IT201600112268A1 - Enthalpy heat exchangers with membrane of aromatic sulfonated polymeric type and process for the preparation of said membranes - Google Patents

Description

"Enthalpy heat exchangers with membranes of the aromatic sulfonated polymeric type and procedure for the preparation of said membranes"

SUMMARY OF THE INVENTION

The present invention relates to enthalpy heat exchangers! for air exchange in buildings, equipped with aromatic sulphonated polymeric membranes, cross-linked or non-cross-linked. The invention also relates to a process for crosslinking, preparing membranes of said polymers and their use.

BACKGROUND OF THE INVENTION

In the international community, the interest in energy saving is certainly significant, to the point that the European Union issued in July 2014 the Regulation 1253/2014 on the specifications for the eco-compatible design of ventilation units, which represents one of the few implementation measures. of Directive 2009/125 / EC relating to the establishment of a framework for the development of specifications for the eco-design of energy-related products.

The construction sector, due to the energy saving policies mentioned, is therefore increasingly pushed to reduce energy consumption, leading to the consequent need to improve the insulation of the envelope ("indoor") to avoid unnecessary energy consumption. However, this insulation can lead to an increase in air tightness, reducing the exchange of air in indoor environments and causing negative effects for buildings and users, with the formation of mold and increased indoor pollution.

In order to avoid the negative effects of the lack of fresh air, many companies offer efficient controlled mechanical ventilation systems, which are usually associated with a heat recovery system (heat exchanger or heat recovery) to increase the energy efficiency of the system. ventilation itself.

In fact, the thermal load for the ventilation systems now represents a significant percentage of the overall energy requirement, and therefore any effort directed towards increasing the efficiency of the ventilation itself, brings significant benefits for the entire building sector.

Through the installation of these systems it is possible to avoid the arbitrary action of opening the windows, pursuing the objective of energy saving by preheating the cold external air with the hot internal air coming out (in winter conditions), or by pre-cooling the hot outdoor air with cold indoor air exiting (in summer conditions).

In recent years, systems have appeared on the market that allow, in addition to heat recovery, to humidify (in winter) and dehumidify (in summer) the outside air. These systems are called enthalpy heat exchangers or recuperators.

The recovery of water vapor is particularly useful from an energy point of view, as it contributes passively to the reduction of the energy load that air conditioning systems (HVAC) must sustain to remove water vapor in the hot season and to increase its presence in the cold season. . Furthermore, enthalpy heat exchangers are useful for improving the thermohygrometric well-being of indoor environments.

Enthalpy heat exchangers exist in two different configurations, namely rotary and static. The static enthalpy heat exchangers, compared to those of the rotary type, have the considerable advantage of the absence of moving parts, thus leading to energy savings, and are made by superimposing matrices of different shape, nature and functions which, once superimposed , they create isolated channels for the passage of hot and humid air and cold and dry air.

Most enthalpy heat exchangers, to have the functionality of water vapor exchange, make use of the use of a membrane permeable to water. This membrane allows heat and moisture to be transferred through fluid currents that flow from opposite sides to the membrane. Dehumidification will then be achieved thanks to the membrane, and this membrane-based dehumidification offers a stable and continuously operating system, which combines long life times with low energy consumption.

The membranes present in state-of-the-art enthalpy heat exchangers are essentially based on perfluorinated materials, such as perfluorosulfonic acid polymers (PFSA, such as Nafion ™). However, these materials have major limitations.

One of these limits concerns their synthesis which involves the use of toxic and non-eco-compatible substances, bringing a disadvantage from the point of view of safety and environmental impact.

Another limitation is their high cost (for example, 200-270 € / m <2> of Nafion ™ depending on the thickness, from 50 to 125 pm).

Finally, these materials are subject to strong swelling in the presence of humidity, with consequent deterioration of the mechanical properties, up to breakage. This obviously leads to a loss of performance of the polymeric membrane, which will no longer be able to efficiently exchange heat and water vapor.

Consequently, there is a growing need for the development of an enthalpy heat exchanger, which possesses a low-cost membrane, characterized by low environmental impact, and which possesses the mechanical and chemical characteristics suitable for a correct transfer of heat and water vapor that lasts over time, through the different thermohygrometric conditions to which it is subjected.

AIMS OF THE INVENTION

It is an object of the present invention to provide an enthalpy heat exchanger that provides for the use of non-toxic materials that can be synthesized through the use of environmentally friendly substances, with considerable advantages from the point of view of safety and environmental impact.

The object of the present invention is also to provide an enthalpy heat exchanger which is economical, while maintaining high technical-mechanical characteristics. Another object of the present invention is to provide an enthalpy heat exchanger which is capable of efficiently exchanging heat and water vapor with efficiency and reliability unchanged over time.

A further object of the present invention is to provide an enthalpy heat exchanger which is not conditioned in its efficiency by the different thermo-hygrometric conditions to which it is subjected.

It is a further object of the present invention to provide a process for the preparation of a membrane for enthalpy heat exchangers.

Finally, an object of the present invention is the use of membranes which, when applied to the technology of enthalpy heat exchangers, allow the latter to achieve the technical advantages listed above.

DESCRIPTION OF THE INVENTION

The present invention relates to an enthalpy heat exchanger comprising at least one polymeric membrane based on sulphonated aromatic polymers (SAP).

In the present invention, by "membrane" is meant a layer of any shape and size that allows the transfer of energy (heat) and / or matter (water vapor) between two streams of air having different temperature and humidity, in a heat exchanger. heat. The membrane of the present invention is envisaged to have any thickness, and said thickness can be a function of the area of the membrane itself and the volume of the two air streams. For a preferred embodiment, the thickness of the membrane ranges from 10 µm to 50 µm, advantageously 20 µm.

In the present invention, by "sulphonated aromatic polymers" or "sulphonated aromatic polymer" or "SAP", it is meant polymers having sulphonic groups linked to aromatic rings. SAPs include for example poly- (ether ether ketone) sulfonate (SPEEK), poly- (phenyl sulfone) sulfonate (SPPSU), poly- (ether sulfone) sulfonate (SPES) and polystyrene sulfonate (SPS ).

SAP polymers are known in the art and examples of their chemical structures are illustrated in Formula 1.

According to a particularly preferred embodiment, the present invention relates to an enthalpy heat exchanger comprising at least one polymeric membrane based on poly- (ether ether ketone) sulfonate (SPEEK).

The SPEEK polymer is known in the art and its chemical structure is reported in the following Formula 2.

Formula 2

In the present invention, SPEEK refers to a polymer based on poly- (ether ether ketone) sulfonate, which has any molecular weight, any ion exchange capacity, any equivalent weight, any polydispersion index, any microstructure and any degree of sulfonation (hereinafter DS, "degree of sulfonation"), that is, any number of -SO3H groups per repetitive unit.

In the present invention, by "ion exchange capacity" or "IEC" (Ionie Exchange Capacity) is meant the milliequivalents of ionic groups, in the specific case of the invention, of sulphonic groups, per gram of polymer.

In the present invention, by "equivalent weight" or "EW" (Equivalent Weight) is meant the reciprocal of IEC; or l / l EC.

In the present invention, by "polydispersion index" or "polydispersion" is meant, as is well known to those skilled in the art, the measure of the uniformity of distribution of molecular weights in a given polymer, expressed through an index calculated from the ratio between the weight average molar mass and the numerical average molar mass of the polymer. A non-limiting example of SPEEK polymer particularly suitable for the purposes of the present invention has the following characteristics: EW of 369 g / eq, polydispersity of 2, microstructure with channels of 5-10 nm, DS of 1 and IEC of 2.71 meq / g.

Object of the present invention are also enthalpy heat exchangers comprising at least one polymeric membrane based on co-polymers containing SAP or SPEEK as defined above. It has surprisingly been found that membranes based on SAP polymer, in particular based on SPEEK polymer as defined above, can be effectively used as heat and water vapor exchangers in enthalpy heat exchangers, as will be fully described and demonstrated below.

In particular, the SPEEK polymer, main constituent of the membrane of the enthalpy heat exchanger according to one of the preferred embodiments of the present invention, can be obtained, for example, starting from commercially available poly- (ether ether ketone) polymer (PEEK), according to the following reaction (Scheme 1) and described in detail in the experimental part:

This reaction is eco-friendly, requires low-cost reagents and does not give rise to the formation of toxic by-products, nor does it involve the use of toxic products. The advantages offered by this material with respect to the perfluorinated alternatives currently available in the state of the art will therefore be clear to the person skilled in the art.

Through this reaction it is also possible to modulate the number of acid sulphonic groups -SO3H present on the skeleton of the SPEEK polymer, thus allowing to easily vary the DS according to the various climatic needs.

The presence of sulfonated acid groups, in the SPEEK polymer as well as in all SAP polymers, allows the material to have a great sensitivity to changes in relative humidity based on the DS reached: the higher the DS, the greater the sensitivity to changes in humidity. relative, since the tendency of the polymer to absorb water is proportional to the number of sulphonic groups per repetitive unit. This makes the SAP polymer, especially the SPEEK polymer, extremely effective and versatile when used in enthalpy heat exchanger membranes.

This heat and water vapor exchange efficacy of the SPEEK polymer membrane has been experimentally demonstrated. Furthermore, it has been observed that the membranes according to the invention offer a more efficient exchange of humidity at the interfaces in the recurring environmental conditions for most of the year, compared to the perfluorinated membranes currently used. The effectiveness of the membranes according to the invention will be discussed and demonstrated in the experimental section reported below.

A further advantage deriving from the use of the SAP polymer, in particular of the SPEEK polymer according to the invention, is represented by its cost, which is much lower than the polymers used in enthalpy heat exchangers according to the state of the art; for example, the cost of SPEEK is about 4-6 € / m <2> for a membrane with a thickness of 20 pm and up to 20-30 € / m <2> for a thickness of about 100 pm, while the cost of Nafion ™, which is a polymer currently used in enthalpy heat exchangers, is about 200-270 € / m <2> for thicknesses ranging from 50 to 125 pm.

As already mentioned in the context of the invention, a limitation of generic polymeric membranes is given by their dimensional variation due to swelling and / or contraction ("de-swelling") in different humidification conditions, which can lead the formation of perforations, fractures or holes. Such defects increase the flow of environmental gases passing through the membrane, negatively affecting the performance of the polymer membrane.

According to the present invention, a further important advantage with respect to the polymers used in the state of the art is represented by the possibility of reducing swelling and / or de-swelling of the polymeric membranes of SAP, in particular of the polymeric membranes of SPEEK through the cross-linking of the SAP itself. .

In fact, it has been observed that the membranes of cross-linked SAP, in particular the membranes of cross-linked SPEEK, show a greater dimensional stability than those of the prior art and pure compared to those made based on non-cross-linked SAP, resulting in a significant improvement of their properties. mechanical, with the result of reducing degradation processes and improving their duration. More specifically, the elastic modulus and the tensile strength and yield strength of crosslinked SAP membranes increase significantly after crosslinking.

For this reason, a further object of the present invention is an enthalpy heat exchanger which comprises at least one polymeric membrane based on cross-linked SAP, said SAP-based polymeric membrane preferably based on SPEEK.

In the present invention, by "cross-linked SAP", as well as by "cross-linked SPEEK", it is meant a polymer of SAP, or of SPEEK, as defined above, which forms any number of cross-links, or which possesses any degree of cross-linking (DXL), with any hydration number and with any elastic modulus.

In the present invention, by "degree of cross-linking" or "DXL" is meant the difference between the IEC of the non-cross-linked (initial) and cross-linked (final) polymer, divided by the IEC of the non-cross-linked (initial) polymer, by 100 ; that is: DXL = (I ECinit-1 ECfin) / l ECinit * 100. In the present invention, by "hydration number" is meant the moles of water divided by the moles of sulphonic groups. In particular, a non-limiting example of cross-linked SPEEK polymer particularly suitable for the purposes of the present invention has the following characteristics: DXL of 8%, hydration number of 12 at 25 ° C and elastic modulus of 1200 MPa. ; The cross-linked SPEEK polymer has sulfone bridges as shown in Formula 3: ;; Initial sample Sample after cross-linking; Formula 3 ;; In Formula 3, the repetitive unit of non-cross-linked SPEEK with DS = 1 can be observed on the left; while on the right the reticulated SPEEK repetitive unit contains the sulphonic groups (x = DS) and the sulphone bridges (y = DXL), highlighted in the figure. It has been surprisingly found that crosslinking does not decrease the ability of the polymer to absorb water vapor, as can be observed in the experimental part reported below. Finally, thanks to crosslinking, there is a better conveyance of water thanks to the modification in the microstructure that is created in the polymer. In fact, this microstructure shows a reduced tortuosity of the membrane channels, compared to the case of the SAP as it is, thus facilitating the passage of water in said channels and improving its conveyance. It is a further object of the invention to provide a process for the preparation of a polymeric membrane based on SAP, possibly cross-linked, being said polymeric membrane based on SAP preferably SPEEK. ; Said process comprises:; a) solubilizing an aliquot of SAP, for example SPEEK, in a suitable solvent, preferably selected from an aprotic polar solvent, a polar protic solvent and mixtures of these, obtaining a solution of SAP polymer, for example a SPEEK polymer solution; ; b) pour said solution obtained according to step (a) on a flat surface and dry it at a temperature between about 80 ° C and about 160 ° C for a period of time necessary for all the solvent to be evaporated, obtaining a SAP membrane, for example a SPEEK membrane; and optionally c) carrying out a heat treatment on said membrane obtained according to said step (b) at temperatures ranging from 160 ° C to 200 ° C for a time ranging from 2 to 33 hours, obtaining a SAP membrane, for example SPEEK, reticulated. In step (a) the solvent used preferably has a dielectric constant between 20 and 60 D, more preferably between 38 and 58 D, and even more preferably 47 D. The solvent is advantageously selected from dimethylsulfoxide (DMSO), dimethylformamide, dimethylacetamide, acetone , or mixtures of DMSO / H20 (1: 1, v / v), DMSO / acetone (1: 1, v / v). According to a preferred embodiment, the solvent used in step (a) is DMSO, and the SPEEK: DMSO ratios range from 1: 5 to 1:20 mg / mL, preferably 1:10 mg / mL. If step (c) is also desired, dimethyl sulfoxide (DMSO) must be used as a solvent, as will be described below. According to a preferred embodiment, it is possible to partially evaporate the solvent used in step (a) before carrying out step (b) under continuous stirring. For example, it is possible to evaporate the solution obtained according to step (a) up to about 1/3 of its initial volume under continuous stirring. This facilitates the following step (b), due to the greater viscosity of the solution, which will be more concentrated, and the smaller volume to be poured. In step (b), the temperature used is between 80 ° C and 160 ° C, preferably between 100 ° C and 140 ° C, and more preferably at 120 ° C. ; Again in step (b), the thickness of the solution poured on the flat surface is not particularly influential, and for example with a thickness of solution poured between 80 and 100 µm it will be obtained, at the end of step (b), or after the evaporation of the solvent, a membrane having a thickness of about 20-30 µm. Still in step (b), the skilled in the art is able to verify whether the reaction solvent is completely evaporated, or if the membrane is solvent-free, with techniques well known in the art. In step (c), the temperature of the heat treatment is preferably 180 ° C and the execution time of this is preferably 10 hours. According to the present invention, it is possible to use both the membrane obtained at the end of step (b) and the membrane obtained according to the optional step (c). In fact, step (c) is optional, but it allows to obtain the SAP crosslinking, for example the SPEEK crosslinking. Cross-linked SAP and even more cross-linked SPEEK is particularly advantageous for use according to the invention for the reasons set out above. ; As previously mentioned, the solvent used in step (a) plays a fundamental role in the formation of cross-links following the heat treatment according to the eventual step (c). In fact, it has been observed that only SAP membranes prepared using DMSO as manufacturing solvent during step a), can give rise to crosslinking. In fact, dissolving the polymer in solvents other than DMSO in step (a) does not lead to any cross-linking reaction following the heat treatment of step (c). Compared to the known crosslinking processes, the SAP crosslinking step (c) according to the present invention uses crosslinking molecules that are not sensitive to the operating conditions, not processed and inexpensive. Furthermore, it is economical, short-lived and easy to make, bringing the further advantage of improving the performance of the cross-linked SAP membranes, in particular SPEEK. The optional process (c) is also suitable for SAPs with high DS values. ; In the optional step (c) it is possible to modulate the degree of crosslinking, which is in fact a function of the temperature and duration of the heat treatment. This aspect constitutes a significant advantage that characterizes the process of the invention, thanks to which it is possible to modify the aforementioned reaction parameters in order to obtain membranes with different characteristics, according to the requirements. Finally, it is evident that the crosslinking performed in the optional step (c) is performed directly in situ during the membrane fabrication process. This characterizes this crosslinking method as very convenient and extremely valid for making membranes to be used in heat exchangers. ; It should be noted that the cross-links that are created between the polymer macromolecules thanks to step (c) according to the invention are of the covalent type, preferred over ionic bonds, as they are more stable and less subject to environmental changes to which the polymer will be subjected to when used according to the invention. A detailed example of the process of the invention for the preparation of a SPEEK membrane will be described below in the experimental section. As mentioned, it has been surprisingly found that the membranes described above are particularly suitable in enthalpy heat exchangers and that their performance is superior to the performance of the membranes present in the current state of the art, as will be amply demonstrated below in the experimental section. . A further object of the present invention is a polymeric membrane for enthalpy heat exchangers based on SAP, preferably cross-linked, being said SAP preferably SPEEK. The present invention also provides for the possibility of incorporating in the polymeric material SAP constituting the membrane, cross-linked or non-cross-linked, one or more organic or inorganic compounds. These compounds can establish different types of interactions with the polymer, depending on their hydrophilic or hydrophobic nature. Interactions can occur either within the same polymer macromolecule or between different macromolecules. The nature and quantity of these interactions determine the tertiary structure of the polymer. ; The self-assembly modulation plays a fundamental role in the characteristics and morphology of the material, as a different microstructure leads to different properties. The presence of said further organic and / or inorganic compounds is of particular interest as it is possible to improve the mechanical properties of the membrane, without significantly sacrificing its water absorption, especially if said compounds are nanometric in size. ; For example, the incorporation of binary oxides with nanometric dimensions such as Si02, Ti02, Zr02 in the SAP, leads to further advantages including: reduction of swelling, permeability and better morphological stability. ; It has in fact been shown that composite membranes of SAP, in particular of SPEEK, with 5% of Zr02 have shown a decrease in water absorption from 30 to 14% and a reduction in permeability from 2xl0 <5> to 5xl0 <4 > Barrer. Furthermore, it has also been shown that the addition of Ti02 with dimensions below 100 nm leads to greater chemical stability, also allowing to modify the hydrophobic / hydrophilic balance in the system, accentuating the phase separation and increasing the water channeling. To improve the dispersion of binary oxides and to have a control at the nanometric level, it is also possible to use oxides functionalized with organic molecules. The use of the latter has several advantages such as, for example: better homogeneity of the system, increased compatibility between the components, lack of agglomeration of the particles and the possibility of modifying the hydrophobic / hydrophilic character of the oxide surface. An example of an organic compound used to modify the surface of binary oxides is tri (hydroxy-methyl) -propane of a hydrophilic nature, while a typical hydrophobic surface modifier is silicone oil, which is extremely stable. Furthermore, for polymeric membranes to be used in enthalpy heat exchangers, it is of particular importance to evaluate the microbiological stability of the membranes themselves. In fact, these membranes can be subjected to high relative humidity values for prolonged times, thus increasing the risk of contamination by microorganisms. ; It may therefore be advisable to insert a compound with an antimicrobial function into the polymeric membrane, in order to avoid the onset of microbiological contamination and to postpone any cleaning and maintenance interventions of the heat exchanger. The present invention also relates to an enthalpy heat exchanger comprising at least one SAP-based polymeric membrane, preferably poly- (ether ether ketone) sulfonate (SPEEK), as defined above, which also comprises one or more different compounds from SAP or SPEEK. Said compounds are selected from: antimicrobial agents, metal oxides, metal particles in ionic form, metal nano fibers, ternary salts. Said SAP or SPEEK polymers can be cross-linked or non-cross-linked and can be used with one or more organic or inorganic compounds, such as for example titanium dioxide and / or particles of ionic silver; preferably having nanometric dimensions. Furthermore, some or all of said compounds preferably exert an antimicrobial action. In the present invention, by nanometric dimensions it is meant that at least one dimension of most of the matter of the compound under examination, for example, at least one dimension of more than 90% of the particles of a compound, is less than 100 nm. The quantity of said one or more compounds inside the membrane is variable. In fact, according to the type of properties they modify, they can be added in different percentages with respect to the total weight of the membrane. Generally, the quantities of said one or more compounds vary from 1% to 10% by weight with respect to the total weight of the membrane and are preferably about 5%. Said one or more compounds can be added at different times in the membrane preparation process. For example, they are added, in the due weight ratios, in step (a) of the process according to the invention. It is a further object of the invention to use SAP, preferably poly- (ether ether ketone) sulfonate (SPEEK), as described above, preferably cross-linked SAP or SPEEK, in membranes for enthalpy heat exchangers. ; It will be understood that the shape, size and type of the exchanger is not critical for the purpose of the application of the membranes according to the invention, provided that, during the passage of the air flows inside it, the mass transfer (water vapor ) and energy (temperature) occurs satisfactorily. Therefore, the enthalpy heat exchanger object of the invention can have any shape and size. The definition of the most suitable forms and types for the optimization of heat and water vapor exchanges is referred to the industrial development process. ; DESCRIPTION OF THE FIGURES; Figure 1 is a graph representing the ambient humidity with respect to the water absorption isotherms by the SPEEK polymer with various degrees of crosslinking (DXL); the symbols represent the experimental data, the lines refer to the model: it is possible to observe how the trend of the experimental data substantially corresponds to that of the models. Figure 2 represents a support including membrane for the base unit (flat plate) of the enthalpy heat exchanger. Figure 3 is a schematic representation of the enthalpy heat exchanger used for the experimental test. Figure 4 represents a test bench for measuring the performance of enthalpy heat exchangers. Figure 5 is a graph that represents the variation of the temperature of the hot flow (inlet in green and outlet in red) and of the cold flow (inlet in gray and outlet in light blue); time is present in the abscissa axis and temperature is present in the ordinate axis. Figure 6 is a graph representing the variation of the relative humidity of the wet flow (input in red and output in green) and of the dry flow (input in light blue and output in gray); time is present in the abscissa axis and relative humidity is present in the ordinate axis. Figure 7 represents a psychrometric diagram representing the variation of the thermodynamic state of the hot and humid flow in the plastic material. Figure 8 represents a psychrometric diagram representing the variation of the thermohygrometric state of the cold and dry flow in the plastic material. Figure 9 represents a psychrometric diagram representing the change in the thermodynamic state of the hot and humid flow in the Nafion ™ NRE-212 (perchlorinated control material). Figure 10 represents a psychrometric diagram representing the change in the thermohygrometric state of the cold and dry flow in the Nafion ™ NRE-212 (perchlorinated control material). ; Figure 11 represents a psychrometric diagram representing the variation of the thermodynamic state of the hot and humid flow in the cross-linked SPEEK (DXL = 0.08). ; Figure 12 represents a psychrometric diagram representing the variation of the thermohygrometric state of the cold and dry flow in the cross-linked SPEEK (DXL = 0.08). ; EXPERIMENTAL SECTION; Example 1; General preparation of membranes of cross-linked SPEEK; Example 1.1; Synthesis of SPEEK; SPEEK was obtained starting from commercially available PEEK according to the synthetic approach described in Scheme 1. ; According to the preparation process, the PEEK polymer is initially dried at 80 ° C for 24 hours to remove traces of moisture and then is slowly added at room temperature of the 96% sulfuric acid present in a three-necked flask, in PEEK / sulfuric acid ratio of 1:35 (mass / volume, g / ml). The mixture is stirred continuously with a mechanical stirrer under an inert atmosphere. After dissolution of the polymer, the mechanical stirrer is removed and replaced with a condenser, then the solution under magnetic stirring is kept at temperatures between 25 ° C and 50 ° C for different times, i.e. between 5 hours and 11 days . In this step, according to the reaction time adopted, different DS will be obtained, up to the maximum value of 1. The solution is then poured into an excess of water and ice under stirring, obtaining a flocculated precipitate. The precipitate is then filtered and washed with dialysis membranes, commercially available, up to neutral pH to completely eliminate the residual sulfuric acid. The sulfonated polymer is then dried at temperatures between 60 ° C and 80 ° C. Finally, the polymer is removed from the dialysis tubes and dried on Teflon plates at 55 ° C for a time of 12 hours. ; Example 1.2; Preparation of SPEEK membranes; A predetermined quantity of SPEEK, deriving directly from the previous example, is dissolved in DMSO to obtain a solution of known concentration with a SPEEK / DMSO ratio of 1:10 mg / mL. The solution is evaporated under continuous stirring up to about 1/3 of its initial volume, then spread on a glass plate and dried in an oven for 24 hours at a temperature of 120 ° C. After cooling to room temperature, the resulting membranes are removed from the glass plate. ; Example 1.3; Crosslinking of SPEEK membranes; The crosslinking reaction is performed directly on the membranes prepared according to the previous example. Said membranes are subjected to thermal treatment, carried out at temperatures between 160 ° C and 180 ° C for a time between 10 and 12 hours, on the plates of the previous step. The membranes are then washed with an aqueous solution of 2 M sulfuric acid and, subsequently, distilled water to eliminate any residues. ; Example 2; Effectiveness of water vapor absorption of cross-linked and non-cross-linked SPEEK; The water uptake data (WU, "water uptake") of cross-linked and non-cross-linked SPEEK with respect to humidity (aH20, " air H2O ") through isopiestic measurements with different salt solutions at a temperature of 25 ° C with equilibrium times of 240 hours., The resulting graph is shown in Figure 1.; Thanks to the high slope of the curve in the graph of Figure 1, It is possible to observe that SPEEK is very sensitive to variations in relative humidity (RH, "relative humidity"; RH = ahhO * 100). It will therefore be obvious to the person skilled in the art that this sensitivity proves the effectiveness of SPEEK as a membrane in heat exchangers enthalpy.

From the same Figure, it can also be observed that the cross-linked SPEEKs have very similar WU values to the non-cross-linked ones. This shows that the crosslinking of SPEEK does not cause a loss in water absorption and consequently a loss in efficacy. The WU values between cross-linked and non-cross-linked SPEEK are comparable up to a value of RH = 80%. When the humidity exceeds this value, only the SPEEKs that have a low degree of cross-linking are able to have an absorption of water vapor similar to non-cross-linked SPEEKs. However, the non-crosslinked SPEEKs, for RH values higher than 90% and contrary to crosslinked ones, begin to show a strong decay of the mechanical properties, no longer sustainable especially for high SD values (over 0.9).

Example 3

Analysis of the effectiveness of the cross-linked SPEEK polymeric membrane in heat exchangers Example 3.1

Preparation of the test bench and construction of the heat exchanger

The analysis of the effectiveness of the SPEEK polymeric membranes for heat exchangers of the invention was carried out preliminarily on a simplified geometry (flat plate). For this purpose a simplified model of the base unit of the enthalpy heat exchanger was constructed (Figure 2, experimental setup and Figure 3, enthalpy heat exchanger scheme of the experimental setup).

The main components of the test bench are shown in Figure 4, and are the humidification chamber (a), which consists of a 50x50x50 cm plexiglass container, with one side that can be opened for positioning the suction fans (b) and connected, through a soft mobile tube, to an ultrasonic humidifier, which allows to control the temperature and relative humidity conditions at the inlet of the exchanger, varying them within the characteristic ranges of applications related to air treatment in buildings. Finally, there is the heat exchanger (c).

In the experimental apparatus it is therefore possible to fix the temperature and relative humidity conditions of the two air flows, also controlling their flow rate, in order to evaluate the ability of the membranes to transfer heat and humidity.

The operating scheme of the test bench is as follows: humid and warm air is produced in the humidification chamber (a) to simulate the conditions of the external air in the summer period. The flow of air sucked in by said chamber will constitute the air flow which will have to exchange heat to the mass (water vapor) with the dry and humid flow which instead comes from the inlet (c).

The two flows are sent to the exchanger and, excluding the initial section of the convergent, they will carry out the exchange of heat and mass, mainly in correspondence with the membrane under examination.

The polymeric membrane is therefore lapped on both sides by the two flows at known temperature and relative humidity, measured at the inlet and outlet of the exchanger itself through four sensors (Galltec - Mela, L series).

The data are acquired through a program developed in the Labview environment, which allows them to be saved, processed and graphically represented.

From the physical point of view, the heat given off by the hot fluid will be given by its thermal capacity due to the decrease in temperature that it undergoes along the passage on the membrane; the water vapor released will instead be given by the decrease in absolute humidity contained in the air flow (absolute humidity is the ratio between the mass of water and the mass of dry air contained in an assigned volume of humid air). The opposite will happen for cold, dry fluid.

Relative humidity is, together with temperature, the thermohygrometric parameter most closely linked to human well-being and is also the simplest parameter to measure with the available instruments.

Relative humidity is indicated with the symbol φ and is defined as the ratio between the mass of water vapor contained in a volume of humid air and the mass of water vapor contained in the same volume of saturated air, at the same temperature:

Considering the approximation of ideal gases valid:

Relative humidity φ is related to absolute humidity (and therefore to the water content in the air stream) through the following relationship:

where P is the total pressure of the humid air and Pw, s is the saturation pressure of the water vapor at the air temperature.

Since from the measurements of temperature and relative humidity of the air it is possible to trace its water content, the analyzes of variation of temperature and relative humidity were carried out in the test bench to measure the performance of the exchanger.

Example 3.2 (Comparative)

Thermohygrometric exchange efficiency obtained from the comparative membrane heat exchanger

The verification of the thermohygrometric exchange efficiency can be carried out both through the separate evaluation of the temperature variations, and through the separate evaluation of the relative humidity variations.

The test bench was first tested with a sheet of waterproof plastic material, in order to validate the experimental setup. The results of this experimental test are reported in Figures 5 to 8.

The first experimental test was carried out with a flow of hot (31.4 ° C) and humid (relative humidity 95%) inlet (green line in Figure 5, red line in Figure 6 and point PI in Figure 7) and a corresponding flow of cold (26.3 ° C) and dry (relative humidity 38%) air entering from the opposite side of the exchanger (gray line in Figure 5, light blue line in Figure 6 and point PI in Figure 8).

Variations in temperature and water content can be visualized even more immediately through the use of the psychrometric chart (Figures 7 and 8). This graph shows the humid air temperature on the abscissa, the absolute humidity in the right ordinate (in grams of water / kg of dry air) and in the curves (in red) that run from the bottom side to left to the upper right, the relative humidity. By setting two of these three parameters, the thermodynamic state of humid air can be defined.

Thanks to the results, it can be seen how the plastic material allows, as expected, the transfer of sensible heat between the two flows (PI - P2 section of the curves in Figures 7 and 8, which testify to the temperature variations), without allowing the transfer of specific humidity. It is in fact possible to note that both the PI - P2 sections of Figure 7 and 8 are horizontal, indicating that the absolute humidity is constant. Thanks to this preliminary test, the experimental setup was validated.

The test was repeated under similar conditions with a Nafion ™ NRE-212 membrane (EW = 1100 g / mol, IEC = 0.91 meq / g) as a comparative reference.

Figures 9 and 10 show the results of said test.

In this case, it is possible to highlight, in addition to heat transfer (temperature variations), also the transport of water vapor, through the modification of the absolute humidity in the section P1-P2 of the curves (increasing in the dry flow, decreasing in the wet flow ). As an example, the wet flow passes, from 0.0260 to 0.0245 g / kg, with a decrease in absolute humidity equal to 0.0015 g / kg.

Example 3.3

Thermo-hygrometric exchange efficiency obtained from the heat exchanger with reticulated SPEEK membrane

The test was finally repeated with a reticulated SPEEK-based membrane (DXL = 8%, DS = 0.9, IEC = 2.5 meq / g).

Figures 11 and 12 show the results obtained.

From this Example it can be seen that temperature variations indicate that, in passing through the SPEEK membrane, the two air flows exchanged sensible heat. The relative humidity variations testify, together with the temperature variations, the mass exchange (water vapor) between the two flows through the membrane according to the equations previously described in Example 3.1. The effectiveness of SPEEK as a membrane in enthalpy heat exchangers was therefore demonstrated.

Furthermore, it is possible to observe that the greater slope of the PI - P2 sections in the tests carried out with cross-linked SPEEK, compared to the slope of the PI - P2 sections of Nafion ™ with EW = 1100 g / mol, results in a more marked variation in the content of water vapor for the individual air flows, thus demonstrating the superiority of the polymer membranes of the invention in terms of water vapor exchange. In fact, the wet flow in this case goes from 0.0250 to 0.0230 g / kg, with a decrease in absolute humidity equal to 0.0020 g / kg.

Claims (10)

CLAIMS 1. Enthalpy heat exchanger comprising at least one polymeric membrane based on sulfonated aromatic polymer (SAP). 2. Heat exchanger according to claim 1, characterized in that said sulphonated aromatic polymer (SAP) is cross-linked. 3. Heat exchanger according to claim 1 or 2, characterized in that said membrane also comprises one or more compounds selected from: antimicrobial agents, metal oxides, metal particles in ionic form, metal nano fibers, ternary salts. 4. Heat exchanger according to claims 1 to 3, characterized in that said sulfonated aromatic polymer (SAP) is poly- (ether ether ketone) sulfonate (SPEEK). 5. Process for the preparation of a polymeric membrane based on sulfonated aromatic polymer (SAP), which includes: a) solubilizing an aliquot of SAP in a solvent selected from an aprotic polar solvent, a polar protic solvent and their mixtures, obtaining a SAP polymer solution; b) pour said solution obtained according to step (a) on a flat surface and dry it at a temperature between about 80 ° C and about 160 ° C, obtaining a SAP membrane, and possibly c) carrying out a heat treatment on said membrane obtained according to said step (b) at temperatures ranging from 160 ° C to 200 ° C for a time ranging from 2 to 33 hours, obtaining a cross-linked SAP membrane. 6. Process according to claim 5, characterized in that said sulfonated aromatic polymer (SAP) is poly- (ether ether ketone) sulfonate (SPEEK). 7. Polymeric membrane for enthalpy heat exchanger based on sulphonated aromatic polymer (SAP). 8. Membrane according to claim 7, characterized in that said SAP is poly- (ether ether ketone) sulfonate (SPEEK). 9. Use of sulphonated aromatic polymer (SAP) in membranes for enthalpy heat exchangers. 10. Use of sulfonated aromatic polymer (SAP) according to claim 9, characterized in that said SAP is poly- (ether ether ketone) sulfonate (SPEEK).