METHOD FOR PRODUCING A MULTICAPILLAR LINING

Description

FIELD OF THE INVENTION

[0001] The invention relates to a method for manufacturing a multicapillary packing suitable for use as a chromatography column and the multicapillary packing obtained by such a method. BACKGROUND OF THE INVENTION

[0002] Packings useful in chromatography are generally composed of a monolithic porous mass, typically made of silica or alumina gel, and a multitude of substantially rectilinear and mutually parallel channels or conduits extending through this porous mass.

[0003] Different methods are known for preparing multicapillary packings that can be used in chromatography.

[0004] For example, it is known that multicapillary packings can be prepared from ablative preforms, for example fibers assembled into a bundle, which are removed after formation of a porous matrix around the fibers (WO2013 / 064754), the whole forming a monolithic structure. The porous matrix can in particular be prepared by a sol-gel process and consist of silica, alumina or an aluminosilicate. Ablation of the preforms by combustion or pyrolysis generates conduits in the mineral matrix.

[0005] The preparation of these linings is difficult due to the fineness of the conduits required for certain applications, and the difficulty of producing monoliths without inherent defects, i.e. without cracks and fissures.

[0006] Thus, a need remains for the provision of a process for preparing a multicapillary packing making it possible to overcome the disadvantages mentioned, in particular minimizing the risks of cracks and fissures. BRIEF DESCRIPTION OF THE INVENTION

[0007] The present invention relates to a method for manufacturing a multi-capillary packing from a substrate of ablative preforms, each preform being adapted to form, upon its ablation, a conduit allowing the convection of a fluid in the packing. The method comprises the following steps: (a) assembling the ablative preforms into at least one bundle; (b) creating a gel between the ablative preforms of the bundle by hydrolysis of an organometallic precursor in the presence of an amount of water not exceeding ten times the stoichiometric amount required for complete hydrolysis of said organometallic precursor; (c) ablation of the preforms, preferably by pyrolysis, oxidation, vaporization, melting and draining, mechanical extraction or chemical etching, so as to form a plurality of conduits in the gel.

[0008] A multicapillary packing obtainable by the method of the present invention is also described.

[0009] Other aspects of the invention are as described in the claims and below. DETAILED DESCRIPTION OF THE INVENTION

[0010] The inventor has developed a process for manufacturing a multicapillary packing from ablative preforms meeting the expressed needs.

[0011] The method of the present invention comprises the following steps: (a) assembling the ablative preforms into at least one bundle; (b) creating a gel between the preforms of the bundle comprising hydrolyzing an organometallic precursor in the presence of an amount of water not exceeding ten times, preferably not exceeding five times, the stoichiometric amount required for complete hydrolysis of said organometallic precursor; (c) ablation of the preforms by pyrolysis, preferably by oxidation, vaporization, melting and draining, mechanical extraction or chemical etching so as to form a plurality of conduits in the gel.

[0012] By stoichiometric amount of water required for complete hydrolysis is meant the amount of water required to convert all the hydrolyzable groups of the organometallic precursor into MOM bonds (M denotes the metal of the organometallic precursor).

[0013] In the case where M is a silicon atom, in particular and in a non-limiting manner, the MOR, MNR, MSR, MOB bonds, where R is an organic group, of the organometallic precursor are considered to be hydrolyzable.

[0014] In the case where M is a silicon atom, in particular and without limitation, the MC- bonds are generally considered non-hydrolyzable. It should be noted, however, that the addition of substituents or heteroatoms such as O, N, S, etc. on the C carbon can make these MC bonds fragile. In the latter case, the bonds will be considered hydrolyzable.

[0015] Thus, for example, for one mole of tetraalkoxysilane of formula M(OR) 4 with M = Si, OR being the alkoxy radical, R being an alkyl, for example a methyl or ethyl group, the stoichiometric quantity of water required is two moles / mole of tetraalkoxysilane: Si(OR) 4 + 2 H 2 O -> SiO 2 + 4 ROH

[0016] Thus, for example, for one mole of trialkoxysilane of formula R'M (OR) 3 with M = Si, OR being the alkoxy radical, R being an alkyl, for example a methyl or ethyl group, R' being an alkyl, for example a methyl or ethyl group, the stoichiometric quantity of water required is 1.5 moles / mole of trialkoxysilane.

[0017] Thus, for example, for one mole of dialkoxysilane of formula R'R"M (OR) 2 with M = Si, OR being the alkoxy radical, R being an alkyl, for example a methyl or ethyl group, R' being an alkyl, for example a methyl or ethyl group, R" being an alkyl, for example a methyl or ethyl group, the stoichiometric quantity of water required is one mole / mole of dialkoxysilane.

[0018] It is noted that the water molecules generated during the hydrolysis and coupling reaction are taken into consideration in determining the stoichiometric amount of water required for complete hydrolysis of said organometallic precursor.

[0019] Thus, in all these estimates, we take into account the fact that the silanol groups resulting from the hydrolysis and present on the silicon couple two by two to form siloxane bridges in order to form silica gel, a reaction which itself restores a water molecule to the reaction medium per siloxane bridge created.

[0020] R' and R" may also advantageously be Dodecyl, Octadecyl, n-Octyl, n-Propyl, n-Butyl, Vinyl, 3-Chloropropyl, 3-Aminopropyl, 2-Aminoethyl-3-aminopropyl, 3-Aminopropyl, 3-Ureidopropyl, 3-Glycidoxypropyl, 3-Glycidoxypropyl, 3-Methacryloxypropyl, Bis(propyl)tetrasulfide, Bis(propyl)disulfide, 3-Mercaptopropyl, Trifluoropropyl radicals, contain epoxy bonds, etc. OR may advantageously be an alkoxy radical (e.g. methoxy, ethoxy), acyloxy, acetoxy, ketoxime, methylethylketoxime, Oximino, etc., (OR) 4 , (OR) 3 , (OR) 2 , which may themselves represent 4, 3, or 2 groups respectively. R previously listed all the same or different.

[0021] The ablative preforms are typically adapted to form, upon their destruction or elimination, axial conduits, substantially rectilinear and parallel to each other, allowing the convection of a fluid (e.g. mobile phase) between an inlet face of the packing and an outlet face of the packing. Preferably, the ablative preforms are in the form of fibers or threads.

[0022] The ablative preforms may be made of, in particular composed of, materials such as carbon (e.g. carbon fibers), polyester, polyamide, polyolefins (e.g. polypropylene, polyethylene), polyacrylate, polymethacrylate, polysulfones, polyurethanes, polyimide, polyether, for example biodegradable polymers (e.g. polydioxanone, polyglycolic acid, polylactic acid). The ablative preforms may be fusible wires, for example wires comprising indium, bismuth, tin, gallium, silver or one of their alloys with other metals, preferably excluding lead, mercury and cadmium.

[0023] Thus, in some embodiments, the preforms comprise polyamide, polyolefin, polyacrylate, polymethacrylate, polysulfone, polyurethane, polyimide, polyether, or polyester yarns.

[0024] Ablative preforms may be made of fibers that may be hollow, porous, or non-porous. The fibers have a preferably circular, but possibly non-circular, cross-section, such as square, rectangular, hexagonal, polygonal, or film-like cross-sections. This list is not exhaustive.

[0025] Ablative preforms preferably have a section between a few tenths of a square micrometer and a few square micrometers.

[0026] Preferably, the diameter of the preforms will be less than 250 µm, advantageously less than 100 µm, and even more advantageously less than 5 µm.

[0027] The diameter considered will be the hydraulic diameter measured perpendicular to the mean direction of fluid flow in the packing.

[0028] The definition of the hydraulic diameter d is as follows: d = 4 A P where A is the area of ​​the passage section of the tube and P is the wetted perimeter of this section.

[0029] In some embodiments, the ablative preforms may extend linearly and without interruption between an input face and an output face of the material.

[0030] In other embodiments, the ablative preforms conform or extend into only a portion of the material and are immersed or occluded therein. Thus, in some embodiments, the preforms may be in the form of sections occluded within the body of the packing.

[0031] In these embodiments, a compact stack of ablative preforms is made in the material in order to promote in the final packing the convective transfer of a fluid circulating in the material between the conduits and towards an outlet face.

[0032] In all cases, the permeability of the material to a circulating fluid is increased.

[0033] Advantageously, the ablative preforms have dimensions that are as uniform as possible. The preforms can be characterized by at least two dimensions: 1. the diameter or hydraulic diameter of the preforms; and 2. the length of the preforms.

[0034] Advantageously, the diameter or hydraulic diameter has a variability characterized by its relative standard deviation less than 30%, preferably less than 10%, even more preferably less than 2% of the average diameter of the preforms. Advantageously, the length has a variability characterized by its relative standard deviation less than 30%, preferably less than 10%, even more preferably less than 2% of the average length of the preforms.

[0035] In some embodiments, the ablative preforms are covered with a porous granular substance, for example silica microbeads, glass, silica gel, alumina gel, titanium gel or zirconium oxide gel. This layer of porous granular substance can have at least two advantages: it avoids contact between the ablative forms, the porous granular substance acting as a spacer, and it can provide a functionality specific to the material (for example a reactive functionality or a catalytic role).

[0036] The pores of the granular substance may be closed by a third body. This third body is preferably a pyrolyzable organic solid, soluble in a solvent or volatile, for example a paraffin. Advantageously, this third body may be removed later in the process (for example before or after removal of the ablative forms or concomitantly with this ablation) and is not found in the final product.

[0037] The preforms, assembled in the form of a bundle, are held together using a gel, acting as a binder, to give a monolithic structure.

[0038] The gel can be based on any mineral compound that provides cohesion to the monolith. Thus, the gel can be a gel based on aluminum oxide, silicon oxide, zirconium oxide, titanium oxide, rare earth oxide such as yttrium, cerium or lanthanum, boron oxide, iron oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, germanium oxide, phosphorus oxide, lithium oxide, potassium oxide, sodium oxide, niobium oxide, copper oxide or a mixture thereof.

[0039] In some embodiments, the gel is a silicon oxide (silica gel) or aluminum oxide (alumina gel) based gel.

[0040] In some embodiments, the gel is a zirconium oxide or titanium oxide based gel.

[0041] In some embodiments, the gel is a multi-component oxide gel. For example, the gel may be comprised of binaries of zirconium and yttrium, zirconium and cerium, zirconium and calcium, barium and titanium, lithium and niobium, phosphorus and sodium, or boron and lithium. The gel may be a gel comprised of silicate, for example, binary silicates based on silica and boron oxide, aluminum oxide, germanium oxide, titanium oxide, zirconium oxide, strontium oxide, or iron oxide, ternary silicates, multi-component silicates having more than three components. In some embodiments, the gel is a multi-component oxide gel, for example, an aluminosilicate gel, for example, a clay.

[0042] The gel is prepared in situ by the well-known sol-gel route (“solution-gelation”).

[0043] The gel is then typically created by immersing the preform bundle(s) in a gel precursor sol which is then cured to form a gel. The sol is typically poured onto the preforms arranged in a mold or tube.

[0044] In another embodiment, the preforms are added to the soil, and the mixture is poured into a mold or into a tube.

[0045] By sol is meant here any mixture comprising an organometallic precursor, and advantageously water in an amount not exceeding ten times the stoichiometric amount required for complete hydrolysis of said organometallic precursor.

[0046] In the context of the present invention, the gel is created between the preforms by hydrolysis of an organometallic precursor. The organometallic precursor comprises at least one, in particular at least two hydroxyl groups or hydrolyzable groups to form metal oxides during their hydrolysis. Thus, the organometallic precursor is typically an organometallic alkoxide, an organometallic acetate, an organometallic carboxylate, an organometallic halide, an organometallic nitrate, an organometallic alkanoate or an organometallic acyloxide.

[0047] Examples of organometallic precursors include, but are not limited to, tetrachlorosilane, aluminum nitrate (which may be hydrolyzed in the presence of urea), tetramethoxysilane, tetraethoxysilane, diethyl(dimethoxy)silane, and triethyl(methoxy)silane.

[0048] The organometallic precursor is preferably an organometallic alkoxide.

[0049] The hydrolysis of the organometallic precursor(s) is carried out in an aqueous medium. The aqueous medium may comprise exclusively water or may comprise a mixture of water and an organic solvent, for example methanol or ethanol, in order to make the mixture homogeneous. The amount of organic solvent is typically less than 12 times the volume of the organometallic precursor, preferably 4 times less than this volume, even more preferably 2 times less than this volume, and in particular less than 0.5 times this volume. In certain embodiments, the organometallic precursor is placed in water with stirring until a homogeneous mixture is formed by partial hydrolysis of the precursor.

[0050] It has been demonstrated that when the gel is created by hydrolysis of an organometallic precursor in the presence of an amount of water not exceeding ten times or six times, or five times, preferably not exceeding four times, even more preferably not exceeding two times, or even 1.25 times the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor, the multicapillary packing / monolithic structure obtained by the method of the present invention has minimal cracking, fissures and defects. In some embodiments, the hydrolysis of the organometallic precursor is carried out in the presence of an amount of water substantially equal to, or even equal to, the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor.In some embodiments, the hydrolysis of the organometallic precursor is carried out in the presence of an amount of water not reaching the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor, for example the amount of water may be half the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor. Thus, the hydrolysis of the organometallic precursor may be carried out in the presence of an amount of water varying from 0.5 times to 10 times or from 0.5 to 5 times the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor.

[0051] The hydrolysis step is typically catalyzed by an acid or a base. The choice of acid or base catalysis typically depends on the precursor(s) used.

[0052] Advantageously, in the case where the metallic part of the organometallic precursor is made up of one or more silicon atoms, a succession of catalysis can be carried out: for example, a first acid hydrolysis can be carried out preferably before insertion of the sol between the preforms of the conduits (i.e., before immersion of the ablative preforms of the bundle in the sol), followed by an addition of base resulting in hydrolysis in a basic medium of the sol between the preforms of the conduits.

[0053] In some embodiments, the gel is created by hydrolysis of an organometallic precursor selected from organometallic derivatives of silicon, aluminum, zirconium, titanium, a rare earth such as yttrium, cerium or lanthanum, boron, iron, magnesium, calcium, strontium, barium, germanium, phosphorus, lithium, potassium, sodium, niobium, copper or a mixture thereof, preferably silicon, zirconium or titanium. The mixtures may be binary, ternary or even comprise more than three organometallic derivatives.

[0054] In some embodiments, the gel is created by hydrolysis of one or more organometallic precursors which may be as described above in the presence of one or more metal salts, for example nitrates or chlorides.

[0055] The choice of the organometallic precursor(s) will depend on the nature of the desired packing. For a chromatography application, the organometallic precursors will be advantageously chosen so as to give the most cohesive and rigid gel possible. The gel will be as dense as possible in order to present the highest possible specific surface area per unit volume of the material and for a given pore size.

[0056] Thus, in other words, step b) of creating a gel can be advantageously formulated as follows: (b1) preparing a sol comprising an organometallic precursor as described above; (b2) immersing the ablative preforms of the bundle in the sol; (c2) hydrolyzing the organometallic precursor in the presence of an amount of water not exceeding ten times or five times the stoichiometric amount required for complete hydrolysis of said organometallic precursor so as to create a gel.

[0057] Once the gel has formed, the preforms can be broken down, advantageously by pyrolysis, oxidation, vaporization, melting and drainage, mechanical extraction or chemical attack. After destruction or removal of the preforms, only the gel traversed by conduits remains.

[0058] Eventually several stages of slaughter or ablation will be implemented, such as an initial hydrolysis stage followed by a pyrolysis stage.

[0059] Optionally, this ablative step can be supplemented or combined with a heat treatment such as sintering in order to consolidate the network and the mechanical resistance of the material. These heat treatments are known to those skilled in the art.

[0060] Typically for a silica gel, such a heat treatment may consist of annealing at temperatures advantageously between 650 and 850°C, for a duration which may vary between a few minutes or tens of minutes to several hours or tens of hours. For example, such a treatment may be carried out at 700°C for 2 hours to 12 hours.

[0061] Optionally, this ablative step or this additional thermal annealing step may, in the case of a silica gel, be followed by a step of rehydroxylation of the surface of the gel, by a treatment with water vapor, by a hydrothermal treatment, or by a treatment in a basic or acidic aqueous medium for example, according to any technique known to those skilled in the art. It is known in fact that high temperatures, above 170 °C, but more particularly above 500 °C, or even 700 °C, promote the dehydroxylation of the surface of the silica gel in a more or less reversible manner. Typically, a silica gel produced at room temperature and dried at 105 °C has between 8 and 4.5 silanol groups per nm 2< . At 170°C, this population begins to decrease slowly, and decreases with the treatment temperature until only 1 silanol group per nm 2< remains at approximately 700°C.This dehydroxylation can impair the final application of the packing, by modifying its adsorption characteristics, the surface becoming less polar, by altering its capacity to receive a functional graft, and by making the surface unstable in the presence of water. Rehydroxylation may therefore be necessary to restore the functionality of the silica gel.

[0062] Before or after removing the preforms, the gel is dried. Drying is carried out under conditions that best guarantee its structural and mechanical integrity, in particular in such a way as to limit as much as possible the formation of cracks and macroscopic or microscopic shrinkage.

[0063] Drying can be carried out under vacuum or at atmospheric pressure, preferably at room temperature. Drying is typically carried out slowly under controlled temperature and partial pressure. The drying time is typically at least one hour, or even more than ten hours, more than 24 hours and can last up to several days. In certain embodiments, the drying time is 48 hours. The drying time will be longer the larger the volume of the material to be dried, in particular the thicker the material. In certain embodiments, drying is carried out at room temperature (20-25°C) under vacuum at a pressure of 1 to 50 kPa for approximately 48 hours.

[0064] The slow drying technology advantageously makes it possible to obtain large packings having a large number of conduits. Thus, the method of the present invention can make it possible to prepare packings comprising more than one hundred conduits, or even more than one thousand conduits, and or even more than ten thousand conduits.

[0065] The method of the present invention can make it possible to prepare packings having a section greater than 0.1 cm 2< , more advantageously greater than 1 cm 2< , even more advantageously greater than 10 cm 2< or even greater than 100 cm 2< .

[0066] In some embodiments, drying is performed after curing to strengthen the gel structure and increase its pore diameter. Curing is typically performed by maintaining the gel at room temperature for a period of about 24 hours or more.

[0067] Generally, a silica gel typically has a specific surface area ranging from 20 to 1200 m 2 < / g, preferably ranging from 20 to 700 m 2 < / g, even more preferably between 70 and 450 m 2 < / g.

[0068] Silica gel typically has a pore volume ranging from 20% to 90% by volume of the gel, more advantageously ranging from 40% to 70% or even 65% by volume of the gel. By "volume of the gel" is meant the volume of gel between the conduits of the monolith delimited by its external contour, distinct from any spacers intended to maintain an open passage to the fluid by maintaining a space between different masses or portions of silica gel, and outside the volume delimiting the contours of the spacers, i.e., the volume of the gel located between the conduits of the monolith. Any spacers are not taken into account in determining the volume of the gel; in other words, in the case where spacers are present, the gel located outside the spacers is considered.

[0069] Silica gel is generally made to obtain pores of large diameters. It is known that the capillary tension forces leading to shrinkage and cracking of the gel during its drying vary as the inverse of this diameter. The pore diameter of the gel before drying is typically greater than 4 nm, preferably greater than 10 nm and generally does not exceed 1000 nm. The pore diameter of the gel after drying is typically greater than 2 nm, preferably greater than 10 nm and generally does not exceed 1000 nm.

[0070] In some embodiments, the silica gel precursor sol comprises additives conventionally used for the preparation of packings. Thus, the sol may comprise surfactants or drying control chemical additives such as formamide. This will reduce cracking upon drying.

[0071] In some embodiments, a solid filler may be added to the gel. The solid filler may mechanically strengthen the resulting gel, limit its shrinkage, and possibly provide the final gel with additional functionality such as additional specific surface area or catalytic functionality.

[0072] The solid filler can be silica gel powder or alumina gel.

[0073] Advantageously, this powder has a high specific surface area, advantageously greater than 250 m 2 < / g, more advantageously greater than 450 m 2 < / g, even more advantageously greater than 700 m 2 < / g. Advantageously, this powder has a very fine particle size, less than 25 µm, preferably less than 3 µm, more preferably less than 0.5 µm.

[0074] The solid filler can be made of fibers, microfibers, or nanofibers, such as whiskers like potassium titanate fibers. These are marketed under the brand name Tismo D. They give greater rigidity to the final material.

[0075] The specific surfaces, pore sizes and pore volumes mentioned in this text are measured by nitrogen adsorption using the BET method.

[0076] The filling obtained by the process of the present invention can then be pyrolyzed at high temperature, for example at temperatures ranging from 300 to 700°C.

[0077] The filling obtained by the method of the present invention can be surface modified.

[0078] Optionally, a silica gel packing can be grafted with a functional silane, in order to modify its adsorption and retention properties for chromatographic application.

[0079] Among the functional silanes that can be used, there may be mentioned, without limitation, dodecyltrimethoxysilane, octadecyltrimethoxysilane, hexadecyltrimethoxysilane, methyltrimethoxysilane, n-octyltriethoxysilane, n-octyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, methyltriacetoxysilane, ethyltriacetoxysilane, vinyltriacetoxysilane, vinyltri(2-methoxyethoxy)silane, 3-chloropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 2-aminoethyl-3-aminopropyltrimethoxysilane, 3-Aminopropyltrimethoxysilane, Bis(trimethoxysilypropyl)amine, 3-Ureidopropyltrimethoxysilane, 3-Glycidoxypropyltrimethoxysilane, 3-Glycidoxypropylmethyldimethoxysilane, 3-Methacryloxypropyltrimethoxysilane, 3-Methacryloxypropylmethyldimethoxysilane, Bis(3-triethoxysilylpropyl)tetrasulfide, Bis(3-triethoxysilylpropyl)disulfide, 3-Mercaptopropyltrimethoxysilane, 3-Mercaptopropylmethyldimethoxysilane,Vinyltris(methylethylketoxime)silane, Vinyl Oximino Silane, Methyltris(methylethylketoxime)silane, Methyl Oximino Silane, Tetra(methylethylketoxime)silane, Trifluoropropylmethyldimethoxylsilane, silanes containing epoxy bonds, etc., Examples of embodiments First embodiment

[0080] In some embodiments, the resulting material, i.e., the gel, is mesoporous and preferably does not exhibit macroporosity. The gel differs in particular from the multimodal silica gels marketed by Merck under the trade name Chromolith, and derived from the research of Mrs. K. Nakanishi [1], [2], and N. Ishizuka [3].

[0081] Such gels are obtained by a standard sol-gel process not involving spinodal decomposition.

[0082] It is generally considered that the microporosity domain includes pores with diameters less than 2 nm, that the mesoporosity domain includes pores with diameters between 2 nm and 50 nm, and that the microporosity domain includes pores with diameters greater than 50 nm.

[0083] However, it is considered here that the microporosity range includes pores with a diameter of less than 2 nm, that the mesoporosity range includes pores with a diameter of between 2 nm and 150 nm, and that the microporosity range includes pores with a diameter of more than 150 nm,

[0084] The silica gel then obtained has a volume fraction of macropores less than 50% of its total pore volume, more advantageously less than 25% of its total pore volume, even more advantageously less than 10% of its total pore volume.

[0085] Advantageously, the silica gel has a volume fraction of micropores less than 30% of its total pore volume, more advantageously less than 10% of its total pore volume, even more advantageously less than 5% of its total pore volume.

[0086] Advantageously, the silica gel has a volume fraction of mesopores greater than 30% of its total pore volume, more advantageously greater than 65% of its total pore volume, even more advantageously greater than 80% of its total pore volume.

[0087] Pore ​​volume fractions are determined by nitrogen adsorption measurements using the Brunauer Emett and Teller method, known as the BET method. This measurement will be carried out on the porous domain constituting the gel itself, excluding the volume of the conduits.

[0088] It has been demonstrated that when a silica gel is created by hydrolysis of an organometallic precursor in the presence of an amount of water not exceeding ten times, preferably not exceeding six times or not exceeding five times, even more preferably not exceeding four times or even twice the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor, the resulting multicapillary packing / monolithic structure or silica gel exhibits minimal cracks, fissures and defects with a gel density, for example having a silica density, high (typically 0.05 to 1.2 g / cm 3< , preferably between 0.1 and 0.8 g / cm 3< ).

[0089] Advantageously, the density of the silica gel obtained by the hydrolysis process will be between 0.1 and 0.40 g / cm 3< . More advantageously, the density of the silica gel obtained by the hydrolysis process will be between 0.15 and 0.35 g / cm 3< .

[0090] This is in fact the density range that results from the hydrolysis of tetramethoxysilane or tetraethoxysilane with quantities of water between 1 and 10 times the required stoichiometric quantity, particularly when the drying is slow drying as described herein, this drying inducing negligible shrinkage. This specificity meets the need to produce monoliths respecting the dimensional dimensions of the preforms, without distortion or cracking or fragmentation of the final dried gel, and having sufficient mechanical strength and the highest possible silica density.

[0091] The density of the gel is an indicator of the possible use of the sol-gel process to produce the multicapillary material.

[0092] It is further noted that the density of the silica gel obtained is higher when R is of low molecular weight.

[0093] Preferably, in this first embodiment, the organometallic precursor of a silica gel is tetramethoxysilane. In this case, the theoretical density in the absence of any shrinkage by syneresis, drying, or heat treatment of the silica gel resulting from said process is between 0.18 and 0.32 g / cm 3.

[0094] Preferably, in this first embodiment, if safety considerations prevail, tetraethoxysilane, which is less toxic and dangerous to handle, will be used as organometallic precursor of silica gel. In this case, the theoretical density in the absence of any shrinkage by syneresis, drying, or heat treatment of the silica gel resulting from said process is between 0.15 and 0.25 g / cm 3.

[0095] Silica gel density means the density of the gel resulting from the hydrolysis process, between the conduits of the monolith delimited by its outer contour and excluding the volume of the conduits, i.e., the density of the gel located between the conduits of the monolith. Any spacers are not taken into account in determining the gel density; in other words, in the case where spacers are present, the gel located outside the spacers is considered.

[0096] On the other hand, if the silica gel contains third bodies such as fibers, microfibers, nanofibers, and particles or nanoparticles, the density considered is the density of the medium external to these third bodies and produced by the sol-gel process itself.

[0097] To measure density, can be used: 1. Either porosimetry using the BET method if the silica gel does not contain such third bodies; 2. Or transmission electron microscopy followed by image analysis, on a section of the material if the silica gel contains such third bodies.

[0098] Advantageously, in this first embodiment, the conduits can extend linearly and without interruption between an inlet face and an outlet face of the material. Second embodiment

[0099] In certain embodiments, the material obtained, i.e., the gel, is macroporous. In particular, these will be multimodal silica gels, of the type marketed by the company Merck under the trade name Chromolith, and derived from the research of Mr Takanishi and Ishizuka [1] [2] [3] in Japan.

[0100] These gels are typically synthesized by spinodal decomposition of silica gel by a sol-gel process in the presence of a polymer such as polyvinyl alcohol, polyethylene glycol, etc. In this way, a macroporous three-dimensional silica skeleton is formed, the macropore size of which can reach several micrometers. The silica skeleton itself is mesoporous. A chromatographic mobile phase can percolate through the micropores, and interact with the surface of the mesopore silica gel.

[0101] These particular silica gels are referred to herein as “multimodal gels.”

[0102] Advantageously, according to the invention, a multimodal silica gel is created by hydrolysis of an organometallic precursor in the presence of an amount of water not exceeding six times, preferably not exceeding five times, even more preferably not exceeding four times, or even twice the stoichiometric amount (stoichiometric molar amount) required for complete hydrolysis of said organometallic precursor. The multicapillary packing / monolithic structure obtained by the method of the present invention then exhibits minimal shrinkage upon drying, maximum compactness, cracks and defects with a gel density, and exhibits, for example, a high silica density (typically 0.05 to 1.2 g / cm 3< , preferably between 0.1 and 0.8 g / cm 3< ).

[0103] It should also be noted that the density of the silica gel obtained is higher when R is of low molecular weight.

[0104] Preferably, in this embodiment leading to a multimodal silica gel, the organometallic precursor is tetramethoxysilane.

[0105] Preferably, if safety considerations prevail, the organometallic precursor of a multimodal silica gel is tetraethoxysilane, which is less toxic and dangerous to handle.

[0106] Density of silica gel means the density of the gel resulting from the hydrolysis process, between the conduits of the monolith delimited by its external contour and excluding the volume of the conduits, i.e., the density of the gel or of the part of the gel resulting from the hydrolysis process, located between the conduits of the monolith. Any spacers are not taken into account in determining the density of the gel; in other words, in the case where spacers are present, the gel located outside the spacers is considered.

[0107] On the other hand, if the silica gel contains third bodies such as fibers, microfibers, nanofibers, and particles or nanoparticles, the density considered is the density of the medium external to these third bodies and produced by the sol-gel process itself.

[0108] To measure density, can be used: 1. Either porosimetry using the BET method if the silica gel does not contain such third bodies 2. Or transmission electron microscopy followed by image analysis, on a section of the material if the silica gel contains such third bodies.

[0109] Advantageously, in the second embodiment, the preforms are preferably pyrolyzable or hydrolyzable yarns or fibers (e.g. sections or segments), for example pyrolyzable or hydrolyzable carbon-based yarns such as in particular carbon fibers, yarns of polymers, polyolefins, polysulfones, polyurethane, polyacrylates and polymethacrylates, polyamides, polyimides, polyethers or polyesters, and their derivatives, which are typically occluded in the gel. The conduits resulting from the ablation of the preforms can extend into a portion of the material only, and be immersed or occluded therein. Indeed, the shrinkage inherent in the drying of such silica gels is thus more easily accompanied, and the stresses that can lead to their cracking are reduced. Furthermore, the presence of large macropores in multimodal gels allows easy convection of a percolating fluid between adjacent conduits.A compact stack of conduits can be made in the material to promote the convective transfer of a fluid circulating in the material between the conduits and towards an outlet face.

[0110] The threads or fibers, more particularly the thread segments, generally have a length between a few micrometers and a few centimeters, typically between one and ten millimeters. Advantageously, these threads have a length greater than the diameter of the final filling.

[0111] The wires are typically statistically oriented in the direction of fluid flow, i.e. from the inlet to the outlet of the packing.

[0112] The wires generally have a diameter of less than 50 µm, more preferably less than 10 µm, even more preferably less than 5 µm.

[0113] The wires may be covered with a spacer to prevent them from touching each other in the packing and producing weak points and preferential passages at these contact points. The spacer may be a layer of porous solid.

[0114] There Figure 1 schematically represents, seen in axial section, a multicapillary packing comprising continuous conduits 2 extending axially between an inlet face 3 and an outlet face 4 in a porous mass 1 obtained by a sol-gel process.

[0115] There Figure 2 schematically represents, seen in axial section, a multicapillary packing comprising discontinuous conduits arranged in the form of sections 5 extending axially between an inlet face 3 and an outlet face 4 and occluded in a porous mass 1 obtained by a sol-gel process.

[0116] Embodiments of the invention are illustrated in the following examples. These examples should not be considered in any way as limiting the present invention. EXAMPLES Example 1

[0117] In this example, the precursor polymer fibers of the conduits are assembled into a bundle, the bundle is immersed in a precursor solution of silica gel, which is then caused to gel around the fibers, and then the fibers are eliminated by pyrolysis and combustion.

[0118] A polyamide monofilament (approximately 100 µm in external diameter) is soaked in an aqueous solution containing 10% polyvinyl alcohol and 15% by weight of glass microbeads supplied by the firm Potters Ballotini with a particle size distribution between 40 and 70 µm in diameter. The monofilament is then dried. In this way, the exterior of the polyamide filament is covered with silica gel microbeads which act as spacers, adhered to its surface by the action of PVA which acts as glue.

[0119] A bundle is made by assembling these filaments into a rectangular cross-section bundle 1700 µm wide, 250 µm deep and 100 mm long. This bundle is created by winding it into a precisely machined conduit made from a 100 mm x 20 mm x 10 mm 316 L stainless steel sheet. The polyamide fiber bundle is impregnated with a mixture of 25 ml of tetraethoxysilane, 10.0 ml of mineralized water and 0.35 ml of 1 N ammonia, previously stirred until a single-phase mixture is formed. The liquid must completely wet and fill the conduit and the packing. The packing is closed by an upper cover made of a flat stainless steel sheet of dimensions identical to those of the base steel sheet, screwed onto it, on which a thickness of approximately 5 micrometers of paraffin melting at 90°C is previously deposited.

[0120] The mixture is left to polymerize and freeze for 24 hours at 80°C.

[0121] The two ends of the lining thus formed are cut flush with the steel sheet so as to release the section of the lining.

[0122] The filling has a length of 100 mm.

[0123] The cover is removed after heating the filling to a temperature of 95°C to melt the paraffin, and the filling is dried under a vacuum of 2 kPa at a temperature of 20°C for 48 hours.

[0124] The resulting product is heated to 550°C in an air atmosphere to convert it into a multi-capillary packing by burning the polymer fibers.

[0125] Once cooled, the filling is closed again on its upper part by a flat sheet of stainless steel of the same dimensions, or cover, screwed onto the one containing the filling. Example 2

[0126] In this example, the precursor polymer fibers of the conduits are assembled into a bundle, the bundle is immersed in a precursor solution of silica gel, which is then caused to gel around the fibers, and then the fibers are eliminated by pyrolysis and combustion.

[0127] A polyamide monofilament (approximately 100 µm in external diameter) is soaked in an aqueous solution containing 10% polyvinyl alcohol and 15% by weight of glass microbeads supplied by Potters Ballotini with a particle size distribution of between 40 and 70 µm in diameter. The monofilament is then dried. In this way, the outside of the polyamide filament is covered with glass microbeads that act as spacers, adhered to its surface by the action of PVA, which acts as glue. A bundle is made by assembling these filaments into a rectangular cross-section bundle 1700 µm wide, 250 µm deep and 100 mm long. This bundle is created by winding it into a conduit precisely machined from a 100 mm x 20 mm x 10 mm sheet of 316 L stainless steel.The polyamide fiber bundle is impregnated with a mixture of 25 ml of tetraethoxysilane, 10.0 ml of mineralized water and 0.35 ml of 1 N ammonia previously stirred until a single-phase mixture is formed, and 5 grams of mesoporous silica nanoparticles with a particle diameter of 20 nm and a specific surface area of ​​600 m 2 < / g, reference 637246 from Sigma Aldrich. The liquid must completely wet and fill the conduit and the packing.

[0128] The packing is closed by an upper cover made of a flat stainless steel sheet of dimensions identical to those of the base steel sheet, screwed onto it, on which a thickness of approximately 5 micrometers of paraffin melting at 90°C is previously deposited.

[0129] The mixture is left to polymerize and freeze for 24 hours at 80°C.

[0130] Both ends of the lining are cut flush with the steel sheet so as to release the lining section.

[0131] The filling has a length of 100 mm.

[0132] The cover is removed after heating the filling to a temperature of 95°C to melt the paraffin, and the filling is dried under a vacuum of 2 kPa at a temperature of 20°C for 48 hours.

[0133] The resulting product is heated to 550°C in an air atmosphere to convert it into a multi-capillary packing by burning the polymer fibers.

[0134] Once cooled, the filling is closed again on its upper part by a flat sheet of stainless steel of the same dimensions, or cover, screwed onto the one containing the filling. Example 3

[0135] In this example, precursor polymer fibers of the conduits are assembled into a bundle, the bundle is immersed in a precursor solution of silica gel, which is then caused to gel around the fibers, and then the fibers are eliminated by pyrolysis and combustion.

[0136] A polyamide monofilament (approximately 100 µm in external diameter) is soaked in an aqueous solution containing 10% polyvinyl alcohol and 15% by weight of glass microbeads supplied by Potters Ballotini with a particle size distribution of between 40 and 70 µm in diameter. The monofilament is then dried. In this way, the outside of the polyamide filament is covered with glass microbeads that act as spacers, adhered to its surface by the action of PVA, which acts as glue. A bundle is made by assembling these filaments into a rectangular cross-section bundle 1700 µm wide, 250 µm deep and 100 mm long. This bundle is created by winding it into a conduit precisely machined from a 100 mm x 20 mm x 10 mm sheet of 316 L stainless steel.The polyamide fiber bundle is impregnated with a mixture of 25 ml of tetraethoxysilane, 10.0 ml of mineralized water and 0.35 ml of 1 N ammonia previously stirred until a single-phase mixture is formed, and 1 g of potassium titanate microfibers, diameter 0.2 µm, length 18 µm, marketed under the brand name TISMO D by Otsuka Chemical Co., Ltd. The liquid must completely wet and fill the conduit and the lining.

[0137] The packing is closed by an upper cover made of a flat stainless steel sheet of dimensions identical to those of the base steel sheet, screwed onto it, on which a thickness of approximately 5 micrometers of paraffin melting at 90°C is previously deposited.

[0138] The mixture is left to polymerize and freeze for 24 hours at 80°C.

[0139] The two ends of the lining thus formed are cut flush with the steel sheet so as to release the section of the lining.

[0140] The filling has a length of 100 mm.

[0141] The cover is removed after heating the filling to a temperature of 95°C to melt the paraffin, and the filling is dried under a vacuum of 2 kPa at a temperature of 20°C for 48 hours.

[0142] The resulting product is heated to 550°C in an air atmosphere to convert it into a multi-capillary packing by burning the polymer fibers.

[0143] Once cooled, the filling is closed again on its upper part by a flat sheet of stainless steel of the same dimensions, or cover, screwed onto the one containing the filling. Example 4

[0144] In this example, precursor polymer fibers of the conduits are assembled into a bundle, the bundle is immersed in a precursor solution of silica gel, which is then caused to gel around the fibers, and then the fibers are eliminated by pyrolysis and combustion.

[0145] A polyamide monofilament (approximately 100 µm in external diameter) is soaked in an aqueous solution containing 10% polyvinyl alcohol and 15% by weight of glass microbeads supplied by Potters Ballotini with a particle size distribution of between 40 and 70 µm in diameter. The monofilament is then dried. In this way, the outside of the polyamide filament is covered with glass microbeads that act as spacers, adhered to its surface by the action of PVA, which acts as glue. A bundle is made by assembling these filaments into a rectangular cross-section bundle 1700 µm wide, 250 µm deep and 100 mm long. This bundle is created by winding it into a conduit precisely machined from a 100 mm x 20 mm x 10 mm sheet of 316 L stainless steel.The polyamide fiber bundle is impregnated with a mixture of 25 ml of tetramethoxysilane and 20.0 ml of mineralized water, previously stirred until a single-phase mixture is formed. The liquid must completely wet and fill the conduit and the lining.

[0146] The packing is closed by an upper cover made of a flat stainless steel sheet of dimensions identical to those of the base steel sheet, screwed onto it, on which a thickness of approximately 5 micrometers of paraffin melting at 90°C is previously deposited.

[0147] The mixture is left to polymerize and freeze for 24 hours at 80°C.

[0148] The two ends of the lining thus formed are cut flush with the steel sheet so as to release the section of the lining.

[0149] The filling has a length of 100 mm.

[0150] The cover is removed after heating the filling to a temperature of 95°C to melt the paraffin, and the filling is dried under a vacuum of 2 kPa at a temperature of 20°C for 48 hours.

[0151] The resulting product is heated to 550°C in an air atmosphere to convert it into a multi-capillary packing by burning the polymer fibers.

[0152] Once cooled, the filling is closed again on its upper part by a flat sheet of stainless steel of the same dimensions, or cover, screwed onto the one containing the filling. Example 5

[0153] In this example, precursor polymer fibers of the conduits are assembled into a bundle, the bundle is immersed in a precursor solution of silica gel, which is then caused to gel around the fibers, and then the fibers are eliminated by pyrolysis and combustion.

[0154] A polyamide monofilament (approximately 100 µm in external diameter) is soaked in an aqueous solution containing 10% polyvinyl alcohol and 15% by weight of glass microbeads supplied by the firm Potters Ballotini with a particle size distribution between 40 and 70 µm in diameter. The monofilament is then dried. In this way, the exterior of the polyamide filament is covered with glass microbeads that act as spacers, adhered to its surface by the action of PVA, which acts as glue. A bundle is made by assembling these filaments into a bundle with a rectangular section of 1700 µm wide, 250 µm deep and 100 mm long. This bundle is created by winding it into such a conduit precisely machined from a titanium sheet (grade 2 ASTM) measuring 100 mm x 20 mm x 10 mm.

[0155] The polyamide fiber bundle is impregnated with a mixture of 1.6 g of Brij 56 (commercial surfactant), 1 g of dodecane, 4 g of tetramethoxysilane, and 2 g of 0.05 N HCl in deionized water. TEOS, dodecane, and Brij are mixed at 50°C until the mixture is homogeneous. 0.5 N acid (HCl) is then added with vigorous stirring. The mixture is poured into the conduit carrying the fibers.

[0156] The packing is closed by an upper cover made of a flat titanium sheet (grade 2 ASTM) of dimensions identical to those of the base titanium sheet, screwed onto it, on which a thickness of approximately 5 micrometers of paraffin melting at 90°C is previously deposited.

[0157] The mixture is left to polymerize and freeze for 24 hours at 20°C.

[0158] Both ends of the packing are cut flush with the titanium sheet to expose the packing section.

[0159] The filling has a length of 100 mm.

[0160] The cover is removed and the filling is dried under a vacuum of 2 kPa at a temperature of 20°C for 48 hours.

[0161] The resulting product is heated to 550°C in an air atmosphere to convert it into a multi-capillary packing by burning the polymer fibers.

[0162] Once cooled, the packing is closed again on its upper part by a flat sheet of titanium (grade 2 ASTM) of the same dimensions, or cover, screwed onto the one containing the packing.

[0163] Once cooled, the filling is closed again on its upper part by a flat sheet of stainless steel of the same dimensions, or cover, screwed onto the one containing the filling. Example 6

[0164] A preform of the monolith ducts is made by creating a bundle composed of sections of carbon fibers 4.8 µm in diameter and five millimeters long.

[0165] The bundle of these sections or needles is then inserted into the bottom of a 2.0 mm wide, 2 mm deep and 75 mm long housing hollowed out of a 20x10x75 mm sheet of 316L stainless steel so as to create a stack of naturally packed needles aligned along the long length of the conduit. A flat cover in a 20x10x75 mm sheet of PTFE is prepared.

[0166] The beam is made with a length of 75 mm long.

[0167] A silicic monolith is synthesized from tetraethoxysilane (TEOS, Aldrich 99%), Polyethylene oxide (PEO, molar mass = 10,000, Aldrich 99%), nitric acid (68%, Aldrich) and NH4OH (analytical purity, Aldrich).

[0168] A 250 mL Erlenmeyer flask is placed in an ice bath at 0°C with a magnetic stir bar. Then demineralized water (36 g, 2 mol) and nitric acid (68% HNO3, 3.60 g, 38.84 mmol) are added and stirred at 500 rpm for 15 min. Then, PEO (4.79 g PEO including 0.11 mol EO unit) is added and the mixture is stirred for one hour at 700 rpm so that all the PEO is dissolved. TEOS (37.70 g, 0.18 mol) is then added and the mixture is stirred for one hour. The resulting clear solution is then poured using a 10 mL pipette into the bundle of sections obtained previously kept in a dry environment at 0°C before filling. The bar is then placed in an oven under a saturated atmosphere of water vapor at 40°C for 72 hours. The PTFE cover is removed

[0169] The bar is immersed in a 2 L beaker with 1500 mL of demineralized water at ambient temperature for 1 h. The monolith is then washed in the same way four times by immersion in demineralized water (500 mL, 1 h) until a neutral pH is obtained. The monolith is then subjected to a basic treatment. It is then immersed in 400 mL of an ammonia solution (0.1 M) in a polypropylene bottle (500 mL). The bottle is then placed in an oven at 40°C for 24 hours.

[0170] The recovered monolith is rinsed with a pipette with distilled water, dried at ambient temperature for 48 h and at 40°C for 24 h on a flat surface.

[0171] It is calcined at 650°C in air for 24 hours (ramp 1°C min-1).

[0172] A flat cover in a 20x10x75 mm sheet of stainless steel is prepared.

[0173] The cover is repositioned with a PEEK gasket at 340°C and cooled.

[0174] The end caps are fixed to the column and the whole thing is sealed with a film of two-component epoxy glue. BIBLIOGRAPHY

[0175] [1] K Nakanishi, Phase separation in silica sol-gel system containing polyacrylic acid, Journal of non-crystalline Solids 139 (1992), 1-13 and 14-24; [2] K. Nakanishi, Phase separation in Gelling Silica-Organic Polymer Solution: Systems Containing Poly(sodium styrenesulfonate), J. Am. Ceram. Soc. 74 (10) 2518-2530-30 (1991); [3] N. Ishizuka, Designing monolithic double pore silica for high-speed liquid chromatography, Journal of Chromatography A, 797 (1998), 133-137.

Claims

1. Method for manufacturing a multi-capillary packing from a substrate of ablative preforms, each preform being suitable for forming, during its ablation, a conduit enabling the convection of a fluid in said packing, said method comprising the following steps: (a) assembling the ablative preforms in the form of at least one bundle; (b) creating a gel between the ablative preforms of the bundle by hydrolysis of an organometallic precursor in the presence of a quantity of water not exceeding ten times the stoichiometric quantity required for complete hydrolysis of said organometallic precursor; (c) ablating the preforms, preferably by pyrolysis, oxidation, vaporization, melting and drainage, mechanical extraction or chemical attack, so as to form a plurality of conduits in the gel.

2. Method according to claim 1, further comprising a drying step between steps (b) and (c) or after step (c).

3. Method according to claim 2, wherein the drying is carried out under vacuum at ambient temperature.

4. Method according to one of the preceding claims, wherein the organometallic precursor is an organometallic alkaloid, organometallic acetate, organometallic carboxylate, organometallic halide, organometallic nitrate, organometallic alkanoate, organometallic acyloxide, or one of the mixtures thereof.

5. Method according to one of the preceding claims, wherein the organometallic precursor is chosen from the organometallic derivatives of silicon, aluminium, zirconium, titanium, a rare earth such as yttrium, cerium or lanthanum, boron, iron, magnesium, calcium, strontium, barium, germanium, phosphorus, lithium, potassium, sodium, niobium, copper, or one of the mixtures thereof.

6. Method according to one of the preceding claims, wherein the organometallic precursor is tetramethoxysilane or tetraethoxysilane.

7. Method according to one of the preceding claims, wherein the gel has a pore volume of between 20% and 90% by volume of the gel, advantageously between 40% and 65% by volume of the gel.

8. Method according to one of the preceding claims, wherein the preforms comprise yarns of polyamide, polyolefin, polyacrylate, polymethacrylate, polysulfone, polyurethane, polyimide, polyether or polyester yarns.

9. Method according to claim 8, wherein the polyester yarns are hydrolysable polyester yarns.

10. Method according to one of the preceding claims, wherein the ablative preforms are covered with a porous granular substance before assembling in bundle form.

11. Method according to one of the preceding claims, wherein the ablative preforms are shaped into segments occluded in the body of the packing.

12. Method according to one of the preceding claims, wherein the gel is a silica gel.

13. Method according to claim 12, wherein the gel is a multimodal silica gel and wherein the quantity of water does not exceed six times the stoichiometric quantity required for complete hydrolysis of said organometallic precursor, preferably wherein the quantity of water does not exceed five times the stoichiometric quantity required for a complete hydrolysis of said organometallic precursor, still more preferably wherein the quantity of water does not exceed four times the stoichiometric quantity required for complete hydrolysis of said organometallic precursor.