IT201900019028A1 - MATERIAL FOR THE ADSORPTION AND DESORPTION OF WATER VAPOR, IN PARTICULAR IN A THERMAL MACHINE OR A SYSTEM WITH ADSORPTION AND HEAT EXCHANGER INCLUDING THIS MATERIAL - Google Patents

Description

MATERIAL FOR THE ADSORPTION AND DESORPTION OF WATER VAPOR, IN PARTICULAR IN A THERMAL MACHINE OR A SYSTEM WITH ADSORPTION AND HEAT EXCHANGER INCLUDING THIS MATERIAL

Field of the invention

The present invention relates to the sector of materials for the adsorption and desorption of water, in particular water vapor. In particular, the invention relates to a material particularly suitable to be used for the construction or coating of a heat exchanger, for example a heat pump.

State of the art

Heat pumps based on the adsorption / desorption of water on micro and mesoporous materials allow an innovative approach to a rational use of energy, for a sustainable energy policy and effective climate protection, through the reduction of environmental impact. of conventional heating and cooling devices.

To date, there are several adsorbent materials, which can be used as a coating, capable of adsorbing water vapor for such applications.

Adequate integration of the adsorbent material in the heat exchanger (HEX) is a key factor in increasing the quality of heat transfer in the adsorber (AdHEX). The use of large HEX surfaces coated with a thin layer of adsorbent is considered an interesting way to design dynamically efficient adsorbers.

However, the solutions currently available allow low contents of adsorbent material, thus implying a lower efficiency of the adsorbent machine. Furthermore, disadvantageously, the coatings that can be made up to now are usually characterized by poor mechanical strength and brittle behavior which favors an easy loss of particles of adsorbent material from the supports following the hydro-thermal cycles to which it is subjected or due to the difference in the coefficients of thermal expansion. This implies that there is often a loss of efficiency of the machine. Frequent maintenance is therefore required. To overcome this problem, thin coatings are often produced which exhibit less brittle behavior. This solution involves as a limit a low quantity of adsorbent material in the adsorber. The need is therefore felt for a material capable of improving the adsorption and desorption performance of a heat exchanger of a heat pump. Summary of the invention

An aim of the present invention is to create an adsorbent material that guarantees high mechanical and chemical resistance and at the same time guarantees high efficiency in terms of adsorption kinetics and hydrothermal stability, and which can also be easily and at low cost.

In particular, an object of the present invention is to provide an adsorbent heat exchanger for heat pumps which guarantees high mechanical and chemical resistance and at the same time guarantees high efficiency in terms of adsorption kinetics and hydrothermal stability, and which is also achievable easily and at low cost.

The present invention achieves at least one of these objects, and other objects which will be evident in the light of the present description, by means of a material, according to claim 1, suitable for adsorbing and desorbing water vapor, in particular in a thermal machine or in a system with adsorption, the material comprising: sulfonated polyetheretherketone (S-PEEK) from 2 to 65% by weight of the material; and particles of an adsorbent filler from 30 to 95% by weight of the material, suitable for adsorbing and desorbing water, in particular water vapor.

The invention also relates to a mixture, according to claim 9, comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the mixture; said particles of adsorbent filler from 3 to 70% by weight of the mixture; and an organic solvent capable of dissolving the sulfonated polyetheretherketone, from 25 to 90% by weight of the mixture.

The invention also relates to a process, according to claim 12, to obtain the material, in which the steps of:

a) providing sulfonated polyetheretherketone (S-PEEK), preferably with a degree of sulfonation from 10 to 50%;

b) solubilizing the sulfonated polyetheretherketone in an organic solvent to obtain a first mixture, the first mixture preferably comprising from 5 to 40% by weight of sulfonated polyetheretherketone;

c1) adding particles of said adsorbent filler to the first mixture to obtain a second mixture, the second mixture preferably comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the second mixture; said particles of adsorbent filler from 3 to 70% by weight of the second mixture; and organic solvent from 25 to 90% by weight of the second mixture;

d) removing the organic solvent from the second mixture, in particular to make it solid.

The invention also relates to a component of a heat engine according to claim 14, the component preferably being a heat exchanger or part of a heat exchanger

The invention also relates to a process, according to claim 15, to obtain the component, in which the steps of:

a) providing sulfonated polyetheretherketone (S-PEEK), preferably with a degree of sulfonation from 10 to 50%;

b) solubilizing the sulfonated polyetheretherketone in an organic solvent to obtain a first mixture, the first mixture preferably comprising from 5 to 40% by weight of sulfonated polyetheretherketone;

c1) adding particles of said adsorbent filler to the first mixture to obtain a second mixture, the second mixture preferably comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the second mixture; said particles of adsorbent filler from 3 to 70% by weight of the second mixture; and organic solvent from 25 to 90% by weight of the second mixture;

c2) placing the second mixture in a mold, or depositing the second mixture on a support using a 3D printer, or depositing the second mixture on the component;

d) removing the organic solvent from the second mixture, in particular to make it solid.

The invention also relates to a thermal machine, in particular a heat pump, according to claim 17.

The material, which is in particular a composite material, comprises or is formed by a thermally conductive and vapor-permeable structural matrix, with the adsorbent filler inside. In this design solution, the choice of a vapor permeable polymer matrix plays a fundamental role in the operation of the heat exchanger itself as the polymer matrix must be able to offer a barrier action to the flow of liquid water in the hydraulic circuit section of the adsorption heat pump but also must be permeable to water vapor in order to guarantee its action in adsorption and desorption in the operating cycle of the machine itself.

For this purpose, the sulphonated polyetherketones (S-PEEK) have been carefully selected, which have relatively low costs and are soluble in numerous organic solvents.

Polyetherketone (PEEK) is a semi-crystalline polymer with good mechanical properties, high thermal stability and chemical resistance.

PEEK is thermostable with a non-fluorinated aromatic chain structure, which can be functionalized by means of a sulfonation reaction, i.e. the insertion reaction of a SO3 <-> sulphonic group on a monomer ring.

One of the main properties that led to the choice of S-PEEK as the main material for the composite matrix is its good permeability to water vapor and its low hydrophilicity, such as to be comparable to commercial ion exchange membranes.

Advantageously, since the polymeric matrix is based on S-PEEK permeable to water vapor, no physical channels are required, for example an open porosity or cracks, to guarantee the adsorption capacity of the composite material based on adsorbent filler. The opportunity to have a monolithic adsorbent material is relevant in order to simplify the manufacturing process, but at the same time also to have a higher density of the composite material. In this way, more adsorbent filler can be added to the heat exchanger without reducing the adsorption kinetics. Furthermore, the material itself can exhibit adequate structural performance in order to be used not only as a cladding but also as a heat exchanger. In fact, the possibility is offered of directly making a heat exchanger in said composite material, and in particular the possibility is offered of eliminating the presence of the metal structure, usually in aluminum, of which the current heat exchangers are made. In other words, the supporting structure of the heat exchanger can be constituted by said composite material. This simplifies operation and considerably increases the performance of the adsorber, i.e. the adsorbent heat exchanger.

Advantageously, the invention offers a heat exchanger for heat pumps, and a process for making it, with significant advantages in terms of cost-effectiveness and flexibility of the manufacturing process, high mechanical and chemical resistance, while still guaranteeing high efficiency in terms of kinetics of adsorption and hydrothermal stability.

The high processing flexibility, i.e. processability, of the developed material allows very wide fields of applications that can diversify both by areas and by techniques of use.

For example, the material can be used for the production of adsorbent foils, in particular for stacked HEX; adsorbent coatings for heat exchangers; a heat exchanger (adsorbent HEX) made directly in the adsorbent monoblock, for example by means of a 3D printer.

In general, some of the advantages related to the material and to an exchanger made of said material or comprising said material are summarized below: high adsorption kinetics; permeability to water in the vapor phase; impermeability to water in the liquid phase; flexible production technique, for example dip coating, liquid casting, 3D printing; excellent mechanical characteristics; high adhesion; high scratch resistance.

Furthermore, the material can advantageously be used for the realization of components for thermal energy storage.

Further features and advantages of the invention will become more evident in the light of the detailed description of exemplary, but not exclusive, embodiments.

The dependent claims describe particular embodiments of the invention.

Description of exemplary embodiments of the invention

A material according to the invention is particularly suitable for adsorbing and desorbing water vapor, in particular in a heat engine, such as a heat pump. In fact, the material can adsorb water, in particular in the vapor state, and subsequently desorb the adsorbed water. The material is, in particular, in a solid form.

The material is in particular a composite material, and comprises polyetheretheretherketone sulfonate (S-PEEK) from 2 to 65%, preferably from 5 to 65%, more preferably from 5 to 15%, for example about 10%, by weight of the material ; and particles of an adsorbent additive or filler from 30 to 95%, preferably from 35 to 90%, more preferably from 65 to 85%, for example about 80%, by weight of the material. The adsorbent filler particles are suitable for adsorbing and desorbing water vapor.

The sulfonated polyetheretherketone is essentially the matrix of the composite material.

The sulfonated polyetheretherketone has been carefully selected, in particular as it has a good permeability to water vapor, so that no physical channels such as an open porosity or slits are required to ensure the adsorption capacity of the composite material comprising the adsorbing filler.

Preferably, the sulfonated polyetheretherketone has a degree of sulfonation from 10 to 50%. With "degree of sulfonation" we mean, in particular, the percentage of monomer units that have been sulphonated. For some applications, it is preferable not to exceed 50% sulfonation as a very high sulfonation value increases the kinetics of water vapor exchange but reduces thermal stability and increases water solubility.

The adsorbent filler is preferably a zeolite or silica gel or activated carbon or a hydrated salt or a metal organic framework (MOF).

Each adsorbent filler particle preferably has a size (also called particle size) from 0.5 to 500 µm.

The zeolite particles preferably each have a size (also called particle size) from 0.5 to 10 µm.

The zeolite can be for example SAPO 34 zeolite, preferably with particle size from 0.5 to 5 µm, for example about 3 µm.

The silica gel particles preferably each have a size (also called particle size) from 1 to 50 µm.

Preferably, the material also comprises particles of a thermally conductive filler or additive. In particular, the material can comprise particles of thermally conductive filler from 0 to 25% by weight of the material, preferably from 0 to 10%, more preferably from 8 to 12%, for example 10%, by weight of the material.

The thermally conductive filler is preferably graphite or graphene or carbon nanotubes (CNT) or a metal, for example but not limited to aluminum powder, copper powder or silver powder.

The thermally conductive filler can be in the form of powder or grains, for example.

The thermally conductive filler improves the thermal conductivity of the material. Preferably, the material has a density from 0.1 g / cm <3> to 4.0 g / cm <3>. The material is particularly homogeneous, i.e. compact. Therefore, the material manufacturing process is particularly smooth, and furthermore the material can comprise a large amount of adsorbent filler without reducing the adsorption kinetics. Moreover, in particular but not only in this density range, the material has excellent structural performance so it can be used both as a coating and for the realization of a component, in particular a monolithic component, such as a heat exchanger, for example by eliminating the presence of the usually aluminum structure of which a conventional heat exchanger is made. Therefore, the operation is simplified and the performance of the heat exchanger is considerably increased.

Below are some non-limiting examples of material according to the invention. In particular, reference is made to substantially solid material, obtained once it has subsequently solidified and substantially all the solvent has evaporated.

The invention also relates to a process for obtaining the aforementioned material in which the phases of:

a) providing polyetheretherketone sulfonate (S-PEEK), preferably by carrying out the sulfonation of polyetheretherketone (PEEK) to obtain polyetheretherketone sulfonate (S-PEEK);

b) solubilizing the sulfonated polyetheretherketone in an organic solvent to obtain a first mixture, the first mixture preferably comprising from 5 to 40% by weight, for example about 10% by weight, of sulfonated polyetheretherketone;

c1) adding particles of said adsorbent filler to the first mixture to obtain a second mixture, the second mixture preferably comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the second mixture; said particles of adsorbent filler from 3 to 70% by weight of the second mixture; and organic solvent from 25 to 90% by weight of the second mixture;

d) removing the organic solvent from the second mixture to consolidate it, i.e. make it solid.

Preferably, the sulfonated polyetheretherketone has a degree of sulfonation from 10 to 50%.

As will also be described hereinafter, the sulfonation of the polyetheretherketone is carried out in particular by means of sulfuric acid, more particularly concentrated sulfuric acid at 95-97%. PEEK is mixed with sulfuric acid, preferably with a mass / volume ratio from 1/5 to 1/40, for example equal to about 1/20. In particular, PEEK is mixed with sulfuric acid at a temperature below 60 ° C, for example at room temperature, for a period of time from 1 to 5 days, depending on the desired degree of sulfonation. The solution thus obtained is then cooled and the precipitate is recovered, which is washed and placed in an oven.

The organic solvent is preferably Dimethylformamide (DMF), in particular CAS: 68-12-2, although other organic solvents can also be used, for example, but not limited to, dimethylsulfoxide (DMSO), Dimethylacetamide (DMA) and ethanol.

Optionally, between step b) and step d), preferably during step c1), particles of said thermally conductive filler are also added to the first mixture, whereby said second mixture also comprises said thermally conductive filler particles, preferably up to 8% by weight of the second mixture.

Below is a non-limiting example of the process according to the invention. In particular, commercially available polyetheretherketone (PEEK) CAS Number: 29658-26-2, and sulfuric acid (95-97%) CAS Number: 7664-93-9 were used.

Sulfonation of polyetheretherketone: S-PEEK samples are obtained by sulfonation of PEEK at room temperature. The sulfonation can also be carried out at higher temperatures, in order to reduce the activation times of the polymer, but in any case lower than 60 ° C.

PEEK is initially mixed with concentrated sulfuric acid with a mass / volume ratio equal to w / V 1/20. For example, 3 g of PEEK are dissolved in 60 ml of concentrated H2SO4, under constant stirring, for the necessary time, in particular from 1 to 5 days, depending on the desired degree of sulfonation.

The solution thus obtained is poured drop by drop into deionized water, under continuous stirring, at a temperature of about 0 ° C maintained in a bath with water and ice.

The precipitated sulfonated polymer (ie the S-PEEK) is recovered by filtration and then washed with deionized water in order to remove the residual sulfuric acid, until it has a pH equal to or approximately equal to 7.

Subsequently, the washed sulfonated polymer is placed in an oven at 60 ° C for 12-24 hours.

Preparation of the mixture (also called second mixture for descriptive purposes or adsorbent mixture): the sulfonated polymer thus obtained is dissolved in Dimethylformamide (DMF) to form a solution at 5-40% by weight, preferably at approximately 10% by weight, and remains under stirring until the complete dissolution of the S-PEEK is obtained, obtaining a first mixture. A period of about 15 minutes under magnetic stirring was sufficient.

The adsorbent filler is then added (in particular zeolite, silica gel or activated carbon) always in constant and vigorous stirring for 15 minutes, until a fluid and homogeneous mixture is obtained. Optionally, in order to improve the thermal conductivity of the composite material, it is possible to add, at the same time as the adsorbent filler, the conductive filler (in particular graphite, CNT or graphene, in powder or grains) preferably in a maximum percentage of 8% or in quantity suitable for obtaining up to 25%, preferably up to 10% of conductive filler in the material after evaporation of the solvent.

The mixture thus obtained can be put in an oven in a temperature range from 45 to 100 ° C, preferably about 60 ° C, for about 24 hours, until the complete removal of the organic solvent.

Before the step of removing the organic solvent, the mixture, or second mixture, can be placed in molds of multiple shapes, for example by casting or injection molding. A compact and cohesive product is advantageously obtained. The product can be, for example, in the form of a monolith.

Alternatively, the deposition can be carried out by dip coating, showering or spraying, obtaining an adsorbent coating. The coating adheres to the substrate on which it is placed, for example of metal, plastic or a paint. The coating can also have high thicknesses or can be in the form of a film. Furthermore, the deposition can alternatively be carried out using a 3D printer. In this case, the resulting product can have particularly complex geometries.

The mixture to be deposited, ie the aforesaid second mixture, comprises polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12%, preferably from 4.0 to 7.0%, by weight of the mixture; said particles of adsorbent filler from 3 to 70%, preferably from 30 to 50%, by weight of the second mixture; and organic solvent from 25 to 90%, preferably from 40 to 60%, by weight of the second mixture.

Optionally, the mixture also comprises particles of said thermally conductive filler from 0 to 8% by weight of the mixture, preferably from 2 to 4% by weight of the mixture.

Below are some non-limiting examples of mixtures according to the invention. Once the solvent is removed, the mixture is consolidated so that the material according to the invention is obtained.

It should be clear that in particular the mass of the components in the tables is given by way of example only, it being possible to obtain the percentages by weight also differently.

Advantageously, the composite material can be used to make at least one part, for example all and only a part, of a component for a thermal machine, such as for example a heat pump. In particular, the composite material can be used to make at least one part, for example all and only a part, of a heat exchanger.

For example, a substantially metallic heat exchanger can be coated with at least one layer of composite material according to the invention.

Advantageously, the characteristics of the composite material allow to realize a coating having a thickness from 0.01 to 4.0 mm.

Furthermore, parts of a heat exchanger can be made with the composite material. For example, one or more adsorbent sheets can comprise or be made of said composite material, and the sheets can for example be used to make an adsorbent heat exchanger, or adsorbent HEX (ad-HEX), in particular comprising modular elements that can be assembled, namely the laminae.

Furthermore, advantageously, an adsorbent heat exchanger, or adsorbent HEX (ad-HEX), can be made substantially completely of said material, ie in the form of a monolithic element, in particular monobloc, for example by 3D printing.

The invention also relates to a heat engine, in particular a heat pump, comprising at least one heat exchanger comprising or consisting of the aforementioned composite material.

Claims (17)

CLAIMS 1. Material suitable for adsorbing and desorbing water vapor, in particular in a heat engine or in an adsorption system, the material comprising: sulfonated polyetheretherketone (S-PEEK) from 2 to 65% by weight of the material; and particles of an adsorbent filler from 30 to 95% by weight of the material, suitable for adsorbing and desorbing water vapor. 2. Material according to claim 1, comprising the sulfonated polyetheretherketone (S-PEEK) from 5 to 15% by weight of the material. 3. Material according to claim 1 or 2, comprising particles of said adsorbent filler from 65 to 85% by weight of the material. A material according to any one of the preceding claims, wherein said adsorbent filler is selected from the group consisting of a zeolite, silica gel, activated carbon, a hydrated salt and a metal-organic structure. 5. Material according to any one of the preceding claims, comprising particles of a thermally conductive filler from 0 to 25% by weight of the material, or from 8 to 12% by weight of the material. A material according to any one of the preceding claims, wherein said thermally conductive filler is selected from the group consisting of graphite, graphene, carbon nanotubes and a metal; the metal preferably being aluminum powder, copper powder or silver powder. 7. Material according to any one of the preceding claims, having a density from 0.1 to 4 g / cm <3>. 8. Material according to any one of the preceding claims, wherein the sulfonated polyetheretherketone (S-PEEK) has a degree of sulfonation from 10 to 50%. 9. Mixture for obtaining a material according to any one of the preceding claims, comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the mixture; said particles of adsorbent filler from 3 to 70% by weight of the mixture; and an organic solvent capable of dissolving the sulfonated polyetheretherketone, from 25 to 90% by weight of the mixture. 10. Blend according to claim 9, comprising particles of said thermally conductive filler from 0 to 8% by weight of the mixture, or from 2 to 4% by weight of the mixture. 11. Blend according to claim 9 or 10, wherein the sulfonated polyetheretherketone (S-PEEK) has a degree of sulfonation of 10 to 50%. 12. Process for obtaining a material according to any one of claims 1 to 8 in which the steps of: a) providing sulfonated polyetheretherketone (S-PEEK), preferably with a degree of sulfonation from 10 to 50%; b) solubilizing the sulfonated polyetheretherketone in an organic solvent to obtain a first mixture, the first mixture preferably comprising from 5 to 40% by weight of sulfonated polyetheretherketone; c1) adding particles of said adsorbent filler to the first mixture to obtain a second mixture, the second mixture preferably comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the second mixture; said particles of adsorbent filler from 3 to 70% by weight of the second mixture; and organic solvent from 25 to 90% by weight of the second mixture; d) removing the organic solvent from the second mixture, in particular to make it solid. 13. Process according to claim 12, wherein between step b) and step d) preferably during step c1), particles of said thermally conductive filler are also added to the first mixture, whereby said second mixture also comprises said particles of thermally conductive filler, preferably up to 8% by weight of the second mixture. 14. Component of a thermal machine, in particular of a heat pump, made of a material according to any one of claims 1 to 8; or comprising at least one coating made of a material according to any one of claims 1 to 8; said component being preferably a heat exchanger or part of a heat exchanger. 15. Process for obtaining a component according to claim 14, in which the steps of: a) providing polyetheretherketone sulfonate (S-PEEK), preferably with a degree of sulfonation from 10 to 50%; b) solubilizing the sulfonated polyetheretherketone in an organic solvent to obtain a first mixture, the first mixture preferably comprising from 5 to 40% by weight of sulfonated polyetheretherketone; c1) adding particles of said adsorbent filler to the first mixture to obtain a second mixture, the second mixture preferably comprising polyetheretherketone sulfonate (S-PEEK) from 2.5 to 12% by weight of the second mixture; said particles of adsorbent filler from 3 to 70% by weight of the second mixture; and organic solvent from 25 to 90% by weight of the second mixture; c2) placing the second mixture in a mold, or depositing the second mixture on a support using a 3D printer, or depositing the second mixture on the component; d) removing the organic solvent from the second mixture, in particular to make it solid. 16. Process according to claim 15, wherein between step b) and step c2), preferably during step c1), particles of said thermally conductive filler are also added to the first mixture, whereby said second mixture also includes said particles of thermally conductive filler, preferably up to 8% by weight of the second mixture. 17. Thermal machine, in particular a heat pump, comprising a component according to claim 14.