EP4271515A1

EP4271515A1 - Continuous flow production of ion exchange membranes immobilized on glass support

Info

Publication number: EP4271515A1
Application number: EP21847540.8A
Authority: EP
Inventors: Luigi Vaccaro; Assunta MARROCCHI; Valeria TROMBETTONI; Riccardo NARDUCCI; Maria Luisa Di Vona
Original assignee: Universita degli Studi di Perugia; Universita degli Studi di Roma Tor Vergata
Current assignee: Universita degli Studi di Perugia; Universita degli Studi di Roma Tor Vergata
Priority date: 2020-12-31
Filing date: 2021-12-23
Publication date: 2023-11-08
Also published as: WO2022144718A1

Abstract

The present invention relates to adsorbent cartridges each one comprising a cross-linked ion exchange membrane anchored to a support material, a process based upon a continuous flow technique for the production of said cartridges as well as the use of the same for the desalination and/or decontamination and/or purification of water.

Description

Continuous flow production of ion exchange membranes immobilized on glass support

DESCRIPTION

The present invention relates to adsorbent cartridges each one comprising cross-linked ion exchange membranes anchored to a support material, a process based upon a continuous flow technique for the production of said cartridges as well as the use of the same for the desalination and/or decontamination and/or purification of water.

STATE OF PRIOR ART

The development of new technical solutions for the purification/reuse of waste water over the years has drawn considerably the attention of researchers due to the increase in the request for such resource as consequence of the increase in the world population. In this context the use of membranes has considerably taken hold in the last decade thanks to their applicability in processes on large scale for the treatment of waste, marine and brackish water (desalination, adsorption of metals, removal of dies, microbicidal actions). The advantages in using the membranes lie in their considerable adaptability in the different operation conditions, apart from the possibility of working under sustainable energy conditions (for example reduced pressure). In this context the membranes based upon poly (ether ether ketone) sulfonate (“SPEEK”), are widely used in processes of nanofiltrations and inverse osmosis. The corresponding covalently cross-linked ones are nowadays substantially unexplored in said fields (Briggs, et al. 2017 DURABLE ASYMMETRIC COMPOSITE MEMBRANE United States HYDROXSYS HOLDINGS LIMITED (Auckland, NZ) 20170086469; Craft, Lenka Benacek et al. 2017 ASYMMETRIC COMPOSITE MEMBRANE AND A METHOD OF PREPARATION THEREOF HYDROXSYS HOLDINGS LIMITED (Auckland, NZ) PCT/IB2016/055899). The high degree of sulfonation (DS) allows to obtain high ion exchange capabilities and the structural polarity limits problems relating the “fouling” of the membranes themselves, which influences directly the durability thereof. The cross-linking of covalent nature can confer on the membrane a considerable chemical stability and physical robustness apart from the capability of limiting the swelling thereof, for example in aqueous means, thus allowing to work under contained pressure conditions.

The low-cost SPEEK-type membranes, thanks to their chemical and physical features are currently used for processes of nanofiltration, inverse osmosis, for the purification of waste water coming from industrial waste and for the desalination of marine and brackish water. Particularly, their polar nature limits the fouling thereof due to the accumulation of hydrophobic substances such as proteins and many other contaminants, thus involving a decrease in management costs and a higher durability with respect to membranes consisting of hydrophobic materials.

The effectiveness as ion exchanger of SPEED-type membranes was further demonstrated in the field of fuel cells, flow batteries, pharmaceutical, textile, food industry. In the last years a simple and cheap method for the cross-linking of such membranes was developed, which uses thermal treatments guided by the solvent, particularly dimethyl sulfoxide, DMSO, which has low costs, it is stable and not toxic and, consequently, particularly suitable to the industrial uses (M.L. Di Vona et al., Analysis of Temperature-Promoted and Solvent-Assisted Cross-Linking in Sulfonated Poly(ether ether ketone) (SPEEK) Proton-Conducting Membranes, J. Phys. Chem.B, 2009, 113, 7505-7512).

The anchoring of membranes on granular materials of different nature (ceramics, glass, anthracite, quartz) is proved and it has as main advantage that of increasing the surface area of the membrane itself by creating more effective adsorption systems. Particularly, the use of glass as anchoring material is considered an economically advantageous method; glass is chemically inert and it has a considerably physical stability in a wide range of pressure conditions, apart from an important hydraulic performance. Such features allow to implement effective and long-lasting systems.

Glass beads as such are used as filtering agents for processes for the removal of suspended solids, by replacing the sand filtration procedures. Their use determines the development of more effective filtration protocols, by allowing the application of better flow rates with a considerable decrease in investment costs. Moreover, they are capable of considerable hydraulic performances and they can be cleaned easily.

Different coating examples on glass with materials having different chemical nature are shown in literature and they can be applied in water purification protocols; for example, chitosan- based “coating” (M. L. G. Vieira et al., Chitosan and cyanoguanidine-crosslinked chitosan coated glass beads and its application in fixed bed adsorption, Chemical Engineering Communication, 2019, 158, 16-24; X. D. Liu et al., Surface modification of nonporous glass beads with chitosan and their adsorption for transition metal ions, Carbohydrates Polymers, 2002, 49, 103-108) and manganese oxides (P. Rose et al., Coating techniques for glass beads as filter media for removal of manganese from water, Water Science and Technology: Water Supply, 2017, 17, 59-75) are used for the adsorption of dyes and metals.

The typical existing processes for coating the membranes on glass, and particularly on glass beads, use immersion, “casting” and “spray” techniques. These are difficult to be applied for protocols on large scale, due to their poor capability of producing a homogeneous coating, apart from the technical difficulties lying in the “scale up” of the technology on itself.

The first one provides the immersion of the glass beads, at constant speed, in a tank containing the material to be put in solution, preferably by avoiding abrupt stirring; the beads then remain still and immersed - in the closed tank - to allow the coating thereof by the material and, at last, they are removed at constant speed, by leaving them to drain to remove the solution excess. The “casting” technique, instead, provides for the use of open tanks which allow the evaporation of the solvent and the consequent formation of a film on the surface of the beads (X. D. Liu et al., Surface modification of nonporous glass beads with chitosan and their adsorption fortransition metal ions, Carbohydrates Polymers, 2002, 49, 103-108). In the “spraying” technique the glass beads are hit by a vaporized flow of the solution to be deposited. In all cases, then step i) of cross-linking the material constituting the film, where applicable, ii) washing and iii) drying the resulting system follow. The low homogeneity/reproducibility of the coating film which is obtained generally represents the greater disadvantage of such techniques.

A coating inhomogeneity, particularly, causes the impossibility of obtaining a uniform distribution of sizes of the pores of the film at issue, involving a not constant response of the system in its application. The not always optimum percentage of coating represents a further limit. Other disadvantages are the material loss and the long process time - above all with reference to the immersion technique - and the exposure to the inhalation of (typically toxic) solvent vapours.

The development of coating technologies in continuous mode is nowadays a widely unexplored field; in literature there is an example of “coating” in continuous mode of glass beads with manganese oxides (P. Rose et al., Coating techniques for glass beads as filter media for removal of manganese from water, Water Science and Technology: Water Supply, 2017, 17, 59-75). The glass beads are introduced in a column (“reactor”) and the manganese-based coating solution is made to flow inside the reactor by using a rotating pump in a “loop”-type closed circuit. At the same time, an oxidizing solution (NaCIO, KMnC ) is made to flow by means of a second dosing pump; in this way filtering systems constituted by MnOx(s) are obtained which are washed (still continuously), dried (discontinuously) and used for removing manganese from water. The water treatment protocols resulted to be more effective than those using the same filtering system by immersion or “casting” techniques.

A continuous process for coating with organic polymer of tubular structures made of ceramics (more expensive than glass) was reported in (S.K. Nataraja et al., Cellulose acetate-coated a- alumina ceramic composite tubular membranes for wastewater treatment, Desalination, 2011 , 281 , 348-353); the polymer, cellulose acetate, has definitely different nature than the ion exchange membranes, and the developed adsorbing system aims at treating waste water coming from industrial waste. In such protocol, the (perforated) tubular supports first of all are immersed for 2-3 h in deionized water, then placed in a baking chamber; the coating material, dissolved in a 17% solution by weight of acetone (volatile and unsafe solvent) is made to flow through the ceramics by using an electric pump for 5 minutes. Washing and drying the adsorbent system instead are carried out discontinuously; particularly, the exceeding solution is removed from the tubular system, the coating is made to gel by immersing it in a thermostated bath and the full system is dried to allow the removal of the solvent(s).

Up to now, embodiment examples in continuous flow of organic polymeric “coating” are not known, with particular reference to cross-linked ion exchange membranes, on glass beads or other granular materials. In such context, therefore, the need for developing effective processes for the production of, preferably cross-linked, ion exchange membranes of organic polymeric type, supported on granular materials, particularly glass beads, remains much felt.

SUMMARY OF THE INVENTION

The present invention relates to the development of a technology for the production of crosslinked ion exchange membranes, particularly membranes of organic polymeric type, anchored to support materials such as glass beads, with variable sizes, to obtain effectively adsorption systems, non-deformable over time, to be used in fixed-bed columns useful in several industrial fields, preferably processes for the decontamination and/or purification of water. Particularly, the authors of the present invention have devised a new process for the production of cross-linked ion exchange membranes anchored on support materials, for example glass beads, based upon a continuous flow technique. Advantageously, the use of systems in continuous mode can guarantee the formation of homogeneous “coating”, in considerably reduced process time.

In an embodiment of the process according to the invention, said ion exchange membranes are cross-linked membranes of poly (ether ether ketone) sulfonate (SPEEK), having a degree of sulfonation comprised between 0.60-0.95 (starting from a Degree of sulfonation, DS, equal to 1 with treatments between 2-33 hours at 180°C) and a structural polarity assisting the anchoring on glass.

As it is clearly highlighted by the results of the studies shown in the experimental section of the present description, the continuous flow technology, the present invention relates to, is effective in the production of ready cartridges of SPEEK-type ion exchange membranes, in the specific case cross-linked, supported on glass beads with variable diameter. More specifically, the present invention provides for the implementation in continuous mode of the following processes in sequence: (i) coating of the support material with ion exchange membrane, (ii) in-situ cross-linking of the ion exchange membrane (iii) system porosity control by means of an inert gas, preferably nitrogen, (iv) washing and (v) drying.

Such “all-in-one" invention, indeed, consists in the possibility of carrying out the above- mentioned steps without interruption, by reducing considerably the material loss, operation time and costs. The inhalation exposure to reagents and solvents is reduced to minimum. Moreover, by using such technology it is possible to modulate and control precisely a wide number of parameters (concentration of the material to be laid in solution, cross-linking time of the material, etc.) and to obtain, for example, glass beads with different sizes coated with membrane films with variable thickness, degree of cross-linking, porosity. The present invention also provides for the incorporation, in the base material constituting the membrane, of micro- and nano-particles made of inorganic materials increasing the adsorbing capability and/or stability thereof, more specifically zirconium phosphates/phosphonates and/or metal organic framework (MOF).

Substantially, the technology allows to implement, in a reproducible way, adsorbent systems based upon low-cost materials, and having ion exchange capability, robustness, porosity varying depending upon the application needs (“tailor-made” systems). An extremely important aspect in this technology is also related to the fact that the flow system, basically, can be automated with a much lower effort than the discontinuous processes (“batch”) and with a more effective control level, which is to be considered an advantage even from the safety point of view.

Additional advantages of the invention are:

1) Possibility of using DMSO as solvent/cross-linking agent for producing adsorbent systems; DMSO is classified as “not dangerous substance” according to the current European legislation (EC Nr. 1272/2008) and this is particularly relevant in fields such as decontamination/purification of water, where traces of residual toxic solvent have to be accurately removed before using said systems.

2) Possibility of implementing adsorbent systems (ready cartridges or other) based upon low-cost membranes, considerable chemical and physical stability and high ion exchange capability. Moreover: the structural polarity of the SPEED-type membranes confers on the material a satisfying durability, by limiting phenomena relating to the membrane “fouling”.

3) Possibility of implementing adsorbent systems anchored on glass beads having reduced costs and operational effectiveness, high durability and resistance under the working conditions.

4) Possibility of implementing water treatment systems wherein the action of the glass beads (for example removal of colloidal particulate in pre-treatment steps) is combined with the action of the ion exchange membranes (for example nano-filtration processes in the treatment of waste water coming from industrial waste and desalination of marine and brackish water).

Therefore, the present invention relates to: an adsorbent cartridge comprising a cross-linked ion exchange membrane anchored to a support material; a process for the preparation of an adsorbent cartridge comprising a cross-linked ion exchange membrane anchored to a support material, comprising the following steps: i. arranging a support material inside a reactor; ii. coating said support material by continuous flow of a solution comprising a polymeric material, so as to form a film of said polymeric material on the surface of said support material; iii. anchoring said film to the surface of said support material; iv. cross-linking said polymeric material; v. washing the adsorbent cartridge obtained in step iv; vi. drying said adsorbent cartridge; and the use of one or more adsorbent cartridges according to any one of the herein described embodiments, for the decontamination and/or purification and/or desalination of water.

Additional advantages, as well as the features and the use modes of the present invention will result evident from the following detailed description of some preferred embodiments.

DETAILED DESCRIPTIOF OF FIGURES

Figure 1. Scheme example of continuous flow reactor for the production of ion exchange membranes immobilized on glass support.

Figure 2. FTIR-ATR spectra of an adsorbent sample obtained in continuous flow (a), in discontinuous flow (b) and of a not supported membrane sample (c) used as reference. The presence of intense signals is noted, typical of the SPEEK-based membrane on the surface of (a).

Figure 3. Evaluation of the homogeneity of “coating” obtained in continuous flow. In the top panel SEM micrographs of the samples’ surface. In the bottom panel the results of the EDS microanalyses on two points of the sample surface are reported; both of them show the presence of sulphur, then of the sulfonate group, characteristic of the SPEED-type membranes.

Figure 4. Evaluation of the homogeneity of “coating” obtained in discontinuous flow. In the top panel the SEM micrographs of the samples’ surface. In the bottom panel the results of the EDS microanalyses on three points of the sample surface are reported; only areas 1 and 2 show the presence of sulphur, then of the sulfonate group, characteristic of the SPEED-type membranes.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the authors of the present invention have devised a new process based upon a continuous flow technique for the production of adsorbent cartridges characterized by cross- linked ion exchange membranes, anchored on support materials.

A first aspect of the present invention then relates to an adsorbent cartridge comprising a crosslinked ion exchange membrane anchored to a support material.

According to an aspect of the present invention, said support material is a material in granular form, that is characterized by a spherical shape, having a diameter of few millimetres.

In a preferred embodiment according to the present invention, said support material is substantially constituted by glass beads, wherein substantially it shows at least 90%, preferably at least 95% still more preferably at least 99%, still more preferably said support material substantially or wholly consists of glass beads. Preferably, said glass beads have a diameter <|) comprised between 1-2 mm.

Under the expression “ion exchange membrane”, also known in English as “Ion Exchange Membrane" (I EM), in the present description a half-permeable membrane is meant, characterized by the presence of functional groups having positive and/or negative charge inside the matrix thereof it consists; the presence of these groups confers on the above-mentioned membrane the capability of allowing the interchange and/or selective passage of some ions. The ion exchange membranes can consist of an organic polymeric matrix or an organic and/or inorganic composite material.

The term “cross-linked”, used in the present description with reference to said ion exchange membrane, relates to the presence of cross-linked chains inside the membrane polymeric matrix, that is chains joined therebetween by covalent bonds (also called crossed bonds) having a bond energy equal to that of the chains’ atoms. The degree of cross-linking (DXL) influences the chemical and mechanical stability of an ion exchange membrane: a higher degree of cross-linking can confer for example on the membrane a greater robustness and size selectivity.

The degree of cross-linking of an ion exchange membrane can be evaluated by means of determination of the ion exchange capability (I EC) of the membrane at the beginning and at the end of the cross-linking process, through the following equation:

DXL = (IEC i - IEC n - IEC i wherein /EC, and / Cf represent the starting and final ion exchange capability of the membrane, respectively. According to an aspect of the invention, an ion exchange membrane suitable to be incorporated inside an adsorbent cartridge according to the present invention, is a membrane having a cross-linking degree at least equal to 10%.

According to an aspect of the present invention, said cross-linked ion exchange membrane is a proton exchange membrane or an anionic exchange membrane. In a preferred embodiment according to the present invention, said cross-linked ion exchange membrane is a membrane consisting of an organic polymer, preferably an organic polymer of polar nature.

Examples of organic polymers which can be used for implementing an ion exchange membrane suitable for the implementation of an adsorbent cartridge according to the present invention include poly (ether ether ketone) sulfonate (SPEEK), poly (ether ketone) sulfonate (SPEK), poly (ether ketone ketone) sulfonate (SPEKK), poly (ether sulfone) sulfonate (SPES), poly (ether sulfone ketone) sulfonate (SPESK), poly (phenyl sulfone) sulfonate (SPPSLI), polyimide sulfonate (SPI), polybenzimidazole benzyl sulfonate (N-benzylsulfonate PBI), polyphenylene oxide sulfonate (SPPO).

In a preferred embodiment, said cross-linked ion exchange membrane is a poly (ether ether ketone) sulfonate (SPEEK) membrane. The poly (ether ether ketone) sulfonate is an organic polymer characterized by the following structure:

As already mentioned, advantageously, SPEEK membranes have low cost and they are characterized by a polar nature limiting “fouling” phenomena of the membrane linked to the accumulation of hydrophobic substances, for example proteins, thus involving a decrease in the management costs and a greater durability with respect to membranes consisting of hydrophobic materials.

An additional aspect of the present invention relates to an adsorbent cartridge comprising a crosslinked ion exchange membrane anchored to a support material, wherein said membrane incorporates, inside the polymeric matrix, micro- and/or nano-particles made of inorganic materials selected from phosphates or zirconium phosphonates and/or metalorganic structures (MOF). In such configuration, the resulting adsorbent cartridge is characterized by greater adsorbent capabilities and stability. According to an aspect of the present invention, said ion exchange membrane has a degree of sulfonation comprised between 0.85 and 0.95%, and/or it has a polarity, expressed in terms of water content (“water uptake”, Wil), at least equal to 110% at room temperature (25°C).

According to an aspect of the present invention, the adsorbent cartridge comprises a cross-linked ion exchange membrane, anchored to said support material so as to form a film on the surface of said support material. Particularly, according to an aspect of the invention, said film consisting of the ion exchange membrane has a thickness comprised between 2-30 micron.

Advantageously, according to an aspect of the present invention, said support material coated with a film of said ion exchange membrane is characterized by a percentage of coating (C%) at least equal to 90%, 95%, 98%, or 99%, wherein said C % is calculated by means of the following formula: c(%): [(Mcc - Msc) - Mti] x 100, wherein Mcc is the mass of the coated support material, Msc is the mass of the uncoated support material, Mti is the mass of said solid ion exchange membrane.

An embodiment according to the present invention, relates to an adsorbent cartridge comprising a plurality of glass beads, each one coated with an ion exchange membrane consisting of an organic polymer.

A preferred embodiment according to the present invention particularly relates to an adsorbent cartridge comprising a plurality of glass beads, each one coated with a cross-linked SPEEK ion exchange membrane. According to an aspect of the present invention, said glass beads are characterized by a percentage of coating C% with cross-linked SPEEK membrane at least equal to 95%, wherein said C% is calculated by means of the following formula: c %)-. [(Mcc - Msc -? Mti] x 100, wherein Mcc is the mass of a coated bead, Msc is the mass of an uncoated bead, Mti is the mass of said solid ion exchange membrane.

According to an additional aspect of the present invention, said cartridge according to any one of the previously described variants comprises an ion exchange membrane characterized by a porosity comprised between 20 and 60%.

The present invention also relates to a process for the preparation of an adsorbent cartridge comprising a cross-linked ion exchange membrane anchored to a support material, comprising the following steps:

I. arranging a support material inside a reactor; ii. coating said support material by continuous flow of a solution comprising a polymeric material, so as to form a film of said polymeric material on the surface of said support material; iii. anchoring said film to the surface of said support material; iv. cross-linking said polymeric material; v. washing the adsorbent cartridge obtained in step iv; vi. drying said adsorbent cartridge.

As previously mentioned, according to an aspect of the present invention, said support material substantially or wholly consists of glass beads, particularly glass beads having a diameter <|) comprised between 1 and 2 mm.

The polymeric material used in step ii. of the above-described process in form of solution preferably is an organic polymer. In a preferred embodiment according to the present invention, said organic polymer is poly (ether ether ketone) sulfonate (SPEEK).

In an embodiment of the process according to the present invention, said solution made of polymeric material further comprises micro- and/or nano-particles made of inorganic materials selected from phosphates or zirconium phosphonates and/or metalorganic structures (MOF), so as to increase the resulting adsorbent capability and/or the stability of the ion exchange membrane.

The step i. of the herein described process can be carried out by inserting the support material inside any reactor suitable to operate in continuous flow mode known in the art. An example of reactor suitable to operate in continuous flow mode is represented by a thermostated reactor, comprising a chamber configured to house the support material to be coated with the ion exchange membrane, and which can be connected to at least a device with pump function capable of pumping one or more reactive flows to specific flow rates inside said chamber.

In an embodiment of the process according to the present invention, in step i. of the process a reactor is used comprising polymeric material, preferably teflon, it has a length comprised between 2-3 m and a diameter <|) comprised between 4 and 6 mm. According to an aspect of the present invention, said reactor is thermostated at a temperature comprised between 30-50°C, and it is connected to a device with pump function.

Preferably, the step i. of the process according to any one of the herein described variants is carried out by means of a flow of inert gas, for example nitrogen. The use of an inert gas flow during the reactor filling step allows to obtain a compact packaging of the support material inside the reactor chamber.

In order to ease the formation of the film made of polymeric material on the surface of said support material, in said step ii. said solution made of polymeric material is made to flow cyclically, by means of a pump system, inside said reactor said reactor.

According to an aspect of the invention, the solution made of polymeric material usable in step ii. of the process is a solution comprising an organic polymer dissolved in an organic solvent. Depending upon the selected organic polymer of interest, the person skilled in the art could use the organic solvent most suitable for the preparation of a polymer solution to be used in the process according to the invention.

In a preferred embodiment of the process according to the present invention, said solution made of polymeric material is a solution of poly (ether ether ketone) sulfonate in dimethyl sulfoxide (DMSO). Said solution is characterized by a SPEEK concentration in a range comprised between 1 :6-1 :15 mg/mL, preferably 1 :8-1 :12 mg/mL.

According to a further aspect of the invention, in said step ii., said solution made of polymeric material is made to flow inside the reactor by using a flow rate comprised in the range 1-10 mL/min, preferably between 3-5 mL/min. Preferably, said step ii., or the contact time between the solution made of polymeric material and the support material, has an overall duration comprised between 100-180 minutes.

In a second moment, the reactor temperature is increased so as increase the viscosity of the solution made of polymeric material (favoured by an increase in the concentration due to the effect of partial evaporation of the solvent) and then to allow the anchoring of the film made of polymeric material on the surface of the support material.

According to an aspect of the invention, the anchoring step iii. is carried out at a temperature at least equal to 140°C.

After the anchoring step, the reactor is heated so as to favour the covalent cross-linking of the film based upon polymeric material which coats the support material. In a preferred embodiment of the process according to the invention, the cross-linking step iv. is carried out at a temperature comprised between 160°C and 180°C for a duration comprised between 2 and 33 hours.

Preferably, during the cross-linking step, inert gas, particularly nitrogen, is made to flow inside the reactor, at a pressure comprised between 1-2 mbar. The nitrogen flow allows the formation of pores inside the coating of polymeric material, with a consequent increase in the surface area thereof and, then, an increase in the contact surface between the adsorbent and adsorbed material. The use of the gas flow during the cross-linking step preferably allows to obtain a degree of porosity of the film made of polymeric material anchored on the surface of the support material comprised in the range 20-60%. Then, according to an aspect of the present invention, the adsorbent cartridge obtained at the end of step iv. comprises a cross-linked ion exchange membrane, anchored to said support material, characterized by a degree of porosity comprised between 20-60%.

The adsorbent cartridge obtained at the end of step iv. can be subjected to washing so as to remove possible residues. According to an aspect of the present invention, in said washing step v. an aqueous solution of sulfuric acid and, subsequently, distilled water are made to flow inside said reactor with a flow rate comprised between 2-3 mL/min.

At this point the adsorbent cartridge can be subjected to a drying process; according to an aspect of the invention the drying step vi. is carried out by means of nitrogen flow at a temperature equal to 120°C.

According to an aspect of the invention, the process according to any one of the previously described embodiments can include an additional step of chemical-physical characterization of the obtained adsorbent cartridge.

Said characterization step can be performed, for example, with the purpose of determining the percentage of coating the glass beads, as well as to evaluate the performances and/or the degree of cross-linking of the coating ion exchange membrane, based upon polymeric material. A characterization method commonly used to evaluate the performances of an ion exchange membrane is represented by the determination of the ion exchange capability (IEC). This quantity is defined as the amount of exchangeable ions, expressed in milliequivalents or millimoles per gram of dry polymer (meq/g or mmol/g, respectively). It represents the total of the active sites or the functional groups responsible for the ion exchange in the ion exchange membrane.

According to an aspect of the present invention, said cartridge characterization step provides for the determination of the ion exchange capability of said coating membrane by means of acidbase titration. By pure way of example, the membrane first of all is immersed in a saline solution, for example a 1.5 N solution of NaCI, under stirring at room temperature, for an overall duration equal to 24 hours. The so-obtained solution is titrated with a base, for example a 0.02 N solution of NaOH. At this point the pH determination by potentiometric route allows to determine the equivalent point. The ion exchange capability of the system then can be determined by multiplying the so-obtained value by the amount of membrane homogenously dispersed in the reactor.

The present invention also relates to an adsorbent cartridge obtainable by a process according to any one of the previously described embodiments.

The adsorbent cartridges according to any one of the herein described variants can be used in water treatment processes, for example nano-filtration processes in the treatment of waste water coming from industrial waste and desalination of marine and brackish water. The present invention then further relates to the use of one or more cartridges according to any one of the previously described embodiments, for the decontamination and/or purification and/or desalination of water.

Particularly, under the term “decontamination” one relates, in the present description, to a process for the treatment and/or filtration of water aimed at removing and/or reducing the amount of harmful substances of chemical nature and/or biological nature inside the same, such as heavy metals, dyes, or pathogen microorganisms. Not limiting examples of pathogen microorganisms include bacteria, viruses, protozoa, fungi.

According to an aspect of the present invention, said water can be waste water, for example water coming from industrial waste, sewage, marine, and/or brackish water.

An aspect of the present invention particularly relates to the use of adsorbent cartridges as previously defined, wherein said adsorbent cartridges are used inside fixed bed columns and/or adsorbers. Not limiting examples of fixed bed columns are tubular reactors inside thereof glass beads coated with SPEEK membrane as described previously are arranged, therethrough a fluid current containing the substance(s) to be adsorbed is made to pass. Preferably, the glass beads coated with SPEEK membrane are packed, still, inside the fixed bed column; vice versa the liquid phase is fed continuously. Through the adsorbent bed, the treated current impoverishes progressively of the unwished solute. The present invention also relates to a process for the decontamination and/or purification and/or desalination of water comprising at least a step of transporting the water to be treated through one or more cartridges according to any one of the previously described embodiments.

Examples are reported herebelow having the purpose of better illustrating the methods shown in the present description, such examples are not in any way to be considered as a limitation of the preceding description and of the subsequent claims.

EXAMPLES

Materials and methods

Production of SPEEK solution in DMSO

A predetermined amount of SPEEK, deriving from the described protocol, (M.L. Di Vona, et al., Front. Energ. Res., 2, 39, 2014, 1-7; R. Narducci, PhD Thesis, University of Rome Tor Vergata, Aix-Marseille University 2014) is solubilized in dimethyl sulfoxide (DMSO) at room temperature and under stirring to obtain a solution at known concentration in the range 1 :8-1 :12 mg/mL, preferably 1 :10 mg/mL.

Creation of the continuous flow system

The method developed for creating the continuous flow system typically comprises the steps described hereinafter:

• Filling a tube made of preferably polymeric material (coil), in the specific case teflon, having length I and diameter comprised in the range 2-3 m and 4-6 mm, respectively, with glass beads having diameter = 1-2 mm (60-70 g); such system is hereinafter designated as reactor.

• Compact packing of the glass beads of said reactor, by means of a flow of inert gas (for example nitrogen);

• Thermostating the so-created reactor and its connection to a device with pump function.

Anchoring of the SPEEK-based membrane on glass beads in continuous mode and cross-linking thereof

The SPEEK solution in DMSO is made to flow cyclically, by means of using the pump system, inside the reactor, thermostated at T= 30-50°C. The flow rate is comprised in the range 1-10 mL/min, more particularly 3-5 mL/min. The contact time between the SPEEK solution and the glass beads is comprised in the range 100-180 min. The reactor temperature, in a second moment, is increased preferably up to 140°C, to make viscous the solution (the concentration increases by partial evaporation of the DMSO) and to allow the membrane anchoring on the glass.

The reactor is then heated at temperatures comprised between 160°C and 180°C for different periods of time, from 2 to 33 hours. In this step the covalent cross-linking of the SPEEK-based film coating the glass beads takes place. At the same time, inert gas, in the specific case nitrogen, is made to flow into the reactor, at a pressure comprised between 1-2 mbar for different periods of time from 2 to 33 hours. The nitrogen flow allows the formation of pores inside the coating, with a consequent increase in the surface area thereof and, then, an increase in the contact surface between adsorbent and adsorbed material. The coating porosity is comprised in the range 20-60%.

Washing and drying of the implemented adsorbent system

The adsorbent system obtained according to the described procedure then is subjected to washing, to remove possible residues. To this purpose, an aqueous solution of sulfuric acid and, subsequently, distilled water is made to flow in the reactor with a rate comprised in the range 2-3 mL/min. The adsorbent system is then dried by making nitrogen flow to pass in the reactor, at different temperatures, preferably at a temperature of 120°C.

Test results

By way of example, the results related to a coating carried out in continuous mode at a feeding flow rate of the solution equal to 5 mL/min are reported hereinafter; the cross-linking is carried out at 180°C, t= 3h.

1. Evaluation of the percentage of coating of the glass beads

The percentage of coating (C) of the glass beads was evaluated, which is given by the difference between the mass of the coated beads (Mcc) and the mass of the uncoated beads (Msc), according to the Equation 1 ; M_tj designates the mass of the solid membrane included in the initial solution in DMSO.

C(%): [(Mcc - - Mti] x 100 ( Eq .1 )

The obtained value is equal to 95%. 2. Evaluation of the ion exchange capability (IEC) and degree of cross-linking of the SPEEK-based coating membrane

The ion exchange capability was measured by acid-base titration (B. Maranesi et al., Cross- Linking of sulfonated poly ether ether ketone by thermal treatments: how does the reaction occur?, Fuel Cells, 2013, 13, 2, 107-117). A known amount of membrane in proton form was then collected by the system and it was converted into Na⁺ form by immersion in 1.5 N solution of NaCI, under stirring at room temperature (24 h). The resulting solution was titrated with a 0.02N solution of NaOH. The pH was determined by potentiometric route, so as to determine the equivalent point. BY multiplying such value by the amount of membrane homogeneously dispersed in the reactor it was possible to evaluate the IEC of the total system. The procedure was carried out on the initial membrane and on the membrane after the thermal treatment, in the specific case carried out at 180°C (3h), inducing (final) cross-linking.

From here it is possible to calculate the degree of cross-linking (DXL) by using the relation in Eq. 2, wherein I ECi and lECf are the ion exchange capability of the initial and final membrane, respectively (S. Holze et al., Influence of TiO2-Layer Thickness of Spray-Coated Glass Beads on Their Photocatalytic Performance. Chemical and Engineering Technology, 2017, 40, 1084-1091). In the specific case a cross-linking degree of 10% was obtained.

DXL = (IEC i - IEC n - IEC i (Eq.2)

3. Evaluation of the homogeneity of the coating material

The presence of the cross-linked SPEEK-type film on the glass beads was confirmed through infrared spectroscopy in Fourier transform, attenuated total reflectance (FTIR-ATR). Figure 3 shows by way of example the results of the analyses for (a) a sample of beads obtained by using the method the present invention relates to, compared to those for (b) a sample obtained by using a discontinuous process (“batch”) and for (c) a sample of not supported membrane. It is clear that its own signals, typical and characteristic of (c) can be recognized in (a), and the intensity of such signals is much higher in (a) than in (b).

The analysis of scanning electron microscopy (SEM) coupled with elementary microanalysis (EDX) supported the evidence of anchoring the membrane on the glass beads, and demonstrated the markedly higher homogeneity of the “coating” obtained in continuous flow with respect to the one obtained with discontinuous process, as shown by way of example in Figure 4 and Figure 5.

4. Evaluation of the system polarity The water content (“water uptake”, Wil) of SPEED-type membranes is usually expressed in grams (of water) per gram of anhydrous polymer (Eq. 3): wherein m(dry) and m(wet) are the dry and humid sample weight, respectively. The Wil value is correlated to the ion exchange capability and then to the number of the sulphonic groups (polar groups); the greater their number is, the greater Wil will be. The cross-linking then allows to modulate suitably this parameter, by allowing to reach the best compromise between the water content, the mechanical resistance and the ion exchange capability. In the specific case a Wil equal to 110% (25°C) was measured.

Claims

CLAIMS An adsorbent cartridge comprising a cross-linked ion exchange membrane anchored to a support material. The cartridge according to claim 1 , wherein said support material is substantially constituted by glass beads. The cartridge according to claim 2, wherein said glass beads have a diameter <|) comprised between 1-2 mm. The cartridge according to any one of claims 1 to 3, wherein said cross-linked ion exchange membrane is anchored to said support material so as to form a film on the surface of said support material, wherein said film has a thickness comprised between 2- 30 micron. The cartridge according to any one of claims 1 to 4, wherein said cross-linked ion exchange membrane is a poly (ether ether ketone) sulfonate (SPEEK) membrane. The cartridge according to any one of claims 1 to 5, comprising a plurality of glass beads each one coated with a cross-linked SPEEK membrane. The cartridge according to any one of claims 2 to 7 wherein said glass beads are characterized by a percentage of coating (C%) at least equal to 95%, wherein said (C%) is calculated by means of the following formula: c(%): [(Mee - Msc) Mti] x 100, wherein Mcc is the mass of a coated bead, Msc is the mass of an uncoated bead, Mti is the mass of said solid ion exchange membrane. The cartridge according to any one of claims 1 to 7, wherein said ion exchange membrane has a degree of cross-linking (DXL) at least equal to 10% and/or it has a porosity comprised between 20-60%. A process for the preparation of an adsorbent cartridge comprising a cross-linked ion exchange membrane anchored to a support material, comprising the following steps: i. arranging a support material inside a reactor; ii. coating said support material by continuous flow of a solution comprising a polymeric material, so as to form a film of said polymeric material on the surface of said support material; iii. anchoring said film to the surface of said support material; iv. cross-linking said polymeric material; v. washing the adsorbent cartridge obtained in step iv; vi. drying said adsorbent cartridge.

10. The process according to claim 9, wherein said support material is represented by glass beads.

11. The process according to claim 10, wherein said glass beads have a diameter <|) comprised between 1 and 2 mm.

12. The process according to any one of claims 9 to 11 , wherein said polymeric material is an organic polymer.

13. The process according to claim 12, wherein said organic polymer is poly (ether ether ketone) sulfonate (SPEEK).

14. The process according to any one of claims 9 to 13, wherein said step i. is carried out by inserting said support material inside a reactor comprising or consisting of polymeric material, preferably teflon, having a length comprised between 2-3 m and a diameter <|) comprised between 4 and 6 mm.

15. The process according to claim 14, wherein said reactor is thermostated at a temperature comprised between 30-50°C and it is connected to a device with pump function.

16. The process according to any one of claims 9 to 15, wherein, in said step ii. said solution made of polymeric material is made to flow cyclically, by means of a pump system, inside said reactor.

17. The process according to any one of claims 9 to 16, wherein said solution made of polymeric material is a solution of poly (ether ether ketone) sulfonate in dimethyl sulfoxide (DMSO).

18. The process according to any one of claims 9 to 17, wherein said step ii. is carried out at a flow rate in the range of 1-10 mL/min, preferably between 3-5 mL/min.

19. The process according to any one of claims 9 to 18, wherein said step ii. has a duration comprised between 100-180 minutes.

20. The process according to any one of claims 9 to 19, wherein said step iii. is carried out at a temperature at least equal to 140°C.

21 . The process according to any one of claims 9 to 20, wherein said step iv. is carried out at a temperature comprised between 160°C and 180°C for a duration comprised between 2 and 33 hours.

22. The process according to claim 21 , wherein, during step iv. inert gas is made to flow, particularly nitrogen, at a pressure comprised between 1-2 mbar inside said reactor.

23. The process according to any one of claims 9 to 22, wherein, in said washing step v., an aqueous solution of sulfuric acid and, subsequently, distilled water are made to flow inside said reactor with a flow rate comprised between 2-3 mL/min.

24. The process according to any one of claims 11 to 23, wherein said solution made of polymeric material comprises micro- and/or nano-particles made of inorganic materials selected from phosphates or zirconium phosphonates and/or metalorganic structures (MOF). 25. Adsorbent cartridge obtainable by a process according to any one of claims 9 to 24.

26. Use of one or more cartridges according to any one of claims 1 to 8 or 25, for the decontamination and/or purification and/or desalination of water.