WO2014128319A1

WO2014128319A1 - Method for producing hollow microfibre membranes and membranes produced in this way

Info

Publication number: WO2014128319A1
Application number: PCT/ES2014/070027
Authority: WO
Inventors: Juan Manuel CROVETTO DE LA TORRE; Juan Esteban DÍAZ GÓMEZ
Original assignee: Porous Fibers, S.L.
Priority date: 2013-02-25
Filing date: 2014-01-17
Publication date: 2014-08-28
Also published as: ES2499117B1; ES2499117A1

Abstract

The invention relates to a method comprising: (a) injecting a first lumen-forming fluid by means of an injection device arranged coaxially inside a nozzle or spinnerette, and injecting a second fluid comprising a gas-separating polymer (PSG) dissolved in at least one solvent coaxially to the first fluid; and (b) generating an electric field gradient between the spinnerette and a second electrode; combining said gradient with the effect of the gravitational field and with the flow of the two fluids, until said first and second fluid detach themselves, forming a protofibre which falls and is collected in the second electrode where the protofibre solidifies, forming the hollow microfibre. The invention also relates to the microfibres produced from said process, and to the use thereof in the production of hollow microfibre membranes.

Description

MANUFACTURING PROCESS OF MEMBRANES OF HOLLOW MICROFIBERS AND

MEMBRANES SO OBTAINED

DESCRIPTION

Technical sector

The present invention relates to the field of hollow microfiber polymer membranes with application in the purification and separation of gases. More specifically, it refers to a new manufacturing process for said membranes, as well as to the membranes obtained therefrom and their use, for example, in methods of gas or fluid separation.

BACKGROUND OF THE INVENTION There are currently major problems in the industry and especially in the environment, for which there is a great interest, both economically and environmentally, for segregating different gas mixtures. In some cases, this segregation is intended to recover these gases and, in others, their confinement. Thus, for example, it is used in order to separate carbon dioxide from combustion gases so that it does not emit into the atmosphere and contributes to the usual greenhouse effect.

No less important are the separations that have to be made in the syngas, where a stream of high temperature water vapor decomposes the carbon in C0 ₂ , CO and H ₂ , the latter being the fuel that is sought for many applications, including and especially the fuel cells.

Other crucial separations in which this technology can be applied are, among other examples, the 0 ₂ and N ₂ separations, or the removal of C0 ₂ from natural gas, which depending on the origin may contain very high amounts of C0 ₂ .

Naturally, in the processes of gas separation, high pressures yield higher flow rates per unit area and, in general, higher temperatures act in the same way on the phenomenon of gas permeation in polymers shaped as a hollow fiber membrane. For this reason, membranes obtained from very rigid polymer structures, even cross-linked, with minimal flexibility and high thermal resistance are preferred for these separation applications. In addition, amorphous (vitreous) and high temperature glass transition polymers are preferred. It is known that there are polymers in which different gases are soluble to a greater or lesser degree. In addition, the gases have greater or lesser affinity for the different polymers based on their molecular structure, the type of bonds that make them up, their free molecular volume, the polar groups or functional groups present in the polymer molecule, and so on.

These polymers can be configured, for practical use, in the form of hollow fibers of small diameter but of great length, offering a large surface area (per unit mass of polymer) of the gases, in addition to presenting small wall thicknesses. This configuration of the polymers is what, classically, allows the separation of gases.

In this way, the greatest possible surface area of the gases with the minimum amount of polymer has to be obtained. Also, the hollow fibers have to be manufactured with the lowest possible thickness, but with sufficient mechanical strength, thus optimizing both the costs of the product and the amount of gas that can be processed.

Currently, the hollow fibers have a maximum diameter, around a millimeter or at least a few tenths of a millimeter and are formed from a viscous polymer solution, or from this molten, by extrusion and forming based on extrusion through nozzles (spinnerets) specially designed for this application. Conventionally, these nozzles consist of two concentric needles, through which the fluid that will lead to the formation of the lumen passes. The dissolution of the polymer or polymers that make up the fibers themselves flows through the space between the inner and outer needles. The outer needle can simply be a solid body in which a coaxial cylinder has been perforated to which the said inner needle carrying the lumen generating fluid is attached. This equipment facilitates the achievement, in the end, of the Hollow Fibers (hereinafter FH) of continuous length, due to a continuous and stable production, but with a diameter of 0.2 to 1 mm or greater.

Economical low-cost polymers that are produced commercially in large quantities and that have often been designed for other applications are cost-effective in that they provide their low-cost factor. However, the low selectivity of these economic polymers to different gases and, above all, the low permeation flow rate that they have, in addition to their limited thermal resistance, make them not useful for many applications.

There are commercial polymers that can make different gas separations and that differ in their gas permeability, mechanical resistance to work at high pressures or temperatures, resistance to certain chemicals or resistance even to the gases themselves. If these properties are not good enough, the degeneration or practical degradation of the polymers can occur, depending on the working conditions.

Virtually all commercial polymers have already been tested as porous flat membrane and porous hollow fiber for gas purification and separation. Examples of these are cellulosic plastics, polysulfones, dialkyl and diphenylsiloxane derivatives, polycarbonates, polyethers (aliphatic and aromatic), polyesters, polyamides (aliphatic and aromatic), polyurethanes, and to a lesser extent other thermoplastics for engineering, such as ABS plastics, acrylic polymers, or in general functional polyphenylene type PPO, PPS or PEEK. High performance polymers have also been tested, such as fluorinated polymers and some polyheterocycles, such as polybenzoxazoles, polybenzimidazoles, or polyimides, and a large number of copolymers or mixtures of the named polymer families. Modernly, some soluble experimental polyimides have aroused great interest for this application, which offer a permeability / selectivity balance far superior to conventional polyimides or commercial polyimides used so far for this application. In principle, all these types of polymers are capable of being transformed into membranes for gases in hollow fiber configuration, as long as they are soluble or can melt below their initial decomposition temperature.

In recent years, various work groups and several companies, generally linked to biomedical applications, have developed electro-spun technology (electrospinning, EE) for the formation of nanowires. This spinning electrohydrodynamic (EHD) technology consists of injecting through a hollow needle a polymer dissolved in one or more solvents, alone or accompanied by other polymers or non-polymeric particles, soluble or not in one or more of those solvents. This polymer, which is at a certain electrical voltage with respect to a second electrode (called a base), which can be connected to ground or to another voltage different from the previous one, causes a gradient of Enough electric field to occur in the "drop" that forms at the distal end of the injection needle (s), a conical shape called the Taylor cone.

For example, in ES2245874 a method for producing composite nanotubes and core-shell structure, from coaxial flows of immiscible or poorly miscible liquids, is described.

In general, the EE process applied to a single polymer comprises providing the polymer from the needle of a syringe (or other type of device that allows to provide precisely the polymer (s), such as a high-precision gear pump, etc.) , towards a conductive device connected to ground or less tension than the syringe-spinnerete, located at the appropriate distance from the needle in question. At the end of the syringe where the polymer outlet is located outside it, an attraction of the injected polymer is generated towards the "base" electrode that is at another potential, generating a conical shape of the polymer protruding from the syringe, called Taylor cone. At the moment when the electric field gradient between the polymer located in the Taylor cone and the base electrode is sufficiently high, the polymer at the end of the Taylor cone leaves it and "falls" towards the second wire-shaped electrode or small sphere, a few nanometers in diameter at least and some mire (micrometer) at most.

The use of this electric field and the subsequent Taylor cone, allows to obtain that the fibers obtained are, in principle, smaller in diameter than those obtained in a completely analogous way but using only gravity to produce the spinning. In the "pure" EE, it is the electrical parameters that determine the size of the wire initially obtained.

In the case of using two fluids, in addition to the conventional needle a second inner needle will be used to the first in order to coaxially provide with the first polymer, a second fluid, which will be confined inside the thread. Thus, by this second coaxial needle with the first, it is injected by a system analogous to the previous one, for example, a second piston pump, a new fluid that can be, among others, an oil or other dissolved (or molten polymer) ) compatible or not with the one injected on the outside. The problem with this method is that during the fiber formation phase the solvent of the polymer used is mostly removed, passing into the atmosphere, the same thing happening to a greater or lesser extent to the solvent of the inner polymer if it is compatible or even coincident with that used for the outside.

When this solvent is lost, the protofiber is ionized, which generates strong repulsions with itself (when presenting the same electrostatic charge and low mass), which translates into a chaotic movement of it. This movement frequently causes discontinuities in the fiber, loss of the lumen or its connection with the outside, being in practice impossible (or practically impossible in conditions of industrial product production) to achieve a continuous and flawless FH that makes it valid for intended use here.

Likewise, the EE presents other drawbacks, among which are not allowing the chemical phase inversion, as well as generating as a consequence of the chaotic movement, diameters of different sizes, breaks or discontinuities in the protofibers (derived from the different inertia generated during repulsions of exterior and lumen fluids). Additionally, said movement causes a lateral arrangement of the lumen in the fiber to be obtained, as well as an excessive thickness of the boundary layer, consequently it is not possible to differentiate between the active surface and its support. The present invention is therefore directed to solve the above difficulties, presenting a manufacturing process of a membrane formed with micro-animal fibers from commercial polymers such as those mentioned above, and possibly also from special polymers of recent development and of very high cost, so that by arranging them in the form of a separating membrane, a large area of permeation of gases (and fluids in general) is achieved per unit mass of polymer used. To do this, it will be the object of the process to generate membranes with a minimum wall thickness, maintaining sufficient strength to withstand the working conditions.

Description of the invention

A first object of the invention is a manufacturing process of composite hollow microfibers comprising:

to. injecting a first lumen-forming fluid with a flow rate between 2 ml / h and 40 ml / h, preferably 7 ml / h at 30 ml / h, through a hollow needle terminal shaped injection device arranged coaxially inside of a mouthpiece or spinerette. Simultaneously, a second fluid characterized by comprise at least one gas separator polymer (PSG) dissolved in at least one solvent forming a viscous solution, with a viscosity value in the order of several thousand cPs (from, for example, 6000 cPs to 20,000 cPs, corresponding to solutions with a percentage by weight of polymer in the solvent of about 10-20% (said variable being variable depending on the polymer and its surface tension), which is injected with a flow rate between 2 ml / h and 40 ml / h, preferably 6 ml / h at 27 ml / h concentrically and coaxially to the first fluid, in particular, the pumping system of the second fluid may comprise a needle of greater diameter than the hollow needle described above or may consist of another equivalent system that allows a specific arrangement of the hollow needle, in addition to allowing the entry of the second fluid.In the case of having two concentric needles, both can have their terminal ends in the same The second needle may not exist and the passage of the second fluid through a foramen made in the body of the nozzle in which, coaxially thereto, the conductive needle of the first fluid is housed. In this case, the body of the nozzle must be executed in a non-conductive and solvent resistant material, such as PP, PEEK and others;

generate an electric field gradient between the electrical voltage of the injection system constituting a first electrode and the voltage of a second electrode consisting preferably of a base cylinder located at a short distance (preferably from 1 cm to 10 cm, and more preferably from 2 to 10 cm) of the injection system, which is connected to ground or other voltage different from the previous one, said gradient being sufficient to generate a deformation at the end or distal surface of the drop formed at the exit of the system Injection As for the second electrode, this can be a fixed or mobile flat system or preferably a rotating cylinder, to facilitate the collection and parallelism of the fibers deposited thereon. Preferably, a non-woven blanket or layer, TNT (preferably, at low temperatures) or appropriate woven fabric may be additionally arranged around it, covering it as a sheath. Said fabric may preferably consist of a material that makes it possible to obtain a sheath that is good conductive, that provides good mechanical resistance and is capable of withstanding high temperatures (in particular, capable of withstanding working conditions of 200 ° C or higher, to which the performance improves considerably, being even essential at times and even exceeding 450 ° C). Preferably, these materials may consist of glass fiber or carbon fiber woven or other type of sintered fiber. For high temperatures, perforated metal (eg perforated aluminum, which is malleable and economical) could also be used;

said electric field gradient is combined with the gravitational field effect and with the flow rate of both fluids, thereby reducing the intensity of the electric field used compared to conventional EE techniques, said electric field being applied until said first and The second fluid eventually detaches itself forming a thread or filament of flow called protofiber that, in this way, is stabilized by the conjunction of the electric field, gravitational field and flow provided by both fluids. This protofiber is constituted by the first fluid (lumen generator) located inside and the second fluid (as a sheath) located outside. The protofiber thus falls into an essentially vertical movement (without typical chaotic movement of the EE) and is collected in the second electrode (or base electrode) comprising a layer of a completely immiscible (non-solvent) fluid with the outer polymer, but perfectly miscible with the solvent (s) used to dissolve the polymer. Thus, upon contact with it, the protofiber solidifies forming a continuous film on the outer surface of the protofiber, without foams or pores, and of a minimum thickness (typically of some nanometers, preferably between 10 and 100 nm, up to or two microns), followed by a porous structure, often sponge type, with interconnected nanometric cavities, which minimize the path of the fluid to be separated by the rigid structure of intrinsic microporosity that is intended in the gas separating polymers. This solidification is due to the gelation / coagulation of the polymer upon contact with the non-solvent fluid thereof, which is however miscible with the solvent of the outer polymer, which escapes and mixes with the fluid that accompanies the base electrode through the outside of it, as a film. Thus, in a particular embodiment in which the base electrode is a rotating cylinder, by rotating it, it is possible to renew the non-solvent fluid of the polymer through, for example, the contact of the fiber formed with a bath located in the bottom of the cylinder or by direct supply of water or other coagulating fluid (which may contain water, alcohol, acetone or a variety of liquids incompatible with the polymer and miscible with several of the solvents thereof) to the cylinder. Thus, the non-solvent is constantly renewed to extract the solvent from the separating polymer that forms the hollow fiber, by means of a "chemical" phase inversion process of the polymer that constitutes the outer sheath or coating. In a particular embodiment of the invention, the polymer solvent used to form the lumen can also change phase. Preferably, said phase change will be avoided, since the object is to leave free the place it occupies, forming a hollow lumen through which the fluid, gas etc., which separates from the initial mixture will move in future applications. In this way, the lumen generating fluid could be removed by different methods, such as dilution or even volatilization in the heat treatment, or both in certain cases.

The described process is also characterized by being carried out in a controlled atmosphere of temperature, humidity and, where appropriate or possibly, a solvent supply by means of a carrier gas, in order to protect against possible evaporation of solvent from the separating polymer. or contact with excessive humidity. Specifically, the process is carried out at a temperature between -10 ° and 85 °, more preferably between 15 ° and 35 °. As a consequence of this controlled atmosphere of solvent, it is possible to control its loss, so that it is minimal or even zero and the uncontrolled ionization of the microfibers and a chaotic movement of the same is avoided, which would cause a great dispersion of the diameter in the fibers and an undesirable decrease in their size (as in the EE of the reference patents described in the "Background of the invention"). Likewise, it is possible to avoid the appearance of microcoagulations on the surface of the protofibers by precipitation of moisture in the outer wall thereof. Finally, thanks to the coagulation of the fibers in a non-solvent, they are obtained free of adhesions with each other, avoiding the creation of tensions that can lead to their breakage or other defects that make them useless, such as fusion or crushing

On the other hand, in the absence of a chaotic movement, it is possible to define exactly the area of the cylinder, which allows the FH to be ordered as best suits (preferably aligned forming small "screw" pitch propellers, controlled by the horizontal movement of the spinnerets ) and not randomly, and do it on a support fabric that, in turn, allows the FH to be manipulated without touching them, ensuring that there are no breaks in its handling.

Throughout the process, the second electrode can rotate at a speed between 0 rpms and 200 rpm, preferably between 10 rpm and 130 rpm, depending on the drop speed and the diameter of the cylinder. Preferably, said control is carried out so that the tangential velocity of the cylinder at the point of fall of the protofiber and that of the protofiber itself are close or coincident, to avoid the formation of unwanted curls or dangerous stretches. At the same time, the injection device can move in a horizontal movement parallel to the surface of the cylinder, achieving a continuous alignment of microfibers with a certain parallel to each other. To achieve this, the deposition or fall velocity of the protofiber on the base cylinder and the tangential velocity thereof must be correctly coordinated, allowing the deposition of the protofiber in an essentially normal way aligned with the generatrices of the collecting cylinder. Said lateral deposition velocity may vary between 0.01 mm / s and 1 mm / s, more preferably between 0.09 mm / s and 0.5 mm / s.

Depending on the initial concentrations of the outer polymer, its characteristics, the presence of other polymers combined with it, the presence of non-solvents, the presence of highly volatile solvents, the evaporation conditions of surface solvents and the characteristics of the non-solvent on which the protofiber is deposited, it is possible to obtain a continuous outer surface of the fibers without pores, suitable for separating gases, and at the same time causing inside nanopores of (typically, but not necessarily) between 10 and 100 nanometers, which allow the free passage inside the fiber of any product, be it gas or other fluid.

By way of example, to determine a case of concentration, distance and working voltage, it is possible to use Matrimid® as an external polymer, which consists of a commercial polyimide used in gas separations. In that case, a concentration of 20% by weight can be used with an aprotic solvent, at 3.5 cm distance between electrodes and 4,500 volts of differential voltage, with a 200 mm diameter cylinder rotating at 100 rpm and using flow rates of 20 ml / h and 20 ml / hour of both lumen and Matrimid®, coagulating in pure water.

For the purposes of this patent, the first lumen-forming fluid is understood as a fluid comprising a solvent that may consist, for example, of viscous oils, polymers such as PPC (volatizable by heat treatment), PVP (water soluble and aprotic ), polyethylene oxide (easily removable), polyvinyl alcohol, and a long etc., being compatible (miscible) or not with the outer separator polymer, which does not occur for example in the conventional EE and represents an important difference between both systems . Even a lumen fluid that induces moderate gelation of the inner wall of the protofiber can be used, generating inner pores that facilitate the transport of permeate fluid, by minimizing the continuous thickness that, on the other hand, is required outside the fiber . This fluid, after the formation of the microfibers, is eliminated giving rise to a lumen or foramen interior with respect to the outer surface or sheath of the microfibers, characterized by their continuity along them.

With respect to the gas separating polymer (PSG), for the purposes of this patent it is understood as a polymer whose structural, spatial and chemical characteristics determine different solubilities to different gas molecules, as well as a differential diffusivity of the different gases in the same. In this way, it is possible to industrially separate gases that are mixed and have sufficiently different permeabilities and flows in practice.

In a particular embodiment, said PSG will consist of a polymer that can be solubilized in organic solvents at a concentration sufficient for the electrowinning process and will be selected from the group of polysulfones, cellulosic plastics, dialkyl and diphenylsiloxane derivatives, polycarbonates, aliphatic polyethers, aromatic polyethers, polyesters, aliphatic polyamides, aromatic polyamides, polyurethanes, ABS plastics, acrylic polymers, liquid crystal polymers, fluorinated polymers, polyheterocycles such as polybenzoxazoles, polybenzimidazoles, or polyimides, and copolymers of the named polymer families or mixtures thereof. Additionally, recently discovered polymers such as TR (thermally rearranged) polymers, PIM polymers, or intrinsic microporosity, or some types of polyimides can be used. In principle, all these types of polymers are capable of being transformed into membranes for gases in hollow fiber configuration, as long as they are soluble or can melt below their initial decomposition temperature and can be transformed into hollow fibers of small thickness and diameter by EE.

Additionally, the system object of the invention allows, when collected on a fabric of e.g. glass, aramid, or carbon fibers, heat treat the polymer in an especially simple manner, which is impossible if systems are used to arrange the polymers that require a support of a conventional UF membrane previously made.

Another advantage of the process is that it is extensible to polymers and conventional mixtures, cheaper, allowing a reduction in costs due to the little material that is necessary to use, in addition to the lower implantation per unit of active surface, less use of adhesives , smaller size of the container system etc. In all cases, and with respect to the conventional methods of manufacturing hollow fibers and gas separation modules from them, it will happen: it will always happen that for the same active surface the conventional system requires one or two orders of magnitude more than material than in the present invention;

it will always happen that for the same surface activates the conventional fiber module, and that derived from this way of processing the polymer, will have much more volume, larger size required for its implantation, etc .;

In most cases, it will occur that the permeability of the polymer used will be greater (ie, the passage of gas per unit of exposed surface) in the case of the present invention compared to any of the conventional ones, since the actual thickness which must pass through the gas or molecule, will be lower in this production system than in any of the conventional ones;

The size of the fiber obtained allows the use of high-priced polymers in the best possible way (at least in an order of magnitude lower than the best that can be achieved by conventional spinning procedures). In the case of the EE, continuous hollow fibers cannot be achieved, nor would they be useful, since their tiny lumen would hardly allow work in separations in which the permeated gas is present in significant quantities;

The heat treatments, recommended to inhibit plasticization or to ensure the closure of cycles in polyheterocycles, controlled crosslinking, controlled carbonization etc., are optimally applied in thinner FH (such as those produced in this procedure), whose handling it does not present, on the other hand, any problem due to the way they are collected after the formation of the fiber, not requiring that they be handled directly by machinery or any operator.

The proposed system with gas protection, which has controlled the temperature, the degree of saturation in solvent of the gas-separating polymer and the humidity throughout the path of the protofiber, allows to work with very volatile solvents, such as chloroform, THF or toluene

In a particular embodiment of the invention, both the first fluid and the second fluid injected into the system can be miscible. Even in certain cases, the lumen can cause controlled coagulation of the external fluid. Thus, in a particular embodiment in the that the outer polymer is Matrimid®, both PPC and PVP or PEO are compatible and are used without problem with aprotic solvents in both solutions.

The lumen fluids and the one used for the cylinder, do not necessarily have to be immiscible, but their contact must generate an infersion (for example, of higher viscosity and even destabilization of the outer polymer solution) such that it facilitates that the lumen Maintain its initial size, that is, the one it has when detached from the spinnerete, with a controllable and moderate decrease thereof, without causing unacceptable off-centering of the lumen with respect to the "outer cylindrical" surface.

One way of implementing the above is to use a rotating cylinder as a collecting electrode, which is partially submerged in the polymer's non-solvent fluid. Given the relatively high speed of rotation of the cylinder, the renewal of the non-solvent is, in this case, very effective.

Likewise, a coagulant fluid can be added directly on the cylinder a few millimeters before the point of fall of the protofiber on the coagulant, and this combined with the previously defined bath that will carry away the non-optimal solvent that can be generated in the coagulant fluid sheet that accompanies the cylinder in its turn.

The hollow microfibers obtained from the process described above are also object of the invention. As a consequence of the new manufacturing process, which combines the harmony and uniformity of hollow fiber production through conventional spinning techniques, with the low diameter allowed by the EE system, obtaining microfibers with diameters of 5 to 120 microns, preferably of 5 to 100 microns and more preferably 5 to 50 microns, perfectly uniform, with a continuous outer surface lacking pores that exist, would be a preferential step for any fluid (in particular gases), and with a preferred active layer thickness of nanometers to one or two microns. Likewise, said microfibers comprise an inner layer located between the outer surface and the lumen of few microns, preferably from 2 to 10 microns or even higher if required, that is porous (thereby minimizing the thickness of polymer that the fluid or the transported molecule has to travel through the polymer separator). Likewise, the membranes obtained from the microfibers are object of the invention by means of the arrangement of a bundle of hollow microfibers essentially oriented in parallel (in an orderly and helical manner) in their deposition in the base electrode. In a preferred embodiment in which the base electrode consists of a cylinder covered with a conductive tissue, a subsequent cut of said tissue and the fiber bundle can be carried out, in a normal way to the assembly (that is, according to a generator of the cylinder , so that the fibers have a beginning and an end, constituting a bundle of aligned fibers and with the lumen open at both ends).

The membranes obtained have a dense outer surface (active face or "skin") and an internal porous structure, with pores or interconnected structures that allow the passage of gases or other fluids with maximum separation efficiency and minimum pressure or load loss. Thus, it is a further object of the invention to use the membranes for the separation of gases and fluids that are presented mixed.

As described, the process of the invention allows, by regulating the deposition rates and the movement of the protofiber collection base (the base electrode), that the protofiber when collected and coagulated does so with an excess of length that, in practice, is transformed into small misalignments of some fibers, the generation of curves, and even the creation of a certain curl or sinusoid formation in the FH (which will depend on the polymers used, the shrinkage they present at drying or heat treatment by the rearrangement of the molecules or the cross-linking or compaction thereof and even by their contraction when their solvent is completely eliminated). This excess length, sometimes necessary to prevent the shortening that occurs when drying or heat treating does not destroy the module to be manufactured with the fiber, is reduced by a heat treatment of the polymer, which frequently results in a shortening of the fiber or shrinking, due to the total elimination of volatile solvents and other additives, as well as a certain rearrangement of molecules that with temperature acquire greater freedom of movement. The curls or sinusoids have to be very controlled, adjusting the tangential speed of the cylinder and the fall of the extruded polymer. In this way, together with the freedom that is achieved in the fibers after cutting them, as they are not connected to each other in any way (when obtained by coagulation or phase inversion), this shortening is not achieved. break or generate minimum acceptable residual stress. Thus, it is possible to shorten the fibers without generating tensions or breaking them. Thus, some of the best membranes to separate gases are obtained from polymers that are subjected, once formed, to heat treatment processes that cause more or less important transformations in their molecular structure, by densification or compaction on occasion of them, or produce reactions of delation, crosslinking or Transposition as described, which gives rise to highly efficient gas separation membranes and, due to their high rigidity at the molecular structure scale, makes them resistant to the degradations that sometimes occur in the separating polymers.

However, this heat treatment frequently causes a shortening of the fibers and often makes them fragile, making their industrial handling difficult, since a low number of breaks can invalidate a complete filter.

In particular, the manufacturing process of the membranes from the protofibers can be interwoven with other yarns deposited by EE in different conditions of tension, solvent, concentration, etc., whose mission is to give consistency to the whole of FH and create spaces for the passage of the gases to be processed. The nature of these threads will preferably be polymeric, and for spinning all polymers capable of being processed by EE, their mixtures in all proportions and using the solvents and additives or fillers advised by experience can be used.

In a further particular embodiment of the invention, there is the possibility of annealing the fibers at high temperature without having to manipulate them. According to the polymers, these temperatures can reach up to 450 ° C, depending on the objectives pursued. For example, to achieve RT, temperatures of 400 ° C and above are required. Certain cross-links are achieved at 250 ° C and total solvent removal usually does not require more than 160 ° C if combined with vacuum in the processing chamber. Depending on the polymer, what allows this process is precisely to reach the values required by the most evolved polymers, both for processing and for subsequent work, once the modules are constituted.

Brief description of the figures

• Figure 1 (Fig. 1) shows the diagram of the process object of the invention.

• Figures 2 to 8 show images obtained by scanning electron microscopy, where the hollow microfibers object of the invention are observed in detail. • Figures 9 to 11 show images of different moments of the manufacturing process of hollow microfibers.

References in Fig. 1

1. First fluid dosage;

2. Dosing second fluid;

3. Injection device (can be by dosing syringe for several injection needles or by high precision gear pump system or similar for systems with many injection needles or spinnerets);

4. Protofiber;

5. Rotary cylinder;

6. Plate (splash remover);

7. Main atmosphere control system (includes air filter, temperature, humidity, solvent and pressure control system);

8. Air or gas inlet suitable for fiber protection;

9. Secondary atmosphere control system.

Detailed description of the invention

A particular embodiment of the object of the invention is described below, with reference to Fig. 1 which accompanies the description by way of illustration.

As shown in Fig. 1, the first fluid (1) and the second fluid (2) are dosed in the injection device (3) through a nozzle that can be single or multiple. In this way, both the first fluid (1) and the second fluid (2) are injected with a flow rate between 2 and 40 ml / min. As a consequence of the (electric) and gravitational field created between the injection system (3) and the rotating cylinder (5) located at a distance of between 1 and 10 cm from the injection system (3), filaments or profibras are detached that they fall on the rotary cylinder (5) at a lateral speed of the injection system (3) with respect to the rotary cylinder (5) of between 0.01 mm / s and 1 mm / s and a deposition or fall rate corresponding to a turn, preferably , from 20 to 200 rpm (depending on the diameter of the cylinder). In a particular embodiment, said rotation speed may be 100 rpm (for a cylinder of, for example, 20 cm in diameter, the deposition rate being 60 m / min in that case). Preferably, the deposition rate can vary, without limitation, between 20 and 150 m / min. By employing a plate (6) located in the lower part of the rotating cylinder (5) is able to remove excess liquid (as a splash, which in principle rarely occur during the process). The protofiber, consisting of the first fluid (lumen generator) located inside and the second fluid (as a sheath) located outside, on contact with the rotating cylinder (5), gels or coagulates as a result of the localized fluid on the surface of the cylinder (immiscible with the polymer of the second fluid, but miscible with the solvent thereof) giving rise to hollow microfibers that, throughout the process, will be distributed evenly along the surface of the rotating cylinder (5) when the injection device moves in a horizontal movement parallel to the surface of the cylinder.

Likewise, the process is carried out in a controlled atmosphere by means of the control system (7) comprising an air filter, as well as a temperature control system (preferably, by electric resistance) and humidity (preferably, by drying the air, followed by the addition of moisture and solvent (if applicable) to the required value). In turn, a condenser or solvent eliminator may be available at the air outlet of the ventilation enclosure, in order to avoid the emission of solvents into the atmosphere. In this way, the air is filtered by removing excess moisture through the air inlet (8) and the temperature is preferably controlled between 0 ° C and 85 ° C. Similarly, the solvent can be recovered for economic or environmental reasons. The process control in the secondary atmosphere control system (9) allows to inject air (or other gas in case the polymer is incompatible with oxygen, eg) in order to control the humidity, temperature and possibly solvent or solvent that It contains to control the surface conditions that the protofiber has when it reaches coagulation.

Whatever the polymer, the actual thickness of the polymer is reduced by one or more orders of magnitude with respect to what is obtained by conventional spinning. Thus, a thickness of tens of microns is a classic value in commercial membranes, and when values close to the mine are achieved, a support is usually required, which leads to high fiber diameters. Likewise, said support consists of another fiber (or flat membrane) that requires a previous formation process and that limits, in general, the temperatures of use. If the membranes in conventional systems are integrally constituted by the separator polymer, said polymer necessarily has a specific surface (surface area polymer mass unit) of two to three orders of magnitude greater than those obtained by the process of the invention, which makes the conventional system more expensive in separating polymer and much higher in module volume for the same active surface.

Claims

1. Manufacturing process of composite hollow microfibers characterized by comprising:

to. injecting a first lumen-forming fluid with a flow rate between 2 ml / h and 40 ml / ha through a hollow needle terminal injection device arranged coaxially inside a nozzle or spinnerete, and a second coaxial fluid to the first fluid, with a flow rate between 2 ml / h and 40 ml / h, wherein said second fluid comprises at least one gas separator polymer (PSG) dissolved in at least one solvent;

b. generate an electric field gradient between the electrical voltage of the spinnerete or first electrode and the voltage of a second electrode located at a distance of the spinnerete from 1 cm to 10 cm, said gradient being sufficient to generate a deformation in the first fluid and second fluid at the distal end of the spinnerets;

C. combining said electric field gradient with the effect of a gravitational field and with the flow rate of both fluids, until said first and second fluid eventually detach forming a continuous filament stabilized by the conjunction of the electric field, gravitational field and flow rate of both fluids, called protofiber, constituted by the first fluid located inside and the second fluid located outside, where said filament falls until it is collected in the second electrode that comprises in its lateral area a fluid immiscible with the PSG polymer, but miscible with the solvent (s) used, so that on contact with it, the protofiber solidifies by a phenomenon of chemical phase inversion, forming a continuous film on the outer surface of the protofiber, and a porous structure inside which constitutes the hollow microfiber itself;

and where said process is carried out under a controlled atmosphere of solvent, temperature, humidity and composition of said atmosphere.

2. Process according to claim 1, wherein the second electrode consists of a base cylinder.

3. Process according to claim 2, wherein the base cylinder is covered by a layer of non-woven fabric (TNT) or woven fabric.

4. Process according to any one of claims 1 to 3, wherein the gas separator polymer (PSG) consists of a polymer that can be solubilized in organic solvents at a concentration sufficient for the electrowinning process.

5. Process according to claims 1 to 4 wherein the polymer selected is from a group consisting of polysulfones, cellulosic plastics, dialkyl and diphenylsiloxanes derivatives, polycarbonates, aliphatic polyethers, aromatic polyethers, polyesters, aliphatic polyamides, aromatic polyamides, polyurethanes , ABS plastics, acrylic polymers, liquid crystal polymers, fluorinated polymers, polyheterocycles, as well as copolymers of the above polymers or any combination thereof.

6. Hollow microfibers obtained from a process according to any one of claims 1 to 5.

7. Microfibers according to claim 6, characterized in that they have a diameter between 5 and 120 microns.

8. Process for obtaining membranes characterized in that it comprises continuously carrying out a process according to any one of claims 1 to 5, during which the base cylinder rotates, while the injection device moves in a horizontal movement parallel to the surface of the cylinder, achieving an orderly and helical alignment of the microfibers in their deposition on the surface of the cylinder.

9. Process according to claim 8, characterized in that it comprises an additional stage of heat treatment at a temperature between 100 and 450 ° C.

10. Membranes obtained from a process according to claim 8 or 9.

1 1. Use of the membranes according to claim 10 for the separation of gases and fluids.