allowing the first recovery container and the compartment to be placed in fluid communication and isolated from each other;

[0026] - the compressor is located downstream of the separation module;

[0027] - the compressor is arranged upstream of the solution device; - the purification device further comprises an expansion valve, a heating member and a cooling member, arranged on the supercritical fluid circuit;

[0028] - the cooling device is arranged downstream of the compressor and upstream of the solution device;

[0029] - the regulator and the heating element are arranged downstream of the solution device and upstream of the separation module.

[0030] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0031] - figure 1 is a schematic representation of a purification device according to one embodiment of the invention;

[0032] - figure 2 is a detailed, schematic view of the purification device of figure 1;

[0033] - Figure 3 is a representation in the form of a flowchart of a purification method according to one embodiment of the invention; and

[0034] - Figure 4 is a phase diagram of CO2, illustrating the variations in enthalpy and pressure during a purification process according to one embodiment of the invention.

[0035] Figure 1 represents a purification device 10 according to one embodiment of the invention.

[0036] The device 10 comprises a circuit 12 capable of receiving a flow of supercritical fluid. In particular, the circuit 12 is configured to maintain temperature and pressure conditions compatible with the supercritical state of a fluid circulating in said circuit 12.

[0037] Preferably, the circuit 12 is capable of accommodating a flow of supercritical CO2.

[0038] Preferably, as in the embodiment shown, circuit 12 forms a closed loop.

[0039] The device 10 further comprises a solution device 14, a separation module 16 and a compressor 18, arranged on the circuit 12.

[0040] In the embodiment shown, the device 10 further comprises an expansion valve 20, a heating member 22 and a cooling member 24, arranged on the circuit 12.

[0041] In the embodiment shown, the device 10 further comprises a supply 26 of supercritical fluid, opening onto the circuit 12.

[0042] The dissolving apparatus 14 is configured to form a supercritical fluid solution containing one or more solutes, as described below. According to one embodiment, the dissolving apparatus 14 is an extractor, capable of extracting a composition using the supercritical fluid. Preferably, the extractor comprises an inlet (not shown) for supplying said extractor with the composition to be extracted.

[0043] According to another embodiment, the dissolution apparatus 14 is a reactor, capable of hosting a chemical reaction in a supercritical medium. Preferably, the reactor comprises one or more inlets (not shown) for supplying said reactor with reactants.

[0044] Preferably, the separation module 16 is in single-block form. The module 16 will be described in more detail below.

[0045] The compressor 18, arranged between the module 16 and the device 14, defines a direction of circulation of fluid in the circuit 12. More precisely, the compressor 18 is arranged downstream of said module 16 and upstream of said device 14. In the present description, the terms “upstream” and “downstream” are understood in relation to said direction of circulation represented by an arrow in FIG. 1.

[0046] In the embodiment shown, the expansion valve 20 and the heating member 22 are arranged downstream of the device 14 and upstream of the module 16. The cooling member 24 is arranged downstream of the compressor 18 and upstream of the device 14.

[0047] The supply 26 comprises, for example, a reserve 28 of fluid and a secondary compressor 29, making it possible to bring said fluid to the supercritical state before it enters the circuit 12. In the embodiment shown, the supply 26 of supercritical fluid opens onto the circuit 12 between the cooling member 24 and the device 14. In a variant not shown, the supply 26 opens onto the circuit 12 between the compressor 18 and the cooling member 24.

[0048] The separation module 16, shown schematically in Figure 2, will now be described.

[0049] The separation module 16 is configured to maintain temperature and pressure conditions compatible with the supercritical state of a fluid circulating in said module. Preferably, the module 16 is capable of receiving a flow of supercritical CO2.

[0050] The separation module 16 comprises: a body 30; a circulation conduit 32, arranged in the body 30; at least one first filtration membrane 34; and at least one first recovery arrangement 36.

[0051] In the embodiment shown in Figure 2, the module 16 further comprises a second filtration membrane 38 and a second recovery arrangement 40. The second membrane and the second arrangement are optional and depend on the solution being treated, as will be described below. The conduit 32 extends between an inlet 42 and an outlet 44. The first filtration membrane 34 is arranged across the conduit 32, between said inlet 42 and outlet 44. In the embodiment shown, the second filtration membrane 38 is arranged across the conduit 32, between the first filtration membrane 34 and the outlet 44.

[0052] The first membrane 34 comprises a first filtration surface 46. Similarly, the second membrane 38 comprises a second filtration surface 47. Each filtration surface 46, 47 is oriented towards the inlet 42.

[0053] Preferably, the or each filtration surface 46, 47 is defined by a generating line 48, 49.

[0054] According to one embodiment, at least one of the filtration surfaces 46, 47 is substantially planar. In the embodiment shown, each filtration surface 46, 47 is substantially planar.

[0055] According to a variant not shown, at least one of the filtration surfaces 46, 47 has the shape of a cylinder or a portion of a cylinder. Hollow or tubular fiber membranes can in particular be used.

[0056] The separation module 16 is configured so that during operation of the purification device 10, the or each filtration surface 46, 47 is arranged substantially vertically. More precisely, the generating line 48, 49 of the or each filtration surface 46, 47 is arranged substantially vertically. By “substantially vertically”, it is meant that the filtration surface 46, 47 deviates from the vertical by an angle of less than 20°, preferably less than 10°, more preferably less than 5°.

[0057] Preferably, each of the first 34 and second 38 membranes is chosen from reverse osmosis (RO) membranes, nanofiltration (NF) membranes and ultrafiltration (UF) membranes, as described for example in the document Techniques de l'ingénieur J2791 of March 10, 2007. In particular, membranes suitable for gas separation or nanofiltration of organic solvents can be used.

[0058] The first 34 and second 38 membranes are associated with the first 36 and second 40 recovery arrangements respectively. Each of said first and second arrangements corresponds to the description below.

[0059] The recovery arrangement 36, 40 comprises a recovery container 50, 52. The separation module 16 is configured so that during operation of the purification device 10, the container is arranged vertically above the corresponding filtration surface 46, 47, preferably in contact with an edge of said surface. The recovery container 50, 52 is for example a cavity provided in the body 30 of the module 16 and opening onto the conduit 32.

[0060] As detailed below, the recovery container 50, 52 is arranged vertically above or below the corresponding filtration surface 46, 47, depending on the operating conditions. In the embodiment shown, the recovery container 50, 52 is arranged below the corresponding filtration surface 46, 47.

[0061] Preferably, the recovery arrangement 36, 40 further comprises a compartment 54, 56 and a valve 58, 60. The valve 58, 60 is movable between open and closed positions, respectively allowing the recovery container 50, 52 and the compartment 54, 56 to be placed in fluid communication and isolated from each other.

[0062] A purification method 100 implemented using the device 10 will now be described. The method 100 is shown schematically in the form of a flowchart in FIG. 3.

[0063] A first step 102 of the method 100 is the obtaining, in the apparatus 14, of a solution 104 comprising a supercritical fluid and a first solute 70, solubilized in said supercritical fluid. More precisely, the solution 104 is a single-phase solution and not a dispersion.

[0064] Preferably, the supercritical fluid is supercritical CO2.

[0065] According to one embodiment, the first step 102 comprises an extraction by the supercritical fluid. According to another embodiment, the first step 102 comprises a chemical reaction in a supercritical medium. If necessary, during the first step 102, the apparatus 14 is supplied with supercritical fluid by means of the supply 26.

[0066] According to one embodiment, in addition to the first solute 70, the solution 104 comprises a second solute 72 and / or any impurities to be removed. Like the first solute 70, the second solute 72 and / or any impurities are solubilized in the supercritical fluid.

[0067] At the outlet of the device 14, the solution 104 is in first conditions Pi, T1 of temperature and pressure, compatible with the supercritical state of the fluid.

[0068] A second optional step 106 of the method 100 is the modification of said conditions, for example by means of the expansion valve 20 and / or the heating member 22. The solution 104 is thus in second temperature and pressure conditions P2, T2 at the inlet 42 of the separation module 16.

[0069] The second conditions P2, T2 are also compatible with the supercritical state of the fluid. Preferably, P2 < Pi.

[0070] In a third step 108, the solution 104 moves in the conduit 32, towards the first membrane 34, in the form of a first flow 74. The first flow 74 is directed from the inlet 42 towards the outlet 44 of the conduit 32. At the inlet 42 of the separation module 16, the temperature and pressure of the solution 104, here T2 and P2, are chosen so that a concentration of the first solute 70, in the solution 104 forming the first flow 74, is close to its saturation concentration in the supercritical fluid of said solution, under said temperature and pressure conditions.

[0071] Preferably, the temperature and pressure of the solution 104, at the inlet 42 of the separation module 16, are chosen so that a concentration C70 of the first solute 70 in the first flow 74 is greater than or equal to 90%, more preferably greater than or equal to 95%, of the saturation concentration C?osat of said first solute 70 in said supercritical fluid.

[0072] The saturation concentration C?osat of the first solute 70 can be measured experimentally using suitable equipment, as described by J.M. Fonseca, R. Dohrn, S. Peper, “High-pressure fluid-phase equilibria: Experimental methods and systems investigated” (2005-2008), Fluid Phase Equilibria, 300, 2011, pages 1-69.

[0073] Alternatively, said saturation concentration can be estimated by a suitable thermodynamic model, as described by S. -A. Hong, J.-D. Kim, J. Kim, J. Won Kang, l.-J. Kang, “Phase equilibria of palm oil, palm kernel oil, and oleic acid+supercritical carbon dioxide and modeling using Peng-Robinson EOS”, Journal of Industrial and Engineering Chemistry, 16, 2010, Pages 859-865.

[0074] Alternatively, said saturation concentration can be estimated using an empirical correlation, as described by JM del Valle, JC de la Fuente, E. Uquiche, “A refined equation for predicting the solubility of vegetable oils in high-pressure CO2”, The Journal of Supercritical Fluids, Q7, 2012, Pages 60-70.

[0075] In a fourth step 110, the first flow 74 passes through the first filtration membrane 34. Said first membrane 34 is chosen so that the first solute 70 contained in the first flow is deposited on the first filtration surface 46, while the supercritical fluid, the possible second solute 72 and any impurities pass through said first membrane 34.

[0076] More specifically, the first solute 70 is deposited on the first filtration surface 46 by a phase separation mechanism from the solution 104, such as precipitation or condensation.

[0077] In a fifth step 112, the first solute 70 flows by gravity along the first filtration surface 46, due to the substantially vertical arrangement of said first surface. The first solute is collected in the container 50 of the first recovery arrangement 36, located vertically above said first surface. It is assumed that the first solute 70 retained on the first surface 46 is in the form of a solution of said first solute saturated with supercritical fluid, making such a flow by gravity possible.

[0078] In the example shown in Figure 2, the first solute 70 retained on the first surface 46 is denser than the solution 104 and flows downwards into the container 50 located below the first surface 46.

[0079] In a variant not shown, the first solute 70 retained on the first surface 46 is less dense than the solution 104 and moves upwards relative to the first flow 74. The recovery container is then advantageously placed above the first surface 46.

[0080] In a sixth step 114, simultaneous with the fifth step 112, the supercritical fluid forms a second flow 76 downstream of the first membrane 34; and said second flow moves in the conduit 32 towards the outlet 44 of the conduit.

[0081] In the embodiment shown, downstream of the first membrane 34, the temperature and pressure of said second flow 76 are preferably chosen so that a concentration C72 of the second solute 72 in the second flow 76 is greater than or equal to 90%, more preferably greater than or equal to 95%, of the saturation concentration C?2sat of said second solute 72 in the supercritical fluid of said second flow.

[0082] In the embodiment shown, during a seventh step 116, the second flow 76 passes through the second filtration membrane 38. Said second membrane 38 is chosen so that the second solute 72 contained in the second flow is deposited on the second filtration surface 47, while the supercritical fluid and any impurities pass through said second membrane 38.

[0083] In an eighth step 118, the second solute 72 flows by gravity along the second filtration surface 47 and is collected in the container 52 of the second recovery arrangement 40, located vertically above said second surface.

[0084] At the end of the seventh step 116, at the outlet 44 of the module 16, the supercritical fluid is in third temperature and pressure conditions P3, T3, compatible with the supercritical state of said fluid. Preferably, P3 S P2 and T3 S T2.

[0085] In the embodiment shown, the method then comprises a ninth step 120 of recycling the supercritical fluid. Said ninth step comprises the modification of the temperature and pressure conditions of the supercritical fluid, to return to the first conditions Pi, T1. Such a modification is for example carried out by means of the compressor 18 and / or the cooling member 24. Optionally, the ninth step comprises the elimination of impurities still solubilized in the supercritical fluid. At the end of the ninth recycling step 120, the supercritical fluid is reintroduced into the dissolution apparatus 14.

[0086] In a tenth 122 and / or an eleventh 124 step, the container 50, 52 of the first 36 and / or of the second 40 recovery arrangement is emptied into the corresponding compartment 54, 56, by means of the corresponding valve 58, 60. The compartment 54, 56 is then isolated from the outside of the module 16, so that the conduit 32 remains in the temperature and pressure conditions compatible with the supercritical state of the fluid.

[0087] The valve 58, 60 is then closed and the compartment 54, 56 can be emptied by means of a discharge device 80, 82, also provided with a valve.

[0088] The tenth 122 and eleventh 124 steps may be repeated regularly during the implementation of the method 100 described above. In this way, the first 70 and / or the second 72 solutes may be recovered continuously, without disturbing the purification process.

[0089] According to an alternative embodiment, the module 16 does not comprise a second membrane 38 and only the first solute 70 is recovered by filtration, using the first membrane 34. In such an alternative, the step of recycling the supercritical fluid is carried out at the end of the sixth step 114. This recycling step comprises the modification of the temperature and pressure conditions of the supercritical fluid, to return to the first conditions Pi, Ti. Such a modification is for example carried out by means of the compressor 18 and / or the cooling member 24.

[0090] According to another embodiment variant, the module 16 comprises a succession of more than two membranes 34, 38 making it possible to recover several solutes by separating them from each other, by successive filtrations of the supercritical fluid flow.

[0091] According to another variant embodiment, the device 10 comprises several purification modules 16, arranged in series on the circuit 12.

[0092] The recovery of solutes 70, 72 by filtration makes it possible to avoid a step of expanding the fluid to the gaseous state. As previously indicated, such expansion is commonly used in supercritical CO2 purification processes to recover solutes.

[0093] Figure 4 shows a phase diagram of CO2, including the gaseous state (area 202) and the supercritical state (area 204).

[0094] A first supercritical CO2 purification cycle 206 is shown, corresponding to a conventional state-of-the-art process. An initial state of CO2 corresponds to point A in Figure 4.

[0095] The first cycle 206 includes in particular a step 208 of expansion of an AP of 100 bars, followed by a heating step 210 to the gaseous state, to recover the solute. The first cycle 206 then includes a compression step 212 to increase the pressure of the CO2 by an AP of 100 bars, then a cooling step 214.

[0096] A second supercritical CO2 purification cycle 220, corresponding to a process similar to the process 100 previously described, is also shown in Figure 4.

[0097] From an initial state corresponding to point A, the second cycle 220 comprises a step 222 of expansion of an AP of 40 bars, a step 224 of compression for an AP of 40 bars, then a step 226 of cooling. Throughout the second cycle 220, the CO2 remains in the supercritical domain.

[0098] Since energy consumption is directly linked to variations in the enthalpy of the fluid (variation of the abscissa of the diagram), it appears in Figure 4 that the energy requirements of the second cycle 220 are considerably lower than the energy requirements of the first cycle 206.

[0099] The purification process according to the present invention, which makes it possible to maintain CO2 in the supercritical state over a purification cycle, is therefore particularly advantageous from an energy point of view.

[0100] The gravity flow of the solutes 70, 72 along the filtration surfaces 46, 47 makes it possible on the one hand to avoid the accumulation of solute, and therefore the obstruction of the membranes 34, 38 during the process, and on the other hand to recover the solutes continuously in the compartments 54, 56, without disturbing the supercritical conditions inside the device 10. Another advantage is to limit the membrane cleaning steps necessary during the accumulation of solutes.

[0101] Processes analogous to process 100 described above are particularly suitable for the purification of apolar or slightly polar compounds, such as oils, in particular from plant matrices.

[0102] EXAMPLE

[0103] A purification device, similar to the device 10 of FIG. 1, is produced with a separation module 16 comprising a single filtration membrane 34.

[0104] The membrane used is a reverse osmosis membrane, which is known for its use in water treatment. Specifically, the membrane used is an AG type membrane manufactured by GE Power. It consists of three polymer layers: a selective polyamide layer synthesized by interfacial polymerization on a PSU polysulfone layer, the whole being supported on a non-woven polyester layer.

[0105] The purification method 100 described above is partially implemented with the purification device.

[0106] Solution 104, obtained in the first step 102 of the process, comprises supercritical CO2 and commercial sunflower oil, solubilized in supercritical CO2 as the first solute 70. The CO2 used is supplied by Air Liquide with a purity > 99.98%.

[0107] The third 108 and fourth 110 steps described above are then implemented, at constant filtration flow.

[0108] Filtration tests are carried out near the saturation concentration of the oil, which is estimated using the Del Valle correlation (JM Del Valle, JM Aguilera, “An improved equation for predicting the solubility of vegetable oils in supercritical carbon dioxide”, Industrial & Engineering Chemistry Research 27 (1988) 1551-1553). The oil flow rates to be injected are then calculated based on the pressure and temperature conditions of the separation tests.

[0109] Table 1 presents a summary of the experimental conditions employed with the AG membrane.

[0110] Table 1

[0111] The experiment was continued for 800 min. The evolution of the transmembrane pressure AP was monitored over time. The results obtained are reported in Table 2:

[0112] *: Reference value for the filtration of pure CO2-SC

[0113] Table 2

[0114] The results show that the measured AP increases from an initial value of 8.9 bar (pure CO2-SC filtration) to a fixed value of approximately 13.5 bar after 400 minutes of filtration. At the end of the 800 minutes, the AP value remains constant, around 13.5 bar, also corresponding to a retention rate of approximately 85%.

[0115] The quasi-stability of the transmembrane pressure AP values ​​for operation at constant feed flow rate indicates that the filtration system has reached a steady state of operation.

[0116] Such a steady state differs from the results obtained in conventional frontal filtration configurations, where on the contrary there is a constant increase in transmembrane pressure to maintain the constant feed flow rate.

[0117] Such transmembrane pressure values ​​suggest an absence of membrane clogging over time. Such a result is consistent with gravity flow of the solute retained on the filtration surface, as described above.

Claims

CLAIMS 1. Purification method (100) comprising the following steps: formation (102) of a solution (104) comprising a first solute (70) and a supercritical fluid; then separation (110) of the first solute and the supercritical fluid; the method being characterized in that: - the method further comprises, after the step of forming the solution, a step of moving (108) a first flow (74) comprising the solution (104); and - the step of separation of the first solute and the supercritical fluid includes: - the passage of said first flow through a first filtration membrane (34), said first membrane comprising a first filtration surface (46), arranged substantially vertically; - retaining the first solute (70) on said first filtration surface, the supercritical fluid passing through the first filtration membrane; and - the movement by gravity of said first retained solute, to a first recovery container (50), arranged vertically above said first filtration surface.

2. The purification method (100) of claim 1, wherein the supercritical fluid is supercritical carbon dioxide.

3. Purification method according to claim 1 or 2, in which a concentration (C70) of the first solute (70) in the first flow (74) is greater than or equal to 90% of a saturation concentration (C?osat) of said first solute in the supercritical fluid, and preferably greater than or equal to 95% of the saturation concentration of said first solute in the supercritical fluid.

4. Purification method according to one of the preceding claims, in which the supercritical fluid has a first pressure (P2) upstream of the first filtration membrane (34) and a second pressure (P3) downstream of said first filtration membrane, the second pressure being less than or equal to the first pressure.

5. Purification method according to claim 4, in which, after passing through the first filtration membrane, the supercritical fluid is subjected to a compression step up to a third pressure (Pi).

6. Purification method according to claim 5, in which a difference between the third pressure (Pi) and the second pressure (P3) is less than 100 bars, preferably less than 70 bars.

7. Purification method according to one of the preceding claims, in which: - the solution (104) further comprises a second solute (72); - during the step (110) of separating the first solute and the supercritical fluid, the second solute passes through the first filtration membrane with said supercritical fluid, to form a second flow (76); and - the method then comprises a step (116) of separating the second solute and the supercritical fluid, said step comprising: - the passage of said second flow through a second filtration membrane (38), said second membrane comprising a second filtration surface (47), arranged substantially vertically; - retention of the second solute on said second filtration surface, the supercritical fluid passing through the second filtration membrane; and - the movement by gravity of said second retained solute, to a second recovery container (52), arranged vertically above said second filtration surface.

8. Purification method according to claim 7, wherein the concentration of the second solute (72) in the second flow is greater than or equal to 90% of a saturation concentration (C?2sat) of said second solute in the supercritical fluid, and preferably greater than or equal to 95% of the saturation concentration of said second solute in the supercritical fluid.

9. Purification device (10) for implementing a method according to one of the preceding claims, said device comprising: - a supercritical fluid circuit (12), said circuit forming a closed loop; and - a solution apparatus (14), a separation module (16) and a compressor (18), arranged on said supercritical fluid circuit; the solution apparatus (14) being suitable for the formation of a solution (104) of the first solute (70) and the supercritical fluid; the separation module (16) comprising: - a conduit (32) for circulating a first flow (74) of supercritical fluid; - a first filtration membrane (34), into which the conduit opens, said first membrane comprising a first filtration surface (46) arranged substantially vertically; and - a first recovery container (50), arranged vertically above said first filtration surface and configured to allow movement by gravity, to said first recovery container, of a solute (70) retained on said first filtration surface; the circulation conduit (32) and the first filtration membrane (34) being arranged on the supercritical fluid circuit (12).

10. A purification device (10, 16) according to claim 9, further comprising a compartment (54) and a valve (58), said valve being movable between open and closed positions, respectively allowing the first recovery container and the compartment to be placed in fluid communication and isolated from each other.

11. Purification device (10) according to claim 9 or claim 10, in which the compressor (18) is arranged downstream of the separation module (16).

12. Purification device (10) according to one of claims 9 to 11, in which the compressor (18) is arranged upstream of the dissolving apparatus (14).

13. Purification device according to one of claims 9 to 12, further comprising an expansion valve (20), a heating member (22) and a cooling member (24), arranged on the supercritical fluid circuit.

14. Purification device according to claim 13, in which the cooling member (24) is arranged downstream of the compressor (18) and upstream of the dissolving apparatus (14).

15. Purification device (10) according to claim 13 or 14, in which the pressure reducer (20) and the heating member (22) are arranged downstream of the dissolution apparatus (14) and upstream of the separation module (16).

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