WO2017140927A1

WO2017140927A1 - Set of hollow-fibre membranes and uses thereof

Info

Publication number: WO2017140927A1
Application number: PCT/ES2017/070039
Authority: WO
Inventors: Mohamed Khayet Souhaimi; María del Carmen GARCÍA PAYO; Julio Antonio SANMARTINO RODRÍGUEZ; Juan Pablo POCOSTALES BUENAVIDA; Rocío RODRÍGUEZ AGUILERA; Abel Riaza Frutos; Francisco Javier BERNAOLA ECHEVARRÍA
Original assignee: Abengoa Water, S.L.
Priority date: 2016-02-19
Filing date: 2017-01-25
Publication date: 2017-08-24
Also published as: ES2633154B1; ES2633154A1

Abstract

The invention relates to a set of hollow-fibre membranes woven into a mesh, and to the application thereof in membrane distillation processes for the treatment and/or desalinisation of fluids.

Description

FIBER HUECA MEMBRANE SET AND ITS APPLICATIONS

DESCRIPTION The present invention relates to a set of hollow fiber membranes entwined in a mesh and its application in the membrane distillation process for the treatment and / or desalination of fluids.

STATE OF THE TECHNIQUE

Membrane distillation (DM) for the treatment and / or desalination of water is a non-isothermal membrane process, whose driving force is the vapor pressure gradient across a membrane that must meet the following characteristics: i) porous with high porosity,

ii) its pores must not "get wet" by the liquids used in the process, iii) it must not alter the liquid / vapor balance of the different components of the solution to be treated,

iv) capillary condensation should not occur inside your pores,

v) at least one side of the membrane must be in direct contact with the solution to be treated, it is at a higher temperature than the permeate.

DM differs from other membrane processes in that the membrane is not an active part in the separation and only serves as a support for a liquid / vapor infer. Due to its hydrophobicity, water in liquid phase or the solution to be treated cannot penetrate inside the pores, unless a hydrostatic pressure greater than the filling pressure of the pores that is determined by the angle is applied of contact of the solution with the membrane (degree of hydrophobicity), the surface tension of the liquid and the maximum pore size. As noted above, the driving force in this process is the difference in vapor pressure between both ends of the pores. To produce the distillation, therefore, a liquid / vapor infer is created at each pore end preventing the hydrostatic pressure from being greater than the filling pressure of the pores.

These DM systems can have one or more membrane modules using flat membranes or hollow fiber membranes. These modules can be flat, spiral or other configurations. Currently, there are different configurations of membrane distillation, such as:

- DMCD: Membrane Distillation by Direct Contact.

- DMCA: Membrane Distillation by Air Chamber.

- DMV: Vacuum Membrane Distillation.

- DMCL: Distillation in Membrane with Liquid Chamber.

- DMGB: Membrane Distillation by Sweeping Gas.

- DMGBT: Membrane Distillation by Thermostatic Sweeping Gas. In US201 10198287 a spiral module with a central recess for collecting the permeate produced is described. This module can work in both DMCA and DMCD as well as serve as a heat exchanger if instead of using hydrophobic and porous hollow fiber membranes they are used in dense capillaries. The layers of hollow fiber membranes are flat sheets, in which the hollow fiber membranes are arranged linearly in an envelope that acts as a contact membrane, and are wrapped around the central tube as well as the spacers to collect the permeate. The linear arrangement of the hollow fiber membranes in a wrap has several limitations: temperature polarization occurs inside the hollow fiber membrane and presents machining difficulties, since the hollow fiber membranes arranged in a wrap when being rolled up to Insert them into the spiral-shaped module and slide in relation to the envelope.

On the other hand, EP20721 12 discloses a distillation system with one or more modules of hollow fiber membranes to obtain distillates from a concentrated liquid as food, arranged in series, in parallel, or in a combination of both options . It consists of a DMCD method, whereby the food (previously heated and pressurized) flows inside the module in which there are flow regulators that cause longer contact time of the food with the hollow fiber membranes and greater turbulence. Inside the hollow fiber membranes the distillate flows at a lower temperature. However, this patent does not describe a set of hollow fiber membranes spirally wound around a condensation surface. WO2003000389 describes a DM system with hollow fiber membranes that works in both DMCD and DMV. This system stands out for being able to recover heat from the permeate vapor (extracted from the module and compressed externally), which is recirculated by an exchanger / condenser to heat the food before it enters the module. However, this patent also does not describe a set of hollow fiber membranes spirally wound around a condensation surface. In addition, the chamber through which the refrigerant fluid circulates does not comprise baffles that create turbulence in the refrigerant fluid to decrease the polarization by temperatures on the permeate side.

One of the major limitations found in the membrane distillation process is the inlet pressure of the liquid in the membrane pores (LEP), so it is necessary to find a suitable module design of hollow fiber membranes that increase turbulence, both the fluid to be treated and the permeate fluid, without increasing the pressure and causing the pores to get wet.

Additionally, modules comprising hollow fiber membranes have another limitation due to their manufacturing process. These modules have hollow fiber membranes arranged in parallel and in a vertical position (parallel to the central axis of the spiral). Specifically, hollow fiber membranes are usually arranged spirally wound around the condensation surface. With this arrangement, it is difficult to introduce and remove the hollow fiber membranes, especially when the condensation surfaces have a certain stiffness, the placement and fixing of the hollow fiber membranes in the module being a challenge.

Therefore, it would be necessary to develop and design hollow fiber membrane modules for membrane distillation systems capable of increasing turbulence, without increasing the pressure preventing the wetting of the pores and the difficulty of the arrangement, placement and fixed of the hollow fiber membrane assembly in the membrane module. BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a set of hollow fiber membranes entwined in a mesh for use in a membrane distillation module.

One of the major limitations found in the process of distillation in hollow fiber membranes is the fluid inlet pressure in the membrane pores (LEP). If the pressure of the water in contact with the hollow fiber membrane exceeds this value, the wetting of the same would occur and consequently the use of the hollow fiber membrane would not be possible. Given the configuration of the module, the small diameter of the capillaries and the number of hollow fiber membranes that can be placed in a mesh and inside the module, a pressure drop that causes the flow of food through the interior of the hollow fiber membranes circulate in a laminar regime. Working in a laminar regime implies a decrease in module performance due to the negative effects of polarization by temperature and concentration. These phenomena originate due to the fact that, with a laminar regime, fluid boundary layers adhered to the internal and external surfaces of the membranes are generated, which causes a temperature and / or concentration gradient. Due to the polarization by temperature, the layers closest to the surface of the membrane will have a temperature very similar to that of the surface, so that the difference in temperatures between both sides of the membrane will be smaller resulting in a decrease in the difference of vapor pressures between both sides of the membrane and therefore a decrease in production. Due to the polarization by concentration, in the layers closest to the surface of the hollow fiber membrane in contact with the food they will have a maximum concentration, which gradually decreases with the distance to the surface. This phenomenon also produces a decrease in the difference in vapor pressures on both sides of the membrane. These phenomena of polarization by temperature and concentration produce a clear decrease in the driving force of the process, obtaining less permeate flow.

Increase the pressure of the fluid in order to overcome the pressure drop caused and increase the flow rate, and therefore the number of Reynolds, inside the hollow fiber membranes could cause them to be wetted with what is not an option acceptable to reduce temperature polarization and / or concentration. This problem is equally extrapolable on the outside of hollow fiber membranes in the direct contact configuration, as the LEP also cannot be overcome on any side of the hollow fiber membrane. The present invention solves the problems due to the laminar regime without increasing the fluid pressure in the hollow fiber membranes. This is achieved by interlacing the hollow fiber membranes in a mesh, which generates some curvature in the hollow fiber membranes so that the turbulence of the flow is increased, decreasing the polarization phenomenon.

In addition, the assembly consisting of a mesh and hollow fiber membranes of the invention is easily removable from the distillation module, which facilitates the assembly of the hollow fiber membranes in the distillation module regardless of the stiffness of the condensation surfaces. The mesh and hollow fiber membrane assembly is highly versatile and manageable, so it can be easily integrated into the spiral structure or other geometries that could be designed.

This design allows the use of all membrane distillation configurations such as DMCD (Direct Contact Membrane Distillation), DMCA (Air Chamber Membrane Distillation), DMV (Vacuum Membrane Distillation), DMCL (Distillation Distillation Membrane with Liquid Chamber), DMGB (Membrane Distillation by Scanning Gas) and DMGBT (Distillation in Membrane by Thermostated Scanning Gas). By "set of hollow fiber membranes" in the context of the invention is meant the set of hollow fiber membranes and a mesh, where the hollow fiber membranes are transversely intertwined in the warp of the mesh.

Therefore, a first aspect of the present invention relates to a set of hollow fiber membranes supported on a mesh characterized in that the hollow fiber membranes are transversely interwoven between the warp of the mesh. A second aspect of the present invention relates to a membrane module comprising the hollow fiber membrane assembly as described above. A third aspect of the present invention relates to a system comprising at least one membrane module of the present invention.

A fourth aspect of the present invention relates to the use of a membrane distillation module as described above or a membrane distillation system as described above for the treatment and / or desalination of fluids.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 Shows a scheme of the mesh and interlacing of the hollow fiber membrane (FIG. 1A) and curvature diameter of the hollow fiber membrane MD (FIG. 1 B); U: warp; T: plot; F: hollow fiber membrane; d _c : curvature diameter.

FIG. 2 Braided in the mesh of hollow fiber membranes and detail of the groups of three interwoven hollow fiber membranes.

FIG. 3. Longitudinal section of a module comprising the set of interwoven hollow fiber membranes of the invention.

FIG. 4. Cross section of a module comprising the set of intertwined hollow fiber membranes of the invention. DETAILED DESCRIPTION OF THE INVENTION

Therefore, a first aspect of the present invention relates to a set of hollow fiber membranes supported on a mesh characterized in that the hollow fiber membranes are transversely interwoven between the warp of the mesh (fig. 1A).

The hollow fiber membrane is a porous membrane in the form of a flexible hollow filament, so it is possible to interlace it in a plastic mesh or of some flexible material with a light greater than the outer diameter of the hollow fiber membrane. The process of interlacing the hollow fiber membrane consists in crosslinking the hollow fiber membrane between the holes of the mesh, leaving or not empty spaces between each interbreeding. This mesh must have an appropriate light size and stiffness so that the hollow fiber membrane can be intertwined without being damaged. The mesh on which the hollow fiber membranes are intertwined performs several functions:

a) Mechanical function: the mesh acts as a support for hollow fiber membranes. By interweaving the hollow fiber membranes, they can be packaged within the body of a membrane distillation module without sliding of the hollow fiber membranes with respect to a condensation surface.

b) Increase in the turbulence of the solutions that circulate both outside and inside the hollow fiber membranes. Increasing the turbulence in the vicinity of the surface of the hollow fiber membrane decreases the polarization by temperatures and concentrations and therefore increases the yield. Energy consumption is lower and therefore the rate of water production increases with respect to the energy used. c) Increase in the packing density of hollow fiber membranes. Being intertwined hollow fiber membranes increases their length with respect to a configuration of linear hollow fiber membranes. Increasing the length increases the membrane surface in the module and therefore the evaporation area, thus increasing water production.

d) Increase in the permeate condensation rate. The hollow fiber membranes being interwoven, form undulations obtaining ridges and valleys. The crest is where it will be easier to remove the vapor that comes out of the pores of the membrane because it is a protruding point. In the valleys that make the hollow fiber membranes the permeate (steam) leaves in convergent directions which causes the union of the vapor drops that increase their size and favors condensation.

In the present invention, "packing density" is understood as the effective membrane area that is available per membrane module volume, excluding the volume occupied by the cooling chamber.

In another preferred embodiment of the first aspect of the present invention the interlacing of the hollow fiber membranes has a curvature diameter (d _c ) of about 2 cm to 5 cm and more preferably 2.5 cm to 3.5 cm (fig. . 1 B). The mesh must be of a flexible material and it must be avoided that it has edges. In another preferred embodiment of the first aspect of the present invention, the mesh is made of plastic to avoid oxidation problems. The materials composing the mesh are preferably selected from fiberglass or a plastic material selected from polyvinylchloride (PVC), polypropylene (PP) or polyethylene (PE).

In another preferred embodiment of the first aspect of the present invention the mesh has a light grid of between 1.5 mm and 8 mm and more preferably from 2 mm to 5 mm and a density of between 0.2 and 2 g / cm ³ and more preferably between 0.4 g / cm ³ and 1 g / cm ³ . More preferably, the mesh has a thickness between 0.1 mm and 0.5 mm, and even more preferably between 0.2 mm and 0.3 mm. The distance between each warp is between 1 mm and 3 mm, more preferably between 1.5 mm and 2.5 mm; the distance between each frame is between 0.1 mm to 1 mm, more preferably between 0.3 mm and 0.8 mm; and a weight between 40 and 150 g / m ² , more preferably between 60 g / m ² and 100 g / m ² .

In another preferred embodiment of the first aspect of the present invention the mesh has a tensile strength greater than 400N.

In another preferred embodiment of the first aspect of the present invention, the hollow fiber membranes are composed of a porous hydrophobic material that It may or may not be combined with a layer of a hydrophilic material. Preferably they are composed of at least one of the following materials selected from polytetrafluoroethylene (PTFE), vinylidene polyfluoride (PVDF), polypropylene (PP), polyvinylidene-co-hexafluoride polypropylene (PVDF-HFPP), fluorinated polyoxadiazoles (POD) , fluorinated polyoxatriazoles (POTF) or any combination thereof. More preferably they are composed of a material selected from polypropylene and vinylidene polyfluoride.

In another preferred embodiment of the first aspect of the present invention, the hollow fiber membranes have a pore size range between 0.01 μηι-5 μηι, preferably between 0.01 μηι and 1 μηι, more preferably between 0.2 μηι -0.6 μηι and even more preferably between 0.3 μηι-0.4 μηι.

A second aspect of the present invention relates to a module comprising the hollow fiber membrane assembly of the present invention as described above.

In a preferred embodiment of the second aspect of the present invention, the module in addition to the hollow fiber membrane assembly of the invention as described above that includes a mesh, comprises:

- a cooling chamber comprising at least two condensation surfaces.

- a module body consisting of a cooling jacket, in addition to covers and connections for refrigerant, food and permeate inlets and outlets.

The cooling chamber is a chamber through which the cooling fluid circulates, and comprising at least two condensing surfaces (preferably one on each side of the chamber). The cooling chamber is fed by the cooling fluid inlet to the chamber and has a cooling fluid outlet.

The cooling chamber has the task of acting as a steam condensation surface in the air and vacuum chamber configurations. In the case of direct contact configuration, its function is to cool the permeate inside the module and favor a higher temperature gradient in the process. In the case of sweeping gas, the cooling chamber must cool the entrainment gas inside the module equally. The cooling jacket on the other hand serves to cool the module, favoring the condensation of the permeate as well as being used as insulation of the module with the outside. In both cases, another objective is to recover heat from the assembly with these chambers, which can be used to preheat the food or the food itself can be used as a refrigerant.

The module construction process consists of the formation of a spiral, constituted by the cooling chamber, inside the membrane distillation module and inserting the mesh with hollow fiber membranes entwined in the spiral chamber of the cooling chamber, so that it is arranged in the form of a spiral wound together with the cooling chamber. In this way, a cooling chamber with sufficient rigidity is available to remain vertically on its own spiral-shaped base. The number of hollow fiber membranes in a module is of the order of several hundred, so the mesh is useful to facilitate packing, preventing the hollow fiber membranes from moving with respect to the cooling chamber that can have various geometries, For example, spiral.

In addition, in another preferred embodiment of the second aspect of the present invention, the membrane module may have an external cooling jacket that allows thermostatizing and better isolating the module, also aiding in condensation and therefore can increase the water production rate. at the same time that heat can be recovered. By thermostatizing in the present invention it is meant to keep the temperature constant within the module and by insulating, minimizing the energy transfer between the module and the exterior thereof.

In a preferred embodiment of the second aspect of the present invention the feed inlet temperature is between 10 ° C and 100 ° C, preferably between 40 ° C and 90 ° C, and more preferably between 60 ° C and 75 ° C. In another preferred embodiment of the second aspect of the present invention, the inlet temperature of the cooling streams is between -25 ° C to 80 ° C, and more preferably between 0 ° C and 50 ° C and more preferably between 10 ° C and 30 ° C.

Therefore, in a preferred embodiment of the second aspect of the present invention the module comprises a food inlet, a food outlet, an inlet and an outlet of the permeate, a spiral-shaped central part composed of a refrigeration chamber having at least two condensation surfaces, and by at least one set of hollow fiber membranes and a mesh described in the present invention, an inlet and an outlet of the cooling fluid from the cooling chamber and, optionally a cooling jacket arranged surrounding the central part. A cooling fluid circulates through the cooling jacket with an inlet and outlet.

Cooling fluid means any fluid used to exchange heat with the walls of the chamber / jacket that contains them. The cooling fluid that circulates through the cooling chamber and the fluid that circulates through the cooling jacket can be the same fluid or different fluids.

In one embodiment of the second aspect of the invention the refrigerant fluid is the food before being heated. In this way the heat of the product obtained in the process is used to preheat the food.

Depending on the membrane distillation configuration chosen, the module will have a permeate outlet for DMCD, which can be air or gas inlet in DMCA, DMGB, DMGBT and permeate outlet in DMCL. In addition to a permeate entry in DMCD, which can be permeate output DMCA, DMGB, DMGBT, DMV (and in DMCL must be closed).

The condensation surfaces are made of a thermal conductive material and compatible with the fluid to be treated as well as the fluid used as a refrigerant.

The thermal conductivity of the condensation surface must be as high as possible to favor the transmission of heat through the surface, increasing the condensation of steam on it and the recovery of that latent heat of condensation in the process itself. The thermal conductivity of the condensation surface must be high in order to keep the permeate at a suitable temperature and prevent it from heating up in the module in the DMCD configuration and, on the other hand, increasing the condensate rate in the condensation surface DMCA and DMV settings. Also in the configuration of entrained gas, the temperature of the gas must be kept as low as possible during its passage through the module. The range of thermal conductivity values that can be used ranges between tens (eg Titanium, 21 W / mK) and hundreds (eg Copper, 385 W / mK). The optimal range is between 200-400 W / m K.

On the other hand, it is important that the materials for the construction of the condensation surface have a moderate-high corrosion resistance of effluents of high salinity, so that seawater or the food itself can be used as cooling fluids.

Examples of materials could range from metals such as copper, aluminum, tin or some type of alloy and, to a lesser extent, plastic materials (they have low conductivity but it is possible to find plastic materials with improved thermal conductivities) or even laminated graphite materials . Other materials that can be used are aluminum-magnesium alloys (eg Magnealtok® 50 with a thermal conductivity of 116 W / mK).

With respect to mechanical properties, the material for the condensation surface is preferably of easy forming and good weldability.

The thickness range of the condensation surfaces of the cooling chamber must be small enough so that the heat transfer is very good and so that it can be easily screwed in (form the spiral) but, at the same time, it must have a sufficient thickness to allow welding without damaging the material. Preferably the range of thicknesses is 0.8 to 1 mm. The material used for the manufacture of the spirally wound refrigeration chamber together with the hollow fiber membrane assembly of the present invention must be rigid enough so that it can be arranged, wound or machined in a spiral and that it keep vertically supported on the base of the spiral without it crumbling or touching the surfaces of it.

Within the mechanical properties we can define the elastic limit, also called the yield limit or yield limit, which is the maximum tension to which a material can be subjected without permanent deformation, that is, when the load ceases the piece recovers Its initial form. In the present invention the condensation surface has a low elastic limit so that it is easily deformable The range of elastic limit may vary between 5 and 150 N / mm ² , for example annealed copper having a value of 9 N / mm ² or an aluminum-magnesium alloy (5052) having an elastic limit of 90 can be used N / mm ² It also has a Brinell Hardness with a maximum of 100 HB, for example for annealed copper it is 35 HB and for the 5052 aluminum-magnesium alloy it is 60 HB.

Therefore, in a preferred embodiment the condensation surface material is a plastic, graphite or metal material, more preferably the condensation surface is a metallic material, even more preferably copper or an aluminum-magnesium alloy.

The hollow fiber membranes next to the mesh, described in the present invention, form a fabric that is preferably spirally arranged. This fabric has to be found together with a spiral-wound flat cooling chamber. In fig. 4 shows a cross-section of the mesh arrangement with the hollow fiber membranes wound from this module. The cooling chamber in turn can function as an internal heat exchanger by preheating the food before being introduced inside the hollow fiber membranes. Inside the hollow fiber membranes circulates the food or solution to be purified, which is at a temperature higher than the condensation surface. The condensation surface is made of a thermally conductive material, preferably metallic, for example copper plate. Water vapor and volatiles from the food solution are able to cross the membrane due to the difference in vapor pressure on both sides of the membrane. The degree of rejection is 100% when the food is electrolytes and non-volatile electrolytes, for example NaCI or glucose, dissolved in water and does not comprise any other volatile element. This vapor reaches the condensation surface by condensing in it as water of greater purity in the DMCA, DMGBT and DMV configurations. In the air chamber configuration, by gravity this permeate ends up being collected at the bottom of the module. You can also apply a certain vacuum in the module (50-100 millibar) to improve the permeate flow, in this case this type of configuration is called vacuum (DMV). In fig. 3 a longitudinal section of this module is shown.

The food is circulated inside the hollow fiber membranes and condense the permeate on a nearby cold surface if working in DMCA or maintaining the permeate (gas or liquid) in contact with hollow fiber membranes for DMCD, DMCL, DMGB and DMGBT. The permeate is kept as cold as possible to increase the driving force of the DM process. The pressure inside the membrane module can be lowered by means of a water tube or a vacuum pump connected to the permeate of the module giving rise to the DMV. In this module, the cooling chamber is a thin hollow chamber of thickness (about 1 cm) formed by condensation surfaces, through which the coolant flows. In this way an increase in the temperature difference within the module can be achieved. Inside the refrigeration chamber there is a number of speakers that give it a mechanical resistance and, at the same time, a better distribution of the fluid inside. The idea is to wind the cooling chamber on a central axis and a mesh with braided hollow fiber membranes to form a roll in a spiral configuration (fig. 4). Also, the module is equipped with an external cooling jacket to insulate the outside and help the condensation phenomenon of the steam produced.

The module can be placed vertically or inclined with a degree between 0 ^or 90 °, preferably between 45 ° and 60 ° on the horizontal, to facilitate the collection of permeate and to guarantee a tangential circulation of the food in contact with the entire membrane.

In a preferred embodiment of the second aspect of the present invention the module as described above can be presented in any configuration and preferably has a selected configuration of DMCD (Direct Contact Membrane Distillation), DMCA (Membrane Distillation by Chamber of Air), DMV (Vacuum Membrane Distillation), DMCL (Liquid Chamber Membrane Distillation), DMGB (Sweep Gas Membrane Distillation) and DMGBT (Thermostatic Swept Membrane Distillation). A third aspect of the present invention relates to a membrane distillation system comprising at least one membrane module of the present invention. Several modules can be arranged in series or in parallel, increasing production. On the other hand, the performance can be increased by arranging several modules in series. A fourth aspect of the present invention relates to the use of a membrane distillation module as described above or a membrane distillation system as described above for the treatment and / or desalination of fluids.

In a preferred embodiment of the fourth aspect of the present invention, the food is a fluid that is to be treated and / or desalinated and that is formed by an aqueous solution containing any type of soluble or insoluble substance that it is desired to remove or decrease from the aqueous solution

In a preferred embodiment of the fourth aspect of the present invention, the feed inlet temperature is between 10 ° C and 100 ° C, preferably between 40 ° C and 90 ° C, and more preferably between 60 ° C and 75 ° C. In another preferred embodiment of the second aspect of the present invention, the inlet temperature of the cooling streams is between -25 ° C to 80 ° C, and more preferably between 2 ° C and 50 ° C and more preferably between 5 ° C and 30 ° C.

The use of the membrane distillation module of the invention or of a system comprising at least one module may have the following applications:

- desalination and treatment of brines from desalination plants, improving the conversion of the plant and reducing the discharge of brine produced;

- wastewater treatment and purification of contaminated effluents of different nature such as pharmaceutical, textile, solutions contaminated with boron, arsenic, etc., and even solutions with low levels or means of radioactivity;

- concentration of solutions, with special relevance for those solutions in which high temperature sensitive compounds are present, for example the concentration of fruit juices or in the dairy industry;

- elimination and / or recovery of volatile organic compounds such as alcohols or halogenated compounds, benzene etc.

- separation of azeotropic mixtures, for example hydrochloric acid - water or formic acid - water.

EXAMPLES OF REALIZATION

1.- Manufacture of membrane distillation module The membrane distillation module comprises the set of hollow fiber membranes entwined in a mesh of the invention and a spirally wound cooling chamber and a body formed by a cooling jacket, 2 stainless steel caps and threads, and connections stainless steel for the exit and entrance of the refrigeration chamber, the cooling jacket, the permeate / condensate and the food. ACCUREL® PP Q3 / 2 hollow fiber membranes were used under the DMCD, DMCA and DMV configurations. However, it could work in the same way with any other type of hollow fiber membranes. Likewise, the ACCUREL® PP Q3 / 2 hollow fiber membranes can be used for other configurations such as DMGB, DMGBT and DMCL.

In fig. 3 (longitudinal section) and 4 (cross section) this embodiment is represented: the module comprises an inlet of the food (1), an outlet (V) of the food, an inlet (2) and an outlet (2 ') of the cooling fluid to the cooling chamber. The central part of the module is composed of the spiral-shaped cooling chamber (2 ") (consisting of two condensing surfaces, 2"') and at least one set of hollow fiber membranes (3) interwoven in one mesh (5). This central part is surrounded by a cooling jacket (4) through which a cooling fluid circulates with an inlet and an outlet (4 ', 4 ", respectively). The module covers have permeate outlet (6) for DMCD, DMCL or air or gas inlet in DMCA, DMGB, DMGBT and permeate inlet (6 ') for DMCD, permeate outlet for DMCA, DMGB, DMGBT, DMV (in DMCL must be closed.) The internal diameter of the cooling jacket is 12.5 cm, with a jacket thickness of 1.25 cm, a spiral-shaped cooling chamber made of copper, annealed copper was placed inside the module because it is the one with the highest thermal conductivity, easily formed and good weldability, to form the cooling chamber.The thickness of each copper plate is 0.8 mm, 30 cm high with an external and internal plate length that forms the walls of the cooling chamber, 71 , 3 cm and 61, 2 cm, respectively (external and internal development of the spiral l) The cooling chamber is formed with three turns around its central axis and a thickness of the hollow cooling chamber of 0.7 cm (2 "in fig. 3). Water is passed through the cooling chamber from the entrance through the bottom of the module to the exit through the top. The intention is to that acts as an internal condensation surface in the case of DMCA. In the DMCD configuration it helps maintain the temperature of the permeate side. The distribution of the refrigerant in the cooling chamber is carried out by means of a perforated flexible tube and located at one end and held between the surfaces of the chamber. In this way, a homogeneous and uniform distribution of the refrigerant in the refrigeration chamber is achieved.

Inside the spiral there is a fiberglass mesh, with a light of 4 mm, dimensions 55 ^χ 30 cm, in which the ACCUREL® PP Q3 / hollow fiber membranes are braided, in groups of three and alternates. 2 (the external and internal diameters of the hollow fiber membrane are 0.9 and 0.6 mm, respectively) (fig. 2). In the braiding process, we try to leave the same length of hollow fiber membrane free on each side of the mesh. The diameter of curvature of the hollow fiber membranes is approximately 3.4 cm, which allows to gain greater membrane surface and, above all, turbulence. The effective surface of the total membrane, taking into account that the effective length of the hollow fiber membranes is approximately 46 cm, amounts to 0.26 m ² .

The technical specifications of the mesh are the following: grid (light): 4 x 4 mm; thickness: 0.2 mm; warp: 1, 7 mm; weft: 0.2 mm; weight: 82 g / m ² ; density: 0.40 g / cm ³ ; and tensile strength (stiffness): ≥ 400 N.

In order to introduce the assembly composed of the hollow fiber membranes and the mesh into the spiral formed by the cooling chamber and it is made to slide through the hollow formed by it, with caution so as not to damage the hollow fiber membranes. Once inside, the mesh is held so that it does not move with a few glue points.

Once you have the spiral formed by the refrigeration chamber and the mesh with interwoven hollow fiber membranes, it is inserted into the module body and the refrigeration tubes of the refrigeration chamber are connected to the connections that are in the covers of the module. The exit and entrance of the module body has a smaller diameter than the module body, this causes the hollow fiber membranes to regroup in the hole. Next, the hollow fiber membranes are glued between them and to the walls of the mouth of the module covers. For this, cotton threads are first introduced between the hollow fiber membranes that will serve as support, and then the glue is added forming a layer that forces the food to circulate only inside the hollow fiber membranes. As an adhesive material for hollow fiber membranes, an epoxy resin resistant to high temperatures has been used. Once the glue is glued and solidified, they are trimmed so that the food circuit connections can be screwed onto the lid. - Density range of hollow fiber membranes.

The number of hollow fiber membranes in the mesh is approximately 300. The length of the mesh is 55 cm long and 30 cm high. If we take into account the length of the mesh, the density of the hollow fiber membranes is 5.45 hollow fiber membranes / cm.

If we take into account that in this example the volume inside the spiral formed by the hollow of the cooling chamber (1 x 55 x 30) is 1650 cm ³ and the effective area of the hollow fiber membranes is 2600 cm ² , the packing density, defined as the effective area of the membrane per volume of membrane module, excluding the volume occupied by the cooling chamber, is 1.58 cm ² / cm ³ .

2.- Example of membrane distillation process with the module of Example 1 Reynolds numbers have been calculated for the feed and permeate flow rates obtained. Feed flows varied between 1 l / min and 5 l / min while those in the permeate varied between 1 l / min and 9 l / min. These Reynolds number values have been calculated for distilled water at a temperature of 25 ° C. The Reynolds numbers obtained for the food varied between 264 and 660 and for the permeate they varied between 528 and 2378.

According to the Reynolds values observed, the most limiting value for the distillation process is the flow of food inside the hollow fiber membranes whose Re is in a clearly laminar regime whereby the effect by temperature polarization and concentration is important. In the current module, taking into account the observed pressure drop and the LEP of the hollow fiber membranes, a maximum of 10 l / min flow could be worked. Higher flows would require higher hydrostatic pressure that could cause wetting of the membrane and consequently render them useless for this application. Even so with a flow rate of 10 l / min we would be in a laminar regime (Re = 1320). However, the fact that the hollow fiber membranes are intertwined in the mesh makes it possible to increase the food regime inside the hollow fiber membranes and minimizes the effects of temperature and concentration polarization. Since the driving force of the membrane distillation process is the difference in vapor pressure on both sides of the membrane and this is temperature dependent, an increase in feed temperature causes an increase in distillate production. The following shows as an example results obtained in the direct contact configuration for the same feed temperature (60 ° C) and different feed rates. With the feed flow rates Qa = 3 l / min and Qa = 5 l / min, the food circulates in a clearly laminar regime, giving Re of 396 and 660 respectively, so that the effect of polarization by temperature and concentration is of importance for the process. For an average feed temperature of 60 ° C and permeate of 30 ° C, distillate flows of 6.5 and 11, 1 LMH (lm ^"2 h ^{" 1} ) have been obtained for feed rates of 3 and 5 l / min respectively, with a permeate flow rate of 5 l / min. This improvement is due to various aspects: the increase in turbulence in the module caused by the interlacing of hollow fiber membranes in the mesh and the increase in feed flow (reducing the effects of polarization by temperature and concentration) and by the decrease of residence times that also has an effect on increasing productivity. This increase in feed flow (from 3 to 5 l / min) also affects the thermal efficiency of the process increased from 45.2% to 71.1%. Likewise, under the same conditions of temperature (60 ° C) and flow rate for the feed (5l / min), distillate flows of 3.7 LMH (lm ^"2 h ^{" 1} ) were obtained in the air chamber configuration and 7.7 LMH (lm ^"2 h ^{" 1} ) in the vacuum configuration using a vacuum pressure of 0.3 bar. The thermal efficiency, ε _τ , has been defined as the ratio between the amount of heat transferred through the membrane and the heat actually used for the permeate flow obtained, that is:

where] is the permeate flow through the membrane obtained in each experiment (kg m ^"2 h ^{" 1} ), A is the area of the membrane (0.26 m ² ), AH _V is the enthalpy of water vaporization at the average temperature of the food (J kg ^"1 ), rh _a is the flow rate of the food through the module (kg h ^{" 1} ), c _pa is the specific heat of the food (distilled water or aqueous solution of 30 g / l of NaCI) at the average food temperature (J kg ^"1 ° C ^{" 1} ) and {T _{a in} - T _{a out} ) is the temperature difference in the food at the entrance and exit of the module (° C) .

It has been assumed that, under stationary conditions, the heat flow transferred through the membrane is equal to the heat flow transferred on the food side along the module.

Claims

1. A set of hollow fiber membranes supported on a mesh characterized in that the hollow fiber membranes are transversely intertwined between the warp of the mesh.

2. The hollow fiber membrane assembly according to claim 1, wherein the interlocking of the hollow fiber membranes has a curvature diameter of 2 to 5 cm.

3. The hollow fiber membrane assembly according to any one of claims 1 or 2, wherein the mesh is composed of fiberglass or a plastic material selected from polyvinyl chloride, polypropylene or polyethylene.

4. The hollow fiber membrane assembly according to any one of claims 1 to 3, wherein the mesh has a light grid of between 1.5 mm and 8 mm and a density of between 0.2 g / cm ³ and 2 g / cm ³ .

5. The hollow fiber membrane assembly according to any one of claims 1 to 4, wherein the mesh is between 0.1 mm and 0.5 mm thick, a distance between each warp between 1 mm and 3 mm, a distance between each frame between 0.1 mm to 1 mm and a weight between 40 and 150 g / m ² .

6. The hollow fiber membrane assembly according to any one of claims 1 to 5, wherein the hollow fiber membranes are composed of a porous hydrophobic material.

7. The set of hollow fiber membranes according to claim 6, wherein the hollow fiber membranes are composed of at least polytetrafluoroethylene, vinylidene polyfluoride, polypropylene, polypropylene vinylidene-co-hexafluoride, fluorinated polyoxadiazoles, fluorinated polyoxatriazoles combination thereof.

8. The hollow fiber membrane assembly according to any one of claims 1 to 7, wherein the hollow fiber membranes are composed of a porous hydrophobic material combined with a layer of a hydrophilic material.

9. The hollow fiber membrane assembly according to any one of claims 1 to 8, wherein the hollow fiber membranes have an average pore size of between 0.01 μηι to 5 μηι, preferably between 0.2 μηι to 0, 6 μηι.

10. A membrane module comprising the set of hollow fiber membranes described in any one of claims 1 to 9.

The module according to claim 10, comprising an inlet of the food (1), an outlet of the food (1 ') and a central part in the form of a spiral composed of at least one cooling chamber (2 ") with a inlet (2) and outlet (2 ') of cooling fluid and by at least one set of hollow fiber membranes (3) entwined in a mesh (5), where the central part is surrounded by a cooling jacket (4) by where a refrigerant fluid circulates with an inlet (4 ') and an outlet (4 ").

12. The module according to claim 1, characterized in that the cooling chamber (2 ") is spirally shaped and formed by two condensing surfaces (2" ').

13. The module according to claim 12, wherein the condensation surface is preferably of a material with a thermal conductivity of between 200 and 400

W / m- K.

14. The module according to any of claims 12 or 13, wherein the condensation surface is formed of a plastic, graphite or metallic material.

15. The module according to claim 14, wherein the condensation surface is formed of a metallic material.

16. A membrane distillation system comprising at least one membrane module according to any of claims 10 to 15.

17. Use of a membrane distillation module according to claims 10 to 15 or a membrane distillation system according to claim 16 for fluid treatment and / or desalination.

18. Use according to claim 17 wherein membrane distillation is carried out in a selected configuration of Direct Contact Membrane Distillation, Air Chamber Membrane Distillation, Vacuum Membrane Distillation, Liquid Chamber Membrane Distillation, Liquid Distillation Membrane by Sweeping Gas and Distillation in Membrane by Thermostatic Sweeping Gas.

19. Use of the module according to claims 17 or 18, wherein the membrane distillation is carried out in a process selected from desalination, treatment of brines from desalination plants, treatment of wastewater, purification of contaminated effluents, concentration of solutions, elimination and / or recovery of volatile organic compounds and separation of azeotropic mixtures.